Reconstruction of a Relict Inlet System and Historical Storm Signatures along Southern Assateague Island, Maryland [article]

(:Unkn) Unknown, University, My, Buynevich, Ilya V. (Ilya Val)
2020
Assateague Island is a classic example of a retrograding barrier island, with its recent geological history punctuated by episodes of overwash and breaching. However, in addition to a number of historical inlets, parts of the island owe their origin to relict (pre-historic) channels. The present study was conducted north of the Virginia-Maryland border, focusing on a narrow segment of the island fronting the Green Run Bay. The site lies north of the historical Green Run Inlet that was active
more » ... il 1880; however, there is no geological evidence of its migration along the island. More than 4 km of high-resolution (250 MHz) ground-penetrating radar (GPR) images, complemented with sediment cores and multi-dating techniques, were used to reconstruct the geological legacy of the Green Run Bay segment of the barrier and to test whether it was the site of an older channel. My findings indicate that a backbarrier paleo-channel still visible within the Green Run Bay corresponds to a large (>380 m wide, 3.0-3.5 m thick) channel cut-and-fill structure revealed in GPR images. The channel fill consists of tangential- to sigmoidal-oblique, southward-dipping reflections downlapping onto channel lag facies, which overlie subhorizontal bay-fill strata. Hummocky reflections in a shore-normal channel transect suggest partial preservation of inlet-related bedforms, believed to be associated with the channel closure. Mollusk shells from the bay fill yield radiocarbon ages of 4630-2400 cal BP (calibrated years before 1950). The paleo-channel facies overlying the bay deposits exhibit a fining-upward sequence, with a mean grain size range of 0.44-2.43 phi. The first set of optical dates indicates that the inlet fill is 660 +/- 70 cal BP (AD 1220-1360). The paleo-channel fill does not extend to the south and therefore is a separate relict feature that predates the historical Green Run Inlet. Based on geophysical and core data, the paleo-tidal prism of the relict channel is 17x10 6 m3. Following the closure of the inlet, a series of bea [...]
doi:10.34944/dspace/2324 fatcat:tazaexf3jvbzva3hayimsnrhxy