LAST SHELF GLACIATION: LITHOLOGIC AND PALEOGEOGRAPHICAL ASPECTS

Late Pleistocene glaciations of the shelves of the western Arctic remain one the most debatable issues of Quaternary geology for the last twenty years. Despite the huge amount of data obtained recently on adjacent land, both the continent and islands, the data on the shelves are still scarce and poorly summarized. Obviously though, regional reconstructions of glacier evolution are unavoidably incomplete and highly hypothetic, unless supported by shelf data. Abundant seismic-acoustic data on the Arctic shelf have been produced by the regional studies conducted by VNI1 Okeangeologia for twenty years. Necessary facilities and methods have been designed, set up and tested, enabling high-quality geological mapping of the sea floor. Based on this, we consider the area of the sea floor in the Barents Sea north of Novaya Zemlya Archipelago and south of St. Anna Trough one of the most informative and promising for the environmental reconstructions of the last glaciation. The whole amount of lately accumulated data indicates that this shelf area was affected by nonglacial rather than glacial environments.

Firstly, the Upper Regional Unconformity (URU) at the base of the Quartenary deposits is strongly eroded here with several generations of ancient valleys dissecting the Mesozoic-Cenozoic basement and filled with Pleistocene sediments. In addition, the character of erosion is considerably different from that in typically glacial regions, such as the Antarctic or Greenland shelves.

Secondly, the glacigenic deposits, the main archive of ice dispersal, are only locally present in this area. Judging by their occurrence, one may suggest few small isolated ice caps topping the topographic highs rather than a continuous ice sheet.

Thirdly, submerged erosional mesoscale landforms are widespread here. But they did not extend deeper than 250 m below sea level. If so, the deepest parts of troughs and depressions on the shelf could not have been affected by glacier ice. In other words, the ice thickness was negligible and glaciers existed locally. This evidence suggests a limited extent of glaciation and, hence, a large ice-free area on the shelf during the last ice age.

Finally, the seismic-acoustic data reveal contrasting neotectonism in the form of uplift and downsagging movements. The amplitudes, and often the direction of movements, may vary within a particular block of the basement confined by faults. This indicates predominance of tectono-eustatic over glacio-eustatic factor of sea level oscillations.

The obtained seismic-acoustic data give sufficient ground to believe that the Late Pleistocene glaciers in the southern Saint-Anna Trough area hardly transgressed the limits of local topographic highs and basements of archipelagos.

Reference:

Rybalko A. Last shelf glaciation: lithologic and paleogeographical aspects. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 80.