9418970 Savin The proposed work is a continuation of ongoing research into the oxygen and hydrogen isotope geochemistry of soil minerals and soil water. The primary immediate goal of the work is to understand the relationships between the isotopic compositions of different pedogenic minerals (especially clay minerals and oxides) and the climate of the weathering environment. A major long term goal of the research is to apply those relationships in the reconstruction of ancient continental climates from the isotopic compositions of minerals in paleosols. An additional goal is to obtain increased insight into the processes involved in the formation and modification of soil minerals. The proposed study is unique in that it will relate measurements of the isotopic composition of pedogenic minerals to the isotopic composition of soil waters and precipitation. Studies of soil minerals begin with very careful field, petrologic and mineralogic examination prior to separation of phases for isotopic analysis. These studies will include an extension of completed work on the oxygen isotopic compositions of Amazonian lateritic kaolinites. Other soil minerals (especially gibbsite, titanium oxides, and iron oxides) from the same pedogenic facies of the same profiles will be analyzed for 18O. All hydrogen-containing phases will be analyzed for D. Studies of soil minerals will also include analysis of a variety of saprolites developed on igneous rocks in the Virginia Piedmont and , in collaboration with colleagues at JPL and Caltech, investigation of the stable isotope systematics of soil minerals developed on basalt on the Kohala Peninsula (Hawaii) along a climatic gradient (rainfall increasing with altitude from 20 cm to 150 cm per year. The isotope geochemistry of soil water and, where possible, precipitation, will be monitored over the course of a year at each of the soil profiles which are studied (Brazil, Virginia Piedmont, Hawaii). Work on the isot ope geochemistry of soil water will focus on the analysis of the liquid water phase (rather than total water as in most previous studies) in the unsaturated zone. This is important distinction when the soil water isotopic data are to be related the isotopic compositions of pedogenic minerals. The analytical technique to be used was developed in the current grant period. It is a laboratory-based CO2 equilibration technique. Additional work is planned on the development and verification of an in situ technique based upon the analysis of soil CO2 and upon the isotopic fractionations that occur when soil water is partitioned into a liquid phase and other components (e.g., adsorbed water).
