Niessen et al: High-Resolution Seismic Stratigraphy of Lake Sediments on the Tavmyr Peninsula
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irregular bottom indicate that the sediments tend to fill depressions and level subbottom
topography.
Interpretation of sequences, depositional environments and unit chronology
Sequence stratigraphy and lake level changes
The sequential stratigraphic approach to linking unit geometry to sea-level changes is well
established for marine records (Bally, 1987). The seismic units of both Lakes Taymyr and
Levinson Lessing include geometric patterns very similar to typical High Stand System Tracks
(HST), Low Stand System Tracks (LST) and Transgressive System Tracks (TST) as outlined
by Bally (1987) for marine shelf and slope environments. Therefore, key profiles from shallow
to deeper water from Lake Taymyr (profile II, Figure 4) and Levinson Lessing (profile 31,
Figure 9) are used to interpret past lake level changes (Figure 11).
The drape-geometry and increase of sediment thicknesses of the units L4, L3 and T4 toward
the present shore are indicative of a higher lake level during deposition (HST) compared to the
present situation. For example, the deposition of large thicknesses of T4 sediments in Lake
Taymyr, as observed in profile II (Figure 4), is hardly possible unless a higher lake level of at
least 20 m above present is assumed. A similar situation is interpreted for Lake Levinson
Lessing during the deposition of unit L4 and L3 (Figure 9).
The high-stand phase is followed by a significant drop of lake levels during which parts of
the HST deposits (e.g. T4) were eroded. In Lake Taymyr, this unconformity forms a typical
system boundary in the sense of Bally (1987) which can be traced down to 40 m b.p.l.l.(Figure
4). Thus, the lake level must have dropped significantly below the present level, possibly to
more than 40 m b.p.!.!.. The geometry of a LST unit is not seen in Lake Taymyr due to limited
sound penetration. However, sequence stratigraphy suggests that a LST unit T3 must be
overlying T4 in the deeper part of the basin (Figure 11) because the truncation of L4 sediments
in shallow areas implies deposition in the basin. Unit T3 probably consists of a large amount of
reworked T4 sediments. Also, the basal sand of core PG 1227, which forms the top of unit T3
(Figure 5), is evidence for a low-stand phase in Lake Taymyr. According to a preliminary
interpretation by Overduin et al. (1996) the deposition of the sand is associated with alluvial
deposition. This suggests a very low lake level or even non-existence of Lake Taymyr at the
time T3 was deposited. In Lake Levinson Lessing, LST deposits are indicated by L2 geometry,
in which adjacent sediments indicate that L2 lenses out between 30 and 40 m b.p.l.l. (Figure
9).
The low-stand is followed by a transgressive phase (Figure 11) where sediments successively
accumulate on the upper slope (Ll, T2). Finally, deposition reappears in present day shallow
water areas of the lakes (Ll, Tl). The lake level remains intermediate (Figure 11) as is indicated
by the increase of unit thicknesses toward the basin (and thus sediment focusing) which is not
seen in HST deposits (Figures 4 and 9). In Lake Taymyr, TST consists of two units, Tl and
T2, of which the boundary is, in places, erosive (Figure 4). This is interpreted to be caused by
erosion following a slight drop in lake level during the transgressional phase as indicated in
Figure 11. Such an unconforiaty is not seen in TST deposits of Lake Levinson Lessing (L 1) so
that a lake level fluctuation during the transgression may not have occurred there.
The Holocene - the transgressive phase
The transgressional phase during which the units Ll, Tl and T2 accumulated is associated with
Holocene deposition. Between 9 and 7 m, core PG 1228 from Levinson Lessing has clear
445
irregular bottom indicate that the sediments tend to fill depressions and level subbottom
topography.
Interpretation of sequences, depositional environments and unit chronology
Sequence stratigraphy and lake level changes
The sequential stratigraphic approach to linking unit geometry to sea-level changes is well
established for marine records (Bally, 1987). The seismic units of both Lakes Taymyr and
Levinson Lessing include geometric patterns very similar to typical High Stand System Tracks
(HST), Low Stand System Tracks (LST) and Transgressive System Tracks (TST) as outlined
by Bally (1987) for marine shelf and slope environments. Therefore, key profiles from shallow
to deeper water from Lake Taymyr (profile II, Figure 4) and Levinson Lessing (profile 31,
Figure 9) are used to interpret past lake level changes (Figure 11).
The drape-geometry and increase of sediment thicknesses of the units L4, L3 and T4 toward
the present shore are indicative of a higher lake level during deposition (HST) compared to the
present situation. For example, the deposition of large thicknesses of T4 sediments in Lake
Taymyr, as observed in profile II (Figure 4), is hardly possible unless a higher lake level of at
least 20 m above present is assumed. A similar situation is interpreted for Lake Levinson
Lessing during the deposition of unit L4 and L3 (Figure 9).
The high-stand phase is followed by a significant drop of lake levels during which parts of
the HST deposits (e.g. T4) were eroded. In Lake Taymyr, this unconformity forms a typical
system boundary in the sense of Bally (1987) which can be traced down to 40 m b.p.l.l.(Figure
4). Thus, the lake level must have dropped significantly below the present level, possibly to
more than 40 m b.p.!.!.. The geometry of a LST unit is not seen in Lake Taymyr due to limited
sound penetration. However, sequence stratigraphy suggests that a LST unit T3 must be
overlying T4 in the deeper part of the basin (Figure 11) because the truncation of L4 sediments
in shallow areas implies deposition in the basin. Unit T3 probably consists of a large amount of
reworked T4 sediments. Also, the basal sand of core PG 1227, which forms the top of unit T3
(Figure 5), is evidence for a low-stand phase in Lake Taymyr. According to a preliminary
interpretation by Overduin et al. (1996) the deposition of the sand is associated with alluvial
deposition. This suggests a very low lake level or even non-existence of Lake Taymyr at the
time T3 was deposited. In Lake Levinson Lessing, LST deposits are indicated by L2 geometry,
in which adjacent sediments indicate that L2 lenses out between 30 and 40 m b.p.l.l. (Figure
9).
The low-stand is followed by a transgressive phase (Figure 11) where sediments successively
accumulate on the upper slope (Ll, T2). Finally, deposition reappears in present day shallow
water areas of the lakes (Ll, Tl). The lake level remains intermediate (Figure 11) as is indicated
by the increase of unit thicknesses toward the basin (and thus sediment focusing) which is not
seen in HST deposits (Figures 4 and 9). In Lake Taymyr, TST consists of two units, Tl and
T2, of which the boundary is, in places, erosive (Figure 4). This is interpreted to be caused by
erosion following a slight drop in lake level during the transgressional phase as indicated in
Figure 11. Such an unconforiaty is not seen in TST deposits of Lake Levinson Lessing (L 1) so
that a lake level fluctuation during the transgression may not have occurred there.
The Holocene - the transgressive phase
The transgressional phase during which the units Ll, Tl and T2 accumulated is associated with
Holocene deposition. Between 9 and 7 m, core PG 1228 from Levinson Lessing has clear