SEDIMENTARY CHARACTERISTICS OF LOESSITE IN NE PANGEA AND ITS IMPLICATION ON PALEOCLIMATE AND PALEOGEOGRAPHY – CAPITANIAN UPPER QUANZIJIE LOW-ORDER CYCLE, BOGDA MOUNTAINS, NW CHINA

Permian sedimentary records provide clues about paleoclimatic conditions during an icehouse to hothouse transition. Seven stratigraphic sections of Middle Permian upper Quanzijie low-order cycle (QZJ LC) in Tarlong-Taodonggou in the south and Dalongkou 70 km to the north in Bogda Mountains, NW China, are used to highlight a major climatic transition from arid-semiarid to humid-subhumid that occurred in NE Pangea from Capitanian to Wuchiapingian. The upper QZJ LC is characterized by laterally persist, thick, and massive red mudrocks interbedded with laterally discontinuous conglomerates. The mudrocks are interpreted as loess deposits because of their massive structure, uniform multi-modal grain size distribution, lateral extent, mineral composition, and uniform detrital zircon ages. Thin conglomerates with a low-relief erosional base are interpreted as ephemeral braided stream deposits; thick conglomerates with a high-relief base as meandering stream deposits. In southern Bogda, Protosols in loess indicate rapid dust accumulation under persistent arid to semiarid conditions, whereas argillic Protosols and Protosols in northern Bogda indicate subhumid conditions alternating with arid-semiarid episodes. A change to Gleysols in the upper part of the LC and persistent Histosols in the overlying Wuchiapingian Wutonggou LC in both study areas indicate a change to subhumid-humid conditions at the Capitanian-Wuchiapingian boundary. The results indicate that loess in NE Pangea shares similar sedimentological characteristics as modern Permian loess in central Pangea. Arid conditions, eolian processes, and dust trapping mechanisms had existed and were persistent in NE Pangea during Capitanian time. The dramatic climatic change from arid-semiarid to humid-subhumid at the end of Capitanian correlates to and is the result of the global demise of the late Paleozoic Ice Age.