Marine and Petroleum Geology ( IF 4.2 ) Pub Date : 2021-05-04 , DOI: 10.1016/j.marpetgeo.2021.105099 Wen Qi , Jia Wu , Yanqing Xia , Xilong Zhang , Zhiyong Li , Jiang Chang , Jie Bai
The geochemical characteristics and distribution of saline lacustrine source rocks are shaped up by the environment and conditions under which they develop. Such environments, in turn, are often heavily influenced by various salt minerals and clay minerals. Therefore, the current study aims to investigate the potential impact of common salt minerals and clays on the formation and chemical changes of source rocks in salt lakes. Instead of relying on conventional classification methods that emphasize salinity, this study divides common petroleum-bearing saline lacustrine sedimentary basins into two types, the carbonate-type and the sulfate-type, based on the hydrochemistry of salt lakes. Experimental comparison of inorganic geochemistry between samples from modern and ancient saline lacustrine sedimentary systems revealed key differences in ion composition, and resultantly in the sedimentary sequences of salt minerals, the transformation of clay minerals, and the evolution of source rocks. It is found that CaCO3-bearing minerals are the first to precipitate in both types of salt lakes. However, secondary mineral deposition in carbonate-type saline lacustrine systems features the precipitation of Na2CO3-bearing alkaline minerals due to the depletion of Ca2+. Meanwhile, the clay in carbonate-type salt lakes contains a relatively high level of smectite and mixed-layer illite/smectite, as well as low content of illite, implying an impediment in smectite illitization. In contrast, sulfate-type salt lakes are enriched in Ca2+ but depleted in CO32−, leading to the abundant development of Ca-bearing sulfate mineral deposits such as gypsum. These geochemical differences could be responsible for the propensity of carbonate-type salt lakes to harbor well-developed oil shale, and for the tendency of source rocks deposited in sulfate-type lacustrine systems to produce oils at the immature stage.
中文翻译:
离子组成对矿物和烃源岩的影响:基于水化学分类的碳酸盐型和硫酸盐型湖相沉积物调查
盐湖相烃源岩的地球化学特征和分布受它们发育的环境和条件的影响。反过来,这样的环境经常受到各种盐矿物和粘土矿物的严重影响。因此,当前的研究旨在调查普通盐矿物和粘土对盐湖中烃源岩的形成和化学变化的潜在影响。本研究没有依靠强调盐度的常规分类方法,而是根据盐湖的水化学将普通的含石油盐湖相沉积盆地分为碳酸盐型和硫酸盐型两种类型。对现代和古代盐水湖沉积系统样品之间的无机地球化学进行的实验比较表明,离子组成存在关键差异,因此在盐矿物的沉积序列,粘土矿物的转化以及烃源岩的演化方面也存在差异。发现碳酸钙含3种矿物质首先在两种类型的盐湖中沉淀。然而,由于Ca 2+的耗尽,碳酸盐型盐湖相系统中的二次矿物沉积具有含Na 2 CO 3的碱性矿物沉淀的特征。同时,碳酸盐型盐湖中的粘土含有较高含量的蒙脱石和混合层伊利石/蒙脱石,并且伊利石含量低,这意味着阻碍了蒙脱石的非法化。相反,硫酸盐型盐湖富含Ca 2+,但富含CO 3 2-导致石膏等含钙硫酸盐矿床的大量开发。这些地球化学差异可能是碳酸盐型盐湖藏有发达的油页岩的倾向,也可能是沉积在硫酸盐型湖相系统中的烃源岩在未成熟阶段产生油的趋势。