中文摘要：

大塘坡组是位于古城冰期和南沱冰期之间的闻冰期沉积，本文应用高精度的SIMS U—Pb锆石定年方法，从湖北长阳大塘坡组中部凝灰岩夹层中获得锆石U—Pb年龄为654．2±2．7Ma，该年龄与从湖南吉首毛坪洞剖面大塘坡组顶部凝灰岩中获得的锆石U—Pb年龄654．5±3．8Ma在误差范围内完全一致，表明该期火山活动可能在华南地区分布广泛．而相同的火山灰年龄，在湖南吉首从大塘坡组顶部获得，而湖北长阳是从大塘坡组中部获得，反映大塘坡组沉积之后所发生的侵蚀作用在台地的不同地区具有显著差异，反映了华南新元古代晚期的裂谷作用一直持续到南沱冰期．此外，当前在大塘坡组中部所获得的这一年龄值，也进一步肯定了南沱冰期的起始时间应远小于654Ma年龄．

英文摘要：

A new SIMS U-Pb zircon age of 654.2 ± 2.7 Ma was reported from the middle Datangpo Formation in Changyang County of Hubei Province, China. The age is identical with that of 654 ± 3.8 Ma from the top Datangpo Formation in western Hunan Province, revealing that the volcanic activities （- 654 Ma） may have occurred widely in South China. The occurrence of the tuff beds （-654 Ma） at different intervals of the Datangpo Formation indicates that the erosion process after the Datangpo deposition varied significantly in different areas. It is thus consequently suggested that the rift in South China was active until the Nantuo glaciation. In addition, the new age confirms that the Nantuo glaciation started much later than 654 Ma.