Diatom biostratigraphy of Lake Baikal during the past 1.25 Ma: new results from BDP-96-2 and BDP-99 drill cores

Abstract

Detailed diatom zonation in the Lake Baikal holostratotype section BDP-96-2 is extended over the interval 0.85–1.25 Ma and compared with diatom assemblage composition from the new BDP-99 drill core. Interglacial diatom assemblages at these two sites over 220 km apart are of similar composition, and the same complete and continuous succession of diatom zones is observed in both drill cores over the 0–800 ka interval. We propose a correlation of Baikal diatomaceous intervals with the marine oxygen isotope stratigraphy and with European climato-stratigraphic divisions of the early Pleistocene. We then use the diatom succession in BDP-96-2 to demonstrate evidence for disconformity in BDP-99 and to establish an approximate age model for this section. Diatom assemblages characteristic of the top of the Matuyama reversed polarity interval and the upper part of the Jaramillo normal polarity subchron are not found in the BDP-99 section below the disconformity boundary. The lack of diatom zones corresponding to the MIS 21-27 of the marine oxygen isotope stratigraphy in BDP-99 section suggests that the estimated age span of missing sediment interval in BDP-99 is ca 150–160 ka. The unusual diatom assemblage of cosmopolitan species during MIS 33 in both BDP-96-2 and BDP-99 drill core sections is indicative of abrupt ecological changes in the time interval 1.12–1.08 Ma.