Chapter 2 - Conventional and Less Conventional Techniques for Hydrogen and Oxygen Isotope Analysis of Clays, Associated Minerals and Pore Waters in Sediments and Soils

Abstract

This chapter discusses the developments of physical and chemical extraction and purification techniques of clays for subsequent stable isotope analysis. Clay minerals form, in a wide range of environments near the earth's surface during weathering, diagenetic processes or hydrothermal alteration. A major difficulty in isotope studies of natural clays is to extract pure, monomineralic clay fractions from rocks as the clays often occur as intimate physical mixtures of inter-grown clay and non-clay minerals. Sample purity is critical to the precise determination of isotope ratios in clays. The major techniques used for clay separation are physical separation techniques and chemical purification. Isotopic analysis of clay minerals for hydrogen and oxygen isotope analysis of clay minerals have been established and yield satisfactory results for most minerals with a precision. Additionally, it includes the isotope analysis of pore waters and associated non-clay minerals in clay-rich rocks. Isotope analysis of pore water in clay-rich rocks is very important in understanding the movements and chemical evolution of interstitial waters in low-permeability rocks or soils, but also their effects on the alteration of rocks. The chapter also reviews the most commonly applied and unconventional techniques related to the isotope analysis of clays. Promising alternatives are the newly developed direct equilibration and the radial diffusion method.