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

Published online by Cambridge University Press:  05 July 2018

A. F. White ,
M. S. Schulz ,
D. A. Stonestrom ,
D. V. Vivit ,
J. Fitzpatrick  and
T. Bullen
A. F. White*
Affiliation:
US Geological Survey, Menlo Park, CA 94025, USA
M. S. Schulz
Affiliation:
US Geological Survey, Menlo Park, CA 94025, USA
D. A. Stonestrom
Affiliation:
US Geological Survey, Menlo Park, CA 94025, USA
D. V. Vivit
Affiliation:
US Geological Survey, Menlo Park, CA 94025, USA
J. Fitzpatrick
Affiliation:
US Geological Survey, Menlo Park, CA 94025, USA
T. Bullen
Affiliation:
US Geological Survey, Menlo Park, CA 94025, USA
*
*E-mail: afwhite@usgs.gov
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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 8.9x10-15 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.

Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 1 , February 2008 , pp. 149 - 153
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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