PRELIMINARY-RESULTS OF THE FIRST SCIENTIFIC DRILLING ON LAKE-BAIKAL, BUGULDEIKA SITE, SOUTHEASTERN SIBERIA

The Baikal Drilling Project (BDP) is a multinational effort to investi gate the paleoclimatic history and tectonic evolution of the Baikal se dimentary basin during the Late Neogene. In March 1993 the Baikal dril ling system was successfuly deployed from a barge frozen into position over a topographic high, termed the Buguldeika saddle, in the souther n basin of Lake Baikal. The BDP-93 scientific team, made up of Russian , American and Japanese scientists, successfully recovered the first l ong (>100 m) hydraulic piston cores from two holes in 354 m of water. High quality cores of 98 m (Hole 1) and 102 m (Hole 2), representing s edimentation over the last 500,000 years, were collected in 78 mm diam eter plastic liners with an average recovery of 72% and 90%, respectiv ely. Magnetic susceptibility logging reveals an excellent hole-to-hole correlation. In this report the scientific team describes the prelimi nary analytical results from BDP-93 hole 1 cores. Radiocarbon dating b y accelerator mass spectrometry provides an accurate chronology for th e upper portion of Hole 1. Detailed lithologic characteristics, rock m agnetic properties and inorganic element distributions show a signific ant change to the depositional environment occuring at 50 m subbottom depth, approximately 250,000 BP. This change may be due to uplift and rotation of the horst block in the Buguldeika saddle. The sedimentary section above 50 m is pelitic with varve-like laminae, whereas the sec tion below 50 m contains a high proportion of sand and gravel horizons often organized into turbidite sequences. Accordingly, high resolutio n seismic records reveal a change in sonic velocity at this depth. It is inferred that sedimentation prior to 250 ka BP was from the west vi a the Buguldeika river system. After 250 ka BP the Buguldeika saddle r eflects an increase in hemipelagic sediments admired with fine-grained material from the Selenga River drainage basin, east of Lake Baikal. Variations in the spore-pollen assemblage, diatoms, biogenic silica co ntent, rock magnetic properties, clay mineralogy and organic carbon in the upper 50 m of BDP-93-1 reveal a detailed record of climate change over approximately the last 250,000 years. These variables alternate in a pattern characteristic of glacial/interglacial climatic fluctuati ons. The present age model suggests that the climate signal recorded i n Lake Baikal sediments is similar to Late Quaternary signals recorded in Chinese loess sections and in marine sediments. Copyright (C) 1996 INQUA/Elsevier Science Ltd