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Hydrocarbons in the frontal and central Ouachitas are in three distinct forms: crude oil, asphaltite, and as organic matter disseminated in potential source rocks. Each of these types has been examined geochemically, in an attempt to correlate oil to asphaltite and oil to source rock. In addition, the general source rock potential of the central Ouachitas has been evaluated. Results show that the crude oil produced to date is chemically mature and largely undergraded, although production is as shallow as 148 ft (45 m) in one field. The asphaltite is predominantly grahamite throughout the Ouachitas, and correlates geochemically to the crude oil, as indicated by similar stable carbon isotope ratios. An examination of the Ouachita section for source potential indicates that everal formations are high enough in organic carbon to have produced oil, although some may be ruled out on the basis of the type of organic matter present.
Association of oil and asphaltite along the strike of the Windingstair fault indicates that this listric reverse fault may have served as a migration conduit. Geochemical similarities between analyses of asphaltite from the Upper Ordovician Bigfork and that from the Mississippian Stanley group further indicate the possibility of vertical migration. Finally, migration along a listric fault, with subsequent near-surface degradation of the oil, would provide a concise explanation for the close association of near-surface solid asphaltite with sightly deeper liquid oil.
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