Sedimentology of the Sturtian icehouse: perspectives from Namibia, Australia and western USA

Marie Busfield

Research output: ThesisDoctoral Thesis

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The Cryogenian icehouse has long attracted significant attention because of the exceptionally widespread distribution of glaciogenic sediments, and the paradoxical accumulation of these sediments at tropical to subtropical palaeolatitudes. As a result, extreme models of global glaciation have been invoked to freeze the tropical latitudes through runaway climate and ice-albedo feedbacks, the eponymous 'Snowball Earth'. However, these predictions conflict with the evidence from the geological record, and cannot be readily
replicated by available palaeoclimatological reconstructions. This thesis examines three exceptionally wellexposed older Cryogenian ('Sturtian') successions in northern Namibia, South Australia and the Death Valley
region of western USA to improve understanding of the scale, mobility and thermal regime of Cryogenian ice masses. Detailed sedimentology, palaeocurrent analyses and thin section micromorphology are utilised to
unravel sedimentological processes active under the Sturtian icehouse. In northern Namibia, these data reveal the first recorded example of subglacial glaciotectonic deformation in the Otavi Mountainland, pre- to synglacial ironstone facies which support photosynthetic microbial communities, and evidence of interglacial conditions interrupting a thick glaciogenic palaeovalley fill. In South Australia, the first known Neoproterozoic trough mouth fan is recorded, alongside evidence of dynamic advance-retreat cyclicity recognised within a glacial sequence stratigraphic framework. Meanwhile, in the Death Valley region, extremely heterolithic, predominantly coarse-grained facies support high debris loads and strong meltwater influence in the glacial depositional environment, clear variation in direct glacial influence across the
depositional basin, and a distinct retrogradational retreat and progradational advance sedimentary architecture. Cumulatively, these data support the presence of grounded, marine-terminating temperate to polythermal ice masses subject to multiple episodes of advance and retreat, including periods of ice minima to open water conditions. These characteristics are more akin to Phanerozoic icehouse intervals than models of extreme global glaciation, and thus militate against the 'hard' snowball Earth hypothesis. In the absence of
reliable geochronological data, diachronous glaciation cannot be inferred, although strong evidence is presented for disparate, dynamic ice masses operating under an active hydrological regime.
Original languageEnglish
Awarding Institution
  • Royal Holloway, University of London
  • le Heron, Daniel, Supervisor
Award date1 Oct 2015
Publication statusUnpublished - 2015

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