The Gulf of Maine (northeast US coast) records shelf evolution since deglaciation ca. 15 ka. Glacial erosion of bedrock left a complex coastline of bays, peninsulas and islands. Till and outwash provided coarse sediment for reworking in littoral systems throughout the Holocene transgression. Glaciomarine mud, the Presumpscot Formation, was an abundant source of fine sediments that were reworked in estuaries, embayments and back-barrier systems. Relative sea-level change was driven by both isostatic and eustatic components. Initial submergence to 70–130 m above present sea level was contemporaneous with marine-based ice-sheet retreat at 15-13 ka. Rapid emergence followed to 60 m below present, during continuing isostatic rebound at 13-11 ka. Finally, submergence and transgression occurred 10.8 ka to present as isostatic rebound was overtaken by eustatic sea-level rise. Reworking during emergence and lowstand brought sand and gravel to the present coast and inner shelf, building paleodeltas at the mouths of the Merrimack River and Kennebec River. Other rivers, such as the Penobscot, drained landscapes with fewer coarse-grained sources, and have primarily mud-filled estuaries, such as Penobscot Bay.
Detailed seismic reflection profiling and sidescan sonar mapping provide data for a model of inner-shelf evolution based on principles of sequence stratigraphy. The lower sequence boundary is the unconformity created on top of the Presumpscot Fm. and other glacial sediments during emergence. Lowstand systems tracts are best recognized in paleodeltas. Transgressive systems tracts are thin, but interrupted by parasequences of prograding deltaic and estuarine facies in some estuaries. Significant examples such as the newly discovered Penobscot Paleodelta (8–9 ka, 30 m below present sea-level) may relate to a slowing of relative sea-level rise. Highstand systems tracts formed in the late Holocene as the rate of sea-level rise slowed and the rate of sediment supply allowed stabilization and progradation of barriers and tidal deltas. Preservation potential of these features is controlled by the open coast ravinement unconformity, and by the tidal ravinement unconformity and bluff ravinement unconformity in embayments. Variability in preservation potential results both from paleotopography and differing energy of modern processes.