PRELIMINARY TEXTURAL ANALYSIS OF THE ANTLERS SANDSTONE, TAYLOR COUNTY, TEXAS

Preliminary textural analysis of an outcrop of the Antlers Sandstone in Taylor County, Texas shows evidence of multiple high-energy events in a distal distributary channel. Samples were collected from an eight-meter-thick outcrop outside of Abilene, Texas, on Highway 277. The Antlers Sandstone is lower Cretaceous in age and belongs to the Trinity Group. The sandstone is composed of coarse to very coarse sands of moderate sorting. Grains are predominantly sub rounded to rounded quartz. Intermittent pebble-rich horizons are quartzose and exhibit a variety of colors. The sandstone is poorly to moderately cemented with a calcite cement. Iron stain and desert varnish presents throughout the outcrop. Thick units of thin trough cross-beds, dipping southward, dominate the section. One unit exhibits weakly defined herringbone cross-beds. Samples were collected, processed in hydrochloric acid to remove carbonate, dried, and crushed. Samples were sieved using a Ro-Tap, in a 0.5 phi sieve set. The resulting fractions on each sieve were massed. The lower portion of the section contains multiple high-energy events. Each event is characterized by a spike in mean grain-size and lower quality sorting. Mean grain-size, sorting, skewness, and kurtosis values fluctuate dramatically in this zone. The upper portion, of the section, shows more stable textural values as grain-sizes fines and sorting improves. Previous works on the Antlers Sandstone indicate a dynamic, clastic coastal system. The 277 section exhibits predominately channel characteristics. Low mud content and sand-rich sediments, unidirectional trough cross-beds, and scour surfaces are common. The rare appearance of herringbone cross-beds may indicate a period of low river flow in which tidal processes of the adjacent coast altered the current in the channel. Proximity to the coast is supported by other local outcrops containing clear evidence of beach deposition. The outcrop represents a distal distributary channel carrying sediment to the lower Cretaceous Coast.