山东平邑盆地古近系湖相微生物碳酸盐岩形成机理

摘要

微生物碳酸盐岩是当前沉积学的研究热点之一,但关于古近系湖相微生物碳酸盐岩的报道还非常少.为探讨山东平邑盆地古近系官庄组中段湖相微生物碳酸盐岩的形成机理,笔者进行了野外实测以及室内偏光显微镜和扫描电镜观察.研究结果认为:(1)研究区微生物碳酸盐岩主要有核形石、叠层石和凝块石；(2)在核形石、叠层石和凝块石内部均发现了球状微生物化石、席状体和凝块状泥晶等微生物成因的显微组构,表明了它们形成过程中共同的生长、粘结和钙化等微生物作用；(3)微生物作用对环境变化比较敏感,水体较小、变化频繁的湖泊环境,对微生物碳酸盐岩结构和形态的发育有很大影响；核形石、叠层石和凝块石的形成环境大致呈现出水动力依次减弱、陆源碎屑物质依次减少、水深依次加大的规律；(4)提出了研究区微生物碳酸盐岩的成因模式,认为这3种微生物碳酸盐岩正是以微生物活动为共同基础,在不同的环境条件下形成的.%The origin of microbial carbonate rocks has become a hot issue of sedimentology, the Pa-leogene lacustrine carbonate rocks, however, are still rarely noticed and studied. In order to study the origin of the Paleogene lacustrine microbial carbonate rocks in the Pingyi Basin, field inspection as well as observations of plain microscope and scanning electron microscope, were carried out. The following re- suits were obtained; (1) Microbial carbonate rocks in the studied section mainly consist of oncolites, thrombolites and stromatolites. (2) In each of these carbonate rocks, coccoid cells, sheet structures and clotted fabric were found, which illuminate the common microbial actions during their formation, including secretion, agglutination and calcification. (3) These 3 microbial carbonate rocks were formed in different environments, which play a great role in the development of textures and shapes of microbial carbonates , because microbial fabrics and microbial actions are sensitive to the instable lacustrine environment. (4) Based on the analyses of the common microbial actions and different forming environments, the genetic model of lacustrine microbial carbonate rocks was presented.