ALBERT

Description: Igneous rocks were recovered from three sites on Hess Rise during Deep Sea Drilling Project Leg 62: altered basalt at Site 464, at the northern end of Hess Rise; and altered trachyte from Site 465, and rounded basalt pebbles in upper Albian to middle Miocene sediments from Site 466, both at the southern end of Hess Rise. Major-, minor-, and trace-element data for basalt from Hole 464 are consistent with these rocks being transitional tholeiites that have undergone low-temperature alteration by reaction with sea water. Trachyte from Hole 465A exhibits as many as three generations of plagioclase along with potash feldspar that are flow aligned in groundmasses alterted to smectites and random mixed-layer clays. Textural evidence indicates that these rocks were eruped subaerially. Chemical data show a range of values when plotted on two- and three-component variation diagrams. The observed variations may result in part from differentiation, but they also reflect the high degree of alteration. Several oxides and elements show strong correlation with H2O+: K2O, SiO2, Rb and Lu decrease and MgO increases with increasing H2O+. These trends, except for that of Lu, are consistent with experimentally determined changes in chemistry that accompany alteration. The trend for Lu has not been previously reported; it may result from a more-intense alteration of the HREE-rich mafic minerals than of the LREE-rich feldspars. Despite their alteration, the trachytes compare favorably with alkalic differentiates from oceanic islands. We interpret Hess Rise as a volcanic platform formed by eruption of off-ridge volcanic rocks onto MORB oceanic crust during the Aptian and Albian stages, after the basement had migrated away from the spreading center. By analogy with present oceanic islands, we propose that early tholeiitic basalts were followed by alkalic basalts and their differentiation products (trachytes), producing a volcanic archipelago of islands and seamounts. Subsequent tectonism and subsidence led to the present state of Hess Rise.

Description: Atomic-absorption spectrophotometry and instrumental neutron activation analysis were used to determine concentrations of SiO2, Al2O3, FeOt, MgO, CaO, Na2O, K2O, MnO, La, Ce, Sm, Eu, Tb, Yb, Lu, Sc, Co, Cr, Th, Hf, and Ta for 14 basalt samples from the lower portion of Hole 462A in the Nauru Basin. The basalts are similar to normal midocean ridge basalt (MORB) for the elements analyzed, and light rare-earth elements (LREE) are depleted relative to heavy rare-earth elements (HREE). Two samples are extensively altered to smectites and show significant reductions in Al2O3, CaO, MnO, Na2O, REE, Sc, Co, and Hf and gains in MgO and FeOt relative to unaltered samples. The increase in MgO and decrease in CaO indicate that alteration was caused by hydrothermal solutions.

Description: The lipids and kerogens of 15 sediment samples from Site 547 (ranging from Pleistocene to Early Jurassic/Triassic) and 4 from Site 545 (Cretaceous) have been analyzed. A strong terrestrial contribution of organic matter was found, and significant autochthonous inputs were also present, especially at Site 545. Both strongly reduced and highly oxidized sediments have been found in the Cenozoic and Jurassic samples of Site 547. On the contrary, all the Cretaceous sections of Sites 547 and 545 are anoxic. Sediments from anoxic paleoenvironments are immature and have a high content of sterenes, diasterenes, steradienes, hopenes, and ßß hopanes. Samples from oxic paleoenvironments are mainly mature and their content of hopenes and steriod structures is below the detection level. Nevertheless, their hopane distributions have the immature ßß homologs as the predominant molecular markers. For Site 545 the most abundant molecular markers are ring A monoaromatic steranes, and their presence is attributed to microbial and chemical transformations during early diagenesis.

Description: At Deep Sea Drilling Project (DSDP) Site 462, from mudline to 447 meters below the sea floor, Cenozoic nannofossil oozes and chalks have acoustic anisotropies such that horizontal sonic velocities are 0 to 2.5% faster than those in the vertical direction. In laminated chalk, anisotropy of 5% is typical, and in limestones, radiolarian oozes, porcellanites, and cherts, the anisotropies range from 4 to 13%. Middle Maestrichtian volcaniclastics from 447 meters to 560 meters below the sea floor have an acoustic anisotropy of 2 to 32%; 4 to 13% is typical. Basalt flows and sills occur between 560 meters and 1068 meters, and have no apparent anisotropy, but minor interbedded volcaniclastics have anisotropies from 0 to 20% (5% is typical). These volcaniclastics frequently have very small anisotropies, however, compared with the volcaniclastic sequence above the basalt section. Data in cross-plots of the laboratory-measured compressional sound velocity versus wet-bulk density, wet-water content, and porosity of sediments and sedimentary rock typically lie between the equations derived by Wyllie et al. (1956) and Wood (1941); the Wyllie et al. (1956) equation has a fair fit with similar basalt velocity cross-plots. Crossplots of thermal conductivity and sound velocity indicate only a fair correlation. Cross-plots of thermal conductivity versus porosity, wet-water content, and wet-bulk density correlate well with equations derived by Maxwell (1904), Ratcliff (1960), Parasnis (1960), and Bullard and Day (1961). Electrical formation factor versus porosity for sediments and sedimentary rock agrees with the Archie (1942) equation, with m values of 2.6; for basalt, an m of about 2.1 is typical. Basalt pore-water resistivities do not appear to be greatly different from sea water. Formation factors are greater than those derived from equations in Maxwell (1904), Winsauer et al. (1952), Boyce (1968), and Kermabon et al. (1969). An "apparent interstitial water resistivity" (Rwa) curve was derived from the density and induction logs. This Rwa curve indicated an anomaly, at 393.5 to 396.5 meters, which could be interpreted as (1) 76% hydrocarbons, (2) relatively fresh pore water (1.8 per mil salinity), or (3) low-grain-density (2.2 g/cm**3) semi-lithified porcellanite-chert. Porcellanite-chert is the most plausible interpretation. In situ temperatures measured by the Uyeda temperature probe were about 2 to 5°C (50%) higher than the equilibrium temperature (Lachenbruch and Brewer, 1959) extrapolated from two Gearhart-Owen continuous temperature logs; this discrepancy probably arises because the hole was washed out in this depth interval, so these extrapolated temperatures are probably not reliable. If one ignores all precautions as to temperature artifacts, then the equilibrium temperatures of the Gearhart-Owen temperature logs suggest that hydrothermal circulation is occurring in at least the upper 40 meters of the basalt section and heat is transferred by convection and not conduction. Hydrothermal circulation is probably not indicated, however, and the temperature anomalies probably result from excessive artificial cooling of the fractured basalt zones by circulation of water during drilling.

Description: The stratigraphic position of the glacially transported 'Scholle' (large-size erratic block) at Schobüll near Husum (Schleswig-Holstein) is now considered to be Devonian rather than 'Rotliegendes'. The 'Scholle', consisting of red clay and dolomite, is overlain by red-colored till without any flint but with up to 90% carbonate clasts (containing 15% dolomite), which indicates an eastern Baltic origin. The relationship of the 'Scholle' with the glacial till also points to an eastern Baltic origin for it, with up to 1 000 km transport distance.

Description: Ferromanganese nodules in the deep-sea and in freshwater lakes usually accrete layers rich in manganese oxides alternating with layers rich in iron oxides. The mechanism producing these alternating layers is unknown; indeed, the mechanism producing the nodules themselves is unknown. In Oneida Lake, New York, precipitants from the lake water and the surfaces of nodules at the sediment-water interface are enriched in Mn, whereas nodules buried in lake sediments have surface layers enriched in Fe. It is hypothesized here, using field and laboratory evidence, that reduction and mobilization of Mn from the nodule surface during periods of anoxic sediment cover produce the high Fe layers observed in the nodules.

Description: Manganese nodules occurring within marine sediments of presumably Upper Miocene-Lower Pliocene age from cores obtained by the Argentine oceanographic vessel ARA Islas Orcadas in 1977 on the Malvinas (Falkland) Plateau and neighbouring Scotia Sea were studied with the aim of comparing them with other fossil nodules found on the mainland of Argentina that were also ascribed to the marine environment. After optical mineralogical, chemical, X-ray and trace element analysis, the studied "nodules" proved to be actually wacke clasts cemented by manganese oxides with a high Fe/Mn ratio corresponding to a continental environment. The studied "nodules" thus differ from the Argentine mainland nodules and are supposed to have been transported from continental environments and then deposited in the marine realms. The wacke clasts became then nuclei for the deposition of the marine manganese oxides of the coatings. The proportion of trace elements, which is high, suggests the growth of the nodules in the marine environment.

Description: Manganese nodules have been analysed at the Scripps Institution of Oceanography after having been ground to to a diameter less than 74 microns. Some analysises were performed on pellets by X-ray Emission Spectroscopy for 1000 Seconds. All concentrations have been corrected to 110 degrees Celsius drying conditions (see: https://doi.pangaea.de/10.1594/PANGAEA.854202).

Description: Morphological, mineralogical and chemical analysis are reported for a metalliferous encrustation from a seamount in the Gulf of Guinea, South Atlantic. The results are compared with published data on encrustation from similar environments. The morphology and mineralogy indicate a crust formed on the exposed rock surface with some agglutination of foram debris. Comparison of the abundance patterns for transition elements with that of known data suggests that some enrichment had resulted from the high primary productivity at this site.

Description: This report is Volume 3 of Descriptions of WHOI rock dredge samples. This series represents a major effort to catalog the rock dredge samples in the WHOI Sea Floor samples collection, and to disseminate this information throughout the scientific community. Volume 3 contains sample descriptions and station data for the dredge stations from five cruises during the period September 1978 through December 1980. The material in this and subsequent volumes of rock descriptions was largely prepared onboard ship by the participating scientists. Volume 3 was printed prior to volumes 1 and 2 because of the excellent documentation of the samples represented in this volume.

Description: The minor-element composition of concentric layers within a single ferromanganese nodule from the eastern North Pacific exhibits strong correlations with Fe and Mn contents but appears to be independent of pronounced mineralogic variations. On the basis of these correlations, the elemental composition of individual layers apparently is controlled by the relative contribution of two sources: seawater, and interstitial water of associated sediment. In contrast, the mineralogy of the nodule, consisting of birnessite in the outer few layers and todorokite in the inner layers, is considered to be a function of nodule diagenesis.

Description: Compositional data for coexisting manganese nodules, micronodules, sediments and pore waters from five areas in the equatorial and S.W. Pacific have been obtained. This represents the largest study of its type ever undertaken to establish the distribution of elements between the various phases within the sediment column. The composition of manganese nodules, micronodules and sediments (on a carbonate-free basis) shows marked differences between the equatorial high productivity zone and the low productivity region of the S.W. Pacific. In the case of the nodules, th is reflects an increased supply of transition elements (notably Ni, Cu and Zn) to the nodules as a result of the in situ dissolution of siliceous tests within the sediment column in the equatorial Pacific high productivity zone. Micronodules display similar, but somewhat different, compositions to those of the associated nodules in each area. Micronodule composition is therefore influenced by the same basic factors that control nodule composition, but is modified by dissolution of the micronodules in situ within the sediment column. Locally, as in the area immediately south of the Marquesas Fracture Zone, the micronodule population is contaminated by small, angular volcanic rock fragments; this leads to apparently anomalous micronodule compositions. Micronodules appear to be a transient feature in the sediment column, especially in the equatorial Pacific. Dissolution of micronodules in the sediment column therefore represents an important source of elements for the growth of manganese nodules in the equatorial Pacific. Sediment composition is markedly influenced by the carbonate content. On a carbonate-free basis, the sediments from the equatorial high productivity zone are quite distinct in composition from those in the S.W. Pacific. This reflects differences in the lithology of the sediments. In the Aitutaki Passage, the local influence of volcanoclastic material in sediment composition has been established. The major cations and anions in pore waters measured here show no major differences between equatorial and S.W. Pacific sediments. Silica is, however, higher in equatorial Pacific pore waters reflecting the dissolution of siliceous tests in these sediments.

Description: Mesozoic benthic foraminifers, recovered from five single-bit holes drilled in the southern Gulf of Mexico on Deep Sea Drilling Project Leg 77 are rare, poorly preserved, and scattered throughout the dominantly redeposited sediments. The Mesozoic sequence at basin Sites 535 and 540 consists largely of laminated limestone with smaller amounts of skeletal limestone and pure pelagic limestone, whereas the Mesozoic sediments at basement Sites 536, 537, and 538 (Hole 538A) consist largely of oolitic-oncolitic limestone.

Description: Initial data on the hydrogen-isotopic compositions in hydrous Mn minerals from various occurrences fall in a wide range from -298 to -84 per mil, relative to SMOW. DeltaD-values of todorokite and cryptomelane from Tertiary deposits show -89 and -150 per mil. 10 Angström-manganite and Delta-MnO2 from deep-sea nodules have relatively restricted DeltaD-values ranging from -96 to -84 per mil. The DeltaD-values for manganese bog ores from recent hot springs show almost -105 per mil. It is recognized that the isotopic values obtained for the deep-sea nodules and recent bog ores are slightly different ranged. Manganite and groutite are unique in their hydrogen-isotopic compositions, having the most depleted DeltaD-values ranging from -298 to -236 per mil. MnO(OH) minerals are more deuterium-depleted hydrous minerals than any other hydrothermal minerals from various ore deposits. Hydrogen-isotope fractionation factors between manganite and water were experimentally determined to be 0.7894, 0.7958 and 0.8078 at 150°, 200° and 250°C, respectively. the present experimental results indicate that if manganites were formed at temperatures below 250°C, under isotopic equilibrium conditions, most of the manganite mineralization in the Tertiary manganese deposits must have precipitated from meteoric hydrothermal solutions.

Description: This report is Volume 1 in the series of reports entitled "Descriptions of W.H.O.I. rock dredge samples". This series represents a major effort to catalog and prepare initial descriptions for all rock dredge samples in the W.H.O.I. Sea Floor Samples Collection, and to distribute this information throughout the scientific community. Volume 1 contains sample descriptions from approximately 382 dredging stations executed during the period 1960 through 1977. It also represents a digitized listing of all dredge station data for the entire W.H.O.I. Dredge Collection through 1980. This data is sorted by Marsden Square and can serve as a regional index for all rock descriptions included in Volumes 1-3.

Description: A submersible study has been conducted in February - March 1978 at the axis of the East Pacific Rise near 21°N. The expedition CYAMEX, the first submersible program to be conducted on the East Pacific Rise, is part of the French-American-Mexican project RITA (Rivera - Tamayo), a 3-year study devoted to detailed geological and geophysical investigations of the East Pacific Rise Crest. On the basis of the 15 dives made by CYANA in the axial area of the Rise, a morphological and tectonic zonation can be established for this moderately-fast spreading center. A narrow, 0.6 to 1.2 km wide zone of extrusion (zone 1), dominated by young lava flows, is flanked by a highly fissured and faulted zone of extension (zone 2) with a width of 1 to 2 km. Further out, zone 3 is dominated by outward tilted blocks bounded by inward-facing fault scarps. Active or recent faults extend up to 12 km from the axis of extrusion of the East Pacific Rise. This represents the first determination from direct field evidence of the width of active tectonism associated with an accreting plate boundary. Massive sulfide deposits, made principally of zinc, copper and iron, were found close to the axis of the Rise. Other signs of the intense hydrothermal activity included the discovery of benthic fauna of giant size similar to that found at the axis of the Galapagos Rift. We emphasize the cyclic character of the volcanicity. The main characteristics of the geology of this segment of the East Pacific Rise can be explained by the thermal structure at depth below this moderately-fast spreading center. The geological observations are compatible with the existence of a shallow magma reservoir centered at the axis of the Rise with a half-width of the order of 10 km.

Description: Of numerous island-arc systems in the western Pacific, the Mariana arc-trench system and the basins and submerged ridges lying west of them in the Philippine Sea seemed to be best suited to answer questions regarding arc-trench and back-arc basin formation. Three years of planning by the JOIDES Active Margin Panel, Ocean Crust Panel, and Planning Committee resulted in a proposed transect of drill sites aligned more or less along the 18th parallel. This South Philippine Sea transect was designed to investigate each major basin and ridge between the central part of the West Philippine Sea and the Mariana Trench and the Pacific Ocean plate immediately to the east.

Description: The goal of Site 462 was to study the paleontologic, sedimentary, petrologic, tectonic, and magnetic histories of that area through Recent to Late Jurassic time by drilling a deep re-entry site into the Nauru Basin west of the Ralik Chain of the Marshall Islands. This area formed at a fast-spreading Pacific Plate boundary 145 to 155 m.y. ago, in the Late Jurassic. Cores from this area allow to better understand the biostratigraphic evolution and sedimentary processes in a Mesozoic open-ocean environment, the petrologic nature of fast-spreading oceanic crust, the tectonic history of the Late Jurassic Pacific Plate, and the nature of the Jurassic magnetic quiet zone.

Description: The four sites drilled during Leg 62 were needed to establish better regional coverage of the North Pacific Ocean. Although paleoenvironments were to be stressed on Leg 62, studies of igneous rocks from acoustic basement were planned, to determine ages, petrogenesis, alteration effects, rock magnetism, and Paleomagnetism of old parts of the Pacific crust. These studies were emphasized in order to establish the early history of oceanic plateaus and whether they are the result of midocean-ridge or intraplate volcanism.

Description: A primary objective of Leg 63 was to investigate the fluctuations of this eastern boundary current along a north-south transect off the Gulf of California. This information would aid in biostratigraphically correlating open-ocean planktonic zones with local California zonations. Spanning the last 30 m.y., the complicated tectonic history of the continental margin off California and Baja California comprises changes from a subduction zone to a transform boundary and then to an inactive margin. A second objective of Leg 63 was to define and clarify this history using information on sedimentation, unconformities, basement ages, and paleomagnetic reconstructions gained from drilling, in conjunction with geophysical data and pre-existing bottom samples.

Description: Undamaged deep-sea manganese nodules were retrieved from a box core from the central North Pacific and quickly preserved in formaldehyde solution. Light and scanning electron microscope studies of the nodule surface reveal the presence of a variety of fragile filamentous and coccoid bacterial morphotypes, associated with an organic film that covers the botryoid surface.

Description: The main objective of the cruise was to study the sediments and sedimentary processes in an area known as Great Meteor East (GME) - part of a feasibility study into the ocean disposal of high-level radioactive waste commissioned by the Department of the Environment. Previous cruises (Discovery 118, 126, 134 and Farnella 3/81) had done much of the ground work, consequently the area was already well known but not necessarily well understood for the purposes of our investigation.

Description: The drilling plan for Leg 74 of the Deep Sea Drilling Project was designed to address three main scientific topics: (1) the history of the deep-water circulation in the southeastern Atlantic, (2) the nature and geologic evolution of the Walvis Ridge, and (3) the biostratigraphy and magnetic stratigraphy of this region. In order to study these subjects, a suite of five sites was drilled on the Walvis Ridge that extended from its crest (near 1000 m water depth) down its northwest flank into the Angola Basin to a depth of 4400 m.

Description: Leg 73 was the middle of five legs on South Atlantic paleoenvironments planned by the JOIDES Ocean Paleoenvironment (OP) Panel during the years from 1975 to 1980. The idea of drilling a transect of holes across the 30°S parallel was entertained soon after the drilling on Leg 3, during the first phase of the Deep Sea Drilling Project (1968/69), when the surprising discovery was made that the middle Miocene sediments of the South Atlantic were largely marls and red clays. The deposition of the red clays was obviously related to the intense dissolution of calcite during the middle Miocene, when the calcite-compensation level was elevated. The objectives and tactical planning for a transect across the east flank of the Mid-Atlantic Ridge just north of 30°S were outlined by the OP Panel more fully to the Planning Committee in July of 1978. After a piston core containing Paleocene sediments was taken in 1979 at the site in the Cape Basin at the foot of the Walvis Ridge this area was designated for DSDP Leg 73 and 74.

Description: Site 530 is located in the southeastern corner of the Angola Basin, about 20 km north of the Walvis Escarpment, near the eastern end of the easternmost (or Frio) segment of the Walvis Ridge. It lies on the abyssal floor of the Angola Basin and exhibits a seismic stratigraphic sequence typical for the entire deep part of the basin. It was selected because it appears to have the oldest strata in the region preserved in a sediment pond between low basement rises.

Description: The drilling of Leg 77 is part of an overall program by the JOIDES Passive Margin Panel to study the evolution of the western North Atlantic passive margin. The history of the central North Atlantic is probably the best known of all ocean basins, but the origin and history of the neighboring Gulf of Mexico are very much uncertain. Some geologists consider it the oldest ocean basin still in existence (Paleozoic), but others doubt the existence of "true" oceanic crust under the central Gulf. The nature and origin of the transitional crust and the overlying Mesozoic sedimentary sequences in the southeastern Gulf, therefore, was the main objective of Leg 77.

Description: The principal goal of Site 543 was definition of an oceanic reference section. One of the specific objectives was to provide a physical-property profile through the undisturbed oceanplate section and thereby a basis for measuring the tectonic consolidation of any offscraped rocks of similar lithology in the area of the Tiburon and Barracuda rises which constitute prominent highs emerging from the Atlantic abyssal plain and presently intersecting the deformation front of the Barbados Ridge complex.

Description: Analyses of the bulk oxidation state of marine manganese nodules indicates that more than 98% of the Mn in deep ocean nodules is present as Mn(IV). The samples were collected from three quite different areas: the hemipelagic environment of the Guatemala Basin, the pelagic area of the North Pacific, and seamounts in the central Pacific. Results of the study suggest that todorokite in marine nodules is fully oxidized and has the following stoichiometry: (K, Na, Ca, Ba)0.33 (Mg, Cu, Ni)0.76 Mn5 O22 (H2O)3.2.

Description: The major and minor element composition of ferromanganese nodules from DOMES Site A has been determined by X-ray fluorescence methods. Three phases appear to control the bulk compositions: Mn and Fe oxyhydroxides and aluminosilicates. Relatively wide compositional variations are evident throughout the area. Nodules with high Mn/Fe ratios, high Cu, Mg, Mo, Ni and Zn concentrations and high todorokite/-MnO2 ratios have gritty surface textures and are confined to an east-west trending depression with thin Quaternary sediment cover. Nodules with low Mn/Fe ratios, high concentrations of As, Ca, Ce, Co, La, P, Sr, Ti, V, Y and Zr and low todorokite/-MnO2 ratios have smooth surfaces and are confined to shallower areas with relatively thick Quaternary sediment to the north and south of the depression. All nodules in the area have compositions which are influenced by diagenesis, but those with the most marked diagenetic signature (high Mn/Fe and Cu/Ni ratios, low Ce/La ratios and more todorokite) are found in areas of very slow or non-existent sedimentation; many of these nodules are actually in contact with outcropping Tertiary sediment. This paradox may be resolved by postulating, by analogy with some shallow-water occurrences, that the nodules accrete from bottom waters which have enhanced particulate and dissolved metal contents derived from diagenetic reaction in areas remote from the site of nodule formation. The metals are supplied in a bottom flow (probably Antarctic Bottom Water) which also erodes, or prevents modern sedimentation in, the depression. Nodules on the flanks of the depression are not evidently affected by this flow and derive at least pan of their constituent metals from diagenetic reaction in the underlying Quaternary sediment. Apparently, abyssal diagenetic nodules can have an immediate and a remote diagenetic metal source. Metal fluxes derived from pore water dissolved metal gradients may not be relevant to particular accreting nodules if a significant fraction of their metals is derived from outside the area in which they form.

Description: The unusual petrological diversity of abyssal lavas erupted along some segments of the Galapagos spreading center is a direct consequence of the propagation (elongation) of these segments into older oceanic crust. With increasing distance behind propagating rift tips, relatively unfractionated MORB erupted close to the tips are joined first by FeTi basalts (bimodal assemblage) and then by a wide range of basaltic and siliceous lavas. Further behind propagating rift tips, this broad range diminishes again, approaching the narrow compositional range of adjacent normal ridge segments. These compositional variations reflect the evolution of the subaxial magmatic system beneath the newly forming spreading center as it propagates through a pre-existing plate. We envisage this evolution as proceeding from small, isolated, ephemeral magma chambers through increasing numbers of larger, increasingly interconnected chambers to the steady-state buffered system of a normal ridge. Throughout this evolution, magma supply rates gradually increase and cooling rates of crustal magma bodies decrease. High degrees of crystal fractionation are favored only when a delicate balance between cooling rate and resupply rate of primitive magma is achieved. At other propagating and non-propagating ridge-transform intersections the degree to which the balance is achieved and the length of ridge over which it evolves control the distribution of fractionated lavas. These effects may be evaluated provided a number of tectonic variables including transform length, spreading and propagation rates are taken into account.

Description: Measurements of Pb-210 activities, in conjunction with micropaleontological, geotechnical and sedimentological observations, on sediment cores have been used to characterize two distinctive bioturbation regimes on the continental slope and rise east of Newfoundland. On the rise (2600 m), excess Pb-210 is confined to the upper few centimeters of the coarser-grained sediments underlying the axis of the Western Boundary Undercurrent. The geological and geochemical evidence for a low rate of bioturbation in this high bottom current regime is consistent with a reduced population of deeper burrowing macrofauna, particularly the species Maldane sarsi. In contrast, a higher flux of organic-rich, fine-grained particulate material to the middle slope (1500 m water depth), and the comparatively stable sedimentological conditions that prevail in this low bottom current regime, have led to the active colonization of the sediment substrate by bioturbating organisms. Enhanced mixing of middle slope deposits is reflected by comparatively lower shear strengths within the upper 30 cm of the sediment column, and by the reduced variability of the sediment-depth distribution of the most abundant species of foraminifera. Excess Pb-210 has been transported downward from the sediment-water interface to depths greater than 12 cm. Some Pb-210 profiles from the middle slope can be interpreted in terms of a diffusion mixing model for which the biological mixing coefficients are of the order of 0.10-1.0 cm2/yr.Measurements of the two and three dimensional distribution of excess Pb-210 in one middle slope box core indicate that the mixing process in these sediments has a pronounced heterogeneous component on time scales of the same order as the half life of Pb-210 (22.3 yr). Spatial correlations between Pb-210 anomalies and artifacts of bioturbation observed in x-radiographs of the core suggest that Pb-210 maxima observed at depth may be the result of an inclined orientation of burrow structures which have introduced a significant lateral component to the downward transport of surficial sediments.

Description: The southernmost part of the Sohm Abyssal Plain in the Northwest Atlantic Basin is geographically distal with respect to the major source of Quaternary terrigenous material transported from the Canadian Maritime Provinces. An assessment of the proportion of more locally introduced sediment relative to that derived from distal sources is based largely on size and compositional analyses of Quaternary piston core samples. These data are supplemented by radiocarbon dating of selected core samples, bottom photographs, conductivity-temperature-depth profiles, and seismic records. The premises of the study are that (a) locally derived sediment should be most abundant near high-relief bathymetric features such as seamounts and abyssal hills, and (b) such material should contain enhanced proportions of reworked volcanic debris and alteration products. Core analyses reveal that the amounts of these are directly related to proximity of volcanic ocean-bottom features, and that a significant, although not total, amount of such volcanic materials recovered from cores are derived from submarine weathering of basalt. Associated with this assemblage are nannofossils, dating from the Quaternary to the Upper Cretaceous, reworked from older strata. This increased proportion of volcanic and related products and reworked faunas near seamounts and basement rises strongly implies that such topographic features continue to serve as major source terrains. Locally derived volcanic materials, however, are usually disseminated and masked on the Sohm Abyssal Plain, particularly in sectors receiving large amounts of terrigenous turbidites and biogenic suspensates, and/or undergoing reworking by bottom currents. We propose that the volcanic fraction can serve as a useful index, or "yardstick," to interpret the role of locally derived material in abyssal plain sedimentation. A sedimentation model is developed to illustrate the premise that as access to land-derived sources diminishes, the proportion of terrigenous components is reduced while pelagic and volcanic fractions are enhanced. Thus, sediment accumulating in abyssal plains almost totally isolated from terrigenous sources would comprise significant amounts of pelagic (including wind-blown) and volcanic components.

Description: Nine nodules collected from throughout the deep North Pacific were analyzed for their mineralogy and major-element composition before and after leaching with Chester-Hughes solution. Data indicate that the mineral phillipsite accounts for the major part (〉 75%) of the aluminosilicate fraction of all nodules. It is suggested that formation of phillipsite takes place on growing nodule surfaces coupled with the oxidation of absorbed manganous ion. All the nodules could be described as ternary mixtures of amorphous iron fraction (Fe-Ti-P), manganese oxide fraction (Mn-Mg Cu-Ni), and phillipsite fraction (Al-Si-K-Na), these fractions accounting for 96% of the variability of the chemical composition.

Description: Crusts composed of nontronite and ferromanganese oxides were recovered from Explorer Ridge, a spreading ridge segment in the northeastern Pacific Ocean located off the west coast of Canada. The chemical and mineralogical composition of the crusts closely resembles that of the mound-like hydrothermal deposits recently discovered at the FAMOUS site on the Mid-Atlantic Ridge and on the Galapagos spreading centre. Compositional anomalies suggest that the crusts are precipitates of hydrothermal vent solutions which were ejected discontinuously and subsequently mixed with seawater.

Description: Submersible exploration on the eastern Pacific Ridge near 21 ° N has revealed an active hydrothermal system. It is manifested by the emission in the marine environment of hot and Highly mineralized fluids (370 ° C maximum). These fluids precipitate on contact with seawater and deposits of massive sulphides are built at the outlet of their sources. The mineralogical and geochemical study of the products associated with the emissions of hot fluids provides an initial evaluation of this type of deposit and leads to a comparison between the hydrothermalism responsible for the formation of sulphides and the hydrothermalism responsible for the formation of metal rich crusts formed of iron smectites and manganese oxides. This study is carried out with conventional mineralogical and geochemical investigations (optical and electronic microscopy, X-ray diffraction, X-ray fluorescence spectrometry, electron microprobe, neutron activation and mass spectrometry).

Description: Relationships among Th and Ra isotopes in nodule, sediment and water phases at MANOP Site S establish the most likely source for Th in the nodules, the frequency of nodule turning, and the similarity of micro and macro nodules. Manganese nodules and bottom waters have 230Th/232Th activity ratios considerably higher than other phases at this site suggesting that sea water is the likely source of Th for the nodules. Similar 230Th/232Th activity ratios in nodule tops and bottoms and in certain cases departure from expected 226Ra/230Th activity ratios in nodule tops and bottoms indicate that the nodules rotate every one to ten thousand years. The micro nodules have diffusion coefficients of Ra similar to macro nodule bottoms. I suggest that they may act as a carrier phase for transporting metals through oxic sediments to nodules.

Description: Ferromanganese micronodules have been found on Georges Bank, off the U.S. northeast coast, distributed throughout the surficial sediments within an area about 125 km long and at least 12 km wide. These coarse, sand-sized concretions have precipitated from metal-rich interstitial waters and contain many of the textural and structural features common to other neritic nodules. Most of the nodules have accreted around detrital grains, and X-ray powder diffraction analyses indicate the presence of geothite and vernadite ( delta -MnO sub(2)) in the ferromanganese layers. Chemical analyses of the micronodules, when compared with similar data on deep-sea manganese nodules, reveal lower Mn/Fe ratios, significantly higher concentrations of V and As, comparable values of Mo, and an order of magnitude less of Co, Ni, Ce and most other, metals.

Description: The sulfide deposit at Site 471 occurs between overlying pelagic sediment and underlying basalt. The deposit is vertically zoned and consists, from top to bottom, of the following mineral assemblages: (1) pyrite, chalcopyrite, and Zn-sulfide in chert and calcite gangue (~ 35 cm thick); (2) a 5-cm-thick metalliferous sediment layer and (3) a 4-cm-thick chert layer. The calcite gangue appears at a later stage than chert gangue in the sequence of deposition, also filling in voids and fractures. The manganese content of calcite is particularly high and varies systematically, reaching a maximum at the top of the massive sulfide portion of the deposit.

Description: Elevated regions in the central parts of ocean basins are excellent for study of accumulation of eolian material. The mass-accumulation rates of this sediment component appear to reflect changes in the influx of volcanic materials through the Early Cretaceous to Recent history of Deep Sea Drilling Project Site 463, on the Mid-Pacific Mountains. Four distinct episodes of eolian accumulation occurred during the Cretaceous: two periods of moderate accumulation, averaging about 0.2 to 0.3 g/cm**2/10**3 yr, 67 to 70.5 m.y. ago and 91 to 108 m.y. ago; a period of low accumulation, approximately 0.03 g/cm**2/10**3 yr, 70.5 to 90 m.y. ago; and a period of high accumulation, about 0.9 g/cm**2/10**3 yr, 109 to 117 m.y. ago (bottom of the hole). Much of the Cenozoic section is missing from Site 463. Upper Miocene to Recent sediments record an upward increase in accumulation rates, from less than 0.01 to about 0.044 g/cm**2/10**3 yr. The late Pliocene-Pleistocene peak may reflect the change to glacial-wind regimes, as well as an increase in volcanic source materials.

Description: Eolian dust preserved in deep-sea sediment can provide a direct historical record of global atmospheric circulation. Data from a reasonably complete Upper Cretaceous section of pelagic sediments recovered at DSDP Site 463 in the central North Pacific provides a good record of eolian activity during the time period between about 112 and 66 m.y. ago. We have isolated the eolian component from these sediments, determined its mass accumulation rate and combined these data with the mineralogy of the inorganic fraction determined by others to construct a record of eolian deposition. Volcanic input is significant during Aptian-Albian and Maastrichtian times, otherwise continentally derived minerals dominate. Mass accumulation rates of the continental eolian component range from over 500 mg/cm**2/kyr during the late Albian to a low of 5 mg/cm**2/kyr during Coniacian time. (For comparison, the upper Miocene to Pleistocene rate averages about 20 mg/cm**2/kyr). The temporal pattern of Late Cretaceous eolian accumulation of Site 463 generally matches known changes in sea level, suggesting that source availability is the dominant control of eolian sedimentation during that time.

Description: We analyzed the oxygen and carbon isotopic composition of planktonic and benthic foraminifers picked from 13 late Eocene to late Oligocene samples from DSDP Site 540 (23°49.73'N, 84°22.25'W, 2926 m water depth) from the Gulf of Mexico. An enrichment occurs in 18O of about 0.5 to 0.8 per mil in both benthic foraminifers and surface-dwelling planktonic foraminifers between the latest Eocene and early Oligocene. This early Oligocene maximum is followed by lower 18O values. A 1.2 per mil d13C decrease in both benthic and planktonic foraminiferal data occurs from the late Eocene to the late Oligocene. There is a correspondence of the 13C signal to deep-sea records; however, the amplitude of this change is greater than previously seen in deep-sea cores, possibly as a result of proximity to terrestrial sources of carbon. The covarying isotopic changes in both benthic and planktonic foraminifers suggest global causes, such as ice volume increases and increased terrestrial carbon input to the ocean. However, during the latter part of the record (early-late Oligocene), the increases in the benthic 18O without accompanying increases observed with planktonic foraminifers suggest that changes in only one part of the system occurred; one potential explanation being a decrease in bottom-water temperatures without concomitant changes in the surface waters. The 18O differences between species of planktonic foraminifers and the difference between planktonic and benthic 18O data indicate that diagenesis problems are minimal. These preliminary results are encouraging given that these cores are partially lithified.