PRELIMINARY RECONSTRUCTION OF MID-TO-HIGH-LATITUDE CONTINENTAL CLIMATIC VARIABILITY RECORDED IN PERMO-TRIASSIC FLUVIAL-LACUSTRINE ROCKS, BOGDA MOUNTAINS, NORTHWESTERN CHINA

Mid-to-high-latitude continental climate variability is critical to understanding Pangean climate evolution. A 1178-m Lower Permian-Lower Triassic fluvial-lacustrine section in southern Bogda Mountains, NW China, deposited in a rift-drift setting on the Junggar microplate at 50^oN paleolatitude, was studied at a cm-dm scale. Lithofacies, paleosols, fauna and flora, cycle stacking patterns, total organic carbon, and type of organic matter were used in depositional environment reconstruction and preliminary climate interpretation. Lower-Permian Taoxigou Group (295 m) consists of orthoconglomerate, sandstone, and non-calcareous paleosols, interpreted as braided stream deposits in a tectonically-active, sub-humid environment. Minor lacustrine limestones suggest periods of semi-arid conditions. Middle-Permian Daheyan Fm. (104 m) contains similar facies but with upward-increasing Calcisols, suggesting a transition to a semi-arid strong-seasonality climate. This condition strengthened upward, as indicated by meter to sub-meter lacustrine cycles composed of littoral sandstone, profundal organic-rich shale, limestone, dolomitic and gypsum-bearing (?) shale of the Middle-Permian Luocaogou Fm. (159 m) and abundant palustrine limestones and Calcisols of the Hongyanchi Fm. (118 m). The condition culminated at base of Quanzhijie Fm. (75 m, end-Guadalupian). Interspersed lacustrine deltaic deposits suggest periods of subhumid conditions in the overall Middle-Permian semi-arid trend. Afterward, climate changed abruptly to subhumid to humid with weak seasonality in Upper-Permian Quanzhijie, Wutonggou, and Guodikeng Fms. (125 and 138 m, respectively), as indicated by abundant deltaic and meandering stream deposits containing highly-eluviated and oxidized Argillisols, hydromorphic paleosols, coals, and petrified wood. The sub-humid to humid conditions persisted into Lower-Triassic Jiuchaiyuan and Shaofanggou Fms. (116 and 46 m, respectively), without significant climatic changes across the Permo-Triassic boundary. The reconstructed record probably represents the evolution of east-coast climatic conditions in northern Pangea.