Sedimentary facies and palaeogeography of the Northern Qilian orogenic during the Silurian

During the Ordovician-Silurian, the northern Qilian orogenic belt underwent a complex transition from subduction to orogeny which influenced by Caledonian tectonic activity.Its Silurian is an important tectonic transition stage of basin-mountain conversion, but the nature and tectonic setting of its Silurian deposition has been controversial. The palaeogeographic analysis in this paper is based on the field and laboratory examination in integration with lithology, textures and structures, and fossil assemblages. Three sedimentary facies,including tidal-flat facies, shallow shelf facies and bathyal facies are discriminated.In addition, based on the previous research and the new data of this study, the new relation map of Silurian sedimentary structure framework, sedimentary basin types and spatial configuration in North Qilian area is compiled. Furthermore, sedimentary basin filling sequence and paleogeographic evolution of the study area are restored on the basis of the regional stratigraphic correlation and lithofacies paleogeographic mapping.