德阳—安岳裂陷槽寒武系筇竹寺组页岩有机质差异富集机制及控制因素定量评价OA

Based on microscopic observations,total organic carbon(TOC)content measurements,and major,trace,and rare earth element analyses of core samples from the Cambrian Qiongzhusi Formation shale at different structural positions within the Deyang-Anyue rift trough of Sichuan Basin,this study employs a combined geochemical and random forest algorithm to qualitatively and quantitatively identify the controlling factors of organic matter enrichment in black shales,and to elucidate the patterns of organic matter enrichment under the influence of tectono-sedimentary differentiation within the rift trough.The results are obtained in four aspects.First,the Qiongzhusi shales were deposited under a warm and humid climate with intense chemical weathering.From the extra-trough to the intra-trough settings,paleoproductivity and sedimentary environmental restriction gradually increased,whereas terrigenous detrital input and redox potential progressively decreased.Moreover,hydrothermal activity intensity diminished from the trough margin toward the extra-trough and intra-trough areas.Second,vertically,layers 1 and 3,which remained under persistently high productivity and reducing conditions,exhibit high organic matter enrichment;layer 5 shows relatively high enrichment due to the high level of organism abundance period;layer 7,characterized by limited marine transgression,exhibits the lowest enrichment,attributed to reduced productivity,weakened reducing conditions,and enhanced activities of terrigenous detritus and hydrothermal inputs.Third,the random forest model demonstrates a satisfactory performance in fitting the organic matter enrichment in black shales,revealing that it is primarily governed by paleoproductivity,secondarily by redox conditions,and to a lesser extent influenced by terrigenous detrital input and hydrothermal activity.Fourth,for organic-rich shale gas exploration,vertically,layers 1 and 3 hold greater exploration potential than layer 5;laterally,priority should be given to the central intra-trough area north of the central zone of the rift trough.These findings contribute to a better understanding of the organic matter enrichment mechanisms in the Qiongzhusi Formation shales of the Sichuan Basin,and provide a geological theoretical basis for shale gas exploration and source rock evaluation.