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Abstract

The upper Miocene (late middle to early late Miocene) depositional episode (UM depisode) records a long-lived family of sediment dispersal systems that persisted for nearly 6 Ma with little modification. In the central Gulf of Mexico basin, this depisode records extensive margin offlap, primarily centered on the paleo-Tennessee River and Mississippi River dispersal axes, that began immediately following the Textularia W/Textularia stapperi flooding and is terminated by a regional flooding event associated with the Robulus E biostratigraphic top. Thickest sediments are deposited in the paleo-Tennessee River delta beneath modern southeast Louisiana, where three major depocenters are recognized. These depocenters have migrated in both strike and dip directions, and margin progradation is very prominent.

The composite fluvial-dominated paleo-Tennessee and Mississippi delta system rapidly built beyond the subjacent middle Miocene shelf margin to construct a sandy delta-fed apron. Margin outbuilding was locally and briefly interrupted by hyper-subsidence due to salt withdrawal and consequent slope mass wasting. Sediments also continuously bypassed into the Mississippi Canyon, Atwater Valley and Green Canyon OCS areas throughout the entire upper Miocene, forming two secondary depocenters composing the McAVLU submarine fan system at the base of the paleo-continental slope. A broad, but relatively thin, sandy strandplain and clastic shelf succession, supplied by reworking of the deltaic deposits, extended eastward and westward from the delta system. Abundant strike-reworked sediment locally prograded the strand plain to the shelf edge, and slope offlap exceeds 30 mi (50 km).

The presence of extremely large volumes of high-quality shelf margin delta and deep-water fan sandstone reservoirs results in the great productivity of the central Gulf of Mexico upper Miocene, and upper Miocene production is dominated by a major deltaic oil and gas trend straddling the southeast Louisiana coast.

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