利用露头、钻井、地震及大量实验分析资料,从现今地层结构、沉降-沉积速率、古水体盐度、岩石组合及沉积相展布、烃源岩有机质类型等方面,论证了柴达木盆地腹部一里坪坳陷与柴西坳陷之间发育大型水下古隆起,并通过构造解析和古地貌恢复,分析其演化过程,最后从油气成藏角度阐述了古隆起对下一步油气勘探的意义.研究表明:①古新世早期,受早喜马拉雅挤压造山运动影响,形成了古隆起雏形,平面上呈北西—南东向展布,分隔了其东、西两侧的一里坪坳陷与柴西坳陷,始新世至渐新世,古隆起具有很好的继承性,下干柴沟组沉积时期隆起区最大面积约为3 500 km2,至中新世晚期,受柴西沉积中心向东迁移及南北向物源补给的影响,古隆起演变为宽缓斜坡.②古隆起对油气成储、成烃、成藏具有控制作用:古隆起南北两端近物源区发育规模三角洲砂体,而中心主体区远离物源,处于欠补偿咸化水体环境,发育规模湖相碳酸盐岩储层,受古隆起的分隔影响,西侧柴西坳陷下干柴沟组上段—上干柴沟组已证实发育优质咸化湖相烃源岩,东侧一里坪坳陷可能发育有效烃源岩,古隆起是油气运移有利指向区,有利于油气聚集成藏,可作为下一步有利勘探区带.

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.