豫西北焦作地区奥陶系马家沟组叠层石发育特征及其环境意义

Characteristics and its environment significance of Stromatolite from ordovician Majiagou formation of Jiaozuo area in the north-west Henan province

豫西北焦作地区中-下奥陶统马家沟组有叠层石发育,在实地观测野外露头剖面的基础上,通过薄片鉴定并结合岩性和生物特征分析对研究区奥陶系马家沟组叠层石的宏观与微观特征进行了研究.结果表明,研究区叠层石主要发育在马七段,形态多样,根据其几何形态可划分为层状、波状、丘状、柱状、指状等多种类型;研究区叠层石主要发育在潮下带上部到潮上带之间,其形态变化揭示叠层石发育段至少经历了3次明显的海平面升降,且当时竞争群落和后生动物较少.此外,在叠层石发育段有机质含量比较高,推测具有较好的生烃潜质.

Many stromatolites were found in the middle-lower ordovician Majiagou formation of Jiaozuo area in northwest Henan.Based on field profile measurement,the macroscopic and microscopic features of the stromatolites were discussed by means of lithologic and paleontologic microscopic analysis.The results show that the stromatolites with various forms in the research area are mainly developed in the seventh member of Majiagou formation.According to geometric shape,these stromatolites can be divided into several types as stratiform,corrugate,domal,columnar and branching.The stromatolites developed between the upper subtidal zone and the supralittoral zone in the research area.Their morphologic changes clearly show at least three times fluctuations of sea level and the competitive community and metazoan were rare at that age.The organic matter was found rich in limestone and dolomite strata with stromatolites developed,and these strata have good potential of hydrocarbon generation.