I am excited to advertise a new paper on the chemical and physical erosion of the northern Apennines: Led by Erica Erlanger.

Rocks exposed to the surface of the Earth break down by physical processes (e.g. through river erosion, cracking under the influence of temperature etc.) and chemical processes (e.g. by dissolution in acidic water). Water, wind, and gravity transport rock fragments and form extensive sedimentary deposits. In turn, rivers carry the dissolved load into lakes and into the ocean, thereby influencing Earth’s chemical cycles. The relative importance of these physical and chemical denudation processes depends on the type of rock. For example, carbonate rocks dissolve much faster than silicates, but they can also be more resistant to physical breakdown. In our study, we asked how physical and chemical denudation are partitioned in mixed carbonate-silicate rock. To address this question, we went to the northern Apennines.

Compared to the Alps or the Himalaya, the northern Apennines are a young mountain range that exposes marine carbonates and silicate rocks. These rocks were deposited by turbidity currents and they experienced only limited burial and metamorphism. The Apennines therefore provide an opportunity to study the evolution of physical and chemical erosion in the early stages of mountain building.

We combined erosion rates from measurements of cosmogenic nuclides in river sediments with analyses of the dissolved load carried by rivers. Compared to more evolved siliciclastic mountain ranges, the Apennines have a larger relative chemical weathering flux; Most likely, due to the rapid dissolution of carbonate.

Interestingly, we also find that up to 90% of the dissolved carbonate re-precipitates as sediment grains. How can that be? We believe this phenomenon can be explained by the saturation of the river water with respect to calcium carbonate. When cool CO₂-laden acidic groundwater discharges into streams, the temperature and CO₂ equilibrate with the atmosphere. Warmer water with less CO₂ can dissolve less carbonate, and the excess precipitates. This mechanism converts a large fraction of the chemical flux back into sediment. As a result, the chemical flux out of the Apennines is not limited by the dissolution of minerals in the subsurface, but by the capacity of the stream to carry the dissolved carbonate; A surprising result.

Shoutout to: Erica Erlanger, Jeremy C. Rugenstein, Vincenzo Picotti, and Sean Willett.

[12] Erlanger E.D., Rugenstein, J.K.C., Bufe A., Picotti V., Willett, S.D. (2021). Controls on Physical and Chemical Denudation in a Mixed Carbonate-Siliciclastic Orogen. Journal of Geophysical Research: Earth Surface. 126(8), e2021JF006064. Journal Link (open access).