A Cenozoic-style scenario for the end-Ordovician glaciation
Abstract
The end-Ordovician was an enigmatic interval in the Phanerozoic, known for massive
glaciation potentially at elevated CO2 levels, biogeochemical cycle disruptions recorded as
large isotope anomalies and a devastating extinction event. Ice-sheet volumes claimed to be
twice those of the Last Glacial Maximum paradoxically coincided with oceans as warm as
today. Here we argue that some of these remarkable claims arise from undersampling of
incomplete geological sections that led to apparent temporal correlations within the relatively
coarse resolution capability of Palaeozoic biochronostratigraphy. We examine exceptionally
complete sedimentary records from two, low and high, palaeolatitude settings. Their
correlation framework reveals a Cenozoic-style scenario including three main glacial cycles
and higher-order phenomena. This necessitates revision of mechanisms for the end-
Ordovician events, as the first extinction is tied to an early phase of melting, not to initial
cooling, and the largest d13C excursion occurs during final deglaciation, not at the glacial apex.
Origin : Publication funded by an institution
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