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Sample records for atlantic continental margins

  1. 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)

  2. Structure of continental margin off Mid-Atlantic states (Baltimore Canyon Trough)

    Science.gov (United States)

    Schlee, John Stevens; Behrendt, John Charles; Mattick, Robert E.; Taylor, P.T.

    1975-01-01

    Increasing interest in the Atlantic continental margin as a future petroleum province has resulted in several recent papers (Emmerich, 1974; Burk and Drake, 1974) that attempt to summarize the structure and stratigraphic framework of this area. Most papers tend to portray the margin as a wedge of Mesozoic and Cenozoic sediment that thins at the edge of the shelf over a "basement ridge" and then thickens again under the continental rise. Off the northeastern United States, the sediment wedge under the shelf attains a thickness of 8-11 km in the Georges Bank basin (Schultz and Glover, 1974; Mattick and others, 1974; Sheridan, 1974b; Behrendt and others, 1974) and 12 km in thickness in the Baltimore Canyon trough off the middle Atlantic states of Delaware, Maryland, Virginia and New Jersey (fig. 1). Seaward of the continental shelf and its sediment prism, Emery and Uchupi (1972, figs. 133-135) infer slump deposits (eroded in some areas) covering a buried ridge thought to extend from the Laurentian Channel to Cape Hatteras, where it splits in two. The lower slope and continental rise are inferred by Drake and later investigators to be a thick prism of deep sea sediment (turbidites, hemipelagic clays, slump deposits) overlying oceanic basement in a welt that parallels the continental edge and reaches a maximum thickness of 6 km (Emery and Uchupi, 1972, fig. 188).

  3. Tectonic Implications of Canyon Directions Over the Northeast Atlantic Continental Margin

    Science.gov (United States)

    Lallemand, Serge; Sibuet, Jean-Claude

    1986-12-01

    The basis of this study is a new bathymetric map of the northeast Atlantic compiled from previously published maps made from conventional echosounder data, plus all Sea Beam data acquired on board the R/V JEAN CHARCOT since 1977. As most of the Sea Beam data have been obtained on the continental margin from Porcupine Seabight to the south of the Iberian Peninsula, a precise picture of the continental slope is given. A statistical analysis of the canyons, based on 750 measurements, reveals that many of the canyons present sharp changes in their direction, indicating a structural control mainly linked to the late Hercynian trends, especially around the Iberian Peninsula. Nevertheless, the paths of canyons may merely reflect recent gravity processes, as in the Porcupine Seabight. Canyons locally follow the directions of listric and associated transecting faults (Permian to Triassic and upper Jurassic to lower Cretaceous), as on the Celtic margin, and every type of tectonic lineament—for example, the North Pyrenean Paleogene thrust front which fringes the Gouf of Cap Breton. A comparison of diagrams for the northern and southern Bay of Biscay margin (especially trends predating the opening) is compatible with a 25° rotation of Iberia with respect to Europe.

  4. Thermal history and evolution of the South Atlantic passive continental margin in northern Namibia

    Science.gov (United States)

    Menges, Daniel; Karl, Markus; Glasmacher, Ulrich Anton

    2013-04-01

    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 (Coward and Daly 1984, Daly et al. 1991), and the deposition of the Nama Group sediments and the Karoo megasequence. The lithostratigraphic units consist of Proterozoic and Cambrian metamorphosed rocks with ages of 534 (7) Ma to 481 (25) Ma (Miller 1983, Haack 1983), as well as Mesozoic sedimentary and igneous rocks. The Early Jurassic Karoo flood basalt lavas erupted rapidly at 183 (1) Ma (Duncan et al. 1997). 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 (Renne et al. 1992, Milner et al. 1995, Stewart et al. 1996, Turner et al. 1996). The "passive" continental margin in northern Namibia is a perfect location to quantify exhumation and uplift rates, model the long-term landscape evolution and provide information on the influence of mantle processes on a longer time scale. The poster will provide first information on the long-term landscape evolution and thermochronological data. References Coward, M. P. and Daly, M. C., 1984. Crustal lineaments and shear zones in Africa: Their relationships to plate movements, Precambrian Research 24: 27-45. Duncan, R., Hooper, P., Rehacek, J., March, J. and Duncan, A. (1997). The timing and duration of the Karoo igneous event, southern Gondwana, Journal of Geophysical Research 102: 18127-18138. Haack, U., 1983. Reconstruction of the cooling history of the Damara Orogen by correlation of radiometric ages with geography and altitude, in H. Martin and F. W. Eder (eds), Intracontinental fold belts, Springer Verlag, Berlin, pp. 837-884. Miller, R. M., 1983. Evolution of the Damara Orogen, Vol. 11, Geological Society, South Africa Spec. Pub.. Milner, S. C., le Roex, A. P. and O'Connor, J. M., 1995. Age of Mesozoic igneous rocks in

  5. NOAA Ship Okeanos Explorer 2013 Field Season on the U.S. Atlantic Continental Margin

    Science.gov (United States)

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

    2013-12-01

    During the 2013 field season, Okeanos Explorer used its suite of state-of-the-art sonars to systematically map and explore our nation's waters off the Atlantic seaboard, specifically the Atlantic Canyons and New England Seamounts. High resolution three dimensional maps created from the ship's sonars were used to select sites for fine-resolution exploration with the new 6000 meter remotely operated vehicle (ROV) Deep Discoverer. Scientists onboard and onshore around the world were actively engaged in all steps of the exploration process, from the identification of broad-scale mapping targets, to the planning and real-time refining of 300 to 1500 meter long planned ROV dive tracks. Live video feeds were available to the general public through the award winning website www.oceanexplorer.noaa.gov. Important exploration milestones during the Okeanos Explorer 2013 Field Season include: the completion of comprehensive, high-resolution multibeam mapping of the continental shelf break from Cape Hatteras to the northern U.S. Atlantic offshore border, totaling over 100,000 square kilometers of new seafloor data within the U.S. Exclusive Economic Zone; the first successful field season of the ROV Deep Discoverer, which conducted over 40 successful dives; and initial mapping site characterization of eight of the outer seamounts of the New England Seamount Chain. All data collected by Okeanos Explorer are available via the NOAA public archives with metadata records within 60 to 90 days of the end of each cruise.

  6. 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)

  7. Data file, Continental Margin Program, Atlantic Coast of the United States: vol. 2 sample collection and analytical data

    Science.gov (United States)

    Hathaway, John C.

    1971-01-01

    The purpose of the data file presented below is twofold: the first purpose is to make available in printed form the basic data relating to the samples collected as part of the joint U.S. Geological Survey - Woods Hole Oceanographic Institution program of study of the Atlantic continental margin of the United States; the second purpose is to maintain these data in a form that is easily retrievable by modern computer methods. With the data in such form, repeate manual transcription for statistical or similar mathematical treatment becomes unnecessary. Manual plotting of information or derivatives from the information may also be eliminated. Not only is handling of data by the computer considerably faster than manual techniques, but a fruitful source of errors, transcription mistakes, is eliminated.

  8. Deep Drilling Results in the Atlantic Ocean: Continental Margins and Paleoenvironment

    Science.gov (United States)

    1979-01-01

    volcanic hydrothermal exhalations. Bemuda Ri -For tiii-pc ds approximately However, the formation at most sites is not- near to- the seli~t traisiti -nfroi...A.C., et al., Initial Re- Greenwood, R., Cristobalite : its relationship to Gse ports Deep Sea Drilling Project, 14, 787-954 chert formation in...Ryan ; , l l l l l4 CONTENTS Preface " Mesozoic-Cerozoic Sedimentary Formations of the North American Basin. Western North Atlantic, L. F. Jansa, P. Enos

  9. 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

    2016-04-01

    In northwest 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 are processed to give 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 amount of denudation in the last 130 Ma

  10. South Atlantic continental margins of Africa: a comparison of the tectonic vs climate interplay on the evolution of equatorial west Africa and SW Africa margins

    CERN Document Server

    Seranne, M; Seranne, Michel; Anka, Zahie

    2005-01-01

    The comparative review of 2 representative segments of Africa continental margin: the equatorial western Africa and the SW Africa margins, helps in analysing the main controlling factors on their development. Early Cretaceous active rifting S of the Walvis Ridge resulted in the formation of the SW Africa volcanic margin. The non-volcanic rifting N of the Walvis ridge, led to the formation of the equatorial western Africa margin, with thick and extensive, synrift basins. Regressive erosion of SW Africa prominent shoulder uplift accounts for high clastic sedimentation rate in Late Cretaceous - Eocene, while dominant carbonate production on equatorial western Africa shelf suggests little erosion of a low hinterland. The early Oligocene climate change had contrasted response in both margins. Emplacement of the Congo deep-sea fan reflects increased erosion in equatorial Africa, under the influence of wet climate, whereas establishment of an arid climate over SW Africa induced a drastic decrease of denudation, and ...

  11. Iberian Atlantic Margins Group investigates deep structure of ocean margins

    Science.gov (United States)

    The Iberian Atlantic Margins Group; Banda, Enric; Torne, Montserrat

    With recent seismic reflection data in hand, investigators for the Iberian Atlantic Margins project are preparing images of the deep continental and oceanic margins of Iberia. In 1993, the IAM group collected near vertical incidence seismic reflection data over a total distance of 3500 km along the North and Western Iberian Margins, Gorringe Bank Region and Gulf of Cadiz (Figure 1). When combined with data on the conjugate margin off Canada, details of the Iberian margin's deep structure should aid in distinguishing rift models and improve understanding of the processes governing the formation of margins.The North Iberian passive continental margin was formed during a Permian to Triassic phase of extension and matured during the early Cretaceous by rotation of the Iberian Peninsula with respect to Eurasia. From the late Cretaceous to the early Oligocene period, Iberia rotated in a counterclockwise direction around an axis located west of Lisbon. The plate boundary between Iberia and Eurasia, which lies along the Pyrenees, follows the north Spanish marginal trough, trends obliquely in the direction of the fossil Bay of Biscay triple junction, and continues along the Azores-Biscay Rise [Sibuet et al., 1994]. Following the NE-SW convergence of Iberia and Eurasia, the reactivation of the North Iberian continental margin resulted in the formation of a marginal trough and accretionary prism [Boillot et al., 1971].

  12. Location of bottom photographs taken along the U.S. Atlantic East Coast as part of the Continental Margin Program (1963-1968, BPHOTOS)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — In 1962, Congress authorized the Continental Margin Program, a joint program between the U.S. Geological Survey (USGS) and the Woods Hole Oceanographic Institution...

  13. 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

  14. The pre-Atlantic Hf isotope evolution of the east Laurentian continental margin: Insights from zircon in basement rocks and glacial tillites from northern New Jersey and southeastern New York

    Science.gov (United States)

    Zirakparvar, N. Alex; Setera, Jacob; Mathez, Edmond; Vantongeren, Jill; Fossum, Ryanna

    2017-02-01

    This paper presents laser ablation U-Pb age and Hf isotope data for zircons from basement rocks and glacial deposits in northern New Jersey and southeastern New York. The purpose is to understand the eastern Laurentian continental margin's Hf isotope record in relation to its geologic evolution prior to the opening of the Atlantic Ocean. The basement samples encompass a Meso- to Neoproterozoic continental margin arc, an anatectic magmatic suite, as well as a Late Ordovician alkaline igneous suite emplaced during post-orogenic melting of the lithospheric mantle. Additional samples were collected from terminal moraines of two Quaternary continental ice sheets. Across the entire dataset, zircons with ages corresponding to the timing of continental margin arc magmatism ( 1.4 Ga to 1.2 Ga) have positive εHf(initial) values that define the more radiogenic end of a crustal evolution array. This array progresses towards more unradiogenic εHf(initial) values along a series of low 176Lu/177Hf (0.022 to 0.005) trajectories during subsequent anatectic magmatism ( 1.2 Ga to 1.0 Ga) and later metamorphic and metasomatic re-working ( 1.0 Ga to 0.8 Ga) of the continental margin arc crust. In contrast, nearly chondritic εHf(initial) values from the Late Ordovician alkaline magmas indicate that the Laurentian margin was underlain by a re-fertilized mantle source. Such a source may have developed by subduction enrichment of the mantle wedge beneath the continental margin during the Mesoproterozoic. Additionally, preliminary data from a metasedimentary unit of unknown provenance hints at the possibility that some of the sediments occupying this portion of the Laurentian margin prior to the Ordovician were sourced from crust older than 1.9 Ga.

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

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, K.S.

    scope for multiple picks of foot-of-slope, it narrows along the eastern continental margin and is clear for single pick of foot-of-slope. Continental slope and rise on western margin and rise on eastern margin were modified to a major extent... boundaries and continental rifting. 231 Active (convergent) continental margin Active continental margins typically have a trench at the foot of the continental slope. The margins are found near...

  16. Phytoplankton community dynamics during late spring coccolithophore blooms at the continental margin of the Celtic Sea (North East Atlantic, 2006–2008)

    OpenAIRE

    Van Oostende, Nicolas; Harlay, Jérôme; Vanelslander, Bart; Chou, Lei; Vyverman, Wim; Sabbe, Koen

    2012-01-01

    We determined the spatial and temporal dynamics of major phytoplankton groups in relation to biogeochemical and physical variables during the late spring coccolithophore blooms (May-June) along and across the continental margin of the northern Bay of Biscay (2006-2008). Photosynthetic biomass (Chla) of the dominant plankton groups was determined by CHEMTAX analysis of HPLC pigment signatures. We used uni- and multivariate statistical techniques to identify the main physical and biogeochemical...

  17. Subduction-driven recycling of continental margin lithosphere.

    Science.gov (United States)

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

    2014-11-13

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

  18. Asymmetry of high-velocity lower crust on the South Atlantic rifted margins and implications for the interplay of magmatism and tectonics in continental break-up

    Directory of Open Access Journals (Sweden)

    K. Becker

    2014-06-01

    Full Text Available High-velocity lower crust (HVLC and seaward dipping reflector sequences (SDRs are typical features of volcanic rifted margins. However, the nature and origin of HVLC is under discussion. Here we provide a comprehensive analysis of deep crustal structures in the southern segment of the South Atlantic and an assessment of HVLC along the margins. Two new seismic refraction lines off South America fill a gap in the data coverage and together with five existing velocity models allow a detailed investigation of the lower crustal properties on both margins. An important finding is the major asymmetry in volumes of HVLC on the conjugate margins. The seismic refraction lines across the South African margin reveal four times larger cross sectional areas of HVLC than at the South American margin, a finding that is in sharp contrast to the distribution of the flood basalts in the Paraná-Etendeka Large Igneous Provinces (LIP. Also, the position of the HVLC with respect to the seaward dipping reflector sequences varies consistently along both margins. Close to the Falkland-Agulhas Fracture Zone a small body of HVLC is not accompanied by seaward dipping reflectors. In the central portion of both margins, the HVLC is below the inner seaward dipping reflector wedges while in the northern area, closer to the Rio Grande Rise/Walvis Ridge, large volumes of HVLC extend far seawards of the inner seaward dipping reflectors. This challenges the concept of a simple extrusive/intrusive relationship between seaward dipping reflector sequences and HVLC, and it provides evidence for formation of the HVLC at different times during the rifting and break-up process. We suggest that the drastically different HVLC volumes are caused by asymmetric rifting in a simple shear dominated extension.

  19. 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.

  20. The chronology and tectonic style of landscape evolution along the elevated Atlantic continental margin of South Africa resolved by joint apatite fission track and (U-Th-Sm)/He thermochronology

    Science.gov (United States)

    Wildman, Mark; Brown, Roderick; Beucher, Romain; Persano, Cristina; Stuart, Fin; Gallagher, Kerry; Schwanethal, James; Carter, Andrew

    2016-03-01

    Atlantic-type continental margins have long been considered "passive" tectonic settings throughout the entire postrift phase. Recent studies question the long-term stability of these margins and have shown that postrift uplift and reactivation of preexisting structures may be a common feature of a continental margin's evolution. The Namaqualand sector of the western continental margin of South Africa is characterized by a ubiquitously faulted basement but lacks preservation of younger geological strata to constrain postrift tectonic fault activity. Here we present the first systematic study using joint apatite fission track and apatite (U-Th-Sm)/He thermochronology to achieve a better understanding on the chronology and tectonic style of landscape evolution across this region. Apatite fission track ages range from 58.3 ± 2.6 to 132.2 ± 3.6 Ma, with mean track lengths between 10.9 ± 0.19 and 14.35 ± 0.22 µm, and mean (U-Th-Sm)/He sample ages range from 55.8 ± 31.3 to 120.6 ± 31.4 Ma. Joint inverse modeling of these data reveals two distinct episodes of cooling at approximately 150-130 Ma and 110-90 Ma with limited cooling during the Cenozoic. Estimates of denudation based on these thermal histories predict approximately 1-3 km of denudation coinciding with two major tectonic events. The first event, during the Early Cretaceous, was driven by continental rifting and the development and removal of synrift topography. The second event, during the Late Cretaceous, includes localized reactivation of basement structures as well as regional mantle-driven uplift. Relative tectonic stability prevailed during the Cenozoic, and regional denudation over this time is constrained to be less than 1 km.

  1. Atlantic NAD 83 Continental Shelf Boundary (CSB)

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains Continental Shelf Boundary (CSB) lines in ESRI shapefile format for the BOEM Atlantic Region. The CSB defines the seaward limit of federally...

  2. Dynamics of the continental margins

    Energy Technology Data Exchange (ETDEWEB)

    1990-11-01

    On 18--20 June 1990, over 70 oceanographers conducting research in the ocean margins of North America attended a workshop in Virginia Beach, Virginia. The purpose of the workshop was to provide the Department of Energy with recommendations for future research on the exchange of energy-related materials between the coastal and interior ocean and the relationship between the ocean margins and global change. The workshop was designed to optimize the interaction of scientists from specific research disciplines (biology, chemistry, physics and geology) as they developed hypotheses, research questions and topics and implementation plans. The participants were given few restraints on the research they proposed other than realistic time and monetary limits. The interdisciplinary structure of the meeting promoted lively discussion and creative research plans. The meeting was divided into four working groups based on lateral, vertical, air/sea and sediment/water processes. Working papers were prepared and distributed before the meeting. During the meeting the groups revised the papers and added recommendations that appear in this report, which was reviewed by an Executive Committee.

  3. Abrupt plate accelerations shape rifted continental margins.

    Science.gov (United States)

    Brune, Sascha; Williams, Simon E; Butterworth, Nathaniel P; Müller, R Dietmar

    2016-08-11

    Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth's major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength--velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time.

  4. Abrupt plate accelerations shape rifted continental margins

    Science.gov (United States)

    Brune, Sascha; Williams, Simon E.; Butterworth, Nathaniel P.; Müller, R. Dietmar

    2016-08-01

    Rifted margins are formed by persistent stretching of continental lithosphere until breakup is achieved. It is well known that strain-rate-dependent processes control rift evolution, yet quantified extension histories of Earth’s major passive margins have become available only recently. Here we investigate rift kinematics globally by applying a new geotectonic analysis technique to revised global plate reconstructions. We find that rifted margins feature an initial, slow rift phase (less than ten millimetres per year, full rate) and that an abrupt increase of plate divergence introduces a fast rift phase. Plate acceleration takes place before continental rupture and considerable margin area is created during each phase. We reproduce the rapid transition from slow to fast extension using analytical and numerical modelling with constant force boundary conditions. The extension models suggest that the two-phase velocity behaviour is caused by a rift-intrinsic strength-velocity feedback, which can be robustly inferred for diverse lithosphere configurations and rheologies. Our results explain differences between proximal and distal margin areas and demonstrate that abrupt plate acceleration during continental rifting is controlled by the nonlinear decay of the resistive rift strength force. This mechanism provides an explanation for several previously unexplained rapid absolute plate motion changes, offering new insights into the balance of plate driving forces through time.

  5. 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

  6. 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.

  7. On the Evolution of Glaciated Continental Margins

    Science.gov (United States)

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

    2016-04-01

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

  8. 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

  9. 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

  10. 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

  11. 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; 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.

  12. 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.

    have a trench at the foot of the continental slope. The margins are found near convergent plate boundaries where the oceanic plate is being pushed down into the Earth’s interior beneath continent lying on another plate. Here the continent and ocean... is narrow to non-existent, dropping off quickly into the depths of the subduction trench. The trench at the foot of the continental slope generally replaces the 4 continental rise found at passive continental margins. This type of continental margin...

  13. Cyclic growth in Atlantic region continental crust

    Science.gov (United States)

    Goodwin, A. M.

    1986-01-01

    Atlantic region continental crust evolved in successive stages under the influence of regular, approximately 400 Ma-long tectonic cycles. Data point to a variety of operative tectonic processes ranging from widespread ocean floor consumption (Wilson cycle) to entirely ensialic (Ampferer-style subduction or simple crustal attenuation-compression). Different processes may have operated concurrently in some or different belts. Resolving this remains the major challenge.

  14. Post-orogenic evolution of the Sierras Septentrionales and the Sierras Australes and links to the evolution of the eastern Argentina South Atlantic passive continental margin constrained by low temperature thermochronometry and 2D thermokinematic modeling

    Science.gov (United States)

    Kollenz, Sebastian; Glasmacher, Ulrich Anton; Rossello, Eduardo A.

    2013-04-01

    The eastern Argentina South Atlantic passive continental margin is distinguished by a very flat topography. Out of the so called Pampean flat two mountain ranges are arising. These mountain ranges, the Sierras Australes and the Sierras Septentrionales, are located in the State of Buenos Aires south of the capital Buenos Aires. North of the Sierras Septentrionales the Salado basin is located. The Sierras Septentrionales and the Sierras Australes are also divided by a smaller intracratonic basin. Further in the South the Colorado basin is located. The Sierras Australes is a variscian fold belt originated by strong phases of metamorphosis, but till now it is unclear by how many tectonic phases the area was influenced (Tomezzoli & Vilas, 1999). It consists of Proterozoic to Paleozoic rocks. The Sierras Septentrionales consists mainly of Precambrian crystalline rocks. The Precambrian sequences are overlain by younger Sediments (Cingolani, 2010). The aim is to understand the long-term landscape evolution of the area by quantifiying erosion- and exhumation-rates and by dating ancient rock-uplift-events. Another goal is to find out how the opening of the south atlantic took effect on this region. To fulfill this goal, thermochronological techniques, such as fission-track dating and (U-Th-Sm)/He dating has been applied to samples from the region. Because there was no low-temperature thermochronology done in this area, both techniques were applied on apatites and zircons. Furthermore, numerical modeling of the cooling history has provided the data base for the quantification of the exhumation rates. The first data-set shows clusters of different ages which can be linked to tectonic activities during late Paleozoic times. Also the thermokinematic modeling is leading to new insights of the evolution of both mountain ranges. References: Renata Nela Tomezzoli and Juan Francisco Vilas (1999): Palaeomagnetic constraints on the age of deformation of the Sierras Australes thrust and

  15. 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...

  16. 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.

    The geochemistry and mineralogy of the potential phospharite deposits recovered from the continental margin off Chennai, Tamil Nadu (India) and their comparison with other offshore phosphorites is given. The phosphorites recovered are classified...

  17. 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.

    The oceans' 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...

  18. Continental margin sedimentation: from sediment transport to sequence stratigraphy

    Science.gov (United States)

    Nittrouer, Charles A.; Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P.M.; Wiberg, Patricia L.; Nittrouer, Charles A.; Austin, James A.; Field, Michael E.; Kravitz, Joseph H.; Syvitski, James P. M.; Wiberg, Patricia L.

    2007-01-01

    This volume on continental margin sedimentation brings together an expert editorial and contributor team to create a state-of-the-art resource. Taking a global perspective, the book spans a range of timescales and content, ranging from how oceans transport particles, to how thick rock sequences are formed on continental margins. - Summarizes and integrates our understanding of sedimentary processes and strata associated with fluvial dispersal systems on continental shelves and slopes - Explores timescales ranging from particle transport at one extreme, to deep burial at the other - Insights are presented for margins in general, and with focus on a tectonically active margin (northern California) and a passive margin (New Jersey), enabling detailed examination of the intricate relationships between a wide suite of sedimentary processes and their preserved stratigraphy - Includes observational studies which document the processes and strata found on particular margins, in addition to numerical models and laboratory experimentation, which provide a quantitative basis for extrapolation in time and space of insights about continental-margin sedimentation - Provides a research resource for scientists studying modern and ancient margins, and an educational text for advanced students in sedimentology and stratigraphy

  19. 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.

  20. On the relationship between sequential faulting, margin asymmetry and highly thinned continental crust

    Science.gov (United States)

    Brune, Sascha; Heine, Christian; Pérez-Gussinyé, Marta; Sobolev, Stephan

    2014-05-01

    The architecture of magma-poor continental margins is remarkably variable. The width of highly thinned continental crust (with a thickness material; (2) Formation of a low viscosity exhumation channel adjacent to the rift centre that is generated by heat transfer from the upwelling mantle and enhanced by viscous strain softening. Rift migration takes place in a steady-state manner and is accomplished by oceanward-younging sequential faults within the upper crust and balanced through lower crustal flow. We demonstrate that the rate of extension has paramount control on margin width. Since higher velocities lead to elevated heat flow within the rift and hence to hot and weak lower crust, a larger low-viscosity exhumation channel is generated that facilitates rift migration leading to wider margins. The South Atlantic is an ideal test bed for the hypothesis of velocity-dependent margin width since rifting was fast in the south, but slow in the northern part. As predicted by our numerical models, the maximum present-day margin width increases almost linearly from the conjugate Equatorial margin segments to the Florianopolis/Walvis ridge. Even though the polarity of the magma-poor South Atlantic margins alternates, the asymmetry and the width of the wider margin are in very good agreement with our simulations. The described rift evolution has three fundamental implications: (1) It implies sustained transfer of material across the extensional plate boundary thereby predicting that large portions of a wide margin originate from its conjugate side. (2) Migration of the deformation locus causes faulting in the distal parts of the margin to postdate that of the proximal parts by as much as 10 million years. This means that syn-rift and post-rift phase are location-dependent. (3) Lateral movement of the rift centre generates drastically different peak heat flow and subsidence histories at the proximal and the distal margin.

  1. 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, resulting in

  2. Continental margin of Andhra Pradesh: Some new problems and perspectives

    Digital Repository Service at National Institute of Oceanography (India)

    Murthy, K.S.R.

    in the K-G basin at the foot of the continental slope, at around 3000 m water depth. These preliminary findings suggest that the exploration of the Andhra Pradesh margin should be followed up more vigorously to infer its neotectonics and geodynamics...

  3. 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.

  4. Formation of the volcanic rifted margin off Argentina/Uruguay, South Atlantic

    Science.gov (United States)

    Franke, D.; Reichert, C.; Ladage, S.; Schnabel, M.; Schreckenberger, B.; Neben, S.; Hinz, K.

    2009-04-01

    The Federal Institute for Geosciences and Natural Resources (BGR), Germany has investigated the passive continental margins offshore Argentina and Uruguay since the early 90ies. Numerous marine geophysical surveys have meanwhile established a databasis of more than 25.000 km of regional multi-channel reflection seismic lines, accompanied with magnetic and gravity profiles. These data document that the Early Cretaceous South Atlantic continental break-up and initial sea-floor spreading were accompanied by large-scale, transient volcanism emplacing voluminous extrusives, manifested in the seismic data by huge wedges of seaward dipping reflectors (SDRs). These deeply buried and 60-120 km wide SDRs were emplaced episodically as suggested by at least three superimposed SDRS units. Distinct along-margin variations in the architecture, volume, and width of the SDRs wedges correlate with large scale margin segmentation. We identify at least four domains bounded by the Falkland Fracture Zone/Falkland Transfer, the Colorado Transfer, the Ventana Transfer and the Salado Transfer. The individual transfer zones may have acted as barriers for propagating rifts during the SDR emplacement phase, selectively directing rift segments in left stepping patterns along the western South Atlantic margin. The rift segments are offset systematically in a left stepping pattern along the western South Atlantic margin. Albeit we found extensive variations in the architecture, style and extent of the seaward dipping reflector sequences a general trend is that the largest volumes are emplaced close to the proposed transfer zones and the width of the SDRs wedges decreases northward within the individual margin segments. The different volcano-tectonic architectures of the margin segments and the distribution of the extruded magmas indicates that the emplacement of the volcanic material was controlled by the tectonic setting and the pre-rift lithosphere configuration within individual margin

  5. Glacial and oceanic history of the polar North Atlantic margins: An overview

    DEFF Research Database (Denmark)

    Elverhøj, A.; Dowdeswell, J.; Funder, S.V.

    1998-01-01

    The five-year PONAl'vl (polar North Atlantic l\\largin: Late Cenozoic Evolution) pr programme was launched by the European Science Foundation in 1989. Its aim was to study the major climate-driven environmental variations in the Norwegian-Greenland (also Nordic) Sea and its continental margins ove...... varying from 100,000 year glacial cycles to millennial-scale nuctuations. C(;, 1998 Elsevier Science Ltd. All rights reserved....

  6. Multiple uplift phases inferred from the Southwest African Atlantic margin

    Science.gov (United States)

    Scheck-Wenderoth, Magdalena; Cacace, Mauro; Dressel, Ingo

    2015-04-01

    The South Atlantic basins offshore Namibia and South Africa stored more than 10 km thick sedimentary successions that are separated by major unconformities into several sequences. These sedimentary units rest on a thinned continental crust of a magmatic passive margin. Using a 3D forward modelling approach considering flexural compensation of a rheologically differentiated lithosphere in response to sedimentary loading after stretching on one hand and the thermal feed-back between cooling of the stretched lithosphere and insulating sediments on the other hand we derive quantitative estimates on how vertical movements have influenced the margin after stretching. The approach combines the consideration of observations on sediment configuration as well as on crustal thickness (ß-factor) with the process of lithosphere thinning and subsequent thermal re-equilibration. These estimates are conservative estimates as they are based on the preserved sediments only whereas eroded sediments are not considered. Nevertheless, the approach considers thermo-mechanical coupling in 3D and both initial conditions as well as sedimentary history are constrained by observations. Specific effects include the delayed thermal re-equilibration of the thinned lithosphere due to deposition of insulating sediments and the related thermal feedback on lithosphere rheology and therefore on the flexural response to sediment loading. Our results indicate that in addition to predominantly continuous subsidence also phases of uplift have affected the southwestern African margin during the syn-rift and post-rift evolution. The spatio-temporal variation of vertical movements is controlled by the amount of initial thinning of the lithosphere, the variation of rheological characteristics (lithology and temperature) but also by the distribution of sediment supply (loading and thermal insulation).

  7. Widespread methane leakage from the sea floor on the northern US Atlantic margin

    Science.gov (United States)

    Skarke, Adam; Ruppel, Carolyn; Kodis, Mali'o; Brothers, Daniel S.; Lobecker, Elizabeth A.

    2014-01-01

    Methane emissions from the sea floor affect methane inputs into the atmosphere, ocean acidification and de-oxygenation, the distribution of chemosynthetic communities and energy resources. Global methane flux from seabed cold seeps has only been estimated for continental shelves, at 8 to 65 Tg CH4 yr−1, yet other parts of marine continental margins are also emitting methane. The US Atlantic margin has not been considered an area of widespread seepage, with only three methane seeps recognized seaward of the shelf break. However, massive upper-slope seepage related to gas hydrate degradation has been predicted for the southern part of this margin, even though this process has previously only been recognized in the Arctic. Here we use multibeam water-column backscatter data that cover 94,000 km2 of sea floor to identify about 570 gas plumes at water depths between 50 and 1,700 m between Cape Hatteras and Georges Bank on the northern US Atlantic passive margin. About 440 seeps originate at water depths that bracket the updip limit for methane hydrate stability. Contemporary upper-slope seepage there may be triggered by ongoing warming of intermediate waters, but authigenic carbonates observed imply that emissions have continued for more than 1,000 years at some seeps. Extrapolating the upper-slope seep density on this margin to the global passive margin system, we suggest that tens of thousands of seeps could be discoverable.

  8. Deformation and seismicity associated with continental rift zones propagating toward continental margins

    Science.gov (United States)

    Lyakhovsky, V.; Segev, A.; Schattner, U.; Weinberger, R.

    2012-01-01

    We study the propagation of a continental rift and its interaction with a continental margin utilizing a 3-D lithospheric model with a seismogenic crust governed by a damage rheology. A long-standing problem in rift-mechanics, known as thetectonic force paradox, is that the magnitude of the tectonic forces required for rifting are not large enough in the absence of basaltic magmatism. Our modeling results demonstrate that under moderate rift-driving tectonic forces the rift propagation is feasible even in the absence of magmatism. This is due to gradual weakening and "long-term memory" of fractured rocks that lead to a significantly lower yielding stress than that of the surrounding intact rocks. We show that the style, rate and the associated seismicity pattern of the rift zone formation in the continental lithosphere depend not only on the applied tectonic forces, but also on the rate of healing. Accounting for the memory effect provides a feasible solution for thetectonic force paradox. Our modeling results also demonstrate how the lithosphere structure affects the geometry of the propagating rift system toward a continental margin. Thinning of the crystalline crust leads to a decrease in the propagation rate and possibly to rift termination across the margin. In such a case, a new fault system is created perpendicular to the direction of the rift propagation. These results reveal that the local lithosphere structure is one of the key factors controlling the geometry of the evolving rift system and seismicity pattern.

  9. Elephant teeth from the atlantic continental shelf

    Science.gov (United States)

    Whitmore, F.C.; Emery, K.O.; Cooke, H.B.S.; Swift, D.J.P.

    1967-01-01

    Teeth of mastodons and mastodons have been recovered by fishermen from at least 40 sites on the continental shelf as deep as 120 meters. Also present are submerged shorelines, peat deposits, lagoonal shells, and relict sands. Evidently elephants and other large mammals ranged this region during the glacial stage of low sea level of the last 25.000 years.

  10. Segmentation of the Levant continental margin, eastern Mediterranean

    Science.gov (United States)

    Ben-Avraham, Z.; Schattner, U.; Lazar, M.; Hall, J. K.; Ben-Gai, Y.; Neev, D.; Reshef, M.

    2006-10-01

    The Levant continental margin is divided into two major segments by the Carmel structure, which extends from the Dead Sea fault into the eastern Mediterranean. New seismic reflection data over the unexplored northern segment are used for completing the structural framework of the Levant area, together with existing data south of it. Inclusive depth structural maps of the area were produced for the base Pliocene and base Messinian evaporites. Previous studies indicate that differences between the two segments are well expressed in the deep crustal structure. The present study, which focuses mainly on the shallow section, shows that these differences are maintained throughout the accumulation of young sedimentary units, and even in the bathymetry. This preservation of segmentation, both in the shallow and in the deep structure, insinuates that the two segments were formed through different continental breakup processes, which continue to dictate the style of sediment accumulation.

  11. How a Curvilinear Continental Margin Influences Its Subsidence History

    Science.gov (United States)

    Sacek, V.; Ussami, N.

    2012-12-01

    Current one-dimensional (1D) and two-dimensional (2D) thermo-mechanical models successfully explain the first-order vertical motions of sedimentary basins created by lithospheric extension. However, the modeling of second-order effects such as extra-subsidence, non-monotonic-subsidence or protracted-subsidence still remains controversial. One aspect that has not been fully considered in the current models is that the rifting direction leading to the continental break-up does not always follow a straight line, which demands a three-dimensional (3D) approach. The aim of this work is to demonstrate the importance of using a 3D model that takes into account the curvature of rifting along the margin and theoretically predicts some of the second-order subsidence observations. Our results indicate that concave oceanward margins tend to subside faster than convex ones. This differential subsidence of the margin is a result of the combined effect of lateral thermal conduction, small-scale mantle (or edge driven) convection and the curvature of the rifting. We have used the finite element code CITCOM (Moresi & Gurnis, 1996; Zhong et al., 2000) to construct 3D numerical models of the mantle convection and its effect on the surface evolution. We observed that the differential subsidence along a curved margin is dependent on the viscosity structure of the mantle: for an asthenospheric viscosity of 5×1020 Pa.s the differential subsidence can reach more than 700 m assuming a sediment filled basin; however, for low asthenospheric viscosity (geometry. As an application of this 3D conceptual model for curved margin, we analysed the stratigraphic evolution of the Santos Basin, offshore Southeastern Brazil, and we propose that the variations in the subsidence history along the margin can be explained by its 3D geometry and the dynamical evolution of the mantle. We conclude that the incorporation of the third dimension in the study of the subsidence history of divergent margins may

  12. 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

  13. GLANAM (Glaciated North Atlantic Margins): A Marie Curie Initial Training Network between Norway, the UK & Denmark

    Science.gov (United States)

    Petter Sejrup, Hans; Oline Hjelstuen, Berit

    2015-04-01

    GLANAM (Glaciated North Atlantic Margins) is an Initial Training Network (ITN) funded under the EU Marie Curie Programme. It comprises 10 research partners from Norway, UK and Denmark, including 7 University research teams, 1 industrial full partner and 2 industrial associate partners. The GLANAM network will employ and train 15 early career researchers (Fellows). The aim of GLANAM is to improve the career prospects and development of young researchers in both the public and private sector within the field of earth science, focusing on North Atlantic glaciated margins. The young scientists will perform multi-disciplinary research and receive training in geophysics, remote sensing, GIS, sedimentology, geomorphology, stratigraphy, geochemistry and numerical modeling through three interconnected work packages that collectively address knowledge gaps related to the large, glacial age, sedimentary depocentres on the North Atlantic margin. The 15 Fellows will work on projects that geographically extend from Ireland in the south to the High Arctic. Filling these gaps will not only result in major new insights regarding glacial age processes on continental margins in general, but will also provide paleoclimate information essential for understanding the role of marine-based ice sheets in the climate system and for the testing of climate models. GLANAM brings together leading European research groups working on glaciated margins in a coordinated and collaborative research and training project. Focusing on the North Atlantic margins, this coordinated approach will lead to a major advance in the understanding of glaciated margins more widely and will fundamentally strengthen European research and build capacity in this field.

  14. Mesozoic Source-to-Sink of the African margin of the Equatorial Atlantic

    Science.gov (United States)

    ye, jing; Chardon, Dominique; rouby, delphine; Guillocheau, François; Robin, Cecile; Loparev, Artiom; Huyghe, damien; Dall'Asta, Massimo; Brown, Roderick; wildman, mark; webster, david

    2016-04-01

    The objective of the Transform Source to Sink Project (TS2P) is to link the dynamics of the erosion of the West African Craton to the offshore sedimentary basins of the African margin of the Equatorial Atlantic at geological time scales. This margin, alternating transform and oblique segments from Guinea to Nigeria, shows a strong structural variability in the margin width, continental geology and relief, drainage networks and subsidence/accumulation patterns. We analyzed this system combining onshore geology and geomorphology as well as offshore sub-surface data. We produced paleogeographic maps at the scale of West Africa spanning the continental domain and offshore basins since 200 Ma. Mapping spatial and temporal distribution of domains either in erosion (sources) or in accumulation (sinks) document the impact of the successive rifting of Central and Equatorial Atlantic on the physiography of the area. We use low temperature thermochronology dating along three transects perpendicular to the margin (Guinea, Ivory Coast and Benin) to determine periods and domains of denudation in that framework. We compare these data to the Mesozoic accumulation histories in passive margin basins and discuss their stratigraphic expression according to the type of margin segment they are preserved in. Syn-rift architectures (Early Cretaceous) are largely impacted by transform faults that define sub-basins with contrasted width of crustal necking zone (narrower in transform segments than in oblique/normal segments). During the Late Cretaceous post-rift, sedimentary wedges record a transgression along the all margin. Proximal parts of the sedimentary wedge are preserved in basins developing on segments with wide crustal necking zone while they were eroded away in basins developing on narrow segments. As a difference, the Cenozoic wedge is everywhere preserved across the whole width of the margin.

  15. Evolution of high Arctic ocean basins and continental margins

    Energy Technology Data Exchange (ETDEWEB)

    Engen, Oeyvind

    2005-08-01

    Taking advantage of the much increased detail offered by new data, the dissertation attempts to answer some of the remaining questions about the ocean basins and continental margins flanking the Eurasia-North America plate boundary. Its four constituent papers result from integrated geophysical analysis of gravity and magnetic anomalies, bathymetry, seismic reflection and refraction profiles, earthquake locations and focal mechanisms, and onshore and offshore geological data. The overall objectives are to: 1) Elucidate aspects of the structure, composition and evolution of the Eurasia Basin and Norwegian-Greenland Sea and their passive continental margins. 2) Relate the findings to fundamental Earth processes, specifically associated with lithospheric break-up and seafloor spreading. Summary of Papers: The present-day global seismograph network is capable of detecting earthquakes with nearly uniform magnitude threshold throughout the Eurasia Basin region. Given that the location of each earthquake is constrained by at least 12 recording stations, global earthquake catalogues confidently show that 1) earthquakes along the oceanic part of the plate boundary occur in swarms; 2) plate boundary stress decreases eastwards, in accordance with decreasing spreading rates; and 3) deformation takes place in a narrow zone in the oceanic domain but is abruptly defocused at the transition to the Laptev Sea continental rift system. When integrated with bathymetry and potential field data, the earthquake distribution indicates four distinct plate boundary provinces. The Spitsbergen Transform System is a series of oblique ridges and transform faults where the seismicity becomes increasingly diffuse to the north. The western Gakkel Ridge (west of 60{sup E}) has clustered and focused seismicity, accentuated topography and highamplitude magnetic anomalies, whereas the eastern Gakkel Ridge has smoother topographic relief, lower magnetic amplitudes, and slightly more focused seismicity

  16. Reconstruction of the East Africa and Antarctica continental margins

    Science.gov (United States)

    Nguyen, Luan C.; Hall, Stuart A.; Bird, Dale E.; Ball, Philip J.

    2016-06-01

    The Early Jurassic separation of Antarctica from Africa plays an important role in our understanding of the dispersal of Gondwana and Pangea. Previous reconstruction models contain overlaps and gaps in the restored margins that reflect difficulties in accurately delineating the continent-ocean-boundary (COB) and determining the amount and distribution of extended continental crust. This study focuses on the evolution of the African margin adjacent to the Mozambique Basin and the conjugate Antarctic margin near the Riiser-Larsen Sea. Satellite-derived gravity data have been used to trace the orientations and landward limits of fracture zones. A 3-D gravity inversion has produced a crustal thickness model that reliably quantifies the extent and amount of stretched crust. Crustal thicknesses together with fracture zone terminations reveal COBs that are significantly closer to the African and Antarctic coasts than previously recognized. Correlation of fracture zone azimuths and identified COBs suggests Antarctica began drifting away from Africa at approximately 171 Ma in a roughly SSE direction. An areal-balancing method has been used to restore the crust to a uniform prerift thickness so as to perform a nonrigid reconstruction for both nonvolcanic and volcanic margins. Both margins reveal a trend of increasing extension from east to west. Our results suggest Africa underwent extension of 60-120 km, while Antarctic crust was stretched by 105-180 km. Various models tested to determine the direction of extension during rifting suggest that Antarctica moved away from Africa in a WNW-ESE direction during the period between 184 and 171 Ma prior to the onset of seafloor spreading.

  17. The character of the glaciated Mid-Norwegian continental margin

    Science.gov (United States)

    Oline Hjelstuen, Berit; Haflidason, Haflidi; Petter Sejrup, Hans

    2010-05-01

    During Pleistocene the development of the NW European continental margin was strongly controlled by the variability in ocean circulation, glaciations and sea-level changes. Repeated occurrence of shelf edge glaciations, from Ireland to Svalbard, started at Marine Isotope Stage 12 (c. 0.5 Ma). During these periods, fast moving ice streams also crossed the Mid-Norwegian continental shelf on a number of locations, and a thick prograding wedge accumulated on the continental slope. During shelf edge glaciations and in early deglaciation phases high sedimentation rates (>2000 cm/ka) existed, and glacigenic debris flows and melt water plumes were deposited. Within these depositional environments we identify three slide events. These slides have affected an area between 2900 and 12000 km2 and involved 580-2400 km3 of sediments, noting that the slide debrites left by the failure events reach a maximum thickness of c. 150 m. The failures have occurred within an area dominated by gradients less than 1 degree, and observation of long run-out distances indicate that hydroplaning was important during slide development. Gas hydrate bearing sediments are identified on the mid-Norwegian continental margin, but appears to be absent in the slide scars. Thus, dissociation of gas hydrates may have promoted conditions for the failures to occur. Within the region of gas hydrate bearing Pleistocene sediments the Nyegga Pockmark Field is observed. This field contains more than 200 pockmarks and is located at a water depth of 600-800 m. The pockmarks identified are up to 15 m deep, between 30 m and 600 m across and reach a maximum area of c. 315 000 m2. The pockmarks are sediment-empty features and are restricted to a <16.2 cal ka BP old sandy mud unit. It seems that the Nyegga Pockmark Field does not show any strong relationship neither to seabed features, sub-seabed structures nor the glacial sedimentary setting. Thus, this implies a more complex development history for the Nyegga

  18. Seaward dipping reflectors along the SW continental margin of India: Evidence for volcanic passive margin

    Indian Academy of Sciences (India)

    K K Ajay; A K Chaubey; K S Krishna; D Gopala Rao; D Sar

    2010-12-01

    Multi-channel seismic reflection profiles across the southwest continental margin of India (SWCMI) show presence of westerly dipping seismic reflectors beneath sedimentary strata along the western flank of the Laccadive Ridge –northernmost part of the Chagos –Laccadive Ridge system. Velocity structure, seismic character, 2D gravity model and geographic locations of the dipping reflectors suggest that these reflectors are volcanic in origin, which are interpreted as Seaward Dipping Reflectors (SDRs). 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 deduced from free-air gravity anomaly suggest that they are genetically related to incipient volcanism during separation of Madagascar from India. We suggest that (i)SWCMI is a volcanic passive margin developed during India –Madagascar breakup in the Late Cretaceous, and (ii)continent –ocean transition lies at western margin of the Laccadive Ridge, west of feather edge of the SDRs. Occurrence of SDRs on western flank of the Laccadive Ridge and inferred zone of transition from continent to ocean further suggest continental nature of crust of the Laccadive Ridge.

  19. Tectonic Evolution of the Northern Continental Margin of North China Platform in Middle Proterozoic

    Institute of Scientific and Technical Information of China (English)

    Xu Zhongyuan; Liu Zhenghong

    2000-01-01

    An orogenic belt developed in late middle Proterozoic in the northern margin of North China Plate extends from Inner Mongolia to Western Liaoning Province and Eastern Jilin Province. It is over 2000km long. The orogenic belt was formed by collision between North China Platform and Siberia Platform during the Rodinian Super- Continent period. From sedimentary formation, magmatic activity and crustal tectonic deformation, it is suggested that along the tectonic belt the paleocontinental margin experienced four stages of tectonic evolution in middle Proterozoic, they are: continental margin rift,passive continental margin, active continental margin and collisional orogenic stages.

  20. 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...

  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. 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 governed solely by temperature, but they may be explained by small amounts of partial melt or enhanced volatile content in the asthenosphere. While an asthenospheric low velocity zone appears to be ubiquitous beneath the continent, minimum velocities (and likely viscosities) within the eastern U.S. asthenosphere are not as low as those in the western U.S. At smaller scales, Sp imaging hints at lithospheric thickness variations that are correlated with tectonic features (e.g. orogenic boundaries, failed rifts) but resolution will be vastly improved with analysis of data from USArray Transportable and 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

  3. Numerical Models of Salt Tectonics and Associated Thermal Evolution of Rifted Continental Margins

    Science.gov (United States)

    Goteti, R.; Beaumont, C.; Ings, S. J.

    2011-12-01

    Salt tectonics at rifted continental margins reflects the interplay between the geometry of the initial evaporite basin and subsequent mobilization of the salt which is partly controlled by the density and strength of the overburden. Salt mobility is also influenced by the overall thermo-mechanical evolution of the margin which includes factors such as: initial seaward tilt of the margin basement owing to crustal thinning; an initial thermal anomaly owing to the rifting and the subsequent long-term postrift thermal subsidence; and the flexural isostatic response to sedimentation which may reverse the basal tilt. The high thermal conductivity of salt also has a significant impact on the thermal evolution of rifted margin sedimentary basins. We present two-dimensional thermo-mechanical finite element models designed to assess salt mobility and its impact on the thermal evolution of the surrounding sediments and underlying crust in the context of an evolving rifted margin, that includes the processes listed above. Model experiments include: the initial geometry of the rifted margin and the embedded autochthonous salt basin, and its subsequent thermal subsidence, sedimentation and water loading and their flexural response, erosion and, sediment compaction. Salt is mobilized by aggrading sediments with a sinusoidally perturbed surface that represents natural bathymetric unevenness. The model results indicate that the presence of a highly conductive salt layer perturbs the initial thermal structure of the rifted margin resulting in a negative thermal anomaly beneath the autochthonous salt basin. For a given thickness of the salt layer, the depth of this perturbation increases with the width of the salt basin. Flow of salt initially occurs by gliding owing to the initial seaward tilt of the margin which is enhanced by thermal subsidence as the margin cools and, subsequently by a combination of gliding and gravitational spreading when loaded by aggrading sediments. Uneven

  4. From rifting to passive margin: the examples of the Red Sea, Central Atlantic and Alpine Tethys

    Science.gov (United States)

    Favre, P.; Stampfli, G. M.

    1992-12-01

    Evolution of the Red Sea/Gulf of Suez and the Central Atlantic rift systems shows that an initial, transtensive rifting phase, affecting a broad area around the future zone of crustal separation, was followed by a pre-oceanic rifting phase during which extensional strain was concentrated on the axial rift zone. This caused lateral graben systems to become inactive and they evolved into rift-rim basins. The transtensive phase of diffuse crustal extension is recognized in many intra-continental rifts. If controlling stress systems relax, these rifts abort and develop into palaeorifts. If controlling stress systems persist, transtensive rift systems can enter the pre-oceanic rifting stage, during which the rift zone narrows and becomes asymmetric as a consequence of simple-shear deformation at shallow crustal levels and pure shear deformation at lower crustal and mantle-lithospheric levels. Preceding crustal separation, extensional denudation of the lithospheric mantle is possible. Progressive lithospheric attenuation entails updoming of the asthenosphere and thermal doming of the rift shoulders. Their uplift provides a major clastic source for the rift basins and the lateral rift-rim basins. Their stratigraphic record provides a sensitive tool for dating the rift shoulder uplift. Asymmetric rifting leads to the formation of asymmetric continental margins, corresponding in a simple-shear model to an upper plate and a conjugate lower plate margin, as seen in the Central Atlantic passive margins of the United States and Morocco. This rifting model can be successfully applied to the analysis of the Alpine Tethys palaeo-margins (such as Rif and the Western Alps).

  5. Atlantic update, July 1986--June 1990: Outer Continental Shelf oil and gas activities

    Energy Technology Data Exchange (ETDEWEB)

    Karpas, R.M.; Gould, G.J.

    1990-10-01

    This report describes outer continental shelf oil and gas activities in the Atlantic Region. This edition of the Atlantic Update includes an overview of the Mid-Atlantic Planning Area and a summary of the Manteo Prospect off-shore North Carolina. 6 figs., 8 tabs.

  6. Gravity and structure of the continental margins of southwestern Mexico and northwestern Guatemala

    Science.gov (United States)

    Couch, Richard; Woodcock, Stephen

    1981-03-01

    Geophysical measurements over the eastern end of the Tehuantepec Ridge and adjacent continental margins of southern Mexico and northern Guatemala indicate that the ridge is a fracture zone and that it marks the boundary between two different subduction provinces. A positive free-air gravity anomaly which extends northwestward along the outer continental shelf of Guatemala curves abruptly landward in the Gulf of Tehuantepec. The positive shelf anomaly is on trend with the positive anomaly of the Nicoya Peninsula, Costa Rica, and suggests that rocks genetically related to Cretaceous rocks of the Nicoya Complex extend northwestward along the continental shelf to the Gulf of Tehuantepec. A crustal and subcrustal cross section of the continental margin of Guatemala, constrained by gravity, magnetic, and seismic refraction data, indicates that the rock strata causing the outer shelf gravity high dip landward, consistent with imbricate thrusting of the oceanic crust beneath and into the continental margin. A model crustal cross section of the continental margin of southern Mexico, north of the Tehuantepec Ridge, shows a markedly different margin structure with a relatively small amount of continental accretion and a continental crustal block extending to within approximately 25 km of the trench axis.

  7. Quaternary phosphorites from the continental margin off Chennai, southeast India: Analogs of ancient phosphate stromatolites

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Rao, K.M.; Raju, D.S.N.

    the continental supply and degradation of organic matter associated with benthic microbial communities. The phosphate stratiform stromatolites thus formed were subsequently reworked into a shelf-margin depression and resulted in the occurrence of condensed...

  8. Sulphur enrichment in a sediment core from the central western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, P.S.; Rao, Ch.M.

    Anomalous sulphur values in relation to organic carbon have been found in the sediments of a core collected from the central western continental margin of India. The relationship between organic carbon and sulphur is similar to that of the sediments...

  9. Scenario of gas-charged sediments and gas hydrates in the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Karisiddaiah, S.M.; SubbaRaju, L.V.

    Echosounding, high-resolution shallow seismic data were collected along track lines spaced at 20 km interval across the western continental margin of India. A detailed analysis of the underway data revealed the occurrence of methane-bearing gas...

  10. 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; Bhattacharya, G.C.; SubbaRaju, L; 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...

  11. 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.

    Inversion of magnetic data was carried out on 40 profiles collected across the continental margin of Visakhapatnam, Andhra Pradesh, India at a spacing of about 10 km and magnetic basement map for this region is prepared. The map reveals complex...

  12. 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...

  13. Larval Transport on the Atlantic Continental Shelf of North America: a Review

    Science.gov (United States)

    Epifanio, C. E.; Garvine, R. W.

    2001-01-01

    This review considers transport of larval fish and crustaceans on the continental shelf. Previous reviews have contained only limited treatments of the physical processes involved. The present paper provides a physical background that is considerably more comprehensive. It includes a discussion of three principal forcing agents: (1) wind stress; (2) tides propagating from the deep ocean; and (3) differences in density associated with the buoyant outflow of estuaries, surface heat flux, or the interaction of coastal and oceanic water masses at the seaward margin of the shelf. The authors discuss the effects of these forcing agents on transport of larvae in the Middle Atlantic and South Atlantic Bights along the east coast of North America. The discussion concentrates on three species (blue crab, menhaden, bluefish) that have been the subject of a very recent multi-disciplinary study. Taken as a whole, the reproductive activities of these three species span the entire year and utilize the entire shelf, from the most seaward margin to the estuarine nursery. The blue crab is representative of species affected by physical processes occurring during summer and early autumn on the inner and mid-shelf. Menhaden are impacted by processes occurring in winter on the outer and mid-shelf. Bluefish are influenced primarily by processes occurring during early spring at the outer shelf margin near the western boundary current. The authors conclude that alongshore wind stress and density differences, i.e. buoyancy-driven flow, are the primary agents of larval transport in the region. Circulation associated with the western boundary current is only important at the shelf margin and tidally driven processes are generally inconsequential.

  14. 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

  15. A time-transgressive Holocene onset from Globorotalia menardii records on Brazilian continental margin sediments

    Science.gov (United States)

    Iwai, F. S.; Costa, K. B.; Toledo, F. A. D. L.; Santarosa, A. C. A.; Chiessi, C. M.; Camillo, E., Jr.; Quadros, J. P.

    2014-12-01

    The planktic foraminifer Globorotalia menardii presents a cyclic behavior within Pleistocene glacial cycles on Atlantic; it disappears during glacial periods and returns to this ocean after deglaciations. Therefore, G. menardii has been used to identify limits between those cycles and the last limit is recognized as the Holocene onset. The Holocene onset has been reported before as being more than 4 kyrs later than expected at the equatorial Atlantic Ocean based on a G. menardii record (Broecker & Pena, 2014). In this study, we explore the time-transgressive Holocene onset of G. menardii in the Atlantic from 21 piston cores collected along the Brazilian continental margin, between 7 ˚N and 33 ˚S. Radiocarbon dating was conducted on Globigerinoides ruber on samples prior to and after G. menardii reappearance in the cores. Reservoir-age corrected 14C dates vary between 17 and 6.5 cal kyrs; the older ages are found at ~14 ˚S and younger ages at 6 ˚N and 33 ˚S. From these ages and latitudes, we hypothesize that G. menardii's population has spread at higher rates southward. From the scenario observed on Brazilian coast it is possible to conclude that although ocean circulation has an important role on dispersion of planktonic foraminifera, it may be superimposed by ecological constraints of the species. G. menardii absence during glacials is linked to the Agulhas Leakage activity, which is prevented from getting to the Atlantic due the northern position of the Subtropical Convergence Zone during glacials. On interglacials, warm and saline waters carrying G. menardii are transported into the Subtropical Gyre currents, achieving Brazil's coast through the South Equatorial Current and spreading south and northward through Brazil Current and North Brazil Current, respectively. Nonetheless, from velocity and volume registered for this currents, we would expect a higher G. menardii dispersion rate northward. A faster southward dispersal during the deglaciation suggests

  16. 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...

  17. New Views of the U.S. Atlantic Margin Mapped for UNCLOS Applications. New Views of the U.S. Atlantic Margin Mapped for UNCLOS Applications

    Science.gov (United States)

    Gardner, J. V.; Mayer, L. A.; Arnstrong, A.; Donaldson, P.; Infantino, J.; Davis, G.; Smith, D.; Lobecker, M.; Cartwright, D.; Iwachiw, J.; Farr, S.; Meadows, D.; Dorsey, S.; Marsh, G.; Owen, W.

    2005-12-01

    Article 76 of the UN Convention on the Law of the Sea (UNCLOS) presents an opportunity to map continental margins. Although mapping the required 2500-m isobath is relatively straight forward, locating the geomorphic foot of the slope is, in many areas, equivocal and requires mapping large areas of the lower slope. The large-area mapping required to support an UNCLOS submission, generates a dataset useful to a wide spectrum of disciplines and the new bathymetric maps will represent roadmaps for the next generation of continental-margin studies. As part of the U.S. UNCLOS effort, the entire U.S. Atlantic margin between the 1 and 5 km isobaths was mapped in 2004 and 2005. A 12-kHz multibeam echosounder was used to provide bathymetry and co-registered backscatter, 3.5-kHz CHIRP profiler and gravity data were also collected. The bathymetric data cover> 600,000 km2 with a spatial resolution of 100 m. Eight New England Seamounts were mapped in their entirety. Talus piles, moats and sediment banks are common features around the seamounts. The northern seamounts fall along two trends; Balanus, Picket and Retriever Seamounts trend 118 deg whereas Retriever , Physalia and Bear Seamounts trend 94 deg. The change in trends occurred about 100 my ago. Mytilus Seamount and two other unnamed seamounts are offset 70 km to the SE and trend 108 deg. The trends and changes in trend suggest that the relationship of the seamounts to a single hotspot trend is too simplistic. Submarine canyon-channel systems (CCS) dominate the northern third of the Atlantic lower slope and rise, are less ubiquitous in the middle third and are rare in the southern third. The northern CCSs are composed of canyon channels distributed along the upper slope that are captured down slope by a single channel. Channel capture has resulted in hanging valleys of 10 to 100 m high. In the northern area, a CCS is composed of a broad channel plain incised by a narrow channel. This rejuvenation of channel cutting suggests

  18. Evolution of magma-poor continental margins from rifting to seafloor spreading.

    Science.gov (United States)

    Whitmarsh, R B; Manatschal, G; Minshull, T A

    2001-09-13

    The rifting of continents involves faulting (tectonism) and magmatism, which reflect the strain-rate and temperature dependent processes of solid-state deformation and decompression melting within the Earth. Most models of this rifting have treated tectonism and magmatism separately, and few numerical simulations have attempted to include continental break-up and melting, let alone describe how continental rifting evolves into seafloor spreading. Models of this evolution conventionally juxtapose continental and oceanic crust. Here we present observations that support the existence of a zone of exhumed continental mantle, several tens of kilometres wide, between oceanic and continental crust on continental margins where magma-poor rifting has taken place. We present geophysical and geological observations from the west Iberia margin, and geological mapping of margins of the former Tethys ocean now exposed in the Alps. We use these complementary findings to propose a conceptual model that focuses on the final stage of continental extension and break-up, and the creation of a zone of exhumed continental mantle that evolves oceanward into seafloor spreading. We conclude that the evolving stress and thermal fields are constrained by a rising and narrowing ridge of asthenospheric mantle, and that magmatism and rates of extension systematically increase oceanward.

  19. Modelling of sea floor spreading initiation and rifted continental margin formation

    Science.gov (United States)

    Tymms, V. J.; Isimm Team

    2003-04-01

    Recent observations of depth dependent (heterogeneous) stretching where upper crustal extension is much less than that of the lower crust and lithospheric mantle at both non-volcanic and volcanic margins plus the discovery of broad domains of exhumed continental mantle at non-volcanic rifted margins are not predicted by existing quantitative models of rifted margin formation which are usually based on intra-continental rift models subjected to very large stretching factors. New conceptual and quantitative models of rifted margin formation are required. Observations and continuum mechanics suggest that the dominant process responsible for rifted continental margin formation is sea-floor spreading of the young ocean ridge, rather than pre-breakup intra-continental rifting. Simple fluid flow models of ocean ridge processes using analytical iso-viscous corner-flow demonstrate that the divergent motion of the upwelling mantle beneath the ocean ridge, when viewed in the reference frame of the young continental margin, shows oceanward flow of the lower continental crust and lithospheric mantle of the young rifted margin giving rise to depth dependent stretching as observed. Single-phase fluid-models have been developed to model the initiation of sea-floor spreading and the thermal, stretching and thinning evolution of the young rifted continental margin. Finite element fluid-flow modelling incorporating the evolving temperature dependent viscosity field on the fluid flow also show depth dependent stretching of the young continental margin. Two-phase flow models of ocean ridges incorporating the transport of both solid matrix and melt fluid (Spiegelman &Reynolds 1999) predict the divergent motion of the asthenosphere and lithosphere matrix, and the focusing of basaltic melt into the narrow axial zone spreading centre at ocean ridges. We are adapting two-phase flow models for application to the initiation of sea-floor spreading and rifted continental margin formation. i

  20. 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)

  1. Holistic Approach Offers Potential to Quantify Mass Fluxes Across Continental Margins

    Science.gov (United States)

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

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

  2. 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.

  3. 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

    2012-10-01

    Full Text Available The complex coastline of the Earth is over 400 000 km long and about 40% of the world's population lives within 100 km of the sea. Past characterizations of the global coastline were constructed either from a continental perspective through an analysis of watershed river basin properties (COSCAT: Coastal Segmentation and related CATchments or from an oceanic perspective, through a regionalization of the proximal and distal continental margins (LME: 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 which 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 fresh water 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. These results can be used for regional analyses and combined with various typologies for upscaling and biogeochemical budgets. In addition, the three levels segmentation can be used for application in Earth System analysis.

  4. 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).

  5. 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.

  6. The Agulhas-Karoo Geoscience Transect: Structures and processes along the southern African continental margin

    OpenAIRE

    N. Parsiegla; Gohl, K.; Uenzelmann-Neben, G.; Jacek Stankiewicz

    2008-01-01

    The southern African continental transform margin is of great interest for the understanding of processes related to continental breakup, transform fault formation and vertical plate motion. Open questions include the cause and consequences for the high topography of southern Africa, neotectonic activity along the Agulhas-Falkland Fracture Zone and the formation of the Outeniqua Basin. As a component of the project “Inkaby yeAfrica”, the 900 km long Agulhas-Karoo Geoscience Transect was carri...

  7. Towards Biogeochemical Modeling of Anaerobic Oxidation of Methane: Characterization of Microbial Communities in Methane-bearing North American Continental Margin Sediments

    Science.gov (United States)

    Graw, M. F.; Solomon, E. A.; Chrisler, W.; Krause, S.; Treude, T.; Ruppel, C. D.; Pohlman, J.; Colwell, F. S.

    2015-12-01

    Methane advecting through continental margin sediments may enter the water column and potentially contribute to ocean acidification and increase atmospheric methane concentrations. Anaerobic oxidation of methane (AOM), mediated by syntrophic consortia of anaerobic methanotrophic archaea and sulfate-reducing bacteria (ANME-SRB), consumes nearly all dissolved methane in methane-bearing sediments before it reaches the sediment-water interface. Despite the significant role ANME-SRB play in carbon cycling, our knowledge of these organisms and their surrounding microbial communities is limited. Our objective is to develop a metabolic model of ANME-SRB within methane-bearing sediments and to couple this to a geochemical reaction-transport model for these margins. As a first step towards this goal, we undertook fluorescent microscopic imaging, 16S rRNA gene deep-sequencing, and shotgun metagenomic sequencing of sediments from the US Pacific (Washington) and northern Atlantic margins where ANME-SRB are present. A successful Illumina MiSeq sequencing run yielded 106,257 bacterial and 857,834 archaeal 16S rRNA gene sequences from 12 communities from the Washington Margin using both universal prokaryotic and archaeal-specific primer sets. Fluorescent microscopy confirmed the presence of cells of the ANME-2c lineage in the sequenced communities. Microbial community characterization was coupled with measurements of sediment physical and geochemical properties and, for samples from the US Atlantic margin, 14C-based measurements of AOM rates and 35S-based measurements of sulfate reduction rates. These findings have the potential to increase understanding of ANME-SRB, their surrounding microbial communities, and their role in carbon cycling within continental margins. In addition, they pave the way for future efforts at developing a metabolic model of ANME-SRB and coupling it to geochemical models of the US Washington and Atlantic margins.

  8. Environmental geologic studies on the southeastern United States Atlantic Outer Continental Shelf, 1977-1978

    Science.gov (United States)

    Popenoe, Peter; Popenoe, Peter

    1981-01-01

    This report is a summary of the second year of marine environmental research activities by the U.S. Geological Survey (USGS) on the southeaster U.S. Atlantic Continental Margin, in accordance with with Memorandum of Understanding (MOU) AA551-MU8-13 between the USGS and the Bureau of Land Management (BLM). The report covers studies whose fieldwork was conducted during the period from 1 October 1977 to 30 September 1978. The results of the first year of study are reported in Popenoe (1978a and b) and as U.S. Department of Commerce NTIS report PB 300-820. The purpose of these investigations is to provide basic geologic and oceanographic data to the BLM Outer Continental Shelf (OCS) Marine Environmental Studies Program in support of management decisions which relate to possible development of oil and gas resources of the continental shelf. The objectives of the USGS-BLM geologic research program for fiscal year 1978 (FY-78) were 1) to determine the sedimentation rates and processes on the upper slope and inner Blake Plateau; 2) to determine the distribution, areal extent, and vertical characteristics of geological features supportive of biological communities; 3) to monitor the transport of bottom sediment across the OCS, evaluate its possible effect on pollutant transfer along the seabed and the potential of sediment as a pollutant sink, determine the implications of erosion/deposition on pipeline emplacement, and aid the interpretation of chemical, biological, and physical data; 4) to determine the concentration levels of chosen trace metals and silica in three chemically defined fractions of the suspended particulate matter (seston); 5) to study the shelf edge and slope near areas of oil and gas interest, and the northern portion of the Blake Plateau for evidence of slope instability and other geologic hazards, and 6) to determine the depth and rate of sediment mixing caused by large storms and/or by benthic organisms and where possible to estimate the rate of

  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.

     edited version of this paper was published by Blackwell Verlag GmbH. Copyright [2010]  2 Problem In the past few decades, considerable attention has been given to the study of continental margin biodiversity (Flach & Thomsen 1998; Tselepides et al. 2000; Palma et al. 2005). The continental margin, extending from the sublittoral... Concepecion (Palma et al. 2005). In addition, one particular morphological adaptation of this species, an expanded branchial structure has been observed only in the OMZ settings, specifically at the lowest level of oxygen concentration on the upper slope...

  10. Lithospheric Thermal Isostasy of North Continental Margin of the South China Sea

    Institute of Scientific and Technical Information of China (English)

    Chen Shi; Zhang Jian; Sun Yujun; Shi Yaolin

    2009-01-01

    Accompanied with rifting and detaching of the north continental margin of the South China Sea,the ernst and the lithosphere become thinner away from the continental margin resulting from the tectonic activities,such as tensile deformation,thermal uplift,and cooling subsidence,etc..Integrated with thermal,gravimetric,and isostatic analysis techniques,based on the seismic interpretation of the deep penetration seismic soundings across the northern margin of the South China Sea,we reconstructed the lithospheric thermal structure and derived the variation of the crust boundary in the east and west parts of the seismic profde by using gravity anomaly data.We mainly studied the thermal isostasy problems using the bathymetry of the profiles and calculated the crust thinning effect due to the thermal variety in the rifting process.The results Indicate that the thermal isostasy may reach 2.5 kin,and the compositional variations in the ilthospheric density and thickness may produce a variation of 4.0 kin.Therefore,the compositional isostatic correction is very important to recover the relationship between surface heat flow and topography.Moreover,because of the high heat flow characteristic of the continental margin,building the model of lithospheric geotherm in this region is of great importan for studying the Cenozoic tectonic thermal evolution of the north passive continental margin of the South China Sea.

  11. Spatial and temporal variability of particle flux at the NW European continental margin

    NARCIS (Netherlands)

    Antia, A.N.; Maaßen, J.; Herman, P.M.J.; Voss, M.; Scholten, J.C.M.; Groom, S.; Miller, P.

    2001-01-01

    A synopsis of results from two sediment trap moorings deployed at the mid- and outer slope (water depths 1450 and 3660 m, respectively) of the Goban Spur (N.E. Atlantic Margin) is presented. Fluxes increase with trap deployment depth; below 1000 m resuspended and advected material contributes increa

  12. Early Eocene climatic optimum: Environmental impact on the North Iberian continental margin

    NARCIS (Netherlands)

    Payros, A.; Ortiz, S.; Millán, I.; Arostegi, J.; Orue-Etxebarria, X.; Apellaniz, E.

    2015-01-01

    The early Eocene climatic optimum, which constituted the peak of the long-term early Cenozoic global warming, had a significant impact on the environmental evolution of terrestrial and oceanic areas. Surprisingly, however, its influence on continental margins is poorly known. New insights are provid

  13. A water column study of methane around gas flares located at the West Spitsbergen continental margin

    DEFF Research Database (Denmark)

    Gentz, Torben; Damm, Ellen; von Deimling, Jens Schneider;

    2014-01-01

    In the Arctic Seas, the West Spitsbergen continental margin represents a prominent methane seep area. In this area, free gas formation and gas ebullition as a consequence of hydrate dissociation due to global warming are currently under debate. Recent studies revealed shallow gas accumulation and...

  14. Magnetic anomalies of offshore Krishna–Godavari basin, eastern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Swamy, K.V.; Murthy, I.V.R.; Krishna, K.S.; Murthy, K.S.R.; Subrahmanyam, A.S.; Rao, M.M.M.

    The marine magnetic data acquired from offshore Krishna-Godavari (K-G) basin, eastern continental margin of India (ECMI), brought out a prominent NE-SW trending feature, which could be explained by a buried structural high formed by volcanic...

  15. 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.

    Gravimetric and bathymetric studies on the southwestern continental margin of India confirm the extension of onshore NW-SE-, NNW-SSE-, N-S-, NE-SW-, ENE-WSW- and E-W-trending lineaments of Precambrian age over a considerable distance...

  16. 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.

    , International Indian Ocean Expedition, Oceanographic Monographs, 2,173 pp. DIESTER-HAASS L. (1976) Quaternary accumulation rates of biogenous and terrigenous components on the East Atlantic continental slope off NW Africa. Marine Geology, 21, 1-24. Dm.... THIEDE (1983) Coastal upwelling its sediment record. Plenum Press, New York, 604 pp. THIEDE J. (1983) Skeletal plankton and nekton in upwelling water masses off north western south America and northwest Africa. In: Coastal upwelling: its sediment record...

  17. Wintertime pytoplankton bloom in the Subarctic Pacific supportedby continental margin iron

    Energy Technology Data Exchange (ETDEWEB)

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

    2004-06-08

    Heightened biological activity was observed in February 1996in the high-nutrient low-chlorophyll (HNLC) subarctic North PacificOcean, a region that is thought to beiron-limited. Here we provideevidence supporting the hypothesis that Ocean Station Papa (OSP) in thesubarctic Pacific received a lateral supply of particulate iron from thecontinental margin off the Aleutian Islands in the winter, coincidentwith the observed biological bloom. Synchrotron X-ray analysis was usedto describe the physical form, chemistry, and depth distributions of ironin size fractionated particulate matter samples. The analysis revealsthat discrete micron-sized iron-rich hotspots are ubiquitous in the upper200m at OSP, more than 900km from the closest coast. The specifics of thechemistry and depth profiles of the Fe hot spots trace them to thecontinental margins. We thus hypothesize that iron hotspots are a markerfor the delivery of iron from the continental margin. We confirm thedelivery of continental margin iron to the open ocean using an oceangeneral circulation model with an iron-like tracer source at thecontinental margin. We suggest that iron from the continental marginstimulated a wintertime phytoplankton bloom, partially relieving the HNLCcondition.

  18. The deep thermal characteristic of continental margin of the northern South China Sea

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Heat flow plays an important role in the study of thermal structure and thermal evolution of continental margin of the northern South China Sea. The analysis of heat flow value shows that margin heat flow in the northern South China Sea is relatively high setting, but the percentage of crustal heat flow is lower than 35% in terrestrial heat flow. The terrestrial heat flow exhibited a current of rise from the Northern Continental Margin to the Southern Central Basin. However, the proportion of crustal heat flow in terrestrial heat flow slowly dropped down in the same direction. It is suggested that the main factor causing high heat flow setting is the moving up of hot material from asthenosphere.

  19. 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

  20. Timing of methane efflux along the Norwegian and US Atlantic margin

    Science.gov (United States)

    Sahy, Diana; Condon, Daniel; Lepland, Aivo; Crémière, Antoine; Noble, Stephen; Ruppel, Carolyn

    2016-04-01

    Methane-related authigenic carbonates (MDAC) provide a robust archive of past methane emissions from cold seeps located along continental margins. MDAC are amenable to U-Th geochronology which can be used to assess the timing and drivers of fluid flow (Teichert et al., 2003; Bayon et al., 2013). The difficulty of sourcing MDAC typically precludes the assembly of datasets with sufficient geographic coverage and resolution to investigate the processes triggering and sustaining methane seeps on a regional scale. To address this, two collaborative projects led by the British, Norwegian and US geological surveys are currently underway, targeting methane seeps located along the Norwegian and US Atlantic margins (Skarke et al., 2014). MDAC samples collected for the two projects come from a range of depths (300-2000 m), and are linked to a variety of processes (e.g. collapse of grounded ice sheet, salt diapirism, dissociation of upper slope gas hydrates, emissions from deep reservoirs through fault networks). MDAC typically present as matrix-supported conglomerate /sandstone/ siltstone, and consist of detrital material of variable grainsize (depending on locality) encased in an aragonite and/or calcite cement. Interconnected voids within the MDAC, which likely represent fluid conduits, are often at least partially filled with clean (>90%), layered aragonite. The latter are ideal materials for U-Th geochronology, and can yield U-Th dates with precision approaching 0.5 % (2σ), with thicker (ca. 2 cm) layered cavity fills showing resolvable growth histories on the order of 1 kyr. While measurements on cavity-filling aragonite give a snapshot of seep activity, quantifying the entire methane emission history of a sample, and crucially, the timing of the onset of emissions, requires the analysis of MDAC groundmass. Such analyses are more challenging as initial detrital 230Th included in the samples must be accounted for. While precise dating of the onset of methane emissions at

  1. 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)

  2. Outer Continental Shelf Official Protraction Diagrams - Atlantic Region NAD 83

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains Official Protraction Diagram (OPD) outlines in ESRI shapefile format. Atlantic Region OPDs are approximately 2 degrees wide by one degree...

  3. Outer Continental Shelf Lease Blocks - Atlantic Region NAD83

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains OCS block outlines in ArcGIS shape file format for the BOEM Atlantic Region. OCS blocks are used to define small geographic areas within an...

  4. Tectonics of the West Iberia continental margin from seismic reflection data

    Science.gov (United States)

    Henning, Alison Teagan

    Continental rifting is a fundamental component of the plate tectonic cycle. The West Iberia passive margin is a classic example of a nonvolcanic rifted margin. The West Iberia margin contains an enigmatic north-south ridge of serpentinized peridotite located within the ocean-continent transition. Interpretation of multichannel seismic data and tectonic subsidence analyses suggests that the ridge is located within a broad zone of exhumed mantle that has been serpentinized. This implies that seafloor spreading does not immediately follow continental breakup. Where the peridotite ridge is well-developed, it parallels a deeply-penetrating, west-dipping normal fault. Hydrodynamic circulation drove seawater down this fault close to the beginning of seafloor spreading and caused a concentration of serpentinization at its base. This water-driven process of formation accounts for the variability of the ridge along strike. Prestack depth migration of a 340 km long seismic reflection profile across the margin served as the basis for stratigraphic interpretation. The proximal margin displays horsts and grabens, with 1--2 km thick synrift deposits from Early Cretaceous (Valanginian) rifting. The deep water margin displays rotated blocks with distinct internal seismic patterns. These blocks formed during the final Cretaceous rifting event that led to continental breakup, and contain earlier Valanginian synrift deposits as part of the rotated blocks, thus providing evidence of two separate rifting stages along this profile. A large mantle-penetrating fault located seaward of the last rotated block of continental crust provides evidence for a third and final Cretaceous rifting event that may have been coeval with early seafloor spreading. Two independent estimates of crustal thickness along this line indicate stretching factors of 50% on the proximal margin (corresponding to a continental crustal thickness of ˜16 km), increasing to 100% in the deep water. Plate tectonics is one

  5. How widely is the Andean type of continental margin represented in the Archean

    Science.gov (United States)

    Burke, Kevin

    1988-01-01

    Application of the principle of uniformitarianism to the Archean was discussed in a search for evidence of Archean-type continental margins in Archean rocks. The author cautioned that Archean rocks represent only 2 percent of the current exposure of the continents, half of which is in the North American Superior Province. Care must be taken in interpreting the global tectonic significance of relatively small exposures of Archean rocks, such as South India. Andean margins were characterized by their elongate shape, magmatic associations, and isotopic signatures. Although the compositional evidence alone will always be ambiguous, it was suggested that supporting structural evidence may aid in the identification of Archean Andean margins. Andean margin remains have been recognized in the Superior Province of Canada by these criteria, and the author suggested that the Closepet granite of South India may represent another example.

  6. Numerical modeling of the development of southeastern Red Sea continental margin

    Institute of Scientific and Technical Information of China (English)

    Sunil Kumar Dwivedi; Daigoro Hayashi

    2009-01-01

    The Red Sea continental margin (RSCM) corresponds to a wide hinge zone between Red Sea and Arabian plate. This margin has been studied through geological and geophysical observations primarily in regard to the evolution of Red Sea rift. This margin is characterized by occurrence of thin sediments, significant onshore uplift, tectonic subsidence of the offshore sedimentary basin, active faulting and seismicity. Studies indicate that sedimentary sequences of the margin are deformed by faults and folds resulting from at least two phases of extension and a phase of uplift. During the two phases of extension due to regional plate stress the sequence was cut by set of extensional faults. While during the phase of uplift the sequence was deformed by folding and faulting. The present paper aims to clear the structural development of RSCM during these tectonic episodes, taken as particular tectonic event, by two-dimensional finite element modeling on plane strain condition. Elastic rheology is assumed for the oceanic, continental and transitional crust along with syntectonic deposits. Stress field, shear stress and fault distribution suggests that mantle plume weakened the crust following rifting due to regional stress and developed the margin. These results are well consistent with those from present seismicity, active faulting and neotec-tonic studies.

  7. 77 FR 5830 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    Science.gov (United States)

    2012-02-06

    ... Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the Atlantic... identify areas that may be most suitable for wind energy leasing on the Outer Continental Shelf (OCS), and... efficient and responsible renewable energy leasing process. In consultation with other Federal agencies...

  8. 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

  9. Northwest margin of California continental borderland: marine geology and tectonic evolution.

    Science.gov (United States)

    Crouch, J.K.

    1981-01-01

    The NW margin of the California continental border land consists of 2 NW-trending pre-Neogene lithologic belts blanketed by Miocene and younger strata. These represent facies corresponding to the subduction complex and forearc-basin deposits of a late Mesozoic and Paleogene continental-margin arc-trench system. The outer belt, which forms the acoustic basement is characterized by: 1) moderately high compressional velocities; 2) discordant and discontinuous seismic reflectors; and 3) nonfossiliferous and diverse rock types. Landward, the inner Great Valley sequence belt is characterized by: 1) intermediate compressional velocities; 2) concordant and relatively continuous reflectors, and 3) a thick turbidite sequence. Well-developed wrench-fault structures in overlying Miocene strata record a transition from Paleogene subduction to Neogene transform faulting. The timing of volcanism and uplift, and of the younger wrenching event, closely matches the plate-tectonic model of Atwater and Molnar.-from Author

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

    Science.gov (United States)

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

    2007-01-01

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

  11. The impact of ocean deoxygenation on iron release from continental margin sediments

    OpenAIRE

    Scholz, Florian; McManus, James; Mix, Alan C; Hensen, Christian; Schneider, Ralph

    2014-01-01

    In the oceans’ high-nitrate–low-chlorophyll regions, such as the Peru/Humboldt Current system and the adjacent eastern equatorial Pacific1, primary productivity is limited by the micronutrient iron. Within the Peruvian upwelling area, bioavailable iron is released from the reducing continental margin sediments2. The magnitude of this seafloor source could change with fluctuations in the extension or intensity of the oxygen minimum zones3, 4. Here we show that measurements of molybdenum, urani...

  12. Geochemistry of the continental margin sediments of the central west coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, Ch.M.; Murty, P.S.N.

    is mainly associated with the clay mineral, montmorillonite. Minor Elements The distribution of Cu, Ni, Zn are very similar in the surface sediments and can be conveniently considered as a single group. Uniformly high concentrations of these elements occur... these variables can be conveniently expressed by means of factor analysis (Harman, 1960). Such an analysis was carried CONTINENTAL MARGIN SEDIMENTS, WEST COAST OF INDIA 29 out on the major and minor element data using the R. mode method developed by Fernandes...

  13. Geometries of hyperextended continental crust in northeastern continental brazilian margin: insights from potential field and seismic interpretation

    Science.gov (United States)

    Magalhães, José; Barbosa, José; Ribeiro, Vanessa; Oliveira, Jefferson; Filho, Osvaldo; Buarque, Bruno

    2016-04-01

    The study region encompasses a set of three basins located at Northeast Brazilian continental margin: Pernambuco (south sector), Paraíba and Natal platform (north sector). These basins were formed during the last stage of separation between South America and African plates during Cretaceous. The continental breakup in these regions occurred probably during the Middle-Upper Albian (~102 m.y). The adjacent basement rocks belong to Borborema Province (BP), which was formed due a complex superposition between Pre-Cambrian orogenic cycles. The structural framework of BP is dominated by large shear zones that divided this province in three main tectonic domains: South, Central and North. The Pernambuco Basin is located in the South Domain and the Paraíba and Natal platform basins are related to the Central Domain. The tectonic and magmatic evolution of the Pernambuco Basin was influenced by oblique rifting (~ 35° to rift axis) and a thermal anomaly probably caused by the Santa Helena hotspot. The north sector represents a continental shelf characterized by basement high with a narrow platform and an abrupt shelf break on transition to the abyssal plain. The continental platform break of this sector was parallel to the rift axis. In this way, we present a regional structural interpretation of these sectors of Brazilian rifted margin based on interpretation and 2D forward modeling of potential field and 2D seismic data. The magnetic maps (Reduction to magnetic pole and Analytic signal) revealed the influence of an alternating pattern of large narrow magnetic and non-magnetic lineaments, oriented NE-SW, E-W and NW-SE. In the Pernambuco Basin these lineaments (NE-SW and E-W) are related to shear zones in the hyperextended basement which is interpreted as a continuation of the granitic-gneissic and metasedimentary rocks of the South Domain of BP. The Paraíba and Natal platform basins show a slight change in the orientation of structures trending E-W (shear zones in

  14. Sn to Sg conversion and focusing along the Atlantic margin, Morocco - Implications for earthquake hazard evaluation

    Science.gov (United States)

    Seber, Dogan; Barazangi, Muawia; Tadili, Ben A.; Ramdani, Mohamed; Ibenbrahim, Aomar; Ben Sari, Driss; El Alami, Sidi O.

    1993-07-01

    Digital data from a telemetered, short-period seismic network in Morocco provide a new perspective for understanding the cause of severe shaking and macroseismic reports in Morocco produced by large offshore earthquakes located along the Azores-Gibraltar seismic zone. Even though the earthquake epicenters are 500-1000 km away from the Moroccan coast, historical records show that such events are capable of producing considerable damage in inland areas. We analyze 15 earthquakes that occurred in this region. The records show multiple S phases with varying frequencies and amplitudes. The S phase with the largest amplitude, usually misinterpreted as Sn, has a phase velocity of 4.2-4.4 km/s. We show that these S arrivals can best be explained as Sn to Sg converted phases. Calculated locations of the conversion points for these phases exhibit two distinct zones almost parallel to the Atlantic coastline: one is located along the passive continental margin and the other is located about 100 km inland from the coastline. We interpret these two zones to be regions where a sudden change in crustal thickness occurs. Such zones act to focus and magnify the amplitudes of seismic phases.

  15. Climate modulated erosion and sediment flux control offshore crustal structure at South China Sea continental margin

    Science.gov (United States)

    Clift, P. D.; Brune, S.; Quinteros, J.

    2015-12-01

    Rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling yet basins on some continental margins experience anomalous subsidence events that postdate active extension. Deep basins on the northern margin of the South China Sea, notably the Baiyun Sag, show basement subsidence accelerating after ~21 Ma, postdating extension by several million years. Similar subsidence events are seen after 5 Ma in the Song Hong Basin and after 11 Ma in the Qiongdongnan Basin. We combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following Early Miocene monsoon intensification is a viable trigger for ductile flow after the cessation of active extension. Loading works in conjunction with onshore uplift to drive flow of the lower crust away from the rift axis. As well as sediment supply rates distribution patterns and drainage capture can be significant in controlling crustal flow and thinning. This illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate-tectonic coupling.

  16. 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

  17. Constraining lithosphere deformation modes during continental breakup for the Iberia-Newfoundland conjugate rifted margins

    Science.gov (United States)

    Jeanniot, Ludovic; Kusznir, Nick; Mohn, Geoffroy; Manatschal, Gianreto; Cowie, Leanne

    2016-06-01

    A kinematic model of lithosphere and asthenosphere deformation has been used to investigate lithosphere stretching and thinning modes during continental rifting leading to breakup and seafloor spreading. The model has been applied to two conjugate profiles across the Iberia-Newfoundland rifted margins and quantitatively calibrated using observed present-day water loaded subsidence and crustal thickness, together with observed mantle exhumation, subsidence and melting generation histories. The kinematic model uses an evolving prescribed flow-field to deform the lithosphere and asthenosphere leading to lithospheric breakup from which continental crustal thinning, lithosphere thermal evolution, decompression melt initiation and subsidence are predicted. We explore the sensitivity of model predictions to extension rate history, deformation migration and buoyancy induced upwelling. The best fit calibrated models of lithosphere deformation evolution for the Iberia-Newfoundland conjugate margins require; (1) an initial broad region of lithosphere deformation with passive upwelling, (2) lateral migration of deformation, (3) an increase in extension rate with time, (4) focussing of the deformation and (5) buoyancy induced upwelling. The model prediction of exhumed mantle at the Iberia-Newfoundland margins, as observed, requires a critical threshold of melting to be exceeded before melt extraction. The preferred calibrated models predict faster extension rates and earlier continental crustal separation and mantle exhumation for the Iberia Abyssal Plain-Flemish Pass conjugate margin profile than for the Galicia Bank-Flemish Cap profile to the north. The predicted N-S differences in the deformation evolution give insights into the 3D evolution of Iberia-Newfoundland margin crustal separation.

  18. Benthic respiration and standing stock on two contrasting continental margins in the western Indian Ocean: the Yemen- Somali upwelling region and the margin off Kenya

    NARCIS (Netherlands)

    Duineveld, G.; De Wilde, P.; Berhuis, E.M.; Kok, A.; Tahey, T.; Kromkamp, J.C.

    1997-01-01

    During the Netherlands Indian Ocean Project (NIOP, 1992-1993) sediment community oxygen consumption (SCOC) was measured on two continental margins in the Indian Ocean with different productivity: the productive upwelling region off Yemen-Somalia and the supposedly less productive Kenyan margin, whic

  19. Causes and consequences of continental breakup in the South Atlantic: lessons learned from the SAMPLE program

    Science.gov (United States)

    Trumbull, Robert B.

    2014-05-01

    Since 2009 the SAMPLE program (www.spp-sample.de) provides a platform for research into the causes and effects of continental breakup and the evolution of passive margins. SAMPLE encompasses 28 projects from 13 German institutions and many international partnerships. The 6-year program will run through 2015. At the core of the program are observational studies that are interlinked by modelling projects examining the interplay of deep mantle dynamics, lithospheric stress fields, pre-rift fabric and melt-weaking on localizing rifting. Geophysics teams collect and integrate existing data from wide-angle seismic profiles, reprocessed multichannel seismics, as well as gravity, magnetics and heat-flow studies to construct self-consistent lithospheric-scale 3-D models along the conjugate margins. Key interests are variations in margin architecture, distribution of magmatic features and the evolution of sedimentary basins (subsidence and thermal histories). An exciting new contribution of SAMPLE geophysics is a linked set of seismic, seismologic and magnetotelluric experiments along the Walvis Ridge, including onshore NW Namibia and the Tristan da Cunha hotspot. In the deep mantle, we examine evidence from global seismic tomography for dramatic low seismic-velocity regions near the core-mantle boundary beneath southern Africa and their implications for dynamics in the deep Earth and the thermo-chemical nature of plumes. Petrologic studies focus on near-primary mantle melts represented by Mg-rich mafic dikes. Projects address the origin of magmas and crust-mantle interaction, and the environmental impact of mega-scale volcanism during breakup. Thermobarometry results from the African margin reveal a N-to-S decrease in mantle potential temperatures from 1520°C (N) to 1380° (S), which supports a thermal plume origin for excessive melt production in the north. Thermochronology data from both conjugate margins reveal complex and puzzling patterns in the denudation history

  20. 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.

    Content-Type text/plain; charset=UTF-8 202 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...: a) the tectonic, lithologic and petrographic demarcation of areas for geological mapping, b) the delimiting of promising zones and areas for more detailed geological and geophysical exploration, c) the discovery of local structures favoring...

  1. Geomorphology and Neogene tectonic evolution of the Palomares continental margin (Western Mediterranean)

    Science.gov (United States)

    Gómez de la Peña, Laura; Gràcia, Eulàlia; Muñoz, Araceli; Acosta, Juan; Gómez-Ballesteros, María; R. Ranero, César; Uchupi, Elazar

    2016-10-01

    The Palomares continental margin is located in the southeastern part of Spain. The margin main structure was formed during Miocene times, and it is currently part of the wide deformation zone characterizing the region between the Iberian and African plates, where no well-defined plate boundary occurs. The convergence between these two plates is here accommodated by several structures, including the left lateral strike-slip Palomares Fault. The region is characterized by sparse, low to moderate magnitude (Mw tectonic history of the margin we analyze new high-resolution multibeam bathymetry data and re-processed three multichannel seismic reflection profiles crossing the main structures. The analysis of seafloor morphology and associated subsurface structure provides new insights of the active tectonic features of the area. In contrast to other segments of the southeastern Iberian margin, the Palomares margin contains numerous large and comparatively closely spaced canyons with heads that reach near the coast. The margin relief is also characterized by the presence of three prominent igneous submarine ridges that include the Aguilas, Abubacer and Maimonides highs. Erosive processes evidenced by a number of scars, slope failures, gullies and canyon incisions shape the present-day relief of the Palomares margin. Seismic images reveal the deep structure distinguishing between Miocene structures related to the formation of the margin and currently active features, some of which may reactivate inherited structures. The structure of the margin started with an extensional phase accompanied by volcanic accretion during the Serravallian, followed by a compressional pulse that started during the Latemost Tortonian. Nowadays, tectonic activity offshore is subdued and limited to few, minor faults, in comparison with the activity recorded onshore. The deep Algero-Balearic Basin is affected by surficial processes, associated to halokinesis of Messinian evaporites.

  2. 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.

    Investigations on green grains from sediments of the western continental margin of India, between Ratnagiri and Cape Comorin, (water depth 37-330 m) indicate the presence of verdine and glaucony facies. Verdine facies occurs over an area of about...

  3. Three-dimensional density model of the Nazca plate and the Andean continental margin

    Science.gov (United States)

    Tassara, AndréS.; GöTze, Hans-Jürgen; Schmidt, Sabine; Hackney, Ron

    2006-09-01

    We forward modeled the Bouguer anomaly in a region encompassing the Pacific Ocean (85°W) and the Andean margin (60°W) between northern Peru (5°S) and Patagonia (45°S). The three-dimensional density model that reproduces the gravity field is a continental-scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic Nazca plate, subducted slab and continental margin with a minimum number of bodies. We predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure-temperature conditions appropriate for the Andean setting. A database of independent geophysical information constrains the geometry of the top of the subducted slab, locally the Moho of the oceanic and continental crusts and, indirectly, the lithosphere-asthenosphere boundary underneath the continental plate. Other boundaries, notably the intracrustal density discontinuity separating upper from lower crust below the continent, were not constrained and their geometry is the result of fitting the observed and calculated Bouguer anomaly during forward modeling. This contribution presents the model to the Andean geoscientific community and contains some tools, like a sensitivity analysis, that helps potential users of the model to interpret its results. We describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena (e.g., modification of oceanic plate structure by hot spots, shape of the subducted slab, thermal structure of the continental lithosphere, compensation mechanism and formation of orogenic relieve, causes of Andean segmentation).

  4. Atlantic Offshore Seabird Dataset Catalog, Atlantic Coast and Outer Continental Shelf, from 1938-01-01 to 2013-12-31 (NODC Accession 0115356)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Several bureaus within the Department of Interior compiled available information from seabird observation datasets from the Atlantic Outer Continental Shelf into a...

  5. The petroleum potential of the passive continental margin of South-Western Africa : a basin modelling study

    OpenAIRE

    Schmidt, Sabine

    2004-01-01

    The Petroleum Potential of the Continental Margin of South-Western Africa - A Basin Modelling Study The hydrocarbon potential of the continental margin of south-western Africa was assessed with means of a 2D basin modelling study of the hydrocarbon generation, migration and accumulation of the Kudu gas field. The basin model is based on well and seismic data from offshore Namibia and constrained by geochemical data on source rocks, natural gas samples and hydrocarbons desorbed from near-surfa...

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

    Science.gov (United States)

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

    2007-01-01

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

  7. Assessment of tsunami hazard to the U.S. Atlantic margin

    Science.gov (United States)

    Ten Brink, Uri; Chaytor, Jason; Geist, Eric L.; Brothers, Daniel S.; Andrews, Brian D.

    2014-01-01

    Tsunami hazard is a very low-probability, but potentially high-risk natural hazard, posing unique challenges to scientists and policy makers trying to mitigate its impacts. These challenges are illustrated in this assessment of tsunami hazard to the U.S. Atlantic margin. Seismic activity along the U.S. Atlantic margin in general is low, and confirmed paleo-tsunami deposits have not yet been found, suggesting a very low rate of hazard. However, the devastating 1929 Grand Banks tsunami along the Atlantic margin of Canada shows that these events continue to occur. Densely populated areas, extensive industrial and port facilities, and the presence of ten nuclear power plants along the coast, make this region highly vulnerable to flooding by tsunamis and therefore even low-probability events need to be evaluated.

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

    Science.gov (United States)

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

    2001-01-01

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

  9. Continental Margins and the Law of the Sea - an `Arranged Marriage' with Huge Research Potential

    Science.gov (United States)

    Parson, L.

    2005-12-01

    The United Nations Convention on the Law of the Sea (UNCLOS) requires coastal states intending to secure sovereignty over continental shelf territory extending beyond 200 nautical miles to submit geological/geophysical data, along with their analysis and synthesis of the relevant continental margin in support of their claim. These submissions are scrutinised and assessed by a UN Commission of experts who decide if the claim is justified, and thereby ultimately allowing the exploitation of non-living resources into this extended maritime space. The amount of data required to support the case will vary from margin to margin, depending on the local geological evolution, but typically will involve the running of new, dedicated marine surveys, mostly bathymetric and seismic. Key geological/geophysical issues revolve around proof of `naturalness' of the prolongation of land mass (cue - wide-angle seismics, deep drilling and sampling programmes) and shelf and slope morphology and sediment section thickness (cue - swath bathymetry and multichannel seismics programmes). These surveys, probably primarily funded by government agencies anxious not to lose out on the `land grab', will generate datasets which will inevitably boost not only the research effort leading to increased understanding of margin evolution in academic terms, but also contribute to wider applied aspects of the work such as those leading to refinement of deepwater hydrocarbon resource potential. It is conservatively estimated that in the region of fifty coastal states world-wide have a significant potential for claiming continental shelf beyond 200 nautical miles, and that the total area available as extended shelf could easily exceed 7 million square kilometres. However, while for the vast majority of these states a UNCLOS deadline of 2009 exists for submitting a claim - to date only four have done so (Russia, Brazil, Australia and Ireland). It is therefore predictable, if not inevitable, that within the

  10. Evidence for extensive methane venting on the southeastern U.S. Atlantic margin

    Science.gov (United States)

    Brothers, L.L.; Van Dover, C.L.; German, C.R.; Kaiser, C.L.; Yoerger, D.R.; Ruppel, C.D.; Lobecker, E.; Skarke, A.D.; Wagner, J.K.S.

    2013-01-01

    We present the first evidence for widespread seabed methane venting along the southeastern United States Atlantic margin beyond the well-known Blake Ridge diapir seep. Recent ship- and autonomous underwater vehicle (AUV)–collected data resolve multiple water-column anomalies (>1000 m height) and extensive new chemosynthetic seep communities at the Blake Ridge and Cape Fear diapirs. These results indicate that multiple, highly localized fluid conduits punctuate the areally extensive Blake Ridge gas hydrate province, and enable the delivery of significant amounts of methane to the water column. Thus, there appears to be an abundance of seabed fluid flux not previously ascribed to the Atlantic margin of the United States.

  11. Oceanographic Time Series Data: Northeast Atlantic Outer Continental Shelf, Gulf of Maine and Georges Bank Marine Sanctuary

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Time-series oceanographic data for the Northeast Atlantic outer continental shelf, Gulf of Maine and Georges Bank collected by the U.S. Geological Survey (USGS) or...

  12. Vestiges of a continental margin ophiolite type in the Novo Oriente region, Borborema Province, NE Brazil

    Science.gov (United States)

    Pitombeira, João Paulo Araújo; Amaral, Wagner da Silva; Uchôa Filho, Evilarde Carvalho; Fuck, Reinhardt Adolfo; Dantas, Elton Luiz; Parente, Clóvis Vaz; da Costa, Felipe Grandjean; Veríssimo, César Ulisses Vieira

    2017-01-01

    The Novo Oriente Group is a restricted well-preserved metasedimentary sequence, composed of two tectonic-stratigraphic sequences in the southwestern portion of the Ceará Central Domain, NE Brazil. The Bonsucesso Formation comprises mainly quartzite and metamafic rocks and the Caraúbas Formation is dominantly metapelitic, with chemical sedimentary contribution, metamafic and metaultramafic rocks. New integrated field, geochemical data and Sm-Nd isotopes of the metaultramafic and metamafic rocks of the two formations have been investigated in order to determine their tectonic setting. The metaultramafic rocks are dominantly composed of deformed and undeformed serpentinites, chloritites, actinolitites, talc-chlorite schists, serpentine-talc schists, talc-rich siliceous rocks and subordinated listwänites. Geochemical data indicate that the serpentinites correspond to rocks resulting from the alteration of dunites depleted in HREE, similar to the pattern presented by subduction-zone serpentinites generated from exhumed sub-continental peridotites and hydrated during ocean-continent transition (OCT) rifting. The metamafic rocks, represented by metagabbros, hornblende metagabbros and metabasalts, consist of basic rocks of basaltic and tholeiitic affinity with signatures between E- and N-MORB and variable contamination by crustal components similar to the rocks formed from the interaction between mantle plumes and heavily thinned continental crust. Isotopic analysis indicates crustal assimilation with negative ɛNd and Paleoproterozoic TDM ages. The data suggest that metaultramafic and metamafic rocks correspond, respectively, to continental sub-lithospheric mantle exhumed in an area of ocean-continent transition (OCT), and mafic magmatism associated with the development of a magma-poor passive margin generated by the break-up of the Rodinia Supercontinent, which was later dismembered by the Brasiliano/Pan-African Orogeny collisional phase and preserved as a Continental

  13. Molybdenum isotope signatures from the Yangtze block continental margin and its indication to organic burial rate

    Science.gov (United States)

    Zhou, L.; Zhou, H. B.; Huang, J. H.

    2007-12-01

    The paper presents the molybdenum isotope data, along with the trace element content, to investigate the geochemical behavior of authigenic Mo during long-term burial in sediments in continental margin settings of the Yangtze block, as well as their indication to the burial of original organic carbon. The burial rate of original organic carbon were estimated on the basis of the amount of sedimentary sulfur (TS content), whilst the carbon loss by aerobic degradation was estimated according to calculated Mn contents. On these points, the original organic carbon flux was calculated, exhibiting a large range of variation (2.54-15.82 mmol/m2/day). The strong correlation between sedimentary Mo isotope values and organic carbon burial rates previously proposed on the basis of the investigations on modern ocean sediments was also used here to estimate the organic carbon burial rate. The data gained through this model showed that organic carbon burial rates have large variations, ranging from 0.43- 2.87mmol/m2/day. Although the two sets of data gained through different geochemical records in the Yangtze block show a deviation of one order of magnitude, they do display a strong correlation. It is thus tempting to speculate that the Mo isotope signature of sediments may serve as a tracer for the accumulation rate of original organic carbon in the continental margin sediments. Keywords: Molybdenum isotopes; organic carbon burial rate; ancient continental margin setting ACKNOWLEDGMENTS We thank Professor Xie Shucheng for his constructive review comments. This research is co-supported by the Program for Changjiang Scholars and Innovative Research Team in University (grants IRT0441), the SinoPec project (grant no. G0800-06-ZS-319) and the National Nature Science Foundation of China (grants 40673020).

  14. Influence of marginal highs on the accumulation of organic carbon along the continental slope off western India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, B; Veerayya, M.

    0.70 to 5.86%. Highest values of organic carbon are recorded on the marginal highs (5.12-5.86%), followed by shelf margin basin (3.53-4.22%) and the continental slope (1.80-3.84%). The organic carbon content is relatively low in the Arabian Basin (0...

  15. Regional gravity and magnetic studies over the continental margin of the Central West Coast of India

    Digital Repository Service at National Institute of Oceanography (India)

    SubbaRaju, L.V.; KameshRaju, K.A.; Subrahmanyam, V.; Rao, D.G.

    Institute of Oceanography, Dona Paula, Goa 403 004, India Abstract Gravity studies over the continental margin of the central west coast of India show a sediment thickness of 2-3 km on the shelf associated with deeper hoest and graben structures, of 6 km... sequence ranges from Palaeocene to Recent. Stratigraphy as obtained from the explor atory wells BH-I, DCS-IA, HI2-1, and R6-110cated in the Bombay offshore basin is shown in Figure 2. Figure 3 depicts the seismogeological section of the Bombay offshore...

  16. 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.

  17. Late Cenozoic evolution of the East China continental margin: Insights from seismic, gravity, and magnetic analyses

    Science.gov (United States)

    Shang, Lu-Ning; Zhang, Xun-Hua; Jia, Yong-Gang; Han, Bo; Yang, Chuan-Sheng; Geng, Wei; Pang, Yu-Mao

    2017-02-01

    Seismic reflection profiles reveal the structural characteristics beneath the East China Sea shelf margin and the Okinawa Trough, and provide new constraints on the Late Cenozoic evolution of the East China continental margin. The Frontal Shelf Basin between the Taiwan-Sinzi Uplift and the trough axis occupies the western half of the Northern-Middle Okinawa Trough. In this basin, the Middle-Late Miocene sediments are confined to grabens or half-grabens dominated by listric faults, whereas the overlying Pliocene-Quaternary sequence is characterized by a uniform thickness and dense planar-type faults, suggesting that rifting of the Northern-Middle Okinawa Trough initiated during the Middle Miocene but slowed down during the earliest Pliocene. Since that time, the opening of the Okinawa Trough has been dominated by diffuse rifting. The Southern Okinawa Trough is predominately filled by Quaternary sediments, indicating that its back-arc rifting began during the earliest Pleistocene. Contractional structures identified in the pre-Quaternary sequence beneath the continental slope, along with an erosional Pleistocene-pre-Pleistocene unconformity in the Southern Okinawa Trough, demonstrate the existence of pre-rifting compression and uplifting in this region. We use this evidence and previously published results, to propose an evolutionary model of the East China continental margin during the Late Cenozoic. The Northern-Middle Okinawa Trough began rifting during the Middle Miocene on a paleo-uplift. The Luzon Arc initially impinged upon the Eurasian continental margin during the Late Miocene near the southeastern end of the Miyako Fault Belt and activated the proto-Taiwan Orogeny in today's Southern Okinawa Trough and adjacent regions. During the Late Miocene-Pliocene, the orogeny quickly propagated southwestward along with the west-northwest-moving Philippine Sea Plate. Subsequently, the rifting of the Southern Okinawa Trough was initiated during the earliest Pleistocene

  18. Post-rift influence of small-scale convection on the landscape evolution at divergent continental margins

    Science.gov (United States)

    Sacek, Victor

    2017-02-01

    After decades of geological and geophysical data acquisition along with quantitative modeling of the long-term evolution of the landscape at divergent continental margins, the search for an explanation for the formation and evolution of steep escarpments bordering the coast is still a challenging task. One difficult aspect to explain about the evolution of these escarpments is the expressive variability of denudation rate through the post-rift phase observed in many margins. Here I propose that the interaction of small-scale convection in the asthenosphere with the base of the continental lithosphere can create intermittent vertical displacements of the surface with magnitude of a few hundreds of meters at the continental margin. These topographic perturbations are sufficient to produce an expressive variability in the rate of erosion of the landscape through the post-rift phase similar to the exhumation history observed along old divergent margins. I show that the vertical motion of the surface is amplified when a mobile belt is present at the continental margin, with lithospheric mantle less viscous than the cratonic lithosphere and, consequently, more prone to be partially eroded by the convective asthenosphere. I conclude that the influence of small-scale convection is not the primary explanation for the formation of high topographic features at divergent continental margins, but can be an important component contributing to sustain a preexistent escarpment. The present results are based on numerical simulations that combine thermochemical convection in the mantle, flexure of the lithosphere and surface processes of erosion and sedimentation.

  19. 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

    Full Text Available The continental margin of West Greenland is similar in many respects to other elevated, passive continental margins (EPCMs around the world. These margins are characterised by extensive regions of low relief at elevations of 1–2 kilometres above sea level sloping gently inland, with a much steeper, oceanward decline, often termed a 'Great Escarpment', terminating at a coastal plain. Recent studies, based on integration of geological, geomorphological and thermochronological evidence, have shown that the high topography of West Greenland was formed by differential uplift and dissection of an Oligo-Miocene peneplain since the late Miocene, many millions of years after continental break-up between Greenland and North America. In contrast, many studies of other EPCMs have proposed a different style of development in which the high plateaux and the steep, oceanward decline are regarded as a direct result of rifting and continental separation. Some studies assume that the elevated regions have remained high since break-up, with the high topography continuously renewed by isostasy. Others identify the elevated plains as remnants of pre-rift landscapes. Key to understanding the development of the West Greenland margin is a new approach to the study of landforms, stratigraphic landscape analysis, in which the low-relief, high-elevation plateaux at EPCMs are interpreted as uplifted peneplains: low-relief surfaces of large extent, cutting across bedrock of different age and resistance, and originally graded to sea level. Identification of different generations of peneplain (re-exposed and epigene from regional mapping, combined with geological constraints and thermochronology, allows definition of the evolution leading to the formation of the modern-day topography. This approach is founded particularly on results from the South Swedish Dome, which document former sea levels as base levels for the formation of peneplains. These results support the view

  20. Inputs of iron, manganese and aluminium to surface waters of the Northeast Atlantic Ocean and the European continental shelf

    NARCIS (Netherlands)

    Jong, Jeroen T.M. de; Boyé, Marie; Gelado-Caballero, Maria D.; Timmermans, Klaas R.; Veldhuis, Marcel J.W.; Nolting, Rob F.; Berg, Constant M.G. van den; Baar, Hein J.W. de

    2007-01-01

    Dissolved Fe, Mn and Al concentrations (dFe, dMn and dAl hereafter) in surface waters and the water column of the Northeast Atlantic and the European continental shelf are reported. Following an episode of enhanced Saharan dust inputs over the Northeast Atlantic Ocean prior and during the cruise in

  1. 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.

  2. 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.

  3. Molybdenum isotope composition from Yangtze block continental margin and its indication to organic burial rate

    Institute of Scientific and Technical Information of China (English)

    ZHOU Lian; HUANG Junhua; Corey Archer; Chris Hawkesworth

    2007-01-01

    The paper presents the molybdenum isotope data,along with the trace element content,to investigate the geochemical behavior of authigenic Mo during long-term burial in sediments in continental margin settings of the Yangtze block,as well as their indication to the burial of original organic carbon.The burial rate of original organic carbon was estimated on the basis of the amount of sedimentary sulfur (TS content),whilst the carbon loss by aerobic degradation was estimated according to calculated Mn contents.On these points,the original organic carbon flux was calculated,exhibiting a large range of variation (0.17-0.67mmol/m2/day).The strong correlation between sedimentary Mo isotope values and organic carbon burial rates previously proposed on the basis of the investigations on modern ocean sediments,was also used here to estimate the organic carbon burial rate.The data gained through this model showed that organic carbon burial rates have large variations,ranging from 0.43-2.87 mmol/m2/day.Although the two sets of data gained through different geochemical records in the Yangtze block show a deviation of one order of magnitude,they do display a strong correlation.It is thus tempting to speculate that the Mo isotope signature of sediments may serve as a tracer for the accumulation rate of original organic carbon in the continental margin sediments.

  4. Biodiversity response to natural gradients of multiple stressors on continental margins.

    Science.gov (United States)

    Sperling, Erik A; Frieder, Christina A; Levin, Lisa A

    2016-04-27

    Sharp increases in atmospheric CO2 are resulting in ocean warming, acidification and deoxygenation that threaten marine organisms on continental margins and their ecological functions and resulting ecosystem services. The relative influence of these stressors on biodiversity remains unclear, as well as the threshold levels for change and when secondary stressors become important. One strategy to interpret adaptation potential and predict future faunal change is to examine ecological shifts along natural gradients in the modern ocean. Here, we assess the explanatory power of temperature, oxygen and the carbonate system for macrofaunal diversity and evenness along continental upwelling margins using variance partitioning techniques. Oxygen levels have the strongest explanatory capacity for variation in species diversity. Sharp drops in diversity are seen as O2 levels decline through the 0.5-0.15 ml l(-1) (approx. 22-6 µM; approx. 21-5 matm) range, and as temperature increases through the 7-10°C range. pCO2 is the best explanatory variable in the Arabian Sea, but explains little of the variance in diversity in the eastern Pacific Ocean. By contrast, very little variation in evenness is explained by these three global change variables. The identification of sharp thresholds in ecological response are used here to predict areas of the seafloor where diversity is most at risk to future marine global change, noting that the existence of clear regional differences cautions against applying global thresholds.

  5. Preliminary digital geologic map of the Penokean (early Proterozoic) continental margin in northern Michigan and Wisconsin

    Science.gov (United States)

    Cannon, W.F.; Ottke, Doug

    1999-01-01

    The data on this CD consist of geographic information system (GIS) coverages and tabular data on the geology of Early Proterozoic and Archean rocks in part of the Early Proterozoic Penokean orogeny. The map emphasizes metasedimentary and metavolcanic rocks that were deposited along the southern margin of the Superior craton and were later deformed during continental collision at about 1850 Ma. The area includes the famous iron ranges of the south shore region of the Lake Superior district. Base maps, both as digital raster graphics (DRG) and digital line graphs (DLG) are also provided for the convenience of users. The map has been compiled from many individual studies, mostly by USGS researchers, completed during the past 50 years, including many detailed (1:24,000 scale) geologic maps. Data was compiled at 1:100,000 scale and preserves most of the details of source materials. This product is a preliminary release of the geologic map data bases during ongoing studies of the geology and metallogeny of the Penokean continental margin. Files are provided in three formats: Federal Spatial Data Transfer format (SDTS), Arc export format (.e00) files, and Arc coverages. All files can be accessed directly from the CD-ROM using either ARC/INFO 7.1.2 or later or Arc View 3.0 or later software. ESRI's Arc Explorer, a free GIS data viewer available at the web site: http://www.esri.com/software/arcexplorer/index.html also provides display and querying capability for these files.

  6. Macrofaunal Biodiversity Response to Natural Gradients of Multiple Stressors on Continental Margins

    Science.gov (United States)

    Sperling, E. A.; Frieder, C.; Levin, L. A.

    2015-12-01

    Sharp increases in atmospheric CO2 are resulting in ocean warming, acidification and deoxygenation. Rates of change are unprecedented, raising questions about whether (and how) communities will adapt and if responses will reflect synergistic interactions among multiple stressors. Changes to benthic biodiversity on continental margins have important implications for carbon cycle processes and other ecosystem services. One strategy to interpret adaptation potential and predict future faunal change is to examine ecological shifts along natural gradients in the modern ocean. Here, we assess the explanatory power of major climate stressors for macrofaunal diversity and evenness along continental margins using variance partitioning techniques. Sharp drops in diversity are seen as O2 levels decline through the 0.5 - 0.15 ml/l (~22 - 6 μM; ~21 - 5 matm) range, and as temperature increases through the 7-10°C range. pCO2 shows a strong effect in the Arabian Sea but very little effect in the Eastern Pacific Ocean. In contrast, very little variation in evenness is explained by these three global change variables. The identification of sharp thresholds in ecological response are used here to predict seafloor areas most at risk to future marine global change, although the existence of clear regional differences cautions against applying global thresholds.

  7. Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust

    Science.gov (United States)

    Von Huene, R.; Scholl, D. W.

    1991-01-01

    At ocean margins where two plates converge, the oceanic plate sinks or is subducted beneath an upper one topped by a layer of terrestrial crust. This crust is constructed of continental or island arc material. The subduction process either builds juvenile masses of terrestrial crust through arc volcanism or new areas of crust through the piling up of accretionary masses (prisms) of sedimentary deposits and fragments of thicker crustal bodies scraped off the subducting lower plate. At convergent margins, terrestrial material can also bypass the accretionary prism as a result of sediment subduction, and terrestrial matter can be removed from the upper plate by processes of subduction erosion. Sediment subduction occurs where sediment remains attached to the subducting oceanic plate and underthrusts the seaward position of the upper plate's resistive buttress (backstop) of consolidated sediment and rock. Sediment subduction occurs at two types of convergent margins: type 1 margins where accretionary prisms form and type 2 margins where little net accretion takes place. At type 2 margins (???19,000 km in global length), effectively all incoming sediment is subducted beneath the massif of basement or framework rocks forming the landward trench slope. At accreting or type 1 margins, sediment subduction begins at the seaward position of an active buttress of consolidated accretionary material that accumulated in front of a starting or core buttress of framework rocks. Where small-to-mediumsized prisms have formed (???16,300 km), approximately 20% of the incoming sediment is skimmed off a detachment surface or decollement and frontally accreted to the active buttress. The remaining 80% subducts beneath the buttress and may either underplate older parts of the frontal body or bypass the prism entirely and underthrust the leading edge of the margin's rock framework. At margins bordered by large prisms (???8,200 km), roughly 70% of the incoming trench floor section is

  8. New Low-Temperature Thermochronology Reveals Contrasting Modes of Continental Extension Across the Sonoran Rifted Margin

    Science.gov (United States)

    Kohn, B. P.; Fletcher, J. M.; Gleadow, A. J.; Calmus, T.; Nourse, J. A.

    2003-12-01

    The Sonoran rifted margin extends 250 km from the western flanks of the Sierra Madre Occidental to the Gulf of California and contains a classic Basin and Range morphology that indicates "broad-rift" mode of continental extension. However, new low-temperature thermochronology reveals that the Sonoran rifted margin is also internally composed of at least two temporally and spatially distinct belts that display other distinct styles of extension. Mountain ranges that lie within a narrow belt (20 km wide) along the coast of the Gulf of California between Puerto Libertad and Bahia Kino yield highly discordant apatite fission track (AFT) ages that range from 5 to 54 Ma and likely reflect the strong tilting of these tectonic blocks. The widespread occurrence of AFT ages between 5 and 7 Ma, which are typically found in the deepest crustal levels of the tilt blocks, and the presence of Quaternary scarps indicate that extension in the coastal region largely occurred from late Miocene to recent times. We infer that this belt is dominated by a "narrow-rift" mode of extension where deformation has been focused to produce the Gulf depression. Well inland from the coast (175 km east) is a belt of metamorphic core complexes that extends more than 200 km from Magdalena to Mazatan and typically yields older and more concordant AFT ages from 14 to 23 Ma. However, the presence of ages as young as 8 to 11 Ma indicate that the "metamorphic-core-complex" mode of extension in this belt likely overlapped in time with the "narrow-rift" mode of extension in the Gulf of California. We conclude that the juxtaposition of major deformation belts each with different modes of continental extension reflects the diverse processes that have affected the Sonoran margin through time.

  9. Plate-tectonic evolution of the deep ocean basins adjoining the western continental margin of India - A proposed model for the early opening scenario

    Digital Repository Service at National Institute of Oceanography (India)

    Bhattacharya, G.C.; Yatheesh, V.

    The available plate-tectonic evolution models suggest that the deep ocean basins adjoining the western continental margin of India have evolved largely due to break-up and dispersal of India, Seychelles and Madagascar continental blocks since Late...

  10. Thermal evolution of a sheared continental margin: Insights from the Ballenas transform in Baja California, Mexico

    Science.gov (United States)

    Seiler, Christian; Gleadow, Andrew J. W.; Fletcher, John M.; Kohn, Barry P.

    2009-07-01

    The Ballenas transform margin in central Baja California offers an unparalleled opportunity to study the thermal behaviour of a sheared continental margin during various stages of its evolution. Apatite fission track and (U-Th)/He results from two transects perpendicular to the coast reveal a pronounced latest Pliocene to Pleistocene (~ 1.8 Ma) heating event related to the Neogene opening of the Gulf of California. Proximity to a regional pre-rift unconformity indicates that samples remained at near-surface levels since Paleogene unroofing, despite having experienced reheating to maximum paleotemperatures within or above the fission track partial annealing zone. In general, maximum paleotemperatures during overprinting decrease from > 100-120 °C near the coast to below 60 °C ca. 5-8 km further inland, suggesting lateral heat flow from a source within the Gulf of California. Heat sources related to the structural development of the Ballenas transform fault, located approximately 1.5-4.5 km offshore from the two sample transects, most likely controlled the observed reheating. Overprinting patterns do not support conductive reheating due to reburial, magmatism or frictional shear. Instead, a pronounced thermal spike in between much less overprinted neighbouring samples strongly favours convective heating by hydrothermal fluids as the dominant overprinting process. Hydrothermal activity may be caused by either deep fluid circulation along newly formed shear zones of the transform fault or, more likely, magmatic leaking along the transform fault. Latest Pliocene to Pleistocene (~ 1.8 Ma) activity on the Ballenas transform fault is closely linked to extension in the Lower and Upper Delfín basins and provides a minimum age for the structural reorganisation and the relocation of extension in the northern Gulf of California. This study shows that hydrothermal activity can cause significant thermal events in a transform margin before the passage of the spreading centre

  11. 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.

  12. Pyrophaeophorbide- a as a tracer of suspended particulate organic matter from the NE Pacific continental margin

    Science.gov (United States)

    Bianchi, Thomas S.; Bauer, James E.; Druffel, Ellen R. M.; Lambert, Corey D.

    Pyrophaeophorbide- a, a degradation product of chlorophyll- a, is predominantly formed by grazing processes in sediments as well as in the water column. Water column profiles of pyrophaeophorbide- a/suspended particulate organic carbon (SPOC) concentrations, at an abyssal site in the northeast (NE) Pacific (Sta M, 34°50'N, 123°00'W; 4100 m water depth), show low concentrations (0.01-0.1 ng/μg SPOC) at surface and mesopelagic depths, and increasing concentrations with closer proximity to the sea floor (0.05-0.6 ng/μg SPOC). However, in June 1992, the deep maximum of pyrophaeophorbide- a/SPOC in the water column of Sta M extended higher into the water column, as much as 1600 m above the bottom (mab) (2500 m water depth); in other seasons they only extended up to 650 mab (3450 m water depth). Previous studies have demonstrated lateral transport of particulate matter from the continental shelf to the deep ocean off the coast of northern California. Recent work suggests that the benthic boundary layer (BBL) extends to 50 mab, based on sediment trap and transmissometry measurements (Smith, K.L., Kaukmann, R.S., Baldwin, R.J., 1994. Coupling of near-bottom pelagic and benthic processes at abyssal depths. Limnology and Oceanography 39, 1101-1118.), and that lateral transport is significant only during summer, which is consistent with our observations. A partial vertical profile of pyrophaeophorbide- a/SPOC from the north central (NC) Pacific provides some evidence that the deep maximum may be absent due to the distance of this site from the continental margin. Thus, the observed deep maximum of pyrophaeophorbide- a/SPOC at Sta M is likely due mainly to lateral transport from the continental slope rather than to local vertical resuspension in the BBL exclusively. Pyrophaeophorbide- a concentrations in SPOC at Sta M were negatively correlated with Δ 14C values of SPOC (SPOC samples from Druffel, E.R.M., Bauer, J.E., Williams, P.M., Griffin, S.A. and Wolgast, D., 1996

  13. Lithospheric thermal-rheological structures of the continental margin in the northern South China Sea

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    Thermal structures of three deep seismic profiles in the continental margin in the northern South China Sea are calculated, their "thermal" lithospheric thicknesses are evaluated based on the basalt dry solidus, and their rheological structures are evaluated with linear frictional failure criterion and power-law creep equation. "Thermal" lithosphere is about 90 km in thickness in shelf area, and thins toward the slope, lowers to 60-65 km in the lower slope, ocean crust and Xisha Trough. In the mid-west of the studied area, the lithospheric rheological structure in shelf area and Xisha Islands is of four layers: brittle, ductile, brittle and ductile. Because of uprising of heat mantle and thinning of crust and lithosphere in Xisha Trough, the bottom of the upper brittle layer is only buried at 16 km. In the eastern area, the bottom of the upper brittle layer in the north is buried at 20 km or so, while in lower slope and ocean crust, the rheological structure is of two layers of brittle and ductile, and crust and uppermost mantle form one whole brittle layer whose bottom is buried at 30-32 km. Analyses show that the characteristics of rheological structure accord with the seismic result observed. The character of rheological stratification implies that before the extension of the continent margin, there likely was a ductile layer in mid-lower crust. The influence of the existence of ductile layer to the evolution of the continent margin and the different extensions of ductile layer and brittle layer should not be overlooked. Its thickness, depth and extent in influencing continent margin's extension and evolution should be well evaluated in building a dynamic model for the area.

  14. 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.

  15. 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.

  16. Neotectonic regime on the passive continental margin of the northern South China Sea

    Science.gov (United States)

    Lüdmann, Thomas; Wong, How Kin

    1999-09-01

    Between 1989 and 1994, more than 6600 km of reflection seismic profiles were obtained in the South China Sea off Hong Kong with the German research vessel Sonne during cruises SO-50B, SO-72A and SO-95. A seismo-stratigraphic interpretation of this data set leads to a new age assignment of the unconformity T 0 which we place within the Pleistocene. Both Neogene unconformities T 1 and T 0 are generated by uplift of the Dongsha Rise and truncation of their overlying strata. This uplift is caused by intrusion of magma into the upper crust. Our seismic profiles show plutons which have penetrated the sedimentary cover, whereby their original stratification in the contact zone is eliminated. These magmato-tectonic events may be correlated to the two main collision phases between Taiwan and the continental margin of East China 5-3 and 3-0 ma ago. The collisional events subsequent to the NNW to WNW drift of Taiwan transformed the compression into strike-slip movements along the continental margin of Southeastern China. The accompanying stress regime is transtensional, with subsidence of the cooling oceanic crust since the cessation of rifting and its consumption beneath the Manila Trench providing the extensional stress. The strike-slip movements remobilized many of the rift and drift faults providing pathways for magma ascent. The tectonic framework of the northern South China Sea is characterized by Miocene faults trending NE-SW. These faults are scarce but are distributed throughout the study area. Pliocene faults striking ENE-WSW to NE-SW are concentrated west of the Dongsha Islands and are mostly strike-slip in character. Recent faults are generally oriented NE-SW subparallel to the synrift faults. They result in part from local uplifts where they are normal in character, but strike-slip motion also occurs. Most of the faults involve the basement and represent reactivated zones of weakness of the rift and drift phases.

  17. Geological and Sediment Thickness Data Sources From the U.S. Continental Margins

    Science.gov (United States)

    Hutchinson, D. R.; Childs, J. R.; Edgar, N. T.; Barth, G.; Hammar-Klose, E.; Dadisman, S. V.; Rowland, R.

    2005-12-01

    Although the United States has not yet ratified the United Nations Convention on the Law of the Sea (UNCLOS), work has begun to assess the geophysical and geological data sources that might be applied to an extended continental shelf submission under Article 76 of the UNCLOS. The U.S. Geological Survey, as a follow-up to the Congressional Report published by the University of New Hampshire on data relevant to a potential U.S. submission (Mayer and others, 2002), has identified existing seismic reflection, seismic refraction, and drill-hole data on the U.S. margins for the areas where an extended continental shelf submission could be considered. This work complements ongoing NOAA efforts to map the foot-of-the-slope. The USGS compilation includes more than 80,000 km of multichannel seismic data, 70,000 km of single-channel seismic reflection data, 25 refraction experiments, and 12 drill holes that penetrate to basement. Data quality varies according to year collected and acquisition system used. Data coverage is generally excellent within the 200-nm EEZ boundary, but new data will be required to adequately assess sediment thickness in the area beyond 200-nm in some of the poorly surveyed regions (e.g., the Arctic). Velocity and drill-hole control for deeper sedimentary units is generally poor; this deficiency will also need to be addressed in new data gathering efforts. Subsea mineral resources that might exist in the region of an extended continental shelf vary by region and include conventional hydrocarbons, gas hydrate, ferro-manganese crusts and nodules, and possibly phosphorite deposits. On-going efforts are directed at interpreting these data with reference to UNCLOS criteria and guidelines, as well as evaluating how recent submissions to the United Nations by other States might affect a possible U.S. submission.

  18. Structural and stratigraphic controls on the origin and tectonic history of a subducted continental margin, Oman

    Science.gov (United States)

    Warren, C. J.; Miller, J. McL.

    2007-03-01

    Eclogites and blueschists exposed in Saih Hatat, Oman, record the subduction and exhumation of continental crustal material beneath the Cretaceous Semail Ophiolite during ophiolite obduction. The eclogite-bearing lower plate, originally part of Oman's distal continental margin, is exposed in two tectonic windows through the less metamorphosed upper plate by a previously mapped low angle, high strain, décollement structure. A major tectonic break, currently poorly exposed, records the juxtaposition of the highest pressure eclogites and garnet blueschists against lower pressure epidote-blueschists. The subsequent exhumation of the entire lower plate to mid crustal levels is marked by a pervasive shearing event associated with a regional greenschist facies overprint. The décollement truncates structures and the metamorphic field gradient in the lower plate, but does not significantly truncate structures or stratigraphy in the upper plate. It is not responsible for the exhumation of the high pressure rocks to mid-crustal levels. Most of the displacement across this structure was accommodated during continuing convergence after the subduction system had ceased to be active, and post ophiolite emplacement onto the platform carbonate sequences. A revised tectonic model is presented which accounts for the structural, geochronological and metamorphic observations.

  19. Uplift, exhumation and erosion along the Angolan continental margin: an integrated approach

    Science.gov (United States)

    Gröger, Heike R.; Machado, Vladimir; Di Pinto, Giuseppe

    2013-04-01

    The topographical development along the SW African margin is not exclusively rift-related. In addition to the onset of rifting in the Early Cretaceous, additional Late Cretaceous and Cenozoic events of uplift, exhumation and erosion are discussed. Thermochronology has proven to be a valuable tool to constrain phases of exhumation in passive continental margins. For South Africa and Namibia a large number of thermochronological data are available. Angola on the other hand is still scarcely investigated. This study is based on thermochronological data from onshore Angola, integrated with quantitative morphotectonic analysis and the on- and offshore stratigraphic record. In South Africa and Namibia published thermochronological data document pronounced Early and Late Cretaceous cooling events, which can be related to 2.5-3.5 km of removed section during the Cretaceous. An additional 1-2 km of removed section are estimated during the Cenozoic. In Angola predominantly Permo-Triassic apatite fission track ages indicate significantly less Cretaceous to Cenozoic erosion (appear directly linked. Cenozoic erosion onshore is mirrored by enhanced Oligocene to Miocene sedimentation offshore. The geomorphological information as well as the stratigraphic record are compatible with the Cenozoic cooling and exhumation as suggested by thermal modelling of apatite fission track data. Although direct indicators for Cretaceous cooling and erosion are missing in Angola, minor amounts of Cretaceous erosion may be disguised by the Miocene final event.

  20. Seamounts along the Iberian continental margins; Los montes submarinos en los margenes continentales de Iberia

    Energy Technology Data Exchange (ETDEWEB)

    Vazquez, J. T.; Alonso, B.; Fernandez-Puga, M. C.; Gomez-Ballesteros, M.; Iglesias, J.; Palomino, D.; Roque, C.; Ercilla, G.; Diaz-del-Rio, V.

    2015-07-01

    Seamounts are first-order morphological elements on continental margins and in oceanic domains, which have been extensively researched over recent decades in all branches of oceanography. These features favour the development of several geological processes, and their study gives us a better understanding of their geological and morphological domains. The seamounts around Iberia are numerous and provide excellent examples of the geo diversity of these morphological elements. Here we present a compilation of 15 seamounts around the Iberian Peninsula. These seamounts have different origins related to the geodynamic evolution (volcanism, extensional or compressive tectonics, and diapirism) of the domains where they are located. The current configuration of their relief has been influenced by Neogene-Quaternary tectonics. Their positioning controls the current morpho-sedimentary processes in the basins and on the margins, and high- lights the fact that downslope processes on seamount flanks (mass flows, turbidite flows, and landslides) and processes parallel to seamounts (contouritic currents) correspond to the major geological features they are associated with them. Biogenic structures commonly develop on the tops of seamounts where occasionally isolated shelves form that have carbonate-dominated sedimentation. (Author)

  1. Magnetic anomalies of offshore Krishna-Godavari Basin, eastern continental margin of India

    Indian Academy of Sciences (India)

    K V Swamy; I V Radhakrishna Murthy; K S Krishna; K S R Murthy; A S Subrahmanyam; M M Malleswara Rao

    2009-08-01

    The marine magnetic data acquired from offshore Krishna–Godavari (K–G) basin, eastern continental margin of India (ECMI), brought out a prominent NE–SW trending feature, which could be explained by a buried structural high formed by volcanic activity. The magnetic anomaly feature is also associated with a distinct negative gravity anomaly similar to the one associated with 85°E Ridge. The gravity low could be attributed to a flexure at the Moho boundary, which could in turn be filled with the volcanic material. Inversion of the magnetic and gravity anomalies was also carried out to establish the similarity of anomalies of the two geological features (structural high on the margin and the 85°E Ridge) and their interpretations. In both cases, the magnetic anomalies were caused dominantly by the magnetization contrast between the volcanic material and the surrounding oceanic crust, whereas the low gravity anomalies are by the flexures of the order of 3–4 km at Moho boundary beneath them. The analysis suggests that both structural high present in offshore Krishna–Godavari basin and the 85°E Ridge have been emplaced on relatively older oceanic crust by a common volcanic process, but at discrete times, and that several of the gravity lows in the Bay of Bengal can be attributed to flexures on the Moho, each created due to the load of volcanic material.

  2. Bathymetric terrain model of the Atlantic margin for marine geological investigations

    Science.gov (United States)

    Andrews, Brian D.; Chaytor, Jason D.; ten Brink, Uri S.; Brothers, Daniel S.; Gardner, James V.; Lobecker, Elizabeth A.; Calder, Brian R.

    2016-01-01

    A bathymetric terrain model of the Atlantic margin covering almost 725,000 square kilometers of seafloor from the New England Seamounts in the north to the Blake Basin in the south is compiled from existing multibeam bathymetric data for marine geological investigations. Although other terrain models of the same area are extant, they are produced from either satellite-derived bathymetry at coarse resolution (ETOPO1), or use older bathymetric data collected by using a combination of single beam and multibeam sonars (Coastal Relief Model). The new multibeam data used to produce this terrain model have been edited by using hydrographic data processing software to maximize the quality, usability, and cartographic presentation of the combined 100-meter resolution grid. The final grid provides the largest high-resolution, seamless terrain model of the Atlantic margin..

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

    Science.gov (United States)

    Archer, D.

    2014-06-01

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

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

    Directory of Open Access Journals (Sweden)

    D. Archer

    2014-06-01

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

  5. Cenozoic ice sheet history from East Antarctic Wilkes Land continental margin sediments

    Science.gov (United States)

    Escutia, C.; De Santis, L.; Donda, F.; Dunbar, R.B.; Cooper, A. K.; Brancolini, Giuliano; Eittreim, S.L.

    2005-01-01

    The long-term history of glaciation along the East Antarctic Wilkes Land margin, from the time of the first arrival of the ice sheet to the margin, through the significant periods of Cenozoic climate change is inferred using an integrated geophysical and geological approach. We postulate that the first arrival of the ice sheet to the Wilkes Land margin resulted in the development of a large unconformity (WL-U3) between 33.42 and 30 Ma during the early Oligocene cooling climate trend. Above WL-U3, substantial margin progradation takes place with early glacial strata (e.g., outwash deposits) deposited as low-angle prograding foresets by temperate glaciers. The change in geometry of the prograding wedge across unconformity WL-U8 is interpreted to represent the transition, at the end of the middle Miocene "climatic optimum" (14-10 Ma), from a subpolar regime with dynamic ice sheets (i.e., ice sheets come and go) to a regime with persistent but oscillatory ice sheets. The steep foresets above WL-U8 likely consist of ice proximal sediments (i.e., water-lain till and debris flows) deposited when grounded ice-sheets extended into the shelf. On the continental rise, shelf progradation above WL-U3 results in an up-section increase in the energy of the depositional environment (i.e., seismic facies indicative of more proximal turbidite and of bottom contour current deposition from the deposition of the lower WL-S5 sequence to WL-S7). Maximum rates of sediment delivery to the rise occur during the development of sequences WL-S6 and WL-S7, which we infer to be of middle Miocene age. During deposition of the two uppermost sequences, WL-S8 and WL-S9, there is a marked decrease in the sediment supply to the lower continental rise and a shift in the depocenters to more proximal areas of the margin. We believe WL-S8 records sedimentation during the final transition from a dynamic to a persistent but oscillatory ice sheet in this margin (14-10 Ma). Sequence WL-S9 forms under a polar

  6. 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.

    terraces and from the Fifty Fathom Flat off Saurashtra-Bombay, authigenic clays from the Kerala continental margin and onshore data. Offshore sea-level data relative to the eustatic sea-level show about 40 m subsidence sometime in the Holocene. Existing sea...

  7. Geoacoustic characteristics at the DH-2 long-core sediments in the Korean continental margin of the East Sea

    Science.gov (United States)

    Ryang, Woo Hun; Kim, Seong Pil; Hahn, Jooyoung

    2015-04-01

    A long core of 27.2 m was acquired at the DH-2 site (37°34.355'N and 129°19.516'E) in the Korean continental margin of the western East Sea. The core site is located near the Donghae City and the water depth is 316.6 m deep. The long-core sediment was recovered using the Portable Remotely Operated Drill (PROD), a fully contained drilling system, remotely operated at the seafloor. The recovered core sediments were analyzed for physical, sedimentological, and geoacoustic properties mostly at 10~30 cm intervals. Based on the long-core data with subbottom and air-gun profiles at the DH-2 core site, geoacoustic characteristics of the deeper sedimentary successions were firstly investigated in the Korean continental margin of the western East Sea. The geoacoustic measurements comprise 86 P-wave velocities and 76 attenuation values. These geoacoustic characteristics of the DH-2 long core probably contribute for reconstruction of geoacoustic models reflecting vertical and lateral variability of acoustic properties in the Korean continental margin of the western East Sea. Keywords: long core, geoacoustic, East Sea, continental margin, P-wave speed Acknowledgements: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025733) and by the Agency of Defense Development (UD140003DD).

  8. 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; 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...

  9. Cretaceous to Quaternary Siliciclastic Sediments of the Tarfaya Basin, Marginal Atlantic, SW Morocco Petrography, Geochemistry, Provenance, Climate and Weathering

    OpenAIRE

    Ali, Sajid

    2012-01-01

    This dissertation is prepared to attain the doctorate under the title "Cretaceous to Quaternary Siliciclastic Sediments of the Tarfaya Basin, Marginal Atlantic, SW Morocco Petrography, Geochemistry, Provenance, Climate and Weathering".

  10. The role of continental margins in the final stages of arc formation: Constraints from teleseismic tomography of the Gibraltar and Calabrian Arc (Western Mediterranean)

    Science.gov (United States)

    Argnani, Andrea; Cimini, Giovanni Battista; Frugoni, Francesco; Monna, Stephen; Montuori, Caterina

    2016-05-01

    The deep seismicity and lateral distribution of seismic velocity in the Central Western Mediterranean, point to the existence under the Alboran and Tyrrhenian Seas of two lithospheric slabs reaching the mantle transition zone. Gibraltar and Calabrian narrow arcs correspond to the slabs. Similarities in the tectonic and mantle structure of the two areas have been explained by a common subduction and roll-back mechanism, in which the two arcs are symmetrical end members. We present a new 3-D tomographic model at mantle scale for the Calabrian Arc and compare it with a recently published model for the Gibraltar Arc by Monna et al. (2013a). The two models, calculated with inversion of teleseismic phase arrivals, have a scale and parametrization that allow for a direct comparison. The inclusion in both inversions of ocean bottom seismometer broadband data improves the resolution of the areas underlying the seafloor networks. This additional information is used to resolve the deep structure and constrain the reconstruction of the Central Western Mediterranean geodynamic evolution. The Gibraltar tomography model suggests that the slab is separated from the Atlantic oceanic domain by a portion of African continental margin, whereas the Calabrian model displays a continuous oceanic slab that is connected, via a narrow passage (~ 350 km), to the Ionian basin oceanic domain. Starting from the comparison of the two models we propose the following interpretation: within the Mediterranean geodynamic regime (dominated by slab rollback) the geometry of the African continental margin, located on the lower plate, represents a critical control on the evolution of subduction. As buoyant continental lithosphere entered the subduction zones, slab pull caused tears in the subducted lithosphere. This tectonic response, which occurred in the final stages of arc evolution and was strongly controlled by the paleogeography of the subducted plates, explains the observed differences between the

  11. The magmatic budget of Atlantic type rifted margins: is it related to inheritance?

    Science.gov (United States)

    Manatschal, Gianreto; Tugend, Julia; Picazo, Suzanne; Müntener, Othmar

    2016-04-01

    In the past, Atlantic type rifted margins were either classified as volcanic or non-volcanic. An increasing number of high quality reflection and refraction seismic surveys and drill hole data show a divergent style of margin architecture and an evolution in which the quantity and distribution of syn-rift magmatism is variable, independently of the amount of extension. Overgeneralized classifications and models assuming simple relations between magmatic and extensional systems are thus inappropriate to describe the formation of rifted margins. More recent studies show that the magmatic evolution of rifted margins is complex and cannot be characterized based on the volume of observed magma alone. On the one hand, so-called "non-volcanic" margins are not necessarily amagmatic, as shown by the results of ODP drilling along the Iberia-Newfoundland rifted margins. On the other hand, magma-rich margins, such as the Norwegian, NW Australian or the Namibia rifted margins show evidence for hyper-extension prior to breakup. These observations suggest that the magmatic budget does not only depend on extension rates but also on the composition and temperature of the decompressing mantle. Moreover, the fact that the magmatic budget may change very abruptly along strike and across the margin is difficult to reconcile with the occurrence of plumes or other deep-seated large-scale mantle phenomena only. These overall observations result in questions on how magmatic and tectonic processes are interacting during rifting and lithospheric breakup and on how far inheritance may control the magmatic budget during rifting. In our presentation we will review results from the South and North Atlantic and the Alpine Tethys domain and will discuss the structural and magmatic evolution of so-called magma-rich and magma-poor rifted margins. In particular, we will try to define when, where and how much magma forms during rifting and lithospheric breakup. The key questions that we aim to address

  12. Chemical Characteristics of Continental Outflow Over the Tropical South Atlantic Ocean from Brazil and Africa

    Science.gov (United States)

    Talbot, R. W.; Bradshaw, J. D.; Sandholm, S. T.; Smyth, S.; Blake, D. R.; Blake, N. R.; Sachse, G. W.; Collins, J. E.; Heikes, B. G.; Anderson, B. E.; Gregory, G. L.; Singh, H. B.; Lefer, B. L.; Bachmeier, A. S.

    1996-01-01

    The chemical characteristics of air parcels over the tropical South Atlantic during September - October 1992 are summarized by analysis of aged marine and continental outflow classifications. Positive correlations between CO and CH3CL and minimal enhancements of C2CL40, and various ChloroFluoroCarbon (CFC) species in air parcels recently advected over the South Atlantic basin strongly suggest an impact on tropospheric chemistry from biomass burning on adjacent continental areas of Brazil and Africa. Comparison of the composition of aged Pacific air with aged marine air over the South Atlantic basin from 0.3 to 12.5 km altitude indicates potential accumulation of long-lived species during the local dry season. This may amount to enhancements of up to two-fold for C2H6, 30% for CO, and 10% for CH3Cl. Nitric oxide and NO(x) were significantly enhanced (up to approx. 1 part per billion by volume (ppbv)) above 10 km altitude and poorly correlated with CO and CH3Cl. In addition, median mixing ratios of NO and NO(x) were essentially identical in aged marine and continental outflow air masses. It appears that in addition to biomass burning, lightning or recycled reactive nitrogen may be an important source of NO(x) to the upper troposphere. Methane exhibited a monotonic increase with altitude from approx. 1690 to 1720 ppbv in both aged marine and continental outflow air masses. The largest mixing ratios in the upper troposphere were often anticorrelated with CO, CH3Cl, and CO2, suggesting CH, contributions from natural sources. We also argue, based on CH4/CO ratios and relationships with various hydrocarbon and CFC species, that inputs from biomass burning and the northern hemisphere are unlikely to be the dominant sources of CO, CH4 and C2H6 in aged marine air. Emissions from urban areas would seem to be necessary to account for the distribution of at least CH4 and C2H6. Over the African and South American continents an efficient mechanism of convective vertical transport

  13. 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

  14. 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.

  15. Gas emissions at the continental margin west off Svalbard: mapping, sampling, and quantification

    Directory of Open Access Journals (Sweden)

    H. Sahling

    2014-05-01

    Full Text Available We mapped, sampled, and quantified gas emissions at the continental margin west of Svalbard during R/V Heincke cruise He-387 in late summer 2012. Hydroacoustic mapping revealed that gas emissions were not limited to a zone just above 396 m below sea level (m b.s.l.. Flares from this depth gained significant attention in the scientific community in recent years because they may be caused by bottom water-warming induced hydrate dissolution in the course of global warming and/or by recurring seasonal hydrate formation and decay. We found that gas emissions occurred widespread between about 80 and 415 m b.s.l. which indicates that hydrate dissolution might only be one of several triggers for active hydrocarbon seepage in that area. Gas emissions were remarkably intensive at the main ridge of the forlandet moraine complex in 80 to 90 m water depths, and may be related to thawing permafrost. Focused seafloor investigations were performed with the remotely operated vehicle (ROV "Cherokee". Geochemical analyses of gas bubbles sampled at about 240 m b.s.l. as well as at the 396 m gas emission sites revealed that the vent gas is primarily composed of methane (> 99.70% of microbial origin (average δ13C = −55.7‰ V-PDB. Estimates of the regional gas bubble flux from the seafloor to the water column in the area of possible hydrate decomposition were achieved by combining flare mapping using multibeam and single beam echosounder data, bubble stream mapping using a ROV-mounted horizontally-looking sonar, and quantification of individual bubble streams using ROV imagery and bubble counting. We estimated that about 53 × 106 mol methane were annually emitted at the two areas and allow a large range of uncertainty due to our method (9 to 118 × 106 mol yr−1. These amounts, first, show that gas emissions at the continental margin west of Svalbard were in the same order of magnitude as bubble emissions at other geological settings, and second, may be used to

  16. 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

  17. Recurrent Pleistocene sub-marine slide events on the south Vøring Plateau, mid-Norwegian continental margin

    Science.gov (United States)

    Hjelstuen, B.; Skaug, M.; Haflidason, H.

    2009-12-01

    Throughout the Pleistocene the sediment input and depositional environments on the continental slope off Norway have been strongly controlled by variability in the ocean circulation, glaciations and sea-level changes. Repeated occurrence of shelf edge glaciations along the whole NW European margin, from Ireland to Svalbard, started at Marine Isotope Stage 12 (c. 0.5 Ma). During these periods, fast moving ice streams crossed the continental shelf on a number of locations, and large submarine fans and prograding wedges accumulated on the continental slope. During glacial maximums and in the early phases of the deglaciations high sedimentation rates, >2000 cm/ka, characterised the Norwegian continental margin. Within these depositional environments more than 30 large-scale mass failures have been identified. Here, we report on three slide events on the south Vøring Plateau, on the mid-Norwegian margin. These slides have affected an area between 2900 and 12000 km2 and involved 580-2400 km3 of sediments, noting that the slide debrites left by the failure events reach a maximum thickness of c. 150 m. For comparison the Holocene Storegga Slide, considered the largest exposed sub-marine slide in the world today, mobilized c. 2500-3500 km3 of masses and affected an area of c. 95 000 km2. The Vøring Plateau sub-marine slides are most likely younger than 0.5 Ma, thus occurring in a time period of repeated ice sheet growth to the shelf edge and high accumulation rates. The failures have occurred within an area dominated by gradients less than 1 degree, and observation of long run-out distances indicate that hydroplaning was important during slide development. Our multichannel seismic profiles further show that gas hydrate bearing sediments are observed on the mid-Norwegian continental margin. Thus, dissociation of gas hydrates and high sedimentation rates may have promoted conditions for failures to occur.

  18. 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.

  19. A mechanism to thin the continental lithosphere at magma-poor margins.

    Science.gov (United States)

    Lavier, Luc L; Manatschal, Gianreto

    2006-03-16

    Where continental plates break apart, slip along multiple normal faults provides the required space for the Earth's crust to thin and subside. After initial rifting, however, the displacement on normal faults observed at the sea floor seems not to match the inferred extension. Here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults. Our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust (< 10 km) by exhumation of mid-crustal and mantle material. This transitional crust is capped by sub-horizontal detachment surfaces over distances exceeding 100 km with little visible deformation. Our rift model is based on numerical experiments constrained by geological and geophysical observations from the Alpine Tethys and Iberia/Newfoundland margins. Furthermore, we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust. The presence of such lower crustal gabbros is well constrained for the Alpine Tethys system. Initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution. This is achieved in our models by the formation of weak ductile shear zones.

  20. Styles of neotectonic fault reactivation within a formerly extended continental margin, North West Shelf, Australia

    Science.gov (United States)

    Whitney, Beau B.; Hengesh, James V.; Gillam, Dan

    2016-08-01

    We have investigated the locations and patterns of neotectonic deformation in the Carnarvon basin along the Mesozoic rifted margin of Western Australia to evaluate the characteristics of post-Neogene tectonic reactivation. Geological, geophysical, geotechnical, and bathymetric data demonstrate that preferentially oriented rift-era structures have been reactivated under the current neotectonic stress regime. The most recent pulse of neotectonic reactivation initiated during the Plio-Pleistocene (4.0 to 1.8 million years ago) and is ongoing. Reactivated structures in the region demonstrate a variety of styles of deformation consistent with dextral-transpression. Structural styles include both positive and negative flower structures, restraining and releasing bends, and hourglass structures. Barrow Island lies within a broad kinematic restraining bend that appears to warp the MIS 5e marine terrace on the island. Fold reconstructions of Neogene strata on the Cape Range and Barrow anticlines yield uplift rates consistent with uplift rates determined from folded late Pleistocene units in the Cape region. Although tectonic rates are low compared to interplate settings, evidence for active tectonic deformation precludes this part of the Australian plate from being classified as a Stable Continental Region.

  1. Thermal history from both sides of the South Atlantic passive margin - A comparison: Argentinean pampa vs. South African escarpement.

    Science.gov (United States)

    Kollenz, Sebastian; Glasmacher, Ulrich A.

    2014-05-01

    The eastern Argentina South Atlantic passive continental margin is distinguished by a very flat topography. Out of the so called Pampean flat two mountain ranges are arising. These mountain ranges, the Sierras Australes and the Sierras Septentrionales, are located in the State of Buenos Aires south of the capital Buenos Aires. In existing literature the Sierras Australes are correlated with the South African cape fold belt (Torsvik 2009; Lopez Gamundi & Rossello 1998). Existing thermochronological data shows different post-breakup cooling histories for both areas and different AFT-ages. Published thermochronological ages (e.g. Raab et al. 2002, 2005, Gallagher et al et al. 1998)from the south African escarpement vary around 150 and 100 Ma (Gallagher et al. 1998). Only some spots in the eastern part of South Africa towards the pacific margin show older ages of 250 Ma and older than 350 Ma (Gallagher et al. 1998). New thermochronological data (AHe, AFT and ZHe) from the Sierras Australes indicate a different cooling history by revealing a range of varying ages due to younger tectonic activity. By comparing the data sets from both areas it is getting clear that the post-rift evolution of both continents is differing very strong. Gallagher, K., Brown, R. and Johnson, C. 1998. Fission track analysis and its application to geological problems. Annual review of Earth and Planetary Science, 26, 519-572. Lopez Gamundi, O.R., Rossello, E.A. (1998): Basin fill evolution and paleotectonic patterns along the Samfrau geosyncline: the Sauce Grande basin-Ventana foldbelt (Argentina) and Karoo basin-Cape foldbelt (South Africa) revisited. Geol Rundsch 86 :819-834. Raab, M.J., Brown, R.W., Gallagher, K., Carter, A. and Webber, K. 2002. late Cretaceous reactivation of major crustal shear zones in northern Namibia: constraints from apatite fission track analysis. Tectonophysics. 349, 75-92. Raab, M.J., Brown, R.W., Gallagher, K., Webber, K. and Gleadow, A.J.W. 2005. denudational and

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

    Science.gov (United States)

    2012-12-03

    ... Bureau of Ocean Energy Management Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on... for wind power on the Outer Continental Shelf offshore Rhode Island and Massachusetts. SUMMARY: This document is the Proposed Sale Notice (PSN) for the sale of commercial wind energy leases on the...

  3. 75 FR 25291 - Outer Continental Shelf (OCS) Mid-Atlantic Proposed Oil and Gas Lease Sale 220

    Science.gov (United States)

    2010-05-07

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Minerals Management Service Outer Continental Shelf (OCS) Mid-Atlantic Proposed Oil and Gas Lease Sale 220 AGENCY: Minerals Management Service (MMS), Interior. ACTION: Notice of indefinite postponement of...

  4. Satellite-Derived Distributions, Inventories and Fluxes of Dissolved and Particulate Organic Matter Along the Northeastern U.S. Continental Margin

    Science.gov (United States)

    Mannino, A.; Hooker, S. B.; Hyde, K.; Novak, M. G.; Pan, X.; Friedrichs, M.; Cahill, B.; Wilkin, J.

    2011-01-01

    Estuaries and the coastal ocean experience a high degree of variability in the composition and concentration of particulate and dissolved organic matter (DOM) as a consequence of riverine and estuarine fluxes of terrigenous DOM, sediments, detritus and nutrients into coastal waters and associated phytoplankton blooms. Our approach integrates biogeochemical measurements, optical properties and remote sensing to examine the distributions and inventories of organic carbon in the U.S. Middle Atlantic Bight and Gulf of Maine. Algorithms developed to retrieve colored DOM (CDOM), Dissolved (DOC) and Particulate Organic Carbon (POC) from NASA's MODIS-Aqua and SeaWiFS satellite sensors are applied to quantify the distributions and inventories of DOC and POC. Horizontal fluxes of DOC and POC from the continental margin to the open ocean are estimated from SeaWiFS and MODIS-Aqua distributions of DOC and POC and horizontal divergence fluxes obtained from the Northeastern North Atlantic ROMS model. SeaWiFS and MODIS imagery reveal the importance of estuarine outflow to the export of CDOM and DOC to the coastal ocean and a net community production of DOC on the shelf.

  5. Measurement of sediment and crustal thickness corrected RDA for 2D profiles at rifted continental margins: Applications to the Iberian, Gulf of Aden and S Angolan margins

    Science.gov (United States)

    Cowie, Leanne; Kusznir, Nick

    2014-05-01

    Subsidence analysis of sedimentary basins and rifted continental margins requires a correction for the anomalous uplift or subsidence arising from mantle dynamic topography. Whilst different global model predictions of mantle dynamic topography may give a broadly similar pattern at long wavelengths, they differ substantially in the predicted amplitude and at shorter wavelengths. As a consequence the accuracy of predicted mantle dynamic topography is not sufficiently good to provide corrections for subsidence analysis. Measurements of present day anomalous subsidence, which we attribute to mantle dynamic topography, have been made for three rifted continental margins; offshore Iberia, the Gulf of Aden and southern Angola. We determine residual depth anomaly (RDA), corrected for sediment loading and crustal thickness variation for 2D profiles running from unequivocal oceanic crust across the continental ocean boundary onto thinned continental crust. Residual depth anomalies (RDA), corrected for sediment loading using flexural backstripping and decompaction, have been calculated by comparing observed and age predicted oceanic bathymetries at these margins. Age predicted bathymetric anomalies have been calculated using the thermal plate model predictions from Crosby & McKenzie (2009). Non-zero sediment corrected RDAs may result from anomalous oceanic crustal thickness with respect to the global average or from anomalous uplift or subsidence. Gravity anomaly inversion incorporating a lithosphere thermal gravity anomaly correction and sediment thickness from 2D seismic reflection data has been used to determine Moho depth, calibrated using seismic refraction, and oceanic crustal basement thickness. Crustal basement thicknesses derived from gravity inversion together with Airy isostasy have been used to correct for variations of crustal thickness from a standard oceanic thickness of 7km. The 2D profiles of RDA corrected for both sediment loading and non-standard crustal

  6. 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 dista

  7. 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.

    , whereas other features like slope, foot of the slope and rise are less explicit (Figure 2). Along profile RE-11, the slope is modified with exposure of basement structures. The seafloor topography in the Laxmi Basin is generally smooth except... continental margin of India. Seismic reflection studies across the Seychelles-Laxmi Ridge margins (Collier et al., 2004) have clearly imaged the SDRs on the southern edge of the Laxmi Ridge and close to the foot of the Seychelles Bank. The presence of SDRs...

  8. Disintegration of the continental margin of northwestern Gondwana: Late Devonian of the eastern Anti-Atlas (Morocco)

    Science.gov (United States)

    Wendt, Jobst

    1985-11-01

    The Devonian early Carboniferous sequence in the eastern Anti-Atlas represents a complete record of the last stage of the depositional and tectonic evolution along the northwestern margin of Gondwana. As a consequence of early Variscan block faulting, a platform and basin topography was established during the Middle and Late Devonian. Platforms were covered by condensed cephalopod limestones; sedimentation in the basins was mainly argillaceous with calcareous and turbiditic intercalations. In the latest Famennian/early Tournaisian the whole area was covered by delta deposits in the south passing into turbidites and olistostromes toward a continental slope farther north. This sedimentary and structural evolution reflects the gradual foundering and disintegration of the northwestern continental margin of Gondwana prior to the collisional stage in the late Visean/late Carboniferous.

  9. Chriolepis prolata, a new species of Atlantic goby (Teleostei: Gobiidae) from the North American continental shelf.

    Science.gov (United States)

    Hastings, Philip A; Findley, Lloyd T

    2015-01-08

    A new species of seven-spined goby of the genus Chriolepis is described from five specimens collected from the continental shelf of the northeastern Gulf of Mexico and Atlantic Ocean off South Carolina in depths of ca 54 to 110 m. The "Platform Goby", Chriolepis prolata, is distinguishable from all other western Atlantic species currently assigned to the genus Chriolepis and the morphologically similar genus Varicus in having pelvic-fin rays one through four branched, the fifth (innermost) pelvic-fin ray unbranched and relatively long (longer than the second ray to longer than all other pelvic-fin rays); most lateral body scales ctenoid, extending anteriorly in a wedge to a level anterior to the first dorsal-fin insertion or nearly to the pectoral-fin axil, with two or more rows of small cycloid scales extending anteriorly to near the pectoral-fin axil, cycloid scales along the bases of the dorsal and anal fins, and no scales on the belly; and the first two anal-fin pterygiophores inserted anterior to the first haemal spine. It closely resembles C. bilix but differs from that species which has a scaled belly, a shorter fifth pelvic-fin ray, prolonged dorsal-fin spines and smaller teeth in the lower jaw. An earlier report of C. bilix from Florida waters apparently refers to C. prolata. 

  10. 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.

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

    Science.gov (United States)

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

    2016-01-01

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

  12. Geoacoustic models of the Donghae-to-Gangneung region in the Korean continental margin of the East Sea

    Science.gov (United States)

    Ryang, Woo Hun; Kim, Seong Pil; Hahn, Jooyoung

    2016-04-01

    Geoacoustic model is to provide a model of the real seafloor with measured, extrapolated, and predicted values of geoacoustic environmental parameters. It controls acoustic propagation in underwater acoustics. In the Korean continental margin of the East Sea, this study reconstructed geoacoustic models using geoacoustic and marine geologic data of the Donghae-to-Gangneung region (37.4° to 37.8° in latitude). The models were based on the data of the high-resolution subbottom and air-gun seismic profiles with sediment cores. The Donghae region comprised measured P-wave velocities and attenuations of the cores, whereas the Gangneung region comprised regression values using measured values of the adjacent areas. Geoacoustic data of the cores were extrapolated down to a depth of the geoacoustic models. For actual modeling, the P-wave speed of the models was compensated to in situ depth below the sea floor using the Hamilton method. These geoacoustic models of this region probably contribute for geoacoustic and underwater acoustic modelling reflecting vertical and lateral variability of acoustic properties in the Korean continental margin of the western East Sea. Keywords: geoacoustic model, environmental parameter, East Sea, continental margin Acknowledgements: This research was supported by the research grants from the Agency of Defense Development (UD140003DD and UE140033DD).

  13. Bathymetric and regional changes in benthic macrofaunal assemblages on the deep Eastern Brazilian margin, SW Atlantic

    Science.gov (United States)

    Bernardino, Angelo Fraga; Berenguer, Vanessa; Ribeiro-Ferreira, Venina P.

    2016-05-01

    Deep-sea continental slopes have valuable mineral and biological resources in close proximity to diverse, undersampled and fragile marine benthic ecosystems. The eastern Brazilian Continental Margin (19.01°S to 21.06°S, 37.88°W to 40.22°W) is an important economic region for both fishing and oil industries, but is poorly understood with respect to the structure of the soft-sediment benthic fauna, their regional distribution and their bathymetric patterns. To identify spatial and temporal patterns of benthic macrofaunal assemblages on the slope (400 to 3000 m), the Espirito Santo Basin Assessment Project (AMBES, coordinated by Cenpes-Petrobras) sampled 42 stations across the Brazilian Eastern Slope during both Summer 2012 and Winter 2013. We found a significant decrease in macrofaunal abundance at the 400 m isobath along the slope near the northern region of the Espirito Santo Basin, suggesting benthic responses to upwelling events towards the south in Campos Basin and southern Espirito Santo Basin. The taxonomic diversity and assemblage composition also changed significantly across depth zones with mid-slope peaks of diversity at 1000-1300 m. In general, macrofaunal assemblages were strongly related to slope depth, suggesting a strong influence of productivity gradients and water mass distribution on this oligotrophic margin. Sediment grain size was marginally important to macrofaunal composition on the upper slope. In general, macrofaunal assemblages on the slope of Espirito Santo Basin are similar to other areas of the SE Brazilian margin, but regional changes in response to productivity and depth need to be considered for management strategies in the face of increasing economic activities off-shore.

  14. Initiation of subduction at Atlantic-type margins: Insights from laboratory experiments

    Science.gov (United States)

    Faccenna, Claudio; Giardini, Domenico; Davy, Philippe; Argentieri, Alessio

    1999-02-01

    We have performed scaled lithospheric experiments to simulate the behavior of a ocean-continent plate system subjected to compressional strain over a geological timescale. Experiments have been constructed using sand and silicone putty, representing the brittle upper crust and the ductile lower crust/upper mantle, respectively; the layers floated on glucose syrup simulating the asthenosphere. Compressional stress is achieved by displacing a piston at constant velocity perpendicular to the plate margin. We investigate the influence of four parameters: (1) the negative buoyancy of oceanic lithosphere, (2) the horizontal body forces between continent and ocean, and (3) the brittle and (4) the ductile strength of the passive margin. Two numbers express the importance of these parameters: the Argand number (Ar), representing the ratio between the body force of continent and its integrated strength, and the buoyancy number (F), representing the ratio between the buoyancy force of ocean and its ductile resistance. We obtain three scenarios. In experiments with Ar 3 and F 1 the continent collapses toward the ocean, producing back-arc extension and subduction, simulating the post-Alpine Neogene evolution of the Mediterranean area. In experiments with Ar 3 and F > 1 the passive margin slowly evolves toward trench nucleation with the formation of a viscous mantle instability. We conclude that the latter model can be applied to the evolution of Atlantic-type margins, where there is evidence of this ongoing process.

  15. Macrofaunal communities associated with chemosynthetic habitats from the U.S. Atlantic margin: A comparison among depth and habitat types

    Science.gov (United States)

    Bourque, Jill R.; Robertson, Craig M.; Brooke, Sandra; Demopoulos, Amanda

    2016-01-01

    Hydrocarbon seeps support distinct benthic communities capable of tolerating extreme environmental conditions and utilizing reduced chemical compounds for nutrition. In recent years, several locations of methane seepage have been mapped along the U.S. Atlantic continental slope. In 2012 and 2013, two newly discovered seeps were investigated in this region: a shallow site near Baltimore Canyon (BCS, 366–412 m) and a deep site near Norfolk Canyon (NCS, 1467–1602 m), with both sites containing extensive chemosynthetic mussel bed and microbial mat habitats. Sediment push cores, suction samples, and Ekman box cores were collected to quantify the abundance, diversity, and community structure of benthic macrofauna (>300 μm) in mussel beds, mats, and slope habitats at both sites. Community data from the deep site were also assessed in relation to the associated sediment environment (organic carbon and nitrogen, stable carbon and nitrogen isotopes, grain size, and depth). Infaunal assemblages and densities differed both between depths and among habitat types. Macrofaunal densities in microbial mats were four times greater than those present in mussel beds and slope sediments and were dominated by the annelid families Dorvilleidae, Capitellidae, and Tubificidae, while mussel habitats had higher proportions of crustaceans. Diversity was lower in BCS microbial mat habitats, but higher in mussel and slope sediments compared to NCS habitats. Multivariate statistical analysis revealed specific sediment properties as important for distinguishing the macrofaunal communities, including larger grain sizes present within NCS microbial mat habitats and depleted stable carbon isotopes (δ13C) in sediments present at mussel beds. These results suggest that habitat differences in the quality and source of organic matter are driving the observed patterns in the infaunal assemblages, including high β diversity and high variability in the macrofaunal community composition. This

  16. Miocene to Present evolution of the Calabria Tyrrhenian continental margin (Southern Tyrrhenian Sea)

    Science.gov (United States)

    Pepe, F.; Sulli, A.; Bertotti, G.; Cella, F.

    2009-04-01

    The Miocene to Present evolution of the Calabria Tyrrhenian Continental Margin (CTCM, Southern Tyrrhenian Sea) are reconstructed using two ENE-WSW oriented, near-vertical seismic profiles (CROP-M27 and SISTER 11 lines). The interpreted profiles were time-to-depth converted, merged and translated in a geological section, which was also extended to the Tyrrhenian bathial plain and the Calabrian arc using wide-angle seismic data [Scarascia et al., 1994], and tested with gravity modelling. Across the CTCM, top of KCU is laterally variable in depth forming basins filled by Oligo-Miocene clastic to terrigenous deposits up to 1500m thick. Basins are separated by major structures with contractional or transcurrent kinematics, where faults are arranged in a positive flower structure fashion, affecting the KCU as well as lower Oligocene to Miocene deposits. The Messinian evaporites display essentially a constant thickness of ~-400m with the exception of the Paola Basin where deep-water Messinian evaporites are up to 1000 m thick. Plio-Quaternary deposits display a remarkable variation in thickness from ~-4.5 km in the Paola Basin to less then 400m in the central sector of the margin. Plio-Quaternary sediments are internally sub-divisible into four sub-units separated by tectonics enhanced angular unconformities. W-ward vergent reverse faults with limited vertical displacement offset the top of KCU as well as the Oligo-Miocene sedimentary and evaporitic units in the eastern side of the Paola basin and in the distal part of the CTCM where a number of closely spaced, W-vergent thrust faults are also observed in the Plio-Pleistocene deposits. Along the CTCM, the only significant normal fault which was identified is located around its central sector, dips to the W and has a displacement of ~-580m. Across the margin, the Moho was inferred at ~-35 km beneath the Calabria Arc and shallows up to 24 km in correspondence with the coastline. Moho deepens again to a depth of ~-28 km in

  17. Is earthquake activity along the French Atlantic margin favoured by local rheological contrasts?

    Science.gov (United States)

    Mazabraud, Yves; Béthoux, Nicole; Delouis, Bertrand

    2013-09-01

    The seismological study of recent seismic crises near Oleron Island confirms the coexistence of an extensional deformation and a transtensive regime in the Atlantic margin of France, which is different from the general western European stress field corresponding to a strike-slip regime. We argue that the switch of the principal stress axes σ1/σ2 in a NW-SE vertical plane is linked with the existence of crustal heterogeneities. Events of magnitude larger than 5 sometimes occur along the Atlantic margin of France, such as the 7 September 1972 (ML = 5.2) earthquake near Oleron island and the 30 September 2002 (ML = 5.7) Hennebont event in Brittany. To test the mechanism of local strain localization, we model the deformation of the hypocentral area of the Hennebont earthquake using a 3D thermo-mechanical finite element code. We conclude that the occurrence of moderate earthquakes located in limited parts of the Hercynian shear zones (as the often reactivated swarms near Oleron) could be due to local reactivation of pre-existing faults. These sporadic seismic ruptures are favoured by stress concentration due to rheological heterogeneities.

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

    Science.gov (United States)

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

    2014-06-01

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

  19. 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.

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

    Science.gov (United States)

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

    2015-12-01

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

  1. Digital data for depth to basement in the deep-sea basins of the Pacific continental margin (cowbsm) based on data collected in 1984.

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Digital vector data for the contours of depth to basement for the deep-sea basins of the Pacific continental margin offshore of Washington, Oregon, and California....

  2. Bathymetric grid (1000 m) of the continental margin offshore of Washington, Oregon, and California based on data available in the late 1980s.

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Cowbatg.tif is a 1000-m resolution bathymetric grid of the continental margin offshore of Washington, California, and Oregon. The grid was generated from bathymetric...

  3. Bathymetric contours of the continental margin offshore of Washington, Oregon, and California based on data available in the late 1980s.

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Bathymetric contours (contour interval 100 m) of the continental margin offshore of Washington, Oregon, and California (cowbat) were compiled from various sources...

  4. The Bay of Bengal and the Statement of Understanding Concerning the Establishment of the Outer Edge of the Continental Margin: Regional Implications for Delimiting the Juridical Continental Shelf

    Science.gov (United States)

    Mridha, M.; Varma, H.; Macnab, R.

    2005-12-01

    The Bay of Bengal is the site of massive depositions of sediment from the Ganga-Brahmaputra river systems, which discharge an estimated 2300 million tons of material into the Indian Ocean every year. The accumulated material comprises an enormous fan that extends some 4000 km from the Mouths of the Ganges, a delta system which encompasses the entire coast of Bangladesh and a segment of the coast of India. The major tectonic elements of the Bay of Bengal and surrounding areas are: the passive eastern continental margin of India; the 85E Ridge; the Ninetyeast Ridge; the intervening basin buried beneath deep sediment; and the Sunda Arc system with the associated back-arc Andaman Basin. Except for the Nikitin Seamounts which rise above the seabed just south of the Equator, the 85E Ridge is totally covered by thick sediment. The Ninetyeast Ridge, on the other hand, protrudes above the seabed as far north as 10N, where it plunges beneath the thickening sediment and separates the deposits into the Bengal Fan and the smaller Nicobar Fan. The 85E and Ninetyeast Ridges present the most significant relief in the crystalline basement underlying the Bay of Bengal, and should therefore figure substantially in any analysis of sediment thickness pursuant to the delimitation of the outer continental shelf. In this region, the sediment thickness provision of Article 76 has been modified by a Statement of Understanding in Annex II of the Final Act of the Third UN Conference on the Law of the Sea. To avoid a perceived inequity that might arise from the application of the standard one percent sediment thickness formula of Article 76, the Statement introduced a new formula: a qualified State in this region, even if it has a narrow physiographic continental shelf, may establish the outer edge of its continental margin by a line where the thickness of sedimentary rock is not less than one km. This presentation will describe the development of a joint formula line for the States that

  5. South Atlantic Margin Processes and Links with Onshore Evolution: Overview of the German Priority Program SAMPLE (Invited)

    Science.gov (United States)

    Trumbull, R. B.

    2013-12-01

    Since 2009 the SAMPLE program (www.spp-sample.de) provides a platform for research into the causes and effects of continental breakup and the evolution of passive margins. SAMPLE encompasses 28 projects from 13 German institutions and many international partnerships. The 6-year program will run through 2015. At the core of the program are observational studies that are interlinked by modelling projects examining the interplay of deep mantle dynamics, lithospheric stress fields, pre-rift fabric and melt-weaking on localizing rifting. Geophysics teams collect and integrate existing data from wide-angle seismic profiles, reprocessed multichannel seismics, as well as gravity, magnetics and heat-flow studies to construct self-consistent lithospheric-scale 3-D models along the conjugate margins. Key interests are variations in margin architecture, distribution of magmatic features and the evolution of sedimentary basins (subsidence and thermal histories). An exciting new contribution of SAMPLE geophysics is a linked set of seismic, seismologic and magnetotelluric experiments along the Walvis Ridge, including onshore NW Namibia and the Tristan da Cunha hotspot. In the deep mantle, we examine evidence from global seismic tomography for dramatic low seismic-velocity regions near the core-mantle boundary beneath southern Africa and their implications for dynamics in the deep Earth and the thermo-chemical nature of plumes. Petrologic studies focus on near-primary mantle melts represented by Mg-rich mafic dikes. Projects address the origin of magmas and crust-mantle interaction, and the environmental impact of mega-scale volcanism during breakup. Thermobarometry results from the African margin reveal a N-to-S decrease in mantle potential temperatures from 1520°C (N) to 1380° (S), which supports a thermal plume origin for excessive melt production in the north. Thermochronology data from both conjugate margins reveal complex and puzzling patterns in the denudation history

  6. The Cryogenian intra-continental rifting of Rodinia: Evidence from the Laurentian margin in eastern North America

    Science.gov (United States)

    McClellan, Elizabeth; Gazel, Esteban

    2014-10-01

    The geologic history of the eastern North American (Laurentian) margin encompasses two complete Wilson cycles that brought about the assembly and subsequent disaggregation of two supercontinents, Rodinia and Pangea. In the southern and central Appalachian region, basement rocks were affected by two episodes of crustal extension separated by > 100 m.y.; a Cryogenian phase spanning the interval 765-700 Ma and an Ediacaran event at ~ 565 Ma. During the Cryogenian phase, the Mesoproterozoic continental crust was intruded by numerous A-type felsic plutons and extensional mafic dikes. At ~ 760-750 Ma a bimodal volcanic sequence erupted onto the uplifted and eroded basement. This sequence, known as the Mount Rogers Formation (MRF), comprises a bimodal basalt-rhyolite lower section and an upper section of dominantly peralkaline rhyolitic sheets. Here, we provide new geochemical evidence from the well-preserved volcanic rocks of the Cryogenian lower MRF, with the goal of elucidating the process that induced the initial stage of the break-up of Rodinia and how this affected the evolution of the eastern Laurentian margin. The geochemical compositions of the Cryogenian lavas are remarkably similar to modern continental intra-plate settings (e.g., East African Rift, Yellowstone-Snake River Plain). Geochemical, geophysical and tectonic evidence suggests that the common denominator controlling the melting processes in these settings is deep mantle plume activity. Thus, evidence from the MRF suggests that the initial phase of extension of the Laurentian margin at ~ 760-750 Ma was possibly triggered by mantle plume activity. It is possible that lithospheric weakness caused by a mantle plume that impacted Rodinia triggered the regional extension and produced the intra-continental rifting that preceded the breakup of the Laurentian margin.

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

    Directory of Open Access Journals (Sweden)

    G. Cowie

    2014-02-01

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

  8. Symposium on North Atlantic Margin Petroleum Resources: Technical Program: Papers Presented

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    2001-07-01

    This program lists the papers presented at a symposium, held as part of the Geological Association--Mineralogical Association of Canada 2001 Joint Annual Meeting. Thirty-nine papers and seven poster exhibits were presented on a wide diversity of subjects dealing with (1) development activities and exploration potential of the North Atlantic margins of Nova Scotia, across the ocean to Ireland and offshore Morocco; (2) recently activated hydrocarbon fields off Canada's eastern shores; (3) integration of local and regional geological data with production data and new and proven technologies; (4) a short course on ichnofossils and fossil footprints and the sedimentology of shallow-and marginal marine systems using core from the Jeanne d'Arc Basin; and (5) modern products and processes that are fundamental to successful production from marginal marine reservoirs. This program lists only the titles of the papers presented in each of the six sessions and the titles of the poster exhibits. The abstracts themselves are available on the Internet at the address cited above.

  9. The Eastern Sardinian Margin (Tyrrhenian Sea, Western Mediterranean) : a key area to study the rifting and post-breakup evolution of a back-arc passive continental margin

    Science.gov (United States)

    Gaullier, Virginie; Chanier, Frank; Vendeville, Bruno; Maillard, Agnès; Thinon, Isabelle; Graveleau, Fabien; Lofi, Johanna; Sage, Françoise

    2016-04-01

    The Eastern Sardinian passive continental margin formed during the opening of the Tyrrhenian Sea, which is a back-arc basin created by continental rifting and oceanic spreading related to the eastward migrating Apennine subduction system (middle Miocene to Pliocene). Up to now, rifting in this key area was considered to be pro parte coeval with the Messinian Salinity Crisis (MSC, 5.96-5.32 Ma). We use the MSC seismic markers and the deformation of viscous salt and its brittle overburden as proxies to better delineate the timing of rifting and post-rift reactivation, and especially to quantify vertical and horizontal movements. On this young, highly-segmented margin, the Messinian Erosion Surface and the Upper and Mobile Units are systematically associated, respectively, to basement highs and deeper basins, showing that a rifted deep-sea domain already existed by Messinian times, therefore a major pre-MSC rifting episode occurred across the entire domain. Data show that there are no signs of Messinian syn-rift sediments, hence no evidence for rifting after Late Tortonian times. Moreover, because salt tectonics creates fan-shaped geometries in sediments, syn-rift deposits have to be carefully re-examined to distinguish the effects of crustal tectonics (rifting) and salt tectonics. We also precise that rifting is clearly diachronous from the upper margin (East-Sardinia Basin) to the lower margin (Cornaglia Terrace) with two unconformities, attributed respectively to the necking and to the lithospheric breakup unconformities. The onshore part of the upper margin has been recently investigated in order to characterize the large crustal faults affecting the Mesozoic series (geometry, kinematics and chronology) and to decipher the role of the structural inheritance and of the early rifting. Seaward, we also try to constrain the architecture and timing of the continent-ocean transition, between the hyper-extended continental crust and the first oceanic crust. Widespread

  10. 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.

    , showing slumping on the continental slope region. (b) Seismic section off Amini Island, Lakshadweep. showing slump deposits at the foot of slope. Please note smoothness of main glide plain. (e) Seismic section off southern tip of India. showing slump...

  11. HyFlux - Part I: Regional Modeling of Methane Flux From Near-Seafloor Gas Hydrate Deposits on Continental Margins

    Science.gov (United States)

    MacDonald, I. R.; Asper, V.; Garcia, O. P.; Kastner, M.; Leifer, I.; Naehr, T.; Solomon, E.; Yvon-Lewis, S.; Zimmer, B.

    2008-12-01

    HyFlux - Part I: Regional modeling of methane flux from near-seafloor gas hydrate deposits on continental margins MacDonald, I.R., Asper, V., Garcia, O., Kastner, M., Leifer, I., Naehr, T.H., Solomon, E., Yvon-Lewis, S., and Zimmer, B. The Dept. of Energy National Energy Technology Laboratory (DOE/NETL) has recently awarded a project entitled HyFlux: "Remote sensing and sea-truth measurements of methane flux to the atmosphere." The project will address this problem with a combined effort of satellite remote sensing and data collection at proven sites in the Gulf of Mexico where gas hydrate releases gas to the water column. Submarine gas hydrate is a large pool of greenhouse gas that may interact with the atmosphere over geologic time to affect climate cycles. In the near term, the magnitude of methane reaching the atmosphere from gas hydrate on continental margins is poorly known because 1) gas hydrate is exposed to metastable oceanic conditions in shallow, dispersed deposits that are poorly imaged by standard geophysical techniques and 2) the consumption of methane in marine sediments and in the water column is subject to uncertainty. The northern GOM is a prolific hydrocarbon province where rapid migration of oil, gases, and brines from deep subsurface petroleum reservoirs occurs through faults generated by salt tectonics. Focused expulsion of hydrocarbons is manifested at the seafloor by gas vents, gas hydrates, oil seeps, chemosynthetic biological communities, and mud volcanoes. Where hydrocarbon seeps occur in depths below the hydrate stability zone (~500m), rapid flux of gas will feed shallow deposits of gas hydrate that potentially interact with water column temperature changes; oil released from seeps forms sea-surface features that can be detected in remote-sensing images. The regional phase of the project will quantify verifiable sources of methane (and oil) the Gulf of Mexico continental margin and selected margins (e.g. Pakistan Margin, South China Sea

  12. Multi-beam backscatter data to characterize the mound and channel provinces of the Porcupine Seabight - northeast Atlantic margin

    Science.gov (United States)

    Beyer, A.; Chakraborty, B.; Schenke, H. W.

    2003-04-01

    Large scale oceanographic explorations are presently continuing around the Porcupine Seabight area, which is located towards the south-west Ireland. This area is an embayment of the north Atlantic continental margins. It's importance due to the dominant hydrocarbon resources are not unknown, and on-going experiments are important due to the involvement of higher order variability (in terms of physical and geological settings) around this area. Multi-beam angular backscatter study to characterize the eastern slope seafloor of the Porcupine Seabight is initiated first time. Backscatter data acquired from twenty-nine locations of the carbonate mounds and associated buried mounds (Belgica province), and channel seafloors like: Kings channel and Gollum channels are analysed in this paper. Processing details of the angular backscatter data was carried out to apply the scattering models to determine seafloor roughness. Employed normalization to the angular backscatter data to obtain shape invariant seafloor indicate distinct grey levels for mound, buried mound, and various channel seafloors (four distinct types of seafloors) within the backscatter dynamic range of 12 dB. The backscatter levels are the highest for the mound areas followed by the buried mounds, channel seafloor, and inter-channel areas. Present study was further substantiated by employing a semi-empirical method to determine the shape aspects of the area backscatter strengths. Estimated three parameters like: predicted 20 degree angular backscatter response, slope and coefficient of variations of the angular backscatter responses are computed to understand general seafloor characteristics of the varying area seafloor. The use of Helmholtz-Kirchhoff's angular backscatter theory which is a functional of the power law are carried out to estimate sea water floor interface roughness parameters. The sediment volume inhomogeneity parameters are also determined by use of curve fitting to the overlaying interface

  13. Geoacoustic model at the DH-1 long-core site in the Korean continental margin of the East Sea

    Science.gov (United States)

    Ryang, Woo Hun; Kim, Seong Pil

    2014-05-01

    A long core of 23.6 m was acquired at the DH-1 site (37°36.651'N and 129°19.709'E) in the Korean continental margin of the western East Sea. The core site is located near the Donghae City and the water depth is 357.8 m deep. The long-core sediment was recovered using the Portable Remotely Operated Drill (PROD), a fully contained drilling system, remotely operated at the seafloor. The recovered core sediments were analyzed for physical, sedimentological, and geoacoustic properties mostly at 10~30 cm intervals. Based on the long-core data with subbottom and air-gun profiles at the DH-1 core site, a geoacoustic model was firstly reconstructed including water mass. The geoacoustic model comprises 7 geoacoustic units of the core sediments, based on the measurements of 125 P-wave velocities and 121 attenuations. The P-wave speed was compensated to in situ depth below the sea floor using the Hamilton method. The geoacoustic model DH-1 probably contributes for reconstruction of geoacoustic models reflecting vertical and lateral variability of acoustic properties in the Korean continental margin of the western East Sea. Keywords: long core, geoacoustic model, East Sea, continental margin, P-wave speed Acknowledgements: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025733) and by the Ministry of Knowledge Economy through the grant of Marine Geology and Geophysical Mapping Project (GP2010-013).

  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. Tectono-stratigraphic analysis of the Malvinas Basin, offshore the southernmost Argentinean continental margin

    Science.gov (United States)

    Baristeas, N.; Anka, Z.; di Primio, R.; Rodriguez, J. F.; Marchal, D.; Dominguez, F.

    2012-04-01

    A detailed tectono-stratigraphic analysis of the Malvinas Basin development, located offshore the Argentinean margin, was carried out. This was achieved through the interpretation of around 65,000 km of 2D seismic reflection profiles, spanning a dense grid on the shelf and the upper-slope of the basin. Five main seismo-stratigraphic units and their sub-units, informally named U1 to U5 a/b, bound by major unconformities were identified and correlated with the Mesozoic to Cenozoic main tectonic phases of the basin. U1 (Pre-168 Ma) represents the seismic basement and deepens gradually southwards. U2 (168-150.5 Ma, syn rift phase) fills regional depressions, onlapping the basement, and it thickens and deepens southwards. U1 and U2 are affected by several syn-rift normal faults, which have a main NE-SW strike direction in the south of the basin and a NW-SE strike direction in the centre of the basin. This suggests that the Malvinas Basin may have been developed initially as a rift basin with two different extensional directions. (1) a NW-SE directed extension probably linked with the opening of the Weddell Sea (Early Mid-Jurassic) and (2) a NE-SW directed extension most likely linked with the opening of the South Atlantic during Mid-Jurassic to Early Cretaceous. U3 (150.5-68 Ma, sag phase) is mainly an aggradational wedge-shaped unit. Some syn-rift faults continue into the Cretaceous. Sedimentation in this unit is mainly derived from the north and during Mid-Cretaceous also from the northeast, as documented by the presence of a southwestward prograding sedimentary fan located in the northeast of the basin. U4 (68-42.5 Ma, transtensional foredeep phase) overlies unconformly U3 and thickens to the south. Sediment input decreases dramatically during that time and only a thin sedimentary succession was deposited over the entire basin. Although a regional compressional regime is established from late Cretaceous to Cenozoic due to the Andean orogenesis, an extensional regime

  16. Reproductive biology of two macrourid fish, Nezumia aequalis and Coelorinchus mediterraneus, inhabiting the NW Mediterranean continental margin (400-2000 m)

    Science.gov (United States)

    Fernandez-Arcaya, U.; Ramirez-Llodra, E.; Rotllant, G.; Recasens, L.; Murua, H.; Quaggio-Grassiotto, I.; Company, J. B.

    2013-08-01

    Nezumia aequalis and Coelorinchus mediterraneus are abundant species on the upper and lower continental slopes, respectively, in the Mediterranean Sea. A study on the reproductive strategy of the two species was conducted on the Catalan margin (NW Mediterranean). The reproductive cycle of both species was investigated using visual analyses of gonads and histological screening. The shallower species, N. aequalis, showed continuous reproduction with a peak of spawning females in winter months. In contrast, the deeper-living species, C. mediterraneus, showed semi-continuous reproduction with a regression period during the spring. Juveniles of N. aequalis were present in all seasons, but most abundant in the spring. Only two juveniles of C. mediterraneus were found. Both species had asynchronous oocyte development. The average fecundity of N. aequalis was 10,630 oocytes per individual, lower than known for the same species in the Atlantic Ocean. The fecundity of C. mediterraneus was measured for the first time in this study, with an average of 7693 oocytes per individual. Males of both species appear to have semi-cystic spermatogenesis.

  17. 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

  18. Methane Gas Hydrate Stability Models on Continental Shelves in Response to Glacio-Eustatic Sea Level Variations: Examples from Canadian Oceanic Margins

    Directory of Open Access Journals (Sweden)

    Jan Safanda

    2013-11-01

    Full Text Available We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource volumes depend on the dynamics of the ocean-atmosphere system as it responds to both natural (glacial-interglacial and anthropogenic (climate change forcing. Our models focus on the interval beginning three million years ago (i.e., Late Pliocene-Holocene. They continue through the current interglacial and they are projected to its anticipated natural end. During the current interglacial the gas hydrate stability zone (GHSZ thickness in each region responded uniquely as a function of changes in water depth and sea bottom temperature influenced by ocean currents. In general, the GHSZ in the deeper parts of the Pacific and Atlantic margins (≥1316 m thinned primarily due to increased water bottom temperatures. The GHSZ is highly variable in the shallower settings on the same margins (~400–500 m. On the Pacific Margin shallow GH dissociated completely prior to nine thousand years ago but the effects of subsequent sea level rise reestablished a persistent, thin GHSZ. On the Atlantic Margin Scotian Shelf the warm Gulf Stream caused GHSZ to disappear completely, whereas in shallow water depths offshore Labrador the combination of the cool Labrador Current and sea level rise increased the GHSZ. If future ocean bottom temperatures remain constant, these general characteristics will persist until the current interglacial ends. If the sea bottom warms, possibly in response to global climate change, there could be a significant reduction to complete loss of GH stability, especially on the shallow parts of the continental shelf. The interglacial GH thinning rates constrain rates at which carbon can be transferred between the GH reservoir and the atmosphere

  19. 138-121 Ma asthenospheric magmatism prior to continental break-up in the North Atlantic and geodynamic implications

    Science.gov (United States)

    Schärer, Urs; Girardeau, Jacques; Cornen, Guy; Boillot, Gilbert

    2000-09-01

    Along the Galicia and Gorringe banks and in the Iberia Abyssal Plain of the North Atlantic, unroofed sub-continental mantle fills the gap between 'true' oceanic crust and the continental crust margin. These lithospheric peridotites are intruded by gabbros and dolerites, and locally covered by basalts. Primary magmatic zircons extracted from gabbros and meta-gabbros of the two banks were dated by the U-Pb chronometer, and initial hafnium isotope signatures ( ɛHf i) were determined on the same grains. For Mt. Gettysburg at Gorringe, gabbro emplacement ages of 137.5±0.5 (2σ) Ma and 135.7±0.8 Ma are obtained, and corresponding ɛHf i lie at +20.5±0.3 (2σ) and +19.5±0.4, substantiating magma formation from severely LILE-depleted mantle domains. Gabbro zircons from Mt. Ormonde at Gorringe yield a much younger age of 77.1±0.4 Ma and the Hf isotopes document an intermediately LILE-depleted mantle source having a ɛHf i of +7.6±0.4. Given its age and Hf signature, emplacement of this rock can be ascribed to the alkaline magmatic event that also affected the Iberian Continent in Upper Cretaceous time. Concerning the Galicia section, zircons from a meta-gabbro yield an emplacement age of 121.7±0.4 Ma and a ɛHf i of +14.0±0.2, and a ɛHf i of +14.6±0.2 is obtained for zircons from a previously dated meta-gabbro of identical age. These results indicate magma extraction from mantle reservoirs that are slightly less LILE-depleted than those sampled by the about 20 Myr older Gorringe gabbros. The data demonstrate that magmatism occurring prior to complete separation of Europe from America was essentially of asthenospheric origin. Both the 138-135 Ma ages for the Gorringe gabbros and 122 Ma ages for the Galicia gabbros are at least 5 Myr older than the oldest sediments on Gorringe, and the break-up unconformity at the Galicia Bank, respectively. Magma source signatures of the syn-rift gabbros are in agreement with values expected for differently depleted Cretaceous

  20. Reconstruction of multiple tectonic events in continental margins by integrated tectonostratigraphic and geochronological analysis: the Mesozoic to Paleogene Caribbean-South American interaction in northeastern Colombia

    Science.gov (United States)

    Cardona, Agustin; Montes, Camilo; Bayona, German; Valencia, Victor; Ramirez, Diego; Zapata, Sebastian; Lara, Mario; Lopez-Martinez, Margarita; Thomson, Stuart; Weber, Marion

    2013-04-01

    Although the older record and successive tectonic scenarios experienced by a continental margin is commonly fragmentary, integrated field, petrological and geochronological analysis can reconstruct the long term tectonic evolution of continental margins and characterized major controls on the orogenic style. We present new geochronological constraints from igneous and low to very low grade metasedimentary rocks from the Caribbean continental margin of northeastern Colombia (Guajira region) in order to reconstruct the different tectonic events recorded by the margin before, during and following the arc-continent collision with the front of the Caribbean plate. Zircon U-Pb LA-ICP-MS geochronology results from leucogranites associated with garnet amphibolites, tonalites and volcanic rocks that made the continental basement of northeastern Colombia reveals and Early to Middle Mesozoic tectonic activity with peaks at ca. 220-230 Ma and 170-180 Ma. This magmatic record is related to a collisional belt link to the final agglutination of Pangea and was followed by an overimposed far field back-arc setting associated to the subduction of the Pacific (Farrallon) plate under the Pangea supercontinent. Muscovite and biotite Ar-Ar geochronology from basement rocks and low grade Mesozoic metasediments also reveals the existence of Middle Jurassic to Early Cretaceous thermal events link to the final opening of the proto-Caribbean ocean. The South American continental margin was subsequently affected by an arc-continent collisional event with the front of the Caribbean plate. This event is recorded by the growth of a Banda-type collisional melange that mixed South American continental margin sediments with mafic and ultramafic blocks of intra-oceanic arc origin, the formation of a coherent metasedimentary belt also made of South American margin sediments, and the mylonitization of the continental basement. Ar-Ar temporal constraints on the low grade metasedimentary rocks and

  1. Fine-scale analysis of shelf -slope physiography across the western continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Chakraborty, B.; Mukhopadhyay, R.; Jauhari, P.; Mahale, V.; Shashikumar, K.; Rajesh, M.

    to characterise the outer shelf, upper slope, shelf margin basin, and several structural rises. The scatter diagram analysis shows that the seafloor can be grouped in two distinct clusters. Distinctly different clustering patterns are observed over the structural...

  2. 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.

    . Subrahmanyam et al. / Marine Geology 253 (2008) 63–72 Charles Mountains. Antarctica. J. Geol. Soc. Aust. 30, 295–304. Stagg,H.M.J., Colwel, J.B., Direen,N.G.,O'Briem,P.E.,Bernardel,G., Borissova, I., Brown, B.J., Ishirara, T., 2004. Geology of the continental...

  3. Geophysical and Geotechnical Determination of Sand Resources on the Florida Atlantic Continental Shelf: Preliminary Results

    Science.gov (United States)

    Finkl, C. W.; Andrews, J. L.; Suthard, B. C.; Robertson, W.

    2007-12-01

    the ability to assess sand resource potential on the shelf. Sand resources on the Florida Atlantic continental shelf amount to something on the order of about 85 x 109 m3. These potential sand volumes, based on average 3 m depth assumptions, break down to about 1 x 109 m3 for the southeast (Miami, Broward, Palm Beach counties), 4.3 x 109 m3 for the central (Martin, St. Lucie, Indian River, Brevard counties), and 78.5 x 109 m3 for the northeast (Volusia, Flagler, St. Johns, Duval, Nassau counties) Florida shelf areas. It is effective to use multiple remote sensing methods to locate large sand bodies, but more detailed geotechnical surveys are required to better estimate these sand resource potentials.

  4. Outer Continental Shelf Oil and Natural Gas Wells - Atlantic Region NAD83

    Data.gov (United States)

    Bureau of Ocean Energy Management, Department of the Interior — This data set contains surface locations for oil and gas wells located in the Atlantic federal waters. All wells in the Atlantic Region were completed and abandoned...

  5. 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

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

    Science.gov (United States)

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

    2013-11-01

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

  7. 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.

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

    Science.gov (United States)

    Huang, Xiaoxia; Jokat, Wilfried

    2016-11-01

    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.

  9. Cenozoic magmatism in the northern continental margin of the South China Sea: evidence from seismic profiles

    Science.gov (United States)

    Zhang, Qiao; Wu, Shiguo; Dong, Dongdong

    2016-06-01

    Igneous rocks in the northern margin of the South China Sea (SCS) have been identified via high resolution multi-channel seismic data in addition to other geophysical and drilling well data. This study identified intrusive and extrusive structures including seamounts and buried volcanoes, and their seismic characteristics. Intrusive features consist of piercement and implicit-piercement type structures, indicating different energy input associated with diapir formation. Extrusive structures are divided into flat-topped and conical-topped seamounts. Three main criteria (the overlying strata, the contact relationship and sills) were used to distinguish between intrusive rocks and buried volcanos. Three criteria are also used to estimate the timing of igneous rock formation: the contact relationship, the overlying sedimentary thickness and seismic reflection characteristics. These criteria are applied to recognize and distinguish between three periods of Cenozoic magmatism in the northern margin of the SCS: before seafloor spreading (Paleocene and Eocene), during seafloor spreading (Early Oligocene-Mid Miocene) and after cessation of seafloor spreading (Mid Miocene-Recent). Among them, greater attention is given to the extensive magmatism since 5.5 Ma, which is present throughout nearly all of the study area, making it a significant event in the SCS. Almost all of the Cenozoic igneous rocks were located below the 1500 m bathymetric contour. In contrast with the wide distribution of igneous rocks in the volcanic rifted margin, igneous rocks in the syn-rift stage of the northern margin of the SCS are extremely sporadic, and they could only be found in the southern Pearl River Mouth basin and NW sub-sea basin. The ocean-continent transition of the northern SCS exhibits high-angle listric faults, concentrated on the seaward side of the magmatic zone, and a sharply decreased crust, with little influence from a mantle plume. These observations provide further evidence to

  10. Formation of Australian continental margin highlands driven by plate-mantle interaction

    Science.gov (United States)

    Müller, R. Dietmar; Flament, Nicolas; Matthews, Kara J.; Williams, Simon E.; Gurnis, Michael

    2016-05-01

    Passive margin highlands occur on most continents on Earth and play a critical role in the cycle of weathering, erosion, and atmospheric circulation. Yet, in contrast to the well-developed understanding of collisional mountain belts, such as the Alps and Himalayas, the origin of less elevated (1-2 km) passive margin highlands is still unknown. The eastern Australian highlands are a prime example of these plateaus, but compared to others they have a well-documented episodic uplift history spanning 120 million years. We use a series of mantle convection models to show that the time-dependent interaction of plate motion with mantle downwellings and upwellings accounts for the broad pattern of margin uplift phases. Initial dynamic uplift of 400-600 m from 120-80 Ma was driven by the eastward motion of eastern Australia's margin away from the sinking eastern Gondwana slab, followed by tectonic quiescence to about 60 Ma in the south (Snowy Mountains). Renewed uplift of ∼700 m in the Snowy Mountains is propelled by the gradual motion of the margin over the edge of the large Pacific mantle upwelling. In contrast the northernmost portion of the highlands records continuous uplift from 120 Ma to present-day totalling about 800 m. The northern highlands experienced a continuous history of dynamic uplift, first due to the end of subduction to the east of Australia, then due to moving over a large passive mantle upwelling. In contrast, the southern highlands started interacting with the edge of the large Pacific mantle upwelling ∼ 40- 50 million years later, resulting in a two-phase uplift history. Our results are in agreement with published uplift models derived from river profiles and the Cretaceous sediment influx into the Ceduna sub-basin offshore southeast Australia, reflecting the fundamental link between dynamic uplift, fluvial erosion and depositional pulses in basins distal to passive margin highlands.

  11. Middle-Late Eocene structure of the southern Levant continental margin — Tectonic motion versus global sea-level change

    Science.gov (United States)

    Segev, Amit; Schattner, Uri; Lyakhovsky, Vladimir

    2011-03-01

    During the Paleogene greenhouse episode Earth experienced the warmest period of the Cenozoic while global sea level rose by more than 100 m. However, geological evidence from the Levant margin, northwestern Arabian plate, indicates that throughout this period seabed deepening exceeded 1000 m. Lithology from Israel, Syria, Lebanon and Jordan is mainly pelagic and neritic, interfered by occasional fossil sub-marine slumps. In order to understand this dissimilarity we quantify the vertical tectonic motion of the Levant continental margin through the Paleogene. The margin began to take shape during the Late Permian and it was reactivated during the Oligocene. Based on information from outcrops, drillholes, seismic reflection and refraction, gravity, and previous publications, a multi-layered model of the Levant lithosphere was established. Layers include the Moho, top of the crystalline basement and covering sediments up to the Late Eocene. The model was restored horizontally by 100 km along the younger Dead Sea transform. Assuming local isostatic compensation, vertical restoration yielded the paleo-bathymetry which prevailed across northwestern Arabia during the Middle-Late Eocene. Results show that following the margin subsidence the Cretaceous Levantine platform became ramp shaped during the Eocene. Most parts of the central Levant were submerged under ~ 200 to ~ 1800 m of water, while the paleo-bathymetric gradients ranged from ~ 2° at the shelf to ~ 6° at the slope. The apparent dissimilarity between sea level and our tectonic-based calculations is up to an order of magnitude. These differences may be resolved by accounting for vertical tectonic motions and sediment supply rates. Our results stress the importance of the presented crustal structure. As opposed to the backstripping procedure, the structural map of the top Eocene interface was constructed upwards from the well established top Turonian (Judea Group) interface since only scarce and sporadic outcrops

  12. 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

  13. Can rifting evolution and passive margins architecture be driven by relative rheological heterogeneities? Insight from analogue modelling focused on South Atlantic margins.

    Science.gov (United States)

    Cappelletti, Alessio; Nestola, Yago; Tsikalas, Filippos; Salvi, Francesca; Argnani, Andrea; Cavozzi, Crisitan; Meda, Marco

    2016-04-01

    Crustal transect joined with lithospherical-scale analogue experiments are used to unreveal the evolution of the Central Segment of the South Atlantic margin. Specifically we analized the Santos and Campos basins along the Brazilian margin, where crustal inhomogeneities affects both rifting evolution and structural architecture of the conjugate margins. The results show that heterogeneities located within the lower crust can have a remarkable impact on the along-margin segmentation promoting focused and deeper basins related to a relatively "weak" rheology, and articulated basins with horsts and grabens in response to a relative "strong" rheology on the equivalent parts of the conjugate pairs. At the early-stage of rift evolution the deformation is concentrated at the proximal margin. At this stage, if a weak lower crust rheology heterogeneity exists, a main deep listric half-graben fault and associated thick and wedge shaped syn-rift basin sequences are developed; on the contrary, a strong lower crust rheology produce a more planar, rotated, domino-type faulted basins with thinner sequences directly controlled by the individual fault-blocks. At the late-stage rift evolution, once the effects of the initial crustal rheology inhomogeneities are reduced due to the lithosperic thinning process, the outer margin records a late syn-rift sequence which shows comparable thicknesses for both cases of lower crust rheologies. This tectono-stratigraphic evolution of the rifting process gives rise to along-margin alterations in symmetry versus asymmetry of the width and structural architecture. The presented models show that the tectono-stratigraphic evolution of rifting process can produces along margin switching of width and structural architecture. The change in architecture is due to the relative rheological contrast with respect to the surrounding in the lower crust. This produces a different, "relative", behavior for the lower crust if next to "weak" or to "strong

  14. The Role of Antecedent Geology in Submarine Slope Failure: Insights from the Currituck Slide Complex along the Central U.S. Atlantic Margin

    Science.gov (United States)

    Hill, J. C.; Brothers, D. S.; Ten Brink, U. S.; Craig, B.; Chaytor, J. D.; Flores, C. H.

    2015-12-01

    To investigate the influence of antecedent geology on the distribution of submarine landslides along the central U.S. Atlantic margin, we examined a suite of multichannel seismic data, including vintage airgun data from Norfolk Canyon to Cape Hatteras and new high-resolution sparker data across the Currituck Slide, as well as regional multibeam bathymetry. Areas north and south of the Currituck Slide are characterized by oblique margin morphology, defined by angular, convex deltaic clinoforms deposited during the Mid-Miocene, which generated an abrupt shelf-break with relatively steep downslope gradients (>8°). As a result, upper slope sediment bypass, closely spaced submarine canyons, and small landslides confined to canyon headwalls and sidewalls characterize these areas. In contrast, the Currituck region is defined by a sigmoidal geometry, with a smooth shelf-edge rollover and more gentle slope gradient (800m of Plio-Pleistocene sediment accumulation across the continental slope prior to failure. Regionally continuous seismic reflectors show little or no evidence of canyonization beneath the Currituck Slide. A significant volume of intact strata on the lower slope suggests the Currituck region was a primary depocenter for fluvial inputs during multiple sea level lowstands. Failure along bedding planes is evident in outcropping strata along the upper and lower headwalls. Buried scarps beneath these headwalls imply repeated cycles of failure. Folds and faults suggest differential compaction across these scarps may have contributed to the most recent failure. These results suggest high sedimentation and subsequent compaction along a sigmoidal margin were critical components in preconditioning the Currituck Slide for failure. Examination of the regional geological framework illustrates the importance of sediment supply and antecedent slope morphology in the development of large, potentially unstable depocenters along passive margins.

  15. Continental Shelf Embayments of the Eastern Margin of the Philippines; Lamon Bay Stratification & Circulation

    Science.gov (United States)

    2014-09-30

    circulation, stratification and the Shelf-Slope interaction within Lamon Bay of the eastern margin of the Philippines, marking the ’ birth ’ of the...blue ship track) and 24 April - 13 May 2012 (green track). The 2011 CTD stations are shown as blue stars for the 2011 cruise, and as green discs for

  16. Epibenthic megacrustaceans from the continental margin and slope of the Southwestern Gulf of Mexico: factors responsible for variability in species composition and diversity

    Science.gov (United States)

    Gaytan-Caballero, A.; Escobar, E.; Villalobos-Hiriart, J. L.

    2007-05-01

    Specimens collected from trawls on board UNAM's R/V Justo Sierra along 4 years has allowed us to describe the community structure of megacrustaceans collected on the continental margin (45 to 156 m) and upper slope (251 to 705m) in the Mexican Ridges and the Campeche Bank of the southern Gulf of Mexico. The species composition, species richness, density and diversity varied among geographic regions and in the depth gradient. A total of 76 species were identified and grouped in 2 orders, 5 infraorders, 37 families and 53 genera. This study extends the known geographic ranges of the species Homolodromia monstrosa and the proposal of Munida constricta and Munidopsis polita. The largest number of species was recorded in the Mexican Ridges (9+3.16) and on the upper continental shelf (10+3.5); lower values were found on the continental margin. The largest densities were recorded on the continental margin in the Mexican Ridges. Megacrustaceans show in general low frequencies and low abundances, characterizing them as rare components of benthic assemblages. In spite of the great similarity among continental shelf and upper continental slope, two subgroups were recognized reflecting specific habitat and time variation

  17. Carbonate Chemistry Dynamics in an Area of Active Gas Seepage: the Hudson Canyon, US Atlantic Margin

    Science.gov (United States)

    Garcia-Tigreros Kodovska, F.; Kessler, J. D.; Leonte, M.; Chepigin, A.; Kellermann, M. Y.; Arrington, E. C.; Valentine, D. L.

    2015-12-01

    The fate of oceanic methane and its impact on the global climate has been of particular interest to the global community. The potential for vast amounts of methane to be emitted from the seafloor into the atmosphere due to gas hydrate decomposition has been under scientific evaluation. However, despite the great extent of these geological reservoirs, much of the methane released from the seafloor in deep ocean environments does not reach the atmosphere. Once dissolved in ocean water, the emitted methane can be microbially converted to either carbon dioxide or assimilated to biomass. Here, we will present results from a research cruise to the Hudson Canyon, northern US Atlantic Margin, where we investigated changes in ocean water carbonate chemistry induced by the oxidation of methane released from gas seeps. We will be presenting high precision pH data as well as methane and DIC concentrations, natural stable isotopes, and methane oxidation rates collected inside and adjacent to the Hudson Canyon in the summer of 2014.

  18. UK Atlantic Margin Environmental Survey: Introduction and overview of bathyal benthic ecology

    Science.gov (United States)

    Bett, Brian J.

    2001-05-01

    The recent expansion of the Oil and Gas Industry in to the deep waters of the UK Atlantic Frontier prompted the industry and its regulator to reappraise the needs and means of environmental monitoring. In concert, deep-sea academics, specialist contractors, the regulator and the Industry, through the Atlantic Frontier Environmental Network (AFEN), devised and implemented a large-scale environmental survey of the deep waters to the north and west of Scotland. The AFEN-funded survey was carried out during the summers of 1996 and 1998, and involved two steps; an initial sidescan sonar mapping of the survey areas, followed up with direct seabed investigations by coring and photography. This contribution deals with the latter step. Seabed samples were collected to assess sediment type, organic content, heavy metals, hydrocarbons and macrobenthos. Photographic and video observations were employed to provide both 'routine' seabed assessments and to investigate particular sidescan features of note. Although essentially intended as a 'baseline' environmental survey, anthropogenic impacts are already evident throughout the areas surveyed. Indications of the effects of deep-sea trawling were frequently encountered (seabed trawl marks and areas of disturbed sediments), being present in almost all of the areas studied and extending to water depths in excess of 1000 m. Evidence of localised contamination of the seabed by drilling muds was also detected, though background hydrocarbon contamination is predominantly of terrestrial origin or derived from shipping. The benthic ecology of the UK Atlantic Margin is dominated by the marked differences in the hydrography of the Faroe-Shetland Channel (FSC) and the Rockall Trough (RT). Comparatively warm North Atlantic Water is common to both areas; however, in the FSC, cold (subzero) waters occupy the deeper parts of the channel (>600 m). The extreme thermal gradient present on the West Shetland Slope has a substantial influence on the

  19. Ascension Submarine Canyon, California - Evolution of a multi-head canyon system along a strike-slip continental margin

    Science.gov (United States)

    Nagel, D.K.; Mullins, H.T.; Greene, H. Gary

    1986-01-01

    Ascension Submarine Canyon, which lies along the strike-slip (transform) dominated continental margin of central California, consists of two discrete northwestern heads and six less well defined southeastern heads. These eight heads coalesce to form a single submarine canyon near the 2700 m isobath. Detailed seismic stratigraphic data correlated with 19 rock dredge hauls from the walls of the canyon system, suggest that at least one of the two northwestern heads was initially eroded during a Pliocene lowstand of sea level ???3.8 m.y. B.P. Paleogeographic reconstructions indicate that at this time, northwestern Ascension Canyon formed the distal channel of nearby Monterey Canyon and has subsequently been offset by right-lateral, strike-slip faulting along the San Gregorio fault zone. Some of the six southwestern heads of Ascension Canyon may also have been initially eroded as the distal portions of Monterey Canyon during late Pliocene-early Pleistocene sea-level lowstands (???2.8 and 1.75 m.y. B.P.) and subsequently truncated and offset to the northwest. There have also been a minimum of two canyon-cutting episodes within the past 750,000 years, after the entire Ascension Canyon system migrated to the northwest past Monterey Canyon. We attribute these late Pleistocene erosional events to relative lowstands of sea level 750,000 and 18,000 yrs B.P. The late Pleistocene and Holocene evolution of the six southeastern heads also appears to have been controlled by structural uplift of the Ascension-Monterey basement high at the southeastern terminus of the Outer Santa Cruz Basin. We believe that uplift of this basement high sufficiently oversteepened submarine slopes to induce gravitational instability and generate mass movements that resulted in the erosion of the canyon heads. Most significantly, though, our results and interpretations support previous proposals that submarine canyons along strike-slip continental margins can originate by tectonic trunction and lateral

  20. Seismic patterns of the Guerrero-Oaxaca, Mexico region, and its relationship to the continental margin structure

    Science.gov (United States)

    Yamamoto, Jaime; González-Moran, Tomas; Quintanar, Luis; Zavaleta, Ana B.; Zamora, Araceli; Espindola, Victor H.

    2013-01-01

    The main purpose of this paper is to enhance awareness on the seismic evidences that suggest a possible segmentation of the continental margin at the Guerrero-Oaxaca, Mexico region. Data from a recent 7 months survey of microseismicity carried out from 2008 December to 2009 June at Ometepec, Guerrero area, using a portable broad-band digital seismographs network added with data of a previous survey and the aftershocks distribution of the 1982 and 1995 major earthquakes permit to infer the characteristics of the seismic patterns of the Acapulco-Pinotepa Nacional portion of the southern Mexico subduction region. Two different seismic regimens are apparent, one in the Acapulco-Marquelia and the other in the Marquelia-Pinotepa Nacional areas. In the Acapulco-Marquelia portion, the seismicity is broader and dispersed starting at the coast up to 160 km inland approximately. Seismicity in the Marquelia-Pinotepa portion, on the other hand, is narrower and concentrates near the coast. The two seismic regimens are separated by a narrow band or strip of low seismic activity, nearly perpendicular to the coast and trench axis. The apparent low seismicity strip that separates the seismic regimens may trace the position either of a seismically inactive fracture zone or a seismic gap. Moreover, careful observation of the epicentres distribution of the Marquelia-Pinotepa segment reveals two clusters of events separated by another low seismicity strip. Thus, the two observed low activity strips, located near the northern tip of the Ometepec submarine canyon and Punta Maldonado, respectively, are interpreted in this paper as corresponding to disruptions of the continental margin. Other low seismic activity strips probably exist but these two are the most conspicuous. Supplementary information on fault mechanisms available for this area seems to substantiate additionally this interpretation. The observations reported are important to understand the mechanics of the major earthquakes

  1. 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

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

    Science.gov (United States)

    Archer, D.

    2015-05-01

    A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial-interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial-interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil

  3. 77 FR 5560 - Commercial Wind Lease Issuance and Site Assessment Activities on the Atlantic Outer Continental...

    Science.gov (United States)

    2012-02-03

    ... activities (geophysical, geotechnical, archaeological, and biological surveys needed to develop specific... identified these WEAs in a Notice of Intent (NOI) to prepare an EA for Mid-Atlantic WEAs (76 FR 7226). The... published in the Federal Register a NOA of a draft of the EA for Mid-Atlantic WEAs (76 FR 40925)....

  4. Distribution and sources of organic matter in surface sediments of the eastern continental margin of India

    Digital Repository Service at National Institute of Oceanography (India)

    Krishna, M.S.; Naidu, S.A.; Subbaiah, Ch.V.; Sarma, V.V.S.S.; Reddy, N.P.C.

    of the northern and western Gulf of Mexico, the north coast of Alaska and the Niger Delta [Gearing et al., 1977], surface sediments from the Beaufort shelf, Beaufort Sea [Goni et al., 2000], coastal sediments from the Gulf of Trieste, N Adriatic Sea [Ogrinc et... the chemical composition of SOC off the Washington margin [Keil et al. 1994; Prahl et al. 1994], Amazon [Goni, 1997], Bengal fans [Lanord and Derry, 1994], and Gulf of Mexico [Goni et al. 1997]. Other possible reason could be preferential removal of N...

  5. Detrital zircon geochronology of the Cretaceous succession from the Iberian Atlantic Margin: palaeogeographic implications

    Science.gov (United States)

    Dinis, Pedro A.; Dinis, Jorge; Tassinari, Colombo; Carter, Andy; Callapez, Pedro; Morais, Manuel

    2016-04-01

    Detrital zircon U-Pb data performed on eight Cretaceous sandstone samples (819 age isotopic results) from the Lusitanian basin (west Portugal) constrain the history of uplift and palaeodrainage of western Iberia following break-up of Pangaea and opening of the North Atlantic Ocean. We examined the links between shifts in provenance and known basinwide unconformities dated to the late Berriasian, Barremian, late Aptian and Cenomanian-Turonian. The detrital zircon record of sedimentary rocks with wider supplying areas is relatively homogenous, being characterized by a clear predominance of late Palaeozoic ages (c. 375-275 Ma) together with variable proportions of ages in the range c. 800-460 Ma. These two groups of ages are diagnostic of sources within the Variscan Iberian Massif. A few samples also reveal significant amounts of middle Palaeozoic (c. 420-385 Ma) and late Mesoproterozoic to early Neoproterozoic (c. 1.2-0.9 Ga) zircon, which are almost absent in the basement to the east of the Lusitanian basin, but are common in terranes with a Laurussia affinity found in NW Iberia and the conjugate margin (Newfoundland). The Barremian unconformity marks a sudden rise in the proportion of c. 375-275 Ma zircon ages accompanied by a decrease in the abundance of the c. 420-385 Ma and c. 1.2-0.9 Ga ages. This shift in the zircon signature, which is contemporaneous with the separation of the Galicia Bank from Flemish Cap, reflects increased denudation of Variscan crystalline rocks and a reduction in source material from NW Iberia and adjoining areas. The late Aptian unconformity, which represents the largest hiatus in the sedimentary record, is reflected by a shift in late Palaeozoic peak ages from c. 330-310 Ma (widespread in Iberia) to c. 310-290 Ma (more frequent in N Iberia). It is considered that this shift in the age spectra resulted from a westward migration of catchment areas following major uplift in northern Iberia and some transport southward from the Bay of

  6. AHC (Active Heave Compensation) - 800 Drilling on the Atlantic (New Jersey) Margin

    Science.gov (United States)

    Austin, J. A.

    2004-12-01

    The New Jersey continental shelf, an old, stable passive margin, has been a focus of latest Pleistocene-Holocene sea-level studies for decades, because eustasy is a major driving force in the production of the surficial stratigraphic record there. This margin is also geographically proximal to diverse oceanographic resources - laboratories, ports and ships - so hypothesis-testing using a "natural laboratory" approach has been suitable for data acquisition, analysis and interpretation. The Office of Naval Research has taken advantage of this shelf's characteristics to support collection and interpretation of a huge and diverse suite of geophysical data off New Jersey since the late 1980's - MCS profiles at multiple frequencies, deep-towed boomer and chirp profiles, multibeam bathymetry/ backscatter control, and most recently sediment samples using a lake-drilling system owned and operated by Drilling, Observation and Sampling of the Earth's Continental Crust (DOSECC), Inc., modified with active heave compensation for deployment off the Woods Hole Oceanographic Institution research vessel Knorr. The goal is to understand how the diverse interaction of depositional and erosional processes culminates in the preserved stratigraphic record. A first test of the AHC-800 drilling system took place in November 2001 in Block Island Sound off southern New England, with the following results: 1) some success was achieved in sampling mud, 2) fall weather was a limiting factor (heave compensation limits of 2.44 m in 8 s were often exceeded), 3) the vessel's dynamic positioning (DP) system was not always capable of maintaining station in shifting winds; precise navigation (beyond differential GPS) was required, and 4) the need for automated drillpipe handling to increase efficiency was recognized. A second test took place on the New Jersey shelf in September-October 2002, using updated software, automated pipe handling, and differential GPS navigation supplemented by a POS/MV 320

  7. Principles of Geological Mapping of Marine Sediments (with Special Reference to the African Continental Margin). Unesco Reports in Marine Science No. 37.

    Science.gov (United States)

    Lisitzin, Alexandre P.

    Designed to serve as a complement to the Unesco Technical Papers in Marine Science, this report concentrates on theoretical and practical problems of geological mapping of the sea floor. An introduction is given to geological mapping procedures at continental margins as well as some practical recommendations taking as an example the African region…

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

    Digital Repository Service at National Institute of Oceanography (India)

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

    organic geochemistry of Indian margin sediments 6687 Station Depth Lat. Long. DO ∗ %salt Corg TN C / N δ13Corg %(BALA +GABA) %AA-TN DI 3∗∗ Median %Clay %Silt %Sand m ◦ N ◦ E (µM) wt% wt% wt% molar ‰ µm (∅) Upriver SPM∗∗∗ Mandovi nd 15.2650 74.0628 nd nd nd... indices of terrigenous (versus autochthonous/marine) OM inputs are plotted in Fig. 4. These include stable C iso- topic compositions (δ13Corg [‰], Fig. 4a), total lignin phenol yields (3, mg 100 mg−1 Corg; Fig. 4b) and molar organic-C- to-total-N ratios...

  9. Seasonal dynamics of Atlantic herring (Clupea harengus L. populations spawning in the vicinity of marginal habitats.

    Directory of Open Access Journals (Sweden)

    Florian Eggers

    Full Text Available Gillnet sampling and analyses of otolith shape, vertebral count and growth indicated the presence of three putative Atlantic herring (Clupea harengus L. populations mixing together over the spawning season February-June inside and outside an inland brackish water lake (Landvikvannet in southern Norway. Peak spawning of oceanic Norwegian spring spawners and coastal Skagerrak spring spawners occurred in March-April with small proportions of spawners entering the lake. In comparison, spawning of Landvik herring peaked in May-June with high proportions found inside the lake, which could be explained by local adaptations to the environmental conditions and seasonal changes of this marginal habitat. The 1.85 km(2 lake was characterized by oxygen depletion occurring between 2.5 and 5 m depth between March and June. This was followed by changes in salinity from 1-7‰ in the 0-1 m surface layer to levels of 20-25‰ deeper than 10 m. In comparison, outside the 3 km long narrow channel connecting the lake with the neighboring fjord, no anoxic conditions were found. Here salinity in the surface layer increased over the season from 10 to 25‰, whereas deeper than 5 m it was stable at around 35‰. Temperature at 0-5 m depth increased significantly over the season in both habitats, from 7 to 14 °C outside and 5 to 17 °C inside the lake. Despite differences in peak spawning and utilization of the lake habitat between the three putative populations, there was an apparent temporal and spatial overlap in spawning stages suggesting potential interbreeding in accordance with the metapopulation concept.

  10. 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)

  11. Multibeam Mapping of the South Atlantic Bight: Georgia 2005, a Proposed MPA on the Continental Shelf

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NOAA Fisheries laboratory in Panama City, Florida coordinated an acoustic survey at the new proposed Marine Protected Areas in the South Atlantic Bight area June...

  12. Rift Structure along the Eastern Continental Margin of India - new constraints on style of breakup of the Indian landmass from the eastern Gondwanaland

    Science.gov (United States)

    Ismaiel, M.; Krishna, K. S.; Karlapati, S.; Mishra, J.; D, S.

    2015-12-01

    The Eastern Continental Margin of India (ECMI), a classical passive margin has evolved after breakup of the Indian landmass from the East Antarctica during the Early Cretaceous. Anomalous thick sediments and lack of cohesive magnetic signatures in the Bay of Bengal hampered delineation of rift-structure and age assignment for the continental breakup between India and East Antarctica. Further, absence of lithological and geochronological information and a few seismic profiles from the margin led to put forward several competing models for the rift initiation and evolution of the ECMI. Here, we analyze long streamer seismic reflection data and deep-water drill well information from the western Bay of Bengal to infer the buried rift structure, crustal architecture and stratigraphy along the ECMI. Following the structural pattern of the margin, the region is divided into four domains as decoupled, coupled, exhumed and oceanic, which in turn helped us to demarcate the variations in rift structure from south to north along the margin. The southern segment in the vicinity of Cauvery Basin consists of steep continental shelf associated with few major normal faults, which indicates that the segment was evolved as mix shear-rifted margin. The central segment off southern part of the Krishna-Godavari Basin is controlled by a series of fault-bounded half-graben structures and presence of thinned continental crust over the exhumed mantle body, revealing that the segment was formed under hyper-rifting process. While the northern segment extends up to Mahanadi Basin shows relatively less gradient continental slope with a few major faults, suggesting that the segment was evolved by hypo-extended process. Variable crustal architecture lying along the ECMI supports each segment of the margin formed in a specific rift process. A breakup unconformity considered as important geological constraint for completion of rift process between India and East Antarctica is clearly mapped on

  13. The Dauki Fault in NE India: A crustal scale thrust-fold reactivating the continental margin

    Science.gov (United States)

    Ferguson, E. K.; Seeber, L.; Akhter, S. H.; Steckler, M. S.; Biswas, A.; Mukhopadhyay, B. P.

    2011-12-01

    New structural data along the central part of the Dauki topographic front supports the hypothesis that the Shillong Plateau is a highly asymmetric south-verging Quaternary anticline driven by a north-dipping blind thrust fault that projects into Bangladesh, south of the topographic front. This thrust-fold is tectonically more important than it appears from the relatively modest accumulated deformation, and may represent a reorganization of the eastern Himalayan front. The Dauki Fault is the most likely source of the 1897 Great Indian Earthquake and poses a hazard to densely populated areas on the Ganges-Brahmaputra Delta region. The sharp linear topographic feature often mapped as the Dauki fault is instead a contact between competent Eocene limestone and much less competent younger clastic units. This contact may be depositional or locally a secondary back thrust. While the Sylhet basin has been rapidly subsiding in the Late Quaternary, the topographic front is marked by raised and eroded river fanglomerates, thus still on the hangingwall side of the fault. Samples from these raised terraces will be dated using optically stimulated luminescence. The exposed structural relief is primarily accounted for by folding, very broad at the culmination on the "plateau," but much sharper at the southern front. In the central and steepest Cherrapunji segment of the Dauki front, the fold is marked by the erosion resistant Cretaceous-Paleocene passive-margin sequence overlying the Sylhet Traps with evidence that the Cretaceous rifting was parallel to the Dauki front. The Dauki fault, therefore, could be a passive margin-related normal fault reactivated as a thrust. The part of the forelimb exposed in the ~20 km Cherrapunji segment exhibits two sharp kinks, suggesting blind imbricates above the main blind fault. The Shillong Plateau is characterized by a two-level drainage morphology. The well-preserved Precambrian surface and its Cretaceous cover along the southern edge of the

  14. Diverse Approaches USED to Characterize the Earthquake and Tsunami Hazards Along the Southern Alaska Continental Margin

    Science.gov (United States)

    Haeussler, P. J.; Witter, R. C.; Liberty, L. M.; Brothers, D. S.; Briggs, R. W.; Armstrong, P. A.; Freymueller, J. T.; Parsons, T.; Ryan, H. F.; Lee, H. J.; Roland, E. C.

    2014-12-01

    Earthquakes and tsunamis are the principal geohazards of southern Alaska. The entire margin has ruptured in megathrust earthquakes, including the M9.2 1964 event, and these earthquakes have launched deadly local and trans-Pacific tsunamis. Tsunamis have been by far the largest killer in these earthquakes. Moreover, the subduction zone displays a range in locking behavior from completely locked beneath Prince William Sound, to ­­­­nearly freely slipping beneath the Shumagin Islands. Characterizing earthquake-related tsunami sources requires a diverse set of methods, and we discuss several examples. One important source for tsunamis is from megathrust splay faults. The Patton Bay splay fault system ruptured during the 1964 earthquake and generated a tsunami that impacted coastlines tens of minutes after the earthquake. A combination of multibeam mapping, high-resolution and crustal-scale seismic data, thermochronology, and detrital zircon geochronology show focused exhumation along this splay fault system for the last 2-3 Ma. Moreover, this long term pattern of exhumation mimics the pattern of uplift in 1964. Submarine landslides are another example of a tsunami source. Numerous devastating slides were triggered by the 1964 earthquake. Multibeam bathymetry, bathymetry difference maps, high-resolution seismic data, and records of paleotsunamis in coastal marshes reveal a long history of submarine landsliding in the coastal fjords of Alaska. The Little Ice Age appears to have had a significant influence on the submarine landslides in the 1964 earthquake through increased sediment production, transport to fjord margins, and, locally, compaction by glacier advances. Glacial retreat before 1964 gave rise to over-steepened slopes susceptible to dynamic failure. Numerous blocks in the submarine landslides were particularly effective in generating high tsunami run up. Finally, regional tectonic displacements of the seafloor have launched trans-Pacific tsunamis. Coastal

  15. Satellite-Based Investigations of the Transition from an Oceanic to Continental Transform Margin

    Science.gov (United States)

    Miller, M. Meghan

    1998-01-01

    Detailed characterization of neotectonics evolution of the Valle de San Felipe and Arroyo Grande regions in northern Baja California. Reoccupied GEOMEX GPS sites, and occupied a regional GPS (Global Positioning System) network. The Baja California peninsula in Mexico offers a unique setting for studying the kinematic evolution of a complex, active strike-slip/rift plate boundary. We are currently conducting remote sensing, geologic, and geodetic studies of this boundary. The combined data sets will yield instantaneous and time integrated views of its evolution. This proposal solicits renewed funding from NASA to support remote sensing and geologic studies. During the late Cenozoic, Baja California has been the locus of changing fault geometry that has accommodated components of the relative motion between the North America and Pacific plates. Contemporary slip between the two plates occurs in a broad zone that encompasses much of southern California and the Baja California Peninsula. The transfer of slip across this zone in southern California is relatively well understood. South of the border, the geometry and role of specific faults and structural provinces in transferring plate margin deformation across the peninsula is enigmatic. Results We use Landsat Thematic Mapper imagery of the Baja California Peninsula to identify recent and active faults, and then conduct field studies that characterize the temporal and spatial structural evolution of the plate margin. These data address questions concerning the neotectonic development of the Gulf of California, the Baja California Peninsula, and their role in evolution of the post-Miocene Pacific - North American plate boundary. Moreover, these studies provide constraints on the geometry of active faults, allowing more exact understanding of the results of ongoing NASA-supported geodetic experiments. In addition, anticipated publication of the TM scenes will provide a widely available geological data base for relatively

  16. Stretching characteristics and its dynamic significance of the northern continental margin of South China Sea

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of South China Sea with data such as whole crustal thickness, depth of Cenozoic sedimentary basement and the horizontal displacement of faults. An isometric line drawing on whole crustal stretching factor is then obtained. Along the seismic Line 1530 in Baiyun sag, we also calculated the stretching factors of the upper and lower crust. The results suggest that the whole crustal thickness decreases seaward while the whole crustal stretching factor increases from shelf to slope. The Moho upwells highest beneath where the crust is thinned most. The value of the whole crustal stretching factor ranges from 1.5 to 6. Two areas were thinned intensely: the center of Yinggehai Basin, and the Baiyun sag in the Pearl River Mouth Basin. The calculation of the upper and lower crustal stretching factors from DSP1530 in Baiyun sag shows that the original crust of Baiyun sag should be thinned before deformation. Its pre-Cenozoic evolution as well as tectonic position during Cenozoic might be responsible for that.

  17. Methane Hydrate and Gas In The Continental Margin of West Svalbard - Preliminary Results of The Hydratech Project

    Science.gov (United States)

    Westbrook, G. K.; Hydratech Consortium

    In July 2001, two sites in the continental margin west of Svalbard were the subject of seismic investigation as part of the EC-FP5-EESD project HYDRATECH - Tech- niques for the Quantification of Methane Hydrate in European Continental Margins. The northern of the two sites, is underlain by a bottom-simulating reflector (BSR), be- lieved to mark the downward transition from sediment containing hydrate to sediment containing free gas [Posewang &Mienert, Geo-Marine Letters, 19, 150-156, 1999]. At the southern site, bright spots, associated with a decrease in seismic velocity, occur above active mud diapirs that intrude a local basin near the foot of the continental margin. At each site, an array of 20 four-component OBS at 400-m spacing was de- ployed at the centre of a grid of seismic lines shot with 200-m line spacing and a 20-m shot spacing. The seismic source comprised two 0.65-litre sleeve guns, and single- channel reflection profiles were recorded along each shot line. At the northern site, a BSR is seen in most of the reflection profiles, at a depth of about 250 ms below the sea bed. It has opposite polarity to the seabed reflector, and obliquely cuts across the reflectors related to bedding, which show increased amplitude and lower frequency content beneath the BSR. Some of these reflectors show a change in polarity where they cross the BSR. Generally, the BSR is a reflector that exists independently of the other reflectors, at the scale of the seismic resolution of the profiles, although in parts of the profiles the hydrate/gas transition is only evident from the change in amplitude of the bedding reflectors. A preliminary inversion of the travel-time data recorded by one OBS from one shot line shows that P-wave velocity increases steadily with depth to 1800 m/s at the BSR, at a depth of 205 m, beneath which the velocity decreases rapidly to about 1460 m/s. This zone of low velocity, about 50-m thick, beneath the BSR is interpreted to be caused by the

  18. 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

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

    Science.gov (United States)

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

    2017-01-01

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

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

    Science.gov (United States)

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

    2006-12-01

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

  1. Gravity anomalies, crustal structure and rift tectonics at the Konkan and Kerala basins, western continental margin of India

    Indian Academy of Sciences (India)

    Sheena V Dev; M Radhakrishna; Shyam Chand; C Subrahmanyam

    2012-06-01

    Litho-stratigraphic variation of sedimentary units constructed from seismic sections and gravity anomaly in the Konkan and Kerala basins of the western continental margin of India (WCMI) have been used to model processes such as lithospheric rifting mechanism, its strength, and evolution of flank uplift topography that led to the present-day Western Ghats escarpment. Based on the process-oriented approach, two lithospheric models (necking and magmatic underplating) of evolution of the margin were tested. Both, necking and underplating models suggest an effective elastic thickness (Te) of 5 km and 10 km along Konkan and Kerala basins, respectively and a deep level of necking at 20 km at both basins. Model study suggests that the necking model better explains the observed gravity anomalies in the southern part of the WCMI. A synthesis of these results along with the previously published elastic thickness estimates along the WCMI suggests that a low-to-intermediate strength lithosphere and a deeper level of necking explains the observed flank-uplift opography of the Western Ghats. Process-oriented gravity modeling further suggests that the lateral variations in the lithospheric strength, though not very significant, exist from north to south within a distance of 600 km in the Konkan and Kerala basins along the WCMI at the time of rifting. A comparison with previous Te estimates from coherence analysis along the WCMI indicates that the lithospheric strength did not change appreciably since the time of rifting and it is low both onshore and offshore having a range of 5–15 km.

  2. Oceanographic parameters in continental margin of the State of Ceará (northeastern Brazil) deduced from C and O isotopes in foraminifers.

    Science.gov (United States)

    Marques, Wanessa S; Menor, Eldemar de A; Sial, Alcides N; Manso, Valdir A V; Freire, Satander S

    2007-03-01

    Specimens of Recent foraminifera of Amphistegina radiata, Peneroplis planatus and Globigerinoides ruber, from fifty samples of surface sediments of the continental margin of the State of Ceará, Brazil, have been analyzed for carbon and oxygen isotopes to investigate oceanographic parameters and determine the values of delta18O of the oceanic water. From a comparison between values of delta18O obtained for ocean water using the linear equations by (Craig and Gordon 1965) and the one by Wolff et al. (1998), it became evident that the former yielded a more reliable value (0.2 per thousand SMOW) than the latter. Lower values of delta18O for the ocean water in this continental margin resulted from continental water influence. Values of 18O (-0.3 per thousand to -1.5 per thousand PDB for benthic foraminifera and -0.6 per thousand to -2.4 per thousand PDB for planktic foraminifera), attest to a variation of temperatures of oceanic water masses, in average, between 20 to 22 degrees C in deep water and 24 to 27 degrees C, in surface water. Values of delta13C from +3.2% to -0.2 per thousand PDB (benthic foraminifera) reflect a variation in the apparent oxygen utilization (AOU) in the continental margin and indicate that the environments of bacteriological decomposition of organic matter are not continuous along the investigated area.

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

    Science.gov (United States)

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

    2016-08-01

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

  4. Organic matter quality and supply to deep-water coral/mound systems of the NW European Continental Margin

    Science.gov (United States)

    Kiriakoulakis, K.; Freiwald, A.; Fisher, E.; Wolff, G. A.

    2007-02-01

    Comparison of five deep-water coral (DWC)/mound ecosystems along the European Continental Margin shows that suspended particulate organic matter (sPOM), a potential food source, is lipid rich and of high quality. However, there are differences between the sites. The Darwin and Pelagia Mounds (N. Rockall Trough and N. Porcupine Bank, respectively) have higher proportions of labile particulate lipids (including high proportions of polyunsaturated fatty acids) in the benthic boundary layer than Logachev, Hovland and Belgica Mounds (Rockall Bank, S. Porcupine Bank and Porcupine Seabight, respectively). The high quality sPOM could be transported downslope from the euphotic zone. There is some evidence for inter-annual variability at some sites (e.g. Hovland and Logachev Mounds) as large differences in suspended lipid and particulate organic carbon concentrations were observed over the sampling period. Elevated total organic carbon contents of sediments at mound sites, relative to control sites in some cases (particularly Darwin Mounds), probably reflect local hydrodynamic control and the trapping of sPOM by the DWC. Fresh POM can be relatively rapidly transferred to significant depth (up to 8 cm) through bioturbation that is evident at all sites. There is no clear evidence of present day hydrocarbon seepage at any of the sites.

  5. Organic matter pools, C turnover and meiofaunal biodiversity in the sediments of the western Spitsbergen deep continental margin, Svalbard Archipelago

    Science.gov (United States)

    Pusceddu, A.; Carugati, L.; Gambi, C.; Mienert, J.; Petani, B.; Sanchez-Vidal, A.; Canals, M.; Heussner, S.; Danovaro, R.

    2016-01-01

    We investigated organic matter (OM) quantity, nutritional quality and degradation rates, as well as abundance and biodiversity of meiofauna and nematodes along the deep continental margin off Spitsbergen, in the Svalbard Archipelago. Sediment samples were collected in July 2010 and 2011 along a bathymetric gradient between 600 m and 2000 m depth, and total mass flux measured at the same depths from July 2010 to July 2011. In both sampling periods sedimentary OM contents and C degradation rates increased significantly with water depth, whereas OM nutritional quality was generally higher at shallower depths, with the unique exception at 600 m depth in 2010. Meiofaunal abundance and biomass (largely dominated by nematodes) showed the highest values at intermediate depths (ca 1500 m) in both sampling periods. The richness of meiofaunal higher taxa and nematode species richness did not vary significantly with water depth in both sampling periods. We suggest here that patterns in OM quantity, C degradation rates, and meiofauna community composition in 2011 were likely influenced by the intensification of the warm West Spitsbergen Current (WSC). We hypothesize that the intensity of the WSC inflow to the Arctic Ocean could have an important role on benthic biodiversity and functioning of deep-sea Arctic ecosystems.

  6. Tectonic isolation of the Levant basin offshore Galilee-Lebanon effects of the Dead Sea fault plate boundary on the Levant continental margin, eastern Mediterranean

    Science.gov (United States)

    Schattner, U.; Ben-Avraham, Z.; Lazar, M.; Hüebscher, C.

    2006-11-01

    The continental margin of the central Levant, offshore northern Israel and southern Lebanon is characterized by a sharp continental-oceanic crustal transition, exhibited on the bathymetry as a steep continental slope. At the base of the slope a narrow zone of faulting deforms the upper Messinian-recent sedimentary sequence. Further into the basin no major deformations are observed. However, onland a restraining bend along the Dead Sea fault plate boundary results in the formation of the Lebanon and anti-Lebanon mountain ranges, which exhibit a large positive isostatic anomaly not compensated at depth. All these geologic features follow a NNE-SSW trend. A dense network of multi-channel and single-channel seismic profiles, covering 5000 km of ship-track offshore northern Israel and southern Lebanon, was analyzed for the purpose of characterizing the continental margin. Additional seismic surveys covering the area between the Levant margin and the Cyprean arc were examined. Data were then incorporated with magnetic, gravity and earthquake measurements to reveal the deep crustal structure of the area and integrated with bathymetry data to describe the behavior of the young sedimentary basin fill. Results indicate that the Levant basin, offshore northern Israel and southern Lebanon (up to Beirut) is more-or-less unaffected by the intense tectonic deformation occurring onland. The transition between the deformed area onland and the undeformed Levant basin occurs along the base of the continental slope. Along the base, the upper Messinian-recent sedimentary sequence is cut by two sets of faults: shallow growth faults resulting from salt tectonics and high angle faults, marking the surface expression of a deeper crustal discontinuity - the marine extension of the Carmel fault zone. The central Levant continental margin is being reactivated by transpressional faulting of the marine continuation of the Carmel fault, at the base of the continental slope. This fault system

  7. Two- and three-dimensional gravity modeling along western continental margin and intraplate Narmada-Tapti rifts: Its relevance to Deccan flood basalt volcanism

    Indian Academy of Sciences (India)

    Somdev Bhattacharji; Rajesh Sharma; Nilanjan Chatterjee

    2004-12-01

    The western continental margin and the intraplate Narmada-Tapti rifts are primarily covered by Deccan flood basalts. 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 an approximate depth of 6.0 ± 0.6km, and its average density is 2935 kg/m3. Calculated dimension of the high density body in the upper crust is 300 ± 30km in length and 25 ± 2.5 to 40 ± 4 km in width. Three-dimensional gravity modeling of +10 mgal to −30 mgal Bouguer gravity highs along the intraplate Narmada-Tapti rift indicates the presence of eight small isolated high density mafic bodies with an average density of 2961 kg/m3. These mafic bodies are convex upward and their top surface is estimated at an average depth of 6.5 ± 0.6 (between 6 and 8 km). These isolated mafic bodies have an average length of 23.8 ± 2.4 km and width of 15.9 ± 1.5 km. Estimated average thickness of these mafic bodies is 12.4 ± 1.2 km. The difference in shape, length and width of these high density mafic bodies along the 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 large, ellipsoidal high density mafic bodies along the western continental margin and small, isolated mafic bodies along the Narmada-Tapti rift are related to lineamentreactivation and subsequent rifting due to interaction of hot mantle plume with the lithospheric weaknesses (lineaments) along the path of Indian plate motion over the R´eunion hotspot. Mafic bodies formed in the upper lithosphere as

  8. 78 FR 8190 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    Science.gov (United States)

    2013-02-05

    ... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF THE INTERIOR Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the Atlantic... Notice of Intent to Prepare an Environmental Assessment (EA) for Commercial Wind Leasing and...

  9. 77 FR 74218 - Commercial Wind Leasing and Site Assessment Activities on the Atlantic Outer Continental Shelf...

    Science.gov (United States)

    2012-12-13

    ... Bureau of Ocean Energy Management Commercial Wind Leasing and Site Assessment Activities on the Atlantic... suitable for wind energy leasing on the OCS, known as Wind Energy Areas (WEAs) and to obtain public and... these areas to achieve an efficient and responsible renewable energy leasing process. More...

  10. Imperfections of the North-Atlantic wind-driven ocean circulation: continental geometry and windstress shape

    NARCIS (Netherlands)

    Dijkstra, H.A.; Molemaker, M.J.

    2001-01-01

    Multiple equilibria of the wind-driven gyres have been found in idealized quasi- geostrophic and shallow water models.In this paper we demonstrate that multiple equilibria persist within a reduced gravity shallow water model under quite realis- tic continental geometry and windstress orcing for the

  11. Effects of energy-related activities on the Atlantic Continental Shelf

    Energy Technology Data Exchange (ETDEWEB)

    Manowitz, B [ed.

    1975-01-01

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

  12. EC_250M_AEA_NAD27.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar composite mosaic (ACEA, 250 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  13. EC_Q09.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (9 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  14. EC_Q01.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (1 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  15. EC_Q08.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (8 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  16. EC_Q13.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (13 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  17. EC_Q06.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (6 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  18. EC_Q02.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (2 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  19. EC_Q07.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (7 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  20. EC_Q05.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (5 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  1. EC_Q10.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (10 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  2. EC_Q17.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (17 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  3. EC_Q21.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (21 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  4. EC_Q23.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (23 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  5. EC_Q22.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (22 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  6. EC_Q19.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (19 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  7. EC_Q12.TIF - U.S. Atlantic East Coast EEZ GLORIA sidescan-sonar data mosaic (12 of 23) (ACEA, 50 m, Clarke1866)

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — From February to May 1987 the U.S. Geological Survey (USGS) conducted five cruises to cover the U.S. Atlantic Continental Margin Exclusive Economic Zone (EEZ)...

  8. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic.

    Science.gov (United States)

    Døssing, Arne; Japsen, Peter; Watts, Anthony; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans

    2016-04-01

    Tectonic models predict that, following breakup, rift margins undergo only decaying thermal subsidence during their post-rift evolution. However, post-breakup stratigraphy beneath the NE Atlantic shelves shows evidence of regional-scale unconformities, commonly cited as outer margin responses to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone - East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic unconformity (IMU), which marks the termination of syn-rift deposition in the deep-sea basins and onset of: (i) thermo-mechanical coupling across the GFZ, (ii) basin compression, and (iii) contourite deposition, north of the EGR. The onset of coupling across the GFZ is constrained by results of 2-D flexural backstripping. We explain the thermo-mechanical coupling and the deposition of contourites by the formation of a continuous plate boundary along the Mohns and Knipovich ridges, leading to an accelerated widening of the Fram Strait. We demonstrate that the IMU event is linked to onset of uplift and massive shelf-progradation on the NE Greenland margin. Given an estimated middle-to-late Miocene (~15-10 Ma) age of the IMU, we speculate that the event is synchronous with uplift of the East and West Greenland margins. The correlation between margin uplift and plate-motion changes further indicates that the uplift was triggered by plate tectonic forces, induced perhaps by a change in the Iceland plume (a hot pulse) and/or by changes in intra-plate stresses related to global tectonics.

  9. Modeling Cape- and Ridge-Associated Marine Sand Deposits; A Focus on the U.S. Atlantic Continental Shelf

    Science.gov (United States)

    Bliss, James D.; Williams, S. Jeffress; Bolm, Karen S.

    2009-01-01

    Cape- and ridge-associated marine sand deposits, which accumulate on storm-dominated continental shelves that are undergoing Holocene marine transgression, are particularly notable in a segment of the U.S. Atlantic Continental Shelf that extends southward from the east tip of Long Island, N.Y., and eastward from Cape May at the south end of the New Jersey shoreline. These sand deposits commonly contain sand suitable for shore protection in the form of beach nourishment. Increasing demand for marine sand raises questions about both short- and long-term potential supply and the sustainability of beach nourishment with the prospects of accelerating sea-level rise and increasing storm activity. To address these important issues, quantitative assessments of the volume of marine sand resources are needed. Currently, the U.S. Geological Survey is undertaking these assessments through its national Marine Aggregates and Resources Program (URL http://woodshole.er.usgs.gov/project-pages/aggregates/). In this chapter, we present a hypothetical example of a quantitative assessment of cape-and ridge-associated marine sand deposits in the study area, using proven tools of mineral-resource assessment. Applying these tools requires new models that summarize essential data on the quantity and quality of these deposits. Two representative types of model are descriptive models, which consist of a narrative that allows for a consistent recognition of cape-and ridge-associated marine sand deposits, and quantitative models, which consist of empirical statistical distributions that describe significant deposit characteristics, such as volume and grain-size distribution. Variables of the marine sand deposits considered for quantitative modeling in this study include area, thickness, mean grain size, grain sorting, volume, proportion of sand-dominated facies, and spatial density, of which spatial density is particularly helpful in estimating the number of undiscovered deposits within an

  10. Record of a Mid-Pleistocene depositional anomaly in West Antarctic continental margin sediments: an indicator for ice-sheet collapse?

    Science.gov (United States)

    Hillenbrand, C.-D.; Kuhn, G.; Frederichs, T.

    2009-06-01

    Modern global warming is likely to cause future melting of Earth's polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5-6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial-interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424-374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial-interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15-MIS 13 (621-478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15-MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15-MIS 13. Some of these

  11. Exploration of the canyon-incised continental margin of the northeastern United States reveals dynamic habitats and diverse communities

    Science.gov (United States)

    Quattrini, Andrea; Nizinski, Martha S.; Chaytor, Jason; Demopoulos, Amanda; Roark, E. Brendan; France, Scott; Moore, Jon A.; Heyl, Taylor P.; Auster, Peter J.; Ruppel, Carolyn; Elliott, Kelley P.; Kennedy, Brian R.C.; Lobecker, Elizabeth A.; Skarke, Adam; Shank, Timothy M.

    2015-01-01

    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 melanotrichosand 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 initial

  12. 350 ka organic 13C record of the monsoon variability on the Oman continental margin, ArabianSea

    Indian Academy of Sciences (India)

    Alfred N N Muzuka

    2000-12-01

    The stable isotope compositions of sedimentary organic carbon and content of organic carbon for sediment cores recovered at two sites (sites 724C and 725C) during Ocean Drilling Program (ODP) Leg. 117 on the Oman continental margin are used to document variability of the monsoon winds for the past 350 ka. Although both sites have a mean 13C value of -20.1%, three zones depleted in 13C are observable at site 724C during isotope stages 3, 8 and 10, while only one zone is recognizable at site 725C. Increased coastal upwelling during isotope stage 3 owing to intense SW monsoon winds resulted in higher concentration of CO2 in the water column causing the formation of organic matter that was depleted in 13C. The other two zones deposited during oxygen isotope stages 8 and 10, which are also characterized by low values of organic carbon, nitrogen and C/N ratios, could be attributed to the dilution by terrestrial material derived from paleosol by transported by northwesterlies. Because of utilization of 13C enriched dissolved CO2 during the last glacial maximum Holocene sedimentary organic materials are depleted in 13C relative to the the fomer. The content of residues organic carbon (ROC) is higher at site 724C (with an average of 2.3 ± 1.2%) relative to site 725C, which averages to 0.9 ± 0.4% probably because of differences in the degree of preservation. Organic material deposited at site 725C has undergone more degradation relative to site 724C as reflected by a systematic downcore decrease in 13C resulting from a loss of 13C enriched organic compounds. Owing to lack of good chronology at site 725C, a zone that is characterized by low 13C values it could not be correlated with the other three zones observed at Site 724C.

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

    Science.gov (United States)

    Quattrini, Andrea M; Nizinski, Martha S; Chaytor, Jason D; Demopoulos, Amanda W J; Roark, E Brendan; France, Scott C; Moore, Jon A; Heyl, Taylor; Auster, Peter J; Kinlan, Brian; Ruppel, Carolyn; Elliott, Kelley P; Kennedy, Brian R C; Lobecker, Elizabeth; Skarke, Adam; Shank, Timothy M

    2015-01-01

    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 initial exploration

  14. The Lamu Basin deepwater fold-and-thrust belt: An example of a margin-scale, gravity-driven thrust belt along the continental passive margin of East Africa

    Science.gov (United States)

    Cruciani, Francesco; Barchi, Massimiliano R.

    2016-03-01

    In recent decades, advances in seismic processing and acquisition of new data sets have revealed the presence of many deepwater fold-and-thrust belts (DW-FTBs), often developing along continental passive margins. These kinds of tectonic features have been intensively studied, due to their substantial interest. This work presents a regional-scale study of the poorly explored Lamu Basin DW-FTB, a margin-scale, gravity-driven system extending for more than 450 km along the continental passive margin of Kenya and southern Somalia (East Africa). A 2-D seismic data set was analyzed, consisting of both recently acquired high-quality data and old reprocessed seismic profiles, for the first detailed structural and stratigraphic interpretation of this DW-FTB. The system originated over an Early to mid-Cretaceous shale detachment due to a mainly gravity-spreading mechanism. Analysis of synkinematic strata indicates that the DW-FTB was active from the Late Cretaceous to the Early Miocene, but almost all of the deformation occurred before the Late Paleocene. The fold-and-thrust system displays a marked N-S variation in width, the northern portion being more than 150 km wide and the southern portion only a few dozen kilometers wide; this along-strike variation is thought to be related to the complex tectonosedimentary evolution of the continental margin at the Somalia-Kenya boundary, also reflected in the present-day bathymetry. Locally, a series of volcanic edifices stopped the basinward propagation of the DW-FTB. A landward change in the dominant structural style, from asymmetric imbricate thrust sheets to pseudo-symmetric detachment folds, is generally observed, related to the landward thickening of the detached shales.

  15. 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.

  16. Episodes of subsidence and uplift of the conjugate margins of Greenland and Norway after opening of the NE Atlantic

    Science.gov (United States)

    Japsen, Peter; Green, Paul F.; Bonow, Johan M.; Chalmers, James A.

    2016-04-01

    We have undertaken a regional study of the thermo-tectonic development of East Greenland (68-75°N; Bonow et al. 2014; Japsen et al. 2014) and of southern Norway (58-64°N) based on integration of apatite fission-track analysis (AFTA), stratigraphic landscape analysis and the geological record onshore and offshore. Volcanic and sedimentary rocks accumulated on the subsiding, East Greenland margin during and following breakup and then began to be exhumed during late Eocene uplift that preceded a major, early Oligocene plate reorganization in the NE Atlantic. The Norwegian margin also experienced Eocene subsidence and burial; there are hemipelagic, deep-marine sediments of Eocene age along the coast of southern Norway. End-Eocene uplift of the NW European margin led to the formation of a major unconformity along the entire margin and to progradation of clastic wedges from Norway towards the south. Our AFTA data from East Greenland and southern Norway reveal a long history of Mesozoic burial and exhumation across the region, with a number of broadly synchronous events being recorded on both margins. AFTA data from East Greenland show clear evidence for uplift at the Eocene-Oligocene transition whereas the data from Norway do not resolve any effects of exhumation related to this event. AFTA data from the East Greenland margin show evidence of two Neogene events of uplift and incision of the in the late Miocene and Pliocene whereas results from southern Norway define Neogene uplift and erosion which began in the early Miocene. A Pliocene uplift phase in southern Norway is evident from the stratigraphic landscape analysis and from the sedimentary sequences offshore. In East Greenland, a late Eocene phase of uplift led to formation of a regional erosion surface near sea level (the Upper Planation Surface, UPS). Uplift of the UPS in the late Miocene led to formation of the Lower Planation Surface (LPS) by incision below the uplifted UPS, and a Pliocene phase led to

  17. DEPSCoR FY 99: 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

    Science.gov (United States)

    2016-06-13

    Distribution of Acoustic and Geotechnical Property Variability in Near Surface Sediments on the East China Sea Continental Margin Louis R. Bartek Department of...East China Sea Continental Margin 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER...collecting data. During survey 221099 in the East China Sea (ECS) and the Yellow Sea (YS) we collected 191 km of 210 cubic inch Generator Injector Air

  18. 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

  19. Distribution, migration and derivation of Mesozoic-Cenozoic regional fault systems in the central continental margin of eastern China

    Institute of Scientific and Technical Information of China (English)

    SUN Xiaomeng; HAO Fujiang; BIAN Weihua; GAO Yi; BAO Yafan

    2007-01-01

    Deep-large faults in the central continental margin of eastern China are well developed. Based on the regularity of spatial and temporal distribution of the faults,four fault systems were divided: the Yanshan orogenic belt fault system, the Qinling-Dabie-Sulu orogenic belt fault system, the Tanlu fault system and the East China Sea shelfbasin-Okinawa trough fault system. The four fault systems exhibit different migration behaviors. The Yanshan orogenic belt fault system deflected from an EW to a NE direction,then to a NNE direction during the Indo-Chinese epoch-Yanshanian epoch. The thrust-nappe strength of the Qinling-Dabie orogenic belt fault system showed the tendency that the strength was greater in the south and east, but weaker in the north and west. This fault system faulted in the east and folded in the west from the Indo-Chinese epoch to the early Yanshanian epoch. At the same time, the faults also had a diachronous migration from east to west from the Indo-Chinese epoch to the early Yanshanian epoch. On the con-trary, the thrust-nappe strength was greater in the north and west, weaker in the south and east during the late Yanshanian epoch-early Himalayan epoch. The Tanlu fault system caused the basin to migrate from west to east and south to north. The migration regularity of the East China Sea shelf basin-Okinawa trough fault system shows that the for mation age became younger in the west. The four fault systems and their migration regularities were respectively the results of four different geodynamic backgrounds. The Yanshan orogenicbelt fault system derived from the intracontinental orogeny.The Qinling-Dabie-Sulu orogenic belt fault system derived from the collision of plates and intracontinental subduction.The Tanlu fault system derived from the strike-slip movement and the East China Sea shelf basin-Okinawa trough fault system derived from plate subduction and retreat of the subduction belt.

  20. Precambrian crustal evolution and Cretaceous–Palaeogene faulting in West Greenland: Evolution of Neoarchaean supracrustal belts at the northern margin of the North Atlantic Craton, West Greenland

    Directory of Open Access Journals (Sweden)

    Stensgaard, Bo Møller

    2006-12-01

    Neoarchaean environments proximal to and on a continental plate, and were amalgamated in a convergent margin setting shortly after their deposition.

  1. 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.

  2. Crustal structure and magnetic lineation along two geo-traverses from western continental margin of India to Eastern Somali Basin, NW Indian Ocean

    Science.gov (United States)

    Chaubey, A. K.; Anshu, A.; Sreejith, K.; Pandey, A.

    2012-12-01

    Shipborne gravity and magnetic data along two parallel geo-traverses spanning from western continental margin of India to off Seychelles are used to delineate crustal structure and magnetic pattern of major structural features - western continental margin of India, Laxmi Basin, Laxmi Ridge, Arabian Basin, slow spreading Carlsberg Ridge and Eastern Somali Basin. The seismically constrained gravity models along the geo-traverses suggest considerable variation in crustal thickness - about 38 km on continental shelf of western India to about 4 km of the Eastern Somali Basin. The Eastern Somali Basin is characterized by thin oceanic crustal thickness (~3 to 4 km) as compared to its conjugate Arabian Basin where thickness varies from 5 to 6 km. The magnetic anomalies along the geo-traverse reveal three distinct zones: (i) a zone of relative high frequency short wavelength younger anomalies over the axial parts of the Carlsberg Ridge, (ii) a zone of well developed Early Tertiary magnetic anomalies in both the Arabian and Eastern Somali basins, and (iii) relative magnetic quiet zone, between the above two zones, representing a hiatus in spreading. Based on the results, we present a comparative analysis of crustal configuration and magnetic pattern of major structural features of the study area and discuss its tectonic evolution.

  3. The Eocene-Oligocene sedimentary record in the Chesapeake Bay impact structure: Implications for climate and sea-level changes on the western Atlantic margin

    Science.gov (United States)

    Schulte, P.; Wade, B.S.; Kontny, A.; ,

    2009-01-01

    A multidisciplinary investigation of the Eocene-Oligocene transition in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville core from the Chesapeake Bay impact basin was conducted in order to document environmental changes and sequence stratigraphic setting. Planktonic foraminifera and calcareous nannofossil biostratigraphy indicate that the Eyreville core includes an expanded upper Eocene (Biozones E15 to E16 and NP19/20 to NP21, respectively) and a condensed Oligocene-Miocene (NP24-NN1) sedimentary sequence. The Eocene-Oligocene contact corresponds to a =3-Ma-long hiatus. Eocene- Oligocene sedimentation is dominated by great diversity and varying amounts of detrital and authigenic minerals. Four sedimentary intervals are identified by lithology and mineral content: (1) A 30-m-thick, smectite- and illite-rich interval directly overlies the Exmore Formation, suggesting long-term reworking of impact debris within the Chesapeake Bay impact structure. (2) Subsequently, an increase in kaolinite content suggests erosion from soils developed during late Eocene warm and humid climate in agreement with data derived from other Atlantic sites. However, the kaolinite increase may also be explained by change to a predominant sediment input from outside the Chesapeake Bay impact structure caused by progradation of more proximal facies belts during the highstand systems tract of the late Eocene sequence E10.Spectral analysis based on gamma-ray and magnetic susceptibility logs suggests infl uence of 1.2 Ma low-amplitude oscillation of the obliquity period during the late Eocene. (3) During the latest Eocene (Biozones NP21 and E16), several lithological contacts (clay to clayey silt) occur concomitant with a prominent change in the mineralogical composition with illite as a major component: This lithological change starts close to the Biozone NP19/20-NP21 boundary and may correspond to sequence boundary E10-E11 as observed in

  4. Authigenic P formation and reactive P burial in sediments of the Nazaré canyon on the Iberian margin (NE Atlantic)

    NARCIS (Netherlands)

    Zee, C. van der; Slomp, C.P.; Raaphorst, W. van

    2002-01-01

    Profiles of different forms of sedimentary phosphorus were measured at four sites at the Iberian margin (NE Atlantic), which were chosen on the basis of differences in depositional environment: a shelf site (113 m), a mid-slope station (1387 m) and two stations at the head (396 m) and base (3097 m)

  5. 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

  6. 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...

  7. 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...

  8. 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...

  9. Cold water corals of the Northeast Atlantic margin: Archives of intermediate water circulation during the Holocene

    Science.gov (United States)

    Frank, N.; Paterne, M.; Ayliffe, L.; Lutringer, A.; Blamart, D.; van Weering, T.

    2003-04-01

    We present combined 230Th/U and 14C dating and stable isotope analyses on benthic corals from the northeastern North Atlantic in order to investigate past changes of the thermohaline circulation. The reef forming cold water corals Lophelia pertusa and Madrepora oculata were raised from intermediate depth (˜750m bsl) from carbonate mounds along Rockall and Porcupine Bank and Porcupine Seabight.The 230Th/U ages range from today to 247,400yr. The δ234U, 230Th/232Th, and X-ray images indicate negligible alteration of the investigated corals, i.e. open system behavior. Very young deep-sea corals were accurately dated by means of 230Th/U dating. One in-situ living Lophelia coral yielded a mean age of 1995AD, matching the date of collection in 1999AD. From this coral, the measured and calculated seawater Δ14C values are indistinguishable, and the reservoir age Rinterm of the upper intermediate waters is 710±80 years. Several modern corals, being dated between 1950AD and 1986AD, recorded the atmospheric 14C/12C increase due to the nuclear tests in the early 60s. The modern pre-bomb Δ14C value of the North Atlantic intermediate waters was determined at an average of -65±7o/oo, and the mean reservoir age at 500±50 years. Finally, several investigated benthic coral grew during the second step of the deglaciation and during the Holocene climate optimum (from 10,900 to about 8,000 CAL yr BP). The reservoir age of average 530±65 years is equivalent to that of today indicating that, during the studied coral growth episodes, a modern type oceanic circulation, as well as the air-sea and surface to deeper adjacent water 14CO2 exchanges prevailed in the Northeast Atlantic Ocean.

  10. Prolonged post-rift magmatism on highly extended crust of divergent continental margins (Baiyun Sag, South China Sea)

    Science.gov (United States)

    Zhao, Fang; Alves, Tiago M.; Wu, Shiguo; Li, Wei; Huuse, Mads; Mi, Lijun; Sun, Qiliang; Ma, Benjun

    2016-07-01

    Three-dimensional (3D) seismic, borehole and geochemical data reveal a prolonged phase of post-rift magmatism on highly extended crust of the Baiyun Sag, South China Sea. Two volcanic complexes are identified and described in the context of continental rifting and diachronous continental breakup of the South China Sea. Biostratigraphic data from exploration wells BY7-1 and BY2, complemented by K-Ar datings from core samples, confirm that magmatic activity in the Baiyun Sag occurred in two main stages: (1) a first episode at the base of the Miocene (23.8 Ma); and (2) a second episode occurring at the end of the Early Miocene (17.6 Ma). The relative location of volcanic complexes in the Baiyun Sag, and their stratigraphic position, reveals prolonged magmatism inboard of the ocean-continent transition zone during continental breakup. We suggest that magmatism in the Baiyun Sag reflects progressive continental breakup in the South China Sea, with the last volcanic episode marking the end of a breakup sequence representing the early post-rift tectonic events associated with the continental breakup process. Seismic and borehole data from this breakup sequence records diachronous magma emplacement and complex changes in depositional environments during continental breakup.

  11. 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.

  12. Spatiotemporal SNP analysis reveals pronounced biocomplexity at the northern range margin of Atlantic cod Gadus morhua

    DEFF Research Database (Denmark)

    Therkildsen, Nina Overgaard; Hansen, Jakob Hemmer; Hedeholm, R.B.;

    2013-01-01

    Accurate prediction of species distribution shifts in the face of climate change requires a sound understanding of population diversity and local adaptations. Previous modeling has suggested that global warming will lead to increased abundance of Atlantic cod (Gadus morhua) in the ocean around...... Greenland, but the dynamics of earlier abundance fluctuations are not well understood. We applied a retrospective spatiotemporal population genomics approach to examine the temporal stability of cod population structure in this region and to search for signatures of divergent selection over a 78-year period...

  13. {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.

  14. Continental Arc Magmatism and its Abrupt Termination by Ridge Subduction or Ridge Jump Along the Proto-Pacific Margin of Gondwana, Marie Byrd Land, Antarctica: A Zircon U-Pb Study

    Science.gov (United States)

    Mukasa, S. B.

    2003-12-01

    The Paleozoic and Mesozoic development and subsequent fragmentation of Gondwanaland's Pacific margin is recorded in igneous and metamorphic rocks cropping out in the Marie Byrd Land (MBL) continental block of West Antarctica, recognized on geologic and paleomagnetic grounds to comprise a distinct microplate. Widespread occurrence of metaluminous granitoids dated by the zircon U-Pb method as mid- to late Paleozoic shows that convergence-related magmatism dominated the early evolution of this margin. Dates for granodiorites, monzogranites and granites from the Ruppert and Hobbs Coasts of western MBL reveal a prolonged period of subduction-related calc-alkaline magmatism between at least 320 ñ 3 Ma (age of the oldest granodiorite dated) and 110 ñ1 Ma (the age of the Mt. Prince granite). The latter is intruded by swarms of mafic and intermediate dikes believed to record the onset of rifting that led to separation of the New Zealand microcontinent from MBL. The dikes have been dated by zircon U-Pb at 101 ñ 1 Ma. Thus, the regime along the Ruppert and Hobbs Coasts had shifted from subduction-related to rift-related magmatism within a mere ~9-m.y. period. In the Kohler Range and the Pine Island Bay areas of eastern MBL, the calc-alkaline magmatism did not terminate until 96 ñ 1 Ma, based on U-Pb dating of zircons from one granitoid sample, or 94 ñ 3 Ma based on zircons from another. No continental separation occurred to the east of MBL. The margins of the Thurston Island and Antarctic Peninsula blocks went directly from convergent to inactive. With their zircon U-Pb ages clustering around 100 ñ 2 Ma, dike-free "anorogenic" syenites and quartz syenites along the Ruppert and Hobbs Coasts show that the transition to extensional magmatism was rapid in the west. This is also reflected by the fact that from the onset of rifting at 101 ñ 1 Ma to formation of oceanic crust between MBL and Greater New Zealand (Campbell Plateau, Chatham Rise, North Island and South Island

  15. Tracking the influence of a continental margin on growth of a magmatic arc, Fiordland, New Zealand, using thermobarometry, thermochronology, and zircon U-Pb and Hf isotopes

    Science.gov (United States)

    Scott, J. M.; Cooper, A. F.; Palin, J. M.; Tulloch, A. J.; Kula, J.; Jongens, R.; Spell, T. L.; Pearson, N. J.

    2009-12-01

    Geothermobarometric, radiogenic isotopic and thermochronologic data are used to track the influence of an ancient continental margin (Western Province) on development of an adjacent Carboniferous-Cretaceous magmatic arc (Outboard Median Batholith) in Fiordland, New Zealand. The data show a record of complicated Mesozoic Gondwana margin growth. Paragneiss within the Outboard Median Batholith is of Carboniferous to Jurassic age and records burial to middle crustal depths in Late Jurassic-Early Cretaceous during subduction-related plutonism and arc thickening. In contrast, Western Province metasedimentary rocks in the area of study immediately west of the Outboard Median Batholith are Late Cambrian-Early Ordovician in age, recrystallized at the amphibolite facies in the Late Devonian-Early Carboniferous and exhibit no evidence for Mesozoic textural or isotopic reequilibration. A phase of deformation, between 128 and 116 Ma deformed, exhumed, and cooled the Outboard Median Batholith to greenschist facies temperatures, while large parts of the Western Province underwent ≥9 kbar metamorphic conditions. Zircon grains from Mesozoic inboard plutons are isotopically more evolved (ɛHf(t) = +2.3 to +4.0) than those in the Outboard Median Batholith (ɛHf(t) = +9.4 to +11.1). The contrasting zircon Hf isotope ratios, absence of S-type plutons or Proterozoic-Early Paleozoic inherited zircon, and the apparent absence of Early Paleozoic metasedimentary rocks indicates that the Outboard Median Batholith is unlikely to be underlain by the Western Province continental lithosphere. The new data are consistent with the Outboard Median Batholith representing an allochthonous (although not necessarily exotic) arc that was juxtaposed onto the Gondwana continental margin along the intervening Grebe Mylonite Zone.

  16. A study on the geochemical characteristics of Upper Permian continental marginal arc volcanic rocks in the northern segment of South Lancangjiang Belt

    Institute of Scientific and Technical Information of China (English)

    SHEN Shangyue; FENG Qinglai; WEI Qirong; ZHANG Zhibin; ZHANG Hu

    2006-01-01

    Geochemical characteristics of the Upper Permian ( P2 ) continental marginal arc volcanic rocks are described, which have been found recently around the areas of Xiaodingxi and Zangli on the eastern side of the Yunxian-Lincang granite, in terms of rock assemblage, petrochemistry, REE, trace elements, Pb isotopes, geotectonic environment and so on. The volcanic rock assemblage is dominated by basalt-andesite-dacite, with minor trachyte andecite-trachyte; the volcanic rock series is predominated by the calc-alkaline series, with minor tholleiite series and alkaline series rocks; the volcanic rocks are characterized by high Al2O3 and low TiO2 , with K2O contents showing extremely strong polarity; the REE distribution patterns are characterized by LREE enrichment and right-inclined type; trace elements and large cation elements are highly enriched, Ti and Cr are depleted, and P and Nb are partially depleted; the Pb composition is of the Gondwana type; the petrochemical points mostly fall within the field of island-arc volcanic rocks, in consistency with the projection of data points of continental marginal volcanic rocks in the southern segment of the South Lancangjiang Belt and the North Lancangjiang Belt. This continental marginal arc volcanic rock belt, together with the ocean-ridge and ocean-island volcanic rocks and ophiolites in the Changning-Menglian Belt, constitute the ocean-ridge volcanic rock, ophiolite-arc rock-magmatic rock belts which are distributed in pairs, indicating that the Lancangjiang oceanic crust subducted eastwards. This result is of great importance in constraining the evolution of the paleo-Tethys in the Lancangjiang Belt.

  17. PBDEs in the atmosphere over the Asian marginal seas, and the Indian and Atlantic oceans

    Science.gov (United States)

    Li, Jun; Li, Qilu; Gioia, Rosalinda; Zhang, Yanlin; Zhang, Gan; Li, Xiangdong; Spiro, Baruch; Bhatia, Ravinder S.; Jones, Kevin C.

    2011-12-01

    Air samples were collected from Jan 16 to Mar 14, 2008 onboard the Oceanic II- The Scholar Ship which navigated an east-west transect from Shanghai to Cape Verde, and polybrominated diphenyl ethers (PBDEs) were analyzed in these samples. PBDE concentrations in the atmosphere over the open seas were influenced by proximity to source areas and land, and air mass origins. The concentrations of Σ 21PBDEs over the East and South China Seas, the Bay of Bengal and the Andaman Sea, the Indian Ocean, and the Atlantic Ocean were 10.8 ± 6.13, 3.22 ± 1.57, 5.12 ± 3.56, and 2.87 ± 1.81 pg m -3, respectively. BDE-47 and -99 were the dominant congeners in all the samples, suggesting that the widely used commercial penta-BDE products were the original sources. Over some parts of Atlantic and Indian Ocean, daytime concentrations of BDE-47 and BDE-99 were higher than the concentrations at night. The strong atmospheric variability does not always coincide with a diurnal cycle, but the variability in air concentrations in such remote areas of the ocean remains strong. No significant trends were found for each of PBDE congener with latitude.

  18. Buried Cold-Water Coral Mound Provinces and Contourite Drifts Along the Eastern Atlantic Margin: Controls, Interactions and Connectivity

    Science.gov (United States)

    Van Rooij, D.; Vandorpe, T.; Delivet, S.; Hebbeln, D.; Wienberg, C.; Martins, I.

    2014-12-01

    The association between cold-water coral mounds and contourite drift deposits has been demonstrated in the Belgica mound province, off Ireland. On that location, IODP expedition 307 was able to drill through the base of a mound, dating mound initiation at 2.65 Ma. However, the Belgica mounds are just one of the many expressions of mound growth. More enigmatic is the buried Magellan mound province, located in the northern part of the Porcupine Basin, featuring over 1000 relatively closely spaced buried mounds, which are all rooted on a common reflector. This indicates a common start-up event, but the true driving forces behind their initial settling, growth and demise are still unknown. The influence of bottom currents cannot be ruled out, since clear obstacle marks are present surrounding the mounds. In 2013, some 3000 km south of the Magellan mounds, a new province of buried mounds was discovered along the Moroccan Atlantic Margin, which may shed new light on the "life" cycle of mounds. Here, we report the preliminary results and propose a first view on the controls, interactions and connectivity between these 2 provinces, assisted by a series of studies of contourite drifts along the Eastern Atlantic Margin. The newly discovered buried mounds can be associated to a vast province of several clusters of seabed mounds. They occur in water depths between 500 and 1000 m, buried under up to 50 m of sediment. With respect to the Magellan mounds, they are smaller, but more importantly, they do not root on one single stratigraphic level. At least 4 different initiation levels were identified. The off-mound reflectors indicate a slight influence of bottom currents, since the mounds are located in a large sediment drift. Moreover, the link between the two buried mound provinces may be found in connecting the evolution of the associated contourite drift systems, respectively in Porcupine Seabight and the Gulf of Cádiz. Intermediate sites on Goban Spur and near Le Danois

  19. Instabilities and deformation in the sedimentary cover on the upper slope of the southern Aquitaine continental margin, north of the Capbreton canyon (Bay of Biscay)

    OpenAIRE

    Gonthier, E; Cirac, P.; Faugeres, J; Gaudin, Mathieu; Cremer, M; Bourillet, Jean-francois

    2006-01-01

    Acoustic and core data have recently been collected on the shelf break and the upper part of the slope of the south Aquitaine continental margin. They reveal the major role played by mass-flow gravity processes in deposit erosion and redistribution, modelling of the sea-bed, and transfer of sediment toward the deep-sea. The study region is bounded in the south by the Capbreton canyon. The northern area, which shows a smooth morphology, is characterised by small-scale deformations due to sedim...

  20. Winter- and summertime continental influences on tropospheric O3 and CO observed by TES over the western North Atlantic Ocean

    Directory of Open Access Journals (Sweden)

    R. Talbot

    2010-04-01

    Full Text Available The distributions of tropospheric ozone (O3 and carbon monoxide (CO, and the synoptic factors regulating these distributions over the western North Atlantic Ocean during winter and summer were investigated using profile retrievals from the Tropospheric Emission Spectrometer (TES for 2004–2006. Seasonal composites of TES retrievals, reprocessed to remove the influence of the a priori on geographical and seasonal structure, exhibited strong seasonal differences. At the 681 hPa level during winter months of December, January and February (DJF the composite O3 mixing ratios were uniformly low (~45 ppbv, but continental export was evident in a channel of enhanced CO (100–110 ppbv flowing eastward from the US coast. In summer months June, July, and August (JJA O3 mixing ratios were variable (45–65 ppbv and generally higher due to increased photochemical production. The summer distribution also featured a channel of enhanced CO (95–105 ppbv flowing northeastward around an anticyclone and exiting the continent over the Canadian Maritimes around 50° N. Offshore O3-CO slopes were generally 0.15–0.20 mol mol−1 in JJA, indicative of photochemical O3 production. Composites for 4 predominant synoptic patterns or map types in DJF suggested that export to the lower free troposphere (681 hPa level was enhanced by the warm conveyor belt airstream of mid-latitude cyclones while stratospheric intrusions increased TES O3 levels at 316 hPa. A major finding in the DJF data was that offshore 681 hPa CO mixing ratios behind cold fronts could be enhanced up to >150 ppbv likely by lofting from the surface via shallow convection resulting from rapid destabilization of cold air flowing over much warmer ocean waters. In JJA composites for 3 map types showed that the general export pattern of the seasonal composites was associated with a synoptic pattern featuring the Bermuda High. However, weak cyclones and frontal troughs could enhance offshore 681 hPa CO

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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...

  6. 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.

  7. 75 FR 61512 - Outer Continental Shelf Official Protraction Diagrams

    Science.gov (United States)

    2010-10-05

    ... Bureau of Ocean Energy Management, Regulation and Enforcement Outer Continental Shelf Official... Outer Continental Shelf Official Protraction Diagrams (OPDs) located within Atlantic Ocean areas, with... informational purposes only. Outer Continental Shelf Official Protraction Diagrams in the North Atlantic,...

  8. 78 FR 33897 - Atlantic Wind Lease Sale 2 (ATLW2) Commercial Leasing for Wind Power on the Outer Continental...

    Science.gov (United States)

    2013-06-05

    ... for Wind Power on the Outer Continental Shelf Offshore Rhode Island and Massachusetts-- Final Sale...) Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Rhode Island and Massachusetts... for Commercial Leasing for Wind Power on the Outer Continental Shelf Offshore Rhode Island...

  9. 75 FR 16830 - Geological and Geophysical Exploration (G&G) on the Mid- and South Atlantic Outer Continental...

    Science.gov (United States)

    2010-04-02

    ... Outer Continental Shelf (OCS) AGENCY: Minerals Management Service, Interior. ACTION: Reopening of... Outer Continental Shelf Lands Act (OCSLA, as amended; 43 U.S.C. 1331-1356, (2007)) and its implementing... Leasing Oil and Natural Gas Resources: Outer Continental Shelf (see...

  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. Distribution and relation of total bacteria, active bacteria, bacterivory, and volume of organic detritus in Atlantic continental shelf waters off Cape Hatteras NC, USA

    Science.gov (United States)

    Sherr, Evelyn B.; Sherr, Barry F.; Verity, Peter G.

    During the Ocean Margins Program, we obtained data on the abundances of bacterioplankton and heterotrophic flagellates, and on rates of bacterivory, across the mid-Atlantic continental shelf off Cape Hatteras, NC, during four spring and summer cruises from 1993 to 1996. Bacterial and grazing parameters were compared for inner, middle, and outer shelf regions. In 1996, we sampled during two seasons: early spring (March) and mid-summer (July), and in addition determined the fractions of in situ bacterioplankton that had visible nucleoids (NV cells), or that had highly active electron transport systems (ETS), i.e. that were positive for reduction of the fluorogenic formazan compound, 5 cyano-2,3 ditolyl tetrazolium chloride (CTC+ cells), as well as the volumetric concentration of organic detrital particles. Detrital volumes and abundances of bacterioplankton and of heterotrophic flagellates, varied by an order of magnitude, and decreased from inshore to offshore shelf regions. In 1996, bacterial abundances and percentages of CTC+ cells were higher across the shelf during the early spring bloom season (March) compared to the post-bloom season (July). In March 1996, percentages of bacterial cells with visible nucleoids varied between 20% and 70%, but showed little change across the shelf; while fractions of total bacteria with highly active ETS were lower and more variable (1-16% CTC+ cells), and on average were twice as high in the inner shelf region compared to the rest of the shelf. Percentages of CTC+ cells were also higher for particle-associated bacteria. There was a strong positive relationship between percent CTC+ cells and volume of organic detrital particles. However, % CTC+ cells and detrital volume were not consistently related to either bulk particulate organic carbon or chlorophyll. Bacterivory, assessed via rate of ingestion of fluorescently labeled bacteria, could remove 2-9% (4-18% accounting for motile cells) of total bacterial stocks per day. If

  12. Pelagic-benthic coupling and diagenesis of nucleic acids in a deep-sea continental margin and an open-slope system of the Eastern Mediterranean.

    Science.gov (United States)

    Dell'anno, Antonio; Corinaldesi, Cinzia; Stavrakakis, Spyros; Lykousis, Vasilis; Danovaro, Roberto

    2005-10-01

    Downward fluxes of nucleic acids adsorbed onto settling particles play a key role in the supply of organic phosphorus and genetic material to the ocean interior. However, information on pelagic-benthic coupling, diagenesis, and processes controlling nucleic acid preservation in deep-sea sediments is practically nonexistent. In this study, we compared nucleic acid fluxes, sedimentary DNA and RNA concentrations, and the enzymatically hydrolyzable fraction of DNA in a bathyal continental margin (North Aegean Sea) and an open-sea system (South Aegean Sea) of the Eastern Mediterranean. The two systems displayed contrasting patterns of nucleic acid fluxes, which increased significantly with depth in the North Aegean Sea and decreased with depth in the South Aegean Sea. These results suggest that in continental margin and open-ocean systems different processes control the nucleic acid supply to the sea floor. Differences in nucleic acid fluxes were reflected by nucleic acid concentrations in the sediments, which reached extremely high values in the North Aegean Sea. In this system, a large fraction of DNA may be buried, as suggested by the large fraction of DNA resistant to nuclease degradation and by estimates of burial efficiency (ca. eight times higher in the North than in the South Aegean Sea). Overall, the results reported here suggest that the preservation of DNA in deeper sediment layers may be favored in benthic systems characterized by high sedimentation rates.

  13. Tectonic and eustatic controls of late quaternary shelf sedimentation along the Central California (Santa Cruz) continental margin: high-resolution seismic stratigraphic evidence

    Science.gov (United States)

    Mullins, Henry T.; Nagel, David K.; Dominguez, Laura L.

    1985-07-01

    A high-resolution "uniboom", seismic stratigraphic investigation of a portion of the central California continental shelf has demonstrated that depositional patterns and sequences are controlled largely by an interplay of glacioeustatic sea-level fluctuations superimposed on local tectonics. Wrench tectonics, associated with active right-lateral shear along the San Gregorio fault zone, and the Pigeon Point Basement High control the location, distribution and overall geometry of depositional sequences via en echelon folding and differential subsidence. Areas of relatively thick and thin late Quaternary sediments conform in large part with structures produced during wrenching. Glacioeustatic sea-level oscillations have also shaped depositional patterns and sequences. Correlation of our seismic stratigraphic data with a southern California continental margin sea-level curve, suggests that during the last glacial maximum, approximately 18,000 yrs ago, a relative lowstand resulted in the erosion of a distinct unconformity upon which late Quaternary sediments have accumulated. A rapid rise of sea level to a relative stillstand, approximately 12,000 yrs ago, produced a concave-up, marine terrace profile across the mid-shelf, that has since been infilled with as much as 22 m of Holocene clastic sediments. A relative drop of sea level, approximately 11,000 yrs ago, allowed sediments to build seaward as a series of prograding clinoforms that form the basal sequences of the late Quaternary sediment fill. The succeeding Holocene transgression partially eroded the top of this earlier regressive sequence, and has now established a typical, wave-graded shelf along which sediments fine in a seaward direction to water depths of 90-100 m. At greater shelf water depths, surface sediments coarsen and appear to be relicts of previous relative sea-level lowstands. The presence of now submerged and buried marine terraces along both the central and southern California continental margins

  14. Sediments overlying exhumed continental mantle: a proxy for the morphotectonic evolution of the Ocean Continent Transition in magma-poor rifted margins

    Science.gov (United States)

    Karpoff, A. M.; Manatschal, G.; Bernoulli, D.; Lagabrielle, Y.

    2003-04-01

    Observations from ancient and present-day magma-poor rifted margins in the Alps and Iberia provide compelling evidence that within the ocean-continent transition (OCT) crustal and sub-continental mantle rocks were exhumed along downward-concave faults which were active during final rifting and accommodated high amounts of extension. The faults are overlain by stranded allochthons of continental origin, pillow basalts, and pelagic sediments, i.e. radiolarites and/or pelagic limestones, and hemipelagic shales. Associated with the faults are tectono-sedimentary breccias and various types of clastic sediments, ranging from debris flow deposits to laminated sandstone, and quartz-rich silt- and claystones. Mineralogical studies of the shales, red jaspers, and red cherts overlying mantle rocks in the Alps of eastern Switzerland are typically quartz-rich and contain variable amounts of phyllosilicates (chlorite and/or mica), feldspars, ± calcite, oxides, pyrite, and epidote. Their main geochemical characteristic is the high silica and low iron and manganese content, which contrasts with that of "metalliferous" Fe-Mn-Si-rich sediments overlying oceanic basalts. High Fe, Ba, REE, U/Th values measured in black shales overlying mantle rocks in the proximal OCT point to a strong hydrothermal activity associated with mantle exhumation. The clastic sediments in the OCT show a wide range of compositions related to mantle, continental crust, and/or pelagic contributions. In particular, the fact that these sediments contain abundant material derived from continental basement rocks seems at odds with their occurrence on top of tectonized mantle rocks. However, drilling in the Iberia margin, where tectonized mantle rocks are overlain by sedimentary breccias (e.g. ODP Sites 1068, 1070), shed new light on the observations in the Alps. Based on drill-hole and seismic data, the tectono-sedimentary breccias drilled in the OCT off Iberia may be interpreted to result from a conveyor

  15. Late Devonian and Triassic basalts from the southern continental margin of the East European Platform, tracers of a single heterogeneous lithospheric mantle source

    Science.gov (United States)

    Chalot-Prat, Françoise; Tikhomirov, Petr; Saintot, Aline

    2007-12-01

    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 during continental rifting periods some 600 km away from expected locations of active oceanic subduction zones. This paper reports a comparative geochemical study of the basaltic rocks, and views them as the best tracers of the involved mantle below the Eastern European Platform. The Late Devonian alkaline basic rocks differ from the calc-alkaline Triassic basic rocks by their higher alkali-silica ratio, their higher TiO2, K2O, P2O5 and FeO contents, their higher trace element contents, a higher degree of fractionation between the most and the least incompatible elements and the absence of Ta-Nb negative anomalies. These general features, clearly distinct from those of partial melting and fractional crystallization, are due to mantle source effects. With similar Nd and Sr isotopic signatures indicating mantle-crust mixing, both suites would originate from the melting of a same but heterogeneous continental mantle lithosphere (refertilized depleted mantle). Accordingly the Nd model ages, the youngest major event associated with mantle metasomatism occurred during Early Neoproterozoic times (˜650Ma).

  16. Late Devonian and Triassic basalts from the southern continental margin of the East European Platform, tracers of a single heterogeneous lithospheric mantle source

    Indian Academy of Sciences (India)

    Françoise Chalot-Prat; Petr Tikhomirov; Aline Saintot

    2007-12-01

    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 during continental rifting periods some 600 km away from expected locations of active oceanic subduction zones. This paper reports a comparative geochemical study of the basaltic rocks, and views them as the best tracers of the involved mantle below the Eastern European Platform. The Late Devonian alkaline basic rocks differ from the calc-alkaline Triassic basic rocks by their higher alkali-silica ratio, their higher TiO2, K2O, P2O5 and FeO contents, their higher trace element contents, a higher degree of fractionation between the most and the least incompatible elements and the absence of Ta-Nb negative anomalies. These general features, clearly distinct from those of partial melting and fractional crystallization, are due to mantle source effects. With similar Nd and Sr isotopic signatures indicating mantle-crust mixing, both suites would originate from the melting of a same but heterogeneous continental mantle lithosphere (refertilized depleted mantle). Accordingly the Nd model ages, the youngest major event associated with mantle metasomatism occurred during Early Neoproterozoic times (∼650Ma).

  17. Subseafloor to Sea-Air Interface Characterization of Methane Dynamics in the northern US Atlantic Margin Seep Province

    Science.gov (United States)

    Ruppel, C. D.; Kluesner, J.; Danforth, W. W.; Casso, M.; Pohlman, J.

    2015-12-01

    Since the discovery of hundreds of northern US Atlantic margin (USAM) cold seeps in 2012 and 2013, the USGS Gas Hydrates Project has undertaken intensive studies of the along-margin gas hydrate/free gas distribution, the plumbing systems sustaining seeps, seafloor gas emissions, and sea-air methane flux. Interest in the USAM is motivated both by climate change (i.e., documented ocean warming may contribute to seepage) and energy resource (i.e., the amount of gas-in-place in hydrates on the USAM is about the same as that in the northern Gulf of Mexico) issues. USGS-led field efforts have included an April 2015 study to acquire high-resolution multichannel seismic data, coincident split-beam water column methane plume imaging data, and real-time sea-air methane flux measurements between Wilmington and Norfolk Canyons and a September 2015 cruise (with OSU, UCLA, and Geomar) to collect piston cores, multicores, heat flow data, subbottom imagery, CTDs, and coincident water column imagery from Block Canyon to the Currituck Slide. In April 2015, we discovered methane seeps not included in the previously-published database, but found that some known seeps were not active. New high-resolution multi-channel seismic data revealed clear differences between the deep gas distribution in mid-Atlantic upper slope zones that are replete with (up to 240 sites) and lacking in seeps. Based on sea-air flux measurements, even shallow-water outer shelf (~125 m water depth) seeps and a 900-m-high methane plume originating on the mid-slope do not contribute methane to the atmosphere. Using thermistors placed on piston core outriggers, we will in September 2015 acquire thermal data to identify zones of high fluid advection and to constrain background geotherms in areas where heat flow has never been measured. During that same cruise, we will collect a series of piston cores across the no-hydrate/hydrate transition on the upper slope to constrain fluid and gas dynamics in this zone.

  18. Oceanographic parameters in continental margin of the State of Ceará (northeastern Brazil deduced from C and O isotopes in foraminifers

    Directory of Open Access Journals (Sweden)

    Wanessa S. Marques

    2007-03-01

    Full Text Available Specimens of Recent foraminifera of Amphistegina radiata, Peneroplis planatus and Globigerinoides ruber, from fifty samples of surface sediments of the continental margin of the State of Ceará, Brazil, have been analyzed for carbon and oxygen isotopes to investigate oceanographic parameters and determine the values of delta18O of the oceanic water. From a comparison between values of delta18O obtained for ocean water using the linear equations by (Craig and Gordon 1965 and the one by Wolff et al. (1998, it became evident that the former yielded a more reliable value (0.2‰ SMOW than the latter. Lower values of delta18O for the ocean water in this continental margin resulted from continental water influence. Values of 18O (-0.3‰ to -1.5‰ PDB for benthic foraminifera and -0.6‰ to -2.4‰ PDB for planktic foraminifera, attest to a variation of temperatures of oceanic water masses, in average, between 20 to 22ºC in deep water and 24 to 27ºC, in surface water. Values of delta13C from +3.2‰ to -0.2‰ PDB (benthic foraminifera reflect a variation in the apparent oxygen utilization (AOU in the continental margin and indicate that the environments of bacteriological decomposition of organic matter are not continuous along the investigated area.Amphistegina radiata, Peneroplis planatus e Globigerinoides ruber, presentes em cinqüenta amostras de sedimentos superficiais da margem continental do Estado do Ceará, Brasil, foram analisados quanto à composição isotópica do Oxigênio e Carbono para investigar parâmetros oceanográficos, e um possível valor de delta18O do oceano. Foi feita uma comparação entre as equações lineares de Craig e Gordon (1965 e de Wolff et al. (1998, e verificou-se que a primeira equação foi mais apropriada para o cálculo de delta18O do oceano, na área estudada, encontrando-se um valor de 0,2‰ SMOW. Os menores valores de delta18O estão associados à desembocadura dos rios, refletindo a influ

  19. High-temperature metamorphism during extreme thinning of the continental crust: a reappraisal of the north Pyrenean paleo-passive margin

    Directory of Open Access Journals (Sweden)

    C. Clerc

    2015-02-01

    Full Text Available An increasing number of field examples in mountain belts show that the formation of passive margins during extreme continent thinning may occur under conditions of high to very high thermal gradient beneath a thin cover of syn-rift sediments. Orogenic belts resulting from the tectonic inversion of distal margins and regions of exhumed continental mantle may exhibit high-temperature, low-pressure (HT-LP metamorphism and coeval syn-extensional, ductile deformation. Recent studies have shown that the northern flank of the Pyrenean belt, especially the North Pyrenean Zone, is one of the best examples of such inverted hot, passive margin. In this study, we provide a map of HT-LP metamorphism based on a dataset of more than one hundred peak-temperature estimates obtained using Raman spectroscopy of the carbonaceous material (RSCM. This dataset is completed by previous PT estimates based on mineral assemblages, and new Ar–Ar (amphibole, micas and U–Pb (titanite ages from metamorphic and magmatic rocks of the North Pyrenean Zone. The implications on the geological evolution of the Cretaceous Pyrenean paleomargins are discussed. Ages range mainly from 110 to 90 Ma and no westward or eastward propagation of the metamorphism and magmatism can be clearly identified. In contrast, the new data reveal a progressive propagation of the thermal anomaly from the base to the surface of the continental crust. Focusing on the key-localities of the Mauléon Basin, Arguenos-Moncaup, Lherz, Boucheville and the Bas-Agly, we analyse the thermal conditions prevailing during the Cretaceous crustal thinning. The results are synthetized into a series of three regional thematic maps, and into two detailed maps of the Arguenos-Moncaup and Lherz areas. The results indicate a first-order control of the thermal gradient by the intensity of crustal thinning. The highest grades of metamorphism are intimately associated with the areas where subcontinental mantle rocks have been

  20. Variations in Organic Matter Burial and Composition in Sediments from the Indian Ocean Continental Margin Off SW Indonesia (Sumatra - Java - Flores) Since the Last Glacial Maximum

    Science.gov (United States)

    Jennerjahn, T. C.; Gesierich, K.; Schefuß, E.; Mohtadi, M.

    2014-12-01

    Global climate change is a mosaic of regional changes to a large extent determined by region-specific feedbacks between climate and ecosystems. At present the ocean is forming a major sink in the global carbon cycle. Organic matter (OM) storage in sediments displays large regional variations and varied over time during the Quaternary. Upwelling regions are sites of high primary productivity and major depocenters of organic carbon (OC), the least understood of which is the Indian Ocean upwelling off Indonesia. In order to reconstruct the burial and composition of OM during the Late Quaternary, we analyzed five sediment cores from the Indian Ocean continental margin off the Indonesian islands Sumatra to Flores spanning the last 20,000 years (20 kyr). Sediments were analyzed for bulk composition, stable carbon and nitrogen isotopes of OM, amino acids and hexosamines and terrestrial plant wax n-alkanes and their stable carbon isotope composition. Sedimentation rates hardly varied over time in the western part of the transect. They were slightly lower in the East during the Last Glacial Maximum (LGM) and deglaciation, but increased strongly during the Holocene. The amount and composition of OM was similar along the transect with maximum values during the deglaciation and the late Holocene. High biogenic opal covarying with OM content indicates upwelling-induced primary productivity dominated by diatoms to be a major control of OM burial in sediments in the East during the past 20 kyr. The content of labile OM was low throughout the transect during the LGM and increased during the late Holocene. The increase was stronger and the OM less degraded in the East than in the West indicating that continental margin sediments off Java and Flores were the major depocenter of OC burial along the Indian Ocean margin off SW Indonesia. Temporal variations probably resulted from changes in upwelling intensity and terrestrial inputs driven by variations in monsoon strength.

  1. What do Great Subduction Earthquakes tell us About Continental Deformation of the Upper Plate in the Central Andes Forearc? Insights From Seismotectonics, Continental Deformation and Coulomb Modelisation Along Southern Peru Margin

    Science.gov (United States)

    Audin, L.; Perfettini, H.; Tavera, H.

    2007-05-01

    Subduction of the Nazca plate beneath the Peruvian margin has produced numerous megathrust earthquakes during the last century and still constitutes mature seismic gaps in some places such as in between Ilo (Peru) and Arica (Chile). The rupture zones of the 1604, 1784 and 1868 southern Peru events were partially reactivated by the Arequipa 2001 (Mw = 8.5) seismic event, whose rupture zone was about 350km-long and stopped its propagation towards the south on Ilo Peninsula. Just after the occurrence of 2001 event, some reactivation of continental fault systems are identified and monitored thanks to the Peruvian seismic network and describe continental deformation processes occurring perpendicularly to the trench or parallel to the trench, traducing the continental plate response to major subduction earthquakes and some partitioning of the deformation. The Chololo and associated ( perpendicular to the trench) fault systems define some 80-km-long margin crustal blocks and the major one coincides with the 2001 earthquake southern limit of the rupture zone as it propagated to the south. These blocks are made from Late Jurassic and Cretaceous plutonic rocks from the Coastal Batholith; these are outcropping in some places and are evidenced by the aeromagnetic mapping elsewhere around the area. Northward along the subduction zone, another boundary between two rupture zones of major subduction earthquake was reactivated recently, perpendicularly to the trench, by the seismic crisis of October 2006, M=6.4, near Lima, right at the southern end of the rupture zone of the 1974 event (Mw=8.1).Those boundaries corresponding to discontinuities (lithospheric fault systems) in the upper plate, trending nearly perpendicular to the trench, act as earthquake barriers during rupture of large seismic events. Additionally occurred on 20 of November 2006 another seismic event (Mw=5.6 Neic, Ml=5.3) in Tacna region, showing a reverse focal mechanism compatible with the trend of the Sama

  2. The MORENA Project: Shelf-ocean exchanges and transport processes along the continental margin in the European coastal upwelling region

    Energy Technology Data Exchange (ETDEWEB)

    Fiuza, A.F.G. [Univ. de Lisboa (Portugal). Inst. de Oceanografia; Perez, F. [Inst. Investigaciones Marinas, Vigo (Spain); Johnson, J. [Univ. East Anglia (United Kingdom)] [and others

    1994-12-31

    The MORENA Project (Multidisciplinary Oceanographic Research in the Eastern Boundary of the North Atlantic) is sponsored by the CEC MAST-2 Programme and has as general objective to measure, understand and model shelf-ocean exchange in a typical coastal upwelling region of the eastern boundary layer of the subtropical ocean. This is being attained through a multidisciplinary approach aimed at the quantitative understanding of the physical, chemical and biological processes involved in the transfer of matter (including salt, particulates, nutrients, organic compounds, biomass), momentum and energy across and along the shelf, the shelf break and the slope, in the Iberian region of the European Atlantic. MORENA has the following components: Observations, Modelling and Combined Analysis.

  3. Impact of organic matter source and quality on living benthic foraminiferal distribution on a river-dominated continental margin: A study of the Portuguese margin

    Science.gov (United States)

    Dessandier, Pierre-Antoine; Bonnin, Jérôme; Kim, Jung-Hyun; Bichon, Sabrina; Deflandre, Bruno; Grémare, Antoine; Sinninghe Damsté, Jaap S.

    2016-06-01

    Living (rose Bengal stained) benthic foraminifera were investigated on surface sediments from 23 stations from the river-dominated northwestern Portuguese margin. Samples were collected in March 2011, following the period of the maximum rainfall over the Iberian Peninsula, between 20 and 2000 m water depth along five cross-margin transects. Four of them are located off the Douro, Mondego, Tagus, and Sado Rivers and one off the Estremadura coast. The major objectives of this study are (1) to assess the impact of organic matter of various origin and quality on the benthic foraminifera and (2) to investigate the spatial differences of faunal distribution from coastal waters to the deep sea under river influences. To do this, sedimentological and biogeochemical characteristics of the sediments were identified by measuring grain size, oxygen penetration depth, total organic carbon (TOC) content, stable carbon isotopic composition of TOC (δ13CTOC) and concentration of pigments and amino acids. Based on the principal component and cluster analyses of the environmental data, three major geographical groups are identified: (1) deep stations, (2) coastal and middle slope stations, and (3) shelf stations under river influence. At the deepest stations, species are associated with high organic matter (OM) quantity but low OM quality, where Uvigerina mediterranea, Hoeglundina elegans, and agglutinated species such as Reophax scorpiurus or Bigenerina nodosaria are dominant. All stations off the Sado River, which is the most affected area by the anthropogenic influence, are also characterized by high quantity but low quality of OM with the minimum faunal density and diversity within the study area. Middle slope stations are associated with low OM content and coarse sediments (Q50) with the predominance of N. scaphum. Shallow shelf stations close to the Douro and Tagus River mouths show a dominance of taxa (e.g., Ammonia beccarii, Bulimina aculeata, Eggerelloides scaber, Nonion

  4. Settling particle fluxes across the continental margin of the Gulf of Lion: the role of dense shelf water cascading

    Directory of Open Access Journals (Sweden)

    C. Pasqual

    2009-07-01

    Full Text Available Settling particles were collected using sediment traps deployed along three transects in the Lacaze-Duthiers and Cap de Creus canyons and the adjacent southern open slope from October 2005 to October 2006. The settling material was analysed to obtain total mass fluxes and main constituent contents (organic matter, opal, calcium carbonate, and siliciclastics. Cascades of dense shelf water from the continental shelf edge to the lower continental slope occurred from January to March 2006. They were traced through strong negative near-bottom temperature anomalies and increased current speeds, and generated two intense pulses of mass fluxes in January and March 2006. This oceanographic phenomenon appeared as the major physical forcing of settling particles at almost all stations, and caused both high seasonal variability in mass fluxes and important qualitative changes in settling material. Fluxes during the dense shelf water cascading (DSWC event ranged from 90.1 g m−2 d−1 at the 1000 m depth station in the Cap de Creus canyon to 3.2 g m−2 d−1 at the canyon mouth at 1900 m. Fractions of organic matter, opal and calcium carbonate components increased seaward, thus diminishing the siliciclastic fraction. Temporal variability of the major components was larger in the canyon mouth and open slope sites, due to the mixed impact of dense shelf water cascading processes and the pelagic biological production. Results indicate that the cascading event remobilized and homogenized large amounts of material down canyon and southwardly along the continental slope contributing to a better understanding of the internal dynamics of DSWC events. While the late winter/early spring bloom signature was diluted when DSWC occurred, the primary production dynamics were observable at all stations during the rest of the year and highlighted the biological community succession in surface waters.

  5. Tsunami Sceanarios from Large Earthquakes in the NE Atlantic: the Gloria Fault and the Southwest Iberia Margin case studies

    Science.gov (United States)

    Baptista, Maria Ana; Omira, Rachid; Miranda, Jorge Miguel; Batllo, Josep; Lourenço, Nuno

    2013-04-01

    In the North East Atlantic (NEA) basin, the threat of tsunami of tectonic origin comes from regional sources located in the South West Iberian Margin (SWIM), far-field sources on the Gloria fault and transoceanic tsunamis from the Caribbean region. SWIM and Gloria source areas were responsible for tsunamigenic earthquakes that affected the coasts of NEA basin. The 1755.11.01 and the 1941.11.26 events remain the most well-known (historical and instrumental) tsunamis in these areas. The SWIM area is the most active seismic area in the NEA basin. It WAS the place of several events in historical times, namely: the 60 B.C. tsunami which reported to flood Portugal and Galicia coasts and the 382 AD tsunami that impacted Portugal and the Atlantic coasts of Morocco and Spain. Recently, the 1969.02.28 earthquake triggered a small tsunami recorded in the tide-gauge network of the area. Among the historical events, of the SWIM region, the November, 1st, 1755 tsunami is probably the most destructive in the history of Europe. The Gloria fault is a segment of the Eurasia-Nubia plate boundary. This is a large strike slip fault, located between 24W and 19W, with scarce seismic activity. Nonetheless, it is the location of several large earthquakes that caused tsunamis, namely the 1941.11.26 earthquake with a magnitude of 8.3 and the 7.9 magnitude earthquake of 1975.05.26. In 1941, the sea overtopped some beaches in the north coast of Portugal; during the 1975 event, eyewitness observations report the fast withdraw of the sea and the subsequent influx over the highest water mark. In this paper, we compute far-field and regional tsunami impact in the NEA Basin based on hydrodynamic simulations of two case studies representing the worst case scenarios for SWIM and Gloria. Both scenarios correspond to the largest earthquakes expected to occur along in these areas. These scenarios are consistent with the two past events of November, 1st, 1755 and of November, 24th, 1941. We assess

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

    Science.gov (United States)

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

    2015-12-01

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

  7. Violent Gas Venting on the Heng-Chun Mud Volcano, South China Sea Active Continental Margin offshore SW Taiwan

    Science.gov (United States)

    Lin, S.; Cheng, W. Y.; Tseng, Y. T.; Chen, N. C.; Hsieh, I. C.; Yang, T. F.

    2014-12-01

    Accumulation of methane as gas hydrate under the sea floor has been considered a major trap for both thermal and biogenic gas in marine environment. Aided by rapid AOM process near the sea floor, fraction of methane escaping the sea floor has been considered at minuscule. However, most studies focused mainly on deepwater gas hydrate systems where gas hydrate remain relatively stable. We have studied methane seeps on the active margin offshore Taiwan, where rapid tectonic activities occur. Our intention is to evaluate the scale and condition of gas seeps in the tectonic active region. Towcam, coring, heat probe, chirp, multibeam bathymetric mapping and echo sounding were conducted at the study areas. Our results showed that gas is violently venting at the active margin, not only through sediments, but also through overlying sea water, directly into the atmosphere. Similar ventings, but, not in this scale, have also been identified previously in the nearby region. High concentrations of methane as well as traces of propane were found in sediments and in waters with flares. In conjunction, abundant chemosynthetic community, life mussel, clams, tube worms, bacterial mats together with high concentrations of dissolve sulfide, large authigenic carbonate buildups were also found. Our results indicate that methane could be another major green house gas in the shallow water active margin region.

  8. 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.

    2016-09-01

    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.

  9. The extent of ocean acidification on aragonite saturation state along the Washington-Oregon continental shelf margin in late summer 2012

    Science.gov (United States)

    Feely, R. A.; Alin, S. R.; Hales, B. R.; Juranek, L.; Greeley, D.

    2012-12-01

    The Washington-Oregon continental shelf region is exposed to conditions of low aragonite saturation state during the late spring/early summer upwelling season. However, the extent of its evolution in late summer/early fall has been largely unknown. Along this continental margin, ocean acidification, upwelling, biological productivity, and respiration processes in subsurface waters are major contributors to the variability in dissolved inorganic carbon (DIC), pH and aragonite saturation state. The persistence of water with aragonite saturation state Washington and Oregon has been previously identified and could have profound ecological consequences for benthic and pelagic calcifying organisms such as mussels, oysters, abalone, echinoderms, and pteropods. In the late summer of 2012 we studied the extent of acidification conditions employing shipboard cruises and profiling gliders. We conducted several large-scale chemical and hydrographic surveys of the region in order to better understand the interrelationships between these natural and human-induced processes and their effects on aragonite saturation. We will compare the results of these new surveys with our previous work in 2011 and 2007.

  10. Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps

    Science.gov (United States)

    Prouty, Nancy G.; Sahy, Diana; Ruppel, Carolyn; Roark, E. Brendan; Condon, Dan; Brooke, Sandra; Ross, Steve W.; Demopoulos, Amanda

    2016-01-01

    The recent discovery of active methane venting along the US northern and mid-Atlantic margin represents a new source of global methane not previously accounted for in carbon budgets from this region. However, uncertainty remains as to the origin and history of methane seepage along this tectonically inactive passive margin. Here we present the first isotopic analyses of authigenic carbonates and methanotrophic deep-sea mussels, Bathymodiolus   sp., and the first direct constraints on the timing of past methane emission, based on samples collected at the upper slope Baltimore Canyon (∼385 m water depth) and deepwater Norfolk (∼1600 m) seep fields within the area of newly-discovered venting. The authigenic carbonates at both sites were dominated by aragonite, with an average  signature of −47‰, a value consistent with microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment–water interface. Authigenic carbonate U and Sr isotope data further support the inference of carbonate precipitation from seawater-derived fluids rather than from formation fluids from deep aquifers. Carbonate stable and radiocarbon ( and ) isotope values from living Bathymodiolus   sp. specimens are lighter than those of seawater dissolved inorganic carbon, highlighting the influence of fossil carbon from methane on carbonate precipitation. U–Th dates on authigenic carbonates suggest seepage at Baltimore Canyon between 14.7±0.6 ka to 15.7±1.6 ka, and at the Norfolk seep field between 1.0±0.7 ka to 3.3±1.3 ka, providing constraint on the longevity of methane efflux at these sites. The age of the brecciated authigenic carbonates and the occurrence of pockmarks at the Baltimore Canyon upper slope could suggest a link between sediment delivery during Pleistocene sea-level lowstand, accumulation of pore fluid overpressure from sediment compaction, and release of overpressure through subsequent venting. Calculations show that

  11. Insights into methane dynamics from analysis of authigenic carbonates and chemosynthetic mussels at newly-discovered Atlantic Margin seeps

    Science.gov (United States)

    Prouty, N. G.; Sahy, D.; Ruppel, C. D.; Roark, E. B.; Condon, D.; Brooke, S.; Ross, S. W.; Demopoulos, A. W. J.

    2016-09-01

    The recent discovery of active methane venting along the US northern and mid-Atlantic margin represents a new source of global methane not previously accounted for in carbon budgets from this region. However, uncertainty remains as to the origin and history of methane seepage along this tectonically inactive passive margin. Here we present the first isotopic analyses of authigenic carbonates and methanotrophic deep-sea mussels, Bathymodiolus sp., and the first direct constraints on the timing of past methane emission, based on samples collected at the upper slope Baltimore Canyon (∼385 m water depth) and deepwater Norfolk (∼1600 m) seep fields within the area of newly-discovered venting. The authigenic carbonates at both sites were dominated by aragonite, with an average δ13C signature of - 47 ‰, a value consistent with microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment-water interface. Authigenic carbonate U and Sr isotope data further support the inference of carbonate precipitation from seawater-derived fluids rather than from formation fluids from deep aquifers. Carbonate stable and radiocarbon (δ13C and Δ13C) isotope values from living Bathymodiolus sp. specimens are lighter than those of seawater dissolved inorganic carbon, highlighting the influence of fossil carbon from methane on carbonate precipitation. U-Th dates on authigenic carbonates suggest seepage at Baltimore Canyon between 14.7 ± 0.6 ka to 15.7 ± 1.6 ka, and at the Norfolk seep field between 1.0 ± 0.7 ka to 3.3 ± 1.3 ka, providing constraint on the longevity of methane efflux at these sites. The age of the brecciated authigenic carbonates and the occurrence of pockmarks at the Baltimore Canyon upper slope could suggest a link between sediment delivery during Pleistocene sea-level lowstand, accumulation of pore fluid overpressure from sediment compaction, and release of overpressure through subsequent venting. Calculations show that the

  12. Droughts in the East Asian summer monsoon margin during the last 6 kyrs: Link to the North Atlantic cooling events

    Science.gov (United States)

    Fan, Jiawei; Xiao, Jule; Wen, Ruilin; Zhang, Shengrui; Wang, Xu; Cui, Linlin; Li, He; Xue, Dingshuai; Yamagata, Hideki

    2016-11-01

    Teleconnections to the high latitudes, forcing by the tropical oceans and solar variability have all been suggested as dominant factors in the sub-millennial global climate changes, yet there is little consensus as to the relative importance of these factors for the East Asian summer monsoon (EASM) variability. This study presents the results of high-resolution analyses of Ca and Mg concentrations, Mg/Ca ratio, δ18O and δ13C values of endogenic calcites from a sediment core from Dali Lake in the EASM margin, in order to investigate the sub-millennial EASM variability and its possible driving forces during the last 6 kyrs. Increases in these chemical proxy data were interpreted as drought events in the region due to the intensive evaporation losses overwhelming the water input to the lake. The chemical proxy data in this study combined with multi-proxy indicators including grain size component and total organic carbon concentrations from the same sediment core imply that declines in the EASM intensity may have played a dominant role in triggering the drought events during the last 6 kyrs. The results indicate that the EASM intensity significantly declined at the intervals of 5.8-4.75, 3.2-2.8, 1.65-1.15 and 0.65-0.2 kyrs BP. Large declines in the EASM intensity during the last 6 kyrs correspond in time to occurrences of ice-rafted debris in the North Atlantic, indicating that millennial-to-centennial scale changes in the EASM intensity were mainly controlled by climatic processes occurring in the northern high latitudes. These data imply that persistent global warming may be favorable for the strengthening of the EASM circulation and for the transportation of more rainfall to the semi-arid regions of northern China on sub-millennial scales.

  13. Temperature and salinity changes associated with the Paleocene-Eocene Carbon Isotope Excursion along the mid Atlantic margin

    Science.gov (United States)

    Makarova, M.; Miller, K. G.; Wright, J. D.; Rosenthal, Y.; Babila, T. L.

    2015-12-01

    The Paleocene-Eocene Thermal Maximum (PETM) was an abrupt warming event, characterized by a global temperature increase of about 5-8°C and associated with the Carbon Isotope Excursion (CIE) of ~2.5-4‰ in marine environments. Here we evaluate temperature and salinity changes across the Paleocene/Eocene boundary in the Millville New Jersey coastal plain core (ODP Leg 174AX) using two independent temperature proxies (the organic paleothermometer TEX86 and Mg/Ca ratio of planktonic foraminifera) and δ18O of planktonic foraminifera. Paleotemperature estimates show warming of 5-7°C during the CIE, though different temperature calibrations provide a broad range of absolute temperatures. We argue that the temperature calibration of TEXL 86 provides the best temperature estimate (warming from 23°C to 30°C) because it is the only one that yields realistic salinities, whereas the TEXH 86 calibration yields extremely high sea surface salinities (~48 psu in the latest Paleocene). In contrast to the previous studies, use of the correct calibration effectively eliminates any temperature increase prior to the CIE suggesting that temperature was not the trigger for the massive release of carbon. A salinity decrease of at least ~4 psu was associated with the onset of the CIE/PETM. This implies freshening of surface and thermocline waters supports the hypothesis of an enhanced hydrological cycle. We conclude that our results are consistent with the hypothesis of Appalachian Amazon river system development and increased river runoff to the New Jersey continental margin during the PETM.

  14. Thermotectonic history of the southeastern Brazilian margin: Evidence from apatite fission track data of the offshore Santos Basin and continental basement

    Science.gov (United States)

    Engelmann de Oliveira, Christie Helouise; Jelinek, Andréa Ritter; Chemale, Farid; Cupertino, José Antônio

    2016-08-01

    The Santos Basin is the largest offshore sedimentary basin in the southeastern Brazilian margin and originated by breakup of West Gondwana in the Early Cretaceous. We carried out a new thermochronological study by apatite fission track analysis from borehole samples of the Santos Basin and its continental basement to constrain the tectonic history of the southeastern Brazilian margin. Apatite fission track central ages of the basement and borehole samples vary from 21.0 ± 1.8 to 157.0 ± 35.0 Ma and from 6.5 ± 1.1 to 208.0 ± 11.0 Ma, respectively. From thermal modeling, the basement samples reached the maximum paleotemperatures during the final breakup of South America and Africa. The onshore basement and offshore basin record an early thermotectonic event during the Late Cretaceous linked to the uplift and denudation of the Serra do Mar and Serra da Mantiqueira. Maturation of the organic matter in the offshore basin is related with the progressive increase of the geothermal gradient due to burial. The thermal modeling indicates that the oil generation window started at 55-25 Ma. The basement samples experienced the final cooling during the Cenozoic, with an estimated amount of denudation linked to the sedimentary influx in the offshore basin. A rapid cooling during the Neogene becomes evident and it is linked to the reactivation along Precambrian shear zones and change of the Paraíba do Sul drainage system.

  15. Multibeam Mapping of the South Atlantic Bight: South Carolina 2005, a Proposed MPA on the Continental Shelf

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The NOAA Fisheries laboratory in Panama City, Florida coordinated an acoustic survey at the new proposed Marine Protected Areas in the South Atlantic Bight area June...

  16. Ostracoda and Foraminifera associated with macrofauna of marginal marine origin in continental sabkha sediments of Tayma (NW Saudi Arabia)

    Science.gov (United States)

    Pint, Anna; Frenzel, Peter; Engel, Max; Plessen, Birgit; Melzer, Sandra; Brückner, Helmut

    2016-04-01

    The oasis Tayma in northwestern Saudi Arabia (27°38'N, 38°33'E) is well known for its rich archaeological heritage and also hosts a key sedimentary record of Holocene environmental change.The palaeontologically investigated material comes from two 5.5 m long sediment cores taken in the northeastern and central part of the sabkha and two outcrops of shoreline deposits at the northeastern and southwestern margin of a large lake. Microfossil-rich layers have an age of about 9.2-ca. 8 ka BP. The sandy and carbonate-dominated sediments contain autochthonous balanids, the gastropods Melanoides tuberculatus and hydrobiids as well as the foraminifers Ammonia tepida (Cushman, 1926), Quinqueloculina seminula (Linnaeus, 1758), and Flintionoides labiosa (d'Orbigny, 1839). This brackish water association is completed by partially mass-occurrence of Cyprideis torosa (JONES, 1850), an euryhaline and generally widely tolerant ostracod species. Only the smooth shelled morphotype littoralis occurs. The association indicates a large brackish water lake with temporary freshwater inflows. All species documented originate in the marginal marine environment of the Red or Mediterranean Sea within the intertidal zone and hence they are adapted for strong environmental changes. We assume negative water balance under arid climatic conditions as cause for the high salinity of this athalassic lake. Sieve-pore analyses and shell chemistry suppose a trend of increasing salinity towards the top of the studied microfossil-bearing sections. This pattern is confirmed by increasing test malformation ratios of foraminifers. The marine origin of the fauna is surprising in this area 250 km away from the sea in an altitude of about 800 m a.s.l. We assume an avian-mediated transport of eggs, larvae or even adult animals to this site. The brackish water character of the lake enabled a permanent settling of marginal marine foraminifers, ostracods and even macrofauna as gastropods and balanids. The studied

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

    Science.gov (United States)

    ,

    1975-01-01

    The area designated for possible oil and gas lease sale as modified from BLM memorandum 3310 #42 (722) and referred to therein as the North Atlantic Outer Continental Shelf (OCS) contains about 58,300 sq km of shelf beneath water depths of less than 200 m and lies chiefly within the Georges Bank basin. The oldest sediments drilled or dredged on the bordering Continental Slope are sandstone, clay, and silt of Upper Cretaceous age. In Upper Cretaceous exposures, on Marthas Vineyard and nearby New England islands, the predominant lithology appears to be clay. About 125 km northeast of the eastern tip of Georges Bank, the Shell B-93 well penetrated clays and silts of Upper and Lower Cretaceous age above dense Jurassic carbonate rocks which overlie a basement of lower Paleozoic slate, schist, quartzite, and granite. Structurally, the Georges Bank basin is a westerly trending trough which opens to the west-southwest. Post-Paleozoic sediments are more than 8 km thick in parts of the basin. Major structural features appear to be directly related to basement structures. Local anticlines, probably caused by differential compaction over basement flexures and horst blocks or by later uplift along basement faults are reflected principally in Lower Cretaceous and older sediments, though some of these features continue upward to within 0.7 of a second (about 650 m) of the seafloor. Tertiary deposits in the Georges Bank basin are probably up to a kilometre thick and are made up of poorly consolidated sand, silt, and clay. The Cretaceous section is inferred to be up to 3.5 km thick and to be mainly clastics -- shale, siltstone, calcareous shale, changing to limestone in the lowest part of the system. Jurassic rocks in the deepest part of the basin appear to be about 3.6 to 4.0 km thick and probably consist mainly of dense carbonates. Potential source rocks in the Georges Bank basin may include organic-rich Cretaceous shale and carbonaceous Jurassic limestone. By analogy with the

  18. Continental outflow from the US to the upper troposphere over the North Atlantic during the NASA INTEX-NA Airborne Campaign

    Directory of Open Access Journals (Sweden)

    S. Y. Kim

    2008-04-01

    Full Text Available A case of continental outflow from the United States (US was examined using airborne measurements from NASA DC-8 flight 13 during the Intercontinental Chemical Transport Experiment – North America (INTEX-NA. Mixing ratios of methane (CH4 and carbon monoxide (CO at 8–11 km altitude over the North Atlantic were elevated to 1843 ppbv and 134 ppbv respectively, while those of carbon dioxide (CO2 and carbonyl sulfide (COS were reduced to 372.4 ppmv and 411 pptv respectively. In this region, urban and industrial influences were evidenced by elevated mixing ratios and good linear relationships between urban and industrial tracers compared to North Atlantic background air. Moreover, low mixing ratios and a good correlation between COS and CO2 showed a fingerprint of terrestrial uptake and minimal dilution during rapid transport over a 1–2 day time period. Analysis of synoptic conditions, backward trajectories, and photochemical aging estimates based on C3H8/C2H6 strongly suggested that elevated anthropogenic tracers in the upper troposphere of the flight region were the result of transport via convection and warm conveyor belt (WCB uplifting of boundary layer air over the southeastern US. This mechanism is supported by the similar slope values of linear correlations between long-lived (months anthropogenic tracers (e.g., C2Cl4 and CHCl3 from the flight region and the planetary boundary layer in the southeastern US. In addition, the aircraft measurements suggest that outflow from the US augmented the entire tropospheric column at mid-latitudes over the North Atlantic. Overall, the flight 13 data demonstrate a pervasive impact of US anthropogenic emissions on the troposphere over the North Atlantic.

  19. Rheological implications of sediment transport for continental rifting and its impact in margin geometry and major unconformities

    Science.gov (United States)

    Andres-Martinez, Miguel; Perez-Gussinye, Marta; Armitage, John; Morgan, Jason

    2016-04-01

    The inner dynamics of the Earth such as mantle convection, geochemical reactions and isostasy have been typically interpreted as the main engine of plate tectonics and crustal deformation. However, nowadays it is well established that processes transporting material along the surface of the Earth influence the inner dynamics. Surface processes play a key role particularly during rifting, where great subsidence rates occur at synrift basins while shoulder uplift provides rock to be eroded for later infilling of these basins. Erosion implies unloading of the crust which favours uplift, and sedimentation at basins results in loading which favours subsidence. Consequently, erosion and sedimentation amplify stresses and the flexural response of the lithosphere in situations with extensive faulting. These changes to the stress field may be large enough to result in changes in the evolution of rifting and its modes of extension. Additionally, higher subsidence rates and thermal blanketing due to sediments may result in higher geotherms and consequently, a weaker/more-viscous behaviour of the crustal rocks. This would also have a large impact on the deformation style during extension. Here, we explore the interactions between surface processes and tectonics using numerical modelling. Experiments are run with the absence of sediment transport and with different sediment transport regimes for 35 and 40 km crustal thicknesses. Tests with higher transport coefficient show more effective localization of deformation into upper crustal faults which results in effective crustal thinning, larger blocks and longer-lived faults. Our experiments also prove that more effective surface processes reduce the length of margins generated by sequential faulting. For our end member situations, high sedimentation rates lead to pure shear extension of the crust induced by high temperatures, which finally results in broad extension and symmetric margins. Furthermore, our model allows for the

  20. Ice-sheet dynamics through the Quaternary on the mid-Norwegian continental margin inferred from 3D seismic data.

    Science.gov (United States)

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

    2017-02-01

    Reconstructing the evolution of ice sheets is critical to our understanding of the global environmental system, but most detailed palaeo-glaciological reconstructions have hitherto focused on the very recent history of ice sheets. Here, we present a three-dimensional (3D) reconstruction of the changing nature of ice-sheet derived sedimentary architecture through the Quaternary Ice Age of almost 3 Ma. An extensive geophysical record documents a marine-terminating, calving Fennoscandian Ice Sheet (FIS) margin present periodically on the mid-Norwegian shelf since the beginning of the Quaternary. Spatial and temporal variability of the FIS is illustrated by the gradual development of fast-flowing ice streams and associated intensification of focused glacial erosion and sedimentation since that time. Buried subglacial landforms reveal a complex and dynamic ice sheet, with converging palaeo-ice streams and several flow-switching events that may reflect major changes in topography and basal thermal regime. Lack of major subglacial meltwater channels suggests a largely distributed drainage system beneath the marine-terminating part of the FIS. This palaeo-environmental examination of the FIS provides a useful framework for ice-sheet modelling and shows that fragmentary preservation of buried surfaces and variability of ice-sheet dynamics should be taken into account when reconstructing glacial history from spatially limited datasets.

  1. Distribution and preservation of black carbon in the East China Sea sediments: Perspectives on carbon cycling at continental margins

    Science.gov (United States)

    Huang, Liang; Zhang, Jing; Wu, Ying; Wang, Jinlong

    2016-02-01

    We determined the concentrations and radiocarbon (14C) compositions of black carbon (BC) in the sediments of the East China Sea (ECS). The BC concentrations, which were in the range of 0.30-1.52 mg/g, accounted for 12-65% of the total organic carbon (TOC). The distribution of BC in ECS sediments was controlled by factors such as grain size, distance from the coast, and deposition rate. Radiocarbon measurements of BC yielded ages of 6350-10,440 years before present (BP), suggesting that the percentage of BC derived from biomass combustion was in the range of 29-48%. The BC burial flux in sediments of the ECS was estimated to be ∼1.39×106 t/yr, which was similar to burial fluxes reported for shelf sediments in other areas. However, the magnitude of the total BC sink was far greater than that of any other shelf regions studied to date, indicating the global importance of BC accumulation in the ECS, and the magnitude of BC input from large rivers (e.g., the Changjiang). The riverine delivery of BC to the ECS (73%) was far greater than that of atmospheric flux (27%). Further study of the BC cycle and the interactions of BC with other organic compounds in marginal seas was required to better understand the role of BC in the global carbon cycle.

  2. Late Pleistocene to Holocene sedimentation and hydrocarbon seeps on the continental shelf of a steep, tectonically active margin, southern California, USA

    Science.gov (United States)

    Draut, Amy E.; Hart, Patrick E.; Lorenson, T.D.; Ryan, Holly F.; Wong, Florence L.; Sliter, Ray W.; Conrad, James E.

    2009-01-01

    Small, steep, uplifting coastal watersheds are prolific sediment producers that contribute significantly to the global marine sediment budget. This study illustrates how sedimentation evolves in one such system where the continental shelf is largely sediment-starved, with most terrestrial sediment bypassing the shelf in favor of deposition in deeper basins. The Santa Barbara-Ventura coast of southern California, USA, is considered a classic area for the study of active tectonics and of Tertiary and Quaternary climatic evolution, interpretations of which depend upon an understanding of sedimentation patterns. High-resolution seismic-reflection data over >570 km2 of this shelf show that sediment production is concentrated in a few drainage basins, with the Ventura and Santa Clara River deltas containing most of the upper Pleistocene to Holocene sediment on the shelf. Away from those deltas, the major factor controlling shelf sedimentation is the interaction of wave energy with coastline geometry. Depocenters containing sediment 5-20 m thick exist opposite broad coastal embayments, whereas relict material (bedrock below a regional unconformity) is exposed at the sea floor in areas of the shelf opposite coastal headlands. Locally, natural hydrocarbon seeps interact with sediment deposition either to produce elevated tar-and-sediment mounds or as gas plumes that hinder sediment settling. As much as 80% of fluvial sediment delivered by the Ventura and Santa Clara Rivers is transported off the shelf (some into the Santa Barbara Basin and some into the Santa Monica Basin via Hueneme Canyon), leaving a shelf with relatively little recent sediment accumulation. Understanding factors that control large-scale sediment dispersal along a rapidly uplifting coast that produces substantial quantities of sediment has implications for interpreting the ancient stratigraphic record of active and transform continental margins, and for inferring the distribution of hydrocarbon resources

  3. New insights into the tectono-stratigraphic evolution of the Malvinas Basin, offshore of the southernmost Argentinean continental margin

    Science.gov (United States)

    Baristeas, N.; Anka, Z.; di Primio, R.; Rodriguez, J. F.; Marchal, D.; Dominguez, F.

    2013-09-01

    A detailed tectono-stratigraphic analysis of the Malvinas Basin was achieved by the interpretation of around 65,000 km of 2D seismic reflection profiles. Five main seismo-stratigraphic units and their sub-units, informally named units U1 to U5 a/b, bound by major unconformities were identified and correlated with the Mesozoic to Cenozoic main tectonic phases of the basin. Unit U1 (Pre-168 Ma) represents the seismic basement. Unit U2 (168-150.5 Ma, syn rift phase) thickens and deepens southwards. Units U1 and U2 are affected by several syn-rift normal faults that exhibit a main NE-SW strike direction in the south of the basin and a NW-SE strike direction in the centre of the basin. This suggests that the Malvinas Basin may have developed initially as a rift basin with two different extensional directions: (1) a NW-SE directed extension probably linked with the opening of the Weddell Sea (Early Mid-Jurassic), and (2) a NE-SW directed extension most likely linked with the Jurassic back-arc extension of Gondwana and probably later with the onset of the opening of the South Atlantic during Late Jurassic to Early Cretaceous time. Unit U3 (150.5-68 Ma, sag phase) is mainly an aggradational wedge-shaped unit. Unit U4 (68-42.5 Ma, transtensional foredeep phase) overlies unconformable unit U3. It deepens in the south because of an N-S/NW-SE directed extensional regime. Accumulation rates decrease during units U2, U3, and U4 from 4.84, to 1.23 to 0.8 km3/Ma × 103. Units U5a and U5b (42.5-5.5 and 5.5-0 Ma, transpressional foredeep phase) finally represent a change from aggradation to progradation sedimentary pattern and to a left-lateral transpressional regime in the south. The sediment supply was considerably higher than before and a thick sedimentary wedge has been deposited until today. Accumulations rates increased in units U5a and U5b from 2.28 to 8.91 km3/Ma × 103.

  4. Geophysical evidence and inferred triggering factors of submarine landslides on the western continental margin of the Ulleung Basin, East Sea

    Science.gov (United States)

    Cukur, Deniz; Kim, Seong-Pil; Kong, Gee-Soo; Bahk, Jang-Jun; Horozal, Senay; Um, In-Kwon; Lee, Gwang-Soo; Chang, Tae-Soo; Ha, Hun-Jun; Völker, David; Kim, Jung-Ki

    2016-12-01

    Submarine landslides form very complex depositional and erosional features on the seafloor, and their dynamics and triggering processes are yet to be understood completely. Numerous studies are being undertaken both because of the scientific significance but also for their potential harm to seafloor infrastructure and coastal areas. This study investigates the styles and causes of landsliding along the western margin of the Ulleung Basin in the East Sea, based on multiple sparker, subbottom profiler, multibeam echosounder and sediment core datasets collected in 2015. The bathymetric analyses indicate that the southern slope of the Ulleung Basin has experienced at least seven submarine failures. These failures left clear arcuate-shaped scarps that initiated at water depths of 600 m. The observed headwall scarps have heights that exceed 60 m and appear to be the result of retrogressive-type failures. Seismic reflection data clearly image the basal sliding surface that is characterized by a prominent high-amplitude reflector. Chaotic-to-transparent seismic facies occur immediately downslope of the headwall scarps; these represent 20 m thick landslide deposits. Gravity cores taken from areas adjacent to the scars suggest that these slides are older than ca. 97 ka. Interpretation of the present data shows that faults appear to cut recent sediments upslope of scarps, and that the slope may still be in an active phase of failure. Seismic data also image various overpressurized gases and/or gas fluids, as evidenced by the occurrence of pockmarks and seismic chimneys in upslope or adjacent areas of the scarps. Hence, earthquakes associated with tectonic activity and development of fluid overpressure may have acted as the main conditioning factor for destabilizing the slope sediments. Geotechnical stability analyses indicate that the sampled slope sediments are exceptionally stable under present-day conditions, even under seismic loading. This finding points to additional

  5. Sedimentary hydrocarbons and sterols in a South Atlantic estuarine/shallow continental shelf transitional environment under oil terminal and grain port influences.

    Science.gov (United States)

    Bet, Rafael; Bícego, Marcia C; Martins, César C

    2015-06-15

    Sterols and hydrocarbons were determined in the surface sediments from the transitional environment between Paranaguá Bay and the shallow continental shelf in the South Atlantic to assess the sources of organic matter (OM) and the contamination status of an area exposed to multiple anthropogenic inputs. Total aliphatic hydrocarbon concentrations were less than 10μgg(-1), which is typical of unpolluted sediments, and related to recent inputs from higher terrestrial plants. Total polycyclic aromatic hydrocarbon ranged from

  6. Kinematics of the South Atlantic rift

    Directory of Open Access Journals (Sweden)

    C. Heine

    2013-01-01

    Full Text Available The South Atlantic rift basin evolved as branch of a large Jurassic-Cretaceous intraplate rift zone between the African and South American plates during the final breakup of western Gondwana. While the relative motions between South America and Africa for post-breakup times are well resolved, many issues pertaining to the fit reconstruction and particular the relation between kinematics and lithosphere dynamics during pre-breakup remain unclear in currently published plate models. We have compiled and assimilated data from these intraplated rifts and constructed a revised plate kinematic model for the pre-breakup evolution of the South Atlantic. Based on structural restoration of the conjugate South Atlantic margins and intracontinental rift basins in Africa and South America, we achieve a tight fit reconstruction which eliminates the need for previously inferred large intracontinental shear zones, in particular in Patagonian South America. By quantitatively accounting for crustal deformation in the Central and West African rift zone, we have been able to indirectly construct the kinematic history of the pre-breakup evolution of the conjugate West African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic Pre-salt sag basin and the São Paulo High. We model an initial E–W directed extension between South America and Africa (fixed in present-day position at very low extensional velocities until Upper Hauterivian times (≈126 Ma when rift activity along in the equatorial Atlantic domain started to increase significantly. During this initial ≈17 Myr-long stretching episode the Pre-salt basin width on the conjugate Brazilian and West African margins is generated. An intermediate stage between 126.57 Ma and Base Aptian is characterised by strain localisation, rapid lithospheric weakening in the

  7. Crustal structure and rift tectonics across the Cauvery–Palar basin, Eastern Continental Margin of India based on seismic and potential field modelling

    Indian Academy of Sciences (India)

    D Twinkle; G Srinivasa Rao; M Radhakrishna; K S R Murthy

    2016-03-01

    The Cauvery–Palar basin is a major peri-cratonic rift basin located along the Eastern Continental Margin of India (ECMI) that had formed during the rift-drift events associated with the breakup of eastern Gondwanaland (mainly India–Sri Lanka–East Antarctica). In the present study, we carry out an integrated analysis of the potential field data across the basin to understand the crustal structure and the associated rift tectonics. The composite-magnetic anomaly map of the basin clearly shows the onshore-tooffshore structural continuity, and presence of several high-low trends related to either intrusive rocks or the faults. The Curie depth estimated from the spectral analysis of offshore magnetic anomaly data gave rise to 23 km in the offshore Cauvery–Palar basin. The 2D gravity and magnetic crustal models indicate several crustal blocks separated by major structures or faults, and the rift-related volcanic intrusiverocks that characterize the basin. The crustal models further reveal that the crust below southeast Indian shield margin is ∼36 km thick and thins down to as much as 13–16 km in the Ocean Continent Transition (OCT) region and increases to around 19–21 km towards deep oceanic areas of the basin. Thefaulted Moho geometry with maximum stretching in the Cauvery basin indicates shearing or low angle rifting at the time of breakup between India–Sri Lanka and the East Antarctica. However, the additional stretching observed in the Cauvery basin region could be ascribed to the subsequent rifting of Sri Lanka from India. The abnormal thinning of crust at the OCT is interpreted as the probable zone of emplaced Proto-Oceanic Crust (POC) rocks during the breakup. The derived crustal structure along with other geophysical data further reiterates sheared nature of the southern part of the ECMI.

  8. Implications for the evolution of continental crust from Hf isotope systematics of Archean detrital zircons

    Science.gov (United States)

    Stevenson, Ross K.; Patchett, P. Jonathan

    1990-01-01

    Results from the fractionation of zircon by sedimentary processes into continental margin sandstone yield information on the preservation of preexisting continental crust in the form of zircon, making it possible to distinguish between the contrasting theories of gradual growth versus constant volume of continental crust over geologic time. In this work, Hf-176/Hf-177 ratios were determined for detrital zircon fractions from 2.0-2.5, 2.6-3.0, and pre-3.0 Gyr old sandstones from the Canadian-Shield, the North-Atlantic, the Wyoming, and the Kaapvaal Cratons. Results pointed to small amounts of continental crust prior to 3.0 Gyr ago and a rapid addition of continental crust between 2.5 and 3.0 Gyr ago, consistent with the gradual growth of continental crust, and giving evidence against no-growth histories.

  9. 77 FR 71621 - Atlantic Wind One (ATLW1) Commercial Leasing for Wind Power on the Outer Continental Shelf...

    Science.gov (United States)

    2012-12-03

    ... Bureau of Ocean Energy Management Atlantic Wind One (ATLW1) Commercial Leasing for Wind Power on the... Management (BOEM), Interior. ACTION: Proposed Sale Notice for Commercial Leasing for Wind Power on the Outer... Assessment (EA) and Finding of No Significant Impact (FONSI) for commercial wind lease issuance and...

  10. Do physical and chemical factors structure the macrobenthic community at a continental slope in the NE Atlantic?

    NARCIS (Netherlands)

    Flach, E.; Thomsen, L.

    1998-01-01

    Macrofauna density, biomass and community structure together with several characteristics of the sediment and flow velocity were estimated in May 1994 and August 1995 at seven stations ranging from 208 m to 4470 m water depth along the OMEX- transect in the Goban Spur area (NE Atlantic). In 1994 fou

  11. Distribution of marine birds on the mid- and North-Atlantic US outer continental shelf. Technical progress report, January 1978-July 1980

    Energy Technology Data Exchange (ETDEWEB)

    Powers, K.D.; Pittman, G.L.; Fitch, S.J.

    1980-09-01

    The species composition, distribution, and abundance of marine birds on continental shelf waters from Cape Hatteras to the Bay of Fundy were examined using ships-of-opportunity. Northern Fulmar, Cory's Shearwater, Greater Shearwater, Sooty Shearwater, Wilson's Storm-Petrel, Gannet, Red Phalarope, Great Black-backed Gull, Herring Gull, and Black-legged Kittiwake were the most abundant and common species. These species were ecologically dominant within the bird community in numbers and biomass. Georges Bank and Gulf of Marine regions generally had greatest estimates of standing stock and biomass; whereas, in the Middle Atlantic region these estimates were consistently lowest. Species diversity throughout the study area was greatest in spring and least in fall. Oceanic fronts at the continental shelf break and at Nantucket Shoals influenced the distribution of Wilson's Storm-Petrels and Red Phalaropes. Fishing activities were particularly important to Larus gull distribution. Fishes, squids, and crustaceans were the most important groups of prey items in diets of nine bird species. An oiled bird or pollution index was developed. According to the index, frequency of oiled birds was greatest in winter and spring, and gulls made up the majority of species with oiled plumages.

  12. Shallow geological environment of Krishna–Godavari offshore, eastern continental margin of India as inferred from the interpretation of high resolution sparker data

    Indian Academy of Sciences (India)

    G Anitha; M V Ramana; T Ramprasad; P Dewangan; M Anuradha

    2014-03-01

    Krishna–Godavari offshore basin, a part of the eastern continental margin of India is a proven petroliferous basin. Recent drilling in this area in search of gas hydrates reveals that the upper ∼300 m thick Quaternary–Recent strata comprised of nannofossil bearing rich clays and, fractures/faults are the suitable zones for gas hydrates accumulation. Therefore, the knowledge about the shallow geological environments and its architecture are significantly important in assessing the gas hydrates potential of this area. In order to enhance the geological understanding, the newly acquired high resolution seismic (HRS) reflection data in this gas hydrates prone area is interpreted. The processed seismic sections show a maximum penetration of 562 ms TWT (∼450 m) underneath the seabed with high resolution stratification. An attempt has been made to: (i) deduce the shallow geological environment from the reflection characteristics, and, (ii) assign tentative ages under the constraints of drilling/coring results. We further explained the observed folded structures on the surface and subsurface through a mechanism linked to shale tectonism and neotectonic activity.

  13. Source and sink characteristics of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

    Science.gov (United States)

    Li, Chao; Lv, Chengfu; Chen, Guojun; Zhang, Gongcheng; Ma, Ming; Shen, Huailei; Zhao, Zhao; Guo, Shuai

    2017-02-01

    The "source-conduit-sink" model is crucial for studying deep-water sedimentary systems along a continental margin. Using seismic data, bulk rare earth element compositions of sediments and zircon U-Pb age data, we examined the supply and deposition (i.e., the source and sink) of the sediments in the Central Canyon of the South China Sea. Five phases of secondary canyon fill are present in the Central Canyon. The natural levees developed at the head of phase 1 of the secondary canyon deposits indicate that the Central Canyon initially developed at 10.5 Ma. The sediments in the Central Canyon were supplied by the Ledong submarine fan, and the provenance of the material in the Ledong submarine fan and Central Canyon was eastern Vietnam. Large amounts of sediments were transported through the Central Canyon to the Shuangfeng Basin and deposited during four phases of submarine fan development. Phases 1-3 of the Shuangfeng submarine fans are composed of deep-water branching channel and inter-channel sediments. Phase 4 of the Shuangfeng submarine fan consists of deep-water channel and lobe sediments. Tectonic events, including the broad uplift of the Tibetan Plateau and central-southern Vietnam during the late Miocene, reversal of the strike-slip Red River Fault, and rapid subsidence in the Qiongdongnan Basin at approximately 5.5 Ma, provided favourable conditions for the growth of the Ledong submarine fan, Central Canyon and Shuangfeng submarine fan system.

  14. Paleomagnetism on the Quaternary marine sediment at the DH-1 long-core site in the Korean continental margin of the East Sea

    Science.gov (United States)

    Ryang, Woo Hun; Lee, Byungju

    2014-05-01

    A long core of 23.6 m was acquired in the Korean continental margin of the western East Sea. The core site of the DH-1 is located in the offshore of the Donghae City and the water depth is 357.8 m deep. In this area, the paleomagnetism and magnetostratigraphy were firstly reported using 420 samples collected from the long-core sediments. Based on the inclination distribution of the depositional remanent magnetization, the DH-1 core could be divided into two upper and lower units at the boundary of 1750 cm below seafloor. The upper unit is characterized by a positive polarity, whereas the lower unit by a negative polarity. The boundary of the upper and lower units was interpreted as the Brunhes-Matuyama boundary (778 ka). The chemical components of tephra layer at 2014 cm below seafloor belong to alkaline series, plotted between the tephra components of the Mount Baekdu and Ulleung Island. Key words: magnetostratigraphy, Brunhes-Matuyama boundary, tephra, East Sea Acknowledgements: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0025733) and by the Ministry of Knowledge Economy through the grant of Marine Geology and Geophysical Mapping Project (GP2010-013).

  15. Diversity and distribution of methane-oxidizing microbial communities associated with different faunal assemblages in a giant pockmark of the Gabon continental margin

    Science.gov (United States)

    Cambon-Bonavita, M. A.; Nadalig, T.; Roussel, E.; Delage, E.; Duperron, S.; Caprais, J. C.; Boetius, A.; Sibuet, M.

    2009-12-01

    A giant 800-m-diameter pockmark named REGAB was discovered on the Gabon continental margin actively emitting methane at a water depth of 3200 m. The microbial diversity in sediments from four different assemblages of chemosynthetic organisms, Mytilidae, Vesicomyidae, Siboglinidae and a bacterial mat, was investigated using comparative 16S rRNA gene sequence analysis. Aggregates of anaerobic methanotrophic archaea (ANME-2) and bacteria of the Desulfosarcina/Desulfococcus cluster were found in all four chemosynthetic habitats. Fluorescence in situ hybridization targeting the ANME-2/ Desulfosarcina/Desulfococcus aggregates showed their presence few centimeters (3-5 cm) below the surface of sediment. 16S rRNA gene sequences from all known marine ANME groups were detected in the pockmark sediments, as well as from both known bacterial partners. The archaeal diversity was limited to the ANME cluster for all investigated samples. The bacterial diversity included members of the Proteobacteria, Bacilliales, Cytophaga/Flavobacteria, Verrucomicrobia, JS1 and Actinobacteria clusters. Bacterial 16S rRNA gene sequences related to those of known sulphide-oxidizing symbionts were recovered from tissues of several invertebrates including vesicomyid clams and siboglinid tubeworms of REGAB.

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

    Directory of Open Access Journals (Sweden)

    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.

  17. Small-scale variability in the coupling/uncoupling of bacteria, phytoplankton and organic carbon fluxes along the continental margin of the Gulf of Lions, Northwestern Mediterranean Sea

    Science.gov (United States)

    Van Wambeke, F.; Heussner, S.; Diaz, F.; Raimbault, P.; Conan, P.

    2002-06-01

    A High Frequency Flux (HFF) experiment was conducted during spring 1997 on the continental slope of the Gulf of Lions (Northwestern Mediterranean Sea) with the aim of examining the dynamical and biological processes controlling particle transfer in this margin environment. Within this general framework, a special attention was paid to short temporal and small spatial variations of phytoplankton and bacterial production through six hydrological and biological surveys performed during a 7-week period at nine sampling stations located on a 10×20-mile grid. Downward fluxes of particulate organic carbon at each station were measured by traps deployed at 240 m depth. The f-ratio and the ratio of integrated bacterial to primary production (IBP/IPP ratio), computed as indexes of biological export for each survey and station, did not provide a clear, unambiguous understanding of the importance of biological processes in the cycling of carbon in the upper water column. However, the data collected allowed to draw up carbon budgets for the different phases of the experiment. The comparison of primary production with measured and estimated organic carbon removal terms (sinking, cycling through the microbial food web, grazing by ciliates and metazoans) showed that a balance was never reached between fluxes of production and removal of organic carbon during the course of the experiment. The system shifted from an initial situation of 'missing' carbon (removal>production) to one of 'excess' carbon (removalimportant factor affecting the budget.

  18. Middle Triassic magma mixing in an active continental margin: Evidence from mafic enclaves and host granites from the Dewulu pluton in West Qinling, central China

    Science.gov (United States)

    Huang, X.; Mo, X.; Yu, X.

    2015-12-01

    The Qinling-Dabie-Sulu orogen was formed through the collision of the North and South China blocks, but the precise timing of the closure of the Paleo-Tethys ocean between the two blocks remains debated. Large volumes of Triassic granites associated with mafic microgranular enclaves (MMEs) were emplaced in the Qinling terrane. This paper presents field observations, petrography, geochronology and geochemistry of the MMEs and their host granites from the Dewulu pluton in West Qinling. The host rocks comprise granodiorite and granodioritic porphyry, and the The MMEs range in composition from gabbroic diorite to diorite. Zircon LA-ICP-MS U-Pb ages suggest that the granites and MMEs were coeval at ca. 245 Ma. The granites are relatively enriched in LILE and depleted in HFSE, and have evolved Sr-Nd-Pb and zircon Hf isotopic compositions [initial 87Sr/86Sr = 0.7070-0.7076, ɛNd(t) = -7.5 to -6.8, ɛHf(t) = -8.2 to -4.2], indicative of an origin from the amphibolitic lower crust. The near-primitive gabbro-dioritic MMEs bear a remarkable geochemical resemblance to the high-magnesium andesite (HMA), such as moderate SiO2 (~55 wt.%), low FeOT/MgO (~0.75), high Cr (268-308 ppm) and MgO (8.58-8.77 wt.%) with Mg# of ~70. Additionally, they exhibit lower initial 87Sr/86Sr, higher ɛNd(t) and ɛHf(t), and more radiogenic Pb isotopes than the dioritic MMEs which share similar isotopic compositions with the granites. These features, together with the presence of the specific minerals in the MMEs (e.g., felsic xenocrysts and acicular apatite), point to mixing process between the lower crust-derived magmas and the melts produced by the reaction of the subducting sediment-derived components and the overlying mantle. Taking into account the regional occurrence of synchronous plutonic-volcanic complexes (250-234 Ma) ranging from basaltic to granitic variants, we suggest that the Dewulu pluton formed in an active continental margin in response to the local extension triggered by the

  19. Sedimentary Environment and Climate Evolution at the Northern Continental Margin of the South China Sea During the Last Glacial Cycle and Holocene

    Science.gov (United States)

    Tomczak, M.; Kaiser, J.; Borowka, R. K.; Chen, H.; Zhang, J.; Harff, J.; Qiu, Y.; Witkowski, A.

    2014-12-01

    Climate, oceanographic and sea level history during last glacial cycle (LGC) and Holocene at the NW continental margin of the South China Sea (SCS) are investigated within the SECEB project. For that purpose two sediment cores (HDQ2 & 83PC) and single-channel seismic sections were selected to serve as a proxy data source for paleoceanographic and paleoclimatic reconstructions. The sedimentary facies is interpreted by multi-proxy approaches considering micropaleontological, sedimentological and geochemical analyses. According to 14C and OSL datings, sediments of shallow water drill core HDQ2 (88.3 m) cover a time span of ca. 115 kyr BP. Seismic images of the sampling site show a series of reflectors which can be correlated with coarse layers of core HDQ2. These layers are interpreted as transgression / regression horizons. Due to the age model it is possible to correlate these horizons with the general sea level dynamics within the SCS as it is displayed in relative sea level excursions for the MIS 5 to 2 from the Sunda Shelf (Hanebuth et al. 2011). Core 83PC (8.6 m) retrieved from the continental slope provide constant record and calm environment. Therefore, this core is used as a source for data proxy for environmental reconstructions. According to δ18O and paleomagnetic analysis, a good age model which indicate age of this core to ca. 110 kyr BP was elaborated and help correlate the paleoenvironmental data with core HDQ2. Alkenones, δ18O, the Mg/Ca ratio, and microfossil proxies serve for paleo-SST curves and monsoon variability reconstructions. δ15N and δ13C indicate nutrient supply to the marine environment. Diatomological analysis outlines the environmental evolution and interrelations between their parameters during the LGC. Interpretation of seismic profiling allowed identification of submarine paleo-delta. It's anticipated that deposited sediments descent from the Hainan Island and allow correlation of the source and sink area.Hanebuth, T.J.J, Voris, H

  20. Current meter data from moored current meter casts in the North Atlantic Ocean as part of the Outer Continental Shelf - South Atlantic (OCS-South Atlantic) project from 01 August 1978 - 20 March 1979 (NODC Accession 7900312)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Current meter data were collected using moored current meter casts in the North Atlantic Ocean from August 1, 1978 to March 20, 1979. Data were submitted by Science...

  1. Structural basins, terrain contacts, and large fault displacements on the central California continental margin, constrained by seismic data and submersible observations

    Science.gov (United States)

    Ramirez, T. M.; Caress, D.; Aiello, I.; Greene, G.; Lewis, S.; Paull, C.; Silver, E.; Stakes, D.

    2002-05-01

    A synthesis of reprocessed multichannel seismic data and lithologies based on ROV sampling defines a series of block faulted basement rocks off-shore central California in the Monterey Bay region with lithologies associated with either Salinia or Franciscan microterrains and their overlying sediments. In 1990, the USGS conducted a multi-channel seismic (MCS) reflection survey (cruise L-3-90-NC) off the central California coast between Monterey Bay and Bodega Bay. Sixty-two MCS lines were collected on the R/V S. P. Lee using a 2.6 km long, 48-channel streamer and a tuned 2400 cubic inch array of ten airguns. We have reprocessed several critical lines and reviewed the entire dataset to map basement structures and the lithostratigraphy of sediments. From preliminary analyses of the MCS data, the development of Smooth Ridge appears controlled by two prominent basement highs forming a trapped basin for sediment accumulation. Meanders in the lower Monterey Canyon, seen in bathymetric data, are constrained by these uplifted basement blocks. The lithologies of basement samples collected by ROV show spatial relationships that correlate with the seismic character. Faulted contacts between the blocks of the Franciscan and Salinia microterrains are consistent with 100+ Km of right slip displacement on the San Gregorio fault zone. These contacts are onlapped by Tertiary sediments forming a series of basins such as Smooth Ridge aligned along the continental margin. On-going analyses of these data will allow for a better understanding of the Monterey Bay regional tectonics and contribute to the mapping of the western edge of the paleo-subduction zone along central California.

  2. Structural and functional study of the nematode community from the Indian western continental margin with reference to habitat heterogeneity and oxygen minimum zone

    Directory of Open Access Journals (Sweden)

    R. Singh

    2015-07-01

    Full Text Available We studied patterns of nematode distribution along the western Indian continental margin to determine the influence of habitat heterogeneity and oxygen minimum 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. Nematodes were identified to species and classified according to biological/functional traits. A total of 110 nematode species belonging to 24 families were found along the transect. Mean nematode density was higher on the shelf (176 ind 10 cm−2, 34 m depth than on the slope (124 ind 10 cm−2 or in the basin 62.9 ind 10 cm−2. Across the entire study area, the dominant species were Terschellingia longicaudata, (15.2 %, Desmodora sp 1, Sphaerolaimus gracilis, and Theristus ensifer; their maximum density was at shelf stations. Multidimensional scaling ordination (nMDS of the nematode species abundance data indicated the effect of different zones (ANOSIM; Global R = 0.607; P = 0.028, but it was not the same in case of functional traits. Only seven species were found exclusively in the oxygen minimum zone: Pselionema sp 1, Choanolaimus sp 2, Halichoanolaimus sp 1, Cobbia dentata, Daptonema sp 1, Trissonchulus sp 1, and Minolaimus sp 1. Moreover, in our study, species diversity was higher on the shelf than on the slope or in the basin. The distinctive features of all three zones as based on nematofaunal abundance were also reflected in the functional traits (feeding types, body shape, tail shape, and life history strategy. Correlation with a number of environmental variables indicated that food quality (measured as the organic carbon content and chlorophyll content and oxygen level were the major factors that influenced the nematode community (structural and functional.

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

    Science.gov (United States)

    Thresher, Ronald; Althaus, Franziska; Adkins, Jess; Gowlett-Holmes, Karen; Alderslade, Phil; Dowdney, Jo; Cho, Walter; Gagnon, Alex; Staples, David; McEnnulty, Felicity; Williams, Alan

    2014-01-01

    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.

  4. Patterns and Dynamics of Rifting on Passive Continental Margin from Shelf to Slope of the Northern South China Sea:Evidence from 3D Analogue Modeling

    Institute of Scientific and Technical Information of China (English)

    Sun Zhen; Zhou Di; Wu Shimin; Zhong Zhihong; Myra Keep; Jiang Jianqun; Fan Hao

    2009-01-01

    Affected by thermal perturbation due to mantle uprising,the rheological structure of the lithosphere could be modified,which could lead to different rifting patterns from shelf to slope in a passive continental margin.From the observed deformation style on the northern South China Sea and analogue modeling experiments,we find that the rift zone located on the shelf is characterized by half grabens or simple grabens controlled mainly by long faults with large vertical offset,supposed to be formed with normal lithasphere extension.On the slope,where the lithosphere is very hot due to mantle upwelling and heating,composite grabens composed of symmetric grabens developed.The boundary and inner faults are all short with small vertical offset.Between the zones with very hot and normal lithosphere,composite half grnbens composed of half grabens or asymmetric grabens formed,whose boundary faults are long with large vertical offset,while the inner faults are relatively short.Along with the thickness decrease of the brittle upper crust due to high temperature,the deformation becomes more sensitive to the shape of a pre-existing weakness zone and shows orientation variation along strike.When there was a bend in the pre-existing weakness zone,and the basal plate was pulled by a clockwise rotating stress,the strongest deformation always occurs along the middle segment and at the transition area from the middle to the eastern segments,which contributes to a hotter lithosphere in the middle segment,where the Baiyun (白云) sag formed.

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

    Directory of Open Access Journals (Sweden)

    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.

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

    Science.gov (United States)

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

    2001-01-01

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

  7. Miocene uplift of the NE Greenland margin linked to plate tectonics: Seismic evidence from the Greenland Fracture Zone, NE Atlantic

    DEFF Research Database (Denmark)

    Døssing Andreasen, Arne; Japsen, Peter; Watts, Anthony B.;

    2016-01-01

    to inner margin episodic uplift, including the formation of coastal mountains. The origin of these events remains enigmatic. We present a seismic reflection study from the Greenland Fracture Zone – East Greenland Ridge (GFZ-EGR) and the NE Greenland shelf. We document a regional intra-Miocene seismic...

  8. Environmental implication of subaqueous lava flows from a continental Large Igneous Province: Examples from the Moroccan Central Atlantic Magmatic Province (CAMP)

    Science.gov (United States)

    El Ghilani, S.; Youbi, N.; Madeira, J.; Chellai, E. H.; López-Galindo, A.; Martins, L.; Mata, J.

    2017-03-01

    The Late Triassic-Early Jurassic volcanic sequence of the Central Atlantic Magmatic Province (CAMP) of Morocco is classically subdivided into four stratigraphic units: the Lower, Middle, Upper and Recurrent Formations separated by intercalated sediments deposited during short hiatuses in volcanic activity. Although corresponding to a Large Igneous Province formed in continental environment, it contains subaqueous lava flows, including dominant pillowed flows but also occasional sheet flows. We present a study of the morphology, structure and morphometry of subaqueous lava flows from three sections located at the Marrakech High-Atlas (regions of Aït-Ourir, Jbel Imzar and Oued Lhar-Herissane), as well as an analysis of the sediments, in order to characterize them and to understand their environmental meaning. The analysis of clays by the diffraction method X-ray revealed the presence of illite, mica, phengite, céladonite, talc and small amounts of quartz, hematite, calcite and feldspar, as well as two pairs of interbedded irregular (chlorite Smectite/chlorite-Mica). Fibrous minerals such as sepiolite and palygorskite were not detected. The peperite of Herissane region (Central High Atlas) provided an excellent overview on the factors favoring the magma-sediment interaction. These are the products of a mixture of unconsolidated or poorly consolidated sediments, low permeability with a low viscosity magma. The attempt of dating palynology proved unfortunately without results.

  9. Relationship between isotopic composition (Δ18O and Δ13C and plaktonic foraminifera test size in core tops from the Brazilian Continental Margin

    Directory of Open Access Journals (Sweden)

    Paula Franco-Fraguas

    2011-12-01

    Full Text Available Stable oxygen (δ18O and carbon (δ13C isotopic signature registered in fossil planktonic foraminifera tests are widely used to reconstruct ancient oceanographic conditions. Test size is a major source of stable isotope variability in planktonic foraminifera found in sediment samples and thus can compromise paleoceanographic interpretations. Test size/stable isotope (δ18O and δ13C relationships were evaluated in two planktonic foraminifer species (Globigerinoides ruber (white and Globorotalia truncatulinoides (right in two core tops from the Brazilian Continental Margin. δ18 Omeasurements were used to predict the depth of calcification of each test size fraction. δ13C offsets for each test size fraction were then estimated. No systematic δ18O changes with size were observed in G. ruber (white suggesting a similar calcification depth range (c.a. 100 m during ontogeny. For G. truncatulinoides (right δ18O values increased with size indicating ontogenetic migration along thermocline waters (250-400 m. δ13C measurements and δ13C offsets increased with size for both species reflecting well known physiological induced ontogenetic-related variability. In G. ruber (white the largest test size fractions (300µm and >355µm more closely reflect δ13C DIC indicating they are best suited for paleoceanographic studies.O tamanho de testa dos foraminíferos é uma importante fonte de variabilidade isotópica (δ18O e δ13C em amostras de sedimento marinho comprometendo as interpretações paloeceanograficas. No presente estudo, avaliou-se a relação entre o sinal isotópico medido em diferentes frações de tamanho de testa das espécies planctônicas, Globigerinoides ruber (branca e Globorotalia truncatulinoides (dextral em amostras de topo de dois testemunhos localizados na Margem Continental Brasileira. Os valores de δ18O foram utilizados para estimar a profundidade de calcificação de cada fração de tamanho. Os desequilíbrios nos valores de

  10. Wave speed structure of the eastern North American margin

    Science.gov (United States)

    Savage, B.; Covellone, B. M.; Shen, Y.

    2017-02-01

    The eastern North American margin (ENAM) is the result of nearly a billion years of continental collision and rifting. To the west of this margin lies thick continental lithosphere of the North American craton, and to the east is oceanic lithosphere in the Atlantic. The substantial changes in lithosphere thickness at this boundary are thought to drive asthenosphere upwelling along the edge of the continent. Through iterative, full-waveform, ambient noise tomography, we observe a heterogeneous low wave speed margin along the continent in the upper mantle. Multiple low wave speed features imaged within the margin are consistent with asthenospeheric upwelling due to edge-driven convection. Also within the margin are high wave speed anomalies that maybe the remnants of eclogitic delamination of the Appalachian crustal root, which contribute to convection at the margin. Edge driven, small-scale convection keeps the margin weak and thus controls the large scale plate tectonic patterns and the crustal deformation. The imaged mantle wave speed anomalies, interpreted as edge-driven convection, correlate with and may increase the likelihood of damaging earthquakes in the eastern portion of North America.

  11. A comparative study of Pleistocene phosphorites from the continental slope off western India

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.; Naqvi, S.W.A.; DileepKumar, M.; Cardinal, D.; Michard, A.; Borole, D.V.; Jacobs, E.; Natarajan, R.

    of Sedimentologists 945 INTRODUCTION Present-day phosphogenesis and phosphorite for- mation occur on the continental margins of Baja California, Peru–Chile and east Australia in the Pacific Ocean, Namibia and south-west Africa in the Atlantic Ocean and south... (Piper et al., 1988) and the phosphorites of Namibia, Cape Province and Agulhas Bank off South Africa (McArthur & Walsh, 1984), which exhibit shale- like patterns. Strontium (Sr), samarium (Sm) and neodym- ium (Nd) isotopes were determined by mass...

  12. Regional seismic stratigraphy and controls on the Quaternary evolution of the Cape Hatteras region of the Atlantic passive margin, USA

    Science.gov (United States)

    Mallinson, D.J.; Culver, S.J.; Riggs, S.R.; Thieler, E.R.; Foster, D.; Wehmiller, J.; Farrell, K.M.; Pierson, J.

    2010-01-01

    Seismic and core data, combined with amino acid racemization and strontium-isotope age data, enable the definition of the Quaternary stratigraphic framework and recognition of geologic controls on the development of the modern coastal system of North Carolina, U.S.A. Seven regionally continuous high amplitude reflections are defined which bound six seismic stratigraphic units consisting of multiple regionally discontinuous depositional sequences and parasequence sets, and enable an understanding of the evolution of this margin. Data reveal the progressive eastward progradation and aggradation of the Quaternary shelf. The early Pleistocene inner shelf occurs at a depth of ca. 20-40 m beneath the western part of the modern estuarine system (Pamlico Sound). A mid- to outer shelf lowstand terrace (also early Pleistocene) with shelf sand ridge deposits comprising parasequence sets within a transgressive systems tract, occurs at a deeper level (ca. 45-70 m) beneath the modern barrier island system (the Outer Banks) and northern Pamlico Sound. Seismic and foraminiferal paleoenvironmental data from cores indicate the occurrence of lowstand strandplain shoreline deposits on the early to middle Pleistocene shelf. Middle to late Pleistocene deposits occur above a prominent unconformity and marine flooding surface that truncates underlying units, and contain numerous filled fluvial valleys that are incised into the early and middle Pleistocene deposits. The stratigraphic framework suggests margin progradation and aggradation modified by an increase in the magnitude of sea-level fluctuations during the middle to late Pleistocene, expressed as falling stage, lowstand, transgressive and highstand systems tracts. Thick stratigraphic sequences occur within the middle Pleistocene section, suggesting the occurrence of high capacity fluvial point sources debouching into the area from the west and north. Furthermore, the antecedent topography plays a significant role in the evolution

  13. Geological studies of the COST No. B-3 Well, United States Mid-Atlantic continental slope area

    Science.gov (United States)

    Scholle, Peter A.

    1980-01-01

    The COST No. B-3 well is the first deep stratigraphic test to be drilled on the Continental Slope off the Eastern United States. The well was drilled in 2,686 ft (819 m) of water in the Baltimore Canyon trough area to a total depth of 15,820 ft (4,844 m) below the drill platform. It penetrated a section composed of mudstones, calcareous mudstones, and limestones of generally deep water origin to a depth of about 8.200 ft (2,500 m) below the drill floor. Light-colored, medium- to coarse-grained sandstones with intercalated gray and brown shales, micritic limestones, and minor coal and dolomite predominate from about 8,200 to 12,300 ft (2,500 to 3,750 m). From about 12,300 ft (3,750 m) to the bottom, the section consists of limestones (including oolitic and intraclastic grainstones) with interbedded fine-to medium-grained sandstones, dark-colored fissile shales, and numerous coal seams. Biostratigraphic examination has shown that the section down to approximately 6,000 ft (1,830 m) is Tertiary. The boundary between the Lower and Upper Cretaceous sections is placed between 8,600 and 9,200 ft (2,620 and 2,800 m) by various workers. Placement of the Jurassic-Cretaceous boundary shows an even greater range based on different organisms; it is placed variously between 12,250 and 13,450 ft (3,730 and 5,000 m). The oldest unit penetrated in the well is considered to be Upper Jurassic (Kimmeridgian) by some workers and Middle Jurassic (Callovian) by others. The Lower Cretaceous and Jurassic parts of the section represent nonmarine to shallow-marine shelf sedimentation. Upper Cretaceous and Tertiary units reflect generally deeper water conditions at the B-3 well site and show a general transition from deposition at shelf to slope water depths. Examination of cores, well cuttings, and electric logs indicates that potential hydrocarbon-reservoir units are present throughout the Jurassic and Cretaceous section. Porous and moderately permeable limestones and sandstones have been

  14. Linking benthic hydrodynamics and cold-water coral occurrences: A high-resolution model study at three cold-water coral provinces in the NE Atlantic

    NARCIS (Netherlands)

    Mohn, C.; Rengstorf, A.; White, M.; Mienis, F.; Soetaert, K.; Grehan, A.; Duineveld, G.

    2014-01-01

    Observations from numerous cold-water coral locations in the NE Atlantic show energetic near-bottom flow dynamics along the European continental margin at individual coral mounds and mound clusters. Dynamics are largely controlled by tide-topography interaction generating and enhancing periodic moti

  15. 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.

  16. A Multitracer Study of Sub Millenial Climate Variability During The Last Glacial-interglacial On The NE Atlantic Margin

    Science.gov (United States)

    Byrne, C.

    The timing of depositional events from the Scottish Ice Sheet are of interest as its rela- tively small size and situation at the limits of the Devensian glaciation will have made it responsive to even small changes in climate. of particular interest are the decay of the ice sheet during the last deglaciation and climate oscillations such as the Younger Dryas and Bølling/Allerød events. Studies of MD 95-2006, from the Barra Fan (5702N, 1004W), have highlighted the rapid fluctuations in climatic/oceanographic conditions and ice sheet dynamics recorded in the core. AMS dates on parallel foraminiferal and sedimentary organic matter samples are currently being prepared for the highly expanded 10-15kyr period (6.5m). A de- tailed chronology will be constructed, allowing more precise interpretation of high- frequency oscillations. Organic biomarker work is being carried out to track the amount and nature of organic matter inputs associated with the expansion of the glaciers and iceberg calving at the edge of the shelf. High-resolution fluctuations have been documented in 13Corg signature, suggesting major changes in the au- tochthonous marine and terrigenous organic matter. Also currently underway are source-specific organic biomarkers such as lignin phenols, algal-specific sterols, n- alkanes and alkenones. These will be used to characterise past changes in productivity and phytoplankton community structure, and to provide a SST record (UK37). It is hoped that this high-resolution record will answer the question whether the Scot- tish Ice Sheet has fluctuated independently from the Laurentide Ice Sheet, and to es- tablish their relative phasing. Also whether the timing of the regional Younger Dryas and Heinrich event 1 are synchronous with the equivalent events in the open North Atlantic Ocean.

  17. 南海大陆边缘动力学:科学实验与研究进展%Dynamics of the continental margins of South China Sea: scientific experiments and research progresses

    Institute of Scientific and Technical Information of China (English)

    李家彪

    2011-01-01

    Comprehensive geophysical survey, including the multi-channel seismic survey with long streamer and large air-gun source and the wide-angle refraction/reflection seismic survey of OBS, has been deployed in the southern margin and Southwest Sub-basin of the South China Sea for the first time. Based on the interpretation of these geophysical data, combined with studies on tectonic structure, geochemistry, and dynamic simulation, etc, our project worked out the dynamics of the continental margin in South China Sea. Major conclusions are as follows: Two sea-floor spreading events occurred in Cenozoic. The first episode happened between 33. 5 ~ 25 Ma, and after a 1. 5 Ma tectonic adjustment, started the second episode of sea-floor spreading between 23. 5~15. 5 Ma. In both episodes the South China Sea experienced propagation rifting and spreading from east to west, resulting in a structural framework featured with blocks innorth-south direction and segments in east-west direction; Cenozoic marginal basins in the northern and southern continental margins show different rift-terminated time, which correspond with the two episodic sea-floor spreading respectively. The continental crust of the South China Sea might have experienced depth-dependent stretching. The lower crust and top of upper mantle have been magnetized and no obvious velocity anomalies of the mantle have been found in oceanic basin. South China Sea margins are a kind of magma-poor rifting, although lower crustal bodies of high-velocity occur in the east of the northern margin, but without SDR. The origin and evolution of sediment basins on northern and southern continental margins are very distinct, and the hydrocarbon accumulations are distributed in a cirque with oil outside and gas inside. We believe that the hydrocarbon-bearing perspectives in southern continental marginal basins are superior to these northern continental marginal basins. In Mesozoic the northern and southern margin of the South

  18. Indian Ocean margins

    Digital Repository Service at National Institute of Oceanography (India)

    Naqvi, S.W.A.

    in the latter two areas. Some of these fluxes are expected to be substantial in the case of Indonesian continental margins and probably also across the eastern coasts of Africa not covered in this chapter. However, a dearth of information makes these margins...

  19. Structure and history of submarine slope failures at the Cape Fear submarine landslide, U.S. Atlantic margin

    Science.gov (United States)

    Miller, N. C.; Chaytor, J. D.; Hutchinson, D. R.; Ten Brink, U. S.; Flores, C. H.

    2015-12-01

    New multi-channel seismic (MCS), chirp sub-bottom, and multibeam bathymetry and backscatter data image the Late Pleistocene-Holocene age Cape Fear submarine landslide (CFS) along its complete ~375 km length, from the multiple headwalls at ~2500 m water depth on the slope to the lobate, low-relief toe at ~5400 m water depth. A surficial chaotic mass transport deposit (MTD) filling the failure scar exceeds 100 m in thickness over large sections of the deposit, thinning towards the margins of the slide. Below 5000 m, the CFS truncates the surficial MTD of the Cape Lookout Landslide in several places, indicating that it post-dates the Cape Lookout Landslide. At depth, the MCS data image the edge of the Cape Fear salt diapir and a seismically transparent region that may be associated with fluid flow focused along the edge of the diapir. This potential fluid pathway sits directly beneath the headwalls of the CFS, supporting the hypothesis that the salt diapir is responsible for the failure, either through deformation of sediments during salt emplacement or by focusing of fluids, or both. The MCS data also image several earlier MTDs. These deposits are confined to sediments younger than the early Cenozoic, consistent with interpretations of major canyon cutting in the Eocene and initiation of intense deep and erosive currents in the Late Paleogene. These processes can over-steepen and redistribute slope sediments, enhancing conditions for slope failures and salt diapirism.

  20. Reefs of the Jurassic-Cretaceous west Atlantic margin : an overview of settings, types, facies trends, depositional styles and terminations (with reservoir implications)

    Energy Technology Data Exchange (ETDEWEB)

    Eliuk, L.S. [GeoTours Consulting Inc., Calgary, AB (Canada)

    2005-07-01

    In the past 40 years, approximately 20 exploratory wells have been drilled in the Jurassic-Cretaceous Abenaki Formation near-margin carbonate sequences off the Atlantic coast. These include the pioneer wells drilled in the 1970s offshore Nova Scotia, a mid-1980s group including 3 Baltimore Canyon wells in the United States, and those following EnCana's Deep Panuke 1998 gas discovery offshore Nova Scotia. A comparison of these wells has revealed 2 margin settings over deep basement highs versus prograded carbonates, 3 reef-reef mound/slope types, and an overall vertical facies trend that reveals an upward progression from microbial-rich slope beds to shallower forereef to reef and reef-flat beds initially rich in coralline sponges, followed by more microsolenid corals and bioeroded stormreworked coral-rich and oncolitic debris beds up to oolitic shoals. The top of carbonate bank sequences may be replaced gradually by shallow-water siliciclastics near deltaic depocentres or abruptly by deeper-water sponge-reef-derived beds. Smaller-scale similar flooding and shoaling patterns exist within this overall style that allow sequence or parasequence subdivision in Nova Scotia following an initial oolitic flooding event immediately above the Misaine shale. The association of deltas and reef termination suggests drowning by nutrient poisoning. The mid-Mesozoic biotas appear more robust by living in close proximity to siliciclastics. Being at the carbonate shelf margin and in a non-argillaceous shallow water reef-associated facies would appear to be necessary requirements for gas-bearing reservoir development in the Abenaki, but they are not sufficient. Originally porous oolitic grainstones are tight in areas where they are deeply buried in the Panuke area. Siliciclastic burial influenced the limestone cementation, resulting in potential stratigraphic trapping where offset by subsurface dolomitization and leaching fed by fractures or faults in coarser reef

  1. Distribution of long-lived radioactive iodine isotope (I-129) in pore waters from the gas hydrate fields on the continental margins: Indication for methane source of gas hydrate deposits

    Science.gov (United States)

    Tomaru, H.; Lu, Z.; Fehn, U.

    2011-12-01

    Because iodine has a strong association with organic matters in marine environments, pore waters in high methane potential region, in particular gas hydrate occurrences on the continental margins, are enriched significantly in iodine compared with seawater. Natural iodine system is composed of stable and radioactive species, I-129 (half-life of 15.7 Myr) has been used for estimating the age of source formations both for methane and iodine, because iodine can be liberated into pore water during the degradation of organic matter to methane in deep sediments. Here we present I-129 age data in pore waters collected from variety of gas hydrate occurrences on the continental margins. The I-129 ages in pore waters from these locations are significantly older than those of host sediments, indicating long-term transport and accumulation from deep/old sediments. The I-129 ages in the Japan Sea and Okhotsk Sea along the plate boundary between the North American and Amurian Plates correspond to the ages of initial spreading of these marginal seas, pointing to the massive deposition of organic matter for methane generation in deep sediments within limited periods. On the Pacific side of these areas, organic matter-rich back stop is responsible for methane in deep-seated gas hydrate deposits along the Nankai Trough. Deep coaly sequences responsible for deep conventional natural gas deposits are also responsible for overlying gas hydrate deposits off Shimokita Peninsula, NE Japan. Those in the Gulf of Mexico are correlative to the ages of sediments where the top of salt diapirs intrude. Marine sediments on the Pacific Plate subducting beneath the Australian Plate are likely responsible for the methane and iodine in the Hikurangi Trough, New Zealand. These ages reflect well the regional geological settings responsible for generation, transport, and accumulation of methane, I-129 is a key to understand the geological history of gas hydrate deposition.

  2. Variability of aerosol, gaseous pollutants and meteorological characteristics associated with continental, urban and marine air masses at the SW Atlantic coast of Iberia

    Directory of Open Access Journals (Sweden)

    J.-M. Diesch

    2011-12-01

    Full Text Available Measurements of the ambient aerosol were performed at the Southern coast of Spain, within the framework of the DOMINO (Diel Oxidant Mechanisms In relation to Nitrogen Oxides project. The field campaign took place from 20 November until 9 December 2008 at the atmospheric research station "El Arenosillo" (37°5'47.76" N, 6°44'6.94" W. As the monitoring station is located at the interface between a natural park, industrial cities (Huelva, Seville and the Atlantic Ocean a variety of physical and chemical parameters of aerosols and gas phase could be characterized in dependency on the origin of air masses. Backwards trajectories were examined and compared with local meteorology to classify characteristic air mass types for several source regions. Aerosol number and mass as well as polycyclic aromatic hydrocarbons and black carbon concentrations were measured in PM1 and size distributions were registered covering a size range from 7 nm up to 32 μm. The chemical composition of the non-refractory submicron aerosol was measured by means of an Aerosol Mass Spectrometer (Aerodyne HR-ToF-AMS. Gas phase analyzers monitored various trace gases (O3, SO2, NO, NO2, CO2 and a weather station provided meteorological parameters.

    Lowest average submicron particle mass and number concentrations were found in air masses arriving from the Atlantic Ocean with values around 2 μg m−3 and 1000 cm−3. These mass concentrations were about two to four times lower than the values recorded in air masses of continental and urban origins. For some species PM1-fractions in marine air were significantly larger than in air masses originating from Huelva, a closely located city with extensive industrial activities. The largest fraction of sulfate (54% was detected in marine air masses and was to a high degree not neutralized. In addition small concentrations of

  3. Net sea-air CO2 fluxes and modelled pCO2 in the southwestern subtropical Atlantic continental shelf during spring 2010 and summer 2011

    Science.gov (United States)

    Ito, Rosane Gonçalves; Garcia, Carlos Alberto Eiras; Tavano, Virginia Maria

    2016-05-01

    Sea-air CO2 fluxes over continental shelves vary substantially in time on both seasonal and sub-seasonal scales, driven primarily by variations in surface pCO2 due to several oceanic mechanisms. Furthermore, coastal zones have not been appropriately considered in global estimates of sea-air CO2 fluxes, despite their importance to ecology and to productivity. In this work, we aimed to improve our understanding of the role played by shelf waters in controlling sea-air CO2 fluxes by investigating the southwestern Atlantic Ocean (21-35°S) region, where physical, chemical and biological measurements were made on board the Brazilian R. V. Cruzeiro do Sul during late spring 2010 and early summer 2011. Features such as discharge from the La Plata River, intrusions of tropical waters on the outer shelf due to meandering and flow instabilities of the Brazil Current, and coastal upwelling in the Santa Marta Grande Cape and São Tomé Cape were detected by both in situ measurements and ocean colour and thermal satellite imagery. Overall, shelf waters in the study area were a source of CO2 to the atmosphere, with an average of 1.2 mmol CO2 m-2 day-1 for the late spring and 11.2 mmol CO2 m-2 day-1 for the early summer cruises. The spatial variability in ocean pCO2 was associated with surface ocean properties (temperature, salinity and chlorophyll-a concentration) in both the slope and shelf waters. Empirical algorithms for predicting temperature-normalized surface ocean pCO2 as a function of surface ocean properties were shown to perform well in both shelf and slope waters, except (a) within cyclonic eddies produced by baroclinic instability of the Brazil Current as detected by satellite SST imagery and (b) in coastal upwelling regions. In these regions, surface ocean pCO2 values were higher as a result of upwelled CO2-enriched subsurface waters. Finally, a pCO2 algorithm based on both sea surface temperature and surface chlorophyll-a was developed that enabled the spatial

  4. Determining how the pelagic ecosystem over the continental shelf of the Bay of Biscay (NE Atlantic) functions: An approach using mesozooplankton enzyme activities as descriptors

    Science.gov (United States)

    Bergeron, Jean-Pierre; Delmas, Daniel; Koueta, Noussithé

    2009-04-01

    A fisheries research cruise conducted in 2000 offered a first opportunity to take simultaneous measurements of the activities of three enzymes in mesozooplankton samples collected at a regional scale over the continental shelf of the Bay of Biscay in the NE Atlantic, with the aim of characterizing main aspects of the functioning of the biotic environment of small pelagic fish populations. The activity of the digestive endopeptidase trypsin was selected to characterize the assimilation rate of proteins, whereas pyruvate kinase (PK) was chosen as an indicator of carbohydrate assimilation and aspartate transcarbamylase (ATC) provided an overall assessment of mesozooplankton productivity. The Bay of Biscay region is subject to various strong physical driving forces that directly affect the primary structure of the pelagic food web. On our cruise, the phytoplankton biomass distribution reflected these different physical influences: diatoms dominated the nutrient-enriched coastal water; picoplankton dominated the northern-central part where nutrients were depleted; and nanoplankton were abundant at the shelf break where internal waves provided an input of nutrients. These and other results (on bacteria, particulate organic carbon distribution, among others) illustrate the differences that exist in the microbial food webs of different sectors of the bay. The living matter produced was characterized by the quality and quantity of the smallest prey items that were available to higher trophic levels. Variations in mesozooplankton enzyme activities may agree well not only with classically expected results, but also present unexpected special features: high ATC specific activities were measured around the mouth of the Gironde, in the nutrient-rich desalted water of the plume, but surprisingly not in front of the Loire river. PK specific activities reflected preponderantly the balance between phytoplankton cells sizes and the related bacterial abundance resulting from nutrient

  5. Regional comparison of syn- and post-rift sequences in salt and salt-free basins offshore Brazil and Angola/Namibia, South Atlantic

    Science.gov (United States)

    Strozyk, Frank; Back, Stefan; Kukla, Peter

    2015-04-01

    The large South Atlantic basins offshore South America and Africa record a highly variable syn- to post-breakup tectono-stratigraphic development. The present-day diversity in the structural and sedimentary architecture of the conjugate margins offshore southern Brazil, Namibia and Angola reflects variations in the interplay of a number of controlling factors, of which the most important are i) the structural configuration of each margin segment at the time of break-up, ii) the post break-up geodynamic history including tectonics and magmatism, and iii) variations in the type, quantity and distribution of sediment input to the respective margin segment. Particularly the basins around the Rio Grande Rise - Walvis Ridge volcanic complex show a pronounced tectono-stratigraphic asymmetry both along the respective continental margin and across the Atlantic. Only a few attempts exist to establish a regional tectono-stratigraphic correlation framework across the South Atlantic Ocean, mainly because of the lack of data across entire margin segments and limited resolution of basin wide geophysics. Still unresolved issues particularly concern the explanation of the basin-specific geological evolution of respective margin segments along the same continental margin, as well as the correlation of conjugate basins and margin segments across the Atlantic Ocean. In our study we present interpretations and first-pass restorations of regional 2D seismic-reflectivity data from the large basins offshore Brazil (Pelotas Basin, Santos Basin, Campos Basin, Espirito Santo Basin), and offshore Namibia and Angola (Walvis Basin, Namibe Basin, Benguela Basin, Kwanza Basin), which represent four adjacent pairs of conjugate basins on both sides of the South Atlantic. Results are used to document and compare on a basin-scale the contrasting styles of rift and post-rift settings during and after the continental breakup.

  6. Methane Gas Hydrate Stability Models on Continental Shelves in Response to Glacio-Eustatic Sea Level Variations: Examples from Canadian Oceanic Margins

    OpenAIRE

    2013-01-01

    We model numerically regions of the Canadian continental shelves during successive glacio-eustatic cycles to illustrate past, current and future marine gas hydrate (GH) stability and instability. These models indicated that the marine GH resource has dynamic features and the formation age and resource volumes depend on the dynamics of the ocean-atmosphere system as it responds to both natural (glacial-interglacial) and anthropogenic (climate change) forcing. Our models focus on the interval b...

  7. Neotectómca transpresiva en la plataforma continental Suribérica Atlántica

    OpenAIRE

    Maestro González, Adolfo; Somoza, L.; Díaz del Río, Víctor; Vázquez Garrido, Juan Tomás; Martín Alfageme, S.; Alveirinho, J. M.; Barnolas, Antonio; Vegas, Ramón

    1997-01-01

    Detailed structural, interpretátioh of a network of high-resolution seismic lines runnig across, , and along the continental shelf of Faro (south-lberian Atlantic margin) provides evidences of recent deformation structures associated with the Africa-Eurasia plate boundary. In these seismic profiles, palm-tree type flower structures interpreted as strike-slip faults affect the non-consolidated Holocene muddy shelf deposits and the underlying semi-cemented sandy shelf-wedges of the Pleistocene ...

  8. Historical developments in marine geology and some aspects of fine-grained sediments along the continental margins of India and Bengal fan

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    of the Deccan Traps and kaolinite-smectite-rich assemblage of the Gneissic province (Fig. 5). The tidal currents operating at the Gulf of Kachchh act as barriers to the along-shore transport of Indus-borne sediments. The influence of SW monsoon current can... on the continental slope of the NW India are an admixture of Indus-borne and Deccan Trap sediments. Sr and Nd isotopes are distinct for the sediments derived from glacial weathering and those derived from chemical weathering and also exhibit distinct variations...

  9. New Insights into SouthWest Africa Margin Evolution; Integrating Reconstructions and Restorations

    Science.gov (United States)

    Paton, Douglas; Markwick, Paul; Hodgson, Neil; Rowlands, Holly; Thompson, Phil

    2015-04-01

    Over the last few years there has been a significant increase in the quality and availability of passive margin scale transect derived from new geophysical techniques. Coupled with plate reconstructions this has unquestionably led to a paradigm shift in our understanding of the architecture of conjugate passive continental margins and the transition from continental to oceanic lithosphere. These sections, however, still commonly only consider architecture of the margin by placing conjugate sections together in their pre-break up position without considering realistic architecture of the margin at the time of deposition. In this study we use plate reconstructions to consider location of sections at a variety of time steps. We then apply stratigraphic and structural techniques to determine the geometry of the depositional sequence to predict the architecture and water depth of the margin at the time of deposition. Our study focuses on the south-eastern Atlantic and we use these techniques to understand key time intervals, including the geometry at the end of the rift phase, the emplacement of seaward dipping reflections, the Barremian sag phase and early Cretaceous deltaic sequences. This provides us with new insights into the Southern Atlantic basin evolution as well as providing better constraints for lithospheric processes and palaeogeographic reconstructions during these intervals that are fundamental to the hydrocarbon prospectivity of the region.

  10. What role does crustal heterogeneity play on continental break-up; the interplay of a foldbelt, rift system and ocean basin in the South Atlantic

    Science.gov (United States)

    Paton, Douglas; Mortimer, Estelle; Hodgson, Neil

    2015-04-01

    Although extensively studied, two key questions remain unanswered regarding the evolution of the southern South Atlantic. Firstly, where is the Cape Foldbelt (CFB) in offshore South Africa? The CFB is part of the broader Gonwanian Orogeny that prior to South Atlantic rifting continued into the Ventana Foldbelt of Argentina but to date its location in the offshore part of South Africa remains enigmatic. Secondly, the conjugate rift basin to South Africa is the Colorado Basin in Argentina but why does it trend east-west despite its perpendicular orientation to the Atlantic spreading ridge? Current plate models and structural understands cannot explain these fundamental questions. We use newly acquired deep reflection seismic data in the Orange Basin, South Africa, to develop a new structural model for the southern South Atlantic. We characterise the geometry of the Cape Foldbelt onshore and for the first time correlate it into the offshore. We show that it has a north-south trend immediately to the north of the Cape Peninsula but then has a syntaxis (Garies syntaxis) that results in a change to an east-west orientation. This forms the missing jigsaw piece of the Atlantic reconstruction as this is directly beside the restored Colorado Basin. When considered within the pre-break up structural configuration our observations imply that prior to the main phase of Atlantic rifting in the Mezosoic there was significant variation in crustal geometry incorporating the Orange Basin of South Africa, the Colorado Basin and the Gariep Belt of Namibia. These faults were active during Gondwana rifting, but the Colorado rift failed resulting in the present day location of the South Atlantic. Not only do our results improve our understanding of the evolution of the South Atlantic ocean, they highlight the importance of differentiating between early rift evolution and strain localisation during the subsequent rift phase prior to seafloor spreading.

  11. Early Cambrian granitoids of North Gondwana margin in the transition from a convergent setting to intra-continental rifting (Ossa-Morena Zone, SW Iberia)

    Science.gov (United States)

    Sánchez-García, T.; Pereira, M. F.; Bellido, F.; Chichorro, M.; Silva, J. B.; Valverde-Vaquero, P.; Pin, Ch.; Solá, A. R.

    2014-07-01

    Two distinct Cambrian magmatic pulses are recognized in the Ossa-Morena Zone (SW Iberia): an early rift-(ER) and a main rift-related event. This Cambrian magmatism is related to intra-continental rifting of North Gondwana that is thought to have culminated in the opening of the Rheic Ocean in Lower Ordovician times. New data of whole-rock geochemistry (19 samples), Sm-Nd-Sr isotopes (4 samples) and ID-TIMS U-Pb zircon geochronology (1 sample) of the Early Cambrian ER plutonic rocks of the Ossa-Morena Zone are presented in this contribution. The ER granitoids (Barreiros, Barquete, Calera, Salvatierra de los Barros and Tablada granitoid Massifs) are mostly peraluminous granites. The Sm-Nd isotopic data show moderate negative ɛNdt values ranging from -3.5 to +0.1 and TDM ages greatly in excess of emplacement ages. Most ER granitoids are crustal melts. However, a subset of samples shows a transitional anorogenic alkaline tendency, together with more primitive isotopic signatures, documenting the participation of lower crust or mantle-derived sources and suggesting a local transient advanced stage of rifting. The Barreiros granitoid is intrusive into the Ediacaran basement of the Ossa-Morena Zone (Série Negra succession) and has yielded a crystallization age of 524.7 ± 0.8 Ma consistent with other ages of ER magmatic pulse. This age: (1) constrains the age of the metamorphism developed in the Ediacaran back-arc basins before the intrusion of granites and (2) defines the time of the transition from the Ediacaran convergent setting to the Lower Cambrian intra-continental rifting in North Gondwana.

  12. Glaciomarine sedimentation and bottom current activity on the north-western and northern continental margins of Svalbard during the late Quaternary

    Science.gov (United States)

    Chauhan, Teena; Noormets, Riko; Rasmussen, Tine L.

    2016-04-01

    Palaeo-bottom current strength of the West Spitsbergen Current (WSC) and the influence of the Svalbard-Barents Sea Ice Sheet (SBIS) on the depositional environment along the northern Svalbard margins are poorly known. Two gravity cores from the southern Yermak Plateau and the upper slope north of Nordaustlandet, covering marine isotope stage (MIS) 1 to MIS 5, are investigated. Five lithofacies, based on grain size distribution, silt/clay ratio, content and mean of sortable silt (SS), are distinguished to characterise the contourite-dominated sedimentary environments. In addition, depositional environments are described using total organic carbon (TOC), total sulphur (TS) and calcium carbonate (CaCO3) contents of sediments. Facies A, containing coarse SS, suggests strong bottom current activity and good bottom water ventilation conditions as inferred from low TOC content. This facies was deposited during the glacial periods MIS 4, MIS 2 and during the late Holocene. Facies B is dominated by fine SS indicating weak bottom current and poor ventilation (cf. high TOC content of 1.2-1.6%), and correlates with the MIS 4/3 and MIS 2/1 transition periods. With an equal amount of clay and sand, fine SS and high content of TOC, facies C indicates reduced bottom current strength for intervals with sediment supply from proximal sources such as icebergs, sea ice or meltwater discharge. This facies was deposited during the last glacial maximum. Facies D represents mass-flow deposits on the northern Svalbard margin attributed to the SBIS advance at or near the shelf edge. Facies E sediments indicating moderate bottom current strength were deposited during MIS 5 and MIS 3, and during parts of MIS 2. This first late Quaternary proxy record of the WSC flow and sedimentation history from the northern Svalbard margin suggests that the oceanographic conditions and ice sheet processes have exerted first-order control on sediment properties.

  13. Milankovitch cyclicity in modern continental margins: stratigraphic cycles in terrigenous shelf settings; El registro de la ciclicidad de Milankovitch en margenes continentales actuales: ciclos estratigraficos en plataformas terrigenas

    Energy Technology Data Exchange (ETDEWEB)

    Lobo, F. J.; Ridente, D.

    2013-06-01

    We present a synthesis of the sedimentary responses to Late Quaternary Milankovitch-type sea-level cycles (100 and 20 kyr periodicities) as a basis for our investigations into the patterns and concepts of composite sequences in shallow-shelf settings. We describe the record of both 100 and 20 kyr cycles as documented worldwide and discuss the pattern of composite cyclicity mainly on the basis of previously published data from the Adriatic Sea and Gulf of Cadiz margins. Cycles of 100 kyr are those most frequently documented in Quaternary margins; they occur in the form of unconformity-bounded depositional sequences dominated by fairly uniform pro gradational-regressive units and more variable, though less well developed, transgressive deposits. Sequence boundaries correspond to prominent polygenic (regressive-transgressive) erosional surfaces that bear witness to considerable transgressive reworking of the original sub-aerial unconformity. Although the progradational units making up the greater part of these sequences have usually been interpreted as a record of a falling sea-level stage, recent evidence is pointing towards a more complex stratigraphic picture, including a distinction between relative highstand and lowstand deposits. The 20-kyr stratigraphic motifs show greater variation compared to that displayed by the more common 100-kyr sequences, particularly in the basic structure of systems tracts and the nature of bounding surfaces. The two case studies described here, the Adriatic Sea and Gulf of Cadiz margins, highlight the fact that, concomitantly with an increase in frequencies of cycles and sequences, sediment supply and the dynamics of their dispersal significantly affected the stratigraphic response to the main controlling factor, which was sea-level, thus determining the variety of expression in the 20 kyr cycles. (Author)

  14. New geochemical and geochronological data of early Cambrian of (SW Iberia): Calc-alkaline magmatism in the transition from active to passive continental margin in North Gondwana

    OpenAIRE

    Sanchez-Garcia, Teresa; Pereira, M. Francisco; Bellido, Felix; Chichorro, Martim; Silva, J. Brandao; Valverde-Vaquero, Pablo; Pin, Christian; Solá, Rita

    2011-01-01

    The Ossa-Morena Zone (SW Iberia) displays a well-preserved record of the history of the northern Gondwana margin in Late Ediacaran-Early Cambrian times. This period of time is marked by the late-stage evolution of the Cadomian magmatic arc and related back-arc basins (c. 590-545 Ma), and the onset of rifting and widespread magmatism (c. 530-500 Ma) that led to the opening of the Rheic Ocean. Here we present new geochemical and geochronological data on some Cambrian granitoids of Ossa-Morena ...

  15. Zooplankton data from zooplankton net casts and other instruments in the Delaware Bay and North Atlantic Ocean as part of the Ocean Continental Shelf (OCS - Mid Atlantic) project, 03 November 1976 - 18 November 1977 (NODC Accession 7800340)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Zooplankton data were collected using zooplankton net casts and other instruments in the Delaware Bay and North Atlantic Ocean from November 3, 1976 to November 18,...

  16. Bacteriology data from moored buoy casts and other instruments in the Delaware Bay and North Atlantic Ocean during the Ocean Continental Shelf (OCS-Mid Atlantic Ocean) project, 05 November 1976 - 16 August 1977 (NODC Accession 7800207)

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — Bacteriology data were collected using moored buoy casts and other instruments in the Delaware Bay and North Atlantic Ocean from November 5, 1976 to August 16, 1977....

  17. 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

  18. The Roles of Advection and In Situ Growth in Determining the Dynamics of Continental Shelf Zooplankton: High Frequency Measurements of Zooplankton Biomass Coupled with Measurements of Secondary Productivity in the Middle Atlantic Bight

    Energy Technology Data Exchange (ETDEWEB)

    Smith, Sharon L.

    1999-03-26

    Evaluation of the role of continental margins in planetary carbon cycles can be approached in various ways, with the extremes being knowledge generated either by large-scale studies of a few basic characteristics of the carbon cycle of shelves worldwide (comparative approach) or by temporally intensive studies of a few sites selected to typify contrasting processes. Mechanisms of cross-shelf transfer, for example, are presently of great interest and within the US there are at least four differing continental shelf environments in which cross-shelf processes are driven by storms (southern Bering Sea, northeastern US), by jets and eddies (northern California coast), by freshwater runoff (Bering Sea, Gulf of Mexico), and by frontal meanders and filaments of the Gulf Stream (southeastern US). Because the type and magnitude of the physical forcing, and its variability on an annual scale, are fundamental to the response of the carbon cycle, investigation of each of these shelves would offer insight useful to predictive global understanding of the carbon cycle on continental shelves.

  19. Arctic and N Atlantic Crustal Thickness and Oceanic Lithosphere Distribution from Gravity Inversion

    Science.gov (United States)

    Kusznir, Nick; Alvey, Andy

    2014-05-01

    The ocean basins of the Arctic and N. Atlantic formed during the Mesozoic and Cenozoic as a series of distinct ocean basins, both small and large, leading to a complex distribution of oceanic crust, thinned continental crust and rifted continental margins. The plate tectonic framework of this region was demonstrated by the pioneering work of Peter Ziegler in AAPG Memoir 43 " Evolution of the Arctic-North Atlantic and the Western Tethys" published in 1988. The spatial evolution of Arctic Ocean and N Atlantic ocean basin geometry and bathymetry are critical not only for hydrocarbon exploration but also for understanding regional palaeo-oceanography and ocean gateway connectivity, and its influence on global climate. Mapping crustal thickness and oceanic lithosphere distribution represents a substantial challenge for the Polar Regions. Using gravity anomaly inversion we have produced comprehensive maps of crustal thickness and oceanic lithosphere distribution for the Arctic and N Atlantic region, We determine Moho depth, crustal basement thickness, continental lithosphere thinning and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir 2008). Gravity anomaly and bathymetry data used in the gravity inversion are from the NGA (U) Arctic Gravity Project and IBCAO respectively; sediment thickness is from a new regional compilation. The resulting maps of crustal thickness and continental lithosphere thinning factor are used to determine continent-ocean boundary location and the distribution of oceanic lithosphere. Crustal cross-sections using Moho depth from the gravity inversion allow continent-ocean transition structure to be determined and magmatic type (magma poor, "normal" or magma rich). Our gravity inversion predicts thin crust and high continental lithosphere thinning factors in the Eurasia, Canada, Makarov, Podvodnikov and Baffin Basins

  20. IODP Expedition 307: A high Resolution Record of Contourite Deposition and Palaeoclimatic Forcing on the Eastern Porcupine Seabight (Irish Continental Margin)

    Science.gov (United States)

    Odonnell, R.; Thierens, M.; Murray-Wallace, C.; Dorschel, B.; Wheeler, A.

    2007-12-01

    In May 2005, IODP Expedition 307 recovered a continuous sediment succession from a contourite drift sequence from the eastern slope of the Porcupine Seabight. The contourite drift is adjacent to the Belgica Mound Province of which one cold-water coral carbonate mound (Challenger Mound) was also drilled. Grain size analysis of 95m of decalcified Pleistocene succession from IODP Core 1318B with 10cm resolution provides a detailed record of grain size distribution and variability for the last ca. 780kyr. Based on these data, we interpret the climatic history, changing sedimentological, hydrodynamic and palaeoenvironmental conditions within the Belgica Mound province. This information, in conjunction with other analyses provides important regional information on palaeoclimatic forcing of sedimentary systems on the NE Atlantic slope during the Pleistocene. So far, End-Member Modelling and sortible silt analyses have identified significant changes in the sedimentary processes over time. Correlations with the abundance of ice rafted detritus highlight the changes in climate condition as the main factor for changes in the slope sedimentary system. Results indicate periods with a coarse sediment input alternating with prolonged finer grained sediment reflecting sporadic periods of along-slope contourite deposition, down-slope terrigenous components and ice- rafted debris linked to ice mass dynamics. Given the proximity of the study area to the Belgica cold-water coral carbonate mounds, this information provide the regional hydrodynamic and paleoenvironmental context for a segment of the mound story and help elucidate carbonate mound growth vs. sediment input throughout the last c. 700kyr. Although much effort has been invested in the study of the Irish offshore in recent years, this project is unique in the detail at which the Pleistocene sediments will be examined and the depth of borehole recovery promises to provide answers on the interplay of sedimentology, climate and

  1. 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

  2. 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

  3. 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)

  4. 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

  5. Genesis of the Madang Cenozoic sodic alkaline basalt in the eastern margin of the Tibetan Plateau and its continental dynamic implications

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    The Madang Cenozoic sodic alkaline basalt occurred in the eastern margin of the Tibetan Plateau, where is a key tectonic transform region of Tibet, North China, and Yangtze blocks. The basalts are characterized by the variation in SiO2=42%―51%, Na2O/K2O>4, belonging to the sodic alkaline basalt series. The rocks are enriched in Ba, Th, Nb, Ta, relative to a slight depletion in K, Rb in the trace and rare earth element (REE) spider diagrams that are similar to the typical oceanic island alkaline basalt. The Sr-Nd-Pb isotopic compositions suggest that they are derived from a mixed mantle reservoir. The western Qinling-Songpan tectonic region was controlled by Tibet, North China and Yangtze blocks since Cenozoic, therefore, the region was in the stage of the substance converge from the mantle to upper crust, producing a mixed mantle reservoir in the studied area. The Madang basalts occurred in the specific tectonic background, they result from partial melting of a mixed asthenospheric mantle reservoir in the western Qinling-Songpan tectonic node.

  6. 活动大陆边缘花岗岩类演化——以福州复式岩体为例%Evolution of Granitoids in the Active Continental Margin : a Case Study of the Fuzhou Compound Complex

    Institute of Scientific and Technical Information of China (English)

    林清茶; 程雄卫; 张玉泉; 汪方跃

    2011-01-01

    中国东南部处于扬子地块、印度板块和太平洋板块的中间地区,位于亚洲东部大陆边缘的最南段,是中生代以来欧亚板块与太平洋板块相互作用非常活跃的区域.本文通过对产在活动大陆边缘的福州复式岩体的花岗岩类中的锆石进行LA-ICP-MS U-Pb定年,得到早期的涧田花岗闪长岩、中期的丹阳二长花岗岩一福州钾长花岗岩和晚期的魁歧晶洞碱性花岗岩年龄分别为110Ma、100~107 Ma、95 Ma,属于燕山晚期,相当于早白垩世中晚期.说明产在活动大陆边缘的福州复式岩体,从早期的钙碱性Ⅰ型花岗岩,到晚期的碱性A型花岗岩,其侵位时间相应从早白垩世中-晚期到晚白垩世早期.表明福州复式岩体岩浆作用的时间持续了15Ma.%Southeast China, located at the interior part of Yangtze block, Indian plate and Pacific plate and the southmost of the continental margin of Eastern Asian, has been most active region due to interaction between Eurasian plate and Pacific plate since the Mesozoic. LA-ICP-MS U-Pb dating of zircons from the granitoids of the Fuzhou compound complex in the active continental margin yields an age of HOMa for the early Jiantian granodiorite, an age of 100~107 Ma for the mid-stage Dangyang monozonitic granite, and an age of 95 Ma for the late-stage Kuiji alkaline granite. All these data suggest they formed in a Yanshanian epoch, equivalent to mid- ot late Late Cretaceous. These data indicate that the Fuzhou compound complex evolved from early calci-alkaline I-type granite to late alkaline A-type granite, and correspondingly, emplacement lasted from mid- and late Early Cretaceous to early Late Cretaceous. Our research shows that magmatism of the Fuzhou compound complex had been active for at least 15 Ma.

  7. Atlantic Offshore Seabird Dataset Catalog

    Data.gov (United States)

    U.S. Geological Survey, Department of the Interior — Several bureaus within the Department of Interior compiled available information from seabird observation datasets from the Atlantic Outer Continental Shelf into a...

  8. Links between the recruitment success of northern European hake (Merluccius merluccius L.) and a regime shift on the NE Atlantic continental shelf

    KAUST Repository

    Goikoetxea, Nerea

    2013-07-01

    The distribution of northern European hake (Merluccius merluccius L.) extends from the Bay of Biscay up to Norwegian waters. However, despite its wide geographical distribution, there have been few studies on fluctuations in the European hake populations. Marine ecosystem shifts have been investigated worldwide and their influence on trophic levels has been studied, from top predator fish populations down to planktonic prey species, but there is little information on the effect of atmosphere-ocean shifts on European hake. This work analyses hake recruitment success (recruits per adult biomass) in relation to environmental changes over the period 1978-2006 in order to determine whether the regime shift identified in several abiotic and biotic variables in the North Sea also affected the Northeast Atlantic shelf oceanography. Hake recruitment success as well as parameters such as the sea surface temperature, wind patterns and copepod abundance changed significantly at the end of the 1980s, demonstrating an ecological regime shift in the Northeast Atlantic. Despite the low reproductive biomass recorded during the last decades, hake recruitment success has been higher since the change in 1989/90. The higher productivity may have sustained the population despite the intense fishing pressure; copepod abundance, warmer water temperatures and moderate eastward transport were found to be beneficial. In conclusion, in 1988/89 the Northeast Atlantic environment shifted to a favourable regime for northern hake production. This study supports the hypothesis that the hydro-climatic regime shift that affected the North Sea in the late 1980s may have influenced a wider region, such as the Northeast Atlantic. © 2013 John Wiley & Sons Ltd.

  9. Elastic thickness estimates at north east passive margin of North America and its implications

    Indian Academy of Sciences (India)

    R T Ratheesh Kumar; Tanmay K Maji; Suresh Ch Kandpal; D Sengupta; Rajesh R Nair

    2011-06-01

    Global estimates of the elastic thickness (Te) of the structure of passive continental margins show wide and varying results owing to the use of different methodologies. Earlier estimates of the elastic thickness of the North Atlantic passive continental margins that used flexural modelling yielded a Te value of ∼20–100 km. Here, we compare these estimates with the Te value obtained using orthonormalized Hermite multitaper recovered isostatic coherence functions. We discuss how Te is correlated with heat flow distribution and depth of necking. The E–W segment in the southern study region comprising Nova Scotia and the Southern Grand Banks show low Te values, while the zones comprising the NE–SW zones, viz., Western Greenland, Labrador, Orphan Basin and the Northern Grand Bank show comparatively high Te values. As expected, Te broadly reflects the depth of the 200–400°C isotherm below the weak surface sediment layer at the time of loading, and at the margins most of the loading occurred during rifting. We infer that these low Te measurements indicate Te frozen into the lithosphere. This could be due to the passive nature of the margin when the loads were emplaced during the continental break-up process at high temperature gradients.

  10. Hydrothermal Mineralization on the Mesoproterozoic Passive Continental Margins of China:A Case Study of the Langshan-Zha'ertaishan Belt, Inner Mongolia, China

    Institute of Scientific and Technical Information of China (English)

    PENG Runmin; ZHAI Yusheng

    2004-01-01

    Most ore-forming characteristics of the Langshan-Zha'ertaishan hydrothermal exhalation belt, which consists of the Dongshengmiao, Huogeqi, Tanyaokou and Jiashengpan large-superlarge Zn-Pb-Cu-Fe sulfide deposits, are most similar to those of Mesoproterozoic SEDEX-type provinces of the world. The characteristics include: (1) All deposits of this type in the belt occur in third-order fault-basins in the Langshan-Zha'ertaishan aulacogen along the northern margin of the North China Platform; (2) these deposits with all their orebodies hosted in the Mesoproterozoic impure dolomite-marble and carbonaceous phyllite (or schists) have an apparent stratabound nature; ores display laminated and banded structures,showing clear depositional features; (3) there is some evidence of syn-sedimentary faulting, which to a certain extent accounts for the temporal and spatial distribution and the size of the orebodies in all deposits and the formation of intrabed conglomerates and breccias; (4) they show lateral and vertical zonation of sulfides; (5) The Cu/(Pb+Zn+Cu) ratio of the large and thick Pb+Zn+Cu orebodies gradually decreases from bottom to top; and (6) barite is interbedded with pyrites and sometimes with sphalerite. However, some characteristics such as the Co/Ni radio of the pyrites, the volcanism, for example, of the Langshan-Zha'ertaishan metallogenic belt, are different from those of the typical SEDEX deposits of the world. The meta-basic volcanic rock in Huogeqi, the sodic bimodal volcanic rocks in the Dongshengmiao and potassic bimodal-volcanic rocks with blastoporphyritic and blasto-glomeroporphyritic texture as well as blasto-amygdaloidal structure in the Tanyaokou deposits have been discovered in the only ore-bearing second formation of the Langshan Group in the past 10 years. The metallogeny of some deposits hosted in the Langshan Group is closely related to syn-sedimentary volcanism based on the following facts: most of the lead isotopes in sphalerite, galena

  11. A harbinger of plate tectonics: a commentary on Bullard, Everett and Smith (1965) 'The fit of the continents around the Atlantic'.

    Science.gov (United States)

    Dewey, John F

    2015-04-13

    In the 1960s, geology was transformed by the paradigm of plate tectonics. The 1965 paper of Bullard, Everett and Smith was a linking transition between the theories of continental drift and plate tectonics. They showed, conclusively, that the continents around the Atlantic were once contiguous and that the Atlantic Ocean had grown at rates of a few centimetres per year since the Early Jurassic, about 160 Ma. They achieved fits of the continental margins at the 500 fathom line (approx. 900 m), not the shorelines, by minimizing misfits between conjugate margins and finding axes, poles and angles of rotation, using Euler's theorem, that defined the unique single finite difference rotation that carried congruent continents from contiguity to their present positions, recognizing that the real motion may have been more complex around a number of finite motion poles. Critically, they were concerned only with kinematic reality and were not restricted by considerations of the mechanism by which continents split and oceans grow. Many of the defining features of plate tectonics were explicit or implicit in their reconstructions, such as the torsional rigidity of continents, Euler's theorem, closure of the Tethyan ocean(s), major continental margin shear zones, the rapid rotation of small continental blocks (Iberia) around nearby poles, the consequent opening of small wedge-shaped oceans (Bay of Biscay), and misfit overlaps (deltas and volcanic piles) and underlaps (stretched continental edges). This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

  12. How the structure of a continental margin affects the development of a fold and thrust belt. 3: evidences from field mapping and geological cross-sections in south-central Taiwan

    Science.gov (United States)

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

    2016-04-01

    The Eurasian Margin is obliquely colliding with the Luzon Arc to form the Taiwan orogen. This configuration is particularly apparent in south-central part of the island providing a case example to investigate the effects of structural inheritance in the development of the thrust and fold belt. The Eurasian Margin evolved from a pre-Cenozoic continental basement that underwent rifting in the Early Eocene and subsequent sea-floor spreading to form the South China Sea during the late Early Oligocene. The margin underwent localized extension in the Middle Miocene, before the initiation of collision with the Luzon Arc by the Early Miocene. The important along-strike changes in structure and topography of south-central Taiwan thrust and fold belt are evidenced in the detailed geological map and 3 balanced geological cross sections. A 3D tomography model is integrated in this study to help constrain the structure at depth. Major along-strike changes seem to be related to structures oriented at a high angle to the thrust system. These include changes in strike of thrusts and fold traces, the changing elevation of thrusts and stratigraphic contacts, and the growing importance of Middle Miocene sediments within the thrust system that take place from north to south. Horizontal slices of the tomography model illustrate that N-S changes in velocity have the orientation of the inherited structural grain of the Eurasian margin. In particular, the inherited location of the Mesozoic margin's shelf-slope transition affects the distribution of seismicity and the location of lateral stratigraphic and structural changes. Also, it appears to be associated with the inversion of Eocene- and Miocene-age extensional faults, deeply rooted in the pre-Cenozoic basement that trend oblique to the thrust belt. The inversion of inherited structures affects the uplift of Miocene syn-extensional and syn-tectonic Plio-Pleistocene foreland basin sediments, and of the pre-Cenozoic basement. Section A

  13. Tectonics and melting in intra-continental settings

    NARCIS (Netherlands)

    Gorczyk, Weronika; Vogt, Katharina

    2015-01-01

    Most of the geodynamic theories of deformation aswell asmetamorphismandmelting of continental lithosphere are concentrated on plate boundaries and are dominated by the effects of subduction upon deformation of the margins of continental lithospheric blocks. However, it is becoming increasingly appar

  14. 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

  15. The continental record and the generation of continental crust

    OpenAIRE

    Cawood, Peter Anthony; Hawkesworth, Chris; Dhuime, Bruno Philippe Marcel

    2013-01-01

    Continental crust is the archive of Earth history. The spatial and temporal distribution of Earth's record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and seawater and atmospheric proxies are distributed about a series of peaks and troughs. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, a...

  16. Dynamics of continental accretion.

    Science.gov (United States)

    Moresi, L; Betts, P G; Miller, M S; Cayley, R A

    2014-04-10

    Subduction zones become congested when they try to consume buoyant, exotic crust. The accretionary mountain belts (orogens) that form at these convergent plate margins have been the principal sites of lateral continental growth through Earth's history. Modern examples of accretionary margins are the North American Cordilleras and southwest Pacific subduction zones. The geologic record contains abundant accretionary orogens, such as the Tasmanides, along the eastern margin of the supercontinent Gondwana, and the Altaïdes, which formed on the southern margin of Laurasia. In modern and ancient examples of long-lived accretionary orogens, the overriding plate is subjected to episodes of crustal extension and back-arc basin development, often related to subduction rollback and transient episodes of orogenesis and crustal shortening, coincident with accretion of exotic crust. Here we present three-dimensional dynamic models that show how accretionary margins evolve from the initial collision, through a period of plate margin instability, to re-establishment of a stable convergent margin. The models illustrate how significant curvature of the orogenic system develops, as well as the mechanism for tectonic escape of the back-arc region. The complexity of the morphology and the evolution of the system are caused by lateral rollback of a tightly arcuate trench migrating parallel to the plate boundary and orthogonally to the convergence direction. We find geological and geophysical evidence for this process in the Tasmanides of eastern Australia, and infer that this is a recurrent and global phenomenon.

  17. 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

  18. Structure of the Gabon Margin from integrated seismic reflection and gravity data

    Science.gov (United States)

    Dupré, Stéphanie; Cloetingh, Sierd; Bertotti, Giovanni

    2011-06-01

    In the South Gabon Basin, deep multi-channel seismic reflection and gravity modeling analysis have shed light on key features of the structure of the margin. The thinned continental crust beneath the Gabon Margin appears to be composed of two distinct layers, separated by a clear, strong and more or less continuous reflector running in the 7-10 s TWT window. The lower crust is characterized by a higher density, intermediate between the lower values of the upper crust and the denser values of the mantle. The lower crust is irregularly shaped and presents lateral thickness variations along the direction of thinning and along the coast. In the offshore thinned continental domain, the lower and upper crust form a 20-25 km thick body. Crustal thicknesses point to a relatively sharp and narrow transition, along a few tens of kilometers, between the unthinned and the thinned continental crust. The high density layer identified offshore Gabon presents similar characteristics in density, geometry and spatial distribution, as the underplated magmatic bodies observed along volcanic margins, e.g. along the South Atlantic Namibia Margin or the North Atlantic Vøring Margin. Although this lower crustal body could possibly represent ultra mafic serpentinized rocks or high grade metamorphic crustal rocks, we suggest that it could be composed of mafic rocks. Magmas resulting from partial melting during rifting may underplate the crust and/or be intruded in the lower crust through a system of dykes and sills. In this view, the present-day crustal thicknesses along rifted margins, characterized by magmatic underplating and/or intrusion, are not representative of the thinning that the crust experienced during rifting. Results of this study point to relatively shallow sedimentary basins along the South Gabon Margin. The deepest offshore depocenters located under the westernmost side of the continental platform appear to be associated with the deepest syn-rift basins These basins seem

  19. Linking benthic hydrodynamics and cold-water coral occurrences: A high-resolution model study at three cold-water coral provinces in the NE Atlantic

    OpenAIRE

    2014-01-01

    Observations from numerous cold-water coral locations in the NE Atlantic show energetic near-bottom flow dynamics along the European continental margin at individual coral mounds and mound clusters. Dynamics are largely controlled by tide-topography interaction generating and enhancing periodic motions such as trapped waves, freely propagating internal tides and internal hydraulic jumps. In this study, linkages between key abiotic parameters and cold water coral occurrences are explored acros...

  20. 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

  1. Authigenic minerals from the continental margins

    Digital Repository Service at National Institute of Oceanography (India)

    Rao, V.P.

    . 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...

  2. Baddeleyite and zircon U Pb ages from the Kærven area, Kangerlussuaq: Implications for the timing of Paleogene continental breakup in the North Atlantic

    Science.gov (United States)

    Holm, Paul Martin; Heaman, Larry M.; Pedersen, Lise E.

    2006-11-01

    We report U-Pb zircon and baddeleyite age results for two mafic units in the Kangerlussuaq area which are part of the Paleogene East Greenland igneous province; the Kangerlussuaq macrodyke, which represents a feeder to some flood basalts, and the nearby Kærven Gabbro. Baddeleyite from the macrodyke yielded a concordant age of 54.7 ± 0.4 (2 σ) Ma and this is among the most precise age determinations from the province. This age is interpreted to reflect the time of emplacement. The macrodyke belongs to a swarm of dykes emplaced perhaps in a failed arm during continental rifting, and the age predates the completion of continental breakup at the end of emplacement of the Plateau Basalts of the East Greenland eruption sequence. Geochemically the macrodyke is correlated with the Milne Land Formation lavas. The magma experienced slight crustal contamination. Based on the age and geochemistry of the macrodyke, the age of the Skaergaard intrusion and Skrænterne Formation lavas, an age span of 1-2 Ma is confirmed for the extrusion of the entire Plateau Basalts. U-Pb analysis of zircon from the Kærven Gabbro yields an age of 53.0 ± 0.3 (2 σ) Ma. The Kærven Gabbro was intruded after extension had ceased in the area and we suggest that the post plateau basalt magmatism did not take place at a distinct later time, but instead that igneous activity continued for some time at a lower rate. Slightly fractionated HREEs indicate that the Kærven Gabbro magma was extracted at relatively shallow levels in the mantle.

  3. Meiofauna and macrofauna community structure in relation to sediment composition at the Iberian margin compared to the Goban Spur (NE Atlantic)

    NARCIS (Netherlands)

    Flach, E.; Muthumbi, A.; Heip, C.H.R.

    2002-01-01

    Meiofauna and macrofauna communities and several sediment characteristics were compared between a slope situated far from the coast (Goban Spur) and two transects across the Iberian Margin with steep slopes and close to the shore. The northern Galician transect (off La Coruña) was situated in an are

  4. Kinematics of the South Atlantic rift

    CERN Document Server

    Heine, Christian; Müller, R Dietmar

    2013-01-01

    The South Atlantic rift basin evolved as branch of a large Jurassic-Cretaceous intraplate rift zone between the African and South American plates during the final breakup of western Gondwana. By quantitatively accounting for crustal deformation in the Central and West African rift zone, we indirectly construct the kinematic history of the pre-breakup evolution of the conjugate West African-Brazilian margins. Our model suggests a causal link between changes in extension direction and velocity during continental extension and the generation of marginal structures such as the enigmatic Pre-salt sag basin and the S\\~ao Paulo High. We model an initial E-W directed extension between South America and Africa (fixed in present-day position) at very low extensional velocities until Upper Hauterivian times ($\\approx$126 Ma) when rift activity along in the equatorial Atlantic domain started to increase significantly. During this initial $\\approx$17 Myr-long stretching episode the Pre-salt basin width on the conjugate Br...

  5. North Atlantic Ocean deep-water processes and depositional environments: A study of the Cenozoic Norway Basin

    Science.gov (United States)

    Oline Hjelstuen, Berit; Andreassen, Elin V.

    2015-04-01

    Despite the enormous areas deep-water basins occupy in modern oceans, our knowledge about them remains poor. At depths of greater than 2000 m, the Cenozoic Norway Basin in the northernmost part of the Atlantic Ocean, is one such basin. Interpretation of 2D multichannel seismic data suggests a three-stage evolution for the Norway Basin. (1) Eocene-Pliocene. This time period is characterised by deposition of ooze-rich sediments in a widening and deepening basin. (2) Early-Middle Pleistocene. A significant shift in sedimentary processes and depositional environments took place in the Early Pleistocene. Mass failures initiated on the Norwegian continental slope, and three Early and Middle Pleistocene slide debrites, with maximum thicknesses of 600 m and sediment volumes of up to 25000 km3, were deposited. With ages estimated at c. 2.7-1.7 Ma, 1.7-1.1 Ma and 0.5 Ma, these slide deposits are among the largest identified worldwide, and among the oldest mapped along the entire NE Atlantic continental margin. (3) Late Pleistocene-Present. Since c. 0.5 Ma the Norway Basin has been effected by glacigenic debris flows, the Storegga Slide and hemipelagic-glacimarine sedimentation. These sedimentary processes were active during a time of repeated shelf-edge ice advances along the NE Atlantic continental margin. This study shows that deep-water basins represent dynamic depositional environments reflecting regional tectonic and climatic changes trough time.

  6. Nova contribuição para o estudo dos nematódeos de peixes do Oceano Atlântico: Costa Continental Portuguesa e Costa do Norte da Africa New contribution for study of nematodes of fishes from Atlantic Ocean: Continental Portuguese Coast and North African Coast

    Directory of Open Access Journals (Sweden)

    H. de Oliveira Rodrigues

    1975-01-01

    Full Text Available São estudadas 4 espécies de nematódeos encontradas em 21 peixes que foram coletados no Oceâno Atlântico na Costa Continental Portuguesa e na Costa Norte da África. Foram encontados 6 peixes dos 21 necropsiados parasitados por nematódeos. Os hospedeiros e os nematódeos encontrados são os seguintes: 3 exemplares de Solea solea, sendo um parasitado por Contraceaecum magnum; 3 exemplares de Batrachoides didactylus, sendo um parasitado por Contracaecum magnum e também por cucullanus hians; 7 exemplares de Pagellus bogaraveo, sendo 2 parasitados por Contracaecum bidentalum; 7 exemplares de Beryx decadactylus, sendo 2 parasitados por Contracaecum seriolae. Soela solea e Batrachoides didacylus são referidos pela primeira vez como hospedeiros de Contracaecum magnum. Contracaecum seriolae é referido pela primeira vez em Beryx decadactylus e no Oceano Atlântico. Batrachoides didactylus é referido pela primeira vez como hospedeiro de Cucullanus hians e Contracaecum bidentatum como parasito de Pagellus gobaraveo.In an examination of 21 fishes from Atlantic Ocean - Continental Portuguese Coast and North African Coast, 6 were parasited by nematodes. The species of fishes and the nematodes recovered are as follows: 3 samples of Solea solea in one of them we recovered Contracaecum magnum; 3 samples of Batrachoides didactylus in one of them we ecovered Contracaecum magnum and Cucullanus hians; 7 samples of Pagellus bogaraveo, two of them we recovered Contracaecum bidentatum; 7 samples of Beryx decadactylus, two of them recovered Contacaecum seriolae. Contracaecum magnum is for the first time reported infecting both Solea solea and Batrachoides didactylus. Contracaecum seriolae is for the first time reported in Beryx decadactylus and Pagellus bogaraveo are the news hosts record for Cucullanus hians and Contracaecum bidentatum respectively.

  7. The Blake Nose Cretaceous-Paleogene (Florida Atlantic margin, ODP Leg 171B): an exemplar record of the Maastrichtian-Danian transition

    Science.gov (United States)

    Bellier, J.-P.; Marca, S.; Norris, R.D.; Kroon, D.; Klaus, A.; Alexander, I.T.; Bardot, L.P.; Barker, C.E.; Blome, C.D.; Clarke, L.J.; Erbacher, J.; Faul, K.L.; Holmes, M.A.; Huber, B.T.; Katz, M.E.; MacLeod, K.G.; Martinez-Ruiz, F. C.; Mita, I.; Nakai, M.; Ogg, J.G.; Pak, D.K.; Pletsch, T.K.; ,; Shackleton, N.J.; Smit, J.; Ussler, W.; Watkins, D.K.; Widmark, J.; Wilson, P.A.

    1997-01-01

    During ODP Leg 171B, devoted to the analysis of the Blake Plateau margin in front of Florida, 16 holes have been drilled in 5 distinct sites. The sites have documented a sedimentary succession ranging in age from Aptian to Eocene. Emphasis has been put on critical periods, comprising the Paleocene-Eocene transition, the Cretaceous-Tertiary boundary which has been cored in excellent conditions, the middle Maastrichtian extinctions and the Albian anoxic episodes.

  8. Hydrographic and ecologic implications of foraminiferal stable isotopic response across the U.S. mid-Atlantic continental shelf during the Paleocene-Eocene Thermal Maximum

    Science.gov (United States)

    Makarova, Maria; Wright, James D.; Miller, Kenneth G.; Babila, Tali L.; Rosenthal, Yair; Park, Jill I.

    2017-01-01

    We present new δ13C and δ18O records of surface (Morozovella and Acarinina) and thermocline dwelling (Subbotina) planktonic foraminifera and benthic foraminifera (Gavelinella, Cibicidoides, and Anomalinoides) during the Paleocene-Eocene Thermal Maximum (PETM) from Millville, New Jersey, and compare them with three other sites located along a paleoshelf transect from the U.S. mid-Atlantic coastal plain. Our analyses show different isotopic responses during the PETM in surface versus thermocline and benthic species. Whereas all taxa record a 3.6-4.0‰ δ13C decrease associated with the carbon isotope excursion, thermocline dwellers and benthic foraminifera show larger δ18O decreases compared to surface dwellers. We consider two scenarios that can explain the observed isotopic records: (1) a change in the water column structure and (2) a change in habitat or calcification season of the surface dwellers due to environmental stress (e.g., warming, ocean acidification, surface freshening, and/or eutrophication). In the first scenario, persistent warming during the PETM would have propagated heat into deeper layers and created a more homogenous water column with a thicker warm mixed layer and deeper, more gradual thermocline. We attribute the hydrographic change to decreased meridional thermal gradients, consistent with models that predict polar amplification. The second scenario assumes that environmental change was greater in the mixed layer forcing surface dwellers to descend into thermocline waters as a refuge or restrict their calcification to the colder seasons. Although both scenarios are plausible, similar δ13C responses recorded in surface, thermocline, and benthic foraminifera challenge mixed layer taxa migration.

  9. Mineral Resource Assessment of Marine Sand Resources in Cape- and Ridge-Associated Marine Sand Deposits in Three Tracts, New York and New Jersey, United States Atlantic Continental Shelf

    Science.gov (United States)

    Bliss, James D.; Williams, S. Jeffress; Arsenault, Matthew A.

    2009-01-01

    Demand is growing in the United States and worldwide for information about the geology of offshore continental shelf regions, the character of the seafloor, and sediments comprising the seafloor and subbottom. Interest in locating sand bodies or high quality deposits that have potential as sources for beach nourishment and ecosystem restoration is especially great in some regions of the country. The Atlantic coast, particularly New York and New Jersey, has been the focus of these studies for the past 40 years with widely varying results. This study is the first attempt at applying probability statistics to modeling Holocene-age cape-and ridge-associated sand deposits and thus focuses on distinct sand body morphology. This modeling technique may have application for other continental shelf regions that have similar geologic character and late Quaternary sea-level transgression history. An estimated volume of 3.9 billion m3 of marine sand resources is predicted in the cape-and ridge-associated marine sand deposits in three representative regions or tracts on the continental shelf offshore of New York and New Jersey. These estimates are taken from probabilistic distributions of sand resources and are produced using deposit models and Monte Carlo Simulation (MCS) techniques. The estimated sand resources presented here are for only three tracts as described below and for Holocene age sand resources contained in cape-and ridge-associated marine sand deposit types within this area. Other areas may qualify as tracts for this deposit type and other deposit types and geologic ages (for example, paleo-stream channels, blanket and outwash deposits, ebb-tide shoals, and lower sea level-stand deltas), which are present on the New Jersey and New York continental shelf area but are not delineated and modeled in this initial evaluation. Admittedly, only a portion of these probable sand resources will ultimately be available and suitable for production, dependent largely on

  10. Wide-angle seismic constraints on the nature, origin and evolution of the SW Iberian margins

    Science.gov (United States)

    Sallares, V.; Gailler, A.; Gutscher, M.; Martínez-Loriente, S.; Bartolome, R.; Graindorge, D.; Diaz, J.; Gracia, E.

    2011-12-01

    We investigate the crustal structure of the SW Iberian margin along two new refraction and wide-angle reflection seismic profiles acquired during the NEAREST-2008 survey; one crossing from the central Gulf of Cadiz to the Variscan continental margin in the Algarve, Southern Portugal (P1), and the other crossing the Gorringe bank from Tagus Abyssal plain to the Seine Abyssal plain (P2). P1 shows shows a sharp transition between the ~30 km-thick Variscan domain in the north and a ~7 km-thick and ~150 km-wide crustal section that is oceanic in nature. The sharp transition between continental and oceanic crust is best explained by an initial rifting setting as a transform margin during the Early Jurassic that followed the continental break-up in the Central Atlantic. The narrow oceanic basin would have formed during an oblique rifting and seafloor spreading episode between Iberia and Africa that lasted up to the initiation of oceanic spreading in the North Atlantic (earliest Cretaceous). This oceanic plate segment could be the last remnant of an oceanic corridor that once connected the Alpine-Tethys with the Atlantic ocean. This interpretation is consistent with geodynamic models suggesting the existence of a narrow oceanic slab beneath the Gibraltar arc-Alboran basin system. In P2, the most striking observation is that the Tagus and Horseshoe Abyssal plains, as well as the Gorringe bank, show the same basement velocity structure, suggesting a common nature and origin. The velocity and density gradient confirms that the basement in these domains is made of highly serpentinized, exhumed mantle, probably emplaced during the initial phases of rifting at the of the North Atlantic in the Early Cretaceous. In contrast, the Seine Abyssal plain south from Coral Patch show evidences for the presence of a well-developed oceanic crust, similar to that described along P1. Therefore, these new observations provide key constraints to better understand the initial phases of rifting

  11. Exploration Status and Major Controlling Factors of Hydrocarbon Accumulation in the Continental Margin Basins of the Bengal Bay%孟加拉湾地区大陆边缘盆地勘探概况与油气富集主控因素

    Institute of Scientific and Technical Information of China (English)

    朱光辉; 李林涛

    2012-01-01

    The Bengal Bay lies in the east of India continent, west of Burma-Andaman-Sumatra area, and south of the Bangladesh. There are two different kinds of continental margins: passive and active continental margin. Many hydrocarbons bearing basins lie in the continental margins of the Bengal Bay, Based on the structure characteristics and plate position, we divided the basins into three types: passive continental margin basin (Mahanadi, Cauvery, and the K-G basins) , active continental margin basin (Rakhine, central Burma, Moattama, Andaman, and the north Sumatra basins) and remnant ocean basin (Bengal Basin). According to the distribution of the volcanic arcs, we further divided the active continental basin into trench, fore-arc and back-arc related basin. Through petroleum exploration analysis of the continental margin basins of the Bengal Bay, we come into the conclusion that the type of hydrocarbon source rocks and abundance of organic matters determined the nature of fluids and abundance of resources. Large river-delta system determined the distribution of big hydrocarbon field. Finally type, property and intensity of tectonic activities (especially of the late stage) determined the potential of exploration zones.%孟加拉湾位于印度大陆以东、缅甸—安达曼—苏门答腊以西、孟加拉国南部海上地区,该区存在主动和被动两种不同类型的大陆边缘,并发育众多大陆边缘含油气盆地.根据板块位置和构造特征将其划分为三大类,分别是:被动大陆边缘盆地(马哈纳迪、K-G和高韦里盆地);主动大陆边缘盆地(若开、缅甸中央、马达班、安达曼和北苏门答腊盆地);残留洋盆地(孟加拉盆地).根据火山岛弧带分布情况进一步将主动大陆边缘盆地划分为:①海沟型——若开盆地;②弧前型——缅甸中央盆地;③弧后型——马达班、安达曼和北苏门答腊盆地.对这些盆地油气勘探情况的统计与分析表明,该区大

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

    Directory of Open Access Journals (Sweden)

    A. Goswami

    2015-04-01

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

  13. Anomalous subsidence at South China Sea rifted margin: Sediments digging their own hole

    Science.gov (United States)

    Brune, Sascha; Clift, Peter; Quinteros, Javier

    2015-04-01

    in the source regions. (2) Weak continental crust: Extension in the South China Sea occurred in wide rift mode, which indicates the existence of a thick, weak crustal layer that decoupled deformation of brittle crust and mantle, ultimately forming symmetric margins with an extraordinary width of more than 300 km. Lateral crustal flow below the Baiyun basin is a consequence of the weakness of the crust, caused by high heat flow, a weak quartz-rheology and is triggered by sediment loading. We suggest that super-deep rift basins, like Baiyun Sag, are likely often linked to the flow of ductile crust in this fashion and would not be expected in cooler rift settings, such as found along the Atlantic margins.

  14. Spongicoloides sp. aff. a Spongicoloides galapagensis (Decapoda: Stenopodidea: Spongicolidae: una nueva especie para la carcinofauna chilena y primer registro de un estenopodido en aguas del margen continental de Chile Spongicoloides sp. aff. to Spongicoloides galapagensis (Decapoda: Stenopodidea: Spongicolidae: a new species for Chilean carcinofauna and the first record of aStenopodid for the Chilean margin

    Directory of Open Access Journals (Sweden)

    Guillermo L Guzmán

    2011-11-01

    Full Text Available Se cita por primera vez para el margen continental de Chile una especie de camarón Stenopodidae, asociado a una esponja hexactinelida. Los especímenes fueron recolectados en dos sitios de Chile central (31°12'S, 71°52'W y 36°00'S, 73°38'W; 922 a 1000 m de profundidad. Las esponjas estaban adheridas al sustrato con probable origen en emanaciones de metano. Spongicoloides sp. aff. a S. gala-pagensis, es el primer registro de la familia en aguas del margen continental del Pacífico suroriental. Los ejemplares coinciden con los rangos de la variación morfológica de S. galapagensis, no obstante difieren en el número de branquias descrito.This is the first record of a species of Stenopodid shrimp along the Chilean margin, associated with a hexactinellid sponge. The specimens were collected at two sites in central Chile (31°12'S, 71°52'W and 36°00'S, 73°38'W; 922 to 1000 m depth. The sponges were attached to the substrate with probable origins in methane seepage. Spongicoloides sp. aff. to S. galapagensis constitutes the first record of the family for the eastern south Pacific continental margin. The specimens coincide with the ranges of morphological variation of S. galapagensis, although they differ in the number of brachia described.

  15. The Carolina Sandhills: Quaternary eolian sand sheets and dunes along the updip margin of the Atlantic Coastal Plain province, southeastern United States

    Science.gov (United States)

    Swezey, Christopher; Fitzwater, Bradley A.; Whittecar, G. Richard; Mahan, Shannon; Garrity, Christopher P.; Aleman Gonzalez, Wilma B.; Dobbs, Kerby M.

    2016-01-01

    The Carolina Sandhills is a physiographic region of the Atlantic Coastal Plain province in the southeastern United States. In Chesterfield County (South Carolina), the surficial sand of this region is the Pinehurst Formation, which is interpreted as eolian sand derived from the underlying Cretaceous Middendorf Formation. This sand has yielded three clusters of optically stimulated luminescence ages: (1) 75 to 37 thousand years ago (ka), coincident with growth of the Laurentide Ice Sheet; (2) 28 to 18 ka, coincident with the last glacial maximum (LGM); and (3) 12 to 6 ka, mostly coincident with the Younger Dryas through final collapse of the Laurentide Ice Sheet. Relict dune morphologies are consistent with winds from the west or northwest, coincident with modern and inferred LGM January wind directions. Sand sheets are more common than dunes because of effects of coarse grain size (mean range: 0.35–0.59 mm) and vegetation. The coarse grain size would have required LGM wind velocities of at least 4–6 m/sec, accounting for effects of colder air temperatures on eolian sand transport. The eolian interpretation of the Carolina Sandhills is consistent with other evidence for eolian activity in the southeastern United States during the last glaciation.

  16. The cold-water coral Lophelia pertusa (Scleractinia) and enigmatic seabed mounds along the north-east Atlantic margin: are they related?

    Science.gov (United States)

    Roberts, J M; Long, D; Wilson, J B; Mortensen, P B; Gage, J D

    2003-01-01

    In this study, an updated distribution of Lophelia pertusa between the Porcupine Seabight and Norwegian shelf is presented. It seems unlikely that enigmatic mound structures observed at water depths of more than 570 m during acoustic seabed surveys, particularly to the west of the Shetland Islands, are related to the occurrence of L. pertusa. At these depths in the Faroe-Shetland Channel, the predominant influence of cold Arctic water precludes its growth. Iceberg dumpsites are also considered unlikely explanations for the origin of these mounds, and they are interpreted as most likely to be related to the release of fluids at the seabed. When mound structures were investigated, no scleractinian corals were recovered at water depths >500 m. This study shows the importance of seabed temperature as an environmental control on cold-water coral distribution. The significance of cold-water coral habitats in sustaining high levels of local-scale biodiversity is now becoming apparent in parallel with increased hydrocarbon extraction and fishing activity beyond the shelf edge. There is growing evidence that these areas have been marked by the passage of deep-water trawls. It seems likely that trawling activity has already reduced the extent of cold-water coral distribution in this region of the north-east Atlantic.

  17. Tectonic-sedimentary evolution of the eastern Brazilian marginal basins: Implications in their petroleum systems

    Energy Technology Data Exchange (ETDEWEB)

    Francisco, N.F.; Azambuja, N.C.; Mello, M.R. (Petrobras, Rio de Janeiro (Brazil))

    1993-02-01

    A geological survey of eastern Brazilian marginal basins using sedimentological, tectonic and geochemical data has been carried out. The almost 4000 km long set of basins can be classified as component of a typical divergent, mature Atlantic-continental margin. Based on their tectonic-sedimentary sequence, they can be linked to a single evolutionary history, which can be divided in three main stages: pre-rift, rift, and drift. The integration of all data allowed the characterization of two major petroleum systems that represent about 90% of the known Brazilian hydrocarbons reserves: (1) the rift (Early Cretaceous) and the drift (Late Cretaceous-Paleogene). With respect to the oil-in-place volume and production, the most significant one is the drift system associated with the siliciclastic deep water turbidites reservoirs deposited in bathyal environments. Such reservoirs are clearly controlled by a favorable relationship of stratigraphic and tectonic settings.

  18. Is the Gop rift oceanic? A reevaluation of the Seychelles-India conjugate margins

    Science.gov (United States)

    Guan, Huixin; Werner, Philippe; Geoffroy, Laurent

    2016-04-01

    Gop Rift axis. We propose that the conspicuous buoyant central part of the Gop Rift is likely associated with a continental C-Block as described in a recent paper on conjugated VPMs8, at least in the southern part of the Gop Rift. The crust below the Laxmi basin is probably transitional continental i.e. strongly intruded. West of India and west of the Laxmi Ridge, the transition to the Carlsberg Basin occurs along a clearly-expressed transform fault, not through an extended and thinned continental margin. We reinterpret the whole system based on those observations and propositions, giving some explanations on controversial magnetic anomalies based on similar observations from the southern Atlantic Ocean. 1: Collier et al., 2008. Age of the Seychelles-India break-up. Earth and Planetary Science Letters. 2: Minshull et al., 2008. The relationship between riftingand magmatism in the northeastern Arabian Sea. Nature Geoscience. 3 : Armitage et al., 2010. The importance of rift history for volcanic margin. Nature. 4 : Krishna et al., 2006. Nature of the crust in the Laxmi Basin (14 degrees-20 degrees N), western continental margin of India. Tectonics. 5 : Misra et al., 2015. Repeat ridge jumps and microcontinent separation: insights from NE Arabian Sea. Marine and Petroleum Geology. 6 : Biswas, 1982. Rift basins in the western margin of India and their hydrocarbon prospects. Bull. Am. Assoc. Pet. Geol. 7 : Chatterjee et al., 2013. The longest voyage: Tectonic, magmatic, and paleoclimatic evolution of the Indian plate during its northward flight from Gondwana to Asia. Gondwana Research. 8 : Geoffroy et al., 2015. Volcanic passive margins: anotherway to break up continents. Scientific Reports.

  19. Modeling the Nd isotopic composition in the North Atlantic basin using an eddy-permitting model

    Science.gov (United States)

    Arsouze, T.; Treguier, A. M.; Peronne, S.; Dutay, J.-C.; Lacan, F.; Jeandel, C.

    2010-09-01

    Boundary Exchange (BE - exchange of elements between continental margins and the open ocean) has been emphasized as a key process in the oceanic cycle of neodymium (Nd) (Lacan and Jeandel, 2005a). Here, we use a regional eddy-permitting resolution Ocean General Circulation Model (1/4°) of the North Atlantic basin to simulate the distribution of the Nd isotopic composition, considering BE as the only source. Results show good agreement with the data, confirming previous results obtained using the same parameterization of the source in a coarse resolution global model (Arsouze et al., 2007), and therefore the major control played by the BE processes in the Nd cycle on the regional scale. We quantified the exchange rate of the BE, and found that the time needed for the continental margins to significantly imprint the chemical composition of the surrounding seawater (further referred as characteristic exchange time) is of the order of 0.2 years. However, the timescale of the BE may be subject to large variations as a very short exchange time (a few days) is needed to reproduce the highly negative values of surface waters in the Labrador Sea, whereas a longer one (up to 0.5 years) is required to simulate the radiogenic influence of basaltic margins and distinguish the negative isotopic signatures of North Atlantic Deep Water from the more radiogenic southern origin water masses. This likely represents geographical variations in erosion fluxes and the subsequent particle load onto the continental margins. Although the parameterization of the BE is the same in both configurations of the model, the characteristic exchange time in the eddy-permitting configuration is significantly lower than the previous evaluations using a low resolution configuration (6 months to 10 years), but however in agreement with the available seawater Nd isotope data. This results highlights the importance of the model dynamics in simulating the BE process.

  20. Post-Glacial Development of Western North Atlant