Calibrating the terminations of Cryogenian global glaciations
Calibrating the terminations of Cryogenian global glaciations
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DOI：
10.1130/g45719.1
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发表时间：
2019-03
期刊：
影响因子：
5.8
通讯作者：
Chuanming Zhou;M. Huyskens;X. Lang;S. Xiao;Q. Yin
中科院分区：
文献类型：
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作者：
Chuanming Zhou;M. Huyskens;X. Lang;S. Xiao;Q. Yin
低温期的斯特阶和马里诺阶冰川及相关地层记录了地球历史上最严重的古气候事件，是雪球地球假说（SEH）的主要试验场。SEH预测，斯特期和马里诺期的冰川消退都是全球同步的、快速的和灾难性的。从冰川杂屑岩到上覆的帽白云岩的急剧过渡代表了这些冰消期的关键事件。因此，一个积极的测试全球同步冰川消退需要高精度的放射性测年，以紧密地括号中的每一个古大陆和每一个实质性的沉积盆地的过渡，然而，这种高分辨率的日期是稀缺的，并有有限的地层和古地理覆盖面。本文报道了中国南方铁四澳杂岩顶帽白云岩（Sturtian年龄）和南沱杂岩顶帽白云岩（Marinoan年龄）凝灰质层中两个高精度锆石化学磨蚀-同位素稀释-热电离质谱年龄（U-Pb），分别为658.80 ± 0.50Ma和634.57 ± 0.88Ma。658.80 ± 0.50Ma的年龄代表了Sturtian期冰川作用终止的高精度最小年龄限制。634.57 ± 0.88Ma的年龄和以前发表的635.23 ± 0.57Ma的年龄在不确定性范围内是不可区分的，它们一起提供了严格的限制，在中国南方的Marinoan冰川的终止约。635 Ma，直接将盖层白云岩的形成时间界定为<106 a。这些新的资料支持了华南地区的Marinoan冰期的快速终止，并与全球低温期冰消事件的同步性相一致。
Cryogenian Sturtian and Marinoan glacial and associated strata record the most severe paleoclimatic events in Earth history and are the main test ground of the snowball Earth hypothesis (SEH). The SEH predicts that both Sturtian and Marinoan deglaciations were globally synchronous, rapid, and catastrophic. The sharp transition from glacial diamictite to the overlying cap dolostone represents a key event during these deglaciations. Thus, a positive test for globally synchronous deglaciation requires high-precision radiometric dates to tightly bracket this transition on each paleocontinent and within every substantial sedimentary basin; however, such high-resolution dates are scarce and have limited stratigraphic and paleogeographic coverage. Here, we report two high-precision U-Pb zircon chemical abrasion–isotope dilution–thermal ionization mass spectrometry ages of 658.80 ± 0.50 Ma and 634.57 ± 0.88 Ma from tuffaceous layers that occur, respectively, within the cap dolostone atop the Tiesi’ao diamictite (Sturtian age) and at the topmost Nantuo diamictite (Marinoan age) in South China. The 658.80 ± 0.50 Ma age represents a high-precision minimum age constraint on the termination of the Sturtian-age glaciation. The 634.57 ± 0.88 Ma age and a previously published age of 635.23 ± 0.57 Ma from the topmost cap dolostone are indistinguishable within uncertainty, and together they provide tight constraints on the termination of the Marinoan glaciation in South China at ca. 635 Ma and directly bracket the duration of the cap dolostone to be <106yr. The new data support the rapid termination of the Marinoan glaciation in South China and are consistent with global synchroneity of Cryogenian deglaciation events.