Plain Fan Complexes in Jurassic-Cretaceous Grabens of the Western Transbaikal Region

Abstract

The paper deals with peculiarities of structure, composition, and formational environment of Jurassic-Lower Cretaceous coaliferous-terrigenous rocks in the Western Transbaikal region. These rocks are commonly considered intermontane molasses. It is proven that, in most cases, these rocks are fan complexes, which fill narrow troughs (grabens) against the background of a plain morphology rather than molasses (indicators of mountain landscape). Models of structure and sedimentation of fan complexes and the reasons favoring the origination of thick coal deposits in them are elaborated. Distinctions of fan complexes from the molasses are revealed. It is shown the discrimination of fan complexes is important for the reconstruction of paleogeographic and paleotectonic environments.