Carbonate-associated sulfate (CAS)—trace SO 4 2- incorporated into carbonate mineral lattices by substituting for CO 3 2— serves as a valuable geochemical proxy for reconstructing seawater chemistry, redox conditions, microbial sulfate reduction activity, and diagenetic sequences in ancient marine environments, cold seeps, and gas hydrate reservoirs. However, conventional CAS extraction methods, which typically use HCl to dige...