INLET-ASSOCIATED MARSH ISLANDS: A 30-YEAR REVIEW

Originally documented by Cleary et al. (1979) along the U.S. Atlantic Coastal Plain, inlet-associated marsh islands have been described in a number of barrier settings around the world. These linear features rise above the vegetated marsh surface and mark the location of active or former tidal inlets. They typically occur along mixed-energy barrier island coasts, where the backbarrier is composed of saltmarsh and tidal creeks systems, and flood-tidal deltas are often poorly developed. In the present review, we summarize the results of recent geological investigations of the classic marsh-island sites in North and South Carolinas, along with findings from Massachusetts and Maine. These studies indicate that the general stratigraphy of the islands exhibits a fining-upward sand-dominated sequence deposited through one or several stages of sediment influx by flood-tidal currents and storms waves, with subsequent aeolian reworking and varying stages of vegetation development. This sequence typically has a sharp contact with underlying saltmarsh peats, which date back to 1,400-400 cal BP and through historical times. Recent satellite image-based morphological analysis of 23 active inlets in contrasting geographic regions (Mid-Atlantic states, western Madagascar, and northern Russia), shows a positive correlation between the distance from inlet throat to the marsh islands and the high-tide inlet width. The average ratio between the two parameters is 1.4 for the Atlantic sites, compared to 0.6-0.7 in the other two regions. The hydraulic radius of the inlet channel, marsh topography, storm wave energy, short-term sea-level changes, and latitude-dependent factors (oyster reefs, mangrove density, ice cover, boat wake wash, and dredging) determine the ultimate geological context and preservation potential of the recent marsh islands. Future research will combine high-resolution georadar imaging with multi-dating techniques (AMS radiocarbon, optically-simulated luminescence, archaeology, and dendrochronology) to assess the age-structure and evolution of relict and historical inlet-associated marsh islands.