Abstract The northern Atlantic coastal plain forms the western margin of the Baltimore Canyon Trough, a large sedimentary basin that underlies the continental shelf along the Middle Atlantic states (Fig. 1). The coastal plain narrows northeastwardly from Virginia to Long Island where it plunges beneath the Atlantic Ocean; small exposures of coastal plain sediments occur on Block, Marthas Vineyard, and Nantucket islands east of Long Island. Deposition in the coastal region is related to the development of the Baltimore Canyon Trough, which took place during the postrift phase of the opening of the Atlantic Ocean. The coastal plain is composed of unconsolidated and semi-consolidated sediments of Cretaceous and Cenozoic age. Sediments of late Jurassic age possibly lie beneath the eastern edge of the coastal plain but this has not been clearly documented. In outcrop, the coastal plain is divided into an inner belt of Cretaceous and early Tertiary formations and an outer belt of younger Tertiary and Quaternary formations. The coastal plain sediments thicken eastwardly into the Baltimore Canyon Trough as a series of basin fills that vary in thickness, along strike. In general the section thins northeastwardly. Near Salisbury, Maryland, the sedimentary section is approximately 2165 m in thickness, whereas at Long Island the thickness is less than 625 m. The variation in thickness along strike is related to structural highs and lows of the underlying basement rocks. Sedimentation began on the coastal plain during Early Cretaceous (Neocomian) or possibly Late Jurassic time with deposition of fluvial sands, gravels, and variegated clays. The Lower Cretaceous stratigraphic sequence is composed almost entirely of sediments of continental (fluvial) origin. In the distal downdip parts of the coastal plain, marine fossils (molluscs, dinoflagellates, and foraminifers) occur in the Lower Cretaceous section in some wells. This suggests that the coastal plain was influenced from time to time by marginal marine incursions.

Abstract The Atlantic and Gulf Coastal Province differs from most other geomorphic provinces in North America in that it has a large suboceanic area (685 × 10 3 km 2 ) in addition to its subaerial segment (1,166 × 10 3 km 2 ; Table 1). The subaerial portion, usually referred to as the Coastal Plain * , extends from Long Island in New York (with outliers in Martha’s Vineyard and Cape Cod) to the Mexico border in Texas and includes all or part of 19 states. The suboceanic portion, which composes part of North America’s Continental Shelf, extends from the Canadian border south and west to the border with Mexico. The unifying character of this province stems mainly from a geologic history that has recorded alternating periods of submergence and emergence. Thus, all parts of the province have experienced coastal processes at one time or another, and most areas several times. However, over many parts of the province the surface expression of these processes has been destroyed or highly modified by erosion or burial. Most of the suboceanic portion of the province was subaerial as recently as 18,000 years ago, whereas parts of the subaerial portion of the Coastal Plain have not been submerged since the Cretaceous. The interface between the two divisions has been near its present elevational position for only some 5,000 to 6,000 years. During most of the province’s history, a number of geomorphic processes have been operative upon a relatively gently sloping surface consisting of rocks that generally increase in age upslope. In addition

Abstract A detailed magnetic study of the U.S. Atlantic continental margin north of Cape Hatteras delineates the pattern of basins and platforms that form the basement structure. A 185,000-km, high-sensitivity aeromagnetic survey acquired in 1975 over the entire U.S. Atlantic continental margin forms the basis of this study. Magnetic depth-to-source estimates were calculated for the entire survey using a Werner "deconvolution" type method. These depth-to-basement estimates are integrated with multichannel seismic reflection profiles to interpolate basement structures between seismic profiles. The deep sediment-filled basins along the margin are bounded on their landward sides by blockfaulted continental crust; their seaward sides are marked by the East Coast magnetic anomaly. The trends of the landward sides of these basins vary from 030° in the south to 040° in the north, consistent with a common pole of opening for all of the basins. The ends of these basins are controlled by sharp offsets in the continental crust that underlie the various platforms. These offsets are the result of the initial breakup of North America and Africa and are preserved as fracture zones under the continental rise. The regions west of the various basins are comprised of platforms of Paleozoic and older crust and embayments of Triassic-Jurassic age. The Long Island platform is a series of ridges and troughs. These troughs are oriented northeastward, parallel with the Baltimore Canyon trough and the Georges Bank trough. The Connecticut Valley Triassic basin has a broad magnetic low associated with it that can be traced across Long Island. A similar magnetic signature is associated with the trough between Martha's Vineyard and Nantucket Island, suggesting that it also may be a Triassic basin. The Salsbury Embayment with its Triassic-Jurassic age sediments lies just west of the Baltimore Canyon trough while the Carolina platform, which has a few smaller Triassic basins within predominantly Paleozoic and older crust, lies landward of the Carolina trough. The area around Charleston is another major embayment of Triassic-Jurassic age, and west of the Blake Plateau is the Florida platform with Paleozoic and older crust. A magnetic basement high associated with the East Coast magnetic anomaly separates oceanic crust from the deep sediment-filled troughs. The minimum depth of this high ranges from 6 to 8 km and the susceptibility contrast suggests that it is more likely an uptilted block of oceanic crust than a massive intrusive body. The magnetic anomaly probably is produced by a combination of a basement high and an "edge effect," where the edge is between the uptilted block and flat-lying, nonmagnetic sediments to the west.

The age of the late Wisconsin maximum of the Laurentide ice sheet off the coast of New England and on Long Island, New York, is not closely designated. Radiocarbon and stratigraphic evidence from Martha’s Vineyard suggests that the glacier margin may have been close to its maximum position as late as 15,300 yrs ago; indirect evidence from Long Island infers that the ice sheet had reached a maximum and had begun to recede prior to 17,000 yrs ago. In any case, by at least 14,200 yrs ago the glacier margin had retreated from its maximum late Wisconsin position at the Ronkonkoma Moraine on Long Island, had constructed recessional frontal deposits, and had retreated north of Rogers Lake on the southern Connecticut coast. Subsequent readvances culminated near Middletown, Connecticut, some time after 15,000 yrs ago, and in Cambridge, Massachusetts, after 14,000 yrs ago. Whether these readvances were synchronous is unknown because of the absence of close limiting dates and because of the lack of evidence for readvance in the intervening area. The northwestward recession of the glacier margin from the present coast in eastern Maine was accompanied by a marine transgression and deposition of hundreds of submarine moraines between 13,500 and 12,500 yrs ago. This general recession was interrupted by a readvance which culminated at the Pineo Ridge Moraine approximately 12,700 yrs ago. Although it may have resulted from general climatic change, the Pineo Ridge readvance just as likely may have been caused by a vastly decreased calving rate associated with isostatic uplift and marine recession from coastal Maine. This is well documented as having occurred simultaneously with the Pineo Ridge readvance. Thereafter, the ice sheet thinned and separated over the highlands of northwestern Maine leaving residual ice to the southeast. Active ice, receding into the St. Lawrence Valley of southeastern Quebec deposited the Highland Front Moraine approximately 12,700 to 12,600 yrs ago. In summary, (1) a major amelioration of climate that began prior to 14,200 yrs ago resulted in very rapid dissipation of the ice sheet in New England at least by 12,500 yrs ago, with the exception of small glaciers that possibly persisted in the highlands; (2) no conclusive evidence has been recognized for any climatic reversals during the dissipation of the ice sheet in New England; and (3) although major events in New England compare with those of the Great Lakes region, no minor events have proven correlation with the possible exception of the Pineo Ridge and Port Huron readvances.

Abstract The first method of exploring the ocean floor and mapping its sediments was the use of tallowed lead weights at the end of sounding lines. Seamen often cast the lead on approaching land during fog, and when they encountered a large area of shallow mud bottom, known as the “Block Island soundings,” between Martha’s Vineyard and Long Island, they knew their position along the coast (Pour-tales, 1871, 1872). The general characteristics of many samples taken with lead line by ships belonging to the Coast and Geodetic Survey were described by Pourtales (1871, 1872), and their content of foraminifers was reported by Pourtales (1850) and Bailey (1851, 1854). On the basis of 9,000 such samples, Pourtales (1870) compiled the first general bottom-sediment chart of the continental shelf for the area between Cape Cod and Key West. Notations of the character of the bottom also were written on field sheets and published navigational charts, and they were used by Shepard (1932) in a general study of the distribution patterns on continental shelves, particularly those of the Atlantic coast of the United States. During World War II these notations also were used for making large-scale bottom-sediment charts to help estimate the probable ranges for acoustic detection between submarines and surface ships. Charts were made by the United States Navy under the direction of H. C. Stetson and also by the German Navy (Oberkommando der Kreigsmarine, 1943).

Abstract The data for this study are derived from 8 traverses across the continental shelf, from Cape Cod to Cape Canaveral, and 3 from the Gulf of Maine. Samples were spaced from 0.5 to 2 miles apart. The source of the present-day sediment is largely reworked glacial debris for the northern lines, and for those outside the limits of the ice advance, reworked Coastal Plain deposits. Although the distribution of the sediments appears very diverse when the shelf is considered in small areas, certain uniformities in their arrangement appear when it is taken by regions. This distribution indicates that the bottom deposits are becoming adjusted to present sea-level, and that the differences are largely dependent on source of supply. Calcium carbonate is present in insignificant amounts north of Cape Hatteras. South of this cape however, it is a main constituent of the bottom deposits, often reaching 50-80 per cent. It is derived from the skeletons of various organisms which have been comminuted to the same sizes as the inorganic particles, and also from oolites. Some of the lime is undoubtedly derived from the reworking of older deposits. The Gulf Stream is the only one of the currents making up part of the main circulatory system of the ocean that has any effect on the sediments of the continental shelf. South of Cape Hatteras the continental slope is, for the most part, swept bare of unconsolidated material by this current. A combination of wave action and tidal currents is sorting the bottom deposits in water shallower than 60 to 70 meters and occasionally to greater depths where the tidal currents are exceptionally strong. Wave action is known to extend to the bottom all over the shelf in winter but is not effective in agitating the sediments below the depths given above. A profile of equilibrium has been developed on the inner halves of the northern lines and is best exemplified on the Marthas Vineyard traverse. The traverses south of Cape Hatteras represent profiles that are still far above wave base. South of New England is a large area in which quartz sand grains, exhibiting a very high degree of rounding, are found in abundance. Most of these grains have a mat surface unless it has been secondarily removed. They are thought to be the remains of ancient dunes formed during the lower stands of the sea during the Pleistocene. Many sediments on the break in slope are coarser than those immediately inshore. They are also considered to be residual from a lowered sea-level. The grade size does not decrease uniformly in an offshore direction. However the bottom deposits, by their very diversity, are merely a modem illustration of conditions that have been in operation throughout the whole history of Coastal Plain deposition. Sedimentation along the margins of a major ocean must not be considered typical of an inland sea.

Abstract The data for this study are derived from 8 traverses across the continental shelf, from Cape Cod to Cape Canaveral, and 3 from the Gulf of Maine. Samples were spaced from 0.5 to 2 miles apart. The source of the present-day sediment is largely reworked glacial débris for the northern lines, and for those outside the limits of the ice advance, reworked Coastal Plain deposits. Although the distribution of the sediments appears very diverse when the shelf is considered in small areas, certain uniformities in their arrangement appear when it is taken by regions. This distribution indicates that the bottom deposits are becoming adjusted to present sea-level, and that the differences are largely dependent on source of supply. Calcium carbonate is present in insignificant amounts north of Cape Hatteras. South of this cape however, it is a main constituent of the bottom deposits, often reaching 50–80 per cent. It is derived from the skeletons of various organisms which have been comminuted to the same sizes as the inorganic particles, and also from oölites. Some of the lime is undoubtedly derived from the reworking of older deposits. The Gulf Stream is the only one of the currents making up part of the main circulatory system of the ocean that has any effect on the sediments of the continental shelf. South of Cape Hatteras the continental slope is, for the most part, swept bare of unconsolidated material by this current. A combination of wave action and tidal currents is sorting the bottom deposits in water shallower than 60 to 70 meters and occasionally to greater depths where the tidal currents are exceptionally strong. Wave action is known to extend to the bottom all over the shelf in winter but is not effective in agitating the sediments below the depths given above. A profile of equilibrium has been developed on the inner halves of the northern lines and is best exemplified on the Marthas Vineyard traverse. The traverses south of Cape Hatteras represent profiles that are still far above wave base. South of New England is a large area in which quartz sand grains, exhibiting a very high degree of rounding, are found in abundance. Most of these grains have a mat surface unless it has been secondarily removed. They are thought to be the remains of ancient dunes formed during the lower stands of the sea during the Pleistocene. Many sediments on the break in slope are coarser than those immediately inshore. They are also considered to be residual from a lowered sea-level. The grade size does not decrease uniformly in an offshore direction. However the bottom deposits, by their very diversity, are merely a modern illustration of conditions that have been in operation throughout the whole history of Coastal Plain deposition. Sedimentation along the margins of a major ocean must not be considered typical of an inland sea.