Grain size distribution in surface sediments samples of the continental shelf and slope of southeast Greenland

During "Meteor" Cruise 6/1966 in the northwest Atlantic a systematic survey of the bottom topography of the southeast Greenland continental margin was undertaken. Eighty-seven profiles transverse to the shelf edge at distances of 3-4 nautical miles and two longitudinal profiles parallel to the coast were carried out with the ELAC Narrow Beam Echo-Sounder giving a reliable record of even steep slopes. On the basis of the echo soundings the topography and morphology of the continental shelf and slope are evaluated. A detailed bathymetric chart and a serial profile chart were designed as working material for the morphological research. These maps along with the original echograms are morphometrically evaluated. The analysis of the sea bottom features is the basis of a subsequent morphogenetical interpretation, verified and extended by means of interpretation of magnetic data and sediment analysis (grain size, roundness, lithology). The results of the research are expressed in a geomorphological map. The primary findings can be summarized as follows: 1) The southeast Greenland shelf by its bottom topography can be clearly designated as a glacially formed area. The glacial features of the shelf can be classified into two zones nearly parallel to the coast: glacial erosion forms on the inner shelf and glacial accumulation forms on the outer shelf. The inner shelf is characterized by the rugged and hummocky topography of ice scoured plains with clear west/east slope asymmetry. On the outer shelf three types of glacial accumulation forms can be recognized: ice margin deposits with clearly expressed terminal moraines, glacial till plains and glaciomarine outwash fans. Both zones of the shelf can be subdivided into two levels of relief. The ice scoured plains, with average depths of 240 meters (m), are dissected to a maximum depth of 1060 m (Gyldenloves Trough) by trough valleys, which are the prolongations of the Greenland fjords. The banks of the outer shelf, with an average depth of 180 m, surround glacial basins with a maximum depth of 670 meters. 2) The sediments of the continental shelf can be classified as glacial due to their grain size distribution and the degree of roundness of the gravel particles. The ice margin deposits on the outer shelf can be recognized by their high percentage of gravels. On the inner shelf a rock surface is suggested, intermittently covered by glacial deposits. In the shelf troughs fine-grained sediments occur mixed with gravels. 3) Topography and sediments show that the southeast Greenland shelf was covered by an ice sheet resting on the sea floor during the Pleistocene ice-age. The large end moraines along the shelf edge probably indicate the maximum extent of the Wurm shelf ice resting on the sea floor. The breakthroughs of the end moraines in front of the glacial basins suggest that the shelf ice has floated further seaward over the increasing depths. 4) Petrographically the shelf sediments consist of gneisses, granites and basalts. While gneisses and granites occire on the nearby coast, basalt is not known to exist here. Either this material has been drifted by icebergs from the basalt province to the north or exists on the southeast Greenland shelf itself. The last interpretation is supported bythe high portion of basalt contained in the sediment samples taken and the strong magnetic anomalies probably caused by basaltic intrusions. 5) A magnetic profile allows the recognition of two magnetically differing areas which approximately coincide with the glacial erosion and accumulation zones. The inner shelf shows a strong and variable magnetic field because the glacially eroded basement forms the sea floor. The outer shelf is characterized by a weak and homogenous magnetic field, as the magnetized basement lies at greater depthy, buried by a thick cover of glacial sediments. The strong magnetic anomalies of the inner shelf are probably caused by dike swarms, similar to those observed further to the north in the Kangerdlugssuaq Fjord region. This interpretation is supported by the high basalt content of the sediment samples and the rough topography of the ice scoured plains which correlates in general with the magnetic fluctuations. The dike structures of the basement have been differentially eroded by the shelf ice. 6) The continental slope, extending from the shelf break at 313 m to a depth of 1270 m with an average slope of 11°, is characterized by delta-shaped projections in front of the shelf basins, by marginal plateaus, ridges and hills, by canyons and slumping features. The projections could be identified as glaciomarine sediment fans. This conclusion is supported by the strong decrease of magnetic field intensity. The deep sea hills and ridges with their greater magnetic intensities have to be regarded as basement outcrops projecting through the glaciomarine sediment cover. The upper continental rise, sloping seaward at about 2°, is composed of wide sediment fans and slump material. A marginal depression on the continental rise running parallel to the shelf edge has been identified. In this depression bottom currents capable of erosion have been recorded. South of Cape Farvel the depression extends to the accumulation zone of the "Eirik" sedimentary ridge. 7) By means of a study of the recent marine processes, postglacial modification of the ice-formed relief can be postulated. The retention effect of the fjord troughs and the high velocity of the East Greenland stream prevents the glacial features from being buried by sediments. Bottom currents capable of active erosion have only been found in the marginal depression on the continental rise. In addition, at the time of the lowest glacio-eustatic sea level, the shelf bottom was not situated in the zone of wave erosion. Only on the continental slope and rise bottom currents, sediment slumps and turbidity currents have led to significant recent modifications. Considering these results, the geomorphological development of the southeast Greenland continental terrace can be suggested as follows: 1. initial formation of a "peneplain", 2. fluvial incision, 3. submergence, and finally 4. glacial modification.

Age data of ODP Site 181-1124

ODP Site 1124, located 600 km east of the North Island of New Zealand, records post-middle Oligocene variations in the Pacific Deep Western Boundary Current (DWBC) and New Zealand's climatic and tectonic evolution. Sediment parameters, such as terrigenous grain size, flux, magnetic fabric, and non-depositional episodes, are used to interpret DWBC intensity and Antarctic climate. Interpretations of DWBC velocities indicate that the Antarctic Circumpolar Current reached modern intensities at ~23 Ma, as the tectonic seaways expanded, completing the thermal isolation of Antarctica. Periods of more intense bottom water formation are suggested by the presence of hiatuses formed under the DWBC at 22.5-17.6, 16.5-15, and 14-11 Ma. The oldest interval of high current intensity occurs within a climatically warm period during which the intensity of thermohaline circulation around Antarctica increased as a result of recent opening of circum-Antarctic gateways. The younger hiatuses represent glacial periods on Antarctica and major fluctuations in the East Antarctic Ice Sheet, whereas intervals around the hiatuses represent times of relative warmth, but with continued current activity. The period between 11 to 9 Ma is characterized by conditions surrounding a high velocity DWBC around the time of the formation and stabilization of the West Antarctic Ice Sheet. The increased terrigenous input may result from either changing Antarctic conditions or more direct sediment transport from New Zealand. The Pacific DWBC did not exert a major influence on sedimentation at Site 1124 from 9 Ma to the present; the late Miocene to Pleistocene sequence is more influenced by the climatic and tectonic history of New Zealand. Despite the apparent potential for increased sediment supply to this site from changes in sediment channeling, increasing rates of mountain uplift, and volcanic activity, terrigenous fluxes remain low and constant throughout this younger period.

Benthic foraminifera of surface sediments from the continental slope off Sierra Leone, North-West Africa

On "Meteor" cruise 30 (1973) 22 piston-cores were collected off Sierra Leone from water-depths between about 5000 m (Sierra Leone Basin) and 500 m (upper continental slope) with the objective to study the sediment composition and age as well as processes of sedimentation on the continental slope in a tropical humid region. Granulometric analysis and determinations of the carbonate contents of the sediment samples were carried out, as well as qualitative and quantitative analysis of the components of the grain size fractions > 63 µm and of the planktonic and benthonic foraminifera > 160 µm. Presently, the cold Canary Current influences the composition of the planktonic foraminifera within the northwestern area of investigation (profile A), whereas the planktonic fauna of the eastern area (profile C) seems to be truly tropical. In all Quaternary sediments from the continental slope off Sierra Leone, species of Globorotalia are less abundant than in truly pelagic sediments. For that reason, the zonation of the Pleistocene sediments based on the presence or absence of Globorotalia cultrata does not always agree with the climatic changes reflected in the sediments. Concerning past climates better results can be obtained by using the changes in percentage abundances of Globigerina sp. sp. and Globigerinoides sp. sp. as indicators for cool and warm temperatures. The Tertiary sediments contain a pelagic foraminiferal assemblage. In the Holocene sediments the benthonic foraminifera do not only serve as good paleodepth indicators, but their communities are also restricted to defined water masses, which change their positions in accordance with climatic changes. Thus, Cassidulina carinata in the area of investigation is an excellent indicator for sediments deposited during times, which were cooler than today; this is true for all cores from the continental slope off Sierra Leone independent of water-depth although this species presently abounds at water-depths around 600 m. The cores from the continental rise and from the Sierra Leone Basin (M30-261, M30-146, M30-147) were deposited below the calcium carbonate compensation depth. Only small sections of the cores consist of the original carbonate-free sediments, whereas the main part of the sediment column is redeposited material, rich in foraminifera, which normally live on the upper continental slope, or even on the shelf. From these cores only M30-261 can be subdivided into biostratigraphic zones ranging from zone V to zone Y. In all cores from the middle and upper continental slope of the eastern area of investigation (profile C; KL 230, 209-204) and in cores KL 183 and KL 184 from the northwestern area (profile A) we observed an undisturbed succession of sediments from the biostratigraphic zones X (partly), Y and Z. All cores from the central area (M30-181, M30-182, M30-262 to 264) and M30-187 from the upper slope of profile A show variable hiatuses in the sedimentary record. Locally, high velocity bottom currents were probably responsible for erosion, nondeposition or minimal sedimentation rates. These currents might have been initiated partly by the somewhat exposed position of this part of the continental slope, where the shelf edge bends from a northwest towards an eastern direction, and partly by very young tectonic movements. Fracture zones with vertically displaced fault blocs are frequent at Sierra Leone continental margin. According to seismic measurements by McMaster et al. (1975) the sites of the central area are located on an uplifted fault bloc explaining the reduced sediment rates or erosion. Unlike the central area, the eastern area (profile C) is situated on a downfaulted bloc with high sediment rates. The sediments from the cores of profile B as well as the turbiditic deep-sea sediments were deposited under a higher flow regime; therefore they are coarser than the extremely fine-grained sediments of the cores from profile C. Since the sand fraction (> 63 µm) is mainly composed of foraminifera, besides pteropods and light-colored fecal pellets, the carbonate content increases with the increasing percentage of the coarse grain fraction. Higher concentrations of quartz were only observed in core sections with considerable carbonate dissolution (mainly in the X-Zone), and, in general, in all sediments from the eastern area with higher terrigenous input including larger concentration of mica. Especially during times transitional between glacials and interglacials (or interstadials) the bottom currents were intensified. The percentages of coarse fraction and carbonate increase with increasing current velocities. Calcium carbonate dissolution becomes important in water depths > 3500 m. During cooler times the lysokline is depressed. Light-colored fecal pellets were redeposited from Late Neogene sediments (M30-187, M30-181). In the area of investigation they occur in the Holocene and mainly the Pleistocene sediments of the cores from the northwestern and central area because only here Tertiary sediments have been eroded at the uppermost continental slope. In the central area there are at least two periods of non-sedimentation and/or erosion which can be confined as being (1) not older than middle Pliocene and not younger than zone V and (2) younger than zone W. The local character of the erosion is documented by the fact that a complete Late Quaternary section is present in the cores of the northwestern and eastern area, each within less than 100 km from incomplete cores from the central area.

Physical properties of sediment core AND-2A

Whole-core measurements of Wet Bulk Density (WBD), compressional (P)-wave velocity (Vp), and Magnetic Susceptibility were measured at a sampling interval of 1 or 2 centimetres (cm) throughout the AND-2A drill core for initial core characterisation and on-site correlation with seismic modeling to predict target-reflector depth. Measurements were made using a GEOTEK (Multi-Sensor-Core-Logger MSCL). Density and velocity standards were measured together with core runs of 3-6 metres (m) (and occasionally up to 18 m) throughout the entire depth range to monitor data quality. Drift of the magnetic susceptibility sensor was also monitored and corrected where necessary. These physical properties show a large range of values, reflecting the different nature of the various lithologies including extremely high velocity and density values in individual clasts, and the effects of cementation on porosity. A downcore increase in WBD and Vp occurs in the upper 200 m, however, no systematic trend exists at greater depths although large fluctuations on a m-decimetre- (dm) scale occur. Magnetic susceptibility is generally low (<100 x 10-5 SI), however, four intervals of high (>600 x 10-5 SI) susceptibility occur at 560, 800, 980 and 1 080 mbsf, indicating a relatively greater contribution of volcanic-derived material to the core site in the lower half of the AND-2A core.

Laboratory investigation of flow structure and resistance of high- and low-angle dunes

A prominent control on the flow over subaqueous dunes is the slope of the downstream leeside. While previous work has focused on steep (~30°), asymmetric dunes with permanent flow separation, little is known about dunes with lower lee-slope angles for which flow separation is absent or intermittent. Here, we present a laboratory investigation where we systematically varied the dune lee-slope, holding other geometric parameters and flow hydraulics constant, to explore effects on the turbulent flow field and flow resistance. Three sets of fixed dunes (lee-slopes of 10°, 20° and 30°) were separately installed in a 15 m long and 1 m wide flume and subjected to 0.20 m deep flow. Measurements consisted of high-frequency, vertical profiles collected with a Laser Doppler Velocimeter (LDV). We show that the temporal and spatial occurrence of flow separation decreases with dune lee-slope. Velocity gradients in the dune leeside depict a free shear layer downstream of the 30° dunes and a weaker shear layer closer to the bed for the 20° and 10° dunes. The decrease in velocity gradients leads to lower magnitude of turbulence production for gentle lee-slopes. Aperiodic, strong ejection events dominate the shear layer, but decrease in strength and frequency for low-angle dunes. Flow resistance of dunes decreases with lee-slope; the transition being non-linear. Over the 10°, 20° and 30° dunes, shear stress is 8%, 33% and 90 % greater than a flat bed, respectively. Our results demonstrate that dune lee-slope plays an important, but often ignored role in flow resistance.

Physical oceanography and current velocity during Nathaniel B. Palmer cruise NBP97-05

An extensive set of conductivity-temperature-depth (CTD)/lowered acoustic Doppler current profiler (LADCP) data obtained within the northwestern Weddell Sea in August 1997 characterizes the dense water outflow from the Weddell Sea and overflow into the Scotia Sea. Along the outer rim of the Weddell Gyre, there is a stream of relatively low salinity, high oxygen Weddell Sea Deep Water (defined as water between 0° and ?0.7°C), constituting a more ventilated form of this water mass than that found farther within the gyre. Its enhanced ventilation is due to injection of relatively low salinity shelf water found near the northern extreme of Antarctic Peninsula's Weddell Sea shelf, shelf water too buoyant to descend to the deep-sea floor. The more ventilated form of Weddell Sea Deep Water flows northward along the eastern side of the South Orkney Plateau, passing into the Scotia Sea rather than continuing along an eastward path in the northern Weddell Sea. Weddell Sea Bottom Water also exhibits two forms: a low-salinity, better oxygenated component confined to the outer rim of the Weddell Gyre, and a more saline, less oxygenated component observed farther into the gyre. The more saline Weddell Sea Bottom Water is derived from the southwestern Weddell Sea, where high-salinity shelf water is abundant. The less saline Weddell Sea Bottom Water, like the more ventilated Weddell Sea Deep Water, is derived from lower-salinity shelf water at a point farther north along the Antarctic Peninsula. Transports of Weddell Sea Deep and Bottom Water masses crossing 44°W estimated from one LADCP survey are 25 ? 10**6 and 5 ? 10**6 m**3/s, respectively. The low-salinity, better ventilated forms of Weddell Sea Deep and Bottom Water flowing along the outer rim of the Weddell Gyre have the position and depth range that would lead to overflow of the topographic confines of the Weddell Basin, whereas the more saline forms may be forced to recirculate within the Weddell Gyre.

Multi-year high-frequency current and water quality in-situ observations at the Guadiana Estuary

High-frequency data collected continuously over a multiyear time frame are required for investigating the various agents that drive ecological and hydrodynamic processes in estuaries. Here, we present water quality and current in-situ observations from a fixed monitoring station operating from 2008 to 2014 in the lower Guadiana Estuary, southern Portugal (37°11.30' N, 7°24.67' W). The data were recorded by a multi-parametric probe providing hourly records (temperature, salinity, chlorophyll, dissolved oxygen, turbidity, and pH) at a water depth of ~1 m, and by a bottom-mounted acoustic Doppler current profiler measuring the pressure, near-bottom temperature, and flow velocity through the water column every 15 min. The time-series data, in particular the probe ones, present substantial gaps arising from equipment failure and maintenance, which are ineluctable with this type of observations in harsh environments. However, prolonged (months-long) periods of multi-parametric observations during contrasted external forcing conditions are available. The raw data are reported together with flags indicating the quality status of each record. River discharge data from two hydrographic stations located near the estuary head are also provided to support data analysis and interpretation.

Penetration velocity and deceleration of penetrometer stations N1 to N97 during cruise Senckenberg_11_2008

In-situ geotechnical measurements of surface sediments were carried out along large subaqueous dunes in the Knudedyb tidal inlet channel in the Danish Wadden Sea using a small free-falling penetrometer. Vertical profiles showed a typical stratification pattern with a resolution of ~1 cm depicting a thin surface layer of low sediment strength and a stiffer substratum below (quasi-static bearing capacity equivalent: 1-3 kPa in the top layer, 20-140 kPa in the underlying sediment; thickness of the top layer ca. 5-8 cm). Observed variations in the thickness and strength of the surface layer during a tidal cycle were compared to mean current velocities (measured using an acoustic Doppler current profiler, ADCP), high-resolution bathymetry (based on multibeam echo sounding, MBES) and qualitative estimates of suspended sediment distributions in the water column (estimated from ADCP backscatter intensity). The results revealed an ebb dominance in sediment remobilization, and a general accretion of the bed towards low water. A loose top layer occurred throughout the tidal cycle, likely influenced by bedload transport and small events of suspended sediment resettlement (thickness: 6 +-2 cm). Furthermore, this layer showed a significant increase in thickness (e.g. from 8 cm to 16 cm) related to periods of overall deposition. These findings imply that dynamic penetrometers can conveniently serve to (1) quantify potentially mobile sediments by determining the thickness of a loose sediment surface layer, (2) unravel sediment strength development in potentially mobile sediments and (3) identify sediment accumulation. Such data are an important complement and add a new geotechnical perspective during investigations of sediment remobilization processes in highly dynamic coastal environments.

High-resolution in situ oxygen microprofiles, porewater and solid phase geochemistry from the Crimean shelf (Black Sea) from Maria S. Merian cruise MSM15/1

The outer western Crimean shelf of the Black Sea is a natural laboratory to investigate effects of stable oxic versus varying hypoxic conditions on seafloor biogeochemical processes and benthic community structure. Bottom-water oxygen concentrations ranged from normoxic (175 µmol O2/L) and hypoxic (< 63 µmol O2/L) or even anoxic/sulfidic conditions within a few kilometers' distance. Variations in oxygen concentrations between 160 and 10 µmol/L even occurred within hours close to the chemocline at 134 m water depth. Total oxygen uptake, including diffusive as well as fauna-mediated oxygen consumption, decreased from 15 mmol/m**2/d on average in the oxic zone, to 7 mmol/m**2/d on average in the hypoxic zone, correlating with changes in macrobenthos composition. Benthic diffusive oxygen uptake rates, comprising respiration of microorganisms and small meiofauna, were similar in oxic and hypoxic zones (on average 4.5 mmol/m**2/d), but declined to 1.3 mmol/m**2/d in bottom waters with oxygen concentrations below 20 µmol/L. Measurements and modeling of porewater profiles indicated that reoxidation of reduced compounds played only a minor role in diffusive oxygen uptake under the different oxygen conditions, leaving the major fraction to aerobic degradation of organic carbon. Remineralization efficiency decreased from nearly 100 % in the oxic zone, to 50 % in the oxic-hypoxic zone, to 10 % in the hypoxic-anoxic zone. Overall, the faunal remineralization rate was more important, but also more influenced by fluctuating oxygen concentrations, than microbial and geochemical oxidation processes.

High-resolution paleomagnetic investigation in the Iceland Basin

Based on discrete samples, we report new high-resolution records of the ~185 kyr Iceland Basin (IB) geomagnetic excursion from Ocean Drilling Project (ODP) Site 1063 on the Bermuda Rise (sedimentation rate 32 cm/kyr) and from ODP Site 983 in the far North Atlantic (sedimentation rate 18 cm/kyr). Two records from Holes 1063A and 1063B are very consistent, and provide the highest resolution of the detailed field behaviour during the IB excursion obtained so far. Inclination records from Holes 983B and 983C in the far North Atlantic are also very consistent, whereas declination anomalies deviate more notably. The pseudo-Thellier (PT) technique was applied along with more conventional palaeointensity proxies (NRM/ARM and NRM/kappa) to recover relative palaeointensity (RPI) estimates from Hole 1063A and Hole 983B. As expected, these proxies indicate that the field intensity generally dropped at both sites during the IB excursion, but also that the history of RPI from the two sites is different. VGPs from Site 1063 indicate that the field at this location experienced some stop-and-go behaviour between patches of intense vertical flux over North America and the tip of South America, areas which coincide fairly well with patches of preferred transitional VGP clustering from reversals and zones of high seismic velocity in the lower mantle. Changes in RPI at this location were generally gradual, possibly due to the proximity of these flux patches, and the first period of VGP-clustering over North America was accompanied by a conspicuous increase in RPI. VGPs from Site 983 track along a different path, and the associated RPI changes are very abrupt and completely synchronous with the onset and termination of the excursion. The differing VGP paths from Sites 1063 and 983 indicate that the global field structure during the IB excursion was not dominated by a single dipole.

(Table 1) Sound velocity, wet-bulk density, and acoustic impedance of some indurated sediment from DSDP Leg 64 Holes

The Pliocene-Quaternary sediments that we drilled at eight sites in the Gulf of California consist of silty clays to clayey silts, diatomaceous oozes, and mixtures of both types. In this chapter I have summarized various measurements of their physical properties, relating this information to burial depth and effective overburden pressure. Rapid deposition and frequent intercalations of mud turbidites may cause underconsolidation in some cases; overconsolidation probably can be excluded. General lithification begins at depths between 200 and 300 meters sub-bottom, at porosities between 55 and 60% (for silty clays) and as high as 70% (for diatomaceous ooze). Diatom-rich sediments have low strength and very high porosities (70-90%) and can maintain this state to a depth of nearly 400 meters (where the overburden pressure = 1.4 MPa). The field compressibility curves of all sites are compared to data published earlier. Where sediments are affected by basaltic sills, these curves clearly show the effects of additional loading and thermal stress (diagenesis near the contacts). Strength measurements on well-preserved hydraulic piston cores yielded results similar to those obtained on selected samples from standard drilling. Volumetric shrinkage dropped to low values at 100 to 400 meters burial depth (0.3 to 2.0 MPa overburden pressure). Porosity after shrinkage depends on the composition of sediments.

Physical properties, velocity and attenuation characteristics, and mineralogy of gabbros from ODP Hole 176-735B

Laboratory compressional wave (Vp) and shear wave (Vs) velocities were measured as a function of confining pressure for the gabbros from Hole 735B and compared to results from Leg 118. The upper 500 m of the hole has a Vp mean value of 6895 m/s measured at 200 MPa, and at 500 meters below seafloor (mbsf), Vp measurements show a mean value of 7036 m/s. Vs mean values in the same intervals are 3840 m/s and 3857 m/s, respectively. The mean Vp and Vs values obtained from log data in the upper 600 m are 6520 and 3518 m/s, respectively. These results show a general increase in velocity with depth and the velocity gradients estimate an upper mantle depth of 3.32 km. This value agrees with previous work based on dredged samples and inversion of rare element concentrations in basalts dredged from the conjugate site to the north of the Atlantis Bank. Laboratory measurements show Vp anisotropy ranging between 0.4% and 8.8%, with the majority of the samples having values less than 3.8%. Measurements of velocity anisotropy seem to be associated with zones of high crystal-plastic deformation with predominant preferred mineral orientations of plagioclase, amphiboles, and pyroxenes. These findings are consistent with results on gabbros from the Hess Deep area and suggest that plastic deformation may play an important role in the seismic properties of the lower oceanic crust. In contrast to ophiolite studies, many of the olivine gabbros show a small degree of anisotropy. Log derived Vs anisotropy shows an average of 5.8% for the upper 600 m of Hole 735B and tends to decrease with depth where the overburden pressure and the age of the crustal section suggests closure of cracks and infilling of fractures by alteration minerals. Overall the results indicate that the average shear wave splitting in Hole 735B might be influenced by preferred structural orientations and the average value of shear wave splitting may not be a maximum because structural dips are <90°. The maximum fast-wave orientation values could be influenced by structural features striking slightly oblique to this orientation or by near-field stress concentrations. However, flexural wave dispersion analyses have not been performed to confirm this hypothesis or to indicate to what extent the near-field stresses may be influencing shear wave propagation. Acoustic impedance contrasts calculated from laboratory and logging data were used to generate synthetic seismograms that aid in the interpretation of reflection profiles. Several prominent reflections produced by these calculations suggest that Fe-Ti oxides and shear zones may contribute to the reflective nature of the lower oceanic crust. Laboratory velocity attenuation (Q) measurements from below 500 m have a mean value of 35.1, which is consistent with previous vertical seismic profile (VSP) and laboratory measurements on the upper 500 m.

Electrical resistivity, formation factors, and sound velocity at DSDP Holes 75-530A and 75-530B

From 0 to 277 m at Site 530 are found Holocene to Miocene diatom ooze, nannofossil ooze, marl, clay, and debrisflow deposits; from 277 to 467 m are Miocene to Oligocene mud; from 467 to 1103 m are Eocene to late Albian Cenomanian interbedded mudstone, marlstone, chalk, clastic limestone, sandstone, and black shale in the lower portion; from 1103 to 1121 m are basalts. In the interval from 0 to 467 m, in Holocene to Oligocene pelagic oozes, marl, clay, debris flows, and mud, velocities are 1.5 to 1.8 km/s; below 200 m velocities increase irregularly with increasing depth. From 0 to 100 m, in Holocene to Pleistocene diatom and nannofossil oozes (excluding debris flows), velocities are approximately equivalent to that of the interstitial seawater, and thus acoustic reflections in the upper 100 m are primarily caused by variations in density and porosity. Below 100 or 200 m, acoustic reflections are caused by variations in both velocity and density. From 100 to 467 m, in Miocene-Oligocene nannofossil ooze, clay, marl, debris flows, and mud, acoustic anisotropy irregularly increases to 10%, with 2 to 5% being typical. From 467 to 1103 m in Paleocene to late Albian Cenomanian interbedded mudstone, marlstone, chalk, clastic limestone, and black shale in the lower portion of the hole, velocities range from 1.6 to 5.48 km/s, and acoustic anisotropies are as great as 47% (1.0 km/s) faster horizontally. Mudstone and uncemented sandstone have anisotropies which irregularly increase with increasing depth from 5 to 10% (0.2 km/s). Calcareous mudstones have the greatest anisotropies, typically 35% (0.6 km/s). Below 1103 m, basalt velocities ranged from 4.68 to 4.98 km/s. A typical value is about 4.8 km/s. In situ velocities are calculated from velocity data obtained in the laboratory. These are corrected for in situ temperature, hydrostatic pressure, and porosity rebound (expansion when the overburden pressure is released). These corrections do not include rigidity variations caused by overburden pressures. These corrections affect semiconsolidated sedimentary rocks the most (up to 0.25 km/s faster). These laboratory velocities appear to be greater than the velocities from the sonic log. Reflection coefficients derived from the laboratory data, in general, agree with the major features on the seismic profiles. These indicate more potential reflectors than indicated from the reflection coefficients derived using the Gearhart-Owen Sonic Log from 625 to 940 m, because the Sonic Log data average thin beds. Porosity-density data versus depth for mud, mudstone, and pelagic oozes agree with data for similar sediments as summarized in Hamilton (1976). At depths of about 400 m and about 850 m are zones of relatively higher porosity mudstones, which may suggest anomalously high pore pressure; however, they are more probably caused by variations in grain-size distribution and lithology. Electrical resistivity (horizontal) from 625 to 950 m ranged from about 1.0 to 4.0 ohm-m, in Maestrichtian to Santonian- Coniacian mudstone, marlstone, chalk, clastic limestone, and sandstone. An interstitial-water resistivity curve did not indicate any unexpected lithology or unusual fluid or gas in the pores of the rock. These logs were above the black shale beds. From 0 to 100 m at Sites 530 and 532, the vane shear strength on undisturbed samples of Holocene-Pleistocene diatom and nannofossil ooze uniformly increases from about 80 g/cm**2 to about 800 g/cm**2. From 100 to 300 m, vane shear strength of Pleistocene-Miocene nannofossil ooze, clay, and marl are irregular versus depth with a range of 500 to 2300 g/cm**2; and at Site 532 the vane shear strength appears to decrease irregularly and slightly with increasing depth (gassy zone). Vane shear strength values of gassy samples may not be valid, for the samples may be disturbed as gas evolves, and the sediments may not be gassy at in situ depths.