COSMOGENIC NUCLIDE DATING OF THE DELTAIC TERRACES ON THE SELENGA RIVER DELTA, LAKE BAIKAL, SIBERIA

The Selenga River flows northward from Mongolia, landing on the southeastern shore of Lake Baikal, in southern Siberia, forming a shelf-edge delta system atop a tectonically active continental rift zone. The approximately 600 km^2 delta region seen today, is the result of a fluvially dominated, high sediment input transport system. The absolute dating of the Selenga River’s deltaic terraces, is an effort to constrain and understand the stratigraphy and geomorphology of the region during the quaternary period. To interpret the stratigraphic history and resulting geomorphology of the delta, field samples from three distinct terrace levels (regionally named: Manzur, Kabansk, and Barani Mis) are currently being analyzed for both particle size and the concentration with depth of the cosmogenic nuclide, Beryllium 10. By analyzing depth profiles for concentration of Beryllium 10, potential surface exposure histories of these terraces can be constrained. The study could yield various results depending on the relative exposure ages of the individual terraces. One hypothesis consistent with the observed stratigraphy and geomorphology, is that repeated avulsions of the delta were caused primarily by the tectonic subsidence associated with the Lake Baikal continental rifting zone, while the formation of the modern terrace system was likely the result of increased erosion due to glacial melt at the beginning of the Holocene as the climate warmed. This study of the Selenga River delta will provide further insight into the importance of tectonic and climatic forcing’s on the behavior of shelf edge delta systems.