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Controls on Physical and Chemical Denudation in a Mixed Carbonate‐Siliciclastic Orogen
Author(s) -
Erlanger E. D.,
Rugenstein J. K. C.,
Bufe A.,
Picotti V.,
Willett S. D.
Publication year - 2021
Publication title -
journal of geophysical research: earth surface
Language(s) - English
Resource type - Journals
eISSN - 2169-9011
pISSN - 2169-9003
DOI - 10.1029/2021jf006064
Subject(s) - weathering , denudation , siliciclastic , carbonate , geology , silicate , lithology , geochemistry , soil production function , erosion , carbonate rock , earth science , geomorphology , sedimentary rock , soil science , chemistry , paleontology , pedogenesis , sedimentary depositional environment , soil water , organic chemistry , structural basin , tectonics
Abstract Mixed siliciclastic‐carbonate active orogens are common on Earth's surface, yet most studies have focused on erosion and weathering in silicate‐rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed‐lithology regions. However, our knowledge of weathering and erosion in mixed carbonate‐silicate lithologies is limited and, thus, so is our understanding of the mechanistic coupling between uplift, weathering, and the carbon cycle. Here, we partition denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennines—a mixed carbonate‐siliciclastic active orogen—using dissolved solutes, the carbonate sand fraction, and existing 10 Be denudation rates. Erosion generally dominates total denudation fluxes relative to weathering by an order of magnitude. Carbonate and silicate contributions to erosion vary between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be kinetically limited, whereas carbonate weathering may be limited by acid supply. Carbonate re‐precipitation estimated by comparing ion ratios (Sr, Ca, Na) from rivers and bedrock suggests that up to 90% of dissolved Ca 2+ is lost from carbonate‐rich catchments. Corresponding [Ca 2+ ] estimates for the weathering zone are high, likely driven by high soil CO 2 partial pressures ( p CO 2 ); however, re‐equilibration with atmospheric p CO 2 in rivers converts solutes back into grains that become part of the physical denudation flux. Weathering limits in this landscape therefore differ between the subsurface weathering zone and riverine exports, and our findings suggest that carbon cycle models may overestimate the sensitivity to erosion of solute exports (Ca 2+ and HCO 3 − ) derived from carbonate weathering.