Paleoenvironmental Factors Of Organic Matter Accumulation In The Lower Part Of Wufeng-Longmaxi Formation In Northern Yunnan And Guizhou

Through previous studies,it has been shown that the lower strata of the Wufeng-lower Longinaxi Formation group in the North of Yunnan Guizhou exploration area are of good resource potential,and the prospect has been universally recognized with the exploration of the research areas being deepened.This paper studies about the relationship between the enrichment rule of shale gas and its sedimentary environment in North of Yunnan Guizhou Research area through data collection,geological survey,experimental test and data analysis,and combined with previous research results,then obtains the following results:Based on the study of the Y1 in North of Yunnan Guizhou Exploration area,the paper establishes the biological strata(WF2-LM3)and considers that the strata of the Wufeng-lower Longmaxi Formation group in the North of Yunnan Guizhou region are two successive sedimentary strata.The vertical variation of litho-facies indicate that the organic matter content is reducing upwards,and there are many benthic fauna appear in the limestone facies interval of the upper member of the LM3,indicating that the sedimentary environment of WF2-LM3 generally varied from anoxic to oxic in the direction of bottom of the WF2-LM3.Geochemical parameters have recorded the sedimentary environment change during Wufeng-lower Longmaxi period.Meanwhile the organic carbon isotopes also keep a good record for the glacial events happened in Himantian and the sea level eustacy(deep-shallow-deep).In this thesis,we use both microelement and geochemical parameters to analyze and reveal the sedimentary environment of our research region.Results show that,during the WF2-WF3 and LM1-LM3,the sedimentary environment of those organic-rich stratum is in a relatively deep water,which is anoxic and highly productive deep water shelf facies,but during WF4,the sedimentary environment is in a oxic shallow shelf facies.Combined with the parameters of Lithofacies and geo-index,the sedimentary facies of the study area were divided as follow:? The lower segment of Wufeng Formation group was(WF2-WF3)the anoxic muddy deep water shelf facies ? The KwanYin Bridge layer in the Wufeng group(WF4)is considered to be the oxic lime-muddy shallow shelf facies ? The Longmaxi Formation group(LM1-LM3)was anoxic muddy deep water shelf facies.The redox conditions,productivity,deposition rate of sedimentary water,fluctuation of sea level,paleogeographic environment and sedimentary facies belt control the accumulation of organic matter in the study area.The enrichment mode of organic matter was established by combining the characteristics of these factors.The palaeoenvironment of the enrichment of organic matter should be the moderate deposition rate,relatively high sea level,and high productivity of the oxygen-deficient deep-sea continental shelf facies belt..In Wufeng-Longmaxi period,the enrichment of organic is mainly during WF2-MWF3 period and LM1-LM3 period.