中—上扬子地区二叠系眼球状石灰岩特征及成因研究  

Origin and Characteristics of Permian Eyeball-shaped Limestones in Middle—Upper Yangtze Region

作　　者：罗进雄[1] 何幼斌[1] 

机构地区：[1]长江大学地球科学学院,湖北荆州434023

出　　处：《地质论评》2010年第5期629-637,共9页Geological Review

基　　金：中国石油化工股份有限公司海相油气勘探前瞻性项目"南方二叠系定量岩相古地理研究及油气预测"(YPH08019)资助

摘　　要：眼球状石灰岩是中—上扬子地区二叠系一种具特殊构造的碳酸盐岩,由"眼球"和"眼皮"组成,广泛分布于中二叠统栖霞组下部和茅口组中—下部。在野外工作的基础上,结合室内薄片鉴定分析,碳、氧同位素分析及微量元素分析,对眼球状石灰岩的野外宏观特征、镜下微观特征、地球化学特征及其形成机理进行了较为详细的研究。"眼球"与"眼皮"宏观及微观特征差异明显,"眼球"颜色较浅,为较纯净的石灰岩,不显层理,生屑以藻类、腕足类、有孔虫和■类等为主,"眼皮"的颜色较深,泥质较"眼球"高,多数为含泥石灰岩,略显波状,生屑以介壳类为主,缺乏藻类,定向排列,且成岩作用相对较强烈;碳、氧同位素研究表明"眼球"与"眼皮"为相似成岩环境的产物;微量元素分析表明"眼球"为富氧沉积,"眼皮"为缺氧沉积;遗迹化石也表明"眼皮"为缺氧沉积。综合分析,提出"眼皮"可能为上升流作用的产物,眼球状石灰岩是受上升流作用的影响,由沉积和差异压实共同作用形成的。Permian eyeball-shaped limestone in Middle—Upper Yangtze region is a kind of carbonate with special structure ,which is composed of ＂eyeball＂ and ＂eyelid＂ ,and develops widely in the lower part of the Middle Permian Qixia Formation and the middle and lower part of the Middle Maokou Formation. Based on field work,combined with thin section analysis,carbon and oxygen isotope data and trace element data,the field macro-characteristics,micro-characteristics,geochemical features and formation mechanism have been studied in detail. And differences of the macro-and micro-characteristics between ＂eyeball＂ and ＂eyelid＂ are obvious. The ＂eyeball＂ is purer limestone without bedding,whose color is relatively light,and the biograins in ＂eyeball＂ mainly are algae,brachiopoda,foraminifera and fusulinids; while the most of ＂eyelid＂ is mud-bearing limestones with slight wavy bedding,its color is darker,the muddy content is higher than ＂eyeball＂ ,the biograins in ＂eyelid＂ dominate by shell which align orientationally,and lack algae,moreover,the diagenesis of ＂eyelid＂ is relatively intensive. Carbon and oxygen isotope research shows that ＂eyeball＂ and ＂eyelid＂ are the products in similar diagenesis environment; the trace element analysis indicates that ＂eyeball＂ is oxygen enriched deposition and ＂eyelid＂ is anoxic deposition; and trace fossil also shows that ＂eyelid＂ is anoxic deposition. According to the comprehensive analysis,the results can be conducted that ＂eyelid＂ may be the product of upwelling,and eyeball-shaped limestones is formed combinatively by sedimentation and diagenesis under the influence of upwelling.

关 键 词：中—上扬子地区 二叠系 眼球状石灰岩 缺氧环境 上升流 

分 类 号：P588.245[天文地球—岩石学]