HOLOCENE EVOLUTION OF THE SOUTHERN-END OF SALISBURY BEACH, MA: SEA-LEVEL RISE AND TIDAL INLET FORCINGS

Barrier island development along the Merrimack Embayment has been studied for over 60 years to determine the influence of the Merrimack River, sea-level changes, geological framework, and the relative sand contribution from the lowstand delta, inner shelf braidplain, and river sources. One model shows that barriers migrated to their present position approximately 4-5,000 yrs BP when sea-level rise slowed sufficiently so that incipient barriers became anchored to bedrock outcrops and glacial deposits, built vertically, and became progradational. In a shorter time scale, historical documents show that Merrimack Inlet has undergone dramatic shifts in shoreline alignment, position of the main ebb channel, and bar migrational trends, all of which have affected sedimentation processes along southern Salisbury Beach.

High resolution geophysical and sedimentological analysis of the southern Salisbury Beach have provided new insights regarding the sedimentary dynamics between the barrier and adjacent inlet system. The internal architecture of the updrift barrier-island terminus was delineated using ground-penetrating radar (200-MHz antenna) and five sediment cores collected using a Geoprobe system recovering up to 9 m of sediment. Organic-rich layers within the cores were sampled for micropaleontological analysis to estimate the influence of the sea-level changes on barrier evolution. Results showed a complex internal architecture, which documents the occurrence of two major phases in the growth history of the barrier island: (1) a first phase dominated by the onshore migration of the barrier driven by sea-level rise, and (2) a second phase characterized by the lateral growth of the barrier island driven by longshore currents and the welding of swash bars to the foreshore.