Promises and
Problems of Two-Dimensional Nonmarine Sequence Stratigraphic Analysis Using
Hierarchical Depositional Cycles – An Example from Outcrop Lower Permian to
Lower Triassic Fluvial-Lacustrine Deposits, Southern Bogda Mountains, Turpan
Intermontane Basin, NW China
Yang, Wan1, Qiao Feng2,
Yiqun Liu3, Neil Tabor4, Stephanie Thomas4, Yi
Yang3, Guozi Sun3, Bei Sun3 (1) Wichita State
University, Wichita, KS (2) Shandong University of Science and Technology,
Qingdao, China (3) Northwestern University, Xian, China (4) Southern Methodist
University, Dallas, TX
Correlation of hierarchical cycles among
individual sections may be effective in sequence stratigraphic analysis of
nonmarine deposits with rapid facies changes and common erosional surfaces. Two
long (1049 and 1616 m) and four short (~100-m each) Lower Permian-Lower
Triassic sections in Bogda Mountains, China, were measured at a
cm-dm scale. 823 high-order fluvial-lacustrine cycles (HCs) have five major
types, interpreted as basic time-stratigraphic units recording fluvial
erosion-deposition and lake expansion-contraction.
Facies and thickness stacking patterns of HCs define 137 intermediate-order and
17 low-order cycles (ICs and LCs). LCs and some ICs are correlative in 6 km;
ICs and many HCs in 1-2 km; HCs in ~100 m. Lithofacies and thickness of HCs
change over 10s-100s m. Three Kungurian Daheyan LCs of mainly braided-stream
HCs filled topographic lows. Fluctuating profundal siliciclastic-carbonate HCs
of Roadian Lucaogou LC thin westward into fluvial and littoral HCs. Fluvial and
littoral HCs of Wordian Hongyanchi LC thin westward into dominantly littoral
HCs. Eastward-thinning Capitanian Quanzijie LC of fluvial HCs overlies a major
Calcisol, indicating a semi-arid-to-humid climate shift. Eastward-thickening
Lopingian Wutonggou LC contains meandering-stream and deltaic HCs with
Spodosols and Histosols indicating humid climate. Fluvial HCs with Calcisols of
Induan Jiucaiyuan LC change eastward into littoral HCs, indicating a return to
semi-arid climate. Olenekian Shaofanggou LC contains littoral HCs with
Calcisols indicating stable tectonic and semi-arid conditions. Delineation and
correlation of LCs and ICs, aided by interpreted lake-type, tectonic, and
climatic trends, are critical to establishing a reliable sequence-stratigraphic
framework for improved correlation of meter-scale HCs.