Diagenetic Evolution Of Siderite Bearing Strata In High Frequency Sequence Of Late Permian Coal Measures In Western Guizhou

This thesis applies theories and methods of mineralogy,sedimentology and petrographic paleogeography,sedimentary geochemistry,sequence stratigraphy,etc,based on comprehensive analysis results of more than 20 drilling geological data in Panxian area of western Guizhou,and various experimental test analysis results of samples sampled from wells with well-developed siderite bearing strata,carrying out research on high-frequency sequence division and sedimentary facies of the Late Permian coal measures in the western Guizhou area,explore the petrological and sedimentary characteristics of the siderite bearing strata developed within it and the development law in the high frequency sequence framework,study on the diagenetic characteristics of various siderite bearing strata,finnally,the diagenetic evolution model of siderite bearing strata controlled by sequence is obtained.Guided by the Milankovich cycle theory,the high frequency sequence division is carried out for the well-developed siderite bearing strata in western Guizhou,and the high frequency sequence stratigraphic framework of the Late Permian coal measures in the study area was established,the types and distribution characteristics of sedimentary facies in the sequence are analyzed.According to the microscopic characteristics of siderite in the siderite bearing strata and their distribution characteristics in the high frequency sequence framework,they are divided into three types,among them,the type?siderite bearing strata is developed near the largest ocean flooding surface in the sequence and contains gelatinous siderite;the type?siderite bearing strata contains micronized crystal siderite,and its distribution in the sequence is more complex,so it can be divided into three subtypes,the type?₁siderite bearing strata developed during the sea level rise period of the transgressive system,it is relatively close to the bottom tertiary sequence interface,the type?₂siderite bearing strata was developed during the sea level rise period of the transgressive system,but it was far away from the third-order sequence boundary below,the type?₃siderite bearing strata was developed in the highstand system tract;the type?siderite bearing strata contain pelletized siderite,which does not show obvious development law in the sequence.Based on the study of the sedimentary water medium properties and sedimentary environment of various kinds of siderite bearing strata,it is found that there are obvious differences in the degree of influence of sea water on the sedimentary period of various kinds of siderite bearing strata,among which the influence of sea water on the type?siderite bearing strata is strong,the type?₁siderite bearing strata is mainly affected by sea water,the type?₂siderite bearing strata is jointly affected by sea water and fresh water,and the type?₃siderite bearing strata are greatly affected by fresh water.Based on the petrological and geochemical characteristics of the siderite bearing strata,the diagenetic characteristics of the siderite bearing strata are studied.At present,all kinds of siderite bearing strata are in the middle diagenetic stage a,but the diagenetic combination types are different,and the diagenetic water medium properties are different.Among them,the diagenetic water medium of the type?siderite bearing strata is more likely to be seawater during the sedimentary period;and the diagenetic water medium of the type?₁siderite bearing strata is more active freshwater fluid,which may be due to compaction,the compacted or fractured water moving in the rock;the properties of the diagenetic water medium of the type?₂siderite bearing strata are similar to those of the type?₁siderite bearing strata;the diagenetic water medium of the type?₃siderite bearing strata is more likely to be dominated by primary pore water;the diagenetic water medium of the type?siderite bearing strata is a more active multi-phase fluid.The diagenetic evolution model of various types of siderite bearing strata under sequence control is summarized,and it is considered that from type?siderite bearing strata?type?₃siderite bearing strata?type?₂siderite bearing strata?type?₁siderite bearing strata?type?siderite bearing strata,the intensity of diagenetic fluid transformation gradually increases,the final formation period of the internal siderite gradually becomes late,and the siderite crystal morphology gradually improves.This paper has 54 pictures,36 tables and 129 references.