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Texture of Surface Sediments from New Jersey to Southern Florida

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Texture of Surface Sediments from New Jersey to Southern Florida Atlantic Continental Shelf and Slope of the United States Texture of Surface Sediments from New Jersey to Southern Florida GEOLOGICAL SURVEY PROFESSIONAL PAPER 529-M , Atlantic Continental Shelf and Slope of the United States­ Texture of Surface Sediments from New Jersey to Southern Florida By CHARLES D. HOLLISTER GEOLOGICAL SURVEY_ PROFESSIONAL PAPER 529-M An interpretation of textural parameters of sediment from the continental shelf and slope and the Blake Plateau and their relationship to modern patterns of oceanic circulation • UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 73-600248 • For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402- Price $1.50 (paper cover) Stock Number 2401-02432 CONTENTS Paee Abstract ---------------------------------------------------------------- ~1 Introduction ------------------------------------------------------------- 1 Acknovvledgynents -------------------------------------------------------- 4 Sediment texture --------------------------------------------------------- 4 Scatter diagrams of grain-size parameters --------------------------------- 11 Discussion -------------------------------------------------------------- 14 Conclusions ------------------------------------------------------------- 21 Selected references ------------------------------------------------------- 22 ILLUSTRATIONS Page PLATE 1. ~aps shovving distribution of general sediment textures and gravel, sand, silt, and clay in surface sedi- ment on the continental margin from Nevv Jers·ey to southe·rn Florida ---------------------- In pocket 2. ~aps shovving distribution of statistical measures of surficial sediments on the continental margin from Nevv Jersey to southern Florida --------------------------------------------------------- In pocket Page FIGURE 1. ~ap of the continental margin from Nevv Jersey to southern Florida shovving sample localities and bot- tom currents ------------------------------------------------------------------------------ ~2 2. Schematic sections of bottom currents and subbottom reflecting horizons along the continental slope off Florida ----------------------------------------------------------------------------------- 5 3. ~ap shovving bottom currents, microphysiography, and s·ediment cores on the continental margin south of Cape Hatteras ------------------------------------------------------------------------- 6 4. Photograph of shells on rippled oolitic sand on the continental shelf -------------------------------- 8 5. Photograph shovving short-crested ripples in sand beneath the Gulf Stream ------------------------- g 6. Ternary diagram of clay-silt-sand or gravel-silt-sand components of continental surficial sediment off the southeastern lJnited States ------------------------------------------------------------- 10 7 2. Scatter diagrams of statistical measures of surficial sediments on the continental margin from Nevv ~ Jersey to southern Florida: 7. ~ean grain size versus standard deviation ----------------------------------------------- 12 8. ~ean grain size versus skevvness -------------------------------------------------------- 13 9. ~ean grain size versus kurtosis -------------------------------------------------------- 14 10. Skevvness versus standard deviation ----------------------------------------------------- 15 11. Kurtosis versus s.tandard deviation ----------------------------------------------------- 16 12. Kurtosis versus ske·vvness -------------------------------------------------------------- 17 13. Photograph shovving current-scoured mangane•se- and phosphate-encrusted slabs on the central Blake Plateau ----------------------------------------------------------------------------------- 18 14. ~ap shovving sand-svvell crests on the continental sheU from Nevv Jersey to southern Florida -------- 19 15. Graph shovving depth of vvater versus mean grain size for sediment beneath the Gulf Stream Counter Current ----------------------------------------------------------------------------------- 20 16. Graph shovving depth of vvater versus standard deviation for sediment beneath the Gulf Stream Coun- ter Current ------------------------------------------------------------------------------- 20 17. Graph shovving depth of water versus skevvness for sediment beneath the Gulf Stream Counter Current_ 21 III ATLANTIC CONTINENTAL SHELF AND SLOPE OF THE UNITED STATES­ TEXTURE OF SURFACE SEDIMENTS FROM NEW JERSEY TO SOUTHERN FLOIUDA1 By CHARLES D. HoLLISTER, Woods Hole Oceanographic Institution ABSTRACT the distribution and nature of ocean-bottom currents. A study of more than 800 bottom-sediment samples col­ In the study area (fig. 1) the continental shelf lected from the continental margin between New Jers·ey and ranges in width from less than 5 kilometers off Florida shows that sand covers almosrt the entire continental southern Florida to nearly 150 km off central Florida shelf. The sand is mainly unimodal, is well sorted, and has a and New Jersey (Veatch and Smith, 1939; Heezen symmetrical grain-size distribution curve. Mean grain size and others, 1959; Jordan, 1952; Uchupi, 1968). The generally increases toward the shelf break. Shelf sands con­ taining an appreciable amount of calcium carbonate on the shelf is smooth (relief less than 50 meters and has continental shelf south of Cape Hatteras are texturally simi­ a seaward gradient of less than 1:1,000. lar to the sands consi,sting mainly of quartz and feldspar An abrupt increase in slope from about 1:1,000 to north of Cape Hatteras, and thus it appears that composition about 1:10 occurs at the "shelf break" marking the does not influence grain-size distribution. The continental seaward limit of the continental shelf and the begin­ s.Iope off the Carolinas is covered by sand; north of there, the slope is covered by clayey and sandy silt. The upper con­ ning of the relatively steep continental slope where tinental rise is veneered by silty clay. gradients range from 1:40 to 1: 6. The depth of the Certain distinctive patterns of textural parameters appear shelf break generally ranges from 10m off Miami to to correlate with patterns of ocean-bottom circulation. The 120 m off Norfolk. In the study area it generally lies continental s.Iope off Florida is covered by poorly sorted clay between 40 to 70 m (Uchupi, 1968). Submarine can­ and silt deposited beneath the Gulf Stream Counter Current. Most fine-grained sediment is removed directly beneath the yons that slice through the continental slope north Gulf Stream. The &ilty sand near the southern margin of the of Cape Hatteras are generally less than 15 km wide Blake Plateau may be winnowed pelagic ooze transported and the largest are about 300 to 500 m deep (Heezen from the eastern Blake Plate·au by the westward-flowing and others, 1959; Rona and others, 1967). Antille·s Current. These two major current systems appear to The continental slope off Florida, along the west­ control sediment texture on the Blake Plateau. ern limit of the Blake Plateau, is about 75 m to INTRODUCTION about 750 m deep. An abrupt decrease in slope from 1:40 to 1: 1,000 marks the boundary with the Blake What are the relations between textural param­ Plateau which lies between 750 and 1,100 m below eters and the environment of deposition? Can one sea level. This major physiographic feature of the establish correlations between a known environment continental margin extends about 300 km seaward and the texture of surficial sediments that could be from the Florida continental slope. The seaward useful to sedimentologists working in ancient ma­ limit of the Blake Plateau is marked by an abrupt rine sediments where the environment has to be increase in slope at a depth of about 1,000 m. This inferred? This report, concerned with patterns of is the top of the precipitous Blake-Bahama Escarp~ bottom-sediment texture, is designed as an attempt ment whose face plunges to a depth of about 5,000 to answer these questions. m. Very little unconsolidated sediment has accumu­ Throughout this study the sediment textures, like lated on this current-swept scarp (Heezen and Sheri~ those of other continental margins, are assumed to dan, 1966). This feature marks the seaward limit of bear a close relation to the associated bottom relief, the study area east of Florida. the underlying geology, sea-level fluctuations, and Various submarine features such as sinuous 1 Contribution 2566 of the Woods Hole Oceanographic Institution, based ridges, sand waves, benches, and terraces found on on work done under a program conducted jointly by the U.S. Geological the continental slope are inferred to be remnants of Survey and the Woods Hole Oceanographic Institution and financed by the U.S. Geological Survey. former stands of sea level. The continental shelf Ml a:: ~ > 'OrO 1-3 t"f z> 1-3 1-4 ~. 0 C'l 0z 1-3 z1-4 'Or: zt:J 1-3> t" 00 ~ t;J ~ > 'Ore z t::l 100 0 100 KILOMETERS 00 t" 0 1-Q t;J ~,.... '01$ ~. ~<9. '\rO 'b. '\,; ~. '\i "'v. '\<:) 0 E X P L A N A T 0 N l:l:j 1-3 ~----- ~~ ~ Sample •location Gulf Stream'counter Current Western Boundary Undercurrent t;J ........_ ~ ~ ~ --+ z Gulf St~m Antilles Current Residual bottom drift 1-4 1-3 (Bottom axis) From Bumpus {1965) and Norcross t;J ~ and Stanley (1967) t::l Photographic current measurement 00 From Pratt (1963} and Heezen, 1-3 Hollister, and Rudd1"man {1966) >1-3 t;J
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