摘要:
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.
Abstract:
Most of lacustrinc carbonate rocks of Mesozoic-Cenozoic era consist of limestone mainly.However in some lake basins such as the Nan-Xiang hasi, it mainly deposited dolomite with a net accumulative thickness of 900 meters.Whilt the entire dolomite sedimentarv, sequence can he more than 2100 meters which formed a set of good oil-generation source rocks, and a small and rich Nan-Yang oil field iashccn found there.This paper descrihes, taking the Bivang depression as an example the genetic conditions of the thick lacustrinc dolomite of stable sedimentary fac ics: 1.A hot palcoclimatc which is semi-wet to wet;2.A water body of carbonate type which contains plenty of K+,Na+,HC03- and C03-but less. Ca2+ and S042- ions; 3.A medium of palcowatcr with a pH value of ≥ 9, and a low water salinity of generally 3‰-10‰, which belongs to the range of slight salty<0.5‰-5‰>to semi-salty<5‰-30‰>,or even higher salinity although the deposition of dolomite may not he so strict on the palcosalinitv: 4.A stable shallow lake and deep lake condition of a broad lake basin: 5.The biological and chemical effect may he strong so that the contents of C032-and HC03-,as well as the pH value will he increased while the content of 042- decreased.
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