The Geology of Texas - Vol. 1

COMANCHE PEAK FORMATION (including Goodland)

Nomenclature.--This formation was called the "Comanche Peak group" in 1860 by Shumard (1463, pp. 583-585), who placed it correctly below the Edwards ("Caprina") limestone and incorrectly above the Austin chalk. Its type locality is at the famous Indian landmark, Comanche Peak, central Hood County, and the formation is best developed in the Brazos and Trinity valleys

Stratigraphic position and contacts.—Thickness relations indicate that the Comanche Peak is a facies of the Fredericksburg, and may be in part laterally continuous with Walnut below and Edwards above. No adequate zonation allows a check of this assumption. but certainly to the south the rudistid facies ("Edwards") invades all levels of the Fredericksburg group, and therefore is presumably equivalent in part to type Comanche Peak. Both upper and lower contacts of the Comanche Peak appear to be concordant, according to published reports.

Facies.—The Comanche Peak is a chalky-limy facies. To the north it is continuous with the "Goodland" limestone, which is of the same lithology and fossils (1575, p. 256). Throughout central Texas and the Callahan divide, it maintains the same lithology; in the marginal areas (Red River valley, southern Oklahoma, north of Fort Stockton and Kent, at Sierra Prieta), it presumably goes into a marginal sandy phase.

Areal outcrop, local section.—The Goodland limestone, first named and described by R. T. Hill (780, p. 88, 1891; 772. p. 514, 1891) in the Red River valley is the same as the Comanche Peak, because (1) Edwards is defined as consisting of the rudistid facies and similar rock, and does not outcrop north of Fort Worth; and (2) the Goodland contains Oxytropidoceras acutocarinatum, a species which marks the middle and lower parts of the Fredericksburg group. At Goodland (803, p. 217) the limestone is less than 20 feet thick. The rock is fractured, crystalline, whitish limestone, resembling Comanche Peak in lithology, and contains undiagnostic fossils: Engonoceras aff. hilli Böhm, Exogyra texana Roemer, Cerithium bosquense Shumard, and many pelecypods and gastropods.

The easternmost outcrop of the Goodland is north and east of Cerro Gordo, Arkansas, and about 4 miles down Little River from it.  It consists of 50 feet or less or of thick-bedded gray sandy limestone, containing some beds of hard, yellow-gray, calcareous sandstone.  At some horizons, the Goodland beds are notably lenticular: lentils of limestone 6 feet long and a foot thick foot thick, of varying degrees of sandiness, stand at small angles with the normal bedding.  The upper 8 feet of the formation, where exposed, is a less sandy limestone.  The top is a ledge a foot thick, of hard, white limestone, which weathers into cavernous slabs.  The Goodland is overlain by about 20 feet of Kiamichi clay containing Gryphaea navia (392, pp. 15-16).

In Grayson County, the Goodland, overlying 6 feet of marl, shale and thin seams of limestone and shell aggregates, consists of about 15 to 20 feet of hard, white, semi-crystalline limestone, generally in four beds each 4 to 6 feet thick. It weathers by conchoidal flaking, and develops a honey-comb surface by erosion of softer pockets. In Marshall County, Oklahoma, 15 to 20 feet is recorded; in Love County, about 25 feet. It contains Oxytropidoceras aff. supani, pelecypods, and gastropods, including a large smooth oyster some-what like Exogyra americana Marcou. In northern Cooke County, the Goodland is 25 feet thick, in southern Cooke County, 40 feet.  At a variable distance (2 to 16 feet) below the top, there is a horizon of Exogyra plexa Cragin. At a variable level (3 to 9 feet) above the base, a zone of abundance of Gryphaea marcoui is recorded.  Oxy. acutocarinatum is reported throughout the formation. Other fossils are: Remondia robbinsi (White), Protocardia, Pholadomya, Pecten, Turritella, Cerithium bosquense, and Heteraster. The Walnut shell aggregate is absent, and the thin Walnut clay rests on sandy beds containing Gryphaea marcoui and Ostrea crenulimargo Roemer. This aggregation of fossils is not diagnostic, but suggests Comanche Peak, not Edwards.  

The formation thickens, from 42 feet in northern Denton County and 75 feet in southwestern Denton County, to 116 feet near Lake Worth, Tarrant County. The marly limestones and limy marls of the Goodland form large hills on the Clear Fork and West Fork of the Trinity in western Tarrant and eastern Parker counties. Near Benbrook, there are large, richly fossiliferous exposures. At Lake Worth Dam, a complete section shows an alternation of more limy and more marly beds, lying above the massive Gryphea marcoui aggregate capping the Walnut and the base of the Kiamichi clay.  Dipoloceras and Oxytropidoceras range from the bottom to the top of this section.  Local zones (9, pp. 15-31) are probably applicable from this area to the Red River valley.