Provenance analysis of Upper Permian-basal Triassic fluviallacustrine sedimentary rocks in the greater Turpan-Junggar Basin, southern Bogda Mountains, NW China
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The Tian Shan region was identified as the source of Permian fluvial-lacustrine fills in the greater Turpan-Junggar basin. Thin-section petrographic study of thirty-six fine to very coarse lithic arenites from Upper Permian-Basal Triassic Wutonggou low-order cycle suggests both distant Tian Shan and local intrabasinal rift shoulders were sources. Two petrofacies are identified on the basis of QFL composition. Petrofacies A (mean Q2F4L94, Qm2F4Lt94, Qm42P57K1, and Qp0Lv49Ls51) occurs in the lower Wutonggou low-order cycle, which is characterized by repetitive shifts between fluvial and deltaic depositional cycles. Petrofacies B (mean Q26F9L65, Qm17F9Lt74, Qm65P25K10, and Qp13Lv55Ls32) occurs in the upper Wutonggou low-order cycle, which is dominated by deltaic depositional cycles. Abundant mudrock and basaltic lithics in Petrofacies A suggest intrabasinal rift shoulders were the primary source for the lower Wutonggou low-order cycle. During the deposition of lower Wutonggou, the greater Turpan-Junggar Basin was probably composed of highly partitioned grabens and half-grabens, similar to the Quaternary Basin and Range Province of the western U.S. The abrupt increase in quartz and decrease in basaltic lithics, coupled with changes in paleocurrents and depositional style in the upper Wutonggou low-order cycle, suggest a different catchment with a larger drainage fed the Wutonggou lake. The grabens and half-grabens during the deposition of upper Wutonggou were more interconnected, receiving sediments derived from both distant Tian Shan and local rift shoulders. The documented data best support a rift model, but the underlying cause of rifting remains to be examined.
Thesis (M.S.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Geology.