四川古蔺芭蕉村二叠系碳酸盐岩微相与沉积环境OA

The classification and combination of carbonate microfacies provide an important basis and means for identifying sedimentary environments.Combined with the paleogeographical background,the sedimentary models of carbonate rocks can be determined.Based on previous studies,field observations,and laboratory analyses,the carbonate microfacies of the Permian section in Bajiaocun,Gulin,Sichuan Province,were studied to further clarify and verify the sedimentary environments and their evolution.A total of 16 types of carbonate microfacies are identified:sparry granular limestone(MF1),sparry-micrite granular limestone(MF2),micrite bioclastic limestone rich in foraminifera and calcareous algae(MF3),micrite bioclastic limestone with multi-type biodetritus(MF4),micrite bioclastic limestone with calcareous algae(MF5),micrite bioclastic limestone with organic laminae(MF6),bioclast micrite limestone with multi-type biodetritus(MF7),bioclast micrite limestone with foraminifera(MF8),bioclast micrite limestone with calcareous algae(MF9),bioclast-bearing micrite limestone(MF10),bioclast-bearing micrite limestone with fenestral features(MF11),bioclast-bearing micrite limestone with organic laminae(MF12),micrite(MF13),stromatolite(MF14),calcite dolomite(MF15),and calcirudite(MF16).From bottom to top,these microfacies are divided into 10 assemblages,indicating distinct sedimentary environments.The Qixia Formation and the first member of the Maokou Formation represent an open shelf-lagoon setting;the second and third members of the Maokou Formation are typical tidal flat-lagoon,sandy beach,and interbeach sea deposits.The Changxing Formation is dominated by a restricted low-energy lagoon sedimentary environment,with a deep steep slope front and an open shelf environment in its upper part.The Qixia Formation and the first member of the Maokou Formation exhibit a gentle slope sedimentary model,which is characterized primarily by the development of an open sea environment with gentle slopes and a restricted sea environment with inner gentle slopes.The second and third members of the Maokou Formation correspond to a platform sedimentary model and are classified as an open inner ramp to a restricted inner ramp environment.High-energy shoals are present within or around the area,with local transitions to a mid-ramp setting.The sedimentary types of the Changxing Formation include inter-platform basins,steep slopes of inter-platform basin margins,open marine settings on the open platform,tidal flat-lagoon of restricted platforms,and open shelf environments.