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A rift basin commonly consists of many grabens and half-grabens. Stratigraphic architecture of sediment fill in individual grabens is a prerequisite to understand that of the entire rift basin and to avoid large-scale stratigraphic miscorrelation within the basin. During the 40-day fieldwork in the remote high-desert of NW China in the first grant year, two undergraduate students and I, along with two Chinese student assistants, have measured five stratigraphic sections, with a total of ~900 m of stratigraphic thickness, in the Tarlong-Taodonggou half-graben. Two intervals of the uppermost Carboniferous-Lower Triassic fluvial-lacustrine stratigraphy were investigated. The first part is the lower Upper Permian Quanzijie low-order cycle (QZJ LC), as a project for student Jonathan Obrist. It represents the transition between two tripartite sequences at the base and the transition within a tripartite sequence at the top, both of which may have a tectonic and/or climatic origin. A total of six sections, three of which were measured in the summer of 2010, illustrate the nature of the transitions, covering 88 km². The QZJ LC thickens from NE to SW Tarlong (68-140 m) and contains 20-42 fining-upward cycles of conglomerate, sandstone, and mudrock. Thin, gray, clast-support conglomerate and very coarse lithic wacke filling channel forms are interpreted as channel-lag deposits; the lack of accretionary point-bar deposits suggests episodic, high-energy, small ephemeral rivers. Monotonically brown-red mudrock includes thick massive mudstone and some thickly-laminated siltstone and silty shale, containing no plant remains and mature paleosols, and minimal clay fraction. It is interpreted as loess-like sediments mixed with overbank deposits in a semiarid-subhumid climate. A paleotopographic low in SW Tarlong is indicated by volcanics-damned lake deposits and the maximum QZJ thickness. The termination of underlying and initiation of overlying tripartite sequences are complex. The basal QZJ contains stacked channel-fill successions, 0-20 m thick, with an erosional base up to 30 m deep, representing lake withdrawal, erosion of lacustrine sediments, and onset of fluvial deposition. Mature Calcisols cap the fluvial deposits graben-wide, signifying a stabilized non-depositional landscape in an arid climate. The basal QZJ transition zone of lenticular fluvial deposits and Calcisols sandwiched by two unconformities represents a short but intense tectonic uplift followed by peneplanation and pedogenesis with a time span of 1-10 Ma. Overlying the Calcisols are thick QZJ fluvial-eolian sediments deposited in an enlarged and stable catchment basin during a long tectonic quiescence. The uppermost 1-2 cycles of QZJ LC contain mature Gleysols with abundant Fe-Mn pisoids, indicating a waterlogged environment and humid climate, which prevailed throughout Late Permian to earliest Triassic. The interfluve deposits of QZJ grade into overlying lake-margin and deltaic deposits. In summary, termination of a tripartite sequence is abrupt and forced by a major tectonic uplift, whereas partite transition within a sequence is gradational through gradual changes of sedimentary, tectonic, and climatic processes.

The second part of the field investigation focused on braided stream deposits of the alluvial-fan low-order cycles, the lower, middle, and upper Daheyan (DHY) low-order cycles, exposed in southern Tarlong, as a project for student Tyler Foster. Two sections were measured. These low-order cycles are the first sediment fill in the half-graben, overlying the pre-rift volcanic and volcaniclastic debris flow deposits. The thickness thins dramatically from east to west in northern Tarlong and northern Taodonggou; and the lower DHY LC was absent to the west, signifying a high-relief paleotopography in the initial half-graben. Preliminary interpretation and correlation indicate that the lower DHY and the majority of the middle DHY LCs are absent in southeastern Tarlong and are likely the case in southwestern Tarlong. The results, combing with those from previously-measured sections in northern Tarlong, suggest a paleovalley in the vicinity of northeastern Tarlong. This paleogeographic configuration changed dramatically in the overlying lacustrine low-order cycles, suggesting major reorganization with progressive rifting. Tyler Foster also investigated a Quaternary cliff face composed of alluvial-fan braided stream deposits through sketching, photographing, and measurement, applying the principle of “Present is the Key to the Past.”

Finally, a 2-day field reconnaissance in southeastern Tarlong found thick lava basalts, possible continental slope and shelf marine shale, chert, and sandstones, and shoreface-beach sandstone deposits, ~1000 m thick. The pre-rift succession is a rare exposure of basement rocks within the Junggar-Turpan microplate, whose basement structures and composition have been in debate.

Laboratory work includes drafting measured sections (completed) and sample preparation for thin-sectioning. An abstract on QZJ LC was submitted to 2011 AAPG Annual Meeting. The fund was used for IDTIMS zircon U-Pb dating of four bentonites and ashfall tuffs collected in previous seasons. Three samples generate very useful radiometric dates, which are critical to establishing a chronostratigraphy of nonmarine strata.

Both students learned much on procedure, methodology, and principles of scientific research, especially, field investigations. Jonathan Obrist enrolled in the MS program in Wichita State in fall of 2010, getting a head start on his thesis research. Tyler Foster has decided to apply for a MS program. The two students have also been exposed to a wide variety of Chinese modern and ancient culture and history, for example, through a 48-hour cross-country train ride. A Chinese student assistant plans to apply for admission into the MS program in Wichita State.

The results of field reconnaissance were used for a grant proposal to Missouri University of Science and Technology. The results of the study were also used in the revision of a NSF grant proposal with me as the lead PI with four co-PIs from four different US universities and five collaborators (3 from China, 2 from US). I was invited to present our research in NW China in Chinese Academy of Sciences, Beijing, which promoted the stature of Wichita State. In addition to the abstract, a paper is in press, where the support of ACS-PRF is acknowledged.

The undergraduate research experience, activities, and presentations associated with this research have “contaminated” many other undergraduate and graduate students in Wichita State University. The degree of positive impact remains to be seen.