『Abstract
Vertisols are clayey, shrink-swell soils that are widely recognized
in the rock record, thus generating the need to better understand
the dynamics of elemental concentrations on the development of
weathering indexes for climate interpretations. We assessed the
weathering performance of the four major base-forming oxides (CaO,
MgO, Na2O, K2O) along
a modern Vertisol climosequence spanning a strong precipitation
gradient and discovered that the concentration of bulk soil CaO
and MgO yields the strongest correlation to mean annual precipitation
(MAP). Based on this finding, we introduce the CALMAG weathering
index, defined as Al2O3/(Al2O3+CaO+MgO)×100, which improves
rainfall estimates for Vertisols relative to the well-established
CIA-K (chemical index of alteration minus potassium) weathering
index. Rather than documenting the hydrolysis of weatherable minerals
common in many other soil orders, in Vertisols CALMAG principally
tracks the flux of calcium and magnesium sourced from calcium
carbonate, detrital clay, and exchangeable Ca2+ and
Mg2+. Application of two Mesozoic paleosols reveals
that in drier climates CIA-K yields higher MAP estimates than
CALMAG, but that the reverse is true in wetter climates. This
work improves paleorainfall estimates from Vertisols and suggests
that a family of weathering indexes is needed for different paleosol
types. 』
Introduction
Setting and methods
Sources of the base-forming oxides
Selection of base oxides for development of weathering indexes
Rainfall estimates from paleovertisols
Conclusions
Acknowledgments
References cited