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 r ecovered a continuous sedimentary record of the past 10 Ma. The entire sect ion is represented by lacustrine sediments, which gradually change from dis tal deltaic facies at the bottom of the section to fine undisturbed hemipel agic sediments of the upper 300-m interval. The entire 10-Ma lacustrine sec tion contains abundant diatoms, thus allowing extension of Plio-Pleistocene diatom and biogenic silica records into the Miocene. Above the Matuyama/Ga uss paleomagnetic reversal boundary, the BDP-98 record contains clearly del ineated glacial/interglacial lithologic cycles. Below this boundary the dia tom signal is quite different: average diatom contents are higher and varia tions 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 M iocene and Early-Middle Pliocene. The continuous BDP-98 drill core, which c overs the hiati present in the composite continental sections of the Baikal region, is a key section for reconstructing the Neogene-Quaternary climati c evolution of continental Asia. The BDP-98 section also places several important time constraints on the ri fting history of Lake Baikal by providing reliable correlation of lithologi cal and physical properties of the drill core sediments with calculated pos itions of the acoustic reflection boundaries interpreted from multichannel seismic studies. The lithologic composition indicates that, on the stable b lock of Academician Ridge where the BDP-96 and BDP-98 drill sites are locat ed, 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 El sevier Science Ltd.