Methane Clathrate Destabilziation in Equatorial Tidalites During Deglaciation

Kennedy, Martin J.¹, David D. Mrofka¹ (1) University of California, Riverside, Riverside, CA

The global-warming induced destabilization of oceanic and terrestrial methane clathrates represents a wild card in the climate system. The climate effects of this potentially non- linear response to subtle warming is difficult to accurately access given that it has not been active in historical time. The deep time record, however, provides multiple candidates for climate induced methane clathrate destabilization, with one of the best candidates during the terminal Proterozoic following what was likely to be the most severe ice age in Earth history. Cold temperatures and expansive intracratonic basins exposed to terrestrial conditions during this severe ice house would have optimized the potential for methane clathrate accumulation in both marine and continental permafrost settings. We have identified numerous global-examples of methane-influenced deglacial sediments at a similar interval. In some cases, methane flux may have been significant enough to establish large, complex deepwater microbial carbonate mounds (> 100 m) on basin margins and drive oceans anoxic. In South Australia, the presence of carbonate cemented seep horizons that formed within active tidal channels within transgressive deglacial deposits imply catastrophic release of methane from secondary clathrates. The low paleolatitude (<15°) and shallow-water occurrence of these deposits require a permafrost origin and indicate a vastly more extensive permafrost methane clathrate pool than developed during the Cenozoic. Episodic catastrophic release of methane after termination of Neoproterozoic glaciation may explain a negative –5‰ carbon isotopic excursion characteristic of Neoproterozoic post glacial carbonates, implying the presence of a strong greenhouse gas feedback capable of expediting the icehouse-to-greenhouse transition.