Wu, Xinxia¹, William E Galloway¹ 
(1) University of Texas at Austin, Austin, TX

ABSTRACT: Depositional and Structural Evolution of the Upper Miocene Depositional Episode, East-Central Gulf of Mexico

Two widespread, transgressive deposits associated with biostratigraphic top Textularia W (12.0 Ma) and Robulus E (6.2 Ma) define the Upper Miocene (Late Middle to Early Late Miocene) depositional episode (UM depisode). The UM depisode records a long-lived family of sediment dispersal systems that persisted for nearly 6 m.y. with little modification. In the east-central Gulf of Mexico, this depisode records extensive margin offlap, primarily centered on the ancestral Tennessee River and Mississippi River dispersal axes. Thickest sediments were deposited in the Tennessee River delta beneath modern SE Louisiana. The composite fluvial-dominated 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 UM, forming a secondary depocenter 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, extends both eastward and westward from the delta system. Abundant strike-reworked sediment locally prograded the strand plain to the shelf edge, with slope offlap exceeding 30 mi (50 km).

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.