Paper No. 6
Presentation Time: 4:55 PM
INTO THE BREACH: PALEO-INLETS AS ARCHIVES OF EXTREME EVENTS IN THE NORTH ATLANTIC BASIN
Extreme oceanographic events, such as intense storms and tsunamis, are responsible for both the origin and major transformations of the vast majority of open-ocean tidal inlets. Every intense storm of the past century, including the 2012 Hurricane Sandy, has resulted in breaching through a combination of wave erosion and ebb-surge. Inlet scars mapped on the Atlantic continental shelf constrain former barrier chain positions and emphasize the punctuated nature of shoreline retreat. Similarly, numerous historical and pre-historic (relict) inlet channels comprise the lithosomes of retrograding barriers and transgressive nuclei of prograded segments. Migrating inlet channels invert the facies architecture of coastal barriers and make vast quantities of sand available for aeolian processes. Understanding the geological legacy of former inlets aids reconstructions of formative event chronology and assessments of vulnerability to future breaching. This study summarizes the results of paleo-inlet research along the Atlantic Seaboard, from mixed-to-tide-dominated systems (northern New England, South Carolina) to wave-dominated barriers (southern Massachusetts, Maryland, and North Carolina). Ground-penetrating radar (GPR) surveys are used to guide the coring efforts and provide unprecedented continuous visualization of the upper 10-15 m of freshwater-saturated portions of coastal sequences. In mixed-sediment paraglacial settings, paleo-channel lithosomes characterized by lithological heterogeneity are ideal for GPR imaging, with buried channels defined by coarse lag deposits. At sand-dominated Coastal Plain sites, subsurface reflections are caused by subtle textural and compositional variations, which also contribute to GPR reflections. In addition to paleo-channels themselves, inlet-associated marsh islands are intimately linked with channel genesis and migration. Their emplacement and longshore growth offer complementary stratigraphic and chronological framework of inlet-related processes. The timing of key evolutionary stages is provided by radiocarbon dating, optically stimulated luminescence, dendrochronology, and historical documents. The growing database points to regional inlet-forming phases during 3,000-2,700 yBP, 1,600-1,300 yBP, and beginning 400 yBP.