According to the Unified Stratigraphic Scheme of Quaternary deposits of the West-Siberian Plain (2000) the Karginsky horizon is subdivided into 5 units, sometimes called subhorizons, which reflect three warmings and two coolings. These climatic events and correspondiong sedimentary units are (Volkova et al, 2003) the Shuryshkary warming 50-44 kyr, Kiryas cooling 43-42 kyr, Zolotoi Mys warming 41-35 kyr, Lokhpodgort cooling 34-30 kyr, Verkhnelobanov warming 29-24 kyr. The optimum of the Karginsky time in this scheme is represented by the Shuryshkary temperate-warm climate, whereas the modern climate is characterized as temperate-cold bordering on the sub-Arctic (Volkova et al, 2005). The age of these strata is determined by ^I4C dating performed in SOAN during 1960-70-s. Already in those times there it was a suspicion that some of those dates were spurious (Zubakov, 1974; Arkhipov et al, 1980). However, the rest of the dates were believed to be valid and served as indication of the stratotypes age. U/Th dating of the Shuryshkary strata has shown their much older age in the stratotype (Astakhov et al, 2005). We have studied the key sections of the Zolotoi Mys and Kiryas strata.

In the Zolotoi Mys section the Karginsky interval is represented from the top downward by oxbow-lake peat, channel alluvium, limnoglacial, upper till and underlying sediments. The underlying sediments served as the stratotype for the Zolotoi Mys strata of the Early Karginsky interval. Eight ¹⁴C dates in the range of 48.9 to 35 kyr have been obtained in Laboratory of Geochronology of St. Petersburg University from the oxbow-lake peat and from peat laminae in the overlying floodplain alluvium. Thus, only these sediments prove to be of the Karginsky age. 2 coolings and 3 warmings have been distinguished from this part of the sequence in a pollen diagram. Vegetation was close to the modern one only in the early warming. The boundary between taiga and forest-tundra shifted southward by 50-80 km during the other warmings, and by 100-150 km during the coolings.

In the Kyrias section «the basal» peat has the ^I4C date >60.7 kyr. The Karginsky interval (by ¹⁴C dates from 46.3 to 27.8 kyr) shows traces of three warmings and two coolings deduced from a pollen diagram. But even in the optimum there was forest-tundra, and during the cool times tundra predominated. Now the Kyrias section is located within typical taiga.

The boundaries between vegetation zones during the warmings moved southward by 300-600 km, and during the coolings by 800 km and more. The Karginsky time on the lower and middle stretches of the Ob was colder than present. In the north the cooling was less pronounced due the incursion of the warm Karginsky sea, and on the middle stretch it was greater, probably due to the influence of stagnant ice from the Zyryanka glaciation.

This work was supported by INTAS, grant 01-0675 and RFBR, grants 06-05-64996 and 04-06-80024.

Reference:

Arslanov Kh.A., Laukhin S.A., Maksimov F.E., Chernov S.B., Tertychnaya T.V. New data on geochronology and paleoclimatic events of the Karginsky time in the Surgut and Lower Ob regions. Correlation of Pleistocene Events in the Russian North. International Workshop Abstracts. 4-6 December 2006. Saint-Petersburg, 2006, p. 10.