塔里木盆地奥陶系岩相古地理演化及沉积模式

Lithofacies palaeogeographic evolution and sedimentary model of the Ordovician in the Tarim Basin

在前人研究基础上,通过对盆地周缘12条野外露头剖面的详细观测,对钻遇奥陶系31口典型井,特别是2016年以来新钻井岩心的详细观察,对盆地内钻遇奥陶系82口井的沉积相精细解释,以及对188条二维地震测线和5个工区三维地震资料的解释与地震相识别,按照从点—线—面的思路,在确定沉积相类型的基础上,开展沉积相对比,进而以组为编图单元,系统编绘塔里木盆地奥陶系各组沉积期岩相古地理图。结果表明:塔里木盆地奥陶系沉积演化过程中依次发育局限台地、开阔台地、淹没台地、台地边缘、台缘斜坡、陆棚和深水盆地等7种沉积相,进一步划分为16种亚相和若干微相。岩相古地理编图揭示了塔里木盆地早期蓬莱坝组—一间房组沉积期并非传统认识的“西台东盆”沉积格局,而是“单台双缘双盆”的沉积格局;塔里木盆地奥陶系碳酸盐台地经历了由统一的碳酸盐台地形成—台地分异形成多台地—台地最终消亡的演化过程。在上述基础上,建立了奥陶系3种沉积充填模式,分别是:单一台地—缓坡、陡坡边缘共存—盆地沉积模式,多台地—多台缘—多盆地沉积模式和陆源碎屑海洋环境沉积模式。

Upon previous researches,insights have been gained through detailed observation of 12 new outcrop sections and cores(mostly gathered after 2016)from 31 typical wells on the perihhery of Tarim Basin as well as fine interpretation of sedimentary facies in 82 wells together with the interpretation and seismic facies identification from 188 two-dimensional seismic lines and three-dimensional seismic data in five acreages focusing on the Ordovician in the Tarim Basin.Firstly,sedimentary facies types and features are determined by observing single outcrop sections and analyzing drilling data of single wells.Secondly,sedimentary facies changes are mapped through correlation between outcrop sections and well profiles.Thirdly,facies boundaries are delineated based on seismic facies types and their planar distribution determined through seismic interpretation and tracing.Finally,the lithofacies paleogeography during the deposition of each formation of the Ordovician are mapped to reveal their paleogeographic and sedimentary patterns.The results show that the sedimentary period of the Penglaiba-Yijianfang Formations in the early Ordovician is rather a pattern of"one platform with two edges and two basins"than a pattern of"a west platform coupled with an east basin"that as previously determined.The Ordovician carbonate platform is suggested to have evolved from a unified carbonate platform to multiple platforms after differentiation and to the final extinction.Based on these understandings,three sedimentary filling models are established for the evolution of the Ordovician,i.e.,the early single platform-coexisting gentle slope and steep slope edge-basin,the middle multiplatform-multiple edge-multiple basin and the late marine environment with terrigenous clastic input.