Carbon isotopic composition of terrestrial plant matter in the Upper Cretaceous Geoncheonri Formation, Gyeongsang Basin, Korea: Implications for Late Cretaceous palaeoclimate on the East Asian continental margin

The Upper Cretaceous Geoncheonri Formation in the Gyeongsang Basin, southeast Korea, was deposited in a lacustrine environment in a continental part of the East Asian continental margin and contains abundant terrestrial plant matter (TPM). Most of δ13CTPM values for the formation corrected to the modern atmospheric δ13C value correspond to that of water-stressed C3 woody plants, which suggests they grew in conditions of limited moisture. The relationship between δ13C value of leaf and mean annual rainfall (MAR) of Stewart et al. (1995) suggests that the climate of the Gyeongsang Basin ranged from semi-arid to sub-humid (MAR: ca. 400–700 mm) during the period of deposition represent by the Geoncheonri Formation. The average δ13CTPM value for the formation is higher than that of coeval strata in the forearc regions (Russian Far East and Hokkaido, Japan), indicating that conditions in the Gyeongsang Basin were more arid conditions than in the forearc regions. This aridity was probably because the basin was in a rain-shadow created by the topographic barrier of an uplifted accretionary complex and active arc volcanism.