GEOLOGIC MAPPING OF PORTIONS OF THE MYRTLE BEACH AND OCEAN FOREST 7.5-MINUTE QUADRANGLES: EDMAP 2002

The purpose of this ongoing USGS-funded EDMAP study is to create a detailed geologic map of the Myrtle Beach, South Carolina area and to obtain a better understanding of the depositional environments and the geologic history of the region. Located in the lower Coastal Plain of the northeast part of South Carolina and containing portions of both the Myrtle Beach and the Ocean Forest 7.5 minute quadrangles, the study area also includes onshore and offshore near-surface stratigraphic deposits. A similar study has been conducted adjacent to the southern boundary of this study (Moses et al., 2003) and is a part of the overall EDMAP project at Coastal Carolina University.

Geomorphically, the area contains portions of the Pleistocene Jaluco and Myrtle Beach barriers. The surficial deposits beneath these landforms have most recently been mapped as entirely Socastee Formation (Owens, 1990) and are approximately 202,000 to 230,000 yrs old (McCartan et al., 1982). Beneath these deposits and in offshore exposures, truncated dipping and folded Cretaceous strata are common. Because this study focuses on large-scale (small area) mapping, it is possible to study boundaries of surficial units with more detail than in previous programs.

In this study the Socastee Formation is divided into two units resurrecting the terminology of DuBar (1968). The first lithostratigraphically distinct unit is a sandy deposit named the Jaluco Formation (DuBar, 1968). The sandy unit was part of an old barrier island system. The second is a muddy unit, which is the Socastee Formation. The mud unit was part of an old backbarrier system and fills the lowland between the Myrtle Beach and Jaluco barrier ridges. The section of beach included in the area is primarily Holocene with a large section of recent fill that was placed there as part of the beach re-nourishment project in the late 1990s.