The new BDP-98 600-m drill core from Lake Baikal: a key late Cenozoic sedimentary section in continental Asia

The new 600-m drill core BDP-98 from the Academician Ridge of Lake Baikal recovered a continuous sedimentary record of the past 10 Ma. The entire section is represented by lacustrine sediments, which gradually change from distal deltaic facies at the bottom of the section to fine undisturbed hemipelagic sediments of the upper 300-m interval. The entire 10-Ma lacustrine section contains abundant diatoms, thus allowing extension of Plio-Pleistocene diatom and biogenic silica records into the Miocene. Above the Matuyama/Gauss paleomagnetic reversal boundary, the BDP-98 record contains clearly delineated glacial/interglacial lithologic cycles. Below this boundary the diatom signal is quite different: average diatom contents are higher and variations are of lower amplitude. Although most likely paleoclimatic in origin, these variation presumably reflect past changes in the moisture regime of southeast Siberia under conditions of warm subtropical climate during the Miocene and Early-Middle Pliocene. The continuous BDP-98 drill core, which covers the hiati present in the composite continental sections of the Baikal region, is a key section for reconstructing the Neogene-Quaternary climatic evolution of continental Asia. The BDP-98 section also places several important time constraints on the rifting history of Lake Baikal by providing reliable correlation of lithological and physical properties of the drill core sediments with calculated positions of the acoustic reflection boundaries interpreted from multichannel seismic studies. The lithologic composition indicates that, on the stable block of Academician Ridge where the BDP-96 and BDP-98 drill sites are located, acoustic reflection boundaries are not associated with major erosional events, but instead result from changes in sediment density and composition. Several lithologic indices further suggest that significant changes have occurred in the physics and chemistry of Lake Baikal waters, affecting the carbonate equilibrium and oxygen regime of Baikal. (C) 2001 Published by Elsevier Science Ltd.