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USGS · 70033138

Solute profiles in soils, weathering gradients and exchange equilibrium/disequilibrium

A. F. White·M. S. Schulz·David A. Stonestrom·D.V. Vivit·J. Fitzpatrick·T. Bullen
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Abstract

The spatial and temporal changes in hydrology and pore water elemental and 87/86 Sr compositions were used to determine contemporary weathering rates in a 65 to 226 ky old soil chronosequence formed from granitic sediments deposited on marine terraces along coastal California. Cl-corrected Na, K and Si increased with depth denoting inputs from the weathering of plagioclase and K-feldspar. Solute 87/86 Sr exhibited progressive mixing of sea water-dominated precipitation with inputs from less radiogenic plagioclase. Linear approximations to these weathering gradients were used to determine plagioclase weathering rates of between 0.38 and 8.9×10 −15 moles m −2 s −1 . The lack of corresponding weathering gradients for Ca and Sr indicated short-term equilibrium with the clay ion exchange pool which requires periodic resetting by natural perturbations to maintain continuity, in spite of soil composition changes reflecting the effects of long-term weathering.

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A. F. White, M. S. Schulz, David A. Stonestrom, D.V. Vivit, J. Fitzpatrick, T. Bullen. 2018-07-05. Solute profiles in soils, weathering gradients and exchange equilibrium/disequilibrium. https://doi.org/10.1180/minmag.2008.072.1.149

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