Large igneous provinces and Earth's carbon cycle: Lessons from the Late Triassic and rapidly emplaced Central Atlantic Magmatic Province

Using stable carbon isotopes of soil carbonates, I demonstrate that the eruption of the Central Atlantic Magmatic Province (CAMP) resulted in a transient perturbation of atmospheric pCO2 in the Late Triassic. I show evidence of a discrete pCO2 pulse (roughly a doubling) immediately after the first CAMP flow-unit preserved in the Newark rift basin, followed by a ∼200 kyr falloff toward pre-eruptive concentrations, a pattern repeated above the second and third flow-units. Observations from the Hartford basin indicate that pCO2 had fallen to concentrations well below background by 400 kyr after the final eruptions in the earliest Jurassic. I use a simple geochemical model to demonstrate that this decrease below pre-eruptive background is most easily accomplished by the extrusion of ∼1.12 x 107 km2 of basalt into the equatorial humid belt, which effectively amplified the increase in global continental weathering rate by perhaps as much as 50%. These results indicate that LIPs can be overall net sinks for CO2. A test of the Late Triassic equilibrium state from a 33-My record of pCO2 broadly shows a ∼3-fold decrease from the Carnian through the Rhaetian. This pCO2 decrease is most consistent with the hypothesis that a Late-Triassic increase in continental area within the tropical humid belt, as a result of the slow northward migration of the Pangean Supercontinent, lead to increased rates of continental weathering and CO 2 consumption. A significant implication of this finding is that changes in degassing rate from variable ocean crust production are not driving the long-term decrease in pCO2 because crustal production rates show little variability through the Late Triassic. Together, the results of this work lay the foundation for a revision of our understanding regarding the driving mechanisms behind Earth’s long-term carbon cycle toward a greater emphasis on weathering processes.