This geographic information system (GIS) data layer shows the generalized lithologic and geochemical, termed lithogeochemical, character of near-surface bedrock in the New England Coastal Basin (NECB) study area of the U.S. Geological Survey's National Water Quality Assessment (NAWQA) Program. The area encompasses 23,000 square miles in western and central Maine, eastern Massachusetts, most of Rhode Island, eastern New Hampshire and a small part of eastern Connecticut. The NECB study area includes the Kennebec, Androscoggin, Saco, Merrimack, Charles, and Blackstone River Basins, as well as all of Cape Cod.
Bedrock units in the NECB study area are classified into lithogeochemical units based on the relative reactivity of their constituent minerals to dissolution and the presence of carbonate or sulfide minerals. The 38 lithogeochemical units are generalized into 7 major groups: (1) carbonate-bearing metasedimentary rocks; (2) primarily noncalcareous, clastic sedimentary rocks with restricted deposition in discrete fault-bounded sedimentary basins of Mississipian or younger age; (3) primarily noncalcareous, clastic sedimentary rocks at or above biotite-grade of regional metamorphism; (4) mafic igneous rocks and their metamorphic equivalents; (5) ultramafic rocks; (6) felsic igneous rocks and their metamorphic equivalents; and (7) unconsolidated and poorly consolidated sediments.