Sedimentary formations and main development stages of the western Transbaikal and southeastern Baikal regions in the late Cretaceous and Cenozoic

Abstract

Upper Cretaceous and Cenozoic formations of the western Transbaikal and southeastern Baikal regions are considered. Molasses and molassoids (molasse-type sediments) were included into these formations in previous works. In our opinion, the following formations are developed in these regions: plain fan formation divided into the terrigenous (Upper Cretaceous) and coaliferous (Upper Oligocene-Lower Pliocene) subformations; plain fine-clastic formation (Paleogene, except the Upper Oligocene); and orogenic molasse formation (Upper Pliocene-Holocene) divided into the lower red-colored and upper gray-colored subformations. Main textural features of these formations are considered. Paleogeographic and paleotectonic settings of their accumulation are reconstructed. It is shown that coarse-clastic sediments of fan formations accumulated in grabens among ancient denudation plains due to the destruction of rocks in near-wall benches. These plains probably hosted in some areas remnants of the mountainous relief. Origination and development of the Baikal rift zone was the main geological event in the Baikal region during the Late Cretaceous and Cenozoic. Based on study of the southeastern Baikal region with the thickest and most representative Cenozoic sections, the prerifting and rifting stages of this zone and correlative events in the adjacent (relatively stable) areas of the western Transbaikal region are characterized.