Origin and stratigraphic architecture of the Middle Permian lower and upper Quanzijie low-order cycles, Bogda Mountains, NW China
"This study is carried out in the Bogda Mountains, NW China, and aims to provide a detailed sedimentary, stratigraphic, environmental, and paleoclimatic reconstruction in the paleo-mid-latitude along the east coast of Pangea. The Middle Permian lower and upper Quanzijie low-order cycles (QZJ LCs) provide a nearly complete sedimentary record in an area were little is known. In the first part of this work, the previously-established QZJ LC is divided into two LCs on the basis of regional stratigraphic correlation and major changes in depositional environments and tectonic and climatic processes. The newly-established lower QZJ LC is mainly composed of meandering streams and associated overbank deposits that formed under a semiarid climate with strong precipitation seasonality and its delineation demonstrates that a process-response approach is effective in time-stratigraphic analysis of complex nonmarine fluvial-lacustrine strata. In the second part of this work, the depositional environments of the upper QZJ LC are interpreted as a mixture of meandering and ephemeral stream and loess deposits. Loess in the region is poorly-documented and its presence indicates persistent arid to semiarid conditions during upper QZJ LC. The uppermost part of the upper QZJ LC records a major climatic change to humid-subhumid as a result of the global icehouse to hothouse transition. Finally, the fluvial conglomerates and sandstones in the lower and upper QZJ LCs are interpreted as being derived from the northern Tian Shan volcanic arc to the south and from local rift shoulders. This study provides a detailed sedimentologic, stratigraphic, environmental, and paleoclimatic reconstruction in an area were little is known and aims to provide a record in an important time period in the Earth's history when major climatic and biotic changes occurred."--Abstract, page iv.
Missouri University of Science and Technology
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