Sedimentary Sequence,Provenance Analysis And Tectonic Evolution Of The Late Mesozoic Wafangdian Basin In Southern Liaoning

Liaodong peninsula in the northeastern north China craton,is the study of the north China craton Mesozoic tectonic evolution of a hot spots,has experienced many times during the Mesozoic tectonic events,main show is from the shrinkage of the early early cretaceous to early late cretaceous stretching,the structure of the development of a series of contraction and stretch,including the thrust nappe,metamorphic core complex,and normal fault control of half graben basin.Wafangdian basin in southern area superimposed basin in Jurassic and cretaceous,bottom-up deposition under-Jura in wafangdian group(J1-2w)formation,lower cretaceous Gui Yun flower group(K1g)volcanic sedimentary formation,lower cretaceous Pu Lan Dian group(K1p)formation,during the period of early cretaceous has developed the thrust nappe and detachment fault system.The strata and different structures of the basin reflect the time of Mesozoic tectonic system transformation in Liaodong Peninsula,which is of great theoretical significance.The stratigraphic sequence of Wafangdian Basin is studied through field geological survey,measured typical stratigraphic profiles and regional data,and the sedimentary facies analysis is carried out.The early-middle Jurassic Wafangdian Formation is a set of coal-bearing strata,mainly composed of sandstone,mudstone,gray shale and marl,and is fluvial lacustrine facies.The Early Cretaceous Guiyunhua formation is volcanic-sedimentary sequence with multiple cycles of overflow,explosion and intermittent sedimentary facies.The Pulandian formation is a set of conglomerate,sandstone,mudstone and shale,reflecting alluvial fan-braided river-lake facies.According to the analysis of gravel composition and paleoflow direction statistics,the gravel in the conglomerate of Pulandian formation mainly comes from the volcanic eruption in the early Cretaceous,the Qingbaikou system and the Cambrian system around the basin,and the basin is a faulted basin controlled by the activity of the detachment fault in Jinzhou.By comparing Wafangdian basin with basins in western liaoning and eastern Liaoning,it is found that different basins in the region show the consistency of sedimentary characteristics and structural characteristics in space and time,indicating that they are the products of the same regional tectonic action.The formation and evolution of the basin may be related to the subduction and retraction of the Western Pacific plate.