THE ORGANIC GEOCHEMISTRY OF KEROGEN AND HUMIC ACIDS IN RECENT SEDIMENTS FROM THE GULF OF MEXICO.

摘要

The kerogen, humic acid and fulvic acid fractions were studied in sediments from three environments in the northwest Gulf of Mexico: the Orca Basin (an anoxic, hyper-saline basin on the continental slope), Baffin Bay, and the continental shelf. The amount of organic carbon present, and its distribution among the three fractions were determined, and stable carbon isotope ratios were determined for the total sediments and the kerogens and humic acids. The kerogen samples and selected humic acids were pyrolyzed at 300(DEGREES) in a vacuum, and the volatile and liquid products characterized. Humic acids were analyzed by 'H-Nuclear Magnetic Resonance (NMR) spectroscopy, and selected humic acids were also analyzed by solid state cross-polarized magic angle spinning (CP/MAS) ('13)C-NMR.; Humic and fulvic acids were abundant, especially in the surface layers of sediment (0-20 cm) in all environments. The humic acids from Orca Basin and the continental shelf are very homogeneous and formed predominantly from marine organic matter. The kerogens from these sites were much more heterogeneous, and appears to be formed organic matter from two different sources. Baffin Bay was found to be a complex sedimentary environment with several possible sources of organic matter.; It was found that the kerogen and humic acid fractions form at the same time, and there is little or no interconversion of kerogen and humic acid in these sediments. Kerogen and humic acid are not always related geochemically.; Pyrolysis and NMR studies showed the kerogens and humics to be highly functionalized, with many easily degraded groups. A large fraction ((TURN)30%) of the total carbon occurred in aromatic groups, with more than one substitution per ring, and more than one ring per molecule. Numerous other structures with no known biological precursors were found, implying a rapid condensation and rearrangement of structural elements. A set of melanoidins was synthesized and compared to authentic humic acids by 'H-NMR; major differences were noted between them.; From these data models of kerogen and humic acid structures, and early organic transformations in the sediment were made.