Sources and distribution of late Quaternary silt in the surficial sediment of the northeastern continental shelf of the United States

Abstract

The sources and distribution of silt in the surficial sediment of the northeastern continental shelf of the United States and the Gulf of Maine were determined by the analysis of quartz grain roundness and surface textures. Three distinct populations of silt are present in the surficial sediment of the continental shelf and the Gulf of Maine. Each population is represented by a suite of quartz silt grains with distinctive roundness and surface texture characteristics, is derived from a different source, and is distributed throughout different parts of the study area. The first population is represented by rounded and subrounded quartz silt grains with weathered surfaces (“quo;end member 1”quo;). It was apparently derived from the Cretacious, Tertiary, and Quaternary sdiments of the Atlantic coastal plain, and is most abundant on the continental shelf between Cape Cod and Cape Hatteras (which is underlain and bordered by coastal plain strata) and on the western and eastern rims of the Gulf of Maine (which are also underlain by coastal plain strata). The second population is represented by very angular quartz silt grains with microfractures and fracture faces (“quo;end member 2”quo;). It was apparently derived from the late Wisconsin glacial and periglacial deposits of the northeast United States, and is most abundant within and downdrift from the glaciated part of the study area and in the modern depocenters of rivers which drain glaciated terranes in New York and New England. The third population is represented by subangular and subrounded quartz silt grains with crystalline nodes, grain embayments, and secondary quartz overgrowths (“quo;end member 3”quo;). It was apparently derived from Precambrian, Paleozoic, and Early Mesozoic crystalline and sedimentary rocks of the Appalachian Mountains, and is most abundant in the modern and ancient depocenters of the Appalachian rivers of the eastern United States