HURRICANES: SPACE MAKERS IN U.S. EAST COAST SALT MARSHES FOR TIDAL SILICICLASTICS AND LOW MARSH PEAT?

Late Holocene salt-marsh deposits along the U.S. east coast have been studied for sedimentary records of hurricane strikes (e.g., Liu and Fearn, 1993; Donnelly et al., 2001), but hardly for evidence of storm erosion. Lithostratigraphic and radiocarbon data from the inland section of Pattagansett River Marsh, Connecticut show that twice during the past 600 yr this sheltered area of the marsh experienced significant erosion, each time followed by rapid and complete infilling of the eroded space with a regressive sequence of tidal mud, low marsh and high marsh peat. Erosive contacts in salt-marsh deposits can result from expansion of the tidal drainage network due to a (temporary) increase in local tidal range, lateral migration of channels, marsh-cliff retreat, pond-hole formation and/or the action of waves and currents under storm-surge conditions.

We argue that the two erosive surfaces in Pattagansett River Marsh cannot be attributed to increases in tidal prism, gradual lateral migration of tidal channels or pond-hole formation. The ±2ó age range (1390–1470 A.D.) for first low marsh growth in the older regressive sequence agrees well with the age range (1400–1440 A.D.) for a hurricane deposit at Succotash Marsh, Rhode Island,60 km to the east (Donnelly et al. 2001). The younger regressive sequence dates with greatest probability to the period 1640–1670 A.D., i.e., shortly after the hurricanes of 1635 and 1638 (Boose et al., 2001). Our conclusion that the most likely cause of the erosion was hurricane activity is relevant to paleo-storm research and the study of marsh sensitivity for and recovery from storm erosion. Furthermore, it offers a basis for reinterpreting lithostratigraphic data, previously thought to reflect variations in the rate of sea-level rise, in terms of changes in the rate of sedimentation related to the passage of a hurricane or other severe storm.