IDENTIFYING CAUSES OF GPR REFLECTIONS IN HURRICANE OVERWASH DEPOSITS, SANTA ROSA ISLAND, FLORIDA

Ground Penetrating Radar is an efficient geophysical device utilized for imaging sedimentary deposits. Under most depositional circumstances, sedimentary deposits are associated with structural and compositional complexities. These complexities are of major concern while interpreting GPR data. Here we investigate the effect of small and large scale depositional features on GPR reflections. We collected 250 MHz GPR profiles over a hurricane overwash deposit in Santa Rosa Island on Florida's Panhandle coast. The GPR data were ground truthed with cores and trenches. This hurricane Ivan deposit is widespread in lateral extent and is primarily composed of 99% quartz sand with some 1% heavy minerals that form thin layers. The base of the overwash is clearly defined in most areas and can be identified with the GPR. Within the overwash deposit, the magnetite -rich layers are thinner than radar wavelengths and are expected to produce interference patterns in GPR records. In this study we examine the relationship between radar returns and layering within packages. The sedimentary packages in this deposit include: (1) high amplitude, laterally discontinuous and discordant bi-directional dipping reflections interpreted to represent truncated and buried dunes, (2) high amplitude, laterally continuous, horizontal to subhorizontal reflections that correlate with stratigraphic bounding surfaces, and (3) high to moderate amplitude, discontinuous, inclined reflections representing internal architecture within discrete washover sediment layers. Less common features include zones of laterally confined, moderate to high amplitude bi-directional concave dipping reflections interpreted to represent washover channel, and scour-hole features.