Sedimentary Characteristics And Tectonic Evolution Of Jiaolai Basin

The Jiaolai Basin is a typical continental basin,located in the Jiaodong Peninsula.The western part of the basin is bounded by the Tanlu fault zone,and the south is adjacent to the Sulu orogenic belt.The northern main part of the basin is overlaid on the Jiaobei uplift.The east extends into the Yellow Sea,and connected with the Qianliyan uplift by Qianliyan fault.In order to reveal whether the post-orogenic effect of the Sulu orogenic belt is related to the formation of the Jiaolai Basin,this paper investigates the sedimentary characteristics and tectonic evolution of the Jiaolai Basin and discusses the dynamic mechanism of basin formation.Based on the analysis of the texture,structure and contact relationships of the sedimentary strata in the basin,Laiyang Group is a set of terrigenous clastic rocks.The basin experienced two complete cycles of water inflow and retreat.The Wawukuang Formation at the bottom of the Laiyang Group experienced a separate water inflow and retreat cycle during its sedimentary period,and formed a sedimentary system of alluvial fan-lacustrine-river.From the lower Linsishan formation to the top Qugezhuang formation,the sedimentary system was successively alluvial fan depositional system,fan delta depositional system,lacustrine depositional system,braided river delta depositional system and braided river depositional system,and formed another complete cycle.The Qingshan Group can be divided into four volcanic cycles,with lithology dominated by volcanic rocks and pyroclastic rocks.The Wangshi Group is a set of red-toned terrigenous clastic rocks,and the basin experienced a complete water inflow and retreat cycle during its stratigraphic sedimentary period,and formed a sedimentary system of alluvial fan-delta-river.In this paper,through the collection,analysis and inversion of fault-slip data,joint data,fold data and synsedimentary fault data in the Jiaolai Basin,six stages of paleotectonic stress field for the basin were obtained: 1)During Early Cretaceous,the NWW-SEE extensional paleotectonic stress controlled the initial deposition of the Laiyang Group;2)At the end of the Laiyang Group's sedimentary,the paleotectonic stress changed to a compression near EW direction;however,3)During Late Early Cretaceous paleotectonic stress changed to EW extensional geological setting,forming four volcanic cycles of the Qingshan Group;4)At the end of the Early Cretaceous,the paleotectonic stress shifted to NW-SE compression;5)The Wangshi Group strata were deposited in the Late Cretaceous under the extensional stress from near N-S to NNESSW,and 6)finally the paleotectonic stress direction changed to NE-SW compression at the end of Wangshi Group deposition.The NWW-SEE extension during the Laiyang Group sedimentary period may be caused by the E-W retreat of the Paleo-Pacific plate during the subduction to the Eurasian plate and the NW-SE post-orogeny of the Sulu orogenic belt,which indicates that the preliminary stage of the Jiaolai basin formation may be influenced by the late orogeny of the Sulu orogenic belt.The changes of paleotectonic stress field in the other stages may be mainly affected by the subduction and retreat of the Paleo-Pacific,and the direction of Paleo-Pacific subduction showed a clockwise change in the process of basin evolution.Under the action of the Cretaceous paleotectonic stress field,the Jiaolai basin is controlled by rifting in the Early Cretaceous and strike-slip pull-apart in the Late Cretaceous,respectively,and the superposition of the two processes made the Jiaolai basin a composite basin.