432
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
The most likely process forming the sandy layers are turbidity currents irregularly initiated by
collapsing delta front sediments and slumping of sediment material from the steep slopes of the
lake bed. As indicated by the absence of erosional channels in sub-bottom profiles crossing the
lake (Niessen et aI., this volume), such turbidity currents did not lead to a significant
resuspension of surface sediments along their flow paths. Differences in the composition of the
sandy layers (massive and graded) may be due to different source areas: whilst graded layers
may represent distal turbidites from the Krasnaya River, massive layers could represent
proximal turbidites or slumping material from littoral areas and delta regions of small rivers
entering the lake at its southwestern shore (Figure 2). Additional mineralogical and geochemical
data which characterize the source area sediment compositions and allow a comparison with the
composition of the sandy layers in the sediment record may support this interpretation.
Similar sediment types (fine-grained laminae and coarse-grained, "surge-type" layers) and
processes were observed in the High Arctic Lake C2, Ellesmere Island, Canada (Zolitschka,
1996; Retelle and Child, 1996). The existence of overflow, interflow, and underflow processes
as described in these investigations and by Sturm and Matter (1978) is not likely in LevinsonLessing Lake due to the very weak stratification of the lake water column.
Whilst the number of sandy layers in core PG 1228 decreases slightly in the Holocene
sediments, their cumulative thickness is comparable to values in Weichselian sediments (Figure
5). This indicates that turbidites were more frequent during the Weichselian, but had no
stronger contribution to the total sediment accumulation, as the individual events were of lower
energy than those during the Holocene. Higher turbidite frequencies together with lower current
energies during the Weichselian could have been caused by a significantly lower lake level at
that time. This interpretation is also supported by sub-bottom profile investigations from
Levinson-Lessing Lake (Niess en et a!., this volume).
Based on the largely constant contribution of sandy layers to sediment accumulation, and on
the with small variations in laminae thicknesses throughout the fine-grained sediments (around
0.7 mm), rather constant long-term sedimentation rates throughout the time interval covered by
the core were determined. This implies that no glaciation occurred in the Levinson-Lessing
Lake area during that time period. The existence of glaciers within the catchment area would
have caused significant changes in both the sedimentation rates and facies.
Moreover, relatively constant sedimentation rates allow an estimation of the ages of
Interstadials 1 and 2 occurring in the lower portion of the core (Figure 5). The linear
extrapolation of the post-Bplling sedimentation rate of 0.7 mm/a towards the underlying
sediments results in ca. 27 and 25 ka BP for Interstadials 1 and 2, respectively. This indicates
that those periods with assumed interstadial conditions could correspond with the youngest
Middle Weichselian warming in Siberia, which, according to Isayeva (1984), occurred between
24 and 30 ka BP. However, since interstadial conditions in Siberia were also described for
several other Middle Weichselian time periods (e.g. Grichuk, 1984; Kind, 1974; Rybakova,
1989) and since a displacement of Holocene material during the coring process cannot be
completely excluded, the absolute ages of Interstadials I and 2 can only be determined by
accurate absolute dating. As bulk sediment 14C dating is regarded to provide unreliable results
due to contamination by fossil coal, radiocarbon dating of defined organic fractions (such as
humic acids) must be performed and is currently in progress.
Geochemical and physical properties
The geochemical and physical properties of sediments in core PG 1228 show a very good
correlation with the palynological results, especially with the ratio of arboreal to non-arboreal
pollen, which, according to Hahne and Melles (this volume), mirrors variations in Late
Pleistocene and Holocene average summer temperatures (Figure 5).
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
The most likely process forming the sandy layers are turbidity currents irregularly initiated by
collapsing delta front sediments and slumping of sediment material from the steep slopes of the
lake bed. As indicated by the absence of erosional channels in sub-bottom profiles crossing the
lake (Niessen et aI., this volume), such turbidity currents did not lead to a significant
resuspension of surface sediments along their flow paths. Differences in the composition of the
sandy layers (massive and graded) may be due to different source areas: whilst graded layers
may represent distal turbidites from the Krasnaya River, massive layers could represent
proximal turbidites or slumping material from littoral areas and delta regions of small rivers
entering the lake at its southwestern shore (Figure 2). Additional mineralogical and geochemical
data which characterize the source area sediment compositions and allow a comparison with the
composition of the sandy layers in the sediment record may support this interpretation.
Similar sediment types (fine-grained laminae and coarse-grained, "surge-type" layers) and
processes were observed in the High Arctic Lake C2, Ellesmere Island, Canada (Zolitschka,
1996; Retelle and Child, 1996). The existence of overflow, interflow, and underflow processes
as described in these investigations and by Sturm and Matter (1978) is not likely in LevinsonLessing Lake due to the very weak stratification of the lake water column.
Whilst the number of sandy layers in core PG 1228 decreases slightly in the Holocene
sediments, their cumulative thickness is comparable to values in Weichselian sediments (Figure
5). This indicates that turbidites were more frequent during the Weichselian, but had no
stronger contribution to the total sediment accumulation, as the individual events were of lower
energy than those during the Holocene. Higher turbidite frequencies together with lower current
energies during the Weichselian could have been caused by a significantly lower lake level at
that time. This interpretation is also supported by sub-bottom profile investigations from
Levinson-Lessing Lake (Niess en et a!., this volume).
Based on the largely constant contribution of sandy layers to sediment accumulation, and on
the with small variations in laminae thicknesses throughout the fine-grained sediments (around
0.7 mm), rather constant long-term sedimentation rates throughout the time interval covered by
the core were determined. This implies that no glaciation occurred in the Levinson-Lessing
Lake area during that time period. The existence of glaciers within the catchment area would
have caused significant changes in both the sedimentation rates and facies.
Moreover, relatively constant sedimentation rates allow an estimation of the ages of
Interstadials 1 and 2 occurring in the lower portion of the core (Figure 5). The linear
extrapolation of the post-Bplling sedimentation rate of 0.7 mm/a towards the underlying
sediments results in ca. 27 and 25 ka BP for Interstadials 1 and 2, respectively. This indicates
that those periods with assumed interstadial conditions could correspond with the youngest
Middle Weichselian warming in Siberia, which, according to Isayeva (1984), occurred between
24 and 30 ka BP. However, since interstadial conditions in Siberia were also described for
several other Middle Weichselian time periods (e.g. Grichuk, 1984; Kind, 1974; Rybakova,
1989) and since a displacement of Holocene material during the coring process cannot be
completely excluded, the absolute ages of Interstadials I and 2 can only be determined by
accurate absolute dating. As bulk sediment 14C dating is regarded to provide unreliable results
due to contamination by fossil coal, radiocarbon dating of defined organic fractions (such as
humic acids) must be performed and is currently in progress.
Geochemical and physical properties
The geochemical and physical properties of sediments in core PG 1228 show a very good
correlation with the palynological results, especially with the ratio of arboreal to non-arboreal
pollen, which, according to Hahne and Melles (this volume), mirrors variations in Late
Pleistocene and Holocene average summer temperatures (Figure 5).