Eastward Shift of Deepwater Fan Axes During the Miocene in the Gulf of Mexico: Possible Causes and Models

John W. Snedden, William E. Galloway, Timothy L. Whiteaker, and Patricia E. Ganey-Curry
¹Institute for Geophysics, University of Texas at Austin, 10100 Burnet Rd., Austin, Texas 78758, U.S.A.
²Center for Research in Water Resources, University of Texas at Austin, 10100 Burnet Rd., Austin, Texas 78758, U.S.A.

Synthesis of the Gulf of Mexico depositional history reveals a notable eastward displacement of sediment transport in the Miocene. The paleo–Tennessee River system deposited over 9800 ft (3000 m) of sediment south of the fluvio-deltaic input point in available shelf/upper slope accommodation. However, the depositional axis of the MCAVLU (Mississippi Canyon Atwater Valley, and Lund protraction areas) submarine fan system is located more than 150 km (90 mi) east of this depocenter, indicating along shelf/upper slope transport prior to entering the deepwater. This anomaly can be variously explained as a function of salt tectonics or, alternatively, development of strong easterly oceanographic currents.

Evidence for development of intensified, clockwise oceanographic flow in the Miocene has been previously recognized but not linked to this apparent deepwater submarine fan shift. Upper Miocene deepwater fan deposits on the western flank of the Gulf of Mexico basin, including north-dipping clinoforms, indicate accelerated current flow from the south. In the eastern Gulf of Mexico, seismic stratigraphic analysis shows a major Middle to Upper Miocene unconformity formed on the western Florida platform margin, well below the influence of subaerial erosion processes.

Linking these observations suggests that oceanographic current velocities were probably elevated, and thus may have caused displacement of transport pathways toward the Mississippi Canyon area. Initiation of intensified current flow could be linked with progressive termination of global equatorial flow beginning in the early Miocene.

Implications for deepwater exploration are substantial, given high interest in the Gulf of Mexico Miocene deepwater play and use of source-to-sink reconstructions that often do not consider oceanographic currents.

AAPG Search and Discovery Article #90158©2012 GCAGS and GC-SEPM 6nd Annual Convention, Austin, Texas, 21-24 October 2012