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Physiography .1· , Atlantic Continental Shelf and Slope ~. of the United States ·- •t.,........_,C',...,.~~~""' 11:'·~~. '"''"' ~.~..-.. ......-.,· ....... ~ ·-,}........ ·. '~':7'n:.~~-... "" • '•ilfl::.t,l.>.o;r,~... ,, ~· ·-·· ·-. - '··~~ ..~-~'·· ··_ -·· ·~~--~----1 .., Physiography GEOLOGICAL SURVEY PROFESSIONAL PAPER 529-C Atlantic Continental · Shelf and Slope of The United States- Physiography By ELAZAR UCHUPI GEOLOGICAL SURVEY PROFESSIONAL PAPER 529-C Description of the submarine physiography of the continental margin between Nova Scotia and the Florida Keys UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director ~ : . For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page Page Abstract __________________________________________ _ C1 Continental margin-Continued Introduction ______________________________________ _ 1 Intermediate provinces _________________________ _ C17 General statement _____________________________ _ 1 Blake Plateau_·____________________________ _ 17 Acknowledgments ______ -.- ______________________ _ 3 Straits of Florida __________________________ _ 19 Continental margin ________________________________ _ 3 Continental slope ______________________________ _ 21 General setting________________________________ _ 3 Provinces seaward of the continental slope ________ _ 27 Continental shelf ______________________________ _ 3 Continental rise ___________________________ _ 27 Scotian Shelf ______________________________ _ 5 Blake Basin and Blake Ridge _______________ _ 28 Summary _________________________________________ _ Georges Bank _____________________________ _ 5 28 Gulf of Maine _____________________________ _ 7 References cited ____________________________________ _ 29 East Coast Shelf ___________________________ _ 10 ILLUSTRATIONS [Plates are in pocket] PLATES 1-3. Maps showing bottom topography of the continental margin: 1. Nova Scotia to New Jersey. 2. New Jersey to South Carolina. 3. South Carolina to the Florida Keys. Page FIGURE 1. Model of the continental margin from Nova Scotia to the Florida Keys ________________ -_------------- C2 2-5. Maps showing: 2. Density of soundings used in construction of charts ___________________ ----------------------- 3 3. Physiographic provinces of the continental margin, Nova Scotia to the Florida Keys______________ 4 4. Distribution of sand waves on Georges Bank-------------------------------------------.,.----- 6 5. Bathymetry of Cultivator ShoaL----------------------------------------------------------- 8 6. Trace of a Precision Depth Recorder profile of a series of small channels along the north slope of the Gulf of Maine--------------------------------------------------------------------------------------- 9 7. Map showing outline of the basins within the Gulf of Maine----------------------------------·------- 10 8. Bottom profile showing sub bottom reflector in the deeper parts of Jordan Basin ______ ------ ------ ____ -- 11 9. Map and profiles showing morphology of the continental shelf from Juniper Inlet to Marquesas Key, Fla_- 12 10. Variation in depth along the shelf-break___________________________________________________________ 13 11. Map showing distribution of sand shoalsand sand waves on Nantucket Shoals and Nantucket Sound_____ 14 12. Detailed map of a section of Nantucket Shoals ________________________________________ ---------_-_- 15 i3. Map showing bathymetry of sand swells south of Long Island ___________ ._____________________________ 16 14. Map showing sand swells on the continental shelf ___________________________________________ --______ 18 15. Bottom profiles of the northern edge of the Blake Plateau___________________________________________ 19 16-19. Maps showing: 16. Bathymetry of the Blake Plateau ___________________________ :.. ____________________ ---_-----_ 20 }, 17. Topography of a part of the rough zone at the base of Florida-Hatteras Slope___________________ 21 18. Zone of rough topography along the western boundary of the Blake Plateau and the northern tip of the Straits of Florida ___________________________________________________ ._______________ 22 19. Bathymetry of the Straits of Florida________________________________________________________ 23 20. Bottom profiles of Miami and Pourtales Terraces___________________________________________________ 24 21. Map showing topography of Miami Terrace________________________________________________________ 25 22. Bottom profiles of the continental slope------------------------------------------------------------ 26 23. Map showing bathymetry of the continental slope and rise near Northeast ChanneL____________________ 27 TABLES Pa~re TABLE 1. Depth, area, and volume of basins in the Gulf of Maine _ _:________________________ C9 2. Depth to outer edge of terraces of the continental shelf, slope, and Florida-Hatteras Slope___________________________________________________________________ 13 III ATLANTIC CONTINENTAL SHELF AND SLOPE OF THE UNITED STATES-PHYSIOGRAPHY 1 By ELAZAR UcHUPI, Woods Hole Oceanographic Institution ABSTRACT scription of the topographic provinces of the margin The continental margin from Nova Scotia to the Florida Keys from Nova Scotia to the Florida Keys and a discussion exhibits a variety of physiographic forms. On the basis of sur­ of the origin of these provinces are the prime objectives face morphology it can be divided into three zones. In the of this report. This paper is one of a series on the ma­ northern zone, the continental shelf extending from Nova Scotia rine geology of the continental margin off the Atlantic to Nantucket Island, has broad basins separated by shallow coast of the United States. Emery ( 1966) discussed the flat-topped banks, undulating swells, and irregularly crested ridges; some of the basins reach depths greater than 200 meters. general aspects of the investigation, and Prn,tt ( 1968) This type of shelf topography is characteristic of shelves off described the physiography and sediments of the ad­ glaciated areas and terminates at or near the southern limit of jacent deep-sea basins. Description of the topographic Pleistocene glaciation. Seaward of the shelf most of the conti­ provinces of the continental margin from Nova Scotia nental slope is deeply entrenched by submarine canyons. At the to the Florida l(eys is based principally on the three foot of the slope is a large sedimentary apron known as the continental rise. charts included with this report and on more than 5,000 The central zone from Nantucket Island to Cape Lookout also kilometers of PDR (Precision Depth Recorder) traces consists of continental shelf, slope, and rise. Although smoother obtained during the present investigation. Physio­ than in the northern zone, the surface of the shelf is disrupted graphic interpretations presented in this paper are based by sand swells, channels, coral mounds, and terraces. Most of largely on published reports. The conclusions are tenta­ these features may be related to lower stands of sea level during the Pleistocene. The continental slope in this zone is as deeply tive and may be affected by the continuous seismic entrenched by submarine canyons as the slope in the northern studies to be undertaken by this and other projects. zone. The continental rise seaward of the continental slope is Studies of the sea bottom along the east coast of similar to that in the northern zone. United States and Canada were initiated well over a The continental margin in the southern zone from Cape Look­ out to the Florida Keys is more complicated than the areas century ago. As early as the middle of the 19th century, farther north. The continental slope is relatively smooth and has leadline soundings were taken by the U.S. Coast: ~nd gradients as high as 20°-five times steeper than the slope Geodetic Survey and the British Admiralty along the farther north. The area landward of the slope does not consist coast, on offshore banks, and on the continental shelf. of a simple continental shelf as it does farther north but instead Later these surveys were extended seaward to include consists of a shelf, a marginal plateau (the Blake Plateau), a trough (the Straits of Florida), and the Bahama Banks. In the continental slope, continental rise, and the abyssal this sector of the continental margin, the topographic position plains. Data from these surveys were used by Agassiz occupied by the continental rise farther north is occupied by (1888) to compile a topographic 1nap of the continental the broad flat-bottomed Blake Basin and Blake Ridge. East of margin from the Gulf of Maine to the Florida l(eys. Nantucket Island, topographic differences are believed to be due Because of the great length of time required to make to glacial erosion, which has deepened the normal shallow shelf; south of Cape Lookout, they are believed to be due to folding wire soundings, the concentration of soundings was so or faulting, erosion by the Gulf Stream, and calcareous low that it prevented accurate determination of the accretion. diagnostic details of the continental margin. Since the INTRODUCTION development of echo-sounding devices and accurate GENERAL STATEMENT navigational methods, enough soundings have been col­ lected for a regional study of the continental margin. The submarine topography of the continental mar­ The first detailed investigation of the physiography gin (fig. 1) offers abundant
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