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| Titel |
Sedimentary Fe/Mn layers buried deeply below the bottom surface in Lake Baikal |
| VerfasserIn |
L. Z. Granina, M. A. Phedorin, V. D. Mats, O. M. Khlystov |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024991
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| Zusammenfassung |
| In Lake Baikal, constantly oxygenated water column results in intensive accumulation of iron
and manganese in surface oxidized sediments. However, in the region of underwater
Academician Ridge Fe/Mn layers and crusts are also found deeply (meters) below the
water-sediment interface. Formation of such crusts was firstly related to climatic fluctuations
in the region (Deike et al. 1997), later - to tectonic events in the lake. We believe that in
Baikal depression, the weathering crust, sub-aerial cover, and accompanied Fe, Mn, and P
ores developed during the Cretaceous-Paleogene and Neogene epochs, characterized by
warm and wet climatic conditions. Later on, the depression’s diurnal surface was
flooded by water basins newly formed in the region, however fragments of this
surface are widely spread both on the land and the lake bottom in the regions of
Olkhon Island and Academician Ridge. As a result of the Late Pleistocene tectonic
movements, the surface of Academician uplift was submerged below the present lake’s
level. Covered this surface ancient (pre-Baikalian) ore-bearing formations were
also submerged. Age of sedimentary Fe/Mn crusts buried deeply below the bottom
surface in the region of Academician Ridge is about 100 Ky (Deike et al. 1997;
Granina et al. 2003), and it agrees with suggestion on the crusts burial due to tectonic
movements that have started in this part of the lake about 120 Ky ago. There are different
evidences supported this hypothesis (Mats et al. 2000; Granina et al. 2003); new ones
presented in this paper are the following: i) A map firstly constructed using the
regional geological data clearly shows that location of the continental Fe and Mn
ores and phosphorites in the Central Western Prebaikalie and shore-land near the
Olkhon Island (Preolkhon’ie) is rather close to nearby area of the lake bottom,
where Fe/Mn crusts are deeply buried within the sediments. This testifies in favor
of their subaerial origin and relation to the continental ores on the western lake
shore. Some of the buried crusts are bedded directly in subaerial sands; the others
were re-deposited under conditions of extremely low content of organic carbon in
ambient sediments. ii) The first data are presented on the elemental composition of
deeply buried Fe/Mn crusts (layers) obtained by SR-XRF method as described in
(Phedorin et al. 2000). They indicate that crusts are enriched compared to ambient
sediments not only in Fe and Mn, but also in Cu, Sr, Cr, and V; in some cases -
in Ni, Pb, and Mo. The Cr and V enrichment needs to be further explained since
these elements show no any accumulation in the recent Baikal sediments (Muller
et al. 2002). The highest enrichment (6-8 times) is found for As and U. Many of
buried crusts are highly enriched in P as may be exemplified by data presented
in (Deike et al. 1997). Some of them were identified as U-bearing phosphorites
(Zhmodik et al. 2001). The highest U content (up to 260 ppm) was recorded in
secondary vivianite found at 316 cm depth in sediment core from Academician
Ridge (Fagel et al. 2005). In general, the concentrations of Fe, Mn, and P oxides in
deeply buried crusts have the same order of magnitude as the highest concentrations
recorded in continental phosphorites of the Sarminsky and Ozersky deposits located on
the western Baikal shore. Thus new data presented show that Fe/Mn crusts buried
deeply below the water-sediment interface in some areas of Lake Baikal may be
inherited from ancient ores formed under quite different climatic and sedimentological
conditions. They could serve as markers of past tectonic events started in the Late
Pleistocene. |
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