VIKING UNST PROJECT: FIELD SEASON 2008 - Nabo

More documents

Recommendations

Info

nature of these infills and any information they may provide on the purpose and use of thegully and the overall use-history of the more severely truncated lower room.4.6 A GEOARCHAEOLOGICAL ASSESSMENT OF DEPOSITS AT HAMAR AND THE UPPERHOUSE, UNDERHOULLZ. Outram & M.J. ChurchA programme of geoarchaeological assessment of occupation deposits was carried out atHamar during the 2007 excavation season, and was continued at both sites in the <strong>2008</strong>season. It was hoped that any activity carried out on these deposits would be reflected in thechemical and magnetic signatures recorded by the samples. A number of techniques havebeen used to analyse the deposits with the aim of identifying evidence that relates to its use,including: magnetic susceptibility and viscosity, organic and inorganic phosphates, pH, andsoil lipid analysis. A multidisciplinary approach is advantageous as it allows theinformation produced by the different techniques to be compared, contrasted andcorrelated, providing a more detailed assessment of the processes that resulted in theformation of the sampled deposits.Samples were collected at regular intervals where possible, spaced 20cm apart from theupper room House 1 and at the Upper House, Underhoull. The exceptions to this relates tothe samples collected using the in situ magnetic susceptibility survey, which was carriedout using a 5cm grid. The deposits sampled at Hamar related to a potential occupationsurface defined by contexts: [369], [389], [401], [402], and [246]. The deposits sampledfrom the interior of the Upper House, Underhoull, collected material from a 2m widetransect through the centre of the structure, and sampling contexts: [070], [123], [143],[168], and [169].4.6.1 Magnetic Susceptibility & ViscosityThe background magnetism of a site is a measure of the concentration and composition ofthe magnetic minerals present, as well as the size and shape of the magnetic grains withinthese minerals. This largely reflects the underlying geology of the area, but the effects ofhuman and natural activities can enhance/alter these different parameters, such as throughheating/burning, fermentation and dehydration (Tite & Mullins 1971; 209; Thompson &Oldfield 1986; 75; Dearing 1999; 60). With this in mind, samples were collected forassessment using both magnetic susceptibility and magnetic viscosity in order to identifyany possible evidence of enhancement to the deposits.Magnetic susceptibility provides a measure of the ability of a material to becometemporarily magnetised when placed within a magnetic field, being dependent on themineralogy, size and concentration of the magnetic minerals present. Enhancement of themagnetic susceptibility of a deposit is largely related to processes of heating/burning,converting non-ferrimagnetic minerals to ferrimagentic minerals, such as magnetite(Thompson & Oldfield 1986; 75; Marwick 2005; 1359). In addition to heating,fermentation/decay processes of organic material within a deposit have been linked to theenhancement of magnetic susceptibility through the action of microbial, organic matter and60
iron within the soils (Gaffney & Gater 2003; 38; Tite & Mullins 1971; 209-210; Linford2004; 178). Both of these processes can occur in archaeological deposits. The patterns ofenhancement across the structure will therefore be useful in the interpretation of the site.In terms of the magnetic viscosity, this provides a measure of the ease of which magneticgrains become aligned with an external magnetic field. Materials with higher magneticviscosity values are dominated by larger magnetic grains, as these take longer/more energyto align with the magnetic field (Gaffney & Gater 2003; 46). It has been noted that therepeated heating and cooling of magnetic materials tends to reduce the size of the magneticgrains, corresponding to a decrease in the magnetic viscosity (Gaffney & Gater 2003; 46).An assessment of this parameter will therefore provide some indication as to the intensityof activity within the area, as well as the occurrence of industrial activities such as metalworking.In addition to the individual measurements of magnetic susceptibility and viscosity, thebenefits of combining the assessments have been demonstrated. By simply determining therelationship between these two parameters, Gaffney and Gater have shown that adistinction can be made between samples enhanced through industrial and domesticactivities, providing further information regarding the intensity of the activities carried outat Hamar and the Upper House, Underhoull (Gaffney & Gater 2003; Figure 157).The measurements of magnetic susceptibility and viscosity are carried out on 50g of driedand sieved samples. The assessment of magnetic susceptibility will be carried out using alow field A.C. susceptibility bridge (Evans & Heller 2003; 63), while the magneticviscosity will be assessed using a pulsed induction meter (P.I.M). In addition to thelaboratory measurements of magnetic susceptibility, in situ assessments were carried out inthe field using an Exploranium KT-9 Kappameter across a 5cm grid of the lower room ofHouse 1.The preliminary results from the use of the Exploranium meter have been very encouragingfor the measurements collected from the lower room of House 1 at Hamar during the 2007season. The background level of magnetic susceptibility was subtracted from the readingsbefore being plotted as a 2-dimensional contour map; higher values were represented as thedarker areas of the plot and therefore highlighted potential ‘hotspots’ of activity within thelower room. It was clear that there were two main areas of high magnetic susceptibilitymeasurements, corresponding to the area adjacent to the southern doorway, and a smallcircle within the upper area of the lower room, which appears to correspond to a small gullyfeature running down the centre towards the upper room (figure 4.1). It is not yet clear whatthese ‘hotspots’ relate as the other geoarchaeological techniques applied to the sampleshave not yet been completed.4.6.2 Phosphate analysisThe use of phosphate for geochemical prospection is a well documented technique (Bethell& Máté 1989). Phosphorus is abundant within soil systems, being present in both inorganicand organic forms, as well as in both soluble and insoluble forms. The use of this elementin prospection is based on the fact that different activities enhance the levels of phosphate61
Page 1 and 2:
VIKING UNST PROJECTEXCAVATIONS AT H
Page 3 and 4:
This is a provisional report on the
Page 5 and 6:
PART TWO: PERSONNEL AND RELATED RES
Page 7 and 8:
PART ONEEXCAVATIONS AT HAMAR &THE U
Page 9 and 10: A geophysical survey of the site wa
Page 11 and 12: The 2006 & 2007 excavation seasonsT
Page 13 and 14: sites are multiperiod settlements s
Page 15 and 16: more complex; geophysics would be a
Page 17 and 18: floor surface included fragments of
Page 19 and 20: Lower room & ash pitWork also concl
Page 21 and 22: Figure 2.2: Plan of the sunken floo
Page 23 and 24: External DepositsA section was exca
Page 25 and 26: along the north edge (open side) of
Page 27 and 28: Figure 2.5: The south east annexe,
Page 29 and 30: At the lower (easternmost) end of t
Page 31 and 32: 3. SUMMARY OF FINDS FROM THE 2008 S
Page 33 and 34: 46mm) with working marks on three s
Page 35 and 36: 3.2.2 A geological assessment of th
Page 37 and 38: minerals are chemically stable in n
Page 39 and 40: the same stone. SF721 (context [117
Page 41 and 42: context [185] is a fine example of
Page 43 and 44: close proximity of steatite outcrop
Page 45 and 46: oom. The three body sherds are fair
Page 47 and 48: Greenland and Iceland that a number
Page 49 and 50: channel changes from U-shaped to V-
Page 51 and 52: 4. ENVIRONMENTAL EVIDENCEJ.M. Bond,
Page 53 and 54: The cereals recovered are hulled si
Page 55 and 56: five barley grains and a single oat
Page 57 and 58: 4.3.2 The Upper House, UnderhoullAs
Page 59: [176]. The identification of microl
Page 63 and 64: 63Figure 4.1: The graphical represe
Page 65 and 66: SitecodeSamplecodeContext SFnumberA
Page 67 and 68: presence of tephra within the depos
Page 69 and 70: has been widely criticised as too g
Page 71 and 72: Outram, Z., Cussans, J.E., Summers,
Page 73 and 74: Level Two StudentsKirsty BennellJoh
Page 75 and 76: 8. BIBLIOGRAPHYAlsvik, H. and Batey
Page 77 and 78: Davidson, D.A. and Simpson, I.A. 20
Page 79 and 80: McDonnell, J.G. 2000. Pyrotechnolog
Page 81 and 82: 700s-800s: a potential alternative
show all

VIKING UNST PROJECT: FIELD SEASON 2008 - Nabo

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?