湘中湘南地区奥陶纪达瑞威尔中晚期-凯迪早期岩相古地理及其油气地质意义

Sedimentary facies and palaeogeography during the middle and late Darriwilian to the early Katian(Ordovician) and hydrocarbon exploration in central and southern Hunan

湘中湘南地区在早古生代时期,由于受海平面变化以及全球古气候的影响,形成了有利于烃源岩形成的沉积环境。笔者通过对湘中湘南地区的奥陶纪达瑞威尔中晚期-凯迪早期开展沉积相、岩相古地理和油气地质等研究,结合前人所取得的相关研究成果,将该区划分为陆架相、盆地相和陆架边缘相。陆架相主要由砂质板岩、砂岩、黑色页岩和硅质岩组成;陆架边缘相为粉砂-细粒石英砂岩、长石石英砂岩夹条带状板岩、炭质板岩和硅质岩等组成;而盆地相为一套炭质页岩和硅质岩组成的黑色岩系,代表了一种平静还原的滞流缺氧环境。该套岩性有机质含量高,具较高的生烃潜力,且分布范围广,是湘中湘南地区达瑞威尔-凯迪阶的富烃沉积区,也是下一步油气地质调查和勘探的重要层位。

The areas of central and southern Hunan sandwiched between the Yangtze and Cathaysian landmasses are believed to be the favourable sedimentary environments for the formation of source rocks due to the sea-level changes and global palaeoclimatic changes during the Early Palaeozoic.The middle and late Darriwilian to the early Katian（Ordovician） sedimentary strata dominantly consist of the Yanxi and Modaoxi Formations in central Hunan,and Baimachong and Shuangjiakou Formations in southern Hunan,and may be divided,on the basis of sedimentary facies and palaeogeography and petroleum geology,into continental shelf facies,basin facies and continental shelf-margin facies.The continental shelf facies is made up of sandy slate,sandstone,black shale and siliceous rocks.The continental shelf-margin facies is built up of silty to fine-grained quartz sandstone and feldspathic quartz sandstone,intercalated with banded slate,carbonaceous slate and siliceous rocks.The basin facies is assembled by a succession of black rock series including carbonaceous shale and siliceous rocks,representing the stagnant and anoxic environment.The above-mentioned rocks have higher contents of organic matter,and greater hydrocarbon potential,and thus are believed to be the key horizons for further petroleum exploration.