THE NEOPROTEROZOIC GHAUB GLACIATION IN NAMIBIA: EVIDENCE FOR A COLD OCEAN ICE PATCH EARTH

The Snowball Earth hypothesis proposes the Earth froze at least twice during the Neoproterozoic isolating the oceans from the atmosphere and closing down the carbon cycle. Atmospheric CO₂ derived from volcanoes generated a super greenhouse climate catastrophically ending these extreme glacial episodes. Globally distributed cap dolostones, with negative δ13C values, overlying glacial diamictites are interpreted as chemical precipitates from a massive alkali influx into the ocean during unprecedented continental weather in super greenhouse periods. Negative isotopic stages are interpreted as global collapse in organic productivity below the ice. The Slushball Earth proposes small gaps in the sea ice to explain how some life survived. But even small areas of open ocean would prevent atmospheric CO₂ ever reaching concentrations needed to generate such an extreme climatic shift (Le Hire et al 2008). This questions if it is possible to ever escape from a Snowball/Slushball glacial scenario. New data from the low latitude Neoproterozoic Ghaub glaciation (635.5Ma; Marinoan Snowball Earth) exposed in NE Namibia, suggest an alternative explanation. The Ghaub diamictite is overlain by the Maieberg cap dolostone (< 10m) and a limestone/dolomite cap carbonate sequence with a negative δ13C signature (-5‰) (~200 m thick). Evidence for continuous life in this interval indicates open ocean coexisted with sea ice, casting doubt on what negative δ13C record and their use for global correlation. Evidence is presented that the Maieberg cap dolostone in the Otavi Mountainland was deposited in cold shallow water conditions indicating the Ghaub glaciation was not ended by a super greenhouse climate. A cold ocean ice patch Earth model is proposed in which low magnitude regional temperature fluctuations in an ambient cold global ocean caused localized dynamic advance/retreat of the polar ice fronts that in places reached low latitudes. Thermohaline circulation may have been sluggish. Small regional changes in sea surface temperature due to changes in wind driven ocean circulation patterns caused localized advance/retreat of the ice fronts. Albedo-ice feed back was insufficient for run away glaciation. Global evidence for low latitude glaciations may be diachronous, recording localized ice advance over an extended period.