A 30 Myr record of Late Triassic atmospheric pCO(2) variation reflects a fundamental control of the carbon cycle by changes in continental weathering

摘要

We generate a detailed similar to 30 Myr record of pCO(2) spanning most of the Late Triassic (Carnian-Norian-Rhaetian) to earliest Jurassic (Hettangian), based on stable carbon isotope ratios of soil carbonate and preserved organic matter from paleosols in the eastern North American Newark rift basin. Atmospheric pCO(2) was near 4500 ppm in the late Carnian, decreasing to below similar to 2000 ppm by the late Rhaetian just before the earliest Jurassic eruption of the Central Atlantic Magmatic Province, which triggered measurable pulses of CO2 outgassing. These data are consistent with published modeling results using the GEOCLIM model, which predict a decrease in pCO(2) over the Late Triassic as a result of the progressive increase in continental area subject to the intense weathering regime of the tropical humid belt due to Pangea's northward motion. The finer-scale pCO(2) changes we observe may be dependent on the lithology introduced to the tropics, such as the dip to similar to 2000 ppm around 212 Ma and its rebound to similar to 4000 ppm at 209 Ma, which can be accomplished by introducing a more weatherable subaerial basaltic terrain. These observations indicate that the consumption of CO2 by continental silicate weathering can force long-term changes in pCO(2) comparable to those driven by presumed changes in mantle degassing.