The Geology of Texas - Vol. 1 - pages 461-462

PECAN GAP CHALK

 Nomenclature.—This chalk was named by Stephenson (1530, p. 156) in 1919. The type locality is near Pecan Gap, Delta County, in a cut of the Gulf, Colorado and Santa Fe Railway ½ mile east of Pecan Gap. Other good localities are on the Cox place 3 miles east by south of Wolfe City; and on the Jim Burnett farm, one mile west of Kellog, Hunt County (see also 1511d).

 Areal outcrop.—The Pecan Gap typically consists of about 50 feet of bluish-gray, slightly bituminous, more or less argillaceous and sandy chalk, weathering to a light gray and white. The lower 10 feet is a blue massive chalk, weathering light gray and white, becoming sandy and containing many phosphatic casts of mollusca in the lower 2 or 3 feet. At the type locality the basal chalk is glauconitic, contains numerous phosphatic nodules, and rests upon the somewhat irregular surface of the top of the Wolfe City sand, which is here a soft, fine-grained argillaceous sand. However at a locality ¾ mile north and ¾ mile west of Rockwall, the lowest 3 feet of the Pecan Gap, which consists of hard blue chalk weathering white and changing to calcareous clay at its base, rests without irregularity on dark argillaceous sand of the Wolfe City. The thickness of the Pecan Gap is here not more than 40 feet.  Southwards the Pecan Gap thins. At a locality on the north side of Mustang Creek 3.1 miles N. 30° W. of Crandall, Kaufman County, the upper part of the Pecan Gap is a hard chalky marl, in part practically chalk (391, p. 44).

 Cephalopods reported from the Pecan Gap in Delta and Hunt counties are: Baculites asper Morton?, Baculites spp., "Turrilites" (2 species), Scaphites (3 to 4 species), and Nautilus sp. Other fossils are: Hemiaster aff. lacunosus Slocum, Gryphaea vesicularis Lamarck var., Ostrea plumosa Morton, Exogyra ponderosa Roemer, E. ponderosa var. erraticostata Stephenson, E. costata Say (a small, non-typical form), Anomia argentaria Morton, Pecten quinquecostatus Sowerby, Cardium spillmani Conrad, Liopistha protexta Conrad?, "Radiolites" austinensis Roemer, and several others.

 Fossils from the Annona and Pecan Gap chalks are listed by Thomas and Rice (1601c). Some Taylor and Austin chalk samples contain "spherical bodies" (p. 365).

 The Pecan Gap-Wolfe City contact is unconformable in Hunt and Collin counties. At a locality 2.6 miles east-southeast of Kingston, Hunt County, the base of the Pecan Gap chalk is highly phosphatic, contains many phosphatic casts of fossils, and many borings filled with chalk extend to a depth of 2 feet into the underlying greenish-gray marine sand. In Bear Creek, ½ mile south of Lavon, Collin County, the base of the Pecan Gap chalk, marked by a thin line of phosphatic casts and nodules, cuts across the edges of the underlying Taylor clay strata (1539, pp. 1330-1331).

 The base of the upper Taylor marl overlying the Pecan Gap chalk contains, at a locality 3 ¾ miles southwest of Clarksville, Red River County, a few smoothly water-worn quartz pebbles (1539, p. 1331). Additional Pecan Gap localities in Red River County are recorded by Spofford (1511d).