New Insight Into the Crustal Structure of the Continental Margin offshore NW Sabah/Borneo

NASA Astrophysics Data System (ADS)

Barckhausen, U.; Franke, D.; Behain, D.; Meyer, H.

2002-12-01

The continental margin offshore NW Sabah/Borneo (Malaysia) has been investigated with reflection and refraction seismics, magnetics, and gravity during the recent cruise BGR01-POPSCOMS. A total of 4000 km of geophysical profiles has been acquired, thereof 2900 km with reflection seismics. The focus of investigations was on the deep water areas. The margin looks like a typical accretionary margin and was presumably formed during the subduction of a proto South China Sea. Presently, no horizontal movements between the two plates are being observed. Like in major parts of the South China Sea, the area seaward of the Sabah Trough consists of extended continental lithosphere which is characterised by a pattern of rotated fault blocks and half grabens and a carbonate platform of Early Oligocene to Early Miocene age. We found evidence that the continental crust also underlies the Sabah Trough and the adjacent continental slope, a fact that raises many questions about the tectonic history and development of this margin. The tectonic pattern of the Dangerous Grounds' extended continental crust can be traced a long way landward of the Sabah Trough beneath the sedimentary succession of the upper plate. The magnetic anomalies which are dominated by the magnetic signatures of relatively young volcanic features also continue under the continental slope. The sedimentary rocks of the upper plate, in contrast, seem to generate hardly any magnetic anomalies. Based on the new data we propose the following scenario for the development of the NW Sabah continental margin: Seafloor spreading in the present South China Sea started at about 30 Ma in the Late Oligocene. The spreading process separated the Dangerous Grounds area from the SE Asian continent and ceased in late Early Miocene when the oceanic crust of the proto South China Sea was fully subducted in eastward direction along the Borneo-Palawan Trough. During Lower and/or Middle Miocene, Borneo rotated counterclockwise and was

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

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

Durophagous Predation by King Crabs on the Continental Slope off Antarctica

NASA Astrophysics Data System (ADS)

Smith, K.; Aronson, R. B.; Steffel, B. V.; McClintock, J. B.; Amsler, M.; Thatje, S.

2016-02-01

For perhaps tens of millions of years, marine communities in Antarctica have been essentially devoid of durophagous (shell-crushing) predators, which have been excluded by low temperatures. In their absence, the resident species have evolved in isolation and are slow-moving with limited defenses. Rapidly rising sea temperatures around Antarctica are now relaxing the cold-thermal barrier and appear to be allowing deep-water king crabs (Lithodidae) to move up the continental slope, into shallower water. Their potential to emerge on the continental shelf could drastically restructure the endemic communities that live there; in other areas of the world, lithodids are typically generalist predators of invertebrates. Their diet in Antarctic waters remains unknown and it has been speculated that they are opportunistic scavengers. We report the findings of a trapping study conducted in deep water off the western Antarctic Peninsula in 2015. Stomach contents were analyzed for 18 adult Paralomis birsteini trapped on the continental slope. P. birsteini feed primarily on invertebrates such as echinoderms, gastropods and polychaetes. By understanding the prey species targeted by slope-dwelling lithodids, we can begin to project the future impact of an expansion of king crabs onto the Antarctic continental shelf.

Geology of continental margins

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

With continued high interest in offshore petroleum exploration, the 1977 AAPG Short Course presents the latest interpretations of new data bearing on the geology and geophysics of continental margins. Seven well-known earth scientists have organized an integrated program covering major topics involved in the development of ocean basins and continental margins with emphasis on the slopes and rises. The discussion of plate tectonics and evolution of continental margins is followed by presentations on the stratigraphy and structure of pull-apart and compressional margins. Prospective petroleum source rocks, their organic content, rate of burial, and distribution on slopes and rises of differentmore » margin types is covered. Prospective reservoir rock patterns are related to depositional processes and to the sedimentary and structural histories for different types of continental margins. Finally, the seismic recognition of depositional facies on slopes and rises for different margin types with varying rates of sediment supply during eustatic sea-level changes are discussed. The course with this syllabus offers an invaluable opportunity for explorationists to refresh their understanding of the geology associated with an important petroleum frontier. In addition, the course sets forth a technical frame of reference for the case-histoy papers to be presented later in the AAPG Research Symposium on the Petroleum Potential of Slopes, Rises, and Plateaus.« less

Can sea level rise cause large submarine landslides on continental slopes?

NASA Astrophysics Data System (ADS)

Urlaub, Morelia

2014-05-01

Submarine landslides are one of the volumetrically most important sediment transport processes at continental margins. Moreover, these landslides are a major geohazard as they can cause damaging tsunamis and destroy seabed infrastructure. Due to their inaccessibility our understanding of what causes these landslides is limited and based on hypotheses that are difficult to test. Some of the largest submarine landslides, such as the Storegga Slide off Norway, occurred during times of eustatic sea level rise. It has been suggested that this global sea level rise was implicated in triggering of the landslides by causing an increase in excess pore pressure in the subseafloor. However, in a homogeneous slope a change in the thickness of the overlying water mass is not expected to affect its stability, as only the hydrostatic pressure component will change, whereas pore pressures in excess of hydrostatic will remain unaltered. Whether sufficiently rapid sea level rise, aided by rather impermeable sediment and complex layering, could cause excess pore pressures that may destabilise a continental slope is more difficult to answer and has not yet been tested. I use Finite Element Modelling to explore and quantify the direct effect of changes in the thickness of the overlying water mass on the stability of a generic sediment column with different stratigraphic conditions and hydro-mechanical properties. The results show that the direct effect of sea level rise on continental slope stability is minimal. Nevertheless, sea level rise may foster other processes, such as lithospheric stress changes resulting in increased seismicity, that could potentially cause large submarine landslides on continental slopes.

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

Onshore-offshore movement of jumbo squid (Dosidicus gigas) on the continental shelf

NASA Astrophysics Data System (ADS)

Stewart, Julia S.; Gilly, William F.; Field, John C.; Payne, John C.

2013-10-01

Jumbo squid (Dosidicus gigas) have greatly extended their range in the California Current System, where they forage on a variety of ecologically and economically important species that inhabit both coastal and offshore mesopelagic regions. Swimming abilities and behavior are important factors in assessing the impacts of this range expansion, particularly in regard to foraging in conjunction with onshore-offshore movement over the continental shelf. Here we describe a study of horizontal movements by jumbo squid along and across the continental shelf off Washington, USA, using acoustic tags in association with the Census of Marine Life's Pacific Ocean Shelf Tracking Program (POST) receiver arrays. We detected frequent movements along the shelf break, movement onto the shelf at night, and no evidence of movement as a cohesive school. Our results demonstrate feasibility of using acoustic tags and arrays to document horizontal movements of jumbo squid along and across the continental shelf. This is important in order to determine how those movements overlap with those of other ecologically and commercially important fish species.

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

Storm-driven delivery of sediment to the continental slope: Numerical modeling for the northern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Harris, C. K.; Kniskern, T. A.; Arango, H.

2016-02-01

The supply of sediment from the continental shelf to deeper waters is of critical importance for building continental margin repositories of sediment, and may also factor into episodic events on the continental slope such as turbidity currents and slope failures. While numerical sediment transport models have been developed for coastal and continental shelf areas, they have not often been used to infer sediment delivery to deeper waters. A three-dimensional coupled hydrodynamic - suspended sediment transport model for the northern Gulf of Mexico has been developed and run to evaluate the types of conditions that are associated with delivery of suspended sediment to the continental slope. Accounting for sediment delivery by riverine plumes and for sediment resuspension by energetic waves and currents, the sediment transport calculations were implemented within the Regional Ocean Modeling System (ROMS). The model domain represents the northern Gulf of Mexico shelf and slope including the Mississippi birdfoot delta and the Mississippi and DeSoto Canyons. To investigate the role of storms in driving down-slope sediment fluxes, model runs that encompassed fall, 2007 through late summer, 2008 the summer and fall of 2008 were analyzed. This time period included several winter storms, and the passage of two hurricanes (Ike and Gustav) over the study area. Preliminary results indicated that sediment delivery to the continental slope was triggered by the passage of these storm events, and focused at certain locations, such as submarine canyons. Additionally, a climatological analysis indicates that storm track influences both the wind-driven currents and wave energy on the shelf, and as such plays an important role in determining which storms trigger delivery of suspended continental shelf sediment to the adjacent slope.

Comparative organic geochemistry of Indian margin (Arabian Sea) sediments: estuary to continental slope

NASA Astrophysics Data System (ADS)

Cowie, G.; Mowbray, S.; Kurian, S.; Sarkar, A.; White, C.; Anderson, A.; Vergnaud, B.; Johnstone, G.; Brear, S.; Woulds, C.; Naqvi, S. W.; Kitazato, H.

2014-02-01

Surface sediments from sites across the Indian margin of the Arabian Sea were analysed for their carbon and nitrogen compositions (elemental and stable isotopic), grain size distributions and biochemical indices of organic matter (OM) source and/or degradation state. Site locations ranged from the estuaries of the Mandovi and Zuari rivers to depths of ~ 2000 m on the continental slope, thus spanning nearshore muds and sands on the shelf and both the semi-permanent oxygen minimum zone (OMZ) on the upper slope (~ 200-1300 m) and the seasonal hypoxic zone that impinges on the shelf. Source indices showed mixed marine and terrigenous OM within the estuaries, and overwhelming predominance (80%+) of marine OM on the shelf and slope. Thus, riverine OM is heavily diluted by autochthonous marine OM and/or is efficiently remineralised within or immediately offshore of the estuaries. Any terrigenous OM that is exported appears to be retained in nearshore muds; lignin phenols indicate that the small terrigenous OM content of slope sediments is of different origin, potentially from rivers to the north. Organic C contents of surface shelf and slope sediments varied from < 0.5 wt % in relict shelf sands to over 7 wt % at slope sites within the OMZ, decreasing to ≤ 1 wt % at 2000 m. Major variability (~ 5 wt %) was found at slope sites within the OMZ of similar depth and near-identical bottom-water oxygen concentration. A strong relationship between organic C and sediment grain size was seen for sediments within the OMZ, but lower C loadings were found for sites on the shelf and below the OMZ. Diagenetic indices confirmed that lower C content below the OMZ is associated with greater extent of OM degradation, but that C-poor shelf sediments are not consistently more degraded than those within the OMZ. Together, the results indicate that OM enrichment on the upper slope can be explained by physical controls (winnowing and/or dilution) on the shelf and progressive OM degradation

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.

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

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.

76 FR 14681 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Massachusetts...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-03-17

... No. BOEM-2010-0063] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore..., Regulation and Enforcement (BOEMRE), Interior. ACTION: Request for Interest (RFI) in Commercial Wind Energy... (BOEMRE) is reopening the comment period on the RFI in Commercial Wind Energy Leasing Offshore...

Submarine landslides along the eastern Mediterranean Israeli continental slope - a possible source for tsunami

NASA Astrophysics Data System (ADS)

Katz, O.; Reuven, E.; Aharonov, E.

2013-12-01

Numerous shallow submarine slope failures (scars and deposits) are observed in recent high resolution bathymetric grids of the continental slope off the Israeli eastern Mediterranean coast. The nature of these slope failures is currently not comprehensively understood as well as the question of whether the eastern Mediterranean continental slope is continuously or episodically unstable. This question is relevant to tsunami hazard along the densely populated eastern Mediterranean shores. We report here first steps towards understanding the present state of this submarine landslide system, which include mapping and analyzing the geology of the landslides and the hosting slopes. The continental slope extends from water depths of about 150 to more than 1000 meters with a slope of less than 5 degrees in general. Bathymetric grids with pixel resolution of 15 m till water depth of 700 m and 50 m till water depth of 1700 m were used. Analyzing the bathymetry revealed three main submarine surface features on the continental slope: (a) numerous shallow landslides, within the upper sequence of the post-Messenian sediments. Landslide widths range between hundreds to thousand of meters at the scar, with scar heights up to hundred meters. The toes of the landslides are not always mapable and lay up to a few kilometers down slope from the scar. Slope angles within the scars are 5 degrees to more than 15 degrees. In general landslides size decreases from south to north where their head scar depth turns to be shallower northwards. At least two types of landslides were detected: presumably young slides with sharp scars and presumably old slides with secondary slides and secondary drainage systems developed within the scar area; (b) a few kilometers long, north striking step-like lineaments. Step heights are up to 100 meters and the slopes are up to 20 degrees. The offset between parallel steps is less than a kilometer to a few kilometers. Analyzing seismic lines, the steps are

Louisiana continental slope: geologic and seismic stratigraphic framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ray, P.K.; Cooke, D.W.

1987-05-01

The continental slope of Louisiana from Green Canyon to Mississippi Canyon was studied by interpreting seismic CDP data and wells in the area. The slope is characterized by blocked canyon intraslope basins of various dimensions with maximum thickness of sediments in excess of 21,000 ft, rotational slump blocks and large-scale submarine slides. In the subsurface, the outer shelf and upper slope show contrasting character with that of the lower slope, especially below the Sigsbee Scarp. The seismic stratigraphic units established for the deep sea area can be recognized in their entirety up to a water depth of 6000 to 5500more » ft. In shallower water salt tectonics obliterates the sequence. Fragmental records of the sequence, especially the top of Challenger boundary, have been recognized in as shallow as 2000 to 3000 ft of water. The Tertiary units often downlap and onlap directly on the Challenger unit, indicating the progradational nature of the clastic slope. The Sigsbee unit has been traced through the entire slope area and can be divided into five subunits of unique acoustical characteristics. The slope constantly regrades in response to Neogene sea level fluctuations. Loading of the shelf by deltaic deposition contributes to salt sill formation and flowage of salt over deep-water sediments on the slope during high sea level. Regressive sea is represented by slope failure, formation of large-scale submarine slides, filling of blocked canyon intraslope basins which show similar seismic facies to that of Orca and Pigmy basins as reported from DSDP studies, and sporadic uplifting of salt diapirs and massifs and the formation of linear transverse salt ridges.« less

Comparative geochemistry of Indian margin (Arabian Sea) sediments: Estuary to continental slope.

NASA Astrophysics Data System (ADS)

Cowie, Greg; Mowbray, Stephen; Kurian, Siby; Sarkar, Amit; White, Carol; Anderson, Amy; Vergnaud, Bianca; Johnstone, Gisele; Brear, Samuel; Woulds, Clare; Naqvi, Wajih; Kitazato, Hiroshi

2014-05-01

Factors controlling the distribution of organic matter in the Arabian Sea have been the subject of much research and debate ever since organic-rich slope deposits were associated with the mid-water oxygen minimum zone (OMZ) However, the debate remains open, and numerous interacting factors have been invoked as important controls. A limitation of most previous studies is that they have been restricted to limited portions of the margin, and have not included molecular-level tracers that allow distinction of organic matter (OM) source and degradation state as factors in OM distribution. We report results from sites across the Indian margin of the Arabian Sea, which were analysed for carbon and nitrogen compositions (elemental and isotopic), grain size and indices of OM source and degradation state. Site locations ranged from the Mandovi/Zuari estuaries to depths of ~2000m on the continental slope, thus spanning both the semi-permanent OMZ on the upper slope (~200-1300m) and the seasonal hypoxic zone that impinges on the shelf. Source indices showed mixed marine and terrigenous OM within the estuaries, but overwhelming predominance (80%+) of marine OM on the shelf and slope, even in nearshore deposits. Thus, riverine OM is heavily diluted or efficiently remineralised within or immediately offshore of the estuaries. Any terrigenous OM that is exported appears to be retained in nearshore muds; lignin phenols indicate that the small terrigenous OM content of slope sediments is of different origin, potentially from rivers to the north. Organic C contents of surface shelf and slope sediments varied from <0.5 wt% in relict shelf sands to a maximum of >7 wt% at upper slope sites within the OMZ, then decreasing to ≤1wt% at 2000m. However, major variability (~5 wt%) occured within the OMZ at sites with near-identical depths and bottom-water oxygen. A strong relationship between organic C and grain size was seen for OMZ sediments, but lower C loadings were found for sites on

Isotope and fatty acid trends along continental shelf depth gradients: Inshore versus offshore hydrological influences on benthic trophic functioning

NASA Astrophysics Data System (ADS)

Chouvelon, T.; Schaal, G.; Grall, J.; Pernet, F.; Perdriau, M.; A-Pernet, E. J.; Le Bris, H.

2015-11-01

consumers) was especially apparent across the northern transect, due to unusual carbon isotope compositions (δ13C) in the compartments. At stations under the cold pool, SI and FA organism compositions indicated benthic trophic functioning based on a microbial food web, including a significant contribution of heterotrophic planktonic organisms and/or of SOM, notably in stations under the cold pool. On the contrary, inshore and shelf break areas were characterised by a microalgae-based food web (at least in part for the shelf break area, due to slope current and upwelling that can favour fresh primary production sinking on site). SIA and FAA were relevant and complementary tools, and consumers better medium- to long-term system integrators than POM samples, for depicting the trophic functioning and dynamics along inshore-offshore transects over continental shelves.

Tidally induced residual current over the Malin Sea continental slope

NASA Astrophysics Data System (ADS)

Stashchuk, Nataliya; Vlasenko, Vasiliy; Hosegood, Phil; Nimmo-Smith, W. Alex M.

2017-05-01

Tidally induced residual currents generated over shelf-slope topography are investigated analytically and numerically using the Massachusetts Institute of Technology general circulation model. Observational support for the presence of such a slope current was recorded over the Malin Sea continental slope during the 88-th cruise of the RRS ;James Cook; in July 2013. A simple analytical formula developed here in the framework of time-averaged shallow water equations has been validated against a fully nonlinear nonhydrostatic numerical solution. A good agreement between analytical and numerical solutions is found for a wide range of input parameters of the tidal flow and bottom topography. In application to the Malin Shelf area both the numerical model and analytical solution predicted a northward moving current confined to the slope with its core located above the 400 m isobath and with vertically averaged maximum velocities up to 8 cm s-1, which is consistent with the in-situ data recorded at three moorings and along cross-slope transects.

Subtidal currents over the central California slope: Evidence for offshore veering of the undercurrent and for direct, wind-driven slope currents

USGS Publications Warehouse

Noble, M.A.; Ramp, S.R.

2000-01-01

In February 1991, an array of six current-meter moorings was deployed for one year across the central California outer shelf and slope. The main line of the array extended 30 km offshore of the shelf break, out to water depths of 1400 m. A more sparsely-instrumented line, displaced 30 km to the northwest, extended 14 km offshore. Though shorter, the northern line spanned similar water depths because the gradient of the topography steepened in the northern region. A poleward flow pattern, typical of the California undercurrent, was seen across both lines in the array over most of the year. The poleward flow was surface intensified. In general, the portion of the undercurrent that crossed the southern line had larger amplitudes and penetrated more deeply into the water column than the portion that crossed the northern line. Transport over the year ranged from 0 to 2.5 Sverdrups (Sv) poleward across the southern line; 0 to 1 Sv poleward across the northern line. We suggest the difference in transport was caused by topographic constraints, which tended to force the poleward flow offshore of the northern measurement sites. The slope of the topography steepened too abruptly to allow the poleward flow to follow isobaths when currents were strong. When current velocities lessened, a more coherent flow pattern was seen across both lines in the array. In general, the poleward flow patterns in the undercurrent were not affected by local winds or by the local alongshore pressure gradient. Nor was a strong seasonal pattern evident. Rather unexpectedly, a small but statistically significant fraction of the current variance over the mid- and outer slope was driven by the surface wind stress. An alongshelf wind stress caused currents to flow along the slope, parallel to the wind field, down to depths of 400 m below the surface and out to distances of 2 Rossby radii past the shelf break. The transfer functions were weak, 3-4 cm/s per dyn cm-2, but comparable to wind-driven current

78 FR 8190 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore North Carolina...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-05

...] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore North Carolina--Call for... Commercial Leasing for Wind Power Offshore North Carolina (Call), published on December 13, 2012 (77 FR 7204). DATES: BOEM must receive your nomination describing your interest in obtaining a commercial wind lease...

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.

Petroleum geology of the mid-Atlantic continental margin, offshore Virginia

USGS Publications Warehouse

Bayer, K.C.; Milici, R.C.

1989-01-01

The Baltimore Canyon Trough, a major sedimentary basin on the Atlantic continental shelf, contains up to 18 km of Mesozoic and Cenozoic strata. The basin has been studied extensively by multichannel common depth point (CDP) seismic reflection profiles and has been tested by drilling for hydrocarbon resources in several places. The Mesozoic and Cenozoic strata contained in the basin were deposited in littoral to bathyal depositional settings and contain immature to marginally mature oil-prone and gas-prone kerogen. The more deeply buried strata of Early Mesozoic age are more likely to be thermally mature than are the younger strata with respect to hydrocarbon generation, but contain terrestrially derived coaly organic matter that would be prone to yield gas, rather than oil. An analysis of available CDP seismic reflection data has indicated that there are several potential hydrocarbon plays in the area offshore of Virginia. These include: (1) Lower Mesozoic synrift basins that appear similar to those exposed in the Appalachian Piedmont, (2) a stratigraphic updip pinchout of strata of Early Mesozoic age in the offshore region near the coast, (3) a deeply buried paleoshelf edge, where seismic reflectors dip sharply seaward; and (4) a Cretaceous/Jurassic shelf edge beneath the present continental rise. Of these, the synrift basins and Cretaceous/Jurassic shelf edge are considered to be the best targets for exploration. ?? 1989.

Sponge assemblages on the deep Mediterranean continental shelf and slope (Menorca Channel, Western Mediterranean Sea)

NASA Astrophysics Data System (ADS)

Santín, Andreu; Grinyó, Jordi; Ambroso, Stefano; Uriz, Maria J.; Gori, Andrea; Dominguez-Carrió, Carlos; Gili, Josep-Maria

2018-01-01

Sponge assemblages on continental shelves and slopes around the world have been known about for centuries. However, due to limitations of the traditional sampling systems, data about individual sponge species rather than assemblages have been reported. This study characterizes sponge assemblages over a wide bathymetric range ( 50-350 m depth) and covering the entire continental shelf and the upper slope of the Menorca Channel, an area soon to be declared a Marine Protected Area (MPA) as part of the Natura 2000 Network. Quantitative analysis of 85 video-transects (a total linear distance of 75 km), together with representative collections to confirm species identifications, allowed us to discriminate six major assemblages. Differences in the assemblages mainly corresponded to differences in substrate type and depth. On the inner continental shelf, a semi-sciaphilous Axinellid assemblage dominated the rocky outcrops. Maërl beds on the inner continental shelf were dominated by Haliclona (Reniera) mediterranea, whereas the horny sponge Aplysina cavernicola and several other haliclonids mostly dominated maërl beds and rocky substrates of the outer shelf. Soft sediments on the shelf break hosted a monospecific Thenea muricata assemblage, whereas rocky substrates of the shelf break were characterized by a mixture of encrusting, columnar and fan-shaped sponges. Finally, the upper slope was dominated by Hamacantha (Vomerula) falcula and the hexactinellid Tretodictyum reiswigi. Overall, sponge diversity showed its highest values above the shelf break, plummeting severely on the upper slope. Despite this diversity decrease, we found very high densities (> 70 ind./m2) of sponges over vast areas of both the shelf break and the upper slope.

Study of southern CHAONAN sag lower continental slope basin deposition character in Northern South China Sea

NASA Astrophysics Data System (ADS)

Tang, Y.

2009-12-01

Northern South China Sea Margin locates in Eurasian plate,Indian-Australia plate,Pacific Plates.The South China Sea had underwent a complicated tectonic evolution in Cenozoic.During rifting,the continental shelf and slope forms a series of Cenozoic sedimentary basins,including Qiongdongnan basin,Pearl River Mouth basin,Taixinan basin.These basins fill in thick Cenozoic fluviolacustrine facies,transitional facies,marine facies,abyssal facies sediment,recording the evolution history of South China Sea Margin rifting and ocean basin extending.The studies of tectonics and deposition of depression in the Southern Chaonan Sag of lower continental slope in the Norther South China Sea were dealt with,based on the sequence stratigraphy and depositional facies interpretation of seismic profiles acquired by cruises of“China and Germany Joint Study on Marine Geosciences in the South China Sea”and“The formation,evolution and key issues of important resources in China marginal sea",and combining with ODP 1148 cole and LW33-1-1 well.The free-air gravity anomaly of the break up of the continental and ocean appears comparatively low negative anomaly traps which extended in EW,it is the reflection of passive margin gravitational effect.Bouguer gravity anomaly is comparatively low which is gradient zone extended NE-SW.Magnetic anomaly lies in Magnetic Quiet Zone at the Northern Continental Margin of the South China Sea.The Cenozoic sediments of lower continental slope in Southern Chaonan Sag can be divided into five stratum interface:SB5.5,SB10.5,SB16.5,SB23.8 and Hg,their ages are of Pliocene-Quaternary,late Miocene,middle Miocene,early Miocene,paleogene.The tectonic evolution of low continental slope depressions can be divided into rifting,rifting-depression transitional and depression stages,while their depositional environments change from river to shallow marine and abyssa1,which results in different topography in different stages.The topographic evolvement in the study

Tectonostratigraphy of the Passive Continental Margin Offshore Indus Pakistan

NASA Astrophysics Data System (ADS)

Aslam, K.; Khan, M.; Liu, Y.; Farid, A.

2017-12-01

The tectonic evolution and structural complexities are poorly understood in the passive continental margin of the Offshore Indus of Pakistan. In the present study, an attempt has been made to interpret the structural trends and seismic stratigraphic framework in relation to the tectonics of the region. Seismic reflection data revealed tectonically controlled, distinct episodes of normal faulting representing rifting at different ages and transpression in the Late Eocene time. This transpression has resulted in the reactivation of the Pre-Cambrian basement structures. The movement of these basement structures has considerably affected the younger sedimentary succession resulting in push up structures resembling anticlines. The structural growth of the push-up structures was computed. The most remarkable tectonic setting in the region is represented by the normal faulting and by the basement uplift which divides the rifting and transpression stages. Ten mappable seismic sequences have been identified on the seismic records. A Jurassic aged paleo-shelf has also been identified on all regional seismic profiles which is indicative of Indian-African Plates separation during the Jurassic time. Furthermore, the backstripping technique was applied which has been proved to be a powerful technique to quantify subsidence/uplift history of rift-type passive continental margins. The back strip curves suggest that transition from an extensional rifted margin to transpression occurred during Eocene time (50-30 Ma). The backstripping curves show uplift had happened in the area. We infer that the uplift has occurred due to the movement of basement structures by the transpression movements of Arabian and Indian Plates. The present study suggests that the structural styles and stratigraphy of the Offshore Indus Pakistan were significantly affected by the tectonic activities during the separation of Gondwanaland in the Mesozoic and northward movement of the Indian Plate, post

Salt structure and sediment thickness, Texas-Louisiana continental slope, northwestern Gulf of Mexico

USGS Publications Warehouse

Martin, Raymond G.

1973-01-01

The objectives of this study were to determine the general configuration of the salt surface beneath the Texas-Louisiana continental slope and to isopach the Mesozoic-Cenozoic sedimentary section lying upon it. The structure contour map discloses that the entire slope province between the shelf edge and Sigsbee Escarpment is underlain by salt structures which interconnect at relatively shallow subbottom depths. Salt structures on the slope south of Louisiana and eastern Texas can be grouped according to structural relief and size which define morphological belts of decreasing deformational maturity in a downslope direction. Off northern Mexico and southernmost Texas, salt structures are anticlinal and their trends suggest a structural relationship with the folds of the Mexican Ridge province to the south. Structural trends in the two slope areas meet in the corner of the northwestern gulf where salt structure may have been influenced by a seaward extension of the San Marcos Arch, or an abrupt change in subsalt structural topography. Sediment thickness above the top of salt on the slope averages about 1,400 m (4,620 ft) which is a smaller average than expected from previous estimates. In some synclinal basins between salt structures, sediments may be as thick as 4,000-5,000 m (12,000-17,000 ft). On the average, sedimentary deposits in basins on the upper slope are thicker than on the lower slope. From the isopach map of sediments above salt it is estimated that the U.S. continental slope off Texas and Louisiana contains a sedimentary volume of about 170,000 km3 (41,000 mi3). The bulk of this volume is situated in synclinal basins between domes and principally in those beneath the upper and middle slope regions.

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.

Mechanical Stability of Stratified Sediments along the upper continental Slope off Vesterålen, northern Norway - Insights from in situ CPTU Tests

NASA Astrophysics Data System (ADS)

Voelker, D.; Stegmann, S.; Kreiter, S.; L'Heureux, J. S.; Vanneste, M. W. B.; Baeten, N. J.; Knudsen, S.; Rise, L.; Longva, O.; Brendryen, J.; Haflidason, H.; Chand, S.; Mörz, T.; Kopf, A.

2015-12-01

High-resolution single channel-seismic data (3.5 kHz) reveal small-scale submarine landslide structures and superficial deformation features (e.g. tension cracks) along the gently dipping (3°) upper continental slope west of the Vesterålen Archipelago off northern Norway. Previous laboratory-based geotechnical studies attest that the slope is per sestable and that seismic events in an order of magnitude M5.7 may have triggered the slope sediments to fail. Here we present geotechnical in situ data (sedimentary strength, pore pressure), which were obtained with RV Poseidon in summer 2014 using the static CPTU system GOST. The CPTU system provided high-resolution geotechnical profiles of the uppermost sediments to a maximum penetration depth of ~ 20 m at six sites within the landslide features and beside them in undisturbed slope sediments as reference. The CPTU data reveal the occurrence of mechanically weaker zones (MWZ) by the drop of sedimentary strength. These zones are interbedded by coarser, more competent layers. The occurrence of sensitive fine-grained material may be responsible for the loss of strength in the deeper portion (appx. 12 to 18 m below seafloor). An 1D infinite pseudo-static stability analysis attests that the mechanically weaker zones (MWZ) correlate well with portions, where the Factor of Safety (FoS) ≤ 1 (meta-stable to unstable) indicates permanent deformation or failure in case additional dynamic load is induced by an earthquake. Thus, the mechanically weak layers can be considered as one important pre-condition for landslide activity. In conclusion, the integration of in situ CPTU data with geophysical data improves soil characterization and hence foster a better understanding of the pre-conditioning factors for slope instability at the upper continental slope off Vesterålen. Risk assessment for the present-day slope off Vesterålen is particularly crucial, because the opening of the region for offshore oil and gas exploration is

Late Cenozoic sea-level changes and the onset of glaciation: impact on continental slope progradation off eastern Canada

USGS Publications Warehouse

Piper, D.J.W.; Normark, W.R.

1989-01-01

Late Cenozoic sedimentation from four varied sites on the continental slopes off southeastern Canada has been analysed using high-resolution airgun multichannel seismic profiles, supplemented with some single channel data. Biostratigraphic ties are available to exploratory wells at three of the sites. Uniform, slow accumulation of hemipelagic sediments was locally terminated by the late Miocene sea-level lowering, which is also reflected in changes in foraminiferan faunas on the continental shelf. Data are very limited for the early Pliocene but suggest a return to slow hemipelagic sedimentation. At the beginning of the late Pliocene, there was a change in sedimentation style marked by a several-fold increase in accumulation rates and cutting of slope valleys. This late Pliocene cutting of slope valleys corresponds to the onset of late Cenozoic growth of the Laurentian Fan and the initiation of turbidite sedimentation on the Sohm Abyssal Plain. Although it corresponds to a time of sea-level lowering, the contrast with the late Miocene lowstand indicates that there must also have been a change in sediment delivery to the coastline, perhaps as a result of increased rainfall or development of valley glaciers. High sedimentation rates continued into the early Pleistocene, but the extent of slope dissection by gullies increased. Gully-cutting episodes alternated with sediment-draping episodes. Throughout the southeastern Canadian continental margin, there was a change in sedimentation style in the middle Pleistocene that resulted from extensive ice sheets crossing the continental shelf and delivering coarse sediment directly to the continental slope. ?? 1989.

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.

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.

Submarine Landslide Hazards Offshore Southern Alaska: Seismic Strengthening Versus Rapid Sedimentation

NASA Astrophysics Data System (ADS)

Sawyer, D.; Reece, R.; Gulick, S. P. S.; Lenz, B. L.

2017-12-01

The southern Alaskan offshore margin is prone to submarine landslides and tsunami hazards due to seismically active plate boundaries and extreme sedimentation rates from glacially enhanced mountain erosion. We examine the submarine landslide potential with new shear strength measurements acquired by Integrated Ocean Drilling Program Expedition 341 on the continental slope and Surveyor Fan. These data reveal lower than expected sediment strength. Contrary to other active margins where seismic strengthening enhances slope stability, the high-sedimentation margin offshore southern Alaska behaves like a passive margin from a shear strength perspective. We interpret that seismic strengthening occurs but is offset by high sedimentation rates and overpressure within the slope and Surveyor Fan. This conclusion is supported because shear strength follows an expected active margin profile outside of the fan, where background sedimentation rates occur. More broadly, seismically active margins with wet-based glaciers are susceptible to submarine landslide hazards because of the combination of high sedimentation rates and earthquake shaking

Atlantic continental margin of the United States

USGS Publications Warehouse

Grow, John A.; Sheridan, Robert E.; Palmer, A.R.

1982-01-01

The objective of this Decade of North American Geology (D-NAG) volume will be to focus on the Mesozoic and Cenozoic evolution of the U.S. Atlantic continental margin, including the onshore coastal plain, related onshore Triassic-Jurassic rift grabens, and the offshore basins and platforms. Following multiple compressional tectonic episodes between Africa and North America during the Paleozoic Era that formed the Appalachian Mountains, the Mesozoic and Cenozoic Eras were dominated by tensional tectonic processes that separated Africa and North America. Extensional rifting during Triassic and Early Jurassic times resulted in numerous tensional grabens both onshore and offshore, which filled with nonmarine continental red beds, lacustrine deposits, and volcanic flows and debris. The final stage of this breakup between Africa and North America occurred beneath the present outer continental shelf and continental slope during Early or Middle Jurassic time when sea-floor spreading began to form new oceanic crust and lithosophere between the two continents as they drifted apart. Postrift subsidence of the marginal basins continued in response to cooling of the lithosphere and sedimentary loading.Geophysical surveys and oil-exploration drilling along the U.S. Atlantic continental margin during the past 5 years are beginning to answer many questions concerning its deep structure and stratigraphy and how it evolved during the rifting and early sea-floor-spreading stages of the separation of this region from Africa. Earlier geophysical studies of the U.S. continental margin used marine refraction and submarine gravity measurements. Single-channel seismic-reflection, marine magnetic, aeromagnetic, and continuous gravity measurements became available during the 1960s.

Impact of sea-level rise on earthquake and landslide triggering offshore the Alentejo margin (SW Iberia)

NASA Astrophysics Data System (ADS)

Neves, M. C.; Roque, C.; Luttrell, K. M.; Vázquez, J. T.; Alonso, B.

2016-12-01

Earthquakes and submarine landslides are recurrent and widespread manifestations of fault activity offshore SW Iberia. The present work tests the effects of sea-level rise on offshore fault systems using Coulomb stress change calculations across the Alentejo margin. Large-scale faults capable of generating large earthquakes and tsunamis in the region, especially NE-SW trending thrusts and WNW-ESE trending dextral strike-slip faults imaged at basement depths, are either blocked or unaffected by flexural effects related to sea-level changes. Large-magnitude earthquakes occurring along these structures may, therefore, be less frequent during periods of sea-level rise. In contrast, sea-level rise promotes shallow fault ruptures within the sedimentary sequence along the continental slope and upper rise within distances of <100 km from the coast. The results suggest that the occurrence of continental slope failures may either increase (if triggered by shallow fault ruptures) or decrease (if triggered by deep fault ruptures) as a result of sea-level rise. Moreover, observations of slope failures affecting the area of the Sines contourite drift highlight the role of sediment properties as preconditioning factors in this region.

The Wide Bay Canyon system: A case study of canyon morphology on the east Australian continental margin

NASA Astrophysics Data System (ADS)

Yu, P. W.; Hubble, T.; Airey, D.; Gallagher, S. J.; Clarke, S. L.

2014-12-01

A voyage was conducted aboard the RV Southern Surveyor in early 2013 to investigate the east Australian continental margin. From the continental slope of the Wide Bay region offshore Fraser Island, Queensland, Australia, remote sensing data and sediment samples were collected. Bathymetric data reveals that the continental slope of the region presents a mature canyon system. Eight dredge samples were recovered from the walls of Wide Bay Canyon and the adjacent, relatively intact continental slope along the entire length of the slope, from the start of the shelf break to the toe, in water depths ranging from 1100-2500 m. For these samples, sediment composition, biostratigraphic age, and bulk mineralogy data are reported. These slope-forming sediments are primarily comprised of calcareous sandy-silts. Occasional terrestrial plant fossils and minerals can be found in a mostly marine-fossiliferous composition, suggesting minor but significant riverine and aeolian input. Biostratigraphic dates extracted from the foraminiferal contents of these samples indicate that the intra-canyon and slope material was deposited between Middle Miocene to Pliocene, implying that the incision of this section of the margin and formation of the erosional features took place no earlier than the Pliocene. In conjunction with bathymetric data of the local continental slope, the depositional origins of this section of the east Australian continental margin, and the timing of major morphological events such as slope failure and canyon incision can be interpreted. The Wide Bay Canyon system can serve as a representative case study of local canyon formation, allowing a better understanding of the past or ongoing processes that are shaping the margin and giving way to similar morphologies.

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.

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

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.

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

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

78 FR 45965 - Research Lease on the Outer Continental Shelf (OCS) Offshore Virginia, Request for Competitive...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-07-30

...; MMAA104000] Research Lease on the Outer Continental Shelf (OCS) Offshore Virginia, Request for Competitive... Unsolicited Request for an OCS Research Lease; Request for Competitive Interest (RFCI); and Request for Public... for wind energy research activities; (2) solicit indications of interest in a renewable energy lease...

Submarine landslides on the north continental slope of the South China Sea

NASA Astrophysics Data System (ADS)

Wang, Weiwei; Wang, Dawei; Wu, Shiguo; Völker, David; Zeng, Hongliu; Cai, Guanqiang; Li, Qingping

2018-02-01

Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea (SCS). In this paper, high-resolution 3D seismic data and multibeam data based on seismic sedimentology and geomorphology are employed to assist in identifying submarine landslides. In addition, deposition models are proposed that are based on specific geological structures and features, and which illustrate the local stress field over entire submarine landslides in deep-water areas of the SCS. The SCS is one of the largest fluvial sediment sinks in enclosed or semi-enclosed marginal seas worldwide. It therefore provides a set of preconditions for the formation of submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. A new concept involving temporal and spatial analyses is tested to construct a relationship between submarine landslides and different time scale trigger mechanisms, and three mechanisms are discussed in the context of spatial scale and temporal frequency: evolution of slope gradient and overpressure, global environmental changes, and tectonic events. Submarine landslides that are triggered by tectonic events are the largest but occur less frequently, while submarine landslides triggered by the combination of slope gradient and over-pressure evolution are the smallest but most frequently occurring events. In summary, analysis shows that the formation of submarine landslides is a complex process involving the operation of different factors on various time scales.

Sedimentological fingerprint of modern and ancient meltwater outbursts across Antarctic continental shelves and slopes

NASA Astrophysics Data System (ADS)

Anderson, J. B.; Simkins, L. M.; Prothro, L. O.

2016-12-01

On formerly glaciated Antarctic continental shelves, the crystalline inner shelf is commonly dissected by linked subglacial lake and channel systems; however, signatures of meltwater are rare within subglacial and glacial-marine deposits on the middle to outer continental shelf. Recent observations of ice-marginal landforms incised by meltwater channels in the western Ross Sea indicate pulses of meltwater outbursts at marine-based grounding lines during deglaciation of the continental shelf. Here we present sedimentological evidence of meltwater outbursts and associated plumes from new and legacy cores collected on the continental shelf and slope within the Ross Sea, Amundsen Sea, and Marguerite Bay. Discrete fine-grained silt deposits are found overlying till and within proximal grounding line deposits and open-marine diatomaceous sediments. The deposits are massive to laminated, contain little to no coarser material, moderately sorted and dominated by a 10 μm grain-size mode. Grain-size measurements show no indication of winnowing; therefore, we interpret these deposits as meltwater deposits, transported by subglacial meltwater drainage systems to the grounding line and dispersed further seaward by meltwater plumes. The similarity of the deposits down-core and between shelf and slope sites within the Ross Sea, Amundsen Sea, and Marguerite Bay indicate that sorting and/or production of the fine silts occurs due to subglacial hydrodynamic processes. These distinctive meltwater deposits within the stratigraphic record provide an accessible proxy for identifying meltwater discharge from the Antarctic Ice Sheet and potentially be used to correlate cores on and off the continental shelf. Dating events on the continental shelf is notoriously difficult; therefore, deeper ocean records offer an easier means of bracketing the timing of meltwater discharge events. Longer records of ice dynamics from off the continental shelf are commonly used to reconstruct IRD records

Submarine slope instability offshore western Calabria, Italy: possible triggering of tsunamigenic landslides by seismic load

NASA Astrophysics Data System (ADS)

Ausilia Paparo, Maria; Armigliato, Alberto; Pagnoni, Gianluca; Zaniboni, Filippo; Gallotti, Glauco; Tinti, Stefano

2017-04-01

The Eastern Tyrrhenian margin offshore western Calabria (Italy) has experienced several mass movements involving varying volumes and shapes, as revealed by several geological surveys identifying slide scars and massive deposits. The hypothesis that at least some of these mass movements was tsunamigenic sounds perfectly reasonable. In this study, we focus on the continental edge offshore the Santa Eufemia Gulf and the Paola Basin, because the area experienced several strong earthquakes (Mw up to 7), some of them in the last centuries (see, for example, the 1905 earthquake and the late shocks of the 1783 sequence). Our aim is to study the seismic load as the trigger mechanism of mass failures: not all earthquakes generate tsunamis, but the conjunction of definite factors as seafloor shaking and pore water pressure could temporarily reduce soil shear stress, inducing failures and submarine tsunamigenic landslides. We have selected several sections of the Calabrian margin with different gradients and studied their slope stability by using the Minimum Lithostatic Deviation (MLD) method. We have applied typical Peak Ground Accelerations (PGAs) obtained from local historical earthquakes by means of regression laws, determining the potentially unstable sectors, as well as the volumes of the material that can be set in motion. This in turn can be used as input for future tsunami modelling and hazard assessment. This work is a contribution to assess local hazard and risk in western Calabrian coast where earthquakes can trigger tsunamigenic submarine mass movements: the impact and the effects of such phenomena could be disastrous for coastal infrastructures and populations without the proper mitigation measures. This work was carried out in the frame of the EU Project called ASTARTE - Assessment, STrategy And Risk Reduction for Tsunamis in Europe (Grant 603839, 7th FP, ENV.2013.6.4-3).

Near-bottom currents over the continental slope in the Mid-Atlantic Bight

USGS Publications Warehouse

Csanady, G.T.; Churchill, J.H.; Butman, B.

1988-01-01

From a set of 28 current meter records we have found that near-bottom currents faster than 0.2 m s-1 occur frequently over the outer continental shelf of the Mid-Atlantic Bight (bottom depth <210 m) but very rarely (<1% of the time) between bottom depths of 500 m and 2 km over the slope. The rarity of strong near-bottom flow over the middle and lower slope allows the accumulation of fine-grained sediment and organic carbon in this region. Fast near-bottom currents which do occur over the slope are invariably associated with topographic waves, although it is often superimposed inertial oscillations which increase current speed above the level of 0.2 m s-1. Episodes of intense inertial oscillations occur randomly and last typically for 10-20 days. Their energy source is unknown. Topographic wave energy exhibits a slight, but statistically significant, minimum over the mid-slope. These waves appear irregularly and vary both along isobaths and in time. The irregularity is presumably a consequence of random topographic wave generation by Gulf Stream instability. The current regime within sea-floor depressions in the slope (canyons and gullies) is distinctly different from that of the open slope; most notable is the near absence of topographic wave motion within depressions. ?? 1988.

Water masses transform at mid-depths over the Antarctic Continental Slope

NASA Astrophysics Data System (ADS)

Mead Silvester, Jess; Lenn, Yueng-Djern; Polton, Jeffrey; Phillips, Helen E.; Morales Maqueda, Miguel

2017-04-01

The Meridional Overturning Circulation (MOC) controls the oceans' latitudinal heat distribution, helping to regulate the Earth's climate. The Southern Ocean is the primary place where cool, deep waters return to the surface to complete this global circulation. While water mass transformations intrinsic to this process predominantly take place at the surface following upwelling, recent studies implicate vertical mixing in allowing transformation at mid-depths over the Antarctic continental slope. We deployed an EM-Apex float near Elephant Island, north of the Antarctic Peninsula's tip, to profile along the slope and use potential vorticity to diagnose observed instabilities. The float captures direct heat exchange between a lens of Upper Circumpolar Deep Water (UCDW) and surrounding Lower Circumpolar Deep Waters (LCDW) at mid-depths and over the course of several days. Heat fluxes peak across the top and bottom boundaries of the UCDW lens and peak diffusivities across the bottom boundary are associated with shear instability. Estimates of diffusivity from shear-strain finestructure parameterisation and heat fluxes are found to be in reasonable agreement. The two-dimensional Ertel potential vorticity is elevated both inside the UCDW lens and along its bottom boundary, with a strong contribution from the shear term in these regions and instabilities are associated with gravitational and symmetric forcing. Thus, shear instabilities are driving turbulent mixing across the lower boundary between these two water masses, leading to the observed heat exchange and transformation at mid-depths over the Antarctic continental slope. This has implications for our understanding of the rates of upwelling and ocean-atmosphere exchanges of heat and carbon at this critical location.

Submarine slope earthquake-induced instability and associated tsunami generation potential along the Hyblean-Malta Escarpment (offshore eastern Sicily, Italy)

NASA Astrophysics Data System (ADS)

Ausilia Paparo, Maria; Pagnoni, Gianluca; Zaniboni, Filippo; Tinti, Stefano

2016-04-01

The stability analysis of offshore margins is an important step for the assessment of natural hazard: the main challenge is to evaluate the potential slope failures and the consequent occurrence of submarine tsunamigenic landslides to mitigate the potential coastal damage to inhabitants and infrastructures. But the limited geotechnical knowledge of the underwater soil and the controversial scientific interpretation of the tectonic units make it often difficult to carry out this type of analysis reliably. We select the Hyblean-Malta Escarpment (HME), the main active geological structure offshore eastern Sicily, because the amount of data from historical chronicles, the records about strong earthquakes and tsunami, and the numerous geological offshore surveys carried out in recent years make the region an excellent scenario to evaluate slope failures, mass movements triggered by earthquakes and the consequent tsunamis. We choose several profiles along the HME and analyse their equilibrium conditions using the Minimun Lithostatic Deviation (MLD) method (Tinti and Manucci, 2006, 2008; Paparo et al. 2013), that is based on the limit-equilibrium theory. Considering the morphological and geotechnical features of the offshore slopes, we prove that large-earthquake shaking may lead some zones of the HME to instability, we evaluate the expected volumes involved in sliding and compute the associated landslide-tsunami through numerical tsunami simulations. This work was carried out in the frame of the EU Project called ASTARTE - Assessment, STrategy And Risk Reduction for Tsunamis in Europe (Grant 603839, 7th FP, ENV.2013.6.4-3).

Cenozoic sedimentation in the Mumbai Offshore Basin: Implications for tectonic evolution of the western continental margin of India

NASA Astrophysics Data System (ADS)

Nair, Nisha; Pandey, Dhananjai K.

2018-02-01

Interpretation of multichannel seismic reflection data along the Mumbai Offshore Basin (MOB) revealed the tectonic processes that led to the development of sedimentary basins during Cenozoic evolution. Structural interpretation along three selected MCS profiles from MOB revealed seven major sedimentary sequences (∼3.0 s TWT, thick) and the associated complex fault patterns. These stratigraphic sequences are interpreted to host detritus of syn- to post rift events during rift-drift process. The acoustic basement appeared to be faulted with interspaced intrusive bodies. The sections also depicted the presence of slumping of sediments, subsidence, marginal basins, rollover anticlines, mud diapirs etc accompanied by normal to thrust faults related to recent tectonics. Presence of upthrusts in the slope region marks the locations of local compression during collision. Forward gravity modeling constrained with results from seismic and drill results, revealed that the crustal structure beneath the MOB has undergone an extensional type tectonics intruded with intrusive bodies. Results from the seismo-gravity modeling in association with litholog data from drilled wells from the western continental margin of India (WCMI) are presented here.

Seismic displacement of gently-sloping coastal and marine sediment under multidirectional earthquake loading

USGS Publications Warehouse

Kayen, Robert E.

2017-01-01

Gentle sediment-laden slopes are typical of the onshore coastal zone and offshore continental shelf and slope. Coastal sediment are commonly young weakly consolidated materials that are well stratified, have low strength, and can mobilize shear displacements at low levels of stress. Seismically-driven plastic displacements of these sediment pose a hazard to coastal cities, buried onshore utilities, and offshore infrastructure like harbor protection and outfalls. One-dimensional rigid downslope-directed Newmark sliding block analyses have been used to predict earthquake deformations generally on steeper slopes that are modeled as frictional materials. This study probes the effect of multidirectional earthquake motions on inertial displacements of gently sloping ground of the coastal and offshore condition where soft-compliant soil is expected. Toward that objective, this investigation seeks to understand the effect on Newmark-type displacements of [1] multidirectional earthquake shaking and [2] soil compliance. In order to model multidirectional effects, the earthquake motions are rotated into the local slope strike- and dip-components. On gently sloping ground, including the strike component of motion always results in a larger and more accurate shear stress vector. Strike motions are found to contribute to downslope deformations on any declivity. Compliant response of the soil mass also influences the plastic displacements. The magnitude of seismic displacements can be estimated with a simplified model using only the estimated soil yield-acceleration (ky) and the peak ground velocity (Vmax) of the earthquake motions. Compliance effects can be effectively mapped using the concept of Plastic Displacement Response Spectra (PDRS).

77 FR 10711 - Safety Zone; KULLUK, Outer Continental Shelf Mobile Offshore Drilling Unit (MODU), Beaufort Sea, AK

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-23

...-AA00 Safety Zone; KULLUK, Outer Continental Shelf Mobile Offshore Drilling Unit (MODU), Beaufort Sea... on location in order to drill exploratory wells at various prospects located in the Beaufort Sea... in order to drill exploratory wells in several prospects located in the Beaufort Sea during the 2012...

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

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.

Geomorphology and Sediment Stability of a Segment of the U.S. Continental Slope off New Jersey.

PubMed

Robb, J M; Hampson, J C; Twichell, D C

1981-02-27

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.

77 FR 47877 - Potential Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Maine...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-08-10

... Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Maine; Request for Interest... Request for a Commercial OCS Wind Lease, Request for Interest, and Request for Public Comment SUMMARY: The... (Statoil NA) to acquire an OCS wind lease; (2) solicit public input regarding the proposal, its potential...

Unusual megafaunal assemblages on the continental slope off Cape Hatteras

NASA Astrophysics Data System (ADS)

Hecker, Barbara

Megafaunal assemblages were studied in August-September 1992 using a towed camera sled along seven cross-isobath transects on the continental slope off Cape Hatteras. A total of 20,722 megafaunal organisms were observed on 10,918 m 2 of the sea floor between the depths of 157 and 1 924 m. These data were compared with data previously collected off Cape Hatteras in 1985 and at other locations along the eastern U.S. coast between 1981 and 1987. Megafaunal populations on the upper and lower slopes off Cape Hatteras were fouond to be similar, in terms of density and species composition, to those observed at the other locations. In contrast, megafaunal abundances were found to be elevated (0.88 and 2.65 individuals per m 2 during 1985 and 1992, respectively) on the middle slope off Cape Hatteras when compared to most other slope locations (<0.5individuals per m 2). These elevated abundances mainly reflect dense populations of three demersal fish, two eel pouts ( Lysenchelys verrilli and Lycodes atlanticus) and the witch flounder Glyptocephalus cynoglossus, and a large anemone ( Actinauge verrilli). These four species dominated the megafauna off Cape Hatteras, whereas they represented only a minor component of megafaunal populations found at other slope locations. Additionally, numerous tubes of the foraminiferan Bathysiphon filiformis were observed off Cape Hatteras, but not elsewhere. The high density of demersal fish found off Cape Hatteras appears to be related to the high densities of infaunal prey reported from this area. The high densities of A. verrilli and B. fuliformis may be related to the same factors responsible for the high infaunal densities, namely enhanced nutrient inputs in the form of fine particles. Extreme patchiness also was observed in the distributions of the middle slope taxa off Cape Hatteras. This patchiness may reflect the habitat heterogeneity of this exceptionally rugged slope and the sedentary nature of the organisms inhabiting it.

Arctic Submarine Slope Stability

NASA Astrophysics Data System (ADS)

Winkelmann, D.; Geissler, W.

2010-12-01

Submarine landsliding represents aside submarine earthquakes major natural hazard to coastal and sea-floor infrastructure as well as to coastal communities due to their ability to generate large-scale tsunamis with their socio-economic consequences. The investigation of submarine landslides, their conditions and trigger mechanisms, recurrence rates and potential impact remains an important task for the evaluation of risks in coastal management and offshore industrial activities. In the light of a changing globe with warming oceans and rising sea-level accompanied by increasing human population along coasts and enhanced near- and offshore activities, slope stability issues gain more importance than ever before. The Arctic exhibits the most rapid and drastic changes and is predicted to change even faster. Aside rising air temperatures, enhanced inflow of less cooled Atlantic water into the Arctic Ocean reduces sea-ice cover and warms the surroundings. Slope stability is challenged considering large areas of permafrost and hydrates. The Hinlopen/Yermak Megaslide (HYM) north of Svalbard is the first and so far only reported large-scale submarine landslide in the Arctic Ocean. The HYM exhibits the highest headwalls that have been found on siliciclastic margins. With more than 10.000 square kilometer areal extent and app. 2.400 cubic kilometer of involved sedimentary material, it is one of the largest exposed submarine slides worldwide. Geometry and age put this slide in a special position in discussing submarine slope stability on glaciated continental margins. The HYM occurred 30 ka ago, when the global sea-level dropped by app. 50 m within less than one millennium due to rapid onset of global glaciation. It probably caused a tsunami with circum-Arctic impact and wave heights exceeding 130 meters. The HYM affected the slope stability field in its neighbourhood by removal of support. Post-megaslide slope instability as expressed in creeping and smaller-scaled slides are

Postglacial sedimentary record of the Southern California continental shelf and slope, Point Conception to Dana Point

USGS Publications Warehouse

Sommerfield, C.K.; Lee, H.J.; Normark, W.R.

2009-01-01

Sedimentary strata on the Southern California shelf and slope (Point Conception to Dana Point) display patterns and rates of sediment accumulation that convey information on sea-level inundation, sediment supply, and oceanic transport processes following the Last Glacial Maximum. In Santa Monica Bay and San Pedro Bay, postglacial transgression is recorded in shelf deposits by wave-ravinement surfaces dated at 13-11 ka and an upsection transition from coastal to shallow-marine sediment facies. Depositional conditions analogous to the modern environment were established in the bays by 8-9 ka. On the continental slope, transgression is evidenced in places by an increase in sediment grain size and accumulation rate ca. 15-10 ka, a consequence of coastal ravinement and downslope resedimentation, perhaps in conjunction with climatic increases in fluvial sediment delivery. Grain sizes and accumulation rates then decreased after 12-10 ka when the shelf flooded and backfilled under rising sea level. The Santa Barbara coastal cell contains the largest mass of postglacial sediment at 32-42 ?? 109 metric tons, most of which occurs between offshore Santa Barbara and Hueneme Canyon. The San Pedro cell contains the second largest quantity of sediment, 8-11 ?? 109 metric tons, much of which is present on the eastern Palos Verdes and outer San Pedro shelves. By comparison, the mass of sediment sequestered within the Santa Monica cell is smaller at ??6-8 ?? 109 metric tons. The postglacial sediment mass distribution among coastal cells reflects the size of local fluvial sediment sources, whereas intracell accumulation patterns reflect antecedent bathymetric features conducive for sediment bypass or trapping. ?? 2009 The Geological Society of America.

Submarine landslide and tsunami hazards offshore southern Alaska: Seismic strengthening versus rapid sedimentation

NASA Astrophysics Data System (ADS)

Sawyer, Derek E.; Reece, Robert S.; Gulick, Sean P. S.; Lenz, Brandi L.

2017-08-01

The southern Alaskan offshore margin is prone to submarine landslides and tsunami hazards due to seismically active plate boundaries and extreme sedimentation rates from glacially enhanced mountain erosion. We examine the submarine landslide potential with new shear strength measurements acquired by Integrated Ocean Drilling Program Expedition 341 on the continental slope and Surveyor Fan. These data reveal lower than expected sediment strength. Contrary to other active margins where seismic strengthening enhances slope stability, the high-sedimentation margin offshore southern Alaska behaves like a passive margin from a shear strength perspective. We interpret that seismic strengthening occurs but is offset by high sedimentation rates and overpressure. This conclusion is supported by shear strength outside of the fan that follow an active margin trend. More broadly, seismically active margins with wet-based glaciers are susceptible to submarine landslide hazards because of the combination of high sedimentation rates and earthquake shaking.

Western Ross Sea continental slope gravity currents

NASA Astrophysics Data System (ADS)

Gordon, Arnold L.; Orsi, Alejandro H.; Muench, Robin; Huber, Bruce A.; Zambianchi, Enrico; Visbeck, Martin

2009-06-01

Antarctic Bottom Water of the world ocean is derived from dense Shelf Water that is carried downslope by gravity currents at specific sites along the Antarctic margins. Data gathered by the AnSlope and CLIMA programs reveal the presence of energetic gravity currents that are formed over the western continental slope of the Ross Sea when High Salinity Shelf Water exits the shelf through Drygalski Trough. Joides Trough, immediately to the east, offers an additional escape route for less saline Shelf Water, while the Glomar Challenger Trough still farther east is a major pathway for export of the once supercooled low-salinity Ice Shelf Water that forms under the Ross Ice Shelf. The Drygalski Trough gravity currents increase in thickness from ˜100 to ˜400 m on proceeding downslope from ˜600 m (the shelf break) to 1200 m (upper slope) sea floor depth, while turning sharply to the west in response to the Coriolis force during their descent. The mean current pathway trends ˜35° downslope from isobaths. Benthic-layer current and thickness are correlated with the bottom water salinity, which exerts the primary control over the benthic-layer density. A 1-year time series of bottom-water current and hydrographic properties obtained on the slope near the 1000 m isobath indicates episodic pulses of Shelf Water export through Drygalski Trough. These cold (<-1 °C), salty (>34.75) pulses correlate with strong downslope bottom flow. Extreme examples occurred during austral summer/fall 2003, comprising concentrated High Salinity Shelf Water (-1.9 °C; 34.79) and approaching 1.5 m s -1 at descent angles as large as ˜60° relative to the isobaths. Such events were most common during November-May, consistent with a northward shift in position of the dense Shelf Water during austral summer. The coldest, saltiest bottom water was measured from mid-April to mid-May 2003. The summer/fall export of High Salinity Shelf Water observed in 2004 was less than that seen in 2003. This

Seismic stratigraphy of the Mississippi-Alabama shelf and upper continental slope

USGS Publications Warehouse

Kindinger, J.L.

1988-01-01

The Mississippi-Alabama shelf and upper continental slope contain relatively thin Upper Pleistocene and Holocene deposits. Five stages of shelf evolution can be identified from the early Wisconsinan to present. The stages were controlled by glacioeustatic or relative sea-level changes and are defined by the stratigraphic position of depositional and erosional episodes. The stratigraphy was identified on seismic profiles by means of geomorphic pattern, high-angle clinoform progradational deposits, buried stream entrenchments, planar conformities, and erosional unconformities. The oldest stage (stage 1) of evolution occurred during the early Wisconsinan lowstand; the subaerially exposed shelf was eroded to a smooth seaward-sloping surface. This paleosurface is overlain by a thin (< 10 m) drape of transgressive deposits (stage 2). Stage 3 occurred in three phases as the late Wisconsinan sea retreated: (1) fluvial channel systems eroded across the shelf, (2) deposited a thick (90 m) shelf-margin delta, and (3) contemporaneously deposited sediments on the upper slope. Stage 4 included the rapid Holocene sea-level rise that deposited a relatively thin transgressive facies over parts of the shelf. The last major depositional episode (stage 5) was the progradation of the St. Bernard delta over the northwestern and central parts of the area. A depositional hiatus has occurred since the St. Bernard progradation. These Upper Quaternary shelf and slope deposits provide models for analogous deposits in the geologic record. Primarily, they are examples of cyclic sedimentation caused by changes in sea level and may be useful in describing short-term, sandy depositional episodes in prograding shelf and slope sequences. ?? 1988.

Sediment Dynamics and Geohazards offshore Uruguay and Northern Argentina: First Results from the multi-disciplinary Meteor-Cruise M78-3

NASA Astrophysics Data System (ADS)

Krastel, Sebastian; Freudenthal, Tim; Hanebuth, Till; Preu, Benedict; Schwenck, Tilmann; Strasser, Michael; Violante, Roberto; Wefer, Gerold; Winkelmann, Daniel

2010-05-01

About 90% of the sediments generated by weathering and erosion on land get finally deposited at the ocean margins. The sediment distribution processes and landscape evolution on land are relatively well understood, but comparably little is known about the role and relative importance of marine sediment dynamics in controlling the architectural evolution of ocean margins. Important players include hemi-pelagic settling, down-slope and current-controlled along-slope sediment transport, depositional and post-depositional sedimentary processes (e.g. consolidation and diagenesis), as well as the destabilization of sediment bodies and their erosion. Submarine landslides in this context thus may represent an important sediment transport process, but also a major geo-hazard due to the increasing number of offshore constructions as well as their potential to instantaneously displace large water masses triggering waves in densely populated coastal areas. Here we present first results from a seagoing expedition that aimed at investigating the interaction processes of sediment redistribution, partitioning, deposition and diagenesis from the coast to the deep-sea along the western South-Atlantic passive continental margin. During RV Meteor Cruise M78/3 in May-July 2009 the shelf, slope and rise offshore Argentina and Uruguay have been investigated by means of hydroacoustic and seismic mapping as well as geological sampling with conventional coring tools as well as the new MARUM seafloor drill rig (MeBo) that revealed recovery of geological strata sampled from up to 50m below seafloor. The working area is characterized by a high amount of fluvial input by the Rio de la Plata river. The continental slope is relatively wide and shows average slope gradients between 1 and 2.5 but locally higher slope gradients may occur (>5). The transition for the continental rise with low slope gradients is found in ~ 3000m water depth. The working area is located in a highly dynamic

California State Waters Map Series: offshore of Refugio Beach, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Cochrane, Guy R.; Golden, Nadine E.; Phillips, Eleyne L.; Ritchie, Andrew C.; Krigsman, Lisa M.; Dieter, Bryan E.; Conrad, James E.; Greene, H. Gary; Seitz, Gordon G.; Endris, Charles A.; Sliter, Ray W.; Wong, Florence L.; Erdey, Mercedes D.; Gutierrez, Carlos I.; Yoklavich, Mary M.; East, Amy E.; Hart, Patrick E.; Johnson, Samuel Y.; Cochran, Susan A.

2015-01-01

Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft, unconsolidated sediment interspersed with isolated areas of rocky habitat that support kelp-forest communities nearshore and rocky-reef communities in deep water. The potential marine benthic habitat types mapped in the Offshore of Refugio Beach map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats, which lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank or continental slope) megahabitats, primarily are composed of soft sediment interrupted by a few carbonate mounds. This homogeneous seafloor of sediment and low-relief bedrock provides promising habitat for groundfish, crabs, shrimp, and other marine benthic organisms.

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

Shelf-Basin Exchange over the Continental Slope of the Chukchi Sea 2003/04 vs. 2016/17

NASA Astrophysics Data System (ADS)

Muenchow, A.; Elmer, C.; Badiey, M.; Eickmeier, J.; Ryan, P.

2017-12-01

The US Navy faces the "New Arctic" as a challenge to predict acoustic propagation from deep to shallow waters, because a less ice-covered Arctic Ocean is more dynamic and creates new and more complex sound channels. We here present context and preliminary results from the Canada Basin Acoustic Propagation Experiment (CANAPE) and focus on the Chukchi Sea between 100-m and 800-m isobaths. We explore temperature and density fields using ocean survey and mooring data that we collected in 2016 and 2017. We compare these "new" data to observations from prior decades.Remote sensing (SSMI and Sentinel-1) of sea ice, winds, and ocean hydrography all document change in large scale ocean forcing in our study area about 150 km west of Barrow, Alaska. The "new" surface forcing impacts both ocean dynamics and sound propagation over the Chukchi Slope. More specifically, we find warm water intrusions at 80-m depth near the 1026 kg/m3 density surface at 160 W longitude. Spatial extend and structure of this water varies both along and across the continental with eddy trains dispersing offshore. Temperature and sound speed signals exceed 1 C and 5 m/s, respectively, and have not been observed before. We note, that our study area is generally ice-covered in November, but was free of ice in 2016.

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

USGS Publications Warehouse

Gartner, John V.; Sulak, K.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 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.

Internal wave scattering in continental slope canyons, part 1: Theory and development of a ray tracing algorithm

NASA Astrophysics Data System (ADS)

Nazarian, Robert H.; Legg, Sonya

2017-10-01

When internal waves interact with topography, such as continental slopes, they can transfer wave energy to local dissipation and diapycnal mixing. Submarine canyons comprise approximately ten percent of global continental slopes, and can enhance the local dissipation of internal wave energy, yet parameterizations of canyon mixing processes are currently missing from large-scale ocean models. As a first step in the development of such parameterizations, we conduct a parameter space study of M2 tidal-frequency, low-mode internal waves interacting with idealized V-shaped canyon topographies. Specifically, we examine the effects of varying the canyon mouth width, shape and slope of the thalweg (line of lowest elevation). This effort is divided into two parts. In the first part, presented here, we extend the theory of 3-dimensional internal wave reflection to a rotated coordinate system aligned with our idealized V-shaped canyons. Based on the updated linear internal wave reflection solution that we derive, we construct a ray tracing algorithm which traces a large number of rays (the discrete analog of a continuous wave) into the canyon region where they can scatter off topography. Although a ray tracing approach has been employed in other studies, we have, for the first time, used ray tracing to calculate changes in wavenumber and ray density which, in turn, can be used to calculate the Froude number (a measure of the likelihood of instability). We show that for canyons of intermediate aspect ratio, large spatial envelopes of instability can form in the presence of supercritical sidewalls. Additionally, the canyon height and length can modulate the Froude number. The second part of this study, a diagnosis of internal wave scattering in continental slope canyons using both numerical simulations and this ray tracing algorithm, as well as a test of robustness of the ray tracing, is presented in the companion article.

New OBS network deployment offshore Ireland

NASA Astrophysics Data System (ADS)

Le Pape, Florian; Bean, Chris; Craig, David; Jousset, Philippe; Horan, Clare; Hogg, Colin; Donne, Sarah; McCann, Hannah; Möllhoff, Martin; Kirk, Henning; Ploetz, Aline

2016-04-01

With the presence of the stormy NE Atlantic, Ireland is ideally located to investigate further our understanding of ocean generated microseisms and use noise correlation methods to develop seismic imaging in marine environments as well as time-lapse monitoring. In order to study the microseismic activity offshore Ireland, 10 Broad Band Ocean Bottom Seismographs (OBSs) units including hydrophones have been deployed in January 2016 across the shelf offshore Donegal and out into the Rockall Trough. This survey represents the first Broadband passive study in this part of the NE Atlantic. The instruments will be recovered in August 2016 providing 8 months worth of data to study microseisms but also the offshore seismic activity in the area. One of the main goal of the survey is to investigate the spatial and temporal distributions of dominant microseism source regions, close to the microseism sources. Additionally we will study the coupling of seismic and acoustic signals at the sea bed and its evolution in both the deep water and continental shelf areas. Furthermore, the survey also aims to investigate further the relationship between sea state conditions (e.g. wave height, period), seafloor pressure variations and seismic data recorded on both land and seafloor. Finally, the deployed OBS network is also the first ever attempt to closely monitor local offshore earthquakes in Ireland. Ireland seismicity although relatively low can reduce slope stability and poses the possibility of triggering large offshore landslides and local tsunamis.

Architecture and sedimentary processes on the mid-Norwegian continental slope: A 2.7 Myr record from extensive seismic evidence

NASA Astrophysics Data System (ADS)

Montelli, A.; Dowdeswell, J. A.; Ottesen, D.; Johansen, S. E.

2018-07-01

Quaternary architectural evolution and sedimentary processes on the mid-Norwegian continental slope are investigated using margin-wide three- and two-dimensional seismic datasets. Of ∼100,000 km3 sediments delivered to the mid-Norwegian shelf and slope over the Quaternary, ∼75,000 km3 comprise the slope succession. The structural high of the Vøring Plateau, characterised by initially low (∼1-2°) slope gradients and reduced accommodation space, exerted a strong control over the long-term architectural evolution of the margin. Slope sediment fluxes were higher on the Vøring Plateau area, increasing up to ∼32 km3 ka-1 during the middle Pleistocene, when fast-flowing ice streams advanced to the palaeo-shelf edge. Resulted in a more rapid slope progradation on the Vøring Plateau, these rates of sediment delivery are high compared to the maximum of ∼7 km3 ka-1 in the adjacent sectors of the slope, characterised by steeper slope (∼3-5°), more available accommodation space and smaller or no palaeo-ice streams on the adjacent shelves. In addition to the broad-scale architectural evolution, identification of more than 300 buried slope landforms provides an unprecedented level of detailed, process-based palaeoenvironmental reconstruction. Channels dominate the Early Pleistocene record (∼2.7-0.8 Ma), during which glacimarine sedimentation on the slope was influenced by dense bottom-water flow and turbidity currents. Morphologic signature of glacigenic debris-flows appear within the Middle-Late Pleistocene (∼0.8-0 Ma) succession. Their abundance increases towards Late Pleistocene, marking a decreasing role for channelized turbidity currents and dense water flows. This broad-scale palaeo-environmental shift coincides with the intensification of Northern Hemispheric glaciations, highlighting first-order climate control on the sedimentary processes in high-latitude continental slopes.

Assessment of submarine landslides hazard through geotechnical and rheological analysis of sediments on the French Atlantic continental slope

NASA Astrophysics Data System (ADS)

Toucanne, S.; Howlett, S.; Garziglia, S.; Silva Jacinto, R.; Courgeon, S.; Sabine, M.; Riboulot, V.; Marsset, B.

2016-12-01

In the aftermath of the devastating tsunami on the Japanese coast in 2011, a French multi-partnership project called TANDEM has been launched to assess the impact of tsunamis generated or propagated in the vicinity of French Channel and Atlantic coastlines. Tsunami are usually generated by earthquakes, but can also be triggered by submarine landslides. This study focuses on submarine landslides along the French Atlantic continental slope using data that were mainly collected in August 2015 during the GITAN cruise (R/V Pourquoi Pas?). Following geomorphological, geophysical and sedimentological analysis of the Bay of Biscay, efforts were oriented towards the determination of the sediment properties controlling landslide dynamics from in situ and laboratory measurements. Preliminary results show over 700 landslide scars on the French Atlantic continental slope, with most of them occurring between 400 and 1000m water depth and in canyon environments. The Plio-Quaternary sediments draping the majority of the Bay of Biscay are generally normally consolidated and composed of high plasticity clays. They show similar geomechanical properties throughout the area studied, with linear evolutions with depth and good reproducibility for rheological parameters such as Storage and Loss modulus. These similarities allow to extend geotechnical and rheological models to a regional scale in the Bay of Biscay. Our multi-disciplinary approach will provide the tools to assess continental slope failures and submarine landslides generation. Finally, we will aim to qualify and quantify the volumes and flow properties of sediment transported obtained through slope-stability modeling on SAMU-3D and rheology modelling on Nixes-SPH. These results will provide the TANDEM actors with the information necessary to simulate tsunami wave generation.

Structure of the Lithosphere-Asthenosphere Boundary Onshore and Offshore the California Continental Margin from Three-Dimensional Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Gomez, C. D.; Escobar, L., Sr.; Rathnayaka, S.; Weeraratne, D. S.; Kohler, M. D.

2016-12-01

The California continental margin, a major transform plate boundary in continental North America, is the locus of complex tectonic stress fields that are important in interpreting both remnant and ongoing deformational strain. Ancient subduction of the East Pacific Rise spreading center, the rotation and translation of tectonic blocks and inception of the San Andreas fault all contribute to the dynamic stress fields located both onshore and offshore southern California. Data obtained by the ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) and the CISN (California Integrated Seismic Network) seismic array are analyzed for azimuthal anisotropy of Rayleigh waves from 80 teleseismic events at periods 16 - 78 s. Here we invert Rayleigh wave data for shear wave velocity structure and three-dimensional seismic anisotropy in the thee regions designated within the continental margin including the continent, seafloor and California Borderlands. Preliminary results show that seismic anisotropy is resolved in multiple layers and can be used to determine the lithosphere-asthenosphere boundary (LAB) in offshore and continental regions. The oldest seafloor in our study at age 25-35 Ma indicates that the anisotropic transition across the LAB occurs at 73 km +/- 25 km with the lithospheric fast direction oriented WNW-ESE, consistent with current Pacific plate motion direction. The continent region west of the San Andreas indicates similar WNW-ESE anisotropy and LAB depth. Regions east of the San Andreas fault indicate NW-SE anisotropy transitioning to a N-S alignment at 80 km depth north of the Garlock fault. The youngest seafloor (15 - 25 Ma) and outer Borderlands indicate a more complex three layer fabric where shallow lithospheric NE-SW fast directions are perpendicular with ancient Farallon subduction arc, a mid-layer with E-W fast directions are perpendicular to remnant fossil fabric, and the deepest layer

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

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

USGS Publications Warehouse

Gartner, John V.; 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.

Observed Oceanic Response over the Upper Continental Slope and Outer Shelf during Hurricane Ivan

DTIC Science & Technology

2007-09-01

the slope and rise. In addition, they were presumed to be along-shelf and cross-shelf components of group veloci- generated by pulsations of the Loop ...hits. Fortunately, all of exchange of mass, momentum, heat , and water proper- the SEED moorings survived this powerful storm and ties across the shelf...15. SUBJECT TERMS SEED, continental shelf, Doppler, waves 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18. NUMBER 19a. NAME OF RESPONSIBLE

Relationship Between Subduction Erosion, Seamount Subduction, Fluid Venting and Mound Formation on the Slope of the Costa Rican Continental Margin

NASA Astrophysics Data System (ADS)

Petersen, C.; Klaucke, I.; Weinrebe, W.

2006-12-01

The oceanic crust off central Costa Rica northwest of the Cocos Ridge is dominated by chains of seamounts rising 1-2 km above the seafloor with diameters of up to 20 km. The subduction of these seamounts leads to strong indentations, scars and slides on the continental margin. A smoother segment of about 80 km width is located offshore Nicoya peninsula. The segment ends at a fracture zone which marks the transition of oceanic crust created at the Cocos-Nazca spreading center (CNS) and at the East Pacific Rise (EPR). Offshore Nicaragua the incoming EPR crust is dominated by bending related faults. To investigate the relationship between subduction erosion, fluid venting and mound formation, multibeam bathymetry and high-resolution deep-tow sidescan sonar and sediment echosounder data were acquired during R/V Sonne cruises SO163 and SO173 (2002/2003). The deep-tow system consisted of a dual-frequency 75/410 kHz sidescan sonar and a 2-12 kHz chirp sub-bottom profiler. The connection of the observed seafloor features to deeper subduction related processes is obtained by analysis of multi-channel streamer (MCS) data acquired during cruises SO81 (1992) and BGR99 (1999). Data examples and interpretations for different settings along the margin are presented. Near the Fisher seamount the large Nicoya slump failed over the flank of a huge subducted seamount. The sidescan and echosounder data permit a detailed characterization of fault patterns and fluid escape structures around the headwall of the slump. Where the fracture zone separating CNS and EPR crust subducts, the Hongo mound field was mapped in detail. Several mounds of up to 100 m height are located in line with a scar possibly created by a subducting ridge of the fracture zone. MCS data image a topographic high on the subducting oceanic crust beneath the mound field which lead to uplift and possibly enabled ascent of fluids from the subducting plate. The combined analysis of geoacoustic and seismic MCS data

New Insight Into The Crustal Structure of The Continental Margin Off NW Sabah/borneo

NASA Astrophysics Data System (ADS)

Barckhausen, U.; Franke, D.; Behain, D.; Meyer, H.

The continental margin offshore NW Sabah/Borneo (Malaysia) has been investigated with reflection and refraction seismics, magnetics, and gravity during the recent cruise BGR01-POPSCOMS. A total of 4000 km of geophysical profiles has been acquired, thereof 2900 km with reflection seismics. Like in major parts of the South China Sea, the area seaward of the Sabah Trough consists of extended continental lithosphere. We found evidence that the continental crust also underlies the continental slope land- ward of the Trough, a fact that raises many questions about the tectonic history and development of this margin. The characteristic pattern of rotated fault blocks and half grabens and the carbon- ates which are observed all over the Dangerous Grounds can be traced a long way landward of the Sabah Trough beneath the sedimentary succession of the upper plate. The magnetic anomalies which are dominated by the magnetic signatures of relatively young volcanic features also continue under the continental slope. The sedimentary rocks of the upper plate, in contrast, seem to generate hardly any magnetic anoma- lies. We suspect that the volcanic activity coincided with the collision of Borneo and the Dangerous Grounds in middle or late Miocene time. The emplacement of an al- lochtonous terrane on top of the extended continental lithosphere could be explained by overthrusting as a result of the collision or it could be related to gravity sliding following a broad uplift of NW Borneo at the same time.

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

A downslope propagating thermal front over the continental slope

NASA Astrophysics Data System (ADS)

van Haren, Hans; Hosegood, Phil J.

2017-04-01

In the ocean, internal frontal bores above sloping topography have many appearances, depending on the local density stratification, and on the angle and source of generation of the carrier wave. However, their common characteristics are a backward breaking wave, strong sediment resuspension, and relatively cool (denser) water moving more or less upslope underneath warm (less dense) water. In this paper, we present a rare example of a downslope moving front of cold water moving over near-bottom warm water. Large backscatter is observed in the downslope moving front's trailing edge, rather than the leading edge as is common in upslope moving fronts. Time series observations have been made during a fortnight in summer, using a 101 m long array of high-resolution temperature sensors moored with an acoustic Doppler current profiler at 396 m depth in near-homogeneous waters, near a small canyon in the continental slope off the Malin shelf (West-Scotland, UK). Occurring between fronts that propagate upslope with tidal periodicity, the rare downslope propagating one resembles a gravity current and includes strong convective turbulence coming from the interior rather than the more usual frictionally generated turbulence arising from interaction with the seabed. Its turbulence is 3-10 times larger than that of more common upslope propagating fronts. As the main turbulence is in the interior with a thin stratified layer close to the bottom, little sediment is resuspended by a downslope propagating front. The downslope propagating front is suggested to be generated by oblique propagation of internal (tidal) waves and flow over a nearby upstream promontory.

Geology of the offshore Southeast Georgia Embayment, U.S. Atlantic continental margin, based on multichannel seismic reflection profiles

USGS Publications Warehouse

Buffler, Richard T.; Watkins, Joel S.; Dillon, William P.

1979-01-01

The sedimentary section is divided into three major seismic intervals. The intervals are separated by unconformities and can be mapped regionally. The oldest interval ranges in age from Early Cretaceous through middle Late Cretaceous, although it may contain Jurassic rocks where it thickens beneath the Blake Plateau. It probably consists of continental to nearshore clastic rocks where it onlaps basement and grades seaward to a restricted carbonate platform facies (dolomite-evaporite). The middle interval (Upper Cretaceous) is characterized by prograding clinoforms interpreted as open marine slope deposits. This interval represents a Late Cretaceous shift of the carbonate shelf margin from the Blake Escarpment shoreward to about its present location, probably due to a combination of co tinued subsidence, an overall Late Cretaceous rise in sea level, and strong currents across the Blake Plateau. The youngest (Cenozoic) interval represents a continued seaward progradation of the continental shelf and slope. Cenozoic sedimentation on the Blake Plateau was much abbreviated owing mainly to strong currents.

Slumping and shallow faulting related to the presence of salt on the Continental Slope and rise off North Carolina

USGS Publications Warehouse

Cashman, K.V.; Popenoe, P.

1985-01-01

Seismic reflection profiles and long- and medium-range sidescan sonar were used to investigate a salt diapir complex and area of slope instability near the base of the Continental Slope off North Carolina. Within the area of investigation three diapirs are bounded on their upslope side by a scarp 60 m high and 50 km long. The slope above the scarp is characterized by a series of shallow rotational normal faults. The bottom below the scarp is furrowed by slide tracks, which were probably carved by large blocks that broke off the scarp face and slid downslope leaving rubble and scree lobes. Extensive slumping in this area appears to be a result of uplift and faulting associated with salt intrusion, which has fractured and oversteepened the slope leading to instability and failure. Sharply defined slide tracks suggest that slope failure above the breached diapir complex is a continuing process, in contrast to much of the surrounding slope area where few instability features were observed. 

Assessment of Submarine Slope Stability on the Continental Margin off SW Taiwan

NASA Astrophysics Data System (ADS)

Hsu, Huai-Houh; Dong, Jia-Jyun; Cheng, Win-Bin; Su, Chih-Chieh

2017-04-01

The abundant gas hydrate reservoirs are distributed in the southwest (SW) off Taiwan. To explore this new energy, geological methods were systematically used and mainly emphasized on the storage potential evaluation. On the other hand, the correlation between gas hydrate dissociation and submarine slope stability is also an important issue. In this study, three submarine profiles on the active and passive continental margin were selected and assessed their slope stabilities by considering two influence factors (seismic forces and number of sedimentary layers). The gravity corers obtained from these three sites (Xiaoliuqiu, Yuan-An Ridge, and Pointer Ridge) to conduct soil laboratory tests. The physical property tests and isotropically consolidated undrained (CIU) triaxial tests were carried out to establish reference properties and shear strength parameters. Before the stability analysis is performed, it is also necessary to construct the seabed profile. For each submarine profile, data from P-waves and from S-waves generated by P-S conversion on reflection from airgun shots recorded along one line of ocean bottom seismometers were used to construct 2-D velocity sections. The seabed strata could be simplified to be only one sedimentary layer or to be multilayer in accordance with the velocity structure profile. Results show the safety factors (FS) of stability analysis are obviously different in considering the number of sedimentary layers, especially for a very thin layer of sediments on a steep slope. The simplified strata condition which treated all seabed strata as only one sedimentary layer might result in the FS lower than 1 and the slope was in an unstable state. On the contrary, the FS could be higher than 10 in a multilayer condition.

78 FR 18614 - National Offshore Safety Advisory Committee

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-27

... Continental Shelf (OCS); (b) Electrical Equipment in Hazardous Areas on Foreign Flag Mobile Offshore Drilling... DEPARTMENT OF HOMELAND SECURITY Coast Guard [Docket No. USCG-2013-0182] National Offshore Safety... Advisory Committee Meetings. SUMMARY: The National Offshore Safety Advisory Committee (NOSAC) will meet on...

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. Copyright © 2014 Elsevier Ltd. All rights reserved.

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, Dennis 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.

Origin of Volcanic Seamounts Offshore California Related to Interaction of Abandoned Spreading Centers with the Continental Margin

NASA Astrophysics Data System (ADS)

Davis, A. S.; Clague, D. A.; Paduan, J. B.; Cousens, B. L.; Huard, J.

2007-12-01

The numerous NE-SW trending volcanic seamounts at the continental margin offshore central to Southern California owe their existence to the complex tectonics that resulted when small spreading ridge segments intersected and partly subducted beneath the continental margin during the Miocene plate reorganization. A limited number of dredged samples had indicated multiple episodes of coeval, alkalic volcanism at geographically widely separated sites (Davis et al., 2002, GSA Bull. 114, 316-333). 450 new samples were collected from 8 seamounts from 37. 5°N to 32.3°N with MBARI's ROV Tiburon. Ar-Ar ages for 50 of these samples extend the ages of volcanism from 18 Ma to 2.8 Ma. The dominant whole rock compositions are differentiated alkalic basalt, hawaiite, and mugearite, but include minor benmoreite, trachyte, and rare tholeiitic basalt. This entire range of compositions is also present in glassy margins or in volcaniclastic breccias, except for the trachyte, which had no glassy margins. Trace element abundances and ratios (e.g. REE, Zr, Nb, Ta, Th, Ba, etc.) are typical for ocean island basalt, whether the seamount is located on the Pacific plate (e.g. Pioneer, Gumdrop, Guide, Davidson, San Juan, San Marcos) or on the continental slope (Rodriguez) or within the Southern Continental Borderland (Northeast Bank). Nine samples, predominantly from Rodriguez Seamount, show a calc-alkaline trend with lower Nb, Ta, and higher Th. These samples may be erratics (Paduan et al., 2007, Marine Geology, in press). Sr, Nd, and Pb isotopic compositions plot within the Pacific N-MORB field for the northern seamounts (Pioneer, Gumdrop, Guide) but suggest progressively more radiogenic sources southward. There is considerable scatter at each site, especially with regard to 87Sr/86Sr, despite severe acid-leaching of the samples. Isotopic and trace element compositions indicate sources that are heterogeneous at a small scale. Chondrite-normalized Ce/Yb suggest smaller degree of melting and

Nitrogen and Phosphorous Flow in Atlantic Forest Covered Watersheds on the Oceanic and Continental Slopes at Serra dos Órgãos mountain, Southeast of Brazil

NASA Astrophysics Data System (ADS)

Vidal, M. M.; De Souza, P.; De Mello, W. Z.; Damaceno, I.; Bourseau, L.; Rodrigues, R. D. A.; Mattos, B. B.

2017-12-01

Concentration of nutrients above natural levels are found even at remote or protected environments due to atmospheric transportation from biomass burning emissions, urban and industrial areas. This study evaluate N and P atmospheric deposition at the oceanic and continental slopes of Serra dos Órgãos mountain, which are influenced by the pollutants emission from the Metropolitan Region of Rio de Janeiro. Flux of dissolved forms of N and P were measured in three watersheds in headwaters of Piabanha basin, southeastern Brazil, to understand the dynamics of the biogeochemical processes of these elements, related to anthropic influences of atmospheric inputs and export via stream flow. Samples of bulk precipitation (weekly; n=47) and stream water (monthly; n=13) were collected along one year (Sept 2014 - Sept 2015). During that period the annual rainfall in the oceanic slope (2163 mm) was the double of the continental one. It is important to stress that the rainfall in the oceanic slope was 13 % and 28% in 2014/15, respectively, lower than the long term average. Atmospheric deposition of total dissolved nitrogen (TDN) on the oceanic and continental slopes were, respectively, 15 and 8.6 kg N ha-1 year-1. The TDN outputs by stream water were 5-7 times lower in oceanic slope and 28 times lower on the continental one. The relative contribution of dissolved organic nitrogen (DON; 65%-70%) was higher than the one of dissolved inorganic nitrogen (DIN; 30-35%) to TDN deposition. Atmospheric deposition of total dissolved phosphorus (TDP) in oceanic and continental slopes were 1.4 and 0.95 kg P ha-1 year-1. Dissolved Organic Phosphorus (DOP; 89-96%) was higher than the inorganic one (PO43-; 5-11%). TDP outputs were 2-4 times lower, regarding to atmospheric contribution. The contribution of DOP (73-77 %) was higher than DIP (23-27 %). Results show variations in quantities and forms of N and P species due to natural and anthropogenic processes which contribute to the cycling of

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.

The role of deep-water sedimentary processes in shaping a continental margin: The Northwest Atlantic

USGS Publications Warehouse

Mosher, David C.; Campbell, D.C.; Gardner, J.V.; Piper, D.J.W.; Chaytor, Jason; Rebesco, M.

2017-01-01

The tectonic history of a margin dictates its general shape; however, its geomorphology is generally transformed by deep-sea sedimentary processes. The objective of this study is to show the influences of turbidity currents, contour currents and sediment mass failures on the geomorphology of the deep-water northwestern Atlantic margin (NWAM) between Blake Ridge and Hudson Trough, spanning about 32° of latitude and the shelf edge to the abyssal plain. This assessment is based on new multibeam echosounder data, global bathymetric models and sub-surface geophysical information.The deep-water NWAM is divided into four broad geomorphologic classifications based on their bathymetric shape: graded, above-grade, stepped and out-of-grade. These shapes were created as a function of the balance between sediment accumulation and removal that in turn were related to sedimentary processes and slope-accommodation. This descriptive method of classifying continental margins, while being non-interpretative, is more informative than the conventional continental shelf, slope and rise classification, and better facilitates interpretation concerning dominant sedimentary processes.Areas of the margin dominated by turbidity currents and slope by-pass developed graded slopes. If sediments did not by-pass the slope due to accommodation then an above grade or stepped slope resulted. Geostrophic currents created sedimentary bodies of a variety of forms and positions along the NWAM. Detached drifts form linear, above-grade slopes along their crests from the shelf edge to the deep basin. Plastered drifts formed stepped slope profiles. Sediment mass failure has had a variety of consequences on the margin morphology; large mass-failures created out-of-grade profiles, whereas smaller mass failures tended to remain on the slope and formed above-grade profiles at trough-mouth fans, or nearly graded profiles, such as offshore Cape Fear.

Caanyon Mediated Cross-Slope Transport

NASA Astrophysics Data System (ADS)

Mihaly, S. F.; Cabrera De Leo, F.; Sastri, A. R.; Matabos, M.; Heesemann, M.; Ogata, B.

2017-12-01

Three current meter and water property stations along the west coast of Vancouver Island along with video and acoustic backscatter observations are used to gain insight into mechanisms of cross-slope transport. The setting is an eastern boundary current region with a active poleward flowing countercurrent. The significant effects of these currents flowing over a strongly incised continental slope along with cross-slope density flows are contrasted with the seasonally varying upwelling and downwelling regime. The video and acoustic backscatter enabled by Ocean Networks Canada's NEPTUNE observatory provide a view on the materials being transported between the abyssal plain and the continental shelf.

Bathymetry Offshore Sumatra First Comprehensive map of International Data Sets

NASA Astrophysics Data System (ADS)

Gaedicke, C.; Ladage, S.; Soh, W.; Weinrebe, W.; Tappin, D. R.; Henstock, T.; McNeill, L.; Sibuet, J.; Klingelhoefer, F.; Singh, S.; Flueh, E.; Djajadihardja, Y.

2006-12-01

Knowledge of the bathymetry offshore Sumatra is of great importance for geohazard risk assessment, modelling of tsunami runup heights and development of tsunami early warning systems as well as for the general understanding of plate boundary processes and morphotectonic features. Since the devastating December 26, 2004 Sumatra-Andaman Islands earthquake and tsunami a number of marine expeditions, funded by Canada, France, Germany, India, Indonesia, Japan, United Kingdom and the United States have acquired bathymetric data over the southern part of the earthquake rupture zone but also along strike the whole Sunda trench. Here we present the first compilation of these bathymetric data sets as one bathymetric map. The bathymetric data acquired up to date covers a vast part of the trench, continental slope and in part also of the fore arc basins. The map incorporates the newest data sets from 2005 of the British high-resolution HMS SCOTT survey, the French Marion-Dufresene "Aftershocks" and the Japanese Natsushima cruises. While these surveys concentrated on the southern rupture zone of the Dec. 26th, 2004 earthquake, the German RV SONNE SeaCause and Sumatra cruises in 2005 and 2006 mapped the March 28th 2005 rupture area as well as large parts of the central Sunda trench and slope and in part the fore arc basins. Surveys reaching back to 1997 covering parts of the Sunda Strait and offshore southern Sumatra are also incorporated. A nearly complete coverage of the Sunda trench and slope area in the north is achieved. In the south data gaps on the slope still exist. This map compilation is a collaborative international effort initiated and partly funded by InterMARGINS. It is a major contribution to the Indonesian and international science community.

Nonhydrostatic simulation of hyperpycnal river plumes on sloping continental shelves: Flow structures and nonhydrostatic effect

NASA Astrophysics Data System (ADS)

Tseng, Chien-Yung; Chou, Yi-Ju

2018-04-01

A three-dimensional nonhydrostatic coastal model SUNTANS is used to study hyperpycnal plumes on sloping continental shelves with idealized domain setup. The study aims to examine the nonhydrostatic effect of the plunging hyperpycnal plume and the associated flow structures on different shelf slopes. The unstructured triangular grid in SUNTANS allows for local refinement of the grid size for regions in which the flow varies abruptly, while retaining low-cost computation using the coarse grid resolution for regions in which the flow is more uniform. These nonhydrostatic simulations reveal detailed three-dimensional flow structures in both transient and steady states. Via comparison with the hydrostatic simulation, we show that the nonhydrostatic effect is particularly important before plunging, when the plume is subject to significant changes in both the along-shore and vertical directions. After plunging, where the plume becomes an undercurrent that is more spatially uniform, little difference is found between the hydrostatic and nonhydrostatic simulations in the present gentle- and mild-slope cases. A grid-dependence study shows that the nonhydrostatic effect can be seen only when the grid resolution is sufficiently fine that the calculation is not overly diffusive. A depth-integrated momentum budget analysis is then conducted to show that the flow convergence due to plunging is an important factor in the three-dimensional flow structures. Moreover, it shows that the nonhydrostatic effect becomes more important as the slope increases, and in the steep-slope case, neglect of transport of the vertical momentum during plunging in the hydrostatic case further leads to an erroneous prediction for the undercurrent.

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.

Textures of water-rich mud sediments from the continental margin offshore Costa Rica (IODP expeditions 334 and 344)

NASA Astrophysics Data System (ADS)

Kuehn, Rebecca; Stipp, Michael; Leiss, Bernd

2017-04-01

During sedimentation and burial at continental margins, clay-rich sediments develop crystallographic preferred orientations (textures) depending on the ongoing compaction as well as size distribution and shape fabrics of the grains. Such textures can control the deformational properties of these sediments and hence the strain distribution in active continental margins and also the frictional behavior along and around the plate boundary. Strain-hardening and discontinuous deformation may lead to earthquake nucleation at or below the updip limit of the seismogenic zone. We want to investigate the active continental margin offshore Costa Rica where the oceanic Cocos plate is subducted below the Caribbean plate at a rate of approximately 9 cm per year. The Costa Rica trench is well-known for shallow seismogenesis and tsunami generation. As it is an erosive continental margin, both the incoming sediments from the Nazca plate as well as the slope sediments of the continental margin can be important for earthquake nucleation and faulting causing sea-floor breakage. To investigate texture and composition of the sediments and hence their deformational properties we collected samples from varying depth of 7 different drilling locations across the trench retrieved during IODP expeditions 334 and 344 as part of the Costa Rica Seismogenesis Project (CRISP). Texture analysis was carried out by means of synchrotron diffraction, as only this method is suitable for water-bearing samples. As knowledge on the sediment composition is required as input parameter for the texture data analysis, additional X-ray powder diffraction analysis on the sample material has been carried out. Samples for texture measurements were prepared from the original drill cores using an internally developed cutter which allows to produce cylindrical samples with a diameter of about 1.5 cm. The samples are oriented with respect to the drill core axis. Synchrotron texture measurements were conducted at the

Late-stage development of the Bryant Canyon turbidite pathway on the Louisiana continental slope

USGS Publications Warehouse

Twichell, David C.; Nelson, Hans; Damuth, John E.

2000-01-01

GLORIA sidescan imagery, multibeam bathymetry, seismic profiles, and piston cores (3–5 m penetration) reveal the near-surface geology of the Bryant Canyon turbidite pathway on the continental margin of Louisiana. This pathway extends from the continental shelf edge, across the continental slope, to a deep-sea fan on the continental rise. The pathway is narrow (<2 km) where it crosses shallow salt deposits. Turbidites have been sampled from these narrow segments, and radiocarbon dates indicate that some of them accumulated as recently as 10,150 yr B.P. The pathway broadens however, where it crosses mini-basins whose floors are covered largely by muddy mass-transport deposits and coarse silt turbidites. Mass-transport deposits in the upper 4.7 m of cores from the floors of mini-basins accumulated 18,140-3,400 yr. BP. Seismic profiles show that the mass-transport deposits in some of the mini-basins are as much as 225 milliseconds thick and that turbidites in the basin floor are buried by these deposits. Salt movement has had a major impact on this pathway, and its thalweg no longer has a continuous down-slope gradient. Some mini-basin floors along the pathway are now more than 500 m deeper than their basin’s spill point. We propose a 6-stage conceptual model to explain our observations for the evolution of a mini-basin along this turbidite pathway. In this model, an active channel feeds sand to a mini-basin (Stabe B). Once the mini-basin is filled, the sand deposit is entrenched by a bypass channel (Stage C). When the turbidite system shuts off, salt migration oversteepens the mini-basin walls (Stage D) which collapse and create a layer of mass-transport deposits on the mini-basin floor (Stage E). The depositional succession is capped by a layer of highstand hemipelagic drape (Stage F). The Bryant Canyon turbidite pathway provides a recent example of a large turbidite pathway in the Gulf of Mexico that crosses an area of active salt tectonics thus providing a

Offshore Tectonics of the St. Elias Mountains: Insights from Ocean Drilling and Seismic Stratigraphy on the Yakutat Shelf

NASA Astrophysics Data System (ADS)

Worthington, L. L.; Gulick, S. P. S.; Montelli, A.; Jaeger, J. M.; Zellers, S.; Walczak, M. H.; Mix, A. C.

2015-12-01

Ongoing collision of the Yakutat (YAK) microplate with North America (NA) in southern Alaska has driven orogenesis of the St. Elias Mountains and the advance of the offshore deformation front to the southeast. The offshore St. Elias fold-thrust belt records the complex interaction between collisional tectonics and glacial climate variability, providing insight for models of orogenesis and the evolution of glacial depocenters. Glacial erosion and deposition have provided sediment that constructed the upper continental shelf, much of which has been reincorporated into the orogenic wedge through offshore faulting and folding. We integrate core and downhole logging data from IODP Expedition 341 (Sites U1420 and U1421) drilled on the Yakutat shelf and slope with high-resolution and regional seismic profiles to investigate the coupled structural and stratigraphic evolution of the St. Elias margin. Site U1420 lies on the Yakutat shelf within the Bering Trough, a shelf-crossing trough that is within primary depocenter for Bering Glacier sediments. Two faults underlie the glacial packages and have been rendered inactive as the depositional environment has evolved, while faulting elsewhere on the shelf has initiated. Site U1421 lies on the current continental slope, within the backlimb of an active thrust that forms part of the modern YAK-NA deformation front. At each of these sites, we recovered glacigenic diamict (at depths up to ~1015 m at Site U1420), much of which is younger than 0.3 Ma. Age models within the trough indicated that initiation of active deformation away from the Bering Trough depocenter likely occurred since 0.3 Ma, suggesting that possible tectonic reorganization due to mass redistribution by glacial processes can occur at time scales on the order of 100kyr-1Myr.

A Holocene record of ocean productivity and upwelling from the northern California continental slope

NASA Astrophysics Data System (ADS)

Addison, J. A.; Barron, J. A.; Finney, B.; Kusler, J. E.; Bukry, D.; Heusser, L. E.; Alexander, C. R., Jr.

2016-12-01

The Holocene upwelling history of the northern California continental slope is examined using a 7-m-long marine sediment core (TN062-O550; 40.9°N, 124.6°W, 550 m water depth) collected offshore from Eureka, CA, that spans the last 7,400 calibrated years before present (cal yrs BP). A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with global Holocene millennial-scale warm intervals. Results show biogenic sediment accumulation in TN062-O550 varied considerably during the Holocene, despite being located within 50 km of the mouth of the Eel River, one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at 2900 cal yr BP indicates the onset of modern upwelling in the CCS, and that this period also corresponds to the most intense period of upwelling in the last 7,400 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification as recorded in TN062-O550 corresponds closely to that seen at nearby ODP Site 1019 as well as in the Santa Barbara Basin of southern California. Other CCS records with less high-quality age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone-derived sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we tentatively suggest that regional CCS warming may be conducive to upwelling intensification in the future.

Change in morphology and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York between 2011 and 2014: Analysis of hurricane impact

USGS Publications Warehouse

Schwab, William C.; Baldwin, Wayne E.; Warner, John C.; List, Jeffrey; Denny, Jane F.; Liste Munoz, Maria; Safak, Ilgar

2017-01-01

Seafloor mapping investigations conducted on the lower shoreface and inner continental shelf offshore of Fire Island, New York in 2011 and 2014, the period encompassing the impacts of Hurricanes Irene and Sandy, provide an unprecedented perspective regarding regional inner continental shelf sediment dynamics during large storm events. Analyses of these studies demonstrate that storm-induced erosion and sediment transport occurred throughout the study area in water depths up to 30 m. Acoustic backscatter patterns were observed to move from ~1 m to 450 m with a mean of 20 m and movement tended to decrease with increasing water depth. These patterns indicate that both of the primary inner continental shelf sedimentary features in the study area, linear sorted bedforms offshore of eastern Fire Island and shoreface-attached sand ridges offshore of central and western Fire island, migrated alongshore to the southwest. The migration of the sorted bedforms represents the modification of an active ravinement surface and is thought to have liberated a significant volume of sediment. Comparison of isopach maps of sediment thickness show that the volume of modern sediment composing the lower shoreface and shoreface-attached sand ridges decreased by ~2.8 × 106 m3 across the ~73 km2 of common seafloor mapped in both surveys. However, a similar analysis for the relatively calmer 15-yr period prior to 2011 revealed significant accretion. This allows speculation that the shoreface-attached sand ridges are maintained over decadal timescales via sediment supplied through erosion of Pleistocene outwash and lower Holocene transgressive channel-fill deposits exposed on the inner continental shelf, but that the sand ridges also periodically erode and move to the southwest during large storm events. Analyses show that significant storminduced erosion and sediment transport occurs far seaward of the 5 to 9 m depth of closure assumed for Fire Island, where it is thought that an onshore

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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,more » just north of the eastern-most tip of Cape Hatteras.« less

77 FR 71621 - Atlantic Wind One (ATLW1) Commercial Leasing for Wind Power on the Outer Continental Shelf...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-03

... Wind One (ATLW1) Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Virginia... Notice for Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Virginia. SUMMARY... (FONSI) for commercial wind lease issuance and site assessment activities on the Atlantic OCS offshore...

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.

Seabed fluid expulsion along the upper slope and outer shelf of the U.S. Atlantic continental margin

USGS Publications Warehouse

Brothers, D.S.; Ruppel, C.; Kluesner, J.W.; ten Brink, Uri S.; Chaytor, J.D.; Hill, J.C.; Andrews, B.D.; Flores, C.

2014-01-01

Identifying the spatial distribution of seabed fluid expulsion features is crucial for understanding the substrate plumbing system of any continental margin. A 1100 km stretch of the U.S. Atlantic margin contains more than 5000 pockmarks at water depths of 120 m (shelf edge) to 700 m (upper slope), mostly updip of the contemporary gas hydrate stability zone (GHSZ). Advanced attribute analyses of high-resolution multichannel seismic reflection data reveal gas-charged sediment and probable fluid chimneys beneath pockmark fields. A series of enhanced reflectors, inferred to represent hydrate-bearing sediments, occur within the GHSZ. Differential sediment loading at the shelf edge and warming-induced gas hydrate dissociation along the upper slope are the proposed mechanisms that led to transient changes in substrate pore fluid overpressure, vertical fluid/gas migration, and pockmark formation.

Surficial sediment character of the New York-New Jersey offshore continental shelf region: a GIS compilation

USGS Publications Warehouse

Williams, S. Jeffress; Arsenault, Matthew A.; Poppe, Lawrence J.; Reid, Jane A.; Reid, Jamey M.; Jenkins, Chris J.

2007-01-01

series of new geologic maps and reports of the sea floor that will provide scientific insights into the character and geologic development of U.S. continental margins and to use these maps and information to assess the potential availability of offshore sand and gravel resources. The mapping and aggregate resource assessments are being conducted on a national scale using the usSEABED data base as described in Williams and others (2003). Potential uses for these data include: (1) defining the geological variability of the sea floor in relation to benthic habitat diversity; (2) improving our understanding of the processes that control the distribution and transport of bottom sediments and benthic habitats; (3) locating aggregate resources for beach nourishment and industrial applications; and (4) providing a detailed geospatial framework for future marine science research, monitoring, and management activities. The initial assessments are in progress for the New York Bight and Louisiana offshore areas.

Phytoplankton community structure in relation to hydrographic features along a coast-to-offshore transect on the SW Atlantic Continental Shelf

NASA Astrophysics Data System (ADS)

Islabão, C. A.; Mendes, C. R. B.; Detoni, A. M. S.; Odebrecht, C.

2017-12-01

The continental shelf in Southern Brazil is characterized by high biological productivity associated with horizontal and vertical density gradients due to the mixing of distinct water masses. Phytoplankton biomass and composition were evaluated in summer 2013 along an on-offshore transect off the mouth of the Patos Lagoon (Lat. 32°12S). Photosynthetic active radiation, temperature, salinity and fluorescence vertical profiles were carried out and Brünt-Väisäla frequency was estimated. Three water bodies were identified: the Subtropical Shelf Water along the entire transect, the Plata Plume Water on the middle shelf surface and the Tropical Water farther offshore. The water was sampled (N = 40) for the analyses of dissolved inorganic nutrients, phytoplankton cell density and composition. Phytoplankton present in the water was identified and quantified by the classical microscope sedimentation technique, complemented with CHEMTAX analysis of high-performance liquid chromatography (HPLC) pigment data. From the results obtained, chlorophyll a concentration was higher at both coastal stations (1.6-2.0 mg m-3) where the water column was homogeneous and diatoms dominated the stations. This group was replaced by dinoflagellates in stratified conditions on the shelf and farther offshore. Along the onshore-offshore gradient, two types of dinoflagellates were found: the peridinin-containing dinoflagellates Prorocentrum and Scrippsiella with a small contribution at the coastal stations, and the fucoxantin-containing small Gymnodiniales cells (< 15 μm) with more than 50% of the total chlorophyll a at the stations on the continental shelf, especially associated with the chlorophyll maximum at the base of the euphotic zone. The positive (negative) relationship between the biomass of dinoflagellates (diatoms) with the Brünt-Väisäla frequency, respectively, support the hypothesis that stratification is the most important environmental factor that determines the biomass of

High-resolution seismic-reflection profiles collected by the R/V Columbus Iselin, cruise CI 7807-1, in the Baltimore Canyon outer continental shelf area, offshore New Jersey

USGS Publications Warehouse

Robb, James M.

1980-01-01

High-resolution seismic-reflection profiles were collected by the U.S. Geological Survey (USGS) aboard R/V COLUMBUS ISELIN, cruise 7807-1, from 18 August to 4 September 1978 over the Continental Slope of the Eastern United States between Wilmington and Hudson Canyons. These data were acquired as part of a study to determine potential geologic hazards to petroleum development of the Baltimore Canyon trough area. On this cruise, the Continental Slope between Lindenkohl and Carteret Canyons was surveyed along lines spaced one-half nautical mile apart to study the size and distribution of mass-wasting features as a guide to assess the importance of mass wasting processes on the Continental Slope. The seismic-reflection profiles were placed to complement other data gathered previously by the USGS.Track-line distances totaled 2,050 km of 40-in3 air-gun (with wave shaper) profiles, 2,100 km of 800-J sparker data, and 2,100 km of 3 .5-kHz data. The air-gun and sparker profiles are of high quality, but the 3.5-kHz system did not function well and achieved no subbottom penetration. The side-scan sonar system was operated along the uppermost Continental Slope to investigate its potential for use in this environment. Data were acquired over 22 km of ship's track.Navigation was by Loran-C (5-minute fix interval).The original records can be examined at the U.S. Geological Survey offices in Woods Hole, Massachusetts 02543. Microfilm copies of the data are available for purchase from the National Geophysical and Solar-Terrestrial Data Center (NGSDC), Boulder, Colorado 80303.

A new method to identify the foot of continental slope based on an integrated profile analysis

NASA Astrophysics Data System (ADS)

Wu, Ziyin; Li, Jiabiao; Li, Shoujun; Shang, Jihong; Jin, Xiaobin

2017-06-01

A new method is proposed to identify automatically the foot of the continental slope (FOS) based on the integrated analysis of topographic profiles. Based on the extremum points of the second derivative and the Douglas-Peucker algorithm, it simplifies the topographic profiles, then calculates the second derivative of the original profiles and the D-P profiles. Seven steps are proposed to simplify the original profiles. Meanwhile, multiple identification methods are proposed to determine the FOS points, including gradient, water depth and second derivative values of data points, as well as the concave and convex, continuity and segmentation of the topographic profiles. This method can comprehensively and intelligently analyze the topographic profiles and their derived slopes, second derivatives and D-P profiles, based on which, it is capable to analyze the essential properties of every single data point in the profile. Furthermore, it is proposed to remove the concave points of the curve and in addition, to implement six FOS judgment criteria.

Searching for Last Glacial Deep-Sea Polar Carbonates in the Ross Sea Continental slope and Their Relevance to Chronological Constraints

NASA Astrophysics Data System (ADS)

Brambati, A.; Bonaccorsi, R.; Quaia, T.; Busetti, M.

2003-12-01

Ice-proximal glacial marine sediments from the Antarctic continental margin retain ice rafting events as proxy record for change in the volume and extension of the Antarctic ice sheet throughout glacial-interglacial cycles. However, the sedimentary sequences from the Ross Sea continental margin remain relatively poorly understood and most research has been focused mainly on continental shelf sequences during the last past decades. We present a data set (i.e., X-ray lithology, Multi Sensor Core Logger physical data, and preservation of biogenic carbonates), obtained from six deep-sea cores (1991-1999 Italian Antarctic Research Programme, PNRA - Summer cruises). Specifically, the cores were collected from a) the central Eastern sector (i.e., Core ANTA95-89C, depth: 2056 m, length: 401 cm and Core ANTA99-c22, depth: 2650 m, length: 851 cm); b) the central Western sector (i.e., Core ANTA99-c23; water depth: 2158 m, length: 548 cm; and ANTA99-c24, water depth: 2750 m, length: 811 cm); and c) the North Western sector (i.e., Core ANTA91-08C, and ANTA91-02C) of the Ross Sea Continental slope. Well-preserved calcareous foraminifers (N. pachyderma, sx) in coarse-grained IRD materials sparsely occur and/or are concentrated in discrete layers (i.e., up to 22 cm-thick) of at least three cores (i.e., Cores ANTA91-08, ANTA91-02, and ANTA95-89C, e.g., at 217-238 cm-depth). Some carbonate layers were deposited during a period of time bracketing Stage3/Stage2. In Core 89C foraminifers are associated to multiple ice rafting episodes and likely occurred with oceanographic changes in the properties of slope water masses. The search of well-preserved, in situ-deposited, polar carbonates is demanded for a reliable C-14 AMS dating of late Pleistocene events in the Ross Sea.

Cascadia Onshore-Offshore Site Response, Submarine Sediment Mobilization, and Earthquake Recurrence

NASA Astrophysics Data System (ADS)

Gomberg, J.

2018-02-01

Local geologic structure and topography may modify arriving seismic waves. This inherent variation in shaking, or "site response," may affect the distribution of slope failures and redistribution of submarine sediments. I used seafloor seismic data from the 2011 to 2015 Cascadia Initiative and permanent onshore seismic networks to derive estimates of site response, denoted Sn, in low- and high-frequency (0.02-1 and 1-10 Hz) passbands. For three shaking metrics (peak velocity and acceleration and energy density) Sn varies similarly throughout Cascadia and changes primarily in the direction of convergence, roughly east-west. In the two passbands, Sn patterns offshore are nearly opposite and range over an order of magnitude or more across Cascadia. Sn patterns broadly may be attributed to sediment resonance and attenuation. This and an abrupt step in the east-west trend of Sn suggest that changes in topography and structure at the edge of the continental margin significantly impact shaking. These patterns also correlate with gravity lows diagnostic of marginal basins and methane plumes channeled within shelf-bounding faults. Offshore Sn exceeds that onshore in both passbands, and the steepest slopes and shelf coincide with the relatively greatest and smallest Sn estimates at low and high frequencies, respectively; these results should be considered in submarine shaking-triggered slope stability failure studies. Significant north-south Sn variations are not apparent, but sparse sampling does not permit rejection of the hypothesis that the southerly decrease in intervals between shaking-triggered turbidites and great earthquakes inferred by Goldfinger et al. (2012, 2013, 2016) and Priest et al. (2017) is due to inherently stronger shaking southward.

California State Waters Map Series: offshore of Salt Point, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Golden, Nadine E.; Hartwell, Stephen R.; Erdey, Mercedes D.; Greene, H. Gary; Cochrane, Guy R.; Kvitek, Rikk G.; Manson, Michael W.; Endris, Charles A.; Dieter, Bryan E.; Watt, Janet T.; Krigsman, Lisa M.; Sliter, Ray W.; Lowe, Erik N.; Chinn, John L.; Johnson, Samuel Y.; Cochran, Susan A.

2015-01-01

Potential marine benthic habitats in the Offshore of Salt Point map area include unconsolidated continental shelf sediments, mixed continental shelf substrate, and hard continental shelf substrate. Rocky-shelf outcrops and rubble are considered to be promising potential habitats for rockfish and lingcod, both of which are recreationally and commercially important species.

California State Waters Map Series—Offshore of Fort Ross, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Golden, Nadine E.; Hartwell, Stephen R.; Erdey, Mercedes D.; Greene, H. Gary; Cochrane, Guy R.; Kvitek, Rikk G.; Manson, Michael W.; Endris, Charles A.; Dieter, Bryan E.; Watt, Janet T.; Krigsman, Lisa M.; Sliter, Ray W.; Lowe, Erik N.; Chin, John L.; Johnson, Samuel Y.; Cochran, Susan A.

2015-12-03

Potential marine benthic habitat types in the Offshore of Fort Ross map area include unconsolidated continental-shelf sediments, mixed continental-shelf substrate, and hard continental-shelf substrate. Rocky shelf outcrops and rubble are considered the primary habitat type for rockfish and lingcod, both of which are recreationally and commercially important species.

California State Waters Map Series—Offshore of Bodega Head, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Golden, Nadine E.; Hartwell, Stephen R.; Erdey, Mercedes D.; Greene, H. Gary; Cochrane, Guy R.; Kvitek, Rikk G.; Manson, Michael W.; Endris, Charles A.; Dieter, Bryan E.; Watt, Janet T.; Krigsman, Lisa M.; Sliter, Ray W.; Lowe, Erik N.; Chin, John L.; Johnson, Samuel Y.; Cochran, Susan A.

2015-08-06

Potential marine benthic habitats in the Offshore of Bodega Head map area include unconsolidated continental-shelf sediments, mixed continental-shelf substrate, and hard continental-shelf substrate. Rocky-shelf outcrops and rubble are considered to be promising potential habitats for rockfish and lingcod, both of which are recreationally and commercially important species.

77 FR 71612 - Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-03

... Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore...), Interior. ACTION: Proposed Sale Notice for commercial leasing for wind power on the Outer Continental Shelf... sale of commercial wind energy leases on the Outer Continental Shelf (OCS) offshore Rhode Island and...

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

An aeromagnetic survey has shown the existence of several basins in which magnetic basement depths are greater than 5 km on the continental shelf off Liberia. Magnetic diabase of 176 to 192 m.y. (Jurassic) in age intruding the Paleozoic (?) rocks and overlain by younger rocks onshore requires the distinction between “magnetic basement” and “basement.” Several lines of evidence suggest that the Paleozoic(?) rocks are less than 1 km thick; this implies that the diabase does not introduce a large error in depth-to-basement estimates. The dikes or their extrusive equivalents are traceable, on the basis of the magnetic data, beneath the younger sedimentary rock in the basins to the edge of the continental slope. The magnetic data also delineate a second zone of diabase dikes 90 km inland, parallel to the coast, which cross the entire country. The intrusion of the younger dikes probably coincides with rifting at the beginning of the separation of Africa and South America, and the associated magnetic anomaly zones appear to be parallel with and continuous into the anomaly bands in the Atlantic. A major northeast-trending break in the magnetic fabric intersects the coast near 9° W. and is associated with Eburnean age rocks (about 2000 m.y.) to the southeast as contrasted with Liberian-age rocks (about 2700 m.y.) to the northwest. Change in magnetic fabric direction inland from northeast to northwest in the coastal area allows recognition of a boundary between the Liberian-age rocks inland and Pan-African-age (about 550 m.y.) rocks in the coastal area northwest of about 9° 20'W. Sets of north-northwest-and west-northwest—trending faults of 1 to 2 km vertical displacement cut the Cretaceous sedimentary rocks onshore and can be traced into the offshore basins. Vertical displacements of several kilometers in the magnetic basement underlying the continental shelf suggest a pattern of block faulting all along the coast and continental shelf. Negative Bouguer

U.S. Geological Survey program of offshore resource and geoenvironmental studies, Atlantic-Gulf of Mexico region, from September 1, 1976, to December 31, 1978

USGS Publications Warehouse

Folger, David W.; Needell, Sally W.

1983-01-01

acromagnetic data, and 39,000 km of gravity data, plus 10,000 samples and logs obtained from U.S. Geological Survey and industry drilling (for example, coreholes of the Atlantic Slope Program, Joint Oceanographic Institutions Deep Earth Sampling, Continental Offshore Stratigraphic Tests, and the Atlantic Margin Coring Program). A sedimentary section of Jurassic and Cretaceous age grades from terrigenous clastic rocks nearshore to carbonate rocks offshore; this section is part of an extensive buried bank-platform complex that could contain large reserves of natural gas and oil. The volume of sediment deposited offshore far exceeds the volume deposited onshore where extensive accumulations of oil, gas, and minerals have been found. Commercial exploratory drilling offshore thus far has been limited to the Baltimore Canyon Trough area off New Jersey, where at least two holes have found gas; leasing has taken place in the Southeast Georgia Embayment, where drilling was scheduled to begin in 1979, and is imminent in the Georges Bank area off New England. In addition, hydrogeologic and hydrochemical data obtained from the drilling studies have delineated freshwater-bearing submarine extensions of land aquifers that are important coastal ground-water resources. Hazards in the Georges Bank area include sand mobility associated with strong currents and storm-driven waves; high concentrations of suspended sediment in the water column that, when mixed with spilled oil, may sink to the bottom; and slumping along the upper slope. In the Baltimore Canyon, high sediment mobility accompanies major winter storms, and slumped material may cover as much as 20 percent of the upper slope. Potentially unstable slope areas are being studied in great detail to provide data on timing, triggering mechanisms, and rates of sediment movement. In the Southeast Georgia Embayment and Blake Plateau Basin, strong Gulf Stream flow poses a major problem to all offshore operations. In the Gulf o

Maps showing bathymetry and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York, pre-Hurricane Sandy

USGS Publications Warehouse

Schwab, William C.; Denny, Jane F.; Baldwin, Wayne E.

2014-01-01

The U.S. Geological Survey mapped approximately 336 square kilometers of the lower shoreface and inner continental shelf offshore of Fire Island, New York, in 2011 by using interferometric sonar and high-resolution chirp seismic-reflection systems. This report presents maps of bathymetry, acoustic backscatter, the coastal plain unconformity, the Holocene marine transgressive surface, and modern sediment thickness. These spatial data support research on the Quaternary evolution of the Fire Island coastal system and provide baseline information for research on coastal processes along southern Long Island.

Clay mineralogical record on the upper continental slope of the northwestern South China Sea since the Last Glacial Maximum

NASA Astrophysics Data System (ADS)

CHEN, Q.; Liu, Z.; Stattegger, K.

2012-12-01

Clay mineralogy of two gravity cores (18428 and 18429) on the upper continental slope of the northwestern South China Sea was investigated in order to understand terrigenous sediment sources and to evaluate the contribution from the Red River since the Late Glacial Maximum. Planktonic foraminiferal oxygen isotope and carbonate stratigraphies suggest that Core 18428 is constrained in Holocene while Core 18429 covers the period of MIS 1-2. Clay mineral assemblages of two cores are composed mainly of smectite (18-57%) and illite (21-41%), with minor chlorite (12-21%) and kaolinite (8-26%). In despite of relatively constant values of illite crystallinity, ranging among 0.14°-0.20° Δ2θ, the time series variation in clay mineral distributions indicates a strong glacial-interglacial shift. Contents of illite, chlorite, and kaolinite (Core 18429) in the Holocene are lower than in the glacial period, and vice versa for the smectite content. The provenance analysis based on clay mineralogy suggests the Red River as a predominant sedimentary source of illite, chlorite, and kaolinite during all the depositional period of MIS 1-2. The sea level change actually controlled the variations of clay mineral assemblages on the upper slope since the Last Glacial Maximum. When the sea level was low during the last glacial period, more terrigenous sediments from the Red River could reach the continental slope in the northwestern South China Sea. However, when the sea level is closed to the present situation during the Holocene, most of Red River sediments could be trapped in the Gulf of Tonkin, instead of draining in the deep South China Sea.

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.

Slump dominated upper slope reservoir facies, Intra Qua Iboe (Pliocene), Edop Field, offshore Nigeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shanmugam, G.; Hermance, W.E.; Olaifa, J.O.

An integration of sedimentologic and 3D seismic data provides a basis for unraveling complex depositional processes and sand distribution of the Intra Qua Iboe (IQI) reservoir (Pliocene), Edop Field, offshore Nigeria. Nearly 3,000 feet of conventional core was examined in interpreting slump/slide/debris flow, bottom current, turbidity current, pelagic/hemipelagic, wave and tide dominated facies. The IQI was deposited on an upper slope in close proximity to the shelf edge. Through time, as the shelf edge migrated seaward, deposition began with a turbidite channel dominated slope system (IQI 1 and 2) and progressed through a slump/debris flow dominated slope system (IQI 3,more » the principal reservoir) to a tide and wave dominated, collapsed shelf-edge deltaic system (IQI 4). Using seismic time slices and corresponding depositional facies in the core, a sandy {open_quotes}fairway{open_quotes} has been delineated in the IQI 3. Because of differences in stacking patterns of sandy and muddy slump intervals, seismic facies show: (1) both sheet-like and mounded external forms (geometries), and (2) parallel/continuous as well as chaotic/hummocky internal reflections. In wireline logs, slump facies exhibits blocky, coarsening-up, fining-up, and serrated motifs. In the absence of conventional core, slump facies may be misinterpreted and even miscorrelated because seismic facies and log motifs of slumps and debris flows tend to mimic properties of turbidite fan deposits. The slump dominated reservoir facies is composed of unconsolidated fine-grained sand. Thickness of individual units varies from 1 to 34 feet, but amalgamated intervals reach a thickness of up to 70 feet and apparently form connected sand bodies. Porosity commonly ranges from 20 to 35%. Horizontal permeability commonly ranges from 1,000 to 3,000 md.« less

Sediment property changes in response to the glacial activity on the continental slope to the eastern side of Pennell-Iselin Bank in the Ross Sea, Antarctica

NASA Astrophysics Data System (ADS)

Ha, Sangbeom; Khim, Boo-Keun; Colizza, Ester; Marci, Patrizia; Sagnotti, Leonardo; Caricchi, Chiara; Langone, Leonardo; Giglio, Federico; Kuhn, Gerhard

2017-04-01

High latitude marine environments including the Antarctic continental margin have sensitively responded to the climate change, and the Ross Sea is one of these examples. Subglacial marine sedimentary changes have been studied extensively in the continental shelf areas of the Ross Sea to understand the growth and retreat of glaciers in response to the glacial-interglacial changes. However, the continental slope areas of the Ross Sea have not been investigated comparatively less. Thus, in order to comprehend the glaciomarine sedimentation change on the continental slope of the Ross Sea, 3 gravity cores (GC1, GC2, GC3) and 3 box cores (BC1, BC2, BC3) were collected from 3 sites (RS14-C1, C2, C3 by decreasing water depth), respectively, across the continental slope to the eastern side of the Pennell-Iselin Bank during XXIX PNRA (Rosslope II) cruise in 2014. A variety of sedimentological (grain size, magnetic susceptibility, XRF) and geochemical (biogenic opal, total organic carbon, CaCO3, δ13C of organic matter) properties were analyzed along with AMS 14C dating of bulk sediments. All core sediments consist of mostly hemipelagic sandy clay or silty clay with scattered IRD (Ice-Rafted Debris). Sediment color of three cores changes consistently downward from brown to gray with some alternations in core GC1. Based on the basic sediment properties such as sediment color, grain size, and magnetic susceptibility, sediment lithology was decided to divide Unit A and Unit B, both of which were further divided into two subunits. Despite old carbon effect, AMS 14C dates confirm that Unit A belongs to the Holocene and Unit B covers the deglacial to last glacial period at the top of cores. Unit A is characterized by low TOC, low CaCO3, low biogenic opal content and low C/N ratios, whereas Unit B is characterized by high TOC, high CaCO3, moderate to high biogenic opal content and high C/N ratios. Consequently, Unit A represents the modern and interglacial sediments deposited mainly

Modification of the Quaternary stratigraphic framework of the inner-continental shelf by Holocene marine transgression: An example offshore of Fire Island, New York

USGS Publications Warehouse

Schwab, William C.; Baldwin, Wayne E.; Denny, Jane F.; Hapke, Cheryl J.; Gayes, Paul T.; List, Jeffrey; Warner, John C.

2014-01-01

The inner-continental shelf off Fire Island, New York was mapped in 2011 using interferometric sonar and high-resolution chirp seismic-reflection systems. The area mapped is approximately 50 km long by 8 km wide, extending from Moriches Inlet to Fire Island Inlet in water depths ranging from 8 to 32 m. The morphology of this inner-continental shelf region and modern sediment distribution patterns are determined by erosion of Pleistocene glaciofluvial sediments during the ongoing Holocene marine transgression; much of the shelf is thus an actively forming ravinement surface. Remnants of a Pleistocene outwash lobe define a submerged headland offshore of central Fire Island. East of the submerged headland, relatively older Pleistocene outwash is exposed over much of the inner-continental shelf and covered by asymmetric, sorted bedforms interpreted to indicate erosion and westward transport of reworked sediment. Erosion of the eastern flank of the submerged Pleistocene headland over the last ~ 8000 years yielded an abundance of modern sand that was transported westward and reworked into a field of shoreface-attached ridges offshore of western Fire Island. West of the submerged headland, erosion of Pleistocene outwash continues in troughs between the sand ridges, resulting in modification of the lower shoreface. Comparison of the modern sand ridge morphology with the morphology of the underlying ravinement surface suggests that the sand ridges have moved a minimum of ~ 1000 m westward since formation. Comparison of modern sediment thickness mapped in 1996–1997 and 2011 allows speculation that the nearshore/shoreface sedimentary deposit has gained sediment at the expense of deflation of the sand ridges.

WIND Toolkit Offshore Summary Dataset

DOE Office of Scientific and Technical Information (OSTI.GOV)

Draxl, Caroline; Musial, Walt; Scott, George

This dataset contains summary statistics for offshore wind resources for the continental United States derived from the Wind Integration National Datatset (WIND) Toolkit. These data are available in two formats: GDB - Compressed geodatabases containing statistical summaries aligned with lease blocks (aliquots) stored in a GIS format. These data are partitioned into Pacific, Atlantic, and Gulf resource regions. HDF5 - Statistical summaries of all points in the offshore Pacific, Atlantic, and Gulf offshore regions. These data are located on the original WIND Toolkit grid and have not been reassigned or downsampled to lease blocks. These data were developed under contractmore » by NREL for the Bureau of Oceanic Energy Management (BOEM).« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 andmore » 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.« less

Morphologic and seismic evidence of rapid submergence offshore Cide-Sinop in the southern Black Sea shelf

NASA Astrophysics Data System (ADS)

Ocakoğlu, Neslihan; İşcan, Yeliz; Kılıç, Fatmagül; Özel, Oğuz

2018-06-01

Multi-beam bathymetric and multi-channel seismic reflection data obtained offshore Cide-Sinop have revealed important records on the latest transgression of the Black Sea for the first time. A relatively large shelf plain within the narrow southern continental shelf characterized by a flat seafloor morphology at -100 water depth followed by a steep continental slope leading to -500 m depth. This area is widely covered by submerged morphological features such as dunes, lagoons, possible aeolianites, an eroded anticline and small channels that developed by aeolian and fluvial processes. These morphological features sit upon an erosional surface that truncates the top of all seismic units and constitutes the seafloor over the whole shelf. The recent prograded delta deposits around the shelf break are also truncated by the similar erosional surface. These results indicate that offshore Cide-Sinop was once a terrestrial landscape that was then submerged. The interpreted paleoshoreline varies from -100 to -120 m. This variation can be explained by not only sea level changes but also the active faults observed on the seismic section. The effective protection of morphological features on the seafloor is the evidence of abrupt submergence rather than gradual. In addition, the absence of coastal onlaps suggests that these morphological features should have developed at low sea level before the latest sea level rise in the Black Sea.

Preliminary results from 2017 OGS Explora cruise to the Ross Sea continental slope

NASA Astrophysics Data System (ADS)

Rebesco, Michele; De Santis, Laura; Gales, Jenny; Kim, Sookwan; Liu, Yanguang; Sauli, Chiara; Cuffaro, Marco; Bergamasco, Andrea; Colleoni, Florence; Kovacevic, Vedrana; Olivo, Elisabetta; Florindo-Lopez, Cristian; Codiglia, Riccardo; Zgur, Fabrizio; Accettella, Daniela; Gordini, Emiliano; Visnovic, Paolo; Tomini, Isabella; Mansutti, Paolo; Sterzai, Paolo

2017-04-01

OGS Explora is back to Antarctica for three projects focused on the Ross Sea eastern continental slope: EU/FP7-EUROFLEETS (http://www.eurofleets.eu) ANTSSS, PNRA (Programma Nazionale Di Ricerche in Antartide) ODYSSEA, and PNRA WHISPERS. These projects employ three main methods: 1) geophysics (multichannel seismic reflection, sub-bottom and multibeam morphobathymetric survey); 2) geology (gravity corer and box-corer); oceanography (CTD, LADCP, turbulence). The general objective is to contribute to the understanding of past and present ocean dynamics and glacial history of this Antarctic sector. In particular, to find evidence (in the geometry and distribution of the stratigraphic sequences) of Miocene-Pleistocene West Antarctic Ice Sheet and East Antarctic Ice Sheet advances and retreats and of their effects on Ross Sea Bottom Water formation and dynamics. The gravity cores provide the chronological control for the Quaternary. Deep sea drilling (through IODP Exp. 374, whose additional alternative sites are surveyed during this cruise) will provide the chronological control for the pre-Quaternary seismic sequences.

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

Offshore oil in the Alaskan Arctic

NASA Technical Reports Server (NTRS)

Weeks, W. F.; Weller, G.

1984-01-01

Oil and gas deposits in the Alaskan Arctic are estimated to contain up to 40 percent of the remaining undiscovered crude oil and oil-equivalent natural gas within U.S. jurisdiction. Most (65 to 70 percent) of these estimated reserves are believed to occuur offshore beneath the shallow, ice-covered seas of the Alaskan continental shelf. Offshore recovery operations for such areas are far from routine, with the primary problems associated with the presence of ice. Some problems that must be resolved if efficient, cost-effective, environmentally safe, year-round offshore production is to be achieved include the accurate estimation of ice forces on offshore structures, the proper placement of pipelines beneath ice-produced gouges in the sea floor, and the cleanup of oil spills in pack ice areas.

A 2.7 Myr record of sedimentary processes on a high-latitude continental slope: 3D seismic evidence from the mid-Norwegian margin

NASA Astrophysics Data System (ADS)

Montelli, A.; Dowdeswell, J. A.; Ottesen, D.; Johansen, S. E.

2017-12-01

An extensive three-dimensional seismic dataset is used to investigate the sedimentary processes and morphological evolution of the mid-Norwegian continental slope through the Quaternary. These data reveal hundreds of buried landforms, including channels and debris flows of variable morphology, as well as gullies, iceberg ploughmarks, slide scars and sediment waves. Slide scars, turbidity currents and debris flows comprise slope systems controlled by local slope morphology, showing the spatial variability of high-latitude sedimentation. Channels dominate the Early Pleistocene ( 2.7-0.8 Ma) morphological record of the mid-Norwegian slope. During Early Plesitocene, glacimarine sedimentation on the slope was influenced by dense bottom-water flow and turbidity currents. Glacigenic debris-flows appear within the Middle-Late Pleistocene ( 0.8-0 Ma) succession. Their abundance increases on Late Pleistocene palaeo-surfaces, marking a paleo-environmental change characterised by decreasing role for channelized turbidity currents and dense water flows. This transition coincides with the gradual shift to full-glacial ice-sheet conditions marked by the appearance of the first erosive fast-flowing ice streams and an associated increase in sediment flux to the shelf edge, emphasizing first-order climate control on the temporal variability of high-latitude sedimentary slope records.

Sea-floor drainage features of Cascadia Basin and the adjacent continental slope, northeast Pacific Ocean

USGS Publications Warehouse

Hampton, M.A.; Karl, Herman A.; Kenyon, Neil H.

1989-01-01

Sea-floor drainage features of Cascadia Basin and the adjacent continental slope include canyons, primary fan valleys, deep-sea valleys, and remnant valley segments. Long-range sidescan sonographs and associated seismic-reflection profiles indicate that the canyons may originate along a mid-slope escarpment and grow upslope by mass wasting and downslope by valley erosion or aggradation. Most canyons are partly filled with sediment, and Quillayute Canyon is almost completely filled. Under normal growth conditions, the larger canyons connect with primary fan valleys or deep-sea valleys in Cascadia Basin, but development of accretionary ridges blocks or re-routes most canyons, forcing abandonment of the associated valleys in the basin. Astoria Fan has a primary fan valley that connects with Astoria Canyon at the fan apex. The fan valley is bordered by parallel levees on the upper fan but becomes obscure on the lower fan, where a few valley segments appear on the sonographs. Apparently, Nitinat Fan does not presently have a primary fan valley; none of the numerous valleys on the fan connect with a canyon. The Willapa-Cascadia-Vancouver-Juan de Fuca deep-sea valley system bypasses the submarine fans and includes deeply incised valleys to broad shallow swales, as well as within-valley terraces and hanging-valley confluences. ?? 1989.

Tree community variation in a tropical continental island according to slope aspect and human interference.

PubMed

Gonçalves, Nathan B; Nettesheim, Felipe C; Conde, Marilena M S

2018-01-01

Associating description of unrecorded tropical tree community structure to sampling approaches that can help determine mechanisms behind floristic variation is important to further the comprehension of how plant species coexist at tropical forests. Thus, this study had the goals of (i) evaluating tree community structure on the continental island of Marambaia (23°4'37.09"S; 43°59'2.15"W) and (ii) testing the prediction that there are local scale changes in a tropical tree community structure between slopes facing different geographic orientation and with distinct human interference history. We established 60 (0.6 ha) sampling units in three different slope sites with distinct predominant geographic orientation and human interference. We sampled all woody trees with diameter at breast height (dbh) ≥ 5 cm. We found a total of 1.170 individuals representing 220 species, 120 genera and 50 families. The overall tree community structure and structural descriptors (abundance of individuals, basal area, species richness and diversity) varied extensively between the sites. The evidence presented here supports that local scale topography variations and human interference history can be important factors contributing to the known floristic heterogeneity of the Atlantic Rainforest. Future work on the study area should focus on disentangling effects from distinct causal factors over tree community variation and species occurrence.

Development and sexual dimorphism of the sonic system in three deep-sea neobythitine fishes and comparisons between upper mid and lower continental slope

NASA Astrophysics Data System (ADS)

Fine, Michael L.; Ali, Heba A.; Nguyen, Thanh Kim; Mok, Hin-Kiu; Parmentier, Eric

2018-01-01

Based on morphology, NB Marshall identified cusk-eels (family Ophidiidae) as one of the chief sound-producing groups on the continental slope. Due to food scarcity, we hypothesized that sonic systems will be reduced at great depths despite their potential importance in sexual reproduction. We examined this hypothesis in the cusk-eel subfamily Neobythitinae by comparing sonic morphology in Atlantic species from the upper-mid (Dicrolene intronigra) and deeper continental slope (Porogadus miles and Bathyonus pectoralis) with three Taiwanese species previously described from the upper slope (Hoplobrotula armatus, Neobythites longipes and N. unimaculatus). In all six species, medial muscles are heavier in males than in females. Dicrolene has four pairs of sonic muscles similar to the shallow Pacific species, suggesting neobythitine sonic anatomy is conservative and sufficient food exists to maintain a well-developed system at depths exceeding 1 km. The sonic system in Porogadus and Bathyonus was reduced to a single pair of ventral medial muscles that connects to a smaller and thinner swimbladder via a long tendon. Small muscle fiber diameters, a likely indicator of rapid contraction, were present in males of five of the species. However, in Bathyonus, the deepest species (pale coloration, reduced eye size, shorter sonic muscles and longer tendons), muscle fibers were larger suggesting an adaptation to facilitate rapid bladder movement for sound production while using slower contractions and less metabolic energy. The six species separate into three groups in length-weight regressions: the three upper slope species have the greatest weights per unit length, Dicrolene is lower, and the two deep species are further reduced consistent with the hypothesis that food limitation affects sonic anatomy at great depths.

Immediate propagation of deglacial environmental change to turbidite systems along the Chilean continental slope

NASA Astrophysics Data System (ADS)

Bernhardt, Anne; Schwanghart, Wolfgang; Hebbeln, Dierk; Stuut, Jan-Berend; Strecker, Manfred

2017-04-01

Understanding how Earth-surface processes respond to past climatic perturbations is crucial for making informed predictions about future impacts of climate change on sediment fluxes. Sedimentary records provide the archives for inferring these processes but their interpretation is compromised by our incomplete understanding of how sediment-routing systems respond to millennial-scale climate cycles. We analyzed seven sediment cores recovered from turbidite depositional sites along the continental slope of the Chile convergent margin. These depositional systems represent the ultimate sedimentary archives before sediment gets recycled during subduction processes and provide relatively continuous and well-dated records. The study sites span a pronounced arid-to-humid gradient with variable topographic gradients and related connectivity of terrestrial and marine landscapes on the continental slope. This setting allowed us to study event-related depositional processes from the Last Glacial Maximum to present in different climatic and geomorphic settings. The turbidite record was quantified in terms of turbidite thickness and frequency. The three studied sites show a steep decline of turbidite deposition during deglaciation. High rates of sea-level rise significantly lag the decline in turbidite deposition by 3-6.5 kyrs. However, comparison to paleoclimate proxies shows that this spatio-temporal sedimentary pattern mirrors the deglacial humidity decrease and concomitant warming with little to no lag times. Our results suggest that the deglacial humidity decrease resulted in a decrease of fluvial sediment supply, which propagated rapidly through the highly connected systems into the marine sink in north-central Chile. In contrast, in south-central Chilean systems, connectivity between the Andean erosional zone and the fluvial transfer zone probably decreased abruptly by the deglaciation of piedmont lakes, resulting in a significant and rapid decrease of sediment supply to

High-resolution seismic-reflection profiles collected by the R/V James M. Gilliss, cruise GS 7903-4, in the Baltimore Canyon outer continental shelf area, offshore New Jersey

USGS Publications Warehouse

Robb, James M.

1980-01-01

High-resolution seismic-reflection profiles were collected by the U.S. Geological Survey (USGS) aboard R/V JAMES M. GILLIS (cruise GS 7903-4) from 27 June to 11 July 1979 over the Continental Slope of the Eastern United States between Lindenkohl and Hudson Canyons. These data were acquired as part of a study to determine potential geologic hazards to petroleum development of the Baltimore Canyon trough area. On this cruise, the Continental Slope between Carteret and South Toms Canyons was surveyed along lines spaced one-half nautical mile apart to study the size and distribution of mass-wasting features as a guide to assess the importance of mass-wasting processes on the Continental Slope. The seimsic-reflection profiles were placed to complement other data gathered previously by the USGS and to continue a survey grid begun in 1978 aboard the R/V COLUMBUS !SELIN, cruise CI 7807-1.Track-line distances totaled 1,555 km of 40-in3 air-gun (with wave shaper) profiles, 1, 750 km of 800-J sparker data, and 1,780 km of 3 .5-kHz data. All data are of high quality. A side-scan sonar system was operated briefly along the uppermost Continental Slope to acquire data over 70 km of ship's track. In addition, experimental profiling data were collected from a hydrophone towed at depth over the midslope on the end of the side-scan cable; the surface-towed sparker was used as a sound source. High-resolution profiles were collected by this method over 105 km of track.Navigation was by Loran-C (5-minute fix interval) and satellite.The original data may be inspected at the offices of the U.S. Geological Survey in Woods Hole, Massachusetts 02543. Microfilm copies of the data from this cruise are available for purchase from the National Geophysical and Solar-Terrestrial Data Center (NGSDC), Boulder, Colorado 80303.

Geology of the continental margin beneath Santa Monica Bay, Southern California, from seismic-reflection data

USGS Publications Warehouse

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

2003-01-01

We interpret seismic-reflection data, which were collected in Santa Monica Bay using a 70-in3 generator-injector air gun, to show the geologic structure of the continental shelf and slope and of the deep-water, Santa Monica and San Pedro Basins. The goal of this research is to investigate the earthquake hazard posed to urban areas by offshore faults. These data reveal that northwest of the Palos Verdes Peninsula, the Palos Verdes Fault neither offsets the seafloor nor cuts through an undeformed sediment apron that postdates the last sea level rise. Other evidence indicates that this fault extends northwest beneath the shelf in the deep subsurface. However, other major faults in the study area, such as the Dume and San Pedro Basin Faults, were active recently, as indicated by an arched seafloor and offset shallow sediment. Rocks under the lower continental slope are deformed to differing degrees on opposite sides of Santa Monica Canyon. Northwest of this canyon, the continental slope is underlain by a little-deformed sediment apron; the main structures that deform this apron are two lower-slope anticlines that extend toward Point Dume and are cored by faults showing reverse or thrust separation. Southeast of Santa Monica Canyon, lower-slope rocks are deformed by a complex arrangement of strike-slip, normal, and reverse faults. The San Pedro Escarpment rises abruptly along the southeast side of Santa Monica Canyon. Reverse faults and folds underpinning this escarpment steepen progressively southeastward. Locally they form flower structures and cut downward into basement rocks. These faults merge downward with the San Pedro Basin fault zone, which is nearly vertical and strike slip. The escarpment and its attendant structures diverge from this strike-slip fault zone and extend for 60 km along the margin, separating the continental shelf from the deep-water basins. The deep-water Santa Monica Basin has large extent but is filled with only a thin (less than 1.5-km

78 FR 27913 - Revision of Crane Regulation Standards for Mobile Offshore Drilling Units (MODUs), Offshore...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-05-13

...The Coast Guard proposes to revise regulations related to the design, certification, inspection, and testing of cranes. These regulations apply to cranes installed on Mobile Offshore Drilling Units (MODUs), Offshore Supply Vessels (OSVs), and floating Outer Continental Shelf (OCS) facilities. This revision would update industry standards incorporated by reference with more recent versions, which are used by industry and incorporated in Bureau of Safety and Environmental Enforcement regulations. Additionally, the Coast Guard proposes to revise regulations regarding certification, inspection, and testing of cranes by allowing use of additional organizations to act in lieu of Coast Guard marine inspectors.

78 FR 48180 - Consolidation of Officer in Charge, Marine Inspection For Outer Continental Shelf Activities...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-07

... for all Mobile Offshore Drilling Units and Floating Outer Continental Shelf Facilities (as defined in... Commander. Vessels requiring Coast Guard inspection include Mobile Offshore Drilling Units (MODUs), Floating... engage directly in oil and gas exploration or production in the offshore waters of the Eighth Coast Guard...

Vertical and horizontal resolution dependency in the model representation of tracer dispersion along the continental slope in the northern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Bracco, Annalisa; Choi, Jun; Kurian, Jaison; Chang, Ping

2018-02-01

A set of nine regional ocean model simulations at various horizontal (from 1 to 9 km) and vertical (from 25 to 150 layers) resolutions with different vertical mixing parameterizations is carried out to examine the transport and mixing of a passive tracer released near the ocean bottom over the continental slope in the northern Gulf of Mexico. The release location is in proximity to the Deepwater Horizon oil well that ruptured in April 2010. Horizontal and diapycnal diffusivities are calculated and their dependence on the model set-up and on the representation of mesoscale and submesoscale circulations is discussed. Horizontal and vertical resolutions play a comparable role in determining the modeled horizontal diffusivities. Vertical resolution is key to a proper representation of passive tracer propagation and - in the case of the Gulf of Mexico - contributes to both confining the tracer along the continental slope and limiting its vertical spreading. The choice of the tracer advection scheme is also important, with positive definiteness in the tracer concentration being achieved at the price of spurious mixing across density surfaces. In all cases, however, the diapycnal mixing coefficient derived from the model simulations overestimates the observed value, indicating an area where model improvement is needed.

The Continental Margins Program in Georgia

USGS Publications Warehouse

Cocker, M.D.; Shapiro, E.A.

1999-01-01

From 1984 to 1993, the Georgia Geologic Survey (GGS) participated in the Minerals Management Service-funded Continental Margins Program. Geological and geophysical data acquisition focused on offshore stratigraphic framework studies, phosphate-bearing Miocene-age strata, distribution of heavy minerals, near-surface alternative sources of groundwater, and development of a PC-based Coastal Geographic Information System (GIS). Seven GGS publications document results of those investigations. In addition to those publications, direct benefits of the GGS's participation include an impetus to the GGS's investigations of economic minerals on the Georgia coast, establishment of a GIS that includes computer hardware and software, and seeds for additional investigations through the information and training acquired as a result of the Continental Margins Program. These addtional investigations are quite varied in scope, and many were made possible because of GIS expertise gained as a result of the Continental Margins Program. Future investigations will also reap the benefits of the Continental Margins Program.From 1984 to 1993, the Georgia Geologic Survey (GGS) participated in the Minerals Management Service-funded Continental Margins Program. Geological and geophysical data acquisition focused on offshore stratigraphic framework studies, phosphate-bearing Miocene-age strata, distribution of heavy minerals, near-surface alternative sources of groundwater, and development of a PC-based Coastal Geographic Information System (GIS). Seven GGS publications document results of those investigations. In addition to those publications, direct benefits of the GGS's participation include an impetus to the GGS's investigations of economic minerals on the Georgia coast, establishment of a GIS that includes computer hardware and software, and seeds for additional investigations through the information and training acquired as a result of the Continental Margins Program. These additional

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

On the Antarctic Slope Front and Current crossing of the South Scotia Ridge

NASA Astrophysics Data System (ADS)

Orsi, A. H.; Palmer, M.; Gomis, D.; Flexas, M. M.; Kim, Y.-S.; Jordà, G.; Wiederwohl, C.; Álvarez, M.

2012-04-01

To unveil the contorted path followed by the Antarctic Slope Current connecting the Weddell and Scotia Seas, hydrographic stations with unprecedented spatial resolution were occupied on a series of sections across the slope and multiple channels in the double-pronged western portion of the South Scotia Ridge. Fieldwork consisted of two cruises from the ESASSI (January 2008) and ACROSS (February 2009) programs, the Spanish and USA/Argentina components of the International Polar Year core project SASSI (Synoptic Antarctic Shelf-Slope Interaction study). In this region the Antarctic Slope Current can be located by the pronounced in-shore deepening of isopycnals over the continental slope, rendering the strong subsurface temperature and salinity gradients characteristic of the Antarctic Slope Front. Before reaching the gaps in the southern Ridge near 51°W and 50°W, the ASC carries about 3 Sv of upper layer waters, but it splits into shallow and deep branches upon turning north through these two gaps. The shallower branch enters the Hesperides Trough at 51°W, then shows a tight cyclonic loop back to that longitude roughly following the slope's 700-m isobath, and turns again westward through a similar gap in the northern Ridge. In the Scotia Sea the westward-flowing Antarctic Slope Current is found as far west as the Elephant Island along slightly deeper levels of slope (1100 m) before it is blocked by the Antarctic Circumpolar Current south of the Shackleton Fracture Zone (56°W). The deeper branch of the ASC in the Powell Basin crosses the southern Ridge near 50°W and roughly follows the 1600-m isobath before entering the Scotia Sea through the Hesperides Gap farther to the east (49°W). Thereafter the deeper waters carried westward by this branch become undistinguishable from those circulating farther offshore. Repeat cross-slope sections at both southern and northern flanks of the South Scotia Ridge showed significant temporal variability in the characteristics

77 FR 5830 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-06

...] Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf Offshore... governments, offshore wind energy developers, and the public in the Department of the Interior's (DOI) ``Smart from the Start'' wind energy initiative offshore Massachusetts. The purpose of the ``Smart from the...

Geophysical Mapping of the South Carolina Atlantic Offshore for Wind Energy Development

NASA Astrophysics Data System (ADS)

Knapp, C. C.; Brantley, D.; Battista, B.; Gayes, P. T.; Knapp, J. H.; White, S. M.

2016-12-01

The submerged continental margin of the southeastern United States records a geologic history of continental collision during Paleozoic time (500-300 Mya), and subsequent continental rifting and break-up with associated magmatism during early Mesozoic time (230-180 Mya). Subsequent development as a passive continental margin has resulted in accumulation of a thick sedimentary cover deposited through numerous cycles of sea level change on the margin. Themost recent phase of deposition (Pleistocene; <1.8 Ma) took place during repeated, large-scale (120 m) sea-level changes which resulted in extensive exposure and inundation of the shelf. The shallow subsurface of the near-shore environment under consideration for wind energy development requires thorough analysis of seabed bottom type, seafloor roughness and geomorphology, potential sites of cultural resources and features such as active and inactive faults, filled channels, and potential slope instabilities which would have a considerable potential impact on siting of installations for wind energy. To this end, a geophysical survey has been conducted to further refine future wind farm locations. The study is focused on the inner shelf from 18 to 26 km offshore of North Myrtle Beach, SC and a second smaller area offshore of Georgetown, SC. The collaborative effort is generating multibeam, side scan sonar, chirp sub-bottom and magnetometer data. Seafloor acoustic backscatter is derived from the same instrument acquiring the bathymetry. Bathymetry shows a radial distribution of coast-perpendicular features that transition between two coastal processes: 1) there is the sediment distribution caused by longshore currents and wave energy, and 2) there are areas related to the coastal inlets that disrupt the primary sedimentation patterns and impose patterns of terrestrial sedimentation such as those from rivers, deltas and estuaries. There are numerous systems tracts and channels acting on the seafloor over time in the

Modeling of Selected Continental Slope Processes

DTIC Science & Technology

1999-09-30

photographs of stratigraphy: AAPG 2000 annual convention Iverson, R.M., and Reid, M.E., 1992. Gravity-driven groundwater flow and slope failure potential; 1...and deposits, in Bouma et al. (eds), Turbidites: AAPG /SEG special publication. Pratson, L., Gouveia, W., Courtney, R., Syvitski, J.P., Paola, C., and...Geophysical Society 15-19 August, 1999, Rio de Janeiro, Brazil Pratson, L., and Gouveia, W., in review. Linking stratigraphic and seismic modeling: AAPG

Using high-resolution multibeam bathymetry to identify seafloor surface rupture along the Palos Verdes fault complex in offshore Southern California

USGS Publications Warehouse

Marlow, M. S.; Gardner, J.V.; Normark, W.R.

2000-01-01

Recently acquired high-resolution multibeam bathymetric data reveal several linear traces that are the surficial expressions of seafloor rupture of Holocene faults on the upper continental slope southeast of the Palos Verdes Peninsula. High-resolution multichannel and boomer seismic-reflection profiles show that these linear ruptures are the surficial expressions of Holocene faults with vertical to steep dips. The most prominent fault on the multibeam bathymetry is about 10 km to the west of the mapped trace of the Palos Verdes fault and extends for at least 14 km between the shelf edge and the base of the continental slope. This fault is informally called the Avalon Knoll fault for the nearby geographic feature of that name. Seismic-reflection profiles show that the Avalon Knoll fault is part of a northwest-trending complex of faults and anticlinal uplifts that are evident as scarps and bathymetric highs on the multibeam bathymetry. This fault complex may extend onshore and contribute to the missing balance of Quaternary uplift determined for the Palos Verdes Hills and not accounted for by vertical uplift along the onshore Palos Verdes fault. We investigate the extent of the newly located offshore Avalon Knoll fault and use this mapped fault length to estimate likely minimum magnitudes for events along this fault.

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.

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.

Observations of internal bores and waves of elevation on the New England inner continental shelf during summer 2001

NASA Astrophysics Data System (ADS)

Pritchard, Mark; Weller, Robert A.

2005-03-01

During July-August 2001, oceanographic variability on the New England inner continental shelf was investigated with an emphasis on temporal scales shorter than tidal periods. Mooring and ship survey data showed that subtidal variation of inner shelf stratification was in response to regional Ekman upwelling and downwelling wind driven dynamics. High-frequency variability in the vertical structure of the water column at an offshore mooring site was linked to the baroclinic internal tide and the onshore propagation of nonlinear solitary waves of depression. Temperature, salinity, and velocity data measured at an inshore mooring detected a bottom bore that formed on the flood phase of the tide. During the ebb tide, a second bottom discontinuity and series of nonlinear internal waves of elevation (IWOE) formed when the water column became for a time under hydraulic control. A surface manifestation of these internal wave crests was also observed in aircraft remote sensing imagery. The coupling of IWOE formation to the offshore solitary waves packets was investigated through internal wave breaking criterion derived in earlier laboratory studies. Results suggested that the offshore solitons shoaled on the sloping shelf, and transformed from waves of depression to waves of elevation. The coupling of inshore bore formation to the offshore solitary waves and the possible impact of these periodic features on mixing on the inner shelf region are discussed.

NOAA Ship Okeanos Explorer 2012 Field Season in the Northern Gulf of Mexico and U.S. Atlantic Continental Margin

NASA Astrophysics Data System (ADS)

Skarke, A. D.; Lobecker, E.; Malik, M.; VerPlanck, N.

2012-12-01

The NOAA Ship Okeanos Explorer, jointly operated by the NOAA Office of Ocean Exploration and Research and the NOAA Office of Marine and Aviation Operations, is America's only federally managed ship dedicated solely to ocean exploration. The 2012 field season was spent exploring the northern Gulf of Mexico and the U.S. Atlantic continental shelf break and slope. In the Gulf of Mexico, mapping and remotely operated vehicle operations focused on the salt domes and canyons offshore Mississippi and Louisiana, and characterized several of the hundreds of seeps that were detected in the water column backscatter data collected with the ship's Kongsberg EM 302 multibeam sonar (30 kHz) during the 2011 field season. A team of NOAA and non-NOAA partners identified priority frontier areas along the continental shelf and slope between North Carolina and Cape Cod, mapping numerous canyons selected for focused mapping exploration in partnership with the North East Fisheries Science Center, the Mid-Atlantic Regional Council on the Ocean (a state level partnership between various states including NY, NJ, DE, MD, and VA), Woods Hole Oceanographic Institution (WHOI) and Virginia Sea Grant. The 2012 mapping efforts built on data collected during the 2011 field season. Okeanos Explorer data were leveraged by NOAA Ship Henry B. Bigelow to conduct towed camera operations to ground truth multibeam backscatter data for deepwater coral habitat assessment. The Blake Ridge and Cape Fear Diapirs offshore North Carolina were a third focus of exploration operations. Seven 900 meter high cold seeps were discovered in the diapir province. Exploration incorporated WHOI's Sentry autonomous underwater vehicle and its full suite of mapping and oceanographic sensors were used to characterize six seep sites. All data collected by Okeanos Explorer are available via the NOAA public archives with metadata records within 60 to 90 days of the end of each cruise.

Bottom currents observed in and around a submarine valley on the continental slope of the northern South China Sea

NASA Astrophysics Data System (ADS)

Wu, Lunyu; Xiong, Xuejun; Li, Xiaolong; Shi, Maochong; Guo, Yongqing; Chen, Liang

2016-12-01

Bottom currents at about 1000 m depth in and around a submarine valley on the continental slope of the northern South China Sea were studied by a 14-month long experiment from July 2013 to September 2014. The observations reveal that bottom currents are strongly influenced by the topography, being along valley axis or isobaths. Power density spectrum analysis shows that all the currents have significant peaks at diurnal and semi-diurnal frequencies. Diurnal energy is dominant at the open slope site, which is consistent with many previous studies. However, at the site inside the valley the semi-diurnal energy dominates, although the distance between the two sites of observation is quite small (11 km) compared to a typical horizontal first-mode internal tide wavelength (200 km). We found this phenomenon is caused by the focusing of internal waves of certain frequencies in the valley. The inertial peak is found only at the open slope site in the first deployment but missing at the inside valley site and the rest of the deployments. Monthly averaged residual currents reveal that the near-bottom currents on the slope flow southwestward throughout the year except in August and September, 2013, from which we speculate that this is a result of the interaction between a mesoscale eddy and the canyon/sag topography. Currents inside the valley within about 10 mab basically flow along slope and in the layers above the 10 mab the currents are northwestward, that is, from the deep ocean to the shelf. The monthly mean current vectors manifest an Ekman layer-like vertical structure at both sites, which rotate counter-clockwise looking from above.

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

Acoustic Velocity Of The Sediments Offshore Southwestern Taiwan

NASA Astrophysics Data System (ADS)

Tsai, C.; Liu, C.; Huang, P.

2004-12-01

Along the Manila Trench south of 21øXN, deep-sea sediments are being underthrusted beneath the Taiwan accretionary prism which is composed of the Kaoping Slope and Hengchun Ridge. Offshore southwestern Taiwan, foreland sediments and Late Miocene strata of the Tainan Basin are being accreted onto the fold-and thrust belt of the syn-collision accretionary wedge of the Kaoping Slope. The Kaoping Slope consists of thick Neogene to Recent siliciclastics deformed by fold-and-thrust structures and mud diapers. These Pliocene-Quaternary sediments deposited in the Kaoping Shelf and upper slope area are considered to be paleo-channel deposits confined by NNE-SSW trend mud diapiric structure. Seismic P-wave velocities of the sediment deposited in the Kaoping Shelf and Kaoping Slope area are derived from mutichannel seismic reflection data and wide-angle reflection and refraction profiles collected by sonobuoys. Sediment velocity structures constrained from mutichannel seismic reflection data using velocity spectrum analysis method and that derived from sonobuoy data using tau-sum inversion method are compared, and they both provide consistent velocity structures. Seismic velocities were analyzed along the seismic profile from the surface to maximum depths of about 2.0 km below the seafloor. Our model features a sediment layer1 with 400 ms in thickness and a sediment layer2 with 600 ms in thickness. For the shelf sediments, we observe a linear interval velocity trend of V=1.53+1.91T in layer1, and V=1.86+0.87T in layer2, where T is the one way travel time within the layer. For the slop sediment, the trend of V=1.47+1.93T in layer1, and V=1.70+1.55T in layer2. The layer1¡¦s velocities gradients are similar between the shelf (1.91 km/sec2) and the slope(1.93 km/sec2). It means layer1 distributes over the slope and shelf widely. The result of the sediment velocity gradients in this area are in good agreement with that reported for the south Atlantic continental margins.

Maps showing the change in modern sediment thickness on the Inner Continental Shelf offshore of Fire Island, New York, between 1996-97 and 2011

USGS Publications Warehouse

Schwab, William C.; Baldwin, Wayne E.; Denny, Jane F.

2015-01-01

The U.S. Geological Survey mapped approximately 336 square kilometers of the lower shoreface and inner continental shelf offshore of Fire Island, New York, in 1996 and 1997, using high-resolution sidescan-sonar and seismic-reflection systems, and again in 2011, using interferometric sonar and high-resolution chirp seismic-reflection systems. This report presents a comparison of sediment thickness and distribution as mapped during these two investigations. These spatial data support research on the Quaternary evolution of the Fire Island coastal system and provide baseline information for research on coastal processes along southern Long Island.

Paleomagnetism and rock magnetism from sediments along a continental shelf-to-slope transect in the NW Barents Sea: Implications for geomagnetic and depositional changes during the past 15 thousand years

NASA Astrophysics Data System (ADS)

Caricchi, C.; Lucchi, R. G.; Sagnotti, L.; Macrì, P.; Morigi, C.; Melis, R.; Caffau, M.; Rebesco, M.; Hanebuth, T. J. J.

2018-01-01

Paleomagnetic and rock magnetic data were measured on glaciomarine silty-clay successions along an E-W sediment-core transect across the continental shelf and slope of the Kveithola paleo-ice stream system (south of Svalbard, north-western Barents Sea), representing a stratigraphic interval spanning the last deglaciation and the Holocene. The records indicate that magnetite is the main magnetic mineral and that magnetic minerals are distinctly less abundant on the shelf than at the continental slope. The paleomagnetic properties allow for the reconstruction of a well-defined characteristic remanent magnetization (ChRM) throughout the sedimentary successions. The stratigraphic trends of rock magnetic and paleomagnetic parameters are used for a shelf-slope core correlation and sediment facies analysis is applied for depositional processes reconstruction. The new paleomagnetic records compare to the PSV and RPI variation predicted for the core sites by a simulation using the global geomagnetic field variation models SHA.DIF.14k and CALS7K.2 and closest PSV and RPI regional stack curves. The elaborated dataset, corroborated by available 14C ages, provides a fundamental chronological framework to constrain the coupling of shelf-slope sedimentary processes and environmental changes in the NW Barents Sea region during and after deglaciation.

Assessment of the U. S. outer continental shelf environmental studies program. 1. Physical oceanography. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

Federal responsibility for oil and gas development on the U.S. outer continental shelf (OCS) resides with the Minerals Management Service (MMS) of the U.S. Department of the Interior (DOI). The DOI's Environmental Studies Program (ESP) is the program through which MMS conducts environmental studies on the OCS and collects information to prepare environmental impact statements (EISs). It appeared to MMS in 1986 that the time was ripe to assess the status of the present program and to explore the needs for future studies. MMS requested an evaluation of the adequacy and applicability of ESP studies, a review of the generalmore » state of knowledge in the appropriate disciplines, and recommendations for future studies. Three panels were established, one of which, the Physical Oceanography Panel, investigated the physical oceanographic aspects of the ESP, the subject of the report, which is the first of three in a series. In reviewing the ESP's physical oceanography program, the panel evaluated the quality and relevance of studies carried out in waters under federal control, which extend from the limits of state jurisdictions (3-12 miles offshore) and include the central and outer continental shelf waters and the continental slope.« less

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 thatmore » 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.« less

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

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

Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska

NASA Astrophysics Data System (ADS)

Daigle, Hugh; Worthington, Lindsay L.; Gulick, Sean P. S.; Van Avendonk, Harm J. A.

2017-04-01

Pore pressures in sediments at convergent margins play an important role in driving chemical fluxes and controlling deformation styles and localization. In the Bering Trough offshore Southern Alaska, extreme sedimentation rates over the last 140 kyr as a result of glacial advance/retreats on the continental shelf have resulted in elevated pore fluid pressures in slope sediments overlying the Pamplona Zone fold and thrust belt, the accretionary wedge resulting from subduction of the Yakutat microplate beneath the North American Plate. Based on laboratory experiments and downhole logs acquired at Integrated Ocean Drilling Program Site U1421, we predict that the overpressure in the slope sediments may be as high as 92% of the lithostatic stress. Results of one-dimensional numerical modeling accounting for changes in sedimentation rate over the last 130 kyr predicted overpressures that are consistent with our estimates, suggesting that the overpressure is a direct result of the rapid sedimentation experienced on the Bering shelf and slope. Comparisons with other convergent margins indicate that such rapid sedimentation and high overpressure are anomalous in sediments overlying accretionary wedges. We hypothesize that the shallow overpressure on the Bering shelf/slope has fundamentally altered the deformation style within the Pamplona Zone by suppressing development of faults and may inhibit seismicity by focusing faulting elsewhere or causing deformation on existing faults to be aseismic. These consequences are probably long-lived as it may take several million years for the excess pressure to dissipate.

Geology report for proposed oil and gas lease sale No. 90; continental margin off the southeastern United States

USGS Publications Warehouse

Dillon, William P.

1983-01-01

This report summarizes our general knowledge of the geology and petroleum potential, as well as potential problems and hazards associated with development of petroleum resources, within the area proposed for nominations for lease sale number 90. This area includes the U.S. eastern continental margin from Raleigh Bay, just south of Cape Hatteras, to southern Florida, including the upper Continental Slope and inner Blake Plateau. The area for possible sales for lease sale number 90, as well as the area for lease sale number 78 and the previous areas leased are shown in figure 1; physiographic features of the region are shown in figure 2. Six exploration wells have been drilled within the proposed lease area (figs. 3 and 4), but no commercial discoveries have been made. All six wells were drilled on the Continental Shelf. No commercial production has been obtained onshore in the region. The areas already drilled have thin sedimentary rock sections, and the deeper strata are dominantly of continental facies. Petroleum formation may have been hindered by a lack of organic material and lack of sufficient burial for thermal maturation. However, analyses of drilling and seismic profiling data presented here indicate that a much thicker section of sedimentary rocks containing a much higher proportion of marine deposits, exists seaward of the Continental Shelf. These geologic conditions imply that the basins farther offshore may be more favorable environments for generating petroleum.

Deep structure of the continental margin and basin off Greater Kabylia, Algeria - New insights from wide-angle seismic data modeling and multichannel seismic interpretation

NASA Astrophysics Data System (ADS)

Aïdi, Chafik; Beslier, Marie-Odile; Yelles-Chaouche, Abdel Karim; Klingelhoefer, Frauke; Bracene, Rabah; Galve, Audrey; Bounif, Abdallah; Schenini, Laure; Hamai, Lamine; Schnurle, Philippe; Djellit, Hamou; Sage, Françoise; Charvis, Philippe; Déverchère, Jacques

2018-03-01

During the Algerian-French SPIRAL survey aimed at investigating the deep structure of the Algerian margin and basin, two coincident wide-angle and reflection seismic profiles were acquired in central Algeria, offshore Greater Kabylia, together with gravimetric, bathymetric and magnetic data. This 260 km-long offshore-onshore profile spans the Balearic basin, the central Algerian margin and the Greater Kabylia block up to the southward limit of the internal zones onshore. Results are obtained from modeling and interpretation of the combined data sets. The Algerian basin offshore Greater Kabylia is floored by a thin oceanic crust ( 4 km) with P-wave velocities ranging between 5.2 and 6.8 km/s. In the northern Hannibal High region, the atypical 3-layer crustal structure is interpreted as volcanic products stacked over a thin crust similar to that bordering the margin and related to Miocene post-accretion volcanism. These results support a two-step back-arc opening of the west-Algerian basin, comprising oceanic crust accretion during the first southward stage, and a magmatic and probably tectonic reworking of this young oceanic basement during the second, westward, opening phase. The structure of the central Algerian margin is that of a narrow ( 70 km), magma-poor rifted margin, with a wider zone of distal thinned continental crust than on the other margin segments. There is no evidence for mantle exhumation in the sharp ocean-continent transition, but transcurrent movements during the second opening phase may have changed its initial geometry. The Plio-Quaternary inversion of the margin related to ongoing convergence between Africa and Eurasia is expressed by a blind thrust system under the margin rising toward the surface at the slope toe, and by an isostatic disequilibrium resulting from opposite flexures of two plates decoupled at the continental slope. This disequilibrium is likely responsible for the peculiar asymmetrical shape of the crustal neck that may thus

Western Continental Margin of India - Re-look using potential field data

NASA Astrophysics Data System (ADS)

Rajaram, M.; S P, A.

2008-05-01

The Western Continental Margin of India (WCMI) evolved as a result of rifting between India and Madagascar that took place during mid Cretaceous (~88Ma).The WCMI is equally important in terms of natural resources as well as research point of view. The major tectonic elements in the western offshore includes the Laxmi and Chagos- Laccadive ridge dividing the WCMI and the adjoining Arabian sea into two basins, Pratap Ridge, Alleppey platform etc. Different theories have been proposed for the evolution of each of these tectonic elements. In the current paper we look at geopotential data on the west coast of India and the western off-shore. The data sets utilized include Satellite derived High Resolution Free Air Gravity data over the off-shore, Bouguer data onland, Champ Satellite Magnetic data, published Marine Magnetic data collected by ONGC, NIO, ground magnetic data over west cost collected by IIG and available aeromagnetic data. From the free air gravity anomaly the structural details of the western offshore can be delineated. The Euler depths of FAG depict deep solutions associated with Pratap Ridge, Comorin Ridge, the west coast fault and the Laxmi Ridge. These may be associated with continental margin and continental fragments. From the aeromagnetic and marine magnetic data it is evident that the West Coast Fault is dissected at several places. The shallow circular feature associated with Bombay High is evident both on the FAG and the analytic signal derived from satellite Magnetic data. The crustal magnetic thickness from MF5 lithospheric model of the Champ appears to suggest that the continental crust extends up to the Chagos- Laccadive ridge. Based on the analysis of these geopotential data sets the various theories for the evolution of the WCMI will be evaluated and these results will be presented.

Low methane concentrations in sediment along the continental slope north of Siberia: Inference from pore water geochemistry

NASA Astrophysics Data System (ADS)

Miller, C.; Dickens, G. R.; Jakobsson, M.; Koshurnikov, A.

2016-12-01

The Eastern Siberian Margin (ESM), a vast region of the Arctic, potentially holds large amounts of methane in sediments as gas hydrate and free gas. Although this CH4 has become a topic of discussion, primarily because of rapid regional climate change, the ESM remains sparingly explored. Here we present pore water chemistry results from 32 cores taken during Leg 2 of the 2014 SWERUS-C3 expedition. The cores come from depth transects across the continental slope of the ESM between Wrangel Island and the New Siberian Islands. Upward CH4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO42-), alkalinity, and the δ13C-dissolved inorganic Carbon (DIC), is negligible at all stations east of where the Lomonosov Ridge abuts the ESM at about 143°E. In the upper eight meters of these cores, downward sulfate flux never exceeds 9.2 mol/m2-kyr, the upward alkalinity flux never exceeds 6.8 mol/m2-kyr, and δ13C-DIC only slowly decreases with depth (-3.6‰/m on average). Additionally, dissolved H2S was not detected in these cores, and nutrient and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment. A single core on Lomonosov Ridge differs, as diffusive fluxes for SO42- and alkalinity were 13.9 and 11.3 mol/m2-kyr, respectively, the δ13C-DIC gradient was 5.6‰/m, and Mn2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that significant quantities of CH4, including gas hydrates, do not exist in any of our investigated depth transects spread out along much of the ESM continental slope. This contradicts previous assumptions and hypothetical models and discussion, which generally have assumed the presence of substantial CH4.

77 FR 24980 - Notice on Outer Continental Shelf Oil and Gas Lease Sales

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-26

... DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Notice on Outer Continental Shelf Oil... Outer Continental Shelf oil and gas lease sales to be held during the bidding period May 1, 2012... Corporation ExxonMobil Exploration Company Group II. Shell Oil Company Shell Offshore Inc. SWEPI LP Shell...

California State Waters Map Series: offshore of San Francisco, California

USGS Publications Warehouse

Cochrane, Guy R.; Johnson, Samuel Y.; Dartnell, Peter; Greene, H. Gary; Erdey, Mercedes D.; Golden, Nadine E.; Hartwell, Stephen R.; Endris, Charles A.; Manson, Michael W.; Sliter, Ray W.; Kvitek, Rikk G.; Watt, Janet Tilden; Ross, Stephanie L.; Bruns, Terry R.; Cochrane, Guy R.; Cochran, Susan A.

2015-01-01

Circulation over the continental shelf in the Offshore of San Francisco map area is dominated by the southward-flowing California Current, an eastern limb of the North Pacific Gyre that flows from Oregon to Baja California. At its midpoint offshore of central California, the California Current transports subarctic surface waters southeastward, about 150 to 1,300 km from shore. Seasonal northwesterly winds that are, in part, responsible for the California Current, generate coastal upwelling. Ocean temperatures offshore of central California have increased over the past 50 years, driving an ecosystem shift from the productive subarctic regime towards a depopulated subtropical environment.

78 FR 73882 - Notice of Determination of No Competitive Interest, Offshore Virginia

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-09

... energy research activities, including wind turbine installation and operational testing and installation... a Proposed Outer Continental Shelf (OCS) Wind Energy Research Lease Offshore Virginia. SUMMARY: This...

Physical oceanography of the US Atlantic and eastern Gulf of Mexico. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Milliman, J.D.; Imamura, E.

The report provides a summary of the physical oceanography of the U.S. Atlantic and Eastern Gulf of Mexico and its implication to offshore oil and gas exploration and development. Topics covered in the report include: meteorology and air-sea interactions, circulation on the continental shelf, continental slope and rise circulation, Gulf Stream, Loop Current, deep-western boundary current, surface gravity-wave climatology, offshore engineering implications, implications for resource commercialization, and numerical models of pollutant dispersion.

The influence of El Niño-Southern Oscillation (ENSO) cycles on wave-driven sea-floor sediment mobility along the central California continental margin

USGS Publications Warehouse

Storlazzi, Curt D.; Reid, Jane A.

2010-01-01

Ocean surface waves are the dominant temporally and spatially variable process influencing sea floor sediment resuspension along most continental shelves. Wave-induced sediment mobility on the continental shelf and upper continental slope off central California for different phases of El Niño-Southern Oscillation (ENSO) events was modeled using monthly statistics derived from more than 14 years of concurrent hourly oceanographic and meteorologic data as boundary input for the Delft SWAN wave model, gridded sea floor grain-size data from the usSEABED database, and regional bathymetry. Differences as small as 0.5 m in wave height, 1 s in wave period, and 10° in wave direction, in conjunction with the spatially heterogeneous unconsolidated sea-floor sedimentary cover, result in significant changes in the predicted mobility of continental shelf surficial sediment in the study area. El Niño events result in more frequent mobilization on the inner shelf in the summer and winter than during La Niña events and on the outer shelf and upper slope in the winter months, while La Niña events result in more frequent mobilization on the mid-shelf during spring and summer months than during El Niño events. The timing and patterns of seabed mobility are addressed in context of geologic and biologic processes. By understanding the spatial and temporal variability in the disturbance of the sea floor, scientists can better interpret sedimentary patterns and ecosystem structure, while providing managers and planners an understanding of natural impacts when considering the permitting of offshore activities that disturb the sea floor such as trawling, dredging, and the emplacement of sea-floor engineering structures.

30 CFR 250.417 - What must I provide if I plan to use a mobile offshore drilling unit (MODU)?

Code of Federal Regulations, 2010 CFR

2010-07-01

... offshore drilling unit (MODU)? 250.417 Section 250.417 Mineral Resources MINERALS MANAGEMENT SERVICE, DEPARTMENT OF THE INTERIOR OFFSHORE OIL AND GAS AND SULPHUR OPERATIONS IN THE OUTER CONTINENTAL SHELF Oil and... a mobile offshore drilling unit (MODU)? If you plan to use a MODU, you must provide: (a) Fitness...

Summary of environmental geologic studies in the Mid-Atlantic outer continental shelf area; results of 1978-1979 field seasons

USGS Publications Warehouse

Robb, James M.

1983-01-01

Because of the need for knowledge of an offshore area that is undergoing exploration for oil and gas resources, since 1975 the U.S. Bureau of Land Management (BLM) has funded studies of the environmental characteristics of the Mid-Atlantic Outer Continental Shelf. This volume briefly summarizes a final report to the BLM on the results of U.S. Geological Survey investigations stemming from data acquired during 1978 and 1979. The parent final report contains complete accounts of those investigations. The subjects of the studies range from the geologic effects of water currents and their capabilities of erosion and transportation, to delineation of potentially hazardous geologic characteristics of the area. Nine specific studies address the complexities of water currents, the nature of materials suspended in the sea waters, rates of mixing-in of material deposited on the bottom, and the sites of probable deposition of such materials, as well as sites and mechanisms of possible submarine landsliding or unstable bottom (engineering characteristics) of the Continental Slope and shelf.

Deep sea sedimentation processes and geomorphology: Northwest Atlantic continental margin

NASA Astrophysics Data System (ADS)

Mosher, David; Campbell, Calvin; Gardner, Jim; Chaytor, Jason; Piper, David; Rebesco, Michele

2017-04-01

Deep-sea sedimentation processes impart a fundamental control on the morphology of the western North Atlantic continental margin from Blake Spur to Hudson Strait. This fact is illustrated by the variable patterns of cross-margin gradients that are based on extensive new multibeam echo-sounder data informed by subbottom profiler and seismic reflection data. Erosion by off-shelf sediment transport in turbidity currents creates gullies, canyons and channels and a steep upper slope. Amalgamation of these conduits produces singular channels and turbidite fan complexes on the lower slope, flattening slope-profile gradients. The effect is an exponentially decaying "graded" slope profile. Comparatively, sediment mass failure produces steeper upper slopes due to head scarp development and a wedging architecture to the lower slope as deposits thin in the downslope direction. This process results in either a "stepped" slope, and/or a significant downslope gradient change where MTDs pinch out. Large drift deposits created by geostrophic currents are developed all along the margin. Blake Ridge, Sackville Spur, and Hamilton Spur are large detached drifts on disparate parts of the margin. They form a linear "above grade" profile along their crests from the shelf to abyssal plain. Deeper portions of the US continental margin are dominated by the Chesapeake Drift and Hatteras Outer Ridge; both plastered elongate mounded drifts. Farther north, particularly on the Grand Banks margin, are plastered and separated drifts. These drifts form "stepped" slope profiles, where they onlap the margin. Trough-mouth fan complexes become more common along the margin with increasing latitude. Sediment deposition and retention, particularly those dominated by glacigenic debris flows, characterize these segments producing an "above grade" slope profile. Understanding these geomorphological consequences of deep sea sedimentation processes is important to extended continental shelf mapping in which

30 CFR 250.417 - What must I provide if I plan to use a mobile offshore drilling unit (MODU)?

Code of Federal Regulations, 2012 CFR

2012-07-01

... offshore drilling unit (MODU)? 250.417 Section 250.417 Mineral Resources BUREAU OF SAFETY AND ENVIRONMENTAL ENFORCEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE OIL AND GAS AND SULPHUR OPERATIONS IN THE OUTER CONTINENTAL... plan to use a mobile offshore drilling unit (MODU)? If you plan to use a MODU, you must provide: (a...

30 CFR 250.417 - What must I provide if I plan to use a mobile offshore drilling unit (MODU)?

Code of Federal Regulations, 2013 CFR

2013-07-01

... offshore drilling unit (MODU)? 250.417 Section 250.417 Mineral Resources BUREAU OF SAFETY AND ENVIRONMENTAL ENFORCEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE OIL AND GAS AND SULPHUR OPERATIONS IN THE OUTER CONTINENTAL... plan to use a mobile offshore drilling unit (MODU)? If you plan to use a MODU, you must provide: (a...

30 CFR 250.417 - What must I provide if I plan to use a mobile offshore drilling unit (MODU)?

Code of Federal Regulations, 2014 CFR

2014-07-01

... offshore drilling unit (MODU)? 250.417 Section 250.417 Mineral Resources BUREAU OF SAFETY AND ENVIRONMENTAL ENFORCEMENT, DEPARTMENT OF THE INTERIOR OFFSHORE OIL AND GAS AND SULPHUR OPERATIONS IN THE OUTER CONTINENTAL... plan to use a mobile offshore drilling unit (MODU)? If you plan to use a MODU, you must provide: (a...

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

Development and sexual dimorphism of the sonic system in deep sea neobythitine fishes: The upper continental slope

NASA Astrophysics Data System (ADS)

Ali, Heba A.; Mok, Hin-Kiu; Fine, Michael L.

2016-09-01

The anatomy of sound production in continental-slope fishes has been ignored since the work of NB Marshall in the 1960s. Due to food scarcity at great depths, we hypothesize that sonic muscles will be reduced in deep-water neobythitine cusk-eels (family Ophidiidae). Here we describe and quantify dimensions of the swimbladder and sonic muscles of three species from the upper slope. They have four pairs of well-developed sonic muscles (two medial and two lateral) with origins on the skull and insertions on the medial swimbladder (medial pair) or on modified epineural ribs that attach to the lateral swimbladder (lateral pair). Despite minor differences, relatively similar swimbladder dimensions, muscle length and external morphology suggest a conservative body plan. However, there are major differences in sonic muscle mass: medial muscles are heavier in males and made of relatively small fibers (ca 10 μm in diameter). Lateral muscles are generally larger in females and consist of larger fibers, as in epaxial trunk muscle. Muscle weight varies between species, and we suggest males produce advertisement calls that vary in amplitude and duration in different species. Due to differences in fiber size, we hypothesize that lateral muscles with larger fibers remain contracted during sound production, and medial muscles with smaller fibers will oscillate to drive swimbladder sound production.

Results of Laboratory Tests on Surficial Sediments from the Upper Continental Slope Northern Gulf of Mexico

USGS Publications Warehouse

Booth, James S.

1979-01-01

The purpose of this report is to present the results of geo­technical, textural, and chemical tests performed on samples from the upper Continental Slope, northern Gulf of Mexico.The samples were collected by a piston corer up to 12 m (40 ft.} in length with a head weight of 908 kg (one ton}. The inside diameter of the C. A. B. liner was 89 mm (3.5 inches}. Upon retrieval, the cores were cut in 1.5 m sections, examined for evidence of disturbance, then, if in acceptable condition, were sealed and placed in their in situ vertical position in a refrigerated van. Once ashore, the sections were opened, sealed with wax, recapped and stored as before.The cores were split lengthwise for analysis. One half of the core was X-rayed and the radiograph was carefully examined as a further check for disturbance. This half was then archived. The other half of the core was used for the laboratory work.

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. Copyright © 2016 Elsevier Ltd. All rights reserved.

High-resolution bathymetry and acoustic geophysical data from Santa Maria di Leuca Cold Water Coral province (Northern Ionian Sea—Apulian continental slope)

NASA Astrophysics Data System (ADS)

Savini, A.; Corselli, C.

2010-03-01

A total of 800 km 2 of multibeam echo-sounder coverage, roughly 800 km of chirp-sonar data and 18 km of side-scan sonar profiles (100/500 kHz) were acquired a few km offshore Santa Maria di Leuca (south-eastern Italy), from 200 m to 1300 m water depth. The explored area belongs to the upper slope of the gently south-eastward dipping Apulian continental margin (northern Ionian Sea). Acoustic datasets were collected, by three different oceanographic expeditions, where evidence of living cold-water coral (CWC) colonies were documented by previous surveys and samples. High-resolution multibeam bathymetry indicated an extensive rough seafloor with an irregular faulted upper surface to the west (reflecting large-scale tectonic control on the margin) and a highly disrupted upper slope formed by prominent downslope mass-movements to the north. A broad area in the east was influenced by mass-transport deposition, which resulted in a very complex hummocky seafloor, mainly shaped by detached block-like features and failure-related bedforms (i.e. low scarps, downslope lineations and compressional ridges). From the shallow seismic-stratigraphic data, failure events appeared to be multiple and recurrent and chaotic reflectors, both buried and exposed at the seafloor, affected most of the investigated area. Drift sedimentation was also recognised along a central large ridge, resulting in an interplay between contour currents and downslope turbidity currents. The spatial distribution of the CWC reefs was inferred from the acoustic facies interpretation based on video images and ground-truthed by sediment samples. It appeared that: (1) within the investigated area, living coral frameworks were located along large topographic highs facing the main flow of the bottom currents, where hard and firm substrata and/or failure-related sediment bedforms occurred; (2) CWC mainly settled on clustered (and isolated) mound-like features, tens to a few hundreds of metres long and no more than 25

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

26 CFR 1.638-1 - Continental Shelf areas.

Code of Federal Regulations, 2013 CFR

2013-04-01

... exploitation of oil and is physically present on an offshore oil drilling platform operated by employees of L... a foreign country, designs equipment for use on oil drilling platforms affixed to the continental... corporation, to engage in exploratory oil drilling activities on a leasehold held by Y Corporation. Such...

26 CFR 1.638-1 - Continental Shelf areas.

Code of Federal Regulations, 2014 CFR

2014-04-01

... exploitation of oil and is physically present on an offshore oil drilling platform operated by employees of L... a foreign country, designs equipment for use on oil drilling platforms affixed to the continental... corporation, to engage in exploratory oil drilling activities on a leasehold held by Y Corporation. Such...

26 CFR 1.638-1 - Continental Shelf areas.

Code of Federal Regulations, 2012 CFR

2012-04-01

... exploitation of oil and is physically present on an offshore oil drilling platform operated by employees of L... a foreign country, designs equipment for use on oil drilling platforms affixed to the continental... corporation, to engage in exploratory oil drilling activities on a leasehold held by Y Corporation. Such...

26 CFR 1.638-1 - Continental Shelf areas.

Code of Federal Regulations, 2011 CFR

2011-04-01

... exploitation of oil and is physically present on an offshore oil drilling platform operated by employees of L... a foreign country, designs equipment for use on oil drilling platforms affixed to the continental... corporation, to engage in exploratory oil drilling activities on a leasehold held by Y Corporation. Such...

Characterization of a Mud Deposit Offshore of the Patos Lagoon, Southern Brazil

DTIC Science & Technology

2009-02-01

Journal Article 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE Characterization of mud deposit offshore of the Patos lagoon, southern Brazil 5a...deposition of mud on the beach along the shoreface of Rio Grande do Sul, Brazil dramatically influences the normal operations in the littoral zone...Continental Shelf Research journal homepage: www.elsevier.com/locate/csr Characterization of a mud deposit offshore of the Patos Lagoon, southern Brazil

Seismic swarms and fluid flow offshore Central America

NASA Astrophysics Data System (ADS)

Dzierma, Yvonne; Thorwart, Martin; Hensen, Christian; Rabbel, Wolfgang; Wolf, Florian

2010-05-01

Offshore Nicaragua and Northern Costa Rica, the Cocos Plate subducts beneath the Caribbean Plate, carrying with it a large amount of fluids and volatiles. While some of these are set free at great depth beneath the volcanic arc, causing the extremely high water content observed in Nicaraguan mafic magmas (Carr et al., 2003; Kutterolf et al., 2007), some early dehydration reactions already release fluids from the subducting plate underneath the continental slope. Unlike in accretionary margins, where these fluids migrate up along the decollement towards the deformation front, fluid release at erosional margins seems to occur through fractures in the overriding plate (Ranero et al., 2008). Fluid seeps in this region have be observed at seafloor mounds, appearing as side-scan sonar backscatter anomalies or revealed by the presence of chemosynthetic communities (Sahling et al., 2008). In the framework of the General Research Area SFB 574 "Volatiles and Fluids in Subduction Zones", a network of 20 ocean-bottom-stations was deployed offshore Sta Elena Peninsula, Northern Costa Rica, from December 2005 to June 2006. Several distinct swarms of small earthquakes were observed at the seismic stations, which occurred clustered over a time period of several days and have very similar seismic waveforms. Since a correlation of fluid-release sites with the occurrence of sporadic seismic swarms would indicate that fluid migration and fracturing is the mechanism responsible for triggering the earthquake swarms, the events are re-analysed by double-difference localisation to enhance the resolution of the earthquake locations. The results are then considered to estimate the migration velocity and direction and compare the localisations with the known mound sites. Carr, M., Feigenson, M. D., Patino, L. C., and Walker, J. A., 2003: Volcanism and geochemistry in Central America: Progress and problems, in Eiler, J. (ed.), Inside the subduction factory, pp. 153-179, American Geophysical

Preliminary Results from Acoustic Survey Offshore Kefken, Southwestern Black Sea Margin

NASA Astrophysics Data System (ADS)

Dondurur, Derman; Karaca, Onur; Nasıf, Aslıhan

2017-04-01

In March 2016, different marine acoustic datasets were collected aboard of R/V K. Piri Reis research vessel of Dokuz Eylül University within the scope of Turkish Research Council (Tübitak) Project (115Y218) to reveal submarine morphology and seismo-acoustical structure of the continental shelf and upper slope of Şile-Kefken region in the southwest of the Black Sea. A total of 1564 km high resolution seismic, multibeam bathymetry and Chirp sub-bottom profiler data were collected. Seismic data was collected using a 1500 m long digital streamer with 240 active channels. Group and shot intervals were 6.25 m and 25 m, respectively. Collected data were analyzed by means of (i) stratigraphic and (ii) structural components, and (iii) the structure of upper slope and shelf break. The stratigraphic elements in the region indicate the existence of Eocene and younger units. A distinctive acoustical basement in the seismic data observed throughout the shelf which is interpreted as uplifted Cretaceous basement of the Black Sea, that is Akveren or Yemişliçay Formation. The basement also outcrops around the Kefken Island. Chirp data is used to map the shallow stratigraphy of the shelf including the Holocene sediment distribution which exists on a very restricted area on the shelf. To the east, there is a large outcrop zone offshore Kefken where no Holocene sediments are observed. Initial evaluation of the collected data indicates that there is no present day delta formation in the area due to a few weak streams observed in the study area. The penetration of Chirp data in the western and the southern parts of the shelf area is very limited while it increases towards to upper continental slope to the North, and east of Kefken Cape. The acoustic data suggests that the study area is under the influence of the Pontide overthrust. Possible existence of reverse faults of Pontide overthrust is evident on the seismic data from southwestern shelf. In addition to the reverse faults to

Aragonite preservation in late Quaternary sediment cores on the Brazilian Continental Slope: implications for intermediate water circulation

NASA Astrophysics Data System (ADS)

Gerhardt, S.; Groth, H.; Rühlemann, C.; Henrich, R.

We present late Quaternary records of aragonite preservation determined for sediment cores recovered on the Brazilian Continental Slope (1790-2585m water depth) where North Atlantic Deep Water (NADW) dominates at present. We have used various indirect dissolution proxies (carbonate content, aragonite/calcite contents, and sand percentages) as well as gastropodal abundances and fragmentation of Limacina inflata to determine the state of aragonite preservation. In addition, microscopic investigations of the dissolution susceptibility of three Limacina species yielded the Limacina Dissolution Index which correlates well with most of the other proxies. Excellent preservation of aragonite was found in the Holocene section, whereas aragonite dissolution gradually increases downcore. This general pattern is attributed to an overall increase in aragonite corrosiveness of pore waters. Overprinted on this early diagenetic trend are high-frequency fluctuations of aragonite preservation, which may be related to climatically induced variations of intermediate water masses.

Basins in ARC-continental collisions

USGS Publications Warehouse

Draut, Amy E.; Clift, Peter D.; Busby, Cathy; Azor, Antonio

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

True Volumes of Slope Failure Estimated From a Quaternary Mass-Transport Deposit in the Northern South China Sea

NASA Astrophysics Data System (ADS)

Sun, Qiliang; Alves, Tiago M.; Lu, Xiangyang; Chen, Chuanxu; Xie, Xinong

2018-03-01

Submarine slope failure can mobilize large amounts of seafloor sediment, as shown in varied offshore locations around the world. Submarine landslide volumes are usually estimated by mapping their tops and bases on seismic data. However, two essential components of the total volume of failed sediments are overlooked in most estimates: (a) the volume of subseismic turbidites generated during slope failure and (b) the volume of shear compaction occurring during the emplacement of failed sediment. In this study, the true volume of a large submarine landslide in the northern South China Sea is estimated using seismic, multibeam bathymetry and Ocean Drilling Program/Integrated Ocean Drilling Program well data. The submarine landslide was evacuated on the continental slope and deposited in an ocean basin connected to the slope through a narrow moat. This particular character of the sea floor provides an opportunity to estimate the amount of strata remobilized by slope instability. The imaged volume of the studied landslide is 1035 ± 64 km3, 406 ± 28 km3 on the slope and 629 ± 36 km3 in the ocean basin. The volume of subseismic turbidites is 86 km3 (median value), and the volume of shear compaction is 100 km3, which are 8.6% and 9.7% of the landslide volume imaged on seismic data, respectively. This study highlights that the original volume of the failed sediments is significantly larger than that estimated using seismic and bathymetric data. Volume loss related to the generation of landslide-related turbidites and shear compaction must be considered when estimating the total volume of failed strata in the submarine realm.

78 FR 8190 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-05

...] Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf (OCS) Offshore... Assessment (EA) for Commercial Wind Leasing and Site Assessment Activities on the OCS Offshore North Carolina... INFORMATION: Background: On December 13, 2012, BOEM published the Notice in the Federal Register (77 FR 74218...

Characteristics and features of the submarine landslides in passive and active margin southwestern offshore Taiwan

NASA Astrophysics Data System (ADS)

Yeh, Y. C.

2016-12-01

In the past decade, numerous multi-channel seismic surveys as well as near seafloor high resolution geophysical investigations were conducted in order to explore and estimate the reserves of gas hydrate southwestern offshore Taiwan. The previous object was focused on searching substitute energy (i.e. gas hydrate) rather than geo-hazards. However, it is suggested that most of the gas hydrate is generally distributed at slope area southwestern offshore Taiwan, which indicates the slope may be failed when steady state was disturbed by some factors, such as sea level or climate change. In addition, once gas hydrate was dissociated, this may induce submarine landslide that further cause devastated tsunami. Thus, it is of great urgency to investigate potential landslide area, particularly, the hydrate-rich continental slope (active and passive margins) in adjacent to populous city like Kaohsiung. In this study, we collected several high resolution multi-channel seismic data with ten seconds shooting rate and 3.125 meters group interval streamer by using R/V ORI and R/V ORV. The seismic data were processed in conventional data processing strategy: bad trace clean, geometry settings, band-pass filter, de-convolution, surface-related multiple rejection, radon filter, stacking,kirchhoff migration and time to depth conversion. Combine the results obtained from the MCS data and subbottom profiles, two major results could be raised in the active margin as followed: (1) Most of the surface creeping and landslide was occurred shallower than 500 meters in water depth, which should be related to the inter-bedded fluid activities. (2) The landslide distribution is lagly affected by the presence of diaper, suggesting the subsequent mud diapirism may destruct slope stability; (3) The submarine landslide deeper than 800 meters in water depth distributes in the thrust fold area, that is probably referred to active thrusting. In the passive margin, large volume mass transportation

77 FR 5545 - Commercial Leasing for Wind Power Development on the Outer Continental Shelf (OCS) Offshore...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-03

... to encourage and incentivize offshore wind energy development. While a state may promote such development through activities such as the creation of financial incentives, an offshore wind project cannot... information resource for the state on Virginia's coastal energy resources, including offshore wind. For more...

Study of crustal structure and stretch mechanism of central continental shelf of northern South China Sea

NASA Astrophysics Data System (ADS)

Cao, J.; Xia, S.; Sun, J.; Wan, K.; Xu, H.

2017-12-01

Known as a significant region to study tectonic relationship between South China block and South China Sea (SCS) block and the evolution of rifted basin in continental margin, the continental shelf of northern SCS documents the evolution from continental splitting to seafloor spreading of SCS. To investigate crustal structure of central continental shelf in northern SCS, two wide-angle onshore-offshore seismic experiments and coincident multi-channel seismic (MCS) profiles were carried out across the onshore-offshore transitional zone in northern SCS, 2010 and 2012. A total of 34 stations consisted of ocean bottom seismometers, portable and permanent land stations were deployed during the survey. The two-dimensional precise crustal structure models of central continental shelf in northern SCS was constructed from onshore to offshore, and the stretching factors along the P-wave velocity models were calculated. The models reveal that South China block is a typical continental crust with a 30-32 km Moho depth, and a localized high-velocity anomaly in middle-lower crust under land area near Hong Kong was imaged, which may reflect magma underplating caused by subduction of paleo-Pacific plate in late Mesozoic. The littoral fault zone is composed of several parallel, high-angle, normal faults that mainly trend northeast to northeast-to-east and dip to the southeast with a large displacement, and the fault is divided into several segments separated by the northwest-trending faults. The shelf zone south of LFZ was consisted of a differential thinning upper and lower continental crust, which indicate stretch thinning of passive continent margin during the Cenozoic spreading of the SCS. The results appear to further confirm that the northern margin of SCS experienced a transition from active margin to passive one during late Mesozoic and Cenozoic.

Gas hydrate and spatial venting variations in the continental margin offshore Southwestern Taiwan

NASA Astrophysics Data System (ADS)

Lin, S.; Lim, Y.; Hsieh, W.; Yang, T.; Wang, Y.

2006-12-01

Strong BSR, high methane contents and rapid sulfate reduction were found in the continental margin sediments offshore southwestern Taiwan. In order to identify the venting phenomena and its relationship with gas hydrate, this research investigate sea floor vent features using WHOI?|s Towcam system as well as piston core in the study region. A total of 10 dives were conducted on board the r/v OR-1. Pore water sulfate, dissolved sulfide, methane, chloride, del O18 ratio, sediment organic carbon, carbonate content and carbonate del C13 ratio, pyrite-S were measured Large spatial variations were found based on pictures obtained from Towcam system and piston cores. Active venting features include bacteria mat, live dense bivalve patches, gas plume, temperature and salinity fluctuations, rapid sulfate reduction and high concentrations of methane in sediments. In addition, vent chimney, pockmark and large authigenic carbonate buildup were also observed in the active venting area. In contrast, in some areas without active venting features, scatter dead chimney, semi- buried carbonate structures, and dead bivalves were found. Total sulfate depletion was found at depth as shallow as 1 meter below sediment water interface in area near active vent whereas almost no sulfate depletion was observed in areas without any vent feature. Stages of carbonate build up existed, with initial phase dominated by small tube, chimney, and later with massive carbonate structures protruding the sea floor. The appearances of massive carbonate buildup structures seemed to indicate the end stage of gas hydrate venting phenomena.

Multiphased extension along continental margins: a case study of the Porcupine Basin, offshore Ireland

NASA Astrophysics Data System (ADS)

Bulois, Cédric; Shannon, Patrick, M.; Manuel, Pubellier; Nicolas, Chamot-Rooke; Louise, Watremez; Jacques, Deverchère

2017-04-01

Mesozoic faulting has been recognised in several Irish sedimentary basins as part of the northward propagation of the Atlantic rift system. However, the contribution of older structural elements remains poorly constrained. The present study documents the succession of extensional phases in the northern part of the Porcupine Basin sensu largo, offshore west of Ireland, in which structural inheritance and fault reactivation is commonly observed. The correlation of 2D and 3D seismic lines with exploration wells enables the precise definition of four overprinted extensional systems that link to specific tectonic stages identified along the Irish margin. The Porcupine Basin opened through a thickened continental crust that evolved during the Palaeozoic with the Caledonian and Variscan orogenic cycles. Extension initiated during the Carboniferous by reactivation of old structures, resulting in the migration of depocentres bounded by E-W, NE-SW and N-S structural trends. Subsequent episodic rifting occurred during several discrete events. The first rift episode, of Late Triassic to Early Jurassic age, is restricted to the North Porcupine Basin and most likely reactivated E-W structures of Caledonian age. Synrift sediments were generally deposited in a littoral setting that progressively deepened through time. The second episode, much more pronounced, occurred during the Upper Jurassic to lowermost Cretaceous (Neocomian). It resulted in shallow to deep marine deposition controlled by structural directions recognised in Caledonian and Variscan terranes. A third rift phase, evidenced by thick clastic deposition, locally occurred during the Aptian and finally died out with the opening of the Bay of Biscay located to the south of the region. A series of extensional megacycles are recognised from seismic unconformities and faulting geometries. Initial extension strongly followed the structural architecture of the continental crust (i.e. ancient folds, thrusts or orogenic fronts

77 FR 74204 - Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore North Carolina-Call for...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-13

...BOEM invites the submission of nominations for commercial wind leases that would allow a lessee to propose the construction of a wind energy project on the Outer Continental Shelf (OCS) offshore North Carolina, and to develop the project if approved after further environmental review. Although this announcement is not itself a leasing announcement, the Call Areas described herein, or portions thereof, may be available for future leasing. BOEM will use responses to this Call to gauge specific interest in acquiring commercial wind leases in some or all of the Call Areas, as required by 43 U.S.C. 1337(p)(3). Parties wishing to submit a nomination in response to this Call should submit detailed and specific information in response to the requirements described in the section entitled, ``Required Nomination Information.'' This announcement also requests comments and information from interested and affected parties about site conditions, resources, and multiple uses in close proximity to, or within, the Call Areas that would be relevant to BOEM's review of any nominations submitted and/or to BOEM's subsequent decision to offer all or part of the Call Areas for commercial wind leasing. The information that BOEM is requesting is described in the section of this Call entitled, ``Requested Information from Interested or Affected Parties.'' This Call is published pursuant to subsection 8(p)(3) of the OCS Lands Act, 43 U.S.C. 1337(p)(3), which was added by section 388 of the Energy Policy Act of 2005 (EPAct), as well as the implementing regulations at 30 CFR part 585. The Call Areas described in this notice are located on the OCS offshore North Carolina and are delineated as Wilmington-West, Wilmington-East and Kitty Hawk (formerly referred to as North Carolina Planning Areas 1, 2, and 5, respectively, during BOEM's North Carolina offshore wind planning efforts). The three Call Areas include 195 whole OCS blocks and 60 partial blocks in total and comprise approximately 1

Mineral resource management of the Outer Continental Shelf : leasing procedures, evaluation of resources, and supervision of production operations on leased lands of the Outer Continental Shelf

USGS Publications Warehouse

Adams, Maurice V.; John, C.B.; Kelly, R.F.; LaPointe, A.E.; Meurer, R.W.

1975-01-01

An important function of the Geological Survey is the evaluation and management of the mineral resources of the Outer Continental Shelf, particularly with respect to oil and gas, salt, and sulfur. Production of oil and gas from the Outer Continental Shelf of the United States has increased substantially over the past 20 years and represents an increasing percentage of total United States production. As discovery of major onshore production of oil and gas has become more difficult, the search has moved into the surrounding waters where submerged sedimentary formations are conducive to the accumulation of oil and gas. Increased energy demands of recent years have accelerated the pace of offshore operations with a corresponding improvement in technology as exploration and development have proceeded farther from shore and into deeper water. While improved technology and enforcement of more stringent regulations have made offshore operations safer, it is unrealistic to believe that completely accident-free operations can ever be achieved. Only slightly more than six percent of the world's continental terrace is adjacent to the United States, but less than one percent has been explored for oil and gas. Since the lead time for the development of offshore oil and gas resources can be as much as a decade, they do not provide an immediate energy supply but should be viewed in the light of a near-term source with a potential of becoming a medium-range source of supply pending the development of alternative energy sources. Revenues from the Outer Continental Shelf are deposited to the general fund of the United States Treasury. A major portion of these funds is allocated to the Land and Water Conservation Fund, the largest Federal grant-in-aid program of assistance to States, counties, and cities for the acquisition and development of public parks, open space, and recreation lands and water.

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. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

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.

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, Steve 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.

Influence of submarine morphology on bottom water flow across the western Ross Sea continental margin

USGS Publications Warehouse

Davey, F.J.; Jacobs, S.S.

2007-01-01

Multibeam sonar bathymetry documents a lack of significant channels crossing outer continental shelf and slope of the western Ross Sea. This indicates that movement of bottom water across the shelf break into the deep ocean in this area is mainly by laminar or sheet flow. Subtle, ~20 m deep and up to 1000 m wide channels extend down the continental slope, into tributary drainage patterns on the upper rise, and then major erosional submarine canyons. These down-slope channels may have been formed by episodic pulses of rapid down slope water flow, some recorded on bottom current meters, or by sub-ice melt water erosion from an icesheet grounded at the margin. Narrow, mostly linear furrows on the continental shelf thought to be caused by iceberg scouring are randomly oriented, have widths generally less than 400 m and depths less than 30m, and extend to water depths in excess of 600 m.

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

Observations of seismicity and ground motion in the northeast U.S. Atlantic margin from ocean bottom seismometer data

USGS Publications Warehouse

Flores, Claudia; ten Brink, Uri S.; McGuire, Jeffrey J.; Collins, John A.

2017-01-01

Earthquake data from two short-period ocean-bottom seismometer (OBS) networks deployed for over a year on the continental slope off New York and southern New England were used to evaluate seismicity and ground motions along the continental margin. Our OBS networks located only one earthquake of Mc∼1.5 near the shelf edge during six months of recording, suggesting that seismic activity (MLg>3.0) of the margin as far as 150–200 km offshore is probably successfully monitored by land stations without the need for OBS deployments. The spectral acceleration from two local earthquakes recorded by the OBS was found to be generally similar to the acceleration from these earthquakes recorded at several seismic stations on land and to hybrid empirical acceleration relationships for eastern North America. Therefore, the seismic attenuation used for eastern North America can be extended in this region at least to the continental slope. However, additional offshore studies are needed to verify these preliminary conclusions.

Morphogenesis of the SW Balearic continental slope and adjacent abyssal plain, Western Mediterranean Sea

NASA Astrophysics Data System (ADS)

Camerlenghi, Angelo; Accettella, Daniela; Costa, Sergio; Lastras, Galderic; Acosta, Juan; Canals, Miquel; Wardell, Nigel

2009-06-01

We present the seafloor morphology and shallow seismic structure of the continental slope south-east of the Balearic promontory and of the adjacent Algero-Balearic abyssal plain from multibeam and chirp sonar data. The main purpose of this research was to identify the sediment pathways from the Balearic promontory to the Algero-Balearic deep basin from the Early Pliocene to the Present. The morphology of the southern Balearic margin is controlled by a SW-NE structural trend, whose main expressions are the Emile Baudot Escarpment transform fault, and a newly discovered WSW-ENE trend that affects the SW end of the escarpment and the abyssal plain. We relate the two structural trends to right-lateral simple shear as a consequence of the Miocene westward migration of the Gibraltar Arc. Newly discovered steep and narrow volcanic ridges were probably enabled to grow by local transtension along the transform margin. Abyssal plain knolls and seahills relate to the subsurface deformation of early stage halokinetic structures such as salt rollers, salt anticlines, and salt pillows. The limited thickness of the overburden and the limited amount of deformation in the deep basin prevent the formation of more mature halokinetic structures such as diapirs, salt walls, bulbs, and salt extrusions. The uppermost sediment cover is affected by a dense pattern of sub-vertical small throw normal faults resulting from extensional stress induced in the overburden by subsurface salt deformation structures. Shallow gas seismic character and the possible presence of an active polygonal fault system suggest upward fluid migration and fluid and sediment expulsion at the seafloor through a probable mud volcano and other piercement structures. One large debris flow deposit, named Formentera Debris Flow, has been identified on the lower slope and rise of the south Formentera margin. Based on current observations, we hypothesize that the landslide originating the Formentera Debris Flow occurred in

A 3-D morphometric analysis of erosional features in a contourite drift from offshore SE Brazil

NASA Astrophysics Data System (ADS)

Alves, Tiago M.

2010-12-01

A contourite drift from offshore Brazil is mapped in detail and investigated using state-of-the-art 3-D seismic data. The aim was to review the relevance of erosional features in contourite drifts accumulated on continental slopes. Topographically confined by growing salt diapirs, the mapped contourite ridge is limited by two erosional features, a contourite moat and a turbidite channel, showing multiple slide scars on it flanks. Associated with the latter features are thick accumulations of high-amplitude strata, probably comprising sandy/silty sediment of Miocene to Holocene age. The erosional unconformities are mostly observed in a region averaging 3.75km away from the axes of a channel and a moat, whose deposits interfinger with continuous strata in central parts of the contourite drift. The multiple unconformities observed are mostly related to slide scars and local erosion on the flanks of the drift. This work demonstrates that the existence of widespread unconformities within contourite drifts on continental slopes: (1) may not be as prominent as often documented, (2) are often diachronic and interfinger with correlative hiatuses or aggraded strata in axial regions of contourite drifts. Although less widespread than regional, or ocean-scale unconformities, these diachronous features result in significant hiatuses within contourite drifts and are, therefore, potentially mappable as relevant (regional-scale) unconformities on 2-D/3-D seismic data. Thus, without a full 3-D morphometric analysis of contourite drifts, significant errors may occur when estimating major changes in the dynamics of principal geostrophic currents based on single-site core data, or on direct correlations between stratigraphic surfaces of distinct contourite bodies.

78 FR 1759 - Notice of Approval of Clean Air Act Outer Continental Shelf Minor Source/Title V Minor Permit...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-09

... Outer Continental Shelf Minor Source/Title V Minor Permit Modification Issued to Shell Offshore, Inc. for the Kulluk Conical Drilling Unit AGENCY: United States Environmental Protection Agency (EPA... decision granting Shell Offshore Inc.'s (``Shell'') request for minor modifications of Clean Air Act Outer...

California State Waters Map Series: offshore of Tomales Point, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Golden, Nadine E.; Hartwell, Stephen R.; Greene, H. Gary; Erdey, Mercedes D.; Cochrane, Guy R.; Watt, Janet Tilden; Kvitek, Rikk G.; Manson, Michael W.; Endris, Charles A.; Dieter, Bryan E.; Krigsman, Lisa M.; Sliter, Ray W.; Lowe, Erik N.; Chinn, John L.; Johnson, Samuel Y.; Cochran, Susan A.

2015-01-01

Potential marine benthic habitats in the Offshore of Tomales Point map area range from unconsolidated continental-shelf sediment, to rocky continental-shelf substrate, to unconsolidated estuary sediments. Rocky-shelf outcrops and rubble are considered to be promising potential habitats for rockfish and lingcod, both of which are recreationally and commercially important species. Dynamic bedforms, such as the sand waves at the mouth of Tomales Bay, are considered potential foraging habitat for juvenile lingcod and possibly migratory fishes, as well as for forage fish such as Pacific sand lance.

Effects of energy-related activities on the Atlantic Continental Shelf

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manowitz, B

1975-01-01

Sixteen papers were presented and are announced separately. Coastal waters, continental shelf geology and aquatic ecosystems are studied for modelling basic data for assessment of possible environmental impacts from offshore energy development. Sediment transport and wave phenomena are modelled for understanding water pollution transport and diffusion. (PCS)

Direct observations of the Antarctic Slope Current transport at 113°E

NASA Astrophysics Data System (ADS)

Peña-Molino, B.; McCartney, M. S.; Rintoul, S. R.

2016-10-01

The Antarctic Slope Current (ASC), defined here as the region of westward flow along the continental slope off Antarctica, forms the southern limb of the subpolar gyres. It regulates the exchange of water across the shelf break and provides a path for interbasin westward transport. Despite its significance, the ASC remains largely unobserved around most of the Antarctic continent. Here we present direct velocity observations from a 17 month current meter moored array deployed across the continental slope between the 1000 and the 4200 m isobaths, in the southeastern Indian Ocean near 113°E. The observed time-mean flow consists of a surface-intensified jet associated with the Antarctic Slope Front (ASF) and a broader bottom-intensified westward flow that extends out to approximately the 4000 m isobath and is strongest along the upper slope. The time-mean transport of the ASC is -29.2 Sv. Fluctuations in the transport are large, typically exceeding the mean by a factor of 2. They are mainly due to changes in the northward extent of the current over the lower slope. However, seasonal changes in the wind also drive variations in the transport of the ASF and the flow in the upper slope. Both mean and variability are largely barotropic, thus invisible to traditional geostrophic methods.

Shelf-Slope Exchanges near Submarine Canyons in the Southern Mid-Atlantic Bight

NASA Astrophysics Data System (ADS)

Wang, H.; Gong, D.

2016-02-01

Shelf-slope exchange processes are major physical drivers of biological productivity near the shelf-break. Observations from two Slocum ocean gliders in Fall 2013 are used to explore the driving mechanisms of cross-shelf-slope exchanges near Norfolk Canyon and Washington Canyon in the southern Mid-Atlantic Bight. Offshore excursion of bottom "cold pool" water, and shoreward intrusion of slope water at surface layer and thermocline depth occurred during northeasterly along-shelf winds. The saline intrusions of surface slope water resided between the cold pool and surface shelf water, and reached the bottom on the outer and mid-shelf, while the offshore excursion of cold pool water was found between the surface and intermediate slope-water over the canyon. Ekman transport calculation shows wind-driven cross-shelf transport can partially explain this interleaving pattern of intrusions. Scaling analysis of double diffusive processes demonstrate that they also likely played a role in the cross-shelf-slope exchange. A unique canyon upwelling event was captured in and around Washington Canyon during a period of southwesterly along-shelf wind and along-shelf flow to the northeast. The water mass distributions and isopycnal responses in both along-canyon and cross-canyon transects are consistent with scaling analysis and numerical studies of canyon upwelling. Temperature-Salinity properties of water masses in the canyon suggest active mixing between shelf and slope water masses near the canyon head. These results point to the importance of wind, double diffusion, and canyon topography on shelf-slope exchange in the MAB.

A method for determining average beach slope and beach slope variability for U.S. sandy coastlines

USGS Publications Warehouse

Doran, Kara S.; Long, Joseph W.; Overbeck, Jacquelyn R.

2015-01-01

The U.S. Geological Survey (USGS) National Assessment of Hurricane-Induced Coastal Erosion Hazards compares measurements of beach morphology with storm-induced total water levels to produce forecasts of coastal change for storms impacting the Gulf of Mexico and Atlantic coastlines of the United States. The wave-induced water level component (wave setup and swash) is estimated by using modeled offshore wave height and period and measured beach slope (from dune toe to shoreline) through the empirical parameterization of Stockdon and others (2006). Spatial and temporal variability in beach slope leads to corresponding variability in predicted wave setup and swash. For instance, seasonal and storm-induced changes in beach slope can lead to differences on the order of 1 meter (m) in wave-induced water level elevation, making accurate specification of this parameter and its associated uncertainty essential to skillful forecasts of coastal change. A method for calculating spatially and temporally averaged beach slopes is presented here along with a method for determining total uncertainty for each 200-m alongshore section of coastline.

Discussion of the paper 'Hydrates offshore Brazil'

USGS Publications Warehouse

Dillon, William P.

1994-01-01

The paper “Hydrates Offshore Brazil” by Rogerio L. Fontana and Alexandre Mussumeci presents some important information that strongly indicates the presence of gas hydrates on the southern Brazilian continental margin. However, the acoustic compressional wave velocity structure reported for the Brazilian margin sediments is highly unusual and quite puzzling. We will discuss a possible explanation related to the presence of gas hydrate and free gas in the sediments.

Concentrations and isotope ratios of mercury in sediments from shelf and continental slope at Campos Basin near Rio de Janeiro, Brazil.

PubMed

Araujo, Beatriz Ferreira; Hintelmann, Holger; Dimock, Brian; Almeida, Marcelo Gomes; Rezende, Carlos Eduardo

2017-07-01

Mercury (Hg) may originate from both anthropogenic and natural sources. The measurement of spatial and temporal variations of Hg isotope ratios in sediments may enable source identification and tracking of environmental processes. In this study we establish the distribution of mercury concentrations and mercury isotope ratios in surface sediments of three transects along the continental shelf and slope in Campos Basin-RJ-Brazil. The shelf showed on average lower total Hg concentrations (9.2 ± 5.3 ng g -1 ) than the slope (24.6 ± 8.8 ng g -1 ). MMHg average concentrations of shelf 0.15 ± 0.12 ng g -1 and slope 0.13 ± 0.06 ng g -1 were not significantly different. Distinct differences in Hg isotope ratio signatures were observed, suggesting that the two regions were impacted by different sources of Hg. The shelf showed more negative δ 202 Hg and Δ 199 Hg values ranging from -0.59 to -2.19‰ and from -0.76 to 0.08‰, respectively. In contrast, the slope exhibited δ 202 Hg values from -0.29 to -1.82‰ and Δ 199 Hg values from -0.23 to 0.09‰. Mercury found on the shelf, especially along the "D" and "I" transects, is depleted in heavy isotopes resulting in more negative δ 202 Hg compared to the slope. Isotope ratios observed in the "D" and "I" shelf region are similar to Hg ratios commonly associated with plants and vegetation and very comparable to those detected in the estuary and adjoining mangrove forest, which suggests that Hg exported from rivers may be the dominating source of Hg in near coastal regions along the northern part of the shelf. Copyright © 2017 Elsevier Ltd. All rights reserved.

77 FR 5552 - Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Maryland-Call for...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-03

... incentivize offshore wind energy development. While a state may promote such development through activities such as the creation of financial incentives, it is important to note that an offshore wind project... evaluate and determine areas of the OCS that may be suitable for offshore wind energy development. This...

Along-slope variability of barotropic transport in the Nordic Seas: Simplified dynamics tested against observations

NASA Astrophysics Data System (ADS)

Aaboe, S.; NøSt, O. A.; Hansen, E.

2009-03-01

The present study combines simple geostrophic considerations and observational data to examine the along-slope evolution of the barotropic transport following the continental slope in the Nordic Seas and Arctic Ocean. Following geostrophic theory, the transport evolution is calculated from bottom densities in five different transects within the Nordic Seas. This theoretically predicted transport evolution is compared with transports estimated directly from velocity measurements. Between the Faroe-Shetland Channel and the Svinøy section off southern Norway, across the Fram Strait (below 800 m), and between the Fram Strait and the Greenland Sea the agreement is generally good between geostrophic theory and observations. This indicates that many aspects of the barotropic flow in these regions are captured by geostrophic dynamics. Between the eastern and western Fram Strait above 800 m and between Svinøy and the eastern Fram Strait the observed flow fields differ to a large extent from the flow field predicted by geostrophic dynamics, indicating that ageostrophic dynamics play a more important role in these regions. The barotropic transport differences between the eastern and western Fram Strait contain information about the barotropic transport evolution along the entire Arctic continental slope. The good agreement between observations and theory across the strait (below 800 m) therefore indicates that the flow along the deeper part of the Arctic continental slope is well described by geostrophic dynamics. According to our results, the noticeably more baroclinic nature of the flow in the western Fram Strait, compared with the eastern strait, can then be ascribed to water mass modifications along the Arctic continental slope.

77 FR 7148 - Notice of Approval of Clean Air Act Outer Continental Shelf Permits Issued to Shell Gulf of...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-10

... Shelf Permits Issued to Shell Gulf of Mexico, Inc., and Shell Offshore, Inc. for the Discoverer... Clean Air Act Outer Continental Shelf (OCS) permit applications, one from Shell Gulf of Mexico, Inc., for operation of the Discoverer drillship in the Chukchi Sea and one from Shell Offshore, Inc...

Wind-driven export of Weddell Sea slope water

NASA Astrophysics Data System (ADS)

Meijers, A. J. S.; Meredith, M. P.; Abrahamsen, E. P.; Morales Maqueda, M. A.; Jones, D. C.; Naveira Garabato, A. C.

2016-10-01

The export of waters from the Weddell Gyre to lower latitudes is an integral component of the southern subpolar contribution to the three-dimensional oceanic circulation. Here we use more than 20 years of repeat hydrographic data on the continental slope on the northern tip of the Antarctic Peninsula and 5 years of bottom lander data on the slope at 1000 m to show the intermittent presence of a relatively cold, fresh, westward flowing current. This is often bottom-intensified between 600 and 2000 dbar with velocities of over 20 cm s-1, transporting an average of 1.5 ± 1.5 Sv. By comparison with hydrography on the continental slope within the Weddell Sea and modeled tracer release experiments we show that this slope current is an extension of the Antarctic Slope Current that has crossed the South Scotia Ridge west of Orkney Plateau. On monthly to interannual time scales the density of the slope current is negatively correlated (r > 0.6 with a significance of over 95%) with eastward wind stress over the northern Weddell Sea, but lagging it by 6-13 months. This relationship holds in both the high temporal resolution bottom lander time series and the 20+ year annual hydrographic occupations and agrees with Weddell Sea export variability observed further east. We compare several alternative hypotheses for this wind stress/export relationship and find that it is most consistent with wind-driven acceleration of the gyre boundary current, possibly modulated by eddy dynamics, and represents a mechanism by which climatic perturbations can be rapidly transmitted as fluctuations in the supply of intermediate-level waters to lower latitudes.

78 FR 760 - Potential Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore New...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-01-04

... Offshore Wind Collaborative,'' a public-private entity consisting of NYPA, the Long Island Power Authority... Island-New York City Offshore Wind Project'', is designed to generate at least 350 megawatts (MW) of electricity from offshore wind resources, with the ability to expand generation capacity to as much as 700 MW...

Supervised classification of continental shelf sediment off western Donegal, Ireland

NASA Astrophysics Data System (ADS)

Monteys, X.; Craven, K.; McCarron, S. G.

2017-12-01

Managing human impacts on marine ecosystems requires natural regions to be identified and mapped over a range of hierarchically nested scales. In recent years (2000-present) the Irish National Seabed Survey (INSS) and Integrated Mapping for the Sustainable Development of Ireland's Marine Resources programme (INFOMAR) (Geological Survey Ireland and Marine Institute collaborations) has provided unprecedented quantities of high quality data on Ireland's offshore territories. The increasing availability of large, detailed digital representations of these environments requires the application of objective and quantitative analyses. This study presents results of a new approach for sea floor sediment mapping based on an integrated analysis of INFOMAR multibeam bathymetric data (including the derivatives of slope and relative position), backscatter data (including derivatives of angular response analysis) and sediment groundtruthing over the continental shelf, west of Donegal. It applies a Geographic-Object-Based Image Analysis software package to provide a supervised classification of the surface sediment. This approach can provide a statistically robust, high resolution classification of the seafloor. Initial results display a differentiation of sediment classes and a reduction in artefacts from previously applied methodologies. These results indicate a methodology that could be used during physical habitat mapping and classification of marine environments.

Erosional unconformity or non-deposition? An alternative interpretation of the Eocene seismic stratigraphy offshore Wilkes Land, East Antarctica

NASA Astrophysics Data System (ADS)

Sauermilch, Isabel; Whittaker, Joanne; Totterdell, Jennifer; Jokat, Wilfried

2017-04-01

The sedimentary stratigraphy along the conjugate Australian-Antarctic continental margins provide insights into their tectonic evolution as well as changes in paleoceanographic conditions in the Southern Ocean. A comprehensive network of multichannel seismic reflection data as well as geological information from drill cores have been used to interpret the stratigraphic evolution of these margins. However, a number of alternative seismic interpretations exist for the Antarctic side, particularly due to sparse drill core information. A prominent high-amplitude reflector observed along the margin, extending from the continental shelf to the foot-of-slope, is at the centre of debate. Recently, two major hiatuses (from 33.6 - 47.9 Ma and 51.06 - 51.9 Ma) were recovered by the IODP drill core U1356A offshore Wilkes Land and correlated to this prominent reflector. Previous seismic stratigraphic investigations interpreted this structure as an erosional unconformity and proposed different events as a possible cause for this formation, including first arrival of the continental glaciation at the coast at about 34 Ma, increase in spreading rate between Australia and Antarctica at about 45 Ma and drastic global sea level drop of 70 m at about 43 Ma. However, such a large-scale erosion must consequently lead to a re-deposition of a significantly large amount of sediment somewhere along the margins, but, to date, no such deposition is observed in the seismic reflection data. Here, we present an alternative seismo-stratigraphic interpretation based on correlation to the sedimentary structures along the Australian margin. We argue that the prominent unconformity is formed due to non-deposition of sediment between 47.8 and 33.6 Ma. The sedimentary units underlying this unconformity show strong similarities in structure, seismic characteristics and variation along the margin with sequences that are partly exposed to the seafloor at the foot of the Australian slope. On the Australian

77 FR 30551 - Commercial Renewable Energy Transmission on the Outer Continental Shelf (OCS) Offshore Rhode...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-23

... electrical power from Deepwater Wind's proposed 30 megawatt (MW) offshore wind energy project located in... (BIWF), a proposed 30 MW offshore wind energy project located in Rhode Island State waters approximately... habitats can be found at: http://www.crmc.ri.gov/samp_ocean.html . There are several species of birds...

Final Scientific/Technical Report: Characterizing the Response of the Cascadia Margin Gas Hydrate Reservoir to Bottom Water Warming Along the Upper Continental Slope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Solomon, Evan A.; Johnson, H. Paul; Salmi, Marie

The objective of this project is to understand the response of the WA margin gas hydrate system to contemporary warming of bottom water along the upper continental slope. Through pre-cruise analysis and modeling of archive and recent geophysical and oceanographic data, we (1) inventoried bottom simulating reflectors along the WA margin and defined the upper limit of gas hydrate stability, (2) refined margin-wide estimates of heat flow and geothermal gradients, (3) characterized decadal scale temporal variations of bottom water temperatures at the upper continental slope of the Washington margin, and (4) used numerical simulations to provide quantitative estimates of howmore » the shallow boundary of methane hydrate stability responds to modern environmental change. These pre-cruise results provided the context for a systematic geophysical and geochemical survey of methane seepage along the upper continental slope from 48° to 46°N during a 10-day field program on the R/V Thompson from October 10-19, 2014. This systematic inventory of methane emissions along this climate-sensitive margin corridor and comprehensive sediment and water column sampling program provided data and samples for Phase 3 of this project that focused on determining fluid and methane sources (deep-source vs. shallow; microbial, thermogenic, gas hydrate dissociation) within the sediment, and how they relate to contemporary intermediate water warming. During the 2014 research expedition, we sampled nine seep sites between ~470 and 520 m water depth, within the zone of predicted methane hydrate retreat over the past 40 years. We imaged 22 bubble plumes with heights commonly rising to ~300 meters below sea level with one reaching near the sea surface. We collected 22 gravity cores and 20 CTD/hydrocasts from the 9 seeps and at background locations (no acoustic evidence of seepage) within the depth interval of predicted downslope retreat of the methane hydrate stability zone. Approximately 300 pore

Offshore teleradiology.

PubMed

Bradley, William G

2004-04-01

Radiologists are responsible for providing prompt emergency radiology interpretations 24 hours a day, every day of the year. As a result of the increasing use of multidetector computed tomography, emergency radiology has increased significantly in volume over the past 5 years. Simultaneously, radiologists are working harder during the day because of the workforce shortage. Although teleradiology services located in the continental United States have been providing efficient coverage until recently, they are now having increasing difficulty recruiting radiologists who are willing to work at night. Addressing this problem is "offshore teleradiology." With the increasing use of several enabling technologies--Digital Imaging and Communication in Medicine, the picture archiving and communication system, and the Internet-it is now possible to cover a domestic radiology practice at night from any location in the world where it is daytime. Setting up such a practice is nontrivial, however. The radiologists must all be American trained and certified by the American Board of Radiology. They must have medical licenses in every state and privileges at every hospital they cover. This article describes some of the details involved in setting up an offshore teleradiology practice. It also attempts to make a financial case for using such a practice, particularly in the current economic environment.

Correlation of offshore seismic profiles with onshore New Jersey Miocene sediments

USGS Publications Warehouse

Monteverde, D.H.; Miller, K.G.; Mountain, Gregory S.

2000-01-01

The New Jersey passive continental margin records the interaction of sequences and sea-level, although previous studies linking seismically defined sequences, borehole control, and global ??18O records were hindered by a seismic data gap on the inner-shelf. We describe new seismic data from the innermost New Jersey shelf that tie offshore seismic stratigraphy directly to onshore boreholes. These data link the onshore boreholes to existing seismic grids across the outer margin and to boreholes on the continental slope. Surfaces defined by age; facies, and log signature in the onshore boreholes at the base of sequences Kw2b, Kw2a, Kw1c, and Kw0 are now tied to seismic sequence boundaries m5s, m5.2s, m5.4s, and m6s, respectively, defined beneath the inner shelf. Sequence boundaries recognized in onshore boreholes and inner shelf seismic profiles apparently correlate with reflections m5, m5.2, m5.4, and m6, respectively, that were dated at slope boreholes during ODP Leg 150. We now recognize an additional sequence boundary beneath the shelf that we name m5.5s and correlate to the base of the onshore sequence Kw1b. The new seismic data image prograding Oligocene clinoforms beneath the inner shelf, consistent with the results from onshore boreholes. A land-based seismic profile crossing the Island Beach borehole reveals reflector geometries that we tie to Lower Miocene litho- and bio-facies in this borehole. These land-based seismic profiles image well-defined sequence boundaries, onlap and downlap truncations that correlate to Transgressive Systems Tracts (TST) and Highstand Systems Tracts (HST) identified in boreholes. Preliminary analysis of CH0698 data continues these system tract delineations across the inner shelf The CH0698 seismic profiles tie seismically defined sequence boundaries with sequences identified by lithiologic and paleontologic criteria. Both can now be related to global ??18O increases and attendant glacioeustatic lowerings. This integration of core

California State Waters Map Series—Offshore of Gaviota, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Cochrane, Guy R.; Hartwell, Stephen R.; Golden, Nadine E.; Kvitek, Rikk G.; Davenport, Clifton W.; Johnson, Samuel Y.; Cochran, Susan A.

2018-04-20

during major winter storms and long periods of low (or no) flow and minimal sediment load between storms. In recent (recorded) history, the majority of high-discharge, high-sediment-flux events have been associated with El Niño phases of the El Niño–Southern Oscillation climatic pattern.Shelf width in the Offshore of Gaviota map area ranges from about 4.3 to 4.7 km, and shelf slopes average about 1.0° to 1.2° but are highly variable because of the presence of the large Gaviota sediment bar. This bar extends southwestward for about 9 km from the mouth of Cañada de la Gaviota to the shelf break, is as wide as 2 km, and is by far the largest shore-attached sediment bar in the Santa Barbara Channel. The shelf is underlain by bedrock and variable amounts (0 to as much as 36 m in the Gaviota bar) of upper Quaternary sediments deposited as sea level fluctuated in the late Pleistocene. The trend of the shelf break changes from about 276° to 236° azimuth over a distance of about 12 km, and it ranges in depth from about 91 m to as shallow as 62 to 73 m where significant shelf-break and upper-slope failure and landsliding has apparently occurred. The shelf break in the western part of the map area is notably embayed by the heads of three large (150- to 300-m-wide) channels that have been referred to as “the Gaviota Canyons” or as “Drake Canyon,” “Sacate Canyon,” and “Alegria Canyon.”Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft, unconsolidated sediment interspersed with isolated areas of rocky habitat that support kelp-forest communities in the nearshore and rocky-reef communities in deeper water. The potential marine benthic habitat types mapped in the Offshore of Gaviota map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank

Morphological responses of macrobenthic polychaetes to low oxygen on the Oman continental slope, NW Arabian Sea

NASA Astrophysics Data System (ADS)

Lamont, Peter A.; Gage, John D.

2000-01-01

Morphological adaptation to low dissolved oxygen consisting of enlarged respiratory surface area is described in polychaete species belonging to the family Spionidae from the Oman margin where the oxygen minimum zone impinges on the continental slope. Similar adaptation is suggested for species in the family Cossuridae. Such morphological adaptation apparently has not been previously recorded among polychaetes living in hypoxic conditions. The response consists of enlargement in size and branching of the branchiae relative to similar species living in normal levels of dissolved oxygen. Specimens were examined in benthic samples from different depths along a transect through the oxygen minimum zone. There was a highly significant trend shown to increasing respiratory area relative to body size in two undescribed spionid species with decreasing depth and oxygen within the OMZ. Yet the size and number of branchiae are often used as taxonomic characters. These within-species differences in size and number of branchiae may be a direct response by the phenotype to intensity of hypoxia. The alternative explanations are that they either reflect a pattern of differential post-settlement selection among a highly variable genotype, or represent early genetic differentiation among depth-isolated sub-populations.

Polychaete/amphipod ratio as an indicator of environmental impact related to offshore oil and gas production along the Norwegian continental shelf.

PubMed

Andrade, Hector; Renaud, Paul E

2011-12-01

Benthic faunal data is regularly collected worldwide to assess the ecological quality of marine environments. Recently, there has been renewed interest in developing biological indices able to identify environmental status and potential anthropogenic impacts. In this paper we evaluate the performance of a general polychaete/amphipod ratio along the Norwegian continental shelf as an environmental indicator for offshore oil and gas impacts. Two main trends are apparent: first, a contamination gradient is discernible from where production takes place compared to stations 10,000 m away. Second, the quality of the marine environment has improved over time. These results are consistent with monitoring reports employing a combination of uni- and multi-variate statistics. Thus, we consider this ratio as a relatively simple, useful and potentially cost-effective complement to other more demanding assessment techniques. Because of its strong theoretical basis, it may also be useful for detecting ecological change as a result of other activities. Copyright © 2011 Elsevier Ltd. All rights reserved.

Pockmark asymmetry and seafloor currents in the Santos Basin offshore Brazil

USGS Publications Warehouse

Schattner, U.; Lazar, M.; Souza, L. A. P.; ten Brink, Uri S.; Mahiques, M. M.

2016-01-01

Pockmarks form by gas/fluid expulsion into the ocean and are preserved under conditions of negligible sedimentation. Ideally, they are circular at the seafloor and symmetrical in profile. Elliptical pockmarks are more enigmatic. They are associated with seafloor currents while asymmetry is connected to sedimentation patterns. This study examines these associations through morphological analysis of new multibeam data collected across the Santos continental slope offshore Brazil in 2011 (353–865 mbsl). Of 984 pockmarks, 78% are both elliptical and asymmetric. Geometric criteria divide the pockmarks into three depth ranges that correlate with a transition between two currents: the Brazil Current transfers Tropical Water and South Atlantic Central Water southwestwards while the Intermediate Western Boundary Current transfers Antarctic Intermediate Water northeastwards. It is suggested that the velocity of seafloor currents and their persistence dictate pockmark ellipticity, orientation and profile asymmetry. Fast currents (>20 cm/s) are capable of maintaining pockmark flank steepness close to the angle of repose. These morphological expressions present direct evidence for an edge effect of the South Atlantic Subtropical Gyre and, in general, provide a correlation between pockmark geometry and seafloor currents that can be applied at other locations worldwide.

Terrigenous sediment supply along the Chilean continental margin: modern regional patterns of texture and composition

NASA Astrophysics Data System (ADS)

Lamy, F.; Hebbeln, D.; Wefer, G.

The regional patterns of texture and composition of modern continental slope and pelagic sediments off Chile between 25°S and 43°S reflect the latitudinal segmentation of geological, morphological, and climatic features of the continental hinterland. Grain-size characteristics are controlled by the grain-size of source rocks, the weathering regime, and mode of sediment input (eolian off northern Chile vs fluvial further south). Bulk-mineral assemblages reveal a low grade of maturity. Regional variations are governed by the source-rock composition of the different geological terranes and the relative source-rock contribution of the Coastal Range and Andes, as controlled by the continental hydrology. The relative abundance of clay minerals is also predominantly influenced by the source-rock composition and partly by continental smectite neoformation. Latitudinal variations of illite crystallinities along the Chilean continental slope (and west of the Peru-Chile trench) clearly reflect modifications of the weathering regime which correspond to the strong climatic zonation of Chile.

Offshore sand resources for coastal erosion control in Louisiana

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ramsey, K.E.; Penland, S.; McBride, R.A.

1990-09-01

An inventory of existing geophysical data supplemented by more than 15,000 km of high-resolution seismic profiles and 400 vibracores collected cooperatively by the Louisiana Geological Survey and US Geological Survey since 1981 indicates that a wide range of aggregate minerals occurs on the continental shelf in a variety of depositional settings. The distribution of these deposits is controlled by the geometry of the preexisting fluvial and deltaic channel systems and the stratigraphic signature of the Holocene Transgression across these features. The geology of coastal and offshore Louisiana is tied to the depositional history of the Mississippi River. Offshore of themore » delta plain, five types of aggregate sources can be identified: inner shelf shoals, submerged barrier islands, tidal inlets, distributary channels, and barrier platforms. This paper describes the geology of offshore Louisiana, the available geophysical data sets, and the distribution of aggregate mineral resources. On the continental shelf of the Mississippi River delta plain, two extensive seismic survey grids have been developed by the Louisiana Geological Survey and US Geological Survey. The most prospective resources found are the huge sand bodies of Ship Shoal and associated distributaries, Cat Island Pass tidal channels and associated tidal deltas, and Barataria Pass/Grand Terre tidal channels and associated tidal deltas. East of the mouth of the Mississippi River are the Chandeleur Islands, where LGS identified seven major sand resource targets, truncated barrier-spit and tidal inlet deposits, submerged beach ridges, and distributaries associated with abandoned St. Bernard delta complexes. Abundant sand resources can be found in offshore Louisiana. Many of the sand bodies contain heavy minerals, but their concentration and distribution is unknown. Other potential sand resources not yet adequately explored include Sabine Bank, the Outer Shoal, and the St. Bernard shoal.« less

Shallow structure and stratigraphy of the carbonate West Florida continental slope and their implications to sedimentation and geohazards

USGS Publications Warehouse

Doyle, Larry J.

1983-01-01

An 1800-joule sparker survey of the West Florida continental slope between about 26?N and 29?15?N showed a top bed of Pleistocene age forming an irregular drape over a surface that is probably Pliocene. The contact between the top two layers is unconformable in the south and, in some places, shows karst collapse and solution features. Karst topography grades into a more hummocky erosional surface to the north, which in turn smoothes out; the contact become conformable still further north. A period of folding, which is widespread over the outer portion of the study area and which may be related to large scale mass wasting, occurred at about the same time represented by the unconformity. Significant subsidence has occurred as late as Pleistocene. The surface layer thins to a minimum (0 in the south) at about 525-meters water depth and then thickens again dramatically to the west, downslope. This thinning is interpreted to be due to the Loop Current, which flows from north to south in the area and which acts to block deposition and scour the bottom. Despite the fact that the margin is dominated by carbonates, usually associated with low sedimentation rates, there is widespread evidence of mass wasting affecting ancient and surficial deposits on the outer part of the upper slope. Three potential groups of geohazards identified are: 1. Potential bottom failure in areas where a thin top layer overlies the karst surface. 2. Potential for sliding and slumping. 3. Scour due to currents which could also affect drilling and engineering activities.

Sediments, structural framework, petroleum potential, environmental conditions, and operational considerations of the United States South Atlantic Outer Continental Shelf

USGS Publications Warehouse

,

1975-01-01

The area designated for possible oil and gas lease sale in Bureau of Land Management memorandum 3310 #43 (722) and referred to therein as part of the United States South Atlantic Outer Continental Shelf (OCS) contains about 98,000 square kilometres of the continental margin seaward of the 3 mile offshore limit and within the 600 metre isobath. The designated area, offshore of North Carolina, South Carolina, Georgia, and Florida, encompasses parts of three physiographic provinces: the Continental Shelf, the Florida-Hatteras Slope, and the Blake Plateau. The structural framework of the U.3. South Atlantic region is dominated by the Southeast Georgia Embayment --an east-plunging depression recessed into the Atlantic Coastal Plain and shelf between Cape Fear, North Carolina and Jacksonville, Florida. The embayment is bounded to the north by the Cape Fear Arch and to southeast by the Peninsular Arch. Refraction data indicate a minor basement(?) ridge beneath the outer shelf between 30? and 32?N at 80?W. Drill hole data also suggest a gentle fold or accretionary structure (reef?) off the east coast of Florida. Several other structural features have been identified by refraction and reflection techniques and drilling. These are the Yamacraw Uplift, Burton High, Stone Arch, and the Suwannee Channel. Gravity and magnetic anomalies within the area probably result from emplacement of magma bodies along linear features representing fundamental crustal boundaries. Of these anomalies, the most prominent, is a segment of the East Coast Magnetic Anomaly which crosses the coast at Brunswick, Georgia. This anomaly has been interpreted as representing an ancient continental boundary where two formerly separate continental plates collided and were welded together. There may be as much as 5,000 m of sedimentary rocks in the Southeast Georgia Embayment out to the 600 m isobath. Basement rocks beneath the Southeast Georgia Embayment are expected to be similar to those exposed in the

Pore water geochemistry along continental slopes north of the East Siberian Sea: inference of low methane concentrations

NASA Astrophysics Data System (ADS)

Miller, Clint M.; Dickens, Gerald R.; Jakobsson, Martin; Johansson, Carina; Koshurnikov, Andrey; O'Regan, Matt; Muschitiello, Francesco; Stranne, Christian; Mörth, Carl-Magnus

2017-06-01

Continental slopes north of the East Siberian Sea potentially hold large amounts of methane (CH4) in sediments as gas hydrate and free gas. Although release of this CH4 to the ocean and atmosphere has become a topic of discussion, the region remains sparingly explored. Here we present pore water chemistry results from 32 sediment cores taken during Leg 2 of the 2014 joint Swedish-Russian-US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions (SWERUS-C3) expedition. The cores come from depth transects across the slope and rise extending between the Mendeleev and the Lomonosov ridges, north of Wrangel Island and the New Siberian Islands, respectively. Upward CH4 flux towards the seafloor, as inferred from profiles of dissolved sulfate (SO42-), alkalinity, and the δ13C of dissolved inorganic carbon (DIC), is negligible at all stations east of 143° E longitude. In the upper 8 m of these cores, downward SO42- flux never exceeds 6.2 mol m-2 kyr-1, the upward alkalinity flux never exceeds 6.8 mol m-2 kyr-1, and δ13C composition of DIC (δ13C-DIC) only moderately decreases with depth (-3.6 ‰ m-1 on average). Moreover, upon addition of Zn acetate to pore water samples, ZnS did not precipitate, indicating a lack of dissolved H2S. Phosphate, ammonium, and metal profiles reveal that metal oxide reduction by organic carbon dominates the geochemical environment and supports very low organic carbon turnover rates. A single core on the Lomonosov Ridge differs, as diffusive fluxes for SO42- and alkalinity were 13.9 and 11.3 mol m-2 kyr-1, respectively, the δ13C-DIC gradient was 5.6 ‰ m-1, and Mn2+ reduction terminated within 1.3 m of the seafloor. These are among the first pore water results generated from this vast climatically sensitive region, and they imply that abundant CH4, including gas hydrates, do not characterize the East Siberian Sea slope or rise along the investigated depth transects. This contradicts previous modeling and discussions, which

Investigation of the Hosgri Fault, offshore Southern California, Point Sal to Point Conception

USGS Publications Warehouse

Payne, C.M.; Swanson, O.E.; Schell, B.A.

1979-01-01

A high-resolution seismic reflection survey of the inner continental shelf between Point Sal and Point Conception has revealed faults that displace post-Wisconsin strata (less than 17,000-20,000 years). These faults are the Hosgri fault, the Offshore Lompoc fault, and smaller unnamed faults. Faults trending offshore from the adjacent shoreline such as the Pezzoni, Lions Head, Honda, and Pacifico faults, do not show post-Wisconsin activity. The Hosgri fault trends directly toward the coastline between Purisima Point and Point Arguello where it appears to merge with folds and smaller faults in the western Transverse Ranges. This trend of offshore structures toward the Point Arguello-Point Conception area is consistent with a hypothesis that the regional structural fabric of the southern California Coast Ranges and its adjacent offshore area merge with the Transverse Ranges.

Oligocene to Holocene sediment drifts and bottom currents on the slope of Gabon continental margin (west Africa). Consequences for sedimentation and southeast Atlantic upwelling

NASA Astrophysics Data System (ADS)

Séranne, Michel; Nzé Abeigne, César-Rostand

1999-10-01

Seismic reflection profiles on the slope of the south Gabon continental margin display furrows 2 km wide and some 200 m deep, that develop normal to the margin in 500-1500 m water depth. Furrows are characterised by an aggradation/progradation pattern which leads to margin-parallel, northwestward migration of their axes through time. These structures, previously interpreted as turbidity current channels, display the distinctive seismic image and internal organisation of sediment drifts, constructed by the activity of bottom currents. Sediment drifts were initiated above a major Oligocene unconformity, and they developed within a Oligocene to Present megasequence of general progradation of the margin, whilst they are markedly absent from the underlying Late Cretaceous-Eocene aggradation megasequence. The presence of upslope migrating sediment waves, and the northwest migration of the sediment drifts indicate deposition by bottom current flowing upslope, under the influence of the Coriolis force. Such landwards-directed bottom currents on the slope probably represent coastal upwelling, which has been active along the west Africa margin throughout the Neogene.

The three scales of submarine groundwater flow and discharge across passive continental margins

USGS Publications Warehouse

Bratton, John F.

2010-01-01

Increased study of submarine groundwater systems in recent years has provided a wealth of new data and techniques, but some ambiguity has been introduced by insufficient distinguishing of the relevant spatial scales of the phenomena studied. Submarine groundwater flow and discharge on passive continental margins can be most productively studied and discussed by distinct consideration of the following three spatial scales: (1) the nearshore scale, spanning approximately 0–10 m offshore and including the unconfined surficial aquifer; (2) the embayment scale, spanning approximately 10 m to as much as 10 km offshore and including the first confined submarine aquifer and its terminus; and (3) the shelf scale, spanning the width and thickness of the aquifers of the entire continental shelf, from the base of the first confined aquifer downward to the basement, and including influences of geothermal convection and glacio-eustatic change in sea level.

High-resolution seismic-reflection profiles from the R/V Columbus Iselin, cruise CI 7-78-2, over the continental shelf and slope in the Georges Bank area

USGS Publications Warehouse

Bailey, Norman G.; Aaron, John M.

1982-01-01

In September 1978, the U. S. Geological Survey (USGS) collected 5,029 km of single-channel seismic-reflection data from the Georges Bank area of the Atlantic Continental Shelf and Slope during the R/V COLUMBUS ISELIN cruise CI 7-78-2. The purpose of the cruise was to determine the location and frequency of mass sediment movement and other geologic hazards along the Continental Slope.Navigation of the COLUMBUS ISELIN was by LORAN-C; position fixes were automatically recorded at 5-minute intervals and manually plotted and recorded at 15-minute intervals. The navigation equipment included a Northstar 6000 LORAN receiver and a Texas Instruments Silent 700 tape and paper recorder.The seismic equipment consisted of a 40-in3 airgun, a 5-in3 airgun, a Teledyne 600-joule mnisparker, and ORE (Ocean Research Equipment Inc.) 3.5-kHz transducer. The seismic profiles obtained were recorded on paper by EPC (EPC Labs Inc.) recorders and on magnetic tape by a 7-channel analog tape recorder. Overall, the data quality is excellent, and penetration and resolution are good although in some areas, the underlying structure was obscured by rough topography.The original records may be viewed at the USGS office in Woods Hole, Massachusetts. Microfilm copies of the data may be purchased only from the National Geophysical and Solar-Terrestrial Data Center, NOAA/EDIS/NGSDC, Code D621, 325 Broadway, Boulder, CO 80303 (Telephone: 303-497-6338).

The worldwide search for petroleum offshore; a status report for the quarter century, 1947-72

USGS Publications Warehouse

Berryhill, Henry L.

1974-01-01

At the end of 1972, offshore petroleum exploration was in progress on the submerged continental margins of 80 countries. Some 780 oil and gas fields had been discovered. Estimated worldwide volume of oil discovered offshore as of January 1, 1973, is 172.8 billion barrels of oil, or about 26 percent of the world total, and 168.4 trillion ft3 of natural gas. Present reserves of oil are 135.5 billion barrels, of which 70 percent is in the Persian Gulf. Some 90 percent of the oil discovered offshore has been found in 60 giant fields having reserves of 500 million or more barrels each.

Origin and extent of fresh paleowaters on the Atlantic continental shelf, USA

USGS Publications Warehouse

Cohen, D.; Person, M.; Wang, P.; Gable, C.W.; Hutchinson, D.; Marksamer, A.; Dugan, Brandon; Kooi, H.; Groen, K.; Lizarralde, D.; Evans, R.L.; Day-Lewis, F. D.; Lane, J.W.

2010-01-01

While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km3 in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (104 km3) and passive margins globally (3 ?? 105 km3). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages. ?? 2009 National Ground Water Association.

Modes of development of slope canyons and their relation to channel and levee features on the Ebro sediment apron, off-shore northeastern Spain

USGS Publications Warehouse

O'Connell, S.; Ryan, William B. F.; Normark, W.R.

1987-01-01

Six submarine slope canyons in an area of the northwestern Mediterranean, offshore from the Ebro River and Delta, were surveyed with bathymetric swathmapping (SeaBeam) and mid-range side-looking sonar (SeaMARC I). All of the canyons have slightly winding paths with concave-upwards gradients that are relatively steep shallower than 1,200 m. Two major types of canyons are identified on the basis of their morphologic character at the base of the slope; Type-I canyons lead to an unchannelled base-of-slope deposit and Type-II canyons are continuous with channel-levee systems that cross the rise. Four Type-I canyons were surveyed in the area. Two of these are broad, U-shaped, steep (average gradients of 1:14), do not indent the shelf, and terminate downslope at debris-flow deposits. These two canyons, the most northern in the area, have rounded heads with extensive gullies separated by knife-edge ridges. Relief of the canyon walls is about equal on both sides of the canyons, although the right-hand walls (looking downslope) are generally steeper. The other two Type-I canyons in the area are similar in that they do not indent the shelf, but they are much smaller and shallower and coalesce before terminating in the base-of-slope region. The two Type-II canyons that feed leveed-channels are U-shaped with flatter floors, longer profiles and gentler gradients than Type-I canyons. They are closer to the Valencia Valley and have relatively small cross-sectional areas. We propose a four-stage evolutionary sequence to explain the development of the canyons observed in this section on the prograding Ebro margin. During the initial stage, slumping and erosion on the slope creates a network of small gullies. During the next stage, headward growth of one (or more) gully leads to a major indentation of the shelf. This is the critical factor for developing a channel that will incise the slope and provide a major conduit for moving sediment to the basin. Stage 3 is characterized by the

Assessing the impact of Hurricanes Irene and Sandy on the morphology and modern sediment thickness on the inner continental shelf offshore of Fire Island, New York

USGS Publications Warehouse

Schwab, William C.; Baldwin, Wayne E.; Denny, Jane F.

2016-01-15

This report documents the changes in seabed morphology and modern sediment thickness detected on the inner continental shelf offshore of Fire Island, New York, before and after Hurricanes Irene and Sandy made landfall. Comparison of acoustic backscatter imagery, seismic-reflection profiles, and bathymetry collected in 2011 and in 2014 show that sedimentary structures and depositional patterns moved alongshore to the southwest in water depths up to 30 meters during the 3-year period. The measured lateral offset distances range between about 1 and 450 meters with a mean of 20 meters. The mean distances computed indicate that change tended to decrease with increasing water depth. Comparison of isopach maps of modern sediment thickness show that a series of shoreface-attached sand ridges, which are the dominant sedimentary structures offshore of Fire Island, migrated toward the southwest because of erosion of the ridge crests and northeast-facing flanks as well as deposition on the southwest-facing flanks and in troughs between individual ridges. Statistics computed suggest that the modern sediment volume across the about 81 square kilometers of common sea floor mapped in both surveys decreased by 2.8 million cubic meters, which is a mean change of –0.03 meters, which is smaller than the resolution limit of the mapping systems used.

The Role of Microfossils in the Compression of Marine Sediments: Implications for Submarine Slope Failure

NASA Astrophysics Data System (ADS)

Reece, J. S.; Shackleton, T.

2016-12-01

mudstone properties. This study has large implications for submarine slope failure due to the possible sudden expulsion of water causing a pore pressure increase, which may destabilize continental slopes, and cause a hazard for coastal communities and offshore infrastructure.

Divergent evolutionary processes associated with colonization of offshore islands.

PubMed

Martínková, Natália; Barnett, Ross; Cucchi, Thomas; Struchen, Rahel; Pascal, Marine; Pascal, Michel; Fischer, Martin C; Higham, Thomas; Brace, Selina; Ho, Simon Y W; Quéré, Jean-Pierre; O'Higgins, Paul; Excoffier, Laurent; Heckel, Gerald; Hoelzel, A Rus; Dobney, Keith M; Searle, Jeremy B

2013-10-01

Oceanic islands have been a test ground for evolutionary theory, but here, we focus on the possibilities for evolutionary study created by offshore islands. These can be colonized through various means and by a wide range of species, including those with low dispersal capabilities. We use morphology, modern and ancient sequences of cytochrome b (cytb) and microsatellite genotypes to examine colonization history and evolutionary change associated with occupation of the Orkney archipelago by the common vole (Microtus arvalis), a species found in continental Europe but not in Britain. Among possible colonization scenarios, our results are most consistent with human introduction at least 5100 bp (confirmed by radiocarbon dating). We used approximate Bayesian computation of population history to infer the coast of Belgium as the possible source and estimated the evolutionary timescale using a Bayesian coalescent approach. We showed substantial morphological divergence of the island populations, including a size increase presumably driven by selection and reduced microsatellite variation likely reflecting founder events and genetic drift. More surprisingly, our results suggest that a recent and widespread cytb replacement event in the continental source area purged cytb variation there, whereas the ancestral diversity is largely retained in the colonized islands as a genetic 'ark'. The replacement event in the continental M. arvalis was probably triggered by anthropogenic causes (land-use change). Our studies illustrate that small offshore islands can act as field laboratories for studying various evolutionary processes over relatively short timescales, informing about the mainland source area as well as the island. © 2013 John Wiley & Sons Ltd.

A model study of sediment transport across the shelf break

NASA Astrophysics Data System (ADS)

Marchal, Olivier

2017-04-01

A variety of dynamical processes can contribute to the transport of material (e.g., particulate matter) across the shelf break - the region separating the continental shelf from the continental slope. Among these processes are (i) the reflection of internal waves on the outer shelf and upper slope, and (ii) the instability of hydrographic fronts, roughly aligned with isobaths, that are often present at the shelf break. On the one hand, internal waves reflecting on a sloping boundary can produce bottom shear stresses that are large enough to resuspend non-cohesive sediments into the water column. On the other hand, eddies shed from unstable shelf break fronts can incorporate into their core particle-rich waters from the outer shelf and upper slope, and transport these waters offshore. Here we present numerical experiments with a three-dimensional numerical model of ocean circulation and sediment transport, which illustrate the joint effect of internal waves and eddies on sediment transport across the shelf break. The model is based on the primitive equations and terrain-following coordinates. The model domain is square and idealized, comprising a flat continental shelf, a constant continental slope, and a flat abyssal basin. The model grid has O(1 km) horizontal resolution, so that (sub)mesoscale eddies observed in the vicinity of shelf breaks, such as south of New England, can be represented in detail. Internal waves are excited through the specification of a periodic variation in the across-slope component of velocity at the offshore boundary of the domain, and eddies are generated from the baroclinic instability of a shelf break jet that is initially in strict thermal wind balance. Numerical experiments are conducted that are characterized by (i) different slopes of internal wave characteristics relative to the continental slope, representing sub-critical, critical, and super-critical regimes, and (ii) different values for the dimensionless ratios that emerge

Geomorphological and sedimentary processes of the glacially influenced northwestern Iberian continental margin and abyssal plains

NASA Astrophysics Data System (ADS)

Llave, Estefanía; Jané, Gloria; Maestro, Adolfo; López-Martínez, Jerónimo; Hernández-Molina, F. Javier; Mink, Sandra

2018-07-01

The offshore region of northwestern Iberia offers an opportunity to study the impacts of along-slope processes on the morphology of a glacially influenced continental margin, which has traditionally been conceptually characterised by predominant down-slope sedimentary processes. High-resolution multibeam bathymetry, acoustic backscatter and ultrahigh-resolution seismic reflection profile data are integrated and analysed to describe the present-day and recent geomorphological features and to interpret their associated sedimentary processes. Seventeen large-scale seafloor morphologies and sixteen individual echo types, interpreted as structural features (escarpments, marginal platforms and related fluid escape structures) and depositional and erosional bedforms developed either by the influence of bottom currents (moats, abraded surfaces, sediment waves, contourite drifts and ridges) or by gravitational features (gullies, canyons, slides, channel-levee complexes and submarine fans), are identified for the first time in the study area (spanning 90,000 km2 and water depths of 300 m to 5 km). Different types of slope failures and turbidity currents are mainly observed on the upper and lower slopes and along submarine canyons and deep-sea channels. The middle slope morphologies are mostly determined by the actions of bottom currents (North Atlantic Central Water, Mediterranean Outflow Water, Labrador Sea Water and North Atlantic Deep Water), which thereby define the margin morphologies and favour the reworking and deposition of sediments. The abyssal plains (Biscay and Iberian) are characterised by pelagic deposits and channel-lobe systems (the Cantabrian and Charcot), although several contourite features are also observed at the foot of the slope due to the influence of the deepest water masses (i.e., the North Atlantic Deep Water and Lower Deep Water). This work shows that the study area is the result of Mesozoic to present-day tectonics (e.g. the marginal platforms

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, in the

pCO2 Observations from a Vertical Profiler on the upper continental slope off Vancouver Island: Physical controls on biogeochemical processes.

NASA Astrophysics Data System (ADS)

Mihaly, S. F.

2016-02-01

We analyse two six month sets of data collected from a vertical profiler on Ocean Networks Canada's NEPTUNE observatory over the summer and early fall of 2012 and 2014. The profiler is in 400 m of water on the upper slope of the continental shelf. The site is away from direct influence of canyons, but is in a region of strong internal tide generation. Both seasonally varying semidiurnal internal tidal currents and diurnal shelf waves are observed. The near surface mean flow is weak and seasonally alternates between the California and Alaskan Currents. Mid-depth waters are influenced by the poleward flowing Californian undercurrent and the deep waters by seasonally varying wind-driven Ekman transport. The profiling package consists of a CTD, an oxygen optode, a pCO2 sensor, Chlorophyll fluorometer/turbidity, CDOM and is co-located with an upward-looking bottom-mounted 75kHz ADCP that measures currents to 30 m below sea surface. With these first deep-sea profiled time series measurements of pCO2, we endeavor to model how the local physical dynamics exert control over the variability of water properties over the slope and shelf and what the variability of the non-conservative tracers of pCO2 and O2 can tell us about the biogeochemistry of the region.

Sandstone and shale compaction curves derived from sonic and gamma ray logs in offshore wells, North Slope, Alaska; parameters for basin modeling

USGS Publications Warehouse

Rowan, Elisabeth L.; Hayba, Daniel O.; Nelson, Philip H.; Burns, W. Matthew; Houseknecht, David W.

2003-01-01

Representative compaction curves for the principle lithologies are essential input for reliable models of basin history. Compaction curves influence estimates of maximum burial and erosion. Different compaction curves may produce significantly different thermal histories. Default compaction curves provided by basin modeling packages may or may not be a good proxy for the compaction properties in a given area. Compaction curves in the published literature span a wide range, even within one lithology, e.g., sandstone (see Panel 3). An abundance of geophysical well data for the North Slope, from both government and private sources, provides us with an unusually good opportunity to develop compaction curves for the Cretaceous-Tertiary Brookian sandstones, siltstones, and shales. We examined the sonic and gamma ray logs from 19 offshore wells (see map), where significant erosion is least likely to have occurred. Our data are primarily from the Cretaceous-Tertiary Brookian sequence and are less complete for older sequences. For each well, the fraction of shale (Vsh) at a given depth was estimated from the gamma ray log, and porosity was computed from sonic travel time. By compositing porosities for the near-pure sand (Vsh99%)from many individual wells we obtained data over sufficient depth intervals to define sandstone and shale 'master' compaction curves. A siltstone curve was defined using the sonic-derived porosities for Vsh values of 50%. These compaction curves generally match most of the sonic porosities with an error of 5% or less. Onshore, the curves are used to estimate the depth of maximum burial at the end of Brookian sedimentation. The depth of sonic-derived porosity profiles is adjusted to give the best match with the 'master' compaction curves. The amount of the depth adjustment is the erosion estimate. Using our compaction curves, erosion estimates on the North Slope range from zero in much of the offshore, to as much as 1500 ft along the coast, and to

Geomorphic response of a continental margin to tectonic and eustatic variations, the Levant margin during the Messinian Salinity Crisis

NASA Astrophysics Data System (ADS)

Ben Moshe, Liran; Ben-Avraham, Zvi; Enzel, Yehouda; Uri, Schattner

2017-04-01

During the Messinian Salinity Crisis (MSC, 5.97±0.01-5.33 Ma) the Mediterranean Levant margin experienced major eustatic and sedimentary cycles as well as tectonic motion along the nearby Dead Sea fault plate boundary. New structures formed along this margin with morphology responding to these changes. Our study focuses on changes in this morphology across the margin. It is based on interpretation of three 3D seismic reflection volumes from offshore Israel. Multi-attribute analysis aided the extraction of key reflectors. Morphologic analysis of these data quantified interacting eustasy, sedimentation, and tectonics. Late Messinian morphologic domains include: (a) continental shelf; (b) 'Delta' anticline, forming a ridge diagonal to the strike of the margin; (c) southward dipping 'Hadera' valley, separating between (a) and (b); (d) 'Delta Gap' - a water gap crossing perpendicular to the anticline axis, exhibiting a sinuous thalweg; (e) continental slope. Drainage across the margin developed in several stages. Remains of turbidite flows crossing the margin down-slope were spotted across the 'Delta' anticline. These flows accumulated with the MSC evaporate sequence and prior to the anticline folding. Rising of the anticline, above the then bathymetry, either blocked or diverted the turbidites. That rising also defined the Hadera valley. In-situ evaporates, covering the valley floor, are, in turn covered by a fan-delta at the distal end of the valley. The fan-delta complex contains eroded evaporites and Lago-Mare fauna. Its top is truncated by dendritic fluvial channels that drained towards the Delta Gap. The Delta Gap was carved through the Delta ridge in a morphological and structural transition zone. We propose that during the first stages of the MSC (5.97±0.01-5.59 ma) destabilization of the continental slope due to oscillating sea level produced gravity currents that flowed through the pre-existing Delta anticline. Subsequent folding of the Delta anticline

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.

Comparison of the tectonics and geophysics of the major structural belts between the northern and southern continental margins of the South China Sea

NASA Astrophysics Data System (ADS)

Xia, Kan-yuan; Huang, Ci-liu; Jiang, Shao-ren; Zhang, Yi-xiang; Su, Da-quan; Xia, Si-gao; Chen, Zhong-rong

1994-07-01

A comparison of the tectonics and geophysics of the major structural belts of the northern and the southern continental margins of South China Sea has been made, on the basis of measured geophysical data obtained by ourselves over a period of 8 years (1984-1991). This confirmed that the northern margin is a divergent one and the southern margin is characterized by clearly convergent features. The main extensional structures of the northern margin are, from north to south: (1) The Littoral Fault Belt, a tectonic boundary between the continental crust and a transitional zone, along the coast of the provinces of Guangdong and Fujian in South China. It is characterised by earthquake activities, high magnetic anomalies and a rapid change in crustal thickness. (2) The Northern and Southern Depression zones (i.e., the Pearl River Mouth Basin), this strikes NE-ENE and is a very large Cenozoic depression which extends from offshore Shantou westwards to Hainan Island. (3) The Central Uplift Zone. This includes the Dongsha Uplift, Shenhu Uplift and may be linked with the Penghu uplift and Taiwan shoals to the east, forming a large NE-striking uplift zone along the northern continental slope. It is characterized by high magnetic anomalies. (4) Southern Boundary Fault Belt of the transitional crust. This has positive gravity anomalies on the land side and negative ones on the sea side. (5) The Magnetic Quiet Zone. This is located south of the southern Boundary Fault Belt and between the continental margin and the Central Basin of the South China Sea. Magnetic anomalies in this belt are of small amplitude and low gradient. We consider the Magnetic Quiet Zone to be a very important tectonic zone. The major structures of southern continental margin southwards are: (1) The Northern Fault Belt of the Nansha Block. This extends along the continental slope north of the Liyue shoal (Reed Bank) and Zhongye reef, and is a tectonic boundary between oceanic crust and the Nansha Block

Summary report on the regional geology, environmental considerations for development, petroleum potential, and estimates of undiscovered recoverable oil and gas resources of the United States southeastern Atlantic continental margin in the area of proposed oil and gas lease sale No. 78

USGS Publications Warehouse

Dillon, William P.

1981-01-01

This report summarizes our general knowledge of the geology and petroleum potential, as well as potential problems and hazards associated with development of petroleum resources, of the area proposed for nominations for lease sale number 78. This area includes the U.S. eastern continental margin from the mouth of Chesapeake Bay to approximately Cape Canaveral, Florida, including the upper Continental Slope and inner Blake Plateau. The area for possible sales and the previous areas leased are shown in figure 1; physiographic features of the region are shown in figure 2. Six exploration wells have been drilled within the proposed lease area (figs. 3 and 4) but no commercial discoveries have been made. All six wells were drilled on the Continental Shelf in the Southeast Georgia Embayment. No commercial production has been obtained onshore in the region. The areas already drilled have thin sedimentary sections, and the deeper rocks are dominantly continental facies. Petroleum formation may have been hindered by a lack of organic material and sufficient burial for thermal maturation. Analysis of drill and seismic profiling data presented here, however, indicates that a much thicker sedimentary rock section containing a much higher proportion of marine deposits exists seaward of the exploratory wells on the Continental Shelf. These geologic conditions imply that the offshore basins may be more favorable environments for generating petroleum.

77 FR 24734 - Outer Continental Shelf (OCS) Renewable Energy Program Leasing for Marine Hydrokinetic Technology...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-25

... Continental Shelf (OCS) Renewable Energy Program Leasing for Marine Hydrokinetic Technology Testing Offshore... found online at: http://www.boem.gov/Renewable-Energy-Program/State-Activities/Florida.aspx . [[Page.... FOR FURTHER INFORMATION CONTACT: Michelle Morin, BOEM Office of Renewable Energy Programs, 381 Elden...

Recent faulting in the Gulf of Santa Catalina: San Diego to Dana Point

USGS Publications Warehouse

Ryan, H.F.; Legg, M.R.; Conrad, J.E.; Sliter, R.W.

2009-01-01

We interpret seismic-reflection profiles to determine the location and offset mode of Quaternary offshore faults beneath the Gulf of Santa Catalina in the inner California Continental Borderland. These faults are primarily northwest-trending, right-lateral, strike-slip faults, and are in the offshore Rose Canyon-Newport-Inglewood, Coronado Bank, Palos Verdes, and San Diego Trough fault zones. In addition we describe a suite of faults imaged at the base of the continental slope between Dana Point and Del Mar, California. Our new interpretations are based on high-resolution, multichannel seismic (MCS), as well as very high resolution Huntec and GeoPulse seismic-reflection profiles collected by the U.S. Geological Survey from 1998 to 2000 and MCS data collected by WesternGeco in 1975 and 1981, which have recently been made publicly available. Between La Jolla and Newport Beach, California, the Rose Canyon and Newport-Inglewood fault zones are multistranded and generally underlie the shelf break. The Rose Canyon fault zone has a more northerly strike; a left bend in the fault zone is required to connect with the Newport-Inglewood fault zone. A prominent active anticline at mid-slope depths (300-400 m) is imaged seaward of where the Rose Canyon fault zone merges with the Newport-Inglewood fault zone. The Coronado Bank fault zone is a steeply dipping, northwest-trending zone consisting of multiple strands that are imaged from south of the U.S.-Mexico border to offshore of San Mateo Point. South of the La Jolla fan valley, the Coronado Bank fault zone is primarily transtensional; this section of the fault zone ends at the La Jolla fan valley in a series of horsetail splays. The northern section of the Coronado Bank fault zone is less well developed. North of the La Jolla fan valley, the Coronado Bank fault zone forms a positive flower structure that can be mapped at least as far north as Oceanside, a distance of ??35 km. However, north of Oceanside, the Coronado Bank

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

Geomorphology of the Eastern North American Continental Margin: the role of deep sea sedimentation processes

NASA Astrophysics Data System (ADS)

Mosher, D. C.; Campbell, C.; Piper, D.; Chaytor, J. D.; Gardner, J. V.; Rebesco, M.

2016-12-01

Deep-sea sedimentation processes impart a fundamental control on the morphology of the western North Atlantic continental margin from Blake Spur to Hudson Strait. This fact is illustrated by the variable patterns of cross-margin gradients that are based on extensive new multibeam echo-sounder data in concert with subbottom profiler and seismic reflection data. Most of the continental margin has a steep (>3o) upper slope down to 1500 to 2500 m and then a gradual middle and lower slope with a general concave upward shape There is a constant interplay of deep sea sedimentation processes, but the general morphology is dictated by the dominant one. Erosion by off-shelf sediment transport in turbidity currents creating channels, gullies and canyons creates the steep upper slope. These gullies and canyons amalgamate to form singular channels that are conduits to the abyssal plain. This process results in a general seaward flattening of gradients, producing an exponentially decaying slope profile. Comparatively, sediment mass failure produces steeper upper slopes due to head scarp development and a wedging architecture to the lower slope as deposits thin in the downslope direction. This process results in either a two-segment slope, and/or a significant downslope gradient change where MTDs pinch out. Large sediment bodies deposited by contour-following currents are developed all along the margin. Blake Ridge, Sackville Spur, and Hamilton Spur are large detached drifts on disparate parts of the margin. Along their crests, they form a linear profile from the shelf to abyssal plain. Deeper portions of the US continental margin are dominated by the Chesapeake Drift and Hatteras Outer Ridge; both plastered elongate mounded drifts. Farther north, particularly on the Grand Banks margin, are plastered and separated drifts. These drifts tend to form bathymetric steps in profile, where they onlap the margin. Stacked drifts create several steps. Turbidites of the abyssal plain onlap

Observation of near-inertial internal waves on the continental slope in the northwestern South China Sea

NASA Astrophysics Data System (ADS)

Zheng, Jie; Tian, Jiwei; Liang, Hui

2017-04-01

Based on nearly 3 months of moored acoustic Doppler current profiler records on the continental slope in the northwestern South China Sea (SCS) in 2006, this study examines temporal and vertical characteristics of near-inertial internal waves (NIW). Rotary frequency spectrum indicates that motions in the near-inertial frequency are strongly polarized, with clockwise (CW) energy exceeding counterclockwise (CCW) by about a factor of 10. Wavelet analysis exhibits an energy peak exceeding the 95% confidence level at the frequency of local inertial during the passage of typhoon Xangsane (24 September to 4 October). This elevated near-inertial kinetic energy (NIKE) event possesses about a 4 days delay correlation with the time integral of energy flux induced by typhoon, indicating an energy source of wind. Further analysis shows that the upward phase velocity of this event is 3.8 m h-1 approximately, corresponding to a vertical wavelength of about 125 m if not taking the redshift of local inertial frequency into account. Rotary vertical wavenumber spectrum exhibits the dominance of clockwise-with-depth energy, indicating downward energy propagation and implying a surface energy source. Dynamical modes suggest that mode 1 plays a dominant role at the growth stage of NIW, whereas major contribution is from higher modes during the penetration of NIKE into the ocean interior.

Continental Affinities of the Alpha Ridge

NASA Astrophysics Data System (ADS)

Jackson, H. Ruth; Li, Qingmou; Shimeld, John; Chian, Deping

2017-04-01

Identifying the crustal attributes of the Alpha Ridge (AR) part of the High Arctic Large Igneous Province and tracing the spreading centre across the Amerasia Basin plays a key role in understanding the opening history of the Arctic Ocean. In this approach, we report the evidence for a continental influence on the development of the AR and reduced ocean crust in the Amerasia Basin. These points are inferred from a documented continental sedimentation source in the Amerasia Basin and calculated diagnostic compressional and shear refraction waves, and from the tracing of the distinct spreading centre using the potential field data. (1) The circum-Arctic geology of the small polar ocean provides compelling evidence of a long-lived continental landmass north of the Sverdrup Basin in the Canadian Arctic Islands and north of the Barents Sea continental margin. Based on sediment distribution patterns in the Sverdrup Basin a continental source is required from the Triassic to mid Jurassic. In addition, an extensive continental sediment source to the north of the Barents Sea is required until the Barremian. (2) Offshore data suggest a portion of continental crust in the Alpha and Mendeleev ridges including measured shear wave velocities, similarity of compressional wave velocities with large igneous province with continental fragments and magnetic patterns. Ocean bottom seismometers recorded shear waves velocities that are sensitive to the quartz content of rocks across the Chukchi Borderland and the Mendeleev Ridge that are diagnostic of both an upper and lower continental crust. On the Nautilus Spur of the Alpha Ridge expendable sonobuoys recorded clear converted shear waves also consistent with continental crust. The magnetic patterns (amplitude, frequency, and textures) on the Northwind Ridge and the Nautilus Spur also have similarities. In fact only limited portions of the deepest water portions of the Canada Basin and the Makarov Basin have typical oceanic layer 2 and

Connecting onshore and offshore near-surface geology: Delaware's sand inventory project

USGS Publications Warehouse

Ramsey, K.W.; Jordan, R.R.; Talley, J.H.

1999-01-01

Beginning in 1988, the Delaware Geological Survey began a program to inventory on-land sand resources suitable for beach nourishment. The inventory included an assessment of the native beach textures using existing data and developing parameters of what would be considered suitable sand textures for Delaware's Atlantic beaches. An assessment of the economics of on-land sand resources was also conducted, and it was determined that the cost of the sand was competitive with offshore dredging costs. In addition, the sand resources were put into a geologic context for purposes of predicting which depositional environments and lithostratigraphic units were most likely to produce suitable sand resources. The results of the work identified several suitable on-land sand resource areas in the Omar and Beaverdam formations that were deposited in barrier-tidal delta and fluvial-estuarine environments, respectively. The identified on-land resources areas have not been utilized due to difficulties of truck transport and development pressures in the resource areas. The Delaware Geological Survey's participation in years 8, 9, and 10 of the Continental Margins Program was developed to extend the known resource areas onshore to offshore Delaware in order to determine potential offshore sand resources for beach nourishment. Years 8 and 9 involved primarily the collection of all available data on the offshore geology. These data included all seismic lines, surface grab samples, and cores. The data were filtered for those that had reliable locations and geologic information that could be used for geologic investigations. Year 10 completed the investigations onshore by construction of a geologic cross-section from data along the coast of Delaware from Cape Henlopen to Fenwick. This cross section identified the geologic units and potential sand resource bodies as found immediately along the coast. These units and resources are currently being extended offshore and tied to known and

Deformation offshore Northern Chile monitored by a seafloor geodetic network (GeoSEA)

NASA Astrophysics Data System (ADS)

Hannemann, Katrin; Lange, Dietrich; Kopp, Heidrun; Petersen, Florian; Contreras-Reyes, Eduardo

2017-04-01

The Nazca-South American plate boundary around 21°S has last ruptured in an earthquake in 1877 and was identified as a seismic gap prior to the 2014 Iquique earthquake (Mw=8.1). The southern portion of this segment is still unbroken. The geodetic monitoring of the Chilean subduction zone is crucial to understand the deformation processes in this area. Most geodetic measurements rely on GPS and are therefore limited to onshore campaigns. In December 2015, we installed the GeoSEA (Geodetic Earthquake Observatory on the SEAfloor) array around 21°S of the Nazca-South American plate boundary with RV SONNE to extend the geodetic observations to the offshore areas. The GeoSEA array consists of autonomous acoustic seafloor transponders mounted on 4 m high tripods. These transponders are able to continuously measure the two-way travel time of acoustic signals between station pairs (baselines) and the properties of the sea water (sound speed, temperature and pressure) at each transponder. These measurements are used to retrieve the distances between the transponders and give insights into the deformation of the seafloor. At the Chilean subduction zone, we installed in total 23 transponders in 3 subarrays with interstation distances of up to 2500 m. On the middle continental slope in 2300 m water depth, an array consisting of 8 transponders measures across crustal faults seen in AUV mapping. A second array of 5 stations located on the outer rise monitors extension across normal plate-bending faults. The deepest deployment in 5000 m water depth located on the lower continental slope with 10 stations is designed to measure diffuse strain build-up. The transponders are intended to monitor the seafloor deformation for 3.5 years. In November 2016 during a cruise of RV Langseth, the first 11 months of data were successfully uploaded via an acoustic modem. Furthermore, an additional component of the network, GeoSURF, a self-steering autonomous vehicle (wave glider), was

Environmental controls on the distribution of living (stained) benthic foraminifera on the continental slope in the Campos Basin area (SW Atlantic)

NASA Astrophysics Data System (ADS)

Yamashita, Cintia; Mello e Sousa, Silvia Helena de; Vicente, Thaisa Marques; Martins, Maria Virgínia; Nagai, Renata Hanae; Frontalini, Fabrizio; Godoi, Sueli Susana; Napolitano, Dante; Burone, Letícia; Carreira, Renato; Figueira, Rubens Cesar Lopes; Taniguchi, Nancy Kazumi; Rezende, Carlos Eduardo de; Koutsoukos, Eduardo Apostolos Machado

2018-05-01

Living (stained) benthic foraminifera from deep-sea stations in the Campos Basin, southeastern Brazilian continental margin, were investigated to understand their distribution patterns and ecology, as well as the oceanographic processes that control foraminiferal distribution. Sediments were collected from 1050 m to 1950 m of water depth during the austral winter of 2003, below the Intermediate Western Boundary Current (IWBC) and the Deep Water Boundary Current (DWBC). Based on statistical analysis, vertical flux of particulate organic matter and the grain size of sediment seem to be the main factors controlling the spatial distribution of benthic foraminifera. The middle slope (1050 m deep) is characterized by relatively high foraminiferal density and a predominance of phytodetritus-feeding foraminifera such as Epistominella exigua and Globocassidulina subglobosa. The occurrence of these species seems to reflect the Brazil Current System (BCS). The above-mentioned currents are associated with the relatively high vertical flux of particulate organic matter and the prevalence of sandy sediments, respectively. The lower slope (between 1350 and 1950 m of water depth) is marked by low foraminiferal density and assemblages composed of Bolivina spp. and Brizalina spp., with low particulate organic matter flux values, muddy sediments, and more refractory organic matter. The distribution of this group seems to be related to episodic fluxes of food particles to the seafloor, which are influenced by the BCS at the surface and are deposited under low deep current activity (DWBC).

Submarine slope failures in the Beaufort Sea; Influence of gas hydrate decomposition

NASA Astrophysics Data System (ADS)

Grozic, J. L.; Dallimore, S.

2012-12-01

The continental shelf of the Beaufort Sea is composed of complex of marine and non-marine sequences of clay, silt, and sand. In many areas of the shelf these sediments contain occurrences of ice-bonded permafrost and associated pressure and temperature conditions that are conducive to the occurrence of methane gas hydrates. This complex environment is undergoing dramatic warming, where changes in sea level, ocean bottom temperatures, and geothermal regimes are inducing permafrost thawing and gas hydrate decomposition. Decomposition is inferred to be occurring at the base and top of the gas hydrate stability zone, which will cause sediment weakening and the generation of excess water and free gas. In such settings, the overlying permafrost cap may act as a permeability barrier, which could result in significant excess pore pressures and reduction in sediment stability. The shelf to slope transition is thought to be an area of extensive regional instability with acoustic records indicating there is upwards of 500 km of slumps and glides extending over the entire Beaufort margin. Some of these slide regions are coincident with up-dip limit of the permafrost gas hydrate stability zone. In this paper, a two dimensional model of the Beaufort shelf was constructed to examine the influence of gas hydrate decomposition on slope stability. The model relies on available data on the Beaufort sediments generated from offshore hydrocarbon exploration in the 1980s and 90s, as well as knowledge available from multidisciplinary marine research programs conducted in the outer shelf area. The slope stability model investigates the influence of marine transgression and ocean bottom warming by coupling soil deformation with hydrate dissociation during undrained conditions. By combining mechanical and thermal loading of the sediment, a more accurate indication of slope stability was obtained. The stability analysis results indicate a relatively low factor of safety for the Beaufort

Marine fish community structure and habitat associations on the Canadian Beaufort shelf and slope

NASA Astrophysics Data System (ADS)

Majewski, Andrew R.; Atchison, Sheila; MacPhee, Shannon; Eert, Jane; Niemi, Andrea; Michel, Christine; Reist, James D.

2017-03-01

Marine fishes in the Canadian Beaufort Sea have complex interactions with habitats and prey, and occupy a pivotal position in the food web by transferring energy between lower- and upper-trophic levels, and also within and among habitats (e.g., benthic-pelagic coupling). The distributions, habitat associations, and community structure of most Beaufort Sea marine fishes, however, are unknown thus precluding effective regulatory management of emerging offshore industries in the region (e.g., hydrocarbon development, shipping, and fisheries). Between 2012 and 2014, Fisheries and Oceans Canada conducted the first baseline survey of offshore marine fishes, their habitats, and ecological relationships in the Canadian Beaufort Sea. Benthic trawling was conducted at 45 stations spanning 18-1001 m depths across shelf and slope habitats. Physical oceanographic variables (depth, salinity, temperature, oxygen), biological variables (benthic chlorophyll and integrated water-column chlorophyll) and sediment composition (grain size) were assessed as potential explanatory variables for fish community structure using a non-parametric statistical approach. Selected stations were re-sampled in 2013 and 2014 for a preliminary assessment of inter-annual variability in the fish community. Four distinct fish assemblages were delineated on the Canadian Beaufort Shelf and slope: 1) Nearshore-shelf: <50 m depth, 2) Offshore-shelf: >50 and ≤200 m depths, 3) Upper-slope: ≥200 and ≤500 m depths, and 4) Lower-slope: ≥500 m depths. Depth was the environmental variable that best explained fish community structure, and each species assemblage was spatially associated with distinct aspects of the vertical water mass profile. Significant differences in the fish community from east to west were not detected, and the species composition of the assemblages on the Canadian Beaufort Shelf have not changed substantially over the past decade. This community analysis provides a framework for testing

Nearshore Phytoplankton Production on the Louisiana Continental Shelf

NASA Astrophysics Data System (ADS)

Fung, M.; Lehrter, J. C.

2017-12-01

Net heterotrophy has been observed across much of the Louisiana continental shelf (LCS) where hypoxic conditions occur. Recent studies suggest that cross-shelf transport of nearshore organic matter derived from phytoplankton production subsidizes this heterotrophy. To investigate this theory, we conducted two cruises in spring and summer of 2017 to assess the spatial and temporal patterns of primary production (PP) and respiration (R). We focused on nearshore waters across the area of the shelf where hypoxia is most frequently observed. Overall, PP rates were highest (median = 35 mmol O2 m-3 d-1) in nearshore surface waters (sites with <15 m depth and riverine plume locations), but temporal and spatial differences were seen in both the magnitude of PP and R. Nearshore waters in spring had the highest production rates (median = 52.3 mmol O2 m-3 d-1) and were an order of magnitude greater than production in offshore waters (>15 m depth), while summer production rates in the nearshore and offshore areas were comparable. Similarly, spring nearshore respiration rates (11.2 mmol O2 m-3 d-1) were an order of magnitude larger than offshore, and summer respiration rates in the nearshore and offshore areas were comparable. P/R was greatest nearshore in the spring (4.7) and lowest offshore in the summer (0.9). These results suggest that nearshore production is potentially a significant source of organic matter for the observed heterotrophy over most of the LCS, supporting the theory that shelf-wide hypoxia may be largely driven by nearshore production.

Assessment of tsunami hazard to the U.S. East Coast using relationships between submarine landslides and earthquakes

USGS Publications Warehouse

ten Brink, Uri S.; Lee, H.J.; Geist, E.L.; Twichell, D.

2009-01-01

.S.) must be located offshore and within 100??km of the continental slope to induce a catastrophic slope failure. Thus, a repeat of the 1755 Cape Anne and 1881 Charleston earthquakes are not expected to cause landslides on the continental slope. The observed rate of seismicity offshore the U.S. Atlantic coast is very low with the exception of New England, where some microseismicity is observed. An extrapolation of annual strain rates from the Canadian Atlantic continental margin suggests that the New England margin may experience the equivalent of a magnitude 7 earthquake on average every 600-3000??yr. A minimum triggering earthquake magnitude of 5.5 is suggested for a sufficiently large submarine failure to generate a devastating tsunami and only if the epicenter is located within the continental slope.

Plate tectonics and offshore boundary delimitation: Tunisia-Libya case at the International Court of Justice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stanley, D.J.

1983-03-01

Advances in the technology for exploiting resources of the oceans, particularly recovery of hydrocarbons and minerals in deep water, is benefiting a growing number of nations. At the same time, however, economic and political pressures have induced concern and there is now a much increased emphasis on jurisdiction to divide the offshore areas between the 132 coastal nations. Negotiations affect research operations at sea and, in consequence, marine scientists have been made aware of offshore problems as highlighted by the Law of the Sea Treaty (UNCLOS III) and complications arising from the legal versus scientific definitions of continental shelves andmore » margins. The first major offshore boundary case of international scope where plate tectonics has constituted a significant argument is the one recently brought before the International Court of Justice by Libya and Tunisia concerning the delimitation of their continental shelves. Of the two parties, Libya placed the greatest emphasis on this concept as a means to determine natural prolongation of its land territory into and under the sea. Tunisia contested Libya's use of the whole of the African continental landmass as a reference unit; in Tunisia's view, considerations of geography, geomorphology, and bathymetry are at least as relevant as are those of geology. In its landmark judgment (February 1982) - which almost certainly will have far-reaching consequences in future such boundary delimitation cases - the court pronounced that It is the outcome, not the evolution in the long-distant past, which is of importance, and that it is the present-day configuration of the coasts and sea bed which are the main factors to be considered, not geology.« less

High-resolution seismic-reflection profiles collected aboard R/V James M. Gilliss Cruise GS-7903-3, over the Atlantic Continental Slope and Rise off New England

USGS Publications Warehouse

Bailey, Norman G.; Aaron, John M.

1982-01-01

During June 1979, the U.S. Geological Survey (USGS) collected 4,032 km of single-channel seismic-reflection data from the Atlantic Continental Slope and Rise off New England. The work was conducted aboard R/V JAMES M. GILLISS (cruise GS-7903-3). The purpose of the cruise was to determine the characteristics of mass sediment movement on the Continental Slope, and to study and correlate the stratigraphy of the Jurassic and Cretaceous strata lying north and south of the New England seamount chain.Seismic instrumentation included 40-in3, 160-in3, and 500-in3 airguns; a Teledyne 800-joule minisparker system; a 3-5-kHz to 7-kHz, hull-mounted tunable transducer; and a 7-channel analog tape recorder.Navigation control during the cruise was provided by a Western Integrated Navigation System capable of integrating satellite, rho-rho Loran-C, hyperbolic Loran-C, gyro compass, and doppler speed-log position data. The prime navigation sensor was the rho-rho Loran-C automatically recorded at 20-second intervals and manually plotted every 15 minutes, backed up by hyperbolic Loran-C fixes automatically recorded every 5 minutes.Of the 4,032 km of data collected, 3,257 km of 3-5-kHz, minisparker and 40-in3 airgun were for the sediment-slump studand the other 775 km of 3-5-kHz, minis parker, 160-in3 air gun and 500-in3 airgun were for the deep stratigraphy study. Overall, the quality of the data is excellent with good resolution and penetration.The original data may be examined at the U.S. Geological Survey, Woods Hole, MA 02543. Copies of the data can be purchased only from the National Geophysical and Solar-Terrestrial Data Center, NOAA/EDIS/NGSDC, Code D621, 325 Broadway, Boulder, CO 80303 (303-497-6338).

Thirty-Three Years of Ocean Benthic Warming Along the U.S. Northeast Continental Shelf and Slope: Patterns, Drivers, and Ecological Consequences

NASA Astrophysics Data System (ADS)

Kavanaugh, Maria T.; Rheuban, Jennie E.; Luis, Kelly M. A.; Doney, Scott C.

2017-12-01

The U.S. Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends, and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982 to 2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4°C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid-Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin-scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf, and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally specific ecological processes.

Thirty-Three Years of Ocean Benthic Warming Along the U.S. Northeast Continental Shelf and Slope: Patterns, Drivers, and Ecological Consequences.

PubMed

Kavanaugh, Maria T; Rheuban, Jennie E; Luis, Kelly M A; Doney, Scott C

2017-12-01

The U.S. Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends, and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982 to 2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4°C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid-Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin-scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf, and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally specific ecological processes.

Filling of a Salt-withdrawal Minibasin on the Continental Slope by Turbidity Currents: Experimental study

NASA Astrophysics Data System (ADS)

Violet, J.; Evans, C.; Sheets, B.; Paola, C.; Pratson, L.; Parker, G.

2001-12-01

We report on the transport and deposition of sediment by turbidity currents in an experimental basin designed to model salt-withdrawal minibasins found along the northern continental slope of the Gulf of Mexico. The experiment was performed in two stages in the subsiding EXperimental EarthScape facility (XES) at St. Anthony Falls Laboratory, University of Minnesota. Stage I consisted of 15 turbidity-current events in the following sequence: one 36-minute continuous event, six 1.85-minute small pulses, one 3.8-minute large pulse, six more small pulses, one more large pulse, and finally one more continuous event. The continuous events and the small pulses had a flow discharge of 1.5 liters/s and the large pulse had a flow discharge of 4.5 liters/s. The flows all had a volume concentration of sediment of 0.05. The sediment comprised three grades of silica with nominal diameters of 20 microns (45%), 45 microns (40%) and 110 microns (15%). The basin subsided continuously during Stage I. Stage II consisted of the same sequence of events as Stage I, but with no further subsidence. The sand content was eliminated during the latter part of Stage II. The deposit was imaged as it developed during the experiment using high-frequency sonar. The sonar records show indications of incipient self-channelization as well as clear erosion, bypass, and deposition. Erosion was promoted by large pulse events and the absence of sand. The deposit shows well developed lamination and normal grading.

Turbulent properties under sloping Ice-wall in polar water

NASA Astrophysics Data System (ADS)

Mondal, Mainak; Gayen, Bishakhdatta; Griffiths, Ross W.; Kerr, Ross C.

2017-11-01

Ice-shelves around West Antarctic basins are the most vulnerable to melting in the presence of warmer continental shelf water. A large extent of slope exists under these ice-shelves, where turbulent transport of salt and heat into the ice wall drives a convective melt-water plume against it. Large scale ice-ocean models neglect the effect of convection which can lead to a wrong estimation of melt rate. We perform direct numerical simulations under sloping ice-shelves with realistic ambient conditions. We estimated the melt rates, boundary layer thicknesses and entrainment coefficients as a function of slope angle. The numerical results are further supported by theoretical predictions. Over the range of slope angles, different mechanisms are active for sustaining turbulence. For near vertical case, buoyancy production is the primary source of turbulent kinetic energy whereas for shallower angles turbulence is produced by velocity shear in the meltwater plume. Australian Research Council.

Chemical and textural characteristics of sediments at an EPA reference site for dredged material on the continental slope SW of the Farallon Islands

USGS Publications Warehouse

Bothner, Michael H.; Gill, P.W.; Boothman, W.S.; Taylor, B.B.; Karl, Herman A.

1997-01-01

A U.S. Environmental Protection Agency (EPA) reference site for dredged material has been established on the Continental Slope off San Francisco in water depths of 800-1500 m. This site, 35 km southwest of the Farallon Islands, serves as a reference for sediment testing in support of dredging and disposal at the San Francisco Deep Ocean Disposal Site (SF-DODS). An estimated 300 million cubic yards of dredged material from San Francisco Bay are expected to be discharged at this site during the next 50 years. Information from the reference site provides an additional baseline for monitoring environmental changes at the SF-DODS. This study provides sediment data on a suite of heavy metals and organic compounds which make up the EPA list of "chemicals of concern" because of their potential toxicity to marine organisms.

Sedimentation across the central California oxygen minimum zone: an alternative coastal upwelling sequence.

USGS Publications Warehouse

Vercoutere, T.L.; Mullins, H.T.; McDougall, K.; Thompson, J.B.

1987-01-01

Distribution, abundance, and diversity of terrigenous, authigenous, and biogenous material provide evidence of the effect of bottom currents and oxygen minimum zone (OMZ) on continental slope sedimentation offshore central California. Three major OMZ facies are identified, along the upper and lower edges of OMZ and one at its core.-from Authors

Three Dimensional Underwater Sound Propagation Over Sloping Bottoms

NASA Astrophysics Data System (ADS)

Glegg, Stewart A. L.; Riley, J. M.

This article reviews the work which has been carried out over the past few years on three dimensional underwater sound propagation over sloping bottoms. When sound propagates across a slope three dimensional effects can cause shadow zones and mode cut off effects to occur, which could not be predicted by a two dimensional model. For many years the theory for this type of propagation over realistic ocean floors, which can support both compressional and shear waves, eluded workers in this field. Recently the complete solution for the acoustic field in a "wedge domain with penetrable boundaries" has been developed, and this has allowed for complete understanding of three dimensional bottom interacting sound propagation. These theories have been verified by a series of laboratory scale experiments and excellent agreement has been obtained. However only one full scale ocean experiment has been carried out on three dimensional, bottom interacting, acoustic propagation. This showed significant horizontal refraction of sound propagating across a continental slope and further verifies the importance of bottom slopes on underwater sound propagation.

Wave and setup dynamics on steeply-sloping reefs with large bottom roughness

NASA Astrophysics Data System (ADS)

Buckley, M. L.; Hansen, J.; Lowe, R.

2016-12-01

High-resolution observations from a wave flume were used to investigate the dynamics of wave setup over a steeply-sloping fringing reef profile with the effect of bottom roughness modeled using roughness elements scaled to mimic a coral reef. Results with roughness were compared with smooth bottom runs across sixteen offshore wave and still water level conditions. The time-averaged and depth-integrated force balance was evaluated from observations collected at seventeen locations across the flume, which was found to consist of cross-shore pressure and radiation stress gradients whose sum was balanced by mean quadratic bottom stresses. We found that when radiation stress gradients were calculated from observations of the radiation stress derived from linear wave theory, both wave setdown and setup were under predicted for the majority of wave and water level conditions tested. Inaccuracies in the predicted setdown and setup were improved by including a wave roller model, which provides a correction to the kinetic energy predicted by linear wave theory for breaking waves and produces a spatial delay in the wave forcing that was consistent with the observations. The introduction of roughness had two primary effects. First, the amount of wave energy dissipated during wave breaking was reduced due to frictional wave dissipation that occurred on the reef slope offshore of the breakpoint. Second, offshore directed mean bottom stresses were generated by the interaction of the combined wave-current velocity field with the roughness elements. These two mechanisms acted counter to one another. As a result, setup on the reef flat was comparable (7% mean difference) between corresponding rough and smooth runs. These findings are used to assess prior results from numerical modelling studies of reefs, and also to discuss the broader implications for how steep slopes and large roughness influences setup dynamics for general nearshore systems.

Pacific-North America plate boundary reorganization in response to a change in relative plate motion: Offshore Canada

NASA Astrophysics Data System (ADS)

Rohr, K. M. M.; Tryon, A. J.

2010-06-01

The transition from subduction in Cascadia to the transform Queen Charlotte fault along western Canada is often drawn as a subduction zone, yet recent studies of GPS and earthquake data from northern Vancouver Island are not consistent with that model. In this paper we synthesize seismic reflection and gravity interpretations with microseismicity data in order to test models of (1) microplate subduction and (2) reorganization of the preexisting strike-slip plate boundary. We focus on the critical region of outer Queen Charlotte Sound and the adjacent offshore. On much of the continental shelf, several million years of subsidence above thin crust are a counterindicator for subduction. An undated episode of compression uplifted the southernmost shelf, but subsidence patterns offshore show that recent subduction is unlikely to be responsible. Previously unremarked near-vertical faults and a mix of extensional and compressional faults offshore indicate that strike-slip faulting has been a significant mode of deformation. Seismicity in the last 18 years is dominantly strike-slip and shows large amounts of moment release on the Revere-Dellwood fault and its overlap with the Queen Charlotte fault. The relative plate motion between the Pacific and North American plates rotated clockwise ˜6 Ma and appears to have triggered formation of an evolving array of structures. We suggest that the paleo-Queen Charlotte fault which had defined this continental margin retreated northward as offshore distributed shear and the newly formed Revere Dellwood fault propagated to the northwest.

Sediment Dispersal Within Poverty Bay, Offshore of the Waipaoa River, New Zealand

NASA Astrophysics Data System (ADS)

Harris, C. K.; Bever, A. J.; McNinch, J. E.

2006-12-01

Transport processes change drastically as sediment crosses the boundary between land and sea. As such, developing conceptual or predictive models of transport and deposition for the shoreline and inner continental shelf is critical to understanding source-to-sink sedimentary systems. In shallow coastal areas, sediment dispersal results from both dilute suspensions driven by energetic waves and current shear stresses, and by gravitationally driven flows of fluid muds. The Waipaoa River, on the east coast of the North Island of New Zealand, delivers approximately 15 million tons per year of sediment to Poverty Bay, a small embayment with water depth less than about 25 m. Instruments deployed during the winter storm season of 2006 captured periods of high discharge from the Waipaoa River that were typically associated with energetic waves and winds from the southeast. During these times, instruments deployed at 9 and 14 m water depths recorded high turbidity. Currents measured in Poverty Bay were correlated with wind velocities, but also showed prolonged periods of offshore flow within the bottom boundary layer. Sediment texture throughout much of Poverty Bay is muddy, and thick deposits have occurred during the Holocene, as evidenced by sub-bottom seismics. Short-lived radioisotopes such as ^7Be have not been found on Poverty Bay sediments during our field work, though depocenters have been identified using ^7Be on the continental shelf. This may imply that muds exist there as ephemeral and spatially patchy deposits that may bypass Poverty Bay. Bypassing mechanisms may include offshore dispersal by dilute suspended sediment, and downslope transport of fluid muds. Energetic waves may resuspend sediment, which is then transported out of Poverty Bay by ambient ocean currents. Alternatively, fluid muds may form and transport material downslope and offshore to the continental shelf. Because of the high sediment loads of the Waipaoa River, these fluid muds may be formed by

California State Waters Map Series: offshore of Coal Oil Point, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Cochrane, Guy R.; Golden, Nadine E.; Phillips, Eleyne L.; Ritchie, Andrew C.; Kvitek, Rikk G.; Dieter, Bryan E.; Conrad, James E.; Lorenson, T.D.; Krigsman, Lisa M.; Greene, H. Gary; Endris, Charles A.; Seitz, Gordon G.; Finlayson, David P.; Sliter, Ray W.; Wong, Florence L.; Erdey, Mercedes D.; Gutierrez, Carlos I.; Leifer, Ira; Yoklavich, Mary M.; Draut, Amy E.; Hart, Patrick E.; Hostettler, Frances D.; Peters, Kenneth E.; Kvenvolden, Keith A.; Rosenbauer, Robert J.; Fong, Grace; Johnson, Samuel Y.; Cochran, Susan A.

2014-01-01

In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology. The Offshore of Coal Oil Point map area lies within the central Santa Barbara Channel region of the Southern California Bight. This geologically complex region forms a major biogeographic transition zone, separating the cold-temperate Oregonian province north of Point Conception from the warm-temperate California province to the south. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and geodetic studies indicate that the region is presently undergoing north-south shortening. Uplift rates (as much as 2.0 mm/yr) that are based on studies of onland marine terraces provide further evidence of significant shortening. The cities of Goleta and Isla Vista, the main population centers in the map area, are in the western part of a contiguous urban area that extends eastward through Santa Barbara to Carpinteria. This urban area is on the south flank of the east-west-trending Santa Ynez Mountains, on coalescing alluvial fans and uplifted marine terraces underlain by folded and

Megabenthic assemblages in the continental shelf edge and upper slope of the Menorca Channel, Western Mediterranean Sea

NASA Astrophysics Data System (ADS)

Grinyó, Jordi; Gori, Andrea; Greenacre, Michael; Requena, Susana; Canepa, Antonio; Lo Iacono, Claudio; Ambroso, Stefano; Purroy, Ariadna; Gili, Josep-Maria

2018-03-01

Highly diverse megabenthic assemblages dominated by passive and active suspension feeders have been recently reported in shelf edge environments of the Mediterranean Sea. Due to their frequent association with species of commercial interest, these assemblages have been heavily impacted by fishing. The vulnerability and low resilience of these assemblages, composed mainly by long-living and slow-growing species, have motivated the implementation of management measures such as the restriction of bottom trawling, and the establishment of large protected areas embracing these environments. The Menorca Channel is one of such areas recently included in the European Union Natura 2000 network. Quantitative analysis of video transects recorded at 95-360 m depth by manned submersible and remotely operated vehicles were used to characterize megabenthic assemblages and to assess their geographical and bathymetric distribution. Six different assemblages were identified, mainly segregated by substrate type and depth. Hard substrates hosted coral gardens and sponge grounds, whereas soft sediments were mainly characterized by large extensions of the crinoid Leptometra phalangium and the brachiopod Gryphus vitreus. The good preservation of most of the observed assemblages is probably related to a low bottom trawling pressure, which mainly concentrates deeper on the adjacent continental slope. Because of their biological and ecological value, management and conservation measures need to be established to preserve these benthic assemblages.

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.

WHISPERS Project on the easternmost slope of the Ross Sea (Antarctica): preliminary results.

NASA Astrophysics Data System (ADS)

Olivo, E.; De Santis, L.; Bergamasco, A.; Colleoni, F.; Gales, J. A.; Florindo-Lopez, C.; Kim, S.; Kovacevic, V.; Rebesco, M.

2017-12-01

The advance and retreat of the West Antarctic Ice Sheet from the outer continental shelf and the oceanic circulation are the main causes of the depositional processes on the Ross Sea continental slope, at present time and during the most of the Cenozoic. Currently the Antarctic Bottom Water formation is directly linked to the relatively warm Circumpolar Deep Water that, encroaching the continental shelf, mixes with the colder Ross Sea Bottom Water. Detailed multibeam and geological surveys useful to locate and characterize peculiar morphological structures on the bottom are essential to study how the glacial and oceanographic processes interact with the seabed sediments. In the framework of the PNRA-WHISPERS project (XXXIIth Italian Antarctic expedition - January/March 2017), new multibeam bathymetric, sub-bottom chirp, were acquired from the easternmost margin of the Ross Sea, on the southeastern side of the Hayes Bank, usually covered by sea ice. We observed on the upper slope erosional features (incised gullies of likely glacial meltwater origin). A broad scar in the upper slope is characterized by an elongated SSW-NNE ridge (10 km long, 850-1200 m water depth, 2 km wide), that may be a remnants of previous glacial or debris flow deposits, eroded by meltwater outwash discharge at the beginning of grounding ice retreat and by RSBW cascading along the slope, as documented by Expandable Bathy-Thermograph and Acoustic Depth Current Profile data. Sub-bottom chirp profiles crossing this ridge show a very low amplitude reflective sea bed, supporting the hypothesis of its soft sediment nature, in good agreement with a very low acoustic velocity obtained by multichannel seismic data reprocessing. The occurrence of internal stratification on 2D multichannel seismic profiles would discount a gas-fluids related mud volcano origin. No sediment cores were collected, due to bad sea conditions and limited ship time, further data collection would be needed to fully understand

Ocean Drilling Program Leg 178 (Antarctic Peninsula): Sedimentology of glacially influenced continental margin topsets and foresets

USGS Publications Warehouse

Eyles, N.; Daniels, J.; Osterman, L.E.; Januszczak, N.

2001-01-01

Ocean Drilling Program Leg 178 (February-April 1998) drilled two sites (Sites 1097 and 1103) on the outer Antarctic Peninsula Pacific continental shelf. Recovered strata are no older than late Miocene or early Pliocene (<4.6 Ma). Recovery at shallow depths in loosely consolidated and iceberg-turbated bouldery sediment was poor but improved with increasing depth and consolidation to allow description of lithofacies and biofacies and interpretation of depositional environment. Site 1097 lies on the outer shelf within Marguerite Trough which is a major outlet for ice expanding seaward from the Antarctic Peninsula and reached a maximum depth drilled of 436.6 m below the sea floor (mbsf). Seismic stratigraphic data show flat-lying upper strata resting on strata that dip gently seaward. Uppermost strata, to a depth of 150 mbsf, were poorly recovered, but data suggest they consist of diamictites containing reworked and abraded marine microfauna. This interval is interpreted as having been deposited largely as till produced by subglacial cannibalization of marine sediments (deformation till) recording ice sheet expansion across the shelf. Underlying gently dipping strata show massive, stratified and graded diamictite facies with common bioturbation and slump stuctures that are interbedded with laminated and massive mudstones with dropstones. The succession contains a well-preserved in situ marine microfauna typical of open marine and proglacial marine environments. The lower gently dipping succession at Site 1097 is interpreted as a complex of sediment gravity flows formed of poorly sorted glacial debris. Site 1103 was drilled in that part of the continental margin that shows uppermost flat-lying continental shelf topsets overlying steeper dipping slope foresets seaward of a structural mid-shelf high. Drilling reached a depth of 363 mbsf with good recovery in steeply dipping continental slope foreset strata. Foreset strata are dominated by massive and chaotically

A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin

DOE PAGES

Archer, D.

2014-06-03

A two-dimensional model of a passive continental margin was adapted to the simulation of the methane cycle on Siberian continental shelf and slope, attempting to account for the impacts of glacial/interglacial cycles in sea level, alternately exposing the continental shelf to freezing conditions with deep permafrost formation during glacial times, and immersion in the ocean in interglacial times. The model is used to gauge the impact of the glacial cycles, and potential anthropogenic warming in the deep future, on the atmospheric methane emission flux, and the sensitivities of that flux to processes such as permafrost formation and terrestrial organic carbonmore » (Yedoma) deposition. Hydrological forcing drives a freshening and ventilation of pore waters in areas exposed to the atmosphere, which is not quickly reversed by invasion of seawater upon submergence, since there is no analogous saltwater pump. This hydrological pump changes the salinity enough to affect the stability of permafrost and methane hydrates on the shelf. Permafrost formation inhibits bubble transport through the sediment column, by construction in the model. The impact of permafrost on the methane budget is to replace the bubble flux by offshore groundwater flow containing dissolved methane, rather than accumulating methane for catastrophic release when the permafrost seal fails during warming. By far the largest impact of the glacial/interglacial cycles on the atmospheric methane flux is attenuation by dissolution of bubbles in the ocean when sea level is high. Methane emissions are highest during the regression (soil freezing) part of the cycle, rather than during transgression (thawing). The model-predicted methane flux to the atmosphere in response to a warming climate is small, relative to the global methane production rate, because of the ongoing flooding of the continental shelf. A slight increase due to warming could be completely counteracted by sea level rise on geologic time

77 FR 1019 - Renewable Energy Alternate Uses of Existing Facilities on the Outer Continental Shelf-Acquire a...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-09

...-0045] RIN 1010-AD79 Renewable Energy Alternate Uses of Existing Facilities on the Outer Continental... rule related to acquiring a lease non-competitively for offshore renewable energy projects. DATES... or Timothy Redding, Renewable Energy, BOEM, at (703) 787-1219 or email [email protected

77 FR 74512 - Interim Policy Leasing for Renewable Energy Data Collection Facility on the Outer Continental...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-12-14

... Policy Leasing for Renewable Energy Data Collection Facility on the Outer Continental Shelf off the Coast..., tribes, local governments, and the public in the preparation of an EA. The EA will consider the environmental consequences associated with issuing a lease for an offshore data collection facility located on...

Bottom trawling and oxygen minimum zone influences on continental slope benthic community structure off Vancouver Island (NE Pacific)

NASA Astrophysics Data System (ADS)

De Leo, Fabio C.; Gauthier, Maéva; Nephin, Jessica; Mihály, Steven; Juniper, S. Kim

2017-03-01

Understanding responses of benthic ecosystems to cumulative impacts of natural stressors, long-term ocean change and increasing resource exploitation is an emerging area of interest for marine ecologists and environmental managers. Few, if any, studies have quantitatively addressed cumulative effects in the deep sea. We report here on a study from the continental slope off Vancouver Island (Canada) in the northeast Pacific Ocean, where the Oxygen Minimum Zone impinges on seabed habitats that are subjected to widespread bottom trawling, primarily by the fishery for thornyhead (Sebastolobus ssp.). We examined how the benthic megafauna in this area was influenced by varying levels of dissolved oxygen and trawling activity, along a depth gradient that was also likely to shape community composition. Continuous video and sonar records from two ROV surveys (50 linear km total; depth range 300-1400 m) respectively provided data on faunal attributes (composition, abundance and diversity) and the frequency of trawl door marks on the seabed. Faunal and trawl data were compiled in a geo-referenced database along with corresponding dissolved oxygen data, and pooled into 500 m segments for statistical analysis. Trawl mark occurrence peaked between 500 and 1100 m, corresponding to areas of slope subjected to hypoxia (<1.4 ml l-1) and severe hypoxia (<0.5 ml l-1). A combined total of 266,251 megafauna organisms from 87 taxa were enumerated in the two transects. Significant megafaunal assemblages according to depth, trawling intensity and bottom water dissolved oxygen concentration were identified by PERMANOVA analyses, with characterizing taxa identified for all three factors. Depth, dissolved oxygen and trawl mark density accounted for 21% to 52% of the variability in benthic community structure according to multiple regression (DISTLM) models. Species richness was highest at intermediate depths and in areas subject to intermediate levels of trawling, and higher under hypoxia

Geologic evolution and sequence stratigraphy of the offshore Pelotas Basin, southeast Brazil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abreu, V.S.

1996-01-01

The Brazilian marginal basins have been studied since the beginning of the 70s. At least nine large basins are distributed along the entire Eastern continental margin. The sedimentary infill of these basins consists of lower Cretaceous (continental/lacustrine) rift section underlying marine upper Cretaceous (carbonate platforms) and marine upper Cretaceous/Tertiary sections, corresponding to the drift phase. The sedimentary deposits are a direct result of the Jurassic to lower Cretaceous break-up of the Pangea. This study will focus on the geologic evolution and sequence stratigraphic analysis of the Pelotas basin (offshore), located in the Southeast portion of the Brazilian continental margin betweenmore » 28[degrees] and 34[degrees] S, covering approximately 50,000 Km[sup 2]. During the early Cretaceous, when the break-up of the continent began in the south, thick basaltic layers were deposited in the Pelotas basin. These basalts form a thick and broad wedge of dipping seaward reflections interpreted as a transitional crust. During Albian to Turonian times, due to thermal subsidence, an extensive clastic/carbonate platform was developed, in an early drift stage. The sedimentation from the upper Cretaceous to Tertiary was characterized by a predominance of siliciclastics in the southeast margin, marking an accentuate deepening of the basin, showing several cycles related to eustatic fluctuations. Studies have addressed the problems of hydrocarbon exploration in deep water setting within a sequence stratigraphic framework. Thus Pelotas basin can provide a useful analogue for exploration efforts worldwide in offshore passive margins.« less

Geologic evolution and sequence stratigraphy of the offshore Pelotas Basin, southeast Brazil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Abreu, V.S.

1996-12-31

The Brazilian marginal basins have been studied since the beginning of the 70s. At least nine large basins are distributed along the entire Eastern continental margin. The sedimentary infill of these basins consists of lower Cretaceous (continental/lacustrine) rift section underlying marine upper Cretaceous (carbonate platforms) and marine upper Cretaceous/Tertiary sections, corresponding to the drift phase. The sedimentary deposits are a direct result of the Jurassic to lower Cretaceous break-up of the Pangea. This study will focus on the geologic evolution and sequence stratigraphic analysis of the Pelotas basin (offshore), located in the Southeast portion of the Brazilian continental margin betweenmore » 28{degrees} and 34{degrees} S, covering approximately 50,000 Km{sup 2}. During the early Cretaceous, when the break-up of the continent began in the south, thick basaltic layers were deposited in the Pelotas basin. These basalts form a thick and broad wedge of dipping seaward reflections interpreted as a transitional crust. During Albian to Turonian times, due to thermal subsidence, an extensive clastic/carbonate platform was developed, in an early drift stage. The sedimentation from the upper Cretaceous to Tertiary was characterized by a predominance of siliciclastics in the southeast margin, marking an accentuate deepening of the basin, showing several cycles related to eustatic fluctuations. Studies have addressed the problems of hydrocarbon exploration in deep water setting within a sequence stratigraphic framework. Thus Pelotas basin can provide a useful analogue for exploration efforts worldwide in offshore passive margins.« less

Sloping fan travertine, Belen, New Mexico, USA

NASA Astrophysics Data System (ADS)

Cook, Megan; Chafetz, Henry S.

2017-05-01

Pliocene to Quaternary age travertines are very well-exposed in quarries near Belen, New Mexico, U.S.A., on the western edge of the Rio Grande Rift system. A series of hillside springs produced travertine tongues tens of meters thick and hundreds of meters long. The accumulations represent deposits from individual springs as well as the amalgamation of deposits. The overall architecture is predominantly composed of sloping fans with a smaller component of terrace mounds. The sloping fan deposits commonly have a dip of < 10°, however, they range from horizontal to near vertical. Individual strata display significant changes in depositional dip, beds pinch and swell, and some are completely truncated. Centimeter to meter scale terrace mounds exhibit the common stair-step morphology. As a consequence of vertical accretion in the pools, terrace mounds morphed into sloping fans. The travertine is composed of a variety of commonly reported constituents, i.e., centimeter thick laminae of bacterial shrubs and oncoids, foam rock, sheets and rafts, and finely crystalline crusts that occur throughout the sloping fan and terrace mound accumulations. Sheets and rafts formed as precipitates in pools on the surfaces of the fans and terraces as well as spelean deposits on the water surfaces of pools within cavities in the overall accumulation. Thus, the spelean rafts provide valuable indicators of original horizontality in the sloping fan strata. In addition, intraformational breccias, composed of locally torn-up travertine intraclastic boulders and deposited in with other travertine, and extraformational breccias, composed of torn-up travertine intraclasts mixed with siliciclastic fines and sand and Paleozoic limestone clasts transported downslope from higher on the hillside, are a common constituent in the sloping fan accumulation. The Belen travertines provide a very well-exposed example of sloping fan travertines and may provide relevant data with regard to the subsurface

Structure and geomorphology of the "big bend" in the Hosgri-San Gregorio fault system, offshore of Big Sur, central California

NASA Astrophysics Data System (ADS)

Johnson, S. Y.; Watt, J. T.; Hartwell, S. R.; Kluesner, J. W.; Dartnell, P.

2015-12-01

The right-lateral Hosgri-San Gregorio fault system extends mainly offshore for about 400 km along the central California coast and is a major structure in the distributed transform margin of western North America. We recently mapped a poorly known 64-km-long section of the Hosgri fault offshore Big Sur between Ragged Point and Pfieffer Point using high-resolution bathymetry, tightly spaced single-channel seismic-reflection and coincident marine magnetic profiles, and reprocessed industry multichannel seismic-reflection data. Regionally, this part of the Hosgri-San Gregorio fault system has a markedly more westerly trend (by 10° to 15°) than parts farther north and south, and thus represents a transpressional "big bend." Through this "big bend," the fault zone is never more than 6 km from the shoreline and is a primary control on the dramatic coastal geomorphology that includes high coastal cliffs, a narrow (2- to 8-km-wide) continental shelf, a sharp shelfbreak, and a steep (as much as 17°) continental slope incised by submarine canyons and gullies. Depth-converted industry seismic data suggest that the Hosgri fault dips steeply to the northeast and forms the eastern boundary of the asymmetric (deeper to the east) Sur Basin. Structural relief on Franciscan basement across the Hosgri fault is about 2.8 km. Locally, we recognize five discrete "sections" of the Hosgri fault based on fault trend, shallow structure (e.g., disruption of young sediments), seafloor geomorphology, and coincidence with high-amplitude magnetic anomalies sourced by ultramafic rocks in the Franciscan Complex. From south to north, section lengths and trends are as follows: (1) 17 km, 312°; (2) 10 km, 322°; (3)13 km, 317°; (4) 3 km, 329°; (5) 21 km, 318°. Through these sections, the Hosgri surface trace includes several right steps that vary from a few hundred meters to about 1 km wide, none wide enough to provide a barrier to continuous earthquake rupture.

Nepheloid Layers: Origin and Development In A Narrow Continental Shelf (nw Portugal)

NASA Astrophysics Data System (ADS)

Oliveira, A.; Vitorino, J.; Rodrigues, A.; Jouanneau, J. M.; Weber, O.; Dias, J. A.

A general hydrographic, nephelometric and sedimentological surveying of the NW Portuguese continental shelf and slope was undertaken, under winter and spring con- ditions in order to elaborate a conceptual model of suspended sediments (nepheloid layer) dynamics. Two major situations were found: 1) Spring/Summer - with northerly winds (upwelling) and low energetic wave regime that favour the deposition of sedi- ments. The northerly winds promote offshore transport in the surface nepheloid layer (SNL) and the establishment of a seasonal thermocline allow the expansion of the SNL to the west. The SNL can reach or even cross the shelf-break (50 km from coastline). Particulate organic carbon (POC) content in this layer highlights the higher contribution of biogenic particles (average concentration of 22%); 2) Winter, with southerly winds (downwelling) and high energetic wave regime that favour mid- shelf sediments resuspension and offshore transport in the bottom nepheloid layer (BNL). In the shelf-break the BNL detached to form intermediate nepheloid layers (INL). The SNL is restricted to the inner shelf. The effect of southerly winds gener- ates shoreward Ekman transport and detains the offshore westward extension of this layer even during high river run-off periods. The POC content indicates a dominance of litogenic particles in suspension (average concentration of 8%). Over the mid- and inner-shelf the dominant resuspension mechanism is associated with surface waves (Vitorino et al., 2002). Estimates based on wave measurements at mid-shelf (86m depth) suggested that, in winter, the wave shear velocity frequently exceeds 1 cm/s, assumed as the critical shear velocity for the resuspension of the fine grained sedi- ments (34m) of the bottom cover. Storm events, such as the one observed in November 1996 easily increase the wave shear velocities over 3 cm/s, leading to the increase of the BNL thickness (20-30m) (Vitorino et al., 2002; Oliveira et al., 2002). Low

A multi-factor approach for process-based seabed characterization: example from the northeastern continental margin of the Korean peninsula (East Sea)

NASA Astrophysics Data System (ADS)

Cukur, Deniz; Um, In-Kwon; Chun, Jong-Hwa; Kim, So-Ra; Lee, Gwang-Soo; Kim, Yuri; Kong, Gee-Soo; Horozal, Senay; Kim, Seong-Pil

2018-04-01

This study investigates sediment transport and depositional processes from a newly collected dataset comprising sub-bottom chirp profiles, multibeam bathymetry, and sediment cores from the northeastern continental margin of Korea in the East Sea (Japan Sea). Twelve echo-types and eleven sedimentary facies have been defined and interpreted as deposits formed by shallow-marine, hemipelagic sedimentation, bottom current, and mass-movement processes. Hemipelagic sedimentation, which is acoustically characterized by undisturbed layered sediments, appears to have been the primary sedimentary process throughout the study area. The inner and outer continental shelf (<150 m water depth) have been influenced by shallow-marine sedimentary processes. Two slope-parallel canyons, 0.2-2 km wide and up to 30 km long, appear to have acted as possible conduits for turbidity currents from the shallower shelf into the deep basins. Bottom current deposits, expressed as erosional moats immediately below topographic highs, are prevalent on the southern lower slope at water depths of 400-450 m. Mass-movements (i.e., slides/slumps, debris flow deposits) consisting of chaotic facies characterize the lower slope and represent one of the most important sedimentary processes in the study area. Piston cores confirm the presence of mass-transport deposits (MTDs) that are characterized by mud clasts of variable size, shape, and color. Multibeam bathymetry shows that large-scale MTDs are chiefly initiated on the lower slope (400-600 m) with gradients up to 3° and where they produce scarps on the order of 100 m in height. Sandy MTDs also occur on the upper continental slope adjacent to the seaward edge of the shelf terrace. Earthquakes associated with tectonic activity and the development of fluid overpressure is considered as the main conditioning factor for destabilizing the slope sediments. Overall, the sedimentary processes show typical characteristics of a fine-grained clastic slope apron and

Geohistory analysis of the Santa Maria basin, California, and its relationship to tectonic evolution of the continental margin

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCrory, P.A.; Arends, R.G.; Ingle, J.C. Jr.

1991-02-01

The Santa Maria basin of central California is a geologically complex area located along the tectonically active California continental margin. The record of Cenozoic tectonism preserved in Santa Maria strata provides an opportunity to compare the evolution of the region with plate tectonic models for Cenozoic interactions along the margin. Geohistory analysis of Neogene Santa Maria basin strata provides important constraints for hypotheses of the tectonic evolution of the central California margin during its transition from a convergent to a transform plate boundary. Preliminary analyses suggest that the tectonic evolution of the Santa Maria area was dominated by coupling betweenmore » adjacent oceanic plates and the continental margin. This coupling is reflected in the timing of major hiatuses within the basin sedimentary sequence and margin subsidence and uplift which occurred during periods of tectonic plate adjustment. Stratigraphic evidence indicates that the Santa Maria basin originated on the continental shelf in early Miocene time. A component of margin subsidence is postulated to have been caused by cessation of spreading on adjacent offshore microplates approximately 19-18 ma. A sharp reduction in rate of tectonic subsidence in middle Miocene time, observed in the Santa Maria basin both onshore and offshore, was coeval with rotation of crustal blocks as major shearing shifts shoreward. Tectonic uplift of two eastern sites, offshore Point Arguello and near Point Sal, in the late Miocene may have been related to a change to transpressional motion between the Pacific and North American plates, as well as to rotation of the western Transverse Ranges in a restraining geometry.« less

76 FR 20367 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Off Delaware...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-12

... No. BOEM-2011-0008] Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Off... determination that no competitive interest exists in acquiring a commercial wind lease in the area offshore... a Request for Interest (RFI) in the Federal Register on April 26, 2010 (75 FR 21653). Bluewater Wind...

Holistic Approach Offers Potential to Quantify Mass Fluxes Across Continental Margins

NASA Astrophysics Data System (ADS)

Kuehl, Steven; Carter, Lionel; Gomez, Basil; Trustrum, Noel

Most humans live on and utilize the continental margin, the surface of which changes continually in response to environmental perturbations such as weather, climate change, tectonism, earthquakes, volcanism, sea level, and human settlement and land use. Part of the margin is above sea level and the rest is submarine, but these land and seascape components are contiguous, and material transport from source to sink occurs as a seamless cascade. The margin responds to environmental perturbations by changing the nature and magnitude of a variety of important functions, including the distribution of soil formation and erosion; biogeochemical functioning (especially the storage and release of water, limiting nutrients and contaminants); and the form and behavior of geomorphic components from hill slopes and floodplains through the coastal zone to the continental rise. While some areas of the margin are eroding-for example, hill slopes-others accumulate sediment, such as tectonic basins and continental slope and rise. These areas record the history of surface changes. A major goal of the Earth science community is to provide quantitative explanations and predictions of the effects of environmental perturbations on surface changes and preserved sedimentary strata of continental margins. In past decades, margins have been investigated piecemeal by researchers who have tended to focus on a particular segment from one disciplinary perspective while eschewing the broader perspective of the margin as an interconnected whole. Recognizing this shortcoming, the U.S. National Science Foundation (NSF) has initiated the MARGINS Source-to-Sink (S2S) program, which, for the first time, will attempt to understand the functioning of entire margin systems through dedicated observational and community modeling studies. Following input from the Earth science community, the Waipaoa Sedimentary System (WSS) of the North Island, New Zealand, was chosen as one of the focus sites for possible

P-wave velocity model of mud volcano on the continental slope of the Canadian Beaufort Sea from frequency-domain full waveform inversion

NASA Astrophysics Data System (ADS)

Jang, U. G.; Kang, S. G.; Hong, J. K.; Jin, Y. K.; Dallimore, S.; Riedel, M.; Paull, C. K.

2017-12-01

2014 Expedition ARA05C was a multidisciplinary undertaking conducted in the Canadian Beaufort Sea, Arctic Ocean on the Korean ice breaker IBRV ARAON from August 30 to September 19, 2014. The program was carried out as collaboration between the Korea Polar Research Institute (KOPRI), Geological Survey of Canada (GSC), Monterey Bay Aquarium Research Institute (MBARI), Department of Fisheries and Ocean (DFO) with participation by Bremen University (BARUM). During this expedition, multi-channel seismic (MCS) data were acquired on the outer continental shelf and upper slope of the Canadian Beaufort Sea, totaling 20 lines with 1,000 line-kilometers from September 1 to September 13, 2014. Three MCS survey lines was designed to cross the three submarine mud volcanoes found in the slope at approximate water depth of 290 m, 460 m and 740 m. Submarine mud volcanoes are seafloor structures with positive topography formed by a combination of mud eruption, gas emission, and water seepage from the subsurface. MCS data will allow image subsurface structures of mud volcanoes as identification of fluid migration pathways, however, imaging its subsurface structure is difficult by using conventional seismic data processing procedure, because it is seismically characterized by acoustically transparent facies. Full waveform inversion (FWI) is non-linear data-fitting procedure to estimate the physical properties of the subsurface by minimizing the difference between the observed and modelled data. FWI uses the two-wave wave equation to compute forward/backward wavefield to calculate the gradient direction, therefore it can derive more detailed velocity model beyond travel-time tomography techniques, which use only the kinematics of seismic data, by additional information provided by the amplitude and phase of the seismic waveform. In this study, we suggest P-wave structure of mud volcanos, which were inverted by 2D acoustic FWI. It will be useful to understand the characterization of mud

Summary of IODP Expedition 344, CRISP-A2, offshore the Osa Peninsula, Costa Rica

NASA Astrophysics Data System (ADS)

Harris, R. N.; Sakaguchi, A.; Petronotis, K. E.

2013-12-01

The Costa Rica Seismogenesis Project (CRISP) is designed to elucidate the processes that control nucleation and seismic rupture of large earthquakes at erosional subduction zones. The CRISP study area is located offshore the Osa Peninsula where the incoming Cocos Ridge has lifted the seismogenic zone to within reach of scientific drilling. The incoming plate is characterized by low sediment supply, a fast convergence rate, abundant plate interface seismicity, and a change in subducting plate relief along strike. In addition to elucidating processes at erosional convergent margins, this project is complementary to other IODP deep fault drilling projects (e.g., NanTroSEIZE and J-FAST). Expedition 344 (23 October - 11 December, 2012) is the second expedition of CRISP Program A (Integrated Ocean Drilling Program Proposal 537A-Full5) that focused on the shallow lithologic, hydrologic, stress, and thermal conditions that lead to unstable slip in the seismogenic zone. With the exception of not reaching the décollement and the underthrust sediment at the toe site (U1412), Expedition 344 exceeded expectations. Material was recovered from the incoming Cocos plate (Sites U1381 and U1414), the toe of the margin (Site U1412), the mid-slope region (Site U1380), and the upper-slope region (Site U1413). Input sites U1381 and U1414 are characterized by anomalously high heat flow and the flow of fluids. These sites contained abundant ash that will be used to assess the impact of Cocos Ridge subduction on the evolution of the Central American volcanic arc. Although toe Site U1412 did not cross the décollement we did penetrate terrigenous sediments interrupted by a Miocene ooze that may reflect accretion of a frontal prism sliver. Mid-slope Site U1380 yielded a major result in that the upper plate material is not a mélange of oceanic material or the offshore extension of the Caribbean large igneous complex, but forearc basin material consisting of lithic sedimentary units. Upper-slope

77 FR 27054 - Notice of Approval of Clean Air Act Outer Continental Shelf Permits Issued to Shell Offshore, Inc...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-05-08

... Shelf Permits Issued to Shell Offshore, Inc. for the Kulluk Conical Drilling Unit AGENCY: United States... (OCS) permit to construct and Title V air quality operating permit to Shell Offshore, Inc. (``Shell'') for operation of the Kulluk conical drilling unit in the Beaufort Sea off the north coast of Alaska...

Work, eat and sleep: towards a healthy ageing at work program offshore.

PubMed

Riethmeister, Vanessa; Brouwer, Sandra; van der Klink, Jac; Bültmann, Ute

2016-02-09

Health management tools need to be developed to foster healthy ageing at work and sustain employability of ageing work-forces. The objectives of this study were to 1) perform a needs assessment to identify the needs of offshore workers in the Dutch Continental Shelf with regard to healthy ageing at work and 2) to define suitable program objectives for a future healthy ageing at work program in the offshore working population. A mixed methods design was used applying an intervention mapping procedure. Qualitative data were gathered in N = 19 semi-structured interviews and six focus-group sessions (N = 49). Qualitative data were used to develop a questionnaire, which was administered among N = 450 offshore workers. Subgroup analyses were performed to investigate age-related differences relating to health status and work-related factors. The importance of good working environments, food, as well as sleep/fatigue management was identified by the qualitative data analysis. A total of 260 offshore workers completed the questionnaire. Significant differences in work ability were found between offshore workers aged <45 and 45-54 years (mean 8.63 vs. 8.19; p = 0.005) and offshore workers aged <45 and >55 years (mean 8.63 vs. 8.22; p = 0.028). Offshore workers had a high BMI (M = 27.06, SD = 3.67), with 46 % classified as overweight (BMI 25-30) and 21 % classified as obese (BMI >30). A significant difference in BMI was found between offshore workers aged <45 and ≥55 years (mean 26.3 vs. 28.6; p <0.001). In total, 73 % of offshore workers reported prolonged fatigue. A significant difference in fatigue scores was found between offshore workers aged <45 and ≥55 years (mean 36.0 vs. 37.6; p = 0.024). Further, a "dip" was reported by 41 % of offshore workers. Dips were mainly experienced at day 10 or 11 (60 %), with 45 % experiencing the dip both as physical and mental fatigue, whereas 39 % experienced the dip as only mental fatigue. Both qualitative and quantitative analyses

Revised oil-spill risk analysis: Beaufort Sea outer continental shelf lease sale 170. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, C.; Johnson, W.; Marshall, C.

1997-11-01

The Federal Government has proposed to offer Outer Continental Shelf lands in the Beaufort Sea for oil and gas leasing. Because oil spills may occur from activities associated with offshore oil production, the Minerals Management Service conducts a formal risk assessment. This report summarizes results of oil-spill risk analysis conducted for the proposed Beaufort Sea lease sale.

Gas hydrates of outer continental margins

DOE Office of Scientific and Technical Information (OSTI.GOV)

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 ofmore » 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.« less

Characterization of H/V Spectral Ratios for the Assessment of Slope Stability in the Gas Hydrate-rich Area: an Example from Offshore SW Taiwan

NASA Astrophysics Data System (ADS)

Lin, J. Y.; Tsia, C. H.; Cheng, W. B.; Chin, S. J.; Lin, S. S.; Liang, C. W.

2015-12-01

The Nakamura's method, which calculates the ratios between horizontal and vertical component spectra of seismic signals (H/V), is widely used in the inland area. However, few related estimations were performed for the offshore area and little knowledge for the marine sediments were obtained. From 2013 to 2015, three passive ocean bottom seismometer (OBS) experiments were conducted in gas hydrate-rich area offshore SW Taiwan in the aim of acquiring information related to the physical properties of seafloor sediments. The H/V of the seafloor sediments in the three areas were estimated by using the ambient noise and seismic signal recorded by OBSs. The resonance frequency of each site was estimated from the main peak of H/V distribution and a range between 5 and 10 Hz were obtained. Based on the empirical law, this resonance frequency range should correspond to a sediment thickness of approximately several to ten of meters. This estimation is consistent with the thickness of the sedimentary cover imaged by chirp sonar survey, suggesting that the site response of seafloor is dominantly controlled by the unconsolidated sedimentary layer on the top of the sea bed. Remarkably, the H/V ratios obtained in our study area are much larger than that calculated for the inland areas. The magnification can reach as high as 50 to more than 100. This observation infers that the sea water movement might emphasize the horizontal motion of the marine sediments, which is crucial for the slope stability assessment. Moreover, for most stations located in the active margin, no distinct peak is observed for the H/V pattern calculated during earthquakes. However, in the passive margin, the H/V peak calculated from ambient noise and earthquakes is mostly identical. This phenomenon may suggest that relatively unclear sedimentary boundary exist in the active margin environment. Estimating H/V spectral ratios of data recorded by the OBSs deployed in the southwest Taiwan offshore area offers a

Heat Content and Ice Draft Variability over the Slope of the Chukchi Sea from 2016-2017 Ocean Moorings

NASA Astrophysics Data System (ADS)

Muenchow, A.; Ryan, P. A.; Badiey, M.; Elmer, C.; Eickmeier, J.

2017-12-01

The shallow-water component of the Canada Basin Acoustic Propagation Experiment (CANAPE) will quantify how ocean properties vary at daily to seasonal time scales over the outer continental shelf of the Chukchi Sea. We here describe initial results related to a weak sound channel above warm Atlantic and below seasonally modulated surface waters. It coincides with the cold halocline layer that often slopes up- or downward at the edge of the continental shelf in response to surface forcing. Sloping topography supports isopycnal oscillations whose time scales vary from hours to months. These Kelvin or Rossby waves will become more pronounced in a increasingly dynamic, wind-forced Arctic Ocean with a diminished, thinner, and more mobile ice cover.

30 CFR 250.224 - What information on support vessels, offshore vehicles, and aircraft you will use must accompany...

Code of Federal Regulations, 2011 CFR

2011-07-01

... 30 Mineral Resources 2 2011-07-01 2011-07-01 false What information on support vessels, offshore vehicles, and aircraft you will use must accompany the EP? 250.224 Section 250.224 Mineral Resources BUREAU... GAS AND SULPHUR OPERATIONS IN THE OUTER CONTINENTAL SHELF Plans and Information Contents of...

77 FR 39164 - Safety Zone; KULLUK, Outer Continental Shelf Mobile Offshore Drilling Unit (MODU), Beaufort Sea, AK

Federal Register 2010, 2011, 2012, 2013, 2014

2012-07-02

... sensitivity of the environmental and subsistence importance to the indigenous population; (4) the lack of any... Outer Continental Shelf Lands Act and 33 C.F.R 147. Accordingly, State and Local law enforcement... due to the location of the MODU KULLUK on the Outer Continental Shelf and its distance from both land...

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.

Submarine canyon formation and evolution in the Argentine Continental Margin between 44°30'S and 48°S

NASA Astrophysics Data System (ADS)

Lastras, G.; Acosta, J.; Muñoz, A.; Canals, M.

2011-05-01

In the framework of the Vulnerable Marine Ecosystems (VME) of the High Seas of the South West Atlantic, large areas of the Argentine Continental Margin (ACM) between 44°30'S and 48°S have been swath-mapped for the first time, obtaining full data coverage of the seafloor in this region between the outermost continental shelf and the middle slope down to 1600 m water depth. The slope is characterized by the presence of smooth terraces (Nagera, Perito Moreno and Piedra Buena) that widen towards the south, limited by morphological steps with evident signs of erosion in the form of scours. These terraces form part of the Argentine contourite depositional systems, generated by the interaction of the northwards flowing Antarctic water masses with the seafloor. Within the studied area, seven canyons and their multiple branches dissect the upper and middle continental slopes, from west to east, across the terraces and the steps. These canyons, which belong to the Patagonia submarine canyon system and are collected at a depth of ~ 3.5 km by a slope-parallel, SSW-NNE-oriented channel known as the Almirante Brown transverse canyon, display a large variety of morphologies. These include incisions from just a dozen of metres to 650 m, straight to highly meandering sections with sharp bends, well-developed levees and walls that reach 35° in slope gradient, hanging branches, conspicuous axial incisions and multiple knickpoints. Only the northernmost canyon indents in the continental shelf, whereas the others start at the limit between the upper and middle slopes, and are often fed by small, straight, leveed gullies. The action of both across-slope processes represented by submarine canyons and along-slope processes represented by terracing and scouring conform the ACM as a peculiar mixed margin, with the presence of both contour and gravity currents at the same place at the same time. We propose that at present, along-slope erosion and transport mainly occurs along the Perito

Numerical simulation of the observed near-surface East India Coastal Current on the continental slope

NASA Astrophysics Data System (ADS)

Mukherjee, A.; Shankar, D.; Chatterjee, Abhisek; Vinayachandran, P. N.

2018-06-01

We simulate the East India Coastal Current (EICC) using two numerical models (resolution 0.1° × 0.1°), an oceanic general circulation model (OGCM) called Modular Ocean Model and a simpler, linear, continuously stratified (LCS) model, and compare the simulated current with observations from moorings equipped with acoustic Doppler current profilers deployed on the continental slope in the western Bay of Bengal (BoB). We also carry out numerical experiments to analyse the processes. Both models simulate well the annual cycle of the EICC, but the performance degrades for the intra-annual and intraseasonal components. In a model-resolution experiment, both models (run at a coarser resolution of 0.25° × 0.25°) simulate well the currents in the equatorial Indian Ocean (EIO), but the performance of the high-resolution LCS model as well as the coarse-resolution OGCM, which is good in the EICC regime, degrades in the eastern and northern BoB. An experiment on forcing mechanisms shows that the annual EICC is largely forced by the local alongshore winds in the western BoB and remote forcing due to Ekman pumping over the BoB, but forcing from the EIO has a strong impact on the intra-annual EICC. At intraseasonal periods, local (equatorial) forcing dominates in the south (north) because the Kelvin wave propagates equatorward in the western BoB. A stratification experiment with the LCS model shows that changing the background stratification from EIO to BoB leads to a stronger surface EICC owing to strong coupling of higher order vertical modes with wind forcing for the BoB profiles. These high-order modes, which lead to energy propagating down into the ocean in the form of beams, are important only for the current and do not contribute significantly to the sea level.

Submarine landslide identified in DLW3102 core of the northern continental slope, South China Sea

NASA Astrophysics Data System (ADS)

Xu, Yuanqin; Liu, Lejun; Zhou, Hang; Huang, Baoqi; Li, Ping; Ma, Xiudong; Dong, Feiyin

2018-02-01

In this paper, we take DLW3101 core obtained at the top of the canyon (no landslide area) and DLW3102 core obtained at the bottom of the canyon (landslide area) on the northern continental slope of the South China Sea as research objects. The chronostratigraphic framework of the DLW3101 core and elemental strata of the DLW3101 core and the DLW3102 core since MIS5 are established by analyzing oxygen isotope, calcium carbonate content, and X-Ray Fluorescence (XRF) scanning elements. On the basis of the information obtained by analyzing the sedimentary structure and chemical elements in the landslide deposition, we found that the DLW3102 core shows four layers of submarine landslides, and each landslide layer is characterized by high Si, K, Ti, and Fe contents, thereby indicating terrigenous clastic sources. L1 (2.15-2.44 m) occurred in MIS2, which is a slump sedimentary layer with a small sliding distance and scale. L2 (15.48-16.00 m) occurred in MIS5 and is a debris flow-deposited layer with a scale and sliding distance that are greater than those of L1. L3 (19.00-20.90 m) occurred in MIS5; its upper part (19.00-20.00 m) is a debris flow-deposited layer, and its lower part (20.00-20.90 m) is a sliding deposition layer. The landslide scale of L3 is large. L4 (22.93-24.27 m) occurred in MIS5; its upper part (22.93-23.50 m) is a turbid sedimentary layer, and its lower part (23.50-24.27 m) is a slump sedimentary layer. The landslide scale of L4 is large.

Observed intraseasonal and seasonal variability of the West India Coastal Current on the continental slope

NASA Astrophysics Data System (ADS)

Amol, P.; Shankar, D.; Fernando, V.; Mukherjee, A.; Aparna, S. G.; Fernandes, R.; Michael, G. S.; Khalap, S. T.; Satelkar, N. P.; Agarvadekar, Y.; Gaonkar, M. G.; Tari, A. P.; Kankonkar, A.; Vernekar, S. P.

2014-06-01

We present current data from acoustic Doppler current profilers (ADCPs) moored on the continental slope off the west coast of India. The data were collected at four locations (roughly at Kanyakumari, Kollam, Goa, and Mumbai) extending from ˜ 7° to ˜ 20°N during 2008-2012. The observations show that a seasonal cycle, including an annual cycle, is present in the West India Coastal Current (WICC); this seasonal cycle, which strengthens northward, shows considerable interannual variability and is not as strongly correlated along the coast as in climatologies based on ship drifts or the altimeter. The alongshore decorrelation of the WICC is much stronger at intraseasonal periods, which are evident during the winter monsoon all along the coast. This intraseasonal variability is stronger in the south. A striking feature of the WICC is upward phase propagation, which implies an undercurrent whose depth becomes shallower as the season progresses. There are also instances when the phase propagates downward. At the two southern mooring locations off Kollam and Kanyakumari, the cross-shore current, which is usually associated with eddy-like circulations, is comparable to the alongshore current on occasions. A comparison with data from the OSCAR (Ocean Surface Currents Analyses Real-time) data product shows not only similarities, but also significant differences, particularly in the phase. One possible reason for this phase mismatch between the ADCP current at 48 m and the OSCAR current, which represents the current in the 0-30 m depth range, is the vertical phase propagation. Current products based on Ocean General Circulation Models like ECCO2 (Estimating the Circulation and Climate of the Ocean, Phase II) and GODAS (Global Ocean Data Assimilation System) show a weaker correlation with the ADCP current, and ECCO2 does capture some of the observed variability.

Potential Offshore Wind Energy Areas in California: An Assessment of Locations, Technology, and Costs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Musial, Walter; Beiter, Philipp; Tegen, Suzanne

This report summarizes a study of possible offshore wind energy locations, technologies, and levelized cost of energy in the state of California between 2015 and 2030. The study was funded by the U.S. Department of the Interior's Bureau of Ocean Energy Management (BOEM), the federal agency responsible for regulating renewable energy development on the Outer Continental Shelf. It is based on reference wind energy areas where representative technology and performance characteristics were evaluated. These reference areas were identified as sites that were suitable to represent offshore wind cost and technology based on physical site conditions, wind resource quality, known existingmore » site use, and proximity to necessary infrastructure. The purpose of this study is to assist energy policy decision-making by state utilities, independent system operators, state government officials and policymakers, BOEM, and its key stakeholders. The report is not intended to serve as a prescreening exercise for possible future offshore wind development.« less

Go to work or report sick? A focus group study on decisions of sickness presence among offshore catering section workers.

PubMed

Krohne, Kariann; Magnussen, Liv Heide

2011-03-18

To identify and explore the factors promoting sickness presenteeism among offshore catering section workers. Twenty men and women, working in the offshore catering section onboard three offshore oil and gas production platforms on the Norwegian Continental Shelf, participated in three focus groups. Data from the focus groups were analysed according to a phenomenological approach, and supported by theories on presenteeism. The results show that the decision to attend work despite illness, first and foremost, was based on the severity of the health complaint. Other factors identified were; the individual's location once the health complaint occurred, job satisfaction, the norms of the team, and experiences of how company policies on sickness absenteeism were implemented by the catering section leaders. Offshore working conditions may promote sickness presenteeism. The factors promoting sickness presenteeism onboard the platforms reflected experiences of a healthy work environment.

Organic geochemistry of sediments from the continental margin off southern New England, U.S.A.--Part I. Amino acids, carbohydrates and lignin

NASA Technical Reports Server (NTRS)

Steinberg, S. M.; Venkatesan, M. I.; Kaplan, I. R.

1987-01-01

Total organic carbon (TOC), lignin, amino acids, sugars and amino sugars were measured in recent sediments for the continental margin off southern New England. The various organic carbon fractions decreased in concentration with increasing distance from shore. The fraction of the TOC that was accounted for by these major components also decreased with increasing distance from shore. The concentration of lignin indicated that only about 3-5% of the organic carbon in the nearshore sediment was of terrestrial origin. The various fractions were highly correlated, which was consistent with a simple linear mixing model of shelf organic matter with material form the slope and rise and indicated a significant transport of sediment from the continental shelf to the continental slope and rise.

New Insights Into Valley Formation and Preservation: Geophysical Imaging of the Offshore Trinity River Paleovalley

NASA Astrophysics Data System (ADS)

Speed, C. M.; Swartz, J. M.; Gulick, S. P. S.; Goff, J.

2017-12-01

The Trinity River paleovalley is an offshore stratigraphic structure located on the inner continental shelf of the Gulf of Mexico offshore Galveston, Texas. Its formation is linked to the paleo-Trinity system as it existed across the continental shelf during the last glacial period. Newly acquired high-resolution geophysical data have imaged more complexity to the valley morphology and shelf stratigraphy than was previously captured. Significantly, the paleo-Trinity River valley appears to change in the degree of confinement and relief relative to the surrounding strata. Proximal to the modern shoreline, the interpreted time-transgressive erosive surface formed by the paleo-river system is broad and rugose with no single valley, but just 5 km farther offshore the system appears to become confined to a 10 km wide valley structure before again becoming unconfined once again 30 km offshore. Fluvial stratigraphy in this region has a similar degree of complexity in morphology and preservation. A dense geophysical survey of several hundred km is planned for Fall 2017, which will provide unprecedented imaging of the paleovalley morphology and associated stratigraphy. Our analysis leverages robust chirp processing techniques that allow for imaging of strata on the decimeter scale. We will integrate our geophysical results with a wide array of both newly collected and previously published sediment cores. This approach will allow us to address several key questions regarding incised valley formation and preservation on glacial-interglacial timescales including: to what extent do paleo-rivers remain confined within a single broad valley structure, what is the fluvial systems response to transgression, and what stratigraphy is created and preserved at the transition from fluvial to estuarine environments? Our work illustrates that traditional models of incised valley formation and subsequent infilling potentially fail to capture the full breadth of dynamics of past river

California State Waters Map Series — Offshore of Point Conception, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Cochrane, Guy R.; Hartwell, Stephen R.; Golden, Nadine E.; Kvitek, Rikk G.; Davenport, Clifton W.; Johnson, Samuel Y.; Cochran, Susan A.

2018-04-20

about 298° to 241° azimuth. Shelf width ranges from about 5 km south of Point Conception to about 11 km northwest of it; the slope ranges from about 1.0° to 1.2° to about 0.7° south and northwest of Point Conception, respectively. Southwest of Point Conception, the shelf break and upper slope are incised by a 600-m-wide, 20- to 30-m-deep, south-facing trough, one of five heads of the informally named Arguello submarine canyon.The map area is located at a major biogeographic transition zone between the east-west-trending Santa Barbara Channel region of the Southern California Bight and the northwest-trending central California coast. North of Point Conception, the coast is subjected to high wave exposure from the north, west, and south, as well as consistently strong upwelling that brings cold, nutrient-rich waters to the surface. Southeast of Point Conception, the Santa Barbara Channel is largely protected from strong north swells by Point Conception and from south swells by the Channel Islands; surface waters are warmer, and upwelling is weak and seasonal.Seafloor habitats in the broad Santa Barbara Channel region consist of significant amounts of soft, unconsolidated sediment interspersed with isolated areas of rocky habitat that support kelp-forest communities in the nearshore and rocky-reef communities in deeper water. The potential marine benthic habitat types mapped in the Offshore of Point Conception map area are directly related to its Quaternary geologic history, geomorphology, and active sedimentary processes. These potential habitats lie primarily within the Shelf (continental shelf) but also partly within the Flank (basin flank or continental slope) megahabitats. The fairly homogeneous seafloor of sediment and low-relief bedrock provides characteristic habitat for rockfish, groundfish, crabs, shrimp, and other marine benthic organisms. Several areas of smooth sediment form nearshore terraces that have relatively steep, smooth fronts, which are

A Holocene record of ocean productivity and upwelling from the northern California continental slope

USGS Publications Warehouse

Addison, Jason A.; Barron, John A.; Finney, Bruce P.; Kusler, Jennifer E.; Bukry, David; Heusser, Linda E.; Alexander, Clark R.

2018-01-01

The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.

Continental margin sedimentation: From sediment transport to sequence stratigraphy

USGS Publications Warehouse

Nittrouer, Charles A.; 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

Trophic Ecology and Movement Patters of Tiger Sharks (Galeocerdo Cuvier) off the Western North Atlantic Coastal and Continental Shelf Waters

NASA Astrophysics Data System (ADS)

Sancho, G.; Edman, R.; Frazier, B.; Bubley, W.

2016-02-01

Understanding the trophic dynamics and habitat utilization of apex predators is central to inferring their influence on different marine landscapes and to help design effective management plans for these animals. Tiger sharks (Galeocerdo cuvier) are abundant in shelf and offshore Gulf Stream waters of the western North Atlantic Ocean, and based on movements from individuals captured in Florida and Bahamas, seem to avoid coastal and shelf waters off South Carolina and Georgia. This contradicts reports of tiger sharks regularly being caught nearshore by anglers in these states, indicating that separate sub-populations may exist in the western North Atlantic. In the present study we captured Tiger Sharks in coastal waters off South Carolina in 2014 and 2015 in order to describe their movement patterns through acoustic and satellite tagging, and trophic dynamics through stable isotope analyses. Movement data show that these tiger sharks repeatedly visit particular inshore areas and mainly travel over the continental shelf, but rarely venture offshore beyond the continental shelf edge. Ongoing C and N stable isotope analyses of muscle, blood and skin tissues from adult and juvenile tiger sharks, as well as from potential prey species and primary producers, will help determine if their diets are based on inshore, shelf or offshore based food webs. Tiger sharks exploiting nearshore environments and shelf waters have much higher probabilities of interacting with humans than individuals occupying far offshore Gulf Stream habitats.

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

Potential role of gas hydrate decomposition in generating submarine slope failures: Chapter 12

USGS Publications Warehouse

Pauli, Charles K.; Ussler, William III; Dillon, William P.; Max, Michael D.

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.

Go to work or report sick? A focus group study on decisions of sickness presence among offshore catering section workers

PubMed Central

2011-01-01

Background To identify and explore the factors promoting sickness presenteeism among offshore catering section workers. Methods Twenty men and women, working in the offshore catering section onboard three offshore oil and gas production platforms on the Norwegian Continental Shelf, participated in three focus groups. Data from the focus groups were analysed according to a phenomenological approach, and supported by theories on presenteeism. Results The results show that the decision to attend work despite illness, first and foremost, was based on the severity of the health complaint. Other factors identified were; the individual's location once the health complaint occurred, job satisfaction, the norms of the team, and experiences of how company policies on sickness absenteeism were implemented by the catering section leaders. Conclusions Offshore working conditions may promote sickness presenteeism. The factors promoting sickness presenteeism onboard the platforms reflected experiences of a healthy work environment. PMID:21418561

Ultrahigh-Resolution 3-Dimensional Seismic Imaging of Seeps from the Continental Slope of the Northern Gulf of Mexico: Subsurface, Seafloor and Into the Water Column

NASA Astrophysics Data System (ADS)

Brookshire, B. N., Jr.; Mattox, B. A.; Parish, A. E.; Burks, A. G.

2016-02-01

Utilizing recently advanced ultrahigh-resolution 3-dimensional (UHR3D) seismic tools we have imaged the seafloor geomorphology and associated subsurface aspects of seep related expulsion features along the continental slope of the northern Gulf of Mexico with unprecedented clarity and continuity. Over an area of approximately 400 km2, over 50 discrete features were identified and three general seafloor geomorphologies indicative of seep activity including mounds, depressions and bathymetrically complex features were quantitatively characterized. Moreover, areas of high seafloor reflectivity indicative of mineralization and areas of coherent seismic amplitude anomalies in the near-seafloor water column indicative of active gas expulsion were identified. In association with these features, shallow source gas accumulations and migration pathways based on salt related stratigraphic uplift and faulting were imaged. Shallow, bottom simulating reflectors (BSRs) interpreted to be free gas trapped under near seafloor gas hydrate accumulations were very clearly imaged.

The saltwater-freshwater interface in the Tertiary limestone aquifer, southeast Atlantic outer-continental shelf of the U.S.A.

USGS Publications Warehouse

Johnston, R.H.

1983-01-01

Hydrologic testing in an offshore oil well abandoned by Tenneco, Inc., determined the position of the saltwater-freshwater interface in Tertiary limestones underlying the Florida-Georgia continental shelf of the U.S.A. Previous drilling (JOIDES and U.S.G.S. AMCOR projects) established the existence of freshwater far offshore in this area. At the Tenneco well 55 mi. (???88 km) east of Fernandina Beach, Florida, drill-stem tests made in the interval 1050-1070 ft. (320-326 m) below sea level in the Ocala Limestone recovered a sample with a chloride concentration of 7000 mg l-1. Formation water probably is slightly fresher. Pressure-head measurements indicated equivalent freshwater heads of 24-29 ft. (7.3-8.8 m) above sea level. At the coast (Fernandina Beach), a relatively thin transition zone separating freshwater and saltwater occurs at a depth of 2100 ft. (640 m) below sea level. Fifty-five miles (???88 km) offshore, at the Tenneco well, the base of freshwater is ???1100 ft. (???335 m) below sea level. The difference in approximate depth to the freshwater-saltwater transition at these two locations suggests an interface with a very slight landward slope. Assuming the Hubbert interface equation applies here (because the interface and therefore freshwater flow lines are nearly horizontal) the equilibrium depth to the interface should be 40 times the freshwater head above sea level. Using present-day freshwater heads along the coast in the Hubbert equation results in depths to the interface of less than the observed 2100 ft. (640 m). Substituting predevelopment heads in the equation yields depths greater than 2100 ft. (640 m). Thus the interface appears to be in a transient position between the position that would be compatible with present-day heads and the position that would be compatible with predevelopment heads. This implies that some movement of the interface from the predevelopment position has occurred during the past hundred years. The implied movement is

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.

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

The Queen Charlotte-Fairweather Fault Zone - Geomorphology of a submarine transform fault, offshore British Columbia and southeastern Alaska

NASA Astrophysics Data System (ADS)

Walton, M. A. L.; Barrie, V.; Greene, H. G.; Brothers, D. S.; Conway, K.; Conrad, J. E.

2017-12-01

The Queen Charlotte-Fairweather (QC-FW) Fault Zone is the Pacific - North America transform plate boundary and is clearly seen for over 900 km on the seabed as a linear and continuous feature from offshore central Haida Gwaii, British Columbia to Icy Point, Alaska. Recently (July - September 2017) collected multibeam bathymetry, seismic-reflection profiles and sediment cores provide evidence for the continuous strike-slip morphology along the continental shelfbreak and upper slope, including a linear fault valley, offset submarine canyons and gullies, and right-step offsets (pull apart basins). South of central Haida Gwaii, the QC-FW is represented by several NW-SE to N-S trending faults to the southern end of the islands. Adjacent to the fault at the southern extreme and offshore Dixon Entrance (Canada/US boundary) are 400 to 600 m high mud volcanos in 1000 to 1600 m water depth that have plumes extending up 700 m into the water column and contain extensive carbonate crusts and chemosynthetic communities within the craters. In addition, gas plumes have been identified that appear to be directly associated with the fault zone. Surficial Quaternary sediments within and adjacent to the central and southern fault date either to the deglaciation of this region of the Pacific north coast (16,000 years BP) or to the last interstadial period ( 40,000 years BP). Sediment accumulation is minimal and the sediments cored are primarily hard-packed dense sands that appear to have been transported along the fault valley. The majority of the right-lateral slip along the entire QC-FW appears to be accommodated by the single fault north of the convergence at its southern most extent.

The Queen Charlotte-Fairweather Fault Zone - Geomorphology of a submarine transform fault, offshore British Columbia and southeastern Alaska

NASA Astrophysics Data System (ADS)

Walton, M. A. L.; Barrie, V.; Greene, H. G.; Brothers, D. S.; Conway, K.; Conrad, J. E.

2016-12-01

The Queen Charlotte-Fairweather (QC-FW) Fault Zone is the Pacific - North America transform plate boundary and is clearly seen for over 900 km on the seabed as a linear and continuous feature from offshore central Haida Gwaii, British Columbia to Icy Point, Alaska. Recently (July - September 2017) collected multibeam bathymetry, seismic-reflection profiles and sediment cores provide evidence for the continuous strike-slip morphology along the continental shelfbreak and upper slope, including a linear fault valley, offset submarine canyons and gullies, and right-step offsets (pull apart basins). South of central Haida Gwaii, the QC-FW is represented by several NW-SE to N-S trending faults to the southern end of the islands. Adjacent to the fault at the southern extreme and offshore Dixon Entrance (Canada/US boundary) are 400 to 600 m high mud volcanos in 1000 to 1600 m water depth that have plumes extending up 700 m into the water column and contain extensive carbonate crusts and chemosynthetic communities within the craters. In addition, gas plumes have been identified that appear to be directly associated with the fault zone. Surficial Quaternary sediments within and adjacent to the central and southern fault date either to the deglaciation of this region of the Pacific north coast (16,000 years BP) or to the last interstadial period ( 40,000 years BP). Sediment accumulation is minimal and the sediments cored are primarily hard-packed dense sands that appear to have been transported along the fault valley. The majority of the right-lateral slip along the entire QC-FW appears to be accommodated by the single fault north of the convergence at its southern most extent.

Global Paleobathymetry Reconstruction with Realistic Shelf-Slope and Sediment Wedge

NASA Astrophysics Data System (ADS)

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

2013-12-01

We present paleo-ocean bathymetry reconstructions in a 0.1°x0.1° resolution, using simple geophysical models (Plate Model Equation for oceanic lithosphere), published ages of the ocean floor (Müller et al. 2008), and modern world sediment thickness data (Divins 2003). The motivation is to create realistic paleobathymetry to understand the effect of ocean floor roughness on tides and heat transport in paleoclimate simulations. The values for the parameters in the Plate Model Equation are deduced from Crosby et al. (2006) and are used together with ocean floor age to model Depth to Basement. On top of the Depth to Basement, we added an isostatically adjusted multilayer sediment layer, as indicated from sediment thickness data of the modern oceans and marginal seas (Divins 2003). We also created another version of the sediment layer from the Müller et al. dataset. The Depth to Basement with the appropriate sediment layer together represent a realistic paleobathymetry. A Sediment Wedge was modeled to complement the reconstructed paleobathymetry by extending it to the coastlines. In this process we added a modeled Continental Shelf and Continental Slope to match the extent of the reconstructed paleobathymetry. The Sediment Wedge was prepared by studying the modern ocean where a complete history of seafloor spreading is preserved (north, south and central Atlantic Ocean, Southern Ocean between Australia-Antarctica, and the Pacific Ocean off the west coast of South America). The model takes into account the modern continental shelf-slope structure (as evident from ETOPO1/ETOPO5), tectonic margin type (active vs. passive margin) and age of the latest tectonic activity (USGS & CGMW). Once the complete ocean bathymetry is modeled, we combine it with PALEOMAP (Scotese, 2011) continental reconstructions to produce global paleoworld elevation-bathymetry maps. Modern time (00 Ma) was assumed as a test case. Using the above-described methodology we reconstructed modern ocean

Geomorphology of the Iberian Continental Margin

NASA Astrophysics Data System (ADS)

Maestro, Adolfo; López-Martínez, Jerónimo; Llave, Estefanía; Bohoyo, Fernando; Acosta, Juan; Hernández-Molina, F. Javier; Muñoz, Araceli; Jané, Gloria

2013-08-01

The submarine features and processes around the Iberian Peninsula are the result of a complex and diverse geological and oceanographical setting. This paper presents an overview of the seafloor geomorphology of the Iberian Continental Margin and the adjacent abyssal plains. The study covers an area of approximately 2.3 million km2, including a 50 to 400 km wide band adjacent to the coastline. The main morphological characteristics of the seafloor features on the Iberian continental shelf, continental slope, continental rise and the surrounding abyssal plains are described. Individual seafloor features existing on the Iberian Margin have been classified into three main groups according to their origin: tectonic and/or volcanic, depositional and erosional. Major depositional and erosional features around the Iberian Margin developed in late Pleistocene-Holocene times and have been controlled by tectonic movements and eustatic fluctuations. The distribution of the geomorphological features is discussed in relation to their genetic processes and the evolution of the margin. The prevalence of one or several specific processes in certain areas reflects the dominant morphotectonic and oceanographic controlling factors. Sedimentary processes and the resulting depositional products are dominant on the Valencia-Catalán Margin and in the northern part of the Balearic Promontory. Strong tectonic control is observed in the geomorphology of the Betic and the Gulf of Cádiz margins. The role of bottom currents is especially evident throughout the Iberian Margin. The Galicia, Portuguese and Cantabrian margins show a predominance of erosional features and tectonically-controlled linear features related to faults.

Morphology and sedimentology of glacigenic submarine fans on the west Greenland continental margin

NASA Astrophysics Data System (ADS)

O'Cofaigh, Colm; Hogan, Kelly A.; Dowdeswell, Julian A.; Jennings, Anne E.; Noormets, Riko; Evans, Jeffrey

2014-05-01

Along the West Greenland continental margin adjoining Baffin Bay, bathymetric data show a series of large submarine fans located at the mouths of cross-shelf troughs. Two of these fans, the Uummannaq Fan and the Disko Fan are trough-mouth fans built largely of debris delivered from ice sheet outlets of the Greenland Ice Sheet during past glacial maxima. On the Uummannaq Fan glacigenic debris flow deposits occur on the upper slope and extend to at least 1800 m water depth in front of the trough-mouth. The debris flow deposits are related to the remobilisation of subglacial debris that was delivered onto the upper slope at times when an ice stream was positioned at the shelf edge. In contrast, sedimentary facies from the northern sector of the fan are characterised by hemipelagic and ice-rafted sediments and turbidites; glacigenic debris flows are notably absent in cores from this region. Further south along the Greenland continental margin the surface of the Disko Fan is prominently channelised and associated sediments are acoustically stratified. Although glacigenic debris flow deposits do occur on the upper Disko Fan, sediments recovered in cores from elsewhere on the fan record the influence of turbidity current and meltwater sedimentation. The channelised form of the Disko fan contrasts markedly with that of the Uummannaq Fan and, more widely, with trough mouth fans from the Polar North Atlantic. Collectively these data highlight the variability of glacimarine depositional processes operating on trough-mouth fans on high-latitude continental slopes and show that glacigenic debris flows are but one of a number of mechanisms by which such large glacially-influenced depocentres form.

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.

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

Geomorphic Thresholds of Submarine Canyons Along the U.S. Atlantic Continental Margin

NASA Astrophysics Data System (ADS)

Brothers, D. S.; ten Brink, U. S.; Andrews, B. D.; Chaytor, J. D.

2011-12-01

Vast networks of submarine canyons and associated channels are incised into the U.S. Atlantic continental slope and rise. Submarine canyons form by differential erosion and deposition, primarily from sedimentary turbidity flows. Theoretical and laboratory studies have investigated the initiation of turbidity flows and their capacity to erode and entrain sedimentary material at distances far from the shelf edge. The results have helped understand the nature of turbidite deposits on the continental slope and rise. Nevertheless, few studies have examined the linkages between down-canyon sediment transport and the morphology of canyon/channel networks using mesoscale analyses of swath bathymetry data. We present quantitative analysis of 100-m resolution multibeam bathymetry data spanning ~616,000 km2 of the slope and rise between Georges Banks and the Blake Plateau (New England to North Carolina). Canyons are categorized as shelf-indenting or slope-confined based on spatial scale, vertical relief and connection with terrestrial river systems during sea level low stands. Shelf-indenting canyons usually represent the trunk-canyon of submerged channel networks. On the rise, shelf-indenting canyons have relatively well-developed channel-levees and sharp inner-thalwag incision suggesting much higher frequency and volume of turbidity flows. Because of the similarities between submarine canyon networks and terrestrial river systems, we apply methods originally developed to study fluvial morphology. Along-canyon profiles are extracted from the bathymetry data and the power-law relationship between thalwag gradient and drainage area is examined for more than 180 canyons along an ~1200 km stretch of the US Atlantic margin. We observe distinct thresholds in the power-law relationship between drainage area and gradient. Almost all canyons with heads on the upper slope contain at least two linear segments when plotted in log-log form. The first segment along the upper slope is flat

3D seismic attribute expressions of deep offshore Niger Delta

NASA Astrophysics Data System (ADS)

Anyiam, Uzonna Okenna

Structural and stratigraphic interpretation of 3D seismic data for reservoir characterization in an area affected by dense faulting, such as the Niger Delta, is typically difficult and strongly model driven because of problems with imaging. In the Freeman field, located about 120km offshore southwestern Niger Delta at about 1300m water depth, 3D seismic attribute-based analogs, and structural and stratigraphic based geometric models are combined to help enhance and constrain the interpretation. The objectives being to show how 3D seismic attribute analysis enhances seismic interpretation, develop structural style and stratigraphic architecture models and identify trap mechanisms in the study area; with the main purpose of producing structural and stratigraphic framework analogs to aid exploration and production companies, as well as researchers in better understanding the structural style, stratigraphic framework and trap mechanism of the Miocene to Pliocene Agbada Formation reservoirs in the deep Offshore Niger Delta Basin. A multidisciplinary approach which involved analyses of calculated variance-based coherence cube, spectral decomposition box probe and root-mean-square amplitude attributes, sequence stratigraphy based well correlation, and structural modeling; were undertaken to achieve these objectives. Studies reveal a massive northwest-southeast trending shale cored detachment fold anticline, with associated normal faults; interpreted to have been folded and faulted by localized compression resulting from a combination of differential loading on the deep-seated overpressured-ductile-undercompacted-marine Akata shale, and gravitational collapse of the Niger delta continental slope due to influx of sediments. Crestal extension resulting from this localized compression, is believed to have given rise to the synthetic, antithetic and newly observed crossing conjugate normal faults in the study area. This structure is unique to the existing types of principal

OC5 Project Phase Ib: Validation of hydrodynamic loading on a fixed, flexible cylinder for offshore wind applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robertson, Amy N.; Wendt, Fabian; Jonkman, Jason M.

This paper summarizes the findings from Phase Ib of the Offshore Code Comparison, Collaboration, Continued with Correlation (OC5) project. OC5 is a project run under the International Energy Agency (IEA) Wind Research Task 30, and is focused on validating the tools used for modelling offshore wind systems through the comparison of simulated responses of select offshore wind systems (and components) to physical test data. For Phase Ib of the project, simulated hydrodynamic loads on a flexible cylinder fixed to a sloped bed were validated against test measurements made in the shallow water basin at the Danish Hydraulic Institute (DHI) withmore » support from the Technical University of Denmark (DTU). The first phase of OC5 examined two simple cylinder structures (Phase Ia and Ib) to focus on validation of hydrodynamic models used in the various tools before moving on to more complex offshore wind systems and the associated coupled physics. As a result, verification and validation activities such as these lead to improvement of offshore wind modelling tools, which will enable the development of more innovative and cost-effective offshore wind designs.« less

OC5 Project Phase Ib: Validation of hydrodynamic loading on a fixed, flexible cylinder for offshore wind applications

DOE PAGES

Robertson, Amy N.; Wendt, Fabian; Jonkman, Jason M.; ...

2016-10-13

This paper summarizes the findings from Phase Ib of the Offshore Code Comparison, Collaboration, Continued with Correlation (OC5) project. OC5 is a project run under the International Energy Agency (IEA) Wind Research Task 30, and is focused on validating the tools used for modelling offshore wind systems through the comparison of simulated responses of select offshore wind systems (and components) to physical test data. For Phase Ib of the project, simulated hydrodynamic loads on a flexible cylinder fixed to a sloped bed were validated against test measurements made in the shallow water basin at the Danish Hydraulic Institute (DHI) withmore » support from the Technical University of Denmark (DTU). The first phase of OC5 examined two simple cylinder structures (Phase Ia and Ib) to focus on validation of hydrodynamic models used in the various tools before moving on to more complex offshore wind systems and the associated coupled physics. As a result, verification and validation activities such as these lead to improvement of offshore wind modelling tools, which will enable the development of more innovative and cost-effective offshore wind designs.« less

Structure, mechanical properties and evolution of the lithosphere below the northwest continental margin of India

NASA Astrophysics Data System (ADS)

Rao, G. Srinivasa; Kumar, Manish; Radhakrishna, M.

2018-02-01

The continental breakup history at the northwest continental margin of India remained conjectural due to lack of clearly discernable magnetic anomaly identifications and the presence of several enigmatic structural/basement features whose structure was partly obscured by the Late Cretaceous Deccan magmatic event. In this study, a detailed analysis of the existing seismic and seismological data covering both onshore and offshore areas of the northwest Indian margin along with 3-D/2-D constrained potential field (gravity, magnetic and geoid) modeling has been carried out. The crustal structure and lithosphere-asthenosphere boundary (LAB) delineated across the margin provided valuable insights on the mechanism of continental extension. An analysis of the residual geoid anomaly (degree-10) map and the modeled LAB below Deccan volcanic province (DVP) revealed significant variation in upper mantle characteristics between the northwest (NW) and south central (SC) parts of DVP having thinner lithosphere in the NW part. The depth to LAB ranges 80-130 km at the margin with gradual thinning towards the western offshore having sharp gradient in the south (SC part of DVP) and gentle gradient in the north (NW part of DVP). The Moho configuration obtained from seismically constrained 3-D gravity inversion reveals that Moho depths vary 34-42 km below DVP and gradually thins to 16-20 km in the western offshore. The effective elastic thickness (Te) map computed through 3-D flexural modeling indicates that the Te values are in general lower in the region and range 12-25 km. Such lower Te values could be ascribed to the combined effect of the lithosphere stretching during Gondwana fragmentation in the Mesozoic and subsequent thermal influence of the Reunion plume. Based on the crustal stretching factors (β), Te estimates and the modeled lithosphere geometry at the margin in this study, we propose that the lithosphere below Laxmi-Gop basin region (β > 3.0) had undergone continuous

Seismic stratigraphic characteristics of upper Louisiana continental slope: an area east of Green Canyon

USGS Publications Warehouse

Bouma, Arnold H.; Feeley, Mary H.; Kindinger, Jack G.; Stelting, Charles E.; Hilde, Thomas W.C.

1981-01-01

A high-resolution seismic reflection survey was conducted in a small area of the upper Louisiana Continental Slope known as Green Canyon Area. This area includes tracts 427, 428, 471, 472, 515, and 516, that will be offered for sale in March 1982 as part of Lease Sale 67.The sea floor of this region is, slightly hummocky and is underlain by salt diapirs that are mantled by early Tertiary shale. Most of the shale is overlain by younger Tertiary and Quaternary deposits, although locally some of the shale protrudes the sea floor. Because of proximity to older Mississippi River sources, the sediments are thick. The sediment cover shows an abundance of geologic phenomena such as horsts, grabens, growth faults, normal faults, and consolidation faults, zones with distinct and indistinct parallel reflections, semi-transparent zones, distorted zones, and angular unconformities.The major feature of this region is a N-S linear zone of uplifted and intruded sedimentary deposits formed due to diapiric intrusion.Small scale graben development over the crest of the structure can be attributed to extension and collapse. Large scale undulations of reflections well off the flanks of the uplifted structure suggest sediment creep and slumping. Dipping of parallel reflections show block faulting and tilting.Air gun (5 and 40 cubic inch) records reveal at least five major sequences that show masked onlap and slumping in their lower parts grading into more distinct parallel reflections in their upper parts. Such sequences can be related to local uplift and sea level changes. Minisparker records of this area show similar sequences but on a smaller scale. The distinct parallel reflections often onlap the diapir flanks. The highly reflective parts of these sequences may represent turbidite-type deposition, possibly at times of lower sea level. The acoustically more transparent parts of each sequence may represent deposits containing primarily hemipelagic and pelagic sediment.A complex ridge

Sediment accumulation on the Southern California Bight continental margin during the twentieth century

USGS Publications Warehouse

Alexander, C.R.; Lee, H.J.

2009-01-01

Sediment discharged into the portion of the Southern California Bight extending from Santa Barbara to Dana Point enters a complex system of semi-isolated coastal cells, narrow continental shelves, submarine canyons, and offshore basins. On both the Santa Monica and San Pedro margins, 210Pb accumulation rates decrease in an offshore direction (from ??0.5 g cm-2yr-1 to 0.02 g cm-2yr -1), in concert with a fining in sediment grain size (from 4.5?? to 8.5??), suggesting that offshore transport of wave-resuspended material occurs as relatively dilute nepheloid layers and that hemiplegic sedimentation dominates the supply of sediment to the outer shelf, slope, and basins. Together, these areas are effectively sequestering up to 100% of the annual fluvial input. In contrast to the Santa Monica margin, which does not display evidence of mass wasting as an important process of sediment delivery and redistribution, the San Pedro margin does provide numerous examples of failures and mass wasting, suggesting that intraslope sediment redistribution may play a more important role there. Basin deposits in both areas exhibit evidence of turbidites tentatively associated with both major floods and earthquakes, sourced from either the Redondo Canyon (San Pedro Basin) or Dume Canyon (Santa Monica Basin). On the Palos Verdes shelf, sediment-accumulation rates decrease along and across the shelf away from the White's Point outfall, which has been a major source of contaminants to the shelf deposits. Accumulation rates prior to the construction of the outfall were ??0.2 g cm-2yr-1 and increased 1.5-3.7 times during peak discharges from the outfall in 1971. The distal rate of accumulation has decreased by ??50%, from 0.63 g cm -2yr-1 during the period 1971-1992 to 0.29 g cm -2yr-1 during the period 1992-2003. The proximal rate of accumulation, however, has only decreased ??10%, from 0.83 g cm -2yr-1 during the period 1971-1992 to 0.73 g cm -2yr-1 during the period 1992-2003. Effluent

Winter ocean-ice interactions under thin sea ice observed by IAOOS platforms during N-ICE2015: Salty surface mixed layer and active basal melt

NASA Astrophysics Data System (ADS)

Koenig, Zoé; Provost, Christine; Villacieros-Robineau, Nicolas; Sennéchael, Nathalie; Meyer, Amelie

2016-10-01

IAOOS (Ice Atmosphere Arctic Ocean Observing System) platforms, measuring physical parameters at the atmosphere-snow-ice-ocean interface deployed as part of the N-ICE2015 campaign, provide new insights on winter conditions North of Svalbard. The three regions crossed during the drifts, the Nansen Basin, the Sofia Deep, and the Svalbard northern continental slope featured distinct hydrographic properties and ice-ocean exchanges. In the Nansen Basin, the quiescent warm layer was capped by a stepped halocline (60 and 110 m) and a deep thermocline (110 m). Ice was forming and the winter mixed layer salinity was larger by ˜0.1 g/kg than previously observed. Over the Svalbard continental slope, the Atlantic Water (AW) was very shallow (20 m from the surface) and extended offshore from the 500 m isobath by a distance of about 70 km, sank along the slope (40 m from the surface) and probably shed eddies into the Sofia Deep. In the Sofia Deep, relatively warm waters of Atlantic origin extended from 90 m downward. Resulting from different pathways, these waters had a wide range of hydrographic characteristics. Sea-ice melt was widespread over the Svalbard continental slope and ocean-to-ice heat fluxes reached values of 400 W m-2 (mean of ˜150 W m-2 over the continental slope). Sea-ice melt events were associated with near 12 h fluctuations in the mixed-layer temperature and salinity corresponding to the periodicity of tides and near-inertial waves potentially generated by winter storms, large barotropic tides over steep topography, and/or geostrophic adjustments.

Southeast Offshore Storage Resource Assessment (SOSRA): Evaluation of CO2 Storage Potential on the Continental Shelf from North Carolina to Florida

NASA Astrophysics Data System (ADS)

Knapp, J. H.; Knapp, C. C.; Brantley, D.; Lakshmi, V.; Howard, S.

2016-12-01

The Southeast Offshore Storage Resource Assessment (SOSRA) project is part of a major new program, funded by the U.S. Department of Energy for the next two and a half years, to evaluate the Atlantic and Gulf of Mexico offshore margins of the United States for geologic storage capacity of CO2. Collaborating organizations include the Southern States Energy Board, Virginia Polytechnic Institute, University of South Carolina, Oklahoma State University, Virginia Department of Mines, Minerals, and Energy, South Carolina Geological Survey, and Geological Survey of Alabama. Team members from South Carolina are focused on the Atlantic offshore, from North Carolina to Florida. Geologic sequestration of CO2 is a major research focus globally, and requires robust knowledge of the porosity and permeability distribution in upper crustal sediments. Using legacy seismic reflection, refraction, and well data from a previous phase of offshore petroleum exploration on the Atlantic margin, we are analyzing the rock physics characteristics of the offshore Mesozoic and Cenozoic stratigraphy on a regional scale from North Carolina to Florida. Major features of the margin include the Carolina Trough, the Southeast Georgia Embayment, the Blake Plateau basin, and the Blake Outer Ridge. Previous studies indicate sediment accumulations on this margin may be as thick as 12-15 km. The study will apply a diverse suite of data analysis techniques designed to meet the goal of predicting storage capacity to within ±30%. Synthetic seismograms and checkshot surveys will be used to tie well and seismic data. Seismic interpretation and geophysical log analysis will employ leading-edge software technology and state-of-the art techniques for stratigraphic and structural interpretation and the definition of storage units and their physical and chemical properties. This approach will result in a robust characterization of offshore CO2 storage opportunities, as well as a volumetric analysis that is

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.

Venezuela offshore oil and gas production development: Past, present and future

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perez La Salvia, H.; Schwartz, E.; Contreras, M.

1995-12-01

This paper presents a short history of offshore oil and gas production in Venezuela starting in Lake Maracaibo in 1923. The main emphasis has been the results of the recent R and D and the exploratory offshore programs in areas like Orinoco Delta located in the Atlantic Ocean, Northeast and Northwest Venezuela in the Caribbean sea. In the R and D offshore program the main objectives were: (1) To establish the local environmental, oceanographical, geotechnical and seismicity conditions for the Venezuelan Continental Platform. (2) To give a technical support to the PDVSA Operating Affiliates during the exploratory programs including: (a)more » to develop accurate drilling vessel positioning systems; (b) evaluation of sea bottom geotechnical conditions for safely operating the jack-ups and drilling vessels involved in the exploratory wells and (c) to identify those areas which because of their special nature require further investigation to establish preliminary type of platforms required for the areas to be developed or to evaluate other solutions proposed by Foreign Consultant Engineering Companies to the PDVSA Operating Affiliated Companies. The main objective of PDVSA for the coming future will be to develop the North of Paria Gas Field through the initially named Christopher Columbus Project now Sucre Gas, S.A., a consortium conformed by LaGoven, S.A. Shell, Exxon and Mitsubishi. objective of this paper is to give an idea of the history of the Venezuelan Oil and Gas Offshore development giving emphasis to the results of the INTEVEP S.A. Red offshore program and to show some results of the particular characteristics of oceanographical, environmental, geotechnical and seismic conditions in the main areas evaluated during the exploratory program: Orinoco Delta, Gulf of Paria and North of Paria.« less

Broadband acoustic wave propagation across sloping topography covered by sea ice

NASA Astrophysics Data System (ADS)

Badiey, M.; Wan, L.; Eickmeier, J.; Muenchow, A.; Ryan, P. A.

2017-12-01

The Canada Basin Acoustic Propagation Experiment (CANAPE) quantifies how sound generated in the deep Basin is received on the continental shelf. The two regimes, deep basin and shallow shelves, are separated by a 30-km wide region where the bottom changes from 1000-m to 100-m. This narrow region focuses and traps kinetic energy that surface wind forcing inputs into the ocean over a wide region with periodicities of days to months. As a result, ocean temperature and speed of sound are more variable near sloping topography than they are over either deep basins or shallow shelves. In contrast to companion CANAPE presentations in this session, here we use sound speed as input to predict likely propagation paths and transmission losses across the continental slope with a two-dimensional parabolic model (2D PE). Intensity fluctuations due to the changing bathymetry, water column oceanography, and the scattering from ice cover for broadband signals are checked against measured broadband acoustic signals that were collected simultaneously with the oceanographic measurements for a long period. Differences between measured and calculated transmission loss can be the result of out of plane acoustic paths requiring 3D PE modeling for future studies. [Work supported by ONR code 322 OA].

Rifting-to-drifting transition of the South China Sea: Moho reflection characteristics in continental-ocean transition zone

NASA Astrophysics Data System (ADS)

Wen, Y.; Li, C.

2017-12-01

Dispute remains on the process of continental rifting to subsequent seafloor spreading in the South China Sea (SCS). Several crust-scale multi-channel seismic reflection profiles acquired in the continent-ocean transition zone (COT) of the SCS provide a detailed overview of Moho and deep crustal reflectors and give key information on rifting-to-drifting transition of the area. Moho has strong but discontinuous seismic reflection in COT. These discontinuities are mainly located in the landward side of continent-ocean boundary (COB), and may own to upwelling of lower crustal materials during initial continental extension, leading to numerous volcanic edifices and volcanic ridges. The continental crust in COT shows discontinuous Moho reflections at 11-8.5 s in two-way travel time (twtt), and thins from 18-20.5 km under the uppermost slope to 6-7 km under the lower slope, assuming an average crustal velocity of 6.0 km/s. The oceanic crust has Moho reflections of moderate to high continuity mostly at 1.8-2.2 s twtt below the top of the igneous basement, which means that the crustal thickness excluding sediment layer in COT is 5.4-6.6 km. Subhorizontal Moho reflections are often abruptly interrupted by large seaward dipping normal faults in southern COT but are more continuous compared with the fluctuant and very discontinuous Moho reflections in northern COT. The thickness of thinned continental crust (4.2-4.8 km) is smaller than that of oceanic crust (5.4-6.0 km) near southern COB, indicating that the continental crust has experienced a long period of rifting before seafloor spreading started. The smaller width of northern COT (0-40 km) than in southern COT (0-60 km), and thinner continental crust in southern COT, all indicate that the continental margin rifting and extension was asymmetric. The COT width in the SCS is narrower than that found in other magma-poor continental margins, indicating a swift transition from the final stage of rifting to the inception of

Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf

PubMed Central

Tomašových, Adam; Kidwell, Susan M.

2017-01-01

The soft-sediment seafloor of the open continental shelf is among the least-known biomes on Earth, despite its high diversity and importance to fisheries and biogeochemical cycling. Abundant dead shells of epifaunal suspension-feeding terebratulid brachiopods (Laqueus) and scallops on the now-muddy mainland continental shelf of southern California reveal the recent, previously unsuspected extirpation of an extensive offshore shell-gravel ecosystem, evidently driven by anthropogenic siltation. Living populations of attached epifauna, which formerly existed in a middle- and outer-shelf mosaic with patches of trophically diverse muds, are restricted today to rocky seafloor along the shelf edge and to the sandier shelves of offshore islands. Geological age-dating of 190 dead brachiopod shells shows that (i) no shells have been produced on the mainland shelf within the last 100 years, (ii) their shell production declined steeply during the nineteenth century, and (iii) they had formerly been present continuously for at least 4 kyr. This loss, sufficiently rapid (less than or equal to 100 years) and thorough to represent an ecosystem collapse, coincides with intensification of alluvial-plain land use in the nineteenth century, particularly livestock grazing. Extirpation was complete by the start of twentieth-century urbanization, warming, bottom fishing and scientific surveys. The loss of this filter-feeding fauna and the new spatial homogeneity and dominance of deposit- and detritus-feeders would have altered ecosystem functioning by reducing habitat heterogeneity and seawater filtering. This discovery, attesting to the power of this geological approach to recent ecological transitions, also strongly increases the spatial scope attributable to the negative effects of siltation, and suggests that it has been under-recognized on continental shelves elsewhere as a legacy of coastal land use. PMID:28592668

Nineteenth-century collapse of a benthic marine ecosystem on the open continental shelf.

PubMed

Tomašových, Adam; Kidwell, Susan M

2017-06-14

The soft-sediment seafloor of the open continental shelf is among the least-known biomes on Earth, despite its high diversity and importance to fisheries and biogeochemical cycling. Abundant dead shells of epifaunal suspension-feeding terebratulid brachiopods ( Laqueus ) and scallops on the now-muddy mainland continental shelf of southern California reveal the recent, previously unsuspected extirpation of an extensive offshore shell-gravel ecosystem, evidently driven by anthropogenic siltation. Living populations of attached epifauna, which formerly existed in a middle- and outer-shelf mosaic with patches of trophically diverse muds, are restricted today to rocky seafloor along the shelf edge and to the sandier shelves of offshore islands. Geological age-dating of 190 dead brachiopod shells shows that (i) no shells have been produced on the mainland shelf within the last 100 years, (ii) their shell production declined steeply during the nineteenth century, and (iii) they had formerly been present continuously for at least 4 kyr. This loss, sufficiently rapid (less than or equal to 100 years) and thorough to represent an ecosystem collapse, coincides with intensification of alluvial-plain land use in the nineteenth century, particularly livestock grazing. Extirpation was complete by the start of twentieth-century urbanization, warming, bottom fishing and scientific surveys. The loss of this filter-feeding fauna and the new spatial homogeneity and dominance of deposit- and detritus-feeders would have altered ecosystem functioning by reducing habitat heterogeneity and seawater filtering. This discovery, attesting to the power of this geological approach to recent ecological transitions, also strongly increases the spatial scope attributable to the negative effects of siltation, and suggests that it has been under-recognized on continental shelves elsewhere as a legacy of coastal land use. © 2017 The Author(s).

Comparison with Offshore and Onshore Mud Volcanoes in the Southwestern Taiwan

NASA Astrophysics Data System (ADS)

Chen, Y. H.; Su, C. C.; Chen, T. T.; Liu, C. S.; Paull, C. K.; Caress, D. W.; Gwiazda, R.; Lundsten, E. M.; Hsu, H. H.

2017-12-01

The offshore area southwest (SW) of Taiwan is on the convergent boundary between the Eurasian and Philippine Sea plates. The plate convergence manifests in this unique geological setting as a fold-and-thrust-belt. Multi-channel seismic profiles, and bathymetry and gravity anomaly data collected from Taiwan offshore to the SW show the presence of a large amount of mud volcanoes and diapirs with NE-SW orientations. In the absence of comprehensive sampling and detailed geochemistry data from submarine mud volcanoes, the relation between onshore and offshore mud volcanoes remains ambiguous. During two MBARI and IONTU joint cruises conducted in 2017 we collected high-resolution multibeam bathymetry data (1-m-resolution) and chirp sub-bottom profiles with an autonomous underwater vehicle (AUV) from submarine Mud Volcano III (MV3), and obtained precisely located samples and video observations with a remotely operated vehicle (ROV). MV3 is an active submarine mud volcano at 465 m water depth offshore SW Taiwan. This cone-shape mud volcano is almost 780 m wide, 150 m high, with 8° slopes, and a 30 m wide mound on the top. Several linear features are observed in the southwest of the mound, and these features are interpreted as a series of marks caused by rolling rocks that erupted from the top of MV3. We collected three rocks and push cores from MV3 and its top with the ROV, in order to compare their chemical and mineralogical composition to that of samples collected from mud volcanoes along the Chishan fault. The surface and X-radiography imaging, 210Pb chronology, grain size and X-ray diffractometer analyses were conducted to compare geochemical and sedimentary properties of offshore and onshore mud volcanoes. The results indicate that the offshore and onshore mud volcanoes have similar characteristics. We suggest that offshore and onshore mud volcanoes of SW Taiwan are no different in the source of their materials and their mechanism of creation and evolution.

Geological history of the west Libyan offshore and adjoining regions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benniran, M.M.; Taleb, T.M.; McCrossan, R.G.

1988-08-01

The continental margin of the African plate north of Libya is separated from the Saharan platform to the south by a major Variscan fault system running along the coastline. The structural evolution of three sedimentary basins within the margin is discussed. The Jeffara basin, onshore western Libya-southern Tunisia, formed as a right-lateral pull-part late in the Variscan event. When the strike-slip motion ceased in the Late Permian, the basin continued to subside thermally. The Sabratah (Tripolitanian) basin, offshore western Libya-southern Tunisia, and the Benghazi basin in the Sirte rise were both formed as left-lateral pull-aparts in the Late Triassic-Early Jurassic.more » From the Middle Jurassic to the present they have subsided thermally. Onshore the lower Mesozoic is characterized by continental and nearshore clastics, separated by an evaporite sequence of Late Triassic-Early Jurassic age. Offshore this sequence is thought to grade northward into open marine carbonates. Uplift along the edge of the Saharan platform during the Early Cretaceous sourced coarse clastics, which grade northward into a thick sequence of shallow-water carbonates. Throughout the Late Cretaceous and early Tertiary, high-energy carbonates were deposited around the flanks of the Sabratah basin, grading into deeper-water, fine-grained clastics and carbonates toward the center of the basin. The late Tertiary succession is dominated by clastics derived from the growing Tellian Atlas to the northwest. During the Mesozoic and Tertiary a thick sequence of carbonates was deposited on the Pelagian platform to the north of the Sabratah basin. Periodically the platform was exposed subaerially.« less

Filling of a Salt-withdrawal Minibasin on the Continental Slope by Turbidity Currents: Futher Research and Results

NASA Astrophysics Data System (ADS)

Violet, J. A.; Sheets, B. A.; Paola, C.; Pratson, L. F.; Parker, G.

2002-12-01

We illustrate further research results on the transport and deposition of sediment by turbidity currents in an experimental basin, designed to model salt-withdrawal minibasins found along the northern continental slope of the Gulf of Mexico. The experiment was performed in 2001 in the subsiding EXperimental EarthScape facility (XES) at St. Anthony Falls Laboratory, University of Minnesota. The run consisted of two stages that each contained the same sequence of events, which were of three different variations (1.85-minute pulses of 1.5 liters/s discharges, 3.8-minute pulses of 4.5 liters/s discharges, or 36 minute events of 1.5 liters/s discharges). The sediment comprised three grades of silica with nominal diameters of 20 microns (45%), 45 microns (40%) and 110 microns (15%) and all flows had a volume concentration of sediment of 5%. The only difference between stage I and II was that no subsidence occurred during stage II, and that the 110 micron sand was removed from the flows late in stage II to study the effects of a smaller mean flow-grainsize. Research since the run has focused on the correction of high-frequency sonar data taken during the run, digital photography taken of dried deposit stratigraphy and grainsize data also taken at various locations in the dried deposit. The sonar data is utilized in the creation of post-event topographies and isopach maps to illustrate what the controls on erosion, deposition, flow path, deposit thickness and even the channelization of early flow events are. Comparisons of the stratigraphy and the grainsize data with the conclusions from the sonar data are made, as sonar is also constructed in a manner that exhibits synthetic or predicted stratigraphy (before compaction). Finally the stratigraphy is structurally described in the proximal, medial, and distal segments of the deposit and comparisons to the field are made.

Bathymetry and acoustic backscatter: outer mainland shelf and slope, Gulf of Santa Catalina, southern California

USGS Publications Warehouse

Dartnell, Peter; Conrad, James E.; Ryan, Holly F.; Finlayson, David P.

2014-01-01

In 2010 and 2011, scientists from the U.S. Geological Survey (USGS), Coastal and Marine Geology Program, acquired bathymetry and acoustic-backscatter data from the outer shelf and slope region offshore of southern California. The surveys were conducted as part of the USGS Marine Geohazards Program. Assessment of the hazards posed by offshore faults, submarine landslides, and tsunamis are facilitated by accurate and detailed bathymetric data. The surveys were conducted using the USGS R/V Parke Snavely outfitted with a 100-kHz Reson 7111 multibeam-echosounder system. This report provides the bathymetry and backscatter data acquired during these surveys in several formats, a summary of the mapping mission, maps of bathymetry and backscatter, and Federal Geographic Data Committee (FGDC) metadata.

Habitat compression and expansion of sea urchins in response to changing climate conditions on the California continental shelf and slope (1994-2013)

NASA Astrophysics Data System (ADS)

Sato, Kirk N.; Levin, Lisa A.; Schiff, Kenneth

2017-03-01

Echinoid sea urchins with distributions along the continental shelf and slope of the eastern Pacific often dominate the megafauna community. This occurs despite their exposure to naturally low dissolved oxygen (DO) waters (<60 μmol kg-1) associated with the Oxygen Limited Zone and low-pH waters undersaturated with respect to calcium carbonate (ΩCaCO3<1). Here we present vertical depth distribution and density analyses of historical otter trawl data collected in the Southern California Bight (SCB) from 1994 to 2013 to address the question: Do changes in echinoid density and species' depth distributions along the continental margin in the SCB reflect observed secular or interannual changes in climate? Deep-dwelling burrowing urchins (Brissopsis pacifica, Brisaster spp. and Spatangus californicus), which are adapted to low-DO, low-pH conditions appeared to have expanded their vertical distributions and populations upslope over the past decade (2003-2013), and densities of the deep pink urchin, Strongylocentrotus fragilis, increased significantly in the upper 500 m of the SCB. Conversely, the shallower urchin, Lytechinus pictus, exhibited depth shoaling and density decreases within the upper 200 m of the SCB from 1994 to 2013. Oxygen and pH in the SCB also vary inter-annually due to varying strengths of the El Niño Southern Oscillation (ENSO). Changes in depth distributions and densities were correlated with bi-monthly ENSO climate indices in the region. Our results suggest that both a secular trend in ocean deoxygenation and acidification and varying strength of ENSO may be linked to echinoid species distributions and densities, creating habitat compression in some and habitat expansion in others. Potential life-history mechanisms underlying depth and density changes observed over these time periods include migration, mortality, and recruitment. These types of analyses are needed for a broad suite of benthic species in order to identify and manage climate

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

High-Resolution Seafloor Observations of an Active Mud Volcano Offshore SW Taiwan - Results of a Repeated Survey after Four Years

NASA Astrophysics Data System (ADS)

Hsu, H. H.; Chen, T. T.; Liu, C. S.; Su, C. C.; Paull, C. K.; Caress, D. W.; Gwiazda, R.; Chen, Y. H.

2017-12-01

Mud Volcano V (MV5) is an active submarine mud volcano sitting on top of a mud diapir ridge at water depths of 600 m in the active margin offshore of southwestern Taiwan. This cone-shape mud volcano is almost 3-km-wide, 200-m-high, with 9.5° slopes, and explosively ejects streams of mud every 1.5-3 minutes. It was first mapped in 2013 with MBARI's mapping AUV (autonomous underwater vehicle). In 2017, a repeated AUV mapping survey was conducted to see if significant bathymetric changes took place since 2013, and to investigate the fluxes of fluids that pass through diapiric structures in an active continental margin. In addition to high-resolution bathymetry (1-m-resolution), sub-bottom profiling and side-scan sonar data acquired by the AUV, and videos and samples collected by MBARI's miniROV, we also incorporate multichannel seismic reflection data and gravity core sample analyses in this study. AUV bathymetry data reveal that there are two gryphons on the eastern slope of MV5. In the 2017 survey the mapped sizes of the two side cones were 80 m wide, 35 m long, 20 m relief and 40 m wide, 40 m long, 12 m relief, respectively. Comparing the bathymetry mapped in the 2017 AUV survey with that surveyed in 2013, no obvious overall morphological changes in MV5 are detected, except around the two gryphons. In the time period between the surveys, due to venting of mud from the two gryphons, two series of flow deposits which can be up to 5 meters thick are observed along the slope in the east side of both gryphons. The center depressions of these two gryphons have increased by 1-5 meters depth in their west side. Seismic and sub-bottom profiles reveal amplitude anomalies in the sub-strata of MV5 which indicate possible fluid migration paths of mud flows from deep. The trace of mud flow from the top of MV5 to its foot can be delineated from the side-scan sonar images. On the basis of 210Pbex chronology dating method, the sedimentation rate on the surface of MV5 is very slow

76 FR 22130 - Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore New Jersey-Call for...

Federal Register 2010, 2011, 2012, 2013, 2014

2011-04-20

... the potential from offshore wind power to other electric power sources, including fossil, nuclear and... for their proposed projects on the OCS. BOEMRE/New Jersey Renewable Energy Task Force BOEMRE formed...

Offshore forcing on the "pressure point" of the West Florida Shelf: Anomalous upwelling and its influence on harmful algal blooms

NASA Astrophysics Data System (ADS)

Liu, Yonggang; Weisberg, Robert H.; Lenes, Jason M.; Zheng, Lianyuan; Hubbard, Katherine; Walsh, John J.

2016-08-01

Gulf of Mexico Loop Current (LC) interactions with the West Florida Shelf (WFS) slope play an important role in shelf ecology through the upwelling of new inorganic nutrients across the shelf break. This is particularly the case when the LC impinges upon the shelf slope in the southwest portion of the WFS near the Dry Tortugas. By contacting shallow water isobaths at this "pressure point" the LC forcing sets the entire shelf into motion. Characteristic patterns of LC interactions with the WFS and their occurrences are identified using unsupervised neural network, self-organizing map, from 23 years (1993-2015) of altimetry data. The duration of the occurrences of such LC patterns is used as an indicator of offshore forcing of anomalous upwelling. Consistency is found between the altimetry-derived offshore forcing and the occurrence and severity of WFS coastal blooms of the toxic dinoflagellate, Karenia brevis: years without major blooms tend to have prolonged LC contact at the "pressure point," whereas years with major blooms tend not to have prolonged offshore forcing. Resetting the nutrient state of the shelf by the coastal ocean circulation in response to deep-ocean forcing demonstrates the importance of physical oceanography in shelf ecology. A satellite altimetry-derived seasonal predictor for major K. brevis blooms is also proposed.

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.

78 FR 59968 - Potential Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Oregon...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-09-30

... DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management [Docket No. BOEM-2013-0050..., Request for Interest AGENCY: Bureau of Ocean Energy Management (BOEM), Interior. ACTION: Public Notice of... demonstration facility offshore Coos Bay, Oregon. The project is designed to generate 30 megawatts (MW) of...

Formation of Fe-Mn crusts within a continental margin environment

USGS Publications Warehouse

Conrad, Tracey A.; Hein, James R.; Paytan, Adina; Clague, David A.

2017-01-01

This study examines Fe-Mn crusts that form on seamounts along the California continental-margin (CCM), within the United States 200 nautical mile exclusive economic zone. The study area extends from approximately 30° to 38° North latitudes and from 117° to 126° West longitudes. The area of study is a tectonically active northeast Pacific plate boundary region and is also part of the North Pacific Subtropical Gyre with currents dominated by the California Current System. Upwelling of nutrient-rich water results in high primary productivity that produces a pronounced oxygen minimum zone. Hydrogenetic Fe-Mn crusts forming along the CCM show distinct chemical and mineral compositions compared to open-ocean crusts. On average, CCM crusts contain more Fe relative to Mn than open-ocean Pacific crusts. The continental shelf and slope release both Fe and Mn under low-oxygen conditions. Silica is also enriched relative to Al compared to open-ocean crusts. This is due to the North Pacific silica plume and enrichment of Si along the path of deep-water circulation, resulting in Si enrichment in bottom and intermediate waters of the eastern Pacific.The CCM Fe-Mn crusts have a higher percentage of birnessite than open-ocean crusts, reflecting lower dissolved seawater oxygen that results from the intense coastal upwelling and proximity to zones of continental slope pore-water anoxia. Carbonate fluorapatite (CFA) is not present and CCM crusts do not show evidence of phosphatization, even in the older sections. The mineralogy indicates a suboxic environment under which birnessite forms, but in which pH is not high enough to facilitate CFA deposition. Growth rates of CCM crusts generally increase with increasing water depth, likely due to deep-water Fe sources mobilized from reduced shelf and slope sediments.Many elements of economic interest including Mn, Co, Ni, Cu, W, and Te have slightly or significantly lower concentrations in CCM crusts relative to crusts from the Pacific

Heavy-Mineral Placer Potential Map of the U.S. Continental Shelf, Western and Northern Gulf of Mexico

USGS Publications Warehouse

Shideler, Gerald L.

1988-01-01

The establishment of the Exclusive Economic Zone (EEZ) in 1983 by Presidential Proclamation opened for natural resource exploration a vast offshore frontier area contiguous to the United States and its territories. The EEZ extends from the seaward limit of state waters (3 nautical mi from shore) to 200 nautical mi offshore, and it includes the continental shelves. Within the context of the EEZ natural resource assessment effort, the purpose of this study is to delineate, on a regional basis, the potential for heavy-mineral placers on the U.S. Continental Shelf in the western and northern Gulf of Mexico from the United States-Mexico border to the Alabama-Florida state line. This map is intended to serve as a general guide for placer exploration. It shows favorable sea-floor areas for placer occurrence in water depths ranging from 0 to 100 fathoms (600 ft). The map can be used as a guide for focusing costly exploratory efforts, such as coring operations and geophysical surveys. The potential economic value of heavy-mineral placer concentrations on the U.S. Continental Shelf is a function of both geologic and economic variables. Geologic variables include the composition and concentration of the heavy-mineral assemblages and their environment of deposition. Economic variables include the current world market price of extracted metals, as well as the cost of mining, processing, and marketing the metals. These economic factors, in turn, are tempered by the nation1s socio-political climate, which determines its need for specific mineral resources at any given time.

Identification of third-order (approx. 10{sup 6} yrs) and fourth-order (approx. 10{sup 5}/10{sup 4} yrs) stratigraphic cycles in the South Addition, West Cameron Lease Area, Louisiana offshore

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lowrie, A.; Meeks, P.; Hoffman, K.

In the highly explored South Addition of the West Cameron Lease Area, Louisiana offshore, interpretation of a six-mile ({approx}10 km) seismic section across a single intraslope basin yielded 20 sediment packages. Several interpretive tools were necessary. Seismic stratigraphy indicated that the shallower zone was an outer shelf marked by 8 major sea level oscillations. In the portion between 1 and 3 seconds, seismic stratigraphy and paleontology led to the interpretation of depositional environments such as upper slope, and paleobathymetrically deeper intervals with descent through the section. The intraslope basin, while small, may be viewed as a micro-continental margin. Each seamore » level oscillation cycle apparently made a distinct progradational unit, decipherable in the seismic data. Fourth order cycles have been provisionally interpreted, throughout most of the entire 3.7 second section. Such precision is possible only in explored basins with excellent seismic data. The sequence thickness showed a seven-fold variability, from 0.08 to 0.58 seconds. The shallower section, deposited along an outer shelf, has an average individual sequence thickness of 0.13 seconds. Individual seismic sequences in the deeper section, interpreted to have been deposited on an upper slope, have average thicknesses of 0.25 seconds. The thinner sequences of the shallower section are compatible with the notion that the outer shelf was a bypass zone during a glacial epoch. The thicker sequences of the deeper section are the result of deposition onto an aggrading upper slope within an intraslope basin during a highstand.« less

Gas hydrate potential of the mid Atlantic outer continental shelf

USGS Publications Warehouse

Shedd, William W.; Hutchinson, Deborah R.

2006-01-01

For the last two years, the Minerals Management Service (MMS) has been studying the resource potential of gas hydrates in federal offshore lands of the Outer Continental Shelf (OCS) off the Atlantic, Gulf of Mexico, Pacific, and Alaska in collaboration with the U.S. Geological Survey (USGS), the Department of Energy (DOE), the National Oceanic and Atmospheric Administration (NOAA), the Naval Research Lab (NRL) and academia. Utilizing its extensive seismic, well, and geochemical databases, the MMS will be reporting the in-place resource numbers within the next few months. Though the methodology of the study was not prospect oriented, discrete prospects have been recognized.

The offshore petroleum industry: The formative years, 1945-1962

NASA Astrophysics Data System (ADS)

Kreidler, Tai Deckner

1997-12-01

This dissertation is the first to examine the offshore oil industry that was born in the calm waters of the Gulf of Mexico. It describes the industry's origins and tracks its development as a consequence of a search for new oil frontiers. In addition, it elaborates how the oil industry moved into the marine province using available technology, and was driven by the economic urgency to compete and develop new territories. Enterprising drilling contractors and operators seized the offshore gamble, finding it possible to lower the economic and technological threshold by drawing directly from wartime research and surplus equipment. Though large oil companies had placed its indelible stamp upon the industry, the smaller, independent oil operators set the pace of early offshore development. As a technological frontier, offshore development depended upon creative and unconventional engineering. Unfamiliar marine conditions tested the imagination of oil industry engineering. The unorthodox methods of John Hayward of Barnsdall Oil and R. G. LeTourneau of LeTourneau, Inc. among others transformed the industry by blending petroleum and marine engineering. Grappling with alien marine conditions and lacking formal training, Hayward and LeTourneau merged a century of practical oil field knowledge and petroleum engineering with 2,000 years of shipbuilding experience. The Gulf of Mexico served as a fertile and protective environment for the development of a fledgling industry. With calm waters, lacking the tempestuous and stormy character of the Atlantic Ocean, with a gradual sea-floor slope and saturated with the highly productive salt dome reservoirs, the Gulf became the birth place of the modern offshore oil industry. Within its protective sphere, companies experimented and developed various technical and business adaptations. Operators used technology and business strategies that increased the opportunity for success. In addition, regional academic research institutes arose as

Physical modelling of tsunamis generated by three-dimensional deformable granular landslides on planar and conical island slopes

PubMed Central

2016-01-01

Tsunamis generated by landslides and volcanic island collapses account for some of the most catastrophic events recorded, yet critically important field data related to the landslide motion and tsunami evolution remain lacking. Landslide-generated tsunami source and propagation scenarios are physically modelled in a three-dimensional tsunami wave basin. A unique pneumatic landslide tsunami generator was deployed to simulate landslides with varying geometry and kinematics. The landslides were generated on a planar hill slope and divergent convex conical hill slope to study lateral hill slope effects on the wave characteristics. The leading wave crest amplitude generated on a planar hill slope is larger on average than the leading wave crest generated on a convex conical hill slope, whereas the leading wave trough and second wave crest amplitudes are smaller. Between 1% and 24% of the landslide kinetic energy is transferred into the wave train. Cobble landslides transfer on average 43% more kinetic energy into the wave train than corresponding gravel landslides. Predictive equations for the offshore propagating wave amplitudes, periods, celerities and lengths generated by landslides on planar and divergent convex conical hill slopes are derived, which allow an initial rapid tsunami hazard assessment. PMID:27274697

Physical modelling of tsunamis generated by three-dimensional deformable granular landslides on planar and conical island slopes.

PubMed

McFall, Brian C; Fritz, Hermann M

2016-04-01

Tsunamis generated by landslides and volcanic island collapses account for some of the most catastrophic events recorded, yet critically important field data related to the landslide motion and tsunami evolution remain lacking. Landslide-generated tsunami source and propagation scenarios are physically modelled in a three-dimensional tsunami wave basin. A unique pneumatic landslide tsunami generator was deployed to simulate landslides with varying geometry and kinematics. The landslides were generated on a planar hill slope and divergent convex conical hill slope to study lateral hill slope effects on the wave characteristics. The leading wave crest amplitude generated on a planar hill slope is larger on average than the leading wave crest generated on a convex conical hill slope, whereas the leading wave trough and second wave crest amplitudes are smaller. Between 1% and 24% of the landslide kinetic energy is transferred into the wave train. Cobble landslides transfer on average 43% more kinetic energy into the wave train than corresponding gravel landslides. Predictive equations for the offshore propagating wave amplitudes, periods, celerities and lengths generated by landslides on planar and divergent convex conical hill slopes are derived, which allow an initial rapid tsunami hazard assessment.

Offshore medicine.

PubMed

Baker, D

2001-03-01

Offshore life can be refreshing for medics who are looking for a little change of pace; however, it is not for everyone. Working offshore can be the easiest or most boring job you'll ever have. It takes a specific type of medic to fit this mold. So, if you are considering a career in the offshore field, take all of the above into consideration. You are not just making a change in jobs, but a change in lifestyle. Once you become accustomed to this lifestyle, it will be hard to go back to the everyday hustle and bustle of the streets. For more information about working offshore, contact Acadian Contract Services at 800/259-333, or visit www.acadian.com.

Heat flow in eastern Egypt - The thermal signature of a continental breakup

NASA Technical Reports Server (NTRS)

Morgan, P.; Boulos, F. K.; Hennin, S. F.; El-Sherif, A. A.; El-Sayed, A. A.

1985-01-01

It is noted that the Red Sea is a modern example of continental fragmentation and incipient ocean formation. A consistent pattern of high heat flow in the Red Sea margins and coastal zone, including Precambrian terrane up to at least 30 km from the Red Sea, has emerged from the existing data. It is noted that this pattern has important implications for the mode and mechanism of Red Sea opening. High heat flow in the Red Sea shelf requires either a high extension of the crust in this zone (probably with major basic magmatic activity) or young oceanic crust beneath this zone. High heat flow in the coastal thermal anomaly zone may be caused by lateral conduction from the offshore lithosphere and/or from high mantle heat flow. It is suggested that new oceanic crust and highly extended continental crust would be essentially indistinguishable with the available data in the Red Sea margins, and are for many purposes essentially identical.

Hanging canyons of Haida Gwaii, British Columbia, Canada: Fault-control on submarine canyon geomorphology along active continental margins

NASA Astrophysics Data System (ADS)

Harris, Peter T.; Barrie, J. Vaughn; Conway, Kim W.; Greene, H. Gary

2014-06-01

Faulting commonly influences the geomorphology of submarine canyons that occur on active continental margins. Here, we examine the geomorphology of canyons located on the continental margin off Haida Gwaii, British Columbia, that are truncated on the mid-slope (1200-1400 m water depth) by the Queen Charlotte Fault Zone (QCFZ). The QCFZ is an oblique strike-slip fault zone that has rates of lateral motion of around 50-60 mm/yr and a small convergent component equal to about 3 mm/yr. Slow subduction along the Cascadia Subduction Zone has accreted a prism of marine sediment against the lower slope (1500-3500 m water depth), forming the Queen Charlotte Terrace, which blocks the mouths of submarine canyons formed on the upper slope (200-1400 m water depth). Consequently, canyons along this margin are short (4-8 km in length), closely spaced (around 800 m), and terminate uniformly along the 1400 m isobath, coinciding with the primary fault trend of the QCFZ. Vertical displacement along the fault has resulted in hanging canyons occurring locally. The Haida Gwaii canyons are compared and contrasted with the Sur Canyon system, located to the south of Monterey Bay, California, on a transform margin, which is not blocked by any accretionary prism, and where canyons thus extend to 4000 m depth, across the full breadth of the slope.

Geologic control of mineral composition of stream waters of the eastern slope of the Southern Coast Ranges, California

USGS Publications Warehouse

Davis, G.H.

1961-01-01

Chemical analyses of waters of streams that drain the semiarid eastern slope of the southern Coast Ranges in California demonstrate that differences in the anion composition, especially in the ratio of bicarbonate to sulfate, are related chiefly to the lithologic character of the rocks exposed in the tributary drainage area. Where more than hall the drainage area of a typical eastern-slope stream is underlain by clastic marine sedimentary rocks of Jurassic and Cretaceous age, bicarbonate generally predominates over sulfate; the ratio of bicarbonate to sullate, both expressed in equivalents per million, in samples of the streams at low-flow stage ranges from 0.8 to 6. Conversely, where more than hall the drainage area is underlain by marine and continental deposits of Tertiary age and continental deposits of Quaternary age, sulfate predominates over bicarbonate, and the ratio of bicarbonate to sulfate in samples taken during the low-flow stage ranges from 0.02 to 0.7. Organic siliceous marine shale of Tertiary age deposited in a reducing environment is probably the primary source of sullate in the region. Secondary deposits of sulfate minerals, chiefly gypsum, which are abundant in the continental deposits of late Tertiary and Quaternary age, also contribute sullate to the stream waters.

Calcareous nannofossil evidence for the existence of the Gulf Stream during the late Maastrichtian

USGS Publications Warehouse

Watkins, D.K.; ,

2005-01-01

Upper Maastrichtian calcareous nannofossil assemblages, from eight cores on the South Carolina Coastal Plain (onshore set) and three deep sea drilling sites from the continental slope and abyssal hills (offshore set), were analyzed by correlation and principal component analysis to examine the ancient surface water thermal structure. In addition, a temperature index derived from independently published paleobiogeographic information was applied to the sample data. All three methods indicate a strong separation of the samples into onshore and offshore sets, with the offshore data set exhibiting significantly warmer paleotemperatures. The great disparity between these two sample sets indicates that there was a strong thermal contrast between the onshore and offshore surface water masses that persisted throughout the late Maastrichtian despite evident shortterm changes in fertility, productivity, and community structure. This suggests the Gulf Stream was present as a major oceanographic feature during the late Maastrichtian. Copyright 2005 by the American Geophysical Union.

Applicability of NASA contract quality management and failure mode effect analysis procedures to the USGS Outer Continental Shelf oil and gas lease management program

NASA Technical Reports Server (NTRS)

Dyer, M. K.; Little, D. G.; Hoard, E. G.; Taylor, A. C.; Campbell, R.

1972-01-01

An approach that might be used for determining the applicability of NASA management techniques to benefit almost any type of down-to-earth enterprise is presented. A study was made to determine the following: (1) the practicality of adopting NASA contractual quality management techniques to the U.S. Geological Survey Outer Continental Shelf lease management function; (2) the applicability of failure mode effects analysis to the drilling, production, and delivery systems in use offshore; (3) the impact on industrial offshore operations and onshore management operations required to apply recommended NASA techniques; and (4) the probable changes required in laws or regulations in order to implement recommendations. Several management activities that have been applied to space programs are identified, and their institution for improved management of offshore and onshore oil and gas operations is recommended.

Tectonic elements of the continental margin of East Antarctica, 38-164ºE

USGS Publications Warehouse

O'Brien, P.E.; Stagg, H.M.J.

2007-01-01

The East Antarctic continental margin from 38–164ºE is divided into western and eastern provinces that developed during the separation of India from Australia–Antarctica (Early Cretaceous) and Australia from Antarctica (Late Cretaceous). In the overlap between these provinces the geology is complex and bears the imprint of both extension/spreading episodes, with an overprinting of volcanism. The main rift-bounding faults appear to approximately coincide with the outer edge of the continental shelf. Inboard of these faults, the sedimentary cover thins above shallowing basement towards the coast where crystalline basement generally crops out. The continental slope and the landward flanks of the ocean basins, are blanketed by up to 9–10 km of mainly post-rift sediments in margin-parallel basins, except in the Bruce Rise area. Beneath this blanket, extensive rift basins are identified off Enderby and Wilkes Land/Terre Adélie; however, their extent and detailed structures are difficult to determine.

Synchronous onset of the Messinian evaporite precipitation: First Mediterranean offshore evidence

NASA Astrophysics Data System (ADS)

Ochoa, Diana; Sierro, Francisco J.; Lofi, Johanna; Maillard, Agnès; Flores, Jose-Abel; Suárez, Mercedes

2015-10-01

The Messinian Salinity Crisis (MSC) was a major ecological crisis affecting shallow and deep-water settings over the entire Mediterranean basin. However, the evolution of the MSC and its ecological impacts have mainly been explained on the basis of sediments from onshore outcrops. Lack of complete and physically connected records from onshore and offshore settings has inhibited comprehensive understanding of basin behaviour during the MSC. Herein we present a continuous record from an intermediate-depth basin on the Balearic Promontory that comprises late Tortonian-Messinian marls and evaporitic beds from the first MSC phase (i.e., Primary Lower Gypsum-PLG stage). Well-log and biostratigraphic data allow us establishing a large-scale calibration to the astronomical solutions, and to correlate pre-MSC sediments with classical rhythmic successions outcropping onshore. Thickness and characteristic sedimentary patterns observed in the offshore evaporitic records resemble those from marginal PLG sequences. Furthermore, seismic reflectors from a Bedded Unit (BU), which corresponds to an evaporitic interval according to well-to-seismic ties, are correlated with the onshore PLG sequences. This correlation constitutes the first attempt to link well-known marginal sequences with intermediate-depth offshore settings, which have previously only been studied through seismic imaging. Our time-calibration provides direct evidence supporting a synchronous onset of the PLG phase between onshore and offshore settings along the southwestern Balearic Promontory margin. Those BU reflectors, which were positively correlated to the PLG, were likely precipitated offshore the continental shelf at Messinian times. These results suggest that gypsum precipitation and/or preservation was not always limited to 200 m water-depths and could occur in non-silled basins. Finally, we only found a major erosion at the top of the PLG sequences, implying that the MSC drawdown occurred after the

The Q-Slope Method for Rock Slope Engineering

NASA Astrophysics Data System (ADS)

Bar, Neil; Barton, Nick

2017-12-01

Q-slope is an empirical rock slope engineering method for assessing the stability of excavated rock slopes in the field. Intended for use in reinforcement-free road or railway cuttings or in opencast mines, Q-slope allows geotechnical engineers to make potential adjustments to slope angles as rock mass conditions become apparent during construction. Through case studies across Asia, Australia, Central America, and Europe, a simple correlation between Q-slope and long-term stable slopes was established. Q-slope is designed such that it suggests stable, maintenance-free bench-face slope angles of, for instance, 40°-45°, 60°-65°, and 80°-85° with respective Q-slope values of approximately 0.1, 1.0, and 10. Q-slope was developed by supplementing the Q-system which has been extensively used for characterizing rock exposures, drill-core, and tunnels under construction for the last 40 years. The Q' parameters (RQD, J n, J a, and J r) remain unchanged in Q-slope. However, a new method for applying J r/ J a ratios to both sides of potential wedges is used, with relative orientation weightings for each side. The term J w, which is now termed J wice, takes into account long-term exposure to various climatic and environmental conditions such as intense erosive rainfall and ice-wedging effects. Slope-relevant SRF categories for slope surface conditions, stress-strength ratios, and major discontinuities such as faults, weakness zones, or joint swarms have also been incorporated. This paper discusses the applicability of the Q-slope method to slopes ranging from less than 5 m to more than 250 m in height in both civil and mining engineering projects.

Sediment-transport events on the northern California continental shelf during the 1990 1991 STRESS experiment

NASA Astrophysics Data System (ADS)

Sherwood, C. R.; Butman, B.; Cacchione, D. A.; Drake, D. E.; Gross, T. F.; Sternberg, R. W.; Wiberg, P. L.; Williams, A. J.

1994-08-01

Measurements of currents and light transmission were made at bottom tripods and moorings arrayed across the northern California continental shelf along the Coastal Ocean Dynamics Experiment (CODE) "C" transect as part of the 1990-1991 Sediment Transport Events on Shelves and Slopes (STRESS) experiment. In combination with meteorological and wave data from the National Data Buoy Center Buoy 46013, these measurements provide information about the physical forcing and resultant resuspension and transport of bottom material between 21 November and 8 March. Sixteen events were identified in the wave, wind and current-meter records for this period. Only two were local storms with southerly winds, but they caused about half of the seasonal net transport. Seven were swell events that combined long-period waves generated by distant storms with local currents. At the 90-m site, swells interacted with the mean northward flow to produce northward transport. During six northerly wind events, upwelling-favorable winds often were sufficient to slow or reverse the mean northward flow and thus caused southward transport. A single current event, which produced moderate southward transport, was observed at the 130-m site. Net transport during the winter experiment was offshore at all sites, northward at the inner- and mid-shelf sites, but southward at the outer-shelf site. The results suggest that local storms with southerly winds may dominate seasonal transport, as on the Washington shelf, but significant transport also can occur during fair weather and during periods of northerly winds.

Sea-floor geology and sedimentary processes in the vicinity of Cross Rip Channel, Nantucket Sound, offshore southeastern Massachusetts

USGS Publications Warehouse

Poppe, L.J.; McMullen, K.Y.; Ackerman, S.D.; Schaer, J.D.; Wright, D.B.

2012-01-01

Gridded multibeam bathymetry covers approximately 10.4 square kilometers of sea floor in the vicinity of Cross Rip Channel in Nantucket Sound, offshore southeastern Massachusetts. Although originally collected for charting purposes during National Oceanic and Atmospheric Administration hydrographic survey H12007, these acoustic data, and the sea-floor sediment sampling and bottom photography stations subsequently occupied to verify them, show the composition and terrain of the seabed and provide information on sediment transport and benthic habitat. This report is part of an expanding series of cooperative studies by the U.S. Geological Survey, National Oceanic and Atmospheric Administration, and Massachusetts Office of Coastal Zone Management that provide a fundamental framework for research and resource-management activities (for example, windfarms, pipelines, and dredging) along the inner continental shelf offshore of Massachusetts.

High sedimentation rates and thrust fault modulation: Insights from ocean drilling offshore the St. Elias Mountains, southern Alaska

NASA Astrophysics Data System (ADS)

Worthington, Lindsay L.; Daigle, Hugh; Clary, Wesley A.; Gulick, Sean P. S.; Montelli, Aleksandr

2018-02-01

The southern Alaskan margin offshore the St. Elias Mountains has experienced the highest recorded offshore sediment accumulation rates globally. Combined with high uplift rates, active convergence and extensive temperate glaciation, the margin provides a superb setting for evaluating competing influences of tectonic and surface processes on orogen development. We correlate results from Integrated Ocean Drilling Program (IODP) Expedition 341 Sites U1420 and U1421 with regional seismic data to determine the spatial and temporal evolution of the Pamplona Zone fold-thrust belt that forms the offshore St. Elias deformation front on the continental shelf. Our mapping shows that the pattern of active faulting changed from distributed across the shelf to localized away from the primary glacial depocenter over ∼300-780 kyrs, following an order-of-magnitude increase in sediment accumulation rates. Simple Coulomb stress calculations show that the suppression of faulting is partially controlled by the change in sediment accumulation rates which created a differential pore pressure regime between the underlying, faulted strata and the overlying, undeformed sediments.

A critical review of the glaciomarine model for Irish sea deglaciation: evidence from southern Britain, the Celtic shelf and adjacent continental slope

NASA Astrophysics Data System (ADS)

Scourse, J. D.; Furze, M. F. A.

2001-07-01

In support of their glaciomarine model for the deglaciation of the Irish Sea basin, Eyles and McCabe cited the occurrence of distal glaciomarine mud drapes onshore in the Isles of Scilly and North Devon, and of arctic beach-face gravels and sands around the shores of the Celtic Sea. Glacial and sea-level data from the southern part of the Irish Sea in the terminal zone of the ice stream and the adjacent continental slope are reviewed here to test this aspect of the model. The suggestion that the glacial sequences of both the Isles of Scilly and Fremington in North Devon are glaciomarine mud drapes is rejected. An actively calving tidewater margin only occurred early in the deglacial sequence close to the terminal zone in the south-central Celtic Sea. Relative sea-levels were lower, and therefore glacio-isostatic depression less, than envisaged in the glaciomarine model. Geochronological, sedimentological and biostratigraphical data indicate that the raised beach sequences around the shores of the Celtic Sea and English Channel were deposited at, or during regression soon after, interglacial eustatic highstands. Evidence for ice-rafting at a time of high relative sea-levels is restricted to a phase(s) earlier than the Late Devensian. These data indicate that the raised beach sequences have no bearing on the style of Irish Sea deglaciation.

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

Significance of anoxic slope basins to occurrence of hydrocarbons along flexure trend, Gulf of Mexico: a reappraisal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dinkelman, M.G.; Curry, D.J.

1987-05-01

Recently, Tertiary anoxic slope basins have been proposed as the sources for much of the oil occurring along the Flexure Trend in the Gulf of Mexico. The intraslope basins are thought to have been formed in response to salt diapirism and concomitant salt withdrawal resulting from differential sediment loading between the basins and the diapirs, as well as due to associated faulting. Of the modern intraslope basins, the black, organic-rich muds accumulating in the Orca basin have especially attracted and are suggested to be modern analogs to late Tertiary source rocks accumulated and buried across the continental slope. Although themore » organic carbon content of the anoxic sediments in the Orca basin is generally high (2 to 3%), the concentration of preserved oil-generative organic matter in these sediments is low. Rock-Eval P2 yields are usually in the range of 340 to 1620 ppm, and hydrogen indices are generally less than 100. Pyrolysis-GC and 13C-NMR data show that up to 30 + % of the organic carbon is contained in carboxyl and other oxygenated groups, which are lost during diagenesis and early catagenesis of the sediments, and that much of the remainder is aromatized and degraded. The degradation was probably by oxidation during settling through the oxic water column. The geochemical data indicate, therefore, that the bulk of the organic carbon in the Orca basin is not capable of forming oil during catagenesis. Published regional cross sections across the Texas-Louisiana continental margin commonly show a thick (0.5-4 km), continuous salt sequence, sourcing salt diapirs and ridges, to underlie the Oligocene(.)/Miocene to Pleistocene sedimentary section of the outer continental shelf and slope.« less

Recent Sedimentary Processes Along the Western Continental Margin of the South Korea Plateau, East Sea of Korea

NASA Astrophysics Data System (ADS)

Cukur, D.; Um, I. K.; Bahk, J. J.; Chun, J. H.; Lee, G. S.; Soo, K. G.; Horozal, S.; Kim, S. P.

2017-12-01

The continental margins of the marginal seas is largely shaped by a complex interplay of sediment transport processes directed both downslope and along-slope. Factors influence the sediment transport from shelf to the deep basin include: (i) seabed morphology, (ii) climate, (iii) sea level changes, (iv) slope stability, (v) oceanographic regime, and (vi) sediment sources. In order to understand the recent sedimentary processes along the western margin of the South Korea Plateau in the East Sea, we collected multiple geophysical datasets including the subbottom profiler and multibeam echosounder as well as geological sampling. Twelve echo types have been defined and interpreted as deposits formed by shallow marine, hemipelagic sedimentation, bottom currents, combined- (mass-movement/hemipelagic and hemipelagic/turbidites) and mass-movement-processes. Hemipelagic sedimentation, which is reflected as undisturbed layered sediments, appears to have been the primary sedimentary process throughout the study area. Two major slope-parallel channels appear to have acted as major conduits for turbidity currents from shallower shelf into the deep basins. Bottom current deposits, which is expressed as undulating seafloor morphology, are prevalent in the southern mid-slope at water depths between 250 to 450 m. Mass-transport deposits, consisting of chaotic seismic facies, occur in the upper and lower parts of the continental slope. Piston cores confirm the presence of MTDs that are characterized by mud clasts of variable size and shape. Multibeam bathymetry data show that these MTDs chiefly initiate on lower-slopes (400-600 m) where the gradient is up to 3°. In addition, subbottom profiles suggest the presence of numerous faults in close vicinity of headwall scarps; some are extending to the seafloor suggesting their recent activity. Earthquakes associated with tectonic activity are considered as the main triggering mechanism for these MTDs. Overall, the acoustic facies

California State Waters Map Series: offshore of Carpinteria, California

USGS Publications Warehouse

Johnson, Samuel Y.; Dartnell, Peter; Cochrane, Guy R.; Golden, Nadine E.; Phillips, Eleyne L.; Ritchie, Andrew C.; Kvitek, Rikk G.; Greene, H. Gary; Endris, Charles A.; Seitz, Gordon G.; Sliter, Ray W.; Erdey, Mercedes D.; Wong, Florence L.; Gutierrez, Carlos I.; Krigsman, Lisa M.; Draut, Amy E.; Hart, Patrick E.; Johnson, Samuel Y.; Cochran, Susan A.

2013-01-01

In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP), designed to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats, and geology within the 3-nautical-mile limit of California’s State Waters. The CSMP approach is to create highly detailed seafloor maps through collection, integration, interpretation, and visualization of swath sonar data, acoustic backscatter, seafloor video, seafloor photography, high-resolution seismic-reflection profiles, and bottom-sediment sampling data. The map products display seafloor morphology and character, identify potential marine benthic habitats, and illustrate both the surficial seafloor geology and shallow (to about 100 m) subsurface geology. The Offshore of Carpinteria map area lies within the central Santa Barbara Channel region of the Southern California Bight. This geologically complex region forms a major biogeographic transition zone, separating the cold-temperate Oregonian province north of Point Conception from the warm-temperate California province to the south. The map area is in the southern part of the Western Transverse Ranges geologic province, which is north of the California Continental Borderland. Significant clockwise rotation—at least 90°—since the early Miocene has been proposed for the Western Transverse Ranges province, and the region is presently undergoing north-south shortening. The small city of Carpinteria is the most significant onshore cultural center in the map area; the smaller town of Summerland lies west of Carpinteria. These communities rest on a relatively flat coastal piedmont that is surrounded on the north, east, and west by hilly relief on the flanks of the Santa Ynez Mountains. El Estero, a salt marsh on the coast west of Carpinteria, is an ecologically important coastal estuary. Southeast of Carpinteria, the coastal zone is narrow strip containing highway and railway transportation corridors

Storm-induced inner-continental shelf circulation and sediment transport: Long Bay, South Carolina

USGS Publications Warehouse

Warner, John C.; Armstrong, Brandy N.; Sylvester, Charlene S.; Voulgaris, George; Nelson, Tim; Schwab, William C.; Denny, Jane F.

2012-01-01

Long Bay is a sediment-starved, arcuate embayment located along the US East Coast connecting both South and North Carolina. In this region the rates and pathways of sediment transport are important because they determine the availability of sediments for beach nourishment, seafloor habitat, and navigation. The impact of storms on sediment transport magnitude and direction were investigated during the period October 2003–April 2004 using bottom mounted flow meters, acoustic backscatter sensors and rotary sonars deployed at eight sites offshore of Myrtle Beach, SC, to measure currents, water levels, surface waves, salinity, temperature, suspended sediment concentrations, and bedform morphology. Measurements identify that sediment mobility is caused by waves and wind driven currents from three predominant types of storm patterns that pass through this region: (1) cold fronts, (2) warm fronts and (3) low-pressure storms. The passage of a cold front is accompanied by a rapid change in wind direction from primarily northeastward to southwestward. The passage of a warm front is accompanied by an opposite change in wind direction from mainly southwestward to northeastward. Low-pressure systems passing offshore are accompanied by a change in wind direction from southwestward to southeastward as the offshore storm moves from south to north.During the passage of cold fronts more sediment is transported when winds are northeastward and directed onshore than when the winds are directed offshore, creating a net sediment flux to the north–east. Likewise, even though the warm front has an opposite wind pattern, net sediment flux is typically to the north–east due to the larger fetch when the winds are northeastward and directed onshore. During the passage of low-pressure systems strong winds, waves, and currents to the south are sustained creating a net sediment flux southwestward. During the 3-month deployment a total of 8 cold fronts, 10 warm fronts, and 10 low

Identification and Classification of Mass Transport Complexes in Offshore Trinidad/Venezuela and Their Potential Anthropogenic Impact as Tsunamigenic Hazards

NASA Astrophysics Data System (ADS)

Moscardelli, L.; Wood, L. J.

2006-12-01

Several late Pleistocene-age seafloor destabilization events have been identified in the continental margin of eastern offshore Trinidad, of sufficient scale to produce tsunamigenic forces. This area, situated along the obliquely-converging-boundary of the Caribbean/South American plates and proximal to the Orinoco Delta, is characterized by catastrophic shelf-margin processes, intrusive-extrusive mobile shales, and active tectonism. A mega-merged, 10,000km2, 3D seismic survey reveals several mass transport complexes that range in area from 11.3km2 to 2017km2. Historical records indicate that this region has experienced submarine landslide- generated tsunamigenic events, including tsunamis that affected Venezuela during the 1700's-1900's. This work concentrates on defining those ancient deep marine mass transport complexes whose occurrence could potentially triggered tsunamis. Three types of failures are identified; 1) source-attached failures that are fed by shelf edge deltas whose sediment input is controlled by sea-level fluctuations and sedimentation rates, 2) source-detached systems, which occur when upper slope sediments catastrophically fail due to gas hydrate disruptions and/or earthquakes, and 3) locally sourced failures, formed when local instabilities in the sea floor trigger relatively smaller collapses. Such classification of the relationship between slope mass failures and the sourcing regions enables a better understanding of the nature of initiation, length of development history and petrography of such mass transport deposits. Source-detached systems, generated due to sudden sediment remobilizations, are more likely to disrupt the overlying water column causing a rise in tsunamigenic risk. Unlike 2D seismic, 3D seismic enables scientists to calculate more accurate deposit volumes, improve deposit imaging and thus increase the accuracy of physical and computer simulations of mass failure processes.

Offshore oil and the coastline

NASA Astrophysics Data System (ADS)

Bell, Peter M.

A radical, accelerated 5-year plan to offer 875 million acres (of which 20 million could actually be leased for oil and gas extraction purposes) on the outer continental shelf (OCS) could result in the release of large volumes of drilling wastes and spillage (Environ. Sci. Tech., Nov. 1981). The actual leasing, under the 5-year plan proposed by Secretary of the Interior James G. Watt, could amount to 4-5 million acres per year—about 10 times as much, on the average, as had been leased over the past 25 years. Regulations on the environmental effects may be less complicated yet more effective in that impact statements will cover large areas instead of the tract-by-tract statements now required. A number of the new offshore leasing areas, for example, the Alaska Coast (Cook Inlet, Beaufort Bay, Gulf of Alaska), the Blake Plateau and Baltimore Canyon, and the Georges Bank, are extremely valuable in terms of renewable resources and potentially fragile in terms of environmental conditions. Fishing interests in these areas have produced considerable controversy over the planned sale of petroleum rights.

Digital depth horizon compilations of the Alaskan North Slope and adjacent Arctic regions

USGS Publications Warehouse

Saltus, Richard W.; Bird, Kenneth J.

2003-01-01

Data have been digitized and combined to create four detailed depth horizon grids spanning the Alaskan North Slope and adjacent offshore areas. These map horizon compilations were created to aid in petroleum system modeling and related studies. Topography/bathymetry is extracted from a recent Arctic compilation of global onshore DEM and satellite altimetry and ship soundings offshore. The Lower Cretaceous Unconformity (LCU), the top of the Triassic Shublik Formation, and the pre-Carboniferous acoustic basement horizon grids are created from numerous seismic studies, drill hole information, and interpolation. These horizons were selected because they mark critical times in the geologic evolution of the region as it relates to petroleum. The various horizons clearly show the major tectonic elements of this region including the Brooks Range, Colville Trough, Barrow Arch, Hanna Trough, Chukchi Platform, Nuwuk Basin, Kaktovik Basin, and Canada Basin. The gridded data are available in a variety of data formats for use in regional studies.

Deposition and Burial Efficiency of Terrestrial Organic Carbon Exported from Small Mountainous Rivers to the Continental Margin, Southwest of Taiwan

NASA Astrophysics Data System (ADS)

Hsu, F.; Lin, S.; Wang, C.; Huh, C.

2007-12-01

Terrestrial organic carbon exported from small mountainous river to the continental margin may play an important role in global carbon cycle and it?|s biogeochemical process. A huge amount of suspended materials from small rivers in southwestern Taiwan (104 million tons per year) could serve as major carbon source to the adjacent ocean. However, little is know concerning fate of this terrigenous organic carbon. The purpose of this study is to calculate flux of terrigenous organic carbon deposited in the continental margin, offshore southwestern Taiwan through investigating spatial variation of organic carbon content, organic carbon isotopic compositions, organic carbon deposition rate and burial efficiency. Results show that organic carbon compositions in sediment are strongly influenced by terrestrial material exported from small rivers in the region, Kaoping River, Tseng-wen River and Er-jan Rver. In addition, a major part of the terrestrial materials exported from the Kaoping River may bypass shelf region and transport directly into the deep sea (South China Sea) through the Kaoping Canyon. Organic carbon isotopic compositions with lighter carbon isotopic values are found near the Kaoping River and Tseng-wen River mouth and rapidly change from heavier to lighter values through shelf to slope. Patches of lighter organic carbon isotopic compositions with high organic carbon content are also found in areas west of Kaoping River mouth, near the Kaoshiung city. Furthermore, terrigenous organic carbons with lighter isotopic values are found in the Kaoping canyon. A total of 0.028 Mt/yr of terrestrial organic carbon was found in the study area, which represented only about 10 percent of all terrestrial organic carbon deposited in the study area. Majority (~90 percent) of the organic carbon exported from the Kaoping River maybe directly transported into the deep sea (South China Sea) and become a major source of organic carbon in the deep sea.

Preliminary interpretation of high resolution 3D seismic data from offshore Mt. Etna, Italy

NASA Astrophysics Data System (ADS)

Gross, F.; Krastel, S.; Chiocci, F. L.; Ridente, D.; Cukur, D.; Bialas, J.; Papenberg, C. A.; Crutchley, G.; Koch, S.

2013-12-01

In order to gain knowledge about subsurface structures and its correlation to seafloor expressions, a hydro-acoustic dataset was collected during RV Meteor Cruise M86/2 (December 2011/January 2012) in Messina Straits and offshore Mt. Etna. Especially offshore Mt. Etna, the data reveals an obvious connection between subsurface structures and previously known morphological features at the sea floor. Therefore a high resolution 3D seismic dataset was acquired between Riposto Ridge and Catania Canyon close to the shore of eastern Sicily. The study area is characterized by a major structural high, which hosts several ridge-like features at the seafloor. These features are connected to a SW-NE trending fault system. The ridges are bended in their NE-SW direction and host major escarpments at the seafloor. Furthermore they are located directly next to a massive amphitheater structure offshore Mt. Etna with slope gradients of up to 35°, which is interpreted as remnants of a massive submarine mass wasting event off Sicily. The new 3D seismic dataset allows an in depth analysis of the ongoing deformation of the east flank of Mt. Etna.

Offshore tsunami deposits signify risk for heavily populated southern Levant Coastline (Gaza and Ashkelon)

NASA Astrophysics Data System (ADS)

Hoffmann, Nadine; Goodman-Tchernov, Beverly; Galanti, Barak; Katz, Oded

2016-04-01

The southern Levantine coastline is exposed to a variety of potential tsunami-generating sources, including far field influences such as large earthquakes and volcanic eruptions as well as near field offshore landslides along the continental slope, where slumping features are present throughout the area. Not only does this coast boast a long history of continuous occupation but also today large cities (e.g. Tel Aviv, Ashdod, Ashkelon, and Gaza) and related critical infrastructure such as ports, power plants, chemical industries, roads, etc. are located along this corridor. In addition, further to the south, the Gaza Strip has one of the highest population densities in the world and is dependent on external assistance for many basic needs, goods and infrastructure. Newly obtained sediment cores from the shallow shelf offshore Ashkelon (~12 km north of Gaza City) exhibit several events that can be linked to historical records. These cores can be subdivided in two general horizon types that show relative changes to one another across different proxies. The continuous input of Nile-delta sands results in a homogenous and stable 'background' sediment represented by well sorted, finer sands, few inclusions, lower proportions of A. parkinsoniana relative to fossil tests, and very few yellow-stained and blackened specimens. Contrasting these normal marine condition deposits are high energy tsunamigenic deposits characterized by poor sorting, with inclusions of a range of whole, articulated, and fragmented shells, wood, charcoal, and sub-angular to rounded pebbles. Newly mapped and quantified offshore bathymetric evidence for landslides and slumping motion has identified features that are large enough to generate tsunamis that would affect the study area. These were modeled as possible sources and compared to different far field events. Some of those tsunamigenic horizons could be assigned to specific events ranging between the youngest at 1202AD to the oldest prehistoric

A source of CO2 to the atmosphere throughout the year in the Maranhense continental shelf (2°30'S, Brazil)

NASA Astrophysics Data System (ADS)

Lefèvre, Nathalie; da Silva Dias, Francisco Jose; de Torres, Audálio Rebelo; Noriega, Carlos; Araujo, Moacyr; de Castro, Antonio Carlos Leal; Rocha, Carlos; Jiang, Shan; Ibánhez, J. Severino P.

2017-06-01

To reduce uncertainty regarding the contribution of continental shelf areas in low latitude regions to the air-sea CO2 exchange, more data are required to understand the carbon turnover in these regions and cover gaps in coverage. For the first time, inorganic carbon and alkalinity were measured along a cross-shelf transect off the coast of Maranhão (North Brazil) in 9 cruises spawning from April 2013 to September 2014. On the last 4 transects, dissolved organic matter and nutrients were also measured. The highest inorganic and organic carbon concentrations are observed close to land. As a result of low productivity and significant remineralization, heterotrophy dominates along the transect throughout the year. Although the temporal variability is significantly reduced at the offshore station with carbon concentrations decreasing seaward, the fugacity of CO2 (fCO2) at this station remains significantly higher, especially during the wet season, than the open ocean values measured routinely by a merchant ship further west. Overall, the continental shelf is a weak source of CO2 to the atmosphere throughout the year with an annual mean flux of 1.81±0.84 mmol m-2 d-1. The highest magnitudes of fCO2 are observed during the wet season when the winds are the weakest. As a result, the CO2 flux does not show a clear seasonal pattern. Further offshore, fCO2 is significantly lower than on the continental shelf. However, the oceanic CO2 flux, with an annual mean of 2.32±1.09 mmol m-2 d-1, is not statistically different from the CO2 flux at the continental shelf because the wind is stronger in the open ocean.

The subsurface geology of the Florida-Hatteras shelf, slope, and inner Blake Plateau

USGS Publications Warehouse

Paull, Charles K.; Dillon, William P.

1979-01-01

The structure and stratigraphy of the Florida-Hatteras Slope and inner Blake Plateau was studied by means of 4,780 km of single-channel air gun seismic reflection profiles. Control for the seismic stratigraphy is provided by correlating reflecting units and paleontologically dated stratigraphic units identified in offshore wells and dredge hauls. Many Tertiary unconformities exist, and major regional unconformities at the end of the Oligocene and in the late Paleocene are mapped. Reflecting surfaces believed to represent the tops of the Cretaceous, Paleocene, and Oligocene extend throughout the region. Upper Cretaceous (pre-Maastrichtian) rocks on the southeastern side of the Carolina Platform form a large seaward-facing progradational wedge. The Upper Cretaceous rocks in the Southeast Georgia Embayment, are seismically transparent and on the inner Blake Plateau are cut by numerous small faults, perhaps due to compaction. Within the survey area relatively flat-lying Maastrichtian and Paleocene strata show no evidence that a feature similar to the present Florida-Hatteras Slope existed at the beginning of the Tertiary. Late Paleocene erosion, related to the initiation of the Gulf Stream flow, probably developed this regional unconformity. Eocene and Oligocene sediments landward of the present Gulf Stream form a thick sequence of seaward-dipping progradational beds. A seaward progradational wedge of Miocene to Holocene age covers a regionally traceable unconformity, which separates the Oligocene from the Miocene sediments. Under and seaward of the present Gulf Stream, the Eocene and younger sediment supply was much smaller and the buildup is comparatively insignificant. The difference in accumulation rates in the Eocene and younger sediments, landward and seaward of the Gulf Stream, is responsible for the Florida-Hatteras Slope. Tertiary isopach maps suggest that there is a well developed triangular depocenter under the shelf. The edges of the depocenter correspond

Environmental geologic studies on the southeastern United States Atlantic Outer Continental Shelf, 1977-1978

USGS Publications Warehouse

Popenoe, Peter; Popenoe, Peter

1981-01-01

This report is a summary of the second year of marine environmental research activities by the U.S. Geological Survey (USGS) on the southeaster U.S. Atlantic Continental Margin, in accordance with with Memorandum of Understanding (MOU) AA551-MU8-13 between the USGS and the Bureau of Land Management (BLM). The report covers studies whose fieldwork was conducted during the period from 1 October 1977 to 30 September 1978. The results of the first year of study are reported in Popenoe (1978a and b) and as U.S. Department of Commerce NTIS report PB 300-820. The purpose of these investigations is to provide basic geologic and oceanographic data to the BLM Outer Continental Shelf (OCS) Marine Environmental Studies Program in support of management decisions which relate to possible development of oil and gas resources of the continental shelf. The objectives of the USGS-BLM geologic research program for fiscal year 1978 (FY-78) were 1) to determine the sedimentation rates and processes on the upper slope and inner Blake Plateau; 2) to determine the distribution, areal extent, and vertical characteristics of geological features supportive of biological communities; 3) to monitor the transport of bottom sediment across the OCS, evaluate its possible effect on pollutant transfer along the seabed and the potential of sediment as a pollutant sink, determine the implications of erosion/deposition on pipeline emplacement, and aid the interpretation of chemical, biological, and physical data; 4) to determine the concentration levels of chosen trace metals and silica in three chemically defined fractions of the suspended particulate matter (seston); 5) to study the shelf edge and slope near areas of oil and gas interest, and the northern portion of the Blake Plateau for evidence of slope instability and other geologic hazards, and 6) to determine the depth and rate of sediment mixing caused by large storms and/or by benthic organisms and where possible to estimate the rate of

Offshore Wind Energy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Strach-Sonsalla, Mareike; Stammler, Matthias; Wenske, Jan

In 1991, the Vindeby Offshore Wind Farm, the first offshore wind farm in the world, started feeding electricity to the grid off the coast of Lolland, Denmark. Since then, offshore wind energy has developed from this early experiment to a multibillion dollar market and an important pillar of worldwide renewable energy production. Unit sizes grew from 450 kW at Vindeby to the 7.5 MW-class offshore wind turbines (OWT ) that are currently (by October 2014) in the prototyping phase. This chapter gives an overview of the state of the art in offshore wind turbine (OWT) technology and introduces the principlesmore » of modeling and simulating an OWT. The OWT components -- including the rotor, nacelle, support structure, control system, and power electronics -- are introduced, and current technological challenges are presented. The OWT system dynamics and the environment (wind and ocean waves) are described from the perspective of OWT modelers and designers. Finally, an outlook on future technology is provided. The descriptions in this chapter are focused on a single OWT -- more precisely, a horizontal-axis wind turbine -- as a dynamic system. Offshore wind farms and wind farm effects are not described in detail in this chapter, but an introduction and further references are given.« less

Multi-year Current Observations on the Shelf Slope off Cape Hatteras, NC

NASA Astrophysics Data System (ADS)

Muglia, M.

2017-12-01

As part of an observing and modeling effort by the North Carolina Renewable Ocean Energy Program to determine if the Gulf Stream is a viable marine hydrokinetic energy resource for the state, upper continental slope current measurements were made over a period of nearly four years off of Cape Hatteras, NC. Velocity profiles were measured by a near-bottom, upward-looking, 150-kHz Acoustic Doppler Current Profiler deployed at a depth of 230-260 m. The mooring was sited at the location where water from the Gulf Stream, Middle Atlantic Bight, South Atlantic Bight, and Slope Sea all converge. Measured tidal amplitudes here are 2 m. These observations are used to consider the temporal variability and vertical structure of the currents at this location at tidal to interannual periods at this complex location. Concurrent near-bottom water mass properties are considered.

Coral forests diversity in the outer shelf of the south Sardinian continental margin

NASA Astrophysics Data System (ADS)

Cau, Alessandro; Moccia, Davide; Follesa, Maria Cristina; Alvito, Andrea; Canese, Simonepietro; Angiolillo, Michela; Cuccu, Danila; Bo, Marzia; Cannas, Rita

2017-04-01

Ecological theory predicts that heterogeneous habitats allow more species to co-exist in a given area, but to date, knowledge on relationships between habitat heterogeneity and biodiversity of coral forests in the outer shelf and upper slope along continental margins is rather limited. We investigated biodiversity of coral forests from 8 sites spread over two different geomorphological settings (namely, pinnacles vs. canyons) in the outer shelf along Sardinian continental margin. Using a combination of multivariate statistical analyses, we show here that differences in the composition of coral assemblages among contrasting geomorphological settings were not statistically significant, whereas significant differences emerged among sites within similar geomorphologies (i.e. among pinnacles and among canyons). Our results reveal that environmental and bathymetric factors such as sediment coverage, slope of the substrate, terrain ruggedness, bathymetric positioning index and aspect were important drivers of the observed patterns of coral biodiversity, in both settings. Spatial variability of coral forests' biodiversity is affected by environmental factors that act at the scale of each geomorphological setting (i.e. within each pinnacle and canyon) rather than by the contrasting geomorphological settings themselves. This result allows us to suggest that simple categorization of benthic communities according topographically defined habitat is unlikely to be sufficient for addressing conservation purposes.

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.

Minimum distribution of subsea ice-bearing permafrost on the US Beaufort Sea continental shelf

USGS Publications Warehouse

Brothers, Laura L.; Hart, Patrick E.; Ruppel, Carolyn D.

2012-01-01

Starting in Late Pleistocene time (~19 ka), sea level rise inundated coastal zones worldwide. On some parts of the present-day circum-Arctic continental shelf, this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates. Relict permafrost has never been systematically mapped along the 700-km-long U.S. Beaufort Sea continental shelf and is often assumed to extend to ~120 m water depth, the approximate amount of sea level rise since the Late Pleistocene. Here, 5,000 km of multichannel seismic (MCS) data acquired between 1977 and 1992 were examined for high-velocity (>2.3 km s−1) refractions consistent with ice-bearing, coarse-grained sediments. Permafrost refractions were identified along <5% of the tracklines at depths of ~5 to 470 m below the seafloor. The resulting map reveals the minimum extent of subsea ice-bearing permafrost, which does not extend seaward of 30 km offshore or beyond the 20 m isobath.

Oil-spill risk analysis: Outer continental shelf lease sale 158, Gulf of Alaska/Yakutat. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, C.M.; Johnson, W.R.; Marshall, C.F.

1995-01-01

The Federal Government has proposed to offer Outer Continental Shelf lands in the Gulf of Alaska/Yakutat for oil and gas leasing. Because oil spills may occur from activities associated with offshore oil production, the Minerals Management Service conducts a formal risk assessment. The report summarizes results of an oil-spill risk analysis conducted for OCS Lease Sale 158, Gulf of Alaska/Yakutat. The objective of this analysis was to estimate relative risks associated with oil and gas production for the proposed lease sale.

Variability of subseafloor viral abundance at the geographically and geologically distinct continental margins.

PubMed

Yanagawa, Katsunori; Morono, Yuki; Yoshida-Takashima, Yukari; Eitoku, Masamitsu; Sunamura, Michinari; Inagaki, Fumio; Imachi, Hiroyuki; Takai, Ken; Nunoura, Takuro

2014-04-01

We studied the relationship between viral particle and microbial cell abundances in marine subsurface sediments from three geographically distinct locations in the continental margins (offshore of the Shimokita Peninsula of Japan, the Cascadia Margin off Oregon, and the Gulf of Mexico) and found depth variations in viral abundances among these sites. Viruses in sediments obtained offshore of the Shimokita and in the Cascadia Margin generally decreased with increasing depth, whereas those in sediments from the Gulf of Mexico were relatively constant throughout the investigated depths. In addition, the abundance ratios of viruses to microbial cells notably varied among the sites, ranging between 10(-3) and 10(1) . The subseafloor viral abundance offshore of the Shimokita showed a positive relationship with the microbial cell abundance and the sediment porosity. In contrast, no statistically significant relationship was observed in the Cascadia Margin and the Gulf of Mexico sites, presumably due to the long-term preservation of viruses from enzymatic degradation within the low-porosity sediments. Our observations indicate that viral abundance in the marine subsurface sedimentary environment is regulated not only by in situ production but also by the balance of preservation and decay, which is associated with the regional sedimentation processes in the geological settings. © 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.

Understanding Variability in Beach Slope to Improve Forecasts of Storm-induced Water Levels

NASA Astrophysics Data System (ADS)

Doran, K. S.; Stockdon, H. F.; Long, J.

2014-12-01

The National Assessment of Hurricane-Induced Coastal Erosion Hazards combines measurements of beach morphology with storm hydrodynamics to produce forecasts of coastal change during storms for the Gulf of Mexico and Atlantic coastlines of the United States. Wave-induced water levels are estimated using modeled offshore wave height and period and measured beach slope (from dune toe to shoreline) through the empirical parameterization of Stockdon et al. (2006). Spatial and temporal variability in beach slope leads to corresponding variability in predicted wave setup and swash. Seasonal and storm-induced changes in beach slope can lead to differences on the order of a meter in wave runup elevation, making accurate specification of this parameter essential to skillful forecasts of coastal change. Spatial variation in beach slope is accounted for through alongshore averaging, but temporal variability in beach slope is not included in the final computation of the likelihood of coastal change. Additionally, input morphology may be years old and potentially very different than the conditions present during forecast storm. In order to improve our forecasts of hurricane-induced coastal erosion hazards, the temporal variability of beach slope must be included in the final uncertainty of modeled wave-induced water levels. Frequently collected field measurements of lidar-based beach morphology are examined for study sites in Duck, North Carolina, Treasure Island, Florida, Assateague Island, Virginia, and Dauphin Island, Alabama, with some records extending over a period of 15 years. Understanding the variability of slopes at these sites will help provide estimates of associated water level uncertainty which can then be applied to other areas where lidar observations are infrequent, and improve the overall skill of future forecasts of storm-induced coastal change. Stockdon, H. F., Holman, R. A., Howd, P. A., and Sallenger Jr, A. H. (2006). Empirical parameterization of setup

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

Influence of dynamic topography on landscape evolution and passive continental margin stratigraphy

NASA Astrophysics Data System (ADS)

Ding, Xuesong; Salles, Tristan; Flament, Nicolas; Rey, Patrice

2017-04-01

Quantifying the interaction between surface processes and tectonics/deep Earth processes is one important aspect of landscape evolution modelling. Both observations and results from numerical modelling indicate that dynamic topography - a surface expression of time-varying mantle convection - plays a significant role in shaping landscape through geological time. Recent research suggests that dynamic topography also has non-negligible effects on stratigraphic architecture by modifying accommodation space available for sedimentation. In addition, dynamic topography influences the sediment supply to continental margins. We use Badlands to investigate the evolution of a continental-scale landscape in response to transient dynamic uplift or subsidence, and to model the stratigraphic development on passive continental margins in response to sea-level change, thermal subsidence and dynamic topography. We consider a circularly symmetric landscape consisting of a plateau surrounded by a gently sloping continental plain and a continental margin, and a linear wave of dynamic topography. We analyze the evolution of river catchments, of longitudinal river profiles and of the χ values to evaluate the dynamic response of drainage systems to dynamic topography. We calculate the amount of cumulative erosion and deposition, and sediment flux at shoreline position, as a function of precipitation rate and erodibility coefficient. We compute the stratal stacking pattern and Wheeler diagram on vertical cross-sections at the continental margin. Our results indicate that dynamic topography 1) has a considerable influence on drainage reorganization; 2) contributes to shoreline migration and the distribution of depositional packages by modifying the accommodation space; 3) affects sediment supply to the continental margin. Transient dynamic topography contributes to the migration of drainage divides and to the migration of the mainstream in a drainage basin. The dynamic uplift

Seismic investigation on the Littoral Faults Zone in the northern continental margin of South China Sea

NASA Astrophysics Data System (ADS)

Sun, J.; Xu, H.; Xia, S.; Cao, J.; Wan, K.

2017-12-01

The continental margin of the northern South China Sea (SCS) had experienced continuous evolution from an active continental margin in the late Mesozoic to a passive continental margin in the Cenozoic. The 1200km-long Littoral Faults Zone (LFZ) off the mainland South China was suggested to represent one of the sub-plate boundaries and play a key role during the evolution. Besides, four devastating earthquakes with magnitude over 7 and another 11 destructive events with M>6 were documented to have occurred along the LFZ. However, its approximity to the shoreline, the shallow water depth, and the heavy fishing activities make it hard to conduct a marine seismic investigation. As a result, understandings about the LFZ before 2000 were relatively poor and mostly descriptive. After two experiments of joint onshore-offshore wide-angle seismic surveys in the 1st decade of this century, several cruses aiming to unveil the deep structure of the LFZ were performed in the past few years, with five joint onshore-offshore wide-angle seismic survey profiles completed. Each of these profiles is perpendicular to the shoreline, with four to five seismometers of campaign mode deployed on the landside and over ten Ocean Bottom Seismometers (OBSs) spacing at 20km deployed on the seaside. Meanwhile, multi-channel seismic (MCS) data along these profiles were obtained simultaneously. Based on these data, velocity models from both forward modeling and inversion were obtained. According to these models, the LFZ was imaged to be a low-velocity fractured zone dipping to the SSE-SE at a high-angle and cutting through the thinned continental crust at some locations. Width of the fractured zone varies from 6km to more than 10km from site to site. With these results, it is suggested that the LFZ accommodates the stresses from both the east side, where the Eurasia/Philippine Sea plate converging and mountain building is ongoing, and the west side, where a strike-slip between the Indochina

Changes in water clarity in response to river discharges on the Great Barrier Reef continental shelf: 2002-2013

NASA Astrophysics Data System (ADS)

Fabricius, K. E.; Logan, M.; Weeks, S. J.; Lewis, S. E.; Brodie, J.

2016-05-01

Water clarity is a key factor for the health of marine ecosystems. The Australian Great Barrier Reef (GBR) is located on a continental shelf, with >35 major seasonal rivers discharging into this 344,000 km2 tropical to subtropical ecosystem. This work investigates how river discharges affect water clarity in different zones along and across the GBR. For each day over 11 years (2002-2013) we calculated 'photic depth' as a proxy measure of water clarity (calibrated to be equivalent to Secchi depth), for each 1 km2 pixel from MODIS-Aqua remote sensing data. Long-term and seasonal changes in photic depth were related to the daily discharge volumes of the nearest rivers, after statistically removing the effects of waves and tides on photic depth. The relationships between photic depths and rivers differed across and along the GBR. They typically declined from the coastal to offshore zones, and were strongest in proximity to rivers in agriculturally modified catchments. In most southern inner zones, photic depth declined consistently throughout the 11-year observation period; such long-term trend was not observed offshore nor in the northern regions. Averaged across the GBR, photic depths declined to 47% of local maximum values soon after the onset of river floods, and recovery to 95% of maximum values took on average 6 months (range: 150-260 days). The river effects were strongest at latitude 14.5°-19.0°S, where river loads are high and the continental shelf is narrow. Here, even offshore zones showed a >40% seasonal decline in photic depth, and 17-24% reductions in annual mean photic depth in years with large river nutrients and sediment loads. Our methodology is based on freely available data and tools and may be applied to other shelf systems, providing valuable insights in support of ecosystem management.

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.

Sedimentary processes on the Storfjorden trough-mouth fan during last deglaciation phase: the role of subglacial meltwater plumes on continental margin sedimentation

NASA Astrophysics Data System (ADS)

Lucchi, Renata G.; Camerlenghi, Angelo; Colmenero-Hidalgo, Elena; Sierro, Francisco J.; Bárcena, Maria Angeles; Flores, José-Abel; Urgeles, Roger; Macrı, Patrizia; Sagnotti, Leonardo; Caburlotto, Andrea

2010-05-01

The continental margin of the Southern Storfjorden trough-mouth fan was investigated within the SVAIS project (BIO Hesperides cruise, August 2007) as a Spanish contribution to IPY Activity N. 367 (Neogene ice streams and sedimentary processes on high- latitude continental margins - NICE STREAMS). The objectives were to investigate the glacially-dominated late-Neogene-Quaternary sedimentary architecture of the NW Barents Sea continental margin and reconstruct its sedimentary system in response to natural climate change. The paleo-ice streams in Storfjorden had a small catchment area draining ice from the southern Spitsbergen and Bear Island. The short distance from the ice source to the calving front produced a short residence time of ice, and therefore a rapid response to climatic changes. Here ground truthing recovered the last few thousands years sedimentary sequence thought to represent last deglaciation phase. Detailed palaeostratigraphic investigations together with paleomagnetic and rock magnetic analyses and AMS dating define the constraints for high-resolution inter-core correlation and dating. Most of the cores contain at the base gravity-mass deposits including debris flows and over-consolidated glacigenic diamicton. Mass deposits are overlain by an oxidized interval originated at the release and sink of fresh, cold and oxygenated melt-waters at the inception of the deglaciation phase. On the upper slope the oxidized interval is overlain by several meters of finely-stratified sediments composed of sandy-silt layers cyclically recurring within finer-grained laminated silty-clay sediments. Textural and compositional analyses suggest preferential deposition by settling from meltwater sediment-laden plumes (plumites) occurred during deglaciation with coarser layers representing episodes of subglacial meltwater discharge (glacial hyperpycnal flows) accompanying the ice streams retreat. The laminated sequence is truncated at uppermost part by a more recent

75 FR 68824 - Commercial Leasing for Wind Power on the Outer Continental Shelf (OCS) Offshore Maryland-Request...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-09

... will use responses to this RFI to enable BOEMRE to gauge specific interest in commercial development of... BOEMRE Maryland Renewable Energy Task Force. A detailed description of the RFI area is found later in... Energy and Alternate Uses of Existing Facilities on the Outer Continental Shelf (REAU) rule. If...

Getting offshoring right.

PubMed

Aron, Ravi; Singh, Jitendra V

2005-12-01

The prospect of offshoring and outsourcing business processes has captured the imagination of CEOs everywhere. In the past five years, a rising number of companies in North America and Europe have experimented with this strategy, hoping to reduce costs and gain strategic advantage. But many businesses have had mixed results. According to several studies, half the organizations that have shifted processes offshore have failed to generate the expected financial benefits. What's more, many of them have faced employee resistance and consumer dissatisfaction. Clearly, companies have to rethink how they formulate their offshoring strategies. A three-part methodology can help. First, companies need to prioritize their processes, ranking each based on two criteria: the value it creates for customers and the degree to which the company can capture some of that value. Companies will want to keep their core (highest-priority) processes in-house and consider outsourcing their commodity (low-priority) processes; critical (moderate-priority) processes are up for debate and must be considered carefully. Second, businesses should analyze all the risks that accompany offshoring and look systematically at their critical and commodity processes in terms of operational risk (the risk that processes won't operate smoothly after being offshored) and structural risk (the risk that relationships with service providers may not work as expected). Finally, companies should determine possible locations for their offshore efforts, as well as the organizational forms--such as captive centers and joint ventures--that those efforts might take. They can do so by examining each process's operational and structural risks side by side. This article outlines the tools that will help companies choose the right processes to offshore. It also describes a new organizational structure called the extended organization, in which companies specify the quality of services they want and work alongside providers

A model of onshore-offshore change in faunal diversity

NASA Technical Reports Server (NTRS)

Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

1991-01-01

Onshore-offshore patterns of faunal change occurred at many taxonomic scales during the Paleozoic Era, ranging from replacement of the Cambrian evolutionary fauna by the Paleozoic fauna to the environmental expansion of many orders and classes. A simple mathematical model is constructed to investigate such change. The environmental gradient across the marine shelf-slope is treated as a linear array of discrete habitats, each of which holds a set number of species, as observed in the fossil record. During any interval of time, some portion of the species in each habitat becomes extinct by background processes, with rates of extinction varying among both clades and habitats, as also observed in the record. After extinction, species are replaced from within the habitat and from immediately adjacent habitats, with proportions dependent on surviving species. This model leads to the prediction that extinction-resistant clades will always diversify at the expense of extinction-prone clades. But if extinction intensity is highest in nearshore habitats, extinction-resistant clades will expand preferentially in the onshore direction, build up diversity there, and then diversify outward toward the offshore. Thus, onshore-offshore patterns of diversification may be the expectation for faunal change quite independently of whether or not clades originate onshore. When the model is parameterized for Paleozoic trilobites and brachiopods, numerical solutions exhibit both a pattern of faunal change and a time span for diversification similar to that seen in the fossil record. They also generate structure similar to that seen in global diversification, including logistic patterns of growth, declining origination but constant extinction within clades through time, and declining overall extinction across clades through time.

The wide-angle seismic image of a complex rifted margin, offshore North Namibia: Implications for the tectonics of continental breakup

NASA Astrophysics Data System (ADS)

Planert, Lars; Behrmann, Jan; Jokat, Wilfried; Fromm, Tanja; Ryberg, Trond; Weber, Michael; Haberland, Christian

2017-10-01

Voluminous magmatism during the South Atlantic opening has been considered as a classical example for plume related continental breakup. We present a study of the crustal structure around Walvis Ridge, near the intersection with the African margin. Two wide-angle seismic profiles were acquired. One is oriented NNW-SSE, following the continent-ocean transition and crossing Walvis Ridge. A second amphibious profile runs NW-SE from the Angola Basin into continental Namibia. At the continent-ocean boundary (COB) the mafic crust beneath Walvis Ridge is up to 33 km thick, with a pronounced high-velocity lower crustal body. Towards the south there is a smooth transition to 20-25 km thick crust underlying the COB in the Walvis Basin, with a similar velocity structure, indicating a gabbroic lower crust with associated cumulates at the base. The northern boundary of Walvis Ridge towards the Angola Basin shows a sudden change to oceanic crust only 4-6 km thick, coincident with the projection of the Florianopolis Fracture Zone, one of the most prominent tectonic features of the South Atlantic ocean basin. In the amphibious profile the COB is defined by a sharp transition from oceanic to rifted continental crust, with a magmatic overprint landward of the intersection of Walvis Ridge with the Namibian margin. The continental crust beneath the Congo Craton is 40 km thick, shoaling to 35 km further SE. The velocity models show that massive high-velocity gabbroic intrusives are restricted to a narrow zone directly underneath Walvis Ridge and the COB in the south. This distribution of rift-related magmatism is not easily reconciled with models of continental breakup following the establishment of a large, axially symmetric plume in the Earth's mantle. Rift-related lithospheric stretching and associated transform faulting play an overriding role in locating magmatism, dividing the margin in a magma-dominated southern and an essentially amagmatic northern segment.

California State Waters Map Series—Offshore of Pigeon Point, California

USGS Publications Warehouse

Cochrane, Guy R.; Watt, Janet T.; Dartnell, Peter; Greene, H. Gary; Erdey, Mercedes D.; Dieter, Bryan E.; Golden, Nadine E.; Johnson, Samuel Y.; Endris, Charles A.; Hartwell, Stephen R.; Kvitek, Rikk G.; Davenport, Clifton W.; Krigsman, Lisa M.; Ritchie, Andrew C.; Sliter, Ray W.; Finlayson, David P.; Maier, Katherine L.; Cochrane, Guy R.; Cochran, Susan A.

2015-12-15

Seafloor habitats in the Offshore of Pigeon Point map area lie within the Shelf (continental shelf) megahabitat. Significant rocky outcrops, which support kelp-forest communities in the nearshore and rocky-reef communities in deeper water, dominate the inner shelf waters. Biological productivity resulting from coastal upwelling supports populations of Sooty Shearwater, Western Gull, Common Murre, Cassin’s Auklet, and many other less populous bird species. In addition, an observable recovery of Humpback and Blue Whales has occurred in the area; both species are dependent on coastal upwelling to provide nutrients. The large extent of exposed inner shelf bedrock supports large forests of “bull kelp,” which is well adapted for high-wave-energy environments. Common fish species found in the kelp beds and rocky reefs include lingcod and various species of rockfish and greenling.

Hyperpycnal plume-derived fans in the Santa Barbara Channel, California

USGS Publications Warehouse

Warrick, Jonathan A.; Simms, Alexander R.; Ritchie, Andy; Steel, Elisabeth; Dartnell, Pete; Conrad, James E.; Finlayson, David P.

2013-01-01

Hyperpycnal gravity currents rapidly transport sediment across shore from rivers to the continental shelf and deep sea. Although these geophysical processes are important sediment dispersal mechanisms, few distinct geomorphic features on the continental shelf can be attributed to hyperpycnal flows. Here we provide evidence of large depositional features derived from hyperpycnal plumes on the continental shelf of the northern Santa Barbara Channel, California, from the combination of new sonar, lidar, and seismic reflection data. These data reveal lobate fans directly offshore of the mouths of several watersheds known to produce hyperpycnal concentrations of suspended sediment. The fans occur on an upwardly concave section of the shelf where slopes decrease from 0.04 to 0.01, and the location of these fans is consistent with wave- and auto-suspending sediment gravity current theories. Thus, we provide the first documentation that the morphology of sediment deposits on the continental shelf can be dictated by river-generated hyperpycnal flows.

An Altimetry-Derived Index of the Offshore Forcing on the "Pressure Point" of the West Florida Shelf: Anomalous Upwelling and Its Influence on Harmful Algal Blooms

NASA Astrophysics Data System (ADS)

Liu, Y.; Weisberg, R. H.; Lenes, J. M.; Zheng, L.; Hubbard, K.; Walsh, J. J.

2017-12-01

Gulf of Mexico Loop Current (LC) interactions with the West Florida Shelf (WFS) slope play an important role in shelf ecology through the upwelling of new inorganic nutrients across the shelf break. This is particularly the case when the LC impinges upon the shelf slope in the southwest portion of the WFS near the Dry Tortugas. By contacting shallow water isobaths at this "pressure point" the LC forcing sets the entire shelf into motion. Characteristic patterns of LC interactions with the WFS and their occurrences are identified from altimetry data using unsupervised neural network, self-organizing map. The duration of the occurrences of such LC patterns is used as an indicator of offshore forcing of anomalous upwelling. Consistency is found between the altimetry-derived offshore forcing and the occurrence and severity of WFS coastal blooms of the toxic dinoflagellate, Karenia brevis: years without major blooms tend to have prolonged LC contact at the "pressure point," whereas years with major blooms tend not to have prolonged offshore forcing. Resetting the nutrient state of the shelf by the coastal ocean circulation in response to deep-ocean forcing demonstrates the importance of physical oceanography in shelf ecology. A satellite altimetry-derived seasonal predictor for major K. brevis blooms is also proposed.

Offshore gas hydrate sample database with an overview and preliminary analysis

USGS Publications Warehouse

Booth, James S.; Rowe, Mary M.; Fisher, Kathleen M.

1996-01-01

Synopsis -- A database of offshore gas hydrate samples was constructed from published observations and measurements. More than 90 samples from 15 distinct regions are represented in 13 data categories. This database has permitted preliminary description of gas hydrate (chiefly methane hydrate) tendencies and associations with respect to their geological environment. Gas hydrates have been recovered from offshore sediment worldwide and from total depths (water depth plus subseabed depth) ranging from 500 m to nearly 6,000 m. Samples have come from subbottom depths ranging from 0 to 400 m. Various physiographic provinces are represented in the data set including second order landforms such as continental margins and deep-sea trenches, and third order forms such as submarine canyons, continental slopes, continental margin ridges and intraslope basins. There is a clear association between fault zones and other manifestations of local, tectonic-related processes, and hydrate-bearing sediment. Samples of gas hydrate frequently consist of individual grains or particles. These types of hydrates are often further described as inclusions or disseminated in the sediment. Moreover, hydrates occur as a cement, as nodules, or as layers (mostly laminae) or in veins. The preponderance of hydrates that could be characterized as 2- dimensional (planar) were associated with fine sediment, either as intercalated layers or in fractures. Hydrate cements were commonly associated with coarser sediment. Hydrates have been found in association with grain sizes ranging from clay through gravel. More hydrates are associated with the more abundant finer-grained sediment than with coarser sediment, and many were discovered in the presence of both fine (silt and clay) and coarse sediment. The thickness of hydrate zones (i. e., sections of hydrate-bearing sediment) varies from a few centimeters to as much as 30 m. In contrast, the thickness of layers of pure hydrate or the dimensions of

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.

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.

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

Geoloogic slip on offshore San Clemente fault, Southern California, understated in GPS data

NASA Astrophysics Data System (ADS)

Legg, M. R.

2005-12-01

The San Clemente fault offshore southern California exhibits prominent geomorphic evidence of major late Quaternary right-slip. Like the San Andreas fault, where modern Pacific-North America transform motion is focused, the San Clemente fault stretches more than 700 km along the continental margin with a well-defined principal displacement zone (PDZ). Lateral offset is generally concentrated in a zone less than about 1 km wide, and linear seafloor fault scarps cutting across active submarine fans and basin-filling turbidites demonstrate Holocene activity. Dextral offset of middle Miocene circular crater structures suggest as much as 60 km of Neogene and younger displacement. Offset submarine fan depositional features suggest a rate of about 4-7 mm/yr of late Quaternary slip. Nearly 75 years of seismograph recording in southern California registered at least three moderate (M~6) earthquakes, activity which exceeds that of the Elsinore fault with a similar measured slip rate. Geodetic data based only on a few decades of GPS observations have been interpreted to show less than 1 mm/yr right-slip on the San Clemente fault, whereas larger rates, of about 5-10 mm/yr are described in the Inner Borderland between Catalina Island and the coast. Extrapolations of data from GPS stations on the Pacific Plate offshore Baja California also suggest larger rates west of San Clemente Island. Because there are few offshore locations (islands) for GPS observations, and San Clemente Island is likely within the broader zone of deformation of its namesake fault, these data miss the full slip rate. Seafloor observations from submersible discovered youthful fault scarps in turbidite muds that are inferred to represent large prehistoric earthquakes, (M~7). The potential for large offshore earthquakes, with tsunami generation that would affect the heavily populated adjacent coastal areas underscores the importance of resolving the slip rate and quantifying the hazard potential.

Comparison of Oceanic and Continental Lithosphere, Asthenosphere, and the LAB Through Shear Velocity Inversion of Rayleigh Wave Data from the ALBACORE Amphibious Array in Southern California

NASA Astrophysics Data System (ADS)

Amodeo, K.; Rathnayaka, S.; Weeraratne, D. S.; Kohler, M. D.

2016-12-01

Continental and oceanic lithosphere, which form in different tectonic environments, are studied in a single amphibious seismic array across the Southern California continental margin. This provides a unique opportunity to directly compare oceanic and continental lithosphere, asthenosphere, and the LAB (Lithosphere-Asthenosphere Boundary) in a single data set. The complex history of the region, including spreading center subduction, block rotation, and Borderland extension, allows us to study limits in the rigidity and strength of the lithosphere. We study Rayleigh wave phase velocities obtained from the ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) offshore seismic array project and invert for shear wave velocity structure as a function of depth. We divide the study area into several regions: continent, inner Borderland, outer Borderland, and oceanic seafloor categorized by age. A unique starting Vs model is used for each case including layer thicknesses, densities, and P and S velocities which predicts Rayleigh phase velocities and are compared to observed phase velocities in each region. We solve for shear wave velocities with the best fit between observed and predicted phase velocity data in a least square sense. Preliminary results indicate that lithospheric velocities in the oceanic mantle are higher than the continental region by at least 2%. The LAB is observed at 50 ± 20 km beneath 15-35 Ma oceanic seafloor. Asthenospheric low velocities reach a minimum of 4.2 km/s in all regions, but have a steeper positive velocity gradient at the base of the oceanic asthenosphere compared to the continent. Seismic tomography images in two and three dimensions will be presented from each study region.

Estimating cross-slope exchange from drifter tracks and from glider sections

NASA Astrophysics Data System (ADS)

Huthnance, John M.

2017-04-01

In areas of complex topography, it can be difficult to define "along-slope" or "cross-slope" direction, yet transport estimates are sensitive to these definitions, especially as along-slope flow is favoured by geostrophy. However, if drifter positions and hence underlying water depths are recorded regularly, we know where and when depth contours are crossed by the drifters, and hence by the water assuming that the drifters follow the water. An approach is discussed for deriving statistics of contour-crossing speed, via depth changes experienced by the drifters and an effective slope. The transport equation for (e.g.) salinity S can be reduced to an explicit equation for effective diffusivity K if we assume steady along-slope flow with known total transport Q, a salinity maximum at its "core" and effective diffusion to less saline waters to either side. Salinity gradients along the flow and to either side are needed to calculate K. Gliders provide a means of measuring salinity gradients in this context. Measurements at the continental shelf edge south-west of England and west of Scotland illustrate the calculation. Both approaches give overall rather than process-related estimates. There is limited scope for process discrimination according to (i) how often drifter locations are recorded and (ii) the time-intervals into which estimates are "binned". (i) Frequent recording may record more crossings owing to processes of short time scale, albeit these are less significant for slowly-evolving water contents. (ii) Sufficient samples for statistically significant estimates of exchange entail "bins" spanning some weeks or months for typically-limited numbers of drifters or gliders.

Nature and distribution of potential heavy-mineral resources offshore of the Atlantic Coast of the United States.

USGS Publications Warehouse

Grosz, A.E.

1987-01-01

The US is dependent on foreign imports of placer heavy minerals for a majority of its ilmenite and rutile, and virtually all of its monazite requirements. Although sand deposits in the SE US are important domestic sources of these heavy minerals (HM) and a number of other less well-known heavy-mineral species, global onshore reserves of placer minerals may fall short of demand in as few as 20 years. Insofar as they are important commodities for the future, offshore HM placers will become more important, but much research on them remains to be done. Results of recent offshore studies, based on surficial grab samples, indicate an average of about 2 weight percent HM in surficial Atlantic Continental Shelf (ACS) sediments, in strong contrast with previous estimates of an average of 0.16% HM. Although provocative, the information from these grab samples does not include the thickness of the HM deposits and thus their volume and tonnage cannot be estimated.-from Author

Towers for Offshore Wind Turbines

NASA Astrophysics Data System (ADS)

Kurian, V. J.; Narayanan, S. P.; Ganapathy, C.

2010-06-01

Increasing energy demand coupled with pollution free production of energy has found a viable solution in wind energy. Land based windmills have been utilized for power generation for more than two thousand years. In modern times wind generated power has become popular in many countries. Offshore wind turbines are being used in a number of countries to tap the energy from wind over the oceans and convert to electric energy. The advantages of offshore wind turbines as compared to land are that offshore winds flow at higher speed than onshore winds and the more available space. In some land based settings, for better efficiency, turbines are separated as much as 10 rotor diameters from each other. In offshore applications where only two wind directions are likely to predominate, the distances between the turbines arranged in a line can be shortened to as little as two or four rotor diameters. Today, more than a dozen offshore European wind facilities with turbine ratings of 450 kw to 3.6 MW exist offshore in very shallow waters of 5 to 12 m. Compared to onshore wind turbines, offshore wind turbines are bigger and the tower height in offshore are in the range of 60 to 80 m. The water depths in oceans where offshore turbines can be located are within 30 m. However as the distance from land increases, the costs of building and maintaining the turbines and transmitting the power back to shore also increase sharply. The objective of this paper is to review the parameters of design for the maximum efficiency of offshore wind turbines and to develop types offshore towers to support the wind turbines. The methodology of design of offshore towers to support the wind turbine would be given and the environmental loads for the design of the towers would be calculated for specific cases. The marine corrosion on the towers and the methods to control the corrosion also would be briefly presented. As the wind speeds tend to increase with distance from the shore, turbines build father

A Model based Examination of Conditions for Ignition of Turbidity Currents on Slopes

NASA Astrophysics Data System (ADS)

Mehta, A. J.; Krishna, G.

2009-12-01

Turbidity currents form a major mechanism for the movement of sediment in the natural environment. Self-accelerating turbidity currents over continental slopes are of considerable scientific and engineering interest due to their role as agents for submarine sediment transportation from the shelf to the seabed. Such currents are called ignitive provided they eventually reach a catastrophic state as acceleration results in high sediment loads due to erosion of the sloping bed. A numerical model, which treats the fluid and the particles as two separate phases, is applied to investigate the effects of particle size, initial flow friction velocity and mild bed slope on the ignitive condition. Laboratory experimental data have been included as part of the analysis for qualitative comparison purposes. Ignition for the smallest of the three selected sizes (0.21mm) of medium sand typical of Florida beaches was found to depend on the initial conditions at the head of the slope as determined by the pressure gradient. Bed slope seemed to be of secondary importance. For the two sands with larger grain sizes (0.28mm and 0.35mm) the slope was found to play a more important role when compared to the initial pressure gradient. For a given pressure gradient, increasing the slope increased the likelihood of self-acceleration. It is concluded that in general ignition cannot be defined merely in terms of positive values of the velocity gradient and the sediment flux gradient along the slope. Depending on particle size the initial pressure gradient can also play a role. For the selected initial conditions (grain size, pressure gradient and bed slope), out of the 54 combinations tested, all except three satisfied the Knapp-Bagnold criterion for auto-suspension irrespective of whether the turbid current was ignitive or non-ignitive. In all 54 cases the current was found to erode the bed. Further use of the model will require accommodation of wider ranges of sediment size and bed density

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-Miocene.

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