Bulletin of the Geological Society of Denmark • Volume 42/1

The Greenland ice sheet - a model for its culmination and decay during and after the last glacial maximum

Funder, S. & Hansen, L.: The Greenland ice sheet - a model for its culmination and decay during and after the last glacial maximum. Bulletin of the Geological Society of Denmark, Vol. 42, pp.137-I52. Copenhagen,1996-02-01.

Abstract: Ice margin reconstructions of the Greenland ice sheet during LGM (c. 21-16 ka) and 10 ka are based on published onshore field evidence supplemented with recent studies on the East Greenland shelf and results of current field work in the Scoresby Sund area. Additional evidence comes from the pattern of Holocene uplift and the frequency distribution of more than 1000 14-C-dates.

During LGM, only southern Greenland (south of lat. 69^o-72^oN) saw a major expansion of the ice sheet with thick cover over the present coastline and onto the shelf. In the north, outlet glaciers filled fjord basins, including the Nares Strait between Canada and Greenland, and piedmont glaciers descended from coastal mountains onto the coastline, but the glaciers did not cover the shelf. Break up probably began after c. 15 ka, and took place in two discrete steps.

First, the shelf and major inlets were cleared of marine based ice. There was little thinning of the ice on land, and in the northern parts there was little change at all. The driving factor during this step was calving caused by rising sea level. This lasted until c.10 ka, but may have been consumated before the Younger Dryas. T

he second step began with a glacier-readvance between 10 and 9.5 ka, and after this the fjord glaciers began to retreat rapidly. Within a few millennia all the presently ice free land was exposed. The frequency distribution of 14-C-dates show that the nearshore marine and terrestrial biotopes emerged in this period. The discharge of ice was both by calving and melting, and the driving force was probably increased insolation.

Maximum Holocene uplift was attained in areas of the 10 ka ice margin, indicating that the uplift is essentially a response to the melting and unloading of ice that began at this time. In suppport of this, recent results in West, North and East Greenland indicate that the age of the marine limits decline towards the outer coasts, away from the 10 ka ice margin.

Address: Svend Funder and Louise Hansen, Geological Museum, University of Copenhagen, Øster- Voldgade 5-7, DK-1350 Copenhagen K, Denmark, l7th November 1995.

Progressive glaciotectonic deformation in Weichselian and Palaeogene deposits at Feggeklit, northern Denmark

Pedersen, S.A.S.: Progressive glaciotectonic deformation in Weichselian and Palaeogene deposits at Feggeklit, northern Denmark. Bulletin of the Geological Society of Denmark, Vol. 42, pp. 153-174, Copenhagen 1996-02-01.

Abstract: Structural analysis of the glaciotectonic deformations at Feggeklit, Mors, Denmark, provide a unique record of successive deformation phases in a progressive glaciotectonic deformation. The Feggeklit profile displays glaciotectonically folded, thrust-faulted and sheared Palaeogene diatomite with thin volcanic ash layers, the Fur Formation, overlain by a glacigene succession.

The combination of stratigraphical and structural analysis shows that the Feggeklit was affected by three glaciodynamic events. The first event is of Saalian age and is represented by the deposition of a till and the formation of a para-authochthonous glacitectonite in the top of the Fur Formation deposits.

The second event is only represented by the deposition of a till, probably of Saalian age. The third event is of Late Weichselian age. It includes: 1) deposition of proglacial glaciolacustrine and -fluvial sediments, 2) the formation of a glaciotectonic unit (the Feggeklit deformation complex) and 3) deposition of a till resting on a tectonic unconformity formed subglacially.

A detailed structural analysis of the glaciotectonic unit provides a subdivision into five successive deformation phases. The first four phases are related to the proglacial deformation and comprise 1) anastamosing jointing, 2) conjugate faulting, 3) buckle folding and listric thrust faulting, and 4) large scale ramp thrusting. The final phase (5) is related to subglacial shear deformation and loading which produced an allochthonous diatomite-glacitectonite at the sole of the overlying lodgement till.

The formation of the structural complex at Feggeklit was caused by two glaciotectonic mechanisms: 1 ) a proglacial gravity spreading deformation, and 2) a subglacial cataclastic shearing. The balanced cross-section of the fold structures related to the first deformation mechanism indicates that the detachment of the dislocation is situated below the base of the diatomite formation in the plastic clay at a depth of 80-100 m below the surface.

Based on the glaciodynamic analysis and considerations on the dating of regional glacigenic setting the velocity of the advancing ice is estimated at 10 m per year. This advance created the gravity spreading deformation reflected in the glaciotectonic structures preserved in the Feggeklit.

Address: S.A. Schack Pedersen. Geological Survey of Denmark and Greenland, Thoravej 8, DK 2400 Copenhagen, Denmark. 9th June 1995.

Distribution and intensity of glaciotectonic deformation in Denmark

Jakobsen P R.: Distribution and intensity of glaciotectonic deformation in Denmark. Bulletin of the Geological Society of Denmark. Vol. 42, pp.175-185. Copenhagen 1996-02-01.

Abstract: Glaciotectonic deformation has a large impact on the stratigraphical and lithological variability of Quaternary deposits and the shallow subsurface pre-Quaternary sediments. Mapping of the distribution of glaciotectonic deformation involving pre-Quaternary and interglacial deposits has been carried out, and the density of glaciotectonic deformation analysed, on the basis of data from the well database ZEUS, at the Geological Survey of Denmark.

Glaciotectonic deformation is widespread in Denmark. It is recognised in glacial terrains within morphological well-defined glaciotectonic complexes, and in areas with no obvious glaciotectonic related morphology as well as in areas covered with postglacial deposits. The dislocated bedrock is usually not transported for long distances, although rafts of pre-Quaternary bedrock may be transported up to 50 km or more.

On a large scale, regions have been located showing high intensity of glaciotectonic deformation. Some of these regions are in good agreement with records from exposures and the geomorphology, others cannot be recognised without well log information.

Address: Peter Roll Jakobsen, Geological Survey of Denmark, Thoravej 8, DK 2400 København NV Denmark. October 27th 1995.

New free-living bryozoans from the northwest European Chalk

Håkansson, E. & Voigt, E.: New free-living bryozoans from the northwest European Chalk. Bulletin of the Geological Society of Denmark, vol. 42, pp. 187-207. Copenhagen 1996- 02-01.

Abstract: Twelve new species of free-living cheilostome bryozoans are described from the white chalk of Denmark and northern Germany: Lunulites pseudocretacea, L. microstoma, L. vespertilio, L. conulus, L. patens, L. immensa, L. foveolata, Pavolunulites parva, P. schmidi, P insolita, P moenensis, P. danica. Eleven species are restricted to the Maastrichtian, while a single species also range down into Upper Campanian strata. The systematic status of the genera Lunulites and Pavolunulites in the Cretaceous is briefly discussed.

Address: Eckart Håkansson, Geological Institute, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. Ehrhard Voigt, Geologisch-Paläontologisches Institut, Universität Hamburg, Bundesstrasse 55, D-20146 Hamburg, Germany. 27th September 1995.