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) ) THE HISTORY OF SEDIMENTATION AND ABYSSAL CI RCULATI ON ON THE GREATER ANTI LLES OUTER RI DGE Brian E. Tucholke Submitted to the Massachusetts Institute of Technology- Woods Hole Oceanographic <strong>Institution</strong> Joint Program in Oceanography on August 13,1973, in partial fulfillment of the requirements for the degree of Doctor of Philosophy. ABSTRACT The Greater Antilles Outer Ridge is an 1800 km long, submarine sedimentary ridge which lies below 5000 m in the southwes tern North At 1 anti c Ocean. Sei smi c refl ecti on profiles and core data indicate that the ridge is composed of more than 6 x 10 km3 of acoustically transparent sediment which has accumulated above a sequence of acoustically ,stratified sediments deposited before late Eocene time. The sediments consist of low-carbonate, homogeneous, terrigenous lutites which have accumulated at rates of up to 30 cm/1000 yr. since the middle Eocene. Clay-mineral analyses indicate that the chlorite-enriched sediment is derived from the northeastern continental margin of North Ameri ca. Abyssal contour-following currents which flow around the Greater Antilles Outer R~dge are interpreted as an extension of the Western Boundary Undercurrent (WBUC) found along the continental rise of eastern North America. This current system is proposed to be the agent which has transported sediment southward for more than 2500 km and deposited it on the Greater Antilles Outer Ridge. Sediment is presently carried in concentrations up to 65 ug/liter in the currents flowing around the outer ridge, and mineral analyses show that the suspended sediment has a northern provenance; it is similar in composition to the bottom sediment and is interpreted as the source of sediment deposited on the Greater Antilles Outer Ridge. The Puerto Ri co Trench began to form in mi ddle Eocene time, and it cut off direct downslope sedimentation to the Greater Antilles Outer Ridge. At the same time, the newly formed WBUC interacted with existing sea-floor topography and the Antarctic Bottom Water (AABW) flowing in from the South Atlantic, and it began to deposit acoustically trans- 2
parent sediment on the eastern outer ridge. This depositional pattern persisted until the middle or late Miocene, when increased AABW flow di verted the WBUC to the northwes t and initiated deposition of the western sector of the Greater Anti lles Outer Ri dge. Shortly thereafter, decreased AABW flow and lower current speeds allowed rapid deposition of sedi ment on the Greater Anti 11 es Outer Ri dge and on the Cai cos Outer Ri dge to the wes t. The bottom topography has controlled the abyssal current pattern, and current-controlled deposition has continued to construct the Greater Antilles Outer Ridge since early Pliocene time. Thesis Supervisor~ Dr. Charles D. Hollister Ti tl e: Associ ate Scienti st 3 )
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Page 15 and 16: Fi gure 6.14 6. 15 7. 1 7.2 7.3 7.4
Page 17 and 18: \ I ) Table 4. 1 4.2 5.1 5.2 5.3 6.
Page 19 and 20: CHAPTER I INTRODUCTION The area inv
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Page 25 and 26: ) ) This is expected since most of
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) ) others, 1973), and the upper po
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) Figure 3.5. CONRAD 8 seismic refl
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. Q) 3W/L NOI.L~ l( . (Y CI s. :: 0
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.) Figure 3.6. Idealized profile al
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) ) Figure 3.7. CONRAD 10 seismic r
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i- (Y (1 ~:: en or- LL 47
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) ) THE TRANSPARENT LAYER The distr
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Fi gure 3.8. CH A I N 34 s e ism i
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co . (Y (l So :: O' "r- Li 51
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) 53
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) Figure 3.9. CONRAD 10 seismic ref
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0' (V CJ s. :: O' ... LL 55
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\ J ) Figure 3.10. Seismic reflecti
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or- . (V Q) S- :: rn Li 58
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ì ) Figure 3.11. CONRAD 10 seismic
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) .I Figure 3.12. Echo-soundi ng pr
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N CV OJ s. :: 01 l. 62
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) ) Figure 3.13. CONRAD 10 seismic
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(' r- (' (j $. :: en 'r- LL 64
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) ) GENERAL LITHOLOGY CHAPTER iv TH
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~ , ) Figure 4.1. General lithology
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.'-/ '..-/ AIr 60-8 A II 60-8 An60~
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average of 80% lutite (~ 2 ~m) and
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10 m2, with an average value of 1.3
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The laminated zones and overlying p
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) ) Figure 4.7. Graph of carbonate
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) ) z 0 N O~ E I i ,,_.' i." I ." .
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) ì i Figure 4.8. Curves of carbon
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currents have transported many Fora
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increased dissolution (elevated lys
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TABLE 4.1. MINERALOGY OF THE c 2 ~m
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the following peaks and weighting f
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Obvi ous ly, di 1 uti on of the nor
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The m i n era log i c a 1 com po si
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gray 1 uti t e s per s i s t n ear
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TABLE 5.1. AVERAGE RATES OF SEDIMEN
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and thus the T-Z zonation (Fig. 5.1
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) ) )
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TABLE 5.2. AVERAGE RATES OF SEDIMEN
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Cl z: c: l/ l. i- c: Cl z: o OJ IX
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consolidated (A.J. Silva, pers. com
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in age, and the ash is probably ass
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122 must result from mixing with th
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eas twa rd flow of NADW between 150
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whi ch recorded currents for about
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,) , ,
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ottom photographs in February, 1972
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Several important features were obs
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141 turn north in the western part
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145 bottle spacing. An example is t
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~() ~ 3.0 ~ ~ ) ~ ~i. ) .. ~ 2.0 ~i
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) ) Figure 6.6. Silicate ("g-atoms/
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,) -) 152 structure persist at and
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) ~) 154 Figure 6.7. Current patter
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) ) 72° DEPTH IN CORR. METERS Fi g
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) ) speeds of 2 cm/sec (the stall s
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) I / Fi gure6. 8. 158 Progressi ve
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) ) ~ 160 Figure 6.9. Polar histogr
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,) B(LOWER) START 22 B(UPPER) START
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) ) Figure 6.11. Polar histogram of
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) 2700 ) 00 1800 F; g u re 6. 11 C
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, ) ) _/ Figure 6.12. 168 Progress
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\ --~ E START 21 5 30 12 XI 21 xu )
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) / i I .~J the flow recorded at cu
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) Figure 6.13. Directions and relat
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') ./ ) ,j 70° 68° 66° ~~oo · "
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Fig u re 6. 14. i 75 Bottom photogr
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S e c t ion 2 (F i g s. 6. 1, 6. 7)
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northwest flow along the west flank
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filter (0.50 lJmpore size). After f
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. '! ) ) ,./ 2.2 ~ 2.i () '- 2.0 ~
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) ) Figure 7.3. Light-scattering pr
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'\. './. V 23-7 V 23-6 V 25-74 V 25
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extensive erosion on the lower cont
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) \/ (SEM) to determine composition
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\ ) ) Figure 7.4. 195 Scanning elec
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The less than 2 ~m (lutite) fractio
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201 In a sample where additional cl
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TAB LE 7. 1. CALCULATE D CLAY MI NE
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cannot always be accepted at face v
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The apparent enrichment of chlorite
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in favor of the concept that the su
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on the north flank of the far easte
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that enough suspended matter has be
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The following pages describe a mode
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) )
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series of ridges associated with an
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Eocene to 01 i gocene (Monroe, 1968
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(Table 8.1). The interbedded silts
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229 Chase and Hersey, 1968). The th
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\ ! Figure 8.3. 231 Schematic diagr
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Downslope sedimentation covered the
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) 235 Fi gure 8.4. Sketch showi ng
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'\ l ) ~z w u w a: o ~ wz w o u ~ w
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) / the same event of current-contr
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) Figure 8.5. Idealized representat
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) \ ) d / 'I i II I Ii I i I i I I
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) \ ) formed earlier depositional s
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) ) homogenei ty of the sediments o
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) ) 2 ) Sou t h S lop e - P u e rt
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248 Biscaye, P.E. and S.L. Eittreim
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Ericson, D.B., M. Ewing, G. Wollin
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Hersey, J.B. (1965) Sediment pondin
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McCullough, J.R. and G.H. Tupper (1
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Swallow, J.C. and L.V. Worthington
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" ) )
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259 approximation of the amount of
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s ~ 0 ~ Q) o '- CO 0 U ~ it \f0 Q)
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) )
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Crui se All 11 All 11 AII 60 Leg 8
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TABLE A2.1. BOTTOM PHOTOGRAPHS (Con
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TABLE A2.1. BOTTOM PHOTOGRAPHS (Con
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TAB LE A2. 1. BOTTOM PHOTOGRAPHS (C
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CH 19 CH 19 CH 19 CH 34 CH 34 TABLE
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KN25 KN 25 KN 25 KN 25 TABLE A2.1.
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LL 8 LL 8 LL 8 LL 8 LL 8 SA C ru is
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) )
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s. .. M i. 0 1. " .. QJ ..- N .. C'
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~.. c. 0' 0 .. Q)+l- ~ 0' 0' 0 ~ M
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TABLE A3.1. SUSPENDED PARTICULATE M
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) -) APPENDIX IV PHYSICAL PROPERTIE
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) ) Figure A4.1. Plots of water con
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) ) C\' 0 § to ~ ~ ~ 0 ~ ~ ~ CI Q:
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) /) 295 Figure A4.5. Plots of wate
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'-. ~, 160 SHEAR STRENGTH 30 50 (g/
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) ) Figure A4.6. Plots of water con
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) , )
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) ) 307 Fi gure A4.11. Plots of wat
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"-, ',, WATER CONTENT (% DRY WEIGHT
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) j 309 Figure A4.12. Plots of wate
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) ) ./
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) 312 WATER CONTENT (%DRY WT) SHEAR
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) J BIOGRAPHY Born: Ma rch 19, 1946
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') \ ) ~UWDATORY DISTRIBUTION LIST
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) J
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UNCLASSI FIED 1/31/74 SECURITY CLAS
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