ENVIRONMENTAL HISTORY OF THE NOVOSIBIRSKIE ISLANDS FOR THE LAST 12 KA
ANISIMOV, MIKHAIL A.. Arctic and Antarctic Research Institute.
Tumskoy, Vladimir E.. Moscow State University, Faculty of Geology.
The presented materials generalize paleo-geographical studies of Kotelnyi and Zhokhov Islands (Makeev et al., 1989, 1999), Bennetta Island (Verkulich et al., 1989,1999) and fieldwork of different years performed by the authors on Bennetta, Zhokhov, Bol. Lyakhovskii and Novaya Sibir Islands.
The New Siberian islands are located on the continental shelf presenting fragments of an extensive plain that existed during the period of the last (Sartanian) cooling. The sea level at that time was 100-120 m as low as the modern one, which determined the coastline location of 700-1000 km to the north compared to the current one.
No thick ice sheet glaciers similar to Scandinavia or North America existed in the region of the New Siberian Islands. Numerous 14C datings in range 24-17 ka confirm its. Small passive ice sheets were only on the northern islands of the archipelago. Their fragments are still preserved on Bennetta, Genrietta and Zhannetta Islands. Unclear traces of the car-near-slope glaciers in the form of unpronounced ice deposits are preserved on Zhokhov Island. Over much of the territory, deposits of different genetic types with high ice content accumulated, whose typical feature was the presence of big ice wedges (Ice-Complex deposits). The thickness of deposits increased southward from 5-10 m to 50-70 m.
As a result of a series of warming events in the end of the Late Pleistocene and the decay of ice sheet glaciers in the north of Europe and America, the sea level rise began in the eastern Arctic with the coastline advancing southward. According to the results of studies in the Laptev Sea region (Degtyarenko et al., 1982; Bauch et al., 2001), the sea level rise began around 17 kyr BP achieving its current position around 5 kyr BP. The coastline was, however, located much more to the north than at present. Thus, rocks with high ice content were not yet destroyed by thermal abrasion. The marine transgression reached its maximum around 4 kyr BP. The sea level at this time was 3-4 m higher than the current one whereas the coastline was in tens and hundreds of kilometers from its present position. Due to the fact that the overwhelming parts of shores was comprised of deposits with high ice contents, the terrace levels formed at this time were destroyed due to thermal abrasion and were preserved only on some segments of bedrock outcrops. For examples, there are radiocarbon datings of driftwood from a laida (with a height of 4-5 m) in the northern part of Zhokhov Island (4.9-3.9 kyr BP). Insignificant climate coolings in the Holocene resulted in slower rates of sea transgression or in some regressions. Due to this, probably around 9 kyr BP, a terrace level at a depth of about 15 m (Zhokhov Island) was formed. The presence of a large quantity of the driftwood fragments at the monument (Zhokhov Island) and the features of depth distribution around Zhokhov Island provide indirect evidence of this. We have recorded one more insignificant sea level rise on Stolbovoy Island. A band of driftwood concentration was dated at a distance of 60-70 m from the shore at a height of about 3 m above the sea level. The radiocarbon age of wood is 1255±40 kyr BP (LE-5850). There was a short-term warming at this time and it is also probable that the driftwood band was formed due to strong storms in the ice-free sea.
During the warming periods of the end of the Late Pleistocene (Raunis, Bolling and Allerod climatic stages) the area of the New Siberian Islands still presented one continental land, which is indicated by dating of the mammoth tusk from Bennetta Island (12.5 kyr BP).
The decrease of climate continentality and increased humidity in the end of the Late Pleistocene resulted in a sharp intensification of thermokarst processes. The accumulation of deposits with high ice content on land was replaced by their melting. On Novaya Sibir Island, a horizontally bedding organic interlayer with an age of 11050±60 (GIN-11246à) overlaps a cast along the ice wedges. On Novaya Sibir Island, there is also a date of 10750±100 years BP (GIN-11247à) obtained from an interlayer of allchthonous peat filling a thermokarst basin. Intensification of solifluction and thermal erosion belongs approximately to this time. There are similar datings from Bol. Lyakhovskii Island.
The formation of peat bogs began synchronously in series with the development of thermokarst depressions. On Kotelnyi Island, they are dated beginning from 12.3 kyr BP (LU-1763) and on Zhokhov Island from 12.2 kyr BP. Milder temperature conditions resulted in the vegetation boundary advance northward. In peat bogs on Zhokhov, Kotelnyi, Novaya Sibir and Bol. Lyahkovskii Islands, numerous remnants of shrubs growing here in the Holocene were encountered. A decrease in intensity of the mass thermokarst development belongs to the middle of the Holocene. Around 3 kyr BP, the accumulation of peat bogs ends (3380±40, LE-5854 - peat bog on Novaya Sibir Island).
Visit of Zhokhov Island by man belongs to the Holocene optimum (around 8 kyr BP). Due to bathymetry features near Zhokhov Island, the distance from the site of ancient people to the seashore was not greater than several kilometers. A large quantity of driftwood remains and bone remnants of a sea animal at the ancient man site serve as indirect evidence.
The available data on the Novosibirskie Islands indicate synchronous climatic changes in the territory of the eastern Arctic shelf. These changes were of a complicated rhythmic character determined not only by temperature fluctuations, but also by climate changing from continental to marine due to sea transgression.
Makeev V.M., Pitulko V.V. and Kasparov A.K. (1999) De-Long Archipelago environment at the end of the Pleistocene and beginning of the Holocene and ancient human. - In: Proceedings RGO, vol. 124, N3, pp. 271-276 (in Russian)
Makeev V.M., Arslanov H.A., Baranovskaya O.F., Kosmodamianskii A.V., Ponomareva D.P., Tertychnaya T.V. (1989) Stratigraphy, geochronology and palaeogeography of Kotel`ny Island at the Late Pleistocene and Holocene. - In: Committee bulletin for the Quaternary time investigation, N58, pp. 58-69
Verkulich S.R., Makeev V.M., Arslanov H.A., Ponomareva D.P., Tertychnaya T.V., Baranovskaya O.F. (1989) Structure and geochronology of the Quaternary deposits on the Bennett Island. - In: Quaternary Geochronology. Abstracts, p.16. Tallin.
Verkulich S.R., Bolshiyanov D.Yu., Makeev V.M., Anisimov M.A. (1995) Investigations of the Arctic in the framework of paleogeographical studies of the AARI. - In: Second Annual PALE Research Meeting, 4-6 February 1995, University of Washington. Abstracts. Washington, p. 5
Previous | Abstract Index | Next
Copyright © 2001 INSTAAR, Univ. of Colorado