Geochemistry of the upper Permian sandstones in the Dalong Formation in the South Yellow Sea Basin, East China: implications to provenance, weathering, and tectonic setting

To reconstruct the paleoenvironment, the petrography and geochemical compositions of the upper Permian Dalong Formation (Fm) (P3d) sandstones in the Central Uplift, South Yellow Sea Basin, was investigated, after which the provenance, tectonic setting, weathering conditions, and diagenetic history were determined. The Dalong Fm is mainly composed of sandstones with a few mudstones and limestones. The petrographic analysis showed that the P3d sandstones are in low maturity and could be classified into feldspar sandstone and lithic sandstone on average framework composition of Q63F16L21. The major and trace element results show that Dalong Fm sandstones are enriched in Rb and depleted in Cr and Ni compared with the upper continental crust (UCC). The chemical weathering intensity is weak to low moderate in the source area as indicated by the chemical index of alteration (CIA) and other results from a variety of methods. The diagenetic process included three main stages: eodiagenesis, mesodiagenesis, and telodiagenesis. Tectonic discrimination plots show that the source areas were an active continental margin (ACM) and a passive continental margin (PCM), which may have been related to the northward movement of the Lower Yangtze Plate (LYP) and the collision between the LYP and the North China Plate (NCP).