Geochemical Climofunctions from North American Soils and Application to Paleosols across the Eocene-Oligocene Boundary in Oregon

摘要

The degree of chemical weathering in soils increases with mean annual precipitation (P; mm) and mean annual temperature (T; deg C). We have quantified these relationships using a datablase 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 = 221.12e~(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-sepcific relationship was found relating P to the molar ratio of calcium to alumina (C) as follows: P = - 130.93 ln (C) + 467.4 with R~2 = 0.59. Relationships between weathering ratios of T are less roubust, but a potentially useful one was found between T and the molecular ratio of potash and soda to alumina (S) where 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 of bases/alumina of < 0.5 or by a chemical index of alternation without potassium < 80. Application of these data to a sequence of Eocene nad Oligocene paleosols from central Oregon yielded refined paleoprecipitation and paleotemperature estimates consistent with those from other pedogenic and paleobotanical transfer functions for paleoclimate.