Cryogenian (717−635 Ma) Snowball Earth glaciations are the most extreme episodes of climate change in the geological record, but their impact on landscapes and environmental change remain uncertain. Some climate models predict thin, cold-based, stable ice sheets, with low sliding velocity and minimal erosion, whereas others predict thick, warm-based ice sheets that were sensitive to orbital forcing and highly erosive. These models make predictions for the stratigraphy, sedimentation rates, and provenance of deep-water deposits. The Zerrissene fan in Namibia is a Cryogenian−Ediacaran turbidite succession that records the deep-sea sedimentary response to the Marinoan (639−635 Ma) glaciation. We report the stratigraphically lowest traceable horizon of dropstones in the upper Brak River Formation of the Zerrissene Group, which we interpret to record Marinoan Snowball glacial onset in a deep-water setting. The youngest zircon grain in a preglacial detrital sample 153 m below this horizon yields a concordant chemical abrasion−isotope dilution−thermal ionization mass spectrometry date of ca. 642 Ma, which is consistent with Marinoan onset at ca. 639 Ma. In contrast with glacially influenced Pleistocene deep-sea fans, for which intensifying glaciation has driven accelerated sedimentation, provenance variability, and sea-level−mediated progradation, the Brak River Formation exhibits none of these responses to glaciation. The insensitivity of deep-sea sedimentary dynamics to Snowball Earth glaciation conflicts with the hypothesis of expansive syn-Snowball continental denudation. Instead, the continuity of deep-sea sediment routing is consistent with a cold-based, stable Snowball ice sheet with low sliding velocity and minimal erosion.
Tasistro-Hart et al. (Tue,) studied this question.