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Mass-Transport Mechanisms and Resulting Deposits in a Deepwater Carbonate Debris Apron: Lower Cretaceous Tamabra Formation, Poza Rica Field Area, Mexico

Loucks, Robrt G.*1; Kerans, Charles 1; Janson, Xavier 1
(1) The Bureau of Economic Geology, The University of Texas at Austin, Austin, TX.

A large carbonate debris apron developed on the west side of the Lower Cretaceous Tuxpan Platform in water depths up to 1,000 m. The transition from the shallow-water, reef-rimmed shelf to the debris apron was abrupt, with slope angles up to 35°. The apron extended more than 20 km from the shelf edge. Near the platform, the apron is approximately 400 m thick, and at the basinward-most edge of data control it is approximately 150 m thick. Density flows and suspension processes were the dominant mechanisms of sedimentation. Accumulations with cobble- to boulder-sized carbonate lithoclasts were deposited by debris and mud flows. Matrix strength was the dominant grain-support mechanism, but pore pressure and buoyancy also contributed. Deposits of this type include clast-bearing lime mudstone and carbonate breccia, with matrix texture ranging from carbonate mud dominated to carbonate grain dominated. Coarse-grained skeletal-grain accumulations were deposited by concentrated and hyperconcentrated density flows. Dispersive pressure was the dominant grain-support mechanism, but buoyancy also contributed. Deposits include coarse-grained packstone to grainstone and rudstone. Grains are of shallow-water origin. Some of the fine-grained carbonate grainstones are associated with deposition by turbidity currents and show components of Bouma sequences. Turbulence was the dominant grain-support mechanism for these flows. Lithofacies group into packages that appear to correspond to stages of relative sea-level changes. Debris-flow deposits dominated during the transgressive to early highstand stages, and concentrated to hyperconcentrated density-flow deposits dominated during stillstand or early, slowly relative falling of sea level.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California