FIELD AND LABORATORY CHARACTERIZATION OF THE ANTLERS FORMATION AND AQUIFER IN SOUTH-CENTRAL OKLAHOMA

The Cretaceous-age Antlers Formation crops out in several counties north of the Texas border in southern and southeastern Oklahoma. The Antlers is composed of sands, conglomerates, clays, and limestones that lie unconformably over Paleozoic rocks. The formation creates the Antlers Aquifer, the fourth largest aquifer in Oklahoma in terms of storage volume. Because of its high permeability and adequate recharge, the Antlers is important to several municipalities that depend on the aquifer for water. The soils in the area are conducive for heavy vegetation growth, obscuring most of the formation on the surface, making a field study of the Antlers difficult. Since 1992, there have been no hydrogeologic investigations of the aquifer. It is the goal of this study to examine the geologic controls on the aquifer‘s hydraulic properties in Marshall, Johnston, and Carter Counties. Field characterization of the formation indicates that the Antlers is a unconsolidated sand dominated formation with varying percentages of silt and clay. The specific lithologies of outcrops differ spatially, even in nearby locations. This makes it difficult to identify trends in the study area. Laboratory characterization used mathematical techniques to calculate the hydraulic conductivity by determining the finest 10% of sediments (d₁₀). Sieve analysis confirms that d₁₀ has a range of .03mm to 4mm. These values suggest that the hydraulic conductivity of the Antlers Aquifer material would be from 1x10^-7 to 4x10^-3 cm/sec.