Abstract
Based on outcrop, drilling, seismic and a large number of experimental analysis data, from the aspects of current stratigraphic structure, subsidence rate, deposition rate, paleo salinity, rock assemblage and sedimentary facies distribution, organic matter types of source rocks, it is demonstrated that a large underwater paleouplift (central paleouplift) is developed between Chaixi Depression and Yiliping Depression in Qaidam Basin. The tectonic evolution of the central paleouplift is analyzed through structural analysis and paleogeomorphic restoration. Finally, the significance of hydrocarbon accumulation in the paleouplift for the next oil and gas exploration is expounded. The results show that: (1) In the early Paleocene, influenced by the early Himalayan compression orogeny, the prototype of paleouplift was formed, which is distributed in a NW-SE direction on the plane, separating the Chaixi Depression on the west side and the Yiliping Depression on the east side. The paleouplift has good inheritance from Eocene to Oligocene, and the maximum area of the uplift area in Lower Ganchaigou period is about 3 500 km2. In the late Miocene, the paleouplift evolved into a wide and gentle slope due to the eastward migration of Chaixi sedimentary center and the north-south provenance supply. (2) The central paleouplift controls the formation of oil and gas reservoirs, hydrocarbons and reservoirs. Large-scale delta sand bodies are developed in the near provenance areas at the north and south ends of the central paleouplift, while the central main area far away from the provenance is in an undercompensated salinized water environment, and large-scale lacustrine carbonate reservoirs are developed there. Influenced by the separation of paleouplift, it has been confirmed that high-quality salinized lacustrine source rocks are developed in Chaixi Depression in the west during Lower Ganchaigou to Upper Ganchaigou period, and effective source rocks may be developed in Yiliping Depression in the east. As a directional area for oil and gas migration, the paleouplift is conducive to hydrocarbon accumulation and can serve as the next favorable exploration zone.
Key words
paleouplift, Chaixi Depression, Yiliping Depression, tectonic evolution, oil-gas exploration, Qaidam Basin
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Formation and evolution of the central paleouplift and its significance for oil-gas exploration in Qaidam Basin[J]. Marine Origin Petroleum Geology. 2023, 28(3): 269-279
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