Hematite U-Pb dating of Snowball Earth meltwater events

• 成果类型: Article
• 署名作者: Courtney-Davies, Liam; Flowers, Rebecca M.; Siddoway, Christine S.; Hart, Adrian Tasistro-; Macdonald, Francis A.
• 署名单位: University of Colorado System; University of Colorado Boulder; Colorado College; University of California System; University of California Santa Barbara; University of California System; University of California Berkeley
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-15334
• DOI: 10.1073/pnas.2410759121
• 发表日期: 2024-11-19
• 关键词: antarctic ice-sheet; hydrothermal hematite; clastic dykes; deformation; sedimentation; EVOLUTION; origin; systematics; constraints; glaciation

摘要

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 similar to 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 similar to 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.