Application of sedimentary carbohydrate residues in a study of organic facies and natural gas occurrences

Abstract

Recent aquatic environments and resulting organic facies can be characterized by types and amounts of carbohydrate residues. Characteristics are based on source organisms, degree and type of degradation, and reactions with associated compounds in the mineral-kerogen-humus complex. Selected modern environments are typified by the following presently known carbohydrate suites: (1) deep sea, mid-Pacific, mid-Atlantic Oceans—glucose, galactose, furfurals, low total carbohydrates (TC); (2) deep gulf, Gulf of California—glu, gal, xylose, mannose, furfurals, moderate to high TC; (3) continental shelf, eastern North America—glu, xyl, gal, furfurals, high TC; (5) oligotrophic lake, Minnesota—furfurals, low TC; (6) eutrophic lake, Minnesota—glu, xyl, arabinose, gal, rhamnose, man, ribose, furfurals, glucuronic acid, high TC; (7) bog, Minnesota—glu, ara, xyl, gal, man, rib, very high TC. Polysaccharides are rare to absent in modern deep sea deposits but have been found in Lower Quaternary and younger deep gulf sediments. Cellulose, alpha- and beta-amylose and laminaran are common in shallow marine and lacustrine sediments. Methane, derived from both terrestrial and aquatic higher plant residues is high in yield in freshwater marshes and bogs and in eutrophic lake sediments, moderate in salt-water marshes and estuaries and relatively low in offshore marine sediments. Nitrogen and carbon dioxide are the commonest non-hydrocarbon gases. In many samples studied, xylans appear to predominate over other plant polysaccharide as methane sources. Carbohydrate residues in ancient rocks, based on examples from North America, show a tentative, but as yet poorly investigated, relationship to environmental organic facies and should prove to be useful in natural gas exploration.