224-5 Denudation of carbonate bedrock as a driver of river basin reorganization

Session: From the Cosmos and Back: Quantifying Processes and Rates of Landscape Change (Posters)

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Abstract:

River basins are dynamic landscape features that shrink, grow and split over geologic time. Such changes can lead to shifts in connectivity between river basins, influencing everything from biological evolution to rates and patterns of sedimentation in depositional basins. River rearrangements are initiated when erosion rates differ across drainage divides, a situation that may arise in the presence of bedrock that varies spatially in physical and chemical properties. If erosion rates are higher in ‘softer’ rocks, the drainage divide will migrate towards the ‘harder’ rocks. Indeed, in many mountain ranges main drainage divides are pinned within these harder-to-erode rocks. While most previous investigations of bedrock erodibility and drainage divide instability have focused on differences in rates of mechanical erosion, the role of chemical weathering, particularly of carbonate bedrock, has not been as thoroughly investigated. Here, I present a case-study from the southeastern United States, where the drainage divide separating the Black Warrior River and the lower Tennessee River system is coincident with the contact between carbonate (the Bangor Limestone) and siliciclastic (the Pottsville Formation) bedrock. I estimate the relative contributions of mechanical erosion and chemical dissolution to total denudation across the drainage divide using water chemistry measurements and a compilation of cosmogenic-nuclide derived erosion rates from the region. The results highlight the importance of chemical dissolution of carbonate bedrock for patterns and rates of denudation in low-relief humid environments. 

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10959

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