Sedimentary Characteristics Of Late Paleozoic Coal-bearing Basins In Xinglong Area,Northern Hebei Province

The Late Palaeozoic coal-bearing basin in Xinglong area,Northern Heibei province,is Located in the Yanshan thrust fold belt of North China plate,which is between Miyun-Xifengkou-Qinglong fault zone and Shangyi-Chicheng-Gubeikou-Pingquan fault zone.The basin is influenced by the Mesozoic Yanshan movement,which is characterized by the development of large complex imbricate fan structure.The formation,evolution,sedimentation and tectonic activities of the basin have attracted the attention of scholars at home and abroad.This paper is based on the study of Carboniferous Permian coal-bearing strata in Xing Long area.With the research methods of particle analysis,geochemistry analysis and paleostreamflow analysis,the sedimentary characteristics,lithologic assemblage and paleosedimentary environment of the Late Palaeozoic coal-bearing basin in Xinglong area are discussed in this paper.And the writer discussed the geographical location,type and tectonic background of the source area of the basin in order to reveal the close relation between coal-bearing basin and source erosion area in the late Paleozoic.The main conclusion of this paper are as follows:(1)The lithology of Jidi section in Benxi formation and Beishan section of Taiyuan formation in the late Paleozoic coal bearing basin in Xinglong area is conglomerate,which is mainly composed of quartz sandstone,quartzite and chert,and a small amount of carbonaceous pebbles.The sandstone types in Benxi formation to the lower Shanxi formation are mainly lithic quartz sandstone and quartz sandstone.And the sandstone types in the upper Shanxi formation and Xiashihezi formation are mainly lithic sandstone and feldspar quartz sandstone.It is noteworthy that It is worth noting that a small amount of volcanic rocks appear in Beishan section of Taiyuan formation,and there are several layers of tuff interlayer in Zhangjiazhuang section of Taiyuan formation and Xiashihezi formation,indicating the existence of the volcanic activity in the source area at the same time.(2)The Carboniferous Permian coal-bearing strata in the Xinglong area are formed in warm and humid climate conditions,which were deposited in fresh water under the condition of weak oxidation.The Benxi formation to the Zhangjiazhuang section of Taiyuan formation is an alluvial fan sedimentary assemblage.The Lamagou section of Taiyuan formation is a barrier island delta plain sedimentary assemblage.And the Xiashihezi formation is a braided river delta plain sedimentary assemblage.This reflects the influence of the regional sea progressive-regression movement of the North China block in the late Paleozoic.The basin had developed a set of marine and terrestrial sedimentary deposits with marginal facies.(3)The result of the provenance analysis in the late Paleozoic coal-bearing basin in Xinglong area shows that the source area was the Inner Mongolia uplift located in the north of the basin,under the tectonic setting of the active continental margin.And its formation is related to the subduction process of Ancient Asian Ocean to the North China block in the late Paleozoic.The source area had been widely distributed in the Upper Proterozoic and Cambrian Ordovician sedimentary rocks composed of clastic rocks and carbonate rich chert rich carbonate rocks.(4)The late Paleozoic coal-bearing basin in Xinglong area belongs to the northern margin of the cratonic basin,which is located in North China plate.The sedimentary evolution of the basin is divided into three stages according to its sedimentary characteristics,sedimentary facies and its source changes.The stage of the alluvial fan in the early Late Carboniferous period recorded the beginning of the Inner Mongolia long period which had volcanic activity in this period.The stage of the barrier island delta plain in the early Late Carboniferous Early Permian recorded the slow uplift and erosion process of the Inner Mongolia uplift during this period.The stage of braided river delta plain in the late Early Permian recorded the strong tectonic uplift and volcano in the Inner Mongolia uplift.