Physiography, surficial sediments and Quaternary stratigraphy of the inner continental shelf and nearshore region of the Gulf of Maine

Abstract

The western margin of the Gulf of Maine is a bedrock-framed, glaciated continental shelf that has only recently been geologically mapped. The bathymetry is divisible into four physiographic areas: nearshore basins, shelf valleys, rocky zones, and outer basins. The nearshore basins are largely floored by mud except near rock outcrops where shelly gravel occurs. Shelf valleys extend seaward from nearshore basins and estuaries and generally possess less sediment than nearshore basins. Abundant exposures of Pleistocene sediment with rippled substrates suggest that contemporary reworking is occurring. Rocky zones are the most abundant physiographic area and include both exposed bedrock and glacial gravel outcrops. Shell material produced by organisms living on or near rocks is common both in the rocky zones and in abutting environments. The outer basin begins at a depth of about 60 m and extends beyond the 100 m isobath. This area is occasionally bordered on its landward side by the late Quaternary lowstand shoreline. Below this shoreline thicker deposits of sediment exist, while all environments landward were reworked by a regression and transgression of the sea.