Geochemical Characterization and Paleoenvironmental Analysis of Black Shale of the Shuijingtuo Formation in Yichang Area, Yangtze Platform, Based on pXRF Core Scanning

This study focuses on fully cored drilling samples from the Yichang area of the Yangtze Platform, targeting the evolution of ecosystems during the Cambrian Explosion. High-resolution geochemical element analysis (sampling interval: 0.05 m) was performed on intact core samples of the Shuijingtuo Formation using a portable X-ray fluorescence spectrometer (pXRF). This allowed for the reconstruction of paleoenvironmental characteristics during the deposition of the Shuijingtuo Formation, including paleoclimate, paleosalinity, paleoredox conditions, paleowater depth, and paleoproductivity. The results demonstrate the following: Variations in the Rb/Sr ratio indicate an overall warm and humid climate during the depositional period, with a gradual transition to a hotter and more arid climate from the base to the top of the Shuijingtuo Formation. Th/U＜2 suggest a predominantly marine saline environment with fluctuating salinity, likely linked to local sea-level changes and the degree of environmental confinement. V/(V+Ni) ＞0.5 and V/Cr ＞2 reflect long-term suboxic to anoxic conditions in the depositional water column. Zr/Rb＜2 reveal a depositional setting at the margin of a shallow marine platform to the outer shelf, characterized by relatively deep water depths. Peaks in Ni/Al and Cu/Al correlate with polymetallic enrichment intervals. Integrated geochemical proxies indicate that the black shales of the Shuijingtuo Formation were deposited in a warm, humid, and reducing shallow marine environment. These conditions promoted the enrichment of organic matter and polymetallic elements, while also providing critical geological prerequisites for the formation and exceptional preservation of the Qingjiang biota, a Burgess Shale-type fossil Lagerstätte. This study establishes preliminary geochemical evidence for reconstructing early Cambrian paleoenvironments and ecosystems in the Yangtze Platform and proposes an efficient analytical approach for deciphering paleoenvironmental conditions in key stratigraphic intervals.