| Thick medium-high quality oil shale and low-quality oil shale and shale layers were well developed in the Middle Permian Lucaogou Formation in the Northern Bogda Mountain,Xinjiang.The rich ancient environmental and lacustrine biological information were well saved in the oil shale bearing series because of the relatively low maturity,which may provide a good experimental site for the study and contract on the aggregation carbon process under the joint control factors of geology and biology between the medium-high quality oil shale and low-quality oil shale and shale.In this paper,a more comprehensive research on the establishment of organic matter aggregation models in the oil shale bearing series of the Lucaogou Formation would be well done based on the detailed sedimentary facies and sequenced stratigraphy division,a large number of mineralogy,element geochemistry,organic geochemistry and biogeochemistry test data.Accurate identification of sedimentary facies and sequence stratigraphy division is the geological basis for the study on the organic matter aggregation mechanism of the oil shale.The delta facies and lake facies were identified in the study sections based on the observation of outcrop,well drilling,well logging data and the test and analysis of organic geochemical parameters.Delta front subfacies were identified in delta facies,including underwater distributary channel microfacies,underwater interchannel microfacies,debouch bar microfacies and frontal sheet sand microfacies.Shallow lake subfacies were identified in lake facies,including sandy shallow lake microfacies and muddy shallow lake microfacies.Sequence stratigraphic framework features indicate that the Lcucaogou Formation is divided into two complete sequence,respectively for sequence I and sequence II.The lowstand systems tract,transgressive systems tract,highstrand systems tract and regressive systems tract were developed in each sequence from bottom to top in turn.And the sedimentary facies types and distribution characteristics of different systems tracts in different areas are different from each other.The spatial distribution of organic matter abundance and organic matter types and the correct discrimination of organic matter maturity is the necessary premise to carry out the study on the organic matter accumulation mechanism.Based on the analysis of a large number of organic geochemical parameters testing,it can be found that the organic matter abundance in the lowstand systems tract is medium and the organic matter type is mainly type ?1 and type ?2.The organic matter abundance in transgressive systems tract and regressive systems tract is relatively good.the organic matter type in transgressive systems tract is mainly type ?1,parts areas is for type I.While the organic matter type in regressive systems tract is for type ?1 and type ?2.The organic matter abundance in highstrand systems tract in the best and the organic matter type is mainly for type I,parts areas is for type ?1.The organic matter maturity of most samples is mainly at the low mature stage.The study on the characteristics of lake biological community structure is the important content of establishment of organic carbon aggregation models.In this paper,the characteristics of lake biological community structure can be semi-quantitatively identified based on biomarkers technology.The analytical results show that four obviously different lake biological communities were observed in the oil shale bearing serises of the Lucaogou Formation.The lake biological community in the stage A is mainly for more-bacteria,benthic macro algae and diatom community.The lake biological community in the stage B is mainly for more-bacteria,diatom and dinoflagellates community.The lake biological community in the stage C is mainly for less-bacteria and dinoflagellates community.The lake biological community in the stage D is mainly for less-bacteria,green algae and dinoflagellates community.The research on the evolution characteristics of various organic matter accumulation control factors is a key link in the inversion of organic matter accumulation process.Various kinds of element geochemistry and organic geochemistry parameters were used for the qualitative and quantitative inversion of the ancient climate,ancient water depth,reducing oxidation,paleosalinity,nutrient elements structure and the productivity.The analytical results show that the humid climate,deep water depth,high salinity and anoxic water environment is the typical sedimentary environments during sequence I sedimentary period(stage A and stage B).In addition,the productivity in this period is high.While the arid climate,shallow water depth,low salinity and oxic water environment is the typical sedimentary environments during sequence II sedimentary period(stage C and stage D),the productivity in this period is relatively lower.And the 12 nutrient elements indicative parameters such as elements P,Fe,Mn,Cr,Co,Ni,Cu,Zn,Cr,Ba,total abundance of major nutrient elements and total abundance of trace nutrient elements reveal that the nutrient elements structure is relatively complex and the total abundance of nutrient elements is relatively higher during the sequence I sedimentary period.Conversely,the nutrient elements structure is relatively simple and the total abundance of nutrient elements is relatively lower during the sequence II sedimentary period.Based on the detail study on the relevance of various controlling factors on the organic matter aggregation process,two organic matter aggregation models in the oil shale bearing series of Permian Lucaogou Formation in the Northern Bogda Mountain were established,respectively for the high organic matter abundance aggregation model and low organic matter abundance aggregation model.The high organic matter abundance aggregation model includes the more-bacteria,benthic macro algae and diatom type and more-bacteria,diatom and dinoflagellates type second aggregation models.The more-bacteria,benthic macro algae and diatom type second aggregation model is formed in the warm and humid climate.The high abundance of nutrient injection(elements P,Fe,Mn,Cu,Zn,Ni,Cr and Ba)promotes the flourishment of more-bacteria,benthic macro algae and diatom,then the high lake primary productivity was formed and saved in the deep water environment with the high salinity and anoxic.Thus the medium-high quality oil shale was formed.The more-bacteria,diatom and dinoflagellates type second aggregation model is also formed in the warm and humid climate.The high abundance of nutrient injection(elements P,Fe,Mn,Cu,Zn,Ni,Cr and Cd)promotes the flourishment of more-bacteria,diatom and dinoflagellates,then the high lake primary productivity was formed and saved in the deep water environment with the high salinity and anoxic.Thus the medium-high quality oil shale was also formed in this model.While the low organic matter abundance accumulation model also contains two second models,respectively for the less-bacteria and dinoflagellates type and less-bacteria,green algae and dinoflagellates type.The less-bacteria and dinoflagellates type second aggregation model is formed in the arid climate.The low abundance of nutrient injection(elements Mn,Ni,Cr and Cd)promotes the flourishment of less-bacteria and dinoflagellates,then the low lake primary productivity was originated from these lake microorganisms and saved in the shallow water environment with the low salinity and oxygen-enriched.Thus the low quality oil shale and shale was formed.In addition,the less-bacteria,green algae and dinoflagellates type second aggregation model is also formed in the arid climate.The low abundance of nutrient injection(elements Mn,Ni,Cr,Co and Cd)promotes the flourishment of less-bacteria,green algae and dinoflagellates,but the lake primary productivity originated from above lake microorganisms was still low and the sedimentary environment was also the shallow water environment with the low salinity and oxygen-enriched.Thus the low quality oil shale and shale was also formed in this aggregation model. |
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