Sedimentary records of intense storms in Holocene barrier sequences, Maine, USA

Abstract

Coastal-morphological, geophysical (ground-penetrating radar [GPR]), and sedimentological data document extreme storm events along the sandy barriers of Maine's south–central (Hunnewell and Flat Point barriers) and southwestern (Saco Bay barriers) coastal compartments. The Hunnewell barrier contains four equally spaced buried storm scarps behind the exposed scarp of the Blizzard of 1978, a 100-year storm that eroded more than 100 m of shoreline, causing extensive property loss. These scarps dip 3–5° steeper than the normal beachface slope and consist of sands with more than 50% heavy minerals. The heavy minerals produce distinct subsurface reflections that facilitate the location of buried supratidal parts of storm scarps and the mapping of ancient poststorm shoreline positions. The imaged scarps likely formed within the past 1.5–2.0 ka BP. The Flat Point barrier consists of a prograded sequence overlain by a laterally extensive, seaward-thinning layer of freshwater peat and capped by aeolian sands. This stratigraphy suggests that the bog varied in size through time, contracting during overwash events and aeolian deposition and expanding across washover sheets during extended periods of barrier stability. The main overwash event accompanied by barrier planation and wetland expansion may be linked to the first historical storm in New England, the “Great Colonial Hurricane” of 1635. Evidence of near-modern and mid-Holocene storm events along Saco Bay includes washover units and marsh ridges. Washovers interfinger with saltmarsh peat that ranges in age from 4.5 ka BP to modern. The presence of isolated sandy ridges behind existing and former tidal inlets reflects overtopping of marshes and high intertidal mudflats during major storms. Radiocarbon ages indicate that this process took place at different locations along the Saco Bay barrier complex from 3 to 1 ka BP.