Characterization of gravity flow deposition of the Lower Triassic Liujiagou Formation in the southwestern Ordos Basin and analysis of its genesis
Through core observation,thin section identification,and X-ray diffraction mineral analysis,the rock types and characteristics,and the genesis were studied.The results show that the core section of Liujia-gou Formation develops grayish purple siltstone,rudaceous mixed rock and black mudstone.The siltstone was mainly composed of quartz,rock debris,feldspar,micrite calcite,and matrix,with a matrix-supported fabric,and developed turbidite sedimentary characteristics such as groove casts,graded bedding,flame structures,convolute bedding,and Bouma sequences,identifying it as turbidite.The mixed rock contained a large a-mount of gravel intraclast and interstitial material,with the latter composed of terrigenous clastic particles,in-traclasts,and matrix.It exhibited sedimentary characteristics such as muddy tear-shaped clasts,matrix-sup-ported structure,randomly oriented particles,and abrupt contact with the overlying and underlying mud-stones,suggesting it was debris flow deposition.The study suggests that the Mianlue Ocean during the Early Triassic was not completely closed and had a marine transgression impact on the southwestern margin of the Er-dos Basin,forming mixed rock strata.Lagoon sediments developed in the Zhengning area,with slopes pres-ent,and gravity flow sediments dominated by debris flow-turbidity current were developed at the place of Well C3.
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