Genesis and quantitative analysis of SiO2 in hydrocarbon source rocks at the Cambrian bottom in Majiang,southeastern Guizhou
Objectives:In the Early Cambrian,a set of gray—black good source rocks developed in the Yangqiao section of Majiang,Guizhou.At present,in view of the lack of systematic research on the genesis and quantitative analysis of source rocks in this stratum.Methods:This paper discusses the types of SiO2 genesis in this section based on the analysis and testing of organic petrology,SEM,major elements and rare earth elements,and establishes relevant models to quantitatively analyze and calculate the SiO2 content from different sources.Results:The results show that:① In the early Cambrian,petrological evidence of hydrothermal activity was found in the source rock samples at the bottom of the Niutitang Formation in the Yangtiao outcrop,indicating that the sedimentary process of the source rock at the bottom of the Niutitang Formation was influenced by hydrothermal activity,including chalcedony and hydrothermal organisms such as sponge spicules and Pogonophoran worms.②The average values of Fe/Ti in siliceous rock and siliceous shale were 51.04 and 17.24,respectively,and the average values of Al/(Al+Fe)were 0.41 and 0.65,respectively.At the same time,ΣLREE/ΣHREE overall greater than 1,and the rare earth element distribution pattern has the characteristics of Eu positive anomaly and Ce negative anomaly,which indicates that siliceous rocks are greatly affected by hydrothermal fluids,while siliceous shales are not affected by hydrothermal fluids or are less affected by hydrothermal fluids.③ The results of quantitative analysis showed that in source rocks;The average value of detrital silicon is 30.52％;The average value of hydrothermal silicon is 34.67％;The average value of biosilicon is 34.81％,which indicated that the source rocks at the bottom of the Niutitang Formation in the Yangqiao section were mainly of biogenetic and hydrothermal fluids origin.Conclusions:The results of the study will provide a reference for identifying favorable shale gas enrichment and production intervals in the area.
genesis of SiO2quantitative analysis of SiO2Cambrian bottomsedimentary environmentsource rocksorganic matter preservation
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