DIAGENESIS OF ORGANIC-MATTER - A STUDY USING STABLE ISOTOPES OF INDIVIDUAL CARBOHYDRATES

This paper presents data on the isotopic compositions of individual carbohydrates which have been isolated from both living organisms and from a depositional environment. Through recent developments in chromatography, isolation of monosaccharides in sufficient quantity for isotopic analysis is possible. Carbohydrates isolated from marine and terrestrial plants and animals have carbon isotopic compositions which clearly indicate biosynthetic processes which are recognized to be associated with isotopic fractionations during the incorporation and metabolism of carbon. Stable nitrogen isotopic compositions of N-acetyl-D-glucosamine, isolated from a variety of chitins, indicate a common fractionation of nitrogen which may be associated with transamination. This fractionation is estimated to be about -9 parts per thousand relative to the whole organism. Through the isotopic label, the source or history of an organic material may be traced through diagenesis. Further, production of non-indigenous carbohydrates, which may be associated with fungal or bacterial action, can be identified through depleted isotopic compositions. Xylose, for example, isolated from a peat, was approximately 8 parts per thousand more depleted in carbon than the whole peat or mannose isolated from the same peat. The isotopic distributions of carbohydrates isolated from living organisms are essential for the interpretation of those characterized in natural mixtures from an environment.