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The AAPG/Datapages Combined Publications Database
Shales rich in organic matter and coalified plant fragments (phytoclasts) in the early Mesozoic basins of the Newark Supergroup of the eastern United States are the topic of a current multidisciplinary study to understand their burial history, their role in ore-forming processes, and their hydrocarbon potential. Samples from the Hartford, Newark, Culpeper, Richmond, Taylorsville, and Deep River basins were analyzed using elemental analysis, nuclear magnetic resonance spectroscopy (NMR), Rock-Eval pyrolysis, stable isotope mass spectrometry, pyrolysis-gas chromatography, and gas chromatography-mass spectrometry.
The composition of the preserved organic matter in these samples is highly variable. Most sedimentary rocks of Triassic to Jurassic age in the Hartford, Newark, Culpeper, Richmond, and Deep River basins are in a catagenetic stage of thermal alteration. Samples from the Lower Jurassic Towaco Formation of the Newark basin are the least thermally altered samples analyzed and are apparently at a late diagenetic stage. Most of the older Triassic samples and a few of the latest Triassic to Jurassic samples, however, are highly thermally altered. Phytoclasts from the Lower Jurassic Feltville and Portland Formations, from the Newark and Hartford basins, respectively, are essentially aromatic; however, phenolic groups were observed in the NMR spectra.
The initial organic geochemical results imply that the organic matter basically exists in two populations, one with a low to medium rank or level of maturation and the other representing a much higher maturation level. No gradual change in maturation from one rock unit to the next was observed for the samples analyzed, and the distribution of maturities apparently is neither stratigraphically nor temporally controlled. The presence of phenolic groups in the phytoclasts from the Feltville and Portland Formations suggests that carbonization rather than coalification processes may have occurred.
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