安徽沿长江地区下三叠统瘤状灰岩成因研究

在研究安徽沿长江地区中、下三叠统碳酸岩-蒸发岩时,发现早三叠世地层的中部,普遍不同程度地发育着结核灰岩(或称瘤状灰岩)。各地露头经风化后,常在灰岩层或泥灰岩层面呈现有疙瘩状凸起,作瘤状,在岩层的断面上可清晰地见到瘤体平行于层理断续排列,瘤体大小常为厘米级,并与泥质物交替成层。

PRELIMINARY STUDY ON ORIGIN OF THE LOWER TRIASSIC NODULAR LIMESTONE IN THE REGION ALONG THE YANGTSE RIVER

This article deals with the origin of the Lower Triassic nodular limestone in the region along the Yangtse River, Anhui Province, the regularity of its distribution and the division of the nodular limestone member. After study on the lithologic and lithofacies characteristics of nodular limestone, the article gives a discussion on the origin and the mechanism of formation of the nodular limestone.These rocks can be explained as the products of material redistributional process during early deagenetic stage under the compactional process. In other words, they have some connection with "resolution and reprecipitation" of the ions(Ca²⁺. HCO₃).On the basis of the lithologic, lithofacies and palaeontologic characters of nodular limestone, the author discusses the tectonic setting and palaeogeographic environment in the date to Middle period of the Late Triassic.The author proposes that these nodular limestones had occurred essentially in deep-water environments. The facies of the nodular limestone in the studied region must belong to basin facies and slope facies or margin facies.