Abstract: Delineation of Delta Types: Norias Delta System, Frio Formation, South Texas

By

Edward A. Duncan

The Norias delta system was the major depositional component of the Frio Formation, South Texas. The Norias was an expansive, sandy, predominantly progradational complex fed by the updip Gueydan fluvial system. This depositional complex effectively filled the Rio Grande Embayment of South Texas by the end of Frio deposition. Norias deltaic sedimentation was probably initiated during the early rise in sea level following a lowstand. The delta system was flanked by time equivalent depositional systems including a northerly strandplain and to the south possibly a delta system in northern Mexico. Incorporated within the complex body of the generally progradational sequence, a well defined evolution of Norias delta types can be documented through the time of Frio deposition. Early Norias deltas developed a strongly dip-oriented lobate geometry interpreted as reflecting a high constructive fluvially dominated regime. Middle Norias deltas continued to be generally high constructive lobate in style, but evidence for significant strike reworking of deltaic sediments can be inferred based on development of a north flanking strandplain system. Late Norias deltas were high destructive wave dominated features. Essentially the Norias delta system had evolved into a broad alluvial plain feeding a strandplain with little physiographic expression of a delta lobe.

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