Sedimentary response of regional tectonic transformation in Late Triassic Yanchang period at the central and southern Ordos Basin

Based on a large number of mineral quantitative identification data,the plane and vertical distribution and changing characteristics of the sandstone types,light minerals,lithic components,etc.have been systematically analyzed in the Group Chang 10-Chang 1Yanchang Formation at the central and southern Ordos Basin.The study revealed that during the deposition of Group Chang 8and Group Chang 7,the Ordos Basin had undergone an obvious sedimentary changing event.Since the Period Chang 7,the deposition zones of southwest and northeast in the basin had became very different in the types of sandstone,the components of minerals and tectonic background of source region,but there was no such difference before Period Chang 7.The boundary of the two regions has been confirmed to be along the Huachi and Huangling line.Considering the tectonic setting of the development and other sedimentary and tectonic events in Ordos Basin,we proposed that the sedimentary changing event in Yanchang Period was closely related to the splicing and collision of North China and Yangtze Craton in the Mid-Late Triassic,causing the closure of Qinling Ocean.In other words,this event is the sedimentary response to the fully collision,strong uplift and denudation of Qingling Orogenic Belt.The study can provide scientific basis for further analyzing the tectonic property of source region,the sedimentary system division in basin,the distribution of sand bodies as well as the prediction of favorable reservoirs in Yanchang Formation. Meanwhile,new evidences and important clues for the construction and reformation of basin evolution and basin-range coupling in the Mesozoic are provided.