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10 m2, with an average value of 1.3 organisms per 10 m2. The abundance of organi sms at these depths and below a water mass of low productivity (southern Sargasso Sea) is very unusual (Rowe, 1971); expected animal densities are probably less than 0.2 organisms per 10 m2 (Rowe and Menzies, 1969). Significant benthic activity is also confirmed by the abundance of burrow mottling in the cores (Fig. 4.1). The va r i e ty and i n ten s i ty 0 f be nth i c act i v i ty s u g g est s t hat the high organic carbon in the sediment may create unusually rich feeding grounds for the organisms. Sediment cores from the Silver and Nares Abyssal Plains show the typical alternation of pelagic and turbidite sequences normally encountered beneath abyssal plains (Ericson and others, 1961). This is most strongly demon- strated in the grain-size distribution (Fig. 4.24 where silt may constitute 80% of the sediment in a turbidite sequence on the Nares Abyssal Plain. The quantity of organic carbon is similar to that on the Greater Antilles Outer Ridge. The Nares Abyssal Plain differs from other abyssal plains in the North Atlantic in that it is isolated from direct downslope sedimentation from continental margin SQurces; Vema Gap is the main tributary through which sediment is funnel ed to thi s area. The i sol ation of the Nares Abyssal Plain probably results in deposition of thin, distal turbidite sequences on its surface. This is indicated by the virtual absence of sand-sized material (Fig. 4.2) and by the thick sequences of fine silt and lutite laminae (Fig. 4.5). 76 ; \, i : /
\ ) ) Figure 4.5. Distal turbidite sequences in MT. MITCHELL core 1GC from the southern edge of the Nares Abyssal Plain: Left, 139-151 cm; right 172-184 em. Each such sequence of fine-grained, finely laminated sediments may represent distal depositi on from dozens of turbi di ty-current events. Sea 1 e: 1 d i vis ion = 1 mm. 77
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I "a f IMods Hole '" ~ o c.,,~tlOGR
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parent sediment on the eastern oute
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esearch. 5 )
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Res u 1 ts. . . . . . . . . . . . .
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Figure 3.12 Echo-sounding profile (
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Fi gure 6.14 6. 15 7. 1 7.2 7.3 7.4
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\ I ) Table 4. 1 4.2 5.1 5.2 5.3 6.
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CHAPTER I INTRODUCTION The area inv
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) \ .1 Fi gure i. 1. Bathymetry of
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~. ~ 71° 70° tI 68 fJ0 25° 7' 25
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) ) This is expected since most of
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GENERAL DES CRI PT I ON CHAPTE R I
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j
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egi onal contours. An area centered
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this region. However, all of these
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'"-, i~ 7t 70° 6f 68 67° 25° 72
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Fig u r e 3. 2 . CON RA D 10 s e is
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sequence corresponds to layered tur
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) . .) Figure 3.3. Map showing domi
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"- '''--.- 25° ................. .
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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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Page 67 and 68: ) ) Figure 3.7. CONRAD 10 seismic r
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Page 71 and 72: ) ) THE TRANSPARENT LAYER The distr
Page 73 and 74: Fi gure 3.8. CH A I N 34 s e ism i
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Page 79 and 80: ) Figure 3.9. CONRAD 10 seismic ref
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Page 83 and 84: \ J ) Figure 3.10. Seismic reflecti
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Page 87 and 88: ì ) Figure 3.11. CONRAD 10 seismic
Page 89 and 90: l UJ .líliiiP',,:... ¡ '"'" ~ ' ~
Page 91 and 92: ) .I Figure 3.12. Echo-soundi ng pr
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Page 95 and 96: ) ) Figure 3.13. CONRAD 10 seismic
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Page 99 and 100: ) ) GENERAL LITHOLOGY CHAPTER iv TH
Page 101 and 102: ~ , ) Figure 4.1. General lithology
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Page 108 and 109: average of 80% lutite (~ 2 ~m) and
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Page 120 and 121: The laminated zones and overlying p
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Page 127 and 128: ) ) Figure 4.7. Graph of carbonate
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Page 131: ) ì i Figure 4.8. Curves of carbon
Page 134 and 135: currents have transported many Fora
Page 136 and 137: increased dissolution (elevated lys
Page 138 and 139: TABLE 4.1. MINERALOGY OF THE c 2 ~m
Page 140 and 141: the following peaks and weighting f
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Page 150 and 151: Obvi ous ly, di 1 uti on of the nor
Page 152 and 153: The m i n era log i c a 1 com po si
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Page 158 and 159: TABLE 5.1. AVERAGE RATES OF SEDIMEN
Page 160 and 161: and thus the T-Z zonation (Fig. 5.1
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Page 164 and 165: 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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) ) ~ 2.2 ~ 2.0 t2 ~ tt ~" 1.8 .. ~
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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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" ) / ) 10 19 17 5 5616 M 5801 M N
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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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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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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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) ) 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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