ESR 15 - Developing a 3D model of regolith formation and use it to interpret weathering intensity data
The regolith is the uppermost part of the Earth’s crust, which, because it is in contact with the hydrosphere, is composed of chemically and physically altered or weathered rocks. It is an essential part of the so-called critical zone in part because it is host to the largest fresh water reservoir on Earth, but also because it sustains most life at the Earth’s surface. The processes that control the formation and thus the present-day thickness of the regolith are, however, poorly quantified and few predictive model exists. Our estimates of regolith geometry are based on very sparse measurements and mostly rely on empirical relationships or correlations. Braun et al (2016) recently proposed a simple parameterization of regolith formation under the assumption that chemical alteration controls the rate of propagation of the weathering front through the ability of the flow of water along the interface to remove the product of the chemical dissolution, therefore keeping the system from complete saturation. Although highly simplified, the model is able to reproduce basic observations such as the control of surface erosion rate on regolith thickness and of surface slope on the distribution of regolith (in our out of phase with the surface topography). The first objective of this project is to generalize this model to 3 dimensions and to include it in an existing landscape evolution model (LEM). One of the challenges will be to find a highly efficient implementation that insures that the resulting LEM can be used in a Bayesian scheme to invert for both climate/tectonic control and model parameter values. For this we will need to improve on existing methods to compute the geometry of the water table in an arbitrary regolith geometry. The second objective is to use existing regolith estimates and data collected in WP1 by ESR5 to validate and calibrate the model and to investigate how an extreme climatic event such as the PETM affects weathering rates and is expressed and recorded in the geological archives.
- A new 3D landscape evolution model that predicts surface and regolith geometry and is hydrologically consistent (i.e. coupling surface and groundwater flow).
- A better understanding and quantification of how weathering efficiency reacts to an extreme climatic event.
Three publications are expected including one describing the methodological development.
- Université Bourgogne FrancheComté (E. Pucéat) - To learn about weathering proxies and how they could be predicted by the model (2 months)
- Université de Genève (S. Castelltort) - To incorporate weathering data into model (4 months)
- Université de Rennes 1 (F. Guillocheau & C. Robin) – African case study (4 months)