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Early Miocene High Island Delta System, Offshore Texas and Louisiana

Abstract

Well logs and 3D seismic reflection data are integrated to image Lower Miocene depocenters of the upper Texas and westernmost Louisiana coastal and offshore areas. Although previously interpreted at a large scale (3rd order cycles) the detailed stratigraphy and depositional history of the early Miocene succession has not been accomplished. The late lower Miocene interval from Amphistegina B (MFS9) to Robulus L (MFS10) has been further subdivided into five 4th order cycles (each 200 to 300 m thick) to provide finer scale stratigraphic detail and help with interpretation of depositional Previous HitenvironmentsNext Hit. Results of the finer scale correlations are presented in a series of sandstone percent maps. Overall, the maps display a strike-elongate (sub-parallel to the present day coastline) geometry for the sandstone bodies which thin to the southeast (basinward). Net sandstone thickness is relatively low in older cycles and increases in younger cycles suggesting an overall progradation of the Previous HitdeltaicNext Hit system into the mapped area through time. Continued marine regression and southward movement of the shoreline are also confirmed by seismic amplitude maps. After a major transgression associated with Robulus L Previous HitdeltaicNext Hit progradation occurred under rising sea level conditions. Previous HitDeltaicNext Hit sediments prograded southward and sandstone brought to the upper Texas coast was distributed laterally by longshore currents to form strandplain coast lines. Maximum regression occurred during the interval MFS9_2 to MFS9_3 when a Previous HitdeltaicNext Hit depocenter formed offshore Texas in east High Island area. However, sandstone progressively decreases laterally to the east (offshore Louisiana) where more shale is present and marine processes rework Previous HitdeltaicTop derived sandstones into shore parallel bars. There is a clear retreat of the shoreline during the youngest cycle marking the beginning of transgression associated with Amphistegina B.