Review of Greenland Avtivities 2001 - Geus

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is abundant and highly diverse, and is referred to the Jumodontus gananda – ?Reutterodus andinus Interval of Ethington & Clark (1981). In the uppermost 100 m of the unit (above the grainstone marker horizon) the conodont fauna is, however, of low diversity and not biostratigraphically distinctive (Smith 1991). Narwhale Sound Formation On Ella Ø the Narwhale Sound Formation was only studied in section 4 (Fig. 1); in section 5 many closely spaced and nearly coast-parallel faults disrupt the succession. The sediments comprise sucrosic dolostones with a vuggy texture, and no original sedimentary structures are preserved. The base of the Narwhale Sound Formation is recorded as a prominent 7 m thick bed of laminated and cross-bedded dolostone and dolomitic bioturbated limestone. The remainder of the 260 m thick succession consists of pale grey to cream grey microcrystalline to sucrosic dolostone, pale grey to grey fine-grained dolomitic limestone and pale grey limestone. Small thrombolitic mounds are present and cross-bedding is common. Individual beds vary in thickness from 5 cm to over 7 m. Throughout the formation beds of brown to black cherts and chert-like silicified dolostones occur. The upper boundary is the Devonian unconformity. Silicified macrofossils are present. The fauna primarily consists of gastropods, cephalopods and occasional brachiopods, sponges and trilobites. Conodonts recorded from the upper part of the formation are Middle Ordovician in age (Smith & Bjerreskov 1994), and the Lower to Middle Ordovician boundary is probably within the lower part of the Narwhale Sound Formation (Fig. 2; Stouge 1978; Smith 1991). Albert Heim Bjerge The Albert Heim Bjerge are bounded by Wordie Gletscher to the north-east and Reservatet to the north (Fig. 1). The major E–W-trending valley of Promenadedal and the river Vibeke Elv form the southern limit of the study area (Fig. 1). The area is noted for the exposures of the Middle Ordovician Heimbjerge Formation, which is the youngest preserved pre-Caledonian unit in this part of North-East Greenland (Bütler 1940; Cowie & Adams 1957; Frykman 1979). As is the case on Ella Ø, Devonian clastic sediments unconformably overlie the Ordovician rocks. Investigations in the Albert Heim Bjerge area were focused on the ‘Black Limestones’ of the Cape Weber Formation and the type area of the Heimbjerge Formation (Fig. 1, section 6; Cowie & Adams 1957). Cape Weber Formation Cowie & Adams (1957) subdivided the Cape Weber Formation in the Albert Heim Bjerge into ‘Lower Limestones’, ‘Black Limestones’, ‘Upper Limestones’ and ‘Dolomites and Dolomitic Limestones’. The ‘Black Limestones’ facies has so far only been distinguished in the Albert Heim Bjerge area (Cowie & Adams 1957), where it is 80−100 m thick and consists of black, bituminous wackestone to grainstone with shaly partings, and with chert in the upper part. Fossils are common and trilobites, including a species of the cosmopolitic genus Carolinites, have been reported (Cowie & Adams 1957). In 2001 macrofossils were collected from the ‘Black Limestones’, and samples were collected throughout the unit for conodont studies. The ‘Black Limestones’ represent a deep-water marine incursion on the outer margins of the platform of North- East Greenland. On Ella Ø the coeval interval may be either the dark limestones and cherts of the upper part of Unit C, or the dark bituminous limestones of Unit D. Heimbjerge Formation The basal 10–15 m of the Heimbjerge Formation are dominated by brown and dark red laminated lime mudstones with birds-eye structures, stromatolites and bioturbated limestones. Above follows c. 50 m of laminated, grey brown lime mudstone with intraclast conglomerates overlain by platy carbonate mudstones with thin layers of calcite. A further 10 m are represented by a heterogeneous succession of massive and platy limestones, in places bioturbated, and marked by the development of small stromatoporoid mounds. Thick beds of light grey, bioturbated clean wacke- to grainstones with discontinuous horizons of chert nodules occur throughout the overlying 80 m of section. The highest exposed 50 m comprise a platy limestone facies dominated by the development of stromatoporoid bioherms. The preserved succession of the Heimbjerge Formation is only 300 m at the type locality in Albert Heim Bjerge, but Frykman (1979) recorded more than 1200 m of strata belonging to the formation on C.H. Ostenfeld Nunatak about 25 km to the north (Fig. 1). The Heimbjerge Formation is Whiterockian in age (Middle Ordovician; Smith & Bjerreskov 1994). 122
Thermal and burial history of the Ella Ø succession Smith (1991) briefly reported on the conodont alteration indices (CAI; Epstein et al. 1977) from the upper Lower to Middle Ordovician rocks of the study area. Low values (CAI 1–1.5) are characteristic for the study area, and higher values (CAI 2) are found in the C.H. Ostenfeld Nunatak succession to the north (Smith 1991). The provisional results of CAI studies on samples collected in 2000 and 2001 are reported below. The sequential change in colour of conodont elements reflects the progressive and irreversible alteration of organic matter preserved in the conodont elements in response to temperature, usually a consequence of thickness of overburden. The CAI values 1–5 have been experimentally calibrated with temperature ranges and correlated with other indices of organic metamorphism by Epstein et al. (1977). Thus, CAI 1 (50–80°C) and CAI 1.5 (50–90°C) are unaltered to nearly unaltered paleyellow to yellow conodont elements, CAI 2 (60–140°C) are yellow to light brown, whereas CAI 3 (110–200°C) comprises brown altered conodont elements. CAI determinations from limestones of the Antiklinalbugt Formation on Ella Ø give values of CAI 3 decreasing upwards to CAI 1.5 in the Cape Weber Formation and CAI 1 in the Middle Ordovician Narwhale Sound Formation. In Albert Heim Bjerge, CAI values are about CAI 1 in the Heimbjerge Formation. The CAI values recorded from the Ordovician succession on Ella Ø suggest that increased depth of burial was the major factor for the organic metamorphism and that the subsidence in the study area occurred during the Early Palaeozoic. A conservative estimate of the overburden responsible for the low CAI values in the Narwhale Sound Formation on Ella Ø and the Heimbjerge Formation in Albert Heim Bjerge is about 1.5 to 1.7 km. Thus, 1–1.5 km of strata of the formerly overlying carbonate sequence has been removed from the area between Albert Heim Bjerge and Ella Ø. It follows that the 1200 m thick sequence of the Heimbjerge Formation reported from C.H. Ostenfeld Nunatak by Frykman (1979) is virtually complete. Overburden estimates are based on the geothermal gradient estimates by Rasmussen & Smith (2001) in the Ordovician carbonates of the northernmost East Greenland Caledonides and the estimates of heat flow by Armstrong et al. (1994). Synthesis The summer of 2001 was devoted mainly to the Ordovician succession overlying the disconformity separating the Antiklinalbugt Formation and the Cape Weber Formation (Stouge et al. 2001). The hiatus corresponds to all of the Demingian Stage and the early part of the Jeffersonian Stage of the Canadian Series (Fig. 2). Faunal evidence from the Cape Weber Formation shows that the four informal units (A–D) represent most of the Jeffersonian and the Cassinian stages of the upper Canadian Series. The Canadian–Whiterockian Series boundary is apparently conformable and can be placed within the lower part of the Narwhale Sound Formation. The Heimbjerge Formation is Whiterockian in age, and sedimentary sequences younger than Whiterockian have not been recorded from the study area. The Ordovician strata below the Demingian disconformity have conodonts with CAI values of about 3, suggesting that organic maturity had been reached. The overlying strata of the upper Canadian – lower Whiterockian above the disconformity are organically mature to immature with CAI values 1.5 to 1. The upper Lower Ordovician – lower Middle Ordovician Cape Weber Formation and Narwhale Sound Formation represent a cycle of sedimentation beginning with subtidal facies and concluding with peritidal facies. There is a change from deposition on a slow subsiding passive margin to a faster subsiding margin characterised by rapid accumulation of carbonates. The cycle concluded with a regression in early Whiterockian time. The ‘Black Limestones’ of Albert Heim Bjerge and the coeval strata on Ella Ø possibly mark the global sea-level rise corresponding to the ‘evae’ transgression (= zones H–I), which is the highest sea-level stand in the Early Ordovician (Stouge 1982; Barnes 1984; Fortey 1984; Nielsen 1992). This sea-level rise can be traced in coeval shelf and slope deposits along the margins around the Laurentian palaeocontinent (Barnes 1984), and is characterised by the appearance of marginal shelf to slope faunal elements in the shallow-water carbonates on the shelf. A second sea-level rise may also be reflected by the ‘Black Limestones’ that correspond to Zone J of the upper Canadian Series. In Greenland, this younger sealevel rise has been recorded from the Nunatami Formation in North-West Greenland (i.e. the ‘Bifidus’ shale of Poulsen 1927) and has also been recognised in western and central North Greenland (Higgins et al. 1991). In western Newfoundland the sea-level rise has been identified on the basis of faunal evidence (Boyce et al. 2000). 123
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GEOLOGY OF GREENLAND SURVEY BULLETI
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Geology of Greenland Survey Bulleti
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Contents Numbers of articles corres
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■ ■ ■ ■ ■ ■ ■ ■ ■
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Canada Pituffik O 1 Thule Air Base
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Publications A complete list of geo
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Canada Greenland Greenland Inland I
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northern Nagssugtoqidian orogen (SN
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western to the north-eastern corner
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group consists of conjugate sets of
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y pure shear. Coincidence of the or
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The Precambrian supracrustal rocks
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68°25′ 52° 68°25′ BIF 0 3 km
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Fig. 4. Dolomitic marble in the sou
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Bugt (Fig. 1; Henderson 1969). The
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Keto, L. 1962: Aerial prospecting b
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▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲ ▲
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increases towards the south. We obs
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Kalsbeek, F. & Taylor, P.N. 1999: R
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Canada Nuussuaq 0 50 km PROTEROZOIC
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deposit. Descriptions of the differ
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Pegmatites The gneisses throughout
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tacts with quartzo-feldspathic coun
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Geological correlation of magnetic
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Fig. 2. The hand-held magnetic susc
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Susceptibility distribution (%) Sus
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have a reducing effect, which hinde
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ancy between the susceptibility val
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67° Sisimiut • 53° 52° 51° 50
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Table 1. Range of Nb concentrations
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chemical composition - may indicate
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Concentration/C1 chondrite 100.00 1
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Menzies, M.A. & Hawkesworth, C.J. (
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72°30´ Aeromag 2001 50 km Upernav
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56° 54° 52° 72° 72° nT 71°30
Page 74 and 75: Conclusions The aeromagnetic survey
Page 76 and 77: 53° 51° Inland Ice Greenland 72°
Page 78 and 79: On the south coast of Nuussuaq, wes
Page 80 and 81: Fig. 5. Blocks and boulders in the
Page 82 and 83: 2000 SW NE 1500 Surface trace 1985
Page 84 and 85: 1979). Along other sections of the
Page 86 and 87: Petroleum geological activities in
Page 88 and 89: Seismic acquisition during summer 2
Page 90 and 91: Other petroleum geological work Alt
Page 92 and 93: A multidisciplinary study of the Pa
Page 94 and 95: Seismic interpretation The grid of
Page 96 and 97: Middle Eocene Lower Eocene Upper Pa
Page 98 and 99: Chalmers, J.A., Dahl, J.T., Bate, K
Page 100 and 101: 95-06 ▲ ▲ 58° 95-12 95-10 56°
Page 102 and 103: 70° 71° 60° 2000 2000 2400 400 1
Page 104 and 105: Storey, M., Duncan, R.A., Pedersen,
Page 106 and 107: 24° 100 km 30° 27° 21 ° Jameson
Page 108 and 109: Oligocene Krabbedalen Fm Eocene Bop
Page 110 and 111: grading. Bivalve shell material is
Page 112 and 113: References Birkenmajer, K. 1972: Re
Page 114 and 115: B A 72° Palaeogene basalts Gl 50 k
Page 116 and 117: a b c d e f g h 20 µm i j k l Fig.
Page 118 and 119: offshore South-East Greenland, onsh
Page 120 and 121: ▲ Albert Heim Bjerge Wordie Gletc
Page 122 and 123: T D A CW NS placed the lowermost c.
Page 126 and 127: The Heimbjerge Formation comprises
Page 128 and 129: Late Permian carbonate concretions
Page 130 and 131: m 25 20 15 B3 L2 B2 Fig. 3. Simplif
Page 132 and 133: (2001), who pointed out the restric
Page 134 and 135: Piasecki, S. 1984: Preliminary paly
Page 136 and 137: 66° 68° • • • • • • 7
Page 138 and 139: absent at Tikeraussaq where a postu
Page 140 and 141: 72° 70° 68° 66° Sample locality
Page 142 and 143: Table 2. Summary of selected elemen
Page 144 and 145: Concluding remarks Observations dur
Page 146 and 147: Lake-catchment interactions with cl
Page 148 and 149: lakes. As in earlier reports (e.g.
Page 150 and 151: Discussion Global climate models pr
Page 152 and 153: Glaciological investigations on ice
Page 154 and 155: Fig. 2. The new one-mast design of
Page 156 and 157: A B N 20 km 1993 1995 Fig. 5. Satel
Page 158 and 159: Krabill, W., Frederick, E., Manizad
Page 160 and 161: 2001/47: Calibration of stream sedi
Page 162 and 163: Hanghøj, K., Kelemen, P., Bernstei
Page 165 and 166: Danmarks og Grønlands Geologiske U
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