泌阳凹陷下第三系湖相白云岩形成条件

中国中、新生代大多数湖盆湖相碳酸盐岩以灰岩沉积为主,但部分湖盆像南-襄盆地泌阳凹陷则主要沉积白云岩,其累计厚度达 90 0余米,而白云岩层系的厚度 (包括白云质、灰质泥岩,白云质粉、细砂岩等夹层 )可达 2 2 0 0m,并成为良好的生油岩系,形成小而肥的南阳油田。本文着重探讨如此巨厚的白云岩形成的古气候、古水体的物理化学性质和古环境条件。在目前湖相碳酸盐岩研究仍处于湖泊沉积学研究的极薄弱领域,湖相白云岩形成条件更是涉及较少的情况下,愿本文的研究能起到抛砖引玉的作用.

Sedimentary Condition of Lacustrine Dolomite in the Lower Tertiary Biyang Depression

Most of lacustrine carbonate rocks of Mesozoic-Cenozoic era consist of limestone mainly. However, in some lake basins such as the Nan-Xiang basin, it mainly dep osited dolomite with a net accumulative thickness of 900 meters. While the entir e dolomite sedimentary, sequence can be more than 2100 meters, which formed a set of good oil-generation source rocks, and a small and rich Nan-Yang oil field iasbeen found there. This paper describes, taking the Biyang depression as an e xample, the genetic conditions of the thick lacustrine dolomite of stable sedim entary fac ies: 1. A hot paleoclimate which is semi-wet to wet ; 2. A water body of carbonate type which contains plenty of K+, Na+, HCO 3 and CO2 -3, but less Ca2+ and SO2-４ ions; 3. A medium of paleowater with a pH value of ≥9, and a low water salinity of generally 3‰～10‰, which b elongs to the range of slight salty <0.5‰～5‰>to semi-salty<5‰～30‰> , or ev en higher salinity, although the deposition of dolomite may not be so strict on the paleosalinity; 4. A stable shallow lake and deep lake condition of a broad l ake basin; 5. The biological and chemical effect may be strong so that the conte nts of CO2-３ and HCO-３, as well as the pH value will be increa sed while the content of SO2-４ decreased.