Glauconite Deposition in the Cambrian Gushan Formation, North China: Insights into Paleoenvironments and Sedimentary Processes

This study investigates the glauconitic ooids of the Cambrian Gushan Formation at the Kelan section (Shanxi Province) through stratigraphic, microscopic, and geochemical analyses to unravel the paleoenvironmental conditions and sedimentary processes governing glauconite formation. The glauconite occurs within oolitic grainstone, which was deposited during the normal regression (highstand systems tract) of a third-order sequence, indicating a moderate to high sedimentation rate in a high-energy setting. Microscopic and geochemical data confirm the presence of glauconite in the form of pellets comparable in size to ooids and reveal their calcitic composition, suggesting simultaneous precipitation with calcite. A key finding of this study is the recognition of the Contrast Temperature Association (CTA), which highlights the coexistence of warm-water oolitic grainstone and traditionally cool-water glauconite, challenging the conventional paradigm of glauconite formation. The current sedimentological and geochemical investigations confirm that the glauconitic ooids of the Cambrian Gushan Formation (Miaolingian Series) at the Kelan section are autochthonous.