Abstract

Depth predictions for geophysical data obtained at the surface of the earth are usually made with the tacit assumption that lateral variations in the intervening strata are negligible. However, the evidence at hand indicates that, over Gulf Coast structures, local mineralization has resulted in appreciable stratigraphic variations which are not inverse functions of the depth nor direct functions of the relief of the underlying structures, but do appear to be excellent indices of the areal extent of deep seated, low relief, traps.More than a generation ago, evidence for this mineralization over and around Gulf Coast oil fields was recognized in the induration responsible for lowered drilling rates, and in the characteristic 'halo' or 'aureole' pattern of surface gas seeps. This mineralization results in increased acoustic speeds in the sediments overlying Gulf Coast traps, and so was responsible for the marginal refraction anomalies discovered from 1928-1930, and has been indicated indirectly by the exaggerated relief frequently predicted by the reflection surveys made in this area to date. This mineralization also modifies the electrical properties of the shallow sediments, and has been responsible for the shallow anomalies discovered by the recently introduced electrical transient method. Recent studies of the distribution of hydrocarbons and associated significant constituents in the surface soils have rediscovered and confirmed the 'halo' pattern of surface gas seeps responsible for the discovery of the Goose Creek oil field in 1907.The recognition that these stratigraphic variations occur at shallow depths even over low relief deep seated structures should result in a material simplification in exploration procedure through affording more easily attainable objectives in the way of shallow but important clues to deep seated traps.

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