Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Rift Basin-Fill Architecture of Fluvial-Lacustrine Lower Permian Lucaogou and Hongyanchi Low-Order Cycles, Southern Bogda Mountains, NW China
(1) Geology, Wichita State University, Wichita, KS.
(2) Department of Geological Sciences & Engineering, Missouri University of Science and Technology, Rolla, MO.
(3) College of Geoinformatics, Shangdong University of Science and Technology, Qingdao, China.
(4) Department of Geology, Northwestern University, Xi'an, China.
Rapid lateral facies change, autogenic processes, and irregular topography of nonmarine rift basins challenge the application of traditional marine sequence stratigraphic techniques. Stratigraphic architecture may be reconstructed with a process-based approach, that is, using interpreted climatic and tectonic controlling processes on sedimentation in addition to observable attributes to correlate sedimentary cycles. This hypothesis is tested for Lower Permian Lucaogou and Hongyanchi low-order cycles (LCs) in the Tarlong-Taodonggou half-graben, using outcrop and petrographic data. The graben fill covers 88 km2. Depositional environments and controlling sedimentary processes were interpreted on 5 measured sections, 0.2-5 km apart. Microscopic and XRD data on grain composition and texture substantiate field interpretations and minimize stratigraphic miscorrelation. Humid to arid climatic conditions are interpreted using climate-sensitive lithologies, such as paleosols; tectonic movement are interpreted in terms of source area uplift, basin subsidence, and spill-point movement.
The base of Lucaogou is transgressive over underlying alluvial-fan deposits of the upper Daheyan LC. The Lucaogou LC is composed of fluctuating profundal siliciclastic and carbonate deposits interspersed with deltaic deposits. The top of Lucaogou is a fluvial-deltaic erosional unconformity, across which the type and magnitude of facies shifts varies greatly across the half-graben. The overlying Hongyanchi LC is composed of fluvial deposits in the basal part and fluctuating profundal siliciclastic and carbonate deposits upward. It is capped by a graben-wide fluvial erosional unconformity overlain by mature Calcisols and fluvial deposits of the Quanzijie LC. The Daheyan-Lucaogou-Hongyanchi LCs constitute the early-rifting tripartite sequence in the half-graben fill. The process-based depositional model may be useful to study other nonmarine rift basin fills. Finally, the outcrop and petrographic results provide data and analogs on the quality and distribution of hydrocarbon source and reservoir rocks in the adjacent petroliferous Turpan and Junggar basins.