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Abstract
Neoproterozoic diamictites at low palaeolatitudes overlain by "Cap Carbonates" led to the hypothesis of at least 2 global glaciations, known as "Snowball Earth". The Cap Carbonates associated with negative -δ13C excursions are a key point of this theory, interpreted as a result of the collapse in organic productivity in the ocean, due to the isolation of global oceans from the atmosphere by the global ice cover. Therefore Cap Carbonates were interpreted as anorganic precipitates produced by the switch from "Snowball Earth" into a super green house – the Neoproterozoic Climatic Paradox.
Palynological studies of Cap Carbonates from the late Neoproterozoic Maieberg Fm in NE-Namibia prove a continuous record of life within the Cap Carbonates, dominated by cyanobacteria with few prasinophytes and acritarchs. The decrease of organic matter (TOC) in the Cap Carbonates is not related to less organic productivity in the oceans, but to facies changes to extremely shallow marginal marine conditions of a proximal carbonate platform. Palynology proves, that cap carbonates are mainly biogenic or at least biomediated deposits (and not solely anorganic precipitates), requiring open oceans and ice-free sea floors during this aftermath of the main glacial interval. Palynofacies analysis gives clear evidence for sea-level fluctuations within the Cap Carbonates. Variations in relative sea-level are recorded by changing proportions of prasinophytes and acritarchs within the generally very shallow, marginal marine environment, dominated by microbial mats (cyanobacteria).
This indicates continued climatic variability during Cap Carbonate deposition, contradicting its interpretation as a deposit of a single large marine transgression at the end of the global glaciation, assumed by the ‘Snowball Earth’ theory. The continuous record of fluctuations in relative sea-level coeval with dropstones contradicts the rapid change from a "Snowball Earth" to a super greenhouse during the Cap Carbonate deposition, but supports a model of long term waxing and waning of glaciers within a relatively slow escape from a widely glaciated Neoproterozoic world. Expanding palynofacies analysis on the whole pre- to postglacial succession will give more information on timing and intensity of the "Marinoan" glacial interval, as an example for Neoproterozoic glaciations.
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