2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 4
Presentation Time: 8:45 AM


FENG, Qiao1, LIU, Yiqun2, LIN, Jinyan2, YANG, Wan3 and ZHOU, Dingwu2, (1)College of Geoinformation Science and Engineering, Shangdong University of Science and Technology, 579 Qianwangang Street, Qingdao, 266510, China, (2)Department of Geology, Northwestern University, Xian, 710069, China, (3)Department of Geology, Wichita State Univ, 1845 Fairmount, Wichita, KS 67260, fengqiao@nwu.edu.cn

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 50oN 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.