The Anacacho Limestone represents an anomaly in the Gulfian-age rocks of Texas. Like the Austin Chalk that it unconformably overlies, the Anacacho is a limestone in a section dominated by terrigenous elastics and mudrocks; unlike the Austin Chalk (which is extensive throughout the margin of the Gulf Basin), the Anacacho is a small carbonate bank that extends less than 96 mi (160 km) along an east-west trend on the flanks of the Uvalde Salient. The formation thins perceptibly to the east toward San Antonio, where it is replaced by rocks of the Taylor Group. The formation reaches its maximum thickness on the flanks of the Uvalde Salient, and terminates abruptly at the western edge of the Anacacho Mountains. West of this termination the Anacacho is replaced by the Upson and San Miguel Formations.
From the Nueces River, west of the Uvalde Salient, westward to the Anacacho Mountains, the limestone outcrop is continuous for approximately 28 mi (46 km). The width of the outcrop varies from 2.4 mi (4 km) to 9 mi (15 km). East of the Uvalde Salient, outcrops of the Anacacho Limestone are discontinuous and scattered. Much of the section is either covered by alluvium or is lost along faults of the Balcones Fault Zone (Bureau of Economic Geology, 1974). This section, from Blanco Creek eastward to San Antonio, is approximately 60 mi (100 km) in length. However, outcrops in this section are limited in length from a few miles to several hundred feet. Exposures are mostly along
Figures & Tables
South-Central Section of the Geological Society of America
One of six volumes generated by each GSA section for the Decade of North American Geology (DNAG) project, this Centennial Field Guide contains descriptions of 100 sites or site clusters representing outstanding geologic locations in Arkansas, Kansas, Oklahoma, and Texas.