Geologic units in Barnwell county, South Carolina

Neogene strata (undifferentiated) (Neogene) at surface, covers 46 % 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.

Huber/Lisbon/Barnwell Formations, undivided (Eocene) at surface, covers 46 % 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.

Alluvial Valley Swamp (Quaternary) at surface, covers 4 % 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.

Penholoway Formation (Pleistocene) at surface, covers 2 % of this area

Similar to Cape May, broad lateral extent underlying terraces in the Carolinas; swamps and ridges on terrace surface were originally barrier islands and back bays. Superimposed on these landforms are swarms of Carolina bays.

Chenier plain and deltas of Suwannee & Chattahoochie Rivers (Holocene) at surface, covers 1 % of this area

Chenier plain and deltas of Suwannee & Chattahoochie Rivers

Socastee Formation (Pleistocene) at surface, covers 0.5 % of this area

Low coastal formation in Carolinas like Penholoway but younger and lower in altitude.

Duplin Formation (Pliocene) at surface, covers 0.3 % of this area

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