Early Diagenesis of Fatty Acids in Mangrove Peats, St. Croix, U.S. Virgin Islands
Samples of fresh leaves, stems, and seeds of the mangroves Rhizophora mangle, Avicennia nitida, and Laguncularia racemosa were analyzed in an attempt to evaluate their potential contribution of fatty acids to the associated peats. In plant tissues, the C18:3 C18:1andC18:2 fatty acids occur in higher percentages than the long-cnain fatty acias derived primarily from the mangrove waxes (n-C20:0 to n-C32:0) Some long-chain unsaturated and branched-chain fatty acids are also present in mangrove tissues. Comparison of fatty acid distributions of mangrove litter and peats with those of the living mangroves suggests that preferential preservation of the normal long–chain fatty acids occurs during early diagenesis. The relative abundances of short-chain saturated, and expecially unsaturated, fatty acids decrease, whereas the relative abundances of normal long-chain fatty acids increase.
Mangroves have been cited as possible progenitors of coals, but the relative stability of long-chain fatty acids in associated depositional environments may be significant also with respect to the gensis of high- wax petroleum.
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This publication represents the proceedings, of a symposium on The Geology, Paleobotany, Geochemistry, and Microbiology of Peats." The symposium was held during the Annual Meeting of the Geological Society of America and associated societies, which took place in Miami, 18-20 November, 1974, and was jointly sponsored by the Coal Geology Division of the Society and the Organic Geochemistry Division of the Geochemical Society. Fourteen papers were presented, and nine are included in this publication. Five authors elected to make other arrangements for publishing their work; but the abstracts of these five papers, as submitted for inclusion in Abstracts with Programs, volume 6, number 7, 1974, are included here for completeness. Peats are of interest to scientists in a variety of disciplines: coal geology, organic geochemistry, soil science, plant ecology, the general ecology of food chains, agronomy, and environmental studies. Workers in many of these fields contributed to this symposium, but it is perhaps fair to say that the central unifying core is the consideration of peat as the precursor of coal. From a broad and general earth science point of view, peats and coals are of special interest because (a) such sediments contain higher concentrations of organic matter than any other common sedimentary deposits, and (b) in most peat beds and coal seams, the greater part of the organic matter and part of the mineral matter are autochthonous in the strictest sense, so that the many biological and chemical fossils that they contain are valid indicators of the organisms from which the organic matter was derived or of the environment of deposition. By contrast, although the reservoir and source rocks of petroleum do contain chemical fossils indicating their origin, reservoir rocks at least, cannot, of their nature, contain relevant fossils in the ordinary biological sense.