INVESTIGATING BARRIER ISLAND EVOLUTION AND INLET FORMATION THROUGH STRATIGRAPHIC ANALYSIS OF VIBRACORES TAKEN FROM ASSATEAGUE AND CHINCOTEAGUE ISLANDS, VA

Barrier islands are dynamic coastal features that provide storm protection, critical habitat, as well as commerce and real estate. To manage these valuable areas, we need to understand their past and project their future evolution. Analysis of sediment cores from barrier islands allows investigations on time scales longer than historical maps and relict geomorphology. Assateague and Chincoteague (AI, CI) islands located on the Mid-Atlantic Delmarva Peninsula, form a unique duplexed barrier island system that is not well understood. We present the results from radiocarbon dating and lithological analysis of six 1-3 meter long vibracores collected in 2015/2016 from the northern tip of CI, a modern salt marsh, and an accretion mound in the North Wash Flats region of AI. We also collected GPR transects of the subsurface of the paleoinlet and the recurved spit of the accretion mound (GSSI SIR 3000, 270 MHz antenna).

The core extracted from CI consists of medium-grained quartz sands (Unit 1) recording high energy conditions, that fine upward through fine sands and silts to bay muds (with a date of 1459 AD) (Units 2 & 3). These are then overlain by modern salt marsh sediments (Unit 5). Truncated paleoshorelines south of our core site suggests the modern Wildcat Marsh stabilized a former high-energy flood tidal delta inside the AI-CI paleoinlet by this time.

On AI, the North Wash Flats accretion mound is characterized by mica-rich bay bottom sandy silts (Units 2 and 3; shell material dates from 1266 to 1865 AD) overlain by bedded medium-grained quartz sands (Unit 4). Finer grained units indicate lower energy conditions and a closed inlet. Coarser sediments were then intermittently deposited on top of highly saturated fine-grained sediments which evidently dewatered upward through crustacean burrows. This suggests storm overwash and/or temporary opening of the inlet. GPR profiles taken between core sites will help to resolve the pattern of deposition in the uppermost units.

These data allow us to better understand the geologic history of this region and contribute to the development of refined models for the evolution of the barrier islands. These models will ultimately provide valuable information to help constrain future forecasts for AI and CI as climate change and global sea level rise continue to impact the region.