Geophysical and stratigraphic analysis of a southeastern salt marsh, North Inlet, SC

Salt marshes are recognized as among the most dynamic, productive and important ecosystems today. This study presents new evidence of a low sea level stand within the North Inlet-Winyah Bay salt marsh system on the South Carolina coast between 4000-6500 yrs BP as well as the first use of high-resolution seismic reflection surveys to map the surficial and sub-bottom geology of this dynamic system. Facies maps based on sediment stratigraphy, lead-210 analyses and radiocarbon dates show the direct impact of sea level on the formation, evolution and stability of a low gradient saltmarsh system.; Parallel to this geological investigation, an evaluation was conducted of Lidar (Light Detecting and Ranging) topographic data accuracy against a statistically representative array of Real-Time Kinematic (RTK) GPS data on the marsh platform. Although airborne Lidar is able to measure micro-topographic features in difficult settings rapidly and accurately, Lidar data were found to overestimate the RTK GPS topographic data by an overall average of 7 cm. Additionally, these data showed little effect from the dominant macrophyte vegetation within the Lidar footprint. From this evaluation, 7 cm appears to be an appropriate vertical adjustment factor for using Lidar data in low gradient salt marshes. However, local ground control will continue to be crucial in studies of intertidal environments incorporating airborne laser data collection.; Reflection surfaces were recorded from the channel bottom to as deep as 25 m below surface. These data were acquired utilizing innovative methodology to investigate the unconsolidated sedimentary lensc from a floating platform. Isopach surfaces derived from interpreted horizons and the present day surface including the RTK GPS/Lidar topographic assessment illustrate quantitatively the spatial and temporal residual control paleo-surfaces have on their latter counterparts. Analysis of these data reveal the integral role that antecedent geology and subsurface topography has played in the area's geomorphological evolution. By defining the shallow-subsurface geologic framework, we hope to provide a foundation for future process-orientated and modeling studies of the evolution of coastal marshes.