泥岩/页岩：中国元古代－古生代海相沉积盆地主要烃源岩

在中国元古宙—古生代海相沉积体系中,碳酸盐岩是最主要的沉积岩类型,长期以来研究的重点也一直是碳酸盐岩,对海相泥岩/页岩的关注比较少,并且认为碳酸盐岩是海相沉积盆地中主要的烃源岩。对中国南方上、中、下扬子地区、滇黔桂地区、塔里木盆地、鄂尔多斯盆地、华北地区等147条剖面、289口探井及浅井约11200余个样品有机碳含量的分析与统计表明,泥岩/页岩有机质丰度高,是中国元古宙—古生代海相沉积盆地中主要的烃源岩类型,而碳酸盐岩有机质丰度普遍较低,仅仅是次要的烃源岩类型。海相碳酸盐岩中有机质的含量与碳酸盐含量呈现弱的负相关性,泥质输入有利于形成高有机质丰度的碳酸盐岩烃源岩,但并不是高有机质丰度碳酸盐岩烃源岩发育的必要条件,决定碳酸盐岩烃源岩有机质丰度的主要因素是有机质的生产率、有机质的沉积与保存环境。中国元古宙—古生代海相沉积盆地中并不缺乏高有机质丰度泥岩/页岩类好烃源岩,上、中、下扬子地区主要发育于上震旦统陡山沱组、下寒武统、上奥陶统—下志留统、上二叠统;华南地区主要发育于中、下泥盆统;塔里木盆地主要发育于下寒武统、下奥陶统及中上奥陶统;华北地区为中新元古界洪水庄组、下马岭组。泥灰岩类碳酸盐岩烃源岩在塔里木盆地相对比较发育,在中国南方地区只有下二叠统相对发育。

Shale and mudstone: the essential source rocks in the Proterozoic to the Paleozoic marine basins in China

Carbonates are dominantly sedimentary rock in the Proterozoic to the Paleozoic marine basins of China, and were put more attentions for a long time and were thought to be primary source rock in many researches, but shales/mudstones were rarely studied. Based on the statistics of more than 11 thousands of samples, according to the geological age and lithological classification, from 147 outcrop sections and 289 wells in the Yangtze area, Yunnan, Guizhou and Guangxi Provinces of the Southern-Western China, Tarim and Ordos basins of the Northwestern-Northern China, it is very clear that shales/mudstones are rich in organic matter and are the essential source rock in the Proterozoic to the Paleozoic marine basins, while the carbonates are poor in organic matter and are secondary source rock. The relation between TOC and carbonate content is weak. It indicates that muddy input is favorable for the formation of organic-rich carbonate source rock, but is not an essential, while the productivity, sedimentary and preservation environments of organic matter are the essential factors to control the concentration of organic matter in the carbonate rocks. It is not lack of organic-rich shales or mudstones in the Proterozoic to the Paleozoic marine basins of China, they occur widely in the Doushantuo formation of the Neoproterozoic, the Lower Cambrian, the Upper Ordovician-Lower Silurian and the Upper Permian in the Yangtze area, the Lower-Middle Devonian in the Yunnan, Guangxi and southern Guizhou provinces, the Lower Cambrian, the Lower Ordovician and the Middle-Upper Ordovician in the Tarim basin; the Hongshuizhuang and Xiamaling formations of the Mesoproterozoic to the Neoproterozoic in the Northern China. Carbonate source rocks, such as lime mudstone, marl and argillaceous limestone, occur locally in the Cambrian and Ordovician, Tarim basin, and in the Lower Permian, Southern China.