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THE CARBON RECORD IN LAKE SEDIMENTS FROM THE TUNGUSKA BASIN

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THE CARBON RECORD IN LAKE SEDIMENTS FROM THE TUNGUSKA BASIN Powered By Docstoc
					Crater Lake in Siberia: A Unique Lacustrine Record Linking Proxy and Trigger of Carbon Isotope
Perturbations at the Permian-Triassic Boundary


     KIRSTEN FRISTAD1, HENRIK SVENSEN1, SVERRE PLANKE 1,2, AND ALEXANDER G. POLOZOV1, 3
1
  Physics of Geological Processes (PGP), University of Oslo, PO Box 1048 Blindern, 0316 Oslo, Norway.
    Kirsten.Fristad@fys.uio.no
2
  Volcanic Basin Petroleum Research (VBPR), Oslo Research Park, 0349 Oslo, Norway
3
  Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry of Russian Academy of
    Sciences (IGEM RAS), 119017 Moscow, Russia

Svensen et al. (EPSL, 2009) have investigated the existence of hundreds of phreatomagmatic breccia
pipes located in the Tunguska Basin, which formed contemporaneously with the Siberian Traps. They
hypothesize a violent formation history caused by sill intrusions into organic rich sediments, which
enabled the release of gigatonnes of greenhouse gases to the atmosphere as the initial trigger for the
end-Permian environmental crisis. Crater lake deposits are preserved in some of these pipes and offer
the first opportunity to precisely constrain the timing and effects of pipe formation. We are studying
the upper 550 m of a core drilled through the center of a former crater lake and underlying brecciated
pipe located in the southern reaches of the Tunguska Basin. The core consists of fine- to coarse-grained
siliciclastic and volcanoclastic sediments interspersed with tuff deposits. The sediments range in TOC
values of up to 4% and contain various well-preserved organic fossils including pollen, algae and
acritarchs. We report on the sequence of carbon isotopes in organic matter throughout the crater lake
sediments. An excursion at the base of the crater sediments temporally links the formation of the pipe
with disturbances in the carbon cycle at the P-T boundary. This constrained timing means the unique
terrestrial environmental and fossil record preserved in this lake can be interpreted in the context of the
end-Permian crisis.

				
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posted:10/7/2011
language:English
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