NEW EVIDENCE FOR POSTGLACIAL RELATIVE SEA-LEVEL CHANGE FROM THE MERRIMACK RIVER PALEODELTA, WESTERN GULF OF MAINE

The formerly glaciated shelf of North America has a complex glacial and postglacial history of sea-level change. During deglaciation, isostatic loading of the land permitted marine incursion as evidenced by uplifted glacial marine deposits along the coast. Following ice retreat, crustal rebound led to a local relative sea-level lowstand of -60 m in the northwestern Gulf of Maine. The present relative sea-level curve of northeastern Massachusetts and its inner continental shelf lack observations between 8,000 and 12,000 BP (sea-level lowstand). This dearth of evidence leaves the chronology and rates of sea-level rise in this region poorly understood. Here, we present high-resolution geophysical data ground-truthed with new radiocarbon dates collected from the Merrimack River paleodelta located in the western Gulf of Maine. Bivalve fossils found in life position have calibrated radiocarbon ages falling between 9,000- 11,500 BP. These data fill a significant knowledge gap and combined with other regional sea-level curves constrain the regional isostatic response of the New England coast and continental shelf glacial retreat.