Neoproterozoic Glaciated Basins: A Critical Review of the Snowball Earth Hypothesis by Comparison with Phanerozoic Glaciations

Abstract

The Neoproterozoic is widely considered to have experienced some of the most severe climatic perturbations recorded in Earth history, with extensive glaciations often referred to as 'Snowball Earth' events. The Snowball Earth and competing hypotheses seek to explain a wide range of geological data on Neoproterozoic pre-, syn-and post-glacial successions including glacial sedimentology, chemostratigraphy, palaeoceanography, geochronology, palaeomagnetism and palaeogeography, geodynamics, tectonics, palaeontology and palaeobiogeochemistry. However, our understanding of the Phanerozoic and particularly the Cenozoic and contemporary glacial geological record is often relatively neglected when evaluating the evidence for apparent severe and prolonged periods of globally synchronous glaciation. This paper presents a review of the available geological data for Neoproterozoic glacial successions in the light of what we know about the Cenozoic and recent glacial record. Most Neoproterozoic successions are shown to exhibit spatial and temporal variability, with sediment stacking patterns and facies associations indicative of dynamic ice masses. These characteristics are typical of sedimentary sequences deposited along glaciated continental margins throughout Earth history, without the need for global synchroneity or necessarily severe climatic excursions. Although recurrent very widespread glaciation is envisaged in the Neoproterozoic, the presence of analogous glacigenic and interglacial successions in the Neoproterozoic and Cenozoic suggest the operation of a similar set of processes across a similar range of depositional environments. Consequently, an unambiguous sedimentary record of hydrological shutdown during a prolonged global glaciation appears to be lacking. This indicates either a preservational bias in Neoproterozoic successions of the advance and recessional stages of glacial epochs, or the occurrence of dynamic, non-global glaciations during the Neoproterozoic.

Events in the Precambrian history of the Earth: Challenges in discriminating their global significance

“…However, opponents of the theory cite a significant number of arguments based on evidence from the rock record, against the SEH (e.g., Williams, 1975Williams, , 1986Williams, , 1998Williams, , 2004Williams, , 2008Williams et al, 2008;Young, 2004): (1) thick successions of diamictites with associated water-laid deposits; (2) evidence supporting glacial cycles and eustasy; (3) the combination of tidalites, tidal rhythmites, and thick glaciomarine successions indicates unfrozen seas over significant areas; (4) evidence for strong seasonality in glaciogenic deposits; (5) indications of gradual palaeoclimatic changes at the start and end of Proterozoic glaciogenic events rather than the rapid and extreme changes inherent in the SEH; (6) a lack of high latitude Proterozoic glacial deposits; (7) cap carbonates and BIF within the expected stratigraphic succession from SE events are not that common, and the stratigraphic position, facies and chemistry of these chemical rock types can equally be explained through alternative genetic models, especially related to rifts as supercontinents begin to break up (e.g., summary in . A recent comparison of Neoproterozoic glaciogenic units with Phanerozoic glacial deposits also provides a strong case against the SEH (Etienne et al, 2008).…”

A new rock-based definition for the Cryogenian Period (circa 720 – 635 Ma)

“…For these reasons, Andrew Knoll, when chair of the Terminal Proterozoic Subcommission, advocated a chronostratigraphic definition for the base of Cryogenian System marked by the first 'Sturtian' glacial rocks (Knoll, 2000). However, even if glacial influence could be demonstrated unambiguously in the chosen section (Etienne et al, 2008), the onset of glaciogenic deposition in one region may not correspond to a globally correlative stratigraphic horizon due to geographic variability and sub-glacial erosion (e.g. Kendall et al, 2009).…”

Glaciogenic reservoirs and hydrocarbon systems: an introduction

“…Despite the supposedly snowball Earth pretext, most Neoproterozoic glacial successions compare closely in facies and stacking patterns to their Phanerozoic counterparts (Etienne et al 2007).…”