Late Cretaceous Paleo-Mississippi Valley Feeder Systems to the North-Central and Northeastern Gulf of Mexico: A Tuscaloosa-Time Sediment Machine

L. J. Wood and K. Woolf
Bureau of Economic Geology, University of Texas at Austin, Austin, Texas 78713

Analysis of 640 wireline logs and 13 whole core across the region of eastern Louisiana, Mississippi, Alabama and parts of Florida, onshore as well as offshore, indicate that a significant paleo-Mississippi River system drained the central and eastern Gulf Coastal Plain feeding coarse-grained fluvial braided and meandering river sediments to shelfedge deltas, developing in a wave- and current- dominated environment in and around several bathymetric highs. The largest valley (> 80 km) roughly parallels the New Madrid fault system, cutting its way across the U.S. as early as 60 mya with several secondary valleys originating off the Ouachita and Appalachian highlands. Isopach maps of Tuscaloosa parasequences; P0, P1, P2, P3 and Stringer, oldest to youngest respectively, show bypass along large valleys (P0 and P1) with pathways to the shelf in SE Louisiana, and the Mississippi and Florida Panhandles. P2 and P3 maps document transgression and flooding of the large estuaries with deposits dissected into channels, bars and interfluves. The Stringer, a transgressive backstepping shelf delta deposit, is incredibly productive with excellent overlying marine sealing shales. Rapidly deposited distal-delta front, hyperpycnal turbidites, are found in core as sharp-based, very fine-grained sandstone beds, (~ 1-2 ft) surrounded by muddy, burrowed siltstone. More proximal to the delta front, channel-mouth-bar facies are composed of fine-grained sandstone, show lowangle, planar stratification and ripple-laminated, fine-grained sandstone. Proximal fluvial facies, found north of the Louisiana-Mississippi state line are very coarse-grained, poorly sorted and abandon upward into mottled thick soil horizons.

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