OCCURRENCES IN THE SOUTHEASTERN ATLANTIC COASTAL PLAIN OF STRATA CORRELATIVE WITH THE TYPE RHEMS FORMATION (LOWER PALEOCENE) OF SOUTH CAROLINA

In South Carolina, the oldest known Paleocene strata are assigned to the Rhems Formation, which was formally named in 1982 and has its type area in Georgetown County, SC. The type Rhems is composed mainly of mudstone and sandstone and contains a distinct palynomorph assemblage that enables the formation to be distinguished from older and younger strata.

We have recognized strata coeval with the type Rhems at several localities in the Carolinas. In USGS Clubhouse Crossroads Corehole no. 1 (CCC1) in Dorchester County, SC, strata assigned by several authors to the Rhems Formation consist (in ascending order) of a sand-shale-sand-limestone sequence 165 ft thick, but only the lower part is correlative with the type Rhems; the upper part of the sequence assigned to the Rhems in CCC1 evidently correlates in part with the type Lower Bridge Member of the Williamsburg Formation. In the two USGS Clark Middle School coreholes in Orangeburg County, SC, strata correlative with the type Rhems consist of sand and clay about 26 ft thick which unconformably overlie the Cretaceous Sawdust Landing Formation and are unconformably overlain by the Eocene Congaree Formation. In the USGS Kure Beach Corehole no. 1, New Hanover County, NC, the unit assigned to the Beaufort Formation is correlative with the type Rhems and consists largely of siltstone and silty sandstone, is 31 ft thick, overlies the Cretaceous Peedee Formation, and is overlain by the Eocene Castle Hayne Formation.

At several localities on the Atlantic Coastal Plain, strata correlative with the type Rhems are missing, but palynomorph assemblages characteristic of the type Rhems have been found reworked into post-Rhems strata, indicating that the Rhems was once there. For example, in corehole P21TA, in Barnwell County, SC, the lowest preserved Paleocene unit is a black clay containing reworked specimens of a marker species for the type Rhems Formation, a reworked Cretaceous dinocyst species, and several in situ palynomorph species restricted to post-Rhems Paleocene strata. Sparse specimens of a pollen marker species for the type Rhems are also found reworked, along with Cretaceous pollen grains, in the Brightseat Formation of Maryland; because the Brightseat belongs to lower Paleocene calcareous nannofossil Zone NP 3, the type Rhems cannot be younger than NP 3.