22 Interstate Stratigraphic Correlation: A Practical Geology Session

Primarily a hands-on display of core and samples with posters, and talks, to facilitate interstate correlation. Concepts covered are related to interstate correlation problems in stratigraphy—mapping, source rocks for REE minerals, geochronology, and regolith.

Tuesday, 10 March 2026
10:30 AM - 12:00 PM
RCC, 103

High-Resolution Dating of Waccamaw Formation Subunits via Correlation to Global δ18O Curves

Paper number: 22-2
Program: Technical Sessions
Time: 11:10 AM – 11:30 AM

Authors

Abstract

The Waccamaw Formation is a Plio-Pleistocene marl with pockets of limestone found in the coastal plain of the Carolinas between the Cape Fear Arch and Georgetown. It is divided based on fauna into two informal subunits (upper and lower). These each include multiple small transgressive-regressive cycles within the larger transgressive pulses, likely corresponding to the ~40 ka Milankovitch cycles.

There is ongoing debate on the exact dating of many Carolinian Neogene units, partly due to a lack of radioisotopes. Strontium dating is usable on them, however, Strontium can be contaminated by freshwater, and thus should be supported by other dating methods. Uranium/Helium dating of Floridian units and correlation of Carolinian units to them is among the simplest options for dating. The Caloosahatchee Formation and the Nashua Formation are clearly contemporaneous with the Waccamaw Formation on the basis of numerous shared index fossils; all three also have faunally-differentiated upper and lower units. The Caloosahatchee has been dated using 238U/4He on corals to 2.53-1.80 Ma. The Caloosahatchee-overlying Bermont Formation has been reliably dated to falling within 1.78-1.0 Ma and including 1.6 Ma. Thus, the Waccamaw should fall within the age range of about 2.5-1.6 Ma. Prior to this study, no sites were known with extensive upper Waccamaw Formation section that had not experienced any winnowing of smaller specimens. The SC Rock Goretown Mine in Horry County preserves this, allowing for detailed paleoenvironmental reconstruction of successive beds. These can be turned into an approximate sea level curve for the site and combined with approximate curves from lower Waccamaw sites to match these curves to global δ18O curves. This shows an extremely close match between the lower Waccamaw and the sea level variation 2.43-2.09 Ma, and the upper Waccamaw to 2.06-1.74 Ma.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411620

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