Stable Isotopes in the Sedimentary Record
This chapter addresses the interpretation of the sedimentary records of several common stable isotopes and their fractionation in natural systems. Of the 258 stable isotopes of the chemical elements, those with the atomic numbers 1–20, hydrogen through calcium, are the main chemical constituents of the atmosphere, continental and oceanic waters, sediments, and upper part of the crystalline continental and oceanic crust. The chapter deals with the isotopes of hydrogen (D/H) and oxygen ( 18 O/ 16 O) that occur in the global water cycle and are fractionated by a number of physical and chemical processes in the gas–liquid–solid H 2 O system, as well as in many mineral–water reactions in sediments; the isotopes of calcium ( 44 Ca/ 40 Ca) in the riverine input to the ocean and biogenic carbonates forming in ocean water; the isotopic fractionation of the elements essential to life, carbon ( 13 C/ 12 C), nitrogen ( 15 N/ 14 N), and sulfur ( 34 S/ 32 S), that have produced variably extensive sedimentary records during Earth's history; and the occurrences of the boron isotopes ( 11 B/ 10 B) in the Earth's surface environment. In addition to the nonradiogenic stable isotopes mentioned, a section in this chapter is devoted to the radiogenic stable 40 Ar because of its importance as a tracer of certain diagenetic processes in sedimentary clay minerals.