--> ABSTRACT: Petrology of Eocene Rocks, Southeastern Georgia Coastal Plain, by Paul A. Thayer and James A. Miller; #91036 (2010)
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Petrology of Eocene Rocks, Southeastern Georgia Coastal Plain

Previous HitPaulTop A. Thayer, James A. Miller

Study of cores from a U.S. Geological Survey test well in Wayne County indicates that Eocene strata represent an overall shallowing-upward, clastic-carbonate sequence. The 1,397-ft (426-m) Eocene section is divided into three units: unnamed lower Eocene rocks, middle Eocene (Claibornian) Lisbon and Avon Park Formations, and upper Eocene (Jacksonian) Ocala Limestone.

Lower Eocene rocks are 141 ft (43 m) thick and consist of sandy, calcareous shale intercalated with glauconitic, sandy wackestone and packstone. Terrigenous quartz, feldspar, and mica form 15-30% of whole-rock volume. Carbonate allochems are foraminifers and abraided echinoderm and molluscan fragments. Lower Eocene strata were deposited in an open-marine environment of shallow to moderate depth.

Middle Eocene strata are 947 ft (289 m) thick and consist of a lower glauconitic sandy clay with thin stringers of glauconitic limestone (Lisbon Formation) disconformably overlain by Avon Park carbonates. Avon Park Formation is a sandy, glauconitic wackestone-packstone that grades upward into skeletal packstone, grainstone, and crystalline dolomite. Dominant allochems are foraminifers and bryozoans with subordinate mollusks, echinoderms, and algae. Nodular chert, wispy argillaceous seams, and thin lignitic layers are common. The Avon Park was deposited on a shallow, warm-water carbonate bank. Lisbon Formation accumulated in deeper water that had a higher influx of terrigenous clastics. Dolomite formed by replacement of micrite-rich limestone; recrystallization occurred in a subsurface shoreline environment by meteoric water-sea water mixing.

The Ocala Limestone is a skeletal grainstone and packstone with minor wackestone and crystalline dolomite. It is 309 ft (94 m) thick and contains abundant larger foraminifera (Asterocyclina sp., Lepidocyclina sp.), bryozoans, mollusks, and algae. Glauconite and terrigenous quartz are rare. The Ocala was deposited in warm, clear water on a shallow carbonate bank.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.