William R. Doar | USGS Science

USGS2026

Last interglacial relative sea-level changes at Myrtle Beach, South Carolina

The peak of the Last Interglacial (Marine Isotope Stage 5e; ∼128–117 ky) provides a valuable analogue for understanding sea level rise under future warming scenarios. Relative sea-level (RSL) indicators from passive margins are essential for constraining past sea levels and refining glacio-hydro-isostatic adjustment (GIA) models, thereby enhancing projections of future sea-level change and associated regional impacts. In this study, we present new luminescence ages from 17 sediment samples in outcrops along the Intracoastal Waterway near Myrtle Beach, South Carolina (USA). The sampling sites lie between a series of paleo beach ridges preserved as successive off-lapping deposits, the scarp toes of which have been previously identified as indicators of the maximum sea level during each associated sea-level highstand. Our results include ages corresponding with Marine Isotope Stages (MIS) 7 (∼200 ka), 5e (∼125 ka), 5c (∼105 ka), and the last deglacial period (∼14–12 ky). These new sea-level indicators, supplemented by the existing scarp elevation data, suggest that relative sea level in this region reached similar levels during MIS 5e and MIS 5c/5a. Comparison with GIA model outputs shows that more models fit our observations (from all time periods) when a peak GMSL of less than 5 m above present during MIS 5e is assumed, which makes those scenarios more likely.

South Carolina↗

USGS2019

Geology of the Hardeeville NW Quadrangle and parts of the Brighton and Pineland Quadrangles, Jasper County, South Carolina

Introduction This publication portrays the geology of the Hardeeville NW quadrangle and parts of the Brighton and Pineland quadrangles that are within Jasper County, South Carolina. The study area is located in the Atlantic Coastal Plain province, approximately 50 to 70 kilometers (km) inland from the coast. The data are compiled from geological field mapping, light detection and ranging (lidar) elevation data, cores, optically stimulated luminescence ages, radiocarbon ages, and biostratigraphic interpretations. Most of the study area is occupied by the valley of the Savannah River, and exposures of geologic units are very limited. Traditional geologic mapping in this area is difficult because of limited access, subdued topography, extensive swamps, and abundant vegetation. The Savannah River flows predominantly southeast, and forms most of the border between the States of South Carolina and Georgia. The river is approximately 483 km long and has a total drainage area of approximately 15,850 square km. Although upstream tributaries drain the southeastern side of the Appalachian Blue Ridge province, the Savannah River begins in the Piedmont province and then flows across the Atlantic Coastal Plain province to the Atlantic Ocean. For much of its extent, the modern channel of the Savannah River is located on the southwestern side of the river valley, and the southwestern bank of the valley is the active cut bank. Within the study area, the valley of the Savannah River trends southeast and is relatively straight. The valley has relatively low relief, although the southwestern valley wall is steeper and has greater relief than the northeastern valley wall. Elevations within the valley mostly range from 3 to 15 meters (m) above sea level, whereas elevations on the high terrace that forms the eastern margin of the Savannah River valley are 15 to 20 m above sea level. The width of the valley is 6 to 7 km in the northern part of the study area and expands to 10 to 12 km farther south. The modern river channel occupies the southwestern side of the valley, and some modern (active) creeks enter the river from the west. Sand hills and low-relief terraces are present to the east of the modern river channel, and the eastern side of the valley is characterized by abandoned meandering and linear channels. Fan-shaped deposits of sand and mud are present where relict (inactive) channels enter the eastern side of the valley. Abandoned meandering channels of low relief (<3 m) are also present to the east on the high terrace (>15 m elevation) that forms the eastern margin of the Savannah River valley. Within the study area, most of the Savannah River valley is covered by alluvial wetland community vegetation dominated by cypress and tupelo trees, although sand hills within the valley are covered by xeric sand community vegetation dominated by pine trees.

South Carolina↗