Abstract
How shallow-marine redox conditions responded to changes in water-column dynamics during the Neoproterozoic remains poorly constrained, limiting process-based understanding of regional marine environmental heterogeneity. Here, we investigate the Neoproterozoic Hejiazhai Formation in western Henan, southern North China, by integrating stratigraphic and sedimentological observations, petrographic analysis, and elemental geochemistry to reconstruct depositional evolution and redox variability and to test their stratigraphic coupling. The Hejiazhai Formation comprises predominantly argillaceous limestone, limestone, and quartz-bearing detrital limestone, recording a shallow-marine carbonate system variably influenced by terrigenous input. Integrated lithofacies and microfacies analysis identifies at least three recurring deepening–shallowing cycles, whereas V/Cr and Ni/Co display stratigraphically coherent fluctuations that broadly track these depositional cycles, with relative deepening generally associated with less oxic conditions and shallowing with more oxic conditions. Although the geochemical proxies remain sensitive to provenance, mineralogical composition, and diagenetic modification, their recurrent correspondence with independently constrained facies changes supports a systematic sedimentary–redox relationship rather than isolated geochemical anomalies. We propose a process-based framework in which relative water-column changes may modify water-column structure and exchange, alter oxygen supply, and consequently influence redox-sensitive elemental responses. This framework reframes Neoproterozoic shallow-marine redox reconstruction from static proxy-based state identification toward sedimentary–redox coupling, providing a testable mechanism for evaluating how depositional and water-column dynamics contributed to the spatial and temporal heterogeneity of marine oxygenation along the southern North China Craton.
