Seismic morphology, a tool for high resolution seismic-sequence stratigraphy: Case study, the Upper Miocene Tortonian successions, OCS310, South Marsh Island, offshore Louisiana

Seismic attribute maps constructed from flattened 3D seismic data have helped to outline the morphology of nine fourth order sequences within the Upper Miocene Tortonian successions, in lease block OCS310 of the South Marsh Island area, offshore Louisiana. These fourth order sequences were deposited on an unstable paleoshelf that was exposed to rapid fluctuations in sediment supply and base level change. The chronostratigraphic seismic attribute maps of amplitude and coherence highlighted incised valley fill, deltaic, prograding upper shoreface and deep-water successions produced during ten major changes in relative sea level. The fourth order cycles in the study area are marked by a shorter sea level fall and a much longer sea level rise. Structural elements in the study area controlled the location and orientation of the Tortonian incised valleys and deltaic channels and their lobes. Lowstand and transgressive plays were identified within the Upper Miocene Tortonian section as upper slope fan, lowstand delta, and strandplain sand facies, and incised valley fills. The interplay between high frequency sea level cycles and sediment supply on the Upper Miocene Tortonian paleoshelf controlled the development, location and orientation of these reservoir facies. This study can be used as an analog for other similar settings of older Cenozoic sections in the Gulf of Mexico that have been heavily disturbed by tectonic movement.