Sediments of the Gulf of Maine: ABSTRACT

Abstract

The Gulf of Maine is a rectangular depression on the continental shelf about 180 miles long and 120 miles wide. Georges Bank, Browns Bank, and the Nova Scotian Shelf, all shallower than 100 meters, separate the Gulf from the Atlantic Ocean to the southeast. Glacial scouring has accentuated the highly irregular bottom topography, and numerous basins 200 to 377 meters deep are present. Large areas between shallow bedrock ridges and the large flat-floored basins are veneered by poorly sorted mixtures of clay, silt, sand, and gravel, probably derived with very little change from glacial till and outwash. These sediments contain moderate amounts of layer silicates but less than 2 per cent organic matter. The sand-size fraction contains 3 to 10 per cent rock fragments and 10 to 15 per cent dark minerals. Post-Pleistocene reworking of poorly sorted glacial material by wave and current action near the coast and End_Page 343------------------------------ on the shallow banks flanking the Gulf has produced relatively well-sorted sand, low in layer silicates and organic matter. Some well-sorted material has also been deposited on the flanks of Georges and Browns Banks and in some coastal areas. Most winnowed fine detritus has accumulated on the flat floors of the deep basins. The sediment there is silty clay composed dominantly of mica, chlorite, and mixed layered mica-montmorillonite. Kaolinite occurs only as traces in a few samples. The minor amounts of sand-size material are composed predominantly of mica and of foraminiferal tests and other biogenic debris. Organic matter exceeds 4 per cent in some of the basins. The carbon/nitrogen ratio of the deposits tends to increase with distance from shore. End_of_Article - Last_Page 344------------