据悉，雪球地球假说预测，全球被冰覆盖。然而，前人对冰川期（720-635 Ma）冰川沉积的描述仅限于大陆边缘和浅海盆地。在美国科罗拉多州的塔瓦卡伊夫（Tava）砂岩注入物和山脊中，保存了一份罕见的低温低纬度冰川作用的陆地记录。
研究显示，在冰下环境中，由于冰川负荷、流体超压和融水事件期间的反复注砂，注入物、脊和化学风化结晶岩表现出流态化和普遍变形的特征。在~690 ~ 660 Ma，受Tava岩脉切割的赤铁矿-石英脉的原地赤铁矿U-Pb年代学限制了注砂。研究小组将Tava早期的注砂事件归因于与裂陷和地热加热相关的基底融化，而后期的注砂事件则被归因于约661Ma Sturtian冰川消退期的融水生成。
南极洲的罗斯海湾提供了一个现代类比的例子，在那里，与裂谷有关的断层与充满沉积物的盆地接壤，超压流体在冰下封闭的承压含水层中循环，并且保留了广泛的冰川前地形。科罗拉多的野外证据和地质年代学进一步强调，元古代基岩的深层化学风化和与大不整合相关的剥蚀作用，早于低温期注入流化砂，与有限的冰川侵蚀相一致。
附：英文原文
Title: Hematite U-Pb dating of Snowball Earth meltwater events
Author: Courtney-Davies, Liam, Flowers, Rebecca M., Siddoway, Christine S., Tasistro-Hart, Adrian, Macdonald, Francis A.
Issue&Volume: 2024-11-11
Abstract: The Snowball Earth hypothesis predicts global ice cover; however, previous descriptions of Cryogenian (720-635 Ma) glacial deposits are limited to continental margins and shallow marine basins. The Tavakaiv (Tava) sandstone injectites and ridges in Colorado, USA, preserve a rare terrestrial record of Cryogenian low-latitude glaciation. Injectites, ridges, and chemically weathered crystalline rock display features characteristic of fluidization and pervasive deformation in a subglacial environment due to glacial loading, fluid overpressure, and repeated sand injection during meltwater events. In situ hematite U-Pb geochronology on hematite-quartz veins, which crosscut and are cut by Tava dikes, constrain sand injection at ~690-660 Ma. We attribute early Tava sand injection episodes to basal melting associated with rifting and geothermal heating, and later injections to meltwater generation during ~661 Ma Sturtian deglaciation. A modern analog is provided by the Ross Embayment of Antarctica, where rift-related faults border sediment-filled basins, overpressurized fluids circulate in confined aquifers below ice, and extensive preglacial topography is preserved. Field evidence and geochronology in Colorado further highlight that deep chemical weathering of Proterozoic bedrock and denudation associated with the Great Unconformity predate Cryogenian injection of fluidized sand, consistent with limited glacial erosion.
DOI: 10.1073/pnas.2410759121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2410759121