492
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
obtained by AMS dating (Table 3): 20400 +300/-290 yr BP, 17320±220 yr BP, 14390+150/140 yr BP and 11810 ±140 yr BP. The first datum quoted is related to silty and sandy deposits
recovered at some sites by core drilling at the broad, dried lake depression to the west of the
Tolton-Pastakh-Yuryukh River (see Figure 2). The investigated sediments consist of laminated
light grey, yellow-grey or brownish grey fine layered silts and silty sands with trace fine plant
remains (mosses, seeds, fine branches of dwarf shrubs). The ground-ice contents range from
30 to 50%. Fine lens-shaped and massive cryostructures are common. In filled lake
depressions, ice wedges were found. Such ice wedges were drilled in LAB4/94, LAB5/94 and
LAB9/95. Their stable isotope ratio range from -26.04%0 to -28.54%0 and from -202.7%0 to
218.54%0 for 0 18 0 and 02H, respectively.
The age of 17.3 ka BP (Table 3, No 1) was obtained from the upper part of vaguely
laminated sandy deposits with ice-wedge polygons in the surroundings of Kokora Lake. The
"ice complex" here forms an esker-like ridge along the eastern lake shore. Primarily fine
residues of seeds, grass roots and branches were found as plant remains. The pollen
assemblages from these sediments represent a dry grass-moss-tundra vegetation dominated by
NAP with significant amounts of Poaceae, Artemisia, Caryophyllaceae, Saxifragaceae, other
herbs and also cryophytic sporophytes, while Aboreal pollen (nearly only shrub pollen) were
present in quite small amounts (10 to 20 %).
Sediments formed at 11800 ka (No 8 in Table 3) were studied in the southern shore zone of
Labaz lake (LAO 13-94 in Figure 1, C). Plant remains are very rare in these well-sorted finegrained sands. However, the pollen assemblage from this horizon, although dominated by
Poacea and Artemisia, indicated that shrubs (primarily Betula sect. Nanaea) and Larix began to
spread in the surroundings at this time. In the underlying sand horizon, the pollen assemblage
suggested a significantly cooler and drier environment which likely existed during the Sartan.
Peat accumulation already took place at this site during the Preboreal, at 9300 yr BP (see No 27
in Table 2).
Unit 4: Holocene deposits
Holocene deposits occur at different geomorphological levels. They are presented primarily by
lacustrine silts and peats formed in thermo karst depressions, lakes and by different slope
deposits. The latter overlie different relief elements and, together with fluvial sediments, fill the
recent river valleys in this area. The wide-spread occurrence of slope deposits blur the older
relief elements and complicate the reconstruction of former lake level stages.
Numerous radiocarbon ages were obtained from Holocene plant material (see Table 2, 3). At
first, these data suggested that the development of thermokarst processes (thawing of buried ice
bodies, other ice-rich permafrost) already started during the warming events at the termination
of the Pleistocene. For example, silty sediments in section LAB2.95, which were characterized
by pollen assemblages relating to the termination of the Sartan, accumulated in a thaw-lake
(thermokarst lake) and were overlain by a peaty horizon dated around 9000 yr BP (Table 2, No
31, 32). The wide-spread occurrence of thick tree trunks, especially of larch at the base of peat
beds with ages of about 7000-8000 yr BP, showed that optimum conditions for their growth in
this area were from the Boreal to the beginning of the Atlantikum. Younger larch trunks were
characterized by a smaller diameter and signs of deformation. The youngest larch wood had a
14C-age of 2880±60 yr BP and was found as a stump at the slope of a thermokarst depression
near the drilling site LAB 13-95 (see Table 2, No 55). Several pollen diagrams of dated
Holocene deposits (for example, Figure 9) also indicated that optimum climatic conditions for
an expansion of trees towards the north in this region existed during the Boreal time. This
corresponds with the results of other investigators (Hahne and Melles, this volume;
Nikolskaya, 1982; Velichko et aI., 1994). Apparently, the progressive swamping of the flat
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
obtained by AMS dating (Table 3): 20400 +300/-290 yr BP, 17320±220 yr BP, 14390+150/140 yr BP and 11810 ±140 yr BP. The first datum quoted is related to silty and sandy deposits
recovered at some sites by core drilling at the broad, dried lake depression to the west of the
Tolton-Pastakh-Yuryukh River (see Figure 2). The investigated sediments consist of laminated
light grey, yellow-grey or brownish grey fine layered silts and silty sands with trace fine plant
remains (mosses, seeds, fine branches of dwarf shrubs). The ground-ice contents range from
30 to 50%. Fine lens-shaped and massive cryostructures are common. In filled lake
depressions, ice wedges were found. Such ice wedges were drilled in LAB4/94, LAB5/94 and
LAB9/95. Their stable isotope ratio range from -26.04%0 to -28.54%0 and from -202.7%0 to
218.54%0 for 0 18 0 and 02H, respectively.
The age of 17.3 ka BP (Table 3, No 1) was obtained from the upper part of vaguely
laminated sandy deposits with ice-wedge polygons in the surroundings of Kokora Lake. The
"ice complex" here forms an esker-like ridge along the eastern lake shore. Primarily fine
residues of seeds, grass roots and branches were found as plant remains. The pollen
assemblages from these sediments represent a dry grass-moss-tundra vegetation dominated by
NAP with significant amounts of Poaceae, Artemisia, Caryophyllaceae, Saxifragaceae, other
herbs and also cryophytic sporophytes, while Aboreal pollen (nearly only shrub pollen) were
present in quite small amounts (10 to 20 %).
Sediments formed at 11800 ka (No 8 in Table 3) were studied in the southern shore zone of
Labaz lake (LAO 13-94 in Figure 1, C). Plant remains are very rare in these well-sorted finegrained sands. However, the pollen assemblage from this horizon, although dominated by
Poacea and Artemisia, indicated that shrubs (primarily Betula sect. Nanaea) and Larix began to
spread in the surroundings at this time. In the underlying sand horizon, the pollen assemblage
suggested a significantly cooler and drier environment which likely existed during the Sartan.
Peat accumulation already took place at this site during the Preboreal, at 9300 yr BP (see No 27
in Table 2).
Unit 4: Holocene deposits
Holocene deposits occur at different geomorphological levels. They are presented primarily by
lacustrine silts and peats formed in thermo karst depressions, lakes and by different slope
deposits. The latter overlie different relief elements and, together with fluvial sediments, fill the
recent river valleys in this area. The wide-spread occurrence of slope deposits blur the older
relief elements and complicate the reconstruction of former lake level stages.
Numerous radiocarbon ages were obtained from Holocene plant material (see Table 2, 3). At
first, these data suggested that the development of thermokarst processes (thawing of buried ice
bodies, other ice-rich permafrost) already started during the warming events at the termination
of the Pleistocene. For example, silty sediments in section LAB2.95, which were characterized
by pollen assemblages relating to the termination of the Sartan, accumulated in a thaw-lake
(thermokarst lake) and were overlain by a peaty horizon dated around 9000 yr BP (Table 2, No
31, 32). The wide-spread occurrence of thick tree trunks, especially of larch at the base of peat
beds with ages of about 7000-8000 yr BP, showed that optimum conditions for their growth in
this area were from the Boreal to the beginning of the Atlantikum. Younger larch trunks were
characterized by a smaller diameter and signs of deformation. The youngest larch wood had a
14C-age of 2880±60 yr BP and was found as a stump at the slope of a thermokarst depression
near the drilling site LAB 13-95 (see Table 2, No 55). Several pollen diagrams of dated
Holocene deposits (for example, Figure 9) also indicated that optimum climatic conditions for
an expansion of trees towards the north in this region existed during the Boreal time. This
corresponds with the results of other investigators (Hahne and Melles, this volume;
Nikolskaya, 1982; Velichko et aI., 1994). Apparently, the progressive swamping of the flat