Sandy Neck is a 10-km-long sheltered mesotidal barrier spit along the southeastern New England coast, bordering Cape Cod Bay. Its stratigraphy contains evidence of relative sea-level (RSL) rise and tidal-inlet development, and enables reconstruction of accretion and progradation of this barrier through time. Core, trench, and ground-penetrating-radar (GPR) data show that the lower boundary of the uppermost, eolian, facies climbs about 9 m from the proximal to the distal part of the spit, away from the mainland anchor point. This change is thought to be related primarily to a comparable rise in RSL. The same boundary also shows a shallowing trend in a seaward direction, indicating net spit progradation through time. The absence of inlet-channel facies in the stratigraphy of the proximal part of the barrier spit, in contrast to the presence of inlet facies in more distal parts of the spit, indicates that some time elapsed after barrier initiation before an inlet thalweg developed. In its earliest stages, this thalweg was poorly defined, wide, and shallow, but its characteristics changed as the barrier spit lengthened. In the central part of Sandy Neck, the assemblage of inlet-channel facies becomes markedly thicker, reflecting thalweg deepening in response to paleotopographic and substrate-lithologic factors. The stratigraphy of the distal part of the spit shows the effects of continued, but more gradual, inlet deepening that may be tied directly to increasing barrier length. The process-controlled stratigraphy presented here differs from current facies models because it accounts for temporal changes in coastal environmental processes and parameters. It suggests a high preservation potential for proximal eolian facies in the spit sequence, underneath a cover of fine-grained and organic back-barrier sediment. Once reliably dated, the new stratigraphic data will help to improve the regional RSL curve for the southern Cape Cod Bay area.

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