Based on data from core observations, thin-section petrography, scanning electron microscopy, whole-rock X-ray diffraction, organic geochemical analysis, and element analysis, in this study, we characterized the mineralogical–petrological features and sedimentary environment of the Lower Cambrian Qiongzhusi Formation shale in Western Hubei Province, and we clarified their relationships with organic matter enrichment. The results are as follows: (1) Five dominant rock types were identified in the Qiongzhusi Formation, namely, siliceous shale, argillaceous–siliceous mixed shale, argillaceous–calcareous shale, calcareous–siliceous shale, and calcareous shale. Vertically, the lithofacies transition follows the sequence of siliceous shale facies → mixed shale facies → calcareous shale facies. Laterally, from the marine trough to the trough margin, the thicknesses of the siliceous shale, argillaceous–siliceous mixed shale, and calcareous–siliceous mixed shale gradually decrease, whereas the thickness of the argillaceous–calcareous mixed shale increases progressively. (2) From the early to late sedimentary periods of the Qiongzhusi Formation and from the marine trough to the trough margin, a consistent evolutionary trend can be observed: gradual shallowing of the water depth, intensified hydrodynamic conditions, increased dissolved oxygen content of the bottom water, weakened upwelling currents, reduced paleoproductivity in the surface water, enhanced water mass stagnation, increased terrigenous input, and a corresponding gradual decrease in the total organic carbon (TOC) content. (3) The formation of the late-stage organic-rich shale was comprehensively controlled by the terrigenous input, redox conditions, paleoproductivity, water mass stagnation, and upwelling activity. Among these factors, the redox conditions, water mass stagnation, and paleoproductivity were the primary drivers responsible for the difference in the TOC contents in the Western Hubei marine trough and its margin, while the terrigenous input played a secondary role.
Lan et al. (Tue,) studied this question.