广西百色盆地东部古近系那读组湖相灰岩

百色盆地东部田东坳陷那坤地区古近系那读组三段下部发育一套数米至数十米厚的湖相灰岩，岩石以浅灰色-灰色、含大量的螺蚌化石和具核形石结构为特征，间夹有薄层的泥岩、钙质泥质粉砂岩。本文在实测地表剖面和详细观察岩心的基础上，仔细研究了此套灰岩的岩石学特征。依据丰富的原生沉积构造、古生物化石标志以及沉积地球化学、测井相特征将湖相灰岩的沉积相划分为滨湖、颗粒滩、浅湖三个亚相以及灰泥坪、沼泽、颗粒坪、滩缘、滩核、滩间水道、灰泥浅湖、泥质浅湖等八个微相，并详细地研究了各微相的沉积特征。结合该灰岩的区域分布和沉积相的平面展布格局指出沉积相主体属于浅湖的颗粒滩，并提出了相应的沉积相模式。

Lacustrine limestone of the Nadu Formation of Paleogene in eastern Baise Basin, Guangxi

A set of lacustrine limestones,several to tens of meters thick,are the main deposits in the lower part of Member 3 of the Nadu Formation in the Tiandong Depression of the Baise Basin The rocks range from light grey to grey in color,with abundant gastropoda shell fossils and oncolites,and are interbedded with thin mudstones and calcareous argillaceous siltstones In this paper, the petrologic characteristics of the lacustrine limestones are studied in detail on the basis of core observation and outcrop According to a large number of features of the primary sedimentary structures,fossils,sedimentary geochemistry and well logging facies,the sedimentary facies of lacustrine limestones are divided into three subfacies,i e ,coastal lake,grain bank and shallow lake Then eight microfacies are recognized,including the calcareous mudstone tidal flat,swamp,grain flat,bank edge,bank ridge,interbank channel,limemud shallow lake and argillaceous shallow lake,and the sedimentary characteristics of each microfacies are also studied in detail It is concluded that the lacustrine limestone was mainly deposited in the grain bank located in the shallow lake and the sedimentary facies model is proposed through mapping the regional distribution of lacustrine limestone and the layout pattern of sedimentary facies