Discovery of large-scale Silurian ancient delta deposition system in Longmu Co area, Qinghai-Tibet Plateau, China and its significance

A complete set of Silurian stratum has been found in Longmu Co area, Qinghai-Tibet Plateau, also authors have established Longmu Co Formation of Lower Silurian, Danmianshan Formation of Middle-Upper Silurian, Xinxinghu Formation of Upper Silurian. During Silurian Period, the environment of study area has experienced four evolution stages: open sea platform, blocking gulf,delta and tidal flat. There is a large ancient delta deposition in the Lower Part of the Danmianshan Formation, and it is made up of the former and delta, the delta front and the delta plain. The triage river of delta plain, natural levee, river burst fan and segregation between the bay and lakes, swamps and other micro-phases of the ancient delta are developed and the sediment thickness is very big. The discovery of the large delta deposits, the frequent change between land and ocean, the unconformity between the Middle-Upper Devonian and Ordovician-Silurian around Wuzhishan, east of Longmu Co, these evidences have proven that the norther side of Longmu Co-Shuanghu suture zone was affected by the late Caledonian movement and it is distinctly different from the sediment structure in southern Qiangtang area. Therefore, the discovery helps to understand better the tectonic evolution of the southern and northern Qiangtang area, and to explore the north and south of the ancient continent plate boundaries.