Wandering, uplifting, and eroding continents: impact on silicate weathering and carbon cycle

English Abstract:

The geological evolution of the carbon cycle is pending on many complex processes. Among them, continental silicate weathering is known to be a controling factor of first importance, able to modulate the atmospheric CO2 and the Earth climate. But this process is itself a function of many processes. Specifically, the role of mountain uplift and basaltic weathering has been particularly discussed in the recent years. But much less attention has been paid to the role of continental drift, which modulates the climate over large regions, and hence the CO2 consumption by silicate weathering.

Here we discuss the combined effects on the Earth climate of two major continental reorganizations: one in the late Neoproterozoic and the other in the late Paleozoic. The investigation tool is the coupled carbon-climate numerical model GEOCLIM. In the first case, the tectonic context is the dislocation of the Rodinia super continent, with the onset of many highly weatherable large igneous provinces, all processes leading to a global cooling. In the second case, antagonistic forcings (the equatorial hercynian range promoting weathering and the Pangea assembly inhibiting weathering through aridification) produces first a global cooling from 330 to 290 Ma. This cooling is concomittant with the Late Paleozoic Ice Age. Then the demise of the range and the rising aridity allows CO2 to rise to high level in the late Permian, ending the glacial episode.

In both case, the scenarios are in agreement with the strontium isotopic ratio evolution, which traces the relative contribution of the weathering of various lithologies to the global strontium and carbon budgets.