Sedimentological and Tectonic Studies on the Nonmarine Sequences of the Tectonic-controlled Cretaceous Gyeongsang Basin, Korea

摘要

The forming and evolving tectonics of the Gyeongsang Basin has been elucidated through sedimentological and tectonic studies of the nonmarine Nakdong Formation of the Gyeongsang sequence in Hadong, Sacheon area of Gyeongsangnam-do, Korea. The twelve lithofacies are recognized - three conglomerate fades (Gel, Gn, Gic), five sandstone facies (Sh-n, Sh-i, Sp, Sr, Sm), four mudstone facies (Mf, Mfn, Me, Mv), and are roughly grouped into five associations. They are interpreted as cohesionless debris flow deposits, turbidity current deposits and sheetflood deposits, and upper or lower flow regime deposits, respectively. The depositional settings of the Nakdong Formation in Hadong, Sachon area are alluvial plains for the lower part of the formation, and low-sinuosity meandering and braided streams for- the middle and upper parts of the formation. Acidic dikes, tuff layers, and growth faults are syntectonically developed in the lowermost portion of the Nakdong Formation in Hadong, Sachon area. Transtensional tectonisrn which caused the formation and evolution of the Cretaceous Gyeongsang Basin was originated from an oblique convergence of the Kula plate. Magmatic intrusions and volcanisms are suggested to have been very active since the beginning stage of the Gyeongsang sequence.