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| Titel |
Environmental changes at the Holocene-Late Pleistocene transition: Sedimentation on Akademicheskii Ridge (Lake Baikal, Russia) |
| VerfasserIn |
Elena G. Vologina, Michael Sturm |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250043825
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| Zusammenfassung |
| Akademicheskii Ridge of Lake Baikal represents a 300 m deep underwater rise, which
separates the Central Basin (1647 m water depth) and the North Basin (970 m water depth) of
640 km long lake. The large distance to the turbid load of particle-carrying tributaries and
coastal areas as well as the absence of slide induced turbidites are responsible for low
sedimentation rates. A large number of short cores (approx. 120 cm) was used to study in
detail the Holocene-Late Pleistocene transition, using lithological composition, magnetic
susceptibility, microfossils, pollen and spores, chemistry, grain size and mineral
composition.
Holocene sediments show sedimentation rates from 0.015 to 0.25 mm y-1 and are
mainly composed of biogenic material with rare admixtures of aeolian and ice-rafted
terrigenous particles [1]. The sediments are characterized by abundant microfossils, such
as diatoms, spicules of sponges, chrysophyte cysts, pollen and spores. Holocene
diatom assemblages are representated by Aulacoseira baicalensis, A. skvortzowii,
Cyclotella minuta, C. baicalensis, Synedra acus var.radians, Stephanodiscus meyerii,
Crateriportula inconspicuus and Cyclostephanos dubius [2]. Concentrations of
Corg.,Ntot.,and Sibiog.indicate clearly higher productivity of the lake during the Holocene
[1].
Late Pleistocene sediments are composed of clastic, fine-grained, clayey material, mainly
of terrigenous origin. This includes also aeolian particles and rare ice-transported sandy
material and rock debris. A peak of the diatom species Stephanodiscus flabellatus, observed
within the upper part of clayey sediments, defines the Late Pleistocene-Holocene transition
[2].
Very low contents of microfossils (diatoms, spicules of sponges, chrysophyte cysts etc.)
within Late Pleistocene deposits indicate lower productivity of Lake Baikal. Glacial
melt-water dominated the sediment transport processes within the lake during this
time.
The main minerals of the sand fraction are quartz, feldspars and mica. The heavy mineral
assemblage contains amphiboles, pyroxenes, epidote, sphene, magnetite, garnet and
chloritoide. Within the Holocene, contents of chloritoide are low (0.6-1.2 %), but they
are distinctly higher within the Late Pleistocene sediments (3.2-14.6 %) [1]. An
increase of chloritoide in sediments points towards an intensification of aeolian
transport by stronger winds and longer-lasting periods of ice cover during the Late
Pleistocene [3]. Results of pollen analyses support these findings. They indicate
that mountain slopes of the catchment of Lake Baikal were mostly uncovered by
vegetation.
A polymineral composition is characteristic for the clay fraction of Late Pleistocene
deposits: hydro-mica, kaolinite, smectite and chlorite. This is caused by extensive glaciation
of the catchment of the lake during this time [4], generating increased transport of terrigenous
material to the lake by glacial melt water [5].
References
[1] Vologina, E.G. and Sturm, M. 2009. Types of Holocene deposits and regional
pattern of sedimentation in Lake Baikal. Russian Geology and Geophysics 50,
1-6.
[2] Bradbury, J.P., Bezrukova, Ye.V., Chernyaeva, G.P. et al. 1994. A synthesis of
post-glacial diatom records from Lake Baikal. J. Paleolimnol. 10, 213-252. |
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