The Sedimentary Environment Evolution And Its Tectonic Significance Of Late Permian To Early Triassic In Yiyang County, Western Henan Province

It is a great time in the process of geologic history from late Paleozoic to early Mesozoic and one of a largest mass extinction events happened during the period.Not only the biosphere,but also other layers(lithosphere,hydrosphere,atmosphere)had happened great changes.Many envelops of geological events can reflect the coupling between layers and it is the most focus for the geologists.At present,due to the wide and continuous,Marine strata distribution in Permian-Triassic research also gradually mature.But the continental strata distribution is still relatively limited and it has no obvious characteristics of the biological indicator.Therefore,continental strata both breadth and depth of research still has a large development space.It is an important carrier in researching continental sedimentary environment in China that we have found the Permian-Triassic strata in Yiyang County,Western Henan Province.Some people had done a lot of works on the structure of MISS in the area.Sedimentology,geochemistry,analysis on the sedimentary basin and other methods were comprehensively used to study the characteristics of lithology,sedimentary structure,palaeosedimentary environment,provenance and we got some conclusions as bellow:The lithology from Sunjiagou Formation to Heshanggou Formation is formed with sandstone,mudstone and conglomeratic sandstone.It has braided delta facies,lacustrine facies,Lake Delta facies and lacustrine facies in turn from below.The depositional characteristics indicate the Formation had undergone progressive-regressive-progressive cycle and it developed continental sedimentary environment.The sedimentary environments shows fresh water by using geochemical approaches.From Sunjiagou Formation to Heshanggou Formation,the climate shows a change from warm-humid to hot-dry and it shows oxidizability.According to the analysis of provenance,the sediments may have come from passive continental margin,active continental margin and continental island arc which reflect the Qinling Mountains micro block to the North China craton basin stage of subduction,Shangdan tectonic evolution characteristics of closed.