Geological Characteristics and Tectonic Significance of Jurassic Yangqu Formation from Alake Lake Area in the Eastern Part of East Kunlun Orogenic Belt

The early Jurassic Yangqu Formation, newly identified at Alake Lake area during the process of 1:50000 geological mapping in the eastern part of East Kunlun orogenic belt, is observed and depicted carefully both outdoor and indoor in the view of sedimentary faciology, which has been subdivided into 3 lithology beds according to their lithological differences from bottom to top, namely, conglomerate lithology bed (J₁y¹), sandstone and siltstone lithology bed (J₁y²) and rhythmic lithology bed (J₁y³). This Formation can be summarized as a stratigraphic sequence of continental faciology with fluvial deposits-lacustrine deposits-fluvial deposits. Based on the regional data, it is supposed that this strata may be the sedimentary response to the strength field transition from compression to extension for the eastern part of East Kunlun orogenic belt during middle Triassic-early Jurassic.