Science.gov

Sample records for adjacent continental slope

  1. Distribution of Pasiphaea japonica larvae in submarine canyons and adjacent continental slope areas in Toyama Bay, Sea of Japan

    NASA Astrophysics Data System (ADS)

    Nanjo, Nobuaki; Katayama, Satoshi

    2014-09-01

    The horizontal and vertical distribution of Pasiphaea japonica larvae, which included larval stages and postlarval or later stages, were investigated in Toyama Bay located in central Japan. The horizontal distributions in the inner part of the bay were investigated by oblique hauls from 10 m above the sea-bottom to the surface using a Remodeled NORPAC net (LNP net) in May, August, November 2005, January, March, April, July, September, December 2006, March-September, November-December 2007, and January-March 2008. The vertical distributions were investigated by concurrent horizontal hauls at the depths of 0, 50, 100, 150, 200, and 250 m using a Motoda net (MTD net) in January, March, April, July, September, and December 2006. Mean density of larvae was higher in submarine canyons which dissect the continental shelf and run to the mouth of river, than adjacent continental slope areas. Larvae densely aggregated in the canyon head. Vertical distribution of the larval stages concentrated in the depth range of 100-150 m in both daytime and nighttime, and larvae in the postlarval or later stages showed diel vertical distribution over a wider depth range than larval stages. Our results indicate the possibility of a larval aggregation in energy-rich habitats, and indicated two important roles of submarine canyons, which were larval retention and high food supply.

  2. Degrading permafrost and gas hydrate under the Beaufort Shelf and marine gas hydrate on the adjacent continental slope

    NASA Astrophysics Data System (ADS)

    Paull, C. K.; Dallimore, S. R.; Hughes Clarke, J. E.; Blasco, S.; Melling, H.; Lundsten, E.; Vagle, S.; Collett, T. S.

    2011-12-01

    The sub-seafloor under the Arctic Shelf is arguably the part of the Earth that is undergoing the most dramatic warming. In the southern Beaufort Sea, the shelf area was terrestrially exposed during much of the Quaternary period when sea level was ~120m lower than present. As a consequence, many areas are underlain by >600m of ice-bonded permafrost that conditions the geothermal regime such that the base of the methane hydrate stability can be >1000m deep. Marine transgression has imposed a change in mean annual surface temperature from -15°C or lower during periods of terrestrial exposure, to mean annual sea bottom temperatures near 0°C. The thermal disturbance caused by transgression is still influencing the upper km of subsurface sediments. Decomposition of gas hydrate is inferred to be occurring at the base and the top of the gas hydrate stability zone. As gas hydrate and permafrost intervals degrade, a range of processes occur that are somewhat unique to this setting. Decomposition of gas hydrate at depth can cause sediment weakening, generate excess pore water pressure, and form free gas. Similarly, thawing permafrost can cause thaw consolidation, liberate trapped gas bubbles in ice bonded permafrost. Understanding the connection between deep subsurface processes generated by transgression, surficial sediment processes near the seafloor, and gas flux into the ocean and atmosphere is important to assessing geohazard and environmental conditions in this setting. In contrast, conditions for marine gas hydrate formation occur on the adjacent continental slope below ~270m water depths. In this paper, we present field observations of gas venting from three geologically distinct environments in the Canadian Beaufort Sea, two on the shelf and one on the slope. A complimentary paper by Dallimore et al reviews the geothermal changes conditioning this environment. Vigorous methane venting is occurring over Pingo-Like-Features (PLF) on the mid-shelf. Diffuse venting of

  3. Habitat use and preferences of cetaceans along the continental slope and the adjacent pelagic waters in the western Ligurian Sea

    NASA Astrophysics Data System (ADS)

    Azzellino, A.; Gaspari, S.; Airoldi, S.; Nani, B.

    2008-03-01

    The physical habitat of cetaceans occurring along the continental slope in the western Ligurian Sea was investigated. Data were collected from two different sighting platforms, one of the two being a whale-watching boat. Surveys, conducted from May to October and from 1996 to 2000, covered an area of approximately 3000 km 2 with a mean effort of about 10,000 km year -1. A total of 814 sightings was reported, including all the species occurring in the area: Stenella coeruleoalba, Balaenoptera physalus, Physeter macrocephalus, Globicephala melas, Grampus griseus, Ziphius cavirostris, Tursiops truncatus, Delphinus delphis. A Geographic Information System was used to integrate sighting data to a set of environmental characteristics, which included bottom gradient, area between different isobaths, and length and linearity of the isobaths within a cell unit. Habitat use was analysed by means of a multi-dimensional scaling, MDS, analysis. Significant differences were found in the habitat preference of most of the species regularly occurring in the area. Bottlenose dolphin, Risso's dolphin, sperm whale and Cuvier's beaked whale were found strongly associated to well-defined depth and slope gradient characteristics of the shelf-edge and the upper and lower slope. The hypothesis of habitat segregation was considered for Risso's dolphin, sperm whale and Cuvier's beaked whale. Canonical discriminant functions using depth and slope as predictors outlined clear and not overlapping habitat preferences for Risso's dolphin and Cuvier's beaked whale, whereas a partial overlapping of the habitat of the other two species was observed for sperm whale. Such a partitioning of the upper and lower slope area may be the result of the common feeding habits and suggests a possible competition of these three species. A temporal segregation in the use of the slope area was also observed for sperm whales and Risso's dolphins. Fin whales, and the occasionally encountered common dolphin and long

  4. Active diapirism and slope steepening, northern Gulf of Mexico continental slope.

    USGS Publications Warehouse

    Martin, R.G.; Bouma, A.H.

    1982-01-01

    Large diapiric and nondiapiric masses of Jurassic salt and Tertiary shale underlie the northern Gulf of Mexico continental slope and adjacent outer continental shelf. Local steepening of the sea floor in response to the vertical growth of these structures is a serious concern to those involved in the site selection and the construction of future oil and gas production and transportation facilities in this frontier petroleum province. The evidence given in this paper supports the conclusion that the present continental slope region of the northern Gulf of Mexico is undergoing active diapirism and consequent slope steepening. Because most of the sediment on the flanks of diapiric structures consists of underconsolidated muds, slumping will take place regularly in response to further diapiric movement.-from Authors

  5. Ocean processes at the Antarctic continental slope.

    PubMed

    Heywood, Karen J; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D; Queste, Bastien Y; Stevens, David P; Wadley, Martin; Thompson, Andrew F; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K; Smith, Walker

    2014-07-13

    The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean-atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

  6. Ocean processes at the Antarctic continental slope

    PubMed Central

    Heywood, Karen J.; Schmidtko, Sunke; Heuzé, Céline; Kaiser, Jan; Jickells, Timothy D.; Queste, Bastien Y.; Stevens, David P.; Wadley, Martin; Thompson, Andrew F.; Fielding, Sophie; Guihen, Damien; Creed, Elizabeth; Ridley, Jeff K.; Smith, Walker

    2014-01-01

    The Antarctic continental shelves and slopes occupy relatively small areas, but, nevertheless, are important for global climate, biogeochemical cycling and ecosystem functioning. Processes of water mass transformation through sea ice formation/melting and ocean–atmosphere interaction are key to the formation of deep and bottom waters as well as determining the heat flux beneath ice shelves. Climate models, however, struggle to capture these physical processes and are unable to reproduce water mass properties of the region. Dynamics at the continental slope are key for correctly modelling climate, yet their small spatial scale presents challenges both for ocean modelling and for observational studies. Cross-slope exchange processes are also vital for the flux of nutrients such as iron from the continental shelf into the mixed layer of the Southern Ocean. An iron-cycling model embedded in an eddy-permitting ocean model reveals the importance of sedimentary iron in fertilizing parts of the Southern Ocean. Ocean gliders play a key role in improving our ability to observe and understand these small-scale processes at the continental shelf break. The Gliders: Excellent New Tools for Observing the Ocean (GENTOO) project deployed three Seagliders for up to two months in early 2012 to sample the water to the east of the Antarctic Peninsula in unprecedented temporal and spatial detail. The glider data resolve small-scale exchange processes across the shelf-break front (the Antarctic Slope Front) and the front's biogeochemical signature. GENTOO demonstrated the capability of ocean gliders to play a key role in a future multi-disciplinary Southern Ocean observing system. PMID:24891389

  7. Continental margin of Western europe: slope progradation and erosion.

    PubMed

    Curray, J R; Moore, D G; Belderson, R H; Stride, A H

    1966-10-14

    Reflection profiling of the continental margin off western Europe shows seaward-dipping continental-slope deposits that have been dissected by submarine canyons west of the English Channel. These records refute previous interpretation of structural benches of older, nearly horizontal strata outcropping on the slope face. PMID:17810307

  8. Circulation and exchange processes over the continental shelf and slope

    SciTech Connect

    Csanady, G.T.

    1988-01-01

    The theme of the work during the past triennium has been the SEEP experiment, data interpretation and modeling related to the goals of the experiment, and was characterized by increasing cooperation with colleagues from other disciplines. The theoretical contributions dealt with shelf-slope interaction, the dynamics and climatology of currents over the continental slope, and the behavior of fate of organic particles. Observational papers discussed various exchange mechanisms at the shelf edge, with special attention to particle exchange, and the quiescence of currents over the mid continental slope which is presumably responsible for the accumulation of organic particles.

  9. The shaping of continental slopes by internal tides

    USGS Publications Warehouse

    Cacchione, D.A.; Pratson, Lincoln F.; Ogston, A.S.

    2002-01-01

    The angles of energy propagation of semidiurnal internal tides may determine the average gradient of continental slopes in ocean basins (???2 to 4 degrees). Intensification of near-bottom water velocities and bottom shear stresses caused by reflection of semi-diurnal internal tides affects sedimentation patterns and bottom gradients, as indicated by recent studies of continental slopes off northern California and New Jersey. Estimates of bottom shear velocities caused by semi-diurnal internal tides are high enough to inhibit deposition of fine-grained sediment onto the slopes.

  10. Observations of energetic turbulence on the Weddell Sea continental slope

    NASA Astrophysics Data System (ADS)

    Fer, Ilker; Darelius, Elin; Daae, Kjersti B.

    2016-01-01

    Turbulence profile measurements made on the upper continental slope and shelf of the southeastern Weddell Sea reveal striking contrasts in dissipation and mixing rates between the two sites. The mean profiles of dissipation rates from the upper slope are 1-2 orders of magnitude greater than the profiles collected over the shelf in the entire water column. The difference increases toward the bottom where the dissipation rate of turbulent kinetic energy and the vertical eddy diffusivity on the slope exceed 10-7 W kg-1 and 10-2 m2 s-1, respectively. Elevated levels of turbulence on the slope are concentrated within a 100 m thick bottom layer, which is absent on the shelf. The upper slope is characterized by near-critical slopes and is in close proximity to the critical latitude for semidiurnal internal tides. Our observations suggest that the upper continental slope of the southern Weddell Sea is a generation site of semidiurnal internal tide, which is trapped along the slope along the critical latitude, and dissipates its energy in a m thick layer near the bottom and within km across the slope.

  11. Nepheloid layers and internal waves over continental shelves and slopes

    USGS Publications Warehouse

    Cacchione, D.A.; Drake, D.E.

    1986-01-01

    Theoretical and laboratory results indicate that bottom velocities within shoaling internal gravity waves intensify upslope approximately inversely proportional to the water depth. The elevated velocities (and bottom stresses) caused by shoaling and, possibly, breaking internal waves might explain the generation and maintenance of near-bottom nepheloid zones and attached turbid plumes that have been observed over certain continental shelves and slopes. This process is proposed as an explanation of zones of relatively low transmissibility that emanate from the upper continental slope near Newport submarine canyon off southern California. ?? 1986 Springer-Verlag New York Inc.

  12. Is there a distinct continental slope fauna in the Antarctic?

    NASA Astrophysics Data System (ADS)

    Kaiser, Stefanie; Griffiths, Huw J.; Barnes, David K. A.; Brandão, Simone N.; Brandt, Angelika; O'Brien, Philip E.

    2011-02-01

    The Antarctic continental slope spans the depths from the shelf break (usually between 500 and 1000 m) to ˜3000 m, is very steep, overlain by 'warm' (2-2.5 °C) Circumpolar Deep Water (CDW), and life there is poorly studied. This study investigates whether life on Antarctica's continental slope is essentially an extension of the shelf or the abyssal fauna, a transition zone between these or clearly distinct in its own right. Using data from several cruises to the Weddell Sea and Scotia Sea, including the ANDEEP (ANtarctic benthic DEEP-sea biodiversity, colonisation history and recent community patterns) I-III, BIOPEARL (BIOdiversity, Phylogeny, Evolution and Adaptive Radiation of Life in Antarctica) 1 and EASIZ (Ecology of the Antarctic Sea Ice Zone) II cruises as well as current databases (SOMBASE, SCAR-MarBIN), four different taxa were selected (i.e. cheilostome bryozoans, isopod and ostracod crustaceans and echinoid echinoderms) and two areas, the Weddell Sea and the Scotia Sea, to examine faunal composition, richness and affinities. The answer has important ramifications to the link between physical oceanography and ecology, and the potential of the slope to act as a refuge and resupply zone to the shelf during glaciations. Benthic samples were collected using Agassiz trawl, epibenthic sledge and Rauschert sled. By bathymetric definition, these data suggest that despite eurybathy in some of the groups examined and apparent similarity of physical conditions in the Antarctic, the shelf, slope and abyssal faunas were clearly separated in the Weddell Sea. However, no such separation of faunas was apparent in the Scotia Sea (except in echinoids). Using a geomorphological definition of the slope, shelf-slope-abyss similarity only changed significantly in the bryozoans. Our results did not support the presence of a homogenous and unique Antarctic slope fauna despite a high number of species being restricted to the slope. However, it remains the case that there may be

  13. An Open-Ocean Wide Analysis of the Slope of the Continental Slope and Internal Tides

    NASA Astrophysics Data System (ADS)

    Pratson, L. F.; Cacchione, D.

    2002-12-01

    Cacchione and others (Science 296, 724 (2002)) show that a correlation exists between the angles of energy propagation of semidiurnal tides and the average gradient of the continental slope in the US STRATAFORM study areas offshore New Jersey and California. Based on this correlation, they propose that internal tides may be a strong influence on the slope of the continental slope worldwide by affecting sedimentation patterns through the bottom shear stresses the tides generate. For the internal tide and other internal waves, the angle of energy propagation, c, is given by c = (σ 2 - f2) / (N2 - σ 2) where σ is the internal wave frequency (0.081 cph for semi-diurnal tides), N is the Brunt VÂäisÂälÂä frequency, and f is the local inertial frequency, which is a function of latitude \\phi, i.e., f=(sinφ )/12 cph. Assuming N is relatively constant with latitude, c will be greatest near the equator (where the angle is undefined) and decrease toward the poles. The gradient of the continental slope should behave similarly if the internal tide is the primary influence on the gradient. We test these hypotheses by computing c and the mean gradient of the continental slope as a function of latitude in the western Pacific, the eastern and western Atlantic, and the Indian Oceans. c is computed from the mean annual temperature and salinity measurements contained in the NOAA 1998 World Ocean Database, while the mean slope gradients are computed from the Scripps/NOAA ETOPO2 2-minute gridded global topography and bathymetry. As hypothesized, c systematically decreases with increasing latitude in all three ocean basins, gradually falling from a high of ~4° near the equator to a low of <2° at 60° latitude, which is the poleward most extent of the ETOPO2 dataset. Over this latitudinal range, N in fact also decreases due to a deepening and smoothing of the main pycnocline, but it decreases slower than f thus causing the decrease in c. By contrast, the mean slope of the

  14. Interaction of dipole eddies with the western continental slope of the Mozambique Channel

    NASA Astrophysics Data System (ADS)

    Roberts, Michael J.; Ternon, Jean-François; Morris, Tamaryn

    2014-02-01

    Sea Level Anomaly (SLA) data were used to track a southward propagating eddy dipole along the western slope of the Mozambique Channel over some 6 months. In April 2005, this dipole (with the cyclone to the south) was close to the continental slope off southern Mozambique. The contact zone between the contra-rotating vortices and the slope was surveyed by ship using onboard (S-)ADCP and CTD lines. The data showed strong (>1.4 m s-1) southward (geostrophic) currents over the slope adjacent to the anticyclone with horizontal divergence over the shelf edge. Significant slope upwelling between the dipole and the shelf was evident, concomitant with enhanced nutrient and chlorophyll levels enriching shelf near-surface waters. Satellite observations depicted a 300 km long surface chlorophyll filament extending offshore in the frontal zone between the contra-rotating vortices. A satellite-tracked drifter deployed at the coastal base of this filament confirmed the offshore advection of chlorophyll-enriched shelf water, which ultimately wrapped around the cyclone and filling its centre. The slope upwelling was also clearly evident in hourly temperature data collected by a recorder deployed on a nearby reef (Zambia Reef) in a depth of 18 m. According to the SLA data, the dipole took several weeks to pass Zambia Reef causing prolonged bouts of upwelling that finally ceased when it left the continental slope and moved southwards into the open ocean. Further analysis showed that lone anticyclones and cyclones against the Mozambique continental shelf also induce slope upwelling as a result of horizontal divergence created by the radial circulation of the vortex. In the case of cyclones, the divergence occurs north of the contact zone. Overall, this case study confirms that eddies moving southwards along the western side of the Mozambique Channel are the main mechanism for pumping nutrients into the otherwise oligotrophic surface waters, and moreover, provide a vigorous mechanism

  15. Constraining the Formation of Submarine Gullies on Continental Slopes

    NASA Astrophysics Data System (ADS)

    Shumaker, L.; Jobe, Z. R.; Graham, S. A.

    2015-12-01

    Submarine gullies are ubiquitous on continental slopes and steep areas of seafloor worldwide, but their role in sediment transport remains unresolved. Direct observation of flows in the submarine realm is rare and expensive, but by analyzing basic geometries of gullies in the sedimentary record, it is possible to gain insight into the behavior of the flows that formed them. In shallow 3D seismic reflection data from the Taranaki Basin, New Zealand, we document gullies preserved in a Pliocene-Pleistocene progradational margin sequence. These gullies commonly form aggradational complexes hundreds of meters thick, showing alternating periods of erosion, inactivity, and roughly self-similar aggradation in response to slope sedimentation. Erosional phases speak of modification by energetic turbidity currents, whereas sediment drapes point to extended periods of flow quiescence and hemipelagic deposition. We pair these observations with morphometrics of over 600 gullies in seafloor bathymetry from continental margins worldwide. The slopes of these modern gullies and interfluves are both well described by a power-law decay with along-profile distance. The decay of slopes with distance (concavity) obtained from power-law relationships for interfluves and gullies are well correlated, although gullies attain higher slopes and are slightly more concave than neighboring interfluves. The self-similar growth of gullies in the subsurface and the strong similarity between gully and interfluve profiles in all datasets suggests a link between the evolution of gullies and of the slopes on which they form. We conclude by presenting a conceptual model in which gully and slope morphology are tightly coupled.

  16. Recent carbonate slope development on southwest Florida continental margin

    SciTech Connect

    Brooks, G.R.; Holmes, C.W.

    1987-05-01

    The southwest Florida continental slope bordering the Florida Strait contains a thick sequence of seaward-prograding sediments. Sediments consist principally of a mixture of shallow water and pelagic carbonate sands and muds deposited rapidly on the upper slope. Sedimentary patterns are interpreted to be a function of high-frequency sea level fluctuations. Most vigorous off-shelf transport and highest sedimentation rates (exceeding 2.5 m/1000 years) occur during early transgressions and late regressions when water depths on the shelf are shallow. During sea level highstands, off-shelf transport is less vigorous and sedimentation rates decrease. During sea level lowstands, no off-shelf transport takes place and erosion of the previously deposited sequence occurs as a result of an increase in erosional capacity of the Florida Current. The presence of at least nine such sequences, all with similar characteristics, indicates that these processes have been occurring since at least the late Pleistocene in response to high-frequency glacial fluctuations. The location of the southwest Florida slope between the rimmed Bahama platform and the nonrimmed remainder of the west Florida margin, as well as similarities with ancient carbonate slope deposits formed during periods when shelf-edge reef-forming organisms were lacking, suggest that depositional patterns on the southwest Florida slope may be indicative of a transition between rimmed and nonrimmed carbonate platform environments. The southwest Florida slope may provide a valuable modern analog for identifying similar transitional environments in the geologic record.

  17. An Experimental Study of Submarine Canyon Evolution on Continental Slopes

    NASA Astrophysics Data System (ADS)

    Lai, S. Y.; Gerber, T. P.; Amblas, D.

    2013-12-01

    Submarine canyons define the morphology of many continental slopes and are conduits for the transport of sediment from shallow to deep water. Though the origin and evolution of submarine canyons is still debated, there is general agreement that sediment gravity flows play an important role. Here we present results from a simple, reduced-scale sandbox experiment designed to investigate how sediment gravity flows generate submarine canyons. In the experiments, gravity flows were modeled using either sediment-free or turbid saline currents. Unconfined flows were released onto an inclined bed of sand bounded on the downstream end by a movable floor that was incrementally lowered during the course of an experiment to produce an escarpment. This design was developed to represent the growth of relief across the continental slope. To monitor canyon evolution on the slope, we placed an overhead DSLR camera to record vivid time-lapse videos. At the end of each experimental stage we scanned the topography by imaging a series of submerged laser stripes, each projected from a motor-driven transverse laser sheet, onto a calibrated Cartesian coordinate system to produce high resolution bathymetry without draining the ambient water. In areas unaffected by the flows, we observe featureless, angle-of-repose submarine slopes formed by retrogressive breaching processes. In contrast, areas influenced by gravity flows cascading across the shelf break are deeply incised by submarine canyons with well-developed channel networks. Our results show that downslope gravity flows and submarine falling base level are both required to produce realistic canyon morphologies at laboratory scale. Though our mechanism for generating relief may be a rather crude analogue for the processes driving slope evolution, we hope our novel approach can stimulate new questions about the coevolution of canyons and slopes and motivate further experimental work to address them.

  18. Morphology, origin and evolution of Pleistocene submarine canyons, New Jersey continental slope

    NASA Astrophysics Data System (ADS)

    Bhatnagar, T.; Mountain, G. S.

    2015-12-01

    Submarine canyons serve as important conduits for transport of detrital sediments from nearshore and shelf environments to adjacent deep marine basins. However, the processes controlling the formation, maintenance, and fill of these sediment pathways are complex. This study presents an investigation of these systems at the New Jersey continental margin using a grid of high-resolution, 48-channel seismic reflection data collected in 1995 on the R/V Oceanus cruise Oc270 as a part of the STRATAFORM initiative. The aim is to shed new light on the origin and role of submarine canyons in Pleistocene sedimentation beneath the outer shelf and upper continental slope. Preliminary investigation of the Pleistocene interval reveals prominent unconformities tied to and dated with published studies at 7 sites drilled by ODP Legs 150 and 174A. The profiles of the continental slope unveil a series of abandoned and now buried submarine canyons that have influenced the development of modern canyons. Mapping these systems has revealed a range of canyon geometries, including U, V-shaped and flat-bottomed cross sections, each suggesting different histories. At least three types of seismic facies constitute the canyon fills: parallel onlap, interpreted as infilling by alternating coarser turbidites and finer hemipelagic sediments, chaotic infill, signifying structureless, massive debris flow deposition, and lateral accretion infill by both turbidity and bottom currents. Canyon formation and development appear to be strongly influenced by variations in sediment supply, grain size, and currents on the continental slope. One goal of our research is to establish if the canyons were initiated by failures at the base of the slope followed by upslope erosion, or by erosion at the shelf slope transition, and then downslope extension by erosive events. No single model accounts for all canyons. The history of these canyons may elucidate the extent to which the shelf was exposed during sea

  19. Coherent sea-level fluctuations along the global continental slope.

    PubMed

    Hughes, Chris W; Meredith, Michael P

    2006-04-15

    Signals in sea-level or, more properly, sub-surface pressure (SSP; sea-level corrected for the inverse barometer effect) are expected to propagate rapidly along the continental slope due to the effect of sloping topography on wave modes, resulting in strongly correlated SSP over long-distances. Observations of such correlations around the Arctic and Antarctic are briefly reviewed, and then extended using satellite altimetry to the rest of the global continental slope. It is shown that such long-distance correlations are common, especially in extra-tropical regions. Simple correlations from altimetry cannot, however, establish the wave speed, or whether waves are responsible for the correlations as opposed to large-scale coherence in the forcing. A case study around South America is used to highlight some of the complications, and is found to strengthen the case for the importance of wave modes in such long-distance SSP coherence, although more detailed in situ data are required to resolve the cause of the correlations. PMID:16537146

  20. Benthic polychaete diversity patterns and community structure in the Whittard Canyon system and adjacent slope (NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Gunton, Laetitia M.; Neal, Lenka; Gooday, Andrew J.; Bett, Brian J.; Glover, Adrian G.

    2015-12-01

    We examined deep-sea macrofaunal polychaete species assemblage composition, diversity and turnover in the Whittard Canyon system (NE Atlantic) using replicate megacore samples from three of the canyon branches and one site on the continental slope to the west of the canyon, all at ~3500 m water depth. A total of 110 polychaete species were recorded. Paramphinome jeffreysii was the most abundant species (2326 ind. m-2) followed by Aurospio sp. B (646 ind. m-2), Opheliidae sp. A (393 ind. m-2), Prionospio sp. I (380 ind. m-2), and Ophelina abranchiata (227 ind. m-2). Species composition varied significantly across all sites. From west to east, the dominance of Paramphinome jeffreysii increased from 12.9% on the slope to 39.6% in the Eastern branch. Ordination of species composition revealed that the Central and Eastern branches were most similar, whereas the Western branch and slope sites were more distinct. High abundances of P. jeffreysii and Opheliidae sp. A characterised the Eastern branch of the canyon and may indicate an opportunistic response to a possible recent input of organic matter inside the canyon. Species richness and diversity indices were higher on the slope compared with inside the canyon, and the slope site had higher species evenness. Within the canyon, species diversity between branches was broadly similar. Despite depressed diversity within the canyon compared with the adjacent slope, the fact that 46 of the 99 polychaete species found in the Whittard Canyon were not present on the adjacent slope suggests that this feature may enhance the regional species pool. However, our sampling effort on the adjacent slope was insufficient to confirm this conclusion.

  1. Role of submarine canyons in the US Atlantic Continental Slope and upper Continental rise development

    SciTech Connect

    McGregor, B.A.

    1984-04-01

    Three areas of the US Atlantic continental slope and rise (seaward of George Bank, Delaware Bay, and Pamlico Sound north of Cape Hatteras) have been studied using seismic reflection profiles and mid-range sidescan-sonar data. The continental slope in all three areas is dissected by numerous submarine canyons. The general sea floor gradient of the slope and the morphology of the rise, however, vary among the areas. Submarine canyons are dominant morphologic features on the slope and have an important function in sediment transport and distribution on the rise. In the study area north of Cape Hatteras, however, the low relief of the rise topography indicates that ocean currents flowing parallel to the margin may also affect sediment distribution on the rise. Morphology and sedimentation patterns suggest that differences in canyon ages exist both within each area and among the areas. Spatial and temporal variability of canyon activity is important in determining sediment sources for the construction of the rise. Although the US Atlantic slope and rise are relatively sediment-starved at present, mid-range sidescan data and submersible observations and samples suggest that periodic sediment transport events occur within the canyons.

  2. Overpressure, Flow Focusing, Compaction and Slope Stability on the continental slope: Insights from IODP Expedition 308

    NASA Astrophysics Data System (ADS)

    Flemings, P. B.

    2010-12-01

    Integrated Ocean Drilling Program Expepedition 308 used direct measurements of pore pressure, analysis of hydromechanical properties, and geological analysis to illuminate how sedimentation, flow focusing, overpressure, and slope stability couple beneath the seafloor on the deepwater continental slope in the Gulf of Mexico. We used pore pressure penetrometers to measure severe overpressures (60% of the difference between lithostatic stress and hydrostatic pressure) that extend from the seafloor for 100’s of meters. We ran uniaxial consolidation experiments on whole core and found that although permeability is relatively high near the seafloor, the sediments are highly compressible. As a result, the coefficient of consolidation (the hydraulic diffusivity) is remarkably constant over a large range of effective stresses. This behavior accounts for the high overpressure that begins near the seafloor and extends to depth. Forward modeling suggests that flow is driven laterally along a permeable unit called the Blue Unit. Calculations suggest that soon after deposition, lateral flow lowered the effective stress and triggered the submarine landslides that we observe. Later in the evolution of this system, overpressure may have pre-conditioned the slope to failure by earthquakes. Results from IODP Expedition 308 illustrate how pore pressure and sedimentation control the large-scale form of continental margins, how submarine landslides form, and provide strategies for designing stable drilling programs.

  3. Evolution of continental slope gullies on the northern california margin

    USGS Publications Warehouse

    Spinelli, G.A.; Field, M.E.

    2001-01-01

    A series of subparallel, downslope-trending gullies on the northern California continental slope is revealed on high-resolution seismic reflection profiles imaging the uppermost 50 m of sediment. The gullies are typically 100 m wide and have 1 to 3 m of relief. They extend for 10 to 15 km down the slope and merge into larger channels that feed the Trinity Canyon. In the lower half of the 50 m stratigraphic section, the gullies increase in both relief and number up section, to maxima at a surface 5 to 10 m below the last glacial maximum lowstand surface. Gully relief increased as interfluves aggraded more rapidly than thalwegs. Erosion is not evident in the gully bottoms, therefore gully growth was probably due to reduced sediment deposition within the gullies relative to that on interfluves. As the gullies increased in relief, their heads extended upslope toward the shelfbreak. At all times, a minimum of 10 km of non-gullied upper slope and shelf stretched between the heads of the gullies and the paleo-shoreline; the gullies did not connect with a subaerial drainage network at any time. Gully growth occurred when the gully heads were in relatively shallow water (??? 200 m paleo-water depth) and were closest to potential sediment sources. We suggest that prior to the last glacial maximum, the Mad River, then within 10 km of the gully heads, supplied sediment to the upper slope, which fed downslope-eroding sediment flows. These flows removed sediment from nearly parallel gullies at a rate slightly slower than sediment accumulation from the Eel River, 40 km to the south. The process or processes responsible for gully growth and maintenance prior to the last glacial maximum effectively ceased following the lowstand, when sea level rose and gully heads lay in deeper water (??? 300 m water depth), farther from potential sediment sources. During sea-level highstand, the Mad River is separated from the gully heads by a shelf 30 km wide and no longer feeds sediment flows

  4. Slope-stability analysis and creep susceptibility of Quaternary sediments on the northeastern United States continental slope

    USGS Publications Warehouse

    Booth, James S.; Silva, Armand J.; Jordan, Stephen A.

    1984-01-01

    The continental slope off the northeastern United States is a relatively steep, morphologically complex surface which shows abundant evidence of submarine slides and related processes. Because this area may be developed by the petroleum industry, questions arise concerning the potential for further slope failures or unacceptable deformations and the conditions necessary to cause such instabilities. Accordingly, a generalized analysis of slope stability and the stress—strain—time-dependent behavior of the sediments is being conducted.

  5. Observational evidence for tidal straining over a sloping continental shelf

    NASA Astrophysics Data System (ADS)

    Endoh, Takahiro; Yoshikawa, Yutaka; Matsuno, Takeshi; Wakata, Yoshinobu; Lee, Keun-Jong; Umlauf, Lars

    2016-04-01

    Straining of a horizontal density gradient by tidal currents acts to periodically produce and destroy near-bottom stratification, which has been shown to modulate turbulence in the bottom boundary layer (BBL). Previous observations of such periodic variations have been limited to the coastal ocean and estuaries, where horizontal density gradients are maintained by river runoff or differential heating. In the present study, we show evidence for the existence of tidal straining over the continental shelf, outside any regions of freshwater influence, where horizontal density gradients are likely to result from the projection of the interior vertical stratification onto sloping topography. Based on microstructure data obtained in the East China Sea, we demonstrate that the tidal current shear interacting with the cross-isobath density gradient results in semidiurnal switching between unstable and stable stratification in the lower part of the BBL. The cycle of turbulent dissipation is quarter-diurnal, corresponding to the semidiurnal variation of tidal current shear. In addition, a noticeable diurnal modulation in stratification as well as a significant diurnal cycle of turbulent dissipation are observed in the upper part of the BBL, where the time evolution of stratification is dominated by tidal advection, rather than tidal straining.

  6. Research activities on submarine landslides in gentle continental slope

    NASA Astrophysics Data System (ADS)

    Morita, S.; Goto, S.; Miyata, Y.; Nakamura, Y.; Kitahara, Y.; Yamada, Y.

    2013-12-01

    In the north Sanrikuoki Basin off Shimokita Peninsula, NE Japan, a great number of buried large slump deposits have been identified in the Pliocene and younger formations. The basin has formed in a very gentle continental slope of less than one degree in gradient and is composed of well-stratified formations which basically parallel to the present seafloor. This indicates that the slumping have also occurred in such very gentle slope angle. The slump units and their slip surfaces have very simple and clear characteristics, such as layer-parallel slip on the gentle slope, regularly imbricated internal structure, block-supported with little matrix structure, widespread dewatering structure, and low-amplitude slip surface layer. We recognize that the large slump deposits group of layer-parallel slip in this area is an appropriate target to determine 'mechanism of submarine landslides', that is one of the subjects on the new IODP science plan for 2013 and beyond. So, we started some research activities to examine the feasibility of the future scientific drilling. The slump deposits were recognized basically by 3D seismic analysis. Further detailed seismic analysis using 2D seismic data in wider area of the basin is being performed for better understanding of geologic structure of the sedimentary basin and the slump deposits. This will be good source to extract suitable locations for drill sites. Typical seismic features and some other previous studies imply that the formation fluid in this study area is strongly related to natural gas, of which condition is strongly affected by temperature. So, detailed heat flow measurements was performed in the study area in 2013. For that purpose, a long-term water temperature monitoring system was deployed on the seafloor in October, 2012. The collected water temperature variation is applied to precise correction of heat flow values. Vitrinite reflectance analysis is also being carried out using sediments samples recovered by IODP

  7. Numerical Internal Tide Scattering, Diffraction, and Dissipation on the Tasman Continental Slope

    NASA Astrophysics Data System (ADS)

    Klymak, J. M.; Simmons, H. L.; MacKinnon, J. A.; Alford, M. H.; Pinkel, R.

    2014-12-01

    Internal tides generated at steep topography tend to propagate far from their source with little local mixing. Where does this energy dissipate? One candidate is via reflection on continental slopes. The upcoming Tasmanian Internal Tide Experiment aims to look at the reflection of internal tide generated near New Zealand and track its reflection from the Tasmanian Continental Slope. Here we consider numerical studies to track the propagation of the internal tide onto this slope and its dissipation. We find a strong interference patterns sets up, as expected from a reflecting tide. The pattern is complicated by the ``Tasman Rise'' positioned near the center of the incoming internal tide beam, causing a diffraction pattern to focus and defocus the tide along the slope. Dissipative mechanisms on the slope include turbulent lee waves from small cross-slope ridges, and along-slope lee-waves trapped and breaking in corrugations in the slope.

  8. The speciation of marine particulate iron adjacent to active and passive continental margins

    NASA Astrophysics Data System (ADS)

    Lam, Phoebe J.; Ohnemus, Daniel C.; Marcus, Matthew A.

    2012-03-01

    We use synchrotron-based chemical-species mapping techniques to compare the speciation of suspended (1-51 μm) marine particulate iron collected in two open ocean environments adjacent to active and passive continental margins. Chemical-species mapping provides speciation information for heterogeneous environmental samples, and is especially good for detecting spectroscopically distinct trace minerals and species that could not be detectable by other methods. The average oxidation state of marine particulate iron determined by chemical-species mapping is comparable to that determined by standard bulk X-ray Absorption Near Edge Structure spectroscopy. Using chemical-species mapping, we find that up to 43% of particulate Fe in the Northwest Pacific at the depth of the adjacent active continental margin is in the Fe(II) state, with the balance Fe(III). In contrast, particulate iron in the eastern tropical North Atlantic, which receives the highest dust deposition on Earth and is adjacent to a passive margin, is dominated by weathered and oxidized Fe compounds, with Fe(III) contributing 90% of total iron. The balance is composed primarily of Fe(II)-containing species, but we detected individual pyrite particles in some samples within an oxygen minimum zone in the upper thermocline. Several lines of evidence point to the adjacent Mauritanian continental shelf as the source of pyrite to the water column. The speciation of suspended marine particulate iron reflects the mineralogy of iron from the adjacent continental margins. Since the solubility of particulate iron has been shown to be a function of its speciation, this may have implications for the bioavailability of particulate iron adjacent to passive compared to active continental margins.

  9. Submarine canyon and slope processes of the U.S. Atlantic continental margin

    USGS Publications Warehouse

    McGregor, B.A.

    1983-01-01

    Two regions on the U.S. Atlantic continental margin were surveyed using single-channel, seismic-reflection profiling techniques: the Mid-Atlantic Continental Slope and Rise seaward of New Jersey in the vicinity of Baltimore Canyon and the Continental Slope and upper Rise just north of Cape Hatteras. Submarine canyons are the dominant morphologic feature in both areas. The Continental Slope in the Baltimore Canyon area has a general sea-floor gradient of 3?-4? and a width of approximately 40 km, whereas the study area north of Cape Hatteras has a general sea-floor gradient of approximately 9? and a width of 20 km. The dominant slope process differs in each area. In the Baltimore Canyon area, subbottom reflectors suggest that sediment deposition with progradation of the slope is related to canyon processes. In the study area north of Cape Hatteras, the canyons appear erosional and mass wasting is the dominant erosional process. Dominant slope processes appear to be correlated with the width and sea-floor gradient of the Continental Slope. Although the absolute age of the canyons is difficult to determine without rotary-drill cores for stratigraphic control, Baltimore Canyon is suggested to be older than the shelf-indenting canyon just north of Cape Hatteras. An anomalously large ridge flanking Baltimore Canyon on the upper rise appears to be related to canyon depositional and erosional processes.

  10. Submarine slope failures along the convergent continental margin of the Middle America Trench

    NASA Astrophysics Data System (ADS)

    Harders, Rieka; Ranero, CéSar R.; Weinrebe, Wilhelm; Behrmann, Jan H.

    2011-06-01

    We present the first comprehensive study of mass wasting processes in the continental slope of a convergent margin of a subduction zone where tectonic processes are dominated by subduction erosion. We have used multibeam bathymetry along ˜1300 km of the Middle America Trench of the Central America Subduction Zone and deep-towed side-scan sonar data. We found abundant evidence of large-scale slope failures that were mostly previously unmapped. The features are classified into a variety of slope failure types, creating an inventory of 147 slope failure structures. Their type distribution and abundance define a segmentation of the continental slope in six sectors. The segmentation in slope stability processes does not appear to be related to slope preconditioning due to changes in physical properties of sediment, presence/absence of gas hydrates, or apparent changes in the hydrogeological system. The segmentation appears to be better explained by changes in slope preconditioning due to variations in tectonic processes. The region is an optimal setting to study how tectonic processes related to variations in intensity of subduction erosion and changes in relief of the underthrusting plate affect mass wasting processes of the continental slope. The largest slope failures occur offshore Costa Rica. There, subducting ridges and seamounts produce failures with up to hundreds of meters high headwalls, with detachment planes that penetrate deep into the continental margin, in some cases reaching the plate boundary. Offshore northern Costa Rica a smooth oceanic seafloor underthrusts the least disturbed continental slope. Offshore Nicaragua, the ocean plate is ornamented with smaller seamounts and horst and graben topography of variable intensity. Here mass wasting structures are numerous and comparatively smaller, but when combined, they affect a large part of the margin segment. Farther north, offshore El Salvador and Guatemala the downgoing plate has no large seamounts but

  11. Circulation and exchange processes over the continental shelf and slope. Final report

    SciTech Connect

    Csanady, G.T.

    1988-12-31

    The theme of the work during the past triennium has been the SEEP experiment, data interpretation and modeling related to the goals of the experiment, and was characterized by increasing cooperation with colleagues from other disciplines. The theoretical contributions dealt with shelf-slope interaction, the dynamics and climatology of currents over the continental slope, and the behavior of fate of organic particles. Observational papers discussed various exchange mechanisms at the shelf edge, with special attention to particle exchange, and the quiescence of currents over the mid continental slope which is presumably responsible for the accumulation of organic particles.

  12. The structure of the mesoplankton community in the area of the continental slope of the St. Anna Trough (Kara Sea)

    NASA Astrophysics Data System (ADS)

    Flint, M. V.; Poyarkov, S. G.; Timonin, A. G.; Soloviev, K. A.

    2015-07-01

    Zooplankton samples and concomitant hydrophysical data have been obtained in the outer Kara shelf over the continental slope and adjacent deepwater region of the western spur of the St. Anna Trough in the last ten days of September in 2007 and 2011. Mesoplankton biomass in the examined regions in 2007, the warmest year of the last three decades, was 1.5-2 times higher than the relatively cold year of 2011. A frontal zone, distinct in temperature, salinity, and chlorophyll fluorescence in the surface sea layer was located over the continental slope. The temperature gradient in the frontal zone reached 0.25-0.67°C/km, and its salinity gradient reached 1.6-4.7 psu/km. An increase in mesoplankton biomass was associated with the frontal zone, which was especially pronounced in the upper layers of the water column. The average biomass content in the upper 50 m in the frontal maximum amounted to 1210 mg/m3 in 2007 and 972 mg/m3 in 2011, being two orders of magnitude higher than the outer shelf and the deepwater domain of the basin. The pteropod Limacina helicina was dominant at the slope maximum, accounting for up to 80% of mesoplankton biomass. The frontal zone over the slope also represented a distinct boundary separating the shelf mesoplankton community from the deepwater community, which drastically differed in composition and biomass.

  13. Spreading and slope instability at the continental margin offshore Mt Etna, imaged by high-resolution 2D seismic data

    NASA Astrophysics Data System (ADS)

    Gross, Felix; Krastel, Sebastian; Behrmann, Jan-Hinrich; Papenberg, Cord; Geersen, Jacob; Ridente, Domenico; Latino Chiocci, Francesco; Urlaub, Morelia; Bialas, Jörg; Micallef, Aaron

    2015-04-01

    Mount Etna is the largest active volcano in Europe. Its volcano edifice is located on top of continental crust close to the Ionian shore in east Sicily. Instability of the eastern flank of the volcano edifice is well documented onshore. The continental margin is supposed to deform as well. Little, however, is known about the offshore extension of the eastern volcano flank and its adjacent continental margin, which is a serious shortcoming in stability models. In order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano, we acquired and processed a new marine high-resolution seismic and hydro-acoustic dataset. The data provide new detailed insights into the heterogeneous geology and tectonics of shallow continental margin structures offshore Mt Etna. In a similiar manner as observed onshore, the submarine realm is characterized by different blocks, which are controlled by local- and regional tectonics. We image a compressional regime at the toe of the continental margin, which is bound to an asymmetric basin system confining the eastward movement of the flank. In addition, we constrain the proposed southern boundary of the moving flank, which is identified as a right lateral oblique fault movement north of Catania Canyon. From our findings, we consider a major coupled volcano edifice instability and continental margin gravitational collapse and spreading to be present at Mt Etna, as we see a clear link between on- and offshore tectonic structures across the entire eastern flank. The new findings will help to evaluate hazards and risks accompanied by Mt Etna's slope- and continental margin instability and will be used as a base for future investigations in this region.

  14. Morphobathymetry and formation processes of sediment waves in the Gulf of Valencia continental slope (NW Mediterranean).

    NASA Astrophysics Data System (ADS)

    Ribó, Marta; Puig, Pere; Lo Iacono, Claudio; Acosta, Juan; Muñoz, Araceli; Van Rooij, David; van Haren, Hans; Gomez-Ballesteros, Maria

    2014-05-01

    Recently acquired swath bathymetry and seismic datasets revealed the presence of a series of very-large undulations over the Gulf of Valencia (GoV) continental slope. Such undulations have already been described in previous studies, interpreted as a result of sliding and/or creeping processes, presumably affected by neotectonic fracture system, which apparently produced mass movements along the continental slope. However, the analysis of previous data could have been misinterpreted similar to other case studies, such as the "Humbolt slide" (northern California) or the Landes Plateau slope. In this study we present newly detailed morphological and geometrical analysis of the sediment undulations observed on the GoV continental slope. Morphological parameters and quantitative measurements of the undulations were computed, measuring the common geomorphic parameters from the multibeam dataset (i.e. wave-length, wave-height, asymmetry index, slope, etc.). In addition, seismic profiles were acquired at different resolutions across the undulations using TOPAS, Sparker and Airguns. The interpretation of the internal structure of such undulations indicated that they correspond to depositional sediment waves that affect a large portion of the continental slope sedimentary record, being preferentially developed in the three major fields separated by structural heights. The sediment waves formation processes has been inferred from contemporary hydrodynamics observations, which indicate that near-inertial internal waves interacting with the GoV continental slope could play an important role in redistribution of near-bottom suspended particles, contributing to the development and/or maintenance of such sediment wave fields. This study will provide a new detailed characterization of the sediment waves observed over the GoV, and suggest a formation model that could be extended to similar sediment waves fields developed in continental slope regions elsewhere.

  15. Shelfbreak current over the Canadian Beaufort Sea continental slope: Wind-driven events in January 2005

    NASA Astrophysics Data System (ADS)

    Dmitrenko, Igor A.; Kirillov, Sergei A.; Forest, Alexandre; Gratton, Yves; Volkov, Denis L.; Williams, William J.; Lukovich, Jennifer V.; Belanger, Claude; Barber, David G.

    2016-04-01

    The shelfbreak current over the Beaufort Sea continental slope is known to be one of the most energetic features of the Beaufort Sea hydrography. In January 2005, three oceanographic moorings deployed over the Canadian (eastern) Beaufort Sea continental slope simultaneously recorded two consecutive shelfbreak current events with along-slope eastward bottom-intensified flow up to 120 cm s-1. Both events were generated by the local wind forcing associated with two Pacific-born cyclones passing north of the Beaufort Sea continental slope toward the Canadian Archipelago. Over the mooring array, the associated westerly wind exceeded 15 m s-1. These two cyclones generated storm surges along the Beaufort Sea coast with sea surface height (SSH) rising up to 1.4 m following the two westerly wind maxima. We suggest that the westerly along-slope wind generated a surface Ekman onshore transport. The associated SSH increase over the shelf produced a cross-slope pressure gradient that drove an along-slope eastward geostrophic current, in the same direction as the wind. This wind-driven barotropic flow was superimposed on the background baroclinic bottom-intensified shelfbreak current that consequently amplified. Summer-fall satellite altimetry data for 1992-2013 show that the SSH gradient in the southeastern Beaufort Sea is enhanced over the upper continental slope in response to frequent storm surge events. Because the local wind forcing and/or sea-ice drift could not explain the reduction of sea-ice concentration over the Beaufort Sea continental slope in January 2005, we speculate that wind-driven sea level fluctuations may impact the sea-ice cover in winter.

  16. Overpressure and fluid flow in the new jersey continental slope: implications for slope failure and cold seeps

    PubMed

    Dugan; Flemings

    2000-07-14

    Miocene through Pleistocene sediments on the New Jersey continental slope (Ocean Drilling Program Site 1073) are undercompacted (porosity between 40 and 65%) to 640 meters below the sea floor, and this is interpreted to record fluid pressures that reach 95% of the lithostatic stress. A two-dimensional model, where rapid Pleistocene sedimentation loads permeable sandy silt of Miocene age, successfully predicts the observed pressures. The model describes how lateral pressure equilibration in permeable beds produces fluid pressures that approach the lithostatic stress where overburden is thin. This transfer of pressure may cause slope failure and drive cold seeps on passive margins around the world. PMID:10894774

  17. Measurements of slope currents and internal tides on the Continental Shelf and slope off Newport Beach, California

    USGS Publications Warehouse

    Rosenberger, Kurt J.; Noble, Marlene A.; Norris, Benjamin

    2014-01-01

    An array of seven moorings housing current meters and oceanographic sensors was deployed for 6 months at 5 sites on the Continental Shelf and slope off Newport Beach, California, from July 2011 to January 2012. Full water-column profiles of currents were acquired at all five sites, and a profile of water-column temperature was also acquired at two of the five sites for the duration of the deployment. In conjunction with this deployment, the Orange County Sanitation District deployed four bottom platforms with current meters on the San Pedro Shelf, and these meters provided water-column profiles of currents. The data from this program will provide the basis for an investigation of the interaction between the deep water flow over the slope and the internal tide on the Continental Shelf.

  18. Changes in abundance and composition of anthropogenic marine debris on the continental slope off the Pacific coast of northern Japan, after the March 2011 Tohoku earthquake.

    PubMed

    Goto, Tomoaki; Shibata, Haruka

    2015-06-15

    Abundance and composition of anthropogenic marine debris were assessed on the basis of six bottom trawl surveys conducted on the continental slope off Iwate Prefecture, Pacific coast of northern Japan, in 2003, 2004 and 2011, and the temporal changes due to the Tohoku earthquake and tsunami in March 2011 evaluated. In 2003 and 2004, 54-94 items km(-2) of marine debris, dominated by sea-base sourced items mainly comprising fishing gear and related items from adjacent fishing grounds on the continental shelf, were quantified. In the post-earthquake period, the density increased drastically to 233-332 items km(-2), due to an increase in land-base sourced items generated by the tsunami. However, a major increase in abundance after the disaster, compared to the total amount of tsunami debris swept into the sea, was not found. Additional sources of land-based debris from the adjacent continental shelf are suggested in the present waters. PMID:25921637

  19. Recent glacially influenced sedimentary processes on the East Greenland continental slope and deep Greenland Basin

    NASA Astrophysics Data System (ADS)

    García, Marga; Dowdeswell, Julian A.; Ercilla, Gemma; Jakobsson, Martin

    2012-08-01

    This paper presents the morpho-sedimentary characterization and interpretations of the assemblage of landforms of the East Greenland continental slope and Greenland Basin, based on swath bathymetry and sub-bottom TOPAS profiles. The interpretation of landforms reveals the glacial influence on recent sedimentary processes shaping the seafloor, including mass-wasting and turbidite flows. The timing of landform development points to a predominantly glacial origin of the sediment supplied to the continental margin, supporting the scenario of a Greenland Ice Sheet extending across the continental shelf, or even to the shelf-edge, during the Last Glacial Maximum (LGM). Major sedimentary processes along the central section of the eastern Greenland Continental Slope, the Norske margin, suggest a relatively high glacial sediment input during the LGM that, probably triggered by tectonic activity, led to the development of scarps and channels on the slope and debris flows on the continental rise. The more southerly Kejser Franz Josef margin has small-scale mass-wasting deposits and an extensive turbidite system that developed in relation to both channelised and unconfined turbidity flows which transferred sediments into the deep Greenland Basin.

  20. Vertical distribution of benthic infauna in continental slope sediments off Cape Lookout, North Carolina

    NASA Astrophysics Data System (ADS)

    Blake, James A.

    The vertical distribution of 30 species of benthic infauna from continental slope (583-3000 m) sediments off Cape Lookout, North Carolina was closely correlated with feeding types. Carnivores, omnivores, filter feeders, and surface deposit feeders were mostly concentrated in the upper 0-2 cm of the cores. The depth distribution of subsurface deposit feeders was more variable, even among related taxa.

  1. Benthic study of the continental slope off Cape Hatteras, North Carolina. Volume 2. Final report

    SciTech Connect

    Diaz, R.J.; Blake, J.A.; Lohse, D.P.

    1993-03-01

    A number of blocks off Cape Hatteras have been leased by Mobil Oil, which has requested permission to drill an exploratory well, at 820-m depth, in a block identified as Manteo 467. The proposed well location is 39 miles from the coast of North Carolina. The possibility of extracting gas from the continental slope off the coast of North Carolina, particularly at slope depths, has raised a number of environmental concerns that cannot be addressed from existing data. The present study was developed by the Minerals Management Service to better define the nature of the continental slope benthic communities off Cape Hatteras and to delineate their areal extent. Emphasis was placed on the area around the proposed drill site in the Manteo 467 lease block.

  2. Slope Stability: Factor of Safety along the Seismically Active Continental Slope Offshore Sumatra

    NASA Astrophysics Data System (ADS)

    Patton, J. R.; Goldfinger, C.; Djadjadihardja, Y.; None, U.

    2013-12-01

    Recent papers have documented the probability that turbidites deposited along and downslope of subduction zone accretionary prisms are likely the result of strong ground shaking from great earthquakes. Given the damaging nature of these earthquakes, along with the casualties from the associated tsunamis, the spatial and temporal patterns of these earthquakes can only be evaluated with paleoseismologic coring and seismic reflection methods. We evaluate slope stability for seafloor topography along the Sunda subduction offshore Sumatra, Indonesia. We use sediment material properties, from local (Sumatra) and analogous sites, to constrain our estimates of static slope stability Factor of Safety (FOS) analyses. We then use ground motion prediction equations (GMPE's) to estimate ground motion intensity (Arias Intensity, AI) and acceleration (Peak Ground Acceleration, PGA), as possibly generated by fault rupture, to constrain seismic loads for pseudostatic slope stability FOS analyses. The ground motions taper rapidly with distance from the fault plane, consistent with ground motion - fault distance relations measured during the 2011 Tohoku-Oki subduction zone earthquake. Our FOS analyses include a Morgenstern method of slices probabilistic analysis for 2-D profiles along with Critical Acceleration (Ac) and Newmark Displacement (Dn) analysis of multibeam bathymetry of the seafloor. In addition, we also use estimates of ground motion modeled with a 2004 Sumatra-Andaman subduction zone (SASZ) earthquake fault slip model, to also compare with our static FOS analyses of seafloor topography. All slope and trench sites are statically stable (FOS < 1) and sensitive to ground motions generated by earthquakes of magnitude greater than 7. We conclude that for earthquakes of magnitude 6 to 9, PGA of 0.4-0.6 to 1.4-2.5 g would be expected, respectively, from existing GMPE's. However, saturation of accelerations in the accretionary wedge may limit actual accelerations to less than 1

  3. Multiple slope failures shaped the lower continental slope offshore NW Svalbard in the Fram Strait

    NASA Astrophysics Data System (ADS)

    Osti, Giacomo; Mienert, Jürgen; Forwick, Matthias; Sverre Laberg, Jan

    2016-04-01

    Bathymetry data show that the lower slope (between 1300 m and 3000 m water depth) of the NW-Svalbard passive margin has been affected by multiple slope failure events. The single events differ in terms of extension, volume of mobilized sediments, morphology of the slide scar, run-out distance and age. As for several mega-scale and minor Arctic slides, the trigger mechanism is still speculative and may include high sedimentation rates, dissociation of gas hydrates, excess pore pressure, or earthquakes caused by isostatic rebound. In this study, we discuss the potential trigger mechanisms that have led to the multiple slope failure events within what we suggest to be named the Fram Strait Slide Complex. The slide complex lies in proximity to the tectonically active Spitsbergen Fracture Zone where earthquakes events, occurrences of potential weak layers in the sediment column, low sedimentation rates, and extended gas hydrate-bearing sediments may all have contributed to the causes leading to multiple slope failures. Preliminary results obtained from 14C dating on N. pachyderma sin. from sediment cores from the Spitsbergen Fracture Zone slides (SFZS 1 and 2), coupled with sub-bottom profiler data (frequency 9 to 15 KHz) show that the two shallowest glide planes within one of the observed slide scars failed ~100,000 and ~115,000 yr BP. Whilst SFZS 1 affected an area of 750 km2 mobilizing a total sediment volume of 40 km3, SFZS 2 moved an area of 230 km2 with a sediment volume of 4.5 km3.

  4. Gulf of Alaska continental slope morphology: Evidence for recent trough mouth fan formation

    NASA Astrophysics Data System (ADS)

    Swartz, John M.; Gulick, Sean P. S.; Goff, John A.

    2015-01-01

    continental shelves are host to numerous morphologic features that help understand past glacier dynamics. Southeastern Alaska is home to the St. Elias mountains, an active orogen that also hosts temperate marine glaciers. During glacial periods ice streams advance across the continental shelf, carving shelf-crossing troughs that reach the shelf edge. We use high-resolution multibeam data to develop the relationship between the Yakutat and Alsek Sea Valleys and the resulting continental slope morphology. The shelf and slope geomorphology can be divided into statistical groupings that relate to the relative balance of erosion and deposition. Our analysis indicates that only the Yakutat system has been able to build an incipient trough-mouth fan. The extreme sediment supply from this region was able to overwhelm the steep initial topography of the transform margin while further to the east sediment slope-bypass dominates. This analysis provides an extreme end member to existing studies of temperate glaciation along continental margins. The unique interplay between rapid uplift due to ongoing collision and the massive erosion caused by temperate glaciers provides for sedimentary flux far above most other systems.

  5. Factors controlling Pliocene-Quaternary sedimentation on the Gulf of Cadiz Continental Slope, Spain

    SciTech Connect

    Baraza, J.; Maldonado, A. ); Nelson, C.H. )

    1990-05-01

    The Pliocene-Quaternary sedimentation on the Gulf of Cadiz continental slope records an interaction between the tectonics responsible for a complex bathymetry, and the Mediterranean outflow undercurrent developed after the opening of the Gibraltar Strait at the end of the Miocene. During periods of low sea level, sedimentation was controlled mainly by changes in the sediment supply from the various rivers that feed the area. During high sea level, periods like the present, deposition is controlled mainly by the Mediterranean undercurrent. The Mediterranean undercurrent flows out from the Strait of Gibraltar toward the northwest and impinges on the Cadiz continental slope at 300- to 500-m depths. Flows are fastest near the Strait of Gibraltar (as much as 200 m/sec) and slow to 10-20 m/sec westward Portugal. The gradual decrease in undercurrent speed from the Strait of Gibraltar to the center of the Gulf of Cadiz results in a westward change from erosional to depositional characteristics on the upper continental slope. Erosion in the southeastern part of the Gulf is characterized by exposed bed rock on the sea floor and by erosional truncation of reflectors on sea-floor slopes. In contrast, several prograding shelf-break types and slope configurations occur in the west, showing the influence of tectonic subsidence, diapir uplift and sediment supply on the Pliocene-Quaternary sedimentation. At middle slope depths, high-energy depositional features, such as cut-and-fill structures, are observed in seismic profiles. Energy decreasing bed-form fields, from east to west, are shown in profiles and sonographic of the most sufficial units on the deep platforms. In addition, sediment drift bodies deposit against basement diapiric ridges near the canyon-ridge central area.

  6. Slope Instability and Gas Hydrates in the Hudson Canyon Region, U.S. Atlantic Continental Margin

    NASA Astrophysics Data System (ADS)

    Rona, P. A.; Robb, J. M.; Butman, B.; Scranton, M. I.; Kingman, K. E.; Tucholke, B. E.; Twichell, D.

    2004-12-01

    The continental slope and the upper rise centered on Hudson Canyon offshore New York and New Jersey lie within a major gas-hydrate province. This region exhibits evidence of gravitational mass movements and possible methane expulsion, as inferred from our bathymetric and water-column surveys conducted in 2002 with support from NOAA/OE, and prior data. The bathymetric data cover our study area (200 km by 110 km; 37\\deg40'N to 39\\deg50'N, 70\\deg00'W to 72\\deg30'W) from the inner edge of the continental slope (depth 200 m) seaward to the middle rise (c.3500 m). The world's largest hub of submarine telecommunications cables partially passes through this area. Evidence of gravitational mass movements and of probable gas release is extensive. Examples of the former include: (1) blocks of landward-dipping strata up to 2-km wide and 150-m high that lie at the base of the continental slope (water depth 2100-2200 m) seaward of an over-pressured zone beneath the continental slope (639 mbsf in ODP Hole 1073A; water depth 650 m; Dugan and Flemings, 2000); (2) boulders of Eocene chalk that litter the lower slope and upper rise; (3) a semicircular, tabular glide block, about 20 km in diameter, which thickens to about 150 m at its seaward margin; the block is centered at 39\\deg23.5'N, 71\\deg10.0'W between 2450 and 2600 m depth on the upper rise, about 15 km downslope from a congruent scarp at 2200 m on the lower slope; (4) apparent penecontemporaneous faulting and gliding in strata inclined sub-parallel to the seafloor along the upper rise; 5) apparent clogging of Hudson Canyon with hummocky sediment at a right-angle turn of the axis (depth 3368 m; 38\\deg39.6'N, 71\\deg01.8'W); 6) changes in stratification from the upper to middle rise; uneven layering beneath the upper rise (seafloor mean inclination 0.75\\deg down to 2700 m) is inferred to reflect disturbance by gravitational mass movements; even layering parallel to the seafloor beneath the middle rise (inclination

  7. Molluskan species richness and endemism on New Caledonian seamounts: Are they enhanced compared to adjacent slopes?

    NASA Astrophysics Data System (ADS)

    Castelin, Magalie; Puillandre, Nicolas; Lozouet, Pierre; Sysoev, Alexander; de Forges, Bertrand Richer; Samadi, Sarah

    2011-06-01

    Seamounts were often considered as 'hotspots of diversity' and 'centers of endemism', but recently this opinion has been challenged. After 25 years of exploration and the work of numerous taxonomists, the Norfolk Ridge (Southwest Pacific) is probably one of the best-studied seamount chains worldwide. However, even in this intensively explored area, the richness and the geographic patterns of diversity are still poorly characterized. Among the benthic organisms, the post-mortem remains of mollusks can supplement live records to comprehensively document geographical distributions. Moreover, the accretionary growth of mollusk shells informs us about the life span of the pelagic larva. To compare diversity and level of endemism between the Norfolk Ridge seamounts and the continental slopes of New Caledonia we used species occurrence data drawn from (i) the taxonomic literature on mollusks and (ii) a raw dataset of mainly undescribed deep-sea species of the hyperdiverse Turridae. Patterns of endemism and species richness were analyzed through quantitative indices of endemism and species richness estimator metrics. To date, 403 gastropods and bivalves species have been recorded on the Norfolk Ridge seamounts. Of these, at least 38 species (˜10%) are potentially endemic to the seamounts and nearly all of 38 species have protoconchs indicating lecithotrophic larval development. Overall, our results suggest that estimates of species richness and endemism, when sampling effort is taken into account, were not significantly different between slopes and seamounts. By including in our analyses 347 undescribed morphospecies from the Norfolk Ridge, our results also demonstrate the influence of taxonomic bias on our estimates of species richness and endemism.

  8. Active mud volcanoes on the continental slope of the Canadian Beaufort Sea

    NASA Astrophysics Data System (ADS)

    Paull, C. K.; Dallimore, S. R.; Caress, D. W.; Gwiazda, R.; Melling, H.; Riedel, M.; Jin, Y. K.; Hong, J. K.; Kim, Y.-G.; Graves, D.; Sherman, A.; Lundsten, E.; Anderson, K.; Lundsten, L.; Villinger, H.; Kopf, A.; Johnson, S. B.; Hughes Clarke, J.; Blasco, S.; Conway, K.; Neelands, P.; Thomas, H.; Côté, M.

    2015-09-01

    Morphologic features, 600-1100 m across and elevated up to 30 m above the surrounding seafloor, interpreted to be mud volcanoes were investigated on the continental slope in the Beaufort Sea in the Canadian Arctic. Sediment cores, detailed mapping with an autonomous underwater vehicle, and exploration with a remotely operated vehicle show that these are young and actively forming features experiencing ongoing eruptions. Biogenic methane and low-chloride, sodium-bicarbonate-rich waters are extruded with warm sediment that accumulates to form cones and low-relief circular plateaus. The chemical and isotopic compositions of the ascending water indicate that a mixture of meteoric water, seawater, and water from clay dehydration has played a significant role in the evolution of these fluids. The venting methane supports extensive siboglinid tubeworms communities and forms some gas hydrates within the near seafloor. We believe that these are the first documented living chemosynthetic biological communities in the continental slope of the western Arctic Ocean.

  9. Circulation and exchange at the continental shelf and slope SEEP-2

    SciTech Connect

    Houghton, R.W.; Ou, Hsien-Wang.

    1991-01-01

    This project was a component of the SEEP-II program. It contributed to the instrumentation of the SEEP-II moored array to the processing and analysis of the time-series data of water temperature and currents, and to a theoretical modeling study of the circulation on the continental margin. We are responsible for nearly half of the current meters and thermistor chains that were deployed in the SEEP-II moored array on the continental margin off the Delmarva peninsula. Data tapes derived from three deployments of the instruments in this array were processed. A second component of this project was a theoretical study of the interaction of the Gulf Stream with the continental margin north of Cape Hatteras. The model shows how the topographic influence on the local vorticity balance leads to back-folding filaments of Gulf Stream water and to the Slope Sea gyre circulation.

  10. Important geological and biological impacts of natural hydrocarbon seeps: Northern Gulf of Mexico continental slope

    SciTech Connect

    Roberts, H.H. )

    1993-11-01

    Large volumes of siliciclastic sediments, input especially during periods of lowered sea level, and compensating salt tectonics have produced a continental slope that is arguably the most complex in today's oceans. Faults associated with deformation of salt and shale provide the primary migration routes for hydrocarbon gases, crude oil, brines, and formation fluids to the modern sea floor. Since the mid 1980s, it has become increasingly clearer that this process has an extremely important impact on the geomorphology, sedimentology, and biology of the modern continental slope. Hydrocarbon source, flux rate, and water depth are important determinants of sea-floor response. Under rapid flux conditions mud volcanoes (to 1 km wide and 50 m high) result, and hydrate hills (rich with authigenic carbonates), carbonate lithoherms, and isolated communities of chemosymbiotic organisms with associated hardgrounds represent much slower flux responses. In numerous moderate- to low-flux cases, cold seep products function to support islands of productivity for communities of chemosymbiotic organisms that contribute both directly (shell material) and through chemical byproducts to the production of massive volumes of calcium-magnesium carbonate in the form of hardgrounds, stacked slabs, and discrete moundlike buildups (commonly >20m). Seep-related carbonates of the Gulf of Mexico continental slope, as well those formed through degassing of accretionary prisms along active margins, are now thought to create hardgrounds and discrete buildups that are excellent analogs for many problematic carbonate buildups in ancient deep-water siliciclastic rocks.

  11. Surface heat flow measurements from the East Siberian continental slope and southern Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    O'Regan, Matt; Preto, Pedro; Stranne, Christian; Jakobsson, Martin; Koshurnikov, Andrey

    2016-05-01

    Surface heat flow data in the Arctic Ocean are needed to assess hydrocarbon and methane hydrate distributions, and provide constraints into the tectonic origins and nature of underlying crust. However, across broad areas of the Arctic, few published measurements exist. This is true for the outer continental shelf and slope of the East Siberian Sea, and the adjoining deep water ridges and basins. Here we present 21 new surface heat flow measurements from this region of the Arctic Ocean. On the Southern Lomonosov Ridge, the average measured heat flow, uncorrected for effects of sedimentation and topography, is 57 ± 4 mW/m2 (n = 4). On the outer continental shelf and slope of the East Siberian Sea (ESS), the average is 57 ± 10 mW/m2 (n = 16). An anomalously high heat flow of 203 ± 28 mW/m2 was measured at a single station in the Herald Canyon. With the exception of this high heat flow, the new data from the ESS are consistent with predictions for thermally equilibrated lithosphere of continental origin that was last affected by thermotectonic processes in the Cretaceous to early Cenozoic. Variability within the data likely arises from differences in radiogenic heat production within the continental crust and overlying sediments. This can be further explored by comparing the data with geophysical constraints on sediment and crustal thicknesses.

  12. Observed bottom boundary layer transport and uplift on the continental shelf adjacent to a western boundary current

    NASA Astrophysics Data System (ADS)

    Schaeffer, A.; Roughan, M.; Wood, J. E.

    2014-08-01

    Western boundary currents strongly influence the dynamics on the adjacent continental shelf and in particular the cross-shelf transport and uplift through the bottom boundary layer. Four years of moored in situ observations on the narrow southeastern Australian shelf (in water depths of between 65 and 140 m) were used to investigate bottom cross-shelf transport, both upstream (30°S) and downstream (34°S) of the separation zone of the East Australian Current (EAC). Bottom transport was estimated and assessed against Ekman theory, showing consistent results for a number of different formulations of the boundary layer thickness. Net bottom cross-shelf transport was onshore at all locations. Ekman theory indicates that up to 64% of the transport variability is driven by the along-shelf bottom stress. Onshore transport in the bottom boundary layer was more intense and frequent upstream than downstream, occurring 64% of the time at 30°S. Wind-driven surface Ekman transport estimates did not balance the bottom cross-shelf flow. At both locations, strong variability was found in bottom water transport at periods of approximately 90-100 days. This corresponds with periodicity in EAC fluctuations and eddy shedding as evidenced from altimeter observations, highlighting the EAC as a driver of variability in the continental shelf waters. Ocean glider and HF radar observations were used to identify the bio-physical response to an EAC encroachment event, resulting in a strong onshore bottom flow, the uplift of cold slope water, and elevated coastal chlorophyll concentrations.

  13. The continental slope off New England: A long-range sidescan-sonar perspective

    USGS Publications Warehouse

    Scanlon, K.M.

    1984-01-01

    The first continuous overview of a large segment of the continental slope and rise off the northeastern United States has been obtained using the GLORIA II long-range sidescan-sonar system. Extensive dissection by canyon and gully systems and evidence of possible large-scale sediment sliding are seen on the slope. The style and degree of incision, as well as the numbers and locations of canyons, have been found to differ significantly from previously published maps. It is suggested that the slope is a significant source of the sediment that has been deposited on the rise, and that some abrupt changes in the courses of canyons may be the result of local structural control. ?? 1984 Springer-Verlag New York Inc.

  14. The Influences of The Continental Slope Geomorphology On The Deep Water Sediment System, Taking the Northern South China Slope for Example

    NASA Astrophysics Data System (ADS)

    liu, L.; Li, P.; Li, J.; Du, J.; Fu, M.

    2013-12-01

    The developing of deepwater sedimentary bodies have been affected by many factors, such as the tectonic evolution, conditions of the sediment supplying as well as the sea-level changes. In the researching of the sedimentary bodies on the continental slope system, there have been found that the degree of slope mould affect the building of those sedimentary bodies. Taking the Northern South China Slope for example, based on the high resolution marine geophysical data, including the multi-beam echo sounder, the sub-bottom profiler and the high-resolution 2D multi-channel seismic reflection sections, the geomorphological patterns of the study Field are interpreted in details, illuminated the types of those sedimentary bodies, the characteristic and the space distributions. Analyzed those influences factors on the deepwater depositional system of the geomorphology. Those geomorphological bodies zonation in the study area generally consistent with the upper part, the middle part and the lower part zoned for the continental slope of the South China Sea. In the upper part of the continental slope with a monocline shape (water depth: 200m~400m), there are sand waves and paleo-coral reefs, whereas in its lower part (water depth: 400m~670m) the seafloor is flat and no unfavourable geological bodies have been recognized. In the continental slope zone with fault terraces, the topography of the seafloor falls into pieces and submarine canyons, fault scarps, landslides and collapses and abrupt slopes are widely developed. At the two slope sides of the canyons landslides and piles of debris can be observed clearly. In the continental slope zone with turbidity current deposits, the seafloor is gentle. The down-cutting depth and width of the submarine canyons become small and disappear gradually. The main geo-hazard risks in this zone are the debris flow (turbidity-current) deposits and the seafloor landslides

  15. Benthic Community Structure and Sediment Geochemical Properties at Hydrocarbon Seeps Along the Continental Slope of the Western North Atlantic

    NASA Astrophysics Data System (ADS)

    Demopoulos, A. W.; Bourque, J. R.; Brooke, S.

    2015-12-01

    Hydrocarbon seeps support distinct benthic communities capable of utilizing reduced chemical compounds for nutrition. In recent years, methane seepage has been increasingly documented along the continental slope of the U.S. Atlantic margin. In 2012 and 2013, two seeps were investigated in this region: a shallow site near Baltimore Canyon (410-450 m) and a deep site near Norfolk Canyon (1600 m). Both sites contain extensive mussel beds and microbial mats. Sediment cores and grab samples were collected to quantify the abundance, diversity, and community structure of benthic macrofauna (>300 mm) in relationship to the associated sediment environment (organic carbon and nitrogen, stable isotopes 13C and 15N, grain size, and depth) of mussel beds, mats, and slope habitats. Macrofaunal densities in microbial mats were four times greater than those present in mussel beds and slope sediments. Macrofaunal communities were distinctly different both between depths and among habitat types. Specifically, microbial mat sediments were dominated by the annelid families Dorvilleidae, Capitellidae, and Tubificidae, while mussel habitats had higher proportions of crustaceans. Diversity was lower in Baltimore microbial mat habitats, but higher in mussel and slope sediments compared to Norfolk seep habitats found at deeper depths. Multivariate statistical analysis identified sediment carbon:nitrogen (C:N) ratios and 13C values as important variables for structuring the macrofaunal communities. Higher C:N ratios were present within microbial mat habitats and depleted 13C values occurred in sediments adjacent to mussel beds found in Norfolk Canyon seeps. Differences in the quality and source of organic matter present in the seep habitats are known to be important drivers in macrofaunal community structure and associated food webs. The multivariate analysis provides new insight into the relative importance of the seep sediment quality in supporting dense macrofaunal communities compared

  16. Transport and transfer rates in the waters of the continental shelf and slope: SEEP. Final report, May 1, 1987--December 31, 1993

    SciTech Connect

    Biscaye, P.E.; Anderson, R.F.

    1993-12-31

    The overall Shelf Edge Exchange Processes (SEEP) Program, which began in 1980 or 1981, had as its goal the testing of a hypothesis with respect to the fate of particulate matter formed in and introduced into the waters of the continental shelf adjacent to the northern east coast of the US, i.e., the MAB. The original hypothesis was that a large proportion of the particles in general, and of the particulate organic carbon (POC) in particular, was exported from the shelf, across the shelf/slope break and front, into the waters of, and, to some degree, deposited in the sediments of the continental slope. This hypothesis was based on budgets of organic carbon and lead-210 that did not account for a large proportion of those species in the waters or sediments of the shelf, and on a carbon-rich band of sediments centered on the slope at {approximately}1,000 m water depth. The results of the first SEEP experiment, south of New England and Long Island (SEEP-1) suggested, but did not prove, that there was only a relatively small proportion of the carbon which was exported from the shelf to the slope. The objective of the second experiment -- SEEP-2 -- done under the subject grant, was to tighten the experiment in terms of the kinds of data collected, and to focus it more on the shelf and only the upper slope, where shelf-derived particles were thought to be deposited.

  17. Submesoscale currents in the northern Gulf of Mexico: Deep phenomena and dispersion over the continental slope

    NASA Astrophysics Data System (ADS)

    Bracco, Annalisa; Choi, Jun; Joshi, Keshav; Luo, Hao; McWilliams, James C.

    2016-05-01

    This study examines the mesoscale and submesoscale circulations along the continental slope in the northern Gulf of Mexico at depths greater than 1000 m. The investigation is performed using a regional model run at two horizontal grid resolutions, 5 km and 1.6 km, over a 3 year period, from January 2010 to December 2012. Ageostrophic submesoscale eddies and vorticity filaments populate the continental slope, and they are stronger and more abundant in the simulation at higher resolution, as to be expected. They are formed from horizontal shear layers at the edges of highly intermittent, bottom-intensified, along-slope boundary currents and in the cores of those currents where they are confined to steep slopes. Two different flow regimes are identified. The first applies to the De Soto Canyon that is characterized by weak mean currents and, in the high-resolution run, by intense but few submesoscale eddies that form near preferentially along the Florida continental slope. The second is found in the remainder of the domain, where the mean currents are stronger and the circulation is highly variable in both space and time, and the vorticity field is populated, in the high-resolution case, by numerous vorticity filaments and short-lived eddies. Lagrangian tracers are deployed at different times along the continental shelf below 1000 m depth to quantify the impact of the submesoscale currents on transport and mixing. The modeled absolute dispersion is, on average, independent of horizontal resolution, while mixing, quantified by finite-size Lyapunov exponents and vertical relative dispersion, increases when submesoscale processes are present. Dispersion in the De Soto Canyon is smaller than in the rest of the model domain and less affected by resolution. This is further confirmed comparing the evolution of passive dye fields deployed in De Soto Canyon near the Macondo Prospect, where the Deepwater Horizon rig exploded in 2010, and at the largest known natural hydrocarbon

  18. Benthic oxygen uptake, hydrolytic potentials and microbial biomass at the Arctic continental slope

    NASA Astrophysics Data System (ADS)

    Boetius, Antje; Damm, Ellen

    1998-02-01

    Oxygen (O 2) uptake and microbial activity in sediments of the eastern Arctic continental slope were investigated in both ice-covered and ice-free areas of the Laptev Sea. Total O 2 flux ( J) decreased markedly from 2 mmol m -2 d -1 at the shelf edge (50 m) to 0.07 mmol m -2 d -1 at the bottom of the slope (3500 m), matched by the more than tenfold decline in chlorophyll pigments (CPE), protein and dissolved amino acids (DFAA). Furthermore, concentrations of these labile organic compounds were strongly correlated with extracellular enzyme potentials (EEA) in the sediments as well as with microbial biomass. The concentrations of labile substances and total microbial biomass (TMB) as well as the rates of O 2 uptake and EEA were independent of the distribution of TOC, probably due to the dominance of non-labile terrigenous compounds. Differences in O 2 uptake and microbial EEA between ice-covered and ice-free transects were relatively small. Values of O 2 uptake, CPE, EEA and TMB at the Laptev Sea slope were considerably lower than at temperate continental slopes but nevertheless higher than in the central Arctic deep-sea basin. Considering newly published data on primary productivity in the central Arctic, our results indicate that the benthic respiratory demand at the Laptev Sea slope and in the Arctic basin could be satisfied by the vertical flux of POC and does not necessarily depend on lateral advection of POC from the shelf seas as previously anticipated.

  19. Estimated oil and gas reserves, Gulf of Mexico outer continental shelf and continental slope, December 31, 1982

    USGS Publications Warehouse

    Hewitt, Jack E.; Brooke, Jeff P.; Knipmeyer, John H.

    1983-01-01

    Remaining recoverable reserves of oil* and gas in the Gulf of Mexico Outer Continental Shelf and Continental Slope have been estimated to be about 2.98 billion barrels of oil and 39.8 trillion cubic feet of gas, as of December 31, 1982. These reserves are recoverable from 468 studied fields under the Federal submerged lands off the coasts of Louisiana and Texas. An additional 53 fields, discovered since December 31, 1980, have not been sufficiently developed to permit a reasonably accurate estimate of reserves. Original recoverable reserves are estimated to have been 8.56 billion barrels of oil and 98.1 trillion cubic feet of gas from 484 fields in the same geographic area. Included in this number are 16 fields that are depleted and were abandoned; not included are the 53 insufficiently developed fields. Estimates were made for individual reservoirs in 382 fields and on a field-wide basis for the other 102 fields. *The term 'oil' as used in this report includes crude oil and condensate.

  20. Cold-seep carbonates of the middle and lower continental slope, northern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Roberts, Harry H.; Feng, Dong; Joye, Samantha B.

    2010-11-01

    Authigenic carbonates from cold seeps on the middle and lower continental slope of the northern Gulf of Mexico (GOM) exhibit a wide range of mineralogical and stable isotopic compositions. These carbonates consist of concretions and nodules in surface sediments, hardgrounds of crusts and isolated slabs, and mounded buildups of blocks and slabs of up to over 10 meters in relief above the surrounding seafloor. Mineralogically, the carbonates are dominated by high-Mg calcite (HMC) and aragonite. However, low levels (<5 wt%) of dolomite are present in most samples. Petrographically, Mg-calcite peloidal matrix and acicular to botryoidal aragonitic void-filling cements are the most frequent associations. The carbon isotopic compositions of the carbonates range from -60.8 to 14.0‰ PDB, indicating complex carbon sources that include 13C-depleted biogenic and thermogenic methane, biodegraded crude oil, seawater CO2, and 13C-enriched residual CO2 from methanogenesis. A similarly large variability in δ18O values (2.5 to 6.7‰ PDB) demonstrates the geochemical complexity of the slope, with some samples pointing toward an 18O-enriched oxygen source that is possibly related to advection of 18O-enriched formation water and/or to the decomposition of gas hydrate. A considerable range of mineralogical and isotopic variations in cold-seep carbonate composition was noted even within individual study sites. However, common trends occur across multiple geographic areas. This situation suggests that local controls on fluid and gas flux, types of seep hydrocarbons, the presence or absence of gas hydrate in the near-surface sediment, and chemosynthetic communities, as well as the temporal evolution of the local hydrocarbon reservoir, all may play a part in determining carbonate mineralogy and isotope geochemistry. The carbon isotope data clearly indicate that between-site variation is greater than within-site variation. Seep carbonates formed on the middle and lower continental slope

  1. Diversity and Distribution Patterns of Cetaceans in the Subtropical Southwestern Atlantic Outer Continental Shelf and Slope.

    PubMed

    Di Tullio, Juliana Couto; Gandra, Tiago B R; Zerbini, Alexandre N; Secchi, Eduardo R

    2016-01-01

    Temporal and spatial patterns of cetacean diversity and distribution were investigated through eight ship-based surveys carried out during spring and autumn between 2009 and 2014 on the outer continental shelf (~150m) and slope (1500m) off southeastern and southern Brazil (~23°S to ~34°S). The survey area was divided into southeast and south areas according to their oceanographic characteristics. Twenty-one species were observed in 503 sightings. The overall number of species was similar between the two areas, though it was higher in the spring in the south area. Five species were dominant and diversity varied more seasonally than spatially. ANOVA and kernel analyses showed that overall cetacean densities were higher in spring compared to autumn. Physeter macrocephalus, the most frequent species, concentrated throughout the south area at depths over 1000m in both seasons. Despite the overlapped occurrence at a broader scale, small delphinids presented latitudinal and in-offshore gradients as well as seasonal variation in distribution patterns, which could indicate habitat partitioning between some species. Delphinus delphis was only recorded in the south and its density decreased in areas where the presence of Stenella frontalis increased, mainly beyond the 250m isobath. Densities of S. longirostris and S. attenuata increased in lower latitudes and beyond the shelf break. The large delphinids Tursiops truncatus and Globicephala melas formed mixed groups in many occasions and were observed along the study area around depths of 500m. Grampus griseus was twice as frequent in the south area and densities increased in waters deeper than 600m. As expected, densities of both small and large migratory whales were higher during spring, over the continental slope, in the southeast area. The results presented here provided strong evidence on the importance of the outer continental shelf and slope to a diverse community of cetaceans occurring in the subtropical Southwestern

  2. Diversity and Distribution Patterns of Cetaceans in the Subtropical Southwestern Atlantic Outer Continental Shelf and Slope

    PubMed Central

    Di Tullio, Juliana Couto; Gandra, Tiago B. R.; Zerbini, Alexandre N.; Secchi, Eduardo R.

    2016-01-01

    Temporal and spatial patterns of cetacean diversity and distribution were investigated through eight ship-based surveys carried out during spring and autumn between 2009 and 2014 on the outer continental shelf (~150m) and slope (1500m) off southeastern and southern Brazil (~23°S to ~34°S). The survey area was divided into southeast and south areas according to their oceanographic characteristics. Twenty-one species were observed in 503 sightings. The overall number of species was similar between the two areas, though it was higher in the spring in the south area. Five species were dominant and diversity varied more seasonally than spatially. ANOVA and kernel analyses showed that overall cetacean densities were higher in spring compared to autumn. Physeter macrocephalus, the most frequent species, concentrated throughout the south area at depths over 1000m in both seasons. Despite the overlapped occurrence at a broader scale, small delphinids presented latitudinal and in-offshore gradients as well as seasonal variation in distribution patterns, which could indicate habitat partitioning between some species. Delphinus delphis was only recorded in the south and its density decreased in areas where the presence of Stenella frontalis increased, mainly beyond the 250m isobath. Densities of S. longirostris and S. attenuata increased in lower latitudes and beyond the shelf break. The large delphinids Tursiops truncatus and Globicephala melas formed mixed groups in many occasions and were observed along the study area around depths of 500m. Grampus griseus was twice as frequent in the south area and densities increased in waters deeper than 600m. As expected, densities of both small and large migratory whales were higher during spring, over the continental slope, in the southeast area. The results presented here provided strong evidence on the importance of the outer continental shelf and slope to a diverse community of cetaceans occurring in the subtropical Southwestern

  3. Paleoecologic implications of chemoautotrophic molluscan-dominated assemblages on the Louisiana continental slope

    SciTech Connect

    Callender, W.R.; Powell, E.N. )

    1991-03-01

    Dense chemoautotrophically based molluscan communities are common at sites of active petroleum seepage in the Green Canyon and Garden Banks lease blocks on the Louisiana upper continental slope. The presence of dense molluscan aggregations has important implications for paleoecology because the continental slope is generally though of as a geologic setting depauperate of macrofossils. Liquid and gaseous petroleum seepage, primarily along faults associated with salt diapirism, provides localized nutrient input which facilitates high molluscan productivity. Authigenic carbonate, formed due to methane oxidation, occurs at and below the sediment-water interface in areas of molluscan concentrations. Trophic structure of these bivalve-dominated communities is based on three separate carbon pathways: chemoautotrophy, utilizing either H{sub 2}S or CH{sub 4}, or autotrophy, utilizing organic food sources. The largest quantity of preservable molluscan biomass is produced by infaunal lucinid and thyasirid clams which utilize H{sub 2}S. Thyasirid and lucinid clams form extensive three-dimensional shell beds which can extend for several tens of meters. Second and third in terms of preservable biomass are vesicomyid clams and mytilid mussels which utilize H{sub 2}S and CH{sub 4} respectively. Vesicomyid clams form shell pavements at a smaller scale then the lucinid and thyasirid shell beds. The least amount of preservable biomass is produced by autotrophs including trochid and nerite gastropods, limid bivalves, crabs, and starfish. Energy flow requirements for benthic communities on the oligotrophic continental shelf and slope settings of the northern Gulf of Mexico require a localized nutrient enrichment, such as a petroleum seep, to support dense concentrations of large individuals. This relationship of nutrient enrichment to enhanced biomass productivity probably also was a dominant factor in the formation of similar autochthonous benthic assemblages in the fossil record.

  4. Seafloor Mapping of the Southeast Iberian Continental Slope and Western Algero-Balearic Abyssal Plain

    NASA Astrophysics Data System (ADS)

    Lastras, G.; Canals, M.; León, C.; Elvira, E.; Pascual, L.; Muñoz, A.; de Cárdenas, E.; Acosta, J.

    2014-12-01

    We present the multibeam bathymetry and derived maps of the southeast Iberian margin from Cabo de Palos to Cabo de Gata, 37º35'N to 35º45'N and 2º10'W to 0º20'E, from the coastline down to the Algero-Balearic abyssal plain at depths exceeding 2,600 m. Data were obtained during different surveys in 2004, 2006 and 2007 on board R/V Vizconde de Eza with a Simrad EM300 multibeam echo-sounder, as part of the CAPESME Project, a collaboration between the Spanish Institute of Oceanography (IEO) and General Secretariat of Fisheries (SGP), aiming at creating maps of the fishing grounds of the Mediterranean continental margins of Spain. The edition of the maps has been carried out within the Complementary Action VALORPLAT (Scientific valorisation of multibeam bathymetry data from the Spanish continental shelf and slope), funded by the Spanish Ministry of Economy and Competitivity. Multibeam bathymetry data from the continental shelf obtained within the ESPACE project, also in a cooperative frame between IEO and SGP, completes the whole picture from the coastline to the deep abyssal plain. The map series is constituted by a general map at 1:400,000 scale and 14 detailed maps at 1:75,000 scale, which include inset maps on slope gradients and seafloor nature (rock or sediment type), the later obtained with rock dredges and Shipeck sediment dredges. Both the detailed maps and the general map are available in paper print, and the whole collection is also distributed in an edited USB. The geological features displayed in the different maps include the continental shelf, with abundant geomorphic features indicative of past sea-level changes, the continental slope carved by a large number of submarine canyons and gullies, including Palos, Tiñoso, Cartagena Este, Cartagena Oeste, Águilas, Almanzora, Alias, Garrucha and Gata submarine canyons, the Mazarrón, Palomares and Al-Mansour escarpments of probable tectonic origin, the Abubácer, Maimonides and Yusuf ridges, the

  5. Benthic study of the continental slope off Cape Hatteras, North Carolina. Volume 3. Appendices

    SciTech Connect

    Diaz, R.J.; Blake, J.A.; Lohse, D.P.

    1993-03-01

    The Point is an area that supports a most productive pelagic fishery, including tuna, swordfish, marlin, and more. The objective of the study is to analyze video tapes from near the Point, in order to provide data on epibenthic, megafaunal invertebrates including species composition, relative abundances, and large scale (1 km) distribution. The Point is not a defined spot on a chart. Although fishermen do use the steep shelf break for location, they generally look for the west wall of the Gulf Stream. The Point and the oil lease site coincidentally occur where the Gulf Stream parts the continental slope, just north of the eastern-most tip of Cape Hatteras.

  6. ON THE WIND-INDUCED EXCHANGE BETWEEN INDIAN RIVER BAY, DELAWARE AND THE ADJACENT CONTINENTAL SHELF. (R826945)

    EPA Science Inventory

    The structure of the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf is examined based on current measurements made at the Indian River Inlet which represents the only conduit of exchange between the bay and the coastal ocean. Local ...

  7. Large-scale fine-grained sediment waves over the Gulf of Valencia continental slope (northwestern Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Ribo, M.; Puig, P.; Muñoz, A.; Lo Iacono, C.; Van Rooij, D.; Palanques, A.; Acosta, J.; Guillén, J.; Gómez-Ballesteros, M.

    2014-12-01

    Recently acquired swath bathymetry on the Gulf of Valencia continental margin (NW Mediterranean Sea) allowed characterizing a large-scale sediment wave field which develops on the continental slope, from 250 m in depth to the continental rise, found at 850 m in depth. Geometric parameters as wavelength, wave height, asymmetry index, and steepness were obtained from the analysis of the bathymetric models. The internal structure of the sediment waves was determined using parametric (TOPAS), single-channel (Sparker) and multi-channel (Airgun) seismic reflection profiles. Sediment wavelengths range between 500 and 1000 m, and maximum wave heights of up to 50 m were observed on the upper-slope, decreasing downslope to just 2 m high on the continental rise. These depositional sediment waves over the continental slope are preferentially developed on the foreset region of the prograding margin clinoform, and are preserved in the sediment record since the Early/Lower Pliocene. Contemporary hydrodynamic data have determined the presence of strong near-inertial internal waves interacting with the continental slope, playing an important role in the redistribution of near-bottom suspended particles. Such hydrodynamic process can contribute to the sediment transport and deposition and to the formation of the sediment waves over the Gulf of Valencia continental slope. These morphological features were previously interpreted as a result of gravitational slope failures. However, the use of adequate seafloor mapping techniques, together with oceanographic and sedimentary dynamics measurements, allowed changing the previous interpretation and providing new insights on the seafloor morphology over this part of the NW Mediterranean continental margin.

  8. Particle fluxes and their drivers in the Avilés submarine canyon and adjacent slope, central Cantabrian margin, Bay of Biscay

    NASA Astrophysics Data System (ADS)

    Rumín-Caparrós, A.; Sanchez-Vidal, A.; González-Pola, C.; Lastras, G.; Calafat, A.; Canals, M.

    2016-05-01

    The Avilés Canyon in the central Cantabrian margin is one of the largest submarine canyons in Europe, extending from the shelf edge at 130 m depth to 4765 m depth in the Biscay abyssal plain. In this paper we present the results of a year-round (March 2012 to April 2013) study of particle fluxes in this canyon and the adjacent continental slope. Three mooring lines equipped with automated sequential sediment traps, high-accuracy conductivity-temperature recorders and current meters allowed measuring total mass fluxes and their major components (lithogenics, calcium carbonate, opal and organic matter) in the settling material jointly with a set of environmental parameters. The integrated analysis of the data obtained from the moorings together with remote sensing images and meteorological and hydrographical data has shed light on the sources of particles and the across- and along margin mechanisms involved in their transfer to the deep. Our results allow interpreting the dynamics of the sedimentary particles in the study area. Two factors play a critical role: (i) direct delivery of river-sourced material to the narrow continental shelf, and (ii) major resuspension events caused by large waves and near bottom currents developing at the occasion of the rather frequent severe storms that are typical of the Cantabrian Sea. Wind direction and subsequent wind-driven currents largely determine the way sedimentary particles reach the canyon. While westerly winds favour the injection of sediments into the Avilés Canyon mainly by building an offshore transport in the bottom Ekman layer, easterly winds ease the offshore advection of particulate matter towards the Avilés Canyon and its adjacent western slope principally through the surface Ekman layer. Furthermore, repeated cycles of semidiurnal tides add an extra amount of energy to the prevailing bottom currents and actively contribute to keep a permanent background of suspended particles in near-bottom waters. High

  9. Methane Hydrate Dissociation and Gas Seepage on Global Upper Continental Slopes Driven by Intermediate Ocean Warming

    NASA Astrophysics Data System (ADS)

    Ruppel, C. D.; Weber, T.; Kessler, J. D.; Pohlman, J.; Skarke, A. D.

    2014-12-01

    Evidence suggests that the short-term temporal pattern of seafloor gas emissions may be largely driven by tidal/barometric pressure fluctuations. However, thermal perturbations in the overlying intermediate waters are a key factor leading to gas hydrate dissociation that liberates methane to feed cold seeps near the updip limit of gas hydrate stability (GHS) on upper continental slopes. Over the past 5 years, studies have documented temperature-driven methane release at intraseasonal to century-long timescales on the West Spitsbergen margin. Our data on the US Arctic margin show that bottom water temperature (BWT) perturbations over ~2.5 months cause the theoretical updip GHS limit to migrate ~1.5 km upslope, a level of dynamism that may manifest as the observed elevated methane concentrations over the upper slope. Given the documented decades-long increase in oceanic heat content due to global warming, it is not surprising that evidence is emerging that upper slope hydrate dissociation is a global, not merely arctic, phenomenon. On the northern US Atlantic margin, most of the ~600 newly-discovered methane seeps mapped between Cape Hatteras and Georges Bank occur on the upper continental slope near the updip limit of GHS (505-575 m). A BWT database based on ~35,000 CTD casts reveals subtle along-margin variations in the theoretical updip GHS limit and first-order agreement with the observed onset of seepage. Other historical datasets provide evidence for short-term BWT variations of >1ºC on the upper slope. Hudson Canyon, the largest US Atlantic margin shelf-break canyon, has reversing current patterns that amplify short-term BWT variations, making this location an apt laboratory for study of possible gas hydrate degradation processes. Hudson Canyon surveys conducted in 2014 identified dozens more seeps than the ~50 described in Skarke et al. (Fall Meeting 2013), particularly at the updip limit of GHS At this depth, CTDs show that BWTs were initially within GHS

  10. Brittle star distribution patterns and population densities on the continental slope off central California (Echinodermata: Ophiuroidea)

    NASA Astrophysics Data System (ADS)

    Summers, Anne C.; Nybakken, James

    2000-05-01

    The ophiuroid communities on the continental slope off central California were examined using box cores and trawls. Box cores were taken between 550 and 3085 m at sites southwest of the Farallon Islands, and otter and beam trawls were used below 2300 m at three sites between the Farallon Islands and Point Sur. Eighteen ophiuroid species from six families were identified. Eighty percent of the individuals collected with box cores belonged to two species, Ophiura leptoctenia and Ophiacantha normani, which were dominant between 1000 and 2000 m. The largest ophiuroid faunal break occurred at around 2000 m and was associated with elevated dissolved oxygen levels, decreasing sediment grain size, and increasing sediment organic content. A comparison of box-core and trawl data from below 2300 m showed that box cores undersampled the ophiuroid community on the continental slope, missing almost 50% of the species collected by trawls within the same area, whereas trawls underestimated ophiuroid densities, reporting on average 243 times fewer ophiuroids per m 2 than did box cores. There was a change in species relative abundance patterns between sampling locations. Ophiuroids exhibited patchy spatial distribution patterns on both a small scale of around 0.1 m 2 and a large scale on the order of 100-1000 s of square meters.

  11. Persistent near-bottom aggregations of mesopelagic animals along the North Carolina and Virginia continental slopes

    USGS Publications Warehouse

    Gartner, John V., Jr.; Sulak, K.J.; Ross, S.W.; Necaise, Ann Marie

    2008-01-01

    Submersible observations during four missions over the North Carolina and Virginia continental slopes (184-900 m) documented the occurrence of large aggregations of mesopelagic fishes and macronektonic invertebrates near or on the bottom. Aggregated mesopelagics formed a layer up to tens of meters deep positioned from a few centimeters to 20 m, usually <10 m, above the substrate. Aggregations were numerically dominated by microvores, notably the myctophid fish Ceratoscopelus maderensis and the penaeid shrimp Sergestes arcticus. Consistently present but in relatively lower numbers, were mesopelagic predators, including the paralepidids Notolepis rissoi and Lestidium atlanticum, the eel Nemichthys scolopaceus, the stomiid fishes Chauliodus sloani and Stomias boa ferox, and squids Illex spp. Near-bottom aggregations do not appear to be an artifact due to attraction to the submersible. Based on submersible observations in three areas in 4 years spanning a decade, near-bottom aggregations of midwater organisms appear to be a geographically widespread and persistent phenomenon along the continental slope of the southeastern US Aggregations may exploit areas of enhanced food resources at the bottom. ?? 2007 Springer-Verlag.

  12. Persistent near-bottom aggregations of mesopelagic animals along the North Carolina and Virginia continental slopes

    USGS Publications Warehouse

    Gartner, John V., Jr.; Sulak, Kenneth J.; Ross, Steve W.; Necaise, Ann Marie

    2008-01-01

    Submersible observations during four missions over the North Carolina and Virginia continental slopes (184–900 m) documented the occurrence of large aggregations of mesopelagic fishes and macronektonic invertebrates near or on the bottom. Aggregated mesopelagics formed a layer up to tens of meters deep positioned from a few centimeters to 20 m, usually <10 m, above the substrate. Aggregations were numerically dominated by microvores, notably the myctophid fishCeratoscopelus maderensis and the penaeid shrimp Sergestes arcticus. Consistently present but in relatively lower numbers, were mesopelagic predators, including the paralepidids Notolepis rissoiand Lestidium atlanticum, the eel Nemichthys scolopaceus, the stomiid fishes Chauliodus sloaniand Stomias boa ferox, and squids Illex spp. Near-bottom aggregations do not appear to be an artifact due to attraction to the submersible. Based on submersible observations in three areas in 4 years spanning a decade, near-bottom aggregations of midwater organisms appear to be a geographically widespread and persistent phenomenon along the continental slope of the southeastern US Aggregations may exploit areas of enhanced food resources at the bottom.

  13. Bathymetric map of the continental slope and uppermost continental rise between Lindenkohl Canyon and South Toms Canyon, offshore Eastern United States

    USGS Publications Warehouse

    Robb, James M.; Kirby, John R.; Hampson, John C.

    1981-01-01

    This map was prepared as part of a study of geologic hazards to resource exploration and development on the Continental Slope in the Baltimore Canyon Trough area, off southern New Jersey.  Detailed bathymetric maps are required for enfineering studies of bottom stability and for geologic  interpretation of the nature of the submarine topography.  This map presents the morphology of the Continental Slope in greater detail than do other available bathymetic maps (Veatch and Smith, 1939; Uchupi, 1965, sheet 2; U.S. Coast and Geodetic Survey, 1967; Belding and Holland, 1970, sheet 1; National Ocean Survey, 1977).

  14. Bioavailability of sinking organic matter in the Blanes canyon and the adjacent open slope (NW Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Lopez-Fernandez, P.; Bianchelli, S.; Pusceddu, A.; Calafat, A.; Sanchez-Vidal, A.; Danovaro, R.

    2012-12-01

    Submarine canyons are sites of intense energy and material exchange between the shelf and the deep adjacent basins. To test the hypothesis that active submarine canyons represent preferential conduits of available food for the deep-sea benthos, two mooring lines were deployed at 1200 m depth from November 2008 to November 2009 inside the Blanes canyon and on the adjacent open slope (Catalan Margin, NW Mediterranean Sea). We investigated the fluxes, biochemical composition and food quality of sinking organic carbon (OC). OC fluxes in the canyon and the open slope varied among sampling periods, though not consistently in the two sites. In particular, while in the open slope the highest OC fluxes were observed in August 2009, in the canyon the highest OC fluxes occurred in April-May 2009. For almost the entire study period, the OC fluxes in the canyon were significantly higher than those in the open slope, whereas OC contents of sinking particles collected in the open slope were consistently higher than those in the canyon. This result confirms that submarine canyons are effective conveyors of OC to the deep sea, particles transferred are predominantly of inorganic origin, significantly higher than that reaching the open slope at a similar water depth. Using multivariate statistical tests, two major clusters of sampling periods were identified: one in the canyon that grouped trap samples collected in December 2008, concurrently with the occurrence of a major storm at the sea surface, and associated with increased fluxes of nutritionally available particles from the upper shelf. Another cluster grouped samples from both the canyon and the open slope collected in March 2009, concurrently with the occurrence of the seasonal phytoplankton bloom at the sea surface, and associated with increased fluxes of total phytopigments. Our results confirm the key ecological role of submarine canyons for the functioning of deep-sea ecosystems, and highlight the importance of canyons

  15. Holocene and deglacial paleoenvironmental history of the Peru-Chile current system and adjacent continental Chile

    NASA Astrophysics Data System (ADS)

    Lamy, F.; Hebbeln, D.; Kim, J.; Mohtadi, M.; Ruehlemann, C.

    2002-12-01

    A combined analysis of terrigenous and biogenic compounds in marine sediments from the Chilean continental slope allows detailed reconstructions of both the paleoclimatic and paleoceanographic history of this region during the last glacial and Holocene. Based on sediment cores recovered during two cruises with the German R/V Sonne, we found evidence for changes both in continental rainfall, most likely induced by latitudinal shifts of the Southern Westerlies, and marine productivity as well as sea surface temperature (SST) changes within the Peru-Chile Current system on time scales ranging from Milankovitch to centennial-scale. On Milankovitch time-scales, we found strong evidence for precession-controlled shifts of the Southern Westerlies implying e.g. more humid conditions during the LGM in the Chilean Norte Chico and a trend towards more arid climates during the deglaciation culminating in the early Holocene. These shifts are paralleled by paleoceanographic changes indicating generally higher productivity during the LGM mainly caused by increased advection of nutrients from the south through an enhanced Peru-Chile current. SSTs off central Chile were about 3.5 C lower than present during the LGM. On shorter time-scales, extremely high resolution sediment cores from the southern Chilean margin provide evidence of significant short-term Holocene climate changes with bands of variability centred at ca. 900 and 1500 years, periodicities also well known from Northern Hemisphere records. Our data point to strong interhemispheric connections of climate change both on multi-centennial to millennial and Milankovitch time-scales with a major role of the tropics for the interhemispheric transfer of climate signals involving changes within the Hadley circulation and/or probably long-term modifications of the El Ni¤o-Southern Oscillation system. The recently drilled ODP Sites 1233 (ca. 41S) and 1234/1235 (ca. 36S) at the southern Chilean margin have the potential to extent

  16. Cleanup Verification Package for the 118-F-8:4 Fuel Storage Basin West Side Adjacent and Side Slope Soils

    SciTech Connect

    L. D. Habel

    2008-03-18

    This cleanup verification package documents completion of remedial action, sampling activities, and compliance with cleanup criteria for the 118-F-8:4 Fuel Storage Basin West Side Adjacent and Side Slope Soils. The rectangular-shaped concrete basin on the south side of the 105-F Reactor building served as an underwater collection, storage, and transfer facility for irradiated fuel elements discharged from the reactor.

  17. Investigation of shallow gas hydrate occurrence and gas seep activity on the Sakhalin continental slope, Russia

    NASA Astrophysics Data System (ADS)

    Jin, Young Keun; Baranov, Boris; Obzhirov, Anatoly; Salomatin, Alexander; Derkachev, Alexander; Hachikubo, Akihiro; Minami, Hrotsugu; Kuk Hong, Jong

    2016-04-01

    The Sakhalin continental slope has been a well-known gas hydrate area since the first finding of gas hydrate in 1980's. This area belongs to the southernmost glacial sea in the northern hemisphere where most of the area sea is covered by sea ice the winter season. Very high organic carbon content in the sediment, cold sea environment, and active tectonic regime in the Sakhalin slope provide a very favorable condition for occurring shallow gas hydrate accumulation and gas emission phenomena. Research expeditions under the framework of a Korean-Russian-Japanese long-term international collaboration projects (CHAOS, SSGH-I, SSGH-II projects) have been conducted to investigate gas hydrate occurrence and gas seepage activities on the Sakhalin continental slope, Russia from 2003 to 2015. During the expeditions, near-surface gas hydrate samples at more than 30 sites have been retrieved and hundreds of active gas seepage structures on the seafloor were newly registered by multidisciplinary surveys. The gas hydrates occurrence at the various water depths from about 300 m to 1000 m in the study area were accompanied by active gas seepage-related phenomena in the sub-bottom, on the seafloor, and in the water column: well-defined upward gas migration structures (gas chimney) imaged by high-resolution seismic, hydroacoustic anomalies of gas emissions (gas flares) detected by echosounders, seafloor high backscatter intensities (seepage structures) imaged by side-scan sonar and bathymetric structures (pockmarks and mounds) mapped by single/multi-beam surveys, and very shallow SMTZ (sulphate-methane transition zone) depths, strong microbial activities and high methane concentrations measured in sediment/seawater samples. The highlights of the expeditions are shallow gas hydrate occurrences around 300 m in the water depth which is nearly closed to the upper boundary of gas hydrate stability zone in the area and a 2,000 m-high gas flare emitted from the deep seafloor.

  18. Provenance and distribution of clay minerals in the sediments of the western continental shelf and slope of India

    NASA Astrophysics Data System (ADS)

    Purnachandra Rao, V.; Ramalingeswara Rao, B.

    1995-12-01

    The distribution of clay minerals from 156 surficial sediments of the western continental margin of India, ranging from 17 to 2000 m water depth, indicate that there are three principal sources of sediments. The illite and chlorite-rich assemblage derived from the Indus (Indus Province) is predominant in the continental margin sediments to the north of the Gulf of Kachchh. An assemblage of smectite with minor kaolinite, illite and chlorite, mostly derived from the Deccan Trap basalts (Deccan Trap Province), occurs all along the inner shelf from Saurashtra to Goa. Illite, however, dominates smectite in the outer shelf of Saurashtra and on the continental slope from Saurashtra to Goa. Some samples on the outer shelf of the Gulf of Cambay-Goa show trace contents of all clay minerals, while others from the same region show the dominance of smectite over illite. A smectite and kaolinite-rich assemblage with minor illite, chlorite and gibbsite derived from the Gneissic Province occurs both on the shelf and slope between Goa and Cochin. It appears that the Indus derived sediments are transported onto the continental slope and, to a lesser extent, the outer shelf of western India by a southerly surface current and admix with clays transported from the hinterland. The influence of the Indus borne sediments on the continental slope decreases from north to south and cross shelf transport processes dominate in the southwestern continental margin between Goa and Cochin.

  19. Dynamic simulations of potential methane release from East Siberian continental slope sediments

    NASA Astrophysics Data System (ADS)

    Stranne, C.; O'Regan, M.; Dickens, G. R.; Crill, P. M.; Miller, C.; Preto, P.; Jakobsson, M.

    2015-12-01

    Sediments deposited along continental margins of the Arctic Ocean presumably host large amounts of CH4 in gas hydrates. Here we apply numerical simulations to assess the potential of gas hydrate dissociation and methane release from the East Siberian slope over the next 100 years. Simulations are based on a hypothesized bottom water warming of 3 °C, and an assumed starting distribution of gas hydrate. The simulation results show that methane hydrate dissociation in these sediments is relatively slow, and that gas fluxes toward the seafloor are limited by low sediment permeability. The latter is true even when sediment fractures are permitted to form through overpressure. With an initial gas hydrate distbution dictated by present-day pressure and temperature conditions, nominally 0.35 gigaton of CH4 are released from the East Siberian slope during the first 100 years of the simulation. However, this methane discharge is reduced significantly (to ~0.05 Gt) if Arctic Ocean history is considered. This is because a lower sea level during the last glacial maximum must result in depleted gas hydrate abundance within the most sensitive region of the modern gas hydrate stability zone. In any case, even if methane reached the atmosphere, amounts coming from East Siberian slopes would be minimal compared to present-day atmospheric methane inputs from other sources.

  20. Collapse of the northern Jalisco continental slope:Subduction erosion, forearc slivering, or subduction beneath the Tres Marias escarpment?

    NASA Astrophysics Data System (ADS)

    Bandy, W. L.; Mortera-Gutierrez, C. A.; Ortiz-Zamora, G.; Ortega-Ramirez, J.; Galindo Dominguez, R. E.; Ponce-Núñez, F.; Pérez-Calderón, D.; Rufino-Contreras, I.; Valle-Hernández, S.; Pérez-González, E.

    2010-12-01

    The Jalisco subduction zone exhibits several interesting characteristics. Among these is that convergence between the Rivera and North American plate is highly oblique, especially north of 20N, the obliquity progressively increasing to the NW. By analogy to other better studied subduction zones, this distribution of forces should produce a NW-SE extension in the overriding plate, especially north of 20N. This has led to the proposal that the trench perpendicular Bahia de Banderas is an expression of this extension [Kostoglodov and Bandy, JGR, vol. 100, 1995]. To further investigate this proposal, multibeam bathymetric data and seafloor backscatter images, seismic reflection sub-bottom profiles and marine magnetic data were collected during the MORTIC08 campaign of the B.O. EL PUMA in March 2009. The bathymetric data provides for 100% coverage (20 to 200 meter spacing of the actual measured depth value depending on the water depth) of the continental slope and trench areas north of 20N. These data indicate that a marked change occurs in the morphology of the continental slope at 20N. To the north the slope consists of a broad, fairly flat plain lying between a steep lower inner trench slope to the west and a steep, concave seaward, escarpment to the east. In contrast, to the south the continental slope exhibits a more gradual deepening until the steep lower inner trench slope. A prominent submarine canyon deeply incises the continental slope between these two morphotectonic domains. This canyon appears to represent the boundary between two NW-SE diverging forearc blocks or slivers, consistent with the presence of oblique convergence. In contrast, the broad, fairly flat plain is better explained by subsidence induced by subduction erosion (i.e. erosion of the base of the overriding plate underneath the continental slope area). The shoaling of the trench axis northward towards the Puerto Vallarta Graben and subsequent deepening may be related to subduction of the

  1. Rippled scour depressions on continental shelf bank slopes off Nordland and Troms, Northern Norway

    NASA Astrophysics Data System (ADS)

    Bellec, Valérie K.; Bøe, Reidulv; Rise, Leif; Slagstad, Dag; Longva, Oddvar; Dolan, Margaret F. J.

    2010-05-01

    Multibeam bathymetry acquired under the MAREANO programme from the continental shelf off Nordland and Troms, northern Norway, show bedforms that we have interpreted as rippled scour depressions. They occur in three areas offshore on bank slopes facing southeast, more than 15 km from land. They are generally found where the slope gradient is low, in water depths of 70-160 m. Individual depressions are up to 3 km long, 1 m deep and up to 300 m wide. They occur in areas where sediments evolve quickly from glacial deposits on the banks to post-glacial muddy sediments on the glacial troughs. Multibeam backscatter and underwater video data show that depression floors are covered by rippled, gravelly, shelly sand. Ripple crests are parallel or slightly oblique to the depression axis orientation. Sand without bedforms is observed between the depressions. TOPAS seismic lines show that the uppermost seismic unit consists of the sand between the depressions. The base of this unit may be the last transgressive/tidal/wave ravinement surface. Physical oceanographic modelling indicates that maximum current velocities are up to 0.6 m/s in the rippled scour depression areas. Stronger currents appear to inhibit the building of these features. Tidal currents play an important role as they trend parallel to the southeast banks slopes and are likely responsible of the gravelly ripples formation inside the depressions as well as the persistence of these depressions which are not covered by finer sediments. On Malangsgrunnen bank, some of the rippled scour depressions are in the extension of NW-SE furrows located on the bank. Simulated bottom currents indicate currents mainly perpendicular to these furrows, as for the rippled scour depressions on the bank slopes. Nevertheless, these features could also highlight currents coming from the northwest which reach the bank margin and continue down to the areas of the rippled scour depressions. These currents could be responsible for the

  2. Morphology and origin of smaller-scale mass movements on the continental slope off northern Norway

    NASA Astrophysics Data System (ADS)

    Baeten, Nicole J.; Laberg, Jan Sverre; Forwick, Matthias; Vorren, Tore O.; Vanneste, Maarten; Forsberg, Carl Fredrik; Kvalstad, Tore J.; Ivanov, Michael

    2013-04-01

    Little attention has been paid to smaller-scale mass movements on continental slopes, even though they occur much more frequently than their large-scale counterparts. Swath bathymetry, side-scan sonar, sub-bottom profiler and seismic data from the continental slope offshore the Lofoten Islands, northern Norway, reveal evidence of repetitive smaller-scale translational sliding, involving spreading and multi-phase retrogression, in water depths between 1100 and 2500 m. Three styles of failure have been identified, occurring in close proximity. Style 1 is characterized by a 4.7 km wide and up to 100 m deep amphitheater shaped headwall, a relatively deep glide plane (± 130 mbsf), detached sediment ridges and a run-out area with rafted sediment blocks. Style 2 consists of a staircase pattern of secondary escarpments, caused by the activation of several glide planes between ± 30 and 110 mbsf. Headwalls and secondary escarpments have a height of up to 30 and 70 m, respectively. The run-out area shows an almost complete sediment evacuation. Style 3 is more subtle, as it is only identified on the side-scan sonar data due to its higher spatial resolution. This style shows different phases of on-going evolution, illustrating the gradual disintegration of a slab of sediments moving over a shallow glide plane at ± 13 mbsf. Zones with sediment slabs are up to several hundreds of meters wide and are sharply delineated by shear margins or escarpments. The spatial variation in the failure style is inferred to have been caused by the activation of different glide planes, which is probably a result of the thinning of contouritic sediments towards the south-west. In the north-east, the mounded contouritic sediments contain more potential glide planes and higher slope angles. The smaller-scale mass movements are suggested to have been triggered by undercutting and removal of support at the foot of the slope due to large-scale mass movements that have occurred immediately south of

  3. Self-advection of density perturbations on a sloping continental shelf

    SciTech Connect

    Ping-Tung Shaw; Csanady, G.T.

    1983-05-01

    Bottom water movement on the continental shelf is modeled by the nonlinear interaction between longshore bottom geostrophic flow and the density field. Bottom geostrophic velocity, subject to linear steady momentum equations with linear bottom friction, can be generated by along-isobath density variations over a sloping bottom. At the same time, the density field is slowly advected by the velocity field. Away from boundary layers, the interplay is governed by Burgers' equation, which shows the formation and self-propulsion of strong density gradients along an isobath. The direction of propagation of a dense water blob is to have shallow water on the right- (left-) hand side facing downstream in the Northern (Southern) Hemisphere. The propagation of a light water blob is opposite to that of a dense water blob.

  4. Variability of PCB burden in 5 fish and sharks species of the French Mediterranean continental slope.

    PubMed

    Cresson, Pierre; Fabri, Marie Claire; Miralles, Françoise Marco; Dufour, Jean-Louis; Elleboode, Romain; Sevin, Karine; Mahé, Kelig; Bouchoucha, Marc

    2016-05-01

    Despite being generally located far from contamination sources, deep marine ecosystems are impacted by chemicals like PCB. The PCB contamination in five fish and shark species collected in the continental slope of the Gulf of Lions (NW Mediterranean Sea) was measured, with a special focus on intra- and interspecific variability and on the driving factors. Significant differences occurred between species. Higher values were measured in Scyliorhinus canicula, Galeus melastomus and Helicolenus dactylopterus and lower values in Phycis blennoides and Lepidorhombus boscii. These differences might be explained by specific abilities to accumulate and eliminate contaminant, mostly through cytochrome P450 pathway. Interindividual variation was also high and no correlation was observed between contamination and length, age or trophic level. Despite its major importance, actual bioaccumulation of PCB in deep fish is not as documented as in other marine ecosystems, calling for a better assessment of the factors driving individual bioaccumulation mechanisms and originating high variability in PCB contamination. PMID:26874319

  5. Geology and potential hazards of the continental slope between Lindenkohl and South Toms canyons, offshore Mid-Atlantic United States

    USGS Publications Warehouse

    Robb, James M.; Hampson, John C., Jr.; Kirby, John R.; Twichell, David C.

    1981-01-01

    Because sediment instability, or slumping, has been identified as a potential hazard to petroleum development of the east-coast Continental Slope, the U.S. Geological Survey, in cooperation with the U.S. Bureau of Land Management, began a detailed study of a segment of the Continental Slope between Lindenkohl and South Toms Canyons off New Jersey. This 40-km x 35-km area was chosen for study because it lies within the area of high interest for petroleum development (Lease sales 49 and 59), and because it includes several wells which provide stratigraphic control. This report discusses the results of geologic mapping, using seismic-reflection data acquired in 1978 and 1979. Some initial results from more recently acquired data are included. The Continental Slope in the study area has a complex surface with ridges, canyons, and valleys. Three slump or slide features were observed in the heads and on the walls of canyons and valleys, and two slides were identified on an intercanyon area. The identified slumps or slides are found in Quaternary sediments and total about 1.3 percent of the Continental Slope area mapped. The slope is generally mantled by less than 2 m of Holocene sediments. Pleistocene sediment (primarily silty clay) is about 450 m thick at the top of the slope and thins to nearly zero or is absent on much of the mid and lower slope, where sediments of Miocene to Eocene age are exposed. Ridges on the midslope (water depths of 800-1,500 m) and parts of the lowr slope (1,500-2,150 m) result primarily from Pleistocene and older deposition. The intervening valleys show evidence of erosion along the deepest parts of their courses. Mid-range sidescan-sonar data show evidence that processes of bottom-current erosion and downcanyon transport of material may be active in the present day. However, major features of the sea floor appear to be unchanged since late-Pleistocene time.

  6. Geomorphology and sediment stability of a segment of the U.S. continental slope off New Jersey

    USGS Publications Warehouse

    Robb, James M.; Hampson, J.C., Jr.; Twichell, D.C.

    1981-01-01

    The morphology of complex deposits of Pleistocene sediments covering the upper continental slope between Lindenkohl Canyon and South Toms Canyon results from both depositional and erosional processes. Small slump or slide features were detected primarily on the flanks of canyons or valleys and were observed to occur only within Pleistocene-aged sediments. Eocene to Miocene sediments are exposed over much of the mid- and lower slope in this area. Copyright ?? 1981 AAAS.

  7. Processes of benthic foraminiferal fossil assemblage formation on the continental slope

    SciTech Connect

    Loubere, P. )

    1991-03-01

    Theoretical analysis of benethic foraminiferal fossil assemblage formation shows that the assemblage eventually preserved in the sediments is an integrated result of species' test production rate, microhabitat behavior, and biogeochemical processes that control the probability of species' test preservation. The biogeochemical processes that influence test preservation in slope sediments are controlled by the flux of organic carbon to the sea-bed and the botton water oxygen concentration. These variables also affect the depth of the biotic habitation zone in the sediments. Therefore, organic carbon flux and bottom water oxygen content should be reflected in benthic foraminiferal fossil assemblages for both ecologic and taphonomic reasons. An integrated study of fossil assemblage generation was conducted on the Gulf of Mexico continental slope using box cores collected along depth transects across the oxygen minimum, and using live and dead assemblage analysis combined with {sup 210}Pb measurements to quantify biotic activity in the sediments and pore water nutrient and metals analysis to quantify biogeochemical processes acting in the sediment habitation zone. The results show that the size of the habitation zone and live standing stock are influenced by organic carbon flux and oxygen supply to the sea-bed. The fossil assemblage is created progressively through the upper 10-20 cm of sediment and biologichemically driven test destruction (taphonomic process) is important in determining the assemblage that enters the geologic record.

  8. Spatial heterogeneity of benthos associated with biogenic structures on the North Carolina continental slope

    NASA Astrophysics Data System (ADS)

    Schaff, T. R.; Levin, L. A.

    The objective of this study was to determine if biogenic features such as mounds, pits and tubes produce small-scale (0.1-100 m) spatial heterogeneity in macrofaunal community structure on the continental slope off North Carolina at 850 m. Macrofaunal and microbial communities associated with sediment mounds, pits and level areas were compared off Cape Lookout, North Carolina. No significant differences were found in sediment microbial counts or total macrofaunal distributions. One paraonid polychaete ( Levensenia gracilis) was more abundant in pits than in the other samples, and infaunal anemones exhibited depressed densities in sediment mounds. At a second site, off Cape Hatteras, North Carolina, infaunal heterogeneity associated with the tube-building foraminiferan Bathysiphon filiformis was examined by comparing an area with high tube densities (93.8 m -2) with an area 100 m away without tubes. No significant differences were found in the distribution and abundances of bacteria between the two areas. The only significant difference found in infaunal densities was the presence of high numbers of reproductive oligochaetes in the 5-10 cm fraction beneath tube beds. Oneterebellid polychaete species ( Nicolea sp.), which lives exclusively on B. filiformis tubes, was absent in the non-tube area. With a few exceptions, the biogenic structures examined at these two sites appeared to exert only minor influence on macrofaunal or microbial community structure. Within each site, slope assemblages examined in this study appeared to be homogeneous on the small scales examined.

  9. Causes of two slope-failure types in continental-shelf sediment, northeastern Gulf of Alaska

    USGS Publications Warehouse

    Schwab, William C.; Lee, Homa J.

    1988-01-01

    Slumps and sediment-gravity flows have been identified in Holocene glaciomarine sediment on declivities less than 1.3 degrees on the Gulf of Alaska continental shelf. Geologic and geotechnical investigation suggest that the processes responsible for these slope failures are earthquake and storm-wave loading, coupled with cyclic degradation of the sediment-shear strength. We propose that the failure type is related to the nature of the failure load. For example, a slump that occurs approximately 30 km seaward of Icy Bay in water depth of 70 to 150 m was most likely caused by earthquake loading, whereas sediment-gravity flows on the Alsek prodelta, which occur in water depths of 35 to 80 m, probably were caused primarily by storm-wave loading. Sediment remolding and redistribution and incorporation of water, which occurs more readily during wave loading from a long storm than during the limited number of loading cycles generated by an earthquake, reduces the shear strength and increases the fluidity of the failed sediment mass. Wave-induced slope failures thereby tend to transform into sediment-gravity flows.

  10. Analysis of bubble plume distributions to evaluate methane hydrate decomposition on the continental slope

    NASA Astrophysics Data System (ADS)

    Johnson, H. Paul; Miller, Una K.; Salmi, Marie S.; Solomon, Evan A.

    2015-11-01

    Cascadia margin sediments contain a rich reservoir of carbon derived both from terrestrial input and sea surface productivity. A portion of this carbon exists as solid gas hydrate within sediment pore spaces which previous studies have shown to be a methane reservoir of substantial size on both the Vancouver Island and Oregon portions of the Cascadia margin. Multichannel seismic reflection profiles on the Cascadia margin show the widespread presence of Bottom Simulating Reflectors (BSRs) within the sediment column, indicating the gas hydrate reservoir extends from the deformation front at 3000 m depth to the upper limit of gas hydrate stability near 500 m water depth. In this study, we compile an inventory of methane bubble plume sites on the Cascadia margin identified in investigations carried out for a range of interdisciplinary goals that also include sites volunteered by commercial fishermen. High plume density anomalies are associated with both the continental shelf (<180 m) and the depth of the upper limit of methane hydrate stability depth (MHSD) that occurs near 500 m in the NE Pacific. The observed anomalies on the Cascadia slope may be due to the warming of seawater at intermediate depths, suggesting that modern climate change has begun to destabilize the climate-sensitive hydrate reservoir within the Cascadia margin sediments. Reanalysis of similar plume images on the North American Atlantic slope suggests a lack of correlation between observed plume depths and the MHSD for much of the latitudinal range.

  11. Organic carbon inputs to the sea bottom of the Mallorca continental slope

    NASA Astrophysics Data System (ADS)

    Pasqual, Catalina; Calafat, Antoni; Lopez-Fernandez, Pilar; Pusceddu, Antonio

    2015-08-01

    To assess the origin and degradation state of the organic particles sinking towards the sea bottom of the Mallorca continental slope, the major inorganic and organic components of the total mass flux and its biochemical composition (in terms of protein, carbohydrate, lipid and phytopigment contents) have been analysed. Two instrumented lines were deployed at the western (Sóller station, Balearic sub-basin) and southern (Cabrera station, Algerian sub-basin) slopes of Mallorca Island, 900 m depth from November 2009 to January 2011. The two locations are characterized by putatively different environmental settings. Settled material at Sóller station has higher lithogenic contents when compared with the Cabrera one. Such difference can be explained by the synergistic presence in the Sóller station of large inputs of resuspended material due to the mesoscale variability of the Balearic current and the impact of bottom trapped waves. On the other hand, at the Cabrera station sinking particles are characterized by OM and opal percentages higher than those recorded at the Sóller station. This result points out that organic particles reaching the sea floor at the Cabrera station have a pre-eminent pelagic origin. Based on analyses of the C and N stable isotopes of the sinking material, our results also highlight that, overall, the OM reaching the sea floor at the Mallorca slope is mostly of marine origin. In general, the OM settled at the Sóller station has a higher nutritional value than that at the Cabrera one. Such a difference, occurring across a relatively reduced spatial scale, let us hypothesizing that the nutritionally richer particles descending in the Cabrera station are exposed to a less energetic environment than that in the Sóller setting. This would lead to higher settling velocity of particles in the Sóller setting which in turn would result in lower degradation rates of particles during their descent towards the sea bottom.

  12. Bioavailability of sinking organic matter in the Blanes canyon and the adjacent open slope (NW Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Lopez-Fernandez, P.; Bianchelli, S.; Pusceddu, A.; Calafat, A.; Sanchez-Vidal, A.; Danovaro, R.

    2013-05-01

    Submarine canyons are sites of intense energy and material exchange between the shelf and the deep adjacent basins. To test the hypothesis that active submarine canyons represent preferential conduits of available food for the deep-sea benthos, two mooring lines were deployed at 1200 m depth from November 2008 to November 2009 inside the Blanes canyon and on the adjacent open slope (Catalan Margin, NW Mediterranean Sea). We investigated the fluxes, biochemical composition and food quality of sinking organic carbon (OC). OC fluxes in the canyon and the open slope varied among sampling periods, though not consistently in the two sites. In particular, while in the open slope the highest OC fluxes were observed in August 2009, in the canyon the highest OC fluxes occurred in April-May 2009. For almost the entire study period, the OC fluxes in the canyon were significantly higher than those in the open slope, whereas OC contents of sinking particles collected in the open slope were consistently higher than those in the canyon. This result confirms that submarine canyons are effective conveyors of OC to the deep sea. Particles transferred to the deep sea floor through the canyons are predominantly of inorganic origin, significantly higher than that reaching the open slope at a similar water depth. Using multivariate statistical tests, two major clusters of sampling periods were identified: one in the canyon that grouped trap samples collected in December 2008, concurrently with the occurrence of a major storm at the sea surface, and associated with increased fluxes of nutritionally available particles from the upper shelf. Another cluster grouped samples from both the canyon and the open slope collected in March 2009, concurrently with the occurrence of the seasonal phytoplankton bloom at the sea surface, and associated with increased fluxes of total phytopigments. Our results confirm the key ecological role of submarine canyons for the functioning of deep-sea ecosystems

  13. Morphobathymetric analysis of the large fine-grained sediment waves over the Gulf of Valencia continental slope (NW Mediterranean)

    NASA Astrophysics Data System (ADS)

    Ribó, Marta; Puig, Pere; Muñoz, Araceli; Lo Iacono, Claudio; Masqué, Pere; Palanques, Albert; Acosta, Juan; Guillén, Jorge; Gómez Ballesteros, María

    2016-01-01

    Detailed analysis of recently acquired swath bathymetry, together with high-resolution seismic profiles and bottom sediment samples, revealed the presence of large-scale fine-grained sediment waves over the Gulf of Valencia continental slope. As many other deep-water sediment waves, these features were previously attributed to gravitational slope failure, related to creep-like deformation, and are here reinterpreted as sediment wave fields extending from 250 m depth to the continental rise, at ~ 850 m depth. Geometric parameters were computed from the high-resolution multibeam dataset. Sediment wave lengths range between 500 and 1000 m, and maximum wave heights of up to 50 m are found on the upper slope, decreasing downslope to minimum values of 2 m high. Sediment waves on the lower part of the slope are quasi-stationary vertically accreting, whereas they show an upslope migrating pattern from the mid-slope to the upper part of the continental slope. High-resolution seismic profiles show continuous internal reflectors, with sediment waves merging down-section and sediment wave packages decreasing in thickness downslope. These sediment packages are thicker on the crest of each individual sediment wave and thinner on the downslope flank. 210Pb analyses conducted on sediment cores collected over the sediment wave fields also indicate slightly higher sediment accumulation rates on the wave crests. Sediment wave formation processes have been inferred from contemporary hydrodynamic observations, which reveal the presence of near-inertial internal waves interacting with the Gulf of Valencia continental slope. Internal wave activity is suggested to be the preferential mechanism for the transport and deposition of sediment, and the maintenance of the observed sediment wave fields.

  14. The geodynamic province of transitional crust adjacent to magma-poor continental margins

    NASA Astrophysics Data System (ADS)

    Sibuet, J.; Tucholke, B. E.

    2011-12-01

    Two types of 'transitional crust' have been documented along magma-poor rifted margins. One consists of apparently sub-continental mantle that has been exhumed and serpentinized in a regime of brittle deformation during late stages of rifting. A second is highly thinned continental crust, which in some cases is known to have been supported near sea level until very late in the rift history and thus is interpreted to reflect depth-dependent extension. In both cases it is typically assumed that formation of oceanic crust occurs shortly after the breakup of brittle continental crust and thus that the transitional crust has relatively limited width. We here examine two representative cases of transitional crust, one in the Newfoundland-Iberia rift (exhumed mantle) and one off the Angola-Gabon margin (highly thinned continental crust). Considering the geological and geophysical evidence, we propose that depth-dependent extension (riftward flow of weak lower/middle continental crust and/or upper mantle) may be a common phenomenon on magma-poor margins and that this can result in a much broader zone of transitional crust than has hitherto been assumed. Transitional crust in this extended zone may consist of sub-continental mantle, lower to middle continental crust, or some combination thereof, depending on the strength profile of the pre-rift continental lithosphere. Transitional crust ceases to be emplaced (i.e., final 'breakup' occurs) only when emplacement of heat and melt from the rising asthenosphere becomes dominant over lateral flow of the weak lower lithosphere. This model implies a two-stage breakup: first the rupture of the brittle upper crust and second, the eventual emplacement of oceanic crust. Well-defined magnetic anomalies can form in transitional crust consisting of highly serpentinized, exhumed mantle, and they therefore are not diagnostic of oceanic crust. Where present in transitional crust, these anomalies can be helpful in interpreting the rifting

  15. Northern Gulf of Mexico Continental Slope study. Final report (year 4). Volume 1. Executive summary. Final report

    SciTech Connect

    Gallaway, B.J.

    1988-09-01

    In 1983, the Minerals Management Service initiated a multi-year program to study the Continental Slope of the northern Gulf of Mexico as part of its Outer Continental Shelf environmental-studies program. This particular program, the Northern Gulf of Mexico Continental Slope Program, has three primary goals: (1) to determine the abundance, structure, and distribution of animal communities in the deep sea Gulf of Mexico; (2) to determine the hydrography and bottom conditions at selected sites within the study area and to relate these to faunal variations; and (3) to measure present levels of hydrocarbon contamination in deep-sea sediments and selected animals. Volume I provides an introduction of the study and summarizes field and laboratory methods; the environmental characterization of the area; meiofauna, macrofauna, megafauna; an overview of the chemosynthetic community; the Bush Hill chemosynthetic community, the general conceptual model; depth patterns of standing stocks; faunal assemblages and zonation; conclusions; sampling deficiencies and recommendations; and literature cited.

  16. OESbathy version 1.0: a method for reconstructing ocean bathymetry with generalized continental shelf-slope-rise structures

    NASA Astrophysics Data System (ADS)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

    2015-09-01

    We present a method for reconstructing global ocean bathymetry that combines a standard plate cooling model for the oceanic lithosphere based on the age of the oceanic crust, global oceanic sediment thicknesses, plus generalized shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to develop a methodology for reconstructing ocean bathymetry in the geologic past that includes heterogeneous continental margins in addition to abyssal ocean floor. First, the plate cooling model is applied to maps of ocean crustal age to calculate depth to basement. To the depth to basement we add an isostatically adjusted, multicomponent sediment layer constrained by sediment thickness in the modern oceans and marginal seas. A three-parameter continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Parameters of the shelf-slope-rise structures at active and passive margins are determined from modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and central Atlantic, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth to basement, ocean bathymetry with an isostatically adjusted multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  17. A benthic carbon budget for the continental slope off Cape Hatteras, N.C.

    SciTech Connect

    Thomas, C.J.; Blair, N.E.; DeMaster, D.J.; Jahnke, R.A.; Martens, C.S.

    1999-01-31

    The continental slope off Cape Hatteras, N.C. from approximately 36{degree} 00 minutes N to 35{degree} 20 minutes N is a region of relatively rapid sediment accumulation, organic matter deposition and subsequent remineralization. The measured fluxes are the highest reported for the slope off the eastern US Sediment accumulation rates range from 40 to 140 cm ky{sup -1}. Organic carbon deposition rates range from 3.5 to 7.4 moles C m{sup -2} yr{sup -1}. The areal coverage of this ''depocenter'' is probably controlled by interactions between physical oceanographic processes and the rugged topography of the seafloor. The organic matter deposited on the seafloor is primarily marine in origin and a mix of old and fresh particles. 73-93% of the depositing detritus is rapidly oxidized near the sediment/water interface. The controls on subsurface remineralization appear to be a complex function of the relative amount of metabolizable carbon delivered to the seabed both now and in the distant past (>=500ybp) and the extent of seabed irrigation. The age of DIC and CH{sub 4} produced within the seabed indicates that relatively young, reactive carbon is advected below the sediment surface and fuels subsurface remineralization. The stable isotopic composition of DIC produced within the seabed indicates the selective degradation of {sup 13}C-enriched fractions of the organic matter. The metabolizable fraction has a carbon isotopic signature of approx. -18{per_thousand};, while the organic matter that survives degradation and is buried has a d{sup 13}C closer to -20{per_thousand}.

  18. C/sup 13/-depleted authigenic carbonate buildups from hydrocarbon seeps, Louisiana Continental Slope

    SciTech Connect

    Roberts, H.H.; Sassen, R.; Aharon, P.; Carney, R.

    1989-03-01

    Geohazard and geochemical survey data consisting of high-resolution profiles, side-scale sonographs, drop cores, dredge samples, and borings have substantiated the consistent association between carbonate buildups and hydrocarbon seeps on the Louisiana continental slope. Analyses indicate a range of carbonate mineralogies including aragonite, Mg-calcite, and dolomite that are extremely depleted in the C/sup 13/ isotope (/approximately/dC/sup 13/ values to /minus/48/per thousand/ PDB). Microbial oxidation of methane (biogenic and thermogenic) and crude oil creates a source of pore water CO/sub 2/ containing isotopically light carbon, which triggers carbonate precipitation. Geophysical and geochemical evidence suggests that both surface and subsurface lithification is taking place. Recent observations and samples collected using a Pisces class research submersible confirm the abundance of C/sup 13/-depleted sedimentary carbonates and massive authigenic buildups associated with the tops and flanks of shallow salt diapirs and gas hydrate hills. Although chemosynthetic communities (including tube worms and bivalves) with isotopically light carbon in tissues have been described from gas seeps, bacterial mats sampled from several seep areas using a submersible have /delta/C/sup 13/ values of /minus/28 to /minus/ /per thousand/ PDB, suggesting a crude oil contribution to microbial biomass. Lithoherms 15 m in vertical dimension are not unusual on dome crests. These features dominate mesoscale sea-floor topography on the slope and have important short-term impacts on platform locations as well as pipeline routing. They are of long-term importance as sites for low sea level reefs. Moreover, these observations provide new insight into the earliest stages of salt-dome cap-rock evolution.

  19. Internal tide transformation across a continental slope off Cape Sines, Portugal

    NASA Astrophysics Data System (ADS)

    Small, Justin

    2002-04-01

    During the INTIFANTE 99 experiment in July 1999, observations were made of a prominent internal undular bore off Cape Sines, Portugal. The feature was always present and dominant in a collection of synthetic aperture radar (SAR) images of the area covering the period before, during and after the trial. During the trial, rapid dissemination of SAR data to the survey ship enabled assessment of the progression of the feature, and the consequent planning of a survey of the bore coincident with a new SAR image. Large amplitude internal waves of 50 m amplitude in 250 m water depth, and 40 m in 100 m depth, were observed. The images show that the position of the feature is linked to the phase of the tide, suggesting an internal tide origin. The individual packets of internal waves contain up to seven waves with wavelengths in the range of 500-1500 m, and successive packets are separated by internal tide distances of typically 16-20 km, suggesting phase speeds of 0.35-0.45 m s -1. The internal waves were coherent over crest lengths of between 15 and 70 km, the longer wavefronts being due to the merging of packets. This paper uses the SAR data to detail the transformation of the wave packet as it passes across the continental slope and approaches the coast. The generation sites for the feature are discussed and reasons for its unusually large amplitude are hypothesised. It is concluded that generation at critical slopes of the bathymetry and non-linear interactions are the likely explanations for the large amplitudes.

  20. Four new Paramphimonhystrella species (Nematoda: Xyalidae) from the continental slope of New Zealand.

    PubMed

    Leduc, Daniel

    2014-01-01

    Four new Paramphimonhystrella species are described from the continental slope of New Zealand. P. glossalga n. sp. is characterised by presence of twelve lips, large buccal cavity, males with short, heavily cuticularised spicules joined distally, and females with large postvulvar sac and hammer-shaped cuticularised piece immediately posterior to vagina. P. barbula n. sp. is characterised by narrow buccal cavity, oval-shaped amphids, conico-cylindrical tail with swollen appearance due to conspicuously enlarged caudal gland, and males with long slender spicules and small gubernaculum. P. scutula n. sp. is characterised by a lozenge-shaped buccal cavity, males with scythe-shaped spicules, females with vulva at almost two thirds of body length from anterior, and a hammer-shaped cuticularised piece immediately posterior to vagina. P. echinocauda n. sp. is characterised by buccal cavity with cylindrical anterior portion and funnel-shaped posterior portion, distal tip of slender spicules with three pointed projections, thin gubernaculum, and tail with several long setae in middle portion, two lateral setae near tail tip and one terminal seta. The presence of a hammer-shaped cuticularised piece in two species of the genus is recorded for the first time; the function of this structure is unknown. The genus diagnosis is emended and a key to all known Paramphimonhystrella species (seven in total) is provided. The present study provides the first record of the genus outside the type locality (Yellow Sea) and extends its depth distribution from <150 m to 1350 m. PMID:24943443

  1. Benthic foraminifers on the continental shelf and upper slope, Russian River area, northern California ( USA).

    USGS Publications Warehouse

    Quinterno, P.J.; Gardner, J.V.

    1987-01-01

    We analyzed benthic foraminifers from 71 surface samples collected from the sea floor of the continental margin. One hundred and six different taxa were identified, and Q-mode factor analysis was used to identify assemblages. Six foraminiferal assemblage factors explain 94% of the variation in the data matrix. The Inner Shelf Assemblage is characterized by Trichohyalus ornatissima, Rotalia columbiensis, Cassidulina limbata, Cibicides fletcheri, Elphidiella hannai and Elphidium sp. 1 and occupies water depths less than 50 m. The Middle Shelf Assemblage is characterized by Nonionella basispinata, Elphidium excavatum and Florilus labradoricus and occupies water depths between 50 and 90 m. A Middle Shelf to Upper Bathyal Assemblage is characterized by Uvigerina juncea, Globobulimina spp. and Nonionella basispinata and occupies depths between about 90 and 450 m. Two overlapping assemblages make up the Upper Middle Bathyal Assemblage and are most abundant between water depths of 500 and 1300 m. They are associated with low- oxygen conditions. The Mid-Bathyal Assemblage is dominated by Uvigerina proboscidea and occurs on the slope at water depths ranging from 1200 to 2500 m. -from Authors

  2. Association of oil seeps and chemosynthetic communities with oil discoveries, upper continental slope, Gulf of Mexico

    SciTech Connect

    Sassen, R.; Brooks, J.M.; MacDonald, I.R.; Kennicutt, M.C. II; Guinasso, N.L. Jr. )

    1993-09-01

    A belt of sea-floor oil seeps and chemosynthetic communities has been mapped across the upper continental slope, offshore Louisiana, at depths ranging from 2000 to 1000 m. Visibly oil-stained sediments and thelmogenic gas hydrates have been recovered using piston cores and research submarines. Biomarker fingerprinting of seep oils suggests an origin from deeply buried Cretaceous or Jurassic source rocks characterized by marine kerogen. The abundance of seeps provides a unique opportunity to define their relationship to oil discoveries including Auger, Cooper, Jolliet, Marquette, Vancouver, Popeye, and Mars. Seeps are preferentially distributed over shallow salt ridges that rim intrasalt basin cooking pots, over salt diapirs, and along shallow fault traces near discoveries. Diagnostic seep-related features on the sea floor include gas hydrate mounds and outcrops, pockmarks and craters, mud volcanoes, and carbonate buildups. Many of the 50 chemosynthetic communities including tube worms, mussels, or clams thus far documented in the gulf occur near discoveries. Recent imagery from orbital platforms, including the space shuttle, shows that natural oil slicks are common on the sea surface in this area. Additional mapping of seep distributions should contribute to better defining of the limits of the deep Gulf play fairway.

  3. Recent benthic foraminifera from the Caribbean continental slope and shelf off west of Colombia

    NASA Astrophysics Data System (ADS)

    Fiorini, Flavia

    2015-07-01

    A quantitative benthic foraminiferal analysis was conducted on 30 sea-floor sediment samples distributed along the continental slope and shelf in Fuerte Area (Colombian Caribbean), between 39 and 2469 m water depth. The aims of the research were to provide data on the distribution of southwestern Caribbean Recent benthic foraminifera, to estimate changes in the foraminiferal distribution related to the bathymetry and the characteristics of the substrate, to define a data-bank on distribution of recent tropical benthic foraminifera from the southwestern Caribbean, to provide reference on foraminiferal distribution that can be used in bathymetric reconstructions of ancient environments. Three different assemblages corresponding to three different environments were identified by cluster analysis. Assemblage A, characterized by variable percentages of porcellaneous, hyaline and agglutinated benthic foraminifera indicative of shelf environments. Assemblage B, dominated by calcareous hyaline foraminifera mainly composed of infaunal foraminifera corresponding to upper bathyal, marine conditions. Assemblage C, composed by agglutinated and calcareous hyaline foraminifera characteristic of normal deep-water marine environments.

  4. Upwelling on the continental slope of the Alaskan Beaufort Sea: Storms, ice, and oceanographic response

    NASA Astrophysics Data System (ADS)

    Pickart, Robert S.; Moore, G. W. K.; Torres, Daniel J.; Fratantoni, Paula S.; Goldsmith, Roger A.; Yang, Jiayan

    2009-01-01

    The characteristics of Pacific-born storms that cause upwelling along the Beaufort Sea continental slope, the oceanographic response, and the modulation of the response due to sea ice are investigated. In fall 2002 a mooring array located near 152°W measured 11 significant upwelling events that brought warm and salty Atlantic water to shallow depths. When comparing the storms that caused these events to other Aleutian lows that did not induce upwelling, interesting trends emerged. Upwelling occurred most frequently when storms were located in a region near the eastern end of the Aleutian Island Arc and Alaskan Peninsula. Not only were these storms deep but they generally had northward-tending trajectories. While the steering flow aloft aided this northward progression, the occurrence of lee cyclogenesis due to the orography of Alaska seems to play a role as well in expanding the meridional influence of the storms. In late fall and early winter both the intensity and frequency of the upwelling diminished significantly at the array site. It is argued that the reduction in amplitude was due to the onset of heavy pack ice, while the decreased frequency was due to two different upper-level atmospheric blocking patterns inhibiting the far field influence of the storms.

  5. Trophic relationship of benthic invertebrate fauna from the continental slope of the Sea of Japan

    NASA Astrophysics Data System (ADS)

    Kharlamenko, Vladimir I.; Brandt, Angelika; Kiyashko, Serguei I.; Würzberg, Laura

    2013-02-01

    The Sea of Japan continental slope food web was examined by analysis of stable C and N isotopes and fatty acid compositions in ten species of common benthic organisms and in sediment and particulate organic matter. A considerable range of δ13C and δ15N values was found for benthic species, with δ13C values of -22.3‰ in crinoids (Heliometra glacialis) to -16.1‰ in asteroids (Ctenodiscus crispatus) and with δ15N values of 5.3‰ in foraminifera (Elphidium sp.) to 15.5‰ in C. crispatus. Polyunsaturated fatty acids were the most abundant of the fatty acids in the total lipids of all investigated species. The organisms' individual fatty acid compositions show the importance of a variety of food sources, including phytoplankton, detritus, foraminiferans and zooplankton, for megabenthic species. Additionally, the presence of considerable amounts of the 20:4(n-6) and 20:1(n-13) fatty acids indicates the importance of the benthic microbial loop in the nutrition of some of the studied animals.

  6. Mercury in sediments from shelf and continental slope at Campos Basin near Rio de Janeiro, Brazil

    NASA Astrophysics Data System (ADS)

    Araujo, Beatriz; Hintelmann, Holger; Dimock, Brian; Gomes de Almeida, Marcelo; Falcão, Ana Paula; de Rezende, Carlos Eduardo

    2016-04-01

    Mercury (Hg) is a global pollutant due to its ability to undergo long-range transport from source regions to remote parts of the world, and its ubiquitous presence in aquatic ecosystems. The Hg isotope ratios could be an effective tool for tracing the sources and process of Hg in the environment. This study aimed to establish the distribution of mercury in surface sediments of three transects (25- 3000m water depth) in continental shelf and slope in Campos Basin-RJ-Brazil, using the Hg isotopes to understand the geochemical processes relating to Hg cycling that occur in a subtropical coastal environment. The study area was divided into three transects: A (located to the south and close to a upwelling area), D (located opposite the mouth of the Paraiba do Sul River) and I (located north near the top of Vitória-ES). Sampling isobaths were 25, 50, 75, 100, 150, 400, 700, 1000, 1300, 1900, 2500 and 3000m. The Total Hg, MMHg and Hg stable isotopes were determined based on EPA Method 1631, EPA method 1630 and Foucher and Hintelmann (2006), respectively. The silt/clay ranged from 0.05 to 95%, and the organic carbon (OC) from 0.07 to 1.43 % for all transects. THg and MMHg concentrations in the shelf were 11.9 ± 7.2 (1.7- 22.2) ng.g‑1 and 0.15 ± 0.12 (0.02 - 0.40) ng.g‑1; in the slope 30.3 ± 9.2 (11.6 - 51.6) ng.g‑1 and 0.13 ± 0.06 (0.03 -0.29) ng.g‑1 , respectively. The δ202Hg and Δ199Hg varied from -0.32 to -1.85 ‰ (-0.79 ± 0.44‰) and -0.41 to 0.09 ‰ (-0.03 ± 0.12 ‰) for all transects, respectively. The delta values between both regions are significantly different, the shelf region showed δ202Hg from -0.59 to -2.19 ‰ (mean: -1.52 ±0.65) and Δ199Hg from - 0.53 to 0.08 ‰ (mean: -0.27 ±0.55) and the slope region were observed δ202Hg values from -0.32 to -1.82 ‰ (mean: -0.73 ±0.39 ‰ n=18) and gΔ199Hg from -0.23 to 0.09‰ (mean: -0.02 ±0.08‰ n=5). The slope appears to be enriched with heavier isotopes compared to the shelf, however

  7. OESbathy version 1.0: a method for reconstructing ocean bathymetry with realistic continental shelf-slope-rise structures

    NASA Astrophysics Data System (ADS)

    Goswami, A.; Olson, P. L.; Hinnov, L. A.; Gnanadesikan, A.

    2015-04-01

    We present a method for reconstructing global ocean bathymetry that uses a plate cooling model for the oceanic lithosphere, the age distribution of the oceanic crust, global oceanic sediment thicknesses, plus shelf-slope-rise structures calibrated at modern active and passive continental margins. Our motivation is to reconstruct realistic ocean bathymetry based on parameterized relationships of present-day variables that can be applied to global oceans in the geologic past, and to isolate locations where anomalous processes such as mantle convection may affect bathymetry. Parameters of the plate cooling model are combined with ocean crustal age to calculate depth-to-basement. To the depth-to-basement we add an isostatically adjusted, multicomponent sediment layer, constrained by sediment thickness in the modern oceans and marginal seas. A continental shelf-slope-rise structure completes the bathymetry reconstruction, extending from the ocean crust to the coastlines. Shelf-slope-rise structures at active and passive margins are parameterized using modern ocean bathymetry at locations where a complete history of seafloor spreading is preserved. This includes the coastal regions of the North, South, and Central Atlantic Ocean, the Southern Ocean between Australia and Antarctica, and the Pacific Ocean off the west coast of South America. The final products are global maps at 0.1° × 0.1° resolution of depth-to-basement, ocean bathymetry with an isostatically adjusted, multicomponent sediment layer, and ocean bathymetry with reconstructed continental shelf-slope-rise structures. Our reconstructed bathymetry agrees with the measured ETOPO1 bathymetry at most passive margins, including the east coast of North America, north coast of the Arabian Sea, and northeast and southeast coasts of South America. There is disagreement at margins with anomalous continental shelf-slope-rise structures, such as around the Arctic Ocean, the Falkland Islands, and Indonesia.

  8. Causes of long-term landscape evolution of "passive" margins and adjacent continental segments at the South Atlantic Ocean.

    NASA Astrophysics Data System (ADS)

    Glasmacher, Ulrich Anton; Hackspacher, Peter C.

    2013-04-01

    During the last 10 years research efforts have been devoted to understand the coupling between tectonic and surface processes in the formation of recent topography. Quantification of the rate at which landforms adapt to a changing tectonic, heat flow, and climate environment in the long term has become an important research object and uses intensively data revealed by low-temperature thermochronology, terrigenous cosmogenic nuclides, and geomorphological analyses. The influence of endogenic forces such as mantle processes as one of the causes for "Dynamic Topography Evolution" have been explored in a few studies, recently. In addition, the increased understanding how change in surface topography, and change in the amount of downward moving cold surface water caused by climate change affects warping isotherms in the uppermost crust allows further interpretation of low-temperature thermochronological data. "Passive" continental margins and adjacent continental segments especially at the South Atlantic ocean are perfect locations to quantify exhumation and uplift rates, model the long-term landscape evolution, and provide information on the influence of mantle processes on a longer time scale. This climate-continental margin-mantle process-response system is caused by the interaction between endogenic and exogenic forces that are related to the mantle-process driven rift - drift - "passive" continental margin evolution of the South Atlantic, and the climate change since the Early/Late Cretaceous climate maximum. Furthermore, the influence of major transform faults (also called: transfer zones, Fracture Zones (FZ)) on the long-term evolution of "passive" continental margins is still very much in debate. The presentation will provide insight in possible causes for the differentiated long-term landscape evolution along the South Atlantic Ocean.

  9. Physical and geotechnical properties and assessment of sediment stability on the continental slope and basin of the Bransfield Basin (Antarctica Peninsula)

    USGS Publications Warehouse

    Casas, D.; Ercilla, G.; Estrada, F.; Alonso, B.; Baraza, J.; Lee, H.; Kayen, R.; Chiocci, F.

    2004-01-01

    Our investigation is centred on the continental slope of the Antarctic Peninsula and adjacent basin. Type of sediments, sedimentary stratigraphy, and physical and geotechnical characterization of the sediments have been integrated. Four different types of sediments have been defined: diamictons, silty and muddy turbidites, muddy, silty and muddy matrix embedded clast contourites. There is a close correspondence between the physical properties (density, magnetic susceptibility and p-wave velocity) and the texture and/or fabric as laminations and stratification. From a quantitative point of view, only a few statistical correlations between textural and physical properties have been found. Within the geotechnical properties, only water content is most influenced by texture. This slope, with a maximum gradient observed (20??), is stable, according to the stability under gravitational loading concepts, and the maximum stable slope that would range from 22?? to 29??. Nevertheless, different instability features have been observed. Volcanic activity, bottom currents, glacial loading-unloading or earthquakes can be considered as potential mechanisms to induce instability in this area. Copyright ?? Taylor & Francis Inc.

  10. Rapid propagation of deglacial precipitation changes to turbidite systems on the Chile continental slope

    NASA Astrophysics Data System (ADS)

    Bernhardt, Anne; Schwanghart, Wolfgang; Strecker, Manfred R.

    2016-04-01

    hemipelagic sediment. Lower magnitude precipitation changes due to changes of the position and strength of the Southern Hemisphere Westerly Winds during the Holocene, however, are not resolved in the turbidite records. The terrestrial sediment routing system has often been described as a "jerky conveyor belt" that generates significant lag times between erosion and sedimentation, and shreds climatic signals. However, our results suggest that major changes during the transition from glacial to interglacial climates propagate rapidly through the tested sediment routing systems and are manifested in the sedimentary record on the continental slope. Hence, we conclude that turbiditic strata can act as reliable recorders of climate change, indicating related changes in sediment supply, and fluvial transport capacity across a wide range of climatic zones and geomorphic conditions.

  11. Recent seasonal hypoxia on the Western Black Sea shelf recorded in adjacent slope sediments

    NASA Astrophysics Data System (ADS)

    Roepert, Anne; Jilbert, Tom S.; Slomp, Caroline P.

    2015-04-01

    Bottom water hypoxia is a major environmental problem afflicting estuarine and marine environments across the globe (Diaz and Rosenberg, 2008). Hypoxia is often attributed to human-induced increased nutrient discharge from rivers and related eutrophication. The Western Black Sea shelf is a typical example of a system where such anthropogenic impacts are thought to have contributed to the development of seasonal hypoxia in the late 20th century. However, due to the lack of spatially and temporally consistent monitoring in the region, questions remain about the evolution, causes and consequences of the seasonal hypoxia on the Western Black Sea shelf and whether or not the ecological state has recently improved (Capet et al., 2013). In this study a resin-embedded sediment core from a location below the chemocline on the Western Black Sea slope (water depth 377 m) was analyzed for its elemental composition by means of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), recovering a continuous geochemical record at a sub-annual resolution for the last 100 years. Relative enrichments in organic carbon, Pb, Fe, S, and Mo were observed in the depth interval corresponding to the 1970s until the 1990s, suggesting an increased carbon flux to the sediments as well as an anthropogenic pollution signal. We propose that the expansion of eutrophication on the Western Black Sea shelf was responsible for the enhanced carbon flux to our study site, while the associated hypoxia enhanced the shuttling of redox-sensitive elements to locations below the chemocline. The subsequent decrease in organic carbon and metal enrichments at the core top suggests a recent rise in oxygen concentrations and improvement of the ecological state of the Western Black Sea shelf. References: Capet, A., Beckers, J.-M., Grégoire, M. (2013). "Drivers, mechanisms and long-term variability of seasonal hypoxia on the Black Sea northwestern shelf-is there any recovery after eutrophication

  12. Macrobenthic assemblages of the Changjiang River estuary (Yangtze River, China) and adjacent continental shelf relative to mild summer hypoxia

    NASA Astrophysics Data System (ADS)

    Liao, Yibo; Shou, Lu; Tang, Yanbin; Zeng, Jiangning; Gao, Aigen; Chen, Quanzhen; Yan, Xiaojun

    2016-06-01

    To assess the effects of hypoxia, macrobenthic communities along an estuarine gradient of the Changjiang estuary and adjacent continental shelf were analyzed. This revealed spatial variations in the communities and relationships with environmental variables during periods of reduced dissolved oxygen (DO) concentration in summer. Statistical analyses revealed significant differences in macrobenthic community composition among the three zones: estuarine zone (EZ), mildly hypoxic zone (MHZ) in the continental shelf, and normoxic zone (NZ) in the continental shelf (Global R =0.206, P =0.002). Pairwise tests showed that the macrobenthic community composition of the EZ was significantly different from the MHZ (pairwise test R =0.305, P =0.001) and the NZ (pairwise test R =0.259, P =0.001). There was no significant difference in macrobenthic communities between the MHZ and the NZ (pairwise test R =0.062, P =0.114). The taxa included small and typically opportunistic polychaetes, which made the greatest contribution to the dissimilarity between the zones. The effects of mild hypoxia on the macrobenthic communities are a result not only of reduced DO concentration but also of differences in environmental variables such as temperature, salinity, and nutrient concentrations caused by stratification.

  13. The biogeochemistry of carbon in continental slope sediments: The North Carolina margin

    SciTech Connect

    Blair, N.; Levin, L.; DeMaster, D.; Plaia, G.; Martin, C.; Fornes, W.; Thomas, C.; Pope, R.

    1999-12-01

    The responses of the continental slope benthos to organic detritus deposition were studied with a multiple trace approach. Study sites were offshore of Cape Fear (I) and Cape Hatteras (III), N.C. (both 850 m water depth) and were characterized by different organic C deposition rates, macrofaunal densities (III>I in both cases) and taxa. Natural abundances of {sup 13}C and {sup 12}C in particulate organic carbon (POC), dissolved inorganic carbon (DIC) and macrofauna indicate that the reactive organic detritus is marine in origin. Natural abundance levels of {sup 14}C and uptake of {sup 13}C-labeled diatoms by benthic animals indicate that they incorporate a relatively young component of carbon into their biomass. {sup 13}C-labeled diatoms (Thalassiorsira pseudonana) tagged with {sup 210}Pb, slope sediment tagged with {sup 113}Sn and {sup 228}Th-labeled glass beads were emplaced in plots on the seafloor at both locations and the plots were sampled after 30 min., 1-1.5 d and 14 mo. At Site I, tracer diatom was intercepted at the surface primarily by protozoans and surface-feeding annelids. Little of the diatom C penetrated below 2 cm even after 14 months. Oxidation of organic carbon appeared to be largely aerobic. At Site III, annelids were primarily responsible for the initial uptake of tracer. On the time scale of days, diatom C was transported to a depth of 12 cm and was found in animals collected between 5-10 cm. The hoeing of tracer from the surface by the maldanid Praxillela sp. may have been responsible for some of the rapid nonlocal transport. Oxidation of the diatom organic carbon was evident to at least 10 cm depth. Anaerobic breakdown of organic matter is more important at Site III. Horizontal transport, which was probably biologically mediated, was an order of magnitude more rapid than vertical displacement over a year time scale. If the horizontal transport was associated with biochemical transformations of the organic matter, it may represent an

  14. Evolution of stocks and massifs from burial of salt sheets, continental slope, northern Gulf of Mexico

    SciTech Connect

    Seni, S.J. )

    1991-03-01

    Salt structures in a 4000-km{sup 2} region of the continental slope, the northeast Green Canyon area, include stocks, massifs, remnant structures, and an allochthonous sheet. Salt-withdrawal basins include typical semicircular basins and an extensive linear trough that is largely salt-free. Counterregional growth faults truncate the landward margin of salt sheets that extend 30-50 km to the Sigsbee Escarpment. The withdrawal basins, stocks, and massifs occur within a large graben between an east-northeast-trending landward zone of shelf-margin growth faults and a parallel trend of counterregional growth faults located 48-64 km basinward. The graben formed by extension and subsidence as burial of the updip portion of a thick salt sheet produced massifs and stocks by downbuilding. Differential loading segmented the updip margin of the salt sheet into stocks and massifs separated by salt-withdrawal basins. Initially, low-relief structures evolved by trap-door growth as half-graben basins buried the salt sheet. Remnant-salt structures and a turtle-structure anticline overlay a salt-weld disconformity in sediments formerly separated by a salt sheet. Age of sediments below the weld is inferred to be be late Miocene to early Pliocene (4.6-5.3 Ma); age of sediments above the weld is late Pliocene (2.8-3.5 Ma). The missing interval of time (1-2.5 Ma) is the duration between emplacement of the salt sheet and burial of the sheet. Sheet extrusion began in the late Miocene to early Pliocene, and sheet burial began in the late Pliocene in the area of the submarine trough to early Pleistocene in the area of the massifs.

  15. Circulation and exchange at the continental shelf and slope SEEP-2. Final report, May 1, 1989--December 31, 1991

    SciTech Connect

    Houghton, R.W.; Ou, Hsien-Wang

    1991-12-31

    This project was a component of the SEEP-II program. It contributed to the instrumentation of the SEEP-II moored array to the processing and analysis of the time-series data of water temperature and currents, and to a theoretical modeling study of the circulation on the continental margin. We are responsible for nearly half of the current meters and thermistor chains that were deployed in the SEEP-II moored array on the continental margin off the Delmarva peninsula. Data tapes derived from three deployments of the instruments in this array were processed. A second component of this project was a theoretical study of the interaction of the Gulf Stream with the continental margin north of Cape Hatteras. The model shows how the topographic influence on the local vorticity balance leads to back-folding filaments of Gulf Stream water and to the Slope Sea gyre circulation.

  16. Paleomagnetism of sedimentary cores from the Ross Sea outer shelf and continental slope (PNRA-ROSSLOPE II Project)

    NASA Astrophysics Data System (ADS)

    Macrì, Patrizia; Sagnotti, Leonardo; Caricchi, Chiara; Colizza, Ester

    2016-04-01

    We carried out a paleomagnetic and rock magnetic study of 4 gravity cores sampled in the Ross Sea continental slope of the area to the east of Pennell-Iselin banks. The cores (RS14-C1, C2, C3 and ANTA99-C20) consist of hemipelagic fine-grained (silty-clays) sediments with an IRD component. Rock magnetic and paleomagnetic measurements were carried out at 1-cm spacing on u-channel samples. The data indicate that the cored sediments carry a well-defined characteristic remanent magnetization (ChRM) and have a valuable potential to reconstruct dynamics and amplitude of the geomagnetic field variation at high southern latitudes (ca. 75°S) during the Holocene and the late Pleistocene. The paleomagnetic and rock magnetic data are integrated in a multidisciplinary context which includes previous geological, geophysical, oceanographic and morpho-bathimetric data obtained in the same area in the frame of the PNRA/ROSSLOPE (Past and present sedimentary dynamic in the ROSS Sea: a multidisciplinary approach to study the continental slope) Project. The main aim of the project is to investigate the relation between present and past water mass circulation and to provide a basis for paleoceanographic reconstructions and for the development of a depositional model of the modern processes active along the continental slope.

  17. Morphology, distribution, and development of submarine canyons on the United States Atlantic continental slope between Hudson arid Baltimore Canyons

    NASA Astrophysics Data System (ADS)

    Twichell, David C.; Roberts, David G.

    1982-08-01

    The distribution and morphology of submarine canyons off the eastern United States between Hudson and Baltimore Canyons have been mapped by long-range sidescan sonar. In this area canyons are numerous, and their spacing correlates with overall slope gradient; they are absent where the gradient is less than 3°, are 2 to 10 km apart where the gradient is 3° to 5°, and are 1.5 to 4 km apart where the gradient exceeds 6°. Canyons range from straight to sinuous; those having sinuous axes indent the edge of the continental shelf and appear to be older than those that head on the upper slope and have straighter axes. A difference in canyon age would suggest that canyons are initiated on the continental slope and only with greater age erode headward to indent the shelf. Shallow gullies on the middle and upper slope parts of the canyon walls suggest that submarine erosion has been a major process in a recent phase of canyon development. *Present address: British Petroleum, Moorgate, London EC2Y 9BU, England

  18. Investigation of the shelf break and continental slope in the Western part of the Black Sea using acoustic methods

    NASA Astrophysics Data System (ADS)

    Dutu, F.; Ion, G.; Jugaru Tiron, L.

    2009-04-01

    The Black Sea is a large marginal sea surrounded by a system of Alpine orogenic chains, including the Balkanides-Pontides, Caucasus, Crimea and North Dobrogea located to the south, northeast, north and northwest, respectively (Dinu et al., 2005). The north-western part of the Black Sea is the main depocentre for sediment supply from Central Europe via the Danube River, but also from Eastern Europe through the Ukrainian rivers Dniepr, Dniestr and Southern Bug (Popescu et al., 2004). The shelfbreak is located at water depths of 120-140 m southward of the Danube Canyon, and up to 170 m northward of the canyon possibly due to recent faulting which is very common in this area. The continental slope is dissected by numerous canyons, each of which is fed by several tributaries. The Danube Canyon (also known as Viteaz Canyon) is a large shelf-indenting canyon located in the north-western Black Sea and connected to the youngest channel-levee system of the Danube Fan (Popescu et al., 2004). The acoustic methods are a useful way for investigate the shelf break and the continental slope giving us information about landslides on the continental slope, the topography of the investigated area, the sedimentary zones affected by instability and to quantify the geometry of the underwater landslides. The measurements made on the continental slope from north-western part of the Black Sea gave us the possibility to make a digital terrain model. After processing the data the model offer information about the main access ways of the sediments through gravitational slide on the submarines canyons, with forming of turbidity currents, debris flows and also other transport/transformation phenomena of the sediments on the continental slope like submarine landslides and submarine collapse. References Dinu, C., Wong, H.K., Tambrea, D., Matenco, L., 2005. Stratigraphic and structural characteristics of the Romanian Black Sea shelf. Tectonophysics 410, 417-435. Popescu, I., Lericolais, G., Panin

  19. Subsurface geology of upper Tertiary and Quaternary deposits, coastal Louisiana and adjacent Continental Shelf

    SciTech Connect

    McFarlan, E. Jr.; Leroy, D.O.

    1988-09-01

    Upper Tertiary and Quaternary deposits thicken seaward from a feather edge on the outcrop in the uplands of southern Louisiana to more than 7000 ft (2134 m) beneath the middle continental shelf. Through a study of cores and cuttings from 100 control wells and electric-log pattern correlations from 350 water and petroleum industry wells with seismic corroboration in the offshore area, these deposits have been divided into six major time-stratigraphic units, four of which correlate to outcropping terraces. This investigation presents a regional stratigraphic framework of the major upper Tertiary and Quaternary units from their updip pinch-outs in and beneath the terraced uplands, into the subsurface, across the coastal plain to the Louisiana offshore area.

  20. Multichannel seismic depth sections and interval velocities over outer continental shelf and upper continental slope between Cape Hatteras and Cape Cod: rifted margins

    USGS Publications Warehouse

    Grow, John A.; Mattick, Robert E.; Schlee, John S.

    1979-01-01

    Six computer-generated seismic depth sections over the outer continental shelf and upper slope reveal that subhorizontal Lower Cretaceous reflectors continue 20 to 30 km seaward of the present shelf edge. Extensive erosion on the continental slope has occurred primarily during the Tertiary, causing major unconformities and retreat of the shelf edge to its present position. The precise age and number of erosional events is not established, but at least one major erosional event is thought to be Oligocene and related to a marine regression in response to a worldwide eustatic lowering of sea level. Velocities derived from the multichannel data reveal distinctive ranges and lateral trends as functions of sediment age, depth of burial, and distance from the coastline. Seismic units beneath the shelf and slope of inferred Tertiary age range from 1.7 to 2.7 km/sec, increasing with age and depth of burial. Units interpreted as Upper Cretaceous rocks beneath the shelf range from 2.3 to 3.6 km/sec and show a distinct lateral increase across the shelf followed by a decrease beneath the present continental slope. Inferred Lower Cretaceous and Upper Jurassic rocks beneath the shelf increase from 3.7 to 4.8 km/sec from nearshore to offshore and indicate a change in facies from clastic units below the inner shelf to carbonate units beneath the outer shelf and upper continental slope. Both reflection and refraction data suggest that thin, high-velocity limestone units (5.0 km/sec) are present within the Lower Cretaceous and Upper Jurassic units beneath the outermost shelf edge, but that these change lithology or pinch out before reaching the middle shelf. Although lateral changes in velocity across the shelf and local velocity inversions appear, the interval velocities along the length of the margin show excellent continuity between Cape Hatteras and Cape Cod. The high-velocity horizons within the Lower Cretaceous and Upper Jurassic shelf-edge complex indicate the presence of a

  1. Metal elements in the bottom sediments of the Changjiang Estuary and its adjacent continental shelf of the East China Sea.

    PubMed

    Cao, Lu; Hong, Gi Hoon; Liu, Sumei

    2015-06-15

    The metal elements (Al, Fe, Mn, Cr, Co, Ni, Cu, Zn, As, Pb and Ca) in the bottom sediment of the Changjiang Estuary and its adjacent continental shelf of the East China Sea were studied to map their spatial distribution and to assess their potential risk to the marine biota. These metal concentrations except Ca were generally higher in the inner shelf and northeastern part, and were found to decrease from the coast to the offshore of the Changjiang Estuary. Sedimentary Ca was most abundant in the outer shelf sediments and decreased in inner shelf. Arsenic (As) appeared to be contaminated due to economic development from 1980s in the inner shelf overall, but the potential ecological risk from the selected metals was low in the coastal sea off the Changjiang. PMID:25869200

  2. Supercritical turbidity-current bedforms in the northeastern continental slope, South China Sea

    NASA Astrophysics Data System (ADS)

    Zhong, Guangfa; Kuang, Zenggui; Cartigny, Matthieu J. B.; Guo, Yiqun; Wang, Liaoliang

    2015-04-01

    Large-scale Supercritical flow bedforms in the northeastern continental slope of the South China Sea were investigated by integrating high-resolution multibeam bathymetric data and multichannel seismic profiles. In the area, many canyons are developed, including the Penghu, West Penghu, Jiulong, South Taiwan Shoal and Dongsha canyons. Most of the canyons downslope join the South Taiwan Shoal canyon, and finally merge into the Penghu canyon. Numerous step-like features were recognized within the South Taiwan Shoal and the West Penghu canyons. The features, ranging from 1.2 to 10.0 km in wave length and 5.4 to 80.9 m in wave height, are mostly interpreted as cyclic steps formed by turbidity currents flowing through the canyons based on their morphological and seismic characteristics. The steps align in trains along the canyon thalwegs or scatter in the canyon terraces. Each thalweg train consists of up to 19 continuous cyclic steps and extends up to 100 km in length, and is separated by a slope break into an upper steeper and a lower gentler segments. Steps in the upper segments are characterized by smaller wavelength and chaotic internal reflections, which contrast to those in the lower segments with a lager wavelength and typical upstream-dipping backset reflections. Aided by a simple numerical modeling exercise, we interpreted the features in the upper segments as net-erosional cyclic steps or transitional bedforms between antidunes and cyclic steps, and those in the lower segments as net-depositional cyclic steps. Nine short trains of scours were identified on a terrace of the South Taiwan Shoal canyon. They are oriented parallel to the tributaries draining over the terrace and roughly perpendicular to the main canyon thalweg, and are presumed as resulting from the tributary flows, indicating a complicated flow pattern within the canyon valley. In addition, four large fields of sediment waves were delineated. They are located on the western and southern flanks of

  3. Polycyclic aromatic hydrocarbon concentrations across the Florida Panhandle continental shelf and slope after the BP MC 252 well failure.

    PubMed

    Snyder, Richard A; Ederington-Hagy, Melissa; Hileman, Fredrick; Moss, Joseph A; Amick, Lauren; Carruth, Rebecca; Head, Marie; Marks, Joel; Tominack, Sarah; Jeffrey, Wade H

    2014-12-15

    The Florida Panhandle continental shelf environment was exposed to oil from the BP oil well failure in the Gulf of Mexico during 2010. Floating mats of oil were documented by satellite, but the distribution of dissolved components of the oil in this region was unknown. Shipek® grab samples of sediments were taken during repeated cruises between June 2010 and June 2012 to test for selected polycyclic aromatic hydrocarbons (PAHs) as indicators of this contamination. Sediments were collected as composite samples, extracted using standard techniques, and PAHs were quantified by GC/MS-SIM. PAHs in samples from the continental slope in May 2011 were highest near to the failed well site and were reduced in samples taken one year later. PAHs from continental shelf sediments during the spill (June 2010) ranged from 10 to 165 ng g(-1). Subsequent cruises yielded variable and reduced amounts of PAHs across the shelf. The data suggest that PAHs were distributed widely across the shelf, and their subsequent loss to background levels suggests these compounds were of oil spill origin. PAH half-life estimates by regression were 70-122 days for slope and 201 days for shelf stations. PMID:25444619

  4. Middle to late Miocene canyon cutting on the New Jersey continental slope: biostratigraphic and seismic stratigraphic evidence

    SciTech Connect

    Miller, K.G.; Melillo, A.J.; Mountain, G.S.; Farre, J.A.; Poag, C.W.

    1987-06-01

    The authors have identified and dated a major Miocene erosional surface (M1) on the New Jersey continental slope. This surface was penetrated at Deep Sea Drilling Project (DSDP) Site 612, which was drilled near the thalweg of a buried V-shaped canyon. Biostratigraphic data at Site 612 firmly constrain the age of strata above the buried canyon surface as Zones CN7 (N=NN9) and N16 (lowermost upper Miocene); the upper Miocene surface at Site 612 lies above lowermost Oligocene strata because of coalesced unconformities. The authors traced the M1 erosional surface to the COST B-3 well where upper middle Miocene strata underlie it. Biostratigraphic studies of other New Jersey continental slope boreholes (ASP 14, ASP 15) suggest that elsewhere the sediments immediately below the M1 surface encompass the Globorotalia fohsi robusta Zone (=Zone N12-earliest N13; middle middle Miocene). The best age estimate is that M1 was eroded between 11.5 and 10.0 Ma. This erosional event apparently correlates with a similar even on the Irish and Florida continental margins and with oxygen-isotope evidence for a glacio-eustatic lowering.

  5. The Alegre Lineament and its role over the tectonic evolution of the Campos Basin and adjacent continental margin, Southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Calegari, Salomão Silva; Neves, Mirna Aparecida; Guadagnin, Felipe; França, George Sand; Vincentelli, Maria Gabriela Castillo

    2016-08-01

    The structural framework and tectonic evolution of the sedimentary basins along the eastern margin of the South American continent are closely associated with the tectonic framework and crustal heterogeneities inherited from the Precambrian basement. However, the role of NW-SE and NNW-SSE structures observed at the outcropping basement in Southeastern Brazil and its impact over the development of those basins have not been closely investigated. In the continental region adjacent to the Campos Basin, we described a geological feature with NNW-SSE orientation, named in this paper as the Alegre Fracture Zone (AFZ), which is observed in the onshore basement and can be projected to the offshore basin. The main goal of this work was to study this structural lineament and its influence on the tectonic evolution of the central portion of the Campos Basin and adjacent mainland. The onshore area was investigated through remote sensing data joint with field observations, and the offshore area was studied through the interpretation of 2-D seismic data calibrated by geophysical well logs. We concluded that the AFZ occurs in both onshore and offshore as a brittle deformation zone formed by multiple sets of fractures that originated in the Cambrian and were reactivated mainly as normal faults during the rift phase and in the Cenozoic. In the Campos Basin, the AFZ delimitates the western side of the Corvina-Parati Low, composing a complex fault system with the NE-SW faults and the NW-SE transfer faults.

  6. Bioturbation, geochemistry and geotechnics of sediments affected by the oxygen minimum zone on the Oman continental slope and abyssal plain, Arabian Sea

    NASA Astrophysics Data System (ADS)

    Meadows, Azra; Meadows, Peter S.; West, Fraser J. C.; Murray, John M. H.

    2000-01-01

    We investigate the way the oxygen minimum zone (OMZ) alters interactions between bioturbation and sediment geochemistry, and geotechnical properties. Sediments are compared within and below the OMZ on the Oman continental slope and adjacent abyssal plain during the post monsoonal autumn season. Quantitative measurements were made of Eh and pH, of total organic matter (TOM) and carbonate, of water content and shear strength, and of bioturbation structures in vertical profiles of subcores taken from spade-box core samples. The OMZ stations had distinctively low redox conditions and high carbonate content, and different geotechnical properties and different bioturbation structures than stations below the OMZ on the abyssal plain. These differences are related to the degree of anoxia and to water depth. Within the OMZ, Eh, pH and carbonate increased with water depth, and TOM and water content decreased. We also noted the presence of subsurface sediment heterogeneity on the continental slope within the OMZ. In the OMZ, Eh, water content and bioturbation decreased with increasing sediment depth. There was a slight decrease in pH in the top 5 cm at all stations. Shear strength nearly always increased with increasing sediment depth. At each water depth correlations show down-core trends in these parameters, while across all water depths correlations were significant at deeper sediment depths (20-30 cm). An Eh-pH diagram identified two water-depth groupings: 391-1008 and 1265-3396 m. Cluster analysis showed the upper and lower sediment depths form separate clusters, the break occurring at 4-7.5 cm; while there are also distinct clusters related to water depth. We relate our results to bottom-water oxygen concentrations reported by other investigators, and to regional-scale geochemical processes.

  7. >Mud mounds on the continental slope, northwestern Gulf of Mexico and their relation to hydrates and seafloor instability

    SciTech Connect

    Neurauter, T.W.

    1988-01-01

    High resolution seismic data delineate acoustically amorphous mounded structures on the continental slope of the Northwest Gulf of Mexico. The thermogenic gas hydrates reported from Green Canyon Block 184 are associated with one of these mounds. This particular mound occurs in a highly faulted area and overlies an extensive chaotic seismic facies. Gas and fluids are migrating up the fault plane to the sea floor. The relief of the mound is partially the result of the throw of the associated faults, but also to a combination of other factors such as the upwelling of gaseous muds, in-place expansion of the hydrates and the generation of diagenic carbonates. The acoustic signature of the known hydrate accumulation of Green Canyon Block 184 was applied to high resolution data in Mississippi Canyon Block 798 and 799 in an attempt to predict the occurrence of hydrates. Piston cores within an acoustically amorphous mound in Block 798 encountered extremely gassy sediments with sizeable chunks of white, presumably biogenic hydrates. The geologic setting in Block 798 was similar to Green Canyon 184 with complex faulting and subsurface sequences of thick chaotic facies. The venting of gas and fluids from overpressured zones appears to be the common factor for all mounds thereby making them mud diapir/mud volcano type structures. No evidence of seafloor instability was directly related to the presence or possible presence of gas hydrates. However, if it can be established that massive hydrate formation exist on the continental slope, then a substantial lowering of sea level such as occurred in the late Pleistocene, would result in decomposition of the hydrates and trigger mass wasting. Such a mechanism could explain abundance of buried erosional scars along the continental slope.

  8. The North Slope of Alaska and Adjacent Arctic Ocean (NSA/AAO) cart site begins operation: Collaboration with SHEBA and FIRE

    SciTech Connect

    Zak, D. B.; Church, H.; Ivey, M.; Yellowhorse, L.; Zirzow, J.; Widener, K. B.; Rhodes, P.; Turney, C.; Koontz, A.; Stamnes, K.; Storvold, R.; Eide, H. A.; Utley, P.; Eagan, R.; Cook, D.; Hart, D.; Wesely, M.

    2000-04-04

    Since the 1997 Atmospheric Radiation Measurement (ARM) Science Team Meeting, the North Slope of Alaska and Adjacent Arctic Ocean (NSA/AAO) Cloud and Radiation Testbed (CART) site has come into being. Much has happened even since the 1998 Science Team Meeting at which this paper was presented. To maximize its usefulness, this paper has been updated to include developments through July 1998.

  9. Late-summer mass deposition of gelatinous phytodetritus along the slope of the N.W. European Continental Margin

    NASA Astrophysics Data System (ADS)

    de Wilde, P. A. W. J.; Duineveld, G. C. A.; Berghuis, E. M.; Lavaleye, M. S. S.; Kok, A.

    1998-12-01

    In the period 1993-1995 the OMEX area has been visited 3 times to address the question of across-slope transport of suspended matter from the shelf to the deep sea. By analyzing phytopigments and nucleic acids in the sediment and water of the N.W. European Continental slope and rise seasonal patterns of benthic food input were investigated and relation between input and the structure and activity of the benthic community were explored. Chloropigments in the surface sediments indicated that a spring bloom effect could be traced down to about 2500 m. During late August 1995 heavy deposits of gelatinous matter, characterized by high concentrations of chloropigments and nucleic acids, were detected all over the ocean floor of the outer slope and continental rise below 3500 m. It is estimated that this mucus layer had a carbon load of 250 mmol C m -2 over an area of 50,000 km 2. The recent state of the mucus allowed us to search for its origin. Characteristic pigment composition and the presence of coccoliths pointed to prymnesiophytes (coccolithophorids) as a major contributor, but dinoflagellates (peridinin) and green algae (chlorophyll-b, lutein) must have contributed as well. Simultaneous observations of the overlying water column, deep chlorophyll maximum, revealed the presence of a coccolithophorid bloom in a recent stage of disintegration at St. III. An obvious relation with the mucus carpet, however, could not be indicated. This, and the significant differences in pigment composition and pigment ratios at the various deep stations lead us to understand that the extended mucus field at the Celtic slope originates from different, more or less synoptically occurring surface blooms. The presence of large `vacuum-cleaning' sea-cucumbers is considered indicative of the occurrence of phytodetritus pulses.

  10. Seamount subduction and related deformation and seismicity of the continental slope off Manzanillo, Mexico, as evidenced by multibeam data

    NASA Astrophysics Data System (ADS)

    Bandy, W. L.; Castillo Maldonado, M.; Mortera-Gutierrez, C. A.

    2014-12-01

    The west coast of Mexico presents a complex pattern of deformation related to the convergence and subduction of the Rivera plate beneath the Jalisco Block/North American plate. Previous single beam bathymetric data have evidenced a large bathymetric high at 104.6218oW, 18.7123oN, in the continental slope region off Manzanillo, Mexico. One school of thought held that this high was the offshore extension of the onshore Manzanillo horst, although the two features are offset in a right-lateral sense. Alternatively, given the presence of a large positive magnetic anomaly near the bathymetric high, the high could also be caused by the collision and subsequent subduction of a large seamount. Given that the offset between the two structures was the main evidence for proposing the existence of a forearc sliver in the offshore area of the Jalisco margin, resolving the nature of this bathymetric high is quite important in our attempts to understand the plate kinematics and tectonics of this region. Thus, to better define the deformation pattern associated with the bathymetric high, multibeam bathymetric data (obtained using the Kongsberg EM300 multibeam system), subbottom profiles (obtained using the Kongsberg TOPAS18 system), and total field magnetic data (obtained using the Geometrics G877 marine proton precession magnetometer) were collected in the continental slope region between Manzanillo, Colima, and Chamela, Jalisco, during several cruises of UNAM´s research vessel the B.O. EL PUMA. The morphology and structural deformation patterns obtained in this study indicate very clearly that a large seamount is in the process of subducting beneath the continental slope off Manzanillo. The results also indicate that not only has the seamount uplifted the slope but has resulted in slumping of the area of the slope landward of the seamount. Given these results the proposal of the existence of an independent forearc sliver in the offshore area of the southern Jalisco block needs

  11. Behaviour of REEs in a tropical estuary and adjacent continental shelf of southwest coast of India: Evidence from anomalies

    NASA Astrophysics Data System (ADS)

    Deepulal, P. M.; Kumar, T. R. Gireesh; Sujatha, C. H.

    2012-10-01

    The distribution and accumulation of the rare earth elements (REE) in the sediments of the Cochin Estuary and adjacent continental shelf were investigated. The rare earth elements like La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the heavy metals like Mg, V, Cr, Mn, Fe, Cu, Zn, U, Th were analysed by using standard analytical methods. The Post-Archean Australian Shale composition was used to normalise the rare earth elements. It was found that the sediments were more enriched with the lighter rare earth elements than the heavier ones. The positive correlation between the concentrations of REE, Fe and Mn could explain the precipitation of oxyhydroxides in the study area. The factor analysis and correlation analysis suggest common sources of origin for the REEs. From the Ce-anomalies calculated, it was found that an oxic environment predominates in all stations except the station No. 2. The Eu-anomaly gave an idea that the origin of REEs may be from the feldspar. The parameters like total organic carbon, U/Th ratio, authigenic U, Cu/Zn, V/Cr ratios revealed the oxic environment and thus the depositional behaviour of REEs in the region.

  12. Slope failure of continental frontal ridges offshore Vancouver Island, British Columbia

    NASA Astrophysics Data System (ADS)

    Scholz, N.; Riedel, M.; Spence, G.; Dugan, B.; Daigle, H.; Hyndman, R. D.; James, T. S.; Naegeli, K.

    2010-12-01

    Bathymetric data from the Northern Cascadia margin offshore Vancouver Island reveal several submarine landslide features on the seaward slopes of frontal ridges. The slides occur just landward of the deformation front of the subducting Juan de Fuca and Explorer plates. Possible trigger mechanisms for the slope failures include earthquakes, pore pressure changes induced by sea-level changes, and the dissociation of gas hydrates. Evidence of gas hydrate has been found beneath the frontal ridges. A bottom simulating reflection (BSR) has been identified in regional seismic data and logging data showed gas hydrate indicators including sonic velocity and high electrical resistivity. The influence of gas hydrate formation and dissociation on slope stability is of special interest since previous studies showed coincident depths of BSRs and failure planes. We investigate two slope failure events in detail using numerical modeling techniques such as finite and discrete element modeling. Hybrid techniques provide a means to model processes ranging from grain-scale interactions up to movements of the sliding body by addressing both the continuous and discontinuous aspects of the problem. These include the internal forces, the evaluation of material failure criterion, deformation, and interaction forces. Furthermore, tensile failure and crack propagation, for example caused by gas hydrate or by the gradual breakdown of the slope material, can be characterized. Particle flow using different shapes and properties can be simulated. By examining the effect of local sea-level changes, glacial rebound, and gas hydrate formation or dissociation on stresses and fluid pressures, the work involves modeling the failure conditions associated with a decrease in shear strength, an increase in pore pressure, and the possible development or re-opening of cracks. Beyond describing the trigger mechanism, we also have interest in reconstructing the dynamics of the slide events to explain their

  13. Benthic faunal assemblages and carbon supply along the continental shelf/shelf break-slope off Cape Hatteras, North Carolina

    NASA Astrophysics Data System (ADS)

    Aller, J. Y.; Aller, R. C.; Green, M. A.

    Patterns of benthic faunal abundances, biomass, and productivity were examined in the continental shelf-break/upper-slope and mid-slope region of the Ocean Margins Program study area off Cape Hatteras, NC in July 1994, and July and August 1996. Macrofaunal abundances were comparable to or slightly higher than other shelf-slope locales in the North Atlantic. Similar to previous studies in the region, there were no clear depth (75-900 m) or latitudinal (36°20'N-35°25') trends. Sta. S300 in 300 m had greatest abundances (539,000±38,400 m -2) for individuals >0.3 mm, more than 3 times higher than the average for all stations. Annelids of all sizes dominated numerically, equaling >80% of all macrofauna regardless of size. The majority of infauna were found in the upper 5 cm, but direct visual observations and geochemical evidence from other studies imply a deep-burrowing benthos. Meiofauna (excluding benthic foraminifera) were twice as abundant at shelf-break/upper-slope stations than mid-slope stations, while foraminifera were more abundant at deeper stations. Meiofaunal-sized polychaetes and nematodes were found to at least 7-8 cm below the sediment surface. Bacterial inventories at shelf-break/upper-slope depths were high relative to other shelf regions, but declined precipitously deeper than 500 m. Relative biomass patterns were similar for all stations, highest for macrobenthos and lowest for bacteria. Although densities were high, the contribution of nematodes to benthic biomass was <1%. Macrofaunal biomass averaged 54±47 g C m -2 and ranged from 6 g C m -2 at station N455 to 188 g C m -2 (>0.3 mm) at station S300, while metazoan meiofauna contributed from 0.6 g C m -2 at station N-274 to 11 g C m -2 at M76, averaging 2.2±2.4 g C m -2. Bacterial biomass over the upper 10 cm was ˜4 times higher at shelf-break/upper-slope stations than mid-slope stations, averaging 1.05±1.14 g C m -2 and ranging from 5 g C m -2 at M76 to 0.12 g C m -2 at MLB-679Rb. Benthic

  14. The complex spreading pattern of Mediterranean Water off the Portuguese continental slope

    NASA Astrophysics Data System (ADS)

    Zenk, Walter; Armi, Lorenz

    1990-12-01

    Two stacked outflow cores of the Mediterranean Water undercurrent pass through a broad "gateway" between Cape St. Vincent and Gettysburg Bank entering the Iberian Basin. The upper core (depth ˜750 m, σ1=31.85) shows a strong tendency to follow the contours of the Portuguese continental rise. Yet, the lower core (depth ˜1250 m, σ1=32.25) primarily meanders west and northwestward forming large blobs of Mediterranean Water. The predominance of isolated Meddy structures embedded in a background field is reflected in a long-term current meter record from the deep Iberian Basin.

  15. Volcanic Rocks Collected With ROV Tiburon From Rodriguez Seamount, Located at the Continental Slope of the California Borderland

    NASA Astrophysics Data System (ADS)

    Davis, A. S.; Clague, D. A.; Paduan, J. B.

    2004-12-01

    Volcanic rocks were collected from Rodriguez Seamount at the outer margin off the Continental Borderland with MBARI's ROV Tiburon in October 2003 and April 2004. Six dives recovered lava and volcaniclastic samples from the deep flanks ( ˜2120 m) to the summit at 630 m. Whole rock compositions of plagioclase-olivine-clionpyroxene bearing lava samples are predominantly alkalic basalt (<8% MgO) and hawaiite with minor mugearite (MgO=1.5%). Glass compositions of pillow rims and of volcaniclastic fragments in breccia and bedded sandstone are predominantly hawaiite, mugearite and minor evolved alkalic basalt. The lava samples include one rhyolite and one basaltic andesite with subduction-related chemistry; they are probably erratics. Other clearly identifiable erratics include granite, quartzite, amphibolite, and bored, erosion-sculpted sandstone, resembling typical beach deposits. Most of these erratics are pebble- to small cobble-size and occur in conglomerate and crossbedded sandstone that surround the summit at a break in slope that most likely marks the shoreline when Rodriguez was an island. The lava outcrops on the gently domed platform of the summit are dense, oxidized àà-like flows without glassy rinds. Sulfur content of glass, collected from the flanks of the volcano, ranges from 1300 ppm of a glass inclusion in an olivine crystal to ˜160 ppm of volcaniclastic grains, indicating extensive degassing. Petrographically and chemically these lavas are virtually identical to those erupted on Miocene seamounts offshore central California (e.g. Davidson, Guide, Pioneer, Gumdrop seamounts, Davis et al, 2002) as well as Northeast Bank on the continental shelf south of Rodriguez and seamounts farther offshore from the Continental Borderland (e.g. Little Joe, San Marcos, San Juan seamounts, Clague et al, unpublished; Davis et al., 1995). Trace element abundances and ratios (e.g. LREE, Zr/Nb, Ta/Nb) also completely overlap with those from the other sites, suggesting

  16. Suggestions for Mitigation of Methane Clathrate Destabilization Along Continental Slopes Offshore and Discrimination Between Fossil and Recent Methane in the Atmosphere with Remote Sensing

    NASA Astrophysics Data System (ADS)

    Vincent, R. K.; Vincent, R. A.

    2010-12-01

    When a hydrocarbon-rich stratum intersects the outer edge of a continental shelf, at the continental slope, methane clathrates act as a partially impermeable barrier that prevents their easy escape at the end of the “layer cake” of continental sediments. If the clathrates on the continental slope melt because of rising sea bottom temperatures, hydrocarbons (natural gas and oil) can escape into the ocean, and finally into the atmosphere in the case of methane. A mitigation method is discussed that would drill vertically into the continental shelf, then horizontally toward the continental slope, and resulting production of oil and gas would reduce the pressure and the amount of methane escape to the ocean and the atmosphere. Remote sensing for lower tropospheric methane plumes will be needed to determine where drilling is needed, as well as to assess the effects of mitigation in reducing methane escape. A remote sensing method employing carbon isotopic ratios is proposed for discriminating fossil methane in natural gas from recent methane produced by decaying organic material. This is important because recent methane is recycled over decadal time frames and does not add greatly to global warming, whereas fossil methane releases carbon that has been sequestered for millions of years and is a principal cause of increased carbon dioxide in the atmosphere and its concomitant global warming.

  17. Temporal and spatial variability of ADCP backscatter on a continental slope

    NASA Astrophysics Data System (ADS)

    Sindlinger, Laurie R.; Biggs, Douglas C.; DiMarco, Steven F.

    2005-01-01

    Previous research has shown that acoustic volume backscatter intensity (ABI) from an acoustic Doppler current profiler (ADCP) can be a proxy for zooplankton and micronekton biomass over time or space. As part of NOAA's Sperm Whale and Acoustic Monitoring Program (SWAMP) and a follow-on ichthyoplankton survey (SEAMAP), a ship-mounted 300-kHz broadband ADCP collected current velocity and ABI data from July to September 2001 in the northeast Gulf of Mexico. The present study sought to compare/contrast the variability in ABI both spatially and temporally using the data obtained from the SWAMP and SEAMAP cruises. The ADCP data were averaged over 2 min and 4 m vertical bins from 16 to 56 m below sea surface. Usually, ABI in this epipelagic realm averaged 3 dB higher at night than during the day because of diel vertical migration of zooplankton and micronekton into these near surface waters, while in a region having cyclonic circulation along the continental margin of the northeast Gulf, ABI averaged 6 dB higher than in an anticyclonic warm filament there. Wet displacement volumes (WDV) were measured using Bongo net tows to estimate that a 6 dB increase in ABI was equivalent to an increase from 9 to 10.5 ml WDV of plankton+micronekton per 100 m 3. Sperm whale abundance has been shown to be positively correlated with regions of locally high ABI, and sperm whale sightings during SWAMP were also compared to our ABI measurements. Spectral and Empirical Orthogonal Function analyses were performed on subsets of the ABI data for which 10-14 day time series were available and showed 2-3 day periodicity near-surface, corresponding to spatial scales of 10 1-10 2 km. During summer 2001, the mesoscale circulation along the subtropical continental margin in the northeastern Gulf was found to be the principal forcing factor for low frequency ABI variation. Increased backscatter observations are also correlated with offshore flow from the continental margin to the deep ocean

  18. Late Pleistocene-Holocene events on the continental slope of the Laptev Sea: Evidence from benthic and planktonic foraminiferal assemblages

    NASA Astrophysics Data System (ADS)

    Ovsepyan, Ya. S.; Taldenkova, E. E.; Bauch, H. A.; Kandiano, E. S.

    2015-11-01

    This work is dedicated to the study of benthic and planktonic foraminifers and is a contribution to the multidisciplinary investigations of Core PS51/154-11 from the Laptev Sea. The paleoecological analysis of foraminiferal assemblages makes it possible to reconstruct in detail environmental changes on the western continental margin of the Laptev Sea during the Late Pleistocene and Holocene. The examined core dated by the AMS radiocarbon method is divided into intervals that reflect main stages in the regional evolution for the last 17.6 k.y.: early deglaciation, Bølling-Allerød warming, Younger Dryas cooling, transition to the Interglacial, Holocene climatic optimum, Middle-Late Holocene. The presence of subpolar planktonic foraminifers and benthic species Cassidulina neoteretis (Tappan) provides grounds to reconstruct for the continental slope area stages of the enhanced activity of subsurface Atlantic-derived water in the intervals of 12.0-14.7 and 0.6-5.4 ka. The benthic assemblage reflects changes in depositional environments related to the postglacial transgression and also climatic change impacts affecting bioproductivity. The events defined on the basis of foraminifers are correlated with climatic oscillations and changes in circulation of water masses.

  19. Neogene depositional processes on the Texas-Louisiana continental slope revealed by high-resolution seismic studies

    SciTech Connect

    Damuth, J.E.; Olson, H.C. ); Twichell, D.C. )

    1991-03-01

    Systematic interpretation of high-resolution seismic profiles (3.5-10 kHz echograms and 100 Hz air gun) from the continental slope and rise of offshore Texas and Louisiana from the shelf break across the highly deformed zone of salt diapirs, folds, and intraslope basins to water depths greater than 3,500 m seaward of the Sigsbee Escarpment reveals the geometries, scales, distributions, and depositional processes of deep-water deposits in this region. The 3.5-10 kHz data indicate that redistribution of sediment by mass-transport processes a ubiquitous, and a wide spectrum of slumps, slide blocks, and debris flows are observed from small, isolated deposits in intraslope basins to large, complex deposits covering hundreds of kilometers. The reflection character (echo character) of many intraslope basin and canyon floors indicates sand-rich deposits; however, aggradational leveed-channel systems, characteristic of deep-sea fans, are not observed in the steep-walled intraslope basins. In contrast, some large submarine-fan channel-levee complexes do extend seaward from the mouths of these large canyons and basins at the base of the Sigsbee Escarpment to form one or more large deep-sea fans on the continental rise. Apparently, large quantities of terrigenous sediments can be transported by turbidity flows through the intricate network of rugged intraslope basins and canyons to feed these fans. Evidence of sediment redistribution by bottom currents (contour currents) is also observed in the form of sediment waves and drift deposits across a large area of the continental rise seaward of the southeastern base of the Sigsbee Escarpment.

  20. Data assimilative modeling investigation of Gulf Stream Warm Core Ring interaction with continental shelf and slope circulation

    NASA Astrophysics Data System (ADS)

    Chen, Ke; He, Ruoying; Powell, Brian S.; Gawarkiewicz, Glen G.; Moore, Andrew M.; Arango, Hernan G.

    2014-09-01

    A data assimilative ocean circulation model is used to hindcast the interaction between a large Gulf Stream Warm Core Ring (WCR) with the Mid-Atlantic Bight (MAB) shelf and slope circulation. Using the recently developed Incremental Strong constraint 4D Variational (I4D-Var) data assimilation algorithm, the model assimilates mapped satellite sea surface height (SSH), sea surface temperature (SST), in situ temperature, and salinity profiles measured by expendable bathythermograph, Argo floats, shipboard CTD casts, and glider transects. Model validations against independent hydrographic data show 60% and 57% error reductions in temperature and salinity, respectively. The WCR significantly changed MAB continental slope and shelf circulation. The mean cross-shelf transport induced by the WCR is estimated to be 0.28 Sv offshore, balancing the mean along-shelf transport by the shelfbreak jet. Large heat/salt fluxes with peak values of 8900 W m-2/4 × 10-4 kg m-2 s-1 are found when the WCR was impinging upon the shelfbreak. Vorticity analysis reveals the nonlinear advection term, as well as the residual of joint effect of baroclinicity and bottom relief (JEBAR) and advection of potential vorticity (APV) play important roles in controlling the variability of the eddy vorticity.

  1. Trophic interactions of fish communities at midwater depths enhance long-term carbon storage and benthic production on continental slopes

    PubMed Central

    Trueman, C. N.; Johnston, G.; O'Hea, B.; MacKenzie, K. M.

    2014-01-01

    Biological transfer of nutrients and materials between linked ecosystems influences global carbon budgets and ecosystem structure and function. Identifying the organisms or functional groups that are responsible for nutrient transfer, and quantifying their influence on ecosystem structure and carbon capture is an essential step for informed management of ecosystems in physically distant, but ecologically linked areas. Here, we combine natural abundance stable isotope tracers and survey data to show that mid-water and bentho-pelagic-feeding demersal fishes play an important role in the ocean carbon cycle, bypassing the detrital particle flux and transferring carbon to deep long-term storage. Global peaks in biomass and diversity of fishes at mid-slope depths are explained by competitive release of the demersal fish predators of mid-water organisms, which in turn support benthic fish production. Over 50% of the biomass of the demersal fish community at depths between 500 and 1800 m is supported by biological rather than detrital nutrient flux processes, and we estimate that bentho-pelagic fishes from the UK–Irish continental slope capture and store a volume of carbon equivalent to over 1 million tonnes of CO2 every year. PMID:24898373

  2. Trophic interactions of fish communities at midwater depths enhance long-term carbon storage and benthic production on continental slopes.

    PubMed

    Trueman, C N; Johnston, G; O'Hea, B; MacKenzie, K M

    2014-07-22

    Biological transfer of nutrients and materials between linked ecosystems influences global carbon budgets and ecosystem structure and function. Identifying the organisms or functional groups that are responsible for nutrient transfer, and quantifying their influence on ecosystem structure and carbon capture is an essential step for informed management of ecosystems in physically distant, but ecologically linked areas. Here, we combine natural abundance stable isotope tracers and survey data to show that mid-water and bentho-pelagic-feeding demersal fishes play an important role in the ocean carbon cycle, bypassing the detrital particle flux and transferring carbon to deep long-term storage. Global peaks in biomass and diversity of fishes at mid-slope depths are explained by competitive release of the demersal fish predators of mid-water organisms, which in turn support benthic fish production. Over 50% of the biomass of the demersal fish community at depths between 500 and 1800 m is supported by biological rather than detrital nutrient flux processes, and we estimate that bentho-pelagic fishes from the UK-Irish continental slope capture and store a volume of carbon equivalent to over 1 million tonnes of CO2 every year. PMID:24898373

  3. Seismic stratigraphy of Pliocene-Pleistocene deposits, continental slope-upper Mississippi Fan, northern Gulf of Mexico

    SciTech Connect

    Walters, R.D.; Buffler, R.T.

    1985-02-01

    Regional multichannel seismic data are used to develop a seismic stratigraphic framework for the continental slope-upper Mississippi fan region in the northern Gulf of Mexico. In the Mississippi canyon area, upper Pliocene and Pleistocene paleontologic zones from wells provide age control for major seismic sequence boundaries. A major unconformity and high-amplitude reflector identified as the base of Pleistocene represents a break in sedimentation and probably marks onset of fan deposition. This unconformity and others within the Pleistocene define sequences showing cyclic patterns of deposition, which are related to Pleistocene sea level changes and salt mobilization. Interpretation of seismic facies and their relationships to sea level changes, glaciations, and salt movement results in a model for the depositional history of the Mississippi fan from the canyon area to the deep-water part of the fan. Low-amplitude, chaotic, onlapping facies are interpreted as slump or debris-flow deposits associated with canyon cutting by retrogressive failure and initiation of large-scale mass movement due to a relative lowering of sea level. High-amplitude, parallel, continuous reflectors at sequence boundaries represent pelagic and hemipelagic sediments associated with a succeeding rise in relative sea level. In the shelf-upper slope area, isolated salt diapirs influence sedimentation on a localized scale. In the lower slope to upper fan, most Pleistocenen section is extensively disrupted by parallel sets of salt ridges that result from differential loading of fan sediments. Shifting depocenters and migratory channel systems funnel sediment through this area onto the lower fan. Salt wedges in the eastern study area appear to represent detached salt masses isolated within the Pleistocene section.

  4. Continental slope morphology in northern Gulf of Mexico mapped with long-range (GLORIA) side-scan data

    SciTech Connect

    McGregor, B.A.; Garrison, L.E.; Kenyon, N.H.

    1985-02-01

    GLORIA II long-range side-scan data provide a mosaic of the continental slope in the northern Gulf of Mexico, seaward of the Texas-Louisiana coast. A swath as wide as 30 km and a 10% overlap of the data between parallel track lines provide a continuous picture of the complex slope morphology, which is largely controlled by salt deformation. Morphologic features range from piercement structures approximately 2 km in diameter to basins as much as 30 km across. The GLORIA data delineate the East Breaks submarine slide, where surface lineations are suggestive of deformation features. High-resolution 10 kHz seismic-reflection profiles indicate that the very irregular surface on the slide has a relief of 10 m. The 3 types of intraslope basins (blocked canyon, interdomal, and collapse) described by A.H. Bouma can be identified on the GLORIA data. The walls of Gyre basin, an example of a blocked canyon, have what are interpreted to be gullies, which are commonly associated with submarine canyons. Another basin downslope has similar gully-like features on the walls, which suggest that it may have been part of the original canyon system. Although many canyon-like features direct the movement of sediment downslope, the present data show that all conduits end in closed basins. No system of basins can be shown to transport sediment across the entire slope between the Mississippi Canyon and the East Breaks slide. Small-scale slumps, which can be identified on the flanks of some of the diapiric structures, also contribute sediments to basins such as Gyre basin.

  5. Macrofaunal abundance and community composition at lower bathyal depths in different branches of the Whittard Canyon and on the adjacent slope (3500 m; NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Gunton, Laetitia M.; Gooday, Andrew J.; Glover, Adrian G.; Bett, Brian J.

    2015-03-01

    We studied benthic macrofaunal abundance and community composition in replicate Megacorer samples obtained from three sites in different branches of the Whittard Canyon (NE Atlantic) and one site on the adjacent slope to the west of the canyon system. All sites were located at a depth of ~3500 m. Abundance (macrobenthos sensu stricto, >300 μm) varied significantly (p<0.001) among sites, and decreased from east to west; highest in the Eastern branch (6249±standard deviation 1363 ind. m-2) and lowest on the slope (2744±SD 269 ind. m-2). Polychaetes were the dominant taxon, making up 53% of the macrofauna, followed by isopods (11%), tanaids (10%), bivalves (7%) and sipunculans (7%). Among the polychaetes, the Amphinomidae was the dominant family (27%), followed by the Spionidae (22%). Assemblage composition changed across the sites. From east to west, the proportion of polychaetes and isopods decreased (by 6% in each case), while sipunculans and tanaids increased (by 13% and 8%, respectively). The ranking of the two dominant polychaete families reversed from east to west (Eastern branch-Amphinomidae 36%, Spionidae 21%; Slope-Spionidae 30%, Amphinomidae 10%). Ordination of faunal groups (macrofaunal higher taxa, and polychaete families) revealed that the Central and Eastern branches were substantially similar, while the Western branch and slope sites were relatively distinct. A very similar pattern was evident in a corresponding ordination of environmental variables across the sites. An analysis of faunal similarities (ANOSIM) indicated that the Western branch/slope and Central branch/Eastern branch groups displayed the highest similarity. The clearest separation was between the slope and the Eastern branch. We conclude that, when compared at the same water depth, macrofaunal abundance and composition varies between open slope and canyon location, as well as among canyon branches. These differences probably reflect the influence of organic enrichment together with

  6. Avalanche Sedimentation in Seas and Oceans, Paper 3: The Second Global Level of Avalanche Sedimentation: The Base of the Continental Slope

    SciTech Connect

    Lisilsyn, A.P.

    1986-03-01

    The paper discusses the sedimentation pattern at the second global hypsometric level - at the base of continental slope, where the bulk of the planet's sedimentary matter is concentrated. Typifying examples are given, and the patterns of quantitative distribution of sedimentary matter at that level are described.

  7. Environmental factors controlling particulate mass fluxes on the Mallorca continental slope (Western Mediterranean Sea)

    NASA Astrophysics Data System (ADS)

    Pasqual, Catalina; Amores, Angel; Flexas, M. Mar; Monserrat, Sebastià; Calafat, Antoni

    2014-10-01

    Settled material recorded by two near bottom sediment traps deployed from November 2009 to February 2011 at northern (Sóller) and southern (Cabrera) slopes of Mallorca Island (Western Mediterranean) is studied with the aim of discerning their possible origin. The total settled particulate mass fluxes (TMF) at Sóller station were found to be, on average, 2.8 times greater than at Cabrera location during the deployment period, although both time series had a similar temporal evolution. It is suggested that wind episodes affecting the entire area were the common forcing, causing a primary production enhancement and being responsible of the similar temporal behavior. The greater sediment amounts collected in Sóller are explained on the basis of two physical mechanisms: 1) a number of successive eddies generated by instabilities of the Balearic Current that are regularly observed on satellite images, some of which have been reported to reach the seabed, thus increasing near bottom velocities and causing sediment resuspension. And 2) bottom trapped waves that are evidenced from a wavelet analysis in Sóller which could affect the TFM by enhancing sediment resuspension or advecting material from the surrounding areas.

  8. Methane sources feeding cold seeps on the shelf and upper continental slope off central Oregon, USA

    NASA Astrophysics Data System (ADS)

    Torres, Marta E.; Embley, Robert W.; Merle, Susan G.; TréHu, Anne M.; Collier, Robert W.; Suess, Erwin; Heeschen, Katja U.

    2009-11-01

    We report on a bathymetric mapping and remotely operated vehicle surveys along the 100-600 m region offshore Oregon from 43°50'N to 44°18'N. We interpret our results in light of available geophysical data, published geotectonic models, and analogous observations of fluid venting and carbonate deposition from 44°30'N to 45°00'N. The methane seepage is defined by juxtaposition of a young prism, where methane is generated by bacterial activity and its release is modulated by gas hydrate dynamics, against older sequences that serve as a source of thermogenic hydrocarbons that vent in the shelf. We hypothesize that collision of a buried ridge with the Siletz Terrane results in uplift of gas hydrate bearing sediments in the oncoming plate and that the resulting decrease in pressure leads to gas hydrate dissociation and methane exolution, which, in turn, may facilitate slope failure. Oxidation of the released methane results in precipitation of carbonates that are imaged as high backscatter along a 550 ± 60 m benthic corridor.

  9. Map and tabulation of quaternary mass movements along the United States-Canadian Atlantic continental slope from 32 degrees 00 minutes to 47 degrees 00 minutes N. latitude

    USGS Publications Warehouse

    Booth, J.S.; O'Leary, D. W.; Popenoe, Peter; Robb, James M.; McGregor, B.A.

    1988-01-01

    Since the initial report on the Grand Banks Slump off southern Newfoundland (Heezen and Ewing, 1952), a large body of data on submarine mass movement along the Atlantic continental margin of the United States and Canada has been published.  These data were compiled to provide this distribution map (sheet 1) and tabulation (sheet 2) of "principal facts" on mass movement of the northwest Atlantic Continental Slope.  Although we prepared this inventory to facilitate our study of Quaternary mass movement along the U.S. Continental Slope, we judged the compilation to be large enough and detailed enough to be published as a generally useful data source and compendium.  Sheet 3 shows examples of mass movement styles.

  10. Gravity deposits in deep sea fans and on Continental Slopes, Black Sea

    SciTech Connect

    Ivanov, M.K.; Konyukhov, A.I.

    1988-08-01

    The Danube fan has a classical structure. It is clearly expressed in the bottom relief and traced by reflection profiles for more than 200 km. The fan body is levee valley, which splits in a mid-fan area into numerous meandering distributaries. The fan consists of gravity and hemipelagic deposits. These are mainly turbidites of various compositions. Channels are filled with grain-flow deposits (sand), debris-flow deposits (sandy clay with shells), and slides from valley walls (mud, sapropelic mud). Levees in upper and mid-fan areas are formed by specific turbidite sequences: mudstone crumbs in the base, thinly laminated silt and clays in the middle, blue mud on the top. Hemipelagic sediments increase noticeably on outer slopes of the levees. In the Pleistocene sequences these are mud; in the Holocene, sapropelic mud and coccolith-diatom ooze. Distal turbidites are widespread in the lower fan areas. In the base of each cycle is a thin sand-silt layer with unclear graded bedding; the upper part is represented by mud. Reflection profiles demonstrate an ancient fan system with buried channels and levees. Configurations of these bodies are very similar to those of the modern fans. The sedimentary lens on the sea floor opposite the mouths of submarine canyons of the Rioni, Inguri, Kodori, Supsa, and Chorokh Rivers was formed by overlapped modern and ancient fans. The Inguri and Rioni produced a practically single submarine fan, the largest in this area. It is rather well expressed morphologically and traced by reflection profiles for more than 100 km. In its lower part it overlays a number of small fans. The Rioni-Inguri fan is smaller than the Danube, but the whole system of overlapped fans occupies an area of about 17,000 km/sup 2/, being more than 3 km thick. The composition and structure of sediments in this deep-sea system change sharply, depending on the geomorphological position.

  11. Observations of second baroclinic mode internal solitary waves on the continental slope of the northern South China Sea

    NASA Astrophysics Data System (ADS)

    Yang, Yiing Jang; Fang, Ying Chih; Chang, Ming-Huei; Ramp, Steven R.; Kao, Chih-Chung; Tang, Tswen Yung

    2009-10-01

    A temperature and current velocity mooring, located on the upper continental slope of the northern South China Sea, recorded a number of second baroclinic mode (mode 2) internal solitary waves (ISWs). These types of waves are seldom observed in nature. The mode 2 ISWs typically showed upward (downward) displacement of isotherms in the upper (lower) water column and three layers of eastward, westward, and eastward current from the uppermost to bottommost portions of a wave. In summer, westward-propagating mode 2 ISWs were observed only occasionally. These waves generally appeared after mode 1 ISWs, a feature that may relate to the diurnal tide with a period of approximately 24 hours. The displacement of isotherms induced by mode 2 ISWs was 20 ± 14 m at 75 m and -22 ± 15 m at 240 m, and the characteristic time scale was approximately 8.0 ± 4.3 min. In winter, mode 2 ISWs were more active but mode 1 ISWs were rarely observed. Isotherm displacement by mode 2 ISWs in winter was 30 ± 18 m at 75 m and -26 ± 16 m at 240 m, and the average characteristic time scale was 6.9 ± 4.6 min. The mode 2 ISWs thus had larger amplitudes and smaller time scales in winter than they did in summer. The observed vertical temperature profile also showed notable seasonal change. The thermocline was shallow in summer and deep in winter. In winter, vertical temperature profiles indicated that the main thermocline was located near middepth over the upper continental slope near the 350 m isobath. Mode 1 ISWs were more active in summer than in winter, reflecting the larger Ursell numbers for mode 1 ISWs in summer. Among mode 2 ISWs in summer, 90% appeared after mode 1 ISWs. These results suggest that mode 2 ISWs could be related to mode 1 ISWs. In contrast, mode 2 ISWs were more active in winter than in summer, with larger mode 2 Ursell numbers also found in winter. Among winter mode 2 ISWs, 72% appeared without mode 1 ISWs. Mode 2 ISWs in winter could be related to the main thermocline

  12. Metazoan meiofauna in deep-sea canyons and adjacent open slopes: A large-scale comparison with focus on the rare taxa

    NASA Astrophysics Data System (ADS)

    Bianchelli, S.; Gambi, C.; Zeppilli, D.; Danovaro, R.

    2010-03-01

    Metazoan meiofaunal abundance, total biomass, nematode size and the richness of taxa were investigated along bathymetric gradients (from the shelf break down to ca. 5000-m depth) in six submarine canyons and on five adjacent open slopes of three deep-sea regions. The investigated areas were distributed along >2500 km, on the Portuguese to the Catalan and South Adriatic margins. The Portuguese and Catalan margins displayed the highest abundances, biomass and richness of taxa, while the lowest values were observed in the Central Mediterranean Sea. The comparison between canyons and the nearby open slopes showed the lack of significant differences in terms of meiofaunal abundance and biomass at any sampling depth. In most canyons and on most slopes, meiofaunal variables did not display consistent bathymetric patterns. Conversely, we found that the different topographic features were apparently responsible for significant differences in the abundance and distribution of the rare meiofaunal taxa (i.e. taxa accounting for <1% of total meiofaunal abundance). Several taxa belonging to the temporary meiofauna, such as larvae/juveniles of Priapulida, Holothuroidea, Ascidiacea and Cnidaria, were encountered exclusively on open slopes, while others (including the Tanaidacea and Echinodea larvae) were found exclusively in canyons sediments. Results reported here indicate that, at large spatial scales, differences in deep-sea meiofaunal abundance and biomass are not only controlled by the available food sources, but also by the region or habitat specific topographic features, which apparently play a key role in the distribution of rare benthic taxa.

  13. New insights into submarine geomorphology and depositional processes along the George V Land continental slope and upper rise (East Antarctica)

    NASA Astrophysics Data System (ADS)

    de Santis, Laura

    2010-05-01

    Swath bathymetry collected by the Italian Antarctic Program (PNRA), in the offshore of the George Vth Land, document evidence of cascading, cold and dense bottom currents, inside continental slope canyons, and suggest an active role of the sea floor morphology on modern and ancient process. The continental slope is incised by canyons locally heading to the shelf edge and bounding sedimentary ridges of Miocene age(ref1,2). Erosion by bottom water masses, up to present times, exhumed or prevented the burial of such relict sedimentary ridges originated by glacial processes. Dense shelf water is formed by coastal polynyas and is exported over the shelf break to produce Antarctic Bottom Water (AABW)(ref3,4). This locally formed AABW (often referred to as Adélie Land Bottom Water) is detected by CTD and mooring measurements up to about 3200 m of depth, in the Jussieu canyon and further to the west(ref5). The speed of the ALBW is enough to transport fine sand and silt from shallow to deep water. Evidence for exporting sediment off the shelf via bottom water, through the Holocene, is inferred by sedimentological and geophysical studies(ref6,7). Morphologic and geological data in the slope and rise confirm that the Jussieu canyon is a main conduit of high energetic bottom current, in present times as well as in the past(ref1,7). Coarse grain material and turbidites (up to 1 meter thick) were sampled from the canyon levees at 2500 and 3000 meters of water depth(ref1). At a depth of 2600 m, the Jussieu canyon converges with two canyons into a single branch, showing a meandering trend, up to about 3200 m of water depth. The asymmetry of the meandering section and the internal geometry of its levees are typical expressions of differential erosion and deposition from downslope flows. Sediment waves characterise the western flank of the Wega Channel, at depth of 2400-2800 meters, to the east of the Jussieu canyon(ref1). The waves are composed by fine grained sediments whose

  14. Cenozoic global sea level, sequences, and the New Jersey transect: Results from coastal plain and continental slope drilling

    USGS Publications Warehouse

    Miller, K.G.; Mountain, Gregory S.; Browning, J.V.; Kominz, M.; Sugarman, P.J.; Christie-Blick, N.; Katz, M.E.; Wright, J.D.

    1998-01-01

    The New Jersey Sea Level Transect was designed to evaluate the relationships among global sea level (eustatic) change, unconformity-bounded sequences, and variations in subsidence, sediment supply, and climate on a passive continental margin. By sampling and dating Cenozoic strata from coastal plain and continental slope locations, we show that sequence boundaries correlate (within ??0.5 myr) regionally (onshore-offshore) and interregionally (New Jersey-Alabama-Bahamas), implicating a global cause. Sequence boundaries correlate with ??18O increases for at least the past 42 myr, consistent with an ice volume (glacioeustatic) control, although a causal relationship is not required because of uncertainties in ages and correlations. Evidence for a causal connection is provided by preliminary Miocene data from slope Site 904 that directly link ??18O increases with sequence boundaries. We conclude that variation in the size of ice sheets has been a primary control on the formation of sequence boundaries since ~42 Ma. We speculate that prior to this, the growth and decay of small ice sheets caused small-amplitude sea level changes (<20 m) in this supposedly ice-free world because Eocene sequence boundaries also appear to correlate with minor ??18O increases. Subsidence estimates (backstripping) indicate amplitudes of short-term (million-year scale) lowerings that are consistent with estimates derived from ??18O studies (25-50 m in the Oligocene-middle Miocene and 10-20 m in the Eocene) and a long-term lowering of 150-200 m over the past 65 myr, consistent with estimates derived from volume changes on mid-ocean ridges. Although our results are consistent with the general number and timing of Paleocene to middle Miocene sequences published by workers at Exxon Production Research Company, our estimates of sea level amplitudes are substantially lower than theirs. Lithofacies patterns within sequences follow repetitive, predictable patterns: (1) coastal plain sequences consist

  15. Hooked from the deep: a rare new species of Taeniogyrus (Holothuroidea, Chiridotidae) from the continental slope of Brazil, southwestern Atlantic.

    PubMed

    Moura, Rafael Bendayan De; Campos, Lúcia De Siqueira; Esteves, André Morgado

    2015-01-01

    Most species of Taeniogyrus Semper, 1867 are known from shallow water in the Indo-Pacific, with other records in Antarctica, Mediterranean Sea, and the Atlantic. A new species of Taeniogyrus is described and illustrated here from the continental slope of Campos Basin, southeast of Brazil. In this species, sigmoid hooks (336-405 µm) are much larger than in any other in the genus, bearing a long and conspicuous hook region. Wheels with six spokes (86-169 µm), inner margin with 60-125 continuous teeth, are confined to round papillae along each interradius. Polian vesicles are ventral, numerous (15-21), of different sizes, and tubular shaped with a terminal round region. This new species represents the deepest record of the genus Taeniogyrus. It increases to three the number of chiridotids in Brazilian waters, and the number of Taeniogyrus species in the Atlantic. Additionally, Taeniogyrus furcipraeditus (Salvini-Plawen, 1972) from the Mediterranean Sea and Taeniogyrus havelockensis (Rao, 1975) from the Andaman Sea are proposed as new combinations. PMID:26249509

  16. Geochemistry of pore waters from Shell Oil Company drill holes on the continental slope of the northern Gulf of Mexico

    USGS Publications Warehouse

    Manheim, F. T.; Bischoff, J.L.

    1969-01-01

    Pore waters were analyzed from 6 holes drilled from M.V. "Eureka" as a part of the Shell Oil Co. deeper offshore study. The holes were drilled in water depths of 600-3,000 ft. (approximately 180-550 m) and penetrated up to 1,000 ft. (300 m) of Pliocene-Recent clayey sediments. Salt and anhydrite caprock was encountered in one diapiric structure on the continental slope. Samples from holes drilled near diapiric structures showed systematic increases of pore-water salinity with depth, suggestive of salt diffusion from underlying salt plugs. Anomalous concentrations of K and Br indicate that at least one plug contains late-stage evaporite minerals. Salinities approaching halite saturation were observed. Samples from holes away from diapiric structures showed little change in pore-water chemistry, except for loss of SO4 and other variations attributable to early-stage diagenetic reactions with enclosing sediments. Thus, increased salt concentrations in even shallow sediments from this part of the Gulf appear to provide an indicator of salt masses at depth. ?? 1969.

  17. Discovery of a recent, natural whale fall on the continental slope off Anvers Island, western Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Smith, Kathryn E.; Thatje, Sven; Singh, Hanumant; Amsler, Margaret O.; Vos, Stephanie C.; McClintock, James B.; Brothers, Cecilia J.; Brown, Alastair; Ellis, Daniel; Anderson, Jeffrey S.; Aronson, Richard B.

    2014-08-01

    Whale falls provide a substantial, nutrient-rich resource for species in areas of the ocean that may otherwise be largely devoid of food. We report the discovery of a natural whale fall at 1430 m depth in the cold waters of the continental slope off the western Antarctic Peninsula. This is the highest-latitude whale fall reported to date. The section of the carcass we observed-the tail fluke-was more complete than any previously reported natural whale fall from the deep sea and in the early stages of decomposition. We estimate the entire cetacean to measure 5-8 m in length. The flesh remained almost intact on the carcass but the skin was missing from the entire section except for the end of the fluke, clearly exposing blubber and soft tissue. The absence of skin indicates rapid and Homogeneous loss. The dominant macrofauna present were crustaceans, including most prominently the lithodid crab Paralomis birsteini, and zoarcid fish typical of the ‘mobile-scavenger' successional stage. The density of mobile macrofauna was greatest on the carcass and declined to background levels within 100 m, indicating that they were attracted to the whale fall. This whale fall offers an important opportunity to examine the decomposition of a carcass under deep-sea conditions at polar latitudes.

  18. The role of horizontal impulses of the faulting continental slope in generating the 26 December 2004 tsunami

    NASA Astrophysics Data System (ADS)

    Song, Y. Tony; Fu, L.-L.; Zlotnicki, Victor; Ji, Chen; Hjorleifsdottir, Vala; Shum, C. K.; Yi, Yuchan

    For a long time, people have believed that the vertical displacement of seafloor due to undersea earthquakes is the primary cause of tsunami genesis. However, seismically-inverted seafloor deformation of the 2004 Sumatra-Andaman earthquake shows that the total vertical displacement is not enough to have generated the powerful Indian Ocean tsunami. Based on the seismically-inverted data and a three-dimensional ocean general circulation model (OGCM), we show that the momentum force, transferred by the horizontal impulses of the faulting continental slope in that earthquake, has accounted for two thirds of the satellite-observed tsunami height and generated kinetic energy 5 times larger than the potential energy due to the vertical displacement. The asymmetric tsunami pattern, recorded by tide-gauges showing leading-elevation waves toward Sri Lanka and leading-depression waves toward Thailand, is best explained by the horizontally-forced mechanism. The same mechanism has also explained the March 2005 Nias earthquake and tsunami data, suggesting that the horizontal motions of faulting have played more important roles in tsunami genesis than previously thought.

  19. Deepwater Program: Studies of Gulf of Mexico lower continental slope communities related to chemosynthetic and hard substrate habitats

    USGS Publications Warehouse

    Ross, Steve W.; Demopoulos, Amanda W.J.; Kellogg, Christina A.; Morrison, Cheryl L.; Nizinski, Martha S.; Ames, Cheryl L.; Casazza, Tara L.; Gualtieri, Daniel; Kovacs, Kaitlin; McClain, Jennifer P.; Quattrini, Andrea M.; Roa-Varon, Adela Y.; Thaler, Andrew D.

    2012-01-01

    This report summarizes research funded by the U.S. Geological Survey (USGS) in collaboration with the University of North Carolina at Wilmington (UNCW) on the ecology of deep chemosynthetic communities in the Gulf of Mexico. The research was conducted at the request of the U.S. Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE; formerly Minerals Management Service) to complement a BOEMRE-funded project titled "Deepwater Program: Investigations of Chemosynthetic Communities on the Lower Continental Slope of the Gulf of Mexico." The overall research partnership, known as "Chemo III," was initiated to increase understanding of the distribution, structure, function, and vulnerabilities of these poorly known associations of animals and microbes for water depths greater than 1,000 meters (m) in the Gulf of Mexico. Chemosynthetic communities rely on carbon sources that are largely independent of sunlight and photosynthetic food webs. Despite recent research directed toward chemosynthetic and deep coral (for example, Lophelia pertusa) based ecosystems, these habitats are still poorly studied, especially at depths greater than 1,000 m. With the progression into deeper waters by fishing and energy industries, developing sufficient knowledge to manage these deep ecosystems is essential. Increased understanding of deep-sea communities will enable sound evaluations of potential impacts and appropriate mitigations.

  20. Subseafloor microbial communities associated with rapid turbidite deposition in the Gulf of Mexico continental slope (IODP Expedition 308).

    PubMed

    Nunoura, Takuro; Soffientino, Bruno; Blazejak, Anna; Kakuta, Jungo; Oida, Hanako; Schippers, Axel; Takai, Ken

    2009-09-01

    The subseafloor microbial communities in the turbidite depositional basins Brazos-Trinity Basin IV (BT Basin) and the Mars-Ursa Basin (Ursa Basin) on the Gulf of Mexico continental slope (IODP holes U1319A, U1320A, U1322B and U1324B) were investigated by PCR-dependent molecular analyses targeted to the small subunit (SSU) rRNA genes, dsrA and mcrA, and hydrogenase activity measurements. Biomass at both basins was very low, with the maximum cell or the SSU rRNA gene copy number <1 x 10(7) cells mL(-1) or copies g(-1) sediments, respectively. Hydrogenase activity correlated with biomass estimated by SSU rRNA gene copy number when all data sets were combined. We detected differences in the SSU rRNA gene community structures and SSU rRNA gene copy numbers between the basin-fill and basement sediments in the BT Basin. Examination of microbial communities and hydrogenase activity in the context of geochemical and geophysical parameters and sediment depositional environments revealed that differences in microbial community composition between the basin-fill and basement sediments in the BT Basin were associated with sedimentation regimes tied to the sea-level change. This may also explain the distributions of relatively similar archaeal communities in the Ursa Basin sediments and basement sediments in the BT Basin. PMID:19583789

  1. The Kongsfjorden Channel System offshore NW Spitsbergen, European Arctic: evidence of down-slope processes in a contour-current dominated setting on the continental margin

    NASA Astrophysics Data System (ADS)

    Forwick, Matthias; Sverre Laberg, Jan; Hass, H. Christian; Osti, Giacomo

    2016-04-01

    The Kongsfjorden Channel System (KCS) is located on the continental slope in the eastern Fram Strait, off northwest Spitsbergen. It provides evidence that the influence of down-slope sedimentary processes locally exceeds regional along-slope sedimentation. Compared to other submarine channel systems on and off glaciated continental margins, it is a relatively short system (~120 km) occurring at a large range of water depths (~250-4000 m). It originates with multiple gullies on the Kongsfjorden Trough Mouth Fan merging to small channels that further downslope merge to a main channel. The overall location of the channel system is controlled by variations in slope gradients (0-20°) and the ambient regional bathymetry: widest and deepest incisions occur in areas of steepest slope gradients. The KCS has probably been active since ~1 Ma when glacial activity on Svalbard increased and grounded ice expanded to the shelf break off Kongsfjorden repeatedly. Activity within the system was probably highest during glacials. However, reduced activity presumably took place also during interglacials. The presentation summarizes the work of Forwick et al. (2015). Reference: Forwick, M., Laberg, J.S., Hass, H.C. & Osti, C., 2015. The Kongsfjorden Channel System offshore NW Svalbard: downslope sedimentary processes in a contour-current-dominated setting. Arktos 1, DOI: 10.1007/s41063-015-0018-4.

  2. Cenozoic climate change and diversification on the continental shelf and slope: evolution of gastropod diversity in the family Solariellidae (Trochoidea).

    PubMed

    Williams, S T; Smith, L M; Herbert, D G; Marshall, B A; Warén, A; Kiel, S; Dyal, P; Linse, K; Vilvens, C; Kano, Y

    2013-04-01

    Recent expeditions have revealed high levels of biodiversity in the tropical deep-sea, yet little is known about the age or origin of this biodiversity, and large-scale molecular studies are still few in number. In this study, we had access to the largest number of solariellid gastropods ever collected for molecular studies, including many rare and unusual taxa. We used a Bayesian chronogram of these deep-sea gastropods (1) to test the hypothesis that deep-water communities arose onshore, (2) to determine whether Antarctica acted as a source of diversity for deep-water communities elsewhere and (3) to determine how factors like global climate change have affected evolution on the continental slope. We show that although fossil data suggest that solariellid gastropods likely arose in a shallow, tropical environment, interpretation of the molecular data is equivocal with respect to the origin of the group. On the other hand, the molecular data clearly show that Antarctic species sampled represent a recent invasion, rather than a relictual ancestral lineage. We also show that an abrupt period of global warming during the Palaeocene Eocene Thermal Maximum (PETM) leaves no molecular record of change in diversification rate in solariellids and that the group radiated before the PETM. Conversely, there is a substantial, although not significant increase in the rate of diversification of a major clade approximately 33.7 Mya, coinciding with a period of global cooling at the Eocene-Oligocene transition. Increased nutrients made available by contemporaneous changes to erosion, ocean circulation, tectonic events and upwelling may explain increased diversification, suggesting that food availability may have been a factor limiting exploitation of deep-sea habitats. Tectonic events that shaped diversification in reef-associated taxa and deep-water squat lobsters in central Indo-West Pacific were also probably important in the evolution of solariellids during the Oligo

  3. Provenance and depositional history of continental slope sediments in the Southwestern Gulf of Mexico unraveled by geochemical analysis

    NASA Astrophysics Data System (ADS)

    Armstrong-Altrin, John S.; Machain-Castillo, María Luisa; Rosales-Hoz, Leticia; Carranza-Edwards, Arturo; Sanchez-Cabeza, Joan-Albert; Ruíz-Fernández, Ana Carolina

    2015-03-01

    The aim of this work is to constrain the provenance and depositional history of continental slope sediments in the Southwestern Gulf of Mexico (~1089-1785 m water depth). To achieve this, 10 piston sediment cores (~5-5.5 m long) were studied for mineralogy, major, trace and rare earth element geochemistry. Samples were analyzed at three core sections, i.e. upper (0-1 cm), middle (30-31 cm) and lower (~300-391 cm). The textural study reveals that the core sediments are characterized by silt and clay fractions. Radiocarbon dating of sediments for the cores at different levels indicated a maximum of ~28,000 year BP. Sediments were classified as shale. The chemical index of alteration (CIA) values for the upper, middle, and lower sections revealed moderate weathering in the source region. The index of chemical maturity (ICV) and SiO2/Al2O3 ratio indicated low compositional maturity for the core sediments. A statistically significant correlation observed between total rare earth elements (∑REE) versus Al2O3 and Zr indicated that REE are mainly housed in detrital minerals. The North American Shale Composite (NASC) normalized REE patterns, trace element concentrations such as Cr, Ni and V, and the comparison of REE concentrations in sediments and source rocks indicated that the study area received sediments from rocks intermediate between felsic and mafic composition. The enrichment factor (EF) results indicated that the Cd and Zn contents of the upper section sediments were influenced by an anthropogenic source. The trace element ratios and authigenic U content of the core sediments indicated the existence of an oxic depositional environment.

  4. Cenozoic climate change and diversification on the continental shelf and slope: evolution of gastropod diversity in the family Solariellidae (Trochoidea)

    PubMed Central

    Williams, S T; Smith, L M; Herbert, D G; Marshall, B A; Warén, A; Kiel, S; Dyal, P; Linse, K; Vilvens, C; Kano, Y

    2013-01-01

    Recent expeditions have revealed high levels of biodiversity in the tropical deep-sea, yet little is known about the age or origin of this biodiversity, and large-scale molecular studies are still few in number. In this study, we had access to the largest number of solariellid gastropods ever collected for molecular studies, including many rare and unusual taxa. We used a Bayesian chronogram of these deep-sea gastropods (1) to test the hypothesis that deep-water communities arose onshore, (2) to determine whether Antarctica acted as a source of diversity for deep-water communities elsewhere and (3) to determine how factors like global climate change have affected evolution on the continental slope. We show that although fossil data suggest that solariellid gastropods likely arose in a shallow, tropical environment, interpretation of the molecular data is equivocal with respect to the origin of the group. On the other hand, the molecular data clearly show that Antarctic species sampled represent a recent invasion, rather than a relictual ancestral lineage. We also show that an abrupt period of global warming during the Palaeocene Eocene Thermal Maximum (PETM) leaves no molecular record of change in diversification rate in solariellids and that the group radiated before the PETM. Conversely, there is a substantial, although not significant increase in the rate of diversification of a major clade approximately 33.7 Mya, coinciding with a period of global cooling at the Eocene–Oligocene transition. Increased nutrients made available by contemporaneous changes to erosion, ocean circulation, tectonic events and upwelling may explain increased diversification, suggesting that food availability may have been a factor limiting exploitation of deep-sea habitats. Tectonic events that shaped diversification in reef-associated taxa and deep-water squat lobsters in central Indo-West Pacific were also probably important in the evolution of solariellids during the Oligo

  5. Distribution and generic composition of culturable marine actinomycetes from the sediments of Indian continental slope of Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Das, Surajit; Lyla, P. S.; Ajmal Khan, S.

    2008-05-01

    Actinomycetes population from continental slope sediment of the Bay of Bengal was studied. Samples were collected during two voyages of FORV Sagar Sampada in 2004 (May-June) and 2005 (July) respectively from 11 transects (each transect had ca. 200 m, 500 m, and 1 000 m depth stations). The physicochemical parameters of overlying water, and sediment samples were also recorded. The actinomycete population ranged from 5.17 to 51.94 CFU/g dry sediment weight and 9.38 to 45.22 CFU/g dry sediment weight during the two cruises respectively. No actinomycete colony was isolated from stations in 1 000 m depth. Two-way analysis of variance showed significant variation among stations (ANOVA two-way, P<0.05), but no significance was found between the two cruises (ANOVA two-way, P<0.05). Populations in stations in 500 m depth in both cruises were higher than that of 200 m depth stations with statistically insignificant difference (ANOVA two-way, P>0.05). Three actinomycetes genera were identified. Streptomyces was found to be the dominating one in both the cruises, followed by Micromonospora, and Actinomyces. The spore of Streptomyces isolates showed the abundance in spiral spore chain. Spore surface was smooth. Multiple regression analysis revealed that the influencing physico-chemical factors were sediment pH, sediment temperature, TOC, porosity, salinity, and pressure. The media used in the present study was prepared with seawater. Thus, they may represent an autochthonous marine flora and deny the theory of land runoff carriage into the sea for adaptation to the salinity of the seawater and sediments.

  6. Records of sedimentary dynamics in the continental shelf and upper slope between Aveiro-Espinho (N Portugal)

    NASA Astrophysics Data System (ADS)

    Martins, Virgínia; Abrantes, Isabel; Grangeia, Carlos; Martins, Paula; Nagai, Renata; Sousa, Sílvia H. M.; Laut, Lazaro L. M.; Dias, João M. Alveirinho; Dias, João M.; da Silva, Eduardo Ferreira; Rocha, Fernando

    2012-08-01

    The sedimentary unconsolidated cover of the Aveiro-Espinho continental shelf and upper slope (NW Portugal) records a complex interplay of processes including wave energy and currents, fluvial input, sediment transport alongshore and cross-shelf, geological and oceanographic processes and sediment sources and sinks. In order to study this record, a set of surface sediment samples was studied. Sediment grain size and composition, as well as the mineralogical composition (by XRD) of the fine (< 63 μm) and clay (< 2 μm) fractions and benthic microfaunal (foraminifera) data were analysed. Cluster analysis applied to the sedimentological data (grain size, sediment composition and mineralogy) allowed the establishment of three main zones corresponding to the: inner-, mid- and outer-shelf/upper slope. On the inner-shelf, the sedimentary coverture is composed of siliciclastic fine to very fine sand, essentially comprising modern (immature) terrigenous particles. The sediment grain size, as well as mineralogical and microfaunal composition, denote the high energetic conditions of this sector in which the alongshore transport of sand is predominantly southward and occurs mostly during the spring-summer oceanographic regime, when the main river providing sediments to this area, the River Douro, undergoes periods of drought. This effect may emphasize the erosive character of this coastal sector at present, since the Ria de Aveiro provides the shelf with few sediments. On the mid-shelf, an alongshore siliciclastic band of coarse sand and gravel can be found between the 40 m and 60 m isobaths. This gravelly deposit includes relic sediments deposited during lower sea-level stands. This structure stays on the surface due to the high bottom energy, which promotes the remobilization of the fine-grained sediments, and/or events of sediments bypassing. Benthic foraminifera density and "Benthic Foraminifera High Productivity" (BFHP) proxy values are in general low, which is consistent

  7. Seed dissemination by frugivorous birds from forest fragments to adjacent pastures on the western slope of Volcán Barva, Costa Rica.

    PubMed

    Barrantes, Gilbert; Pereira, Ana

    2002-06-01

    Logging, cattle raising, and agricultural activities have caused the destruction of most forested areas in Costa Rica. In some middle and highlands the abrupt topography delayed the complete destruction of montane forest. Consequently, some fragments of almost pristine forest remain along streams that run in deep canyons. Frequently, these remnants serve as corridors between larger forested areas and as routes for movement of frugivorous birds. Eighteen bird species, e.g., Turdus plebejus, Elaenia frantzii and Ptilogonys caudatus are common dwellers of forest patches throughout the Pacific slope of the Volcán Barva. These species fly frequently from forest fragments to adjacent pastures. They defected and regurgitated seeds of 28 plant species on stumps scattered on pasture areas. Isolated trees and specially the stumps are suitable microhabitats for germination of seeds and establishment of seedings. PMID:12298287

  8. Observed internal tides and near-inertial waves on the continental shelf and slope off Jaigarh, central west coast of India

    NASA Astrophysics Data System (ADS)

    Subeesh, M. P.; Unnikrishnan, A. S.

    2016-05-01

    The characteristics of internal tides (ITs) and near-inertial waves (NIWs) on the continental shelf and slope off Jaigarh (17∘N), central west coast of India were studied. Eight-month (March-October) long Acoustic Doppler Current Profiler (ADCP) measurements made in the year 2008 were used in the present study. Analysis of sea surface heights from satellite altimeter data, where the tracks of the satellites are oriented nearly in the direction of the semimajor axis of barotropic tides, reveals the presence of diurnal and semidiurnal internal tides with surface amplitudes of about 2 cm. Baroclinic current spectra of horizontal velocities show peaks in IT frequencies of M2, S2, K1 and O1 and in inertial frequency (f). The observed current spectra show higher energies than those in Garrett-Munk reference spectra by about 2-3 times. Based on the estimates of "critical topography" (where the topographic slope is equal to the slope of IT) and computed barotropic body force (Baines, 1982), the shelf-edge, mid-slope and deep part of the slope region are found to be the possible generation sites of internal tides in the region. Over the period of observation, the IT on the slope is found to be energetic, with a strong IT during March to mid-April (pre-monsoon period). Whereas, on the shelf, IT is weak during the pre-monsoon and found to be strong in the southwest monsoon. The available hydrographic data and model simulated hydrography suggest that this difference is linked with the stratification changes on the shelf and slope during these seasons, where the stratification is found to be weak on the shelf and strong on the slope during pre-monsoon. Strong low-mode NIW is observed on the shelf associated with the storm events while the NIW is found to be less energetic on the slope.

  9. Evidence of low density sub-crustal underplating beneath western continental region of India and adjacent Arabian Sea: Geodynamical considerations

    NASA Astrophysics Data System (ADS)

    Pandey, O. P.; Agrawal, P. K.; Negi, J. G.

    1996-07-01

    The known high mobility of the Indian subcontinent during the period from 80 to 53 Ma has evoked considerable interest in recent times. It appears to have played an important role in shaping the subcontinental structures of western India and the adjoining Arabian Sea. During this period, a major catastrophic event took place in the form of Deccan volcanism, which coincides with the biological mass extinction at the K-T boundary, including the death of dinosaurs. The origin of Deccan volcanism is still being debated. Geophysically, western India and its offshore regions exhibit numerous prominent anomalies which testify to the abnormal nature of the underlying crust-lithosphere. In this work, we develop a two-dimensional structural model of these areas along two long profiles extending from the eastern basin of the Arabian Sea to about 1000 km inland. The model, derived from the available gravity data in the oceanic and continental regions, is constrained by seismic and other relevant information in the area, and suggests, for the first time, the presence of an extensive low-density (2.95-3.05 g/cm 3) sub-crustal underplating. Such a layer is found to occur between depths of 11 and 20 km in the eastern basin of the Arabian Sea, and betweeen 45 and 60 km in the continental region where it is sandwiched in the lower lithosphere. The low density may have been caused as a result of serpentinization or fractionation of magma by a process related in some way to the Deccan volcanic event. Substantial depletion of both oceanic and continental lithosphere is indicated. We hypothesize that the present anatomy of the deformed lithosphere of the region at the K-T boundary is the result of substantial melt generated owing to frictional heat possibly giving rise to a hot cell like condition at the base of the lithosphere, resulting from the rapid movement of the Indian subcontinent between 80 and 53 Ma.

  10. Mesobathic chondrichthyes of the Juan Fernández seamounts: are they different from those of the central Chilean continental slope?

    PubMed

    Andrade, Isabel; Pequeño, Germán

    2008-03-01

    We compared the geographic distribution of groups of chondrychthid fishes of two physically proximal, although geographically different, regions that include the Juan Fernández seamounts and the central Chilean continental slope, both sampled at mesopelagic and mesobenthonic depths. The ridge is in the Nazca Plate, while the slope region in on the South American Plate, and is closer to the South American continent. We found six species of Chondrichthyes for the seamounts (four orders, four families). The slope sampling produced ten species of Chondrichthyes, of which Torpedo tremens De Buen 1959, was the only species in common with the Juan Fernandez area. There are clear differences between the Chondrichthyes of the two regions. These fisheries require adequate administrative modes. PMID:18624236

  11. iSIMM (Integrated Seismic Imaging and Modelling of Margins): Seismic Acquisition on the Faroes Shelf, Hatton Bank and adjacent Continental Margins

    NASA Astrophysics Data System (ADS)

    White, B.; Kusznir, N.; Christie, P.; Roberts, A. M.; Lunnon, Z.; Roberts, A. W.; Hurst, N.; Smith, L.; Parkin, C.; Surendra, A.; Davies, A.

    2002-12-01

    The iSIMM project is using state-of-the art seismic techniques with long-offset and wide-angle data, to image the crust formed on volcanic continental margins in parallel with developing and testing new quantitative models of rifted margin formation, incorporating heterogeneous stretching, the effects of melt generation and emplacement and varying thermal anomalies in the mantle. During June-July 2002, we used RRS Discovery to acquire wide angle and normal incidence seismic data on the Faroes Shelf and adjacent continental margin, Hatton-Rockall Basin, Hatton Bank and the adjacent oceanic crust using OBS and MCS. In August 2002, WesternGeco's Topaz used three single-sensor, Q-Marine streamers, 12km plus two 4km, to overshoot the wide-angle profiles on the Faroes Shelf and adjacent continental margin. In the Faroes region we deployed 85 4-component ocean bottom seismometers (OBS) and 5 vertical arrays along a 350km-long profile extending from the Faroes-Shetland Channel across the Faroes Shelf and continental margin into the oceanic crust of the Norwegian Sea. The entire profile was shot twice. First with a 6,300 cubic inch airgun array towed at 20 m depth and tuned to enhance the initial peak output pressure pulse. Second, with the airguns reconfigured to enhance the low-frequency bubble waveform, producing a source rich in low frequency energy (centred on 10-12 Hz), and with a broad bandwidth. Shots were spaced at either 75 m or 100 m, giving shot repetition rates in excess of 60 secs, thus avoiding contaminating with wrap-round energy from the previous shot. The Q-Marine acquisition used a 48-gun, 10,170 cu. in. airgun array, also tuned to enhance the low-frequency bubble signature, shooting at 50m/20s intervals and recorded on individual sensors for optimal grouping. The streamer configuration provides swath coverage at shorter offsets, while the long offsets record diving waves and wide-angle reflections. Shot-by-shot source signature recording will facilitate

  12. Geochemical characteristics of the barite deposits at cold seeps from the northern Gulf of Mexico continental slope

    NASA Astrophysics Data System (ADS)

    Feng, Dong; Roberts, Harry H.

    2011-09-01

    Although less common than the occurrence of authigenic carbonate, barite has been observed frequently at cold seeps on continental margins worldwide. It is understood that barite forms by the interaction of barium-rich and sulfate-free seeping fluids with dissolved sulfate of pore water near the seafloor, but questions remain about the geochemical processes and mode(s) of the barite formation. Here, we report geochemical characteristics of barite deposits at 11 cold seep locations from the northern Gulf of Mexico continental slope. Samples from these sites of fluid and gas expulsion provide environmental information on barite formation. Seafloor observations and samples acquired indicate that barites occur as chimneys, cones, crusts, irregular mound-like buildups up to 2-meters high, and as a material disseminated in host sediment. Most barite samples are white-to-gray and usually have a porous fabric and layered internal structure. Mineralogically, samples of barite may contain a significant amounts of carbonate minerals, such as calcite and dolomite, but aragonite is absent in all samples analyzed in this study. Negative δ 13C values (as low as - 46.4‰ V-PDB) of the associated carbonates strongly suggests that methane is the primary carbon source. The δ 34S and δ 18O values of the barites have large variations, ranging from 18‰ to 80.4‰ V-CDT, and 7.5‰ to 26.7‰ V-SMOW, respectively. On δ 34S versus δ 18O plots, many barite deposits show a linear trend that projects down toward the isotopic composition of seawater sulfate. The trend suggests that barite formed from seawater sulfate that has been isotopically modified to varying degrees by biological sulfate reduction. The δ 34S/δ 18O ratios vary between 2.4 and 4.1. The variations are interpreted to reflect local controls on the flux of barium-rich seep fluids, changes in the rate of bacterial sulfate reduction, and/or the openness of pore fluid system. The 87Sr/ 86Sr values of the barites

  13. Vertical and lateral flux on the continental slope off Pakistan: correlation of sediment core and trap results

    NASA Astrophysics Data System (ADS)

    Schulz, H.; von Rad, U.

    2014-06-01

    Due to the lack of bioturbation, the varve-laminated muds from the oxygen minimum zone (OMZ) off Pakistan provide a unique opportunity to precisely determine the vertical and lateral sediment fluxes in the nearshore part of the northeastern Arabian Sea. West of Karachi (Hab area), the results of two sediment trap stations (EPT and WPT) were correlated with 16 short sediment cores on a depth transect crossing the OMZ. The top of a distinct, either reddish- or light-gray silt layer, 210Pb-dated as AD 1905 ± 10, was used as an isochronous stratigraphic marker bed to calculate sediment accumulation rates. In one core, the red and gray layer were separated by a few (5-10) thin laminae. According to our varve model, this contributes < 10 years to the dating uncertainty, assuming that the different layers are almost synchronous. We directly compared the accumulation rates with the flux rates from the sediment traps that collected the settling material within the water column above. All traps on the steep Makran continental slope show exceptionally high, pulsed winter fluxes of up to 5000 mg m-2 d-1. Based on core results, the flux at the seafloor amounts to 4000 mg m-2 d-1 and agrees remarkably well with the bulk winter flux of material, as well as with the flux of the individual bulk components of organic carbon, calcium carbonate and opal. However, due to the extreme mass of remobilized matter, the high winter flux events exceeded the capacity of the shallow traps. Based on our comparisons, we argue that high-flux events must occur regularly during winter within the upper OMZ off Pakistan to explain the high accumulations rates. These show distribution patterns that are a negative function of water depth and distance from the shelf. Some of the sediment fractions show marked shifts in accumulation rates near the lower boundary of the OMZ. For instance, the flux of benthic foraminifera is lowered but stable below ~1200-1300 m. However, flux and sedimentation in the

  14. Flux and budget of BC in the continental shelf seas adjacent to Chinese high BC emission source regions

    NASA Astrophysics Data System (ADS)

    Fang, Yin; Chen, Yingjun; Tian, Chongguo; Lin, Tian; Hu, Limin; Huang, Guopei; Tang, Jianhui; Li, Jun; Zhang, Gan

    2015-07-01

    This study conducted the first comprehensive investigation of sedimentary black carbon (BC) concentration, flux, and budget in the continental shelves of "Bohai Sea (BS) and Yellow Sea (YS)," based on measurements of BC in 191 surface sediments, 36 riverine water, and 2 seawater samples, as well as the reported data set of the atmospheric samples from seven coastal cities in the Bohai Rim. BC concentrations in these matrices were measured using the method of thermal/optical reflectance. The spatial distribution of the BC concentration in surface sediments was largely influenced by the regional hydrodynamic conditions, with high values mainly occurring in the central mud areas where fine-grained particles (median diameters > 6 Φ (i.e., <0.0156 mm)) were deposited. The BC burial flux in the BS and YS ranged from 4 to 1100 µg/cm2 yr, and averaged 166 ± 200 µg/cm2 yr, which was within the range of burial fluxes reported in other continental shelf regimes. The area-integrated sedimentary BC sink flux in the entire BS and YS was ~325 Gg/yr, and the BS alone contributed ~50% (~157 Gg/yr). The BC budget calculated in the BS showed that atmospheric deposition, riverine discharge, and import from the Northern Yellow Sea (NYS) each contributed ~51%, ~47%, and ~2%. Therefore, atmospheric deposition and riverine discharge dominated the total BC influx (~98%). Sequestration to bottom sediments was the major BC output pattern, accounting for ~88% of the input BC. Water exchange between the BS and the NYS was also an important BC transport route, with net BC transport from the BS to the NYS.

  15. A regional assessment of potential environmental hazards to and limitations on petroleum development of the Southeastern United States Atlantic continental shelf, slope, and rise, offshore North Carolina

    USGS Publications Warehouse

    Popenoe, Peter; Coward, E.L.; Cashman, K.V.

    1982-01-01

    More than 11,000 km of high-resolution seismic-reflection data, 325 km of mid-range sidescan-sonar data, and 500 km of long-range sidescan-sonar data were examined and used to construct an environmental geology map of the Continental Shelf, Slope, and Rise for the area of the U.S. Atlantic margin between lats. 32?N. and 37?N. Hardgrounds and two faults described in previous literature also are shown on the map. On the Continental Shelf, at least two faults, the Helena Banks fault and the White Oak lineament, appear to be tectonic in origin. However, a lack of historical seismicity associated with these faults indicates that they are probably not active at the present time. Hardgrounds are widely scattered but are most abundant in Onslow Bay. Although paleostream channels are common nearshore, they do not appear to be common on the central and outer shelf except off Albemarle Sound where extensive Pleistocene, Pliocene, and late Miocene channels extend across the shelf. Mobile bottom sediments are confined mainly to the shoals off Cape Romain, Cape Fear, Cape Lookout, and Cape Hatteras. Elsewhere the sand cover is thin, and older more indurated rocks are present in subcrop. No slope-instability features were noted on the Florida-Hatteras slope off North Carolina. The lack of features indicates that this slope is relatively stable. Evidence for scour by strong currents is ubiquitous on the northern Blake Plateau although deep-water reefs are sparse. The outer edge of the plateau is dominated by a major growth fault and numerous splay and antithetic faults. These faults are the product of salt tectonism in the Carolina trough and thus are not associated with seismicity. Displacements observed near the sea floor and breached diapirs offshore indicate that the main fault is still moving. Associated with the faults are collapse features that are interpreted to be caused by karst solution and cavernous porosity in Eocene and Oligocene limestones at depth. Major slumps

  16. Chemical composition of North American microtektites and tektite fragments from Barbados and DSDP site 612 on the continental slope off New Jersey

    NASA Astrophysics Data System (ADS)

    Koeberl, C.; Glass, B. P.

    1988-02-01

    The major element and trace element content of tektite fragments and microtektites found in deep-sea sediments from Barbados and DSDP (Deep Sea Drilling Project) Site 612 on the continental slope off New Jersey have been determined. The compositions are consistent with the conclusion that the samples from both occurrences belong to the North American tektite strewn field. However, the chemistry of the samples from both occurrences is not identical with the bediasite or georgianite chemistry. These differences show that there are geographical variations in composition in the North American strewn field.

  17. Gulf of Mexico continental slope study annual report, year 2. Volume 2. Primary volume. Interim report 1985-1986. [Sampling for hydrocarbons

    SciTech Connect

    Not Available

    1986-09-01

    This report, which was prepared in three volumes (Executive Summary, Primary Volume, and Appendix), details the findings of two years of sampling on the continental slope of the northern Gulf of Mexico at depths of 300-3000 m. Preliminary results from a third year of sampling are also presented. Physical and chemical measurements included: CTD casts at 35 stations; sediment characteristics, including hydrocarbons and bulk sediment parameters from 60 stations; tissue hydrocarbon levels of representative benthic organisms; and delta carbon-13 values from sediments and organisms, including comparison of areas of natural petroleum seepage to prevailing slope conditions. The biological oceanography section provides detailed enumeration of megafaunal specimens collected by trawling and of macro- and meiofaunal specimens collected with a 600 sq cm box core. Major megafaunal groups treated are Arthropoda, Echinodermata, and demersal fishes.

  18. Seafloor morphology of the continental slope in front the Petacalco Bay and its tsunamigenic relationship at the Mexican sector of the Middle American subduction zone

    NASA Astrophysics Data System (ADS)

    Mortera-Gutierrez, C. A.; Bandy, W. L.; Millan-Motolinia, C.; Ponce-Nuñez, F.; Ortega-Ramirez, J.

    2014-12-01

    The recent occurrence of offshore, large, earthquake ruptures in the western limit of the Guerrero Seismic Gap and the scattered data of seafloor morphology of the continental slope along this sector at the Mexican Mid American subduction zone have encouraged the UNAM marine geophysical group to initiate a mapping program at the Guerrero margin, from the shelf break to the Middle American Trench. The main objective of this initiative is to have a complete cover of the seafloor morphology of the Guerrero slope as the background data for comparative studies of the seafloor deformation in case of future offshore earthquake ruptures in this region. At he first stage of this initiative, we have mapped the continental slope in front the Petacalco Bay, west of the Guerrero Seismic Gap, where three important large earthquakes occurred and caused great damages in Mexico City: Petatlán earthquake (Mw=7.6) at 1979, Michoacán earthquake (Mw=8.1) and its aftershock (Mw=7.9) at 1985. Geophysical results of two campaigns carry in 2012 (MAMRIV12) and 2013 (BABPET13) on board the BO EL PUMA are presented which include multibeam data and subbottom profiles. These data sets cover an area between 101°W and 103°W, and from the shelf-slope break to the trench. The multibeam chart shows details of the hydrological erosion induced by many submarine cannons at the upper slope, whereas the seafloor relief in the lower slope is dominated by tectonic structures. The subbottom profiles and the seafloor morphology evidence zones of big slumps and faults. For first time the Rio Balsas submarine cannon is completed chart, reaching the trench basin. The river course is deflected, possibly by shear faulting. There are slump sites near the trench that probably one is associated to the 1925 tsunami at Zihuatanejo, Guerrero. The 1985 Michoacán aftershock was accompany by a small Tsunami. At that time, the lack of morphology data in this slope inhibited further studies of seafloor-deformation and

  19. Deposition of bomb 14C in continental slope sediments of the Mid-Atlantic Bight: assessing organic matter sources and burial rates

    NASA Astrophysics Data System (ADS)

    DeMaster, D. J.; Thomas, C. J.; Blair, N. E.; Fornes, W. L.; Plaia, G.; Levin, L. A.

    As part of the Ocean Margins Program (OMP), organic carbon 14C measurements have been made on benthic fauna and kasten core sediments from the North Carolina continental slope. These analyses are used to evaluate the nature and burial flux of organic matter in the OMP study area off Cape Hatteras. Despite the fact that surface sediment 14C contents ranged from -41 to -215 per mil, the benthic fauna (primarily polychaetes) all contained significant amounts of bomb- 14C (body tissue 14C contents ranging from +20 to +82 per mil). Bomb- 14C clearly is reaching the seabed on the North Carolina slope, and the labile planktonic material carrying this signal is a primary source of nutrition to the benthic ecosystem. The enrichment of 14C in benthic faunal tissue relative to the 14C content of bulk surface-sediment organic matter (a difference of ˜150 per mil) is attributed to a combination of particle selection and selective digestive processes. Organic carbon burial rates from 12 stations on the North Carolina slope varied from 0.02 to 1.7 mol of C m -2 yr -1, with a mean value of 0.7 mol of C m -2 yr -1. The accumulation of organic matter on the upper slope accounts for <1% of the primary production in the entire continental margin system. The North Carolina margin was deliberately selected because of its potential for offshore transport and high sediment deposition rates, and even in this environment, burial of organic carbon accounts for a very small fraction of the primary production occurring in surface waters.

  20. Geologic Assessment of Undiscovered, Technically Recoverable Coalbed-Gas Resources in Cretaceous and Tertiary Rocks, North Slope and Adjacent State Waters, Alaska

    USGS Publications Warehouse

    Roberts, Stephen B., (compiler)

    2008-01-01

    The purpose of the U.S. Geological Survey's (USGS) National Oil and Gas Assessment is to develop geology-based hypotheses regarding the potential for additions to oil and gas reserves in priority areas of the United States, focusing on the distribution, quantity, and availability of oil and natural gas resources. The USGS has completed an assessment of the undiscovered, technically recoverable coalbed-gas resources in Cretaceous and Tertiary rocks underlying the North Slope and adjacent State waters of Alaska (USGS Northern Alaska Province 5001). The province is a priority Energy Policy and Conservation Act (EPCA) province for the National Assessment because of its potential for oil and gas resources. The assessment of this province is based on geologic principles and uses the total petroleum system concept. The geologic elements of a total petroleum system include hydrocarbon source rocks (source rock maturation, hydrocarbon generation and migration), reservoir rocks (stratigraphy, sedimentology, petrophysical properties), and hydrocarbon traps (trap formation and timing). In the Northern Alaska Province, the USGS used this geologic framework to define one composite coalbed gas total petroleum system and three coalbed gas assessment units within the petroleum system, and quantitatively estimated the undiscovered coalbed-gas resources within each assessment unit.

  1. Foraminiferal biodiversity associated with cold-water coral carbonate mounds and open slope of SE Rockall Bank (Irish continental margin—NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Morigi, C.; Sabbatini, A.; Vitale, G.; Pancotti, I.; Gooday, A. J.; Duineveld, G. C. A.; De Stigter, H. C.; Danovaro, R.; Negri, A.

    2012-01-01

    Cold-water coral (CWC) ecosystems are hotspots of macro- and microfaunal biodiversity and provide refuge for a wide variety of deep-sea species. We investigated how the abundance and biodiversity of 'live' (Rose Bengal stained) foraminifera varies with, and is related to, the occurrence of CWC on the Rockall Bank (NE Atlantic). Qualitative and quantitative analyses were performed on 21 replicate samples from 8 deep-sea stations, including 4 stations on CWC-covered carbonate mounds at depths of 567-657 m, and 4 stations on the adjacent slope at depths of 469-1958 m where CWC were absent. This sampling strategy enabled us to demonstrate that sediments surrounding the living CWC were characterised by higher foraminiferal abundance and biodiversity than open-slope sediments from the same area. A total of 163 foraminiferal species was identified. The dominant species in CWC sediments were: Spirillina vivipara, Allogromiid sp. 1, Globocassidulina subglobosa, Adercotryma wrighti, Eponides pusillus, Ehrenbergina carinata, Planulina ariminensis, Trochammina inflata and Paratrochammina challengeri. Foraminifera were nearly absent in adjacent open slope areas subject to strong tidal currents and characterised by coarse grained deposits. We suggest that CWC create a heterogeneous three-dimensional substrate offering microhabitats to a diverse benthic foraminiferal community.

  2. Sediment movement and dispersal patterns on the Grand Banks continental shelf and slope were tied to the dynamics of the Laurentide ice-sheet margin

    NASA Astrophysics Data System (ADS)

    Rashid, H.; MacKillop, K.; Piper, D.; Vermooten, M.; Higgins, J.; Marche, B.; Langer, K.; Brockway, B.; Spicer, H. E.; Webb, M. D.; Fournier, E.

    2015-12-01

    The expansion and contraction of the late Pleistocene Laurentide ice-sheet (LIS) was the crucial determining factor for the geomorphic features and shelf and slope sediment mobility on the eastern Canadian continental margin, with abundant mass-transport deposits (MTDs) seaward of ice margins on the upper slope. Here, we report for the first time sediment failure and mass-transport deposits from the central Grand Banks slope in the Salar and Carson petroleum basins. High-resolution seismic profiles and multibeam bathymetry show numerous sediment failure scarps in 500-1600 m water depth. There is no evidence for an ice margin on the upper slope younger than MIS 6. Centimeter-scale X-ray fluorescence analysis (XRF), grain size, and oxygen isotope data from piston cores constrain sediment processes over the past 46 ka. Geotechnical measurements including Atterberg limit tests, vane shear measurements and triaxial and multi-stage isotropic consolidation tests allowed us to assess the instability on the continental margin. Cores with continuous undisturbed stratigraphy in contourite silty muds show normal downcore increase in bulk density and undrained peak shear strength. Heinrich (H) layers are identifiable by a marked increase in the bulk density, high Ca (ppm), increase in iceberg-rafted debris and lighter δ18O in the polar planktonic foram Neogloboquadrina pachyderma (sinistral): with a few C-14 dates they provide a robust chronology. There is no evidence for significant supply of sediment from the Grand Banks at the last-glacial maximum. Mass-transport deposits (MTD) are marked by variability in the bulk density, undrained shear strength and little variation in bulk density or Ca (ppm) values. The MTD are older than 46 ka on the central Grand Banks slope, whereas younger MTDs are present in southern Flemish Pass. Factor of safety calculations suggest the slope is statically stable up to gradients of 10°, but more intervals of silty mud may fail during earthquake

  3. Morphology and shallow geological structure of the continental slope located between Manzanillo, Colima and Chamela, Jalisco, Mexico, using multibeam bathymetry and high resolution seismic reflection data

    NASA Astrophysics Data System (ADS)

    Castillo, M.; Bandy, W. L.; Mortera-Gutierrez, C. A.

    2013-05-01

    The west coast of Mexico presents a complex array of tectonic processes related with the subduction of the Rivera plate beneath the Jalisco Block/North American plate including seamount subduction and forearc slivering. To better understand these processes and related deformation, an analysis and integration of marine geophysical data was undertaken to map the morphology and shallow geologic structure of the continental slope located between Manzanillo, Colima and Chamela, Jalisco, Mexico (Longitude: 104 ° 20 'to 106 ° 0 Latitude: 18 ° 24 'to 19 ° 48'). These data include multibeam bathymetry and seafloor backscatter data (Kongsberg EM300 system) and high-resolution seismic reflection data (Kongsberg TOPAS system) collected during the MORTIC07 campaign aboard the oceanographic vessel "El Puma". 3D models of the bathymetry and acoustic backscatter strength were constructed along with maps of the major geological and structural features, such as landslides and active faults and folds. The analysis indicates that the continental slope in this area has undergone significant vertical and horizontal movements producing several large slump blocks, a prominent sedimentary filled basin, and a series of transpressional ridges suggestive of a recent collision and subduction of a seamount, or similar bathymetric features.

  4. Following the Cantabrian (Ventaniella) fault into the Bay of Biscay: a deeply incised canyon, a change of trend, and 20002 km of unstable continental slope

    NASA Astrophysics Data System (ADS)

    Fernandez Viejo, G.; Lopez-Fernandez, C.; Dominguez-Cuesta, M.

    2012-12-01

    The Cantabrian fault, known traditionally with the local name of Ventaniella fault is a long-lived rectilinear feature that runs in a NW-SE direction for more than 200 km across northwest Spain. Its origins are linked to the end of the Variscan orogeny, but its important role took place during the extensional processes of the Mesozoic that led Iberia to become a microplate separated from Europe and Africa. With the initiation of the alpine orogeny Iberia converges with Europe pushed from the south by Africa, and the Ventaniella fault acted as a dextral strike slip fault with an important reverse component. It has a relatively low topographic expression, although its NE block is slightly uplifted with respect to the SW one. Traditionally it has been mapped offshore following the trace of the Aviles canyon, a deeply incised canyon 7 miles from the coast, oblique to the E-W coast trend and which descents from 160 m in the continental shelf , down to 4750 m in the abyssal plain of the Bay of Biscay . All this incision occurs along just 50 km length of the narrow continental shelf in this area, making the Aviles canyon one of the steepest in the Atlantic. Through seismic reflection lines across the continental shelf and slope, a bathymetric model up to date and a 3D geological model the fault has been mapped into the sea integrating the seismicity associated to its SW block and the newest geological mapping on land. At the same time, what is observed in the northwest prolongation and termination of the fault against the oceanic crust of the abyssal plain is a continental slope that is full of mass-wasting processes along more than 80 km length, showing gravitational and submarine slide processes in an area that roughly occupies 2000 km 2 and involves a volume of unstable mass estimated in more than 1000 km3 . One of the biggest displaced masses made the Aviles canyon change its trend to N-S in an almost 90° bend close to the middle slope. Although the displaced masses

  5. Physico-chemical parameters of the SW and post NE monsoon (2009) seawater along the continental slope, Tamil Nadu, east coast of India, Bay of Bengal

    NASA Astrophysics Data System (ADS)

    Nisha, V.; Achyuthan, H.

    2014-01-01

    Variations in sea water temperature, salinity, light intensity and availability of nutrients strongly influence the phytoplankton distribution that forms an important part of the coastal food chain. In this paper, we present the results of the physico-chemical parameters and nutrient concentrations in seawaters sampled during the 2009 South West (SW) and post North East (NE) monsoon periods along the continental shelf from Chennai to Nagapattinam, east coast, Tamil Nadu. This study was conducted to assess the status of the coastal biogeochemical environment and for this purpose, seawater samples were collected from the sea surface and also at varying depths (surface to 150 m depth) at six different locations. The nutrient analyses and the CTD data reveal a distinct variation with water depth along the continental slope and also the physico-chemical properties of seawater are not homogenous. The observed values of nutrients for the post NE monsoon period are low compared to the SW monsoon period. Contour plots indicate seasonal and spatial variations in physico-chemical parameters along the continental shelf of the east coast of India. The data suggests that during the 2009 SW monsoon period, a significant increase of freshwater input into the Bay of Bengal could have elevated nutrient concentration compared to that observed during the post 2009 NE monsoon.

  6. Geotechnical properties and preliminary assessment of sediment stability on the continental slope of the northwestern Alboran Sea

    USGS Publications Warehouse

    Baraza, J.; Ercilla, G.; Lee, H.J.

    1992-01-01

    Laboratory analysis of core samples from the western Alboran Sea slope reveal a large variability in texture and geotechnical properties. Stability analysis suggests that the sediment is stable under static gravitational loading but potentially unstable under seismic loading. Slope failures may occur if horizontal ground accelerations greater than 0.16 g are seismically induced. The, Alboran Sea is an active region, on which earthquakes inducing accelerations big enough to exceed the shear strength of the soft soil may occur. Test results contrast with the apparent stability deduced from seismic profiles. ?? 1992 Springer-Verlag New York Inc.

  7. Sedimentary features of the south Texas continental slope as revealed by side-scan sonar and high-resolution seismic data

    SciTech Connect

    Rothwell, R.G.; Kenyon, N.H. ); McGregor, B.A. )

    1991-02-01

    Sedimentary provinces on the south Texas slope have been identified by their acoustic character on long-range side-scan sonar records and high-resolution seismic profiles. Probable lithofacies within these provinces have been identified by core data and by analogy with previously cored acoustic facies. In the northern part of the study area, the East Breaks Slide is a prominent mass-transport feature. Revised bathymetry shows that the slide originated on the upper slope (200-1,000 m), in front of a sandy late Wisconsinan shelf-margin delta, where the gradient is up to 3{degree}. Side-scan sonar data indicates that the slide is a strongly backscattering feature extending more than 110 km downslope from the shelf edge. it consists of two lobes that are separated by a diapiric high. Diapiric highs on the middle slope have blocked most of the flow. borehole data shows that the slide deposit contains intercalated sands and contorted bedding. The slide is therefore attributed to failure of sandy deltaic material deposited close to the shelf edge during the last period of low sea level (late Wisconsinan, circa 11-29 Ka). Core data suggests that the weakly backscattering acoustic facies adjacent to the slide are fine-grained sediments (mudturbidites and hemipelagites) of a slope mud drape. The middle slope in front of the sandy late Wisconsinan shelf-margin delta of the Rio Grande has an intermediate level of backscattering with numerous channels leading to the Sigsbee Deep. Acoustic facies mapping using long-range side-scan sonar matches well with acoustic facies mapping using 3.5-kHz high-resolution seismic profiles.

  8. Association of Syscenus infelix (Crustacea: Isopoda: Aegidae) with benthopelagic rattail fishes, Nezumia spp. (Macrouridae), along the western North Atlantic continental slope

    USGS Publications Warehouse

    Ross, S.W.; Sulak, K.J.; Munroe, T.A.

    2001-01-01

    During submersible surveys along the continental slope (summers of 1991 and 1992, 184-847 m) between False Cape, Virginia, and Cape Hatteras, North Carolina, USA, we observed the aegid isopod, Syscenus infelix Harger, attached to the macrourid Nezumia bairdii (Goode and Bean). This is the first report of S. infelix attached to fishes in the western North Atlantic. The association of this blind isopod with its host appears species specific. The large, conspicuous isopod always attached to a fish in the same location, the dorsal midline, immediately behind the first dorsal fin. Attachment appears to be long term, with the isopod forming a characteristic scar consisting of a distinct discolored oval depression with seven small, dark impressions that coalesce as the fish grows. Only one S. infelix was found on each host fish. The isopod occurred on 23.7% of N. bairdii observed from submersible on the middle continental slope off Virginia and North Carolina, compared with 16.6% of 1236 museum specimens of the same species (based on inspection for scars) collected at latitudes 26??-64??N. Prevalence of the fish-isopod association was not correlated with depth or latitude. We also found identical scars on preserved specimens of N. aequalis (2.6% of 660 specimens), N. sclerorhynchus (1.2% of 86 specimens), and N. suilla (14.3% of 7 specimens), mostly from areas outside the range of N. bairdii. No scars were found on museum specimens of N. atlantica (n = 27), N. cyrano (n = 57), or N. longebarbata (n = 7). The low incidence of isopod attachment on these species suggests that N. bairdii is the preferred host. Infestation by the isopod appears to result in erosion of host fish scales and tissue. We propose that S. infelix is an obligate associate of its host fish and should be considered parasitic.

  9. Structural framework, stratigraphy, and petroleum geology of the area of oil and gas lease Sale No. 49 on the U.S. Atlantic continental shelf and slope

    USGS Publications Warehouse

    Mattick, Robert E.; Hennessy, Jacqueline L.

    1980-01-01

    On September 23, 1977, the U.S. Department of the Interior announced the tentative selection of 136 tracts for Sale No. 49 of oil and gas leases in the Baltimore Canyon Trough on the U.S. Atlantic Continental Shelf and Slope. This report summarizes the geology and petroleum potential of the area. The Baltimore Canyon Trough is an elongate, seaward-opening sedimentary basin filled by as much as 14 km of Mesozoic and Cenozoic sedimentary rocks. The basin first formed under the New Jersey shelf and gradually spread west and south as the area subsided after the rifting that formed the Atlantic basin. Rocks of the Triassic and Jurassic Systems together are more than 8 km thick in a depocenter areally restricted to the northern part of the trough. Basal Jurassic rocks are apparently nonmarine sedimentary rocks bedded with evaporite deposits. Direct evidence that some salt is in the basal Jurassic section comes from the Houston Oil and Minerals 676-1 well, which penetrated salt at a depth of about 3.8 km. During the Middle and Late Jurassic, more open marine conditions prevailed than in the Early Jurassic, and carbonate banks and reefs formed discontinuously along the seaward side of the shelf. Sand flats likely occupied the central part of the shelf, and these probably graded shoreward into nonmarine red beds that accumulated in a bordering coastal plain. Thick nonmarine sands and silty shales of Late Jurassic age were deposited in what is now the nearshore and midshelf area. These sedimentary rocks probably grade into thick marine carbonate rocks near the present shelf edge. During the Cretaceous, less sediment accumulated (about 4 km) than during the Jurassic, and most was deposited during Early Cretaceous time. The Cretaceous units show two main trends through time-a diminishing rate of sediment accumulation and an increase in marine character of sediments. During the Middle and Late Cretaceous, calcareous sand and mud filled the basin, buried the shelf-edge reefs and

  10. Distribution of otoliths in surficial sediments of the U.S. Atlantic Continental Shelf and slope and potential for reconstructing Holocene fish stocks

    NASA Astrophysics Data System (ADS)

    Elder, Kathryn L.; Jones, Glenn A.; Bolz, George

    1996-06-01

    We examined more than 1100 surface sediment samples from the Atlantic continental margin of the United States to determine the feasibility of using fossil fish otoliths as diagnostic tools in reconstructing paleoenvironments and latitudinal distribution of fish stocks during the Holocene. Although 63% of the 1107 samples collected were from shelf areas (<140 m), the total number of shelf-derived otoliths represents only 0.3% of the entire sampled assemblage. The majority of otoliths occurred on the continental slope (400-2000 m), with a maximum concentration in sediments at 500 to 600-m water depth. Otoliths of the most commonly occurring species, Ceratoscopelus maderensis, exhibit a marked distributional boundary just south of Cape Hatteras, North Carolina (33°N), which mimics the distribution of their living counterparts. North of this boundary, C. maderensis constitutes greater than 70% of the preserved otolith assemblage, whereas more southerly regions contain no otoliths of this species. Although C. maderensis typically migrates diurnally over a depth of 300-600 m, otoliths taken from live-captured C. maderensis exhibit Δ14C values comparable to that of the dissolved inorganic carbon (DIC) of surface seawater in the study area. Accelerator mass spectrometry radiocarbon analyses of cooccurring otoliths and planktonic foraminifera from a sediment core collected south of Martha's Vineyard (40°15'N 70°51'W, 265 m) demonstrate temporal concordance throughout the Holocene. Otoliths appear to be viable, underutilized paleoceanographic tools. Specimens are found in sufficient abundance to permit temporal reconstructions of the distribution of C. maderensis and potentially several other icthyospecies along the U.S. Atlantic continental margin.

  11. Ecohydrological interactions in the evolution of constructed slopes in a Mediterranean-Continental environment: the role of runoff

    NASA Astrophysics Data System (ADS)

    Nicolau, José Manuel; Merino-Martín, Luis; Moreno de las Heras, Mariano; Espigares, Tíscar

    2013-04-01

    It is well known that overland flow plays a major role in the functioning of natural ecosystems in drylands, where water is the main limiting factor. However, in reclaimed ecosystems its role is not so well understood. This study shows a synthesis of the research conducted in constructed slopes from coal mining reclamation at El Moral field site (Teruel coalfield, Spain). Three trajectories have been identified and modeled, associated to runoff volume, particularly to external run-on coming from the upper part of slopes. When rill networks are formed, arrested succession occurs. Rills efficiently drain runoff away from slopes, reducing rainfall infiltration and increasing water deficit. Vegetation dynamics becomes severely affected: seedling emergence, plant establishment and seed production are limited along a gradient of rill erosion. Soil moisture content is spatially redistributed, being higher near rills and lower on inter-rills. This determines the spatial pattern of the dominant species (Medicago sativa). At intermediate levels of runoff amount, micro-landforms as rill fans and splays are generated. Vegetation is adapted to the micro-geomorphology developing a patchy mosaic structure. Seven types of ecohydrological units (classified as runoff sources or sinks) have been identified. A functional interaction between sources and sinks following the Trigger Transfer Reserve Pulse approach (Ludwig et al. 2005)* has been demonstrated. When runoff does not develop micro-landforms, natural plant colonization leads to another patchy mosaic structure based on individuals of the shrub Genista scorpius, which can be considered as natural islands of hydrological enhanced biotic productivity. This species develops a biotic control of the main hydrological processes, playing a key role in the succession of the ecosystem. These findings allow us to conclude that runoff can be considered as a driving force in the ecological succession of reclaimed ecosystems; therefore, an

  12. Origin of shallow submarine mass movements and their glide planes—Sedimentological and geotechnical analyses from the continental slope off northern Norway

    NASA Astrophysics Data System (ADS)

    Baeten, Nicole J.; Laberg, Jan Sverre; Vanneste, Maarten; Forsberg, Carl Fredrik; Kvalstad, Tore J.; Forwick, Matthias; Vorren, Tore O.; Haflidason, Haflidi

    2014-11-01

    Submarine landslides are often characterized by a basal surface of rupture parallel to the stratigraphy, in which downslope movement is initiated. However, little is known about the sedimentology and physical properties of the sediments within these surfaces. In this study, we present a multiproxy analysis of the sediments collected from a giant piston core penetrating a shallow submarine mass transport deposit, in combination with high-resolution seismoacoustic data to identify and characterize the basal glide plane and the weaker sediments in which movement was initiated. The initial phase of instability consists of a single fracture that formed due to the downslope movement of a mostly intact slab of sediments. The 16 m long core, comprising mostly undisturbed massive and laminated ice-rafted debris-rich clay penetrated this slab. The base of the slab is characterized by a high-amplitude semicontinuous reflection visible on the subbottom profiler data at about 12.5 m depth, interpreted to originate from the glide plane on top of a plumite deposit. This plumite has dilative behavior with pore pressure decrease with increasing shear strain and high undrained shear strength. Movement probably started within contouritic sediments immediately above the glide plane, characterized by higher sensitivities and higher water contents. The occurrence of the mass movements documented in this study are likely affected by the presence of a submarine landslide complex directly downslope. The slide scar of this landslide complex promoted retrogressive movement farther upslope and progressive spreading of strain softening along the slide base and in the slide mass. Numerical models (infinite slope, BING, and retrogressive slope models) illustrate that the present-day continental slope is essentially stable and allow reconstruction of the failure processes when initiated by an external trigger.

  13. Seasonal reproduction and feeding ecology of giant isopods Bathynomus giganteus from the continental slope of the Yucatán peninsula

    NASA Astrophysics Data System (ADS)

    Barradas-Ortiz, Cecilia; Briones-Fourzán, Patricia; Lozano-Álvarez, Enrique

    2003-04-01

    The reproduction and feeding habits of giant isopods Bathynomus giganteus [range in body length (BL): 43-363 mm] from the continental slope of the Yucatán Peninsula, México, were studied from samples collected at depths of 359-1050 m during three research cruises conducted in winter, spring, and summer of different years. Samples taken in winter and spring yielded a large proportion of mancas and juveniles, as well as high percentages of adult females with functional oostegites and males with appendices masculinae, suggesting a peak in reproductive activity during these seasons. In contrast, the virtual absence in the summer samples of (a) mancas and small juveniles, (b) females with functional oostegites, and (c) small adult males (210-290 mm BL) with appendices masculinae, suggests a low reproductive activity of B. giganteus during summer. Stomach contents analyses were conducted on five life phases (mancas, small juveniles, large juveniles, adult females and adult males) in winter and summer. Mancas and juveniles had fuller stomachs than adults during winter, and all isopods had emptier stomachs during summer than during winter. The diet of B. giganteus was broad, but the most important food categories in all life phases were fish and squid remains, underlining the main scavenging habits of B. giganteus. However, the remaining food categories show that this species is a facultative rather than a strict scavenger and suggest some ontogenetic dietary shifts. These results were further supported by diet (Horn's) overlap indices. In the winter, high diet overlap occurred between all life phases. In the summer, adult males had a low diet overlap with adult females and large juveniles. Adult males also had a low diet overlap between summer and winter. Results from this and other studies suggest that the main reproductive activity of B. giganteus in the Yucatán slope occurs during winter and spring, when the food supply on the upper-slope is highest, particularly

  14. Quaternary sea-level lowstand features on the southern Florida Keys upper continental slope: Seismic, submersible, and outcrop data

    SciTech Connect

    Toscano, M.A.; Hine, A.C. . Dept. of Marine Science)

    1992-01-01

    The low-gradient slope, seaward of the Holocene reef tract and latest Pleistocene outlier reefs, is superimposed by mounds or bumps. These range in depth from 60 to 100 m MSL, and resemble reefal or dune deposits, or shoreline nickpoints. Seismic data were recently augmented by a series of 2-man submersible dives (DELTA) in and around these features, providing invaluable first-hand dimensional perspective on the undersea outcrops, as well as providing invaluable first-hand dimensional perspective on the undersea outcrops, as well as extensive video, still photography, and in situ outcrop samples. The outcropping grainstones contain abundant subtropical and tropical skeletal components useful for paleoclimatic and age analyses, paleoenvironmental and diagenetic studies, and interpretation of these deposits in terms of sea level position and relationship to climate. Quaternary sea-level lowstand deposits have not previously been sampled from the south Florida Platform, a current-dominated windward carbonate margin. Because this platform is neither subject to isostatic adjustments associated with glacial boundaries and clastic (deltaic) loading, nor with any dynamic tectonic regime, it should preserve a relatively pure signal of the amplitudes of sea level-fluctuations. High-frequency sea-level changes recorded by slope features provide data on modes for long-term platform development. Florida lowstand amplitudes in combination with available highstand data can be used to establish a maximum range for Quaternary sea level fluctuations. When considered in the context of paleoclimatic and paleoenvironmental data from outcrop samples, the magnitude, timing, and duration of Quaternary sea levels in south Florida may be viewed as critical to a general understanding of processes associated with rapid climate change.

  15. Benthic foraminifers from the continental shelf and slope of the Gulf of Mexico: An indicator of shelf hypoxia

    USGS Publications Warehouse

    Osterman, L.E.

    2003-01-01

    Benthic foraminifers from 74 core-top sediment samples collected primarily from the continental shelf of the Gulf of Mexico were analyzed to determine a microfaunal indicator for shelf hypoxia to be used in future paleoenvironmental studies. Principal component analysis (PCA) and cluster analysis (CA) of 93 species recognized factors/clusters that were similar to previous investigations of the benthic foraminifers, except that both analyses also identified PCA6/CA6 in the area where hypoxic conditions have been observed. Three low-oxygen-tolerant species, Pseudononion atlanticum, Epistominella vitrea, and Buliminella morgani have high factor loadings in PCA6. The cumulative percentage of three species is defined as the PEB (PEB, Pseudononion, Epistominella, Buliminella) index. The highest PEB values observed in the 74 surface sediment samples occur in the zone of recognized hypoxia on the Louisiana shelf. Values of the PEB index are also elevated along the southern Texas coastline, suggesting that this area may experience periodic hypoxia as well. ?? 2003 Elsevier Ltd. All rights reserved.

  16. Dynamic processes observed at a gas hydrate outcropping on the continental slope of the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Vardaro, Michael F.; MacDonald, Ian R.; Bender, Leslie C.; Guinasso, Norman L.

    2006-03-01

    A deep-sea time-lapse camera and several temperature probes were deployed on the Gulf of Mexico continental shelf at a biological community associated with a gas hydrate outcropping to study topographic and hydrologic changes over time. The deployment site, Bush Hill (GC-185), is located at 27°47.5' N and 91°15.0' W at depths of ˜540 m. The digital camera recorded one still image every 6 h for July-October in 2001, every 2 h for the month of June 2002, and every 6 h for the month of July 2002. Temperature probes were in place at the site for the entire experimental period. The data recovered provide a record of processes that occur at gas hydrate mounds. Sediment resuspension over the mound causes significant variation in luminosity of the time-lapse photographs. A marked diurnal pattern can be seen in the temperature and luminosity records. No major change in shape or size of the gas hydrate outcrop at this site was observed during this study. Stable topography of the gas hydrate mound, combined with high bacterial activity and sediment turnover, appears to focus biological activity in the mound area. Frequency and recurrence of sediment resuspension indicate that short-term change in the depth and distribution of surface sediments is a feature of the benthos at the site. Because the sediment interface is a critical environment for hydrocarbon oxidation and chemosynthesis, short-term variability and heterogeneity may be important characteristics of these settings.

  17. Demersal fishes associated with Lophelia pertusa coral and hard-substrate biotopes on the continental slope, northern Gulf of Mexico

    USGS Publications Warehouse

    Sulak, Kenneth J.; Allen, Brooks R.; Luke, Kirsten E.; Norem, April D.; Randall, Michael; Quaid, Andrew J.; Yeargin, George E.; Miller, Jana M.; Harden, William M.; Caruso, John H.; Ross, Steve W.

    2007-01-01

    The demersal fish fauna of Lophelia pertusa (Linnaeus, 1758) coral reefs and associated hard-bottom biotopes was investigated at two depth horizons in the northern Gulf of Mexico using a manned submersible and remote sampling. The Viosca Knoll fauna consisted of at least 53 demersal fish species, 37 of which were documented by submersible video. On the 325 m horizon, dominant taxa determined from frame-by-frame video analysis included Stromateidae, Serranidae, Trachichthyidae, Congridae, Scorpaenidae, and Gadiformes. On the 500 m horizon, large mobile visual macrocarnivores of families Stromateidae and Serranidae dropped out, while a zeiform microcarnivore assumed importance on reef "Thicket" biotope, and the open-slope taxa Macrouridae and Squalidae gained in importance. The most consistent faunal groups at both depths included sit-and-wait and hover-and-wait strategists (Scorpaenidae, Congridae, Trachichthyidae), along with generalized mesocarnivores (Gadiformes). The specialized microcarnivore, Grammicolepis brachiusculus Poey, 1873, appears to be highly associated with Lophelia reefs. The coral "Thicket" biotope was extensively developed on the 500 m site, but fish abundance was low with only 95 fish per hectare. In contrast to Lophelia reefs from the eastern the North Atlantic, the coral "Rubble" biotope was essentially absent. This study represents the first quantitative analysis of fishes associated with Lophelia reefs in the Gulf of Mexico, and generally in the western North Atlantic.

  18. Illustrations of the importance of mass wasting in the evolution of continental margins

    SciTech Connect

    Pratson, L.; Ryan, W. ); Twichell, D. )

    1990-05-01

    Side-looking sonar imagery and swath bathymetry from a variety of contemporary continental slopes all display erosional scars and debris aprons, illustrating the importance of mass wasting in the evolution of continental margins. The continental slopes examined include slopes fed directly from the fronts of ice sheets, slopes adjacent to continental shelves that were the sites of glacial outwash, slopes supplied exclusively by fluvial drainage, slopes at carbonate platforms, and slopes on accretionary prisms. Examples are drawn from the Atlantic Ocean, the Gulf of Mexico, and the Mediterranean Sea in both passive and active continental margin settings. The sonar imagery and bathymetry used in this study indicate that continental slopes in different tectonic and climatic environments show similar forms of mass wasting. However, in some cases the dominant mode of erosion and/or the overall degree of mass wasting appears to be distinct to particular sedimentary environments. Timing of both recent and older exhumed erosional surfaces identified in the imagery and in seismic reflection profiles is obtained by ground truth observations using submersibles, towed camera sleds, drilling, and coring. These observations suggest that eustatic fluctuations common to all the margins examined do not explain the range in magnitude and areal density of the observed mass wasting. More localized factors such as lithology, diagenesis, pore fluid conditions, sediment supply rates, and seismic ground motion appear to have a major influence in the evolution of erosional scars and their corresponding unconformities.

  19. Comparison of baited longlines and baited underwater cameras for assessing the composition of continental slope deepwater fish assemblages off southeast Australia

    NASA Astrophysics Data System (ADS)

    McLean, D. L.; Green, M.; Harvey, E. S.; Williams, A.; Daley, R.; Graham, K. J.

    2015-04-01

    Expansion of demersal fisheries into the deep sea has driven a need for methods to provide information on the status of deepwater fish assemblages, especially for vulnerable species. For this purpose, we compared co-located sampling by baited longlines and baited remote underwater video systems (BRUVs) off southeastern Australia and found these techniques observed different elements of the continental slope fish assemblage, but were complementary for monitoring needs. Of the 94 species surveyed in total, only 32% were common to both survey techniques, with BRUVs sampling fewer species, with 51 species detected compared with 73 species captured by longlines. Species detected exclusively by BRUVs (21 spp) included those not vulnerable to longline hooks, and those with large-body size-including several chondrichthyans. One group of chondrichthyans, gulper sharks (Centrophorus) were the focus of this study because they are listed as conservation dependent under Australia's Environmental Protection and Biodiversity Conservation Act, and are subject to a management plan that requires their recovery to be monitored. Very few gulper sharks were observed by BRUVs (n=10). Longlines captured 773 gulper sharks suggesting this technique provides a more effective means of sampling. However, most longline caught sharks were either dead or in poor condition on capture, further depleting this vulnerable species. BRUVs are non-lethal, but a high sampling intensity is likely to be needed to detect changes in gulper shark abundance within typical management timeframes (years).

  20. Short-term hydrophysical and biological variability over the northeastern Black Sea continental slope as inferred from multiparametric tethered profiler surveys

    NASA Astrophysics Data System (ADS)

    Ostrovskii, Alexander; Zatsepin, Andrey

    2011-06-01

    This presentation introduces a new ocean autonomous profiler for multiparametric surveys at fixed geographical locations. The profiler moves down and up along a mooring line, which is taut vertically between a subsurface flotation and an anchor. This observational platform carries such modern oceanographic equipment as the Nortek Aquadopp-3D current meter and the Teledyne RDI Citadel CTD-ES probe. The profiler was successfully tested in the northeastern Black Sea during 2007-2009. By using the profiler, new data on the layered organization of the marine environment in the waters over the upper part of the continental slope were obtained. The temporal variability of the fine-scale structure of the acoustic backscatter at 2 MHz was interpreted along with biooptical and chemical data. The patchy patterns of the acoustic backscatter were associated with physical and biological processes such as the advection, propagation of submesoscale eddy, thermocline displacement, and diel migration of zooplankton. Further applications of the multidisciplinary moored profiler technology are discussed.

  1. Occurrence, distribution and expression of gas seeps and gas hydrates on the northeastern continental slope of Sakhalin Island, Sea of Okhotsk

    NASA Astrophysics Data System (ADS)

    Jin, Y.; Hong, J.; Baranov, B.; Shoji, H.; Obzhirov, A.

    2012-12-01

    The northeastern Sakhalin continental slope (NESS), Okhotsk Sea is characterized by an abundant occurrence of gas hydrate and gas seeps. Under the frameworks of Korea-Russia-Japan international projects (CHAOS and SSGH), we have carried out multidisciplinary surveys to investigate gas hydrate accumulation and active gas seepage phenomena on the NESS since 2003. During the surveys, about moe than nine hundred gas seeps were detected in a 2,650 km2 area of the NESS. Active gas seeps on the NESS were evident from features in the water column, on the seafloor, and in the subsurface by geophysical methods: well-defined hydroacoustic anomalies (gas flares), side-scan sonar seafloor structures with high backscatter intensity (seepage structures), bathymetric structures (pockmarks and mounds), and gas- and gas-hydrate-related seismic features (bottom-simulating reflectors, gas chimneys, high-amplitude reflectors, and acoustic blanking). They are also evident from ground-truths; high methane concentrations in seawater, near-bottom gas hydrates and antigenic carbonates. These features are generally related; a gas flare emits at a topographic mound with high backscatter intensity, below which a gas chimney is present. We interpret that gas chimneys producing enhanced reflection on high-resolution seismic profiles are active pathways for upward gas migration to the seafloor.

  2. Fatty acid profiles of marine benthic microorganisms isolated from the continental slope of bay of bengal: a possible implications in the benthic Food web

    NASA Astrophysics Data System (ADS)

    Das, Surajit; Lyla, P. S.; Khan, S. Ajmal

    2007-12-01

    Marine bacteria, actinomycetes and fungal strains were isolated from continental slope sediment of the Bay of Bengal and studied for fatty acid profile to investigate their involvement in the benthic food-web. Fifteen different saturated and unsaturated fatty acids from bacterial isolates, 14 from actinomycetes and fungal isolates were detected. The total unsaturated fatty acids in bacterial isolates ranged from 11.85 to 37.26%, while the saturated fatty acid ranged between 42.34 and 80.74%. In actinomycetes isolates, total unsaturated fatty acids varied from 27.86 to 38.85% and saturated fatty acids ranged from 35.29 to 51.25%. In fungal isolates unsaturated fatty acids ranged between 44.62 and 65.52% while saturated FA ranged from 20.80 to 46.30%. The higher percentages of unsaturated fatty acids from the microbial isolates are helpful in anticipating the active participation in the benthic food-web of Bay of Bengal.

  3. Stable C and N isotopic composition of cold-water corals from the Newfoundland and Labrador continental slope: Examination of trophic, depth and spatial effects

    NASA Astrophysics Data System (ADS)

    Sherwood, Owen A.; Jamieson, Robyn E.; Edinger, Evan N.; Wareham, Vonda E.

    2008-10-01

    With the aim of understanding of the trophic ecology of cold-water corals, this paper explores the tissue δ13C and δ15N values of 11 'coral' species (8 alcyonacean, 1 antipatharian, 1 pennatulacean, 1 scleractinian) collected along the Newfoundland and Labrador continental slope. Isotopic results delimit species along continua of trophic level and food lability. With an isotopic signature similar to macrozooplankton, Paragorgia arborea occupies the lowest trophic level and most likely feeds on fresh phytodetritus. Primnoa resedaeformis occupies a slightly higher trophic level, likely supplementing its diet with microzooplankton. Bathypathes arctica, Pennatulacea and other alcyonaceans ( Acanella arbuscula, Acanthogorgia armata, Anthomastus grandiflorus, Duva florida, Keratoisis ornata, Paramuricea sp.) had higher δ13C and δ15N values, suggesting these species feed at higher trophic levels and on a greater proportion of more degraded POM. Flabellum alabastrum had an isotopic signature similar to that of snow crab, indicating a primarily carnivorous diet. Isotopic composition did not vary significantly over a depth gradient of 50-1400 m. Coral δ13C increased slightly (<1‰) from the Hudson Strait to the southern Grand Banks, but δ15N did not. By modulating the availability and quality of suspended foods, substrate likely exerts a primary influence on the feeding habits of cold-water corals.

  4. Seasonal Control of Surface-Water Dissolved Iron Concentrations by Suspended Particle Concentrations on the Northern Gulf of Alaska Continental Shelf and Slope

    NASA Astrophysics Data System (ADS)

    Crusius, J.; Schroth, A. W.; Campbell, R.; Cullen, J. T.; Dillman, D.; Resing, J.

    2012-12-01

    shelf break suggest offshore transport of Fe in this location. These outer shelf and slope Fe concentrations are substantially higher than observed on the outer shelf and slope along the GAK line (offshore of Seward, AK) by Wu et al 2009 and Lippiatt et al, 2010. We suggest that the higher concentrations over the outer shelf and slope region in our work are due to offshore transport, whereas the GAK line experienced Ekman-induced onshore transport. We will explore possible mechanisms for offshore transport of Fe in surface waters in in our work. All of these studies have in common the suggestion that particles from the continental shelf exert an important control on dFe concentrations both over and beyond the shelf. Understanding the processes of cross-shelf transport will be important for understanding the high productivity in the region.

  5. Arctic Submarine Slope Stability

    NASA Astrophysics Data System (ADS)

    Winkelmann, D.; Geissler, W.

    2010-12-01

    the consequence. Its geometrical configuration and timing is different from submarine slides on other glaciated continental margins. Thus, it raises the question whether slope stability within the Arctic Ocean is governed by processes specific to this environment. The extraordinary thick slabs (up to 1600 m) that were moved translationally during sliding rise the question on the nature of the weak layers associated with this process. Especially theories involving higher pore pressure are being challenged by this observation, because either extreme pore pressures or alternative explanations (e.g. mineralogical and/or textural) can be considered. To assess the actual submarine slope stability and failure potential in the Arctic Ocean, we propose to drill and recover weak layer material of the HYM from the adjacent intact strata by deep drilling under the framework of Integrated Ocean Drilling Program. This is the only method to recover weak layer material from the HYM, because the strata are too thick. We further propose to drill into the adjacent deforming slope to identify material properties of the layers acting as detachment and monitor the deformation.

  6. Massive Rock Detachments from the Continental slope of the Balsas River Submarine Delta that occur due to Instability of Sediments which Produce Turbidity Currents and Tsunamis

    NASA Astrophysics Data System (ADS)

    Sandoval-Ochoa, J.; Aguayo-Camargo, J.

    2007-05-01

    During the NOAA oceanographic delivery cruise of the US R/V "Roger Revelle" to the Scripps Institution of Oceanography at the University of California in San Diego, California USA, in July 1996; a well calibrated bathymetric equipment, the SeaBeam* 2012, was tested. Good resolutions in data allowed bathymetric mapping to visualize the sea floor relief. Detailed colorful chartographic images showed a portion of the continental slope between the Balsas River Delta and the Middle America Trench and between the Balsas Canyon and La Necesidad Canyon. The surveyed area covered more than 3 000 square kilometers. After the delivery cruise, one of the goals was to measure and analyze the Morphobathymetry of the uneven lower portion of the Balsas River Submarine Delta. So far some of the findings with the morphometric analyses consist of several isolated slump scars that each comprise more than 12 cubic kilometers in volume and a multiple slump scar with an evident steep hollow about 200 cubic kilometers absent of rock. These volumes of rock apparently underwent a remobilization from the slope during the Late Quaternary. The rock detachments occured in relatively small portions but in instantaneous massive displacements because of their instability as well as other identified factors in the region. Over time more and more authors have accepted that coastal cuts or submarine slump scars have been left by sudden movements of rock and fluids. The phenomena that occur in the region in general, are accompanied on one side by potential and kinetic energies like falling bodies, flows and gravity waves, and on the other side, by mass transfer of rock and fluid mobilization like turbidity currents, accumulations, sea wave surges or tsunamis. In some cases the phenomena is produced by another natural triggering forces or by an earthquake. We propose that events like these, i.e. massive detachments and their products such as accumulations, turbidity currents and depositional debrites

  7. Seismic velocity increase and deep-sea gas hydrate concentration above a bottom-simulating reflector on the northern Cascadia continental slope

    NASA Astrophysics Data System (ADS)

    Yuan, T.; Hyndman, R. D.; Spence, G. D.; Desmons, B.

    1996-06-01

    The amount of gas hydrates in the accretionary wedge sediments of the northern Cascadia subduction zone off Vancouver Island has been estimated from multichannel seismic (MCS) and Ocean Drilling Program (ODP) data. Detailed semblance velocity analyses and full waveform inversion of MCS data, combined with previously published ODP Sites 889/890 sonic log and vertical seismic profile (VSP) data, show that sediment velocities increase downward more rapidly than the no-hydrate/no-gas reference profile from about 1500 m/s near the seafloor to a maximum of 1900 m/s just above the bottom-simulating reflector (BSR) at a subbottom depth of 224 m. Immediately below the BSR, the MCS velocities drop to ˜1700 m/s. A low velocity of ˜1500 m/s from the VSP data probably represents a thin layer, ˜20 m, containing free gas. The difference between the reference and observed velocities is used to estimate hydrate concentration, which reaches a maximum of 20-30% of the pore space above the BSR. A simple interpretation of the drill core chlorinity dilution data at the ODP site yields a similar hydrate concentration of 35%. The estimated hydrate concentration with subbottom depth represents about 7 m3 of hydrate per square meter of seafloor. The total methane gas at STP, including hydrate above the BSR and the small amount of free gas below, is about 800 m3 per square meter of seafloor, or 200 TCF (trillion cubic feet) on the Vancouver Island continental slope. Application of the same method in the Blake-Bahama region of the eastern U.S. margin indicates that the velocity enhancement and inferred hydrate concentration are very similar.

  8. 20,000 years of Nile River dynamics and environmental changes in the Nile catchment area as inferred from Nile upper continental slope sediments

    NASA Astrophysics Data System (ADS)

    Revel, Marie; Ducassou, E.; Skonieczny, C.; Colin, C.; Bastian, L.; Bosch, D.; Migeon, S.; Mascle, J.

    2015-12-01

    Multi-proxy analysis of two marine sediment cores (MS27PT and MD04-2726) from the Nile continental slope provides evidence of changes in Nile sediment discharge related to changes in Ethiopian African Monsoon (EAM) precipitation, and allows us to reconstruct changes in Nile River runoff, vegetation and erosion in the Nile headwaters. Sediment element composition and neodymium isotopic composition reveal significant changes in clastic sediment provenance, with sources oscillating between a Saharan aeolian contribution during the Last Glacial Maximum/deglacial transition and during the Late Holocene, and a Blue/Atbara Nile fluvial contribution during the African Humid Period (AHP). This study provides a new understanding of past environmental changes. Between 14.6 and 14.13 ka there was a major input of sediments from the Ethiopian Highlands, consistent with a stronger EAM at that time. Climate in the Nile basin was wetter between 14.8 and 8.4 ka, with a corresponding increase in Blue Nile water and sediment discharge via the main Nile into the Eastern Mediterranean. The gradual climatic transition from the AHP to the present-day dry climate was reflected in a decrease in Blue Nile sediment deposition and flood discharge between 8.4 and 3.7 ka, with aridity at a maximum between 3.7 and 2.6 ka. The onset of drier conditions in the Blue Nile basin seems to have begun before the 8.2 ka cooling event in the North Atlantic. We speculate that the climatic change from the wet AHP to the dry late Holocene may have been a result of a break in the low latitude dynamic equilibrium between climate, vegetation and erosion, which may in turn have affected the climate in higher latitudes. Reduced Nile flow may also have had an impact on Levantine Intermediate Water originating in the Eastern Mediterranean through an increase in intermediate water formation.

  9. Morphology and formation mechanism of pyrite induced by the anaerobic oxidation of methane from the continental slope of the NE South China Sea

    NASA Astrophysics Data System (ADS)

    Zhang, Mei; Konishi, Hiromi; Xu, Huifang; Sun, Xiaoming; Lu, Hongfeng; Wu, Daidai; Wu, Nengyou

    2014-10-01

    In order to understand the response of authigenic pyrite to gas hydrate geo-systems, pyrite tubes or rods at the sulfate-methane transition (SMT) zone of core GC10 from the northern continental slope of the South China Sea (SCS) were investigated. In situ X-ray diffraction (XRD) results show that the pyrite tube consists of pyrite micro-crystals with trace amount of graphite in the inner tube. Scanning electron microscope (SEM) observations of pyrite tubes indicate various aggregations in the form of framboidal, euhedral, and colloidal pyrite microcrystals. Typical framboidal pyrite is considered as packing of octahedral microcrystals. Interestingly, many framboids in the tubes consist of round or irregular microcrystals and have an outer crust that consists of secondary pyrite. The size of the framboids in the inner wall of the tube is larger than that in the middle wall or foraminifer-filled pyrite. High-resolution transmission electron microscopic (HRTEM) images show marcasite lamellae defects in the spherulitic pyrite crystals, which reveal different solution conditions during the pyrite precipitation. Nano-foil-like graphitic carbon was observed to be closely associated with the pyrite spherules. The occurrence of both marcasite layers and nano-foil-like graphitic carbon suggest that the migration of methane from deep sediment. It is suggested that the formation of pyrite serves as a catalyst during the reaction from methane to elemental carbon under the anaerobic oxidation of methane. Meanwhile, this reaction results in local acidification of the solution inside the pyrite tubes, which favors marcasite lamellae growth on the host pyrite substrate.

  10. North Atlantic slope and canyon study. Volume 2. Final report

    SciTech Connect

    Butman, B.

    1986-12-01

    A field program to investigate the currents and sediment transport along the outershelf and upper slope along the southern flank of Georges Bank was conducted between 1980 and 1984. A major part of the field experiment was conducted in Lydonia Canyon, a large submarine canyon which cuts northward about 20 km into the continental shelf from the shelfbreak. A smaller experiment was conducted in Oceanographer Canyon to compare the currents in these two major canyons. Long-term current observations were made at 20 locations in or adjacent to Lydonia Canyon, and at 9 stations on the continental slope. Detailed semi-synoptic hydrographic observations were made on 9 cruises. The currents associated with Gulf Stream warm core rings (WCR's) strongly affect the flow along the outer shelf and upper slope; eastward currents in excess of 75cm/s were associated with WCR's.

  11. Productivity and sedimentary δ15N variability for the last 17,000 years along the northern Gulf of Alaska continental slope

    USGS Publications Warehouse

    Addison, Jason A.; Finney, Bruce P.; Dean, Walter E.; Davies, Maureen H.; Mix, Alan C.; Stoner, Joseph S.; Jaeger, John M.

    2012-01-01

    Biogenic opal, organic carbon, organic matter stable isotope, and trace metal data from a well-dated, high-resolution jumbo piston core (EW0408–85JC; 59° 33.3′N, 144° 9.21′W, 682 m water depth) recovered from the northern Gulf of Alaska continental slope reveal changes in productivity and nutrient utilization over the last 17,000 years. Maximum values of opal concentration (∼10%) occur during the deglacial Bølling-Allerød (B-A) interval and earliest Holocene (11.2 to 10.8 cal ka BP), moderate values (∼6%) occur during the Younger Dryas (13.0 to 11.2 cal ka BP) and Holocene, and minimum values (∼3.5%) occur during the Late Glacial Interval (LGI). When converted to opal mass accumulation rates, the highest values (∼5000 g cm−2 kyr−1) occur during the LGI prior to 16.7 cal ka BP, which points to a strong influence by LGI glacimarine sedimentation regimes. Similar patterns are also observed in total organic carbon and cadmium paleoproductivity proxies. Mid-Holocene peaks in the terrestrial organic matter fraction at 5.5, 4.7, 3.5, and 1.2 cal ka BP indicate periods of enhanced delivery of glaciomarine sediments by the Alaska Coastal Current. The B-A and earliest Holocene intervals are laminated, and enrichments of redox-sensitive elements suggest dysoxic-to-anoxic conditions in the water column. The laminations are also associated with mildly enriched sedimentary δ15N ratios, indicating a link between productivity, nitrogen cycle dynamics, and sedimentary anoxia. After applying a correction for terrestrial δ15N contributions based on end-member mixing models of terrestrial and marine organic matter, the resulting B-A marine δ15N (6.3 ± 0.4 ‰) ratios are consistent with either mild denitrification, or increased nitrate utilization. These findings can be explained by increased micronutrient (Fe) availability during episodes of rapid rising sea level that released iron from the previously subaerial coastal plain; iron input from enhanced

  12. Crustal structure of the eastern Algerian continental margin and adjacent deep basin: implications for late Cenozoic geodynamic evolution of the western Mediterranean

    NASA Astrophysics Data System (ADS)

    Bouyahiaoui, B.; Sage, F.; Abtout, A.; Klingelhoefer, F.; Yelles-Chaouche, K.; Schnürle, P.; Marok, A.; Déverchère, J.; Arab, M.; Galve, A.; Collot, J. Y.

    2015-06-01

    We determine the deep structure of the eastern Algerian basin and its southern margin in the Annaba region (easternmost Algeria), to better constrain the plate kinematic reconstruction in this region. This study is based on new geophysical data collected during the SPIRAL cruise in 2009, which included a wide-angle, 240-km-long, onshore-offshore seismic profile, multichannel seismic reflection lines and gravity and magnetic data, complemented by the available geophysical data for the study area. The analysis and modelling of the wide-angle seismic data including refracted and reflected arrival travel times, and integrated with the multichannel seismic reflection lines, reveal the detailed structure of an ocean-to-continent transition. In the deep basin, there is an ˜5.5-km-thick oceanic crust that is composed of two layers. The upper layer of the crust is defined by a high velocity gradient and P-wave velocities between 4.8 and 6.0 km s-1, from the top to the bottom. The lower crust is defined by a lower velocity gradient and P-wave velocity between 6.0 and 7.1 km s-1. The Poisson ratio in the lower crust deduced from S-wave modelling is 0.28, which indicates that the lower crust is composed mainly of gabbros. Below the continental edge, a typical continental crust with P-wave velocities between 5.2 and 7.0 km s-1, from the top to the bottom, shows a gradual seaward thinning of ˜15 km over an ˜35-km distance. This thinning is regularly distributed between the upper and lower crusts, and it characterizes a rifted margin, which has resulted from backarc extension at the rear of the Kabylian block, here represented by the Edough Massif at the shoreline. Above the continental basement, an ˜2-km-thick, pre-Messinian sediment layer with a complex internal structure is interpreted as allochthonous nappes of flysch backthrusted on the margin during the collision of Kabylia with the African margin. The crustal structure, moreover, provides evidence for Miocene

  13. The limits of seaward spreading and slope instability at the continental margin offshore Mt Etna, imaged by high-resolution 2D seismic data

    NASA Astrophysics Data System (ADS)

    Gross, Felix; Krastel, Sebastian; Geersen, Jacob; Behrmann, Jan Hinrich; Ridente, Domenico; Chiocci, Francesco Latino; Bialas, Jörg; Papenberg, Cord; Cukur, Deniz; Urlaub, Morelia; Micallef, Aaron

    2016-01-01

    Mount Etna is the largest active volcano in Europe. Instability of its eastern flank is well documented onshore, and continuously monitored by geodetic and InSAR measurements. Little is known, however, about the offshore extension of the eastern volcano flank, defining a serious shortcoming in stability models. In order to better constrain the active tectonics of the continental margin offshore the eastern flank of the volcano, we acquired a new high-resolution 2D reflection seismic dataset. The data provide new insights into the heterogeneous geology and tectonics at the continental margin offshore Mt Etna. The submarine realm is characterized by different blocks, which are controlled by local- and regional tectonics. A compressional regime is found at the toe of the continental margin, which is bound to a complex basin system. Both, the clear link between on- and offshore tectonic structures as well as the compressional regime at the easternmost flank edge, indicate a continental margin gravitational collapse as well as spreading to be present at Mt Etna. Moreover, we find evidence for the offshore southern boundary of the moving flank, which is identified as a right lateral oblique fault north of Catania Canyon. Our findings suggest a coupled volcano edifice/continental margin instability at Mt Etna, demonstrating first order linkage between on- and offshore tectonic processes.

  14. H.R. 73: A Bill to protect the ecologically fragile coastal resources of south Florida by prohibiting offshore oil and gas activities and by cancelling Federal leases in the area of the Outer Continental Shelf adjacent to the south Florida coast. Introduced in the House of Representatives, One Hundred Fourth Congress, First session

    SciTech Connect

    1995-12-31

    This document contains H.R. 73, A Bill to protect the ecologically fragile coastal resources of south Florida by prohibiting offshore oil and gas activities and by cancelling Federal leases in the area of the Outer Continental Shelf adjacent to south Florida. This Bill was introduced in the House of Representatives, 104th Congress, First Session, January 4, 1995.

  15. Are deep-sea organisms dwelling within a submarine canyon more at risk from anthropogenic contamination than those from the adjacent open slope? A case study of Blanes canyon (NW Mediterranean)

    NASA Astrophysics Data System (ADS)

    Koenig, Samuel; Fernández, Pilar; Company, Joan B.; Huertas, David; Solé, Montserrat

    2013-11-01

    Due to their geomorphological structure and proximity to the coastline, submarine canyons may act as natural conduit routes for anthropogenic contaminants that are transported from surface waters to the deep-sea. Organisms dwelling in these canyon environments might thus be at risk of experiencing adverse health effects due to higher pollution exposure. To address this question, chemical and biochemical analyses were conducted on two of the most abundant deep-sea fish species in the study area, namely Alepocephalus rostratus and Lepidion lepidion, and the most abundant deep-sea commercial decapod crustacean Aristeus antennatus sampled inside Blanes canyon (BC) and on the adjacent open slope (OS). Persistent organic pollutants (POPs) levels, including polychlorinated biphenyl (PCB), dichlorodiphenyltrichloroethane (DDT) and derivatives, hexachlorocyclohexanes (HCHs) and hexachlorobenzene (HCB) were determined in muscle tissue of selected samples from 900 m and 1500 m depth. Potential effects resulting from contaminant exposure were determined using hepatic biomarkers such as ethoxyresorufin-O-deethylase (EROD), pentoxyresorufin-O-deethylase (PROD), catalase (CAT), carboxylesterase (CbE), glutathione-S-transferase (GST), total glutathione peroxidase (GPX), glutathione reductase (GR) and superoxide-dismutase (SOD) enzyme activities and lipid peroxidation levels (LP). L. lepidion and A. antennatus tissues exhibited higher POP levels inside BC compared to the OS at 900 m depth. These findings were consistent with biomarker data (i.e. enzymatic response to presence of contaminant agents). Elevated xenobiotic-metabolizing (EROD and PROD) and antioxidant enzymes (CAT and GPX) indicated higher contaminant exposure in both species caught within BC. No difference in POP accumulation between sites was observed in L. lepidion at 1500 m depth, nor in biomarker data, suggesting that the pollution gradient was less pronounced at greater depths. This trend was further corroborated

  16. Spectral analysis of the efficiency of vertical mixing in the deep ocean due to interaction of tidal currents with a ridge running down a continental slope

    SciTech Connect

    Ibragimov, Ranis N.; Tartakovsky, Alexandre M.

    2014-10-29

    Efficiency of mixing, resulting from the reflection of an internal wave field imposed on the oscillatory background flow with a three-dimensional bottom topography, is investigated using a linear approximation. The radiating wave field is associated with the spectrum of the linear model, which consists of those mode numbers n and slope values α, for which the solution represents the internal waves of frequencies ω = nω0 radiating upwrad of the topography, where ω0 is the fundamental frequency at which internal waves are generated at the topography. The effects of the bottom topography and the earth’s rotation on the spectrum is analyzed analytically and numerically in the vicinity of the critical slope, which is a slope with the same angle to the horizontal as the internal wave characteristic. In this notation, θ is latitude, f is the Coriolis parameter and N is the buoyancy frequency, which is assumed to be a constant, which corresponds to the uniform stratification.

  17. Crustal architecture and deep structure of the Namibian continental shelf and adjacent oceanic basins around the landfall of Walvis Ridge from wide-angle seismic and marine magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Planert, L.; Behrmann, J.; Jegen, M.; Heincke, B.; Jokat, W.; Bialas, J.; Marti, A.

    2012-12-01

    The opening of the South Atlantic ocean basin resulted in voluminous magmatism on the conjugate continental margins of Africa and South America, including the formation of the Parana and Entendeka large igneous provinces (LIPs), the formation of up to 100 km wide volcanic wedges characterized by seaward dipping reflector sequences (SDRs), as well as the formation of paired hotspot tracks on the rifted African and South American plates, the Walvis Ridge and the Rio Grande Rise. Hence, the passive margins bordering the South Atlantic are today considered as type examples for models involving hotspot related continental break-up. However, the presence of volcanic features (SDRs, LIPs) appears to be limited south of the hotspot trails. The resulting segmentation of the margins offers a prime opportunity to study the magmatic signal in space and time, and investigate the interrelation with rift-related deformation. A globally significant question to be adressed here is whether magmatism is the driving force for continental break-up, or whether even rifting with abundant hotspot related magmatism is in principle in response to crustal and lithospheric stretching. In 2010/11, a combination of on-/offshore wide-angle seismic, marine magnetotelluric and on-/offshore seismological data were acquired around the landfall of Walvis Ridge at the Namibian passive continental margin. The set of experiments was designed to provide crustal velocity and conductivity information and to investigate the structure of the upper mantle. In particular, we aimed at identifying deep fault zones and variations in Moho depth, the presence of interleaved sediment layers in SDR sequences as well as magmatic intrusions and underplated material near the continent-ocean transition. The sedimentary portions down to the igneous basement were additionally constrained by coincident single-channel reflection seismic data. Here, we present preliminary results for two wide-angle seismic transects and first

  18. The use of Rn-222 as a tracer of mixing in the waters of the continental shelf and slope of the Middle Atlantic Bight

    SciTech Connect

    Carson, S.R.

    1989-01-01

    Production of {sup 222}Rn by the surface sediments of the shelf generally increases with increased fraction of fine-grained sediments. Unusually high radon production found in some areas of shelf sands appears to be the result of mineralogically-controlled coatings on grain surfaces that contain radium in association with manganese. Radon fluxes from the shelf sediments are enhanced relative to fluxes expected from molecular diffusion alone. The flux enhancement from the largest body of high production sands is greater than that from normal-production sands and is variable with season and/or current strength. On the slope the production of radon by the surface sediments tends to increase with water depth. Excess radon standing crops in the waters of the lower slope are consistent with fluxes from the underlying sediments due to molecular diffusion alone, while on the upper slope excess radon standing crops indicate enhanced fluxes. The seasonally variable vertical distributions of radon in the shelf waters show a general association between radon gradients and density gradients. Horizontal distributions of radon in the shelf waters are tied to the laterally inhomogeneous sediment source with some redistribution due to horizontal advection. Short term variability of radon distributions is lowest in the waters of the middle shelf and highest on portions of the outer shelf. Modeling of both vertical and horizontal radon distributions is limited by the time variability of those distributions and by the sensitivity of the models. During stratified periods the vertical eddy diffusion coefficients in the lower pycnocline of the middle shelf average 0.025-0.050 cm{sup 2}/sec. During winter the vertical eddy diffusion coefficients in well-mixed, middle shelf waters are probably greater than the 100 cm{sup 2}/sec upper limit on sensitivity of the model.

  19. Compositional variability of selected sandy intervals in a muddy continental shelf-to-slope succession, Canterbury Basin, South Island, New Zealand

    NASA Astrophysics Data System (ADS)

    Marsaglia, K. M.; Bender-Whitaker, C.; Bailey, C. H.; Nolasco, J.

    2012-12-01

    Integrated Ocean Drilling Program (IODP) Expedition 317 drilled four sites in the Canterbury Basin off South Island, New Zealand. The goal of the expedition was to provide a complete stratigraphic record of the shelf and slope for correlation with interpreted seismic stratigraphy. Recovered lithologies were mostly mud and sandy mud with lesser shell hash, sand, and muddy sand (Fulthorpe et al., 2010). The objective of our study was to determine the compositional variability of Holocene to Pliocene sandy intervals from both shelf (U1351, U1353, U1354) and slope (U1352) sites. Sandy sediment was sampled systematically throughout recovered intervals, which included several potential seismic sequence boundaries. Samples were sieved and sand fractions were made into thin sections. Thin sections were stained for feldspar identification and point counted (400 points) using the Gazzi-Dickinson method to minimize effects of grain size variation. A detailed classification scheme of monomineralic, lithic and bioclastic components was used. The sand samples are fairly uniform in composition: predominantly feldspathic, with lesser quartz and lithic components (average QFL%Q= 39; F= 48; % L= 13). The feldspar includes both plagioclase and potassium varieties, whereas the quartz is predominantly monocrystalline. Lithic components are mainly metamorphic (e.g., quartz-mica tectonite) and sedimentary (mudstone), with rare volcanic fragments. Other common minerals include chlorite and mica, with lesser dense minerals. Bioclastic debris ranges from 0 to 70% of the sand fraction. There are no significant differences in composition among the samples from shelf and slope sites. Sand samples near or at horizons linked to seismic sequence boundaries showed no consistent compositional trends in terrigenous components or percent carbonate (bioclastic debris) as compared to others. This is in contrast to results from other workers focusing on the composition of muddy lithofacies within the

  20. Downslope Eulerian mean flow associated with high-frequency current fluctuations observed on the outer continental shelf and upper slope along the northeastern United States continental margin: implications for sediment transport

    USGS Publications Warehouse

    Butman, B.

    1988-01-01

    Eulerian current measurements made 5-7 m above bottom at six stations along the United States east coast continental margin show a net downslope flow of 1-5 cm s-1. Although the scalar current speed decreases with water depth and toward the bottom, fluctuations in the cross-isobath flow were stronger and increasingly asymmetric near the bottom. Maximum downslope flow exceeded maximum upslope flow by a factor of two to three. The strength of the low-passed downslope flow was proportional to the upslope Reynolds flux of density as well as to the amplitude of the current fluctuations that have periods shorter than 30 h. These flow characteristics may be caused by differential vertical mixing in the bottom boundary layer where a stratified fluid flows upslope (unstable) and downslope (stable). The asymmetry in current strength clearly favors net downslope transport of sediments that move as bedload. ?? 1988.

  1. Hydrographic and biological observations on the Washington continental shelf and slope during the periods: 30 March-5 April, 8-15 June, and 6-11 September 1978

    SciTech Connect

    Postel, J.R.; Peterson, W.K.

    1981-01-01

    During 1978 several cruises were successfully completed along a shelf-slope section off the Washington coast. These cruises were undertaken to collect seasonal information on the processes affecting phytoplankton production and distribution and data on the settling rate of organic matter in the sea during spring, early summer, and autumn conditions. This report summarizes the data collected on three cruises aboard the R/V CAYUSE, which was operated by Oregon State University. All three cruises originated and terminated in Newport, Oregon. Sampling was conducted at established station locations along a transect off Copalis Beach, Washington. Water depth varied from about 10 m at the innermost station (approx. 3 km from the beach) to over 1500 m at the outermost station (approx. 120 km from the beach).

  2. Processes controlling very low sedimentation rates on the continental slope of the Gonone-Orosei canyon system, NE Sardinia—terrestrial and oceanic significance

    NASA Astrophysics Data System (ADS)

    Giresse, Pierre; Pascucci, Vincenzo; Lymer, Gaël; Gaullier, Virginie; Thinon, Isabelle

    2014-12-01

    The narrow shelf and upper slope immediately above the Gonone canyon head off NE Sardinia represent areas of very low sedimentation rates. Along the sides of the canyon head (1,600 m water depth), the sediment deposits are homogeneous but show alternating light-grey intervals rich in carbonate and dark-grey ones rich in organic matter, possibly related to distal turbidite processes. Deposits older than 50,000 years are already encountered at core depths of 2.50 m, the sedimentation rates varying from 6-21 cm/103 years in the lower parts of two cores and from 1.5-3 cm/103 years in the upper parts. At about 35,000 years BP, both cores show a simultaneous drop in sedimentation rate by a factor of 3, probably in response to local mechanisms of channel avulsion. Lithological, mineralogical and geochemical properties reveal the environmental factors which are responsible for the extremely slow sediment accumulation. The southernmost sector of the coast, and partly also of the shelf, consists of Jurassic limestones which supply only small amounts of fine-grained material transported in suspension. During the last sea-level highstand, the accumulation of the Cedrino River pro-delta remained restricted to the coast, the low siliciclastic sediment yields resulting in poor shelf sediment trapping. The present morphology of the canyon head prevented the occurrence of gravity processes in the deeper part of the canyon system, including the coring sites. Accordingly, deposition was mainly fed by hemipelagic material of planktonic origin, together with only moderate terrigenous inputs. On a wider late Pleistocene timescale, seismic data indicate the occurrence of a coarse-grained, layered turbidite facies, implying a very different architecture of the canyon drainage system probably prior to 60,000 years BP.

  3. Late Quaternary changes of the oxygen conditions in the bottom and intermediate waters on the western Kamchatka continental slope, the Sea of Okhotsk

    NASA Astrophysics Data System (ADS)

    Matul, A.; Abelmann, A.; Khusid, T.; Chekhovskaya, M.; Kaiser, A.; Nürnberg, D.; Tiedemann, R.

    2016-03-01

    Microfossil data on the foraminifers and radiolarians in the sediment core KOMEX LV28-44-3, the Kamchatka slope in the eastern Sea of Okhotsk, exhibit the changes in the water oxygen conditions during the last 146 ky. The paleoenvironmental proxies are the radiolarian species Cycladophora davisiana as indicator of the upper intermediate water ventilation, and the benthic/planktonic foraminifers as indicators of the bioproductivity and bottom water oxygenation. In case of sediment core LV28-44-3, the bottom water represents the lower intermediate one, so that conclusions on paleoenvironments are applicable for the most range of the local intermediate water. The well-oxygenated intermediate and near-bottom waters existed in the area of study during the penultimate glaciation of MIS 6, Early Weichselian initiation of the last glaciation within MIS 5b-d, and last glacial stages of MIS 3-2. The intervals of the short low-O2 bottom events with suboxic conditions (dissolved O2 in water 0.3-1.2 ml/l) occur during the last interglacial MIS 5e (Eemian stage) 125 to 113 ka, and during the last deglaciation 17.5 to 6.5 ka. Eemian low-O2 bottom events are associated with the high bioproductivity of the subsurface water but poor ventilation on the upper intermediate depths. The low-O2 bottom events during the last deglaciation occurred at the high bioproductivity of the subsurface water and active ventilation on the upper intermediate depths.

  4. Partitioning the contributions of mega-, macro- and meiofauna to benthic metabolism on the upper continental slope of New Zealand: Potential links with environmental factors and trawling intensity

    NASA Astrophysics Data System (ADS)

    Leduc, Daniel; Pilditch, Conrad A.; Nodder, Scott D.

    2016-02-01

    Understanding and predicting change in deep-sea benthic ecosystem function remains a major challenge. Here, we conducted analyses combining data on the abundance and biomass of benthic fauna and sediment community oxygen consumption (SCOC) on New Zealand's continental margin to estimate and compare the contributions of meio-, macro-, and megafauna to total benthic metabolism and identify potential links with environmental factors and trawling intensity. We focussed on two regions in close proximity-the high surface primary productivity Chatham Rise and low surface productivity Challenger Plateau. Mean megafauna biomass was twenty times greater on Chatham Rise than Challenger Plateau, likely reflecting differences in food supply between the two regions; this contrast in megafaunal biomass was mainly due to differences in mean body weight rather than abundance. Meio- and macrofauna made similar contributions to SCOC and together accounted for 12% of benthic metabolism on average. In contrast, the estimated contribution of megafauna never exceeded 1.5%. Significant positive correlations between faunal respiration and food availability indicate a link between food supply and benthic community function. Our analyses also show that fauna made a greater contribution to SCOC in conditions of high food availability, and that microorganisms (i.e., the proportion of SCOC not accounted for by the fauna) tended to be more dominant at sites with low food availability. These findings provide support for the concept that large organisms are more strongly affected by a reduction in food resources than small organisms, which in turn underlies one of the most widely described patterns in the deep-sea benthos, i.e., the reduction in organism body size with depth. Because metabolism in deep-sea sediments is typically dominated by microorganisms and small fauna, the absence of a relationship between bottom trawling intensity and the respiration of benthic fauna in the present study may

  5. Influence of explosive volcanic events on the activation versus de-activation of a modern turbidite system: the example of the Dohrn canyon-fan in the continental slope of the Campania volcanic district (Naples Bay, Italy - Western Mediterranean)

    NASA Astrophysics Data System (ADS)

    Roca, M.; Budillon, F.; Pappone, G.; Insinga, D.

    2015-12-01

    The interplay between volcanic activity, volcano-clastic yield and activation/deactivation of a turbidite system can be evaluated along the continental margin of Campania region (Tyrrhenian Sea - Italy), an active volcanic area, where three wide canyon-fans occur at short distances one to another. Actually, the Dohrn, Magnaghi and Cuma canyons cut the continental slope and shelf off Ischia and Procida volcanic islands and off the Campania Plain where Phlegraean Field and Mt. Vesuvius active vents are located. This research, partly supported by the Italian Flagship Project Ritmare, is based on single-channel, high-resolution seismic profiles (Sparker-One 16 kJ, 0.5 s twtt), swath-bathymetry and litho- and tephra-stratigraphy of gravity cores. We focused on the stratigraphic constraint of paleo-thalweg features and channel/levees deposits in seismics, debris flow, turbidites and hemipelagites in cores, to learn more on the activation/deactivation stages of the canyon Dohrn, in the frame of relative eustatic sea level variations over the Middle Pleistocene-Holocene time span.Preliminary outcomes suggest that even major volcanic events occurred in the last 300 ky, such as ignimbrite eruptions or large fallouts, have caused the infilling of the canyon head and the cover of pre-existing seabed morphology. As a consequence, the temporary deactivation of the turbidite system has occurred, despite the volcano-clastic overload in the coastal environment. Phases of renewed activities of the thalweg are observed to be in step with falling stages of sea level, which have driven the re-incision of canyon valleys through continuous volcano-clastic debris and turbidites down-flows. Since Holocene, the quiescence of the Dohrn Canyon has been documented, despite the intense volcano-tectonic activity in the area.

  6. Long-Term Aspect of 1980's Submersible-Observed Methane Venting on the Northern Gulf of Mexico Upper Continental Slope: Mapping of Areal Extent and Aggregation: R/V Okeanos Explorer EX1203

    NASA Astrophysics Data System (ADS)

    Carney, R. S.; Roberts, H. H.; Malik, M.

    2012-12-01

    Since the initial discovery of hydrocarbon seeps and associated communities on the upper Louisiana continental slope in 1984 there has been extensive and nearly continuous multidisciplinary exploration of these systems for scientific and regulatory purposes. Four sites within a 45km by 25km rectangle centered at 27° 41' 26.92"N, 91° 28' 4.26"W in the Green Canyon seafloor leasing area were the initial sites confirmed as seep systems by direct observation using the submersible Johnson SeaLink. Hydrocarbon gas venting at these sites ranged from small volume intermittent flow to continuous bubble plumes. The points of emergence ranged from consolidated sediment in mineral-prone environments to fluid muds and brine. The latter two fluid-prone environments represented an active and a quiescent expulsion features. The NOAA Okeanos Explorer Program 2012 expedition 1203 carried out multibeam mapping of this region 6-8 May using both a Konsberg EM 302 288 beam system and a Simrad EK60 scientific echo sounder. Returns from both systems were processed for water column signals. More than 75 indications of bubble plumes were observed representing one of the highest densities as well as magnitudes of individual plumes found to date in the Gulf of Mexico. The plumes were aggregated on the flanks of salt diapirs, ridges between salt-withdrawal basins and areas of multiple slope failures. Correlation with observations begun in the 1980's is good indicating long-term venting. Previous research on gas mix and isotopic content indicated a regionally complex pattern of biogenic and thermogenic methane sources.

  7. Stages in evolution of Paleozoic carbonate platform and basin margin types - western United States passive Continental Margin

    SciTech Connect

    Cook, H.E.; Taylor, M.E.

    1987-05-01

    Late Precambrian rifting along the western edge of North America established a passive continental margin that became the site of 5000 m of platform and basin carbonate sediments over a 150-m.y. interval (Cambrian-Devonian). This megaplatform evolved through several stages: (1) Cambrian-Silurian, distally steepened nonrimmed ramp with base-of-slope fan (Hales Limestone) to homoclinal ramp (Hanson Creek Formation); to (2) Silurian-Devonian, rimmed platform (Lone Mountain Dolomite) having low-angle depositional slopes and slope aprons (Roberts Mountains Formation) and basinal debris sheets (Tor Limestone); to (3) Devonian, rimmed platforms having high-angle bypass slopes, slides, and base-of-slope aprons (McColley Canyon Formation and Devils Gate Limestone). The position of the rifted continental margin controlled the overall trend of the platform-slope break. Postrift subsidence with superimposed eustatic sea level changes allowed the platform to accumulate 5000 m of sediment. The stratigraphic progression from nonrimmed ramps in the Cambrian to rimmed platforms with high-angle bypass slopes in the Devonian was a function of both the gradual steepening of the slope, as the platform margin built up and prograded seaward, and the evolution of reef and bank-building organisms through time. Evolution of adjacent basinal carbonates was strongly influenced by slope declivity and relative sea level changes. As slope declivity increased through time, sedimentary processes on the slope changed from small-scale sediment gravity flows that accreted on the slope (ex: Roberts Mountains Formation slope apron) to large-scale sediment gravity flows that deposited debris in base-of-slope settings (ex: Devils Gate Limestone base-of-slope apron).

  8. North Atlantic slope and canyon study. Volume 1. Executive summary

    SciTech Connect

    Butman, B.

    1986-12-01

    A field program to investigate the currents and sediment transport along the outershelf and upper slope along the southern flank of Georges Bank was conducted between 1980 and 1984. A major part of the field experiment was conducted in Lydonia Canyon, a large submarine canyon which cuts northward about 20 km into the continental shelf from the shelfbreak. A smaller experiment was conducted in Oceanographer Canyon to compare the currents in these two major canyons. The long-term current observations made in Lydonia and Oceanographer Canyons show that the current regime in these topographic features differs from the adjacent slope, and between canyons. Sediments near the head (depths shallower than about 600 m) in both Lydonia and Oceanographer are frequently resuspended. This frequent resuspension may allow the sediments to strip pollutants from the water column. Currents in Oceanographer Canyon are stronger and the sediments coarser than in Lydonia at comparable depths.

  9. A seismic-reflection investigation of gas hydrates and sea-floor features of the upper continental slope of the Garden Banks and Green Canyon regions, northern Gulf of Mexico: report for cruise G1-99-GM (99002)

    USGS Publications Warehouse

    Cooper, Alan; Twichell, David; Hart, Patrick

    1999-01-01

    During April 1999, the U.S. Geological Survey (USGS) conducted a 13-day cruise in the Garden Banks and Green Canyon regions of the Gulf of Mexico. The R/V Gyre, owned by Texas A&M University, was chartered for the cruise. The general objectives were (1) to acquire very high resolution seismic-reflection data and side-scan sonar images of the upper and middle continental slope (200-1200-m water depths), (2) to study the acoustic character and features of the sea floor for evidence of sea-floor hazards, and (3) to look for evidence of subsurface gas hydrates and their effects. The Gulf of Mexico is well known for hydrocarbon resources, with emphasis now on frontier deep-water areas. For water depths greater than about 250 m, the pressure-termperature conditions are correct for the development of shallow-subsurface gas hydrate formation (Anderson et al., 1992). Gas hydrates are ice-like mixtures of gas and water (Kvenvolden, 1993). They are known to be present from extensive previous sampling in sea-floor cores and from mound-like features observed on the sea floor in many parts of the northern Gulf, including the Green Canyon and Garden Banks areas (e.g., Roberts, 1995). Seismic-reflection data are extensive in the Gulf of Mexico, but few very-high-resolution data like those needed for gas-hydrate studies exist in the public domain. The occurrence and mechanisms of gas hydrate formation and dissociation are important to understand, because of their perceived economic potential for methane gas, their potential controls on local and regional sea-floor stability, and their possible effects on earth climates due to massive release of methane greenhouse gas into the atmosphere. Three high-resolution seismic-reflection systems and one side-scan sonar system were used on the cruise to map the surface reflectance and features of the sea floor and the acoustic geometries and character of the shallow sub-surface. The cruise was designed to acquire regional and detailed local

  10. Late Mesozoic and Cenozoic thermotectonic evolution of the central Brooks Range and adjacent North Slope foreland basin, Alaska: Including fission track results from the Trans-Alaska Crustal Transect (TACT)

    USGS Publications Warehouse

    O'Sullivan, P. B.; Murphy, J.M.; Blythe, A.E.

    1997-01-01

    Apatite fission track data are used to evaluate the thermal and tectonic history of the central Brooks Range and the North Slope foreland basin in northern Alaska along the northern leg of the Trans-Alaska Crustal Transect (TACT). Fission track analyses of the detrital apatite grains in most sedimentary units resolve the timing of structures and denudation within the Brooks Range, ranging in scale from the entire mountain range to relatively small-scale folds and faults. Interpretation of the results indicates that rocks exposed within the central Brooks Range cooled rapidly from paleotemperatures 110?? to 50??C during discrete episodes at ???100??5 Ma, ???60??4 Ma, and ???24??3 Ma, probably in response to kilometer-scale denudation. North of the mountain front, rocks in the southern half of the foreland basin were exposed to maximum paleotemperatures 110??C in the Late Cretaceous to early Paleocene as a result of burial by Upper Jurassic and Cretaceous sedimentary rocks. Rapid cooling from these elevated paleotemperatures also occurred due to distinct episodes of kilometer-scale denudation at ???60??4 Ma, 46??3 Ma, 35??2 Ma, and ???24??3 Ma. Combined, the apatite analyses indicate that rocks exposed along the TACT line through the central Brooks Range and foreland basin experienced episodic rapid cooling throughout the Late Cretaceous and Cenozoic in response to at least three distinct kilometer-scale denudation events. Future models explaining orogenic events in northern Alaska must consider these new constraints from fission track thermochronology. Copyright 1997 by the American Geophysical Union.

  11. Layered Slope

    NASA Technical Reports Server (NTRS)

    2005-01-01

    28 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a frost-covered slope in the south polar region of Mars. The layered nature of the terrain in the south polar region is evident in a series of irregular, somewhat stair-stepped bands that run across the image.

    Location near: 84.3oS, 27.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  12. Downward Slope

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This false-color image from NASA's Mars Exploration Rover Opportunity panoramic camera shows a downward view from the rover as it sits at the edge of 'Endurance' crater. The gradual, 'blueberry'-strewn slope before the rover contains an exposed dark layer of rock that wraps around the upper section of the crater. Scientists suspect that this rock layer will provide clues about Mars' distant past. This mosaic image comprises images taken from 10 rover positions using 750, 530 and 430 nanometer filters, acquired on sol 131 (June 6, 2004).

  13. Gullied Slope

    NASA Technical Reports Server (NTRS)

    2005-01-01

    20 May 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows gullies formed on an equator-facing slope among mounds in Acidalia Planitia. Similar gullies occur in a variety of settings at middle and polar latitudes in both martian hemispheres.

    Location near: 49.8oN, 22.7oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Summer

  14. A reevaluation of the Munson-Nygren-Retriever submarine landslide complex, Georges bank lower slope, western north Atlantic

    USGS Publications Warehouse

    Chaytor, Jason D.; Twichell, David C.; ten Brink, Uri S.

    2012-01-01

    The Munson-Nygren-Retriever (MNR) landslide complex is a series of distinct submarine landslides located between Nygren and Powell canyons on the Georges Bank lower slope. These landslides were first imaged in 1978 using widely-spaced seismic reflection profiles and were further investigated using continuous coverage GLORIA sidescan imagery collected over the landslide complex in 1987. Recent acquisition of highresolution multibeam bathymetry across these landslides has provided an unprecedented view of their complex morphology and allows for a more detailed investigation of their evacuation and deposit morphologies and sizes, modes of failure, and relationship to the adjacent sections of the margin, including the identification of an additional landslide within the MNR complex, referred to here as the Pickett slide. The evacuation zone of these landslides covers an area of approximately 1,780 km2 . The headwalls of these landslides are at a depth of approximately 1,800 m, with evacuation extending for approximately 60 km downslope to the top of the continental rise. High-relief debris deposits, in the form of blocks and ridges, are present down the length of the majority of the evacuation zones and within the deposition area at the base of the slope. On the continental rise, the deposits from each of the most recent failures of the MNR complex landslides merge with debris from earlier continental slope failures, canyon and alongslope derived deposits, and prominent upper-rise failures.

  15. Preliminary report on geology along Atlantic Continental Margin of northeastern United States

    USGS Publications Warehouse

    Minard, J.P.; Perry, W.J.; Weed, E.G.A.; Rhodehamel, E.C.; Robbins, E.I.; Mixon, R.B.

    1974-01-01

    The U.S. Geological Survey is conducting a geologic and geophysical study of the northeastern United States outer continental shelf and the adjacent slope from Georges Bank to Cape Hatteras. The study also includes the adjacent coastal plain because it is a more accessible extension of the shelf. The total study area is about 324,000 sq km, of which the shelf and slope constitute about 181,000 sq km and the coastal plain constitutes 143,000 sq km. The shelf width ranges from about 30 km at Cape Hatteras to about 195 km off Raritan Bay and on Georges Bank. Analyses of bottom samples make it possible to construct a preliminary geologic map of the shelf and slope to a water depth of 2,000 m. The oldest beds cropping out in the submarine canyons and on the slope are of early ate Cretaceous age. Beds of Early Cretaceous and Jurassic age are present in deep wells onshore and probably are present beneath the shelf in the area of this study. Such beds are reported beneath the Scotian shelf on the northeast where they include limestone, salt, and anhydrite. Preliminary conclusions suggest a considerably thicker Mesozoic sedimentary sequence than has been described previously. The region is large; the sedimentary wedge is thick; structures seem favorable; and the hydrocarbon potential may be considerable.

  16. Continental magnetic anomaly constraints on continental reconstruction

    NASA Technical Reports Server (NTRS)

    Vonfrese, R. R. B.; Hinze, W. J.; Olivier, R.; Bentley, C. R.

    1985-01-01

    Crustal magnetic anomalies mapped by the MAGSAT satellite for North and South America, Europe, Africa, India, Australia and Antarctica and adjacent marine areas were adjusted to a common elevation of 400 km and differentially reduced to the radial pole of intensity 60,000 nT. These radially polarized anomalies are normalized for differential inclination, declination and intensity effects of the geomagnetic field, so that in principle they directly reflected the geometric and magnetic polarization attributes of sources which include regional petrologic variations of the crust and upper mantle, and crustal thickness and thermal perturbations. Continental anomalies demonstrate remarkably detailed correlation of regional magnetic sources across rifted margins when plotted on a reconstruction of Pangea. Accordingly, they suggest further fundamental constraints on the geologic evolution of the continents and their reconstructions.

  17. Habitat Specialization in Tropical Continental Shelf Demersal Fish Assemblages

    PubMed Central

    Fitzpatrick, Ben M.; Harvey, Euan S.; Heyward, Andrew J.; Twiggs, Emily J.; Colquhoun, Jamie

    2012-01-01

    The implications of shallow water impacts such as fishing and climate change on fish assemblages are generally considered in isolation from the distribution and abundance of these fish assemblages in adjacent deeper waters. We investigate the abundance and length of demersal fish assemblages across a section of tropical continental shelf at Ningaloo Reef, Western Australia, to identify fish and fish habitat relationships across steep gradients in depth and in different benthic habitat types. The assemblage composition of demersal fish were assessed from baited remote underwater stereo-video samples (n = 304) collected from 16 depth and habitat combinations. Samples were collected across a depth range poorly represented in the literature from the fringing reef lagoon (1–10 m depth), down the fore reef slope to the reef base (10–30 m depth) then across the adjacent continental shelf (30–110 m depth). Multivariate analyses showed that there were distinctive fish assemblages and different sized fish were associated with each habitat/depth category. Species richness, MaxN and diversity declined with depth, while average length and trophic level increased. The assemblage structure, diversity, size and trophic structure of demersal fishes changes from shallow inshore habitats to deeper water habitats. More habitat specialists (unique species per habitat/depth category) were associated with the reef slope and reef base than other habitats, but offshore sponge-dominated habitats and inshore coral-dominated reef also supported unique species. This suggests that marine protected areas in shallow coral-dominated reef habitats may not adequately protect those species whose depth distribution extends beyond shallow habitats, or other significant elements of demersal fish biodiversity. The ontogenetic habitat partitioning which is characteristic of many species, suggests that to maintain entire species life histories it is necessary to protect corridors of connected

  18. Continental Margins of the Arctic Ocean: Implications for Law of the Sea

    NASA Astrophysics Data System (ADS)

    Mosher, David

    2016-04-01

    A coastal State must define the outer edge of its continental margin in order to be entitled to extend the outer limits of its continental shelf beyond 200 M, according to article 76 of the UN Convention on the Law of the Sea. The article prescribes the methods with which to make this definition and includes such metrics as water depth, seafloor gradient and thickness of sediment. Note the distinction between the "outer edge of the continental margin", which is the extent of the margin after application of the formula of article 76, and the "outer limit of the continental shelf", which is the limit after constraint criteria of article 76 are applied. For a relatively small ocean basin, the Arctic Ocean reveals a plethora of continental margin types reflecting both its complex tectonic origins and its diverse sedimentation history. These factors play important roles in determining the extended continental shelves of Arctic coastal States. This study highlights the critical factors that might determine the outer edge of continental margins in the Arctic Ocean as prescribed by article 76. Norway is the only Arctic coastal State that has had recommendations rendered by the Commission on the Limits of the Continental Shelf (CLCS). Russia and Denmark (Greenland) have made submissions to the CLCS to support their extended continental shelves in the Arctic and are awaiting recommendations. Canada has yet to make its submission and the US has not yet ratified the Convention. The various criteria that each coastal State has utilized or potentially can utilize to determine the outer edge of the continental margin are considered. Important criteria in the Arctic include, 1) morphological continuity of undersea features, such as the various ridges and spurs, with the landmass, 2) the tectonic origins and geologic affinities with the adjacent land masses of the margins and various ridges, 3) sedimentary processes, particularly along continental slopes, and 4) thickness and

  19. Block glides offshore Newport Beach, Southern California continental margin

    SciTech Connect

    Greene, H.G.; Clarke, S.H. Jr.; Kennedy, M.P.

    1988-01-01

    The continental slope offshore Newport Beach, California, is characterized by a relatively gentle (approximately 1/sup 0/) grade and is dissected by numerous channels and canyons, of which the most conspicuous is Newport Canyon. An unusual series of block-glide landslides have developed on this lope adjacent to many of these channels. Locally, secondary channels that develop along pull-apart fractures between the slide blocks may service as conduits for downslope sediment movement. A detailed seismic-reflection survey of the area shows that the slope is underlain by soft water-saturated unstable sediment of Quaternary age. The block-glides lie wholly within this sediment; displaced blocks appear to have moved only a short distance downslope and are preserved as intact masses that exhibit downward increasing internal deformation. This deformation reaches a maximum near the front of the displaced mass and in basal beds nearest the slip surface. The morphology of the blocks and their intervening channellike erosional scarps is similar to that of glacial blocks and their associated bergschrunds. The formation of new scarps and the widening of channels formed as pull-aparts by the ongoing process of block movement may contribute to headward erosion and widening of Newport Canyon and its tributaries. Slope failure might be greatly enhanced by strong ground motion associated with nearby earthquakes. The authors suspect that renewed movement occurs on these blocks during major seismic events on the nearby Newport-Inglewood fault (e.g., 1933 M/sub L/ 6.3 event).

  20. Adjacent segment disease.

    PubMed

    Virk, Sohrab S; Niedermeier, Steven; Yu, Elizabeth; Khan, Safdar N

    2014-08-01

    EDUCATIONAL OBJECTIVES As a result of reading this article, physicians should be able to: 1. Understand the forces that predispose adjacent cervical segments to degeneration. 2. Understand the challenges of radiographic evaluation in the diagnosis of cervical and lumbar adjacent segment disease. 3. Describe the changes in biomechanical forces applied to adjacent segments of lumbar vertebrae with fusion. 4. Know the risk factors for adjacent segment disease in spinal fusion. Adjacent segment disease (ASD) is a broad term encompassing many complications of spinal fusion, including listhesis, instability, herniated nucleus pulposus, stenosis, hypertrophic facet arthritis, scoliosis, and vertebral compression fracture. The area of the cervical spine where most fusions occur (C3-C7) is adjacent to a highly mobile upper cervical region, and this contributes to the biomechanical stress put on the adjacent cervical segments postfusion. Studies have shown that after fusion surgery, there is increased load on adjacent segments. Definitive treatment of ASD is a topic of continuing research, but in general, treatment choices are dictated by patient age and degree of debilitation. Investigators have also studied the risk factors associated with spinal fusion that may predispose certain patients to ASD postfusion, and these data are invaluable for properly counseling patients considering spinal fusion surgery. Biomechanical studies have confirmed the added stress on adjacent segments in the cervical and lumbar spine. The diagnosis of cervical ASD is complicated given the imprecise correlation of radiographic and clinical findings. Although radiological and clinical diagnoses do not always correlate, radiographs and clinical examination dictate how a patient with prolonged pain is treated. Options for both cervical and lumbar spine ASD include fusion and/or decompression. Current studies are encouraging regarding the adoption of arthroplasty in spinal surgery, but more long

  1. Freshwater peat on the continental shelf

    USGS Publications Warehouse

    Emery, K.O.; Wigley, R.L.; Bartlett, A.S.; Rubin, M.; Barghoorn, E.S.

    1967-01-01

    Freshwater peats from the continental shelf off northeastern United States contain the same general pollen sequence as peats from ponds that are above sea level and that are of comparable radiocarbon ages. These peats indicate that during glacial times of low sea level terrestrial vegetation covered the region that is now the continental shelf in an unbroken extension from the adjacent land areas to the north and west.

  2. Freshwater peat on the continental shelf.

    PubMed

    Emery, K O; Wigley, R L; Bartlett, A S; Rubin, M; Barghoorn, E S

    1967-12-01

    Freshwater peats from the continental shelf off northeastern United States contain the same general pollen sequence as peats from ponds that are above sea level and that are of comparable radiocarbon ages. These peats indicate that during glacial times of low sea level terrestrial vegetation covered the region that is now the continental shelf in an unbroken extension from the adjacent land areas to the north and west. PMID:17801856

  3. Comparison of observed and predicted slope winds

    SciTech Connect

    Horst, T.W.; Doran, J.C.

    1980-07-01

    Nocturnal drainage winds begin when air adjacent to an inclined surface flows down the slop because it is cooled more than the free air at some distance horizontally from the surface. These slope winds merge and are channeled by the topography to form the larger-scale drainage or mountain winds. This paper discusses the slope flow phase of the drainage wind. The predictions of a simple model for flow down a two-dimensional slope are compared to observations of the drainage wind obtained during the July 1979 ASCOT field study near Middletown, CA.

  4. Structure and development of the southern Moroccan continental shelf

    USGS Publications Warehouse

    Dillon, William P.

    1974-01-01

    The structure of the continental shelf off southern Morocco was studied by means of 2,100 km of seismic reflection profiles, magnetic and bathymetric surveys, and dredge samples. The research area lies off four geologic divisions adjacent to the coast: the Atlas Mountains; the Souss Trough; the Anti-Atlas Mountains; and the Aaiun Basin. The continental shelf, along with the western Atlas Mountains, the western Souss Trough, and the entire Aaiun Basin, has subsided along a normal fault-flexure system. This system runs along the shore at the Anti-Atlas Mountains, and cuts off this cratonic block from the shelf subsidence. The shelf is narrow and characterized by out-building off the Anti-Atlas range, whereas it is broader and characterized by upbuilding to the north and south. Deposition was essentially continuous at least from Early Cretaceous through Eocene time. Published work suggests that the last cycle of sedimentation began during Permian rifting. After Eocene time, most sediments carried to the shelf must have bypassed it and gone to construct the slope and rise or to the deep sea. Tertiary orogenies caused extensive folding of Mesozoic and early Tertiary deposits off the Atlas Mountains. ?? 1974.

  5. Crustal structure of the Peruvian continental margin from wide-angle seismic studies

    NASA Astrophysics Data System (ADS)

    Krabbenhöft, A.; Bialas, J.; Kopp, H.; Kukowski, N.; Hübscher, C.

    2004-11-01

    Active seismic investigations along the Pacific margin off Peru were carried out using ocean bottom hydrophones and seismometers. The structure and the P-wave velocities of the obliquely subducting oceanic Nazca Plate and overriding South American Plate from 8°S to 15°S were determined by modelling the wide-angle seismic data combined with the analysis of reflection seismic data. Three detailed cross-sections of the subduction zone of the Peruvian margin and one strike-line across the Lima Basin are presented here. The oceanic crust of the Nazca Plate, with a thin pelagic sediment cover, ranging from 0-200 m, has an average thickness of 6.4 km. At 8°S it thins to 4 km in the area of Trujillo Trough, a graben-like structure. Across the margin, the plate boundary can be traced to 25 km depth. As inferred from the velocity models, a frontal prism exists adjacent to the trench axis and is associated with the steep lower slope. Terrigeneous sediments are proposed to be transported downslope due to gravitational forces and comprise the frontal prism, characterized by low seismic P-wave velocities. The lower slope material accretes against a backstop structure, which is defined by higher seismic P-wave velocities, 3.5-6.0 km s-1. The large variations in surface slope along one transect may reflect basal removal of upper plate material, thus steepening the slope surface. Subduction processes along the Peruvian margin are dominated by tectonic erosion indicated by the large margin taper, the shape and bending of the subducting slab, laterally varying slope angles and the material properties of the overriding continental plate. The erosional mechanisms, frontal and basal erosion, result in the steepening of the slope and consequent slope failure.

  6. The Brazilian continental margin

    NASA Astrophysics Data System (ADS)

    Martins, L. R.; Coutinho, P. N.

    1981-04-01

    The Brazilian continental margin, with its interesting morphology, structure and sediments, has become better known only during the last two decades. Six physiographical provinces can be recognized at the continental margin and the adjacent coast: (1) Cabo Orange-Parnaiba delta; (2) Parnaiba delta-Cabo Sa˜o Roque; (3) Cabo Sa˜o Roque-Belmonte; (4) Belmonte-Cabo Frio; (5) Cabo Frio-Cabo Santa Marta; and (6) Cabo Santa Marta-Chui. The shelf is rather wide near the Amazon Mouth, becoming narrower eastwards, continuing very narrow along the northeastern and eastern coast, and becoming wider again in the south towards the Plate River. Prominent morphological features along the margin are the Amazon cone, the marginal plateaus off northeastern Brazil, the Sa˜o Francisco cone and canyon, the Abrolhos Bank, and the deep-sea plateaus of Pernambuco and Sa˜o Paulo. On the shelf proper a number of relief elements exist, such as sand waves east of the Amazon, submarine terraces at various places, and irregularities of structural origin. The shelf break is rather smooth in the far north and south, more abrupt in the remainder. Surface sediments of the Brazilian shelf show five distinct facies types: littoral quartz sands, mud, transition sand-mud, coralline algae, and biodetrital. The terrigenous elastic fractions dominate off the Amazon and in southern Brazil; between these areas they occupy a very narrow strip near the coast. The carbonate facies, predominantly composed of calcareous algae, is abundant between the Parnaiba delta and Cabo Frio; to the south this facies is more biodetrital and restricted to the outer shelf. Economically important on the Brazilian continental margin besides oil, are sands and gravels, carbonate deposits, evaporites and some subsurface coal. Other possible mineral resources could be phosphate, heavy minerals and clays for ceramics.

  7. Phytoplankton Communities in Louisiana coastal waters and the continental shelf

    EPA Science Inventory

    Louisiana coastal waters and the adjacent continental shelf receive large freshwater and nutrient inputs from the Mississippi and Atchafalaya Rivers, creating favorable conditions for increased phytoplankton productivity. To examine inshore-offshore patterns in phytoplankton comm...

  8. Reproductive biology and recruitment of the deep-sea fish community from the NW Mediterranean continental margin

    NASA Astrophysics Data System (ADS)

    Fernandez-Arcaya, U.; Rotllant, G.; Ramirez-Llodra, E.; Recasens, L.; Aguzzi, J.; Flexas, M. M.; Sanchez-Vidal, A.; López-Fernández, P.; García, J. A.; Company, J. B.

    2013-11-01

    Temporal patterns in deep-sea fish reproduction are presently unknown for the majority of deep continental margins. A series of seasonal trawling surveys between depths of 300 to 1750 m in the Blanes submarine canyon and its adjacent open slope (NW Mediterranean) were conducted. The bathymetric size distributions and reproductive cycles of the most abundant species along the NW Mediterranean margin were analyzed to assess the occurrence of (i) temporal patterns in reproduction (i.e., spawning season) along a bathymetric gradient and (ii) preferential depth strata for recruitment. The fish assemblages were grouped in relation to their bathymetric distribution: upper slope, middle slope and lower slope species. Middle-slope species (i.e., 800-1350 m) showed short (i.e., highly seasonal) reproductive activity compared to the upper (300-800 m) and lower (1350-1750 m) ones. Our results, together with those previously published for megabenthic crustacean decapods in the area, suggest a cross-phyla depth-related trend of seasonality in reproduction. In the middle and lower slope species, the reproductive activity reached a maximum in the autumn-winter months and decreased in the spring. The observed seasonal spawning patterns appear to be ultimately correlated with changes in the downward transport of organic particles and with seasonal changes in the physicochemical characteristics of the surrounding water masses. The distribution of juveniles was associated with the bathymetric stratum where intermediate nepheloid layers interact with the continental margins, indicating that this stratum acts as a deep-sea fish nursery area.

  9. Continental Rifts

    NASA Astrophysics Data System (ADS)

    Rosendahl, B. R.

    Continental Rifts, edited by A. M. Quennell, is a new member of the Benchmark Papers in Geology Series, edited in toto by R. W. Fairbridge. In this series the individual volume editors peruse the literature on a given topic, select a few dozen papers of ostensibly benchmark quality, and then reorder them in some sensible fashion. Some of the original papers are republished intact, but many are chopped into “McNuggets™” of information. Depending upon the volume editor, the chopping process can range from a butchering job to careful and prudent pruning. The collecting, sifting, and reorganizing tasks are, of course, equally editor-sensitive. The end product of this series is something akin to a set of Reader's Digest of Geology.

  10. Structure and petroleum potential of the continental margin between Cross Sound and Icy Bay, northern Gulf of Alaska

    USGS Publications Warehouse

    Bruns, T.R.

    1982-01-01

    Major structural features of the Yakutat segment, the segment of the continental margin between Cross Sound and Icy Bay, northern Gulf of Alaska, are delineated by multichannel seismic reflection data. A large structural high is centered on Fairweather Ground and lies generally at the edge of the shelf from Cross Sound to west of the Alsek Valley. A basement uplift, the Dangerous River zone, along which the seismic acoustic basement shallows by up to two kilometers, extends north from the western edge of Fairweather Ground towards the mouth of the Dangerous River. The Dangerous River zone separates the Yakutat segment into two distinct subbasins. The eastern subbasin has a maximum sediment thickness of about 4 km, and the axis of the basin is near and parallel to the coast. Strata in this basin are largely of late Cenozoic age (Neogene and Quaternary) and approximately correlate with the onshore Yakataga Formation. The western subbasin has a maximum of at least 9 km of sediment, comprised of a thick (greater than 4.5 km) Paleogene section overlain by late Cenozoic strata. The Paleogene section is truncated along the Dangerous River zone by a combination of erosion, faulting, and onlap onto the acoustic basement. Within the western subbasin, the late Cenozoic basin axis is near and parallel to the coast, but the Paleogene basin axis appears to trend in a northwest direction diagonally across the shelf. Sedimentary strata throughout the Yakutat shelf show regional subsidence and only minor deformation except in the vicinity of the Fairweather Ground structural high, near and along the Dangerous River zone, and at the shoreline near Lituya Bay. Seismic data across the continental slope and adjacent deep ocean show truncation at the continental slope of Paleogene strata, the presence of a thick (to 6 km) undeformed or mildly deformed abyssal sedimentary section at the base of the slope that in part onlaps the slope, and a relatively narrow zone along the slope or at

  11. Interior Slopes of Copernican Craters

    NASA Astrophysics Data System (ADS)

    Robinson, M. S.; Burns, K.; Stelling, R.; Speyerer, E.; Mahanti, P.

    2012-12-01

    The Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) routinely acquires high resolution (50 to 200 cm pixel scales) stereo pairs from adjacent orbits through spacecraft slews; parallax angles are typically >20°, and the local incidence angle between 40° and 65°. These observations are reduced to digital elevation models (DEM) using a combination of ISIS (USGS) and SOCET Set (BAE Systems). For this study DEMs originally sampled at 2 m scales were reduced (averaging technique) to 5 m scales to provide slopes calculated over 3x3 pixel boxes (15 m x 15 m). The upper 50% of interior walls of Copernican craters (2 to 20 km diameter) typically have average slopes of 36°, with slopes locally above 40° not uncommon (i.e. Fig 1: 2.3 km diam, 17.68°S, 144.41°E). Giordano Bruno (GB; 35.97N°, 102.86°E) is likely the youngest 20-km diameter class crater on the Moon. Its floor is dominated by impact forms (ponds and flows), and inner walls exhibit a series of coalesced flow lobes emanating from steep upper slopes. The lobes appear to be composed of dry granular material based on the observation of boulder trails superposed on many examples. The upper slopes average 36° or more, with some slopes above 40°. For much of GB, slopes exceed 30° all the way to the crater floor (especially in the SE). The high slopes imply angular grains, some level of cohesion, and/or higher angles of repose due to the Moon's relatively low gravity. Larmor Q (28.56°N, 176.33°E), another large Copernican crater, is elliptical in plan (23 x 18 km diameter), with an interior floor dominated by large slump blocks. Like GB its walls exhibit overlapping lobes (granular materials) emanating from interior wall slopes that range from 30° to 36°. Other Copernican craters exhibit similar steep slopes on interior walls: Moore F (23 km diam), Necho (30 km), and two unnamed craters (9 km,13.31°S, 257.55°E; 9 km, 15.72°, 177.39°E). Slopes of the central peaks of Tycho crater (0

  12. Geologic development and characteristics of continental margins, Gulf of Mexico

    SciTech Connect

    Coleman, J.M.; Prior, D.B.; Roberts, H.H.

    1986-09-01

    The continental slope of the Gulf basin covers more than 500,000 km/sup 2/ and consists of smooth and gently sloping surfaces, prominent escarpments, knolls, intraslope basins, and submarine canyons and channels. It is an area of extremely diverse topographic and sedimentologic conditions. The slope extends from the shelf break, roughly at the 200-m isobath, to the upper limit of the continental rise at a depth of 2800 m. The most complex province in the basin, and the one of most interest to the petroleum industry, is the Texas-Louisiana slope, occupying 120,000 km/sup 2/ and in which bottom slopes range from less than 1/sup 0/ to greater than 20/sup 0/ around the knolls and basins. The near-surface geology and topography of the slope is a function of the interplay between episodes of rapid shelf-edge and slope progradation and contemporaneous modification of the depositional sequence by diapirism. Development of discrete depocenters throughout the Neogene results in rapid shelf-edge progradation, often exceeding 15-20 km/m.y. This rapid progradation of the shelf edge leads to development of thick wedges of sediment accumulation on the continental slope. Slope oversteepening, high pore pressures in rapidly deposited soft sediments, and changes in eustatic sea level cause subaqueous slope instabilities such as landslides and debris flows. Large-scale features such as shelf-edge separation scars and landslide-related canyons often result from such processes.

  13. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

    Levander, A.; Bezada, M. J.; Niu, F.; Palomeras, I.; Thurner, S.; Humphreys, E.; Miller, M. S.; Carbonell, R.; Gallart, J.; Schmitz, M.

    2014-12-01

    While subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, recycling continental lithosphere appears far more complicated and is less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we describe another process that can lead to the loss of continental lithosphere adjacent to a subduction zone: Subducting oceanic plates can entrain and recycle lithospheric mantle from an adjacent continent and disrupt the continental lithosphere far inland from the subduction zone. Seismic images from recent dense broadband arrays on opposite sides of the Atlantic show higher than expected volumes of positive anomalies identified as the subducted Atlantic (ATL) slab under northeastern South America (SA), and the Alboran slab beneath the Gibraltar arc region (GA). The positive anomalies lie under and are aligned with the continental margins at depths greater than 200 km. Closer to the surface we find that the continental margin lithospheric mantle is significantly thinner than expected beneath the orogens adjacent to the subduction zones. Thinner than expected lithosphere extends inland as far as the edges of nearby cratonic cores. These observations suggest that subducting oceanic plates viscously entrain and remove continental mantle lithosphere from beneath adjacent continental margins, modulating the surface tectonics and pre-conditioning the margins for further deformation. The latter can include delamination of the entire lithospheric mantle, as around GA, inferred by results from active and passive seismic experiments. Secondary downwellings develop under the continental interior inland from the subduction zone: We image one under SA and one or more in the past were likely under GA. The process of subduction-driven continental margin lithosphere removal reconciles numerous, sometimes mutually

  14. Fuzzy slope stability method

    SciTech Connect

    Kacewicz, M.

    1987-11-01

    An approach for the description of uncertainty in geology using fuzzy-set theory and an example of slope stability problem is presented. Soil parameters may be described by fuzzy sets. The fuzzy method of slope stability estimation is considered and verified in the case of one of Warsaw's (Poland) slopes.

  15. Detailed analysis of the Valdes slide: a landward facing slope failure off Chile

    NASA Astrophysics Data System (ADS)

    Anasetti, Andrea; Krastel, Sebastian; Weinrebe, Willy; Klaucke, Ingo; Bialas, Jorge

    2010-05-01

    The Chilean continental margin is a very active area interested by important tectonic movements and characterized by a fast morphological evolution. Geophysical data acquired during cruise JC 23, aboard RV JAMES COOK in March/April 2008 and previous cruises cover most of the active Chilean continental margin between 33° and 37° S. Integrated interpretation of multi-beam bathymetric, sub-bottom profiles, side-scan sonar and seismic data allowed the identification of a number of slope failures. The main topic of this project is the morphological and sedimentological analysis of the Valdes slide, a medium-sized submarine landslide offshore the city of Talcahuano (300 km south of Santiago). In contrast to most other slides along continental margins, the Valdes slide is located on the landward facing eastern slope of a submarine ridge. This setting has important implications for the associated tsunami wave field (first arrival of positive amplitude). We measured geometrical parameters of the failure and adjacent slope. The slide affected an area of 19 km2 between ~1060 m and >1700 m water depths. Its is ~ 6 km long, up to 3 km wide and involved a total sedimentary volume of about 0,8 km3. The failure process was characterized by a multiple-event and we assume its tsunami potential to be high. Using the high resolution bathymetric data and the seismic profiles along the slide deposit it was possible to reconstruct the original morphology of the area in order to understand the relation between the slide event and the structural evolution of the ridge. Through the analysis of the data and bibliographic information about the Chilean margin, we analyzed potential trigger mechanisms for the landslide. The Valdes slide is situated on a steep ridge flank. The ridge follows an elongated fault zone running app. parallel to the margin. This fault zone has a dextral component which in combination with the faults elongation results in a compressional regime that is superimposed on

  16. Benthic infaunal communities across the Weddell Sea Basin and South Sandwich Slope, Antarctica

    NASA Astrophysics Data System (ADS)

    Blake, James A.; Narayanaswamy, Bhavani E.

    2004-07-01

    informative because so few species were collected. Two stations in the Weddell Abyssal Basin were the only ones to exhibit a high level of similarity due to two shared polychaetes. Data on reproductive status of some polychaetes suggest that species limited to abyssal depths are reproducing there. Other species with broader depth ranges may be receiving recruits from slope depths. The results suggest that the deep-water infauna in Antarctica is largely endemic, but has some components that occur along other continental margins and adjacent abyssal basins.

  17. Large-scale penetration of Gulf Stream water onto the continental shelf north of Cape Hatteras

    NASA Technical Reports Server (NTRS)

    Gawarkiewicz, Glen; Church, Thomas M.; Luther, George W., III; Ferdelman, Timothy G.; Caruso, Michael

    1992-01-01

    The presence of Gulf Stream water on the continental shelf as much as 60 km north of Cape Hatteras was observed during a hydrographic cruise in the summer of 1990. Gulf Stream water was concentrated at mid-depth between 10 and 30 m and penetrated the shelfbreak front which normally separates the shelf water from slope water and Gulf Stream water. Velocities of Gulf Stream water in the upper 110 m of the water column along the 1000 m isobath indicated a flow of 18 to 25 cm/s directed towards the northwest. Gulf Stream water on the shelf is considered to be associated with low values of fluorescence, transmissivity, and nutrient concentrations relative to adjacent shelf water.

  18. Lomonosov Ridge as a Natural Component of Continental Margin

    NASA Astrophysics Data System (ADS)

    Poselov, V.; Kaminsky, V. D.; Butsenko, V. V.; Grikurov, G. E.

    2010-12-01

    .7 km/; its thickness is 8-9 km on shelf, 5 km under continental slope and gradually increases to 9 km on Lomonosov Ridge. The velocity in upper mantle is approximately 8.0 km/s; the depth to Moho changes from 28 km on the shelf to 22 km on Lomonosov Ridge. Our data demonstrate that principal features of deep crustal structure recognized on Lomonosov Ridge can continuously be traced along its length onto adjacent Siberian shelf, and in orthogonal direction across the periphery of Amundsen Basin. Recognition of these features beneath the Siberian continental slope is somewhat obscured by normal faults but the latter do not appreciably affect the seismic stratigraphy and/or seismic facies characteristics of the distinguished sequences. The northward prolongation of the Kotelny Island horst is articulated by a chain of elevated blocks expressed in the Lomonosov Ridge surface; this offers an additional confirmation of uninterrupted connection between the ridge and the New Siberian Islands shelf. The evidence presented herein suggests an autochtonous position of Lomonosov Ridge which can therefore be regarded a part of submerged natural prolongation of the Russian Arctic landmass.

  19. Subduction-driven recycling of continental margin lithosphere.

    PubMed

    Levander, A; Bezada, M J; Niu, F; Humphreys, E D; Palomeras, I; Thurner, S M; Masy, J; Schmitz, M; Gallart, J; Carbonell, R; Miller, M S

    2014-11-13

    Whereas subduction recycling of oceanic lithosphere is one of the central themes of plate tectonics, the recycling of continental lithosphere appears to be far more complicated and less well understood. Delamination and convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we relate oceanic plate subduction to removal of adjacent continental lithosphere in certain plate tectonic settings. We have developed teleseismic body wave images from dense broadband seismic experiments that show higher than expected volumes of anomalously fast mantle associated with the subducted Atlantic slab under northeastern South America and the Alboran slab beneath the Gibraltar arc region; the anomalies are under, and are aligned with, the continental margins at depths greater than 200 kilometres. Rayleigh wave analysis finds that the lithospheric mantle under the continental margins is significantly thinner than expected, and that thin lithosphere extends from the orogens adjacent to the subduction zones inland to the edges of nearby cratonic cores. Taking these data together, here we describe a process that can lead to the loss of continental lithosphere adjacent to a subduction zone. Subducting oceanic plates can viscously entrain and remove the bottom of the continental thermal boundary layer lithosphere from adjacent continental margins. This drives surface tectonics and pre-conditions the margins for further deformation by creating topography along the lithosphere-asthenosphere boundary. This can lead to development of secondary downwellings under the continental interior, probably under both South America and the Gibraltar arc, and to delamination of the entire lithospheric mantle, as around the Gibraltar arc. This process reconciles numerous, sometimes mutually exclusive, geodynamic models proposed to explain the complex oceanic-continental tectonics of these subduction zones

  20. Geotechnical characteristics and slope stability in the Gulf of Cadiz

    USGS Publications Warehouse

    Lee, H.; Baraza, J.

    1999-01-01

    Sedimentological and geotechnical analyses of thirty-seven core samples from the Gulf of Cadiz continental margin were used to define the regional variability of sediment properties and to assess slope stability. Considering the sediment property data set as a whole, there is an association between grain size, plasticity and water content. Any one of these properties can be mapped regionally to provide an indication of the dominant surface sediment lithology. Based on static sediment strength, a simplified slope stability analysis showed that only steep slopes (> 16??for even the most vulnerable sediment) can fail under static loading conditions. Accordingly, transient loads, such as earthquakes or storms, are needed to cause failure on more moderate slopes. A regional seismic slope stability analysis of the Cadiz margin was performed based on detailed geotechnical testing of four gravity core samples. The results showed that the stability of these slopes under seismic loading conditions depends upon sediment density, the cyclic loading shear strength, the slope steepness, and the regional seismicity. Sediment density and cyclic loading shear strength are dependent upon water content, which can act as a proxy for plasticity and texture effects. Specifically, Sediment in the water content range of 50-56% is most vulnerable to failure under cyclic loading within the Cadiz margin. As a result, for a uniform seismicity over the region, susceptibility to failure during seismic loading conditions increases with increasing slope steepness and is higher if the sediment water content is in the 50-56% range than if it is not. The only sampled zone of failure on the continental slope contains sediment with water content in this critical range. Storm-wave-induced instability was evaluated for the continental shelf. The evaluation showed that a storm having hundreds of waves with a height in the range of 16 m might be capable of causing failure on the shelf. However, no

  1. Limiting equilibrium and liquefaction potential in infinite submarine slopes

    USGS Publications Warehouse

    Denlinger, R.P.; Iverson, R.M.

    1990-01-01

    Stability evaluation of submarine slopes is hampered by the difficulty of making field measurements. Owing to the scarcity of detailed field data, stability is commonly assessed by assuming homogenous infinite slopes with steady seepage. For these conditions, it is necessary to measure only the slope angle, friction angle, cohesion, and pore pressure at some distance into the sediment to evaluate stability. Examination of available data shows that conditions close to those required for liquefaction are necessary for Coulomb failure in many continental shelf areas. This favors long landslide runouts and flow of sediment subsequent to failure. -from Authors

  2. Slope evolution at the Calvert Cliffs, Maryland -- measuring the change from eroding bluffs to stable slopes

    USGS Publications Warehouse

    Herzog, Martha; Larsen, Curtis E.; McRae, Michele

    2002-01-01

    Despite a long history of geomorphic studies, it is difficult to ascertain the time required for slopes to change from near vertical exposures to relatively stable slopes due to inadequate age control. Actively eroding coastal bluffs along the western shore of the Chesapeake Bay provide a key for understanding the centennial-scale development of stable slopes from eroding bluff faces. The Calvert Cliffs are composed of sandy silts, silty sands, and clayey silts of Miocene-age. Active wave erosion at the bluff toes encourages rapid sloughing from bluff faces and maintains slope angles of 70-80 degrees and relatively constant bluff-retreat rates. Naturally stabilized slopes are preserved as a fossil bluff line inland from a prograding cuspate foreland at Cove Point. The foreland is migrating southward at a rate of ca. 1.5 m/yr. As it moves south, it progressively protects bluffs from wave action as new beaches are deposited at their toes. Wave erosion is reinitiated at the northern end of the complex as the landform passes. An incremental record of slope change is preserved along the fossil bluff line. 14C dating of swales between beach ridges shows the complex to span 1700 years of progressive migration history. We hypothesized that slopes would change from steep, eroding faces to low-angle slopes covered with vegetation and sought to document the rate of change. Our team measured slope angles at intervals along the fossil bluff line and dated profiles by interpolating 14C ages of adjacent beach ridges. There was no progressive decrease in slope with age. All slopes along the fossil bluff line were 30-40 degrees with a mean of 35 degrees. Constancy in slope angle suggests that steep, actively eroding bluffs were quickly changed to stable slopes by landslides and slumping once they were protected. Given the accuracy of our age control, we conclude that the time required to attain a stable slope under natural processes is less than one century. This indicates that

  3. NASA Now: SLOPE

    NASA Video Gallery

    Welcome to the SLOPE facility at NASA’s Glenn Research Center in Cleveland, Ohio. In this building, NASA engineers experiment with different wheel designs for lunar rovers. They use a simulated c...

  4. Rock slope stability

    SciTech Connect

    Kliche, C.A.

    1999-07-01

    Whether you're involved in surface mine design, surface mine production, construction, education, or regulation, this is an important new book for your library. It describes the basic rock slope failure modes and methods of analysis--both kinematic and kinetic techniques. Chapters include geotechnical and geomechanical analysis techniques, hydrology, rock slope stabilization techniques, and geotechnical instrumentation and monitoring. Numerous examples, drawings and photos enhance the text.

  5. New Insights into the Sedimentary Dynamics along Carbonate Slopes

    NASA Astrophysics Data System (ADS)

    Wunsch, Marco; Betzler, Christian; Lindhorst, Sebastian; Lüdmann, Thomas; Eberli, Gregor

    2016-04-01

    Hydroacoustic, sedimentological and seismic data of the leeward slope of Great Bahama Bank and the windward slope of the adjacent Cay Sal Bank provide new insights into carbonate platform slope sedimentation. Our study focuses on the diversity and complexity of the slope morphologies and sedimentary patterns which characterize the youngest high-frequency sequence, forming since the Last Glacial Maximum. It is shown that both carbonate platform slopes are dissected by furrows, gullies and channels which are genetically not related. Along the windward slope of Cay Sal Bank, toe of slope erosion, in conjunction with the local tectonic regime is responsible for channel incisions. Our data show that these channels were active during the regression after the last interglacial highstand of sea level. During this regression, downwelling transported platform sediment downslope, which was redistributed along the slope by contour currents. It is also shown that large mass transport complexes at the leeward slope of Great Bahama Bank formed during the last sea level lowstand, probably triggered by the release of pore-water pressure. These MTC created a complex slope morphology of gullies and scarps. These gullies act as a point source by confining the exported platform sediments during the present day sea level highstand.

  6. A Geo-traverse at a Passive Continental Margin: the Tagus Abyssal Plain, West Iberia

    NASA Astrophysics Data System (ADS)

    Afilhado, A.; Matias, L.; Mendes-Victor, L.

    2006-12-01

    transitional domain suggests a layered structure for the lithospheric mantle. The location of the main features and trend changes seen on the magnetic anomaly and the Bouguer anomaly maps are compatible to the seismically defined transition to the oceanic domain. Both magnetic and free air profiles modeling are also consistent to a major rock property contrast at this location. Minor features within the oceanic domain indicate some variability of the mass and magnetic dipoles distribution that might be related to different cross cutting of the segment axis and/or non stationary thermo-mechanical conditions of the sea floor spreading process. From 9.4W to the foot of the continental slope, at 10.2W, in a 65km distance, the Bouguer anomaly strongly increases due both to continental crust thinning and Moho shallowing. Magnetic anomalies having peak to peak values of 30 to 90nT and wave length of at least 30km plus the high density blocks modeled at shallow levels, indicate that dense and magnetic rocks should be present at the continental margin. A large body of exhumed continental mantle at the OCT is hardly supported by the data. Even so, the eastern 35km segment of the abyssal plain adjacent to the continental margin is a mass excess segment, bordered by significant magnetic anomalies, in good agreement to an intruded and partly ultramafic lower transitional crust, as suggested by the seismic data.

  7. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

    Levander, Alan; Bezada, Maximiliano; Niu, Fenglin; Palomeras, Imma; Thurner, Sally; Humphreys, Eugene; Carbonell, Ramon; Gallart, Josep; Schmitz, Michael; Miller, Meghan

    2015-04-01

    Subduction recycling of oceanic lithosphere, a central theme of plate tectonics, is relatively well understood, whereas recycling continental lithosphere is more difficult to recognize, and appears far more complicated. Delamination and localized convective downwelling are two widely recognized processes invoked to explain the removal of lithospheric mantle under or adjacent to orogenic belts. Here we describe another process that can lead to the loss of continental lithosphere adjacent to a subduction zone: Subducting oceanic plates can entrain and recycle lithospheric mantle from an adjacent continent and disrupt the continental lithosphere far inland from the subduction zone. Seismic images from recent dense broadband seismograph arrays in northeastern South America (SA) and in the western Mediterranean show higher than expected volumes of positive anomalies identified as the subducted Atlantic slab under northeastern SA, and the Alboran slab beneath the Gibraltar arc region (GA). The positive anomalies lie under and are aligned with the continental margins at depths greater than 200 km. Closer to the surface we find that the continental margin lithospheric mantle is significantly thinner than expected beneath the orogens adjacent to the subduction zones. The thinner than expected lithosphere extends inland as far as the edges of nearby cratonic cores. These observations suggest that subducting oceanic plates viscously entrain and remove continental mantle lithosphere from beneath adjacent continental margins, modulating the surface tectonics and pre-conditioning the margins for further deformation. The latter can include delamination of the entire lithospheric mantle, as around GA, inferred by results from active and passive seismic experiments. Viscous removal of continental margin lithosphere creates lithosphere-asthenosphere boundary (LAB) topography which can give rise to secondary downwellings under the continental interior far inland from the subduction

  8. Aeromagnetic and gravity investigations of the Coastal Area and Continental Shelf of Liberia, West Africa, and their relation to continental drift

    USGS Publications Warehouse

    Behrendt, John C.; Wotorson, Cletus S.

    1970-01-01

    anomalies exist over two Cretaceous basins in the coastal area; a negative Bouguer anomaly exists over one of the basins southwest of Monrovia, as shown by a marine traverse, suggesting that Cretaceous or younger sedimentary rocks fill these basins also. A 50 to 60 mgal positive Bouguer anomaly area exists along the coast from Sierra Leone to Ivory Coast. This anomaly correlates with mafic granulites in the Monrovia region, where the gradient is too steep to be entirely due to crustal thickening at the continental margin and may be related to tectonic activity associated with the basins. The only major break in this positive anomaly above basement rocks along the entire coast of Liberia is over granite gneiss adjacent to (and presumably underlying) the only onshore basins on the Liberian coast. Three seismic reflection profiles support the interpretation of a substantial section of sedimentary rock offshore. A suggested sequence of events indicates tectonic activity in the periods about 2700, about 2000, and about 550 m.y. B.P.; uplift and exposure of deep crustal rocks; deposition of Paleozoic sediments; intrusion of diabase dikes in inland zones; intrusion of 176 to 192 m.y.-old dikes and sills accompanying separation of Africa and South and North America; block faulting along coast and continental shelf, and active sea-floor spreading; filling of basins in Cretaceous and Tertiary(?) time; basaltic extrusion on spreading sea floor and sedimentation on continental shelf and slope.

  9. Efficient deinterlacing method using simple edge slope tracing

    NASA Astrophysics Data System (ADS)

    Khan, Sajid; Lee, Dongho

    2015-10-01

    This paper presents a low-complexity interpolation method that minimizes image quality losses at edges, which are easily perceivable by the human eye. Deinterlacing, which converts an interlaced video into a progressive video, is a problem in image interpolation that doubles the number of vertical lines. Applying averaging, or any linear algorithm, achieves time-efficient deinterlacing but produces artifacts. However, applying other complex methods tends to reduce unwanted artifacts but at the cost of high computation time. The proposed deinterlacing scheme is based on an algorithm called "edge slope tracing" which simply predicts the slope on the basis of information on adjacent slopes. Predicted slopes are used to perform deinterlacing in slope-based line averaging. The simulation results show that this scheme provides better results and reduces complexity compared to conventional state-of-the-art algorithms.

  10. New High-Resolution Mapping of Submarine Canyons in the Mid-Atlantic Continental Margin

    NASA Astrophysics Data System (ADS)

    ten Brink, U. S.; Chaytor, J. D.; Brothers, D. S.; Twichell, D. C.; Ross, S. W.; Brooke, S.

    2011-12-01

    During June 2011, a BOEMRE/NOAA/USGS -funded multibeam bathymetry survey mapped the upper reaches (<900-m depths) of the Norfolk, Washington, and Baltimore canyons. Combined with existing multibeam bathymetry of the continental slope and rise, the new data provide a detailed view of the sedimentary processes that shaped the mid-Atlantic margin. The shelf-breaching canyon heads are surrounded by two terraces at depths of 95-100 m and 115-125 m in the Norfolk and Washington canyons and at depths of 115-125 m and 135-145 m in the Baltimore canyon. These terraces may represent paleo-shorelines formed during sea level stillstands. The canyon thalwegs within the shelf appear to be filled with sand in accord with old core results. The gradient of their thalweg profile is variable and relatively low across the shelf, slope, and upper rise, in contrast to the concave gradient of most non-shelf breaching canyons in the region. A few of the non-shelf breaching canyons in the mid-Atlantic margin also have relatively low and variable gradients suggesting that they once breached the shelf but are now completely filled. The seaward extensions of the Norfolk, Washington, and Baltimore canyons onto the continental rise are characterized by channels bordered by 100-200 m high levees. In places, these channels meander tightly. The extensions of other canyons onto the rise are either defined by subtle, linear depressions or cannot be traced. Channel-capture by adjacent canyons and channel abandonment originate in the lower slope and were prompted by either landslides or levee breaching. These observations indicate dynamic outer shelf deltas fed by large rivers, which were active at the last glacial maximum (LGM). The river channels on the shelf have been progressively filled during the Holocene. The clear expression of levied channels on the continental rise that extend from shelf-breaching canyons suggests that these canyons were the last ones to deliver turbidity flows to the rise

  11. Deep continental margin reflectors

    USGS Publications Warehouse

    Ewing, J.; Heirtzler, J.; Purdy, M.; Klitgord, Kim D.

    1985-01-01

    In contrast to the rarity of such observations a decade ago, seismic reflecting and refracting horizons are now being observed to Moho depths under continental shelves in a number of places. These observations provide knowledge of the entire crustal thickness from the shoreline to the oceanic crust on passive margins and supplement Consortium for Continental Reflection Profiling (COCORP)-type measurements on land.

  12. Freshly brewed continental crust

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Hayes, J. L.; Caddick, M. J.; Madrigal, P.

    2015-12-01

    Earth's crust is the life-sustaining interface between our planet's deep interior and surface. Basaltic crusts similar to Earth's oceanic crust characterize terrestrial planets in the solar system while the continental masses, areas of buoyant, thick silicic crust, are a unique characteristic of Earth. Therefore, understanding the processes responsible for the formation of continents is fundamental to reconstructing the evolution of our planet. We use geochemical and geophysical data to reconstruct the evolution of the Central American Land Bridge (Costa Rica and Panama) over the last 70 Ma. We also include new preliminary data from a key turning point (~12-6 Ma) from the evolution from an oceanic arc depleted in incompatible elements to a juvenile continental mass in order to evaluate current models of continental crust formation. We also discovered that seismic P-waves (body waves) travel through the crust at velocities closer to the ones observed in continental crust worldwide. Based on global statistical analyses of all magmas produced today in oceanic arcs compared to the global average composition of continental crust we developed a continental index. Our goal was to quantitatively correlate geochemical composition with the average P-wave velocity of arc crust. We suggest that although the formation and evolution of continents may involve many processes, melting enriched oceanic crust within a subduction zone, a process probably more common in the Achaean where most continental landmasses formed, can produce the starting material necessary for juvenile continental crust formation.

  13. Estimating Slope and Level Change in N = 1 Designs

    ERIC Educational Resources Information Center

    Solanas, Antonio; Manolov, Rumen; Onghena, Patrick

    2010-01-01

    The current study proposes a new procedure for separately estimating slope change and level change between two adjacent phases in single-case designs. The procedure eliminates baseline trend from the whole data series before assessing treatment effectiveness. The steps necessary to obtain the estimates are presented in detail, explained, and…

  14. Recent tectonics of the Eastern Sakhalin Slope

    NASA Astrophysics Data System (ADS)

    Rukavishnikova, D.

    2014-12-01

    Eastern Sakhalin slope belongs to an active strike-slip boundary between Amur and Okhotsk plates, which is marked by an active tectonics and seismicity. In the east the slope joints to the Okhotsk Sea deep basins. This continental margin has a complex structural geometry formed by the strike-slip tectonics of the active plate boundary and the deep sea basins formation. Geophysical data in this region show a system of the NS, NE and NW-striking faults in the basement that is covered by sediments of 3-5 km thickness. These faults reflect structure of the strike-slip system at the time of its origin. According to focal mechanism solutions the Sakhalin region is characterized by transition from pure strike-slip motion in the north to compression motion in the south, while Okhotsk Sea deep basins had formed by regional extension. The recent tectonic activity and kinematics of those processes along this continental margin are under discussion We present results of many years research of the upper part of sedimentary cover structure. Bathymetry and seismic data was interpreted using geomorphology and structural geology approach. Based on the results of the research we distinguished recent fault system, including NS, north-east and north-west faults with significant vertical offset. According to faults kinematics we suggest that this system is formed as a surface manifestation of the recent displacement along deep-seated strike-slip faults. While some of them could be connected to reactivation of the faults originated during the deep-basins formation. Obtained data allows us make suggestions about recent tectonic conditions and lithospheric dynamics In the Eastern Sakhalin slope.

  15. Structure of the North American Atlantic Continental Margin.

    USGS Publications Warehouse

    Schlee, J.S.; Klitgord, K.K.

    1986-01-01

    Off E N America, where the structure of the continental margin is essentially constructional, seismic profiles have approximated geologic cross sections up to 10-15km below the sea floor and revealed major structural and stratigraphic features that have regional hydrocarbon potential. These features include a) a block-faulted basement hinge zone; b) a deep, broad, rifted basement filled with clastic sediment and salt; and c) a buried paleoshelf-edge complex that has many forms. The mapping of seismostratigraphic units over the continental shelf, slope, and rise has shown that the margin's developmental state included infilling of a rifted margin, buildup of a carbonate platform, and construction of an onlapping continental-rise wedge that was accompanied by erosion of the slope. -from Authors

  16. Gas hydrates of outer continental margins

    SciTech Connect

    Kvenvolden, K.A. )

    1990-05-01

    Gas hydrates are crystalline substances in which a rigid framework of water molecules traps molecules of gas, mainly methane. Gas-hydrate deposits are common in continental margin sediment in all major oceans at water depths greater than about 300 m. Thirty-three localities with evidence for gas-hydrate occurrence have been described worldwide. The presence of these gas hydrates has been inferred mainly from anomalous lacoustic reflectors seen on marine seismic records. Naturally occurring marine gas hydrates have been sampled and analyzed at about tensites in several regions including continental slope and rise sediment of the eastern Pacific Ocean and the Gulf of Mexico. Except for some Gulf of Mexico gas hydrate occurrences, the analyzed gas hydrates are composed almost exclusively of microbial methane. Evidence for the microbial origin of methane in gas hydrates includes (1) the inverse relation between methane occurence and sulfate concentration in the sediment, (2) the subparallel depth trends in carbon isotopic compositions of methane and bicarbonate in the interstitial water, and (3) the general range of {sup 13}C depletion ({delta}{sub PDB}{sup 13}C = {minus}90 to {minus}60 {per thousand}) in the methane. Analyses of gas hydrates from the Peruvian outer continental margin in particular illustrate this evidence for microbially generated methane. The total amount of methane in gas hydrates of continental margins is not known, but estimates of about 10{sup 16} m{sup 3} seem reasonable. Although this amount of methane is large, it is not yet clear whether methane hydrates of outer continental margins will ever be a significant energy resource; however, these gas hydrates will probably constitute a drilling hazard when outer continental margins are explored in the future.

  17. Geotechnical Properties of Submarine Sediments from Submarine Landslides on the Eastern Australian Continental Margin and Implications for Slide Initiation

    NASA Astrophysics Data System (ADS)

    Clarke, S. L.; Hubble, T.; Airey, D.

    2014-12-01

    Geomechanical test data are presented for 12 gravity cores, up to 5 m long, taken at sites from the upper slope (<1200 m) of the east Australian continental margin in or adjacent to five submarine landslide features. Sediments uniformly consist of olive grey to grey sandy silts (MH-ML), with clay content ranging from 2-12% (using the Unified Soil Classification System - USCS). Total unit weight varies between 14.1 to 17.4 kNm-3, bulk density 715-2065 kgm-3, water content 43-90+%, and specific gravity 2.5-2.74. Sediments present low plasticity, liquid limits 43-63%, and plasticity indices of 8.7-34%. Measured strength values, friction angle (Ф') and apparent cohesion (c'), vary between 30-40°, and 0-10 kPa respectively. One slide-adjacent core, and four within-landslide cores present boundary surfaces located at depths of 0.8 to 2.2 meters below the present-day seafloor that are identified by a sharp, colour-change boundary; small increases in sediment stiffness; slight increases in sediment bulk density of 0.1 gcm-3; and distinct gaps in AMS 14C age of at least 25 ka. Compression testing indicates that the sediment above and below the boundary surface is slightly overconsolidated. Triaxial tests indicate a significant increase in the brittleness of the shear response of the sediment with increasing vertical stress, which would cause a progressive increase of pore pressure if the sediment was subjected to cyclic (earthquake) loading. The boundary surfaces are interpreted to represent detachment surfaces or slide plane surfaces. Slope stability models based on classical soil mechanics and measured sediment shear-strengths indicate that the upper slope sediments should be stable. However, multibeam bathymetry data reveal that many upper slope landslides occur across the margin and that submarine landsliding is a common process. We infer from these results that: a) the margin experiences seismic events that act to destabilise the slope sediments, and/or b) an

  18. A numerical investigation of continental collision styles

    NASA Astrophysics Data System (ADS)

    Ghazian, Reza Khabbaz; Buiter, Susanne J. H.

    2013-06-01

    Continental collision after closure of an ocean can lead to different deformation styles: subduction of continental crust and lithosphere, lithospheric thickening, folding of the unsubducted continents, Rayleigh-Taylor (RT) instabilities and/or slab break-off. We use 2-D thermomechanical models of oceanic subduction followed by continental collision to investigate the sensitivity of these collision styles to driving velocity, crustal and lithospheric temperature, continental rheology and the initial density difference between the oceanic lithosphere and the asthenosphere. We find that these parameters influence the collision system, but that driving velocity, rheology and lithospheric (rather than Moho and mantle) temperature can be classified as important controls, whereas reasonable variations in the initial density contrast between oceanic lithosphere and asthenosphere are not necessarily important. Stable continental subduction occurs over a relatively large range of values of driving velocity and lithospheric temperature. Fast and cold systems are more likely to show folding, whereas slow and warm systems can experience RT-type dripping. Our results show that a continent with a strong upper crust can experience subduction of the entire crust and is more likely to fold. Accretion of the upper crust at the trench is feasible when the upper crust has a moderate to weak strength, whereas the entire crust can be scraped-off in the case of a weak lower crust. We also illustrate that weakening of the lithospheric mantle promotes RT-type of dripping in a collision system. We use a dynamic collision model, in which collision is driven by slab pull only, to illustrate that adjacent plates can play an important role in continental collision systems. In dynamic collision models, exhumation of subducted continental material and sediments is triggered by slab retreat and opening of a subduction channel, which allows upward flow of buoyant materials. Exhumation continues

  19. SLOPE--a real-time ECG data compressor.

    PubMed

    Tai, S C

    1991-03-01

    An ECG sampled at a rate of 250 samples s-1 or more produces a large amount of redundant data that are difficult to store and transmit. In the paper, a real-time ECG data compressor, SLOPE, is presented. SLOPE considers some adjacent samples as a vector, and this vector is extended if the coming sample falls in a fan spanned by this vector and a threshold angle; otherwise, it is delimited as a linear segment. By this means SLOPE repeatedly delimits linear segments of different lengths and different slopes. The Huffman codes for the parameters to describe this linear segment are transmitted for that linear segment. SLOPEa, which is a slightly modified version of SLOPE, is used to compress ambulatory ECG data. All the operations used by SLOPE and SLOPEa are simple integer operations, both SLOPE and SLOPEa being real-time compressors. Experimental results show that an average of 192 bits per channel per second (bpcs) for each ECG signal is obtained by SLOPE and an average of 148 bpcs for each ECG signal is obtained by SLOPEa. PMID:1857123

  20. The Probable Whole of Slope Submarine Landslides of Southeast Queensland, Australia.

    NASA Astrophysics Data System (ADS)

    Hubble, T.

    2015-12-01

    A research cruise aboard the RV Southern Surveyor (SS2013-V01) conducted in January 2013 offshore east Australia collected regional bathymetric data for the seabed of the continental margin of southern Queensland for the seabed bounded by Noosa Heads in the south and Indian Head, Fraser Island in the north. This newly mapped area presents a particularly steep portion of continental slope (5o to 10 o) that presents numerous submarine landslides, including two 'whole-of-slope' features (The Wide Bay Canyon, and Inskip Slides. The slope is also dissected by three large submarine canyons offshore northern Fraser Island, Wide Bay and Noosa Heads (i.e. the Fraser Canyons, the Wide Bay Canyon and the Noosa Canyon). Dredge and core samples were collected from slide scars in the northern, central and southern areas of the bathymetric survey area. The initial examination of the area's bathymetry, the core and dredge sample sedimentology, and determination of biostratigraphic ages for these sediment samples indicates that the larger, submarine slides present in this study area have probably been shed from the slope since the late Pliocene and that canyon incision is currently active on this portion of the slope. In one case, canyon incision is partly responsible for generating slides due to undercutting and removal of the toe of the slope. Slope sediments are dominantly comprised of hemipelagic muds but the presence of massive coarse sands and graded sands in some cores above erosion surfaces that cut into slope mud units is interpreted to indicate that areas of the southern Queensland continental slope are probably subjected to abrasion by grain-flows and turbidites comprised of shelf-derived sands and upper slope sediment. The results from this voyage confirms and extends previous work on the southeastern Australian continental margin that indicates that sediment transport from the shelf to deep water on this margin is dominated by gravity mass transport and that the margin

  1. The Antarctic Slope Current near 30°E

    NASA Astrophysics Data System (ADS)

    Dong, Jun; Speer, Kevin; Jullion, Loic

    2016-02-01

    The Antarctic Slope Current flows westward above the continental slope of Antarctica, entering the Weddell Sea near 30°E and supplying dense water to the deep overturning cell there, and contributing to global Antarctic Bottom Water formation. Observations from the 2008 I6S hydrographic section are used to investigate the strength of the Slope Current near 30°E. A prominent topographic feature, the Gunnerus Bank, diverts the Slope Current upstream of this longitude, and has a large effect on the current's structure, splitting it into a coastal and offshore component. The bank also enhances water mass mixing and lateral exchange across the slope. As part of the 2008 occupation, an additional line was made along the crest of the bank, forming a closed volume over the western side. By combining hydrographic and Lowered Acoustic Doppler Current Profiler measurements in this box using an inverse method, the Slope Current transport is estimated to be 9.6 ± 2.3 Sv; the transport associated with the Antarctic Slope Front is 4.0 ± 0.3 Sv, of which 1.8 ± 0.3 Sv enters the Weddell Gyre as recently formed dense water.

  2. Geology and petroleum potential of Shumagin continental margin, western Gulf of Alaska

    SciTech Connect

    Bruns, T.R.; Von Huene, R.; Culotta, R.D.; Lewis, S.D.; Ladd, J.W.

    1986-07-01

    Interpretations of multichannel seismic reflection data indicate that the Shumagin continental margin seaward of the Border Ranges fault is underlain by two major seismic sequences, separated by an erosional unconformity beneath the shelf and by the time-correlative conformity seaward. Rocks above the unconformity are late Miocene and younger. Rocks below the unconformity can be as young as middle Miocene beneath the outer shelf and slope, seaward of a paleoshelf break. However, beneath the shelf they are primarily Late Cretaceous turbidites of the Shumagin Formation and Paleocene granodiorite. Late Miocene and younger structures of the Shumagin margin include Shumagin, Sanak, and Unimak basins and Unimak Ridge, a midslope structural high. Strata in Sanak and Unimak basins were deposited on a subsiding outer shelf and slope, and trapped behind Unimak Ridge and its now-buried structural continuation. Sanak and Unimak basins are in part bounded by northwest-trending extensional faults that parallel both the early Tertiary Beringian margin and a transverse tectonic boundary that segments the fore-arc. These faults may have developed during collapse and extension along the southeastward continuation of the old Beringian margin, analogous to the processes that created the Bering Shelf basins. The most promising areas of the Shumagin margin for petroleum potential are Sanak, and Unimak basins, which contain strata 8 and 4.5 km thick, respectively, and beneath the outer shelf and slope. Paleogene source rocks like those on the adjacent Alaska Peninsula may be preserved offshore, seaward of the inferred paleoshelf break. Reservoir rocks might have formed from granitic-rich erosional products derived during Oligocene and Miocene erosion of the shelf plutons.

  3. Linking margin morphology to sedimentary processes along the US East Coast passive continental margin

    NASA Astrophysics Data System (ADS)

    Brothers, D. S.; ten Brink, U. S.; Andrews, B.; Twichell, D.

    2010-12-01

    The morphology of the US East Coast continental slope and rise has a surprising amount of along-margin variation. Multibeam bathymetry datasets that cover the slope and rise from Cape Hatteras to Georges Bank provide a unique opportunity to analyze both first-order and higher-order morphologies, including submarine canyons, landslides, slumps and sedimentary bedforms. Using the morphological characterization coupled with seismic and core data, we hope to better understand how ancient and modern sedimentary processes control the shape of the margin. As a first step, the margin bathymetry was subdivided into 20 shelf-perpendicular regions from which several statistical parameters were analyzed. Within each region, the slope gradient was computed separately for down-slope and across-slope aspect directions. Distribution curves in each region for down- and across-slope gradients and seafloor roughness as functions of depth were grouped according to their statistical similarities. Four basic groups emerge and each approximately corresponds to known regions of Quaternary glacial, fluvial, current-controlled and gravity-driven sedimentary transport. In the second part of the study, published lithologic and chronostratigraphic frameworks of this margin were used to examine the relationship between seafloor morphology and the underlying geology. Along the upper continental rise, thick Quaternary deposits appear to have a strong influence on the short- and long-wavelength variation in rise topography, revealing a complex interplay between down-slope and along-slope sediment transport. Despite the close correlation between continental slope morphology and Quaternary environmental conditions, initial results suggest that the underlying, older, stratigraphy also plays a primary role. Along the continental slope, Quaternary processes appear to control the relief of slope-confined canyons and other short-wavelength (<5 km) topography, but the first order morphology of the slope

  4. Structure and petroleum potential of the Yakutat segment of the northern Gulf of Alaska continental margin

    SciTech Connect

    Bruns, T.R.

    1983-01-01

    This report discusses the structure, geologic history, and petroleum potential of the Yakutat segment, the part of the continental margin between Cross Sound and Icy Bay, northern Gulf of Alaska. As part of a program of geological and geophysical investigations of the continental margin in the northern Gulf of Alaska, the US Geological Survey collected multichannel seismic reflection data along about 2000 km of tracklines in the study area during 1975, 1977, and 1978. In addition, dredge samples from the continental slope were acquired during the 1977, 1978, and 1979 field seasons. The first part of this paper presents an interpretation of the seismic reflection and refraction data, including structure contour maps, isopach maps, and interpreted seismic sections; the second part is a discussion of the implications for petroleum potential. The primary area of interest is the continental shelf and slope, but some data from strata at the base of the slope are also included.

  5. Sediment deformation related to the submarine failure in northeastern South China Sea continental margin

    NASA Astrophysics Data System (ADS)

    Chiu, J.

    2012-12-01

    In northeastern South China Sea continental margin, geological structure is complex due to the passive continental margin meets the Taiwan mountain belt. Submarine slope failures, turbidity flows and so on are the main sedimentary processes in this continental slope, but these processes play different roles along the passive continental slope. So Chirp subbottom profiles, include analog and digital data, and cores collected in this region were analyzed to study the difference of sedimentation of the Late Quaternary. We found that more sediment deformations near seafloor, e.g. sediment layer pulled by sliding block and formed a shape like "pinch-out", were observed in the west region of the study area. This phenomenon could be related to finer sediments from mainland China, comparing with coarser sediments from Taiwan mountain belt deposited in the east region of the study area.

  6. Basins in ARC-continental collisions

    USGS Publications Warehouse

    Draut, Amy E.; Clift, Peter D.

    2012-01-01

    Arc-continent collisions occur commonly in the plate-tectonic cycle and result in rapidly formed and rapidly collapsing orogens, often spanning just 5-15 My. Growth of continental masses through arc-continent collision is widely thought to be a major process governing the structural and geochemical evolution of the continental crust over geologic time. Collisions of intra-oceanic arcs with passive continental margins (a situation in which the arc, on the upper plate, faces the continent) involve a substantially different geometry than collisions of intra-oceanic arcs with active continental margins (a situation requiring more than one convergence zone and in which the arc, on the lower plate, backs into the continent), with variable preservation potential for basins in each case. Substantial differences also occur between trench and forearc evolution in tectonically erosive versus tectonically accreting margins, both before and after collision. We examine the evolution of trenches, trench-slope basins, forearc basins, intra-arc basins, and backarc basins during arc-continent collision. The preservation potential of trench-slope basins is low; in collision they are rapidly uplifted and eroded, and at erosive margins they are progressively destroyed by subduction erosion. Post-collisional preservation of trench sediment and trench-slope basins is biased toward margins that were tectonically accreting for a substantial length of time before collision. Forearc basins in erosive margins are usually floored by strong lithosphere and may survive collision with a passive margin, sometimes continuing sedimentation throughout collision and orogeny. The low flexural rigidity of intra-arc basins makes them deep and, if preserved, potentially long records of arc and collisional tectonism. Backarc basins, in contrast, are typically subducted and their sediment either lost or preserved only as fragments in melange sequences. A substantial proportion of the sediment derived from

  7. 30 CFR 282.6 - Disclosure of data and information to an adjacent State.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 2 2010-07-01 2010-07-01 false Disclosure of data and information to an adjacent State. 282.6 Section 282.6 Mineral Resources MINERALS MANAGEMENT SERVICE, DEPARTMENT OF THE INTERIOR OFFSHORE OPERATIONS IN THE OUTER CONTINENTAL SHELF FOR MINERALS OTHER THAN OIL, GAS, AND...

  8. Geologic development and characteristics of the continental margins, Gulf of Mexico. Research report, 1983-1986

    SciTech Connect

    Coleman, J.M.; Prior, D.B.; Roberts, H.H.

    1986-01-01

    The continental slope of the Gulf Basin covers more than 500,000 sq km and consists of smooth and gently sloping surfaces, prominent escarpments, knolls, intraslope basins, and submarine canyons and channels. It is an area of extremely diverse topographic and sedimentologic conditions. The slope extends from the shelf break, roughly at the 200 m isobath, to the upper limit of the continental rise, at a depth of 2800 m. The most-complex province in the basin, and the one of most interest to the petroleum industry, is the Texas-Louisiana slope, occupying 120,000 sq km and in which bottom slopes range from < 1 deg to > 20 deg around the knolls and basins. The near-surface geology and topography of the slope are functions of the interplay between episodes of rapid shelf-edge and slope progradation and contemporaneous modification of the depositional sequence by diapirism. Development of discrete depo-centers throughout the Neogene results in rapid shelf-edge progradation, often in excess of 15-20 km/my. This rapid progradation of the shelf edge leads to development of thick wedges of sediment accumulation on the continental slope. Oversteeping, high pore pressures in rapidly deposited soft sediments and changes in eustatic sea level cause subaqueous slope instabilities such as landsliding and debris flows. Large scale features such as shelf edge separation scars and landslide related canyons often results from such processes.

  9. Synchronous oceanic spreading and continental rifting in West Antarctica

    NASA Astrophysics Data System (ADS)

    Davey, F. J.; Granot, R.; Cande, S. C.; Stock, J. M.; Selvans, M.; Ferraccioli, F.

    2016-06-01

    Magnetic anomalies associated with new ocean crust formation in the Adare Basin off north-western Ross Sea (43-26 Ma) can be traced directly into the Northern Basin that underlies the adjacent morphological continental shelf, implying a continuity in the emplacement of oceanic crust. Steep gravity gradients along the margins of the Northern Basin, particularly in the east, suggest that little extension and thinning of continental crust occurred before it ruptured and the new oceanic crust formed, unlike most other continental rifts and the Victoria Land Basin further south. A preexisting weak crust and localization of strain by strike-slip faulting are proposed as the factors allowing the rapid rupture of continental crust.

  10. Terra Sirenum Slope

    NASA Technical Reports Server (NTRS)

    2004-01-01

    16 July 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the layered rocks and boulders exposed on the wall of a trough in the Terra Sirenum region. The layers that erode to produce large boulders are harder and more resistant to weathering and erosion than those that do not. The slope is located near 25.8oS, 139.8oW. The image covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  11. On the Evolution of Glaciated Continental Margins

    NASA Astrophysics Data System (ADS)

    Sverre Laberg, Jan; Rydningen, Tom Arne; Safronova, Polina A.; Forwick, Matthias

    2016-04-01

    Glaciated continental margins, continental margins where a grounded ice sheet repeatedly has been at or near the shelf break, are found at both northern and southern high-latitudes. Their evolution are in several aspects different from their low-latitude counterparts where eustatic sea-level variations possess a fundamental control on their evolution and where fluvial systems provide the main sediment input. From studies of the Norwegian - Barents Sea - Svalbard and NE Greenland continental margins we propose the following factors as the main control on the evolution of glaciated continental margins: 1) Pre-glacial relief controlling the accommodation space, 2) Ice sheet glaciology including the location of fast-flowing ice streams where source area morphology exerts a fundamental control, 3) Composition of the glacigenic sediments where the clay content in previous studies have been found to be important, and 4) Sea-level controlled both by eustacy and isostacy. From three case studies, 1) the western Barents Sea, 2) part of the North Norwegian (Troms), and 3) the Mid-Norwegian margin, the influence on these factors for the sea-floor morphology, sedimentary processes of the continental slope - deep sea and continental margin architecture are discussed. The pre-glacial relief of the mid-Norwegian and Troms margins relates to the onset of rifting and plate break-up from the early Cenozoic while for the SW Barents Sea, plate shear was followed by rifting. A wide zone of extended continental crust occurs offshore mid-Norway while this zone is much narrower offshore Troms leading to a more pronounced pre-glacial relief. Regarding sediment delivery and ice sheet glaciology the western Barents Sea exemplifies very high sediment input corresponding to an estimated average erosion of the source area of ~0.4 mm/yr (SW Barents Sea), much of which is related to subglacial erosion of Mesozoic - Cenozoic sedimentary rocks from large paleo-ice streams. The mid-Norwegian margin

  12. Geomorphic characterization of the U.S. Atlantic continental margin

    USGS Publications Warehouse

    Brothers, Daniel S.; ten Brink, Uri S.; Andrews, Brian D.; Chaytor, Jason D.

    2013-01-01

    The increasing volume of multibeam bathymetry data collected along continental margins is providing new opportunities to study the feedbacks between sedimentary and oceanographic processes and seafloor morphology. Attempts to develop simple guidelines that describe the relationships between form and process often overlook the importance of inherited physiography in slope depositional systems. Here, we use multibeam bathymetry data and seismic reflection profiles spanning the U.S. Atlantic outer continental shelf, slope and rise from Cape Hatteras to New England to quantify the broad-scale, across-margin morphological variation. Morphometric analyses suggest the margin can be divided into four basic categories that roughly align with Quaternary sedimentary provinces. Within each category, Quaternary sedimentary processes exerted heavy modification of submarine canyons, landslide complexes and the broad-scale morphology of the continental rise, but they appear to have preserved much of the pre-Quaternary, across-margin shape of the continental slope. Without detailed constraints on the substrate structure, first-order morphological categorization the U.S. Atlantic margin does not provide a reliable framework for predicting relationships between form and process.

  13. Meso and small-scale variations of 210Pb fluxes on the Northwestern Mediterranean continental margins

    NASA Astrophysics Data System (ADS)

    Radakovitch, O.; Sanchez-Cabeza, J. A.; Abassi, A.; Masqué, P.; Heussner, S.

    2003-05-01

    210Pb was analysed in samples collected from (16) sediment traps, deployed during 1 year on the Northwestern Mediterranean continental margins, within the framework of the (MTP I)-EUROMARGE-NB programme. The traps were moored within (5) submarine canyons and their adjacent open slope, corresponding to contrasting conditions of particle inputs (fluxes and constituents). The major meso-scale observation (at the margin) is the variation in 210Pb fluxes along the slope, increasing by a factor of 2-3 between the entrance and the exit of the slope, in relation to the general (water) circulation. At a smaller scale (canyon), the 210Pb fluxes showed trends which were common to the various sites, i.e. a seaward decrease at 500 m depth and an increase, with depth, in the canyons. All these features are related to mass flux variations, except for periods with huge mass fluxes, when 210Pb fluxes reached a constant value. 210Pb activities decreased with increasing mass flux; then did not show clear relationship with the concentration of the major constituents of the flux. 210Pb fluxes, obtained from the traps were mainly in excess of the theoretical 210Pb flux, available in the overlying water column. Since 210Pb inventories, measured on the basis of the shelf and slope bottom sediments, were also in excess in relation to the available flux. The margin, as a whole, appears as a sink for 210Pb. This boundary-scavenging process appears to be controlled completely by the mass flux of particles. Differences were observed between 210Pb fluxes in the near-bottom traps and in the underlying sediments; there can be linked to mass flux and/or morphobathymetry (the trap flux is higher than the sediment flux in the canyon, but lower on the open slope). Overall, the differences were not in excess of 50%, confirming good representation of data collected by the sediment traps. However, this finding must be taken into account when comparing organic carbon or other constituent fluxes, between

  14. Continental rift jumps

    NASA Astrophysics Data System (ADS)

    Wood, Charles A.

    1983-05-01

    Continental rift jumps, analogous to jumps of oceanic spreading ridges, are here proposed to be common. Good examples exist in Iceland and Afar (both transitional from ridge to rift jumps), West Africa (Benue Trough and Cameroon Volcanic Line), and Kenya. Indeed, the Kenya rift appears to have jumped c. 100 km eastward c. 10 m.y. ago and is currently jumping further to the east. Possible jumps exist in the Baikal rift, the Limagne-Bresse rift pair, and parallel to ancient continental margins (e.g., the Triassic basins of the eastern U.S. to Baltimore Canyon and Georges Bank). Continental rifts jump distances that are approximately equal to local lithosphere thickness, suggesting that jumped rifts are controlled by lithosphere fracturing, but there appears to be no reason for the fracturing except migration of hot spots.

  15. Influence of the Atlantic inflow and Mediterranean outflow currents on late Quaternary sedimentary facies of the Gulf of Cadiz continental margin

    USGS Publications Warehouse

    Nelson, C.H.; Baraza, J.; Maldonado, A.; Rodero, J.; Escutia, C.; Barber, J.H., Jr.

    1999-01-01

    The late Quaternary pattern of sedimentary facies on the Spanish Gulf of Cadiz continental shelf results from an interaction between a number of controlling factors that are dominated by the Atlantic inflow currents flowing southeastward across the Cadiz shelf toward the Strait of Gibraltar. An inner shelf shoreface sand facies formed by shoaling waves is modified by the inflow currents to form a belt of sand dunes at 10-20 m that extends deeper and obliquely down paleo-valleys as a result of southward down-valley flow. A mid-shelf Holocene mud facies progrades offshore from river mouth sources, but Atlantic inflow currents cause extensive progradation along shelf toward the southeast. Increased inflow current speeds near the Strait of Gibraltar and the strong Mediterranean outflow currents there result in lack of mud deposition and development of a reworked transgressive sand dune facies across the entire southernmost shelf. At the outer shelf edge and underlying the mid-shelf mud and inner shelf sand facies is a late Pleistocene to Holocene transgressive sand sheet formed by the eustatic shoreline advance. The late Quaternary pattern of contourite deposits on the Spanish Gulf of Cadiz continental slope results from an interaction between linear diapiric ridges that are oblique to slope contours and the Mediterranean outflow current flowing northwestward parallel to the slope contours and down valleys between the ridges. Coincident with the northwestward decrease in outflow current speeds from the Strait there is the following northwestward gradation of contourite sediment facies: (1) upper slope sand to silt bed facies, (2) sand dune facies on the upstream mid-slope terrace, (3) large mud wave facies on the lower slope, (4) sediment drift facies banked against the diapiric ridges, and (5) valley facies between the ridges. The southeastern sediment drift facies closest to Gibraltar contains medium-fine sand beds interbedded with mud. The adjacent valley floor

  16. Deep-sea drilling on the upper continental rise off New Jersey, DSDP Sites 604 and 605

    NASA Astrophysics Data System (ADS)

    van Hinte, Jan E.; Wise, Sherwood W., Jr.; Biart, Brian N. M.; Mitchener Covington, J.; Dunn, Dean A.; Haggerty, Janet A.; Johns, Mark W.; Meyers, Philip A.; Moullade, Michel R.; Muza, Jay P.; Ogg, James G.; Okamura, Makoto; Sarti, Massimo; von Rad, Ulrich

    1985-06-01

    Deep Sea Drilling Project Sites 604 and 60S on the upper continental rise are the first of a series of cored holes along the “New Jersey transect” which, when completed, will provide the first comprehensive dipwise suite of drill holes across a passive margin from the coastal plain to the abyssal plain. Our drilling results document the age of important seismic sequence boundaries and allow their correlation with wells on the continental shelf and slope as well as with the regional oceanic seismic stratigraphy. Hole 605,156 km (97 mi) southeast of Atlantic City, New Jersey, and drilled 816.7 m down to mid-Maestrichtian limestones, penetrated a near-complete Cretaceous/Tertiary boundary section overlain by a 200-m expanded Paleocene sequence. Unusually high amounts of terrigenous silts and glauconite are present at the boundary and immediately above. Among the several hypotheses discussed, we suggest that the terrigenous silts and glauconite may represent a high-energy event such as a tsunami caused by a Cretaceous/Tertiary impact. Site 604, 5 km (3 mi) seaward of Site 605, was terminated in upper Miocene glauconitic sands and debris flows at 294.5 m by unstable hole conditions. These sediments contain shelf-derived gravels and exotic blocks of Eocene chalk (up to 50 cm across) eroded from bedrock that is today widely exposed on the adjacent slope. Our drilling results show that denudation of the Eocene units was not limited to the Oligocene Au erosional event, but that major loss occurred during late Miocene and later glacial sea-level lowstands.

  17. Slope stability and stabilization methods

    SciTech Connect

    Abramson, L.W.; Lee, T.S.; Boyce, G.M.; Sharma, S.S.

    1995-12-01

    Slope stability can be a major problem during the construction of surface facilities. Cutting into existing ground disturbs the mechanics of the surrounding area, which can result in landslides and rock falls. This practical reference gives you the comprehensive information you need for slope stability analysis, suitable methods of analysis with and without the use of computers, and examples of common stability problems and stabilization methods for cuts and fills. It includes detailed discussions of methods used in slope stability analysis, including the Ordinary Method of Slices, Simplified Janbu Method, Simplified Bishop Method, Spencer`s Method, other limit equilibrium methods, numerical methods, total stress analysis, effective stress analysis, and the use of computer programs to solve problems. Chapters include: General Slope Stability Concepts; Engineering Geology Principles; Groundwater Conditions; Geologic Site Exploration; Laboratory Testing Interpretation; Slope Stability Concepts; Slope Stabilization Methods; and Design, Construction and Maintenance.

  18. The Continental Crust.

    ERIC Educational Resources Information Center

    Burchfiel, B. Clark

    1983-01-01

    Continental crust underlies the continents, their margins, and also small shallow regions in oceans. The nature of the crust (much older than oceanic crust) and its dynamics are discussed. Research related to and effects of tectonics, volcanism, erosion, and sedimentation on the crust are considered. (JN)

  19. Continental Flood Basalts

    NASA Astrophysics Data System (ADS)

    Continental flood basalts have been receiving considerable scientific attention lately. Recent publications have focused on several particular flood-basalt provinces (Brito-Arctic, Karoo, Parana', Deccan, and Columbia Plateau), and much attention has been given to the proposed connection between flood-basalt volcanism, bolide impacts, and mass extinctions. The editor of Continental Flood Basalts, J. D. Macdougall, conceived the book to assemble in a single volume, from a vast and scattered literature, an overview of each major post-Cambrian flood-basalt province.Continental Flood Basalts has 10 chapters; nine treat individual flood-basalt provinces, and a summary chapter compares and contrasts continental flood-basalts and mid-oceanic ridge basalts. Specifically, the chapters address the Columbia River basalt, the northwest United States including the Columbia River basalt, the Ethiopian Province, the North Atlantic Tertiary Province, the Deccan Traps, the Parana' Basin, the Karoo Province, the Siberian Platform, and Cenozoic basaltic rocks in eastern China. Each chapter is written by one or more individuals with an extensive background in the province.

  20. Continental drift before 1900.

    PubMed

    Rupke, N A

    1970-07-25

    The idea that Francis Bacon and other seventeenth and eighteenth century thinkers first conceived the notion of continental drift does not stand up to close scrutiny. The few authors who expressed the idea viewed the process as a catastrophic event. PMID:16057953

  1. Geology of the Continental Margin Beneath Santa Monica Bay, Southern California, from Small-Airgun, Seismic-Reflection Data

    NASA Astrophysics Data System (ADS)

    Fisher, M. A.; Normark, W. R.; Bohannon, R. G.; Sliter, R. W.; Calvert, A. J.

    2001-12-01

    Small-airgun, multichannel-seismic-reflection (MCS) data collected in Santa Monica Bay reveal the geologic structure of the continental shelf and of the adjacent basin slope and deep-water basins. The Palos Verdes fault under the northern, shallow part of the bay cannot be identified in seismic-reflection data, even though many studies suggest its presence. This fault neither offsets the seafloor nor cuts through an undeformed sediment apron. Other major faults, such as the east-west Dume fault under the northern part of Santa Monica Bay, show evidence for recent activity. Tomographic-velocity data, derived from arrivals along the LARSE, deep-crustal MCS streamer, show that metamorphic rocks, probably the Catalina schist, underlie Santa Monica Bay and the deep-water Santa Monica basin to the south. The Santa Monica canyon marks a significant change in deformation of the lower slope of the Santa Monica Basin. North and northwest of this canyon, the slope is underlain by a little-deformed sediment apron; the main apron structures are two anticlines that extend toward Point Dume and are cored by reverse or thrust faults. Southeast of the canyon, lower-slope rocks are deformed by a complex zone of strike-slip, normal and reverse faults. The San Pedro bathymetric escarpment rises abruptly along the southeast side of Santa Monica Canyon. Structures underpinning this escarpment steepen progressively southeastward; they cut downward into basement rocks, and merge with the San Pedro Basin fault zone, which is nearly vertical and possibly strike-slip. The escarpment and its attendant structures extend for 60 km along the margin, separating the continental shelf from the mid-bathyal Santa Monica and San Pedro basins. The Santa Monica Basin, the more extensive of the two, contains about 1.5 km of turbidite fill that is deformed only near the northern basin margin. Data from ODP site 1015 indicate that this fill is most likely no older than Quaternary, and possibly no older

  2. Convective Removal of Continental Margin Lithosphere at the Edges of Subducting Oceanic Plates

    NASA Astrophysics Data System (ADS)

    Levander, A.; Bezada, M. J.; Palomeras, I.; Masy, J.; Humphreys, E.; Niu, F.

    2013-12-01

    Although oceanic lithosphere is continuously recycled to the deeper mantle by subduction, the rates and manner in which different types of continental lithospheric mantle are recycled is unclear. Cratonic mantle can be chemically reworked and essentially decratonized, although the frequency of decratonization is unclear. Lithospheric mantle under or adjacent to orogenic belts can be lost to the deeper mantle by convective downwellings and delamination phenomena. Here we describe how subduction related processes at the edges of oceanic plates adjacent to passive continental margins removes the mantle lithosphere from beneath the margin and from the continental interior. This appears to be a widespread means of recycling non-cratonic continental mantle. Lithospheric removal requires the edge of a subducting oceanic plate to be at a relatively high angle to an adjacent passive continental margin. From Rayleigh wave and body wave tomography, and receiver function images from the BOLIVAR and PICASSO experiments, we infer large-scale removal of continental margin lithospheric mantle from beneath 1) the northern South American plate margin due to Atlantic subduction, and 2) the Iberian and North African margins due to Alboran plate subduction. In both cases lithospheric mantle appears to have been removed several hundred kilometers inland from the subduction zones. This type of ';plate-edge' tectonics either accompanies or pre-conditions continental margins for orogenic activity by thinning and weakening the lithosphere. These processes show the importance of relatively small convective structures, i.e. small subducting plates, in formation of orogenic belts.

  3. CDP seismic sections of the western Beaufort continental margin

    USGS Publications Warehouse

    Eittreim, S.; Grantz, A.

    1979-01-01

    The continental rise, slope, and shelf in the Beaufort Sea off northern Alaska were surveyed with 5600 km of common-depth-point (CDP) seismic data by the U.S. Geological Survey in 1977. The lower continental rise consists of a wedge of at least 4.5 km of low-velocity, generally flat-lying, parallel-bedded sediments. Slump-related diapiric folds, probably cored by shale, occur on the upper rise and lower slope. The observed minimum depth to oceanic basement in the Canada Basin requires an age for this basin of at least 120 m.y., assuming it to be floored by oceanic crust with a subsidence history similar to that of the Atlantic and Pacific oceans. ?? 1979.

  4. The geomorphic evolution of slopes and sediment chutes on forereefs

    NASA Astrophysics Data System (ADS)

    Hall, Douglas B.

    1999-03-01

    Frequent slope failures of the forereef dropoff occur in living coral reefs on the island of Bonaire in the southern Caribbean. Topographic profiles of ten sites were taken perpendicular to shore, followed by an estimation of coral ages ( M. annularis) along the topographic profiles. The coral ages were estimated from published rates of growth and sizes of the sampled corals. Comparisons of coral age and adjacent slope angle indicated that the steeper slopes are older and that mass failure of the slope reduces the steepness of the forereef front and destroys the coral community along the disturbed slope. Slopes grow until reaching a critical steepness, after which underwater sliding of the over-steepened forereef front results. In observed slides, the mechanical weakness in the reef structure that facilitates a slide failure was the result of a weak mud and coral rubble layer deposited 2 m below the living coral cover. The remaining slide scarp evolves into a sediment chute that conveys the resulting flow of biogenic sands from the shallow forereef terrace down the forereef edge. Because of the constant flow of sand down these channels, no corals can recolonize the sediment chutes and the chutes become stable topographic features. In addition, these indentations in the forereef front also serve as channels for the vertical density mixing of water of varying salinities and temperatures.

  5. 46 CFR 148.445 - Adjacent spaces.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 46 Shipping 5 2013-10-01 2013-10-01 false Adjacent spaces. 148.445 Section 148.445 Shipping COAST... THAT REQUIRE SPECIAL HANDLING Additional Special Requirements § 148.445 Adjacent spaces. When... following requirements must be met: (a) Each space adjacent to a cargo hold must be ventilated by...

  6. 46 CFR 148.445 - Adjacent spaces.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 46 Shipping 5 2014-10-01 2014-10-01 false Adjacent spaces. 148.445 Section 148.445 Shipping COAST... THAT REQUIRE SPECIAL HANDLING Additional Special Requirements § 148.445 Adjacent spaces. When... following requirements must be met: (a) Each space adjacent to a cargo hold must be ventilated by...

  7. 46 CFR 148.445 - Adjacent spaces.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 46 Shipping 5 2012-10-01 2012-10-01 false Adjacent spaces. 148.445 Section 148.445 Shipping COAST... THAT REQUIRE SPECIAL HANDLING Additional Special Requirements § 148.445 Adjacent spaces. When... following requirements must be met: (a) Each space adjacent to a cargo hold must be ventilated by...

  8. 46 CFR 148.445 - Adjacent spaces.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 46 Shipping 5 2011-10-01 2011-10-01 false Adjacent spaces. 148.445 Section 148.445 Shipping COAST... THAT REQUIRE SPECIAL HANDLING Additional Special Requirements § 148.445 Adjacent spaces. When... following requirements must be met: (a) Each space adjacent to a cargo hold must be ventilated by...

  9. Early Continental Rifting of the South China Sea

    NASA Astrophysics Data System (ADS)

    Lee, C.; Chiu, M.; Chan, C.

    2010-12-01

    Combined two years (2007 and 2008) of OBS and MCS studies in the northern slope of the South China Sea, we suggest that the early rifting, probably during 60 - 30 mabp, is an asymmetrical Atlantic-type continental rifting. The crust thin out from 35-40 km of possible continental crust to about 10-15 km of typical oceanic crust. Along the continent-ocean boundary, we observe an intrusion of the high P-wave velocity (about 7.5-8.0 km/sec). This is possible of mantle exhumation as comparable to other Atlantic-type continental margins. The OBS result is revealed by the gravity data. Along the upper layers of the continental crust as well as the oceanic crust, the MCS and multi-beam bathymetry data show that they are covered by numerous submarine seamounts. This probably relate to a volcanic origin of the Cenozoic sea-floor spreading during 30-15 mabp as mapped by previous magnetic anomalies in this region. The sea-floor spreading spread apart in the central, NW and SW sub-basins with several different episodes. Lack of the deep crustal data in the southern slope of the South China Sea, particularly around the Sprately area, the interpretation is speculative. However, several very large-size atolls (150 - 200 km in diameter), such as the Chen-Ho, Shun-Zu, Chung-Yeh and Chiu-Cheng fringing reefs, are sub-parallel located along the south margins. We interpret that these are the upper portions of the continental rifting. Combined the two tectonic stories in the northern and southern slope of the South China Sea, we believe that it is in consistent with the complicate nature of the South China Sea crust.

  10. Cruise report; RV Coastal Surveyor Cruise C1-99; multibeam mapping of the Long Beach, California continental shelf; April 12 through May 19, 1999

    USGS Publications Warehouse

    Gardner, James V.; Hughes-Clarke, John E.; Mayer, Larry A.

    1999-01-01

    The greater Los Angeles area of California is home to more than 10 million people. This large population puts increased pressure on the adjacent offshore continental shelf and margin with activities such as ocean disposal for dredged spoils, explosive disposal, waste-water outfall, and commercial fishing. The increased utilization of the shelf and margin in this area has generated accelerated multi-disciplinary research efforts in all aspects of the environment of the coastal zone. Prior to 1996 there were no highly accurate base maps of the continental shelf and slope upon which the research activities could be located and monitored. In 1996, the United States Geological Survey (USGS) Pacific Seafloor Mapping Project began to address this problem by mapping the Santa Monica shelf and margin (Fig. 1) using a state-of-the-art, high-resolution multibeam sonar system (Gardner, et al., 1996; 1999). Additional seafloor mapping in 1998 provided coverage of the continental margin from south of Newport to the proximal San Pedro Basin northwest of Palos Verdes Peninsula (Gardner, et al., 1998) (Fig. 1). The mapping of the seafloor in the greater Los Angeles continental shelf and margin was completed with a 30-day mapping of the Long Beach shelf in April and May 1999, the subject of this report. The objective of Cruise C-1-99-SC was to completely map the broad continental shelf from the eastern end of the Palos Verdes Peninsula to the narrow shelf south of Newport Beach, from the break in slope at about 120-m isobath to the inner shelf at about the 10-m isobath. Mapping the Long Beach shelf was jointly funded by the U.S. Geological Survey and the County of Orange (CA) Sanitation District and was conducted under a Cooperative Agreement with the Ocean Mapping Group from the University of New Brunswick (OMG/UNB). The OMG/UNB contracted with C&C Technologies, Inc. of Lafayette, LA for use of the RV Coastal Surveyor and the latest evolution of high-resolution multibeam sonars, a

  11. Nonlocal impacts of the Loop Current on cross-slope near-bottom flow in the northeastern Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Nguyen, Thanh-Tam; Morey, Steven L.; Dukhovskoy, Dmitry S.; Chassignet, Eric P.

    2015-04-01

    Cross-slope near-bottom motions near De Soto Canyon in the northeastern Gulf of Mexico are analyzed from a multidecadal ocean model simulation to characterize upwelling and downwelling, important mechanisms for exchange between the deep ocean and shelf in the vicinity of the 2010 BP Macondo well oil spill. Across the continental slope, large-scale depression and offshore movement of isopycnals (downwelling) occur more frequently when the Loop Current impinges upon the West Florida Shelf slope farther south. Upwelling and onshore movement of isopycnals occurs with roughly the same likelihood regardless of Loop Current impingement on the slope. The remote influence of Loop Current on the De Soto Canyon region downwelling is a consequence of a high-pressure anomaly that extends along the continental slope emanating from the location of Loop Current impact.

  12. Interplay between down-slope and along-slope sedimentary processes during the late Quaternary along the Capo Vaticano margin (southern Tyrrhenian Sea, Italy)

    NASA Astrophysics Data System (ADS)

    Martorelli, Eleonora; Bosman, Alessandro; Casalbore, Daniele; Falcini, Federico

    2016-04-01

    Late Quaternary along-slope and down-slope sedimentary processes and structures in the upper slope-shelf sector of the Calabro-Tyrrhenian continental margin off Capo Vaticano have been investigated using very high-resolution single-channel seismic profiles and multibeam bathymetric data. The results show that a competition among along-slope bottom currents-vs down-slope mass-wasting mostly contributed in shaping the seafloor and controlling deposition of sedimentary units during the Late Quaternary. Along-slope processes mostly formed elongated drifts located on the upper continental slope and outer shelf, between -90 and -300 m. The contourite deposits and associated erosive elements indicate the presence of a northwestward geostrophic flow that can be related to the modified-LIW issued by the Messina Strait. According to the proposed stratigraphic reconstruction it is likely that the activity of bottom-currents off Capo Vaticano was intensified around the LGM period and during the post-glacial sea-level rise, whereas they were less intense during the Holocene. Gravity-driven down-slope processes formed mass-transport deposits and turbidite systems with erosive channels, locally indenting the present-day shelf. Several slide events affected the upper 10-20 m of the stratigraphic record, dismantling considerable volume of contourite sediment. High-resolution seismic profiles indicate that failure processes appear to be dominated by translational sliding with glide plains mainly developed within contourite deposits. The most striking feature is the Capo Vaticano slide complex, which displays a large spatial coverage (area of about 18 km2) and is composed by several intersecting slide scars and overlapping deposits; these characteristics are peculiar for the Tyrrhenian continental margins, where slide events developed in open-slope areas are usually less complex and smaller in size. The presence of high-amplitude reflectors within contourite deposits (representing

  13. Stability of submarine slopes in the northern South China Sea: a numerical approach

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Luan, Xiwu

    2013-01-01

    Submarine landslides occur frequently on most continental margins. They are effective mechanisms of sediment transfer but also a geological hazard to seafloor installations. In this paper, submarine slope stability is evaluated using a 2D limit equilibrium method. Considerations of slope, sediment, and triggering force on the factor of safety (FOS) were calculated in drained and undrained ( Φ=0) cases. Results show that submarine slopes are stable when the slope is <16° under static conditions and without a weak interlayer. With a weak interlayer, slopes are stable at <18° in the drained case and at <9° in the undrained case. Earthquake loading can drastically reduce the shear strength of sediment with increased pore water pressure. The slope became unstable at >13° with earthquake peak ground acceleration (PGA) of 0.5 g; whereas with a weak layer, a PGA of 0.2 g could trigger instability at slopes >10°, and >3° for PGA of 0.5 g. The northern slope of the South China Sea is geomorphologically stable under static conditions. However, because of the possibility of high PGA at the eastern margin of the South China Sea, submarine slides are likely on the Taiwan Bank slope and eastern part of the Dongsha slope. Therefore, submarine slides recognized in seismic profiles on the Taiwan Bank slope would be triggered by an earthquake, the most important factor for triggering submarine slides on the northern slope of the South China Sea. Considering the distribution of PGA, we consider the northern slope of the South China Sea to be stable, excluding the Taiwan Bank slope, which is tectonically active.

  14. Linking Slope Sedimentation, Gradient, Morphology, and Active Faulting: An Integrated Example from the Palos Verdes Slope, Southern California Borderland

    NASA Astrophysics Data System (ADS)

    Maier, K. L.; Brothers, D. S.; Paull, C. K.; McGann, M.; Caress, D. W.; Conrad, J. E.

    2015-12-01

    Seafloor gradient variations associated with restraining and releasing bends along the active (1.6-1.9 mm/yr) right-lateral Palos Verdes Fault appear to control Holocene sediment thickness, depositional environment, and morphodynamic processes along a section of the continental slope offshore Los Angeles, California. Autonomous underwater mapping vehicle (AUV), remotely operated vehicle (ROV), and shipboard methods were used to acquire a dense grid of high-resolution chirp profiles (150 m line spacing; 11 cm vertical resolution), multibeam bathymetry (2 m grid), and targeted sediment core samples (<2 m length). Detailed interpretation of Holocene deposits in the chirp profiles combined with radiocarbon dating and laser particle-size analyses allow correlation of Holocene sediment thickness and seafloor gradient with sediment gravity flow deposits. Holocene down-slope flows appear to have been generated by mass wasting processes, primarily on the upper slope (~100-200 m water depth) where shipboard multibeam bathymetry reveals submarine landslide headwall scarps in a region that has been isolated from terrigenous sediment sources throughout the Holocene. Submarine landslides appear to have transformed into sandy and organic-rich turbidity currents that created up-slope migrating sediment waves, a low relief (<5 m) fault-bounded channel, and a series of depocenters. A down-slope gradient profile and a Holocene isopach down-slope profile show that the primary depocenter occurs within a small pull-apart basin associated with a decrease in seafloor gradient of ~1.5°. Holocene sediment-flow deposits vary in number, thickness, and character with subtle changes in seabed gradient (<0.5°) and depositional environment. These results help quantify morphodynamic sensitivity to seafloor gradients and have implications for down-slope flow dynamics, deep-water depositional architecture, Holocene sediment, nutrient, and contaminant transport, and turbidite paleoseismology along

  15. The role of sediment composition and behavior under dynamic loading conditions on slope failure initiation: a study of a subaqueous landslide in earthquake-prone South-Central Chile

    NASA Astrophysics Data System (ADS)

    Wiemer, Gauvain; Moernaut, Jasper; Stark, Nina; Kempf, Philipp; De Batist, Marc; Pino, Mario; Urrutia, Roberto; de Guevara, Bruno Ladrón; Strasser, Michael; Kopf, Achim

    2015-07-01

    Subaqueous slope failure mechanisms are still poorly understood partly because they are difficult to study due to the remote location of submarine landslides. Landslides in lakes are smaller in size and more readily accessible and therefore represent a good alternative to their marine counterparts. Lake Villarrica, located in South-Central Chile, experienced significant slope failure and serves here as an exemplary study area for subaqueous landslide initiation mechanisms in tectonically active settings. Coring and CPTU testing were undertaken with the MARUM free-fall CPTU deployed adjacent to the coring sites where all lithological units involved in the slope failure were sampled. Using geotechnical methods such as pseudo-static factor of safety analysis and cyclic triaxial testing, three types of soils (i.e., diatomaceous ooze, volcanic ash, and quick clay) were analyzed for their role in slope failure, and earthquake shaking was identified as the primary trigger mechanism. The investigated landslide consisted of two distinct phases. During the first phase, slope failure was initiated above a tephra layer. In the second phase, retrogression led to the shoreward extension of the slide scarp along a second failure plane located in a stratigraphically deeper, extremely sensitive lithology (i.e., quick clay). Results show that liquefaction of buried tephra layers was unlikely, but such layers might still have contributed to a reduction in shear strength along the contact area with the neighboring sediment. Furthermore, cyclic shaking-induced pore pressure in diatomaceous ooze may be similar to that in granular soils. We generally infer that failure mechanisms observed in this study are equally important for landslide initiation in submarine settings as diatomaceous ooze intercalated with volcanic ash may be abundantly present along active continental margins.

  16. Evolution of Submarine Gullies on a Prograding Slope: Insights from 3D Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Shumaker, L.; Jobe, Z. R.

    2014-12-01

    Submarine gullies are common features on continental slopes on both passive and active margins, but the processes dictating gully formation and the role of gullies in deep-water sediment transport are topics of debate. The geometries of gullies can provide clues to understanding the processes by which they initiate and grow, particularly when considered in the context of surrounding submarine geomorphology. Further confidence in these interpretations can be gained by tracking the temporal history of gullies with evolution of the continental margin. The 500 km2 Tui 3D seismic survey from the Taranaki Basin, New Zealand, shows continental slope gullies and other channel features in a ~1 km-thick package of prograding shelf-slope clinoforms that developed over Pliocene-Pleistocene time. This dataset allows for documentation of gullies over ~3 Ma, through numerous cycles of initiation and burial. For this study, we manually interpreted clinoform packages to generate 'paleo-seafloor' surfaces that provide context such as position of the shelf edge, slope gradient and azimuth, and relative progradation and aggradation magnitudes. Gully geometries were obtained from detailed seismic interpretation guided by semblance and RMS amplitude imaging on these surfaces. Gullies are low sinuosity, with widths ranging from ~50-150 m and depths from a few tens to <100 m. Gullies are observed to grow in width and relief downslope without evidence for aggradational confinement (levees), and in some cases form gully 'complexes' hundreds of m wide in the lower slope region. These complexes are present through >150 m of stratigraphy, indicating that they are long-lived features on the slope. This further indicates that the frequency of flows along the gullies was enough to maintain their topographic expression during slope progradation and aggradation, and suggests that gullies play an integral role in transport processes on the slope.

  17. Light and Dark Slope Streaks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    21 July 2004 Dark slope streaks are a common feature on slopes thickly-mantled by dust, especially in the Tharsis, Arabia, and western Amazonis regions of Mars. Less common are light-toned slope streaks, which often occur in the same area as dark streaks. They are most common in Arabia Terra, and some are shown in this Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image. Slope streaks are probably the result of sudden avalanches of extremely dry dust. The behavior of the avalanching dust is somewhat fluid-like, and new streaks have been observed to form over intervals of a few months to a Mars year. This image is located near 13.4oN, 340.3oW, and covers an area about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  18. Blake's Slope-Intercept Surprise.

    ERIC Educational Resources Information Center

    Misener, Jeff P.

    2000-01-01

    Describes a student's unique perspective on the algorithm for finding equations of non-vertical lines given one point and the slope. Indicates that students had a better understanding of what they were doing. (KHR)

  19. Measurements of slope current and environmental geochemistry near the western boundary of the Gulf of the Farallones National Marine Sanctuary

    USGS Publications Warehouse

    Noble, Marlene A.; Xu, Jingping; Kolak, Jon; Gartner, Anne L.; Rosenberger, Kurt J.

    2007-01-01

    For nearly a decade, dredged material from San Francisco Bay has been deposited at the U.S. Environmental Protection Agency (EPA) Region IX designated disposal site on the continental slope west of the Farallon Islands. Over the past several years, annual disposal volumes have ranged from 136,170 m3 (61 barge loads) to 2,407,600 m3 (1,173 barge loads) (Ota, personal communication, 2000). The EPA has conducted extensive studies to evaluate the fate and effects of the disposed material (Abdelrhman, 1992; Tetra-Tech, 1992; SAIC, 1992). The EPA has also maintained a long-term monitoring program to collect hydrodynamic, sedimentary, chemical, and biological data that are used to determine whether the dredged material adversely affects the ecology of adjacent water bodies and whether it moves from the disposal site, especially into the Gulf of the Farallones National Marine Sanctuary. As part of this monitoring program, the U.S. Geological Survey (USGS) Coastal and Marine Geology Program (CMGP) deployed arrays of instruments on three moorings near the EPA disposal site from November 1997 to November 1998. This report describes the results and findings of this field monitoring experiment.

  20. Convergent tectonics and coastal upwelling: a history of the Peru continental margin ( Pacific).

    USGS Publications Warehouse

    Von Huene, R.; Suess, E.; Emeis, K.C.

    1987-01-01

    Late in 1986, scientists on the ODP drillship JOIDES Resolution confirmed that the upper slope of the Peruvian margin consists of continental crust whereas the lower slope comprises an accretionary complex. An intricate history of horizontal and vertical movements can be detected, and the locations of ancient centers of upwelling appear to have varied, partly due to tectonic movements of the margin. In this review of Leg 112, the 3 scientific leaders on this cruise discuss their results. -from Journal Editor

  1. Evidence of a dense water vein along the Libyan continental margin

    NASA Astrophysics Data System (ADS)

    Gasparini, G. P.; Bonanno, A.; Zgozi, S.; Basilone, G.; Borghini, M.; Buscaino, G.; Cuttitta, A.; Essarbout, N.; Mazzola, S.; Patti, B.; Ramadan, A. B.; Schroeder, K.; Bahri, T.; Massa, F.

    2008-02-01

    For the first time it was possible to investigate a still poorly known region of the eastern Mediterranean Sea, the Libyan continental margin. An oceanographic cruise, performed during summer 2006, revealed an important and novel feature: a dense vein flowing along the continental slope. The paper describes the vein evolution with some insights on its dynamic and furnishes an estimate of its transport, which results to be comparable with the Adriatic Deep Water production rate. The cascading into a steep canyon which incises the continental shelf suggests that the vein may play an important role in ventilating the deep layers of the Ionian Sea.

  2. The Continental Distillery: Building Thick Continental Crust in the Central Andes (Invited)

    NASA Astrophysics Data System (ADS)

    Wagner, L. S.; Beck, S. L.; Zandt, G.; Long, M. D.; Tavera, H.; Minaya, E.; Biryol, C. B.; Bishop, B.; Eakin, C. M.; Franca, G.; Knezevic Antonijevic, S.; Kumar, A.; Ryan, J. C.; Scire, A. C.; Ward, K. M.; Young, B. E.

    2013-12-01

    The formation of stable continental crust and the associated development and destruction of mantle lithospheric roots is central to our understanding of plate tectonics, both at its inception and as an ongoing process today. Subduction zones play an important role in the creation and refinement of continental crust, and also serve as a possible mechanism for the removal of residual mantle material. The central Andes provide an intriguing laboratory for the study of these processes. Up to 400 km wide, 1500 km long, and with an average elevation of 4 km, the Altiplano Plateau is the largest orogen on earth associated with an ocean-continent subduction zone. This is much larger than adjacent 'normal' sections of the Andes, raising the question of why this portion of South American crust became so much more substantial than surrounding areas. Over the past several years, new seismic data have made it possible for us to develop a more complete picture of the lithospheric and asthenospheric processes involved in the development of the Altiplano Plateau and the adjacent narrower orogen further to the north. The 'Central Andean Uplift and the Geodynamics of High Topography' (CAUGHT) comprises in part a broadband deployment of 50 stations across the northern flank of the Altiplano Plateau in southern Peru and northern Bolivia. The adjacent 'PerU Lithosphere and Slab Experiment' (PULSE) includes 40 broadband stations that cover the region directly north of the CAUGHT deployment, encompassing the northern edge of the Altiplano, the transition to 'normal' width orogen, and the transition in slab geometry from normal to flat from south to north across the study area. Uplift of the Altiplano Plateau is likely due to some combination shortening, isostasy due to lithospheric destruction or changes in crustal density, magmatic addition to the crust, and/or flow within the thickened crust. Our studies indicate pervasive low velocities across the Altiplano consistent with a

  3. Converting your Continental

    SciTech Connect

    Wirz, B.M.

    1981-07-01

    Inflation and higher fuel and environmental costs make conventional-generated power as unaffordable (as a Lincoln Continental in the automobile market) for retail and industrial customers, many of whom are looking for alternatives to purchase electric power. The loss of revenue from competing energy sources eliminates the monopoly status that utilities have enjoyed and is forcing utilities to provide what customers want and do it better than the competition. Utilities have only research and development or fuel switching to improve efficiency unless they rethink their approach and come up with new alternatives. 1 table. (DCK)

  4. North Slope (Wahluke Slope) expedited response action cleanup plan

    SciTech Connect

    Not Available

    1994-02-01

    The purpose of this action is to mitigate any threat to public health and the environment from hazards on the North Slope and meet the expedited response action (ERA) objective of cleanup to a degree requiring no further action. The ERA may be the final remediation of the 100-I-3 Operable Unit. A No Action record of decision (ROD) may be issued after remediation completion. The US Department of Energy (DOE) currently owns or administers approximately 140 mi{sup 2} (about 90,000 acres) of land north and east of the Columbia River (referred to as the North Slope) that is part of the Hanford Site. The North Slope, also commonly known as the Wahluke Slope, was not used for plutonium production or support facilities; it was used for military air defense of the Hanford Site and vicinity. The North Slope contained seven antiaircraft gun emplacements and three Nike-Ajax missile positions. These military positions were vacated in 1960--1961 as the defense requirements at Hanford changed. They were demolished in 1974. Prior to government control in 1943, the North Slope was homesteaded. Since the initiation of this ERA in the summer of 1992, DOE signed the modified Hanford Federal Agreement and Consent Order (Tri-Party Agreement) with the Washington Department of Ecology (Ecology) and the US Environmental Protection Agency (EPA), in which a milestone was set to complete remediation activities and a draft closeout report by October 1994. Remediation activities will make the North Slope area available for future non-DOE uses. Thirty-nine sites have undergone limited characterization to determine if significant environmental hazards exist. This plan documents the results of that characterization and evaluates the potential remediation alternatives.

  5. Impact of gravity processes on the initial post-rift stages of construction and evolution of a continental margin: Insights from the eastern Gulf of Aden

    NASA Astrophysics Data System (ADS)

    Baurion, Celine; Gorini, Christian; Leroy, Sylvie; Migeon, Sebastien; Lucazeau, Francis; Bache, Francois; Zaragosi, Sebastien; Smit, Jeroen; Al-Toubi, Khalfan; dos Reis, Antonio

    2013-04-01

    The study of the post-rift sediment architecture and continental slope morphology leads to a reconstruction of the initial stages of formation and evolution of gravity-driven processes on the northern margin of the eastern Gulf of Aden. The slope-related features and associated deposits in the deep basin along this young passive margin are investigated through the analysis of a set of seismic-reflection and multibeam bathymetry data. This study demonstrates how preconditioning and triggering factors (tectonics, climate and eustatic variations) can interact and control the margin morphology and post-rift sediment architecture in a source-to-sink perspective. The combined geomorphological and stratigraphic study of this margin allows us to identify three morphological domains inherited from the structural segmentation. The monsoon climate combined with a major eustatic lowstand is proposed as the most likely set of factors preconditioning slope destabilisation on the whole margin. These factors also enhance the effect of the late post-rift uplift of the eastern morphological domain of the studied margin. The formation and distribution of the slope-related features are thus mainly controlled by active faults on the continental slope and the potential effect of bottom currents at the base of the continental slope. The oversteepening of the continental slope in the eastern domain of the studied margin is probably the main triggering factor controlling the generation of failure processes and subsequent canyon formation by upslope erosion. The analysis of canyon location and morphology along the uplifted part of the continental slope reveals the long-term influence of secondary slope-related features, contour currents and turbidite flows on the development of canyons. As a consequence of the late post-rift uplift that only affected the eastern part of the studied margin, huge volumes of sediment were accumulated in mass-transport complexes at the foot of numerous slope

  6. Coordination: southeast continental shelf studies. Progress report

    SciTech Connect

    Menzel, D.W.

    1980-03-01

    The GABEX I experiment is designed to provide synoptic coverage of a series of Gulf Stream wave-like disturbances, the effect of these on the circulation of the entire shelf, and on biological and chemical processes. This study was initiated in February 1980 when current meter arrays were deployed. These meters will be removed in July 1980. In April three ships will simultaneously study the effects of Gulf Stream disturbances on the hydrography, chemistry, and biology of the shelf. One vessel will track a specific wave-like disturbance and provide synoptic coverage of the shelf area. The second vessel will determine the effect of shelf break processes on adjacent shelf water; and the third will study trace metal distributions in and outside of disturbances. Research progress is reported in continental shelf studies, nearshore and estuarine studies (diffusion of freshwater out of nearshore zone), tidal currents and material transport, and mixing of inlet plumes.

  7. Slope Instability on the French Guiana Transform Margin from Swath-Bathymetry and 3.5 kHz Echograms

    NASA Astrophysics Data System (ADS)

    Gaullier, Virginie; Loncke, Lies; Droz, Laurence; Basile, Christophe; Maillard, Agnès.; Patriat, Martin; Roest, Walter R.; Loubrieu, Benoît.

    2010-05-01

    Although transform margins represent ˜30% of rifted margins around the world, few studies have investigated mass-movement processes in such areas and their links with this specific structural context. The French Guiana transform margin and adjacent Demerara abyssal plain have been surveyed during the GUYAPLAC cruise, collecting multibeam bathymetric data, backscatter imagery, 3.5 kHz echograms and 6-channel seismic profiles. The study area is divided into three domains: the shallow Demerara plateau, the Guiana slope and rise, and the Demerara abyssal plain. The dataset emphasizes the importance of slope instability in shaping the French Guiana transform margin. Sizes and styles of these mass-movements differ between the studied sectors. The Guiana slope and rise (transform segment), south of the Demerara Plateau, are mainly affected by huge and successive mass-movements, with slope failures generating large stacked debris flows, sometimes buried and reworked by creeping processes. Fluid escape is ubiquitous there, suggesting a dewatering of debris flows due to sediment loading. The whole Demerara plateau is affected by multi-scale mass-movement processes. The rough surface of the plateau is mainly deformed by creeping folds perpendicular to the slope and pockmarks with giant elongated ones. At a deeper scale, study in progress (Basile et al. 2009) shows repetitive slumping creating seaward collapse of the upper 500 m of sediments. The driving mechanism seems to be the tilting of the plateau in relation with increasing subsidence northeastward (Loncke et al. 2009). This tilting may allow the upper part of the sedimentary section to glide on décollements sub-parallel to the bedding. The northern part of the Demerara plateau is mainly affected by small valley networks and debris flows. The lack of massive failure deposits probably indicates that the slow sliding on the plateau did not evolve, at least recently, in huge catastrophic events. Two main types of

  8. Geologic history of the continental margin of North America in the Bering Sea

    USGS Publications Warehouse

    Scholl, D. W.; Buffington, E.C.; Hopkins, D.M.

    1968-01-01

    The North American continental margin beneath the Bering Sea is nearly 1,300 km long and extends from Alaska to eastern Siberia. The margin is a canyon-scarred 3,200-3,400-m high escarpment separating one of the world's largest epicontinental seas (the shallow Bering Sea) and the Aleutian Basin (the deep-water Bering Sea), a marginal oceanic basin distinguished by having its southern boundary formed by the Aleutian Ridge. Three geomorphic provinces can be recognized: a southeastern province characterized by a gentle continental slope (lacking V-shaped canyons) and an outlying continental borderland (formed by Umnak Plateau); a central province distinguished by a steep canyon-scarred slope, and a northwestern province having a gentler and, apparently, less eroded continental slope. Continuous seismic reflection profiles show that the margin is constructed of three major structural-stratigraphic units: (1) an acoustic basement underlying the outer shelf and upper slope; (2) an overlying main layered sequence; and (3) a stratified rise unit underlying and forming the continental rise at the base of the slope. The existing margin evolved with downbowing and faulting of the acoustic basement, an older margin probably of Late Mesozoic age, consisting in part of well-indurated siltstone and mudstone, in Early Tertiary time. Concomitant with subsidence as much as 1,500 m of main-layered-sequence strata were draped over the basement. Intense canyon cutting, presumed to have been caused by the rapid deposition of unstable masses of riverborn sediment over the outer shelf and upper slope, is thought to have begun in Late Tertiary and Quaternary time. Concurrent with canyon cutting, submarine fans, consisting of turbidites forming the rise unit, accrued at the base of the continental slope. Subsidence of the continental margin during the Tertiary may be related to foundering ("oceanization") of a continental block to form the Aleutian Basin, or to simple isostatic depression

  9. Contrasts Between Precipitation over Mediterranean Sea and Adjacent Continental Areas Based on Decadal Scale Satellite Estimates

    NASA Technical Reports Server (NTRS)

    Smith, Eric A.

    2007-01-01

    Most knowledge concerning the last century's climatology and climate dynamics of precipitation over the Mediterranean Sea basin is based on observations taken from rain gauges surrounding the sea itself. In turn, most of the observations come from Southern Europe, with many fewer measurements taken from widely scattered sites situated over North Africa, the Middle East, and the Balkans. This aspect of research on the Mediterranean Sea basin is apparent in a recent compilation of studies presented in book form concerning climate variability of the Mediterranean region [Lionello, P., P. Malanotte-Rizzoli, and R. Boscolo (eds.), 2006: Mediterranean Climate Variability. Elsevier, Amsterdam, 9 chapters.] In light of this missing link to over-water observations, this study (in conjunction with four companion studies by Z. Haddad, A. Mugnai, T. Nakazawa, and G. Stephens) will contrast the nature of precipitation variability directly over the Mediterranean Sea to precipitation variability over the surrounding land areas based on three decades of satellite-based precipitation estimates which have stood up well to validation scrutiny. The satellite observations are drawn from the Global Precipitation Climatology Project (GPCP) dataset extending back to 1979 and the TRMM Merged Algorithm 3b42 dataset extending back to 1998. Both datasets are mostly produced from microwave measurements, excepting the period from 1979 to mid-1987 when only infrared satellite measurements were available for the GPCP estimates. The purpose of this study is to emphasize how the salient properties of precipitation variability over land and sea across a hierarchy of space and time scales, and the salient differences in these properties, might be used in guiding short-term climate models to better predictions of future climate states under different regional temperature-change scenarios.

  10. Phytoplankton assemblages within the Chesapeake Bay plume and adjacent waters of the continental shelf

    NASA Technical Reports Server (NTRS)

    Marshall, H. G.

    1981-01-01

    The Chesapeake Bay plume was identified and plotted in relation to the presence and high concentrations of phytoplankton assemblages. Seasonal differences occurred within the plume during the collection period, with Skeletonema costatum and an ultraplankton component the dominant forms. Patchiness was found along the transects, with variations in composition and concentrations common on consecutive day sampling within the plume in its movement along the shelf. The presence of 236 species is noted, with their presence indicated for plume and shelf stations during the March, June, and October 1980 collections.

  11. Dynamics of continental collision: influence of the plate contact

    NASA Astrophysics Data System (ADS)

    De Franco, Roberta; Govers, Rob; Wortel, Rinus

    2008-09-01

    Observations shows that continental collision may evolve in different ways, resulting in a wide range of tectonic responses. In search of the controlling conditions and parameters, we start from the results of our previous work, which demonstrated that the properties of the plate contact are important for the overall dynamics of convergent plate margins. Two fundamental types of subduction plate contact can be distinguished: one based on a fault and the other based on a weak subduction channel. In this study, we investigate how the plate contact affects the initial stage of continental collision. We use a finite element method to solve the heat and the time-dependent momentum equations for elastic, (power-law) viscous and plastic rheologies. For the same rheological properties and driving forces, varying the nature of the plate contact leads to three types of responses. The presence of a subduction channel promotes coherent and, when the boundary conditions allow it, plate-like subduction of the continental margin. In models with a subduction fault, coherent subduction of the incoming continental lithosphere occurs when the colliding passive margin has a gentle slope. The approaching continental sliver starts to subduct and the subduction is characterized by a non-plate like behaviour-slower subduction velocity than in channel models and strong slab deformation. If the continental margin is steep and the strength of the incoming continental crust is high, fault models result in locking of the trench, eventually leading to slab break-off. If the crustal strength is relatively low, shear delamination of part of the crust is expected. In the channel model, this type of delamination never occurs. The tectonic settings used in our experiments (prescribed plate velocity of the subducting plate versus fixed subducting plate corresponding to a landlocked basin setting) do not significantly influence the nature of the model response. We conclude that initial stages of

  12. Slope sensitivities for optical surfaces

    NASA Astrophysics Data System (ADS)

    Rogers, John R.

    2015-09-01

    Setting a tolerance for the slope errors of an optical surface (e.g., surface form errors of the "mid-spatial-frequencies") requires some knowledge of how those surface errors affect the final image of the system. While excellent tools exist for simulating those effects on a surface-by-surface basis, considerable insight may be gained by examining, for each surface, a simple sensitivity parameter that relates the slope error on the surface to the ray displacement at the final image plane. Snell's law gives a relationship between the slope errors of a surface and the angular deviations of the rays emerging from the surface. For a singlet or thin doublet acting by itself, these angular deviations are related to ray deviations at the image plane by the focal length of the lens. However, for optical surfaces inside an optical system having a substantial axial extent, the focal length of the system is not the correct multiplier, as the sensitivity is influenced by the optical surfaces that follow. In this paper, a simple expression is derived that relates the slope errors at an arbitrary optical surface to the ray deviation at the image plane. This expression is experimentally verified by comparison to a real-ray perturbation analysis. The sensitivity parameter relates the RMS slope errors to the RMS spot radius, and also relates the peak slope error to the 100% spot radius, and may be used to create an RSS error budget for slope error. Application to various types of system are shown and discussed.

  13. Stacking attributes from local slopes

    NASA Astrophysics Data System (ADS)

    Ghosh, S.; Gajewski, D.; Dell, S.; Nath, S. K.; Wave Inversion Technology (Wit) Consortium

    2010-12-01

    CMP stacking is controlled by the stacking velocity which is determined by a one-dimendional optimization procedure using semblance as a coherence criterion. New multi-parameter stacking formulas like the Common Reflection Surface (CRS) operator consider neighboring CMP locations in the stack. These methods stack considerably more traces than conventional CMP processing leading to stacked sections with an improved signal-to-nose ratio and better image quality. The corresponding stacking trajectories are controlled by three stacking attributes for the 2-D case and eight for the 3-D case. The determination of these attributes requires a multi-dimensional optimization procedure which is time consuming. If we know good starting values, we can limit the search intervals considerably and speed up the process. It was shown that the stacking attributes are linked to local slopes in seismic zero offset and constant offset sections. Therefore, the determination of local slopes can guide the choice of the search intervals in the optimization procedure. We use structural tensors for the determination of local slopes. Structural tensors represent a versatile tool to investigate coherent features in the data superior to other slop determination tools like slant stacking or plane wave destructors. The window size is adjustable and allows to optimize smoothing and smearing in the slope determination process where the smoothing can be performed along structural events (directional smoothing). This smart feature helps to consider complex geologies and acknowledges faults and conflicting dips without any significant change in computation time. Different variants of the algorithm are used to determine slopes in CMP gathers, stacked and time or depth migrated sections. The results of the local slope determinations are used to compute stacking attributes for the CRS method. We compare these to stacking attributes obtained from optimization. The attributes determined from local slopes

  14. Bathyal ostracodes from the Florida-Hatteras slope, the Straits of Florida, and the Blake Plateau

    USGS Publications Warehouse

    Cronin, T. M.

    1983-01-01

    Epibathyal ostracodes from the Florida-Hatteras slope, the Blake Plateau and the Straits of Florida were studied to determine the relationship of numerous genera and species to bottom-water environmental conditions such as dissolved oxygen and bottom-water temperatures. From a total of 100 samples, 44 samples evenly distributed between 200 and 1100 m water depth and having an average of 325 specimens were examined in detail. Using occurrence data from the adjacent continental shelf, carapace preservation, Rose Bengal staining and population data, indigenous death assemblages were distinguished from transported or reworked fossil specimens. The percent of transported specimens varied as follows: Blake Plateau 90% of the samples and usually constitute 10 to 30% of each. Trachyleberidea, Bairdoppilata, Saida, Paranesidea, Ambocythere, Bythocypris, Cytherella, Bradleya, Henryhowella, and Polycopidae occur in 45 to 80% of the samples in varying percentages. The upper depth limits of 39 taxa occur at or just below the thermocline suggesting a relationship to temperature. Australoecia, Quasibuntonia, Cytheropteron, Ruggieriella, Saida, Ambocythere, Trachyleberidea, Macrocypris, Krithe, "Thalassocythere", and Cytherella are most common or restricted to the O2 minimum zone. Conversely, Anchistrocheles, Bradleya, Henryhowella, and Rockallia are most common below 750 m in well oxygenated water with temperatures below 8??C. The results show that: (1) ostracodes display a narrow depth zonation controlled by dissolved oxygen and water temperature; (2) species diversity is very high for a bathyal zone; (3) ostracodes can be used to identify the source of sediment that has been transported downslope; and (4) some taxa are useful in recognizing low oxygenated water in Cenozoic deposits. ?? 1983.

  15. Map of Distribution of Bottom Sediments on the Continental Shelf, Gulf of Alaska

    USGS Publications Warehouse

    Evans, Kevin R.; Carlson, Paul R.; Hampton, Monty A.; Marlow, Michael S.; Barnes, Peter W.

    2000-01-01

    floor structures. Sea-floor sediment on shallow banks is eroded by seasonal wave-generated currents. The winnowing action of the large storm waves results in concentrations of gravel over broad segments of the Kodiak shelf. Northeastern Gulf of Alaska -- Tectonic framework studies demonstrate that rocks of distant origin (Yakutat terrane) are currently attached to and moving with the Pacific Plate, as it collides with and is subducted beneath southern Alaska. This collision process has led to pronounced structural deformation of the continental margin and adjacent southern Alaska. Consequences include rapidly rising mountains and high fluvial and glacial sedimentation rates on the adjacent margin and ocean floor. The northeastern Gulf of Alaska shelf also has concentrations of winnowed (lag) gravel on Tarr Bank and on the outer shelf southeast of Yakutat Bay. Between Kayak Island and Yakutat Bay the outer shelf consists of pebbly mud (diamict). This diamict is a product of glacial marine sedimentation during the Pleistocene and is present today as a relict sediment. A prograding wedge of Holocene sediment consisting of nearshore sand grading seaward into clayey silt and silty clay covers the relict pebbly mud to mid-shelf and beyond. Shelf and slope channel systems transport glacially derived sediment across the continental margin into Surveyor Channel, an abyssal fan and channel system that reaches over 1,000 km to the Aleutian Trench.

  16. 43 CFR 420.3 - Adjacent lands.

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 43 Public Lands: Interior 1 2014-10-01 2014-10-01 false Adjacent lands. 420.3 Section 420.3 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF RECLAMATION, DEPARTMENT OF THE INTERIOR...-managing agencies on adjacent lands (both public and private)....

  17. 43 CFR 420.3 - Adjacent lands.

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 43 Public Lands: Interior 1 2013-10-01 2013-10-01 false Adjacent lands. 420.3 Section 420.3 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF RECLAMATION, DEPARTMENT OF THE INTERIOR...-managing agencies on adjacent lands (both public and private)....

  18. 43 CFR 420.3 - Adjacent lands.

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 43 Public Lands: Interior 1 2011-10-01 2011-10-01 false Adjacent lands. 420.3 Section 420.3 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF RECLAMATION, DEPARTMENT OF THE INTERIOR OFF-ROAD VEHICLE USE § 420.3 Adjacent lands. When administratively feasible, the regulation of off-road vehicle use on Reclamation lands will...

  19. 43 CFR 420.3 - Adjacent lands.

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 43 Public Lands: Interior 1 2012-10-01 2011-10-01 true Adjacent lands. 420.3 Section 420.3 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF RECLAMATION, DEPARTMENT OF THE INTERIOR...-managing agencies on adjacent lands (both public and private)....

  20. 43 CFR 420.3 - Adjacent lands.

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 43 Public Lands: Interior 1 2010-10-01 2010-10-01 false Adjacent lands. 420.3 Section 420.3 Public Lands: Interior Regulations Relating to Public Lands BUREAU OF RECLAMATION, DEPARTMENT OF THE INTERIOR OFF-ROAD VEHICLE USE § 420.3 Adjacent lands. When administratively feasible, the regulation of...

  1. Anatomy of gravitationally deformed slopes

    NASA Astrophysics Data System (ADS)

    Chigira, Masahiro; Yamasaki, Shintaro; Hariyama, Takehiro

    2010-05-01

    Deep-seated gravitational slope deformation is the deformation of rocks as well as slope surfaces, but the internal structures have not been well observed and described before. This is mainly due to the difficulty in obtaining undisturbed samples from underground. We analyzed the internal deformational structures of gravitationally deformed slopes by using high quality drilled cores obtained by hybrid drilling technique, which has been recently developed and can recover very fragile materials that could not be taken by the conventional drilling techniques. Investigated slopes were gravitationally deformed out-facing slopes of pelitic schist and shale. The slope surfaces showed deformational features of small steps, depressions, knobs, and linear depressions, but had no major main scarp and landslide body with well-defined outline. This is indicative of slow, deep-seated gravitational deformation. Most of these small deformational features are hidden by vegetations, but they are detected by using airborne laser scanner. Drilled cores showed that the internal deformation is dominated by the slip and tearing off along foliations. Slippage along foliations is conspicuous in pelitic schist: Pelitic schist is sheared, particularly along black layers, which are rich in graphite and pyrite. Graphite is known to be a solid lubricant in material sciences, which seems to be why shearing occurs along the black layers. Rock mass between two slip layers is sheared, rotated, fractured, and pulverized; undulation of bedding or schistosity could be the nucleation points of fracturing. Tearing off along foliations is also the major deformation mode, which forms jagged morphology of rock fragments within shear zones. Rock fragments with jagged surface are commonly observed in "gouge", which is very different from tectonic gouge. This probably reflects the low confining pressures during their formation. Microscopic to mesoscopic openings along fractures are commonly observed with

  2. Mapping Shallow Landslide Slope Inestability at Large Scales Using Remote Sensing and GIS

    NASA Astrophysics Data System (ADS)

    Avalon Cullen, C.; Kashuk, S.; Temimi, M.; Suhili, R.; Khanbilvardi, R.

    2015-12-01

    Rainfall induced landslides are one of the most frequent hazards on slanted terrains. They lead to great economic losses and fatalities worldwide. Most factors inducing shallow landslides are local and can only be mapped with high levels of uncertainty at larger scales. This work presents an attempt to determine slope instability at large scales. Buffer and threshold techniques are used to downscale areas and minimize uncertainties. Four static parameters (slope angle, soil type, land cover and elevation) for 261 shallow rainfall-induced landslides in the continental United States are examined. ASTER GDEM is used as bases for topographical characterization of slope and buffer analysis. Slope angle threshold assessment at the 50, 75, 95, 98, and 99 percentiles is tested locally. Further analysis of each threshold in relation to other parameters is investigated in a logistic regression environment for the continental U.S. It is determined that lower than 95-percentile thresholds under-estimate slope angles. Best regression fit can be achieved when utilizing the 99-threshold slope angle. This model predicts the highest number of cases correctly at 87.0% accuracy. A one-unit rise in the 99-threshold range increases landslide likelihood by 11.8%. The logistic regression model is carried over to ArcGIS where all variables are processed based on their corresponding coefficients. A regional slope instability map for the continental United States is created and analyzed against the available landslide records and their spatial distributions. It is expected that future inclusion of dynamic parameters like precipitation and other proxies like soil moisture into the model will further improve accuracy.

  3. Shelf-Slope Exchange in the Mid-Atlantic Bight

    NASA Astrophysics Data System (ADS)

    Goodman, P. J.; Wilkin, J.

    2004-12-01

    A high resolution model (ROMS, the Regional Ocean Modeling System) of U.S. East Coast circulation from Newfoundland to Cuba is used to explore features of alongshelf freshwater transport, residence time, and shelf-sea/deep-ocean exchange. The focus of the analysis is the Mid-Atlantic Bight (MAB) shelf-slope system which, like continental shelves throughout the world, contributes to the oceanic budgets of heat, salt, and fresh water. In addition, the "continental shelf pump" transfers carbon from the atmosphere to the deep ocean through fluxes of dissolved organic carbon and particulate organic carbon off the shelves. Solar radiation, evaporation, rainfall, riverine input, gas exchange with the atmosphere, and biological production all modify the character of shelf waters. In the MAB, the shelf-slope front separates shallow coastal waters from slope waters and the Gulf Stream, extending residence times on the shelf and maintaining coastal salinities at significantly lower levels than those offshore. The southwestward coastal mean flow exchanges weakly with slope waters along most of the MAB, with the strongest offshore flow occurring at Cape Hatteras where much of the flow is entrained into the Gulf Stream front. The shelf circulation is influenced by input from the Hudson and Delaware Rivers and Chesapeake Bay. Along the shelf break, exchange is modulated by warm-core rings from the Gulf Stream and variability of the shelf-break front. Key features of the seasonal circulation such as the MAB "Cold Pool" are captured by the simulation. Measurements suggest that DOC in shelf and shallow slope waters of the MAB include both old marine carbon and a young terrestrial-riverine-estuarine component, and these carbon cycling processes are being studied with a companion primary production, nitogen and carbon cycle model directly coupled to ROMS. Results showing salinity, idealized dye and Lagrangian float tracking results from a ROMS simulation of the MAB shelf circulation

  4. A new vision of carbonate slopes: the Little Bahama Bank

    NASA Astrophysics Data System (ADS)

    Mulder, Thierry; Gillet, Hervé; Hanquiez, Vincent; Reijmer, John J.; Tournadour, Elsa; Chabaud, Ludivine; Principaud, Mélanie; Schnyder, Jara; Borgomano, Jean; Fauquembergue, Kelly; Ducassou, Emmanuelle

    2016-04-01

    Recent high-quality multibeam and seismic data allow to image a large part of the uppermost slope of Northeastern Little Bahama Bank between 30 and 400 m water depth and to characterize the uppermost slope (Rankey and Doolitle, 1992) over a surface of 170 km2. The new data set includes multibeam bathymetry and acoustic imagery, 3.5 kHz very-high resolution (VHR) seismic reflexion lines (1120 km), 21 gravity cores and 11 Van Veen grabs. This dataset completes the recent surveys of the slope adjacent to LBB (Carambar cruise, Mulder et al, 2012). The data provide insight into sediment transfer from the shallow carbonate bank to the adjacent slope. Four major terraces and escarpments dominate the morphology of the slope. The terraces are located at 22 m, 27-33 m, 40-46 and 55-64 m below present water depth (mpwd). They could either be related to periods of stagnating sea-level and therefore increased erosion by waves, or periods of accelerated sea-level rise since the Last Glacial Maximum. Escarpments bound the terraces. The deepest one (64-56 mpwd) is also the steepest 35-50°). It corresponds to the marginal scarp of Rankey and Doolitle (1992). The lower part of the uppermost slope shows a discontinuous Holocene sediment wedge with varying thickness between 0 and 35 m. It forms a blind or very crudely stratified echo facies. This Holocene unit can be thicker than 20 m and consists of mud that forms most of the present sediment export. This unit fills small depressions in the substratum and thickens in front of gullies that cut the carbonate platform edge. It forms by off-bank export initiated when a cold front passes by, resulting in density cascading currents. The associated sediment fall-out and convective sedimentation can generate density currents that flow through linear structures on the upper slope. The survey reveals the presence of recently active channels that extend laterally over the entire uppermost slope and interrupt the density cascading fall

  5. Western Slope of Andes, Peru

    NASA Technical Reports Server (NTRS)

    2008-01-01

    Along the western flank of the Andes, 400 km SE of Lima Peru, erosion has carved the mountain slopes into long, narrow serpentine ridges. The gently-sloping sediments have been turned into a plate of worms wiggling their way downhill to the ocean.

    The image was acquired September 28, 2004, covers an area of 38 x 31.6 km, and is located near 14.7 degrees south latitude, 74.5 degrees west longitude.

    The U.S. science team is located at NASA's Jet Propulsion Laboratory, Pasadena, Calif. The Terra mission is part of NASA's Science Mission Directorate.

  6. Patterns of deep-water coral diversity in the Caribbean Basin and adjacent southern waters: an approach based on records from the R/V Pillsbury expeditions.

    PubMed

    Hernández-Ávila, Iván

    2014-01-01

    The diversity of deep-water corals in the Caribbean Sea was studied using records from oceanographic expeditions performed by the R/V Pillsbury. Sampled stations were sorted according to broad depth ranges and ecoregions and were analyzed in terms of species accumulation curves, variance in the species composition and contributions to alpha, beta and gamma diversity. According to the analysis of species accumulation curves using the Chao2 estimator, more diversity occurs on the continental slope (200-2000 m depth) than on the upper continental shelf (60-200 m depth). In addition to the effect of depth sampling, differences in species composition related to depth ranges were detected. However, the differences between ecoregions are dependent on depth ranges, there were fewer differences among ecoregions on the continental slope than on the upper continental shelf. Indicator species for distinctness of ecoregions were, in general, Alcyonaria and Antipatharia for the upper continental shelf, but also the scleractinians Madracis myriabilis and Cladocora debilis. In the continental slope, the alcyonarian Placogorgia and the scleractinians Stephanocyathus and Fungiacyathus were important for the distinction of ecoregions. Beta diversity was the most important component of gamma diversity in the Caribbean Basin. The contribution of ecoregions to alpha, beta and gamma diversity differed with depth range. On the upper continental shelf, the Southern Caribbean ecoregion contributed substantially to all components of diversity. In contrast, the northern ecoregions contributed substantially to the diversity of the Continental Slope. Strategies for the conservation of deep-water coral diversity in the Caribbean Basin must consider the variation between ecoregions and depth ranges. PMID:24671156

  7. Patterns of Deep-Water Coral Diversity in the Caribbean Basin and Adjacent Southern Waters: An Approach based on Records from the R/V Pillsbury Expeditions

    PubMed Central

    Hernández-Ávila, Iván

    2014-01-01

    The diversity of deep-water corals in the Caribbean Sea was studied using records from oceanographic expeditions performed by the R/V Pillsbury. Sampled stations were sorted according to broad depth ranges and ecoregions and were analyzed in terms of species accumulation curves, variance in the species composition and contributions to alpha, beta and gamma diversity. According to the analysis of species accumulation curves using the Chao2 estimator, more diversity occurs on the continental slope (200–2000 m depth) than on the upper continental shelf (60–200 m depth). In addition to the effect of depth sampling, differences in species composition related to depth ranges were detected. However, the differences between ecoregions are dependent on depth ranges, there were fewer differences among ecoregions on the continental slope than on the upper continental shelf. Indicator species for distinctness of ecoregions were, in general, Alcyonaria and Antipatharia for the upper continental shelf, but also the scleractinians Madracis myriabilis and Cladocora debilis. In the continental slope, the alcyonarian Placogorgia and the scleractinians Stephanocyathus and Fungiacyathus were important for the distinction of ecoregions. Beta diversity was the most important component of gamma diversity in the Caribbean Basin. The contribution of ecoregions to alpha, beta and gamma diversity differed with depth range. On the upper continental shelf, the Southern Caribbean ecoregion contributed substantially to all components of diversity. In contrast, the northern ecoregions contributed substantially to the diversity of the Continental Slope. Strategies for the conservation of deep-water coral diversity in the Caribbean Basin must consider the variation between ecoregions and depth ranges. PMID:24671156

  8. What triggers large submarine landslides on <2° slopes? A study on overpressure generation in slow deposition environments

    NASA Astrophysics Data System (ADS)

    Urlaub, M.; Talling, P. J.; Zervos, A.; Masson, D. G.; Clayton, C. R.

    2012-12-01

    Large submarine landslides that exceed in size landslides on land by up to two orders of magnitude occur on slope angles of less than 2°. Mechanically, failure of soil on nearly flat slopes is only possible when high ratios of excess pore pressure to effective stress prevail which significantly reduce the shearing resistance of the sediment. It has been suggested that the combinations of rapid deposition of low permeability sediment with lateral fluid flow precondition the slope to a tipping point, and that earthquakes act as final trigger to cause failure of low gradient slopes. However, slope failure is also observed at continental margins that experience comparatively low rates of sediment deposition. We develop a fully coupled 2D stress-fluid flow finite element model of an entire continental slope in order to investigate excess pore pressure generation due to consolidation under slow sediment deposition. Different permeability-porosity relationships, permeability anisotropies, compressibility, sediment strengths or inclusion of aquifers are modelled, but resulting excess pore pressures are too low to significantly decrease effective stress anywhere along the slope. This result indicates that we may miss out a dominant pore pressure generating process in areas of slow deposition, or that factors other than overpressure drive slope failure.

  9. Modeling the voice source in terms of spectral slopes.

    PubMed

    Garellek, Marc; Samlan, Robin; Gerratt, Bruce R; Kreiman, Jody

    2016-03-01

    A psychoacoustic model of the voice source spectrum is proposed. The model is characterized by four spectral slope parameters: the difference in amplitude between the first two harmonics (H1-H2), the second and fourth harmonics (H2-H4), the fourth harmonic and the harmonic nearest 2 kHz in frequency (H4-2 kHz), and the harmonic nearest 2 kHz and that nearest 5 kHz (2 kHz-5 kHz). As a step toward model validation, experiments were conducted to establish the acoustic and perceptual independence of these parameters. In experiment 1, the model was fit to a large number of voice sources. Results showed that parameters are predictable from one another, but that these relationships are due to overall spectral roll-off. Two additional experiments addressed the perceptual independence of the source parameters. Listener sensitivity to H1-H2, H2-H4, and H4-2 kHz did not change as a function of the slope of an adjacent component, suggesting that sensitivity to these components is robust. Listener sensitivity to changes in spectral slope from 2 kHz to 5 kHz depended on complex interactions between spectral slope, spectral noise levels, and H4-2 kHz. It is concluded that the four parameters represent non-redundant acoustic and perceptual aspects of voice quality. PMID:27036277

  10. Exploring Slope with Stairs & Steps

    ERIC Educational Resources Information Center

    Smith, Toni M.; Seshaiyer, Padmanabhan; Peixoto, Nathalia; Suh, Jennifer M.; Bagshaw, Graham; Collins, Laurena K.

    2013-01-01

    As much as ever before, mathematics teachers are searching for ways to connect mathematics to real-life scenarios within STEM contexts. As students develop skill in proportional reasoning, they examine graphical representations of linear functions, learn to associate "slope" with "steepness" and rate of change, and develop…

  11. Pleistocene slope instability of gas hydrate-laden sediment on the Beaufort Sea margin

    USGS Publications Warehouse

    Kayen, R.E.; Lee, H.J.

    1991-01-01

    In oceanic areas underlain by sediment with gas hydrate, reduction of sea level initiates disassociation along the base of the gas hydrate, which, in turn, causes the release of large volumes of gas into the sediment and creates excess pore-fluid pressures and reduced slope stability. Fluid diffusion properties dominate the disassociation process in fine-grained marine sediment. Slope failure appears likely for this sediment type on moderate slopes unless pressures can be adequately vented away from the gas hydrate base. Pleistocene eustatic-sea level regressions, likely triggered seafloor landslides on the continental slope of the Beaufort Sea and other margins where gas hydrate is present in seafloor sediment. -from Authors

  12. Potential role of gas hydrate decomposition in generating submarine slope failures: Chapter 12

    USGS Publications Warehouse

    Pauli, Charles K.; mUssler, William III; Dillon, William P.

    2003-01-01

    Gas hydrate decomposition is hypothesized to be a factor in generating weakness in continental margin sediments that may help explain some of the observed patterns of continental margin sediment instability. The processes associated with formation and decomposition of gas hydrate can cause the strengthening of sediments in which gas hydrate grow and the weakening of sediments in which gas hydrate decomposes. The weakened sediments may form horizons along which the potential for sediment failure is increased. While a causal relationship between slope failures and gas hydrate decomposition has not been proven, a number of empirical observations support their potential connection.

  13. Continental margin sedimentation: from sediment transport to sequence stratigraphy

    USGS Publications Warehouse

    Nittrouer, Charles A., (Edited By); Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P.M.; Wiberg, Patricia L.

    2007-01-01

    This volume on continental margin sedimentation brings together an expert editorial and contributor team to create a state-of-the-art resource. Taking a global perspective, the book spans a range of timescales and content, ranging from how oceans transport particles, to how thick rock sequences are formed on continental margins. - Summarizes and integrates our understanding of sedimentary processes and strata associated with fluvial dispersal systems on continental shelves and slopes - Explores timescales ranging from particle transport at one extreme, to deep burial at the other - Insights are presented for margins in general, and with focus on a tectonically active margin (northern California) and a passive margin (New Jersey), enabling detailed examination of the intricate relationships between a wide suite of sedimentary processes and their preserved stratigraphy - Includes observational studies which document the processes and strata found on particular margins, in addition to numerical models and laboratory experimentation, which provide a quantitative basis for extrapolation in time and space of insights about continental-margin sedimentation - Provides a research resource for scientists studying modern and ancient margins, and an educational text for advanced students in sedimentology and stratigraphy

  14. Dynamics of Continental Accretion

    NASA Astrophysics Data System (ADS)

    Moresi, L. N.; Betts, P. G.; Miller, M. S.

    2013-12-01

    Subduction zones become congested when they try to swallow buoyant exotic crust. Accretionary mountain belts (orogens) that form at these convergent plate margins are the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North and South American Cordilleras and southwest Pacific. The geologic record is riddled with accretionary orogens, such as the Tasmanides along the eastern margin of the supercontinent Gondwana and the Altaides that formed on the southern margin of Laurasia. Both the modern and ancient examples are characterised by episodic switches between extension and shortening associated with transitions from collision of exotic crust and subduction related rollback. We present three-dimensional dynamic models that show for the first time how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back arc region. The complexity of the morphology and evolution of the system are driven by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonal to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, but infer that this is a global phenomena throughout Earth's evolution.

  15. Dynamics of continental accretion.

    PubMed

    Moresi, L; Betts, P G; Miller, M S; Cayley, R A

    2014-04-10

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon. PMID:24670638

  16. Erosive Margins: The Link between the Nature of oceanic Plate and Slope Surface at the Peruvian Margin and the Margin's Mechanical State

    NASA Astrophysics Data System (ADS)

    Kukowski, N.; Hampel, A.; Bialas, J.; Huebscher, C.; Bourgois, J.

    2003-04-01

    a lower possibility to bend a plate. The lower slope up to about 1500m above the trench, is very similar along the margin, while escarpments on the middle slope become wider and more distinct from north to south. Whereas the morphology and dip of the Nazca Ridge differs significantly from those of the areas north of the collision zone, the continental slope opposite to the collision zone very much resembles the portions of the margin north of it. The morphology of seamounts on Nazca Ridge as well as normal faults close to the trench in the collision zone can be quantified from a combination of the dip angle and shape index attributes. These attributes also help to detect overstep areas at the lower Yaquina slope. This analysis shows that steepness is varying significantly locally with over-steep portion close to the trench being adjacent to smoother portions, the latter comprising features of recent to sub-paleo failure.

  17. Upper Devonian depositional system of Bel'kov Island (New Siberian Islands): An intracontinental rift or a continental margin?

    NASA Astrophysics Data System (ADS)

    Danukalova, M. K.; Kuzmichev, A. B.; Aristov, V. A.

    2014-09-01

    The archipelago of New Siberian Islands situated on the northeastern continental shelf of Eurasia is considered a part of an exotic terrane that collided with Siberia in the Early Cretaceous. Bel'kov Island is located close to the inferred western boundary of this terrane and thus should demonstrate attributes of its localization at the margin of the Paleozoic oceanic basin. The Upper Devonian section on Bel'kov Island is a continuous sequence of deepwater terrigenous rocks, which indicates a tendency toward deepening of the basin previously revealed on adjacent Kotel'ny Island. The lowermost Upper Devonian unit on Bel'kov Island is represented by thin Domanik-like strata resting on the Middle Devonian carbonate platform. The main body of the Upper Devonian sequence, more than 4 km in total thickness, is made up of gravity-flow sediments including turbidites, clay and block diamictites, and olistostromes in the upper part of the section, which accumulated at the slope of the basin or its rise. At many levels, these sediments have been redeposited by along-slope currents. The uppermost unit of organogenic limestone is evidence for compensation of the trough. According to conodont assemblages, the deepwater terrigenous rocks were deposited from the early Frasnian to the early Tournaisian. This time is known for extensive rifting in the eastern Siberian Platform. The data obtained allowed us to reconstruct a NNW-trending Late Devonian rift basin on the Laptev Sea shelf similar to other rifts at the eastern margin of the Siberian Platform.

  18. Planktonic ecosystem response to meso and submesoscale dynamics above a shelf slope.

    NASA Astrophysics Data System (ADS)

    Pennel, Romain; Rivière, Pascal; Pondaven, Philippe; Carton, Xavier

    2015-04-01

    In this numerical process study, we examine the impact of the relative positions of a coastal current and the continental slope on the dynamics of a planktonic ecosystem. In the open ocean, previous studies have evidenced the importance of mesoscale and submesoscale turbulence on the structure and functioning of planktonic ecosystem (Rivière et Pondaven, 2006; Perruche et al, 2011). In coastal areas, the presence of the continental slope induces a complex ocean dynamics and impacts the spreading of biochemical tracers between the shallow continental shelf and the deep open ocean. The topographic parameter (ratio between the shelf slope and the isopycnal slope), the vertical aspect ratio (ratio between the depth of the current and the total depth) and the Burger number control the stability of surface coastal currents and the emergence of meso and submesoscale structures (Pennel et al, 2012; Poulin et al, 2014). Thus, different positions of the current above the shelf slope, by changing the local depth or the local slope, induce different dynamical regimes that may imply a large impact on ecosystems through changes in nutrient inputs from the deep ocean into the euphotic layer or changes in the cross-shelf transport. Simulations of a geostrophically balanced gravity current with a mixed layer are carried out using the Regional Ocean Modeling System (ROMS). The domain consists of a re-entrant channel with an hyperbolic tangent shelf bathymetry. The 600 m horizontal resolution (12 grid points per radius of deformation) and the 60 vertical levels allow the model to resolve both the meso and submesoscale dynamics. An idealized biological model is included and accounts for the existence of two different trophic chains involving small and large species (NP2Z2D). A suite of few months long simulations is performed with different positions of the coastal current above the bottom topography. The results are discussed in terms of primary production, cross-shore export of

  19. Geodynamic settings of microcontinents, non-volcanic islands and submerged continental marginal plateau formation

    NASA Astrophysics Data System (ADS)

    Dubinin, Evgeny; Grokholsky, Andrey; Makushkina, Anna

    2016-04-01

    Complex process of continental lithosphere breakup is often accompanied by full or semi isolation of small continental blocks from the parent continent such as microcontinents or submerged marginal plateaus. We present different types of continental blocks formed in various geodynamic settings. The process depends on thermo-mechanical properties of rifting. 1) The continental blocks fully isolated from the parent continent. This kind of blocks exist in submerged form (Elan Bank, the Jan-Mayen Ridge, Zenith Plateau, Gulden Draak Knoll, Batavia Knoll) and in non-submerged form in case of large block size. Most of listed submerged blocks are formed in proximity of hot-spot or plume. 2) The continental blocks semi-isolated from the parent continent. Exmouth Plateau, Vøring, Agulhas, Naturaliste are submerged continental plateaus of the indicated category; Sri Lanka, Tasmania, Socotra are islands adjacent to continent here. Nowadays illustration of this setting is the Sinai block located between the two continental rifts. 3) The submerged linear continental blocks formed by the continental rifting along margin (the Lomonosov Ridge). Suggested evolution of this paragraph is the rift propagation along existing transtensional (or another type) transform fault. Future example of this type might be the California Peninsula block, detached from the North American plate by the rifting within San-Andreas fault. 4) The submerged continental blocks formed by extensional processes as the result of asthenosphere flow and shear deformations. Examples are submerged blocks in the central and southern Scotia Sea (Terror Bank, Protector Basin, Discovery Bank, Bruce Bank etc.). 5) The continental blocks formed in the transform fault systems originated in setting of contradict rifts propagation in presence of structure barriers, rifts are shifted by several hundreds kilometers from each other. Examples of this geodynamic setting are Equatorial Atlantic at the initial development stage

  20. Carbonate slope gully system on the Westside Great Bahama Bank

    NASA Astrophysics Data System (ADS)

    Principaud, Mélanie; Mulder, Thierry; Borgomano, Jean; Ducassou, Emmanuelle; Hanquiez, Vincent; Gillet, Hervé; Marieu, Vincent; Sorriaux, Patrick

    2013-04-01

    Gullies are commonly observed on submarine slopes along many continental margins. They are generally small, straight, shallow channels with a depth that does not exceed a few tens of meters. They form on relatively steep slopes. They are important features for downslope sediment transfer from the outer continental shelf to the continental slope and rise. Data collected during the first leg of the Carambar cruise (Nov. 1st - Nov. 15th, 2010) on the RV "Le Suroît" show that the western slope of the Great Bahamas Bank is characterized by the presence of gullies that extend about 100 km from North to South along the carbonate platform. Gullies appear on the upper slope at approximately 410 m water depth in a carbonated mud-dominated environment. Their initiation follows the presence of sediment waves. They extend over a 3° steeped slope down to 610 m water depth. The gully heads are not connected to the platform and to any significant carbonate depositional system. They are relatively linear, sub-parallel, with a symmetric to asymmetric V-shaped cross section and incision does not exceed 30 m. Average gully length and spacing are 4000 and 800 m respectively. A detailed morphometric study based on EM302 multibeam bathymetry and very-high resolution seismic data (Chirp sub bottom profiler) combined with a statistical analysis allowed the gullied slope to be divided into two distinct areas. (1) The northern area characterized by regularly-spaced gullies (spacing varies from 750 to 800 m from North to South). They are generally linear and sub-parallel with an average length of 4 km. Their depth are usually lower than 10 m. Asymmetry is greater in the central region of gullies (northern flank is steeper than southern flank) and seems to be correlated with an increase in gully depth and a decrease in gully spacing. (2) The southern area is characterized by irregularly-shaped gullies that are usually truncated by a large 40 m high N-S deformation escarpment. Gullies have

  1. A new integrated tectonic model for the Mesozoic-Early Cenozoic subduction, spreading, accretion and collision history of Tethys adjacent to the southern margin of Eurasia (NE Turkey)

    NASA Astrophysics Data System (ADS)

    Robertson, Alastair; Parlak, Osman; Ustaömer, Timur; Taslı, Kemal; İnan, Nurdan; Dumitrica, Paulian; Karaoǧlan, Fatih

    2014-05-01

    Cretaceous age for the E Pontide ophiolites, with important implications for alternative tectonic hypotheses. The two-subduction-zone hypothesis is supported by sedimentological and structural studies of the volcanic-sedimentary melange and of the sedimentary thrust sheets within the suture zone. Geochemical studies of oceanic basaltic rocks in the melange and also new biostratigraphic dating of radiolarites and calcareous microfossils within pelagic and redeposited deep-sea/slope sediments add to the picture. Taken together, the evidence suggests the former existence of both an oceanic and a continental margin subduction complex that are now amalgamated within the suture zone. We propose the following tectonic hypothesis: Fragments of oceanic basaltic lithologies and their deep-sea sedimentary cover accreted to form a Jurassic-Cretaceous intra-oceanic subduction complex. Terrigenous and arc-derived volcaniclastic gravity flows and pelagic carbonates accumulated in a continental margin forearc basin, mainly during the Cretaceous. Subduction melange was first emplaced over the distal Eurasian margin during the Late Cretaceous owing to thickening of the accretionary prism. During suturing, the continental margin forearc basin was emplaced southwards over the oceanic-derived accretionary wedge. The Eurasian continental margin was imbricated and thrust northwards as collision proceeded. Final closure of the adjacent Tethys took place prior to late Middle Eocene. This was followed by marine transgression and the accumulation of non-marine to shallow-marine sediments, including Nummulitic limestones. Regional correlations suggest that the double subduction zone hypothesis, notably involving Jurassic intra-oceanic spreading, is applicable to >1000 km of the Eurasian margin, specifically the Lesser Caucasus and possibly also the Central Pontides.

  2. Geotechnical characteristics and slope stability on the Ebro margin, western Mediterranean

    USGS Publications Warehouse

    Baraza, J.; Lee, H.J.; Kayen, R.E.; Hampton, M.A.

    1990-01-01

    Sedimentological and geotechnical analyses of core samples from the Ebro continental slope define two distinct areas on the basis of sediment type, physical properties and geotechnical behavior. The first area is the upper slope area (water depths of 200-500 m), which consists of upper Pleistocene prodeltaic silty clay with a low water content (34% dry weight average), low plasticity, and high overconsolidation near the seafloor. The second area, the middle and lower slope (water depths greater than 500 m), contains clay- and silt-size hemipelagic deposits with a high water content (90% average), high plasticity, and a low to moderate degree of overconsolidation near the sediment surface. Results from geotechnical tests show that the upper slope has a relatively high degree of stability under relatively rapid (undrained) static loading conditions, compared with the middle and lower slopes, which have a higher degree of stability under long-term (drained) static loading conditions. Under cyclic loading, which occurs during earthquakes, the upper slope has a higher degree of stability than the middle and lower slopes. For the surface of the seafloor, calculated critical earthquake accelerations that can trigger slope failures range from 0.73 g on the upper slope to 0.23 g on the lower slope. Sediment buried well below the seafloor may have a critical acceleration as low as 0.09 g on the upper slope and 0.17 g on the lower slope. Seismically induced instability of most of the Ebro slope seems unlikely given that an earthquake shaking of at least intensity VI would be needed, and such strong intensities have never been recorded in the last 70 years. Other cyclic loading events, such as storms or internal waves, do not appear to be direct causes of instability at present. Infrequent, particularly strong earthquakes could cause landslides on the Ebro margin slope. The Columbretes slide on the southwestern Ebro margin may have been caused by intense earthquake shaking

  3. Rayleigh wave tomography of China and adjacent regions

    NASA Astrophysics Data System (ADS)

    Huang, Zhongxian; Su, Wei; Peng, Yanju; Zheng, Yuejun; Li, Hongyi

    2003-02-01

    This paper presents a tomographic study on the S wave velocity structure of China and adjacent regions. Group velocity dispersions of fundamental Rayleigh waves along more than 4000 paths were determined with frequency-time analysis. The study region was divided into a 1° × 1° grid, and velocities in between grid nodes were calculated by bilinear interpolation. The Occam's inversion scheme was adopted to invert for group velocity distributions. This method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern. Checkerboard tests were carried out, and the lateral resolution was estimated to be 4°-6° in China and its eastern continental shelves. The resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features. The pure path dispersion curves at each node were inverted for shear wave velocity structures. The three-dimensional velocity model indicates thick lithospheres in the Yangtze and Tarim platforms and hot upper mantles in Baikal and western Mongolia, coastal area and continental shelves of eastern China, and Indochina and South China Sea regions. The Tibetan Plateau has a very thick crust with a low-velocity zone in its middle. Beneath the crust a north dipping high-velocity zone, mimicking a subducting plate, reaches to 200 km in depth and reaches to the Kunlun Mountains northward. In northern Tibet a low-velocity zone immediately below the Moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low-velocity area in Indochina and the South China Sea.

  4. Skate assemblage on the eastern Patagonian Shelf and Slope: structure, diversity and abundance.

    PubMed

    Arkhipkin, A; Brickle, P; Laptikhovsky, V; Pompert, J; Winter, A

    2012-04-01

    The eastern Patagonian Shelf and continental slope of the south-west Atlantic Ocean support a high biodiversity and abundance of skates. In this study, meso-scale differences in the assemblages, spatial and seasonal distributions of skates are revealed among six habitat zones of the eastern Patagonian Shelf characterized by distinctive oceanographic conditions. Most skates belonged to temperate fauna, and their abundance was much greater in habitats occupied by temperate waters (north-western outer shelf) or mixed waters (northern slope) than in habitats occupied by sub-Antarctic waters (SASW) (south-eastern outer shelf and southern slope). Sub-Antarctic skates were not abundant on the shelf even in habitats occupied by SASW, occurring mainly in deep areas of the lower continental slope. The majority of temperate skates migrated seasonally, shifting northward in winter and spreading southward with warming waters in summer. Most temperate species had two peaks in female maturity (mainly spring and autumn) and spawned in the same habitats where they fed. It is hypothesized that the high biodiversity and abundance of skates on the Patagonian Shelf and Slope are due to the practical absence of their natural competitors, flatfishes, which occupy similar eco-niches elsewhere. PMID:22497404

  5. Coordination: Southeast continental shelf studies

    SciTech Connect

    Menzel, D.W.

    1989-01-26

    The objective of this investigation is to obtain model descriptions of the flow modifications in the Southeast Atlantic continental shelf due to Gulf Stream fluctuations and topographic effects. 2 refs., 4 figs.

  6. Potential causes for slope instabilities of under-consolidated marine sediments

    SciTech Connect

    Quemeneur, P.; Tisot, J.P.; Cochonat, P.; Bourillet, J.F.; d`Oultremont, V.; Colliat, J.L.; Tofani, R.

    1995-12-31

    Offshore studies have been completed in the Gulf of Guinea, off West Africa. An area has been selected over the Gabon continental slope. A morpho-sedimentological zonation is made regarding acoustic data and geotechnical characteristics of sampled sediments. An old slide has been considered as a criteria for estimating realistic slope failure conditions. Both drained and undrained formulations tend to prove that fluid escape is the most realistic explanation for slides occurrence. Regional hazard charts also allow them to present unstable zones and build up criteria for structures implantation.

  7. Framework for North Slope Seminar II

    SciTech Connect

    Tailleur, I.L.

    1985-04-01

    This meeting focuses on a province with enormous potential for fuels and minerals. Oil reserves approach 10% of the total oil already produced in the rest of the country. Estimated coal resources could store a thousand times the 70-80 quads of energy the US uses every year. Potential yields of silver, lead, and zinc range from 10 to 100% of the amounts produced domestically since the middle of the 19th century. Prospects for copper are also large. The province is dominated by the east-trending Brooks Range, whose structures formed during the late Mesozoic Brookian orogeny and are now being shortened longitudinally. Flanking basins succeeded the uplift; the northern one is bounded by a passive continental margin. Early in the orogeny, a relatively thin early Paleozoic through Jurassic megasequence of clastic-wedge, carbonate, and siliceous sediments was telescoped into a fivefold stacking of allochthons and beneath allochthons of volcanic and mafic-ultramafic rocks. The greater than 500-km breadth of sialic crust that had underlain the allochthons disappeared. At about the same time, the Arctic ocean basin replaced the northern provenance. A mid-Paleozoic sialic source area on the opposite margin of the megasequence disappeared by the end of the Carboniferous and near the beginning of siliceous deposition. Basement beneath the North Slope part of the megasequence was created when the Devonian Ellesmerian orogeny added to the crust the late precambrian to early Paleozoic clastic, carbonate, and volcanic rocks of an older megasequence. The northern successor basin accumulated large amounts of coal. Truncation and sealing of potential reservoir rocks on replacement of the northern landmass led to huge pools of hydrocarbons. Late Paleozoic rocks in the lowest allochthon host stratabound base-metal deposits. A narrow belt of reportedly Devonian shallow-seated felsic rocks contain deposits of copper.

  8. Hydrological heterogeneity in Mediterranean reclaimed slopes: runoff and sediment yield at the patch and slope scales along a gradient of overland flow

    NASA Astrophysics Data System (ADS)

    Merino-Martín, L.; Moreno-de Las Heras, M.; Pérez-Domingo, S.; Espigares, T.; Nicolau, J. M.

    2011-11-01

    Hydrological heterogeneity is recognized as a fundamental ecosystem attribute in drylands controlling the flux of water and energy through landscapes. Therefore, mosaics of runoff and sediment sinks and source patches are frequently identified in these dry environments. There is a remarkable scarcity of studies about hydrological spatial heterogeneity in restored slopes, where ecological succession and overland flow are interacting. We conducted a field research to study the hydrological role of patches and slopes along an overland flow gradient in three reclaimed slopes coming from mining reclamation in a Mediterranean-continental climate. We found that runoff generation and routing in non-rilled slopes showed a pattern of source and sink areas of runoff. Such hydrological microenvironments were associated to seven vegetation patches (characterized by plant community types and cover). Two types of sink patches were identified: shrub Genista scorpius patches could be considered as a "deep sink", while patches where the graminoids Brachypodium retusum and Lolium perenne dominate were classified as "surface sinks" or "runoff splays". A variety of source patches were also identified spanning from "extreme sources" (Medicago sativa patches; equivalent to bare soil) to "poor sources" (areas scattered by dwarf-shrubs of Thymus vulgaris or herbaceous tussocks of Dactylis glomerata). Finally, we identified the volume of overland flow routing along the slope as a controlling major factor of hydrological diversity: when overland flow increases at the slope scale hydrological diversity diminishes.

  9. -induced continental warming

    NASA Astrophysics Data System (ADS)

    Kamae, Youichi; Watanabe, Masahiro; Kimoto, Masahide; Shiogama, Hideo

    2014-11-01

    In this the second of a two-part study, we examine the physical mechanisms responsible for the increasing contrast of the land-sea surface air temperature (SAT) in summertime over the Far East, as observed in recent decades and revealed in future climate projections obtained from a series of transient warming and sensitivity experiments conducted under the umbrella of the Coupled Model Intercomparison Project phase 5. On a global perspective, a strengthening of land-sea SAT contrast in the transient warming simulations of coupled atmosphere-ocean general circulation models is attributed to an increase in sea surface temperature (SST). However, in boreal summer, the strengthened contrast over the Far East is reproduced only by increasing atmospheric CO2 concentration. In response to SST increase alone, the tropospheric warming over the interior of the mid- to high-latitude continents including Eurasia are weaker than those over the surrounding oceans, leading to a weakening of the land-sea SAT contrast over the Far East. Thus, the increasing contrast and associated change in atmospheric circulation over East Asia is explained by CO2-induced continental warming. The degree of strengthening of the land-sea SAT contrast varies in different transient warming scenarios, but is reproduced through a combination of the CO2-induced positive and SST-induced negative contributions to the land-sea contrast. These results imply that changes of climate patterns over the land-ocean boundary regions are sensitive to future scenarios of CO2 concentration pathways including extreme cases.

  10. Manganese flux from continental margin sediments in a transect through the oxygen minimum

    SciTech Connect

    Johnson, K.S. Monterey Bay Aquarium Research Inst., Pacific Grove, CA ); Berelson, W.M.; Iams, H.D.; Kilgore, T.E. ); Coale, K.H.; Coley, T.L.; Elrod, V.A.; Fairey, W.R.; Nowicki, J.L. )

    1992-08-28

    The flux of manganese from continental margin sediments to the ocean was measured with a free-vehicle, benthic flux chamber in a transect across the continental shelf and upper slope of the California margin. The highest fluxes were observed on the shallow continental shelf. Manganese flux decreased linearly with bottom water oxygen concentration, and the lowest flux occurred in the oxygen minimum zone (at a depth of 600 to 1,000 meters). Although the flux of manganese from continental shelf sediments can account for the elevated concentrations observed in shallow, coastal waters, the flux from sediments that intersect the oxygen minimum cannot produce the subsurface concentration maximum of dissolved manganese that is observed in the Pacific Ocean.

  11. Exhumation and continental strike-slip fault systems: Introduction

    USGS Publications Warehouse

    Roeske, S.M.; Till, A.B.; Foster, D.A.; Sample, J.C.

    2007-01-01

    Metamorphic rocks adjacent to and within strike-slip faultsystems occur in a wide range of tectonic settings. Detailed studies show that for a number of these locales a significant part of the exhumation occurred during strike-slip fault motion, but the specific processes involved are often cryptic. Although some sites share characteristic features, such as metamorphic rocks exhumed in extensional step-overs within overall transtensional systems, no one common theme emerges from all of the studies. Our understanding of the variables that control continental strike-slip faults' interaction with mid- to lower-crustal structures is still primitive.

  12. Modes of continental decretion in western Canada

    NASA Astrophysics Data System (ADS)

    Cook, F. A.

    2010-12-01

    Between the Archean Slave Province and the Pacific Ocean, the North American continent in Canada appears to have ‘grown’ westward during Paleoproterozoic (Wopmay) and Paleozoic-Mesozoic (Cordilleran) orogenesis. However, results from geological observations combined with regional geophysical surveys lead to interpretations in which pre-orogenic basement in both the Wopmay and the Cordillera projects far beneath proposed ‘accreted’ terranes. In the Wopmay orogen (1.89-1.84 Ga), deep geophysical images indicate that Archean Slave basement projects in the subsurface up to 50 km west of the Medial zone (formerly Wopmay fault), a boundary that was previously interpreted as the transition from Slave basement to accreted terrane basement. The Slave basement appears as a west-tapering tectonic wedge into accreted(?) rocks, consistent with an interpretation by Hildebrand and Bowring (Geology, 1999) that the Archean lithosphere that was formerly west of the wedge broke off and was recycled. In the Cordillera, cross sections of the lithosphere illustrate that lower crustal and upper mantle rocks as much as 2/3 of the distance across the orogen can be stratigraphically, geologically and seismically correlated to the ancient cratonic margin. Retrodeformation of rocks that were deposited on or adjacent to the craton leads to the conclusion that, prior to the onset of terrane accretion, the North American margin and associated rocks projected even farther west (today’s coordinates) - at least as far as the modern margin. Apparently, as flakes of terranes were added to the surface in the western regions of the Cordillera, the North American lithosphere, which may have been foreshortened during contraction, was tectonically and/or thermally eroded from below. As a result, terrane accretion in the Cordillera apparently resulted in a net decretion of continental lithosphere. Together, these observations lead to the interpretation that the processes responsible for

  13. On the time-course of adjacent and non-adjacent transposed-letter priming

    PubMed Central

    Ktori, Maria; Kingma, Brechtsje; Hannagan, Thomas; Holcomb, Phillip J.; Grainger, Jonathan

    2014-01-01

    We compared effects of adjacent (e.g., atricle-ARTICLE) and non-adjacent (e.g., actirle-ARTICLE) transposed-letter (TL) primes in an ERP study using the sandwich priming technique. TL priming was measured relative to the standard double-substitution condition. We found significantly stronger priming effects for adjacent transpositions than non-adjacent transpositions (with 2 intervening letters) in behavioral responses (lexical decision latencies), and the adjacent priming effects emerged earlier in the ERP signal, at around 200 ms post-target onset. Non-adjacent priming effects emerged about 50 ms later and were short-lived, being significant only in the 250-300 ms time-window. Adjacent transpositions on the other hand continued to produce priming in the N400 time-window (300-500 ms post-target onset). This qualitatively different pattern of priming effects for adjacent and non-adjacent transpositions is discussed in the light of different accounts of letter transposition effects, and the utility of drawing a distinction between positional flexibility and positional noise. PMID:25364497

  14. Regional variability of slope stability: Application to the Eel margin, California

    USGS Publications Warehouse

    Lee, H.; Locat, J.; Dartnell, P.; Israel, K.; Florence, Wong

    1999-01-01

    Relative values of downslope driving forces and sediment resisting forces determine the locations of submarine slope failures. Both of these vary regionally, and their impact can be addressed when the data are organized in a Geographic Information System (GIS). The study area on the continental margin near the Eel River provides an excellent opportunity to apply GIS spatial analysis techniques for evaluation of slope stability. In this area, swath bathymetric mapping shows seafloor morphology and distribution of slope steepness in fine detail, and sediment analysis of over 70 box cores delineates the variability of sediment density near the seafloor surface. Based on the results of ten geotechnical studies of submarine study areas, we developed an algorithm that relates surface sediment density to the shear strength appropriate to the type of cyclic loading produced by an earthquake. Strength and stress normalization procedures provide results that are conceptually independent of subbottom depth. Results at depth are rigorously applicable if sediment lithology does not vary significantly and consolidation state can be estimated. Otherwise, the method applies only to shallow-seated slope failure. Regional density, slope, and level of anticipated seismic shaking information were combined in a GIS framework to yield a map that illustrates the relative stability of slopes in the face of seismically induced failure. When a measure of predicted relative slope stability is draped on an oblique view of swath bathymetry, a variation in this slope stability is observed on an otherwise smooth slope along the mid-slope region north of a plunging anticline. The section of slope containing diffuse, pockmarked gullies has a lower measure of stability than a separate section containing gullies that have sharper boundaries and somewhat steeper sides. Such an association suggests that our slope-stability analysis relates to the stability of the gully sides. The remainder of the

  15. Slope Streaks in Terra Sabaea

    NASA Technical Reports Server (NTRS)

    2007-01-01

    [figure removed for brevity, see original site] Figure 1 Click on image for larger version

    This HiRISE image shows the rim of a crater in the region of Terra Sabaea in the northern hemisphere of Mars.

    The subimage (figure 1) is a close-up view of the crater rim revealing dark and light-toned slope streaks. Slope streak formation is among the few known processes currently active on Mars. While their mechanism of formation and triggering is debated, they are most commonly believed to form by downslope movement of extremely dry sand or very fine-grained dust in an almost fluidlike manner (analogous to a terrestrial snow avalanche) exposing darker underlying material.

    Other ideas include the triggering of slope streak formation by possible concentrations of near-surface ice or scouring of the surface by running water from aquifers intercepting slope faces, spring discharge (perhaps brines), and/or hydrothermal activity.

    Several of the slope streaks in the subimage, particularly the three longest darker streaks, show evidence that downslope movement is being diverted around obstacles such as large boulders. Several streaks also appear to originate at boulders or clumps of rocky material.

    In general, the slope streaks do not have large deposits of displaced material at their downslope ends and do not run out onto the crater floor suggesting that they have little reserve kinetic energy. The darkest slope streaks are youngest and can be seen to cross cut and superpose older and lighter-toned streaks. The lighter-toned streaks are believed to be dark streaks that have lightened with time as new dust is deposited on their surface.

    Observation Geometry Image PSP_001808_1875 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on 15-Dec-2006. The complete image is centered at 7.4 degrees latitude, 47.0 degrees East longitude. The range to the target site was 272.1 km

  16. A statistical overview of mass movement characteristics on the North American atlantic outer continental margin

    USGS Publications Warehouse

    Booth, James S.; O'Leary, Dennis W.

    1992-01-01

    An analysis of 179 mass movements on the North American Atlantic continental slope and upper rise shows that slope failures have occurred throughout the geographic extent of the outer margin. Although the slope failures show no striking affinity for a particular depth as an origination level, there is a broad, primary mode centered at about 900 m. The resulting slides terminate at almost all depths and have a primary mode at 1100 m, but the slope/rise boundary (at 2200 m) also is an important mode. Slope failures have occurred at declivities ranging from 1° to 30° (typically, 4°); the resultant mass movement deposits vary in width from 0.2 to 50 km (typically, 1-2 km) and in length from 0.3 to 380 km (typically, 2–4 km), and they have been reported to be as thick as 650 m. On a numeric basis, mass movements are slightly more prevalent on open slopes than in other physiographic settings, and both translational and rotational failure surfaces are common. The typical mass movement is disintegrative in nature. Open slope slides tend to occur at lower slope angles and are larger than canyon slides. Further, large‐scale slides rather than small‐scale slides tend to originate on gentle slopes (≍ 3-4°). Rotational slope failures appear to have a slightly greater chance of occurring in canyons, but there is no analogous bias associated with translational failures. Similarly, disintegrative slides seem more likely to be associated with rotational slope failures than translational ones and are longer than their nondisintegrative counterparts. The occurrence of such a variety of mass movements at low declivities implies that a regional failure mechanism has prevailed. We suggest that earthquakes or, perhaps in some areas, gas hydrates are the most likely cause of the slope failures.

  17. Constraining Depositional Slope From Sedimentary Structures in Sandy Braided Streams

    NASA Astrophysics Data System (ADS)

    Lynds, R. M.; Mohrig, D.; Heller, P. L.

    2003-12-01

    Determination of paleoslopes in ancient fluvial systems has potentially broad application to quantitatively constraining the history of tectonics and paleoclimate in continental sequences. Our method for calculating paleoslopes for sandy braided streams is based upon a simple physical model that establishes depositional skin-frictional shear stresses from assemblages of sedimentary structures and their associated grain size distributions. The addition of a skin-frictional shear stress, with a geometrically determined form-drag shear stress results in a total boundary shear stress which is directly related to water-surface slope averaged over an appropriate spatial scale. In order to apply this model to ancient fluvial systems, it is necessary to measure the following: coarsest suspended sediment size, finest grain size carried in bed load, flow depth, dune height, and dune length. In the rock record, suspended load and bed load can be accurately assessed by well-preserved suspended load deposits ("low-energy" ripples) and bed load deposits (dune foresets). This model predicts an average slope for the North Loup River near Taylor, Nebraska (modern case study) of 2.7 x 10-3. The measured reach-averaged water surface slope for the same reach of the river is 1.37 x 10-3. We suggest that it is possible to calculate the depositional slope of a sandy fluvial system by a factor of approximately two. Additionally, preliminary application of this model to the Lower Jurassic Kayenta Formation throughout the Colorado Plateau provides a promising and consistent evaluation of paleoslope in an ancient and well-preserved, sandy braided stream deposit.

  18. Gravity-induced stresses in finite slopes

    USGS Publications Warehouse

    Savage, W.Z.

    1994-01-01

    An exact solution for gravity-induced stresses in finite elastic slopes is presented. This solution, which is applied for gravity-induced stresses in 15, 30, 45 and 90?? finite slopes, has application in pit-slope design, compares favorably with published finite element results for this problem and satisfies the conditions that shear and normal stresses vanish on the ground surface. The solution predicts that horizontal stresses are compressive along the top of the slopes (zero in the case of the 90?? slope) and tensile away from the bottom of the slopes, effects which are caused by downward movement and near-surface horizontal extension in front of the slope in response to gravity loading caused by the additional material associated with the finite slope. ?? 1994.

  19. Gravitational deformation and inherited structural control on slope morphology, north-central Chile (~29-33°S)

    NASA Astrophysics Data System (ADS)

    Peña Gomez, M. A.; Becerra, J.; Arriagada, C.; Contreras-Reyes, E.; Gómez, I.; Bascunan, S. A.; Manriquez, P. M.

    2015-12-01

    We studied the structure of the subduction zone system offshore the Pampean flat-slab segment (~29-33°S) using seismic and bathymetric constraints. Bathymetric data reveals three structural domains: (1) NW, NNW and NS oriented ridges and contractional geometries in the frontal prism and below the lower slope, (2) an extensional system controlled by NNW, NS and NE oriented westward dipping faults at the lower and middle slope, and (3) NNW-NS and NE oriented eastward dipping extensional faults at the upper continental slope. Overlying the acoustic top of the continental basement, at least two syn-extensional seismic sequences have been recognized that were correlated with onshore geological units and the Valparaíso Forearc Basin seismic sequences: Pliocene and Pre-Pliocene syn-extensional sequences. These sequences are separated by an erosional unconformity. Seismic reflection data reveal that the eastward dipping extensional system recognized at the upper slope can be extended to the middle slope and controlled the older seismic package. The westward dipping extensional system is essentially restricted to the middle slope. The tectonic boundary between the middle and upper continental slope is a prominent system of trenchward-dipping normal fault scarps (~1 km offset). This abrupt structural change can be readily detected along the Chilean erosive margin as well as the two extensional sets. Otherwise, evidences of positive inversion tectonics and thrusting have been recognized in the slope domain locally restricted to some eastern dipping faults. These contractional features could be related to gravitational deformation, which is favored by the regional inclination of the pre-Pliocene sequences. We propose that the structural configuration of the study area is dominantly controlled by tectonic erosion as well as the uplift of the Coastal Cordillera, and partially controlled by inherited architecture.

  20. The Current Tectonics of the Yukon and Adjacent Area

    NASA Astrophysics Data System (ADS)

    Hyndman, R. D.; Leonard, L. J.

    2014-12-01

    The current tectonics across the Yukon and adjacent areas of western Northwest Territories (NWT) and northern British Columbia appear to be driven primarily by the Yakutat Terrane collision, an "indenter" in the corner of the Gulf of Alaska. GPS data show 1-10 mm/yr northward and eastward, decreasing inland. The rates from earthquake statistics are similar although there are important discrepancies. The eastern Cordillera earthquake mechanisms are mainly thrust in the Mackenzie Mountains of southwestern NWT where the Cordillera upper crust is overthrusting the craton. To the north, the mechanisms are mainly strike-slip in the Richardson Mountains that appear to lie along the edge of the craton. The deformation appears to be limited to the hot and weak Cordillera with the strong craton providing an irregular eastern boundary. For example, there is an eastward bow in the craton edge and the deformation in the Mackenzie Mountains. On the Beaufort Sea margin in the region of the Mackenzie Delta there appears to be a type of "subduction zone" with the continent very slowly overthrusting the oceanic plate, a process that has continued since at least the Cretaceous. A northward moving continental margin block is bounded by left lateral faulting in the west (Canning Displacement Zone of eastern Alaska) and right lateral faulting in the east (Richardson Mountains in eastern Yukon). There is almost no seismicity on this thrust belt but as for some other subduction zones such as Cascadia there is the potential for very infrequent great earthquakes.

  1. Continental crust beneath the Agulhas Plateau, Southwest Indian Ocean

    SciTech Connect

    Tucholke, B.E.; Houtz, R.E.; Barrett, D.M.

    1981-05-10

    The Agulhas Plateau lies 500 km off the Cape of Good Hope in the southwestern Indian Ocean. Acoustic basement beneath the northern one third of this large, aseismic structural high has rugged morphology, but basement in the south is anomalously smooth, excepting a 30- to 90-km-wide zone with irregular relief that trends south-southwest through the center of the plateau. Seismic refraction profiles across the southern plateau indicate that the zone of irregular acoustic basement overlies thickened oceanic crust and that continental crust, locally thinned and intruded by basalts, underlies several regions of smooth acoustic basement. Recovery of quartzo-feldspathic gneisses in dredge hauls confirms the presence of continental crust. The smoothness of acoustic basement probably results from erosion (perhaps initially subaerial) of topographic highs with depositions and cementation of debris in ponds to form high-velocity beds. Basalt flows and sills also may contribute locally to form smooth basement. The rugged basement of the northern plateau appears to be of oceanic origin. A plate reconstruction to the time of initial opening of the South Atlantic places the continental part of the southern plateau adjacent to the southern edge of the Falkland Plateau, and both abut the western Mozambique Ridge. Both the Agulhas and Falkland plateaus were displaced westward during initial rifting in the Early Cretaceous. Formation of an RRR triple junction at the northern edge of the Agulhas continental fragment during middle Cretaceous time may explain the origin of the rugged, thickened oceanic crust beneath plateau as well as the apparent extension of the continental crust and intrusion of basaltic magmas beneath the southern plateau.

  2. The northern Egyptian continental margin

    NASA Astrophysics Data System (ADS)

    Badawy, Ahmed; Mohamed, Gad; Omar, Khaled; Farid, Walid

    2015-01-01

    Africa displays a variety of continental margin structures, tectonics and sedimentary records. The northern Egyptian continental margin represents the NE portion of the North African passive continental margin. Economically, this region is of great importance as a very rich and productive hydrocarbon zone in Egypt. Moreover, it is characterized by remarkable tectonic setting accompanied by active tectonic processes from the old Tethys to recent Mediterranean. In this article, seismicity of the northern Egyptian continental margin has been re-evaluated for more than 100-years and the source parameters of three recent earthquakes (October 2012, January 2013 and July 2013) have been estimated. Moment tensor inversions of 19th October 2012 and 17th January 2013 earthquakes reveal normal faulting mechanism with strike-slip component having seismic moment of 3.5E16 N m and 4.3E15 N m respectively. The operation of the Egyptian National Seismic Network (ENSN) since the end of 1997 has significantly enhanced the old picture of earthquake activity across northern Egyptian continental margin whereas; the record-ability (annual rate) has changed from 2-events/year to 54-event/year before and after ENSN respectively. The spatial distribution of earthquakes foci indicated that the activity tends to cluster at three zones: Mediterranean Ridge (MR), Nile Cone (NC) and Eratosthenes Seamount (ERS). However, two seismic gaps are reported along Levant Basin (LEV) and Herodotus Basin (HER).

  3. 76 FR 2919 - Outer Continental Shelf Official Protraction Diagram and Supplemental Official Outer Continental...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-18

    ... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf Official Protraction Diagram and Supplemental Official Outer Continental Shelf Block Diagrams AGENCY: Bureau of Ocean... American Datum of 1983 (NAD 83) Outer Continental Shelf Official Protraction Diagram and...

  4. Bioenergetics of Continental Serpentinites

    NASA Astrophysics Data System (ADS)

    Cardace, D.; Meyer-Dombard, D. R.

    2011-12-01

    Serpentinization is the aqueous alteration of ultramafic (Fe- and Mg-rich) rocks, resulting in secondary mineral assemblages of serpentine, brucite, iron oxyhydroxides and magnetite, talc, and possibly carbonate and silica-rich veins and other minor phases-all depending on the evolving pressure-temperature-composition of the system. The abiotic evolution of hydrogen and possibly organic compounds via serpentinization (McCollom and Bach, 2009) highlights the relevance of this geologic process to carbon and energy sources for the deep biosphere. Serpentinization may fuel life over long stretches of geologic time, throughout the global seabed and in exposed, faulted peridotite blocks (as at Lost City Hydrothermal Field, Kelley et al., 2005), and in obducted oceanic mantle units in ophiolites (e.g., Tiago et al., 2004). Relatively little work has been published on life in continental serpentinite settings, though they likely host a unique resident microbiota. In this work, we systematically model the serpentinizing fluid as an environmental niche. Reported field data for high and moderate pH serpentinizing fluids were modeled from Cyprus, the Philippines, Oman, Northern California, New Caledonia, Yugoslavia, Portugal, Italy, Newfoundland Canada, New Zealand, and Turkey. Values for Gibbs Energy of reaction (ΔGr), kJ per mole of electrons transferred for a given metabolism, are calculated for each field site. Cases are considered both for (1) modest assumptions of 1 nanomolar hydrogen and 1 micromolar methane, based on unpublished data for a similar northern California field site (Cardace and Hoehler, in prep.) and (2) an upper estimate of 10 nanomolar hydrogen and 500 micromolar methane. We survey the feasibility of microbial metabolisms for key steps in the nitrogen cycle, oxidation of sulfur in pyrite, iron oxidation or reduction reactions, sulfate reduction coupled to hydrogen or methane oxidation, methane oxidation coupled to the reduction of oxygen, and

  5. SOLIDS TRANSPORT BETWEEN ADJACENT CAFB FLUIDIZED BEDS

    EPA Science Inventory

    The report gives results of an experimental investigation of a pulsed, dense-phase pneumatic transport system for controlled circulation between adjacent fluidized beds. A model was developed to predict performance. The program provides technical support for EPA's program to demo...

  6. Border separation for adjacent orthogonal fields

    SciTech Connect

    Werner, B.L.; Khan, F.M.; Sharma, S.C.; Lee, C.K.; Kim, T.H. )

    1991-06-01

    Field border separations for adjacent orthogonal fields can be calculated geometrically, given the validity of some important assumptions such as beam alignment and field uniformity. Thermoluminescent dosimetry (TLD) measurements were used to investigate dose uniformity across field junctions as a function of field separation and, in particular, to review the CCSG recommendation for the treatment of medulloblastoma with separate head and spine fields.

  7. Changes in deep-water epibenthic megafaunal assemblages in relation to seabed slope on the Nigerian margin

    NASA Astrophysics Data System (ADS)

    Jones, Daniel O. B.; Mrabure, Charles O.; Gates, Andrew R.

    2013-08-01

    Local-scale habitat heterogeneity associated with changes in slope is a ubiquitous feature of bathyal continental margins. The response of deep-sea species to high habitat heterogeneity is poorly known and slope can be used as a proxy for many important ecological variables, such as current flow, sedimentation and substratum type. This study determines how slope angle effects megafaunal species density and diversity at the Usan field, offshore Nigeria, between 740 and 760 m depth. This deep-water area is increasingly exploited for hydrocarbons, yet lacking in baseline biological information. Replicated remotely operated vehicle video transect surveys were carried out using industry infrastructure (through the SERPENT Project) at a representative range of slopes (1°, 3°, 11° and 29°). Twenty-four species of benthic megafaunal invertebrate were found, numerically dominated by the echinoid Phormosoma placenta, and nine species of fish were observed. Megafaunal invertebrate deposit feeder density decreased significantly with increasing slope (density range 0.503-0.081 individuals m-2). Densities of megafaunal suspension feeders were very low except at the highest slope site (mean density 0.17 m-2). Overall species richness was greater on steeper slopes, although the richness of deposit feeders was not affected. Reduced labile organic matter in sediments on steeper slopes likely reduced deposit feeder densities, but increased current flow at higher slopes allowed both increased richness and density of suspension feeders.

  8. Understanding continental margin biodiversity: a new imperative.

    PubMed

    Levin, Lisa A; Sibuet, Myriam

    2012-01-01

    Until recently, the deep continental margins (200-4,000 m) were perceived as monotonous mud slopes of limited ecological or environmental concern. Progress in seafloor mapping and direct observation now reveals unexpected heterogeneity, with a mosaic of habitats and ecosystems linked to geomorphological, geochemical, and hydrographic features that influence biotic diversity. Interactions among water masses, terrestrial inputs, sediment diagenesis, and tectonic activity create a multitude of ecological settings supporting distinct communities that populate canyons and seamounts, high-stress oxygen minimum zones, and methane seeps, as well as vast reefs of cold corals and sponges. This high regional biodiversity is fundamental to the production of valuable fisheries, energy, and mineral resources, and performs critical ecological services (nutrient cycling, carbon sequestration, nursery and habitat support). It is under significant threat from climate change and human resource extraction activities. Serious actions are required to preserve the functions and services provided by the deep-sea settings we are just now getting to know. PMID:22457970

  9. Continental crust: a geophysical approach

    SciTech Connect

    Meissner, R.

    1986-01-01

    This book develops an integrated and balanced picture of present knowledge of the continental crust. Crust and lithosphere are first defined, and the formation of crusts as a general planetary phenomenon is described. The background and methods of geophysical studies of the earth's crust and the collection of related geophysical parameters are examined. Creep and friction experiments and the various methods of radiometric age dating are addressed, and geophysical and geological investigations of the crustal structure in various age provinces of the continents are studied. Specific tectonic structures such as rifts, continental margins, and geothermal areas are discussed. Finally, an attempt is made to give a comprehensive view of the evolution of the continental crust and to collect and develop arguments for crustal accretion and recycling. 647 references.

  10. The continental drift convection cell

    NASA Astrophysics Data System (ADS)

    Whitehead, J. A.; Behn, Mark D.

    2015-06-01

    Continents on Earth periodically assemble to form supercontinents and then break up again into smaller continental blocks (the Wilson cycle). Previous highly developed numerical models incorporate fixed continents while others indicate that continent movement modulates flow. Our simplified numerical model suggests that continental drift is fundamental. A thermally insulating continent is anchored at its center to mantle flow on an otherwise stress-free surface for infinite Prandtl number cellular convection with constant material properties. Rayleigh numbers exceed 107, while continent widths and chamber lengths approach Earth's values. The Wilson cycle is reproduced by a unique, rugged monopolar "continental drift convection cell." Subduction occurs at the cell's upstream end with cold slabs dipping at an angle beneath the moving continent (as found in many continent/subduction regions on Earth). Drift enhances vertical heat transport up to 30%, especially at the core-mantle boundary, and greatly decreases lateral mantle temperature differences.

  11. Mycorrhizal aspects in slope stabilisation

    NASA Astrophysics Data System (ADS)

    Graf, Frank

    2016-04-01

    In order to re-colonise and stabilise slopes affected by superficial soil failure with plants essential requirements have to be met: the plants must grow the plants must survive sustainably plant succession must start and continuously develop These requirements, however, are anything but easy given, particularly under the often hostile environmental conditions dominating on bare and steep slopes. Mycorrhizal fungi, the symbiotic partners of almost all plants used in eco-engineering, are said to improve the plants' ability to overcome periods governed by strongly (growth) limiting factors. Subsequently, results of investigations are presented of mycorrhizal effects on different plant and soil functions related to eco-engineering in general and soil and slope stabilisation in particular. Generally, inoculation yielded higher biomass of the host plants above as well as below ground. Furthermore, the survival rate was higher for mycorrhized compared to non-mycorrhized plants, particularly under extreme environmental conditions. However, the scale of the mycorrhizal impact may be species specific of both the plant host as well as the fungal partner(s) and often becomes evident only after a certain time lag. Depending on the plant-fungus combination the root length per soil volume was found to be between 0 and 2.5 times higher for inoculated compared to non-inoculated specimens. On an alpine graded ski slope the survival of inoculated compared to non-treated Salix herbacea cuttings was significant after one vegetation period only for one of the three added mycorrhizal fungus species. However, after three years all of the inoculated plantlets performed significantly better than the non-inoculated controls. The analysis of the potential for producing and stabilising soil aggregates of five different ectomycorrhizal fungi showed high variation and, for the species Inocybe lacera, no significant difference compared to untreated soil. Furthermore, inoculation of Salix

  12. Deep water challenges: Oil industry moves off continental shelf; meets new oceanographic data-gathering challenges

    SciTech Connect

    Mardell, G.; Flynn, J.

    1995-08-01

    While offshore oil industry activities move from the continental shelves to the continental slope and even onto the abyssal plains of the deep oceans, new oceanographic problems arise - from riser-deforming internal waves to ocean-floor avalanches. As well as soliton-induced currents, other subsurface flows need to be monitored to provide data in support of wide ranging underwater activities, including exploration drilling, deployment of subsea systems, diver and ROV operations, and pipe design, lay and inspection. This article examines some of the work carried out over the past year or so with data-gathering deep water moorings.

  13. Slope gradient and lithology as controls on the initiation of submarine slope gullies; Insights from the North Carnarvon Basin, Offshore NW Australia

    NASA Astrophysics Data System (ADS)

    Prélat, Amandine; Pankhania, Shyam S.; Jackson, Christopher A.-L.; Hodgson, David M.

    2015-11-01

    Slope-confined submarine gullies are present on many continental margins, yet the controls on their initiation and demise are poorly understood because modern or recently active systems are rarely if ever monitored, and exhumed systems, typically formed in very fine-grained successions, are poorly preserved at outcrop. We use 3D seismic reflection and borehole data from offshore NW Australia to investigate long-term (~ 40 Myr) variations in the geomorphology of Eocene-to-Miocene gullies that developed in mixed carbonate-clastic clinothems. Through time, clinoform slope gradient increases from 1.6° to 3.2°, with gullies forming when the clinoform slope exceeds 2.5°. After their inception, gullies increase in width (from 350 m to 770 m) and depth (from 37 m to 60 m). Slope steepening appears to coincide with a change from poorly cemented, fine-grained carbonate to better-cemented, coarse-grained carbonate, implying a secondary, lithological control on slope dip and, ultimately, gully formation.

  14. Mesozoic Bivalvia from Clerke and Mermaid Canyons, northwest Australian continental slope

    NASA Astrophysics Data System (ADS)

    Grant-Mackie, J. A.

    Four sets of rock samples from two sites off the northwest Australian shelf in 3625-4480 m of water contain macrofaunas, mainly bivalves, of warm shallow-water origin. Mermaid Canyon (16 deg 19 min S, 118 deg 23 min E) provided many samples of oolitic calcarenite containing Pseudopecten (Pseudopecten) dugong n.sp., indicating an Early Jurassic age and Tethyan relationship. Three hand-specimens from the ridge forming the western edge of Clerke Canyon (16 deg 29 min S, 118 deg 30 min E) yielded a Norian coral-?Lima-oyster assemblage and the Norian-Rhaetian bivalve Palaeocardita aff. globiformis (Boettger). The latter shows relationship with south-east Asian (Indonesia-Vietnam-south China) forms.

  15. Benthic study of the continental slope off Cape Hatteras, North Carolina. Volume 1. Executive summary

    SciTech Connect

    Diaz, R.J.; Blake, J.A.; Rhoads, D.C.

    1993-03-01

    Because of the potential impact on the environment associated with development and production activities, the Oil Pollution Act of 1990 mandated that a panel of experts, the North Carolina Environmental Sciences Review Panel (NCESRP), be convened. Their purpose was to consider whether the availability of scientific information was adequate for making decisions about oil and gas leasing, exploration, and development off North Carolina. The present study was developed by the Minerals Management Service because of concern raised by the NCESRP (1992) that not more than 5 percent of the unusual benthic community be covered by drill muds and cuttings. The principal task of the study was to determine if the communities extended over an area of the sea floor that was 20 time larger then the area estimated to be covered by drill muds and cuttings. If more than 5 percent of the unusual benthic community were covered by drill muds and cuttings, the NCESRP recommended that a study be carried out to determine the recovery rate of this community.

  16. Transport and transfer rates in the waters of the continental shelf and slope: SEEP

    SciTech Connect

    Biscaye, P.E.; Anderson, R.F.

    1990-12-01

    At this writing we are in the midst of the first year of the present funding period. This period was approved as a three year grant, but, with the planned restructuring of the DOE regional programs, it will undoubtedly be less than that. With the exception of some relatively minor participation in connection with the French ECOMARGE programme and finishing of some work on SEEP-1 samples, all of our efforts in the current year have been in the preparation and analysis of samples and data obtained during the SEEP-2 field experiment in 1988--1989. We review briefly the progress on these sediment trap samples and transmissometer data at present and the status anticipated at the end of the current funding year with respect to the several kinds of analyses planned for them. We also briefly review the status of the last of the work on SEEP-1 samples and data, and of our participation in other collaborative projects. 14 refs.

  17. Transient seafloor venting on continental slopes from warming-induced methane hydrate dissociation

    NASA Astrophysics Data System (ADS)

    Darnell, K. N.; Flemings, P. B.

    2015-12-01

    Methane held in frozen hydrate cages within marine sediment comprises one of the largest carbon reservoirs on the planet. Recent submarine observations of widespread methane seepage may record hydrate dissociation due to oceanic warming, which consequently may further amplify climate change. Here we simulate the effect of seafloor warming on marine hydrate deposits using a multiphase flow model. We show that hydrate dissociation, gas migration, and subsequent hydrate formation cangenerate temporary methane venting into the ocean through the hydrate stability zone. Methane seeps venting through the hydrate stability zone on the eastern Atlantic margin may record this process due to warming begun thousands of years ago. Our results contrast with the traditional view that venting occurs only updip of the hydrate stability zone.

  18. Histopathological assessment of liver and gonad pathology in continental slope fish from the northeast Atlantic Ocean.

    PubMed

    Feist, S W; Stentiford, G D; Kent, M L; Ribeiro Santos, A; Lorance, P

    2015-05-01

    The deep-sea environment is a sink for a wide variety of contaminants including heavy metals and organic compounds of anthropogenic origin. Life history traits of many deep-water fish species including longevity and high trophic position may predispose them to contaminant exposure and subsequent induction of pathological changes, including tumour formation. The lack of evidence for this hypothesis prompted this investigation in order to provide data on the presence of pathological changes in the liver and gonads of several deep-water fish species. Fish were obtained from the north east region of the Bay of Biscay (north east Atlantic Ocean) by trawling at depths between 700 and 1400 m. Liver and gonad samples were collected on board ship and fixed for histological processing and subsequent examination by light microscopy. Hepatocellular and nuclear pleomorphism and individual cases of ovotestis and foci of cellular alteration (FCA) were detected in black scabbardfish (Aphanopus carbo). Six cases of FCA were observed in orange roughy (Hoplostethus atlanticus) (n = 50) together with a single case of hepatocellular adenoma. A wide variety of inflammatory and degenerative lesions were found in all species examined. Deep-water fish display a range of pathologies similar to those seen in shelf-sea species used for international monitoring programmes including biological effects of contaminants. This study has confirmed the utility of health screening in deep-water fish for detecting evidence of prior exposure to contaminants and has also gained evidence of pathology potentially associated with exposure to algal toxins. PMID:25756900

  19. Gas hydrate that breaches the sea floor on the continental slope of the Gulf of Mexico

    SciTech Connect

    MacDonald, I.R.; Guinasso, N.L. Jr.; Sassen, R.; Brooks, J.M.; Lee, L. ); Scott, K.T. )

    1994-08-01

    We report observations that concern formation and dissociation of gas hydrate near the sea floor at depths of [minus]540 m in the northern Gulf of Mexico. In August 1992, three lobes of gas hydrate were partly exposed beneath a thin layer of sediment. By May 1993, the most prominent lobe had evidently broken free and floated away, leaving a patch of disturbed sediment and exposed hydrate. The underside of the gas hydrate was about 0.2[degree]C warmer than ambient sea water and had trapped a large volume of oil and free gas. An in situ monitoring device, deployed on a nearby bed of mussels, recorded sustained releases of gas during a 44 day monitoring period. Gas venting coincided with a temporary rise in water temperature of 1[degree]C, which is consistent with thermally induced dissociation of hydrate composed mainly of methane and water. We conclude that the effects of accumulating buoyant force and fluctuating water temperature cause shallow gas hydrate alternately to check and release gas venting. 18 refs., 3 figs., 1 tab.

  20. The Influence of Shales on Slope Instability

    NASA Astrophysics Data System (ADS)

    Stead, Doug

    2016-02-01

    Shales play a major role in the stability of slopes, both natural and engineered. This paper attempts to provide a review of the state-of-the-art in shale slope stability. The complexities of shale terminology and classification are first reviewed followed by a brief discussion of the important physical and mechanical properties of relevance to shale slope stability. The varied mechanisms of shale slope stability are outlined and their importance highlighted by reference to international shale slope failures. Stability analysis and modelling of anisotropic rock slope masses are briefly discussed and the potential role of brittle rock fracture and damage highlighted. A short review of shale slopes in open pits is presented.

  1. Drifter observations in the summer time Bay of Biscay slope current

    NASA Astrophysics Data System (ADS)

    Porter, M.; Inall, M. E.; Green, J. A. M.; Simpson, J. H.; Dale, A. C.; Miller, P. I.

    2016-05-01

    During the summer of 2012, 20 surface drifters drogued at 50 m depth were deployed on the continental slope to the north of the Bay of Biscay. Initially after release the drifters all crossed the slope, with 14 continuing equatorward, parallel to the slope following an absolute dynamic topography feature and 6 returning to the slope, in an eddy, visible in chlorophyll-a maps. Lagrangian statistics show an anisotropic flow field that becomes less tied to the absolute dynamic topography and increasingly dominated by diffusion and eddy processes. A weaker tie to the absolute dynamic topography allowed for total of 8 of the drifters crossed from the deep water onto the shelf, showing pathways for flow across the slope. A combination of drifter trajectories, absolute dynamic topography and chlorophyll-a concentration maps has been used to show that small anticyclonic eddies, tied to the complex slope topography provide a mechanism for on shelf transport. During the summer, the presence of these eddies can be seen in surface chlorophyll-a maps.

  2. Analysis and retracking of continental ice sheet radar altimeter waveforms

    NASA Technical Reports Server (NTRS)

    Martin, T. V.; Brenner, A. C.; Zwally, H. J.; Bindschadler, R. A.

    1983-01-01

    The Seasat-1 radar altimeter data set acquired over both the Antarctic and Greenland continental ice sheets is analyzed to obtain corrected ranges to the ice surface. The radar altimeter functional response over the continental ice sheets is considerably more complex than over the oceans. Causal factors identified in this complicated response include sloping surfaces, undulating ice surfaces with characteristic wavelengths on the same spatial scale as the altimeter beam-limited footprint, off-track reflections, and dynamic lag of the altimeter tracking circuit. Retracking methods using the altimeter return pulse waveforms give range corrections that are typically several meters. The entire set of Seasat-1 altimetry over the continental ice sheets is being retracked by fitting a multi-parameter function to each waveform. Many waveforms have double ramps indicating near-normal reflections from two distinct portions of the ice surface within the altimeter beam. Two independent range measurements differing by less than 25 m are obtained from retracking the double-ramp waveforms.

  3. A geophysical study of the northern Svalbard continental margin

    NASA Astrophysics Data System (ADS)

    Geissler, Wolfram H.; Jokat, Wilfried

    2004-07-01

    In the summer of 1999, the first systematic seismic profiles were acquired across the northern Svalbard continental margin east of 15°E. Approximately 1470 km of multi-channel seismic reflection data as well as sonobuoy wide-angle data were collected up to 82°N. With few exceptions the signals imaged the whole sedimentary cover down to the acoustic basement. The uppermost sedimentary deposits of the inner shelf yield P-wave velocities of 2 km s-1 and higher, indicating erosion and compaction due to a former ice load. The inner shelf east of Hinlopen Strait has only a thin veneer of over-consolidated sediments above the acoustic basement. Beneath the outer shelf, up to 3.5 km of sedimentary deposits cover the down-faulted acoustic basement. The continental slope is heavily eroded due to bottom current activity and slumping. At about 30°E the morphology of the continental slope has a smooth appearance. Shelf progradation only in the vicinity of glacial troughs crossing the shelf (associated with submarine fans) indicates main sediment transport by ice streams during former glacial periods. The maximum sedimentary thickness in the Sophia Basin is more than 9 km, and the Nansen Basin has a sediment thickness of 4.5 km close to the margin. Gravity modelling along the seismic profiles was performed to constrain the position of the continent-ocean transition. Existing sedimentary thickness and structural maps were extended over the area investigated. The new data provide no evidence for the presence of former extensive subaerial volcanic sequences (seaward-dipping reflectors), which would have been emplaced during the break-up along the margin. Thus, we consider this part of the margin as non-volcanic.

  4. Estimation of continental precipitation recycling

    NASA Technical Reports Server (NTRS)

    Brubaker, Kaye L.; Entekhabi, Dara; Eagleson, P. S.

    1993-01-01

    The total amount of water that precipitates on large continental regions is supplied by two mechanisms: 1) advection from the surrounding areas external to the region and 2) evaporation and transpiration from the land surface within the region. The latter supply mechanism is tantamount to the recycling of precipitation over the continental area. The degree to which regional precipitation is supplied by recycled moisture is a potentially significant climate feedback mechanism and land surface-atmosphere interaction, which may contribute to the persistence and intensification of droughts. Gridded data on observed wind and humidity in the global atmosphere are used to determine the convergence of atmospheric water vapor over continental regions. A simplified model of the atmospheric moisture over continents and simultaneous estimates of regional precipitation are employed to estimate, for several large continental regions, the fraction of precipitation that is locally derived. The results indicate that the contribution of regional evaporation to regional precipitation varies substantially with location and season. For the regions studied, the ratio of locally contributed to total monthly precipitation generally lies between 0. 10 and 0.30 but is as high as 0.40 in several cases.

  5. The Magnetic Signature of Zones of Continental Collision

    NASA Astrophysics Data System (ADS)

    Purucker, M. E.; Whaler, K. A.

    2007-12-01

    Near-surface and satellite maps of the crustal component of the magnetic field can be interpreted in terms of thermal conditions at depth because the magnetic properties of rocks depend on their temperature. Observations related to continental deformation at diffuse plate boundaries are often considered in relation to three length scales: the thickness of the seismogenic upper crust, the entire continental crust, and the mechanical lithosphere. The lower boundary of the magnetic crust coincides with the Moho, or in the presence of an elevated geotherm, with the Curie isotherm. New global perspectives on the magnetic signature of zones of continental collision are afforded by the recently published Magnetic Anomaly Map of the World (Purucker, 2007, EOS, 88, 263), the MF-5 satellite magnetic field (Maus et al., 2007, Gcubed), and NASA's ST-5 constellation mission in 2006. The thickness of the magnetic crust can be estimated by integrating the MF-5 satellite magnetic field into the 3SMAC compositional and thermal model of the lithosphere, and a minimum estimate of the magnetization can be estimated using a Greens function approach. We compare our magnetic maps with the diffuse plate boundary maps of Gordon (1998) and Dumoulin et al. (1998). The diffuse plate boundary zones exhibit intermediate (22-31 km) magnetic thicknessses, significantly less than those of the adjacent stable plate. The diffuse NE Asia plate boundary zone, from the Lena River delta to the Sea of Okhotsk, is especially well- expressed in both satellite and near-surface magnetic maps.

  6. 3-D view of erosional scars on U. S. Mid-Atlantic continental margin

    SciTech Connect

    Farre, J.A.; Ryan, W.B.

    1985-06-01

    Deep-towed side-scan and bathymetric data have been merged to present a 3-D view of the lower continental slope and upper continental rise offshore Atlantic City, New Jersey. Carteret Canyon narrows and becomes nearly stranded on the lower slope where it leads into one of two steep-walled, flat-floored erosional chutes. The floors of the chutes, cut into semilithified middle Eocene siliceous limestones, are marked by downslope-trending grooves. The grooves are interpreted to be gouge marks formed during rock and sediment slides. On the uppermost rise, beneath the chutes, is a 40-m deep depression. The origin of the depression is believed to be related to material moving downslope and encountering the change in gradient at the slope/rise boundary. Downslope of the depression are channels, trails, and allochthonous blocks. The lack of significant post-early Miocene deposits implies that the lower slope offshore New Jersey has yet to reach a configuration conducive to sediment accumulation. The age of erosion on the lower slope apparently ranges from late Eocene-early Miocene to the recent geologic past.

  7. Hydrological heterogeneity in Mediterranean reclaimed slopes: runoff and sediment yield at the patch and slope scales along a gradient of overland flow

    NASA Astrophysics Data System (ADS)

    Merino-Martín, L.; Moreno-de las Heras, M.; Pérez-Domingo, S.; Espigares, T.; Nicolau, J. M.

    2012-05-01

    Hydrological heterogeneity is recognized as a fundamental ecosystem attribute in drylands controlling the flux of water and energy through landscapes. Therefore, mosaics of runoff and sediment source patches and sinks are frequently identified in these dry environments. There is a remarkable scarcity of studies about hydrological spatial heterogeneity in restored slopes, where ecological succession and overland flow are interacting. We conducted field research to study the hydrological role of patches and slopes along an "overland flow gradient" (gradient of overland flow routing through the slopes caused by different amounts of run-on coming from upslope) in three reclaimed mining slopes of Mediterranean-continental climate. We found that runoff generation and routing in non-rilled slopes showed a pattern of source and sink areas of runoff. Such hydrological microenvironments were associated with seven vegetation patches (characterized by plant community types and cover). Two types of sink patches were identified: shrub Genista scorpius patches could be considered as "deep sinks", while patches where the graminoids Brachypodium retusum and Lolium perenne dominate were classified as "surface sinks" or "runoff splays". A variety of source patches were also identified spanning from "extreme sources" (Medicago sativa patches; equivalent to bare soil) to "poor sources" (areas scattered by dwarf-shrubs of Thymus vulgaris or herbaceous tussocks of Dactylis glomerata). Finally, we identified the volume of overland flow routing along the slope as a major controlling factor of "hydrological diversity" (heterogeneity of hydrological behaviours quantified as Shannon diversity index): when overland flow increases at the slope scale hydrological diversity diminishes.

  8. Adjacent Segment Pathology after Lumbar Spinal Fusion.

    PubMed

    Lee, Jae Chul; Choi, Sung-Woo

    2015-10-01

    One of the major clinical issues encountered after lumbar spinal fusion is the development of adjacent segment pathology (ASP) caused by increased mechanical stress at adjacent segments, and resulting in various radiographic changes and clinical symptoms. This condition may require surgical intervention. The incidence of ASP varies with both the definition and methodology adopted in individual studies; various risk factors for this condition have been identified, although a significant controversy still exists regarding their significance. Motion-preserving devices have been developed, and some studies have shown their efficacy of preventing ASP. Surgeons should be aware of the risk factors of ASP when planning a surgery, and accordingly counsel their patients preoperatively. PMID:26435804

  9. Geomorphological features in the southern Canary Island Volcanic Province: The importance of volcanic processes and massive slope instabilities associated with seamounts

    NASA Astrophysics Data System (ADS)

    Palomino, Desirée; Vázquez, Juan-Tomás; Somoza, Luis; León, Ricardo; López-González, Nieves; Medialdea, Teresa; Fernández-Salas, Luis-Miguel; González, Francisco-Javier; Rengel, Juan Antonio

    2016-02-01

    The margin of the continental slope of the Volcanic Province of Canary Islands is characterised by seamounts, submarine hills and large landslides. The seabed morphology including detailed morphology of the seamounts and hills was analysed using multibeam bathymetry and backscatter data, and very high resolution seismic profiles. Some of the elevation data are reported here for the first time. The shape and distribution of characteristics features such as volcanic cones, ridges, slides scars, gullies and channels indicate evolutionary differences. Special attention was paid to recent geological processes that influenced the seamounts. We defined various morpho-sedimentary units, which are mainly due to massive slope instability that disrupt the pelagic sedimentary cover. We also studied other processes such as the role of deep bottom currents in determining sediment distribution. The sediments are interpreted as the result of a complex mixture of material derived from a) slope failures on seamounts and submarine hills; and b) slides and slumps on the continental slope.

  10. Post-Ellesmerian depositional sequences of central North Slope subsurface

    SciTech Connect

    Noonan, W.G.

    1985-04-01

    Detailed electrical-log correlations of bedding in the Mesozoic to recent intervals define nearly time-equivalent stratigraphic units. Basinal depositional minima separate them into depositional cycles of 15 to 40-m.y. duration, and sequences of similar cycles correspond to the major episodes of Arctic tectonism. The close of the Sag River cycle in Pleinsbachian time ended the Ellesmerian sequence of accretionary tectonics and northerly continental provenance. Long,oscillating uplift to the northwest during the Jurassic Kingak cycle, and five or more subcycles of emergence along an ancestral Barrow arch rift shoulder during the Lower Cretaceous Kup River cycle show that the Barrovian sequence accompanied Arctic rifting. The Brookian sequence records a time of Arctic seafloor spreading coincident with underthrusting of the North Slope block toward a convergent Pacific margin. A series of major overthrusts onto the block from this margin were sources for Lower Torok, Nanushuk, Schrader Bluff, Prince Creek, and Franklin Bluffs cycles. The lower Torok source was in a distant westerly direction, and those of the following cycles became progressively closer and more southerly, ending near the present position of the central and western Brooks Range. A collision between Alaska and Siberia in mid-Tertiary time initiated the Eurekan sequence of circum-arctic compressional tectonics. The North Slope block was tilted northeast, and the Nuwok cycle was derived from the resulting regional erosion. Similar tilting and erosion beginning in the Pleistocene started the Gubik cycle that is still being deposited.

  11. Adjacent Segment Pathology after Anterior Cervical Fusion

    PubMed Central

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon

    2016-01-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of motion preservation technologies like total disc arthroplasty. The true nature and scope of ASP remains poorly understood. The etiology of ASP is most likely multifactorial. Various factors including altered biomechanical stresses, surgical disruption of soft tissue and the natural history of cervical disc disease contribute to the development of ASP. General factors associated with disc degeneration including gender, age, smoking and sports may play a role in the development of ASP. Postoperative sagittal alignment and type of surgery are also considered potential causes of ASP. Therefore, a spine surgeon must be particularly careful to avoid unnecessary disruption of the musculoligamentous structures, reduced risk of direct injury to the disc during dissection and maintain a safe margin between the plate edge and adjacent vertebrae during anterior cervical fusion. PMID:27340541

  12. Adjacent Segment Pathology after Anterior Cervical Fusion.

    PubMed

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon; Kim, Sung Kyu

    2016-06-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of motion preservation technologies like total disc arthroplasty. The true nature and scope of ASP remains poorly understood. The etiology of ASP is most likely multifactorial. Various factors including altered biomechanical stresses, surgical disruption of soft tissue and the natural history of cervical disc disease contribute to the development of ASP. General factors associated with disc degeneration including gender, age, smoking and sports may play a role in the development of ASP. Postoperative sagittal alignment and type of surgery are also considered potential causes of ASP. Therefore, a spine surgeon must be particularly careful to avoid unnecessary disruption of the musculoligamentous structures, reduced risk of direct injury to the disc during dissection and maintain a safe margin between the plate edge and adjacent vertebrae during anterior cervical fusion. PMID:27340541

  13. HDMR methods to assess reliability in slope stability analyses

    NASA Astrophysics Data System (ADS)

    Kozubal, Janusz; Pula, Wojciech; Vessia, Giovanna

    2014-05-01

    Stability analyses of complex rock-soil deposits shall be tackled considering the complex structure of discontinuities within rock mass and embedded soil layers. These materials are characterized by a high variability in physical and mechanical properties. Thus, to calculate the slope safety factor in stability analyses two issues must be taken into account: 1) the uncertainties related to structural setting of the rock-slope mass and 2) the variability in mechanical properties of soils and rocks. High Dimensional Model Representation (HDMR) (Chowdhury et al. 2009; Chowdhury and Rao 2010) can be used to carry out the reliability index within complex rock-soil slopes when numerous random variables with high coefficient of variations are considered. HDMR implements the inverse reliability analysis, meaning that the unknown design parameters are sought provided that prescribed reliability index values are attained. Such approach uses implicit response functions according to the Response Surface Method (RSM). The simple RSM can be efficiently applied when less than four random variables are considered; as the number of variables increases, the efficiency in reliability index estimation decreases due to the great amount of calculations. Therefore, HDMR method is used to improve the computational accuracy. In this study, the sliding mechanism in Polish Flysch Carpathian Mountains have been studied by means of HDMR. The Southern part of Poland where Carpathian Mountains are placed is characterized by a rather complicated sedimentary pattern of flysh rocky-soil deposits that can be simplified into three main categories: (1) normal flysch, consisting of adjacent sandstone and shale beds of approximately equal thickness, (2) shale flysch, where shale beds are thicker than adjacent sandstone beds, and (3) sandstone flysch, where the opposite holds. Landslides occur in all flysch deposit types thus some configurations of possible unstable settings (within fractured rocky

  14. Furrowed outcrops of Eocene chalk on the lower continental slop offshore New Jersey

    USGS Publications Warehouse

    Robb, James M.; Kirby, John R.; Hampson, John C., Jr.; Gibson, Patricia R.; Hecker, Barbara

    1983-01-01

    A sea bottom of middle Eocene calcareous claystone cut by downslope-trending furrows was observed during an Alvin dive to the mouth of Berkeley Canyon on the continental slope off New Jersey. The furrows are 10 to 50 m apart, 4 to 13 m deep, linear, and nearly parallel in water depths of 2,000 m. They have steep walls and flat floors 3 to 5 m wide, of fine-grained sediment. Mid-range sidescan-sonar images show that similarly furrowed surfaces are found on nearby areas of the lower continental slope, not associated with canyons. The furrows are overlain in places by Pleistocene sediments. Although they show evidence of erosional origin, they do not appear to be related to observed structures, and their straight, parallel pattern is not well understood. A general cover of flocky unconsolidated sediments implies that bottom-current erosion is not active now.

  15. Submarine processes of the middle Atlantic continental rise based on GLORIA imagery

    USGS Publications Warehouse

    Schlee, J.S.; Robb, James M.

    1991-01-01

    Approximately 6100 km of 3.5-kHz echo-sounding profiles was correlated with a GLORIA side-scan sonar image of the mid-Atlantic United States (34??N, 70??W) lower slope-upper continental rise. The image allows us to map the major erosional and depositional features and to identify major processes that have shaped the area. Interpretation of GLORIA imagery and echo-sounding profiles indicates that mass movement is the predominant process affecting sediment on the United States east coast mid-Atlantic slope and upper rise and that isobath-parallel sediment movement by geostrophic currents is restricted mainly to the lower continental rise. The mass-movement processes evident on the rise probably were most active during the Pleistocene, when sea level was lower and sediment input more active. -from Authors

  16. Fluid-escape structures and slope instabilities along the French Guiana margin

    NASA Astrophysics Data System (ADS)

    Loncke, L.; Gaullier, V.; Basile, C.; Maillard, A.; Patriat, M.; Vendeville, B. C.; Folens, L.; Roest, W.

    2009-04-01

    Many of the world's passive margins are shear margins. Those margins present a very steep ocean-continent boundary which is expressed by high surface-slope gradients. In this type of margins, complex rift structures including wrench and strike-slip faults affect the continental crust. These rift basins usually trap organic matter, hence kerogen that later become hydrocarbons. Along the Guiana margin, late cretaceous black Shales provide additional organic matter. The French Guiana margin has been recently surveyed (GUYAPLAC cruise, 2003) allowing the discovery of a giant pockmark field likely caused by active degassing of deep reservoirs and expressed at the surface through giant elongated pock-marks. These pockmarks are systematically associated with massive slope instabilities and underlying polygonal fault network. Major seaward collapses seem to have affected the margin, and the breakup unconformity is tilted seaward. We believe that fluid overpressure above Cretaceous under-consolidated organic rocks may have destabilized part of the sedimentary cover, allowing massive escape of fluids toward the surface, as is suggested further North by geotechnical analyses made after leg ODP 207 (O'Regan & Moran, 2007). A compactional origin of fluids is also possible. In any case, the specific structural pattern of the Guiana transform margin, with a seaward tilted geometry and no marginal ridge, may favour particularly active fluid releases and slope instabilities (favoured by the decrease in sediment's strength related to high pore-fluid pressure). As suggested by O'Regan & Moran (2007) it is possible also that fluid migration occurs along the break-up unconformity, which crops out along the very steep continental slope. If this is correct, a great part of fossil hydrocarbon resources may escape to the surface along of the Guiana and Surinam continental margins. References: O'Regan M. & K. Moran, 2007. Compressibility, permeability and stress history of sediments from

  17. Biodiversity and ecological composition of macrobenthos on cold-water coral mounds and adjacent off-mound habitat in the bathyal Porcupine Seabight, NE Atlantic

    NASA Astrophysics Data System (ADS)

    Henry, Lea-Anne; Roberts, J. Murray

    2007-04-01

    The cold-water scleractinian corals Lophelia pertusa and Madrepora oculata form mound structures on the continental shelf and slope in the NE Atlantic. This study is the first to compare the taxonomic biodiversity and ecological composition of the macrobenthos between on- and off-mound habitats. Seven box cores from the summits of three mounds and four cores from an adjacent off-mound area in the Belgica Mound Province in the Porcupine Seabight yielded 349 species, including 10 undescribed species. On-mound habitat was three times more speciose, and was richer with higher evenness and significantly greater Shannon's diversity than off-mound. Species composition differed significantly between habitats and the four best discriminating species were Pliobothrus symmetricus (more frequent off-mound), Crisia nov. sp, Aphrocallistes bocagei and Lophelia pertusa (all more frequent on-mound). Filter/suspension feeders were significantly more abundant on-mound, while deposit feeders were significantly more abundant off-mound. Species composition did not significantly differ between mounds, but similarity within replicates decreased from Galway Mound

  18. Dip-slope and Dip-slope Failures in Taiwan - a Review

    NASA Astrophysics Data System (ADS)

    Lee, C.

    2011-12-01

    Taiwan is famous for dip-slope and dip-slope slides. Dip-slopes exist at many places in the fold-and-thrust belt of Taiwan. Under active cutting of stream channels and man-made excavations, a dip-slope may become unstable and susceptible for mass sliding. Daylight of a bedding parallel clay seam is the most dangerous type for dip-slope sliding. Buckling or shear-off features may also happen at toe of a long dip-slope. Besides, a dip-slope is also dangerous for shallow debris slides, if the slope angle is between 25 to 45 degrees and the debris (colluvium or slope wash) is thick (>1m). These unstable slopes may slide during a triggering event, earthquake or typhoon storm; or even slide without a triggering event, like the 2010 Tapu case. Initial buckling feature had been found in the dip-slope of the Feitsui arch dam abutment after detailed explorations. Shear-off feature have also been found in dip-slope located in right bank of the Nahua reservoir after field investigation and drilling. The Chiufengerhshan slide may also be shear-off type. On the other hand, the Tapu, the Tsaoling slides and others are of direct slide type. The Neihoo Bishan slide is a shallow debris slide on dip-slope. All these cases demonstrate the four different types of dip-slope slide. The hazard of a dip-slope should be investigated to cover these possible types of failure. The existence of bedding parallel clay seams is critical for the stability of a dip-slope, either for direct slide or buckling or shear-off type of failure, and is a hot point during investigation. Because, the stability of a dip-slope is changing with time, therefore, detailed explorations to including weathering and erosion rates are also very necessary to ensure the long-term stability of a dip-slope.

  19. Potential geologic hazards on the eastern Gulf of Cadiz slope (SW Spain)

    USGS Publications Warehouse

    Baraza, J.; Ercilla, G.; Nelson, C.H.

    1999-01-01

    Geologic hazards resulting from sedimentary, oceanographic and tectonic processes affect more than one third of the offshore Gulf of Cadiz, and are identified by interpreting high-resolution seismic profiles and sonographs. Hazards of sedimentary origin include the occurrence of slope instability processes in the form of single or multiple slumps occupying up to 147 km2 mainly concentrated in the steeper, upper slope area. Besides the presence of steep slopes, the triggering of submarine landslides is probably due to seismic activity and favoured by the presence of biogenic gas within the sediment. Gassy sediments and associated seafloor pockmarks cover more than 240 km2 in the upper slope. Hazards from oceanographic processes result from the complex system of bottom currents created by the interaction of the strong Mediterranean Undercurrent and the rough seafloor physiography. The local intensification of bottom currents is responsible for erosive processes along more than 1900 km2 in the upper slope and in the canyons eroded in the central area of the slope, undermining slopes and causing instability. The strong bottom currents also create a mobile seafloor containing bedforms in an area of the Gulf that extends more than 2500 km2, mostly in the continental slope terraces. Hazards of tectonic origin are important because the Gulf of Cadiz straddles two major tectonic regions, the Azores-Gibraltar fracture zone and the Betic range, which results in diapir uplift over an area of more than 1000 km2, and in active seismicity with earthquakes of moderate magnitude. Also, tsunamis produced by strong earthquakes occur in the Gulf of Cadiz, and are related to the tectonic activity along the Azores-Gibraltar fracture zone.

  20. Production and remineralization in continental shelf ecosystems: A test of the SEEP hypothesis

    SciTech Connect

    Rowe, G.T.

    1986-09-01

    The hypothesis that continental shelf ecosystems export a major fraction of the carbon produced by the phytoplankton during the spring bloom was tested during the Shelf Edge Exchange Processes (SEEP) experiment off the northeast US coast in 1984. This study, along with a reanalysis of traditional concepts, leads to the conclusion that only a small fraction of continental shelf phytodetritus is exported across a distinct shelf-slope hydrographic frontal system. What is not consumed in the spring is utilized on the shelf during the ensuing stratified season. More open ended ecosystems may export production more readily. The total benthic standing stocks in terms of organic carbon (macrofauna, meiofauna, and bacteria) have been estimated in the SEEP area. Their preponderance on the continental shelf was partial evidence that little organic matter escapes to the upper continental slope. Measurements of the metabolism of the biota allowed calculation of turnover times of organic detritius and the total biota. The turnover time of detritus increased as grain size decreased, suggesting that fine-grained deposits contain mostly refractory, nonreactive compounds, especially on the deep slope. Turnover times of the total biota were about the same in the coarse versus fine-grained shelf deposits, but a far larger fraction of the turnover was attributed to the bacteria in the fine sediments than in the coarse. On average, about 25% of the primary production appeared to be utilized by the aerobic benthos on the continental shelf in the SEEP area. The role of anaerobes at depth in the sediments remains uncertain.

  1. Transport and transfer rates in the waters of the continental shelf. Annual report

    SciTech Connect

    Biscaye, P.E.

    1980-09-01

    The goal of govern project is to understand and quantify the processes that the transport and dispersal of energy-related pollutants introduced to the waters of the continental shelf and slope. The report is divided into sections dealing with processes associated with suspended solids; processes associated with sediments sinks for radionuclides and other pollutants; and spreading of water characteristics and species in solution. (ACR)

  2. Arctic and Antarctic submarine gullies—A comparison of high latitude continental margins

    NASA Astrophysics Data System (ADS)

    Gales, J. A.; Forwick, M.; Laberg, J. S.; Vorren, T. O.; Larter, R. D.; Graham, A. G. C.; Baeten, N. J.; Amundsen, H. B.

    2013-11-01

    Submarine gullies are common features of high latitude continental slopes and, over the last decade, have been shown to play a key role in continental margin evolution, submarine erosion, downslope sediment transport, slope deposits, and the architecture of petroleum reservoirs. However, the processes that form these gullies, the timescales over which they develop, and the environmental controls influencing their morphology remain poorly constrained. We present the first systematic and comparative analysis between Arctic and Antarctic gullies with the aim of identifying differences in slope character, from which we infer differences in processes operating in these environments. Quantitative analysis of multibeam echosounder data along 2441 km of the continental shelf and upper slope and morphometric signatures of over 1450 gullies show that six geomorphically distinct gully types exist on high latitude continental margins. We identify distinct differences between Arctic and Antarctic gully morphologies. In the Arctic data sets, deep relief (> 30 m gully incision depth at 50 m below the shelf edge) and shelf-incising gullies are lacking. These differences have implications for the timescales over which the gullies were formed and for the magnitude of the flows that formed them. We consider two hypotheses for these differences: (1) some Antarctic gullies developed through several glacial cycles; and (2) larger Antarctic gullies were formed since the Last Glacial Maximum as a result of erosive flows (i.e., sediment-laden subglacial meltwater) being more abundant on parts of the Antarctic margin over longer timescales. A second difference is that unique gully signatures are observed on Arctic and on Antarctic margins. Environmental controls, such as the oceanographic regime and geotechnical differences, may lead to particular styles of gully erosion observed on Arctic and Antarctic margins.

  3. Plankton blooms, ocean circulation and the European slope current: Response to weather and climate in the Bay of Biscay and W English Channel (NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Pingree, Robin D.; Garcia-Soto, Carlos

    2014-08-01

    The flow of upper-layer surface water and circulation for the Bay of Biscay, continental slope and in the wider region of the NE Atlantic is presented, as well as the seasonality of flow and internal tides. The marine plankton environments of Biscay Ocean, Biscay Eddies, Biscay Slope and Biscay Shelf are defined. The Shelf region (Armorican and Celtic) is further divided into Stratified Shelf, Frontal and Tidally Mixed. Seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data. Mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined. Some regional responses for the slope current, dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the Bay of Biscay and around the British Isles are suggested and discussed. An example of the Eastern European Ocean Margin continental slope response to winter weather (sea level atmospheric pressure forcing) resulting in warm winter water in the southern Bay of Biscay (Navidad, with eddy production) and off the Shetland continental slopes (the warm-water supply route to the Arctic) is given from the slope climate observation series.

  4. The continental margin is a key source of iron to the HNLC North Pacific Ocean

    SciTech Connect

    Lam, P.J.; Bishop, J.K.B

    2008-01-15

    Here we show that labile particulate iron and manganese concentrations in the upper 500m of the Western Subarctic Pacific, an iron-limited High Nutrient Low Chlorophyll (HNLC) region, have prominent subsurface maxima between 100-200 m, reaching 3 nM and 600 pM, respectively. The subsurface concentration maxima in particulate Fe are characterized by a more reduced oxidation state, suggesting a source from primary volcagenic minerals such as from the Kuril/Kamchatka margin. The systematics of these profiles suggest a consistently strong lateral advection of labile Mn and Fe from redox-mobilized labile sources at the continental shelf supplemented by a more variable source of Fe from the upper continental slope. This subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing, and is likely a key source of bioavailable Fe to the HNLC North Pacific.

  5. The continental margin is a key source of iron to the HNLC North Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Lam, Phoebe J.; Bishop, James K. B.

    2008-04-01

    Here we show that labile particulate iron and manganese concentrations in the upper 500 m of the Western Subarctic Pacific, an iron-limited High Nutrient Low Chlorophyll (HNLC) region, have prominent subsurface maxima between 100-200 m, reaching 3 nM and 600 pM, respectively. The subsurface concentration maxima in particulate Fe are characterized by a more reduced oxidation state, suggesting a source from primary volcagenic minerals such as from the Kuril/Kamchatka margin. The systematics of these profiles suggest a consistently strong lateral advection of labile Mn and Fe from redox-mobilized labile sources at the continental shelf supplemented by a more variable source of Fe from the upper continental slope. This subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing, and is likely a key source of bioavailable Fe to the HNLC North Pacific.

  6. Reconstructing genome mixtures from partial adjacencies.

    PubMed

    Mahmoody, Ahmad; Kahn, Crystal L; Raphael, Benjamin J

    2012-01-01

    Many cancer genome sequencing efforts are underway with the goal of identifying the somatic mutations that drive cancer progression. A major difficulty in these studies is that tumors are typically heterogeneous, with individual cells in a tumor having different complements of somatic mutations. However, nearly all DNA sequencing technologies sequence DNA from multiple cells, thus resulting in measurement of mutations from a mixture of genomes. Genome rearrangements are a major class of somatic mutations in many tumors, and the novel adjacencies (i.e. breakpoints) resulting from these rearrangements are readily detected from DNA sequencing reads. However, the assignment of each rearrangement, or adjacency, to an individual cancer genome in the mixture is not known. Moreover, the quantity of DNA sequence reads may be insufficient to measure all rearrangements in all genomes in the tumor. Motivated by this application, we formulate the k-minimum completion problem (k-MCP). In this problem, we aim to reconstruct k genomes derived from a single reference genome, given partial information about the adjacencies present in the mixture of these genomes. We show that the 1-MCP is solvable in linear time in the cases where: (i) the measured, incomplete genome has a single circular or linear chromosome; (ii) there are no restrictions on the chromosomal content of the measured, incomplete genome. We also show that the k-MCP problem, for k ≥ 3 in general, and the 2-MCP problem with the double-cut-and-join (DCJ) distance are NP-complete, when there are no restriction on the chromosomal structure of the measured, incomplete genome. These results lay the foundation for future algorithmic studies of the k-MCP and the application of these algorithms to real cancer sequencing data. PMID:23282028

  7. Continental collisions and seismic signature

    NASA Astrophysics Data System (ADS)

    Meissner, R.; Wever, Th.; Sadowiak, P.

    1991-04-01

    Reflection seismics in compressional belts has revealed the structure of crustal shortening and thickening processes, showing complex patterns of indentation and interfingering of colliding crusts and subcrustal lithospheres. Generally, in the upper crust large zones of detachments develop, often showing duplexes and 'crocodile' structures. The lower crust from zones of active collision (e.g. Alps, Pyrenees) is characterized by strongly dipping reflections. The base of the crust with the Moho must be continuously equilibrating after orogenic collapse as areas of former continental collision exhibit flat Mohos and subhorizontal reflections. The depth to the Moho increases during collision and decreases after the onset of post-orogenic extension, until finally the crustal root disappears completely together with the erosion of the mountains. Processes, active during continental collisions and orogenic collapse, create distinct structures which are imaged by reflection seismic profiling. Examples are shown and discussed.

  8. Inorganic geochemistry of surface sediments of the Ebro shelf and slope, northwestern Mediterranean

    USGS Publications Warehouse

    Gardner, J.V.; Dean, W.E.; Alonso, B.

    1990-01-01

    Distributions of major, minor, and trace elements in surface sediment of the continental shelf and upper slope of the northeastern Spanish continental margin reflect the influences of discharge from the Ebro River and changes in eustatic sea levels. Multivariate factor analysis of sediment geochemistry was used to identify five groupings of samples (factors) on the shelf and slope. The first factor is an aluminosilicate factor that represents detrital clastic material. The second factor is a highly variable amount of excess SiO2 and probably represents a quartz residuum originating from winnowing of relict detrital sediments. A carbonate factor (Factor 3) has no positive correlation with other geochemical parameters but is associated with the sand-size fraction. The carbonate in these sediments consists of a mixture of biogenic calcite and angular to subangular detrital grains. Organic carbon is associated with the aluminosilicate factor (Factor 1) but also factors out by itself (Factor 4); this suggests that there may be two sources of organic matter, terrestrial and marine. The fifth factor comprises upper slope sediments that contain high concentrations of manganese. The most likely explanation for these high manganese concentrations is precipitation of Mn oxyhydroxides at the interface between Mn-rich, oxygen-deficient, intermediate waters and oxygenated surface waters. During eustatic low sea levels of the glacial Pleistocene, the Ebro Delta built across the outer continental shelf and deposited sediment with fairly high contents of organic carbon and continental components. The period of marine transgression from eustatic low (glacial) to eustatic high (interglacial) sea levels was characterized by erosion of the outer shelf delta and surficial shelf sediments and the transport of sediment across the slope within numerous canyons. Once eustatic high sea level was reached, delta progradation resumed on the inner shelf. Today, coarse-grained sediment (silt and

  9. Low-frequency currents and continental shelf waves in the southern Weddell Sea

    SciTech Connect

    Middleton, J.H.; Foster, T.D.; Foldvik, A.

    1982-07-01

    The salient features of low-frequency current fluctuations, obtained from an analysis of eight current meter records from the continental shelf and slope of the southern Weddell sea, are compared to baroclinic and barotropic theories. A simple baroclinic theory of internal waves is used successfully to predict high-frequency spectral cutoff values from low-frequency velocity ellipse calculations made from the continental slope mooring data. The success of this theory indicates that the higher spectral energy levels observed over the slope compared to the shelf are probably due to baroclinic motions. A barotropic model of free continental shelf waves proposed by Saint-Guily (1976) is adapted for the local topography and the predictions of the model compared to observations. Coherences and phases between moorings separated by 10 and 160 km in the long-shelf direction provide substantial evidence of the existence of shelf waves as predicted by the theory for periods of 3--60 days and for the lowest three modes. For periods of 3--8 days rotary spectral levels indicate anticlockwise rotating current vectors over the shelf as predicted by theory, but for longer periods current vectors rotate clockwise. It is speculated that fluctuations in along-shelf wind stress drive the shelf waves but that the longer period motions are driven directly by the wind stress.

  10. Why does continental convergence stop

    SciTech Connect

    Hynes, A.

    1985-01-01

    Convergence between India and Asia slowed at 45 Ma when they collided, but continues today. This requires that substantial proportions of the Indian and/or Asian lithospheric mantle are still being subducted. The resulting slab-pull is probably comparable with that from complete lithospheric slabs and may promote continued continental convergence even after collision. Since descending lithospheric slabs are present at all collision zones at the time of collision such continued convergence may be general after continental collisions. It may cease only when there is a major (global) plate reorganization which results in new forces on the convergent continents that may counteract the slab-pull. These inferences may be tested on the late Paleozoic collision between Gondwanaland and Laurasia. This is generally considered to have been complete by mid-Permian time (250 Ma). However, this may be only the time of docking of Gondwanaland with North America, not that of the cessation of convergence. Paleomagnetic polar-wander paths for the Gondwanide continents exhibit consistently greater latitudinal shifts from 250 Ma to 200 Ma than those of Laurasia when corrected for post-Triassic drift, suggesting that convergence continued through late Permian well into the Triassic. It may have been accommodated by crustal thickening under what is now the US Coastal Plain, or by strike-slip faulting. Convergence may have ceased only when Pangea began to fragment again, in which case the cause for its cessation may be related to the cause of continental fragmentation.

  11. Continental crust beneath southeast Iceland.

    PubMed

    Torsvik, Trond H; Amundsen, Hans E F; Trønnes, Reidar G; Doubrovine, Pavel V; Gaina, Carmen; Kusznir, Nick J; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D; Griffin, William L; Werner, Stephanie C; Jamtveit, Bjørn

    2015-04-14

    The magmatic activity (0-16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland--and especially the Öræfajökull volcano--is characterized by a unique enriched-mantle component (EM2-like) with elevated (87)Sr/(86)Sr and (207)Pb/(204)Pb. Here, we demonstrate through modeling of Sr-Nd-Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2-6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  12. Continental crust beneath southeast Iceland

    PubMed Central

    Torsvik, Trond H.; Amundsen, Hans E. F.; Trønnes, Reidar G.; Doubrovine, Pavel V.; Gaina, Carmen; Kusznir, Nick J.; Steinberger, Bernhard; Corfu, Fernando; Ashwal, Lewis D.; Griffin, William L.; Werner, Stephanie C.; Jamtveit, Bjørn

    2015-01-01

    The magmatic activity (0–16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Iceland—and especially the Öræfajökull volcano—is characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of Sr–Nd–Pb abundances and isotope ratios that the primitive Öræfajökull melts could have assimilated 2–6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of ∼350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume. PMID:25825769

  13. Outer Continental Shelf environmental assessment program. Final reports of principal investigators. Volume 33

    SciTech Connect

    Not Available

    1985-07-01

    This ccompilation of five final reports deals with the distribution and dynamics of heavy metals in Alaskan Shelf environments; characterization of organic matter in sediments; distribution of trace elements in bottom sediment of the Northern Bering Sea; aspects of size distributions, clay mineralogy, and geochemistry of sediments of the Beaufort Sea and adjacent deltas; and the natural distribution and dynamics of hydrocarbons on the Alaskan continental shelf.

  14. Continental basaltic volcanoes — Processes and problems

    NASA Astrophysics Data System (ADS)

    Valentine, G. A.; Gregg, T. K. P.

    2008-11-01

    Monogenetic basaltic volcanoes are the most common volcanic landforms on the continents. They encompass a range of morphologies from small pyroclastic constructs to larger shields and reflect a wide range of eruptive processes. This paper reviews physical volcanological aspects of continental basaltic eruptions that are driven primarily by magmatic volatiles. Explosive eruption styles include Hawaiian and Strombolian ( sensu stricto) and violent Strombolian end members, and a full spectrum of styles that are transitional between these end members. The end-member explosive styles generate characteristic facies within the resulting pyroclastic constructs (proximal) and beyond in tephra fall deposits (medial to distal). Explosive and effusive behavior can be simultaneous from the same conduit system and is a complex function of composition, ascent rate, degassing, and multiphase processes. Lavas are produced by direct effusion from central vents and fissures or from breakouts (boccas, located along cone slopes or at the base of a cone or rampart) that are controlled by varying combinations of cone structure, feeder dike processes, local effusion rate and topography. Clastogenic lavas are also produced by rapid accumulation of hot material from a pyroclastic column, or by more gradual welding and collapse of a pyroclastic edifice shortly after eruptions. Lava flows interact with — and counteract — cone building through the process of rafting. Eruption processes are closely coupled to shallow magma ascent dynamics, which in turn are variably controlled by pre-existing structures and interaction of the rising magmatic mixture with wall rocks. Locations and length scales of shallow intrusive features can be related to deeper length scales within the magma source zone in the mantle. Coupling between tectonic forces, magma mass flux, and heat flow range from weak (low magma flux basaltic fields) to sufficiently strong that some basaltic fields produce polygenetic

  15. Large slope failures in the La Paz basin, Bolivian Andes

    NASA Astrophysics Data System (ADS)

    Roberts, N. J.; Hermanns, R. L.; Rabus, B.; Guzmán, M. A.; Minaya, E.; Clague, J. J.

    2014-12-01

    The La Paz basin in the eastern Bolivian Andes has been a hotspot for large-scale, deep-seated gravitational slope deformation during the Holocene. In less than 2 Ma, a network of steep-sided valleys up to 800 m deep formed in sediments of the Altiplano Plateau and underlying basement rocks. We characterize the distribution, extent, mechanisms, and modern activity of large-scale failures within this landscape using optical image interpretation, existing geologic maps, synthetic RADAR interferometry (InSAR), and field investigation. Deposits of nearly 20 landslides larger than 100 Mm3 occur within the basin. Most failures have occurred in weakly lithified Late Miocene to Pliocene sedimentary rocks and include earth flows, translational and rotational landslides, and plug flows. Failures in underlying tectonized Paleozoic sedimentary rocks include bedding-parallel rockslides. The largest failure is the 3 km3 Achcocalla earth flow (ca. 11 ka BP), which ran out ~20 km. Other dated events span the period from the early Holocene to nearly the Colonial historic period. InSAR results show that many large slope failures, including the Achocalla earth flow, are currently moving at rates of a few centimeters to a few decimeters per year. Rapid deposition, shallow burial, and rapid incision of the basin fills produced steep slopes in weak geologic materials that, coupled with groundwater discharge from the valley walls, are the primary controls on instability. In contrast, the Altiplano surface has changed little in 2 Ma and the adjacent slopes of the Cordilleran Real, although steep, are relatively stable. Of the over 100 landslides that have occurred in the city of La Paz since the early twentieth century, most are at the margins of large, deep-seated prehistoric failures, and two of the most damaging historic landslides (Hanko-Hanko, 1582; Pampahasi, 2011) were large-scale reactivations of previously failed slopes. Improved understanding of large, deep-seated landslides in

  16. Numerical investigation of large amplitude second mode internal solitary waves over a slope-shelf topography

    NASA Astrophysics Data System (ADS)

    Guo, C.; Chen, X.

    A numerical study of the propagation and transformation of large amplitude second mode concave internal solitary waves (ISWs) over a slope-shelf topography is presented. A fully nonlinear and non-hydrostatic numerical model is employed and solved. The fluid stratification, amplitude of the incident wave, and inclination of the bottom topography are taken close to those in the northern South China Sea (SCS), where the continental slope and shelf span quite a large area. It is found that the incoming wave adjusts permanently to the changing depth in deep water without essential changes of the wave profile until it gets close to the shelf break, where the frontal face becomes flatter and the rear face steeper. A very steep wave structure is formed at the leading edge just after the wave passes by the shelf break. This steep structure does not progress into a new soliton of concave type, but slopes more and more gently. The trailing edge of the initial concave wave becomes steeper and steeper and gradually develops into a packet of convex ISWs. Finally the rear convex wave packet catches up with the frontal concave wave. The two wave systems then "merge" and travel forward steadily with almost permanent profile. No events of wave breaking occur with the model configuration close to the realistic slope-shelf of the northern SCS. Finally, amplitudes of the incident wave and inclination of the slope are varied, and different scenarios take place before and after the wave reaches the shelf break.

  17. PERCENT OF CROPLAND ON STEEP SLOPES

    EPA Science Inventory

    Clearing land for agriculture tends to increase soil erosion. The amount of erosion is related to the steepness of the slope, farming methods used and soil type. High amounts of cropland on steep slopes can increase the amount of soil erosion leading to increased sediment in sur...

  18. PERCENT AGRICULTURAL LAND COVER ON STEEP SLOPES

    EPA Science Inventory

    Clearing land for agriculture tends to increase soil erosion. The amount of erosion is related to the steepness of the slope, farming methods used and soil type. High amounts of agriculture on steep slopes can increase the amount of soil erosion leading to increased sediment in ...

  19. Lithologic variations in slope development theory

    USGS Publications Warehouse

    Scheidegger, Adrian E.

    1964-01-01

    This paper presents a comprehensive review and amplification of the writer's earlier slope development theory. In particular, the influence of lithology on evolving slope profiles is investigated and calculations are made for various conditions, such as presence of caprock, soft bottom, and hard and soft intermediate layers.

  20. Slope Stability. CEGS Programs Publication Number 15.

    ERIC Educational Resources Information Center

    Pestrong, Raymond

    Slope Stability is one in a series of single-topic problem modules intended for use in undergraduate and earth science courses. The module, also appropriate for use in undergraduate civil engineering and engineering geology courses, is a self-standing introduction to studies of slope stability. It has been designed to supplement standard…

  1. Modelling continental deformation within global plate tectonic reconstructions

    NASA Astrophysics Data System (ADS)

    Williams, S.; Whittaker, J.; Heine, C.; Müller, P.

    2010-12-01

    A limitation of regional and global plate tectonic models is the way continental deformation is represented. Continental blocks are typically represented as rigid polygons - overlaps or gaps between adjacent continental blocks represent extension or compression respectively. Full-fit reconstructions of major ocean basins result in large overlaps between the conjugate continental plates, on the basis that the continental margins are highly extended compared to their pre-rift state. A fundamental challenge in generating more robust global-scale plate reconstructions is the incorporation of a more quantitative description of the kinematics within extended passive margins, based on observations. We have used the conjugate Southern Australia and Wilkes Land, Antarctica margins as a case study, and as part of this work have generated revised sediment thickness maps for these margins. These datasets are used to test different approaches for generating full-fit reconstructions in order to create a framework of methodologies that is globally applicable. One approach is to restore two conjugate continent-ocean boundaries (COBs) to their pre-rift configuration and then use the geometric fitting method of Hellinger (1981) and Royer and Chang (1991), used to generate fits of seafloor isochrons, to generate a “full-fit” Euler pole. To quantitatively restore the COBs to their palinspastic pre-rift configuration we integrate estimates of crustal thickness along small circle paths, defined by an initial estimate of the Euler stage pole describing plate motions during continental rifting. We then use the conjugate sets of restored COB’s as inputs to the geometric fitting method, treating them as isochrons, and so generate poles of rotation for the plate configuration prior to rifting. Two potential shortcomings of this methodology are that (1) the conjugate margins are treated independently, whereas in reality they were actually one continuous continental basin during rifting

  2. Slope-scale dynamic states of rockfalls

    NASA Astrophysics Data System (ADS)

    Agliardi, F.; Crosta, G. B.

    2009-04-01

    Rockfalls are common earth surface phenomena characterised by complex dynamics at the slope scale, depending on local block kinematics and slope geometry. We investigated the nature of this slope-scale dynamics by parametric 3D numerical modelling of rockfalls over synthetic slopes with different inclination, roughness and spatial resolution. Simulations were performed through an original code specifically designed for rockfall modeling, incorporating kinematic and hybrid algorithms with different damping functions available to model local energy loss by impact and pure rolling. Modelling results in terms of average velocity profiles suggest that three dynamic regimes (i.e. decelerating, steady-state and accelerating), previously recognized in the literature through laboratory experiments on granular flows, can set up at the slope scale depending on slope average inclination and roughness. Sharp changes in rock fall kinematics, including motion type and lateral dispersion of trajectories, are associated to the transition among different regimes. Associated threshold conditions, portrayed in "phase diagrams" as slope-roughness critical lines, were analysed depending on block size, impact/rebound angles, velocity and energy, and model spatial resolution. Motion in regime B (i.e. steady state) is governed by a slope-scale "viscous friction" with average velocity linearly related to the sine of slope inclination. This suggest an analogy between rockfall motion in regime B and newtonian flow, whereas in regime C (i.e. accelerating) an analogy with a dilatant flow was observed. Thus, although local behavior of single falling blocks is well described by rigid body dynamics, the slope scale dynamics of rockfalls seem to statistically approach that of granular media. Possible outcomes of these findings include a discussion of the transition from rockfall to granular flow, the evaluation of the reliability of predictive models, and the implementation of criteria for a

  3. Geometry and significance of stacked gullies on the northern California slope

    USGS Publications Warehouse

    Field, M.E.; Gardner, J.V.; Prior, D.B.

    1999-01-01

    Recent geophysical surveys off northern California reveal patterns of gullies on the sea floor and preserved within continental-slope deposits that represent both erosional and aggradational processes. These surveys, conducted as part of the STRATAFORM project, combined multibeam bathymetry and backscatter with high-resolution seismic profiles. These data provide a new basis for evaluating gully morphology, distribution, and their significance to slope sedimentation and evolution. The continental margin off northern California exhibits an upper slope that has undergone both progradation and aggradation. The slope surface, which dips at <2??to 4.0??, contains a set of straight, evenly spaced, and parallel to sub-parallel gullies that begin at the 380-m isobath and extend onto the Eel and Klamath plateaus and into Trinity Canyon. The surface gullies are typically 100-m wide or more and only 1-2 m deep. The gullied slope is underlain by a sedimentary sequence that contains abundant buried gullies to subsurface depths of over 150 m. Although some of the buried gullies are distinctly erosional, most are part of the aggradational pattern responsible for the overall growth of the slope. The latest phase of gully erosion is marked by a gullied surface lying <20 m below the present-day sea floor. These erosional gullies locally truncate individual reflectors, have small depositional levees, and exhibit greater relief than do overlying gullies exposed on the sea floor. The older subsurface gullies document a period of widespread, but minor, erosion and downslope transport, presumably from a large, proximal sediment source. The cycles of downcutting and gully excavation are a minor part of the stratigraphic section, and are likely related to the combined influence of lower sea levels and higher sediment yields. During aggradation of the slope depositional sequences, sediment was draped over the gully features, producing sediment layers that mimic the underlying gully form

  4. Controls on slope-wash erosion rates in the Mojave Desert

    NASA Astrophysics Data System (ADS)

    Crouvi, O.; Polyakov, V. O.; Pelletier, J. D.; Rasmussen, C.

    2014-06-01

    This study estimates the rates of soil erosion by slope wash in an arid region and the various factors that control these rates. Decadal-scale erosion rates were estimated on hillslope scales using inventories of 137Cs that were sampled from 46 soil profiles in four different study sites in the Mojave Desert. Calculated mean soil erosion rates per site range from -3.6 to -24.3 t ha-1 yr-1. Higher mean rates were associated with gently sloping sites that exhibit low percentage of rock and vegetation coverage, whereas lower mean rates corresponded to steep and rocky sites. Individual erosion rates were not correlated to slope gradient or curvature but were negatively correlated with the volume fraction of rocks in the upper soil profile (i.e., upslope rock coverage). Since the slopes get rockier as they get steeper, any increase in erosion rates with increasing slope is outweighed by the inhibiting effect of greater rock cover. This, together with sandy-loam soil texture on the steep slopes hinders runoff and erosion. Our findings are supported by soil data that show greater heterogeneity in the degree of calcic soil development and higher soluble salt contents in more gently sloping sites that are characterized by high erosion rates. The erosion rates reported here for the gently sloping sites are higher than rates calculated for semi-arid regions, probably due to the lower rock and vegetation coverage in these sites compared to wetter areas. These rates are also higher than millennial-scale rates estimated for the Mojave Desert on watershed scales, and suggest that at least part of the eroded sediments are stored in the adjacent streams and do not reach the piedmonts.

  5. Alaskan North Slope petroleum systems

    USGS Publications Warehouse

    Magoon, L.B.; Lillis, P.G.; Bird, K.J.; Lampe, C.; Peters, K.E.

    2003-01-01

    Six North Slope petroleum systems are identified, described, and mapped using oil-to-oil and oil-to-source rock correlations, pods of active source rock, and overburden rock packages. To map these systems, we assumed that: a) petroleum source rocks contain 3.2 wt. % organic carbon (TOC); b) immature oil-prone source rocks have hydrogen indices (HI) >300 (mg HC/gm TOC); c) the top and bottom of the petroleum (oil plus gas) window occur at vitrinite reflectance values of 0.6 and 1.0% Ro, respectively; and d) most hydrocarbons are expelled within the petroleum window. The six petroleum systems we have identified and mapped are: a) a southern system involving the Kuna-Lisburne source rock unit that was active during the Late Jurassic and Early Cretaceous; b) two western systems involving source rock in the Kingak-Blankenship, and GRZ-lower Torok source rock units that were active during the Albian; and c) three eastern systems involving the Shublik-Otuk, Hue Shale and Canning source rock units that were active during the Cenozoic. The GRZ-lower Torok in the west is correlative with the Hue Shale to the east. Four overburden rock packages controlled the time of expulsion and gross geometry of migration paths: a) a southern package of Early Cretaceous and older rocks structurally-thickened by early Brooks Range thrusting; b) a western package of Early Cretaceous rocks that filled the western part of the foreland basin; c) an eastern package of Late Cretaceous and Paleogene rocks that filled the eastern part of the foreland basin; and d) an offshore deltaic package of Neogene rocks deposited by the Colville, Canning, and Mackenzie rivers. This petroleum system poster is part of a series of Northern Alaska posters on modeling. The poster in this session by Saltus and Bird present gridded maps for the greater Northern Alaskan onshore and offshore that are used in the 3D modeling poster by Lampe and others. Posters on source rock units are by Keller and Bird as well as

  6. Effect of sea-level variation on upper-slope depositional processes offshore of Tiber delta, Tyrrhenian Sea, Italy

    USGS Publications Warehouse

    Chiocci, F.L.; Normark, W.R.

    1992-01-01

    The upper slope and outer shelf in front of the Tiber River mouth (east-central Tyrrhenian Sea) exhibits a series of about 15 gullies that are not clearly related to present-day erosional or depositional processes. An extensive, high-resolution, seismic-reflection profiling survey of a 450 km2 area in front of the Tiber delta shows several generations of similar features within the older depositional sequences underlying the outer continental shelf. The gully relief appears dominantly depositional, probably developed during lowstand periods when the Tiber River mouth was relatively near the shelf break. The position of the gullied intervals, including those on the modern slope relict from the last lowstand, shows a successive northward shift with time. This northward shift indicates continued tilting of this part of the eastern Tyrrhenian continental margin, probably resulting from a continued subsidence to the north. ?? 1992.

  7. Exchange coupling between laterally adjacent nanomagnets.

    PubMed

    Dey, H; Csaba, G; Bernstein, G H; Porod, W

    2016-09-30

    We experimentally demonstrate exchange-coupling between laterally adjacent nanomagnets. Our results show that two neighboring nanomagnets that are each antiferromagnetically exchange-coupled to a common ferromagnetic bottom layer can be brought into strong ferromagnetic interaction. Simulations show that interlayer exchange coupling effectively promotes ferromagnetic alignment between the two nanomagnets, as opposed to antiferromagnetic alignment due to dipole-coupling. In order to experimentally demonstrate the proposed scheme, we fabricated arrays of pairs of elongated, single-domain nanomagnets. Magnetic force microscopy measurements show that most of the pairs are ferromagnetically ordered. The results are in agreement with micromagnetic simulations. The presented scheme can achieve coupling strengths that are significantly stronger than dipole coupling, potentially enabling far-reaching applications in Nanomagnet Logic, spin-wave devices and three-dimensional storage and computing. PMID:27535227

  8. Seismicity in Azerbaijan and Adjacent Caspian Sea

    SciTech Connect

    Panahi, Behrouz M.

    2006-03-23

    So far no general view on the geodynamic evolution of the Black Sea to the Caspian Sea region is elaborated. This is associated with the geological and structural complexities of the region revealed by geophysical, geochemical, petrologic, structural, and other studies. A clash of opinions on geodynamic conditions of the Caucasus region, sometimes mutually exclusive, can be explained by a simplified interpretation of the seismic data. In this paper I analyze available data on earthquake occurrences in Azerbaijan and the adjacent Caspian Sea region. The results of the analysis of macroseismic and instrumental data, seismic regime, and earthquake reoccurrence indicate that a level of seismicity in the region is moderate, and seismic event are concentrated in the shallow part of the lithosphere. Seismicity is mostly intra-plate, and spatial distribution of earthquake epicenters does not correlate with the plate boundaries.

  9. Boundary Layers of Air Adjacent to Cylinders

    PubMed Central

    Nobel, Park S.

    1974-01-01

    Using existing heat transfer data, a relatively simple expression was developed for estimating the effective thickness of the boundary layer of air surrounding cylinders. For wind velocities from 10 to 1000 cm/second, the calculated boundary-layer thickness agreed with that determined for water vapor diffusion from a moistened cylindrical surface 2 cm in diameter. It correctly predicted the resistance for water vapor movement across the boundary layers adjacent to the (cylindrical) inflorescence stems of Xanthorrhoea australis R. Br. and Scirpus validus Vahl and the leaves of Allium cepa L. The boundary-layer thickness decreased as the turbulence intensity increased. For a turbulence intensity representative of field conditions (0.5) and for νwindd between 200 and 30,000 cm2/second (where νwind is the mean wind velocity and d is the cylinder diameter), the effective boundary-layer thickness in centimeters was equal to [Formula: see text]. PMID:16658855

  10. The Peruvian Continental Margin: Results from wide angle seismic Data

    NASA Astrophysics Data System (ADS)

    Krabbenhoeft, A.; Bialas, J.; Kopp, H.; Kukowski, N.; Huebscher, C.

    2003-04-01

    Within the scope of the GEOPECO (Geophysical Experiments at the Peruvian Continental Margin) project, seismic investigations along the Pacific margin of Peru were carried out using ocean bottom hydrophones (OBH) and seismometers (OBS) recording marine airgun shots. The structure and the P- wave velocity of the oblique subducting Nazca and overriding South-American Plates from 8°S to 15°S were determined by forward modeling and tomographic inversion of the wide-angle seismic data combined with the analysis of reflection seismic data. The region south of 12°S has been influenced by the southward migration of the aseismic Nazca Ridge the past 11 Ma. The oceanic Nazca Plate is divided by Mendana Fracture Zone (MFZ) which marks a transition zone of a different crustal age of approximately 28 Ma in the north to 38 Ma in the south at the Peruvian trench. North of MFZ the oceanic crust is influenced by Trujillo Trough trending N15E and the surrounding extensional stresses leading to a crustal thinning as can be seen in the northernmost refraction seismic model. The oceanic crust south of MFZ is overall homogeneous with a thin pelagic sedimentary layer and normal oceanic crustal layers. The P-wave velocity of the mantle is overall 7.9-8.1km/s. The Peruvian Continental Margin is characterized by the continental slope and several basins, Trujillo and Yaquina basin, Lima basin and Pisco basin, which are partly affected by the southward migration of the subducting Nazca Ridge. This caused uplift and subsidence along the margin leading to erosional tectonic features. The basins and continental basement could be mapped with forward modeling and tomographic inversion as well as the continental backstop on each profile. An accretionary prism is set up with a width of 20 to 30 km and 4 to 5 km thickness which does not further increase in size as revealed by the profiles recorded further north of Nazca Ridge. This and a taper of 14- 17 degrees at the collision zone indicates that

  11. 30 CFR 56.9103 - Clearance on adjacent tracks.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Clearance on adjacent tracks. 56.9103 Section..., Hauling, and Dumping Traffic Safety § 56.9103 Clearance on adjacent tracks. Railcars shall not be left on side tracks unless clearance is provided for traffic on adjacent tracks....

  12. 30 CFR 57.9103 - Clearance on adjacent tracks.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Clearance on adjacent tracks. 57.9103 Section..., Hauling, and Dumping Traffic Safety § 57.9103 Clearance on adjacent tracks. Railcars shall not be left on side tracks unless clearance is provided for traffic on adjacent tracks....

  13. 30 CFR 56.9103 - Clearance on adjacent tracks.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 30 Mineral Resources 1 2011-07-01 2011-07-01 false Clearance on adjacent tracks. 56.9103 Section..., Hauling, and Dumping Traffic Safety § 56.9103 Clearance on adjacent tracks. Railcars shall not be left on side tracks unless clearance is provided for traffic on adjacent tracks....

  14. 30 CFR 57.9103 - Clearance on adjacent tracks.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Clearance on adjacent tracks. 57.9103 Section..., Hauling, and Dumping Traffic Safety § 57.9103 Clearance on adjacent tracks. Railcars shall not be left on side tracks unless clearance is provided for traffic on adjacent tracks....

  15. 33 CFR 80.1395 - Puget Sound and adjacent waters.

    Code of Federal Regulations, 2010 CFR

    2010-07-01

    ... 33 Navigation and Navigable Waters 1 2010-07-01 2010-07-01 false Puget Sound and adjacent waters... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1395 Puget Sound and adjacent waters. The 72 COLREGS shall apply on all waters of Puget Sound and adjacent waters, including Lake...

  16. 33 CFR 80.1395 - Puget Sound and adjacent waters.

    Code of Federal Regulations, 2013 CFR

    2013-07-01

    ... 33 Navigation and Navigable Waters 1 2013-07-01 2013-07-01 false Puget Sound and adjacent waters... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1395 Puget Sound and adjacent waters. The 72 COLREGS shall apply on all waters of Puget Sound and adjacent waters, including Lake...

  17. 33 CFR 80.1395 - Puget Sound and adjacent waters.

    Code of Federal Regulations, 2011 CFR

    2011-07-01

    ... 33 Navigation and Navigable Waters 1 2011-07-01 2011-07-01 false Puget Sound and adjacent waters... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1395 Puget Sound and adjacent waters. The 72 COLREGS shall apply on all waters of Puget Sound and adjacent waters, including Lake...

  18. 33 CFR 80.1395 - Puget Sound and adjacent waters.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... 33 Navigation and Navigable Waters 1 2014-07-01 2014-07-01 false Puget Sound and adjacent waters... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1395 Puget Sound and adjacent waters. The 72 COLREGS shall apply on all waters of Puget Sound and adjacent waters, including Lake...

  19. 33 CFR 80.1395 - Puget Sound and adjacent waters.

    Code of Federal Regulations, 2012 CFR

    2012-07-01

    ... 33 Navigation and Navigable Waters 1 2012-07-01 2012-07-01 false Puget Sound and adjacent waters... INTERNATIONAL NAVIGATION RULES COLREGS DEMARCATION LINES Thirteenth District § 80.1395 Puget Sound and adjacent waters. The 72 COLREGS shall apply on all waters of Puget Sound and adjacent waters, including Lake...

  20. Organic geochemistry of continental margin and deep ocean sediments

    SciTech Connect

    Whelan, J.K.; Hunt, J.M.; Eglinton, T.; Dickinson, P.; Johnson, C.; Buxton, L.; Tarafa, M.E.

    1990-08-01

    The objective of this research continues to be the understanding of the complex processes of fossil fuel formation and migration. DOE funded research to date has focused on case histories'' of down-hole well profiles of light hydrocarbons, pyrograms, pyrolysis-GC and -GCMS parameters, and biomarker data from wells in the Louisiana and Texas Gulf Coasts the Alaskan North Slope. In the case of the Alaskan North Slope, geological data and one-dimensional maturation modeling have been integrated in order to better constrain possible source rocks, timing, and migration routes for oil and gas generation and expulsion processes.This period, biomarker analyses and organic petrographic analyses were completed for the Ikpikpuk well. In the case of the Gulf Coast, we have obtained a one-dimensional maturation model of the Cost B-1 well in E. Cameron field of the Louisiana Gulf Coast. The completed E. Cameron data set adds to the enigma of the Gulf Coast oils found on the continental shelf of Louisiana. If significant quantities of the oil are coming from relatively organic lean Tertiary rocks, then non-conventional'' expulsion and migration mechanisms, such as gas dissolved in oil must be invoked to explain the Gulf Coast oils reservoired on the Louisiana continental shelf. We are designing and starting to assemble a hydrous pyrolysis apparatus to follow, the laboratory, rates of generation and expulsion of sediment gases. Initiation of some new research to examine {delta}{sup 13}C of individual compounds from pyrolysis is also described. We are beginning to examine both the laboratory and field data from the Gulf Coast in the context of a Global Basin Research Network (GBRN). The purpose is to better understand subsurface fluid flow processes over geologic time in sedimentary basins and their relation to resource accumulation (i.e., petroleum and metal ores). 58 refs.

  1. Uncovering the glacial history of the Irish continental shelf (Invited)

    NASA Astrophysics Data System (ADS)

    Dunlop, P.; Benetti, S.; OCofaigh, C.

    2013-12-01

    In 1999 the Irish Government initiated a €32 million survey of its territorial waters known as the Irish National Seabed Survey (INSS). The INSS is amongst the largest marine mapping programmes ever undertaken anywhere in the world and provides high-resolution multibeam, backscatter and seismic data of the seabed around Ireland. These data have been used to provide the first clear evidence for extensive glaciation of the continental shelf west and northwest of Ireland. Streamlined drumlins on the mid to outer shelf record former offshore-directed ice flow towards the shelf edge and show that the ice sheet was grounded in a zone of confluence where ice flowing onto the shelf from northwest Ireland merged with ice flowing across the Malin Shelf from southwest Scotland. The major glacial features on the shelf are well developed nested arcuate moraine systems that mark the position of the ice sheet margin and confirm that the former British Irish Ice Sheet was grounded as far as the shelf edge around 100 km offshore of west Donegal at the last glacial maximum. Distal to the moraines, on the outermost shelf, prominent zones of iceberg plough marks give way to the Barra/Donegal fan and a well developed system of gullies and canyons which incise the continental slope. Since 2008 several scientific cruises have retrieved cores from the shelf and slope to help build a more detailed understanding of glacial events in this region. This presentation will provide an overview of the glacial history of the Irish shelf and will discuss ongoing research programmes that are building on the initial research findings to produce a better understanding of the nature and timing of ice sheet events in this region.

  2. Database on unstable rock slopes in Norway

    NASA Astrophysics Data System (ADS)

    Oppikofer, Thierry; Nordahl, Bo; Bunkholt, Halvor; Nicolaisen, Magnus; Hermanns, Reginald L.; Böhme, Martina; Yugsi Molina, Freddy X.

    2014-05-01

    Several large rockslides have occurred in historic times in Norway causing many casualties. Most of these casualties are due to displacement waves triggered by a rock avalanche and affecting coast lines of entire lakes and fjords. The Geological Survey of Norway performs systematic mapping of unstable rock slopes in Norway and has detected up to now more than 230 unstable slopes with significant postglacial deformation. This systematic mapping aims to detect future rock avalanches before they occur. The registered unstable rock slopes are stored in a database on unstable rock slopes developed and maintained by the Geological Survey of Norway. The main aims of this database are (1) to serve as a national archive for unstable rock slopes in Norway; (2) to serve for data collection and storage during field mapping; (3) to provide decision-makers with hazard zones and other necessary information on unstable rock slopes for land-use planning and mitigation; and (4) to inform the public through an online map service. The database is organized hierarchically with a main point for each unstable rock slope to which several feature classes and tables are linked. This main point feature class includes several general attributes of the unstable rock slopes, such as site name, general and geological descriptions, executed works, recommendations, technical parameters (volume, lithology, mechanism and others), displacement rates, possible consequences, hazard and risk classification and so on. Feature classes and tables linked to the main feature class include the run-out area, the area effected by secondary effects, the hazard and risk classification, subareas and scenarios of an unstable rock slope, field observation points, displacement measurement stations, URL links for further documentation and references. The database on unstable rock slopes in Norway will be publicly consultable through the online map service on www.skrednett.no in 2014. Only publicly relevant parts of

  3. SLOPE PROFILOMETRY OF GRAZING INCIDENCE OPTICS.

    SciTech Connect

    TAKACS,P.Z.

    2003-01-14

    Profiling instruments are well-suited to the measurement of grazing incidence optics, such as those found in synchrotron radiation beam lines. Slope measuring profilers, based upon the principle of the pencil beam interferometer, have proven to be especially useful in measuring the figure and slope errors on cylindrical aspheres. The Long Trace Profiler, in various configurations, is the most widely used of this class of profiler. Current performance provides slope measurement accuracy at the microradian level and height measurements accurate to 25 nm over 1 meter trace lengths.

  4. Thermal models pertaining to continental growth

    NASA Technical Reports Server (NTRS)

    Morgan, Paul; Ashwal, Lew

    1988-01-01

    Thermal models are important to understanding continental growth as the genesis, stabilization, and possible recycling of continental crust are closely related to the tectonic processes of the earth which are driven primarily by heat. The thermal energy budget of the earth was slowly decreasing since core formation, and thus the energy driving the terrestrial tectonic engine was decreasing. This fundamental observation was used to develop a logic tree defining the options for continental growth throughout earth history.

  5. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction

    PubMed Central

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-01-01

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins. PMID:24301173

  6. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    PubMed

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-01-01

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins. PMID:24301173

  7. Continental aggregation, subduction initiation, and plume generation

    NASA Astrophysics Data System (ADS)

    Heron, P. J.; Lowman, J. P.

    2013-12-01

    Several processes unfold during the supercontinent cycle, more than one of which might result in an elevation in subcontinental mantle temperatures through the generation of mantle plumes. Paleogeographic plate reconstructions have indicated that sub-continental mantle upwellings appear below large continents that are extensively ringed by subduction zones. Moreover, several numerical simulations of supercontinent formation and dispersal attribute the genesis of sub-continental plumes to the generation of subduction zones on the edges of the supercontinent, rather than resulting from continental insulation. However, the role of the location of downwellings in producing a return-flow upwelling, and on increasing sub-continental mantle temperatures, is not fully understood. In this mantle convection study, we examine the evolution of mantle dynamics after supercontinent accretion over a subduction zone (analogous to the formation of Pangea) for a range of continental coverage. We present 2D and 3D Cartesian geometry mantle convection simulations, featuring geotherm- and pressur