摘要
四川盆地东部(以下简称川东)海相三叠系地层广泛分布,与其有关的油气、盐卤、天青石及硬石膏等矿产资源丰富,是一个具有重要经济价值的层位。笔者于1981—1985年间在20万km^2范围的盐类矿产普查工作中,采集了近150件零星样品进行碳、氧、硫稳定同位素分析(图1),积累的数据展示了在极其复杂的地史背景下各种地质-地球化学作用产生的物质交换效应及同位素分馏,形成不同元素在不同层位(地质体)的丰度特征。
The carbon isotope values (δ^(13)C) of Triassic marine carbonate rocks in the Sichuan Basin range from -8.5 to 5.92‰, generally from -2 to 2‰, in equilibrium with those of sea water. The organic-rich carbonate rocks exhibit lower δ^(13)C values, indicating a closed reducing environment. The δ^(13)C values tend to increase with shallowing of water body, salinization of sea water and oxidation of the environments. The δ^(18)O values vary between - 19.71 and 2.77‰, usually between -2 and -7‰. The higher δ^(18)O values may suggest a low-temperature, highly salinized and organic-rich environment. The above-mentioned carbon and oxygen isotope values of Triassic marine carbonate rocks may reflect the variations in sea water depth, temperature and salinity, and be employed as a tool to determine marinity of the sediments and lateral facies changes and to understand the evolution of the sedimentary basin. The δ^(34)S values of Triassic evaporites in the Sichuan Basin range between 14.5 to 34.9‰. The higher δ^(34)S values in this paper may contribute to the modification and refinement of the worldwide sulfur isotope curves for Triassic evaporites, and be used as the basis for the stratigraphic division and correlation. The δ^(34)S values of anhydrite developed in No. 4 Member of the Lower Triassic Jialingjiang Formation and in No. 1 Member of the Middle Triassic Badong Formation vary around 28‰, showing the steady supply of soluble sulphates into ancient saline lakes. This has been for geological interpretation of a shallow saline lake model. The decrease in δ^(34)S values from 34.9 to 14.5‰ is responsible for the sulfur isotopic depletion in the brines and sediments in the ancient saline lakes. It is inferred that the salt minerals formed during high salinization stage may occur in No.4 Member of the Leikoupo Formation.
出处
《沉积与特提斯地质》
CAS
CSCD
1990年第4期16-25,共10页
Sedimentary Geology and Tethyan Geology
