examining the relationship between human activities and climate

heritagecouncil.ie

examining the relationship between human activities and climate

Project Number 16718

EXAMINING THE RELATIONSHIP BETWEEN HUMAN ACTIVITIES

AND CLIMATE CHANGE IN THE WETLANDS OF IRELAND: FINAL

TECHNICAL REPORT

Edited by: N.P. Branch 1 and I. Matthews 2

Contributions to sections (in alphabetical order):

C.R. Batchelor 1 , S. Black 1 , N.P. Branch 1 , A. Brown 1 , K. Denton 2 , L. Dolding 2 , G.

Dormer 1 , S. Elias 2 , A. Field 2 , A. Griggs 2 , I. Matthews 2 , N. Riddiford 2 , O. Pritchard 1 , T.S.

Watson 2 , J. Whitaker 3 and D.Young 1

1 School of Human and Environmental Sciences, University of Reading, Whiteknights, PO Box 227,

Reading, RG6 6AB, UK

2 Department of Geography, Royal Holloway University of London, Egham Hill, Egham, Surrey, TW20

OEX, UK

3 Archaeological Development Services Ltd, 110 Amiens Street, Dublin 1, Co Dublin, Ireland

__________________________________________________________________________

INTRODUCTION

This technical report presents the results of a collaborative research project involving staff

and students from the University of Reading (School of Human and Environmental

Sciences), University of London (Royal Holloway) and Archaeological Development Services

Ltd.. Archaeological excavation of six ombrogenous mires at Gilltown, Lullymore East,

Kinnegad, Ballykean, Ballybeg and Littleton revealed the presence of wooden structures

(toghers, platforms and trackways, and a settlement) of prehistoric and historic age (Figure

1). Palaeoenvironmental and geochronological investigations as part of the post-excavation

analysis programme have reconstructed the environmental context of past human activities,

and examined the relationships between structure construction, reconstruction and

abandonment, and changes in bog surface wetness and climate history. To achieve these

aims, the team (known as the ‘wetland ALLIANCE’) have conducted, and are continuing to

conduct, a multi-proxy approach, involving analysis of:-

1. Peat stratigraphy

2. Peat humification and organic matter content

3. Pollen grains and spores

4. Plant macrofossils, including wood, Sphagna and monocotyledonous remains

5. Insects

6. Testate amoeba

7. Peat geochemistry e.g. phosphates

8. Stable and radiogenic isotopes

9. Radiocarbon and dendrochronological dating.

Funding was secured from the Irish Heritage Council (INSTAR programme) in 2009 for a

continuation of the tephrochronological studies initiated in 2008, with the aim of providing a

precise chronological framework for the archaeological remains and the palaeoenvironmental

records.

This technical report has been divided into two parts; PART A presents a summary of the

results of the main palaeoenvironmental records for each site; PART B presents the results

of the tephrochronological studies.

The forthcoming MONOGRAPH publication will provide a fully integrated discussion of

PARTS A and B, and further publications will be generated for individual sites, themes or

techniques in peer reviewed academic journals.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Project Number 16718

PART A: SUMMARY OF THE PALAEOENVIRONMENTAL DATA

1.0 KINNEGAD BOG

D. Young, N.P. Branch, K. Denton, S. Elias, A. Brown and J. Whitaker

This section summarises the findings arising out of the litho- and bio-stratigraphical analysis

of samples taken from archaeological sites 07E0501 (ME-KND0016) and 07E0497 (ME-

KND002) at Kinnegad Bog, Co. Meath, Ireland. In total ten sites were excavated during 2007

at Kinnegad Bog by Archaeological Development Services (ADS) Ltd., five of which were

dated to the Middle to Late Bronze Age. The sites were located in two clusters, one group of

sites in the southwest corner, and one trackway spanning the southeast corner of the bog

(Figure 2). Kinnegad Bog, 1km south of Kinnegad village, is part of the Allen group of bogs

with a production area of 330 hectares (Rohan, 2008). The surrounding topography is

predominantly low-lying, undulating ground with an average elevation of 85 to 95m OD

(Rohan, 2008). A dryland ridge separates the southwest and southeast corners of the bog; at

least two of the excavated trackways are orientated towards this ridge (Rohan, 2008). The

investigation at Kinnegad Bog had two main aims: (1) To reconstruct the environmental

context of past human activities; (2) To elucidate the relationship, if any, between structure

construction and abandonment, and climate change.

Figure 2: Location of Kinnegad Bog, Co. Meath. Western and eastern sets of

archaeological sites and Recorded Monuments (blue) are shown (adapted from Rohan,

2008).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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The results, supported by several radiocarbon dates (Table 1), indicate:

1. That the development pathway of Kinnegad Bog is broadly consistent across the basin

and that borehole is representative of the main sedimentary units in this part of the

bog.

2. The Fen-Bog Transition (FBT) is recorded towards the top of zone KBH3-2, beginning at

c. 280cm (at c. 5500 cal yrs BP).

3. The FBT is followed immediately by a dry shift from c. 280 to 260cm, during which time

well humified wood peat formed.

4. Following the period of drier conditions after the FBT, a major wet shift is indicated by low

humification (35.5%) values at c. 235cm in borehole .

5. The humification record indicates wet shifts at c. 197cm (46.9%) and c. 172cm (45%),

which may be synchronous with increases in the abundance of the low lawn/pool species

S. papillosum towards the top of the zone.

6. The plant macrofossil analysis has indicated that zone KBH3-4 experienced relatively dry

conditions with desiccation of the peat surface during the summer indicated by the

dominance of E. vaginatum.

7. A significant dry shift at 3690-3470 cal yrs BP, towards the top of zone KBH3-4, was

followed by a significant wet shift at 3340-3070 cal yrs BP (at c. 69cm). The humification

record and peat stratigraphy from borehole indicate that during this event the bog

surface became significantly wetter, with poorly humified Sphagnum peat following a

period of drier conditions dominated by more humified wood peat.

8. The peat stratigraphy of plant macrofossil zone KBH3-5, beginning at c. 3170 cal yrs BP

and lasting until c. 2600 cal yrs BP, is dominated by poorly humified Sphagnum peat, with

S. papillosum becoming the dominant species, replacing E. vaginatum, whose presence

declines to the lowest levels recorded in any of the post-FBT plant macrofossil zones.

The humification record (


Project Number 16718

because they are reliably dated, are supported by the plant macrofossil and pollen

records, and occur after the fen-bog transition (FBT).

12. Radiocarbon dating of trackway 07E0501 (ME-KND0016) returned an age range of 3460-

3210 cal yrs BP. This trackway is located close to borehole , and the linear age/depth

model created using four radiocarbon dates from borehole places the trackway at a

depth range of 61-81cm (midpoint 71 ±10cm). This inferred depth places the trackway

construction in plant macrofossil zone KBH3-4, and pollen zone 2/3, a period of relatively

dry conditions with desiccation of the peat surface during the summer indicated by the

dominance of E. vaginatum and the presence of Ericales rootlets throughout the zone.

The presence of S. tenellum throughout zone KBH3-4 indicates regular disturbance of

the peat surface (see McMullen et al., 2004), which may indicate fire events or

anthropogenic activity on the dry bog surface. This significant dry shift is dated to 3690-

3470 cal yr BP and coincides with the construction of trackway 07E0501 (ME-KND0016),

trackway 07E0496 (ME-KND001; 3700-3380 cal yrs BP), platform 07E0499 (ME-

KND011) and trackway 07E0497 (ME-KND002). At this time, the bog surface was

composed of highly humified wood peat and supported a mixture of E. vaginatum,

Scirpus cespitosus and C. vulgaris, indicating drier conditions on the bog surface. The

presence of S. papillosum, albeit in reduced abundance, indicates that low lawn

conditions may have been present nearby, although this species has been known to

survive on drier hummock sides in reduced quantities (Godwin and Conway, 1939). This

dry shift, and the construction of the trackways and platform, was followed by a significant

change at 3340-3070 cal yrs BP, during which the bog surface became significantly

wetter (c. 40-200 years), with poorly humified Sphagnum peat and E. vaginatum being

replaced as the dominant taxa by S. papillosum. This wet shift is considered to have

preceded a significant change in climatic conditions, with greatly increased climatic

wetness between c. 3170 to c. 2600 cal yrs BP. This interpretation is supported by data

from several sites across NW Europe, which indicates worsening climatic conditions at

this time (Chambers, 1987; Hughes et al., 2000; Barber et al., 2003; Caseldine and

Gearey, 2005; Plunkett, 2006). It was during this time that platform 07E0501 (ME-

KND0015) was constructed.

13. Since trackway 07E0501 (ME-KND0016), trackway 07E0496 (ME-KND001), platform

07E0499 (ME-KND011) and trackway 07E0497 (ME-KND002) were constructed during

an especially dry period, following perhaps several hundred years of drier conditions at

Kinnegad Bog, it is reasonable to suggest that they were constructed as a response to

increased demand for the exploitation of Kinnegad Bog, not as a response to a shift in

climatic conditions. The climatic deterioration that followed their construction probably

rendered the bog surface less desirable as an area for grazing, settlement or agriculture.

Although continued human activity on the bog surface is indicated by the pollen record

and the presence of platform 07E0501 (ME-KND0015), suggesting that the adverse

climatic conditions may have initiated a change in subsistence practices. According to

Turney et al (2006), archaeological visibility tends to increase during the Bronze and Iron

Ages in Ireland, especially during periods of increased wetness, with crannogs (lake-side

dwellings) and forts seemingly constructed in response to a dramatic reduction in

available resources. This model does not seem to apply to Kinnegad Bog. Instead

construction occurred during periods of both drier and wetter bog surface conditions.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Project Number 16718

Table 1: Radiocarbon dates from borehole with associated calibrated age ranges

Lab. Code Core Depth below 13C (per 14C age BP Cal. range BP (2)

surface (cm) mil.) (uncal.)

BETA233290 BH3B 20-21 -24.4 2730 ±40 2930-2760

BETA233291 BH3B 60-61 -26.0 3150 ±40 3440-3310/3300-3260

BETA233292 BH3B 68-69 -27.2 3050 ±40 3340-3070

BETA233293 BH3B 92-93 -26.2 3370 ±40 3690-3470

ME-KND001 -- c. 65-115 -- -- 3540±160

ME-KND002 -- c. 81-96 -- -- 3519±9

ME-KND011 -- c. 43.5-63.5 -- -- 3155±205

ME-KND0015 -- c. 24.8-58.8 -- -- 3030±180

ME-KND0016 -- c. 61-81 -- -- 3460-3210

Figure 3: Stratigraphic transect (boreholes to ) at Kinnegad Bog, Co. Meath.

The transect is orientated north-south.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 4: Stratigraphy of boreholes , and (distal to 07E0501, 07E0500,

07E0499 and 07E0496) at Kinnegad Bog, Co. Meath.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

7


Project Number 16718

Figure 5: Plant macrofossil diagram for Kinnegad Bog, borehole (8cm resolution) showing peat stratigraphy from this core and

% humification data from core BH3A.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

8


Project Number 16718

Figure 6: Pollen diagram from Kinnegad Bog, borehole (top 1.50m, 4cm resolution). The stratigraphic position of the trackways

and platforms is shown (shaded bar).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

9


Project Number 16718

2.0 BALLYKEAN BOG

N.P. Branch, D. Young, K. Denton, S. Elias, A. Brown and J. Whitaker

This section summarises the findings arising out of the litho- and bio-stratigraphical analysis

of samples taken from a habitation site (07E0274) at Ballykean Bog, Co. Offaly, Ireland. The

habitation site was excavated in 2007 by Archaeological Development Services (ADS) Ltd.

and consists of a central sub-rectangular hearth (2.3x1.4m) surrounded by a double arc of

stakes and wattling, probably representing an exterior wall of a house 9m in diameter, and an

exterior circular palisade 22-24m in diameter (Turrell, 2008). Ballykean Bog, 5km southeast

of Daingean and 4km east of Geashill, is part of the Derrygreenagh Group of bogs, and

covers and area of 415 hectares (Figure 7). The bog is bordered to the east by elevated

ground and Walsh Island, and to the north by a narrow gravel ridge, which separates it from

Mountlucas Bog (Turrell, 2008). The investigation at Ballykean Bog had two main aims: (1)

To reconstruct the environmental context of past human activities; (2) To elucidate the

relationship, if any, between structure construction and abandonment, and climate change.

Figure 7: Location of Ballykean Bog, Co. Offaly (adapted from Turrell, 2008).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

10


Project Number 16718

The results indicate:

1. The chronological information available for the Ballykean Bog habitation site indicates an

Early Christian age (1270 ±100 cal yrs BP and 1395 ±125 cal yrs BP).

2. The environmental archaeological data derived from borehole is particularly

important with respect to the reconstruction of the local and regional environmental

context of human activities at Ballykean Bog habitation site. The plant macrofossil record

from borehole is especially interesting because it confirms data from the column

samples ( and ) indicating the presence of an extensive pool complex with

Scheuchzeria palustris and drier hummocks (zones BK37-1 and BK37-2, and BKZ-1 and

BKZ-2). This mosaic of pools and hummocks persisted into the top 30cm of the

sequence, which represents the possible transition between the pre-habitation (zones

BK37-3 and BKZ-3) and habitation (zone BK37-3) surface. However, within this horizon,

slightly drier bog surface conditions are suggested in borehole , whilst in column

sample , an extensive pool complex is inferred.

3. The pollen data from column samples and also indicate a local, bog surface

dominated by mosses, sedges and grasses. The extra-local and regional vegetation

cover comprised open mixed deciduous woodland with Corylus, Quercus, Ulmus,

Fraxinus and Betula. Between 35-15cm (zone 2), there is an excellent correlation with the

plant macrofossil data indicating a slight shift to drier bog surface conditions, which

accompanied a clear decline in woodland cover. The evidence for further woodland

decline persisted into zone 3 (0-15cm). Although there are no pollen-stratigraphic

indicators of human activity, the decline in woodland cover could be attributed to human

interference with the vegetation cover prior to the construction of the habitation site.

However, given the plant macrofossil evidence for extensive pool systems, it is entirely

possible that some of the pools, including those recorded in column samples and

, were infilling with peat during the period of occupation. Therefore, the pollen record

for woodland decline may be broadly contemporaneous with the structure. An alternative

explanation for the woodland decline, and the slight shift to drier bog surface conditions,

however, may be climate change prior to 1270 ±100 cal yrs BP and 1395 ±125 cal yrs BP

or broadly contemporaneous with the structure. The insect data from the same section

sampled for pollen and plant macrofossil analyses indicates a mosaic of standing water

with Sphagnum, woodland (e.g. Salix and Betula), as well as dung, arable land, carrion

and dry deadwood, which broadly supports the overall findings.

4. Although there is strong evidence for anthropogenic activities prior to and during

occupation of the Ballykean Bog habitation site, it is interesting to note that the timing of

occupation (1270 ±100 cal yrs BP and 1395 ±125 cal yrs BP) coincides with a possible

shift to wetter climatic conditions in Ireland (see Turney et al., 2006). This period

witnesses a rise in the number of settlement sites, crannogs and forts, possibly a

response to stress placed on existing subsistence strategies and the need to exploit new

ecosystems. If the occupation at Ballykean Bog occurred as a response to this event, it

might also explain the changes in vegetation cover that occurred on the bog surface (i.e.

the development of the extensive pool system), and on nearby dryland. Therefore, the

decline in woodland cover, and the evidence for cultivation and pastoralism, could be

interpreted as a response to worsening climatic conditions.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 8: Organic matter content, borehole , Ballykean Bog, Co. Offaly.

Figure 9: Organic matter content, column samples and , Ballykean Bog, Co.

Offaly.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

12


Project Number 16718

Figure 10: Plant macrofossil diagram for Ballykean Bog, 07E0487 core borehole (top 1.06m, 8cm resolution) showing peat

stratigraphy and % humification data.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

13


Project Number 16718

Figure 11: Plant macrofossil diagram for Ballykean Bog, 07E0487 columns and (8cm resolution) showing peat stratigraphy

and % humification data for the top 0.65m.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

14


Project Number 16718

Figure 12: Pollen diagram from Ballykean Bog, 07E0487, column samples and .

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

15


Project Number 16718

3.0 GILLTOWN BOG

N.P. Branch, D. Young, K. Denton, S. Elias, A. Brown, C.R. Batchelor and J. Whitaker

This section summarises the findings arising out of the litho- and bio-stratigraphical analysis

of samples taken from archaeological site 07E0632 (KD-GT005c) at Gilltown Bog, Co.

Kildare, Ireland (Figure 13). Forming part of the Coolnamona Group of bogs, Gilltown Bog

lies 2km northwest of Staplestown, and is surrounded predominantly by farmland (Corcoran,

2008). It covers a total area of 355 hectares. Two archaeological sites were excavated at

Gilltown Bog by Archaeological Development Services (ADS) Ltd. Both of these were

sections of substantial wooden toghers, one (07E0631) of Early Medieval age, dated to 1175

±115 cal yrs BP, the other (07E0632) dated to 3295 ±145 cal yrs BP and equated to the

Middle Bronze Age cultural period. Trackway 07E0631 was orientated northwest to

southeast across the northeast corner of Gilltown Bog, while trackway 07E0632 was

orientated northeast to southwest across the southeast corner. This section focuses on the

analysis of togher 07E0632 (Middle Bronze Age). The investigation at Gilltown Bog had two

main aims: (1) To reconstruct the environmental context of past human activities; (2) To

elucidate the relationship, if any, between structure construction and abandonment, and

climate change.

Figure 13: Location of Gilltown Bog, Co. Kildare, Ireland (adapted from Corcoran,

2008).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

16


Project Number 16718

The results indicate:

1. The results of the stratigraphic descriptions of the transect borehole core samples

indicates a clear distinction between those locations indicative of the fen edge of the

ombrogenous bog, and those points that were more central to the original peat dome.

Boreholes and , and trackway (togher) 07E0632 (3295 ±145 cal yrs BP), were

located within the fen edge according to the stratigraphic descriptions.

2. This interpretation is supported by the pollen and plant macrofossil data for borehole

, and the plant macrofossil results for borehole , which indicate Betula and

Alnus mature fen carr woodland prior to the trackway construction (pollen zone 1), which

persisted throughout the sequence despite pronounced changes in bog surface wetness.

3. This is confirmed by the insect analysis, which indicates the presence of Salix, Betula

and Alnus carr woodland from 105cm upwards (post trackway construction but possibly

contemporaneous with its use), with open pools of duckweed, mud banks, damp

woodland, leaf litter, Sphagnum mosses and reeds.

4. On nearby dryland, Quercus and Corylus with Ulmus and Fraxinus were present, forming

mixed deciduous woodland, prior to the trackway construction at 3295 ±145 cal yrs BP.

5. Following construction and use, the pollen evidence indicates a decline in Corylus,

Quercus, Ulmus and Fraxinus during a period of cereal cultivation. Thereafter, the hazel

dominated woodland recovers, possibly due to the decline in human activity on the

wetland and dryland.

6. The pollen and plant macrofossil results indicate that the trackway was constructed

during a wetter phase of fen peat accumulation, with Scheuchzeria palustris, Menyanthes

trifoliata, Phragmites australis and Sphagnum. If the timing of the trackway construction

(3295 ±145 cal yrs BP) is compared with the Holocene climate model proposed by

Turney et al (2006), then the wetter phase proposed for Gilltown Bog contradicts the drier

phase they identified at this time. This apparent contradiction may be due to the sampling

location at Gilltown Bog, with the fen carr being less sensitive to changes in atmospheric

precipitation and greatly influenced by surface runoff from nearby dryland. Indeed, the

wetter phase identified at Gilltown Bog may be due to human activities on adjacent dry

ground (identified by the pollen and insect analyses), resulting in increased overland flow

of water, and causing localised changes in the mire hydrology. Support for this

interpretation may be found in the apparent contradiction in evidence for bog surface

conditions following trackway abandonment, with borehole indicating wetter

conditions, whilst borehole indicates a dry phase.

7. This suggest that fen areas are less sensitive to changes in climate due to the complex

effects of localised hydrological changes. Therefore, although the trackway was

constructed at Gilltown Bog during a phase of wetter bog surface conditions, these

conditions were not necessarily initiated by climate change. According to the Turney et al

(2006) model, the climate during this time was drier, which perhaps created favourable

conditions for trackway construction and the exploitation of wetland resources.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

17


Project Number 16718

Figure 14: Transect A, Gilltown Bog, Co. Kildare. Borehole is located at the southern end of Gilltown bog, Borehole is

located at the northern end of the bog.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

18


Project Number 16718

Figure 15: Organic matter data from Gilltown Bog, borehole .

Figure 16: Organic matter data from Gilltown Bog borehole .

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

19


Project Number 16718

Figure 17: Plant macrofossil and humification analysis of Gilltown Bog borehole (top 1.70m, 8cm resolution). Plant macrofossil

assemblage zones are displayed; these were defined with the aid of stratigraphically constrained proportional cluster analysis with

no data transformation, using CONISS within TILIA v.2.02.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

20


Project Number 16718

Figure 18: Plant macrofossil and humification analysis of Gilltown Bog borehole (top 1.70m, 8cm resolution). Plant macrofossil

assemblage zones are displayed; these were defined with the aid of stratigraphically constrained proportional cluster analysis with

no data transformation, using CONISS within TILIA v.2.02.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

21


Project Number 16718

Figure 19: Pollen analysis of Gilltown Bog borehole .

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

22


Project Number 16718

4.0 LULLYMORE EAST BOG

N.P. Branch, D. Young, K. Denton, S. Elias, A. Brown, C.R. Batchelor and J. Whitaker

This section summarises the findings arising out of the litho- and bio-stratigraphical analysis

of samples taken from archaeological site 07E0630 (KD-LYE001 and KD-LYE002) at

Lullymore East Bog, Co. Kildare, Ireland (Figure 20). Lullymore East Bog forms part of the

Derrygreenagh Group of bogs. It is bordered to the northeast by the Lullymore island and to

the west by the dryland island of Lullybeg. It has a production area of approximately 80

hectares, with 38 production fields orientated east to west (Corcoran, 2008). Of the three

archaeological sites recorded during the 2004 survey by Archaeological Development

Services Ltd. (ADS), gravel and wooden trackway KD-LYE001 was selected for excavation.

During the excavation, wooden trackway KD-LYE002 was also exposed, sited c. 0.29m

above the gravel and wooden trackway at the western end of the cutting. Gravel and wooden

trackway KD-LYE001 is of Late Iron Age/Early Medieval age, dated to 1430 ±140 cal yrs BP,

while wooden trackway KD-LYE002 is equated to the Early Medieval cultural period, dated to

920 ±130 cal yrs BP (Corcoran, 2008). Both trackways were orientated northeast to

southwest across Lullymore East Bog, between the dryland islands of Lullymore and

Lullybeg. The investigation at Lullymore East Bog had two main aims: (1) To reconstruct the

environmental context of past human activities; (2) To elucidate the relationship, if any,

between structure construction and abandonment, and climate change.

Figure 20: Location of Lullymore East Bog, Co. Kildare (adapted from Corcoran, 2008).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

23


Project Number 16718

The results indicate:

1. The multi-proxy environmental archaeological analysis of trackways KD-LYE001 (1430

±140 cal yrs BP; AD 330-660) and KD-LYE002 (920 ±130 cal yrs BP; AD 900-1160) has

provided a valuable insight into the Late Holocene environmental history of Lullymore

East Bog.

2. The dryland vegetation throughout the period-represented (c. 600-1100 AD) was open

mixed deciduous woodland, dominated by Corylus but with Ulmus, Quercus and

Fraxinus, and short turf grassland and meadowland.

3. The bog surface was a mosaic of open pools, lawns and hummocks, with damp

woodland (Alnus and Salix carr), reeds (Phragmites australis; Poaceae), Carex

(Cyperaceae), Sphagnum and duckweed (Lemna), and drier areas having Erica sp. and

Calluna vulgaris.

4. The plant macrofossil evidence indicates that a wet Sphagnum bog existed prior to and

during use of trackway KD-LYE001 (AD 330-660), which is supported by the pollen data.

Following its abandonment, the bog surface became significantly wetter, with a body of

standing water on the peat surface. This increase in bog surface wetness is possibly

supported by the model for Holocene climate change in Ireland advocated by Turney et al

(2006). The model suggests that during the Late Iron Age to Early Medieval period there

was a shift from drier to wetter climatic conditions.

5. Therefore, the results from Lullymore East Bog may indicate that the changes in

hydrology of the bog surface coincided with wetter climatic conditions. Whether these

changes caused the abandonment of the gravel and wooden trackway remains uncertain.

6. During the period of construction and use of trackway KD-LYE002, c. 500 years after the

construction of the gravel and wooden trackway, drier bog surface conditions are

indicated by the plant macrofossil data at Lullymore East Bog.

7. Comparison with the Turney et al (2006) model once again reveals a strong correlation

with a period of climate change from wetter to drier conditions (Medieval Warm Period).

Therefore, it is possible that trackway KD-LYE002 was constructed on a relatively dry,

stable peat surface following the onset of the Medieval Warm Period.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 21: Transect A, Lullymore Bog, Co. Kildare.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 22: Transect B, Lullymore Bog, Co. Kildare.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 23: Organic matter content, Lullymore Bog, borehole .

Figure 24: Organic matter content, Lullymore Bog, borehole .

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 25: Plant macrofossil and humification analysis of Lullymore East Bog borehole (top 0.90m, 8cm resolution). Plant

macrofossil assemblage zones are displayed; these were defined with the aid of stratigraphically constrained proportional cluster

analysis with no data transformation, using CONISS.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 26: Plant macrofossil and humification analysis of Lullymore East Bog borehole (top 1.30m, 8cm resolution). Plant

macrofossil assemblage zones are displayed; these were defined with the aid of stratigraphically constrained proportional cluster

analysis with no data transformation, using CONISS within TILIA.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 27: Pollen analysis of Lullymore East Bog borehole (top 0.90m).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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5.0 BALLYBEG BOG

D. Young, N.P. Branch, K. Denton, A. Brown, S. Elias and J. Whitaker

This section summarises the findings arising out of the litho- and bio-stratigraphical analysis

of samples taken from Ballybeg Bog, Co. Tipperary, Ireland (Figure 28). In total eight sites

were excavated at Ballybeg Bog in 2008 by Archaeological Development Services (ADS)

Ltd. These sites were identified as three platforms, two short toghers, one possible togher,

one hurdle panel and a deposit of archaeological wood (Rohan, 2008). Following excavation,

two of these sites were dated to between 3830-2945 BP (Rohan, 2008), and date therefore

to the Middle to Late Bronze Age. The archaeological sites at Ballybeg Bog were situated in

two groups: one further north, in proximity to dryland woodland, the other further south. Both

groups are situated within a narrow part of the bog separating the eastern and western sides.

Ballybeg Bog is located 1.3km southeast of Littleton village, and forms part of the Littleton

Group of bogs (Rohan, 2008). The surrounding topography is predominantly low-lying,

undulating ground with an average elevation of 120m OD, but dominating the view to the

east is the Slieveardagh Hills, 4km to the southeast (Rohan, 2008). The production area of

the bog is 146 hectares. The investigation at Ballybeg Bog had two main aims: (1) To

reconstruct the environmental context of past human activities; (2) To elucidate the

relationship, if any, between structure construction and abandonment, and climate change.

Figure 28: Location of Ballybeg Bog, Co. Tipperary (adapted from Rohan, 2008)

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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The results indicate:

1. The multi-proxy analytical approach adopted here has revealed significant changes in

bog surface wetness, and the local and regional vegetation cover. The timing of these

events remains uncertain but it is highly likely, given the depth of the peat stratigraphy,

and the location and age of the archaeological structures (08E0394 (TN-BLG002) 2945

±9 BP; 08E0397 (TN-BLG0016) 3700 ±130 BP, 08E0396 (TN-BLG009a-b) 3485 ±155

BP) relative to borehole , that organic-rich sediment accumulation commenced in

borehole during the later Middle Holocene.

2. This may reflect its position towards the edge of this part of Ballybeg Bog. This

interpretation is possibly supported by the pollen analyses at Littleton Bog conducted by

Mitchell (1965), who identified a decline in Pinus during the Late Neolithic / Early Bronze

Age, which may be present at Ballybeg Bog during the zone 1 to 2 transition.

3. The development of fen and fen carr woodland during the early stages of sedimentation

was accompanied by the growth of Betula and Alnus with evidence for standing water on

the bog surface (plant macrofossil zone BBBH-1, and pollen zone 1). This was

succeeded by fluctuating bog surface wetness and changes in the local vegetation cover

prior to the fen-bog transition at c. 134cm. The plant macrofossil evidence suggests that

the bog surface became drier during zones BBBH-2 and BBBH-4, between 213-175cm

and 152-134cm respectively.

4. Both of these events correspond to an increase in importance of Erica dwarf shrubland

on the bog surface during pollen zone 2. The wetter bog surface conditions recorded by

the plant macrofossils in zone BBBH-3 are not present in the pollen data.

5. Unfortunately, the timing of these bog surface wetness changes remain uncertain, but

based upon the location, age and stratigraphic depth of togher 08E0394 (TN-BLG002;

2945 ±9 BP) with respect to borehole , it is highly likely that these events occurred

prior to c. 3000 BP, and probably during the period of use of structures 08E0397 (TN-

BLG0016; 3700 ±130 BP) and 08E0396 (TN-BLG009a-b; 3485 ±155 BP).

6. During this time, the dryland vegetation cover comprised Quercus and Corylus with

Ulmus and Fraxinus forming mixed deciduous woodland.

7. The transition to ombrotrophic conditions at Ballybeg Bog was accompanied by a

significant change to wetter surface conditions, which is indicated by the plant

macrofossil and pollen data (zones BBBH-5 and zone 3, respectively). It is highly likely,

based upon the location, age and stratigraphic depth of togher 08E0394 (TN-BLG002;

2945 ±9 BP) with respect to borehole , that this transition occurred post-3000 BP.

During this time, Corylus, Quercus, Ulmus and Fraxinus continued to dominate, possibly

with Erica, the dryland taxa, although there is some evidence for an overall decline in

woodland cover. This trend continued into pollen zone 4 (30-0cm), where there is decline

in dryland taxa, namely Corylus, Quercus, Ulmus and Fraxinus.

8. Based upon the known age of the structures at Ballybeg Bog, we can correlate these

records with the palaeoclimatic model proposed for Ireland based upon bog oak and pine

records (Turney et al., 2006). The model suggests that during the construction of togher

08E0394 (TN-BLG002) at 2945 ±9 BP, the climate in Ireland was wetter. The

palaeoecological records from Ballybeg Bog broadly support a shift to wetter surface

conditions at this time and given the weak anthropogenic signal in the pollen data, it is

tempting to suggest that the general decline in dryland woodland cover was climatically

induced.

9. However, for toghers 08E0397 (TN-BLG0016; 3700 ±130 BP), and 08E0396 (TN-

BLG009a-b; 3485 ±155 BP), the situation is less clear. The former was constructed

during a period of wetter conditions according to the Turney et al (2006) model, but the

latter corresponds to a period of drier conditions. This seems to suggest a lack of

consistency between the climatic model and the archaeological evidence. Due the

absence of radiocarbon dates and tephrochronological data for borehole , at present

it is not possible to test the Turney et al model or establish whether the shifts in surface

wetness noted above correspond to periods of togher construction.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 29: Stratigraphy of borehole ¸ Ballybeg Bog; lake basin sediments were not

retained but are considered to underlie the lowest unit described, since the coring

device could not be penetrated further, and had clearly entered a clay/gravel sediment.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 30: Plant macrofossil diagram for Ballybeg Bog, borehole (8cm resolution), showing peat stratigraphy and % humification

data.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 31: Pollen diagram from Ballybeg Bog, borehole .

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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6.0 LITTLETON BOG

N.P. Branch, D. Young, K. Denton, G. Dormer, S. Elias, A. Brown, S. Black, O. Pritchard and

J. Whitaker

This section summarises the findings arising out of the litho- and bio-stratigraphical analysis

of samples taken from Littleton Bog, Co. Tipperary, Ireland (Figure 32). At Littleton Bog,

Archaeological Development Services (ADS) Ltd excavated thirteen sites during 2008, with

ages ranging from Late Bronze Age to Early Medieval. These included three trackways

orientated east to west, a smaller brushwood and roundwood trackway, five platform sites, a

large wooden vessel and three sites that had largely been removed by peat harvesting

(Turrell, 2008). Littleton Bog is the largest of the Littleton Group of bogs, with a total area of

1,013 hectares. Located 8km northeast of Littleton Village, Co. Tipperary, Littleton Bog is

located near the centre of the Littleton Group, where two dryland islands within a narrow

neck of bog provide a convenient east-west crossing (Turrell, 2008). The investigation at

Littleton Bog had two main aims: (1) To reconstruct the environmental context of past human

activities; (2) To elucidate the relationship, if any, between structure construction and

abandonment, and climate change.

Figure 32: Location of Littleton Bog, Co. Tipperary (adapted from Turrell, 2008).

The results indicate:

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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1. Based upon the chronological information provided for the trackways and platforms near

borehole , namely 08E0408, 08E0410 and 09E0411, we can perhaps assume that

the upper 2m of peat stratigraphy in borehole is Late Holocene in age (last 3000

years).

2. This is supported by the pollen-stratigraphic studies of Mitchell (1965), which show a

broadly similar composition and structure to the vegetation cover. During this period, the

plant macrofossil analysis has identified four distinct shifts in the composition of the local

vegetation cover. The first (zone L25-1) probably pre-dates the construction of 08E0410

(AD130-420), and represents a fen community dominated by rushes, sedges and

grasses, such as Scheuchzeria and Eriophorum. Zone L25-2, marks the transition to

acidic, ombrotrophic bog, with Sphagnum moss species dominating lawns, pools and

hummocks. The third shift suggests the formation of much wetter surface conditions

(zone L25-3), with extensive pools and standing water, which is also highlighted by a

sustained reduction in peat humification. Finally, during zone L25-4, the plant

macrofossils indicate the dominance of Sphagnum imbricatum and Eriophorum

vaginatum, suggesting drier surface conditions. The precise relationship between these

shifts in bog surface wetness and the construction and abandonment of the various

structures near to borehole remains to be established. Nevertheless, the changes in

plant macrofossil assemblages do indicate that the period of structure use occurred

following the transition from fen to fully developed raised bog conditions.

3. The pollen (borehole ) and insect (trackway 08E0411) analyses support this

interpretation, indicating the presence of Sphagnum dominated bog with acidic pools

containing reeds, duckweed and decaying plant matter prior to, during and following the

use of trackway 08E0411, and possibly the other structures. This suggests that the

trackway sequence may be tentatively correlated with zones L25-2 and L25-3 (plant

macrofossils), and zones LTNBH2-2 and possibly LTNBH2-3 (pollen), of borehole .

During this period, wet woodland, probably growing mainly in the lagg area of the bog, is

indicated by the presence of Alnus, Salix and Betula in both the pollen and insect

assemblages. On dryland, the pollen data indicate that mixed deciduous woodland with

Corylus, Quercus, Ulmus, Fraxinus and Betula (zone LTNBH2-1) declined during zones

LTNBH2-2 and LTNBH2-3, which facilitated the expansion of both grassland and Ericadominated

heathland. This period coincided with a shift to wetter bog surface conditions

recorded in the plant macrofossil data (zones L25-2 and L25-3), which suggests that

there is a correlation between changes in dryland vegetation and changes in the

hydrology and vegetation cover of the bog surface.

4. Borehole , which is distal to trackway 08E0399 (dated to c. 2995 cal yrs BP), has

provided a detailed record of the local vegetation cover during the Late Devensian

Lateglacial and Holocene based upon the plant macrofossil assemblages. The full

stratigraphic sequence will not be discussed here because only the top 70cm (zone L01-

6) is relevant to the study of trackway 08E0399. The plant macrofossils indicate a bog

surface dominated by species of Sphagnum, creating abundant low lawns and pools.

This record is confirmed by the humification values (Figure 5), which indicate generally

lower levels of humification suggesting an increase in bog surface wetness. Based upon

previous pollen-stratigraphic work at Littleton Bog (Mitchell, 1965), the Late Bronze Age

and Early Iron Age was characterised by open mixed deciduous woodland dominated by

Corylus, with Betula, Quercus, Ulmus and Fraxinus. However, there is clear evidence

that the extent of the woodland was reduced by comparison with earlier periods, and that

grassland (either pasture or meadowland) formed a major component of the community

structure.

5. During the Holocene, several distinct shifts to drier bog surface conditions have been

recorded in Ireland by the presence of macrofossils of oak and pine within raised peat

bogs (Turney et al., 2006). These occur at 800, 1700, 2650, 3200, 4100, 5000, 5600,

6200-7300, 8000 and 9000 cal yrs BP, and are believed to reflect periods of climate

change. Between these drier shifts, bog surfaces would have been wetter and it is during

these periods that structures in many wetlands across Ireland apparently become

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Project Number 16718

common. Based upon the bog oak and pine records, trackway 08E0410, constructed

between AD130-420 (c. 1580-1870 cal yrs BP), seemingly spans the transition from a

period of drier to wetter climatic conditions. Indeed the palaeoecological evidence

presented here for increasing bog surface wetness may provide support for this

interpretation.

6. Therefore, if the remaining structures in this part of Littleton Bog, namely 08E0408 and

08E0411, are of a broadly similar age, then it may suggest that construction and

abandonment occurred during a period of climatic change. However, due to the poor

chronological control that currently exists it remains unclear whether climate change was

the main forcing factor behind structure construction and abandonment, and whether this

stimulated the human activities noted in the proxy records. Indeed, given the outstanding

palaeoecological evidence for woodland clearance, cereal cultivation and possible

pastoral farming over a prolonged period, it seems entirely plausible that the construction

of the structures occurred at a time when there was simply ongoing or possibly increasing

use of both the wetland and dryland during the Late Iron Age and Dark Ages.

7. Both the plant macrofossil (borehole ) and pollen records (Mitchell, 1965) for the Late

Bronze Age and Early Iron Age from Littleton Bog indicate that construction and

abandonment was occurring during a period of increased bog surface wetness,

deforestation and cereal cultivation. The records of Turney et al. (2006) support this,

indicating a period of climatic deterioration during the Late Bronze Age followed by a drier

phase centred on 2650 cal yrs BP. This suggests that the trackway construction was

possibly initiated by climate change to wetter conditions, which coincided with a period of

intensive human activity on the dryland, probably as a response to the worsening climatic

conditions.

8. There has been no documented mining activity within Ireland during the periods identified

above (Schettler and Romer, 2006), suggesting that the Lead peaks identified in this

study are probably sourced from a wider geographical area, with the largest peaks

probably originating from Roman mining within the British Isles or Continental Europe,

which corresponds to the late Iron Age in Ireland. These results show that the application

of rapid ICP-MS Lead analysis to Irish peat sequences serve as an invaluable resource

into understanding both the transportation of pollutants within our atmosphere and as an

important chronological marker.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.

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Figure 33: Organic matter content, Littleton Bog, Co. Tipperary, borehole .

Figure 34: Stratigraphy and organic matter content, borehole , Littleton Bog, Co.

Tipperary.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship 39

between Human Activities and Climate Change in the Wetlands of Ireland: Final Technical Report.

Irish Heritage Council INSTAR Thematic programme.


Project Number 16718

Figure 35: Plant macrofossil diagram for Littleton Bog borehole (8cm resolution, top 2.00m) showing peat stratigraphy and %

humification data.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Project Number 16718

Figure 36: Plant macrofossil diagram for Littleton Bog borehole (8cm resolution) showing peat stratigraphy and % humification

data.

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 37: Pollen diagram from Littleton Bog borehole (0.00-0.45m 4cm resolution; 0.45-2.00m 8cm resolution).

Format for referencing: Branch, N.P. and Matthews, I. (eds.) (2009) Examining the Relationship between Human Activities and Climate Change in the

Wetlands of Ireland: Final Technical Report. Irish Heritage Council INSTAR Thematic programme.

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Figure 38: 208 Pb and 206 Pb/ 207 Pb ratio from Littleton Bog, borehole , Littleton Bog, C.

Tipperary.

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CONCLUDING COMMENTS

1. Kinnegad Bog

a. The results of the palaeoenvironmental analysis indicates that dry conditions

persisted on the bog surface prior to and during the use of trackway 07E0501

(ME-KND0016), trackway 07E0496 (ME-KND001), platform 07E0499 (ME-

KND011) and trackway 07E0497 (ME-KND002). Bog surface conditions became

much wetter at c. 3170 cal yrs BP and persisting for at least 500 years. The shift

to wet bog surface conditions is thought to be a response to increased climatic

wetness, which affected raised and blanket bogs across NW Europe (Chambers,

1987; Hughes et al., 2000; Barber et al., 2003; Caseldine and Gearey, 2005;

Plunkett, 2006).

2. Ballykean Bog

a. The palaeoenvironmental data indicates that during the period of occupation the

peat surface was probably a mosaic of open pools and dry hummocks. The timing

of occupation (1270 ±100 cal yrs BP and 1395 ±125 cal yrs BP) coincides with a

major climatic change to wetter conditions, which may be reflected in the pool,

Scheuchzeria and Sphagnum-rich surface vegetation cover. The pollen and insect

records also indicate a decline in the woodland cover during this time,

accompanied by a strong anthropogenic signal for arable and pastoral activities. It

is suggested here that these human activities may have been a response to

climatic deterioration, which involved the need to exploit a wider range of natural

ecosystems.

3. Gilltown Bog

a. The dating evidence provided for trackway 07E0632 combined with the

palaeoenvironmental records suggests that the sequences in boreholes and

date from the late Middle Holocene. Trackway construction occurred during

a period of much wetter conditions on the bog surface, which are believed to have

been caused by localised factors, in particular human activities on nearby dryland.

This is no evidence from Gilltown Bog to suggest that climate change initiated

trackway construction or abandonment, although it is possible that construction

occurred during a period of drier climatic conditions (see Turney et al., 2006).

4. Lullymore East Bog

a. The palaeoenvironmental analysis of trackways KD-LYE001 (AD 330-660) and

KD-LYE002 (AD 900-1160) has revealed that during the Late Iron Age/Early

Medieval period, trackway KD-LYE001 may have been abandoned during a

period of climatic deterioration to wetter conditions, whilst trackway KD-LYE002

may have been constructed during a period of climatic amelioration. During this

time, there is unequivocal evidence for human impact on the surrounding

environment, which included cereal cultivation and animal husbandry.

5. Ballybeg Bog

a. The dating evidence provided for the archaeological structures combined with the

palaeoenvironmental records suggest that the sequence in borehole dates

from the late Middle Holocene. The records have provided an interesting

reconstruction of the transition from fen to bog conditions, and the corresponding

changes in surface wetness and vegetation. However, it remains unclear how

these changes relate to the timing of togher construction, especially for toghers

08E0397 (TN-BLG0016; 3700 ±130 BP) and 08E0396 (TN-BLG009a-b; 3485

±155 BP). For togher 08E0394 it is tempting to suggest that construction occurred

during a period of sustained climatic deterioration after 3000 BP, which

corresponds to the development of fully ombrotrophic conditions at Ballybeg Beg

and a decline in dryland woodland cover.

6. Littleton Bog

a. The plant macrofossil (borehole ), pollen (borehole ) and insect (trackway

08E0411) analyses have provided a record of environmental change during the

Late Holocene. The records indicate the presence of a Sphagnum dominated bog

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with acidic pools containing reeds, duckweed and decaying plant matter prior to,

during and following the use of trackway 08E0411, and possibly the other

structures (trackway 08E0410 has been dated to AD130-420). During the period

of trackway use, the dryland vegetation, comprising mixed deciduous woodland,

declined, which resulted in the expansion of both grassland and Erica-dominated

heathland. This also coincided with a sustained period of cereal cultivation on the

dryland and increased bog surface wetness. It remains unclear whether the

construction and abandonment of the structures was triggered by climate change

to wetter conditions, or simply formed part of ongoing human activities on the

dryland and wetland at Littleton Bog during the Late Holocene.

b. The plant macrofossil (borehole ) and pollen records distal to trackway

08E0399 (dated to c. 2995 cal yrs BP), indicate a bog surface dominated by

species of Sphagnum, creating abundant low lawns and pools, and with the

dryland vegetation dominated by Corylus, with Betula, Quercus, Ulmus and

Fraxinus. There is unequivocal evidence for cereal cultivation and grassland

expansion, suggesting that human activities were widespread on both the dryland

and wetland. Trackway construction occurred during a period of climate change to

wetter conditions, which is possibly reflected in the plant macrofossil records from

borehole . This event coincided with a period of intensive human activity on

the dryland, probably as a response to the worsening climatic conditions.

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BIBLIOGRAPHY

This includes all literature consulted for PART A of the report; please note that only selected

references appear in the text.

Alexander, K.N.A. (1994) An Annotated Checklist of British Lignicolous & Saproxylic

Invertebrates. National Trust Estates Advisors' Office, Cirencester (Draft).

Andrus, R. E., Wagner, D. J., and Titus, J. E. (1983) Vertical zonation of Sphagnum mosses

along hummock-hollow gradients. Canadian Journal of Botany 61, 3128–3139.

Atty, D.B. (1983) Coleoptera of Gloucestershire. Cheltenham.

Barber, K.E. (1981) Peat stratigraphy and climatic change: a palaeoecological test of the

theory of cyclic peat bog regeneration. Balkema, Rotterdam.

Barber, K.E., Chambers, F.M. and Maddy, D. (2003) Holocene palaeoclimates from peat

stratigraphy: macrofossil proxy climate records from three oceanic raised bogs in England

and Ireland. Quaternary Science Reviews 22, 521-539.

Bengtsson, L. and Enell, M. (1986) Chemical analysis, In (B.E. Berglund ed.) Handbook of

Holocene Palaeoclimatology and Palaeohydrology, 423-454. Cichester: Wiley.

Berggren, G. (1969) Atlas of Seeds Part 2: Cyperaceae. Swedish Natural Science Research

Council, Stockholm.

Berggren, G. (1981) Atlas of Seeds Part 3: Salicaceae-Cruciferae. Swedish Natural Science

Research Council, Stockholm.

Bilton, D.T. (1988) A survey of aquatic Coleoptera in central Ireland and the Burren. Bulletin

of the Irish Biogeographical Society, 11, 77-94.

Blackford, J.J. (1990) Blanket mires and climatic change: a palaeoecological study based on

peat humification and macrofossil analyses. Unpublished Ph.D. Thesis, Keele University.

Boatman, D.J. (1983) The Silver Flowe National Nature Reserve, Galloway, Scotland.

Journal of Biogeography 10, 163–274.

Buckland P.I. & Buckland P.C. (2006) Bugs Coleopteran Ecology Package, (Versions:

BugsCEP v7.63; Bugsdata v7.11; BugsMCR v2.02; BugStats v1.22), [Downloaded Nov

2007] www.bugscep.com.

Brundin, L. (1934). Die Coleopteren des Tornetraskgebietes. Ein Beitrag zur Okologie und

Geschichte der Kaferwelt in Schwedisch-Lappland. Lund.

Campbell, J. M. (1982) A revision of the North American Omaliinae (Coleoptera:

Staphylinidae). 3. The genus Acidota Stephens. Canadian Entomologist, 114, 1003-1029.

Caseldine, C.J. and Gearey, B.R. (2005) Evaluation of a multi-proxy approach to

reconstructing surface wetness changes in a complex raised mire system at Derryville bog,

Co. Tipperary, Ireland: identification of responses to a series of prehistoric bog bursts. The

Holocene 15, 4.

Caseldine, C.J., Baker, A., Charman, D.J. and Hendon, D. (2000) A comparative study of

optical properties of NaOH peat extracts: implications for humification studies. The Holocene

10, 649-658.

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Caseldine, C. and Gearey, B. (2005) A multiproxy approach to reconstructing surface

wetness changes and prehistoric bog bursts in a raised mire system at Derryville Bog, Co.

Tipperary, Ireland. The Holocene 15, 585-601.

Chambers, F.M. and Charman, D.J. (2004) Holocene environmental change: contributions

from the peatland archive. The Holocene 14, 1-6.

Corcoran, E. (2008) Archaeological Excavations Gilltown Bog, Derryarogue and Gilltown

Townlands, Co. Kildare. Archaeological Development Services Ltd., Dublin.

Corcoran, E. (2008) Archaeological Excavations, Lullymore East Bog and Lullymore East

Townland, Co. Kildare.. Archaeological Development Services Ltd., Dublin.

Clymo, R.S. (1984) The limits to peat bog growth. Philosophical Transactions of the Royal

Society of London B 303, 605-654.

Clymo, R.S. (1991) Peat growth. In: Shane, L.C.K., Cushing, E.J. (Eds.), Quaternary

Landscapes. Belhaven Press, London: 76–112.

Davis, L.R. (1980) Notes on beetle distributions, with a discussion of Nicrophorus

americanus Olivier and its abundance in collections (Coleoptera: Scarabaeidae, Lampyridae,

and Silphidae). Coleopterists Bulletin, 34, 245-251.

Donisthorpe, H.St.J.K. (1939) A Preliminary list of the Coleoptera of Windsor Forest. Lloyd &

Co., London.

Duff, A.G. (1993). Carcinops pumilo (Erichson) (Histeridae), an uninvited dinner guest.

Coleopterist, 2, 80-81.

Elias, S.A. (1994) Quaternary Insects and their Environments. Smithsonian.

Friday, L.E. (1988) A key to the adults of British water beetles. Field Studies 7, 1-151.

Flatberg, I. (1986) Taxonomy, morphovariation, distribution and ecology of the Sphagnum

imbricatum complex with main reference to Norway. Gunneria 54, 1–118.

Godwin, H. (1975) History of the British Flora. A Factual Basis for Phytogeography. Second

edition. Cambridge University Press, Cambridge.

Gore, A.J.P., and Urquhart, C. (1966) The effects of waterlogging on the growth of Molinia

caerulea and Eriophorum vaginatum. Journal of Ecology 54, 617–633.

Green, B.H. (1968) Factors influencing the spatial and temporal distribution of Sphagnum

imbricatum Hornsch ex. Russ in the British Isles. Journal of Ecology 56, 47-58.

Handl.(6) B, 4. Goteborg. (reprinted as English translation (1992) Intercept, Andover.

Harde, K.W. (1984) A Field Guide in Colour to Beetles. Octopus, London.

Haslam, S.M. (1972) Biological Flora of the British Isles: Phragmites communis Trin. (Arundo

phragmites L., ? Phragmites australis (Cav.) Trin. Ex Steudel). Journal of Ecology 60, 585-

610.

Hewett, D.G. (1964) Menyanthes trifoliata L. Journal of Ecology 52, 723-735.

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Horion, A. (1953) Faunistik der Mitteleuropäischen Käfer, 3. Malacodermata, Sternoxia

(Elateridae - Throscidae). G. Frey, Munich.

Hughes, P.D.M., Mauquoy, D., Barber, K.E. and Langdon, P.G. (2000) Mire-development

pathways and palaeoclimatic records from a full Holocene peat archive at Walton Moss,

Cumbria, England. The Holocene 10, 465-479.

Hughes, P. D. M., and Barber, K. E. (2004) Contrasting pathways to ombrotrophy in three

raised bogs from Ireland and Cumbria, England. The Holocene 14, 65–77.

Hill, M.O. (1976) A key for the identification of British Sphagna using macroscopic

characters. Journal of the British Bryological Society 27, 22-31

Hill, M.O., Hodgetts, N.G. and Payne A.G. (1992) Sphagnum: A Field Guide. The UK Joint

Nature Conservation Committee, Peterborough.

Hyman, P.S. (1992) A review of the scarce and threatened Coleoptera of Great Britain, Part

1 (Revised & updated by M.S.Parsons). UK Joint Nature Conservation Committee,

Peterborough.

Janssens, J.A. (1992). Development of a raised bog complex. In The Patterned Peatlands of

Minnesota (H. E. Wright, B. A. Coffin and N. E. Aaseng, Eds.), pp. 189–221. University of

Minnesota Press, Minneapolis.

Jessop, L. (1986) Coleoptera: Scarabaeidae. Handbooks for the Identification of British

Insects 5,11. Royal Entomological Society of London.

Jones, F.G.W. & Jones, M.G. (1974). Pests of Field Crops (2nd ed.). Arnold, London.

Kenward, H.K., Hall, A.R., Jones, A.K.G (1980) A tested set of techniques for the extraction

of plants and animal macrofossils from waterlogged archaeological deposits, Science and

Archaeology, 22, 3-15.

Kilian, M.R., van Geel, B., and Van der Plicht, J. (2000) 14 C AMS wiggle matching of raised

bog deposits and models of peat accumulation. Quaternary Science Reviews 19, 1011–

1033.

Koch, K. (1989) Die Käfer Mitteleuropas. Ökologie, 1. Goecke & Evers, Krefeld.

Koch, K. (1992) Die Käfer Mitteleuropas. Ökologie 3. Goecke & Evers, Krefeld.

Lindroth, C.H. (1945) Die Fennoskandischen Carabidae I-II. Goteborgs K. Vetensk. o

VitterhSamh.

Luff, M.L. (1998) Provisional atlas of the ground beetles (Coleoptera, Carabidae) of Britain.

Centre for Ecology & Hydrology, Biological Records Centre, Abbots Ripton.

Mauquoy, D., and Barber, K.E. (1999) Evidence for climatic deteriorations associated with

the decline of Sphagnum imbricatum Hornsch. Ex Russ. in six ombrotrophic mires from

Northern England and the Scottish Borders. The Holocene 9, 423–437.

Mauquoy, D. and van Geel, B. (2007) Mire and peat macros. In: Elias, S. (Ed.)

Encyclopaedia of Quaternary Science, Volume 3. Elsevier, Amsterdam.

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Met Office (2007) Summer 2007 Summary (Viewed 30/1/09) www.metoffice.gov.uk/weather/

seasonal/summer2007

McMullen, J.A., Barber, K.E. and Johnson, B. (2004) A palaeoecological perspective of

vegetation succession on raised bog microforms. Ecological Monographs 74, 45-77.

Moore, J.J. (1955) The distribution and ecology of Scheuchzeria palustris on a raised bog in

Offaly. The Irish Naturalists’ Journal 12, 321–329.

Morris, M.G. (1997). Broad-Nosed Weevils. Coleoptera : Curculionidae (Entiminae)

Handbooks for the Identification of British Insects, 5, part 17a. Royal Entomological Society,

London.

Moore, P.D., Webb, J.A. and Collinson, M.E. (1991) Pollen Analysis, 2 nd Edition, Blackwell

Scientific Publication, London.

Økland, R.H. (1990) A phytoecological study of the mire Northern Kisselbergmosen, SE

Norway. III. Diversity and habitat niche relationships. Nordic Journal of Botany 10, 191–220.

Palm, T. (1959) Die Holz und Rindenkäfer der sud- und mittelschwedischen Laubbaume.

Opuscula Entomologica Suppl. 16.

Reille, M. (1992) Pollen et Spores d’Europe et d’Afrique du Nord, Laboratoire de Botanique

Historique et Palynologie, Marseille.

Rodwell, J.S. (Ed.) (1991) British Plant Communities. Vol. 2. Mires and Heaths. Cambridge

University Press, Cambridge.

Rohan, N. (2008) Report on Archaeological Excavations in Knockersally and Moydrum or

Bogstown townlands: Kinnnegad Bog, Co. Meath. Archaeological Development Services

Ltd., Dublin.

Rohan, N. (2008) Report on Archaeological Excavations in Ballybeg Townland, Ballybeg

Bog, Co. Tipperary. Archaeological Development Services Ltd., Dublin.

Schettler, G. and Romer, R.L. 2006 Atmospheric Pb-pollution by pre-medieval mining

detected in the sediments of the brackish karst lake An Loch Mor, western Ireland. Applied

Geochemistry 21, 58-82.

Skidmore, P. (1991) Insects of the British Cow-Dung Community. Field Studies Council.

Stace, C. (1997) New Flora of the British Isles, Cambridge University Press, Cambridge.

Tallis, J.H., and Birks, H.J.B. (1965). The past and present distribution of Scheuchzeria

palustris L. in Europe. Journal of Ecology 53, 287–298.

Turrell, S. (2008) Preliminary Report on Archaeological Excavations at Ballintemple

Townland, Ballykean Bog 2007. Archaeological Development Services Ltd., Dublin.

Turrell, S. (2008) Excavations in Littleton Bog, Co. Tipperary. Archaeological Development

Services Ltd., Dublin.

Troels-Smith, J. (1955) Karakterisering af løse jordater (Characterisation of unconsolidated

sediments), Danm. Geol. Unders., Ser IV 3, 73.

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Turney, C.S.M., Baillie, M., Palmer, J. and Brown, D. (2006) Holocene climatic change and

past Irish societal response. Journal of Archaeological Science 33, 34-38.

van der Molen, P.C. and Hoekstra, S.P. (1988) A palaeoecological study of the hummockhollow

complex from Engbertsdyksueen in the Netherlands. Review of Palaeobotany and

Palynology 56, 213–274.

van der Molen, P.C., Schalkoort, M., and Smit, R. (1994) Vegetation and ecology of

hummock-hollow complexes on an Irish raised bog. Biology and Environment: Proceedings

of the Royal Irish Academy 94B, 145–175.

Wein, R.W. (1973) Biological Flora of The British Isles: Eriophorum Vaginatum L. Journal of

Ecology 61, 601-615.

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PART B: CHRONOLOGY

I. Matthews and colleagues at Royal Holloway

1 Chronology

1.1 Archaeological chronology

Four of the six bogs have existing information about the archaeological chronology at each

site in the form of radiocarbon and dendrochronological dates obtained on the structures

excavated (trackways, platforms and worked wood). The dates were undertaken as part of

the ADS Ltd survey of the sites in 2005 (for details see Whitaker, 2006), apart from Ballykean

Bog where the dates were generated during the IAWU survey in 2003 (IAWU, 2003), and the

dates for Lullymore East which are from (Whitaker, 2004). The existing chronological

information is summarised in Table 2 and Figure 39.

Table 2: Radiocarbon and Dendrochronological Dates from Kinnegad bog (Co. Meath),

Gilltown and Lullymore East bogs (Co. Kildare), and Ballykean bog (Co. Offaly). All

dates were processed in OxCal v4. using the INTCAL 04 calibration curve (Reimer et

al., 2004; Bronk Ramsey, 2007). Samples identified as ‘R_Date’ refer to calibrated

radiocarbon determinations, while those referred to as ‘C_Date’ are

Dendrochronological dates. Samples OF-KLG0001cc and OF-KLG0001ee lacked the

outer sapwood and are presented as a Terminus Post Quem (TPQ) also termed an

‘after’ event in OxCal v4.


























200 500

These dates show two periods of human activity on the bogs, which can broadly be thought

of as periods of construction; the first occurs in the Bronze Age beginning between ca. 3700-

3500 cal yr BP (1750-1500 BC) and ending ca. 3000-2700 cal yr BP (1050-800BC), while the

second occurs over a broad timescale in the Early Christian and Medieval periods ca. 1750-

1000 cal. yr BP (AD 200-950).

These two construction periods occur during several shifts in hydrological conditions as

suggested by Charman et al. (2006) (Figure 41). The Charman et al. (2006) record is based

on stacked reconstructions of water table depths using testate amoebae for twelve records in

Northern Britain. It recognises major shifts to wetter conditions at 3600, 2760, and 1600 cal

yr BP, with more minor ‘wet shifts’ recognised at 3060, 2050, 1260, 860, and 260 cal yr BP,

these periods are consistent with similar hydrological shifts identified in other records (Barber

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et al., 2003; Borgmark, 2005). The first two major shifts occur at the start and end of the

Bronze Age construction period, while the last major wet shift is coincident with the later

Early Christian and Medieval construction periods. These shifts are thought to be coincident

with changes in lake levels across mid-latitude Europe (Magny, 2004) and may be driven by

solar variability, a mechanism of environmental change suggested by other peatland records

(Chambers and Blackford, 2001; Blundell et al., 2008) although others have suggested that

solar forcing is not directly linked to climatic variability (Turney et al., 2005; Swindles et al.,

2007). These shifts in regional climate records are coincident with the archaeological

structures identified in the four bogs, but this does not mean that the structures were

constructed as a response to environmental changes. This broad-scale chronological

approach does not integrate the archaeological and environmental chronologies and makes

no attempt to consider the potential spatial variations in climate between northern Britain and

Ireland, in fact it is little better than wiggle-matching broad time zones to environmental

events and indeed the earlier Bronze Age construction period could have occurred in wet

conditions, dry conditions, or in a transitional phase between wet to dry or dry to wet

conditions. In fact, it may have occurred across all or none of these events as it is only

comparing to a regional record and does not integrate the local hydrological conditions. The

stacked record approach used by Charman et al. (2006) minimises local hydrological

influences in order to generate a smoothed regional climatic signal; however local

hydrological influences may have paid a crucial role in timing of the construction of trackways

and may be largely autogenic processes removed from wider climatic signals.

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Figure 39. Calibrated radiocarbon and dendrochronological dates for

archaeological structures identified at four raised bog sites, presented

alongside two regional climate records. The grey bars represent periods of

construction, one focused on the Bronze Age, and the second on the Early

Christian and Medieval periods. OF-KLG001cc+ee represent limiting age

dendrochronological information and so are presented as an ‘after’ function.

All dates were calibrated using the INTCAL04 calibration curve (Reimer et al.,

2004) in OxCal v4. (Bronk Ramsey, 2007). Construction in both periods

appears to span several shifts between wet and dry conditions as represented

in the stacked testate amoebae record (b.).

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In order to resolve this the most refined archaeological chronologies are required in order to

integrate with firstly local and subsequently regional climate records. The next section will

refine site-specific archaeological chronologies using Bayesian statistical models; this will

facilitate the definition of statistically meaningful phases of trackway construction allowing the

beginning and end of each phase to be delimited.

1.1.1. Site-specific chronologies

The archaeological chronology of each site was firstly defined into two groups: 1) Bronze

Age activity (BA), and 2) Early Christian and Medieval activity (EC+M). The best-dated sites

were Kinnegad Bog and Ballykean Bog with only minimal information from Gilltown Bog and

Lullymore East Bog. Kinnegad Bog contained dated archaeology from both phases but had

more dated archaeology in the Bronze Age period, while Ballykean Bog exclusively

contained dated archaeology from the Bronze Age period. Gilltown Bog had single dates

from the BA and from the EC+M while Lullymore East Bog only contained dated sites from

the EC+M period. Lullymore East Bog, Gilltown Bog, and the EC+M part of the Kinnegad

Bog archaeology contain too little chronological information to refine the beginning and end

of construction activity and must be considered provisional age rangefinder information for

subsequent evaluation. Further dendrochronological and radiocarbon information is being

obtained alongside tephrochronological research at these sites and once this is available

further chronological modelling will be undertaken. The rest of this section considers Bronze

Age activity at Kinnegad Bog and Ballykean Bog.

Kinnegad Bog

Six radiocarbon determinations and one dendrochronological age have been collected for the

Bronze Age structures at Kinnegad Bog. Two of these dates relate to longitudinal plank

trackways (ME-KND001B and ME-KND002), while the rest of the dates reflect radiocarbon

determinations on brushwood and roundwood structures provisionally interpreted as

platforms. Several uncertainties still exist regarding the phasing of events at this site. Firstly,

the two plank trackways are on very similar alignments and may actually reflect a single

structure, this cannot be easily tested as the trackways are separated by a wooded area and

can not be directly linked to one another. Secondly, the platform structures are clustered

around ME-KND001 and may be concurrent with the construction of the trackway or may

post-date it being constructed after the trackways made this area of the bog accessible. The

unknown nature of the phasing of archaeological structures means that two alternative

chronologies can be suggested: 1) the sampled structures are not related to one another but

occurred at approximately the same time, or 2) the trackway/s were constructed first and this

was immediately followed by construction of the platform structures. Both of these theories

can be modelled using functions available in OxCal v4.

In the first scenario, all dates are treated equally and modelled using a ‘Phase’, this

command assumes that the dates are associated to each other but makes no assumptions

on the ordering of the dates (Bronk Ramsey, 1995, 2001, 2007). This process allows the

beginning and end of the phase of activity to be defined by boundaries calculated to 95.4%

confidence intervals; the minimum and maximum span of the dated events can also be

calculated. If the single Phase approach is used on the dated material at Kinnegad Bog it

suggests that the construction of the archaeological structures began between 3840-3502 cal

yr BP (1891-1553 BC) and concluded between 3319-2767 cal yr BP (1370-818 BC) (Table 3

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and Figure 40-41). The minimum length of the construction span is 198 years with the

maximum construction span of 618 years (Figure 41).

Table 3: OxCal v4. Single phase output for Kinnegad Bog’s Bronze Age archaeology

(scenario one in text). Rows in red text highlight the start and end ranges for the

construction phase while the phase span is presented in blue text. Dates were

calibrated as before, see text for the model specifications.






















Figure 40: Single Phase model for Bronze Age human activity at Kinnegad Bog, Co.

Meath (See text for details).

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Figure 41: Start and end date envelopes for Bronze Age construction based on a

single phase model compared to the stacked testate ameobae record of Charman et

al., (2006). The green bar represents the 95.4% confidence interval for the beginning

of construction, while the red bar indicates the envelope for the end of the Bronze Age

construction phase. Construction must have continued for a minimum of 198 years.

The second scenario requires a more sophisticated model that utilises two phases which are

considered sequential i.e. the second phase can only occur when the first phase has finished

although not necessarily instantly after the first phase. The first phase contains the trackway

dates from ME-KND001 and ME-KND002, while the second phase contains the platform

dates. With the model set-up in this manner, the platforms can only have been constructed

after the completion of the trackway/s. Table 4 presents the results of this model which

suggests that trackways construction took place between 3722-3498 cal yr BP and 3536-

3421 cal yr BP (1772-1548 and 1586-1471 BC), with platform construction beginning

between 3517-3341 cal yr BP (1567-1391 BC) and ending between 3352-2891 cal yr BP

(1402-941 BC). The span of the trackway phase is 0-86 years which further shows the

proximity in the age of the two structures. The span of the phase of construction of the

platform structures is 0-417 years which may indicate they were either constructed

simultaneously or over several centuries. The total envelope for Bronze Age Human activity

at Kinnegad bog using this model is between 3722-3498 cal yr BP (1772-1548 BC) and

3352-2891 cal yr BP (1402-941 BC), with a span of events between 178-738 years modelled

at 95.2% confidence with a 0.2% chance that the span is less than 156 years.

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Table 4: OxCal v4. Multiple phase output for Kinnegad Bog’s Bronze Age archaeology

(scenario two in text). Rows in red text highlight the start and end ranges for the

construction phase while the phase span is presented in blue text. Dates were

calibrated as in scenario 1, see text for the model specifications.




























If the age ranges presented by these two scenarios are compared to the regional climate

dataset presented by Charman et al. (2006) it is clear that in scenario one Bronze Age

construction could have begun across any hydrological conditions or transition (Figure 43),

while it concluded across variable hydrological conditions across a background of longer

term shift to wetter conditions. In scenario two, trackway construction occurs over an

envelope covering hydrological shifts from relatively dry to wetter conditions and back to drier

conditions this phase is centred on the wetter conditions recognised by Charman et al.

(2006) at ca. 3600 cal yr BP. Platform construction commenced against a climatic signal that

suggests increasingly drier hydrological conditions and concluded either in drier conditions or

across variable hydrological conditions across a background of longer-term shift to wetter

conditions.

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Figure 43: Two phase model of Bronze Age archaeology at Kinnegad Bog Co. Meath.

Phase one represents trackway construction, while phase two indicates construction

of platforms around the trackways (see text for details).

An age modelling approach using phases is more sophisticated than just looking at the entire

chronological dataset; however, this approach still does not attempt to integrate local

hydrological evidence with the proposed regional climate record, or does not attempt to

quantify the period of use of trackways or platforms. It is clear that in both scenarios

construction continues for at least 178 years (198 years minimum in scenario one)

suggesting an extended period of human activity in Kinnegad Bog. To fix this period into the

local and environmental records radiocarbon dating of the peat sequences collected and

tephrochronological assessments have been undertaken and are ongoing (see below).

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Figure 44: Start and end date envelopes for Bronze Age construction based on a two

phase model compared to the stacked testate amoebae record of Charman et al.

(2006). The first green bar represents the 95.4% confidence interval for the beginning

of trackway construction, while the first red bar indicates the envelope for the end of

the Bronze Age trackway construction phase. The second green and red bars

represent the envelope for platform construction. In this model, total construction

must have continued for a minimum of 178 years (see text for details).

Ballykean Bog

Bronze Age archaeology at Ballykean Bog consisted of primary trackways (OF-KLG001 and

OF-KLG002) that were thought to run between areas of relatively dry ground (Whitaker and

Turrell, 2004). Three dendrochronological dates are available for OF-KLG001 and a single

dendrochronological dates is available for OF-KLG002; these dates were obtained by the

IAWU during the original site survey and are currently being supplemented by further

radiocarbon and dendrochronological dates undertaken by ADS Ltd (IAWU, 2003; Whitaker

and Turrell, 2004). The Iron Age/Early Christian habitation site has been radiocarbon dated

to ca. AD200-500. The current chronological information available for OF-KLG001 can be

deconstructed into one dendrochronological age determination with incomplete sapwood that

dates to 1454±9 BC, while the other two dendrochronological dates had no sapwood

available for measurement and were dated to 1600±9 and 1589±9 BC or later. These last

two determination are effectively terminus post quem (TPQ) dates and may well have been

felled at the same time or after the apparently younger first date of 1454±9 BC, these earlier

dates form a ‘phantom’ period of construction activity and cannot be used to attempt to

understand the period of use of the trackway (Baillie, 1995). OF-KLG002 was dated to

1425±9 BC and may be contemporaneous with OF-KLG001.

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These dates were further analysed using the OxCal v4. ‘Phase’ function. In this case

because several dates were available for OF-KLG001 two phases were nested within one

another. The first phase (OF-KLG001) used the dates with no sapwood as TPQ limiting

ages (After function in OxCal v4.). This phase suggests an envelope of construction for OF-

KLG001 of 3483-3318 cal yr BP (1534-1369 BC), while the overall timing of the Bronze Age

activity at Ballykean covers the intervals 3587-3202 cal yr BP (1638-1253 BC) at 95.4%

confidence intervals. The two trackways at Ballykean bog could have been

contemporaneous but the difference in trackways based around the ‘span’ of events could

have been as great as 140 years (Figure 45).

Figure 45: Nested phase model for Bronze Age activity at Ballykean Bog Co. Offaly

(see text for details).

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Table 5: OxCal v4. Phase output for Ballykean Bog’s Bronze Age archaeology. Rows

in red text highlight the start and end ranges for the construction phase while the

phase span is presented in blue text. Dates were calibrated as before, see text for the

model specifications.























If this is compared to the climate records it becomes clear that the two trackways at

Ballykean Bog were constructed after the wet climatic conditions at 3600 cal yr BP, with the

beginning of the construction phase occurring during either a shift to drier conditions, or

during dry conditions centred on 3400 cal yr BP. Trackway construction was concluded

either in this dry period or during the subsequent return to wetter conditions. The lack of

precision of the timing of the construction of the trackways is mostly down to the nature of the

dates, while dendrochronological dates are very precise only two separate structures have

been dated in this phase and the separation of the two trackways is difficult to understand,

hence broad age ranges of construction. Further stratigraphic and chronological

investigations are currently underway alongside the generation of site-specific hydrological

proxy records; this information will allow the refinement of the sequencing of the

archaeological and environmental events (Table 5).

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Figure 46: Start and end date envelopes for Bronze Age construction based on a

nested two phase model compared to the stacked testate amoebae record of Charman

et al. (2006). The first green bar represents the 95.4% confidence interval for the

beginning Bronze Age construction, while the second green bar represents the

beginning envelope for the construction of OF-KLG001. The first red bar represents

the end of the construction phase of OF-KLG001 while the second red bar the

envelope for the end of the Bronze Age construction phase. In this model total

construction could have taken place simultaneously with a very short period of

construction (in as little time as a single year); the maximum period of Bronze Age

activity at Ballykean Bog is 140 years, centred on the drier period of climate centred

on 3400 cal yr BP.

1.1.2. Integrating archaeological and environmental chronologies

Age-depth models for peat sequences have been constructed in a variety of ways, including

linear and polynomial regression lines through dates (Barber et al., 2003), wiggle-match

radiocarbon dating (Davies et al., 2005), and Bayesian approaches (Blockley et al., 2004).

When dealing with relatively short peat sequences linear accumulation of sediment is often

assumed, this is a gross simplification as peat growth is often complex being related to

specific position of a bog water-table and the variable growth rates between hummock and

hollow systems. In peat sequences that contain archaeological features must be considered

to have non-linear sedimentation as human activities can significantly affect the hydrological

profile of a bog. Similarly, bogs often have evidence of modern and palaeo peat cutting, and

this may remove whole sections of peat. This introduces additional concerns over linear

sedimentation and hence approaches to age-models that require this prerequisite (linear

regression, wiggle-match 14 C dating) were avoided. Consequently, environmental agemodels

were constructed using the principles suggested in Blockley et al. (2007), where

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initially the dates available were explored using an unconstrained Bayesian approach,

namely the ‘Sequence’ function in OxCal v4. This model makes no assumptions regarding

sedimentation rate, and only relies upon the simple prior assumption of age increasing with

depth. Should any of the dates collected disagree with this assumption then they were

excluded from subsequent analyses. The age-models were then constructed using the

‘P_Sequence’ function in the OxCal program. This approach uses the relative position of a

dated layer to help produce a constrained age-depth model. The model employs a Poisson

depositional principle that allows episodic and variable depositional rates between dated

horizons and constructs realistic age estimates for undated levels. The model provides

overall agreement indices for the constructed age-depth models. If these indices do not total

60% or greater the model was rejected (Bronk-Ramsey, 2007). The ‘P_Sequence’ allows

the age-depth modeller to have a degree of control over the assumed sedimentation rate, by

varying the value of ‘k’. ‘k’ reflects the number of events that occur between dated levels and

reflects the evenness of deposition. A low k value means that sedimentation rates can vary

and is suitable in very variable depositional environments, a higher k value assumes less

extreme variations in sedimentation rate (i.e. closer to linear sedimentation) and is more

appropriate when age-depth modelling fine grained sediments like peats (Blockley pers.

comm.). Appropriate k values can further constrain undated levels but must be based on

sound sedimentological knowledge; and hence during this research sequences that

displayed little lithostratigraphical variation were modelled using high k values. Where

lithostratigraphy or other evidence suggest that sedimentation rates may have been variable,

boundaries were added to the sequence at the identified change in the rate of deposition, the

use of boundaries is discussed more fully in Blockley et al. (2004).

Kinnegad Bog

Four radiocarbon dates were obtained from core BH3B from Kinnegad bog (Table 6).

Samples were dated using Accelerator Mass Spectrometry (AMS) of 1cm deep core sections

at the Beta Analytic inc. Laboratory, Miami. The resultant age estimates have been

calibrated with OxCal v4. using the INTCAL04 calibration dataset (Reimer et al., 2004; Bronk

Ramsey, 2007). All radiocarbon dates referred to in the text are given as calibrated years

before present (cal yr BP) with their 2 calibrated ranges.

The four samples for radiocarbon dating were obtained from levels estimated to correlate to

the level of trackway ME-KND001, and which showed significant variations in hydrology

indicated by minimum or maximum values in the humification graph.

Table 6: Radiocarbon dates with associated calibrated age ranges from core BH3B

Kinnegad Bog, Co. Meath.









The calibrated ranges of these dates suggest that a reversal is present in sequence, with

Beta-233292 apparently too young for the rest of the dates. When modelled as a Sequence

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this data has an agreement index of 49.4 and hence is in poor agreement with the other

dates, however the Sequence overall agreement is 59.5 which when rounded up just falls

within the model acceptance cut-off value of sixty. Consequently, Beta-233292 does not

concur with the other dates a probably should be rejected from subsequent models;

however, the overall agreement index figure is above the cut-off value, Beta-233292 appears

to be adversely affected by the shape of the calibration curve over this time period, and this

model is based only on standard laboratory error estimates given to 68.2%. If laboratory

errors are represented to 95.4% confidence interval all dates have an agreement index

above sixty and consequently are accepted by the model. If the dates are modelled using a

P_Sequence then a well constrained age-depth model can be generated for the core (Table

7 and Figure 47).

Table 7. Modelled dates for core sequence BH3B from Kinnegad Bog. The Age-model

was generated using the P_Sequence model in OxCal v4. with a ‘k-factor’ value of 6

(see text for details).

Name

Indices

A model =61.1

A overall =69.3

Unmodelled (BP) Modelled (BP) Modelled (BC/AD)

Show all

Show structure from to m from to m from to m A comb A L P C

Boundary 2936 15 1476 2936 1346 2440 -986 604 -490 100 97.4

R_Date Beta-233290 2951 2751 2832 2953 2753 2839 -1003 -803 -889 96.9 99.4

Boundary change to Tb 3188 2792 2965 -1238 -842 -1015 98.1

R_Date Beta-233291 3479 3219 3376 3381 3210 3277 -1431 -1260 -1327 54 99.6

R_Date Beta-233292 3381 3078 3263 3443 3281 3345 -1493 -1331 -1395 87.1 99.6

R_Date Beta-233293 3821 3466 3611 3681 3460 3567 -1731 -1510 -1617 96.7 98.6

Boundary 4036 3586 3808 -2086 -1636 -1858 96.7

Interpreting humification data:

Humification is a measurement of organic decay. Organic material in the aerobic acrotelm of

a bog decomposes through rotifer activity and oxidation processes; however once the

organic material has moved into the anaerobic catotelm decomposition is negligible. This

means that organic material that remains in the acrotelm for an extended period of time is

more highly decomposed than organic material that has quickly passed into the catotelm.

Decomposed organic material contains humic acids that can be extracted via chemical

processes and then measured as a proxy for decomposition (Blackford and Chambers,

1995). Highly decomposed material releases more humic acid and are referred to as more

highly humified while relatively undecomposed material releases less humic acid and would

be termed poorly or in extreme cases unhumified. The humification signal may be linked to

past climate, in ombrotrophic bogs changes in precipitation, and therefore climate, alter the

water-table depths and peat accumulation rates, which in turn determine the residence time

of organic material in the acrotelm.

Samples from Kinnegad Bog BH3B were taken at 8cm resolution and processed for

humification analysis following the standard method of Blackford and Chambers (1993).

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Figure 47. Bayesian age-model from sequence BH3B, Radiocarbon dates are identified

as R_Dates while intervals of interest are referred to by their depth (cm). A change in

stratigraphy between herbaceous and moss peats is delimited by a boundary at 26cm.

The sequence is modelled using a Poison depositional approach in OxCal v4.

(P_Sequence). The sedimentation rate has been constrained using a ‘k’ factor of 6

reflecting the fine grained nature of the peat sediments.

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Humification results:

The humification data were integrated into the P_Sequence age-model for core BH3B (see

also Figure 3). In general the errors on the age estimates for undated intervals encountered

in the core range between 155-339 years within the dated core section (20.5-92.5cm), these

error ranges exponentially increase the further any interpolation occurs outside of this dated

interval, with the largest error range given for the 4cm humification sample (2940-1771 cal yr

BP) which has a range of 1169 years. The precision of the resulting model is limited by the

radiocarbon dates available and an inferred change in sedimentation rate at 26cm (identified

as a shift from herbaceous to moss peat). If the Charman et al. (2006) model of

environmental change is credible then the precision of the chronology is less than the

duration of some of the climatic events identified. This increases uncertainties regarding the

phasing and correlation of events. A good example of this problem is the phasing of the

3600 cal yr BP wet shift; humification values for BH3B across this period could either be

showing: 1) a shift to wetter conditions; 2) wet conditions; 3) a shift to drier conditions; or

even 4) dry stable conditions (Figure 48).

Figure 48. Humification data for BH3B at Kinnegad Bog Co. Offaly, compared to a

regional climate record (Charman et al., 2006). Humification data is presented with

95.4% age ranges. The dashed blue lines represent wet periods in the Charman et al

record, the second of which occurs at ca. 2800 cal yr BP and appears to exist in the

Kinnegad record. Absolute correlation of events is problematic due to the

chronological uncertainties in both records.

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If the errors generated for the chronology of the Charman et al (2006) study are included

then the problem becomes even more complex. In summary over this section of the core

Kinnegad Bog may be in phase with, anti-phased with, or unaffected by the suggested

climatic change (Figure 49). Fortunately more secure interpretations can be made from the

humification data over the directly dated section of the core sequence as this part has

smaller chronological uncertainties. Firstly, a drier period at ca. 3400 cal yr BP that is

followed by increasingly wetter conditions can be recognised in BH3B and the regional

climate record, this trend to wetter conditions continues until the lowest humification values

are recorded between 2950-2730 cal yr BP. This wet shift has been identified in numerous

peat bog records across Ireland and Europe where it is consistently dated to between 2890-

2690 cal. BP.

Interpretation of the archaeological structures identified at Kinnegad Bog alongside the local

and regional environmental data is not dependant on which Phase model is used (either a

single unordered Phase vs two phases based on trackway and platforms). Based on the

humification data from BH3B construction could have begun on wet, dry, or transitional peat

conditions. Construction continued although possibly sporadically through at least one drywet-dry

shifts in peat conditions. These shifts may have been consistent with construction

phases however the current chronological resolution is not sufficient to conclusively assign

construction of any of the archaeological structures to changing climatic conditions.

The synchronicity of these events can be tested using tephrochronological principles, just

prior to and during this shift to wetter conditions five tephra layers have been recognised in

peat sites across Ireland. These ash layers have been recognised in sequences where the

2890-2690 cal yr BP ‘wet shift is recorded (Plunkett, 2006), and currently form part of the

revised Irish Midlands tephrochronological framework (see below). Additionally, if tephra

layers can be identified in both the environmental and archaeological sequences then the

chronologies can be directly linked without complex age-models and this enables the more

successful phasing of events.

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Figure 49: Humification records and regional climate information against Kinnegad

Bronze Age archaeology based around Bayesian Phase models.

1.2. Tephrochronology in Ireland

Initial tephrochronological research has been undertaken which has identified the known

distribution of tephra layers across the study areas, this has been based on published and

unpublished research and this information has been used to construct outline

tephrostratigraphic frameworks for the study regions. The regions have been broken down

into two groups; 1) the Irish Midlands including Kinnegad Bog, Ballykean Bog and Ballybeg

Bogs, and 2) the Tipperary bogs (Littleton and Ballybeg Bogs). The outline

tephrostratigraphic frameworks are currently under revision based on the findings of borehole

sequences collected in this research from Kinnegad, Ballykean and Littleton Bogs, the

findings of this work are presented below. Additionally, the age-estimates for many of the

common tephra layers identified across NW Europe and specifically Ireland have been

reviewed and refined using state of the art Bayesian depositional and sequence age

modelling techniques. This will facilitate the generation of the highest quality age-models

from the archaeological and environmental sequences in this research. These models will

be the most statistically valid attempt to integrate archaeology with the local environmental

information and then to correlate these with regional and continental climatic records.

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1.2.1. Tephra distribution

A total of 38 separate tephra layers covering the last 15,000 years have been identified

across Ireland, a further 14 layers have been identified in the British Isles during this period

(Figure 50). This only represents approximately half of the total number of distal tephra

layers identified in northwest Europe (Matthews, unpublished PhD research). The 38 tephra

layers identified for Ireland are mostly thought to be derived from Iceland with the exception

of five layers that are believed to be from the Jan Mayen volcanic system (Chambers et al.,

2004). The ash layers identified in Ireland are not evenly geographically or chronologically

spaced with clear groupings of studied sites in Northern Ireland and in the Irish Midlands,

although this probably reflects the number of suitable sites and researchers in these

respective areas (Figure 51). The majority of tephra studies have focussed on specific time

periods (Historical, Bronze Age - Iron transition, or Lateglacial), and the few studies where

whole Holocene sequences have been investigated have identified new tephra layers and

significantly improved the known distribution of well characterised ash layers (Chambers et

al., 2004). This section reviews the known distribution of Holocene ash layers across the

Midlands and Co. Tipperary with a view to construct outline tephrochronological frameworks

for this study.

Figure 50. Theoretical tephrostratigraphy for Ireland. A total of 38 separate layers

have been identified although the distribution of individual layers is uneven across the

country.

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Irish Midlands

Seven sites have been investigated for tephra content within the Irish Midlands, these are: All

Saints bog, Clara bog and Mongan bog in County Offaly, Clonfert bog in County Galway,

Clonenagh bog in County Laois, Corlea in County Longford, and Lollymore in County Kildare

(Caseldine et al., 1998; Hall and Pilcher, 2002; Cole and Mitchell, 2003; Hall and Mauquoy,

2005). These studies identified between 1-3 layers and many of the layers were not

duplicated between sites. A total of 5 chemically distinct tephra layers were identified (table

8). These layers can be considered as a basic regional tephro-stratotype.

Table 8. The current published regional Tephrochronological framework for the Irish

Midlands. The dates quoted for the eruptions are based on historic records,

interpolation from radiocarbon dates or by wiggle match radiocarbon dating (WMD). 1

= Thorarinsson, 1967; 2 = Hall and Pilcher, 2002; 3 = Plunkett, 2006; AS = All Saints

bog, C = Clara bog, M = Mongan bog, CH = Clonenagh Bog CT = Clonfert bog, L =

Lollymore, CO = Corlea










Research completed by Matthews as part of his PhD studies of raised bogs sites in County

Offaly and County Westmeath identified the presence of at least a further eight tephra layers

with the suggestion of a further three layers that were sparsely represented in these records.

This raises the possibility that sixteen tephra layers may be available for the correlation of

sequences in the Irish Midlands and this research alongside published work forms an outline

regional tephrochronological framework for the Irish Midlands. However, not all the tephra

layers could be geochemically characterised and it is suggested this new regional

tephrochronological framework remains provisional. All of the identified tephra layers occur

within the last 5000 cal yr BP with groupings in the Medieval period and during the Bronze

Age and Bronze Age to Iron Age transition (ca. 2800 cal yr BP).

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Figure 51: Distribution of sites containing the Hekla 1104AD tephra layer. Shaded

contours refer to kernel density values based on the number of sites containing the

tephra layer within a ca. 50km radius cell size. The high densities in certain areas may

reflect site selection rather than true distribution

Tipperary bogs

The region around Littleton and Ballybeg Bogs has received fewer tephrochronological

investigations, and those that have been undertaken have focussed on the historic period.

This is reflected in the current regional tephrochronological framework that only consists of

one tephra layer (Hekla AD 1104). The initial tephra research in this region has attempted to

generate an outline tephrochronological framework for this region concentrating on the entire

Holocene sequence (Table 9).

Table 9. The current published regional Tephrochronological framework for Co.

Tipperary. The dates quoted for the eruptions are based on historic records,

interpolation from radiocarbon dates or by wiggle match radiocarbon dating (WMD). 1

= Thorarinsson, 1967; 2 = Picher et al., 1995. AS = All Saints bog, CH = Clonenagh

Bog, DE = Derryville bog, MO = Monaincha



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Figure 52. Construction of a new regional tephrochronological framework for the Irish Midlands a. represents the current regional

tephrostratigraphy as outlined in section 3.1, b+c presents the borehole data collected from Toar and Daingean bogs during I. Matthews’

PhD research, and d. presents the new revised tephrochronological framework. DGN2-107 is included in the new tephrostratigraphy as it

has been identified at Toar and Daingean bogs where it is stratigraphically constrained by the BMR-190 and GB4-150 tephra layers. DGN2-

39 and DGN2-41 are tentatively included in the new stratigraphy, as they represent two ash layers identified at both sites but with

geochemical information for DGN2-39 at Daingean bog only. DGN2-41 consists of microlitic intermediate shards and forms a clear optical

marker in the sediments. Age estimates for the DGN2 layers are considered section 1.2.2.

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1.2.2. Tephra age estimates

Distal tephra layers cannot be directly dated, easily. Attempts have been made to date

tephra layers at their sources using Argon-Argon, Potassium-Argon, and fission track dating

(Alloway et al., 2007). Frequently in Late Quaternary deposits the ages derived from these

techniques do not offer high enough precision to provide useful ages. Similarly the

increasing number of tephra layers identified in distal form only means the applicability of this

approach is limited. Consequently when dating distal tephra layers, where no suitable

proximal deposits have been identified for dating, other dating methods are used on the

sediments encasing the ash layer.

In northwest Europe four approaches to assigning ages to micro-tephra layers have been

used:

1. HISTORICAL RECORDS: In the last ca. 1000 years historical records exist for

volcanic eruptions that are derived form Iceland. These often provide annual ages or

better for tephra layers (Thórarinsson, 1967, 1981).

2. INCREMENTAL SEQUENCES: Tephra layers outside the historical age range have

been identified in annually derived incremental records (varves and ice cores). These

have the potential to produce annual ages for tephra layers, but the counting errors

involved in constructing these chronologies must be considered (Wulf et al., 2004;

Zillen et al., 2002; Mortensen et al., 2005). This approach has great potential for

constructing accurate and precise age estimates for tephra layers, but as yet only a

few of the numerous tephra layers identified in northwest Europe have been located

in these types of records.

3. RADIOCARBON DATING: Dates have been derived for tephra layers based on

single or multiple radiocarbon dates encasing an ash layer, which are used as limiting

ages or via interpolation from linear radiocarbon age-depth models. These dates are

frequently imprecise and hence have limited use when utilising tephra layers to

support and test chronologies (Dugmore et al., 1995).

4. WIGGLE-MATCH RADIOCARBON DATING (WMD): This approach uses the

probability distributions of multiple radiocarbon dates combined with depth

information to exploit variations in the calibration curve. This can produce very

precise age estimates for tephra layers, but requires linear deposition to occur. Two

WMD approaches exist, firstly the visual wiggle-match which is essentially an ad hoc

approach which requires the researcher to assign a sedimentation rate to a sequence

and to vary it until the best match to the calibration curve can be achieved. It is often

difficult to calculate errors using this approach and secure stratigraphic knowledge is

essential (Pilcher et al., 1995, 1996). A second approach to WMD is to use Bayesian

statistics to produce the best match to the calibration curve. This approach allows

errors to be quantified, but as of yet has had limited application in assigning ages to

tephra layers (Blockley et al., 2007). The majority of tephra layers that have been

dated by WMD have been produced for tephra layers identified in Irish peat

sequences, with WMD available for 8 tephra layers from Ireland (Lairg A+B, Hekla 4,

BMR-190, OMH-185, GB4-150 and the AD860 a+b layers), and a further six layers

from British and European lake and peat sequences (Glen Garry, the ‘microlite

tephra’, Hekla 3, Hekla Selsund/Kebister, Askja, and Hasseldalen). The majority of

these layers were dated using the ad hoc WMD approach although some attempt

was made to quantify errors, the exception being the Glen Garry, Askja, and

Hasseldalen tephra layers where the Bayesian WMD approach was used.

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For this research the age estimates for non historical tephra layers were reappraised. Many

of the WMD layers were produced using older calibration curves (Pilcher et al., 1995), or the

assumption of linear sedimentation could not be supported. In these cases the original

radiocarbon dates were re-calibrated using the functions available in OxCal v4. If a linear

sedimentation rate could be supported then the ‘U_Sequence’ function available in OxCal v4.

was used. This approach has been demonstrated to be comparable to a Bayesian WMD

(Blockley et al., 2007) and produces very precise age estimates, although typically the errors

produced were greater than those originally published. Where the assumption of linear

sedimentation could not be supported the less constrained P_Sequence function was used,

this typically produced less precise dates than the U_Sequence but is theoretically sounder

in these situations.

Result:

Table 10 presents age-estimates for 13 ash layers based around recalibration and

refinement of existing data. This process has led to the generation of new age estimates for

many of the Holocene tephra layers frequently encountered across NW Europe, significant

improvements have been made in the precision of age-estimates for the BMR-190, OMH-

185, Hekla 4, Lairg B, and Lairg A ashes. Not all remodelled ages offer higher precision, the

BMR-90, 860AD layers, SILK-YN and Hekla 3 ash layers have poorer precision than the

previous estimates although they represent more realistic assessments of ‘true age’ of the

events. The BMR-90 layer was the only reported ash layer encountered that did not have a

historical or WMD available, being previously dated by linear interpolation from the 860AD

layers and presented as a spot figure (920AD) (Hall and Pilcher, 2002). The age estimate for

this layer represents the first attempt to date this ash layer using Bayesian age-modelling.

Three other age-estimates merit further comment:

860AD layers

The original visual WMD generated for the 860AD layers was produced by Pilcher et al.,

(1995), and suggested an age of 860AD ±20 years. The age-estimate was based around

eight bulk-peat radiocarbon determinations which appear to suggest a linear sedimentation

rate. When recalibrated using OxCal v4 the dates are all accepted in an U_Sequence and a

very tight age distribution may be achieved. However, the distribution of the 860AD layer in

the core studied by Pilcher et al. (1995) was spread over several centimetres merging with

the deposition of Hekla 1104AD identified above. This was attributed to drainage and cutting

of the peat, but as seen in chapter seven this disturbance has the potential to reposition

organic material increasing the uncertainty of the accuracy of the radiocarbon determinations

as well as adding to the uncertainty of the stratigraphic position that represents the eruption.

These uncertainties mean that the assumption of linear sedimentation can not be supported

and hence a P_Sequence was used. This example illustrates that although radiocarbon

dating evidence supports an assumption greater consideration must be given to the

stratigraphic integrity of tephra sequences when attempting to generate age-estimates.

OMH-185 and the ‘Microlite’ (DOM6) tephra layers

The OMH-185 and ‘Microlite tephra layers are thought to represent the same eruption, and

have been dated using visual WMD techniques by two operators in Ireland and Germany.

An age of 2705-2630 cal. yr BP was produced for the OMH-185 tephra at Glen West in

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Ireland by Plunkett, et al. (2004), whilst an age of 2680-2614 cal. yr BP was generated for

the ‘Microlite’ tephra at Dosenmoor in Germany by van den Bogaard et al., (2002). This

close agreement between the ages supported the theory that the ashes were derived from

the same eruption. Reinvestigating the radiocarbon dates used to produce these age

estimates and remodelling the sequences have produced refined age estimates of 2633-

2592 cal. yr BP for the OMH-185 layer in Ireland, and 2733-2656 cal. yr BP. These ageestimates

suggest there is no overlap in ages for the two layers and that the ashes represent

separate eruptions. Stratigraphic evidence from Daingean and Toar Bogs support the notion

of several closely spaced eruptions which may indicate that the two ash layers represent

separate events. Alternatively the dating evidence from either location may be generating

falsely precise age-estimates. The dates used to generate the age-estimate for the OMH-

185 were from the humin fraction of samples rich in Sphagnum and Eriophorum. These

were processed using standard procedures (see Plunkett et al., 2004). The dates supported

a linear sedimentation rate and were observed to have undergone little vertical displacement

occurring below the drained upper section. The dates used to generate an age-estimate for

the ‘microlite’ tephra were bulk-peat samples where humic and humin samples were dated

and showed good agreement with each other, however the dates could not support a linear

sedimentation rate and pollen evidence from the same core indicates shifts in local aquatic

taxa through the dated section suggesting changes in hydrology and sedimentation rate in

the sequence. The Microlite tephra was age-modelled using a relatively unconstrained

P_Sequence model. Unfortunately, many of the radiocarbon dates were coincident with a

14 C plateau which meant high levels of precision could not be achieved.

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Table 10: Revised age estimates for Holocene tephra layers across Northwest Europe. Original dates were derived from a variety of

techniques including interpolation from radiocarbon dates, combined probabilities of radiocarbon dates and wiggle match dates (WMD)

using visual and Bayesian techniques. In the majority of cases the new age estimates have been produced using U_Sequence and

P_Sequence Bayesian models (in OxCal v4.), the exception is the dating of SILK-YN where the dates were not in stratigraphic sequence but

rather formed two phases that encapsulated the ash layer. The dates used to create these estimates are from: 1= Hall and Pilcher, 2002; 2 =

Pilcher et al., 1995; 3 = Dugmore et al., 2000; 4 = Barber et al., 2008; 5 = Plunkett et al., 2004; 6 = van den Bogaard et al., 2002; 7 = Matthews,

unpublished PhD research; 8 = Wastegard et al., 2008 ; 9 = Pilcher et al., 1996; 10 = Wohlfarth et al., 2006.




























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With the current data it is difficult to resolve the ages of the OMH-185 and Microlite tephra

layers any further. The lack of humic and humin dates from Glen West does not allow for the

assessment of movement of carbon through the peat, similarly it is not clear if rootlets

especially of Eriophorum were included in the samples. Eriophorum is known to have deep

roots that can lead to artificially young ages. Similarly, although the age-estimates for

Dosenmoor show agreement between the humic and humin fractions the pollen evidence

and radiocarbon dates suggest changes in sedimentation rate that hinder age-modelling.

Alternatively, the age-estimates could be ‘correct’ and the deposits may reflect two separate

eruptions. Until this can be further resolved it is suggested that the OMH-185 and ‘Microlite’

tephra layers are considered separately and the most appropriate age-estimate for any

particular site is used, for example the age-estimate for the OMH-185 will be used in this

research.

Lairg A and Lairg B

The precision of the age-estimates of the Lairg A and Lairg B tephra layers have been

significantly improved. The original estimates were 6998-6809, and 6728-6564 cal. yr BP

spanning 189 and 164 years respectively. The layers were remodelled using an

U_Sequence model which generated age-estimates of 6951-6807, 6610-6535 cal. yr BP

spanning 144 and 75 years respectively. The generated age-distributions for these layers

are non-normal and cannot be represented by a simple mean value, although the model

predicts median values of 6903 and 6579 cal. yr BP for the two layers.

Re-modelling the age of Lairg B highlights some of the issues surrounding the naming of

tephra layers. It has been suggested that Lairg B is renamed the ‘Torfajökull 4700BC tephra’

(Pilcher et al., 2005). The 4700BC date fits with the old age-estimate, but is outside the

errors of the age-estimate generated in this research. Operators should be aware that any

age-estimate is only an approximation and subject to change based on further research; this

also applies to the 860AD layers which may or may not occur at this time, and the fixed age

of this layer has led to research searching for it immediately below the Landnam tephra

(875AD) in Iceland (Wastegård et al, 2003). Based on the less constrained age-estimate for

this layer it may occur any time between 805-878AD and the ‘860AD’ name tag is

misleading. High-precision age-estimates and annual ages for events are attractive

especially when extolling the virtues of tephra layers as opposed to radiocarbon dates

however, potentially misleading names of tephra layers actually cause confusion in agemodelling

and detract from the advantages tephra layers offer as isochronous marker

horizons.

Summary

The Bayesian sequence modelling has allowed high-precision estimates of tephra

deposition, in some cases it has refined the age-estimate reducing uncertainties in precision,

whilst at other sites it has produced less precise estimates which are a more realistic

reflection of the ‘true’ age of the event. This approach allows age estimates from tephra

layers to be incorporated into further age-modelling but highlights some of the problems with

doing this. One particular problem is the naming of tephra layers with annual ages where the

age is not an historical account e.g. the 860AD layers and the Torfajökull 4700BC tephra

(Lairg B), this approach ignore the difficulties of assigning ages to tephra layers and can

lead to confusion when incorporating this layer into age-models. As this age-modelling

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approach uses stratigraphic information it is recommended that the core number and

stratigraphic depth be included in the tephra layer name.

The calculated ages for the tephra layers must remain provisional; in most cases they reflect

a single occurrence of the tephra in a single core sequence. In these cases the ageestimates

are vulnerable to even the slightest inaccuracy of radiocarbon determinations as

these will lead to changes in the depositional model. This is not the case with the Hekla 4

eruption which has been dated at multiple sites across Europe (Pilcher et al. 1995). This

potential for inaccuracy is highlighted by the OMH-185 and Microlite tephra age estimates.

These were considered to represent the same eruption due to the similar ages recorded.

Recalculation of the ages using the above method suggests they cannot be the same event,

although this may reflect inaccuracies in either chronology. Until equivalency can be

determined between ash layers it is recommended that regional age-estimates are employed

and dates from geographically disparate sites are not combined. The Bayesian WMD

derived for the Glen Garry tephra takes such an approach, age-estimates for the ash were

determined for eight peat bogs in Scotland and Northern England (Barber et al. 2008). The

authors conclude that dating single sites to determine ages for ash layers may not constrain

the event to the correct age.

Consideration should also be given to the dated material that constrain the tephra layer or

indeed in any radiocarbon dates. The dates used in these models include radiometric dates

from bulk peats, and AMS dates on: gyttja, bulk peat, and picked macrofossils. The most

suitable material is debatable but ideally to avoid issues of humic acid mobilisation and/or

rootlet penetration humic and humic fractions should be dated alongside macrofossil age

determinations. This is often not practical as sample preparation is time consuming and

expensive. The reliability of these dates can be assessed using other tephra layers, as long

as these layers have reliable age-estimates.

When sampling a core sequence to determine a tephra age it is desirable to have as much

information as possible available. The following are a recommended list of requirements:

1. At least two sequences

2. Detailed lithostratigraphic descriptions, humification, plant macrofossil and

palynological data that may help interpret changing depositional conditions which

affect the sedimentation rate.

3. At least 6 dates bracketing the tephra layer at each site with preferable at least

two sites for comparison.

If these recommendations are followed then dating tephra layers by Bayesian age-modelling

requires at least 12 radiocarbon dates across two sequences. If the ca. 100 tephra layers

identified across NW Europe were to be dated in this manner then a total of at least 1200

radiocarbon dates would be needed. This requires significant financial investment but must

be seen as an important area for future research if tephrochronology is to be utilised as a

standardised chronological tool. Although it is important to stress that tephra layers without

this level of dating information still provide valuable stratigraphic markers that can be used to

test other chronological methods.

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1.3. Tephra investigations of raised bog sequences

1.3.1. Introduction

This section of the report will deal with the data produced during 2009 and its integration with

the data generated in 2008. It will present the findings of tephra research which has focused

on generating tephrochronological frameworks for each of the study regions and applying the

resulting stratigraphic and chronological information to the archaeological structures. Initially,

three bogs were selected for tephrochronological studies: Kinnegad Bog, Ballykean Bog and

Littleton Bog. It was felt that these sites provided the best opportunity to enhance and refine

the tephrochronological and archaeological record. This has subsequently been expanded

to include Ballybeg Bog in Co. Offaly and Ballybeg Bog in Co. Tipperary. The findings

presented within this section reflect the preliminary analysis of a large body of data and will

be refined for publication of the monograph and subsequent peer reviewed publications.

1.3.2. Sample selection

Kinnegad Bog, Co. Westmeath

Sub-samples were extracted from the BH3B sequence between 0-490cm, a second ‘control’

sequence of 130cm taken ca. 50m from BH3B (fulfilling the category E core (CAT-E) remit

for Kinnegad Bog also termed BH9) and KND column 1+2 which relates to the archaeological

structures (ME-KND001 and ME-KND011), these were processed for microtephra

examination. Samples of 1cm thickness were systematically cut from the sequence to

minimise the risk of missing very thin microtephra layers.

Ballykean Bog, Co. Offaly

Sub-samples were extracted from the BH37 sequence between 0-370cm were processed for

microtephra examination. Additional samples were taken from point TS3 between 0-260cm

(surface to base of the sequence). This second core sample fulfils the CAT-E requirement

for Ballykean Bog. These key marker sequences were combined with an investigation of a

further nine 130cm core sequences (transect TS) across 1000m of the bog surface. This

was carried out to assess lateral continuity in peat stratigraphy and tephra deposition across

Ballykean Bog. Contiguous samples of 4cm thickness were systematically cut from both

sequences to identify peaks in tephra shard content. Counts in areas of the sequence where

tephra shards were identified were subsequently refined and quantified to 1cm resolution in

BH37. Samples from TS3 were analysed at 4cm resolution and then correlated with the

layers detected in BH37. The selection of samples from TS3 was selected because it

represented a point >250 metres from the nearest identified archaeological structure. It also

occurs along the 1km TS transect begun by Denton (unpublished data figure 51). The

stratigraphy exposed in the drain faces alongside this transect was recorded every 50 metres

with palaeoenvironmental samples taken at every 100m interval.

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Figure 51. Lithostratigraphic survey carried out across Ballykean Bog, Co. Offaly (data

and diagram produced by K. Denton). Sample point TS3 has been processed and

analysed for tephra content to the base of the bog, while BH37 is located between TS5

and 6. Each of these core sequences has been analysed for tephra content to a depth

of 130cm and will allow the integration of palaeoenvironmental, archaeological and

chronological data across a wide area of Ballykean Bog.

Ballybeg Bog, Co. Offaly

Sub samples were extracted from the BH3 sequence between 0-262cm, they were

subsequently processed for microtephra examination. Contiguous samples of 10cm

thickness were systematically cut from whole sequence. Slides were subsequently assessed

for tephra content and were fully quantified.

Littleton Bog, Co. Tipperary

Sub-samples were extracted from the LTN-01D sequence between 0-506cm, they were

subsequently processed for microtephra examination. Contiguous samples of 4cm thickness

were systematically cut from the upper metre of the sequence whiles 8cm thickness samples

were taken from the rest of the sequence to identify peaks in tephra shard content. These

sampling intervals were selected due to the greater likelihood of identifying tephra layers in

the uppermost metre. Counts in areas of the sequence where tephra shards were identified

were subsequently refined and quantified to 1cm resolution.

Ballybeg Bog, Co. Tipperary

Sub samples were extracted from the BH4 sequence between 0-240cm, they were

subsequently processed for microtephra examination. Contiguous samples of 10cm

thickness were systematically cut from whole sequence. Slides were subsequently assessed

for tephra content and tephra shard numbers were fully quantified.

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1.3.3. Methods

Optical assessment

Samples were incinerated in a furnace at 550˚ for four hours to remove organic matter.

The resulting ash residue was then processed according to a modified version of the

procedure outlined in Blockley et al. (2005). All procedures followed Blockley et al. (2005)

with one principal exception: due to the small diameter of tephra shards frequently

encountered in Ireland a 15 micron (μm) sieve mesh was preferred to guard against loss of

tephra shards during the extraction procedure. To prevent airborne contamination of the

samples in the laboratory all sieving was conducted in a laminar flow cabinet (providing clean

filtered air), and the samples were stored in sealed centrifuge tubes.

Slides of the extracted material were mounted in Canada Balsam and examined optically

using an Olympus CX-41 microscope fitted with cross-polarising filters. Tephra shards were

initially classified by their optical properties (e.g. colour and morphology); three shard type

groups were identified:

1. ‘Colourless’ shards that tended to be vesicular and contained mineral inclusions

2. ‘Intermediate’ shards that ranged from yellowish-brown to olive-brown in colour with

fluted and vesicular morphologies

3. ‘Brownish’ shards that were deep brown in colour and had a characteristic ‘blocky’

morphology.

Geochemical preparation

Some preparation techniques used during the optical examination phase are known to cause

alterations in tephra geochemical properties. For instance, the ashing process alters shard

chemistry as the high temperatures involved lead to alkali mobilisation (Dugmore and

Newton, 1992). Alternative preparation procedures are therefore required for accurate

geochemical data. Two approaches frequently used are the Pilcher and Hall (1992) acid

digestion procedure (modified by Chambers et al., 2004) for organic rich sediment and the

Turney (1997) floatation procedure (modified into stepped floatation by Blockley et al., 2005).

These approaches also have limitations. The acid digestion procedure exposes tephra

shards to low pH’s that are thought to have the potential to alter shards geochemical profiles

(Pollard et al., 2003; Blockley et al., 2005), whereas the Blockley et al., (2005) approach has

limited success on relatively unhumified organic sediments.

Wetlands frequently generate the relatively unhumified organic matter that is difficult to

disaggregate when using the Blockley et al., (2005) approach. As a result most tephra layers

detected in these depositional contexts have been prepared using acid digestion. Concerns

over the geochemical integrity of data obtained using this approach during this research has

led to experimentation to develop an extraction procedure that minimises exposure of

samples to extreme pH values. This preparation method uses weak dispersant (0.1%

Calgon pH 8) for four hours at 60°c to break down the organic matter. Tests have shown

that this procedure should not alter tephra chemistry. Subsequently the samples were

sieved through three mesh sizes, the first and second meshes (200μm and 125μm) removes

coarse fibrous matter, whilst the third (15μm) retains finer organic matter and hopefully

tephra shards. The mineral component of the sample is separated from the organic residue

using floatation and the mineral matter examined for tephra content. If this approach yields

sufficient tephra shards for geochemical analysis then no further processing is required. In

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some samples very little tephra was yielded by this approach. These tended to be relatively

unhumified Sphagnum rich samples, and it is hypothesised that the angular tephra shards

become lodged in the organic material and float off during the floatation stage. When this

occurs it is then necessary to further break down the organic material and so the samples

are treated using the Chambers et al., (2004) acid digestion procedure. This is carried out

using concentrated nitric acid which has a low pH and the potential to alter tephra shards.

Hence, it is important to reduce the exposure time of tephra shards to these conditions as

much as possible. The sieved sample sizes undergo acid digestion until the mixture

becomes a clear yellow colour; usually the finer fraction (125-15μm) clears first, often within

just 15 minutes, due to its large surface area to volume ratio. The larger size fractions may

take up to 2 hours to clear and significantly increase acid exposure times. The 125-15μm

fraction is examined first and recovered shards added to those already identified prior to acid

digestion, which usually produces enough shards for analysis. Should this fail to yield

sufficient shards, however, then the larger size fractions are examined. It should be noted

that acid digestion usually takes place on bulk, un-sieved samples and frequently takes 2 or

more hours to be completed (Blockley et al., 2005), and consequently this approach outlined

here significantly reduces exposure time to low pH. Samples that underwent the acid

digestion procedure were noted and the resulting geochemical data are presented with the

caveat that chemical alteration may have occurred.

The samples were prepared for geochemical analysis using the following procedure:

1. A phenolic ring was placed within a rubber mould and Specifix-40 resin poured into

the mould.

2. This was then placed in an oven to cure at 50°c for 3.5 hours or until set.

3. The resulting stub was flattened using P400 and P1200 silicon carbide grinding papers

with the stub gripped in a Buehler hand polishing guide until the grade across the

surface was not more than 10μm.

4. The stub was then labelled by scribing the sample code into the side and base.

5. The sample was placed upon the stub surface allowed to dry, covered by Specifix-40

resin and cured according to step 2.

6. The cured resin was ground down using P400 and P1200 silicon carbide grinding

papers until shards were sectioned, checked using Olympus CX-41 transmitted and

reflected light microscope.

7. The stub was then polished using a 9μm diamond suspension, cleaned in an ultrasonic

bath and then polished again using a 3μm diamond suspension.

8. When only small scratches (ca. 3μm) remained on the shards (checked in reflected

light), the stub was cleaned in an ultrasonic bath and finally polished using 0.3μm

Aluminium oxide powder.

9. Before analysis, the sample was immersed in ethanol and cleaned using an ultrasonic

bath, and subsequently carbon coated.

10. To avoid sample charging during analysis, a colloidal graphite paste was attached to

the edge of the stub surface leading to an earthed conductor (provided by the sample

holder).

Geochemical analysis was firstly undertaken at the Begbroke Earth Sciences facility in the

University of Oxford using a Jeol JXA8800R microprobe system fitted with 4 wavelength

dispersive spectrometers (WDS). The operating conditions for this system were a defocused

10μm beam with a voltage of 10na and accelerating voltage of 15KV checked by a Faraday

cup. The system was calibrated using pure metals and silicate minerals as primary

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standards. To measure system instability or drifts in readings, secondary glass standards

consisting of internally assayed obsidians and anthropogenic glasses (e.g the USGS NIST

612 and STHS (mount St Helens Obsidian) were measured before, after and within sample

measurements. During analysis count times were 15 seconds, with sodium measured first to

mitigate against sodium mobilisation, a known problem when analysing tephra using EPMA

(Dugmore et al., 1995). Due to the small size of many of the tephra shards encountered

further analyses were carried out in the Tephra Analytical Unit (TAU) in Edinburgh University.

This facility allows the analysis of very small shards via a 5μm beam diameter. Probe

analytical conditions were comparable to the Oxford University system and analyses were

checked using Lipari obsidian as a secondary standard. This second set of analyses

generated results from a basaltic tephra and thus the BHVO-2G basaltic glass was also

employed as a secondary standard. WDS EPMA was preferred to energy dispersive

spectroscopy (EDS) as it affords higher precision in classifying geochemical data (Turney, et

al., 2005).

Nine major elements were routinely measured during analyses at Oxford: SiO 2 , TiO 2 , Al 2 O 3 ,

FeO (total) , MnO, MgO, CaO, Na 2 O, and K 2 O, while at TAU a further four elements were also

included (F, Cl, P 2 O 5 , SO 2 ) these represent the widest selection of elements analysed in

Northwest European tephrochronology. Water content of tephra shards and trace elements

cannot be quantified by EPMA so individual analyses of shards frequently give totals of

under 100%. Typically water content is around 1-3% but can be as high as 5.5% (Harms

and Schmincke, 2000).

When collecting EPMA data from a tephra layer it is advantageous to acquire as much

information from a sample as possible in order to capture as much of the samples

geochemical variability as possible. Unfortunately, in distal tephra studies the amount of

tephra available for geochemical characterisation is often low and the generation of robust

statistical data-sets difficult. Typically, during this research, 30 targets per sample were

selected for geochemical analyses, a sample size considered large enough for application of

statistical procedures. In layers where shards were sparse, fewer targets were available and

hence the resulting datasets were smaller.

Geochemical data has been obtained on ash layers from Ballykean, Kinnegad, Ballybeg (Co.

Offaly), Ballybeg (Co. Tipperary) and Littleton Bogs. The results and correlations outlined

below are based on these chemical determinations and comparisons of the morphological

features of the tephra layers identified to the regional stratotype, especially in particularly

diagnostic intermediate tephra layers. This approach has been used successfully in Ireland

(Plunkett, et al., 2004; Plunkett, 2006). The large amount of data generated during this study

will receive further analysis over the coming months and the correlations presented here

should be considered provisional.

1.3.4. Results

1.3.4.1 Irish Midlands

Kinnegad Bog BH3B

Tephra shards were identified in three zones within BH3B; the first zone was at 10-26cm, the

second at 50-60cm and the third at 110-120cm.

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Zone 1: 10-26cm

Low numbers of colourless and intermediate shard types were identified between 10-25cm.

These shards could not be resolved into discrete peaks in tephra shard concentrations. The

area was re-sampled in order to resolve the shard concentrations, no discrete peaks could

be identified through this zone, although it is likely based on the radiocarbon age-model and

shard morphologies that these shards represent the BMR-190, OMH-185, and GB4-150

tephra layers. This can only be tested through geochemical analysis, which is currently

ongoing. However, should the correlations with the BMR-190 and GB4-150 be verified these

layers have the potential to constrain the age model of BH3B and the archaeological column

samples (CAT-A and CAT-B samples).

Zone 2: 50-60cm

The second area of tephra deposition was 50-60cm with a discrete peak in colourless shards

identified at 52-53cm. The shards had a long axis that was 50-70m in length on average

and were exclusively colourless and fluted in morphology. The shards occur at

approximately 3100 cal yr BP based on the current radiocarbon chronology, and the

numbers of possible correlatives are limited. The only distally identified tephra layer across

NW Europe at this time is Hekla 3, which has a refined date generated in this study of 3090-

2970 cal yr BP. This tephra layer has been identified in Ireland although not in the Irish

Midlands. However, a tephra layer deposited around 3100 cal yr BP was identified at

Daingean Bog during I. Matthews’ PhD research, this layer only produced a single

geochemical analysis which suggested a source of the layer of Hekla but wasn’t sufficient to

confidently correlate with the Hekla 3 eruption. It may be that the Hekla 3 tephra is

widespread across Ireland but hitherto has not been identified in the Irish Midlands, or

conversely it may be that the tephra layers identified at Daingean bog and in core BH3B at

Kinnegad bog represent tephra layers that have not previously been recognised in Ireland.

Zone 3: 110-120cm

The third zone of tephra deposition was at 110-120cm with a peak in exclusively colourless

shards at 116cm (Figure 52). The shards identified were usually platey to fluted in

morphology and were less than 60m in length. Based around the current radiocarbon

chronology this tephra layer was deposited around 3700 cal yr BP, although this requires

considerable interpolation below the last dated interval and the uncertainties around this date

are in the order of 155 years (3838-3683 cal yr BP based on the P_Sequence generated for

the humification data). Only one tephra layer has been identified distally during this period,

the eruption of Hekla variously known as the Hekla Selsund, Hekla-S, Kebister, or KAL-X

layer that has been re-dated in this research to 3778-3704 cal yr BP. This layer has been

identified in continental Europe and the Shetland Isles, but to date, has not been identified in

Mainland Britain or Ireland (Wastegård et al., 2008). Although high concentrations of shards

were identified in this sample the small grain sizes present meant that obtaining geochemical

information was problematic and hence was undertaken at TAU.

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50m

Figure 52. Examples of tephra shards identified at Kinnegad Bog sample BH3B.

These shards were identified at 115-116cm, which represents approximately 3700 cal

yr BP based on the current radiocarbon chronology.

Kinnegad Bog CAT-E core (BH9)

Tephra shards were identified in four zones within the BH9 core; the first zone was at 0-

12cm, the second at 26-32cm, the third at 40-52cm and the last between 80-84cm.

Zone 1: 0-12cm

Low numbers of colourless and brown shard types were identified between 0-12cm. These

shards could not be resolved into discrete peaks in tephra shard concentrations. It is likely

based on the shard morphologies that these shards represent the OMH-185 tephra layer and

associated ash layers. This was tested via geochemical analysis.

Zone 2: 26-32cm

The second area of tephra deposition was 26-32cm. The shards were exclusively colourless

and were usually platey to fluted in morphology, all shards observed were less than 60m in

length. This zone best equates with zone 3 identified in BH3B based on the morphological

characteristics recognised in the shards.

Zone 3: 40-52cm

The third zone of tephra deposition was at 40-52cm. The shards identified were usually

platey, vesicular and fluted in morphology and were less than 100m in length. These

shards formed no discrete peak and displayed mixed morphologies, suggesting some degree

of reworking of older shards into younger sediments.

Zone 4: 80-84cm

The forth zone consists of low numbers of large colourless shards (ca. 80 m in length) that

are usually vesicular in nature. This layer appears to have no correlative in BH3B, but based

in the regional tephrochronological framework it is feasible that it equates with the widely

detected Hekla 4 eruption that has been re-dated in this research to 4291-4221 cal yr BP.

This layer was prepared for geochemical analysis but yielded no successful analyses.

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Implications

Three zones of tephra shards were identified in Kinnegad core BH3B, while four zones have

been detected in BH9. In BH3B two zones could be resolved into peaks in shard

concentrations at 52-53cm and 116-117cm, while one zone 10-26cm contained a mix of

shard types and could not be resolved into clear peaks of distribution.

Kinnegad Bog Columns 1+2

Columns 1 and 2 were sampled for tephra shard content and a total of four tephra layers

were identified: These were between 10-15, 15-20, 20-25 and 45-50cm. These samples

were taken adjacent to ME-KND011and stratigraphically above ME-KND001 (Figure 53).

Figure 53. Columns 1+2 from Kinnegad bog, Co. Meath. The lower wood band

represents trackway ME-KND001+2 while the upper wood band represents platform

ME-KND011. The uppermost part of the section was not sampled because it displayed

considerable variation thought to be derived by the mechanical peat processing. The

platform was recorded at 23-35cm while the trackway was recorded at 60-70cm.

Zone 1: 10-15cm

18 colourless and 54 intermediate tephra shards were identified between10-15cm. These

could not be resolved into a peak within a single centimetre and are best considered as a

5cm zone of tephra deposition. The colourless shards were highly vesicular, while the

intermediate shards were fluted-highly vesicular in appearance with infrequent microlitic

inclusions. Morphologically the intermediate shards are most like those correlated with the

reference material for the BMR-190 tephra layer. This tephra was thought to be present in

BH3B and is represented in the regional tephrostratotype (identified at Toar Bog Co.

Westmeath by I. Matthews).

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Zone 2: 15-20cm

The second zone of tephra deposition was represented by purely colourless shards that were

highly vesicular and had infrequent microlite inclusions. If the correlation to the BMR-190

tephra can be supported then a correlation of this zone to either the OMH-185 tephra or

DGN2-107 tephra layer is feasible, especially when considering the tephra identified in zone

3.

Zone 3: 20-25cm

This zone comprises colourless and intermediate shard-types, with a total of 22 shards

identified. The colourless tephra shards displayed highly vesicular morphologies and were

not diagnostic; the intermediate shards were morphologically consistent with the GB4-150

tephra that forms part of the current regional tephrostratotype. The lowermost shards

recorded in this zone were found in the centimetre of peat above platform ME-KND011 and

provide a limiting age for the use of the structure.

Zone 4: 45-50cm

This zone comprises colourless tephra shards with a peak value of 23 shards at 49cm. The

layer has been tentatively correlated with the tephra identified at 52cm in BH3B (tephra zone

2) based on the series of layers identified above, this would place a tentative age of 3000-

3100 cal. yr BP on this interval of the column sample. This layer occurs above the trackway

ME-KND001+2 and provides a limiting age for the use of this structure, while occurring below

ME-KND011 and hence constraining the age of construction for this platform.

Implications

Tephra zone 3 identified in BH3B (dated to ca. 3700 cal yr BP) was not detected in these

samples and this would suggest that the base of the column samples post-date this event.

The tephra layers identified in Columns 1+2 have the potential to constrain the timing of

construction and use of the archaeological structures represented in the column samples,

additionally; this can provide information regarding human responses to environmental

stimuli. This is explored further in the sections below.

Geochemical data from Kinnegad Bog

The four tephra layers detected in BH9 were prepared for geochemical analysis. Further

preparations from BH3 were not viable within the remit of this project and material from BH3

was limited. Two of the prepared ash layers (10cm and 34cm) yielded successful

geochemical data (Table 11).

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Table 11. Geochemical data derived from BH9 Kinnegad Bog, Co. Offaly.























Kinnegad Bog BH9 10cm

A total of three analyses were obtained from this level (table 11). The geochemical signature

of the tephra demonstrates that it is a sub-alkali basalt from the low potassic range (Figure

54). This indicates that the ash layer is most probably derived from the Iceland volcanic

province in the central-eastern volcanic zone. In fact this ash has similar chemical properties

to others tephras identified across Europe that have been correlated with products of the

Veidivötn volcano. The geochemical properties displayed in table 11and figure 54 suggest

that this eruption from the Veidivötn volcano correlates with a known eruption in this case the

eruption of Veidivötn ca. 2400-2700 cal BP. This layer has only been identified in Lake

Svinivatn in Iceland and has been termed the SvV tephra. The correlation to this layer

remains provisional due to the lack of available geochemical data on this layer. The SvV

tephra is not part of the current Irish Midlands regional tephrochronological framework and

thus has the potential to add another valuable isochron to the Bronze-Iron Age transition

period.

CaO

11.4 11.6 11.8 12.0 12.2

11.1 11.2 11.3 11.4 11.5 11.6 11.7

Figure 54. Bi-plot of KND10cm (Red) against the SvV tephra identified in Iceland (data

accessed through Tephrabase (www.tephrabase.org) [last visited 01.12.09]).

FeO

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Kinnegad Bog BH9 34cm

A total of five analyses were obtained from this level (table 11). The geochemical signature

of the tephra demonstrates that it is a sub-alkali rhyolite from the medium potassic range

(figures 55-56). This indicates that the ash layer is most probably derived from the Iceland

volcanic province in the central-eastern volcanic zone. This ash has few potential

correlatives and no known correlatives in Iceland; hence its source volcano is unknown. The

ash is chemically most similar to the GB4-182 ash layer recognised in the north of Ireland

and dated to ca. 3300 cal. BP. The chemistry identified at Kinnegad matches this layer

better than any other in the Northwest European tephrochronological stratigraphy.

Additionally, another layer of very similar chemistry was identified in Daingean Bog Co.

Offaly (Matthews, 2009). The correlation to this layer cannot be supported due to the

differences observed between the Daingean Bog and Kinnegad Bog CaO and K 2 O values.

These differences may reflect the different analytical conditions, however until this can be

clarified it is recommended that this layer is considered a separate ash fall event dated to

3838-3683 cal. BP. Henceforth it is suggested that this ash layer is now referred to as the

KND9-34 tephra after the site, core, and depth where the layer was first recognised,

successfully characterised and dated. This ash layer can now be added to the regional

tephrochronological framework.

TiO 2

0.2 0.3 0.4 0.5 0.6

DGN2 190cm

GB4-182 Tephra

Kinnegad Bog BH9 34cm

1.0 1.5 2.0 2.5 3.0

Figure 55. Geochemical data for Kinnegad Bog BH9 34cm compared with Daingean

Bog (DGN) and the GB4-182 tephra layers. On these elements correlation is plausible.

FeO

K 2O

1.8 2.0 2.2 2.4 2.6 2.8 3.0

DGN2 190cm

GB4-182 Tephra

Kinnegad Bog BH9 34cm

1.4 1.5 1.6 1.7 1.8

Figure 56. Geochemical data for Kinnegad Bog BH9 34cm compared with Daingean

Bog (DGN) and the GB4-182 tephra layers. The data from GB4-182 differs on CaO and

K 2 O.

CaO

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Implications

The tephrochronological study at Kinnegad Bog has positively identified two ash layers via

geochemistry. These suggest that the upper parts of the bog covers the period 2400-3800

cal. BP and potentially contains a total of 6 ashes that, based around age and morphological

data, are consistent with the BMR-190, OMH-185, GB4-150, SvV, Hekla 3, and KND9-34

tephra layers. These layers provide a unique opportunity to age model the archaeological

structures at this site.

Ballykean Bog BH37

A 360cm core sequence was obtained from Ballykean Bog Co. Offaly 5m from the habitation

site. The sample was taken on an adjacent peat field and the surficial sediments were

thought to be contemporaneous with the archaeological structures (AD 200-500). A total of

nine separate peaks in tephra shard numbers were recorded between ca. 10-260cm (figure

57). These peaks comprise colourless and intermediate tephra shard-types and have been

prepared for geochemical characterisation. A summary of the tephra layers identified is

presented in table 1.

Table 12. Tephra layers identified and potential correlatives for Ballykean Bog BH37,

Co. Offaly.












Tephra layers 1-7 occur in the uppermost 50cm were prepared for geochemical analysis,

however only the layer identified at 10-11cm yielded chemical data in the initial study

(presented below). However, based on the alternating colourless and intermediate layers

and the distinctive morphology of the intermediate tephra shards, when compared to

reference material, tentative correlations are drawn with the Hekla AD 1104, BMR-90, AD

860, and GA4-85 tephra layers. Using the same approach the intermediate tephra layer

identified at 117cm (tephra layer 7) is tentatively correlated with the BMR-190 layer. All of

these layers with the exception of the GA4-85 tephra are represented within the current

regional tephrostratotype.

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Figure 57. Peat stratigraphy, organic matter content and tephra shard counts for BH37

Ballykean Bog, Co. Offaly. Due to the dominant peaks in colourless shards at 25 and

260cm some of the smaller peaks in shard concentrations are not distinct on this

diagram, for absolute counts and depths of each tephra layer see table 12.

Geochemical data from BH37

All nine layers identified in BH37 were prepared for geochemical analysis, however only the

colourless layer at 10-11cm yielded successful geochemical analyses. A total of twelve

analyses were obtained from this level (table 13). The geochemical signature of the tephra

demonstrates that it is a sub-alkali rhyolite from the medium potassic range/ calc-Alkaline

series (figures 58-59). This indicates that the ash layer is most probably derived from the

Iceland volcanic province in the central-eastern volcanic zone. In fact this ash has similar

chemical properties to others tephras identified across Europe that have been correlated with

products of the Hekla volcano.

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Table 13. Geochemical data derived from BH37 Ballykean Bog, Co. Offaly.

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Total

1 73.03 0.19 14.74 3.15 0.13 0.09 1.97 4.26 2.64 100.20

2 72.04 0.20 15.98 2.88 0.09 0.10 1.91 3.41 2.65 99.27

3 71.87 0.28 14.54 3.08 0.14 0.11 1.99 4.21 2.69 98.92

4 71.77 0.19 14.68 3.03 0.12 0.11 1.96 4.26 2.66 98.78

5 71.55 0.21 14.53 3.09 0.11 0.10 1.96 4.07 2.76 98.38

6 71.47 0.22 14.39 3.02 0.13 0.11 1.95 3.98 2.69 97.94

7 71.40 0.22 14.32 3.14 0.08 0.09 1.98 3.93 2.65 97.80

8 70.71 0.20 14.39 3.02 0.12 0.08 1.94 3.88 2.64 96.97

9 70.31 0.19 14.37 2.99 0.08 0.11 1.88 4.04 2.58 96.56

10 69.82 0.18 13.93 2.97 0.10 0.11 1.82 3.74 2.69 95.35

11 68.98 0.18 14.04 2.93 0.09 0.10 1.89 3.81 2.61 94.62

12 68.39 0.19 13.86 3.00 0.12 0.10 1.86 3.42 2.64 93.57

Mean 70.94 0.20 14.48 3.02 0.11 0.10 1.93 3.92 2.66 97.36

St Dev 1.35 0.03 0.55 0.08 0.02 0.01 0.05 0.29 0.04 2.01

The geochemical properties displayed in table 13 and figures 58-60 suggest that this

eruption from the Hekla volcano correlates with a known eruption in this case the eruption of

Hekla in AD 1104. This layer was predicted to equate with this eruption based on matching

of the layers in BH37 to the regional tephrochronological framework. This adds credence to

the other correlations that have already been made.

TAS (Le Bas et al. 1986)

Ultrabasic Basic Intermediate Acid

Na 2 O + K 2 O

0 5 10 15

Alkaline

Foidite

Picrobasalt

Basaltic

Tephrite

trachyandesite

Basanite

Trachybasalt

Basalt

Phonotephrite

Tephriphonolite

Basaltic

andesite

Phonolite

Trachyandesite

Andesite

Trachyte

Trachydacite

Subalkaline/Tholeiitic

Dacite

Rhyolite

40 50 60 70 80

Figure 58. A total alkali vs. Silica biplot of the geochemical data generated for BKN37-

10cm, the classification scheme used follows Le Bas (1986) and was produced using

the GCD toolkit computer program (Janousek et al., 2006).

SiO 2

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SiO 2− K 2O plot (Peccerillo and Taylor 1976)

K 2O

0 1 2 3 4 5 6 7

Shoshonite Series

High-K calc-alkaline

Series

Calc-alkaline

Series

Tholeiite Series

45 50 55 60 65 70 75

Figure 59. A potassium classification plot for the geochemical data from BKN37-10cm.

This suggests that the ash layer has medium potassic chemistry from the Calc-

Alkaline series. This plot follows the classification system of Peccerillo and Tayler

(1976) and was produced using the GCD toolkit computer program (Janousek et al.,

2006).

SiO 2

CaO

1.6 1.8 2.0 2.2 2.4

BH37 10cm

Hekla 1104 AD

2.0 2.5 3.0 3.5

FeO

Figure 60. A FeO vs. CaO bi-plot comparing the data generated from BKN37-10cm to

the geochemistry obtained for the Hekla 1104AD eruption. The close match between

these chemistries supports this correlation (Hekla AD 1104 data from

www.tephrabase.org/ last visited 01-11-2009).

Implications

These tentative allocations have implications for the archaeological interpretation of the

habitation structure identified at Ballykean. This structure dated to AD 200-500 is exposed at

the current bog surface (a period where very few ash layers are known to be deposited in

Ireland), it was expected that BH37 would represent sediment from ca. AD 200-500 and

further back in time. The identification of Medieval tephra layers in BH37 raises some

interesting questions regarding the peat stratigraphy which may be interpreted in three ways:

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i. The peat outside of the habitation structure has deflated (due to drainage) differently

to the sediments that occur inside the structure.

ii. The structure stood out of the surrounding peat or had open pools of water

surrounding it, which only became overgrown/infilled later than AD 200-500.

iii. The date for the habitation site is inaccurate.

All of these options may contribute to the uncertainties regarding interpreting the chronology

of the habitation site; however, an examination of the peat stratigraphy may explain the

situation. A major change in the stratigraphy between highly humified substania humosa and

moderately to poorly humified herb and moss peat occurs at 75cm. If the correlations to all

of the tephra layers can be verified then the age of this transition can be Bayesian age

modelled using a P_Sequence to AD 332-437, within the dated age range of construction of

the habitation site. This may indicate that the site was constructed in an area where open

pools of water and Sphagnum peats existed, which later infilled to record the later tephra

layers. Whatever, the reason for the later tephrostratigraphy recorded at BH37 it provides

the perfect opportunity to constrain the chronology of the habitation site and place it within

the wider environmental context. The correlations suggested here are more fully discussed

below.

Core TS3

Several zones of tephra deposition are recognised in core TS3 (figure 61). In total five areas

of interest have been identified, the first a diffuse zone of colourless and intermediate tephra

shards located between 24-52cm, a peak of 10 colourless shards identified between 96-

100cm, followed by 36 colourless shards identified between 140-144cm. A forth peak of 124

colourless vesicular shards was identified between 152-156cm and lastly a peak of both

colourless and intermediate tephra shards between 192 and 200cm.

Zone 1: 24-52cm

This diffuse zone of mixed shard morphologies displays several shard types that are

consistent with upper four peaks identified in BH37, of particular note are the intermediate

shards recognised at 24-28cm and those between 48-52cm which are consistent with layers

2 and 4 from BH37 respectively. This indicates that the TS3 core covers approximately the

same time period as BH37.

Peak 2: 96-100cm

This is a sparsely represented peak in shard concentrations with only ten ash grains

detected in the sample. The morphology of the grains was fluted to vesicular in nature. It is

likely this ash relates to peak 6 in BH37 where it is recognised between 109-110cm and is

characterised by 34 shards.

Peak 3: 140-144cm

This peak of 36 colourless shards contains predominantly small shards (long axis


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Peak 4: 152-156cm

The peak contains large numbers of colourless vesicular shards (124 shards). The shards

are not morphologically distinctive and could correlate with either peaks 7,8 or 9 identified in

BH37. Due to the stratigraphic position of the layer a match with peak 9 is plausible.

Figure 61. Outline tephra content of core BKN TS3. Both colourless and intermediate

tephra shards are observed in zone 1 and 4 while only colourless shards are identified

in peak 2 and 3.

Peak 5: 192-200cm

Peak 4 is represented by two mixed shard morphologies, the first a colourless vesicular

shard type with a subordinate intermediate population. It is unclear whether this layer

equates with any of the horizons identified in BH 37, although very low numbers of

intermediate shards were identified at 270cm depth in BH37 and it is possible this may be a

correlative.

Geochemical data from TS3

Three peaks in tephra shard concentrations identified in BH37 were prepared for

geochemical analysis (96-100cm, 140-144cm and 152-156cm), the two lower peaks yielded

geochemical information (table 14).

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140-144cm:

The geochemical signature of the tephra demonstrates that it is a sub-alkali rhyolite from the

high-k potassic range (Figure 62). This indicates that the ash layer is most probably derived

from the Iceland volcanic province in the central-eastern volcanic zone. The high alkali

values would suggest an off-axis source for the layer. In fact this ash has similar chemical

properties to others tephras identified across Europe that have been correlated with products

of the Torfajokull volcano. The best match for this ash layer based on its geochemistry and

stratigraphic position is the Lairg B tephra (6500 cal. BP). This ash has not been previously

recognised in the Irish Midlands and thus presents a unique opportunity to date and correlate

Late Mesolithic archaeology.

152-156cm:

The geochemical signature of the tephra demonstrates that it is a sub-alkali rhyolite from the

medium potassic range/ calc-Alkaline series (Figure 62). This indicates that the ash layer is

most probably derived from the Iceland volcanic province in the central-eastern volcanic

zone. In fact this ash has similar chemical properties to others tephras identified across

Europe that have been correlated with products of the Hekla volcano. The most robust

correlative for this ash layer based on chemical and stratigraphic grounds is the Lairg A

tephra (ca. 6900 cal. BP). This ash has not been previously recognised in the Irish Midlands

and thus presents a unique opportunity to date and correlate Late Mesolithic archaeology.

Table 14. Geochemical data from Core sample TS3 Ballykean Bog, Co. Offaly.





































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CaO

0.5 1.0 1.5 2.0 2.5 3.0

Ballykean Bog TS3 142cm

Ballykean Bog TS3 154cm

Hoy Tephra

Lairg Tephra A

Lairg Tephra B

2 3 4 5 6

FeO

Figure 62. A CaO-FeO biplot of the BKN TS3 geochemical data. This would suggest a

correlation between the tephra layers recorded in BKN TS3 with the Lairg A and Lairg

B ash layers and thus date this part of the sequence to ca. 6500-6900 cal. BP. These

represent the first identification of these ash layers in the Irish Midlands

Implications

The greatest difference between BH37 and TS3 is in shard numbers and how defined each

individual peak is within a sequence. These variations are to be expected as each part of the

bog will have more or less effective traps of tephra dependant on the surface vegetation and

surface water extent at the time of deposition. However these small differences apart it is

clear that the records have broad similarities that suggest establishing tephra counts for the

rest of the samples along the transect will provide valuable tephrochronological data and

palaeoenvironmental data.

Ballykean Column samples

The tephra identified in the Ballykean column (CAT-A) samples from beneath the Ballykean

Bog habitation site yielded low numbers of shards alongside a persistent background signal

of tephra input. This is common in archaeological samples where human activities disturb

the stratigraphy. Several observations can be made regarding the material:

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i. The upper layers (1-5) observed in BH37 and TS3 were not recorded, this suggests

that these have been removed and the archaeological structures must pre-dates

these events

ii. The peak in shard numbers at 45cm may reflect primary input and can be tentatively

correlated with the peak at 96-100cm in core sample TS3.

iii. The lower layer identified in TS3 are not present in this sequence.

iv. These data suggest that the palaeoecological data from this site can be constrained

to the Middle Holocene period.

v. The dates on the archaeological structures are probably not in error and the

sedimentation rate around the site must have influenced the exposure of the

habitation site alongside the upper ash layers (i.e. the rate of deposition was severly

reduced across the habitation site leading to its exposure alongside younger peats

directly surrounding the location.

0

5

10

15

20

25

30

Depth (cm)

35

40

45

50

55

60

65

70

75

0 10 20 30 40 50 60

shard numbers

Figure 63. Shard numbers detected in Ballykean Bog column samples and .

These samples underlie the habitation structure. A persistent background signal is

noted, however the peak in shards at 45cm may represent primary ash fall.

Ballykean TS samples

The sequences sampled across the 1000m transect of Ballykean Bog were processed for

tephra content and where appropriate ash layers were sampled for chemical analysis in

order to test the correlations suggested in BH37 and TS3. Of the sequences studied nine

yielded tephra the only layer that did not produce any tephra was TS0 which is closest to the

edge of the Bog. Slow accumulation of peat at this site combined with disturbance through

the mechanised processing of the peat may have removed the tephra record from this

sample. The initial tephra counts are presented in figure 64. Ash layers 1-5 in BH37 were

traced across the other boreholes and this suggests that the AD1104 land surface is

preserved across Ballykean Bog. This period is significantly after the construction of the

habitation site (ca. AD 580-680) and allows the assessment of the environment at Ballykean

Bog before, during and crucially after the occupation of the habitation site.

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Figure 64. Tephra layers identified across TS3 in Ballykean Bog Co. Offaly.

Geochemical data obtained from Ballykean Bog TS cores.

In order to test the correlations to ash layers suggested in BH37 two random samples were

selected for geochemical analysis. These were BKN TS5 40-45cm and BKN TS10 60-65cm.

Only the first yielded geochemical data and had been visually correlated with the AD860 ash

layer. Although some scatter is observed in the geochemical data a correlation to the AD

860 layer is plausible and no other known ash layer from this period can be considered a

better equivalent (Table 15, Figure 65).

Table 15. Geochemical data obtained from Ballykean Bog TS5 40-45cm. The chemistry

displays a mixed chemical population.













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K 2 O

0 1 2 3 4 5 6 7

860 AD Layer part A Tephra

860 AD Layer part B Tephra

Ballykean Bog TS5 42.5cm

Hekla 1104 Tephra

Shoshonite Series

High-K calc-alkaline

Series

Calc-alkaline

Series

Tholeiite Series

45 50 55 60 65 70 75

Figure 65. SiO 2 vs K 2 O plot for geochemical data from 40-45cm in BKN TS5. The best

match to the data is the AD860 ash layers (parts a+b).

SiO 2

Conclusions

The identification of the same tephra isochrons across archaeological, control and transect

samples is unique to Ballykean Bog. This provides an excellent opportunity to examine the

palaeoenvironmental proxy data on the same timescales. Plant macrofossil, palynological,

macroscopic charcoal, and elemental chemistry data has been produced for BH37, TS3, and

column samples and . These data will be integrated in order to provide a detailed

record of bog development and human exploitation of the landscape. At this stage it is

possible to suggest that Ballykean Bog at the point of construction of the habitation site had a

relatively dry surface dominated by grasses, and heather, however, these conditions

deteriorated to include higher amounts of taxa that live in wetter conditions as indicated by

relatively unhumified moss peat dominated by Sphagnum species (Figure 65). This

transition was not synchronous across the bog surface and the surface got progressively

dominated by sphagnum moss through until the current surface sediments (shortly after

Hekla AD 1104). This non-uniform response has profound implications for

palaeoenvironmental reconstructions from single core studies as it suggests these types of

study are not representative.

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Figure 65. Correlation of the ash layers identified across Ballykean Bog along the TS3

transect. The peat stratigraphy from Column samples and are included for

reference. The period correlated with the construction of the habitation site is marked

in grey. The data suggests that the habitation site was constructed on a relatively dry

bog surface that subsequently became wetter.

Additionally, the study of tephra layers at Ballykean Bog has identified two ash layers that

had not been previously detected in the Irish Midlands. These layers were correlated with

the Lairg A and Lairg B tephras and date to between 6500-6900 cal. BP. These layers

provide the opportunity to correlate human activities and environmental change during the

Late Mesolithic and Early Neolithic periods.

Ballybeg Bog Co. Offaly

Three peaks in tephra shard concentration were identified in the Ballybeg Bog Co. Offaly

sequence. These layers were sparsely populated and in order to obtain geochemical

analysis samples were not refined to 1cm samples. The peaks in shard concentrations

between the intervals 80-90 and 100-110cm were prepared for geochemical analysis as it

was considered that these provided the best opportunity to obtain geochemical data (Figure

66).

Figure 66. Shard counts for Ballybeg Co. Offaly. Samples prepared for geochemical

analysis are marked by a star.

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Geochemistry from Ballybeg Co. Offaly

The sample from 85cm was geochemically characterised and five successful analyses were

obtained. The geochemical signature of the tephra demonstrates that three of the analyses

are sub-alkali rhyolites from the high-k potassic range (Figure 67), while a further two

analyses are sub-alkali rhyolite from the medium potassic range/ calc-Alkaline series. This

indicates that two ash layers are represented within the sample. Both types of shards can be

attributed to Iceland volcanic province in the central-eastern volcanic zone. The high alkali

values for the first type would suggest an off-axis source for the layer. In fact this ash has

similar chemical properties to others tephras identified across Europe that have been

correlated with products of the Torfajokull volcano. The best match for this ash layer based

on its geochemistry and stratigraphic position is the Lairg B tephra (6500 cal. BP). This ash

has been recognised in Ballykean Bog during this study and thus presents a unique

opportunity to date and correlate these two sites. The second shard population been

correlated with products of the Hekla volcano. The most robust correlative for this ash layer

based on chemical and stratigraphic grounds is the Lairg A tephra (ca. 6900 cal. BP). The

appearance of these ash layers together is common in bog sites in Ireland and reflect their

close temporal spacing. This, combined with Lairg B, allows for direct comparison between

Ballykean and Ballybeg Bogs.

The ash characterised at 105cm produced three successful analyses. The tephra

demonstrates a sub-alkali rhyolitic chemistry from the high-k potassic range. The high alkali

values for the first type would suggest an off-axis source for the layer. In fact this ash has

similar chemical properties to others tephras identified across Europe that have been

correlated with products of the Torfajokull volcano. The best match for this ash layer based

on its geochemistry is the Lairg B tephra (6500 cal. BP), however, this correlation cannot be

supported due to the identification of the Lairg A and Lairg B ash layers in the 85cm sample.

It is suggested that this ash layer represents a new previously unrecognised tephra layer

derived from the Torfajokull volcano, the age of this layer is uncertain and it can only be

stated that it must pre-date 6900 cal. BP. Henceforth this tephra will be referred to as the

BBO1-105 tephra layer.

Table 16. Geochemical data from Ballybeg Bog, Co. Offaly.

Name SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O F Cl P2O5 SO2 Total

Ballybeg Bog Co.

Offaly BH3 85cm 73.00 0.30 11.75 2.42 0.09 0.25 1.56 4.26 2.53 0.09 0.06 0.04 0.01 96.35

Ballybeg Bog Co.

Offaly BH3 85cm 70.37 0.21 13.26 2.19 0.07 0.16 0.70 5.33 4.25 0.35 0.21 0.01 0.01 97.10

Ballybeg Bog Co.

Offaly BH3 85cm 70.09 0.21 13.61 2.30 0.06 0.14 0.74 5.16 4.45 0.29 0.22 0.02 0.00 97.28

Ballybeg Bog Co.

Offaly BH3 85cm 70.33 0.19 13.66 2.05 0.07 0.20 0.61 4.96 4.35 0.35 0.21 0.02 0.01 97.02

Ballybeg Bog Co.

Offaly BH3 85cm 73.64 0.31 12.11 2.49 0.09 0.20 1.53 2.63 2.50 0.09 0.06 0.04 0.02 95.71

Mean 71.48 0.24 12.88 2.29 0.08 0.19 1.03 4.47 3.62 0.23 0.15 0.03 0.01 96.69

St.Dev 3.39 0.12 1.77 0.35 0.02 0.08 0.95 2.21 2.01 0.27 0.16 0.03 0.01 1.30

Ballybeg Bog Co.

Offaly 105cm 71.31 0.20 14.01 2.15 0.07 0.13 0.71 4.93 4.41 0.14 0.22 0.02 0.00 98.30

Ballybeg Bog Co.

Offaly 105cm 70.46 0.21 14.15 2.19 0.06 0.11 0.61 4.71 4.61 0.15 0.21 0.01 0.00 97.48

Ballybeg Bog Co.

Offaly 105cm 69.64 0.22 13.79 2.09 0.06 0.20 0.74 5.20 4.26 0.29 0.21 0.02 0.00 96.74

Mean 70.47 0.21 13.98 2.14 0.06 0.15 0.69 4.95 4.43 0.19 0.21 0.02 0.00 97.51

St.Dev 1.67 0.02 0.36 0.10 0.01 0.10 0.13 0.50 0.34 0.17 0.01 0.01 0.00 1.56

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K 2 O

1 2 3 4 5 6

Ballybeg Bog Co. Offaly 105cm

Ballybeg Bog Co. Offaly BH3 85cm

Hoy Tephra

Lairg Tephra A

Lairg Tephra B

12.0 12.5 13.0 13.5 14.0 14.5 15.0

Figure 67. Al2O3 vs K2O Biplot of the Ballybeg, Co. Offaly. geochemical data for both

intervals. The data has been plotted against plausible correlatives namely Lairg A,

Lairg B, and the Hoy tephra layers

Al 2 O 3

Implications

The identification of Lairg A and B has provided supporting information for the identification

of these layers in Ballykean Bog. This, alongside a new Torfajokull ash layer (BBO3-105),

has led to a significant advance in the tephrostratigraphy of the Irish Midlands.

Implicatons for the Irish Midlands tephrostratigraphy

The identification of multiple tephra layers closely associated with archaeological structures

at both Kinnegad and Ballykean Bog’s points toward the potential for tephrochronology to

constrain human activities across these and the other Midlands bog selected for study in

2009.

Geochemical correlation of the tephra layers identified has currently allowed a partial

assessment of how these sites compare with the Midlands tephrostratotype, however, the

identification of an unknown intermediate tephra at Ballykean Bog and potentially prehistoric

tephra layers identified at both sites, support previous research carried out in the Irish

Midlands and indicate that there are more tephra layers available for correlation than are

currently recognised. Figure 68 displays the revised Irish Midlands tephrostratigraphic

framework and demonstrates that this research has added a further seven ash layers to this

framework including some not previously recognised across Northern Europe. This

significant advance has produced the opportunity to correlate human-environmental

interactions across a variety of sites and time frames.

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Figure 68. Potential correlations between the existing Midlands tephrostratigraphy

and the tephra layers identified at Kinnegad and Ballykean Bogs. These correlations

will be verified via geochemical data.

1.3.4.2 Co. Tipperary

Littleton Bog LTN-01TD

Three zones of tephra deposition have been detected at Littleton Bog, Co. Tipperary (figure

69). The upper and lower layers (20 and 240cm) comprise highly vesicular colourless

shards, while an intermediate tephra layer was detected at 80cm. The upper and lower layer

were not morphologically distinctive, however, the intermediate layer was morphologically

similar to the reference material for the BMR-190 tephra. This reference material was

generated from geochemically typed shards from Toar Bog Co. Westmeath in the Irish

Midlands and hence due to the morphological variations that would be expected across a

region the correlation of the BMR-190 with the layer detected at 80cm very tentative.

The entire sequence was sampled for tephra content including the basal sediments that

display a tri-partite sediment sequence which suggest that this part of the core covers the

Nahanaghan Stadial and Woodgrange Interstadial (broadly equivalent with GS-1 and GI-1

between ca.14,500-11,700 cal. yr BP) (Mitchell and Ryan, 1997). This core section provides

the first opportunity to detect lateglacial tephra layers in Co. Tipperary. During this period,

six tephra layers are recorded for the north of Ireland, however, no tephra layers have been

detected southern Ireland. No tephra layers were detected in these sediments and this

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would suggest that lateglacial tephra layers in southern Ireland are absent or so sparsely

represented that they fall below the detection level.

Figure 69. Peat stratigraphy, organic content, and tephra shard counts for Littleton

Bog, Co. Tipperary.

Geochemical data from Littleton Bog.

All three tephra layers were prepared for geochemical characterisation, however only the

upper layer yielded successful analyses (table 17).

Table 17. Geochemical data derived from LTN Littleton Bog, Co. Tipperary.

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O Total

1 75.19 0.16 13.07 1.68 0.06 0.08 0.8 3.83 3.91 98.82

2 74.46 0.18 13.42 1.87 0.04 0.08 0.94 4.01 3.65 98.69

3 73.58 0.14 13.29 0.97 0.08 0.18 1.42 3.75 3.48 96.85

4 72.42 0.22 14.67 1.42 0.02 0.37 1.81 3.81 3.06 97.83

5 71.99 0.2 14.46 2.79 0.09 0.09 1.94 4.38 2.72 98.69

6 71.76 0.18 14.42 3.08 0.09 0.1 1.96 3.89 2.74 98.28

7 70.89 0.11 12.79 0.95 0.04 0.19 1.36 3.33 3.54 93.24

Mean 72.9 0.17 13.74 1.84 0.05 0.16 1.46 3.86 3.3 97.48

St Dev 1.56 0.04 0.76 0.84 0.03 0.11 0.47 0.31 0.46 1.99

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A total of seven analyses were obtained from this level (table 17). The geochemical

signature of the tephra demonstrates that it is a sub-alkali rhyolite from the medium to high

potassic range/ High-K to calc-Alkaline series (figures 70 and 71). This indicates that the ash

layer is most probably derived from the Iceland volcanic province and the Eastern volcanic

zone. In fact this ash has similar chemical properties to others tephras identified across

Europe which, to date; have not been located in proximal exposures.

TAS (Le Bas et al. 1986)

Ultrabasic Basic Intermediate Acid

Na 2 O + K 2 O

0 5 10 15

Alkaline

Foidite

Picrobasalt

Basaltic

Tephrite

trachyandesite

Basanite

Trachybasalt

Basalt

Phonotephrite

Tephriphonolite

Basaltic

andesite

Phonolite

Trachyandesite

Andesite

Trachyte

Trachydacite

Subalkaline/Tholeiitic

Dacite

Rhyolite

40 50 60 70 80

Figure 70. A total alkali vs. Silica biplot of the geochemical data generated for LTN-

22cm, the classification scheme used follows Le Bas (1986) and was produced using

the GCD toolkit computer program (Janousek et al., 2006).

SiO 2

SiO 2 − K 2 O plot (Peccerillo and Taylor 1976)

K 2 O

0 1 2 3 4 5 6 7

Shoshonite Series

High-K calc-alkaline

Series

Calc-alkaline

Series

Tholeiite Series

45 50 55 60 65 70 75

Figure 71. A potassium classification plot for the geochemical data from BKN37-10cm.

This suggests that the ash layer has a medium potassic chemistry from the Calc-

Alkaline series. This plot follows the classification system of Peccerillo and Tayler

(1976) and was produced using the GCD toolkit computer program (Janousek et al.,

2006).

SiO 2

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A correlation of the ash layer identified in LTN-22cm is possible based on a database of

distally identified tephra layers. Based on this database a correlation with the OMH-185

tephra layer is made (figure 72). This tephra layer (also identified in the Irish Midlands

tephrochronological framework) has not previously been recognised in Co. Tipperary. If it

can be identified in other sites in the region it has the potential to constrain human activities

and environmental change during the Bronze Age – Iron Age transition. The OMH-185

tephra has been identified in Ireland where it has been dated by wiggle-match radiocarbon

dating to 755-680 cal. BC (2705-2630 cal. BP) (Plunkett et al., 2004). This layer has also

been identified in Germany where it is termed the ‘DOM-6 microlite-tephra’; this is because of

the large numbers of mineral inclusions that are typically observed in the shards (van den

Bogaard and Schminke, 2002). It is also recorded in Scotland where it is known as the

BGMT-3 tephra (Langdon and Barber, 2001), while a geochemically similar layer dating to

600 BC, derived from Vatnajökull, has been identified in Iceland (Larsen & Eiríksson, 2008).

K 2 O

0 2 4 6

BGMT-3

LTN 22cm

Microlite tephra

OMH-185 Tephra Ireland

0.0 0.1 0.2 0.3 0.4 0.5

TiO 2

Figure 72. A TiO 2 vs. K 2 O bi-plot comparing the data generated from LTN-22cm to the

geochemistry obtained for layers correlated with the OMH-185 tephra. The close

match between these chemistries supports this correlation (OMH-185 and BGMT-3

data from www.tephrabase.org/ last visited 01-12-2009, ‘Microlite’ tephra data from

van den Bogaard and Schminke, 2002).

Ballybeg, Co. Tipperary

A tephrostratigraphy was developed for BH4 at Ballybeg, Co. Tipperary. This exercise

attempted to identify the presence and absence of tephra at the site and link it to Littleton

Bog. A single ash layer was identified between 30-40cm which contained abundant microlite

inclusions. This interval was sampled for geochemical analysis and due to the small size of

the shards was analysed in TAU, Edinburgh.

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Geochemical analysis

A total of two successful analyses were obtained from Ballybeg Bog, Co. Tipperary. The

geochemical signature of the tephra demonstrates that it is a sub-alkali rhyolite from the

medium to high potassic range/ High-K to calc-Alkaline series (Figure 73). This indicates

that the ash layer is most probably derived from the Iceland volcanic province and the

Eastern volcanic zone. In fact this ash has similar chemical properties to others tephras

identified across Europe which, to date; have not been located in proximal exposures.

Table 18. Geochemical data obtained from Ballbeg Bog, Co, Tipperary.






Ballybeg Bog Co. Tipperary BH1 35cm

Littleton Bog 20cm

OMH-185 (Microlite) Tephra

CaO

1 2 3 4

1 2 3 4 5 6

FeO

Figure 73. Geochemical data from tephra layers identified in Littleton and Ballybeg

Bogs, Co. Tipperary. The data is compared with chemical data from the OMH-185

tephra layer.

This ash layer appears to be consistent with that geochemically characterised in Littleton Bog

and thus a correlation to the OMH-185 ash layer is made. This doubles the number of sites

where this ash has been recognised in Co. Tipperary.

Implications for the Co. Tipperary tephrostratigraphy

Prior to this investigation only one tephra layer (Hekla AD 1104) had been detected in the

Co. Tipperary region. With the identification of the OMH-185 tephra layer at Littleton and

Ballybeg Bogs the number of tephra isochrones available for comparison has been doubled.

If all of the layers detected at Littleton Bog and Ballybeg Bogs can be geochemically

characterised then they could potential add 2 or 3 further tephra layers to the regional

stratotype and increase the ability of tephrochronology to constrain palaeoenvironmental and

archaeological events.

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1.4 Tephrochronological conclusions and age modelling implications

The three sites that have detailed investigations for tephra content have all yielded multiple

tephra layers, many of which can be used to constrain archaeological and environmental

events. Once they have all been geochemically characterised these layers can be formally

included into age models of human activity in the Irish Midlands and Co. Tipperary. The

current visual correlations can be integrated into the Bayesian age models specifically at

Kinnegad Bog, where dendrochronological dates and radiocarbon dates from the

archaeology can be constrained using the tephra layers identified.

Revised tephra-based age models

The tephra layers identified at Kinnegad Bog occur close to archaeological structures and

from sequences where palaeoenvironmental data have been generated. The relationships

between these structures and records can be refined using the tephra layers identified.

Figure 74 displays the revised age model for Kinnegad BH3B using the inferred presence of

the GB4-150, BMR-190 and SvV tephra layers between 10-20cm. The lack of a clear peak

in shard concentrations from these ash layers means that identifying the stratigraphic

intervals that represent the volcanic eruption cannot be accurately determined. In this case

the upper and lower stratigraphic interval that represents the tephra layer are modelled as a

‘before’ and ‘after’ function i.e. the volcanic event occurs after the first appearance of the

tephra layer but before the last occurrence of shards related to that layer. Although this

lowers the overall precision, when this approach is combined with several tephra layers

acceptable precision is achievable.

Figure 74. P_Sequence depositional model for Kinnegad BH3B constrained using

radiocarbon dates and the presence of the GB4-150 and BMR-190 tephra layers. This

model provides significant improvements to the precision of the humification data

especially in the upper 24cm.

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This age model allows a better assessment of the phasing of palaeoenvironmental and

archaeological events than was hitherto possible and reduces the error ranges for the upper

part of BH3B from ca. 900 years to ca. 300 years with the tephra layers.

The timing of archaeological and palaeoenvironmental events at Kinnegad Bog.

The archaeological structures recorded at column 1+2 and across Kinnegad Bog can be

constrained by the tephra layers (figure 75), and this allows inferences to be made regarding

human activities at this site. The 2008 annual report outlined how Bayesian Phase models

can be used to integrate disparate archaeological structures, and how multi-phase models

can be used to further constrain the timing of construction of archaeological structures. With

the proposed tephra correlations now available for this site especially at Columns 1+2 these

relationships can be further refined.

Figure 75. Columns 1+2 from Kinnegad Bog Co. Meath with all the chronological

information against the stratigraphy (archaeological structures are shaded yellow).

The trackway must have been abandoned prior to the deposition of the colourless

tephra layer at 52cm depth in BH3B (inferred age 3294-3117 cal. yr BP). This pre-dates

the platform ME-KND011 dated to 3356-2975 cal. yr BP which in turn must have been

abandoned prior to the deposition of the GB4-150 tephra (2735-2693 cal. yr BP). In this

example the tephra layers can be used to directly constrain the age of construction

and abandonment of the archaeological structures.

The trackway identified at Kinnegad must have been abandoned and become overgrown by

the time that the colourless tephra recognised in Column 1 (50cm) and BH3B (52cm) was

deposited. This tephra has an age estimate of 3294-3117 cal. yr BP meaning that the

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maximum period that the trackway could have remained in use is 421 years. In fact, the

likely period of use of the trackway is significantly less than this due to the ca. 10cm of peat

deposited after the trackway was overgrown, but before the deposition of the tephra. When

further geochemical information for this tephra becomes available and its correlative can be

determined the chronology may be further refined using a P_Sequence approach. The

timing of trackway construction and maximum period of use is displayed in figure 75. This,

alongside the Humification records for BH3B and the regional climate record, suggests the

trackway was constructed on a wet but drying peat surface during the regionally identified

‘wet conditions’ at ca. 3600 cal. yr BP (Charman et al., 2006). The trackway must have been

abandoned during a period of dry stable conditions in the regional record, but in a fluctuating

wet and dry peat conditions in the local record. The lithostratigraphy for this section would

indicate that the abandonment occurred in the relatively dry peat conditions.

Apart from the use of the tephra layer as a limiting age for the use and abandonment of the

trackways this part of the phase sequence is the same as used in section 3.2.1.1, however

the identification of this tephra below platform ME-KND011 has implications for the modelling

of the platform phase. The age assigned to the tephra means that ME-KND011 cannot be

coincident with the earlier platforms (ME-KND006, ME-KND010 and ME-KND016), and ME-

KND016 is reported to occur below ME-KND015. Additionally, if the platform constructing

Phase occurred over a single period then all of the platform dates would occur after the

tephra age. If the platforms and tephra are placed within a Bayesian Phase model then

platforms ME-KND006, ME-KND010 and ME-KND016 do not agree with the modelled prior

assumptions, hence these archaeological structures are considered an earlier phase of

human activity than that represented by ME-KND011 and ME-KND015 (represented as two

phases named ‘platforms 1 and 2’ in figure 76). This indicates that the earlier platform

construction occurred at the same time or slightly post-dating the construction of the

trackway in regionally dry conditions (Charman et al., 2006). However, the local humification

record suggests oscillating wet and dry conditions possibly with localised pool formation. No

tephra layers have been detected that limit the use of these structures, however, based on

the tephra layers identified in the upper 15-20cm of BH3B and Columns 1+2 it would indicate

that they are likely to have been abandoned some time prior to 2800 cal. yr BP, in the case

of ME-KND016 its use is limited by the date for ME-KND015 which is stratigraphically above

the earlier platform. This limits the age abandonment for this structure to earlier than ca.

3400 cal. yr BP. The latest phase of platform construction occurs at ca. 3400 cal. yr BP and

concludes at ca. 2900 cal. yr BP with the platforms being abandoned prior to the deposition

of the GB4-150 at 2735-2693 cal. yr BP. This indicates that the platforms were constructed

on a peat bog that had increasingly wet conditions and were abandoned during the wettest

conditions centred on a regional climatic shift at ca. 2800 cal. yr BP.

In summary, all archaeological structures and human activities recorded at Kinnegad Bog are

constrained by two widespread regional shifts to wetter conditions at ca. 3600 and 2800 cal.

yr BP (during the Late Bronze Age and Bronze Age to Iron Age transition). The trackway

appears to have been constructed on a drying peat surface and is subsequently abandoned

either, during dry stable peat conditions, or during oscillating dry and wet conditions. This

may indicate that trackway construction occurred due to previously inaccessible parts of the

bog becoming more accessible due to drier peat conditions, or offsite stimuli indirectly linked

to this oscillation. This initial activity was closely followed by the construction of platforms on

an oscillating dry and wet peat surface but during a period of regionally dry climatic

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conditions. The first phase of platform construction ends with the structures abandonment

probably at ca. 3400 cal. yr BP during locally and regionally dry peat conditions. The local

and regional proxy data then indicate a shift to wetter conditions, during this period a second

set of platforms are constructed and subsequently abandoned during a regionally detected

shift to wetter conditions dated to ca. 2800 cal. yr BP.

This indicates that human activities in Kinnegad Bog are related to environmental stimuli with

trackway and platform construction occurring during regionally and locally recognised

environmental shifts. However, this relationship is not simple, different strategies for bog

navigation are used at different times, and the local environmental record does not always

reflect regional patterns. The tephra layers identified at this site and the Bayesian age




Figure 76. Three Phase model for the archaeological events and tephra layers

identified at Kinnegad Bog, Co. Meath. This is compared with the revised tephra and

radiocarbon based age model for the humification record collected for BH3B and the

regional climate curve of Charman et al., (2006). The upper and lower boundaries for

the three phases are presented alongside the limiting tephra dates (in red), and these

are converted into construction and abandonment envelopes (green and red bars).

Human activities are bounded by two regionally recognised shifts to wetter conditions

at ca. 3600 and 2800 cal. yr BP.

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4.0 CONCLUSIONS

Currently, the available chronological information for archaeological structures in wetland

sites is insufficient; it frequently relies on radiocarbon dates (e.g. Kinnegad Bog) and

dendrochronological dates that are effectively only limiting ages for the construction of

structures (e.g. Ballykean Bog). These dates allow the defining of phases of human activity

on bogs based around Bayesian age-models; however, the phase approach only

concentrates on the construction of structure and does not consider the length of use, timing

of abandonment, or environmental stimuli that may have influenced those who built it.

Ultimately, this approach can only offer limited information and does not integrate

archaeological and environmental chronologies in way that facilitates the testing of the

phasing and sequencing of archaeological and environmental events. This project has so far

demonstrated that tephra layers have been deposited in bogs across Ireland, and that more

tephra layers than are currently known exist within the study regions. The initial stages of

this research at Kinnegad, Ballykean and Littleton Bog have indicated that human activities in

raised bogs appear to be related to environmental stimuli, however this relationship is not

simple and different local and regional environmental stimuli result in different human

activities.

The key findings of this research are:

• Frequently too few dates are available to truly constrain archaeological and

environmental data, without improved chronologies the driving factors surrounding

human occupation and exploitation of wetlands remain unclear.

• Tephrochronology provides a robust basis for the correlation of archaeological and

Palaeoenvironmental sequences and thus allows the phasing and sequencing of

environmental change and human activities to be fully explored.

• The chronological data need to be constrained within appropriate Bayesian age

models in order to fully implement the improved chronological precision they

potentially offer.

• Robust regional palaeoenvironmental data is lacking and/or contains large

chronological errors there is a immediate need for the improvement of these records.

• The tephrochronological resource in Ireland has not been fully explored and requires

further refinement.

• A total of seven previously undetected tephra layers were recorded in the Irish

Midlands alone, these provide enhanced chronological control of peat sequences

during this time.

• The unique tephra transect study undertaken at Ballykean Bog suggest that bog

vegetation response is not uniform across distances of 100m or even 100m and

although clear trends ion peat stratigraphy may be identified they cannot be

considered isochronous. This research suggests lags in response between two

samples in the order of 200 years.

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