NEW OBSERVATIONS ON EOCENE STRATA AND MACROFOSSILS AT PLANT VOGTLE, BURKE COUNTY, EASTERN GEORGIA

Excavations for Unit 3 and Unit 4 at Plant Vogtle, Burke County, Georgia exposed Eocene strata last seen here more than 20 years ago (Huddlestun and Hetrick, 1986). The base is in the upper 8 to 10 feet of the middle middle Eocene, informal Blue Bluff unit. The lowest beds of Blue Bluff seen are hard, grayish green, fossiliferous, calcareous siltstone to quartz sandstone with the oyster Cubitostrea sellaeformis, two species of turritellids, other mollusks, and acorn and scalpelloid barnacles. Abundant tubular-conical cnidarian (scyphozoan?) polyps and fewer acorn barnacles coat pieces of a lignitic driftwood log from the Blue Bluff. The uppermost 4 to 6 feet of the Blue Bluff are altered to white or light gray by waters percolated down from the partly karstic, informal Utley unit, which unconformably overlies the Blue Bluff at planar to contorted or burrowed (Glossifungites ichnofacies) contacts to 18 inches deep. The Utley is white to pale tan, glauconitic, moldic, fossil-rich packstone to soft, brown or green, silt and clay residue and is up to 12 feet thick but is dissolved to absent locally. The Utley unconformably underlies the calcareous Griffins Landing Member of the upper Eocene Dry Branch Formation with sharp to irregular contact. The Utley fauna includes a coral, a barnacle, and 15 molluscan species including Bathytormus protextus, Callista aequora, Glycymeris idonea, Linga pomilia alveata, Nucula magnifica, Doliocassis nupera, Neverita limula, and Ranellina maclurii, which correlate with the upper middle Eocene Gosport Sand in Alabama and the informal Orangeburg District bed in South Carolina. Other characteristic Gosport taxa include Athleta sayana, Levifusus trabeatus, and Crepidula lirata (Crepidula is not known from overlying Jackson or Vicksburg groups). Unconformable lower and upper contacts and the Gosport-equivalent molluscan fauna confirm the Utley as a depositional sequence separate from the Blue Bluff.

Hard, calcareous limestone with oyster Crassostrea gigantissima, other mollusks, acorn and scalpelloid barnacles, and other fossils is at the base of Griffins Landing Member and in bioherms in overlying quartz sand. Higher quartz sand without bioherms is Irwinton Sand Member of the Dry Branch Formation and underlies red, clayey quartzose, upper Eocene Tobacco Road Sand at a granule and pebble bed with minor disconformity.