Kienel: Late Weichselian to Holocene Diatom Succession in a Sediment Core
379
This study presents the first diatom sequence from the northwest Siberian region that spans to
the late Weichselian (ca. 11.000 y BP). Little and only very general information about the large
lakes of Taymyr Peninsula and the Putoran Plateau has been collected (Aleksyuk and Bekman,
1981; Chernyaeva, 1981; Shur and Sid 'ko, 1985). Most of the studies describe modern flora or
use lake sediment sequences of less than 1.5 m. In order to infer relative changes in the past
development of Lama Lake (northeast Norilsk, northwest Putoran Plateau) from fossil diatom
assemblages, the conventional methods using diatom indices and categories of life form,
trophic and pH preferences were used. Within the context of palynological (Hahne and Melles,
1997; Hahne and Melles, this volume), sedimentological and geochemical data (Hagedorn et
aI., this volume; Harwart et aI., 1997; Harwart et aI., subm.), the diatom-inferred lake history
can yield indications of the paleoenvironmental processes influencing Lama Lake and its
catchment since the late Weichselian.
Material and methods
Site, Coring
The sediment core PG 1111 was recovered during the summer of 1993 from a water depth of 52
m, 2.2 km from the shore of Lama Lake (69°32.9' N; 90°12.7' E; Figure I). To avoid
disturbing the soft upper sediments during sampling (PG 1111-1, max. depth: 0.54 m), a
gravity corer was used. A 10.6 m sediment sequence was recovered by repeated deployment of
a piston corer operating from a floating platform. The individual cores from overlapping
sediment depths were correlated to the complete sequence on the basis of whole-core physical
measurements, core descriptions, and analytical results. For a more detailed description see
Melles et al. (1994b).
Chronology, Palynology, Sedimentology and Geochemistry
The chronology for core PG 1111 is provided by regional pollen assemblage zones in
correlation with radiometrically dated profiles. Together with the combined chronozones of
Mangerud et al. (1974) and Khotinsky (1984), they provide the chronological framework (see
Hahne and Melles, this volume; Hahne and Melles, 1997).
Generally, grain size remains almost uniform, varying only from silty clay to clayey silt. A
major change in sediment colour from olive brown to greyish and black occurs synchronously
with a transition in sediment structure from densely laminated to a coarser stratification around
7.2 m depth. According to palynology, this section is placed in the Aller¢d (Hahne and Melles,
1997). Geochemical analyses of main elements (Harwart et aI., 1997) revealed a change from
high contents in Fe and Mg to high contents in Si, AI, Ti, Na and K synchronous to the
mentioned change in sediment colour and structure. From these results a change in weathering
regime is inferred. Prevailing physical weathering is replaced to an increasing degree by
chemical weathering processes accompanied by soil formation (Harwart et aI., 1997).
Dating
From radioisotopic 2lOPb investigations of the uppermost part of PG 1111, mean sedimentation
rates of 0.62 ± 0.01 mm y-i have been calculated (Hagedorn et aI., this volume). i4C dating of
the older sediments provided extremely old ages throughout the profile, resulting from the high
coal particle content. Even dating of pollen grains was impossible, since not all coal particles
could be removed. The chronozones employed, from Oldest Dryas to Subatlantic, are based on
comparison of vegetation development with radiometrically dated Siberian pollen profiles
(Hahne and Melles, this volume; Hahne and Melles, 1997).
379
This study presents the first diatom sequence from the northwest Siberian region that spans to
the late Weichselian (ca. 11.000 y BP). Little and only very general information about the large
lakes of Taymyr Peninsula and the Putoran Plateau has been collected (Aleksyuk and Bekman,
1981; Chernyaeva, 1981; Shur and Sid 'ko, 1985). Most of the studies describe modern flora or
use lake sediment sequences of less than 1.5 m. In order to infer relative changes in the past
development of Lama Lake (northeast Norilsk, northwest Putoran Plateau) from fossil diatom
assemblages, the conventional methods using diatom indices and categories of life form,
trophic and pH preferences were used. Within the context of palynological (Hahne and Melles,
1997; Hahne and Melles, this volume), sedimentological and geochemical data (Hagedorn et
aI., this volume; Harwart et aI., 1997; Harwart et aI., subm.), the diatom-inferred lake history
can yield indications of the paleoenvironmental processes influencing Lama Lake and its
catchment since the late Weichselian.
Material and methods
Site, Coring
The sediment core PG 1111 was recovered during the summer of 1993 from a water depth of 52
m, 2.2 km from the shore of Lama Lake (69°32.9' N; 90°12.7' E; Figure I). To avoid
disturbing the soft upper sediments during sampling (PG 1111-1, max. depth: 0.54 m), a
gravity corer was used. A 10.6 m sediment sequence was recovered by repeated deployment of
a piston corer operating from a floating platform. The individual cores from overlapping
sediment depths were correlated to the complete sequence on the basis of whole-core physical
measurements, core descriptions, and analytical results. For a more detailed description see
Melles et al. (1994b).
Chronology, Palynology, Sedimentology and Geochemistry
The chronology for core PG 1111 is provided by regional pollen assemblage zones in
correlation with radiometrically dated profiles. Together with the combined chronozones of
Mangerud et al. (1974) and Khotinsky (1984), they provide the chronological framework (see
Hahne and Melles, this volume; Hahne and Melles, 1997).
Generally, grain size remains almost uniform, varying only from silty clay to clayey silt. A
major change in sediment colour from olive brown to greyish and black occurs synchronously
with a transition in sediment structure from densely laminated to a coarser stratification around
7.2 m depth. According to palynology, this section is placed in the Aller¢d (Hahne and Melles,
1997). Geochemical analyses of main elements (Harwart et aI., 1997) revealed a change from
high contents in Fe and Mg to high contents in Si, AI, Ti, Na and K synchronous to the
mentioned change in sediment colour and structure. From these results a change in weathering
regime is inferred. Prevailing physical weathering is replaced to an increasing degree by
chemical weathering processes accompanied by soil formation (Harwart et aI., 1997).
Dating
From radioisotopic 2lOPb investigations of the uppermost part of PG 1111, mean sedimentation
rates of 0.62 ± 0.01 mm y-i have been calculated (Hagedorn et aI., this volume). i4C dating of
the older sediments provided extremely old ages throughout the profile, resulting from the high
coal particle content. Even dating of pollen grains was impossible, since not all coal particles
could be removed. The chronozones employed, from Oldest Dryas to Subatlantic, are based on
comparison of vegetation development with radiometrically dated Siberian pollen profiles
(Hahne and Melles, this volume; Hahne and Melles, 1997).