Abstract The geologic strip-map for Transect E-l cuts a swath from the Thousand Islands region on the New York-Ontario border to the Atlantic Ocean floor off Georges Bank (see Fig. 1). It includes portions of New York, Ontario and of all of the New England states. The western part, mainly in New York, belongs to the North American craton. The remainder of the onland portion, east of Logan's Line, belongs to the Appalachian Orogen. Southeastward from Logan's Line the transect crosses a series of distinctive terranes. Several of these terranes are believed to be exotic, and to have been accreted to the North American craton during the Paleozoic. Superposed on these are several grabens and half-grabens containing early Mesozoic sediments and mafic volcanics. There are also Mesozoic eruptive complexes of an alkalic nature cutting across the Appalachian Orogen from southern Quebec, across New England, and continuing as a chain of seamounts offshore. Cenozoic rocks are limited to a small, but significant occurrence near Brandon, Vermont (BL on Fig. 2) and a few occurrences in the Cape Cod region and on the adjacent islands in southeastern Massachusetts. Offshore the corridor passes over the Gulf of Maine and Long Island Platforms, thence across Georges Bank and into the North Atlantic Basin. The Gulf of Maine and Long Island Platforms (Fig. 2) are underlain by Paleozoic metamorphic and plutonic rocks and early Mesozoic grabens, as in the adjacent onland regions, but are partially covered offshore by a 1-3 km section of late Mesozoic and

Abstract DNAG Transect E-1. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

Abstract E-4 is one of eight Geodynamics transects that cross the Atlantic margin of North America between Georgia and Newfoundland. Five of the transects are in the United States and three are in Canada. Transect E-4, which is 110 km wide and more than 1,100 km long, extends from the stable North American craton just west of the Grenville front near Lexington, Kentucky southeastward across Cape Fear, North Carolina, on the Atlantic coast to oceanic crust east of the Blake Spur magnetic anomaly. Like all of the other U.S. Atlantic coast transects, it crosses Cambrian and Jurassic continental margins of North America as well as the Appalachian orogen. The display, based upon published information, portrays the geology, tectonic style and geophysical expression of this segment of the eastern North American continental margin and interprets its Phanerozoic history. The Decade of North American Geology 1983 geologic time scale (Palmer, 1983) is used throughout the display and text.

Abstract DNAG Transect E-4. Part of GSA’s DNAG Continent-Ocean Transect Series, this transect contains all or most of the following: free-air gravity and magnetic anomaly profiles, heat flow measurements, geologic cross section with no vertical exaggeration, multi-channel seismic reflection profiles, tectonic kindred cross section with vertical exaggeration, geologic map, stratigraphic diagram, and an index map. All transects are on a scale of 1:500,000.

The U.S. Atlantic and Gulf of Mexico continental margins are thickly sedimented passive margins that formed when Pangea split apart during Middle Jurassic time to create the Atlantic Ocean and Gulf of Mexico. Keys to understanding the process of continental breakup and its relation to preexisting structure are found in the structure of the crust beneath the sediment-filled basins and adjacent platforms and embayments that outline the margins. Because of the great thickness of post-rift sedimentary rock in the basins and the presence of massive reef carbonates and salt layers and diapirs, the crustal structure beneath the basins in the region of the transition between oceanic and continental crust is poorly known at present. Recent advances in seismic reflection and refraction data collection techniques (both sources and receivers), however, are just beginning to yield new data to look at the crustal structure in this important region. One of the most important results on the deep structure of continental margins obtained in recent years is recognition of a thick, high-velocity (7.2 to 7.5 km/sec) layer at the base of the crust beneath the U.S. Atlantic continental margin as well as beneath several other margins worldwide. This layer is observed beneath both extended continental crust and early oceanic crust and has been interpreted to indicate that extensive intrusive magmatism was associated with the late stage of rifting and early sea-floor spreading. Only a weak suggestion of such a layer has been observed beneath the Gulf of Mexico margin, although this may be in part due to the difficulty of observing lower crustal arrivals because of the extensive presence of salt in the shallow section.

Abstract Baltimore Canyon Trough is the deepest depocenter for Mesozoic and Cenozoic sedimentary rocks along the U.S. Atlantic continental margin, with up to 18 km deposited beneath the continental shelf off New Jersey (Figs. 1,2, and 3). The landward edge of the trough is marked by a hinge zone where an abrupt increase in depth to basement is observed on seismic reflection profiles. The depth to the top of basement at the hinge zone usually occurs between 4 and 6 km, but secondary hinge zones in places are observed where basement is as shallow as 1 km or as deep as 8 km. The depth to basement increases toward the East Coast Magnetic Anomaly (ECMA), which marks the landward edge of oceanic crust. The width of the trough, as measured by the distance between the hinge zone and the main axis of the ECMA, varies from 60 km off Virginia to 100 km off New Jersey. In the northern half of the trough, the Jurassic paleoshelf edge complex has prograded seaward of the ECMA onto the oceanic crust by as much as 40 km (Figs. 2 and 4). During the late Cenozoic, the shelf edge, as defined by the present 200-m isobath, has retreated by 10 to 20 km from its prior position during Late Jurassic through early Cenozoic. The distance from the hinge zone to the Jurassic shelf edge varies from 50 km off Virginia to 140 km off New Jersey (Fig. 2).

Abstract Multichannel seismic-reflection data together with two-dimensional gravity and magnetic models suggest that the crustal structure off North Carolina consists of normal continental crust landward of the Brunswick magnetic anomaly (BMA), rift-stage crust in the 80-km-wide zone between the BMA and the East Coast magnetic anomaly (ECMA), and normal oceanic crust seaward of the ECMA.