Sedimentary features and evolution of the Dongying Formation in the tidal area of the Liaohe Basin

An analysis was carried out on the sedimentary features of the Paleogene Dongying Formation in the tidal area of Liaohe Basin based on core,drilling and seismic data as well as modern sedimentology concepts and methods.Six sedimentation types are identified in the Dongying Formation in the tidal area,namely fan delta,braided delta,delta,lake,beach bar and sublacustrine fan.The temporal and spatial distribution as well as the evolutionary features of the sedimentary system in the Formation was controlled by the structural background and lake level variation.The third member of the Formation was deposited in the early stage of lake expansion when the basin was experiencing the most intense subsidence.The sedimentary facies are dominated by fan delta,braided delta and sublacustrine fan.The second member was formed during the lake expansion when the tectonic movement weakened and the lake basin was shallower.Sedimentary facies during the time were mainly braided delta and shallow lake-beach bar.The first member was deposited during lake shrinking and braided delta dominated except for shallow lake-beach bar in local deep sags.