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Sample records for adjacent continental margin

  1. Crustal structure and development of the SW Barents Sea and the adjacent continental margin

    Energy Technology Data Exchange (ETDEWEB)

    Breivik, Asbjoern Johan

    1998-12-31

    Because of its expected petroleum potential, the western Barents Sea has been extensively mapped and investigated. The present thesis deals with many aspects of the geological development of this area. The emphasis is on Late Paleozoic structuring, Late Mesozoic basin formation, and early Tertiary margin formation including geodynamical response to the late Cenozoic sedimentation. The thesis begins with a review of the literature on the Late Palaeozoic structural development of the south-western Barents Sea, Svalbard and eastern Greenland. A structural map is developed for the Upper Carboniferous rift system in the southwestern Barents Sea that shows the interference of the northeasterly and the northerly structural grain. A discussion of the Ottar Basin uses a combination of seismic interpretation and gravity modelling to investigate this important structural element of the Upper Palaeozoic rift system. Previous work on Late Mesozoic basin formation in the southwestern Barents Sea is extended by incorporating new seismic reflection data and gravity modelling. Finally, the focus is shifted from the Barents Sea shelf to the continental-ocean transition and the oceanic basin. Gridded free-air gravity data from the ERS-1 enables the construction of a Bouguer gravity map of unprecedented resolution. The relationship between isostacy and gravity was resolved by modelling the thermal structure across the margin. Admittance analysis of the relationship between bathymetry and free-air gravity indicates an elastic thickness of the oceanic Lithosphere of 15-20 km, which is compatible with the depth to the 450{sup o}C isotherm obtained from thermal modelling. It is concluded that the southwestern Barents Sea margin does not deviate in any significant respects from passive rifted margins, except for a very straight and narrow continent-ocean transition zone. 332 refs., 55 figs., 7 tabs.

  2. Deep continental margin reflectors

    Science.gov (United States)

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

    1985-01-01

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

  3. The role of tectonic inheritance in the morphostructural evolution of the Galicia continental margin and adjacent abyssal plains from digital bathymetric model (DBM) analysis (NW Spain)

    Science.gov (United States)

    Maestro, A.; Jané, G.; Llave, E.; López-Martínez, J.; Bohoyo, F.; Druet, M.

    2017-09-01

    The identification of recent major tectonic structures in the Galicia continental margin and adjacent abyssal plains was carried out by means of a quantitative analysis of the linear structures having bathymetric expression on the seabed. It was possible to identify about 5800 lineaments throughout the entire study area, of approximately 271,500 km2. Most lineaments are located in the Charcot and Coruña highs, in the western sector of the Galicia Bank, in the area of the Marginal Platforms and in the northern sector of the margin. Analysis of the lineament orientations shows a predominant NE-SW direction and three relative maximum directions: NW-SE, E-W and N-S. The total length of the lineaments identified is over 44,000 km, with a mode around 5000 m and an average length of about 7800 m. In light of different tectonic studies undertaken in the northwestern margin of the Iberian Peninsula, we establish that the lineaments obtained from analysis of the digital bathymetric model of the Galicia continental margin and adjacent abyssal plains would correspond to fracture systems. In general, the orientation of lineaments corresponds to main faults, tectonic structures following the directions of ancient faults that resulted from late stages of the Variscan orogeny and Mesozoic extension phases related to Triassic rifting and Upper Jurassic to Early Cretaceous opening of the North Atlantic Ocean. The N-S convergence between Eurasian and African plates since Palaeogene times until the Miocene, and NW-SE convergence from Neogene to present, reactivated the Variscan and Mesozoic fault systems and related physiography.

  4. Contributions to knowledge of the continental margin of Uruguay. Uruguayan continental margin: Physiographic and seismic analysis

    International Nuclear Information System (INIS)

    Preciozzi, F

    2014-01-01

    This work is about the kind of continental margins such as a )Atlantic type passive margins which can be hard or soft b) An active or Pacific margins that because of the very frequent earthquakes develop a morphology dominated by tectonic processes. The Uruguayan continental margin belongs to a soft Atlantic margin

  5. Exploration of the continental margins of India

    Digital Repository Service at National Institute of Oceanography (India)

    Siddiquie, H.N.; Hashimi, N.H.; Vora, K.H.; Pathak, M.C.

    In mid 1970's the National Institute of Oceanography, Goa, India prepared a plan for systematic regional, geological and geophysical surveys of the continental margins of India. This involved over 75,000 km of underway (bathymetric, side scan sonar...

  6. Continental transform margins : state of art and future milestones

    Science.gov (United States)

    Basile, Christophe

    2010-05-01

    to be emphasized. There is not only one type of transform margins, but as for divergent margins huge changes from one margin to another in both structure and evolution. Multiple types have to be evidenced together with the various parameters that should control the variability. As for divergent margins, special attention should be paid to conjugated transform margins as a tool to assess symmetrical / asymmetrical processes in the oceanic opening. Attention should also be focused on the three-dimensional structure of the intersections between transform and divergent margins, such as the one where the giant oil field Jubilee was recently discovered. There is almost no 3D data available in these area, and their structures still have to be described. An other key point to develop is the mechanical behavior of the lithosphere in and in the vicinity of transform margins. The classical behaviors (isostasy, elastic flexure) have be tested extensively. The localization of the deformation by the transform fault, and the coupling of continental and oceanic lithosphere across the transform fault have to be adressed to understand the evolution of these margins. Again as for divergent margins, new concepts are needed to explain the variations in the post-rift and post-transform subsidence, that can not always be explained by classical subsidence models. But the most remarkable advance in our understanding of transform margins may be related to the study of interactions between the lithosphere and adjacent envelops : deep interactions with the mantle, as underplating, tectonic erosion, or possible lateral crustal flow ; surficial interactions between structural evolution, erosion and sedimentation processes in transform margins may affect the topography and bathymetry, thus the oceanic circulation with possible effects on regional and global climate.

  7. Atlantic continental margin of the United States

    Science.gov (United States)

    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.

  8. Reconstructing Rodinia by Fitting Neoproterozoic Continental Margins

    Science.gov (United States)

    Stewart, John H.

    2009-01-01

    Reconstructions of Phanerozoic tectonic plates can be closely constrained by lithologic correlations across conjugate margins by paleontologic information, by correlation of orogenic belts, by paleomagnetic location of continents, and by ocean floor magmatic stripes. In contrast, Proterozoic reconstructions are hindered by the lack of some of these tools or the lack of their precision. To overcome some of these difficulties, this report focuses on a different method of reconstruction, namely the use of the shape of continents to assemble the supercontinent of Rodinia, much like a jigsaw puzzle. Compared to the vast amount of information available for Phanerozoic systems, such a limited approach for Proterozoic rocks, may seem suspect. However, using the assembly of the southern continents (South America, Africa, India, Arabia, Antarctica, and Australia) as an example, a very tight fit of the continents is apparent and illustrates the power of the jigsaw puzzle method. This report focuses on Neoproterozoic rocks, which are shown on two new detailed geologic maps that constitute the backbone of the study. The report also describes the Neoproterozoic, but younger or older rocks are not discussed or not discussed in detail. The Neoproterozoic continents and continental margins are identified based on the distribution of continental-margin sedimentary and magmatic rocks that define the break-up margins of Rodinia. These Neoproterozoic continental exposures, as well as critical Neo- and Meso-Neoproterozoic tectonic features shown on the two new map compilations, are used to reconstruct the Mesoproterozoic supercontinent of Rodinia. This approach differs from the common approach of using fold belts to define structural features deemed important in the Rodinian reconstruction. Fold belts are difficult to date, and many are significantly younger than the time frame considered here (1,200 to 850 Ma). Identifying Neoproterozoic continental margins, which are primarily

  9. Behaviour of REEs in a tropical estuary and adjacent continental ...

    Indian Academy of Sciences (India)

    The distribution and accumulation of the rare earth elements (REE) in the sediments of the Cochin. Estuary and adjacent continental shelf ... in petroleum cracking catalysis, for the produc- tion of light weight hydrocarbons such as ...... Physics and Chemistry of the Earth (eds) Ahrens L H,. Press F, Runcorn S K and Urey H C ...

  10. Investigating Continental Margins: An Activity to Help Students Better Understand the Continental Margins of North America

    Science.gov (United States)

    Poli, Maria-Serena; Capodivacca, Marco

    2011-01-01

    Continental margins are an important part of the ocean floor. They separate the land above sea level from the deep ocean basins below and occupy about 11% of Earth's surface. They are also economically important, as they harbor both mineral resources and some of the most valuable fisheries in the world. In this article students investigate North…

  11. Geological features and geophysical signatures of continental margins of India

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.

    margins of India, with which some of the main geological features of continental margins have been modified. This article provides a brief review on theory of plate tectonics for understanding the process of intra- continental breakup..., thereby the results are discussed for classification of the margins. The Theory of Plate Tectonics The theory of continental drift, which paves the way for discovery of plate tectonics, was put forward by Alfred Lother Wegener as early as in 1912...

  12. Contributions to knowledge of the continental margin of Uruguay. Description of background samples in the continental margin of Uruguay

    International Nuclear Information System (INIS)

    Preciozzi, F

    2015-01-01

    This study provide data concerning of the background sediments of the continental margin of Uruguay. There were carried out different works with witnesses in order to extract various sediment samples from the continental shelf

  13. Understanding Continental Margin Biodiversity: A New Imperative

    Science.gov (United States)

    Levin, Lisa A.; Sibuet, Myriam

    2012-01-01

    Until recently, the deep continental margins (200-4,000 m) were perceived as monotonous mud slopes of limited ecological or environmental concern. Progress in seafloor mapping and direct observation now reveals unexpected heterogeneity, with a mosaic of habitats and ecosystems linked to geomorphological, geochemical, and hydrographic features that influence biotic diversity. Interactions among water masses, terrestrial inputs, sediment diagenesis, and tectonic activity create a multitude of ecological settings supporting distinct communities that populate canyons and seamounts, high-stress oxygen minimum zones, and methane seeps, as well as vast reefs of cold corals and sponges. This high regional biodiversity is fundamental to the production of valuable fisheries, energy, and mineral resources, and performs critical ecological services (nutrient cycling, carbon sequestration, nursery and habitat support). It is under significant threat from climate change and human resource extraction activities. Serious actions are required to preserve the functions and services provided by the deep-sea settings we are just now getting to know.

  14. Anomalous heat flow belt along the continental margin of Brazil

    Science.gov (United States)

    Hamza, Valiya M.; Vieira, Fabio P.; Silva, Raquel T. A.

    2018-01-01

    A comprehensive analysis of thermal gradient and heat flow data was carried out for sedimentary basins situated in the continental margin of Brazil (CMB). The results point to the existence of a narrow belt within CMB, where temperature gradients are higher than 30 °C/km and the heat flow is in excess of 70 mW/m2. This anomalous geothermal belt is confined between zones of relatively low to normal heat flow in the adjacent continental and oceanic regions. The width of the belt is somewhat variable, but most of it falls within the range of 100-300 km. The spatial extent is relatively large in the southern (in the basins of Pelotas, Santos and Campos) and northern (in the basins of Potiguar and Ceará) parts, when compared with those in the central parts (in the basins of South Bahia, Sergipe and Alagoas). The characteristics of heat flow anomalies appear to be compatible with those produced by thermal sources at depths in the lower crust. Hence, magma emplacement at the transition zone between lower crust and upper mantle is considered the likely mechanism producing such anomalies. Seismicity within the belt is relatively weak, with focal depths less than 10 km for most of the events. Such observations imply that "tectonic bonding" between continental and oceanic segments, at the transition zone of CMB, is relatively weak. Hence, it is proposed that passive margins like CMB be considered as constituting a type of plate boundary that is aseismic at sub-crustal levels, but allows for escape of significant amounts of earth's internal heat at shallow depths.

  15. Vertical tectonics at an active continental margin

    Science.gov (United States)

    Houlié, N.; Stern, T. A.

    2017-01-01

    Direct observations of vertical movements of the earth's surface are now possible with space-based GPS networks, and have applications to resources, hazards and tectonics. Here we present data on vertical movements of the Earth's surface in New Zealand, computed from the processing of GPS data collected between 2000 and 2015 by 189 permanent GPS stations. We map the geographical variation in vertical rates and show how these variations are explicable within a tectonic framework of subduction, volcanic activity and slow slip earthquakes. Subsidence of >3 mm/yr is observed along southeastern North Island and is interpreted to be due to the locked segment of the Hikurangi subduction zone. Uplift of 1-3 mm/yr further north along the margin of the eastern North Island is interpreted as being due to the plate interface being unlocked and underplating of sediment on the subduction thrust. The Volcanic Plateau of the central North Island is being uplifted at about 1 mm/yr, which can be explained by basaltic melts being injected in the active mantle-wedge at a rate of ∼6 mm/yr. Within the Central Volcanic Region there is a 250 km2 area that subsided between 2005 and 2012 at a rate of up to 14 mm/yr. Time series from the stations located within and near the zone of subsidence show a strong link between subsidence, adjacent uplift and local earthquake swarms.

  16. Modern sedimentary processes along the Doce river adjacent continental shelf

    Directory of Open Access Journals (Sweden)

    Valéria da Silva Quaresma

    Full Text Available In areas of the continental shelf where sediment supply is greater than the sediment dispersion capacity, an extensive terrigenous deposits and consequently submerged deltas can be formed. The Eastern Brazilian shelf is characterized by the occurrence of river feed deltas in between starving coasts. Herein, modern sedimentary processes acting along the Doce river adjacent continental shelf are investigated. The main objective was to understand the shelf sediment distribution, recognizing distinct sedimentary patterns and the major influence of river sediment discharge in the formation of shelf deposits. The study used 98 surficial samples that were analyzed for grain size, composition and bulk density. Results revealed 3 distinct sectors: south - dominated by mud fraction with a recent deposition from riverine input until 30 m deep and from this depth bioclastic sands dominate; central north - sand mud dominated, been recognized as a bypass zone of resuspended sediment during high energy events; and north - relict sands with high carbonate content. The modern sedimentation processes along the Doce river continental shelf is dominated by distinct sedimentary regimes, showing a strong fluvial influence associated with wave/wind induced sediment dispersion and a carbonate regime along the outer shelf. These regimes seem to be controlled by the distance from the river mouth and bathymetric gradients.

  17. Glacier-influenced sedimentation on high-latitude continental margins

    National Research Council Canada - National Science Library

    Dowdeswell, J. A; Cofaigh, C. Ó

    2002-01-01

    This book examines the process and patterns of glacier-influenced sedimentation on high-latitude continental margins and the geophysical and geological signatures of the resulting sediments and landform...

  18. U.S. East Coast Continental Margin (CONMAR) Sediment Data

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The USGS/WHOI Continental Margin (CONMAR) Data set was compiled by the U.S. Geological Survey and the Woods Hole Oceanographic Institution as a joint program of...

  19. Seismic structure and tectonics of the continental margins of India

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Chaubey, A.K.; Rao, D.G.; Reddy, P.R.

    floor belong to different lithospheric plates. Active margins are commonly the sites of tectonic activity such as earthquakes, volcanoes, mountain building and formation of new igneous rocks. Because of the mountainous terrain the continental shelf... greater proportion of the river borne sediments occur on the shelves, continental slopes, and deep sea fans where terrigenous sedimentation is dominant process. On lower slopes and continental rises, fine-grained siliciclastics commonly mixed...

  20. Crustal growth at active continental margins: Numerical modeling

    NARCIS (Netherlands)

    Vogt, Katharina; Gerya, Taras; Castro, Antonio

    The dynamics and melt sources for crustal growth at active continental margins are analyzed by using a 2D coupled petrological–thermomechanical numerical model of an oceanic-continental subduction zone. This model includes spontaneous slab retreat and bending, dehydration of subducted crust, aqueous

  1. Magma-Assisted Continental Break-up Encroached on Previously Stretched Continental Lithosphere - the NE Greenland Composite Passive Margin

    Science.gov (United States)

    Mazur, S.; Rippington, S.; Houghton, P.

    2014-12-01

    Volcanic continental margins have a number of distinctive features that are different from those typical of magma-poor continental margins. However, in some places volcanic margins may develop parallel to older, highly extended rift systems. In such situations the resultant continental margin shows a complex structure that merges the characteristics of volcanic and non-volcanic margins. Furthermore, the evolution of this younger magma-rich margin is restricted by the pre-existing lithospheric architecture, causing it to diverge from the generally assumed formation model. We use the case of NE Greenland to demonstrate the structure of a composite margin firstly subjected to extensive extension and later overprinted by magma-assisted continental break-up. The NE Greenland continental margin is a highly extended margin, that is up to 250km wide, with crystalline crust attaining the maximum thickness near to the coast of Greenland and at the Danmarkshaven Ridge. The latter represents a major basement horst formed during an Early Cretaceous rifting event. To the east of the Danmarkshaven Ridge, crust is stretched and onlapped by the Early Cretaceous sedimentary basin. The effects of Tertiary break-up are observable in a relatively narrow zone 80 km wide that usually includes an extended edge of continental crust and an adjacent section of oceanic crust. A volcano-sedimentary succession produced during the break-up reaches the maximum thickness of c. 8000 m above a continent-ocean transition (COB). Oceanic crust overlain by mixed volcanic and sedimentary rocks is thicker than usual. No observable SDRs or igneous transitional crust are present near to the COB. Instead, a chain of high density bodies follow the COB at the base of crust. The features observed suggest relatively little extension associated with the Tertiary break-up. Instead localised mantle melting presumably led to rapid break-up with crustal dilatation promptly balanced by production of thick oceanic

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

    Science.gov (United States)

    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

  3. Comparative biogeochemistry-ecosystem-human interactions on dynamic continental margins

    Science.gov (United States)

    Levin, Lisa A.; Liu, Kon-Kee; Emeis, Kay-Christian; Breitburg, Denise L.; Cloern, James; Deutsch, Curtis; Giani, Michele; Goffart, Anne; Hofmann, Eileen E.; Lachkar, Zouhair; Limburg, Karin; Liu, Su-Mei; Montes, Enrique; Naqvi, Wajih; Ragueneau, Olivier; Rabouille, Christophe; Sarkar, Santosh Kumar; Swaney, Dennis P.; Wassman, Paul; Wishner, Karen F.

    2014-01-01

    The ocean’s continental margins face strong and rapid change, forced by a combination of direct human activity, anthropogenic CO2-induced climate change, and natural variability. Stimulated by discussions in Goa, India at the IMBER IMBIZO III, we (1) provide an overview of the drivers of biogeochemical variation and change on margins, (2) compare temporal trends in hydrographic and biogeochemical data across different margins (3) review ecosystem responses to these changes, (4) highlight the importance of margin time series for detecting and attributing change and (5) examine societal responses to changing margin biogeochemistry and ecosystems. We synthesize information over a wide range of margin settings in order to identify the commonalities and distinctions among continental margin ecosystems. Key drivers of biogeochemical variation include long-term climate cycles, CO2-induced warming, acidification, and deoxygenation, as well as sea level rise, eutrophication, hydrologic and water cycle alteration, changing land use, fishing, and species invasion. Ecosystem responses are complex and impact major margin services including primary production, fisheries production, nutrient cycling, shoreline protection, chemical buffering, and biodiversity. Despite regional differences, the societal consequences of these changes are unarguably large and mandate coherent actions to reduce, mitigate and adapt to multiple stressors on continental margins.

  4. Closing the North American Carbon Budget: Continental Margin Fluxes Matter!

    Science.gov (United States)

    Najjar, R.; Benway, H. M.; Siedlecki, S. A.; Boyer, E. W.; Cai, W. J.; Coble, P. G.; Cross, J. N.; Friedrichs, M. A.; Goni, M. A.; Griffith, P. C.; Herrmann, M.; Lohrenz, S. E.; Mathis, J. T.; McKinley, G. A.; Pilskaln, C. H.; Smith, R. A.; Alin, S. R.

    2015-12-01

    Despite their relatively small surface area, continental margins are regions of intense carbon and nutrient processing, export and exchange, and thus have a significant impact on global biogeochemical cycles. In response to recommendations for regional synthesis and carbon budget estimation for North America put forth in the North American Continental Margins workshop report (Hales et al., 2008), the Ocean Carbon and Biogeochemistry (OCB) Program and North American Carbon Program (NACP) began coordinating a series of collaborative, interdisciplinary Coastal CARbon Synthesis (CCARS) research activities in five coastal regions of North America (Atlantic Coast, Pacific Coast, Gulf of Mexico, Arctic, Laurentian Great Lakes) to improve quantitative assessments of the North American carbon budget. CCARS workshops and collaborative research activities have resulted in the development of regional coastal carbon budgets based on recent literature- and model-based estimates of major carbon fluxes with estimated uncertainties. Numerous peer-reviewed papers and presentations by involved researchers have highlighted these findings and provided more in-depth analyses of processes underlying key carbon fluxes in continental margin systems. As a culminating outcome of these synthesis efforts, a comprehensive science plan highlights key knowledge gaps identified during this synthesis and provides explicit guidance on future research and observing priorities in continental margin systems to help inform future agency investments in continental margins research. This presentation will provide an overview of regional and flux-based (terrestrial inputs, biological transformations, sedimentary processes, atmospheric exchanges, lateral carbon transport) synthesis findings and key recommendations in the science plan, as well as a set of overarching priorities and recommendations on observations and modeling approaches for continental margin systems.

  5. Climatic controls on arid continental basin margin systems

    Science.gov (United States)

    Gough, Amy; Clarke, Stuart; Richards, Philip; Milodowski, Antoni

    2016-04-01

    Alluvial fans are both dominant and long-lived within continental basin margin systems. As a result, they commonly interact with a variety of depositional systems that exist at different times in the distal extent of the basin as the basin evolves. The deposits of the distal basin often cycle between those with the potential to act as good aquifers and those with the potential to act as good aquitards. The interactions between the distal deposits and the basin margin fans can have a significant impact upon basin-scale fluid flow. The fans themselves are commonly considered as relatively homogeneous, but their sedimentology is controlled by a variety of factors, including: 1) differing depositional mechanisms; 2) localised autocyclic controls; 3) geometrical and temporal interactions with deposits of the basin centre; and, 4) long-term allocyclic climatic variations. This work examines the basin margin systems of the Cutler Group sediments of the Paradox Basin, western U.S.A and presents generalised facies models for the Cutler Group alluvial fans as well as for the zone of interaction between these fans and the contemporaneous environments in the basin centre, at a variety of scales. Small-scale controls on deposition include climate, tectonics, base level and sediment supply. It has been ascertained that long-term climatic alterations were the main control on these depositional systems. Models have been constructed to highlight how both long-term and short-term alterations in the climatic regime can affect the sedimentation in the basin. These models can be applied to better understand similar, but poorly exposed, alluvial fan deposits. The alluvial fans of the Brockram Facies, northern England form part of a once-proposed site for low-level nuclear waste decommissioning. As such, it is important to understand the sedimentology, three-dimensional geometry, and the proposed connectivity of the deposits from the perspective of basin-scale fluid flow. The developed

  6. Neogene sedimentation on the outer continental margin, southern Bering Sea

    Science.gov (United States)

    Vallier, T.L.; Underwood, M.B.; Gardner, J.V.; Barron, J.A.

    1980-01-01

    Neogene sedimentary rocks and sediments from sites on the outer continental margin in the southern Bering Sea and on the Alaska Peninsula are dominated by volcanic components that probably were eroded from an emergent Aleutian Ridge. A mainland continental source is subordinate. Most sediment in the marine environment was transported to the depositional sites by longshore currents, debris flows, and turbidity currents during times when sea level was near the outermost continental shelf. Fluctuations of sea level are ascribed both to worldwide glacio-eustatic effects and to regional vertical tectonics. Large drainage systems, such as the Yukon and Kuskokwim Rivers, had little direct influence on sedimentation along the continental slope and Unmak Plateau in the southern Bering Sea. Sediments from those drainage systems probably were transported to the floor of the Aleutian Basin, to the numerous shelf basins that underlie the outer continental shelf, and to the Arctic Ocean after passing through the Bering Strait. Environments of deposition at the sites along the outer continental margin have not changed significantly since the middle Miocene. The site on the Alaska Peninsula, however, is now emergent following shallow-marine and transitional sedimentation during the Neogene. ?? 1980.

  7. Slumping on the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Guptha, M.V.S.; Mohan, R.; Muralinath, A.S.

    continental margin is believed to have set in motion during the beginning of Holocene. Besides, it infers that after 6 k.y. B.P. the magnitude of slumping is minimal. The slumping may be attributed to the evolution of methane gas as one of the important causes...

  8. Early diagenesis of phosphorus in continental margin sediments

    NARCIS (Netherlands)

    Slomp, C.P.

    1997-01-01

    Most of the organic material in the oceans that reaches the sea floor is deposited on continental margins and not in the deep sea. This organic matter is the principal carrier of phosphorus (P) to sediments. A part of the organic material is buried definitely. The other part decomposes,

  9. Ooid turbidites from the Central Western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, P.S.

    Gravity displaced debris flows/turbidites have been observed in five box cores collected between water depths of 649 and 3,627 m from the Central Western continental margin of India. Studies on grain size, carbonate content, and coarse fraction...

  10. Holocene subsurface temperature variability in the eastern Antarctic continental margin

    NARCIS (Netherlands)

    Kim, J.H.; Crosta, X.; Willmott, V.; Renssen, H.; Bonnin, J.; Helmke, P.; Schouten, S.; Sinninghe Damsté, J.S.

    2012-01-01

    We reconstructed subsurface (similar to 45-200 m water depth) temperature variability in the eastern Antarctic continental margin during the late Holocene, using an archaeal lipid-based temperature proxy (TEX86 L). Our results reveal that subsurface temperature changes were probably positively

  11. Contributions to knowledge of the continental margin of Uruguay. Uruguayan continental margin: morphology, geology and identification of the base of the slope

    International Nuclear Information System (INIS)

    Preciozzi, F.

    2014-01-01

    This work is about the morphology, geology and the identification of the base of the slope in the The Uruguayan continental margin which corresponds to the the type of divergent, volcanic and segmented margins. Morphologically is constituted by a clearly defined continental shelf, as well as a continental slope that presents configuration changes from north to south and passes directly to the abyssal plain

  12. Tectonic Evolution of Mozambique Ridge in East African continental margin

    Science.gov (United States)

    Tang, Yong

    2017-04-01

    Tectonic Evolution of Mozambique Ridge in East African continental margin Yong Tang He Li ES.Mahanjane Second Institute of Oceanography,SOA,Hangzhou The East Africa passive continental margin is a depression area, with widely distributed sedimentary wedges from southern Mozambique to northern Somali (>6500km in length, and about 6km in thickness). It was resulted from the separation of East Gondwana, and was developed by three stages: (1) rifting in Early-Middle Jurassic; (2) spreading from Late Jurassic to Early Cretaceous; (3) drifting since the Cretaceous period. Tectonic evolution of the Mozambique continental margin is distinguished by two main settings separated by a fossil transform, the Davie Fracture Zone; (i) rifting and transform setting in the northern margin related to opening of the Somali and Rovuma basins, and (ii) rifting and volcanism setting during the opening of the Mozambique basin in the southern margin. 2D reflection seismic investigation of the crustal structure in the Zambezi Delta Depression, provided key piece of evidence for two rifting phases between Africa and Antarctica. The magma-rich Rift I phase evolved from rift-rift-rift style with remarkable emplacement of dyke swarms (between 182 and 170 Ma). Related onshore outcrops are extensively studied, the Karoo volcanics in Mozambique, Zimbabwe and South Africa, all part of the Karoo "triple-junction". These igneous bodies flow and thicken eastwards and are now covered by up to 5 km of Cretaceous and Tertiary sediments and recorded by seismic and oil exploration wells. Geophysical and geological data recorded during oceanographic cruises provide very controversial results regarding the nature of the Mozambique Ridge. Two conflicting opinions remains open, since the early expeditions to the Indian Ocean, postulating that its character is either magmatic (oceanic) or continental origin. We have carried out an China-Mozambique Joint Cruise(CMJC) on southern Mozambique Basin on 1st June to

  13. Rockall Continental Margin Report. Final geological report (5 volumes)

    OpenAIRE

    Stoker, M.S.; Hitchen, K.

    1995-01-01

    The Rockall Continental Margin Project was a 3-year research programme, undertaken between April 1992 and March 1995, designed to investigate the geology and resource potential of part of the frontier area west of Scotland. The programme was funded by a consortium comprising the British Geological Survey (BGS) and 8 exploration companies - BP, British Gas, Conoco, EE Caledonia, Elf, Enterprise, Esso and Mobil. The study has focused on the central and northern Rockall Trough, al...

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

    Science.gov (United States)

    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

  15. Paleogene continental margin truncation in southwestern Mexico: Geochronological evidence

    Science.gov (United States)

    Schaaf, Peter; MoráN-Zenteno, Dante; HernáNdez-Bernal, Maria Del Sol; SolíS-Pichardo, Gabriela; Tolson, Gustavo; KöHler, Hermann

    1995-12-01

    The reasons for, and mechanisms of, continental margin truncation in SW Mexico where Mesozoic-Cenozoic plutons are situated directly on the Pacific coast, are not yet well understood. Large-scale dextral and/or sinistral displacements of the continental margin terranes, now forming parts of Baja California or the Chortis block, have been proposed. The well-defined along-coast NW-SE decreasing granitoid intrusion age trend (˜1.2 cm/yr in the 100 Ma-40 Ma time interval) between Puerto Vallarta and Zihuatanejo is interpreted by us to be a geometric artifact of oblique continental margin truncation rather than the consequence of a sinistral offset of the Chortis block from those latitudes toward the SE. Changes in the dip and velocity of the NNW-SSE trending Cretaceous-Tertiary subduction zone resulted in a landward migration of the magmatic arc. Taking into account certain stratigraphic affinities of Chortis and the Oaxaca and Mixteca terranes, together with the known displacement rates along the North America-Caribbean Plate boundary, the northwesternmost paleoposition of the Chortis block with respect to SW Mexico was near Zihuatanejo. In contrast, between Zihuatanejo and the Isthmus of Tehuantepec, the cessation of the Tertiary magmatism decreased more rapidly (˜7.7 cm/yr), although the trend is not so obvious. Starting in the late Eocene, Chortis moved about 1100 km to the SE along a transform boundary associated with the opening of the Cayman Trough. Based on our geochronological data and structural relationships between mylonite zones and plutons in the Acapulco-Tehuantepec area, we propose an approximately 650 km SE movement of Chortis from about 40-25 Ma, with a velocity of 6.5-4.3 cm/yr. Since this is considerably slower than the decreasing age trend obtained by us using the geochronological data, we consider batholith formation in this segment to predate and postdate the offshore passage of the North America-Farallon-Caribbean triple junction. Geological

  16. Continental margin radiography from a potential field and sediment thickness standpoint: the Iberian Atlantic Margin

    Energy Technology Data Exchange (ETDEWEB)

    Catalan, M.; Martos, Y. M.; Martin-Davila, J.; Munoz-Martin, A.; Carbo, A.; Druet, M.

    2015-07-01

    This study reviews the state of knowledge in the Iberian Atlantic margin. In order to do this, the margin has been divided into three provinces: the Galicia margin, the southern Iberian abyssal plain, and the Tagus abyssal plain. We have used potential field and sediment thickness data. This has allowed us to study the crust, setting limits for the continental crust domain, and the amplitude of the so-called ocean-continent transition, whose end marks the beginning of the oceanic crust. The study shows the continental crust in the Galician margin to be the widest, about 210 km in length, whilst the ocean-continent transition varies slightly in this province: between 65 km wide in the south and 56 km wide in the north. This result shows up some differences with the hypothesis of other authors. The situation in the southern Iberian abyssal plain is nearly the opposite. Its continental crust extends approximately 60 km, whilst the ocean-continent transition zone is 185 km long. The Tagus abyssal plain study shows a faster morphological evolution than the others, according with the amount of crustal thinning β, the ocean-continent transition domain spanning 100 km. These results support a transitional intermediate character for almost the whole Tagus plain, in contrary to what other authors have stated. (Author)

  17. Tectonostratigraphy of the Passive Continental Margin Offshore Indus Pakistan

    Science.gov (United States)

    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

  18. Structure of shumagin continental margin, Western Gulf of Alaska

    Energy Technology Data Exchange (ETDEWEB)

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

    1985-04-01

    The Shumagin margin is characterized by five major structural features or trends: (1) Shumagin basin, containing about 2.5 km of late Miocene and younger strata above acoustic basement; (2) Sanak basin, containing as much as 8 km of dominantly late Cenozoic strata in two subbasins separated by a basement high; (3) cenozoic shelf-edge and upper-slope sedimentary wedges that are 3-4 km thick and possibly as thick as 6 km; (4) a midslope structural trend, Unimak ridge, that is characterized by numerous surface and subsurface structural highs; and (5) a 30-km wide accretionary complex at the base of the slope. A thin (less than 1-2 km) sediment cover of Miocene and younger age covers the continental shelf areas outside of Shumagin and Sanak basins. The tectonic history of the margin includes: (1)j late Cretaceous or early Tertiary removal of the seaward part of the Cretaceous Alaska Peninsula margin along the Border Ranges fault and accretion of the Shumagin Formation against the truncated margin; (2) Miocene uplift and erosion of the shelf; (3) middle or late Miocene uplift of Unimak ridge; and (4) late Miocene and younger subsidence and infilling of Sanak and Shumagin basins, and subduction-accretion along the Aleutian Trench.

  19. Preface: Biogeochemistry–ecosystem interaction on changing continental margins in the Anthropocene

    Digital Repository Service at National Institute of Oceanography (India)

    Liu, K-K.; Emeis, K.-C.; Levin, L.A.; Naqvi, S.W.A.; Roman, M.

    This special issue presents case studies of different continental marginswith different settings and problems. The domains examined cover awide spectrumof continental margin environments, fromwatersheds, estuaries and wetlands on the landward side...

  20. The Continental Margin of East Asia: a collage of multiple plates formed by convergence and extension from multiple directions

    Science.gov (United States)

    Mao, J.; Wang, T.; Ludington, S.; Qiu, Z.; Li, Z.

    2017-12-01

    East Asia is one of the most complex regions in the world. Its margin was divided into 4 parts: Northeast Asia, North China, South China and Southeast Asia. During the Phanerozoic, continental plates of East Asia have interacted successively with a) the Paleo Tethyan Ocean, b) the Tethyan and Paleo Pacific Oceans and c) the Pacific and Indian. In the Early Mesozoic, the Indosinian orogeny is characterized by the convergence and extension within multiple continental plates, whereas the Late Mesozoic Yanshanian orogeny is characterized by both convergence and compression due to oceanic subduction and by widespread extension. We propose this combination as "East Asia Continental Margin type." Except in Northeast Asia, where Jurassic and Cretaeous accretionary complexes are common, most magmatic rocks are the result of reworking of ancient margins of small continental plates; and oceanic island arc basalts and continental margin arc andesites are largely absent. Because South China is adjacent to the western margin of the Pacific Plate, some effects of its westward subduction must be unavoidable, but juvenile arc-related crust has not been identified. The East Asian Continental Margin is characterized by magmatic rocks that are the result of post-convergent tectonics, which differs markedly from the active continental margins of both South and North America. In summary, the chief characteristics of the East Asian Continental Margin are: 1) In Mesozoic, the periphery of multiple blocks experienced magmatism caused by lithospheric delamination and thinning in response to extension punctuated by shorter periods of convergence. 2) The main mechanism of magma generation was the partial melting of crustal rocks, due to underplating by upwelling mafic magma associated with the collapse of orogenic belts and both extension and compression between small continental blocks. 3) During orogeny, mostly high Sr/Y arc-related granitoids formed, whereas during post-orogenic times, A

  1. Mapping Mesophotic Reefs Along the Brazilian Continental Margin

    Science.gov (United States)

    Bastos, A.; Moura, R.; Amado Filho, G.; Ferreira, L.; Boni, G.; Vedoato, F.; D'Agostini, D.; Lavagnino, A. C.; Leite, M. D.; Quaresma, V.

    2017-12-01

    Submerged or drowned reefs constitute an important geological record of sea level variations, forming the substrate for the colonization of modern benthic mesophotic communities. Although mapping mesophotic reefs has increased in the last years, their spatial distribution is poorly known and the worldwide occurrence of this reef habitat maybe underestimated. The importance in recognizing the distribution of mesophotic reefs is that they can act as a refuge for corals during unsuitable environmental conditions and a repository for shallow water corals. Here we present the result of several acoustic surveys that mapped and discovered new mesophotic reefs along the Eastern and Equatorial Brazilian Continental Margin. Seabed mapping was carried out using multibeam and side scan sonars. Ground truthing was obtained using drop camera or scuba diving. Mesophotic reefs were mapped in water depths varying from 30 to 100m and under distinct oceanographic conditions, especially in terms of river load input and shelf width. Reefs showed distinct morphologies, from low relief banks and paleovalleys to shelf edge ridges. Extensive occurrence of low relief banks were mapped along the most important coralline complex province in the South Atlantic, the Abrolhos Shelf. These 30 to 40m deep banks, have no more than 3 meters in height and may represent fringing reefs formed during sea level stabilization. Paleovalleys mapped along the eastern margin showed the occurrence of coralgal ledges along the channel margins. Paleovalleys are usually deeper than 45m and are associated with outer shelf rhodolith beds. Shelf edge ridges (80 to 120m deep) were mapped along both margins and are related to red algal encrusting irregular surfaces that have more than 3m in height, forming a rigid substrate for coral growth. Along the Equatorial Margin, off the Amazon mouth, shelf edge patch reefs and rhodolith beds forming encrusting surfaces and shelf edge ridges were mapped in water depths greater

  2. The Role of the Submarine Channel Pernambuco in the Brazilian Continental Margin East

    International Nuclear Information System (INIS)

    Torres, L.; Villena, H.

    2010-01-01

    The Brazilian Continental Margin, which coastline measures more than 8,500km gives to Brazil continental dimensions. This huge region is conditioned by the action of process such as, sedimentals, tectonics, geomorphological and climatical, as example, which direct or in conjunction with other ones, since of continental break up between South America and Africa are going on and may be responsible for the current morphology of the margin. In accordance with this point of view, the Oriental part of the Brazilian Continental Margin, presents characteristics of a passive margin and fisiographically ''starved'', in which the continental break occur no more than 100km from de coastline and the sedimentary coverage is mainly carbonatic. The continental slope does not present great extension if compared with other parts of the Brazilian Margin and sharp gradient. The remark presence of the continental plateaus (Rio Grande Plateau and Pernambuco Plateau), which link with the continental rise and additionally the Paraiba, Pernambuco e Bahia seamounts, are the majors features in the morphology of the region between the slope and the continental rise. This paper will concentrate its focus on Bahia Seamount, with emphasis in the mainly erosive feature which cut transversally the seamounts, named Pernambuco Submarine Channel. It will be employed bathymetric multibeam and seismic data carried out by the Brazilian Continental Shelf Project (LEPLAC) in the current year and pieces of information from bibliographic researches in order to present a discussion by the hole of the Pernambuco Submarine Channel in the Occidental region of the Brazilian Continental Margin

  3. Particle flux across the mid-European continental margin

    CERN Document Server

    Antia, A N; Peinert, R

    1999-01-01

    Results are presented from particle flux studies using sediment trap and current meter moorings along a transect at the European continental margin at 49 degrees N within the Ocean Margin Exchange (OMEX) project. Two moorings were placed, at the mid- and outer slope in water depths of 1500 and 3660 m, with traps at 600 and 1050 m and at 580, 1440 and 3220 m, respectively. Residual currents at the mid- slope follow the slope contour, whereas seasonal off-slope flow was registered at the outer slope. At 600 m on the slope fluxes are similar to those in the abyssal North Atlantic. The flux of all components (bulk dry weight, particulate organic and inorganic carbon, lithogenic matter and opal) increased with water depth. Highest fluxes were recorded at 1440 m at the outer slope, where off- slope residual currents mediate particle export. The injection of biogenic and lithogenic particles below the depth of winter mixing results in the export of particles from shallower waters. Calculated lateral fluxes of partic...

  4. Cenozoic tectonic jumping and implications for hydrocarbon accumulation in basins in the East Asia Continental Margin

    Science.gov (United States)

    Suo, Yanhui; Li, Sanzhong; Yu, Shan; Somerville, Ian D.; Liu, Xin; Zhao, Shujuan; Dai, Liming

    2014-07-01

    Tectonic migration is a common geological process of basin formation and evolution. However, little is known about tectonic migration in the western Pacific margins. This paper focuses on the representative Cenozoic basins of East China and its surrounding seas in the western Pacific domain to discuss the phenomenon of tectonic jumping in Cenozoic basins, based on structural data from the Bohai Bay Basin, the South Yellow Sea Basin, the East China Sea Shelf Basin, and the South China Sea Continental Shelf Basin. The western Pacific active continental margin is the eastern margin of a global convergent system involving the Eurasian Plate, the Pacific Plate, and the Indian Plate. Under the combined effects of the India-Eurasia collision and retrogressive or roll-back subduction of the Pacific Plate, the western Pacific active continental margin had a wide basin-arc-trench system which migrated or ‘jumped’ eastward and further oceanward. This migration and jumping is characterized by progressive eastward younging of faulting, sedimentation, and subsidence within the basins. Owing to the tectonic migration, the geological conditions associated with hydrocarbon and gashydrate accumulation in the Cenozoic basins of East China and its adjacent seas also become progressively younger from west to east, showing eastward younging in the generation time of reservoirs, seals, traps, accumulations and preservation of hydrocarbon and gashydrate. Such a spatio-temporal distribution of Cenozoic hydrocarbon and gashydrate is significant for the oil, gas and gashydrate exploration in the East Asian Continental Margin. Finally, this study discusses the mechanism of Cenozoic intrabasinal and interbasinal tectonic migration in terms of interplate, intraplate and underplating processes. The migration or jumping regimes of three separate or interrelated events: (1) tectonism-magmatism, (2) basin formation, and (3) hydrocarbon-gashydrate accumulation are the combined effects of the

  5. Origin of volcanic seamounts at the continental margin of California related to changes in plate margins

    Science.gov (United States)

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

    2010-05-01

    Volcanic samples collected with the Monterey Bay Aquarium Research Institute's ROV Tiburon from eight seamounts at the continental margin offshore central to southern California comprise a diverse suite of mainly alkalic basalt to trachyte but also include rare tholeiitic basalt and basanite. All samples experienced complex crystal fractionation probably near the crust/mantle boundary, based on the presence in some of mantle xenoliths. Incompatible trace elements, poorly correlated with isotopic compositions, suggest variable degrees of partial melting of compositionally heterogeneous mantle sources, ranging from MORB-like to relatively enriched OIB. High-precision 40Ar/39Ar ages indicate episodes of volcanic activity mainly from 16 to 7 Ma but document one eruption as recent as 2.8 Ma at San Juan Seamount. Synchronous episodes of volcanism occurred at geographically widely separated locations offshore and within the continental borderland. Collectively, the samples from these seamounts have age ranges and chemical compositions similar to those from Davidson Seamount, identified as being located atop an abandoned spreading center. These seamounts appear to have a common origin ultimately related to abandonment and partial subduction of spreading center segments when the plate boundary changed from subduction-dominated to a transform margin. They differ in composition, age, and origin from other more widespread near-ridge seamounts, which commonly have circular plans with nested calderas, and from age progressive volcanoes in linear arrays, such as the Fieberling-Guadalupe chain, that occur in the same region. Each volcanic episode represents decompression melting of discrete enriched material in the suboceanic mantle with melts rising along zones of weakness in the oceanic crust fabric. The process may be aided by transtensional tectonics related to continued faulting along the continental margin.

  6. Sedimentation on continental margins: An integrated program for innovative studies during the 1990s

    Science.gov (United States)

    Nittrourer, Charles A.; Coleman, James M.; Rouge, Baton; Flood, Roger D.; Ginsburg, Robert N.; Gorsline, Donn S.; Hine, Albert C.; Sternberg, Richard W.; Swift, Donald J. P.; Wright, L. Donelson

    Continental margins are of great scientific interest, and they represent the focus of human interaction with the ocean. Their deep structure forms the transition from continental to oceanic crust, and their surface expression extends from coastal environments of estuaries and shorelines across the continental shelf and slope to either the base of a continental rise or a marginal trough. Modern continental margins represent natural laboratories for investigation of complex relationships between physical, chemical, and biological phenomena, which are sensitive to environmental conditions both on the land and in the ocean. The history of these conditions is preserved within the sedimentary deposits of continental margins. The deposits form repositories for much of the particulate material transported off the world's land masses and produced from dissolved components in the world ocean. Past deposits of continental margins have been uplifted to form many mountain ranges and sedimentary terrains of the world, which record details of Earth history and contain valuable natural resources, such as petroleum and natural gas. Modern deposits of continental margins record the more recent events that have influenced Earth and also contain natural resources (for instance, minerals, sand, and gravel), as well as anthropogenic pollutants (for example, heavy metals and pesticides). The fates of many materials beneficial and deleterious to humans are dependent on the pathways followed by sedimentary particles on continental margins.

  7. Rare-earth elements and uranium in phosphatic nodules from the continental margins of India

    Digital Repository Service at National Institute of Oceanography (India)

    Nath, B.N.; Rao, B.R.; Rao, K.M.; Rao, Ch.M.

    and rare-earth elements (REEs) by inductively coupled plasma-mass spectrometry (ICP-MS). Total REE contents are very low (8-21 ppm) in western continental margin nodules and only slightly in eastern continental margin nodules (maximum is 42 ppm). REE...

  8. Stratigraphic landscape analysis, thermochronology and the episodic development of elevated, passive continental margins

    Directory of Open Access Journals (Sweden)

    Green, Paul F.

    2013-12-01

    that peneplains grade towards base level, and that in the absence of other options (e.g. widespread resistant lithologies, the most likely base level is sea level. This is particularly so at continental margins due to their proximity to the adjacent ocean. Studies in which EPCMs are interpreted as related to rifting or break-up commonly favour histories involving continuous denudation of margins following rifting, and interpretation of thermochronology data in terms of monotonic cooling histories. However, in several regions, including southern Africa, south-east Australia and eastern Brazil, geological constraints demonstrate that such scenarios are inappropriate, and an episodic development involving post-breakup subsidence and burial followed later by uplift and denudation is more realistic. Such development is also indicated by the presence in sedimentary basins adjacent to many EPCMs of major erosional unconformities within the post-breakup sedimentary section which correlate with onshore denudation episodes. The nature of the processes responsible is not yet understood, but it seems likely that plate-scale forces are required in order to explain the regional extent of the effects involved. New geodynamic models are required to explain the episodic development of EPCMs, accommodating post-breakup subsidence and burial as well as subsequent uplift and denudation, long after break-up which created the characteristic, modern-day EPCM landscapes.

  9. Hydrogenetic Ferromanganese Crusts of the California Continental Margin

    Science.gov (United States)

    Conrad, Tracey A.

    Hydrogenetic Ferromanganese (Fe-Mn) crusts grow from seawater and in doing so sequester elements of economic interest and serve as archives of past seawater chemistry. Ferromanganese crusts have been extensively studied in open-ocean environments. However, few studies have examined continent-proximal Fe-Mn crusts especially from the northeast Pacific. This thesis addresses Fe-Mn crusts within the northeast Pacific California continental margin (CCM), which is a dynamic geological and oceanographic environment. In the first of three studies, I analyzed the chemical and mineralogical composition of Fe-Mn crusts and show that continental-proximal processes greatly influence the chemistry and mineralogy of CCM Fe-Mn crusts. When compared to global open-ocean Fe-Mn crusts, CCM crusts have higher concentrations of iron, silica, and thorium with lower concentrations of many elements of economic interest including manganese, cobalt, and tellurium, among other elements. The mineralogy of CCM Fe-Mn crusts is also unique with more birnessite and todorokite present than found in open-ocean samples. Unlike open-ocean Fe-Mn crusts, carbonate-fluorapatite is not present in CCM crusts. This lack of phosphatization makes CCM Fe-Mn crusts excellent candidates for robust paleoceanography records. The second and third studies in this thesis use isotope geochemistry on select CCM Fe-Mn crusts from four seamounts in the CCM to study past terrestrial inputs into the CCM and sources and behavior of Pb and Nd isotopes over the past 7 million years along the northeast Pacific margin. The second study focuses on riverine inputs into the Monterey Submarine Canyon System and sources of the continental material. Osmium isotopes in the crusts are compared to the Cenozoic Os seawater curve to develop an age model for the samples that show the crusts range in age of initiation of crust growth from approximately 20 to 6 Myr. Lead and neodymium isotopes measured in select Fe-Mn crusts show that

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1986-07-01

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

  11. A Spatial Model of Erosion and Sedimentation on Continental Margins

    National Research Council Canada - National Science Library

    Pratson, Lincoln

    1999-01-01

    .... A computer model that simulates the evolution of continental slope morphology under the interaction of sedimentation, slope failure, and sediment flow erosion has been constructed and validated...

  12. Aeolian deposition of Arabia and Somalia sediments on the southwestern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Chauhan, O.S.

    Kaolinite, smectite, illite and chlorite as major clay minerals and palygorskite and gibbsite in minor quantities have been recorded from the slope of southwestern continental margin of India. Contribution of kaolinite, smectite and gibbsite is from...

  13. Marine geophysical studies along a transect across the continental margin off Bombay coast, west of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, D.G.; Ramana, M.V.; Bhattacharya, G.C.; SubbaRaju, L.V.; KameshRaju, K.A.; Ramprasad, T.

    Study of underway geophysical data along a transect of 415 km across the continental margin off Bombay, (Maharashtra, India), between 800 and 3600 m water depths reveals seven seismic sequences consisting of parallel and continuous wavy reflections...

  14. Holocene sea level fluctuations on western Indian continental margin: An update

    Digital Repository Service at National Institute of Oceanography (India)

    Hashimi, N.H.; Nigam, R.; Nair, R.R.; Rajagopalan, G.

    A new Holocene curve is generated for the western Indian continental margin. While constructing this curve careful selection of the dates were made by giving due considerations to the genetic characteristics of the dated material. This new curve...

  15. Morphology of pockmarks along the western continental margin of India: Employing multibeam bathymetry and backscatter data

    Digital Repository Service at National Institute of Oceanography (India)

    Dandapath, S.; Chakraborty, B.; Karisiddaiah, S.M.; Menezes, A.A.A.; Ranade, G.; Fernandes, W.A.; Naik, D.K.; PrudhviRaju, K.N.

    This study addresses the morphology of pockmarks along the western continental margin of India using multibeam bathymetry and backscatter data. Here, for the first time we have utilized the application of ArcGIS (Geographical Information System...

  16. Wintertime phytoplankton bloom in the Subarctic Pacific supported by continental margin iron

    International Nuclear Information System (INIS)

    Lam, Phoebe J.; Bishop, James K.B.; Henning, Cara C.; Marcus, Matthew A.; Waychunas, Glenn A.; Fung, Inez

    2004-01-01

    Heightened biological activity was observed in February 1996 in the high-nutrient low-chlorophyll (HNLC) subarctic North Pacific Ocean, a region that is thought to be iron-limited. Here we provide evidence supporting the hypothesis that Ocean Station Papa (OSP) in the subarctic Pacific received a lateral supply of particulate iron from the continental margin off the Aleutian Islands in the winter, coincident with the observed biological bloom. Synchrotron X-ray analysis was used to describe the physical form, chemistry, and depth distributions of iron in size fractionated particulate matter samples. The analysis reveals that discrete micron-sized iron-rich hotspots are ubiquitous in the upper 200m at OSP, more than 900km from the closest coast. The specifics of the chemistry and depth profiles of the Fe hot spots trace them to the continental margins. We thus hypothesize that iron hotspots are a marker for the delivery of iron from the continental margin. We confirm the delivery of continental margin iron to the open ocean using an ocean general circulation model with an iron-like tracer source at the continental margin. We suggest that iron from the continental margin stimulated a wintertime phytoplankton bloom, partially relieving the HNLC condition

  17. Holocene phosphorites of the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Nair, R.R.

    continental shelf from Saurashtra to Kerala. Prominent apatite peak was present only in the algal limestones off Goa. These occur as nodules and are similar in appearence to rhodoliths. Minerals present, in order of abundance, are high-magnesium calcite...

  18. The influence of tectonic and volcanic processes on the morphology of the Iberian continental margins

    International Nuclear Information System (INIS)

    Maestro, A.; Bohoyo, F.; Lopez-Martinez, J.; Acosta, J.; Gomez-Ballesteros, M.; Llaave, E.; Munoz, A.; Terrinha, P. G.; Dominguez, M.; Fernandez-Saez, F.

    2015-01-01

    The Iberian continental margins are mainly passive margins. Nevertheless, the northern sector of the margin was active during some stages of its geological evolution. The southern sector is considered as a transformed margin, which defines the boundary between the Iberian and African plates. This margin was also an active margin in the past. The different types, origins and intensities of the endogenic processes that have affected he Iberian continental margins have led to the development of various tectonic and volcanic morphologies. The North Atlantic rifting allowed the development of large marginal platforms in the Cantabrian and Galician margins the North-Atlantic Ocean spreading. The reactivation of Variscan faults during the Mesozoic and Cenozoic controlled the strike of some of the largest canyons in the Iberian margins. The Gulf of Cadiz margin is characterized by the development of morphologies related to salt tectonic, fluid seepage, thrust fronts and strike-slip fault lineaments hundreds of kilometres long. The Alboran basin and the Betic margin show morphologies connected with the Miocene rift phase, which generated volcanic edifices and various structural reliefs, and with the subsequent compressive phase, when folds and strike-slip, reverse faults, diapirs and mud volcanoes were developed. Finally, the Catalan-Valencian margin and the Balearic promontory are characterized by the presence of horst and graben structures related to the development of the Valencia trough during the Paleogene. The morphological features of endogenic origin have largely controlled the location and extent of the sedimentary processes and morphological products along the Iberian margins. (Author)

  19. Kinematic and thermal evolution of the Moroccan rifted continental margin: Doukkala-High Atlas Transect

    NARCIS (Netherlands)

    Gouiza, M.; Bertotti, G.V.; Hafid, M.; Cloetingh, S.A.P.L.

    2010-01-01

    The Atlantic passive margin of Morocco developed during Mesozoic times in association with the opening of the Central Atlantic and the Alpine Tethys. Extensional basins formed along the future continental margin and in the Atlas rift system. In Alpine times, this system was inverted to form the High

  20. Gravity anomalies over a segment of Pratap ridge and adjoining shelf margin basin, western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Rao, D.G.; Ramprasad, T.; KameshRaju, K.A.; Rao, M.G.

    Bathymetric and gravity data totalling 2000 line km on the continental margin off Goa and Mulki, west of India have been studied. The free-air gravity anomalies vary between -60 to 25 mgals with prominent NNW-SSE trends in the outer shelf region...

  1. Influence of dynamic topography on landscape evolution and passive continental margin stratigraphy

    Science.gov (United States)

    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

  2. Seaward dipping reflectors along the SW continental margin of India ...

    Indian Academy of Sciences (India)

    The SDRs; 15 to 27 km wide overlain by ∼1 km thick sediment; are observed at three locations and characterized by stack of laterally continuous, divergent and off-lapping reflectors. Occurrence of SDRs along western flank of the Laccadive Ridge adjacent to oceanic crust of the Arabian Basin and 2D crustal model ...

  3. Potential tsunamigenic hazard associated to submarine mass movement along the Ionian continental margin (Mediterranean Sea).

    Science.gov (United States)

    Ceramicola, S.; Tinti, S.; Praeg, D.; Zaniboni, F.; Planinsek, P.

    2012-04-01

    Submarine mass movements are natural geomorphic processes that transport marine sediment down continental slopes into deep-marine environments. Type of mass wasting include creep, slides, slump, debris flows, each with its own features and taking place over timescale from seconds to years. Submarine landslides can be triggered by a number of different causes, either internal (such as changes in physical chemical sediment properties) or external (e.g. earthquakes, volcanic activity, salt movements, sea level changes etc.). Landslides may mobilize sediments in such a way as to form an impulsive vertical displacement of a body of water, originating a wave or series of waves with long wavelengths and long periods called tsunamis ('harbor waves'). Over 600 km of continental margin has been investigated by OGS in the Ionian sea using geophysical data - morpho-bathymetry (Reson 8111, 8150) and sub-bottom profiles (7-10 KHz) - collected aboard the research vessel OGS Explora in the framework of the MAGIC Project (Marine Geohazard along the Italian Coasts), funded by the Italian Civil Protection. The objective of this project is the definition of elements that may constitute geological risk for coastal areas. Geophysical data allowed the recognition of four main types of mass wasting phenomena along the slopes of the ICM: 1) mass transport complexes (MTCs) within intra-slope basins. Seabed imagery show the slopes of all the seabed ridges to be marked by headwall scarps recording widespread failure, multiple debris flows in several basins indicate one or more past episodes of failure that may be linked to activity on the faults bounding the structural highs. 2) submarine landslide - a multiple failure event have been identified (Assi landslide) at about 6 km away from the coastline nearby Riace Marina. Headwall scars up to 50 m high across water depths of 700 to 1400 m, while sub-bottom profiles indicate stacked slide deposits at and near seabed. 4) canyon headwalls - in the

  4. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    KAUST Repository

    Laruelle, G. G.

    2012-10-04

    Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric pro- files. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.

  5. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    Directory of Open Access Journals (Sweden)

    G. G. Laruelle

    2013-05-01

    Full Text Available Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems. Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation and 149 sub-units (COSCATs. Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air–water interface combining global and regional average emission rates derived from local studies.

  6. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    KAUST Repository

    Laruelle, G. G.

    2013-05-29

    Past characterizations of the land-ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LMEs: large marine ecosystems). Here, we present a global-scale coastal segmentation, composed of three consistent levels, that includes the whole aquatic continuum with its riverine, estuarine and shelf sea components. Our work delineates comprehensive ensembles by harmonizing previous segmentations and typologies in order to retain the most important physical characteristics of both the land and shelf areas. The proposed multi-scale segmentation results in a distribution of global exorheic watersheds, estuaries and continental shelf seas among 45 major zones (MARCATS: MARgins and CATchments Segmentation) and 149 sub-units (COSCATs). Geographic and hydrologic parameters such as the surface area, volume and freshwater residence time are calculated for each coastal unit as well as different hypsometric profiles. Our analysis provides detailed insights into the distributions of coastal and continental shelf areas and how they connect with incoming riverine fluxes. The segmentation is also used to re-evaluate the global estuarine CO2 flux at the air-water interface combining global and regional average emission rates derived from local studies. © 2013 Author(s).

  7. Identifying the "Foot of the Continental Slope" of high-latitude continental margins influenced by trough mouth fans

    Science.gov (United States)

    Sverre Laberg, Jan

    2017-04-01

    The continental slope of high-latitude margins often include trough mouth fans, which are sediment fans situated in front of large troughs crossing the continental shelf. The troughs acted as corridors for paleo-ice streams, sectors of fast-flowing ice within the large ice sheets of the last glacial maximum as well as previous glacials. The paleo-ice streams were highly efficient erosional agents, eroding and transporting large volumes of sediments to the continental shelf edge. Here, these sediments were released to move downslope as large debris flows, the "building blocks" of these fans. Due to the very large sediment volume included within these fans, they represent prominent depocenters forming low-gradient sectors (axial gradient often being as low as 1 degree or less) with no clear morphological distinction of the continental slope including its lower limit. Under the UN Convention on the Law of the Sea, the criteria provided in Article 76 includes the lower limit or "foot" of the continental slope as one important parameter in the extended Continental Shelf delineation (i.e. beyond the 200 M exclusive economic zone). Because of this, the Norwegian submission regarding the outer limits of the continental shelf in the Norwegian Sea and the Arctic Ocean argued that the origin of the sub-sea floor sediments on the slope needed to be considered when identifying the location of the foot of the continental slope. This was done by mapping the outer limits of the large debris flow deposits of the trough mouth fans, deposits that without doubt have their origin from the continental shelf. Thus, in these cases, the foot of the continental slope coincide with the downslope termination of the large debris flow deposits and the outer limit of the continental shelf lies 60 M beyond this point. The data used for mapping includes swath bathymetry, sub-bottom profiles and short sediment samples (< 10 m), and we present and discuss examples from the Bear Island Trough Mouth

  8. Dating recent sediments from the subaqueous Yangtze Delta and adjacent continental shelf, China

    Directory of Open Access Journals (Sweden)

    Zhang-Hua Wang

    2014-04-01

    Full Text Available In this study we analyzed sediment lithology, fallout of 210Pb and 137Cs, and spheroidal carbonaceous particles (SCPs for two short cores, YZE and CX38, obtained by gravity corer from the Yangtze River mouth offshore and adjacent continental shelf, to compare geochronological methods on the recent sediments of this area. Lithology and grain size changes in YZE suggested the re-discharging of the North Channel of the Yangtze River mouth by flood events during 1949–1954 and associated accretion in the offshore area. This event was validated by a remarkable zone of declination in both 137Cs and 210Pb activities and the absolute ages derived from the 137Cs and SCPs. In contrast, 210Pb results show obvious disturbance of grain size by sediment mixing and cannot be interpreted above 100 cm. In CX38, absolute ages for the early- and mid-1950s were derived by the 137Cs and the SCP profile respectively, which occurred in a reasonable sequence. The excess 210Pb distribution shows exponentially decreasing activities with depth, and the mean sedimentation rate agrees roughly with the one inferred from the SCP profile. We suggest that the limitation of the 210Pb method needs consideration while the SCP profile has the potential to provide a useful and independent dating method for recent Yangtze offshore and adjacent shelf sediments.

  9. Wilson cycle passive margins: Control of orogenic inheritance on continental breakup

    DEFF Research Database (Denmark)

    Petersen, Kenni D.; Schiffer, Christian

    2016-01-01

    such tectonic inheritance is generally appreciated, causative physical mechanisms that affect the localization and evolution of rifts and passive margins are not well understood. We use thermo-mechanical modeling to assess the role of orogenic structures during rifting and continental breakup. Such inherited...... thinning in the mantle lithosphere rather than in the crust, and continental breakup is therefore preceded by magmatism. This implies that whether passive margins become magma-poor or magma-rich, respectively, is a function of pre-rift orogenic properties. The models show that structures of orogenic...

  10. Constraining Lithosphere Deformation Modes during Continental Breakup for the Iberia-Newfoundland Conjugate Margins

    Science.gov (United States)

    Jeanniot, L.; Kusznir, N. J.; Mohn, G.; Manatschal, G.

    2014-12-01

    How the lithosphere and asthenosphere deforms during continental rifting leading to breakup and sea-floor spreading initiation is poorly understood. Observations at present-day and fossil analogue rifted margins show a complex OCT architecture which cannot be explained by a single simplistic lithosphere deformation modes. This OCT complexity includes hyper-extended continental crust and lithosphere, detachments faults, exhumed mantle, continental slivers and scattered embryonic oceanic crust. We use a coupled kinematic-dynamic model of lithosphere and asthenosphere deformation to determine the sequence of lithosphere deformation modes leading to continental breakup for Iberia-Newfoundland conjugate margin profiles. We quantitatively calibrate the models using observed present-day water loaded subsidence and crustal thickness, together with subsidence history and the age of melt generation. Flow fields, representing a sequence of lithosphere deformation modes, are generated by a 2D finite element viscous flow model (FE-Margin), and used to advect lithosphere and asthenosphere temperature and material. FE-Margin is kinematically driven by divergent deformation in the upper 15-20 km of the lithosphere inducing passive upwelling below. Buoyancy enhanced upwelling (Braun et al. 2000) is also kinematically included. Melt generation by decompressional melting is predicted using the methodology of Katz et al., 2003. The extension magnitudes used in the lithosphere deformation models are taken from Sutra et al (2013). The best fit calibrated models of lithosphere deformation evolution for the Iberia-Newfoundland conjugate margins require (i) an initial broad region of lithosphere deformation and passive upwelling, (ii) lateral migration of deformation, (iii) an increase in extension rate with time, (iv) focussing of deformation and (v) buoyancy induced upwelling. The preferred calibrated models predict faster extension rates and earlier continental crustal rupture and

  11. Benthic assemblages of mega epifauna on the Oregon continental margin

    Science.gov (United States)

    Hemery, Lenaïg G.; Henkel, Sarah K.; Cochrane, Guy R.

    2018-01-01

    Environmental assessment studies are usually required by a country's administration before issuing permits for any industrial activities. One of the goals of such environmental assessment studies is to highlight species assemblages and habitat composition that could make the targeted area unique. A section of the Oregon continental slope that had not been previously explored was targeted for the deployment of floating wind turbines. We carried out an underwater video survey, using a towed camera sled, to describe its benthic assemblages. Organisms were identified to the lowest taxonomic level possible and assemblages described related to the nature of the seafloor and the depth. We highlighted six invertebrate assemblages and three fish assemblages. For the invertebrates within flat soft sediments areas we defined three different assemblages based on primarily depth: a broad mid-depth (98–315 m) assemblage dominated by red octopus, sea pens and pink shrimps; a narrower mid-depth (250–270 m) assemblage dominated by box crabs and various other invertebrates; and a deeper (310–600 m) assemblage dominated by sea urchins, sea anemones, various snails and zoroasterid sea stars. The invertebrates on mixed sediments also were divided into three different assemblages: a shallow (~100 m deep) assemblage dominated by plumose sea anemones, broad mid-depth (170–370 m) assemblage dominated by sea cucumbers and various other invertebrates; and, again, a narrower mid-depth (230–270 m) assemblage, dominated by crinoids and encrusting invertebrates. For the fish, we identified a rockfish assemblage on coarse mixed sediments at 170–370 m and another fish assemblage on smaller mixed sediments within that depth range (250–370 m) dominated by thornyheads, poachers and flatfishes; and we identified a wide depth-range (98–600 m) fish assemblage on flat soft sediments dominated by flatfishes, eelpouts and thornyheads. Three of these assemblages (the two

  12. Benthic assemblages of mega epifauna on the Oregon continental margin

    Science.gov (United States)

    Hemery, Lenaïg G.; Henkel, Sarah K.; Cochrane, Guy R.

    2018-05-01

    Environmental assessment studies are usually required by a country's administration before issuing permits for any industrial activities. One of the goals of such environmental assessment studies is to highlight species assemblages and habitat composition that could make the targeted area unique. A section of the Oregon continental slope that had not been previously explored was targeted for the deployment of floating wind turbines. We carried out an underwater video survey, using a towed camera sled, to describe its benthic assemblages. Organisms were identified to the lowest taxonomic level possible and assemblages described related to the nature of the seafloor and the depth. We highlighted six invertebrate assemblages and three fish assemblages. For the invertebrates within flat soft sediments areas we defined three different assemblages based on primarily depth: a broad mid-depth (98-315 m) assemblage dominated by red octopus, sea pens and pink shrimps; a narrower mid-depth (250-270 m) assemblage dominated by box crabs and various other invertebrates; and a deeper (310-600 m) assemblage dominated by sea urchins, sea anemones, various snails and zoroasterid sea stars. The invertebrates on mixed sediments also were divided into three different assemblages: a shallow ( 100 m deep) assemblage dominated by plumose sea anemones, broad mid-depth (170-370 m) assemblage dominated by sea cucumbers and various other invertebrates; and, again, a narrower mid-depth (230-270 m) assemblage, dominated by crinoids and encrusting invertebrates. For the fish, we identified a rockfish assemblage on coarse mixed sediments at 170-370 m and another fish assemblage on smaller mixed sediments within that depth range (250-370 m) dominated by thornyheads, poachers and flatfishes; and we identified a wide depth-range (98-600 m) fish assemblage on flat soft sediments dominated by flatfishes, eelpouts and thornyheads. Three of these assemblages (the two broad fish assemblages and the deep

  13. Structure and tectonics of the southwestern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Rao, D.G.; Ramana, M.V.; Krishna, K.S.; Murty, G.P.S.; Rao, M.G.

    and (c) seismic data; (d) composite map. 276 V. Subrahmanyam el all/Tecmnot~hysics 249 (1995) 267-282 feature by Naini and Talwani (1982) who named it the Prathap Ridge Complex (Fig. lb). In places the ridge may have three peaks. A pile of sediments..., another basin with a 2.3-km-thick pile of sediments is also noticed between the Prathap Ridge Complex and the Chagos-Laccadive Ridge system. The inner-shelf graben, mid-shelf basement ridge, shelf-margin basin and the Prathap Ridge Complex (Fig. 8a...

  14. Survival Of Magnetic Paleoclimatic Signals From Shallow To Deep Water Marine Redoxomorphic Sediments Across The Northwest Iberian Continental Margin

    Science.gov (United States)

    Mohamed Falcon, K. J.; Rey, D.; Rubio, B.

    2013-05-01

    The magnetic properties of marine sediments on the North Atlantic Iberian continental Margin are strongly dependent on the organic matter input to the sediments and the onset of reductive diagenesis. An onshore-offshore gradient in the intensity of early diagenesis was recently described for the Ría de Vigo, matched by similar patterns in the adjacent rias of Pontevedra and Muros. In the ria environments of NW Iberia, early diagenetic dissolution of magnetic minerals can lead to magnetite half-lives of a few decades, and virtually obliterates any paleoenvironmental signal carried by magnetic minerals, rendering magnetic properties especially useful for the study of early diagenesis dynamics. Early diagenesis has also been identified in sediments of the adjacent continental shelf and deeper environments of the Galician Bank and Iberian Abyssal Plain. However, in these settings, slower dissolution of magnetic minerals allows the preservation of paleoclimatic signatures on different temporal scales. For instance, magnetic properties of continental shelf sediments reveal periods of enhanced rainfall and continental sediment input to the shelf, coincident with the Roman Warm Period and Medieval Climatic Optimum. On the contrary, cold periods are associated with less detrital input. Furthermore, levels of intensified diagenesis are also recorded during cold periods, which have been interpreted as periods of intensified coastal upwelling probably related to long-term North Atlantic Oscillation positive state. At the Galician Bank and Iberian Abyssal Plain sediments early diagenesis is also pervasive, although a paleoceanographic record of changes in the concentration of magnetic minerals transported by water masses flowing from the Portuguese Margin can still be identified. In addition to the progressive dissolution of magnetic minerals with depth, bulk magnetic properties in these deep marine settings show strong dependence on the pelagic carbonate sedimentation and low

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

    Science.gov (United States)

    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.

  16. Geophysical studies over the continental margins of the east coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, T.C.S.; Rao, V.B.

    Results of six profiles of continuous echosounding, magnetic and gravity data collected across the continental margin of the east coast of India between 10 degrees and 20 degrees N in the Bay of Bengal aboard R.V. Chain in 1973 are presented...

  17. Morphology and tectonics of Mahanadi Basin, northeastern continental margin of India from geophysical studies

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Subrahmanyam, A.S.; Murty, G.P.S.; Murthy, K.S.R.

    The bathymetry, total intensity magnetic and satellite free-air gravity data over the eastern continental margin of India between the latitudes 18 degrees 30 minutes N and 20 degrees N within the water depths of 25-2300 m (between Paradip...

  18. Gravity anomalies and crustal structure of the western continental margin off Goa and Mulki, India

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Rao, D.G.; Ramprasad, T.; KameshRaju, K.A.; Rao, M.G.

    Bathymetric and gravity data totalling 2000 line kilometres on the continental margin off Goa and Mulki, India, have been studied and prominent NNW-SSE and ENE-WSW trending free-air gravity anomalies varying between -60 + 25 mGal have been...

  19. The continental margin is a key source of iron to the HNLC North Pacific Ocean

    Energy Technology Data Exchange (ETDEWEB)

    Lam, P.J.; Bishop, J.K.B

    2008-01-15

    Here we show that labile particulate iron and manganese concentrations in the upper 500m of the Western Subarctic Pacific, an iron-limited High Nutrient Low Chlorophyll (HNLC) region, have prominent subsurface maxima between 100-200 m, reaching 3 nM and 600 pM, respectively. The subsurface concentration maxima in particulate Fe are characterized by a more reduced oxidation state, suggesting a source from primary volcagenic minerals such as from the Kuril/Kamchatka margin. The systematics of these profiles suggest a consistently strong lateral advection of labile Mn and Fe from redox-mobilized labile sources at the continental shelf supplemented by a more variable source of Fe from the upper continental slope. This subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing, and is likely a key source of bioavailable Fe to the HNLC North Pacific.

  20. Marginal tissue response adjacent to Astra Dental Implants supporting overdentures in the mandible

    DEFF Research Database (Denmark)

    Gotfredsen, K; Holm, B; Sewerin, I

    1993-01-01

    The aim of this study was to evaluate the marginal tissue response adjacent to implant supported overdentures. Twenty edentulous patients had 2 Astra Dental Implants placed in the canine region of the lower jaw. New overdentures were retained by individual ball attachments in 11 patients...... and by a bar attachment in 9 patients. Periodontal registrations were recorded 0 months, 6 months, 12 months and 24 months after the overdentures were inserted. One of the 40 fixtures was lost at the stage of abutment connection. No fixtures were lost during the 2- to 4-year observation period and no fixtures...... showed any periodontal signs of failure. At the 2-year examination, no pocket depths adjacent to the implants exceeded 4 mm and no bone loss exceeded 3 mm. The mean annual bone loss was less than 0.2 mm during the first 2 years. The preliminary results from this limited study were promising and showed...

  1. Marginal tissue response adjacent to Astra Dental Implants supporting overdentures in the mandible

    DEFF Research Database (Denmark)

    Gotfredsen, K; Holm, B; Sewerin, I

    1993-01-01

    The aim of this study was to evaluate the marginal tissue response adjacent to implant supported overdentures. Twenty edentulous patients had 2 Astra Dental Implants placed in the canine region of the lower jaw. New overdentures were retained by individual ball attachments in 11 patients...... that two osseointegrated Astra Dental Implants could successfully retain an overdenture in the lower jaw. However, long-term observation is needed for a definitive evaluation of this treatment concept....... showed any periodontal signs of failure. At the 2-year examination, no pocket depths adjacent to the implants exceeded 4 mm and no bone loss exceeded 3 mm. The mean annual bone loss was less than 0.2 mm during the first 2 years. The preliminary results from this limited study were promising and showed...

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

    Science.gov (United States)

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

    2001-01-01

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

  3. Potential of radioactive and other waste disposals on the continental margin by natural dispersal processes

    International Nuclear Information System (INIS)

    Ryan, W.B.F.; Farre, J.A.

    1983-01-01

    Mass wasting, an erosional process, has recently been active at deepwater waste disposal sites on the mid-Atlantic margin of the United States. On the continental slope there is a subsea drainage network consisting of canyons, gullies, and chutes, and there are meandering channels, erosional scars, and debris aprons present on the continental rise. Fresh-looking blocks of 40 to 45 million-year-old marl and chalk (from cobble to boulder size) are strewn among canisters of low-level radioactive wastes. Some of the blocks have traveled from their original place of deposition for distances in excess of 170 km. Waste containers on the continental slope and rise cannot be considered to be disposed of permanently. The drainage network of the slope provides a natural process for collecting wastes over a catchment area, and for concentrating it with interim storage in canyons. Erosion by slumping, sliding, and debris flows ultimately will transport the wastes from the continental slope and disperse it over potentially large areas on the continental rise and abyssal plain. If it is desirable that the wastes be buried in the seafloor and isolated from the environment, then the continental slope and rise are not attractive repositories. If, however, it is deemed beneficial that the wastes ultimately be dispersed over a wide area, then the continental slope could be used as a disposal site

  4. Shallow gas in the Iberian continental margin; Gas somero en el margen continental Iberico

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Gil, S.; Cartelle, V.; Blas, E. de; Carlos, A. de; Diez, R.; Duran, R.; Ferrin, A.; Garcia-Moreiras, I.; Garcia-Garcia, A.; Iglesias, J.; Martinez-Carreno, N.; Munoz Sobrino, C.; Ramirez-Perez, A. M.

    2015-07-01

    The shallow gas reservoirs in marine sediments from the Iberian margin or their escapes can be detected by using direct methods: (1) the measurement of high concentrations of methane or other hydrocarbons in the water column or sediment cores, (2) the identification of chemosynthetic communities and/or authigenic car- bonates in the seafloor, and (3) identification (using underwater videos) of pockmarks or carbonate mounds and mud volcanoes associated with the fluid escapes; or by indirect technical characterization of anomalies in acoustic records such as: (1) the presence of acoustic plumes in echo-sounders records, (2) the identification of acoustic blanking and/or acoustic turbidity in the high resolution seismic records, (3) the interpretation of reflectivity and (4) morphologies of pockmarks or seamounts in sidescan sonar and multibeam echo sounder records. This article is a compilation of acoustic-seismic, sedimentologic and morphologic evidence associated to the presence of shallow gas (accumulations or escapes) that appear in the Iberian margin and hat have been published in various papers. The description is divided into geographical sectors, beginning in the north-eastern end of the Mediterranean margin and ending at the easternmost area of the Cantabrian margin, following a clockwise direction around the Iberian Peninsula. (Author)

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

    Science.gov (United States)

    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.

  6. Anthropogenic impacts on continental margins: New frontiers and engagement arena for global sustainability research and action

    Science.gov (United States)

    Liu, K. K.; Glavovic, B.; Limburg, K.; Emeis, K. C.; Thomas, H.; Kremer, H.; Avril, B.; Zhang, J.; Mulholland, M. R.; Glaser, M.; Swaney, D. P.

    2014-12-01

    There is an urgent need to design and implement transformative governance strategies that safeguard Earth's life-support systems essential for long-term human well-being. From a series of meetings of the Continental Margins Working Group co-sponsored by IMBER and LOICZ of IGBP, we conclude that the greatest urgency exists at the ocean-land interface - the continental margins or the Margin - which extends from coastlands over continental shelves and slopes bordering the deep ocean. The Margin is enduring quadruple squeeze from (i) Population growth and rising demands for resources; (ii) Ecosystem degradation and loss; (iii) Rising CO2, climate change and alteration of marine biogeochemistry and ecosystems; and (iv) Rapid and irreversible changes in social-ecological systems. Some areas of the Margin that are subject to the greatest pressures (e.g. the Arctic) are also those for which knowledge of fundamental processes remains most limited. Aside from improving our basic understanding of the nature and variability of the Margin, priority issues include: (i) investment reform to prevent lethal but profitable activities; (ii) risk reduction; and (iii) jurisdiction, equity and fiscal responsibility. However, governance deficits or mismatches are particularly pronounced at the ocean-edge of the Margin and the prevailing Law of the Sea is incapable of resolving these challenges. The "gold rush" of accelerating demands for space and resources, and variability in how this domain is regulated, move the Margin to the forefront of global sustainability research and action. We outline a research strategy in 3 engagement arenas: (a) knowledge and understanding of dynamic Margin processes; (b) development, innovation and risk at the Margin; and (c) governance for sustainability on the Margin. The goals are (1) to better understand Margin social-ecological systems, including their physical and biogeochemical components; (2) to develop practical guidance for sustainable development

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

    Science.gov (United States)

    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

  8. Reactivation of precambrian faults on the southwestern continental margin of India: Evidence from gravity anomalies

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Ramana, M.V.; Rao, D.G.

    con- fi~ration of the western continental margin, with various structural styles, has been considered as a single unit, even though there exists a difference of opinion about the origin and evolution of the Chagos-Laccadive Ridge complex...’tVATION OF PRECAMBRIAN FAULTS ON THE SW CON~~E~AL MARGIN OF INDIA 337 shelf break due to the steep topographic relief of shelf. Furthermore, the gradients might have played a dominant role in shaping the bathymetry when the block movement took place along the pre...

  9. Deep crustal structure and continent-ocean boundary along the Galicia continental margin (NW Iberia)

    Science.gov (United States)

    Druet, María; Muñoz-Martín, Alfonso; Carbó, Andrés; Acosta, Juan; Granja Bruña, José Luis; Llanes, Pilar; Vázquez, Juan-Tomás; Ercilla, Gemma

    2016-04-01

    The Galicia continental margin is a magma-poor rifted margin with an extremely complex structure. Its formation involves several rifting episodes during the Mesozoic in the vicinity of a ridge triple junction, which produces a change in the orientation of the main structures. In addition, there is an overimposed Cenozoic partial tectonic inversion along its northern border. Although this continental margin has been widely studied since the 70's, most studies have focused on its western part in the transition to the Iberia Abyssal Plain, and there is a significant lack of information on the north and northwestern flanks of this margin. This fact, along with its great structural complexity, has resulted in the absence of a previous comprehensive regional geodynamic model integrating all the processes observed. In the present study we integrate a large volume of new geophysical data (gravity, swath bathymetry and 2D multichannel reflection seismic). Data come from the systematic mapping of the Spanish EEZ project which provides a dense grid of gravity data and full seafloor coverage with swath bathymetry, and from the ERGAP project which provides serially-arranged 2D seismic reflection profiles across the NW Iberia margin. The combined interpretation and modelling of this new information has arisen significant constraints on the origin, the deep crustal structure and the physiographic complexity of the margin, as well as on the characterization of the along- and across-strike variation of the ocean-continent transition along NW Iberia margin. The analysis of this information leads us to propose a conceptual model for the initiation of the tectonic inversion of a magma-poor rifted margin. Finally, a framework for the geodynamic evolution of the Galicia margin has been constructed, involving three main stages: A) an early stage from the end of rifting and oceanic drift in the Bay of Biscay (Santonian); B) an intermediate stage with the beginning of tectonic inversion in

  10. Importance of Microbial Iron Reduction in River-Dominated Continental Margin Sediments

    Science.gov (United States)

    Taillefert, M.; Beckler, J. S.; Eitel, E. M.; Owings, S.; Craig, J. D.; Fields, B.; Cathalot, C.; Rassmann, J.; Bombled, B.; Corvaisier, R.; Michalopoulos, P.; Nuzzio, D. B.; Rabouille, C.

    2016-02-01

    Remineralization of organic carbon in continental margin sediments exposed to fast deposition processes is thought to proceed primarily via aerobic respiration and sulfate reduction because the supply of nitrate and metal oxides is not usually significant in deep-sea sediments. Dissimilatory metal reduction, on the other hand, may represent a dominant pathway in coastal and continental shelf sediments where delivery of terrigenous Fe(III) and Mn(IV/III) oxides is sufficiently high or mixing processes near the sediment-water interface recycle these minerals efficiently. Passive continental margin sediments receiving outflow from large rivers are well-known deposition centers for organic carbon, but may also be hot spots for metal-reducing microbial activity considering the simultaneous high deposition rates of unconsolidated metal oxides of terrigenous origin. Interestingly, only a few studies have examined the role of microbial metal reduction in carbon remineralization processes in these environments. In this study, a combination of in situ depth profiles, benthic flux measurements, and ex situ measurements in the Rhône River Delta (Metal reduction dominated carbon remineralization processes in the top 20 cm of sediment subject to high deposition, while evidence for sulfate reduction was lacking. These findings suggest that dissimilatory Fe(III) reduction may be more significant than previously thought in continental slope sediments, which may have important implications on carbon cycling in marine environments.

  11. Seismic structure of the northern continental margin of Spain from ESCIN deep seismic profiles

    Science.gov (United States)

    Alvarez-Marrón, J.; Pérez-Estaún, A.; Danñobeitia, J. J.; Pulgar, J. A.; Martínez^Catalán, J. R.; Marcos, A.; Bastida, F.; Ayarza^Arribas, P.; Aller, J.; Gallart, A.; Gonzalez-Lodeiro, F.; Banda, E.; Comas, M. C.; Córdoba, D.

    1996-10-01

    By the end of the Carboniferous, the crust of the continental shelf in northwestern Spain was made up of deeply rooted structures related to the Variscan collision. From Permian to Triassic times the tectonic setting had changed to mainly extensional and the northern Iberian continental margin underwent rifting during Late Jurassic-Early Cretaceous times, along with sea-floor spreading and the opening of the Bay of Biscay until the Late Cretaceous. Subsequently, the northern Iberian margin was active during the north-south convergence of Eurasia and Iberia in the Tertiary. A multichannel seismic experiment, consisting of two profiles, one north-south (ESCIN-4) crossing the platform margin offshore Asturias, and another (ESCIN-3) crossing the platform margin to the northwest of Galicia, was designed to study the structure of the northern Iberian margin. The ESCIN-4 stacked section reveals inverted structures in the upper crust within the Le Danois Basin. North of the steep continental slope, ESCIN-4 shows a thick sedimentary package from 6 to 9.5 s, two-way travel time (TWT). Within this latter package, a 40-km-long, north-tapering wedge of inclined, mainly south-dipping reflections is thought to represent a buried, Alpine-age accretionary prism. In the north western part of the ESCIN-3 (ESCIN-3-1) stacked section, horizontal reflections from 6.5 to 8.5 s correspond to an undisturbed package of sediments lying above oceanic-type basement. In this part of the line, a few kilometres long, strong horizontal reflection at 11.2 s within the basement may represent an oceanic Moho reflection. Also, a band of reflections dips gently towards the southeast, from the base of the gently dipping continental slope. The part of ESCIN-3 line that runs parallel to the NW-Galicia coast (ESCIN-3-2), is characterized by bright, continuous lower crustal reflections from 8 to 10 s. Beneath the lower crustal reflectivity, a band of strong reflections dips gently toward the southwest from

  12. Initiation of Extension in South China Continental Margin during the Active-Passive Margin Transition: Thermochronological and Kinematic Constraints

    Science.gov (United States)

    Zuo, X.; Chan, L. S.

    2015-12-01

    The South China continental margin is characterized by a widespread magmatic belt, prominent NE-striking faults and numerous rifted basins filled by Cretaceous-Eocene sediments. The geology denotes a transition from active to passive margin, which led to rapid modifications of crustal stress configuration and reactivation of older faults in this area. Our zircon fission-track data in this region show two episodes of exhumation: The first episode, occurring during 170-120Ma, affected local parts of the Nanling Range. The second episode, a more regional exhumation event, occurred during 115-70Ma, including the Yunkai Terrane and the Nanling Range. Numerical geodynamic modeling was conducted to simulate the subduction between the paleo-Pacific plate and the South China Block. The modeling results could explain the fact that exhumation of the granite-dominant Nanling Range occurred earlier than that of the gneiss-dominant Yunkai Terrane. In addition to the difference in rock types, the heat from Jurassic-Early Cretaceous magmatism in Nanling may have softened the upper crust, causing the area to exhume more readily than Yunkai. Numerical modeling results also indicate that (1) high lithospheric geothermal gradient, high slab dip angle and low convergence velocity favor the reversal of crustal stress state from compression to extension in the upper continental plate; (2) late Mesozoic magmatism in South China was probably caused by a slab roll-back; and (3) crustal extension could have occurred prior to the cessation of plate subduction. The inversion of stress regime in the continental crust from compression to crustal extension imply that the Late Cretaceous-early Paleogene red-bed basins in South China could have formed during the late stage of the subduction, accounting for the occurrence of volcanic events in some sedimentary basins. We propose that the rifting started as early as Late Cretaceous, probably before the cessation of subduction process.

  13. Rollback of an intraoceanic subduction system and termination against a continental margin

    Science.gov (United States)

    Campbell, S. M.; Simmons, N. A.; Moucha, R.

    2017-12-01

    The Southeast Indian Slab (SEIS) seismic anomaly has been suggested to represent a Tethyan intraoceanic subduction system which operated during the Jurassic until its termination at or near the margin of East Gondwana (Simmons et al., 2015). As plate reconstructions suggest the downgoing plate remained coupled to the continental margin, this long-lived system likely experienced a significant amount of slab rollback and trench migration (up to 6000 km). Using a 2D thermomechanical numerical code that includes the effects of phase transitions, we test this interpretation by modeling the long-term subduction, transition zone stagnation, and rollback of an intraoceanic subduction system in which the downgoing plate remains coupled to a continental margin. In addition, we also investigate the termination style of such a system, with a particular focus on the potential for some continental subduction beneath an overriding oceanic plate. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-735738

  14. Great earthquakes along the Western United States continental margin: implications for hazards, stratigraphy and turbidite lithology

    Science.gov (United States)

    Nelson, C. H.; Gutiérrez Pastor, J.; Goldfinger, C.; Escutia, C.

    2012-11-01

    We summarize the importance of great earthquakes (Mw ≳ 8) for hazards, stratigraphy of basin floors, and turbidite lithology along the active tectonic continental margins of the Cascadia subduction zone and the northern San Andreas Transform Fault by utilizing studies of swath bathymetry visual core descriptions, grain size analysis, X-ray radiographs and physical properties. Recurrence times of Holocene turbidites as proxies for earthquakes on the Cascadia and northern California margins are analyzed using two methods: (1) radiometric dating (14C method), and (2) relative dating, using hemipelagic sediment thickness and sedimentation rates (H method). The H method provides (1) the best estimate of minimum recurrence times, which are the most important for seismic hazards risk analysis, and (2) the most complete dataset of recurrence times, which shows a normal distribution pattern for paleoseismic turbidite frequencies. We observe that, on these tectonically active continental margins, during the sea-level highstand of Holocene time, triggering of turbidity currents is controlled dominantly by earthquakes, and paleoseismic turbidites have an average recurrence time of ~550 yr in northern Cascadia Basin and ~200 yr along northern California margin. The minimum recurrence times for great earthquakes are approximately 300 yr for the Cascadia subduction zone and 130 yr for the northern San Andreas Fault, which indicates both fault systems are in (Cascadia) or very close (San Andreas) to the early window for another great earthquake. On active tectonic margins with great earthquakes, the volumes of mass transport deposits (MTDs) are limited on basin floors along the margins. The maximum run-out distances of MTD sheets across abyssal-basin floors along active margins are an order of magnitude less (~100 km) than on passive margins (~1000 km). The great earthquakes along the Cascadia and northern California margins cause seismic strengthening of the sediment, which

  15. Great earthquakes along the Western United States continental margin: implications for hazards, stratigraphy and turbidite lithology

    Directory of Open Access Journals (Sweden)

    C. H. Nelson

    2012-11-01

    Full Text Available We summarize the importance of great earthquakes (Mw ≳ 8 for hazards, stratigraphy of basin floors, and turbidite lithology along the active tectonic continental margins of the Cascadia subduction zone and the northern San Andreas Transform Fault by utilizing studies of swath bathymetry visual core descriptions, grain size analysis, X-ray radiographs and physical properties. Recurrence times of Holocene turbidites as proxies for earthquakes on the Cascadia and northern California margins are analyzed using two methods: (1 radiometric dating (14C method, and (2 relative dating, using hemipelagic sediment thickness and sedimentation rates (H method. The H method provides (1 the best estimate of minimum recurrence times, which are the most important for seismic hazards risk analysis, and (2 the most complete dataset of recurrence times, which shows a normal distribution pattern for paleoseismic turbidite frequencies. We observe that, on these tectonically active continental margins, during the sea-level highstand of Holocene time, triggering of turbidity currents is controlled dominantly by earthquakes, and paleoseismic turbidites have an average recurrence time of ~550 yr in northern Cascadia Basin and ~200 yr along northern California margin. The minimum recurrence times for great earthquakes are approximately 300 yr for the Cascadia subduction zone and 130 yr for the northern San Andreas Fault, which indicates both fault systems are in (Cascadia or very close (San Andreas to the early window for another great earthquake.

    On active tectonic margins with great earthquakes, the volumes of mass transport deposits (MTDs are limited on basin floors along the margins. The maximum run-out distances of MTD sheets across abyssal-basin floors along active margins are an order of magnitude less (~100 km than on passive margins (~1000 km. The great earthquakes along the Cascadia and northern California margins

  16. A new integrated tectonic model for the Mesozoic-Early Cenozoic subduction, spreading, accretion and collision history of Tethys adjacent to the southern margin of Eurasia (NE Turkey)

    Science.gov (United States)

    Robertson, Alastair; Parlak, Osman; Ustaömer, Timur; Taslı, Kemal; İnan, Nurdan; Dumitrica, Paulian; Karaoǧlan, Fatih

    2014-05-01

    Cretaceous age for the E Pontide ophiolites, with important implications for alternative tectonic hypotheses. The two-subduction-zone hypothesis is supported by sedimentological and structural studies of the volcanic-sedimentary melange and of the sedimentary thrust sheets within the suture zone. Geochemical studies of oceanic basaltic rocks in the melange and also new biostratigraphic dating of radiolarites and calcareous microfossils within pelagic and redeposited deep-sea/slope sediments add to the picture. Taken together, the evidence suggests the former existence of both an oceanic and a continental margin subduction complex that are now amalgamated within the suture zone. We propose the following tectonic hypothesis: Fragments of oceanic basaltic lithologies and their deep-sea sedimentary cover accreted to form a Jurassic-Cretaceous intra-oceanic subduction complex. Terrigenous and arc-derived volcaniclastic gravity flows and pelagic carbonates accumulated in a continental margin forearc basin, mainly during the Cretaceous. Subduction melange was first emplaced over the distal Eurasian margin during the Late Cretaceous owing to thickening of the accretionary prism. During suturing, the continental margin forearc basin was emplaced southwards over the oceanic-derived accretionary wedge. The Eurasian continental margin was imbricated and thrust northwards as collision proceeded. Final closure of the adjacent Tethys took place prior to late Middle Eocene. This was followed by marine transgression and the accumulation of non-marine to shallow-marine sediments, including Nummulitic limestones. Regional correlations suggest that the double subduction zone hypothesis, notably involving Jurassic intra-oceanic spreading, is applicable to >1000 km of the Eurasian margin, specifically the Lesser Caucasus and possibly also the Central Pontides.

  17. Characterization of the Brazilian continental shelf adjacent to Rio Grande do Norte state, NE Brazil

    Directory of Open Access Journals (Sweden)

    Helenice Vital

    2010-01-01

    Full Text Available This study focuses on the analysis of high-resolution seismic profiles, integrated with sedimentological, echosounder, SRTM and satellite image datasets, of the Brazilian continental shelf adjacent to the Rio Grande do Norte State, NE Brazil. Located in the northeast of Brazil, the State of Rio Grande do Norte is bounded by two main coastal and shelf systems: the eastern coastal-shelf, from the Sagi River to the Touros High, and the northern coastal-shelf, extending from Touros High to Tibau. This shelf represents a modern, highly dynamic mixed carbonate-siliciclastic system characterized by reduced width and shallow depths as compared with other parts of the Brazilian shelf. It has an average width of 40 km, the shelf-break lying at a depth of ~ 60 m. This shelf is subject to the full strength of the westerly South Equatorial current combined with high winds and moderate to high tides and waves. A sharply defined stratigraphic boundary, probably between the Pleistocene and Holocene deposits, is clearly to be observed in the seismic record. Incised-valleys extending from the main river mouths (e.g.the Potengi, Açu, and Apodi to the shelf break dominate the area investigated and may indicate periods of lower sea level.Este estudo está direcionado ao conhecimento da plataforma continental brasileira adjacente ao Estado do Rio Grande do Norte, NE do Brasil, através da analise de perfis sismicos de alta resolução integrados a dados sedimentológicos, batimétricos, SRTM e imagens de satélites. O Estado do Rio Grande do Norte, localizado no nordeste do Brasil, apresenta dois sistemas costeiros-plataformais: Setor Este, do Rio Sagi (divisa PB-RN ao Alto de Touros e Setor Norte, do Alto de Touros a Tibau (divisa RN-CE. Esta plataforma representa um sistema plataformal moderno misto (carbonático-siliciclástico, altamente dinâmico. É caracterizado por sua reduzida largura e águas rasas, quando comparado com outras partes da plataforma

  18. Role of carbonate platforms, continental margin sediments/volcanics and oceanic units in Tethyan assembly: evidence from the Eastern Taurides, Turkey

    Science.gov (United States)

    Robertson, A. H. F.; Metin, Y.; Parlak, O.; Vergili, O.; Taslı, K.; Inan, N.; Soycan, H.

    2012-04-01

    We focus here on the palaeotectonic development of the Eastern Tauride region in its wider regional setting related to the opening and closure of Neotethys. Continental margin-type, ophiolitic and melange units are widely exposed in eastern central Turkey (Gürün, Darende, Hekimhan and Pinarbaşı areas). These units restore as a Triassic rifted continental margin that underwent passive margin subsidence during Jurassic-Early Cretaceous. Ophiolitic rocks (e.g. Pınarbaşı, Gürün area, Kuluncak, Hekimhan, Divriği) formed by spreading above a northward-dipping intra-oceanic subduction zone during Late Cretaceous time. Melanges associated with the emplaced ophiolites are interpreted as parts of the former rifted margins and the early formed (Triassic) oceanic crust that were assembled into an accretionary prism during latest Cretaceous time. The emplacement of the continental margin units, melanges and ophiolites onto the Eastern Tauride platform (e.g. Gürün Autochthon) was driven by trench-margin collision during latest Cretaceous time (Campanian-Maastrichtian). The allochthonous units were re-thrust further south during Early to Mid-Eocene time related to regional continental collision. Eocene thrusting strongly affected the western (Pınarbaşı) and central (Gürün) areas of the region studied, whereas areas further east mainly experienced folding. Specifically, there is little evidence of Eocene thrusting Darende Basin in the east. This suggests that the thrusting was focused by the collision of irregularly shaped microcontinents while intervening areas remained less affected. The complex present-day Eastern Tauride outcrop then reflects post-collisional suture tightening (Miocene) and Plio-Quaternary strike-slip (transpression/transtension) related to the westward 'escape' of Anatolia. As a result of this, different levels of the thrust stack are commonly juxtaposed complicating reconstruction. After taking account of several alternative tectonic models

  19. Sources and distributions of tetraether lipids in surface sediments across a large river-dominated continental margin

    NARCIS (Netherlands)

    Zhu, C.; Weijers, J.W.H.; Wagner, T.; Pan, J.-M.; Chen, J.-F.; Pancost, R.D.

    2011-01-01

    Glycerol dialkyl glycerol tetraether (GDGT)-based proxies are increasingly used in modern carbon cycling and palaeoenvironmental investigations. It is therefore crucial to examine the robustness (sources, transport and degradation) of all GDGT-based proxies in continental margins, where

  20. Changing sedimentary environments during Pleistocene-Holocene in a core from the eastern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Rao, Ch.M.; Mascarenhas, A.; Rao, K.M.; Reddy, N.P.C.; Das, H.C.

    Sedimentological and geochemical investigations of the sediments in a core from the eastern continental margin of India, at a water depth of 1200 m, revealed two distinct types. The Late Pleistocene sediments are greyish-black in colour and consist...

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

    Science.gov (United States)

    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

  2. Thermochronological constraints on the Cambrian to recent geological evolution of the Argentina passive continental margin

    Science.gov (United States)

    Kollenz, Sebastian; Glasmacher, Ulrich A.; Rossello, Eduardo A.; Stockli, Daniel F.; Schad, Sabrina; Pereyra, Ricardo E.

    2017-10-01

    Passive continental margins are geo-archives that store information from the interplay of endogenous and exogenous forces related to continental rifting, post-breakup history, and climate changes. The recent South Atlantic passive continental margins (SAPCMs) in Brazil, Namibia, and South Africa are partly high-elevated margins ( 2000 m a.s.l.), and the recent N-S-trending SAPCM in Argentina and Uruguay is of low elevation. In Argentina, an exception in elevation is arising from the higher topography (> 1000 m a.s.l.) of the two NW-SE-trending mountain ranges Sierras Septentrionales and Sierras Australes. Precambrian metamorphic and intrusive rocks, and siliciclastic rocks of Ordovician to Permian age represent the geological evolution of both areas. The Sierras Australes have been deformed and metamorphosed (incipient - greenschist) during the Gondwanides Orogeny. The low-temperature thermochronological (LTT) data (history of the Gondwanides and the Mesozoic and Cenozoic South Atlantic geological evolution. Upper Carboniferous zircon (U-Th/He)-ages (ZHe) indicate the earliest cooling below 180 °C/1 Ma. Most of the ZHe-ages are of Upper Triassic to Jurassic age. The apatite fission-track ages (AFT) of Sierras Septentrionales and the eastern part of Sierras Australes indicate the South Atlantic rifting and, thereafter. AFT-ages of Middle to Upper Triassic on the western side of the Sierras Australes are in contrast, indicating a Triassic exhumation caused by the eastward thrusting along the Sauce Grande wrench. The corresponding t-T models report a complex subsidence and exhumation history with variable rates since the Ordovician. Based on the LTT-data and the numerical modelling we assume that the NW-SE-trending mountain ranges received their geographic NW-SE orientation during the syn- to post-orogenic history of the Gondwanides.

  3. 210Pb and 210Po as tracers of particle transport mechanisms on continental margins

    International Nuclear Information System (INIS)

    Radakovitch, O.; Heussner, S.; Biscaye, P.; Abassi, A.

    1997-01-01

    The natural radionuclides 210 Po and 210 Pb, members of the 238 U decay chain, are particularly helpful to the understanding of particle transport processes in the ocean. These isotopes were analysed on sediment trap particles collected during 3 one-year experiments on continental margins. In the Bay of Biscay (Northeastern Atlantic) and in the Gulf of Lion (Northwestern Mediterranean Sea) both as part of the French ECOMARGE programme, and in the Middle Atlantic Bight (Northwestern Atlantic) as part of the SEEP programme. They yielded great insights into scenarios of particle transfer at each site, mainly based on the spatial and temporal distribution of 210 Pb particulate concentrations and fluxes. (author)

  4. Map showing bottom topography of the Pacific Continental Margin, Cape Mendocino to Point Conception

    Science.gov (United States)

    Chase, T.E.; Wilde, Pat; Normark, W.R.; Evenden, G.I.; Miller, C.P.; Seekins, B.A.; Young, J. D.; Grim, M.S.; Lief, C.J.

    1992-01-01

    All contours, geographic outlines, and political boundaries shown on this map of the bottom topography, or bathymetry, of the Pacific continental margin between 34? and 41? N. latitudes were plotted from digital data bases in the library of the U.S. Geological Survey (USGS)-National Oceanic and Atmospheric Administration (NOAA) Joint Office for Mapping and Research (JOMAR). These digital data were obtained and compiled from many sources; consequently, data quality varies within particular data bases as well as from one data base to another.

  5. Structure and tectonics of western continental margin of India: Implication for geologic hazards

    Digital Repository Service at National Institute of Oceanography (India)

    Chaubey, A.K.; Ajay, K.K.

    , and Coastal Processes ofIndian. Coast" Structure and Tectonics ofWestern Continental Margin ofIndia: Implication for Geologic Hazards A.K. Chaubey and K.K. Ajay National Institute ojOceanography. DOM Paula, Goa-403 004 The geomorphological and geological....D., Kroon, D., Gaedicke, c., Craig, J. (Eds.), The Tectonic and Climatic Evolution of the Arabian Sea Region, vol. 195. Geological Society, London, pp. 71"':85 (Special Publications). Chaubey, A.K., Gopala Rao, D., Srinivas, K., Ramprasad, T., Ramana, M...

  6. Distribution patterns of Recent planktonic foraminifera in surface sediments of the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.

    derived from organisms living as benthos on the seafloor, and shells of organisms which once had lived as plankton in the surface waters (Diester-Haass et al., 1973). Thus the sedi- ments of continental margins show features typical 0025... surface waters contrast sharply with low salinity waters along the south Indian coast and in the Bay of Bengal (Fig. 3A). The North Equato- rial Current sets-in during the northeastern mon- soon period and it penetrates into the southern Arabian Sea...

  7. Decadal changes in carbon fluxes at the East Siberian continental margin: interactions of ice cover, ocean productivity, particle sedimentation and benthic life

    Science.gov (United States)

    Boetius, A.; Bienhold, C.; Felden, J.; Fernandez Mendez, M.; Gusky, M.; Rossel, P. E.; Vedenin, A.; Wenzhoefer, F.

    2015-12-01

    The observed and predicted Climate-Carbon-Cryosphere interactions in the Arctic Ocean are likely to alter productivity and carbon fluxes of the Siberian continental margin and adjacent basins. Here, we compare field observations and samples obtained in the nineties, and recently in 2012 during the sea ice minimum, to assess decadal changes in the productivity, export and recycling of organic matter at the outer East Siberian margin. In the 90s, the Laptev Sea margin was still largely ice-covered throughout the year, and the samples and measurements obtained represent an ecological baseline against which current and future ecosystem shifts can be assessed. The POLARSTERN expedition IceArc (ARK-XXVII/3) returned in September 2012 to resample the same transects between 60 and 3400 m water depth as well as stations in the adjacent deep basins. Our results suggest that environmental changes in the past two decades, foremost sea ice thinning and retreat, have led to a substantial increase in phytodetritus sedimentation to the seafloor, especially at the lower margin and adjacent basins. This is reflected in increased benthic microbial activities, leading to higher carbon remineralization rates, especially deeper than 3000 m. Besides a relative increase in typical particle degrading bacterial types in surface sediments, bacterial community composition showed little variation between the two years, suggesting that local microbial communities can cope with changing food input. First assessments of faunal abundances suggest an increase in polychaetes,holothurians and bivalves at depth, which fits the prediction of higher productivity and particle deposition rates upon sea ice retreat. The presentation also discusses the controversial issue whether there is evidence for an Arctic-wide increase in carbon flux, or whether we are looking at a spatial shift of the productive marginal ice zone as the main factor to enhance carbon flux to the deep Siberian margin.

  8. Phosphorite concretions in a sediment core from a bathymetric high off Goa, western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, Ch.M; Rao, B.R.

    A sediment core collected from a bathymetric high off Goa on the western continental margin of India, has yielded phosphorite concretions with an average Pd2O5 content of 32.75%, the P2O5 concentrations being highest ever reported from the margins...

  9. First evidence for the presence of iron oxidizing zetaproteobacteria at the Levantine continental margins.

    Directory of Open Access Journals (Sweden)

    Maxim Rubin-Blum

    Full Text Available During the 2010-2011 E/V Nautilus exploration of the Levantine basin's sediments at the depth of 300-1300 m, densely patched orange-yellow flocculent mats were observed at various locations along the continental margin of Israel. Cores from the mat and the control locations were collected by remotely operated vehicle system (ROV operated by the E/V Nautilus team. Microscopic observation and phylogenetic analysis of microbial 16S and 23S rRNA gene sequences indicated the presence of zetaproteobacterial stalk forming Mariprofundus spp.-like prokaryotes in the mats. Bacterial tag-encoded FLX amplicon pyrosequencing determined that zetaproteobacterial populations were a dominant fraction of microbial community in the biofilm. We show for the first time that zetaproteobacterial may thrive at the continental margins, regardless of crustal iron supply, indicating significant fluxes of ferrous iron to the sediment-water interface. In light of this discovery, we discuss the potential bioavailability of sediment-water interface iron for organisms in the overlying water column.

  10. First discovery of a cold seep on the continental margin of the central Red Sea

    KAUST Repository

    Batang, Zenon B.

    2012-06-01

    A new cold brine seep system with microbial mats and metazoan assemblages was discovered by a remotely operated vehicle (ROV) on the Saudi continental margin of central Red Sea. Now named as Thuwal Seeps, it has a shallow brine pool between 840 and 850. m water depths that is formed by focused brine expulsions from two sites (Seep I: 22°17.3\\'N, 38°53.8\\'E; Seep II: 22°16.9\\'N, 38°53.9\\'E). The seep is located at the base of a steep wall rock closer to the shore (20. km) than to the axial trough (120. km). The brine pool does not exhibit a significant thermal anomaly (<. 0.3°C) and is so far the coldest (21.7°C) and least saline (74‰) among brine pools in the Red Sea. This discovery provides the first direct evidence of a cold seep with associated biota on the continental margin of the Red Sea. © 2011 Elsevier B.V.

  11. Ocean-Continent Transition Structure of the Pelotas Magma-Rich Continental Margin, South Atlantic

    Science.gov (United States)

    Harkin, Caroline; Kusznir, Nick; Roberts, Alan; Manatschal, Gianreto; McDermott, Ken

    2017-04-01

    Rifted continental margins in the southern South Atlantic are magma-rich showing well developed volcanic extrusives known as seaward dipping reflectors (SDRs). Here we examine the magma-rich continental rifted margin of the Pelotas Basin, offshore Brazil. Deep seismic reflection data displays a large package of seaward dipping reflectors with an approximate width of 200 km and a varying thickness of 10 km to 17 km that have previously been interpreted as volcanic SDRs. We examine these SDRs to explore if they are composed predominantly of basaltic or sedimentary-volcaniclastic material. We also study the thickness of the crustal basement beneath the SDRs. Additionally we investigate if these SDRs are underlain by thin 'hyper-extended' continental crust or if they have been deposited on new magmatic basement. The answers to these questions are important in understanding the structure and formation processes of magma-rich continental margins. We use gravity inversion to investigate SDR composition by varying the proportion of basalt to sediments-volcaniclastics (basalt fraction) which determines the SDR densities in the gravity inversion. By matching the Moho depth and two-way travel time from gravity inversion and deep seismic reflection data, we determine the lateral variation in basalt fraction of the SDRs. Our analysis suggests: 1) There is an overall pattern of SDR basalt fraction and bulk density decreasing oceanward. This could be due to increasing sediment content oceanward or it could result from the change in basalt flows to hyaloclastites as water depth increases. 2) The SDR package can be split into two distinct sub packages based on the basalt fraction results, where the proximal side of each package has a higher basalt fraction and density. 3) The inner SDR package contains reflectors that bear a resemblance to the SDRs described by Hinz (1981) corresponding to syn-tectonic volcanic eruptions into an extensional basin, while the outer SDR package has

  12. Spatiotemporal relationships between earthquakes of the mid-Atlantic Ridge and the Atlantic continental margins

    Science.gov (United States)

    Bolarinwa, Oluwaseyi J.

    The seismicity of the mid Atlantic Ridge (MAR) was compared in space and time with the seismicity along the Atlantic continental margins of Europe, Africa, North America, the Carribean and South America in a bid to appraise the level of influence of the ridge push force at the MAR on the Atlantic coastal seismicity. By analyzing the spatial and temporal patterns of many earthquakes (along with the patterns in their stress directions) in diverse places with similar tectonic settings, it is hoped that patterns that might be found indicate some of the average properties of the forces that are causing the earthquakes. The spatial analysis of the dataset set used shows that areas with higher seismic moment release along the north MAR spatially correlate with areas with relatively lower seismic moment release along the north Atlantic continental margins (ACM) and vice versa. This inverse spatial correlation observed between MAR seismicity and ACM seismicity might be due to the time (likely a long time) it takes stress changes from segments of the MAR currently experiencing high seismic activity to propagate to the associated passive margin areas presently experiencing relatively low seismic activity. Furthermore, the number of Atlantic basin and Atlantic coast earthquakes occurring away from the MAR is observed to be independent of the proximity of earthquake's epicenters from the MAR axis. The effect of local stress as noted by Wysession et al. (1995) might have contributed to the independence of Atlantic basin and Atlantic coast earthquake proximity from the MAR. The Latchman (2011) observation of strong earthquakes on a specific section of the MAR being followed by earthquakes on Trinidad and Tobago was tested on other areas of the MAR and ACM. It was found that that the temporal delay observed by Latchman does not exist for the seismicity along other areas along the MAR and ACM. Within the time window used for this study, it appears that seismicity is occurring

  13. Gas Hydrates Accumulations on the South Shetland Continental Margin: New Detection Possibilities

    Directory of Open Access Journals (Sweden)

    V. D. Solovyov

    2011-01-01

    Full Text Available The results of investigations in 2006–2010 for hydrocarbon and gas hydrates on the Antarctic Peninsula continental margin are given. In 2004 and 2006, the marine geoelectric researches by methods of forming a short-pulsed electromagnetic field (FSPEF and vertical electric-resonance sounding (VERS had been conducted in this region. The “deposit” type anomaly was mapped by FSPEF survey, and anomalous polarized layers of “hydrocarbon deposit” type were chosen by VERS sounding within this anomaly on Antarctic margin in the region of UAS “Academician Vernadsky.” Anomalous zones of “gas hydrate deposit” type were detected on the South Shetland margin due to the special technology of satellite data processing and interpretation using. These results confirm the high gas hydrates potential of the West Antarctica region. Some practical results of the experimental approbation of these original technologies for the “direct” prospecting and exploration of hydrocarbon (HC and gas hydrates accumulations in different oil-and-gas bearing basins of Russia and Gulf of Mexico are proposed. The integration of satellite data processing and materials of FSPEF-VERS methods enable improving their efficiency for different geological and geophysical problems solving.

  14. Microseismicity in Southern South Island, New Zealand: Implications for the Mechanism of Crustal Deformation Adjacent to a Major Continental Transform

    Science.gov (United States)

    Warren-Smith, Emily; Lamb, Simon; Stern, Tim A.; Smith, Euan

    2017-11-01

    Shallow (New Zealand, as a consequence of distributed shear and thickening in the obliquely convergent Australian-Pacific plate boundary zone. It has recently been proposed that continental convergence here is accommodated by oblique slip on a low-angle detachment that underlies the region, and as such, forms a previously unrecognized mode of oblique continental convergence. We test this model using microseismicity, presenting a new, 15 month high-resolution microearthquake catalog for the Southern Lakes and northern Fiordland regions adjacent to the Alpine Fault. We determine the spatial distribution, moment release, and style of microearthquakes and show that seismicity in the continental lithosphere is predominantly shallower than 20 km, in a zone up to 150 km wide, but less frequent deeper microseismicity extending into the mantle, at depths of up to 100 km is also observed. The geometry of the subducted oceanic Australian plate is well imaged, with a well-defined Benioff zone to depths of 150 km. In detail, the depth of continental microseismicity shows considerable variation, with no clear link with major active surface faults, but rather represents diffuse cracking in response to the ambient stress release. The moment release rate is 0.1% of that required to accommodate relative plate convergence, and the azimuth of the principal horizontal axis of contraction accommodated by microseismicity is 120°, 15-20° clockwise of the horizontal axis of contractional strain rate observed geodetically. Thus, short-term microseismicity, independent of knowledge of intermittent large-magnitude earthquakes, may not be a good guide to the rate and orientation of long-term deformation but is an indicator of the instantaneous state of stress and potential distribution of finite deformation. We show that both the horizontal and vertical spatial distribution of microseismicity can be explained in terms of a low-angle detachment model.

  15. Lithospheric thickness jumps at the S-Atlantic continental margins from satellite gravity data and modelled isostatic anomalies

    Science.gov (United States)

    Shahraki, Meysam; Schmeling, Harro; Haas, Peter

    2018-01-01

    Isostatic equilibrium is a good approximation for passive continental margins. In these regions, geoid anomalies are proportional to the local dipole moment of density-depth distributions, which can be used to constrain the amount of oceanic to continental lithospheric thickening (lithospheric jumps). We consider a five- or three-layer 1D model for the oceanic and continental lithosphere, respectively, composed of water, a sediment layer (both for the oceanic case), the crust, the mantle lithosphere and the asthenosphere. The mantle lithosphere is defined by a mantle density, which is a function of temperature and composition, due to melt depletion. In addition, a depth-dependent sediment density associated with compaction and ocean floor variation is adopted. We analyzed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively. Together with topography data and an averaged crustal density at the conjugate margins these jumps are interpreted as isostatic geoid anomalies and yield best-fitting crustal and lithospheric thicknesses. In a grid search approach five parameters are systematically varied, namely the thicknesses of the sediment layer, the oceanic and continental crusts and the oceanic and the continental mantle lithosphere. The set of successful models reveals a clear asymmetry between the South Africa and Argentine lithospheres by 15 km. Preferred models predict a sediment layer at the Argentine margin of 3-6 km and at the South Africa margin of 1-2.5 km. Moreover, we derived a linear relationship between, oceanic lithosphere, sediment thickness and lithospheric jumps at the South Atlantic margins. It suggests that the continental lithospheres on the western and eastern South Atlantic are thicker by 45-70 and 60-80 km than the oceanic lithospheres, respectively.

  16. Identification and inversion of converted shear waves: case studies from the European North Atlantic continental margins

    Science.gov (United States)

    Eccles, Jennifer D.; White, Robert S.; Christie, Philip A. F.

    2009-10-01

    Wide-angle shear wave arrivals, converted from compressional to shear waves at crustal interfaces, enable crustal Vp/Vs ratios to be determined which provide valuable constraint on geological interpretations. Analysis of the converted shear wave phases represents the next logical step in characterizing the crustal structure and composition following multichannel seismic structural imaging and tomographic inversion of the wide-angle compressional wave phases. In this offshore study across two passive margins extending from stretched continental to fully oceanic crust, the high-data density (2-10 km ocean bottom seismometer, OBS, spacing) and a consistent, efficient conversion interface produced shear wave data sets suitable for traveltime inversion. The shear waves were recorded by three orthogonal geophones in each OBS. Arrival phases, visible to 180 km offset, were identified using their arrival times, moveout velocities and particle motions. Across the North Atlantic volcanic rifted continental margins studied, breakup was accompanied by the eruption of large volumes of basalts of the North Atlantic Igneous Province. The interface between post-volcanic sediments and the top of the basalts provides the dominant conversion boundary across the oceanic crust and the continent-ocean transition. However, the shear wave data quality was significantly diminished at the continental ends of the profiles where the thick basalt flows and hence this conversion interface feathers out and crustal attenuation increases. Initial modelling of the converted shear wave phases was carried out using a layer-based approach with arrivals converted on the way up used to constrain the Vp/Vs ratio of the post-volcanic sedimentary sequence beneath each OBS. To produce a model with continuous crustal S-wave velocities, the compressional wave velocities beneath the sediment-top basalt interface were transformed into starting shear wave velocities using a constant value of Vp/Vs and the

  17. Trace metals and organochlorines in sediments near a major ocean outfall on a high energy continental margin (Sydney, Australia).

    Science.gov (United States)

    Matthai, C; Birch, G F

    2000-12-01

    Sewage effluent from a large ocean outfall south of Sydney, southeastern Australia, is efficiently dispersed on this high energy continental margin. An enrichment of Ag, Cu, Pb and Zn is only detectable in the fine fraction (mud content of surficial sediment, making an identification of the anthropogenic trace metal source difficult using total sediment analyses. The concentrations of HCB and DDE in the total sediment are also slightly elevated near the outfall. In the vicinity of the outfall, the estimated sewage component in the fine fraction of sediment, using Ag, Cu and Zn in a conservative, two-endmember physical mixing model, is sewage to Sydney continental margin sediments.

  18. {sup 210}Pb and {sup 210}Po as tracers of particle transport mechanisms on continental margins

    Energy Technology Data Exchange (ETDEWEB)

    Radakovitch, O.; Heussner, S. [Perpignan Univ., 66 (France). Lab. de Sedimentologie et Geochimie Marines; Biscaye, P.; Abassi, A. [Columbia Univ., Palisades, NY (United States). Lamont Doherty Earth Observatory

    1997-12-31

    The natural radionuclides {sup 210}Po and {sup 210}Pb, members of the {sup 238}U decay chain, are particularly helpful to the understanding of particle transport processes in the ocean. These isotopes were analysed on sediment trap particles collected during 3 one-year experiments on continental margins. In the Bay of Biscay (Northeastern Atlantic) and in the Gulf of Lion (Northwestern Mediterranean Sea) both as part of the French ECOMARGE programme, and in the Middle Atlantic Bight (Northwestern Atlantic) as part of the SEEP programme. They yielded great insights into scenarios of particle transfer at each site, mainly based on the spatial and temporal distribution of {sup 210}Pb particulate concentrations and fluxes. (author) 11 refs.

  19. Chirostylidae of Australia's western continental margin (Crustacea : Decapoda: Anomura), with the description of five new species.

    Science.gov (United States)

    Mccallum, Anna W; Poore, Gary C B

    2013-01-01

    Five new species from the squat lobster family Chirostylidae are described from the continental margin of western Australia: Uroptychus albus sp. nov., Uroptychus bardi sp. nov., Uroptychus jawi sp. nov., Uroptychus taylorae sp. nov., and Uroptychus worrorra sp. nov. New records of Indo-West Pacific species for Australia are: Gastroptychus brachyterus Baba, 2005, Gastroptychus investigatoris Alcock, 1899, Uroptychodes grandirostris (Yokoya, 1933), Uroptychodes inortenseni (Van Dam, 1939), Uroptychus scandens Benedict, 1902, Uroptychus ciliatus (Van Dam, 1933) and Uroptychus vandamae Baba, 1988. New distributional records are given for species previously recorded from Australia: Uroptychus flindersi Ahyong & Poore, 2004, Uroptychus hesperius Ahyong & Poore, 2004, Uroptychusjoloensis Van Dam, 1939, Uroptychus nigricapillis Alcock, 1901, and Uroptychus spinirostris (Ahyong & Poore, 2004). These new records expand the number of chirostylid species in Australia from 34 to 46. Keys to Australian species of the genera Gastroptychus, Uroptychodes and Uroptychus are provided.

  20. Exploring the Continental Margin of Israel: “Telepresence” at Work

    Science.gov (United States)

    Coleman, Dwight F.; Austin, James A., Jr.; Ben-Avraham, Zvi; Ballard, Robert D.

    2011-03-01

    A multidisciplinary team of American and Israeli scientists conducted ocean exploration with a “telepresence” component offshore Israel in September 2010 on board the new E/V Nautilus, which is a reincarnation of the former East German R/V Alexander von Humboldt. This was the first comprehensive geological and biological exploration of the Israel continental margin using deep submergence vehicle systems. Diverse seafloor environments in water depths between 500 and 1300 meters were sampled and imaged using two remotely operated vehicle (ROV) systems, Hercules and Argus. The ROV dives within three areas (Figure 1) investigated high-priority acoustic targets representing geological, biological, or archaeological features as identified by the onboard scientific team. During the dives, biological and geological samples and more than 100 kilometers of high-resolution side-scan sonar data were collected.

  1. Earth-System Scales of Biodiversity Variability in Shallow Continental Margin Seafloor Ecosystems

    Science.gov (United States)

    Moffitt, S. E.; White, S. M.; Hill, T. M.; Kennett, J.

    2015-12-01

    High-resolution paleoceanographic sedimentary sequences allow for the description of ecosystem sensitivity to earth-system scales of climate and oceanographic change. Such archives from Santa Barbara Basin, California record the ecological consequences to seafloor ecosystems of climate-forced shifts in the California Current Oxygen Minimum Zone (OMZ). Here we use core MV0508-20JPC dated to 735,000±5,000 years ago (Marine Isotope Stage 18) as a "floating window" of millennial-scale ecological variability. For this investigation, previously published archives of planktonic δ18O (Globigerina bulloides) record stadial and interstadial oscillations in surface ocean temperature. Core MV0508-20JPC is an intermittently laminated archive, strongly influenced by the California Current OMZ, with continuously preserved benthic foraminifera and discontinuously preserved micro-invertebrates, including ophiuroids, echinoderms, ostracods, gastropods, bivalves and scaphopods. Multivariate statistical approaches, such as ordinations and cluster analyses, describe climate-driven changes in both foraminiferal and micro-invertebrate assemblages. Statistical ordinations illustrate that the shallow continental margin seafloor underwent predictable phase-shifts in oxygenation and biodiversity across stadial and interstadial events. A narrow suite of severely hypoxic taxa characterized foraminiferal communities from laminated intervals, including Bolivina tumida, Globobulimina spp., and Nonionella stella. Foraminiferal communities from bioturbated intervals are diverse and >60% similar to each other, and they are associated with echinoderm, ostracod and mollusc fossils. As with climate shifts in the latest Quaternary, there is a sensitive benthic ecosystem response in mid-Pleistocene continental margins to climatically related changes in OMZ strength.

  2. Bubble composition of natural gas seeps discovered along the Cascadia Continental Margin

    Science.gov (United States)

    Baumberger, T.; Merle, S. G.; Embley, R. W.; Seabrook, S.; Raineault, N.; Lilley, M. D.; Evans, L. J.; Walker, S. L.; Lupton, J. E.

    2016-12-01

    Gas hydrates and gas-filled pockets present in sedimentary deposits have been recognized as large reservoirs for reduced carbon in the Earth's crust. This is particularly relevant in geological settings with high carbon input, such as continental margins. During expedition NA072 on the E/V Nautilus (operated by the Ocean Exploration Trust Inc.) in June 2016, the U.S. Cascadia Continental Margin (Washington, Oregon and northern California) was explored for gas seepage from sediments. During this expedition, over 400 bubble plumes at water depths ranging from 125 and 1640 m were newly discovered, and five of them were sampled for gas bubble composition using specially designed gas tight fluid samplers mounted on the Hercules remotely operated vehicle (ROV). These gas bubble samples were collected at four different depths, 494 m (rim of Astoria Canyon), 615 and 620 m (SW Coquille Bank), 849 m (floor of Astoria Canyon) and 1227 m (Heceta SW). At the two deeper sites, exposed hydrate was present in the same area where bubbles were seeping out from the seafloor. Other than the escaping gas bubbles, no other fluid flow was visible. However, the presence of bacterial mats point to diffuse fluid flow present in the affected area. In this study we present the results of the currently ongoing geochemical analysis of the gas bubbles released at the different sites and depths. Noble gas analysis, namely helium and neon, will give information about the source of the helium as well as about potential fractionation between helium and neon associated with gas hydrates. The characterization of these gas samples will also include total gas (CO2, H2, N2, O2, Ar, CH4 and other hydrocarbons) and stable isotope analysis (C and H). This dataset will reveal the chemical composition of the seeping bubbles as well as give information about the possible sources of the carbon contained in the seeping gas.

  3. Crustal structure of the North Iberian continental margin from seismic refraction/wide-angle reflection profiles

    Science.gov (United States)

    Ruiz, M.; Díaz, J.; Pedreira, D.; Gallart, J.; Pulgar, J. A.

    2017-10-01

    The structure and geodynamics of the southern margin of the Bay of Biscay have been investigated from a set of 11 multichannel seismic reflection profiles, recorded also at wide angle offsets in an onshore-offshore network of 24 OBS/OBH and 46 land sites. This contribution focuses on the analysis of the wide-angle reflection/refraction data along representative profiles. The results document strong lateral variations of the crustal structure along the margin and provide an extensive test of the crustal models previously proposed for the northern part of the Iberian Peninsula. Offshore, the crust has a typical continental structure in the eastern tip of the bay, which disappears smoothly towards the NW to reach crustal thickness close to 10 km at the edge of the studied area ( 45°N, 6°W). The analysis of the velocity-depth profiles, altogether with additional information provided by the multichannel seismic data and magnetic surveys, led to the conclusion that the crust in this part of the bay should be interpreted as transitional from continental to oceanic. Typical oceanic crust has not been imaged in the investigated area. Onshore, the new results are in good agreement with previous results and document the indentation of the Bay of Biscay crust into the Iberian crust, forcing its subduction to the North. The interpreted profiles show that the extent of the southward indentation is not uniform, with an Alpine root less developed in the central and western sector of the Basque-Cantabrian Basin. N-S to NE-SW transfer structures seem to control those variations in the indentation degree.

  4. The De Long Trough: a newly discovered glacial trough on the East Siberian continental margin

    Directory of Open Access Journals (Sweden)

    M. O'Regan

    2017-09-01

    Full Text Available Ice sheets extending over parts of the East Siberian continental shelf have been proposed for the last glacial period and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean have left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish – Russian – US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions. The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a  >  65 m thick sequence of glacio-genic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough – the first to be reported on the East Siberian margin, here referred to as the De Long Trough because of its location due north of the De Long Islands. Stratigraphy and dating of sediment cores show that a drape of acoustically laminated sediments covering the glacial deposits is older than ∼ 50 cal kyr BP. This provides direct evidence for extensive glacial activity on the Siberian shelf that predates the Last Glacial Maximum and most likely occurred during the Saalian (Marine Isotope Stage (MIS 6.

  5. Crustal Structure of the Gulf of Aden Continental Margins, from Afar to Oman, by Ambient Noise Seismic Tomography

    Science.gov (United States)

    Korostelev, F.; Weemstra, C.; Boschi, L.; Leroy, S. D.; Ren, Y.; Stuart, G. W.; Keir, D.; Rolandone, F.; Ahmed, A.; Al Ganad, I.; Khanbari, K. M.; Doubre, C.; Hammond, J. O. S.; Kendall, J. M.

    2014-12-01

    Continental rupture processes under mantle plume influence are still poorly known although extensively studied. The Gulf of Aden presents volcanic margins to the west, where they are influenced by the Afar hotspot, and non volcanic margins east of longitude 46° E. We imaged the crustal structure of the Gulf of Aden continental margins from Afar to Oman to evaluate the role of the Afar plume on the evolution of the passive margin and its extent towards the East. We use Ambient Noise Seismic Tomography to better understand the architecture and processes along the Gulf of Aden. This recent method, developed in the last decade, allows us to study the seismic signal propagating between two seismic stations. Ambient Noise Seismic Tomography is thus free from artifacts related to the distribution of earthquakes. We collected continuous records from about 200 permanent or temporary stations since 1999 to compute Rayleigh phase velocity maps over the Gulf of Aden.

  6. Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean

    OpenAIRE

    Gholamrezaie, Ershad; Scheck-Wenderoth, Magdalena (Dr.); Sippel, Judith (Dr.); Strecker, Manfred R. (Prof. Dr.)

    2018-01-01

    Abstract. The aim of this study is to investigate the shallow thermal field differences for two differently aged passive continental margins by analyzing regional variations in geothermal gradient and exploring the controlling factors for these variations. Hence, we analyzed two previously published 3-D conductive and lithospheric-scale thermal models of the Southwest African and the Norwegian passive margins. These 3-D models differentiate various sedimentary, crustal, and mantle units and i...

  7. Gas hydrate quantification from ocean-bottom seismometer data along the continental margin of Western Svalbard.

    Science.gov (United States)

    Chabert, A.; Minshull, T. A.; Westbrook, G. K.; Berndt, C.

    2009-04-01

    The stability of shallow gas hydrate in the Arctic region is expected to be affected by the warming of the bottom-water in the next decades. It is, therefore, important to evaluate how the gas hydrate systems will react to future increases in bottom-water temperature and the impact on climate of the spatial and temporal variability of the release of methane from these reservoirs. As part of the International Polar Year initiative, a multidisciplinary marine expedition was carried out in September 2008 along the continental margin west of Svalbard in the Arctic. One of the objectives was to investigate the extent of the gas hydrate stability zone (GHSZ) along and across the continental slope and to estimate the quantity of methane present using the geophysical properties of methane hydrate- and gas-bearing sediments, which occur in and beneath the GHSZ. Three seismic experiments employing ocean-bottom seismometers (OBS) were carried out across and along the continental margin as part of the project. Seismic data from 13 OBS in closely spaced arrays were acquired from 5 representative sites off west Svalbard, above and below the upper limit of the GHSZ. Two to four OBSs were deployed at each site, with a spacing of 200 m. The high frequency airguns were fired at 5-s intervals, concurrently with the acquisition of multi-channel seismic reflection profiles. The OBSs were equipped with a 3-component 4.5 Hz geophone package and a broadband hydrophone; the data-loggers were operated at 1 kHz sample rate. The OBS experiments were designed to recover P- and S-wave velocities to depths of a few hundreds metres below the seabed in order to estimate the amount of hydrate in the region, hydrate increasing both the P- and S-wave velocities of the sediments in which it is present. The data show clearly recorded P reflections at short offsets, as well as refracted arrivals at larger offsets, from depths of 1 to 2 kilometres below the seabed. S waves, generated by P-S conversion on

  8. Subsidence and eustasy at the continental margin of eastern North America

    Science.gov (United States)

    Watts, A. B.; Steckler, M. S.

    1979-01-01

    Biostratigraphic data from the COST B-2 well off New York and four deep commercial wells off Nova Scotia have been used to remove the effect of sediment loading at the Atlantic-type continental margin off the East Coast of North America. The resulting subsidence contains terms due to both 'tectonic' and 'eustatic' effects. By assuming the tectonic subsidence is thermal in origin these effects can be separated. The 'eustatic' effects have been isolated by least squares fitting an exponential curve to the subsidence data. The resulting sea-level curve shows a maximum rise in sea level during the Late Cretaceous era which probably does not exceed 150 m. The tectonic subsidence has been interpreted in terms of a simple thermal model for the cooling lithosphere. Based on this model the thermal thickness of the lithosphere and the total amount of crustal thinning are estimated. These estimates which are consistent with surface ship gravity and GEOS-3 altimeter measurements are used to define the structural elements which control the tectonic evolution of the margin.

  9. Distribution, abundance and trail characteristics of acorn worms at Australian continental margins

    Science.gov (United States)

    Anderson, T. J.; Przeslawski, R.; Tran, M.

    2011-04-01

    Acorn worms (Enteropneusta), which were previously thought to be a missing link in understanding the evolution of chordates, are an unusual and potentially important component of many deep-sea benthic environments, particularly for nutrient cycling. Very little is known about their distribution, abundance, or behaviour in deep-sea environments around the world, and almost nothing is known about their distribution within Australian waters. In this study, we take advantage of two large-scale deep-sea mapping surveys along the eastern (northern Lord Howe Rise) and western continental margins of Australia to quantify the distribution, abundance and trail-forming behaviour of this highly unusual taxon. This is the first study to quantify the abundance and trail behaviour of acorn worms within Australian waters and provides the first evidence of strong depth-related distributions. Acorn worm densities and trail activity were concentrated between transect-averaged depths of 1600 and 3000 m in both eastern and western continental margins. The shallow limit of their depth distribution was 1600 m. The deeper limit was less well-defined, as individuals were found in small numbers below 3000 down to 4225 m. This distributional pattern may reflect a preference for these depths, possibly due to higher availability of nutrients, rather than a physiological constraint to greater depths. Sediment characteristics alone were poor predictors of acorn worm densities and trail activity. High densities of acorn worms and trails were associated with sandy-mud sediments, but similar sediment characteristics in either shallower or deeper areas did not support similar densities of acorn worms or trails. Trail shapes varied between eastern and western margins, with proportionally more meandering trails recorded in the east, while spiral and meandering trails were both common in the west. Trail shape varied by depth, with spiral-shaped trails dominant in areas of high acorn worm densities

  10. Organic matter diagenesis and hydrocarbon generation on outer Continental Margin of northwestern Australia

    Energy Technology Data Exchange (ETDEWEB)

    Meyers, P.A.; Snowdon, L.R.; Heggie, D.; Bent, A.

    1989-03-01

    Organic geochemical analyses of sediments and rocks obtained from drill sites on the Exmouth and Wombat Plateaus and the Argo Abyssal Plain on the northwestern margin of Australia were done onboard the JOIDES Resolution during Ocean Drilling Program Legs 122 and 123. These analyses provide information about the sources of organic matter to these offshore locations from Triassic to Holocene times and also indicate the degree of postdepositional diagenesis and maturation the organic matter has experienced. Because this margin has interest to petroleum explorationists, these data have practical as well as fundamental significance. Triassic claystones (equivalent to the onshore Mungeroo Formation) from the Wombat Plateau contain up to several percent of land-derived organic carbon. Neocomian siltstones and claystones (equivalent to the Barrow Group and Muderong Shale) from the Exmouth Plateau hold similar organic matter but at lower concentrations. Younger sediments are generally very lean in organic matter. Gas chromatographic analysis of extractable hydrocarbons shows a large and often dominant contribution of continental components, notably n-alkanes with a strong odd/even ratio and tricyclic diterpanes. Both Rock-Eval and hydrocarbon results agree in indicating low to moderate levels of thermal maturity. Locations on the Exmouth Plateau typically contain large amounts of thermogenic gaseous hydrocarbons dominated by methane. Concentrations peak in Senonian chalk sequences. In Neocomian siltstones and claystones, methane-ethane ratios diminish as concentrations decrease. The source of these hydrocarbons is likely to be the Triassic coals and coaly material below the Dingo claystone, which was not drilled during these legs but has been characterized from industry wells on this passive margin.

  11. Late-Quaternary variations in clay minerals along the SW continental margin of India: Evidence of climatic variations

    Digital Repository Service at National Institute of Oceanography (India)

    Chauhan, O.S.; Sukhija, B.S.; Gujar, A.R.; Nagabhushanam, P.; Paropkari, A.L.

    Down-core variations in illite, chlorite, smectite and kaolinite (the major clays) in two sup(14)C-dated cores collected along the SW continental margin of India show that illite and chlorite have enhanced abundance during 20-17, 12.5, 11-9.5, and 5...

  12. Feeding types of the benthic community and particle transport across the slope of the NW European Continental Margin (Goban Spur)

    NARCIS (Netherlands)

    Flach, E.; Lavaleye, M.; De Stigter, H.; Thomsen, L.

    1998-01-01

    Densities and biomass of feeding guilds of benthic foraminifera, macrofauna and megafauna were estimated at seven stations ranging from 208 m to 4460 m water depth along the OMEX-transect at the continental margin of the Goban Spur N.E. Atlantic. At the same stations flow velocities in the Bottom

  13. Structural interpretation of the Konkan basin, southwestern continental margin of India, based on magnetic and bathymetric data

    Digital Repository Service at National Institute of Oceanography (India)

    Subrahmanyam, V.; Krishna, K.S.; Murty, G.P.S.; Rao, D.G.; Ramana, M.V.; Rao, M.G.

    Magnetic and bathymetric studies on the Konkan basin of the southwestern continental margin of India reveal prominent NNW-SSE, NW-SE, ENE-WSW, and WNE-ESE structural trends. The crystalline basement occurs at about 5-6 km below the mean sea level. A...

  14. Circum-Pacific accretion of oceanic terranes to continental blocks: accretion of the Early Permian Dun Mountain ophiolite to the E Gondwana continental margin, South Island, New Zealand

    Science.gov (United States)

    Robertson, Alastair

    2016-04-01

    Accretionary orogens, in part, grow as a result of the accretion of oceanic terranes to pre-existing continental blocks, as in the circum-Pacific and central Asian regions. However, the accretionary processes involved remain poorly understood. Here, we consider settings in which oceanic crust formed in a supra-subduction zone setting and later accreted to continental terranes (some, themselves of accretionary origin). Good examples include some Late Cretaceous ophiolites in SE Turkey, the Jurassic Coast Range ophiolite, W USA and the Early Permian Dun Mountain ophiolite of South Island, New Zealand. In the last two cases, the ophiolites are depositionally overlain by coarse clastic sedimentary rocks (e.g. Permian Upukerora Formation of South Island, NZ) that then pass upwards into very thick continental margin fore-arc basin sequences (Great Valley sequence, California; Matai sequence, South Island, NZ). Field observations, together with petrographical and geochemical studies in South Island, NZ, summarised here, provide evidence of terrane accretion processes. In a proposed tectonic model, the Early Permian Dun Mountain ophiolite was created by supra-subduction zone spreading above a W-dipping subduction zone (comparable to the present-day Izu-Bonin arc and fore arc, W Pacific). The SSZ oceanic crust in the New Zealand example is inferred to have included an intra-oceanic magmatic arc, which is no longer exposed (other than within a melange unit in Southland), but which is documented by petrographic and geochemical evidence. An additional subduction zone is likely to have dipped westwards beneath the E Gondwana margin during the Permian. As a result, relatively buoyant Early Permian supra-subduction zone oceanic crust was able to dock with the E Gondwana continental margin, terminating intra-oceanic subduction (although the exact timing is debatable). The amalgamation ('soft collision') was accompanied by crustal extension of the newly accreted oceanic slab, and

  15. Germanium-silicon fractionation in a river-influenced continental margin: The Northern Gulf of Mexico

    Science.gov (United States)

    Baronas, J. Jotautas; Hammond, Douglas E.; Berelson, William M.; McManus, James; Severmann, Silke

    2016-04-01

    In this study we have sampled the water column and sediments of the Gulf of Mexico to investigate the effects of high riverine terrigenous load and sediment redox conditions on the cycling of Ge and Si. Water column Ge/Si ratios across the Gulf of Mexico continental shelf range from 1.9 to 25 μmol/mol, which is elevated compared to the global ocean value of 0.7 μmol/mol. The Ge enrichment in the Gulf of Mexico seawater is primarily due to anthropogenic contamination of the Mississippi river, which is the main Ge and Si source to the area, and to a smaller extent due to discrimination against Ge during biogenic silica (bSi) production (Ge/Si = 1.2-1.8 μmol/mol), especially by radiolarians and siliceous sponges (Ge/Si = 0.6-1.1 μmol/mol). Most sediment pore waters (Ge/Si = 0.3-4.5 μmol/mol) and sediment incubation experiments (benthic flux Ge/Si = 0.9-1.2 μmol/mol) indicate precipitation of authigenic phases that sequester Ge from pore waters (non-opal sink). This process appears to be independent of oxidation-reduction reactions and suggests that authigenic aluminosilicate formation (reverse weathering) may be the dominant Ge sink in marine sediments. Compilation of previously published data shows that in continental margins, non-opal Ge burial flux is controlled by bSi supply, while in open ocean sediments it is 10-100 times lower and most likely limited by the supply of lithogenic material. We provide a measurement-based estimate of the global non-opal Ge burial flux as 4-32 Mmol yr-1, encompassing the 2-16 Mmol yr-1 needed to keep the global marine Ge cycle at steady state.

  16. A Comparison of Continental Extension Estimates Across the Margins of the Woodlark Basin, Papua New Guinea

    Science.gov (United States)

    Nazlim, B.; Goodliffe, A. M.

    2016-12-01

    Previous studies have shown that depth dependent extension is commonly observed across rifted margins. This has resulted in a discrepancy between the estimates of extension made through whole lithosphere/crust vs fault heave calculations (for example northwest Australia, South China Sea, Galicia). In the Woodlark Basin, the amount of extension estimated from observed subsidence and brittle extension also do not match. Taking into account sub-seismic resolution and poly-phase faulting reduces this mismatch. In the Woodlark Basin continental extension can also be estimated by extending Euler pole kinematics from the oceanic domain. Previous studies show that this predicts almost double the extension calculated from subsidence and brittle extension. Extension in the Woodlark Basin began at 8.4 Ma and transitioned to sea-floor spreading in the east at 6 Ma. The basin is an ideal place to study the extension discrepancy because of its young age and thin sediments. Seismic reflection easily images basement and fault structures. High resolution bathymetry permits tracing of major faults on the seafloor. A previous study focused on the extension discrepancy at the rifting to spreading transition. This study will focus on the discrepancy further east where seafloor spreading began just after 2 Ma and opening rates are faster. Data used in this study include bathymetry, magnetics, gravity, and low-fold 2-D seismic reflection data. Using the available data, extension estimates have been calculated through brittle extension and subsidence. Euler pole derived extension rates from previous studies were used for comparison. Results indicate that Euler pole kinematics predict far more extension than estimates calculated through subsidence and brittle extension. This provides important insights into processes in the low crust and supports earlier hypotheses that the mantle lithosphere and upper crust may be moving at different rates prior to continental breakup.

  17. 3D thermal structure of the continental lithosphere beneath China and adjacent regions

    Science.gov (United States)

    Sun, Yujun; Dong, Shuwen; Zhang, Huai; Li, Han; Shi, Yaolin

    2013-01-01

    Based on the Crust2.0 model and the topography data of Chinese continent and its adjacent regions, a three-dimensional finite element model is constructed in terms of the spherical coordinate system. In our numerical model, the average annual ground temperature from 195 meteorological stations and temperature of upper mantle derived from the seismic velocities are adopted as the top and bottom boundary conditions, respectively. The observed thermal conductivity and heat production from P wave velocity based on empirical formula are employed in our numerical model as well. The comparison between the calculated and observed surface heat flow proved that our results are reliable. The temperature beneath the Precambrian cratons is lower than that of other areas for 100-300 °C also. The typical temperature rang at the Moho is estimated to be 800-1000 °C beneath the Tibetan plateau and 500-700 °C beneath the Precambrian cratons (such as Indian plate, Sichuan basin, South China, North China and Tarim), respectively. The thermal state in the eastern part of Sino-Korean craton at the depth deeper than 60 km indicates that it was destructed. The thermal structure in center of Tibetan plateau (especially beneath Qiangtang area) supports the proposed flow of lower crustal or upper mantle material to the east. Generally, the distribution of volcanoes in Chinese continent is consistent with the high temperature areas in the crust or upper mantle. There are many obvious thermal transition zones across the orogenic belts. The thermal transition zone between eastern and western parts in the crust of Chinese continent is consistent with the north-south seismic zone.

  18. Three-Dimensional Numerical Modeling of Crustal Growth at Active Continental Margins

    Science.gov (United States)

    Zhu, G.; Gerya, T.; Tackley, P. J.

    2011-12-01

    Active margins are important sites of new continental crust formation by magmatic processes related to the subduction of oceanic plates. We investigate these phenomena using a three-dimensional coupled petrological-geochemical-thermomechanical numerical model, which combines a finite-difference flow solver with a non-diffusive marker-in-cell technique for advection (I3ELVIS code, Gerya and Yuen, PEPI,2007). The model includes mantle flow associated with the subducting plate, water release from the slab, fluid propagation that triggers partial melting at the slab surface, melt extraction and the resulting volcanic crustal growth at the surface. The model also accounts for variations in physical properties (mainly density and viscosity) of both fluids and rocks as a function of local conditions in temperature, pressure, deformation, nature of the rocks, and chemical exchanges. Our results show different patterns of crustal growth and surface topography, which are comparable to nature, during subduction at active continental margins. Often, two trench-parallel lines of magmatic activity, which reflect two maxima of melt production atop the slab, are formed on the surface. The melt extraction rate controls the patterns of new crust at different ages. Moving free water reflects the path of fluids, and the velocity of free water shows the trend of two parallel lines of magmatic activity. The formation of new crust in particular time intervals is distributed in finger-like shapes, corresponding to finger-like and ridge-like cold plumes developed atop the subducting slabs (Zhu et al., G-cubed,2009; PEPI,2011). Most of the new crust is basaltic, formed from peridotitic mantle. Granitic crust extracted from melted sediment and upper crust forms in a line closer to the trench, and its distribution reflects the finger-like cold plumes. Dacitic crust extracted from the melted lower crust forms in a line farther away from the trench, and its distribution is anticorrelated with

  19. The Hatton Basin and continental margin: Crustal structure from wide-angle seismic and gravity data

    Science.gov (United States)

    Vogt, Ulrike; Makris, Jannis; O'Reilly, Brian M.; Hauser, Franz; Readman, Peter W.; Jacob, A. W. Brian; Shannon, Pat M.

    1998-06-01

    Results from a wide-angle seismic and gravity study between the Rockall Bank and the Iceland Basin in the North Atlantic are presented. Crustal and sedimentary structures are resolved in the Hatton Basin and across the Hatton continental margin (HCM) east of magnetic anomaly 24. The structure of the oceanic crust west of the anomaly is also determined. Gravity data support the seismic model in areas of good seismic coverage and are used to control the model where the wide-angle seismic data are poor. A two-layer sedimentary sequence is present both in the Hatton Basin and across the continental margin. The lower layer, with P wave velocity of about 4 km/s, is interpreted as pre-Eocene synrift sediments and is up to 3.5 km thick. A younger and thinner (1-2.5 km) postrift sequence, with a velocity of about 2 km/s, defines a strong velocity contrast, which suggests an erosional unconformity surface. The sedimentary structure is distinctly different from that in the Rockall Trough, where a third intermediate layer (Vp ≈ 3 km/s) occurs. The three-layer crust, characterized by two intracrustal reflections (PiP1 and PiP2) varies from 30 km thick under the Rockall Bank to about 15 km below the Hatton Basin, where it is stretched by a factor of 2 relative to onshore Ireland. The crust is thinnest below the Hatton Bank, where the presence of a single intracrustal reflection indicates that the lower crustal layer thins to below the seismic resolution limit. Below the HCM a region of thick lower crust with anomalously high velocity (Vp ≈ 7.2 km/s) is resolved by the seismic and gravity data. It is connected (west of anomaly 24) to a region of oceanic crust, which is thicker than in the Iceland Basin. These relationships between the thick lower crust below the HCM and the oceanic crust in the Iceland Basin are interpreted as evidence for magmatic underplating, consistent with previous models for the HCM. The inferred unconformity surface between the synrift and postrift

  20. Cretaceous-Eocene provenance connections between the Palawan Continental Terrane and the northern South China Sea margin

    Science.gov (United States)

    Shao, Lei; Cao, Licheng; Qiao, Peijun; Zhang, Xiangtao; Li, Qianyu; van Hinsbergen, Douwe J. J.

    2017-11-01

    The plate kinematic history of the South China Sea opening is key to reconstructing how the Mesozoic configuration of Panthalassa and Tethyan subduction systems evolved into today's complex Southeast Asian tectonic collage. The South China Sea is currently flanked by the Palawan Continental Terrane in the south and South China in the north and the two blocks have long been assumed to be conjugate margins. However, the paleogeographic history of the Palawan Continental Terrane remains an issue of uncertainty and controversy, especially regarding the questions of where and when it was separated from South China. Here we employ detrital zircon U-Pb geochronology and heavy mineral analysis on Cretaceous and Eocene strata from the northern South China Sea and Palawan to constrain the Late Mesozoic-Early Cenozoic provenance and paleogeographic evolution of the region testing possible connection between the Palawan Continental Terrane and the northern South China Sea margin. In addition to a revision of the regional stratigraphic framework using the youngest zircon U-Pb ages, these analyses show that while the Upper Cretaceous strata from the Palawan Continental Terrane are characterized by a dominance of zircon with crystallization ages clustering around the Cretaceous, the Eocene strata feature a large range of zircon ages and a new mineral group of rutile, anatase, and monazite. On the one hand, this change of sediment compositions seems to exclude the possibility of a latest Cretaceous drift of the Palawan Continental Terrane in response to the Proto-South China Sea opening as previously inferred. On the other hand, the zircon age signatures of the Cretaceous-Eocene strata from the Palawan Continental Terrane are largely comparable to those of contemporary samples from the northeastern South China Sea region, suggesting a possible conjugate relationship between the Palawan Continental Terrane and the eastern Pearl River Mouth Basin. Thus, the Palawan Continental

  1. The tectonic significance of the Cabo Frio Tectonic Domain in the SE Brazilian margin: a Paleoproterozoic through Cretaceous saga of a reworked continental margin

    Directory of Open Access Journals (Sweden)

    Renata da Silva Schmitt

    Full Text Available ABSTRACT: The Cabo Frio Tectonic Domain is composed of a Paleoproterozoic basement tectonically interleaved with Neoproterozoic supracrustal rocks (Buzios-Palmital successions. It is in contact with the Neoproterozoic-Cambrian Ribeira Orogen along the SE Brazilian coast. The basement was part of at least three continental margins: (a 1.97 Ga; (b 0.59 - 0.53 Ga; (c 0.14 Ga to today. It consists of continental magmatic arc rocks of 1.99 to 1.94 Ga. Zircon cores show a 2.5 - 2.6 Ga inheritance from the ancient margin of the Congo Craton. During the Ediacaran, this domain was thinned and intruded by tholeiitic mafic dykes during the development of an oceanic basin at ca. 0.59 Ma. After the tectonic inversion, these basin deposits reached high P-T metamorphic conditions, by subduction of the oceanic lithosphere, and were later exhumed as nappes over the basement. The Cabo Frio Tectonic Domain collided with the arc domain of the Ribeira Orogen at ca. 0.54 Ga. It is not an exotic block, but the eastern transition between this orogen and the Congo Craton. Almost 400 m.y. later, the South Atlantic rift zone followed roughly this suture, not coincidently. It shows how the Cabo Frio Tectonic Domain was reactivated as a continental margin in successive extensional and convergent events through geological time.

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

    Science.gov (United States)

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

    2014-08-01

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

  3. Global multi-scale segmentation of continental and coastal waters from the watersheds to the continental margins

    NARCIS (Netherlands)

    Laruelle, G.G.; Dürr, H.H.; Lauerwald, R.; Hartmann, J.; Slomp, C.P.; Goossens, N.; Regnier, P.A.G.

    2013-01-01

    Past characterizations of the land–ocean continuum were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCATs: COastal Segmentation and related CATchments) or from an oceanic perspective, through a regionalization of the proximal and

  4. Rapid Sedimentation, Overpressure, and Focused Fluid Flow, Gulf of Mexico Continental Margin

    Directory of Open Access Journals (Sweden)

    Cédric M. John

    2006-09-01

    Full Text Available Expedition 308 of the Integrated Ocean Drilling Program (IODP was the fi rst phase of a two-component project dedicated to studying overpressure and fl uid fl ow on the continental slope of the Gulf of Mexico. We examined how sedimentation, overpressure, fl uid fl ow, and deformation are coupled in a passive margin setting and investigated how extremely rapid deposition of fi ne-grained mud might lead to a rapid build-up of pore pressure in excess of hydrostatic (overpressure, underconsolidation, and sedimentary masswasting. Our tests within the Ursa region, where sediment accumulated rapidly in the late Pleistocene, included the first-ever in situ measurements of how physical properties, pressure, temperature,and pore fluid compositions vary within low-permeability mudstones that overlie a permeable, overpressured aquifer, and we documented severe overpressure in the mudstones overlying the aquifer. We also drilled and logged three references sites in the Brazos-Trinity Basin IV and documented hydrostatic pressure conditions and normalconsolidation. Post-expedition studies will address how the generation and timing of overpressure control slope stability, seafl oor seeps, and large-scale crustal fluid fl ow. The operations ofExpedition 308 provide a foundation for future long-term in situ monitoring experiments in the aquifer and bounding mudstones.

  5. Deep structure of the Mid-Norwegian continental margin (the Vøring and Møre basins) according to 3-D density and magnetic modelling

    Science.gov (United States)

    Maystrenko, Yuriy Petrovich; Gernigon, Laurent; Nasuti, Aziz; Olesen, Odleiv

    2018-03-01

    A lithosphere-scale 3-D density/magnetic structural model of the Møre and Vøring segments of the Mid-Norwegian continental margin and the adjacent areas of the Norwegian mainland has been constructed by using both published, publically available data sets and confidential data, validated by the 3-D density and magnetic modelling. The obtained Moho topography clearly correlates with the major tectonic units of the study area where a deep Moho corresponds to the base of the Precambrian continental crust and the shallower one is located in close proximity to the younger oceanic lithospheric domain. The 3-D density modelling agrees with previous studies which indicate the presence of a high-density/high-velocity lower-crustal layer beneath the Mid-Norwegian continental margin. The broad Jan Mayen Corridor gravity low is partially related to the decreasing density of the sedimentary layers within the Jan Mayen Corridor and also has to be considered in relation to a possible low-density composition- and/or temperature-related zone in the lithospheric mantle. According to the results of the 3-D magnetic modelling, the absence of a strong magnetic anomaly over the Utgard High indicates that the uplifted crystalline rocks are not so magnetic there, supporting a suggestion that the entire crystalline crust has a low magnetization beneath the greater part of the Vøring Basin and the northern part of the Møre Basin. On the contrary, the crystalline crust is much more magnetic beneath the Trøndelag Platform, the southern part of the Møre Basin and within the mainland, reaching a culmination at the Frøya High where the most intensive magnetic anomaly is observed within the study area.

  6. Abbot Ice Shelf, the Amundsen Sea Continental Margin and the Southern Boundary of the Bellingshausen Plate Seaward of West Antarctica

    Science.gov (United States)

    Cochran, J. R.; Tinto, K. J.; Bell, R. E.

    2014-12-01

    The Abbot Ice Shelf extends 450 km along the coast of West Antarctica between 103°W and 89°W and straddles the boundary between the Bellingshausen Sea continental margin, which overlies a former subduction zone, and Amundsen Sea rifted continental margin. Inversion of NASA Operation IceBridge airborne gravity data for sub-ice bathymetry shows that the western part of the ice shelf, as well as Cosgrove Ice Shelf to the south, are underlain by a series of east-west trending rift basins. The eastern boundary of the rifted terrain coincides with the eastern boundary of rifting between Antarctica and Zealandia and the rifts formed during the early stages of this rifting. Extension in these rifts is minor as rifting quickly jumped north of Thurston Island. The southern boundary of the Cosgrove Rift is aligned with the southern boundary of a sedimentary basin under the Amundsen Embayment continental shelf to the west, also formed by Antarctica-Zealandia rifting. The shelf basin has an extension factor, β, of 1.5 - 1.7 with 80 -100 km of extension occurring in an area now ~250 km wide. Following this extension early in the rifting process, rifting centered to the north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf has been tectonically quiescent and has primarily been shaped though subsidence, sedimentation and the passage of the West Antarctic Ice Sheet back and forth across it. The former Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to its incorporation into the Antarctic Plate at ~62 Ma. During the latter part of its existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence between the Bellingshausen and Antarctic plates east of 102°W. Seismic reflection and gravity data show that this convergence is expressed by an area of intensely deformed sediments beneath the continental slope from 102°W to 95°W and

  7. Evidence of slope failure in the Sines Contourite Drift area (SW Portuguese Continental Margin) - preliminary results

    Science.gov (United States)

    Teixeira, Manuel; Roque, Cristina; Terrinha, Pedro; Rodrigues, Sara; Ercilla, Gemma; Casas, David

    2017-04-01

    Slope instability, expressed by landslide activity, is an important natural hazard both onshore as well as offshore. Offshore processes create great concern on coastal areas constituting one of the major and most prominent hazards, directly by the damages they generate and indirectly by the possibility of generating tsunamis, which may affect the coast line. The Southwest Portuguese Continental Margin has been identified as an area where several mass movements occurred from Late Pleistocene to Present. Recently, an area of 52 km long by 34 km wide, affected by slope failure has been recognized in the Sines contourite drift located off the Alentejo. SWIM and CONDRIBER multibeam swath bathymetry has been used for the geomorphologic analysis and for recognition of mass movement scars on the seabed. Scars' areas and volumes were calculated by reconstructing paleo-bathymetry. The net gain and net loss were calculated using both paleo and present day bathymetry. Geomorphologically, the study area presents 4 morphologic domains with landslide scars: I) Shelf and upper slope display an irregular boundary with domain II with a sharp step ( 150m - 600m); II) Smooth area with gentle slope angles making the transition from smoother area to the continental slope (scarp), with large scars, suggesting slow rate and distributed mass wasting processes over this area ( 600 - 1200m); III) Scarp with high rates of retrograding instability, where faster processes are verified and a great number of gullies is feeding downslope area (1200m - 3200m); IV) Lebre Basin where mass movements deposits accumulate (> 3200m). A total of 51 landslide scars were identified with a total affected area of 137.67 km2, with 80.9 km2 being located in the continental slope with about 59% of the disrupted area, between 1200 and 3200m, and 41% (56.6 km2) lies in the continental shelf and upper slope, on a range of depths between 150 and 800m. The mean scar area is 2.7 km2 and the maximum area recorded on a

  8. Interpretation of free-air gravity anomaly data for determining the crustal structure across the continental margins and aseismic ridges: Some examples from Indian continental margins and deep-sea basins

    Digital Repository Service at National Institute of Oceanography (India)

    Ramana, M.V.

    diagnostic anomaly pattern, and is independent of the location of the boundary with respect to the shelf edge. Robinowitz and Labrecque (1977) computed isostatic gravity anomalies across Argentine and southern African continental margins. The profiles... anomalies over the shelf edge were explained in several ways. For example, Worzel and Shurbet (1955) suggested that that basement ridge and crustal thinning account for gravity high near the shelf edge. High density belts in the basement have been...

  9. Late Neogene and Quaternary evolution of the northern Albemarle Embayment (mid-Atlantic continental margin, USA)

    Science.gov (United States)

    Mallinson, D.; Riggs, S.; Thieler, E.R.; Culver, S.; Farrell, K.; Foster, D.S.; Corbett, D.R.; Horton, B.; Wehmiller, J. F.

    2005-01-01

    Seismic surveys in the eastern Albemarle Sound, adjacent tributaries and the inner continental shelf define the regional geologic framework and provide insight into the sedimentary evolution of the northern North Carolina coastal system. Litho- and chronostratigraphic data are derived from eight drill sites on the Outer Banks barrier islands, and the Mobil #1 well in eastern Albemarle Sound. Within the study area, parallel-bedded, gently dipping Miocene beds occur at 95 to > 160 m below sea level (m bsl), and are overlain by a southward-thickening Pliocene unit characterized by steeply inclined, southward-prograding beds. The lower Pliocene unit consists of three seismic sequences. The 55–60 m thick Quaternary section unconformably overlies the Pliocene unit, and consists of 18 seismic sequences exhibiting numerous incised channel-fill facies. Shallow stratigraphy (paleo-Roanoke River valley. Radiocarbon and amino-acid racemization (AAR) ages indicate that the valley-fill is latest Pleistocene to Holocene in age. At least six distinct valley-fill units are identified in the seismic data. Cores in the valley-fill contain a 3–6 m thick basal fluvial channel deposit that is overlain by a 15 m thick unit of interlaminated muds and sands of brackish water origin that exhibit increasing marine influence upwards. Organic materials within the interlaminated deposits have ages of 13–11 cal. ka. The interlaminated deposits within the valley are overlain by several units that comprise shallow marine sediments (bay-mouth and shoreface environments) that consist of silty, fine- to medium-grained sands containing open neritic foraminifera, suggesting that this area lacked a fronting barrier island system and was an open embayment from ∼10 ka to ∼4.5 ka. Seismic data show that initial infilling of the paleo-Roanoke River valley occurred from the north and west during the late Pleistocene and early Holocene. Later infilling occurred from the south and east and is

  10. Dural invasion of meningiomas adjacent to the tumor margin on Gd-DTPA-enhanced MR images: histopathologic correlation

    International Nuclear Information System (INIS)

    Hutzelmann, A.; Palmie, S.; Freund, M.; Heller, M.; Buhl, R.

    1998-01-01

    In intracranial meningiomas a flat, contrast-enhancing, dural structure adjacent to the tumor can occasionally be observed on gadolinium-DTPA-enhanced MR images. We wished to evaluate whether there is a correlation between MR images and meningeal invasion of intracranial meningiomas. The study included 54 patients with intracranial meningioma and the meningeal sign. MR studies included T2-weighted and gadolinium-DTPA-enhanced T1-weighted images in axial, coronal, and sagittal planes. Histopathologic examinations were done on the meningiomas adjacent to the dura mater. The meningeal sign on MRI was observed from 2 up to 35 mm from the main tumor mass in 31 (57 %) of the 54 patients. In 20 of these 31 the histopathologic examination showed tumor invasion, while 11 patients had no tumor invasion but tissue proliferation, hypervascularity, and vascular dilatation. Seven of the 23 meningiomas without the meningeal sign had histologically proven infiltration of the adjacent dura. MR imaging is not able to determine definitive whether or not there is dural infiltration of the meningiomas. In conclusion, resection of the tumor with a wide margin is necessary to achieve complete excision of meningioma and to avoid recurrence. (orig.)

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

    Science.gov (United States)

    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

  12. Estimated post-Messinian sediment supply and sedimentation rates on the Ebro continental margin, Spain

    Science.gov (United States)

    Nelson, C.H.

    1990-01-01

    Because of the extensive data base of seismic profiles, radiometric ages, and stratigraphic time markers such as the subaerial Messinian surface, sedimentation rates and Ebro River sediment discharge can be estimated for different periods and environments of the Ebro continental margin. New values for sediment discharge (i.e., 6.2 versus previous estimates of 2-3.5 million t/yr) for the Holocene highstand are more reliable but remain minimum estimates because a small proportion of Ebro sediment advected to the Balearic Rise and Abyssal Plain cannot be accounted for, especially during lowstands. The general highstand conditions of the Pliocene, which were similar to those of the Holocene, resulted in a low discharge of Ebro River sediment (ca. 6.5 million t/yr) and an even thickness of sediment across the margin that deposited at rates of about 24-40 cm/ky. In contrast, sediment supply increased two-three times during the Pleistocene, the margin prograded rapidly and deposition occurred at rates of 101-165 cm/ky on the outer shelf and slope, but basin floor rates remained anomalously low (21-26 cm/ky) because sediment was drained and broadly dispersed eastward in Valencia Trough. During the late Pleistocene rise of sea level, the main depocenters progressively shifted shoreward and sedimentation rates greatly decreased from 175 cm/ky on the upper slope during the early transgression to 106 cm/ky on the outer shelf and then to 63 cm/ky on the mid-shelf during the late transgression as the river sediment discharge dropped to half by Holocene time. Maximal sedimentation rates occurred in active depocenters of sediment dispersal such as the Holocene delta (370 cm/ky) or the youngest Pleistocene Oropesa channel-levee complex (705 cm/ky) where deposition rates increased by an order of magnitude or more compared to average Ebro shelf (38 cm/ky) or base-of-slope rates in the Pleistocene (21 cm/ky). The sedimentation rates verify the importance of sea-level control on the

  13. Relationship between radionuclides and sedimentological variables in the South Atlantic Continental Margin; Relacoes entre radionuclideos e variaveis sedimentologicas na Margem Continental do Atlantico Sul

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Paulo A.L.; Figueira, Rubens C.L., E-mail: paulo.alves.ferreira@usp.br, E-mail: rfigueira@usp.br [Universidade de Sao Paulo (IO/USP), SP (Brazil). Instituto Oceanografico

    2015-07-01

    There is a lack of information regarding marine radioactivity in sediments of the Continental Margin of the South Atlantic. {sup 137}Cs and {sup 40}K radioactivity and sedimentological variables were determined in superficial sediment samples. It was demonstrated that {sup 40}K is a good indicator for sediment granulometry, whilst {sup 137}Cs presents a good correlation with its chemical composition. Moreover, it was identified through the radiometric data the occurrence of input of allochtonous matter to the Brazilian southernmost compartment from the Rio de La Plata estuary, as previously reported in the literature. (author)

  14. Sulfur Cycling in an Iron Oxide-Dominated, Dynamic Marine Depositional System: The Argentine Continental Margin

    Directory of Open Access Journals (Sweden)

    Natascha Riedinger

    2017-05-01

    Full Text Available The interplay between sediment deposition patterns, organic matter type and the quantity and quality of reactive mineral phases determines the accumulation, speciation, and isotope composition of pore water and solid phase sulfur constituents in marine sediments. Here, we present the sulfur geochemistry of siliciclastic sediments from two sites along the Argentine continental slope—a system characterized by dynamic deposition and reworking, which result in non-steady state conditions. The two investigated sites have different depositional histories but have in common that reactive iron phases are abundant and that organic matter is refractory—conditions that result in low organoclastic sulfate reduction rates (SRR. Deposition of reworked, isotopically light pyrite and sulfurized organic matter appear to be important contributors to the sulfur inventory, with only minor addition of pyrite from organoclastic sulfate reduction above the sulfate-methane transition (SMT. Pore-water sulfide is limited to a narrow zone at the SMT. The core of that zone is dominated by pyrite accumulation. Iron monosulfide and elemental sulfur accumulate above and below this zone. Iron monosulfide precipitation is driven by the reaction of low amounts of hydrogen sulfide with ferrous iron and is in competition with the oxidation of sulfide by iron (oxyhydroxides to form elemental sulfur. The intervals marked by precipitation of intermediate sulfur phases at the margin of the zone with free sulfide are bordered by two distinct peaks in total organic sulfur (TOS. Organic matter sulfurization appears to precede pyrite formation in the iron-dominated margins of the sulfide zone, potentially linked to the presence of polysulfides formed by reaction between dissolved sulfide and elemental sulfur. Thus, SMTs can be hotspots for organic matter sulfurization in sulfide-limited, reactive iron-rich marine sedimentary systems. Furthermore, existence of elemental sulfur and iron

  15. Nature of the crust in the Laxmi Basin (14°-20°N), western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.; Rao, D.G.; Sar, D.

    Kanya, respectively, across the northwest continental margin of India (Figure 1). Line drawings of interpreted seismic reflection profiles are stacked with free-air gravity and magnetic anomaly profiles, thereby an integrated analyses has been carried... for determining the crust below the shelf, Laxmi Basin and Western Basin. 3. Crustal structure ? associated gravity and magnetic anomalies In the present study we have integrated the new datasets with published geophysical data: Conrad 1707 profiles (Naini...

  16. Characterization of a stratigraphically constrained gas hydrate system along the western continental margin of Svalbard from ocean bottom seismometer data

    OpenAIRE

    Chabert, Anne; Minshull, Tim A.; Westbrook, Graham K.; Berndt, Christian; Thatcher, Kate E.; Sarkar, Sudipta

    2011-01-01

    The ongoing warming of bottom water in the Arctic region is anticipated to destabilize some of the gas hydrate present in shallow seafloor sediment, potentially causing the release of methane from dissociating hydrate into the ocean and the atmosphere. Ocean-bottom seismometer (OBS) experiments were conducted along the continental margin of western Svalbard to quantify the amount of methane present as hydrate or gas beneath the seabed. P- and S-wave velocities were modeled for five sites alon...

  17. IODP Expedition 307 Drills Cold-Water Coral Mound Along the Irish Continental Margin

    Directory of Open Access Journals (Sweden)

    Trevor Williams

    2006-03-01

    Full Text Available Introduction Over the past decade, oceanographic and geophysical surveys along the slope of the Porcupine Seabight off the southwestern continental margin of Ireland have identified upwards of a thousand enigmatic mound-like structures (Figs. 1 and 2. The mounds of the Porcupine Seabight rise from the seafl oor in water depths of 600–900 m and formimpressive conical bodies several kilometers wide and up to 200 m high. Although a few mounds such as Thérèse Mound and Galway Mound are covered by a thriving thicket of coldwater corals, most mound tops and fl anks are covered by dead coral rubble or are entirely buried by sediment (De Mol et al., 2002; Fig. 2, Beyer et al., 2003. Lophelia pertusa (Fig.3 and Madrepora oculata are the most prominent cold-water corals growing without photosynthetic symbionts. The widespread discovery of large and numerous coral-bearing banks and the association of these corals with the mounds have generated signifi cant interest as to the composition, origin and development of these mound structures.Challenger Mound, in the Belgica mound province, has an elongated shape oriented along a north-northeast to south-southwest axis and ispartially buried under Pleistocene drift sediments. In high-resolution seismic profiles the mounds appear to root on an erosion surface (van Rooij et al., 2003. During IODP Expedition307 the Challenger Mound in the Porcupine Seabight was drilled with the goal of unveiling the origin and depositional processes withinthese intriguing sedimentary structures. Challenger Mound, unlike its near neighbors the Thérèse and Galway mounds, has little to no livecoral coverage and, therefore, was chosen as the main target for drilling activities, so that no living ecosystem would be disturbed.

  18. Continental margin subsidence from shallow mantle convection: Example from West Africa

    Science.gov (United States)

    Lodhia, Bhavik Harish; Roberts, Gareth G.; Fraser, Alastair J.; Fishwick, Stewart; Goes, Saskia; Jarvis, Jerry

    2018-01-01

    Spatial and temporal evolution of the uppermost convecting mantle plays an important role in determining histories of magmatism, uplift, subsidence, erosion and deposition of sedimentary rock. Tomographic studies and mantle flow models suggest that changes in lithospheric thickness can focus convection and destabilize plates. Geologic observations that constrain the processes responsible for onset and evolution of shallow mantle convection are sparse. We integrate seismic, well, gravity, magmatic and tomographic information to determine the history of Neogene-Recent (age depths of +2 km and oceanic heat flow anomalies of +16 ± 4 mW m-2 are centered on Cape Verde. Residual depths decrease eastward to zero at the fringe of the Mauritania basin. Backstripped wells and mapped seismic data show that 0.4-0.8 km of water-loaded subsidence occurred in a ∼500 × 500 km region centered on the Mauritania basin during the last 23 Ma. Conversion of shear wave velocities into temperature and simple isostatic calculations indicate that asthenospheric temperatures determine bathymetry from Cape Verde to West Africa. Calculated average excess temperatures beneath Cape Verde are > + 100 °C providing ∼103 m of support. Beneath the Mauritania basin average excess temperatures are < - 100 °C drawing down the lithosphere by ∼102 to 103 m. Up- and downwelling mantle has generated a bathymetric gradient of ∼1/300 at a wavelength of ∼103 km during the last ∼23 Ma. Our results suggest that asthenospheric flow away from upwelling mantle can generate downwelling beneath continental margins.

  19. Crustal stress field perturbations in the continental margin around the Korean Peninsula and Japanese islands

    Science.gov (United States)

    Lee, Junhyung; Hong, Tae-Kyung; Chang, Chandong

    2017-10-01

    Seismic activity and focal mechanisms are governed by the effective stress field that is a combined result of regional tectonic processes and local stress perturbation. This study investigates the regional variation in the stress field in the eastern continental margin of the Eurasian plate around the Korean Peninsula and Japanese islands using a damped stress inversion technique based on the focal mechanism solutions of regional earthquakes. The dominant compressional stress is directed ENE-WSW around the Korean Peninsula and eastern China, E-W at the central East Sea and northern and southern Japan, NW-SE at central Japan, and N-S around the northern Nankai trough. The dominant compression direction changes rapidly in the East Sea and Japanese islands, which may be due to the combined effects of tectonic loading in the subduction zones off the Japanese islands and the India-Eurasia plate boundary. The crustal stress fields around the subduction zones off the Japanese islands present characteristic depth-dependent orientations. The orientations of the largest horizontal stress components, σH, in the subduction zones are subparallel with the plate convergence directions at shallow depths. The σH orientations are observed to rotate clockwise with the depth owing to slab subduction and lithospheric deformation. The regional stress field around the Japanese islands was perturbed temporally by the 2011 M9.0 Tohoku-Oki megathrust earthquake. The regional stress field was recovered in a couple of years. The stress field and tectonic structures are mutually affected, causing stress field distortion and a localized mixture of earthquakes in different faulting types.

  20. Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean: the Southwest African and the Norwegian margins

    Science.gov (United States)

    Gholamrezaie, Ershad; Scheck-Wenderoth, Magdalena; Sippel, Judith; Strecker, Manfred R.

    2018-02-01

    The aim of this study is to investigate the shallow thermal field differences for two differently aged passive continental margins by analyzing regional variations in geothermal gradient and exploring the controlling factors for these variations. Hence, we analyzed two previously published 3-D conductive and lithospheric-scale thermal models of the Southwest African and the Norwegian passive margins. These 3-D models differentiate various sedimentary, crustal, and mantle units and integrate different geophysical data such as seismic observations and the gravity field. We extracted the temperature-depth distributions in 1 km intervals down to 6 km below the upper thermal boundary condition. The geothermal gradient was then calculated for these intervals between the upper thermal boundary condition and the respective depth levels (1, 2, 3, 4, 5, and 6 km below the upper thermal boundary condition). According to our results, the geothermal gradient decreases with increasing depth and shows varying lateral trends and values for these two different margins. We compare the 3-D geological structural models and the geothermal gradient variations for both thermal models and show how radiogenic heat production, sediment insulating effect, and thermal lithosphere-asthenosphere boundary (LAB) depth influence the shallow thermal field pattern. The results indicate an ongoing process of oceanic mantle cooling at the young Norwegian margin compared with the old SW African passive margin that seems to be thermally equilibrated in the present day.

  1. Variability of the geothermal gradient across two differently aged magma-rich continental rifted margins of the Atlantic Ocean: the Southwest African and the Norwegian margins

    Directory of Open Access Journals (Sweden)

    E. Gholamrezaie

    2018-02-01

    Full Text Available The aim of this study is to investigate the shallow thermal field differences for two differently aged passive continental margins by analyzing regional variations in geothermal gradient and exploring the controlling factors for these variations. Hence, we analyzed two previously published 3-D conductive and lithospheric-scale thermal models of the Southwest African and the Norwegian passive margins. These 3-D models differentiate various sedimentary, crustal, and mantle units and integrate different geophysical data such as seismic observations and the gravity field. We extracted the temperature–depth distributions in 1 km intervals down to 6 km below the upper thermal boundary condition. The geothermal gradient was then calculated for these intervals between the upper thermal boundary condition and the respective depth levels (1, 2, 3, 4, 5, and 6 km below the upper thermal boundary condition. According to our results, the geothermal gradient decreases with increasing depth and shows varying lateral trends and values for these two different margins. We compare the 3-D geological structural models and the geothermal gradient variations for both thermal models and show how radiogenic heat production, sediment insulating effect, and thermal lithosphere–asthenosphere boundary (LAB depth influence the shallow thermal field pattern. The results indicate an ongoing process of oceanic mantle cooling at the young Norwegian margin compared with the old SW African passive margin that seems to be thermally equilibrated in the present day.

  2. Edge-driven Rayleigh Taylor Instabilities at Transtensional Continental Margins: Western North Island, New Zealand

    Science.gov (United States)

    Stern, T. A.; Houseman, G. A.; Evans, L.

    2011-12-01

    At a continental transform system with an element of extension, regular and thinned lithosphere are juxtaposed. Such a system will be gravitationally unstable as negative buoyancy is created by the regular mantle lithosphere terminating at an abrubt edge with less dense asthenospheric mantle. Finite element experiments with dimensionless ratios of viscosity and density show that such a gravitational instability can grow, migrate and eventually drip off into the lower density asthenosphere providing two criteria are met: lithospheric thinning across the edge is at least 30% or more; and that viscosity at the top of the mantle lithosphere is no more than 2.4 or 4.5 x1021 Pa s, for lithospheric thicknesses of 100 and 200 km respectively. These are low values for regular mantle lithosphere, but are in keeping with mantle lithosphere found adjacent to plate boundaries, or paleo subduction zones. As the mantle lithosphere deforms and migrates away from an edge it both thins and thickens different portions of the overlying crust. At the surface regions of subsidence and uplift migrated in concert with the subjacent gravitational instability. A dimensionless variable analysis of instability development shows that 3 critical dimensionless ratios control the shape, migration speed and form of the instability: η' = ratio of viscosity between crust and mantle; m' = ratio of crust to lithosphere thickness; and d' = portion of mantle lithosphere thinning to initiate the instability. Western North Island, New Zealand, displays characteristics of uplift and subsidence in the past 10-12 Ma, which can be explained by a migrating instability that initiated from the Auckland-Hauraki area around 10 Ma. Transtensional faults developed in mid-North Island from 5 Ma as back-arc spreading from the oceanic Lau Havre trough penetrated into the continental lithosphere of New Zealand. It is this transtensional phase that we argue started the edge-driven instability. The present position of

  3. Morphosedimentary expression of the Giant Pock Mark structure known as the "Gran Burato" (Transitional Zone, Galicia continental margin)

    Science.gov (United States)

    Lopez, Angel Enrique; Rubio, Belén; Rey, Daniel; Mohamed, Kais; Alvarez, Paula; Plaza-Morlote, Maider; Bernabeu, Ana; Druet, Maria; Martins, Virginia

    2016-04-01

    This paper presents the characterization of the sedimentary environment and other sedimentological features of the Transitional Zone of the Galicia continental margin, in the vicinity of the giant pock -mark structure known as the Gran Burato. The area is characterized by marginal platforms and a horst-graben system controlled by NW-SE oriented normal faults. In this zone, three giant pockmark structures, one of them known as the Gran Burato, were reported as associated to large-scale fluid escapes. The study area is located on the Transitional Zone (TZ) of the Galicia passive continental margin, which extends from Cape Finisterre (43o N) in the North to around 40oN in the South. This margin shows a complex structural configuration, which is reflected in the seabed, owing to tectonic movements from Mesozoic rifting phases and Eocene compression (Pyrennean Orogeny). Sedimentological, geochemical and physical properties analysis and 14C AMS-dating of a 4 m piston core extracted in the vicinity of the Gran Burato complemented by multibeam and TOPAS surveys allowed characterizing of the sedimentary environment in the study area. The interpretation of these data showed that the sedimentary and tectonic evolution of the area controlled by the activity of fluid dynamics.

  4. Quaternary development of resilient reefs on the subsiding kimberley continental margin, Northwest Australia

    Directory of Open Access Journals (Sweden)

    Lindsay B. Collins

    2010-01-01

    Full Text Available The Kimberley region in remote northwest Australia has poorly known reef systems of two types; coastal fringing reefs and atoll-like shelf-edge reefs. As a major geomorphic feature (from 12ºS to 18ºS situated along a subsiding continental margin, the shelf edge reefs are in a tropical realm with warm temperatures, relatively low salinity, clear low nutrient waters lacking sediment input, and Indo-West Pacific corals of moderate diversity. Seismic architecture of the Rowley Shoals reveals that differential pre-Holocene subsidence and relative elevation of the pre-Holocene substrate have controlled lagoon sediment infill and reef morphology, forming an evolutionary series reflecting differential accommodation in three otherwise similar reef systems. The Holocene core described for North Scott Reef confirms previous seismic interpretations, and provides a rare ocean-facing reef record. It demonstrates that the Indo-Pacific reef growth phase (RG111 developed during moderate rates of sea level rise of 10 mm/year from 11 to about 7-6.5 ka BP until sea level stabilization, filling the available 27 m of pre-Holocene accommodation. Despite the medium to high hydrodynamic energy imposed by the 4m tides, swell waves and cyclones the reef-building communities represent relatively low-wave energy settings due to their southeast facing and protection afforded by the proximity of the South Reef platform. This study demonstrates the resilience of reefs on the subsiding margin whilst linking Holocene reef morphology to the relative amount of pre-Holocene subsidence.Kimberly é uma região remota e pouco conhecida, localizada no noroeste da Austrália, ali são encontrados dois sistemas recifais: recifes costeiros de franja e os tipo-atois localizados na margem da plataforma continental. Esses recifes formam a feição geomórfica mais importante entre 12ºS a 18ºS estando localizados ao longo de uma margem continental em subsidência. Esses recifes encontram

  5. Historical changes in terrestrially derived organic carbon inputs to Louisiana continental margin sediments over the past 150 years

    Science.gov (United States)

    Sampere, Troy P.; Bianchi, Thomas S.; Allison, Mead A.

    2011-03-01

    Major rivers (and associated deltaic environments) provide the dominant pathway for the input of terrestrial-derived organic carbon in sediments (TOCT) to the ocean. Natural watershed processes and land-use changes are important in dictating the amount and character of carbon being buried on continental margins. Seven core sites were occupied on the Louisiana continental margin aboard the R/V Pelican in July 2003 along two major sediment transport pathways south and west of the Mississippi River mouth. Lignin profiles in these age-dated cores (210Pb geochronology) indicate artificial reservoir retention as a primary control on organic carbon quantity and quality reaching the margin post-1950, whereas pre-1950 sediments may reflect soil erosion due to land clearing and farming practices. Lignin (Λ8) concentrations (range 0.2 to 1.7) also indicate that TOCT delivery rates/decay processes have probably remained relatively consistent from proximal to distal stations along transects. The down-core profile at the Canyon station seems to be temporally linked and connected to inner shelf deposition, suggestive of rapid cross-shelf transport. Sources of terrestrially derived organic carbon were reflective of mixed angiosperms over the last 150 years in cores west and south of the Mississippi River delta. The lignin-phenol vegetation index (LPVI) (range 130.0 to 510) proved to be a sensitive indicator of source changes in these sediments and eliminated some of the variability compared to C/V (range 0.01 to 0.4) and S/V (range 0.9 to 2.1) ratios. Stochastic events such as hurricanes and large river floods have a measurable, albeit ephemeral, effect on the shelf TOCT record. Burial of TOCT on the river-dominated Louisiana continental margin is largely driven by anthropogenic land-use alterations in the last 150 years. Land-use changes in the Mississippi River basin and river damming have likely affected carbon cycling and TOCT burial on the Louisiana continental margin over a

  6. Structural characteristics of pre-Cenozoic erathem on continental margins of the Southwest Sub-basin, South China Sea and its geological implications

    Science.gov (United States)

    Zhu, Rongwei; Liu, Hailing; Yan, Pin; Yao, Yongjian; Zhou, Yang; Wang, Yin; Li, Yuhan

    2017-04-01

    Pre-Cenozoic structural characteristics on the conjugated continental margins, Zhongsha- Xisha block (ZSXSB) in the northwest and Nansha block (NSB) in the southeast, of the Southwest Sub-basin is fundamental to understand their tectonic contact relationship before the formation of the South China Sea. Some unpublished and published multi-channel seismic profiles together with published drillings and dredge data were correlated for interpretation. The strata of the study region can be divided into the upper, middle and lower structural layers. The upper and middle structural layers with extensional tectonics are Cenozoic, while the lower structural layer suffering compression is Mesozoic-Paleozoic in ZSXSB and Mesozoic in NSB, respectively. These compressional structures were formed mainly in Late Mesozoic Era. Further structural restoration was done to remove the Cenozoic tectonic influence and to calculate the pre-Cenozoic tectonic compression ratios. It is shown that tectonic compression ratios of NNW or NWW orientations gradually increase from the south to the north in the ZSXSB and southern NSB. While tectonic compression ratios of SSE orientations southward gradually decrease in the northern NSB. The variations of the compression ratios may be related to a spreading of the proto-South China Sea in late Jurassic to Early Cretaceous (then located in south of the NSB), which probably had pushed the NSB drifted northward and led to a soft collision suture between the ZSXSB and NSB. Thus the spreading of the Southwest Sub-basin may have started along suture zone pre-existed between the ZSXSB and NSB, which is tectonically weakness zone. Key words: Southwest Sub-basin of the South China Sea, conjugated continental margins, pre-Cenozoic compressive deformation structure, structural restoration, soft collision suture, proto-South China Sea Key words: Southwest Sub-basin of the South China Sea, Conjugated continental margins, Pre-Cenozoic structure, Structural

  7. Morphology and lithology of the continental slope north of the Demerara marginal plateau: results from the DRADEM cruise

    Science.gov (United States)

    Basile, Christophe; Girault, Igor; Heuret, Arnauld; Loncke, Lies; Poetisi, Ewald; Graindorge, David; Deverchère, Jacques; Klingelhoefer, Frauke; Frédéric Lebrun, Jean; Perrot, Julie; Roest, Walter

    2017-04-01

    The DRADEM scientific cruise was carried out from July 9th to 21th 2016 on board the R/V Pourquoi Pas?, in the Exclusive Economic Zones of Suriname and French Guiana. This cruise is part of a program dedicated to geological investigations of the continental margin, including the Demerara plateau, following the GUYAPLAC (2003) and IGUANES (2013) cruises, and before the MARGATS cruise (2016). The aims of DRADEM were to map the continental slope of the transform margin north of the Demerara plateau, and to dredge the rocks outcropping on the slope. We completed the bathymetric mapping of the continental slope, including part of the edge of the Demerara plateau. These new bathymetric data confirm the segmentation of the transform margin in three parts with very different morphologies. In addition, two circular structures were interpreted as mud volcanoes, one on the northern edge of the plateau, the other one in the distal part of the Orinoco deep sea fan. Twelve dredges were performed between 4700 and 3500 m water depths. Four from these twelve did not recovered rocks. The eight others recovered variable amounts of rocks, often encrusted, but of various nature: sediments (breccia, coarse sandstones, sandstones with plants debris, sandstones with shells, clayey ooze), micro-granular rocks and metamorphic rocks (including mylonite). The nature of the rocks was determined from macroscopic observation of the altered rocks. Of course, these determinations need to be validated and refined by further studies onshore. In any case, most of these rocks were previously unknown in this area, and they will strongly influence our understanding of the structure and evolution of this margin. They provide evidence for large vertical displacements that brought to the surface some of these rocks, that were formed in a deep setting.

  8. Geology and physiography of the continental margin north of Alaska and implications for the origin of the Canada Basin

    Science.gov (United States)

    Grantz, Arthur; Eittreim, Stephen L.; Whitney, O.T.

    1979-01-01

    The continental margin north of Alaska is of Atlantic type. It began to form probably in Early Jurassic time but possibly in middle Early Cretaceous time, when the oceanic Canada Basin of the Arctic Ocean is thought to have opened by rifting about a pole of rotation near the Mackenzie Delta. Offsets of the rift along two fracture zones are thought to have divided the Alaskan margin into three sectors of contrasting structure and stratigraphy. In the Barter Island sector on the east and the Chukchi sector on the west the rift was closer to the present northern Alaska mainland than in the Barrow sector, which lies between them. In the Barter Island and Chukchi sectors the continental shelf is underlain by prisms of clastic sedimentary rocks that are inferred to include thick sections of Jurassic and Neocomian (lower Lower Cretaceous) strata of southern provenance. In the intervening Barrow sector the shelf is underlain by relatively thin sections of Jurassic and Neocomian strata derived from northern sources that now lie beneath the outer continental shelf. The rifted continental margin is overlain by a prograded prism of Albian (upper Lower Cretaceous) to Tertiary clastic sedimentary rocks that comprises the continental terrace of the western Beaufort and northern Chukchi Seas. On the south the prism is bounded by Barrow arch, which is a hingeline between the northward-tilted basement surface beneath the continental shelf of the western Beaufort Sea and the southward-tilted Arctic Platform of northern Alaska. The Arctic platform is overlain by shelf clastic and carbonate strata of Mississippian to Cretaceous age, and by Jurassic and Cretaceous clastic strata of the Colville foredeep. Both the Arctic platform and Colville foredeep sequences extend from northern Alaska beneath the northern Chukchi Sea. At Herald fault zone in the central Chukchi Sea they are overthrust by more strongly deformed Cretaceous to Paleozoic sedimentary rocks of Herald arch, which trends

  9. Hypoxia over the Continental Margin in the Northern California Current: The Role of Shelf-Deep Ocean Exchange

    Science.gov (United States)

    Barth, J. A.; Chan, F.; Pierce, S. D.; Adams, K.; Shearman, R. K.; Erofeev, A.

    2016-02-01

    Near-bottom waters over the continental shelf off Oregon in the northern California Current have become increasingly hypoxic over the last decade, including the appearance of anoxia in summer 2006. Observed ecosystem impacts include the absence of fish and invertebrate die-offs. Near-bottom, inner-shelf hypoxia is driven by upwelling of low-oxygen, nutrient-rich source water onto the continental shelf, followed by the decay of organic matter from surface phytoplankton blooms. We are using data from moorings, ship surveys, and from over 60,000 kilometers of autonomous underwater glider tracks to understand the temporal and spatial distribution of dissolved oxygen over the continental margin off Oregon. The inshore side of Heceta Bank, a submarine bank that deflects the coastal upwelling jet seaward creating a region of weaker velocities inshore, is particularly vulnerable to hypoxia. Near-bottom dissolved oxygen variability is driven by changes in both the dissolved oxygen concentrations in offshore upwelling source water and local wind forcing. "Source water" is defined as being seaward of the continental shelf break on density surfaces that upwell onto the continental shelf. The strength and depth of the onshore source water flux due to wind-driven upwelling can vary through the upwelling season, influencing near-bottom shelf hypoxia. Late in the upwelling season, upwelled source waters can become lower in oxygen due to off-shelf flux of continental shelf water that has undergone respiration and is, therefore, lower in oxygen than unmodified upwelling source water. For present day source water dissolved oxygen concentrations ( 2.3 ml/l), hypoxia over the inner shelf on the inshore side of Heceta Bank during the summer upwelling season is observed about 50% of the time. Given the recent declining trend in source water dissolved oxygen concentration, in 50 years the frequency of the hypoxia over the inner shelf on the inshore side of Heceta Bank is predicted to be

  10. From hyperextended rift to convergent margin types: mapping the outer limit of the extended Continental Shelf of Spain in the Galicia area according UNCLOS Art. 76

    Science.gov (United States)

    Somoza, Luis; Medialdea, Teresa; Vázquez, Juan T.; González, Francisco J.; León, Ricardo; Palomino, Desiree; Fernández-Salas, Luis M.; Rengel, Juan

    2017-04-01

    Spain presented on 11 May 2009 a partial submission for delimiting the extended Continental Shelf in respect to the area of Galicia to the Commission on the Limits of the Continental Shelf (CLCS). The Galicia margin represents an example of the transition between two different types of continental margins (CM): a western hyperpextended margin and a northern convergent margin in the Bay of Biscay. The western Galicia Margin (wGM 41° to 43° N) corresponds to a hyper-extended rifted margin as result of the poly-phase development of the Iberian-Newfoundland conjugate margin during the Mesozoic. Otherwise, the north Galicia Margin (nGM) is the western end of the Cenozoic subduction of the Bay of Biscay along the north Iberian Margin (NIM) linked to the Pyrenean-Mediterranean collisional belt Following the procedure established by the CLCS Scientific and Technical Guidelines (CLCS/11), the points of the Foot of Slope (FoS) has to be determined as the points of maximum change in gradient in the region defined as the Base of the continental Slope (BoS). Moreover, the CLCS guidelines specify that the BoS should be contained within the continental margin (CM). In this way, a full-coverage multibeam bathymetry and an extensive dataset of up 4,736 km of multichannel seismic profiles were expressly obtained during two oceanographic surveys (Breogham-2005 and Espor-2008), aboard the Spanish research vessel Hespérides, to map the outer limit of the CM.In order to follow the criteria of the CLCS guidelines, two types of models reported in the CLCS Guidelines were applied to the Galicia Margin. In passive margins, the Commission's guidelines establish that the natural prolongation is based on that "the natural process by which a continent breaks up prior to the separation by seafloor spreading involves thinning, extension and rifting of the continental crust…" (para. 7.3, CLCS/11). The seaward extension of the wGM should include crustal continental blocks and the so

  11. Factors controlling late Cenozoic continental margin growth from the Ebro Delta to the western Mediterranean deep sea

    Science.gov (United States)

    Nelson, C.H.; Maldonado, A.

    1990-01-01

    The Ebro continental margin sedimentation system originated with a Messinian fluvial system. This system eroded both a major subaerial canyon cutting the margin southeastward from the present Ebro Delta and an axial valley that drained northeastward down Valencia Trough. Post-Messinian submergence of this topography and the Pliocene regime of high sea levels resulted in a marine hemipelagic drape over the margin. Late Pliocene to Pleistocene glacial climatic cycles, drainagebasin deforestation, and sea-level lowstands combined to increase sediment supply, cause the margin to prograde, and create a regime of lowstand sediment-gravity flows in the deeper margin. The depositional patterns of regressive, transgressive and highstand sea-level regimes suggest that location of the sediment source near the present Ebro Delta throughout the late Cenozoic, southward current advection of sediment, and greater subsidence in the southern margin combined to cause generally asymmetric progradation of the margin to the southeast. Thicker, less stable deposits filling the Messinian subaerial canyon underwent multiple retrograde failures, eroded wide gullied canyons and formed unchanneled base-of-slope sediment aprons in the central margin area; other margin areas to the north and south developed a series of channel-levee complexes. On the basin floor, the formation of Valencia Valley over the Messinian subaerial valley and earlier faults led to draining of about 20% of the Ebro Pleistocene sediment from channel-levee complexes through the valley to prograde Valencia Fan as much as 500 km northeast of the margin. Thus, the Ebro margin has two growth directions, mainly southeastward during higher sea levels, and eastward to northeastward during lower sea levels. The northeastward draining of turbidity currents has produced unusually thin and widely dispersed turbidite systems compared to those on ponded basin floors. During the past few centuries, man's impact has exceeded natural

  12. Peridotites and mafic igneous rocks at the foot of the Galicia Margin: an oceanic or continental lithosphere? A discussion

    Energy Technology Data Exchange (ETDEWEB)

    Korprobst, J.; Chazot, G.

    2016-10-01

    An ultramafic/mafic complex is exposed on the sea floor at the foot of the Galicia Margin (Spain and Portugal). It comprises various types of peridotites and pyroxenites, as well as amphibole-diorites, gabbros, dolerites and basalts. For chronological and structural reasons (gabbros were emplaced within peridotites before the continental break-up) this unit cannot be assigned to the Atlantic oceanic crust. The compilation of all available petrological and geochemical data suggests that peridotites are derived from the sub-continental lithospheric mantle, deeply transformed during Cretaceous rifting. Thus, websterite dykes extracted from the depleted MORB mantle reservoir (DMM), were emplaced early within the lithospheric harzburgites; subsequent boudinage and tectonic dispersion of these dykes in the peridotites, during deformation stages at the beginning of rifting, resulted in the formation of fertile but isotopically depleted lherzolites. Sterile but isotopically enriched websterites, would represent melting residues in the peridotites, after significant partial melting and melt extraction related to the thermal erosion of the lithosphere. The latter melts are probably the source of brown amphibole metasomatic crystallization in some peridotites, as well as of the emplacement of amphibole-diorite dykes. Melts directly extracted from the asthenosphere were emplaced as gabbro within the sub-continental mantle. Mixing these DMM melts together with the enriched melts extracted from the lithosphere, provided the intermediate isotopic melt-compositions - in between the DMM and Oceanic Islands Basalts reservoir - observed for the dolerites and basalts, none of which are characterized by a genuine N-MORB signature. An enriched lithospheric mantle, present prior to rifting of the Galicia margin, is in good agreement with data from the Messejana dyke (Portugal) and more generally, with those of all continental tholeiites of the Central Atlantic Magmatic Province (CAMP

  13. Resolving the fine-scale velocity structure of continental hyperextension at the Deep Galicia Margin using full-waveform inversion

    Science.gov (United States)

    Davy, R. G.; Morgan, J. V.; Minshull, T. A.; Bayrakci, G.; Bull, J. M.; Klaeschen, D.; Reston, T. J.; Sawyer, D. S.; Lymer, G.; Cresswell, D.

    2018-01-01

    Continental hyperextension during magma-poor rifting at the Deep Galicia Margin is characterized by a complex pattern of faulting, thin continental fault blocks and the serpentinization, with local exhumation, of mantle peridotites along the S-reflector, interpreted as a detachment surface. In order to understand fully the evolution of these features, it is important to image seismically the structure and to model the velocity structure to the greatest resolution possible. Traveltime tomography models have revealed the long-wavelength velocity structure of this hyperextended domain, but are often insufficient to match accurately the short-wavelength structure observed in reflection seismic imaging. Here, we demonstrate the application of 2-D time-domain acoustic full-waveform inversion (FWI) to deep-water seismic data collected at the Deep Galicia Margin, in order to attain a high-resolution velocity model of continental hyperextension. We have used several quality assurance procedures to assess the velocity model, including comparison of the observed and modeled waveforms, checkerboard tests, testing of parameter and inversion strategy and comparison with the migrated reflection image. Our final model exhibits an increase in the resolution of subsurface velocities, with particular improvement observed in the westernmost continental fault blocks, with a clear rotation of the velocity field to match steeply dipping reflectors. Across the S-reflector, there is a sharpening in the velocity contrast, with lower velocities beneath S indicative of preferential mantle serpentinization. This study supports the hypothesis that normal faulting acts to hydrate the upper-mantle peridotite, observed as a systematic decrease in seismic velocities, consistent with increased serpentinization. Our results confirm the feasibility of applying the FWI method to sparse, deep-water crustal data sets.

  14. Map showing bottom topography of the Pacific Continental Margin, Strait of Juan de Fuca to Cape Mendocino

    Science.gov (United States)

    Grim, M.S.; Chase, T.E.; Evenden, G.I.; Holmes, M.L.; Normark, W.R.; Wilde, Pat; Fox, C.J.; Lief, C.J.; Seekins, B.A.

    1992-01-01

    All contours, geographic outlines, and political boundaries shown on this map of the bottom topography, or bathymetry, of the Pacific continental margin between 34° and 41° N. latitudes were plotted from digital data bases in the library of the U.S. Geological Survey (USGS)-National Oceanic and Atmospheric Administration (NOAA) Joint Office for Mapping and Research (JOMAR). These digital data were obtained and compiled from many sources; consequently, data quality varies within particular data bases as well as from one data base to another.

  15. Bottom current processes along the Iberian continental margin; Procesos sedimentarios por corrientes de fondo a lo largo del margen continental iberico

    Energy Technology Data Exchange (ETDEWEB)

    Llave, E.; Hernandez-Molina, F. J.; Ercilla, G.; Roque, C.; Van Rooij, D.; Garcia, M.; Juan, C.; Mena, A.; Brackenridge, R.; Jane, G.; Stow, D.; Gomez-Ballesteros, M.

    2015-07-01

    The products of bottom current circulation around the Iberian continental margin are characterised by large erosional and depositional features formed under a variety of geological and oceanographic contexts. The Iberian margins are influenced by several water masses that mainly interact along the upper and middle con- tinental slopes, as well as along the lower slope with the abyssal plains being influenced to a lesser extent. The main depositional features occur along the Ceuta Contourite Depositional System (CDS) within the SW Alboran Sea, in the Gulf of Cadiz (the most studied so far), the western margins of the Portugal/Galician mar- gin, the Ortegal Spur and the Le Danois Bank or Cachucho. Moreover, erosional contourite features have also been recently indentified, most notably terraces, abraded surfaces, channels, furrows and moats. The majority of these features are formed under the influence of the Mediterranean water masses, especially by the interaction of the Mediterranean Outflow Water (MOW) with the seafloor. The MOW is characterized as relatively warm (13 degree centigrade) and with a high salinity (∼36.5), giving it a high density relative to the surrounding water masses, hence constituting an important contribution to the global thermohaline circulation, making it one of the most studied water masses surrounding Iberia. The development of both depositional and ero- sional contourite features does not only depend on the bottom-current velocity but also on several other important controlling factors, including: 1) local margin morphology affected by recent tectonic activity; 2) multiple sources of sediment supply; 3) water-mass interphases interacting with the seafloor; and 4) glacioeustatic changes, especially during the Quaternary, when the increasing influence of the bottom cur- rent has been observed during the cold stages. The main objective of this special volume contribution is to provide a review and description of the regional along

  16. Origin and transport of trace metals deposited in the canyons off Lisboa and adjacent slopes (Portuguese Margin) in the last century

    NARCIS (Netherlands)

    Costa, A.M.; Mil-Homens, M.; Lebreiro, S.M.; Richter, T.O.; de Stigter, H.; Boer, W.; Trancoso, M.A.; Melo, Z.; Mouro, F.; Mateus, M.; Canário, J.; Branco, V.; Caetano, M.

    2011-01-01

    Submarine canyons play an important role in the transfer of contaminated sediments from shelf areas to the deeper ocean. To evaluate the importance of submarine canyons adjacent to the Tagus and Sado estuaries (Portuguese Margin) as sediment pathway major and trace elements, (210)Pb radionuclides,

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

    Science.gov (United States)

    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

  18. Quantitative restoration the Gulf of Mexico continental margins based on a newly-derived, basin-wide, crustal thickness map

    Science.gov (United States)

    Nguyen, L. C.; Mann, P.

    2016-12-01

    For decades, one of the main difficulties for understanding the tectonic evolution of the Gulf of Mexico (GOM) is quantifying the amount of crustal thinning of its deeply-buried and salt-covered continental margins formed during the Triassic-Jurassic rifting. In this study, we present a new crustal thickness map for the entire GOM and its surrounding areas based on integration of: 1) depth to basement compilation of previous seismic refraction and well data; and 2) regional estimation of Moho depths from 3D gravity inversion. Gravity modeling of salt thickness and Moho depth provide new constraints on crustal thickness in areas where refraction and well data are not available from both the US and Mexican GOM. Our derived crustal thickness map shows a zone of stretched continental crust with an average thickness of 20 km extending 700 km from the Ouachita foldbelt to the Sigsbee escarpment and in a 200-km-wide zone along the north and NW edge of the Yucatan block. To fully reconstruct the GOM to its pre-rift stage, we first close the late Jurassic oceanic part of the deep GOM using the traces of oceanic transform faults mapped from satellite gravity data. We then use our crustal thickness map to restore the thinned continental crust of the conjugate margins. Restoring the Yucatan block in a NW-SE direction produces the optimal, closed-fit model which supports a two-phase, GOM opening concept with early asymmetrical rifting across a broader, more extended, North American lower plate ( 250 km) in the northern, US GOM and a narrower, less extended, Yucatan upper plate ( 100 km) in the southern, Mexican GOM. Our full-fit reconstruction shows a single, post-rift Louann-Campeche salt-filled sag basin and re-aligned Paleozoic magnetic trends between the Yucatan block and Florida.

  19. Crustal structure variations along the NW-African continental margin: A comparison of new and existing models from wide-angle and reflection seismic data

    Science.gov (United States)

    Klingelhoefer, Frauke; Biari, Youssef; Sahabi, Mohamed; Aslanian, Daniel; Schnabel, Michael; Matias, Luis; Benabdellouahed, Massinissa; Funck, Thomas; Gutscher, Marc-André; Reichert, Christian; Austin, James A.

    2016-04-01

    Deep seismic data represent a key to understand the geometry and mechanism of continental rifting. The passive continental margin of NW-Africa is one of the oldest on earth, formed during the Upper Triassic-Lower Liassic rifting of the central Atlantic Ocean over 200 Ma. We present new and existing wide-angle and reflection seismic data from four study regions along the margin located in the south offshore DAKHLA, on the central continental margin offshore Safi, in the northern Moroccan salt basin, and in the Gulf of Cadiz. The thickness of unthinned continental crust decreases from 36 km in the North to about 27 km in the South. Crustal thinning takes place over a region of 150 km in the north and only 70 km in the south. The North Moroccan Basin is underlain by highly thinned continental crust of only 6-8 km thickness. The ocean-continent transition zone shows a variable width between 40 and 70 km and is characterized by seismic velocities in between those of typical oceanic and thinned continental crust. The neighbouring oceanic crust is characterized by a thickness of 7-8 km along the complete margin. Relatively high velocities of up to 7.5 km/s have been imaged between magnetic anomalies S1 and M25, and are probably related to changes in the spreading velocities at the time of the Kimmeridgian/Tithonian plate reorganization. Volcanic activity seems to be mostly confined to the region next to the Canary Islands, and is thus not related to the initial opening of the ocean, which was associated to only weak volcanism. Comparison with the conjugate margin off Nova Scotia shows comparable continental crustal structures, but 2-3 km thinner oceanic crust on the American side than on the African margin.

  20. Heat flow in the rifted continental margin of the South China Sea near Taiwan and its tectonic implications

    Science.gov (United States)

    Liao, Wei-Zhi; Lin, Andrew T.; Liu, Char-Shine; Oung, Jung-Nan; Wang, Yunshuen

    2014-10-01

    Temperature measurements carried out on 9 hydrocarbon exploration boreholes together with Bottom Simulating Reflectors (BSRs) from reflection seismic images are used in this study to derive geothermal gradients and heat flows in the northern margin of the South China Sea near Taiwan. The method of Horner plot is applied to obtain true formation temperatures from measured borehole temperatures, which are disturbed by drilling processes. Sub-seafloor depths of BSRs are used to calculate sub-bottom temperatures using theoretical pressure/temperature phase boundary that marks the base of gas hydrate stability zone. Our results show that the geothermal gradients and heat flows in the study area range from 28 to 128 °C/km and 40 to 159 mW/m2, respectively. There is a marked difference in geothermal gradients and heat flow beneath the shelf and slope regions. It is cooler beneath the shelf with an average geothermal gradient of 34.5 °C/km, and 62.7 mW/m2 heat flow. The continental slope shows a higher average geothermal gradient of 56.4 °C/km, and 70.9 mW/m2 heat flow. Lower heat flow on the shelf is most likely caused by thicker sediments that have accumulated there compared to the sediment thickness beneath the slope. In addition, the continental crust is highly extended beneath the continental slope, yielding higher heat flow in this region. A half graben exists beneath the continental slope with a north-dipping graben-bounding fault. A high heat-flow anomaly coincides at the location of this graben-bounding fault at the Jiulong Ridge, indicating vigorous vertical fluid convection which may take place along this fault.

  1. Tectono-Magmatic Evolution of the South Atlantic Continental Margins with Respect to Opening of the Ocean

    Science.gov (United States)

    Melankholina, E. N.; Sushchevskaya, N. M.

    2018-03-01

    The history of the opening of the South Atlantic in Early Cretaceous time is considered. It is shown that the determining role for continental breakup preparation has been played by tectono-magmatic events within the limits of the distal margins that developed above the plume head. The formation of the Rio Grande Rise-Walvis Ridge volcanic system along the trace of the hot spot is considered. The magmatism in the South Atlantic margins, its sources, and changes in composition during the evolution are described. On the basis of petrogeochemical data, the peculiarities of rocks with a continental signature are shown. Based on Pb-Sr-Nd isotopic studies, it is found that the manifestations of magmatism in the proximal margins had features of enriched components related to the EM I and EM II sources, sometimes with certain participation of the HIMU source. Within the limits of the Walvis Ridge, as magmatism expanded to the newly formed oceanic crust, the participation of depleted asthenospheric mantle became larger in the composition of magmas. The role played by the Tristan plume in magma generation is discussed: it is the most considered as the heat source that determined the melting of the ancient enriched lithosphere. The specifics of the tectono-magmatic evolution of the South Atlantic is pointed out: the origination during spreading of a number of hot spots above the periphery of the African superplume. The diachronous character of the opening of the ocean is considered in the context of northward progradation of the breakup line and its connection with the northern branch of the Atlantic Ocean in the Mid-Cretaceous.

  2. Sedimentology of seismo-turbidites off the Cascadia and northern California active tectonic continental margins, Pacific Ocean

    Science.gov (United States)

    Gutierrez Pastor, Julia; Nelson, Hans; Goldfinger, Chris; Escutia, Carlota

    2013-04-01

    Holocene turbidites from turbidite channel systems along the active tectonic continental margins of the Cascadia subduction zone (offshore Vancouver Island to Mendocino Triple Junction) and the northern San Andreas Transform Fault (the Triple Junction to San Francisco Bay), have been analyzed for sedimentologic features related to their seismic origin. Centimeter thick silt/sand beds (turbidite base) capped by mud layers (turbidite tail) and interbedded with hemipelagic silty clay intervals with high biogenic content have been characterized by visual core descriptions, grain-size analysis, X-ray radiographs and physical properties. Along the northern California margin in upstream single tributary canyons and channels, most turbidites are uni-pulsed (classic fining up) whereas downstream below multiple tributary canyon and channel confluences, most deposits are stacked turbidites. Because each set of stacked turbidites has no hemipelagic sediment between each turbidite unit and each unit has a distinct mineralogy from a different tributary canyon, we interpret that a stacked turbidite is deposited by several coeval turbidity currents fed by multiple tributary canyons and channels with synchronous triggering from a single San Andreas Fault earthquake. The Cascadia margin is characterized by individual multi-pulsed turbidites that contain multiple coarse-grained sub-units without hemipelagic sediment between pulses. Because the number and character of multiple coarse-grained pulses for each correlative multi-pulsed turbidite is almost always constant both upstream and downstream in different channel systems for 600 km along the margin,we interpret that the earthquake shaking or aftershock signature is usually preserved, for the much stronger Cascadia (≥9 Mw) compared to weaker California (≥8Mw) earthquakes, which result in upstream uni-pulsed turbidites and downstream stacked turbidites. Consequently, both the strongest (≥9 Mw) great earthquakes and downstream

  3. Sedimentation and potential venting on the rifted continental margin of Dronning Maud Land

    Science.gov (United States)

    Huang, Xiaoxia; Jokat, Wilfried

    2016-12-01

    The relief of Dronning Maud Land (DML), formed by Middle and Late Mesozoic tectonic activity, had a strong spatial control on the early fluvial and subsequent glacial erosion and deposition. The sources, processes, and products of sedimentation along the DML margin and in the Lazarev Sea in front of the DML mountains have been barely studied. The onshore mountain belt parallel to the coast of the DML margin acts as a barrier to the transport of terrigenous sediments from the east Antarctic interior to the margin and into the Lazarev Sea. Only the Jutul-Penck Graben system allows a localized ice stream controlled transport of material from the interior of DML across its old mountain belt. Offshore, we attribute repeated large-scale debris flow deposits to instability of sediments deposited locally on the steep gradient of the DML margin by high sediment flux. Two types of canyons are defined based on their axial dimensions and originated from turbidity currents and slope failures during glacial/fluvial transport. For the first time, we report pipe-like seismic structures in this region and suggest that they occurred as consequences of volcanic processes. Sedimentary processes on the DML margin were studied using seismic reflection data and we restricted the seismic interpretation to the identification of major seismic sequences and their basal unconformities.

  4. Aedes (Stegomyia) aegypti in the continental United States: a vector at the cool margin of its geographic range.

    Science.gov (United States)

    Eisen, Lars; Moore, Chester G

    2013-05-01

    After more than a half century without recognized local dengue outbreaks in the continental United States, there were recent outbreaks of autochthonous dengue in the southern parts of Texas (2004-2005) and Florida (2009-2011). This dengue reemergence has provoked interest in the extent of the future threat posed by the yellow fever mosquito, Aedes (Stegomyia) aegypti (L.), the primary vector of dengue and yellow fever viruses in urban settings, to human health in the continental United States. Ae. aegypti is an intriguing example of a vector species that not only occurs in the southernmost portions of the eastern United States today but also is incriminated as the likely primary vector in historical outbreaks of yellow fever as far north as New York, Philadelphia, and Boston, from the 1690s to the 1820s. For vector species with geographic ranges limited, in part, by low temperature and cool range margins occurring in the southern part of the continental United States, as is currently the case for Ae. aegypti, it is tempting to speculate that climate warming may result in a northward range expansion (similar to that seen for Ixodes tick vectors of Lyme borreliosis spirochetes in Scandinavia and southern Canada in recent decades). Although there is no doubt that climate conditions directly impact many aspects of the life history of Ae. aegypti, this mosquito also is closely linked to the human environment and directly influenced by the availability of water-holding containers for oviposition and larval development. Competition with other container-inhabiting mosquito species, particularly Aedes (Stegomyia) albopictus (Skuse), also may impact the presence and local abundance of Ae. aegypti. Field-based studies that focus solely on the impact of weather or climate factors on the presence and abundance of Ae. aegypti, including assessments of the potential impact of climate warming on the mosquito's future range and abundance, do not consider the potential confounding

  5. Deformation of plate boundaries associated with subduction of continental margins: insights from 3D thermo-mechanical laboratory experiments (Invited)

    Science.gov (United States)

    Boutelier, D. A.; Cruden, A. R.

    2013-12-01

    The general sequence of tectonic events leading to the formation of collisional mountain belts includes closure of an ocean basin through oceanic subduction, subduction of a continental margin and deformation of the lithosphere. Laboratory experiments reproducing this fundamental chain of events investigate the three-dimensional and thermo-mechanical mechanics of the associated processes. Experiments reveal that this basic scenario can be considerably modified at the beginning of continental subduction. The buoyancy of the subducted passive margin causes a strong horizontal compression in the plates, which can lead to the formation of new thrusts in the magmatic arc or back-arc spreading center if the collision was preceded by oceanic subduction in the tensile regime. Several complex scenarios can develop, depending on the polarity of the new thrusts. If the new thrust in the arc or back-arc has the same polarity as the main subduction zone, the entire area located between the trench and the new thrust can be subducted, leaving little evidence of its former existence in the geological record. This process also modifies the thermal and mechanical regime of the subducted lithosphere, resulting in lower temperatures in the subducted crust thereby allowing deeper subduction. If the polarity of the new thrust is opposite to that of the existing subduction zone, the two slabs collide at depth, with the new slab generally cutting through the pre-existing slab. The distribution of convergence across several thrusts necessarily leads to a reduction of the convergence rate on the pre-existing subduction thrust. This leads to a reduction of the viscous coupling supporting the subducted lithosphere, causing an increase in downdip tension in the slab, and a rapid decrease of the slab strength due to temperature increase, eventually leading to slab break-off. Finally, the deformation caused by the subduction of the buoyant continental crust is fundamentally three

  6. Cenozoic unconformities and depositional supersequences of North Atlantic continental margins: testing the Vail model

    Science.gov (United States)

    Poag, C. Wylie; Ward, Lauck W.

    1987-01-01

    Integrated outcrop, borehole, and seismic reflection stratigraphy from the U.S. and Irish margins of the North Atlantic basin reveals a framework of Cenozoic depositional supersequences and interregional unconformities that resembles the Vail depositional model. Paleo-bathymetric and paleoceanographic analyses of associated microfossil assemblages indicate a genetic link between the depositional framework and the relative position of sea level.

  7. The upwelling record in the sediments of the westen continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Naidu, P.D.; PrakashBabu, C.; Rao, Ch.M.

    margin of India. In: Petroleum geochemistry and exploration in the Afro-Asian region, R. K. KUMAR et al., editors, Balkema, Rotterdam, pp. 347-361. PRELL W. L. (1984) Variation of monsoonal upwelling: a response to changing solar radiation. Climate...

  8. Echinodermata, Ophiuroidea, Gorgonocephalus Leach, 1815: First report of the genus for the Brazilian continental margin

    Directory of Open Access Journals (Sweden)

    Barboza, C. A. M.

    2010-01-01

    Full Text Available The Gorgonocephalidae includes 38 genera, five of them reported for Brazilian waters. Gorgonocephalus chilensishas a wide distribution throughout Antartica and Subantartican regions and its northern limit was restricted to the coast ofUruguay. This work aims to report the first occurrence of the Gorgonocephalus genus for the Brazilian continental marginand extend the northern limit of distribution of G. chilensis to the coast of Santa Catarina. Tolerance to a large temperatureand bathimetric range are crucial to understand the distributions patterns of ophiuroids from the polar circle that alsooccur at southern South America.

  9. Macrofaunal community structure in the western Indian continental margin including the oxygen minimum zone

    Digital Repository Service at National Institute of Oceanography (India)

    Ingole, B.S.; Sautya, S.; Sivadas, S.; Singh, R.; Nanajkar, M.

    and Prof. Lisa Levin helped in improving the manuscript. Our special thanks to Ms. Jennifer Gonzalez, Scripps Institution of Oceanography, La Jolla, California and Andy Gooday, National Oceanography Centre, UK for meticulously going through... caused by El Nino. In: R.V. Tyson & T.H. Pearson (Eds). Modern and Ancient Continental Shelf Anoxia. Geological Society Special Publication No. 58, London, 131-154. Bange H.W., Naqvi S.W.A., Codispoti L.A. (2005) The nitrogen cycle in the Arabian Sea...

  10. 3D thermal effect of late Cenozoic erosion and deposition within the Lofoten-Vesterålen segment of the Mid-Norwegian continental margin

    Science.gov (United States)

    Maystrenko, Yuriy Petrovich; Gernigon, Laurent; Olesen, Odleiv; Ottesen, Dag; Rise, Leif

    2018-01-01

    A 3D subsurface temperature distribution within the Lofoten-Vesterålen segment of the Mid-Norwegian continental margin and adjacent areas has been studied to understand the thermal effect of late Cenozoic erosion of old sedimentary and crystalline rocks and subsequent deposition of glacial sediments during the Pleistocene. A lithosphere-scale 3D structural model of the Lofoten-Vesterålen area has been used as a realistic approximation of the geometries of the sedimentary infill, underlying crystalline crust and lithospheric mantle during the 3D thermal modelling. The influence of late Cenozoic erosion and sedimentation has been included during the 3D thermal calculations. In addition, the 3D thermal modelling has been carried out by taking also into account the influence of early Cenozoic continental breakup. The results of the 3D thermal modelling demonstrate that the mainland is generally colder than the basin areas within the upper part of the 3D model. The thermal influence of the early Cenozoic breakup is still clearly recognisable within the western and deep parts of the Lofoten-Vesterålen margin segment in terms of the increased temperatures. The thermal effects of the erosion and deposition within the study area also indicate that a positive thermal anomaly exists within the specific sub-areas where sedimentary and crystalline rocks were eroded. A negative thermal effect occurs in the sub-areas affected by subsidence and subsequent sedimentation. The erosion-related positive thermal anomaly reaches its maximum of more than + 27° C at depths of 17-22 km beneath the eastern part of the Vestfjorden Basin. The most pronounced deposition-related negative anomaly shows a minimum of around -70° C at 17-20 km depth beneath the Lofoten Basin. The second negative anomaly is located within the northeastern part of the Vøring Basin and has minimal values of around -48° C at 12-14 km depth. These prominent thermal anomalies are associated with the sub-areas where

  11. Biogeochemistry and ecosystems of continental margins in the western North Pacific Ocean and their interactions and responses to external forcing - an overview and synthesis

    Science.gov (United States)

    Liu, K.-K.; Kang, C.-K.; Kobari, T.; Liu, H.; Rabouille, C.; Fennel, K.

    2014-12-01

    In this special issue we examine the biogeochemical conditions and marine ecosystems in the major marginal seas of the western North Pacific Ocean, namely, the East China Sea, the Japan/East Sea to its north and the South China Sea to its south. They are all subject to strong climate forcing as well as anthropogenic impacts. On the one hand, continental margins in this region are bordered by the world's most densely populated coastal communities and receive tremendous amount of land-derived materials. On the other hand, the Kuroshio, the strong western boundary current of the North Pacific Ocean, which is modulated by climate oscillation, exerts strong influences over all three marginal seas. Because these continental margins sustain arguably some of the most productive marine ecosystems in the world, changes in these stressed ecosystems may threaten the livelihood of a large population of humans. This special issue reports the latest observations of the biogeochemical conditions and ecosystem functions in the three marginal seas. The studies exemplify the many faceted ecosystem functions and biogeochemical expressions, but they reveal only a few long-term trends mainly due to lack of sufficiently long records of well-designed observations. It is critical to develop and sustain time series observations in order to detect biogeochemical changes and ecosystem responses in continental margins and to attribute the causes for better management of the environment and resources in these marginal seas.

  12. Surficial clay mineral distribution on the southwestern continental margin of India: evidence of input from the Bay of Bengal

    Science.gov (United States)

    Chauhan, Onkar S.; Gujar, A. R.

    1996-03-01

    Analyses of spatial distribution of clay minerals, sediment texture, and > 63 μm fractions of the grab samples from the S W continental margin of India exhibit: (i) higher contents of illite and chlorite on the lower slope and (ii) a well-defined no-clay zone on the entire shelf. Kaolinite and smectite are also present in significant quantities on the slope with traces of gibbsite and palygorskite in some samples. The high contents of illite and chlorite (clay minerals which are not abundant in the soils and estuarine sediments of this region) in the southern region of the study area are evidence for sediment contribution from the Bay of Bengal waters (BBW), which enter this region after the SW monsoon. Distribution trends of kaolinite, smectite, gibbsite, and laterite granules on the slope are suggestive of contribution from chemically weathered soils of Peninsular India.

  13. Volcano-sedimentary processes operating on a marginal continental arc: the Archean Raquette Lake Formation, Slave Province, Canada

    Science.gov (United States)

    Mueller, W. U.; Corcoran, P. L.

    2001-06-01

    The 200-m thick, volcano-sedimentary Raquette Lake Formation, located in the south-central Archean Slave Province, represents a remnant arc segment floored by continental crust. The formation overlies the gneissic Sleepy Dragon Complex unconformably, is laterally interstratified with subaqueous mafic basalts of the Cameron River volcanic belt, and is considered the proximal equivalent of the turbidite-dominated Burwash Formation. A continuum of events associated with volcanism and sedimentation, and controlled by extensional tectonics, is advocated. A complex stratigraphy with three volcanic and three sedimentary lithofacies constitute the volcano-sedimentary succession. The volcanic lithofacies include: (1) a mafic volcanic lithofacies composed of subaqueous pillow-pillow breccia, and subaerial massive to blocky flows, (2) a felsic volcanic lithofacies representing felsic flows that were deposited in a subaerial environment, and (3) a felsic volcanic sandstone lithofacies interpreted as shallow-water, wave- and storm-reworked pyroclastic debris derived from explosive eruptions. The sedimentary lithofacies are represented by: (1) a conglomerate-sandstone lithofacies consistent with unconfined debris flow, hyperconcentrated flood flow and talus scree deposits, as well as minor high-energy stream flow conglomerates that formed coalescing, steep-sloped, coarse-clastic fan deltas, (2) a sandstone lithofacies, interpreted as hyperconcentrated flood flow deposits that accumulated at the subaerial-subaqueous interface, and (3) a mudstone lithofacies consistent with suspension sedimentation in a small restricted lagoon-type setting. The Raquette Lake Formation is interpreted as a fringing continental arc that displays both high-energy clastic sedimentation and contemporaneous effusive and explosive mafic and felsic volcanism. Modern analogues that develop along active plate margins in which continental crust plays a significant role include Japan and the Baja California

  14. Submarine geo-hazards on the eastern Sardinia-Corsica continental margin based on preliminary pipeline route investigation

    Science.gov (United States)

    Cecchini, S.; Taliana, D.; Giacomini, L.; Herisson, C.; Bonnemaire, B.

    2011-03-01

    The understanding of the morphology and the shallow geo-hazards of the seafloor is a major focus for both academic and private industry research. On November and December 2009 a geophysical pipeline survey was carried out by Fugro Oceansismica S.p.A. (FOSPA) and FUGRO France (FFSA) for DORIS Engineering on behalf of GRTgaz (Engineering centre, Transmission Pipe Department; http://www.grtgaz.com) which are currently investigating the possibility of laying a pipeline between Sardinia and Corsica as a spur line from the planned GALSI Project. The Project, "Alimentation de la Corse en gaz naturel", consists of a corridor 100 km long and 1.0 km wide along the Corsica-Sardinia shelf. The integration of the multibeam, sidescan sonar and sparker data provided a high resolution seafloor mapping for geo-hazard assessment. In this article the data acquired along a break of slope section (approximately 20 km × 1.5 km), in the eastern sector of the Strait of Bonifacio are described. The area was abandoned during the survey, because of its unsuitability. Indeed, in this area the continental shelf, approximately 100 m deep and deepening gently eastward, is characterized by an uneven morphology, with different seabed features such as Beach- rocks mainly NNW-SSE oriented. Also, the continuity of the continental margin, identified around -110/-115 m, is interrupted by four canyon heads which incise the slope and are associated with glide deposits.

  15. 3D thermal modelling within the Lofoten-Vesterålen segment of the Mid-Norwegian continental margin

    Science.gov (United States)

    Maystrenko, Yuriy P.; Gernigon, Laurent; Gradmann, Sofie; Olesen, Odleiv

    2017-04-01

    A lithosphere-scale 3D structural model has been constructed based on the available structural data to reveal a deep structure of the Lofoten-Vesterålen segment and the northern part of the Vøring segment of the Mid-Norwegian continental margin. The constructed model covers the Vestfjorden, Ribban and Røst basins, the northern parts of the Vøring Basin and the Trøndelag Platform. The model also extends from the Fennoscandian Shield to the north-eastern part of the North Atlantic Ocean. The initial 3D structural model has been refined using a 3D gravity modelling over the whole study area. The final gravity-consistent model has been used as a structural base for a further 3D thermal modelling, which has been made by use of commercial software package COMSOL Multiphysics. As an upper thermal boundary condition, time-dependent temperature at the Earth's surface and sea bottom has been set, considering palaeoclimatic changes due to the last two Europe-scale glaciations (the Saalian and Weichselian glacial periods). The lithosphere-asthenosphere boundary has been used as a lower thermal boundary which corresponds to the 1300 °C isotherm. In addition to the above-mentioned paleoclimatic scenario, the effects of late Cenozoic erosion onshore and sedimentation offshore have been taken into account during the 3D thermal modelling. Results of this thermal modelling indicate that the continent is generally colder than the basin areas within the upper part of the 3D model. In particular, considering the transient perturbations in the near-surface thermal regime, as a result of the post-Paleogene erosion and sedimentation, helps us to understand additional details of subsurface temperature distribution within the study area. The thermal effects of the simultaneous erosion over the mainland and deposition within the basin areas indicate that a positive thermal anomaly should exist onshore, whereas the negative one must occur in the offshore part. These two thermal

  16. Basement configuration of Visakhapatnam - Paradip continental margin from inversion of magnetic anomalies

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, M.M.M.; Rao, S.J.; Venkateswarlu, K.; Murthy, K.S.R.; Murthy, I.V.R.; Subrahmanyam, A.S.

    . References 1 Curray J R, Emmel F J, Moore D G & Raitt R W, in: Ocean basins and margins, 6 (Plenum, New York) 1982, pp. 399-450. 2 Rao T C S & Murthy K S R, Magnetic surveys over the con- tinental shelf off Visakhapatnam, Mahasagar - Bull Nat Inst... Visakhapatnam, east coast of India, Indian J Earth Sci, 14(1987) 109-113. 8 Murthy K S R, Rao M M M, Rao T C S & Subrahmanyam A S, A comparative study of Werner deconvolution and con- ventional modelling of marine magnetic data, Geophy Res Bull, 25(1987) 152...

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

    Science.gov (United States)

    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.

  18. Recent Sedimentary Processes Along the Western Continental Margin of the South Korea Plateau, East Sea of Korea

    Science.gov (United States)

    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

  19. Intense biological phosphate uptake onto particles in subeuphotic continental margin waters

    Science.gov (United States)

    Sokoll, S.; Ferdelman, T. G.; Holtappels, M.; Goldhammer, T.; Littmann, S.; Iversen, M. H.; Kuypers, M. M. M.

    2017-03-01

    Elucidating the processes that affect particulate phosphorus (P) export from the euphotic zone and burial in sediments is important for models of global phosphorus, nitrogen, and carbon cycling. We investigated dissolved inorganic Pi incorporation into particles (>0.2 µm) in the subeuphotic zone and benthic boundary layer of high-productivity Mauritanian and Namibian shelf waters, using 33PO43- tracer experiments combined with a sequential chemical extraction analysis. Pi uptake (5.4 to 19.9 nmol P L-1 d-1) by particulate matter was biologically mediated ( 50% into the organic fraction) and similar to estimated rates of heterotrophic growth. Thus, a substantial fraction of Pi must be recycled through a particle-associated microbial pool. Rapid adsorption of 33P in the anoxic waters of Namibia indicated the additional existence of a large pool of surface exchangeable P. Particle-associated Pi recycling and adsorption may influence the export flux and ultimate fate of particle bound P in continental shelf waters.

  20. Authigenic carbonates in the sediments of Goa offshore basin, western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Kocherla, M.

    in all the studied locations. The methane con- centration varied from 0.45–5.25 nM (top) to 11.25 nM (middle) and 0.64–13.23 nM (bottom). The CaCO 3 content of the sediments ranged from 33.6% to 69.9% and TOC varied from 0.21% to 0.86%. The porosity.... G. and Almeida, F., Detection of gas charged sediments and gas hydrate horizons in high resolution seismic profiles from the western con- tinental margin of India. Spec. Publ. Geol. Soc. Lond., 1998, 137, 239–253. 15. Satyavani, N., Thankur, N. K...

  1. Multifractal detrended fluctuation analysis to compare coral bank and seafloor seepage area-related characterization along the central Western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Chakraborty, B.; VishnuVardhan, Y.; Haris, K.; Menezes, A.A.A.; Karisiddaiah, S.M.; Fernandes, W.A.; Kurian, J.

    exponent of a second-order moment. The two coral banks are located around the buried channels off Malpe, western continental margin of India (WCMI). The Gaveshani bank is lying on a submerged headland with high backscatter strength. The presence of greater...

  2. Structural features of the Southwest African continental margin according to results of lithosphere-scale 3D gravity and thermal modelling

    Science.gov (United States)

    Maystrenko, Yuriy P.; Scheck-Wenderoth, Magdalena; Hartwig, Alexander; Anka, Zahie; Watts, Antony B.; Hirsch, Katja K.; Fishwick, Stewart

    2013-09-01

    To understand the structure of the Southwest African continental margin, a lithosphere-scale 3D structural model has been developed, covering the marginal Cretaceous-Cenozoic Orange, Luderitz, Walvis and Namibe basins, the easternmost Walvis Ridge offshore. Onshore, the model includes two late-Proterozoic Owambo (Etosha) and Nama basins. This 3D model integrates published thickness maps (sediment isopach maps), shallow seismic and well data as well as published deep seismic information and has been additionally constrained by 3D gravity and thermal modelling. Using 3D gravity modelling, the first order configuration of the crystalline crust has been resolved with respect to the location of the continent-ocean boundary. The distribution of a high-density lower crustal layer indicates a continuous body extending below the Cretaceous-Cenozoic depocentres and aligned parallel to the coast line. In addition, high-density zones within the continental crystalline crust had to be included in the model to fit observed and calculated gravity. The obtained Moho topography correlates with the major tectonic units of this continental margin. The results of the 3D thermal modelling indicate that there is a clear relationship between the location of thickened sediments and areas with increased temperatures within the upper 10 km of the 3D model. This indicates that the low thermal conductivity of the sediments increases heat storage within the areas covered by thick sediments. Within the deeper crust, the main feature of the temperature distribution is the transition across the continental margin from the relatively cold oceanic part to the warm continental one. This regional pattern is controlled by the thickness of the crystalline continental crust, which is characterized by an increased radiogenic heat production. At a depth of 80-90 km, the temperature becomes higher beneath the oceanic domain than beneath the continent, reflecting the configuration of the lower thermal

  3. Modelling of Continental Lithosphere Breakup and Rifted Margin Formation in Response to an Upwelling Divergent Flow Field Incorporating a Temperature Dependent Rheology

    Science.gov (United States)

    Tymms, V. J.; Kusznir, N. J.

    2005-05-01

    We numerically model continental lithosphere deformation leading to breakup and sea floor spreading initiation in response to an imposed upwelling and divergent flow field applied to continental lithosphere and asthenosphere. The model is used to predict rifted continental margin lithosphere thinning and temperature structure. Model predictions are compared with observed rifted margin structure for four diverse case studies. Prior to application of the upwelling divergent flow field the continental lithosphere is undeformed with a uniform temperature gradient. The upwelling divergent flow field is defined kinematically using boundary conditions consisting of the upwelling velocity Vz at the divergence axis and the half divergence rate Vx . The resultant velocity field throughout the continuum is computed using finite element (FE) code incorporating a Newtonian temperature dependent rheology. The flow field is used to advect the continental lithosphere material and lithospheric and asthenospheric temperatures. Viscosity structure is hence modified and the velocities change correspondingly in a feedback loop. We find the kinematic boundary conditions Vz and Vx to be of first order importance. A high Vz/Vx (greater than10), corresponding to buoyancy assisted flow, leads to minimal mantle exhumation and a well defined continent ocean transition consistent with observations at volcanic margins. For Vz/Vx near unity, corresponding to plate boundary driven divergence, mantle exhumation over widths of up to 100 km is predicted which is consistent with observations at non-volcanic margins. The FE method allows the upwelling velocity Vz to be propagated upwards from the top of the asthenosphere to the Earth's surface without the requirement of imposing Vx. When continental breakup is achieved the half divergence velocity Vx can be applied at the lithosphere surface and the upwelling velocity Vz left free. We find this time and space dependent set of boundary conditions is

  4. Low temperature thermochronology and topographic evolution of the South Atlantic passive continental margin in the region in eastern Argentina

    Science.gov (United States)

    Pfister, Sabrina; Kollenz, Sebastian; Glasmacher, Ulrich A.

    2014-05-01

    To understand the evolution of the passive continental margin in Argentina low temperature thermochronology is an appropriate method, which will lead to new conclusions in this area. The Tandilia System, also called Sierras Septentrionales, is located south of the Río de la Plato Craton in eastern Argentina in the state of Buenos Aires. North of the hills Salado basin is located whereas the Claromecó basin is situated south of the mountain range. In contrary to most basins along the southamerican passive continental margin the Tandilia-System and the neighbouring basins trend perpendicular to the coast line. The topography is fairly flat with altitudes of. The igneous-metamorphic basement is pre-proterozoic in age and build up of mainly granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks and granitoid plutons it is overlain by a series of Neoproterozoic to early Paleozoic sediments (Cingolani, 2010), like siliciclastics, dolostones, shales and limestones (Demoulin et al., 2005). The aim of the study is to quantify the long-term landscape evolution of the passive continental margin in eastern Argentina in terms of thermal history, exhumation and tectonic activities. For that purpose, samples were taken from the Sierra Septentrionales and analyzed with the apatite fission-track method. Further 2-D thermokinematic modeling was conducted with the computer code HeFTy (Ketcham, 2005; Ketcham 2007; Ketcham et al., 2009). The results indicate apatite fission track ages between 101.6 (9.4) to 228.9 (22.3) Ma, what means all measured ages are younger as their formation age. That shows all samples have been reset. Six samples accomplished enough confined tracks and were used to test geological t-T models against the AFT data set. These models give a more detailed insight on the cooling history and tectonic activities in the research area. References: Cingolani C. A. (2010): The Tandilia System of Argentina as a southern extension of the Río de la

  5. The Pan-African continental margin in northeastern Africa: Evidence from a geochronological study of granulites at Sabaloka, Sudan

    International Nuclear Information System (INIS)

    Kroener, A.

    1987-01-01

    Ion microprobe zircon ages, a Nd model age and Rb-Sr whole-rock dates are reported from the high-grade gneiss terrain at Sabaloka on the River Nile north of Khartoum, formally considered to be part of the Archaean/early Proterozoic Nile craton. The granulites, which are of both sedimentary and igneous derivation, occur as remnants in migmatites. Detrital zircon ages range from ≅ 1000 to ≅ 2650 Ma and prove the existence of Archaean to late Proterozoic continental crust in the sedimentary source region. The Nd model age for one sedimentary granulite is between 1.26 (T CHUR ) and 1.70 (T DM ) Ga and provides a mean crustal residence age for the sedimentary precursor. Igneous zircons in enderbitic gneiss crystallized at 719±81 Ma ago, an age that also corresponds to severe Pb loss in the detrital zircons and whic probably reflects the granulite event at Sabaloka. The Rb-Sr data indicate isotropic homogenization at about 700 Ma ago in the granulites and severe post-granulite disturbance at ≅ 570 Ma in the migmatites. We associate this disturbance with hydration, retrograde metamorphism and anatexis that produced undeformed granites ≅ 540 Ma ago. The ≅ 700 Ma granulite event at Sabaloka suggests that this part of the Sudan belongs to the Pan-African Mozambique belt while the ancient Nile craton lay farther west. The gneisses studied here may represent the infrastructure of the ancient African continental margin onto which the juvenile arc assemblage of the Arabian-Nubian shield was accreted during intense horizontal shortening and crustal interstacking of a major collision event. (orig.)

  6. Reconstruction of an early Paleozoic continental margin based on the nature of protoliths in the Nome Complex, Seward Peninsula, Alaska

    Science.gov (United States)

    Till, Alison B.; Dumoulin, Julie A.; Ayuso, Robert A.; Aleinikoff, John N.; Amato, Jeffrey M.; Slack, John F.; Shanks, W.C. Pat

    2014-01-01

    The Nome Complex is a large metamorphic unit that sits along the southern boundary of the Arctic Alaska–Chukotka terrane, the largest of several micro continental fragments of uncertain origin located between the Siberian and Laurentian cratons. The Arctic Alaska–Chukotka terrane moved into its present position during the Mesozoic; its Mesozoic and older movements are central to reconstruction of Arctic tectonic history. Accurate representation of the Arctic Alaska–Chukotka terrane in reconstructions of Late Proterozoic and early Paleozoic paleogeography is hampered by the paucity of information available. Most of the Late Proterozoic to Paleozoic rocks in the Alaska–Chukotka terrane were penetratively deformed and recrystallized during the Mesozoic deformational events; primary features and relationships have been obliterated, and age control is sparse. We use a variety of geochemical, geochronologic, paleontologic, and geologic tools to read through penetrative deformation and reconstruct the protolith sequence of part of the Arctic Alaska–Chukotka terrane, the Nome Complex. We confirm that the protoliths of the Nome Complex were part of the same Late Proterozoic to Devonian continental margin as weakly deformed rocks in the southern and central part of the terrane, the Brooks Range. We show that the protoliths of the Nome Complex represent a carbonate platform (and related rocks) that underwent incipient rifting, probably during the Ordovician, and that the carbonate platform was overrun by an influx of siliciclastic detritus during the Devonian. During early phases of the transition to siliciclastic deposition, restricted basins formed that were the site of sedimentary exhalative base-metal sulfide deposition. Finally, we propose that most of the basement on which the largely Paleozoic sedimentary protolith was deposited was subducted during the Mesozoic.

  7. A comparison of geochemical exploration techniques and sample media within accretionary continental margins: an example from the Pacific Border Ranges, Southern Alaska, U.S.A.

    Science.gov (United States)

    Sutley, S.J.; Goldfarb, R.J.; O'Leary, R. M.; Tripp, R.B.

    1990-01-01

    The Pacific Border Ranges of the southern Alaskan Cordillera are composed of a number of allochthonous tectonostratigraphic terranes. Within these terranes are widespread volcanogenic, massive sulfide deposits in and adjacent to portions of accreted ophiolite complexes, bands and disseminations of chromite in accreted island-arc ultramafic rocks, and epigenetic, gold-bearing quartz veins in metamorphosed turbidite sequences. A geochemical pilot study was undertaken to determine the most efficient exploration strategy for locating these types of mineral deposits within the Pacific Border Ranges and other typical convergent continental margin environments. High-density sediment sampling was carried out in first- and second-order stream channels surrounding typical gold, chromite and massive sulfide occurrences. At each site, a stream-sediment and a panned-concentrate sample were collected. In the laboratory, the stream sediments were sieved into coarse-sand, fine- to medium-sand, and silt- to clay-size fractions prior to analysis. One split of the panned concentrates was retained for analysis; a second split was further concentrated by gravity separation in heavy liquids and then divided into magnetic, weakly magnetic and nonmagnetic fractions for analysis. A number of different techniques including atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and semi-quantitative emission spectrography were used to analyze the various sample media. Comparison of the various types of sample media shows that in this tectonic environment it is most efficient to include a silt- to clay-size sediment fraction and a panned-concentrate sample. Even with the relatively low detection limits for many elements by plasma spectrometry and atomic absorption spectrometry, anomalies reflecting the presence of gold veins could not be identified in any of the stream-sediment fractions. Unseparated panned-concentrate samples should be analyzed by emission

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

    Energy Technology Data Exchange (ETDEWEB)

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

    1999-12-01

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

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

    Science.gov (United States)

    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

  10. Barite-forming environments along a rifted continental margin, Southern California Borderland

    Science.gov (United States)

    Hein, James R.; Zierenberg, Robert A.; Maynard, J. Barry; Hannington, Mark D.

    2007-01-01

    The Southern California Continental Borderland (SCCB) is part of the broad San Andreas transform-fault plate boundary that consists of a series of fault-bounded, petroleum-generating basins. The SCCB has high heat flow and geothermal gradients produced by thinned continental crust and Neogene volcanism. Barite deposits in the SCCB occur along faults. Barite samples from two sea-cliff sites and four offshore sites in the SCCB were analyzed for mineralogy, chemical (54 elements) and isotopic (S, Sr) compositions, and petrography. Barite from Palos Verdes (PV) Peninsula sea-cliff outcrops is hosted by the Miocene Monterey Formation and underlying basalt; carbonate rocks from those outcrops were analyzed for C, O, and Sr isotopes and the basalt for S isotopes. Cold-seep barite from Monterey Bay, California was analyzed for comparison. SCCB offshore samples occur at water depths from about 500 to 1800 m. Those barites vary significantly in texture and occurrence, from friable, highly porous actively growing seafloor mounds to dense, brecciated, vein barite. This latter type of barite contrasts with cold-seep barite in being much more coarse grained, forms thick veins in places, and completely replaced rock clasts in breccia. The barite samples range from 94 to 99 wt% BaSO4, with low trace-element contents, except for high Sr, Zr, Br, U, and Hg concentrations compared to their crustal abundances. δ34S for SCCB offshore barites range from 21.6‰ to 67.4‰, and for PV barite from 62‰ to 70‰. Pyrite from PV sea-cliff basalt and sedimentary rocks that host the barites averages 7.8‰ and 2.2‰, respectively. Two offshore barite samples have δ34S values (21.6‰, 22.1‰) close to that of modern seawater sulfate, whereas all other samples are enriched to strongly enriched in 34S. 87Sr/86Sr ratios for the barites vary over a narrow range of 0.70830–0.70856 and are much lower than that of modern seawater and also lower than the middle Miocene seawater ratio, the time

  11. Crustal structure variations along the NW-African continental margin: a comparison of new and existing models from wide angle and reflection seismic data

    Science.gov (United States)

    Biari, Y.; Klingelhoefer, F.; Sahabi, M.; Aslanian, D.; Philippe, S.; Louden, K. E.; Berglar, K.; Moulin, M.; Mehdi, K.; Graindorge, D.; Evain, M.; Benabellouahed, M.; Reichert, C. J.

    2014-12-01

    Deep seismic data represent a key to understand the geometry and mechanism of continental rifting. The passive continental margin of NW-Africa is one of the oldest on earth, formed during the Upper Triassic-Lower Liassic rifting of the central Atlantic Ocean over 200 Ma. We present new and existing wide-angle and reflection seismic data from three study regions along the margin located in the North Moroccan salt basin, on the central continental margin offshore Safi and in the south, offshore Dakhla. In each of the study areas several combined wide-angle and reflection seismic profiles perpendicular and parallel to the margin have been acquired and forward modelled using comparable methods. The thickness of unthinned continental crust decreases from 36 km in the North to about 27 km in the South. In the North Moroccan Basin continental crust thins from originally 36 km to about 8 km in a 150 km wide zone. The basin itself is underlain by highly thinned continental crust. Offshore safi thinning of the continental crust is confined to a 130 km wide zone with no neighboring sedimentary basin underlain by continental crust. In both areas the zone of crustal thinning is characterised by the presence of large blocks and abundant salt diapirs. In the south crustal thinning is more rapid in a zone of 90 km and asymmetric with the upper crust thinning more closely to the continent than the lower crust, probably due to depth-dependent stretching and the presence of the precambrian Reguibat Ridge on land. Oceanic crust is characterised by a thickness of 7-8 km along the complete margin. Relatively high velocities of up to 7.5 km/s have been imaged between magnetic anomalies S1 and M25, and are probably related to changes in the spreading velocities at the time of the Kimmeridgian/Tithonian plate reorganisation. Volcanic activity seems to be confined to the region next to the Canary Islands, and is thus not related to the initial opening of the oceanic, which was related to no

  12. Tracing Late Holocene Warm Periods in the Galician Continental Margin (NW Spain): Detrital Control vs. Early Diagenetic Modulation.

    Science.gov (United States)

    Mohamed, K.; Rey, D.; Rubio, B.; Vilas, F.

    2007-12-01

    The sediments of the Galician continental margin (NW Spain) exhibit great but variable degrees of early diagenetic dissolution of magnetic minerals. This process completely erases any detrital magnetic signal at time-scales that range from about 1,000 years to less than 50 years in the highly productive estuarine-like environment of the Galician Rias Baixas. The more open marine conditions encountered in the adjoining continental shelf exhibit however a significantly different behavior. The singular balance between early diagenetic dissolution and lower sedimentation rates allows partial and variable preservation of the also variable detritally controlled magnetic inputs. In this context it is possible to reconstruct the recent environmental history of the area attending to the changes in the concentration of magnetically-interesting iron oxides. High-resolution magnetic and geochemical measurements carried out in 6 cores from the continental self evidenced the occurrence of correlatable peaks of magnetic mineral concentration that were interpreted as periods of enhanced detrital input. Magnetically depleted sediments were related to lower detrital input and/or to enhanced productivity that intensified the reductive conditions. The magnetic concentration peaks occurred within the Medieval (MWP) and Roman Warm Periods. Similar concentrations of hematite in the MWP and the RWP suggest that the lower concentration-dependent magnetic properties in the RWP are most likely caused by a greater degree of dissolution of magnetic detrital oxides due to a longer exposure to reducing conditions. These features could be traced over all the studied area, despite the great heterogeneity of the shelf sediments. This highlights the potential of magnetic properties as proxies of paleoenvironmental conditions in areas of similar complexity. This approach can be used as a rapid and cost-effective tool to screen large areas in the search for suitable settings for more precise, but time

  13. Benthic-pelagic coupling: effects on nematode communities along southern European continental margins.

    Directory of Open Access Journals (Sweden)

    Ellen Pape

    Full Text Available Along a west-to-east axis spanning the Galicia Bank region (Iberian margin and the Mediterranean basin, a reduction in surface primary productivity and in seafloor flux of particulate organic carbon was mirrored in the in situ organic matter quantity and quality within the underlying deep-sea sediments at different water depths (1200, 1900 and 3000 m. Nematode standing stock (abundance and biomass and genus and trophic composition were investigated to evaluate downward benthic-pelagic coupling. The longitudinal decline in seafloor particulate organic carbon flux was reflected by a reduction in benthic phytopigment concentrations and nematode standing stock. An exception was the station sampled at the Galicia Bank seamount, where despite the maximal particulate organic carbon flux estimate, we observed reduced pigment levels and nematode standing stock. The strong hydrodynamic forcing at this station was believed to be the main cause of the local decoupling between pelagic and benthic processes. Besides a longitudinal cline in nematode standing stock, we noticed a west-to-east gradient in nematode genus and feeding type composition (owing to an increasing importance of predatory/scavenging nematodes with longitude governed by potential proxies for food availability (percentage of nitrogen, organic carbon, and total organic matter. Within-station variability in generic composition was elevated in sediments with lower phytopigment concentrations. Standing stock appeared to be regulated by sedimentation rates and benthic environmental variables, whereas genus composition covaried only with benthic environmental variables. The coupling between deep-sea nematode assemblages and surface water processes evidenced in the present study suggests that it is likely that climate change will affect the composition and function of deep-sea nematodes.

  14. Passive acoustic records of two vigorous bubble-plume methane seeps on the Oregon continental margin

    Science.gov (United States)

    Dziak, R. P.; Matsumoto, H.; Merle, S. G.; Embley, R. W.; Baumberger, T.; Hammond, S. R.

    2016-12-01

    We present preliminary analysis of the acoustic records of two bubble-plume methane seeps recorded by an autonomous hydrophone deployed during the E/V Nautilus expedition (NA072) in June 2016. The goal of the NA072 expedition was to use the Simrad 302 as a survey tool to map bubble plumes at a regional scale along the Oregon and northern California margins, followed by in situ investigation of bubble-plume sites using the ROV Hercules. The exploration carried out during NA072 resulted in the discovery of hundreds of new individual methane seep sites in water depths ranging from 125 to 1725 m depth. A Greenridge Acousonde 3B™ hydrophone was deployed via ROV within two vigorous bubble-plume sites. Despite persistent ship and ROV propeller noise, the acoustic signature of the bubble-plume can be seen in the hydrophone record as a broadband (0.5 - 4.5 kHz) series of short duration ( 0.2-0.5 msec) pulses that occur in clusters of dozens of pulses lasting 2-3 secs. Previous studies of the passive acoustics of seep bubble-plumes indicate sound is generated during bubble formation, where detachment of the gas bubble from the end of a tube or conduit causes the bubble to oscillate, producing sound. The peak frequency f (the zeroth oscillatory mode) and the bubble equivalent spherical radius r for a given pressure P are: f = (2πr)-1 [(3γP/ρ)]1/2 where γ is the ratio of gas specific heat at constant pressure to constant volume and ρ is the water density (Leifer and Tang, 2006). Thus the frequency of a bubble's oscillation is proportional to the bubble's volume, and therefore it may be possible to use our acoustic data to obtain an estimate of the volume of methane being released at these seafloor plume sites.

  15. Fission track dating: methodology and thermo-chronological applications in alpine and continental margin contexts

    International Nuclear Information System (INIS)

    Sabil, N.

    1995-06-01

    the thermal history of the massifs considered since the last cooling below 120 C of the samples analysed. In the works done before 1994, we have shown that, on the one hand, the transform margin of Cote d'Ivoire-Ghana had known a heating period between 250 C and 60 C post-dating by far its scanning by an oceanic ridge and on the other hand, in the Elbe Island, we have brought the first 'fission track' data in the cooling history of the Monte Capanne granodiorite. In the beginning of the 90's, the fission track method still lacked good reference samples for volcanic glass dating. At the suggestion of the Geochronology Commission of the International Union of Geological Sciences we have studied macusanites, obsidians of the SE Peru. The results of this work suggest that these glasses are not convenient as potential age standards, even if they keep some value as a material for laboratory intercalibration purposes. (author)

  16. Origin of increased terrigenous supply to the NE South American continental margin during Heinrich Stadial 1 and the Younger Dryas

    Science.gov (United States)

    Zhang, Yancheng; Chiessi, Cristiano M.; Mulitza, Stefan; Zabel, Matthias; Trindade, Ricardo I. F.; Hollanda, Maria Helena B. M.; Dantas, Elton L.; Govin, Aline; Tiedemann, Ralf; Wefer, Gerold

    2015-12-01

    We investigate the redistribution of terrigenous materials in the northeastern (NE) South American continental margin during slowdown events of the Atlantic Meridional Overturning Circulation (AMOC). The compilation of stratigraphic data from 108 marine sediment cores collected across the western tropical Atlantic shows an extreme rise in sedimentation rates off the Parnaíba River mouth (about 2°S) during Heinrich Stadial 1 (HS1, 18-15 ka). Sediment core GeoB16206-1, raised offshore the Parnaíba River mouth, documents relatively constant 143Nd/144Nd values (expressed as εNd(0)) throughout the last 30 ka. Whereas the homogeneous εNd(0) data support the input of fluvial sediments by the Parnaíba River from the same source area directly onshore, the increases in Fe/Ca, Al/Si and Rb/Sr during HS1 indicate a marked intensification of fluvial erosion in the Parnaíba River drainage basin. In contrast, the εNd(0) values from sediment core GeoB16224-1 collected off French Guiana (about 7°N) suggest Amazon-sourced materials within the last 30 ka. We attribute the extremely high volume of terrigenous sediments deposited offshore the Parnaíba River mouth during HS1 to (i) an enhanced precipitation in the catchment region and (ii) a reduced North Brazil Current, which are both associated with a weakened AMOC.

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

    Science.gov (United States)

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

    2014-12-01

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

  18. Sensitivity analysis of a variability in rock thermal conductivity concerning implications on the thermal evolution of the Brazilian South Atlantic passive continental margin

    Science.gov (United States)

    Stippich, Christian; Krob, Florian; Glasmacher, Ulrich Anton; Hackspacher, Peter Christian

    2017-04-01

    The aim of the research is to quantify the long-term evolution of the western South Atlantic passive continental margin (SAPCM) in SE-Brazil. Excellent onshore outcrop conditions and extensive pre-rift to post-rift archives between São Paulo and Laguna allow a high precision quantification of exhumation, and rock uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. The research integrates published (Karl et al., 2013) and partly published thermochronological data from Brazil, and test lately published new concepts on causes of long-term landscape and lithospheric evolution in southern Brazil. Six distinct lithospheric blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos), which are separated by fracture zones (Karl et al., 2013) are characterized by individual thermochronological age spectra. Furthermore, the thermal evolution derived by numerical modeling indicates variable post-rift exhumation histories of these blocks. In this context, we will provide information on the causes for the complex exhumation history of the Florianópolis, and adjacent blocks. Following up on our latest publication (Braun et al., 2016) regarding the effect of variability in rock thermal conductivity on exhumation rate estimates we performed a sensitivity analysis to quantify the effect of a differentiated lithospheric crust on the thermal evolution of the Florianópolis block versus exhumation rates estimated from modelling a lithospheric uniform crustal block. The long-term landscape evolution models with process rates were computed with the software code PECUBE (Braun, 2003; Braun et al., 2012). Testing model solutions obtained for a multidimensional parameter space against the real thermochronological and geomorphological data set, the most likely combinations of parameters, values, and rates can be constrained. References Braun, J., 2003. Pecube: A new finite element code to solve the 3D heat transport

  19. The wide-angle seismic image of a complex rifted margin, offshore North Namibia: Implications for the tectonics of continental breakup

    Science.gov (United States)

    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.

  20. Resolving the fine-scale deformation structure of continental hyperextension at the deep Galicia rift margin using seismic full waveform inversion.

    Science.gov (United States)

    Davy, R. G.; Morgan, J. V.; Minshull, T. A.; Bull, J. M.; Bayrakci, G.

    2016-12-01

    Hyperextension of the continental crust during ultra-slow, magma-poor rifting is accommodated by a series of complex fault geometries, preceding continental breakup. At such margins there exists a discrepancy between the extension observed along these fault systems and the total observed thinning of the continental lithosphere, with several competing hypotheses on the responsible mechanism. Despite this, it is agreed that a significant amount of the observed discrepancy is the result of unaccounted sub-seismic fault structure. In order to seismically image these fine scale structures it is imperative to develop accurate and well resolved velocity models of the subsurface, for the purpose of migrating reflection seismic images. Velocity models with the required resolution are unattainable using classic travel time tomography. However, seismic full waveform inversion could provide a suitable alternative to produce the required velocity models, with the method having the ability to resolve velocity structure up to an order of magnitude greater than that of travel time tomography. In this study we apply acoustic full waveform inversion to a 2D wide-angle seismic data set, collected at the hyperextended domain of the deep Galicia rift margin. Despite the challenging environment and dataset, our results show promising increases in the resolution of existing velocity models, particularly in correlation to the normal faulting associated with highly deformed continental fault blocks in the distal hyperextended domain.

  1. Exploration of the Canyon-Incised Continental Margin of the Northeastern United States Reveals Dynamic Habitats and Diverse Communities.

    Directory of Open Access Journals (Sweden)

    Andrea M Quattrini

    Full Text Available The continental margin off the northeastern United States (NEUS contains numerous, topographically complex features that increase habitat heterogeneity across the region. However, the majority of these rugged features have never been surveyed, particularly using direct observations. During summer 2013, 31 Remotely-Operated Vehicle (ROV dives were conducted from 494 to 3271 m depth across a variety of seafloor features to document communities and to infer geological processes that produced such features. The ROV surveyed six broad-scale habitat features, consisting of shelf-breaching canyons, slope-sourced canyons, inter-canyon areas, open-slope/landslide-scar areas, hydrocarbon seeps, and Mytilus Seamount. Four previously unknown chemosynthetic communities dominated by Bathymodiolus mussels were documented. Seafloor methane hydrate was observed at two seep sites. Multivariate analyses indicated that depth and broad-scale habitat significantly influenced megafaunal coral (58 taxa, demersal fish (69 taxa, and decapod crustacean (34 taxa assemblages. Species richness of fishes and crustaceans significantly declined with depth, while there was no relationship between coral richness and depth. Turnover in assemblage structure occurred on the middle to lower slope at the approximate boundaries of water masses found previously in the region. Coral species richness was also an important variable explaining variation in fish and crustacean assemblages. Coral diversity may serve as an indicator of habitat suitability and variation in available niche diversity for these taxonomic groups. Our surveys added 24 putative coral species and three fishes to the known regional fauna, including the black coral Telopathes magna, the octocoral Metallogorgia melanotrichos and the fishes Gaidropsarus argentatus, Guttigadus latifrons, and Lepidion guentheri. Marine litter was observed on 81% of the dives, with at least 12 coral colonies entangled in debris. While

  2. Syn-collisional felsic magmatism and continental crust growth: A case study from the North Qilian Orogenic Belt at the northern margin of the Tibetan Plateau

    Science.gov (United States)

    Chen, Shuo; Niu, Yaoling; Xue, Qiqi

    2018-05-01

    The abundant syn-collisional granitoids produced and preserved at the northern Tibetan Plateau margin provide a prime case for studying the felsic magmatism as well as continental crust growth in response to continental collision. Here we present the results from a systematic study of the syn-collisional granitoids and their mafic magmatic enclaves (MMEs) in the Laohushan (LHS) and Machangshan (MCS) plutons from the North Qilian Orogenic Belt (NQOB). Two types of MMEs from the LHS pluton exhibit identical crystallization age ( 430 Ma) and bulk-rock isotopic compositions to their host granitoids, indicating their genetic link. The phase equilibrium constraints and pressure estimates for amphiboles from the LHS pluton together with the whole rock data suggest that the two types of MMEs represent two evolution products of the same hydrous andesitic magmas. In combination with the data on NQOB syn-collisional granitoids elsewhere, we suggest that the syn-collisional granitoids in the NQOB are material evidence of melting of ocean crust and sediment. The remarkable compositional similarity between the LHS granitoids and the model bulk continental crust in terms of major elements, trace elements, and some key element ratios indicates that the syn-collisional magmatism in the NQOB contributes to net continental crust growth, and that the way of continental crust growth in the Phanerozoic through syn-collisional felsic magmatism (production and preservation) is a straightforward process without the need of petrologically and physically complex processes.

  3. Ophiolitic basement to the Great Valley forearc basin, California, from seismic and gravity data: Implications for crustal growth at the North American continental margin

    Science.gov (United States)

    Godfrey, N.J.; Beaudoin, B.C.; Klemperer, S.L.; Levander, A.; Luetgert, J.; Meltzer, A.; Mooney, W.; Tréhu, A.

    1997-01-01

    The nature of the Great Valley basement, whether oceanic or continental, has long been a source of controversy. A velocity model (derived from a 200-km-long east-west reflection-refraction profile collected south of the Mendocino triple junction, northern California, in 1993), further constrained by density and magnetic models, reveals an ophiolite underlying the Great Valley (Great Valley ophiolite), which in turn is underlain by a westward extension of lower-density continental crust (Sierran affinity material). We used an integrated modeling philosophy, first modeling the seismic-refraction data to obtain a final velocity model, and then modeling the long-wavelength features of the gravity data to obtain a final density model that is constrained in the upper crust by our velocity model. The crustal section of Great Valley ophiolite is 7-8 km thick, and the Great Valley ophiolite relict oceanic Moho is at 11-16 km depth. The Great Valley ophiolite does not extend west beneath the Coast Ranges, but only as far as the western margin of the Great Valley, where the 5-7-km-thick Great Valley ophiolite mantle section dips west into the present-day mantle. There are 16-18 km of lower-density Sierran affinity material beneath the Great Valley ophiolite mantle section, such that a second, deeper, "present-day" continental Moho is at about 34 km depth. At mid-crustal depths, the boundary between the eastern extent of the Great Valley ophiolite and the western extent of Sierran affinity material is a near-vertical velocity and density discontinuity about 80 km east of the western margin of the Great Valley. Our model has important implications for crustal growth at the North American continental margin. We suggest that a thick ophiolite sequence was obducted onto continental material, probably during the Jurassic Nevadan orogeny, so that the Great Valley basement is oceanic crust above oceanic mantle vertically stacked above continental crust and continental mantle.

  4. Evidence of a Neoproterozoic active continental margin - Geochemistry and isotope geology of high-grade paragneiss from the Ribeira Orogen, SE Brazil

    Science.gov (United States)

    Capistrano, G. G.; Schmitt, R. S.; Medeiros, S. R.; Fernandes, G. L. F.

    2017-08-01

    Ediacaran paragneisses from the Palmital Unit are located in a key region, between two major tectonic domains of the Ribeira Orogen (in Rio de Janeiro, SE Brazil): the Cabo Frio Tectonic Domain and the Oriental Terrane. We present here petrographic, geochemical and isotopic data in order to partially unravel the origin and tectonic nature of the protoliths from these metamorphic rocks. Litharenites interpreted as immature sediments, mostly derived from the erosion of felsic rocks (granites/rhyolites and diorites/andesites) are here described. Multi-elements patterns and trace elements ratios reinforce an upper continental crust nature for the composition of the protoliths. These were probably located close to the source area and accommodated in semi-arid climate and high topography conditions. Tectonic discrimination diagrams indicate that the Palmital basin developed in an active continental margin, corroborated by the zircon detrital spectra. The main population of detrital zircon (ca. 750-550 Ma) is partially coeval with the age of the Rio Negro continental magmatic arc, resident in the Oriental Terrane. The Palmital basin could represent a forearc environment with no oceanic crust material, but only a continuous sedimentation of turbidites derived from the arc, with gradational bedding signifying a subaqueous environment, without outside tectonic disturbances. On the other hand, TDM ages of 1.6-1.8 Ga suggest that these sediments are not juvenile, indicating also a contribution from an ancient crust. This recycled continental crust could come either from the basement of the Oriental Terrane (which was not identified yet) or from the basement of the Cabo Frio Tectonic Domain. In the last assumption the Palmital deposition would be concomitant with the initiation of continental collision and the subduction of the passive margin of the Cabo Frio Tectonic Domain towards west. This unit was subsequently metamorphosed/deformed during the ca. 540 Ma collision between

  5. Distribution and composition of verdine and glaucony facies from the sediments of the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.

    on the outer shelf. The distribution of verdine and glaucony facies on the southwestern margin of India is different from those of the distribution along the east coast of India, Senegal, and French Guiana margins, suggesting different paleogeography...

  6. IODP workshop: developing scientific drilling proposals for the Argentina Passive Volcanic Continental Margin (APVCM) - basin evolution, deep biosphere, hydrates, sediment dynamics and ocean evolution

    Science.gov (United States)

    Flood, Roger D.; Violante, Roberto A.; Gorgas, Thomas; Schwarz, Ernesto; Grützner, Jens; Uenzelmann-Neben, Gabriele; Hernández-Molina, F. Javier; Biddle, Jennifer; St-Onge, Guillaume; Workshop Participants, Apvcm

    2017-05-01

    The Argentine margin contains important sedimentological, paleontological and chemical records of regional and local tectonic evolution, sea level, climate evolution and ocean circulation since the opening of the South Atlantic in the Late Jurassic-Early Cretaceous as well as the present-day results of post-depositional chemical and biological alteration. Despite its important location, which underlies the exchange of southern- and northern-sourced water masses, the Argentine margin has not been investigated in detail using scientific drilling techniques, perhaps because the margin has the reputation of being erosional. However, a number of papers published since 2009 have reported new high-resolution and/or multichannel seismic surveys, often combined with multi-beam bathymetric data, which show the common occurrence of layered sediments and prominent sediment drifts on the Argentine and adjacent Uruguayan margins. There has also been significant progress in studying the climatic records in surficial and near-surface sediments recovered in sediment cores from the Argentine margin. Encouraged by these recent results, our 3.5-day IODP (International Ocean Discovery Program) workshop in Buenos Aires (8-11 September 2015) focused on opportunities for scientific drilling on the Atlantic margin of Argentina, which lies beneath a key portion of the global ocean conveyor belt of thermohaline circulation. Significant opportunities exist to study the tectonic evolution, paleoceanography and stratigraphy, sedimentology, and biosphere and geochemistry of this margin.

  7. 16 Years, 16 Cruises, 1.6 Billion Soundings: a Compilation of High-Resolution Multibeam Bathymetry of the Active Plate Boundary Along the Chilean Continental Margin

    Science.gov (United States)

    Weinrebe, W.; Flueh, E. R.; Hasert, M.; Behrmann, J. H.; Voelker, D.; Geersen, J.; Ranero, C. R.; Diaz-Naveas, J. L.

    2011-12-01

    Chile, a country stranding the active plate boundary between the South-American and the Nazca Plate is afflicted by recurrent earthquakes and hazardous volcanic eruptions. The strongest earthquake ever recorded occurred here, and volcanic hazards are frequent. Consequently, this area has been studied by geoscientists for many years to improve the understanding of subduction zone processes. Swath bathymetry mapping of the ocean floor has proven to bear a large potential for the interpretation of subduction-related processes, such as tectonic deformation of the marine forearc, release and migration of fluids as well as earthquake-triggered mass wasting. Multibeam bathymetry data of 16 major cruises of German, British, and Chilean research vessels recorded between 1995 and December 2010, in total more than 10,000 data files comprising about 1.6 billion soundings, have now been carefully reprocessed, compiled and merged into a unifying set of high-resolution bathymetric maps of the Chilean continental margin from latitude 40°S to 20°S. The imprint of subsurface processes on the surface morphology is well displayed in the case of the Chilean continental margin. The 3,500 km long Chilean convergent margin is not uniform, as various segments with different tectonic characteristics can be distinguished. Major factors that control margin morphology and thus the style of subduction are (1) relief and structure of the incoming oceanic plate, (2) supply of trench sediment, (3) turbidite transport within the trench, and (4) the input of terrigeneous sediments down the continental slope. A major segment boundary occurs at latitude 32°-33° S where the hotspot-related volcanic chain of Juan Fernandez is presently subducting. South of the area of ridge subduction the trench is filled with turbidites, and accretionary ridges develop across the base of the slope along most of the segment, whereas north of this boundary the turbiditic infill is reduced and subduction erosion is

  8. Classification of sea-floor features associated with methane seeps along the Gulf of Cádiz continental margin

    Science.gov (United States)

    León, Ricardo; Somoza, Luis; Medialdea, Teresa; Maestro, Adolfo; Díaz-del-Río, Victor; Fernández-Puga, María del Carmen

    2006-06-01

    Based on recently gathered swath-bathymetry, high- to ultra-high-resolution seismic, and underwater camera data, along with dredging and coring samples, this paper examines the relationship between sea-floor features and the nature of hydrocarbon-enriched fluid and gas leaks from degassing of deeply buried sediments along the continental margin of the Gulf of Cádiz (eastern Central Atlantic). A classification into three main groups is proposed on the basis of the morphology and nature of deposits: (1) mud volcanoes, (2) methane-derived authigenic carbonates (MDAC) mounds, and (3) crater-like pockmarks. Mud volcanoes are, topographically, cone-shaped sea-floor edifices, built up from catastrophic mud and fluid degassing, intercalated with periods of inactivity. So far more than 25 mud volcanoes have been discovered in the Gulf of Cádiz, named in memory of deceased colleagues (e.g., Ginsburg and Baraza), or researchers' birth places (e.g. Faro, Cibeles, Almazán, San Petersburgh, Yuma, Rabat, Bonjardim, Coruña, Gades). These structures range from 800 to 2500 m in diameter and tower 150-300 m above the seabed. The volcanoes consistently feature a well-defined outer ring or circular terrace and an inner dome. All mud volcanoes are built up of episodes of mud-breccia flows, intercalated with deep-current deposits, with evident indications of gas saturation: degassing structures, a strong H 2S smell, and chemosynthetic fauna (such as Pogonophora sp. tube worms and Calyptogena sp.). Commonly observed carbonate crusts and slabs overlying some mud volcanoes are thought to have been formed by slow, diffuse venting during periods of inactivity or slower rates of fluid venting following the ejection of mud. A "fermentation" process, the result of microbial-mediated oxidation of hydrocarbon-enriched fluids, seems to play an important role in the growth of large deep-water carbonate mounds and chimneys during periods of low methane-seep fluid pressure. More than 400 crater

  9. Structure and function of nematode communities across the Indian western continental margin and its oxygen minimum zone

    Science.gov (United States)

    Singh, R.; Ingole, B. S.

    2016-01-01

    We studied patterns of nematode distribution along the western Indian continental margin to determine the influence of habitat heterogeneity and low oxygen levels on the community's taxonomic and functional structure. A single transect, perpendicular to the coast at 14° N latitude was sampled from 34 to 2546 m depth for biological and environmental variables during August 2007. The oxygen minimum zone extended from 102 to 1001 m. Nematodes (described and undescribed) were identified to species and classified according to biological and functional traits. A total of 110 nematode species belonging to 24 families were found along the transect. Three depth zones were identified: the shelf (depth range: 34-102 m; highest nematode mean density: 176.6 ± 37 ind 10 cm-2), the slope (525-1524 m; 124.3 ± 16 ind 10 cm-2), and the basin (2001-2546 m; 62.9 ± 2 ind 10 cm-2). Across the entire study area, the dominant species were Terschellingia longicaudata, Desmodora sp. 1, Sphaerolaimus gracilis, and Theristus ensifer; their maximum density was at shelf stations. Nematode communities in different zones differed in species composition. Chromadorita sp. 2 (2.78 %) and Sphaerolaimus gracilis (2.21 %) were dominant on the shelf, whereas Terschellingia longicaudata (4.73 %) and Desmodora sp. 1 (4.42 %) were dominant on the slope, but in the basin, Halalaimus sp. 1(1.11 %) and Acantholaimus elegans (1.11 %) were dominant. The information in a particular functional group was not a simple reflection of the information in species abundance. Ecological information captured by adult length, adult shape, and life-history strategy was less site-specific and thus differed notably from information contained in other taxonomic groups. The functional composition of nematodes was strongly linked to the organic-carbon and dissolved-oxygen concentration. Seven species were found exclusively in the oxygen minimum zone: Pselionema sp. 1, Choanolaimus sp. 2, Halichoanolaimus sp. 1, Cobbia dentata

  10. Uplift history of a transform continental margin revealed by the stratigraphic record: The case of the Agulhas transform margin along the Southern African Plateau

    Science.gov (United States)

    Baby, Guillaume; Guillocheau, François; Boulogne, Carl; Robin, Cécile; Dall'Asta, Massimo

    2018-04-01

    The south and southeast coast of southern Africa (from 28°S to 33°S) forms a high-elevated transform passive margin bounded to the east by the Agulhas-Falkland Fracture Zone (AFFZ). We analysed the stratigraphic record of the Outeniqua and Durban (Thekwini) Basins, located on the African side of the AFFZ, to determine the evolution of these margins from the rifting stage to present-day. The goal was to reconstruct the strike-slip evolution of the Agulhas Margin and the uplift of the inland high-elevation South African Plateau. The Agulhas transform passive margin results from four successive stages: Rifting stage, from Late Triassic to Early Cretaceous ( 200?-134 Ma), punctuated by three successive rifting episodes related to the Gondwana breakup; Wrench stage (134-131 Ma), evidenced by strike- and dip-slip deformations increasing toward the AFFZ; Active transform margin stage (131-92 Ma), during which the Falkland/Malvinas Plateau drifts away along the AFFZ, with an uplift of the northeastern part of the Outeniqua Basin progressively migrating toward the west; Thermal subsidence stage (92-0 Ma), marked by a major change in the configuration of the margin (onset of the shelf-break passive margin morphology). Two main periods of uplift were documented during the thermal subsidence stage of the Agulhas Margin: (1) a 92 Ma short-lived margin-scale uplift, followed by a second one at 76 Ma located along the Outeniqua Basin and; (2) a long-lasting uplift from 40 to 15 Ma limited to the Durban (Thekwini) Basin. This suggests that the South African Plateau is an old Upper Cretaceous relief (90-70 Ma) reactivated during Late Eocene to Early Miocene times (40-15 Ma).

  11. Pre-existing oblique transfer zones and transfer/transform relationships in continental margins: New insights from the southeastern Gulf of Aden, Socotra Island, Yemen

    Science.gov (United States)

    Bellahsen, N.; Leroy, S.; Autin, J.; Razin, P.; d'Acremont, E.; Sloan, H.; Pik, R.; Ahmed, A.; Khanbari, K.

    2013-11-01

    Transfer zones are ubiquitous features in continental rifts and margins, as are transform faults in oceanic lithosphere. Here, we present a structural study of the Hadibo Transfer Zone (HTZ), located in Socotra Island (Yemen) in the southeastern Gulf of Aden. There, we interpret this continental transfer fault zone to represent a reactivated pre-existing structure. Its trend is oblique to the direction of divergence and it has been active from the early up to the latest stages of rifting. One of the main oceanic fracture zones (FZ), the Hadibo-Sharbithat FZ, is aligned with and appears to be an extension of the HTZ and is probably genetically linked to it. Comparing this setting with observations from other Afro-Arabian rifts as well as with passive margins worldwide, it appears that many continental transfer zones are reactivated pre-existing structures, oblique to divergence. We therefore establish a classification system for oceanic FZ based upon their relationship with syn-rift structures. Type 1 FZ form at syn-rift structures and are late syn-rift to early syn-OCT. Type 2 FZ form during the OCT formation and Type 3 FZ form within the oceanic domain, after the oceanic spreading onset. The latter are controlled by far-field forces, magmatic processes, spreading rates, and oceanic crust rheology.

  12. Decadal fCO2 trends in global ocean margins and adjacent boundary current-influenced areas

    Science.gov (United States)

    Wang, Hongjie; Hu, Xinping; Cai, Wei-Jun; Sterba-Boatwright, Blair

    2017-09-01

    Determination of the rate of change of sea surface CO2 fugacity (fCO2) is important, as the fCO2 gradient between the atmosphere and the ocean determines the direction of CO2 flux and hence the fate of this greenhouse gas. Using a newly available, community-based global CO2 database (Surface Ocean CO2 Atlas Version 3 coastal data set) and a newly developed statistical method, we report that the global ocean margins (within 400 km offshore, 30°S-70°N) fCO2 temporal trends on decadal time scales (1.93 ± 1.59 μatm yr-1) closely follow the atmospheric fCO2 increase rate (1.90 ± 0.06 μatm yr-1) in the Northern Hemisphere but are lower (1.35 ± 0.55 μatm yr-1) in the Southern Hemisphere, reflecting dominant atmospheric forcing in conjunction with different warming rates in the two hemispheres. In addition to the atmospheric fCO2 forcing, a direct warming effect contributes more to fCO2 increase in the western boundary current-influenced areas, while intensified upwelling contributes more to fCO2 increase in eastern boundary current-influenced areas.

  13. Mineralogy and Origin of Sediments From Drill Holes on the Continental Margin Off Florida, 1965-1969 (NODC Accession 7100714)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Drill cores obtained during the Joint Oceanographic Institutions' Deep Earth Sampling Program from the continental shelf, the Florida-Hatteras Slope, and the Blake...

  14. EX1205L2: Northeast Canyons and Continental Margins Exploration on NOAA Ship Okeanos Explorer between 20120728 and 20120803

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — EX1205 Leg 2 is the final cruise of the 2012 season for Okeanos Explorer (EX). It will be primarily focused on supplementing Northeast canyon and continental shelf...

  15. EX1204: Northeastern Canyons and Continental Margins Exploration on NOAA Ship Okeanos Explorer between 20120529 and 20120613

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — During the Okeanos Explorer (EX) mission EX1204, the vessel will sail from Norfolk, VA, along the continental shelf break of the U.S. East Coast from Virginia to...

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

    Science.gov (United States)

    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

  17. Past sea level changes along the western continental margins of India: Evidences from morphology of the sea bed

    Digital Repository Service at National Institute of Oceanography (India)

    Vora, K.H.

    , foraminifers, etc. and certain geomorphological features such as submarine terraces, reefs, notches, raised marine deposits, beach rocks and buried channels, etc. Glacio-eustatic sea-level fluctuations, along with relief, lithology, sedimentation..., tectonic movements etc., have governed depositional and erosional patterns and thereby, topography of the continental shelf. The continental shelves world over are marked by the presence of a variety of geomorphological features that are the net...

  18. The influence of tectonic and volcanic processes on the morphology of the Iberian continental margins; Influencia de los procesos tectonicos y volcanicos en la morfologia de los margenes continentales ibericos

    Energy Technology Data Exchange (ETDEWEB)

    Maestro, A.; Bohoyo, F.; Lopez-Martinez, J.; Acosta, J.; Gomez-Ballesteros, M.; Llaave, E.; Munoz, A.; Terrinha, P. G.; Dominguez, M.; Fernandez-Saez, F.

    2015-07-01

    The Iberian continental margins are mainly passive margins. Nevertheless, the northern sector of the margin was active during some stages of its geological evolution. The southern sector is considered as a transformed margin, which defines the boundary between the Iberian and African plates. This margin was also an active margin in the past. The different types, origins and intensities of the endogenic processes that have affected he Iberian continental margins have led to the development of various tectonic and volcanic morphologies. The North Atlantic rifting allowed the development of large marginal platforms in the Cantabrian and Galician margins the North-Atlantic Ocean spreading. The reactivation of Variscan faults during the Mesozoic and Cenozoic controlled the strike of some of the largest canyons in the Iberian margins. The Gulf of Cadiz margin is characterized by the development of morphologies related to salt tectonic, fluid seepage, thrust fronts and strike-slip fault lineaments hundreds of kilometres long. The Alboran basin and the Betic margin show morphologies connected with the Miocene rift phase, which generated volcanic edifices and various structural reliefs, and with the subsequent compressive phase, when folds and strike-slip, reverse faults, diapirs and mud volcanoes were developed. Finally, the Catalan-Valencian margin and the Balearic promontory are characterized by the presence of horst and graben structures related to the development of the Valencia trough during the Paleogene. The morphological features of endogenic origin have largely controlled the location and extent of the sedimentary processes and morphological products along the Iberian margins. (Author)

  19. Mesozoic architecture of a tract of the European-Iberian continental margin: Insights from preserved submarine palaeotopography in the Longobucco Basin (Calabria, Southern Italy)

    Science.gov (United States)

    Santantonio, Massimo; Fabbi, Simone; Aldega, Luca

    2016-01-01

    The sedimentary successions exposed in northeast Calabria document the Jurassic-Early Cretaceous tectonic-sedimentary evolution of a former segment of the European-Iberian continental margin. They are juxtaposed today to units representing the deformation of the African and Adriatic plates margins as a product of Apenninic crustal shortening. A complex pattern of unconformities reveals a multi-stage tectonic evolution during the Early Jurassic, which affected the facies and geometries of siliciclastic and carbonate successions deposited in syn- and post-rift environments ranging from fluvial to deep marine. Late Sinemurian/Early Pliensbachian normal faulting resulted in exposure of the Hercynian basement at the sea-floor, which was onlapped by marine basin-fill units. Shallow-water carbonate aprons and reefs developed in response to the production of new accommodation space, fringing the newborn islands which represent structural highs made of Paleozoic crystalline and metamorphic rock. Their drowning and fragmentation in the Toarcian led to the development of thin caps of Rosso Ammonitico facies. Coeval to these deposits, a thick (> 1 km) hemipelagic/siliciclastic succession was sedimented in neighboring hanging wall basins, which would ultimately merge with the structural high successions. Footwall blocks of the Early Jurassic rift, made of Paleozoic basement and basin-margin border faults with their onlapping basin-fill formations, are found today at the hanging wall of Miocene thrusts, overlying younger (Middle/Late Jurassic to Late Paleogene) folded basinal sediments. This paper makes use of selected case examples to describe the richly diverse set of features, ranging from paleontology to sedimentology, to structural geology, which are associated with the field identification of basin-margin unconformities. Our data provide key constraints for restoring the pre-orogenic architecture of a continental margin facing a branch of the Liguria-Piedmont ocean in the

  20. The Thermal Evolution of the Southeast Baffin Island Continental Margin: An Integrated Apatite Fission Track and Apatite (U-Th)/He Study

    Science.gov (United States)

    Jess, S.; Stephenson, R.; Brown, R. W.

    2017-12-01

    The elevated continental margins of the North Atlantic continue to be a focus of considerable geological and geomorphological debate, as the timing of major tectonic events and the age of topographic relief remain controversial. The West Greenland margin, on the eastern flank of Baffin Bay, is believed by some authors to have experienced tectonic rejuvenation and uplift during the Neogene. However, the opposing flank, Baffin Island, is considered to have experienced a protracted erosional regime with little tectonic activity since the Cretaceous. This work examines the thermal evolution of the Cumberland Peninsula, SE Baffin Island, using published apatite fission track (AFT) data with the addition of 103 apatite (U-Th)/He (AHe) ages. This expansion of available thermochronological data introduces a higher resolution of thermal modelling, whilst the application of the newly developed `Broken Crystals' technique provides a greater number of thermal constraints for an area dominated by AHe age dispersion. Results of joint thermal modelling of the AFT and AHe data exhibit two significant periods of cooling across the Cumberland Peninsula: Devonian/Carboniferous to the Triassic and Late Cretaceous to present. The earliest phase of cooling is interpreted as the result of major fluvial systems present throughout the Paleozoic that flowed across the Canadian Shield to basins in the north and south. The later stage of cooling is believed to result from rift controlled fluvial systems that flowed into Baffin Bay during the Mesozoic and Cenozoic during the early stages and culmination of rifting along the Labrador-Baffin margins. Glaciation in the Late Cenozoic has likely overprinted these later river systems creating a complex fjordal distribution that has shaped the modern elevated topography. This work demonstrates how surface processes, and not tectonism, can explain the formation of elevated continental margins and that recent methodological developments in the field of

  1. {sup 137}Cs as tracer of the origin of allochthonous sediments in the Southeast Continental Margin of Brazil; {sup 137}Cs como tracador da origem de sedimentos aloctones na Margem Continental Sudeste do Brasil

    Energy Technology Data Exchange (ETDEWEB)

    Ferreira, Paulo A.L.; Mahiques, Michel M.; FIgueira, Rubens C.L., E-mail: paulo.alves.ferreira@usp.br, E-mail: mahiques@usp.br, E-mail: rfigueira@usp.br [Universidade de Sao Paulo (IO/USP), SP (Brazil). Instituto Oceanografico; Franca, Elvis J., E-mail: ejfranca@cnen.gov.br [Centro Regional de Ciencias Nucleares do Nordeste (CRCN-NE/CNEN-PE), Recife, PE (Brazil)

    2015-07-01

    The distribution of {sup 137}Cs, artificial radionuclide for which there is no current source, can inform on the origin and destination of sediments. This study analyzed about 60 samples of surface sediment to generate a model of spatial distribution of {sup 137}Cs in the Southeast Continental Margin of Brazil and surroundings for evaluating possible sediment sources for this region. The model showed that the levels of {sup 137}Cs in the southern compartment of the Southeast Brazilian Margin (south of Sao Sebastiao Island) are statistically similar to those of the Rio de la Plata river mouth region, indicating sediment entry due to the seasonal intrusion of the plume of Rio de la Plata, a phenomenon already studied by other authors.

  2. A facies distribution model controlled by a tectonically inherited sea bottom topography in the carbonate rimmed shelf of the Upper Tithonian-Valanginian Southern Tethyan continental margin (NW Sicily, Italy)

    Science.gov (United States)

    Basilone, Luca; Sulli, Attilio

    2016-08-01

    The Upper Tithonian-Valanginian shallow-water carbonates outcropping in the Palermo Mts (NW Sicily) consist of several facies associations reflecting different depositional environments of a carbonate rimmed shelf, pertaining to the Southern Tethyan continental margin. The reconstructed depositional model, based on the sedimentological features, cyclic facies arrangement and biota distribution, shows that a wide protected lagoon, dominated by algae, molluscs and scattered patch reefs, was bordered landward by a tidal flat, where stromatolitic algal mats were cyclically subaerial exposed, and seaward by a marine sand belt and reef complex. Oolitic packstone-grainstone lithofacies, cyclically subjected to subaerial exposure, suggests the occurrence of a barrier island, located nearly to the lagoonal carbonate shoreline, allowing the development of narrow embayments with restricted circulation. In the outer platform, the oolitic lithofacies of the marine sand belt pass landward into the protected lagoon, where washover oolite sands occur, and seaward into a high-energy zone (back-reef apron) gradually merging in the reef complex. In the latter, coral framestone occupied the inner sector (reef flat), while the facies association dominated by boundstone with Ellipsactinia sp. developed in the outer sectors (reef wall), adjacent to the fore-reef and upper slope environments. Stratigraphic evidence, associated with the recognized facies associations, helped to reconstruct the geo-tectonic setting of the carbonate platform, where the distribution of the depositional facies along the shelf and their extension were influenced by the tectonically-inherited sea bottom topography. In a regime of extensional tectonics, localized and thin succession of high-energy prograding oolite sand belt depositional facies occupied structural highs (footwall uplift), while the largely diffused and thick low energy aggrading peritidal-to-lagoonal depositional facies developed in subsiding

  3. Long-term subsidence, cooling, and exhumation history along the South Atlantic passive continental margin in NW-Namibia

    Science.gov (United States)

    Menges, Daniel; Glasmacher, Ulrich Anton; Salomon, Eric; Hackspacher, Peter Christian; Schneider, Gabi

    2017-04-01

    In northwestern Namibia the Kaoko Belt is one of the most important Precambrian crustal segments that have stored the subsidence, cooling, and exhumation history of Namibia since the Neoproterozoic. ZFT-ages, with ages between 292.7 (46.0) and 436.8 (45.9) Ma, are giving new insights on this early evolution. Paleozoic to Mesozoic sedimentary rocks of the Karoo Supergroup and the Lower Cretaceous volcanic rocks of the Etendeka sequence overlay the Proterozoic metamorphic and intrusive rocks (1). New apatite fission-track (AFT) ages range from 390.9 (17.9) Ma to 80.8 (6.0) Ma. Along the coast apatites of Proterozoic rock samples reveal the youngest ages. Further inland the ages increase significantly. In addition, rapid change of AFT-ages occurs on both sides of major thrust and shear zones. Using the oldest thermochronological data the revealed t-T paths indicate a long era of exhumation, starting at the end of the Pan-African Orogeny in the Neoproterozoic and continuing into the Permo-Carboniferous. The subsequent sedimentation of the Karoo Supergroup initiates a new era of subsidence until the end of Triassic (2).The subsequent period of denudation ends abruptly with the rapid deposition of the Etendeka basalts in the Early Cretaceous (3). The maximum thickness of the Etendeka volcanic suite has been estimated, using the apatite fission-track data, to about 3.2 (1.2) km. With the ongoing opening of the South Atlantic and the formation of the continental margin the Kaoko Belt went through a rapid cooling event starting 130 Ma and ending 80 Ma, at a mean rate of 0.034 km/Ma for the western, and 0.018 km/Ma for the northern and eastern Kaoko Belt. This cooling event was accompanied by a reactivation of major fault zones, like the Purros Mylonite Zone (4). Thereafter, stable conditions were established, with denudation rates generally lower than 0.010 km/Ma, until the Neogene, where a second cooling event led to increased exhumation rates around 0.042 km/Ma. The total

  4. Acoustic wipeouts over the continental margins off Krishna, Godavari and Mahanadi river basins, East coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.; Rao, T.C.S.

    wipeouts. Behrens (1988) reported occurrence of gas/oil seepages beneath such ridges associated with underlying salt diapir ofT Gulf of Mexico. Acoustic wipeouts in the sub-surface layers due to a faulted continental slope are also observed of... the figures. References BEHRESS, E. W., (1988) Geology of a continental slope oil seep, Northern Gulf of Mexico. Amer. Assoc. Petrot Geo!. Bulletin. v. 72, pp. 105-114. 568 K. S. R. MURTHY AND T. C. S. RAO BRYANT, W. R. and L. B. ROEMER, (1983) Structure...

  5. Long-term evolution of the western South Atlantic passive continental margin in a key area of SE Brazil revealed by thermokinematic numerical modeling using the software code Pecube

    Science.gov (United States)

    Stippich, Christian; Krob, Florian; Glasmacher, Ulrich A.; Hackspacher, Peter C.

    2016-04-01

    The aim of the research is to quantify the long-term evolution of the western South Atlantic passive continental margin (SAPCM) in SE-Brazil. Excellent onshore outcrop conditions and extensive pre-rift to post-rift archives between São Paulo and Laguna allow a high precision quantification of exhumation, and rock uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. Research will integrate published1 and partly published thermochronological data from Brazil, and test lately published new concepts on causes of long-term landscape and lithospheric evolution in southern Brazil. Six distinct lithospheric blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos), which are separated by fracture zones1 are characterized by individual thermochronological age spectra. Furthermore, the thermal evolution derived by numerical modeling indicates variable post-rift exhumation histories of these blocks. In this context, we will provide information on the causes for the complex exhumation history of the Florianópolis, and adjacent blocks. The climate-continental margin-mantle coupled process-response system is caused by the interaction between endogenous and exogenous forces, which are related to the mantle-process driven rift - drift - passive continental margin evolution of the South Atlantic, and the climate change since the Early/Late Cretaceous climate maximum. Special emphasis will be given to the influence of long-living transform faults such as the Florianopolis Fracture Zone (FFZ) on the long-term topography evolution of the SAPCM's. A long-term landscape evolution model with process rates will be achieved by thermo-kinematic 3-D modeling (software code PECUBE2,3 and FastScape4). Testing model solutions obtained for a multidimensional parameter space against the real thermochronological and geomorphological data set, the most likely combinations of parameter rates, and values can be constrained. The

  6. Heat Flow and Gas Hydrates on the Continental Margin of India: Building on Results from NGHP Expedition 01

    Energy Technology Data Exchange (ETDEWEB)

    Trehu, Anne; Kannberg, Peter

    2011-06-30

    The Indian National Gas Hydrate Program (NGHP) Expedition 01 presented the unique opportunity to constrain regional heat flow derived from seismic observations by using drilling data in three regions on the continental margin of India. The seismic bottom simulating reflection (BSR) is a well-documented feature in hydrate bearing sediments, and can serve as a proxy for apparent heat flow if data are available to estimate acoustic velocity and density in water and sediments, thermal conductivity, and seafloor temperature. Direct observations of temperature at depth and physical properties of the sediment obtained from drilling can be used to calibrate the seismic observations, decreasing the uncertainty of the seismically-derived estimates. Anomalies in apparent heat flow can result from a variety of sources, including sedimentation, erosion, topographic refraction and fluid flow. We constructed apparent heat flow maps for portions of the Krishna-Godavari (K-G) basin, the Mahanadi basin, and the Andaman basin and modeled anomalies using 1-D conductive thermal models. Apparent heat flow values in the Krishna-Godavari (K-G) basin and Mahanadi basin are generally 0.035 to 0.055 watts per square meter (W/m2). The borehole data show an increase in apparent heat flow as water depth increases from 900 to 1500 m. In the SW part of the seismic grid, 1D modeling of the effect of sedimentation on heat flow shows that ~50% of the observed increase in apparent heat flow with increasing water depth can be attributed to trapping of sediments behind a "toe-thrust" ridge that is forming along the seaward edge of a thick, rapidly accumulating deltaic sediment pile. The remainder of the anomaly can be explained either by a decrease in thermal conductivity of the sediments filling the slope basin or by lateral advection of heat through fluid flow along stratigraphic horizons within the basin and through flexural faults in the crest of the anticline. Such flow probably plays a role in

  7. Heat Flow and Gas Hydrates on the Continental Margin of India: Building on Results from NGHP Expedition 01

    Energy Technology Data Exchange (ETDEWEB)

    Anne Trehu; Peter Kannberg

    2011-06-30

    The Indian National Gas Hydrate Program (NGHP) Expedition 01 presented the unique opportunity to constrain regional heat flow derived from seismic observations by using drilling data in three regions on the continental margin of India. The seismic bottom simulating reflection (BSR) is a well-documented feature in hydrate bearing sediments, and can serve as a proxy for apparent heat flow if data are available to estimate acoustic velocity and density in water and sediments, thermal conductivity, and seafloor temperature. Direct observations of temperature at depth and physical properties of the sediment obtained from drilling can be used to calibrate the seismic observations, decreasing the uncertainty of the seismically-derived estimates. Anomalies in apparent heat flow can result from a variety of sources, including sedimentation, erosion, topographic refraction and fluid flow. We constructed apparent heat flow maps for portions of the Krishna-Godavari (K-G) basin, the Mahanadi basin, and the Andaman basin and modeled anomalies using 1-D conductive thermal models. Apparent heat flow values in the Krishna-Godavari (K-G) basin and Mahanadi basin are generally 0.035 to 0.055 watts per square meter (W/m{sup 2}). The borehole data show an increase in apparent heat flow as water depth increases from 900 to 1500 m. In the SW part of the seismic grid, 1D modeling of the effect of sedimentation on heat flow shows that {approx}50% of the observed increase in apparent heat flow with increasing water depth can be attributed to trapping of sediments behind a 'toe-thrust' ridge that is forming along the seaward edge of a thick, rapidly accumulating deltaic sediment pile. The remainder of the anomaly can be explained either by a decrease in thermal conductivity of the sediments filling the slope basin or by lateral advection of heat through fluid flow along stratigraphic horizons within the basin and through flexural faults in the crest of the anticline. Such flow

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

    Energy Technology Data Exchange (ETDEWEB)

    Solomon, Evan A. [Univ. of Washington, Seattle, WA (United States); Johnson, H. Paul [Univ. of Washington, Seattle, WA (United States); Salmi, Marie [Univ. of Washington, Seattle, WA (United States); Whorley, Theresa [Univ. of Washington, Seattle, WA (United States)

    2017-11-10

    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 how 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 water

  9. Cretaceous–Eocene provenance connections between the Palawan Continental Terrane and the northern South China Sea margin

    NARCIS (Netherlands)

    Shao, Lei; Cao, Licheng; Qiao, Peijun; Zhang, Xiangtao; Li, Qianyu; van Hinsbergen, Douwe J.J.

    2017-01-01

    The plate kinematic history of the South China Sea opening is key to reconstructing how the Mesozoic configuration of Panthalassa and Tethyan subduction systems evolved into today's complex Southeast Asian tectonic collage. The South China Sea is currently flanked by the Palawan Continental Terrane

  10. Structural lineaments from the magnetic anomaly maps of the eastern continental margin of India (ECMI) and NW Bengal Fan

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.; Rao, T.C.S.; Subrahmanyam, A.S.; Rao, M.M.M.; Lakshminarayana, S.

    degrees E. Analysis of magnetic data associated with these trends suggests that (1) trend1, located at the foot of the continental slope (around 3000 m water depth) represents the ocean-continent boundary (OCB) of ECMI, (2) trend 2 represents the northern...

  11. Evidences of late quaternary neotectonic activity and sea-level changes along the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Veerayya, M.; Thamban, M.; Wagle, B.G.

    The offshore data on sea-level changes along the western margin of India have been reviewed and evidences of Late Quaternary neotectonic activity and subsidence are documented, based on the diagenetic textures of limestones from deeper submarine...

  12. Land-ocean tectonics (LOTs) and the associated seismic hazard over the Eastern Continental Margin of India (ECMI)

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.; Subrahmanyam, V.; Subrahmanyam, A.S.; Murty, G.P.S.; Sarma, K.V.L.N.S.

    are hence more predominant on the east coast. Recent geophysical studies delineated land-ocean tectonics (LOTs) over the eastern margin, in some cases associated with moderate seismicity as a result of the compressional stress acting on the Indian Plate...

  13. Abbot Ice Shelf, structure of the Amundsen Sea continental margin and the southern boundary of the Bellingshausen Plate seaward of West Antarctica

    Science.gov (United States)

    Cochran, James R.; Tinto, Kirsty J.; Bell, Robin E.

    2015-05-01

    Inversion of NASA Operation IceBridge airborne gravity over the Abbot Ice Shelf in West Antarctica for subice bathymetry defines an extensional terrain made up of east-west trending rift basins formed during the early stages of Antarctica/Zealandia rifting. Extension is minor, as rifting jumped north of Thurston Island early in the rifting process. The Amundsen Sea Embayment continental shelf west of the rifted terrain is underlain by a deeper, more extensive sedimentary basin also formed during rifting between Antarctica and Zealandia. A well-defined boundary zone separates the mildly extended Abbot extensional terrain from the deeper Amundsen Embayment shelf basin. The shelf basin has an extension factor, β, of 1.5-1.7 with 80-100 km of extension occurring across an area now 250 km wide. Following this extension, rifting centered north of the present shelf edge and proceeded to continental rupture. Since then, the Amundsen Embayment continental shelf appears to have been tectonically quiescent and shaped by subsidence, sedimentation, and the advance and retreat of the West Antarctic Ice Sheet. The Bellingshausen Plate was located seaward of the Amundsen Sea margin prior to incorporation into the Antarctic Plate at about 62 Ma. During the latter part of its independent existence, Bellingshausen plate motion had a clockwise rotational component relative to Antarctica producing convergence across the north-south trending Bellingshausen Gravity Anomaly structure at 94°W and compressive deformation on the continental slope between 94°W and 102°W. Farther west, the relative motion was extensional along an east-west trending zone occupied by the Marie Byrd Seamounts. The copyright line for this article was changed on 5 JUN 2015 after original online publication.

  14. How the structure of a continental margin affects the development of a fold and thrust belt. 1: A case study in south-central Taiwan

    Science.gov (United States)

    Brown, Dennis; Alvarez-Marron, Joaquina; Biete, Cristina; Camanni, Giovanni; Kuo-Chen, Hao; Ho, Chun-Wei

    2016-04-01

    Studies of mountain belts worldwide have shown that the structural, mechanical, and kinematic evolution of their foreland fold and thrust belts are strongly influenced by the structure of the continental margins that are involved in the deformation. The area on and around the island of Taiwan provides an unparalleled opportunity to investigate this because the entire profile of the Eurasian margin, from the shelf in the north to the slope and continent-ocean transition in the south and the offshore, is currently involved in the collision. Taiwan, then, can provide key insights into how such features as rift basins on the shelf, the extensional faults that form the shelf-slope break in the basement, or the structure of the extended crust and morphology of the sedimentary carapace of the slope can be directly reflected in the location and pattern of its seismicity, in its topography, and in its structural architecture, among other things. The continental margin of the Eurasian Plate that is currently involved in the Taiwan orogeny is thought to have evolved from a sub-continental subduction system in the Late Cretaceous to a rifting margin by the Early Eocene and, during the late Early Oligocene, to sea-floor spreading and the formation of the South China Sea, followed by localized extension in the Middle Miocene and, finally, collision with the Luzon Arc by the Early Miocene. Imaging features of the margin's structure in the Taiwan orogen is possible with seismic tomography, which shows, for example, that there are notable changes in velocity that can be directly attributed to structures in the basement. For example, there is a marked increase in Vp beneath the Hsuehshan Range which can be interpreted to be related to the uplift of higher velocity basement rocks by basin inversion. This is accompanied by significant seismicity that reaches a depth of more than 30 km's, and by surface uplift to form the highest topography in Taiwan. Furthermore, beginning at 8 km

  15. Modeling sulfate reduction in methane hydrate-bearing continental margin sediments: Does a sulfate-methane transition require anaerobic oxidation of methane?

    Science.gov (United States)

    Malinverno, A.; Pohlman, J.W.

    2011-01-01

    The sulfate-methane transition (SMT), a biogeochemical zone where sulfate and methane are metabolized, is commonly observed at shallow depths (1-30 mbsf) in methane-bearing marine sediments. Two processes consume sulfate at and above the SMT, anaerobic oxidation of methane (AOM) and organoclastic sulfate reduction (OSR). Differentiating the relative contribution of each process is critical to estimate methane flux into the SMT, which, in turn, is necessary to predict deeper occurrences of gas hydrates in continental margin sediments. To evaluate the relative importance of these two sulfate reduction pathways, we developed a diagenetic model to compute the pore water concentrations of sulfate, methane, and dissolved inorganic carbon (DIC). By separately tracking DIC containing 12C and 13C, the model also computes ??13C-DIC values. The model reproduces common observations from methane-rich sediments: a well-defined SMT with no methane above and no sulfate below and a ??13C-DIC minimum at the SMT. The model also highlights the role of upward diffusing 13C-enriched DIC in contributing to the carbon isotope mass balance of DIC. A combination of OSR and AOM, each consuming similar amounts of sulfate, matches observations from Site U1325 (Integrated Ocean Drilling Program Expedition 311, northern Cascadia margin). Without AOM, methane diffuses above the SMT, which contradicts existing field data. The modeling results are generalized with a dimensional analysis to the range of SMT depths and sedimentation rates typical of continental margins. The modeling shows that AOM must be active to establish an SMT wherein methane is quantitatively consumed and the ??13C-DIC minimum occurs. The presence of an SMT generally requires active AOM. Copyright 2011 by the American Geophysical Union.

  16. New insights on the geological evolution of the continental margin of Southeastern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

    Science.gov (United States)

    Krob, Florian; Stippich, Christian; Glasmacher, Ulrich A.; Hackspacher, Peter

    2017-04-01

    New insights on the geological evolution of the continental margin of Southeastern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data Krob, F.C.1, Stippich, C. 1, Glasmacher, U.A.1, Hackspacher, P.C.2 (1) Institute of Earth Sciences, Research Group Thermochronology and Archaeometry, Heidelberg University, INF 234, 69120, Heidelberg, Germany (2) Instituto de Geociências e Ciências Exatas, Universidade Estadual Paulista, Av. 24-A, 1515 Rio Claro, SP, 13506-900, Brazil Passive continental margins are important geoarchives related to mantle dynamics, the breakup of continents, lithospheric dynamics, and other processes. The main concern yields the quantifying long-term lithospheric evolution of the continental margin between São Paulo and Laguna in southeastern Brazil since the Neoproterozoic. We put special emphasis on the reactivation of old fracture zones running into the continent and their constrains on the landscape evolution. In this contribution, we represent already consisting thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4) Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 427.6 (1.8) Ma whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0) Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.52) and 92.0 (1.86) Ma. These thermochronological ages from metamorphic, sedimentary and intrusive rocks show six distinct blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos) with different evolution cut by old fracture zones. Furthermore, models of time-temperature evolution illustrate the differences in Pre- to post-rift exhumation histories of these blocks. The presented data will provide an insight into the complex exhumation history of the continental margin based on the existing literature data on the evolution of the Paraná basin in Brazil and the latest

  17. Oceanic anoxic events of the Cretaceous period and their role in the formation of source rocks in the basins of continental margins

    Directory of Open Access Journals (Sweden)

    A.I. Konyukhov

    2017-09-01

    Full Text Available The Cretaceous period was marked not only by the dominance of warm climate, vast transgressions of the sea and widespread occurrence of carbonate deposits, but also by the formation of the richest petroleum formations, which are associated with the generation of a huge amount of hydrocarbons in the largest oil and gas basins of modern continental margins. Both early and late Cretaceous epochs were marked by several oceanic anoxic events (OAE of global and regional scale, accompanied by the accumulation of sediments enriched in organic matter, and by significant shifts in the ratios of stable isotopes C, O, and Sr. Various aspects of these events are considered in a huge number of articles published in recent years in major scientific publications. Unfortunately, their role in the formation of oil reservoirs has remained outside the scope of scientific analysis. Meanwhile Cretaceous OAE’s had led to the spreading of black shale and other sediments with high content of organic matter on the floor of Tethys ocean, central part of Atlantic and on the seamounts in the Pacific ocean. Among them only OAE 1a (Selli and OAE 2 (Bonarelli are known as more large anoxic events. The first occurred in the middle of Aptian time, the second near the Cenomanian-Turonian boundary (CTB. The analysis of the spreading of source rocks in the largest oil-and-gas bearing basins on the continental margins at that time – the Persian Gulf, Maracaibo, Middle and Upper Magdalena river, Putumayo and other basins – showed that episodes of OAE’s had not always found a reflection in the succession of major source rock’s formations. In the Persian Gulf a list of source rocks includes Hanifa, Garau, Gadvan, Kazhdumi, Ahmadi member and Gurpi formations of Cretaceous age. Thus it is certain that OAE’s were only separate parts of more complex history of accumulation of black shale and carbonate deposits with high content of total organic carbon on the continental margins

  18. Surficial clay mineral distribution on the southwestern continental margin of India: Evidence of input from the Bay of Bengal

    Digital Repository Service at National Institute of Oceanography (India)

    Chauhan, O.S.; Gujar, A.R.

    Continental Shelf Research, Vol. 16, No. 3, pp. 321-333, 1996 Copyright © 1995 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0278-4343/96 $9.50 + 0.00 0278-4343(95)00015-1 Surficial clay mineral distribution on the southwestern...) having nickel-filtered CuKa radiation (21.514 A). 326 O.S. Chauhan and A. R. Gujar Standard methods of ethylene glycol treatment were used to aid in identification of expanded clay minerals (Biscaye, 1965; Carol, 1970; Brindly et al., 1968). Weighted...

  19. Record of Permian-Early Triassic continental arc magmatism in the western margin of the Jiamusi Block, NE China: petrogenesis and implications for Paleo-Pacific subduction

    Science.gov (United States)

    Yang, Hao; Ge, Wenchun; Dong, Yu; Bi, Junhui; Wang, Zhihui; Ji, Zheng; Yang, H.; Ge, W. C.; Dong, Y.; Bi, J. H.; Wang, Z. H.; Ji, Z.

    2017-09-01

    In this paper, we report zircon U-Pb ages, Hf isotopes and whole-rock geochemical data for the Permian to Early Triassic granitoids from the western margin of the Jiamusi Block (WJB), NE China. The intermediate to felsic (SiO2 = 59.67-74.04 wt%) granitoids belong to calc-alkaline series and are characterized by enrichments in light rare earth elements and large ion lithophile elements with pronounced negative Nb, Ta and Ti anomalies, revealing typical continental magmatic arc geochemical signatures. The zircon U-Pb determinations on the granodiorite, monzogranite, syenogranite and quartz diorite samples yielded ages between ca. 275-245 Ma, which, together with the published coeval intrusive rocks, indicates that Permian to Early Triassic continental arc magmatism occurred extensively in the WJB. The low and mainly negative zircon ɛ Hf( t) values between -7.6 and +1.6 and the zircon Hf model ages of 1.2-1.8 Ga, which are significantly older than their crystallization ages, suggest that they were mainly derived from reworking of ancient crustal materials with a limited input of juvenile components. The geochemical systematics and petrogenetic considerations indicate that the studied granitoids were generated from a zone of melting, assimilation, storage, and homogenization, i.e., a MASHed zone at the base of Paleo- to Mesoproterozoic continental crust, where large portions of igneous rocks and minor clay-poor sediments involved in the source region. In combination with regional geological data, we argue that the Jiamusi Block was unlikely the rifted segment of the Songliao Block and two possible geodynamical models were proposed to interpret the formation of the ca. 275-245 Ma granitoids in the WJB. In the context of Permian global plate reconstruction, we suggest that Paleo-Pacific plate subduction was initiated in the Permian to Early Triassic beneath the Jiamusi Block, and even whole eastern NE China.

  20. Bathymetric highs in the mid-slope region of the western continental margin of India - Structure and mode of origin

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, D.G.; Paropkari, A.L.; Krishna, K.S.; Chaubey, A.K.; Ajay, K.K.; Kodagali, V.N.

    -filled depression of ~0.2 km wide. Over all the seafloor relief’s shows a broad anticline with gentle and evenly deepening flanks on either side overlain by ~2 s (TWT) thick sediments. The seismic reflectors of relatively wide structure E (Fig. 7) show a series... 'horst' structure that is bounded on both sides by steep faults. Sediments thickness patterns and faulted basement are confirmed from the fault-bounded trough, named the 'Kori-Comorin Depression' (Biswas, 1989) or "eastern part of shelf margin basin...

  1. Continental basement inheritance and multiscale rifted ocean margin architectures: case studies from the N Atlantic-Greenland region (Invited)

    Science.gov (United States)

    Holdsworth, R. E.; Wilson, R.; McCaffrey, K. J.; Imber, J.; Jones, R.

    2009-12-01

    It is widely believed that pre-existing basement structures significantly influence the development of rifts in both intracontinental and margin settings, but this hypothesis remains to be tested in many areas.We first investigate how fault reactivation controls the distribution and growth of individual faults in the post-breakup cover sequence of the Norwegian margin. We then use a combined onshore and offshore approach to address the wider problem of how intraplate basement structures control subsequent regional-scale fault patterns and kinematics. The influence of pre-existing, rift-related normal faults upon the early stages of fault growth in the post-breakup cover sequence is well illustrated offshore in the Vøring basin. Here Maastrichtian to Palaeocene age rift-related normal faults on the Nyk High were blanketed by Plio-Pleistocene sediments, which are cut locally by small (maximum throw directly above points of maximum throw or offsets along underlying rift-related faults, which therefore clearly control the location and architecture of later structures. Both upward and downward fault propagation from basement to cover and vice versa are recognised during this reactivation. Elastic interactions between en-echelon fault segments situated above basement heterogeneities are likely to promote the rapid growth of reactivated fault systems. Basement structures are often oriented significantly oblique to later rifting directions and can lead to transtensional deformation patterns. The Davis Strait of West Greenland contains the Ungava transform fault zone, which separates the failed spreading centres of the Labrador Sea and Baffin Bay. Detailed onshore studies of fault patterns and kinematics, at regional to outcrop scales, reveal the key roles played by two main transtensional fault systems. An older system of N-S trending en echelon normal faults bound a series of deep sedimentary basins of mid- upper-Cretaceous age that are linked by ESE-trending normal

  2. Use of Stochastic Modeling of Stratigraphic Relationships in High Resolution Seismic Reflection Data for Prediction of the Distribution of Acoustic and Geotechnical Property Variability in Near Surface Sediments on the East China Sea Continental Margin

    National Research Council Canada - National Science Library

    Bartek, Louis

    2004-01-01

    During cruises in May and June of 1999, 7991 km of single channel high resolution seismic data and 5278 km of chirp sub-bottom and side-scan sonar data were collected from the continental margin of the East China Sea (ECS) and Yellow Sea...

  3. Long-term landscape evolution of the South Atlantic "passive" continental margin in Eastern Argentina using apatite fission-track thermochronology

    Science.gov (United States)

    Pfister, Sabrina; Kollenz, Sebastian; Glasmacher, Ulrich A.

    2015-04-01

    To understand the evolution of the "passive" continental margin in Argentina low temperature thermochronology is an appropriate method, which might lead to new insights in this area. The Tandilia System, also called Sierras Septentrionales, is located south of the Río de la Plato Craton in eastern Argentina in the state of Buenos Aires. North of the hills the Salado basin is located whereas the Claromecó basin is situated south of the mountain range. In contrary to most basins along the South American "passive" continental margin, the Tandilia-System and the neighbouring basins trend perpendicular to the coast line. The topography is fairly flat with altitudes up to 350 m. The igneous-metamorphic basement is pre-Proterozoic in age and build up of mainly granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks and granitoid plutons. It is overlain by a series of Neoproterozoic to early Paleozoic sedimentary rocks (Cingolani 2011), like siliciclastic rocks, dolostones, shales and limestones (Demoulin 2005). The aim of the study is to quantify the long-term landscape evolution of the "passive" continental margin in eastern Argentina in terms of thermal, exhumation and tectonic evolution. For that purpose, samples were taken from the basement of the Sierra Septentrionales and analyzed with the apatite fission-track method. Further 2-D thermokinematic modeling was conducted with the computer code HeFTy (Ketcham 2005; Ketcham 2007; Ketcham et al. 2009). Because there are different hypotheses in literature regarding the geological evolution of this area two different models were generated, one after Demoulin et al. (2005) and another after Zalba et al.(2007). All samples were taken from the Neoproterozoic igneous-metamorphic basement. Apatite fission-track ages range from 101.6 (9.4) to 228.9 (22.3) Ma, and, therefore, are younger than their formation age, indicating all samples have been thermally reset. Six samples accomplished enough confined

  4. Generation of felsic rocks of bimodal volcanic suites from thinned and rifted continental margins: Geochemical and Nd, Sr, Pb-isotopic evidence from Haida Gwaii, British Columbia, Canada

    Science.gov (United States)

    Dostal, Jaroslav; Hamilton, Tark S.; Shellnutt, J. Gregory

    2017-11-01

    The compositionally bimodal volcanic rocks of the Eocene-Miocene Masset Formation from Queen Charlotte basin, Haida Gwaii, British Columbia, Canada, underlie an area greater than 5000 km2 where their exposed sections are up to 1.6 km thick. The suite of mafic and felsic rocks (dacites and rhyolites) that erupted closely spaced in time, in both submarine and subaerial conditions, was associated with significant crustal extension and thin continental crust ( 19-24 km thick), with volcanism persisting for 35 Ma (from 46 to 11 Ma). Predominant mafic types (mafic:felsic 2:1) are moderately enriched mid-ocean-ridge-like basalts that were derived by a partial melting of a heterogeneous spinel peridotite source. Felsic rocks are plagioclase-phyric, two pyroxene-bearing, mainly peraluminous types which have Nd, Pb and Sr isotopic compositions overlapping those of basalts including high positive ƐNd(t) values (up to >+6). The chondrite-normalized REE patterns show light REE enrichment but flat heavy REE along with a variable negative Eu anomaly. Mineralogy, major and trace elements, Nd-Sr-Pb isotopic data and model calculations using MELTS are consistent with a derivation of felsic rocks from the basalts by fractional crystallization. The intercalation of basaltic and felsic rocks suggests the existence of separate, simultaneously active plumbing and feeder systems and relatively stable magma chamber(s) to generate large volumes of differentiated felsic magmas by fractional crystallization. The Masset rocks provide an example for the generation of felsic magmas of bimodal volcanic suites during rifting along a thinned continental margin. Appendix 1b Representative analyses of minerals of the Masset Formation felsic rocks

  5. U-Pb thermochronology of rutile from Alpine Corsica: constraints on the thermal evolution of the European margin during Jurassic continental breakup

    Science.gov (United States)

    Ewing, T. A.; Beltrando, M.; Müntener, O.

    2017-12-01

    U-Pb thermochronology of rutile can provide valuable temporal constraints on the exhumation history of the lower crust, given its moderate closure temperature and the occurrence of rutile in appropriate lithologies. We present an example from Alpine Corsica, in which we investigate the thermal evolution of the distal European margin during Jurassic continental rifting that culminated in the opening of the Alpine Tethys ocean. The Belli Piani unit of the Santa Lucia nappe (Corsica) experienced minimal Alpine overprint and bears a striking resemblance to the renowned Ivrea Zone lower crustal section (Italy). At its base, a 2-4 km thick gabbroic complex contains slivers of granulite facies metapelites that represent Permian lower crust. Zr-in-rutile temperatures and U-Pb ages were determined for rutile from three metapelitic slivers from throughout the Mafic Complex. High Zr-in-rutile temperatures of 850-950 °C corroborate textural evidence for rutile formation during Permian granulite facies metamorphism. Lower Zr-in-rutile temperatures of 750-800 °C in a few grains are partly associated with elongate strings of rutile within quartz ribbons, which record recrystallisation of some rutile during high-temperature shearing. Zr thermometry documents that both crystallisation and re-crystallisation of rutile occurred above the closure temperature of Pb in rutile, such that the U-Pb system can be expected to record cooling ages uncomplicated by re-crystallisation. Our new high-precision single-spot LA-ICPMS U-Pb dates are highly consistent between and within samples. The three samples gave ages from 160 ± 1 Ma to 161 ± 2 Ma, with no other age populations detected. The new data indicate that the Santa Lucia lower crust last cooled through 550-650 °C at 160 Ma, coeval with the first formation of oceanic crust in the Tethys. The new data are compared to previous depth profiling rutile U-Pb data for the Belli Piani unit1, and exploited to cast light on the tectonothermal

  6. Impact of the Paleocene-Eocene Thermal Maximum on Continental Margins and Implications for the Carbon Cycle in Near-Shore Environments

    Science.gov (United States)

    John, C. M.; Bohaty, S. M.; Zachos, J. C.; Sluijs, A.; Gibbs, S.; Brinkhuis, H.; Bralower, T. J.

    2006-12-01

    We present a multi-proxy study of continental shelf and slope deposits from the eastern and western margins of North America across the Paleocene-Eocene Thermal Maximum (PETM, about 55 Ma). The PETM is characterized by rapid global warming, of 5-6 ° C but locally by as much as 8 ° C, and a transient 2.5-6 ‰ global negative excursion in the stable isotopic composition of marine and terrestrial sedimentary carbon (carbon isotope excursion, CIE). The CIE is best explained by the rapid transfer of a large mass of methane from gas hydrate reservoirs into the exogenic carbon pool. The rise in temperature associated with the addition of this carbon appears to have also altered global humidity and precipitation patterns, a feature impacting near-shore depositional facies. The sections investigated are dominanted by siliciclastic sediments with sufficient planktonic and benthic foraminifera, and/or organic matter to construct carbon isotope stratigraphies. Oxygen isotope and TEX86- based estimates of surface water temperatures (SST) on the shelf suggest that average SSTs in mid-latitude near shore environments increased significantly, by more than 5 ° C. Salinities may have decreased as a result of increased runoff. Vertical temperature gradients in the water column appear to have weakened along with deepening of the thermocline, resulting in a weaker stratification The magnitude of the CIE in these coastal sections ranges from 3.5 to 4.5 ‰ , which is slightly larger than in the deep-sea, particularly in planktonic foraminifers. The larger magnitude of the CIE in shelf areas likely reflects a combination of enhanced runoff and higher respiration rates that lowered the mean carbon isotope composition of dissolved inorganic carbon (DIC) in coastal waters during the CIE relative to the open ocean. However, we must not rule out that there may also be truncation of deep-water records, making the CIE less complete. In addition, sedimentation rates and preservation

  7. Simbiontes associados com Anomalocardia brasiliana (Gmelin (Mollusca, Bivalvia, Veneridae na Ilha de Santa Catarina e região continental adjacente, Santa Catarina, Brasil Symbionts associated with Anomalocardia brasiliana (Gmelin (Mollusca, Bivalvia, Veneridae on Santa Catarina Island and adjacent continental region, Santa Catarina, Brazil

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    Guisla Boehs

    2004-12-01

    Full Text Available Berbigões, Anomalocardia brasiliana (Gmelin, 1791, de bancos naturais da Ilha de Santa Catarina e região continental adjacente (SC, Brasil, foram examinados quanto a presença de simbiontes. Holothuriophilus tomentosus (Ortmann, 1894 (Brachyura, Sphenia antillensis Dall & Simpson, 1901 (Bivalvia e poliquetos espionídeos (Polychaeta foram observados macroscopicamente. A análise das secções histológicas evidenciou esporocistos de trematódeos (Digenea, um metacestóide (Cestoda e dois ciliados (Ciliophora.Pointed venus, Anomalocardia brasiliana (Gmelin, 1791, from natural beds of Santa Catarina Island and adjacent continental region (SE Brazil were examined in respect of symbiotic associations. Holothuriophilus tomentosus (Ortmann, 1894 (Brachyura, Sphenia antillensis Dall & Simpson, 1901 (Bivalvia, and polychaete worms (Polychaeta were found by macroscopic diagnosis. By analysis of histological sections, it was noted trematode sporocysts (Digenea, a metacestode (Cestoda and two ciliates (Ciliophora.

  8. Long-term landscape evolution of the South Atlantic passive continental margin along the Kaoko- and Damara Belts, NW-Namibia

    Science.gov (United States)

    Menges, Daniel; Glasmacher, Ulrich Anton; Hackspacher, Peter; Schneider, Gabriele; Salomon, Eric

    2015-04-01

    The Kaoko Belt in northwestern Namibia originates in the collision of the Rio de la Plata and Kongo Craton during the Pan-African Orogeny in the Neoproterozoic (1) and represents the northern arm of the Damara Orogen. NW-Namibias continental crust mainly consists of the NE-SW striking intracontinental branch of the Pan-African Damara mobile belt, which separates the Congo from the Kalahari craton. The Damara Orogen is divided into several tectonostratigraphic zones that are bounded by steeply dipping, ductile shear zones. These regional lineaments can be traced at least 150 km offshore (2). The lithostratigraphic units consist of Proterozoic and Cambrian metamorphosed rocks (534 (7) Ma - 481 (25) Ma (3) as well as Mesozoic sedimentary and igneous rocks. From Permo-Carboniferous to Mid Jurassic northern Namibia was affected by deep erosion of the Damara Orogen, Permo-Triassic collisional processes along the southern margin of Gondwana and eastern margin of Africa (4), and the deposition of the Nama Group sediments and the Karoo megasequence (5). Between the Otjihorongo and the Omaruru Lineament-Waterberg Thrust early Mesozoic tectonic activity is recorded by coarse clastic sediments deposited within NE trending half-graben structures. The Early Jurassic Karoo flood basalt lavas erupted rapidly at 183±1 Ma (6). The Early Cretaceous Paraná-Etendeka flood basalts (132±1 Ma) and mafic dike swarms mark the rift stage of the opening of the South Atlantic (7). Early Cretaceous alkaline intrusions (137-124 Ma) occur preferentially along Mesozoic half-graben structures and are called the Damaraland Igneous Province (8). Late Cretaceous alkaline intrusions and kimberlite pipes occur in northern Namibia. Post Early Paleocene siliciclastic sedimentation in Namibia was largely restricted to a 150 km wide zone (9) and is represented by the Tsondab Sandstone Formation (~ 300 m thickness). The oldest part has an age of early Paleocene and the upper part span from middle Miocene

  9. Meso-/Cenozoic long-term landscape evolution at the southern Moroccan passive continental margin, Tarfaya Basin, recorded by low-temperature thermochronology

    Science.gov (United States)

    Sehrt, Manuel; Glasmacher, Ulrich A.; Stockli, Daniel F.; Jabour, Haddou; Kluth, Oliver

    2017-10-01

    This paper presents the first regional study of low-temperature thermochronology to be undertaken in the Tarfaya Basin at the southern Moroccan passive continental margin. The basin is characterised by vast subsidence since Mid-Triassic times, whereby up to 12 km of Meso- to Cenozoic sedimentary rocks accumulated. The study focused on the post-rift vertical movements along a typical ;passive; margin and besides dealt with the timing and maximum temperature reached by potential source rocks of the basin. To unravel the t-T development, thermochronological analyses were performed on 50 outcrop and well samples from Meso-Cenozoic rocks. Thermochronological data reveal a continuous subsidence phase in the offshore basin from Mid-Triassic to recent times. In contrast, apatite (U-Th-Sm)/He and apatite fission-track data as well as thermal modelling point to an inversion of the northeastern onshore basin starting in the Palaeogene at 65-55 Ma. The rock uplift and exhumation period resulted in the erosion of a 1.0-1.4 km thick Cretaceous-Palaeogene sedimentary pile contemporaneously with peak Atlas surface uplift in the Cenozoic. The exhumation stage could be an explanation for the increasing periodic influx of detrital material into the offshore and southern onshore Tarfaya Basin since Palaeocene. Detrital apatite fission-track ages from 92 (± 16) to 237 (± 35) Ma of the Upper Cretaceous-Neogene succession indicate no heating above 60 °C confirming immature to early mature Cenomanian to Campanian and Eocene source rocks in the onshore Tarfaya Basin.

  10. Sulfate reduction and methane oxidation activity below the sulfate-methane transition zone in Alaskan Beaufort Sea continental margin sediments: Implications for deep sulfur cycling

    Science.gov (United States)

    Treude, Tina; Krause, Stefan; Maltby, Johanna; Dale, Andrew W.; Coffin, Richard; Hamdan, Leila J.

    2014-11-01

    Two ∼6 m long sediment cores were collected along the ∼300 m isobath on the Alaskan Beaufort Sea continental margin. Both cores showed distinct sulfate-methane transition zones (SMTZ) at 105 and 120 cm below seafloor (cmbsf). Sulfate was not completely depleted below the SMTZ but remained between 30 and 500 μM. Sulfate reduction and anaerobic oxidation of methane (AOM) determined by radiotracer incubations were active throughout the methanogenic zone. Although a mass balance could not explain the source of sulfate below the SMTZ, geochemical profiles and correlation network analyses of biotic and abiotic data suggest a cryptic sulfur cycle involving iron, manganese and barite. Inhibition experiments with molybdate and 2-bromoethanesulfonate (BES) indicated decoupling of sulfate reduction and AOM and competition between sulfate reducers and methanogens for substrates. While correlation network analyses predicted coupling of AOM to iron reduction, the addition of manganese or iron did not stimulate AOM. Since none of the classical archaeal anaerobic methanotrophs (ANME) were abundant, the involvement of unknown or unconventional phylotypes in AOM is conceivable. The resistance of AOM activity to inhibitors implies deviation from conventional enzymatic pathways. This work suggests that the classical redox cascade of electron acceptor utilization based on Gibbs energy yields does not always hold in diffusion-dominated systems, and instead biotic processes may be more strongly coupled to mineralogy.

  11. Differences in meiofauna communities with sediment depth are greater than habitat effects on the New Zealand continental margin: implications for vulnerability to anthropogenic disturbance

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    Norliana Rosli

    2016-07-01

    Full Text Available Studies of deep-sea benthic communities have largely focused on particular (macro habitats in isolation, with few studies considering multiple habitats simultaneously in a comparable manner. Compared to mega-epifauna and macrofauna, much less is known about habitat-related variation in meiofaunal community attributes (abundance, diversity and community structure. Here, we investigated meiofaunal community attributes in slope, canyon, seamount, and seep habitats in two regions on the continental slope of New Zealand (Hikurangi Margin and Bay of Plenty at four water depths (700, 1,000, 1,200 and 1,500 m. We found that patterns were not the same for each community attribute. Significant differences in abundance were consistent across regions, habitats, water and sediment depths, while diversity and community structure only differed between sediment depths. Abundance was higher in canyon and seep habitats compared with other habitats, while between sediment layer, abundance and diversity were higher at the sediment surface. Our findings suggest that meiofaunal community attributes are affected by environmental factors that operate on micro- (cm to meso- (0.1–10 km, and regional scales (> 100 km. We also found a weak, but significant, correlation between trawling intensity and surface sediment diversity. Overall, our results indicate that variability in meiofaunal communities was greater at small scale than at habitat or regional scale. These findings provide new insights into the factors controlling meiofauna in these deep-sea habitats and their potential vulnerability to anthropogenic activities.

  12. Age and composition of the UHP garnet peridotites in the Dabie orogenic belt (central China) record complex crust-mantle interaction in continental margin

    Science.gov (United States)

    Zhao, Y.; Zheng, J.; Wang, B.

    2017-12-01

    The Dabie-Sulu UHP belt was created by the collision between the North and South China cratons in Middle Triassic time (240-225 Ma). There are lots of garnet-bearing ultramafic body occurs as a lens in the belt. Age and composition of the Maowu garnet peridotites in the Dabie orogenic belt are reported. The garnet harzburgites are main moderately refractory (Mg#Ol=92) and minor fertile (Mg#Ol=88) with high Ni (2344-2603 ppm) and low Al2O3 (0.35-0.54 wt.%), CaO (0.76-2.19 wt.%) and TiO2 (˜0.01 wt.%). Zircons in the harzburgites mainly document metamorphism at 230 ± 2 Ma, 275 ± 5 Ma, 357 ± 4 Ma, and complex minor populations of ages including: 1.8 Ga, 1.3 Ga, and Neoproterozic-early Paleozoic ages (901-420 Ma). The early Meszosic and late Paleozoic zircons have similar trace-element patterns and ranges in ɛHf(t) (+0.6 to +3.4), Th/U ratio (0.2-0.7) and Hf depleted-mantle model ages (TDM ) mainly cluster in the interval 1.2-0.9 Ga. In contrast, the Paleo-Mesoproterozoic zircons have negative ɛHf(t) (-24.9 to -2.7) and oldest Hf TDM = 3.4Ga. Zircons of Neoproterozic-early Paleozoic have a wide range of Hf depleted-mantle model ages (2.4-0.7Ga) and ɛHf(t) (-15.3 to +9.5). Above of the all, we suggest that the Maowu garnet harzburgites are interpreted as a fragment of the metasomatized ancient lithospheric mantle beneath the southern margin of the North China Craton. They experienced the Proterozoic thermal event (1.9-1.8Ga), which is coeval with the assembly of the supercontinent Columbia. And then 1.3Ga mantle metasomatism with asthenospheric materials resulted in the final breakup of the Columbia supercontinent. Neoproterozic-early Paleozoic (901-420 Ma), deep parts of the south margin of the craton were metasomatized during the assembly and breakup of the Rodinia supercontinent. Then, the southern margin of the craton occurred oceanic crust subduction ( 357 Ma), subsequent continental deep subduction and final continent-continent collision in Triassic.

  13. Tectonic setting of the pebble and other copper-gold-molybdenum porphyry deposits within the evolving middle cretaceous continental margin of Northwestern North America

    Science.gov (United States)

    Goldfarb, Richard J.; Anderson, Eric; Hart, Craig J.R.

    2013-01-01

    The Pebble Cu-Au-Mo deposit in southwestern Alaska, containing the largest gold resource of any known porphyry in the world, developed in a tectonic setting significantly different from that of the present-day. It is one of a series of metalliferous middle Cretaceous porphyritic granodiorite, quartz monzonite, and diorite bodies, evolved from lower crust and metasomatized lithospheric mantle melts, which formed along much of the length of the North American craton suture with the Peninsular-Alexander-Wrangellia arc. The porphyry deposits were emplaced within the northernmost two of a series of ca. 130 to 80 Ma flysch basins that define the suture, as well as into arc rocks immediately seaward of the two basins. Deposits include the ca. 100 to 90 Ma Pebble, Neacola, and other porphyry prospects along the Kahiltna basin-Peninsula terrane boundary, and the ca. 115 to 105 Ma Baultoff, Carl Creek, Horsfeld, Orange Hill, Bond Creek, and Chisna porphyries along the Nutzotin basin-Wrangellia terrane boundary.The porphyry deposits probably formed along the craton margin more than 1,000 km to the south of their present latitude. Palinspastic reconstructions of plate kinematics from this period are particularly difficult because magmatism overlaps the 119 to 83 Ma Cretaceous Normal Superchron, a period when sea-floor magnetic data are lacking. Our favored scenario is that ore formation broadly overlaps the cessation of sedimentation and contraction and the transition to a transpressional continental margin regime, such that the remnant ocean basins were converted to strike-slip basins. The basins and outboard Peninsular-Alexander-Wrangellia composite superterrane, which are all located seaward of the deep crustal Denali-Farewell fault system, were subjected to northerly dextral transpression for as long as perhaps 50 m.y., beginning at ca. 95 ± 10 Ma. The onset of this transpression was marked by development of the mineralized bodies along fault segments on the seaward side

  14. The Two Subduction Zones of the Southern Caribbean: Lithosphere Tearing and Continental Margin Recycling in the East, Flat Slab Subduction and Laramide-Style Uplifts in the West

    Science.gov (United States)

    Levander, A.; Bezada, M. J.; Niu, F.; Schmitz, M.

    2015-12-01

    The southern Caribbean plate boundary is a complex strike-slip fault system bounded by oppositely vergent subduction zones, the Antilles subduction zone in the east, and a currently locked Caribbean-South American subduction zone in the west (Bilham and Mencin, 2013). Finite-frequency teleseismic P-wave tomography images both the Atlanic (ATL) and the Caribbean (CAR) plates subducting steeply in opposite directions to transition zone depths under northern South America. Ps receiver functions show a depressed 660 discontinuity and thickened transition zone associated with each subducting plate. In the east the oceanic (ATL) part of the South American (SA) plate subducts westward beneath the CAR, initiating the El Pilar-San Sebastian strike slip system, a subduction-transform edge propagator (STEP) fault (Govers and Wortel, 2005). The point at which the ATL tears away from SA as it descends into the mantle is evidenced by the Paria cluster seismicity at depths of 60-110 km (Russo et al, 1993). Body wave tomography and lithosphere-asthenosphere boundary (LAB) thickness determined from Sp and Ps receiver functions and Rayleigh waves suggest that the descending ATL also viscously removes the bottom third to half of the SA continental margin lithospheric mantle as it descends. This has left thinned continental lithosphere under northern SA in the wake of the eastward migrating Antilles subduction zone. The thinned lithosphere occupies ~70% of the length of the El Pilar-San Sebastian fault system, from ~64oW to ~69oW, and extends inland several hundred kilometers. In northwestern SA the CAR subducts east-southeast at low angle under northern Colombia and western Venezuela. The subducting CAR is at least 200 km wide, extending from northernmost Colombia as far south as the Bucaramanga nest seismicity. The CAR descends steeply under Lake Maracaibo and the Merida Andes. This flat slab is associated with three Neogene basement cored, Laramide-style uplifts: the Santa Marta

  15. Cretaceous high-pressure metamorphic belts of the Central Pontides (northern Turkey): pre-collisional Pacific-type accretionary continental growth of Laurasian Margin

    Science.gov (United States)

    Aygul, Mesut; Okay, Aral I.; Oberhaensli, Roland; Sudo, Masafumi

    2014-05-01

    Cretaceous blueschist-facies metamorphic rocks crop out widely in the central part of the Pontides, an east-west trending mountain belt in northern Turkey. They comprise an accretionary wedge along to the southern Laurasian active continental margin and predate the opening of Black Sea basin. From North to South, the wedge consists of a low grade metaflysch unit with marble, Na-amphibole-bearing metabasite and serpentinite blocks. An extensional shear zone separates the accreted distal terrigenous sediments from HP/LT micaschists and metabasites of oceanic origin, known as Domuzdaǧ Complex. The shear zone reaches up to one km in thickness and consists of tectonic slices of serpentinite, metabasite, marble, phyllite and micaschist with top to the NW sense of shear. The Domuzdaǧ Complex predominantly consists of carbonaceous micaschist and metabasite with serpentinite, and minor metachert, marble and metagabbro. Metabasites consist mainly of epidote-blueschists sometimes with garnet. Fresh lawsonite-blueschists are found as blocks within the shear zone. Peak metamorphic assemblages in the micaschists are chloritoid-glaucophane and garnet-chloritoid-glaucophane-lawsonite in addition to phengite, paragonite, quartz, chlorite and rutile (P: 17 ± 1 Kbar, T: 390-450 °C). To the south, lithologies change slightly, with metabasite and thick, pale marble with few metachert and metapelitic horizons. The degree of metamorphism also changes. The metabasites range from high-pressure upper-greenschist facies with growth of sodic-amphibole to lower greenschist without any HP index mineral, suggesting a general decrease in pressure toward south within the prism. While Domuzdaǧ Complex represents deep-seated underplated oceanic sediments and basalts, the carbonate-rich southern parts can be interpreted as seamounts integrated into the accretionary prism. Ar/Ar dating on phengite separates both from terrigenous and oceanic metasediments give consistent plateau ages of 100 ± 2

  16. Strong depth-related zonation of megabenthos on a rocky continental margin (∼700-4000 m off southern Tasmania, Australia.

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    Ronald Thresher

    Full Text Available Assemblages of megabenthos are structured in seven depth-related zones between ∼700 and 4000 m on the rocky and topographically complex continental margin south of Tasmania, southeastern Australia. These patterns emerge from analysis of imagery and specimen collections taken from a suite of surveys using photographic and in situ sampling by epibenthic sleds, towed video cameras, an autonomous underwater vehicle and a remotely operated vehicle (ROV. Seamount peaks in shallow zones had relatively low biomass and low diversity assemblages, which may be in part natural and in part due to effects of bottom trawl fishing. Species richness was highest at intermediate depths (1000-1300 m as a result of an extensive coral reef community based on the bioherm-forming scleractinian Solenosmilia variabilis. However, megabenthos abundance peaked in a deeper, low diversity assemblage at 2000-2500 m. The S. variabilis reef and the deep biomass zone were separated by an extensive dead, sub-fossil S. variabilis reef and a relatively low biomass stratum on volcanic rock roughly coincident with the oxygen minimum layer. Below 2400 m, megabenthos was increasingly sparse, though punctuated by occasional small pockets of relatively high diversity and biomass. Nonetheless, megabenthic organisms were observed in the vast majority of photographs on all seabed habitats and to the maximum depths observed--a sandy plain below 3950 m. Taxonomic studies in progress suggest that the observed depth zonation is based in part on changing species mixes with depth, but also an underlying commonality to much of the seamount and rocky substrate biota across all depths. Although the mechanisms supporting the extraordinarily high biomass in 2000-2500 m depths remains obscure, plausible explanations include equatorwards lateral transport of polar production and/or a response to depth-stratified oxygen availability.

  17. An improved 3-D constrained stochastic gravity inversion method, adapted to the crustal-scale study of offshore rifted continental margins

    Science.gov (United States)

    Geng, Meixia; Welford, J. Kim; Farquharson, Colin

    2017-04-01

    While seismic methods provide the best geophysical methods for characterizing crustal structure, regional potential field studies and, specifically, constrained 3-D potential field inversion studies, provide an efficient means of bridging between seismic lines and obtaining regional views of deep structure. Most existing potential field inversion codes have been developed for the mining industry with the goal of delineating dense bodies within less dense half-spaces. While these codes can be successfully applied to crustal-scale targets, they are not designed to generate models with the kind of depth-dependent layering expected within the crust and upper mantle and consequently, the results must be interpreted with such limitations in mind. The development of improved inversion codes that will produce results that better conform to known density distributions within the crust and uppermost mantle will revolutionize the application of potential field methods for the study of rifted continental margins where only limited seismic constraints are available. Through insights gained from using existing inversion codes, we have developed a 3D inversion algorithm based on the constrained stochastic method and adapted it for use in regional crustal-scale studies. The new method honours existing sparse seismic constraints and generates models that can reproduce sharp boundaries at the base of the crust as well as more gradational density variations with depth for the crust to upper mantle transition. The improved regional crustal models provide crustal thickness estimates and crustal stretching factors that agree with the sparsely available seismic constraints, while also generating more realistic Earth models. Both synthetic and real examples from offshore eastern Canada, will be used to demonstrate the power of the new method.

  18. The influence of a biomaterial on the closure of a marginal hard tissue defect adjacent to implants. An experimental study in the dog.

    Science.gov (United States)

    Botticelli, Daniele; Berglundh, Tord; Lindhe, Jan

    2004-06-01

    The present experiment was performed to determine the influence of Bio-Oss on hard tissue formation at sites that, following implant installation, presented a 1-1.25 mm wide marginal defect. Four Labrador dogs were used. The premolars and first molars on both sides of the mandible were extracted. After 3 months, mucoperiosteal flaps were elevated and three experimental sites were prepared for implant installation in each side of the mandible. A step drill was used to widen the marginal 5 mm of the canal. Thus, following the placement of the implant (3.3 x 10 mm, SLA surface, Straumann AG, Waldenburg, Switzerland) a circumferential gap, about 1-1.25 wide and 5 mm deep, remained lateral to the titanium rod. The test sites in the left side of the mandible were first filled with a deproteinized cancellous bone mineral (Bio-Oss). The defect sites in the right side of the mandible (control sites) were left for spontaneous healing. A resorbable barrier membrane (Bio-Gide) was placed to cover the implant and the bone tissue in two sites of each quadrant, while the third site was left without membrane placement. The flaps were repositioned to cover all defect sites and were sutured. After 4 months of healing, block biopsies of each implant site were dissected and processed for ground sectioning. It was demonstrated that at 4 months, all types of defects were filled with newly formed bone and that the biomaterial placed in the marginal defect in conjunction with implant installation during healing became incorporated in the newly formed bone tissue. A high degree of contact was established between the Bio-Oss particles and the newly formed bone. Bio-Oss became integrated with the newly formed bone. In the model used, Bio-Oss did not enhance the process of bone formation and defect closure.

  19. Incorporating Cutting Edge Scientific Results from the Margins-Geoprisms Program into the Undergraduate Curriculum, Rupturing Continental Lithosphere Part II: Introducing Euler Poles Using Baja-North America Relative Plate Motion Across the Gulf of California

    Science.gov (United States)

    Loveless, J. P.; Bennett, S. E. K.; Cashman, S. M.; Dorsey, R. J.; Goodliffe, A. M.; Lamb, M. A.

    2014-12-01

    The NSF-MARGINS Program funded a decade of research on continental margin processes. The NSF-GeoPRISMS Mini-lesson Project, funded by NSF-TUES, is designed to integrate the significant findings from the MARGINS program into open-source college-level curriculum. The Gulf of California (GOC) served as the focus site for the Rupturing Continental Lithosphere (RCL) initiative, which addressed several scientific questions: What forces drive rift initiation, localization, propagation and evolution? How does deformation vary in time and space, and why? How does crust evolve, physically and chemically, as rifting proceeds to sea-floor spreading? What is the role of sedimentation and magmatism in continental extension? We developed two weeks of curriculum, including lectures, labs, and in-class activities that can be used as a whole or individually. This component of the curriculum introduces students to the Euler pole description of relative plate motion (RPM) by examining the tectonic interactions of the Baja California microplate and North American plate. The plate boundary varies in rift obliquity along strike, from highly oblique and strike-slip dominated in the south to slightly less oblique and with a larger extensional component in the north. This Google Earth-based exercise provides students with a visualization of RPM using small circle contours of the local direction and magnitude of Baja-North America movement on a spherical Earth. Students use RPM to calculate the fault slip rates on transform, normal, and oblique-slip faults and examine how the varying faulting styles combine to accommodate RPM. MARGINS results are integrated via comparison of rift obliquity with the structural style of rift-related faults around the GOC. We find this exercise to fit naturally into courses about plate tectonics, geophysics, and especially structural geology, given the similarity between Euler pole rotations and stereonet-based rotations of structural data.

  20. Characterization of Sedimentary Deposits Using usSEABED for Large-scale Mapping, Modeling and Research of U.S.Continental Margins

    Science.gov (United States)

    Williams, S. J.; Reid, J. A.; Arsenault, M. A.; Jenkins, C.

    2006-12-01

    Geologic maps of offshore areas containing detailed morphologic features and sediment character can serve many scientific and operational purposes. Such maps have been lacking, but recent computer technology and software to capture diverse marine data are offering promise. Continental margins, products of complex geologic history and dynamic oceanographic processes, dominated by the Holocene marine transgression, contain landforms which provide a variety of important functions: critical habitats for fish, ship navigation, national defense, and engineering activities (i.e., oil and gas platforms, pipeline and cable routes, wind-energy sites) and contain important sedimentary records. Some shelf areas also contain sedimentary deposits such as sand and gravel, regarded as potential aggregate resources for mitigating coastal erosion, reducing vulnerability to hazards, and restoring ecosystems. Because coastal and offshore areas are increasingly important, knowledge of the framework geology and marine processes is useful to many. Especially valuable are comprehensive and integrated digital databases based on data from original sources in the marine community. Products of interest are GIS maps containing thematic information such as seafloor physiography, geology, sediment character and texture, seafloor roughness, and geotechnical engineering properties. These map products are useful to scientists modeling nearshore and shelf processes as well as planners and managers. The USGS with partners is leading a Nation-wide program to gather a wide variety of extant marine geologic data into the usSEABED system (http://walrus.wr.usgs/usseabed). This provides a centralized, fully integrated digital database of marine geologic data collected over the past 50 years by USGS, other federal and state agencies, universities and private companies. To date, approximately 325,000 data points from the U.S. EEZ reside in usSEABED. The usSEABED, which combines a broad array of physical data

  1. Melt Origin Across a Rifted Continental Margin: A Case for Subduction-related Metasomatic Agents in the Lithospheric Source of Alkaline Basalt, Northwest Ross Sea, Antarctica

    Science.gov (United States)

    Panter, K. S.; Castillo, P.; Krans, S. R.; Deering, C. D.; McIntosh, W. C.; Valley, J. W.; Kitajima, K.; Kyle, P. R.; Hart, S. R.; Blusztajn, J.

    2017-12-01

    Alkaline magmatism within the West Antarctic rift system in the NW Ross Sea (NWRS) includes a chain of shield volcanoes extending 260 km along the coast, numerous seamounts located on the continental shelf and hundreds more within the oceanic Adare Basin. Dating and geochemistry confirm that the seamounts are Pliocene‒Pleistocene in age and petrogenetically akin to the mostly Miocene volcanism on the continent as well as to a much broader region of alkaline volcanism that altogether encompasses areas of West Antarctica, Zealandia and Australia. All of these regions were contiguous prior to Gondwana breakup at 100 Ma, suggesting that the magmatism is interrelated. Mafic alkaline magmas (> 6 wt.% MgO) erupted across the transition from continent to ocean in the NWRS show a remarkable systematic increase in Si-undersaturation, P2O5, Sr, Zr, Nb and light rare earth element (LREE) concentrations, LREE/HREE and Nb/Y ratios. Radiogenic isotopes also vary with Nd and Pb ratios increasing and Sr ratios decreasing ocean-ward. The variations are not explained by crustal contamination or by changes in degree of mantle partial melting but are likely a function of the thickness and age of mantle lithosphere. The isotopic signature of the most Si-undersaturated and incompatible element enriched basalts best represent the composition of the sub-lithospheric source with low 87Sr/86Sr (≤ 0.7030) and δ18Oolivine (≤ 5.0 ‰), high 143Nd/144Nd ( 0.5130) and 206Pb/204Pb (≥ 20) ratios. The isotopic `endmember' is derived from recycled material and was transferred to the lithospheric mantle by small degree melts to form amphibole-rich metasomes. Later melting of the metasomes produced silica-undersaturated liquids that reacted with the surrounding peridotite. This reaction occurred to a greater extent as the melt traversed through thicker and older lithosphere continent-ward. Ancient or more recent ( 550‒100 Ma) subduction along the margin of Gondwana supplied the recycled

  2. Reliability of AMS and ARM/KARM to reconstruct the relative vigor and variability of sea-bottom currents during the Last Glacial Period in the North-West Iberian Continental Margin.

    Science.gov (United States)

    Rey, D.; Plaza-Morlote, M.; Mohamed Falcon, K. J.; Pares, J. M.; Bernabeu, A. M.; El Mekadem, N.; Rubio, B.

    2017-12-01

    We explore the potential and reliability of the anisotropy of magnetic susceptibility (AMS) to reconstruct the relative vigor of the sea-bottom currents by comparison with the widely-used paleo current proxy `sortable silt' mean (SS) grain size. SS and AMS are used as two independent proxies to determine relative changes in bottom-current speed, and their consistency tested against each other. The suitability of the magnetic grainsize proxy ARM/KARM ratio as a proxy for bottom-current variability is also investigated. The results are based on CI12PC3 core from the Galicia Interior Basin (North West Iberian Continental Margin) spanning the last 80 ka. The majority of AMS ellipsoid minimum axes (K3) in core CI12PC3 are close to vertical (INCmean= 80o) and nearly orthogonal to the bedding plane. Maximum axes (K1) are well-grouped marking two main magnetic lineation directions. Their orientations are consistent with present-day bottom-currents flow directions along the continental margin. Down-core variations in the degree of anisotropy (Pj) showed significantly higher values during Heinrich Stadials (cold) than during interstadials (warm). CI12PC3 also shows systematically lower ARM/KARM values during the stadials than during interstadials, indicating provenance induced coarsening of the magnetic fraction during the cold periods. We have noted that Pj down-core changes are independent of magnetic grain size, and interpreted them as the result of differences in the degree of grain alignment. These changes can be attributed to the variability in the strength of the bottom currents, indicating that they are stronger during stadials, which is consistent with the SS results. Magnetic properties and AMS of core CI12PC3 are climatically modulated on a millennial time scale reflecting the evolution in the near bottom-currents of the North West Iberian Continental Margin. Their variability exposes unchartered links with the AMOC and with the North Atlantic climate variability

  3. Indian Ocean margins

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.W.A.

    The most important biogeochemical transformations and boundary exchanges in the Indian Ocean seem to occur in the northern region, where the processes originating at the land-ocean boundary extend far beyond the continental margins. Exchanges across...

  4. The Ocean-Continent Transition at the North Atlantic Volcanic Margins

    Science.gov (United States)

    White, R. S.; Christie, P. A.; Kusznir, N. J.; Roberts, A. M.; Eccles, J.; Lunnon, Z.; Parkin, C. J.; Smith, L. K.; Spitzer, R.; Roberts, A. W.

    2005-05-01

    The continental margins of the northern North Atlantic are the best studied volcanic margins in the world. There is a wealth of integrated wide-angle and deep seismic profiles across the continent-ocean transition and the adjacent oceanic and continental crust, several of which form conjugate margin studies. We show new results from the integrated Seismic Imaging and Modelling of Margins (iSIMM) profiles across the Faroes continental margin which image both the extruded volcanics which generate seaward dipping reflector sequences and the underlying lower-crustal intrusions from which the extruded basalts are fed. This enables estimation of the degree of continental stretching and the total volume of melt generated from the mantle at the time of continental breakup. The new results are set in the context of profiles along the entire northern North Atlantic margins. The pattern of melt generation during continental breakup and the initiation of seafloor spreading allows us to map the pattern of enhanced sub-lithospheric mantle temperatures caused by initiation of the Iceland mantle plume over this period. The initial mantle plume thermal anomalies have the shape of rising hot sheets of mantle up to 2000 km in length, which focus into a more axisymmetric shape under the present location of Iceland. These spatial and temporal variations in the mantle temperature exert important controls on the history of uplift and subsidence and thermal maturation of the sediments near the continental margin and its hinterland. The iSIMM Scientific Team comprises NJ Kusznir, RS White, AM Roberts, PAF Christie, R Spitzer, N Hurst, ZC Lunnon, CJ Parkin, AW Roberts, LK Smith, V Tymms, J Eccles and D Healy. The iSIMM project is supported by Liverpool and Cambridge Universities, Schlumberger Cambridge Research, Badley Technology Limited, WesternGeco, Amerada Hess, Anadarko, BP, ConocoPhillips, ENI-UK, Statoil, Shell, the NERC and DTI. We thank WesternGeco for provision of Q-streamer data.

  5. Zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotopes from the metamorphic basement in the Wuhe Complex: Implications for Neoarchean active continental margin along the southeastern North China Craton and constraints on the petrogenesis of Mesozoic granitoids

    Directory of Open Access Journals (Sweden)

    Andong Wang

    2013-01-01

    Full Text Available We report zircon U-Pb geochronology, geochemistry and Sr-Nd-Pb isotope data from mafic granulites and garnet amphibolites of the Wuhe Complex in the southeastern margin of the North China Craton (NCC. In combination with previous data, our results demonstrate that these rocks represent fragments of the ancient lower crust, and have features similar to those of the granulite basement in the northern margin of the NCC. A detailed evaluation of the Pb isotope data shows that Pb isotopes cannot effectively distinguish the role of the Yangtze Craton basement from that of the NCC basement with regard to the source and generation of magmas, at least for southeastern NCC. The age data suggest that the protoliths of the granulites or amphibolites in the Wuhe Complex were most likely generated in Neoarchean and that these rocks were subjected to Paleoproterozoic (1.8–1.9 Ga high-pressure granulite facies metamorphism. This study also shows that the Precambrian metamorphic basement in the southeastern margin of the NCC might have formed in a tectonic setting characterized by a late Neoarchean active continental margin.

  6. Evolution of the South Atlantic passive continental margin and lithosphere dynamic movement in Southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

    Science.gov (United States)

    Krob, Florian; Stippich, Christian; Glasmacher, Ulrich A.; Hackspacher, Peter C.

    2016-04-01

    Passive continental margins are important geoarchives related to mantle dynamics, the breakup of continents, lithospheric dynamics, and other processes. The main concern yields the quantifying long-term lithospheric evolution of the continental margin between São Paulo and Laguna in southeastern Brazil since the Neoproterozoic. We put special emphasis on the reactivation of old fracture zones running into the continent and their constrains on the landscape evolution. In this contribution, we represent already consisting thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons. The zircon fission-track ages range between 108.4 (15.0) and 539.9 (68.4) Ma, the zircon (U-Th-Sm)/He ages between 72.9 (5.8) and 427.6 (1.8) Ma whereas the apatite fission-track ages range between 40.0 (5.3) and 134.7 (8.0) Ma, and the apatite (U-Th-Sm)/He ages between 32.1 (1.52) and 92.0 (1.86) Ma. These thermochronological ages from metamorphic, sedimentary and intrusive rocks show six distinct blocks (Laguna, Florianópolis, Curitiba, Ilha Comprida, Peruibe and Santos) with different evolution cut by old fracture zones. Furthermore, models of time-temperature evolution illustrate the differences in Pre- to post-rift exhumation histories of these blocks. The presented data will provide an insight into the complex exhumation history of the continental margin based on the existing literature data on the evolution of the Paraná basin in Brazil and the latest thermochronological data. We used the geological model of the Paraná basin supersequences (Rio Ivaí, Paraná, Gondwana I-III and Bauru) to remodel the subsidence and exhumation history of our consisting thermochronological sample data. First indications include a fast exhumation during the early Paleozoic, a slow shallow (northern blocks) to fast and deep (Laguna block) subduction from middle Paleozoic to Mesozoic time and a extremely fast exhumation during the opening of the South Atlantic

  7. Submarine mass movements around the Iberian Peninsula. The building of continental margins through hazardous processes; Inestabilidades sedimentarias submarinas alrededor de la Peninsula Iberica. Construccion de margenes a traves de procesos peligrosos

    Energy Technology Data Exchange (ETDEWEB)

    Casas, D.; Casalbore, D.; Yenes, M.; Urgeles, R.

    2015-07-01

    Submarine mass movements, such as those which occur in all environments in every ocean of the world, are widely distributed across the Iberian continental margins. A lack of consistent data from various areas around the Iberian Peninsula makes it difficult to precisely understand their role in the sedimentary record. However, all the studies carried out over the past two decades reveal that they are a recurrent and widespread sedi- mentary process that may represent a significant geohazard. The majority of submarine mass movements observed in both the Mediterranean and Atlantic margins of the Iberian Peninsula have been generically identified as Mass Transport Deposits, but debris flows, slides, slumps and turbidites are common. Only a few remarkable examples involve huge volumes of sediment covering large areas (such as ∼500 km{sup 3} and ∼6x10{sup 4} km{sup 2}), but more moderate deposits (<200 km{sup 2}) are frequently found on the seafloor or embedded in the sedi- mentary sequences, building margins and basins. (Author)

  8. How does continental lithosphere break-apart? A 3D seismic view on the transition from magma-poor rifted margin to magmatic oceanic lithosphere

    Science.gov (United States)

    Emmanuel, M.; Lescanne, M.; Picazo, S.; Tomasi, S.

    2017-12-01

    In the last decade, high-quality seismic data and drilling results drastically challenged our ideas about how continents break apart. New models address their observed variability and are presently redefining basics of rifting as well as exploration potential along deepwater rifted margins. Seafloor spreading is even more constrained by decades of scientific exploration along Mid Oceanic Ridges. By contrast, the transition between rifting and drifting remains a debated subject. This lithospheric breakup "event" is geologically recorded along Ocean-Continent Transitions (OCT) at the most distal part of margins before indubitable oceanic crust. Often lying along ultra-deepwater margin domains and buried beneath a thick sedimentary pile, high-quality images of these domains are rare but mandatory to get strong insights on the processes responsible for lithospheric break up and what are the consequences for the overlying basins. We intend to answer these questions by studying a world-class 3D seismic survey in a segment of a rifted margin exposed in the Atlantic. Through these data, we can show in details the OCT architecture between a magma-poor hyper-extended margin (with exhumed mantle) and a classical layered oceanic crust. It is characterized by 1- the development of out-of-sequence detachment systems with a landward-dipping geometry and 2- the increasing magmatic additions oceanwards (intrusives and extrusives). Geometry of these faults suggests that they may be decoupled at a mantle brittle-ductile interface what may be an indicator on thermicity. Furthermore, magmatism increases as deformation migrates to the future first indubitable oceanic crust what controls a progressive magmatic crustal thickening below, above and across a tapering rest of margin. As the magmatic budget increases oceanwards, full-rate divergence is less and less accommodated by faulting. Magmatic-sedimentary architectures of OCT is therefore changing from supra-detachment to magmatic

  9. Mastritherium (Artiodactyla, Anthracotheriidae) from Wadi Sabya, southwestern Saudi Arabia; an earliest Miocene age for continental rift-valley volcanic deposits of the Red Sea margin

    Science.gov (United States)

    Madden, Gary T.; Schmidt, Dwight Lyman; Whitmore, Frank C.

    1983-01-01

    A lower jaw fragment with its last molar (M/3) from the Baid formation in Wadi Sabya, southwestern Saudi Arabia, represents the first recorded occurrence in the Arabian Peninsula of an anthracotheriid artiodactyl (hippo-like, even-toed ungulate). This fossil is identified as a primitive species of Masritherium, a North and East African genus restricted, previously to the later early Miocene. This identification indicates that the age of the Baid formation, long problematical, is early Miocene and, moreover, shows that the age of the fossil site is earliest Miocene (from 25 to 21Ma). The Wadi Sabya anthracothere is the first species of fossil mammal recorded from western Saudi Arabia, and more important, it indicates an early Miocene age for the volcanic deposits of a continental rift-valley that preceded the initial sea-floor spreading of the Red Sea.

  10. Crustal structure and sedimentation history over the Alleppey platform, southwest continental margin of India: Constraints from multichannel seismic and gravity data

    Directory of Open Access Journals (Sweden)

    P. Unnikrishnan

    2018-03-01

    Full Text Available The Alleppey Platform is an important morphological feature located in the Kerala-Konkan basin off the southwest coast of India. In the present study, seismic reflection data available in the basin were used to understand the sedimentation history and also to carry out integrated gravity interpretation. Detailed seismic reflection data in the basin reveals that: (1 the Alleppey Platform is associated with a basement high in the west of its present-day geometry (as observed in the time-structure map of the Trap Top (K/T boundary, (2 the platform subsequently started developing during the Eocene period and attained the present geometry by the Miocene and, (3 both the Alleppey platform and the Vishnu fracture zone have had significant impact on the sedimentation patterns (as shown by the time-structure and the isochron maps of the major sedimentary horizons in the region. The 3-D sediment gravity effect computed from the sedimentary layer geometry was used to construct the crustal Bouguer anomaly map of the region. The 3-D gravity inversion of crustal Bouguer anomaly exhibits a Moho depression below the western border of the platform and a minor rise towards the east which then deepens again below the Indian shield. The 2-D gravity modelling across the Alleppey platform reveals the geometry of crustal extension, in which there are patches of thin and thick crust. The Vishnu Fracture Zone appears as a crustal-scale feature at the western boundary of the Alleppey platform. Based on the gravity model and the seismic reflection data, we suggest that the basement high to the west of the present day Alleppey platform remained as a piece of continental block very close to the mainland with the intervening depression filling up with sediments during the rifting. In order to place the Alleppey platform in the overall perspective of tectonic evolution of the Kerala-Konkan basin, we propose its candidature as a continental fragment.

  11. Determination of the Anthropogenic Carbon Signal to the Total Change in Dissolved Carbon in the Coastal Upwelling Region Along the Washington-Oregon-California Continental Margin

    Science.gov (United States)

    Feely, R. A.

    2016-02-01

    The continental shelf region off the Washington-Oregon-California coast is seasonally exposed to water with a low aragonite saturation state by coastal upwelling of CO2-rich waters. To date, the spatial and temporal distribution of anthropogenic CO2 (Canthro) contribution to the CO2-rich waters is largely unknown. Here we use an adaptation of the linear regression approach described in Feely et al (2008) along with the GO-SHIP Repeat Hydrography data sets from the northeast Pacific to establish an annually updated relationship between Canthro and potential density. This relationship was then used with the NOAA Ocean Acidification Program west coast cruise data sets from 2007, 2011, 2012 and 2013 to determine the spatial variations of Canthro in the upwelled water. Our results show large spatial differences in Canthro in surface waters along the coast with the lowest surface values (40-45 µmol kg-1) in strong upwelling regions of off northern California and southern Oregon and higher values (50-70 µmol kg-1) to the north and south. Canthro contributes an average of about 70% of the increased amount of dissolved inorganic carbon in the upwelled waters at the surface. In contrast, at 50 m the Canthro contribution is approximately 31% and at 100 m it averages about 16%. The remaining contributions are primarily due to respiration processes in the water that was upwelled and transported to coastal regions or underwent respiration processes that occurred locally during the course of the upwelling season. The uptake of Canthro has caused the aragonite saturation horizon to shoal by approximately 30-50 m since preindustrial period so that the undersaturated waters are well within the regions that affect the biological communities on the continental shelf.

  12. Assessment of canyon wall failure process from multibeam bathymetry and Remotely Operated Vehicle (ROV) observations, U.S. Atlantic continental margin: Chapter 10 in Submarine mass movements and their consequences: 7th international symposium part II

    Science.gov (United States)

    Chaytor, Jason D.; Demopoulos, Amanda W. J.; ten Brink, Uri S.; Baxter, Christopher D. P.; Quattrini, Andrea M.; Brothers, Daniel S.; Lamarche, Geoffroy; Mountjoy, Joshu; Bull, Suzanne; Hubble, Tom; Krastel, Sebastian; Lane, Emily; Micallef, Aaron; Moscardelli, Lorena; Mueller, Christof; Pecher, Ingo; Woelz, Susanne

    2016-01-01

    Over the last few years, canyons along the northern U.S. Atlantic continental margin have been the focus of intensive research examining canyon evolution, submarine geohazards, benthic ecology and deep-sea coral habitat. New high-resolution multibeam bathymetry and Remotely Operated Vehicle (ROV) dives in the major shelf-breaching and minor slope canyons, provided the opportunity to investigate the size of, and processes responsible for, canyon wall failures. The canyons cut through thick Late Cretaceous to Recent mixed siliciclastic and carbonate-rich lithologies which impart a primary control on the style of failures observed. Broad-scale canyon morphology across much of the margin can be correlated to the exposed lithology. Near vertical walls, sedimented benches, talus slopes, and canyon floor debris aprons were present in most canyons. The extent of these features depends on canyon wall cohesion and level of internal fracturing, and resistance to biological and chemical erosion. Evidence of brittle failure over different spatial and temporal scales, physical abrasion by downslope moving flows, and bioerosion, in the form of burrows and surficial scrape marks provide insight into the modification processes active in these canyons. The presence of sessile fauna, including long-lived, slow growing corals and sponges, on canyon walls, especially those affected by failure provide a critical, but as yet, poorly understood chronological record of geologic processes within these systems.

  13. Aspects of the distribution, population structure and reproduction of the gastropod Tibia delicatula (Nevill, 1881) inhabiting the oxygen minimum zone of the Oman and Pakistan continental margins

    Science.gov (United States)

    Ramirez-Llodra, Eva; Olabarria, Celia

    2005-11-01

    The present study describes some aspects of the distribution and biology of Tibia delicatula (Nevill), a gastropod belonging to the family Strombidae. This species has been found in large numbers in the upper oxygen minimum zone (OMZ) of the Oman margin, and has also been collected from the OMZ of the Pakistan margin. The highest abundance of adult specimens in the Oman OMZ was found between 300 and 450 m. Numbers dropped rapidly below 450 m, to zero below 500 m depth. Similarly dense populations were not observed in the Pakistan OMZ. Multiple regression with oxygen concentration and depth indicates that depth (and its related variables) is the main factor explaining the variation in abundance of T. delicatula. The populations from the Oman and Pakistan OMZs were dominated by juveniles. This suggests a unimodal size structure with evidence of a marked recruitment event. Basic reproductive aspects were analysed. All specimens had a penis and sperm groove. The gonad wall consisted of reticular tissue that might be used for nutrient storage or as an irrigation system. Only vitellogenic oocytes were present. The large oocyte sizes observed (200-300 μm) suggest a lecithotrophic larval development.

  14. Distribution and transport of particle-bound polycyclic aromatic hydrocarbons in a river-influenced continental margin: the northern Gulf of Mexico

    Science.gov (United States)

    Adhikari, P. L.; Maiti, K.

    2017-12-01

    Polycyclic aromatic hydrocarbons (PAHs) are particle-reactive and get preferentially sorbed on particulate organic carbon (POC), thus, the transport and fate of POC in aquatic systems plays an important role in biogeochemical cycling of PAHs. In this study, we examine POC and PAHs in finer suspended particulate matter collected from the Louisiana coast, shelf and slope - progressively south-west transect along the direction of the Mississippi River plume, and also from a transect of Atchafalaya River. The concentrations of total particulate PAHs (ΣPAH43) varied between 0.92 to 7.04 ng/L, while POC varied between 4 to 131 µg/L. The concentrations of total particulate ΣPAH43 as well as individual PAH analytes were significantly positively correlated to the concentrations of POC which indicates that the concentrations and transport of POC plays an important role in distribution of PAHs in marine systems. The river influence, characterized by the change in salinity, had significant negative correlation with both the concentrations of particulate PAHs and POC. These results show that the Mississippi River derived particle influx can be an important vector in delivering particle-reactive hydrophobic organic pollutants such as PAHs into the river dominated continental ecosystems in the northern Gulf of Mexico. The underlying seafloor sediment PAHs' concentration and accumulation rates were not correlated to the water column particulate PAH and POC concentrations, which is attributed to re-mineralization during vertical transport, sediment resuspension/redistribution and different timescales of comparison.

  15. Southernmost evidence of large European Ice Sheet-derived freshwater discharges during the Heinrich Stadials of the Last Glacial Period (Galician Interior Basin, Northwest Iberian Continental Margin)

    Science.gov (United States)

    Plaza-Morlote, M.; Rey, D.; Santos, J. F.; Ribeiro, S.; Heslop, D.; Bernabeu, A.; Mohamed, K. J.; Rubio, B.; Martíns, V.

    2017-01-01

    Reconstruction of circum-Atlantic ice-sheet motion and instabilities is crucial to understanding the mechanisms that triggered and/or enhanced abrupt climate changes. Using enviromagnetic and geochemical data, we provide a continuous and well-dated record of the evolution of glacial/interglacial sedimentation on the Northwest Iberian Margin during the last glacial period, covering the last six Heinrich Stadials. The record shows European sediments that were related to meltwater pre-events during the initial stages of HS1, HS2, and HS4 that corroborate the Channel River depositional history. The record also includes IRD from the Laurentide Ice Sheet and the European Ice Sheet during the final stages of these stadials, i.e., Heinrich Events. Therefore, this study provides insight into one of the potential forcing mechanisms for Heinrich Events and, by inference, for Heinrich Stadials.

  16. Preservación y abundancia de escamas de peces en sedimentos del margen continental de Chile (21-36° S Fish scale preservation and abundance in sediments from the continental margin off Chile (21-36° S

    Directory of Open Access Journals (Sweden)

    JAVIER A DÍAZ-OCHOA

    2008-12-01

    Full Text Available Con el objetivo de evaluar la relación entre la preservación de escamas de peces y las variaciones en las condiciones redox en sedimentos del margen continental de Chile, este trabajo presenta recuentos de escamas de peces y concentraciones normalizadas de elementos redox sensibles (Mo/Al, S/Al, Fe/Al en ocho testigos de sedimento recolectados en la zona de minimo oxígeno frente a Chile (Iquique: 20°15' S, bahía de Mejillones: 23° S y Concepción: 36° S. En el norte de Chile (Iquique y Mejillones predominan las escamas de anchoveta (Engraulis ringens y de peces de la familia Myctophidae (media = 90 y 120 escamas 1.000 cm-3, respectivamente mientras que en Chile centro-sur (Concepción son más abundantes las escamas de jurel (Trachurus murphy; media = 140 escamas 1.000 cm-3. La abundancia de escamas de merluza común (Merluccius gayi gayi y de sardina (Sardinops sagax es aproximadamente un orden de magnitud más baja que la de anchoveta o jurel. En general, los valores más altos y los rangos más amplios de variación en las razones Mo/Al, S/Al y Fe/Al se encuentran en Mejillones (Mo/Al ~0,8-12 mg g-1, S/Al 0,2-4,6 g g-1, Fe/Al 0,3-0,7 g g-1 seguidos por Iquique (Mo/Al -0,2-1,8; S/Al 0,2-0,7, Fe/Al 0,5-0,8, mientras que Concepción revela valores más bajos y poco variables (Mo/Al ~0,07, S/Al ~0,15 y Fe/Al ~0,5. La razón Mo/Al, utilizada como indicador de paleo-oxigenación, permite inferir condiciones reductoras relativamente más intensas en los sedimentos de la Bahía de Mejillones e Iquique que en Concepción. En las tres localidades de muestreo se evidencia una asociación estadísticamente significativa entre la abundancia de escamas de anchoveta y el logaritmo de la razón Mo/Al (r²= 0,46; P 1 mg g-1.The relationship between fish scale preservation and variations in the sediment redox conditions on Chile's continental shelf are evaluated herein through fish scale counts and normalized concentrations of redox sensitive elements

  17. Techniques for the non-destructive and continuous analysis of sediment cores. Application in the Iberian continental margin; Tecnicas para el analisis no destructivo y en continuo de testigos de sedimento. Aplicacion en el Margen Continental de Iberia

    Energy Technology Data Exchange (ETDEWEB)

    Frigola, J.; Canals, M.; Mata, P.

    2015-07-01

    Sediment sequences are the most valuable record of long-term environmental conditions at local, regional and/or global scales. Consequently, they are amongst the best archives of the climatic and oceanographic his- tory of the Earth. In the last few decades a strong effort has been made, both in terms of quantity and quality, to improve our knowledge regarding the evolution of our planet from marine and lake sediment records, and also from other records such as ice cores. Such an effort requires reinforcing the geographical coverage and achieving the highest possible robustness in the reconstruction of past environments. Such a target requires the optimization of the time resolution of the records and reconstructions so that fast, high frequency shifts, such as those occurring nowadays due to the on-going global warming, can be disentangled. Beyond paleoenvironmental research, other disciplines have also contributed significantly to the fast growing number of sediment cores already available worldwide. Knowing the physical state and the chemical composition of sedimentary deposits is essential for land management purposes and for many industrial applications. A number of key technological developments are now allowing the acquisition for the first time of massive amounts of multiple parameters from sediment cores in a non-destructive, fast, continuous, repetitive and high-resolution form. In this paper we provide an overview of the state-of-the-art continuous and non-destructive analytical techniques used by the geo scientific community for the study of sediment cores and we present some examples of the application of these methods in several studies carried out around the Iberian Margin. (Author)

  18. Imaging continental shelf shallow stratigraphy by using different high-resolution seismic sources: an example from the Calabro-Tyrrhenian margin (Mediterranean Sea

    Directory of Open Access Journals (Sweden)

    Eleonora Martorelli

    2010-01-01

    Full Text Available High-resolution seismic reflection profiles of the Calabro-Tyrrhenian continental shelf were collected using different seismic sources (Sub-Bottom Profiler, Uniboom, Sparker 0.5-1-4.5 kJ. Noticeable differences and results were obtained both from a geophysical and geological-interpretative point of view. The availability of different sources permitted the definition of the most suitable seismostratigraphic characterization in terms of resolution, penetration and acoustic facies. Very high resolution stratigraphy was defined through profiles produced by different seismic systems used in parallel. This permitted the application of sequence-stratigraphy concepts with the reconstruction of a thick postglacial depositional sequence, formed by a transgressive and a high-stand systems tract. The thickness distribution of postglacial deposits reveals that the main depocenter (55-65 m is located offshore of the Coastal Range, along a stretch of coast supplied by several small and seasonal streams ("fiumare" and characterized by the lack of a coastal plain. This suggests the greater efficiency of sediment supply and bypass in this area relatively to sectors located offshore of the main rivers. The transgressive systems tract, usually thin or nearly absent, is particularly well developed (up to 33 m and is composed of up to three parasequences with a retrogradational stacking pattern. The high-stand systems tract, up to 30 m thick, is made up of two parasequences and has a quite regular geometry and acoustic facies.Perfis de reflexão sísmica de alta resolução da plataforma continental tirreniana de Calabro foram obtidos utilizando-se recursos sísmicos diversos (Perfilador de Sub-superfície, Uniboom, Sparker 0.5-1-4.5 kJ. Diferenças evidentes foram encontradas sob o ponto de vista geofísico e geológico-interpretativo. A disponibilidade de diferentes fontes permitiu a definição de uma caracterização sismo-estratigráfica mais acurada em termos

  19. Geochemical evidence for enhanced preservation of organic matter in the oxygen minimum zone of the continental margin of northern California during the Late Pleistocene

    Science.gov (United States)

    Dean, Walter E.; Gardner, James V.; Anderson, Roger Y.

    1994-01-01

    The present upper water mass of the northeastern Pacific Ocean off California has a well-developed oxygen minimum zone between 600 and 1200 m wherein concentrations of dissolved oxygen are less than 0.5 mL/L. Even at such low concentrations of dissolved oxygen, benthic burrowing organisms are abundant enough to thoroughly bioturbate the surface and near-surface sediments. These macro organisms, together with micro organisms, also consume large quantities of organic carbon produced by large seasonal stocks of plankton in the overlying surface waters, which are supported by high concentrations of nutrients within the California Current upwelling system. In contrast to modern conditions of bioturbation, laminated sediments are preserved in upper Pleistocene sections of cores collected on the continental slope at water depths within the present oxygen minimum zone from at least as far north as the California-Oregon border and as far south as Point Conception. Comparison of sediment components in the laminae with those delivered to sediment traps as pelagic marine “snow” demonstrates that the dark-light lamination couplets are indeed annual (varves). These upper Pleistocene varved sediments contain more abundant lipid-rich “sapropelic” (type II) organic matter than the overlying bioturbated, oxidized Holocene sediments. The baseline of stable carbon isotopic composition of the organic matter in these slope cores does not change with time, indicating that the higher concentrations of type II organic matter in the varved sediments represent better preservation of organic matter rather than any change in the source of organic matter.

  20. NOAA Office of Ocean Exploration and Research'sOkeanos Explorer Program 2014 Discoveries - U.S. Atlantic Continental Margin and Gulf of Mexico

    Science.gov (United States)

    Lobecker, E.; McKenna, L.; Sowers, D.; Elliott, K.; Kennedy, B.

    2014-12-01

    NOAA ShipOkeanos Explorer, the only U.S. federal vessel dedicated to global ocean exploration, made several important discoveries in U.S. waters of the North Atlantic Ocean and Gulf of Mexico during the 2014 field season. Based on input received from a broad group ofmarine scientists and resource managers, over 100,000 square kilometers of seafloor and associated water column were systematically explored using advanced mapping sonars. 39 ROV diveswere conducted, leading to new discoveries that will further ourunderstanding of biologic, geologic, and underwater-cultural heritage secrets hidden withinthe oceans. In the Atlantic, season highlights include completion of a multi-year submarine canyons mapping effort of the continental shelf break from North Carolina to the U.S.-Canada maritime border;new information on the ephemerality of recently discovered and geographically extensive cold water seeps; and continued exploration of the New England Seamount chain; and mapping of two potential historically significant World War II wreck sites. In the Gulf of Mexico, season highlights includecompletion of a multi-year mapping effort of the West Florida Escarpment providing new insight into submarine landslides and detachment zones;the discovery of at least two asphalt volcanoes, or 'tar lilies'; range extensions of deep-sea corals; discovery of two potential new species of crinoids; identification of at least 300 potential cold water seeps; and ROV exploration of three historically significant19th century shipwrecks. In both regions, high-resolution mapping led to new insight into the geological context in which deep sea corals develop,while ROV dives provided valuable observations of deep sea coral habitats and their associated organisms, and chemosynthetic habitats. All mapping and ROV data is freely available to the public in usable data formats and maintained in national geophysical and oceanographic data archives.

  1. Continental weathering as a driver of Late Cretaceous cooling: new insights from clay mineralogy of Campanian sediments from the southern Tethyan margin to the Boreal realm

    Science.gov (United States)

    Chenot, Elise; Deconinck, Jean-François; Pucéat, Emmanuelle; Pellenard, Pierre; Guiraud, Michel; Jaubert, Maxime; Jarvis, Ian; Thibault, Nicolas; Cocquerez, Théophile; Bruneau, Ludovic; Razmjooei, Mohammad J.; Boussaha, Myriam; Richard, James; Sizun, Jean-Pierre; Stemmerik, Lars

    2018-03-01

    New clay mineralogical analyses have been performed on Campanian sediments from the Tethyan and Boreal realms along a palaeolatitudinal transect from 45° to 20°N (Danish Basin, North Sea, Paris Basin, Mons Basin, Aquitaine Basin, Umbria-Marche Basin and Tunisian Atlas). Significant terrigenous inputs are evidenced by increasing proportions of detrital clay minerals such as illite, kaolinite and chlorite at various levels in the mid- to upper Campanian, while smectitic minerals predominate and represented the background of the Late Cretaceous clay sedimentation. Our new results highlight a distinct latitudinal distribution of clay minerals, with the occurrence of kaolinite in southern sections and an almost total absence of this mineral in northern areas. This latitudinal trend points to an at least partial climatic control on clay mineral sedimentation, with a humid zone developed between 20° and 35°N. The association and co-evolution of illite, chlorite and kaolinite in most sections suggest a reworking of these minerals from basement rocks weathered by hydrolysis, which we link to the formation of relief around the Tethys due to compression associated with incipient Tethyan closure. Diachronism in the occurrence of detrital minerals between sections, with detrital input starting earlier during the Santonian in the south than in the north, highlights the northward progression of the deformation related to the anticlockwise rotation of Africa. Increasing continental weathering and erosion, evidenced by our clay mineralogical data through the Campanian, may have resulted in enhanced CO2 consumption by silicate weathering, thereby contributing to Late Cretaceous climatic cooling.

  2. Crustal structure and inferred extension mode in the northern margin of the South China Sea

    Science.gov (United States)

    Gao, J.; Wu, S.; McIntosh, K. D.; Mi, L.; Spence, G.

    2016-12-01

    Combining multi-channel seismic reflection and satellite gravity data, this study has investigated the crustal structure and magmatic activities of the northern South China Sea (SCS) margin. Results show that a broad continent-ocean transition zone (COT) with more than 140 km wide is characterized by extensive igneous intrusion/extrusion and hyper-extended continental crust in the northeastern SCS margin, a broader COT with 220-265 km wide is characterized by crustal thinning, rift depression, structural highs with igneous rock and perhaps a volcanic zone or a zone of tilted fault blocks at the distal edge in the mid-northern SCS margin, and a narrow COT with 65 km wide bounded seawards by a volcanic buried seamount is characterized by extremely hyper-extended continental crust in the northwestern SCS margin, where the remnant crust with less than 3 km thick is bounded by basin-bounding faults corresponding to an aborted rift below the Xisha Trough with a sub-parallel fossil ridge in the adjacent Northwest Sub-basin. Results from gravity modeling and seismic refraction data show that a high velocity layer (HVL) is present in the outer shelf and slope below extended continental crust in the eastern portion of the northern SCS margin and is thickest (up to 10 km) in the Dongsha Uplift where the HVL gradually thins to east and west below the lower slope and finally terminates at the Manila Trench and Baiyun sag of the Pearl River Mouth Basin. The magmatic intrusions/extrusions and HVL may be related to partial melting caused by decompression of passive, upwelling asthenosphere which resulted primarily in post-rifting underplating and magmatic emplacement or modification of the crust. The northern SCS margin is closer to those of the magma-poor margins than those of volcanic margins, but the aborted rift near the northwestern continental margin shows that there may be no obvious detachment fault like that in the Iberia-Newfoundland type margin. The symmetric aborted

  3. Postcollisional mafic igneous rocks record crust-mantle interaction during continental deep subduction.

    Science.gov (United States)

    Zhao, Zi-Fu; Dai, Li-Qun; Zheng, Yong-Fei

    2013-12-04

    Findings of coesite and microdiamond in metamorphic rocks of supracrustal protolith led to the recognition of continental subduction to mantle depths. The crust-mantle interaction is expected to take place during subduction of the continental crust beneath the subcontinental lithospheric mantle wedge. This is recorded by postcollisional mafic igneous rocks in the Dabie-Sulu orogenic belt and its adjacent continental margin in the North China Block. These rocks exhibit the geochemical inheritance of whole-rock trace elements and Sr-Nd-Pb isotopes as well as zircon U-Pb ages and Hf-O isotopes from felsic melts derived from the subducted continental crust. Reaction of such melts with the overlying wedge peridotite would transfer the crustal signatures to the mantle sources for postcollisional mafic magmatism. Therefore, postcollisonal mafic igneous rocks above continental subduction zones are an analog to arc volcanics above oceanic subduction zones, providing an additional laboratory for the study of crust-mantle interaction at convergent plate margins.

  4. Modelling continental deformation within global plate tectonic reconstructions

    Science.gov (United States)

    Williams, S.; Whittaker, J.; Heine, C.; Müller, P.

    2010-12-01

    A limitation of regional and global plate tectonic models is the way continental deformation is represented. Continental blocks are typically represented as rigid polygons - overlaps or gaps between adjacent continental blocks represent extension or compression respectively. Full-fit reconstructions of major ocean basins result in large overlaps between the conjugate continental plates, on the basis that the continental margins are highly extended compared to their pre-rift state. A fundamental challenge in generating more robust global-scale plate reconstructions is the incorporation of a more quantitative description of the kinematics within extended passive margins, based on observations. We have used the conjugate Southern Australia and Wilkes Land, Antarctica margins as a case study, and as part of this work have generated revised sediment thickness maps for these margins. These datasets are used to test different approaches for generating full-fit reconstructions in order to create a framework of methodologies that is globally applicable. One approach is to restore two conjugate continent-ocean boundaries (COBs) to their pre-rift configuration and then use the geometric fitting method of Hellinger (1981) and Royer and Chang (1991), used to generate fits of seafloor isochrons, to generate a “full-fit” Euler pole. To quantitatively restore the COBs to their palinspastic pre-rift configuration we integrate estimates of crustal thickness along small circle paths, defined by an initial estimate of the Euler stage pole describing plate motions during continental rifting. We then use the conjugate sets of restored COB’s as inputs to the geometric fitting method, treating them as isochrons, and so generate poles of rotation for the plate configuration prior to rifting. Two potential shortcomings of this methodology are that (1) the conjugate margins are treated independently, whereas in reality they were actually one continuous continental basin during rifting

  5. Retrospective of fossil dinoflagellate studies in Brazil: their relationship with the evolution of petroleum exploration in the Cretaceous of continental margin basins; Historico do estudo de dinoflagelados fosseis no Brasil: sua relacao com a evolucao da exploracao petrolifera no Cretaceo das bacias da margem continental

    Energy Technology Data Exchange (ETDEWEB)

    Arai, Mitsuru; Lana, Cecilia Cunha [PETROBRAS, Rio de Janeiro, RJ (Brazil). Centro de Pesquisas. Gerencia de Bioestratigrafia e Paleoecologia]. E-mail: arai@cenpes.petrobras.com.br

    2004-05-01

    Palynostratigraphy of the Brazilian Cretaceous was mainly based on terrestrial palynomorphs (mostly spores and pollen grains) until the end of the nineteen eighties. This was so because, for several decades, petroleum exploration in Brazil was focused on the essentially non marine sediments of the Reconcavo Basin. During the nineteen sixties, PETROBRAS extended oil exploration to the Brazilian continental shelf (offshore areas). Nevertheless, at that time the company did not invest immediately in marine palynostratigraphy, because it was believed that bio stratigraphic schemes based on foraminifera and calcareous nanno fossils would be more efficient than palynology in marine sequences. This belief changed only in the seventies, when commercial oil reservoirs were discovered in the Campos Basin, within the Macae Formation, a rock unit deposited in a carbonate shelf environment. Its environmental conditions were certainly hostile to the development and post-mortem preservation of foraminifera and calcareous nanno fossil-producing algae. As a result, no more than two or three bio zones could be identified in the Macae carbonate section on the basis of such organisms. Besides, carbonate shelf sediments, subject to only minor terrigenous input, are usually poor in terrestrial palynomorphs. On the other hand, the palynological content of some Macae strata consists mainly (up to 100%) of such marine palynomorphs as dino flagellates, acritarchs e palynoforaminifera. Consequently, PETROBRAS recognized the importance of developing a zonal framework based on these organisms. The first Cretaceous dinoflagellate zonation in Brazil was erected in 1976, and since the nineteen eighties, marine Cretaceous palynostratigraphy has made significant advances mainly due to the use of dino flagellates. Hundreds of Cretaceous dinoflagellate index species have been introduced into PETROBRAS databanks, becoming widely applicable to the bio stratigraphy of all Brazilian continental margin

  6. Study of the particulate matter transfer and dumping using 210 Po et le 210 Pb. Application to the Gulf of Biscary (NE Atlantic Ocean) and the Gulf of Lion (NW Mediterranean Sea) continental margins

    International Nuclear Information System (INIS)

    Radakovitch, O.

    1995-01-01

    210 Po and 210 Pb activities and fluxes were measured on seawater, sediment-trapped material collected during one year and sediment. Focalization of 210 Pb is clearly noticed on the Cap-Ferret canyon (Gulf of Biscary) and the Lacaze-Duthiers canyon (western part of the Gulf of Lion). In both sites, 210 Pb fluxes in traps and sediment are always higher than 210 Pb flux available from atmospheric and in situ production. On the contrary, Grand-Rhone canyon and its adjacent open slope exhibit a 210 Pb budget near equilibrium in the near-bottom sediment traps, but focalization is important in the sediment. For the entire Gulf of Lion margin, focalization of 210 Pb in the sediment occurred principally between 500 and 1500 m water depth on the slope, and on the middle shelf mud-patch. 210 Po and 210 Pb have been used in the Cap Ferret and Grand-Rhone canyons to characterize the origin of the particulate trapped material. Two main sources feed the water column. The first source, localized in surface waters, is constituted by biogenic particles from primary production and lithogenic material. The second source, deeper, is due to resuspension at the shelf break and/or on the open slope. In each site, 210 Po and 210 Pb activities of the trapped particles did not show any relations with the major constituents. Quantity of particles appeared to be the main factor regulating adsorption processes of these nuclides. Sedimentation rates based on 210 Po profiles decreased with increasing water depth, from 0.4 ti 0.06 cm y-1 on the Cap Ferret canyon (400 to 3000 m water depth) and from 0.5 to 0.05 cm y-1 for the entire Gulf of Lion margin (50 to 2000 m water depth). (author)

  7. Real-Time PCR Quantification and Diversity Analysis of the Functional Genes aprA and dsrA of Sulfate-Reducing Prokaryotes in Marine Sediments of the Peru Continental Margin and the Black Sea.

    Science.gov (United States)

    Blazejak, Anna; Schippers, Axel

    2011-01-01

    Sulfate-reducing prokaryotes (SRP) are ubiquitous and quantitatively important members in many ecosystems, especially in marine sediments. However their abundance and diversity in subsurface marine sediments is poorly understood. In this study, the abundance and diversity of the functional genes for the enzymes adenosine 5'-phosphosulfate reductase (aprA) and dissimilatory sulfite reductase (dsrA) of SRP in marine sediments of the Peru continental margin and the Black Sea were analyzed, including samples from the deep biosphere (ODP site 1227). For aprA quantification a Q-PCR assay was designed and evaluated. Depth profiles of the aprA and dsrA copy numbers were almost equal for all sites. Gene copy numbers decreased concomitantly with depth from around 10(8)/g sediment close to the sediment surface to less than 10(5)/g sediment at 5 mbsf. The 16S rRNA gene copy numbers of total bacteria were much higher than those of the functional genes at all sediment depths and used to calculate the proportion of SRP to the total Bacteria. The aprA and dsrA copy numbers comprised in average 0.5-1% of the 16S rRNA gene copy numbers of total bacteria in the sediments up to a depth of ca. 40 mbsf. In the zone without detectable sulfate in the pore water from about 40-121 mbsf (Peru margin ODP site 1227), only dsrA (but not aprA) was detected with copy numbers of less than 10(4)/g sediment, comprising ca. 14% of the 16S rRNA gene copy numbers of total bacteria. In this zone, sulfate might be provided for SRP by anaerobic sulfide oxidation. Clone libraries of aprA showed that all isolated sequences originate from SRP showing a close relationship to aprA of characterized species or form a new cluster with only distant relation to aprA of isolated SRP. For dsrA a high diversity was detected, even up to 121 m sediment depth in the deep biosphere.

  8. Transfer/transform relationships in continental rifts and margins and their control on syn- and post-rift denudation: the case of the southeastern Gulf of Aden, Socotra Island, Yemen

    Science.gov (United States)

    Pik, Raphael; Bellahsen, Nicolas; Leroy, Sylvie; Denele, Yoann; Razin, Philippe; Ahmed, Abdulhakim; Khanbari, Khaled

    2013-04-01

    Transfer zones are ubiquist features in continental rifts and margins, as well as transform faults in oceanic lithosphere. Here, we present the structural study of such a structure (the Hadibo Transfer Zone, HTZ) from the southeastern Gulf of Aden, in Socotra Island, Yemen. There, from field data, the HTZ is interpreted as being reactivated, obliquely to divergence, since early rifting stages. Then, from a short review of transfer/transform fault zone geometries worldwide, we derive a classification in terms of relative importance (1st, 2nd, 3rd order), geometry, and location. We suggest that the HTZ is a 1st order transfer fault zone as it controls the initiation of a 1st order oceanic transform fault zone. We then investigate the denudation history of the region surrounding the HTZ in order to highlight the interplay of normal and transfer/transform tectonic structures in the course of rift evolution. Samples belong from two distinct East and West domains of the Socotra Island, separated by the (HTZ). Tectonic denudation started during the Priabonian-Rupelian along flat normal faults and removed all the overlying sedimentary formations, allowing basement exhumation up to the surface (~ 1.2 - 1.6 km of exhumation). Forward t-T modelling of the data requires a slightly earlier date and shorter period for development of rifting in the E-Socotra domain (38 - 34 Ma), compared to the W-Socotra domain (34 - 25 Ma), which suggests that the HTZ was already active at that time. A second major event of basement cooling and exhumation (additional ~ 0.7 - 1 km), starting at about ~ 20 Ma, has only been recorded on the E-Socotra domain. This second denudation phase significantly post-dates local rifting period but appears synchronous with Ocean Continent Transition (OCT: 20 - 17.6 Ma). This late syn-OCT uplift is maximum close to the HTZ, in the wedge of hangingwall delimited by this transfer system and the steep north-dipping normal faults that accommodated the vertical

  9. Stratigraphy of Atlantic coastal margin of United States north of Cape Hatteras; brief survey

    Science.gov (United States)

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

    1975-01-01

    A synthesis of studies of sea-floor outcrops of the sedimentary wedge beneath the northeastern United States continental shelf and slope and a reassessment of coastal plain Mesozoic stratigraphy, particularly of the coastal margin, provide insight for estimating the oil and gas potential and provide geologic control for marine seismic investigations of the Atlantic continental margin. The oldest strata known to crop out on the continental slope are late Campanian in age. The Cretaceous-Tertiary contact along the slope ranges from a water depth of 0.6 to 1.5 km south of Georges Bank to 1.8 km in Hudson Canyon. Few samples are available from Tertiary and Late Cretaceous outcrops along the slope. Sediments of the Potomac Group, chiefly of Early Cretaceous age, constitute a major deltaic sequence in the emerged coastal plain. This thick sequence lies under coastal Virginia, Maryland, Delaware, southeastern New Jersey, and the adjacent continental shelf. Marine sands associated with this deltaic sequence may be present seaward under the outer continental shelf. South of the Norfolk arch, under coastal North Carolina, carbonate rocks interfinger with Lower Cretaceous clastic strata. From all available data, Mesozoic correlations in coastal wells between coastal Virginia and Long Island have been revised. The Upper-Lower Cretaceous boundary is placed at the transition between Albian and Cenomanian floras. Potential hydrocarbon source beds are present along the coast in the subsurface sediments of Cretaceous age. Potential reservoir sandstones are abundant in this sequence.

  10. Authigenic minerals from the continental margins

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    . Garrels, RM., Thompson, ME., 1962. A chemical model for sea water at 25 C and one atmospheric pressure. Am. J. Sci., 260, 57-66. Hardie, LA., 1987 Dolomitization: a critical view of some current views. J. Sediment. Petrol., 57, 166-183. Humphery, JD.... Chemistry and environment of dolomitization – a reappraisal. Earth-Sci. Reviews, 23, 175-222. Melim, LA., Scholle, PA., 2002. Dolomitization of the Capitan formation forereef facies (Permian, west Texas and New Mexico): seepage reflux revisited...

  11. Cervical Adjacent Segment Disease

    OpenAIRE

    Özbek, Zühtü; Özkara, Emre; Yağmur, İpek; Arslantaş, Ali

    2017-01-01

    Cervical adjacent segment disease; is the general name ofdisc pathologies that develop in adjacent levels after cervical surgery. If thecervical adjacent segment disease that do not require reoperation and it doesnot cause clinical signs is called radiological cervical adjacent segmentpathology, but those causing radiculopathy, myelopathy or instability is calledclinic cervical adjacent segment pathology. The incidence of cervical adjacentsegment disease in 10-year follow-up is 2.4% -2.9%. Wh...

  12. and three-dimensional gravity modeling along western continental ...

    Indian Academy of Sciences (India)

    R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22

    western continental margin and the intraplate Narmada-Tapti rifts suggests that the migration and concentration of high density magma in the upper lithosphere was much more dominant along the western continental margin rift. Based on the three-dimensional gravity modeling, it is conjectured that the emplacement of ...

  13. Continental tectonics and continental kinetics

    International Nuclear Information System (INIS)

    Allegre, C.J.; Jaupart, C.; Paris-7 Univ., 75

    1985-01-01

    We present a model of continental growth which combines the results of geochemical studies and tectonic ideas about the evolution of continents through geological time. The process of continental growth is mainly controlled by surface phenomena. Continental material is extracted from the mantle along subduction zones at the periphery of oceans, and is destroyed in collision zones where it is remobilized and made available for subduction. We derive an equation for S, the portion of the Earth's surface occupied by continents, which reads as follows: dS/dt=a . √(1-S)-b . S. Coefficients a and b depend on the geometry of plates, on their number and on their velocities. We assume that they decrease exponentially with time with the same time-scale α. This model satisfies both geochemical and tectonic constraints, and allows the integration of several current observations in a single framework. (orig.)

  14. Behaviour of REEs in a tropical estuary and adjacent continental ...

    Indian Academy of Sciences (India)

    Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and the heavy metals like Mg, V, Cr, Mn, Fe, Cu, Zn, U, Th were analysed by using standard analytical ... heavy metals and REEs in cultivated soils and in cereal crops of Alberts, Canada. ...... Klinkhammer G P and Palmer M R 1991 Uranium in the oceans: Where it goes and why?;

  15. Continental Rifts

    Science.gov (United States)

    Rosendahl, B. R.

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

  16. Late Permian to Triassic intraplate orogeny of the southern Tianshan and adjacent regions, NW China

    Directory of Open Access Journals (Sweden)

    Wei Ju

    2014-01-01

    Based on previous studies and recent geochronogical data, we suggest that the final collision between the Tarim Craton and the North Asian continent occurred during the late Carboniferous. Therefore, the Permian was a period of intracontinental environment in the southern Tianshan and adjacent regions. We propose that an earlier, small-scale intraplate orogenic stage occurred in late Permian to Triassic time, which was the first intraplate process in the South Tianshan Orogen and adjacent regions. The later large-scale and well-known Neogene to Quaternary intraplate orogeny was induced by the collision between the India subcontinent and the Eurasian plate. The paper presents a new evolutionary model for the South Tianshan Orogen and adjacent regions, which includes seven stages: (I late Ordovician–early Silurian opening of the South Tianshan Ocean; (II middle Silurian–middle Devonian subduction of the South Tianshan Ocean beneath an active margin of the North Asian continent; (III late Devonian–late Carboniferous closure of the South Tianshan Ocean and collision between the Kazakhstan-Yili and Tarim continental blocks; (IV early Permian post-collisional magmatism and rifting; (V late Permian–Triassic the first intraplate orogeny; (VI Jurassic–Palaeogene tectonic stagnation and (VII Neocene–Quaternary intraplate orogeny.

  17. Adjacent segment disease.

    Science.gov (United States)

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

    2014-08-01

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

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

    Science.gov (United States)

    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.

  19. Tracking small mountainous river derived terrestrial organic carbon across the active margin marine environment

    Science.gov (United States)

    Childress, L. B.; Blair, N. E.; Orpin, A. R.

    2015-12-01

    Active margins are particularly efficient in the burial of organic carbon due to the close proximity of highland sources to marine sediment sinks and high sediment transport rates. Compared with passive margins, active margins are dominated by small mountainous river systems, and play a unique role in marine and global carbon cycles. Small mountainous rivers drain only approximately 20% of land, but deliver approximately 40% of the fluvial sediment to the global ocean. Unlike large passive margin systems where riverine organic carbon is efficiently incinerated on continental shelves, small mountainous river dominated systems are highly effective in the burial and preservation of organic carbon due to the rapid and episodic delivery of organic carbon sourced from vegetation, soil, and rock. To investigate the erosion, transport, and burial of organic carbon in active margin small mountainous river systems we use the Waipaoa River, New Zealand. The Waipaoa River, and adjacent marine depositional environment, is a system of interest due to a large sediment yield (6800 tons km-2 yr-1) and extensive characterization. Previous studies have considered the biogeochemistry of the watershed and tracked the transport of terrestrially derived sediment and organics to the continental shelf and slope by biogeochemical proxies including stable carbon isotopes, lignin phenols, n-alkanes, and n-fatty acids. In this work we expand the spatial extent of investigation to include deep sea sediments of the Hikurangi Trough. Located in approximately 3000 m water depth 120 km from the mouth of the Waipaoa River, the Hikurangi Trough is the southern extension of the Tonga-Kermadec-Hikurangi subduction system. Piston core sediments collected by the National Institute of Water and Atmospheric Research (NIWA, NZ) in the Hikurangi Trough indicate the presence of terrestrially derived material (lignin phenols), and suggest a continuum of deposition, resuspension, and transport across the margin

  20. Root zone of a continental rift

    DEFF Research Database (Denmark)

    Kirsch, Moritz; Svenningsen, Olaf

    2016-01-01

    Mafic magmatic rocks formed between ca. 615 and 560 Ma along the Neoproterozoic margins of Baltica and Laurentia are classically attributed to continental rifting heralding the opening of the Iapetus Ocean. We report new data for the Kebnekaise Intrusive Complex (KIC) exposed in the Seve Nappes i...

  1. MARGINS: Toward a novel science plan

    Science.gov (United States)

    Mutter, John C.

    A science plan to study continental margins has been in the works for the past 3 years, with almost 200 Earth scientists from a wide variety of disciplines gathering at meetings and workshops. Most geological hazards and resources are found at continental margins, yet our understanding of the processes that shape the margins is meager.In formulating this MARGINS research initiative, fundamental issues concerning our understanding of basic Earth-forming processes have arisen. It is clear that a business-as-usual approach will not solve the class of problems defined by the MARGINS program; the solutions demand approaches different from those used in the past. In many cases, a different class of experiment will be required, one that is well beyond the capability of individual principle investigators to undertake on their own. In most cases, broadly based interdisciplinary studies will be needed.

  2. Real-time PCR quantification and diversity analysis of the functional genes aprA and dsrA of sulfate-reducing bacteria in marine sediments of the Peru continental margin and the Black Sea

    OpenAIRE

    Axel eSchippers; Anna eBlazejak

    2011-01-01

    A quantitative, real-time PCR (Q-PCR) assay for the functional gene adenosine 5´-phosphosulfate reductase (aprA) of sulfate-reducing bacteria (SRB) was designed. This assay was applied together with described Q-PCR assays for dissimilatory sulfite reductase (dsrA) and the 16S rRNA gene of total Bacteria to marine sediments from the Peru margin (0 – 121 meters below seafloor (mbsf)) and the Black Sea (0 – 6 mbsf). Clone libraries of aprA show that all isolated sequences originate from SRB...

  3. Morphology and kinematics of the rifted margin of West Antarctica in relation to separation from Zealandia and Bellingshausen plate motion

    Science.gov (United States)

    Wobbe, F.; Gohl, K.; Chambord, A.; Sutherland, R.

    2012-04-01

    The final breakup of Gondwana occurred during Late Cretaceous time as rifted continental crust of New Zealand separated from West Antarctica. Geophysical data acquired using R/V Polarstern constrain the structure and age of Antarctica's rifted oceanic margin. The Marie Byrd Land sector resembles a typical magma-poor margin with a narrow steep slope and a 145 km wide continent-ocean transition zone (COTZ). Our transect modelled from gravity and seismic reflection data indicates initial continental crust of thickness 24 km that was stretched 90 km. The Bellingshausen sector, east of the Antipodes Fault, is broad and complex with abundant evidence for later volcanism. The COTZ is ~670 km wide and substantial uncertainty remains as to the nature of crust within the COTZ. Extension estimates fall in the range of 106-304 km for this sector. Seafloor magnetic anomalies adjacent to the Marie Byrd Land sector at the longitude of the Pahemo Fracture Zone indicate a full-spreading rate during c33-c31 (80-68 Myr) of 60 mm/yr, increasing to 74 mm/yr at c27 (62 Myr), and then dropping to 22 mm/yr by c22 (50 Myr). Spreading rates were lower to the west. Extrapolation towards the continental margin indicates that initial oceanic crust formation was at ~c34y (84 Myr). The high extension rate of 30-60 mm/yr during the initial margin formation is consistent with the relatively sharp and symmetrical margin morphology, but subsequent motion of the Bellingshausen plate relative to Antarctica was slow and complex, and modified the rift morphology through migrating deformation and volcanic centres to create a broad and complex COTZ.

  4. Off-shore to near-shore transects of ferromanganese crusts adjacent to the California margin Tracey A. Conrad1, James R. Hein2, Adina Paytan1 1University of California Santa Cruz, CA, 95064 (tconrad@ucsc.edu) 2USGS, Menlo Park, CA, 94025, USA (jhein@usgs.gov)

    Science.gov (United States)

    Conrad, T. A.; Hein, J. R.; Paytan, A.

    2012-12-01

    Marine ferromanganese (Fe-Mn) crusts growing on seamounts along the California Margin (CM) are influenced by terrestrial and biogenic input. These continental margin crusts have higher concentrations of Si, K, Fe, Na, Ag, Cr, B, and Ba than Fe-Mn crusts from the global open-ocean. Al is also higher but only relative to Pacific open-ocean crusts. These relative enrichments may reflect the high primary productivity near the CM caused by seasonal upwelling and high sediment transport to the region from river/eolian input and cliff erosion. Two transects with samples from five seamounts each are used to compare seaward changes. Transect A includes analyses of 66 bulk samples from Flint, Ben, and Little Joe seamounts, Patton Escarpment, and Northeast Bank. It spans ~400 km of seafloor heading ~58N and coming within ~220 km of the shoreline with samples collected at water depths ranging from 570-2925 m. Transect B includes analyses of 136 bulk samples from Adam, Hoss, San Marcos, San Juan, and Rodriguez seamounts at water depths ranging from 692-3880 m. This transect spans ~240 km heading ~10N and comes within ~75 km of the shoreline near the base of the continental slope. For both transects, mean water depth increases with mean longitude, and latitude is fairly constant varying by approximately 2 degree latitude for transect A and 1degree for B. Both transects show statistically significant trends at the 99% confidence level for element concentrations versus water depth. Concentrations of Fe, Ca, P, Co, and Pb increase as water depth decreases. For transect (A), Mn and Mg also follow this trend, as do Mo and Al for transect (B); Mn also shows this trend for transect (B) but at the 95% confidence level. For both transects, Cu and Zn show the opposite trend, with concentrations increasing in crusts with increasing water depth. For Transect (B), Ni and Al also show this trend. Si and K show no statistically significant trends for either transect. In open-ocean samples

  5. Marginal Matter

    Science.gov (United States)

    van Hecke, Martin

    2013-03-01

    All around us, things are falling apart. The foam on our cappuccinos appears solid, but gentle stirring irreversibly changes its shape. Skin, a biological fiber network, is firm when you pinch it, but soft under light touch. Sand mimics a solid when we walk on the beach but a liquid when we pour it out of our shoes. Crucially, a marginal point separates the rigid or jammed state from the mechanical vacuum (freely flowing) state - at their marginal points, soft materials are neither solid nor liquid. Here I will show how the marginal point gives birth to a third sector of soft matter physics: intrinsically nonlinear mechanics. I will illustrate this with shock waves in weakly compressed granular media, the nonlinear rheology of foams, and the nonlinear mechanics of weakly connected elastic networks.

  6. Adjacent segment degeneration

    OpenAIRE

    Birjandi, Alireza

    2012-01-01

    Abstract: Adjacent segment disease (ASD) is defined as degeneration that develops at mobile segments above or below a fused spinal segment and usually develops after spinal fusion or other back surgeries. Nearly 5 decades ago, the medical findings related to ASD were usually released in case reports as a relatively unusual complication of lumbar or lumbosacral fusions. Since the initial reports, ASD has been found to occur more often than the earlier predictions for its prospect incidence. It...

  7. Continental Divide Trail

    Data.gov (United States)

    Earth Data Analysis Center, University of New Mexico — This shapefile was created to show the proximity of the Continental Divide to the Continental Divide National Scenic Trail in New Mexico. This work was done as part...

  8. Real-time PCR quantification and diversity analysis of the functional genes aprA and dsrA of sulfate-reducing bacteria in marine sediments of the Peru continental margin and the Black Sea

    Directory of Open Access Journals (Sweden)

    Axel eSchippers

    2011-12-01

    Full Text Available A quantitative, real-time PCR (Q-PCR assay for the functional gene adenosine 5´-phosphosulfate reductase (aprA of sulfate-reducing bacteria (SRB was designed. This assay was applied together with described Q-PCR assays for dissimilatory sulfite reductase (dsrA and the 16S rRNA gene of total Bacteria to marine sediments from the Peru margin (0 – 121 meters below seafloor (mbsf and the Black Sea (0 – 6 mbsf. Clone libraries of aprA show that all isolated sequences originate from SRB showing a close relationship to aprA of characterised species or form a new cluster with only distant relation to aprA of isolated SRB. Below 40 mbsf no aprA genes could be amplified. This finding corresponds with results of the applied new Q-PCR assay for aprA. In contrast to the aprA the dsrA gene could be amplified up to sediment depths of 121 mbsf. Even in such an extreme environment a high diversity of this gene was detected. The 16S rRNA gene copy numbers of total Bacteria were much higher than those of the functional genes at all sediment depths and used to calculate the proportion of SRB to the total Bacteria. The aprA and dsrA copy numbers comprised in average 0.5 - 1 % of the 16S rRNA gene copy numbers of total Bacteria in the sediments up to a depth of ca. 40 mbsf. Depth profiles of the aprA and dsrA copy numbers were almost equal for all sites. Gene copy numbers decreased concomitantly with depth from around 108 / g sediment close to the sediment surface to less than 105 / g sediment at 5 mbsf. In the zone without detectable sulfate in the pore water from ca. 40 – 121 mbsf (Peru margin ODP site 1227, only dsrA (but not aprA was detected with copy numbers of less than 104 / g sediment, comprising ca. 14 % of the 16S rRNA gene copy numbers of total Bacteria. In this zone sulfate might be provided for SRB by anaerobic sulfide oxidation.

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

    Science.gov (United States)

    ,

    1975-01-01

    Appalachian Piedmont province. Triassic deposits are likely to exist beneath the inner Continental Shelf, and probably consist of nonmarine arkosic sandstones, shales, basalt flows, and diabase intrusions deposited in relatively narrow northeast-trending grabens. Jurassic marine carbonates in the Bahamas grade northward to carbonates, shales, sand, and arkose in North Carolina. Salt may be present in the basal Jurassic section in the Southeast Georgia Embayment. Up to 4,000 m of Jurassic-Lower Cretaceous rocks are expected out to the 600 m water depth. Lower Cretaceous rocks in southern Florida are shallow-water marine limestone and dolomites with beds of anhydrite. In coastal North Carolina the Lower Cretaceous is a marine section made up of shales, sand, and sandy limestone. The Upper Cretaceous is composed almost entirely of marine carbonates in southern Florida grading northward to nonmarine to marginal marine, sandstones and shales with minor amounts of carbonates. In general, Upper Cretaceous rocks will probably maintain a fairly constant thickness (600 m) on the Continental Shelf and grade downdip from terrigeneous sands and shales to more marine chalks, limestones, and dolomites. The Cenozoic rocks are predominantly shallow-water marine carbonates in Florida grading northward into a marginal marine to marine clastic facies composed of sands, marls, and limestones. The offshore Cenozoic section is expected to range in thickness from 600 to 1100 m. A reconstruction of the geologic history suggests that the present continental margin is a result of a collision of the North American and African continental plates during late Paleozoic time and later modification during Late Triassic time when the continental plates separated, forming the present Atlantic Ocean. No commercial production of hydrocarbons has been developed on the Atlantic Coastal Plain immediately adjacent to the studied area even though hydrocarbon shows have been encountered in ons

  10. Continental fragmentation and the strontium isotopic evolution of seawater.

    Science.gov (United States)

    Eric, H.; Jean Pascal, C.

    2008-12-01

    The time evolution of the strontium isotopic composition of seawater over the last 600 million years has the form of an asymmetric trough. The values are highest in the Cambrian and recent and lowest in the Jurassic. Superimposed on this trend are a number of smaller oscillations. The mechanisms responsible for these global isotopic fluctuations are subject to much debates. In order to get a quantitative picture of the changing paleogeography, we have characterized land-ocean distributions over Late Proterozoic to Phanerozoic times from measurement of perimeters and areas of continental fragments, based on paleomagnetic reconstructions. These measurements served to calculate geophysically constrainted breakup and scatter indexes of continental land masses from 0 to 1100 Ma (Cogne and Humler, 2008). Both parameters (strontium isotopic ratios of seawater and continental fragmentation indexes) are obviously highly correlated during the last 600 Ma. Low continental dispersion (that is large continental land masses) are associated with low seawater strontium isotopic ratios (that is when the continental inputs to oceans are minimum) and high continental dispersion (that is relatively small and widely distributed continents) with high seawater strontium isotopic ratios (that is when the continental input to ocean is maximum). Importantly, this first order evolution appears to conflict with the common idea of mountains erosion as a source for radiogenic strontium to oceans because high strontium isotopic ratios in seawater correspond to period of maximum dispersion of continents and not with period of general collisions. At first glance, it would seem that continental erosion increases with the degree of continental dispersion. Models showing that continental precipitation increases when continental masses are smaller and more widely dispersed and/or the length of continental margins available for rivers to carry continental material to oceans are thus favoured in order

  11. Phanerozoic continental growth and gold metallogeny of Asia

    Science.gov (United States)

    Goldfarb, Richard J.; Taylor, Ryan D.; Collins, Gregory S.; Goryachev, Nicolay A.; Orlandini, Omero Felipe

    2014-01-01

    The Asian continent formed during the past 800 m.y. during late Neoproterozoic through Jurassic closure of the Tethyan ocean basins, followed by late Mesozoic circum-Pacific and Cenozoic Himalayan orogenies. The oldest gold deposits in Asia reflect accretionary events along the margins of the Siberia, Kazakhstan, North China, Tarim–Karakum, South China, and Indochina Precambrian blocks while they were isolated within the Paleotethys and surrounding Panthalassa Oceans. Orogenic gold deposits are associated with large-scale, terrane-bounding fault systems and broad areas of deformation that existed along many of the active margins of the Precambrian blocks. Deposits typically formed during regional transpressional to transtensional events immediately after to as much as 100 m.y. subsequent to the onset of accretion or collision. Major orogenic gold provinces associated with this growth of the Asian continental mass include: (1) the ca. 750 Ma Yenisei Ridge, ca. 500 Ma East Sayan, and ca. 450–350 Ma Patom provinces along the southern margins of the Siberia craton; (2) the 450 Ma Charsk belt of north-central Kazakhstan; (3) the 310–280 Ma Kalba belt of NE Kazakhstan, extending into adjacent NW Xinjiang, along the Siberia–Kazakhstan suture; (4) the ca. 300–280 Ma deposits within the Central Asian southern and middle Tien Shan (e.g., Kumtor, Zarmitan, Muruntau), marking the closure of the Turkestan Ocean between Kazakhstan and the Tarim–Karakum block; (5) the ca. 190–125 Ma Transbaikal deposits along the site of Permian to Late Jurassic diachronous closure of the Mongol–Okhotsk Ocean between Siberia and Mongolia/North China; (6) the probable Late Silurian–Early Devonian Jiagnan belt formed along the margin of Gondwana at the site of collision between the Yangtze and Cathaysia blocks; (7) Triassic deposits of the Paleozoic Qilian Shan and West Qinling orogens along the SW margin of the North China block developed during collision of South China

  12. Moroccan crustal response to continental drift.

    Science.gov (United States)

    Kanes, W H; Saadi, M; Ehrlich, E; Alem, A

    1973-06-01

    The formation and development of a zone of spreading beneath the continental crust resulted in the breakup of Pangea and formation of the Atlantic Ocean. The crust of Morocco bears an extremely complete record of the crustal response to this episode of mantle dynamics. Structural and related depositional patterns indicate that the African margin had stabilized by the Middle Jurassic as a marine carbonate environment; that it was dominated by tensile stresses in the early Mesozoic, resulting in two fault systems paralleling the Atlantic and Mediterranean margins and a basin and range structural-depositional style; and that it was affected by late Paleozoic metamorphism and intrusion. Mesozoic events record the latter portion of African involvement in the spreading episode; late Paleozoic thermal orogenesis might reflect the earlier events in the initiation of the spreading center and its development beneath significant continental crust. In that case, more than 100 million years were required for mantle dynamics to break up Pangea.

  13. Intra-continental subduction and contemporaneous lateral extrusion of the upper plate: insights into Alps-Adria interactions

    Science.gov (United States)

    van Gelder, Inge; Willingshofer, Ernst; Sokoutis, Dimitrios; Cloetingh, Sierd

    2017-04-01

    A series of physical analogue experiments were performed to simulate intra-continental subduction contemporaneous with lateral extrusion of the upper plate to study the interferences between these two processes at crustal levels and in the lithospheric mantle. The lithospheric-scale models are specifically designed to represent the collision of the Adriatic microplate with the Eastern Alps, simulated by an intra-continental weak zone to initiate subduction and a weak confined margin perpendicular to the direction of convergence in order to allow for extrusion of the lithosphere. The weak confined margin is the analog for the opening of the Pannonian back-arc basin adjacent to the Eastern Alps with the direction of extension perpendicular to the strike of the orogen. The models show that intra-continental subduction and coeval lateral extrusion of the upper plate are compatible processes. The obtained deformation structures within the extruding region are similar compared to the classical setup where lateral extrusion is provoked by lithosphere-scale indentation. In the models a strong coupling across the subduction boundary allows for the transfer of abundant stresses to the upper plate, leading to laterally varying strain regimes that are characterized by crustal thickening near a confined margin and dominated by lateral displacement of material near a weak lateral confinement. During ongoing convergence the strain regimes propagate laterally, thereby creating an area of overlap characterized by transpression. In models with oblique subduction, with respect to the convergence direction, less deformation of the upper plate is observed and as a consequence the amount of lateral extrusion decreases. Additionally, strain is partitioned along the oblique plate boundary leading to less subduction in expense of right lateral displacement close to the weak lateral confinement. Both oblique and orthogonal subduction models have a strong resemblance to lateral extrusion

  14. Gulf of Mexico: Dealing with Change in a Marginal Sea

    Science.gov (United States)

    Rabalais, N. N.

    2017-12-01

    The Gulf of Mexico is shared by the United States, Mexico and Cuba and requires collaborative work for integrated management to conserve its natural assets and derived benefits, as well as to foster the overall regional economic wealth. Many rivers drain into the Gulf, most notably the Mississippi, which ranks among global rivers 4th in discharge, 7th in sediment load and 3rd in drainage area, and accounts for about 90 percent of the freshwater inflow to the Gulf. The Mississippi River proper empties onto a narrow ( 20 km wide) continental shelf, and its tributary, the Atchafalaya River, that carries about one third of the total flow discharges onto the broad ( 200 km) and shallow part of the shelf. The entrainment of the Mississippi River discharge into the Louisiana Coastal Current results in the semblance of an extended estuary across much of the inner to mid continental shelf for much of the year. The nitrogen load from the Mississippi River to the adjacent continental shelf over the last half century has increased by 300 per cent. As a result, eutrophication and hypoxia have developed in this stratified coastal system with implications for biogeochemical cycles and valued resources. While there is recognition that over half of the nitrogen sources come from agricultural practices widespread across the watershed, the environmental goal of bringing a 32-year average 13,800 square kilometers of bottom-water hypoxia to less than 5,000 square kilometers is being realized through voluntary and incentive-based activities, designed within a series of subbasin and state strategies. Some activities funded by the US Department of Agriculture for directed nutrient reduction projects and several small-scale voluntary actions towards sustainable and ecologically sound agriculture show promise, but large-scale social-political solutions do not exist now nor will they for the forseeable future. The coastal waters adjacent to the Mississippi River are just one of many such

  15. Regional tectonic trends on the inner continental shelf off Konkan and central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Ramana, M.V.

    Satellite imagery and offshore magnetic data were analysed to correlate regional tectonic elements on the inner continental shelf off Konkan and the adjacent Deccan plateau. Three statistically important lineament trends N-S, WNW-ESE and ENE...

  16. Cretaceous rifting of the Ghana transform margin - Evidence from on ...

    African Journals Online (AJOL)

    The denudation was the result of faults and landslides produced by increases in bathymetric step between the continental margin and the oceanic crust. The latter ... Instead, cooling of ODP samples from the offshore marginal ridge is the consequence of coeval hydrothermal circulation within intracontinental fault acting ...

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

    Science.gov (United States)

    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

  18. Adjacent Segment Pathology after Anterior Cervical Fusion.

    Science.gov (United States)

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon; Kim, Sung Kyu

    2016-06-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of motion preservation technologies like total disc arthroplasty. The true nature and scope of ASP remains poorly understood. The etiology of ASP is most likely multifactorial. Various factors including altered biomechanical stresses, surgical disruption of soft tissue and the natural history of cervical disc disease contribute to the development of ASP. General factors associated with disc degeneration including gender, age, smoking and sports may play a role in the development of ASP. Postoperative sagittal alignment and type of surgery are also considered potential causes of ASP. Therefore, a spine surgeon must be particularly careful to avoid unnecessary disruption of the musculoligamentous structures, reduced risk of direct injury to the disc during dissection and maintain a safe margin between the plate edge and adjacent vertebrae during anterior cervical fusion.

  19. Adjacent Segment Pathology after Anterior Cervical Fusion

    Science.gov (United States)

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon

    2016-01-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of motion preservation technologies like total disc arthroplasty. The true nature and scope of ASP remains poorly understood. The etiology of ASP is most likely multifactorial. Various factors including altered biomechanical stresses, surgical disruption of soft tissue and the natural history of cervical disc disease contribute to the development of ASP. General factors associated with disc degeneration including gender, age, smoking and sports may play a role in the development of ASP. Postoperative sagittal alignment and type of surgery are also considered potential causes of ASP. Therefore, a spine surgeon must be particularly careful to avoid unnecessary disruption of the musculoligamentous structures, reduced risk of direct injury to the disc during dissection and maintain a safe margin between the plate edge and adjacent vertebrae during anterior cervical fusion. PMID:27340541

  20. Western Ross Sea continental slope gravity currents

    Science.gov (United States)

    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 (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 difference, if real

  1. Fluxes and budget of organic matter in the benthic boundary layer over the northwestern Mediterranean margin

    Science.gov (United States)

    Buscail, R.; Pocklington, R.; Daumas, R.; Guidi, L.

    1990-09-01

    Sediment traps were deployed at depths of 26 and 645 m at two stations on the continental margin of the Gulf of Lions (northwestern Mediterranean). During the same period, surficial sediments were sampled by box corer. The material collected by bottom sediment traps and in corresponding surface sediments was analysed for total organic carbon, hydrolysable organic carbon, nitrogen, sugars, amino acids and lignin-derived compounds. Seasonal variations in organic inputs and the difference between particles from bottom layers and sediment were compared. For the continental shelf station, the annual averages of organic compound fluxes were found to be: 552 mg m -2 d -1 (orgC), 183 mg m -2 d -1 (N), 283 mg m -2 d -1 (hydrolysable orgC), 181 mg m -2 d -1 (Ceq. glucose) and 478 mg m -2 d -1 (amino acids). These values would have to be reduced by half if the large fluxes of autumn, due to resuspension during storm events, were excluded. For the slope, the average annual fluxes were evaluated as: 92.7 mg m -2 d -1 (orgC); 9.4 mg m -2 d -1 (N); 74.1 mg m -2 d -1 (hydrolysable orgC); 11.8 mg m -2 d -1 (Ceq.glucose); and 68.2 mg m -2 d -1 (amino acids). The values obtained for material trapped over the shelf are 4-7 times (orgC and amino acids) and 15-19 times (sugars and nitrogen) higher than for the slope. In contrast, the content in organic compounds of surficial sediments on the slope is 2-3 times higher than that of the shelf deposits. Budgets of orgC transformation at the sediment-water interface were based on calculations which include bottom orgC fluxes, sedimentation rates and orgC content for the first centimetre of deposits. For the continental shelf area, 5.3 g m -2 y -1 have accumulated and 16.7 g m -2 y -1 are mineralized. For the canyon and adjacent slope, the figures are 0.4 and 0.6 g m -2 y -1, respectively. Over the upper adjacent slope, the major part of organic matter is transported by advective processes, which contribute to the sediment interface

  2. Passive margins through earth history

    Science.gov (United States)

    Bradley, Dwight C.

    2008-12-01

    Passive margins have existed somewhere on Earth almost continually since 2740 Ma. They were abundant at 1900-1890, 610-520, and 150-0 Ma, scarce at ca. 2445-2300, 1600-1000, and 300-275 Ma, and absent before ca. 3000 Ma and at 1740-1600. The fluctuations in abundance of passive margins track the first-order fluctuations of the independently derived seawater 87Sr/ 86Sr secular curve, and the compilation thus appears to be robust. The 76 ancient passive margins for which lifespans could be measured have a mean lifespan of 181 m.y. The world-record holder, with a lifespan of 590 m.y., is the Mesoproterozoic eastern margin of the Siberian craton. Subdivided into natural age groups, mean lifespans are 186 m.y. for the Archean to Paleoproterozoic, 394 m.y. for the Mesoproterozoic, 180 m.y. for the Neoproterozoic, 137 m.y. for the Cambrian to Carboniferous, and 130 m.y. for the Permian to Neogene. The present-day passive margins, which are not yet finished with their lifespans, have a mean age of 104 m.y. and a maximum age of 180 m.y. On average, Precambrian margins thus had longer, not shorter, lifespans than Phanerozoic ones—and this remains the case even discounting all post-300 Ma margins, most of which have time left. Longer lifespans deeper in the past is at odds with the widely held notion that the tempo of plate tectonics was faster in the Precambrian than at present. It is entirely consistent, however, with recent modeling by Korenaga [Korenaga, J., 2004. Archean geodynamics and thermal evolution of Earth. Archean Geodynamics and Environments, AGU Geophysical Monograph Series 164, 7-32], which showed that plate tectonics was more sluggish in the Precambrian. The abundance of passive margins clearly tracks the assembly, tenure, and breakup of Pangea. Earlier parts of the hypothesized supercontinent cycle, however, are only partly consistent with the documented abundance of passive margins. The passive-margin record is not obviously consistent with the proposed

  3. Pathways of organic carbon oxidation in three continental margin sediments

    DEFF Research Database (Denmark)

    Canfield, Donald Eugene; Jørgensen, Bo Barker; Fossing, Henrik

    1993-01-01

    We have combined several different methodologies to quantify rates of organic carbon mineralization by the various electron acceptors in sediments from the coast of Denmark and Norway. Rates of NH4+ and Sigma CO2 liberation sediment incubations were used with O2 penetration depths to conclude tha...

  4. Continental margin neotectonics in South Africa: a nuclear siting approach

    International Nuclear Information System (INIS)

    Andreoli, M.A.G.; Hambleton-Jones, B.B.; Anderson, N.J.B.; Faurie, J.N.; Raubenheimer, E.; Antoine, L.; Von Veh, M.W.; McMillan, I.K.

    1990-01-01

    Neotectonic activity in South Africa has only recently received attention despite the fact that a rigorous knowledge of this phenomenon could have a major impact on industrial development within certain areas. Since the early 1980s the Atomic Energy Corporation of South Africa has addressed this specific problem in the process of detailed site investigations for the licensing of six facilities related to the nuclear industry. The data indicates that there is a general correspondence in five selected areas along the South African coast between the development of Quarternary joints/faults and the degree of seismic activity recorded in each geological domain. Finally, the results provide new data that may add to a recent survey of global tectonic stresses. 13 refs., 1 fig

  5. Polymetallic ferromanganese deposits research on the Atlantic Spanish continental margin

    OpenAIRE

    Torres Pérez-Hidalgo, Trinidad José; Ortiz Menéndez, José Eugenio; González, F.J.; Somoza, L.; Lunar, R.; Martínez-Frías, J.; Medialdea, T.; León, R.; Martín-Rubí, J.A.; Marino, E.

    2014-01-01

    Seamounts, submarine banks, volcanoes and undercurrent channels are prominent geomorphic features that have become an important target for minerals research and exploration with the goal of future exploitation. Polymetallic ferromanganese deposits are common types of mineralization on these settings. Co-rich ferromanganese crusts are important as potential resources of Mn and Co, but also Ti, Ni, Tl, REEs, PGEs, and other metals. Many seamounts and channels along the Atlantic Spanish continen...

  6. Comparative biogeochemistry–ecosystem–human interactions on dynamic continental margins..

    Digital Repository Service at National Institute of Oceanography (India)

    Levin, L.A; Liu, K-K.; Emeis, K.-C.; Breitburg, D.L.; Cloern, J.; Deutsch, C.; Giani, M.; Goffart, A.; Hofmann, E.E.; Lachkar, Z.; Limburg, K.; Liu, Su-Mei; Montes, E.; Naqvi, S.W.A.; Ragueneau, O.; Rabouille, C.; Sarkar, S.K.; Swaney, D.P.; Wassman, P.; Wishner, K.F.

    Northern 2.5 3.0 3.5 4.0 4.5 5.0 2.6 2.8 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 Total N loadings (log10 kg km-2 surface year-1) La nd in gs fi sh + m ob ile in ve rte br at es (lo g 1 0 kg k m - 2 su rfa ce a re a ye ar - 1 ) <2% hypoxia4-19% hypoxia 22... of China, Qingdao 266100, PR China m College of Marine Science, University of South Florida, St. Petersburg, FL, USA n National Institute of Oceanography, Goa, India o Laboratoire des Sciences de l'Environnement Marin, Institut Universitaire Européen de la...

  7. Pathways of organic carbon oxidation in three continental margin sediments

    DEFF Research Database (Denmark)

    Canfield, Donald Eugene; Jørgensen, Bo Barker; Fossing, Henrik

    1993-01-01

    that O2 respiration accounted for only between 3.6-17.4% of the total organic carbon oxidation. Dentrification was limited to a narrow zone just below the depth of O2 penetration, and was not a major carbon oxidation pathway. The processes of Fe reduction, Mn reduction and sulfate reduction dominated...... organic carbon mineralization, but their relative significance varied depending on the sediment. Where high concentrations of Mn-oxide were found (3-4 wt% Mn), only Mn reduction occurred. With lower Mn oxide concentrations more typical of coastal sediments, Fe reduction and sulfate reduction were most...

  8. A potential phosphorite deposit on the continental margin off Chennai

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Rao, K.M.; Vora, K.H.; Almeida, F.; Subramaniam, M.M.; Souza, C.G.A.

    sands. Quartz, feldspar and high magnesium calcite are the accessory minerals. EDAX (energy dispersive x-ray analysis) carried out for 9 elements on JEOL 840 SEM/EDAX, reveal that measurable S contents (0.9%) occur in only algal nodules....

  9. Continental margin of Andhra Pradesh: Some new problems and perspectives

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.

    -basina! part, and also delineated Pranhita- Godavari Gondwana graben and two other oldest Pre-Cambrian Chintalapudi and Avanigadda cross trends into the offshore K-G basin. An isolated volcanic source of limited lateral extent is also located off Machilipatnam...

  10. Structure and breakup history of the rifted margin of West Antarctica in relation to Cretaceous separation from Zealandia and Bellingshausen plate motion

    Science.gov (United States)

    Wobbe, F.; Gohl, K.; Chambord, A.; Sutherland, R.

    2012-04-01

    Geophysical data acquired using R/V Polarstern constrain the structure and age of the rifted oceanic margin of West Antarctica. West of the Antipodes Fracture Zone, the 145 km wide continent-ocean transition zone (COTZ) of the Marie Byrd Land sector resembles a typical magma-poor margin. New gravity and seismic reflection data indicates initial continental crust of thickness 24 km, that was stretched 90 km. Farther east, the Bellingshausen sector is broad and complex with abundant evidence for volcanism, the COTZ is ˜670 km wide, and the nature of crust within the COTZ is uncertain. Margin extension is estimated to be 106-304 km in this sector. Seafloor magnetic anomalies adjacent to Marie Byrd Land near the Pahemo Fracture Zone indicate full-spreading rate during c33-c31 (80-68 Myr) of 60 mm yr-1, increasing to 74 mm yr-1 at c27 (62 Myr), and then dropping to 22 mm yr-1 by c22 (50 Myr). Spreading rates were lower to the west. Extrapolation towards the continental margin indicates initial oceanic crust formation at around c34y (84 Myr). Subsequent motion of the Bellingshausen plate relative to Antarctica (84-62 Myr) took place east of the Antipodes Fracture Zone at rates <40 mm yr-1, typically 5-20 mm yr-1. The high extension rate of 30-60 mm yr-1 during initial margin formation is consistent with steep and symmetrical margin morphology, but subsequent motion of the Bellingshausen plate was slow and complex, and modified rift morphology through migrating deformation and volcanic centers to create a broad and complex COTZ.

  11. Continental drift before 1900.

    Science.gov (United States)

    Rupke, N A

    1970-07-25

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

  12. A new tectono-magmatic model for the Lofoten/Vesterålen Margin at the outer limit of the Iceland Plume influence

    Science.gov (United States)

    Breivik, Asbjørn Johan; Faleide, Jan Inge; Mjelde, Rolf; Flueh, Ernst R.; Murai, Yoshio

    2017-10-01

    The Early Eocene continental breakup was magma-rich and formed part of the North Atlantic Igneous Province. Extrusive and intrusive magmatism was abundant on the continental side, and a thick oceanic crust was produced up to a few m.y. after breakup. However, the extensive magmatism at the Vøring Plateau off mid-Norway died down rapidly northeastwards towards the Lofoten/Vesterålen Margin. In 2003 an Ocean Bottom Seismometer profile was collected from mainland Norway, across Lofoten, and into the deep ocean. Forward/inverse velocity modeling by raytracing reveals a continental margin transitional between magma-rich and magma-poor rifting. For the first time a distinct lower-crustal body typical for volcanic margins has been identified at this outer margin segment, up to 3.5 km thick and ∼50 km wide. On the other hand, expected extrusive magmatism could not be clearly identified here. Strong reflections earlier interpreted as the top of extensive lavas may at least partly represent high-velocity sediments derived from the shelf, and/or fault surfaces. Early post-breakup oceanic crust is moderately thickened (∼8 km), but is reduced to 6 km after 1 m.y. The adjacent continental crystalline crust is extended down to a minimum of 4.5 km thickness. Early plate spreading rates derived from the Norway Basin and the northern Vøring Plateau were used to calculate synthetic magnetic seafloor anomalies, and compared to our ship magnetic profile. It appears that continental breakup took place at ∼53.1 Ma, ∼1 m.y. later than on the Vøring Plateau, consistent with late strong crustal extension. The low interaction between extension and magmatism indicates that mantle plume material was not present at the Lofoten Margin during initial rifting, and that the observed excess magmatism was created by late lateral transport from a nearby pool of plume material into the lithospheric rift zone at breakup time.

  13. Basement and climate controls on proximal depositional systems in continental settings

    NARCIS (Netherlands)

    Ventra, D.

    2011-01-01

    This doctoral dissertation discusses the sedimentology and dynamics of selected, modern and ancient clastic depositional systems (alluvial fans and colluvial aprons) at continental basin margins. The focus on single depositional systems gave the opportunity to devote particular attention to

  14. Late Devonian and Triassic basalts from the southern continental ...

    Indian Academy of Sciences (India)

    In Late Devonian and Early-to-Late Triassic times, the southern continental margin of the Eastern. European Platform was the site of a basaltic volcanism in the Donbas and Fore-Caucasus areas respectively. Both volcanic piles rest unconformably upon Paleoproterozoic and Late Paleozoic units respectively, and emplaced ...

  15. and three-dimensional gravity modeling along western continental ...

    Indian Academy of Sciences (India)

    Three-dimensional gravity modeling of +70 mgal Bouguer gravity highs extending in the north-south direction along the western continental margin rift indicates the presence of a subsurface high density, mafic-ultramafic type, elongated, roughly ellipsoidal body. It is approximately 12.0 ± 1.2 km thick with its upper surface at ...

  16. Late Devonian and Triassic basalts from the southern continental ...

    Indian Academy of Sciences (India)

    In Late Devonian and Early-to-Late Triassic times, the southern continental margin of the Eastern European Platform was the site of a basaltic volcanism in the Donbas and Fore-Caucasus areas respectively. Both volcanic piles rest unconformably upon Paleoproterozoic and Late Paleozoic units respectively, and emplaced ...

  17. Regional magnetic anomaly constraints on continental rifting

    Science.gov (United States)

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

    1985-01-01

    Radially polarized MAGSAT anomalies of North and South America, Europe, Africa, India, Australia and Antarctica demonstrate remarkably detailed correlation of regional magnetic lithospheric sources across rifted margins when plotted on a reconstruction of Pangea. These major magnetic features apparently preserve their integrity until a superimposed metamorphoric event alters the magnitude and pattern of the anomalies. The longevity of continental scale magnetic anomalies contrasts markedly with that of regional gravity anomalies which tend to reflect predominantly isostatic adjustments associated with neo-tectonism. First observed as a result of NASA's magnetic satellite programs, these anomalies provide new and fundamental constraints on the geologic evolution and dynamics of the continents and oceans. Accordingly, satellite magnetic observations provide a further tool for investigating continental drift to compliment other lines of evidence in paleoclimatology, paleontology, paleomagnetism, and studies of the radiometric ages and geometric fit of the continents.

  18. Modelling passive margin sequence stratigraphy

    Science.gov (United States)

    Steckler, M.S.; Reynolds, D.; Coakley, B.; Swift, B.A.; Jarrard, R.D.

    1993-01-01

    We have modelled stratigraphic sequences to aid in deciphering the sedimentary response to sea-level change. Sequence geometry is found to be most sensitive to sea level, but other factors, including subsidence rate and sediment supply, can produce similar changes. Sediment loading and compaction also play a major role in generating accommodation, a factor often neglected in sequence-stratigraphic models. All of these parameters can control whether a type 1 or type 2 sequence boundary is produced. The models indicate that variations in margin characteristics produce systematic shifts in sequence boundary timing and systems tract distribution. The timing of the sequence boundary formation and systems tracts may differ by up to one-half of a sea-level cycle. Thus correlative sequence boundaries will not be synchronous. While rates of sea-level change may exceed the rate of thermal subsidence, isostasy and compaction may amplify the rate of total subsidence to several times greater than the thermal subsidence. Thus, total subsidence does not vary uniformly across the margin since it is modified by the sediment load. The amplitude of sea-level changes cannot be determined accurately without accounting for the major processes that affect sediment accumulation. Backstripping of a seismic line on the New Jersey margin is used to reconstruct continental margin geometry. The reconstructions show that the pre-existing ramp-margin geometry, rather than sea level, controls clinoform heights and slopes and sedimentary bypass. Backstripping also reveals progressive deformation of sequences due to compaction. Further work is still needed to understand quantitatively the role of sea level and the tectonic and sedimentary processes controlling sequence formation and influencing sequence architecture.

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

    Science.gov (United States)

    Behrendt, John C.; Wotorson, Cletus S.

    1970-01-01

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

  20. Continental Mathematics League.

    Science.gov (United States)

    Quartararo, Joseph

    2002-01-01

    This article describes the activities of the Continental Mathematics League, which offers a series of meets for children in grades 3 though 9. In addition, a Calculus League and a Computer Contest are offered. The league allows schools to participate by mail so that rural schools can participate. (CR)

  1. Outer Continental Shelf Lands Act

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — This data represents geographic terms used within the Outer Continental Shelf Lands Act (OCSLA or Act). The Act defines the United States outer continental shelf...

  2. Evolution of the Southern Margin of the Donbas (Ukraine) from Devonian to early Carboniferous Times.

    NARCIS (Netherlands)

    McCann, T.; Saintot, A.N.

    2003-01-01

    A Devonian-Early Carboniferous succession comprising thick clastic and carbonate sediments with interbedded volcanics was examined along the southern margin of the Donbas fold belt. Ukraine. Following initial rifting and subsidence, a continental (fluvial, lacustrine) succession was established.

  3. Tectonic subsidence analyses of miogeoclinal strata from mesozoic marginal basin of Peru

    Energy Technology Data Exchange (ETDEWEB)

    Devlin, W.J.

    1988-01-01

    The Western Peruvian trough is composed of an eastern miogeoclinical facies of carbonate and clastic strata, and a western eugeoclinal facies consisting of a succession of volcanic and sedimentary rocks. In norther and central Peru, the miogeocline is located between a tectonic hinge adjacent to platformal facies of the Maranon geanticline on the east, and an outer marginal high bounded by the Cordillera Blanca fault and Tapacocha axis on the west. Miogeoclinal and platformal strata in southern Peru occur in a broad belt between Arequipa and Lago Titicaca. A marginal basin setting has been proposed for the Western Peruvian trough and the several kilometers of subsidence in the basin has been attributed to back-arc extension and crustal thinning. As a test of this model, quantitative tectonic subsidence curves were constructed from representative sections within miogeoclinar strata from four localities. Preliminary results indicate that the calculated curves have the same overall form as the age-depth curve for ocean floor, suggesting that subsidence was controlled by cooling and thermal contraction of heated lithosphere. The slopes of the curves are less than those for subsidence of oceanic lithosphere. However, they are in agreement with geologic evidence that the miogeocline accumulated on continental crust. Significant variations in the timing of onset, duration, and magnitude of subsidence are observed between sections from northern and southern Peru.

  4. Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin

    Digital Repository Service at National Institute of Oceanography (India)

    Ajay, K.K.; Chaubey, A.K.; Krishna, K.S.; Rao, D.G.; Sar, D.

    T, Dallmeyer R D and Joseph M 1994 Paleomagnetism and 36 Ar/ 40 Ar vs. 39 Ar/ 40 Ar isotope correlation ages of dyke swarms in central Kerala, India: Tectonic implications; Earth Planet. Sci. Lett. 121 213–226. Raval U and Veeraswamy K 2003 India...

  5. Climate Variability and Siliciclastic Deposition on a Carbonate Margin - Neogene of the Northwest Shelf of Australia

    Science.gov (United States)

    Tagliaro, G.; Fulthorpe, C.; Gallagher, S. J.; McHugh, C.; Kominz, M. A.; Lavier, L.

    2017-12-01

    The Bare Formation represents a unique episode of Neogene siliciclastic deposition on the carbonate-dominated Australian Northwest Shelf (NWS). International Ocean Discovery Program (IODP) Expedition 356 drilling results, coupled with interpretation of 3D seismic data, allow us to constrain the timing of siliciclastic deposition and the associated sedimentary processes. IODP Sites U1462, U1463 and U1464 provide age control that reveals the relationship of the Bare Fm. to the adjacent carbonate sediments. The Bare Fm. is preceded by middle to late Miocene shelf exposure and karstification. Elongate beach barrier deposits with small lobate deltas to the NE developed during the late Miocene. However, fluvial deposition increased markedly in the Zanclean, resulting in development of a large tide-and-wave-influenced delta, with evidence of tidal channels, comprising the thickest component of the Bare Fm. Siliciclastic input decreased in the Piacenzian, leading to margin retreat and final termination near the Plio-Pleistocene boundary. The results correlate with regional climate and sedimentary records derived from Sites U1459, U1463 and U1464, that indicate an arid middle to late Miocene, followed by a humid interval in the Zanclean and a return to arid conditions during the Piacenzian. Therefore, we suggest that fluctuation of surface runoff patterns in the continental hinterlands is the primary control of Bare Fm. evolution. Hence, Neogene siliciclastic distribution is a result of regional climate variability on the NWS. Up to 40 km of shoreline advance is verified in the Late Miocene and Pliocene, an example of climate-driven modification of a continental margin. Additionally, longshore transport intensifies during the Pliocene humid interval, causing NE migration of the deltaic system. Sedimentary and climate transitions are linked to reorganization of Indian Ocean paleoceanography, accompanying northward migration of the Australian continent and progressive

  6. ethiopian rift and adjacent highlands

    African Journals Online (AJOL)

    ABSTRACT: Remotely sensed thermal-infrared spectral data can be used to derive surface temperature of any object if the optical and thermal properties are known. In this study 1M band six has been used to assess the spatial variability of the kinetic temperature of the central Ethiopian rift lakes and adjacent highlands.

  7. Fault linkage and continental breakup

    Science.gov (United States)

    Cresswell, Derren; Lymer, Gaël; Reston, Tim; Stevenson, Carl; Bull, Jonathan; Sawyer, Dale; Morgan, Julia

    2017-04-01

    The magma-poor rifted margin off the west coast of Galicia (NW Spain) has provided some of the key observations in the development of models describing the final stages of rifting and continental breakup. In 2013, we collected a 68 x 20 km 3D seismic survey across the Galicia margin, NE Atlantic. Processing through to 3D Pre-stack Time Migration (12.5 m bin-size) and 3D depth conversion reveals the key structures, including an underlying detachment fault (the S detachment), and the intra-block and inter-block faults. These data reveal multiple phases of faulting, which overlap spatially and temporally, have thinned the crust to between zero and a few km thickness, producing 'basement windows' where crustal basement has been completely pulled apart and sediments lie directly on the mantle. Two approximately N-S trending fault systems are observed: 1) a margin proximal system of two linked faults that are the upward extension (breakaway faults) of the S; in the south they form one surface that splays northward to form two faults with an intervening fault block. These faults were thus demonstrably active at one time rather than sequentially. 2) An oceanward relay structure that shows clear along strike linkage. Faults within the relay trend NE-SW and heavily dissect the basement. The main block bounding faults can be traced from the S detachment through the basement into, and heavily deforming, the syn-rift sediments where they die out, suggesting that the faults propagated up from the S detachment surface. Analysis of the fault heaves and associated maps at different structural levels show complementary fault systems. The pattern of faulting suggests a variation in main tectonic transport direction moving oceanward. This might be interpreted as a temporal change during sequential faulting, however the transfer of extension between faults and the lateral variability of fault blocks suggests that many of the faults across the 3D volume were active at least in part

  8. Volcanic passive margins: another way to break up continents.

    Science.gov (United States)

    Geoffroy, L; Burov, E B; Werner, P

    2015-10-07

    Two major types of passive margins are recognized, i.e. volcanic and non-volcanic, without proposing distinctive mechanisms for their formation. Volcanic passive margins are associated with the extrusion and intrusion of large volumes of magma, predominantly mafic, and represent distinctive features of Larges Igneous Provinces, in which regional fissural volcanism predates localized syn-magmatic break-up of the lithosphere. In contrast with non-volcanic margins, continentward-dipping detachment faults accommodate crustal necking at both conjugate volcanic margins. These faults root on a two-layer deformed ductile crust that appears to be partly of igneous nature. This lower crust is exhumed up to the bottom of the syn-extension extrusives at the outer parts of the margin. Our numerical modelling suggests that strengthening of deep continental crust during early magmatic stages provokes a divergent flow of the ductile lithosphere away from a central continental block, which becomes thinner with time due to the flow-induced mechanical erosion acting at its base. Crustal-scale faults dipping continentward are rooted over this flowing material, thus isolating micro-continents within the future oceanic domain. Pure-shear type deformation affects the bulk lithosphere at VPMs until continental breakup, and the geometry of the margin is closely related to the dynamics of an active and melting mantle.

  9. Role of magmatism in continental lithosphere extension: an introduction to tectnophysics special issue

    Energy Technology Data Exchange (ETDEWEB)

    Van Wijk, Jolante W [Los Alamos National Laboratory

    2008-01-01

    The dynamics and evolution of rifts and continental rifted margins have been the subject of intense study and debate for many years and still remain the focus of active investigation. The 2006 AGU Fall Meeting session 'Extensional Processes Leading to the Formation of Basins and Rifted Margins, From Volcanic to Magma-Limited' included several contributions that illustrated recent advances in our understanding of rifting processes, from the early stages of extension to breakup and incipient seafloor spreading. Following this session, we aimed to assemble a multi-disciplinary collection of papers focussing on the architecture, formation and evolution of continental rift zones and rifted margins. This Tectonophysics Special Issue 'Role of magmatism in continental lithosphere extension' comprises 14 papers that present some of the recent insights on rift and rifted margins dynamics, emphasising the role of magmatism in extensional processes. The purpose of this contribution is to introduce these papers.

  10. The Myanmar continental shelf

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.; Rao, P.S.

    the International Indian Ocean Expedition (IIOE) of the 1960’s and a more recent expedition of the Indian research Vessel ORV Sagar Kanya in 2002. The IIOE results from the Andaman Sea have been summarized by Rodolfo (1969a, 1969b) while the ORV Sagar Kanya... on the Ayeyarwady Delta also occurs during exceptional rain events. Bank overflow and Myanmar Continental Shelf 7 flooding have been controlled by construction of numerous embankments which aid freshwater and sediment discharge to the sea...

  11. The lithosphere of the Appalachian orogen and Atlantic passive margin

    Science.gov (United States)

    Fischer, K. M.; MacDougall, J. G.; Hawman, R. B.; Parker, E. H.; Wagner, L. S.

    2012-12-01

    The lithosphere of the Appalachian orogen and Atlantic passive margin has recorded repeated episodes of continental collision and break-up. Improved resolution of crust and mantle structure in this region holds promise for better understanding of orogenesis, rifting and passive margin development. At a broad scale, tomographic models manifest a decrease in lithospheric thickness from the central U.S. craton into the Appalachian orogen. Migration of Sp scattered waves indicates that a significant drop in shear-wave velocity typically occurs at depths of 80-120 km in the eastern U.S., and where these phases fall within the transition from high velocity lid to lower velocity mantle obtained from tomography, they are interpretable as the seismological lithosphere-asthenosphere boundary. Beneath the Appalachians and coastal plain, Sp-derived lithospheric thicknesses are larger than those found in the tectonically active western U.S. where values range from 40-90 km. The vertical shear velocity gradients required to produce the observed Sp phases are sharp (drops of 4-10% over Flexible Arrays. The goal of the Southeastern Suture of the Appalachian Margin Experiment (SESAME) is to better understand lithospheric structures produced by accretion and rifting processes, with a particular focus on the Laurentia-Gondwana suture proposed in southern Georgia, adjacent regions of Mesozoic extension and magmatism, and the architecture of southern Appalachian orogenic crust. SESAME comprises 85 broadband EarthScope Flexible Array stations deployed in two N-S lines that cross the proposed Laurentia-Gondwana suture and extend into Florida; a third line is oriented roughly normal to Appalachian crustal terranes from northern Georgia to eastern Tennessee. Stations were installed in three phases from 2010-2012, and will remain in the field until 2014. Preliminary data analyses reveal significant shear-wave splitting in SKS and SKKS phases beneath the western SESAME stations. Fast

  12. Relation between denudation history and sediment supply from apatite fission track thermochronology in the northeast Brazilian Margin

    Science.gov (United States)

    Jelinek, Andrea; Chemale, Farid; Bueno, Gilmar

    2014-05-01

    The aim of this study is to provide a quantitative overview of Mesozoic-Cenozoic morphotectonic evolution and sediment supply to the northeast Brazilian margin. Landscape evolution and denudation histories for the northeastern Brazilian continental margin (Sergipe, Alagoas, Bahia, and Espírito Santo states) were detailed by apatite fission track thermochronology and thermal-history modeling and related with the sedimentological record of the offshore basins of the passive margin for a comparison with their denudational history. Approximately one hundred basement samples were analyzed from the coast to the inland of the Brazilian margin. The apparent fission track ages vary from 360 to 61 Ma and confined fission track lengths vary between 10 and 14.6 µm, indicating that not all of the samples recorded the same cooling events. The results of apatite fission track ages indicate that the area has been eroded regionally since the Mesozoic (Sergipe-Alagoas basins. Samples from the Conquista and Borborema Plateaus, and Mantiqueira Range record a Cretaceous-Paleogene onset of exhumation. This timing is consistent with the offshore sedimentary record, wherein a large clastic wedge started forming in the northeastern Sergipe-Alagoas basin, which suggests Sergipe-Alagoas basin records drainage reorganization and extension of the São Francisco River catchment. Interestingly, the Camamu basin, adjacent to the section of the margin does not record syn/post-rift exhumation, does contain a 6-km thick sedimentary succession, which should thus have been derived from more distal sources. The Neogene final denudation is observed throughout the study area and show conspicuous recent exhumation. The post-rift (<40 Ma) offshore sedimentation rates are generally lower than during preceding phases. This final sedimentary succession is thinner in all basins, consistent with limited onshore erosion during this time.

  13. Mafic dykes at the southwestern margin of Eastern Ghats belt ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Earth System Science; Volume 119; Issue 6. Mafic dykes at the southwestern margin of ... LREE enrichment. In view of the chemical signatures of OIB source, the ma fic dykes could as well be related to continental rifting, around 1.3 Ga, which may have been initiated by intra-plate volcanism.

  14. Clay sediment accumulation rates on the monsoon-dominated western continental shelf and slope region of India

    Digital Repository Service at National Institute of Oceanography (India)

    Borole, D.V.

    Clay accumulation rates shown in sediment cores from the nearshore to outer continental shelf and slope regions in water depths of 10-1246 m on the western continental margins of India were determined by the 210Pb dating technique. The 210Pb excess...

  15. The continental waters pollution

    International Nuclear Information System (INIS)

    Marsily, G. de

    1996-01-01

    This work deals with the continental water pollution. The sewage affect considerably the quality of some rivers water and of some basins. Moreover, a slow and general damage of natural waters has been established. The direct effects on men and on the natural medium (climatic change, aquatic ecosystems, water cycle) are given as well as the protection means (waste processing, the water-bearing bed and underground water protection, the aquatic ecosystems protection and planning) used and future to abate the water pollution. (O.L.). 17 refs., 6 tabs

  16. Megabenthic assemblages at the Hudson Canyon head (NW Atlantic margin): Habitat-faunal relationships

    Science.gov (United States)

    Pierdomenico, Martina; Gori, Andrea; Guida, Vincent G.; Gili, Josep-Maria

    2017-09-01

    The distribution of megabenthic communities at the head of Hudson Canyon and adjacent continental shelf was studied by means of underwater video transects and still photo imagery collected using a towed camera system. The goal was to explore the relationships between faunal distribution and physical seafloor conditions and to test the hypothesis that increased seafloor heterogeneity in the Hudson Canyon supports a larger diversity of benthic communities, compared with the adjacent continental shelf. Hierarchical cluster analysis was performed to identify benthic assemblages as defined in imagery. The BIO-ENV procedure and the Canonical Correspondence Analysis were carried out to elucidate species groupings in relation to terrain variables extracted from bathymetric data. Species accumulation curves were generated to evaluate species turn over in and out of Hudson Canyon. The results indicate that seafloor morphology is the main physical factor related to benthic community composition and distribution. Assemblages dominated by sponges, zoanthids and cup corals colonized the canyon margins and flanks, and were associated with coarse-grained sediments, while sea pen assemblages were observed along muddy seafloor within the thalweg. An assemblage dominated by sea stars occurred on the shelf, associated with a sandy seafloor. Some assemblages were exclusively observed in the canyon area, suggesting that the increased variability of seafloor composition, together with the oceanographic processes specific to the canyon area, enhance beta diversity. The colonization by benthic suspension feeders within the canyon, in contrast to shelf assemblages, mainly composed of carnivores and detritus feeders could be favored the intense hydrodynamics at the canyon head that increase the availability of suspended organic matter. From the perspective of management and conservation of marine resources, the results obtained support the relevance of Hudson Canyon as a biodiversity hotspot

  17. Uplift along the western margin of the Deccan Basalt Province: Is ...

    Indian Academy of Sciences (India)

    are common along many passive continental margins around the world, denudational unloa- ding and marginal isostatic uplift are commonly assumed to be the ..... The analysis based on Euclidian distance and centroid method reveals that majority of the rivers have, more or less iden- tical geomorphometric characteristics.

  18. The Cadiz margin study off Spain: An introduction

    Science.gov (United States)

    Nelson, C.H.; Maldonado, A.

    1999-01-01

    The Cadiz continental margin of the northeastern Gulf of Cadiz off Spain was selected for a multidisciplinary project because of the interplay of complex tectonic history between the Iberian and African plates, sediment supply from multiple sources, and unique Mediterranean Gateway inflow and outflow currents. The nature of this complex margin, particularly during the last 5 million years, was investigated with emphasis on tectonic history, stratigraphic sequences, marine circulation, contourite depositional facies, geotechnical properties, geologic hazards, and human influences such as dispersal of river contaminants. This study provides an integrated view of the tectonic, sediment supply and oceanographic factors that control depositional processes and growth patterns of the Cadiz and similar modem and ancient continental margins.

  19. Determining the COB location along the Iberian margin and Galicia Bank from gravity anomaly inversion, residual depth anomaly and subsidence analysis

    Science.gov (United States)

    Cowie, Leanne; Kusznir, Nick; Manatschal, Gianreto

    2015-11-01

    Knowledge and understanding of the ocean-continent transition (OCT) structure, continent-ocean boundary (COB) location and crustal type are of critical importance in evaluating rifted continental margin formation and evolution. OCT structure, COB location and magmatic type also have important implications for the understanding of the geodynamics of continental breakup and in the evaluation of petroleum systems in deep-water frontier oil and gas exploration at rifted continental margins. Mapping the distribution of thinned continental crust and lithosphere, its distal extent and the start of unequivocal oceanic crust and hence determining the OCT structure and COB location at rifted continental margins is therefore a generic global problem. In order to assist in the determination of the OCT structure and COB location, we present methodologies using gravity anomaly inversion, residual depth anomaly (RDA) analysis and subsidence analysis, which we apply to the west Iberian rifted continental margin. The west Iberian margin has one of the most complete data sets available for deep magma-poor rifted margins, so there is abundant data to which the results can be calibrated. Gravity anomaly inversion has been used to determine Moho depth, crustal basement thickness and continental lithosphere thinning; subsidence analysis has been used to determine the distribution of continental lithosphere thinning; and RDAs have been used to investigate the OCT bathymetric anomalies with respect to expected oceanic bathymetries at rifted continental margins. These quantitative analytical techniques have been applied to the west Iberian rifted continental margin along profiles IAM9, Lusigal 12 (with the TGS-extension) and ISE-01. Our predictions of OCT structure, COB location and magmatic type (i.e. the volume of magmatic addition, whether the margin is `normal' magmatic, magma-starved or magma-rich) have been tested and validated using ODP wells (Legs 103, 149 and 173), which provide

  20. Tectonics and sedimentary process in the continental talud in Uruguay

    International Nuclear Information System (INIS)

    De Santa Ana, H.; Soto, M.; Morales, E.; Tomasini, J.; Hernandez-Molina, F.; Veroslavsky, G.

    2012-01-01

    The morphology and evolution of the continental margin of Uruguay is due to the interaction of an important set of sedimentary processes. The contourite and turbiditic are the most significant processes which are associated with the development of submarine canyons as well as the gravitational mass respect to major landslides. These processes generate erosional and depositional features with a direct impact on different areas of application, which have potential environmental risks (gravitational landslides, earthquakes, tsunamis) and potential economic resources

  1. Zircon and monazite geochronology of the granulites and associated gneisses from the Rengali Province, India: Growth of the southern margin of the Singhbhum Craton

    Science.gov (United States)

    Bose, S.; Das, K.; Kimura, K.; Hayasaka, Y.; Hidaka, H.; Dasgupta, A.; Ghosh, G.; Mukhopadhyay, J.

    2013-12-01

    continental margin setting at ca. 2820 Ma before being cratonized at ca. 2800 Ma during the Rengali orogeny (ca. 2820-2800 Ma). Sedimentation in this basin appeared to be short-lived (~ 130 Ma). The geochronological history of the Rengali Province thus bears the signatures of crustal growth of Singhbhum Craton during the Neoarchean time which is similar to that of the North China Craton. Distinct monazite growth at ca. 500 Ma in leucogranite further implies rejuvenation of the continental margin during the Pan African orogeny. Interestingly, the studied craton-margin rocks were not affected by the tectonothermal pulses of the Meso-Neoproterozoic hot orogeny (1000-900 Ma) of the presently adjacent Eastern Ghats Province.

  2. Study of the particulate matter transfer and dumping using {sup 210} Po et le {sup 210} Pb. Application to the Gulf of Biscary (NE Atlantic Ocean) and the Gulf of Lion (NW Mediterranean Sea) continental margins; Etude du transfert et du depot du materiel particulaire par le {sup 210} Po et le {sup 210} Pb. Application aux marges continentales du Golfe de Gascogne (NE Atlantique) et du Golfe du Lion (NW Mediterranee)

    Energy Technology Data Exchange (ETDEWEB)

    Radakovitch, O.

    1995-07-07

    {sup 210} Po and {sup 210} Pb activities and fluxes were measured on seawater, sediment-trapped material collected during one year and sediment. Focalization of {sup 210} Pb is clearly noticed on the Cap-Ferret canyon (Gulf of Biscary) and the Lacaze-Duthiers canyon (western part of the Gulf of Lion). In both sites, {sup 210} Pb fluxes in traps and sediment are always higher than {sup 210} Pb flux available from atmospheric and in situ production. On the contrary, Grand-Rhone canyon and its adjacent open slope exhibit a {sup 210} Pb budget near equilibrium in the near-bottom sediment traps, but focalization is important in the sediment. For the entire Gulf of Lion margin, focalization of {sup 210} Pb in the sediment occurred principally between 500 and 1500 m water depth on the slope, and on the middle shelf mud-patch. {sup 210} Po and {sup 210} Pb have been used in the Cap Ferret and Grand-Rhone canyons to characterize the origin of the particulate trapped material. Two main sources feed the water column. The first source, localized in surface waters, is constituted by biogenic particles from primary production and lithogenic material. The second source, deeper, is due to resuspension at the shelf break and/or on the open slope. In each site, {sup 210} Po and {sup 210} Pb activities of the trapped particles did not show any relations with the major constituents. Quantity of particles appeared to be the main factor regulating adsorption processes of these nuclides. Sedimentation rates based on {sup 210} Po profiles decreased with increasing water depth, from 0.4 ti 0.06 cm y-1 on the Cap Ferret canyon (400 to 3000 m water depth) and from 0.5 to 0.05 cm y-1 for the entire Gulf of Lion margin (50 to 2000 m water depth). (author). 243 refs.

  3. ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

    Science.gov (United States)

    Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

    2014-12-01

    The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS

  4. Marginalization of the Youth

    DEFF Research Database (Denmark)

    Jensen, Niels Rosendal

    2009-01-01

    The article is based on a key note speach in Bielefeld on the subject "welfare state and marginalized youth", focusing upon the high ambition of expanding schooling in Denmark from 9 to 12 years. The unintended effect may be a new kind of marginalization.......The article is based on a key note speach in Bielefeld on the subject "welfare state and marginalized youth", focusing upon the high ambition of expanding schooling in Denmark from 9 to 12 years. The unintended effect may be a new kind of marginalization....

  5. Gas hydrate formation and dissipation histories in the northern margin of Canada: Beaufort-Mackenzie and the Sverdrup Basins

    Czech Academy of Sciences Publication Activity Database

    Majorowicz, J.; Osadetz, K.; Šafanda, Jan

    2012-01-01

    Roč. 2012, č. 1 (2012), 879393/1-879393/17 ISSN 1687-8833 Institutional research plan: CEZ:AV0Z30120515 Keywords : gas hydrates * Canadian Arctic continental margin * permafrost Subject RIV: DC - Siesmology, Volcanology, Earth Structure

  6. Neotectonics in the northern equatorial Brazilian margin

    Science.gov (United States)

    Rossetti, Dilce F.; Souza, Lena S. B.; Prado, Renato; Elis, Vagner R.

    2012-08-01

    An increasing volume of publications has addressed the role of tectonics in inland areas of northern Brazil during the Neogene and Quaternary, despite its location in a passive margin. Hence, northern South America plate in this time interval might have not been as passive as usually regarded. This proposal needs further support, particularly including field data. In this work, we applied an integrated approach to reveal tectonic structures in Miocene and late Quaternary strata in a coastal area of the Amazonas lowland. The investigation, undertaken in Marajó Island, mouth of the Amazonas River, consisted of shallow sub-surface geophysical data including vertical electric sounding and ground penetrating radar. These methods were combined with morphostructural analysis and sedimentological/stratigraphic data from shallow cores and a few outcrops. The results revealed two stratigraphic units, a lower one with Miocene age, and an upper one of Late Pleistocene-Holocene age. An abundance of faults and folds were recorded in the Miocene deposits and, to a minor extent, in overlying Late Pleistocene-Holocene strata. In addition to characterize these structures, we discuss their origin, considering three potential mechanisms: Andean tectonics, gravity tectonics related to sediment loading in the Amazon Fan, and rifting at the continental margin. Amongst these hypotheses, the most likely is that the faults and folds recorded in Marajó Island reflect tectonics associated with the history of continental rifting that gave rise to the South Atlantic Ocean. This study supports sediment deposition influenced by transpression and transtension associated with strike-slip divergence along the northern Equatorial Brazilian margin in the Miocene and Late Pleistocene-Holocene. This work records tectonic evidence only for the uppermost few ten of meters of this sedimentary succession. However, available geological data indicate a thickness of up to 6 km, which is remarkably thick for

  7. Isotopic characterisation of the sub-continental lithospheric mantle beneath Zealandia, a rifted fragment of Gondwana

    Science.gov (United States)

    Waight, Tod E.; Scott, James M.; van der Meer, Quinten H. A.

    2013-04-01

    The greater New Zealand region, known as Zealandia, represents an amalgamation of crustal fragments accreted to the paleo-Pacific Gondwana margin and which underwent significant thinning during the subsequent split from Australia and Antarctica in the mid-Cretaceous following opening of the Tasman Sea and the Southern Ocean. We present Sr, Nd and Pb isotopes and laser ablation trace element data for a comprehensive suite of clinopyroxene separates from spinel peridotite xenoliths (lherzolite to harzburgite) from the sub-continental lithospheric mantle across southern New Zealand. These xenoliths were transported to the surface in intra-plate alkaline volcanics that erupted across the region in the Eocene and Miocene (33-10 m.y.a.). Most of the volcanic suites have similar geochemical and isotopic properties that indicate melting of an OIB-like mantle source in the garnet stability zone and that contained a HIMU component. The volcanics have tapped two adjacent but chemically contrasting upper mantle domains: a fertile eastern domain and an extremely depleted western domain. Both domains underlie Mesozoic metasedimentary crust. Radiogenic isotope compositions of the clinopyroxene have 87Sr/86Sr between 0.7023 to 0.7035, 143Nd/144Nd between 0.5128 and 0.5132 (corresponding to ?Nd between +3 and +13) with a few samples extending to even more depleted compositions, 206Pb/204 Pb between ca. 19.5 to 21.5 and 208Pb/204 Pb between ca. 38.5 to 40.5. No correlations are observed between isotopic composition, age or geographical separation. These isotopic compositions indicate that the sub-continental lithospheric mantle under southern New Zealand has a regionally distinct and pervasive FOZO to HIMU - like signature. The isotopic signatures are also similar to those of the alkaline magmas that transported the xenoliths and suggest that most of the HIMU signature observed in the volcanics could be derived from a major source component in the sub-continental lithospheric mantle

  8. Matthew and marginality

    Directory of Open Access Journals (Sweden)

    Denis C. Duling

    1995-12-01

    Full Text Available This article explores marginality theory as it was first proposed in  the social sciences, that is related to persons caught between two competing cultures (Park; Stonequist, and, then, as it was developed in sociology as related to the poor (Germani and in anthropology as it was related to involuntary marginality and voluntary marginality (Victor Turner. It then examines a (normative scheme' in antiquity that creates involuntary marginality at the macrosocial level, namely, Lenski's social stratification model in an agrarian society, and indicates how Matthean language might fit with a sample inventory  of socioreligious roles. Next, it examines some (normative schemes' in  antiquity for voluntary margi-nality at the microsocial level, namely, groups, and examines how the Matthean gospel would fit based on indications of factions and leaders. The article ,shows that the author of the Gospel of Matthew has an ideology of (voluntary marginality', but his gospel includes some hope for (involuntary  marginals' in  the  real world, though it is somewhat tempered. It also suggests that the writer of the Gospel is a (marginal man', especially in the sense defined by the early theorists (Park; Stone-quist.

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

    Science.gov (United States)

    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

  10. Impacts of continental arcs on global carbon cycling and climate

    Science.gov (United States)

    Lee, C. T.; Jiang, H.; Carter, L.; Dasgupta, R.; Cao, W.; Lackey, J. S.; Lenardic, A.; Barnes, J.; McKenzie, R.

    2017-12-01

    On myr timescales, climatic variability is tied to variations in atmospheric CO2, which in turn is driven by geologic sources of CO2 and modulated by the efficiency of chemical weathering and carbonate precipitation (sinks). Long-term variability in CO2 has largely been attributed to changes in mid-ocean ridge inputs or the efficiency of global weathering. For example, the Cretaceous greenhouse is thought to be related to enhanced oceanic crust production, while the late Cenozoic icehouse is attributed to enhanced chemical weathering associated with the Himalayan orogeny. Here, we show that continental arcs may play a more important role in controlling climate, both in terms of sources and sinks. Continental arcs differ from island arcs and mid-ocean ridges in that the continental plate through which arc magmas pass may contain large amounts of sedimentary carbonate, accumulated over the history of the continent. Interaction of arc magmas with crustal carbonates via assimilation, reaction or heating can significantly add to the mantle-sourced CO2 flux. Detrital zircons and global mapping of basement rocks shows that the length of continental arcs in the Cretaceous was more than twice that in the mid-Cenozoic; maps also show many of these arcs intersected crustal carbonates. The increased length of continental arc magmatism coincided with increased oceanic spreading rates, placing convergent margins into compression, which favors continental arcs. Around 50 Ma, however, nearly all the continental arcs in Eurasia and North America terminated as India collided with Eurasia and the western Pacific rolled back, initiating the Marianas-Tonga-Kermadec intra-oceanic subduction complex and possibly leading to a decrease in global CO2 production. Meanwhile, extinct continental arcs continued to erode, resulting in regionally enhanced chemical weathering unsupported by magmatic fluxes of CO2. Continental arcs, during their magmatic lifetimes, are thus a source of CO2, driving

  11. Tourist preferences for ecotourism in rural communities adjacent to Kruger National Park: A choice experiment approach

    NARCIS (Netherlands)

    Chaminuka, P.; Groeneveld, R.A.; Selomane, A.O.; Ierland, van E.C.

    2012-01-01

    This paper analyses the potential for development of ecotourism in rural communities adjacent to Kruger National Park (KNP) in South Africa. We determine preferences of tourists, according to origin and income levels, for ecotourism and their marginal willingness to pay (MWTP) for three ecotourism

  12. Magma-poor vs. magma-rich continental rifting and breakup in the Labrador Sea

    Science.gov (United States)

    Gouiza, M.; Paton, D.

    2017-12-01

    Magma-poor and magma-rich rifted margins show distinct structural and stratigraphic geometries during the rift to breakup period. In magma-poor margins, crustal stretching is accommodated mainly by brittle faulting and the formation of wide rift basins shaped by numerous graben and half-graben structures. Continental breakup and oceanic crust accretion are often preceded by a localised phase of (hyper-) extension where the upper mantle is embrittled, serpentinized, and exhumed to the surface. In magma-rich margins, the rift basin is narrow and extension is accompanied by a large magmatic supply. Continental breakup and oceanic crust accretion is preceded by the emplacement of a thick volcanic crust juxtaposing and underplating a moderately thinned continental crust. Both magma-poor and magma-rich rifting occur in response to lithospheric extension but the driving forces and processes are believed to be different. In the former extension is assumed to be driven by plate boundary forces, while in the latter extension is supposed to be controlled by sublithospheric mantle dynamics. However, this view fails in explaining observations from many Atlantic conjugate margins where magma-poor and magma-rich segments alternate in a relatively abrupt fashion. This is the case of the Labrador margin where the northern segment shows major magmatic supply during most of the syn-rift phase which culminate in the emplacement of a thick volcanic crust in the transitional domain along with high density bodies underplating the thinned continental crust; while the southern segment is characterized mainly by brittle extension, mantle seprentinization and exhumation prior to continental breakup. In this work, we use seismic and potential field data to describe the crustal and structural architectures of the Labrador margin, and investigate the tectonic and mechanical processes of rifting that may have controlled the magmatic supply in the different segments of the margin.

  13. Lithosphere structure and subsidence evolution of the conjugate S-African and Argentine margins

    Science.gov (United States)

    Dressel, Ingo; Scheck-Wenderoth, Magdalena; Cacace, Mauro; Götze, Hans-Jürgen; Franke, Dieter

    2016-04-01

    The bathymetric evolution of the South Atlantic passive continental margins is a matter of debate. Though it is commonly accepted that passive margins experience thermal subsidence as a result of lithospheric cooling as well as load induced subsidence in response to sediment deposition it is disputed if the South Atlantic passive margins were affected by additional processes affecting the subsidence history after continental breakup. We present a subsidence analysis along the SW African margin and offshore Argentina and restore paleobathymetries to assess the subsidence evolution of the margin. These results are discussed with respect to mechanisms behind margin evolution. Therefore, we use available information about the lithosphere-scale present-day structural configuration of these margins as a starting point for the subsidence analysis. A multi 1D backward modelling method is applied to separate individual subsidence components such as the thermal- as well as the load induced subsidence and to restore paleobathymetries for the conjugate margins. The comparison of the restored paleobathymetries shows that the conjugate margins evolve differently: Continuous subsidence is obtained offshore Argentina whereas the subsidence history of the SW African margin is interrupted by phases of uplift. This differing results for both margins correlate also with different structural configurations of the subcrustal mantle. In the light of these results we discuss possible implications for uplift mechanisms.

  14. Synchronous alkaline and subalkaline magmatism during the late Neoproterozoic-early Paleozoic Ross orogeny, Antarctica: Insights into magmatic sources and processes within a continental arc

    Science.gov (United States)

    Hagen-Peter, Graham; Cottle, John M.

    2016-10-01

    Extensive exposure of intrusive igneous rocks along the Ross orogen of Antarctica-an ancient accretionary orogen on the margin of East Gondwana-provides an exceptional opportunity to study continental arc magmatism. There is significant petrologic and geochemical variability in igneous rocks within a 500-km-long segment of the arc in southern Victoria Land. The conspicuous occurrence of carbonatite and alkaline silicate rocks (nepheline syenite, A-type granite, and alkaline mafic rocks) adjacent to large complexes of subalkaline granitoids is not adequately explained by traditional models for continental arc magmatism. Extensive geochemical analysis (> 100 samples) and zircon U-Pb geochronology (n = 70) confirms that alkaline and carbonatitic magmatism was partially contemporaneous with the emplacement of large subduction-related igneous complexes in adjacent areas. Major pulses of subalkaline magmatism were compositionally distinct and occurred at different times along the arc. Large bodies of subalkaline orthogneiss and granite (sensu lato) were emplaced over similar time intervals (ca. 25 Myr) to the north (ca. 515-492 Ma) and south (ca. 550-525 Ma) of the alkaline magmatic province, although the initiation of these major pulses of magmatism was offset by ca. 35 Myr. Alkaline and carbonatitic magmatism spanned at least ca. 550-509 Ma, overlapping with voluminous subalkaline magmatism in adjacent areas. The most primitive rocks from each area have similarly enriched trace element compositions, indicating some common characteristics of the magma sources along the arc. The samples from the older subalkaline complex have invariably low Sr/Y ratios (generation and differentiation. The younger subalkaline complex and subalkaline rocks within the area of the alkaline province extend to higher Sr/Y ratios (up to 300), indicative of generation and differentiation at deeper levels. The significant spatial and temporal diversity in magmatism can be explained by a tectono

  15. Patents and Antitrust: Application to Adjacent Markets

    OpenAIRE

    Nicholas Economides; William N. Hebert

    2007-01-01

    We examine the intersection of patents and antitrust where a patent holder uses the monopoly power it possesses in the market for a patented product to exclude competitors in an adjacent market and attempt to monopolize or monopolize the adjacent market. The present scheme for awarding patents cannot judge when the issuance of a patent will lead to the appropriate balance between innovation and efficiency. Where a patent holder’s invention uses an interface with adjacent products, the patent ...

  16. Geology and exploration in southwest Pacific Australian region: Western and Northwestern Margin basins of Australia

    Energy Technology Data Exchange (ETDEWEB)

    Woollands, M.A. (BHP Petroleum Pty Ltd., Melbourne (Australia))

    1991-03-01

    The Marginal basins of Western and Northwestern Australia extend approximately 3,800 km along the coast and comprise both continental shelf and adjacent deepwater plateau areas. From north to south, the principal basins are the Sahul/Malita, Browse, Carnarvon, and Perth basins. The stratigraphic sequence within each basin is broadly similar, with initial widespread Triassic-Early Jurassic deposition in broad regional pre-rift sags. Middle Jurassic to Late Jurassic rifting on the Northwest Shelf and early Cretaceous rifting in the Perth basin varies in intensity across the region, and provides the primary control of hydrocarbon distribution through trap type, reservoir, and source rock quality. The best-developed oil source rocks of the region are found in these Jurassic rifted sequences. Although drilling to date has been generally sparse, with only some 824 wells throughout the entire area, significant accumulations of gas and oil have been found in the offshore Carnarvon basin and the Vulcan Graben area of the Browse basin. Recent discoveries of commercial oil at Jabiru in the Vulcan graben and Griffin in the Carnarvon basin have again focused activity on the area's oil potential. Many structural traps remain to be drilled and the potential for stratigraphic trapping has been only slightly explored. Large, poorly explored frontier areas, between the established producing areas and in the Perth basin, as well as adjacent deepwater, are available. However, present data suggest that not all key success factors, notably mature oil source rocks and good reservoirs, may be present in these areas.

  17. Continental United States Hurricane Strikes

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The Continental U.S. Hurricane Strikes Poster is our most popular poster which is updated annually. The poster includes all hurricanes that affected the U.S. since...

  18. The Ebro margin study, northwestern Mediterranean Sea - an introduction

    Science.gov (United States)

    Maldonado, A.; Hans, Nelson C.

    1990-01-01

    The Ebro continental margin from the coast to the deep sea off northeastern Spain was selected for a multidisciplinary project because of the abundant Ebro River sediment supply, Pliocene and Quaternary progradation, and margin development in a restricted basin where a variety of controlling factors could be evaluated. The nature of this young passive margin for the last 5 m.y. was investigated with particular emphasis on marine circulation, sediment dynamics, sediment geochemistry, depositional facies, seismic stratigraphy, geotechnical properties, geological hazards and human influences. These studies show the importance of marine circulation, variation in sediment supply, sea-level oscillation and tectonic setting for the understanding of modern and ancient margin depositional processes and growth patterns. ?? 1990.

  19. Refining margins: recent trends

    International Nuclear Information System (INIS)

    Baudoin, C.; Favennec, J.P.

    1999-01-01

    Despite a business environment that was globally mediocre due primarily to the Asian crisis and to a mild winter in the northern hemisphere, the signs of improvement noted in the refining activity in 1996 were borne out in 1997. But the situation is not yet satisfactory in this sector: the low return on invested capital and the financing of environmental protection expenditure are giving cause for concern. In 1998, the drop in crude oil prices and the concomitant fall in petroleum product prices was ultimately rather favorable to margins. Two elements tended to put a damper on this relative optimism. First of all, margins continue to be extremely volatile and, secondly, the worsening of the economic and financial crisis observed during the summer made for a sharp decline in margins in all geographic regions, especially Asia. Since the beginning of 1999, refining margins are weak and utilization rates of refining capacities have decreased. (authors)

  20. "We call ourselves marginalized"

    DEFF Research Database (Denmark)

    Jørgensen, Nanna Jordt

    2014-01-01

    In recent decades, indigenous knowledge has been added to the environmental education agenda in an attempt to address the marginalization of non-western perspectives. While these efforts are necessary, the debate is often framed in terms of a discourse of victimization that overlooks the agency o...... argue that researchers not only need to pay attention to how certain voices are marginalized in Environmental Education research and practice, but also to how learners as agents respond to, use and negotiate the marginalization of their perspectives.......In recent decades, indigenous knowledge has been added to the environmental education agenda in an attempt to address the marginalization of non-western perspectives. While these efforts are necessary, the debate is often framed in terms of a discourse of victimization that overlooks the agency...

  1. Slope failure of chalk channel margins

    DEFF Research Database (Denmark)

    Gale, A.; Anderskouv, Kresten; Surlyk, Finn

    2015-01-01

    The importance of mass transport and bottom currents is now widely recognized in the Upper Cretaceous Chalk Group of Northern Europe. The detailed dynamics and interaction of the two phenomena are difficult to study as most evidence is based on seismic data and drill core. Here, field observations...... the south, here interpreted as gravitational settling of the chalk immediately adjacent to the channel margin. Detailed biostratigraphic studies and sedimentological observations provide evidence for at least two discrete collapse events and suggest the slumping to be the result of channel margin...... oversteepening rather than evidence for a regional tectonic phase. The described example thus serves as an analogue for processes commonly only inferred from subsurface data....

  2. Areaplanning in marginal areas

    OpenAIRE

    Janneau, Thibaut; Arborg, Pernille; Sandberg, Rina

    2007-01-01

    This project is also a comparative analysis between two cases: Lolland Kommune and Venise Verte, having both a marginal characteristic. The analyze of these two marginal areas makes us able to found out some dilemmas showing the crucial issues of planners between economic development, social equity, cultural evolution and finally environmental enhancer. We also tried to see the different views of nature between two paradigms: widleness of nature and cultural landscapes as well as graduate dif...

  3. Pickering seismic safety margin

    International Nuclear Information System (INIS)

    Ghobarah, A.; Heidebrecht, A.C.; Tso, W.K.

    1992-06-01

    A study was conducted to recommend a methodology for the seismic safety margin review of existing Canadian CANDU nuclear generating stations such as Pickering A. The purpose of the seismic safety margin review is to determine whether the nuclear plant has sufficient seismic safety margin over its design basis to assure plant safety. In this review process, it is possible to identify the weak links which might limit the seismic performance of critical structures, systems and components. The proposed methodology is a modification the EPRI (Electric Power Research Institute) approach. The methodology includes: the characterization of the site margin earthquake, the definition of the performance criteria for the elements of a success path, and the determination of the seismic withstand capacity. It is proposed that the margin earthquake be established on the basis of using historical records and the regional seismo-tectonic and site specific evaluations. The ability of the components and systems to withstand the margin earthquake is determined by database comparisons, inspection, analysis or testing. An implementation plan for the application of the methodology to the Pickering A NGS is prepared

  4. SOCIAL MARGINALIZATION AND HEALTH

    Directory of Open Access Journals (Sweden)

    Marjana Bogdanović

    2007-04-01

    Full Text Available The 20th century was characterized by special improvement in health. The aim of WHO’s policy EQUITY IN HEALTH is to enable equal accessibility and equal high quality of health care for all citizens. More or less some social groups have stayed out of many social systems even out of health care system in the condition of social marginalization. Phenomenon of social marginalization is characterized by dynamics. Marginalized persons have lack of control over their life and available resources. Social marginalization stands for a stroke on health and makes the health status worse. Low socio-economic level dramatically influences people’s health status, therefore, poverty and illness work together. Characteristic marginalized groups are: Roma people, people with AIDS, prisoners, persons with development disorders, persons with mental health disorders, refugees, homosexual people, delinquents, prostitutes, drug consumers, homeless…There is a mutual responsibility of community and marginalized individuals in trying to resolve the problem. Health and other problems could be solved only by multisector approach to well-designed programs.

  5. Deep lithospheric structure and hypogene metallogeny at convergent plate margins

    Czech Academy of Sciences Publication Activity Database

    Hanuš, Václav; Vaněk, Jiří; Špičák, Aleš

    2003-01-01

    Roč. 8, 1/4 (2003), s. 141-149 ISSN 0163-3171 R&D Projects: GA ČR GA205/95/0264; GA ČR GA205/97/0898; GA AV ČR IAA3012805; GA AV ČR IAA3012002 Institutional research plan: CEZ:AV0Z3012916 Keywords : continental lithosphere * hypogene metallogeny * convergent plate margins Subject RIV: DC - Siesmology, Volcanology, Earth Structure

  6. Direct measurement of nitrogen gas fluxes from continental shelf sediments

    Science.gov (United States)

    Devol, Allan H.

    1991-01-01

    IT has been suggested that denitrification in continental shelf and slope sediments is the most important sink in the marine nitrogen cycle1-4. This conclusion has been reached, not from direct measurements of denitrification in these areas, but rather from indirect estimates derived from pore-water models of diagenetic processes. In highly bioturbated continental shelf and slope sediments with steep pore-water gradients, such indirect estimates may not be applicable5,6.1 have now made direct, in situ measurements of denitrification in sediments of the eastern North Pacific continental margin by determining the flux of molecular nitrogen out of the sediments into the overlying water. Denitrification rates in continental shelf sediments measured in this fashion averaged 3.7 pmol N cm-2s-1. The flux of nitrate from the overlying water into the sediments was only 1.5 pmol N cm-2s-1, showing that most of the nitrogen gas production is coupled to nitrification within the sediments. The denitrification rates observed here are four to five times those estimated previously by indirect methods for these same sediments, and indicate the limitations of such indirect estimates. My results suggest that the global denitrification rate in shelf and slope sediments may be greater than previously thought, and confirm the importance of sedimentary denitrification in the marine nitrogen budget.

  7. Late Quaternary sea level and environmental changes from relic carbonate deposits of the western margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Rajagopalan, G.; Vora, K.H.; Almeida, F.

    the entire margin. The age of these deposits on the continental shelf off Cape Comorin and Mangalore, between 110 and 18m depth, ranges between 12, 610 ¹4C yr BP and 6,390 ¹4C yr BP. On the northwestern margin of India, especially on the carbonate platform...

  8. Ocean Margins Programs, Phase I research summaries

    Energy Technology Data Exchange (ETDEWEB)

    Verity, P. [ed.

    1994-08-01

    During FY 1992, the DOE restructured its regional coastal-ocean programs into a new Ocean Margins Program (OMP), to: Quantify the ecological and biogeochemical processes and mechanisms that affect the cycling, flux, and storage of carbon and other biogenic elements at the land/ocean interface; Define ocean-margin sources and sinks in global biogeochemical cycles, and; Determine whether continental shelves are quantitatively significant in removing carbon dioxide from the atmosphere and isolating it via burial in sediments or export to the interior ocean. Currently, the DOE Ocean Margins Program supports more than 70 principal and co-principal investigators, spanning more than 30 academic institutions. Research funded by the OMP amounted to about $6.9M in FY 1994. This document is a collection of abstracts summarizing the component projects of Phase I of the OMP. This phase included both research and technology development, and comprised projects of both two and three years duration. The attached abstracts describe the goals, methods, measurement scales, strengths and limitations, and status of each project, and level of support. Keywords are provided to index the various projects. The names, addresses, affiliations, and major areas of expertise of the investigators are provided in appendices.

  9. Geophysical imaging of buried volcanic structures within a continental back-arc basin

    DEFF Research Database (Denmark)

    Stratford, Wanda Rose; Stern, T.A.

    2008-01-01

    Hidden beneath the ~2 km thick low-velocity volcaniclastics on the western margin of the Central Volcanic Region, North Island, New Zealand, are two structures that represent the early history of volcanic activity in a continental back-arc. These ~20×20 km structures, at Tokoroa and Mangakino, fo...

  10. A Thirty-Year Perspective on Washington Continental-Shelf Sedimentation: The Impact of Recent Environmental Changes

    Science.gov (United States)

    Davies, M. H.; Nittrouer, C. A.

    2006-12-01

    The Washington continental shelf is on a collision margin, adjacent to a historically accreting shoreline. A thorough study of shelf sedimentation performed in 1975/1976 found that sediment accumulation was steady- state at that time. Over the past 30 years, onset of coastal erosion, an increasingly energetic wave climate, and human impacts on the Columbia River have potentially changed shelf sedimentation. To examine this, sixteen sites from the 1975/1976 study were reoccupied in 2005, and the same analyses for accumulation rates and grain-size distribution were performed. The use of Pb-210 (half-life 22.3 years) as a sedimentological tool was pioneered on the Washington shelf, providing a special opportunity to look at changes in sedimentation over the past several decades. However, Pb-210 profiles are remarkably similar to those from 1975/1976, and sediment accumulation rates on the shelf have remained constant within a 95% confidence limit. Surficial sediment was found to be on average 8-9% coarser than in 1975/1976, perhaps due to the increase in wave energy. The increasing seaward transport of nearshore sand may be causing a serendipitous balance with decreases in sediment supply resulting from anthropogenic impacts on the sediment dispersal system (e.g., damming of the Columbia River).

  11. Quaternary nanofossils on the Brazilian continental shelf; Nanofosseis calcarios do quaternario da margem continental brasileira

    Energy Technology Data Exchange (ETDEWEB)

    Antunes, Rogerio Loureiro [PETROBRAS S.A., Rio de Janeiro, RJ (Brazil). Centro de Pesquisas (CENPES). Gerencia de Bioestratigrafia e Paleoecologia], E-mail: rlantunes@petrobras.com.br

    2007-07-01

    The study of calcareous nanofossils occurring in the deposits on the Brazilian continental margin began in the late 1960s, undertaken solely by PETROBRAS. Instead of presenting an academic outlook, the purpose of these investigations is first to formulate a biostratigraphic framework to apply to oil well samples. The initial result was the first zoning for the Brazilian continental margin, which considered the deposits formed between the Aptian and Miocene series. Since the 1960s to date, many papers have been written either with details of that original zoning or applying nanofossil biostratigraphy to solve stratigraphic problems. Regardless of all the papers and studies undertaken, little attention has been paid to the Quaternary, since these deposits are normally of no interest to petroleum geology stricto sensu, especially in a large part of the Brazilian margin. On the other hand, there are a few articles and some Master's dissertations and PhD theses that were written and/or are in progress in Brazilian universities. On the other hand, elsewhere in the world, Quaternary nanofossils have been thoroughly investigated in terms of biostratigraphy and paleoceanography. It is, therefore, very clear that there is a gap between what is being done elsewhere in the world and what has been done in Brazil. In fact, this gap is not larger simply because of a few researchers in Brazilian universities who are studying this topic. The intention of this paper is to contribute toward a richer study of Quaternary nanofossils. It, therefore, contains illustrations and taxonomic descriptions of many species observed in the younger strata of the Brazilian margin basins. This article not only aspires to portray and disseminate the potential of nanofossils for the marine Quaternary study but is also an invitation to students (under and post-graduates) and university researchers - an invitation to learn a little more about the subject and spend some time studying these real gems

  12. The Outcropping Basement of the Demerara Marginal Plateau (French Guiana-Surinam): Results from DRADEM Dredges

    Science.gov (United States)

    Klingelhoefer, F.; Basile, C.; Girault, I.; Bernet, M.; Jean-Louis, P.; Agranier, A.; Loncke, L.; Heuret, A.; Poetisi, E.

    2017-12-01

    At the connection between the Central and the Equatorial Atlantic, the Demerara marginal plateau is a continental margin that resulted from both Jurassic and Cretaceous rifting. The DRADEM cruise (2016) dredged the northern continental slope from 4700 to 3500 m depths. Three dredges recovered magmatic rocks, six dredges recovered sedimentary rocks. In two adjacent dredges, magmatic rocks correspond to fresh basalts and rhyolites belonging to a calc-alcaline, Ti-rich suite. Zircons in rhyolites were dated at 173,4 ± 1,6 Ma. In a third dredge, magmatic rocks are trachy-basalts and basaltic trachy-andesites. All samples share similar patterns in trace elements. They are Light Rare Earth-enriched, and present positive anomalies in Nb, Ta, Zr and Hf, indicative of Ocean Island Basalt magmas, and consequently an hot spot-related magmatic origin. The trachy-basalts were altered, eroded, and sedimented in a carbonate platform forming clasts in a bioclastic and lithoclastic rudstone. Large aragonitic shells were dissolved, and the moldic porosity is partially filled by vadose silts, indicating post-sedimentation outcropping above sea-level. The other sites recovered sandstones : either coarse, or from a delta shoreface, or from an oolithic platform. Cooling ages of detrital zircons from three sites indicate in each site three main peaks interpreted as cooling ages of the detrital sources. They roughly coincide with (1) the lower Cretaceous Equatorial Atlantic rifting, (2) the Central Atlantic Magmatic Province event at the Trias-Jurassic boundary and the subsequent Central Atlantic Rifting and (3) the Panafrican exhumation, possibly in the Hercynian orogen. Cristallisation ages inferred from 206Pb/238U dating of detrital zircons are mainly distributed around 650 Ma and may indicate detrital source from the Panafrican belt in West Africa, prior to the opening of the Equatorial Atlantic. These findings allow to discuss the subsidence of the northern edge of the Demerara

  13. Full-fit Reconstruction of North America-Greenland conjugate margins and implications for reconstructing the North Atlantic

    Science.gov (United States)

    Hosseinpour, Maral; Müller, Dietmar; Williams, Simon

    2013-04-01

    Many reconstruction models for opening of the Labrador Sea and Baffin Bay between North America and Greenland incorporate poles of rotation derived using identifications of magnetic anomalies C28-C33 in the Labrador Sea. However, recent seismic and geological data suggest the crust in which these spreading anomalies have been interpreted is not oceanic crust; the magnetic anomalies may instead delineate igneous penetrations into thinned and fragmented crust within the continent-ocean transition zone. These data suggest a more seaward extension of extended continental material in the Greenland margin near the Davis Strait than assumed in previous full-fit reconstructions. These uncertainties are an important consideration for deriving full-fit reconstruction of this region and adjacent plates. Our study focuses on the full-fit configuration of Greenland and North America using an approach that considers continental deformation in a quantitative manner, in contrast to traditional models that treat continents as rigid blocks. We redefined the continent-ocean boundary by assimilating observations from available seismic profiles and potential field anomaly maps. A limit was then set between stretched and un-stretched continental crust using the crustal thickness map derived from the gravity inversion method, constrained by crustal thickness estimates from available seismic refraction and receiver functions. The COBs were restored to their pre-stretched locations by generating small circle motion paths between these crustal boundaries. Restored COBs were matched together using the quantitative least-squares methodology of Hellinger (1981), and correlating Precambrian bedrock units and fracture zones in both margins, to compute the total-fit Euler pole of rotation. A preferred full-fit model was chosen based on the strongest compatibility with geological and geophysical data. Changing relative plate motions between North America and Greenland before the start of seafloor

  14. Polyphase Rifting and Breakup of the Central Mozambique Margin

    Science.gov (United States)

    Senkans, Andrew; Leroy, Sylvie; d'Acremont, Elia; Castilla, Raymi

    2017-04-01

    The breakup of the Gondwana supercontinent resulted in the formation of the Central Mozambique passive margin as Africa and Antarctica were separated during the mid-Jurassic period. The identification of magnetic anomalies in the Mozambique Basin and Riiser Larsen Sea means that post-oceanisation plate kinematics are well-constrained. Unresolved questions remain, however, regarding the initial fit, continental breakup process, and the first relative movements of Africa and Antarctica. This study uses high quality multi-channel seismic reflection profiles in an effort to identify the major crustal domains in the Angoche and Beira regions of the Central Mozambique margin. This work is part of the integrated pluri-disciplinary PAMELA project*. Our results show that the Central Mozambique passive margin is characterised by intense but localised magmatic activity, evidenced by the existence of seaward dipping reflectors (SDR) in the Angoche region, as well as magmatic sills and volcanoclastic material which mark the Beira High. The Angoche region is defined by a faulted upper-continental crust, with the possible exhumation of lower crustal material forming an extended ocean-continent transition (OCT). The profiles studied across the Beira high reveal an offshore continental fragment, which is overlain by a pre-rift sedimentary unit likely to belong to the Karoo Group. Faulting of the crust and overlying sedimentary unit reveals that the Beira High has recorded several phases of deformation. The combination of our seismic interpretation with existing geophysical and geological results have allowed us to propose a breakup model which supports the idea that the Central Mozambique margin was affected by polyphase rifting. The analysis of both along-dip and along-strike profiles shows that the Beira High initially experienced extension in a direction approximately parallel to the Mozambique coastline onshore of the Beira High. Our results suggest that the Beira High results

  15. Marginal kidney donor

    Directory of Open Access Journals (Sweden)

    Ganesh Gopalakrishnan

    2007-01-01

    Full Text Available Renal transplantation is the treatment of choice for a medically eligible patient with end stage renal disease. The number of renal transplants has increased rapidly over the last two decades. However, the demand for organs has increased even more. This disparity between the availability of organs and waitlisted patients for transplants has forced many transplant centers across the world to use marginal kidneys and donors. We performed a Medline search to establish the current status of marginal kidney donors in the world. Transplant programs using marginal deceased renal grafts is well established. The focus is now on efforts to improve their results. Utilization of non-heart-beating donors is still in a plateau phase and comprises a minor percentage of deceased donations. The main concern is primary non-function of the renal graft apart from legal and ethical issues. Transplants with living donors outnumbered cadaveric transplants at many centers in the last decade. There has been an increased use of marginal living kidney donors with some acceptable medical risks. Our primary concern is the safety of the living donor. There is not enough scientific data available to quantify the risks involved for such donation. The definition of marginal living donor is still not clear and there are no uniform recommendations. The decision must be tailored to each donor who in turn should be actively involved at all levels of the decision-making process. In the current circumstances, our responsibility is very crucial in making decisions for either accepting or rejecting a marginal living donor.

  16. EXPLOITATION OF THE CONTINENTAL SHELF IN DISPUTED AREAS AN EXAMPLE OF THE ARCTIC OCEAN

    Directory of Open Access Journals (Sweden)

    M. S. Peters

    2016-01-01

    Full Text Available This paper aims to examine the legal regime related to define the outer limits of the continental shelf beyond 200 NM. Firstly, special focus will be on the development of the legal concept of the continental shelf. Relevant provisions of the LOS Convention and Article76 inparticular will be scrutinized. Subsequently there is an assumption on which the principles of the Arctic outer continental margin delimitation will be conducted in relation of hypothetic application during the practice of an international adjudicative body. The delimitation within 200 NM and beyond200 NM will be compared. The fourth chapter will be concentrated on the role of the Commission as an important participant of delimitation process. Also there will be a general overview of the state practice concerning the establishment of the outer continental margin in theArctic, the reaction of other Arctic States and recommendations of the Commission.It will be concluded that 'there are some difficulties in implementing the Article 76 (locating the foot of the slope and dealing with ridge issues, however it is possible to delimit the continental margin of the world based on the Article 76.' Difficulties in implementing and some discrepancies in provisions of the Article 76 do not constitute grounds for considering of a new legal approach. Discrepancies are mainly con tained in the Rules of Procedure and in the Scientific and Technical Guidelines of the Commission. They can be disposed practically without considering the legal concept. In case of unresolved land or maritime dispute the cooperation among coastal states is the best way to avoid conflicts while delimiting the outer continental margin.

  17. Peridotite weathering is the missing ingredient of Earth's continental crust composition.

    Science.gov (United States)

    Beinlich, Andreas; Austrheim, Håkon; Mavromatis, Vasileios; Grguric, Ben; Putnis, Christine V; Putnis, Andrew

    2018-02-12

    The chemical composition of the continental crust cannot be adequately explained by current models for its formation, because it is too rich in Ni and Cr compared to that which can be generated by any of the proposed mechanisms. Estimates of the crust composition are derived from average sediment, while crustal growth is ascribed to amalgamation of differentiated magmatic rocks at continental margins. Here we show that chemical weathering of Ni- and Cr-rich, undifferentiated ultramafic rock equivalent to ~1.3 wt% of today's continental crust compensates for low Ni and Cr in formation models of the continental crust. Ultramafic rock weathering produces a residual that is enriched in Ni and also silica. In the light of potentially large volumes of ultramafic rock and high atmospheric CO 2 concentrations during the Archean, chemical weathering must therefore have played a major role in forming compositionally evolved components of the early Earth's crust.

  18. From Borders to Margins

    DEFF Research Database (Denmark)

    Parker, Noel

    2009-01-01

    upon Deleuze's philosophy to set out an ontology in which the continual reformulation of entities in play in ‘post-international' society can be grasped.  This entails a strategic shift from speaking about the ‘borders' between sovereign states to referring instead to the ‘margins' between a plethora...

  19. Masculinity at the margins

    DEFF Research Database (Denmark)

    Jensen, Sune Qvotrup

    2010-01-01

    This article analyses how young marginalized ethnic minority men in Denmark react to the othering they are subject to in the media as well as in the social arenas of every day life. The article is based on theoretically informed ethnographic fieldwork among such young men as well as interviews an...

  20. Maintaining plant safety margins

    International Nuclear Information System (INIS)

    Bergeron, P.A.

    1989-01-01

    The Final Safety Analysis Report Forms the basis of demonstrating that the plant can operate safely and meet all applicable acceptance criteria. In order to assure that this continues through each operating cycle, the safety analysis is reexamined for each reload core. Operating limits are set for each reload core to assure that safety limits and applicable acceptance criteria are not exceeded for postulated events within the design basis. These operating limits form the basis for plant operation, providing barriers on various measurable parameters. The barriers are refereed to as limiting conditions for operation (LCO). The operating limits, being influenced by many factors, can change significantly from cycle to cycle. In order to be successful in demonstrating safe operation for each reload core (with adequate operating margin), it is necessary to continue to focus on ways to maintain/improve existing safety margins. Existing safety margins are a function of the plant type [boiling water reactor/pressurized water reactor (BWR/PWR)], nuclear system supply (NSSS) vendor, operating license date, core design features, plant design features, licensing history, and analytical methods used in the safety analysis. This paper summarizes the experience at Yankee Atomic Electric Company (YAEC) in its efforts to provide adequate operating margin for the plants that it supports

  1. Oceanography of marginal seas

    Digital Repository Service at National Institute of Oceanography (India)

    DileepKumar, M.

    The North Indian Ocean consists of three marginal seas; The Persian Gulf and the Red Sea in the west and the Andaman Sea in the east. Oceanographic features of these semi-enclosed basins have been discussed in this article. While circulation...

  2. Marginally Deformed Starobinsky Gravity

    DEFF Research Database (Denmark)

    Codello, A.; Joergensen, J.; Sannino, Francesco

    2015-01-01

    We show that quantum-induced marginal deformations of the Starobinsky gravitational action of the form $R^{2(1 -\\alpha)}$, with $R$ the Ricci scalar and $\\alpha$ a positive parameter, smaller than one half, can account for the recent experimental observations by BICEP2 of primordial tensor modes....

  3. Adjacent segment disease following cervical spine surgery.

    Science.gov (United States)

    Cho, Samuel K; Riew, K Daniel

    2013-01-01

    Cervical spine surgery is broadly divided into fusion and nonfusion procedures. Anterior cervical diskectomy and fusion (ACDF) is a common procedure, although adjacent segment disease following the surgery is an ongoing clinical concern. Adjacent segment cervical disease occurs in approximately 3% of patients per year, with an expected incidence of 25% within the first 10 years following fusion. Nonfusion procedures such as anterior diskectomy and posterior foraminotomy do not decrease the rate of adjacent segment disease compared with ACDF. Recently, enthusiasm has developed for artificial disk replacement as a motion-sparing alternative to fusion. To date, however, multiple clinical trials and subsequent follow-up studies have failed to demonstrate significant reduction of adjacent segment disease when artificial disk replacement is performed instead of fusion.

  4. Adjacent Segment Pathology after Lumbar Spinal Fusion

    OpenAIRE

    Lee, Jae Chul; Choi, Sung-Woo

    2015-01-01

    One of the major clinical issues encountered after lumbar spinal fusion is the development of adjacent segment pathology (ASP) caused by increased mechanical stress at adjacent segments, and resulting in various radiographic changes and clinical symptoms. This condition may require surgical intervention. The incidence of ASP varies with both the definition and methodology adopted in individual studies; various risk factors for this condition have been identified, although a significant contro...

  5. Adjacent Segment Pathology after Anterior Cervical Fusion

    OpenAIRE

    Chung, Jae Yoon; Park, Jong-Beom; Seo, Hyoung-Yeon; Kim, Sung Kyu

    2016-01-01

    Anterior cervical fusion has become a standard of care for numerous pathologic conditions of the cervical spine. However, subsequent development of clinically significant disc disease at levels adjacent to fused discs is a serious long-term complication of this procedure. As more patients live longer after surgery, it is foreseeable that adjacent segment pathology (ASP) will develop in increasing numbers of patients. Also, ASP has been studied more intensively with the recent popularity of mo...

  6. What are volcanic passive margins? A discussion based on seismic and field examples

    Science.gov (United States)

    Zalan, Pedro

    2014-05-01

    Volcanic or magma-rich passive margins are continental margins whose underlying rift basins, developed during the stretching and thinning phases that affected the continental crust before breakup, are totally or predominantly filled by volcanic and volcanic-derived rocks. The type of magma is usually fissural tholeiitic basalts, eventually bi-modal basaltic-rhyolitic. This is in strong contrast with the definition of sedimentary or magma-poor passive margins, whose rift basins are predominantly filled with sedimentary rocks. As the name states, magma-poor margins may display a certain amount of magmatism, but which is clearly secondary with respect to the dominant sedimentary nature of the syn-rift filling. These are two end-members in the classification of passive margins, and as such, transitional members represented by passive margins displaying characteristics of both extremes are recognizable. The significant difference in the nature of the syn-rift strata gives rise to strikingly different seismic facies in seismic sections that cross the entire width of passive margins, allowing a relatively easy visual distinction between the end-members, as well as of the transitional members. Typical growth volcanic strata dip seawards and fill grabens controlled by landward dipping listric faults, giving rise to the well known laterally accreted wedges of seaward-dipping reflectors (SDR). The amount of magmatism in volcanic margins is so high that it impacts a large area surrounding the continental margin, thus, also easing the recognition of this end-member through the analysis of the neighboring surface geology. Volcanic margins are characterized by Large Igneous Provinces (LIPs) that present pre-rift (lava deltas, tabular lava flows, trap-stage), syn-rift (seaward-dipping growth strata, extrusive centers, SDR-stage) and post-rift (volcanos, punctual lava flows) magmatism. Breakup of the continental crust takes place at the climax of the SDR-stage. Volcanism is

  7. Tectonic growth of a Cretaceous-Eocene accretionary orogen formed at the southern margin of the Caribbean Plate: integrated geological insights from northernmost Colombia

    Science.gov (United States)

    Cardona, A.; Weber, M. B.; Bayona, G.; Jaramillo, C.; Montes, C.; Ojeda, G.; Duque, J. F.; Salazar, C. A.

    2007-05-01

    Geological characteristics from the Cretaceous to Eocene metamorphic and igneous basement rocks from the Guajira and the NW corner of the Sierra Nevada de Santa Marta massifs in the northern Colombian Caribbean region, and the stratigraphy of adjacent basins, reveal different stages of growth of a segmented Late Cretaceous to Eocene accretionary orogen formed by interaction between the NW margin of South America and the Caribbean plate. Extensive intercalations of metavolcano-sedimentary rocks in the Santa Marta region, chemical composition of spinels and pyroxenes from serpentinized mantle tectonites and gabbros, as well as whole rock geochemistry from basaltic dykes from the Guajira massifs, record the evolution of a Cretaceous intra-oceanic arc in a succesion of Mariana- and Chile-type subduction styles. Geological and positive gravity signatures suggest that this arc was accreted and tectonically underplated to the continental margin of South America, creating a Maastrichian-Paleocene syn-orogenic basin, presently cropping out in the Cesar-Rancheria valley. After this collisional event, subduction of the Caribbean plate under South America started, as revealed by intrusion of composite stitched Late Paleocene-Eocene granitoids in the NW corner of the SNSM and Guajira massifs. These plutons show continental calc-alkaline geochemical signatures and more evolved Sr and Nd isotopic compositions than juvenile and older intra-oceanic arc magmatic rocks. This new subduction environment is linked to the convergence between North and South America at this time. Low pressure estimations and fast cooling rates between 450-250° for the Eocene granitoids in the Guajira and Santa Marta regions, indicate shallow < 7 Km depths of intrusion. Local unconformable stratigraphic relationships with Eocene-Miocene sediments at the Guajira region and overimposed post-magmatic low temperature deformation in some of these granitoids suggest an important Late Eocene unroofing and

  8. The open sea as the main source of methylmercury in the water column of the Gulf of Lions (Northwestern Mediterranean margin)

    Science.gov (United States)

    Cossa, Daniel; Durrieu de Madron, Xavier; Schäfer, Jörg; Lanceleur, Laurent; Guédron, Stéphane; Buscail, Roselyne; Thomas, Bastien; Castelle, Sabine; Naudin, Jean-Jacques

    2017-02-01

    Despite the ecologic and economical importance of coastal areas, the neurotoxic bioaccumulable monomethylmercury (MMHg) fluxes within the ocean margins and exchanges with the open sea remain unassessed. The aim of this paper is to address the questions of the abundance, distribution, production and exchanges of methylated mercury species (MeHgT), including MMHg and dimethylmercury (DMHg), in the waters, atmosphere and sediments of the Northwestern Mediterranean margin including the Rhône River delta, the continental shelf and its slope (Gulf of Lions) and the adjacent open sea (North Gyre). Concentrations of MeHgT ranged from <0.02 to 0.48 pmol L-1 with highest values associated with the oxygen-deficient zone of the open sea. The methylated mercury to total mercury proportion (MeHgT/HgT) increased from 2% to 4% in the Rhône River to up to 30% (averaging 18%) in the North Gyre waters, whereas, within the shelf waters, MeHgT/HgT proportions were the lowest (1-3%). We calculate that the open sea is the major source of MeHgT for the shelf waters, with an annual flux estimated at 0.68 ± 0.12 kmol a-1 (i.e., equivalent to 12% of the HgT flux). This MeHgT influx is more than 80 times the direct atmospheric deposition or the in situ net production, more than 40 times the estimated "maximum potential" annual efflux from shelf sediment, and more than 7 times that of the continental sources. In the open sea, ratios of MMHg/DMHg in waters were always <1 and minimum in the oxygen deficient zones of the water column, where MeHg concentrations are maximum. This observation supports the idea that MMHg could be a degradation product of DMHg produced from inorganic divalent Hg.

  9. Drift of continental rafts with asymmetric heating.

    Science.gov (United States)

    Knopoff, L; Poehls, K A; Smith, R C

    1972-06-02

    A laboratory model of a lithospheric raft is propelled through a viscous asthenospheric layer with constant velocity of scaled magnitude appropriate to continental drift. The propulsion is due to differential heat concentration in the model oceanic and continental crusts.

  10. Marginalized Youth. An Introduction.

    OpenAIRE

    Kessl, Fabian; Otto, Hans-Uwe

    2009-01-01

    The life conduct of marginalized groups has become subject to increasing levels of risk in advanced capitalist societies. In particular, children and young people are confronted with the harsh consequences of a “new poverty” in the contemporary era. The demographic complexion of today’s poverty is youthful, as a number of government reports have once again documented in recent years in Australia, Germany, France, Great Britain, the US or Scandinavian countries. Key youth studies have shown a ...

  11. Rio+20, biodiversity marginalized

    OpenAIRE

    Carrière, Stéphanie M.; Rodary, Estienne; Méral, Philippe; Serpantié, Georges; Boisvert, Valérie; Kull, C.A.; Lestrelin, Guillaume; Lhoutellier, Louise; Moizo, Bernard; Smektala, G.; Vandevelde, Jean-Christophe

    2013-01-01

    At the Rio+20 Conference (June 2012), the biodiversity conservation agenda was subsumed into broader environmental issues like sustainable development, “green economy,” and climate change. This shoehorning of biodiversity issues is concomitant with a trend toward market-based instruments and toward standardized biodiversity assessment and monitoring. This article raises concern that these trends can marginalize important and specific aspects of biodiversity governance, including other policy ...

  12. Containment safety margins

    International Nuclear Information System (INIS)

    Von Riesemann, W.A.

    1980-01-01

    Objective of the Containment Safety Margins program is the development and verification of methodologies which are capable of reliably predicting the ultimate load-carrying capability of light water reactor containment structures under accident and severe environments. The program was initiated in June 1980 at Sandia and this paper addresses the first phase of the program which is essentially a planning effort. Brief comments are made about the second phase, which will involve testing of containment models

  13. Deep seismic studies of conjugate profiles from the Nova Scotia - Moroccan and the Liguro-Provencal margin pairs

    Science.gov (United States)

    Klingelhoefer, F.; Biari, Y.; Sahabi, M.; Aslanian, D.; Philippe, S.; Schnabel, M.; Moulin, M.; Louden, K. E.; Funck, T.; Reichert, C. J.

    2014-12-01

    The structure of conjugate passive margins provides information about rifting styles, opening of an ocean and formation of it's associated sedimentary basins. In order to distinguish between tectonic inheritance and structures directly related to rifting of passive margins conjugate profiles have to be acquired on margins on diverse locations and different ages. In this study we use new and existing reflection and wide-angle seismic data from two margin pairs, the 200 Ma year old Nova-Scotia - Morocco margin pair and the only 20 Ma Gulf of Lions - Sardinia margin pair. On both margin pairs wide-angle seismic data combined with reflection seismic data were acquired on conjugate profiles on sea and extended on land. Forward modelling of the deep crustal structure along the four transects indicates that a high velocity zone (HVZ) (> 7.2 km/s) is present at the base of the lower crust on all four margins along the ocean-continental transition zone (OCT). This may represent either exhumed upper mantle material or injection of upper mantle material into proto-oceanic crust at the onset of sea-floor spreading. However the width of the HVZ might strongly differ between conjugates, which may be the result of tectonic inheritance, for example the presence of ancient subduction zones or orogens. Both margin pairs show a similar unthinned continental crustal thickness. Crustal thinning and upper-to-lower crustal thickness vary between margin pairs, but remain nearly symmetric on conjugate profiles and might therefore depend on the structure and mechanical properties of the original continental crust. For the Mediterranean margin pair, the oceanic crust is similar on both sides, with a thickness of only 4-5 km. For the Atlantic margin pair, oceanic crustal thickness is higher on the Moroccan Margin, a fact that can be explained by either asymmetric spreading or by the volcanic underplating, possibly originating from the Canary Hot Spot.

  14. Crustal structure of an exhumed IntraCONtinental Sag (ICONS): the Mekele Basin in Northern Ethiopia.

    Science.gov (United States)

    Alemu, T. B.; Abdelsalam, M. G.

    2017-12-01

    The Mekele Sedimentary Basin (MSB) in Ethiopia is a Paleozoic-Mesozoic IntraCONtinental Sag (ICONS) exposed due to Cenozoic domal and rift flank uplift associated with the Afar mantle plume and Afar Depression (AD). ICONS are formed over stable lithosphere, and in contrast to rift and foreland basins, show circular-elliptical shape in map view, saucer shaped in cross section, and concentric gravity minima. Surface geological features of the MSB have been shown to exhibit geologic characteristics similar to those of other ICONS. We used the World Gravity Map (WGM 2012) data to investigate subsurface-crustal structure of the MSB. We also used 2D power spectrum analysis and inversion of the gravity field to estimate the Moho depth. Our results show the Bouguer anomalies of the WGM 2012 ranges between 130 mGal and - 110 mGal with the highest values within the AD. Despite the effect of the AD on the gravity anomalies, the MSB is characterized by the presence of gravity low anomaly that reaches in places -110 mGal, especially in its western part. The Moho depth estimates, from both spectral analysis and inversion of the gravity data, is between 36 and 40 km depth over most of the western and southern margins of the MSB. However, as the AD is approached, in the eastern margins of the MSB, crustal thickness estimates are highly affected by the anomalously thin and magmatic segment of the AD, and the Moho depth range between 30 and 25 km. Our results are consistent with that of seismic studies in areas far from the MSB, but within the Northwestern Ethiopian Plateau where the MSB is located. Those studies have reported an abrupt decrease in Moho depth from 40 km beneath the Northwestern plateau, to 20 km in the adjacent AD. Though the MSB is small (100 kmX100 km) compared to other ICONS, and affected by the neighboring AD, it is characterized by elliptical gravity minima and a relatively thicker crust that gradually thickens away from the rift. In addition, seismic imaging

  15. Particle flux during the southwest monsoon on the western margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Ramaswamy, V.

    Three sediment traps on a mooring were deployed on the outer shelf at a depth of 115 m from May to September 1985 on the western continental margin of India to study the particle flux during the southwest monsoon The morphology and mineralogy...

  16. Continental Growth and Recycling in Convergent Orogens with Large Turbidite Fans on Oceanic Crust

    Directory of Open Access Journals (Sweden)

    Ben D. Goscombe

    2013-07-01

    Full Text Available Convergent plate margins where large turbidite fans with slivers of oceanic basement are accreted to continents represent important sites of continental crustal growth and recycling. Crust accreted in these settings is dominated by an upper layer of recycled crustal and arc detritus (turbidites underlain by a layer of tectonically imbricated upper oceanic crust and/or thinned continental crust. When oceanic crust is converted to lower continental crust it represents a juvenile addition to the continental growth budget. This two-tiered accreted crust is often the same thickness as average continental crustal and is isostatically balanced near sea level. The Paleozoic Lachlan Orogen of eastern Australia is the archetypical example of a tubidite-dominated accretionary orogeny. The Neoproterozoic-Cambrian Damaran Orogen of SW Africa is similar to the Lachlan Orogen except that it was incorporated into Gondwana via a continent-continent collision. The Mesozoic Rangitatan Orogen of New Zealand illustrates the transition of convergent margin from a Lachlan-type to more typical accretionary wedge type orogen. The spatial and temporal variations in deformation, metamorphism, and magmatism across these orogens illustrate how large volumes of turbidite and their relict oceanic basement eventually become stable continental crust. The timing of deformation and metamorphism recorded in these rocks reflects the crustal thickening phase, whereas post-tectonic magmatism constrains the timing of chemical maturation and cratonization. Cratonization of continental crust is fostered because turbidites represent fertile sources for felsic magmatism. Recognition of similar orogens in the Proterozoic and Archean is important for the evaluation of crustal growth models, particularly for those based on detrital zircon age patterns, because crustal growth by accretion of upper oceanic crust or mafic underplating does not readily result in the addition of voluminous zircon

  17. Asymmetric rifting, breakup and magmatism across conjugate margin pairs: insights from Newfoundland to Ireland

    Science.gov (United States)

    Peace, Alexander L.; Welford, J. Kim; Foulger, Gillian R.; McCaffrey, Ken J. W.

    2017-04-01

    Continental extension, subsequent rifting and eventual breakup result in the development of passive margins with transitional crust between extended continental crust and newly created oceanic crust. Globally, passive margins are typically classified as either magma-rich or magma-poor. Despite this simple classification, magma-poor margins like the West Orphan Basin, offshore Newfoundland, do exhibit some evidence of localized magmatism, as magmatism to some extent invariably accompanies all continental breakup. For example, on the Newfoundland margin, a small volcanic province has been interpreted near the termination of the Charlie Gibbs Fracture Zone, whereas on the conjugate Irish margin within the Rockall Basin, magmatism appears to be more widespread and has been documented both in the north and in the south. The broader region over which volcanism has been identified on the Irish margin is suggestive of magmatic asymmetry across this conjugate margin pair and this may have direct implications for the mechanisms governing the nature of rifting and breakup. Possible causes of the magmatic asymmetry include asymmetric rifting (simple shear), post-breakup thermal anomalies in the mantle, or pre-existing compositional zones in the crust that predispose one of the margins to more melting than its conjugate. A greater understanding of the mechanisms leading to conjugate margin asymmetry will enhance our fundamental understanding of rifting processes and will also reduce hydrocarbon exploration risk by better characterizing the structural and thermal evolution of hydrocarbon bearing basins on magma-poor margins where evidence of localized magmatism exists. Here, the latest results of a conjugate margin study of the Newfoundland-Ireland pair utilizing seismic interpretation integrated with other geological and geophysical datasets are presented. Our analysis has begun to reveal the nature and timing of rift-related magmatism and the degree to which magmatic asymmetry

  18. Amphetamine margin in sports

    Energy Technology Data Exchange (ETDEWEB)

    Laties, V.G.; Weiss, B.

    1981-10-01

    The amphetamines can enhance athletic performance. That much seem clear from the literature, some of which is reviewed here. Increases in endurance have been demonstrated in both humans and rats. Smith and Beecher, 20 years ago, showed improvement of running, swimming, and weight throwing in highly trained athletes. Laboratory analogs of such performances have also been used and similar enhancement demonstrated. The amount of change induced by the amphetamines is usually small, of the order of a few percent. Nevertheless, since a fraction of a percent improvement can make the difference between fame and oblivion, the margin conferred by these drugs can be quite important.

  19. Barrier displacement on a neutral landscape: Towards a theory of continental biogeography

    Science.gov (United States)

    Albert, James S.; Schoolmaster, Donald; Tagliacollo, Victor; Duke-Sylvester, Scott M.

    2017-01-01

    Macroevolutionary theory posits three processes leading to lineage diversification and the formation of regional biotas: dispersal (species geographic range expansion), speciation (species lineage splitting), and extinction (species lineage termination). The Theory of Island Biogeography (TIB) predicts species richness values using just two of these processes; dispersal and extinction. Yet most species on Earth live on continents or continental shelves, and the dynamics of evolutionary diversification at regional and continental scales are qualitatively different from those that govern the formation of species richness on biogeographic islands. Certain geomorphological processes operating perennially on continental platforms displace barriers to gene flow and organismal dispersal, and affect all three terms of macroevolutionary diversification. For example, uplift of a dissected landscape and river capture both merge and separate portions of adjacent areas, allowing dispersal and larger geographic ranges, vicariant speciation and smaller geographic ranges, and extinction when range sizes are subdivided below a minimum persistence threshold.

  20. The life cycle of continental rifting as a focus for U.S.-African scientific collaboration

    Science.gov (United States)

    Abdelsalam, Mohamed G.; Atekwana, Estella A.; Keller, G. Randy; Klemperer, Simon L.

    2004-11-01

    The East African Rift System (EARS) provides the unique opportunity found nowhere else on Earth, to investigate extensional processes from incipient rifting in the Okavango Delta, Botswana, to continental breakup and creation of proto-oceanic basins 3000 km to the north in the Afar Depression in Ethiopia, Eritrea, and Djibouti.The study of continental rifts is of great interest because they represent the initial stages of continental breakup and passive margin development, they are sites for large-scale sediment accumulation, and their geomorphology may have controlled human evolution in the past and localizes geologic hazards in the present. But there is little research that provides insights into the linkage between broad geodynamic processes and the life cycle of continental rifts: We do not know why some rifts evolve into mid-ocean ridges whereas others abort their evolution to become aulacogens. Numerous studies of the EARS and other continental rifts have significantly increased our understanding of rifting processes, but we particularly lack studies of the embryonic stages of rift creation and the last stages of extension when continental breakup occurs.

  1. Adjacent stimulation and measurement patterns considered harmful

    International Nuclear Information System (INIS)

    Adler, Andy; Maimaitijiang, Yasheng; Gaggero, Pascal Olivier

    2011-01-01

    We characterize the ability of electrical impedance tomography (EIT) to distinguish changes in internal conductivity distributions, and analyze it as a function of stimulation and measurement patterns. A distinguishability measure, z, is proposed which is related to the signal-to-noise ratio of a medium and to the probability of detection of conductivity changes in a region of interest. z is a function of the number of electrodes, the EIT stimulation and measurement protocol, the stimulation amplitude, the measurement noise, and the size and location of the contrasts. Using this measure we analyze various choices of stimulation and measurement patterns under the constraint of medical electrical safety limits (maximum current into the body). Analysis is performed for a planar placement of 16 electrodes for simulated 3D tank and chest shapes, and measurements in a saline tank. Results show that the traditional (and still most common) adjacent stimulation and measurement patterns have by far the poorest performance (by 6.9 ×). Good results are obtained for trigonometric patterns and for pair drive and measurement patterns separated by over 90°. Since the possible improvement over adjacent patterns is so large, we present this result as a call to action: adjacent patterns are harmful, and should be abandoned. We recommend using pair drive and measurement patterns separated by one electrode less than 180°. We describe an approach to modify an adjacent pattern EIT system by adjusting electrode placement

  2. POLA KEBERAGAMAAN MASYARAKAT MARGINAL

    Directory of Open Access Journals (Sweden)

    Ahmad Muttaqin

    2016-11-01

    Full Text Available This is a research on sociology of religion, focusing on the issue of religious practices in a local community. Kampung Laut was chosen as the setting of this research for two reasons. First, the rituals of religion practices in the region are different from mainstream practices, which result in label and justification that their religiosity is not a part of or only a fragment of the mainstream religion and tend to be the target of correction. Second, this region raises conflicts among government institutions in relation to the rights of natural resources possession and utilization. The bad image built through this marginalization has formed Kampung Laut community as the one that is resistant and latent. This research used descriptive qualitative method with sociological approach. Rituals of religious practices that are different from the mainstream are explained on the basis of Weber’s theory of behavior categorized into value-oriented rationality. This kind of practices is considered to be more beneficial in the context of struggling for identity among the practices of marginalization experienced by Kampung Laut community. This condition gives a description to public that Kampung Laut community receives unfair treatments for their natural resources. Religious issues is made an entry for its massive, communal, and related to transcendental values.

  3. Density Sorting During the Evolution of Continental Crust

    Science.gov (United States)

    Kelemen, P. B.; Behn, M. D.; Hacker, B. R.

    2015-12-01

    We consider two settings - in addition to "delamination" of arc lower crust - in which dense, mafic eclogites founder into the convecting mantle while buoyant, felsic lithologies accumulate at the base of evolving continental crust. Arc processes play a central role in generating continental crust, but it remains uncertain how basaltic arc crust is transformed to andesitic continental crust. Dense, SiO2-poor products of fractionation may founder from the base of arc crust by "delamination", but lower arc crust after delamination has significantly different trace elements compared to lower continental crust (LCC). In an alternative model, buoyant magmatic rocks generated at arcs are first subducted, mainly via subduction erosion. Upon heating, these buoyant lithologies ascend through the mantle wedge or along a subduction channel, and are "relaminated" at
the base of overlying crust (e.g., Hacker et al EPSL 11, AREPS 15). Average buoyant lavas and plutons
for the Aleutians, Izu-Bonin-Marianas, Kohistan and Talkeetna arcs fall within the range of estimated LCC major and trace elements. Relamination is more efficient in generating continental crust than delamination. Himalayan cross-sections show Indian crust thrust beneath Tibetan crust, with no intervening mantle. There is a horizontal Moho at ca 80 km depth, extending from thickened Indian crust, across the region where Tibetan crust overlies Indian crust, into thickened Tibetan crust. About half the subducted Indian crust is present, whereas the other half is missing. Data (Vp/Vs; Miocene lavas formed by interaction of continental crust with mantle; xenolith thermometry) indicate 1000°C or more from ca 50 km depth to the Moho since the Miocene. We build on earlier studies (LePichon et al Tectonics 92, T'phys 97; Schulte-Pelkum et al Nature 05; Monsalve et al JGR 08) to advance the hypothesis that rapid growth of garnet occurs at 70-80 km and 1000°C within subducting Indian crust. Dense eclogites founder

  4. New results from a 3D seismic academic dataset across the west Galicia margin

    Science.gov (United States)

    Lymer, Gaël; Cresswell, Derren; Reston, Tim; Stevenson, Carl; Sawyer, Dale

    2016-04-01

    The west Galicia margin (western Spain) is a magma-poor margin and has limited sedimentary cover, providing ideal conditions to study the processes of continental extension and break-up through seismic imaging. The margin is characterised by hyper-extended continental crust, well defined rotated faults blocks with associated syn-kinematic sedimentary wedges, and exhumed serpentinized continental mantle. Faulted blocks overlie a bright reflection, the S reflector, generally interpreted as both a detachment and the crust-mantle boundary. But open questions remain concerning the role of the S detachment in extension leading to breakup. To study further the S reflection and its role in continental breakup, a new 3D high-resolution multi-channel seismic dataset has been acquired over the Galicia margin during summer 2013. It consists in 800 inlines and 5000 crosslines distributed on a ~680 km2 areal. This 3D dataset is thus the largest academic one of its kind. It extends across the edge of the continental crust and captures the 3D nature of extension and break-up of the northern Atlantic continental margins. Here we present some results from our interpretations of the 3D volume, which allow various horizons, including the base of the post-rift sedimentary cover, the top basement and the S reflector, to be mapped out in 3D. These maps provide 3D views of the margin structure and also reveal the texture of each horizon. We also focus on the internal structure of some of the faulted blocks through interpretation of the crustal normal faults. The main normal faults are generally connected downward on the S reflector, revealing strong interactions between crustal thinning and the S. The half-grabens and the fault blocks are dominantly N-S oriented, but the crustal structures vary both along strike and cross strike. We particularly observe an intriguingly NW-SE trend, highlighted by a pronounced low within the crest of the fault blocks. We also observe this trend from

  5. Breakup magmatism on the Vøring Margin, mid-Norway: New insight from interpretation of high-quality 2D and 3D seismic reflection data

    Science.gov (United States)

    Abdelmalak, M. M.; Planke, S.; Millett, J.; Jerram, D. A.; Maharjan, D.; Zastrozhnov, D.; Schmid, D. W.; Faleide, J. I.; Svensen, H.; Myklebust, R.

    2017-12-01

    The Vøring Margin offshore mid-Norway is a classic volcanic rifted margin, characterized by voluminous Paleogene igneous rocks present on both sides of the continent-ocean boundary. The margin displays (1) thickened transitional crust with a well-defined lower crustal high-velocity body and prominent deep crustal reflections, the so-called T-Reflection, (2) seaward dipping reflector (SDR) wedges and a prominent northeast-trending escarpment on the Vøring Marginal High, and (3) extensive sill complexes in the adjacent Cretaceous Vøring Basin. During the last decade, new 2D and 3D industry seismic data along with improved processing techniques, such as broadband processing and noise reduction processing sequences, have made it possible to image and map the breakup igneous complex in much greater detail than previously possible. Our interpretation includes a combination of (1) seismic horizon picking, (2) integrated seismic-gravity-magnetic (SGM) interpretation, (3) seismic volcanostratigraphy, and (4) igneous seismic geomorphology. The results are integrated with published wide-angle seismic data, re-analyzed borehole data including new geochronology, and new geodynamic modeling of the effects of magmatism on the thermal history and subsidence of the margin. The extensive sill complexes and associated hydrothermal vent complexes in the Vøring Basin have a Paleocene-Eocene boundary age based on high-precision U/Pb dating combined with seismic mapping constraints. On the marginal high, our results show a highly variable crustal structure, with a pre-breakup configuration consisting of large-scale structural highs and sedimentary basins. These structures were in-filled and covered by basalt flows and volcanogenic sediments during the early stages of continental breakup in the earliest Eocene. Subsequently, rift basins developed along the continent-ocean boundary and where infilled by up to ca. 6 km thick basalt sequences, currently imaged as SDRs fed by a dike swarm

  6. 3D numerical simulations of multiphase continental rifting

    Science.gov (United States)

    Naliboff, J.; Glerum, A.; Brune, S.

    2017-12-01

    Observations of rifted margin architecture suggest continental breakup occurs through multiple phases of extension with distinct styles of deformation. The initial rifting stages are often characterized by slow extension rates and distributed normal faulting in the upper crust decoupled from deformation in the lower crust and mantle lithosphere. Further rifting marks a transition to higher extension rates and coupling between the crust and mantle lithosphere, with deformation typically focused along large-scale detachment faults. Significantly, recent detailed reconstructions and high-resolution 2D numerical simulations suggest that rather than remaining focused on a single long-lived detachment fault, deformation in this phase may progress toward lithospheric breakup through a complex process of fault interaction and development. The numerical simulations also suggest that an initial phase of distributed normal faulting can play a key role in the development of these complex fault networks and the resulting finite deformation patterns. Motivated by these findings, we will present 3D numerical simulations of continental rifting that examine the role of temporal increases in extension velocity on rifted margin structure. The numerical simulations are developed with the massively parallel finite-element code ASPECT. While originally designed to model mantle convection using advanced solvers and adaptive mesh refinement techniques, ASPECT has been extended to model visco-plastic deformation that combines a Drucker Prager yield criterion with non-linear dislocation and diffusion creep. To promote deformation localization, the internal friction angle and cohesion weaken as a function of accumulated plastic strain. Rather than prescribing a single zone of weakness to initiate deformation, an initial random perturbation of the plastic strain field combined with rapid strain weakening produces distributed normal faulting at relatively slow rates of extension in both 2D and

  7. The relative influence of road characteristics and habitat on adjacent lizard populations in arid shrublands

    Science.gov (United States)

    Hubbard, Kaylan A.; Chalfoun, Anna D.; Gerow, Kenneth G.

    2016-01-01

    As road networks continue to expand globally, indirect impacts to adjacent wildlife populations remain largely unknown. Simultaneously, reptile populations are declining worldwide and anthropogenic habitat loss and fragmentation are frequently cited causes. We evaluated the relative influence of three different road characteristics (surface treatment, width, and traffic volume) and habitat features on adjacent populations of Northern Sagebrush Lizards (Sceloporus graciosus graciosus), Plateau Fence Lizards (S. tristichus), and Greater Short-Horned Lizards (Phrynosoma hernandesi) in mixed arid shrubland habitats in southwest Wyoming. Neither odds of lizard presence nor relative abundance was significantly related to any of the assessed road characteristics, although there was a trend for higher Sceloporus spp. abundance adjacent to paved roads. Sceloporus spp. relative abundance did not vary systematically with distance to the nearest road. Rather, both Sceloporus spp. and Greater Short-Horned Lizards were associated strongly with particular habitat characteristics adjacent to roads. Sceloporus spp. presence and relative abundance increased with rock cover, relative abundance was associated positively with shrub cover, and presence was associated negatively with grass cover. Greater Short-Horned Lizard presence increased with bare ground and decreased marginally with shrub cover. Our results suggest that habitat attributes are stronger correlates of lizard presence and relative abundance than individual characteristics of adjacent roads, at least in our system. Therefore, an effective conservation approach for these species may be to consider the landscape through which new roads and their associated development would occur, and the impact that placement could have on fragment size and key habitat elements.

  8. Marginally Stable Nuclear Burning

    Science.gov (United States)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

  9. Additional decompression at adjacent segments leads to adjacent segment degeneration after PLIF.

    Science.gov (United States)

    Miyagi, Masayuki; Ikeda, Osamu; Ohtori, Seiji; Tsuneizumi, Yoshikazu; Someya, Yukio; Shibayama, Masataka; Ogawa, Yasufumi; Inoue, Gen; Orita, Sumihisa; Eguchi, Yawara; Kamoda, Hiroto; Arai, Gen; Ishikawa, Tetsuhiro; Aoki, Yasuchika; Toyone, Tomoaki; Ooi, Toshio; Takahashi, Kazuhisa

    2013-08-01

    Adjacent segment degeneration (ASD) is one of the major complications of lumbar fusion. Several previous retrospective studies reported ASD after PLIF. However, few reports evaluated whether decompression surgery combined with fusion surgery increases the rate of complications in adjacent segments. The purpose of the current study was to investigate the degeneration in decompressed adjacent segments after PLIF. A total of 23 patients (12 men, 11 women; average age, 58.6) who underwent PLIF surgery [1 level (n = 9), 2 levels (n = 8), 3 levels (n = 4), 4 levels (n = 2)] were included. Additional adjacent decompression above or below the level of interbody fusion was performed at 25 levels and no adjacent decompression was performed at 15 levels. We retrospectively investigated ASD by X-ray films of all 40 adjacent segments (above and below fusion level) and clinical outcomes of all 23 cases. Of the 40 adjacent segments, 19 (47.5%) showed ASD and 9 (22.5%) showed symptomatic ASD. In the 19 segments with ASD, ASD occurred in 16 of 25 (64.0%) segments at decompressed sites compared with 3 of 15 (20.0%) non-decompressed sites. The ratio of ASD in adjacent segments was significantly higher at decompressed sites than at non-decompressed sites (p < 0.01). ASD occurs frequently in association with additional decompression above or below the level of PLIF. In cases in which the adjacent segments require decompression, a surgical strategy that preserves as much of the posterior complex as possible should be selected.

  10. Intracontinental Deformation in the NW Iranian Plateau and Comparisons with the Northern Margin of the Tibetan Plateau

    Science.gov (United States)

    Chen, L.; Jiang, M.; Talebian, M.; Wan, B.; Ai, Y.; Ghods, A.; Sobouti, F.; Xiao, W.; Zhu, R.

    2017-12-01

    This study investigates the intracontinental deformation and its relationship with the structure of the crust and uppermost mantle in the NW Iranian plateau by combining new seismic and geological observations, to understand how this part of the plateau deformed to accommodate the Arabia-Eurasia plate collision and how the property of the lithosphere controls the deformation pattern. In contrast to the adjacent Anatolian block that exhibits westward large-scale extrusion, the northwesternmost part of the Iranian plateau shows dispersed intracontinental deformations with the development of numerous small-scale and discontinuous right-lateral strike-slip faults. The dispersed surface structures and deformation pattern correspond well to the active volcanism and seismically slow crust and uppermost mantle, and hence a weak lithosphere of the area. Further to the southeast are the western part of the Alborz Mountains and the southern Caspian Sea, both of which are characterized by stronger and more rigid lithosphere with relatively fast crust and uppermost mantle and absence of Quaternary volcanoes. A sharp Moho offset of 18 km has been imaged at the border of the Alborz and southern Caspian Sea using teleseismic receiver function data from a dense seismic array deployed under a collaborative project named "China-Iran Geological and Geophysical Survey in the Iranian Plateau (CIGSIP)". The sharp Moho offset and the minor undulations of the Moho on both sides indicate insignificant intracrustal deformation but mainly relative crustal movements between the Alborz Mountains and southern Caspian Sea, a behavior consistent with the relatively rigid nature of the lithosphere. Similar Moho offsets and lithospheric structures have been reported at the borders between the Kunlun Mountains and Qaidam or Tarim Basins in the northern margin of the Tibetan plateau, suggesting the occurrence of relative crustal movements with the effects of rigid continental lithosphere in the region

  11. Colorado Basin Structure and Rifting, Argentine passive margin

    Science.gov (United States)

    Autin, Julia; Scheck-Wenderoth, Magdalena; Loegering, Markus; Anka, Zahie; Vallejo, Eduardo; Rodriguez, Jorge; Marchal, Denis; Reichert, Christian; di Primio, Rolando

    2010-05-01

    partly supports this hypothesis and shows two main directions of faulting: margin-parallel faults (~N30°) and rift-parallel faults (~N125°). A specific distribution of the two fault sets is observed: margin-parallel faults are restrained to the most distal part of the margin. Starting with a 3D structural model of the basin fill based on seismic and well data the deeper structure of the crust beneath the Colorado Basin can be evaluate using isostatic and thermal modelling. Franke, D., et al. (2002), Deep Crustal Structure Of The Argentine Continental Margin From Seismic Wide-Angle And Multichannel Reflection Seismic Data, paper presented at AAPG Hedberg Conference "Hydrocarbon Habitat of Volcanic Rifted Passive Margins", Stavanger, Norway Franke, D., et al. (2006), Crustal structure across the Colorado Basin, offshore Argentina Geophysical Journal International 165, 850-864. Gladczenko, T. P., et al. (1997), South Atlantic volcanic margins Journal of the Geological Society, London 154, 465-470. Hinz, K., et al. (1999), The Argentine continental margin north of 48°S: sedimentary successions, volcanic activity during breakup Marine and Petroleum Geology 16(1-25). Hirsch, K. K., et al. (2009), Tectonic subsidence history and thermal evolution of the Orange Basin, Marine and Petroleum Geology, in press, doi:10.1016/j.marpetgeo.2009.1006.1009

  12. Time-constrained project scheduling with adjacent resources

    NARCIS (Netherlands)

    Hurink, Johann L.; Kok, A.L.; Paulus, J.J.; Schutten, Johannes M.J.

    2008-01-01

    We develop a decomposition method for the Time-Constrained Project Scheduling Problem (TCPSP) with Adjacent Resources. For adjacent resources the resource units are ordered and the units assigned to a job have to be adjacent. On top of that, adjacent resources are not required by single jobs, but by

  13. Time-constrained project scheduling with adjacent resources

    NARCIS (Netherlands)

    Hurink, Johann L.; Kok, A.L.; Paulus, J.J.; Schutten, Johannes M.J.

    We develop a decomposition method for the Time-Constrained Project Scheduling Problem (TCPSP) with adjacent resources. For adjacent resources the resource units are ordered and the units assigned to a job have to be adjacent. On top of that, adjacent resources are not required by single jobs, but by

  14. Crustal stress pattern in China and its adjacent areas

    Science.gov (United States)

    Hu, Xingping; Zang, Arno; Heidbach, Oliver; Cui, Xiaofeng; Xie, Furen; Chen, Jiawei

    2017-11-01

    During the update of the World Stress Map (WSM) database, we integrated the China stress database by strictly using the internationally developed quality ranking scheme for each individual stress data record. This effort resulted in a comprehensive and reliable dataset for the crustal stress of China and its adjacent areas with almost double the amount of data records from the WSM database release 2008, i.e., a total of 8228 data records with reliable A-C qualities in the region of 45-155° East and 0-60° North. We use this dataset for an analysis of the stress pattern for the orientation of maximum compressive horizontal stress (SHmax). In contrast to earlier findings that suggested that the mean SHmax orientation would be aligned with the direction of plate motion, we clearly see from our results that the plate boundary forces, as well as topography and faulting, are important control factors for the overall stress pattern. Furthermore, the smoothing results indicate that the SHmax orientation in China rotates clockwise from the west to the east, which results in a fan-shaped crustal stress pattern for the continental scale. The plate boundary forces around China, which are the Indian-Eurasian plate collision in the west and the Pacific plate subduction and the push from the Philippine plate in the east, can still be seen as the key driving processes and the first-order controls for the crustal stress pattern. The South-North seismic zone can be seen as the separation zone for the western and eastern plate boundary forces. Topographic variation and faulting activity, however, provide second-order changes, and lead to local variations and different inhomogeneity scales for the stress pattern. Due to differences in these factors, Northeast China and the central part of the Tibetan plateau have notably homogeneous stress patterns, while the South-North seismic zone, the Hindu Kush-Pamir region, and the Taiwan region have extremely inhomogeneous stress patterns

  15. Global Mapping of Oceanic and Continental Shelf Crustal Thickness and Ocean-Continent Transition Structure

    Science.gov (United States)

    Kusznir, Nick; Alvey, Andy; Roberts, Alan

    2017-04-01

    The 3D mapping of crustal thickness for continental shelves and oceanic crust, and the determination of ocean-continent transition (OCT) structure and continent-ocean boundary (COB) location, represents a substantial challenge. Geophysical inversion of satellite derived free-air gravity anomaly data incorporating a lithosphere thermal anomaly correction (Chappell & Kusznir, 2008) now provides a useful and reliable methodology for mapping crustal thickness in the marine domain. Using this we have produced the first comprehensive maps of global crustal thickness for oceanic and continental shelf regions. Maps of crustal thickness and continental lithosphere thinning factor from gravity inversion may be used to determine the distribution of oceanic lithosphere, micro-continents and oceanic plateaux including for the inaccessible polar regions (e.g. Arctic Ocean, Alvey et al.,2008). The gravity inversion method provides a prediction of continent-ocean boundary location which is independent of ocean magnetic anomaly and isochron interpretation. Using crustal thickness and continental lithosphere thinning factor maps with superimposed shaded-relief free-air gravity anomaly, we can improve the determination of pre-breakup rifted margin conjugacy and sea-floor spreading trajectory during ocean basin formation. By restoring crustal thickness & continental lithosphere thinning to their initial post-breakup configuration we show the geometry and segmentation of the rifted continental margins at their time of breakup, together with the location of highly-stretched failed breakup basins and rifted micro-continents. For detailed analysis to constrain OCT structure, margin type (i.e. magma poor, "normal" or magma rich) and COB location, a suite of quantitative analytical methods may be used which include: (i) Crustal cross-sections showing Moho depth and crustal basement thickness from gravity inversion. (ii) Residual depth anomaly (RDA) analysis which is used to investigate OCT

  16. Regional geomorphology of the continental slope of NW India: Delineation of the signatures of deep-seated structures

    Digital Repository Service at National Institute of Oceanography (India)

    Chauhan, O.S.; Almeida, F.; Moraes, C.

    Geomorphological features (derived from 16,000 lkm of echo-sounding and bathymetric data) and deep-seated tectonic tectonic structures of the continental margin off NW India are presented. The shelf break over the entire region occurs between 80...

  17. Hydrocarbon prospects of the western continental slope of India as indicatEd. by surficial enrichment of organic carbon

    Digital Repository Service at National Institute of Oceanography (India)

    Paropkari, A.L.; Mascarenhas, A.; PrakashBabu, C.

    The sediments from the continental mid-slope (150-1500 m depth) of the western margin are highly enriched in organic carbon (upto 16%) occurring as a long and wide band off Bombay to southern tip of India. Organic carbon is essentially of marine...

  18. Reconstruction of late Quaternary monsoon oscillations based on clay mineral proxies using sediment cores from the western margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Thamban, M.; Rao, V.P.; Schneider, R.R.

    (GC-3 and GC-5) used in this study were collected during the sixth cruise of M/VA.A.Siderenkofrom the western continental margin of India (Fig. 1). The core GC-3 (length, 4.45 m) was raised from an isolated topographic high on the continental slope o...¡ Goa at 355 m water depth, whereas core GC-5 (length, 3.33 m) was recovered from 280 m water depth on the upper continental slope o¡ Cochin (Thamban et al., 1997). Both the core sites are located within the present day Oxygen Minimum Zone (OMZ V150...

  19. Geochemical variability of copper and iron in Oman margin sediments

    Digital Repository Service at National Institute of Oceanography (India)

    Alagarsamy, R.

    .D.Thesis, University of Liverpool, 1984. [19] R.E. Sturgeon, C.L. Chakrabarti, Recent advances in electrothermal atomisation in a graphite furnace atomic adsorption spectrophotometer, Progr. Anal. Atom. Spectroscopy 1 (1978) 5-9. [20] C.R. Smith, L.A. Levin, D... in immature sediments along the continental margins of Peru and Oman. Part I: Results of petrographical and bulk geochemical data, Org. Geochem. 24 (1996) 437-451. [36] R. Raiswell, D.E. Canfield, Sources of iron for pyrite formation in marine sediments...

  20. The Cambrian-Ordovician rocks of Sonora, Mexico, and southern Arizona, southwestern margin of North America (Laurentia): chapter 35

    Science.gov (United States)

    Page, William R.; Harris, Alta C.; Repetski, John E.; Derby, James R.; Fritz, R.D.; Longacre, S.A.; Morgan, W.A.; Sternbach, C.A.

    2013-01-01

    Cambrian and Ordovician shelf, platform, and basin rocks are present in Sonora, Mexico, and southern Arizona and were deposited on the southwestern continental margin of North America (Laurentia). Cambrian and Ordovician rocks in Sonora, Mexico, are mostly exposed in scattered outcrops in the northern half of the state. Their discontinuous nature results from extensive Quaternary and Tertiary surficial cover, from Tertiary and Mesozoic granitic batholiths in western Sonora, and from widespread Tertiary volcanic deposits in the Sierra Madre Occidental in eastern Sonora. Cambrian and Ordovician shelf rocks were deposited as part of the the southern miogeocline on the southwestern continental margin of North America.

  1. Adjacent Segment Pathology after Lumbar Spinal Fusion

    Science.gov (United States)

    Lee, Jae Chul

    2015-01-01

    One of the major clinical issues encountered after lumbar spinal fusion is the development of adjacent segment pathology (ASP) caused by increased mechanical stress at adjacent segments, and resulting in various radiographic changes and clinical symptoms. This condition may require surgical intervention. The incidence of ASP varies with both the definition and methodology adopted in individual studies; various risk factors for this condition have been identified, although a significant controversy still exists regarding their significance. Motion-preserving devices have been developed, and some studies have shown their efficacy of preventing ASP. Surgeons should be aware of the risk factors of ASP when planning a surgery, and accordingly counsel their patients preoperatively. PMID:26435804

  2. The Continental Drift Convection Cell

    Science.gov (United States)

    Whitehead, J. A.; Behn, M. D.

    2014-12-01

    Continents on Earth periodically assemble to form supercontinents, and then break up again into smaller continental blocks (the Wilson Cycle). Highly developed but realistic numerical models cannot resolve if continents respond passively to mantle convection or whether they modulate flow. Our simplified numerical model addresses this problem: A thermally insulating continent floats on a stress-free surface for infinite Prandtl number cellular convection with constant material properties in a chamber 8 times longer than its depth. The continent moves back and forth across the chamber driven by a "continental drift convection cell" of a form not previously described. Subduction exists at the upstream end with cold slabs dipping at an angle beneath the moving continent. Fluid moves with the continent in the upper region of this cell with return flow near the bottom. Many continent/subduction regions on Earth have these features. The drifting cell enhances vertical heat transport by approximately 30% compared to a fixed continent, especially at the core-mantle boundary, and significantly decreases lateral mantle temperature differences. However, continent drift or fixity has smaller effects on profiles of horizontally averaged temperature. Although calculations are done at Rayleigh numbers lower than expected for Earth's mantle (2x105 and 106), the drift speed extrapolates to reasonable Wilson Cycle speeds for larger Ra.

  3. Habitat specialization in tropical continental shelf demersal fish assemblages.

    Directory of Open Access Journals (Sweden)

    Ben M Fitzpatrick

    Full Text Available 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

  4. From continental to oceanic rifting in the Gulf of California

    Science.gov (United States)

    Ferrari, Luca; Bonini, Marco; Martín, Arturo

    2017-11-01

    The continental margin of northwestern Mexico is the youngest example of the transition from a convergent plate boundary to an oblique divergent margin that formed the Gulf of California rift. Subduction of the Farallon oceanic plate during the Cenozoic progressively brought the East Pacific Rise (EPR) toward the North America trench. In this process increasingly younger and buoyant oceanic lithosphere ente