ABSTRACT: Ingleside Barriers on East Texas- SW Louisiana Pleistocene Coast? Old Assumptions - New Evidence

OTVOS, ERVIN G., and WADE E. HOWAT

In sharp contrast with our study results on southwest Texas Pleistocene barriers, detailed core and field data from landforms earlier mapped in the Galveston Bay-Sulphur area of Texas-SW Louisiana as Ingleside indicated that they were not barrier ridges. Fannett Barrier, the sole exception, consists of subdued, eastward-concave ridge arcs on an old embayment, perpendicular to the assumed "barrier trend". The Fannett ridges are composed of muddy sand. Correlatives of the underlying Sangamonian fossiliferous muddy nearshore deposits (Biloxi Fm.) and well sorted shoal sands occur at shallow depths under alluvial Prairie (Beaumont) deposits. Locally they are exposed in the land surface. A pre-Biloxi estuarine-nearshore marine unit also occurs at shallow depth in the Houston Ridge-Calcasieu Lake area.

On aerial photos between Smith Point-Pine Island and in Orange County, Texas, close faint (joint?-) lineaments very superficially mimic barrier ridge trends. At Smith Point-Pine Island, the alleged barrier deposits represent exposed nearshore fossiliferous and shoal sand facies, not blanketed by Beaumont alluvium. Such features, occasionally oblique to the shore, had been also described as Pleistocene barriers at Vidor, TX, in the Houston Ridge, W and E of Lake Calcasieu, Louisiana, and other locations. Erosional excavation of subdued topographic highs from the Beaumont-Prairie coastal plain alluvium took place along intersecting lineaments, likely of tectonic origin. Most of these numerous landforms are unrelated to shore zone deposits of the Isotope Stage 5, Sangamonian marine highstand.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana