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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 delta C-13(Tpm) values for the formation corrected to the modern atmospheric delta C-13 value correspond to that of water-stressed C-3 woody plants, which suggests they grew in conditions of limited moisture. The relationship between delta C-13 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 delta C-13(Tpm) 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. (C) 2011 Elsevier Ltd. All rights reserved.