Geologic units in Wilcox county, Alabama

Alluvial, coastal and low terrace deposits (Holocene) at surface, covers 26 % of this area

Varicolored fine to coarse quartz sand containing clay lenses and gravel in places. Gravel composed of quartz and chert pebbles and assorted metmorphic and igneous rock fragments in streams near the Piedmont. In areas of the Valley and Ridge province gravel composed of angular to subrounded chert, quartz, and quartzite pebbles. Coastal deposits include fine to medium quartz sand with shell fragments and accessory heavy minerals along Gulf beaches and fine to medium quartz sand, silt, clay, peat, mud and ooze in the Mississippi Sound, Little Lagoon, bays, lakes, streams, and estuaries.

Midway Group; Clayton Formation (Paleocene) at surface, covers 16 % of this area

White to yellowsih-gray argillaceous limestone occurs in the upper part (McBryde Limestone Member): the lower part is medium-gray fossiliferous calcareous silt, glauconitic sand and thin beds of sandy limestone and calcareous sandstone (Pine Barren Member). At the base of the formation in southeast AL is a gravelly medium to coarse sand containing clay pebbles. The formation thins west of Wilcox County and westward from Thomaston in eastern Marengo County is mapped with the Porters Creek Formation. The formation is generally deeply weathered and fresh exposures are rare. In western areas exposures consist of weathered white to yellowish-gray argillaceous, fossiliferous sandy limestone, ferruginous sand, and fossiliferous sandstone. In eastern areas exposures consist of residual accumulations of chert boulders, moderate-reddish-orange sand, and clay containing masses and thin layers of iron minerals (limonite-goethite).

Wilcox Group; Nanafalia Formation (Paleocene) at surface, covers 13 % of this area

Members of the Nanafalia Formation follow in descending order. Grampian Hills Member - medium-gray massive clay, claystone, sandy fossiliferous clay, and fossiliferous fine sand. "Ostrea thirsae beds" - glauconitic, abundantly fossiliferous, quartzose fine to medium sand. Gravel Creek Sand Member - pale-yellowish-orange to moderate-reddish-brown micaceous cross-bedded fine to very coarse sand containing gravel and clay pebbles in some exposures. Gravel Creek Member is absent locally and near the base may contain thin beds of lignite. Updip deposits in northern Henry County and southern Barbour County include beds of alternating medium-gray and white clay, carbonaceous clay, white and grayish-yellow fine to coarse sand and lenses of bauxite and bauxitic clay. Sand beds commonly are cross-bedded, gravelly, and contain numerous clay pebbles. The sequence of beds is often obscured by weathering and the collapse of beds into sinkholes in the underlying Clayton Formation.

Midway Group; Porters Creek Formation (Paleocene) at surface, covers 13 % of this area

Dark-gray massive plastic clay in western AL with a thin bed of glauconitic shell marl at the top (Mathews Landing Marl Member). Becomes calcareous eastward grading into light-greenish-gray calcareous, micaceous, clayey fine to medium sand, medium-gray sandy, calcareous clay and white to light-gray thin bedded partly clayey, fossiliferous limestone. East of Crenshaw County, owing to lithologic similarity, beds correlative with the Porters Creek are included in the Clayton Formation.

Wilcox Group; Tuscahoma Sand (Paleocene) at surface, covers 12 % of this area

Light-gray to light-olive-gray laminated and thin-bedded carbonaceous silt and clay interbedded with fine sand; thin lignite beds occur locally. Lower part of the formation includes beds of fossiliferous, glauconitic fine quartz sand containing speroidal sandstone concretions, gravel and clay pebbles.

Midway Group; Naheola Formation (Paleocene) at surface, covers 11 % of this area

The Naheola Formation is restricted to western AL and pinches out in western Butler County. Descriptions of the members of the formation follow in descending order. Coal Bluff Marl Member - glauconitic sand, thin-bedded silty clay, and sandy fossiliferous marl; Oak Hill Member - laminated silt, clay, and fine sand; contains a prominent bed of lignite near the top. The Coal Bluff Marl Member in Sumter County and in parts of Marengo County is mostly cross-bedded fine to coarse sand that is indistinguishable from the overlying lower beds of the Nanafalia Formation. Therefore, in these areas, the contact between the two is mapped at the top of the Oak Hill Member of the Naheola.

Selma Group; Ripley Formation (Cretaceous) at surface, covers 5 % of this area

Light-gray to pale-olive massive, micaceous, glauconitic, fossiliferous fine sand; sandy calcareous clay; and thin indurated beds of fossiliferous sandstone.

High terrace deposits (Pleistocene) at surface, covers 2 % of this area

Varicolored lenticular beds of poorly sorted sand, ferruginous sand, silt, clay, and gravelly sand. Sand consists primarily of very fine to very coarse poorly sorted quartz grains; gravel composed of quartz, quartzite, and chert pebbles.

Selma Group; Prairie Bluff Chalk (Upper Cretaceous) at surface, covers 2 % of this area

Very light-gray to light-bluish-gray firm sandy, fossiliferous brittle chalk and grayish-black silty sandy calcareous glauconitic, fossiliferous clay; semi-indurated beds of sandy, clayey limestone are present in some exposures. Abscent locally in parts of Marengo, Dallas and Wilcox Counties where overlapped by the Clayton Formation or eroded. The Prairie Bluff thins eastward from southwestern Lowndes County to northern Pike County where it interfingers with the Providence Sand.

Wilcox Group; Hatchetigbee Formation (Eocene) at surface, covers 0.7 % of this area

Light to dark-gray laminated carbonaceous clay, silt and very fine to fine sand, and cross-bedded glauconitic sand; one or more thin beds of fossiliferous marly glauconitic sand and sandstone occur in the upper part. Near the base is a prominent bed of glauconitic calcareous sand containing abundant fossils and spheroidal to pillow-shaped sandstone concretions (Bashi Marl Member). In parts of southeast AL the upper beds of the Th were either eroded or not deposited and the overlying Tt formation directly overlies the Bashi Marl Member.