Sedimentary Characteristics Of Shale Reservoir Of Lower Paleozoic In Fenggang Region Of Northern Guizhou Province

Fenggang region is located in northern Guizhou Province,belongs to the tectonic unit of Yangtze Block.Two sets of organic-rich black shales developed at the lower part of lower Cambrian niutitang Formation and lower Silurian longmaxi formation.Given the lack of the research in geological theory of shale gas in Fenggang Region of northern Guizhou Province,for instance,the shale depositional cause of formation,sedimentary and lithofacies characteristics,sequence stratigraphy.Guide by the theory of sedimentary,seque nce stratigraphy,combiend with regional geological data,through this methods for field outcrop geological survey,black shale profile measure,thin section identification,mineralogy,trace element geochemistry,organic geochemical testing,we carry out the studies of sequence stratigraphy and sedimentary characteristics and reservoir geological to the black shale of niutitang and longmaxi formation in Fenggang Region of northern Guizhou Province,and discussed he shale depositional cause of formation.The spatial distribution pattern of the black shales of niutitang formation and longmaxi formation are find out in in Fenggang Region of northern Guizhou Province,and its distribution and composition characteristics in the longitudinal profile is studied,and the mineral composition of shale is researched.The trace organic---inorganic geochemical study shows that the sedimentary environment of lower niutitang shale is deepwater,anaerobic,strong reducing and moist environment,upper niutitang shale is deposit in the e nvironment that is weak reduction-weak oxidation,shallow-water.The sedimentary environment of lower longmaxi shale is semi-deepwater,hypoxia,wet environment,and upper longmaxi shale is deposit in the environment that is shal ow-water,weak oxidation,dry.The paper has made the study of measured sections sequence stratigraphy,through the combination of biology,lithologic features and geochemical characteristics of samples.We divide the niutitang and longmaxi formation into two megasequence,and divide the niutitang sequences into transgressive system tract and high-stand system tract.The longmaxi contains a transgressive system tract longmaxi contains a transgressive system tract at the lower part and a high-stand system tract at the upper part.Through the microscope work of rock section,N iutitang and longmaxi petrological characteristics can be drawn.Then sedimentary facies signs have been studied through sedimentary structures flag,sample geochemical test and paleontology markers.Thus,the depositional environment of neritic shelf fades has been identified,which can be subdivided into deepwater shelf,semi-deepwater shelf,shallow water shelf phase and tidal flat facies.Landform characteristic combination pattern of the niutitang formation is identified,from northwest to southeast,which show deepwater shelf,semi-deep water shelf and shallow water shelf.Its deposition and subsidence center is located in the north-western region of the study area,and thesource is mainly from the southwest.Longmaxi formation shows tidal flat facies in local,and is identified,from south to north,which show shallow water shelf,semi-deep water shelf.Deposition and subsidence center is located in the north-western region of the study area,and thesource is mainly from the southwest.Deposition and subsidence center is located in the east-central region of the study area,and thesource is mainly from the northwest and south.Sedimentary origin of black shale in the niutitang formation involves paleotructural revolution,ascending current,paleoclimate,sea-level change,seafloor hydrothermalactivity.Through analysis of vertical evolution paleostructure,combined with the reflection of ascending current,sedimentary diagram of the longmaxi formation can be drawn,which can study origin of black shale of the longmaxi formation in study area.