Topics in Geobiology Volume 11, 1993, pp 73-98

Isotope Fractionation during Primary Production

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Abstract

The biological source of sedimentary organic matter can be inferred from detailed chemical studies on the structure of individual molecules extracted from sediments. These inferences are drawn from established relationships between biological source materials and diagenetically altered compounds (de Leeuw and Largeau, this volume, Chapter 2). A second method for inferring the biological source and the ecological setting in which organisms existed is with isotopic tracers of carbon, nitrogen, oxygen, hydrogen, and sulfur in organic matter and inorganic substances that have been processed by living organisms. Stable isotope compositions of bulk organic matter have integrative signals from processes that have occurred over the life of the organism, whereas those of individual compounds can record specific events in life. In this chapter, we will review recent advances in biological isotope fractionations of the light stable isotopes and attempt to offer an interpretation of processes that affected the isotopic signature of organic substances in living organisms that were preserved in the fossil record.