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制约扬子地台早寒武世地层的精确锆石U-Pb年龄稀少,对最近于遵义松林地区下寒武统牛蹄塘组底部发现的凝灰岩中的锆石斑晶进行SHRIMP U-Pb测年,结果显示凝灰岩的就位年龄为(518±5)Ma(MSWD=0.37),从而提供了扬子地台下寒武统第二个精确锆石U-Pb年龄数据,构建了该区下寒武统以精确锆石U-Pb年龄为基础的时间框架雏形.结合区域地层对比,凝灰岩年龄数据显示澄江生物群及三叶虫首现(FAD)的绝对年龄应该晚于(518±5)Ma.该年龄数据同时表明,遵义松林地区牛蹄塘组底部Ni-Mo-PGE多金属富集层的Re-Os等时线年龄数据(537～542Ma)不代表地层的年龄.
The precise zircon U-Pb ages that restrict the Early Cambrian stratigraphy of the Yangtze platform are SHRIMP U-Pb dating of the zircon porphyrites in the tuffs recently found in the lower part of the Niutitang Formation in the Songlin area The results show that the tuff in situ age is (518 ± 5) Ma (MSWD = 0.37), which provides the second accurate zircon U-Pb age data of the Lower Cambrian in the Yangtze platform. The Lower Cambrian Based on the accurate U-Pb dating of zircons, the time frame of zircon U-Pb age was taken into account.Comparing with the regional stratigraphic data, the age data of tuff show that the absolute age of the FAD of the Chengjiang biota and Trilobite should be later than (518 ± 5) Ma. The age data also show that the Re-Os isochron age data (537-542 Ma) of Ni-Mo-PGE polymetallic enrichment layer at the bottom of Niutitang Formation in Songlin area do not represent the age of the strata.