Study On The Middle Permian Lithofacies Palaeogeography In Songliao Basin And Its Adjacent Areas

Songliao basin is a large rhombic continental basin in Northeast China.It is about 750 kilometers of long axis,350 kilometers wide,with an area of more than 26 square kilometers.The Middle Permian is an important period of basin evolution.The former basins in the Middle Permian were marine sediments.By the end of the Middle Permian,the Jiamusi and the North China platform were closed to the continental sediments.The study is based on the measured profiles and drilling data,regional data,geological data and paleontological data.We complete lithofacies palaeogeography in strict accordance with the principles of isochronous comparison.Through field reconnaissance we found the Middle Permian strata are widely distributed.In Inner Mongolia,Heilongjiang,Jilin,the Middle East,these strata are distributed.The formation mainly contain shallow water carbonate platform facies(open platform facies),platform margin slope facies,braided delta facies(delta front underwater distributary channel),meandering river delta facies(delta distributary channel,mouth bar,front delta facies,shallow marine facies,semi deep)marine turbidite fan.The thickness of Middle Permian mudstone is between 130 m and 1470 m.The characteristics of mudstone thickness variation include that in western Arxan,Dongwuqi area eastward thickening,the northern basin handaqi area southward direction of mudstone mudstone thickening,Eastern Mishan and Shangzhi basin area to the southwest thickening.Mud ratio also contain the same relationship,reflecting the deepening of the central water in the basin.The sandstone thickness of the basin is 200 m to 1300 m.The characteristics of sandstone thickness variation include western Erenhot,Arxan area to the East,Dongwuqi thinning,reflecting a provenance system from west to east.In the north of the basin,from Baoshan to Nenjiang,the sandstone is thinned to the South,reflecting a provenance system from north to south.The characteristics of sandstone thickness variation include Hunchun to Shangzhi,reflecting a provenance system from southeast to northwest.We restore the lithofacies palaeogeography through the lithofacies classification scheme.The results show that the western part of the Middle Permian Basin is mainly in the delta,neritic environment,The littoral neritic environment including mudstone facies,sandstone and mudstone facies.The Qigihar area,in the northern part of the basin is mainly a shallow sea environment.The mudstone sandstone facies and shallow platform carbonate facies are developed in this neritic environment.The northern part of the basin is mainly in the delta,neritic environment.In the eastern part of the basin,Mishan,Shangzhi area is mainly shallow sea delta,shallow water environment.In this shallow water environment,mudstone sandstone,sandstone mudstone facies and carbonate facies were developed.