近日，加拿大卡尔顿大学Peter W. Crockford团队研究了阿曼斯图特盖碳酸盐岩中地幔样Sr同位素。这一研究成果发表在2025年6月24日出版的《地质学》杂志上。

在成冰纪（720-635 Ma）的斯图田冰川期和马里诺安冰川期，冰盖两次向赤道纬度延伸了数百万年。这些极端气候被解释为记录了雪球气候状态，在这种状态下，地球上的所有海洋都被冰覆盖。在雪球地球期间，水文循环会被缩短，硅酸盐风化会大大减少。在这种情况下，深海化学应该通过大洋中脊的热液交换向地幔值进化。具体而言，海水锶同位素（⁸⁷Sr/⁸⁶Sr）预计将表现出非放射性地幔样值。然而，覆盖在成冰纪冰川沉积物上的盖层碳酸盐产生了与冰川作用前海水相似的放射性⁸⁷Sr/⁸⁶Sr值，这与雪球地球假说的中心地球化学预测不一致。 

研究组报告了在阿曼佐法尔Sturtian冰川沉积物正上方的海洋碳酸盐和自生重晶石中发现的⁸⁷Sr/⁸⁶Sr值为0.7034。这些值记录了以前未发现的当地非放射性源或雪球地球深水值。如果这是一个全球信号，这些新的数据和地球化学建模支持了一种极端的雪球地球情景，即接近完全的冰盖，并定义了地球历史上对海水最大的地球化学扰动之一。

附：英文原文

Title: Mantle-like Sr isotopes in a Sturtian cap carbonate in Oman

Author: Francis A. Macdonald, Ellery Renger, Adrian R. Tasistro-Hart, Benjamin L. Byerly, Matthew G. Jackson, Kristin D. Bergmann, Tristan J. Horner, Peter W. Crockford

Issue&Volume: 2025-06-24

Abstract: Twice in the Cryogenian Period (720635 Ma), during the Sturtian and Marinoan glaciations, ice sheets extended to equatorial latitudes for millions of years. These climate extremes have been interpreted to record the Snowball climate state, in which all of Earth’s oceans were covered with ice. During a Snowball Earth, the hydrological cycle would have been curtailed and silicate weathering greatly reduced. In this scenario, deep ocean chemistry should have evolved toward mantle values through hydrothermal exchange at mid-ocean ridges. Specifically, seawater strontium isotopes (87Sr/86Sr) are predicted to exhibit unradiogenic mantle-like values. However, cap carbonates that overlie the Cryogenian glacial deposits have yielded radiogenic 87Sr/86Sr values similar to those of seawater prior to glaciation, inconsistent with the central geochemical prediction of the Snowball Earth hypothesis. Here we report the discovery of 87Sr/86Sr values of 0.7034 in marine carbonate and authigenic barite that rest directly above Sturtian glacial deposits in Dhofar, Oman. These values record either a local unradiogenic source or Snowball Earth deep-water values that have not been previously identified. If it is a global signal, these new data and geochemical modeling support an extreme Snowball Earth scenario with near-complete ice cover and define one of the largest geochemical perturbations to seawater in Earth history.

DOI: 10.1130/G53385.1

Source: https://pubs.geoscienceworld.org/gsa/geology/article/doi/10.1130/G53385.1/659183/Mantle-like-Sr-isotopes-in-a-Sturtian-cap