Geologic units in Marlboro county, South Carolina

Duplin Formation (Pliocene) at surface, covers 35 % of this area

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

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

One of the older coastal terrace sequences in the Carolinas. Equivalent to Windsor Fm.

Alluvial Valley Swamp (Quaternary) at surface, covers 15 % 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.

Cape Fear/Eutaw Formations (Cretaceous) at surface, covers 11 % of this area

Poorly sorted clayey sand and gravel deposited in delta-dominated fluvial- and restricted marine environments. Unit is characterized by an abundance of smoky quartz gravel, feldspar, monazite, and garnet typically concentrated in placer deposits. Generally non-marine from North Carolina to central Georgia but contains shallow-water delta-front deposits in western Georgia.

Penholoway Formation (Pleistocene) at surface, covers 8 % 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.

Peedee Formation - Black Creek Group, undivided (Cretaceous) at surface, covers 7 % of this area

Peedee Formation - Black Creek Group, undivided

Socastee Formation (Pleistocene) at surface, covers 1 % of this area

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

Flat Swamp Formation (AKA Flat Swamp Member of Cid Formation) (Ordovician to Neoproterozoic) at surface, covers 0.3 % of this area

Crystal and lithic metatuff of rhyolite to rhyodacite composition

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

Sand, sandstone, and mudstone, gray to pale gray with an orange cast, mottled; clay balls and iron-cemented concretions common, beds laterally discontinuous, cross-bedding common.

Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic) at surface, covers < 0.1 % of this area

Thin to thick bedded; bedding plane and axial-planar cleavage common; interbedded with metasandstone, metaconglomerate, and metavolcanic rock.

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

Clay, gray to black, lignitic; contains thin beds and laminae of fine-grained micaceous sand and thick lenses of cross-bedded sand. Glauconitic, fossiliferous clayey sand lenses in upper part.

Yorktown Formation and Duplin Formation, Undivided (Tertiary) at surface, covers < 0.1 % of this area

Yorktown Formation: fossiliferous clay with varying amounts of fine-grained sand, bluish gray, shell material commonly concentrated in lenses; mainly in area north of Neuse River. Duplin Formation: shelly, medium- to coarse-grained sand, sandy marl, and limestone, bluish gray; mainly in area south of Neuse River.