Halverson Galen P, Porter Susannah M, Gibson Timothy M
Department of Earth and Planetary Sciences, McGill University, 3450 University St., Montréal, QC, Canada H3A 0E8.
Earth Dynamics Research Group, The Institute for Geoscience Research (TIGeR), School of Earth and Planetary Sciences, Curtin University, GPO Box U1987, WA 6845, Australia.
Emerg Top Life Sci. 2018 Sep 28;2(2):137-147. doi: 10.1042/ETLS20170167.
The Tonian and Cryogenian periods (ca. 1000-635.5 Ma) witnessed important biological and climatic events, including diversification of eukaryotes, the rise of algae as primary producers, the origin of Metazoa, and a pair of Snowball Earth glaciations. The Tonian and Cryogenian will also be the next periods in the geological time scale to be formally defined. Time-calibrating this interval is essential for properly ordering and interpreting these events and establishing and testing hypotheses for paleoenvironmental change. Here, we briefly review the methods by which the Proterozoic time scale is dated and provide an up-to-date compilation of age constraints on key fossil first and last appearances, geological events, and horizons during the Tonian and Cryogenian periods. We also develop a new age model for a ca. 819-740 Ma composite section in Svalbard, which is unusually complete and contains a rich Tonian fossil archive. This model provides useful preliminary age estimates for the Tonian succession in Svalbard and distinct carbon isotope anomalies that can be globally correlated and used as an indirect dating tool.
拉伸纪和成冰纪时期（约10亿至6.355亿年前）见证了重要的生物和气候事件，包括真核生物的多样化、藻类作为主要生产者的兴起、后生动物的起源以及两次雪球地球冰川作用。拉伸纪和成冰纪也将是地质年代表中下一个正式定义的时期。对这一时期进行时间校准对于正确排列和解释这些事件以及建立和检验古环境变化假说至关重要。在此，我们简要回顾了元古宙地质年代表的定年方法，并提供了有关拉伸纪和成冰纪时期关键化石首次和末次出现、地质事件及地层的年龄限制的最新汇编。我们还为斯瓦尔巴德群岛一个约8.19亿至7.4亿年的复合剖面建立了一个新的年龄模型，该剖面异常完整，包含丰富的拉伸纪化石档案。这个模型为斯瓦尔巴德群岛的拉伸纪层序提供了有用的初步年龄估计，以及可进行全球对比并用作间接定年工具的独特碳同位素异常。
