Atlantic Continental Shelf and Slope of the United States - Physiography

Abstract

The continental margin from Nova Scotia to the Florida Keys exhibits a variety of physiographic forms. On the basis of surface morphology it can be divided into three zones. In the northern zone, the continental shelf extending from Nova Scotia to Nantucket Island, has broad basins separated by shallow flat-topped banks, undulating swells, and irregularly crested ridges; some of the basins reach depths greater than 200 meters. This type of shelf topography is characteristic of shelves off glaciated areas and terminates at or near the southern limit of Pleistocene glaciation. Seaward of the shelf most of the continental slope is deeply entrenched by submarine canyons. At the foot of the slope is a large sedimentary apron known as the continental rise. The central zone from Nantucket Island to Cape Lookout also consists of continental shelf, slope, and rise. Although smoother than in the northern zone, the surface of the shelf is disrupted by sand swells, channels, coral mounds, and terraces. Most of these features may be related to lower stands of sea level during the Pleistocene. The continental slope in this zone is as deeply entrenched by submarine canyons as the slope in the northern zone. The continental rise seaward of the continental slope is similar to that in the northern zone. The continental margin in the southern zone from Cape Lookout to the Florida Keys is more complicated than the areas farther north. The continental slope is relatively smooth and has gradients as high as 20°-five times steeper than the slope farther north. The area landward of the slope does not consist of a simple continental shelf as it does farther north but instead consists of a shelf, a marginal plateau (the Blake Plateau), a trough (the Straits of Florida), and the Bahama Banks. In this sector of the continental margin, the topographic position occupied by the continental rise farther north is occupied by the broad flat-bottomed Blake Basin and Blake Ridge. East of Nantucket Island, topographic differences are believed to be due to glacial erosion, which has deepened the normal shallow shelf; south of Cape Lookout, they are believed to be due to folding or faulting, erosion by the Gulf Stream, and calcareous accretion.

Clinoforms and clinoform systems: Review and dynamic classification scheme for shorelines, subaqueous deltas, shelf edges and continental margins

“…Following the onset of the "middle Cretaceous" climate warming and global oceanic anoxia (e.g., Patruno et al, 2015d;Unida and Patruno, 2016), a major Late Cretaceous eustatic rise (c. 100-200 m) caused the shelfedge to be shifted up to 300 km landward, giving rise to a detached shelf-edge clinoform (Florida-Hatteras Slope) and a compound passive/ draping continental margin clinoform (Blake Escarpment), separated by the wide submarine Blake Plateau (Figs. 10A, C, 18A -B, 19A;Uchupi, 1968;Shipley et al, 1978;Schlee et al, 1979;Dillon et al, 1983).…”

“…(Legler et al, 2013) Jones et al, 2013;Pellegrini et al, 2018). This includes large-scale sediment transfer to the basin-floor of continental-margin clinoforms (e.g., oceanic abyssal plains), as in the Niger Delta and the Cretaceous Tres Pasos-Dorotea formations, Chile (Uchupi, 1968;Damuth, 1994;Hiscott, 2001;Covault et al, 2009;Hubbard et al, 2010). More generally, in continental-margin clinoforms, only negligible river-derived sediment transport towards the abyssal plain takes place, particularly during highstands (e.g., < 5% in the Recent Gulf of Papua), but the presence of submarine canyons extending in proximity of river mouths changes dramatically this sediment balance (e.g., about 90% of Recent sediment off the Sepik River) (Walsh and Nittrouer, 2003;Sweet and Blum, 2016).…”

Shallow stratigraphic control on pockmark distribution in north temperate estuaries

“…As these topographic lows extend seaward they become scoured, seaward sloping troughs, termed 'shelf valleys' Barnhardt et al, 1996Barnhardt et al, , 2009. The origin of underlying depressions is unknown, though they may reflect faulting (Osberg et al, 1985), fluvial erosion (Johnson, 1925), glacial scour (Shepard, 1931), some combination of the three mechanisms (Uchupi, 1968), or even subglacial meltwater pathways as inferred elsewhere (Boyd et al, 1988).…”

Potential geologic hazards and constraints for blocks in South Atlantic OCS oil and gas lease sale 43 (sale held March 28, 1978)

“…2). The regional physiography of the Atlantic Continental Shelf and Slope has been described in detail by Uchupi (1968) and additional source material and discussion can be found in Emery and Uchupi (1972). The most prominent morphologic element within the survey area is the shelf break, which occurs at depths between 50 and 60 m and demarcates the transition between shelf and slope physiographic and sedimentary provinces.…”