MORPHOSEDIMENTARY FRAMEWORK OF THE FORMER GREEN RUN INLET: ASSATEAGUE ISLAND, MD

The morphosedimentary framework of the historical Green Run Inlet was investigated by analyzing 10 sediment cores along with a GPR survey within the inlet complex. The former inlet was located along Assateague Island National Seashore, MD, and was open from 1852 to 1880. This inlet system is characterized by relict geomorphic features including a flood-tidal delta, recurved spits, inlet channel scar, and inlet-closure ridges. GPR surveys revealed that the inlet migrated 700 m before in-filling. Textural analysis was performed on the sand portion of the sediment cores at 10 cm intervals to groundtruth the GPR data. Core 1 was collected from the south recurved spit of the former inlet. This core contained two coarsening upward successions, separated by a mud unit. The upper 60 cm were characterized by an upward increase in mean grain size from 2.7ɸ to 1.6ɸ. The lower coarsening upward succession spanned 89 cm with a mean grain size increasing from 2.3ɸ to 1.8ɸ. These sediments are interpreted as spit platform and foreshore deposits. Core 2 was collected from the former inlet throat and penetrated 200 cm in depth. The upper 60 cm are representative of tidal creek deposits that coarsen upward from 2ɸ to 1.8ɸ. Inlet-fill deposits span from a depth of 60 to 150 cm and are characterized by a fining upward succession with a mean grain size decreasing from 2.4ɸ to 1.5ɸ. An estuarine deposit highlights the lower portion of the core from 150 to 200 cm and is delineated by a sharp decrease in mean grain size. Core 3 penetrated 298 cm within the former inlet channel. The upper 80 cm are representative of an aeolian deposit, demonstrating an overall coarsening upward succession with mean grain size increasing from 2.4ɸ to 1.9ɸ. The lower 218 cm are interpreted as an inlet-fill deposit characterized by sediments fining upward from 0.4ɸ to 2.4ɸ. Finally, Core 4 was collected within the relict flood-tidal delta reaching a depth of 378 cm. This core was characterized by a mean grain size fining upward from 1.5ɸ to 2.2ɸ within the top 190 cm, representing a channel-fill depositional environment. The lower half of the core contained a 188 cm mud unit with heavy bioturbation in the top 30 cm. The sediment cores and GPR data complemented each other and also revealed a need for continued sediment coring to further reconstruct the sedimentary framework of the former inlet.