ABSTRACT

The Georgetown Formation, of Cretaceous age, is composed of irregularly-interbedded fossiliferous micrite (microcrystalline limestone) and marl beds; they are prolifically burrowed. Beds can be recognized over great distances and are practically synchronous through out their lateral extent, at least in the area of this report.

The Georgetown Formation is divisible into five members. They are, in ascending order, the Duck Creek Member, the Fort Worth Member, the Denton Member, the Weno Member, and the Main Street Member. The Members are lithologically consistent throughout northern Travis County and Williamson and Bell counties, Texas, and they maintain an almost constant thickness, except the upper two members which thin slightly southward. The Formation is approximately 95 feet thick in northernmost Bell County and approximately 70 feet thick at Austin, central Travis County; 75 per cent of this southward thinning is in the Weno and Main Street members.

The Georgetown conformably overlies the Kiamichi Formation in the area of the Round Rock Syncline; it disconformably overlies the Edwards Formation over the Belton High and on the northeastern flank of the San Marcos Arch. The Georgetown is conformably overlain by the Del Rio Formation. Deposition was continuous throughout the time of accumulation of the Georgetown Formation, save for minor interruptions that produced bedding planes.

The Georgetown was deposited in an environment that contained abundant life and no coarse terrigenous debris.