A 30 MILLION-YEAR RECORD OF LATE TRIASSIC PCO2 VARIATION SUPPORTS A FUNDAMENTAL CONTROL OF THE CARBON-CYCLE BY CHANGES IN CONTINENTAL WEATHERING

A ~30 My continuous record of pCO₂ spanning the Late Triassic to Earliest Jurassic, based on paleosols from the eastern North American Newark rift basin, shows high pCO₂ levels near 4500 ± 1400 ppm (at S(z) = 3000 ± 1000 ppm) in the late Carnian, decreasing to ~2000 ± 700 ppm by the late Rhaetian, just before the eruption of the Central Atlantic Magmatic Province. These data are consistent with the results of the GEOCLIM model that predicts falling pCO₂ through the Late Triassic as a result of the progressive increase in continental area in the tropical humid belt due to Pangea’s slow northward motion, which Godderis et al (2008 EPSL) incorporated into GEOCLIM using paleolatitudes from the Newark Basin. With a sub-500 kyr average sampling resolution, the more detailed < 3 Myr-scale pCO₂ changes we observe, such as the dip to ~2000 ± 700 ppm around 212 Ma and its rebound at 209 Ma, can be accomplished by introducing a relatively small highly weatherable basaltic terrain into the tropical humid belt. These observations indicate that the consumption of CO₂ by continental silicate weathering can force long-term changes in pCO₂ comparable to those driven by mantle degassing.