Aptian Depositional Patterns Influenced by Salt Tectonics, Central East Texas Basin

A. J. Lomando, T. P. Birdsall

Salt tectonics, which lead both directly and indirectly to the formation of paleobathymetric highs, peripheral sinks, and persistent structural highs, strongly influenced carbonate and siliciclastic depositional patterns of the Aptian Rodessa Formation. This study has focused on northern Anderson County, located in the axial portion of what was the broad, shallow East Texas basin shelf during deposition of the Rodessa. Five Louann (Bathonian-Callovian) Salt diapirs were active and had significant impact on Aptian depositional patterns. Concord and Keechi domes were active beginning in the Late Jurassic to Early Cretaceous, creating peripheral salt withdrawal sinks which filled with Cotton Valley and Travis Peak clastics. Continued growth of the initial salt pillows result d in salt withdrawal from the flanks of the pillows and collapse of the overlying sediment limbs. A trend of elongate turtle structure anticlines cored with siliciclastics were thus formed, resulting in structural features which manifested themselves as paleotopographic highs during deposition of the Rodessa. Brushy Creek, Boggy Creek, and Larue domes acted in consort, expanding and adding to the initial Concord and Keechi peripheral sinks during deposition of the early Travis Peak (Hauterivian). Their continued growth during Rodessa deposition led to Aptian-Albian peripheral sinks which formed bathymetric lows (shelf lagoons).

During deposition of the Rodessa, shoreface and inner shelf siliciclastics were ponded landward (west-northwest) of the turtle structure system. The crests of the turtle structures were the focus of ooid and ooskeletal grainstone shoal development. Periodic (short-term) exposure, erosion, and reworking of sediment on these highs are the interpreted reasons for thin grainstone units being preserved on the crests while thicker and better quality reservoir rocks were developed and preserved on the flanks. Tidal channels, incised on the turtle structure systems, and their associated tidal bars and deltas were the sites of active ooid and skeletal grainstone development while also acting as avenues of siliciclastic sand transport from nearshore areas out to the shelf. As a result, channel reas often contain high-energy mixed carbonate-siliciclastic lithologies which were reworked and transported along the seaward side of turtle structures. East and southeast of the turtle structures, around active peripheral sinks, a relative balance between subsidence and carbonate deposition was reached, allowing for the accumulation of relatively thick, porous grainstone-boundstone sequences. The thickness of these sink-rim buildups contrasts markedly with the thin zones associated with the tops of turtle structures where little subsidence was occurring. In the deeper, central portions of the sink, sedimentation was dominated by black, argillaceous mudstones, wackestones, and shales. From sink rim to sink center, this system provides the juxtaposition of reservoir, seal, and potential ource and serves as a stratigraphic play model applicable in many salt basins.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.