Sedimentary Characteristics, Evolution And The Studies Of Paleoclimate And Palaeoenvironment Of The Late Carboniferous Carbonate Platform In The Anhui Segment Of The Lower Yangtze Area

The Anhui segment of the Lower Yangtze Area is located in Lower Yangtzedivision. The strata of Late Carboniferous is well outcropped, complete andwidespread in the area, which includes Huanglong Group and lower ChuanshanGroup, carbonate rocks are the major component and clastic rocks distribute rarelyin the area.According to the research of field profiles and microscopical pictures, eightkinds of microfacies are identified: bioclasts grainstones/bioclastspackstones(MF1), oncolites grainstones/oncolites packstones(MF2), bioclasticwackestones(MF3), calcilutytes/calcilutytes with a few bioclasts(MF4), micriticbag shell packstones(MF5), crinoid wackstones(MF6), dolomites(MF7), rudstones(MF8).It was mainly open-sea platform carbonate rock facies of the LateCarboniferous in the Anhui segment of the Lower Yangtze Area. In the early stageof Huanglong period, some areas were littoral detrital facies and its sourceprovenance areas was Jiangnan ancient land. then it developed widely tidal-flatdolostone facies, which was composed of powder-fine dolomites, coarse crystallimestones and breccia dolomites, especially it developed obviously in thesouthwest. Later, it was covered by thick limestones of open-sea platform carbonaterock facies. According to the analysis of biological fossils characteristics andhydrodynamic conditions, it also could be divided into platform flat facies,platform basin facies and platform shoal facies. In the early stage of Chuanshanperiod, it developed widely tidal-flat breccia facies, which had thin thickness, thenit deposited thick platform facies limestone and contained platform flat facies andplatform shoal facies. in the late stage, it was mainly platform shoal facies.Through the analysis of Mg/Ca ratios, Fe/Mn ratios and the content of Mn andNa, in the early stage of Late Carboniferous, climates of the area was hot and dry,then it was warm and wet in late stage. The temperature and salinity of ancient seashowed that it was tropical-subtropical climate of the Late Carboniferous in theAnhui segment of the Lower Yangtze Area, which were calculated by carbon isotopes and oxygen isotopes.It was all exposed in the late Early Carboniferous in the Anhui segment of theLower Yangtze Area and the weathering and erosion was apparent. Affected by theextensional forces, the both sides of ancient land began to sink in the LateCarboniferous and the entire district began to accept deposits, there were twolarge-scale transgressions in the Late Carboniferous. In the early stage ofHuanglong period, tidal-flat dolostones was commonly developed in the area, withthe continuous expansion of transgressions, The thick carbonate rocks produced inthe middle-late stage of Huanglong period, carbonate platform developed rapidly.Affected by extrusions, the development of carbonate platform had a short break inthe late stage of Huanglong period. there was a small-scale transgression inChuanshan period, the thick oncolitic limestones produced in carbonate platform,with the quit of sea water, the development of carbonate platform of the latecarboniferous was over.