Geologic units in McNairy county, Tennessee

McNairy Sand (Cretaceous) at surface, covers 42 % of this area

Predominantly sand, in places interbedded with silty light-gray clays. Fine-grained sand at base, locally contains heavy minerals. Thickness about 300 feet.

Coon Creek Formation (Cretaceous) at surface, covers 19 % of this area

Fossiliferous, micaceous sand, silty and glauconitic; locally fossiliferous sandy clay at base. Siderite concretions common in upper part. Thickness about 140 feet.

Alluvial deposits (Quaternary) at surface, covers 17 % of this area

Sand, silt, clay, and gravel. In flood plain of Mississippi River more than 100 feet thick; in smaller streams generally less than 20 feet thick.

Demopolis Formation (Cretaceous) at surface, covers 10 % of this area

Marl and calcareous clay, light-gray, fossiliferous, locally glauconitic and sandy. Merges northward into sands mapped as Kcc. Maximum thickness 180 feet.

High-level alluvial deposits (Quaternary-Tertiary) at surface, covers 5 % of this area

Iron-stained gravel, sand, silt, and clay; variable in thickness but generally less then 60 feet thick.

Coffee Sand (Cretaceous) at surface, covers 3 % of this area

Loose fine-grained sand, light-gray, sparsely glauconitic, locally interbedded with laminated lignitic clay. Thickness 25 to 200 feet; thins northward.

Midway Group including Porters Creek Clay and Clayton Formation (Tertiary) at surface, covers 2 % of this area

Midway Group - includes Porters Creek Clay - Pale-brown to brownish-gray, massive, blocky clay; locally contains glauconitic sand. Thickness 130 to 170 feet. Also includes Clayton Formation- Glauconitic sand, argillaceous and locally fossiliferous; at base in Hardeman County is an impure fossiliferous limestone. Thickness 30 to 70 feet.

Owl Creek Formation (Cretaceous) at surface, covers 1 % of this area

Sandy clay, greenish gray, glauconitic, fossiliferous; merges northward into unfossiliferous clays and sands. Thickness 0 to about 40 feet.

Sardis Formation (Cretaceous) at surface, covers < 0.1 % of this area

Quartz sand and glauconite sand, argillaceous and locally fossiliferous. (Mapped with Kcc north of Beech River.) Maximum thickness 70 feet.

Claiborne and Wilcox Formation (Tertiary) at surface, covers < 0.1 % of this area

Irregularly bedded sand, locally interbedded with lenses and beds of gray to white clay, silty clay, lignitic clay, and lignite. Thickness more than 400 feet.