Geologic units in Calhoun county, South Carolina

Huber/Lisbon/Barnwell Formations, undivided (Eocene) at surface, covers 33 % of this area

Poorly to well sorted sand, clay and carbonates deposited in delta-dominated fluvial- and open-marine environments. Unit is characterized by commercial kaolin bodies in older strata from westernmost South Carolina to central Georgia. Younger strata are cyclic marine deposits which deeper water facies exposed in western Georgia. Carbonate facies are locally mined in western Georgia for agricultural lime.

Duplin Formation (Pliocene) at surface, covers 23 % of this area

Coastal terrace of Carolinas. Pliocene equivalent to Yorktown. Deeply weathered.

Neogene strata (undifferentiated) (Neogene) at surface, covers 14 % of this area

Poorly sorted clayey sand and gravel deposited in a fluvial environment in South Carolina but becoming more fluvio-marine in Georgia. Unit is characterized by insitu weathered feldspar and an abundance of quartzite gravel and cobbles.

Black Mingo/Clayton Formations (Tertiary) at surface, covers 13 % of this area

Poorly to well sorted sand and clay deposited in delta-dominated fluvial- and shallow marine environments. Older parts of unit are characterized by an abundance of feldspar and local sillimanite. Unit is generally delta plain and lagoon deposits in South Carolina becoming open marine calcareous sand and clay in western Georgia. In central Georgia, unit contains an abundance of commercial kaolin deposits formed in lower delta plain environments.

Peedee Formation (Cretaceous) at surface, covers 7 % of this area

Peedee Formation

Alluvial Valley Swamp (Quaternary) at surface, covers 7 % of this area

Unconformable on all underlying units, fluvial sand and gravel at base, grading upwards into fine sands and silts, local peat. May be overrun with recent sediments from forest cutting and agriculture.

Black Creek/Cusseta/Blufftown Formations (Cretaceous) at surface, covers 3 % of this area

Moderately to poorly sorted sand and clay deposited in delta-dominated shallow marine environments. Unit is characterized by sands containing locally abundant (F-VC grained) tourmaline and (F-VC grained) muscovite with some monazite and garnet. Clay layers are also common and some lower delta plain deposits form commercial kaolin bodies. Generally very restricted marine in eastern Georgia becoming more open marine to the east and west.