Geochemistry of Cretaceous nonmarine mudrocks of the Gyeongsang Basin, SE Korea and its implications for provenance, landscape evolution, and paleoclimatic conditions

Fluvial systems that develop in active continental margin settings are characterized by relatively short lengths and high gradients, and the geochemical compositions of fine-grained sediments in these tectonic environments are expected to faithfully record the geochemical characteristics of the provenance and weathering conditions of the drainage basin. The Cretaceous Gyeongsang Basin, located in southeastern Korea, was formed as a forearc basin, and the basin fill was deposited in a fluvio-lacustrine environment. The mudrocks of the Gyeongsang Basin generally show similar geochemical compositions, reflecting relatively stable and similar sedimentary sources (mostly intermediate compositions). Most of the mudrocks in the Gyeongsang Basin originated from the Yeongnam Massif (formerly a volcanic arc) located to the northwest of the Gyeongsang Basin, where the non-steady state weathering regime was dominant due to active uplift, and the overall weathering conditions were influenced by orographic effects. The source terrain experienced more intense weathering in the early stages of basin filling, with mild to moderate weathering dominating in later stages. Estimates of paleotemperature and paleoprecipitation support the above time-dependent changes in weathering conditions.