皖南震旦系冰期地层的再认识

<正> 近年来我国关于震旦系冰期地层的研究,除已公认的峡东的南沱冰期地层外,在华南各地陆续在“南沱组”之下,发现了间冰期大塘坡组和下冰期长安组。这些新成果使扬子板块及其周边晚元古代冰期地层和国际上许多经典的层序具备了共同的三段式结构,即上、下两个冰期,中间夹一段间冰期。已知三段式结构广布于湖北、湖南、贵州、江西和浙江西部(陆松年等1985)。

New contribution to the knowledge of the Sinian strata of glacial age in southern Anhui

Southern Anhui is one of the important areas of Sinian stratigraphy in China. By now it was reported that there was only a single unit of glacial record, whereas three units have long been established around its neighbouring areas, representing the occurrence of three palaeoclimatological events, i. e, two glacial epochs with an interglacial epoch in between. Is it really that there is only one glacial unit? This problem has long puzzling geologists interested in the area. This paper shows that it is not the case. Southern Anhui actually is the same with the adjacent regions. Good records of the three palaeoclimatological events are found. Thickness of these units varies greatly. The thickest section, the Yanqian section of Taiping County is more than 700m, and the thinnest one, the Shiyu section of Yi County, is less than 30m. These units are named after the nomenclature erected in Western Zhejiang. They are, in ascending order, Xiayapu, Yangan, and Leigongwu Formations. Xiayapu and Leigongwu are the lower and upper glacial horizons, composed mainly of diamictites with thicknesses range in 3-300m and 9.7-401m, respectively. Yangan Formation, the interglacial horizon, however, only ranges from 10m to 35m. The most important evidence of the interglacial event is the stable fine-grained laminated sedimentary rocks occurred across the whole region and without clasts, and occasionally intercalated with a layer of carbonate rock, however, the typical black carbonaceous manganese shale popular in other areas is absent in this region.