IBRARY CO Atlantic Continental Shelf and Slope of the United States Shallow Structure GEOLOGICAL SURVEY PROFESSIONAL PAPER 529·1 Atlantic Continental . r.. Shelf and Slope of The United States- Shallow Structure By ELAZAR UCHUPI GEOLOGICAL SURVEY PROFESSIONAL PAPER 529-I Description of the subsurface morphology of the shelf and slop~ (continental terrace) ·and some speculations on the evolution of the sedimentary framework of the terrace UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1970 • UNITED STATES DEPARTMENT OF THE INTERIOR WALTER J. HICKEL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price $1 (paper cover) CONTENTS P11ge Pllge Abstract------------------------------------------- 11 Continental shelf from Cape lioa to Virginia___________ 113 Introduction---------------------~----------------- 1 Continental slope from· Georges Bank to Cape Hatteras_ 15 Acknowledgments _____________________________ _ 2 Continental shelf from Cape Hatteras to Cape Romain___ 19 Topographic setting ___________________ --- _____ ---- __ 2 Blake Plateau area__________________________________ 19 Methods of study __________________________________ _ 2 Straits of Florida ___________ :... _______________ :._______ 30 Scotian Shelf area _________________________________ _ 5 Geologic maP-------------------------------------- 31 5 Isopach maps_ _ _ _ _ __ _ _ _ _ __ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 33 Gulf of Maine and Bay of FundY-------------~------­ Northeast and Great South Channels----------------- 9 Conclusion___ _ _ _ _ _ _ __ _ _ _ _ _ __ _ _ __ _ _ _ _ __ __ _ _ _ _ _ _ _ _ _ _ _ 38 Georges Bank _____________________________________ _ 11 Nature of the con tinen tal shelf and slope_ - _ _ _ _ _ _ _ _ 38 Long Island, Block Island, Rhode Island, and Vineyard Formation of the continental terrace-_____________ 38 Sounds, and Buzzards Bay ________________________ _ 12 References cited____________________________________ 41 ILLUSTRATIONS Pal{e PLATE 1. Bathymetric map of the shelf, slope, and rise between Nantucket Shoals and Chesapeake Bay____ -____ In pocket FIGURE 1. Bathymetric chart showing physiographic provinces of the continental margin _______________________ -__ I3 2. Bathymetric chart showing locations of seismic-reflection profiles ___________________________ --- ___ ---- 4 3-5. Seismic profiles: ' 3. Off Nova Scotia and south of Georges Bank_________________________________________________ 5 4. Off Nova Scotia, Maine, and Long Island _______________________________________ --_-- ___ ---- 6 5. In the Gulf of Maine ________________________________________________________________ -____ 7 6. Bathymetric chart showing locations of seismic profiles in the Gulf of Maine ___________________ - _____ -- 8 7. Echo-sounding profile in the Gulf of Maine-------------------------------------------------------- 9 8. Map and seismic-pro filer record showing buried erosional remnants in Cape Cod Bay ___________ - ______ - 9 9-11. Seismic profiles: . · 9. Northeast Channel and Georges and Franklin Basins---------------------------------------- 10 10. Great South Channel-------------------------------------------------------------------- 11 11. Across Georges Bank-------------------------------------------------------------------- 12 12. Bathymetric map showing sand shoals on Georges Bank and Nantucket Shoals_________________________ 13 13. Seismic profiles of Long Island Sound and other sounds off New England__________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 14 14. Seismic profiles across the inface slope of the shelf cuesta_____________________________________________ 16 15. Bathymetric map showing locations of profiles across cuesta----------------------------------.-------- 17 16. Seismic profiles across zone of disturbed sediments south of Martha's Vineyard ________________________ - 18 17. Photograph of seismic recording across zone of disturbed sediments____________________________________ 18 18. Seismic profiles of outer shelf and slope between Georges Bank and western Long Island ________ :_________ 19 19. Seismic profiles of lower slope and rise------------------------------------------------------------- 19 20. Photographs of two seismic-reflection profiles ________________________________ ~______________________ 20 21. Bathymetric map showing location of profiles in figures 19 and 20------------------------------------ 21 22-28. Seismic profiles: 22. Shelf, slope, and upper rise between New Jersey and Chesapeake Bay_________________________ 22 23. Between Chesapeake Bay and Cape Lookout----------------------------------------------- 22 24. Shelf parallel to shore _______________________________________________________ -~-___________ 22 25. Continental margin between Capes Lookout and Fear________________________________________ 23 26. Depressions and coral bank on Blake Plateau----------------------------------------------- 23 27. Across Florida-Hatteras Slope____________________________________________________________ 24 28. Continental margin from Charleston to Cape KennedY--------------------------------------- 25 m IV CONTENTS Page FIGURE 29. Bathymetric map showing locations of profiles in figures 28, 30, and 3L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I26 30. Seismic profiles in area of JOIDES holes----------------------------------------------------------- 27 31. Stratigraphic units from JOIDES holes superimposed on seismic profile________________________________ 28 32. Echo-sounding profiles across algal ridge along the shelf-break________________________________________ 29 33. Seismic profiles of Straits of Florida-------------------------------------------------------------- 30 34. Pre-Quaternary geologic map of the margin________________________________________________________ 32 35. Seismic profiles across the Fundian fault zone______________________________________________________ 34 36-37. Isopach maps: 36. Triassic and post-Triassic strata_________________________________________________________ 35 37. Tertiary sediments______________________________________________________________________ 36 38. Sediment distribution and isopach maps of Holocene deposits in Gulf of Maine and cross section_________ 37 39. Schematic diagrams showing structural cross sections off New Jersey, Blake Plateau, and Straits of Florida__ 40 ATLANTIC CONTINENTAL SHELF AND SLOPE OF THE UNITED STATES-SHALLOW STRUCTURE 1 By ELAZAR UcHUPI, Woods Hole Oceanographic Institute ABSTRACT INTRODUCTION The con tinental terrace (con tinental shelf and slope) off the The continental m·argin off the east coast of the east coast of the United States can be qivided into two segments. North of Cape Hatteras, N.C., the shelf is immed.ia.tely adjacent tJ nited States is probably one of the best surveyed to the continental slope; south of Cape Hatteras, the shelf is submarine areas in the world. Its bathymetry has either separated from the sl·ope by a marginal plateau (Blake been described in considerable detail (Garrison and Plateau) or is cut in two by a marginal trough (Straits of McMaster, 1966; Heezen and others, 1959; Hurley, FlOTida). The northern segment of the continental terrace was formed 1964; Hurley and others, 1962; Jordan and others, 1964; by upbuilding on the shelf and outbuilding on the slope atop Jordan and Stewart, 1961; Murray, 1947; Pratt, 1968; subsiding Triassic and Jurassic rocks and the Paleoroic base­ Pratt ·and Heezen, 1964; U.S. Coast ·and Geod. Survey ment. Strata .on some sections of the shelf, in both the northern and U.S. Bur. Commercial Fisheries, 1967; Uchupi, and southern segments, have been slightly worked into broad 1965, 1966a--e; Veatch and Smith, 1939). Total sediment ridges at right angles and parallel to shore. Within the southern segment, the slope east of the Blake Plateau (Blake Es:caTJ)ment) thickness atop the pre-Triassic basement has been deter­ was formed by carbonate accretion or reef buildup. Carbonate mined for most of the margin by seismic-refraction accretion, possibly accompanied by folding and faulting, alSIO methods (Antoine and Henry, 1965; Drake and others, formed the side slope of the S·tJraits of Florida. The shelf and 1959; Hersey ·and others, 1959; Sheridan and others, }"'lorida-Hatteras Slope west of the Blake Plateau were formed by 1966). Systematic coring, dredging (Ericson and others, upbuilding on the shelf .and outbuilding on the slope in the direction of .the Blake Plateau. 1952, 1961; Gibson, 1965; Gibson and others, 1968; The framework of the continental terrace was modified con­ Heezen and Sheridan, 1966; Northrop and Heezen, siderably during the Pleistocene. Progl·acial fluvial and glacial 1951; Stetson, 1949), and drilling (Joint Oceanog. Inst. e~sion deepened the normally shallow shelf east of New York. Deep Earth Sampling Program, 1965) have yielded Fluvial and marine erosion and deposition formed the channels, data on the stratigraphy of the region. Recent surveys deltas, ·and .terraces on the shelf's surface west of Georges Bank. Turbidity currents, slumping, and gravitational sliding deeply using seismic-reflection profilers have added consider­ eroded ·and steepened the normally gentle continental slope narth able information on the subsurface of several segments of Cape Hatteras. Erosion by the Gulf Stream modified the Blake of the margin (Emery and Uchupi, 1965; Ewing and Plateau and Florida-Hatteras Slope. lf'arther south, deposition