山东平邑盆地古近系湖相核形石的沉积环境分析

摘要

There are a great many oncoids in the limestone of Pingyi basin. By means of field inspection and microscope observations, the host rocks as well as associated fossils and sedimentary structures were investigated. Some of the chemical compositions were also measured to discuss the environmental features. Oncoids were found intensively distributed in the environment which was characterized by shallow water, medium or mediumlow energy. Slight amount terrigenous influx was discovered to contribute to the growth of oncoids, while superfluous influx was found adverse. Oncoids were divided into 3 types: regular micrite laminaes oncoids (type A), regular microspar laminaes oncoids ( type B), irregular micrite laminaes oncoids ( type C). Type A, which was mainly represented by macro-size, multi-nucleus, regular multi-laminaes, could be considered as the mark of shallow water, medium-energy, slight amount influx. Type B, which was characterized by light color, well-sorted micro-size, microspar laminaes, could represent shallow water, relatively high-energy environment. Type C was identified by irregular laminaes, and could represent the low energy condition. Type A and B indicated lowporosity rocks, while type C indicated comparatively favorable pore space.%山东省平邑盆地古近系官庄组湖相碳酸盐岩露头发育有大量的核形石.为分析其沉积环境,采用野外观测、地球化学测试、偏光显微镜和扫描电镜观察等方法,研究其岩性背景、伴生的生物、沉积构造以及元素地球化学特征.研究表明,核形石主要发育于浅水、中等偏低能量的环境.有少量陆源碎屑物的环境有利于核形石生长;但较多的陆源碎屑物则对其不利.将核形石分为3类:规则泥晶纹层核形石(简称A类核形石),具有大颗粒、多层的规则纹层、复合核心等特点,可以指示浅水、中能、低陆源环境;规则微亮晶纹层核形石(B类),以色浅、粒径小、分选好、微亮晶纹层为特点,可指示浅水、较高能环境;不规则泥晶纹层核形石(C类),以色深、外形不规整、凝块状不规则纹层为特征,指示较深水、低能环境.发育A类和C类核形石的岩石,孔隙发育较差;发育B类核形石的岩石,孔隙发育较好,表现出相对较好的储层潜力.