Central West Greenland Research Articles

Interpretation of flat-lying Precambrian structure by geological photogrammetry along a 65 km coastal profile in Nuussuaq, West Greenland

Photogrammetry employing several unequal models was used in the study of a c. 65 km long coastline of Precambrian basement rocks along Qarajaq Isfjord in northeastern Nuussuaq, central West Greenland. A geological profile was drawn parallel to a steep and inaccessible coastline at a scale of 1:50 000, on the basis of photographs at scale c. 1:175 000 taken with a hand-held camera from a helicopter. Two short profiles along the same coast were drawn at a scale of 1:25 000 from photographs at scale c. 1:40 000. The multi-model photogrammetry provided an accurate, flexible and powerful geological mapping tool in inaccessible terrain, whereby the general flat-Iying structure could be analysed. Broken-up remnants of an extensive anorthosite-gabbro complex could be correlated, and several geological features not recognised in the field were discerned. However the application of multi-model photogrammetry along irregular cliff faces is less suitable in folded rocks with complex three-dimensional structures, than in flat-Iying sequences of undeformed rocks.

Geological setting of Precambrian supracrustal belts: a fundamental part of mineral resource evaluation in Greenland

In Precambrian shield areas the economic potential of supracrustal rocks is well documented, and some of the world's largest metal deposits are found within these sequences. The Black Angel lead-zinc stratabound mineralisation at Mårmorilik in central West Greenland (71° 10'N, Fig. 1), hosted in the Proterozoic Karrat Group, is one commercial enterprise that confirms that this potential can be realised in Greenland. In last year's volume of Report of Activities, Thomassen (1991a) gave a history of the geology and mineral exploration of the Black Angel deposit.

Petroleum geological activities in 1991: reassessment of earlier exploration, and improvement of information service to industry

The shift of emphasis in the petroleum-geological activities of the Geological Survey of Greenland (GGU) from East to West Greenland that was described in the Report of Activities 1990 was consolidated in 1991 in so far as onshore activity is concerned, as the main onshore field activity was in the Cretaceous-Tertiary outcrops in central West Greenland. Offshore West Greenland, reinterpretation of industry data from the 1970s was continued (see Chalmers, 1990). In May processing of the 5200 km seismic data acquired offshore West Greenland in 1990 was completed and interpretation of the data began, and in July two supplementary lines totalling 336 km were acquired offshore West Greenland using the KANUMAS project's vessel Thettis prior to its departure to North-East Greenland. Any geographical bias there may be towards West Greenland is however subsidiary and largely coincidental to the overall current emphasis in GGU's petroleum-geological activities, which is the reassessment of areas of earlier exploration with regard to coming licensing rounds in Greenland. In November 1991 the Mineral Resources Administration for Greenland (MRA) issued a press release in which the time-table for coming licensing rounds offshore West Greenland was outlined. The first of these rounds was announced formally in early April 1992, with the closing date for submission of applications 15 January 1993. The Jameson Land basin in East Greenland has been declared 'open acreage' , and interested companies are invited to contact MRA to discuss licensing terms. An exploration report on the Jameson Land basin specifically designed for management has been prepared by GGU and is now on sale.

Photogrammetric mapping of fluvial channel sand-bodies in the Atane Formation at Paatuut, Nuussuaq, central West Greenland

Upper Cretaceous deltaic sediments from the Atane Formation are well exposed in a series of steep-sided gullies at Paatuut on the south coast of Nuussuaq. The large exposures within the gullies allowed a large-scale sedimentological investigation of delta stratigraphy, sand-body geometry and fluvial style of the distributary channels. Multi-model photogrammetry was applied in several ways. Photogrammetric mapping of good exposures within the area produced accurate vertical sections up to 2 km long and 0.5 km high. A bed to bed stratigraphy of the delta cycles was established and the sand-bodies within each cycle correlated. The horizontal extent of the sand-bodies was subsequently mapped photogrammetrically using the already orientated stereomodels. This mapping allowed a three-dimensional interpretation of the sand-body geometry. Cross-sections of the sand-bodies and the sand-body geometry formed the basis for the interpretation of the fluvial style of the distributary channels. Using the three-dimensional photogrammetric data the width/thickness ratio, the sinuosity and the shape of sand-bodies as well as of palaeochannels are described. These data are useful when modelling the reservoir geometry in deltaic hydrocarbon fields.

New methods for the geological analysis of Tertiary volcanic formations on Nuussuaq and Disko, central West Greenland, using multi-model photogrammetry

A series of experiments with multi-model photogrammetry were made during the compilation of a 80 km long section along the south coast of Nuussuaq. The section covers a range of Tertiary volcanic lithologies which overlie Mesozoic to Tertiary clastic sediments. The multi-model method allows the geological analyses of flat-lying lithologies in steep or inaccessible terrain and the compilation of detailed sections, profiles, and block diagrams. Drawing of sections or maps is combined with accurate structural measurements to document the flow directions of both subaerial and subaqueous volcanic units and to demonstrate syn-and post-volcanic basin movements and the location of volcanic eruption sites. Multi-model photogrammetry experiments made by compiling the geology of areas already covered by field work has led to major new discoveries. Similar experiments made on areas, which had not been visited in the field before the compilation, but which were visited later, demonstrates that the method is an important new tool in geological reconnaissance.

Disko Bugt Project 1991, West Greenland

One of GGU's major field activities in 1991 took place in July and August in the Disko Bugt region of central West Greenland. This was the third year of field investigations under the 'Disko Bugt Project', planned for 1999–1992, with one summer's break in 1990. The project spreads over various activities and over two very different geological provinces: the Archaean-Proterozoic basement east and north-east of Disko Bugt, and the onshore part of the Cretaceous-Tertiary basin in the west, on Disko and the western part of Nugssuaq (Fig. 1). In 1989, the second year of the project, work was concentrated in the eastern basement part of the study area, and in 1991 this work was brought to conclusion. In 1992 field work (including a shallow core drilling campaign) will be concentrated in the sediments and volcanics on Nugssuaq and Svartenhuk Halvø to the north. The main aim of the Disko Bugt Project is to provide a background for the evaluation of the economic potential of the regional mineral resources, mainly in the Precambrian basement, and the hydrocarbon potential of the neighbouring basin offshore (see Kalsbeek, 1989. 1990).

The occurrence of marine fossils in the Upper Cretaceous deltaic sediments at Pautut, central West Greenland

Finds of Upper Cretaceous marine macrofossils from Pautut have been reported since 1874. Subsequent investigations have led to contrasting views concerning the stratigraphic position of the fossils, the general depositional environment, and the amount of marine influence. During a brief visit to Pautut in the summer of 1989, a section of the exposed sediments was described. The sediments can be divided into 4 facies associations reflecting deposition on a prograding delta front, in distributary channels, on a subaerial to limnic delta plain and on an abandoned delta lobe during a marine transgression. The sedimentological model predicts that marine fossils, if present, should occur in the delta front association. The sediments were thoroughly searched for marine macrofossils, which were found in the lower part of the prominent coarsening-upward delta front sequences. The number of fossils is generally low. Bivalves and echinoids constitute the dominant groups of fossils and seem to have been well adapted to a life in muddy marine bays, subject to fluctuations in salinity and rate of deposition and with much suspended sediment. The fossils indicate that the beds at Pautut were deposited during latest Santonian to earliest Campa­nian times. Sediment accumulation rates were high. The stratigraphy within the Pautfit area is discussed and all the Cretaceous sediments are referred to the Atane Formation.

A new, detailed ice-age oxygen-18 record from the ice-sheet margin in central West Greenland

A new detailed oxygen-18 record measured on surface-ice samples from a West Greenland ice-margin location reveals the hitherto longest climatic record from the Greenland ice sheet, spanning the last c. 150,000 years. The new record implies that the Greenland deep ice-core records from Dye3 and Camp Century need to be re-interpreted. A comparison with the deuterium record from the Vostok deep ice core, Antarctica indicates that climate behaved differently in the northern and southern hemispheres during the last glacial/interglacial cycle, with major differences occurring in Emiliani isotopic stage 5.

A new, detailed ice-age oxygen-18 record from the ice-sheet margin in central West Greenland

A new detailed oxygen-18 record measured on surface-ice samples from a West Greenland ice-margin location reveals the hitherto longest climatic record from the Greenland ice sheet, spanning the last c. 150,000 years. The new record implies that the Greenland deep ice-core records from Dye3 and Camp Century need to be re-interpreted. A comparison with the deuterium record from the Vostok deep ice core, Antarctica indicates that climate behaved differently in the northern and southern hemispheres during the last glacial/interglacial cycle, with major differences occurring in Emiliani isotopic stage 5.

Age of growth of two pingos, Sarqaq Dalen, West Central Greenland

AbstractThe aim of this note is to identify the beginnings of growth of two pingos located in Sarqaq Dalen, west‐central Greenland. One is located at the toe of an alluvial fan, and seems to be active; the other is on a river bed, and already collapsed. Marine sand covers the pingos and indicates that the Holocene transgression predates their growth. The pingos are located approximately 2 km from the present coastline. Pollen analysis of the overlying sediments of the two pingos leads to the following conclusions: (1) although the study area had already emerged from the sea at Post Fjord stage (7800 years BP), it was submerged again sometime between 7000‐5000 years BP; (2) one pingo started its growth approximately 4500 years BP; (3) the other pingo started its growth approximately 6000‐5500 years BP.

Ice drilling and mass balance at Pâkitsoq, Jakobshavn, central West Greenland

Hot water drilling and mass-balance measurements were made on the Inland Ice at Pakitsoq north-east of Jakobshavn. Two arrays of moderate and shallow-depth thermistor strings have been installed in the ice to map the englacial temperature from the ice margin to the equilibrium line. Water fluctuations were observed in a drill hole connecting to the ice bed. The measurements indicate a high subglacial water pressure dose to the ice overburden pressure.

A Detailed Oxygen-18 Profile From The Greenland Ice-Sheet Margin Through The Wisconsinan-Holocene Transition

About 1500 surface-ice samples for δ18O analysis were collected in the 1988 field season along a 750 m profile perpendicular to the margin of the Greenland ice sheet at Pakitsoq, ca 40 km north-east of Jakobshavn, central West Greenland. The purpose of the study was to evaluate how well the continuity of the layer sequence is preserved in ice-margin records, a question of crucial importance for evaluating the potential yield of using ice margins as “mining areas” for easily accessible old ice for climate and environmental studies. More than half of the 1500 samples were taken continuously as 20 cm samples along a 170 m section through the Wisconsinan-Holocene transition which, previously, had been located at the surface of the ice margin. Along this transition section δ18O values decrease by about 6‰ from −31.5 to 37.5‰ on an average. Detailed studies were made of surface elevations and surface structures (e.g. blue bands) along the “horizontal core” profile which, moreover, was photographed section by section, thus enabling the δ-record to be correlated with surface features. Results of the δ18O analyses are promising. Even though ice from the blue bands has δ-values that are 7–8‰ higher than those of the surrounding white ice, there seems to be no discontinuity in the white-ice δ-record across the blue bands.

A Detailed Oxygen-18 Profile From The Greenland Ice-Sheet Margin Through The Wisconsinan-Holocene Transition

About 1500 surface-ice samples for δ18O analysis were collected in the 1988 field season along a 750 m profile perpendicular to the margin of the Greenland ice sheet at Pakitsoq, ca 40 km north-east of Jakobshavn, central West Greenland. The purpose of the study was to evaluate how well the continuity of the layer sequence is preserved in ice-margin records, a question of crucial importance for evaluating the potential yield of using ice margins as “mining areas” for easily accessible old ice for climate and environmental studies.More than half of the 1500 samples were taken continuously as 20 cm samples along a 170 m section through the Wisconsinan-Holocene transition which, previously, had been located at the surface of the ice margin. Along this transition section δ18O values decrease by about 6‰ from −31.5 to 37.5‰ on an average. Detailed studies were made of surface elevations and surface structures (e.g. blue bands) along the “horizontal core” profile which, moreover, was photographed section by section, thus enabling the δ-record to be correlated with surface features.Results of the δ18O analyses are promising. Even though ice from the blue bands has δ-values that are 7–8‰ higher than those of the surrounding white ice, there seems to be no discontinuity in the white-ice δ-record across the blue bands.

A new anorthosite/gabbro complex at Nûgssuaq, central West Greenland

As part of the GGU activity in the Disko Bugt region, central West Greenland (Kalsbeek, 1989), the authors carried out helicopter-supported geological reconnaissance mapping and stream sediment sampling for geochemical mapping in the area between Jakobshavn Isfjord and Qarajaq Isfjord (fig. 1). A considerable part of the season was spent in the eastern part of the Nûgssuaq peninsula, partly to complete the stream sediment sampling initiated in 1986 (see Steenfelt, 1988) and also because previous geological field work in eastern Nûgssuaq was very limited. The existing geological map at a Rapp. Grønlands geol. Unders. 145. 16-20 (1989) scale of 1:500 000 covering Nûgssuaq is almost entirely based on interpretation of aerial photographs. During the field work large occurrences of hitherto unknown anorthosite/gabbro rocks and supracrustal sequences were discovered in the gneiss terrain. Both the anorthosite/gabbro and supracrustal units appear to be tectonically interleaved with strongly foliated, flat-Iying or shallowly south-dipping orthogneisses, which themselves contain numerous shear zones suggesting substantial subhorizontal movements.

Reinvestigation of the Cretaceous boundary fault in Sarqaqdalen, Nûgssuaq, central West Greenland

A reinvestigation of the major fauIt in Sarqaqdalen was undertaken in 1988 in response to a renewed interest in the style and timing of the whole fault system that marks the easterly limit of Cretaceous sediments in central West Greenland. This interest stems in turn from the reinterpretation ofseismic lines from the 1970s that has recently been initiated in GGU (Chalmers, 1988; 1989). Dating of seismic sequences isinfiuenced greatly by what ean be learnt from the nearest onshore outcrops, for example proven unconformities in onshore sequences, and demonstrable relationships between sedimentation and fauIt movements.

Continued stable isotope studies on the Greenland ice-sheet margin at Pâkitsoq, north-east of Jakobshavn, central West Greenland

In close cooperation with the GGU glacier-hydrologicaI field team a small group from the Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven, West Germany, worked for four weeks in July-August 1988 on the West Greenland ice-sheet margin at Paakitsup Akuliarusersua, about 40 km northeast of Ilulissat/Jakobshavn. Previous stable isotope studies in the area by GGU (Reeh & Thomsen, 1986) have documented that ice deposited in the inland regions of the ice sheet during the last ice age is now exposed as a roughly 600 m wide band at the surfaee of the ice sheet near the ice edge (Reeh et al., 1987a). The main purpose of the AWI expedition was to perform detailed (continuous) surfaee sampling for stable isotope analysis (bIBO) through the transition from the last glacial period (Wisconsinan) to the present post-glacial period (Holocene). A comparison of such a detailed isotopic record from the surface of the ice margin with similar records from deep Greenland ice cores should tell how well the continuity of the layer sequence is preserved in the ice-margin record. This question is of crucial importance for evaluating the potential yield of the ice margin as a source of easily accessibie old ice.

Gravity and magnetic susceptibility survey over the northern part of the supracrustal rocks in the Disko Bugt area, central West Greenland

As part of the Disko Bugt project (Kalsbeek, 1989) a survey of gravity and magnetic susceptibility was carried out over parts of the supracrustal rocks and the Atå granite/tonalite (fig. 1). The objective of the survey was to acquire new geophysical data that, together with the existing regional aeromagnetic survey in the area (Thorning, 1988), can be used to study the deeper structures related to the granite and the supracrustal belts in the area.

Sedimentological studies in the Upper Cretaceous coal-bearing strata of southern Nûgssuaq, central West Greenland

During the 1988 field scason coal-bearing strata in the Upper Cretaccous Atanc Formation an southern Nûgssuaq, West Greenland (fig. I) were investigated in order to describe and interpret the sedill1cntological features. an the basis af this, it was hoped that a more refined synthesis of the regional geology could bc made. Previous work in the area has dealt mainly with thc dating of the formation (earlier references in Rosenkrantz, 1970), its assemblage of plant fossils (Heer, 1983; Seward, 1926), marine macrofossils (Steenstrup, 1874; Ravn, 1918) and its coal potential and petrography (Shekhar et al., 1982). The general depositional environment was discussccl by Sehiener (1975) and Henderson et al. (1976). The GGU coal project (Shekhar er al., 1982) adopted the models presentcd in these papers but despite impressive field work did not shed much new light on the origin of these sediments.

Measurements of ice thickness on glaciers at Isortuarssûp tasia, southern West Greenland and Pâkitsoq, central West Greenland

Two separate geophysical projects were carried out in 1988 as part of glacier-hydrological investigations of the margin of the Inland Ice. We made a reconnaissance electromagnetic resonance survey over the ice margin adjacent to Sermilik and Isortuarssup tasia, south-east of Nuuk/Godthåb and measured ice thickness along some lines in the area of Qamanârssûp serrnia, Kangiata nunâta sermia and Kangaussarssup sermia a short distance to the north, as well as a few profiles over a local ice cap just east of Isortuarssup tasia. In the Pâkitsoq area, north east of Ilulissat/Jakobshavn, we finished the mono-pulse ice radar work started last year (Thorning & Hansen, 1988a).

Greenland ice-margin programme, a pilot study at Pâkitsoq, north-east of Jakobshavn, central West Greenland

A glaciological field programme was carried out from 24 July to 21 August 1988 on the Greenland ice-sheet margin at Pakitsoq, north-east of Ilulissat/Jakobshavn, West Greenland. Glaciological investigations for planning hydropower at Pakitsoq have been made by GGU since 1982. The investigations include six years of mass-balance measurements, repeated photogrammetric and satellite mapping, ice-thickness mapping by radio-echo sounding, stable-isotope studies, hot-water-jet drillings and measurements of ice velocity and englacial temperatures (Thomsen, 1986, 1988; Thorning & Hansen, 1987; Olesen & Clausen, 1988). Simulations of runoff, glacier dynamics and glacier hydraulics are also carried out (Reeh, 1983; Thomsen et al., 1988). The aim of the 1988 field programme was to extend and confirm assumptions in the previous work.