Elemental Measurement With Quantitative Analysis And Paleoenvironment Analysis Of The Jurassic Of Yangye Formation At Washixia Sag In Southeast Depression Of The Tarim Basin

The research status of Southeast region of Tarim Basin was relatively insufficient due to complex the regional tectonic evolution.With only seven deployed exploration wells,the basic understanding of the depositional environment and source rock development condition during the Jurassic was limited.As the region's two biggest oil and gas exploration target zone as well as one of the great depression,Washixia sag deposited large sets of Jurassic Yangye Formation which mainly consisted of lacustrine mudstone with high proportion of organic matter.For the benefit of hydrocarbon exploration,this paper was focused on the study of sedimentary environment of source rocks of Yangye Formation from the perspective of paleo-environment analysis.Based on the geochemical data collected from the 5 cross-sections of Jurassic selected from field investigation,the study of the environment of Yangye Formation was carried out.The lithology of Yangye Formation was mainly black mudstone and argillaceous siltstone,the mudstone in the middle was thick.The grain-size presented the coarse-fine-coarse sequence from bottom to top.Through the data of drilling and logging,the Yangye Formation was mainly lacustrine deposit,and the sedimentary facies of the section from bottom to top were shallow lake-middle-deep lake-shallow lake.The XRF portable element gun was used for the determination of elements.The data of 53 element points in the Dinghushan cross-section were measured.By the multivariate statistical method of factor analysis,the salinity factors was in the predominant controlling position of the sedimentary environment as the second was the water depth factor.The feedback information of the elements of Sr,Fe,Mn and Ba to the paleo-environment was of the most importance.According to the display of the element in abundance and ratio change curve the.The Jurassic Yangye Formation was freshwater lacustrine sedimentary environment with stronger reducibility and deeper water body;The paleo-climate was warm and humid as a whole,which was provided an ideal environment for source rock development.There were two major fluctuations on the element curve in the middle part of the stratum,which was characterized by the change of water depth and corresponding to the change of sedimentary facies.The total organic carbon(TOC)and pyrolysis of the samples of the 18 pieces of the rock samples collected at Dinghushan cross-section had been tested.Most of the samples have high TOC content and medium hydrocarbon potential,which belongs to medium-good hydrocarbon source rocks.The relationship between the abundance of organic matter and the enrichment of elements is analyzed.The correlation of the Ni element was of the best correlation with hydrocarbon potential,followed by three elements of Ti,V and K,which indicates that these elements have certain directive significance to the organic matter abundance of the source rocks.