UNRAVELING THE EFFECTS OF POTASSIUM METASOMATISM IN SEDIMENTARY-ROCKSAND PALEOSOLS, WITH IMPLICATIONS FOR PALEOWEATHERING CONDITIONS AND PROVENANCE

Lutites are commonly metasomatized during diagenesis, but the analysis presented here accounts for most postdepositional change. Potassium m etasomatism is particularly common, and typically involves the convers ion of kaolin (residual weathering product) to illite by reaction with Kc-bearing pore waters. Sandstones also undergo K metasomatism, which involves the replacement of plagioclase by potassium feldspar. These changes can be identified petrographically and are quantitatively acco unted for by techniques discussed herein. Bulk chemical analyses and t ernary diagrams are used to determine the amount of K addition, premet asomatized sediment composition, and composition of provenance areas. The premetasomatized mineralogy of paleosols fan be compared with the mineralogy of recent soil profiles and thus, climate and topographic c onditions determined for past weathering events. Some weathering indic es lead to erroneous conclusions because, by excluding K2O from consid eration, correction cannot be made for metasomatic effects.