Analysis of geochemical characteristics, provenance, and tectonic background of black shale in the Silurian Longmaxi Formation of the Mingsheng section in the Yanyuan area, Sichuan Province

The graptolitic shales of the Longmaxi Formation were widely deposited during the Silurian transition in the Yanyuan area. This study selected fresh outcrops of the Silurian Longmaxi Formation at the Mingsheng section in the Yanyuan area, systematically sampled them, and analyzed the vertical variation characteristics of major, trace, and rare earth elements in the section. Moreover, this study discussed the perspective of geochemical characteristics, provenance characteristics, and tectonic environment of that period. Research results show that the Longmaxi Formation at the Mingsheng section in the Yanyuan area is predominantly siliciclastic shale facies (sections L1, L3, and L4), with higher carbonate mineral content in sections L2 and L5, and brittle minerals such as quartz and feldspar are less abundant in sections L2 and L5, while clay minerals show a significant increasing trend from bottom to top. The sediments of the Longmaxi Formation at the Mingsheng section have a dual source of mafic and felsic materials: sections L3 and L4 are of mafic or ultramafic provenance, while sections L1, L2, and L5 are more felsic or a mixture of felsic and mafic sources. The tectonic background of the source rock formation is continental margin, and the sediments exhibit dual characteristics of both active and passive continental margins. The variation in provenance indicates that the composition of the Kangdian paleocontinent was complex in the Early Silurian.