Alexander Prokopenko, University of South Carolina (United States)
Galina Khursevich, Institute of Geological Sciences (Belarus)
Elena Bezrukova, Institute of Geochemistry (Russian Federation)
Linda Hinnov, John Hopkins University (United States)
Mikhail Kuzmin, Institute of Geochemistry (Russian Federation)
Here we discuss the paleoclimate record from Lake Baikal, SE Siberia, as a regional (Eurasian) standard of reference of continental Plio-Pleistocene stratigraphy. The first deep rift lake to be drilled in the 1990-ties using the ODP-style advance piston coring technology, Lake Baikal produced a continental sedimentary archive of unmatched continuity, duration and resolution. The most remarkable record recovered by double-cored BDP-96 drill section and single-cored BDP-98 drill section comes from the bathymetric high of an underwater Academician Ridge; this area, currently under 300 meters of water, was characterized by the most stable hemipelagic depositional setting during the past 5 Ma unaffected by lake-level variations, direct riverine input and turbidite deposition. Glacial/interglacial cycles are recorded in Lake Baikal as cycles of diatom productivity seen in diatom abundance, organic carbon accumulation, but best exemplified by changes in biogenic silica as a major component of bulk sediment. Biogenic silica content in sediments varying from zero during glacials to 40-50% dry sediment weight during interglacials. With highly reproducible patterns from core to core and with high signal-two-noise ratio, biogenic silica is the leading proxy for developing stratigraphy and orbitally-tuned timescales.
The new orbitally-tuned composite record of the entire Pleistocene interval, now freely available online, provides a robust continental timescale independent of peak-to-peak correlations with marine oxygen isotope templates. Because of the providential location in high latitudes and in the interior of the largest continent, Lake Baikal productivity and sediment deposition systems were highly responsive to both obliquity and precessional forcing. As a result, even with minimal tuning approach (precession only with September perihelia timing) the age model solution confines high signal power to narrow orbital frequency bands. We will demonstrate that essentially every precessional cycle during the Pleistocene can be recognized in the Baikal record, which makes it a benchmark template for correlation of marine and continental Plio-Pleistocene records based on the recognition of the terrestrial equivalents of marine oxygen isotope stages and substages. With this new timescale as a basis, we will discuss major regional Plio-Pleistocene climatic and biostratigraphic boundaries seen in major terrestrial vegetation changes recorded in pollen records and in major extinctions of the dominant diatom assemblages.