四川盆地中二叠世栖霞期—茅口期岩相古地理特征及其地球动力学机制探讨

Lithofacies and paleogeographic characteristics of Middle Permian Qixia and Maokou Periods in Sichuan Basin and the geodynamic mecheanism

通过对野外露头剖面、岩心、钻测井资料与区域地震大剖面资料的综合分析,以岩石地层划分中的段为研究单元,编制了四川盆地栖霞期—茅口期6张岩相古地理图,详细剖析了岩相古地理特征及其时空演化,并系统讨论了其地球动力学机制.研究表明,四川盆地中二叠世栖霞期—茅口期总体为一套碳酸盐岩台地沉积,古地理格局总体上表现为西南高、北东低,由西南向北东依次发育局限台地相、开阔台地相、陆棚相.岩相古地理环境受峨眉地幔柱、海平面升降变化综合作用的影响,其演化具有明显的继承性和阶段性.栖霞期早期以开阔台地相为主,华蓥山—云阳、安边—宜宾—营昌一带发育深水陆棚;栖霞期晚期的海退作用造就了早期陆棚的萎缩和生屑滩的大面积发育.栖霞期,围绕深水陆棚的台地边缘高部位区域以及沿彭州—江油—广元地区是台缘滩大面积发育的区域.茅口期早期受峨眉地幔柱隆升而在外缘形成张性作用带和全球性海泛事件的双重影响,成为台棚分异的重要时期,发育多个深水陆棚;随后,因峨眉地幔柱持续、快速隆升及其诱发隐伏基底断裂的复活作用,海平面快速下降,早期陆棚持续萎缩,茅口期中-晚期成为了碳酸盐岩滩相储层发育的主要时期,围绕深水陆棚的台地边缘地形较高部位发育大量生屑滩,是四川盆地中二叠统天然气勘探的重要目标.

Based on the comprehensive research of field profiles, well cores, drilling logs and regional seismic sections, analyzed the features and evolution, deduced the geodynamical mode of Sichuan Basin, we compiled 6 lithofacies and paleogeography maps, from Qixia Period up to Maokou Period of Sichuan Basin, segment as a unit. According to the research, Sichuan Basin was a sedimentary platform of carbonatite, sloped from southwest to northeast, developed restricted platform facies, open platform facies and shelf facies, during the Middle Permian. Paleo-environment evolution has evidential succession and periodicity, due to the effects by the Emei mantle plume and sea level eustacy. Early Qixia Period was basically occupied by open platform, deep-water shelf developed along the Huaying Mountain-Yunyang and Anbian-Yibin-Yingchang ribbon, and bio-clastic shoal had fully developed due to the marine regression and shelf exposed during the Late Qixia Period. Platform-margin shoal had massively developed around the high ground of deep-water shelf and along the Pengzhou-Jiangyou-Guangyuan ribbon. The extension fracture zone forced by the Emei mantle plume uplifting, and the global marine transgression are the major events in the Early Maokou Period: the main period of platform-shelf fractionation, developed multiple deep-water shelfs. Then the mantle plume kept lifting fast, caused the sole fault, marine regression, and early shelf exposed. Middle-Late Maokou Period was the prime period of carbonate shoal facies reservoir development:the primary exploration target of Middle Permian of Sichuan Basin.