Toward a Better Understanding of Gulf Coast Miocene Deep-Water Sediments: ABSTRACT

Abstract

Deep-water sands are known from many localities in the lowest Miocene of the Gulf Coast. They are recognized by a combination of paleontologic, conventional core, wireline log, and regional setting criteria. Almost invariably, subsurface geologic interpretations are difficult to make because of correlation problems. Turbidite deposition probably took place in deep-sea fan environments in most cases, but conventional models for these fans are over-simplified for application in studies of the Gulf Coast Miocene. The Miocene outer continental shelf and slope were not characterized by smooth, simple topography, but were extremely irregular, due principally to salt and shale tectonics. Thus the Walker and Mutti and Ricci-Lucchi fan model is inadequate and serves only as a star ing point for Miocene studies. Turbidite sand bodies in this setting can be classified into three major types: major channel deposits, levees, and suprafan lobes. In the Walker model, major incised channels with levees are characteristic of the upper fan, and suprafan lobes in the mid-fan, but in the Miocene they occur together in a complex manner. In the simplest cases we might anticipate that the channels cut through the lobes, resulting in rapid lateral facies change. Recommended procedure for mapping and interpretation involves preparation of panel diagrams after initial correlations have been made as completely as the data permit. Reduced-scale log segments are pinned on a large-scale base map, channel trends are identified, and the channel sands contoured, to the exclusion of other data. Lobe sand bodies are then contoured as a secondary operation and a composite sand or net sand isopach prepared. Abrupt changes in contour trend will occur where lobe and channel sands meet, and the two stage contouring process will yield much more accurate isopachs, and give a better tool for prediction of sand body extensions. End_of_Article - Last_Page 1433------------