Impact of stylolite cementation on weathering rates of carbonate rocks

Abstract

Abstract The weathering of carbonate rocks plays a significant role in the evolution of Earth’s surface. Such weathering is often accelerated by the presence of stylolites, which are rough, serated surfaces that form by dissolution under burial or tectonic stresses. Stylolites are thought to represent zones of mechanical weakness in rocks, as well as regions in which chemical weathering is enhanced. However, a quantitative framework capable of predicting how stylolites accelerate weathering in carbonates has yet to be achieved. In this study, we first used scanning electron microscopy and wavelength dispersive spectroscopy to characterize the way in which the two sides of individual stylolites are connected at the microscopic scale. In the samples we examined, we found that micrometer-scale calcite bridges span the opposing sides of the stylolites, effectively cementing the rock together. This cement filled 1%-30% of the stylolite volume. We then used a numerical cellular automaton model to simulate the effect that the degree of carbonate cementation has on stylolitic carbonate rock weathering. Our results show that weathering rates decrease non-linearly as the degree of stylolite cementation increases. The effect on overall rock weathering rates is significant: stylolite-bearing rocks with 1% cementation weathered as much as 37 times faster than limestone without stylolites, primarily because of accelerated mechanical erosion. Our results indicate that stylolites could be as important as joints and fractures in accelerating carbonate rock weathering and in the development of karst landscapes, potentially making a major contribution to global carbonate weathering.