450
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
(transition from L2 to Ll). However, the effect of lake level changes on sedimentation in the
central part of Levinson Lessing was probably minor because there is no change in the drape
geometry visible between units Ll and L2 (Figure 8). This can be explained by the small
shallow-water area of the lake compared to the large area of more than 30 m water depth
(Figure 3).
In Lake Taymyr, preliminary pollen results from two samples of the basal sand of core
PG 1227 (top of unit T3) suggest a Pleistocene age. The pollen assemblage is extremely poor in
arboreal pollen and thus indicates a cold climate (Hahne, pers. comm.). Therefore, the lowstand phase of Lake Taymyr also occurred in Pre-Holocene time. There is no direct information
about the duration and possible causes of very low lake levels of Lake Taymyr. Other evidence
(M\'!ller et aI., submitted) may indirectly suggest that there is only a relatively short time
window of Latest Pleistocene age during which the low stand might have persisted. M\'!ller et
aI. (submitted) describe a section of massive non-glacial lacustrine silts rich in organic detritus
which is exposed along the north-western shore of Lake Taymyr. This section is radiocarbon
dated as 33.8 ka BP to 16.8 ka BP and associated with pro-deltaic sedimentation in a palaeoLake Taymyr characterised by a much higher lake level of up to 60 m compared to today. This
implies that a significant drop of the Taymyr lake level can only have occurred after 16.8 ka BP
and may have persisted until the beginning of the Holocene. Post-depositional erosion of unit
T4 sediments by glacier ice during the low-stand phase can be excluded because the sound
penetration of the Chirp system into T4 and the lack of deformation of T4 sediments suggest
that no overconsolidation by moving ice has occurred. Consistently, there is no evidence of
glacier-derived deposits in the sedimentary record of PG 1227.
Since M\'!ller et aI. (submitted) describe sediments and chronological evidence that a palaeoLake Taymyr with lake levels up to 60 m above present existed prior to 16.8 ka., it seems to be
likely that the deposits of T4 correlate with the above profile. This would imply that unit T4 is
of Mid to Late Weichselian age. There is a further seismic indication that the deposits and the
palaeo-environment of T4 sediments are indeed similar to that described by M\'!ller et aI. Both
strong reflectors discontinuous to the stratification and back-scatter hyperbolae associated with
pock marks indicate a relatively high sedimentary gas content in unit T4 (Figure 6). This
suggests that T4 sediments are rich in organic matter. Thus, a glacial or proglacial origin for T4
seems unlikely because such sediments would be poor in organic matter. It is interesting to note
that the organic-rich sediments found by M\'!ller et al. (submitted) are terrestrial in origin and
associated with a deltaic type of sedimentation. In our study, the seismic evidence of a high
content of sedimentary gas and thus organic matter in T4 may also be terrestrial in origin
because the location of profile 10 (fig. 6) is close to a larger stream delta.
It is difficult to assume that the drastic changes of the Lake Taymyr level from 60 m above the
present level prior to 16.8 ka BP to about 40 m b.p.I.I. thereafter, followed by a Holocene
transgression, were controlled by climatically induced changes in the hydrology. Since the
present outlet of the lake is only a few metres above sea level, and more than 70% of the
present lake area is less than 3 m deep (Overduin et aI., 1996), a drop of water level by 40 m
would reduce the lake size to only a very small fraction of the present area and volume. If the
outlet was similar to that of today, the low-stand Lake Taymyr would have been a closed basin
system. Considering seasonal runoff from the large catchment of the lake in combination with
low evaporation rates under cold Arctic conditions, this scenario seems to be unlikely. Thus,
tectonic control on the altitude of the outlet of lake Taymyr might be invoked. Also, if our
interpretation of the chronology of the different units in Lake Taymyr and Levinson Lessing is
more or less correct, the low-stand units L2 and T3 did not occur at the same time. L2 probably
comprises the entire Mid to Late Weichselian whereas T3 represents only a relatively short
period during the Latest Weichselian. Because both lakes are part of a larger drainage system, it
is difficult to imagine that Lake Levinson-Lessing had a low stand during the Mid-Weichselian
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
(transition from L2 to Ll). However, the effect of lake level changes on sedimentation in the
central part of Levinson Lessing was probably minor because there is no change in the drape
geometry visible between units Ll and L2 (Figure 8). This can be explained by the small
shallow-water area of the lake compared to the large area of more than 30 m water depth
(Figure 3).
In Lake Taymyr, preliminary pollen results from two samples of the basal sand of core
PG 1227 (top of unit T3) suggest a Pleistocene age. The pollen assemblage is extremely poor in
arboreal pollen and thus indicates a cold climate (Hahne, pers. comm.). Therefore, the lowstand phase of Lake Taymyr also occurred in Pre-Holocene time. There is no direct information
about the duration and possible causes of very low lake levels of Lake Taymyr. Other evidence
(M\'!ller et aI., submitted) may indirectly suggest that there is only a relatively short time
window of Latest Pleistocene age during which the low stand might have persisted. M\'!ller et
aI. (submitted) describe a section of massive non-glacial lacustrine silts rich in organic detritus
which is exposed along the north-western shore of Lake Taymyr. This section is radiocarbon
dated as 33.8 ka BP to 16.8 ka BP and associated with pro-deltaic sedimentation in a palaeoLake Taymyr characterised by a much higher lake level of up to 60 m compared to today. This
implies that a significant drop of the Taymyr lake level can only have occurred after 16.8 ka BP
and may have persisted until the beginning of the Holocene. Post-depositional erosion of unit
T4 sediments by glacier ice during the low-stand phase can be excluded because the sound
penetration of the Chirp system into T4 and the lack of deformation of T4 sediments suggest
that no overconsolidation by moving ice has occurred. Consistently, there is no evidence of
glacier-derived deposits in the sedimentary record of PG 1227.
Since M\'!ller et aI. (submitted) describe sediments and chronological evidence that a palaeoLake Taymyr with lake levels up to 60 m above present existed prior to 16.8 ka., it seems to be
likely that the deposits of T4 correlate with the above profile. This would imply that unit T4 is
of Mid to Late Weichselian age. There is a further seismic indication that the deposits and the
palaeo-environment of T4 sediments are indeed similar to that described by M\'!ller et aI. Both
strong reflectors discontinuous to the stratification and back-scatter hyperbolae associated with
pock marks indicate a relatively high sedimentary gas content in unit T4 (Figure 6). This
suggests that T4 sediments are rich in organic matter. Thus, a glacial or proglacial origin for T4
seems unlikely because such sediments would be poor in organic matter. It is interesting to note
that the organic-rich sediments found by M\'!ller et al. (submitted) are terrestrial in origin and
associated with a deltaic type of sedimentation. In our study, the seismic evidence of a high
content of sedimentary gas and thus organic matter in T4 may also be terrestrial in origin
because the location of profile 10 (fig. 6) is close to a larger stream delta.
It is difficult to assume that the drastic changes of the Lake Taymyr level from 60 m above the
present level prior to 16.8 ka BP to about 40 m b.p.I.I. thereafter, followed by a Holocene
transgression, were controlled by climatically induced changes in the hydrology. Since the
present outlet of the lake is only a few metres above sea level, and more than 70% of the
present lake area is less than 3 m deep (Overduin et aI., 1996), a drop of water level by 40 m
would reduce the lake size to only a very small fraction of the present area and volume. If the
outlet was similar to that of today, the low-stand Lake Taymyr would have been a closed basin
system. Considering seasonal runoff from the large catchment of the lake in combination with
low evaporation rates under cold Arctic conditions, this scenario seems to be unlikely. Thus,
tectonic control on the altitude of the outlet of lake Taymyr might be invoked. Also, if our
interpretation of the chronology of the different units in Lake Taymyr and Levinson Lessing is
more or less correct, the low-stand units L2 and T3 did not occur at the same time. L2 probably
comprises the entire Mid to Late Weichselian whereas T3 represents only a relatively short
period during the Latest Weichselian. Because both lakes are part of a larger drainage system, it
is difficult to imagine that Lake Levinson-Lessing had a low stand during the Mid-Weichselian