STRAWN-CANYON (PENNSYLVANIAN) BOUNDARY IN NORTH-CENTRAL TEXAS

The Strawn–Canyon (Pennsylvanian) boundary in north-central Texas is evaluated from surface studies in the Colorado River and Brazos River valleys. Zonation based on fusulinids is the best criterion for defining the boundary. Strawn series is characterized by the genus Fusulina, Canyon series by Triticites. The brachiopod Mesolobus and bryozoan Prismopora, found in pre-Canyon beds, supplement the evidence. Because upper Strawn and lower Canyon units are generally not persistent in the outcrop area, the boundary is placed at three different stratigraphic positions so that locally prominent surfaces, which agree with paleontologic evidence, may be used as the contact. The Strawn-Canyon boundary in the Colorado River valley is considered to be the top of the Capps limestone, which is continuous to the north through Comanche County and most of Eastland County. In the southern part of the Brazos River valley the boundary is placed at the top of the “boulder” bed (of other investigators). This bed, which is present in northeastern Eastland County and southwestern Palo Pinto County, lies about 20 feet above the Capps limestone. It is correlated with, and designated as, the Village Bend limestone of central Palo Pinto County. In eastern Palo Pinto County, the boundary is placed at the base of the Lake Pinto sandstone, which overlies the Village Bend limestone.