中国东南部新元古代冰碛岩地层

THE NEOPROTEROZOIC TILLITE IN SOUTHEASTERN CHINA

中国东南部新元古代冰碛岩地层分布于扬子板块的皖南、浙北、浙西和赣东地区,其中皖南休宁、歙县、浙北富阳、浙西建德及开化等地保存有两套冰碛岩和含锰碳酸盐岩地层,自下而上四分,而非以往认为的三分,分别记录了冰期-解冻期-冰期-解冻期四个阶段的沉积,这两个冰期分别为古城冰期和南沱冰期,相当于国外的司图特冰期(Sturtian glaciation)和马林诺冰期(Marinoan glaciation)。浙西江山和赣东广丰等地则只保存了一套冰碛岩和含锰碳酸盐岩地层,记录了冰期-解冻期两个阶段的沉积,地质年代为南沱冰期。由上可见,南沱冰期比古城冰期规模更大,冰碛沉积的范围更广泛,对铁、锰、硅及磷的富集成矿有更加重要的意义。

The Neoproterozoic tillites outcrop on the Yangtze Platform in southeastern China from southern Anhui Province to northern Zhejiang, weatern Zhejiang and eastern Jiangxi provinces. The Neoproterozic sequences included two tillite intervals in Xiuning and Shexian of southern Anhui, Fuyang of northern Zhejiang, and Jiande and Kaihua of western of Zhejiang. These sequences record four paleoclimatic stages： glaciation-deglaciation-glaciation-deglaciation, rather than tree stages as previously believed. The two tillites may represent two glaciations corresponding to the Sturtian （710-730 Ma） and Marinoan （590- 600 Ma） ice ages, respectively. Where Neoproterozic sequences include only one tillite interval, for example in Jiangshan of western Zhejiang and Guangfeng of eastern Jiangxi, only one glaciation-deglaciation cy cle is recorded and this glaciation event is likely equivalent to the Marinoan ice age. The Marinoan glaciation was much greater in geographic extent than the Sturtian glaciation, and it played an important role in the accumulation and mineralization of iron, manganese, phosphate, and silicon.