Sedimentation processes and new age constraints on rifting stages in Lake Baikal: results of deep-water drilling |
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| Authors: | M I Kuzmin E B Karabanov A A Prokopenko V F Gelety V S Antipin D F Williams A N Gvozdkov |
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| Institution: | (1) Institute of Geochemistry, Siberian Branch of Russian Academy of Sciences, Irkutsk, Russia, RU;(2) Baikal Drilling Project, Department of Geological Sciences, University of South Carolina, Columbia, SC 29208, USA e-mail: ekarab@geol.sc.edu, US;(3) United Institute of Geology, Geophysics and Mineralogy, Siberian Branch of Russian Academy of Sciences, Novosibirsk, Russia, RU |
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| Abstract: | With this paper we present a first attempt to combine the direct results on lithology, composition and age dating in the
boreholes BDP-93, BDP-96 and BDP-97 with geological and seismic data from the areas where those sections were drilled. The
sedimentary environments represented by the BDP boreholes are markedly different and possess characteristic lithological features.
The results of the deep drilling provide the essential means for testing numerous age models used in geological reconstructions
of the Lake Baikal rifting dynamics. Neither the basin-wide unconformity interpreted from seismic data, nor the interpreted
change from shallow-water to deep-water facies at the boundary of the seismic stratigraphic complexes were found in the BDP-96
boreholes on Academician Ridge. Also, lithology does not support the proposed reconstructions of intense lake level fluctuations
and transgressions during the Pliocene at Academician Ridge. The continuous deep-water hemipelagic sedimentation at Academician
Ridge has existed for the past 5 Ma. The beginning of an intense rifting phase of the Neobaikalian sub-stage and related drastic
changes in sedimentation processes were interpreted on seismic sections as the basin-wide unconformity B10. Different age
estimates for this boundary ranged from Late Pliocene (3.5 Ma) to Plio-Pleistocene boundary. As shown by BDP-96 borehole,
B10 is associated with a lithological change from diatomaceous ooze to dense silty clay and not with an erosional contact.
The new age for this boundary in BDP-96 is approximately 2.5 Ma. This new age constraint suggests that the upper sedimentary
strata of Northern Baikal (1.5–1.7 km thick) have formed during the past 2.5 Ma with average sedimentation rates of 60–70 cm/ka.
The BDP-93 boreholes at Buguldeika suggest that uplift in Primorsky Range took place prior to 1.07–1.31 Ma, a date which exceeds
the age of previous geological models.
Received: 12 March 1999 / Accepted: 10 February 2000 |
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| Keywords: | Rifting stages Lake Baikal Sedimentary environments Lithology |
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