As bedrock is exposed at Earth’s surface, it weathers to form regolith. One of the biggest challenges in predicting the depth and chemistry of regolith is relating the chemistry of weathering to changes in the size and distribution of the weathering particles. We have developed simple models that relate the fracture spacing of bedrock to the formation of weathering rock particles in the weathering zone. These models simulate the size diminution of such fragments of rock as they move up and out of the regolith. The models are being compared to models of chemical transformation versus depth using either soil grain chemistry or mineralogy for granitic, basaltic, and shale systems. Particle size versus depth patterns can thus be related to chemistry versus depth patterns. In fact, however, not only are particles moving up and out of the Critical Zone, but water ‘particles’ – i.e. pores – move down and through the underlying bedrock. We need to understand the chemistry, size, and distribution of these pores. To do this, we use neutron scattering, microscopy, and tomography to probe the distribution of pores. These efforts are painting a picture of the mineral-water interface during weathering that has both mass and surface fractal character. Such a model for this interface elucidates how to make more accurate projections of weathering and erosion.
Brantley, S.L., Jin, L., Ma, L., Bhatt, M., Fletcher, R., Rother, G., Cole, D., Navarre-Sitchler, A. (2010): The movement of rock particles up and water pores down through weathering bedrock (Keynote). Goldschmidt.
This Paper/Book acknowledges NSF CZO grant support.