Evolution of the Academician Ridge Accommodation Zone in the central part of the Baikal Rift, from high-resolution reflection seismic profiling and geological field investigations

New high-resolution seismic reflection data from the central part of Lake B aikal provide new insight into the structure and stratigraphy of Academicia n Ridge, a large intra-rift accommodation zone separating the Central and N orth Baikal basins. Four seismic packages are distinguished above the basem ent: a thin top-of-basement unit; seismic-stratigraphic unit X; seismic-str atigraphic unit A; and seismic-stratigraphic unit B. Units A and B were cor ed on selected key locations. The four packages are correlated with a serie s of deposits exposed on the nearby western shores: the Ularyar Sequence (O ligocene); the Tagay Sequence (Lower to Middle Miocene); the Sasa Sequence (Upper Miocene to Lower Pliocene); the Kharantsy Sequence (Upper Pliocene); and the Nyurga Sequence (Lower Pleistocene). Based on stratal relationship s, sedimentary geometries, distribution patterns and principal morphostruct ural elements - both onshore and offshore - we propose a new palaeogeograph ic evolution model for the area. In this model progressive tectonic subside nce of the Baikal basins and successive pulses of uplift of various segment s of the rift margins lead to: (a) formation of the ridge as a structural a nd morphological feature separating the Central and North Baikal basins dur ing the Middle to Late Miocene; (b) gradual flooding of the main parts of t he ridge and establishment of a lacustrine connection between the two rift basins during the Late Miocene; and (c) total submergence of the top parts of the crest of the ridge during the latest Pleistocene. This new model hel ps to better constrain numerous phases in the structural evolution of the B aikal Rift, in which the Academician Ridge as an accommodation zone plays a crucial role.