Abstract

Data from cores and 1.4- and 3.5-kHz sub-bottom profiles from the western Gulf of Maine are used to interpret the late Wisconsin (<23,000 yr B.P.) and Holocene geologic history of the area. Radiocarbon dates and analyses of sediments in two cores containing a continuous sequence of sediments down to 22 m beneath the sea floor in Stellwagen Basin suggest that grounded glacial ice advanced through the southwestern Gulf of Maine no earlier than 18,900 ± 600 yr B.P. The ice probably persisted on Martha's Vineyard until 15,300 ± 800 yr B.P. During this time, scour and deposition of till occurred in the former marine basins to the north. The lobate character of the glacial margin was accentuated during deglaciation, resulting in the accumulation of glacial sediment as interlobate deposits on outer Cape Cod and perhaps on Stellwagen Bank. Marine transgression and ice degrounding occurred in Stellwagen Basin prior to 14,250 ± 250 yr B.P., and rapid glaciomarine sedimentation followed. Continuous marine deposition in the basin since that time indicates that crustal rebound in the present marine provinces was never rapid enough to raise the sills between the western basins above sea level.

Fine-grained sediment winnowed from areas of elevated submarine topography by marine action eventually replaced glaciomarine detritus as the primary sediment source for the basins. A warming trend about 13,000 yr B.P. is indicated by the disappearance of the frigid-water pelecypod Yoldia arctica. Sedimentation rates in the present marine basins have steadily decreased since 13,000 yr B.P. to a modern rate of a few centimeters per thousand years.

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