Enigmatic CO2 Weathering Consumption and Climatic Response of the Central Atlantic Magmatic Province (CAMP) Straddling the Tropics of Pangea

Earth's long-term climate under the CO2 paradigm is maintained within a relatively narrow temperature range by Walker feedback whereby greenhouse response to CO2 outgassing modulates opposing sinks from CO2 consumption from silicate weathering toward an equilibrium atmospheric pCO2 concentration. Most of Phanerozoic time is characterized by equable climate punctuated by a few cold episodes with continental ice sheets, such as the Late Paleozoic Ice Age (LPIA) ending at ~270 Ma and the ensuing Late Cenozoic Ice Age (LCIA) continuing today from 34 Ma. A leading hypothesis is that cooling can be triggered by significant amounts of alkaline-rich mafic rocks showing up in the tropical humid belt where CO2 weathering consumption can be sufficiently intense to overcome Walker feedback and allow polar ice to eventually form and amplify the cooling. For the LCIA, this may have been a continental LIP (Deccan1) or arc-continent collision mafic rocks (Kohistan-Ladakh2) as India drifted northward and converged with Asia. However, a recent analysis3 showed that the 201 Ma CAMP, perhaps the largest continental LIP that extended over ~10 Mkm2 straddling the tropics between 30° N and 20° S paleolatitude did not flip non-glacial climate between the LPIA and the LCIA. The lack of evidence for high CO2 weathering consumption attributable to the well-studied CAMP poses a fundamental problem to our understanding of long-term controls on atmospheric pCO2 concentrations. However, paleogeographic and related considerations for CAMP offer several explanations for the discrepancy: 1) There may have been relatively few surface expressions (lava flows) associated with the aerially extensive intrusions marking CAMP activity; 2) CAMP lavas were mostly emplaced in the subtropical arid belts with low silicate weathering potential; 3) CAMP lavas were commonly emplaced in rift basins and rapidly buried by sediment; 4) degassing from CAMP activity resulted in a substantial atmospheric pCO2 perturbation4 that had to be removed before a long-term effect on climate could be realized. The net result is that pCO2 levels comparable to pre-eruptive values are attained within a few million years after CAMP activity5.

1Kent & Muttoni 2013 CP 2Macdonald et al. 2019 Science 3Park et al. 2021 Geophys. Mono. 4Schaller et al. 2011 Science 5Schaller et al. 2012 EPSL.