--> --> Depositional Architecture of Inland Lacustrine Facies in Sanhu Area of Qaidam Basin, North of Qinghai-Tibet Plateau, Northwest China

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Depositional Architecture of Inland Lacustrine Facies in Sanhu Area of Qaidam Basin, North of Qinghai-Tibet Plateau, Northwest China

Abstract

The Sanhu depocentre of the SE Qaidam Basin, Northwest China preserves a well-exposed at most 3500 m thick succession of Quaternary strata that record the filling of a basin in a salt lake environment. The clastic deposits of Qigequan Formation, the main Quaternary formation, were derived from near-field granitic or metamorphic sources, mainly in Kunlun Mountain and Qilian Mountain. Five 3rd-order sequences, each hundreds of meters thick, formed during episodic progradation and retrogradation of deltaic shorelines, have been recognized through comprehensive analysis of cores, well logs and seismic volume in the instruction of classic sequence stratigraphy theory. The laterally uniform sequences are separated by regional unconformable stratigraphic interface. It means a relative steady Depositional environment. The distribution regularity of sedimentary systems is dominated by different tectonic zones. Extensive alluvial fan deposit is located on south slope, adjacent to Kunlun Mountain and Yaber tectonic zone, southeastern of study area. The beach and bar sedimental system lacking of terrigenous supply distributes in Sebei tectonic zone. Lacustrine sedimentation is the main succession during the period of development of Qigequan formaition. Shallow lacustrine facies widely distributes in a narrow belt. In contrast to relatively narrow distribution of shallow lacustrine, offshore lacustrine sedimentation is developed in regressive stacking pattern along tendency. Incised valley is obvious in front of Golmud basin-ward in Sanhu area, with a wide lateral extension and deep incision. Based on sedimentary facies, we established two deposition architecture models. River-dominated east model whose main facies are deltaic system and shallow lacustrine, and lake-dominated west model whose main facies is shallow lacustrine. The main control on stratigraphic development is interpreted as rising of the base level and the erosion.