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

Abstract

The degree of chemical weathering in soils increases with mean annual precipitation (P; mm) and mean annual temperature (T; ЊC). 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): with. Another strong relationship was found between P and 0.0197(CIA-K) 2 P p 221.12e Rp 0.72 the molecular ratio of bases/alumina (B): with. A Mollisol-specific relationship 2 P p Ϫ259.34 ln (B) ϩ 759.05 R p 0.66 was found relating P to the molar ratio of calcium to aluminum (C) as follows: with P p Ϫ130.93 ln (C) ϩ 467.4. 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 2 T p Ϫ18.516(S) ϩ 17.298 R p. Our data also showed that most Alfisols can be distinguished from Ultisols by a molecular weathering ratio of 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.

Response of Soils and Soil Ecosystems to the Pennsylvanian–Permian Climate Transition in the Upper Fluvial Plain of the Dunkard Basin, Southeastern Ohio, USA

“…The results were reported as weight percentages of oxides which were then normalized to molecular weights (Supplement 1). These were used to semi-quantitatively assess chemical weathering and climate by calculating several molecular weathering ratios, the chemical index of alteration and mean annual precipitation [25][26][27] (Table 1). Base loss was calculated as Al 2 (Table 1) [25,27].…”

“…These were used to semi-quantitatively assess chemical weathering and climate by calculating several molecular weathering ratios, the chemical index of alteration and mean annual precipitation [25][26][27] (Table 1). Base loss was calculated as Al 2 (Table 1) [25,27]. MAP was calculated using equations derived from geochemical relationships found in modern soils and reported in mm/year [25,27].…”

“…Base loss was calculated as Al 2 (Table 1) [25,27]. MAP was calculated using equations derived from geochemical relationships found in modern soils and reported in mm/year [25,27]. Table 1.…”

“…Table 1. Molecular weathering ratios and paleoprecipitation proxies used in this study and their significance equations after [3,25,26].…”

“…Abundant plant matter and horizontal grayish-green rhizohaloes indicate high soil moisture, e.g., [2,3,32,33]. The abundance of kaolinite also indicates a high soil moisture regime, e.g., [9,25,39]. PT1 plasmic microfabrics indicate some downward illuviation of clay minerals in Ustifluvents, but a lack of illuviation in Epiaquents, e.g., [3].…”