Geologic units in Escambia county, Alabama

Miocene Series undifferentiated (Miocene) at surface, covers 56 % of this area

Moderate-yellowish-orange thin-bedded to massive fine to coarse sand, gravelly sand, thin-bedded to massive clay and sandy clay. Clays are plastic in part. Limonite pellets occur in places along clay-sand contacts. Gravel is composed of quartz and chert granules and pebbles. Locally the upper part of the unit is Pliocene in age.

Citronelle Formation (Pleistocene-Pliocene) at surface, covers 25 % of this area

Moderate-reddish-brown deeply weathered fine to very coarse quartz sand and varicolored typically mottled lenticular beds of clay and clayey gravel. Limonite pebbles and lenses of limonite cemented sand occur locally in weathered exposures. Gravel is composed of chert and quartz pebbles.

Alluvial, coastal and low terrace deposits (Holocene) at surface, covers 18 % 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.

Claiborne/Jackson Group; Residuum (Eocene-Oligocene) at surface, covers 0.6 % of this area

White to moderate-reddish-orange locally mottled sandy clay and residual clay with scattered layers of gravelly medium to coarse sand, fossiliferous chert and limestone boulders and limonitic sand masses. Derived from solution and collapse of limestone in the Jackson Group and Oligocene Series and the slumping of Pliocene and Miocene sediments.

High terrace deposits (Pleistocene) at surface, covers < 0.1 % 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.

Oligocene Series undifferentiated (Oligocene) at surface, covers < 0.1 % of this area

Descriptions of the units of the Oligocene Series follow in descending order. Paynes Hammock Sand - locally fossiliferous, calcareous, argillaceous medium to coarse sand; pale-blue-green clay; and thin-bedded sandy limestone; exposed at Paynes Hammock and at St. Stephens. Chickasawhay Limestone - white to yellowish-gray fossiliferous, glauconitic limestone and soft marl. Byram Formation includes three members in descending order: Bucatunna Clay Member - dark, bentonitic, carbonaceous, sparsely fossiliferous clay and greyish-yellow sand; unnamed marl member - light-grey to yellowish-grey sandy, glauconitic , fossiliferous marl; Glendon Limestone Member - irregularly indurated coquinoid and crystalline limestone, weathering to indurated rock containing large tubular cavities, locally known as 'horsebone'. Marianna Limestone - white to yellowish-grey soft, porous, very fossiliferous limestone. Forest Hill sand - dark-greenish-grey carbonaceous clay with lenses of glauconitic fossiliferous sand; extends eastward from MS into Choctaw, Clarke and Washington Counties. Red Bluff Clay - greenish-gray calcareous clay locally containing selenite crystals, yellowish-grey glauconitic, fossiliferous limestone; and light-gray silty clay with interbeds of sand (Forest Hill equivalent); from Tombigbee River eastward grades into glauconitic fossiliferous limestone equivalent to the Bumpnose Limestone. Bumpnose Limestone - very light-gray to yellowish-gray chalky, subcoquinoid, glauconitic, argillaceous, fossiliferous limestone; intertongues with Red Bluff Clay in vicinity of the Alabama River and is readily differentiated eastward from the Sepulga River.

Jackson Group undifferentiated (Eocene) at surface, covers < 0.1 % of this area

The units of the Jackson Group are the Yazoo Clay and Crystal River and Moodys Branch Formations. Descriptions of the members of the Yazoo Clay follow in decending order. Shubuta Member - in western Alabama consists of light-greenish-gray to white plastic fossiliferous, calcareous clay containing irregular calcareous nodules. From the Tombigbee River eastward the Shubuta becomes more calcareous and grades into massive clayey glauconitic limestone. Eastward from the Alabama River, equivalent beds grade into the Crystal River Formation. Pachuta Marl Member - light-greenish-grey glauconitic, fossiliferous clayey sand and sandy limestone traceable from western Alabama eastward to Covington County where it grades into the Crystal River Formation. Cocoa Sand Member - yellowish-gray firm calcareous, fossiliferous fine to medium sand or sandy limestone or greenish-grey micaceous, calcareous, very clayey sand. Calcareous and clayey sand equivalent to the Cocoa is traceable from western Alabama to the Conecuh River area. North Twistwood Creek Clay Member - greenish-gray plastic calcareous, sparsely fossiliferous, blocky massive clay; grades into Crystal River formation in southeast AL. Crystal River Formation - white to yellowish-grey medium-grained to coquinoid limestone that is soft and chalky to compact and brittle; principally in southeastern AL but interfingers westward with members of the Yazoo Clay. Moodys Branch Formation - greenish-gray to pale-yellowish-orange glauconitic, calcareous, fossiliferous sand and sandy limestone; underlies the Yazoo Clay and the Crystal River Formation.