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Sample records for european atlantic margin

  1. Atlantic marginal basins of Africa

    SciTech Connect

    Moore, G.T.

    1988-02-01

    The over 10,000-km long Atlantic margin of Africa is divisible into thirty basins or segments of the margin that collectively contain over 18.6 x 10/sup 6/ km/sup 3/ of syn-breakup and post-breakup sediments. Twenty of these basins contain a sufficiently thick volume of sediments to be considered prospects. These basins lie, at least partially, within the 200 m isobath. The distribution of source rocks is broad enough to give potential to each of these basins. The sedimentation patterns, tectonics, and timing of events differ from basin to basin and are related directly to the margin's complex history. Two spreading modes exist: rift and transform. Rifting dates from Late Triassic-Early Jurassic in the northwest to Early Cretaceous south of the Niger Delta. A complex transform fault system separated these two margins. Deep-water communication between the two basins became established in the middle Cretaceous. This Mesozoic-Cenozoic cycle of rifting and seafloor spreading has segmented the margin and where observable, basins tend to be bounded by these segments.

  2. Earthquakes at North Atlantic passive margins

    SciTech Connect

    Gregersen, S. ); Basham, P.W. )

    1989-01-01

    The main focus of this volume is the earthquakes that occur at and near the continental margins on both sides of the North Atlantic. The book, which contains the proceedings of the NATO workshop on Causes and Effects of Earthquakes at Passive Margins and in Areas of Postglacial Rebound on Both Sides of the North Atlantic, draws together the fields of geophysics, geology and geodesy to address the stress and strain in the Earth's crust. The resulting earthquakes produced on ancient geological fault zones and the associated seismic hazards these pose to man are also addressed. Postglacial rebound in North America and Fennoscandia is a minor source of earthquakes today, during the interglacial period, but evidence is presented to suggest that the ice sheets suppressed earthquake strain while they were in place, and released this strain as a pulse of significant earthquakes after the ice melted about 9000 years ago.

  3. Evolution of Northeast Atlantic magmatic continental margins

    NASA Astrophysics Data System (ADS)

    England, Richard; Cornwell, David; Ramsden, Alice

    2014-05-01

    One of the major problems interpreting the evolution of magmatic continental margins such as those which dominate the Irish, UK and Norwegian margins of the NE Atlantic is that the structure which should record the pre-magmatic evolution of the rift and which potentially influences the character of the rifting process is partially or completely obscured by thick basalt lava flows and sills. A limited number of deep reflection seismic profiles acquired with tuned seismic sources have penetrated the basalts and provide an image of the pre-magmatic structure, otherwise the principle data are lower resolution wide-angle/refraction profiles and potential field models which have greater uncertainties associated with them. In order to sidestep the imaging contraints we have examined the Ethiopian ñ Afar rift system to try to understand the rifting process. This magmatic rift system provides, along its length, a series of ësnapshotsí into the possible tectonic evolution of a magmatic continental margin which are associated with different amounts of extension. The Main Ethiopian rift contains an embryonic magmatic passive margin dominated by faulting at the margins of the rift and en-echlon magmatic zones at the centre. Further north toward Afar the rift becomes infilled with extensive lava flows fed from fissure systems in the widening rift zone. Deep seismic profiles crossing the NE Atlantic margins reveal ocean dipping reflector sequences (ODRS) of basaltic lavas overlying extended crust and lower crustal sill complexes of intruded igneous rock, often referred to as underplate, which extend back beneath the continental margin. The ODRS show a variety of morphologies and settings but frequently occur in fault bounded rift structures along the margins. We suggest, by analogy to the observations that can be made in the Ethiopia Afar rift that these fault bounded basins largely form at the embryonic rift stage and are then partially or completely filled with lavas fed

  4. Structure of the North American Atlantic Continental Margin.

    ERIC Educational Resources Information Center

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

    1986-01-01

    Offers explanations on the origin of the North American Atlantic continental margin. Provides an analysis and illustrations of structural and strategraphic elements of cross sections of the Atlantic continental margin. Also explains the operations and applications of seismic-relection profiles in studying ocean areas. (ML)

  5. Northeast Atlantic Igneous Province volcanic margin development

    NASA Astrophysics Data System (ADS)

    Mjelde, R.; Breivik, A. J.; Faleide, J. I.

    2009-04-01

    Early Eocene continental breakup in the NE Atlantic Volcanic Province (NAIP) was associated with voluminous extrusive and intrusive magmatism, and initial seafloor spreading produced anomalously thick oceanic crust. Recent publications based on crustal-scale wide-angle seismic data show that there is a positive correlation between igneous crustal thickness (H) and average P-wave velocity (Vp) on all investigated margins in the NAIP. Vp can be used as a proxy for crustal composition, which can be related to the mode of mantle melting. A positive H-Vp correlation indicates that excessive mantle melting the first few million years after breakup was driven by an initial increased temperature that cools off as seafloor spreading develops, consistent with a mantle plume model. Variations in mantle composition can explain excess magmatism, but will generate a negative H-Vp correlation. Active mantle convection may increase the flux of mantle rocks through the melting zone above the rate of passive corner flow, which can also produce excessive magmatism. This would produce little H-Vp correlation, and place the curve lower than the passive flow melting curve in the diagram. We have compiled earlier published results with our own analyses of published and unpublished data from different groups to look for systematic variations in the mantle melting mode along the NAIP margins. Earlier studies (Holbrook et al., 2002, White et al, 2008) on the southeast Greenland conjugate system, indicate that the thick igneous crust of the southern NAIP (SE Greenland ? Hatton Bank) was dominated by increased mantle temperature only, while magmatism closer to the southern side of and including the Greenland-Iceland-Færøy Ridge (GIFR) was created by combined temperature increase and active mantle convection. Recent publications (Breivik et al., 2008, White et al, 2008) north of the GIFR for the Norway Basin segment, indicate temperature dominated magmatism between the Jan Mayen Fracture

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

    NASA Astrophysics Data System (ADS)

    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.

  7. On isostasy at Atlantic-type continental margins

    NASA Technical Reports Server (NTRS)

    Karner, G. D.; Watts, A. B.

    1982-01-01

    The concept of isostasy describes the manner in which topographic features on the earth's surface are compensated at depth. The present investigation is concerned with the isostatic mechanism at Atlantic-type continental margins. Particular attention is given to the question whether the flexure model of isostasy, which has successfully been used at other geological features in oceans, is applicable at margins. Cross-spectral techniques are used to analyze the relationship between free air gravity and topography at Atlantic-type continental margins. The relatively old eastern North America is found to be associated with the highest value of the effective elastic thickness in the range 10-20 km, while the relatively young Coral Sea/Lord Howe rise is associated with the lowest value of less than 5 km. The differences in estimates of effective elastic thickness between margins can be explained by a simple model in which the flexural strength of the basement increases with age.

  8. The Continental Margins of the Western North Atlantic.

    ERIC Educational Resources Information Center

    Schlee, John S.; And Others

    1979-01-01

    Presents an interpretation of geological and geophysical data, which provides a summary of the structural and sedimentary history of the United States Atlantic Margin. The importance of an understanding of the development of the outer continental shelf to future hydrocarbon exploration is detailed. (BT)

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

    USGS Publications Warehouse

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

    2013-01-01

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

  10. Buried Mesozoic rift basins of Moroccan Atlantic continental margin

    SciTech Connect

    Mohamed, N.; Jabour, H.; El Mostaine, M.

    1995-08-01

    The Atlantic continental margin is the largest frontier area for oil and gas exploration in Morocco. Most of the activity has been concentrated where Upper Jurassic carbonate rocks have been the drilling objectives, with only one significant but non commercial oil discovery. Recent exploration activities have focused on early Mesozoic Rift basins buried beneath the post-rift sediments of the Middle Atlantic coastal plain. Many of these basins are of interest because they contain fine-grained lacustrine rocks that have sufficient organic richness to be classified as efficient oil prone source rock. Location of inferred rift basins beneath the Atlantic coastal plain were determined by analysis of drilled-hole data in combination with gravity anomaly and aeromagnetic maps. These rift basins are characterized by several half graben filled by synrift sediments of Triassic age probably deposited in lacustrine environment. Coeval rift basins are known to be present in the U.S. Atlantic continental margin. Basin modeling suggested that many of the less deeply bored rift basins beneath the coastal plain are still within the oil window and present the most attractive exploration targets in the area.

  11. Atlantic Mesozoic marginal basins: an Iberian view

    SciTech Connect

    Wilson, R.C.L.

    1987-05-01

    In the light of theoretical models for crustal stretching that precedes ocean opening, it is unlikely that Iberian basins have mirror image counterparts beneath North American or other European continental shelves. However, certain Iberian sedimentary sequences are comparable to those found in other basins. Of particular note are (1) the almost identical pre-rift sequences in all these areas, (2) the development of Upper Jurassic carbonate buildups in Portugal, Morocco, and beneath the Scotian Shelf, and (3) the hydrocarbon-bearing Upper Jurassic and Lower Cretaceous synrift and postrift siliciclastics of North America, Iberia, and Aquitaine. In the prerift sequences, Triassic red beds are capped by evaporites, which subsequently influenced the structural development of basins. Intertidal and supratidal carbonates occur at the base of the Jurassic and are overlain by Lower and Middle Jurassic limestone-shale sequences, which in places contain bituminous shales. In Portugal only, resedimented carbonates of Toarcian-Aalenian age are associated with an uplifted basement horst. In Portugal, Aquitaine, and eastern Canada, Middle Jurassic high-energy carbonate platforms developed. Synrift siliciclastic sequences show spectacular evidence for deposition within fault-bounded basins. In Portugal, lower Kimmeridgian clastics are up to 3 km thick, but Upper-Lower Cretaceous sequences are relatively thin (ca. 1 km), in contrast to those of the Basco-Cantabrian region where they exceed 10 km. In the latter region occurs the fluvially dominated Wealden (Upper Jurassic-Neocomian) and Urgonian carbonate platforms and associated basinal sediments. In the Asturias basin, Kimmeridgian shales and fluvially dominated deltaic sandstones succeed conglomeratic fluvial sandstones of uncertain age.

  12. Investigating the Asymmetry of Northern North Atlantic Volcanic Continental Margins

    NASA Astrophysics Data System (ADS)

    Smith, L. K.; White, R. S.

    2005-12-01

    The Hatton Bank continental margin is a typical example of the volcanic margins present in the northern North Atlantic where voluminous magmatism occurred at the time of continental break-up. The upper crust exhibits characteristically large volumes of extruded lava imaged as seaward-dipping reflectors, which have in the past proved problematic for seismic imaging of the deeper crustal structure. The integrated Seismic Imaging and Modelling of Margins (iSIMM) project recorded profiles in 2002 designed to map specifically the poorly constrained lower crustal structure in this region. 29 four-component ocean-bottom seismometers (OBS) were deployed along a strike line over the region of thickest extrusive and intruded igneous material; 53 OBS were deployed through the mid-point of the strike line, along a dip line extending from the stretched continental crust of the Hatton Basin into the fully oceanic crust of the Iceland Basin. We present a new seismic velocity model for the Hatton Bank volcanic continental margin. Joint wide-angle refraction and reflection tomography was used to determine the seismic velocity structure and depth to Moho across the continent-ocean transition (COT) in both the dip and strike directions. The lower crust beneath the margin exhibits elevated crustal velocities in the range of 7.0-7.4 km/s, which represent new igneous material added to the lower crust in this region at the time of continental break-up. The iSIMM survey is located close to the site of a previous survey carried out in 1986. A comparison of the 1986 results and the results from the 1996 SIGMA survey carried out on the conjugate southeast Greenland margin show a marked asymmetry in crustal structure: the Greenland margin appears to have a COT stretched over ~ 150 km compared to the narrower COT of the Hatton Bank margin, which extends for only ~ 50 km. The new iSIMM survey results provide a refined estimate of crustal structure of the Hatton Bank margin and improved

  13. Neotectonism along the Atlantic passive continental margin: A review

    NASA Astrophysics Data System (ADS)

    Gardner, Thomas W.

    1989-09-01

    An extensive body of geologic data including the modern state of stress, historical seismicity, surface and subsurface stratigraphy, numerical models of crustal deformation, surficial geomorphic systems, and historical precise leveling and tidal gauge records constrain the style and rate of neotectonic deformation for the Appalachians and Atlantic passive continental margin. There are two major styles of neotectonism in the eastern United States. The northeastern United States is dominated by isostatic uplift and northward migration of peripheral bulge collapse in response to deglaciation. This locally rapid, but decreasing rate of deformation is superimposed upon slower, long-term deformation along the Atlantic margin. Most of the long-term, continental margin deformation is attributed to lithospheric flexuring in response to sediment loading in sedimentary basins (especially the Baltimore Canyon Trough and Carolina Trough), isostatic deformation in response to continental denudation and water loading of the shelf, and stress from far-field plate tectonic sources. Significant deformational features include an uplift anomaly near Cape Fear, N.C.; northward and southward tilting of the Coastal Plain into the Salisbury and Southeast Georgia Embayments respectively; seaward tilting of the Coastal Plain/Piedmont, and a complex pattern of postglacial uplift and later subsidence in the northeast. Estimates of vertical crustal velocities for similar locations vary over several orders of magnitude. Measurement interval bias and systematic leveling errors may account for some of the discrepancies. Evidence for periodic deformation in the eastern United States in substantial and it is possible that historic data indicate a period of accelerated deformation along the Atlantic continental margin.

  14. Tectonic structure and evolution of the Atlantic continental margin

    SciTech Connect

    Klitgord, K.D.; Schouten, H.; Hutchinson, D.R.

    1985-01-01

    The Atlantic continental margin developed across the boundary between continental and oceanic crust as rifting and then sea-floor spreading broke apart and separated the North American and African plates, forming the Atlantic Ocean Basin. Continental rifting began in Late Triassic with reactivation of Paleozoic thrust faults as normal faults and with extension across a broad zone of subparallel rift basins. Extension became localized in Early to Middle Jurassic along the zone that now underlies the large marginal basins, and other rift zones, such as the Newark, Hartford, and Fundy basins, were abandoned. Rifting and crustal stretching between the two continents gave way to sea-floor spreading Middle Jurassic and the formation of oceanic crust. This tectonic evolution resulted in formation of distinctive structural features. The marginal basins are underlain by a thinner crust and contain a variety of fault-controlled structures, including half-grabens, seaward- and landward-tilted blocks, faults that die out within the crust, and faults that penetrate the entire crust. This variable structure probably resulted from the late Triassic-Early Jurassic pattern of normal, listric, and antithetic faults that evolved from the Paleozoic thrust fault geometry. The boundary between marginal basins and oceanic crust is marked approximately by the East Coast Magnetic Anomaly (ECMA). A major basement fault is located in the Baltimore Canyon trough at the landward edge of the ECMA and a zone of seaward dipping reflectors is found just seaward of the ECMA off Georges Bank. The fracture zone pattern in Mesozoic oceanic crust can be traced landward to the ECMA.

  15. Lower-crustal intrusion on the North Atlantic continental margin.

    PubMed

    White, R S; Smith, L K; Roberts, A W; Christie, P A F; Kusznir, N J; Roberts, A M; Healy, D; Spitzer, R; Chappell, A; Eccles, J D; Fletcher, R; Hurst, N; Lunnon, Z; Parkin, C J; Tymms, V J

    2008-03-27

    When continents break apart, the rifting is sometimes accompanied by the production of large volumes of molten rock. The total melt volume, however, is uncertain, because only part of it has erupted at the surface. Furthermore, the cause of the magmatism is still disputed-specifically, whether or not it is due to increased mantle temperatures. We recorded deep-penetration normal-incidence and wide-angle seismic profiles across the Faroe and Hatton Bank volcanic margins in the northeast Atlantic. Here we show that near the Faroe Islands, for every 1 km along strike, 360-400 km(3) of basalt is extruded, while 540-600 km(3) is intruded into the continent-ocean transition. We find that lower-crustal intrusions are focused mainly into a narrow zone approximately 50 km wide on the transition, although extruded basalts flow more than 100 km from the rift. Seismic profiles show that the melt is intruded into the lower crust as sills, which cross-cut the continental fabric, rather than as an 'underplate' of 100 per cent melt, as has often been assumed. Evidence from the measured seismic velocities and from igneous thicknesses are consistent with the dominant control on melt production being increased mantle temperatures, with no requirement for either significant active small-scale mantle convection under the rift or the presence of fertile mantle at the time of continental break-up, as has previously been suggested for the North Atlantic Ocean. PMID:18368115

  16. The Northwestern Atlantic Moroccan Margin From Deep Multichannel Seismic Reflection

    NASA Astrophysics Data System (ADS)

    Malod, J. A.; Réhault, J. P.; Sahabi, M.; Géli, L.; Matias, L.; Zitellini, N.; Sismar Group

    The NW Atlantic Moroccan margin, a conjugate of the Nova Scotia margin, is one of the oldest passive margins of the world. Continental break up occurred in the early Jurassic and the deep margin is characterized by a large salt basin. The SISMAR cruise (9 April to 4 May 2001) acquired 3667 km of 360 channel seismic reflection profiles. In addition, refraction data were recorded by means of 48 OBH/OBS deployments. Simultaneously, some of the marine profiles were extended onshore with 16 portable seismic land stations. WNW-ESE profiles 4 and 5 off El Jadida show a good section of the margin. The crustal thinning in this region is fairly abrupt. These profiles image the crust above a strong seismic reflector at about 12 s.twt., interpreted as the Moho. The crust exhibits several different characteristics from the continent towards the ocean.: - highly diffractive with a thickness larger than 25 km beneath the shelf. - stratified at a deep level and topped by few "tilted blocks" with a diffractive acoustic facies and for which 2 hypotheses are proposed: either continental crust tilted during the rifting or large landslides of crustal and sedimentary material slid down later. Liassic evapor- ites are present but seem less thick than to the south. - layered with seaward dipping reflectors: this type of crust correlates with the magnetic anomaly S1 and corresponds to the continent-ocean transition. - diffractive with an oceanic character. Oceanwards, the crust becomes more typically oceanic, but shows internal reflectors that may be re- lated to compressional reactivation during the Tertiary attested by large scale inverted basins. Our results allow us to discuss the nature and location of the continent-ocean transition at a regional scale and the rifting to spreading evolution of the very ma- ture continental margin off El Jadida. This provide us with some constraints for the initial reconstruction between Africa, North America and Iberia. Moreover, these re- sults help

  17. Depositional patterns of kerogen, Atlantic Margin, North America

    SciTech Connect

    Armentrout, J.M.

    1985-02-01

    Geochemical and biostratigraphic data from offshore wells along the Atlantic margin of North America define a depositional history dominated by coastal-plain and shallow-shelf facies containing degraded and residual continent-derived kerogen. Exceptions to this generalization are 4 depositional facies containing hydrogen-rich amorphous kerogen assemblages. The rocks containing hydrogen-rich amorphous kerogen assemblages are: (1) Upper Jurassic inner-shelf facies probably deposited in algal-rich lagoonlike environments, (2) Lower Cretaceous nonmarine coaly facies, probably deposited in algal-rich swamplike environments, (3) middle Cretaceous abyssal-plain facies probably deposited by turbidity currents that originated on an algal-rich slope, and (4) Miocene outer-shelf to upper-slope facies probably deposited under algal-rich upwelling systems. Correlations of these facies to seismic packages allows for extrapolation of probable organic facies distribution throughout the continental margin. Such modeling of organic facies distributions in conjunction with plate-tectonic and ocean-circulation models permits refinement of strategies for hydrocarbon exploration.

  18. Investigations of the bottom current sculpted margin of Hatton Bank, NE Atlantic

    NASA Astrophysics Data System (ADS)

    MacLachlan, S. E.; Elliott, G. M.; Parson, L. M.

    2007-12-01

    The NW Hatton Bank in the NE Atlantic represents a unique opportunity to examine the interaction of bottom currents with complex seabed topography and to analyse the affects on the morphology and distribution of sediments along the margin. The NW Hatton Bank margin is a slope located remote from any major terrigenous sediment supply and at present is over 200 NM from the closest sediment source onshore. The data presented in this study were collected on the research vessel R.R.S. Charles Darwin in 1999, for the purpose of determining the outer limit of the legal continental shelf according to the United Nations Convention on the Law of the Sea. Swath bathymetry and high resolution acoustic data allow us to evaluate both local and regional controls on slope sedimentation and the possible mechanisms for bottom current velocity variability across a slope setting within the NW European continental margin. The slope is characterised by an intense bottom current flow related to the Deep Northern Boundary Current. Along the slope, bottom-current sedimentation is dominant, leading to the development of the Hatton drift and sediment wave fields. Non-depositional and erosional features related to bottom current activity were also identified and include moats encircling the volcanic cones and deep erosional scours. The interaction between bottom current circulation and complex margin morphology controls the distribution, geometry and scale of the sediment wave fields.

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

    NASA Astrophysics Data System (ADS)

    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).

  20. Temperature anomalies under the Northeast Atlantic rifted volcanic margins

    NASA Astrophysics Data System (ADS)

    Clift, Peter D.

    1997-01-01

    Subsidence analysis of ODP/DSDP drill sites located on oceanic crust on the Southeast Greenland, Edoras Bank, and Vøring Plateau margins, as well as on the Iceland-Faeroe Ridge, shows that the subsidence of these areas does not follow the agerelationship of normal oceanic crust. By correcting for the effect of thickened oceanic crust in raising the level to which subsidence will occur and analyzing the rate of thermal subsidence, it is possible to provide maximum temperature estimates for the underlying asthenosphere through time by identifying periods of anomalous depth to basement. Isostatic models predict crustal thicknesses of 27 km under the Iceland-Faeoe Ridge, around 20 km at Edoras Bank and Southeast Greenland, and 16-17 km at the Vøring Plateau. Asthenospheric temperatures at the time of continental break-up range from 50°C to 100°C above normal mantle, which are insufficient to account for the crustal thicknesses if melting is purely a passive adiabatic process. Asthenospheric upwelling must thus have been more rapid than spreading following break-up. At Edoras Bank the thermal anomaly dissipated within 5 Myr of rifting, similar to that inferred from the eastern US margin, where no plume is considered to have affected the rifting process. The need to invoke thermal input from the Iceland Plume in generating the thickened crust at Edoras Bank, and possibly elsewhere in the Northeast Atlantic, is called into question. However, a 14-20 Myr anomaly, peaking at 12 Myr post-rift, in Southeast Greenland suggests that, although the plume did provide heat to this margin, its strongest influence post-dated break-up.

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Alkalinity distribution in the western North Atlantic Ocean margins

    NASA Astrophysics Data System (ADS)

    Cai, Wei-Jun; Hu, Xinping; Huang, Wei-Jen; Jiang, Li-Qing; Wang, Yongchen; Peng, Tsung-Hung; Zhang, Xin

    2010-08-01

    Total alkalinity (TA) distribution and its relationship with salinity (S) along the western North Atlantic Ocean (wNAO) margins from the Labrador Sea to tropical areas are examined in this study. Based on the observed TA-S patterns, the mixing processes that control alkalinity distribution in these areas can be categorized into a spectrum of patterns that are bracketed by two extreme mixing types, i.e., alongshore current-dominated and river-dominated. Alongshore current-dominated mixing processes exhibit a segmented mixing line with a shared mid-salinity end-member. In such cases (i.e., Labrador Sea, Gulf of Maine, etc.), the y-intercept of the high salinity segment of the mixing line is generally higher than the local river alkalinity values, and it reflects the mixing history of the alongshore current. In contrast, in river-dominated mixing (Amazon River, Caribbean Sea, etc.), good linear relationships between alkalinity and salinity are generally observed, and the zero salinity intercepts of the TA-S regressions roughly match those of the regional river alkalinity values. TA-S mixing lines can be complicated by rapid changes in the river end-member value and by another river nearby with a different TA value (e.g., Mississippi-Atchafalaya/Gulf of Mexico). In the wNAO margins, regression intercepts and river end-members have a clear latitudinal distribution pattern, increasing from a low of ˜300 μmol kg-1 in the Amazon River plume to a high value between ˜500-1100 μmol kg-1 in the middle and high latitude margins. The highest value of ˜2400 μmol kg-1 is observed in the Mississippi River influenced areas. In addition to mixing control, biological processes such as calcification and benthic alkalinity production may also affect ocean margin alkalinity distribution. Therefore, deriving inorganic carbon system information in coastal oceans using alkalinity-salinity relationships, in particular, those of generic nature, may lead to significant errors.

  3. Petroleum systems of the Brazilian South Atlantic margin

    SciTech Connect

    Mello, M.R.; Koutsoukos, E.A.M.; Mohriak, W.U.; Bacoccoli, G.

    1996-08-01

    The characterization of a major petroleum system in the Sergipe Basin, NE Brazil, was undertaken using a multidisciplinary approach. The Lura-Muriboca (!) petroleum system, taken as a representative example for the proto-marine evaporitic stage in the South Atlantic margin, comprises the Carmopolis oil field, which is the largest onshore oil field in Brazil, with about 1.2 MM bbl of oil in place. The hydrocarbons sourced by the proto-marine Aptian marls and calcareous black shales, started migration during the Paleocene, reaching the maximum at the late Oligocene continuing up to now in some parts of the basin. The hydrocarbons were mainly accumulated in Lower Cretaceous alluvial fans/fan deltas coarse clastics reservoirs, and fractured Precambrian basement. The reservoirs trapping were structured during the Cretaceous. Seals are the evaporates and marine shales deposited during the Aptian and Albian times. Mapping the geographic extent of the petroleum system emphasizes the association of the Carmopolis oil field with the proposed offshore pod of active Aptian source rocks. The integration of these data with a geochemical modelling allowed the prediction and characterization, in time and space, of the petroleum pathways from source to trap in the basin.

  4. Crustal structure of Edoras Bank continental margin and mantle thermal anomalies beneath the North Atlantic

    NASA Astrophysics Data System (ADS)

    Barton, A. J.; White, R. S.

    1997-02-01

    We discuss the structure of the continent-ocean transition of the Edoras Bank area of the NE Atlantic margin and the influence of the Iceland mantle plume during continental breakup. Edoras Bank lies close to the present-day limit of influence of the Iceland plume. Sequences of seaward dipping reflectors imaged on multichannel seismic profiles are well-developed over much of the margin. They form aerially extensive, dipping sheets, with individual reflectors imaged on margin-parallel profiles as laterally continuous and subhorizontal features. We interpret them as basalt flows extruded from linear fissure vents close to sea level at the time of continental breakup. A crustal velocity model for the margin was developed by travel time modeling of wide-angle refractions and reflections recorded on digital ocean bottom hydrophones and the structure confirmed by gravity modeling. Oceanic crust formed immediately after breakup is 10 km thick and exhibits classic layer 2 and layer 3 seismic velocities. The crustal thickness increases to the SE reaching 17 km beneath the continental fragment of Edoras Bank. The continent-ocean transition is dominated in the lower crust by a lens up to 8 km thick of high-velocity material (7.2-7.5 km s-1), which exhibits a very low velocity gradient. It extends over a 60 km wide region beneath the seaward dipping reflectors. The high velocities and densities of the lower crust are probably caused by igneous rock with a high MgO content that underplated the margin or heavily intruded pre-existing crustal material during continental breakup. Both the addition of large quantities of melt to the margin and the subsidence curves inferred from postrift sediments sampled by Deep Sea Drilling Project (DSDP) boreholes on the margin indicate the presence of abnormally hot mantle beneath the area at the time of continental breakup. Comparison of the structure and subsidence history of the Edoras Bank margin with other areas of the NW European margin

  5. Imaging the lithosphere of rifted passive margins using waveform tomography: North Atlantic, South Atlantic and beyond

    NASA Astrophysics Data System (ADS)

    Lebedev, Sergei; Schaeffer, Andrew; Celli, Nicolas Luca

    2016-04-01

    Lateral variations in seismic velocities in the upper mantle reflect variations in the temperature of the rocks at depth. Seismic tomography thus provides a proxy for lateral changes in the temperature and thickness of the lithosphere. It can map the deep boundaries between tectonic blocks with different properties and age of the lithosphere. Our 3D tomographic models of the upper mantle and the crust at the Atlantic and global scales are constrained by an unprecedentedly large global dataset of broadband waveform fits (over one million seismograms) and provide improved resolution of the lithosphere, compared to other available models. The most prominent high-velocity anomalies, seen down to 150-200 km depths, indicate the cold, thick, stable mantle lithosphere beneath Precambrian cratons, including those in North America, Greenland, northern and eastern Europe, Africa and South America. The dominant, large-scale, low-velocity feature is the global system of mid-ocean ridges, with broader low-velocity regions near hotspots, including Iceland. Currently active continental rifts show highly variable expression in the upper mantle, from pronounced low velocities to weak anomalies; this correlates with the amount of magmatism within the rift zone. Rifted passive margins have typically undergone cooling since the rifting and show more subtle variations in their seismic-velocity structure. Their thermal structure and evolution, however, are also shaped by 3D geodynamic processes since their formation, including cooling by the adjacent cratonic blocks inland and heating by warm oceanic asthenosphere.

  6. Ireland's Atlantic Margin: An Investigation of the Structure of Magma-rich and Magma-poor Margins using Gravity, Magnetic and Seismic Data

    NASA Astrophysics Data System (ADS)

    Rippington, S.; Warner, J.; Rands, J.; Herbert, H.

    2014-12-01

    Ireland and its continental shelves are located in a structurally complex part of the European North Atlantic Margin. The northern part of the margin (e.g. the Rockall Basin) is considered to be magma-rich, whereas the southern part of the margin (e.g. the Porcupine Basin) is relatively magma-poor. Despite this fundamental difference, the Rockall and Porcupine regions have much in common: both have a dominant structural grain inherited from the Caledonian Orogeny, and were variably deformed by Variscan compression and multiple phases of extension and rifting. Rifting culminated in continental breakup between the North American and European plates in the Paleogene. Following continental breakup, both regions were further deformed by phases of Cenozoic compression, which have been attributed to many different causes, including the Alpine Orogeny. Hydrocarbon exploration in the region has met with limited success. This is in part due to the complex structure of the margin, and a number of persisting questions regarding the location, age, and nature of potential source and reservoir rocks, and the timing and evolution of structural traps. This study aims to re-evaluate the structural framework that underpins hydrocarbon exploration in the region. The study is based on a compilation of georeferenced maps and cross-sections, a newly merged set of marine gravity and aeromagnetic data, as well as published seismic and public domain data gravity and magnetic data, all of which are integrated in GIS. The integration of seismic and potential field data allows us to use the strengths of these different geophysical methods to investigate the crustal architecture from the seabed to the Moho. Quantitative interpretation of the crust is achieved by 2D gravity and magnetic modelling along key B.I.R.P.S seismic lines in the Rockall and Porcupine basins. These models are used to highlight similarities and differences between these areas and to suggest how the structure of the Irish

  7. Scientific Ocean Drilling to Assess Submarine Geohazards along European Margins

    NASA Astrophysics Data System (ADS)

    Ask, M. V.; Camerlenghi, A.; Kopf, A.; Morgan, J. K.; Ocean DrillingSeismic Hazard, P. E.

    2008-12-01

    Submarine geohazards are some of the most devastating natural events in terms of lives lost and economic impact. Earthquakes pose a big threat to society and infrastructure, but the understanding of their episodic generation is incomplete. Tsunamis are known for their potential of striking coastlines world-wide. Other geohazards originating below the sea surface are equally dangerous for undersea structures and the coastal population: submarine landslides and volcanic islands collapse with little warning and devastating consequences. The European scientific community has a strong focus on geohazards along European and nearby continental margins, especially given their high population densities, and long historic and prehistoric record of hazardous events. For example, the Mediterranean is surrounded by very densely-populated coastline and is the World's leading holiday destination, receiving up 30% of global tourism. In addition, its seafloor is criss-crossed by hydrocarbon pipelines and telecommunication cables. However, the governing processes and recurrence intervals of geohazards are still poorly understood. Examples include, but are not limited to, earthquakes and volcanic eruptions along the active tectonic margins of the Mediterranean and Sea of Marmara, landslides on both active and passive margins, and tsunamites and seismites in the sedimentary record that suggest a long history of similar events. The development of geophysical networks, drilling, sampling and long-term monitoring are crucial to the understanding of earthquake, landslide, and tsunami processes, and to mitigate the associated risks in densely populated and industrialized regions such as Europe. Scientific drilling, particularly in the submarine setting, offers a unique tool to obtain drill core samples, borehole measurements and long-term observations. Hence, it is a critical technology to investigate past, present, and possible future influences of hazardous processes in this area. The

  8. Development of passive volcanic margins of the Central Atlantic and initial opening of ocean

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    Geological and geophysical data on the Central Atlantic are discussed in order to elucidate the tectonic setting of the initial magmatic activity, rifting, and breakup resulting in the origination of Mesozoic ocean. The structural, magmatic, and historical aspects of the problem are considered. It has been established that the initial dispersed rifting and low-capacity magmatism at proximal margins was followed by the migration of the process toward the central part of region with the formation of distal zones and the development of vigorous magmmatism, further breakup of the lithosphere and ocean opening. Magmatism, its sources, and the features of newly formed magmatic crust at both the rifting and breakup stages of margin development are discussed and compared with subsequent spreading magmatism. Sr, Nd, and Pb isotopic compositions show that the magmatic evolution of the Central Atlantic proximal margins bears the features of two enriched components, one of which is related to the EM-1 source, developing only at the North American margin. Another enriched component typical of the province as a whole is related to the EM-2 source. To a lesser extent, this component is expressed in igneous rocks of Guyana, which also bear the signature of the MORB-type depleted source typical of spreading tholeiites in the Atlantic Ocean. Similar conditions are assumed for subsequent magmatism at the distal margins and for the early spreading basalts in the adjacent Atlantic belt, which also contain a small admixture of enriched material. A comparison of the magmatism at the margins of Central and North Atlantic reveals their specificity distinctly expressed in isotopic compositions of igneous rocks. In contrast to the typical region of the North Atlantic, the immediate melting of the enriched lithospheric source without the participation of plume-related melts is reconstructed for the proximal margins of the Central Atlantic. At the same time, decompression and melting in the

  9. Petrophysical models of high velocity lower crust on the South Atlantic rifted margins: whence the asymmetry?

    NASA Astrophysics Data System (ADS)

    Trumbull, Robert B.; Franke, Dieter; Bauer, Klaus; Sobolev, Stephan V.

    2015-04-01

    Lower crustal bodies with high seismic velocity (Vp > 7km/s) underlie seaward-dipping reflector wedges on both margins of the South Atlantic, as on many other volcanic rifted margins worldwide. A comprehensive geophysical study of the South Atlantic margins by Becker et al. (Solid Earth, 5: 1011-1026, 2014) showed a strong asymmetry in the development of high-velocity lower crust (HVLC), with about 4 times larger volumes of HVLC on the African margin. That study also found interesting variations in the vertical position of HVLC relative to seaward-dipping reflectors which question a simple intrusive vs. extrusive relationship between these lower- and upper crustal features. The asymmetry of HVLC volumes on the conjugate margins is paradoxically exactly the opposite to that of surface lavas in the Paraná-Etendeka flood basalt province, which are much more voluminous on the South American margin. This contribution highlights the asymmetric features of magma distribution on the South Atlantic margins and explores their geodynamic significance. Petrophysical models of the HVLC are presented in the context of mantle melt generation, based on thickness-velocity (H-Vp) relations. These suggest that the greater volumes and average Vp values of HVLC on the African margin are due to active upwelling and high temperature, whereas passive upwelling under a thick lithospheric lid suppressed magma generation on the South American margin. The contrast in mantle upwelling rate and lithospheric thickness on the two margins predictably causes differential uplift, and this may help explain the greater accomodation space for surface lavas on the South American side although melt generation was strongest under the African margin.

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

    USGS Publications Warehouse

    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. Extreme Precipitation Events over the Iberian Atlantic Margin: The Role of Atmospheric Rivers

    NASA Astrophysics Data System (ADS)

    Eiras, Jorge; Miguez-Macho, Gonzalo

    2014-05-01

    Between 90%-95% of precipitable water meridional transport is concentrated in narrow and elongated structures (hundred of km wide and thousands of km long), labelled as Atmospheric Rivers (ARs). These areas, classically associated to the pre-cold frontal warm conveyor belt region; are located within the warmest and wettest sector of extra-tropical cyclones. Such cyclones are mostly associated to the polar front but occasionally originated as tropical storms, acquiring baroclinic structures when leaving the tropical latitudes. ARs inject water vapor and latent heat from the tropics to mid-latitudes, with a predominant zonal-wind component tracking. The Northern Hemisphere has its main impact areas on the West US and European coast. Atmospheric Rivers are associated to extreme precipitation events (EPE) within the continents. This association is due to the huge amount of precipitable water that they carry and the fact that they are located in a 850hPa-900hPa level, exposing them to an orographic lift that is usually translated into heavy rainfall and flood events. We examine the impact of the advent of Atmospheric Rivers from the North Atlantic Corridor (with origin in the Gulf of Mexico), over the Iberian Peninsula, and its relationship with extreme precipitation and flood events over the Iberian Atlantic Margin. We precisely investigate the Extreme Precipitation Event-Atmospheric River advent ratio, and analyze the advent-annual cycle and the correlation with the NAO-Index. We use a Spain-Portugal interpolated precipitation Database, together with ECMWF ERA-Interim (0.7°× 0.7° horizontal resolution) vertical integrated column of eastward and northward water vapor flux to identificate the AR presence, extreme precipitation and EPE-AR coincidence events, using a detection algorithm based on water vapor integrated flux. We find a substantial EPE-AR coincidence ratio, with an slight correlation with negative NAO and running predominantly in the winter time of the

  12. Late Cenozoic flexural deformation of the middle U.S. Atlantic passive margin

    NASA Technical Reports Server (NTRS)

    Pazzaglia, Frank J.; Gardner, Thomas, W.

    1994-01-01

    Despite the century-long recognition of regional epeirogeny along the middle Atlantic passive margin, relatively few studies have focused on understanding postrift uplift mechanisms. Here, we demonstrate that epeirogenic uplift of the central Appalachian Piedmont and subsidence of the Salisbury Embayment represent first-order, flexural isostatic processes driven by continental denudation and offshore deposition. Our results show that regional epeirogenic processes, present on all Atlantic-type passive margins, are best resolved by specific stratigraphic and geomorphic relationships, rather than topography. A simple one-dimensional geodynamic model, constrained by well-dated Baltimore Canyon trough, Coastal Plain, and lower Susquehanna River (piedmont) stratigraphy, simulates flexural deforamtion of the U.S. Atlantic margin. The model represents the passive margin lithosphree as a uniformly thick elastic plate, without horizontal compressive stresses, that deforms flexurally under the stress of strike-averaged, vertically applied line loads. Model results illustrate a complex interaction among margin stratigraphy and geomorphology, the isostatic repsonse to denudational and depositional processes, and the modulating influence of exogenic forces such as eustasy. The current elevation, with respect to modern sea level, of fluvial terraces and correlateive Coastal Plain deposits or unconformities is successfully predicted through the synthesis of paleotopography, eustatic change, and margin flexure. Results suggest that the middle U.S. Atlantic margin landward of East Coast Magnetic Anomaly is underlain by lithoshpere with an average elastic thickness of 40 km (flexural rigidity, D = 4 X 10(exp 23) N m), the margin experience an average, long-term denudation rate of approximately 10m/m.y., and the Piedmont has been flexurally upwaped between 35 and 130 meters in the last 15 m.y. Long term isostatic continental uplift resulting rom denudation and basin subsidence

  13. Late Cenozoic flexural deformation of the middle U.S. Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Pazzaglia, Frank J.; Gardner, Thomas W.

    1994-06-01

    Despite the century-long recognition of regional epeirogeny along the middle Atlantic passive margin, relatively few studies have focused on understanding postrift uplift mechanisms. Here, we demonstrate that epeirogenic uplift of the central Appalachian Piedmont and subsidence of the Salisbury Embayment represent first-order, flexural isostatic processes driven by continental denudation and offshore deposition. Our results show that regional epeirogenic processes, present on all Atlantic-type passive margins, are best resolved by specific stratigraphic and geomorphic relationships, rather than topography. A simple one-dimensional geodynamic model, constrained by well-dated Baltimore Canyon trough, Coastal Plain, and lower Susquehanna River (Piedmont) stratigraphy, simulates flexural deformation of the U.S. Atlantic margin. The model represents the passive margin lithosphere as a uniformly thick elastic plate, without horizontal compressive stresses, that deforms flexurally under the stress of strike-averaged, vertically applied line loads. Model results illustrate a complex interaction among margin stratigraphy and geomorphology, the isostatic response to denudational and depositional processes, and the modulating influence of exogenic forces such as eustasy. The current elevation, with respect to modern sea level, of fluvial terraces and correlative Coastal Plain deposits or unconformities is successfully predicted through the synthesis of paleotopography, eustatic change, and margin flexure. Results suggest that the middle U.S. Atlantic margin landward of East Coast Magnetic Anomaly is underlain by lithosphere with an average elastic thickness of 40 km (flexural rigidity, D = 4 × 1023 N m), the margin experiences an average, long-term denudation rate of approximately 10 m/m.y., and the Piedmont has been flexurally upwarped between 35 and 130 meters in the last 15 m.y. Long-term isostatic continental uplift resulting from denudation and basin subsidence

  14. Growth of Transgressive Sills in Mechanically Layered Media: Faroe Islands, NE Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Walker, R. J.

    2014-12-01

    Igneous sills represent an important contribution to upper crustal magma transport, acting as magma conduits and stores (i.e. as sill networks, or as nascent magma chambers). Complex sill-network intrusion in basin settings can have significant impact on subsurface fluid flow (e.g., water aquifer and hydrocarbon systems), geothermal systems, the maturation of hydrocarbons, and methane release. Models for these effects are critically dependent on the models for sill emplacement. This study focuses on staircase-geometry sills in the Faroe Islands, on the European Atlantic Margin, which are hosted in mechanically layered lavas (1-20 m thick) and basaltic volcaniclastic units (1-30 m thick). The sills range from 20-50 m thick, with each covering ~17 km2, and transgressing a vertical range of ~480 m. Steps in the sills are elliptical in cross section, and discontinuous laterally, forming smooth transgressive ramps, hence are interpreted as representing initial stages of sill propagation as magma fingers, which inflate through time to create a through-going sheet. Although steps correspond to the position of some host rock layer interfaces and volcaniclastic horizons, most interfaces are bypassed. The overall geometry of the sills is consistent with ENE-WSW compression, and NNW-SSE extension, and stress anisotropy-induced transgression. Local morphology indicates that mechanical layering suppressed tensile stress ahead of the crack tip, leading to a switch in minimum and intermediate stress axes, facilitating lateral sill propagation as fingers, and resulting in a stepped transgressive geometry.

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

    NASA Astrophysics Data System (ADS)

    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

  16. North Atlantic Ocean drivers of the 2015 European heat wave

    NASA Astrophysics Data System (ADS)

    Duchez, Aurélie; Frajka-Williams, Eleanor; Josey, Simon A.; Hirschi, Joël; Evans, Gwyn

    2016-04-01

    Major European heat waves have occurred on several occasions in the past two decades, including the summer of 2015, with dramatic socioeconomic impacts and in a globally warming world, heat waves are expected to become longer, more frequent and more intense. Nevertheless, our understanding of heat wave causes remains at a basic level, limiting the usefulness of event prediction. We show that 2015 was the most extreme heat wave in central Europe in the past 35 years. We find that the heat wave was preceded by cold mid-latitude North Atlantic Ocean surface temperatures, which contributed to its development. In order to explain the genesis of the cold ocean anomaly, we consider surface heat loss, ocean heat content and wind driven upwelling. The anomaly is primarily due to extreme ocean heat loss in the preceding two winters and re-emergent cold ocean water masses. Further analysis indicates that this ocean anomaly was a driver for the 2015 heat wave as it favoured a stationary position of the Jet Stream, which steered Atlantic cyclones away from central Europe towards northern Europe. The cold Atlantic anomaly was also present during the most devastating European heat waves since the 1980s indicating that it is a common factor in the development of these extreme events.

  17. Structure of the North American Atlantic Continental Margin.

    USGS Publications Warehouse

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

    1986-01-01

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

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

    USGS Publications Warehouse

    Poag, C. Wylie; Ward, Lauck W.

    1987-01-01

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

  19. Atlantic Margin Coring Project 1976: preliminary report on shipboard and some laboratory geotechnical data

    USGS Publications Warehouse

    Richards, Adrian F.

    1977-01-01

    This report presents reduced shipboard geotechnical data collected during the 1976 Atlantic Margin Coring Project; results of laboratory tests of specific gravity, water content, bulk density, and Atterberg limits; and sedimentation-compression e log p curves showing consolidation. A description of the procedures used at sea and in the laboratory and a short preliminary summary of the shipboard results also is included.

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

    SciTech Connect

    Poag, C.W.; Ward, L.W.

    1987-02-01

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

  1. Post-breakup Basin Evolution along the South-Atlantic Margins

    NASA Astrophysics Data System (ADS)

    Strozyk, Frank; Back, Stefan; Kukla, Peter

    2014-05-01

    The post-breakup tectono-stratigraphic evolution of large offshore basins along the South American and African continental margins record strongly varying post-rift sedimentary successions. The northernmost segment of the South Atlantic rift and salt basins is characterized by a pronounced asymmetry, with the Brazilian margin comprising narrower and deeper rift basins with less salt in comparison to the Congo-Gabon conjugate margin. Another important observation is that multiple phases of uplift and subsidence are recorded after the break-up of the southern South Atlantic on both sides of the Florianopolis-Walvis Ridge volcanic complex, features that are regarded as atypical when compared to published examples of other post-breakup margin successions. A regional comparison based on tectonic-stratigraphic analysis of selected seismic transects between the large basins offshore southern Brazil (Espirito Santo Basin, Campos Basin, Santos Basin, Pelotas Basin) and southwest Africa (Lower Congo Basin, Kwanza Basin, Namibe Basin, Walvis Basin) provides a comprehensive basin-to-basin documentation of the key geological parameters controlling ocean and continental margin development. This comparison includes the margin configuration, subsidence development through time, sediment influx and storage patterns, type of basin fill (e.g. salt vs. non-salt systems; carbonate-rich vs. clastics-dominated systems) and finally major tectonic and magmatic events. Data from the salt basins indicate that salt-related tectonic deformation is amongst the prime controls for the non-uniform post-rift margin development. The diversity in the stratigraphic 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 (a) the structural configuration of each margin segment at the time of break-up, (b) the post break-up subsidence history of the respective margin segment

  2. Atlantic Ocean forcing of North American and European summer climate.

    PubMed

    Sutton, Rowan T; Hodson, Daniel L R

    2005-07-01

    Recent extreme events such as the devastating 2003 European summer heat wave raise important questions about the possible causes of any underlying trends, or low-frequency variations, in regional climates. Here, we present new evidence that basin-scale changes in the Atlantic Ocean, probably related to the thermohaline circulation, have been an important driver of multidecadal variations in the summertime climate of both North America and western Europe. Our findings advance understanding of past climate changes and also have implications for decadal climate predictions. PMID:15994552

  3. European warming linked to Greenland melting during the Last Interglacial North Atlantic climate optimum

    NASA Astrophysics Data System (ADS)

    Sanchez Goni, M.; Michel, E.; Desprat, S.; Carlson, A. E.; Naughton, F.; Fletcher, W. J.; Rossignol, L.

    2010-12-01

    Recent models and data synthesis suggest that the Last Interglacial North Atlantic warm optimum, ~130 ±2 ka, corresponded with a sea level stand of 4-9 m higher than that of the present-day implying that a substantial part of the Greenland Ice Sheet (GIS) melted at that time. This makes this interglacial a good analogue for understanding the impact of the ongoing global warming and GIS melting on the Atlantic Meridional Overturning Circulation (AMOC) and adjacent landmasses. Here we provide new insights on the impact of insolation and AMOC changes on western European ecosystems and climate and their regional transmission during an episode of GIS melting that can be considered somehow similar to that predicted for 2100 C.E. from IPCC projections. We have revisited three pollen-rich western European margin sequences distributed from 37 to 45°N, MD04-2845, MD95-2042 and MD99-2331, which span all of MIS 5 and are directly affected by the descending branch of the North Atlantic Drift. The analysis of these sequences allows us to directly correlate marine tracers of AMOC variability and changes in ice volume, sea surface temperature (SST), iceberg discharges and pollen-derived European vegetation and climate. The comparison of these observations with those inferred from other locations in the North Atlantic region directly affected by the AMOC and records from the Eirik Drift off southern Greenland document the response of North Atlantic climate to GIS melting during the Last Interglacial. Large and rapid increase in the Western European forest cover and mid-latitude North Atlantic SST at the beginning of MIS 5e benthic isotopic plateau following the YD-like event coincide with strong GIS melting. Despite continued GIS melting during this interval, AMOC strength gradually increases. The dramatic expansion of western European forest could be the result of both AMOC and insolation increase. Subsequently sustained warm SSTs and strong AMOC do not preclude the long term

  4. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

    NASA Astrophysics Data System (ADS)

    van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

    2016-02-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.

  5. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

    PubMed Central

    van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

    2016-01-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval. PMID:26906670

  6. The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin.

    PubMed

    van Hengstum, Peter J; Donnelly, Jeffrey P; Fall, Patricia L; Toomey, Michael R; Albury, Nancy A; Kakuk, Brian

    2016-01-01

    Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval. PMID:26906670

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

    NASA Astrophysics Data System (ADS)

    Skarke, A.; Ruppel, C.; Kodis, M.; Brothers, D.; Lobecker, E.

    2014-09-01

    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. Geodynamics of passive margins: insights from the DFG Schwerpunktprogramm SAMPLE for the South Atlantic and beyond

    NASA Astrophysics Data System (ADS)

    Bunge, Hans-Peter

    2016-04-01

    The DFG Priority Program SAMPLE (South Atlantic Margin Processes and Links with onshore Evolution: http://www.sample-spp.de/), which is to be completed 2016, has studied the evolution of the South Atlantic from its Cretaceous inception to the present day. The program has an explicit interdisciplinary focus, drawing on constraints from deep Earth geophysics, lithosphere and basin dynamics, petrology, landscape evolution and geodesy, thus linking processes that are commonly studied in isolation. Starting from the premise that passive margins are first-order geo-archives, the program has placed the South Atlantic opening history into an observational and theoretical context that considers seismic imaging, plate motion histories, uplift and subsidence events, magmatic and surface evolution, together with models of mantle convection and lithosphere dynamics. A primary lesson is that passive margins are active, displaying a range of vertical motion (i.e. dynamic topography) events, apparently correlated with plate motion changes, that do not conform to traditional rifting models of passive margins. I will summarize some observational results of the program, and place them into a geodynamic context.

  9. Structure and evolution of the NE Atlantic conjugate margins off Norway and Greenland (Invited)

    NASA Astrophysics Data System (ADS)

    Faleide, J.; Planke, S.; Theissen-Krah, S.; Abdelmalak, M.; Zastrozhnov, D.; Tsikalas, F.; Breivik, A. J.; Torsvik, T. H.; Gaina, C.; Schmid, D. W.; Myklebust, R.; Mjelde, R.

    2013-12-01

    The continental margins off Norway and NE Greenland evolved in response to the Cenozoic opening of the NE Atlantic. The margins exhibit a distinct along-margin segmentation reflecting structural inheritance extending back to a complex pre-breakup geological history. The sedimentary basins at the conjugate margins developed as a result of multiple phases of post-Caledonian rifting from Late Paleozoic time to final NE Atlantic breakup at the Paleocene-Eocene transition. The >200 million years of repeated extension caused comprehensive crustal thinning and formation of deep sedimentary basins. The main rift phases span the following time intervals: Late Permian, late Middle Jurassic-earliest Cretaceous, Early-mid Cretaceous and Late Cretaceous-Paleocene. The late Mesozoic-early Cenozoic rifting was related to the northward propagation of North Atlantic sea floor spreading, but also linked to important tectonic events in the Arctic. The pre-drift extension is quantified based on observed geometries of crustal thinning and stretching factors derived from tectonic modeling. The total (cumulative) pre-drift extension amounts to in the order of 300 km which correlates well with estimates from plate reconstructions based on paleomagnetic data. Final lithospheric breakup at the Paleocene-Eocene transition culminated in a 3-6 m.y. period of massive magmatic activity during breakup and onset of early sea-floor spreading, forming a part of the North Atlantic Volcanic Province. At the outer parts of the conjugate margins, the lavas form characteristic seaward dipping reflector sequences and lava deltas that drilling has demonstrated to be subaerially and/or neritically erupted basalts. The continent-ocean transition is usually well defined as a rapid increase of P-wave velocities at mid- to lower-crustal levels. Maximum igneous crustal thickness of about 18 km is found across the outer Vøring Plateau on the Norwegian Margin, and lower-crustal P-wave velocities of up to 7.3 km

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

    NASA Astrophysics Data System (ADS)

    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.

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

    USGS Publications Warehouse

    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..

  12. Coherency of European speleothem δ18O records linked to North Atlantic ocean circulation

    NASA Astrophysics Data System (ADS)

    Deininger, Michael; McDermott, Frank

    2016-04-01

    Speleothem δ18O records can provide valuable information about past continental environmental and climatic conditions. In recent decades a European speleothem network has been assembled that allows us to reconstruct past climate variability in both space and time. In particular climate variability during the Holocene was investigated by these studies. The Holocene is thus an ideal period to apply sophisticated statistical methods to derive spatio-temporal pattern of common climate variability in the European speleothem record. Here we evaluate a compilation of 10 speleothem δ18O records covering the last 4.5 ka for their shared variability. The selected speleothem δ18O records must satisfy certain quality criteria to be included: (i) a robust age model; (ii) a temporal intra-sampling resolution of smaller than 30 years; and (iii) the record should be published. A Monte Carlo based Principal Component Analysis (MC-PCA) that accounts for uncertainties in individual speleothem age models and for the different and varying temporal resolutions of each speleothem δ18O record was used for this purpose. Our MC-PCA approach allows not only the identification of temporally coherent changes in δ18O records, but it also facilitates their depiction and evaluation spatially. The compiled speleothem δ18O records span almost the entire European continent (with the exception of the circum-Mediterranean region) ranging from the western Margin of the European continent (stalagmite CC-3, Ireland) to Northern Turkey (SO-1) and from Northern Italy (CC-26) to Norway (FM-3). For the MC-PCA analysis, the 4.5 ka period was sub-divided into eight 1 ka long time windows that overlap the subsequent time window by 500 years to allow a comparison of the temporal evolution of the common signal. In this study we only interpreted the 1st principal component (PC) that depict the spatio-temporal pattern with the highest explained variability of all speleothem δ18O records. Our MC-PCA results

  13. Cenozoic Source-to-Sink of the African margin of the Equatorial Atlantic

    NASA Astrophysics Data System (ADS)

    Rouby, Delphine; Chardon, Dominique; Huyghe, Damien; Guillocheau, François; Robin, Cecile; Loparev, Artiom; Ye, Jing; Dall'Asta, Massimo; Grimaud, Jean-Louis

    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. Mapping and regional correlation of dated lateritic paleo-landscape remnants allows us to reconstruct two physiographic configurations of West Africa during the Cenozoic. We corrected those reconstitutions from flexural isostasy related to the subsequent erosion. These geometries show that the present-day drainage organization stabilized by at least 29 Myrs ago (probably by 34 Myr) revealing the antiquity of the Senegambia, Niger and Volta catchments toward the Atlantic as well as of the marginal upwarp currently forming a continental divide. The drainage rearrangement that lead to this drainage organization was primarily enhanced by the topographic growth of the Hoggar swell and caused a major stratigraphic turnover along the Equatorial margin of West Africa. Elevation differences between paleo-landscape remnants give access to the spatial and temporal distribution of denudation for 3 time-increments since 45 Myrs. From this, we estimate the volumes of sediments and associated lithologies exported by the West African Craton toward different segments of the margin, taking into account the type of eroded bedrock and the successive drainage reorganizations. We compare these data to Cenozoic accumulation histories in the basins and discuss their stratigraphic expression according to the type of margin segment they are preserved in.

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

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  15. Wavelet and multitaper coherence methods for assessing the elastic thickness of the Irish Atlantic margin

    NASA Astrophysics Data System (ADS)

    Daly, E.; Brown, C.; Stark, C. P.; Ebinger, C. J.

    2004-11-01

    There have been some inconsistencies in estimates of the effective elastic thickness of the continental lithosphere Te based upon admittance or coherence relationships between gravity and topography. This paper compares multitaper and wavelet methods to analyse the coherence between Bouguer gravity and bathymetric data over the Irish Atlantic margin. The analyses show that similar lateral Te variations can be recovered from the data, but demonstrate that the size of the data window can give rise to a significant downward bias in Te estimates. A seismically constrained 3-D gravity inversion over the Rockall basin shows the presence of surface and subsurface loads whose ratio is loosely correlated with load ratio variations generated from the wavelet coherence method. The Te and load ratio, f variations can be plausibly related to major geological structures on the margin. If the load ratio variations can be interpreted geologically, it implies that spectral based methods to estimate effective elastic thickness must incorporate subsurface loads within the underlying theoretical model. On the Irish Atlantic margin, Te is generally low (6-18 km) and is associated with a NE-SW Caledonian trend. The weakest lithosphere is in the southern Rockall basin, Porcupine bank and Porcupine basin and the strongest lithosphere is along the Rockall-Hatton region. The low Te values are consistent with results from other passive margins. The reasons for such low Te values on the Irish Atlantic margin remain unclear, but may be the consequence of Te being frozen into the lithosphere when loads were emplaced during continental breakup and temperature gradients were high. The process of sedimentation and the presence of fluids may be contributory factors. There is an indication of a geological and rheological divide between the Rockall-Hatton region and the Rockall basin, possibly associated with the Caledonian orogenic front.

  16. Boundary scavenging at the East Atlantic margin does not negate use of 231Pa/230Th to trace Atlantic overturning

    NASA Astrophysics Data System (ADS)

    Lippold, Jörg; Mulitza, Stefan; Mollenhauer, Gesine; Weyer, Stefan; Heslop, David; Christl, Marcus

    2012-06-01

    The 231Pa/230Th method is a promising tool to reconstruct Ocean circulation over the past Glacial-Interglacial cycle. However, marine particle flux may constrain the applicability of this ratio as a direct quantitative proxy for the strength of Atlantic Meridional Overturning Circulation (AMOC) by influencing the fractionation between the in situ produced 231Pa and 230Th in ocean water. Here we present 231Pa/230Th down-core profiles from high particle flux areas off Namibia and Senegal covering the past ∼35 ka. The 231Pa/230Th profiles at these sites show very different responses to temporal variations of particle fluxes and to changes in water masses. Our results show that sedimentary 231Pa/230Th in the Eastern Atlantic margin is linked to particle flux, but controlled primarily by the mode of the AMOC. Our data suggest that during the past ∼30 ka the high productivity Eastern margin was not capable of importing and storing significant amounts of 231Pa from the open Ocean. Consequently, the applicability of the 231Pa/230Th proxy to reconstruct past ocean circulation is not hampered by this potentially additional 231Pa sink.

  17. Predicting Rifted Continental Margin Subsidence History From Satellite Gravity Derived Crustal Thinning: Application to North Atlantic Margins

    NASA Astrophysics Data System (ADS)

    Hurst, N. W.; Kusznir, N. J.; Roberts, A. M.; White, R. S.

    2004-05-01

    3D spectral inversion of satellite derived gravity anomaly data (Smith and Sandwell 1997) and bathymetry data (Gebco 2003) has been used to determine oceanic and continental margin crustal thickness for the North Atlantic between 50 and 70 degrees N. The inverse technique incorporates a correction for the large negative thermal gravity anomaly present in the oceanic and stretched continental lithosphere. This correction can be determined using ocean isochron data for oceanic lithosphere, and margin rift age and beta stretching estimates derived iteratively from crustal basement thickness determined from the gravity inversion for the stretched continental lithosphere. A correction for the gravity anomaly contribution from sediments may be determined using thickness estimates derived from seismic reflection MCS data. Density depth variation within sediments is predicted assuming compaction. Crustal thicknesses determined using a thermal gravity correction derived from ocean isochron data give crustal thicknesses that are consistent with seismic observations. The resulting basement thickness determined from gravity inversion for the thinned continental margin lithosphere may be used to produce estimates of crustal thinning and stretching. Flexural backstripping and reverse post-breakup thermal subsidence modelling may be used to restore present 2D (or 3D) stratigraphic cross sections to earlier post-breakup times. Thermal subsidence arises from the cooling of stretched continental lithosphere and the recently formed oceanic lithosphere, and may be predicted from beta stretching factor (McKenzie 1978) and rift age. Beta stretching factors derived from gravity anomaly inversion have been used to predict reverse thermal subsidence for N Atlantic rifted margins. The resulting palaeo-bathymetric restorations show emergence of the Hatton Bank and NE Faroes rifted margins in early post-breakup times. The predicted palaeo-bathymetries are consistent with palaeo

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

    NASA Astrophysics Data System (ADS)

    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

  19. Styles of extension and oceanization: Examples from the South Atlantic margins

    NASA Astrophysics Data System (ADS)

    Perez-Gussinye, Marta; Neto Araujo, Mario; Thoaldo Romeiro, Marco; Andres Martinez, Miguel; Phipps Morgan, Jason; Ros, Elena

    2015-04-01

    Along the margins of the South Atlantic from the Camamu/Gabao to the North Santos/South Kwanza conjugate margin, rift architecture changes considerably. On the Brazilian side, from North to South, the margin width increases, syn-rift subsidence decreases and the degree of conjugate margin asymmetry varies. Here we suggest that these changes in architectonical styles can be explained with a combination of extensional modes: core-complex, wide and narrow rift modes with sequential faulting mode, which arises at the last stages of extension and accounting for conjugate margin asymmetry. The prevalence of any of these modes during extension depends on the strength of the lower crust at the start of rifting and during extension. Melting and serpentinisation are also strongly linked with lower crustal rheology, with weaker rheologies leading to less coupling between lithospheric layers and a slower mantle uplift, hence relatively less melting and serpentinisation. Here we show how likely changes in crustal strength and lithospheric configuration from the northern San Francisco craton to the southern Ribeira belt, may have led to the rich variety in extensional and oceanization styles observed in this margin sector.

  20. Ocean - ice sheet interaction along the NW European margin during the last glacial phases

    NASA Astrophysics Data System (ADS)

    Becker, L. W. M.; Sejrup, H. P.; Haflidason, H.; Hjelstuen, B. O. B.

    2015-12-01

    The NW European continental margin was repeatedly covered by shelf edge glaciations during the last glacial cycles. Here, we present a compilation of new and previously published data from a SW to NE transect of 8 sediment cores raised along the upper continental slope. This study aims to investigate the interaction between sea surface conditions and the variability seen in the British Irish Ice Sheet (BIIS) and the Fennoscandian Ice Sheet (FIS) during the last 13-40 ka BP. Ice Rafted Debris (IRD) counts, IRD flux data, grain size data, the content of the polar planktonic foraminifera Neogloboquadrina pachyderma (sin) and ∂18O measurements were compiled and combined with new Bayesian age models. From 40-24.5 ka BP the build up and consecutive confluence of the BIIS and the FIS are reflected in sediment composition and flux data. Pulses of large quantities of fine material to the southern part of the transect suggest riverine BIIS related influx. The sediment composition in cores close to the Norwegian channel indicates that the Norwegian Channel Ice Stream (NCIS) was only active between 24.5-18.5 ka BP during the last glacial stage. The planktonic foraminifera data during this period strongly suggests a dependence of NCIS extent variability and pulses in warm Atlantic water entering the Nordic Seas. In the northernmost cores rapidly deposited, laminated sediments and ∂18O spikes in planktonic foraminifera dated to 18.5 ka BP were interpreted as meltwater plume deposits. This may reflect NCIS retreat allowing BIIS and FIS to unzip and route ice dammed lake- and meltwater to the margin. In conclusion, the investigation suggests a close co-variation in extent of marine based parts of the BIIS, the FIS and ocean circulation while demonstrating the strong influence of the local glacial history on standard open marine proxies. This suggests that tuning chronologies of single marine records to ice cores in some regions might be more challenging than previously

  1. Controls on hydrocarbon generation and leakage in South Atlantic conjugate margins: A comparative approach.

    NASA Astrophysics Data System (ADS)

    Marcano, Gabriela; Anka, Zahie; di Primio, Rolando

    2013-04-01

    We present a regional comparative analysis of the possible first-order internal and external factors controlling source rock (SR) maturation and hydrocarbon (HC) generation and leakage in two pairs of conjugate margins across the South Atlantic: the Brazil (Campos Basin)-Angola (Lower Congo Basin) margins located in the "central segment", and the Argentina (Colorado Basin)-South Africa (Orange Basin) in the "southern segment". Our approach is based on the analysis and integration of borehole data, numerical modeling, 2D seismic reflection data, and published reports. Coupling of modeling results, sedimentation rate calculation and seal-bypass system analysis reveals that: (1) oil window is reached by syn-rift SRs in the southern segment during the Early to Late Cretaceous when thermal subsidence is still active, whilst in the central segment they reach it in Late-Cretaceous- Neogene during a salt remobilization phase, and (2) early HC generation from post-rift SRs in the southern segment and from all SRs in the central segment appears controlled mainly by episodes of increased sedimentation rates. These latter seem associated to the Andes uplift history for the western South Atlantic basins (Campos and Colorado) and to a possibly climate-driven response for the eastern South Atlantic basins (Orange and Lower Congo). Interestingly, Paleogene leakage indicators, which were identified in the Argentina-South Africa conjugate margins, occur contemporaneously to low sedimentation rates periods. Nonetheless, present-day leakage indicators, which were also identified in both pair of conjugate margins, might be related to seal failure events associated to eustatic sea-level drops.

  2. Crustal composition of the Møre Margin and compilation of a conjugate Atlantic margin transect

    NASA Astrophysics Data System (ADS)

    Kvarven, Trond; Mjelde, Rolf; Hjelstuen, Berit Oline; Faleide, Jan Inge; Thybo, Hans; Flueh, Ernst R.; Murai, Yoshio

    2016-01-01

    The inner part of the volcanic, passive Møre Margin, mid-Norway, expresses an unusual abrupt thinning from high onshore topography with a thick crust to an offshore basin with thin crystalline crust. Previous P-wave modeling of wide-angle seismic data revealed the presence of a high-velocity (7.7-8.0 km/s) body in the lower crust in this transitional region. These velocities are too high to be readily interpreted as Early Cenozoic intrusions, a model often invoked to explain lower crustal high-velocity bodies in the region. We present a Vp/Vs model, derived from the modeling of wide-angle seismic data, acquired by use of Ocean Bottom Seismograph horizontal components. The modeling suggests dominantly felsic composition of the crust. An average Vp/Vs value for the lower crustal body is modeled at 1.77, which is compatible with a mixture of continental blocks and Caledonian eclogites. The results are compiled with earlier results into a transect extending from onshore Norway to onshore Greenland. Back-stripping of the transect to Early Cenozoic indicates asymmetric conjugate magmatism related to the continental break-up. Further back-stripping to the time when most of the Caledonian mountain range had collapsed indicates that the thinning during the first phase of extension was about 25% higher for proto Norway than proto Greenland.

  3. Geologic Significance of Newly Discovered Methane Seeps on the Northern US Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Skarke, A. D.; Ruppel, C. D.; Kodis, M.; Lobecker, E.; Malik, M.

    2013-12-01

    Analysis of multibeam water column backscatter data collected by NOAA Ship Okeanos Explorer in 2011, 2012, and 2013 has revealed the presence of several hundred methane gas plumes on the US Atlantic margin between Cape Hatteras and Cape Cod (see abstract by Kodis et al., 'US Atlantic Margin Methane Plumes Identified From Water Column Backscatter Data Acquired by NOAA Ship Okeanos Explorer'). Acoustic imagery indicates that these vertically elongate methane plumes extend hundreds of meters above the seafloor and are often deflected by ocean currents. Visual and acoustic observation of the base of select plumes by the NOAA remotely operated vehicle (ROV) Deep Discoverer in 2013 confirmed that they are generated by emission of gas bubbles at seafloor seeps. Prior to this discovery, the only observed cold seeps on the central and northern extents of the US Atlantic margin were at shallow water depths in Baltimore Canyon, and no deepwater (>1000 m) seeps were known to exist. The new seeps are observed at depths ranging from 100 m on the Nantucket Shelf to 1400 m in the vicinity of Norfolk, Baltimore, and Veatch Canyons. The seeps occur in isolation as well as in clusters, and particularly high seep concentrations are observed in the upper portions of Hudson Canyon. Along-margin seep distribution is not uniform and higher overall seep concentrations are observed north of Veatch Canyon and south of Wilmington Canyon, with substantially fewer seep occurrences on the intervening part of the Mid-Atlantic Bight. Lithology (e.g., coarse-grained vs. fine-grained sediment), underlying geology, and shelf-slope morphology appear to be correlated with the spatial distribution of cold seeps along the margin. Numerous shallow water (~500 m) seep locations are roughly coincident with seafloor pockmark features identified by D. Brothers (personal communication) and are proximal to the upslope extent of the gas hydrate stability zone (GHSZ). Multiple deepwater seep locations are

  4. Burial, Uplift and Exhumation History of the Atlantic Margin of NE Brazil

    NASA Astrophysics Data System (ADS)

    Japsen, Peter; Bonow, Johan M.; Green, Paul F.; Cobbold, Peter R.; Chiossi, Dario; Lilletveit, Ragnhild

    2010-05-01

    We have undertaken a regional study of landscape development and thermo-tectonic evo-lution of NE Brazil. Our results reveal a long history of post-Devonian burial and exhuma-tion across NE Brazil. Uplift movements just prior to and during Early Cretaceous rifting led to further regional denudation, to filling of rift basins and finally to formation of the Atlantic margin. The rifted margin was buried by a km-thick post-rift section, but exhumation began in the Late Cretaceous as a result of plate-scale forces. The Cretaceous cover probably extended over much of NE Brazil where it is still preserved over extensive areas. The Late Cretaceous exhumation event was followed by events in the Paleogene and Neogene. The results of these events of uplift and exhumation are two regional peneplains that form steps in the landscape. The plateaux in the interior highlands are defined by the Higher Surface at c. 1 km above sea level. This surface formed by fluvial erosion after the Late Cretaceous event - and most likely after the Paleogene event - and thus formed as a Paleogene pene-plain near sea level. This surface was reburied prior to the Neogene event, in the interior by continental deposits and along the Atlantic margin by marine and coastal deposits. Neo-gene uplift led to reexposure of the Palaeogene peneplain and to formation of the Lower Surface by incision along rivers below the uplifted Higher Surface that characterise the pre-sent landscape. Our results show that the elevated landscapes along the Brazilian margin formed during the Neogene, c. 100 Myr after break-up. Studies in West Greenland have demonstrated that similar landscapes formed during the late Neogene, c. 50 Myr after break-up. Many passive continental margins around the world are characterised by such elevated plateaus and it thus seems possible, even likely, that they may also post-date rifting and continental separation by many Myr.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    We have undertaken a regional study of the thermo-­tectonic development of East Greenland (68-75°N) and of southern Norway (58-64°N). We take advantage of the general observation that that the effects of uplift often are reflected more clearly onshore than offshore, and of the specific condition that the mountains of southern East Greenland expose thick basalts that were extruded onto a largely horizontal lava plain near sea level during breakup of the NE Atlantic at the Paleocene-Eocene transition. It is thus clear that the present-­day elevation of these basalts up to 3.7 km a.s.l. were reached after breakup. Our results based on apatite fission-­track analysis (AFTA) data from East Greenland reveal a long history of post-­Palaeozoic burial and exhumation across the region and show that the terrains of Palaeozoic and older rocks were buried below a 2-3 km­-thick cover prior to a series of Mesozoic events of uplift and exhumation. The AFTA results from southern Norway reveal events of Mesozoic uplift and exhumation that are broadly simultaneous with those in Greenland. 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. Our AFTA data from southern Norway show evidence of an event of mid­Cenozoic uplift and exhumation that overlap with the early Oligocene onset of progradation of clastic wedges towards the south and with the formation of a major, late Eocene unconformity along the NW European margin. The uplift event at the Eocene-Oligocene transition that affected wide areas in the NE Atlantic domain was followed by two regional events of uplift and incision of the East Greenland margin in the late Miocene and Pliocene whereas the Neogene uplift of southern Norway began in the early Miocene and was

  6. Major Paleostress Field Differences on Complementary Margins of the South Atlantic

    NASA Astrophysics Data System (ADS)

    Salomon, E.; Koehn, D.; Passchier, C. W.; Hackspacher, P. C.; Glasmacher, P. A.

    2013-12-01

    We present a detailed study of paleostress fields of the Namibian and Brazilian passive continental margins of the South Atlantic to address a general debate on whether or not these complementary margins experienced similar tectonic histories (e.g. Cobbold et al., 2001; Al-Hajri et al., 2009; Japsen et al., 2012). In our study, we compare the NW of Namibia and the SE of Brazil with each other. These areas are largely covered by the flood basalts of the Paraná-Etendeka-Large Igneous Province overlying Neo-Proterozoic basement of the Pan-African orogeny. With an age of ~133 Ma the basalts were emplaced just before or during the onset of the South Atlantic opening and thus serve as a good time marker for rift- and post-rift-related tectonics. We studied mainly fault planes and associated striations within the flood basalts and compared the resulting stress patterns of both margins. Results reveal remarkable differences in the stress patterns for SE Brazil and NW Namibia. In NW Namibia, a WSW-ENE directed extensional stress field dominates and fits well with extension of the original continental rift and the passive margin. A second extensional stress field (σ3 SSW oriented) and a strike-slip system (σ1 NW oriented) appear only subdued. In contrast, the SE of Brazil is mainly characterized by two strike-slip systems (σ1 oriented SW and E, respectively) whereas an extensional stress field is almost non-existent. The strike-slip faulting of the Brazilian study area occur widespread across SE Brazil as they are also evident in other paleostress studies of the region and might thus be the result of far-field stresses. Margin-parallel faults are scarce, so it appears that rift-related extension was restricted to a narrower strip along the continent-ocean boundary, now lying offshore. In NW Namibia, the faults of the extensional stress regime run parallel to the sub-margin-parallel basement structure (i.e. shear zones and foliation) and hence indicate a reactivation of

  7. Meso-Cenozoic Source-to-Sink analysis of the African margin of the Equatorial Atlantic

    NASA Astrophysics Data System (ADS)

    Chardon, Dominique; Rouby, Delphine; Huyghe, Damien; Ye, Jing; Guillocheau, François; Robin, Cécile; Dall'Asta, Massimo; Brown, Roderick; Webster, David

    2015-04-01

    The Transform Source to Sink Project (TS2P) objective is to link the evolution of the offshore sedimentary basins of the African margin of the Equatorial Atlantic and their source areas on the West African Craton. The margin consists in alternating transform and oblique margin portions from Guinea, in the West, to Nigeria, in the East. Such a longitudinal structural variability is associated with variation in the margin width, continental geology and relief, drainage networks and subsidence/accumulation patterns that we analyzed using offshore seismic data and onshore geology and geomorphology. We compare syn- to post rift offshore geometry and long-term stratigraphic history of each of the margin segments. Transform faults appear to play a major role in shaping Early Cretaceous syn-rift basin architectures. Immediate post-rift Late Cretaceous sedimentary wedges record a transgression and are affected by the reactivation of some of transform faults. We produced A new type of inland paleogeographic maps for key periods since the end of the Triassic, allowing delineation of intracratonic basins having accumulated material issued from erosion of the marginal upwarps that have grown since break-up along the margin. We use offshore and onshore basin analysis to estimate sediment accumulation and integrate it in a source-to-sink analysis where Mesozoic onshore denudation will be estimated by low-temperature thermochronology. Cenozoic erosion and drainage history of the continental domain have been reconstructed from the spatial analysis of dated and regionally correlated geomorphic markers. The stationary drainage configuration of the onshore domain since 30 Ma offers the opportunity to correlate the detailed onshore morphoclimatic record based on the sequence of lateritic paleolandsurfaces to offshore stratigraphy, eustasy and global climatic proxies since the Oligocene. Within this framework, we simulate quantitative solute / solid erosional fluxes based on the

  8. Rapid late pleistocene incision of Atlantic passive-margin river gorges

    USGS Publications Warehouse

    Reusser, L.J.; Bierman, P.R.; Pavich, M.J.; Zen, E.-A.; Larsen, J.; Finkel, R.

    2004-01-01

    The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid downcutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial melt-water, initiated incision.

  9. Rapid Late Pleistocene Incision of Atlantic Passive-Margin River Gorges

    NASA Astrophysics Data System (ADS)

    Reusser, Luke J.; Bierman, Paul R.; Pavich, Milan J.; Zen, E.-an; Larsen, Jennifer; Finkel, Robert

    2004-07-01

    The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid downcutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial meltwater, initiated incision.

  10. Giardia and Cryptosporidium in cetaceans on the European Atlantic coast.

    PubMed

    Reboredo-Fernández, Aurora; Ares-Mazás, Elvira; Martínez-Cedeira, José A; Romero-Suances, Rafael; Cacciò, Simone M; Gómez-Couso, Hipólito

    2015-02-01

    The occurrence of Giardia and Cryptosporidium was investigated in cetacean specimens stranded on the northwestern coast of Spain (European Atlantic coast) by analysis of 65 samples of large intestine from eight species. The parasites were identified by direct immunofluorescence antibody test (IFAT) and by PCR amplification of the β-giardin gene, the ITS1-5.8S-ITS2 region and the SSU-rDNA gene of Giardia and the SSU-rDNA gene of Cryptosporidium. Giardia and Cryptosporidium were detected in 7 (10.8 %) and 9 samples (13.8 %), respectively. In two samples, co-infection with both parasites was observed. Giardia duodenalis assemblages A, C, D and F, and Cryptosporidium parvum were identified. This is the first report of G. duodenalis in Balaenoptera acutorostrata, Kogia breviceps and Stenella coeruleoalba and also the first report of Cryptosporidium sp. in B. acutorostrata and of C. parvum in S. coeruleoalba and Tursiops truncatus. These results extend the known host range of these waterborne enteroparasites. PMID:25418072

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

    NASA Astrophysics Data System (ADS)

    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

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

    USGS Publications Warehouse

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

    2014-01-01

    Tsunamis caused by atmospheric disturbances and by coastal earthquakes may be more frequent than those generated by landslides, but their amplitudes are probably smaller. Among the possible far-field earthquake sources, only earthquakes located within the Gulf of Cadiz or west of the Tore-Madeira Rise are likely to affect the U.S. coast. It is questionable whether earthquakes on the Puerto Rico Trench are capable of producing a large enough tsunami that will affect the U.S. Atlantic coast. More information is needed to evaluate the seismic potential of the northern Cuba fold-and-thrust belt. The hazard from a volcano flank collapse in the Canary Islands is likely smaller than originally stated, and there is not enough information to evaluate the magnitude and frequency of flank collapse from the Azores Islands. Both deterministic and probabilistic methods to evaluate the tsunami hazard from the margin are available for application to the Atlantic margin, but their implementation requires more information than is currently available.

  13. Breakup magmatism style on the North Atlantic Igneous Province: insight from Mid-Norwegian volcanic margin

    NASA Astrophysics Data System (ADS)

    Mansour Abdelmalak, Mohamed; Faleide, Jan Inge; Planke, Sverre; Theissen-Krah, Sonja; Zastrozhnov, Dmitrii; Breivik, Asbjørn Johan; Gernigon, Laurent; Myklebust, Reidun

    2014-05-01

    The distribution of breakup-related igneous rocks on rifted margins provide important constraints on the magmatic processes during continental extension and lithosphere separation which lead to a better understanding of the melt supply from the upper mantle and the relationship between tectonic setting and volcanism. The results can lead to a better understanding of the processes forming volcanic margins and thermal evolution of associated prospective basins. We present a revised mapping of the breakup-related igneous rocks in the NE Atlantic area, which are mainly based on the Mid-Norwegian (case example) margin. We divided the breakup related igneous rocks into (1) extrusive complexes, (2) shallow intrusive complexes (sills/dykes) and (3) deep intrusive complexes (Lower Crustal Body: LCB). The extrusive complex has been mapped using the seismic volcanostratigraphic method. Several distinct volcanic seismic facies units have been identified. The top basalt reflection is easily identified because of the high impedance contrast between the sedimentary and volcanic rocks resulting in a major reflector. The basal sequence boundary is frequently difficult to identify but it lies usually over the intruded sedimentary basin. Then the base is usually picked above the shallow sill intrusions identified on seismic profile. The mapping of the top and the base of the basaltic sequences allows us to determine the basalt thickness and estimate the volume of the magma production on the Mid- Norwegian margin. The thicker part of the basalt corresponds to the seaward dipping reflector (SDR). The magma feeder system, mainly formed by dyke and sill intrusions, represents the shallow intrusive complex. Deeper interconnected high-velocity sills are also mappable in the margin. Interconnected sill complexes can define continuous magma network >10 km in vertical ascent. The large-scale sill complexes, in addition to dyke swarm intrusions, represent a mode of vertical long-range magma

  14. Physical Conditions Associated with Widespread Seafloor Methane Discharge on the Northern US Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Skarke, A. D.; Ruppel, C. D.; Brothers, D. S.

    2014-12-01

    Recent analysis of water column backscatter data and remotely operated vehicle (ROV) video imagery collected by NOAA Ship Okeanos Explorer between 2011 and 2013 revealed methane discharge from the seafloor at over 570 gas seep locations along the northern US Atlantic margin. To the best of our knowledge, such large-scale seepage has not previously been observed on a passive margin outside the Arctic or not spatially associated with a petroleum basin. This seepage has implications for the global carbon cycle, ocean chemistry (e.g., acidification), and in some cases, the climate system. Using data collected by Okeanos Explorer and NOAA's Deep Discoverer ROV, we combine water column backscatter data with video imagery and seafloor backscatter data to estimate gas flux and constrain the geoacoustic properties of the seabed at methane discharge sites. The total methane flux from the northern US Atlantic margin seeps is conservatively estimated at ~15-90 Mg y-1, based on observations of gas bubble volume, discharge rates, and discharge points per site. However, fewer than 1% of the identified seep sites have been inspected with a ROV, and this estimate is likely to be revised upward as the characteristics of the seeps are further constrained. Another important observation to emerge from our analysis is the lack of spatial correlation between seep sites and the ~5000 pockmarks mapped on the northern part of the US Atlantic margin. In this region, pockmarks, which are often easily identified by geophysical imaging of the seafloor, should not be considered potential target sites for finding undiscovered areas of seepage. Conversely, discrete patches of elevated relative seafloor acoustic backscatter amplitude do appear to be correlated with the spatial distribution of methane seeps, implying anomalous seafloor characteristic at seep loci. This finding is consistent with ROV video observations of authigenic carbonate outcrops and extensive chemosynthetic bivalve communities

  15. Influence of the Iceland mantle plume on North Atlantic continental margins

    NASA Astrophysics Data System (ADS)

    White, R. S.; Isimm Team

    2003-04-01

    Early Tertiary breakup of the North Atlantic was accompanied by widespread magmatism. The histories of the Iceland mantle plume, of rifting and of magmatism are intimately related. The magmatism provides a challenge both to imaging structure, and to modelling the subsidence and development of the continental margins. We report new work which integrates state-of-the-art seismic imaging and new acquisition on the Atlantic volcanic margins with new techniques for modelling their evolution. We discuss the distribution of igneous rocks along the North Atlantic margins and discuss the temporal and spatial variations in the Iceland mantle plume in the early Tertiary, which have largely controlled this pattern of magmatism. Igneous rocks are added to the crust on rifted margins as extrusive lavas, as sills intruded into the sub-surface and as lower crustal intrusions or underplate. Each provide different, but tractable problems to seismic imaging. We show that many of these difficulties can be surmounted by using very long offsets (long streamers or two-ship methods) with a broad-band, low-frequency source, and by using fixed ocean bottom receivers. We report results from surveys on the North Atlantic continental margins using these methods. Imaging results are shown from the recent FLARE project and from the iSIMM project, which recorded new seismic data recorded in summer 2002. The iSIMM project acquired two seismic surveys, using 85 4-component ocean bottom seismometers with long streamers for wide-angle data, and vertical arrays for far-field source signature recording. One survey crosses the Faroes Shelf and adjacent continental margin, and a second the Hatton-Rockall Basin, Hatton Bank and adjacent oceanic crust. The Faroes wide-angle profiles were overshot by WesternGeco's Topaz using three single-sensor, Q-Marine streamers, 12km plus two 4km. We designed deep-towed, broad-band low-frequency sources tuned to enhance the bubble pulses, with peak frequencies at 8

  16. Extreme Precipitation Events Over the Iberian Atlantic Margin: The Role of Atmospheric Rivers

    NASA Astrophysics Data System (ADS)

    Eiras-Barca, J.; Miguez-Macho, G.

    2014-12-01

    Atmospheric Rivers (ARs), elongated structures of high values of water vapor flux carried along the warm conveyor belt of extratropical cyclones, are a prominent feature in the poleward transport of moisture, and are often associated to extreme precipitation events (EPEs). Here we examine the link between EPEs on the Atlantic Margin of the Iberian Peninsula and ARs in the period 1979-2007, and show that for about 75% of cases there is a direct relation, and for many others, a second order or indirect connection; that is, they originate from moisture transported by an AR to a neighboring region the previous days that feeds another cyclone causing the actual event. EPEs in western Iberia present a pronounced seasonal cycle, being much more likely to occur in the autumn and practically inexistent in the summer. The incidence of ARs is however much higher and doesn't show the same temporal frequency as EPEs, with a maximum in winter and a minimum, very marked in the south but not so much in the north, in summer. Only about 30% of ARs result in EPEs in autumn-winter and less than 10% in summer, likely due to differences in forcing, duration and thermodynamic characteristics of the ARs themselves. The interannual variability of EPEs and ARs can be quite large and uncorrelated, with years of high AR activity not necessarily years with high number of EPEs; nevertheless, EPEs are consistently linked to ARs. The interannual variability of AR arrivals to the Iberian Peninsula mirrors that of AR activity in the southeast North Atlantic and it's enhanced by negative NAO conditions. There are uncorrelated and important yearly variations in other quadrants of the North Atlantic, some being favored over others depending on persistent circulation anomalies. For periods of several years the entire North Atlantic can also present a significant amount of interannual variability in AR activity.

  17. Evolution of North Atlantic Passive Margins Controlled by the Iceland Mantle Plume

    NASA Astrophysics Data System (ADS)

    Parnell-Turner, R. E.; White, N. J.; Henstock, T.; Murton, B. J.; Jones, S. M.

    2015-12-01

    Evolution of North Atlantic passive margins has been profoundly influenced by the Iceland mantle plume over the past 60 Ma. Residual depth anomalies of oceanic lithosphere, long wavelength gravity anomalies and seismic tomographic models show that upwelling mantle material extends from Baffin Bay to Western Norway. At fringing passive margins such as Northwest Scotland, there is evidence for present-day dynamic support of the crust. The Iceland plume is bisected by the Reykjanes Ridge ridge, which acts as a tape-recorder of the temporal variability of the plume. We present regional seismic reflection profiles that traverse the oceanic basin between northwest Europe and Greenland. A diachronous pattern of V-shaped ridges and troughs are imaged beneath marine sediments, revealing a complete record of transient periodicity that can be traced continuously back to ~55 Myrs. This periodicity increases from ~3 to ~8 Ma with clear evidence for minor, but systematic, asymmetric crustal accretion. V-shaped ridges grow with time and reflect small (5-30°C) changes in mantle temperature, consistent with episodic generation of hot solitary waves triggered by growth of thermal boundary layer instabilities within the mantle. Our continuous record of convective activity suggests that the otherwise uniform thermal subsidence of sedimentary basins, which fringe the North Atlantic Ocean, has been punctuated by periods of variable dynamic topography. This record can explain a set of diverse observations from the geologic record. Paleogene unconformities in the Faroe-Shetland Basin, the punctuated deposition of contourite drifts and variations in deep-water current strength can all be explained by transient mantle plume behavior. These signals of convective activity should lead to improved insights into the fluid dynamics of the mantle, and into the evolution of volcanic passive margins.

  18. Observational constraints and models for conjugate North Atlantic volcanic rifted margins formation

    NASA Astrophysics Data System (ADS)

    Huismans, R. S.; Faleide, J. I.; Planke, S.

    2009-12-01

    The amount of breakup-related magmatism in the northeast Atlantic cannot be explained by passive decompression melting of sub-lithospheric mantle with a normal potential temperature. Three competing end-member hypotheses are proposed for the formation of this excess magmatic activity: 1) excess magmatism results from elevated mantle potential temperatures associated with mantle plume processes, 2) rifting induced small scale convection at the base of the lithosphere enhances the flux of material through the melt window during rifting and mid-oceanic ridge spreading, and 3) mantle heterogeneities with lower melt temperatures of the melt source may produce larger than expected magmatic productivity. We review observations and present forward numerical models of passive margin formation including melt production. Key characteristics that require explanation include: 1) igneous crustal thickness versus mean igneous seismic velocity relationships for magmatic underplated bodies on the Norwegian-Greenland conjugate margins that indicate a cooling trend and seismic velocities that point to a moderate or non-existent mantle thermal anomaly during and after breakup; 2) rapid along margin variations in the observed igneous crustal thickness that suggest a local lithospheric control on melt productivity; 3) significant asymmetries in melt production existing between the Norwegian-Greenland conjugate margins; 4) post rift magmatic activity 30 my after breakup with igneous seismic velocity indicating normal mantle temperature; 5) anomalous low magmatic productivity in the oceanic Norway basin following moderate excess productivity that suggests anomalous low mantle temperatures following breakup, 6) anomalous mantle lithosphere thinning in the distal margin in the late syn-rift, 7) uplift and erosion of highly thinned crustal blocks in the distal margin. Forward numerical models of passive margin formation and melt productivity suggest the following key controls: 1) rifting

  19. Isostatic and dynamic support of high topography on a North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Kathrine Pedersen, Vivi; Huismans, Ritske S.; Moucha, Robert

    2016-04-01

    Substantial controversy surrounds the origin and recent evolution of high topography along passive continental margins in the North Atlantic, with suggested age of formation ranging from early Paleozoic Caledonian orogenesis to Neogene uplift of a Mesozoic peneplain. Here we focus on the well-documented high passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that most topography is compensated by the crustal structure, suggesting a topographic age related to ~400 Myr old Caledonian orogenesis. In addition, we infer that dynamic uplift (~300 m) has rejuvenated existing topography locally in the coastal region within the last ~10 Myr due to mantle convection. Such uplift has, in combination with a general eustatic sea-level fall and concurrent erosion-driven isostatic rock-column uplift, the potential to increase erosion of coastal-near regions and explain observations that have traditionally been interpreted in favor of the peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last ~20 Myr. Topography must have been high since the Caledonian orogeny.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Evolution of Northeast Atlantic Magmatic Continental Margins from an Ethiopian-Afar Perspective

    NASA Astrophysics Data System (ADS)

    England, R. W.; Cornwell, D. G.; Ramsden, A. M.

    2014-12-01

    One of the major problems interpreting the evolution of magmatic continental margins is that the structure which should record the pre-magmatic evolution of the rift and which potentially influences the character of the rifting process is partially or completely obscured by thick basalt lava flows and sills. A limited number of deep reflection seismic profiles acquired with tuned seismic sources have penetrated the basalts and provide an image of the pre-magmatic structure, otherwise the principle data are lower resolution wide-angle/refraction profiles and potential field models which have greater uncertainties associated with them. In order to sidestep the imaging constraints we have examined the Ethiopian - Afar rift system to try to understand the rifting process. The Main Ethiopian rift contains an embryonic magmatic passive margin dominated by faulting at the margins of the rift and en-echelon magmatic zones at the centre. Further north toward Afar the rift becomes in-filled with extensive lava flows fed from fissure systems in the widening rift zone. This rift system provides, along its length, a series of 'snapshots' into the possible tectonic evolution of a magmatic continental margin. Deep seismic profiles crossing the NE Atlantic margins reveal ocean dipping reflector sequences (ODRS) overlying extended crust and lower crustal sill complexes of intruded igneous rock, which extend back beneath the continental margin. The ODRS frequently occur in fault bounded rift structures along the margins. We suggest, by analogy to the observations that can be made in the Ethiopia-Afar rift that these fault bounded basins largely form at the embryonic rift stage and are then partially or completely filled with lavas fed from fissures which are now observed as the ODRS. Also in the seismic profiles we identify volcanic constructs on the ODRS which we interpret as the equivalent of the present day fissure eruptions seen in Afar. The ocean ward dip on the ODRS is

  2. Deep Stucture of the Northwestern Atlantic Moroccan Margin Studied by OBS and Deep Multichannel Seismic Reflection.

    NASA Astrophysics Data System (ADS)

    MALOD, J. A.; Réhault, J.; Sahabi, M.; Géli, L.; Matias, L.; Diaz, J.; Zitellini, N.

    2001-12-01

    The Northwestern Atlantic Moroccan margin, a conjugate of the New Scotland margin, is one of the oldest passive margin of the world. Continental break up occurred at early Liassic time and the deep margin is characterized by a large salt basin. A good knowledge of this basin is of major interest to improve the initial reconstruction between Africa, North America and Iberia (Eurasia). It is also a good opportunity to study a mature passive margin and model its structure and evolution.Moreover, there is a need to assess the geological hazards linked to the neotectonic activity within the Africa-Eurasia plate boundary. These topics have been adressed during the SISMAR cruise carried out from April 9th to May 4th 2001.During this cruise, 3667 km of multichannel seismic reflection (360 channels, 4500 m long streamer, 4800 ci array of air guns) were recorded together with refraction records by means of 48 OBH/OBS drops. Simultaneously, some of the marine profiles have been extended onshore with 16 portable seismic land stations. We present the initial results of this study. Off El Jadida, the Moho and structures within the thinned continental crust are well imaged on both the reflection and refraction records. In the northern area, off Casablanca, we follow the deepening of the moroccan margin beneath the up to 9 sec (twtt) allochtonous series forming a prism at the front the Rif-Betic chain. Sismar cruise has been also the opportunity to record long seismic profiles making the junction between the Portuguese margin and the Moroccan one, and crossing the Iberian-African plate boundary. This allows to observe the continuity of the sedimentary sequence after the end of the large inter-plate motion in Early Cretaceous. In addition to the authors, SISMAR Group includes: AMRHAR Mostafa, BERMUDEZ VASQUEZ Antoni, CAMURRI Francesca, CONTRUCCI Isabelle, CORELA Carlos, DIAZ Jordi, DORVAL Philippe, EL ARCHI Abdelkrim, EL ATTARI Ahmed, GONZALEZ Raquel, HARMEGNIES Francois, JAFFAL

  3. Dynamic support by the Icelandic plume and vertical tectonics of the northeast Atlantic continental margins

    NASA Astrophysics Data System (ADS)

    Clift, Peter D.; Turner, Jonathan

    1995-12-01

    Late Paleocene-early Eocene continental rifting in the northeast Atlantic differs significantly from earlier episodes of margin formation in the Central Atlantic. At a nonvolcanic margin, rifting occurs over a wide area, with little associated magmatism. Postrift subsidence decreases in a predictable, exponential pattern with time. In contrast, subsidence analysis of Ocean Drilling Program and Deep Sea Drilling Project drill sites from the Vøring Plateau, Hatton Bank, and East Greenland Margin show that in these areas the continent-ocean transition (COT) is very sharp, with ß increasing over a horizontal distance of 30-50 km from values of 1.1-1.50 on the continent side to ∞ at the COT. Drilling penetrated the thick seaward dipping basaltic sequences that typify the East Greenland Margin at Site 917. Fluvial sandstones underlying the basalts show that the area was subaerially exposed prior to continental breakup, but the amount and timing of any uplift are presently unconstrained. Sediment backstripping techniques allow a comparison between the reconstructed and predicted subsidence histories and thus an estimate of the thermal anomaly through time. Anomalous slow subsidence in the early postrift period at 63°N offshore East Greenland is attributed to support by the Icelandic plume. Dynamic support is weaker on the Hatton Bank and on the Vøring Plateau. Variations in the strength and duration of the support suggest that the plume was a large, 1000-km-radius structure that lay under the Greenland craton at the time of breakup. Current data suggest that it may have crossed the East Greenland coast at 40 Ma. Discrepancies between uniform stretching models and the reconstructed subsidence for sites on the East Greenland shelf and the Vøring Plateau allow the amount of igneous underplating at the time of breakup to be estimated. Calculations suggest a maximum of around 8.8 km of gabbroic underplating occurred at the time of breakup under the East Greenland shelf

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

    NASA Astrophysics Data System (ADS)

    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

  5. Electrical resistivity image of the South Atlantic continental margin derived from onshore and offshore magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Kapinos, G.; Weckmann, U.; Jegen-Kulcsar, M.; Meqbel, N.; Neska, A.; Katjiuongua, T. T.; Hoelz, S.; Ritter, O.

    2016-01-01

    We present a deep electrical resistivity image from the passive continental margin in Namibia. The approximately 700 km long magnetotelluric profile follows the Walvis Ridge offshore, continues onshore across the Kaoko Mobile Belt and reaches onto the Congo Craton. Two-dimensional inversion reveals moderately resistive material offshore, atypically low for oceanic lithosphere, reaching depths of 15-20 km. Such moderate resistivities are consistent with seismic P wave velocity models, which suggest up to 35 km thick crust. The Neoproterozoic rocks of the Kaoko Mobile Belt are resistive, but NNW-striking major shear-zones are imaged as subvertical, conductive structures in the upper and middle crust. Since the geophysical imprint of the shear zones is intact, opening of the South Atlantic in the Cretaceous did not alter the middle crust. The transition into the cratonic region coincides with a deepening of the high-resistive material to depths of more than 60 km.

  6. Rapid late Pleistocene incision of Atlantic passive-margin river gorges.

    PubMed

    Reusser, Luke J; Bierman, Paul R; Pavich, Milan J; Zen, E-an; Larsen, Jennifer; Finkel, Robert

    2004-07-23

    The direct and secondary effects of rapidly changing climate caused large rivers draining the Atlantic passive margin to incise quickly into bedrock beginning about 35,000 years ago. Measured in samples from bedrock fluvial terraces, 10-beryllium shows that both the Susquehanna and Potomac Rivers incised 10- to 20-meter-deep gorges along steep, convex lower reaches during the last glacial cycle. This short-lived pulse of unusually rapid down-cutting ended by 13,000 to 14,000 years ago. The timing and rate of downcutting are similar on the glaciated Susquehanna and unglaciated Potomac Rivers, indicating that regional changes, not simply glacial meltwater, initiated incision. PMID:15273389

  7. Biologic Indicators of Seabed Methane Venting Along the US Mid-Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Prouty, N.; Roark, E. B.; Demopoulos, A. W.; Condon, D. J.; Davis, K.; Ross, S.; Brooke, S.

    2014-12-01

    Evidence of seabed methane venting along the US Mid-Atlantic Margin is confirmed by the presence of authigenic carbonates and methantrophic deep-sea mussels, Bathymodiolus childressi, collected near areas of methane seepage. The biological indicators of methane venting presented here expand the understanding of widespread seepage identified by previous geophysical data. Both dead and living chemosynthetic mussels as well as authigenic carbonate samples were collected from Baltimore Canyon (360-430 m) and on the Virginia outer continental shelf (1600-1475 m). Stable isotope (carbon and sulfur) composition of mussel tissue material illustrates that the chemosynthetic communities are metabolically-dependent on methane rather than sulphide-oxidizing microbial symbionts. Average δ13C from tissue material was -62.80 ‰ and average δ34S was 12.58 ‰. Shell δ13C values were depleted relative to seawater dissolved inorganic carbon, highlighting the influence of methane concentration from cold seeps on shell growth. Lighter stable oxygen isotope values from shells collected at Baltimore Canyon reflect warmer temperatures relative to the colder and deeper Virginia seep site. However, at both sites isotopic disequilibrium relative to seawater δ18O suggests influence of enriched δ18O pore water. The chemical composition of the authigenic carbonates at both sites is dominated by aragonite rather than calcite, with an average δ13C signature of -46 ‰, a value expected from the microbially driven anaerobic oxidation of methane-rich fluids occurring at or near the sediment-water interface. This interpretation is supported by strontium isotope values close to modern seawater values. U/Th data are also reported from the authigenic carbonate stratigraphy to assess the timing and duration of methane venting along the US Mid-Atlantic Margin.

  8. Landscape Response to Changes in Dynamic Topography on the U.S. Atlantic Passive Margin

    NASA Astrophysics Data System (ADS)

    Ruetenik, G.; Moucha, R.; Hoke, G. D.

    2014-12-01

    Recent global backwards-in time models of mantle convection have resulted in vastly different interpretations of the transient state of dynamic topography on the U.S. Atlantic passive margin over the past 30 Myr (Moucha et al., 2008; Spacejovic et al., 2008; Rowley et al., 2013; Liu, 2014) . A promising way of benchmarking these geodynamic models is by reconciling them with the observed offshore sedimentary record. However, it is difficult to deconvolve the erosional response produced by changes in dynamic topography from other sources of landscape change because the erosional response is a convolution of dynamic topography changes, tectonic uplift/subsidence, flexural response to erosional unloading and depositional loading, rock properties, and climate. Herein, we present results from a new landscape evolution model that is capable of producing simulations that are required at the scale and resolution necessary to quantify the landscape response to various models of dynamic topographic change on the U.S. Atlantic passive margin in the presence of flexural unloading and loading due to erosion and deposition. We perform a sensitivity study on the effects of geodynamic modeling parameters including effective elastic thickness, climate and rock properties. We find that, while models of dynamic topography are difficult to discern from the available sedimentary record at the scale of the continent in part due to induced topologic (stream geometry) change, at the catchment scale deposition rates are vastly different through time with differing dynamic topography models. At this scale, all models show distinct peaks in deposition rates, and varying elastic thickness has a significant effect on altering the timing of peak deposition.

  9. Shelf basin exchange along the Siberian continental margin: Modification of Atlantic Water and Lower Halocline Water

    NASA Astrophysics Data System (ADS)

    Bauch, Dorothea; Cherniavskaia, Ekaterina; Timokhov, Leonid

    2016-09-01

    Salinity and stable oxygen isotope (δ18O) evidence shows a modification of Atlantic Water in the Arctic Ocean by a mixture of sea-ice meltwater and meteoric waters along the Barents Sea continental margin. On average no further influence of meteoric waters is detectable within the core of the Atlantic Water east of the Kara Sea as indicated by constant δ18O, while salinity further decreases along the Siberian continental slope. Lower Halocline Waters (LHW) may be divided into different types by Principal Component Analysis. All LHW types show the addition of river water and an influence of sea-ice formation to a varying extent. The geographical distribution of LHW types suggest that the high salinity type of LHW forms in the Barents and Kara seas, while other LHW types are formed either in the northwestern Laptev Sea or from southeastern Kara Sea waters that enter the northwestern Laptev Sea through Vilkitsky Strait. No further modification of LHW is seen in the eastern Laptev Sea but the distribution of LHW-types suggest a bifurcation of LHW at this location, possibly with one branch continuing along the continental margin and a second branch along the Lomonosov Ridge. We see no pronounced distinction between onshore and offshore LHW types, as the LHW components that are found within the halocline over the basin also show a narrow bottom-bound distribution at the continental slope that is consistent with a shelf boundary current as well as a jet of water entering the western Laptev Sea from the Kara Sea through Vilkitsky Strait.

  10. Buried Mesozoic rift basins of the U. S. middle Atlantic continental margin

    SciTech Connect

    Benson, R.N. )

    1991-08-01

    The Atlantic continental margin is one of the frontier areas for oil and gas exploration in the US. Most the activity has been offshore where Upper Jurassic-Lower Cretaceous siliciclastic and carbonate rocks have been the drilling objectives, with only one significant but noncommercial gas discover. Onshore, recent exploration activities have focused on early Mesozoic rift basins buried beneath the postrift sediments of the middle Atlantic coastal plain. Many of the basins are of interest because they contain fine-grained lacustrine rocks that have sufficient organic richness, if not lost through hydrocarbon generation, to be classified as source beds for oil or gas. Locations of inferred rift basins beneath the middle Atlantic coastal plain were determined by analysis of drill-hole data in combination with gravity anomaly and aeromagnetic maps. Two basins in Delaware and the Queen Anne basin of Maryland are imaged on a regional Vibroseis profile. Areas enclosing inferred rift basins in the offshore region were mapped from interpretation of seismic reflection profiles. Assuming that petroleum source beds are present in the basin (synrift) rocks, hydrocarbon-generation models (Lopatin method) indicate that for a basin just offshore Delaware that is buried by 7 km of postrift sediments, only dry gas would be present in reservoir rocks; for the Norfolk basin of the Virginia coast buried by only 3 km of postrift rocks, the upper few hundred meters of synrift rocks are still within the oil-generation window. The less deeply buried basins beneath the coastal plain likely are still within the oil window.

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

    USGS Publications Warehouse

    McGregor, B.A.

    1983-01-01

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

  12. Geomorphology and shallow structure of a segment of the Atlantic Patagonian margin

    NASA Astrophysics Data System (ADS)

    Muñoz, A.; Acosta, J.; Cristobo, J.; Druet, M.; Uchupi, E.

    2013-06-01

    We study an area little known of the Atlantic Patagonian margin from 44°30'S to 47°40'S and from 59°W to nearly 61°W. The multi-beam bathymetry coupled with high resolution seismic reflection profiles, has provided details on the morphology and shallow acoustic structure on this area. The main morphological characteristics of the seafloor features on the shelf and middle slope are described. The Atlantic Patagonian continental shelf north of 45°40'S is located at a depth of 170-200 m, south of this latitude the shelf edge is at 128 to 200 m. The shelf surface is marred by circular depression and ridges oriented oblique to the shelf edge. The upper slope and upper middle slope are plowing by icebergs from Antarctica in Pleistocene and local reefs of cold-water coral further enhance the topography of the area. In the middle slope there are two terraces, the 20 to 60 km wide Nágera and the 15 to 60 km wide Perito Moreno terraces, showing moats, hollows, pot holes, sediment drifts and sediment waves. The terraces may have been formed in Late Miocene whereas the other forms are of Pleistocene age. Other features are a sediment swell south of 47°S and seven submarine canyons on the middle slope. These incipient canyons have been developed in the middle slope by retrogressive erosion, some terminating on the upper middle slope, and others on the upper slope and the Canyon 6 breaching the shelf edge. Individual seafloor features existing on the Atlantic Patagonian Margin have been classified into two main groups according to their origin: along and across-slope processes. These primary agents were supplemented by endogenic processes such as expulsion of gas/water, diapirism of high-pressure mud and folding/faulting. The results suggest that today down-slope processes on the slope are practically non-existent and that the morphology of the upper and middle slope is slowly being remolded by along-slope bottom currents.

  13. Post-breakup Basin Evolution along the South-Atlantic Margins in Brazil and Angola/Namibia

    NASA Astrophysics Data System (ADS)

    Kukla, P. A.; Strozyk, F.; Back, S.

    2013-12-01

    The post-breakup tectono-stratigraphic evolution of large offshore basins along the South American and African continental margins record strongly varying post-rift sedimentary successions. The northernmost segment of the South Atlantic rift and salt basins is characterized by a pronounced asymmetry, with the Brazilian margin comprising narrower and deeper rift basins with less salt in comparison to the Congo-Gabon conjugate margin. Another important observation is that multiple phases of uplift and subsidence are recorded after the break-up of the southern South Atlantic on both sides of the Florianopolis-Walvis Ridge volcanic complex, features that are regarded as atypical when compared to published examples of other post-breakup margin successions. A regional comparison based on tectonic-stratigraphic analysis of selected seismic transects between the large basins offshore southern Brazil (Espirito Santo Basin, Campos Basin, Santos Basin, Pelotas Basin) and southwest Africa (Lower Congo Basin, Kwanza Basin, Namibe Basin, Walvis Basin) provides a comprehensive basin-to-basin documentation of the key geological parameters controlling ocean and continental margin development. This comparison includes the margin configuration, subsidence development through time, sediment influx and storage patterns, type of basin fill (e.g. salt vs. non-salt systems; carbonate-rich vs. clastics-dominated systems) and finally major tectonic and magmatic events. Data from the salt basins indicate that salt-related tectonic deformation is amongst the prime controls for the non-uniform post-rift margin development. The diversity in the stratigraphic 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 (a) the structural configuration of each margin segment at the time of break-up, (b) the post break-up subsidence history of the respective margin segment

  14. Cretaceous source rock characterization of the Atlantic Continental margin of Morocco

    SciTech Connect

    Jabour, H. )

    1993-02-01

    Characterization of the petroleum potential for the Atlantic margin of Morocco has been based primarily on limited, antiently acquired organic geochemical data. These indicate the area of drilling behind the paleoshelf edge to be only fair in organic carbon and C15+ extract values with predominantly terrestrial kerogen types. Recently acquired geochemical data obtained from relatively recent drilling both behind and beyond the paleoshelf edge indicate 4 depositional facies containing hydrogen rich amorphous kerogen assemblages. These are: (1) Lower to Mid Jurassic inner shelf facies probably deposited in algal rich lagoon-like, (2) Lower Cretaceous non marine coaly facies probably deposited in algal rich swamplike environments, (3) Middle Cretaceous facies characterized by restrited anoxic environment with sediments rich in marine kerogen types deposited under sluggish wather circulation, (4) Upper Cretaceous to Tertiary outer-shelf to Upper slope facies probably deposited under algal-rich upwelling systems. Of these, the Cretaceous facies is the most widespread and represents the best source rock potential characteristics. Correlation of these facies to recently acquired good quality seismic packages allows for extrapolation of probable organic facies distribution throughout the continental margin. This should enhance the hydrocarbon potential of the Mesozoic and Cenozoic sediments both landward and seaward of the paleoshelf edge and thus permits refinement of strategies for hydrocarbon exploration in the area.

  15. Preliminary summary of the 1976 Atlantic Margin Coring Project of the U.S. Geological Survey

    USGS Publications Warehouse

    Hathaway, John Cummins; Schlee, J.J.; Poag, C.W.; Valentine, P.C.; Weed, E.G.A.; Bothner, Michael H.; Kohout, F.A.; Manheim, F. T.; Schloam, R.; Miller, R.E.; Schultz, D.M.

    1976-01-01

    The U.S. Geological Survey Atlantic Margin Coring Project, 1976, a 60-day expedition to obtain core samples by drilling beneath the floor of the Continental Shelf and Slope of the eastern United States, was carried out in July, August, and September 1976 aboard D/V GLOMAR CONCEPTION. The coring penetrated as much as 310 meters below the sea floor at 19 sites along the continental margin from Georgia to Georges Bank off New England in water depths ranging from 20 to 300 meters; 1,020 meters of material were recovered in 380 cores, ranging in age from Late Cretaceous to Holocene. One of the major findings was the discovery of relatively fresh water (salinities less than 3 parts per thousand) extending beneath the Continental Shelf as much as 60 nautical miles seaward from the New Jersey coast. Water of about 1 part per thousand salinity was found beneath the shelf more than 7 nautical miles off Ocean City, Maryland and Barnegat Inlet, New Jersey. Analyses for light hydrocarbons in the cores show the highest concentrations (as much as 412,000 ppm) at sites in water depth greater than 200 meters (the shelf-slope break), principally in Pleistocene sediments, although methane concentrations greater than 400,000 ppm also were found in Miocene sediments at one site near the shelf edge. (Woodard-USGS)

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

    USGS Publications Warehouse

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

    1975-01-01

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

  17. Post-rift unroofing of the NW Africa passive continental margin during the Central Atlantic opening

    NASA Astrophysics Data System (ADS)

    Ghorbal, B.; Bertotti, G.; Andriessen, P. A. M.

    2009-04-01

    Many passive margins considered as being stable for long times, show however late uplift and exhumation at regional scale as assessed by low temperature geochronometry. A large amount of Lower Cretaceous terrigeneous sediments laid down in most of basins along the NW Africa continental margins indicate that a major episode of erosion occurred during early post-rift period in the Central Atlantic. AFT and (U-Th)/He dating performed, along a roughly >500 km N-S transect, on pre-Mesozoic basement rocks from Western Meseta to the Anti-Atlas (Morocco, NW Africa) document a fully unexpected widespread unroofing during the Middle-Late Jurassic to early Late Cretaceous, with AFT and (U-Th)/He ages ranging respectively between 120-170Ma and 115-165Ma. A well documented age cluster of 140±20Ma measured for the Moroccan Meseta, Atlas domains and Anti-Atlas belt designates those domains as potentially being the source areas of the detritic sediments considering the proximity of the depositional basins. Absence of major fault separating the Anti-Atlas from the rest of the Western African Craton during the Mesozoic suggests the unroofing region to extend further in Morocco, as far south as the Reguibat (Mauritania) or even New Guinea, documented by our investigation, and perhaps even further when confirmed by additional AFT and AHe data.

  18. Preliminary assessment of a Cretaceous-Paleogene Atlantic passive margin, Serrania del Interior and Central Ranges, Venezuela/Trinidad

    SciTech Connect

    Pindell, J.L.; Drake, C.L. ); Pitman, W.C. )

    1991-03-01

    For several decades, Cretaceous arc collision was assumed along northern Venezuela based on isotopic ages of metamorphic minerals. From subsidence histories in Venezuelan/Trinidadian basins, however, it is now clear that the Cretaceous metamorphic rocks were emplaced southeastward as allochthons above an autochthonous suite of rocks in the Cenozoic, and that the pre-Cenozoic autochthonous rocks represent a Mesozoic passive margin. The passive margin rocks have been metamorphosed separately during overthrusting by the allochthons in central Venezuela, but they are uplifted but not significantly metamorphosed in Eastern Venezuela and Trinidad. There, in the Serrania del Interior and Central Ranges of Venezuela/Trinidad, Mesozoic-Paleogene passive margin sequences were uplifted in Neogene time, when the Caribbean Plate arrived from the west and transpressionally inverted the passive margin. Thus, this portion of South America's Atlantic margin subsided thermally without tectonism from Jurassic to Eocene time, and these sections comprise the only Mesozoic-Cenozoic truly passive Atlantic margin in the Western Hemisphere that is now exposed for direct study. Direct assessments of sedimentological, depositional and faunal features indicative of, and changes in, water depth for Cretaceous and Paleogene time may be made here relative to a thermally subsiding passive margin without the complications of tectonism. Work is underway, and preliminary assessments presented here suggest that sea level changes of Cretaceous-Paleogene time are not as pronounced as the frequent large and rapid sea level falls and rises that are promoted by some.

  19. Asymmetry and polarity of the South Atlantic conjugated margins related to the presence of cratons: a numerical study

    NASA Astrophysics Data System (ADS)

    Andrés-Martínez, Miguel; Pérez-Gussinyé, Marta; de Monserrat Navarro, Albert; Morgan, Jason P.

    2015-04-01

    Tectonic asymmetry of conjugated passive margins, where one margin is much narrower than the conjugate one, is commonly observed at many passive margins world-wide. Conjugate margin asymmetry has been suggested to be a consequence of lateral changes in rheology, composition, temperature gradient or geometries of the crust and lithosphere. Here we use the South Atlantic margins (from Camamu/Gabon to North Santos/South Kwanza) as a natural laboratory to understand conjugate margin asymmetry. Along this margin sector the polarity of the asymmetry changes. To the North, the Brazilian margin developed in the strong Sao Francisco craton, and this constitutes the narrow side of the conjugate pair. To the South, the Brazilian margin developed in the Ribeira fold belt, and the margin is wide. The opposite is true for the African side. We have thus numerically analysed how the relative distance between the initial location of extension and the craton influences the symmetry/asymmetry and polarity of the conjugate margin system. Our numerical model is 2D visco-elasto-plastic and has a free surface, strain weakening and shear heating. The initial set-up includes a cratonic domain, a mobile belt and a transition area between both. We have run tests with different rheologies, thickness of the lithosphere, and weak seeds at different distances from the craton. Results show asymmetric conjugated margins, where the narrower margin is generally the closest to the craton. Our models also allow us to study how the polarity is controlled by the distance between the initial weakness and the craton, and help to understand how the presence of cratonic domains affects the final architecture of the conjugated margins.

  20. Temporal Variation in Population Size of European Bird Species: Effects of Latitude and Marginality of Distribution

    PubMed Central

    Cuervo, José J.; Møller, Anders P.

    2013-01-01

    In the Northern Hemisphere, global warming has been shown to affect animal populations in different ways, with southern populations in general suffering more from increased temperatures than northern populations of the same species. However, southern populations are also often marginal populations relative to the entire breeding range, and marginality may also have negative effects on populations. To disentangle the effects of latitude (possibly due to global warming) and marginality on temporal variation in population size, we investigated European breeding bird species across a latitudinal gradient. Population size estimates were regressed on years, and from these regressions we obtained the slope (a proxy for population trend) and the standard error of the estimate (SEE) (a proxy for population fluctuations). The possible relationships between marginality or latitude on one hand and slopes or SEE on the other were tested among populations within species. Potentially confounding factors such as census method, sampling effort, density-dependence, habitat fragmentation and number of sampling years were controlled statistically. Population latitude was positively related to regression slopes independent of marginality, with more positive slopes (i.e., trends) in northern than in southern populations. The degree of marginality was positively related to SEE independent of latitude, with marginal populations showing larger SEE (i.e., fluctuations) than central ones. Regression slopes were also significantly related to our estimate of density-dependence and SEE was significantly affected by the census method. These results are consistent with a scenario in which southern and northern populations of European bird species are negatively affected by marginality, with southern populations benefitting less from global warming than northern populations, thus potentially making southern populations more vulnerable to extinction. PMID:24147048

  1. Meso-Cenozoic uplifts on the Atlantic margin of South Morocco

    NASA Astrophysics Data System (ADS)

    Lepretre, R.; Missenard, Y.; Barbarand, J.; Gautheron, C.; Saddiqi, O.

    2013-12-01

    Passive margins are key areas to investigate the relationships between the continental interiors and the marine realm. A careful study of their stratigraphic record is then expected to reveal the complex interplays between subsidence, climate and eustasy (Dauteuil et al., 2013). The eastern passive margin of Central Atlantic initiated in the Early Jurassic and has been subsequently witnessing the evolution of the continental interior during the Meso-Cenozoic drifting of Africa and North America. This passive margin is bounded by the West African Craton to the East, and its geometry and evolution are poorly known (Labails et al., 2009). We have focused our study on the vertical evolution of the onshore part of the basin, in order to improve our knowledge with regards to the dynamics of the basin's infill. The purpose was to identify the main uplift vs. subsidence events impacting the margin during Meso-Cenozoic times and to correlate them to the geodynamic context. We used low-temperature thermochronology on apatites with fission tracks and (U-Th)/He dating to constrain the evolution of the margin during Meso-Cenozoic. These analyses have been performed on samples coming from the onshore basin detrital formations and basement formations from the craton. Modeled thermal histories were then carried through the use of QTQt, a recent program taking into account the most recent developments on apatite thermochronology (Gallagher, 2012). We obtained fission tracks ages ranging from 107×8 Ma to 160×11 Ma and (U-Th)/He ages from 14×1 Ma to 97×9 Ma. The scattered repartition of (U-Th)/He ages is explained by the distribution of effective uranium in the samples and reveal a quite young signal. The fission tracks ages are not so scattered and show a consistent signal. Thermal histories characterize for the first time the polyphased vertical evolution of the basin throughout its Meso-Cenozoic history. Two major steps of exhumation are recorded. First, a Late Jurassic

  2. Structural comparison of archetypal Atlantic rifted margins (Angola - Esperito Santo, Iberia - Newfoundland, mid.Norway - East Greenland)

    NASA Astrophysics Data System (ADS)

    Peron-Pinvidic, Gwenn; Manatschal, Gianreto; Terje Osmundsen, Per

    2013-04-01

    In the last decade, a number of new geological and numerical models have been proposed to explain intriguing observations from deep margin settings that were previously not well understood. These new models, together with the increasing amount of high-quality geophysical data, now allow to compare observations from different margins. Key areas are the Iberia-Newfoundland conjugates, the North-East and South Atlantic systems. A first-order structural similarity appears between the architectures of these rifted margins, including magma-poor as well as magma-rich ones. Typical is the seawards arrangement of characteristic entities such as platforms, necking zones, ocean-continent transitions and marginal/outer highs. The arrangement appears to reflect a commonality with respect to the tectonic processes involved in rifted margin formation. The study of magma-poor and magma-rich margins notably suggests that hyper-extension does not preclude a magmatic breakup. We propose to clarify the definition of a number of terms typically used in rifted margin studies. Then we will present a review of available information from the Angola-Gabon, Iberia-Newfoundland and Norway-Greenland margins, usually referred to as the archetypes of hyper-extended, magma-poor or volcanic margins. We will discuss their similarities and differences and review the related deformation modes.

  3. The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature

    NASA Astrophysics Data System (ADS)

    Yamamoto, Ayako; Palter, Jaime B.

    2016-03-01

    Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air-sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline.

  4. The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature.

    PubMed

    Yamamoto, Ayako; Palter, Jaime B

    2016-01-01

    Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air-sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline. PMID:26975331

  5. The absence of an Atlantic imprint on the multidecadal variability of wintertime European temperature

    PubMed Central

    Yamamoto, Ayako; Palter, Jaime B.

    2016-01-01

    Northern Hemisphere climate responds sensitively to multidecadal variability in North Atlantic sea surface temperature (SST). It is therefore surprising that an imprint of such variability is conspicuously absent in wintertime western European temperature, despite that Europe's climate is strongly influenced by its neighbouring ocean, where multidecadal variability in basin-average SST persists in all seasons. Here we trace the cause of this missing imprint to a dynamic anomaly of the atmospheric circulation that masks its thermodynamic response to SST anomalies. Specifically, differences in the pathways Lagrangian particles take to Europe during anomalous SST winters suppress the expected fluctuations in air–sea heat exchange accumulated along those trajectories. Because decadal variability in North Atlantic-average SST may be driven partly by the Atlantic Meridional Overturning Circulation (AMOC), the atmosphere's dynamical adjustment to this mode of variability may have important implications for the European wintertime temperature response to a projected twenty-first century AMOC decline. PMID:26975331

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  7. New Insights into the Temporal Variability of Seafloor Methane Discharge on the Northern US Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Skarke, A. D.

    2015-12-01

    Multibeam echosounder water column backscatter data and remotely operated vehicle (ROV) video imagery collected from 2011 through 2013 by NOAA Ship Okeanos Explorer and ROV Deep Discoverer revealed methane discharge at over 570 seafloor gas seep locations on the US Atlantic margin between Cape Hatteras and Georges Bank. Subsequent water column surveys and video imaging conducted by Okeanos Explorer and ROV Deep Discoverer in 2014 as well as R/V Atlantis and DSV Alvin, as part of the SeepC program in 2015, re-imaged a majority of these gas seep locations providing an opportunity to make preliminary assessments of gas plume ephemerality and the variability of seafloor methane discharge as a function of time. Analysis of newly collected water column backscatter data indicates that some previously imaged gas plumes are no longer present and that a number of new gas plumes are present in locations where they were previously determined to be absent. Additionally, newly acquired video imagery demonstrates that seafloor gas emission at seep locations can vary between absence and abundant effusively on time scales as short as minutes and that this variability is not correlated with that of in situ temperature and pressure observations. These new results indicate that individual methane plume features can be ephemeral on intra-annual to much shorter time scales. Additionally, these results suggest that short-term variability in gas discharge at individual plumes, away from the upper limit of the gas hydrate stability zone, is not mediated by fluctuations in hydrostatic pressure or thermal perturbations. Despite evidence for high temporal variability in the discharge rates of individual gas plumes, video imagery of robust chemosynthetic communities and thick carbonate crusts suggests an overall persistence of methane emissions at seep sites on time scales of hundreds to thousands of years. Collected data are insufficient to fully constrain the temporality of gas discharge on

  8. Sn to Sg Conversion at the U.S. Atlantic Continental Margin

    NASA Astrophysics Data System (ADS)

    Gallegos, A. C.; Long, M. D.; Benoit, M. H.; Ni, J.

    2015-12-01

    Isacks and Stephens [1975] observed a secondary phase with high frequency Lg characteristics that arrived soon after the Sn wave on seismograms generated by events in the West Indies. They concluded that an Sn-to-Lg conversion occurred at the continental margin, where the crust suddenly thickens. A later study on conversion along the continental margin was done by Seber et al. [1993] in Morocco. They noted that historically Morocco has experienced more damage from earthquakes occurring at the Azores-Gibraltar seismic zone (e.g. the M 8.7-9.0 Lisbon earthquake) at distances up to 500-1000 km than from those within the country. They conclude in their study that there are two parallel Sn-to-Sg conversion zones along the coast and interior of Morocco, where Sg is equivalent to Lg at shorter distances. We have seen similar Sn-to-Sg conversions for a M 5.2 event occurring ~1400 km off the Atlantic Coast on Dec. 23, 2013 using EarthScope's Transportable Array (TA). We perform a travel time back-projection based on the geometry of the raypaths, similar to Seber et al. [1993], to determine the location of the conversion points for several Atlantic events and compare with seismograms generated by continental events. We also investigate the possibility of a second conversion at the crustal boundary between the Appalachians and the Coastal Plain. The MAGIC Array is used in tandem with TA to closely observe the propagation characteristics of the converted wave as it travels through the continent. With the sizeable increase in station coverage we are in a position to study this conversion in greater detail. Understanding the causes of Sn-to-Sg conversion and the conditions needed to produce it can lead to insight into the geometry and characteristics of the continental shelf and inland crustal boundaries. Learning about this conversion is also needed to determine seismic hazard along coastal areas, where high amplitude converted shear waves can cause unexpected levels of damage.

  9. Updated size distribution of submarine landslides along the U.S. Atlantic margin

    NASA Astrophysics Data System (ADS)

    Ten Brink, U. S.; Chaytor, J. D.; Andrews, B. D.; Brothers, D. S.; Geist, E. L.

    2012-12-01

    The volume of failed material in submarine landslides is one of the primary factors controlling tsunami amplitude, hence the cumulative volume distribution of submarine landslides on the U.S. Atlantic continental slope and rise provides information important for the evaluation of tsunami hazard potential for U.S. the East Coast. Landslide size distributions also help constrain the initiation mechanisms of submarine landslides in siliciclastic and carbonate environments [1,2], and thus improve our understanding of the pre-conditioning and propagation of landslides. Previous compilations of landslide distributions along the Atlantic continental margin used regional side-scan sonar data, seismic reflection profiles and multibeam bathymetry data that lacked coverage of large portions of the upper continental slope [3, 4]. We updated this regional database by compiling and merging multibeam echosounder data from 36 surveys conducted by various federal agencies and academia between Georges Banks and Cape Hatteras from 1990-2012. The result is a continuous 594,000 km2 digital bathymetric surface with a spatial resolution of 100 m spanning water depths between 55-6150 m. The new grid allows better identification and delineation of the areas and heights of the headwall scarps, and more precise volume estimates of the evacuated slide regions. Acoustic backscatter derived from the multibeam data and an updated compilation of sub-bottom seismic profiles and core logs improve the identification of the extent of mass transport deposits. The updated analysis includes uncertainties in the determination of the landslide areas. The cumulative area and volume distributions of the landslides excavations, their area/volume ratio, the water depth of the head wall, and the fraction of slope and rise areas covered by headwall scarps and landslide deposits, are quantified and discussed. Combining landslide size distribution with the overall rate of occurrence of landslides derived from age

  10. The biology and fisheries of European hake, Merluccius merluccius, in the north-east Atlantic.

    PubMed

    Murua, Hilario

    2010-01-01

    The aim of this chapter is to review the biology and fishery, including the management, of European hake in the north-east Atlantic. The European hake is widely distributed throughout the north-east Atlantic, from Norway in the north to the Guinea Gulf in the south, and throughout the Mediterranean and Black Sea, being more abundant from the British Isles to the south of Spain. In this area, ICES (International Council for the Exploration of the Sea) recognises the existence of two stocks: the northern stock and the southern stock. Both stocks have been extensively and intensively harvested and since the beginning of the 90s have been considered to be outside safe biological limits. The northern stock, however, is currently considered to lie within safe biological limits. In any case, recovery plans were implemented for the northern stock in 2004 and for the southern stock in 2006. Despite its commercial importance, knowledge of the biology and ecology of the European hake in the North Atlantic is still quite scarce. For example, recent investigations suggest that European hake grows much faster, by a factor of two, than was considered previously. This faster growth also affects the maturity-at-age pattern of hake and the agreed maturity-at-age ogive used in the assessments. European hake is a top predator in the demersal community in the north-east Atlantic area; mainly preying on blue whiting, horse mackerel and other cupleids. In relation to the reproductive biology, European hake is considered to be a batch spawner species with indeterminate fecundity and spawning activity all year round. All these characteristics could, in turn, be interpreted as European hake adopting a more opportunistic life strategy, which is unusual for a gadoid and demersal species, and raises several questions about hake biology and ecology that require further investigation. PMID:20959157

  11. Contrasting red bed diagenesis: the southern and northern margin of the Central European Basin

    NASA Astrophysics Data System (ADS)

    Schöner, Robert; Gaupp, Reinhard

    2005-12-01

    We compare the diagenetic evolution of deeply buried Rotliegend (Permian) red bed sandstones at the southern and northern margin of the Central European Basin (CEB) in Germany. Main target is to evaluate the influence of maturation products from hydrocarbon (HC) source rocks during red bed diagenesis. At the southern margin of the CEB, thick coal-bearing Carboniferous source rocks are omnipresent beneath the Rotliegend. They contain dominantly gas-prone terrigenous organic material and some oil source rocks. Hydrocarbons were generated from Late Carboniferous onwards throughout most of basin subsidence. At the northern margin of the CEB, source rocks are almost absent due to deep erosion of Carboniferous rocks and a low TOC of local Lower Carboniferous relics. Early diagenetic processes are comparable at both basin margins. Significant differences in burial diagenetic evolution are spatially correlated to the occurrence of hydrocarbon source rocks. Burial diagenesis at the southern margin of the CEB is characterized especially by bleaching of red beds, major dissolution events, pervasive illite formation, impregnation of pore surfaces with bitumen, and formation of late Fe-rich cements. Almost none of these features were detected at the northern basin margin. Instead, relatively early cements are preserved down to maximum burial depths. This suggests that major diagenetic mineral reactions in deeply buried red bed sandstones are controlled by the presence or absence of maturing hydrocarbon source rocks.

  12. Benthic metazoan biomass, community structure and bioturbation at three contrasting deep-water sites on the northwest European continental margin

    NASA Astrophysics Data System (ADS)

    Hughes, D. J.; Gage, J. D.

    2004-10-01

    Size structure, taxonomic composition and bioturbation potential of benthic metazoan communities were examined at three contrasting sites on the northwest European continental margin as part of a wider study of biogeochemical cycling in the deep-sea benthic boundary layer. Sampling was conducted in the Hatton-Rockall Basin (1100 m depth), on the North Feni Ridge (1920 m) and in the South Rockall Trough (3580 m) on two cruises bracketing the expected 1998 spring phytodetrital flux. Density and biomass of epibenthic megafauna declined with depth and were consistent with previous data from the deep northeast Atlantic. Aggregations of the hexactinellid sponge Pheronema carpenteri occurred at 1100 m. The percentage contribution of suspension-feeders to megafaunal biomass at the lower slope sites was much higher than expected for these depths. Macrofauna (sensu stricto) were consistently undersampled by a box corer relative to an hydraulically damped multiple corer. Estimated macrofaunal densities declined with depth. Polychaete trophic group structure was very different at the three sites, with more small carnivores at 1100 m, surface deposit and interface-feeders at 1920 m, and a higher representation of subsurface deposit-feeders at 3580 m. Meiofaunal densities were low in comparison with published data from comparable depths in the northeast Atlantic. Meiofaunal numbers increased at all three sites from May to July 1998. The increase at 1920 m was statistically significant and was associated with the greatest phytodetrital accumulation observed during the study period. The relative contribution of the mega-, macro- and meiofauna to benthic metazoan biomass did not vary consistently with depth, and no trend was apparent in a review of data from other studies in the North Atlantic. Depth-related patterns in community size structure recorded from previous North Atlantic studies were not all replicated, suggesting the importance of local hydrodynamics and other

  13. Submarine Landslides along the U.S. Atlantic Margin: Their Distribution, Failure Processes, and Age

    NASA Astrophysics Data System (ADS)

    Chaytor, J. D.; ten Brink, U. S.; Twichell, D. C.; Baxter, C. D.; Hallam, T. D.; Brothers, D. S.

    2011-12-01

    We have investigated the size, distribution, failure mode, and age of submarine landslides on the seafloor along the U.S. Atlantic continental slope and rise, using near-complete multibeam bathymetry coverage, together with new and existing seismic reflection, core, and photographic data sets. These data show that open-slope and canyon-related landslides are ubiquitous features of the continental margin and in places have been a dominant mechanism of downslope sediment transport and slope-rise modification. Retrogressive and translational mechanisms are prevailing modes of failure, although earth-flows, rare in the marine realm, are present along seafloor gradients of less than 1o on the upper rise. Individual and composite open-slope landslides with scar dimensions that exceed 900 km2 in area and 100 km3 in volume and deposit run-out distances greater than 200 km are present off Georges Bank (Munson-Nygren-Retriever complex), southern New England, Cape Hatteras (Currituck and Cape Lookout landslides), and the Blake Plateau (Cape Fear landslide). While dating of several landslides along the margin suggests a link to mechanisms driven by environmental changes at the end of the Last Glacial Maximum, the ages of the majority of the observed landslides are still unknown. In an effort to address the scarcity of age information required to investigate failure process and geohazards, we are utilizing both absolute (radiocarbon and oxygen isotope) and relative dating techniques. Radiocarbon dating of shallow water mollusks from recently collected piston cores in landslide scars and debris deposits offshore of southern New England record multiple landslide events over the last 50,000 years originating from both the continental slope and upper rise. Relative ages of landslide features are obtained from cross-cutting relationships between canyons and landslide scars and related mass-transport deposits.

  14. Triggering mechanism and tsunamogenic potential of the Cape Fear Slide complex, U.S. Atlantic margin

    NASA Astrophysics Data System (ADS)

    Hornbach, Matthew J.; Lavier, Luc L.; Ruppel, Carolyn D.

    2007-12-01

    Analysis of new multibeam bathymetry data and seismic Chirp data acquired over the Cape Fear Slide complex on the U.S. Atlantic margin suggests that at least 5 major submarine slides have likely occurred there within the past 30,000 years, indicating that repetitive, large-scale mass wasting and associated tsunamis may be more common in this area than previously believed. Gas hydrate deposits and associated free gas as well as salt tectonics have been implicated in previous studies as triggers for the major Cape Fear slide events. Analysis of the interaction of the gas hydrate phase boundary and the various generations of slides indicates that only the most landward slide likely intersected the phase boundary and inferred high gas pressures below it. For much of the region, we believe that displacement along a newly recognized normal fault led to upward migration of salt, oversteepening of slopes, and repeated slope failures. Using new constraints on slide morphology, we develop the first tsunami model for the Cape Fear Slide complex. Our results indicate that if the most seaward Cape Fear slide event occurred today, it could produce waves in excess of 2 m at the present-day 100 m bathymetric contour.

  15. Provenance of Pliocene clay deposits from the Iberian Atlantic Margin and compositional changes during recycling

    NASA Astrophysics Data System (ADS)

    Dinis, Pedro; Oliveira, Álvaro

    2016-05-01

    The XRD mineralogy and geochemistry of recycled fine-grained deposits from the West Iberia Atlantic Margin are used to establish sediment provenance and evaluate the features that most closely reflect the nature of the source areas and the transformations during the last depositional cycle. A set of Pliocene sediment samples is organized according to grain size distribution, geochemistry, and mineralogy, and their chemical composition is compared with the composition of possible source rocks. Most deposits located to the north of the Mondego River were derived from the uplifted Precambrian metapelites of the basin edge, while to the south of the Mondego River they result mainly from recycling of Cretaceous and Cenozoic clastic units, which, in turn, were derived from Precambrian-Paleozoic granitoids and metasedimentary rocks. This differentiation is supported by several element ratios and biplots involving La, Sm, Gd, Sc, Th, U, Y, Yb, and Zr. For the specific grain size range of the deposits studied, which are mainly made up of silt and clay particles, composition is not substantially affected by the grain size distribution of the sediment. Multi-element diagrams designed to discriminate the tectonic setting and the nature of source rocks are of little use in the interpretation of provenance but help to trace geochemical and mineralogical transformations during the last depositional cycles. Despite the evidence of element leaching during the Pliocene depositional cycle, the geochemical and mineralogical indicators of weathering intensities are largely determined by the nature of the previous cycle units.

  16. Triggering mechanism and tsunamogenic potential of the Cape Fear Slide complex, U.S. Atlantic margin

    USGS Publications Warehouse

    Hornbach, Matthew J.; Lavier, Luc L.; Ruppel, Carolyn D.

    2007-01-01

    Analysis of new multibeam bathymetry data and seismic Chirp data acquired over the Cape Fear Slide complex on the U.S. Atlantic margin suggests that at least 5 major submarine slides have likely occurred there within the past 30,000 years, indicating that repetitive, large-scale mass wasting and associated tsunamis may be more common in this area than previously believed. Gas hydrate deposits and associated free gas as well as salt tectonics have been implicated in previous studies as triggers for the major Cape Fear slide events. Analysis of the interaction of the gas hydrate phase boundary and the various generations of slides indicates that only the most landward slide likely intersected the phase boundary and inferred high gas pressures below it. For much of the region, we believe that displacement along a newly recognized normal fault led to upward migration of salt, oversteepening of slopes, and repeated slope failures. Using new constraints on slide morphology, we develop the first tsunami model for the Cape Fear Slide complex. Our results indicate that if the most seaward Cape Fear slide event occurred today, it could produce waves in excess of 2 m at the present-day 100 m bathymetric contour.

  17. Data file: the 1976 Atlantic Margin Coring (AMCOR) Project of the U.S. Geological Survey

    USGS Publications Warehouse

    Poppe, Lawrence J.

    1981-01-01

    In 1976, the U.S. Geological Survey conducted the Atlantic Margin Coring Project (AMCOR) to obtain information on stratigraphy, hydrology and water chemistry, mineral resources other than petroleum hydrocarbons, and geotechnical engineering properties at sites widely distributed along the Continental Shelf and Slope of the Eastern United States (Hathaway and others, 1976, 1979). This program's primary purpose was to investigate a broad variety of sediment properties, many of which had not been previously studied in this region. Previous studies of sediments recovered by core drilling in this region were usually limited to one or two aspects of the sediment properties (Hathaway and others, 1979, table 2). The AMCOR program was limited by two factors: water depth and penetration depth. Because the ship selected for the program, the Glomar Conception, lacked dynamic positioning capability, its anchoring capacity determined the maximum water depth in which drilling could take place. Although it was equipped to anchor in water 450 m deep and did so successfully at one site, we attmepted no drilling in water depths greater than 300 m. Strong Gulf Stream currents at the one attempted deep (443 m) site frustrated attempts to "spud in" to begin the hole.

  18. Anaerobic oxidation of methane related to methane seepage along the northern US Atlantic margin

    NASA Astrophysics Data System (ADS)

    Treude, T.; Krause, S.; Colwell, F. S.; Graw, M. F.; Pohlman, J.; Ruppel, C. D.

    2015-12-01

    Microbial anaerobic oxidation of methane (AOM), coupled to sulfate reduction, is an important mechanism in marine sediments for reducing methane emissions into the atmosphere. Here we report on AOM and sulfate reduction activity determined from sediments collected at recently-discovered methane seeps along the northern US Atlantic margin (USAM), where more than 550 gas plumes rise from the seafloor. Many of these gas plumes lie within or above the upper limit of gas hydrate stability on the continental slope. Samples were taken by TV-multicorer and a piston corer aboard the R/V Sharp during a September 2015 expedition that was jointly organized by the US Geological Survey, the Oregon State University, GEOMAR, and UCLA. This presentation will display preliminary data of AOM activity from selected seeps at the USAM to discuss (1) the capacity of the methane biofilter in relation to well-known seep sites, (2) its influence on geochemistry (e.g., sulfide accumulation, carbonate formation) and biology (established chemosynthetic communities), and (3) its potential response to recent methane mobilization from dissociating gas hydrates.

  19. Timing of occurrence of large submarine landslides on the Atlantic Ocean margin

    USGS Publications Warehouse

    Lee, H.J.

    2009-01-01

    Submarine landslides are distributed unevenly both in space and time. Spatially, they occur most commonly in fjords, active river deltas, submarine canyon-fan systems, the open continental slope and on the flanks of oceanic volcanic islands. Temporally, they are influenced by the size, location, and sedimentology of migrating depocenters, changes in seafloor pressures and temperatures, variations in seismicity and volcanic activity, and changes in groundwater flow conditions. The dominant factor influencing the timing of submarine landslide occurrence is glaciation. A review of known ages of submarine landslides along the margins of the Atlantic Ocean, augmented by a few ages from other submarine locations shows a relatively even distribution of large landslides with time from the last glacial maximum until about five thousand years after the end of glaciation. During the past 5000??yr, the frequency of occurrence is less by a factor of 1.7 to 3.5 than during or shortly after the last glacial/deglaciation period. Such an association likely exists because of the formation of thick deposits of sediment on the upper continental slope during glacial periods and increased seismicity caused by isostatic readjustment during and following deglaciation. Hydrate dissociation may play a role, as suggested previously in the literature, but the connection is unclear.

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

    NASA Astrophysics Data System (ADS)

    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.

  1. Crustal structure of the Mid-Atlantic Margin from the MAGIC seismic array

    NASA Astrophysics Data System (ADS)

    Benoit, M. H.; Long, M. D.; Kirby, E.; King, S. D.; Miller, S. R.

    2015-12-01

    The eastern United States continental margin has undergone two full supercontinental cycles over the last billion years. While the scars of the repeated episodes of rifting, subduction, and collision are evident in the surficial geology of the eastern United States, the deeper crust and mantle lithospheric structure of the region also was altered during this tectonism. In general, the bulk crustal structure of the eastern US has largely remained uncharacterized before the arrival of the EarthScope, other than through analysis of a handful of regional seismic arrays. We present results of receiver function stacking of seismic data recorded from the MAGIC EarthScope Flex Array, composed of 27 STS-2 broadband stations located in a linear array that spans roughly SE-NE from Richmond,VA to Fort Wayne, Indiana. The array traverses several physiographic provinces, including the Atlantic Piedmont, Blue Ridge, Appalachian Valley and Ridge, and Appalachian Plateau. Preliminary results suggest that the crustal thickness varies significantly over short lateral distances in Virginia, and that the crust within the Appalachian Valley and Ridge contains significant layering. Characterization of the crustal thickness can help address long-standing questions regarding the relative contribution of isostasy in sustaining Appalachian topography.

  2. Comparative analysis of post-breakup basin evolution along the South-American and South-African margins, southern Atlantic

    NASA Astrophysics Data System (ADS)

    Strozyk, F.; Back, S.; Kukla, P. A.

    2012-04-01

    Recently, considerable attempts have been made to compare the sedimentary basin evolution and the associated tectonic framework on both sides of the South-Atlantic. However, yet there are still unresolved questions concerning the tectono-sedimentary styles of margin basin evolution that markedly differ from north to south. Amongst the most striking observations is that multiple phases of uplift and subsidence are recorded after the break-up of the southern South Atlantic margin segment on both sides of the Florianopolis-Walvis Ridge volcanic complex, features that are regarded as atypical when compared to published examples of other post-breakup margin successions. Adding to the heterogeneity of the system, the northernmost segment of the South Atlantic rift and salt basins is also characterized by a pronounced asymmetry, with the Brazilian margin now comprising narrower and deeper rift basins with less salt than the Congo-Gabon conjugate margin. This project deals with a large-scale comparison of this very different post-breakup tectono-stratigraphic development of the southern and northern South American and African continental margins that both record thick post-rift sedimentary successions. To gain detail of the basin margin evolution, we focus on a regional comparison between the post-breakup records archived in the large offshore southern Brazil basins (Pelotas, Santos, Campos) and the post-breakup continental margin successions of offshore Namibia (e.g. Orange Basin) and southern Angola (e.g. Kwanza Basin). A tectonic-stratigraphic comparison of representative geological transects provides a comprehensive basin-to-basin documentation of key factors influencing margin development which include the subsidence development through time, the sediment (in-)flux and storage patterns and the respective type of basin fill (e.g. salt vs. non-salt systems; carbonate-rich vs. clastics-dominated systems). Data from the salt-prone areas offshore South America and southern

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

    NASA Astrophysics Data System (ADS)

    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

  4. Influence of margin segmentation upon the break-up of the Hatton Bank rifted margin, NE Atlantic

    NASA Astrophysics Data System (ADS)

    Elliott, Gavin M.; Parson, Lindsay M.

    2008-10-01

    The Hatton Bank margin, flanking the Iceland Basin, is an example of a volcanic rifted margin and has been studied to examine the along margin tectono-magmatic variability. Integration of 5660 km of new seismic reflection profiles with > 60,000 km 2 of new multibeam bathymetry has allowed the margin to be divided into three segments, each of which are flanked by oceanic crust. The southernmost segment is characterised by a series of inner and outer seaward dipping reflector (SDR) packages, which are separated by an "Outer High" feature. The outer SDRs are truncated by Endymion Spur, a chain of steep sided, volcanic cones connected by narrow septa or necks. The central segment has no Inner SDR package and is characterised by the presence of a continental block, the Hatton Bank Block (HBB). The northern segment is adjacent to Lousy Bank, with a wider region of SDRs recognised than to the south, and characterised by many volcanic cones. The variations in the distribution of the SDRs along the margin, the presence of the HBB and Endymion Spur all suggest that the break-up process was not a uniform smooth process along-strike. Structural segmentation controlled the variations along the margin with break-up initiated in the south, producing the SDR packages. The HBB prompted the focus of break-up to relocate outboard of the block. The northern segment was closest to the Iceland "hot-spot", and regular seafloor spreading did not become established until Chron 21. Shortly after break-up, the eruption of Endymion Spur occurred and may have been triggered by the passage of a pulse of hot asthenospheric material along the margin. The margin segmentation pattern we describe controlled the location of the enhanced volcanism along the Endymion Spur to the southern sector. In addition the segmentation has influenced the break-up style (presence or absence of SDR) and also the location and nature of post break-up volcanism.

  5. High-resolution modelling of ocean-shelf exchange: assessment of a 1/60th NEMO configuration of the Atlantic margin (AMM60)

    NASA Astrophysics Data System (ADS)

    Guihou, Karen; Harle, James; Holt, Jason; O'Dea, Enda; Polton, Jeffrey

    2015-04-01

    The North West European shelf-break is a barrier to the transport and exchange between the open ocean and the coastal waters. The tides, the complex bathymetry, the winds, the slope current, mesoscale processes and internal tides play a key role in the variability of the shelf-sea exchanges. A better understanding of these various processes is a first step towards a better quantification of the seasonal, inter-annual and climate variability of the European continental shelf seas. The FASTNEt (Fluxes Across Sloping Topography of the North East Atlantic) project is a Directed Research Grant funded by the Natural Environment Research Council. It is a collaboration between SAMS, NOC, PML, and the universities of Bangor, Liverpool and Plymouth and aims at elucidate the key processes controlling seasonal, inter-annual and regional variations in ocean-shelf exchange, through a combined strategy of observations and modelling. In this context, a new 1/60th degree resolution (~1.8km) NEMO configuration has been developed: AMM60 extends on the same domain as the UK Met Office operational Atlantic Margin Model (~7km), from 40°N to 64°N, and 20°W to 10°E, enveloping the whole North West European Atlantic margin. With 51 sigma levels, it reproduces high-resolution processes such as internal tides, slope current meanders and eddies, as well along the slope as on the shelf. The capability of AMM60 to reproduce these processes has been assessed through strict validation with observations. The tidal cycle is well reproduced, as well as the seasonal variability of stratification on the shelf. The spatio-temporal variability of high-resolution structures, such as internal tides, is compared against measurements conducted in the frame of the FASTNEt project. This work allows us to quantify the spatio-temporal variability of the ocean-shelf exchanges at several scales and aims to highlight the importance of fine scale processes in controlling the wide area across-shelf budgets.

  6. Evidence for cooler European summers during periods of changing meltwater flux to the North Atlantic.

    PubMed

    Heiri, Oliver; Tinner, Willy; Lotter, André F

    2004-10-26

    We analyzed fossil chironomids (nonbiting midges) and pollen in two lake-sediment records to reconstruct and quantify Holocene summer-temperature fluctuations in the European Alps. Chironomid and pollen records indicate five centennial-scale cooling episodes during the early- and mid-Holocene. The strongest temperature declines of approximately 1 degrees C are inferred at approximately 10,700-10,500 and 8,200-7,600 calibrated 14C years B.P., whereas other temperature fluctuations are of smaller amplitude. Two forcing mechanisms have been presented recently to explain centennial-scale climate variability in Europe during the early- and mid-Holocene, both involving changes in Atlantic thermohaline circulation. In the first mechanism, changes in meltwater flux from the North American continent to the North Atlantic are responsible for changes in the Atlantic thermohaline circulation, thereby affecting circum-Atlantic climate. In the second mechanism, solar variability is the cause of Holocene climatic fluctuations, possibly triggering changes in Atlantic thermohaline overturning. Within their dating uncertainty, the two major cooling periods in the European Alps are coeval with substantial changes in the routing of North American freshwater runoff to the North Atlantic, whereas quantitatively, our climatic reconstructions show a poor agreement with available records of past solar activity. Thus, our results suggest that, during the early- and mid-Holocene, freshwater-induced Atlantic circulation changes had stronger influence on Alpine summer temperatures than solar variability and that Holocene thermohaline circulation reductions have led to summer-temperature declines of up to 1 degrees C in central Europe. PMID:15492214

  7. Passive margin uplift around the North Atlantic region and its role in Northern Hemisphere late Cenozoic glaciation

    NASA Astrophysics Data System (ADS)

    Eyles, Nicholas

    1996-02-01

    Tectonic-climatic models of late Cenozoic global cooling emphasize the importance of middle latitude uplifts (e.g., Tibetan Plateau and the American west) but ignore widespread tectonic events on the margins of the North Atlantic Ocean. Pleistocene glaciations, after 2.5 Ma, are characterized by circum North Atlantic continental ice sheets that formed by the coalescence of perennial snow fields on extensive plateau surfaces in eastern Canada, northwest Britain, and Scandinavia. Plateaus record Cenozoic uplift of peneplains in response to semisynchronous magmatic underplating and thermal buoyancy of rifted continental margins. High-standing plateaus are very sensitive to small reductions in summer temperature. As late Cenozoic climate cooling proceeded, driven by uplift in regions external to the North Atlantic region, elevated plateaus became sites for extensive snow fields and ultimately ice sheets. Circum-Atlantic uplift took place in the key latitudinal belt that is most sensitive to orbitally forced changes in solar irradiation; this, together with albedo effects from large snow fields, could have amplified the relatively weak Milankovitch signal.

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

    NASA Astrophysics Data System (ADS)

    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

  9. Seasonal Dynamics of Atlantic Herring (Clupea harengus L.) Populations Spawning in the Vicinity of Marginal Habitats

    PubMed Central

    Eggers, Florian; Slotte, Aril; Libungan, Lísa Anne; Johannessen, Arne; Kvamme, Cecilie; Moland, Even; Olsen, Esben M.; Nash, Richard D. M.

    2014-01-01

    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 km2 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. PMID:25372461

  10. A statistical overview of mass movement characteristics on the North American atlantic outer continental margin

    USGS Publications Warehouse

    Booth, James S.; O'Leary, Dennis W.

    1992-01-01

    An analysis of 179 mass movements on the North American Atlantic continental slope and upper rise shows that slope failures have occurred throughout the geographic extent of the outer margin. Although the slope failures show no striking affinity for a particular depth as an origination level, there is a broad, primary mode centered at about 900 m. The resulting slides terminate at almost all depths and have a primary mode at 1100 m, but the slope/rise boundary (at 2200 m) also is an important mode. Slope failures have occurred at declivities ranging from 1° to 30° (typically, 4°); the resultant mass movement deposits vary in width from 0.2 to 50 km (typically, 1-2 km) and in length from 0.3 to 380 km (typically, 2–4 km), and they have been reported to be as thick as 650 m. On a numeric basis, mass movements are slightly more prevalent on open slopes than in other physiographic settings, and both translational and rotational failure surfaces are common. The typical mass movement is disintegrative in nature. Open slope slides tend to occur at lower slope angles and are larger than canyon slides. Further, large‐scale slides rather than small‐scale slides tend to originate on gentle slopes (≍ 3-4°). Rotational slope failures appear to have a slightly greater chance of occurring in canyons, but there is no analogous bias associated with translational failures. Similarly, disintegrative slides seem more likely to be associated with rotational slope failures than translational ones and are longer than their nondisintegrative counterparts. The occurrence of such a variety of mass movements at low declivities implies that a regional failure mechanism has prevailed. We suggest that earthquakes or, perhaps in some areas, gas hydrates are the most likely cause of the slope failures.

  11. Assessing the potential of the European Atlantic sturgeon Acipenser sturio to control bivalve invasions in Europe.

    PubMed

    Ferreira-Rodriguez, N; Gessner, J; Pardo, I

    2016-08-01

    This pilot study explored the potential of juvenile European Atlantic sturgeon Acipenser sturio to feed on two invasive bivalve species, the Asian clam Corbicula fluminea and the Eurasian zebra mussel Dreissena polymorpha. Preliminary results indicate that native A. sturio were feeding on D. polymorpha at a very limited rate and their potential to prevent the establishment of invasive bivalve species, in new and previously invaded areas, is considered limited. PMID:27238016

  12. Extreme storm activity in North Atlantic and European region

    NASA Astrophysics Data System (ADS)

    Vyazilova, N.

    2010-09-01

    The extreme storm activity study over North Atlantic and Europe includes the analyses of extreme cyclone (track number, integral cyclonic intensity) and extreme storm (track number) during winter and summer seasons in the regions: 1) 55°N-80N, 50°W-70°E; 2) 30°N-55°N, 50°W-70°E. Extreme cyclones were selected based on cyclone centre pressure (P<=970 mbar). Extreme storms were selected from extreme cyclones based on wind velocity on 925 mbar. The Bofort scala was used for this goal. Integral cyclonic intensity (for region) includes the calculation cyclone centers number and sum of MSLP anomalies in cyclone centers. The analyses based on automated cyclone tracking algorithm, 6-hourly MSLP and wind data (u and v on 925 gPa) from the NCEP/NCAR reanalyses from January 1948 to March 2010. The comparision of mean, calculated for every ten years, had shown, that in polar region extreme cyclone and storm track number, and integral cyclonic intensity gradually increases and have maximum during last years (as for summer, as for winter season). Every ten years means for summer season are more then for winter season, as for polar, as for tropical region. Means (ten years) for tropical region are significance less then for polar region.

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

    NASA Astrophysics Data System (ADS)

    Glasmacher, Ulrich Anton; Hackspacher, Peter C.

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

    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

  15. Crustal Rheology and Rifted Margin Architecture: Comparing Iberia-Newfoundland, Central South Atlantic, and South China Sea

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Crustal rheology controls the style of rifting and ultimately the architecture of rifted margins: Hot, weak, or thick continental crust is dominated by ductile deformation and extends symmetrically into a wide rift system. Extension in cold, strong, or thin crust is accommodated by brittle faults and ductile shear zones that facilitate narrow rifts with asymmetric fault geometries. This recipe provides the standard framework to understand 2D rift geometry, however, a variety of processes exert significant control on subsequent rift evolution and ultimately on the architecture of rifted margins: inherited structures, melting and volcanism, 3D effects, extension rate, and weakening mechanisms. Numerical forward modelling studies have the opportunity to evaluate the influence of these processes on rift evolution in order to understand the complex interaction between rheology and tectonic history of specific margins. Here I compare the formation of three different magma-poor margin pairs, Iberia-Newfoundland, the Central South Atlantic Rift Segment, and the South China Sea margins within a numerical forward modelling framework. I apply a 2D version of the finite element code SLIM3D, which includes nonlinear temperature- and stress-dependent elasto-visco-plastic rheology and is able to reproduces a wide range of rift-related deformation processes such as flexure, lower crustal flow, and faulting. The Iberia-Newfoundland rifted margins are marked by moderate crustal asymmetry, with ~70 km of hyper-extended crust (less than 10 km thick) on the Iberian side and a very narrow margin on the Newfoundland counterpart. Similar to the Iberia-Newfoundland conjugates, the Central South Atlantic margins are predominantly asymmetric, however involve a much stronger degree of asymmetry with more than 200 km of hyper-extended crust offshore Angola, but only few tens of km at the Brazilian side. Kinematic and numerical modelling suggests that the asymmetry is caused by lateral

  16. Control of hyper-extended passive margin architecture on subduction initiation with application to the Alps and present-day North Atlantic ocean

    NASA Astrophysics Data System (ADS)

    Candioti, Lorenzo; Bauville, Arthur; Picazo, Suzanne; Mohn, Geoffroy; Kaus, Boris

    2016-04-01

    Hyper-extended magma-poor margins are characterized by extremely thinned crust and partially serpentinized mantle exhumation. As this can act as a zone of weakness during a subsequent compression event, a hyper-extended margin can thus potentially facilitate subduction initiation. Hyper-extended margins are also found today as passive margins fringing the Atlantic and North Atlantic ocean, e.g. Iberia and New Foundland margins [1] and Porcupine, Rockwall and Hatton basins. It has been proposed in the literature that hyper-extension in the Alpine Tethys does not exceed ~600 km in width [2]. The geodynamical evolution of the Alpine and Atlantic passive margins are distinct: no subduction is yet initiated in the North Atlantic, whereas the Alpine Tethys basin has undergone subduction. Here, we investigate the control of the presence of a hyper-extended margin on subduction initiation. We perform high resolution 2D simulations considering realistic rheologies and temperature profiles for these locations. We systematically vary the length and thickness of the hyper-extended crust and serpentinized mantle, to better understand the conditions for subduction initiation. References: [1] G. Manatschal. New models for evolution of magma-poor rifted margins based on a review of data and concepts from West Iberia and the Alps. Int J Earth Sci (Geol Rundsch) (2004); 432-466. [2] G. Mohn, G. Manatschal, M. Beltrando, I. Haupert. The role of rift-inherited hyper-extension in alpine-type orogens. Terra Nova (2014); 347-353.

  17. Postrift history of the eastern central Atlantic passive margin: Insights from the Saharan region of South Morocco

    NASA Astrophysics Data System (ADS)

    Leprêtre, Rémi; Missenard, Yves; Barbarand, Jocelyn; Gautheron, Cécile; Saddiqi, Omar; Pinna-Jamme, Rosella

    2015-06-01

    The passive margin of South Morocco is a low-elevated passive margin. It constitutes one of the oldest margins of the Atlantic Ocean, with an Early Jurassic breakup, and little geological data are available concerning its postrift reactivation so far. We investigated the postrift thermal history of the onshore part of the margin with low-temperature thermochronology on apatite crystals. Fission track and (U-Th-Sm)/He ages we obtained are significantly younger than the breakup (~190 Ma). Fission track ages range from 107 ± 8 to 175 ± 16 Ma, with mean track lengths from 10.7 ± 0.3 to 12.5 ± 0.2 µm. (U-Th-Sm)/He ages range from 14 ± 1 to 185 ± 15 Ma. Using inverse modeling of low-temperature thermochronological data, we demonstrate that the South Moroccan continental margin underwent a complex postrift history with at least two burial and exhumation phases. The first exhumation event occurred during Late Jurassic/Early Cretaceous, and we attribute this to mantle dynamics rather than to intrinsic rifting-related processes such as flexural rebound. The second event, from Late Cretaceous to early Paleogene, might record the onset of Africa/Europe convergence. We show a remarkably common behavior of the whole Moroccan passive margin during its early postrift evolution. The present-day differences result from a segmentation of the margin domains due to the Africa/Europe convergence. Finally we propose that varying retained strengths during rifting and also the specific crustal/lithospheric geometry of stretching explain the difference between the topographical expressions on the continental African margin compared to its American counterpart.

  18. The impact of North Atlantic wind and cyclone trends on European precipitation and significant wave height in the Atlantic.

    PubMed

    Trigo, Ricardo M; Valente, Maria A; Trigo, Isabel F; Miranda, Pedro M A; Ramos, Alexandre M; Paredes, Daniel; García-Herrera, Ricardo

    2008-12-01

    An analysis of the frequency of cyclones and surface wind velocity for the Euro-Atlantic sector is performed by means of an objective methodology. Monthly and seasonal trends of cyclones and wind speed magnitude are computed and trends between 1960 and 2000 evaluated. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February, and March. Seasonal and monthly analysis of wind magnitude trends shows similar spatial patterns. We show that these changes in the frequency of low-pressure centers and the associated wind patterns are partially responsible for trends in the significant height of waves. Throughout the extended winter months (October-March), regions with positive (negative) wind magnitude trends, of up to 5 cm/s/year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for January-March are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of lat 50 degrees N up to -3 cm/year, and positive up to 5 cm/year just north of Scotland). Trends in European precipitation are assessed using the Climatic Research Unit data set. The results of the assessment emphasize the link with the corresponding tendencies of cyclone frequencies. Finally, it is shown that these changes are associated, to a large extent, with the preferred phases of major large-scale atmospheric circulation modes, particularly with the North Atlantic Oscillation, the eastern Atlantic pattern, and the Scandinavian pattern. PMID:19076417

  19. Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Gooday, A. J.; Aranda da Silva, A.; Pawlowski, J.

    2011-12-01

    Xenophyophores are abundant on a terrace of the lower Nazaré Canyon (4300 m water depth) on the Portuguese margin. Here, the most abundant species, Reticulammina cerebreformis sp. nov., occurs in densities of up to 21 individuals/m 2. This large species has a soft, friable hemispherical test up to 10 cm in diameter consisting of curved, sinuous plates (lamellae) that branch and anastomose. The plates are separated by deep furrows and other depressions to form a distinctive 'brain-like' structure. The outer test layer is thin, weakly cemented and is dominated by fine sediment particles; the internal xenophyae include a higher proportion of larger mineral grains. The second new species at the 4300-m site, Nazareammina tenera gen. et sp. nov., is much less common. The test is basically plate-like, but towards the interior it is perforated by oval spaces, which typically merge into complex system of bar-like features, sometimes with irregular excrescences. The granellare system (cell body and its organic envelope) is packed with tiny mineral grains of various sizes and shapes, including titanium-bearing particles. Also common at this deep site are clusters, with a maximum diameter up to 10 cm or occasionally more, of irregular tubes belonging to Aschemonella ramuliformis Brady 1884, a species previously known mainly from isolated tubes. Rather than being single individuals, these clusters comprise a large number of separate branched tubes. Finally, Syringammina fragillissima Brady 1883, a well-known species that is widely distributed on the NW European margin, occurred on steep sediment-covered slopes at a shallower (1555 m water depth) site in the upper canyon. Almost complete SSU rDNA gene sequences obtained from A. ramuliformis and R. cerebreformis confirm that these xenophyophores are foraminifera. Together with two previously sequenced xenophophores ( Shinkaia lindsayi Lecroq, Gooday, Tsuchiya, Pawlowski 2009 and Syringammina corbicula Richardson 2001), and the

  20. What is reactivated when at rifted margins? comparing the Northwest Svalbard and Møre segments of the NE Atlantic margin.

    NASA Astrophysics Data System (ADS)

    Terje Osmundsen, Per; Braathen, Alvar; Redfield, Thomas F.; Peron-Pinvidic, Gwenn; Maher, Harmon

    2016-04-01

    The opening of oceans along ancient mountain belts was stated as fundamental in the Wilson cycle and appears to be justified in the case of the North Atlantic. The question of what is actually inherited appears as much more difficult. We consider 3 aspects of inheritance as pertinent to the evolution of the Svalbard and Mid-Norwegian rifted margins: 1) inheritance of the post-orogenic rheological and structural template into later stages of rifting, 2) inheritance of the early rift configuration, including variations in crustal thickness and rheology, into the stage of crustal necking and 3) inheritance of the post-rift crustal template into the `passivé margin phase dominated by vertical movements. The Northwest Svalbard and Møre margins share some fundamental similarities in the arrangement of onshore and offshore structures. Both areas host inherited extensional complexes of detachment faults, strongly aligned extension-parallel fabrics including mineral lineations, doubly plunging extension-parallell folds and fold-parallel brittle faults. These fabrics developed during phases of orogenic `collapsé, suggested to be characterized by constrictional strains and regional transtension in the Norwegian case, but that have only recently been identified in Svalbard. In both areas, faults incised into the flanks of extension-parallel folds display a long history of reactivation. The necking domain of the Møre margin developed on a template of NE-SW-trending, warped detachment fabrics and sinistral strike-slip faults, which were reactivated from the Jurassic into the Cretaceous to define the inner boundary for the distal margin. Onshore these structures were reactivated in the Late Cretaceous and/or in the Cenozoic. Considerable topographic and geomorphic contrasts developed across reactivated fault strands since the Latest Cretaceous, demonstrating relationships between inherited structure and Scandinavian topography and landscape. In Svalbard, the N-S trending

  1. Impact of ship emissions on air pollution and AOD over North Atlantic and European Arctic

    NASA Astrophysics Data System (ADS)

    Kaminski, Jacek W.; Struzewska, Joanna; Jefimow, Maciej; Durka, Pawel

    2016-04-01

    The iAREA project is combined of experimental and theoretical research in order to contribute to the new knowledge on the impact of absorbing aerosols on the climate system in the European Arctic (http://www.igf.fuw.edu.pl/iAREA). A tropospheric chemistry model GEM-AQ (Global Environmental Multiscale Air Quality) was used as a computational tool. The core of the model is based on a weather prediction model with environmental processes (chemistry and aerosols) implanted on-line and are interactive (i.e. providing feedback of chemistry on radiation and dynamics). The numerical grid covered the Euro-Atlantic region with the resolution of 50 km. Emissions developed by NILU in the ECLIPSE project was used (Klimont et al., 2013). The model was run for two 1-year scenarios. 2014 was chosen as a base year for simulations and analysis. Scenarios include a base run with most up-to-date emissions and a run without maritime emissions. The analysis will focus on the contribution of maritime emissions on levels of particulate matter and gaseous pollutants over the European Arctic, North Atlantic and coastal areas. The annual variability will be assessed based on monthly mean near-surface concentration fields. Analysis of shipping transport on near-surface air pollution over the Euro-Atlantic region will be assessed for ozone, NO2, SO2, CO, PM10, PM2.5. Also, a contribution of ship emissions to AOD will be analysed.

  2. Chirp seismic-reflection data from the Baltimore, Washington, and Norfolk Canyons, U.S. mid-Atlantic margin

    USGS Publications Warehouse

    Obelcz, Jeffrey B.; Brothers, Daniel S.; ten Brink, Uri S.; Chaytor, Jason D.; Worley, Charles R.; Moore, Eric M.

    2014-01-01

    A large number of high-resolution geophysical surveys between Cape Hatteras and Georges Bank have been conducted by federal, state, and academic institutions since the turn of the century. A major goal of these surveys is providing a continuous view of bathymetry and shallow stratigraphy at the shelf edge in order to assess levels of geological activity during the current sea level highstand. In 2012, chirp seismic-reflection data was collected by the U.S. Geologial Survey aboard the motor vessel Tiki XIV near three United States mid-Atlantic margin submarine canyons. These data can be used to further our understanding of passive continental margin processes during the Holocene, as well as providing valuable information regarding potential submarine geohazards.

  3. The MIRROR cruise (2011): Deep crustal structure of the Moroccan Atlantic Margin from wide-angle and reflection seismic data

    NASA Astrophysics Data System (ADS)

    Klingelhoefer, F.; Aslanian, D.; Sahabi, M.; Moulin, M.; Schnurle, P.; Berglar, K.; Biari, Y.; Feld, A.; Graindorge, D.; Corela, C.; Mehdi, K.; Zourarah, B.; Perrot, J.; Alves Ribeiro, J.; Reichert, C. J.

    2011-12-01

    The study of conjugate margins is important to test different hypotheses of rifting and initial opening of an ocean. In this scope, seven wide-angle seismic profiles were acquired on the Moroccan Atlantic margin (at the latitudes between 32° and 33° N) together with coincident deep frequency reflection seismic data during the MIRROR cruise in May and June 2011. The main seismic profile is conjugate to an existing wide-angle seismic profile off Nova Scotia (SMART 2). Further objectives of the cruise were to image ocean-continent transition zone, to detect and eventually quantify exhumed upper mantle material present in this zone and to determine the origin of the high amplitude West African Magnetic Anomaly, which is conjugate to the north American East Coast Magnetic Anomaly and can be linked to the opening of the Atlantic. Two of the newly acquired profiles are located perpendicular and five parallel to the Moroccan margin. The seismic profiles are between 130 and 260 km in length and between 28 and 13 ocean-bottom seismometers were deployed on each one. One profile was extended on land by 15 landstations in order to better image the zone of continental thinning. A 4.5 km digital streamer and a 7200 cu inch tuned airgun array were used for the acquisition of the seismic data. Additionally magnetic, bathymetric and high resolution seismic data were acquired in the study region. Preliminary results from tomographic inversion of the first arrivals from the ocean-bottom seismometer data image the zone of crustal thinning from about 25 km to 6 km in the basin along about 70 kilometers of the profiles which are located perpendicular to the margin. The oceanic crust can be divided into 2 regions, based on the lower crustal velocities. Upper mantle velocities are about 8.0 km/s. The coincident reflection seismic data show the fine basement and sedimentary structures including salt tectonics in the basin. The comparative study of the two conjugate profiles on the

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

    Døssing, Arne; Japsen, Peter; Watts, Anthony B.; Nielsen, Tove; Jokat, Wilfried; Thybo, Hans; Dahl-Jensen, Trine

    2016-02-01

    Tectonic models predict that following breakup, rift margins undergo only decaying thermal subsidence during their postrift evolution. However, postbreakup 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 synrift deposition in the deep-sea basins and onset of (i) thermomechanical 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 thermomechanical 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 intraplate stresses related to global tectonics.

  6. Correlation and zonation of miocene strata along the atlantic margin of North America using diatoms and silicoflagellates

    USGS Publications Warehouse

    Abbott, W.H.

    1978-01-01

    Six Atlantic Miocene siliceous microfossil zones are proposed based on onshore and offshore samples from the United States Atlantic Margin. Diatoms and silicoflagellates are used to establish the zones. These zones are from oldest to youngest: 1. Zone I Actinoptychus heliopelta Concurrent Range Zone - Early Miocene 2. Zone II Delphineis ovata Partial Range Zone - late Early to early Middle Miocene 3. Zone III Delphineis ovata/Delphineis penelliptica Concurrent Range Zone - early Middle Miocene 4. Zone IV Delphineis penelliptica Partial Range Zone - Middle Miocene 5. Zone V Delphineis penelliptica/Coscinodiscus plicatus Concurrent Range Zone - Middle Miocene 6. Zone VI Coscinodiscus plicatus Partial Range Zone - Middle Miocene. The six zones are easily traced along the Southern and Middle Atlantic Seaboard, but the older three are found for the most part between Cape Hatteras and New Jersey. There is some suggestion of sea-level change during Zone IV. Using rare planktonic diatoms that are index species from other regions and the zonal markers established in this study, correlation can be made with the Standard Foraminiferal Zones, the North Pacific Diatom Zones and with DSDP core 391A in the Blake-Bahama Basin. ?? 1978.

  7. Morphology and environment of cold-water coral carbonate mounds on the NW European margin

    NASA Astrophysics Data System (ADS)

    Wheeler, A. J.; Beyer, A.; Freiwald, A.; de Haas, H.; Huvenne, V. A. I.; Kozachenko, M.; Olu-Le Roy, K.; Opderbecke, J.

    2007-02-01

    Cold-water coral carbonate mounds, owing their presence mainly to the framework building coral Lophelia pertusa and the activity of associated organisms, are common along the European margin with their spatial distribution allowing them to be divided into a number of mound provinces. Variation in mound attributes are explored via a series of case studies on mound provinces that have been the most intensely investigated: Belgica, Hovland, Pelagia, Logachev and Norwegian Mounds. Morphological variation between mound provinces is discussed under the premise that mound morphology is an expression of the environmental conditions under which mounds are initiated and grow. Cold-water coral carbonate mounds can be divided into those exhibiting “inherited” morphologies (where mound morphology reflects the morphology of the colonised features) and “developed” morphology (where the mounds assume their own gross morphology mainly reflecting dominant hydrodynamic controls). Finer-scale, surface morphological features mainly reflecting biological growth forms are also discussed.

  8. Impact of observed North Atlantic multidecadal variations to European summer climate: a linear baroclinic response to surface heating

    NASA Astrophysics Data System (ADS)

    Ghosh, Rohit; Müller, Wolfgang A.; Baehr, Johanna; Bader, Jürgen

    2016-07-01

    The observed prominent multidecadal variations in the central to eastern (C-E) European summer temperature are closely related to the Atlantic multidecadal variability (AMV). Using the Twentieth Century Reanalysis project version 2 data for the period of 1930-2012, we present a mechanism by which the multidecadal variations in the C-E European summer temperature are associated to a linear baroclinic atmospheric response to the AMV-related surface heat flux. Our results suggest that over the north-western Atlantic, the positive heat flux anomaly triggers a surface baroclinic pressure response to diabatic heating with a negative surface pressure anomaly to the east of the heat source. Further downstream, this response induces an east-west wave-like pressure anomaly. The east-west wave-like response in the sea level pressure structure, to which we refer as North-Atlantic-European East West (NEW) mode, is independent of the summer North Atlantic Oscillation and is the principal mode of variations during summer over the Euro-Atlantic region at multidecadal time scales. The NEW mode causes warming of the C-E European region by creating an atmospheric blocking-like situation. Our findings also suggest that this NEW mode is responsible for the multidecadal variations in precipitation over the British Isles and north-western Europe.

  9. Weather Regimes and cyclonic activity in the North Atlantic European region: present and future climates

    NASA Astrophysics Data System (ADS)

    Rodrigues, Tiago; Rocha, Alfredo; Melo-Gonçalves, Paulo; Santos, João A.; Pinto, Joaquim G.

    2014-05-01

    Damages associated with extratropical storms are amongst the most important natural hazards on Western Europe. Thus, in this work we analyse: (i) the relationships between several cyclone characteristics: intensity, depth, radius, cyclogenesis, cyclolysis, and total number of cyclones (identified by applying the Murray and Simmonds method to 6-hourly 850 hPa geopotential height); (ii) their links to four large-scale weather regimes (WRs) over a North Atlantic-European sector (NAE, 90W-30E, 20N-80N); and (iii) the projected changes for future climates under emission scenarios. Four WRs are identified by a 4-means clustering of the daily 500 hPa geopotential height fields (Blocking, Zonal or NAO+, Atlantic Ridge, and Greenland Anticyclonic). Furthermore, daily 500 hPa geopotential height from four CMIP3 simulations are clustered using the ERA centroids, for both the recent-past climate (1961-1990) and two future climates: 2021-2050 and 2069-2098. The impact of anthropogenic forcing on the cyclonic activity over the NAE sector is thereby quantified for each of the four weather regimes. Acknowledgments: this work is supported by European Union Funds (FEDER/COMPETE - Operational Competitiveness Programme) and by national funds (FCT - Portuguese Foundation for Science and Technology) under the project CLIPE (PTDC/AAC-CLI/111733/2009).

  10. European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling

    NASA Astrophysics Data System (ADS)

    Bastos, Ana; Janssens, Ivan A.; Gouveia, Célia M.; Trigo, Ricardo M.; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W.

    2016-01-01

    Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO-EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models.

  11. European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling.

    PubMed

    Bastos, Ana; Janssens, Ivan A; Gouveia, Célia M; Trigo, Ricardo M; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W

    2016-01-01

    Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO-EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models. PMID:26777730

  12. European land CO2 sink influenced by NAO and East-Atlantic Pattern coupling

    PubMed Central

    Bastos, Ana; Janssens, Ivan A.; Gouveia, Célia M.; Trigo, Ricardo M.; Ciais, Philippe; Chevallier, Frédéric; Peñuelas, Josep; Rödenbeck, Christian; Piao, Shilong; Friedlingstein, Pierre; Running, Steven W.

    2016-01-01

    Large-scale climate patterns control variability in the global carbon sink. In Europe, the North-Atlantic Oscillation (NAO) influences vegetation activity, however the East-Atlantic (EA) pattern is known to modulate NAO strength and location. Using observation-driven and modelled data sets, we show that multi-annual variability patterns of European Net Biome Productivity (NBP) are linked to anomalies in heat and water transport controlled by the NAO–EA interplay. Enhanced NBP occurs when NAO and EA are both in negative phase, associated with cool summers with wet soils which enhance photosynthesis. During anti-phase periods, NBP is reduced through distinct impacts of climate anomalies in photosynthesis and respiration. The predominance of anti-phase years in the early 2000s may explain the European-wide reduction of carbon uptake during this period, reported in previous studies. Results show that improving the capability of simulating atmospheric circulation patterns may better constrain regional carbon sink variability in coupled carbon-climate models. PMID:26777730

  13. Lipid Biomarkers and Carbon Isotopic Composition from Authigenic Carbonates and Seep Sediments from the US Mid-Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Campbell, P.; Prouty, N.; Demopoulos, A. W.; Roark, B.; Coykendall, K.

    2015-12-01

    Anaerobic oxidation of methane (AOM), mediated by Archaea and sulfate-reducing bacteria, is common in continental margin sediment and can result in authigenic carbonate precipitation. A lipid biomarker study was undertaken in Mid-Atlantic submarine canyons, focusing specifically on Baltimore and Norfolk canyons, to determine biomarker variability of carbonate rock and the associated sediment in cold seep communities dominated by chemosynthetic mussels, Bathymodiolus childressi. Preliminary 16S metagenomic results confirm the presence of free-living sulfur-reducing bacteria and methantrophic endosymbiotic bacteria in the mussels. Depleted d13C values in both the mussel tissue (-63 ‰) and authigenic carbonates (-48 ‰) support methanotrophy as the dominant nutritional pathway and AOM as the main driver of carbonate precipitation. In addition, paired 14C and 230Th dates are highly discordant, reflecting dilution of the 14C pool with fossil hydrocarbon derived carbon. Seep and canyon sediment, as well as authigenic carbonates, were collected and analyzed for a suite of biomarkers, including sterols, alcohols, alkanes and fatty acids, as well as δ13C values of select biomarkers, to elucidate pathways of organic matter cycling. A comparison of terrestrial biomarker signatures (e.g., n-alkane carbon preference index and C23 / (C23 + C29) values, HMW n-alkanes and C29 sterols) suggests that terrestrial inputs dominate the submarine canyon surface sediment, whereas seep sediment is predominantly marine autochthonous (i.e., cholesterol and 5α-cholestanol). Lipid biomarker profiles (e.g., n-alkanes in the C15 to C33 range) from authigenic carbonates mirror those found in the seep sediment, suggesting that the organisms mediating carbonate precipitation on the seafloor are characteristic of the assemblages present in the sediment at these sites. With widespread methane leakage recently discovered along the Atlantic Margin, the presence of AOM-mediated carbonate

  14. Comparative analysis of the Late Cretaceous to Recent post-breakup basin evolution of the South-American and South-African margin of the southern Atlantic

    NASA Astrophysics Data System (ADS)

    Kukla, Peter; Back, Stefan

    2010-05-01

    Recently, considerable attempts have been made to compare the sedimentary basin evolution and the associated tectonic framework on both sides of the South-Atlantic (e.g. Mohriak et al., 2008, and references therein). Yet there are still unresolved questions. Amongst the most striking observations is that multiple phases of volcanism, uplift and subsidence are recorded after the break-up of the southern South Atlantic margin segment on both sides of the Florianopolis - Walvis Ridge volcanic complex, features that are regarded as atypical when compared to published examples of other post-breakup continental margin successions. However, the tectono-sedimentary and magmatic styles markedly differ from south to north across the volcanic complex. In seismic reflection data, voluminous extrusives are manifested by the occurrence of large wedges of seaward dipping reflector sequences south of the volcanic complex, whilst large volumes of Cretaceous mafic alkaline rocks only occur north of the Florianopolis - Walvis Ridge complex. It can be expected that these differences are of a broad importance for the understanding of both break-up and post-breakup processes. This presentation focuses on a comparison of the post-breakup stratigraphic development of the South American and South African continental margins that both record thick post-rift sedimentary successions. Basins along the southern African margin are much narrower in comparison to their South American counterparts, constituting a pronounced margin asymmetry across the Atlantic. Adding to the heterogeneity of the system, the northernmost segment of the South Atlantic rift and salt basins is also characterized by a pronounced asymmetry, with the Brazilian margin now comprising narrower and deeper rift basins with less salt than the Congo-Gabon conjugate margin. In general, it seems that in the salt-prone areas both offshore South America and southern Africa, salt-related tectonics are amongst the key parameters

  15. Isostatic and dynamic support of high topography on a North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Pedersen, Vivi K.; Huismans, Ritske S.; Moucha, Robert

    2016-07-01

    Substantial controversy surrounds the origin of high topography along passive continental margins. Here we focus on the well-documented elevated passive margin in southwestern Scandinavia, and quantify the relative contributions of crustal isostasy and dynamic topography in controlling the present topography. We find that majority of the topography is compensated by the crustal structure, suggesting a topographic age that is in accord with the 400 Myr old Caledonian orogenesis. In addition, we propose that dynamic uplift of ∼300 m has rejuvenated existing topography locally in the coastal region over the last 10 Myr. Such uplift, combined with a general sea level fall, can help explain a variety of observations that have traditionally been interpreted in favor of a peneplain uplift model. We conclude that high topography along the Scandinavian margin cannot represent remnants of a peneplain uplifted within the last 20 Myr. The topography must have been high since the Caledonian orogeny.

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

    USGS Publications Warehouse

    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.

  17. Key controls of surface carbonate system dynamics around the northwest European continental margin

    NASA Astrophysics Data System (ADS)

    Jiang, Z.; Hydes, D. J.; Hartman, S. E.; Hartman, M. C.

    2011-12-01

    Monthly sampling coupled to continuous underway observation from a ship-of-opportunity (Pride of Bilbao) provides new insights into the relative importance of processes controlling the seasonal to inter-annual variability of the carbonate system around the northwest European continental margin. Total alkalinity (TA) and total dissolved inorganic carbon (DIC) were determined alongside measurements of nutrients and continuous records of temperature, salinity, chlorophyll-fluorescence, and dissolved oxygen (DO). The northwest European continental margin is temperate latitude system with a strong seasonal cycle in biological productivity determined by light, nutrient supply, and stratification. Here we contrast findings in two areas: the shallow non stratified English Channel (depth ~50 m) and seasonally stratified oligotrophic waters of the central Bay of Biscay (depth >3000 m). In the Bay of Biscay, the seasonal variations of the carbonate system, nutrient, and DO were mainly controlled by the winter mixing and spring phytoplankton bloom. DIC and nutrients in the Bay increased from autumn and reached the annual maxima in later winter, they then decreased significantly during the spring bloom corresponding to the biological uptake. DIC fell during the spring bloom with a near Redfield ratio in relation to the nutrient uptake. In contrast, post bloom in summer, a continued decrease in DIC in the absence of measurable nitrate was possibly related to the nutrient supply from the turbulent mixing. pCO2 and pH showed a double peak in the annual cycles modulated by temperature which counterbalanced the influence of winter mixing and biological production. The inter-annual biogeochemical variability was closely related to the changes in winter mixed layer depth and the phytoplankton biomass. The Bay of Biscay acted as a sink for atmospheric CO2 in all seasons, with higher air-to-sea CO2 fluxes observed in cold winter and the productive spring season. In the more dynamic

  18. Late Cretaceous-Paleocene strike-slip faults along the East Greenland margin (63°N to 75°N): constraints for the North East Atlantic opening

    NASA Astrophysics Data System (ADS)

    Guarnieri, P.

    2012-04-01

    The East Greenland margin is a long stretch starting from 60°N up to 81°N in a distance of almost 3000 km. It represents the conjugate of the European margin now separated by the North East Atlantic (NEA). After a long period of E-W extension and almost N-S oriented rift basins since Early Cretaceous, separation between Greenland and Europe began at 55 Ma following a NE-SW oriented line of breakup and the emplacement of the North Atlantic Igneous Province (NAIP). Post-breakup thermal subsidence followed in the Eocene, and the Oligocene initiated a period of plate re-organization together with the initial separation of Jan Mayen microcontinent, a complex tectonic history with inversion structures and uplifts along both the East Greenland and European margins. The effect of this history is represented by exhumed sedimentary basins, dyke swarms, fault systems, intrusive centers, shield volcanoes and plateau lavas constituting highest mountain of Greenland with some peaks up to 3700 m (e.g. Watkins Bjerge). During expeditions for fieldwork in East Greenland (2009 to 2011) to collect new geological and structural data related to the North East Atlantic tectonics, four areas were visited: Skjoldungen 63°N, Kangerlussuaq 68°N, Traill Ø 72°N and Wollaston Forland 75°N. More than 1000 measurement of fault-slip data for structural analysis along major faults were collected and helicopter flights to collect oblique pictures for 3D-photogeology and 3D-mapping were taken. Kinematic analysis of brittle deformation associated with Late Cretaceous-Paleocene rift shows strike-slip movements. Palaeo-stress tensors reconstructed from fault-slip data highlight a NE-SW maximum horizontal stress in a strike-slip tectonic setting along the entire East Greenland margin (Guarnieri 2011a; Guarnieri 2011b; Guarnieri et al. 2011). Structural data show clear evidence for oblique rifting that corresponds in time to the "volcanic rift" (61-55 Ma) with in some cases the magmatic

  19. Structure, Function and Floristic Relationships of Plant Communities in Stressful Habitats Marginal to the Brazilian Atlantic Rainforest

    PubMed Central

    SCARANO, FABIO R.

    2002-01-01

    The Brazilian Atlantic rainforest consists of a typical tropical rainforest on mountain slopes, and stands out as a biodiversity hotspot for its high species richness and high level of species endemism. This forest is bordered by plant communities with lower species diversity, due mostly to more extreme environmental conditions than those found in the mesic rainforest. Between the mountain slopes and the sea, the coastal plains have swamp forests, dry semi‐deciduous forests and open thicket vegetation on marine sand deposits. At the other extreme, on top of the mountains (>2000 m a.s.l.), the rainforest is substituted by high altitude fields and open thicket vegetation on rocky outcrops. Thus, the plant communities that are marginal to the rainforest are subjected either to flooding, drought, oceanicity or cold winter temperatures. It was found that positive interactions among plants play an important role in the structuring and functioning of a swamp forest, a coastal sandy vegetation and a cold, high altitude vegetation in the state of Rio de Janeiro. Moreover, only a few species seem to adopt this positive role and, therefore, the functioning of these entire systems may rely on them. Curiously, these nurse plants are often epiphytes in the rainforest, and at the study sites are typically terrestrial. Many exhibit crassulacean acid metabolism. Conservation initiatives must treat the Atlantic coastal vegetation as a complex rather than a rainforest alone. PMID:12324276

  20. Faults, fault rocks and fractures in basalts: a macro- to micro-analysis of fault rock evolution on the NE Atlantic Margin

    NASA Astrophysics Data System (ADS)

    Walker, R. J.; Holdsworth, R. E.; Imber, J.

    2009-12-01

    Many upper crustal fault zones contain significant volumes of brecciated wall rock formed in the vicinity of dilational jogs, which can form permeability pathways for the migration of mineralising hydrothermal fluids or hydrocarbons. Such fault-breccia formation is commonly assumed to be a geologically instantaneous process, resulting from a sudden differential in fluid pressures between a dilational jog and its surrounding country rock, which leads to inward implosion. However, at shallow crustal depths (0-2km, and potentially deeper with increased fluid pressures) mechanically strong rocks (e.g. crystalline/carbonate rocks) may be able to support dilational jogs as persistent, high permeability, open subterranean cavities that become more gradually filled by fragments of the surrounding wall rocks through time. Understanding the development of fault breccias is therefore scientifically and economically important, as the two breccia models have markedly contrasting sealing and fluid flow histories. The Faroe Islands - the location of the present study - sit above the Jurassic-Palaeogene-age Faroe-Shetland basin on the European NE Atlantic margin. The islands are largely made up of Palaeocene-age basaltic lava units (the Faroe Islands Basalt Group: FIBG; part of the North Atlantic Igneous Province: NAIP) that were emplaced as a precursor to continental break up, and sea-floor spreading in the NE Atlantic. Deformation structures developed on the islands include variously oriented fault-sets (relating to anticlockwise rotation of the extension direction through time) and broad anticlines that form a trilete pattern centred on the islands. These deformation structures were formed and evolved immediately before, during and following continental break-up. This study documents the development of regionally syn-magmatic fault arrays, and contrasts these with later post-magmatic fault-reactivation at shallow burial depths and the development of, potentially, very high

  1. Contrasting geochemical and isotopic observations on the East Greenland and Hatton-Rockall conjugate margins, North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Kempton, P. D.; Chambers, L. M.; Hitchen, K.

    2003-04-01

    Basalts from the East Greenland margin show a temporal transition from N-MORB-like to Icelandic compositions, indicating that the Iceland plume was chemically zoned at the time of continental rupture, having a relatively undepleted core and a more depleted margin [1]. Using Hf-Nd isotope systematics, Kempton et al. [2] showed that the depleted margin is not, in fact, shallow N-MORB source mantle, but rather a depleted sheath surrounding the Iceland plume, probably derived from the thermal boundary layer at the base of the upper mantle. Furthermore, they found that basalts from SW of the Rockall Plateau (DSDP Site 553) and from Goban Spur (DSDP Sites 550-551) were isotopically distinct from those throughout the rest of the NAIP, plotting within the field of N-MORB in Hf-Nd isotope space. From this, Kempton et al. [2] suggested that the compositional influence of the Iceland plume did not reach this far south and east ~55 m.y. ago. However, the apparent lack of a compositional influence from the plume at Hatton Bank is surprising, considering the presence of seaward dipping reflector sequences. In an attempt to address this question, we have initiated a more comprehensive geochemical investigation of the volcanic rocks from the Rockall region, including new samples recently acquired from Rockall Bank (Aug. 2001) using the BGS rockdrill as well as previously existing core and dredge samples from in and around the Rockall Trough. Our new Nd and Hf isotope data show that magmas derived from both the N-MORB-source and the Iceland plume are present in the region. Interesting in this context is the recent observations of Hooper et al. (in press) that the early accretion history of N. Atlantic oceanic crust was asymmetrical: nearly twice the volume of material was emplaced on the Greenland margin relative to Hatton Bank, which may indicate east-directed ridge migration during initial opening. If so, this may explain the presence of both mantle types on the Rockall margin

  2. A comparative study of the particulate trace element geochemistry in two contrasting ocean margin environments in the Northeastern Atlantic

    NASA Astrophysics Data System (ADS)

    Chou, L.; Wollast, R.; Roevros, N.

    2003-04-01

    The present study was conducted during the Phases I and II of the Ocean Margin EXchange (OMEX) project, supported by the European Union in the framework of the MAST programme. The objective was to characterise the suspended matter by its composition with emphasis on trace elements in order to evaluate the sources, biogeochemical behaviour in the water column and fate of particulate material in two contrasting ocean margin environments: the Biscay margin and the Iberian margin. The Biscay margin is bordered by a wide continental plateau and a steep continental slope and rise, and is characterised by strong internal tides among many other physical processes with limited riverine input. In contrast, the Iberian margin is characterised by a narrow continental plateau receiving regularly continental input and by seasonal upwelling/downwelling that could influence significantly the chemical composition, transport and fluxes of particles in this region. Suspended matter in the water column along the two margins was sampled by various methods. These include 1) continuous centrifugation of surface waters, 2) in-situ filtration of large volumes of water at various depths using Stand Alone Pumps (SAPs), and 3) sediment traps. In addition to trace elements (Cr, Co, Ni, Cu, Zn Cd, Pb), the chemical composition of particulate matter collected was determined for major (Si, Al, Fe, Ca, POC/PN) and minor (Mg, Na, K, Mn) elements. Centrifugation samples allow the determination of the composition of surface suspended matter dominated by phytoplankton. SAP samples permit the assessment of the vertical evolution of suspended matter composition in the water column. Settling material intercepted by the sediment traps, are associated with large particles such as faecal pellets, marine snow and other aggregates. Trace metal geochemistry of the particulate matter in relation to the carbon cycle will be compared in the two margin environments investigated. Processes affecting the transfer

  3. Upper Jurassic and Lower Cretaceous facies relationships in a passive margin basin, western North Atlantic

    SciTech Connect

    Prather, B.E.

    1988-02-01

    Correlation of facies from hydrocarbon-bearing continental and transitional marine sandstones to time-equivalent high-energy shelf-margin carbonates provide insight into hydrocarbon habitats of the Baltimore Canyon basin. These facies occur within a thick (> 10,000 ft) prograded wedge of shelf sediments in this passive margin basin. Wells drilled to test structural closures in shallow-water (< 600 ft) areas of Baltimore Canyon penetrate clastic facies which are time-equivalent to the downdip carbonate facies tested in deep-water wells. Numerous hydrocarbon shows, including a noncommercial gas and gas-condensate accumulation, occur with sandstone units that were deposited in prograding continental/fluvial and transitional marine environments located updip of the Oxfordian/Kimmeridgian carbonate shelf edge. The continental and transitional facies are overlain by a fine-grained deltaic complex which forms a regionally extensive top seal unit. The deltaic complex was deposited during aggradation of the Kimmeridgian through Berriasian shelf-margin carbonates penetrated by the deep-water wells. Deep-water wells (> 5000 ft) drilled off the continental shelf edge to test large structural closures along the downdip termination of the Upper Jurassic/Lower Cretaceous carbonate shelf edge encountered no significant hydrocarbon shows. Reservoir rocks in these wells consist of (1) oolite grainstone which was deposited within a shoal-water complex located at the Aptian shelf edge, and (2) coral-stromatoporoid grainstone and boundstone which formed an aggraded shelf-margin complex located at the Kimmeridgian through Berriasian shelf edge. Structural closures with reservoir and top seals are present in both updip and downdip trends. The absence of hydrocarbon shows in downdip carbonate reservoirs suggests a lack of source rocks available to charge objectives at the shelf margin.

  4. Passive Seismic Experiment "13 BB Star" in the Margin of the East European Craton, Northern Poland

    NASA Astrophysics Data System (ADS)

    Polkowski, M.; Grad, M.; Wilde-Piórko, M.; Suchcicki, J.; Arant, T.

    2014-12-01

    Passive experiment "13 BB star" is dedicated to study deep structure of the Earth's interior in the marginal zone of the East European Craton in northern Poland. The seismic network consists of 13 broadband stations on the area of c. 120 km in diameter. The network is located in the area well recognized from the point of view velocities of sedimentary cover and crustal structure. Good records obtained since summer 2013, and expected during next 1.5 years long recording campaign, should yield images of detailed structure of the lithosphere-asthenosphere boundary (LAB), „410", "?520", and „660" km discontinuities, as well as mantle-core boundary and inner core. The LAB is investigated recently very effectively, mostly using seismic methods because their deep penetration and relatively good resolution. The nature of LAB is still debated, particularly under "cold" Precambrian shields and platforms. We show examples of local and teleseismic records, array transfer function of "13 BB star" network and preliminary noise analysis. National Science Centre Poland provided financial support for this work by NCN grant DEC- 2011/02/A/ST10/00284.

  5. Benthic foraminiferal assemblage formation: Theory and observation for the European Arctic margin

    NASA Astrophysics Data System (ADS)

    Loubere, Paul; Rayray, Shan

    2016-09-01

    We use theory and observation to determine how benthic foraminiferal populations living in a range of sedimentary microenvironments are translated into fossil assemblages along the continental margin of the European Arctic. We examine downcore stained (cell tracker green and rose Bengal) and total species shell abundances through the sediment mixing (bioturbation) zone. This, in combination with porewater geochemical measurements, allows us to establish zones of production and destruction for species' shells, and deduce how the fossil record is being generated by the living community. For many taxa, shell production is high in the upper, oxic, sedimentary layer, but destruction in this zone is also high. Hence, contribution to the fossil record is biased to more infaunal populations and species. Taxa producing near, or below, the anoxic boundary of the sediments are particularly important to the developing fossil record of the fjord environment. We find that taxon relative and absolute abundances change continuously through the biologically active sediment profile. This has implications for reconstructing paleoenvironments using benthic foraminiferal assemblages, and potentially for the geochemistry of individual fossil taxa.

  6. Did Upper Cretaceous Intrusions reactivate Pre-Cretaceous structures at the South Atlantic passive continental margin of Brazil?

    NASA Astrophysics Data System (ADS)

    Glasmacher, Ulrich Anton; De Souza Silva, Jaqueline; Hackspacher, Peter Christian; Doranti-Tiritan, Carolina

    2014-05-01

    "Passive" continental margins especially of the South Atlantic Ocean are perfect locations to quantify exhumation, rock uplift, and surface uplift rates, model the long-term landscape evolution and provide information on the influence of mantle processes on a longer time scale. Furthermore, these passive margin allow to study the influence of large intrusions on the reactivation of Pre-Intrusion structures. In Southern Brazil, the Poços de Caldas intrusion (83 Ma) took place in Neoproterozoic para-metamorphic rocks of amphibolite facies, which are deformed and metamorphosed during the Central Brazilian Orogeny (630 Ma - 510 Ma). The compressional deformation caused major N-S trending transform faults, and related perpendicular structures. In the Serra da Mantiqueira and Serra do Mar to the East, these N-S trending transform structures are reactivated at about 120 Ma. Together with the surrounding Precambrian metamorphic rocks the Poços de Caldas Intrusion forms the Poços de Caldas Plateau reaching elevatiosn between 900 m.a.s.l. and 1300 m.a.s.l. The intrusion covers an area of 800 km². The presentation will provide data and discuss the influence of the large intrusion on Pre-Intrusion structures within the surrounding metamorphic basement.

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

    NASA Astrophysics Data System (ADS)

    Shahraki, Meysam; Schmeling, Harro; Haas, Peter

    2016-04-01

    Isostatic equilibrium is a good approximation for passive continental margins. In these regions, geoid anomalies are proportional to the local dipole moment of density-depth distributions, which can be used to constrain the thickness of lithospheric jumps and corresponding tectonic stress. We analysed satellite derived geoid data and, after filtering, extracted typical averaged profiles across the Western and Eastern passive margins of the South Atlantic. They show geoid jumps of 8.1 m and 7.0 m for the Argentinian and African sides, respectively. Together with topography data and reasonable assumptions about densities these jumps are interpreted as isostatic geoid anomalies and yield best-fitting crustal and lithospheric thicknesses. They reveal a small asymmetry between the African and S-American crusts and lithospheres by a few kilometers. On both sides, the continental lithosphere is about 15 - 30km thicker than the oceanic lithosphere. To keep such geoid jumps stable over O(100Ma) fully dynamic models show that lithospheric viscosities must be of the order of 1e23 Pa s.

  8. K-Ar ages and the opening of the South Atlantic Ocean: Basaltic rock from the Brazilian margin

    USGS Publications Warehouse

    Fodor, R.V.; McKee, E.H.; Asmus, H.E.

    1983-01-01

    New K-Ar ages for 13 samples of basalt, gabbro, wehrlite, and trachyandesite drilled from the Brazilian continental shelf and coastline yield information about the timing of the opening of the South Atlantic and the nature of the crust seaward from the Brazil margin. The oldest basalt is 138.1 ?? 3.5 m.y. old and from offshore at 24.5??S; it represents Serra Geral flood basalt on attenuated crust in the Santos basin. Basalts from the coastline at 19.5??S are mixed with terrigenous graben sediments, and their ages confirm that rifting was underway before 130 m.y. Offshore sites in the Campos basin, ???22??-23??S, 41??W, have basalt ranging from 124 to 112 m.y. in age and mostly continental flood basalt in composition. One 112-m.y. basalt, however, is MORB-like and could therefore represent oceanic lithosphere mixed with continental crust about 50 km from the shoreline at ???22.5??S. Other samples reveal compositionally varied intraplate, passive-margin magmatism occurring 75-43 m.y. ago. They correlate with profuse contemporary alkalic magmatism on the southeastern Brazil coast and probably represent reactivation of zones of "weakness" (i.e., fracture zone-lineaments). ?? 1983.

  9. Astronomical tuning for the upper Messinian Spanish Atlantic margin: Disentangling basin evolution, climate cyclicity and MOW

    NASA Astrophysics Data System (ADS)

    van den Berg, B. C. J.; Sierro, F. J.; Hilgen, F. J.; Flecker, R.; Larrasoaña, J. C.; Krijgsman, W.; Flores, J. A.; Mata, M. P.; Bellido Martín, E.; Civis, J.; González-Delgado, J. A.

    2015-12-01

    We present a new high-resolution cyclostratigraphic age model for the Messinian sediments of the Montemayor-1 core. This core was drilled in the Guadalquivir Basin in southern Spain, which formed part of the marine corridor linking the Mediterranean with the Atlantic in the Late Miocene. Tuning of high-resolution geochemical records reveals a strong precessional cyclicity, with maximum clastic supply from river run off coinciding with maximum summer insolation. We recognize a gradual change in the nature of the typical cyclic fluctuations in elemental compositions of the sediments through the core, which is associated with a gradual change in depositional environment as the basin infilled. After applying the new age model, the upper Messinian glacial stages and deglaciation are clearly identified in the oxygen isotope records of the Montemayor-1 core. Reinterpretation of existing planktonic and benthic oxygen isotope records for the core and comparison with equivalent successions in the Rifian Corridor in northern Morocco allow the re-evaluation of the influence of the different water masses in the region: North Atlantic Central Water and Mediterranean Outflow Water. We observe no direct influence of MOW immediately before or during the Messinian Salinity Crisis.

  10. Modeling study of North-Atlantic millennial-timescale variability imprint on Western European loess deposits

    NASA Astrophysics Data System (ADS)

    Sima, A.; Rousseau, D.-D.; Kageyama, M.; Ramstein, G.; Schultz, M.; Balkanski, Y.; Antoine, P.; Dulac, F.; Hatté, C.

    2009-04-01

    Studies on loess sequences of Western Europe have shown (i) that the loess sedimentation pattern over the last glaciation (approximately 100 to 15 thousand years before present (kyr BP)) has been very similar throughout the European loess belt, indicating a common climate control, and (ii) that the rapid environmental changes on the continent are correlated with the North-Atlantic millennial-timescale variations, the so-called Dansgaard-Oeschger (DO) and Heinrich (H) events. Here we test, by means of numerical modelling, if, and by which mechanisms, the dust cycle response to the environmental changes induced by the DO and H events could have led to the recording of these events in the loess deposits of the Western Europe. The LMDZ atmosphere general circulation model, in a version with a stretched grid enhancing the resolution over Western Europe to 60km, is used to simulate (a) a reference glacial state, assimilated to a DO stadial (DOS), (b) a cold perturbation over the North Atlantic, resembling a H event, and (c) a warm perturbation, assimilated to a DO interstadial (DOI). The reference state corresponds to the 40-kyr BP context, in the middle of the typical glacial period (approximately 75 to 15 kyr BP). The subsequent perturbations are obtained by applying cold or warm anomalies of up to 2°C in absolute value to the North-Atlantic sea-surface temperatures in the latitudinal band 30° - 63°N. The three simulated climate states are compared from the point of view of the initial driver of the dust cycle, the dust emission. A detailed analysis is provided for the English Channel and the south of the North Sea (ECSNS), important deflation areas in glacial times, and a source for the Western European loess deposits. In our experiments, the impact of altering the North-Atlantic surface conditions is weak over the ECSNS and loess areas (roughly, the latitudinal band 48° - 53°N) with respect to wind and precipitation. When only considering these factors, and the

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

    NASA Astrophysics Data System (ADS)

    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.

  12. US Atlantic Margin Methane Plumes Identified From Water Column Backscatter Data Acquired by NOAA Ship Okeanos Explorer

    NASA Astrophysics Data System (ADS)

    Kodis, M.; Skarke, A. D.; Ruppel, C. D.; Weber, T.; Lobecker, E.; Malik, M.

    2013-12-01

    The NOAA Office of Ocean Exploration and Research routinely uses NOAA Ship Okeanos Explorer to collect EM302 (30 kHz) multibeam bathymetric data and water column backscatter imagery. These backscatter data have been used to identify gas plumes associated with seafloor methane seeps as part of previous investigations in the Gulf of Mexico and at Blake Ridge. Here, we use QPS Fledermaus Midwater software to analyze over 200,000 km2 of multibeam data acquired on the continental slope and outer shelf of the US Atlantic margin in 2011, 2012, and 2013. Preliminary application of this analytical methodology in late 2012 revealed the first deepwater (> 1000 m water depth) cold seeps found on the US Atlantic margin north of Cape Hatteras as well as 47 new upper slope seeps (http://www.noaanews.noaa.gov/stories2012/20121219_gas_seeps.html). In this new analysis, we identify over 500 water column backscatter anomalies (WCA) originating at the seafloor and extending to various heights in the water column between Cape Hatteras and the Nantucket margin. Data set quality control was achieved through secondary independent analysis of all WCA backscatter records by a highly experienced researcher who assigned a quality factor to each anomaly. Additionally, a subset of the data was analyzed using a Matlab code designed to automatically detect WCA in backscatter data. These quality-control and WCA comparison procedures provide confidence that several hundred of the WCA are robust picks. The observed WCA are structurally consistent with previously confirmed gas bubble plumes, being vertically elongate, rooted at the seafloor, and deflected by currents. They are not structurally consistent with other common WCA such as schooling or swarming organisms. Additionally, the bases of selected WCA that were identified in this analysis have recently been visually and acoustically confirmed to be associated with emission of gas bubbles from the seafloor by the NOAA remotely operated vehicle

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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

  15. Geomorphic characterization of four shelf-sourced submarine canyons along the U.S. Mid-Atlantic continental margin

    USGS Publications Warehouse

    Obelcz, Jeffrey; Brothers, Daniel S.; Chaytor, Jason D.; ten Brink, Uri S.; Ross, Steve W.; Brooke, Sandra

    2013-01-01

    Shelf-sourced submarine canyons are common features of continental margins and are fundamental to deep-sea sedimentary systems. Despite their geomorphic and geologic significance, relatively few passive margin shelf-breaching canyons worldwide have been mapped using modern geophysical methods. Between 2007 and 2012 a series of geophysical surveys was conducted across four major canyons of the US Mid-Atlantic margin: Wilmington, Baltimore, Washington, and Norfolk canyons. More than 5700 km2 of high-resolution multibeam bathymetry and 890 line-km of sub-bottom CHIRP profiles were collected along the outer shelf and uppermost slope (depths of 80-1200 m). The data allowed us to compare and contrast the fine-scale morphology of each canyon system. The canyons have marked differences in the morphology and orientation of canyon heads, steepness and density of sidewall gullies, and the character of the continental shelf surrounding canyon rims. Down-canyon axial profiles for Washington, Baltimore and Wilmington canyons have linear shapes, and each canyon thalweg exhibits morphological evidence for recent, relatively small-scale sediment transport. For example, Washington Canyon displays extremely steep wall gradients and contains ~100 m wide, 5–10 m deep, v-shaped incisions down the canyon axis, suggesting modern or recent sediment transport. In contrast, the convex axial thalweg profile, the absence of thalweg incision, and evidence for sediment infilling at the canyon head, suggest that depositional processes strongly influence Norfolk Canyon during the current sea-level high-stand. The north walls of Wilmington, Washington and Norfolk canyons are steeper than the south walls due to differential erosion, though the underlying cause for this asymmetry is not clear. Furthermore, we speculate that most of the geomorphic features observed within the canyons (e.g., terraces, tributary canyons, gullies, and hanging valleys) were formed during the Pleistocene, and show only

  16. SeepC: Preliminary Characterization of Atlantic Margin Seep Ecosystems from Norfolk Canyon to New England Seep Sites.

    NASA Astrophysics Data System (ADS)

    Turner, P. J.; Ball, B.; Cole, E.; LaBella, A.; Wagner, J.; Van Dover, C. L.; Skarke, A. D.; Ruppel, C. D.

    2015-12-01

    Since 2013, more than 500 seep sites have been located along the continental margin of the eastern US using acoustic signals of gas plumes in the water column. During a July 2015 R/V Atlantis expedition, scientists used the submersible Alvin to explore seep sites at depths of 300 to 1500 m. Study sites ranged from Norfolk Canyon north to New England Seep 2 and included Baltimore, Veatch, and Shallop Canyon sites, as well as new unnamed sites between Norfolk and Baltimore Canyons. Mussels dominated the seep sites (cf ''Bathymodiolus'' childressi) but only small populations (<10s of individuals) were observed at seep sites associated with Shallop Canyon. B. heckerae, the dominant mussel at the Blake Ridge and Cape Fear seep sites (sites associated with salt diapirs off the Carolinas), appear to be present at only one of the Atlantic Margin seeps. At the Norfolk Canyon site, dead B. heckerae shells were observed and live individuals may be within the explored area. The abundant vesicomyid clam of Blake Ridge and Cape Fear sites was absent at the continental margin seeps. Apart from B. childressi, the most conspicuous megafaunal invertebrate species at the newly explored seeps was the red crab, Chaceon sp. and the rock crab, Cancer sp. These crabs are not seep endemic but they were especially abundant at the seeps and were observed to feed and mate on the seep grounds. Molecular tools will be used to explore the genetic structure of mussel populations from Norfolk to New England seeps, and stable isotope methods will be used to test for differences among sites in the source of carbon used by mussels. Alvin video transects and photo-mosaics will be used to collect data on macrofauna associated with seeps and to test the hypothesis that shallow seeps (300-500m) support more diverse assemblages than deep sites (1000-1500m).

  17. Parasites as biological tags in marine fisheries research: European Atlantic waters.

    PubMed

    Mackenzie, K; Hemmingsen, W

    2015-01-01

    Studies of the use of parasites as biological tags for stock identification and to follow migrations of marine fish, mammals and invertebrates in European Atlantic waters are critically reviewed and evaluated. The region covered includes the North, Baltic, Barents and White Seas plus Icelandic waters, but excludes the Mediterranean and Black Seas. Each fish species or ecological group of species is treated separately. More parasite tag studies have been carried out on Atlantic herring Clupea harengus than on any other species, while cod Gadus morhua have also been the subject of many studies. Other species that have been the subjects of more than one study are: blue whiting Micromesistius poutassou, whiting Merlangius merlangus, haddock Melanogrammus aeglefinus, Norway pout Trisopterus esmarkii, horse mackerel Trachurus trachurus and mackerel Scomber scombrus. Other species are dealt with under the general headings redfishes, flatfish, tunas, anadromous fish, elasmobranchs, marine mammals and invertebrates. A final section highlights how parasites can be, and have been, misused as biological tags, and how this can be avoided. It also reviews recent developments in methodology and parasite genetics, considers the potential effects of climate change on the distributions of both hosts and parasites, and suggests host-parasite systems that should reward further research. PMID:24722002

  18. North-Atlantic millennial-timescale variability imprint on Western European loess deposits: a modeling study

    NASA Astrophysics Data System (ADS)

    Sima, A.; Rousseau, D.; Kageyama, M.; Ramstein, G.; Schulz, M.; Balkanski, Y.; Antoine, P.; Dulac, F.; Hatte, C.

    2008-12-01

    We test if the dust cycle response to the North-Atlantic abrupt climate changes, the Dansgaard-Oeschger (DO) and Heinrich (H) events, could have led to the recording of these events in the Western European loess deposits. The LMDZ AGCM is used to simulate a reference glacial state "DOS", assimilated to a DO stadial, a cold perturbation "HE", resembling a H event, and a warm perturbation "DOI", assimilated to a DO interstadial. The reference state corresponds to the 40-kyr BP context, in the middle of the typical glacial period (75-15 kyr BP). The two perturbations are obtained by applying cold, respectively warm anomalies of up to 2°C to the North-Atlantic surface temperatures in the latitudinal band 30°- 63°N. The simulated climates are compared from the point of view of dust emission, with a focus on the English Channel and the south of the North Sea (ECSNS), important dust sources for the Western European loess deposits. When only considering the changes in wind, precipitation, soil moisture and snow cover over the ECSNS and loess deposit areas, the differences of dust emission flux between the simulations are small, in contradiction with the observed stadial-interstadial loess sedimentation rate variations. However, when including the vegetation effect of inhibiting the eolian erosion, the three climates are clearly differentiated, the dust flux for DOI becoming less than half of that for DOS and HE. This shows that vegetation changes have played a key role in the stadial-interstadial dust cycle variations.

  19. Storm activity in North Atlantic and precipitation anomalies in European region during winter seasons

    NASA Astrophysics Data System (ADS)

    Vyazilova, N. A.; Vyazilova, A. E.

    2009-09-01

    The purpose of this paper is to show the storm activity influence on the formation of wet and dry zone in North Atlantic and European region during winter seasons 1994/95, 2006/07 and 2007/08 years with positive mode of NAO, 1995/96, 2000/01 and 2005/06 years with negative mode of NAO. The study of storm activity includes the analyses of cyclonic intensity and cyclone track number. Analyses of cyclonic intensity based on calculation cyclone centers number (CCN) and sum of cyclone centers MSLP anomalies (CCMA). This analyses based on automated cyclone tracking algorithm and the 6-hourly MSLP from the NCEP/NCAR reanalyses 2 from 1979 to 2009. Precipitation anomalies were calculated from CMAP archive. Analyses had included the calculation of cyclone track number in all region [30°N-80°N, 50°W-70°E]and selected latitude zone for long cyclones (with lifetime more 2 day) and short cyclones (with lifetime less 2 day). The study had shown the special features of CCN and CCMA patterns in region for long and short cyclones. The study shows, that every winter season short cyclone track number twice as much long cyclone track number. However, the contribution of long cyclones in main determines the CCMA in region. Study had shown that winter seasons with positive NAO mode Nord Europe were outstanding by strong positive precipitation anomalies and strong cyclonic intensity, and during winter seasons with negative NAO mode in this region were observed negative precipitation anomalies and weak cyclonic activity. Standartizide anomalies of integral CCMA for selected latitude zone [55°N-80°N, 50°W-70°E] had shown the intensification of cyclonic activity over North Atlantic and North European region in last years.

  20. European high-impact weather caused by the downstream response to the extratropical transition of North Atlantic Hurricane Katia (2011)

    NASA Astrophysics Data System (ADS)

    Grams, Christian M.; Blumer, Sandro R.

    2015-10-01

    Tropical cyclones undergoing extratropical transition (ET) are thought to cause high-impact weather (HIW) close to the transitioning tropical cyclone and in remote regions. However, no study so far clearly attributed European HIW to the downstream impact of North Atlantic ET. When Hurricane Katia underwent ET in September 2011, severe thunderstorms occurred downstream in Central Europe. We quantify the role of Katia in the European HIW, using numerical sensitivity experiments. Results show that Katia was crucial for the evolution of a narrow downstream trough. Large-scale forcing for ascent ahead of this trough triggered deep convection. In the absence of ET, no trough was present over Europe and no HIW occurred. This study is the first unambiguous documentation that European HIW is caused by the downstream impact of North Atlantic ET and would not occur otherwise. It likewise corroborates the crucial role of ET in altering the large-scale midlatitude flow in downstream regions.

  1. European high-impact weather caused by the downstream response to the extratropical transition of North Atlantic Hurricane Katia (2011)

    NASA Astrophysics Data System (ADS)

    Blumer, Sandro R.; Grams, Christian M.

    2016-04-01

    Tropical cyclones undergoing extratropical transition (ET) are thought to cause high-impact weather (HIW) close to the transitioning tropical cyclone and in remote regions. However, no study so far clearly attributed European HIW to the downstream impact of North Atlantic ET. When Hurricane Katia underwent ET in September 2011, severe thunderstorms occurred downstream in Central Europe. We quantify the role of Katia in the European HIW, using numerical sensitivity experiments. Results show that Katia was crucial for the evolution of a narrow downstream trough. Large-scale forcing for ascent ahead of this trough triggered deep convection. In the absence of ET, no trough was present over Europe and no HIW occurred. This study is the first unambiguous documentation that European HIW is caused by the downstream impact of North Atlantic ET and would not occur otherwise. It likewise corroborates the crucial role of ET in altering the large-scale midlatitude flow in downstream regions.

  2. Deep sea corals and carbonate mounds of the nw european margin: a biogeochemical perspective

    NASA Astrophysics Data System (ADS)

    Kiriakoulakis, K.; White, M.; Bett, B.; Wolff, G. A.

    2003-04-01

    The deep-sea, scleractinian, reef-forming coral Lophelia pertusa is widespread along the NW European Continental Margin and its presence has been documented since the 19th century. However little is known about its ecology, biochemistry and particularly its relationship with the carbonate mounds it is often associated with. The characterisation of particulate organic matter (POM), which fuels the Lophelia pertusa ecosystems and the sediments on and around the coral/mound sites, may potentially shed light on the biogeochemical processes of the deep water coral (DWC) ecosystems. In this study, POM (20--40 m above bottom) and sediments have been collected from five mound/coral sites along the European Continental Slope (water depth ˜500--1000 m) with distinct oceanographic and sedimentological conditions, (Darwin, Logachev, Pelagia, Hovland and Belgica Mounds located around the Rockall Trough and Porcupine Seabight). Coral densities and mound sizes, shapes and conditions vary significantly from site to site. POM at these sites are significantly different, particularly with respect to the lipid concentrations relative to organic carbon, which are much higher at the Darwin Mounds (N.Rockall Trough; ˜1000m depth) than the rest of the sites (46.63 -- 225.11 mg g-1 and 0.49 -- 14.21 mg g-1 respectively). Polyunsaturated fatty acids (PUFAs), which are used as proxies of labile organic matter are also abundant at the Darwin Mounds, indicating that POM is 'fresh'. Scanning electron microscopy carried out on filtered material from this area confirms this. These mounds are affected by a branch of the poleward slope current, which, in combination with enhanced Ekman downwelling, could transport appreciable amounts of high quality organic matter to the depth that they are found. Lipid (including PUFAs) concentrations at the Pelagia Mounds (SE Rockall Trough; ˜700 m) although lower than at the Darwin Mounds are higher than at the other sites. This location is also influenced by

  3. Analysis of Submarine Landslides and Canyons along the U.S. Atlantic Margin Using Extended Continental Shelf Mapping Data

    NASA Astrophysics Data System (ADS)

    Chaytor, J. D.; Brothers, D. S.; Ten Brink, U. S.; Hoy, S. K.; Baxter, C.; Andrews, B.

    2013-12-01

    U.S. Geological Survey (USGS) studies of the U.S. Atlantic continental slope and rise aim to understand the: 1) the role of submarine landslides in tsunami generation, and 2) the linkages between margin morphology and sedimentary processes, particularly in and around submarine canyon systems. Data from U.S. Extended Continental Shelf (ECS) and numerous subsequent mapping surveys have facilitated the identification and characterization of submarine landslides and related features in fine detail over an unprecedented spatial extent. Ongoing analysis of USGS collected piston cores, sub-bottom and multichannel seismic (MCS) reflection profiles, and an extensive suite of legacy MCS data from two landslides, the Southern New England landslide zone and the Currituck Landslide, suggest that the most recent major landslide events are pre-Holocene, but that failures were complex and most likely multi-phase, at times resulting in extensive overlapping debris deposits. Piston core records plus visual observations of the seafloor from recent TowCam deployments and NOAA Ship Okeanos Explorer ROV dives reveal ongoing development of colluvial wedge-style debris aprons at the base of scarps within these landslides, showing that these regions continue to evolve long after the initial failure events. Multibeam bathymetry data and MCS profiles along the upper slope reveal evidence for vertical fluid migration and possible seabed gas expulsion. These observations underscore the need to reevaluate the sources of pore fluid overpressure in slope sediments and their role in landslide generation. ECS and more recent multibeam mapping have provided the opportunity to investigate the full extent of submarine canyon morphology and evolution from Cape Hatteras up to the US-Canadian EEZ, which has led to better understanding of the important role of antecedent margin physiography on their development. Six submarine canyon systems along the margin (Veatch, Hydrographer, Hudson, Wilmington

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

    NASA Astrophysics Data System (ADS)

    Trumbull, R. B.

    2013-12-01

    after breakup. Unexpected are the implied short time and spatial scales of topographic variations, which challenge conventional wisdom on how passive margins evolve. These variations in surface topography are critical observables for testing models of shallow vs. deep-mantle buoyancy effects. Studies of sedimentary basins offshore complement the denudation studies and are linked with 3D lithospheric models of the margins. A group of projects examines structures, sedimentary sequences and thermal/subsidence histories of selected conjugate basins, and finds major asymmetries. Allied studies of hydrocarbon systems in the basins involve mapping present and paleo gas escape/sequestration features (mud volcanoes, pockmarks, gas chimneys) combined with 3D petroleum systems models. Relating the offshore sedimentary record to lithospheric dynamics requires understanding effects of paleo-oceanography. Major changes in Atlantic circulation due to tectonic events and the geometry of the ocean basin are recorded in erosive and depositional features of offshore sediments. SAMPLE projects use high-resolution seismic data to map and date these features, and in a further step, to study the influence of paleo-ocean circulation on global climate using coupled atmosphere-ocean models.

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

    PubMed Central

    Therkildsen, Nina Overgaard; Hemmer-Hansen, Jakob; Hedeholm, Rasmus Berg; Wisz, Mary S; Pampoulie, Christophe; Meldrup, Dorte; Bonanomi, Sara; Retzel, Anja; Olsen, Steffen Malskær; Nielsen, Einar Eg

    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 spanning major demographic changes. Analyzing >900 gene-associated single nucleotide polymorphisms in 847 individuals, we identified four genetically distinct groups that exhibited varying spatial distributions with considerable overlap and mixture. The genetic composition had remained stable over decades at some spawning grounds, whereas complete population replacement was evident at others. Observations of elevated differentiation in certain genomic regions are consistent with adaptive divergence between the groups, indicating that they may respond differently to environmental variation. Significantly increased temporal changes at a subset of loci also suggest that adaptation may be ongoing. These findings illustrate the power of spatiotemporal population genomics for revealing biocomplexity in both space and time and for informing future fisheries management and conservation efforts. PMID:23789034

  6. 3-D view of erosional scars on U. S. Mid-Atlantic continental margin

    SciTech Connect

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

    1985-06-01

    Deep-towed side-scan and bathymetric data have been merged to present a 3-D view of the lower continental slope and upper continental rise offshore Atlantic City, New Jersey. Carteret Canyon narrows and becomes nearly stranded on the lower slope where it leads into one of two steep-walled, flat-floored erosional chutes. The floors of the chutes, cut into semilithified middle Eocene siliceous limestones, are marked by downslope-trending grooves. The grooves are interpreted to be gouge marks formed during rock and sediment slides. On the uppermost rise, beneath the chutes, is a 40-m deep depression. The origin of the depression is believed to be related to material moving downslope and encountering the change in gradient at the slope/rise boundary. Downslope of the depression are channels, trails, and allochthonous blocks. The lack of significant post-early Miocene deposits implies that the lower slope offshore New Jersey has yet to reach a configuration conducive to sediment accumulation. The age of erosion on the lower slope apparently ranges from late Eocene-early Miocene to the recent geologic past.

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

    USGS Publications Warehouse

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

    2016-01-01

    study is the first investigation of seep infauna along the U.S. Atlantic slope north of the Blake Ridge Diapir and provides a baseline for future regional comparisons to other seep habitats along the Atlantic margin.

  8. Thermal history and long-term evolution of the South Atlantic passive continental margin, Kaoko belt, NW Namibia

    NASA Astrophysics Data System (ADS)

    Menges, D. P.; Glasmacher, P. A.

    2013-12-01

    From Permo-Carboniferous to Mid Jurassic the Kaoko belt in northwestern Namibia was affected by deep erosion of the Damara Sequence, Permo-Triassic collisional processes along the southern margin of Gondwana (Coward & Daly 1984), and the deposition of the Karoo Supergroup. The lithostratigraphic units consist of Proterozoic and Cambrian metamorphosed rocks with ages of 534 (7) Ma to 481 (25) Ma (Miller 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 (Stewart 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 about the major processes controlling the landscape evolution in this region. The poster will present thermochronological data, t-T-models and exhumation rates for the Kaoko belt, NW Namibia. 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. Miller, R. M., 1983. Evolution of the Damara Orogen, Vol. 11, Geological Society, South Africa Spec. Pub.. Stewart, K. S., Turner, S., Kelly, S., Hawkesworth, C. J., Kirstein, L. and Mantovani, M. S. M., 1996. 3D 40Ar-39Ar geochronology in the Paraná continental flood basalt province, Earth and Planetary Science Letters 143: 95-110.

  9. Benthic foraminiferal distributions on the Uruguayan continental margin (South-western Atlantic) and controlling environmental factors

    NASA Astrophysics Data System (ADS)

    de Mello, Camila; Burone, Leticia; Ortega, Leonardo; Franco-Fraguas, Paula; Lahuerta, Nuria; Mahiques, Michel; Marin, Yamandu

    2014-12-01

    The data on benthic foraminifera analysed from 110 box-core samples collected on the Uruguayan continental margin (outer shelf and upper and middle slope, between 36.54-34.64°S and 51.66-53.71°W) were used to evaluate the distribution of the benthic foraminiferal fauna and its relationship with selected abiotic parameters. Primary productivity (PP) and the organic flux (Jz) reaching the sea floor were also estimated for comparison with the foraminiferal distributions. The study area was characterised by elevated PP and Jz values, mainly in the southernmost region, which were associated with thermohaline fronts due to the presence of the Subtropical Shelf Front. The dominant identified taxa were Rhumblerella sepetibaensis (this is the first study recording the ecology of this species) and the opportunistic species Epistominella exigua, Bulimina spp. and Reophax fusiformis, which displayed maximal densities at the southernmost stations, concurrent with the highest Jz levels. The dominant species and vertical foraminiferal distributions responded to the different environmental conditions impacting the area (e.g. PP, grain size, nutrient content), which were most likely related to the hydrodynamic conditions. Hydrodynamic conditions cause differences in PP according to the locations of water masses and their fronts at the surface, according to the depth and current intensity; they determined energetic differences across the benthic environment, controlling organic matter sedimentation as well as grain size, which influenced oxygen availability within sediments.

  10. Behavioural adaptations of two sympatric sandhoppers living on a mesotidal European Atlantic sandy beach

    NASA Astrophysics Data System (ADS)

    Bessa, Filipa; Marques, João Carlos; Scapini, Felicita

    2014-06-01

    Behavioural adaptations of supralittoral species on sandy beaches are expressed as responses to environmental changes and constitute a key factor in their survival and evolution. Two sympatric talitrid amphipods (Talitrus saltator and Britorchestia brito) from a mesotidal exposed sandy beach on the European Atlantic coast (Portugal) were compared as regards orientation and littoral zonation patterns under natural conditions. Orientation experiments were carried out during spring and summer 2011 and 2012 at Quiaios beach, a highly dynamic exposed sandy beach. Multiple regression models were fitted to the angular data and the environmental effects on orientation were investigated for each species. Both talitrids were shown to be well orientated towards the shoreline and finely adapted to the mesotidal environment but a different use of local cues and climatic features between the two species was apparent. T. saltator showed a lower precision in the orientation performance (with a bimodal distribution sea- and land-wards), with less dependence on the sun cues and higher dependence on climatic features. In addition, the zonation of T. saltator was across the land-sea axis during both seasons. For B. brito the landscape vision, sun visibility and the tidal range enhanced the orientation to the shoreline. On this mesotidal Atlantic beach, T. saltator appeared to have a more flexible orientation with respect to B. brito, which appeared to be more dependent on the conditions offered by the intertidal zone, a behaviour confirmed by its restricted zonation below the high tide mark. Consequently, T. saltator showed a more flexible behaviour that may be considered an important evolutionary adaptation to dynamic and mesotidal sandy beaches.

  11. The deep structure of the South Atlantic rifted margins and the implications of the magmatic processes for the break-up

    NASA Astrophysics Data System (ADS)

    Becker, Katharina; Dieter, Franke; Trumbull, Robert; Schnabel, Michael; Heyde, Ingo; Schreckenberger, Bernd; Koopmann, Hannes; Bauer, Klaus; Jokat, Wilfried; Krawczyk, Charlotte

    2014-05-01

    The high velocity lower crust HVLC (Vp > 7km/s) together with seaward dipping reflectors (SDRs) and continental flood basalts are specific characteristics of volcanic rifted margins. The nature and origin of the HVLC is still under discussion. Here we provide a comprehensive study of the deep crustal structure of the South Atlantic rifted margins in which we focus on variations in the distribution and size of HVLC bodies along and across the margins. Two new and five existing refraction lines complemented by gravity models cover the area between the Rio Grande Rise - Walvis Ridge to the Falkland Agulhas Fracture Zone. Three seismic lines on the South American margin outline the change from a non-magmatic margin (lacking seaward dipping reflectors) in the south to a well-developed volcanic rifted margin off Uruguay in the north. While the HVLC exhibit a consistent increase in the cross-sectional area along both margins from South to North, we observe a major asymmetry across the margins. The African margin has about two-three times thicker and four times more voluminous HVLC than the South American margin. Importantly, the erupted lavas in the Etendeka-Paraná Provinces show the opposite asymmetry. Also the spatial position of the HVLC with regard to the inner SDRs 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 segment, HVLC is centered under the SDRs inner wedge but in the north, HVLC also extends further seawards. These observations question a simple extrusive/intrusive relationship between SDRs and HVLC, and they imply differences in the timing of the HVLC formation during the rifting and break-up process. We conclude that the HVLC is predominantly a magmatic feature related mantle melting during break-up. Melt generation models suggest that the greater thickness of HVLC on the African margin is due to active upwelling combined with elevated

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  13. The North American Atlantic outer continental margin landslides data base: Summary and observations

    SciTech Connect

    Booth, J.S.; O'Leary, D.W. )

    1990-06-01

    A compilation of published data from 179 Quaternary mass movement features was analyzed to determine the common attributes of the slides, to reveal general trends, and to classify and compare slide types. The data set was derived primarily from high-resolution, seismic-reflection data and sidescan-sonar images. In general, evidence of slope failure is found throughout the length of the margin and in all water depths. Slides have occurred on slope angles ranging from 1{degree} to 30{degree} (avg.{approximately}5{degree}); they vary in width from 0.2 to 50 km (avg. {approximately}4 km) and in length from 0.3 to 380 km (avg. {approximately}10 km) and have been reported to be as thick as 650 m. They are slightly more prevalent on open slopes than in other physiographic settings (e.g., canyons, ridges, spurs) and more commonly translational than rotational (i.e., slumps). The slides show no striking affinity for a particular depth range, either in the data set as a whole or when analyzed in terms of physiographic setting, size, slope angle, or other basis for classification. Comparison of slides found on the open slope with those found within canyons shows that the average open slope slide tends to occur at lower slope angles and is much larger (by an order of magnitude) than the average canyon slide. Regardless of the physiographic setting or other characteristic, large-scale slides (area >100 km{sup 2}) rather than small-scale slides (area <10 km{sup 2}) tend to be associated with gentle slopes ({approximately}3-4{degree}) Similarly, slides generated on steep slopes ({>=}10{degree}), regardless of other attributes, tend to be small (avg. area <5 km{sup 2}). With few exceptions, comparisons between slide categories show only minor differences.

  14. The Iceland plume in space and time: a Sr-Nd-Pb-Hf study of the North Atlantic rifted margin

    NASA Astrophysics Data System (ADS)

    Kempton, P. D.; Fitton, J. G.; Saunders, A. D.; Nowell, G. M.; Taylor, R. N.; Hardarson, B. S.; Pearson, G.

    2000-04-01

    New Sr-Nd-Pb-Hf data require the existence of at least four mantle components in the genesis of basalts from the the North Atlantic Igneous Province (NAIP): (1) one (or more likely a small range of) enriched component(s) within the Iceland plume, (2) a depleted component within the Iceland plume (distinct from the shallow N-MORB source), (3) a depleted sheath surrounding the plume and (4) shallow N-MORB source mantle. These components have been available since the major phase of igneous activity associated with plume head impact during Paleogene times. In Hf-Nd isotope space, samples from Iceland, DSDP Leg 49 (Sites 407, 408 and 409), ODP Legs 152 and 163 (southeast Greenland margin), the Reykjanes Ridge, Kolbeinsey Ridge and DSDP Leg 38 (Site 348) define fields that are oblique to the main ocean island basalt array and extend toward a component with higher 176Hf/ 177Hf than the N-MORB source available prior to arrival of the plume, as indicated by the compositions of Cretaceous basalts from Goban Spur (˜95 Ma). Aside from Goban Spur, only basalts from Hatton Bank on the oceanward side of the Rockall Plateau (DSDP Leg 81) lie consistently within the field of N-MORB, which indicates that the compositional influence of the plume did not reach this far south and east ˜55 Ma ago. Thus, Hf-Nd isotope systematics are consistent with previous studies which indicate that shallow MORB-source mantle does not represent the depleted component within the Iceland plume [Thirlwall, J. Geol. Soc. London 152 (1995) 991-996; Hards et al., J. Geol. Soc. London 152 (1995) 1003-1009; Fitton et al., Earth Planet. Sci. Lett. 153 (1997) 197-208]. They also indicate that the depleted component is a long-lived and intrinsic feature of the Iceland plume, generated during an ancient melting event in which a mineral (such as garnet) with a high Lu/Hf was a residual phase. Collectively, these data suggest a model for the Iceland plume in which a heterogeneous core, derived from the lower

  15. Dynamics of Mid-Palaeocene North Atlantic rifting linked with European intra-plate deformations.

    PubMed

    Nielsen, Søren B; Stephenson, Randell; Thomsen, Erik

    2007-12-13

    The process of continental break-up provides a large-scale experiment that can be used to test causal relations between plate tectonics and the dynamics of the Earth's deep mantle. Detailed diagnostic information on the timing and dynamics of such events, which are not resolved by plate kinematic reconstructions, can be obtained from the response of the interior of adjacent continental plates to stress changes generated by plate boundary processes. Here we demonstrate a causal relationship between North Atlantic continental rifting at approximately 62 Myr ago and an abrupt change of the intra-plate deformation style in the adjacent European continent. The rifting involved a left-lateral displacement between the North American-Greenland plate and Eurasia, which initiated the observed pause in the relative convergence of Europe and Africa. The associated stress change in the European continent was significant and explains the sudden termination of a approximately 20-Myr-long contractional intra-plate deformation within Europe, during the late Cretaceous period to the earliest Palaeocene epoch, which was replaced by low-amplitude intra-plate stress-relaxation features. The pre-rupture tectonic stress was large enough to have been responsible for precipitating continental break-up, so there is no need to invoke a thermal mantle plume as a driving mechanism. The model explains the simultaneous timing of several diverse geological events, and shows how the intra-continental stratigraphic record can reveal the timing and dynamics of stress changes, which cannot be resolved by reconstructions based only on plate kinematics. PMID:18075591

  16. Lack of genetic structure in greylag goose (Anser anser) populations along the European Atlantic flyway

    PubMed Central

    Pellegrino, Irene; Follestad, Arne; Boos, Mathieu

    2015-01-01

    Greylag goose populations are steadily increasing in north-western Europe. Although individuals breeding in the Netherlands have been considered mainly sedentary birds, those from Scandinavia or northern Germany fly towards their winter quarters, namely over France as far as Spain. This study aimed to determine the genetic structure of these birds, and to evaluate how goose populations mix. We used mitochondrial DNA and microsatellites from individuals distributed throughout the European Atlantic flyway, from breeding sites in Norway and the Netherlands to stopover and wintering sites in northern and south-western France. The mtDNA marker (CR1 D-Loop, 288 bp sequence, 144 ind.) showed 23 different haplotypes. The genetic distances amongst individuals sampled in Norway, northern France and the Netherlands were low (range 0.012–0.013). Individuals in south-western France showed a slightly higher genetic distance compared to all other sampling areas (ranges 0.018–0.022). The NJ tree does not show evidence of any single clades grouping together all individuals from the same geographic area. Besides, individuals from each site are found in different branches. Bayesian clustering procedures on 14 microsatellites (169 individuals) did not detect any geographically distinct cluster, and a high genetic admixture was recorded in all studied areas except for the individuals from the breeding sites in Norway, which were genetically very close. Estimation of migration rates through Bayesian inference confirms the scenario for the current mixing of goose populations. PMID:26339543

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

    USGS Publications Warehouse

    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

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

    NASA Astrophysics Data System (ADS)

    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

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

    NASA Astrophysics Data System (ADS)

    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

  20. Integrated geophysical and petrological characterization of mud volcanoes at the Morrocan Atlantic margin - linking morphology to fluid flow.

    NASA Astrophysics Data System (ADS)

    Depreiter, D.; van Rensbergen, P.; Poort, J.; de Boever, E.; Swennen, R.; Henriet, J.

    2005-12-01

    Detailed geophysical, geochemical and petrological data over a cluster of large mud volcanoes at the Moroccan North Atlantic margin document the activity of sea floor mud volcanoes in relation to its morphology and structural setting. Mud volcanoes are often long-lived systems; their changing morphology bears witness of the evolution of fluid flow expulsion. The El Arraiche mud volcano field is a cluster of 9 mud volcanoes. It was discovered in 2002 at the Morrocan Atlantic margin in water depths from 200 m to 700 m. The largest mud volcano in the field is 255 m high and 5.4 km wide. Marine surveys between 2002 and 2005 yielded detailed geophysical, geochemical, sedimentological, and petrological data. The geophysical data include multibeam bathymetry, high-resolution seismics, deep-tow sub bottom profiles and side-scan sonar mosaics. Video imagery lines, video guided grab samples, dredge samples, gravity cores, and box cores were collected for groundtruthing purposes. Petrological and geochemical analysis of authigenic carbonates provided a record of hydrocarbon sources, fluid characteristics, processes of mixing and the mode of venting. The El Arraiche mud volcanoes cluster around two subparallel anticlines and are associated active extensional faults. Extruded rock clasts and regional seismic data locate the El Arraiche field over a Late Miocene to Pliocene extensional basin. The onset of mud volcanic activity is estimated at about 2.4 Ma and probably roots in the Cretacous to Miocene accretionary wedge. Stacked outflows are visible up to a depth of about 500 m below the sea floor. Stratigraphic correlation of the outflow lenses over the entire mud volcano field indicate that although large outflow events are not synchronized between the individual mud volcanoes, eruptions occurred more frequently during periods of active extensive tectonics. The morphology of the sea floor mud volcanoes is the result of a combination of extrusive and intrusive processes

  1. Lateglacial and early Holocene climates of the Atlantic margins of Europe: Stable isotope, mollusc and pollen records from Orkney, Scotland

    NASA Astrophysics Data System (ADS)

    Whittington, Graeme; Edwards, Kevin J.; Zanchetta, Giovanni; Keen, David H.; Bunting, M. Jane; Fallick, Anthony E.; Bryant, Charlotte L.

    2015-08-01

    The margins of mainland Europe, and especially those areas coming under the influence of North Atlantic weather systems, are ideally placed to record changing palaeoclimates. Cores from an infilled lake basin at Crudale Meadow in Mainland, Orkney, revealed basal deposits of calcareous mud ('marl') beneath sedge peat. Stable isotope, palynological and molluscan analyses allowed the establishment of palaeoenvironmental changes through the Devensian Lateglacial and the early Holocene. The δ18Omarl record exhibited the existence of possibly four climatic oscillations in the Lateglacial (one of which, within event cf. GI-1c, is not often commented upon), as well as the Preboreal Oscillation and other Holocene perturbations. The cold episodes succeeding the Preboreal Oscillation were demarcated conservatively and one of these (event C5, ∼11.0 ka) may have previously been unremarked, while the putative 9.3 and 8.2 ka events seem not to produce corresponding palynologically visible floristic changes. The events at Crudale Meadow are consistent with those recorded at other sites from Britain, Ireland and elsewhere, and can be correlated with isotopic changes shown by the Greenland ice cores. The multi-proxy approach enriches the environmental reconstructions from the site, although the synchronicity of the response of the various proxies is sometimes equivocal, depending upon the time period concerned, taphonomy, and the nature of the deposits. The site may contain the most northerly Lateglacial isotope record from northwest Europe, and it has yielded one of the best archives for the demonstration of abrupt early Holocene events within Britain.

  2. Rise and demise of the Bahama-Grand Banks gigaplatform, northern margin of the Jurassic proto-Atlantic seaway

    USGS Publications Warehouse

    Poag, C. Wylie

    1991-01-01

    An extinct, > 5000-km-long Jurassic carbonate platform and barrier reef system lies buried beneath the Atlantic continental shelf and slope of the United States. A revised stratigraphic framework, a series of regional isopach maps, and paleogeographic reconstructions are used to illustrate the 42-m.y. history of this Bahama-Grand Banks gigaplatform from its inception in Aalenian(?) (early Middle Jurassic) time to its demise and burial in Berriasian-Valanginian time (early Early Cretaceous). Aggradation-progradation rates for the gigaplatform are comparable to those of the familiar Capitan shelf margin (Permian) and are closely correlated with volumetric rates of siliciclastic sediment accumulation and depocenter migration. Siliciclastic encroachment behind the carbonate tracts appears to have been an important impetus for shelf-edge progradation. During the Early Cretaceous, sea-level changes combined with eutrophication (due to landward soil development and seaward upwelling) and the presence of cooler upwelled waters along the outer shelf appear to have decimated the carbonate producers from the Carolina Trough to the Grand Banks. This allowed advancing siliciclastic deltas to overrun the shelf edge despite a notable reduction in siliciclastic accumulation rates. However, upwelling did not extend southward to the Blake-Bahama megabank, so platform carbonate production proceeded there well into the Cretaceous. Subsequent stepwise carbonate abatement characterized the Blake Plateau Basin, whereas the Bahamas have maintained production to the present. The demise of carbonate production on the northern segments of the gigaplatform helped to escalate deep-water carbonate deposition in the Early Cretaceous, but the sudden augmentation of deep-water carbonate reservoirs in the Late Jurassic was triggered by other agents, such as global expansion of nannoplankton communities. ?? 1991.

  3. Thermal history, exhumation and long-term landscape evolution of the South Atlantic passive continental margin, Kaoko Belt, NW Namibia

    NASA Astrophysics Data System (ADS)

    Menges, Daniel; Glasmacher, Ulrich A.; Hackspacher, Peter C.; Schneider, Gabriele; Zentner, Henning; Karl, Markus

    2014-05-01

    After the Damara Orogeny at the end of the Neoproterozoic the Kaoko Belt in northwestern Namibia was affected by deep erosion of the Damara Sequence, followed by the depositon of the Karoo Supergroup from Permo-Carboniferous to Early Cretaceous. The lithostratigraphic units consist of Late Proterozoic to Cambrian metamorphosed rocks and intrusive complexes of the Damara Group, with ages of 534 (7) Ma to 481 (25) Ma (Miller 1983), that are unconformably overlain by terrestrial deposits of the Karoo Supergroup (Stollhofen 1999), comprising two flood basalt events: the Karoo flood basalts, at 183 (1) Ma (Duncan et al. 1997), and the Early Cretaceous Paraná-Etendeka flood basalts, at 132 (1) Ma (Renne et al. 1996). The latter marking the rift stage of the opening of the South Atlantic. The "passive" continental margin along the Kaoko Belt in northern Namibia is a perfect location to quantify exhumation and uplift rates, model the long-term landscape evolution and provide information about the major processes controlling the landscape evolution in this region. The poster/talk will present thermochronological data, t-T-models and exhumation rates for the Kaoko belt, NW Namibia. References Miller, R. M., 1983. Evolution of the Damara Orogen, Vol. 11, Geol. Soc., South Africa Spec. Pub.. Renne, P.R., Glen, J.M., Milner, S.C., Duncan, A.R., 1996. Age of Etendeka flood volcanism and associated intrusions in southwestern Africa, Geology 24 (7): 659- 662. Duncan, R., Hooper, P., Rehacek, J., March, J. and Duncan, A., 1997. The timing and duration of the Karoo igneous event, southern Gondwana, J. Geophys. Res. 102: 18127-18138. Stollhofen, H., 1999. Karoo Synrift-Sedimentation und ihre tektonische Kontrolle am entstehenden Kontinentalrand Namibias, Z.dt.geol.Ges. 149: 519-632.

  4. Sea floor cycling of organic matter in the continental margin of the mid-Atlantic Bight. Final report, May 1, 1995--April 30, 1998

    SciTech Connect

    Jahnke, R.A.

    1998-12-31

    The objective of this project was to examine quantitatively the cycling of organic matter at the sea floor of the mid-Atlantic Bight continental margin. This information would be used to better understand sedimentary geochemical processes and, when used in conjunction with other measurements made within the DOE Ocean Margins Program, would be used to constrain the offshore and surface-to-deep water transport of organic carbon in this region. The latter information is critical in assessing the role of continental margins in the sequestration of anthropogenic carbon dioxide, the dominant greenhouse gas, in the deep ocean. Because the build-up of greenhouse gases in the atmosphere may cause significant changes in climate, this project had major societal importance.

  5. Major controlling factors on hydrocarbon generation and leakage in South Atlantic conjugate margins: A comparative study of Colorado, Orange, Campos and Lower Congo basins

    NASA Astrophysics Data System (ADS)

    Marcano, Gabriela; Anka, Zahie; di Primio, Rolando

    2013-09-01

    We present a supra-regional comparative study of the major internal and external factors controlling source rock (SR) maturation and hydrocarbon (HC) generation and leakage in two pairs of conjugate margins across the South Atlantic: the Brazil (Campos Basin)-Angola (Lower Congo Basin) margins located in the "central segment", and the Argentina (Colorado Basin)-South Africa (Orange Basin) in the "southern segment". Our approach is based on the analysis and integration of borehole data, 1D numerical modeling, 2D seismic reflection data, and published reports. Coupling of modeling results, sedimentation rate calculation and seal-bypass system analysis reveal that: (1) oil window is reached by syn-rift SRs in the southern segment during the Early to Late Cretaceous when thermal subsidence is still active, while in the central segment they reach it in Late-Cretaceous-Neogene during a salt remobilization phase, and (2) early HC generation from post-rift SRs in the southern segment and from all SRs in the central segment appears to be controlled mainly by episodes of increased sedimentation rates. The latter seems to be associated with the Andes uplift history for the western South Atlantic basins (Campos and Colorado) and to a possibly climate-driven response for the eastern South Atlantic basins (Orange and Lower Congo). Additionally, we observe that the effect of volcanism on SR maturation in the southern segment is very local. The comparison of Cretaceous mass transport deposit (MTD) episodes with HC peak of generation and paleo-leakage indicators in the southern segment revealed the possible causal effect that HC generation and leakage have over MTD development. Interestingly, Paleogene leakage indicators, which were identified in the Argentina-South Africa conjugate margins, occur contemporaneously to low sedimentation rate periods. Nonetheless, present-day leakage indicators which were also identified in both pairs of conjugate margins might be related to seal

  6. Drivers of exceptionally cold North Atlantic Ocean temperatures and their link to the 2015 European heat wave

    NASA Astrophysics Data System (ADS)

    Duchez, Aurélie; Frajka-Williams, Eleanor; Josey, Simon A.; Evans, Dafydd G.; Grist, Jeremy P.; Marsh, Robert; McCarthy, Gerard D.; Sinha, Bablu; Berry, David I.; J-M Hirschi, Joël

    2016-07-01

    The North Atlantic and Europe experienced two extreme climate events in 2015: exceptionally cold ocean surface temperatures and a summer heat wave ranked in the top ten over the past 65 years. Here, we show that the cold ocean temperatures were the most extreme in the modern record over much of the mid-high latitude North-East Atlantic. Further, by considering surface heat loss, ocean heat content and wind driven upwelling we explain for the first time the genesis of this cold ocean anomaly. We find that it is primarily due to extreme ocean heat loss driven by atmospheric circulation changes in the preceding two winters combined with the re-emergence of cold ocean water masses. Furthermore, we reveal that a similar cold Atlantic anomaly was also present prior to the most extreme European heat waves since the 1980s indicating that it is a common factor in the development of these events. For the specific case of 2015, we show that the ocean anomaly is linked to a stationary position of the Jet Stream that favours the development of high surface temperatures over Central Europe during the heat wave. Our study calls for an urgent assessment of the impact of ocean drivers on major European summer temperature extremes in order to provide better advance warning measures of these high societal impact events.

  7. Starting a DNA barcode reference library for shallow water polychaetes from the southern European Atlantic coast.

    PubMed

    Lobo, Jorge; Teixeira, Marcos A L; Borges, Luisa M S; Ferreira, Maria S G; Hollatz, Claudia; Gomes, Pedro T; Sousa, Ronaldo; Ravara, Ascensão; Costa, Maria H; Costa, Filipe O

    2016-01-01

    Annelid polychaetes have been seldom the focus of dedicated DNA barcoding studies, despite their ecological relevance and often dominance, particularly in soft-bottom estuarine and coastal marine ecosystems. Here, we report the first assessment of the performance of DNA barcodes in the discrimination of shallow water polychaete species from the southern European Atlantic coast, focusing on specimens collected in estuaries and coastal ecosystems of Portugal. We analysed cytochrome oxidase I DNA barcodes (COI-5P) from 164 specimens, which were assigned to 51 morphospecies. To our data set from Portugal, we added available published sequences selected from the same species, genus or family, to inspect for taxonomic congruence among studies and collection location. The final data set comprised 290 specimens and 79 morphospecies, which generated 99 Barcode Index Numbers (BINs) within Barcode of Life Data Systems (BOLD). Among these, 22 BINs were singletons, 47 other BINs were concordant, confirming the initial identification based on morphological characters, and 30 were discordant, most of which consisted on multiple BINs found for the same morphospecies. Some of the most prominent cases in the latter category include Hediste diversicolor (O.F. Müller, 1776) (7), Eulalia viridis (Linnaeus, 1767) (2) and Owenia fusiformis (delle Chiaje, 1844) (5), all of them reported from Portugal and frequently used in ecological studies as environmental quality indicators. Our results for these species showed discordance between molecular lineages and morphospecies, or added additional relatively divergent lineages. The potential inaccuracies in environmental assessments, where underpinning polychaete species diversity is poorly resolved or clarified, demand additional and extensive investigation of the DNA barcode diversity in this group, in parallel with alpha taxonomy efforts. PMID:26129849

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

    NASA Astrophysics Data System (ADS)

    Becker, K.; Franke, D.; Trumbull, R.; Schnabel, M.; Heyde, I.; Schreckenberger, B.; Koopmann, H.; Bauer, K.; Jokat, W.; Krawczyk, C. M.

    2014-10-01

    High-velocity lower crust (HVLC) and seaward-dipping reflector (SDR) sequences 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 for 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 cross-sectional areas of HVLC 4 times larger than at the South American margin, a finding that is opposite to the asymmetric distribution of the flood basalts in the Paraná-Etendeka Large Igneous Province. Also, the position of the HVLC with respect to the SDR sequences varies consistently along both margins. Close to the Falkland-Agulhas Fracture Zone in the south, a small body of HVLC is not accompanied by SDRs. In the central portion of both margins, the HVLC is below the inner SDR wedges while in the northern area, closer to the Rio Grande Rise-Walvis Ridge, large volumes of HVLC extend far seaward of the inner SDRs. This challenges the concept of a simple extrusive/intrusive relationship between SDR sequences and HVLC, and it provides evidence for formation of the HVLC at different times during the rifting and breakup process. We suggest that the drastically different HVLC volumes are caused by asymmetric rifting in a simple-shear-dominated extension.

  9. 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

    NASA Astrophysics Data System (ADS)

    Becker, K.; Franke, D.; Trumbull, R. B.; Schnabel, M.; Heyde, I.; Schreckenberger, B.; Koopmann, H.; Bauer, K.; Jokat, W.; Krawczyk, C. M.

    2014-06-01

    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.

  10. Factors associated with quality of services for marginalized groups with mental health problems in 14 European countries

    PubMed Central

    2014-01-01

    Background Different service characteristics are known to influence mental health care delivery. Much less is known about the impact of contextual factors, such as the socioeconomic circumstances, on the provision of care to socially marginalized groups. The objectives of this work were to assess the organisational characteristics of services providing mental health care for marginalized groups in 14 European capital cities and to explore the associations between organisational quality, service features and country-level characteristics. Methods 617 services were assessed in two highly deprived areas in 14 European capital cities. A Quality Index of Service Organisation (QISO) was developed and applied across all sites. Service characteristics and country level socioeconomic indicators were tested and related with the Index using linear regressions and random intercept linear models. Results The mean (standard deviation) of the QISO score (minimum = 0; maximum = 15) varied from 8.63 (2.23) in Ireland to 12.40 (2.07) in Hungary. The number of different programmes provided was the only service characteristic significantly correlated with the QISO (p < 0.05). The national Gross Domestic Product (GDP) was inversely associated with the QISO. Nearly 15% of the variance of the QISO was attributed to country-level variables, with GDP explaining 12% of this variance. Conclusions Socioeconomic contextual factors, in particular the national GDP are likely to influence the organisational quality of services providing mental health care for marginalized groups. Such factors should be considered in international comparative studies. Their significance for different types of services should be explored in further research. PMID:24490720

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

    NASA Astrophysics Data System (ADS)

    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

  12. Heterogeneous Cenozoic cooling of central Britain: insights into the complex evolution of the North Atlantic passive margin

    NASA Astrophysics Data System (ADS)

    Łuszczak, Katarzyna; Persano, Cristina; Stuart, Finlay

    2015-04-01

    The western flank of the North Atlantic passive margin has experienced multiple episodes of rock uplift and denudation during the Cenozoic that have been locally variable in scale. Two regional scale exhumation events have been identified: early Palaeogene and Neogene [see 1 for review]. The former has been identified both onshore and offshore and it appears to be temporally coincident with basaltic magmatism related to the arrival of the proto-Iceland mantle plume beneath thinned continental lithosphere, which may have cause long wavelength, low amplitude dynamic uplift. Quantifying the amount of early Palaeogene exhumation using mineral thermochronometers may be complicated by elevated heat flow. The magnitude and timing of exhumation during the Neogene is even less clear, as is the driving mechanism. Quantifying the amount of early Palaeogene exhumation, determining the precise timing as well as the amount of uplift and erosion in the Neogene, require detailed application of low temperature thermochronometers. Here we present the first multiple low temperature thermochronometer study from S Scotland, N England and N Wales. New apatite fission track (AFT) data are integrated with apatite and zircon (U-Th-Sm)/He (AHe and ZHe, respectively) ages to establish regional rock cooling history from 200°C to 30°C. To precisely constrain the early Palaeogene cooling history, and to better define the possible Neogene cooling event, >20 single grain AHe ages have been produced on key samples and modelled using the newly codified HelFrag technique. The new AFT and AHe ages confirm earlier studies that show the Lake District and North Pennines experienced rapid cooling from >120°C in the Palaeogene. The amount of cooling/exhumation gradually decreases northwards into S Scotland and southwards in N Wales; there is no evidence for the rapid Palaeogene event in areas ~70 km from the Lake District centre. Inverse modelling of the AHe and AFT data suggest that the rapid cooling

  13. Deep structure of the U.S. Atlantic continental margin, offshore South Carolina, from coincident ocean bottom and multichannel seismic data

    NASA Astrophysics Data System (ADS)

    Holbrook, W. Steven; Reiter, E. C.; Purdy, G. M.; Sawyer, D.; Stoffa, P. L.; Austin, J. A., Jr.; Oh, J.; Makris, J.

    1994-05-01

    We present the results of a combined multichannel seismic reflection (MCS) and wide-angle, ocean bottom seismic profile collected in 1988 across the Carolina Trough on the U.S. Atlantic continental margin. Inversion of vertical-incidence and wide-angle travel time data has produced a velocity model of the entire crust across the continent-ocean transition. The margin consists of three structural elements: (1) rifted continental crust, comprising 1-4 km of post-rift sedimentary rocks overlying a 30-34 km thick subsedimentary crust, (2) transitional crust, a 70- to 80-km-wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10- to 24-km-thick subsedimentary crust, and (3) oceanic crust, comprising 8 km of sedimentary rocks overlying an 8-km-thick crystalline crust. The boundary between rifted continental and transitional crust, marked by the Brunswick magnetic anomaly, represents an abrupt change in physical properties, with strong lateral increases in seismic velocity, density, and magnetic susceptibility. The transitional crust contains mid-crustal seaward-dipping reflections observed on the MCS section and has seismic velocities of 6.5-6.9 km/s in the midcrust and 7.2-7.5 km/s in the lower crust. Modeling of potential field data shows that transitional crust also produces the prominent, margin-parallel gravity anomaly and the Brunswick and East Coast magnetic anomalies. These observations support the interpretation that the transitional crust was formed by magmatism during continental breakup. The prodigious thickness (up to 24 km) of igneous material rivals that interpreted on continental margins of the North Atlantic (e.g., Hatton Bank and Vøring Plateau), which formed in the vicinity of the Iceland hotspot. These observations, when combined with other transects across the margin, confirm previous suggestions that the U.S. Atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long-lived mantle

  14. Ancient impact structures on modern continental shelves: The Chesapeake Bay, Montagnais, and Toms Canyon craters, Atlantic margin of North America

    USGS Publications Warehouse

    Poag, C. Wylie; Plescia, J.B.; Molzer, P.C.

    2002-01-01

    Three ancient impact craters (Chesapeake Bay - 35.7 Ma; Toms Canyon - 35.7 Ma; Montagnais - 51 Ma) and one multiring impact basin (Chicxulub - 65 Ma) are currently known to be buried beneath modern continental shelves. All occur on the passive Atlantic margin of North America in regions extensively explored by seismic reflection surveys in the search for oil and gas reserves. We limit our discussion herein to the three youngest structures. These craters were created by submarine impacts, which produced many structural and morphological features similar in construction, composition, and variability to those documented in well-preserved subaerial and planetary impact craters. The subcircular Chesapeake Bay (diameter 85 km) and ovate Montagnais (diameter 45-50 km) structures display outer-rim scarps, annular troughs, peak rings, inner basins, and central peaks similar to those incorporated in the widely cited conceptual model of complex impact craters. These craters differ in several respects from the model, however. For example, the Montagnais crater lacks a raised lip on the outer rim, the Chesapeake Bay crater displays only small remnants of a raised lip, and both craters contain an unusually thick body of impact breccia. The subtriangular Toms Canyon crater (diameter 20-22 km), on the other hand, contains none of the internal features of a complex crater, nor is it typical of a simple crater. It displays a prominent raised lip on the outer rim, but the lip is present only on the western side of the crater. In addition, each of these craters contains some distinct features, which are not present in one or both of the others. For example, the central peak at Montagnais rises well above the elevation of the outer rim, whereas at Chesapeake Bay, the outer rim is higher than the central peak. The floor of the Toms Canyon crater is marked by parallel deep troughs and linear ridges formed of sedimentary rocks, whereas at Chesapeake Bay, the crater floor contains

  15. Productivity and river flux variability in response to the PETM on Atlantic margin at Bass River, NJ.

    NASA Astrophysics Data System (ADS)

    Stoll, H.; Shimizu, N.; Savain, R.; Zachos, J.; Ziveri, P.

    2009-04-01

    While the dramatic climate warming of the Paleocene-Eocene Thermal Maximum has been well characterized, changes in the hydrological cycle and the broader biogeochemical feedbacks (weathering, nutrients, productivity) are less well constrained. Here we describe new geochemical results from a coastal section on the midlatitude Atlantic margin of the U.S. at Bass River, NJ. We measured the elemental geochemistry of coccoliths to probe the productivity of these algae in response to the changing nutrient dynamics on the shelf in the time interval preceding and during the PETM. Coccoliths extracted from the siliclastic coastal section at Bass River NJ exhibit exceptionally good preservation and negligible overgrowth compared to typical ocean carbonate-rich sediments. Analysis of individual coccoliths using secondary ion mass spectrometry (SIMS) facilitates reliable trace element measurements in this low-carbonate section. Published sequence stratigraphy and microfossil analysis have revealed several third order sea level cycles in the late Paleocene including a highstand during the PETM. Consequently we extend our paleoproductivity records far below the PETM to characterize this background variability. We recognize a pattern of generally maximum productivity during lowstands and minimal productivity during highstands. Because nutrient concentrations decrease significantly with distance from the coast, highstands reduce productivity by shifting the highest nutrient levels landward, away from the site. This is likely due to greater distance from river sources as well as reduced wave turbulence which mixes nutrients into the photic zone. This general pattern is broken during the PETM, which features high productivity despite a sea level highstand. This anomalous high productivity may reflect enhanced riverine nutrient delivery, and potentially changes in wind strength and mixing intensity. Riverine nutrient delivery could increase with higher precipitation or precipitation

  16. Post-rift uplift, paleorelief and sedimentary fluxes: the case example of the African margin of the South Atlantic

    NASA Astrophysics Data System (ADS)

    Guillocheau, F.; Dauteuil, O.

    2012-04-01

    volume of eroded sediments. This can explain abnormal stratigraphic response along the African South Atlantic passive margins, such as thin clayey basin floor fans at time of uplift and erosion of weathering profiles. Keywords: Africa, Cenozoic, Siliciclastic sediment fluxes, Tectonics, Climate

  17. The problems of the kinematic restoration of hyper-extended rifted margins: the example of the southern North-Atlantic

    NASA Astrophysics Data System (ADS)

    Nirrengarten, Michael; Manatschal, Gianreto; Tugend, Julie; Kusznir, Nick

    2016-04-01

    The development in space and time of hyper-extended lithosphere is fundamental to our understanding of the 3D development and propagation of rifting and lithospheric breakup. Hyper-extended domains, consisting of extremely thinned continental crust and exhumed mantle with possible minor magmatic addition, often extend over wide areas, sometimes up to 400 km, continentward of the first unequivocal oceanic crust. Although considerable work has been done in the last decades to describe the evolution of hyper-extended domains, there is yet no generally accepted approach to kinematically restore them. Indeed, in contrast to oceanic crust, where the kinematics can be defined by isochronal magnetic anomalies, in hyper-extended well-defined consistent magnetic anomalies are lacking. Therefore in order to restore these domains, we need to define alternative approaches. The main questions to be addressed to solve this problem are: 1) how can hyper-extended domains be restored, 2) which kinematic markers could be used 3) what are the implications for the 3D propagation of hyper-extended systems. We use the example of the southern North-Atlantic to develop and apply an approach to kinematically analyse the evolution of hyper-extended domains. We combine seismic dataset and drill hole data available with crustal thickness maps determined from gravity inversion to define and map rift domains and rift domain boundaries. We distinguish between the proximal domain (weakly thinned continental crust), thinned continental crust, exhumed mantle, and oceanic crust. From this mapping, we observe that the width of each domain is variable along the margins and that domain boundaries are not always straight lines. It implies that these boundaries, in particular the edge of the continental crust cannot be easily superimposed at a specific time. Therefore, rift domain boundaries cannot be considered as isochrones and do not represent kinematical markers. The restoration of hyper

  18. ENSO influence on the North Atlantic European climate: a non-linear and non-stationary approach

    NASA Astrophysics Data System (ADS)

    López-Parages, Jorge; Rodríguez-Fonseca, Belén; Dommenget, Dietmar; Frauen, Claudia

    2015-12-01

    El Niño Southern Oscillation (ENSO) impact on the North Atlantic European sector (NAE) is still under discussion. Recent studies have found a non stationary feature of this teleconnection, suggesting an effective modulating role of the ocean mean state. Nevertheless, physical explanations about the underlying mechanisms have been little studied in the available literature. In addition, ENSO events show different SST spatial patterns, phases, and amplitudes, which can also influence on the related remote impacts. In view of all this, in the present study a set of partially coupled experiments have been performed with a global atmospheric general circulation model in which different SST ENSO patterns are superimposed over distinct Pacific and Atlantic SST mean states. These SST background conditions are constructed according to the observational difference between periods with a distinct impact of ENSO on the leading Euro-Mediterranean rainfall mode in late winter-early spring. Our results point to two distinct mechanisms associated with ENSO that can be modulated by the SST mean state: (1) the thermally driven direct circulation (Walker and Hadley cells) connecting the Atlantic and Pacific basins, and (2) the Rossby wave propagation from the tropical Pacific to the North Atlantic. The former elucidates that the positive NAO-like pattern usually related to La Niña events could be only valid for selected decades. The latter explains a reinforced signature of Eastern Pacific Niños on the Euro-Mediterranean rainfall when the tropical Pacific is warmer than usual and the North Atlantic is colder than usual. This feature is consistent with the changing ENSO impact identified in previous studies and demonstrates how the ENSO teleconnection with the NAE climate at interannual timecales could be modulated by multidecadal changes in the SST. According to our results, the assumption of stationarity which is still common to many studies of ENSO teleconnections clearly has to

  19. Plankton blooms, ocean circulation and the European slope current: Response to weather and climate in the Bay of Biscay and W English Channel (NE Atlantic)

    NASA Astrophysics Data System (ADS)

    Pingree, Robin D.; Garcia-Soto, Carlos

    2014-08-01

    The flow of upper-layer surface water and circulation for the Bay of Biscay, continental slope and in the wider region of the NE Atlantic is presented, as well as the seasonality of flow and internal tides. The marine plankton environments of Biscay Ocean, Biscay Eddies, Biscay Slope and Biscay Shelf are defined. The Shelf region (Armorican and Celtic) is further divided into Stratified Shelf, Frontal and Tidally Mixed. Seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data. Mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined. Some regional responses for the slope current, dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the Bay of Biscay and around the British Isles are suggested and discussed. An example of the Eastern European Ocean Margin continental slope response to winter weather (sea level atmospheric pressure forcing) resulting in warm winter water in the southern Bay of Biscay (Navidad, with eddy production) and off the Shetland continental slopes (the warm-water supply route to the Arctic) is given from the slope climate observation series.

  20. Lower crustal high-velocity bodies along North Atlantic passive margins, and their link to Caledonian suture zone eclogites and Early Cenozoic magmatism

    NASA Astrophysics Data System (ADS)

    Mjelde, Rolf; Kvarven, Trond; Faleide, Jan Inge; Thybo, Hans

    2016-02-01

    In this study we use crustal-scale Ocean Bottom Seismic models to infer the presence of two types of lower crustal bodies at North Atlantic passive margins; Type I, primarily interpreted as Early Eocene magmatic intrusions, and Type II, interpreted as Caledonian eclogites. We discuss how these eclogites might be related to the main Caledonian Suture Zone and other tectonic features in a conjugate North Atlantic setting. Based on the first-order approximation that P-wave velocities can be related to rock strength, the narrower continental margin at the southern (Møre) transect may be explained by stronger lower crust there, compared with the northern (Vøring) transect. This difference in strength, possibly resulting in a steeper dip in the subducting Baltica Plate south of the proto-Jan Mayen Lineament, may explain the asymmetry in extensional style observed across this lineament. Our interpretation locates the main suture off mid-Norway close to the Møre Trøndelag Fault Zone on the Møre Margin, along the western boundary of the Trøndelag Platform on the Vøring Margin, and further northwards beneath the Lofoten Ridge. The Lower Crustal Body Type I is about 60% thicker on the Greenland side, for both transects, and its thickness along the northern transect is more than twice that of the southern transect. These differences are consistent with sub-lithospheric interaction between the Icelandic hotspot and the continental rift/oceanic accretion system around the time of continental break-up.

  1. Quantification of the effects of eustasy, subsidence, and sediment supply on Miocene sequences, mid-Atlantic margin of the United States

    USGS Publications Warehouse

    Browning, J.V.; Miller, K.G.; McLaughlin, P.P.; Kominz, M.A.; Sugarman, P.J.; Monteverde, D.; Feigenson, M.D.; Hernandez, J.C.

    2006-01-01

    We use backstripping to quantify the roles of variations in global sea level (eustasy), subsidence, and sediment supply on the development of the Miocene stratigraphic record of the mid-Atlantic continental margin of the United States (New Jersey, Delaware, and Maryland). Eustasy is a primary influence on sequence patterns, determining the global template of sequences (i.e., times when sequences can be preserved) and explaining similarities in Miocene sequence architecture on margins throughout the world. Sequences can be correlated throughout the mid-Atlantic region with Sr-isotopic chronology (??0.6 m.y. to ??1.2 m.y.). Eight Miocene sequences correlate regionally and can be correlated to global ??18O increases, indicating glacioeustatic control. This margin is dominated by passive subsidence with little evidence for active tectonic overprints, except possibly in Maryland during the early Miocene. However, early Miocene sequences in New Jersey and Delaware display a patchwork distribution that is attributable to minor (tens of meters) intervals of excess subsidence. Backstripping quantifies that excess subsidence began in Delaware at ca. 21 Ma and continued until 12 Ma, with maximum rates from ca. 21-16 Ma. We attribute this enhanced subsidence to local flexural response to the progradation of thick sequences offshore and adjacent to this area. Removing this excess subsidence in Delaware yields a record that is remarkably similar to New Jersey eustatic estimates. We conclude that sea-level rise and fall is a first-order control on accommodation providing similar timing on all margins to the sequence record. Tectonic changes due to movement of the crust can overprint the record, resulting in large gaps in the stratigraphic record. Smaller differences in sequences can be attributed to local flexural loading effects, particularly in regions experiencing large-scale progradation. ?? 2006 Geological Society of America.

  2. Rates, causes, and dynamic of long-term landscape evolution of the South Atlantic "passive continental margin", Brazil and Namibia, as revealed by thermo-kinematic numerical modeling.

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The aim of the research is to quantify the long-term landscape evolution of the South Atlantic passive continental margin (SAPCM) in SE-Brazil and NW-Namibia. Excellent onshore outcrop conditions and complete rift to post-rift archives between Sao Paulo and Porto Alegre and in the transition from Namibia to Angola (onshore Walvis ridge) allow a high precision quantification of exhumation, and uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. Research will integrate the published and partly published thermochronological data from Brazil and Namibia, and test lately published new concepts on causes of long-term landscape evolution at rifted margins. 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 PECUBE and FastCape). 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 data and models will allow separating the exogenous and endogenous forces and their process rates.

  3. Comparison of the feeding apparatus and diet of European sardines Sardina pilchardus of Atlantic and Mediterranean waters: ecological implications.

    PubMed

    Costalago, D; Garrido, S; Palomera, I

    2015-04-01

    In this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000 µm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500 µm) that include phytoplankton and copepods, particularly during summer months, and S. pilchardus eggs during the winter. The marked difference between the trophic ecology of S. pilchardus in the two areas studied appears to have originated from different dietary strategies that the two populations have adopted in contrasting feeding environments. These differences are shown to profoundly affect the size and quality of prey consumed, and the effect of cannibalism on the populations. PMID:25846858

  4. The tectono-stratigraphic evolution of the mid-Norway shelf in an Atlantic margin context, and its implications for prospectivity

    SciTech Connect

    Dore, A.G.; Birkeland, O.; Lundin, E.

    1995-08-01

    Source rock, reservoir rock and trap formation along the Atlantic margin between offshore Ireland and the northern part of the Mid-Norwegian shelf can be related to repeating tectonic motifs. Interaction of N-S and NE-SW fault and basin trends and NW-SE transfer lineaments is particularly significant. At least some of this structural grain can be related to basement anisotrophy dating back to the late Caledonian or earlier. Using tectonic maps, facies maps and profiles we demonstrate the establishment and exploitation of these structural elements in response to successive extensional episodes will varying stress fields, magmatic episodes and transtension/transpression. The following key tectonic episodes are selected for discussion: Late Caledonian establishment of basement grain; Carboniferous - Triassic extension; Late Jurassic rifting with a dominant E-W extension vector; Cretaceous extension and magmatism with a dominant NW-SE extension vector; Latest Cretaceous-Eocene tectonism, magmatism and break-up; Cenozoic (primarily Oligocene-Miocene) compression/inversion; and Late Cenozoic uplift. The analysis is described with special reference to the new exploration areas offshore Mid-Norway - the More Basin, Voring Basin and Lofoten area. The potential for play analogies and transfer of exploration models along the Atlantic margin trend is particularly emphasised.

  5. Post-rift vertical movements and horizontal deformations in the eastern margin of the Central Atlantic: Middle Jurassic to Early Cretaceous evolution of Morocco

    NASA Astrophysics Data System (ADS)

    Bertotti, Giovanni; Gouiza, Mohamed

    2012-11-01

    Wide regions of Morocco, from the Meseta to the High Atlas, have experienced km-scale upward vertical movements during Middle Jurassic to Early Cretaceous times following the appearance of oceanic crust in the Central Atlantic. The area experiencing exhumation was flanked to the W by a domain of continuous subsidence, part of which is named the Essaouira-Agadir basin. Comparison with vertical movement curves predicted by lithospheric thinning models shows that only 50-60 % of the subsidence documented in the Essaouira basin can be explained by post-rift thermal relaxation and that <30-40 % of the observed exhumation can be explained by processes (in)directly related to the evolution of the Central Atlantic rifted margin. Syn-sedimentary structures in Middle Jurassic to Lower Cretaceous formations of the Eassouira-Agadir basin are common and range from m-scale folds and thrusts to km-scale sedimentary wedges. These structures systematically document coeval shortening generally oriented at high angle to the present margin. As a working hypothesis, it is suggested that regional shortening can explain the structural observations and the enigmatic vertical movements.

  6. Genetic stock identification of Atlantic salmon (Salmo salar) populations in the southern part of the European range

    PubMed Central

    2010-01-01

    Background Anadromous migratory fish species such as Atlantic salmon (Salmo salar) have significant economic, cultural and ecological importance, but present a complex case for management and conservation due to the range of their migration. Atlantic salmon exist in rivers across the North Atlantic, returning to their river of birth with a high degree of accuracy; however, despite continuing efforts and improvements in in-river conservation, they are in steep decline across their range. Salmon from rivers across Europe migrate along similar routes, where they have, historically, been subject to commercial netting. This mixed stock exploitation has the potential to devastate weak and declining populations where they are exploited indiscriminately. Despite various tagging and marking studies, the effect of marine exploitation and the marine element of the salmon lifecycle in general, remain the "black-box" of salmon management. In a number of Pacific salmonid species and in several regions within the range of the Atlantic salmon, genetic stock identification and mixed stock analysis have been used successfully to quantify exploitation rates and identify the natal origins of fish outside their home waters - to date this has not been attempted for Atlantic salmon in the south of their European range. Results To facilitate mixed stock analysis (MSA) of Atlantic salmon, we have produced a baseline of genetic data for salmon populations originating from the largest rivers from Spain to northern Scotland, a region in which declines have been particularly marked. Using 12 microsatellites, 3,730 individual fish from 57 river catchments have been genotyped. Detailed patterns of population genetic diversity of Atlantic salmon at a sub-continent-wide level have been evaluated, demonstrating the existence of regional genetic signatures. Critically, these appear to be independent of more commonly recognised terrestrial biogeographical and political boundaries, allowing reporting

  7. Allostratigraphy of the U.S. middle Atlantic continental margin; characteristics, distribution, and depositional history of principal unconformity-bounded upper Cretaceous and Cenozoic sedimentary units

    USGS Publications Warehouse

    Poag, C. Wylie; Ward, Lauck W.

    1993-01-01

    Publication of Volumes 93 and 95 ('The New Jersey Transect') of the Deep Sea Drilling Project's Initial Reports completed a major phase of geological and geophysical research along the middle segment of the U. S. Atlantic continental margin. Relying heavily on data from these and related published records, we have integrated outcrop, borehole, and seismic-reflection data from this large area (500,000 km^2 ) to define the regional allostratigraphic framework for Upper Cretaceous and Cenozoic sedimentary rocks. The framework consists of 12 alloformations, which record the Late Cretaceous and Cenozoic depositional history of the contiguous Baltimore Canyon trough (including its onshore margin) and Hatteras basin (northern part). We propose stratotype sections for each alloformation and present a regional allostratigraphic reference section, which crosses these basins from the inner edge of the coastal plain to the inner edge of the abyssal plain. Selected supplementary reference sections on the coastal plain allow observation of the alloformations and their bounding unconformities in outcrop. Our analyses show that sediment supply and its initial dispersal on the middle segment of the U. S. Atlantic margin have been governed, in large part, by hinterland tectonism and subsequently have been modified by paleoclimate, sea-level changes, and oceanic current systems. Notable events in the Late Cretaceous to Holocene sedimentary evolution of this margin include (1) development of continental-rise depocenters in the northern part of the Hatteras basin during the Late Cretaceous; (2) the appear ance of a dual shelf-edge system, a marked decline in siliciclastic sediment accumulation rates, and widespread acceleration of carbonate production during high sea levels of the Paleogene; (3) rapid deposition and progradation of thick terrigenous delta complexes and development of abyssal depocenters during the middle Miocene to Quaternary interval; and (4) deep incision of the

  8. Benthic-Pelagic Coupling: Effects on Nematode Communities along Southern European Continental Margins

    PubMed Central

    Pape, Ellen; Jones, Daniel O. B.; Manini, Elena; Bezerra, Tania Nara; Vanreusel, Ann

    2013-01-01

    Along a west-to-east axis spanning the Galicia Bank region (Iberian margin) and the Mediterranean basin, a reduction in surface primary productivity and in seafloor flux of particulate organic carbon was mirrored in the in situ organic matter quantity and quality within the underlying deep-sea sediments at different water depths (1200, 1900 and 3000 m). Nematode standing stock (abundance and biomass) and genus and trophic composition were investigated to evaluate downward benthic-pelagic coupling. The longitudinal decline in seafloor particulate organic carbon flux was reflected by a reduction in benthic phytopigment concentrations and nematode standing stock. An exception was the station sampled at the Galicia Bank seamount, where despite the maximal particulate organic carbon flux estimate, we observed reduced pigment levels and nematode standing stock. The strong hydrodynamic forcing at this station was believed to be the main cause of the local decoupling between pelagic and benthic processes. Besides a longitudinal cline in nematode standing stock, we noticed a west-to-east gradient in nematode genus and feeding type composition (owing to an increasing importance of predatory/scavenging nematodes with longitude) governed by potential proxies for food availability (percentage of nitrogen, organic carbon, and total organic matter). Within-station variability in generic composition was elevated in sediments with lower phytopigment concentrations. Standing stock appeared to be regulated by sedimentation rates and benthic environmental variables, whereas genus composition covaried only with benthic environmental variables. The coupling between deep-sea nematode assemblages and surface water processes evidenced in the present study suggests that it is likely that climate change will affect the composition and function of deep-sea nematodes. PMID:23565176

  9. Imprint of North-Atlantic abrupt climate changes on western European loess deposits as viewed in a dust emission model

    NASA Astrophysics Data System (ADS)

    Sima, Adriana; Rousseau, Denis-Didier; Kageyama, Masa; Ramstein, Gilles; Schulz, Michael; Balkanski, Yves; Antoine, Pierre; Dulac, François; Hatté, Christine

    2009-12-01

    Western European loess sequences of the last glaciation (˜100,000-15,000 years BP) exhibit strong, cyclic variations of the sedimentation rate, which are coeval to the Greenland stadial/interstadial cycles and the Heinrich events. These North-Atlantic rapid climate changes appear, thus, as a potential cause for the sedimentation variations, via changes in dust intensity cycle. Here we make a first step in testing this hypothesis, by modelling the impact of the North-Atlantic abrupt climate variations on dust emission. Our dust emission calculations use meteorological fields generated by the LMDZ atmospheric general circulation model at a resolution down to 60 km over Western Europe. Three numerical experiments are run, representing a Greenland stadial, an interstadial and a Heinrich event. Orbital parameters and ice-sheet configuration correspond to conditions from Marine Isotope Stage 3 (˜60,000-25,000 years BP), a period characterized by strong millennial-scale climate variability. The only differences we impose in the boundary conditions regard the North-Atlantic surface temperature and sea-ice cover in the latitudinal band 30°-63°N. The changes in wind, precipitation, soil moisture and snow cover from one simulated state to another result in small differences in dust emission intensity. In contrast, when the inhibition of the aeolian erosion by vegetation is taken into account, the dust fluxes for the cold climate states (Greenland stadial and Heinrich event) become generally more than twice higher than those for the relatively warmer Greenland interstadial, in agreement with the loess data. These results support the hypothesis that the North-Atlantic millennial-scale variability is imprinted in Western European loess profiles, and point to vegetation changes as the main factor responsible for millennial-scale sedimentation variations. An analysis for the English Channel and southern North Sea areas, major potential dust sources, shows that the seasonality

  10. Post-glacial coast development and human settling of the North European Ice Marginal Landscape (IML)

    NASA Astrophysics Data System (ADS)

    Bregman, I. Kant Baltic Federal State University, Kaliningrad, Russia, E. P. H.; Netherlands, Utrecht University, the; Druzhinina, I. Kant Baltic Federal State University, Kaliningrad, Russia, O. A.

    2012-04-01

    In North Europe, in the Ice Marginal Landscapes (IML) from the Netherlands to Estonia, human settling is in the Late-Pleistocene - Holocene strongly influenced by post-glacial relative coast development(MESO, 2010; SINCOS, 2002-2009; Machu, 2006-2009, IGCP project 346, CoPaF, 2009-2012) and glacio-isostasy. Geological processes like updoming and tectonic block displacements not only influenced sedimentation of river systems in delta's (e.g. Cohen, 2003), but influenced coastal development and human settling too in the North Sea area (e.g. Peeters, 2009; Hijma e.a., 2011) the Wadden areas (e.g. de Langen, 2011) and lagoons (e.g. Druzhinina, 2010). An overview of shoreline development at the distal side of the Late Glacial forbulge related to glaciological and geophysical processes however does not exist and coastal development models are also not correlated with human settling. Our project( 2012 - 2018) has the aim to describe the influence of shifting coast on the way of settling and living of ancient man in the IML. The main questions to be answered are as follow: (i) Is coast development influenced by glaciations a result of interaction between endo- and exogenic (glaciological-, geological-, and geophysical) forces in general and at the local scale of morphological elements? (ii) Did ancient man adept to changes in natural circumstances and what did that mean for his social behavior and economy? (iii) Were forms of human society and economy in the IML primarily dependent on the natural environment with regard to geophysical and geological differences and related to post-glacial response of the earth crust? Detailed integrated studying of "key-areas", with attention to deep geology, will allow to get new insight of the impact of post-glacial shoreline changes and history of man on the coast in the IML with focus on his past (history of relations) and future (impact of climate change. The project is an international project, with participation of institutes all

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

    NASA Astrophysics Data System (ADS)

    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 (<6°) that allowed >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.

  12. Structure of the SE Greenland margin from seismic reflection and refraction data: Implications for nascent spreading center subsidence and asymmetric crustal accretion during North Atlantic opening

    NASA Astrophysics Data System (ADS)

    Hopper, John R.; Dahl-Jensen, Trine; Holbrook, W. Steven; Larsen, Hans Christian; Lizarralde, Dan; Korenaga, Jun; Kent, Graham M.; Kelemen, Peter B.

    2003-05-01

    Seismic reflection and refraction data from the SE Greenland margin provide a detailed view of a volcanic rifted margin from Archean continental crust to near-to-average oceanic crust over a spatial scale of 400 km. The SIGMA III transect, located ˜600 km south of the Greenland-Iceland Ridge and the presumed track of the Iceland hot spot, shows that the continent-ocean transition is abrupt and only a small amount of crustal thinning occurred prior to final breakup. Initially, 18.3 km thick crust accreted to the margin and the productivity decreased through time until a steady state ridge system was established that produced 8-10 km thick crust. Changes in the morphology of the basaltic extrusives provide evidence for vertical motions of the ridge system, which was close to sea level for at least 1 m.y. of subaerial spreading despite a reduction in productivity from 17 to 13.5 km thick crust over this time interval. This could be explained if a small component of active upwelling associated with thermal buoyancy from a modest thermal anomaly provided dynamic support to the rift system. The thermal anomaly must be exhaustible, consistent with recent suggestions that plume material was emplaced into a preexisting lithospheric thin spot as a thin sheet. Exhaustion of the thin sheet led to rapid subsidence of the spreading system and a change from subaerial, to shallow marine, and finally to deep marine extrusion in ˜2 m.y. is shown by the morphological changes. In addition, comparison to the conjugate Hatton Bank shows a clear asymmetry in the early accretion history of North Atlantic oceanic crust. Nearly double the volume of material was emplaced on the Greenland margin compared to Hatton Bank and may indicate east directed ridge migration during initial opening.

  13. Revealing the long-term landscape evolution of the South Atlantic passive continental margin, Brazil and Namibia, by thermokinematic numerical modeling using the software code Pecube.

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    The aim of the research is to quantify the long-term landscape evolution of the South Atlantic passive continental margin (SAPCM) in SE-Brazil and NW-Namibia. Excellent onshore outcrop conditions and complete rift to post-rift archives between Sao Paulo and Porto Alegre and in the transition from Namibia to Angola (onshore Walvis ridge) allow a high precision quantification of exhumation, and uplift rates, influencing physical parameters, long-term acting forces, and process-response systems. Research will integrate the published and partly published thermochronological data from Brazil and Namibia, and test lately published new concepts on causes of long-term landscape evolution at rifted margins. 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 PECUBE1,2 and FastScape3). 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 data and models will allow separating the exogenous and endogenous forces and their process rates. References 1. Braun, J., 2003. Pecube: A new finite element code to solve the 3D heat transport equation including the effects of a time-varying, finite amplitude surface topography. Computers and Geosciences, v.29, pp.787-794. 2. Braun, J., van der Beek, P., Valla, P., Robert, X., Herman, F., Goltzbacj

  14. High-level landscapes along the margin of southern East Greenland-A record of tectonic uplift and incision after breakup in the NE Atlantic

    NASA Astrophysics Data System (ADS)

    Bonow, Johan M.; Japsen, Peter; Nielsen, Troels F. D.

    2014-05-01

    Elevated plateaux and deeply incised valleys characterise the large-scale landscapes along the East Greenland margin as in many elevated, passive continental margins around the world. The absence of syn- or post-rift rocks in, for example, the mountains of Norway, hampers the assessment of the age of these landscapes and of the present-day elevation. The mountains of southern East Greenland (68-71°N), however, expose thick basalts that were extruded onto a largely horizontal lava plain near sea level during breakup of the NE Atlantic at the Paleocene-Eocene transition. We take advantage of these favourable geological conditions to investigate the uplift history after continental breakup. In particular, it is clear that present-day elevations of these basalts up to 3.7 km above sea level (a.s.l.) were reached after breakup. We have mapped regional erosion surfaces and integrated the information about the landscape with the stratigraphic record (i.e. stratigraphic landscape analysis). The analysis led to the following relative denudation chronology for southern East Greenland: At breakup, the margin subsided and underwent km-scale burial. Around the Eocene-Oligocene transition, the first phase of uplift, tilting and subsequent erosion led to the formation of an extensive, low-relief erosion surface (the Upper Planation Surface, UPS) that was graded towards the base level of the adjacent ocean before the eruption of Miocene lavas onto that surface. A second uplift that most likely occurred after the Miocene produced a new erosion surface (the Lower Planation Surface, LPS) by incision below the UPS. Finally, a third event in the late Cenozoic lifted the UPS and the LPS to their present elevations of up to 3 and 2 km a.s.l., respectively and shaped the present-day valleys and fjords by incision of rivers and glaciers below the LPS. The general picture of landscape development is highly similar to West Greenland and the common characteristics between the stepped

  15. Genomewide single nucleotide polymorphism discovery in Atlantic salmon (Salmo salar): validation in wild and farmed American and European populations.

    PubMed

    Yáñez, J M; Naswa, S; López, M E; Bassini, L; Correa, K; Gilbey, J; Bernatchez, L; Norris, A; Neira, R; Lhorente, J P; Schnable, P S; Newman, S; Mileham, A; Deeb, N; Di Genova, A; Maass, A

    2016-07-01

    A considerable number of single nucleotide polymorphisms (SNPs) are required to elucidate genotype-phenotype associations and determine the molecular basis of important traits. In this work, we carried out de novo SNP discovery accounting for both genome duplication and genetic variation from American and European salmon populations. A total of 9 736 473 nonredundant SNPs were identified across a set of 20 fish by whole-genome sequencing. After applying six bioinformatic filtering steps, 200 K SNPs were selected to develop an Affymetrix Axiom(®) myDesign Custom Array. This array was used to genotype 480 fish representing wild and farmed salmon from Europe, North America and Chile. A total of 159 099 (79.6%) SNPs were validated as high quality based on clustering properties. A total of 151 509 validated SNPs showed a unique position in the genome. When comparing these SNPs against 238 572 markers currently available in two other Atlantic salmon arrays, only 4.6% of the SNP overlapped with the panel developed in this study. This novel high-density SNP panel will be very useful for the dissection of economically and ecologically relevant traits, enhancing breeding programmes through genomic selection as well as supporting genetic studies in both wild and farmed populations of Atlantic salmon using high-resolution genomewide information. PMID:26849107

  16. Influence of the Atlantic Multidecadal Variability on the Winter European Climate in EC-Earth 3.1

    NASA Astrophysics Data System (ADS)

    Davini, Paolo; von Hardenberg, Jost; Corti, Susanna

    2015-04-01

    Atlantic Multidecadal Variability (AMV) is known for being able to influence the mid-latitude climate variability, especially over the European region. In this work we assess the impact of the wintertime AMV in a group of 200-year atmospheric-only simulation performed with EC-Earth 3.1. We force the atmosphere with positive and negative AMV-like SSTs and Sea Ice Concentrations patterns: firstly we apply the AMV anomalies to the whole North Atlantic ocean, hence only to the extratropics (north of 30°N) and finally only to the tropics (between 0° and 30°N), for a total of 6 experiments. Preliminary results show a wintertime NAO-like signal associated with a shift of the jet stream and changes in the blocking frequencies, leading to a negative NAO during positive AMV and viceversa. Surprisingly, the bulk of the signal is caused by the tropical anomalies, and it is associated with the changes in tropical precipitation along the Equator. Indeed, the NAO-like response is almost negligible when the AMV anomalies are applied only to the extratropics.

  17. Sedimentary and structural control on pockmark development—evidence from the Nyegga pockmark field, NW European margin

    NASA Astrophysics Data System (ADS)

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

    2010-06-01

    The Nyegga region, located at water depths of about 600-800 m on the NW European continental margin, contains more than 200 pockmarks. Recently collected TOPAS seismic profiles and EM1002 bathymetric records now provide high-resolution information on their seabed and shallow sub-seabed geological setting. The identified pockmarks are up to 15 m deep, between 30 m and 600 m across and reach a maximum area of ca. 315,000 m2. The pockmarks are sediment-empty features. They do not have any preferred direction of orientation and show large variations in their shape. The pockmarks are restricted to a <16.2 cal. ka old sediment unit. This unit comprises sandy mud and is characterised by sedimentation rates of ca. 1 mm/year. The pockmarks are localised over a thick late Plio-Pleistocene prograding sediment package and a polygonal faulted Miocene-Oligocene ooze-rich unit. The late Plio-Plistocene deposits host bottom simulating reflectors, indicative of gas hydrate-bearing sediments. Inspection of the newly collected high-resolution dataset, combined with previously analysed sediment cores and 2D multichannel seismic profiles, reveals that the Nyegga pockmark field does not show any strong relationship between seabed features, sub-seabed structures and the sedimentary setting. This suggests a more complex evolution history of the Nyegga pockmark field then previously thought.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Effect of gas-transfer-velocity parameterization choice on CO2 air-sea fluxes in the North Atlantic and European Arctic

    NASA Astrophysics Data System (ADS)

    Wróbel, I.; Piskozub, J.

    2015-11-01

    The ocean sink is an important part of the anthropogenic CO2 budget. Because the terrestrial biosphere is usually treated as a residual, understanding the uncertainties the net flux into the ocean sink is crucial for understanding the global carbon cycle. One of the sources of uncertainty is the parameterization of CO2 gas transfer velocity. We used a recently developed software tool, FluxEngine, to calculate monthly net carbon air-sea flux for the extratropical North Atlantic, European Arctic as well as global values (or comparison) using several available parameterizations of gas transfer velocity of different dependence of wind speed, both quadratic and cubic. The aim of the study is to constrain the uncertainty caused by the choice of parameterization in the North Atlantic, a large sink of CO2 and a region with good measurement coverage, characterized by strong winds. We show that this uncertainty is smaller in the North Atlantic and in the Arctic than globally, within 5 % in the North Atlantic and 4 % in the European Arctic, comparing to 9 % for the World Ocean when restricted to functions with quadratic wind dependence and respectively 42, 40 and 67 % for all studied parameterizations. We propose an explanation of this smaller uncertainty due to the combination of higher than global average wind speeds in the North Atlantic and lack of seasonal changes in the flux direction in most of the region. We also compare the available pCO2 climatologies (Takahashi and SOCAT) pCO2 discrepancy in annual flux values of 8 % in the North Atlantic and 19 % in the European Arctic. The seasonal flux changes in the Arctic have inverse seasonal change in both climatologies, caused most probably by insufficient data coverage, especially in winter.

  20. The evolution of the southern margin of the East European Craton based on seismic and potential field data

    NASA Astrophysics Data System (ADS)

    Kostyuchenko, S. L.; Morozov, A. F.; Stephenson, R. A.; Solodilov, L. N.; Vedrentsev, A. G.; Popolitov, K. E.; Aleshina, A. F.; Vishnevskaya, V. S.; Yegorova, T. P.

    2004-03-01

    This paper presents an integrated geophysical study of the southern margin of the East European Craton (EEC) in the Karpinksy Swell-North Caucasus area. It presents new interpretations of deep refraction and wide-angle reflection "deep seismic sounding" (DSS) data as well as conventional seismic and CDP profiling and new analyses of potential field data, including three-dimensional gravity and magnetic modelling. An integrated model of the physical properties and structure of the Earth's crust and, partially, upper mantle displays distinct features that are related to tectonic history of the study area. The Voronezh Massif (VM), the Ukrainian Shield and Rostov Dome (RD) of the EEC as well as the Donbas Foldbelt (DF), Karpinsky Swell (KS), Scythian Plate (SP) and Precaspian Basin (PCB) constitute the geodynamic ensemble that developed on the southern margin of the continent Baltica. There proposed evolutionary model comprises a stage of rifting during the middle to late Devonian, post-rift extension and subsidence during Carboniferous-early Permian times (synchronous with and related to the southward displacement of the Rostov Dome and extension in a palaeo-Scythian back-arc basin), and subsequent Mesozoic and younger evolution. A pre-Ordovician, possibly Riphean (?), mafic magmatic complex is inferred on a near vertical reflection seismic cross-section through the western portion of the Astrakhan Dome in the southwest part of the Precaspian Basin. This complex combined with evidence of a subducting slab in the upper mantle imply the presence of pre-Ordovician (Riphean?) island arc, with synchronous extension in a Precaspian back-arc basin is suggested. A middle Palaeozoic back-arc basin ensemble in what is now the western Karpinsky Swell was more than 100 km to the south from its present location. The Stavropol High migrated northwards, dislocating and moving fragments of this back-arc basin sometime thereafter. Linear positive magnetic anomalies reflect the

  1. Plio-Quaternary paleostresses in the Atlantic passive margin of the Moroccan Meseta: Influence of the Central Rif escape tectonics related to Eurasian-African plate convergence

    NASA Astrophysics Data System (ADS)

    Chabli, Ahmed; Chalouan, Ahmed; Akil, Mostapha; Galindo-Zaldívar, Jesús; Ruano, Patricia; Sanz de Galdeano, Carlos; López-Garrido, Angel Carlos; Marín-Lechado, Carlos; Pedrera, Antonio

    2014-07-01

    The Atlantic Moroccan Meseta margin is affected by far field recent tectonic stresses. The basement belongs to the variscan orogen and was deformed by hercynian folding and metamorphism followed by a post-Permian erosional stage, producing the flat paleorelief of the region. Tabular Mesozoic and Mio-Plio-Quaternary deposits locally cover the Meseta, which has undergone recent uplift, while north of Rabat the subsidence continues in the Gharb basin, constituting the foreland basin of the Rif Cordillera. The Plio-Quaternary sedimentary cover of the Moroccan Meseta, mainly formed by aeolian and marine terraces deposits, is affected by brittle deformations (joints and small-scale faults) that evidence that this region - considered up to date as stable - is affected by the far field stresses. Striated faults are recognized in the oldest Plio-Quaternary deposits and show strike-slip and normal kinematics, while joints affect up to the most recent sediments. Paleostress may be sorted into extensional, only affecting Rabat sector, and three main compressive groups deforming whole the region: (1) ENE-WSW to ESE-WNW compression; (2) NNW-SSE to NE-SW compression and (3) NNE-SSW compression. These stresses can be attributed mainly to the NW-SE oriented Eurasian-African plate convergence in the western Mediterranean and the escape toward the SW of the Rif Cordillera. Local paleostress deviations may be related to basement fault reactivation. These new results reveal the tectonic instability during Plio-Quaternary of the Moroccan Meseta margin in contrast to the standard passive margins, generally considered stable.

  2. ENAM: A community seismic experiment targeting rifting processes and post-rift evolution of the Mid Atlantic US margin

    NASA Astrophysics Data System (ADS)

    Van Avendonk, H. J.; Magnani, M. B.; Shillington, D. J.; Gaherty, J. B.; Hornbach, M. J.; Dugan, B.; Long, M. D.; Lizarralde, D.; Becel, A.; Benoit, M. H.; Harder, S. H.; Wagner, L. S.; Christeson, G. L.

    2014-12-01

    The continental margins of the eastern United States formed in the Early Jurassic after the breakup of supercontinent Pangea. The relationship between the timing of this rift episode and the occurrence of offshore magmatism, which is expressed in the East Coast Magnetic Anomaly, is still unknown. The possible influence of magmatism and existing lithospheric structure on the rifting processes along margin of the eastern U.S. was one of the motivations to conduct a large-scale community seismic experiment in the Eastern North America (ENAM) GeoPRISMS focus site. In addition, there is also a clear need for better high-resolution seismic data with shallow penetration on this margin to better understand the geological setting of submarine landslides. The ENAM community seismic experiment is a project in which a team of scientists will gather both active-source and earthquake seismic data in the vicinity of Cape Hatteras on a 500 km wide section of the margin offshore North Carolina and Virginia. The timing of data acquisition in 2014 and 2015 facilitates leveraging of other geophysical data acquisition programs such as Earthscope's Transportable Array and the USGS marine seismic investigation of the continental shelf. In April of 2014, 30 broadband ocean-bottom seismometers were deployed on the shelf, slope and abyssal plain of the study site. These instruments will record earthquakes for one year, which will help future seismic imaging of the deeper lithosphere beneath the margin. In September and October of 2014, regional marine seismic reflection and refraction data will be gathered with the seismic vessel R/V Marcus Langseth, and airgun shots will also be recorded on land to provide data coverage across the shoreline. Last, in the summer of 2015, a land explosion seismic refraction study will provide constraints on the crustal structure in the adjacent coastal plain of North Carolina and Virginia. All seismic data will be distributed to the community through IRIS

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

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

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

  4. The complex post-rift evolution of the South Atlantic margin, South Africa: new insights from joint inversion of apatite (U-Th)/He and fission track thermochronometry.

    NASA Astrophysics Data System (ADS)

    Wildman, Mark; Brown, Roderick; Persano, Cristina; Beucher, Romain; Stuart, Finlay

    2013-04-01

    The continental edge of southwestern Africa has long been seen as a type example of a high elevation passive margin, with its characteristic topography forming during or shortly after rifting (c. 130 Ma). Recent work along the South Atlantic passive margin has highlighted the importance of interactions between rift-tectonics, mantle flow and dynamic topography on controlling margin evolution, however, the temporal relationship between these processes is still poorly understood. There is now increasing evidence from satellite imagery, onshore field observations (e.g. Viola et al., 2012) and offshore sedimentary basin analysis (e.g. Hirsch et al., 2010) that suggests that these processes have resulted in a much more complex structural and thermal history along the margin than previously thought. A critical step towards developing a better understanding of the post-rift evolution of this margin is to quantify the surface response (i.e. uplift and erosion) to these major structural and thermal events. Apatite fission track analysis (AFTA) has been used world-wide as a powerful means of extracting quantitative constraints on the timing and rate of major episodes of onshore denudation. Previous AFTA studies in SW Africa have identified two distinct cooling events occurred during early and late Cretaceous, respectively. However, in places AFT ages vary significantly over relatively short distances and this has been interpreted to indicate local differential erosion levels controlled by tectonic displacements related to fault reactivation. A limitation of the AFT system is that it is sensitive to a temperature range of c. 120-60°C and therefore is unable to evaluate the magnitude of denudation episodes where the amounts are less than c. 1.5-2 km. So while the Cretaceous history of erosion is well established from existing AFTA data, the details of the timing and amount of erosion occurring during the Cenozoic remain relatively poorly constrained. The apatite (U

  5. Instabilities in the relation between European Weather Types and mid-latitude circulation in the Atlantic

    NASA Astrophysics Data System (ADS)

    Alvarez Castro, Maria del Carmen; Gallego, David; Trigo, Ricardo M.; García-Herrera, Ricardo; Ribera, Pedro

    2015-04-01

    Recently, a new instrumental index (Westerly Index or "WI") measuring the frequency of the westerlies over the English Channel has been developed for the period 1685-1750 (Wheeler et al. 2009) and further extended to the present (Barriopedro et al. 2014). This index holds a climatic signal similar to the North Atlantic Oscillation (NAO) in the temperature and precipitation over large areas of Europe. Nevertheless we are confident that the WI offers two major advantages: first the WI signatures are not restricted to the winter being significant during the entire year and second, the WI does not rely on proxy data and, as such, it is less prone to the uncertainties associated to the calibration process of the NAO reconstructions. During the last decades, regional mid-latitude circulation has also been quantified objectively through the widespread use of so-called Weather Types (WT). WT are used to identify and classify the different patterns of Sea Level Pressure configurations originating particular weather in a given area. In consequence, WT over most Western Europe should be closely related to atmospheric circulation indexes such as the WI. Here we adopted a similar WT classification of the classical WTs developed empirically by Hubert Lamb for the UK and automated by Jones et al. (1993) but centered at the English Channel latitudinal band to be compatible with the window used to define the WI (Wheeler et al., 2009). In this work we compare the long-term (1850-2003) monthly values of WI with the corresponding monthly frequency of directional weather types in the WI area. As expected, we found significant positive (negative) correlation values with WTs dominated by a westerly (easterly) component but interestingly, some quasi periodic intervals of lack of correlation have been found, suggesting an oscillating behaviour on the lack of stationarity between the large-scale north Atlantic circulation and local weather types. Wheeler, D.; García-Herrera, R.; Wilkinson

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

    USGS Publications Warehouse

    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

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

    NASA Astrophysics Data System (ADS)

    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

  8. Is the Atlantic surface temperature a good proxy for forecasting the recruitment of European eel in the Guadalquivir estuary?

    NASA Astrophysics Data System (ADS)

    Gutiérrez-Estrada, Juan Carlos; Pulido-Calvo, Inmaculada

    2015-01-01

    This study analysed the possibility of using the sea surface temperature (SST) of the Atlantic Ocean to predict the recruitment of European eels in one of the most important estuaries of the south of Europe. For this purpose, two different time series concerning glass eel in the Guadalquivir estuary (the first obtained from a set of fishery-independent experimental samplings in this estuary and the second from an unofficial database on commercial catches provided by one of the main local marketer-buyers) were standardised to obtain a single time series on a monthly scale. This series was correlated with a total of 368 SST time series for 368 sectors of 1.95° × 1.95° of the Atlantic Ocean covering the possible migration routes of adult eels and leptocephalous larvae. The significant sectors were clustered and selected as inputs for artificial neural network models (ANNs) with the objective of obtaining a model to forecast glass eel recruitment. Globally, the best result was given by an ANN with only 12 clusters as input variables and 35 neurons in the hidden layer. For this configuration, the explained variance in the test phase was slightly higher than 79%. These results were significantly better than those obtained with classical methods. The strong correlation between predicted and observed glass eel abundance suggests that: (a) there is a marked non-linear relationship between SST and glass eel recruitment in the Guadalquivir estuary; (b) SST is a good proxy for predicting glass eel recruitment and; (c) one of the main factors responsible for the changes in abundance of this species is changes in the ocean conditions.

  9. Geometry of relict surfaces in Northern Norway: Implications for the extensional evolution of the NE Atlantic margin

    NASA Astrophysics Data System (ADS)

    Schermer, Elizabeth; Redfield, Tim

    2013-04-01

    The distribution and geometry of relict surfaces adjacent to the northern Norwegian passive margin can help constrain the post-rift evolution of the onshore region. A swath map of relict surfaces, covering the coast of Senja Island and extending SE to the drainage divide, was constructed from DEMs, aerial photos and an NGU digital map database of Quaternary features. The map and histograms of elevation distribution depict three distinctly stepped, coast-parallel belts of preserved relict surfaces. The belts increase in mean elevation from coast to the southeast and, to a certain degree, correlate with the bedrock geology. Overall, the relict surfaces dip to the NW. Locally SE dipping surfaces in the coastal and central belts may be controlled by post-surface reactivation of normal faults. The coastal belt coincides with a fault-bounded horst of Precambrian rock. Although deeply incised by Alpine glaciers and fjords, relict surfaces are preserved on ridge tops and local broad peaks at 700-800 m. A central belt of much lower relief and with surfaces averaging 900-1100 m high coincides with Caledonian nappe rocks and exhibits few preserved surfaces. An inner belt of extensive and well preserved surfaces averaging 1300-1400m high coincides with peaks and the gently rolling upland of the Scandinavian mountain crest. Here, NW-trending paleoridges and paleovalleys are evident in contours of the highest surfaces. NW-SE topographic profiles (perpendicular to the COB) show distinct steps in the maximum height of the relict surfaces, interpreted to coincide with mapped normal faults whose vertical offsets (throw) may be up to 600-700 m. The geometry of relict surfaces is consistent with multiple rock column uplift events. Published apatite fission track (AFT) apparent ages are ~200 Ma (range ~170-220 Ma), indicating the onshore bedrock was within ~2-3 km of the surface since Early Jurassic time. No distinct AFT age offsets can be resolved within the data, limiting net throw

  10. Tropospheric mid-latitude geopotential wave characteristics associated with strong wind events in the North Atlantic/European region

    NASA Astrophysics Data System (ADS)

    Wild, Simon; Simmonds, Ian; Leckebusch, Gregor C.

    2015-04-01

    The variability of strong synoptic scale wind events in the mid-latitudes have long been linked to baroclinic wave activity in the mid troposphere. Previous studies have also shown that greater amplitudes of planetary waves in the mid troposphere are likely to increase the occurrence of regional extremes in temperature and precipitation. In this study we examine whether characteristics of planetary and synoptic mid-latitude waves show systematic anomalies in the North Atlantic/ European region which can be related to the occurrence of a strong surface wind event. We will mainly focus on two questions: 1) Do amplitudes for waves with different wave lengths show a systematic anomaly when a strong wind event occurs? 2) Can phases of the individual wave components be detected that favour strong wind events? In order to decompose the mid-tropospheric flow into longitudinal waves we employ the fast Fourier transform to the meridional mean of the geopotential height in 500hPa between 35° and 60°N for i) the entire latitude belt and ii) for a North Atlantic/European sector (36°W to 36°E). Our definition of strong wind events is based on the Storm Severity Index (SSI) alongside a wind tracking algorithm identifying areas of exceedances of the local 98th percentile of the 10m wind speed. First results using ERA-Interim Reanalysis from 1979 - 2014 for the extended winter season (ONDJFM) for the 50 most intense strong wind systems with respect to the SSI reveal a greater amplitude for all investigated wave numbers. Especially waves with wave lengths below 2000km show an increase of about 25% of the daily standard deviation on average. The distribution of wave phases for the different wave numbers with respect to the location of a strong wind event shows a less homogenous picture. There is however a high proportion of events that can be associated with phases around 3π/4 and 5π/4 of waves with lengths of around 6000km, equivalent to wave number 5 on a planetary scale

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

    USGS Publications Warehouse

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

    1979-01-01

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

  12. Genetic isolation by distance among populations of the netted dog whelk Nassarius reticulatus (L.) along the European Atlantic coastline.

    PubMed

    Couceiro, Lucía; Barreiro, Rodolfo; Ruiz, José M; Sotka, Erik E

    2007-01-01

    Estimates of the average distances by which marine larvae disperse are generally poorly described, despite the central role that larval dispersal plays in the demographic connectivity of populations across geographic space. Here, we describe the population genetic structure and average dispersal distance of the netted dog whelk Nassarius reticulatus (L.) (Mollusca, Gastropoda, Prosobranchia), a widespread member of European intertidal communities, using DNA sequence variation in a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). An analysis of 156 individuals from 6 locations spread across approximately 1700 km of the European Atlantic coastline revealed weak and nonsignificant population structure (overall Phi(ST) = 0.00013). However, pairwise Phi(ST) values revealed a slight but significant increase in genetic isolation with geographic distance (IBD), suggesting that populations are not panmictic across the sampled geographic range. If we assume that the isolation by distance is maintained by a stable, stepping stone model of gene flow, then the slope of the IBD is consistent with an average larval dispersal distance of approximately 70 km per generation. The spatial scale of larval dispersal in N. reticulatus is consistent with the life cycle of the species (planktotrophic veliger lasting 30-60 days before competent to settle). A mismatch analysis of the COI sequences revealed a signature of an ancient demographic expansion that began 61 500-160,000 years ago, well before the most recent Pleistocene glaciation event. The greatest levels of genetic diversity occur within the middle latitudes of the whelk's geographic range, consistent with the notion that historic populations of N. reticulatus might have expanded northward and southward from the centrally located Bay of Biscay. PMID:17728274

  13. Deep seismic reflection data of EDGE U.S. mid-Atlantic continental-margin experiment: Implications for Appalachian sutures and Mesozoic rifting and magmatic underplating

    NASA Astrophysics Data System (ADS)

    Sheridan, Robert E.; Musser, Douglas L.; Glover, Lynn, III; Talwani, Manik; Ewing, John I.; Holbrook, W. Steven; Purdy, G. Michael; Hawman, Robert; Smithson, Scott

    1993-06-01

    The EDGE seismic experiment across the Virginia continental margin delineated a Paleozoic suture, buried Appalachian terranes, and Mesozoic rifting and magmatic events. The seismic grid revealed that the Mesozoic Norfolk rift basin exists only in the northern one-third of the previously mapped area. The north-striking listric border fault of the Norfolk basin half-graben parallels seismic laminations in the basement. The Jurassic volcanic wedge pinches out just landward of the Baltimore Canyon trough hinge zone and downlaps on the hummocky oceanic basement under the continental rise. Under the continental slope, the volcanic wedgereaches depths >9 s (20 km). Two distinct intracrustal reflections at 4.0-5.0 s and at 7.0 s TWIT (two-way traveltime) dip southeastward at low angles (˜15°). The Moho reflection is disrupted where it is intersected by the 7.0 s reflection. Northwest of this point the Moho dips landward; seaward it is horizontal. Seaward of this point, the lower-crustal boundary laminations exist in a narrow interval (10.5-11.0 s) and are of strong amplitude. These changes in the Moho and lower crust represent the seaward edge of the Grenville-age North American crust and the landward edge of Jurassic magmatic underplating. A northwest-dipping reflection observed for the first time on the U.S. Atlantic margin may be the top of the Jurassic magmatic- underplating layer; the northwest-dipping reflection truncates the southeast- dipping 7.0 s TWTT reflection. Landward projection of the 7.0 s reflection yields a north-south trace on the postrift unconformity under the center of lower Chesapeake Bay. This trace is near a basement fault between low-grade metamorphic rocks (Carolina slate-Avalonia) on the east and high-grade rocks (Goochland terrane) on the west. This fault boundary and the southeastdipping 7.0 s reflection probably represent the Taconic suture.

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

    NASA Astrophysics Data System (ADS)

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  16. Multiple, discrete inversion episodes revealed by apatite fission track analysis along the southernmost Atlantic margin of South Africa

    NASA Astrophysics Data System (ADS)

    Wildman, M.; Brown, R. W.; Persano, C.; Stuart, F. M.

    2013-12-01

    The morpho-tectonic history of the western South African continental margin and interior plateau remains enigmatic. Recent investigations of offshore sediment accumulation and interpretations of onshore structural and geomorphological observations have highlighted the complex geological evolution of South Africa throughout the Mesozoic and Cenozoic. Moreover, advances in geodynamic modelling approaches have explored the crustal response to varying styles of rifting and the influence of mantle upwelling beneath the African plate. These geological observations and models, however, require validation from quantitative constraints on the surface response (i.e. uplift and erosion) to syn- and post rift thermal and tectonic processes Over the last two decades, low temperature thermochronometry, particularly apatite fission track analysis (AFTA) and apatite (U-Th)/He, have been effective tools in providing these constraints by tracking the time-temperature history of rocks through c. 60 - 110°C and 80 - 40°C, respectively. The unique ability of AFTA to constrain both the timing and nature of sample cooling rests largely on the sensitivity of fission track annealing to temperature. Here, we present new AFT data from a suite of samples across the entire western continental margin of South Africa which contributes to a now extensive AFT dataset spanning the entire sub-continent. This dataset broadly invokes at least two discrete episodes of cooling driven by km scale denudation at c. 130 Ma, following rifting and break up of West Gondwana, and 90 Ma as a response to renewed tectonic uplift. However, the apparent lack of correlation of AFT age with elevation or with distance from the coast highlight the spatial and temporal variability of post-rift cooling that may be related to Mid-Cretaceous structural reactivation along the margin. We also present thermal history modelling using the Bayesian transdimensional inverse modelling approach of QTQt (Gallagher, 2012). Modelling

  17. Structure and history of submarine slope failures at the Cape Fear submarine landslide, U.S. Atlantic margin

    NASA Astrophysics Data System (ADS)

    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.

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

    USGS Publications Warehouse

    Schulte, P.; Wade, B.S.; Kontny, A.; Self-Trail J.M.

    2009-01-01

    other northwest Atlantic margin sections. It could result from a shift to more distal depositional environments and condensed sedimentation during maximum fl ooding, rather than refl ecting a climatic change in the hinterland. The distinct 1% increase of the oxygen isotopes may correspond to the short-term latest Eocene "precursor isotope event." (4) The abrupt increase of sediment grainsize, carbonate content, and abundance of authigenic minerals (glauconite) across the major unconformity that separates Eocene from Oligocene sediments in the Eyreville core refl ects deposition in shallower settings associated with erosion, winnowing, and reworking. Sediments within the central crater were affected by the rapid eustatic sea-level changes associated with the greenhouse-icehouse transition, as well as by an abrupt major uplift event and possibly enhanced current activity on the northwestern Atlantic margin. ?? 2009 The Geological Society of America.

  19. Organic matter budget in the Southeast Atlantic continental margin close to the Congo Canyon: In situ measurements of sediment oxygen consumption

    NASA Astrophysics Data System (ADS)

    Rabouille, C.; Caprais, J.-C.; Lansard, B.; Crassous, P.; Dedieu, K.; Reyss, J. L.; Khripounoff, A.

    2009-12-01

    A study of organic carbon mineralization from the Congo continental shelf to the abyssal plain through the Congo submarine channel and Angola Margin was undertaken using in situ measurements of sediment oxygen demand as a tracer of benthic carbon recycling. Two measurement techniques were coupled on a single autonomous platform: in situ benthic chambers and microelectrodes, which provided total and diffusive oxygen uptake as well as oxygen microdistributions in porewaters. In addition, sediment trap fluxes, sediment composition (Org-C, Tot-N, CaCO 3, porosity) and radionuclide profiles provided measurements of, respectively input fluxes and burial rate of organic and inorganic compounds. The in situ results show that the oxygen consumption on this margin close to the Congo River is high with values of total oxygen uptake (TOU) of 4±0.6, 3.6±0.5 mmol m -2 d -1 at 1300 and 3100 m depth, respectively, and between 1.9±0.3 and 2.4±0.2 mmol m -2 d -1 at 4000 m depth. Diffusive oxygen uptakes (DOU) were 2.8±1.1, 2.3±0.8, 0.8±0.3 and 1.2±0.1 mmol m -2 d -1, respectively at the same depths. The magnitude of the oxygen demands on the slope is correlated with water depth but is not correlated with the proximity of the submarine channel-levee system, which indicates that cross-slope transport processes are active over the entire margin. Comparison of the vertical flux of organic carbon with its mineralization and burial reveal that this lateral input is very important since the sum of recycling and burial in the sediments is 5-8 times larger than the vertical flux recorded in traps. Transfer of material from the Congo River occurs through turbidity currents channelled in the Congo valley, which are subsequently deposited in the Lobe zone in the Congo fan below 4800 m. Ship board measurements of oxygen profiles indicate large mineralization rates of organic carbon in this zone, which agrees with the high organic carbon content (3%) and the large sedimentation rate (19

  20. Syn-tectonic sequence generation in low-gradient desert margin systems - the Lower Triassic Buntsandstein of the Central European Basin

    NASA Astrophysics Data System (ADS)

    Radies, D.; Stollhofen, H.; Hollmann, G.; Kukla, P.

    2004-12-01

    The Late Permian/Early Triassic succession of the Central European Basin (CEB) was repeatedly affected by tectonic pulses associated with the earliest phases of Tethyan and Arctic-North Atlantic rifting. Effects of differential tectonic subsidence are particularly well recorded by unconformities, which form widespread sequence boundaries. In the lowermost Triassic the Hardegsen Unconformity (H-unconformity) represents the most prominent unconformity that can be traced over a distance of 1200 km from southern Germany as far north as the Irish Sea Basin. This hiatus is best expressed on intra-basinal highs that are associated with "stratigraphic losses" of whole formations down to Permian strata and a calculated erosional downcutting of up to several hundreds of meters. This study investigates the controlling mechanisms of unconformity development in a predominantly continental environment. 3D-seismic data from the eastern margin of the East-Netherlands Palaeo-High reveal that differential subsidence during the Middle and Upper Buntsandstein was induced by basement tectonics. Core- and log-based facies analysis of 18 cores from the Ems Area in northwestern Germany identifies the effects of differential subsidence and growth faulting on the generation of sedimentary sequences of the Middle Buntsandstein. Lineaments of synsedimentary tectonic movements are observed in seismic sections and drillcores. They originate from deep rooting, north-south extending basement faults in Upper Carboniferous strata that were decoupled by intercalated Permian evaporits. The sedimentary sequences of the Middle Buntsandstein Group are characterised by the fining upward sequences of the Volpriehausen-, Detfurth- and Solling Formations. Beginning with basal sandstone units that represent either fluvial or aeolian dune sandstones the depositional environment changes into ephemeral fluvial or playa type deposits. The H-unconformity is expressed by a stratigraphic gap underlying the Solling

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

    NASA Astrophysics Data System (ADS)

    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.

  2. Sulfate reduction and methane oxidation in continental margin sediments influenced by irrigation (south-east Atlantic off Namibia)

    SciTech Connect

    Fossing, H.; Ferdelman, T.G.; Berg, P.

    2000-03-01

    Sulfate reduction rates (SRR) and concentrations of SO{sub 4}{sup 2{minus}}, H{sub 2}S, pyrite sulfur, total sulfur, CH{sub 4}, and organic carbon were measured with high depth resolution through the entire length of the SO{sub 4}{sup 2{minus}}-zone and well into the CH{sub 4}-xone at two continental slope stations in the eastern South Atlantic (Benguela upwelling area). The sediments were characterized by a high organic carbon content of approx. 7.5% at GeoB 3703 and 3.7% at GeoB 3714. At GeoB 3703 SO{sub 4}{sup 2{minus}} concentrations decreased linearly with depth to about 40 {micro}M at the sulfate-methane transition zone (SMT) at 3.5 m, while at GeoB 3714, SO{sub 4}{sup 2{minus}} remained at sea water concentration in the top 2 m of the sediment and then decreased linearly to about 70 {micro}M at the SMT at 6 m. Direct rate measurements of SRR ({sup 35}SO{sub 4}{sup 2{minus}}) showed that the highest SRR occurred within the surface 3--5 cm with peak rates of up to 20 and 7 nmol SO{sub 4}{sup 2{minus}} cm{sup 3}/day at GeoB 3703 and GeoB 3714, respectively. SRR decreased quasi-exponentially with depth at GeoB 3703 and the cumulative SRR over the length of the SO{sub 4}{sup 2{minus}} zone resulted in an areal SRR of 1114--3493 {micro}mol/m{sup 2} day at GeoB 3703 with more than 80% of the total sulfate reduction proceeding in the top 30 cm sediment. Modeled SRR balanced both methane oxidation rates and measured SRR within the SMT, but severely underestimated by up to 89% the total SRR{sub area} that were obtained from direct measurements. Modeled and measured SRR were reconciled by including solute transport by irrigation described by a non-local pore water exchange function ({alpha}) which had values of up to 0.3 year{sup {minus}1} in the top sediment, and decreased exponentially to zero (i.e., no irrigation) at 2--3 meters (i.e., above SMT). These results suggested that co-existing sulfate reduction processes and linear SO{sub 4}{sup 2{minus}} gradients can be

  3. Subglacial geomorphology reveals connections between glacial dynamics and deeper hydrocarbon reservoir leakages at the Polar north Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Andreassen, Karin; Deryabin, Alexey; Rafaelsen, Bjarne; Richarsen, Morten

    2014-05-01

    Three-dimensional (3D) seismic data from the Barents Sea continental shelf and margin reveal spatial links between subsurface distributions of inferred glacitectonic geomorphic landforms and seismic indications of fluid flow from deeper hydrocarbon reservoirs. Particularly 3D seismic techniques allow detailed mapping and visualization of buried glacial geomorphology and geophysical indications of fluid flow and gas accumulations. Several subsurface glacitectonic landforms show pronounced depressions up to 200 m deep and several km wide. These appear in many locations just upstream from hills of similar sizes and volumes, and are inferred to be hill-hole pairs. The hills are interpreted as thrusted and compressed slabs of sediments and bedrock which have been removed from their original location by moving glaciers during the last glacial, leaving the holes as depressions. The mapped depressions seem often to appear in sediments of different lithology and age. The appearance of mega-scale glacial lineations indicates that fast-flowing ice streams, draining the former Barents Sea and Fennoscandian ice sheets were the main agents of these glacitectonic landforms. Mapped fluid flow migration pathways from deeper reservoirs and shallow gas accumulations show evidence of active fluid migration systems over longer time periods, and their spatial relationship with the glacitectonic landforms is documented for several areas of the Barents Sea continental shelf. A conceptual model is proposed for the depressions, where brittle glacitectonic deformation takes place along a weak layer at the base of gas-hydrate cemented sediments. Fluid flow from deeper hydrocarbon reservoirs is inferred to be associated with cycles of glaciations and unloading due to glacial erosion and ice retreat, causing gas to expand, which in turn potentially breaks the traps, reactivates faults and creates new faults. Gas hydrate stability modeling indicates that the south-western Barents Sea is today

  4. European summer heatwaves and North Atlantic weather regimes in the last Millennium

    NASA Astrophysics Data System (ADS)

    Alvarez Castro, Maria del Carmen; Trasancos, Romain; Yiou, Pascal

    2015-04-01

    The European summer heatwaves have been increasing in frequency and magnitude in the past decades. A higher confidence in future changes in such extremes necessitates to have a better knowledge about extremes behavior in the past climate. The last millennium is well documented in terms of climate forcings. Modelling efforts have provided a wealth of climate simulations covering the last millennium. We want to exploit such data in order to assess how models simulate extreme summer heatwaves. The surface temperature and precipitation are closely related to atmospheric patterns. It has been shown that rainy winter/spring seasons reduce the frequency of hot summer days whereas dry seasons can be followed by summers with high or low frequency of hot days. In this poster, we show the relation between winter/spring precipitation with the frequency of hot days in the 10 hottest summers in Europe and Southern Europe during the Medieval Warm Period (MWP 1150-1250), the Little Ice Age (LIA 1650-1750), and the historical-present period (1850-2005). We first focus on a millennium simulations with the IPSL model (IPSL-CM5). We use daily temperature, precipitation, and SLP data from CMIP5 (Coupled Model Intercomparison Project phase 5) and a couple of IPSL simulations with diferents forcings. Summer weather regimes has been computed as well for NCEP sea level pressure data in order to compare observations with the same period (1948-2005) in CMIP5 and IPSL simulations outputs. We discuss and present the results comparing the effects of hydrological deficits in the preceding season, and the occurrence of specific weather regimes, during the hottest summers over Europe and SouthWestern Europe. This analysis compares differents climate forcings simulations.

  5. Evolution of the South Atlantic passive continental margin in southern Brazil derived from zircon and apatite (U-Th-Sm)/He and fission-track data

    NASA Astrophysics Data System (ADS)

    Karl, Markus; Glasmacher, Ulrich A.; Kollenz, Sebastian; Franco-Magalhaes, Ana O. B.; Stockli, Daniel F.; Hackspacher, Peter C.

    2013-09-01

    The area between São Paulo and Porto Alegre in southeastern Brazil plays a key area to understand and quantify the evolution of the South Atlantic passive continental margin (SAPCM) in Brazil. In this contribution, we present new thermochronological data attained by fission-track and (U-Th-Sm)/He analysis on apatites and zircons from metamorphic, sedimentary and intrusive rocks. 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 525.1(2.4) 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 (1.5) and 93.0 (2.5) Ma. The spatial distribution of these ages shows three distinct blocks with a different evolution cut by old fracture zones. While the central block exhibits an old stable block, the Northern and especially the Southern block underwent complex post-rift exhumation. The sample of the Northern block shows two distinct cooling phases in the Upper Cretaceous and the Paleogene to Neogene. After sedimentation of the Permian sandstones the samples of the Central block were never heated up over 100 °C with a following moderate to fast cooling phase in Cretaceous to Eocene time and a fast cooling between Oligocene to Miocene. The five thermal models obtained in the Southern block indicate a complex evolution with three cooling phases. The exhumation events of the three blocks correspond with the Paraná-Etendekka event, the alkaline intrusions due to the Trinidad hotspot, and the evolution of the continental rift basins in SE Brazil and are, therefore, most likely to be the major force for the post-rift evolution of the passive continental margin in SE Brazil, which therefore corresponds to the three main phases of the Andean orogeny.

  6. The development of cold-water coral mounds along the Moroccan Atlantic and Mediterranean margins revealed by MeBo drillings

    NASA Astrophysics Data System (ADS)

    Hebbeln, Dierk; Wienberg, Claudia; Frank, Norbert

    2015-04-01

    Cold-water corals (CWC) mostly occur in intermediate water depths between 200 m and 1000 m and are capable of forming substantial seafloor structures, so-called coral carbonate mounds. These mounds can reach heights from a few meters up to >300 m and are composed of a mixture of CWC (and other shell) fragments and hemipelagic sediments, that both individually serve as distinct paleo-archives. IODP Leg 307 drilled through Challenger Mound at the Irish margin and revealed for the first time the full life history of a coral mound. However, although CWC occur almost worldwide, the 155 m long Challenger Mound record was for many years the only record from a coral mound exceeding 10 m in length. During expedition MSM36 with the German R/V MARIA S. MERIAN in spring 2014, several coral mounds along the Moroccan margin, both in the Atlantic Ocean and in the Mediterranean Sea, were drilled (actually: push-cored) by applying the Bremen Seafloor Drill Rig MeBo. The MeBo is a remotely controlled drilling system that is lowered from the vessel to the seafloor. Energy supply and video control are secured by an umbilical linking the MeBo to the vessel. The scientific foci of expedition MSM36 were to investigate (1) the long-term development of CWC mounds in both areas over the last several 100,000 years in relation to changes in the ambient environmental conditions in the respective intermediate waters, (2) the life time history of these mounds, and (3) the forcing factors for the initiation and decease of individual mounds. In both working areas, a total amount of 11 sites were successfully drilled with MeBo. Eight drillings were conducted at CWC mounds (on-mound sites) and 3 drillings in the direct vicinity of the mounds (off-mound sites) in order to obtain continuous paleoceanographic records. Drilling depths ranged between 17 m and 71 m with the latter corresponding to the maximum drilling depth of MeBo. The core recoveries varied between the sites and ranged between 47% and

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

    USGS Publications Warehouse

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

    1999-01-01

    facies is composed of gravelly, shelly coarse to medium sand lags and large sand dunes on the valley margins. By comparison, the northwestern drift contains coarse silt interbeds and the adjacent valley floors exhibit small to medium sand dunes of fine sand. Because of the complex pattern of contour-parallel and valley-perpendicular flow paths of the Mediterranean outflow current, the larger-scale bedforms and coarser-grained sediment of valley facies trend perpendicular to the smaller-scale bedforms and finer-grained contourite deposits of adjacent sediment drift facies. Radiocarbon ages verify that the inner shelf shoreface sand facies (sedimentation rate 7.1 cm/kyr), mid-shelf mud facies (maximum rate 234 cm/kyr) and surface sandy contourite layer of 0.2-1.2 m thickness on the Cadiz slope (1-12 cm/kyr) have deposited during Holocene time when high sea level results in maximum water depth over the Gibraltar sill and full development of the Atlantic inflow and Mediterranean outflow currents. The transgressive sand sheet of the shelf, and the mud layer underlying the surface contourite sand sheet of the slope, correlate, respectively, with the late Pleistocene sea level lowstand and apparent weak Mediterranean outflow current.

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

    NASA Astrophysics Data System (ADS)

    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

  9. Integrated seismic, geophysical and geological interpretation of Meso-Atlantic Gulf of Guinea continental margin evolution, and hydrocarbon potential of the Cotonou (Dahomey or Benin) basin

    SciTech Connect

    Babalola, O.O.

    1990-01-01

    The assembled aeromagnetic, reflection-seismic, well-log, and gravity data, eliminate the large, problematic gaps in published geophysical data over the shallow-marine and coastal onshore. Data interpretation reveal discordant fracture zones beneath the Niger Delta region, indicating the Gulf of Guinea basins originated as a series of pull-apart basins, that favorable maturation estimates, migration pathways to good source-rocks, and trapping stratigraphic and structural configurations exist for the accumulation of hydrocarbons in several parts of the basin. Depth-to-basement data from exploratory wells in the basins were evaluated with thermo-mechanical subsidence models, to make geodynamic estimates of lithospheric extension. Seismic stratigraphic and structural analysis illustrate tectonic control of clastic and carbonate sedimentation, and the interplay of basinal subsidence with eustatic sea-level changes. The results support a hypothesis that during the breakup of Africa and South America, the Gulf of Guinea cul-de-sac consisted of several microplates, generated from brittle deformation of continental crust in response to mantle convection stresses from below, as well as torsional stresses from the northward of the South Atlantic rip into the Brasilo-West African region. Relative motion between five of these plates is invoked as the evolutionary model, accounting for the observed tectonic physiography as well as the extensional and compressional features of the Cotonou basin and the peri-Niger Delta region. The generation of short-lived continental microplates is also advanced as a model for breakup of large continental plates, as sea-floor spreading is established along nascent continental margins.

  10. A record of Appalachian denudation in postrift Mesozoic and Cenozoic sedimentary deposits of the U.S. Middle Atlantic continental margin

    USGS Publications Warehouse

    Poag, C.W.; Sevon, W.D.

    1989-01-01

    The complex interplay between source-terrain uplift, basin subsidence, paleoclimatic shifts, and sea-level change, left an extensive sedimentary record in the contiguous offshore basins of the U.S. middle Atlantic margin (Salisbury Embayment, Baltimore Canyon Trough, and Hatteras Basin). Isopach maps of 23 postrift (Lower Jurassic to Quaternary) a allostratigraphic units, coupled with a revised stratigraphic framework, reveal that tectonism, by regulating sediment supply (accumulation rate), dominated the interplay of forcing mechanisms. Tectonic pulses are evidenced by abruptly accelerated sediment accumulation, marked latitudinal shifts in the location of depocenters, and regional changes in lithofacies. Relatively rapid tectonic subsidence during the Early and Middle Jurassic history of the basins may have enhanced sediment accumulation rates. Beginning in the Late Jurassic, however, subsidence rates decreased significantly, though occasional short pulses of subsidence may have effected relative sea-level rises. Sea-level change heavily influenced the distribution and redistribution of sediments one they reached the basins, and paleoclimate regulated the relative abundance of carbonates and evaporites in the basins. We conclude that source terrains of the central Appalachian Highlands were tectonically uplifted, intensely weathered, and rapidly eroded three times since the Late Triassic: (1) Early to Middle Jurassic (Aalenian to Callovian); (2) mid-Early Cretaceous (Barremian); and (3) Late Cenozoic (Middle Miocene). Intervals of tectonic quiescence following these three tectonic pulses provided conditions suitable for the formation of regional erosion surfaces, geomorphic features commonly reported to characterize the central Appalachian Highlands. This series of three, irregularly spaced, tectonic/quiescent cycles does not, however, match the traditional four-cycle concept of post-Triassic Appalachian "peneplanation". ?? 1989.

  11. Statistical Regularities in the Distribution of Faults and Earthquakes in the Central Atlantic and Marginal Seas of the Euro-Asian Continent

    NASA Astrophysics Data System (ADS)

    Maslov, L. A.; Anokhin, V.

    2011-12-01

    Based on a large amount of observed data, cumulative and probability distribution graphs were constructed for the distribution of faults and lineaments by length. The areas of study are: Central Atlantic, Canary Islands, Iberian Peninsula, Russian Platform, Magellan Mountains (Pacific Ocean), marginal seas: Chukchi, Barents, and the Sea of Japan. Also, in the same locations already mentioned, cumulative and probability distribution graphs were constructed for the distribution of earthquakes by their magnitude. The following well-known statistical distribution functions were used to approximate and study the observed data: the normal distribution, log-normal, log-logistic, Gamma-distribution, and the Weibull. The generalized logistic equation, describing the evolution of systems of faults and earthquakes, was written as: dF(x)/dx=aM[1-F(x)/M]F(x)x↑c (*) A number of different distributions can be obtained from the general solution of this equation. Thus, at c = 0 it is the logistic function, at c = -1 it is the log-logistic function. For -1 < c <0 the solution of (*) represents an intermediate case. Our studies showed that the best approximation of the observed data, for both earthquakes and faults, is with a solution of the equation presented above. The figure shows the result of the approximation of the observed data in the Sea of Japan by the solution of equation (*). The survival and hazard functions corresponding to the solution of (*) were derived. Study of these functions showed that there exist a certain combination of parameters, coefficients of equation (*), marking a boundary between stable and unstable developments of a system

  12. Age estimates of the seaward-dipping volcanic wedge, earliest oceanic crust, and earliest drift-stage sediments along the North American Atlantic continental margin

    NASA Astrophysics Data System (ADS)

    Benson, Richard N.

    Owing to their depths of burial along and adjacent to the North American continental margin, there is no direct evidence obtained from boreholes for the ages of the seaward-dipping volcanic wedge, earliest drift-stage sediments overlying the wedge, and the earliest Atlantic oceanic crust between the East Coast (ECMA) and Blake Spur (BSMA) magnetic anomalies. Maximum ages of late Sinemurian for drift-stage sediments have been determined from exploration wells in the Scotian Basin. A similar age is postulated for those sediments in the Georges Bank Basin, but palynomorphs from exploration wells may indicate that earliest drift-stage sediments, in places associated with volcanic rocks, are of Bajocian age and occur higher in the section above the postrift unconformity as recognized on seismic lines. In the Southeast Georgia Embayment of the Blake Plateau Basin, the oldest drift-stage sediments overlying the postrift unconformity that were drilled are of Kimmeridgian-Tithonian age. In the Baltimore Canyon Trough, the volcanic wedge overlies the postrift unconformity which truncates buried synrift rocks that may be as young as Sinemurian. In the Carolina Trough and Blake Plateau Basin, a possible offshore flood basalt marking the postrift unconformity and traced as a reflector to the volcanic wedge may correspond to a subsurface flood basalt onshore that may be part of CAMP (Hettangian). Alternatively, its magmatic source may have been that of the possibly younger volcanic wedge. Sea-floor-spreading-rate lines based on the latest Jurassic time scales and extended to the BSMA and ECMA indicate ages of 166 and 171 Ma for the BSMA and 172 and 179 Ma for the ECMA. An alternative model suggests a middle Pliensbachian/early Toarcian age (188-190 Ma) for the igneous activity that produced the volcanic wedge and earliest oceanic crust.

  13. What can otolith shape analysis tell us about population structure of the European sardine, Sardina pilchardus, from Atlantic and Mediterranean waters?

    NASA Astrophysics Data System (ADS)

    Jemaa, Sharif; Bacha, Mahmoud; Khalaf, Gaby; Dessailly, David; Rabhi, Khalef; Amara, Rachid

    2015-02-01

    The European sardine, Sardina pilchardus, exhibits a complex population structure, which has produced conflicting results in previous genetic studies. Despite its importance in the fisheries industry, stock delineation for management and conservation purposes is still a matter of debate throughout the distribution range of the species. This study examines whether otolith shapes are more efficient than genetic markers to detect population structure in pelagic species with large population sizes. Sardines were analyzed from 15 sampling localities in the Northeast Atlantic and Mediterranean Sea covering almost the whole distribution range of the species. A combination of otolith shape indices and elliptic Fourier descriptors was investigated by multivariate statistical procedures. Within the studied area, three distinct groups were identified with an overall correct classification of 77%. Group A: northern Mediterranean Sea and Gulf of Gabès; group B: Atlantic Morocco-south Alboran-Algero-provençal coasts; and group C: European Atlantic coast. The Almeria-Oran front and the Gibraltar strait are not an efficient barrier for sardine population separation as there seems to be exchanges between populations of the south-western Mediterranean Sea and those of the Moroccan Atlantic Ocean coast or Gulf of Cadiz. The results are discussed in relation to environmental conditions, oceanographic features, and physical barriers to dispersal in the study area, and compared with those obtained by previous genetic, morphometric, and meristic data. For pelagic species with high gene flow, present results highlighted the need to take into account the identification of phenotypic stocks to ensure sustainable fishery benefits and efficient conservation as they may have unique demographic properties and responses to exploitation.

  14. Crustal high-velocity anomaly at the East European Craton margin in SE Poland (TESZ) modelled by 3-D seismic tomography of refracted and reflected arrivals

    NASA Astrophysics Data System (ADS)

    Środa, Piotr; Dec, Monika

    2016-04-01

    The area of Trans-European Suture Zone in SE Poland represents a contact of major tectonic units of different consolidation age - from the Precambrian East European Craton, through Palaeozoic West European Platform to Cenozoic Carpathian orogen. The region was built by several phases of crustal accretion, which resulted in a complex collage of tectonic blocks. In 2000, this region was studied by several seismic wide-angle profiles of CELEBRATION 2000 experiment, providing a dense coverage of seismic data in SE Poland and allowing for detailed investigations of the crustal structure and properties in this area. Beneath the marginal part of the EEC, the 2-D modelling of in-line data form several CELEBRATION profiles revealed a prominent high P-wave velocity anomaly in the upper crust, with Vp of 6.7-7.1 km/s, starting at 10-16 km depth (e.g., Środa et al., 2006). Anomalously high velocities are observed in the area located approximately beneath Lublin trough, to the NE of Teisseyre-Tornquist Zone. Based on 3-D tomography of first arrivals of in- and off-line CELEBRATION 2000 recordings (Malinowski et al., 2008), elevated velocities are also reported in the same area and seem to continue to the SW, off the craton margin. Gravimetric modelling also revealed anomalously high density in the same region at similar depths. High seismic velocities and densities are interpreted as indicative for a pronounced mafic intrusion, possibly related to extensional processes at the EEC margin. Previous 3-D models of the high-velocity intrusion were based on first arrivals (crustal refractions) only. In this study, also off-line reflections (not modelled up to now) are used, in order to enlarge the data set and to better constrain the geometry and properties of the velocity anomaly. A code for 3-D joint tomographic inversion of refracted and reflected arrivals, with model parametrization allowing for velocity discontinuities was used (Rawlinson, 2007). With this approach, besides the

  15. Sensitivity of advective transfer times across the North Atlantic Ocean to the temporal and spatial resolution of model velocity data: Implication for European eel larval transport

    NASA Astrophysics Data System (ADS)

    Blanke, Bruno; Bonhommeau, Sylvain; Grima, Nicolas; Drillet, Yann

    2012-05-01

    European eel (Anguilla anguilla) larvae achieve one of the longest larval migrations of the marine realm, i.e., more than 6000 km from their spawning grounds in the Sargasso Sea to European continental shelves. The duration of this migration remains debated, between 7 months and 3 years. This information is, however, crucial since it determines the period over which larvae are affected by environmental conditions and hence the subsequent recruitment success. We investigate the pathways and duration of trans-Atlantic connections using 3 years of high-resolution (daily, 1/12°) velocity fields available from a Mercator-Océan model configuration without data assimilation. We study specifically the effect of spatial and temporal resolutions on our estimates by applying various filters in time (from daily to 12-day averages) and space (from 1/12° to 1° gridcell aggregation) to the nominal model outputs. Numerical particles are released in the presumed European eel spawning area and considered as passive tracers at three specific depths (around 0, 50, and 200 m). We diagnose particularly the intensity of the water transfer between suitable control sections that encompass the eel larva distribution. Transit ages are also investigated, with a particular focus on the pathways that minimize the connection times between the western and eastern North Atlantic. We show that small-scale structures (eddies and filaments) contribute to faster connections though they also correspond to additional complexity in trajectories. The shortest pathways mostly follow the Gulf Stream and the North Atlantic Drift, whereas interior connections require longer transfers that prove less compatible with biological observations.

  16. Protection of drinking water reservoirs in buried glacial valleys in the ice-marginal landscape for securing future demand in the European perspective (ENCORE-Project).

    NASA Astrophysics Data System (ADS)

    Smit, F. W. H.; Bregman, E. P. H.

    2012-04-01

    Quaternary glaciations have left a significant sedimentological fingerprint in the subsurface of north Europe, in the form of buried glacial valleys. These structures are important drinking water reservoirs for millions of people in the ice-marginal landscape, but are increasingly threatened by anthropogenic pollution (nitrate, sulphate and organic pollutants) and geogenic pollution (salinization). That is one of the conclusion of a recent overview study in the IML of northern Europe from the North Sea to the southern Baltic area. Adequate policy making is yet not possible for several reasons: - Large amounts of data are needed to get a good grip on the lateral continuity of the complex infill. - The BurVal Working Group (2006) has shown that a combination of high resolution seismic survey, together with transient electromagnetic (TEM) surveys can provide realistic data for 3D hydrogeological models. However, these data have not yet been retrieved on a European scale. - Available borehole data can only be used as control points in 3D hydrological models, since the infill of buried glacial valleys is often lateral too complex to make sound interpolations possible. Pollution in buried glacial valleys crosses national borders in northern Europe and therefore national geological surveys have to cooperate in a newly formed European project on protection of these structures. The ENCORE - project (Environmental Conference of the European Regions) has shown in the past that it can facilitate fruitful European cooperation, which is urgently needed due to the costs of gathering data and due to knowledge gaps between different countries. By working together in a European context, these problems can be reduced so that better policy making is possible in order to secure our future drinking water availability.

  17. Complete mitochondrial genome sequences of Atlantic sturgeon, Acipenser oxyrinchus oxyrinchus, Gulf sturgeon, A. o. desotoi and European sturgeon A. sturio (Acipenseriformes: Acipenseridae) obtained through next generation sequencing.

    PubMed

    Popović, Danijela; Baca, Mateusz; Panagiotopoulou, Hanna

    2016-07-01

    Complete mitochondrial genome sequences of European sturgeon and two subspecies of the North American, Atlantic and Gulf sturgeons were determined using MiSeq Illumina technology. All three genomes show typical vertebrate organization. They possess 22 tRNA genes, 13 protein-coding genes, 2 rRNA (ribosomal RNA) genes and a non-coding control region. Excluding ND6, all protein-coding genes are on the heavy strand. The whole mitogenome sequences have been deposited in GenBank under accession numbers KP997216-KP997218. PMID:26017050

  18. Comparing momentum and mass (aerosol source function) fluxes for the North Atlantic and the European Arctic using different parameterizations

    NASA Astrophysics Data System (ADS)

    Wróbel, Iwona; Piskozub, Jacek

    2016-04-01

    Wind speed has a disproportionate role in the forming of the climate as well it is important part in calculate of the air-sea interaction thanks which we can study climate change. It influences on mass, momentum and energy fluxes and the standard way of parametrizing those fluxes is use this variable. However, the very functions used to calculate fluxes from winds have evolved over time and still have large differences (especially in the case of aerosol sources function). As we have shown last year at the EGU conference (PICO presentation EGU2015-11206-1) and in recent public article (OSD 12,C1262-C1264,2015) there is a lot of uncertainties in the case of air-sea CO2 fluxes. In this study we calculated regional and global mass and momentum fluxes based on several wind speed climatologies. To do this we use wind speed from satellite data in FluxEngine software created within OceanFlux GHG Evolution project. Our main area of interest is European Arctic because of the interesting air-sea interaction physics (six-monthly cycle, strong wind and ice cover) but because of better data coverage we have chosen the North Atlantic as a study region to make it possible to compare the calculated fluxes to measured ones. An additional reason was the importance of the area for the North Hemisphere climate, and especially for Europe. The study is related to an ESA funded OceanFlux GHG Evolution project and is meant to be part of a PhD thesis (of I.W) funded by Centre of Polar Studies "POLAR-KNOW" (a project of the Polish Ministry of Science). We have used a modified version FluxEngine, a tool created within an earlier ESA funded project (OceanFlux Greenhouse Gases) for calculating trace gas fluxes to derive two purely wind driven (at least in the simplified form used in their parameterizations) fluxes. The modifications included removing gas transfer velocity formula from the toolset and replacing it with the respective formulas for momentum transfer and mass (aerosol production

  19. Natural variability of pCO2 and pH in the Atlantic and Pacific coastal margins of the U.S

    NASA Astrophysics Data System (ADS)

    Sutton, A. J.; Sabine, C. L.; Feely, R. A.; Newton, J.; Salisbury, J.; Vandemark, D. C.; Musielewicz, S. B.; Maenner-Jones, S.; Bott, R.; Lawrence-Slavas, N.

    2011-12-01

    The discovery that seawater chemistry is changing as a result of carbon dioxide (CO2) emissions, referred to as "ocean acidification", has prompted a large effort to understand how this changing chemistry will impact marine life. Changes in carbon chemistry have been documented in the open ocean; however, in dynamic coastal systems where many marine species live, ocean acidification and the natural biogeochemical variability that organisms are currently exposed to are poorly quantified. In 2010 we began equipping coastal moorings currently measuring pCO2 with pH and other biogeochemical sensors to measure ocean acidification parameters at 3 hour intervals in the surface water. Here we present the magnitude and diurnal to seasonal variability of pCO2 and pH during the first year of observations at 2 sites in the Atlantic and Pacific coastal margins of the U.S.: the Gulf of Maine and outer coast of Washington state. Both the magnitude and range of pCO2 and pH values were much greater at the coastal moorings compared to the open ocean mooring at Ocean Station Papa in the North Pacific and also varied between the two coastal mooring sites. We observed maximum pCO2 values in coastal waters exceeding predicted values for the open ocean at 2x pre-industrial CO2 levels. The range of pCO2 and pH values during this time series was approximately 4 times the range observed at open ocean mooring Papa (2007-2011 time series). In many cases, large variance was observed at short time scales, with values fluctuating more than 200 μatm pCO2 and 0.2 pH between 3-hour cycles. These types of observations are critical for understanding how ocean acidification will manifest in naturally dynamic coastal systems and for informing the experimental design of species response studies that aim to mimic carbon chemistry experienced by coastal marine organisms.

  20. An approach to assess the marginal environmental costs for flow regulation: an example in three European rivers

    NASA Astrophysics Data System (ADS)

    de Jalon Diego, Garcia; de Jalon Silvestre, Garcia; Tanago Marta, Gonzalez

    2015-04-01

    In the last decades there has been a growing concern about water environmental costs. 'Polluter should pay' has been a phrase repeated in numerous policy-making processes. Water abstraction for Irrigation, Hydropower or water supply for Domestic or Industrial porpoises alters natural flow regimes impacting severely fluvial Ecosystems. The objective of this paper is to develop an evaluation of the marginal environmental costs for flow regulation. This approach is based on the idea 'who regulates flows should pay' and the amount to be paid should be proportional on the intensity, duration and frequency of the resulting regulated flows. The methodology proposed includes three separated steps: (i) estimating the natural flow regime of a river segment through studying the hydrologic conditions before the river is affected by a determined anthropogenic impact, (ii) assessing the hydrologic alteration of the river segment according to the estimated natural flow regime, and (iii) calculating marginal environmental costs of water supply. The three different case studies where the methodology was applied were the Esla River (Spain), the Upper River Tyne (England) and the Marna River (Norway).

  1. New clues to the evolutionary history of the main European paternal lineage M269: dissection of the Y-SNP S116 in Atlantic Europe and Iberia.

    PubMed

    Valverde, Laura; Illescas, Maria José; Villaescusa, Patricia; Gotor, Amparo M; García, Ainara; Cardoso, Sergio; Algorta, Jaime; Catarino, Susana; Rouault, Karen; Férec, Claude; Hardiman, Orla; Zarrabeitia, Maite; Jiménez, Susana; Pinheiro, Maria Fátima; Jarreta, Begoña M; Olofsson, Jill; Morling, Niels; de Pancorbo, Marian M

    2016-03-01

    The dissection of S116 in more than 1500 individuals from Atlantic Europe and the Iberian Peninsula has provided important clues about the controversial evolutionary history of M269. First, the results do not point to an origin of M269 in the Franco-Cantabrian refuge, owing to the lack of sublineage diversity within M269, which supports the new theories proposing its origin in Eastern Europe. Second, S116 shows frequency peaks and spatial distribution that differ from those previously proposed, indicating an origin farther west, and it also shows a high frequency in the Atlantic coastline. Third, an outstanding frequency of the DF27 sublineage has been found in Iberia, with a restricted distribution pattern inside this peninsula and a frequency maximum in the area of the Franco-Cantabrian refuge. This entire panorama indicates an old arrival of M269 into Western Europe, because it has generated at least two episodes of expansion in the Franco-Cantabrian area. This study demonstrates the importance of continuing the dissection of the M269 lineage in different European populations because the discovery and study of new sublineages can adjust or even completely revise the theories about European peopling, as has been the case for the place of origin of M269. PMID:26081640

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

    NASA Astrophysics Data System (ADS)

    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

  3. Salt tectonics in the SW Alps (Italy-France): From rifting to the inversion of the European continental margin in a context of oblique convergence

    NASA Astrophysics Data System (ADS)

    Decarlis, A.; Maino, M.; Dallagiovanna, G.; Lualdi, A.; Masini, E.; Seno, S.; Toscani, G.

    2014-12-01

    The SW Alps result from the inversion of the European continental margin during the oblique convergence between Europe and Adria since the Cretaceous. The orogenic deformation is controlled by two factors: the inherited sedimentary and structural record and the geodynamic interaction between the two plates. In this paper we present a stratigraphic and structural analysis of the external SW Alps (Ventimiglia-Menton area) in order to define the sedimentary and deformational geometries of the chain and to reconstruct the evolutionary history. The field-data highlight the preeminent role played by inherited salt-structures, which derive from the depositional history experienced by the European margin since the Mesozoic onwards. From Late Triassic to Jurassic, evaporites and carbonates deposited as a response to the Thetyan rifting. The following emplacement of the Cretaceous flysch and of the Eocene foreland basin succession was strongly influenced by the extensionally-triggered salt diapirism and by the interactions with deformations connected to the Pyrenees dynamics. The resulting geologic discontinuities (i.e. diapir-induced highs and basins, inherited normal and trasform faults) strongly influenced the successive Oligo-Miocene evolution of the belt in the study area. Observed changes in the thrusts and folds kinematics are considered as the results of rotation during their approaching to inherited highs. Furthermore, the overturning of thrusts and folds in the front of the diapiric flanks are associated with the progressively salt squeezing into the anticlines cores promoted by ongoing Alpine compression. Finally, the kinematic data from the study area show radical differences in the tectonic transport direction with respect to the rest of the SW Alps (NW- to W-ward in the Ventimiglia-Menton area, S- to SW-ward in Provence and Ligurian Alps). This difference is interpreted to be caused by the relative motions of crustal blocks dominated by transpressive tectonics

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

    NASA Astrophysics Data System (ADS)

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

    1998-12-01

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

  5. Climate change impairs processes of soil and plant N cycling in European beech forests on marginal soil

    NASA Astrophysics Data System (ADS)

    Tejedor, Javier; Gasche, Rainer; Gschwendtner, Silvia; Leberecht, Martin; Bimüller, Carolin; Kögel-Knabner, Ingrid; Pole, Andrea; Schloter, Michael; Rennenberg, Heinz; Simon, Judy; Hanewinkel, Marc; Baltensweiler, Andri; Bilela, Silvija; Dannenmann, Michael

    2014-05-01

    Beech forests of Central Europe are covering large areas with marginal calcareous soils, but provide important ecological services and represent a significant economical value. The vulnerability of these ecosystems to projected climate conditions (higher temperatures, increase of extreme drought and precipitation events) is currently unclear. Here we present comprehensive data on the influence of climate change conditions on ecosystem performance, considering soil nitrogen biogeochemistry, soil microbiology, mycorrhiza ecology and plant physiology. We simultaneously quantified major plant and soil gross N turnover processes by homogenous triple 15N isotope labeling of intact beech natural regeneration-soil-microbe systems. This isotope approach was combined with a space for time climate change experiment, i.e. we transferred intact beech seedling-soil-microbe mesocosms from a slope with N-exposure (representing present day climate conditions) to a slope with S exposure (serving as a warmer and drier model climate for future conditions). Transfers within N slope served as controls. After an equilibration period of 1 year, three isotope labeling/harvest cycles were performed. Reduced soil water content resulted in a persistent decline of ammonia oxidizing bacteria in soil (AOB). Consequently, we found a massive five-fold reduction of gross nitrification in the climate change treatment and a subsequent strong decline in soil nitrate concentrations as well as nitrate uptake by microorganisms and beech. Because nitrate was the major nutrient for beech in this forest type with little importance of ammonium and amino acids, this resulted in a strongly reduced performance of beech natural regeneration with reduced N content, N metabolite concentrations and plant biomass. These findings provided an explanation for a large-scale decline of distribution of beech forests on calcareous soils in Europe by almost 80% until 2080 predicted by statistical modeling. Hence, we

  6. Lithosphere structure of the Donbas Fodbelt and Karpinsky Swell region (the southern margin of the East-European Craton), Ukraine and Russia, from seismic and gravity data

    NASA Astrophysics Data System (ADS)

    Yegorova, T.; Baranova, E.; Starostenko, V.

    2003-04-01

    LITHOSPHERE STRUCTURE OF THE DONBAS FOLDBELT AND KARPINSKI SWELL REGION (THE SOUTHERN MARGIN OF THE EAST-EUROPEAN CRATON), UKRAINE AND RUSSIA, FROM SEISMIC AND GRAVITY DATA T.Yegorova (1), E.Baranova (1), V.Starostenko (1) (1) Institute of Geophysics, National Academy of Sciences of Ukraine egorova@igph.kiev.ua Along the southern margin of the East-European platform (EEC) super deep Late Devonian rift basins Dnieper-Donets Basin (DDB) and Peri-Caspian Basin (PCB) are located. The structures are adjacent to a zone along which crust was reworked and/or accreted to the EEC during Late Palaeozoic-Triassic times. The objective of the present study is deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the EEC. The study area includes the inverted southernmost part of the intracratonic DDB Donbas Foldbelt (DF), its south-eastern prolongation along the margin of the EEC the sedimentary succession of the Karpinsky Swell (KS), the south-western part of the Peri-Caspian Basin (PCB) and the Scythian Plate. According to the structure of the sedimentary basin, the DF and the KS form a single linear structure, represented by the uplift of Palaeozoic rocks, with the exposure of Carboniferous coal-bearing rocks in the DF, and by deep trough (down to the depth of 20 km and more) on the top of the crystalline Precambrian basement. The 3D gravity back-stripping analysis, implemented to test the sediment structure, reveals a distinct elongate zone of positive sediment corrected anomalies along the axis of the DF-KS and strong positive anomaly in the PCB. This is caused by heterogeneous lithosphere structure below the basin: Moho topography and/or the existence of a high density material in the crystalline crust and uppermost mantle. Our previous investigations have supported the existence of high-density body in the crystalline crust along the DDB axis. The

  7. Influence of the North Atlantic oceanograghic and climatic parameters on the Spanish European Eel population recruitment: relationships in the past and for a future climate change

    NASA Astrophysics Data System (ADS)

    Ribalaygua, Jaime; Pórtoles, Javier; Monjo, Robert; Díaz, Estíbaliz; Korta, María; Chust, Guillem

    2016-04-01

    The status of the European eel population is critical.; the annual recruitment of glass eel to European waters in 2015 is 1.2% of the 1960-1979 level in the 'North Sea' area, and 8.4% in the rest of Europe (ICES 2015) . There are a number of anthropogenic impacts potentially affecting eel population including commercial exploitation, habitat loss, dam and weir construction, hydropower, pumping stations and surface water abstractions. Furthermore, the first eel stages and larval migration and marine survival are heavily influenced by oceanic and climatic factors since the species breeds in the Sargasso Sea and migrates to the continental shelf of the Atlantic coast of Europe and North Africa. Therefore, the study of the relations between recruitment and oceanic conditions may allow to study the potential effect of climatic change on the future eel recruitment and therefore stock. In the present study, the relation between glass eel recruitment and oceanic and climatic factors has been studied. Historic glass eel catches data beginning in the 50s from two Mediterranean and two Atlantic estuaries have been used as a proxy of recruitment. The relation of catches with the main oceanographic and climatic factors identified in the literature was established using an ocean reanalysis, the Simple Ocean Data Assimilation (SODA) and determined which variables are significantly related to the number of catches. The analysis shows significant relationships between catches and oceanic (Surface Downward Stress, Sea Water Temperature and Sea Water Velocity) and atmospheric (NAO Index, AMO Index) variables. Subsequently, we applied the results of three climate models (GFDL-ESM2M, CanESM2 and CNRM-CM5), associated with the Coupled Model Intercomparison Project Phase 5 (CMIP5) under two simulations of climate change (RCP4.5 and RCP8.5), both associated with the 5th Assessment Report of the IPCC, for possible future influences on the eel. This research was funded by the Spanish

  8. Structure of the lithosphere below the southern margin of the East European Craton (Ukraine and Russia) from gravity and seismic data

    NASA Astrophysics Data System (ADS)

    Yegorova, T. P.; Stephenson, R. A.; Kostyuchenko, S. L.; Baranova, E. P.; Starostenko, V. I.; Popolitov, K. E.

    2004-03-01

    The present study was undertaken with the objective of deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the East European Craton (EEC). The study area includes the inverted southernmost part of the intracratonic Dnieper-Donets Basin (DDB)-Donbas Foldbelt (DF), its southeastern prolongation along the margin of the EEC-the sedimentary succession of the Karpinsky Swell (KS), the southwestern part of the Peri-Caspian Basin (PCB), and the Scythian Plate (SP). These structures are adjacent to a zone, along which the crust was reworked and/or accreted to the EEC since the late Palaeozoic. In the Bouguer gravity field, the southern margin of the EEC is marked by an arc of gravity highs, correlating with uplifted Palaeozoic rocks covered by thin Mesozoic and younger sediments. A three-dimensional (3D) gravity analysis has been carried out to investigate further the crustal structure of this area. The sedimentary succession has been modelled as two heterogeneous layers—Mesozoic-Cenozoic and Palaeozoic—in the analysis. The base of the sedimentary succession (top of the crystalline Precambrian basement) lies at a depth up to 22 km in the PCB and DF-KS areas. The residual gravity field, obtained by subtracting the gravitational effect of the sedimentary succession from the observed gravity field, reveals a distinct elongate zone of positive anomalies along the axis of the DF-KS with amplitudes of 100-140 mGal and an anomaly of 180 mGal in the PCB. These anomalies are interpreted to reflect a heterogeneous lithosphere structure below the supracrustal, sedimentary layers: i.e., Moho topography and/or the existence of high-density material in the crystalline crust and uppermost mantle. Previously published data support the existence of a high-density body in the crystalline crust along the DDB axis, including the DF, caused by an intrusion of mafic and

  9. A margin transformed: Pure extension to pure translation along the North Falklands Escarpment. Results of Article 76 surveying in the South Atlantic.

    NASA Astrophysics Data System (ADS)

    Parson, L. M.; Richards, P.; Kimbell, G.; MacLachlan, I.

    2007-12-01

    The Falklands Plateau comprises an elongate continental block extending eastwards from the Falkland Islands to the Maurice Ewing Bank, 900 kilometres away. While complicated by the transpressive convergence of the Scotia Sea Plate in the South, its margin in the north is characterised by the extreme rectilinearity resulting from its transform separation from the South African craton along the Agulhas Plateau/Ridge system. The translational regime is flanked in the west by the well documented seaward dipping reflector sequences dominating the south Argentine margin, but new and extensive swath bathymetric surveying along the escarpment reveals a transition between the two opening modes characterised by a complex of sheared crustal segments, offset zones, and transform discontinuities. Within this 60 km wide margin parallel zone, en echelon arrays of crustal "tears", many defining a crude tension gash geometry, host submarine elevations, which show varying degrees of rotation in response to the increasing development of shear moment toward the east. We examine the tectonic origin of the ridges in the context of the geological evolution of the margin, their connectivity to the margin, and the comparison with the latest data from the conjugate Agulhas margin off South Africa.

  10. 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

    NASA Astrophysics Data System (ADS)

    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.

  11. Lead isotopes in trade wind aerosols at Barbados: the influence of European emissions over the North Atlantic

    SciTech Connect

    Hamelin, B.; Grousset, F.E.; Biscaye, P.E.; Zindler, A. ); Prospero, J.M. )

    1989-11-15

    Previous studies have shown that Pb can be used as a transient tracer in the atmosphere and the ocean because of strong time-variability of industrial inputs and because Pb isotopic composition can be used to identify contribution from different sources. We present Pb isotopic measurements on aerosols collected from the North Atlantic Ocean in the trade wind belt. Aerosols sampled at Barbados during the 1969--1985 period have a Pb isotopic compositions different from that observed by previous investigators in Bermuda corals and Sargasso Sea waters. Barbados aerosols appear to contain significant amounts of relatively unradiogenic industrial and automotive Pb that is derived from Europe and carried to Barbados by the trade winds. In contrast, Bermuda corals and Sargasso sea waters are influenced mainly by U.S.-derived emissions, which contain more radiogenic Pb originating from Missouri-type ores. This difference generates a strong latitudinal Europe-U.S.A. isotopic gradient, thus allowing study of trans-Atlantic atmospheric transport and ocean mixing processes. {copyright} American Geophysical Union 1989

  12. Lead isotopes in trade wind aerosols at Barbados - The influence of European emissions over the North Atlantic

    NASA Technical Reports Server (NTRS)

    Hamelin, B.; Grousset, F. E.; Biscaye, P. E.; Zindler, A.; Prospero, J. M.

    1989-01-01

    Previous studies have shown that Pb can be used as a transient tracer in the atmosphere and the ocean because of strong time-variability of industrial inputs and because Pb isotopic composition can be used to identify contributions from different sources. Pb isotopic measurements on aerosols collected from the North Atlantic Ocean in the trade wind belt are presented. Aerosols sampled at Barbados during the 1969-1985 period have a Pb isotopic composition different from that observed by previous investigators in Bermuda corals and Sargasso Sea waters. Barbados aerosols appear to contain significant amounts of relatively unradiogenic industrial and automotive Pb that is derived from Europe and carried to Barbados by the trade winds. In contrast, Bermuda corals and Sargasso sea waters are influenced mainly by U.S.-derived emissions, which contain more radiogenic Pb originating from Missouri-type ores. This difference generates a strong latitudinal Europe-U.S.A. isotopic gradient, thus allowing study of trans-Atlantic atmospheric transport and ocean mixing processes.

  13. Introductions of a European parasitoid, Peristenus relictus (=P. stygicus), against tarnished plant bug in the mid-Atlantic states

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Populations of tarnished plant bug, Lygus lineolaris, in alfalfa have declined by 65% in New Jersey since the establishment by 1990 of Peristenus digoneutis, a European nymphal parasitoid of Lygus species. Although it has expanded its distribution substantially to the NE and NW, P. digoneutis has n...

  14. Geophysical constraints on the crustal structure of the East European Platform margin and its foreland based on the POLCRUST-01 deep reflection seismic profile

    NASA Astrophysics Data System (ADS)

    Malinowski, M.; Guterch, A.; Narkiewicz, M.; Petecki, Z.; Janik, T.; Środa, P.; Maksym, A.; Probulski, J.; Grad, M.; Czuba, W.; Gaczyński, E.; Majdański, M.; Jankowski, L.

    2015-06-01

    A new 240-km long, deep seismic reflection profile (POLCRUST-01) was recently acquired in SE Poland crossing the East European Platform (EEP) margin south-east of the North-German-Polish Caledonides (NGPC). Here we document geophysical field work and subsequent data processing and modeling. Results obtained from reflection seismic data are augmented by results of the first-arrival tomography applied to co-located extended-offset refraction data, as well as potential field modeling and comparison with the available wide-angle reflection/refraction data. Our preferred model of the crustal structure, derived by integrating seismic, potential field and geological data, is composed of crustal blocks (terranes) separated by nearly-vertical faults. These are: (I) intact part of the EEP; (II) Łysogóry Terrane; (III) Małopolska Terrane; and (IV) Carpathian Mts. with their basement. Reflective lower crust of the EEP can be an inherited feature of crustal extension (rifting) or compressional tectonics acting at the cratonic margin. The Teisseyre-Tornquist Zone (TTZ) is depicted as a Caledonian transcurrent accretion zone corresponding with the near-vertical Tomaszów Fault, bounding the Łysogóry Terrane to the east. The crust of the Łysogóry Terrane suggests EEP affinity, although its middle/lower crust thickness is highly reduced. The Małopolska Terrane seems to be internally subdivided into blocks of different magnetic properties of the lower crust. The Carpathian frontal thrust is associated with a change in the rock properties in the deep basement (an unknown crustal block?) which is not visible in seismic data alone. The interpreted structure of the Caledonian terranes and their tectonic boundaries favors a transcurrent style of a crustal accretion along the central and SE Polish segments of the TTZ, implying a very complex nature of the Caledonian accretionary belt of Central Europe: from an array of terranes displaced along the TTZ to an accretionary wedge of

  15. The Blake Nose Cretaceous-Paleogene (Florida Atlantic margin, ODP Leg 171B): an exemplar record of the Maastrichtian-Danian transition

    USGS Publications Warehouse

    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.; Self-Trail J.M.; Shackleton, N.J.; Smit, J.; Ussler, W., III; 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.

  16. 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

    NASA Astrophysics Data System (ADS)

    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

  17. Behaviour of Talitrus saltator (Crustacea: Amphipoda) on a rehabilitated sandy beach on the European Atlantic Coast (Portugal)

    NASA Astrophysics Data System (ADS)

    Bessa, Filipa; Rossano, Claudia; Nourisson, Delphine; Gambineri, Simone; Marques, João Carlos; Scapini, Felicita

    2013-01-01

    Environmental and human controls are widely accepted as the main structuring forces of the macrofauna communities on sandy beaches. A population of the talitrid amphipod Talitrus saltator (Montagu, 1808) was investigated on an exposed sandy beach on the Atlantic coast of Portugal (Leirosa beach) to estimate orientation capabilities and endogenous rhythms in conditions of recent changes in the landscape (artificial reconstruction of the foredune) and beach morphodynamics (stabilization against erosion from the sea). We tested sun orientation of talitrids on the beach and recorded their locomotor activity rhythms under constant conditions in the laboratory. The orientation data were analysed with circular statistics and multiple regression models adapted to angular distributions, to highlight the main factors and variables influencing the variation of orientation. The talitrids used the sun compass, visual cues (landscape and sun visibility) to orient and the precision of orientation varied according to the tidal regime (rising or ebbing tides). A well-defined free-running rhythm (circadian with in addition a bimodal rhythmicity, likely tidal) was highlighted in this population. This showed a stable behavioural adaptation on a beach that has experienced a process of artificial stabilization of the dune through nourishment actions over a decade. Monitoring the conditions of such dynamic environments and the resilience capacity of the inhabiting macroinfauna is a main challenge for sandy beach ecologists.

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

    NASA Astrophysics Data System (ADS)

    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.

  19. Trophic ecology of European sardine Sardina pilchardus and European anchovy Engraulis encrasicolus in the Bay of Biscay (north-east Atlantic) inferred from δ13C and δ15N values of fish and identified mesozooplanktonic organisms

    NASA Astrophysics Data System (ADS)

    Chouvelon, T.; Chappuis, A.; Bustamante, P.; Lefebvre, S.; Mornet, F.; Guillou, G.; Violamer, L.; Dupuy, C.

    2014-01-01

    European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) are two species of economical and ecological significance in the Bay of Biscay (north-east Atlantic). However, the trophic ecology of both species is still poorly known in the area, and more generally, few studies have considered the potential trophic overlap between sardines and anchovies worldwide. This study aims to highlight the trophic links between the mesozooplankton and adults of these two pelagic fish in the Bay of Biscay, through carbon and nitrogen stable isotope analysis (SIA). Mesozooplankton and individuals of sardines and anchovies were collected during one season (spring 2010), over spatially contrasted stations within the study area. First, the potential effect of preservation (ethanol vs. freezing) and of delipidation (by cyclohexane) on mesozooplankton δ13C and δ15N values was assessed. Results demonstrated the necessity to correct for the preservation effect and for lipid contents in mesozooplankton for further analyses of sardines' and anchovies' diet through SIA. Next, this study highlighted the interest of working on identified mesozooplanktonic organisms instead of undetermined assemblages when unravelling food sources of planktivorous fish using stable isotopes. The inter-specific variability of isotope values within a planktonic assemblage was effectively high, probably depending on the various feeding behaviours that can occur among mesozooplankton species. Intra-specific variability was also significant and related to the spatial variations of baseline signatures in the area. To investigate the foraging areas and potential diet overlap of S. pilchardus and E. encrasicolus, mixing models (SIAR) were applied. Both fish species appeared to feed mainly in the neritic waters of the Bay of Biscay in spring and to select mainly small- to medium-sized copepods (e.g. Acartia sp., Temora sp.). However, E. encrasicolus showed a greater trophic plasticity by

  20. 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

    NASA Astrophysics Data System (ADS)

    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

  1. Characterization of marine boundary layer aerosol from North Atlantic and European sources: Physical and chemical properties and climate forcing parameters

    NASA Astrophysics Data System (ADS)

    Dusek, Ulrike

    This thesis focuses on aerosol properties measured in Southwestern Portugal during the second Aerosol Characterization Experiment. Fundamental aerosol physical properties such as particle size distribution and hygroscopic properties are related to possible sources and aerosol transformation processes. From these fundamental properties we derive aerosol properties that are important for aerosol forcing of climate. First, a new method for calculating CCN spectra is proposed in this work and tested using sensitivity studies and comparisons to direct measurements. The measured and calculated CCN spectra differ on average by 30%, which at small supersaturations is similar to the measurement uncertainties. Second, aerosol number to volume ratios (R) are calculated and the fact that values of R are relatively constrained is explained based on observed correlations between size distribution parameters. Third, a simple parameterization of the humidity dependence of the submicron aerosol scattering coefficient has been derived, depending only on a volume weighted average diameter growth factor and the volume mean diameter of the dry size distribution. One set of empirical parameters can be used to parameterize all aerosol types characterized during the ACE-2 measurement period. Aerosol physical properties and climate forcing parameters in the North-East Atlantic Ocean were clearly affected by pollution outbreaks from Europe. The submicron particle volume increased by a factor of 5 in polluted conditions, the light scattering coefficient of dry particles increased on average by a factor of up to 10, CCN concentrations at supersaturations of 0.2% increased by a factor of 3--5. The aerosol fundamental properties vary often strongly with air mass history, but also show short-term variability that often has a characteristic diurnal scale. The number concentration of fine particles below 50nm and the particle hygroscopic growth factors are mostly dominated by diurnal processes

  2. Apatite fission track dating and long-term landscape evolution of the South Atlantic passive continental margin in the region of the Sierras Septentrionales in eastern Argentina

    NASA Astrophysics Data System (ADS)

    Pfister, S.; Glasmacher, P. A.; Kollenz, S.

    2013-12-01

    To understand the evolution of the passive continental margin in Argentina apatite fission track dating is an appropriate method, which will lead to new conclusions in this area. The Tandilia System, also called Sierras Septentrionales, is located south of the Río de la Plato Craton in eastern Argentina in the state of Buenos Aires. North of the hills Salado basin is orientated whereas the Claromeó basin is located south of the mountain range. In contrary to most basins along the southamerican passive continental margin the Tandilia-System and the neighbouring basins trend perpendicular to the coast line. The topography ranges between 50 and 250m within the study area and is therefore fairly flat. The igneous-metamorphic basement is pre-proterozoic in age build up of mainly granitic-tonalitic gneisses, migmatites, amphibolites, some ultramafic rocks and granitoid plutons and is overlain by a series of Neoproterozoic to early Paleozoic sediments (Cingolani, 2010). The aim of the study is to evaluate the long-term landscape evolution of the passive continental margin in eastern Argentina in terms of thermal history and exhumation. For that purpose samples were taken from the Sierra Septentrionales basement analyzed for the apatite-FT method. The results so far indicate apatite fission track ages between 146.2 (10.1) Ma and 200.4 (12.7) Ma, which shows all samples have been reseted. Still ongoing length measurements will lead to 2D thermo kinematic Hefty (Ketcham, 2005; Ketcham et al., 2009; Ketcham, 2007) models. This will leads to further more insights on the cooling history and tectonic activities in the research area. References: Cingolani C. A. (2010): The Tandilia System of Argentina as a southern extension of the Río de la Plata craton: an overview. Int. J. Earth Sci. (Geol. Rundsch.) (2011) 100:221-242, doi 10.1007/s00531-010-0611-5. Ketcham, R. A. (2005): Forward and inverse modeling of low-temperature thermochronometry data, in Low

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  4. Successful eradication of the European rabbit (Oryctolagus cuniculus) and house mouse (Mus musculus) from the island of Selvagem Grande (Macaronesian archipelago), in the Eastern Atlantic.

    PubMed

    Olivera, Paulo; Menezes, Dilia; Trout, Roger; Buckle, Alan; Geraldes, Pedro; Jesus, José

    2010-03-01

    The Portuguese island of Selvagem Grande (Great Salvage) in Macaronesia is an important seabird breeding station in the eastern Atlantic. Significant populations of Cory's shearwater Calonectris diomedea (Scopoli, 1769), Bulwer's petrel Bulweria bulweria (Jardine & Selby, 1828) and little shearwater Puffinus assimilis baroli (Bonaparte, 1857) are present, and white-faced storm-petrel Pelagodroma marina (Latham, 1790) and Madeiran storm-petrel Oceanodroma castro (Harcourt, 1851) populations are of global significance. Selvagem Grande also provides diverse habitats for an extensive flora, including 11 endemic species. The 270-ha island was also inhabited by two alien invasive mammals: the European rabbit Oryctolagus cuniculus (Linnaeus, 1758) and the house mouse Mus musculus (Linnaeus, 1758). Both are known to have had adverse impacts on breeding seabirds and island vegetation. In 2002, the Natural Park of Madeira conducted a program using brodifacoum bait formulations aimed at rabbit and mouse eradication. Approximately 17 000 individual baiting points were established on a 12.5 × 12.5 m grid. Baits were also applied by hand "seeding" on steep slopes and cliffs where bait stations could not be placed. Rabbits were removed after a month. However, mice persisted for considerably longer and strategic bait applications against them continued for a further six months. Subsequent assessments by trapping, bait takes and systematic observation of signs over three years, has confirmed the removal of both alien invasive species. This paper presents information on these operations, on measures adopted to mitigate adverse impacts of the eradication program on important vertebrate non-target species, including Berthelot's pipit Anthus berthelotii Bolle, 1862 and a species of gecko Tarentola bischoffi Joger, 1984 and on the initial response of the island's ecosystem to the eradication of rabbits and mice. PMID:21392324

  5. Timing and Kinematics of Cretaceous to Paleogene inversion at the SE margin of the Central European Basin System: Part 2, Thermochronology

    NASA Astrophysics Data System (ADS)

    Hoffmann, V.-E.; Dunkl, I.; von Eynatten, H.; Jähne, F.; Voigt, T.; Kley, J.

    2009-04-01

    During the Late Cretaceous to Early Tertiary some parts of the Central European Basin System (CEBS) were uplifted along NW-SE to WNW-ESE striking compressive fault systems. As a result Pre-Zechstein (Permian) basement is exposed at the southern border of the CEBS from Central Germany to the sudetes still further east (e.g. Harz Mountains, Thuringian Forest). Thrust-related basins like the Subhercynian Cretaceous Basin (SCB) in the foreland of the Harz Mountains accumulated up to 2500m of siliciclastic and chemical sediments in only 10 million years (Late Turonian to Lower Campanian, Voigt et al., 2006). By means of low-temperature thermochronology it is possible to characterise these basin inversion processes with respect to timing, pattern and rates of cooling and exhumation. Differed authors have already applied Apatite Fission Track analysis (AFT) in certain areas of the southern margin of CEBS. Thomson and Zeh (2000) published AFT apparent ages of 69 to 81 Ma for the Ruhla Crystalline Complex in the Thuringian Forest. Similar AFT-ages (73-84 Ma) of granitoids from the Harz Mountains were reported by Thomson et al. (1997). The late Carboniferous felsic volcanic rocks near Halle yield a much broader range of AFT apparent ages (75-108 Ma; Jacobs and Breitkreuz, 2003). Comparable AFT-ages (84-90 Ma) had been also observed for gabbros from the north-eastern part of the Mid German Crystalline High (Ventura et al. 2003). The present study tries to bridge some of the major gaps in the regional distribution of thermochronological data by analysing samples from central and southern parts of the CEBS. Overall almost 50 AFT-ages from Saxony-Anhalt, Lower Saxony, Thuringia, Hesse and North Rhine-Westphalia were measured. Emphasis is placed on the regions from the Harz Mountains to the Rhenish Uplands and the Thuringian Forest and its foreland. Furthermore, apatite (U-Th)/He thermochronology is used to better constrain the time-temperature history models. Apart from some

  6. Paleostress states at the south-western margin of the Central European Basin System — Application of fault-slip analysis to unravel a polyphase deformation pattern

    NASA Astrophysics Data System (ADS)

    Sippel, Judith; Scheck-Wenderoth, Magdalena; Reicherter, Klaus; Mazur, Stanislaw

    2009-05-01

    We analyse the deformation pattern along the south-western margin of the Central European Basin System (CEBS) where Upper Carboniferous-Mesozoic rocks are uplifted due to the Late Cretaceous basin inversion. The geometry of mesoscale faults and associated striae are used to calculate the stress state(s) responsible for the observed deformation. Each reduced stress tensor obtained comprises (i) the directions of the principal stress axes σ1, σ2, and σ3 ( σ1 ≥ σ2 ≥ σ3) and (ii) the ratio of principal stress differences R = ( σ2 - σ3) / ( σ1 - σ3). We present a stress inversion technique that allows each stress state inherent in a heterogeneous fault population to be identified by integrating the results of the PBT-Method [Turner, F.J., 1953. Nature and dynamic interpretation of deformation lamellae in calcite of three marbles. American Journal of Sciences, 251(4): 276-298; Sperner, B., Ratschbacher, L. and Ott, R., 1993. Fault-striae analysis: a Turbo Pascal program package for graphical presentation and reduced stress tensor calculation. Computers & Geosciences, 19: 1361-1388] and the Multiple Inverse Method [Yamaji, A., 2000. The multiple inverse method; a new technique to separate stresses from heterogeneous fault-slip data. Journal of Structural Geology, 22(4): 441-452]. This comprehensive approach not only facilitates the separation of complex data sets into homogeneous subsets but also guarantees that each stress state derived fulfils both the criteria of low-misfit angles (Wallace-Bott hypothesis) and high shear-to-normal-stress ratios (Mohr-Coulomb criterion). The reliability of our technique is confirmed by the fact that irrespective of (i) the number of fault-slip data from an outcrop, (ii) the number of subsets they represent and (iii) the proportion of newly formed and reactivated faults, we obtain consistent results from outcrops of variously aged rocks. This consistency concerns both calculated stress states as well as locally observed

  7. Biodiversity and life strategies of deep-sea meiofauna and nematode assemblages in the Whittard Canyon (Celtic margin, NE Atlantic Ocean)

    NASA Astrophysics Data System (ADS)

    Gambi, Cristina; Danovaro, Roberto

    2016-02-01

    An extensive sampling strategy has been carried out along bathymetric transects in two branches (Eastern middle and Western) of the Whittard Canyon and in two adjacent open slopes to investigate meiofaunal assemblages (including nematode diversity and their life strategy) in the Celtic margin, Northern Gulf of Biscay. Our results show the presence of differences in terms of meiofaunal abundance and biomass among habitats even when located at the same depth. Meiofaunal abundance and biomass in the upper and middle (1000-2000 m) part of the branches of the Whittard Canyon are typically higher than those reported in adjacent open slopes while, in deeper sediments (ca. 3000 m), an opposite pattern is detected. The availability of food sources (both in term of quantity and quality) plays a key role in explaining such differences. Diversity expressed either as the richness of meiofaunal taxa and of nematode species is typically higher in slopes than in the branches of the Whittard Canyon. Turnover diversity is high (40-100% for meiofaunal rare taxa and 61-78% for nematode species, respectively) either among habitats and depths. Although a general dominance of deposit feeders, predators are more abundant in slopes (9-12% of total nematode abundance) than in both branches of the Whittard Canyon (4-7%). The higher fraction of predators of the nematode assemblages inhabiting the slopes determined higher values of the maturity index (i.e., more persisters, c-p=4/5). We hypothesize that the life strategies of nematode assemblages are influenced by gravity flows, sediment instability and the 2-3 times higher availability of phytopigments, which characterize the upper part of the Whittard Canyon, favoring opportunist/colonizer species. Our findings indicate that different deep-sea habitats are associated to different life strategies, thus contributing to increase the functional diversity of deep-sea ecosystems.

  8. Biodiversity of the Deep-Sea Continental Margin Bordering the Gulf of Maine (NW Atlantic): Relationships among Sub-Regions and to Shelf Systems

    PubMed Central

    Kelly, Noreen E.; Shea, Elizabeth K.; Metaxas, Anna; Haedrich, Richard L.; Auster, Peter J.

    2010-01-01

    Background In contrast to the well-studied continental shelf region of the Gulf of Maine, fundamental questions regarding the diversity, distribution, and abundance of species living in deep-sea habitats along the adjacent continental margin remain unanswered. Lack of such knowledge precludes a greater understanding of the Gulf of Maine ecosystem and limits development of alternatives for conservation and management. Methodology/Principal Findings We use data from the published literature, unpublished studies, museum records and online sources, to: (1) assess the current state of knowledge of species diversity in the deep-sea habitats adjacent to the Gulf of Maine (39–43°N, 63–71°W, 150–3000 m depth); (2) compare patterns of taxonomic diversity and distribution of megafaunal and macrofaunal species among six distinct sub-regions and to the continental shelf; and (3) estimate the amount of unknown diversity in the region. Known diversity for the deep-sea region is 1,671 species; most are narrowly distributed and known to occur within only one sub-region. The number of species varies by sub-region and is directly related to sampling effort occurring within each. Fishes, corals, decapod crustaceans, molluscs, and echinoderms are relatively well known, while most other taxonomic groups are poorly known. Taxonomic diversity decreases with increasing distance from the continental shelf and with changes in benthic topography. Low similarity in faunal composition suggests the deep-sea region harbours faunal communities distinct from those of the continental shelf. Non-parametric estimators of species richness suggest a minimum of 50% of the deep-sea species inventory remains to be discovered. Conclusions/Significance The current state of knowledge of biodiversity in this deep-sea region is rudimentary. Our ability to answer questions is hampered by a lack of sufficient data for many taxonomic groups, which is constrained by sampling biases, life

  9. The morphotectonic history of the Atlantic continental margin of South Africa: insights from combined (U-Th)/He and fission track thermochronometry

    NASA Astrophysics Data System (ADS)

    Wildman, M.; Beucher, R.; Brown, R.; Persano, C.; Stuart, F.; Roelofse, F.

    2012-04-01

    The morphotectonic evolution of the South African continental margins and the interior plateau remains unresolved, with the crux of the debate being whether the present day topography represents an eroded remnant of a Cretaceous elevated interior or if the topography is much younger, developed as a result of Miocene epeirogenic-style uplift. In recent years, advances in the understanding of mantle dynamics have led to an appreciation of its importance as a major controlling factor on the evolution of the South African plateau since the break-up of Gondwana. However, constraints on the timing and amount of uplift derived from geodynamical models are still controversial due to a lack of tight constraints on mantle viscosity and density structure and because of differences in the way the plate motions at the surface are incorporated into the different models. It is therefore essential to obtain more directly relevant empirical observations that can be used to test these models. Low temperature thermochronology (LTT) is a powerful tool well able to address this question by providing constraints on the time-temperature history of rocks, denudation, landscape evolution and tectonic history. Over the past two decades, the main focus of LTT analysis in South Africa has been on Apatite Fission Track Analysis (AFTA) which generally supports a dominant Cretaceous (c. 90Ma) uplift event with km-scale erosion, but spatially as well as temporally variable, in the interior of the plateau. However, AFTA data is unable to provide robust constraints on the Tertiary cooling history due to the temperature range covered by the fission track system (e.g. 60-110°C). The (U-Th)/He method with a lower temperature range (c. 40-75°C) will therefore be more sensitive to more recent and smaller amounts of erosion offers a new opportunity to evaluate the magnitude of Cenozoic denudation in southern Africa. Here we present the first (U-Th)/He ages from SW South Africa, obtained from a transect

  10. 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

    NASA Astrophysics Data System (ADS)

    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

  11. Dual Symbiosis in a Bathymodiolus sp. Mussel from a Methane Seep on the Gabon Continental Margin (Southeast Atlantic): 16S rRNA Phylogeny and Distribution of the Symbionts in Gills

    PubMed Central

    Duperron, Sébastien; Nadalig, Thierry; Caprais, Jean-Claude; Sibuet, Myriam; Fiala-Médioni, Aline; Amann, Rudolf; Dubilier, Nicole

    2005-01-01

    Deep-sea mussels of the genus Bathymodiolus (Bivalvia: Mytilidae) harbor symbiotic bacteria in their gills and are among the dominant invertebrate species at cold seeps and hydrothermal vents. An undescribed Bathymodiolus species was collected at a depth of 3,150 m in a newly discovered cold seep area on the southeast Atlantic margin, close to the Zaire channel. Transmission electron microscopy, comparative 16S rRNA analysis, and fluorescence in situ hybridization indicated that this Bathymodiolus sp. lives in a dual symbiosis with sulfide- and methane-oxidizing bacteria. A distinct distribution pattern of the symbiotic bacteria in the gill epithelium was observed, with the thiotrophic symbiont dominating the apical region and the methanotrophic symbiont more abundant in the basal region of the bacteriocytes. No variations in this distribution pattern or in the relative abundances of the two symbionts were observed in mussels collected from three different mussel beds with methane concentrations ranging from 0.7 to 33.7 μM. The 16S rRNA sequence of the methanotrophic symbiont is most closely related to those of known methanotrophic symbionts from other bathymodiolid mussels. Surprisingly, the thiotrophic Bathymodiolus sp. 16S rRNA sequence does not fall into the monophyletic group of sequences from thiotrophic symbionts of all other Bathymodiolus hosts. While these mussel species all come from vents, this study describes the first thiotrophic sequence from a seep mussel and shows that it is most closely related (99% sequence identity) to an environmental clone sequence obtained from a hydrothermal plume near Japan. PMID:15811991

  12. Diversity and trans-arctic invasion history of mitochondrial lineages in the North Atlantic Macoma balthica complex (Bivalvia: Tellinidae).

    PubMed

    Nikula, Raisa; Strelkov, Petr; Väinölä, Risto

    2007-04-01

    The history of repeated inter- or transoceanic invasions in bivalve mollusks of the circumpolar Macoma balthica complex was assessed from mtDNA COIII sequences. The data suggest that four independent trans-Arctic invasions, from the Pacific, gave rise to the current lineage diversity in the North Atlantic. Unlike in many other prominent North Atlantic littoral taxa, no evidence for (postinvasion) trans-Atlantic connections was found in the M. balthica complex. The earliest branch of the mtDNA tree is represented by the temperate-boreal North American populations (=Macoma petalum), separated from the M. balthica complex proper in the Early Pliocene at latest. The ensuing trans-Arctic invasions established the North European M. b. rubra, which now prevails on the North Sea and northeast Atlantic coasts, about two million years ago, and the currently northwest Atlantic M. balthica lineage in the Canadian Maritimes, in the Middle Pleistocene. The final reinvasion(s) introduced a lineage that now prevails in a number of North European marginal seas and is still hardly distinguishable from North Pacific mtDNA (M. b. balthica). We used coalescence simulation analyses to assess the age of the latest invasion from the Pacific to the northeast Atlantic. The results refute the hypothesis of recent, human-mediated reintroductions between northeast Pacific and the North European marginal seas in historical times. Yet they also poorly fit the alternative hypotheses of an early postglacial trans-Arctic invasion (< 11 thousand years ago), or an invasion during the previous Eemian interglacial (120 thousand years ago). Divergence time estimates rather fall in the Middle Weichselian before the Last Glacial Maximum, in conflict with the conventional thinking of trans-Arctic biogeographical connections; an early Holocene reinvasion may still be regarded as the most plausible scenario. Today, the most recently invaded Pacific mtDNA lineage is found admixed with the earlier established

  13. Decadal variability in the Eastern North Atlantic

    NASA Astrophysics Data System (ADS)

    Köllner, Manuela; Klein, Birgit; Kieke, Dagmar; Klein, Holger; Rhein, Monika; Roessler, Achim; Denker, Claudia

    2016-04-01

    The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the subpolar gyre and stronger inflow of waters from the subtropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses. We examine the decadal variability in the eastern North Atlantic based on Argo data from 2000-2015 and have constructed time series for four water masses (Subpolar Mode Water (SPMW), Intermediate Water (IW), upper Labrador Sea Water (uLSW) and deep Labrador Sea Water (dLSW)) at selected locations along the Northwest European shelf. Data from the Rockall Trough and the Iceland Basin are chosen to represent advective pathways in the subpolar gyre at two major branches of the North Atlantic Current towards the Nordic Seas and the Arctic Ocean. Temporal variability of subtropical waters transported northward along the eastern boundary is studied at Goban Spur around 48°N. The Argo data are extended in time with long-term hydrographic observations such as the Extended Ellet Line data and other climatological sources in the region. For the study of transport fluctuations time series from the RACE (Regional circulation and Global change) program (2012-2015) and predecessor programs have been used. These programs have monitored the subpolar gyre in the western basin and provide time series of transports and hydrographic anomalies from moored instruments at the western flank of the Mid Atlantic Ridge (MAR). First results show that the temperatures and salinities remained at high levels for the upper waters (SPMW and IW) until 2010 and have been decreasing since

  14. Comparing the deformation and hydrothermal alteration record of tectonic exhumation of mantle-derived ultramafic rocks from the Mid-Atlantic Ridge and from Ocean Continent Transitions (Central Alps and Western Iberia Margin)

    NASA Astrophysics Data System (ADS)

    Picazo, S. M.; Cannat, M.; Manatschal, G.

    2012-12-01

    The exhumation of mantle-derived rocks is widespread at slow and ultraslow Mid-Ocean Ridges and at the Ocean-Continent Transition (OCT) of rifted continental margins. It occurs along large offset normal faults also called detachment faults. Thermo-mechanical models indicate that significant strain softening of the fault rocks in the footwall is required in order to produce such large fault offsets. Our work focuses on actual deformation textures, and the associated mineralogy in ultramafic rocks sampled in the upper levels of the footwall next to the exhumation fault at two contrasted exhumation settings: the Mid-Atlantic Ridge (MAR) at lat. 13°N and 15°N (next to the Ashadze and Logatchev vent sites); and two OCT examples, the Totalp relict of a paleo-Tethys OCT exposed in SE Switzerland, and the Iberian distal margin (ODP Leg 173 Site 1070). These two settings differ by a number of characteristics, most notably the nature of the exhumed mantle (sub-continental mantle at OCTs, oceanic mantle at the ridge) and the extent of magmatic activity during exhumation (extensive magmatism at the MAR, few magmatic rocks at OCTs). Our comparative approach aims at identifying possible differences in the deformation processes during exhumation. We show that in both settings the ultramafic rocks in the upper levels of the footwall next to the detachment fault undergo a series of plastic to semi-brittle and brittle deformations. In samples from OCT settings, we find a cataclasites to gouges-sequence that affects the serpentinized peridotites. It involves a component of plastic deformation of serpentine following pronounced brittle grain-size reduction responsible for matrix-supported gouges formation in the most highly strained intervals. In this case the rheology of serpentine therefore controls the detachment fault. A similar sequence of serpentinite cataclasites and gouges is found in a few samples at one of the studied MAR locations, but in most samples from the MAR we find

  15. Potential use of the invasive European green crab (Carcinus maenas) as an ingredient in Atlantic Salmon (Salmo salar) diets; a preliminary analysis

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Atlantic salmon (Salmo salar) is an important cultured carnivorous species with wide comsumer acceptance. With the finite supply of available fishmeal and fish oil available for aquafeeds, research on and utilization of alternative protein and lipid sources is expandingWe examined the nutritional p...

  16. Tectonic provinces of the Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Pushcharovsky, Yu. M.

    2009-05-01

    The tectonic structure of the floor of the Atlantic Ocean beyond the continental margins is insufficiently studied. This is also true of its tectonic demarcation. The segmentation of the floor into regional-scale tectonic provinces of several orders proposed in this paper is primarily based on structural and historical geological features. It is shown that deep oceanic basins and fault tectonics are of particular importance in this respect. Tectonic provinces of two orders are distinguished by a set of attributes. The first-order provinces are the North, Central, South, and Antarctic domains of the Atlantic Ocean. They are separated by wide demarcation fracture zones into Transatlantic (transverse) second-order tectonic provinces. Ten such provinces are recognized (from the north southward): Greenland-Lofoten, Greenland-Scandinavia, Greenland-Ireland, Newfoundland-European, North American-African, Antilles-African, Angola-Brazil, Cape-Argentine, North Antarctic, and South Antarctic. This subdivision demonstrates significant differentiation in the geodynamic state of the oceanic lithosphere that determines nonuniform ocean formation and the tectonic features of the ocean floor. The latitudinal orientation of the second-order provinces inherits the past tectonic pattern, though newly formed structural units cannot be ruled out. The Earth rotation exerts a crucial effect on the crust and the mantle.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  18. The Evolution of the South Atlantic.

    ERIC Educational Resources Information Center

    McCoy, Floyd W.; Rabinowitz, Philip D.

    1979-01-01

    The development of the South Atlantic continental margins through geological time is discussed in a series of three time slices, all of which depict various characteristics in the initial formation of this margin during the Cretaceous period (180 to 65 million years ago) of the Mesozoic era. (BT)

  19. Teaching Atlantic Studies in American High Schools.

    ERIC Educational Resources Information Center

    Foster, Charles R.

    1980-01-01

    Stresses the importance of Atlantic studies within the framework of United States history, European history, and the contemporary world scene. Ways of integrating Atlantic studies into the high school social studies curriculum are suggested. Topics discussed include objectives, audiovisual aids, supplementary reading material, and global political…

  20. Hyperactive neotectonic near the South Rifian front. Lifted Late Quaternary lagunal deposits (Atlantic Morocco)

    NASA Astrophysics Data System (ADS)

    Benmohammadi, Aïcha; Griboulard, Roger; Zourarah, Bendahhou; Carruesco, Christian; Mehdi, Khalid; Mridekh, Aziz; Moussaoui, Abderahmane El; Alaoui, Asmae Mhamdi; Carbonel, Pierre; Londeix, Laurent

    2007-10-01

    The recent discovery of emerged and lifted lagunal deposits near the Moulay Bouselham lagoon (North Moroccan Atlantic coast), up to 32 m above sea level, requires a new model to explain the evolution of this ecosystem. All the studies on these deposits seem to indicate that we are dealing with very recent lagoonal levels. The main problem is to explain the altitude of these deposits. Likely explanations are a historical tsunami, tempest, and/or a very strong neotectonics in this area. We choose the later hypothesis because it matches the occurrence of an argilokinetic tectonic in front of the North Atlantic Moroccan margin. In this tectonic context, results of 14C analysis data, i.e. 2400 ± 250 BP for one outcrop and 2170 ± 215 BP for a value in a core taken in the lagoon, we obtain a rate of uplift of about 14 mm/yr. Therefore, this region corresponds to an important tectonic junction between the stable Meseta to the south, the Rifian domain to the north and the accretionary prism, in relation with the subduction of the Atlantic crust under the African and European plates to the west. Moreover, in front of the studied site, many mud volcanoes have been observed in the Gulf of Cadiz, near the Moroccan margin.

  1. Genetic identification and distribution of the parasitic larvae of Anisakis pegreffii and Anisakis simplex (s. s.) in European hake Merluccius merluccius from the Tyrrhenian Sea and Spanish Atlantic coast: implications for food safety.

    PubMed

    Cipriani, Paolo; Smaldone, Giorgio; Acerra, Virginia; D'Angelo, Luisa; Anastasio, Aniello; Bellisario, Bruno; Palma, Giuseppe; Nascetti, Giuseppe; Mattiucci, Simonetta

    2015-04-01

    The consumption of the hake Merluccius merluccius is widespread in European countries, where this fish has a high commercial value. To date, different larval species of Anisakis have been identified as parasites in M. merluccius from European waters, Anisakis pegreffii and Anisakis simplex (s. s.) being the two most common. The aim of the study is to present data on the occurrence of Anisakis spp. larvae in the viscera and flesh of M. merluccius. Consequently, the distribution and infection rates of different species of Anisakis in different sites (viscera, and dorsal and ventral fillets) were investigated in hake caught in the central Tyrrhenian Sea (FAO 37.1.3) and the NE Atlantic Ocean (FAO 27 IXa). A sample of N=65 fish individuals (length>26 cm) was examined parasitologically from each fishing ground. The fillets were examined using the pepsin digestion method. A large number (1310) of Anisakis specimens were identified by multilocus allozyme electrophoresis (MAE) and mtDNA cox2 sequence analysis; among these, 814 larvae corresponded to A. simplex (s. s.) and 476 to A. pegreffii. They were found to infect both the flesh and the viscera. The two species co-infected the same individual fish (both in the viscera and in the flesh) from the FAO 27 area, whereas only A. pegreffii was found in hake from the Tyrrhenian Sea. The average parasite burden of A. pegreffii in hake from the Tyrrhenian Sea was significantly lower to that observed from hake off the Atlantic coast of Spain, both in prevalence and in abundance. In addition, whereas no significant difference in overall prevalence values was recorded between the two Anisakis species in the viscera of the FAO 27 sample, significant differences were found in the abundance levels observed between these species in the flesh, with A. simplex (s. s.) exhibiting significantly higher levels than that observed for A. pegreffii (p<0.001). Given that the pathogenic role in relation to man is known for these two species of

  2. Velocity model of the crust and upper mantle at the southern margin of the East European Craton (Azov Sea-Crimea-Black Sea area), DOBRE-2 & DOBRE'99 transect

    NASA Astrophysics Data System (ADS)

    Starostenko, Vitaly; Janik, Tomasz; Stephenson, Randell; Gryn, Dmytro; Tolkunov, Anatoliy; Czuba, Wojciech; Środa, Piotr; Sydorenko, Grigoriy; Lysynchuk, Dmytro; Omelchenko, Victor; Grad, Marek; Guterch, Aleksander; Kolomiyets, Katerina; Thybo, Hans; Dannowski, Anke; Flűh, Ernst R.; Legostaeva, Olga

    2013-04-01

    The southern part of the eastern European continental landmass consists mainly of a thick platform of Vendian and younger sediments overlying Precambrian basement, part of the East European Craton (EEC). The Scythian Platform (SP) lies between the EEC and the (mainly Alpine) deformed belt running from Dobrudja (Romania) to Crimea (Ukraine) and the Greater Caucasus (Russia), along the northern margin of the Black Sea. Hard constraints on the Palaeozoic history on the SP are very sparse and little is known of its crustal structure in this area. The poster presents the seismic results of a multidisciplinary project that fills some of this gap. The project is called DOBRE-2 (as it forms a prolongation of the successful DOBRE project executed in 1999-2001). The main objectives of DOBRE-2 were to elucidate the deep-seated structure of the lithosphere and geodynamic setting of the shelf zones of the Azov and Black seas and the Crimean peninsula and to study the deep controls on the structure of basement and sedimentary cover. DOBRE-2 traverses a number of major faults and suture zones separating the EEC from the SP, the Crimean Mountains, and the Black Sea depression. Significant hydrocarbon reserves occur in the basins traversed by DOBRE-2. Deep seismic reflection profiling (30 second, Vibroseis) has been completed on a 100-km segment of the profile on the Azov massif (part of the Ukrainian Shield) as well as a 47-km segment in Crimea. These are complemented by refraction profiling on the shelf zones of the Azov (~53 km) and Black (~160 km) seas and coincident near-vertical (CDP) in the Black Sea, using a combination of onshore seismograph stations, ocean-bottom seismometers, onshore explosive energy sources (6 shot points), as well as ship-borne seismic acquisition. We present a 2-D seismic velocity model (Vp in the crust, depth to the Moho and depth to the intracrustal reflectors) along (~780 km) the DOBRE-2 & DOBRE'99 transect. Our model extends the model published

  3. Benthic response of Munnopsurus atlanticus (Crustacea Isopoda) to the carbon content of the near-bottom sedimentary environment on the southern margin of the Cap-Ferret Canyon (Bay of Biscay, northeastern Atlantic Ocean)

    NASA Astrophysics Data System (ADS)

    Elizalde, M.; Weber, O.; Pascual, A.; Sorbe, J. C.; Etcheber, H.

    1999-10-01

    The response of benthic organisms to organic carbon fluxes in a continental margin region was studied by investigating the diet of the suprabenthic isopod Munnopsurus atlanticus, which is well represented on the southern margin of the Cap-Ferret Canyon (Bay of Biscay). The grain-size distribution, foraminiferal assemblages, particulate organic carbon and pigments found in the sediment and in the gut of the isopods were analyzed. These results suggest that M. atlanticus feeds on benthic agglutinated foraminifers which are in a high "nourishment state" and represent a link between primary and secondary producers.

  4. Modelling non-analogue elements of Pliocene North Atlantic warming

    NASA Astrophysics Data System (ADS)

    Hill, D. J.

    2013-12-01

    the North Atlantic, including the Barents Sea. North American and European rivers have changed course, due to the newly created marginal seas and glacial rerouting, potentially affecting the salinity balance in the North Atlantic. We present simulations using the Hadley Centre coupled atmosphere-ocean HadCM3 model to estimate the impact of these changes on Atlantic Meridional Overturning Circulation (AMOC) and SST in the North Atlantic. By applying palaeogeographic changes to the standard PlioMIP Experiment 2 simulation individually and as a whole, we show that these can produce North Atlantic SST changes of a similar magnitude to data-model discrepancies. Palaeoclimate model simulations can only reproduce global and regional climate accurately if the boundary conditions given to the model are sufficient to capture all the significant changes in climate processes and dynamics. Incorporation of other important boundary condition changes and proper quantification of the model uncertainties due to unknown boundary conditions could explain existing data-model mismatches in the Pliocene North Atlantic.

  5. The North Atlantic Cold Bias

    NASA Astrophysics Data System (ADS)

    Greatbatch, Richard; Drews, Annika; Ding, Hui; Latif, Mojib; Park, Wonsun

    2016-04-01

    The North Atlantic cold bias, associated with a too zonal path of the North Atlantic Current and a missing "northwest corner", is a common problem in coupled climate and forecast models. The bias affects the North Atlantic and European climate mean state, variability and predictability. We investigate the use of a flow field correction to adjust the path of the North Atlantic Current as well as additional corrections to the surface heat and freshwater fluxes. Results using the Kiel Climate Model show that the flow field correction allows a northward flow into the northwest corner, largely eliminating the bias below the surface layer. A surface cold bias remains but can be eliminated by additionally correcting the surface freshwater flux, without adjusting the surface heat flux seen by the ocean model. A model version in which only the surface fluxes of heat and freshwater are corrected continues to exhibit the incorrect path of the North Atlantic Current and a strong subsurface bias. Removing the bias impacts the multi-decadal time scale variability in the model and leads to a better representation of the SST pattern associated with the Atlantic Multidecadal Variability than the uncorrected model.

  6. Vitellogenin gene expression in the intertidal blenny Lipophrys pholis: a new sentinel species for estrogenic chemical pollution monitoring in the European Atlantic coast?

    PubMed

    Ferreira, F; Santos, M M; Castro, L Filipe C; Reis-Henriques, M A; Lima, D; Vieira, M N; Monteiro, N M

    2009-01-01

    The presence of estrogenic chemicals (ECs) in the aquatic environment is a growing problem. While most attention was initially given to fresh water and estuarine ecosystems, it is now evident that coastal marine areas are also vulnerable to these pollutants. The use of vitellogenin induction in male fish, a specific biomarker of EC exposure, has been the most widely applied methodology. However, in some occasions, the high mobility and migratory behaviour of common sentinel fish species makes data interpretation difficult. Hence, there is the need to validate new sentinel marine fish species which should display, among other features, a strong homing behaviour. The shanny, Lipophrys pholis, is an intertidal fish that combines many of the required characteristics for a sentinel species: abundance and easy of catch, wide geographical distribution and restricted home range. Thus, in order to evaluate, in the field, the species sensitivity to ECs, L. pholis males were collected at two sites reflecting different degrees of anthropogenic contamination. The vitellogenin II gene (VTGII) was isolated and its liver expression evaluated by RT-PCR in the field samples. A significant induction of gene expression was observed in the specimens collected in the urban area, if compared to the reference site, which suggests exposure to ECs. Moreover, a 21-days laboratory exposure to environmental relevant concentrations of ethinylestradiol (EE2) was also performed. A significant induction of L. pholis VTGII gene in EE2 exposed males was observed suggesting similar sensitivity to that of other marine/estuarine fishes. Even though further validation is currently in progress, the available data indicates that L. pholis is responsive to ECs, thus favouring its future integration in monitoring programmes designed to evaluate the presence of ECs in European marine ecosystems. PMID:18672093

  7. Wave observation in the marginal ice zone with the TerraSAR-X satellite

    NASA Astrophysics Data System (ADS)

    Gebhardt, Claus; Bidlot, Jean-Raymond; Gemmrich, Johannes; Lehner, Susanne; Pleskachevsky, Andrey; Rosenthal, Wolfgang

    2016-05-01

    This article investigates the penetration of ocean waves into the marginal ice zone (MIZ), observed by satellite, and likewise provides a basis for the future cross-validation of respective models. To this end, synthetic aperture radar images from the TerraSAR-X satellite (TS-X) and numerical simulations of the European Centre for Medium-Range Weather Forecasts (ECMWF) are used. The focus is an event of swell waves, developed during a storm passage in the Atlantic, penetrating deeply into the MIZ off the coast of Eastern Greenland in February 2013. The TS-X scene which is the basis for this investigation extends from the ice-free open ocean to solid ice. The variation of the peak wavelength is analysed and potential sources of variability are discussed. We find an increase in wavelength which is consistent with the spatial dispersion of deep water waves, even within the ice-covered region.

  8. Wave observation in the marginal ice zone with the TerraSAR-X satellite

    NASA Astrophysics Data System (ADS)

    Gebhardt, Claus; Bidlot, Jean-Raymond; Gemmrich, Johannes; Lehner, Susanne; Pleskachevsky, Andrey; Rosenthal, Wolfgang

    2016-07-01

    This article investigates the penetration of ocean waves into the marginal ice zone (MIZ), observed by satellite, and likewise provides a basis for the future cross-validation of respective models. To this end, synthetic aperture radar images from the TerraSAR-X satellite (TS-X) and numerical simulations of the European Centre for Medium-Range Weather Forecasts (ECMWF) are used. The focus is an event of swell waves, developed during a storm passage in the Atlantic, penetrating deeply into the MIZ off the coast of Eastern Greenland in February 2013. The TS-X scene which is the basis for this investigation extends from the ice-free open ocean to solid ice. The variation of the peak wavelength is analysed and potential sources of variability are discussed. We find an increase in wavelength which is consistent with the spatial dispersion of deep water waves, even within the ice-covered region.

  9. From Europe to America: pliocene to recent trans-atlantic expansion of cold-water north atlantic molluscs.

    PubMed

    Vermeij, Geerat J

    2005-12-01

    Data on the geographical distribution, phylogeny and fossil record of cool-temperate North Atlantic shell-bearing molluscs that live in waters shallower than 100 m depth belong to two biogeographic provinces, one in eastern North America north of Cape Cod, the other in northern Europe. Amphi-Atlantic species, which are found in both provinces, comprise 30.8% of the 402 species in the northeastern Atlantic and 47.3% of the 262 species in the northwestern Atlantic. Some 54.8% of these amphi-Atlantic species have phylogenetic origins in the North Pacific. Comparisons among fossil Atlantic faunas show that amphi-Atlantic distributions became established in the Middle Pliocene (about 3.5 million years ago), and that all represent westward expansions of European taxa to North America. No American taxa spread eastward to Europe without human assistance. These results are in accord with previous phylogeographic studies among populations within several amphi-Atlantic species. Explanations for the unidirectional expansion of species across the Atlantic remain uncertain, but may include smaller size and greater prior extinction of the North American as compared to the European fauna and biased transport mechanisms. Destruction of the European source fauna may jeopardize faunas on both sides of the Atlantic. PMID:16271981

  10. New insights on shear margin gravitational evolution through time. The case of the equatorial margins

    NASA Astrophysics Data System (ADS)

    Loncke, L.; Basile, C.; Gaullier, V.; Maillard, A.; Patriat, M.; Sage, F.; Roest, W.

    2009-04-01

    30% of passive margins in the world correspond to shear margins. Unlike divergent margins, those margins present a very sharp ocean-continent boundary which is expressed by steep surface slopes and complex rift structures. In addition of tilted blocks, wrench and strike-slip faults frequently deform the continental crust. High marginal ridges, rising 1-3 km over the adjacent margin typically form along the continental side of the margin. The best known example of transform margin is the Côte d'Ivoire-Ghana margin, highly investigated in the 1980's. New observations along the French-Guiana shear margin (GUYAPLAC survey, 2003) have evidenced massive early (immediately after rifting) and late collapses of the margin. These collapses concern huge volumes: remobilized masses that reach nearly 15000 km3 have been identified in the abyssal plain. No marginal ridge has been observed there. These observations have been compared to results published for the Surinam prolongation of this shear segment (Gouyet, 1988; Erbacher et al., 2004). There also, collapses and slope instabilities are evident, though part of a marginal ridge remains present. Finally, published data from the western Côte d'Ivoire transform margin (De Caprona, 1992) show wide collapses, some deep-seated, and other shallow. Sinking of entire parts of shear margins by gravity collapses appears thus rather common. These observations show that the post-rift gravity collapse of shear margins has been largely underestimated, and has even not been considered in evolutional models of transform margins, despite the fact this has important implications on the geometry and balance of those margins. On the basis of these observations, we propose a tentative scenario for the equatorial Atlantic shear margin gravitational evolution. References: Gouyet, S., 1988. Evolution tectono-sédimentaire des marges guyannaise et Nord-Brésilienne au cours de l'ouverture de l'Atlantique Sud. PhD Thesis, univ Pau et des pays de l

  11. Comparative assessment of endocrine modulators with oestrogenic activity: I. Definition of a hygiene-based margin of safety (HBMOS) for xeno-oestrogens against the background of European developments.

    PubMed

    Bolt, H M; Janning, P; Michna, H; Degen, G H

    2001-01-01

    A novel concept - the hygiene-based margin of safety (HBMOS) - is suggested for the assessment of the impact of potential endocrine modulators. It integrates exposure scenarios and potency data for industrial chemicals and naturally occurring dietary compounds with oestrogenic activity. An HBMOS is defined as a quotient of estimated daily intakes weighted by the relative in vivo potencies of these compounds. The Existing Chemicals Programme of the European Union provides Human and Environmental Risk Assessments of Existing Chemicals which include human exposure scenarios. Such exposure scenarios, along with potency estimates for endocrine activities, may provide a basis for a quantitative comparison of the potential endocrine-modulating effects of industrial chemicals with endocrine modulators as natural constituents of human diet. Natural phyto-oestrogens exhibit oestrogenic activity in vitro and in vivo. Important phyto-oestrogens for humans are isoflavones (daidzein, genistein) and lignans, with the highest quantities found in soybeans and flaxseed, respectively. Daily isoflavone exposures calculated for infants on soy-based formulae were in the ranges of 4.5-8 mg/kg body wt.; estimates for adults range up to 1 mg/kg body wt. The Senate Commission on the Evaluation of Food Safety (SKLM) of the Deutsche Forschungsgemeinschaft has also indicated a wide range of dietary exposures. For matters of risk assessment, the SKLM has based recommendations on dietary exposure scenarios, implying a daily intake of phyto-oestrogens in the order of 1 mg/kg body wt. On the basis of information compiled within the Existing Chemicals Programme of the EU, it appears that a daily human exposure to nonylphenol of 2 microg/kg body wt. may be a worst-case assumption, but which is based on valid scenarios. The intake of octylphenol is much lower, due to a different use pattern and applications, and may be neglected. Data from migration studies led to estimations of the daily human

  12. The Geodynamic Evolution of the Central and South East European Tethyan Chains

    NASA Astrophysics Data System (ADS)

    Sandulescu, M.

    2003-04-01

    Together with the Main Tethyan Suture Zone (disrupted fragments of the Tethyan oceanic domain ), built up of ophiolitic complexes and their overlying sedimentary sequences, three deformed continental margins (continental crust overlaped by tethyan sedimentary formations) may be recognized within the Central and South-East European area, i.g. the European, the Fore-Apulian and the Apulian margins. The Main Tethyan Suture Zone groups together the : Vardar Zone, South Pannonian-Insubric Suture, Transylvaniadian and Pienidian units. The European Margin cover the Northern and Eastern Carpathains, the South Carpathians,the Balkan, Rhodope and Serebo-Maceonein Massiv. To the Fore-Apulian microcontinent belogs the North Apuseni, Central West Carpathians and Austrialpine units, as well as the most important basement of the Pannonian Depression. Apulia covers the most important part of the Dinarides and Hellenides. The Tethyan Ocean opened, in the central and southern part of the area, during the Late Anisian or Early Ladinian and spread, with different rates since the early Upper Jurassic. The rifting which precede the opening may be Late Permian (?) and Lower Triassic. In the same time within the European Plate the intracontinental aulacogene north Dobrogea-South Crimea start to develop as a pull-apart basin connected with the southeasternmost segment of the Tornquist-Teisseyre Zone. In the northern part (West Carpathains and Alps) the Tethyan Ocean opened in the Middle Jurassic being a prolongation (?) of the Central Atlantic opening. The Bukk Terrane drifted since the end of the Lower Triasic from the Apulian Margin and collided the Fore-Apulian microcontinent until the earlly Jurassic. The first compressive events occur at the Jurassic/Cretaceous boundary stressed out by kalk-alkaline volcanics developed upon oceanic crust (Mariane-type subduction) and the “closing” of the North Dobrogea-South Crimea Aulacogene. Since the Middle Jurassic within the European

  13. Dynamic variability of dissolved Pb and Pb isotope composition from the U.S. North Atlantic GEOTRACES transect

    NASA Astrophysics Data System (ADS)

    Noble, Abigail E.; Echegoyen-Sanz, Yolanda; Boyle, Edward A.; Ohnemus, Daniel C.; Lam, Phoebe J.; Kayser, Rick; Reuer, Matt; Wu, Jingfeng; Smethie, William

    2015-06-01

    United States historically tend to carry 206Pb/207Pb signatures >1.17 (Hurst, 2002), subsurface signatures as low as 1.1563 in 206Pb/207Pb were observed in this feature. This signature appears to be carried westward within saline Subtropical Underwater (STUW), that ventilates from the Central Eastern part of the North Atlantic Subtropical Gyre where the lowest surface isotope 206Pb/207Pb ratios are observed. Along the western boundary, deep water masses of different ages carry distinct isotope ratios corresponding to their respective times of ventilation. Finally, a low 206Pb/207Pb signature in bottom water along the Eastern margin suggests that there may be some mobilization of European-derived anthropogenic Pb from recent surface deposits on the ocean floor.

  14. Atlantic impasse

    SciTech Connect

    Berkhout, F.; Walker, W.

    1994-09-01

    Nuclear trade relations between the United States and The European Union are in danger of falling apart. The U.S. - Euratom Cooperation agreements, under which trade in nuclear materials and technology has been conducted since the 1950s, lapse at the end of 1996. Negotiations to renew the agreement, under way since mind-1992, are in trouble. Failure to agree on a new accord will have serious consequences for all nuclear trade. The issue of `prior consent` is the principal striking point. American negotiators insist that, in the future, Europeans must obtain permission of the U.S. government before they can separate, use, or transfer plutonium from fuel that originated in the U.S. European negotiators do not want to accept greater U.S. control over their nuclear activities at a time when the mood in Washington is so firmly against reprocessing. European attitudes are also colored by commercial considerations. The European nuclear industry has supported the European Union`s tough line. The spetacle of allies and supporters of the Nuclear Non-Proliferation Treaty (NPT) squabbling over each others` rights to control civil nuclear activities would send the wrong signal to the NPT Extension Conference. This disput has the potential for boiling up into a highly damaging standoff in which there will only be losers.

  15. Marginalization and health geomatics.

    PubMed

    Alexander, Gregory L; Kinman, Edward L; Miller, Louise C; Patrick, Timothy B

    2003-01-01

    Marginalized groups have been defined as groups that have been peripheralized from the center of society. Increasing nursing knowledge of marginalized groups and the dynamics of population diversity will enable nurses to better recognize shifting health patterns, plan for utilization of health services, and determine ethnic and cultural differences that exist in marginalized populations. The authors of this article review theoretical models responsible for defining the concept marginalization, describe geographical information systems as a recommended tool to evaluate marginalized groups, and provide a case study utilizing tools and maps as a means of assessing marginal situations. PMID:14643736

  16. The basins on the Argentine continental margin

    SciTech Connect

    Urien, C.M.

    1996-08-01

    After the stabilization of the central Gondwana Craton, orogenic belts were accreted, as a result of convergence events and an extensive passive margin developed in southwestern Gondwana. Thermal subsidence in Parana, Karoo-Ventania basins and the Late Paleozoic-Early Mesozoic rifts, were modified by the Gondwana breakup and the South Atlantic opening. Early Paleozoic marine transgressions deposited the Table Mountain Group in Ventania. In southwestern Patagonia foreland clastics were deposited. Magmatic arcs and marine units indicate a tectonic trough was formed, alternating with continental sequences, over Late Paleozoic metamorphics and intrusives, resulting from plastered terrains along the Gondwana margin. In Patagonia, Permo-Carboniferous continental and glacio marine clastics infill the basins, while in Ventania, paralic sequences, grade from neritic to continental to the northeast, extending beneath the continental margin. The Triassic-Jurassic rift basins progressed onto regional widespread acid lavas and were infilled by lagoonal organic-rich sequences. Early drift phase built basins transverse to the margin, with fluvio-lacustrine sequences: Salado, Colorado, Valdes-Rawson, San Julian and North Malvinas intracratonic basins, which underwent transtensional faulting. Post-Oxfordian to Neocomian brackish sequences, onlapped the conjugate basins during the margin`s drift, with petroleum systems, as in Austral and Malvinas. In the Valanginian, basic extrusions commenced to form on the continental border, heralding the oceanic phase. Due to thermal subsidence, offlaping sediments prograded onto the remaining half-grabens. Several petroleum systems, proven and hypothetical, are identified in this region.

  17. Trans-Atlantic exchanges have shaped the population structure of the Lyme disease agent Borrelia burgdorferi sensu stricto

    PubMed Central

    Castillo-Ramírez, S.; Fingerle, V.; Jungnick, S.; Straubinger, R. K.; Krebs, S.; Blum, H.; Meinel, D. M.; Hofmann, H.; Guertler, P.; Sing, A.; Margos, G.

    2016-01-01

    The origin and population structure of Borrelia burgdorferi sensu stricto (s.s.), the agent of Lyme disease, remain obscure. This tick-transmitted bacterial species occurs in both North America and Europe. We sequenced 17 European isolates (representing the most frequently found sequence types in Europe) and compared these with 17 North American strains. We show that trans-Atlantic exchanges have occurred in the evolutionary history of this species and that a European origin of B. burgdorferi s.s. is marginally more likely than a USA origin. The data further suggest that some European human patients may have acquired their infection in North America. We found three distinct genetically differentiated groups: i) the outgroup species Borrelia bissettii, ii) two divergent strains from Europe, and iii) a group composed of strains from both the USA and Europe. Phylogenetic analysis indicated that different genotypes were likely to have been introduced several times into the same area. Our results demonstrate that irrespective of whether B. burgdorferi s.s. originated in Europe or the USA, later trans-Atlantic exchange(s) have occurred and have shaped the population structure of this genospecies. This study clearly shows the utility of next generation sequencing to obtain a better understanding of the phylogeography of this bacterial species. PMID:26955886

  18. Trans-Atlantic exchanges have shaped the population structure of the Lyme disease agent Borrelia burgdorferi sensu stricto.

    PubMed

    Castillo-Ramírez, S; Fingerle, V; Jungnick, S; Straubinger, R K; Krebs, S; Blum, H; Meinel, D M; Hofmann, H; Guertler, P; Sing, A; Margos, G

    2016-01-01

    The origin and population structure of Borrelia burgdorferi sensu stricto (s.s.), the agent of Lyme disease, remain obscure. This tick-transmitted bacterial species occurs in both North America and Europe. We sequenced 17 European isolates (representing the most frequently found sequence types in Europe) and compared these with 17 North American strains. We show that trans-Atlantic exchanges have occurred in the evolutionary history of this species and that a European origin of B. burgdorferi s.s. is marginally more likely than a USA origin. The data further suggest that some European human patients may have acquired their infection in North America. We found three distinct genetically differentiated groups: i) the outgroup species Borrelia bissettii, ii) two divergent strains from Europe, and iii) a group composed of strains from both the USA and Europe. Phylogenetic analysis indicated that different genotypes were likely to have been introduced several times into the same area. Our results demonstrate that irrespective of whether B. burgdorferi s.s. originated in Europe or the USA, later trans-Atlantic exchange(s) have occurred and have shaped the population structure of this genospecies. This study clearly shows the utility of next generation sequencing to obtain a better understanding of the phylogeography of this bacterial species. PMID:26955886

  19. Factors controlling structural style and magmatism in passive margins

    NASA Astrophysics Data System (ADS)

    Lu, Gang; Huismans, Ritske S.

    2015-04-01

    Comparing volcanic and non-volcanic passive margins, the distinct variability in geometry and subsidence history implies that the thermo-mechanical conditions vary at the time of rifting. Volcanic rifted margins (such as in the North Atlantic) show large magmatic activity and shallow water condition at the rift-drift transition, implying high geothermal gradients. For non-volcanic rifted margins where the initial thermal condition is potentially colder, it may develop in two end-member styles (Type I and Type II). Type-I margin with limited magmatism can be observed at Iberia-Newfoundland conjugate margins where the continental crustal thins across a narrow region and large tracts of continental mantle lithosphere are exposed at the seafloor. Type-II margin as observed in the ultra-wide central South Atlantic margins, in contrast, has normal magmatic activity and has a strongly thinned continental crust that span very wide regions (>250 km) below which the continental mantle lithosphere was removed. Here we perform thermo-mechanical finite element numerical experiments to investigate factors that are potentially important for the formation of volcanic and non-volcanic passive margins. Forward numerical models are used to predict the structural styles and characteristic magmatism associated with each of these end members. A number of parameters including different rheological stratifications and thermal gradients are tested and factors that control the degree of magmatism and structural style during rifting are focused.

  20. Fine scale sediment structure and geochemical signature between eastern and western North Atlantic during Heinrich events 1 and 2

    NASA Astrophysics Data System (ADS)

    Rashid, H.; Saint-Ange, F.; Barber, D. C.; Smith, M. E.; Devalia, N.

    2012-07-01

    Heinrich iceberg-rafting events 1 and 2 (H1 and H2) in the Labrador Sea are identified by their typical nepheloid-flow deposit sedimentary structure, high bulk carbonate, increase in iceberg-rafted detritus (IRD), and depletion of δ18O in the surface-dwelling foraminifer, Neogloboquadrina pachyderma (s). H-layers in this region have sedimentological characteristics different than those in the North Atlantic, and consist of IRD interspersed in pelagic sediments. High resolution 14C-AMS dates allowed us to delineate the leads and lags in instability between different ice-streams of the former Laurentide ice-sheet (LIS). Our data suggest that the discharge from the Hudson Strait ice-stream was followed by Cumberland Sound ice-sheet during H1 and H2. New radiogenic isotopes from the ice-proximal and surficial sediments of the greater Hudson Strait region and Labrador Sea H0, H1 and H2 layers suggest that carbonate-rich layers were only derived from Hudson Strait, not Baffin Bay. Fine scale structure of H1 and H2 intervals in Labrador Sea slope cores is characterized by two lithic peaks dominated by detrital carbonate grains and a single peak in cores from the central Labrador Sea. A similar pattern in the structure of H1 and H2 is observed along the western European margin. These findings contrast with North Atlantic H1 and H2 intervals, which are characterized by a peak of carbonate-rich grains, followed by a peak of quartz and volcanic grains. This comparison with North Atlantic and western European margin cores leads us to suggest that the coupling or lack thereof, between the LIS and European ice-sheet, is related to the depositional processes occurring along the margins, as well as the distance from the sources and the ability of the oceanic currents to disperse icebergs. Any significant change in ice-sheet dynamics would be recorded close to the ice-sheet margin, while distal locations would only record extreme events. We hypothesize that the discordance between

  1. Coupling Between Deglacial Shifts in the Position of the North Atlantic Arctic Front and Precipitation in Western Europe

    NASA Astrophysics Data System (ADS)

    Boessenkool, K. P.; Brinkhuis, H.; Visscher, H.

    2001-12-01

    . Pollen/spore records from marginal marine sediments contain terrestrial environmental information (composition of regional vegetation, temperature, precipitation, transport mode), while the study of the organic remains of marine dinoflagellates (dinocysts) from the same samples gives insight in coeval sea-surface conditions, including temperature and nutrient availability. Concurrent terrestrial and marine environmental signals indicate two phases of increased runoff corresponding to Heinrich event 1 and the YD in southwest Europe. Results show that intensified and possibly prolonged wet winter seasons contrasted with intensified anticyclonic summer aridity at these times. Increased wintertime precipitation associated with the YD is in harmony with the modelled southward migration of the trajectories of North Atlantic cyclones during this cooling event. No atmospheric general circulation models are as yet available for Heinrich events, but a similar relation is conceivable. The pattern of shifting atmospheric belts is confirmed by a similar marine palynological study from a latitudinally contrasting site on the Scottish margin (core MD95-2006). Renssen, H., Lautenschlager, M. and Schuurman, C.J.E., 1996. The atmospheric winter circulation during the Younger Dryas stadial in the Atlantic/European sector. Clim. Dyn., 12: 813-824.

  2. [Marginalization and health. Introduction].

    PubMed

    Yunes, J

    1992-06-01

    The relationship between marginalization and health is clear. In Mexico, for example, life expectancy is 53 years for the poorest population sectors and 20 years more for the wealthiest. Infant mortality in poor Colombian families is twice that of wealthier families, and one-third of developing countries the rural population is only half as likely as the urban to have access to health services. Women in the Southern hemisphere are 12 times likelier than those in the Northern to die of maternal causes. The most important step in arriving at a solution to the inequity may be to analyze in depth the relationship between marginality and health. Marginality may be defined as the lack of participation of individuals or groups in certain key phases of societal life, such as production, consumption, or political decision making. Marginality came to be viewed as a social problem only with recognition of the rights of all individuals to participate in available social goods. Marginality is always relative, and marginal groups exist because central groups determine the criteria for inclusion in the marginal and central groups. Marginality thus always refers to a concrete society at a specific historical moment. Marginal groups may be of various types. At present, marginal groups include women, rural populations, people with AIDS or mental illness or certain other health conditions, refugees, ethnic or religious groups, homosexuals, and the poor, who are the largest group of marginal persons in the world. Even in developed countries, 100-200 million persons live below the poverty line. Latin America is struggling to emerge from its marginal status in the world. The economic crisis of the 1980s increased poverty in the region, and 40% are not considered impoverished. Latin America is a clear example of the relationship between marginality and health. Its epidemiologic profile is intimately related to nutrition, availability of potable water, housing, and environmental

  3. Unraveling the Interaction Between Mantle Processes and the Tectono-Sedimentary Evolution During Final Rifting Based on the Study of Remnants of the Alpine Tethys Rifted Margins Exposed in the Alps

    NASA Astrophysics Data System (ADS)

    Mohn, G.; Masini, E.; Manatschal, G.; Muntener, O.; Kusznir, N.

    2007-12-01

    The tectonic, sedimentary and isostatic evolution of distal rifted margins are poorly constrained and the available data from present-day magma-poor rifted margins, such as the Iberia-Newfoundland or the Southern Atlantic margins suggest that its evolution is complex and very different from that of proximal margins. In contrast to present-day rifted margins, where rift structures are covered by sediments and are at abyssal depth, remnants of ancient margins preserved in collisional orogens bear, if not overprinted by later deformation, important information on the stratigraphic, tectonic and mantle evolution during rifting. This is particularly true for the Adriatic and parts of the European margins exposed in the Alps in Central Europe. From these margins remnants of the first oceanic crust, the subcontinental mantle, from lower crustal rocks, detachment systems, remnants of the distal and proximal margins and the stratigraphic record of rifting, including pre-, syn- and post-rift sediments are preserved. A paleogeographic reconstruction of all these structures including the associated stratigraphy and the underlying basement represents a unique opportunity to study the relations between shallow crustal and mantle processes during rifting. Previous studies suggested that the margins in the Alps resulted from a complex poly-phase evolution that initiated with distributed stretching (220 to 190 Ma), continued with localized thinning (around 180 Ma) and terminated with exhumation of mantle rocks and first MOR-type magmatism (at 160 Ma). Thus, rifting leading to breakup and opening of the Alpine Tethys was shown to be the result of strain localization and to include a transition from decoupled to coupled deformation in which detachment faulting played an important role. How crustal thinning is linked in detail with strain localization, uplift of distal domains and melt infiltration in the rising mantle during crustal thinning is, however, not yet understood. We will

  4. The North Atlantic Population Project

    PubMed Central

    RUGGLES, STEVEN; ROBERTS, EVAN; SARKAR, SULA; SOBEK, MATTHEW

    2011-01-01

    The North Atlantic Population Project (NAPP) is a massive database of historical census microdata from European and North American countries. The backbone of the project is the unique collection of completely digitized censuses providing information on the entire enumerated populations of each country. In addition, for some countries, the NAPP includes sample data from surrounding census years. In this article, the authors provide a brief history of the project, describe their progress to data and plans for the future, and discuss some potential implications of this unique data resource for social and economic research. PMID:22199411

  5. A Crustal Cross Section over the Central North Iberian Margin: New Insights into the Bay of Biscay Inverted Hyperextended Rift

    NASA Astrophysics Data System (ADS)

    Cadenas Martínez, P.; Fernandez Viejo, G.; Pulgar, J. A.; Minshull, T. A.

    2015-12-01

    The Bay of Biscay is a V-shape failed arm of the Atlantic rift which was opened during the Mesozoic and partially closed during the Alpine orogeny in the Cenozoic, when the convergence of the Iberian and European Plates drove to the formation of the Pyrenean-Cantabrian realm in the North Iberian peninsula. A complete crustal cross section through the central part of the North Iberian Margin, representing the southern margin of the Bay of Biscay, is presented here from the interpretation of a high quality deep seismic reflection profile together with boreholes and well logs, acquired for oil and gas exploration purposes. The studied segment of this margin includes a basement high so called Le Danois Bank, and the Asturian basin, one of the sedimentary basins developed during the Mesozoic extensional processes, which was subsequently inverted during the Alpine orogeny. Most of the compression seems to have taken place through uplift of the continental platform and slope and the formation of an accretionary wedge at the bottom of the slope, so it is still possible to elucidate both extensional and compressional features. The basin appears as an asymmetric bowl bounded by synsedimentary normal faults with a maximum thickness of about 6 s TWT, which has been estimated to be equivalent to about 7 km. Depth migration of the seismic profile has revealed the presence of a deeper trough, with a maximum thickness of 13. 5 km at its main depocenter, which closely resembles the sedimentary thickness proposed for other contemporaneous proximal basins. These results support the high degree of extension and the exhumation processes proposed for this margin, deduced from refraction velocities and from the upper crustal and mantle rocks dredged at the slopes of Le Danois High. They will bring new insights to, and further constraints on, geodynamical models for this margin, where the amount of shortening linked with Cenozoic compression and the role of the rift structure during the

  6. Modelling the Oceanic Nd Isotopic Composition With a North Atlantic Eddy Permitting Model

    NASA Astrophysics Data System (ADS)

    Peronne, S.; Treguier, A.; Arsouze, T.; Dutay, J.; Lacan, F.; Jeandel, C.

    2006-12-01

    The oceanic water masses differ by their temperatures, salinity, but also a number of geochemical tracers characterized by their weak concentrations and their ability to quantify oceanic processes (mixing, scavenging rates etc). Among these tracers, the Nd isotopic composition (hereafter epsilon-Nd) is a (quasi) conservative tracer of water mass mixing in the ocean interior, far from any lithogenic inputs. It has been recently established that exchange of Nd at the oceanic margins could be the dominant process controlling both its concentration and isotopic composition distribution in the ocean. This was demonstrated using in situ measurements and budget calculations and has recently been confirmed by a low resolution (2°) modeling approach (Arsouze et al., 2006). However, the currents flowing on the ocean margins are not correctly represented in coarse ocean models. It is the case in the North Atlantic ocean, which is of particular interest since i) it is the area of deep water formation and ii) these deep waters are characterized by the most negative epsilon-Nd values of the world ocean, which are used as "imprint" of the present and past thermohaline circulation. It is therefore essential to understand how these water masses acquire their epsilon-Nd signature. We propose here the first results of the modeling of oceanic Nd isotopic composition at eddy-permitting resolution, with the North Atlantic 0.25° version of the NEMO model used for the DRAKKAR European project. A 150 years off-line experiment and a shorter on-line experiment are performed. Simulated Nd distributions are compared to the present-day data base, vertical profiles, and the results of the low resolution model (in the North Atlantic). The eddy permitting model generally provides improved results, provided a high enough exchange rate is imposed in the deep ocean. Deficiencies of the simulated distribution in the Nordic Seas and the subpolar gyre are explained by errors in the input function on

  7. Plate-wide stress relaxation explains European Palaeocene basin inversions.

    PubMed

    Nielsen, Søren B; Thomsen, Erik; Hansen, David L; Clausen, Ole R

    2005-05-12

    During Late Cretaceous and Cenozoic times, many Palaeozoic and Mesozoic rifts and basin structures in the interior of the European continent underwent several phases of inversion (the process of shortening a previously extensional basin). The main phases occurred during the Late Cretaceous and Middle Palaeocene, and have been previously explained by pulses of compression, mainly from the Alpine orogen. Here we show that the main phases differed both in structural style and cause. The Cretaceous phase was characterized by narrow uplift zones, reverse activation of faults, crustal shortening, and the formation of asymmetric marginal troughs. In contrast, the Middle Palaeocene phase was characterized by dome-like uplift of a wider area with only mild fault movements, and formation of more distal and shallow marginal troughs. A simple flexural model explains how domal, secondary inversion follows inevitably from primary, convergence-related inversion on relaxation of the in-plane tectonic stress. The onset of relaxation inversions was plate-wide and simultaneous, and may have been triggered by stress changes caused by elevation of the North Atlantic lithosphere by the Iceland plume or the drop in the north-south convergence rate between Africa and Europe. PMID:15889089

  8. Lithosphere structure and subsidence evolution of the conjugate S-African and Argentine margins

    NASA Astrophysics Data System (ADS)

    Dressel, Ingo; Scheck-Wenderoth, Magdalena; Cacace, Mauro; Götze, Hans-Jürgen; Franke, Dieter

    2016-04-01

    The bathymetric evolution of the South Atlantic passive continental margins is a matter of debate. Though it is commonly accepted that passive margins experience thermal subsidence as a result of lithospheric cooling as well as load induced subsidence in response to sediment deposition it is disputed if the South Atlantic passive margins were affected by additional processes affecting the subsidence history after continental breakup. We present a subsidence analysis along the SW African margin and offshore Argentina and restore paleobathymetries to assess the subsidence evolution of the margin. These results are discussed with respect to mechanisms behind margin evolution. Therefore, we use available information about the lithosphere-scale present-day structural configuration of these margins as a starting point for the subsidence analysis. A multi 1D backward modelling method is applied to separate individual subsidence components such as the thermal- as well as the load induced subsidence and to restore paleobathymetries for the conjugate margins. The comparison of the restored paleobathymetries shows that the conjugate margins evolve differently: Continuous subsidence is obtained offshore Argentina whereas the subsidence history of the SW African margin is interrupted by phases of uplift. This differing results for both margins correlate also with different structural configurations of the subcrustal mantle. In the light of these results we discuss possible implications for uplift mechanisms.

  9. Ocean margins workshop

    SciTech Connect

    1990-12-31

    The Department of Energy (DOE) is announcing the refocusing of its marine research program to emphasize the study of ocean margins and their role in modulating, controlling, and driving Global Change phenomena. This is a proposal to conduct a workshop that will establish priorities and an implementation plan for a new research initiative by the Department of Energy on the ocean margins. The workshop will be attended by about 70 scientists who specialize in ocean margin research. The workshop will be held in the Norfolk, Virginia area in late June 1990.

  10. Organizing marginalized workers.

    PubMed

    Taylor, A K

    1999-01-01

    Figures from the U.S. Department of Labor show that low-wage or marginalized workers are more likely to be injured on the job and suffer more work-related medical conditions than better-paid workers. Despite an increasingly hostile organizing climate, market globalization, and corporate downsizing, significant progress has been made in organizing marginalized workers. A multifaceted, comprehensive organizing strategy, incorporating union-building strategies that include (but are not limited to) safety and health, must be used by unions to successfully organize marginalized workers and obtain the first contract. PMID:10378982

  11. Mantle Plume Temperature Variations Immediately Following Continental Breakup of the Northern North Atlantic

    NASA Astrophysics Data System (ADS)

    Parkin, C. J.; White, R. S.; Kusznir, N.

    2004-12-01

    North Atlantic from breakup to mature seafloor spreading. With no apparent decrease in spreading rate thinning of the crust oceanwards suggests a temperature decrease of 70K from immediate post rift formation to normal oceanic crustal thickness 17Myr after breakup. Mantle plume temperature variations during this period would cause rapid changes in uplift of the north-west European margin and probably controls much of the Tertiary sedimentation patterns west of Britain.

  12. Tectonic significance of Synrift sediment packages across the Congo continental margin

    SciTech Connect

    McGinnis, J.P.; Karner, G.D.; Driscoll, N.W. ); Brumbaugh, W.D. ); Cameron, N. )

    1993-09-01

    The tectonic and stratigraphic development of the Congo continental margin reflects the timing, magnitude, and distribution of lithospheric extension responsible for its formation. Details of the lithospheric extension process are recorded in the stratigraphic successions preserved along and across the margin. By using the stratal relationships (e.g., onlap, downlap, and truncation) and lithofacies determined from seismic reflection and exploratory well data as input into our basin-modeling strategy, we have developed an integrated approach to determine the relationship between the timing, magnitude, and distribution of lithospheric extension across the margin. Two hinge zones, an eastern and Atlantic hinge formed along the Congo margin in response to discrete extensional events occurring from the Berriasian to the Aptian. The eastern hinge zone demarcates the eastern limit of the broadly distributed Berriasian extension. This extension resulted in the formation of deep anoxic, lacustrine systems. In contrast, the Atlantic hinge, located [approximately]90 km west of the eastern hinge, marks the eastern limit of a second phase of extension, which began in the Hauterivian. Consequent footwall uplift and rotation exposed the earlier synrift and prerift stratigraphy to at least wave base causing varying amounts of erosional truncation across the Atlantic hinge zone along much of the Gabon, Congo, and Angola margins. The absence of the Melania Formation across the Congo margin implies that uplift of the Atlantic hinge was relatively minor compared to that across the Angola and Gabon margins. In addition, material eroded from the adjacent and topographically higher hinge zones may in part account for the thick wedge of sediment deposited seaward of the Congo Atlantic hinge. A third phase of extension reactivated both the eastern and Atlantic hinge zones and was responsible for creating the accommodation space for Marnes Noires source rock deposition.

  13. Marginalization of Vocational Psychology.

    ERIC Educational Resources Information Center

    Tinsley, Howard E. A.

    2001-01-01

    Although vocational psychology has diverse theoretical models and an empirical tradition, it is marginalized within counseling psychology. Its vitality is weakened by those who take a dabbler, pundit, or booster approach to scholarship. (Contains 46 references.) (SK)

  14. High pressure flexible pipes for marginal oilfield development

    SciTech Connect

    Griffiths, A.D.

    1985-01-01

    The major fields in the North Sea are currently in production and the average size of prospective development fields will decrease with time. The smaller or 'marginal' field development technology will represent a major factor in the future of oil and gas development in the North West European Continental Shelf area. Worldwide the number of exploitable marginal discoveries to date is believed to exceed 800. In the North West European Continental Shelf it is forecast by Hoare Govett that more than 45 marginal developments will be underway before 1990 in this area. These will be chosen from a known potential of 200 discoveries. The sub-sea completion of marginal oilfield production facilities is simplified by the use of high pressure flexible pipes. Short pipes are used to ''Tie-In'' rigid pipelines to sub-sea structures and continuous length pipes are used increasingly as a replacement for rigid, steel, pipelines.

  15. Differential response of continental stock complexes of Atlantic salmon (Salmo salar) to the Atlantic Multidecadal Oscillation

    NASA Astrophysics Data System (ADS)

    Friedland, Kevin D.; Shank, Burton V.; Todd, Christopher D.; McGinnity, Philip; Nye, Janet A.

    2014-05-01

    Atlantic salmon, Salmo salar, in the North Atlantic are managed as a set of population complexes distributed in North America and Europe. In recent years, these complexes have experienced reduced marine survival and many populations within the complexes are at risk, especially those at the southern ends of the species amphi-Atlantic range. Atlantic salmon is an anadromous fish dividing its life history between residence in freshwater and the marine environment. The freshwater portion of the life history includes spawning and the rearing of juveniles where in-river production has tended to be relatively stable, whereas the first year at sea, termed the post-smolt year, is characterized by more variable rates of mortality. Although their habitats are widely separated geographically along the North Atlantic seaboards, strong recruitment coherence exists between North American and European stock complexes. This recruitment coherence is correlated with ocean temperature variation associated with the Atlantic Multidecadal Oscillation (AMO). The North Atlantic Oscillation (NAO) appears to be relatively unimportant as a driver of salmon abundance. The mechanism determining the link between AMO-related thermal variation and abundance appears to differ fundamentally for the two continental stock groupings. Whereas ocean climate variability during the first springtime months of juvenile salmon migration to sea appears to be important to the survival of North American stocks, summer climate variation appears to be central to adult recruitment variation for European stocks. This contrast in seasonal effects appears to be related to the varying roles of predation pressure and size-related mortality on the continental stock complexes. The anticipated warming due to global climate change will impose thermal conditions on salmon populations outside historical context and challenge the ability of many populations to persist.

  16. Seasonal predictability of the North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Vellinga, Michael; Scaife, Adam

    2015-04-01

    Until recently, long-range forecast systems showed only modest levels of skill in predicting surface winter climate around the Atlantic Basin and associated fluctuations in the North Atlantic Oscillation at seasonal lead times. Here we use a new forecast system to assess seasonal predictability of winter North Atlantic climate. We demonstrate that key aspects of European and North American winter climate and the surface North Atlantic Oscillation are highly predictable months ahead. We demonstrate high levels of prediction skill in retrospective forecasts of the surface North Atlantic Oscillation, winter storminess, near-surface temperature, and wind speed, all of which have high value for planning and adaptation to extreme winter conditions. Analysis of forecast ensembles suggests that while useful levels of seasonal forecast skill have now been achieved, key sources of predictability are still only partially represented and there is further untapped predictability. This work is distributed under the Creative Commons Attribution 3.0 Unported License together with an author copyright. This license does not conflict with the regulations of the Crown Copyright.

  17. Post-Rift Compressional Deformation on the Passive Margin of a young Mediterranean Backarc Basin (Eastern Sardinian Margin, Tyrrhenian Sea)

    NASA Astrophysics Data System (ADS)

    Chanier, F.; Gaullier, V.; Maillard, A.; Thinon, I.; Sage, F.; Lymer, G.; Vendeville, B.; Giresse, P.; Bassetti, M. A.; Lofi, J.

    2014-12-01

    Compressional deformation has been reported on many passive margins, mostly attributed to thin-skinned tectonics in response to gravity gliding or spreading from viscous layers (overpressured shales, salt décollement). However some of the reported structures are obviously related to regional stress and also affect the basement, not only the upper sedimentary cover. Such deformation has been documented and discussed in the last decade mainly from the northern Atlantic margins (Doré et al., 2008 ; Pereira et al., 2011, & ref. herein). The compressional structures on passive margins have been notably considered as linked to tectonomagmatic and active asthenospheric upwelling, post-breakup compression and compactional stresses. The western margin of the Tyrrhenian Sea (Central Mediterranean) is a passive margin formed during the late Miocene opening of a back-arc basin in relation with the roll-back and retreat of the Ionian subducting lithosphere (African Plate). From our new data, we can show evidence for compressional features that developed in the Pliocene, shortly after the main rifting period on the western Tyrrhenian Sea (Middle to Late Miocene) and beginning of oceanic spreading (Earliest Pliocene). We could describe such structures across the inner margin onshore, from field analysis, as well as offshore, from newly acquired seismic data (METYSS 1 & 3; Gaullier et al. 2014). The characters and distribution of such compressional deformation, occurring very shortly after the onset of oceanic spreading in the deep basin (earliest Pliocene), allow us to discuss the possible interactions between breakup processes and inversion episodes on passive margins. Doré A.G., Lundin E.R., Kusznir N.J., & Pascal C., 2008. Potential mechanisms for the genesis of Cenozoic domal structures on the NE Atlantic margin: Pros and cons and some new ideas. Geol. Soc. London Spec. Pub., 306, 1-26. Gaullier V., Chanier F., et al., 2014. Salt tectonics and crustal tectonics along the

  18. Origin of the northern Atlantic`s Heinrich events

    SciTech Connect

    Broecker, W.; Bond, G.; Klas, M.

    1992-01-01

    As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments of foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50{degrees}N and 24{degrees}W. Their ages are respectively 15000 radiocarbon years, 20000 radiocarbon years, 27000 radiocarbon years, about 40000 years, and about 50000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet. 7 refs., 3 figs., 2 tabs.

  19. Marginal energy prices report

    SciTech Connect

    Chaitkin, Stuart; Biermayer, Peter; Bretz, Sarah; Brown, Steve; Constantine, Sachu; Fisher, Diane; Hakim, Sajid; Liew, Lucy; Lutz, Jim; Marnay, Chris; McMahon, James E.; Moezzi, Mithra; Osborn, Julie; Rawner, Esther; Roberson, Judy; Rosenquist, Greg; Ryan, Nancy; Turiel, Isaac; Wiel, Stephen

    1999-06-24

    This report responds to a recommendation from the Department of Energy's (DOE) Advisory Committee on Appliance Energy Efficiency Standards. It presents the derivation of estimated consumer marginal energy prices for the commercial and residential sectors for use in the life-cycle cost (LCC) analyses for four of the high priority appliances' energy efficiency standards rule makings --clothes washers, water heaters,fluorescent lamp ballasts, and central airconditioners/heat pumps. Marginal prices as discussed here are those prices consumers pay (or save) for their last units of energy used (or saved). Marginal prices reflect a change in a consumer's bill (that might be associated with new energy efficiency standards) divided by the corresponding change in the amount of energy the consumer used.

  20. AtlantOS - Optimizing and Enhancing the Integrated Atlantic Ocean Observing System

    NASA Astrophysics Data System (ADS)

    Reitz, Anja; Visbeck, Martin; AtlantOS consortium, the

    2016-04-01

    Ocean Cooperation. The EU Horizon 2020 AtlantOS project pools the efforts of 57 European and 5 non-European partners (research institutes, universities, marine service providers, multi-institutional organisations, and the private sector) from 18 countries to collaborate on optimizing and enhancing Atlantic Ocean observing. The project has a budget of € 21M for 4 years (April 2015 - June 2019) and is coordinated by GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany (Prof. Dr. Martin Visbeck). The project is organized along work packages on: i) observing system requirements and design studies, ii) enhancement of ship-based and autonomous observing networks, iii) interfaces with coastal ocean observing systems, iv) integration of regional observing systems, v) cross-cutting issues and emerging networks, vi) data flow and data integration, vii) societal benefits from observing /information systems, viii) system evaluation and resource sustainability. Engagement with wider stakeholders including end-users of Atlantic Ocean observation products and services will also be key throughout the project. The AtlantOS initiative contributes to achieving the aims of the Galway Statement on Atlantic Ocean Cooperation that was signed in 2013 by the EU, Canada and the US, launching a Transatlantic Ocean Research Alliance to enhance collaboration to better understand the Atlantic Ocean and sustainably manage and use its resources.

  1. Deep continental margin reflectors

    USGS Publications Warehouse

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

    1985-01-01

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

  2. Predicting service life margins

    NASA Technical Reports Server (NTRS)

    Egan, G. F.

    1971-01-01

    Margins are developed for equipment susceptible to malfunction due to excessive time or operation cycles, and for identifying limited life equipment so monitoring and replacing is accomplished before hardware failure. Method applies to hardware where design service is established and where reasonable expected usage prediction is made.

  3. Hourly marginal emissions tool

    EPA Science Inventory

    The hourly marginal emissions tool is an excel workbook that estimates the hourly NOx, SO2 and CO2 emission reductions of energy efficiency and renewable energy policies and programs in the electric power sector. It will be based on EPA's proposed "Road map for Incorporating ene...

  4. Marginalization and School Nursing

    ERIC Educational Resources Information Center

    Smith, Julia Ann

    2004-01-01

    The concept of marginalization was first analyzed by nursing researchers Hall, Stevens, and Meleis. Although nursing literature frequently refers to this concept when addressing "at risk" groups such as the homeless, gays and lesbians, and those infected with HIV/AIDS, the concept can also be applied to nursing. Analysis of current school nursing…

  5. Contribution Margin Budgeting.

    ERIC Educational Resources Information Center

    Tambrino, Paul A.

    2001-01-01

    Describes Iowa Valley Community College District's Contribution Margin Budgeting (CMB) program, successfully implemented to stave off bankruptcy. In this program, each responsibility center receives credit for all income generated and is charged for all expenditures, and each must build its own reserve against revenue shortfalls and unanticipated…

  6. Marginality and Triangle Inequality

    NASA Astrophysics Data System (ADS)

    Nánásiová, O. L̆ga; Valášková, L̆ubica

    2010-12-01

    In this paper we study conditions for the existence of a 3-dimensional s-map on a quantum logic under assumption that marginal s-maps are known. We show that the existence of such a 3-dimensional s-map depends on the triangle inequality of d-map, which on a Boolean algebra represents a measure of symmetric difference.

  7. Volcanic passive margins

    NASA Astrophysics Data System (ADS)

    Geoffroy, Laurent

    2005-12-01

    Compared to non-volcanic ones, volcanic passive margins mark continental break-up over a hotter mantle, probably subject to small-scale convection. They present distinctive genetic and structural features. High-rate extension of the lithosphere is associated with catastrophic mantle melting responsible for the accretion of a thick igneous crust. Distinctive structural features of volcanic margins are syn-magmatic and continentward-dipping crustal faults accommodating the seaward flexure of the igneous crust. Volcanic margins present along-axis a magmatic and tectonic segmentation with wavelength similar to adjacent slow-spreading ridges. Their 3D organisation suggests a connection between loci of mantle melting at depths and zones of strain concentration within the lithosphere. Break-up would start and propagate from localized thermally-softened lithospheric zones. These 'soft points' could be localized over small-scale convection cells found at the bottom of the lithosphere, where adiabatic mantle melting would specifically occur. The particular structure of the brittle crust at volcanic passive margins could be interpreted by active and sudden oceanward flow of both the unstable hot mantle and the ductile part of the lithosphere during the break-up stage. To cite this article: L. Geoffroy, C. R. Geoscience 337 (2005).

  8. The Brazilian continental margin

    NASA Astrophysics Data System (ADS)

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

    1981-04-01

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

  9. Neotectonics in the northern equatorial Brazilian margin

    NASA Astrophysics Data System (ADS)

    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

  10. The crustal structure of the southern Argentine margin

    NASA Astrophysics Data System (ADS)

    Becker, Katharina; Franke, Dieter; Schnabel, Michael; Schreckenberger, Bernd; Heyde, Ingo; Krawczyk, Charlotte M.

    2012-06-01

    Multichannel reflection seismic profiles, combined with gravimetric and magnetic data provide insight into the crustal structure of the southernmost Argentine margin, at the transition from a rifted to a transform margin and outline the extent of the North Falkland Graben. Based on these data, we establish a regional stratigraphic model for the post-rift sediments, comprising six marker horizons with a new formation in the Barremian/Lower Cretaceous. Our observations support that a N-S trending subsidiary branch of the North Falkland Graben continues along the continental shelf and slope to the Argentine basin. During the rift phase, a wide shelf area was affected by the E-W extension, subsequently forming the North Falkland Graben and the subsidiary branch along which finally breakup occurred. We propose the division of the margin in two segments: a N-S trending rifted margin and an E-W trending transform margin. This is further underpinned by crustal scale gravity modelling. Three different tectono-dynamic processes shaped the study area. (1) The Triassic/Early Jurassic extensional phase resulting in the formation of the North Falkland Graben and additional narrower rift grabens ended synchronously with the breakup of the South Atlantic in the early Valanginian. (2) Extensional phase related to the opening of the South Atlantic. (3) The transform margin was active in the study area from about Hauterivian times and activity lasted until late Cretaceous/early Cenozoic. Both, the rifted margin and the transform margin are magma-poor. Very limited structures may have a volcanic origin but are suggested to be post-rift. The oceanic crust was found to be unusually thin, indicating a deficit in magma supply during formation. These findings in combination with the proposed breakup age in the early Valanginian that considerably predates the formation of the Paraná-Etendeka continental flood basalt provinces in Brazil and Namibia question the influence of the Tristan da

  11. Rifted continental margins: geometric control on crustal architecture and melting

    NASA Astrophysics Data System (ADS)

    Lundin, Erik; Redfield, Tim; Peron-Pinvidic, Gwenn

    2014-05-01

    A new model is provided for the distribution of magma-poor and magma-rich rifted margins. The South Atlantic, Central Atlantic, North Atlantic - Arctic (Eurasia Basin), and Red Sea all are magma-rich at their distal ends and magma-poor at their proximal ends (with respect to their poles of rotation). The well-known architectural zonation across fully developed magma-poor margins (limited crustal stretching, hyperextension, exhumed mantle, oceanic crust) is also observed along the lengths of many margins at the super-regional scale. Zones of exhumed mantle, marking magma-poor margin, can be mapped for thousands of kilometers. Likewise can zones of seaward dipping reflectors (SDR) marking magma-rich margins. At this scale, the age of the oceanic crust becomes younger in the direction of the rotation pole, implying that the continents ruptured by rift tip propagation (and rotation pole propagation). Propagation is also manifested by the age of pre-break-up magmatism, break-up unconformity, and margin uplift. Hence, the classic cross-sectional depiction of margin evolution has a third dimension. The degree of melting follows the same pattern. At the distal end of e.g. the South Atlantic, SDR zones are wide and gradually thin toward the rotation pole. Eventually exhumed mantle takes over, marking the transition to the magma-poor margins, which remain to the proximal end of rifting. SDR zones also thin laterally from ca 10-15 km thickness at the continent-ocean boundary (COB) to ca 7 km thick oceanic crust beyond the SDRs. Outcrop data demonstrate that also exhumed mantle contains up to ca 12% melt, infiltrated in the peridotites. Thus, melting is largest at the distal ends near the COB, and decreases both laterally toward the evolving ocean and along strike toward the rift tip. Accepting that continents are rigid to a first order, the linear rate of extension at any given location along an evolving rift and ocean, is governed by the angular rate of opening, the distance

  12. A predictive relationship between early season North Atlantic hurricane activity and the upcoming winter North Atlantic Oscillation

    NASA Astrophysics Data System (ADS)

    Boyd, Jessica; Saunders, Mark

    2016-04-01

    The winter North Atlantic Oscillation (NAO) is linked strongly to European winter climate including windstorms. Predicting the winter NAO is key to making successful seasonal predictions of European winter climate. We observe that in recent decades there are many instances of an inverse relationship between the strength of the North Atlantic hurricane season and the strength of the subsequent European winter windstorm season. Stormy European winter seasons often follow quiet Atlantic hurricane seasons and calm European winters follow active hurricane seasons. We explore the strength and temporal stability of this inverse relationship, consider a facilitating physical mechanism, and briefly discuss the implications of our findings for end users, in particular global reinsurers. We find there is a statistically significant link between North Atlantic hurricane activity and the upcoming winter NAO. The relationship is established by the midway point of the hurricane season in early September. The link is strongest when hurricane activity is in the upper or lower tercile and when summer ENSO (El Niño Southern Oscillation) is neutral. The relationship works well going back 40 years to the mid 1970s. The early winter (October-November-December) NAO is predicted best but since the early 1980s the predictive link extends to the main winter (December-January-February) NAO. The inverse link can be facilitated by a persistence and slow evolution of atmospheric circulation patterns and sea surface temperature anomalies over the North Atlantic between the summer and the winter. This persistence is best when hurricane seasons are more extreme and when summer ENSO is neutral. Our findings offer the potential for predicting the early winter and winter NAO from early September. The implied inverse relationship between US hurricane activity and European windstorm activity may enable more effective offsetting of risks between territories.

  13. 3. VIEW LOOKING NORTH WEST OVER CENTRAL ATLANTIC WITH ATLANTIC ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. VIEW LOOKING NORTH WEST OVER CENTRAL ATLANTIC WITH ATLANTIC OCEAN IN THE FOREGROUND. DENNIS HOTEL, BLENHEIM HOTEL, AND MARLBOROUGH HOTEL (LEFT TO RIGHT) ARE LOCATED IN THE CENTER OF THE PHOTOGRAPH. THE CLARIDGE HOTEL IS THE HIGHRISE IMMEDIATELY TO THE RIGHT OF THE MARLBOROUGH HOTEL - Marlborough, Blenheim & Dennis Hotels (aerial views), Between Park Place, Michigan Avenue & Boardwalk, Atlantic City, Atlantic County, NJ

  14. Strategies for managing margins.

    PubMed

    2012-08-01

    Potential Medicare and Medicaid reimbursement cuts have made it critical for home health agencies to manage their gross and net operating profit margins. Agencies need to develop tools to analyze their margins and make sure they are following best practices. Try as you may, your agency might still face the question, "Why am I not meeting my budget?" Get some answers in this session from David Berman and Andrea L. Devoti. Berman is a principal at Simione Healthcare Consultants in Hamden, CT, where he is responsible for merchant acquisitions, business valuation due diligence, and oversight of the financial monitor benchmarking tool besides serving as interim chief financial officer. Devoti is chairman of the NAHC board and President & CEO of Neighborhood Health Visiting Nurse Association in West Chester PA. PMID:23074756

  15. Tectonic evolution of Brazilian equatorial continental margin basins

    SciTech Connect

    Azevedo, R.P. )

    1993-02-01

    The structural style and stratigraphic relationships of sedimentary basins along the Brazilian Equatorial Atlantic Continental Margin were used to construct an empirical tectonic model for the development of ancient transform margins. The model is constrained by detailed structural and subsidence analyses of several basins along the margin. The structural framework of the basins was defined at shallow and deep levels by the integration of many geophysical and geological data sets. The Barreirinhas and Para-Maranhao Basins were divided in three tectonic domains: the Tutoia, Caete, and Tromai subbasins. The Caete area is characterized by northwest-southeast striking and northeast-dipping normal faults. A pure shear mechanism of basin formation is suggested for its development. The structure of the Tutoia and Tromai subbasins are more complex and indicative of a major strike-slip component with dextral sense of displacement, during early stages of basin evolution. These two later subbasins were developed on a lithosphere characterized by an abrupt transition (<50 km wide) from an unstretched continent to an oceanic lithosphere. The subsidence history of these basins do not comply with the classical models developed for passive margins or continental rifting. The thermo-mechanical model proposed for the Brazilian equatorial margin includes heterogeneous stretching combined with shearing at the plate margin. The tectonic history comprises: (1) Triassic-Jurassic limited extension associated with the Central Atlantic evolution; (2) Neocomian intraplate deformation consisting of strike-slip reactivation of preexisting shear zones; (3) Aptian-Cenomanian two-phase period of dextral shearing; and (4) Late Cretaceous-Cenozoic sea-floor spreading.

  16. Conjugate margins of Canada and Europe: Results from deep reflection profiling

    NASA Astrophysics Data System (ADS)

    Keen, C.; Peddy, C.; de Voogd, B.; Matthews, D.

    1989-02-01

    Deep seismic reflection profiles have been collected across the conjugate margins of the North Atlantic Ocean. The eastern North Atlantic margin is traversed in the Goban Spur region, and the western North Atlantic margin is crossed in the vicinity of Flemish Cap in the Grand Banks region. These seismic profiles allow us to examine the deep structures and mode of extension in crust that was once contiguous. The Flemish Cap and Goban Spur margins have different structural styles: thick and relatively unfaulted crust is present on the Flemish Cap margin west of the continent-ocean boundary, whereas the Goban Spur margin exhibits a zone of extensional faulting and thinned continental crust. The restored rift zone displays overall symmetry in which a bridge of thin crust (< 15 km thick), about 60 km wide, joins the two crustal blocks of normal continental thickness (˜28 km). The configuration of the Moho, the geometry and distribution of the lower crustal reflections, and the overall symmetry of the rift zone favor pure-shear stretching in the lower lithosphere, although either pure or simple shear could accommodate crustal extension.

  17. Turbidity distribution in the Atlantic Ocean

    USGS Publications Warehouse

    Eittreim, S.; Thorndike, E.M.; Sullivan, L.

    1976-01-01

    The regional coverage of Lamont nephelometer data in the North and South Atlantic can be used to map seawater turbidity at all depths. At the level of the clearest water, in the mid-depth regions, the turbidity distribution primarily reflects the pattern of productivity in the surface waters. This suggests that the 'background' turbidity level in the oceans is largely a function of biogenic fallout. The bottom waters of the western Atlantic generally exhibit large increases in turbidity. The most intense benthic nepheloid layers are in the southwestern Argentine basin and northern North American basin; the lowest bottom water turbidity in the western Atlantic is in the equatorial regions. Both the Argentine and North American basin bottom waters appear to derive their high turbidity largely from local resuspension of terrigenous input in these basins. In contrast to the west, the eastern Atlantic basins show very low turbidities with the exception of three regions: the Mediterranean outflow area, the Cape basin, and the West European basin. ?? 1976.

  18. Phylogeography of the European sturgeon (Acipenser sturio): A critically endangered species.

    PubMed

    Chassaing, Olivier; Desse-Berset, Nathalie; Hänni, Catherine; Hughes, Sandrine; Berrebi, Patrick

    2016-01-01

    The European sturgeon (Acipenser sturio) was once a common species throughout Europe, but the sole remaining natural population presently inhabits the Gironde Estuary in France (Atlantic coast). The species was classified as 'Critically Endangered' in 1996, and the Gironde population is now on the verge of extinction. In this setting, and for the first time, we present the past phylogeographical features of this species throughout Europe along with an assessment of its former genetic diversity. This study was based on a molecular analysis (mtDNA CR sequencing) of 10 living specimens from the Gironde Estuary, 55 museum specimens that had been caught along 19th and 20th centuries, and 59 archaeological remains dating back to 260-5000years BP, from which mitochondrial DNA was extracted and amplified. Although discontinuous, the produced data provided a realistic image of the former structure of A. sturio in Europe. Reconstruction of the phylogenetic trees and haplotypes network led to the identification of several clades. The mitochondrial genetic diversity of this species was found to be much greater at the core (Iberian Peninsula, Mediterranean and Adriatic regions) than along the margins (Atlantic-Northern Europe, Black Sea) of its range. A series of hypotheses on the dates and causes of changes in the species' major structures are put forward on the basis of these data. Finally, competition with A. oxyrinchus, a sibling species whose presence in Northern Europe was recently reconsidered, is presented as a major factor in the evolution of this species. PMID:26424382

  19. Diagnosing overflow waters in the North Atlantic

    NASA Astrophysics Data System (ADS)

    Guo, Chuncheng; Ilicak, Mehmet; Bentsen, Mats; Fer, Ilker

    2015-04-01

    Danmark Strait overflow water (DSOW) and Iceland Faroe overflow water (ISOW) are important for the formation and transformation of deep waters in the North Atlantic. In this work the volume transport, variability, and pathways of DSOW and ISOW are diagnosed using the one degree ocean-ice coupled Norwegian Earth System Model (NorESM) that is forced by CORE2 inter-annual forcing. The oceanic component (MICOM) features an isopycnal coordinate that is referenced to 2000 db. The issues related to the coarse resolution such as the southward transport of ISOW to the western European Basin, the lack of overflow water in the western North Atlantic, and the western boundary detachment of the deep western boundary current are addressed. The effects of diapycnal mixing on the behavior of overflow descent at Denmark Strait and Faroe Bank Channel and its downstream evolution are examined.

  20. A lithospheric 3D temperature study from the South Atlantic

    NASA Astrophysics Data System (ADS)

    Hirsch, K. K.; Scheck-Wenderoth, M.; Maystrenko, Y.; Sippel, J.

    2009-04-01

    The East African continental margin is a passive volcanic margin that experienced a long post-rifting history after break up in Early Cretaceous times. The break up resulted in the formation of a number of basins along the margin. The by far largest depocentre in the South Atlantic, the Orange Basin, was the location of previously performed studies. These studies of the Orange Basin have been performed to investigate the crustal structure and the temperature evolution of the basin. In this way, they gave way to new insights and to a number of questions. With 3D gravity modelling we found the crust to include high density bodies. Furthermore, a rifting model was developed which explained both the geometry and the thermal constraints of the basin. Now, this study has been extended spatially to cover a larger area and into depth to include the deep lithosphere. The main goal is to combine information on the geometry and properties of the sedimentary part of the system with data on the geometry and physical properties of the deep crust. It was also aimed to integrate both the continental and the oceanic parts of the margin into a consistent 3D structural model on a lithospheric scale. A 3D temperature model was evaluated for the passive continental margin of the South Atlantic including the lithospheric structure of the margin. We evaluate a case study for different scenarios to estimate the influence of sediments and crustal structures on the thermal field. The calculated conductive field is constrained by temperature measurements and 3D gravity modelling. At the Norwegian continental margin it has been found that a differentiation of the physical properties of the lower crust and the mantle is needed between the oceanic and continental domains to explain the observations. We aim to compare the younger setting of the Norwegian continental margin with the old passive margin in the South Atlantic. In particular, the South Atlantic is interesting since the southern half

  1. Mesozoic and Cenozoic evolution of the SW Iberian margin

    NASA Astrophysics Data System (ADS)

    Ramos, Adrià; Fernández, Oscar; Terrinha, Pedro; Muñoz, Josep Anton; Arnaiz, Álvaro

    2016-04-01

    The SW Iberian margin lies at the eastern termination of the Azores-Gibraltar Fracture Zone (AGFZ), the diffuse transform plate boundary between Africa and Iberia (Sartori et al., 1994). It comprises the Gulf of Cadiz and the Algarve Basin, which were developed under two main different regional stages of deformation. During the Mesozoic, the SW Iberian margin evolution since the Late Triassic was dominated by the Pangea break-up and the Central Atlantic opening up to Early Jurssic, followed by the westernmost Tethyan opening up to Mid/Late Jurassic, and the North Atlantic rifting from Late Jurassic to Early Cretaceous (e.g., Schettino and Turco, 2010). This phase of extension led to the formation of E-W to NE-SW trending, basement-involved extensional faults, the triggering of salt tectonics and the uplifting of basement highs (e.g., Guadalquivir Bank). This extensional phase was responsible not only for the sedimentary depocenter distribution, but also for the crustal configuration of this passive margin, extending from continental crust in the proximal part, to oceanic crust in the distal and deepest portion of the margin. Since the Late Cretaceous, the margin was inverted due to the N-S convergence between Africa and Iberia, being still undergoing collision given the dominance of reverse fault earthquake mechanisms (e.g., Zitellini et al., 2009). The shortening in the margin is mainly accommodated by the north-dipping foliation of the basin, expressed by south-directed blind thrusts affecting the present-day bathymetry, re-activating the basement highs and the salt tectonics, and controlling the Cenozoic depocenters. The emplacement of the Betics to the east led to the westward emplacement of the gravitational unit partially overlying the sedimentary basins, corresponding to the Allochthonous Unit of the Gulf of Cadiz (AUGC). Our observations of the margin configuration have been based on the interpretation of 2D and 3D seismic reflection surveys throughout the

  2. East Africa continental margins

    SciTech Connect

    Bosellini, A.

    1986-01-01

    New well data from Somalia, together with the history of sea-floor spreading in the Indian Ocean derived from magnetic anomalies, show that the East African margins from latitude 15/sup 0/S into the Gulf of Aden comprise four distinct segments that formed successively by the southward drift of Madagascar from Somalia during the Middle to Late Jurassic and Early Cretaceous, by the northeastward drift of India along the Owen Transform during the Late Cretaceous and Paleocene, and by the opening of the Gulf of Aden during the Neogene.

  3. Amphetamine margin in sports

    SciTech Connect

    Laties, V.G.; Weiss, B.

    1981-10-01

    The amphetamines can enhance athletic performance. That much seem clear from the literature, some of which is reviewed here. Increases in endurance have been demonstrated in both humans and rats. Smith and Beecher, 20 years ago, showed improvement of running, swimming, and weight throwing in highly trained athletes. Laboratory analogs of such performances have also been used and similar enhancement demonstrated. The amount of change induced by the amphetamines is usually small, of the order of a few percent. Nevertheless, since a fraction of a percent improvement can make the difference between fame and oblivion, the margin conferred by these drugs can be quite important.

  4. Structural Margins Assessment Approach

    NASA Technical Reports Server (NTRS)

    Ryan, Robert S.

    1988-01-01

    A general approach to the structural design and verification used to determine the structural margins of the space vehicle elements under Marshall Space Flight Center (MSFC) management is described. The Space Shuttle results and organization will be used as illustrations for techniques discussed. Given also are: (1) the system analyses performed or to be performed by, and (2) element analyses performed by MSFC and its contractors. Analysis approaches and their verification will be addressed. The Shuttle procedures are general in nature and apply to other than Shuttle space vehicles.

  5. Orogenic structural inheritance and rifted passive margin formation

    NASA Astrophysics Data System (ADS)

    Salazar Mora, Claudio A.; Huismans, Ritske S.

    2016-04-01

    Structural inheritance is related to mechanical weaknesses in the lithosphere due to previous tectonic events, e.g. rifting, subduction and collision. The North and South Atlantic rifted passive margins that formed during the breakup of Western Gondwana, are parallel to the older Caledonide and the Brasiliano-Pan-African orogenic belts. In the South Atlantic, 'old' mantle lithospheric fabric resulting from crystallographic preferred orientation of olivine is suggested to play a role during rifted margin formation (Tommasi and Vauchez, 2001). Magnetometric and gravimetric mapping of onshore structures in the Camamu and Almada basins suggest that extensional faults are controlled by two different directions of inherited older Brasiliano structures in the upper lithosphere (Ferreira et al., 2009). In the South Atlantic Campos Basin, 3D seismic data indicate that inherited basement structures provide a first order control on basin structure (Fetter, 2009). Here we investigate the role of structural inheritance on the formation of rifted passive margins with high-resolution 2D thermo-mechanical numerical experiments. The numerical domain is 1200 km long and 600 km deep and represents the lithosphere and the sublithospheric mantle. Model experiments were carried out by creating self-consistent orogenic inheritance where a first phase of orogen formation is followed by extension. We focus in particular on the role of varying amount of orogenic shortening, crustal rheology, contrasting styles of orogen formation on rifted margin style, and the time delay between orogeny and subsequent rifted passive formation. Model results are compared to contrasting structural styles of rifted passive margin formation as observed in the South Atlantic. Ferreira, T.S., Caixeta, J.M., Lima, F.D., 2009. Basement control in Camamu and Almada rift basins. Boletim de Geociências da Petrobrás 17, 69-88. Fetter, M., 2009. The role of basement tectonic reactivation on the structural evolution

  6. A contourite depositional system along the Uruguayan continental margin

    NASA Astrophysics Data System (ADS)

    Hernández Molina, F. J.; Soto, M.; Piola, A. R.; Tomasini, J.; Preu, B.; Thompson, P.; Badalini, G.; Creaser, A.; Violante, R.; Morales, E.; Paterlini, M.; de Santa Ana, H.

    2015-12-01

    For the first time, a multidisciplinary approach for evaluating the influence of bottom currents in the Uruguayan continental margin is presented. Bathymetric data and multichannel 2D and 3D seismic reflection profiles were used to construct a morphosedimentary map to interpret and decode sedimentary and oceanographic processes along the Uruguayan continental margin. Based on these results a significant contourite depositional system on the margin is described, which contains a spectacular array of large erosive, depositional (drifts) and mixed (terrace) features, which have been generated primarily by water masses of Antarctic and subantarctic origin. From the Eocene-Oligocene boundary up to present time, the long-term influence of water masses from higher southern latitudes, in combination with down-slope sedimentary processes have strongly controlled the overall margin morphology. Most of the features described here, were formed during the middle/late Miocene epoch due to paleoceanographic shifts that include the arrival of Antarctic Intermediate Water (AAIW) along the margin, which in combination with deeper Antarctic Bottom Water (AABW) are fundamental in the margin evolution. In combination with Quaternary climatic and eustatic changes in sea level, fluctuations of the Brazil-Malvinas Confluence influenced subsequently glacial and interglacial stages that appear in sedimentary features defined here. These paleoceanographic changes controlled the sedimentary stacking pattern and the locations of high amplitude reflections (HAR) along the contourite terraces, which could be associated to sandier deposits. Fundamental understanding of the above described margin morphologies and the development of associated bedforms in deep marine environments are essential to fully leverage their conceptual implications for hydrocarbon exploration efforts. Futhermore, a more detailed understanding of the margin and its ancient to modern day current dynamics will improve

  7. South Atlantic interbasin exchange

    NASA Technical Reports Server (NTRS)

    Rintoul, Stephen Rich

    1991-01-01

    The exchange of mass and heat between the South Atlantic and the neighboring ocean basins was estimated using hydrographic data and inverse methods, in order to gain information on the links between the deep-water formation processes occurring within the Atlantic and the global thermohaline circulation. Results demonstrate that the global thermohaline cell associated with the formation and export of North Atlantic deep water (NADW) is closed primarily by a 'cold water path' in which deep water leaving the Atlantic ultimately returns as intermediate water entering the basin through Drake Passage. This conclusion conflicts with the suggestion by Gordon (1986) that the global thermohaline circulation associated with the formation of NADW is closed primarily by a 'warm water path', in which the export of NADW is compensated by an inflow of warm Indian Ocean thermocline water south of Africa.

  8. Polychaete abundance, biomass and diversity patterns at the Mid-Atlantic Ridge, North Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    Shields, Mark A.; Blanco-Perez, Raimundo

    2013-12-01

    Recent studies have revealed that the Mid-Atlantic Ridge (MAR) in the North Atlantic Ocean accounts for a large proportion of available bathyal soft-sediment habitat. When comparing the MAR to the continental margins of the North Atlantic, it is apparent that very little is known about the soft-sediment macrofaunal community associated with the MAR. In the present study, as part of the ECOMAR (Ecosystems of the Mid-Atlantic Ridge at the Sub-Polar Front and Charlie-Gibbs Fracture Zone) project, the polychaete component of the MAR macrofaunal community was investigated. A total of 751 polychaete specimens and 133 species were identified from megacorer samples collected at four MAR sites (48-54°N, depth: 2500-2800 m) sampled during the RRS James Cook 48 cruise in the summer of 2010. Polychaetes were the most abundant member of the macrofaunal community, and there was no significant difference in polychaete abundance, biomass and diversity between any of the MAR sites. In addition, the MAR did not appear to provide a physical barrier to the distribution of bathyal polychaetes either side of the ridge.

  9. Magmatic-tectonic evolution of a volcanic rifted margin

    SciTech Connect

    Eldholm, O. )

    1990-05-01

    Many North Atlantic margins are underlain by huge volcanic edifices near the continent-ocean boundary. A crustal hole drilled at the outer Voering Plateau during ODP (Ocean Drilling Project) Leg 104 has provided important constraints on the breakup history and the subsequent margin evolution by penetrating more than 900 m of igneous rocks and interbedded sediment below a post-early Eocene cover. The recovered basement rocks constitute two different volcanic series. The Upper Series, comprising a seaward-dipping reflector wedge, consists of transitional mid-oceanic tholeiitic lava flows and thin volcaniclastic sediments. Dacitic flows, some dikes and thicker sediments constitute the Lower Series. The margin evolved by Paleocene crustal extension, uplift and pervasive intrusion in the rift zone. Just prior to breakup, magma from shallow crustal melts produced the Lower Series. The Upper Series was constructed during an intense, rapidly waning subaerial surge following breakup in the earliest Eocene. The Upper Series covers both new oceanic crust and large areas of continental crust. The dipping wedge was formed by subsidence due to loading and thermal contraction probably amplified by a tectonic force. When the surge had abated, the injection center subsided and a normal oceanic crust was formed. A direct temporal and compositional relationship exists between the onshore North Atlantic Volcanic Province and the volcanic margins. Whereas the central transverse part of the province, near the Iceland hotspot has been active for 60 m.y., the volcanic margins reflect a 2,000-km-long transient phenomenon lasting only 3 m.y. The breakup volcanism and lack of initial subsidence are related to a regional, about 50C{degree}, increased temperature at the base of the lithosphere (hot carpet) combined with opening in previously extended crust.

  10. Subduction-Driven Recycling of Continental Margin Lithosphere

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  11. European Mistletoe

    MedlinePlus

    ... gov Key References American mistletoe. Natural Medicines Comprehensive Database Web site. Accessed at www.naturaldatabase.com on July 7, 2009. European mistletoe. Natural Medicines Comprehensive Database Web site. Accessed at www.naturaldatabase.com on July ...

  12. The multifaceted West Greenland passive margin

    NASA Astrophysics Data System (ADS)

    Breuer, Sonja; Damm, Volkmar; Block, Martin; Schreckenberger, Bernd; Heyde, Ingo; Nelson, Catherine; Kouwe, Wim

    2013-04-01

    The Baffin Bay located between Greenland and Canada, is the northward extension of the Labrador Sea. The Davis Strait High separates these two marine basins. The evolution of these basins is closely linked, and is as well affiliated to the opening of the North Atlantic Ocean. The opening history started in the Cretaceous with the formation of several terrestrial rift basins with a block-faulted, metamorphic Precambrian basement. The further opening of the Baffin Bay coincides with the volcanic activity (60.9-52.5 Ma) along the West Greenland margin (Storey et al., 1998). The subsequent seafloor spreading in the Baffin Bay is linked to the Labrador Sea by the Ungava Fault Zone (UFZ), which is the most prominent transform fault in this region. Two main problems are still unsolved: 1) There are clear indications for normal seafloor spreading in the Baffin Bay like the seaward dipping reflectors (SDRs) on the Canadian side (Skaarup et al., 2006) and on the Greenland side based on our data. On the other hand, associated magnetic spreading anomalies are not yet discovered in the Baffin Bay or are not formed. These findings may either point to slow or ultraslow spreading or underlying strongly extended continental crust and/or serpentinised mantle. 2) The Greenlandic margin is much wider than the Canadian. In addition, a breakup unconformity can only be traced on the Greenland side and is not reported for the Canadian side. Which process causes this asymmetric margin and differences in shelf width? Is it a result of asymmetric spreading or connected to volcanic activity during breakup processes? In summer 2008, a marine geoscientific expedition (MSM09/03) was conducted with the research vessel "Maria S. Merian" in the Davis Strait and southern Baffin Bay. Approximately 1800 km of multichannel reflection seismic data were acquired. To supplement the database, a subsequent marine geoscientific expedition ARK-XXV/3 with RV POLARSTERN in summer 2010 was conducted. In our

  13. Subsidence, extension and thermal history of the West African margin in Senegal

    NASA Astrophysics Data System (ADS)

    Brun, Marie Véronique Latil; Lucazeau, Francis

    1988-10-01

    The subsidence of the Atlantic margin in Senegal clearly shows two rapid stages related to the formation of (1) the Central Atlantic during the early Jurassic (around 200 Ma), and (2) the Equatorial Atlantic during the Cretaceous (100 Ma). A simple model of extension is used to interpret the subsidence history and to derive the thermal evolution of this basin. The present-day gravity, bathymetry, bottom hole temperatures (BHT) in oil exploration boreholes and heat flow density are used to control the validity of the model. Two cross sections from the outcropping basement to oceanic crust are used, one in Casamance and the other one at the south to latitude of Dakar. The model can fully explain the first-order subsidence history as well as the present-day observations, and therefore can provide valuable information about the thermal evolution of sediments and about the structure of the continental crust along the margin. Comparisons with the opposite margin in North America (Blake Plateau and Carolina trough) indicate a rather different evolution (the North American margin did not undergo the second stage of rifting) and a different crustal structure (crustal thinning is less important on the African margin).

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

    NASA Astrophysics Data System (ADS)

    Gouiza, M.; Bertotti, G.; Hafid, M.; Cloetingh, S.

    2010-10-01

    The Atlantic passive margin of Morocco developed during Mesozoic times in association with the opening of the Central Atlantic and the Alpine Tethys. Extensional basins formed along the future continental margin and in the Atlas rift system. In Alpine times, this system was inverted to form the High and Middle Atlas fold-and-thrust belts. To provide a quantitative kinematic analysis of the evolution of the rifted margin, we present a crustal section crossing the Atlantic margin in the region of the Doukkala Basin, the Meseta and the Atlas system. We construct a post-rift upper crustal section compensating for Tertiary to present vertical movements and horizontal deformations, and we conduct numerical modeling to test quantitative relations between amounts and distribution of thinning and related vertical movements. Rifting along the transect began in the Late Triassic and ended with the appearance of oceanic crust at 175 Ma. Subsidence, possibly related to crustal thinning, continued in the Atlas rift in the Middle Jurassic. The numerical models confirm that the margin experienced a polyphase rifting history. The lithosphere along the transect preserved some strength throughout rifting with the Effective Elastic Thickness corresponding to an isotherm of 450°C. A mid-crustal level of necking of 15 km characterized the pre-rift lithosphere.

  15. European Community.

    PubMed

    1987-05-01

    The European Community was established in 1951 to reconcile France and Germany after World War II and to make possible the eventual federation of Europe. By 1986, there were 12 member countries: France, Italy, Belgium, the Federal Republic of Germany, Luxembourg, the Netherlands, Denmark, Ireland, the United Kingdom, Greece, Spain, and Portugal. Principal areas of concern are internal and external trade, agriculture, monetary coordination, fisheries, common industrial and commercial policies, assistance, science and research, and common social and regional policies. The European Community has a budget of US$34.035 billion/year, funded by customs duties and 1.4% of each member's value-added tax. The treaties establishing the European Community call for members to form a common market, a common customs tariff, and common agricultural, transport, economic, and nuclear policies. Major European Community institutions include the Commission, Council of Ministers, European Parliament, Court of Justice, and Economic and Social Committee. The Community is the world's largest trading unit, accounting for 15% of world trade. The 2 main goals of the Community's industrial policy are to create an open internal market and to promote technological innovation in order to improve international competitiveness. The European Community aims to contribute to the economic and social development of Third World countries as well. PMID:12177941

  16. Marginally Stable Nuclear Burning

    NASA Technical Reports Server (NTRS)

    Strohmayer, Tod E.; Altamirano, D.

    2012-01-01

    Thermonuclear X-ray bursts result from unstable nuclear burning of the material accreted on neutron stars in some low mass X-ray binaries (LMXBs). Theory predicts that close to the boundary of stability oscillatory burning can occur. This marginally stable regime has so far been identified in only a small number of sources. We present Rossi X-ray Timing Explorer (RXTE) observations of the bursting, high- inclination LMXB 4U 1323-619 that reveal for the first time in this source the signature of marginally stable burning. The source was observed during two successive RXTE orbits for approximately 5 ksec beginning at 10:14:01 UTC on March 28, 2011. Significant mHz quasi- periodic oscillations (QPO) at a frequency of 8.1 mHz are detected for approximately 1600 s from the beginning of the observation until the occurrence of a thermonuclear X-ray burst at 10:42:22 UTC. The mHz oscillations are not detected following the X-ray burst. The average fractional rms amplitude of the mHz QPOs is 6.4% (3 - 20 keV), and the amplitude increases to about 8% below 10 keV.This phenomenology is strikingly similar to that seen in the LMXB 4U 1636-53. Indeed, the frequency of the mHz QPOs in 4U 1323-619 prior to the X-ray burst is very similar to the transition frequency between mHz QPO and bursts found in 4U 1636-53 by Altamirano et al. (2008). These results strongly suggest that the observed QPOs in 4U 1323-619 are, like those in 4U 1636-53, due to marginally stable nuclear burning. We also explore the dependence of the energy spectrum on the oscillation phase, and we place the present observations within the context of the spectral evolution of the accretion-powered flux from the source.

  17. 76 FR 1153 - Atlantic Grid Operations A LLC, Atlantic Grid Operations B LLC, Atlantic Grid Operations C LLC...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-01-07

    ... Energy Regulatory Commission Atlantic Grid Operations A LLC, Atlantic Grid Operations B LLC, Atlantic Grid Operations C LLC, Atlantic Grid Operations D LLC and Atlantic Grid Operations E LLC; Notice of... (Commission) Rules of Practice and Procedure, 18 CFR 385.207, and Order No. 679,\\1\\ Atlantic Grid Operations...

  18. Paleoceanography. Onset of Mediterranean outflow into the North Atlantic.

    PubMed

    Hernández-Molina, F Javier; Stow, Dorrik A V; Alvarez-Zarikian, Carlos A; Acton, Gary; Bahr, André; Balestra, Barbara; Ducassou, Emmanuelle; Flood, Roger; Flores, José-Abel; Furota, Satoshi; Grunert, Patrick; Hodell, David; Jimenez-Espejo, Francisco; Kim, Jin Kyoung; Krissek, Lawrence; Kuroda, Junichiro; Li, Baohua; Llave, Estefania; Lofi, Johanna; Lourens, Lucas; Miller, Madeline; Nanayama, Futoshi; Nishida, Naohisa; Richter, Carl; Roque, Cristina; Pereira, Hélder; Sanchez Goñi, Maria Fernanda; Sierro, Francisco J; Singh, Arun Deo; Sloss, Craig; Takashimizu, Yasuhiro; Tzanova, Alexandrina; Voelker, Antje; Williams, Trevor; Xuan, Chuang

    2014-06-13

    Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics. PMID:24926012

  19. Does the Fukushima NPP disaster affect the caesium activity of North Atlantic Ocean fish?

    NASA Astrophysics Data System (ADS)

    Kanisch, G.; Aust, M.-O.

    2013-08-01

    Fillet samples of marine fish collected from the East/West Greenland currents (GC) and from the Baltic Sea (BS) have been investigated by gamma-ray spectrometry within the regular German monitoring programme. In samples of the second half of 2011, 134Cs traces have been detected that are suggested to originate from the Fukushima fallout that was deposited in March/April 2011 over the northern North Atlantic and accumulated by fish. The radionuclide 134Cs (half-life 2 yr) was indeed detected with quite small activities at about 0.0036 Bq kg-1 w.w. Existing box models describing the transport of Cs within seawater boxes of the northeast Atlantic allowed for estimation of 134Cs contributions from other sources, i.e. from the Chernobyl fallout and from discharges by the two major European nuclear reprocessing plants; both were negligible around Greenland, while for the Chernobyl fallout a small 134Cs background contribution to BS fish was estimated. Model results confirmed the level of 134C measured in BS fish and showed its maximum to have occurred in winter 2011/2012 followed by a continuous decrease. It was also determined that 134Cs activity, but not that of 134Cs, showed a significant negative correlation with sampling depth (150-400 m) of GC fish; this strengthens our Fukushima fallout assumption. As a result, the Fukushima fallout in these sea areas only marginally enhanced (GC: 4%; BS: 0.1%) pre-Fukushima levels of individual dose rates received by human fish consumers; the addition was around 0.001 μSv following the consumption of 10 kg of fish per year, which is not expected to cause concern according to present guidelines for radiation protection.

  20. Does the Fukushima NPP disaster affect the caesium activity of North Atlantic Ocean fish?

    NASA Astrophysics Data System (ADS)

    Kanisch, G.; Aust, M.-O.

    2013-03-01

    Fillet samples of marine fish collected from the East/West Greenland current (GC) and from the Baltic Sea (BS), have been investigated by gamma-ray spectrometry within the regular German monitoring program. In samples of the second half of 2011 134Cs traces have been detected, suggested to originate from the Fukushima fallout being deposited in March/April 2011 over the northern North Atlantic and accumulated by fish. The radionuclide 134Cs (half-live 2 yr) was indeed detected with quite small activities at about 0.0036 Bq kg-1 w.w. Existing box-models describing the transport of Cs within seawater boxes of the NE Atlantic allowed estimating that 134Cs contributions from other sources, i.e. from the Chernobyl fallout and from discharges by the two major European nuclear reprocessing plants, both were negligible around Greenland, while for the Chernobyl fallout a small 134Cs background contribution to BS fish was estimated. Model results confirmed the level of 134Cs measured in BS fish and showed its maximum to have occurred in winter 2011/2012 followed by a continuous decrease. It was also determined that 134Cs activity, but not that of 134Cs, showed a significant negative correlation with sampling depth (150-400 m) of GC fish; this strengthens our Fukushima fallout assumption. As a result, the Fukushima fallout in these sea areas only marginally enhanced (GC: 4%; BS: 0.1%) pre-Fukushima levels of individual dose rates received by human fish consumers; the addition was around 0.001 μSv following the consumption of 10 kg fish per year, which is not expected to cause concern according to present guidelines for radiation protection.

  1. Ivory Coast-Ghana margin: model of a transform margin

    SciTech Connect

    Mascle, J.; Blarez, E.

    1987-05-01

    The authors present a marine study of the eastern Ivory Coast-Ghana continental margins which they consider one of the most spectacular extinct transform margins. This margin has been created during Early-Lower Cretaceous time and has not been submitted to any major geodynamic reactivation since its fabric. Based on this example, they propose to consider during the evolution of the transform margin four main and successive stages. Shearing contact is first active between two probably thick continental crusts and then between progressively thinning continental crusts. This leads to the creation of specific geological structures such as pull-apart graben, elongated fault lineaments, major fault scarps, shear folds, and marginal ridges. After the final continental breakup, a hot center (the mid-oceanic ridge axis) is progressively drifting along the newly created margin. The contact between two lithospheres of different nature should necessarily induce, by thermal exchanges, vertical crustal readjustments. Finally, the transform margin remains directly adjacent to a hot but cooling oceanic lithosphere; its subsidence behavior should then progressively be comparable to the thermal subsidence of classic rifted margins.

  2. Fault Orientations at Obliquely Rifted Margins: Where? When? Why?

    NASA Astrophysics Data System (ADS)

    Brune, Sascha

    2015-04-01

    Present-day knowledge of rifted margin formation is largely based on 2D seismic lines, 2D conceptual models, and corroborated by 2D numerical experiments. However, the 2D assumption that the extension direction is perpendicular to the rift trend is often invalid. In fact, worldwide more than 75% of all rifted margin segments have been formed under significant obliquity exceeding 20° (angle measured between extension direction and rift trend normal): During formation of the Atlantic Ocean, oblique rifting dominated at the sheared margins of South Africa and Patagonia, the Equatorial Atlantic margins, separation of Greenland and North America, and it played a major role in the protracted rift history of the North East Atlantic. Outside the Atlantic Ocean, oblique rifting occurred during the split between East and West Gondwana, the separation of India and Australia, India and Madagascar, Australia and Antarctica, as well as Arabia and Africa. It is presently observed in the Gulf of California, the Aegean and in the East African Rift. Despite its significance, the degree to which oblique lithospheric extension affects first-order rift and passive margin properties like surface stress pattern, fault azimuths, and basin geometry, is still not entirely clear. This contribution provides insight in crustal stress patterns and fault orientations by applying a 3D numerical rift model to oblique extensional settings. The presented forward experiments cover the whole spectrum of oblique extension (i.e. rift-orthogonal extension, low obliquity, high obliquity, strike-slip deformation) from initial deformation to breakup. They are conducted using an elasto-visco-plastic finite element model and involve crustal and mantle layers accounting for self-consistent necking of the lithosphere. Results are thoroughly compared to previous analogue experiments, which yields many similarities but also distinct differences for late rift stages and for high obliquity. Even though the model

  3. The marginalization of hormesis.

    PubMed

    Calabrese, E J; Baldwin, L A

    2000-01-01

    Despite the substantial development and publication of highly reproducible toxicological data, the concept of hormetic dose-response relationships was never integrated into the mainstream of toxicological thought. Review of the historical foundations of the interpretation of the bioassay and assessment of competitive theories of dose-response relationships lead to the conclusion that multiple factors contributed to the marginalization of hormesis during the middle and subsequent decades of the 20th century. These factors include: (a) the close-association of hormesis with homeopathy lead to the hostility of modern medicine toward homeopathy thereby creating a guilt by association framework, and the carry-over influence of that hostility in the judgements of medically-based pharmacologists/ toxicologists toward hormesis; (b) the emphasis of high dose effects linked with a lack of appreciation of the significance of the implications of low dose stimulatory effects; (c) the lack of an evolutionary-based mechanism(s) to account for hormetic effects; and (d) the lack of appropriate scientific advocates to counter aggressive and intellectually powerful critics of the hormetic perspective. PMID:10745293

  4. The marginalization of hormesis.

    PubMed

    Calabrese, E J; Baldwin, L A

    1999-01-01

    Despite the substantial development and publication of highly reproducible toxicological data, the concept of hormetic dose-response relationships was never integrated into the mainstream of toxicological thought. Review of the historical foundations of the interpretation of the bioassay and assessment of competitive theories of dose-response relationships lead to the conclusion that multiple factors contributed to the marginalization of hormesis during the middle and subsequent decades of the 20th Century. These factors include the following: (a) the close association of hormesis with homeopathy, which led to the hostility of modern medicine toward homeopathy, thereby creating a guilt-by-association framework, and the carryover influence of that hostility toward hormesis in the judgements of medically based pharmacologists/toxicologists; (b) the emphasis of high-dose effects linked with a lack of appreciation of the significance of the implications of low-dose stimulatory effects; (c) the lack of an evolution-based mechanism(s) to account for hormetic effects; and (d) lack of appropriate scientific advocates to counter aggressive and intellectually powerful critics of the hormetic perspective. PMID:10207983

  5. The importance of rift history for volcanic margin formation.

    PubMed

    Armitage, John J; Collier, Jenny S; Minshull, Tim A

    2010-06-17

    Rifting and magmatism are fundamental geological processes that shape the surface of our planet. A relationship between the two is widely acknowledged but its precise nature has eluded geoscientists and remained controversial. Largely on the basis of detailed observations from the North Atlantic Ocean, mantle temperature was identified as the primary factor controlling magmatic production, with most authors seeking to explain observed variations in volcanic activity at rifted margins in terms of the mantle temperature at the time of break-up. However, as more detailed observations have been made at other rifted margins worldwide, the validity of this interpretation and the importance of other factors in controlling break-up style have been much debated. One such observation is from the northwest Indian Ocean, where, despite an unequivocal link between an onshore flood basalt province, continental break-up and a hot-spot track leading to an active ocean island volcano, the associated continental margins show little magmatism. Here we reconcile these observations by applying a numerical model that accounts explicitly for the effects of earlier episodes of extension. Our approach allows us to directly compare break-up magmatism generated at different locations and so isolate the key controlling factors. We show that the volume of rift-related magmatism generated, both in the northwest Indian Ocean and at the better-known North Atlantic margins, depends not only on the mantle temperature but, to a similar degree, on the rift history. The inherited extensional history can either suppress or enhance melt generation, which can explain previously enigmatic observations. PMID:20559385

  6. Biogeographic provinces in the Atlantic deep sea determined from cumacean distribution patterns

    NASA Astrophysics Data System (ADS)

    Watling, Les

    2009-09-01

    Cumacean species abundance and presence-absence data were compiled from samples taken along the US northeast slope and rise, from around the Faroe Islands, and from deep-sea transects throughout the Atlantic Ocean. These data were analyzed using hierarchical cluster techniques, the results being used to help determine the boundaries of zoogeographic units in the deep sea. Comparing the results of these analyses with previous studies on protobranchs, tunicates, and sea stars, supports dividing the deep Atlantic Ocean into the following biogeographic units: (1) Norwegian Basin; (2) North Atlantic Upper Bathyal; (3) West European Basin Northern Bathyal; (4) Lusitanian Bathyal; (5) North American Basin Bathyal; (6) West European Basin Abyssal; (7) North American Basin Abyssal; and (8) Angola, Cape, Brazil, and Argentine Basins occupying the more or less isolated basins of the South Atlantic Ocean. These latter are not well-sampled for most groups but appear to be separated from each other.

  7. The French Tsunami warning center for the Mediterranean and North-East Atlantic: CENALT

    NASA Astrophysics Data System (ADS)

    Roudil, Pascal; Schindele, Francois; Duperray, Pierre; Gailler, Audrey; Hebert, Helene; Loevenbruck, Anne; Gutierrez, Emmanuel; Damicis, Adeline

    2013-04-01

    The CENALT (CENtre d'ALerte aux Tsunamis) is responsible for the French NTWC (National Tsunami Warning Centre). Its objective is to transmit a message in less than fifteen minutes for any earthquake that could trigger a tsunami in the Western Mediterranean Sea and the North-East Atlantic Ocean. The data collected from French installations and from institutions from five European countries are processed with software that permit to make an early location of the seismic events and to measure the expected sea level effect on the shore. The on-duty analysts interactively revise all the information produced and use references based on historical tsunami and earthquake databases as well as computed tsunami scenario to be able to send the more comprehensive message possible. Communication tests are performed monthly to test and validate the different transmission mode latencies (Global telecommunication system, email and fax). In November 2012, CENALT have participated to the international NEAMWave12 tsunami exercise organized by the Intergovernmental Oceanographic Commission (Unesco/IOC). A scenario of a magnitude 7.5 earthquake located on the north Algerian margin was modeled , and messages were disseminated to the tsunami warning focal points of the Member states of the Mediterranean region.

  8. Cenozoic uplift on the West Greenland margin: active sedimentary basins in quiet Archean terranes.

    NASA Astrophysics Data System (ADS)

    Jess, Scott; Stephenson, Randell; Brown, Roderick

    2016-04-01

    The North Atlantic is believed by some authors to have experienced tectonically induced uplift within the Cenozoic. Examination of evidence, onshore and offshore, has been interpreted to imply the presence of kilometre scale uplift across the margins of the Barents Sea, North Sea, Baffin Bay and Greenland Sea. Development of topography on the West Greenland margin (Baffin Bay), in particular, has been subject to much discussion and dispute. A series of low temperature thermochronological (AFT and AHe) studies onshore and interpretation of seismic architecture offshore have suggested uplift of the entire margin totalling ~3km. However, challenges to this work and recent analysis on the opposing margin (Baffin Island) have raised questions about the validity of this interpretation. The present work reviews and remodels the thermochronological data from onshore West Greenland with the aim of re-evaluating our understanding of the margin's history. New concepts within the discipline, such as effect of radiation damage on Helium diffusivity, contemporary modelling approaches and denudational mapping are all utilised to investigate alternative interpretations to this margins complex post rift evolution. In contrast to earlier studies our new approach indicates slow protracted cooling across much of the region; however, reworked sedimentary samples taken from the Cretaceous Nuussuaq Basin display periods of rapid reheating and cooling. These new models suggest the Nuussuaq Basin experienced a tectonically active Cenozoic, while the surrounding Archean basement remained quiet. Faults located within the basin appear to have been reactivated during the Palaeocene and Eocene, a period of well-documented inversion events throughout the North Atlantic, and may have resulted in subaerial kilometre scale uplift. This interpretation of the margin's evolution has wider implications for the treatment of low temperature thermochronological data and the geological history of the North

  9. The dynamics of continental extension and divergent margin formation

    SciTech Connect

    Sawyer, D.S. )

    1990-05-01

    Continental breakup is a highly variable process. Differences occur in the relative timing and extent of volcanism, uplift, and graben formation as well as in the mode and amount of continental extension before breakup. The authors propose a model that reconciles this variability with the previously recognized tendency for breakup to occur along preexisting weak trends. Continental lithosphere is viewed as a composite material composed of two strong layers, one in the upper mantle and one in the middle crust. Finite element simulation indicates that extensional failure at weaknesses in the mantle causes concentrated extension in the mantle and diffuse extension in the crust. This leads to early melt segregation and volcanism, margin uplift during the late stages of the extension process, and relatively narrow symmetrical extended margins. In contrast, failure at weaknesses in the crustal strong zone causes focused extension in the crust and diffuse extension in the mantle. This produces initial graben formation, cooling in the lower crust and upper mantle, and broad asymmetrical extended margins. Volcanism only occurs late in the process. Failure at laterally offset weaknesses within both strong layers, perhaps the most common case, leads to a deformation pattern dominated by simple shear. Thus, differences in the prerift configuration of the continental lithosphere can control the overall style of continental breakup. They find that certain features of the evolution of the US Atlantic margin, particularly the formation of the hinge zone and the distribution and timing of extension may be better explained using these models.

  10. North Atlantic, ITCZ, and Monsoonal Climate Links

    NASA Astrophysics Data System (ADS)

    Haug, G. H.; Deplazes, G.; Peterson, L. C.; Brauer, A.; Mingram, J.; Dulski, P.; Sigman, D. M.

    2008-12-01

    Major element chemistry and color data from sediment cores in the anoxic Cariaco Basin off Venezuela record with (sub)annual resolution large and abrupt shifts in the hydrologic cycle of the tropical Atlantic during the last 80 ka. These data suggest a direct connection between the position of the ITCZ over northern South America, the strength of trade winds, and the temperature gradient to the high northern latitudes, ENSO, and monsoonal climate in Asia. The mechanisms behind these decadal-scale ITCZ-monsoon swings can be further explored at major climate transitions such as the onset of Younger Dryas cooling at ~12.7 ka, one of the most abrupt climate changes observed in ice core, lake and marine records in the North Atlantic realm and much of the Northern Hemisphere. Annually laminated sediments from ideally record the dynamics of abrupt climate changes since seasonal deposition immediately responds to climate and varve counts accurately estimate the time of change. We compare sub-annual geochemical data from a lake in Western Germany, which provides one of the best-dated records currently available for this climate transition, with the new the Cariaco Basin record and a new and higher resolution record from Lake Huguang Maar in China, and the Greenland ice core record. The Lake Meerfelder Maar record indicates an abrupt increase in storminess, occurring from one year to the next at 12,678 ka BP, coincident with other observed climate changes in the region. We interpret this shift of the wintertime winds to signify an abrupt change in the North Atlantic westerlies to a stronger and more zonal jet. The observed wind shift provides the atmospheric mechanism for the strong temporal link between North Atlantic overturning and European climate during the last deglaciation, tightly coupled to ITCZ migrations observed in the Cariaco Basin sediments, and a stronger east Asian Monsoon winter monsoon as seen in lake Huguang Maar, when cave stalagmite oxygen isotope data

  11. Oceanic spawning migration of the European eel (Anguilla anguilla).

    PubMed

    Aarestrup, Kim; Okland, Finn; Hansen, Michael M; Righton, David; Gargan, Patrik; Castonguay, Martin; Bernatchez, Louis; Howey, Paul; Sparholt, Henrik; Pedersen, Michael I; McKinley, Robert S

    2009-09-25

    European eels (Anguilla anguilla) undertake a approximately 5000-kilometer (km) spawning migration from Europe to the Sargasso Sea. The larvae are transported back to European waters by the Gulf Stream and North Atlantic Drift. However, details of the spawning migration remain unknown because tracking eels in the Atlantic Ocean has, so far, eluded study. Recent advances in satellite tracking enable investigation of migratory behavior of large ocean-dwelling animals. However, sizes of available tags have precluded tracking smaller animals like European eels. Here, we present information about the swimming direction, depth, and migratory behavior of European eels during spawning migration, based on a miniaturized pop-up satellite archival transmitter. Although the tagging experiment fell short of revealing the full migration to the Sargasso Sea, the data covered the first 1300 km and provided unique insights. PMID:19779192

  12. Geochemical insights into the provenance of large scale North Atlantic turbidites

    NASA Astrophysics Data System (ADS)

    Watts, Millie; Hunt, James; Talling, Peter; Allin, Josh; Pope, Ed

    2015-04-01

    The North Atlantic margin has been subject to several very large (>100 km3) submarine landslides. Motion of some of these slides has been shown to generate damaging tsunamis, which travelled long distances across the ocean, such as that generated by the Storegga slide at 8.15 ka BP. If such a tsunami occurred again, it would pose a major hazard to northern European coastlines. Therefore identifying the source and age of past slide deposits is important to quantifying the risk to UK and the rest of coastal Europe. In this study we analyse the distal deposits of slides (turbidites) to assess their provenance. We present initial results from a new shallow piston core dataset from the Storegga slide, Trænadjupet slide, Lofoten Drift and basin, and the outer edge of the Voring plateau. Turbidite mudcaps were analysed using both the non-destructive, semi-quantitative Itrax micro-XRF core scanner at BOSCORF for major elements. In addition ICP-MS was used to determine the rare earth element (REE) abundances, allowing the relationship of distal turbidite deposits to be established. REEs are a good source discriminator due to the stability and immobility of lanthanide group elements, and the preservation of elemental ratios during transport. Due to hydraulic fractionation only the finest mud fraction was analysed to avoid the bias associated with heavy mineral concentrations . Clusters of distinct elemental ratios indicate different provenances for the distal turbidites, notably the Eu/Eu* anomaly and (Gd/Yb)N. The clusters demonstrate each deposit has a unique geochemical signature and provide insights into the history of past large-volume slides in the region and the influence of contour current-reworking of deep-water deposits. The Norwegian margin has a long record of large-scale landslides, which are commonly linked to glacial-interglacial transitions. This margin is also an important location of deep-water formation, with strong currents capable of transporting

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

    NASA Astrophysics Data System (ADS)

    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.

  14. Massive icebergs & freshening of the subtropical North Atlantic

    NASA Astrophysics Data System (ADS)

    Hill, J. C.; Condron, A.

    2013-12-01

    New evidence from high-resolution seafloor bathymetry and a state-of-the-art numerical ocean circulation model shows that a significant amount of iceberg-laden meltwater flowed south from northern hemisphere ice sheets in a narrow coastal boundary current along the U.S. Atlantic margin, to the southern tip of Florida, following the Last Glacial Maximum (LGM). It is commonly assumed that meltwater would freshen the subpolar North Atlantic (50° - 70°N), but have little or no penetration to subtropical latitudes, south of 40°N. Using a combination of high-resolution multibeam bathymetry data and a state-of-the-art, high-resolution numerical ocean model, we are able to trace the pathway of icebergs and meltwater released from the Laurentide Ice Sheet (LIS) along the southern U.S. Atlantic margin. The bathymetry data show numerous well-defined relict iceberg scours from Cape Hatteras to the southern tip of Florida (~24.5°N) in water depths of 170 - 380 m, and are traceable for more than 30 km along the margin, suggesting that icebergs up to 300m thick reached these subtropical locations. The scour marks are oriented SSW along regional bathymetric contours and decrease in size and abundance moving south along the margin, concordant with increased iceberg melt as the distance from the ice calving margin increased. Our numerical model simulations confirm that iceberg laden meltwater can penetrate into the subtropical North Atlantic by flowing south, inshore of the Gulf Stream, as a narrow coastal boundary current that can significantly freshen this region and reduce the northward heat transport of the Gulf Stream. This evidence suggests a stronger influence of cold meltwater in the southern latitudes than previously recognized and highlights a distinct shift in paleocirculation patterns, including major adjustments in the Gulf Stream, since the LGM. Our findings strongly indicate that the freshening of the subtropical North Atlantic by icebergs and meltwater played an

  15. Atlantic City memories.

    PubMed

    Epstein, Franklin H

    2008-04-01

    Fifty years ago, the Atlantic City meetings, held the first week in May of every year, were attended by all the elite of American academic medicine and all who wanted to join that group. Part of the magic of those meetings was that professors and neophytes took each other seriously and talked to each other. PMID:18382726

  16. Introgressive hybridization and latitudinal admixture clines in North Atlantic eels

    PubMed Central

    2014-01-01

    Background Hybridization, the interbreeding of diagnosably divergent species, is a major focus in evolutionary studies. Eels, both from North America and Europe migrate through the Atlantic to mate in a vast, overlapping area in the Sargasso Sea. Due to the lack of direct observation, it is unknown how these species remain reproductively isolated. The detection of inter-species hybrids in Iceland suggests on-going gene flow, but few studies to date have addressed the influence of introgression on genetic differentiation in North Atlantic eels. Results Here, we show that while mitochondrial lineages remain completely distinct on both sides of the Atlantic, limited hybridization is detectable with nuclear DNA markers. The nuclear hybridization signal peaks in the northern areas and decreases towards the southern range limits on both continents according to Bayesian assignment analyses. By simulating increasing proportions of both F1 hybrids and admixed individuals from the southern to the northern-most locations, we were able to generate highly significant isolation-by-distance patterns in both cases, reminiscent of previously published data for the European eel. Finally, fitting an isolation-with-migration model to our data supports the hypothesis of recent asymmetric introgression and refutes the alternative hypothesis of ancient polymorphism. Conclusions Fluctuating degrees of introgressive hybridization between Atlantic eel species are sufficient to explain temporally varying correlations of geographic and genetic distances reported for populations of the European eel. PMID:24674242

  17. Acidalia Planitia Channel Margin

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site]

    The THEMIS VIS camera is capable of capturing color images of the Martian surface using five different color filters. In this mode of operation, the spatial resolution and coverage of the image must be reduced to accommodate the additional data volume produced from using multiple filters. To make a color image, three of the five filter images (each in grayscale) are selected. Each is contrast enhanced and then converted to a red, green, or blue intensity image. These three images are then combined to produce a full color, single image. Because the THEMIS color filters don't span the full range of colors seen by the human eye, a color THEMIS image does not represent true color. Also, because each single-filter image is contrast enhanced before inclusion in the three-color image, the apparent color variation of the scene is exaggerated. Nevertheless, the color variation that does appear is representative of some change in color, however subtle, in the actual scene. Note that the long edges of THEMIS color images typically contain color artifacts that do not represent surface variation.

    This false color image shows craters and a channel margin, in the region of southern Acidalia Planitia where Tiu and Ares Valles empty into the planitia. This image was collected during the Northern Spring season.

    Image information: VIS instrument. Latitude 23.8, Longitude 327.5 East (32.5 West). 37 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion

  18. Atlantic tropical cyclones revisited

    NASA Astrophysics Data System (ADS)

    Mann, Michael E.; Emanuel, Kerry A.; Holland, Greg J.; Webster, Peter J.

    Vigorous discussions have taken place recently in Eos [e.g., Mann and Emanuel, 2006; Landsea, 2007] and elsewhere [Emanuel, 2005; Webster et al., 2005; Hoyos et al., 2006; Trenberth and Shea, 2006; Kossin et al., 2007] regarding trends in North Atlantic tropical cyclone (TC) activity and their potential connection with anthropogenic climate change. In one study, for example [Landsea, 2007], it is argued that a substantial underestimate of Atlantic tropical cyclone counts in earlier decades arising from insufficient observing systems invalidates the conclusion that trends in TC behavior may be connected to climate change. Here we argue that such connections are in fact robust with respect to uncertainties in earlier observations.Several recent studies have investigated trends in various measures of TC activity. Emanuel [2005] showed that a measure of total power dissipation by TCs (the power dissipation index, or PDI) is highly correlated with August-October sea surface temperatures (SST) over the main development region (MDR) for Atlantic TCs over at least the past half century. Some support for this conclusion was provided by Sriver and Ruber [2006]. Webster et al. [2005] demonstrated a statistically significant increase in recent decades in both the total number of the strongest category cyclones (categories 4 and 5) and the proportion of storms reaching hurricane intensity. Hoyos et al. [2006] showed that these increases were closely tied to warming trends in tropical Atlantic SST, while, for example, the modest decrease in vertical wind shear played a more secondary role. Kossin et al. [2007] called into question some trends in other basins, based on a reanalysis of past TC data, but they found the North Atlantic trends to be robust.

  19. Stratigraphic signature of lithospheric deformation style in post-rift passive margin basins

    NASA Astrophysics Data System (ADS)

    Rouby, Delphine; Huismans, Ritske; Robin, Cecile; Braun, Jean; Granjeon, Didier

    2016-04-01

    We revise commonly accepted models explaining long-term stratigraphic trends along Atlantic-type passive margins by including the impact of complex lithosphere deformation at depth and it's coupling with surface processes. To achieve this, we simulated the evolution of a passive margin basin using a cascade of three modeling tools: a thermo-mechanical model of the syn-rift stretching of the lithosphere, a flexural and thermal model of the post-rift stage that includes coupling with surface processes and, finally, a stratigraphic model of the associated sedimentary basin architecture. We compare two necking styles that lead to different margin geometries: wide and narrow margins that form by heterogeneous stretching. Wide margins, forming thinner and wider sedimentary wedges, show significantly larger aggradation component and longer preservation duration, in more continental/proximal depositional facies. Narrow margins are characterized by enhanced erosion and by-pass during transgression. Through a parametric analysis we constrain the relative contribution of lithosphere deformation and surface processes on the stratigraphic trends and show that both may contribute equally to the stratigraphic architecture. For example, enhanced erosion in narrow margins impacts the volume of sediments delivered to the basin, which, in turn, significantly increases the subsidence. Our simulations also underline the importance of the assumed sediment transport length, which controls whether the main depocentres remain in the necking zone or reach the more distal parts of the margin.

  20. The role of the Gulf Stream in European climate.

    PubMed

    Palter, Jaime B

    2015-01-01

    The Gulf Stream carries the warm, poleward return flow of the wind-driven North Atlantic subtropical gyre and the Atlantic Meridional Overturning Circulation. This northward flow drives a significant meridional heat transport. Various lines of evidence suggest that Gulf Stream heat transport profoundly influences the climate of the entire Northern Hemisphere and, thus, Europe's climate on timescales of decades and longer. The Gulf Stream's influence is mediated through feedback processes between the ocean, atmosphere, and cryosphere. This review synthesizes paleoclimate archives, model simulations, and the instrumental record, which collectively suggest that decadal and longer-scale variability of the Gulf Stream's heat transport manifests in changes in European temperature, precipitation, and storminess. Given that anthropogenic climate change is projected to weaken the Atlantic Meridional Overturning Circulation, associated changes in European climate are expected. However, large uncertainty in the magnitude of the anticipated weakening undermines the predictability of the future climate in Europe. PMID:25560606

  1. Colorado Basin Structure and Rifting, Argentine passive margin

    NASA Astrophysics Data System (ADS)

    Autin, Julia; Scheck-Wenderoth, Magdalena; Loegering, Markus; Anka, Zahie; Vallejo, Eduardo; Rodriguez, Jorge; Marchal, Denis; Reichert, Christian; di Primio, Rolando

    2010-05-01

    partly supports this hypothesis and shows two main directions of faulting: margin-parallel faults (~N30°) and rift-parallel faults (~N125°). A specific distribution of the two fault sets is observed: margin-parallel faults are restrained to the most distal part of the margin. Starting with a 3D structural model of the basin fill based on seismic and well data the deeper structure of the crust beneath the Colorado Basin can be evaluate using isostatic and thermal modelling. Franke, D., et al. (2002), Deep Crustal Structure Of The Argentine Continental Margin From Seismic Wide-Angle And Multichannel Reflection Seismic Data, paper presented at AAPG Hedberg Conference "Hydrocarbon Habitat of Volcanic Rifted Passive Margins", Stavanger, Norway Franke, D., et al. (2006), Crustal structure across the Colorado Basin, offshore Argentina Geophysical Journal International 165, 850-864. Gladczenko, T. P., et al. (1997), South Atlantic volcanic margins Journal of the Geological Society, London 154, 465-470. Hinz, K., et al. (1999), The Argentine continental margin north of 48°S: sedimentary successions, volcanic activity during breakup Marine and Petroleum Geology 16(1-25). Hirsch, K. K., et al. (2009), Tectonic subsidence history and thermal evolution of the Orange Basin, Marine and Petroleum Geology, in press, doi:10.1016/j.marpetgeo.2009.1006.1009

  2. Susceptibility of pear to European pear sawfly fruit infestation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The European pear sawfly, Hoplocampa brevis (Klug), is a relatively new pest in the Mid-Atlantic fruit production region. A plot containing twelve Pyrus communis pear cultivars and one breeder’s selection in a randomized block design was surveyed for fruit damage. Infestation frequency ranged from...

  3. Divergent/passive margin basins

    SciTech Connect

    Edwards, J.D. ); Santogrossi, P.A. )

    1989-01-01

    This book discusses the detailed geology of the four divergent margin basins and establishes a set of analog scenarios which can be used for future petroleum exploration. The divergent margin basins are the Campos basin of Brazil, the Gabon basin, the Niger delta, and the basins of the northwest shelf of Australia. These four petroleum basins present a wide range of stratigraphic sequences and structural styles that represent the diverse evolution of this large and important class of world petroleum basins.

  4. Steel Industry Marginal Opportunity Analysis

    SciTech Connect

    none,

    2005-09-01

    The Steel Industry Marginal Opportunity Analysis (PDF 347 KB) identifies opportunities for developing advanced technologies and estimates both the necessary funding and the potential payoff. This analysis determines what portion of the energy bandwidth can be captured through the adoption of state-of-the-art technology and practices. R&D opportunities for addressing the remainder of the bandwidth are characterized and plotted on a marginal opportunity curve.

  5. Lithosphere extension and magmatism at volcanic passive margins

    NASA Astrophysics Data System (ADS)

    Geoffroy, Laurent; Gernigon, Laurent; Werner, Philippe

    2014-05-01

    We present onshore and offshore evidences suggesting that volcanic passive margins are distinct in origin and evolution from non-volcanic hyper-extended margins. Consecutively, they should not be integrated in a single evolutionary process and do not necessarily represent the ultimate stage of an hyper-extension with or without mantle exhumation. Volcanic passive margins usually form in mobile areas between cratonic areas which may have been submitted to long-term periods of divergence and convergence or strike-slip tectonics. In the NE-Atlantic, for example, a complete illustration of a Wilson cycle is illustrated between Greenland and Baltica cratonic areas. From the Devonian to the end of the Jurassic, the Caledonian orogenic crust has suffered from a number of wrench and extensional tectonic stretching episodes. The late-Jurassic/Early Cretaceous extension was severe, leading to extreme crustal thinning (e.g. Rockall Through, Vøring Basin, Lofoten Basin) and was followed by a long-term regional thermal subsidence of the NE-Atlantic lithosphere. Meanwhile, pre-thinning lithospheric thickness was restored progressively during ~80 Myr, in spite of some tectonic reactivation occurring in Late Cretaceous (e.g. Outer Vøring Basin) resulting in little coeval stretching and thinning. During the Paleocene (or even earlier, especially in the Rockall area) a regional mantle melting event occurred. The mantle melted in specific locations but led ultimately to a large igneous province formation during the onset of breakup. The NE-Atlantic continental crust was at this time extremely heterogeneous due to its tectonic inheritance but we think that generally the lithosphere was much thicker than during the Jurassic-Cretaceous event, and thus much stronger. Although we must consider the existence of some extension during the latest Cretaceous and Paleocene, the main stretching and thinning event leading to volcanic passive margins formations and successful break-up occurred

  6. Millennial-scale fluctuations of the European Ice Sheet at the end of the last glacial, and their potential impact on global climate

    NASA Astrophysics Data System (ADS)

    Toucanne, Samuel; Soulet, Guillaume; Freslon, Nicolas; Silva Jacinto, Ricardo; Dennielou, Bernard; Zaragosi, Sébastien; Eynaud, Frédérique; Bourillet, Jean-François; Bayon, Germain

    2015-09-01

    Reconstructing Northern Hemisphere ice-sheet oscillations and meltwater routing to the ocean is important to better understand the mechanisms behind abrupt climate changes. To date, research efforts have mainly focused on the North American (Laurentide) ice-sheets (LIS), leaving the potential role of the European Ice Sheet (EIS), and of the Scandinavian ice-sheet (SIS) in particular, largely unexplored. Using neodymium isotopes in detrital sediments deposited off the Channel River, we provide a continuous and well-dated record for the evolution of the EIS southern margin through the end of the last glacial period and during the deglaciation. Our results reveal that the evolution of EIS margins was accompanied with substantial ice recession (especially of the SIS) and simultaneous release of meltwater to the North Atlantic. These events occurred both in the course of the EIS to its LGM position (i.e., during Heinrich Stadial -HS- 3 and HS2; ˜31-29 ka and ˜26-23 ka, respectively) and during the deglaciation (i.e., at ˜22 ka, ˜20-19 ka and from 18.2 ± 0.2 to 16.7 ± 0.2 ka that corresponds to the first part of HS1). The deglaciation was discontinuous in character, and similar in timing to that of the southern LIS margin, with moderate ice-sheet retreat (from 22.5 ± 0.2 ka in the Baltic lowlands) as soon as the northern summer insolation increase (from ˜23 ka) and an acceleration of the margin retreat thereafter (from ˜20 ka). Importantly, our results show that EIS retreat events and release of meltwater to the North Atlantic during the deglaciation coincide with AMOC destabilisation and interhemispheric climate changes. They thus suggest that the EIS, together with the LIS, could have played a critical role in the climatic reorganization that accompanied the last deglaciation. Finally, our data suggest that meltwater discharges to the North Atlantic produced by large-scale recession of continental parts of Northern Hemisphere ice sheets during HS, could have

  7. A new species of Bathynomus Milne Edwards, 1879 (Isopoda: Cirolanidae) from The Bahamas, Western Atlantic.

    PubMed

    Shipley, Oliver N; Bruce, Niel L; Violich, Mackellar; Baco, Amy; Morgan, Nicole; Rawlins, Scott; Brooks, Edward J

    2016-01-01

    A new species of cirolanid isopod, Bathynomus maxeyorum sp. nov., from The Bahamas, Western Atlantic, is described. This species represents the fourth species of Bathynomus to be described from the tropical and sub-tropical Western Atlantic. Bathynomus maxeyorum sp. nov. is characterized by 7 broad short pleotelsonic spines, with setation running along ~80% of the posterior margin of the pleotelson. Genetic analysis indicates a ~14% sequence divergence from the sympatric species Bathynomus giganteus. PMID:27515606

  8. New Insights into SouthWest Africa Margin Evolution; Integrating Reconstructions and Restorations

    NASA Astrophysics Data System (ADS)

    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.

  9. Rifted Continental Margins: The Case for Depth-Dependent Extension

    NASA