Pg. 530, 700-727. Gueydan group. Miss Ellisor has identified about 80 typical Vicksburg species of Foraminifera from lower Oligocene subsurface strata of Texas. The Oligocene beds above this Vicksburg zone carry fauna of younger age and constitute a major part of Oligocene section in Texas. The name Vicksburg group is therefore likely to be misleading. Gueydan group is proposed to designate all strata between Fayette formation (Eocene) and Oakville formation (Miocene). Gueydan of Bailey (applied to the clays and tuffs of southwestern Texas now referred to Catahoula) has been dropped in favor of older name, and Gueydan is therefore available and appropriate to apply to all strata between Fayette below and Oakville above. In East Texas the group comprises only Catahoula formation. In southwestern Texas it is divided into Frio formation below and Catahoula formation above. In subsurface sections in deep wells along the coast it is divided into (descending): Catahoula (lower Miocene or upper Oligocene); unnamed subsurface strata of middle Oligocene age (DISCORBIS zone, HETEROSTEGINA zone, and MARGINULINA zone); Frio (middle or lower Oligocene); and subsurface Vicksburg strata (lower Oligocene). The subsurface middle Oligocene strata may be the down-dip extension of lower and middle part of Catahoula formation in outcrop. Age is considered Oligocene and Miocene(?). Recognized in southern Texas Coastal Plain.

Source: US geologic names lexicon (USGS Bull. 896, p. 888).