The Formation Mechanism Of Coal-bearing Cyclothems In Late Paleozoic In Western Shandong And Its Comparison With North America

In the late carboniferous to early Permian,the North of China plate was located in the low latitude of the earth,and a large number of Coal-bearing cyclothems did not appear until the Early Permian,while the Coal-bearing cyclothems developed in the Early Late Carboniferous in North America at the same latitude,and were greatly reduced until the early Permian.Aiming at this scientific problem,this paper studies the Late Carboniferous-early Permian coal measure deposits in the Western Shandong,and finally reveals the reasons for the different coal measure cycles of the two regions(north China and North America).Based on the study of lithofacies and lithofacie assemblages carried out by field outcrops and drilling cores,the Benxi-Shanxi formation in the Western Shandong is divided into six coal-bearing cyclothems,which are type A-F.Type D and F in the district development,Other types are sporadically distributed in individual mines.In the Middle Late Carboniferous,types A and B affected by gradual transgression,types C and D affected by sudden transgression developed;In the latest Carboniferous and Early Permian,types D and E affected by sudden transgression developed;In the Middle Early Permian,type F affected by small-scale transgression developed.Through Western Shandong coal-measure cycles contrast with North America,a large number of coal-bearing cyclothems developed in North America in the Early Late Carboniferous,while the coal-measure cycles developed in western China in the Middle Late Carboniferous.In terms of the formation time of coal-bearing cyclothems,the north American region is earlier than the Western Shandong,because the Western Shandong in Early Late Carboniferous is dominated by residual facies due to the slow uplift of the structure,and there is no palaeostructure and palaeogeographical conditions suitable for the development of coal seam.In terms of the type of coal-measure cycls,only type A in Linyi area of Western Shandong is similar to type Kansas in North America.The Coal-bearing cyclothems is mainly controlled by tectonic and sea-level changes,and also affected by paleogeography.When tectonic action is significant,Appalachian type cycle is formed;when tectonic action is not significant,Climate plays a dominant role,and the change of glacial sea level controls the coal-bearing cyclothems,Kansas type and type A-F cycles are formed,which are controlled by paleogeographic conditions.Only type A is similar to Kansas type cycle,and both are affected by marginal sea.The Illinois type cycle is formed when tectonic processes and sea level changes occur simultaneously.The results provide a basis for the study of global scale coal measure sedimentary characteristics and paleoclimate changes.