Geochemical climofunctions from North American soils and application to paleosols across the Eocene-Oligocene boundary in Oregon

The degree of chemical weathering in soils increases with mean annual precipitation (P; mm) and mean annual temperature (T; degreesC). We have quantified these relationships using a database of major-element chemical analyses of 126 North American soils. The most robust relationship found was between P and the chemical index of alteration without potash (CIA-K): P = 22.112e(0.0197(CIA-K)) with R-2 = 0.72. Another strong relationship was found between P and the molecular ratio of bases/alumina (B): P = -259.34 ln(B) + 759.05 with R-2 = 0.66. A Mollisol-specific relationship was found relating P to the molar ratio of calcium to aluminum (C) as follows: with P = -130.93 ln (C) +467.4 with R-2 = 0.59. Relationships between weathering ratios and T are less robust, but a potentially useful one was found 2 R p 0.59 between T and the molecular ratio of potash and soda to alumina (S) where with T = -18.516(S) +17. 298 with R-2 = 0.37. Our data also showed that most Alfisols can be distinguished from Ultisols by a molecular weathering ratio 0.37 bases/alumina of <0.5 or by a chemical index of alteration without potassium <80. Application of these data to a sequence of Eocene and Oligocene paleosols from central Oregon yielded refined paleoprecipitation and paleotemperature estimates consistent with those from other pedogenic and paleobotanical transfer functions for paleoclimate.