Late Quaternary geology of northeastern Massachusetts and the Merrimack Embayment, western Gulf of Maine
Edwards, Gerald B.
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The Merrimack Embayment in the western Gulf of Maine is the site of three late-Quaternary paleodeltas. Each delta was deposited by the Merrimack River as its mouth migrated from west to east across the continental shelf during the post-glacial transgression and regression of the sea, In the Merrimack River Valley, a raised, glaciomarine ice-contact delta 33m above present sea level represents deposition of sediments by glacial meltwater at the transgressive marine limit about 13,000 yrs BP. An adjacent delta, preserved at 16m above present sea level, represents the deposition of sediments eroded from the 33m glaciomarine delta during the early stages of marine regression sometime after 13,000 yrs BP. A drowned delta, formed when sea-level was about 50m below present sea-level, is located offshore of the Merrimack River and represents deposition of sediments eroded from the 16m delta and from glacial deposits in the Merrimack Valley during the post-glacial maximum marine regression about 10,500 yrs BP. Major controls on the locations of the deltas include eastward shoreline translation induced by crustal rebound and relative sea-level lowering, and bedrock induced channel entrenchment. The orientation of the deltas and other paleoshoreline features, generally elongate to the south, indicates that a southerly alongshore current was a significant factor in the control of nearshore erosion and deposition. A similar configuration in the present Plum Island and linear sand ridges in the shallow, nearshore zone suggests that the alongshore current has influenced sediment distribution since the retreat of late-Wisconsinan ice from the area.
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