UPPER PLEISTOCENE TO HOLOCENE DEPOSITS OF THE TUNKA RIFT (SOUTHERN BAIKAL REGION)

Abstract

The Tunka rift valley extending from the SW termination of Lake Baikal by 200 km westward represents a series of large and smaller troughs separated by subordinate elevations. Inversely uplifted bedrock exposures exhibit the Neogene to Quaternary basalts, Pliocene pebblestones, and poorly lithified conglomeratic breccias. Large depressions are filled with sandy, boulder-pebbly, and covering loess deposits. Relationships between these lithological complexes and results of thermoluminescence dating show that they accumulated concurrently during the Pleistocene-Holocene, beginning since 70 000 years ago. Alluvial deposits bearing characteristic mollusks are dominant in the sandy complex. These data disprove the idea of a large Tunka Lake (Baikal bay) existence during the Pleistocene time. Proluvial and glacial to fluvioglacial deposits are most characteristic of the boulder-pebbly complex. Eolian processes led to accumulation of loess cover and relevant slope deposits. Alluvial terrace deposits accumulated at various distinct levels of the Irkut River and confluent valleys during the last 40 000 years.