DROWNED FOREDUNE RIDGES AS EVIDENCE OF PRE- HISTORICAL BARRIER-ISLAND STATE CHANGES BETWEEN MIGRATION AND PROGRADATION

Abstract

Abstract: The processes driving barrier-island state changes between erosion/migration and growth/progradation are poorly understood. Stratigraphic and chronologic data are used to infer past state changes of Cedar Island, VA, USA. These data indicate that Cedar Island formed seaward of its present position approximately 5000–6000 years ago. Following a period of net landward migration, the north-central section of the island was breached prior to ca. 450 years ago. During this time, an extensive flood tidal delta was deposited in the backbarrier. After inlet closure, the island migrated landward atop these flood delta deposits, and aggraded, eventually entering a phase of net progradation. From 1852 to present the island has eroded and migrated landward ~1 km. The modern barrier is located stratigraphically above a shallow antecedent high (-5.5 m MSL). The state changes and antecedent geology observed here are discussed and used to infer potential future sediment sources to the island.