ALBERT

Description: Analysis of individual laminae in Recent sediments from the slopes of the Guaymas Basin indicates an increased abundance of the larger sizes (〉60 µm) of Coscinodiscus nodulifer when upwelling conditions persist over the depositional site and an increase of the smaller sizes (〈60 µm) when nonupwelling conditions exist. The size distributions of C. nodulifer in 10-cm composite samples from Hole 480 show a greater abundance of the large sizes (〉60 µm) associated with well-laminated sections and more of the smaller sizes (〈60 µm) in samples from the homogeneous sections. We have tentatively correlated the pronounced homogeneous zones with late Pleistocene glacial periods. These results indicate a persistence of nonupwelling conditions over Hole 480 during glacial periods (homogeneous zones) and a predominance of upwelling conditions during interglacial periods (laminated zones). Other evidence from diatom and silicoflagellate floral analysis seems to support these preliminary conclusions.

Description: Four species of gammaridean Amphipoda are recorded from the Iberian deep sea basin at about 5000 m depth: Bathyceradocus iberiensis sp. n., Paracallisoma platepistomum sp. n., Parandaniexis cf. mirabilis Schellenberg, 1929, and Paragissa galatheae Barnard, 1961. The biology of the four species is discussed.

Description: From 12 radiolarian-rich claystone samples of the DSDP-Leg 25, Site 249, situated in the western Indian Ocean southwest of Madagascar 4 species of agglutinated and 38 species of calcareous benthonic foraminifera are described, 13 of them in open nomenclature. As a lot of Valanginian species and Gavelinella barremiana occur in the foraminiferal faunas described here a Valanginian-Hauterivian age is assigned to them. These microfaunas investigated here yield some index species characteristic in the Lower Cretaceous deposits of Northern Germany and also from the near-by Madagascar. Nodosariids dominate in a striking way with 36 species, especially of Astacolus, Citharina, Lenticulina, Lingulina, Marginulinopsis, Nodosaria, Saracenaria, and Vaginulina. Important Neocomian species well-known from other DSDP sites, namely Praedorothia ouachensis (SIGAL) and planktonic foraminifers, are missing. The microfaunas of Site 249 have to be derived from shelf areas.

Description: The genus Hinia is divided in 4 subgenera; other subgenera are not represented in the area studied. It was possible to find criteria for a better discrimination of the highly variable species H. (Hinia) schlotheimi and H. (Hinia) turbinella. The species "fuchsi" has been placed in the synonymy of H. (Hinia) turbinella. The species H. (Hinia) schlotheimi (BEYRICH) and H. (Telasco) schroederi (KAUTSKY) have been united under the name H. (Hinia) schlotheimi. The easily distinguishable species H. (Tritonella) tenuistriata and H. (Hinia) sulcata belong to two different genera. H. (Tritonella) cimbrica andersoni of the Viol- and Katzheide-Beds (Reinbek-stage) is separable from the population found in the Hemmoor-stage, it turned out to be a valuable guide subspecies for the Reinbek-stage. The species H. (Tritonella) serraticosta, H. (Tritonella) catulli, H. (Hinia) holsatica, and H. (Telasco) syltensis are all similar in respect to shape and ornamentation. Criteria have been found for a better discrimination of these species. The species contabulata, effusa and seminodifera described by SPEYER (1864), turned out to be contogenetic stages of H. (Tritonella) pygmaea. H. (Tritonella) cavata, previously described from the Tertiary of the North sea area, was proven to be absent from the area investigated. The forms described under that name, belong to H. (Tritonella) woodwardi.

Description: Analyses of stable isotopes of monospecific planktonic foraminifers (G. quadrilobatus group) and monogeneric benthic foraminifers (Cibicidoides spp.) from late Neogene Atlantic Site 502 and Pacific Site 503 were conducted in order to determine the paleoceanographic changes resulting from the late Neogene uplift of the Panama Isthmus and from climatic cooling. In general, results at each site are similar to those from previous studies for the late Miocene and late Pliocene time interval, documenting the late Miocene (6 Ma) shift in carbon isotopes and the inferred growth of permanent Northern Hemisphere continental ice sheets beginning about 3.2 Ma. Comparison of Atlantic-Pacific planktonic-benthic isotope data for four stratigraphic intervals (~6-8, ~5-6, ~3-5, and ~2-3 Ma) suggests that increasing isolation of Atlantic and Pacific low-latitude waters may be related to the emergence of the Panama Isthmus. The contrast between Atlantic and Pacific benthic foraminiferal d13C increased in two steps from 0.60 per mil to 1 per mil (the modern contrast) at about 6 Ma and 3 Ma. The first increase (0.15 per mil) may represent the end of previously limited deep-water communication between the Atlantic and Pacific at the present location of Panama. The second increase (0.25 per mil) may be due to increased production of North Atlantic Deep Water. This probably reflects the development of modern deep-sea circulation. The d18O of planktonic foraminifers begins to increase in Atlantic Site 502 at 4.2 Ma and may reflect the increasing salinity of the North Atlantic Ocean arising from diminishing surface-water exchange across Panama. This increase is clearly shown by contrasting the d18O of Atlantic and Pacific planktonic foraminifers, as well as the d18O of planktonic and benthic foraminifers at Site 502. This inferred increase in surface-water salinity begins at the time of increasing provinciality of Atlantic and Pacific planktonic foraminifers.

Description: Heavy and light minerals were examined in 29 samples from Sites 494, 498, 499, 500, and 495 on the Deep Sea Drilling Project Leg 67 Middle America Trench transect; these sites represent lower slope, trench, and oceanic crust environments off Guatemala. All samples are Quaternary except those from Hole 494A (Pliocene) and Hole 498A (Miocene). Heavy-mineral assemblages of the Quaternary sediments are characterized by an immature pyroxene-amphibole suite with small quantities of olivine and epidote. The Miocene sediments yielded an assemblage dominated by epidote and pyroxene but lacking olivine; the absence of olivine is attributed to selective removal of the most unstable components by intrastratal solution. Light-mineral assemblages of all samples are predominantly characterized by volcanic glass and plagioclase feldspar. The feldspar compositions are compatible with andesitic source rocks and frequently exhibit oscillatory zoning. The heavy- and light-mineral associations of these sediments suggest a proximal volcanic source, most probably the Neogene highland volcanic province of Guatemala. Sand-sized components from Site 495 are mainly biogenic skeletons and volcanic glass and, in one instance (Section 495-5-3), euhedral crystals of gypsum.

Description: Mineralogical and oxygen isotopic analyses of samples from Deep Sea Drilling Project Sites 477, 481, and 477 in the Guaymas Basin indicate the existence of two distinct hydrothermal systems. In the first, at Sites 481 and 478, hot dolerite sills intruded into highly porous hemipelagic siliceous mudstones that were moderately rich in organic matter, thermally altered the adjacent sediments, and expelled hydrothermal pore fluids. The second, at Site 477 and active at present, is most probably caused by a recent igneous intrusion forming a magma chamber at shallow depth. In the first hydrothermal system, the main thermal reactions above and below the sills are dissolution of opal-A and formation of quartz, either directly or through opal-CT; formation of smectite; formation of analcime only above the sills; dissolution and recrystallization of calcite and occasional formation of dolomite or protodolomite. The d18O values of the hydrothermally altered sediments range from 9.9 to 12.2 per mil (SMOW). The d18O values of recrystallized calcites above the first sill complex, Site 481, indicate temperatures of 140° to 170°C. No fluid recharge is required in this system. The thickness of the sill complexes and the sequence and depth of intrusion into the sediment column determine the thickness of the alteration zones, which ranges from 2 or 3 to approximately 50 meters. Generally, the hydrothermally altered zone is thicker above than below the sill. In the second type, the sediments are extensively recrystallized. The characteristic greenschist-facies mineral assemblage of quartz-albite-chlorite-epidote predominates. Considerable amounts of pyrite, pyrrhotite, and sphene are also present. The lowest d18O value of the greenschist facies rocks is 6.6 per mil, and the highest d18O value of the associated pore fluids is +1.38 per mil (SMOW). The paragenesis and the oxygen isotopes of individual phases indicate alteration temperatures of 300 ± 50°C. On the basis of the oxygen isotopes of the solids and associated fluids, it is concluded that recharge of fluids is required. The water/rock ratio in wt.% is moderate, approximately 2/1 to 3/1 - higher than the calculated water/rock ratio of the hydrothermal system at the East Pacific Rise, 21 °N.

Description: Nontronite, the main metalliferous phase of the Galapagos mounds, occurs at a subsurface depth of ~2–20 m; Mn-oxide material is limited to the upper 2 m of these mounds. The nontronite forms intervals of up to a few metres thickness, consisting essentially of 100% nontronite granules, which alternate with intervals of normal pelagic sediment. The metalliferous phases represent essentially authigenic precipitates, apparently formed in the presence of upwelling basement-derived hydrothermal solutions which dissolved pre-existent pelagic sediment. Electron microprobe analyses of nontronite granules from different core samples indicate that: (1) there is little difference in major-element composition between nontronitic material from varying locations within the mounds; and (2) adjacent granules from a given sample have very similar compositions and are internally homogeneous. This indicates that the granules are composed of a single mineral of essentially constant composition, consistent with relatively uniform conditions of solution Eh and composition during nontronite formation. The Pb-isotopic composition of the nontronite and Mn-oxide sediments indicates that they were formed from solutions which contained variable proportions of basaltic Pb, introduced into pore waters by basement-derived solutions, and of normal-seawater Pb. However, the Sr-isotopic composition of these sediments is essentially indistinguishable from the value for modern seawater. On the basis of 18O/16O ratios, formation temperatures of ~20–30°C have been estimated for the nontronites. By comparison, temperatures of up to 11.5°C at 9 m depth have been directly measured within the mounds and heat flow data suggest present basement-sediment interface temperatures of 15–25°C.

Description: Constants of calcium, magnesium, zinc, cobalt, copper, and nickel exchange for sodium in iron-manganese nodules taken from different parts of the Pacific Ocean were determined under static conditions at constant ionic strength (?=0.05). These determinations revealed high capacity of nodules for sorbing the referred ions (their exchange constants range from 1.93 to 20.85). Obtained data demonstrate the major role of MnO and Fe2O3 in sorption processes in iron-manganese nodules.

Description: The usefulness of cosmogenic beryllium-10 (half life = 2.5 Ma) for studying the rates of accumulation of ferromanganese nodules is reported based on its measured depth distribution in the top 20 mm of these deposits. Accumulation rates have been obtained in the range of 1 to 4 mm/Ma, which are in good agreement with rates determined using the 230Th method on the same nodules. The use of 10Be offers promise in extending the dating to the outer few cm of the nodules. This contrasts with conventional methods using 230Th and 231Pa isotopes which, due to their comparatively short half lives, are limited to a few mm at the surface of the nodules. Detailed studies of 10Be in the manganese deposits coupled with other trace element analyses should prove valuable in understanding the processes of formation of these deposits and the chronology of events recorded by them.

Description: Nodules occur in the siliceous calcareous ooze and siliceous marl at Site 503 in the eastern equatorial Pacific. They are present below a depth of about 11 meters throughout the green-colored reduced part of the section down to 228 meters, although they are most abundant between 30 and 85 meters. They are cylindrical or barrel-shaped, up to 70 mm long, and usually have an axial channel through them or are hollow. They appear to have formed around and/or within burrows. XRD studies and microprobe analyses show that they are homogeneous and consist of calcian rhododrosite and minor calcite; Mn is present to the extent of about 30%. Isotopic analyses of the carbonate give carbon values which range from -1.2 per mil to -3.8 per mil, and oxygen isotope compositions vary from +4.0 per mil to +6.0 per mil. These values are different from those for marine-derived carbonates as exemplified by the soft sediment filling of a burrow: d13C, -0.26 per mil; d18O, +1.05 per mil. The carbon isotope data indicate that carbonate derived (possibly indirectly) from seawater was mixed with some produced by organic diagenesis to form the nodules. The d18O values suggest that although they formed near the sediment surface, some modification or the introduction of additional diagenetic carbonate occurred during burial.

Description: Deep sea manganese nodules from the Central Pacific Basin are mainly composed of 10Å manganite and d-MnO2 Two zones equivalent to the minerals are evidently distinguishable according to their optical properties. Microscopic and microprobe analyses revealed quite different chemical compositions and textnral characteristics of the two zones. These different feature of the two zones of nodules suggest the different conditions under which they were formed. Concentrations of 11 metal elements in the zones and inter-element relationships show that the 10Å manganite zone is a monomineralic oxide phase containing a large amount of manganese and minor amounts of useful metals, and that the d-MnO2 zone which is apparently homogeneous under the microscope is a mixture of three or more different minerals. The chemical characteristics of the two zones can explain the variation of bulk composition of deep sea manganese nodules and inter-element relationships previously reported, suggesting that the bulk compositions are attributable to the mixing of the 10Å manganite and d-MnO2 zones in various ratios. Characteristic morphology and surface structure of some types of nodules and their relationships to chemistry are also attribut able to the textural and chemical features of the above mentioned two phases. Synthesis of hydrated manganese oxides was carried out in terms of the formation of manganese minerals in the ocean. The primary product which is an equivalent to d-MnO2 was precipitated from Mn 2+ -bearing alkaline solution under oxigenated condition by air bubbling at one atmospheric pressure and room temperature. The primary product was converted to a l0Å manganite equivalent by contact with Ni 2+, Cu 2++ or CO2+ chloride solutions. This reaction caused the decrease of Ni2+, Cu2+ or CO2+ concentrations and the increase of Na+ concentration in the solution. The reaction also proceeded even in diluted solutions of nickel chloride and resulted in a complete removal of Ni2+ from the solution. Reaction products were exclusively 10Å manganite equivalents and their chemical compositions were very similar to those of 10Å manganite in manganese nodules. The maximum value of(Cu+Ni+Co)/Mn ratio of 10Å manganite zones in manganese nodules is 0.16, and the Ni/Mn ratio of synthetic 10Å manganite ranges from 0.15 to 0.18 with the average of 0.167.

Description: In 1970 a large deposit of ferromanganese nodules was discovered on the floor of the Indian Ocean southwest of Cape Leeuwin by the research vessel USNS Eltanin. This discovery, which was based largely on bottom photographs from about 20 stations, was discussed by Frakes (1975) and Kennett and Watkins (1975, 1976). The photographs suggest that the deposit spreads, nearly continuously, over 900 000km^2, and cores showed that the nodules are essentially confined to the sediment surface. Kennett and Watkins (op. cit.) pointed to the abundance of ripple and scour marks and current-formed lineations on the present surface, and of extensive disconformities in the cores, as evidence of strong present and past bottom currents in the region. They suggested that the current action had resulted in very low sedimentation rates, which had allowed the nodule field, named by them (1976) the 'Southeast Indian Ocean Manganese Pavement', to develop. In early 1976 the authors used the research vessel HMAS Diamantina for a 10-day cruise in the region to sample the nodules in order to study their chemistry and mineralogy. During the cruise 9 stations were occupied, 8 of them successfully (Figure 1), and about 2000 nodules were recovered from the sea bed. The apparatus used was a light box dredge on the ships hydrowire, which had a breaking strain of about one tonne. Although an attempt was made to reoccupy Eltanin photographic stations, it should be noted that positioning was by celestial navigation, so errors of up to 10 km are possible.

Description: The major and minor element compositions of a suite of abyssal sea-floor ferromanganese nodules and associated sediments from the eastern central Pacific have been used to examine inter-element relationships and the mineralogy of the nodules, the relationship between the composition of nodules, and their associated sediments and regional variations in composition with respect to likely modes for formation of such deposits. Apart from Mn and Fe, significant proportions of the total Ti, Ca, Mg, K, Ba, Sr, Th and Y and almost all the P, As, Ce, Co, Cu, Mo, Ni, Pb, Zn and Zr are present in the oxide fractions of the nodules. The Mg, Ba, Cu, Mo, Ni and Zn contents are significantly correlated with the total Fe content. Nodules from the northeastern tropical Pacific have Mn/Fe ratios highter than those in the oxide fractions of their associated sediments, todorokite as the principal Mn phase and relatively high concns of minor elements associated with Mn. Nodules from the south central Pacific have Mn/Fe ratios similar to those in the oxide fractions of the associated sediments, {delta}-MnO Sub(2) as the only Mn-phase, and relatively high concns of minor elements associated with Fe. There appears to be a smooth gradation in composition in the tropical Pacific between these 2 end members. The retional compositional variation is interpreted as a reflection of different sources of metals for, and different growth mechanisms of, sea-floor nodules. The oxide precipitate from sea water consists of {delta}-MnO Sub(2), has a relatively low Mn/Fe ratio and minor element contents related to the total Fe and Mn({delta}-MnO Sub(2)) content. The oxide precipitate forming in areas of very low sedimentation as a result of diagenetic remobilisation in the surface sediment consists of todorokite, and has a high Mn/Fe ratio and enhanced metal content in the Mn-(todorokite) phase. Available information on the morphology and compositional variation of individual nodules from the tropical Pacific corroborates these contrasting metal sources and suggests that they can be resolved on the scale of an individual oxide concretion.

Description: Considerable regional variations in the chemical composition of manganese nodules from a wide range of the Pacific Ocean have been observed. These variations can be more exactly expressed in terms of inter-element relationships. In particular, Cu-Mn and Cu-Ni associations reveal that Cu content in pelagic nodules increases rapidly in proportion to those of Mn or Ni. In nodules from continental borderland and hemipelagic areas, even if Mn or Ni contents increase, that of Cu increases only slightly. It is suggested that the considerable chemical differences within individual nodules and between nodules from the same site, at a limited pelagic area where there is no marked change in depositional conditions of nodules, are due to the role of hydrolyzable trace elements in the formation of nodules.

Description: Twenty-four manganese nodules from the surface of the sea floor and fifteen buried nodules were studied. With three exceptions, the nodules were collected from the area covered by Valdivia Cruise VA 04 some 1200 nautical miles southeast of Hawaii. Age determinations were made using the ionium method. In order to get a true reproduction of the activity distribution in the nodules, they were cut in half and placed for one month on nuclear emulsion plates to determine the alpha-activity of the ionium and its daughter products. Special methods of counting the alpha-tracks resolution to depth intervals of 0.125 mm. For the first time it was possible to resolve zones of rapid growth (impulse growth) with growth rates, s 〉 50 mm/106 yr and interruptions in growth. With few exceptions the average rate of growth of all nodules was surprisingly uniform at 4-9 mm/10 yr. No growth could be recognized radioactively in the buried nodules. One exceptional nodule has had recent impulse growth and, in the material formed, the ionium is not yet in equilibrium with its daughter products. Individual layers in one nodule from the Indian Ocean could be dated and an average time interval of t = 2600±400 yr was necessary to form one layer. The alternation between iron and manganese-rich parts of the nodules was made visible by colour differences resulting from special treatment of cut surfaces with HCl vapour. The zones of slow growth of one nodule are relatively enriched in iron. Earlier attempts to find paleomagnetic reversals in manganese nodules have been continued. Despite considerable improvement in areal resolution, reversals were not detected in the nodules studied. Comparisons of the surface structure, microstructure in section and the radiometric dating show that there are erosion surfaces and growth surfaces on the outer surfaces of the manganese nodules. The formation of cracks in the nodules was studied in particular. The model of age-dependent nodule shrinkage and cracking surprisingly indicates that the nodules break after exceeding a certain age and/or size. Consequently, the breaking apart of manganese nodules is a continuous process not of catastrophic or discontinuous origin. The microstructure of the nodules exhibits differences in the mechanism of accretion and accretion rate of material, shortly referred to as accretion form. Thus non-directional growth inside the nodules as well as a directional growth may be observed. Those nodules with large accretion forms have grown faster than smaller ones. Consequently, parallel layers indicate slow growth. The upper surfaces of the nodules, protruding into the bottom water appear to be more prone to growth disturbances than the lower surfaces, immersed in the sediment. Features of some nodules show, that as they develop, they neither turned nor rolled. Yet unknown is the mechanism that keeps the nodules at the surface during continuous sedimentation. All in all, the nodules remain the objects of their own distinctive problems. The hope of using them as a kind of history book still seems to be very remote.

Description: Bulk composition of ferromanganese nodules from the pelagic environment of the Pacific Ocean is apparently related to nodule-growth rate, sediment-accumulation rate, and biologic productivity in the overlying seawater. Nodules with a high Mn/Fe ratio and high Ni and Cu concns tend to occur in areas where primary productivity in the surface layer of the ocean is high and the sediment accumulation rate low. They may have a Mn/Fe ratio as low as one and accrete at rates as low as 1 mm/10 M yrs. Nodules with a larger Mn/Fe ratio apparently have growth rates that are greater by as much as a factor of 10.

Description: The cores and dredges described in this report were taken on Cruise 128 of the R.R.S. "Discovery" in May 1982 by the National Institute of Oceanography, Wormley, United Kingdom. A total of 12 cores were recovered and are available through the British Oceanographic Data Centre for sampling and study.

Description: This chapter discusses the formation and distribution of some metals in ocean-floor manganese nodules in the light of the observed data in the literature and thermodynamic and kinetic considerations of the oxidation of metal ions in the oceanic environment. There are, in general, two major schools of thought on the mechanism of incorporation of the minor elements such as nickel, copper, and cobalt with the major elements such as manganese and iron. One is the lattice substitution mechanism and the other the adsorption mechanism. If the mechanism is lattice substitution, extraction of the metal ions is not possible unless the lattice of the major elements is first broken and exchanged with other ions from the bulk solution. Consequently, the leaching behavior of minor elements should display a very close relationship with that of major elements.

Description: A complete processing method has been experimentally developed at laboratory scale for the future extraction of metlas from manganese nodules. The digestion of the nodules is performed by pressured sulfuric acid leaching at 200° C., nickel, copper, cobalt, and zinc being selectively dissolved in solution along with iron and manganese. The subsequent separation and recovery of the valuable metals is carried out with a combination of ion exchange and precipitation processes. Estimates for this methodology based on an annual throughput of 2 million tonnes of manganese nodules should lead to the production of about 24000 tonnes of nickel, 20000 tonnes of copper, and 3000 tonnes of cobalt and zinc. The authors conclude that, despite all uncertainty regarding the metal processing costs and the future metal prices, the exploitation of manganese nodules is economically viable.

Description: In the summer of 1974, upon returning to Woods Hole from the Azores, the submersible Alvin had the opportunity to make brief dives on Corner Rise and the New England seamount chain. This was the first time man had directly viewed the expanse of the Earth between the Mid-Atlantic Ridge and the North of the American continent. Single dives were made on seven seamounts: Corner Rise and Nashville, Gilliss, Rehoboth, Manning, Balanus, and Mytilus.

Description: This DSDP leg was originally conceived by the Antarctic Advisory Panel in order to investigate the geologic histories of the Scotia Arc and of the Argentine Basin. Site 326 (Drake Passage) was drilled in 3812 meters of water about 150 km southeast of Cape Horn. The main objective was to check the magnetic-reversal dating of the opening of Drake Passage by determining basement age. Site 327 is in 2400 meters of water on the western nose of the elevated eastern part of the Falkland Plateau, the Maurice Ewing Bank and was chosen to examine Southern Ocean shallow-water pre-Neogene biostratigraphy. Site 328, in 5103 meters of water in the Malvinas Outer Basin immediately to the east of the Falkland Plateau and to the south of the Falkland Fracture Zone, was chosen to examine correlatives of Argentine Basin acoustic reflectors, to obtain a deep-water southerly biostratigraphic section, and if possible, to date the underlying oceanic basement. Site 330, in 2626 meters of water at the western end of the elongate rise forming the eastern end of the Falkland Plateau, the Maurice Ewing Bank, was selected to elucidate the pre-Aptian history of the Falkland Plateau and to obtain a biostratigraphic section older than that cored at Sites 327 and 329.

Description: Deep-sea echinoderms of the Tongue of the Ocean, Bahama Islands, have been studied, using trawled collections made by the University of Miami together with observations from the deep submersible Alvin. Transect runs in the submersible permitted studies of population densities and behaviour of approximately 38 species of larger invertebrates, of which 27 were echinoderms. Several echinoderm species show a patchy distribution pattern which is apparently not related to available food resources. Some species are exclusively herbivores, feeding on fragments of turtle grass, Thalassia testudinata and sargassum weed, Sargassum spp. Feeding habits of some Tongue of the Ocean echinoderms are compared with those of the same species from further north, where supplies of plant material are not nearly so abundant.

Description: Unlike most previous Deep Sea Drilling Project cruises, Leg 39 was not scientifically planned as a "theme" cruise, on which a number of sites are drilled to address a single scientific problem area, namely, to improve our knowledge of paleocirculation changes and the overall geologic history of the South Atlantic Ocean. This would be done along more specific objectives: 1) collect a biostratigraphic section on the Ceará Rise (Site 354), determine the nature and age of a prominent reflector there, and determine the nature and age of basement; 2) date basement between magnetic anomalies 32 and 33 in the Argentine Basin (Site 358), and 33 and 34 in the Brazil Basin (Site 355); obtain as complete sedimentary sections as time would permit at the Ceará Rise, Brazil Basin, the Argentine Basin and Sào Paulo Plateau (Site 356).

Description: From a structural and morphological point of view, the continental margin of southwestern Africa is a middle-aged "pull-apart" or "passive-type" margin which was initially created during the breakup of the supercontinent of Gondwanaland in the Mesozoic. The most important objective of the Leg 40 expedition was the attainment of strata laid down when the newly formed ocean was very young and only a few hundred kilometers wide. Site 361 was drilled at the fall of continental platform into the Cape Basin, to a sub-sea floor depth of 1314 meters and yielded sediments that range in age from upper Eocene to lower Aptian and possibly slightly older.

Description: he forty-first cruise of Glomar Challenger was devoted to the study of the evolution of the eastern basins of the North Atlantic, off the continental margin of West Africa. As the available data a the time was showing that most litho-stratigraphic units in the deep basins of the Atlantic had enough lateral extension, the drilling of a limited number of sites in key areas would allow for large-scale regional interpretation. One of the sites was loacted in the Cape Verde deep Basin (Site 367) while others were located in shallower waters such as, the Sierra Leone Rise (Site 366), the Cape Verde Rise (Site 368) or the Continental Slope off Spanish Sahara (Site 369).

Description: On cruises 10 and 15 of Academic Kurchatov (1971, 1973) at the Jan-Mayen Ridge, a large number of samples was obtained. Most of them contained sedimentary rocks. From their study, it is safe to assume that the rocks of the Jan-Mayen Ridge were, at first, subjected to subsidence to a considerable depth, and then uplifted to their contemporary position, by the ascending tectonic movements. Thus, the Jan-Mayen Ridge is in contrast to other Atlantic submarine ridges, not only in the sedimentary rock composition, but in the character of the tectonic movements.

Description: Leg 42, Part 1 of the Deep Sea Drilling Project was scheduled to continue the geological exploration of the Mediterranean. The strategy was to search for areas where the Mediterranean Evaporite formation had been largely or completely removed by erosion, such is the case for Site 372. For Leg 42, Part 2, the project entered the Black Sea. In particular, Site 379 was located the central portion of the Black Sea.

Description: The western part of the North Atlantic Ocean holds clues to some of the most intriguing questions in marine geology. But because the geologic problems are many and varied, the sites of Leg 44 were multipurpose in nature. In particular, some of the targets were : 1) the Blake Nose, a spur of the Blake Plateau, to determine the nature, age, and origin of reef-like structures recognized on seismic profiles and 2) the Blake Outer Ridge, a long low ridge of sediments that forms the eastern boundary of the Blake-Bahama Basin, where we hoped to study the stratigraphy and sample supposed clathrates.

Description: Scientists from the Woods Hole Oceanographic Institution, the U.S. Navy, the State University of New York at Albany, Wesleyan University, Nine dives in the research submersible ?Alvin? were made into Great Abaco Submarine Canyon to depths ranging from 1850 to 3666 m. Our observations indicate that the walls of this canyon are distinctly terraced, consisting of nearly vertical to overhanging rock cliffs and intervening, less steep sediment-covered slopes. The wall rock consists mostly of massive, shallow-water limestones and dolostones of Cretaceous age, coated on exposed surfaces with manganese oxides. These rocks are heavily jointed/fractured and thus very blocky to angular in appearance, with sponges and other sessile organisms commonly attached. Talus slopes and sedimentary breccia deposits containing angular boulders are present at the base of these steep escarpments. Short-term bottom current measurements in the axis of the eastern part of the canyon indicate that currents are relatively weak, reaching velocities of only 10 cm/sec. This relatively placid setting is further corroborated by the abundance of turtle grass (Thalassia) found along the canyon axis. However, abundant subdued, symmetrical ripple marks and large scour depressions at the base of boulders, indicate that high-energy events sporadically impact the canyon axis. Contemporary erosional activity along the axis of the western (headward) part of the canyon appears to be more significant, as evidenced by asymmetrical ripple marks, sand waves and bioerosion. Great Abaco Canyon has evolved with time via a variety of processes, including: (1) faulting: (2) subsidence; (3) defacement; and (4) erosional down-cutting. The location, orientation and initiation of this canyon appear to be structurally controlled by the Great Abaco Fracture Zone during pre-Santonian time. Regional subsidence during the Mesozoic allowed the walls of Great Abaco Canyon to build vertically by accretion of shallow-water limestones, whereas joint-controlled defacement has widened the canyon while maintaining steep walls. Erosional down-cutting in the canyon axis by carbonate sediment gravity flows also appears to have been important episodically, particularly during the Miocene and Pleistocene.

Description: Two consecutive drilling legs (Legs 59 and 60) were assigned to drill an east-west transect of sites along latitude 18°N, from the Mariana Basin of the Pacific Ocean to the oldest inactive island arcs and back-arc spreading basins of the Philippine Sea. The western (older, inactive) half of this transect (Philippine Sea, Palau-Kyushu Ridge, Parece Vela Basin, and the West Mariana Ridge-Sites 447-451) was drilled during Leg 59. The objective of Leg 60 was to sample the tectonically active eastern portion of the transect in a closely spaced series of holes across the presently opening back-arc basin (Mariana Trough, Site Survey Target SP-4: Sites 453-456), the Mariana arc itself (Site Survey Target SP-3b: Site 457), the Mariana fore-arc region (Site Survey Target SP-3, Sites 458 and 459), and deep within the Mariana Trench (Site Survey Target SP-2: Sites 460 and 461). In addition, one site (Site Survey Target SP-1: Site 452) was drilled on the Pacific plate seaward of the trench to obtain a reference section of sediments and oceanic crust being delivered to the trench.

Description: The origin and evolution of passive continental margins are of great scientific interest and economic importance. During DSDP Leg 64 the Glomar Challenger drilled at eight sites (474-481) in the Gulf of California region. The Gulf of California presented a singular example of tectonics and sedimentation in a very young ocean, being formed by translation and oblique rifting. The sedimentation of the region is hemipelagic, rapid, and largely dominated by siliceous microfossils.Sites 474, 475, and 476 form a transect from oceanic crust to continental crust at the southern tip of Baja California in order to define passive-margin subsidence during the early post-rifting phase. Sites 477, 478, and 481 investigate of the nature of young ocean crust in the Guaymas Basin, where high accumulation rates are common and variable high heat flow indicates active rifting and hydrothermal activity. Sites 479 and 480, are situated on the Guaymas Basin Slope above the proto-Gulf sequences. Interest focused on the paleoceanography of laminated, homogeneous diatom-rich, anoxic sediments within the zone of low oxygen.

Description: Leg 66 was part of two broader investigations of subduction complexes and convergent margin geology, one led by the Active Margin Panel (AMP) of the International Phase of Ocean Drilling (IPOD) to drill selected convergent margins to elucidate structure and evolution and the other, led by the University of Texas Marine Science Instituted (UTMSI) Galveston Geophysical Laboratory (GGL) to investigate the tectonics of the Middle America Trench from the Cocos Fracture Zone to the Riviera Fracture Zone. In this context, the specific objective at Site 487 was the coring of pelagic and hemipelagic sediment section and underlying oceanic basement. It is the farthest offshore site off the Cocos Fracture Zone.

Description: The Oaxaca transect, located off southern Mexico and drilled during Leg 66, sampled a truncated margin and subduction complex. In contrast, the Guatemala transect was selected because accretion was thought to have continued in this area during most of the Tertiary. Site surveys conducted by the University of Texas Marine Science Institute provided multichannel seismic records, among which profile GUA-13 was chosen as the location for Leg 67 drill holes. Selection of this transect arises in part from the fact that it includes a portion of the San José Canyon, thus layers of hemipelagic drape may have been stripped away by erosion, allowing quicker access to deep horizons. By studying the continental margin off Guatemala it was hoped to strengthen the tie between offshore and onshore geology, to describe the stratigraphic sequence from the continental slope to the subducting oceanic plate beneath, to recover in ash layers a record of Central American volcanism.

Description: The general objectives of this cruise were to use the newly developed HPC to recover two undisturbed, continuous records of the late Neogene and Quaternary, one from the western Caribbean and the other from the eastern equatorial Pacific, and to test the coring capabilities of the HPC. At site 502 in the Caribbean an hemipelagic facies with accumulation rates of about 3 cm/k.y near site 154 were a coarse-grained volcanogenic turbidite sequence had been recovered at a depth equivalent to a strong seismic reflector. Site 503 was located as close as possible to previously rotary-drilled Site 83 in the eastern equatorial Pacific.

Description: The recovery of hydrothermal sediments at depth beneath the mounds of hydrothermal origin during a brief period of drilling on Deep Sea Drilling Project (DSDP) Leg 54 provided some evidence suggesting that hydrothermal material may be pervasive over a relatively large region inclusive of the mounds but also incorporating adjacent seafloor presently covered by pelagic sediments. As a result of the incomplete recovery of sediments at some sites and the poor recovery of basement rocks during Leg 54, it was suggested that a more carefully planned program be designed to drill a broader range of sites in the Galapagos mounds field. The major objectives of the first part of Leg 70 were to collect data and sediment representative of the hydrothermal mounds and ridges located about 20 km south of the Galapagos spreading axis.

Description: Fragments of a hydrothermal deposit, partly moulded on pieces of basalt lava, were dredged from the edge of the median valley in the centre of the Gulf of Aden. The deposit consists of two main components, manganese oxide in the form of spongy brown to hard black lumps and coatings, and friable green massive smectite. There are smaller amounts of an iron-oxide component, and mixed manganese-oxide-smectite material. Contents of the less mobile trace elements in the smectite are too low for it to have formed by alteration of basalt glass, and it is interpreted as a direct precipitate from hydrothermal solution. None of the components is enriched in Cu or Zn, or contains appreciable amounts of sulphur. If there are sulphides in this deposit, they must lie beneath the parts sampled.

Description: he three-site Leg 64 Deep Sea Drilling transect at the tip of the Peninsula of Baja California straddled the transition from continental to oceanic crust. The outer site, 474, penetrated mainly mud turbidites and bottomed in "middle" Pliocene oceanic crust about 3 m.y. old. Two sites on the lower continental slope penetrated hemipelagic muddy sediments, a thin section of low-oxygen, phosphoritic, and glauconitic sediments, and a metamorphic cobble conglomerate; one of the sites, 476, bottomed in deeply weathered granite. The oldest marine sediments at this site are early Pliocene, about 4.5 m.y. old. Depth indicators in these holes suggest that all sites were in almost 1000 meters of water by the time oceanic crust was first generated and sea-floor spreading began. Block faulting, subsidence, and deposition of marine sediments on continental crust had preceded the start of sea-floor spreading. Close examination of lineated magnetic anomalies demonstrates that the transition from continental to oceanic crust in this region is diachronous, as early as 4.9 m.y. in some places, but as young as 3.2 m.y. along the line of the transect. We propose a geological history scenario which involves termination of subduction along the western margin of Baja California at 12.5 Ma, a period of transform motion between the Pacific and North American plates along the Tosco Abreojos Transform Fault zone along the west side of Baja California, and a jump of the Pacific-North American plate edge to the alignment of the Gulf at 5.5 Ma. Between 5.5 Ma and about 3.2 Ma, separation of the blocks occurred locally by sea-floor spreading, but elsewhere by "diffuse extension", largely involving listric normal faulting and thinning of the continental crust, accompanied by subsidence and marine inundation. Thus, the plate edge system in the mouth and southern part of the Gulf evolved as early as 5.5 Ma, but the transition from rifting to drifting was diachronous, starting only 3.2 Ma along the line of the transect.

Description: A detailed geophysical and geological survey of the Mariana Trough, an actively extensional back-arc basin, was conducted in 1976 and 1977 to provide data for selection of drilling sites for DSDP Leg 60. These surveys revealed large-scale bathymetric trends, sediment distribution, crustal seismic veolocity structure, and earthquake activity that suggest the basin is opening around an axial spreading center tectonically similar to the slowly spreading Mid-Atlantic Ridge. There are, however, significant differences in the character of the trough, such as poorly defined magnetic anomalies, extreme bathymetric relief, and the frequent occurrence of low-magnitude earthquakes but absence of larger seismic events. Seafloor spreading in the Mariana Trough may be characteristic of the initial opening stages of any oceanic rift system, whether or not it is in a back-arc setting.

Description: Submarine photography and box cores described in this report were taken during the R/V Oceanographer Cruise RP-8-OC-76 in October 1976 over area C of the DOMES project (Deep Ocean Mining Environmental Study). This cruise was part of Phase I of the DOMES project which was conducted by the U.S. Geological Survey under the auspices of the National Oceanic and Atmospheric Administration (NOAA). The purpose of DOMES project was to acquire the information necessary to provide both a timely and an independent assessment of the impact of deep ocean manganese nodule mining on the marine ecosystem before commercial mining operations begin. It was formulated in cooperation with the academic community and the mining industry. It consisted of a two-phase study, first to obtain basic information on the deep ocean environment and then to assess the impact of prototype mining operations on that environment.

Description: Three ferromanganese nodules handpicked from the tops of 2500 cm**2 area box cores taken from the north equatorial Pacific have been analysed for their U-Th series nuclides. 230Thexc concentrations in the surface 1-2 mm of the top side of the nodules indicate growth rates of 1.8-4.6 mm/10**6 yr. In two of the nodules a significant discontinuity in the 230Th exc depth profile has been observed at ~0.3 m.y. ago, suggesting that the nodule growth has been episodic. The concentration profiles of 231Pa exc (measured via 227Th) yield growth rates similar to the 230Th exc data. The bottom sides of the nodules display exponential decrease of 230Th exc/232Th activity ratio with depth, yielding growth rates of 1.5-3.3 mm/10**6 yr. The 230Th exc and 231Pa exc concentrations in the outermost layer of the bottom face are significantly lower than in the outermost layer of the top face. Comparison of the extrapolated 230Thexc/232Th and 230Th exc/231Pa exc activity ratios for the top and bottom surfaces yields an "age" of (5-15) x 10**4 yr for the bottom relative to the top. This "age" most probably represents the time elapsed since the nodules have attained the present orientation. The 210Pb concentration in the surface ~0.1 mm of the top side is in large excess over its parent 226Ra. Elsewhere in the nodule, up to ~1 mm depth in both top and bottom sides, 210Pb is deficient relative to 226Ra, probably due to 222Rn loss. The absence of 210Pbexc below the outermost layer of the top face rules out the possibility of a sampling artifact as the cause of the observed exponentially decreasing 230Thexc and 231Paexc concentration profiles. The flux of 210Pbexc to the nodules ranges between 0.31 and 0.58 dpm/cm**2/yr. The exhalation rate of 222Rn, estimated from the 226Ra-210Pb disequilibrium is ~570 dpm/cm**2/yr from the top side and 〉2000 dpm/cm**2/yr from the bottom side. 226Ra is deficient in the top side relative to 230Th up to ~0.5-1 mm and is in large excess throughout the bottom. The data indicate a net gain of 226Ra into the nodule, corresponding to a flux of (24-46) x 10**-3 dpm/cm**2/yr. On a total area basis the gain of 226Ra into the nodules is 〈20% of the 226Ra escaping from the sediments. A similar gain of 228Ra into the bottom side of the nodules is reflected by the high 228Th/232Th activity ratios observed in the outermost layer in contact with sediments.

Description: Quaternary sediments cored in the northeast Pacific nodule area (DOMES site C, 14°N, 126°W) contain a significant amount of hydrothermal metalliferous mud. Water content, color, mineralogy, and chemical composition are analogous to metalliferous sediments of the subequatorial East Pacific Rise. Correction for contribution of pelagic clay indicates the metalliferous fraction to be about 40% of the sediment. SiO2 and Mg are major components in the corrected composition, as they are for other metalliferous sediments similarly corrected from a variety of East Pacific Rise and DSDP metalliferous sediments. A correlation between Mg and SiO2 for these corrected sediments could indicate a hydrothermal origin for a significant portion of the SiO2. Results from DSDP in the nodule area suggest that metalliferous globules are a ubiquitous minor component of the Clipperton Oceanic Formation, which underlies much of the Pacific ferromanganese nodule belt. This indicates that deposition of hydrothermal precipitates is not confined to spreading centers.

Description: The bulk chemical compositions of ferromanganese nodules recovered from 14 of 38 sediment cores collected from a 230 km2 area of abyssal hill topography in the northern equatorial Pacific (8° 20'N, 153° 0'W; regional depth 5000 m) vary nonrandomly between fairly wide limits. The nodules have Mn/Fe ratios ranging from 2.60 to 5.38 and all samples contain todorokite and delta-MnO2 . The variation in the Mn/Fe ratio is governed by the total Fe contents of the nodules; Mn varies to a much smaller extent. Cu and Ni contents average about 1% and vary independently of the Mn contents. The compositional variation in the nodules is related to two features of the associated sediments, which are siliceous pelagic clays. The total Fe contents correlate positively with the oxalate-soluble Fe contents of the surface (0-2 cm) sediments; and their Mn/Fe ratios correlate negatively with the accumulation rates of the sediments. It is suspected that the composition of the nodules is influenced to a considerable extent by diagenetic reactions in the sediments, the clearest manifestation of this being the transformation of oxyhydroxide Fe into an insoluble form, possibly by the formation of smectite. This in turn leads to the formation of relatively Fe-poor ferromanganese nodules. Such nodules occur on slowly accumulating sediments where relatively more diagenetic reaction in the sediments has taken place.

Description: Excess 230Th dominates the alpha activity of the surface regions of manganese nodules and deep sea sediments. If uranium series eguilibrium is maintained, total alpha activity depth profiles should be as useful in determining sedimentation rates as are 230Th measurements. We have used cellulose nitrate alpha track recorders pressed against manganese nodule slabs to record high resolution alpha activity "maps' of a large number of nodules. Total alpha activity profiles have also been obtained for several sediment cores. From the approximately 90 nodule profiles measured to date, 73 show simple, approximately exponential depth dependence; about 2/3 of these have inferred deposition rates of 4-10 mm/10power6 yr. Ten profiles show statistically significant breaks in slope, suggesting growth rate changes. Within single dredge hauls there is little variation in growth rates, although different portions of the same nodule sometimes exhibit different growth rates. There is no correlation between depth and measured growth rate, except for a general tendency for the few Atlantic Ocean nodules we have measured to have slightly lower rates than Pacific or Indian Ocean samples. For a number of nodules and sediments the alpha track results have been compared with 230Th-based deposition rates measured by other workers. Two nodules have 230Th rates (W. S. Broecker et al., pers. comm.) identical within errors to the alpha track determinations. A third nodule (S. Krishnaswami, pers. comm. ) and two sediment cores previously measured by Goldberg and Koide (E. Sci. and Meteoritics, 1963, p. 90} all have much slower rates based on 230Th measurements compared with the alpha track results.

Description: This report presents megascopic descriptions of deep-sea sediment cores obtained by personnel of the Hawaii Institute of Geophysics on cruises of the R/V Kana Keoki in the eastern Pacific Ocean during the year 1978.

Description: Fossil Mn nodules of Cretaceous age from western Timor exhibit chemical, structural and radioisotope compositions consistent with their being of deep-sea origin. These nodules show characteristics similar to nodules now found at depths of 3,500-5,000 m in the Pacific and Indian Oceans. Slight differences in the fine structure and chemistry of these nodules and modern deep-sea nodules are attributed to diagenetic alteration after uplift of enclosing sediments.

Description: The usually high concentrations of Zn, Pb, Cd, and Cu in the most recently accreted portions of ferromanganese nodules from the western Baltic Sea are thought to reflect increased metal input due to anthropogenic mobilization. If so, the point of increase represents a time horizon within the structure of the nodule. Similar trace metal distributions of radiometrically dated sediments from the same area suggest that the ferromanganese nodules have grown in thickness between 0.02 and 0.16 mm yr-1. From this growth rate anthropogenic Zn flux to the nodule surface was calculated to be 80 mg m-2 yr-1.

Description: Mineralogical (microprobe) and geochemical (X-ray fluorescence, neutron activation analyses) data are given for 18 samples of volcanic rocks from the Guatemala Trench area (Deep Sea Drilling Project Leg 67). Typical fresh oceanic tholeiites occur in the trench itself (Hole 500) and in its immediate vicinity on the Cocos Plate (Site 495). Several samples (often reworked) of "spilitic" oceanic tholeiites are also described from the Trench: their mineralogy (greenschist facies association - actinolite + plagioclase + chlorite) and geochemistry (alteration, sometimes linked to manganese and zinc mineralization) are shown to result from high-temperature (300°-475°C) hydrothermal sea water-basalt interactions. The samples studied are depleted in light rare-earth elements (LREE), with the exception of the slightly LREE-enriched basalts from Hole 500. The occurrence of such different oceanic tholeiites in the same area is problematic. Volcanic rocks from the Guatemala continental slope (Hole 494A) are described as greenschist facies metabasites (actinolite + epidote + chlorite + plagioclase + calcite + quartz), mineralogically different from the spilites exposed on the Costa Rica coastal range (Nicoya Peninsula). Their primary magmatic affinity is uncertain: clinopyroxene and plagioclase compositions, together with titanium and other hygromagmaphile element contents, support an "active margin" affinity. The LREE-depleted patterns encountered in the present case, however, are not frequently found in orogenic samples but are typical of many oceanic tholeiites.

Description: Manganese nodules are considered to have accumulated in general very slowly: surface layers of nodules contain a large excess of 230Th, more than would be produced by uranium decay. The decrease of excess 230Th with depth within a nodule is generally interpreted to be due to the radioactive decay, and nodule accumulation rates were then estimated from this to be a few mm/Myr. How then do these nodules escape from burial by associated marine sediments which accumulate 3 orders of magnitude faster than the nodules? One possible explanation is that the radionuclides of interest were not incorporated in the nodule matrix during its growth but were adsorbed later. Subsequent inward diffusion of the radionuclides might result in an apparent radioactive decay. We have tested this hypothesis by measuring simultaneously two radionuclides of different half lives. If the gradients of the radionuclides are really due to the radioactive decay, then, assuming a constant growth rate for a nodule, we expect the profile of the shortlived nuclide to be steeper (because of its faster decay) than that of the longlived nuclide.

Description: Manganese nodules from 36 stations in the Cape Leeuwin field were analyzed for Mn, Fe, Ni, Cu and Co and the results were combined with earlier work to demonstrate quantitative and geographic variations. Nodules in this field are moderately enriched in Ni, moderately depleted in Cu, and contain intermediate values of Co. The sum of Ni + Cu vs. Mn/Fe plots along a hyperbolic regression line derived from nodules of the southeastern Pacific, suggesting that this relationship has general applicability. Regional variations in nodule grade (Ni + Cu + Co) assist in defining pathways of Antarctic Bottom Water between the Southeast Indian Ridge and the Wharton basin.

Description: Information on possible resource value of sea floor manganese nodule deposits in the eastern north Pacific has been obtained by a study of records and collections of the 1972 Sea Scope Expedition.

Description: The purpose of the expedition was to test new techniques to determine thickness, distribution and quality of mineral deposits on the Blake Plateau with special reference to manganese nodules and manganese-phosphate pavements.

Description: Sample preparation technique is critical for valid chemical analyses. A main source of error comes from the fact that the great specific surface area of crusts or nodules enhances their tendency to retain or attract hygroscopic moisture. Variable treatment of this moisture can in extreme cases lead to analytical value differences as great as 40-50 %. In order to quantify these influences, samples of ferromanganese oxide-phosphorite pavement from the Blake Plateau have been subjected to various drying techniques before analysis using X-ray fluorescence.

Description: A preliminary report on the manganese nodule field southwest of Western Australia published in this Journal recently (Frakes, Exon and Granath, 1977) quoted chemical analyses which were carried out on air-dried material. Significantly higher metal values have been recorded in some later analyses done on nodules dried at 105°C. Tests have shown that the ground, air-dried material retains considerable moisture, which accounts for the higher metal values of the later analyses. The average water content (after drying at 105°C) has been determined at 16 percent. The relevant chemical data now available on this material are summarised in the accompanying table: in this table metal values (by atomic absorption spectrophotometry) have been recalculated assuming a moisture content of 16 percent.

Description: An initial investigation has been undertaken on the chemical composition of the manganese nodules. The results of chemical analyses on each layer of single nodules reveal the periodic patterns of distribution for Mn, Fe, Cu, Pb, Zn, Ni and Co contents. The variations strongly suggest that those of the elements in nodules from this region are, at least, climatically controlled.

Description: Ferromanganese deposits, mostly manganese crusts, are common in elevations along the northeastern Brazilian continental margin. Association of the deposits with more or less altered basaltic rock can be observed. On the Pernambuco Plateau and Ceara Guyot, ferromanganese deposits occur associated with phosphatic material and nodules. The mineralogical composition of the ferromanganese deposits indicates a predominance of the manganese oxide phase dMnO2. Low contents of Mn and Cu are characteristic of their chemical composition. Fe and Mn in the deposits probably precipitated from the sea water.

Description: The report is divided into three sections: morphology, mineralogy and elemental composition. The nodule morphology section defines what is considered a nodule for the study, and details the external characteristics and internal structure. Nodule mineralogy is discussed in three sections: manganese minerals, iron oxide minerals, and accessory minerals. The major manganese minerals discussed are todorokite, birnessite, and vernadite. The iron oxide minerals are less well known and include feroxyhyte, goethite, and lepidocrocite. Accessory minerals present include quartz, clays, and other silicates and nonsilicates. A discussion on moisture content is also included. The elemental composition section presents data on 74 elements occurring as cations or anions. Summary data, histograms, and interelement correlation coefficients are presented.

Description: It is the purpose of this chapter to present information available at the time of publication on the internal features of manganese nodules, to offer genetic interpretations of these features, and to suggest new lines of research. To judge from the limited data available on ocean floor crusts rich in manganese and iron (see, for example, Aumento et al., 1968, doi:10.1594/PANGAEA.862565 ), much of what is learnt about nodules may be applied eventually to an understanding of the origin of these more continuous masses. A genetic relationship between these two is likely.

Description: Two types of deep-sea dredges are currently under development for the mining of the manganese nodules, a deep-sea hydraulic dredge and a mechanical cable-bucket system. Both systems offer some advantages with the hydraulic system appearing to be advantageous in themining of a specific deposit for which it is designed while the cable-bucket system appears to be somewhat more flexible in working in a variety of deposits, topographic environments, and water depths. Environmental studies conducted in conjunction with deep-sea tests of the two types of mining systems currently indicate that substantially no environmental damage will be done in the mining of the deep-sea nodules. Because of the nature of the deposits and the way in which they can be mined, the manganese nodules appear to be a relatively pollution free and energy-saving source of a number of industrially important metals.

Description: Manganese nodules from the Suiko Seamount exhibit the significant characteristics in mineral compositions. Well crystallized todorokite and birnessite, which are principal manganese mineral phase in nodules, only occur in the oxide layer directly incasing pebbles and coarse sand. The preferential formation of todorokite or birnessite phases seem to be principally controlled by the reaction rate of iron-manganese oxides with trace elements such as Cu, Ni, Co, Zn, Pb concentrated in nodules, rather than redox characteristics of sedimentary environment or mineralogical diagenetic process.

Description: In 1972, the Sea Scope Expedition was commissioned by Hughes Tool Company and carried out by Global Marine Development, Inc. The object was to gather detailed information on manganese nodules, including distribution, metallic content, methods of recovery, and sea floor bathymetry in noduliferous areas. Five of six planned cruise legs were successful. The resulting report is divided into three sections.

Description: Basalt samples obtained from the Siqueiros transform fault/fracture zone and the adjacent East Pacific Rise are mostly very fresh oceanic tholeiite and fractionated oceanic tholeiite with Fe+3/ Fe+2 ? 0.25; however, alkali basalts occur in the area as well. The rocks of the tholeiitic suite are ol + pl phyric and ol + pl + cpx phyric basalts, while the alkali basalts are ol and ol + pl phyric. Microprobe analyses of the tholeiitic suite phenocrysts indicate that they are Fo68-Fo86, An58-An75, and augite (Ca34Mg50Fe16). The range of olivine and plagioclase compositions represents the chemical variation of the phenocryst compositions with fractionation. The phenocyrsts in the alkali basalts are Fo81 and An69. The suite of tholeiites comprises a fractionation series characterized by relative enrichment of Fe, Ti, Mn, V, Na, K, and P and depletion of Ca, Al, Mg, Ni, and Cr. The fractionated tholeiites occur on the median ridge (which is a sliver of normal oceanic crust) of the double Siqueiros transform fault, on the western Siqueiros fracture zone, and on the adjoining East Pacific Rise, while the two transform fault troughs contain mostly unfractionated or only slightly fractionated tholeiite. We suggest that the fractionated tholeiites are produced by fractional crystallization of more 'primitive' tholeiitic liquid in a crustal magma chamber below the crest of the East Pacific Rise. This magma chamber may be disrupted by the transform fault troughs, thus explaining the paucity of fractionated tholeiites in the troughs. The alkali basalts are found only on the flanks of a topographic high near the intersection of the northern transform trough with the East Pacific Rise.

Description: The eleventh research cruise of Japanese Geodynamics Project in the West Pacific was carried out by the R/V Tokaidaigaku-maru II in August, 1974. During this cruise, in which the authors participated, many traverses of echo sounding and seismic reflection profiling and frequent sampling of bottom sediments were undertaken.