New high-resolution seismic reflection data from northern Lake Baikal and detailed land-based morphological and sedimentological data reveal a variety of coarse-grained deposits in the northern Baikal Rift. Each depositional facies is assigned to a specific structural domain. Alluvial fans (onshore) and small fan deltas (offshore) dominate the western border-fault flank. Glacial deposits (onshore) and large glacio-lacustrine fans (offshore) characterize the eastern flexural margin. In the north, the axial rift termination comprises a large fluvial delta. This distinct pattern of depositional environments reflects the pronounced asymmetry of the rift and emphasizes the role of rift structure in controlling drainage and the location and type of rift-basin fill. Climate, however, exerts a profound influence on the generation and availability of coarse-grained material. This is best documented along the eastern rift margin where Pleistocene valley glaciers advanced at >50, 40-35, and 26-13 ka from the high rift shoulders down to, and beyond, the present shore into the Baikal Basin. During these phases, large volumes of glacial sediment were introduced into the basin, accumulating in extensive glacio-lacustrine outwash fans. About one-third of the seismically penetrated rift fill is glacial-outwash material derived from the eastern shoulder. Under present-day nonglacial conditions, however, the fans are inactive because of insufficient sediment supply; this documents the importance of major climatic fluctuations with respect to the magnitude of sediment discharge and accumulation. The sedimentary history also underscores the modifying effects of climate-driven processes on the typical structure-dominated aspects of rift sedimentation. |
