The Seafloor Revealed

Summary

The geological history of the seafloor of the Maine inner continental shelf has both young and old components. The bedrock regions are the oldest and date back hundreds of millions of years to their formation. These hard crystalline rocks are primarily igneous or metamorphic. Ancient faults and folds, along with varying resistance to erosion over millennia, have resulted in an irregular shape to the Maine coastline and its offshore shoals, canyons, and basins. Until our recent compilation of scientific studies, many of these unique features were hidden beneath the sea and only known by a few who made their livelihood fishing the seafloor.

Continental glaciation repeatedly scoured the state over the last two million years. The most recent retreat of glacial ice produced a variety of mud, sand, and gravel landforms as well as thick sequences of sediments both inland and offshore. These sedimentary deposits have been modified slightly in the last few thousand years.

Land adjustments due to the loading and unloading of the last ice sheet caused the shoreline of the Gulf of Maine to shift considerably in the last 14,000 years. As a result, coastal processes associated with waves, tides, and currents reworked glacial deposits from elevations as high as 80 m above to as low as 60 m below the present shore. This oscillation in sea level resulted in the surf zone first falling and then rising across the inner continental shelf in the recent geological past. Recent sedimentary deposits cover bedrock in some places while in other locations submarine or subaerial erosion exposes boulders and bedrock, particularly on shoals. During this ice-free period, coastal processes have redistributed some glacial sediments to form easily recognized modern sedimentary deposits such as beaches, mud flats, and a few river deltas.

Scientific study has revealed a complex seafloor with many dynamic environments. With the geological past as a key to the future, the recent changes to the seafloor and coastal zone are expected to continue in the near future. Following its recent trend, sea level will rise further along the Maine coast. Rising tides, waves, and currents will rework sediments along the shifting shoreline and continue coastal erosion of beaches and bluffs. Eroded glacial materials will be supplied to mud flats, beaches, and nearshore environments of the inner continental shelf as the shoreline advances inland. As we continue to live, work, and recreate on or beneath the sea, there is much value in knowing our natural resources. The imprint of geological history is revealed in a variety of seafloor types in the western Gulf of Maine. These marine environments form different seascapes or physiographic environments that are inherited from the geologic framework. Each of these regions, such as gravelly plains, muddy basins, sandy beaches, or rocky shoals are some of the many physical habitats that support life in the marine realm.

Contents Introduction Methods Physiography Surficial Geology Geological History Summary Glossary References

Last updated on October 6, 2005