OBSERVED RELATIONSHIPS BETWEEN MODERN SOIL CHEMISTRY AND ENVIRONMENTAL HEAT TRANSFER AND ITS APPLICATION TO SOIL ECOSYSTEMS UPON A GREENHOUSE WORLD

We consider bulk soil chemistry to be a function of environmental heat transfer, or energy input (E_IN) to the soil, which is related to mean annual precipitation (MAP) and temperature (MAT), according to the following empirical relationship that is derived from the IAEA global climate database: (1) E_IN(KJ/m²yr) = 347,135e^{-0.5[((MAT-21.5)/-10)^2+((MAP-4,413)/1704)^2]} (R² = 0.96; P<0.0001). Chemical Index of Alteration minus Potassium (CIA-K = [Al₂O₃/(Al₂O₃+MgO+CaO+Na₂O)*100]) values of B-horizons from 18 soil profiles sampled along four soil climosequences on parent material compositions ranging from granitic to basaltic in the western United States and Mexico exhibit a high degree of linear correlation with E_IN values: (2) E_IN= 422*(CIA-K) -7982 (R² = 0.81, P < 0.0001), suggesting (i) the chemical composition of soil B-horizons does proceed according to environmental heat transfer that is expressed in a manner similar to Eqn (1) above, (ii) the CIA-K values of paleosol B horizons might be used to estimate environmental heat transfer in ancient ecosystems and (iii) CIA-K values may be used in conjunction with independent estimates of MAT from stable isotope geochemistry in order to provide quantitative estimates of MAP (using Eqn 1 above). Paleosol B-horizon samples from Paleocene through Miocene-age laterite profiles that formed at paleolatitudes ranging from ~65°N to ~60°S have CIA-K values >90%, which correspond to E_INvalues >30,000 kJ/m²yr. Such high E_IN values are typical of highly weathered soils such as Ultisols, Oxisols and Spodosols in modern climate regimes. Therefore, the higher-latitude paleosol CIA-K and E_IN data might represent paleoecosystems characterized by more vigorous weathering and greater environmental energy transfer than is typically recorded in modern high-latitude soil ecosystems. Indeed, oxygen and hydrogen isotope compositions of kaolinites from the paleosol B horizons range from 15.4 to 19.0‰ and –71 to -100‰, respectively, which corresponds to kaolinite crystallization temperatures ranging from 21±3° to 29±3°C – temperatures that are much higher than any modern high-latitude soil-forming environments. These paleotemperature and CIA-K estimates of paleo- E_IN will be used to provide new paleoprecipitation estimates within the context of Eqn (1) above.