No abstract

Lateral structural variability and partitioning of fold–thrust belts often reflects lateral variations in the stratigraphy of the deforming foreland and interaction with inherited structures. The Keping Shan Thrust Belt, NW China, was initiated during the late Cenozoic and is a spectacular example of contractional deformation in a foreland setting. The belt is characterized by a series of imbricate thrusts which form a broadly arcuate salient and deform the thick (3–6 km) Phanerozoic sedimentary succession of the NW Tarim Basin (SW Tien Shan foreland). Abrupt lateral changes in the thickness of the sedimentary succession are associated with a series of major pre-existing basement faults which cross-cut the belt and which were probably initiated during early Permian times. These lateral variations in the basin template have impacted strongly on the structural architecture of the superimposed thrust belt. Variations in the thickness of the sediment pile affect the spatial distribution of thrusts, which increase in abundance where the sediment is thinnest. The inherited cross-cutting basement faults and the associated abrupt changes in sediment thickness combine to generate partitioning of the thrust belt.

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Recent contraction in the NW Tarim Basin, China, has exhumed a thick (2-3 km) sequence of Upper Neoproterozoic to Lower Palaeozoic sediments that provide a unique insight into the early evolution of the basin. The sedimentary sequence was examined in outcrop and consists of a lower, 500-m-thick fluvial-lacustrine clastic and volcanic succession, conformably overlain by a 2000-m-thick shallow marine carbonate succession which records a major rifting event that initiated in the Late Neoproterozoic. This rifting event probably corresponds to the breakup of East Gondwana and the separation of the Tarim Block from a conjugate margin equivalent in NW Australia. The generation and infilling of rift basins creates a number of potential hydrocarbon plays, although analysis of individual play elements indicates a relatively high risk, despite the prevalence of hydrocarbons derived from the same rift sequence elsewhere in the basin.