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华南扬子地台下寒武统(相当于寒武系新划分方案的纽芬兰统和第二统)对于揭示早期生命演化、全球生物地球化学循环以及古海洋环境变化等一系列全球性的重大科学问题具有重要研究价值.其中,对该区下寒武统进行精确的绝对年龄标定是多学科交叉研究中至关重要的一个方面.对最近于贵州江口平引剖面老堡组顶部发现的钾质斑脱岩中锆石进行SHRIMPU-Pb年代学研究,其年龄结果为(536±5)Ma(MSWD=0.75),初步认为该钾质斑脱岩可以与前人集中研究的云南梅树村剖面朱家菁组中谊村段中部(第5层)钾质斑脱岩进行区域对比,这一对比结果显示过去仅发现于内部台地浅水环境的第5层钾质斑脱岩在扬子地台较深水环境亦存在沉积记录.平引剖面老堡组顶部钾质斑脱岩的年龄结果直接约束了该剖面牛蹄塘组底部Ni-Mo多金属层的绝对年龄应年轻于(536±5)Ma,表明将Ni-Mo多金属层作为前寒武系-寒武系界线是不适宜的.结合区域对比及碳同位素化学地层学全球对比研究成果,认为朱家菁组中谊村段中部(第5层)及其相当层位的钾质斑脱岩、石岩头组底部及其可对比层位的钾质斑脱岩以及Ni-Mo多金属层可作为扬子地台区域地层对比的三个重要标志层,它们相互一致的绝对年龄初步构建了华南下寒武统的时间框架.
The Lower Cambrian of the Yangtze Platform in South China (Newfoundland and the Second System, equivalent to the new division of the Cambrian system) are a series of major global sciences that reveal the evolution of early life, the global biogeochemical cycle, and the change of paleoceanic environment The problem is of great research value.Among them, accurate absolute age calibration of the Lower Cambrian in this area is an important aspect in the interdisciplinary research.For the most recent discovery of potassium SHRIMPU-Pb geochronology of zircons from bentamorphic rocks shows an age of (536 ± 5) Ma (MSWD = 0.75), suggesting that the karat out of rock can be compared with the previously studied Meishu Cun section of Yunnan The regional comparison of the potassic plagioclase rocks in the middle part of the Zhongyicun section of the Zhujiajing Formation (the fifth layer) shows that the fifth-stage karstified plagioclase rock that was only found in shallow terraces in the past was found in the deeper water environment of the Yangtze platform The sedimentary records also show that the age of the top of karst rock in Pingpu section of Laobao Formation directly constrains the absolute age of Ni-Mo multimetal layer at the bottom of Niutitang Formation in this section to be younger than (536 ± 5) Ma, The Ni-Mo multimetal layer It is not suitable for the Precambrian-Cambrian boundary.Based on the regional contrast and the global comparative study of carbon isotope chemical stratigraphy, it is concluded that the central part of the middle part of the middle member of Zhuyijing Formation (layer 5) Gansu plagioclase and Ni-Mo multimetallic layers can be used as the three important markers of stratigraphic correlation in the Yangtze platform area, and their absolute absolute age is consistent with each other Constructed the time frame of the Lower Cambrian in South China.