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South of 19"N, the McKENZIE pole no longer applies. The magnetic survey of ROESER(1975, 1976) suggests that the pole for the southern Red Sea must lie to the south. The best fit to hisisochrons gives a pole position of 7"N, 50.5"E, with a rate of opening for the past 2 m.y. of 5 x 10-7deg yrl. The corresponding half-spreading rate decreases from 0.75 cm yrl at 19"N to less than 0.6cm yrl south of 16"N.The pole just stated for the southern Red Sea has the important implication in that it predicts adifferent motion at 19"N from the Nubia-Arabia pole. We are therefore forced to conclude that a plateexists between Arabia and Nubia in the southern Red Sea, which as been named the North DanakilPlate, separated from Nubia by a zone of extension (Fig. 12). This extensional boundary is assumedto run along the western rift (discussed earlier from seismic data) through the Gulf of Zula to theDanakil Depression. As morphology suggests that the motion between the North Danakil and Nubianplates become negligible near 19"N since the zone of irregular topography terminates to the north near19"N, the rate of opening between Nubia and Arabia may be determined. This is 3.2 x deg yr-1,which corresponds to a spreading rate of 0.7 cm yr-l near 22"N and 0.5 cm yr-l at the northernextremity ofthe Red Sea.Since the orientation and motion along the Levant Shear System precludes it from being thetransform boundary between Nubia and Arabia, a separate plate, the Sinai Plate, must be assumed.The Sinai-Arabia pole may then be determined by assuming that the Levant Shear between the Lebanonand Anti-Lebanon Mountains and the Araba Depression lies on the same line of pure slip. This polecan thereby be estimated to be at 32.5"N, 4.4"W. The predicted motion along the Levant Shear is thenas follows: pure strike-slip in the Gulf of Aqaba and the Araba Depression, strike-slip with extensionin the Dead Sea and Jordan River area, compression with minor slip in Lebanon, pure strike-slip in theHoms region, and strike-slip with minor extension in Er-Rharb. The Arabia-Sinai rate of motion isthen determined by minimizing the motion between these two plates.The Sinai-Nubia pole obtained by vector composition can be determined to be at 35.9"N,42.6"E, with a rate of 1.65 x deg yr-l. A total rate of opening of 0.3 cm yrl in the Gulf of Suezin a WNW-ESE direction then results.The Arabia-Somalia pole (26.5"N, 21.5"E) can be determined from the magnetic anomalies inthe Gulf of Aden. The angular opening rate is 4 x deg yrl. The remaining Somalia-Nubia andNorth Danakil-Nubia poles can then be computed by vector addition.The total motion since early Miocene based on this kinematic pattern (Fig. 12) agreesreasonably well with the available data. Of particular interest is that the extension rates acrosscontinental grabens (e. . in the Ethiopian Rift), the western Red Sea Rift and in the Gulf of Suez is ofthe order of 0.3 cm yr- B . At this slow rate, features commonly associated with seafloor spreading arenot observed.REMARKS ON THE STRUCTURAL EVOLUTION OF THE RED SEA,GULF OF ADEN, AND EAST AFRICAN RIFT SYSTEMFigure 13 summarizes the structural evolution in the Red Sea, Gulf of Aden and the EastAfrican Rift. Both the Red Sea and the Gulf of Aden have been undergoing more-or-less synchronousseafloor spreading in one or more phases. In contrast, the East African Rift does not appear to becharacterized by active plate accretion, or else the accretion rate is so small that features common toactive spreading centers are not observable at present. Instead, intensive normal faulting, uplift andalkaline volcanism are the basic structural styles.Based on the idea of CLOOS (1939), we have proposed a sequence of events leading toseafloor spreading (DEGENS et al., 1971; WONG and VON HERZEN, 1974). These events are:1) uplift or arching caused by thermally activated volume increase resulting fromconvective upwelling in the asthenosphere (Fig. 14 I);2) block faulting and the propagation of normal faults from the top of the lithospheredownwards (Fig. 14 1);3) igneous and hydrothermal activity (regulated by the availability of meteoric water) andsubsequent erosion and non-marine deposition (Fig. 14 111);4) lithospheric thinning, possibly by divergent convective flow in the asthenosphere,perhaps accompanied by "diffuse extension" (COCHRAN, 198 1, 1982b);3.16
~5) continued thinning and rifting causing subsidence (McKENZIE, 1978), horst andgraben formation, and the tilting of blocks. This leads to an extensive marine incursionand a thick sedimentary sequence; and6) seafloor spreading with basaltic intrusions and hydrothermal convection (Fig. 14 IV).It has been suggested that in the early stages of continental rupture a three-arm-system oftendevelops in a more or less symmemc pattern (BURKE and DEWEY, 1973; BURKE, 1977, 1978). Inthe normal course of events, two of these arms develop while the third arm "fails". Tectonic activity inthe failed arm comes to a stop after a period of active development. It could have reached the seafloorspreading stage and then the spreading axis died out (e.g. in the Benui Trough in Nigeria) or it may noteven have reached the spreading stage (as has been postulated for the East African Rift System). InEast Africa, a number of triple junctions have been recognized. The Red Sea, Gulf of Aden and theEast African Rift constitute one such junction. Sedimentation in the failed arm is particularly rapid sothat conditions are inducive to mineralization and fluid hydrocarbon accumulation (ROBBINS, 1983).In the Benui Trough mineralization is in the form of lead, zinc and copper sulphides in the cross-jointsof anticlines formed in relation to the Benui Ocean closure. The oil fields there are well-known.REFERENCESALLEN, T.D. (1964). A preliminary magnetic survey in the Red Sea and Gulf of Aden. Boll. diGeof. Teorica ed Applicata, 6, 199.ALLEN, T.D. (1970). Magnetic and gravity fields over the Red Sea. Phil. Trans. R. Soc. Lond., A,267, 153-180.ANDERSON, R.N., HONNOREZ, J., BECKER, K., ADAMSON, A.C., ALT, J.C.,EMMERMANN, R., KEMPTON, P.D., KINOSHITA, H., LAVERNE, C., MOTTL, M.J.and NEWMARK, R.L. (1982). DSDP Hole 504B, the first reference section over 1 kmthrough Layer 2 of the oceanic crust. Nature, 300,589-594.BACKER, H. (1976). Fazies und chemische Zusammensetzung rezenter Ausfiillungen ausMineralquellen im Roten Meer. Geol. Jb., D, 17, 151-172.BACKER, H. (1979). Metalliferous sediments in the Red Sea, occurrence, exploration and resourceassessment. In:Proceedings of the International Seminar on Offshore Mineral Resources,Germinal and BRGM, Document BRGM No. 7, Chlians, 319-338.BACKER, H. and RICHTER, 1973. Die rezente hydrothermal-sedimentiire Lagerstatte AtlantisII-Tiefim Roten Meer. Geol. Rundschau, 62,697-741.BACKER, H. and SCHOELL, M. (1972). New deeps with brines and metalliferous sediments in theRed Sea. Nature, 240, 153-158.BACKER, H., LANGE, K. and RICHTER, H. (1975). Morphology of the Red Sea central grabenbetween Subair Island and Abul Kizaan. Geol. Jb., D 13,79-123.BALLARD, R.D. and VAN ANDEL, T.N. (1977). Morphology and tectonics of the inner rift valleyat lat. 36'50'N on the Mid-Atlantic Ridge. Bull. Geol. Soc. Amer., 88(4), 507-530.BARBERI, F., BORSI, S., FERRARA, G., MARINELLI, G., SANTACROCE, R., TAZIEFF, H.and VARET, J. (1972). Evolution of the'Danaki1 Depression (Afar, Ethiopia) in light ofradiometric age determinations. J. Geol., 80,720.BARBERI, F., FERRARA, G., SANTACROCE, R. and VARET, J. (1975). Structural evolution ofthe Afar triple junction. In: A. Pilger and A. Rosler (eds.), Afar Depression of Ethiopia,Schweizerbart, Stuttgart, 1, 38-54.317
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Intergovernmental Oceanographic Com
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of the IOC Marine Pollution Monitor
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PageMARGINAL SEASSTORM SURGES IN TH
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Marine PollutionAt present, marine
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THE INDIAN OCEAN --- AN ENVIRONMENT
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The subtropical anticyclonic gyre i
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GEOLOGICALBecause of its asymmetric
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RADIOACTIVE AND THERMAL WASTESIn co
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RESEARCH AND MONITORING ACTIVITIESM
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2-5, Mn 3-7, Zn 8-31, Fe 35-94, Pb
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Localized problems, both short-term
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HOLEMAN, J.N. (1968). The sediment
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UNEP/UNIDO (1982a). Industrial sour
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0-5-24 -I I I I I I I I I 11--25- A
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I*in '0( U N '0- '0 '0 N , p d'0I I
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C'EO IIFigure 6. Observations of oi
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Table 2.Ranges of Dissolved heavy m
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d.2 W2n2 n z0U.IzIO N m mENmIYEE*Ed
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Table 6. Population and related dat
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PROBLEMS IN THE PHYSICAL OCEANOGRAP
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B2: How does the Agulhas Current in
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0Q0mbWbvx(U49
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Figure 6 Average wind stress curl f
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THE DESTRUCTION OF THE TETHYS AND P
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part of the Seychelles-Mascarene bl
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Much of the old Tethys seafloor has
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when there was little or no movemen
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scouring of the sediments by cold b
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CANDE, S.C. and MUTTER, J.C. (1982)
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SHACKLETON, N.J. and KENNETT, J.P.
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0EYNz 10c2XaYWeKB20LuUz a5 cl300 10
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CALCAREOUS FORAMINIFERANANNOFOSSIL
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GEOLOGICAL-GEOPHYSICAL MAPPING OF T
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The latest tectonic generalization
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LE PICHON, X. and HEIRTZLER, J.R. (
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AN EXAMINATION OF THE FACTORS THAT
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is the specific volume anomaly. Po
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circulation. At Nagappattinam, Madr
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Table 1.MarmagaoCochin1969-781958-7
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tFigure 2. An idealized coastal cur
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STATION : BOMBAY~ J , F I M .- , A
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STATION : COCHIN, J , F , M , A , M
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3007STATION : MADRASI J I F , M I A
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STATION : CALCUTTA, J l F , M , A ,
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RED TIDE§ IN THE INDO-WEST PACIFIC
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were observed as early as 1770 duri
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diarrhetic shellfish poisoning (DSP
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GACUTAN, R.Q., TABBU, M.Y., AUJERO,
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Table 1.Clinical symptoms of variou
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Table 3. Fish species implicated in
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FIGURE CAPTIONSFigure la. Trichodes
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(*14aEE15aHH15c120
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MINERAL RESOURCES OF THE INDIAN OCE
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tonnes of monazite. Similar deposit
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Madagascar and the Red Sea. Within
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South Australian Basin: (Figs. 10-1
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Offshore placers are likely to occu
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MILLIMAN, J.D. (1974). Marine Carbo
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Thailand Tin 5560 (1980) NA 4.2 (19
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Table 2. The range (in percent) of
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Table 4. Chemical composition of po
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141FIGURE - 1
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~IT 73qw p' le' IS IFigure 4. Map s
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@A5 3 9 93 3 s 3 m4P 8O C ' . .' ,
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Figure 10. Map showng the abundance
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Figure 14. Map showing the distribu
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IFigure 17. Marine mineral explorat
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central are corals to the integrity
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Very little information is availabl
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leaving little trace of their exist
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REFERENCESAGASSIZ, A. (1903). The c
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PILLAI, C.S.G. (1969b). Studies on
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Table 1.Extent of damage to coral r
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STATUS OF CRITICAL MARINE HABITATS
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OCCURRENCEThe distribution of reefs
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Mining of Reef RockMining of reef r
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-resource. Their significance deriv
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Coating of Aerial Roots by Fine Sed
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associated with the roots (e.g. GOE
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Temperature and SalinityThe effects
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significant numbers in the Red Sea,
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mersas are known to serve as nurser
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BURCHARD, J.E. (1979). Coral fauna
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HIRTH, H.F., KLIKOFF, L.G. and HARP
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MacNAE, W. (1974). Mangrove forests
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RINKEVITCH, B. and LOYA, Y. (1977).
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WALKER, D.I. and ORMOND, R.F.G. (19
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DAMMING AND DIVERSION OF RIVERSIn d
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FUTURE STUDIESWhat can marine scien
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!0OD9 -8 Nc80,a,u-3(dcab(Dbrr)8brr)
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0 0-0 00 O0O 0% LD d- m cu 0 0202
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STORM SURGES IN THE BAY OF BENGAL*T
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low pressure centres over the Bay i
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ACKNOWLEDGEMENTSThe writers wish to
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Table 1.Latitude and longitude of p
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214
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0Poa9nU0m0Yan-I2li7mYUVQk?401mc0mYm
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0In218
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221
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Table 3. Nomenclature used by India
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ANDHRAB A Y OFB E N G A L ,.16'LO 4
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INDIABAY OF-Point CalirnereLanka L-
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pressure in the South Pacific and l
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SWALLOW, J.C. (1983). Arabian Sea c
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234
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236
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scale wind phenomenon that occurs w
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Several two-dimensional models of t
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HARTMANN, M., LANGE, H., SEIBOLD, E
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Y-Model Domaint=6hrs.b-250 0 59 Xw-
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UELEVATIONS (m) ai 18 HOURS L2:-+EL
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HARMONIC CONSTITUENT K,Figure 8. Ob
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Age of Semi-Diurnal Tide (hrs)28".+
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! 5"BOTTOMFigure 13. Predicted mode
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OCEANOGRAPHIC CONDITIONS PELAGIC PR
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Low oxygen content in subsurface wa
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R/V Dr. F. Nansen trawl of 41 m hea
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thermocline temperature decreases s
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Nitrate - NitrogenSimilarly to phos
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Page 260 and 261: in 6 months when spawning occurs. T
Page 262 and 263: REFERENCES3BANSE, K. (1968). Hydrog
Page 264 and 265: GILSON, H.C., (1937). The nitrogen
Page 266 and 267: ROYAL SOCIETY (1963). International
Page 268 and 269: APPENDIX:REGIONAL COOPERATIVE INVES
Page 270 and 271: 20 015 20 25FEBOC015 20 25 30 35M A
Page 272 and 273: W0-8w0-Inww[r3a+eW281
Page 274 and 275: B35 36 a7 XlO+ 35 36 a7- Mar--- Fob
Page 276 and 277: a, A
Page 278 and 279: ...... :'I. .. ,... .. 8.*.. ... ._
Page 280 and 281: ASTAT.Si -Si (OH14 in p M - d ~ n -
Page 282 and 283: YU0IwYY->02(33-1 II 1amLyY>02(33amL
Page 284 and 285: I I I I I10 Ic L0U0mI(dw -rlo u0w m
Page 286 and 287: III I I I0. 1....w'3...-0U-J..,....
Page 288 and 289: 297
Page 290 and 291: clearly is too low. Because of low
Page 292 and 293: KARBE, L., THIEL, H., WEIKERT, H. a
Page 294 and 295: 50010001 scoOxygen (rnl/l)0I1I2I3I4
Page 296 and 297: c1 oc50C10001500_j_///.///II:I? 0:3
Page 298 and 299: THE RED SEAPHYSIOGRAPHYThe Red Sea
Page 300 and 301: intensity of magnetization which co
Page 302 and 303: 1969; SEARLE and ROSS, 1975). This
Page 304 and 305: y normal faulting. This is most int
Page 308 and 309: BAUMANN, A., RICHTER, H. and SCHOEL
Page 310 and 311: EYAL, M., EYAL, Y., BARTOV, Y. and
Page 312 and 313: LEWIS, B.T.R. (1983). The process o
Page 314 and 315: TARLING, D.H. and MITCHELL, J.G. (1
Page 316 and 317: mC- 1000- 2000- 3000E0Figure 2.Sche
Page 318 and 319: -20b-0,20wFigure 4. Seismicity and
Page 320 and 321: kmaFigure 6. Summary of seismic ref
Page 322 and 323: kQ)Um 5U0c04 3N 4COQ)k3M*rlk332
Page 324 and 325: 5 b'o w-Y EO'i Ii04!I 0I0I334
Page 326 and 327: II,'{34/,'0SOMALIAND: N. DANAKILFig
Page 328 and 329: spreadingvulcanismmblock faultingII
Page 330 and 331: SUPERFICIAL SEDIMENTS OF NORTHERN R
Page 332 and 333: normally sorted, with median diamet
Page 334 and 335: EL-SAYED (1983) used the trace meta
Page 336 and 337: BEHAIRY, AKA. (1983). Marine transg
Page 338 and 339: SHUKRI, N.M. (1953). Bottom deposit
Page 340 and 341: Table 2 Heavy metal concentrations
Page 342 and 343: EGYPTEl-Morgan 1Bargan IBargan 2Yub
Page 344 and 345: Figure 4. Distribution of minerals
Page 346 and 347: ARAGONITEHIGH HG-CALCITEFigure 6. T
Page 348 and 349: MARINE LIVING RESOURCES OF THE RED
Page 350 and 351: This elevated productivity may resu
Page 352 and 353: REVELLE (1981) mentioned that the p
Page 354 and 355: FISHELSON, L. (1964). Observation o
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