Submarine geology and geophysics

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especially the sediment problem. Fachbereich Biol., Univ. Rostock, F R G . 92:3041 Picer, M. and N. Picer, 1991. Long-term trends of DDTs and PCBs in sediment smnples collected from the eastern Adriatic coastal waters. Bull. environ. Contamin. Toxicol~ 47(6):864-873. Center for Mar. Res., 'Ruder Boskovie Inst., Zagreb, Croatia, Yugoslavia.

92:3042 Readman, J.W. and L.D. Mee, 1991. The reliability of analytical data for tributyltin (TBT) in sea water and its implications on water quality criteria. Mar. environ. Res, 32(i-4):19-28. To investigate the reliability of analytical data for TBT in sea water, split water samples were distributed to ten laboratories in six countries. The sub-surface samples comprised an offshore water sample; the same sample but spiked with an undisclosed quantity of TBT standard compound; and a sample taken from a yacht marina. The seven acceptable data sets were in good agreement for the spiked sample but showed greater variation in concentrations reported for the yacht marina sample. The spread in values reported by the laboratories demonstrates inherent difficulties in obtaining good precision below ~ 2 0 ng TBT + L -~. IAEA Mar. Environ. Lab., 19 Ave. des Casteilans, MC 98000, Monaco. 92:3043 Schulz, D.E., 1990. Chlorinated blphenyls in North Atlantic and North Sea water. Ber. Inst. Meeresk. Christian-Albrechts-Univ, 197:ca. 100pp. (In German, English abstract.) Out of 209 theoretically possible chlorobiphenyls, 132 were found in the mixtures at concentrations

>0.05% (w/w); each pesticide congener was present in at least one commercial mixture. PCB concentrations and composition in North Atlantic surface and deep water were determined; concentrations were one to three orders of magnitude below previously reported data. Deep water concentrations were lower and less variable than those of surface waters. PCB concentrations in the North Sea were 2-3 times higher than values in the open North Atlantic; most concentrations in suspended matter were below detection limits. Inst. fur Meereskunde Abt. Meereschem., Dusternbrooker Weg 20, W-2300 Kiel, FRG. (lit)

C240. Corrosion 92:3044 Pedersen, Amelie and Malte Hermansson, 1991. Bacterial corrosion of iron in seawater in-sltu and in aerobic and anaerobic model systems. FEMS Microbiol. Ecol, 86(2): 139-148. A screening of twenty-two marine isolates was made to examine their effects on corrosion of carbon steel ASTM A619. Sixteen of the isolates gave a lower corrosion than the control. The effects of biofilms depended on a balance between the presence of oxygen and the type of population. An anaerobic population attached to the surface increased the corrosion rate if immersed in a suspension of Vibrio sp. DW 1. The vibrio population probably 'protected' the anaerobic population from oxygen and may have provided nutrients, thereby creating conditions that allowed production of corrosive metabolites close to the metal. In contrast, a surface without a biofilm showed a decrease in corrosion when immersed in the same vibrio suspension. Dept. of Genl. and Mar. Microbiol., Carl Skottsbergs gata 22, S-413 19 Goteborg, Univ. Goteborg, Sweden.

D. S U B M A R I N E GEOLOGY AND G E O P H Y S I C S

D60. Geomorphology (fans, canyons, etc.) 92:3045 Goff, J.A., 1991. A global and regional stochastic analysis of near-ridge abyssal hill morphology. J. geophys. Res~ 96(B13):21,713-21,737.

Results of global and regional stochastic analysis of 64 Sea Beam swaths near the Rivera, Cocos, and Nazca spreading sections of the East Pacific Rise, Mid-Atlantic Ridge and Central Indian Ridge are presented. Use of Sea Beam data for estimating stochastic parameters up to order 4 provides important quantitative information regarding abyssal hills,

496

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including rms height, azimuthal orientation, width, aspect ratio, Hausdorff dimension, skewness, tilt, and peakiness. In addition, the results emphasize a strong uniqueness of Pacific-Cocos data relative to the rest of the data global set, and it is found that abyssal hill parameters are correlated with the depth of the adjacent ridge axis, indicating that the abundance in magma supply, which likely controls ridge axis depth, may influence the formation of abyssal hills. WHOI, Woods Hole, MA 02543, USA.

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transport in near-shore sediments inhabited by sedentary polychaetes. Earth planet. Sci. Letts, 105(4):463-473. Dept. of Mar. Sci., Univ. of Connecticut, Groton, CT 06340, USA.

D130. Sediments (rocks, formations, type, composition, etc.) 92:3050 Abu El-Ella, Ramadan, 1991. Relationship between

clay mineralogy and thermal

D70. Coasts, beaches, marshes 92:3046 Shi, Zhong and H.F. Lamb, 1991. Post-giacial sedimentary evolution of a microtidal estuary, Dyfi Estuary, west Wales, U.K. Sedim. Geol, 73(3-4):227-246. Inst. of Earth Studies, Univ. Coll. of Wales, Aberystwyth, Dyfed SY23 3DB, UK. 92:3047 Sunamura, Tsuguo, 1991. The elevation of shore platforms: a laboratory approach to the unsolved problem. J. Geol, 99(5):761-766. A wave-flume experiment was conducted to investigate the influence of wave height and rock strength upon the elevation of shore platforms having a marked scarp at the seaward margin. Breaking waves were allowed to act on a steep model cliff to produce a platform. Results indicated that platform elevation increases with increasing rock strength if other factors are constant. It was suggested that a considerable difference in platform elevation in the field can arise depending on wave height and rock strength. The water depth in front of platforms proved to be important for the study of platform elevation. 9 by the University of Chicago. Inst. of Geosci., Univ. of Tsukuba, Ibaraki 305, Japan.

92:3048 Zhang, Guangwei, 1991. Formation and evolution of sand ridges in the south Huanghai Sea shelf. Mar. GeoL Quat. Geol, 11(2):24-35. (In Chinese, English abstract.) Inst. of Mar. Geol., Ministry of Geol. and Min. Resour., Qingdao, 266071, People's Republic of China.

D120. Sedimentary processes (deposition, diagenesis, etc.) 92:3049 Benoit, J.M., Thomas Torgersen and James O'Donnell, 1991. An advection/diffusion model for U2Rn

maturity

of

Neogene--Quaternary shales in Ras EI-Barr well, offshore Nile Delta, Egypt. Mar. Petrol. Geol., 8(3):296-301. 23 Hassan Kamel St., Miami, Alexandria, Egypt. 92:3051 Ehrenberg, S.N., 1991. Kaolinized, potassium-leached zones at the contacts of the Gain Formation, Haitenbanken, mid-Norwegian continental shelf. Mar. Petrol. Geol~ 8(3):250-269. Geol. Lab., Statoil, Postboks 300, N-4001, Stavanger, Norway. 92:3052 Liu, Zhenxia, 1991. Sedimentation of Mariana Trough. Mar. Geol. Quat. Geol~ 11(2):67-78. (In Chinese, English abstract.) First Inst. of Oceanogr., SOA, Qingdao, 266071, People's Republic of China. 92:3053 McMurtry, G.M., E.H. De Carlo and K.H. Kim, 1991. Accumulation rates, chemical partitioning, and Q-mode factor analysis of metalliferous sediments from the North Fiji Basin. Mar. Geol, 98(2-4):271-295. North central North Fiji Basin and Vanuatu Archipelagic Apron surface samples were chemically and mineralogically analyzed, and sediment cores were analyzed for accumulation rate by the excess "~ method. Phase and size partitioning indicate that metal concentration in the < 2 ittm fraction approach those from the eastern Pacific. Iron accumulation rates are similar to those from the EPR; mean Mn accumulation rate is about lwice the global authigenie rate; A1 is accumulating about ten times faster than in the eastern equatorial Pacific. Q-mode factor analysis produced three major factors--hydrothermal, authigenic, and detrital--for :>90% of sample variance in both size fractions of non-carbonates. Aerial distribution of the < 2 /zm fraction factor components reveals a major hydrothermal source associated with the South Pandora Ridge spreading

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D. Submarine Geology and Geophysics

center. Dept. of Oceanogr., Univ. of Hawaii, Honolulu, HI 96822, USA. 92:3054 Schlungbaum, Gt~nter et al., 1989. Chemical sediment studies in GDR coastal waters. XXX. The quality of the sediment surface layer in the Greifswalder Bodden. Wiss. Z. Univ. Rostock, MeeresbioL Beitr. naturw. Reihe, 38(5):1-2. (In German, English abstract.) Sektion Biol., Univ. Rostock, Freiligrathstr. 7/8, Rostock 0-2500, FRG. 92:3055 Shaw, H.F. and T.J. Primmer, 1991. Diagenesis of mudrocks from the Kimmeridge Clay Formation of the Brae Area, UK North Sea. Mar. Petrol. Geol, 8(3):270-277. Dept. of Geol., Imperial College of Sci., Tech. and Med., Prince Consort Rd., London SW7 2BP, UK. 92:3056 Zuo, Zhizheng, Doeke Eisma and G.W. Berger, 1991. Determination of sediment accumulation and mixing rates in the Gulf of Lions, Mediterranean Sea. Oceanologica Acta, 14(3):253-262. Netherlands Inst. for Sea Res., P.O. Box 59, 1790 AB, Den Burg, Texel, Netherlands.

D140. Submarine hydrology (springs, hyd r o t h e r m a l deposits, etc.) 92:3057 Auzende, J.-M. et al., 1991. In-situ geological and geochemical study of an active hydrothermal site on the North Fiji Basin Ridge. Mar. Geol, 98(2-4):259-269. The axial graben between 16058 , and 17~ consists of alternating Nl5-trending horsts and grabens. Extinct hydrothermal sites all along the graben consist of fossil chimneys, oxide staining and dead shells. At 16~ an active chimney was discovered; this chinmey expels a peculiar water characterized by low chlorinity and a 2850C maximum temperature. In the northern extremity of the NI5 axis a wide fossil hydrothermal site was explored and sampled. Mar. Geosci. Dept., Brest I F R E M E R Centre, BP 70, 29280 Plouzane, France. 92:3058 Baker, P.A. et al., 1991. Large-scale lateral advection of seawater through oceanic crust in the central equatorial Pacific. Earth planet. Sci. Letts, 105(4):522-533.

497

The existence of large-scale lateral advection of water through basaltic crust in the central equatorial Pacific is demonstrated by the Ca, Mg, Sr, sulfate and Sr isotopic compositions of pore waters from the overlying sediments. The advection is believed to extend throughout the region from about 110 to 160~ and 5~ to 8~ The corresponding crustal ages of this region vary from east to west from about 15 to about 70 Ma, respectively. Fluid flow in basement is rapid, having a calculated average residence time in oceanic crust of about 20,000 years and an inferred pore fluid velocity between 1 and 10 m y-L Because of the short reaction time between basement rocks and fluids, as well as the low temperature of this fluid, the chemistry of basement water remains similar to seawater. As a result, despite the important impact of this process on oceanic heat flow, the flow may have little effect on the long-term major element composition of seawater. Duke Univ., Dept. of Geol., Durham, NC 27706, USA. 92:3059 Bourl~s, D.L. et al., 1991. Beryllium isotope systematics of submarine hydrothermal systems. Earth planet. Sci. Letts, 105(4):534-542. While the 9Be concentrations from the sedimentstarved EPR at 21*N and from the sediment-covered Guaymas Basin and Escanaba Trough hydrothermal systems are comparable, their t~ concentrations are significantly different. The t~ concentration from the EPR hydrothermal fluid is at least two times lower than that of the Pacific bottom water. By contrast, the t~ concentration in hydrothermal solutions from sediment-hosted environments are enriched over ambient seawater and are at least one order of magnitude higher than that measured in the 210N fluid. These data demonstrate that 1~ is an unambiguous tracer of interactions between hydrothermal fluids and recent sediments. Centre de Spectrom. de Masse et de Spectrom. Nucl. Batiment 108, 91405 Campus Orsay, France. 92:3060 Crane, Kathleen, Barbara Hecker and Vladimir Golubev, 1991. Heat flow and hydrothermal vents in Lake Baikal, U.S.S.R. Eos, 72(52):585, 588589. Many authors suspect that the Baikal Rift formed in response to the India-Eurasia collision, which deformed the lithosphere in central Asia creating the Himalayas in the south and an extensional province in Siberia. Others believe that the Baikal Rift is primarily an active phenomenon, citing updoming around Lake Baikal and the presence of Cenozoic volcanics as an example of slightly elevated partial

498

D. SubmarineGeologyand Geophysics

melting in underlying asthenospheric material. More than 50 hot springs have been mapped on the periphery of Lake Baikal. Their flux may remove a substantial amount of heat from the subjacent mantle, thus explaining the relatively low regional heat flux (60 mW/m2). The controversy over the thermal nature of the Baikal Rift stimulated our search for hydrothermal activity within the lake itself via a cooperative project involving both surface and submersible vessels. The Frolikha Bay vent field is described. Dept. of Geol. and Geogr., Hunter College, 695 Park Ave., New York, NY 10025, USA. 92:3061 German, C.R., A.C. Campbell and J.M. Edmond, 1991. Hydrothermal scavenging at the MidAtlantic Ridge: modification of trace element dissolved fluxes. Earth planet. Sci. Letts, 107(1): 101-114. Comparison of particulate trace element distributions with particulate Fe concentrations within the neutrally buoyant plume reveals that the distribution of trace elements within the plume is controlled by the following processes: (l) co-precipitation from vent-fluids, (2) scavenging from seawater, and (3) preferential settling from the plume and oxidative dissolution within the water column. For Y and Be, continuous scavenging appears to be important, whereas for V, As and Cr it appears that conditions suitable for uptake into particles may be restricted to the buoyant portion of the hydrothermal plume. It appears that for many elements (e.g., Cu, Co, Ag, Pb, Al, Cd, Be and Zn) the flux of dissolved material from vent-fluids is matched closely by the precipitation of hydrothermai particulate phases. Of the various elements studied here, hydrothermal activity appears to act as a significant source only for dissolved Ca and dissolved Mn. Dept. of Earth and Atmos. and Planetary Sci., MIT, Cambridge, MA 02139, USA. 92:3062 Hodkinson, R.A. and D.S. Cronan, 1991. Geochemistry of recent hydrothermal sediments in relation to tectonic environment in the Lau Basin, southwest Pacific. Mar. Geol, 98(2-4):353-366. Sediments from the Lau Basin have been investigated in relation to the tectonic evolution of its eastern and central spreading centers (ELSC and CLSC). Highest concentrations of hydrothermally associated Fe, Cu and Zn all occur in sediments from the CLSC; highest concentrations of Mn and Ni occur west of the spreading centers. Along the CLSC and ELSC axes, non-detrital P, Mn and Ni all

OLR (1992)39 (6)

increase toward the propagating tips, where maximum values occur. This could be due to a hydrothermal supply of Mn with Ni being scavenged from seawater by the Mn. Phosphorus may be similarly scavenged by ferromanganese oxides. Dept. of Geol., Imperial College, London SW7 2AZ, UK. 92:3063 Jean-Baptiste, P. et al., 1991. Helium and methane measurements in hydrothermal fluids from the Mid-Atlantic Ridge: the Snake Pit site at 23~ Earth planet. Sci. Letts, 106(1-4):17-28. The samples contain large quantities of helium and methane with endmember values of 4.6• 10-5 cm 3 STP/g for helium and 1.38• -3 cm 3 S T P / g for methane. The helium isotopic ratio 3He/4He is 8.4 times the atmospheric ratio. These values are strikingly similar to those already obtained on the EPR. Assuming that the range of variation of the ~He concentration data obtained so far from various tectonic settings is close to the genuine range of values encountered on mid-ocean ridges, the global mass flow involved in the hydrothermal circulation at the ridge's axis is estimated between 1000 and 3000 m 3 of water/see, leading to a residence time of the global ocean with respect to the hydrothermal circulation between 15 and 45 million years. This implies that, in addition to the individual vents (smokers), there is an extensive diffuse circulation of hydrothermal fluids along the ridges, in agreement with recent observations. Lab. de Geochim. Isotop., DSM-CEA/Saclay, 91191 Gif sur Yvette cedex, France. 92:3064 Nelsen, T.A. and E.B. Forde, 1991. The structure, mass and interactions of the hydrothermal plumes at 26~ on the Mid-Atlantic Ridge. Earth planet. Sci. Letts, 106(1-4):1-16. The results of 29 combined nephelometer/CTD cast/tows, covering 25-30 km 2 of ridge segment, indicate the presence of additional sources based on suspended particulate matter (SPM) concentration gradients and plume-top doming over source areas. Plume doming, documented here for the first time, conforms strikingly with laboratory experiments and can serve as a marker for source field location. A comparison of the plumes" SPM with potential temperature and salinity distributions indicates close correlation in water-column anomaly patterns for each, confirming modification of the regional potential temperature and salinity structure by hydrothermal plumes, which is expressed by wide separation and sloping of isotherms and isohalines. NOAA, AOML, OCD, 4301 Rickenbacker Cswy, Miami, F L 33149, USA.

OLR (1992)39 (6)

D. SubmarineGeologyand Geophysics

92:3065 Puteanus, D. et al., 1991. Hydrothermal iron-rich deposits from the Teahltia-Mehitia and Macdonald hot spot areas, southwest Pacific. Mar. Geol., 98(2-4):389-409. The iron oxyhydroxide crusts show complex layering and incorporate volcanic ash layers. It is believed that the crusts were deposited from relatively low temperature hydrothermal fluids. These low temperatures preclude the formation of sulphide deposits. The type of hydrothermal mineral recovered may be a function of the thermal regime of the system and the elevation, which controls the pressure of the venting fluids. The shallower depths of these seamounts compared to the axes of mid-ocean ridges may therefore be responsible for the style of mineralization. T h e Fe oxyhydroxide deposits are the residual low-temperature deposits formed when the spent hydrothermal fluid reached the crest of the seamount. Geol.-Palaontol. Inst., Univ. Kiel, Olshausenstr. 40/60, W-2300 Kiel, FRG. 92:3066 Stakes, Debra and W.S. Moore, 1991. Evolution of hydrothermal activity on the Juan de Fuca Ridge: observations, mineral ages, and Ra isotope ratios. J. geophys. Res., 96(B13):21.,739-21,752. Observations of hydrothermal activity from Juan de Fuca Ridge sites and ages and radium isotope ratios of samples from eight sites collected during 1! dives are reported. It is concluded that individual chimneys form rapidly and that presently active structures are <:2 yr old. In the Fairycastle Site at least one episode of hydrothermal activity occurred 20 yr ago; large Endeavour Site sulfide edifices probably record a discharge of 20 yr or more; chimneys in the southern ridge may be older. The results also suggest that chimneys of diverse mineralogy can be dated by measuring ingrowth of 2zsTh from 2ZSRa decay. Variations in the Z28Ra/Z26Ra ratios reflect differences in fluid residence time, depth of fluid generation, or interaction with basalts altered at low temperatures. Dept. of Geol. Sci., Univ. of South Carolina, Columbia, SC 29208, USA. 92:3067 Vanek, Vladimir and D.R. Lee, 1991. Mapping submarine groundwater discharge areas---an example from Laholm Bay, southwest Sweden. Limnol. Oceanogr., 36(6): 1250-1262. We conducted a broad reconnaissance for freshwater upwelling along the southeastern coast of Sweden from Bfistad 5 km northward. Results were similar regardless of whether measurements were taken with a bottom-contact electrical-conductance

499

sediment probe, by suction of the upper centimeter of the seabed, or with seepage meters. While the point measurements (suction samples and seepage meters) provided an estimate of seepage flux, the sediment-probe reconnaissance provided confidence that a large area of groundwater discharge was not overlooked. The nearshore discharge (0-50 m offshore) probably originates from a shallow aquifer and the offshore discharge (50-220 m offshore) from a buried, confined aquifer. Dept. of Limnol., Univ. of Lund, P.O. Box 65, S-221 00 Lund, Sweden.

D170. Historical geology, stratigraphy 92:3068 Chen, Jiyu, Lichen Wu and Cangzi Liu, 1991. Development of the Yangtze and Yellow river estuaries during the Holocene. Quat. Sci. Revs, 10(6):523-526. Inst. of Estuarine and Coastal Res., East China Normal Univ., Shanghai, People's Republic of China. 92.'3069 Derbyshire, E. (guest editor), 1991. Quaternary environments in China. Q,tat. Sci. Revs, 10(6): 479-554; 9 papers. The volume and detail of data on the evolution of the Chinese mainland, presently available only in the Chinese language, represent an impressive amount of research over the past three decades. The selected papers in this issue cover a broad scale of geographical and temporal studies. Three papers describe the uplift, glaciation, and permafrost of the Qinghai-Xizang Plateau, a fourth describes the paleolithic cultures, two examine the effects of rising sea level on the lower reaches of the Yangtze and Huang He; and two others review palynological and dendrochronological information on Holocene climates. A final paper evaluates the 1000-yr written record of climatic changes in China. 0abf) 92:3070 Fang, Jinqi, 1991. Influence of sea level rise on the middle and lower reaches of the Yangtze River since 12,100 BP. Quat. Sci. Revs, 10(6):527-536. There was intensive headward channel aggradation and water-stage rise in the middle and lower reaches of the Yangtze River after the last glacial maximum (LGM), likely resulting from sea level rise after the LGM. A model is presented, designed to recreate what happened to the river in response to sea level rise. Dept. of Geogr., Nanjing Univ., Nanjing, Jiangsu 210008, People's Republic of China.

500

D. SubmarineGeologyand Geophysics

92:3071 Hamelin, Bruno et al., 1991. z34U/USU mass spectrometry of corals: how accurate is the U-Th age of the last interglacial period? Earth planet. Sci. Letts, 106(1-4): 169-180. The accuracy of U-Th age dating of the last interglacial is examined using very high precision mass spectrometry on Late Pleistocene corals. Results show that most corals have 2J4U/2~sU ratios significantly higher than modern values; differences in the U initial ratio is the most significant cause of uncertainty in the age determinations. All ages measured occur in a tight cluster between 122 and 133 kyr but the data could be explained by even slight contamination of corals that are significantly older than 125 kyr. Geosci. de l'Environn., case 431, Univ. St. Jerome, 13397 Marseille, France. (rjw) 92:3072 Horrell, M.A., 1991. Phytogeography and paleoclimatic interpretation of the Maestrichtian. Palaeogeogr. Palaeoelimatol. Palaeoecol., 86(1-2):87138. This study focuses on reconstructing the climate of the Maestrichtian (latest Cretaceous) based on the abundant published information from the geologic record. Specifically, the approach taken was to reconstruct the general patterns of the terrestrial ecological biomes based on the fossil megaflora and pollen record. Once the biomes were delineated, the climatic constraints on the present counterparts of these biomes were used to determine the prevailing climate of each region. Biome boundaries were recognized by discontinuities in the phytogeographic distributions of a variety of fossil plant groups. Detailed comparisons of fossil plant assemblages with present-day climatic preferences of nearest living relatives allowed each region to be assigned to a modern biome. Altogether, 12 climatic zones corresponding to 7 major biome types have been recognized for the Late Cretaceous period. Dept. of Geophys. Sci., Univ. of Chicago, 5734 S. Ellis Ave., Chicago, IL 60637, USA. 92:3073 Jones, D.S. et al., 1991. Integrated geochronology of a classic Pliocene fossil site in Florida: linking marine and terrestrial blochronologies. J. Geol~ 99(5):637-648. In a large shell pit near Sarasota, Florida, on the order of 1000 well-preserved, shallow marine species are found. Sandwiched between extensive shell beds is a unit containing a rich vertebrate fauna (ca. 100 species) with a distinctive mammalian component indicative of the late Blancan Land Mammal Age (2.5-2.0 Ma). In contrast, the surrounding shell beds

OLR (1992)39 (6)

have traditionally been assigned an older (Early to Mid-Pliocene) age based upon biocorrelation of the benthic invertebrate (molluscan) fauna. In a multifaceted approach, we integrated invertebrate and vertebrate biochronology, paleomagnetism and Sr isotope chronostratigraphy with existing age data from the literature in an attempt to resolve this chronologic dichotomy and link the marine and terrestrial records. 9 by the University of Chicago. Florida Mus. of Nat. Hist., Univ. of Florida, Gainesville, FL 32611, USA. 92:3074 MOiler, D.W. and P.A. Mueller, 1991. Origin and age of the Mediterranean Messinlan evaporites: implications from Sr isotopes. Earth planet. Sci. Lefts, 107(l): 1-12. The Messinian evaporites of the Mediterranean Basin are examined using strontium isotope techniques. Results show a lower evaporite unit (LEV) of marine origin and an upper evaporite (UEV) with strontium ratios below those of Messinian seawater. These findings support the 'deep desiccated basin' model for the Mediterranean where early marine conditions are replaced over time by variable desiccation and continental runoff. Timing of deposition is also examined using Sr data; LEV deposition began ~5.65 Ma ago and UEV deposition ended ~ 4 . 9 Ma ago. Geol. Inst., Swiss Fed. Inst. of Tech., ETH-Zentrum, 8092 Zurich, Switzerland. (rjw) 92:3075 Nowaezyk, N.R., 1991. High-resolution magnetostratigraphy of Late Quaternary Arctic marine sediments. Repts polar Res. (Ber. Polarforsch.), 78:187pp. (In German, English abstract.) Paleomagnetic investigation of 24 cores from the Greenland Sea, Fram Strait, and eastern Arctic Ocean indicate high-frequent variations of the g e o m a g n e t i c field over the last 400 kyr and show that complete stepwise demagnetization of samples and detailed vector analysis of remanence components is needed for reliable information. Results for the Fram Strait confirm polarity events at 23-25 ka, 34--43 ka, 65-77 ka, 115-123 ka, 171-181 ka and 292-298 ka and suggest an event at 152-160 ka, a full reversed polarity event at 98-102 ka, and short excursions at 235 ka and 320 ka. Calculated sedimentation rates for sites in the Fram Strait, Yermak Plateau, and Nansen Basin are on the order of 4 cm/kyr, whereas values of up to 10 c m / k y r were obtained for the continental slope northeast of Svalbard and the northern edge of the Yermak Plateau. Fachbereich Geowissenschaften, Univ. Bremen, Klagenfurther Str., 2800 Bremen, F R G . 0abf)

OLR (1992)39 (6)

D. SubmarineGeologyand Geol~hysics

92:3076 Vorren, T.O. et al., 1991. Cenozoic erosion and sedimentation In the western Barents Sea. Mar. Petrol. Geol, 8(3):317-340. Multichannel seismic reflection lines in the vicinities of Hammerfest and Egga basins are interpreted to identify Cenozoic sediment sources, transport paths, and depositional environments and to estimate rates of sedimentation and erosion and their influences on the evolution of the Barents Sea relative to hydrocarbon potential. The investigation reveals that the Loppa Iligh and adjacent areas served as a sediment source, that as much as 3 km of rock have been eroded from the Svalbard area and the Stappen tligh during the Early Cenozoic, and that in the Late Pliocene and Pleistocene erosion was greatest in the southeast and adjacent to areas fed by glacial ice streams. Dept. of Geol., Univ. of Tromso, N-9000 Tromso, Norway. (hbf) 92:3077 Yan, Jun, Lijuan tte and Shengji Xue, 1991. Characteristics of elements in marginal.sea strata of the west Pacific Ocean and their palaeooceanological significance. Mar. Geol. Quat. Geol, !1(2):56-67. (In Chinese, English abstract.) Sixteen elements in four cores from the west Pacific Ocean were analyzed using XRF. The results show that the elements change regularly, and these changes are periodic with climatic fluctuations in the region. Inst. of Oceanol., Acad. Sinica, Qingdao 266071, People's Republic of China. D 1 8 0 . Paleontology (see also E-BIOLOGICAL OCEANOGRAPIIY) 92:3078 Beaufort, Luc, 1991. Adaptation of the random settling method for quantitative studies of calcaxeous nannofossiis. Micropaleontology, 37(4): 415-418. The techniques available for the preparation of microscopic slides that may be used for absolute counts of nannofossils are discussed. A slide preparation method inspired by the random settling technique of Moore is described. Lab. de Geol. du Quat., Ctre. Natl. de la Rech. Sci., Luminy, Case 907, 13288 Marseille cedcx 9, France. 92:3079 Malumifin, N., Carolina Nfi~ez and Andrea Caramrs, 1991. Uniloeular Foraminifera of retitular surface from Argentina. MicropaleontoloD', 37(4):393-406. Dir. Nae. de Geol. y Min.,

501

Tte. Fgta. Benito Correa 1194, 1107 Buenos Aires, Argentina. 92:3080 Nederbragt, A.J., 1991. Late Cretaceous biostratigraphy and development of lleterohelicidae (planktic Foraminifera). Micropaleontology, 37(4):329372. This paper presents a biostratigraphie and taxonomic analysis of Late Cretaceous planktic foraminiferal Heterohelicidae from Tethyan and SW Atlantic sections. Albian and Cenomanian heterohelicids are small opportunists. Since the Turonian, an overall gradual increase in numeric importance and species richness can be observed, with iterative introduction of chamber proliferation. The Early Turonian, Mid Santonian and -Early Maastrichtian are periods of rapid speciation. Differences between localities are attributed to paleo-environmental conditions. A new genus, Laeviheterohelix, groups the smooth, microperforate heterohelicids. Four species and one variety are new: Heterohelix label-

iosa, Laeviheterohelix flabelliformis, L. turgida, Pseudoguembelina hariaensis and Sigalia deflaensis rugocostata. Geomar. Ctr., Inst. voor Aardwetenschappen, Vrije Univ., de Boelelaan 1085 1081 HV Amsterdam, Netherlands. 92:3081 Stancliffe, R.P.W. and K. Matsuoka, 1991. Note on the preparation of small calcareous tests and shells using hydrofluoric acid. Micropaleontology, 37(4):419-421. The study of small calcareous shells and tests (<150/tm) is hindered by their size and the inability to resolve their internal structure without destroying the outer wall. This note outlines a method that makes their opaque walls almost transparent, allowing the study of the internal morphology including organic linings in relation to the exterior. The process is especially applicable to the study of microforaminiferal linings. Dept. of Geol., Nagasaki Univ., 1-14 Bunkyo machi, Nagasaki, 852, Japan. 92:3082 Zippi, P.A., 1991. S E M and light microscope mounting and specimen location technique for samespecimen study of palynological strew mounts. Mieropaleontology, 37(4):407-413. Dept. of Geol., Univ. of Toronto, ON M5S 3BI, Canada.

D200. Gravity, geodesy, magnetism 92:3083 Genrich, J.F. and J.-B. Minster, 1991. Near-real time

502

D. SubmarineGeologyand Geophysics reduction of shipboard gravity using Kalmanfiltered GPS measurements. Geophysics, 56(12): 1971-1979.

This paper reports on the development and testing of a Kalman filter for Global Positioning Sysiem (GPS) data used in conjunction with a Finite Impulse Response (FIR) filter to obtain near-real time, underway gravity estimates. Application of the technique to two sets of shipboard data shows that both gravimeters yield results with root mean square differences of less than 1 mGal. Horizontal accelerations generate transient signals that can be modeled to an accuracy on the order of 5 mGal. Elimination of transients may be addressed analytically or empirically and will greatly improve data quality. Inst. of Geophys. and Planet. Phys., Scripps Inst. of Oceanogr., A-025, La Jolla, CA 92093, USA. (rjw)

D210. Heat flow 92:3084 Sclater, J.G. and Seiichi Nagihara, 1991. Comment on 'Heat flow in the Caribbean and Gulf of Mexico,' by D. Epp, P.J. Grim, and M.G. Langseth, Jr. J. geophys~ Res, 96(B13):21,80721,810. The original data presentation of Epp et al. (1970) was sufficiently complete that it is now possible to reevaluate their measurements in the light of recent information. We reexamine the heat flow measurements from the western gulf concentrating, first, on the occurrence of nonlinear gradients. We follow by discussing the position of the salt structures and the effect of the now known rate of sedimentation. We finish by arguing that the implications of these revised values are so important for thermal models of the oceanic lithosphere that they need additional validation. Dept. of Geol. Sci., Univ. of Texas, Austin, TX 78712, USA.

D240. Local or regional tectonics 92:3085 Fujii, Yoichiro, 1991. Contemporary crustal deformations in the Izu Peninsula, Honshu, Japan and acceleration of plate bending in the northernmost part of the Philippine Sea Plate. Pure appL Geophys~ 136(2-3):315-342. Detailed geophysical and geodetic observations indicate that the Izu Peninsula, located on the northernmost Philippine Sea Plate where it collides

OLR (1992)39 (6)

with Honshu, Japan, has recently been a region of significant tectonic activity. Results of a new technique to adjust for levelling of different epochs and rapid vertical crustal movements, indicate that the peninsula is inclining southwest at a rate many times higher than from 1929-1972 and that deformation is concentrated in the area where there is a bending of the plate. It is postulated that accelerated bending is responsible for changes within the crust and subcrust, intrusion of magma to shallower depths, seismic swarms, and destructive earthquakes in and around the region. Dept. of Earth Sci., Ibaraki Univ., Mito, Japan. (hbf) 92:3086 Girdler, R.W., 1991. The Afro-Arabian rift system-an overview. Tectonophysics, 197(2-4): 139-153.

The Afro-Arabian rift system is reviewed beginning with the Dead Sea transform and Gulf of Suez in the north, followed by the Gulf of Aden and Red Sea and ending with a brief mention of rifting through eastern and southern Africa. A consistent interpretation is obtained for geophysical data from the Gulf of Aden and Red Sea and geological data for the Dead Sea transform, Suez graben and Red Sea and Gulf of Aden margins. Locations of the ocean-continent boundaries in the northern Red Sea coincide when the total 107 km shear along the Dead Sea is restored. The Red Sea is therefore reconstructed in stages beginning with the 45 km postMiocene shear and 62 km Early-Miocene shear along the Dead Sea transform followed by estimates for extension in the early Red Sea-Suez graben. When this is done, there is a remarkable alignment of various features revealed on Landsat TM imagery for both sides of the northern Red Sea. NASA/Goddard Space Flight Ctr., Code 920, Greenbelt, MD 20771, USA. 92:3087 Huang, C.-Y. and Y.-C. Yin, 1990. Bathymetdc ridges and troughs in the active arc-continent collision region off southeastern Taiwan. Proc. geol. Soc. China, Taiwan, 33(4):351-372. In the region bounded by 21~176 and 120 ~ 122~ three ridges and three troughs of varied origins, all oriented roughly N-S, have been identified by echogram studies and single channel seismic profiling. The position, trend, bathymetry, and approximate dimensions of each of these features are described, and the geologic characteristics of the arc-continent collision region off southeastern Taiwan is compared with the PlioPleistocene collision geology of eastern Taiwan. Inst. of Geol., Natl. Taiwan Univ., Taipei, Taiwan. (hbf)

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D. SabmadneGeoIogyand Get,physics

92:3088 Hughes, G.W., Osman Varol and Z.R. Beydoun, 1991. Evidence for Middle Oiigocene rifting of the Gulf of Aden and for Late Oligocene rifting of the southern Red Sea. Mar. Petrol. Geol~ 8(3): 354-358. Conventional concepts regarding the opening of the Red Sea are based on a model in which a connection existed only with the Mediterranean Sea during the Early to Late Miocene; the present day connection with the Indian Ocean, via the Gulf of Aden, is known to have existed since the Early Pliocene. This study, based on detailed biostratigraphy of exploration wells in the Red Sea and Gulf of Aden regions, reveals the existence of a connection with the Gulf of Aden during the Late Oligocene, the Gulf of Aden itself being the result of a Middle Oligocene event. Robertson Group, Llandudno, Gwynedd LL30 ISA, UK, 92:3089 Jiang, Shaoren et al., 1990. Characterlisticls of the tectonic sequence in Zcngmu Basin [South China Sea]. Tropic Oceanol~ 9(2):23-30. (In Chinese, English abstract.)

Multichannel seismic profile .data indicate the presence of two regional unconformities subdividing the basin fill into three sequences: an upper level Oligocene-Recent marine sequence, averaging 3--6 km in thickness and consisting of deltaic littoral and neritic clastics, terrace reefs and carbonates in the south and abyssal turbidity-current argillaceous deposits to the north; a Middle Paleocene-Eocene sequence of tilted fault blocks reaching a thickness of 4.5 km in the south and thinning northward; and a lower, pre-Tertiary deformed sequence of metamorphic and igneous rocks. The evidence supports Lower Eocene uplift of the basin, followed by subsidence from the Oligocene to the present. South China Sea Inst. of Oceanol., Acad. Sin., People's Republic of China. (hbf) 92:3090 Okamura, Yukinobu, 1991. Large-scale melange formation due to seamount subduction: an example from the Mesozoic accretionary complex in central Japan. J. Geol., 99(5):661-674. The extensive Mesozoic melanges in central Japan, and in particular, the accretionary complex in the Mino terrace, which includes large-scale melanges of seamount fragments and stacked successions of chert, siliceous shale, and turbidites, are interpreted as the result of deformation of the forearc wedge due to seamount subduction. A hypothetical model to

505

account for large-scale melange formation is proposed. Geol. Surv. of Japan, 1-1-3, Higashi, Tsukuba, Ibaraki 305, Japan. (hbf) 92:3091 Qiu, Yuanxi et al., 1991. Meso-Cenozoie taphrogeny and dispersion in the continental margin of southeast China and adjacent seas. Tectonophysics, 197(2-4):257-269. The area from the continental margin of South China to the central basin of the South China Sea can be divided into several Meso-Cenozoic fault-sag zones. The fault-sags are of five types: continental upwarp fault-sags, embryonic continental rifts, intracontinental rifts, continental slope (transitional) rifts and oceanic rifts. These extensional structures are the products of different stages of taphrogeny. The study area lies within the interaction zone of the Eurasia, Pacific and lndo-Australia plates, where the extensional structures are related to this interaction but not directly to the subduction mechanism. The distribution of the fault-sags is controlled by the previous tectonic framework. Dept. of Geol., Zhongshan Univ., Guangzhou, People's Republic of China. 92:3092 Shoberg, Tom, Seth Stein and Jill Karsten, 1991. Constraints on rift propagation history at the Cobb Offset, Juan de Fuca Ridge, from numerical modeling of tectonic fabric. Tectonophysics, 197(2-4):295-308. Magnetic anomalies in the Cobb Offset region of the ridge have been interpreted in terms of a complex 'dueling propagator' history in which rift propagation has occurred alternately in opposing directions on adjacent ridge segments. The overall propagation history has been inferred from magnetic data. More detailed resolution within polarity chrons is obtained by using seafioor tectonic fabric from acoustic imagery. The fabric is best fit for propagation rates between 400 and 900 mm/yr, and results are in accord with the interpretation, based on magnetics alone, that rates of rift propagation significantly exceeded spreading rates. The complex tectonic fabric is reasonably well fit on this scale (~1 kin) by simple rift propagation models which do not invoke shear zone behavior and thus deviate from rigid plate tectonics. Dept. of Geol. Sci., Northwestern Univ., Evanston, IL 60208, USA. 92:3093 Stein, R.S. et al., 1991. Contemporary, Hoiocene, and Quaternary deformation of the Asal Rift, Djibouti: implications for the mechanics of slow spreading ridges. J. geophys. Res., 96(B13): 21,789-21,806.

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D. SubmarineGeologyand Geophysics

The Asal Rift provides the world's best subaerial analog for young, slow-spreading mid-ocean ridges. Seismic, geodetic, and field observations of a seismovolcanic event there in 1978 yielded estimates of fault and dike geometry, displacement, and volume of extruded basalt. Rift valley faults are active. Events on individual faults recur every 200-300 yr; half the rift faults slipped during the 1978 event. If this is typical, then groups of faults are activated every 100-150 yr. For the past 35 kyr, rift axis subsidence has been 8-9 m m / y r and infilling by volcanic extrusion < ! mm/yr. The observations imply that vertical rift deformation has not been steady state and there is a rifting/filling cycle with the most recent filling episode ending ~ 3 5 kyr. USGS, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025, USA.

D250. Plate and global tectonics 92:3094 Gangi, A.F. (ed.), 1991. World rift systems. Special issue. Selected symposium papers, Texas A&M University, College Station, Texas, April 27-28, 1989. Tectonophysics, 197(2-4):99-390; 17 papers. The symposium's purpose was to illustrate structural forms and processes common to rift systems throughout the world and to consider processes and structures characteristic of the rifts of Africa and the Red Sea area, east Asia and western Pacific, and North America. The selected papers include general discussions on graben formation, lithospheric thinning, uplift, heat flow, and petrological aspects of active rifting. Regional treatments cover the A f r o Arabian rift systems, the Dead Sea rift, the Red Sea rift, the Anza rift and continental rifts of Africa, rifting in China, the Reelfoot rift of the south central U.S., the Cobb Offset at the Juan de Fuca Ridge, and the dynamics of the Rio Grande as compared with East African and Kenya rifts. (hbf) 92:3095 Hatcher, R.D. Jr. and L. Zonenshain (eds.), 1991. Special issue. Accretionary tectonics and composite continents. Tectonophysics, 196(3-4):397411; 9 papers. This special volume contains a series of papers originally presented at a 1989 symposium held during the 28th Geological Congress, in Washington, D.C. The papers cover a geographic range from Antarctica to central Asia and include traditional field studies as well as paleomagnetic, geochemical and isotopic investigations. (rjw)

OLR (1992)39 (6)

92:3096 Mart, Yossi, 1991. The Dead Sea Rift: from continental rift to incipient ocean. Tectonophysics, 197(2-4): 155-179. The Dead Sea Rift, a 600-km-long, 20-km-wide depression, which is the northern extension of the Red Sea oceanic spreading center, is built of a series of internal basins. The Pliocene transition of tectonic activity from the Suez to the Dead Sea is probably due to a clockwise jump of the spreading center. Part of the data suggests that the rift is an extensional structure, whereas another part indicates that the rift is a product of regional sinistral strike-slip faulting. Reconstructed Mesozoic depositional facies, seismic reflection profiles, and the series of secondary internal basins in the rift which seem equivalent to the linear system of axial basins in the northern Red Sea, together with the 25-50% reduction of crustal thickness underneath the rift, indicate an incipient oblique oceanic spreading center. Natl. Inst. of Oceanogr., IOLR, Tel Shikmona, Haifa, Israel. 92:3097 Tatsumi, Yoshiyuki and Nobukazu Kimura, 1991. Backarc extension versus continental breakup: petrological aspects for active rifting. Tectonophysics, 197(2-4): 127-137. The active mechanism of rifting is proposed, based on petrological constraints from backarc spreading in the Japan Sea and continental separation in the East African rift system. Secular variation in volcanic activities on the NE Japan arc indicates steepening of subducted oceanic lithosphere and anomalously high temperatures in the mantle wedge at the prerifting stage, requiring that injection of hot asthenosphere into the mantle wedge antedated formation of the backarc rift system. Kenya Rift volcanic activity started earlier than domal uplift and formation of rift systems. It follows that this continental breakup is governed by active rifting. Two magmatic cycles are recognized in the Kenya Rift and attributed to increasing degree of partial melting of mantle source material in association with lithospheric thinning. Dept. of Geol. and Mineralogy, Kyoto Univ., Kyoto 606, Japan.

D280. Volcanism, magmatism 92:3098 Baldridge, W.S. et al., 1991. Miocene magmatism of Sinai related to the opening of the Red Sea. Tectonophysics, 197(2-4): 181-201.

OLR (1992)39 (6)

D. Submarine Geology and Geophysics

Extension during Early Miocene opening of the Red Sea resulted in a widespread system of dikes and smaller bodies, mainly basaltic but with some granophyres, primarily along the northeastern margin of the Red Sea/Gulf of Suez axis. Whether the main trough is underlain by modified continental or oceanic crust is controversial. It is suggested that the Sinai basalts were generated within, but near, the base of subcrustal continental lithosphere, perhaps indicating thermal thinning of lithospheric mantle above upwelled asthenosphere and requiring a lithosphere at least 35-50 km thick during initial rifting and asthenospherie upwarping broad enough for all magmas to derive from roughly the same depth. Yemen-Ethiopian volcanism began about 30 mya and was much more voluminous, suggesting that underlying mantle upwelling accompanied rifting. 92:3099 Coulbourn, W.T. and P.J. Hill, 1991. A field of volcanoes on the Manihiki Plateau: mud or lava? Mar. Geol., 98(2-4):367-388. A field of volcanoes surrounding a seamount on the Manihiki Plateau are examined using seismic and sidescan data. The cones are steep-sided, ~ 1 km in diameter and many appear to be composed of multiple flow units. Some have summit depressions and are surrounded by moats. The number of volcanoes increases toward the seamount which is formed by coalescence of ~ 4 0 individual cones. Coring and dredging recovers only forarniniferal ooze and limestone; it is therefore not clear whether the cones are primarily igneous or sedimentary features. Hill: Bur. of Min. Resources, Geol. and Geophys., GPO Box 378, Canberra, ACT, Australia. (rjw) 92:3100 Dosso, Laure et al., 1991. S r - N d - P b geochemical morphology between 10 ~ and 17~ on the Mid-Atlantic Ridge: a new MORB isotope signature. Earth planet. Sci. Letts, 106(i-4):29-43. Samples coming from the 14~ topographic high show new MORB Sr-Nd isotopic characteristics which, pictured in a classical mantle array diagram, put their representative points close to H I M U sources of ocean islands such as St. Helena, Tubuar and Mangaia. The 14~ mantle source presents geochemical characteristics which indicate mantle differentiation processes and a mantle history that are more distinct than so far envisaged from typical MORB data. Pb data indicate that the 14~ mantle source cannot be the result of binary mixing between a depleted mantle and a HIMU-type source; rather, the enriched endmember could itself be a mixture of

505

Walvis-like and HIMU-like materials. G.D.R. Genese et Evol. des Domaines Ocean., I F R E M E R , BP 70, 29263 Plouzane, France. 92:3101 Gerlach, T.M. (comment), David Graham and Philippe Sarda (reply), 1991. [Discussion oil 'Mid-ocean ridge popping rocks: implications for degassing at ridge crests.' Earth planet. Sci. Letts, 105(4):566-567. This paper is a comment on vesicle size and rare gas abundance in 'popping rocks' samples from the Mid-Atlantic Ridge. Sarda and Graham (1990) report bulk CO 2 concentrations in the rocks, as determined from the gas content of the vesicles, that are 4-5 times larger than the 0.21 wt% value they cited in their discussion and calculations; a value which had been reported elsewhere. This discrepancy is large enough to have a significant effect on mid-ocean-ridge carbon flux calculations and other findings based on the 'popping rocks' compositions. (rjw) 92:3102 Goldstein, S.J. et al., 1991. Geochronology and petrogenesis of MORB from the Juan de Fuca and Gorda ridges by 23sU-2-WYh disequilibrium. Earth planet. Sci. Letts, 107(1):25-41. A highly precise mass spectrometric method of analysis was used to determine 23sU-234U-2~~ in axial and off-axis basalt glasses from the Juan de Fuca and Gorda ridges. Initial 23~ activity excesses in axial samples generally lie within a range of 12 to 15%. Secondary alteration effects, evaluated using 8234U, appear to be negligible. Direct dating of MORB was accomplished by measuring the decrease in excess 23~ in off-axis samples. The full spreading rate based on U - T h ages for the Endeavour segment is 5.9 __.1/2 cm/yr. Initial 23~ ratios and 23~ activity were also used to examine the recent T h / U evolution and extent of melting of mantle sources beneath the ridges. Isotope Geoehem., Grp. INC-7, Los Alamos Natl. Lab., Los Alamos, N M 87545, USA. 92:3103 Marsh, B.D. et al., 1991. Hawaiian basalt and Icelandic rhyolite: indicators of differentiation and partial melting. Geologische Rdsch~ 80(2): 481-510. Although Icelandic and Hawaiian hotspot magmatism have many common characteristics, Icelandic magmas are 10-12% rhyolite, whereas no rhyolitic lavas have been found on Hawaii, and lavas containing > 5 3 % silica are very rare. A study of

506

D. Submarine Geology and Geophysics

Hawaiian lava lakes and the Shonkin Sag laccolith in Montana leads to consideration of the concepts of solidification fronts and crystal size distribution. It is suggested that the principal differences between Icelandic and Hawaiian lavas result from the periodic remelting and recycling of Icelandic crust due to jumps of the spreading axis, which leads to melts forming at or near solidus temperatures. Dept. of Earth and Planetary Sci., Johns Hopkins Univ., Baltimore, MD 21218, USA. 0abf) 92:3104 McDonough, W.F. and C. Chauvel, 1991. Sample contamination explains the Pb isotopic composition of some Rurutu Island and Sasha seamount basaits. Earth planet. Sci. Letts, 105(4):397-404. Palaez and Saunders reported Pb isotopic compositions for Rurutu Island basalts that form a trend oblique to the main oceanic basalt array. Detailed leaching experiments on aliquots of the same rock powders demonstrate that these powders have been heavily contaminated by a foreign Pb component providing ~80% of the total Pb present in the sample. Pb isotopic compositions similar to those of Rurutu basalts were reported by Fornari et al. for Lamont seamount basalts. Strong leaching of glass chips from one of their samples demonstrates that these glass chips also were contaminated by a foreign Pb component. In both cases the contamination most likely occurred prior to the initiation of isotope analyses. We suggest using acid-washed rock chips for even the freshest looking lavas for Pb isotopic analyses. Max Planck Inst. fur Chem., Postfach 3060, D-6500 Mainz, FRG. 92:3105 Metrich, Nicole et al., 1991. The 1783 Lakagigar eruption in Iceland: geochemistry, CO 2 and sulfur degassing. Contr. Miner. Petrology, 107(4):435447. During the 1783 eruption, the largest historic lava flow on Earth, 12.3 km 3 of tholeiite lava flowed from a 25-km-long fissure near Grimsvotn Volcano, accompanied by emission of as much as 10u kg of H2SO 4 atmospheric aerosol. A study of matrix glasses and melt inclusions in phenocrysts provides new data on major element and volatile compositions of the Lakagigar magmas. Compositions ranging from primitive olivine tholeiite, quartz tholeiite, to Fe-Ti olivine basalt indicate a heterogeneous magma reservoir with quartz tholeiite dominant. Vesicularity, water content, CO 2, and Ci 2 vary with degree of differentiation. FeO and sulfur also vary with composition; a loss of at least 75% of sulfur during eruption is indicated. The data also imply that during eruption and following magma

OLR ( 1992} 39 (6)

withdrawal from the reservoir, sulfur degassing was controlled by COz-induced vesicularity of the magma. Lab. Pierre Sue, Grp. des Sci. de la Terre, CEN-Saclay F-91191, Gif sur Yvette, France. (hbf)

92:3106 Monjaret, M.C., H. Bellon and P. Maillet, 1991. Magmatism of the troughs behind the New llebrides Island Arc 0tV Jean Charcot SEAPSO 2 cruise): K-Ar geochronology and petrology. J. Volcanol. geotherm. Res~ 46(3-4):265-280. In every area, volcanism from the troughs precedes that of the adjacent islands. Four main periods of volcanic activity have been defined; volcanic affinity is generally orogenic. But some variation exists and two geochemical types (Mg-IAT basalts and hyperK acid lavas) seem to mark the trough structuration. Only the Vanikoro area (the most northern one) shows basalts with geochemical characteristics intermediate between MORB and island-are tholeiites and acid lavas near primitive island-arc lavas, which illustrate the initiation of the arc in this area. The New Hebrides back-arc troughs must be considered as intra-arc troughs and are back-arc structures only because of their location at the rear of the active emerging arc. U R A n.1278 'Genese et Evolution des Domaines Oceaniques,' Univ. de Bretagne Oceidentale, 6 Ave. Le Gorgeu, 29287 Brest Cedex, France. 92:3107 Niu, Yaoling and Rode)' Batiza, 1991. An empirical method for calculating melt compositions produced beneath mid-ocean ridges: application for axis and off-axis (seamounts) melting. J. geophys. Res, 96(B 13):21,753-21,777. A new method for calculating the major element composition of primary melts parental to MORB is presented in an effort to understand the origin of MORB and the magmatie processes at ridge axes and to provide a self-consistent set of MORB melt compositions for use in physical models of upwelling, flow, and other processes beneath mid-ocean ridges. The method is empirical and employs solid-liquid partition coefficients obtained from experiments. The model is used to interpret MORB compositions and mantle upwelling patterns beneath a fast ridge (the East Pacific Rise), a slow ridge (the Mid-Atlantic Ridge at 26~ and seamounts (the Lamont seamount chain); some conclusions regarding magmatic processes occurring below the plate boundary zone are presented. Dept. of Geol. and Geophys., Univ. of Hawaii at Manoa, Honolulu, HI 96822, USA.

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D. SubmarineGeologyand Geophysics

92:3108 Price, R.C. and L.W. Kroenke, 1991. Tectonics and magma genesis in the northern North Fijl Basin. Mar. Geol, 98(2-4):241-258. In the complex back-arc North Fiji Basin, active seafloor spreading occurs along two N-S ridge systems and extension occurs along the Fiji Fracture Zone, a transform fault, and South Pandora Ridge, a tectonic feature best explained in terms of slowspreading ridge segments within a broad transform domain. The southern end of the central ridge has a profile normally associated with fast-spreading, steady-state, mid-ocean ridges. Basalts are moderately evolved normal MORB. Where fast-spreading, large-scale mantle upwelling leads to extensive melting of asthenosphere-derived depleted mantle, MORB-like compositions dominate. Other settings are characterized by basalts enriched in large ion lithophile and high field strength minor and trace elements. The spectrum of compositions can be related to the range of back-arc environments. Dept. of Geol., La Trobe Univ., Bundoora, Vie. 3083, Australia. 92:3109 Sano, Yuji et al., 1991. Secular variations in helium isotope ratios in an active volcano: eruption and plug hypothesis. Earth planet. Sci. Letts, 107(1): 95-100. Lab. for Earthquake Chem., Univ. of Tokyo, Bunkyo-Ku, Tokyo ! 13, Japan. 92:3110 Tamura, Yoshihiko, Masato Koyama and R.S. Fiske, 1991. Paleomagnetic evidence for hot pyroclastic debris flow in the shallow submarine Shirahama Group (upper Miocene-Pliocene), Japan. J. geophys. Res, 96(B13):21,779-21,787. The cooling history of coarse andesite blocks deposited proximally in the shallow marine environment has been investigated by paleomagnetic studies and heat conductivity calculations. Six to thirteen samples were measured on cores of six andesite blocks. Thermal demagnetization techniques were used to detect directional change of remanence through demagnetization steps. On the basis of the remanence direction of each component, different blocking temperature, and petrography, the first component of remanence is interpreted as secondary viscous remanence, whereas the other two components were obtained during and immediately after emplacement and as the blocks continued cooling after they came to rest. Heat conductivity calculations suggest that the blocks were emplaced less than an hour after being erupted. Dept. of Earth and Planetary Phys., Univ. of Tokyo, Bunkyo, Tokyo 113, Japan.

507

92:3111 Wilkinson, J.F.G., 1991. Mauna Loan and Kilauean tholeiites with low 'ferromagnesian-fractionated' 100 M g / ( M g + F e 2+) ratios: primary liquids from the upper mantle? J. Petrology, 32(5):863-907. Crystal fractionation and primary magma models for the shield-building low-M tholeiites of Mauna Loa and Kitauea volcanoes are compared, and several lines of evidence, which do not support crystal fractionation, are presented. Instead, the lava spectra are interpreted as the result of variable low-pressure (10-15 kb) equilibrium melting of Ti-amphibole spinel lherzolites with fraction crystallization playing only a minor role. It is suggested that the most voluminous tholeiites are products of a mantle source which represent 'lowest-pressure heteromorphs' of the Hawaiian mantle plume that originated in the lower mantle. Dept. of Geol. and Geophys., Univ. of New England, Armidale, NSA 2351, Australia. (hbf)

D290. Crust, mantle,

core

92:3112 Ben-Avraham, Zvi and Mario Grasso, 1991. Crustal structure variations and transcurrent faulting at the eastern and western margins of the eastern Mediterranean. Tectonophysics, 196(3-4):269-277. Crustal structure variations have caused segmentation of the collision zones which extend from Sicily through the Calabrian Arc, the Hellenic Arc and the Cyprian Arc to the Taurus chain. On both sides of the eastern Mediterranean, in southeastern Sicily and in the Levant, similar tectonic features have developed. Hinge faults exist along both margins due to the different modes of collision. Landward of the margins, two large transcurrent fault systems, the Scicli Fault Zone and the Dead Sea Rift, have developed; these units are more buoyant than the adjacent crust and resist underthrusting. The initial faulting along both transcurrent fault systems probably started at the collision zone in the north and propagated to the south where large extensional areas, the Pantelleria Rift and the Red Sea, exist. Dept. of Geophys. and Planet. Sci., Tel Aviv Univ., Tel Aviv 69978, Israel. 92:3113 Campden, D.A. and Stuart Crampin, 1991. Observations of shear-wave splitting from marine VSPs in the southern North Sea. Geophys. J. int~ 107(3):465-473.

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D. SubmarineGeologyand Geophysics

Four offset marine Vertical Seismic Profiles are analysed using mode-converted shear waves. Automatic estimates of fast shear-wave polarizations and time delays indicate the presence of stressinduced cracks striking at between N35~ and N60~ corresponding to independent measurements of stress from borebole breakout data and earthquake studies. Time delays suggest that shearwave splitting occurs only in the overlying sealing rock with no measurable anisotropy in the reservoir sands. All measurements are contaminated by scattered energy, probably resulting from non-planar interfaces and/or lateral variations in lithology. RR/34, KSEPL (Shell Res.), Volmerlann 6, 228 GD, Rijswijk, Ilolland. 92:3114 Crampin, Stuart and J.H. Lovell (eds.), 1991. Seismic anlsotropy. Proceedings of the Fourth International Workshop, Edinburgh, 2-6 July 1990. Geophys. J. int, 107(3):385-714; 30 papers. This volume, which includes almost a third of the papers and posters presented at the workshop, documents the significant advances in seismic anisotropie research since the 1988 workshop, and in particular, details the important developments in processing shear-wave splitting in records and their applications for oil and gas production. Although shear-wave anisotropy of the upper crust may be only 0.5 to 5%, it has great significance for many industrial and geological operations because of its bearing on the interpretation of crack and stress structures within rock bodies. The inclusion of anisotropy in seismic interpretation is hailed as a turning point in seismological research. (hbf) 92:3115 Eissen, J.-P. et al., 1991. Petrology and geochemistry of the central North Fiji Basin spreading centre (southwest Pacific) between 16~ and 22~ Mar. Geol~ 98(2-4):201-239. The main N-S segment of the 12 m.y. old North Fiji Basin is morphologically, petrologically, and geochemically similar to other medium-rate oceanic ridges, whereas other segments have been severely disturbed by a triple junction at 16"45"S, overlapping spreading centers, and propagating rifts and produce basalts of more variable petrology and geochemistry. The spreading rate diminishes from 7.8 cm/yr near 20~ to 4.6 cm/yr near 18~ Mineralogical, petrological and geochemical data from 24 new stations indicate that petrogenesis is essentially controlled by low.pressure crystal fractionation. Beneath recently formed segments, the mantle source is heterogeneous and has some back-arc basin basalt affinities; beneath the more

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steady-state N-S segment the magma source is more homogeneous. Centre ORSTOM, BP A5, Noumea Cedex, New Caledonia. 92:3116 Ferraes, S.G., 1991. A procedure to estimate the probability distribution of [earthquake] recurrence times in the west-northwestern ilellenic Arc. Earth planet. Sci. Letts, 106(!-4):181-190. Inst. of Geophys., Ciudad Univ., Mexico City, Mexico. 92:3117 Hoernle, Kaj, George Tilton and H.-U. Schmincke, 1991. S r - N d - P b Isotopic evolution of Gran Canada: evidence for shallow enriched mantle beneath the Canary Islands. Earth planet. Sci. Letts, 106(1-4):44-63. Sr, Nd, and Pb isotopic compositions of 66 lava flows and dikes spanning the 15 Myr subaerial volcanic history of Gran Canaria and five Miocene through Cretaceous sediment samples from DSDP Site 397, 100 km south of Gran Canaria, are reported. The Miocene and Pliocene-Recent volcanics form distinct trends on isotope correlation diagrams. Although the two age groups have overlapping Sr and Nd isotope ratios, the PlioceneRecent volcanics have less radiogenic Pb. Variation in isotope ratios with age, degree of differentiation, SiO2-saturation in basalts, and magma production rates constrain the composition of the lithosphere, asthenosphere and plume beneath the islands. The study suggests that enriched mantle components may be stored in shallow mantle, whereas the HIMU component may have a deeper origin. Dept. of Earth Sci., Univ. of California, Santa Cruz, CA 95064, USA. 92:3118 Kagan, Y.Y. and D.D. Jackson, 1991. Seismic gap h)]~othesis: ten years after. J. geophys. Res, 96(B 13):21,419-21,43 !.

Based on the seismic gap theory, McCann et al. (1979) postulated zones of high, medium, and low seismic potential around the Pacific rim. In the 10 years since, there have been over 40 large (3//>7.0) earthquakes, enough to test statistically the earlier forecast. We also analyze another forecast of long-term earthquake risk, that by Kelleher et al. (1973). The hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence. The data suggest that, contrary to these forecasts, places of recent earthquake activity have larger than usual seismic hazard, whereas the segments of the eircum-Pacific belt with

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D. SubmarineGeologyand Geophysics

no large earthquakes in recent decades have remained relatively quiet. The 'clustering' of earthquake times does not contradict the plate tectonic model, which constrains only the long-term average slip rate, not the regularity of earthquakes. Inst. of Geophys. and Planetary Phys., Univ. of California, Los Angeles, CA 90024-1567, USA. 92:3119 Kao, Honn and W.-P. Chen, 1991. Earthquakes along the Ryukyu-Kyushu Arc: strain segmentation, lateral compression, and the thermomechanical state of the plate interface. J. geophys. Res, 96(B 13):21,443-21,485. Focal depths and mechanisms of 49 earthquakes of mb >__5.4 along the Ryukyu-Kyushu Arc, determined by inverting waveforms and amplitudes of P and SH wave trains at teleseismic distances, are sufficiently precise to reveal features not predicted by plate kinematics. The interplate thrust zone was found to be simple, despite the presence of a second layer of seismicity beneath the plate interface, and it was shown that at depths > 8 0 km deformation of the subducted slab along the northern arc is completely downdip extensional, whereas along the southern part the arc deforms in an opposite manner. The observed pattern of strain segmentation requires a major accommodation structure, such as a tear fault, in the slab near the Tokara channel. Dept. of Geol., Univ. of Illinois, 245 Nat. Hist. Bldg., 1301 W. Green St., Urbana, IL 61801, USA. 92:3120 Lyzenga, G.A., Arthur Raefsky and S.G. Mulligan, 1991. Models of recurrent strike-slip earthquake cycles and the state of crustal stress. J. geophys. Res~ 96(B 13):2 !,623-21,640. Numerical models of the strike-slip earthquake cycle, assuming a viscoelastic asthenosphere coupling model, are examined. The time-dependent simulations incorporate a stress-driven fault, which leads to tectonic stress fields and earthquake recurrence histories that are mutually consistent. The models predict a local near-fault stress maximum at greater depths, sustained by the cyclic transfer of strain from the elastic crust to the ductile asthenosphere. Models incorporating both low-stress and high-stress fault strength assumptions are examined, under Newtonian and non-Newtonian rheology assumptions. Model results suggest a preference for low-stress (a shear stress level of ~ 1 0 MPa) fault models, in agreement with previous estimates based on heat flow measurements and other stress indicators. Jet Propulsion Lab., M / S 238-332, Pasadena, CA 91109, USA.

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92:3121 Meissner, Rolf and W.D. Mooney, 1991. Speculations on continental crustal evolution. Eos, 72(52):585, 590. Each of the three processes discussed here has its own merits in terms of how effectively it produces 'typical' continental crust from accreted island arcs. We suggest that differentiation is the most common process, followed by injection of alkaline magmas in connection with crustal extension. Geophysical evidence for the widespread occurrence of the lithospheric delamination process remains elusive but continues to gain favor. Inst. for Geophys., Univ. of Kiel, Olshausen Str. 40-60, 2300 Kiel, F R G . 92:3122 Nicholson, Hugh et al., 1991. Geochemical and isotopic evidence for crustal assimilation beneath Krafla, Iceland. J. Petrology, 32(5):1005-1020. K20 and the very incompatible trace elements, Rb, Th, and U, are all enriched beyond the extent expected by closed-system fractional crystallization. Fractionation coupled with periodic replenishment and tapping of the reservoir is unlikely to be responsible for this enrichment, despite the geophysical evidence suggesting a large number of inflations and deflations of a shallow magma reservoir. Th- and O-isotope results confirm that crustal assimilation is operating on a local scale beneath Krafla. A model is suggested, fitting both the Th- and O-isotopic data, which involves the partial melting and incorporation of a hydrothermally altered wall-rock contaminant during fractional crystallization. This process of partial melting is likely to enhance the most highly incompatible element concentrations more than expected by closed-system fractional crystallization. BP Res. Centre, Chertsey Rd., Sunbury on Thames, Middlesex T W I 6 7LN, UK. 92:3123 Nicolaidis, Argyris, Mohammed Jannane and Albert Tarantola, 1991. Neutrino tomography of the Earth. J. geophys. Res, 96(B13):21,811-21,817. Neutrino oscillations inside matter are very sensitive to the density of the medium traversed by the neutrinos. If the neutrino mixing angle (so far unknown) is not very small, then the neutrino oscillation length is of the size of the Earth, and we can use the phenomenon of neutrino matter oscillations to study the Earth's density distribution. Although neutrino attenuation data have already been proposed as a means to infer the density structure of the Earth, we show that neutrino oscillation data could also be used to make a density

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tomograph of the Earth. Theoretical Phys, Dept., Univ. of Thessaloniki, GR-54006 Thessaloniki, Greece. 92:3124 Niu, Yaoling and Rodey Batiza, 1991. In-sltu densities of MORB melts and residual mantle: implications for buoyancy forces beneath midocean ridges. J. Geol, 99(5):767-775. Density differences between silicate melt and solid phases and between fertile and residual mantle may be important controls on the upward flow of upper mantle and separation of melt from the upwelling matrix. To assess quantitatively the magnitude of these effects, we have compiled the available data for calculating densities of silicate melts and solid phases as a function of composition, temperature, and pressure. We include measured and calculated values of thermal expansion and compressibility for both solids and liquids. Our calculations show that density differences between instantaneous melt and residual solids increase toward the surface, implying an increasing melt migration rate with continuing upwelling and melting. However, the density difference is significantly less than the value of ~0.5 g cm -3 commonly assumed in theoretical models. 9 by The University o f Chicago. Univ. of Hawaii at Manoa, tlonolulu, HI 96822, USA. 92:3125 Scholz, C.H. and T. Mikumo (eds.), 1991. Modelling the earthquake source. Selected papers, IASPEI Symposium, lstanbul, Turkey, August 24, 1989. Tectonophysics, 197(1):98pp; 7 papers. These papers in this volume reflect four approaches to the study of earthquake sources: modelling; analysis of source processes of individual large earthquakes; investigations of source processes in general; and work in experimental and theoretical mechanics. Topics include an application of Green's function method and the nonlinear inversion technique; minimum sizes and values for earthquakes rupture velocity; inferences from aftershock sequences; scaling relations; a simplified hypocenter model; and inversions of near-source broadband accelograms. (hbf) 92:3126 Singh, S.K. and F. Mortera, 1991. Source time functions of large Mexican subduction earthquakes, morphology of the Benioff zone, age of the plate, and their tectonic implications. J. geophys. Res. 96(B13):21,487-21,502. Modelling of P waves to obtain source parameters of large Mexican subduction zone earthquakes between

OLR (1992) 39 (6)

95~ and 106~ from 1928 and 1986 shows that all earthquakes are shallow and suggests a change in plate interface characteristics near 99~ at the intersection of the O'Gorman Fracture Zone and the trench. Length of the Benioff zone, which decreases northwest of Oaxaca, can be explained by the correlation between length of subducted slab, age of lithosphere, and convergence rate. The complexity of sources, weaker background seismicity, and fewer aftershocks northwest of Oaxaca may be explained by a stronger interface coupling resulting from subduction of younger oceanic slabs. This, however, neither explains M o s / M o P values northwest of Oaxaca, nor low stress drop estimates, which indicate weaker coupling of the interface. Inst. de Geofis., Univ. Nac. Auton. de Mexico, Ciudad Univ. Codigo 04510, Mexico, DF, Mexico. 92-3127 Sparks, D.W. and E.M. Parmentier, 1991. Melt extraction from the mantle beneath spreading centers. Earth planet. Sci. Letts, 105(4):368-377. Melt migration beneath a mid-oceanic spreading center must be rapid and it must focus melt to the narrow ridge axis. We show that dilation, or decompaction, of the porous matrix creates a high-porosity boundary layer beneath an impermeable cap of cooler, solid mantle. The thickness of the layer, 200-300 m, is determined by a balance between the buoyancy of the melt and the viscous stresses resisting deeompaetion. The parameters that control the layer thickness include the upwelling velocity, mantle viscosity and density difference between the melt and solid. This layer exists near the solidus where melt is being frozen, and therefore deepens with distance from the ridge axis. The along-layer component of gravity drives melt in this highly permeable layer toward the ridge axis. Dept. of Geol. Sci., Brown Univ., Providence, RI 02912, USA.

92:3128 Stoffa, P.L. et al., 1991. Three-dimensional seismic imaging of the Costa Pica accretionary prism: field program and migration examples. J. geophys. Res, 96(B 13):21,693-21,712. To image the complex geologic structures of an active continental margin, a 3-D seismic survey was conducted off Nicoya Peninsula, Costa Pica. Over 60,000 shot points of 96-trace multichannel data were collected in a 9 • 22 km grid located over the accretionary prisms. The data acquisition program and the seismic processing methodology are outlined. Images of two complex geologic a r e a s - - a mud volcano and reflections near the top of the accretionary prism and the top of the subducting oceanic

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D. SubmarineGeologyand Geophysics

basement beneath the prism--illustrate the improvements in imaging and interpretation. Dept. of Geol. Sci., Univ. of Texas, 8701 Mopac Blvd., Austin, TX 78759, USA. 92:3129 Tanahashi, M. et al., 1991. Geological structure of the central spreading system, North Fiji Basin. Mar. Geol, 98(2-4): 187-200. Currently active spreading systems north-northwest and south-southwest of a triple junction at about 17~ 174~ where active hydrothermal activity was discovered, jumped to their present positions possibly in the Late Quaternary. The spreading ridge south-southwest of the triple junction, which is oriented NI5~176 has a 0.7-3.5 km wide axial graben and a 15-35 km wide trapezoidal morphological profile. It cuts into a wide N40~176 oriented graben whose side walls themselves sharply cut previously formed structures, including a high seamount which is now separated into three highs. Geol. Survey of Japan, 1-1-3, Higashi, Tsukuba 305, Japan. 92:3130 Ward, S.N., 1991. A synthetic seismicity model for the Middle America Trench. J. geophys. Res~ 96(B 13) :21,433-21,442. This paper develops a new iterative technique to build models of seismicity and fault interaction. The first step constructs generic models which randomly draw segment strengths and lengths from a 2-D probability distribution. The second step constructs predictive models in which segment lengths and strengths are adjusted to mimic the actual geography and timing of large historical earthquakes. Both types of models not only reproduce the statistics of seismicity over five units of magnitude but also duplicate other aspects including foreshock and aftershock sequences, and migration of focci. However, over a period of about 150 years the complex interaction of fault segments and the nonlinear failure conditions conspire to transform an apparently deterministic model into a chaotic one in that small changes in initial conditions ultimately lead to very different patterns of events. Inst. of Tectonics, Univ. of California, Santa Cruz, CA 95064, USA.

D 3 2 0 . E c o n o m i c g e o l o g y (see also D 3 3 0 Oil and gas, D 3 4 0 - M a n g a n e s e nodules) 92:3131 Coleman, P.J., 1991. Dynamic strike-slip fault systems with respect to the Solomon Islands, and

511

their effect on mineral potential. Mar. Geol~ 98:167-176. Piecemeal slicing of the arc system by complexes of major strike-slip faults and the translation of slices can threaten the process of accumulation of protopetroleum and also the integrity of established reservoirs. However, the same vigorous fault action can result in enhanced development of reef complexes and large-scale growth of organic materials along marginal marine areas. The resultant biomass is swept periodically into deep grabens adjacent to reefs. The sediments may become sufficiently thick and lie at sufficiently great depths to be sites of favourable "oil kitchens'; from these, young oil can be fed into nearby reefal reservoirs. Epithermal and other hydrothermal deposits probably reflect normal, even necessary, episodes in arc growth. The realisation of the vigour of vertical, lateral and rotational movements between fault blocks of the arc system should be a part of the search strategy for arc metals. Univ. of Western Australia, Nedlands, WA 6009, Australia.

D330. Oil and gas 92:3132 Curiale, J.A., Robert Alexander and P.W. Brooks (eds.), 1991. Special issue. Organic geochemistry of hydrocarbon basins. Selected papers from a symposium held at the 1989 International Chemical Congress of Pacific Basin Societies, Honolulu, Hawaii, December 17-22, 1989. Chem. Geol, 93(!-2):206pp; 13 papers. A cross-section of symposium papers provides a state-of-the-art summary of recent organic geochemical research in recent sediments and early diagenesis, petroleum generation and migration, organic geochemistry of the Pacific rim, and novel methods and concepts of petroleum geochemistry. Specific geological/geographical studies include reports on the Canadian Beaufort Tertiary, Tertiary melange on the western Olympic Peninsula of Washington State, the Permian Basin shales, and the Sirikit Oil Field in the Phisanulok Basin of Thailand. (hbf) 92:3133 Hovland, Martin, 1991. Large pockmarks, gascharged sediments and possible clay diapirs in the Skagerrak. Mar. Petrol. Geol., 8(3):311-316. Extensive patches of shallow gas-charged sediments have previously been documented in the eastern Skagerrak (the strait between Norway and Denmark). Recently obtained high resolution side-scan

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sonar and sub-bottom profiler data presented here document several surface and sub-surface features at the border and inside zones of such gas-charged shallow sediments. Four examples are presented and discussed: (1) a low profile, 3 m deep pockmark and gas-charged sediments; (2) a low profile, 6 m deep pockmark associated with a rugged sub-surface reflector; (3) large, up to 24 m deep and 500 m wide pockmarks; and (4) patches of exposed material from the rugged sub-surface reflector. From similarities with previously described features and also with features found in the Kattegat, further south, it is concluded that the pockmarks are formed by gas eruption and seepage and that the rugged subsurface reflector could possibly represent the upper surface of a diapirically deformed unit of gascharged plastic clays. Statoil, P.O. Box 300, N-4001 Stavanger, Norway. 92:3134 Johnson, ttoward, 1991. Petroleum geology of Fiji. Mar. Geol, 98(2-4):313-352. Most petroleum exploration in Fiji has been directed toward shallow-water sedimentary basins; five deep wells drilled offshore and on Viti Levu were dry. The wells penetrated :>2500 m of sedimentary rocks, largely Miocene and younger, which comprise mainly volcaniclastics. Sedimentary series off Viti Levu are cut by large faults; pre-Pliocene rocks are affected by folding. Anomalous amounts of pentane in seabed sediments off northern Viti Levu suggest that some thermogenic hydrocarbons have been generated. Because of the limited seismic resolution, no traps with lower to Middle Miocene shallowwater limestone facies have been identified, but mudstones are widespread in offshore basins and seals are likely to be good. British Geol. Surv., Edinburgh EH9 2LF, UK. 92:3135 Johnson, Howard and John Pflueger, 1991. Potential Mio-Piiocene reef traps in the Iron Bottom Basin, Solomon Islands. Mar. Geol, 98(2-4):177186. 92:3136 Telnaes, Nils and B.S. Cooper, 1991. Oil-source rock correlation using biological markers, Norwegian continental shelf. Mar. Petrol. Geol. 8(3):302310. This paper reports three case studies which illustrate some of the inherent problems in oil-source rock correlations. In the first study an oil is compared directly with mature source rocks on the structure, showing that the oil must have been expelled very early. In the second, oils are compared with

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immature source rock units on the structure, showing the potential of multivariate analysis for correlation problems. Finally an unusual Barents Sea oil is compared with Triassic source rocks from Spitsbergen. It is shown that correlations based on individual characteristics can only be supported in rare cases. Multivariate analysis is a safer method of correlation of oils to a typical potential source rock of mixed kerogen facies and low maturity. Norsk Hydro Res. Ctr., Bergen, Norway. 92:3137 Underhill, J.R., 1991. Implications of MesozoicRecent basin development in the western Inner Moray Firth, UK. Mar. Petrol. Geol, 8(3):359369. Dept. of Geol. and Geophys., Univ. of Edinburgh, West Mains Rd., Edinburgh EH9 3JW, UK.

D340. Manganese nodules, etc. 92:3138 Amakawa, lliroshi et al., 1991. Isotopic composition of Ce, Nd and Sr in ferromanganese nodules from the Pacific and Atlantic oceans, the Baltic and Barents seas, and the Gulf of Bothnla. Earth planet. Sei. Letts, 105(4):554-565. Dept. of Chem., Univ. of Tokyo, Hongo, Tokyo 113, Japan. 92:3139 Cronan, D.S., R.A. Hodkinson and S. Miller, 1991. Manganese nodules in the EEZ's of island countries in the southwestern equatorial Pacific. Mar. Geol, 98(2-4):425-435. Ni and Cu reach their greatest combined abundances (>2%) between 2 ~ and 8~ on the southern margin of the equatorial zone of high biological productivity in the Cook, Line and Phoenix island areas, as a result of biological fluxing of Ni and Cu to the nodules at and just below the CCD. By contrast, Co reaches its greatest abundance (0.6%) south of 8~ in the Cook Islands area in slowly growing nodules on non-biogenic clays well below the CCD. Nodule abundances are greatest (up to 30 kg/m 2) in the Co-rich area, in part due to A A B W flow, giving highest overall metal quantities, particularly of Co. EIlice Islands nodules show features more typical of hydrogenetic ferromanganese oxide crusts than of diagenetically influenced nodules. Dept. of Geol., Imperial College, London SW7 2BP, UK.

92:3140 De Carlo, E.H., 199 !. Paleoceanographic implications of rare earth element variability within a F e - M n

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D. SubmarineGeologyand Geophysics

crust from the central Pacific Ocean. Mar. Geol, 98(2-4):449-467. Geochemical analyses of central Pacific F e - M n oxide crusts suggest that variations in composition and microstructure reflect the influence of environmental conditions during formation. Current crust growth rate estimates of 1-3 mm/m.y, imply that 6-10 cm thicknesses represent a growth record of 20 to 100 m.y. Detailed analyses on successive layers of a 95-mm-thick F e - M n crust from Schumann Seamount reveal variations in elemental distribution and abundance of major constituents and REEs as a function of depth within the crust, which can be explained by mineralogical control but can also reflect differing depositional conditions. Variations in the Ce anomaly and REE fractionation patterns of major element composition and mineralogy and anomalies observed by other workers are used to reconstruct the growth history of the crust. School of Ocean and Earth Sci. and Tech., 10000 Pope Rd., Univ. of Hawaii, Honolulu, HI 96822, USA. 92:3141 Hodkinson, R.A. and D.S. Cronan, 1991. Regional and depth variability in the composition of cobalt-rich ferromanganese, crusts from the SOPAC area and adjacent parts of the central equatorial Pacific. Mar. Geol~ 98(2-4):437-447. Co-rich crust analyses (333, including new analyses from 56 locations) with data comprising Mn, Fe, Co, Ni and Cu concentrations and water depth, have been subjected to a one-way analysis of variance technique to assess factors controlling crust variability in the central Pacific. The two predominant influences on crust composition appear to be water depth and latitude. A model of crust composition variation related to the oxygen minimum zone appears applicable; this model, however, does not explain the observed variations in the data with latitude. Variations in biological productivity about the equator, in addition to the oxygen minimum zone, can be held to account for the observed crust compositional variation with latitude. Mar. Min. Resources Prog., Dept. of Geol., Imperial College, London SW7 2AZ, UK.

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deposition at 128 + 18 kaBP has been determined by excess 23~ dating. Calculated metal accumulation rates are comparable to, or exceed, rates from other hydrothermal areas. Rare earth element results indicate a partial hydrogenetie contribution to a predominantly hydrothermal signature, and vertical element distributions reveal variations in hydrothermal activity. R-mode factor analysis shows that low-temperature hydrothermal, volcanic ash-detrital, and high-temperature hydrothermal factors account for :>95% of sample variability. The combined data reveal a sequence of deposition of initial volcanism followed by high-temperature and then low-temperature hydrothermal mineralization lasting up to 128 ka. Dames and Moore, ! 144 10th Ave., Honolulu, HI 96816, USA. 92:3143 von Stackelberg, Ulrich and Helmut Beiersdorf, 1991. The formation of manganese nodules between the Clarion and Ciipperton fracture zones southeast of Hawaii. Mar. Geol, 98(24):411-423. Growth of most of the nodules found in three Clarion and Clipperton areas began during Oligocene and Miocene breaks in sedimentation. An ample supply of organic matter and skeletal material was important for diagenetic growth of nodules rich in Cu, Ni, and Cu. Also, a large amount of organic matter stimulated bioturbation and lifting by benthic organisms, which kept nodules atop the sediment. The development of minor or local nodule facies is determined mainly by nodule position relative to the calcite compensation depth, post-hiatus sediment thickness, degree of reworking, potential for formation of nuclei during hiatuses, and supply or decomposition of organic matter--factors strongly controlled by seafloor morphology and bottom current activity. Bundesanstalt fur Geowissenschaften und Rohstoffe, W-3000 Hannover 51, FRG.

D360. Books, collections (general)

92:3142 Murphy, Edward et al., 1991. Geochemistry and geochronology of a hydrothermal ferromanganese deposit from the North Fiji Basin. Mar. Geol, 98(2-4):297-312.

92:3144 Crook, K.A.W. (ed.), 1991. Special issue. The geology, geophysics and mineral resources of the South Pacific. Mar. Geol~ 98(2-4):155-467; 17 papers.

A core from the basin contains a 38-cm-thick ferromanganese oxide deposit that conformably overlies foraminiferal ooze. Onset of hydrothermal

Many of the papers in this issue derive from a 1989 workshop held at the Australian National University in Canberra. The subject matter covers many topics

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and encompasses a large area of the Pacific. Two papers relate, respectively, to strike-slip fault systems and Mio--Pliocene reef traps in the Solomon Islands; a second group treats the spreading system, petrology and geochemistry, tectonics and magma genesis, hydrothermal activity, and metalliferous sediments of the North Fiji Basin and the petroleum geology of Fiji; other papers consider hydrothermal

sediments in the Lau Basin, volcanoes on the Manihiki Plateau, hydrothermal and iron-rich deposits from the Teahitia-Mehitia and Macdonald hot spot areas; and a final group takes up the formation and implications of manganese nodules and ferromanganese crusts found in the Clarion and Clipperton fracture zones, the southwest equatorial Pacific, the SOPAC area, and central Pacific. (hbf)

E. BIOLOGICAL OCEANOGRAPHY

El0. Apparatus and methods 92:3145 PahI-Wostl, Claudia, 1991. Patterns in space and t i m e - - a new method for their characterization. Ecol. Model., 58(1-4): 141-157. A method based on information theory and network analysis was recently introduced to quantify the functional changes associated with certain spatiotemporal patterns in ecological networks. The method's potential is illustrated with a simple model system describing the space and time-dependent growth of phytoplankton species as a function of changes in light availability, and with the evaluation of data for the spatiotemporal pattern of N uptake by grassland species. It is proposed to aggregate species into functional ataxonomic assemblages according to their functional and spatiotemporal characteristics; this classification scheme may render data from food webs and network analysis better suited for comparative studies. Zurich Inst. for Aquatic Sci., Ueberlandstr. 133, CH-8600 Dubendoff, Switzerland. 92:3146 Yund, P.O., S.D. Gaines and M.D. Bertness, 1991. Cylindrical tube traps for larval sampling. LimnoL Oceanogr~ 36(6): 1167-1177. A simple modification of the cylindrical tube trap utilizes a high aspect (height-to-width) ratio and an internal Formalin layer to limit the potential resuspension of collected larvae. Tests both in a laboratory flow tank and under field conditions suggest that capture rate scales linearly with both larval concentration and horizontal advection--two components of larval flux. The important role of horizontal advection has additional implications for

the use of such traps to measure sedimentation rates, where only vertical particle flux is of interest. These traps, like sediment traps, may exhibit a particle-size bias in collection" efficiency. Consequently, this technique is probably most appropriate for examining intraspecific spatial and temporal variation in the dynamics of a given larval stage. Dept. of Biol. Sci., Univ. of New Orleans, LA 70148, USA.

E40. Area studies, s u r v e y s (baselines, ecology, etc.) 92:3147 H0pner, Thomas, 1991. The ecological state of the Wadden Sea. An assessment. Int. Revue ges. ttydrobiol., 76(3):317-326. The nutrient load into the Wadden Sea and trend of the load are assessed. Biological indicators of the ecological state of the Wadden Sea are examined; there are signs of a bad as well as a good state, because quality standards are absent. Self-protection mechanisms of the Wadden Sea are discussed with respect to their responsibility for the relatively good state. A qualitative model is proposed to explain the long-term behaviour of the ecosystem. Inst. fur Chem. und Biol. des Meeres, Univ. Oldenburg, FRG. 92:3148 Schiewer, U. (ed.), 1991. Special issue. Eutrophication of the Baltic Sea. Int. Revue ges. Hydrobiol, 76(3):293-472; 17 papers. Once oligotrophic, the Baltic Sea is now considered one of the world's most severely eutrophic seas. Changes due to eutrophication are most evident in