Solute profiles in soils, weathering gradients and exchange equilibrium/disequilibrium
Authors: White, A.F.; Schulz, M.S.; Stonestrom, D.A.; Vivit, D.V.; Fitzpatrick, J.; Bullen, T.
Source: Mineralogical Magazine, Volume 72, Number 1, February 2008 , pp. 149-153(5)
Publisher: Mineralogical Society
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Abstract:
The spatial and temporal changes in hydrology and pore water elemental and 87/86Sr 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 87/86Sr 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.Document Type: Research article
DOI: 10.1180/minmag.2008.072.1.149
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