Development model of the Lower Cambrian source rocks in northeastern Tarim basin:A case study from Well Tadong1
The Lower Cambrian consists of organic-rich mudstone,which is one of the major source rocks in the Tarim basin.At present,the source rocks in northeastern Tarim basin are poorly studied compared with those in northwestern Tarim basin.Based on the experimental study of mineralogy and geochemical characteristics of Lower Cambrian mudstone in Well Tadong1,the main factors controlling the formation of Cambrian source rocks are analyzed based on the experimental results,the development model of the source rocks is established,and its differences with other source rocks in Tarim basin are compared.The results showed that,the Lower Cambrian in Well Tadong1 consists of siliceous and calcareous mudstone.The concentrations of Al2O3,TiO2,Zr and total rare earth element are low,and Lan/Ybn shows heavy rare earth elements enrichment,indicating that they are less affected by terrestrial debris.Crossplots of Cd/Mo-Co*Mn and TOC-geochemical diagram suggest that the northeastern Tarim basin is affected by widespread upwelling The high TOC content TOC,averaging at 3.52％,as well as the concentration of P2O5 and Sibio,indicating that the Lower Cambrian mudstone has high palaeoproductivity,with extremely high palaeoproductivity in the lower part.The trace mental enrichment of U,V,Mo are much higher than those in post Archean Australian shale(PAAS),and the average ratio of organic carbon to phosphorus(Corg:P)is 242,suggesting anoxic bottom water during the Early Cambrian.In combination with regional tectonic evolution,it is believed that the Lower Cambrian source rocks in the northeastern Tarim basin are influenced by various factors such as palaeotopography,eustacy,and upwelling.The Lower Cambrian source rocks in different areas of the Tarim basin are mainly different in sedimentary facies belt and hydrothermal influence.
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