Summary

The interpretations presented in this report represent a unique geologic dataset for a nearshore area of the Massachusetts sea floor between Nahant and Salisbury, including a portion of western Massachusetts Bay and the southern Merrimack Embayment. The sediment texture and physiographic zone maps document the sedimentary environments of the Massachusetts inner continental shelf at a resolution that was previously not possible because of a lack of high-resolution, regional geophysical data. Previously published geologic interpretations, high-resolution geophysical data, sediment samples, aerial photographs, lidar, and bottom photographs were used to generate these interpretations. The sea-floor geology within western Massachusetts Bay is a complex and variable distribution of sediments and geomorphic features that can be primarily attributed to the advances, occupations, and retreats of Pleistocene glaciers and to the reworking of glacial sediments during sea-level change. Modern processes continue to shape the sea floor. However, in the southern Merrimack Embayment, the sea floor geology is more attributable to lowstand fluvial and subsequent marine transgressive processes that blanketed the sea floor with sand and gravel. The high-resolution geologic interpretations provided in this report are valuable input for defining marine resources and improving our understanding of coastal evolution in the region.