1,721,185 research outputs found
Windermere Multibeam Bathymetry Data
No full textMultibeam Bathymetry Data was collected by the British Geological Survey in September 2010 in association with the University of Southampton in both the north and south basins of Windermere in the English Lake District. Data was analysed by Helen Miller and Jonathan Bull from the University of Southampton as well as Carol Cotterill from the British Geological Survey. The data is freely available for download and it would be appropriate to cite the following reference when using the data:
Miller, Helen, Bull, Jonathan M., Cotterill, Carol J., Dix, Justin K., Winfield, Ian J., Kemp, Alan E.S. and Pearce, Richard B. (2013) Lake bed geomorphology and sedimentary processes in glacial lake Windermere, UK. Journal of Maps, 9, (2), 299-312. (doi:10.1080/17445647.2013.780986).
The data is not appropriate for navigational use.
Further information on the survey is available at:
http://www.bgs.ac.uk/research/highlights/2013/lakeWindermere.html
A pdf map of the multibeam data is available for download, and the data can be downloaded here at 1 m and 5 m resolutions from the north and south basins of Windermere.</span
Cruise Report RRS James Cook 152 - JC152: CHIMNEY – Characterisation of major overburden pathways above sub-seafloor CO2 storage reservoirs in the North Sea. Scanner and Challenger Pockmark Complexes
No full textCruise JC152 collected the major data sets for the CHIMNEY (Characterisation of major overburden leakage pathways above sub-seafloor CO2 storage reservoirs in the North Sea) NERC highlight topics research programme. The cruise investigated the Scanner and Challenger pock marks in the northern North Sea, which were previously known to be the locations of vigorous Methane venting. The cruise objectives were to collect data that could be used to constrain the geometry and internal structures of fluid flow, “Chimney” structures, with the eventual aim of determining the current permeability of the sub-surface. The cruise successfully completed two anisotropy experiments over the Scanner and Challenger pock marks by shooting various seismic sources into a grid of 25 and 7 ocean bottom seismometers respectively. Five different seismic sources (Bolt airguns, GI guns, Squid surface sparker, Duraspark surface sparker, and Deep Tow Sparker) were recorded by the ocean bottom seismometers, and an acoustic recorder deployed c. 25 m above the seabed. Multichannel seismic reflection profiles were collected with GI guns and both surface sparker sources, and single channel seismic reflection profiles were collected with the Deep Tow Sparker source. Single and multibeam echo sounder data were collected along all seismic profiles
Buckling of the oceanic lithosphere from geophysical data and experiments
No full textTwo major hypothesis have been advanced for the formation of the long wavelength (100-300) km undulations of oceanic basement and overlying sediments developed in the central Indian Ocean: whole layer folding (buckling) and local thickening (inverse boudinage). Using appropriately scaled two layer models of the oceanic lithosphere comprising a brittle layer overlying a ductile lower layer, we show that buckling of the entire brittle layer is likely to be the mode of deformation. However the lithosphere-asthenosphere boundary remains undisturbed. We find a relationship between the thickness of the brittle layer and the wavelength of folding such that the wavelength is 7 times the brittle layer thickness
Modelling rough interfaces on seismic reflection profiles - the application of fractal concepts
No full textThe distortion of reflection continuity and amplitude by overburden structure in seismic reflection images of the sub- surface is easily recognised and modelled when the wavelength of the shallower structure is relatively large. The effects of shorter wavelength structure although giving rise to little reflective response itself, cause significant distortion of the propagating wavefield, particularly when a moderate or strong acoustic impedance contrast is present in the shallow sub-surface. Here we show how short as well as long spatial wavelengths of horizon roughness affect deeper reflection continuity, and develop a new method using fractal interpolation techniques to predict the total roughness of sub-surface horizons from information contained in seismic reflection sections. Fractally complete depth-velocity models are used in forward models, using the finite difference technique, to produce synthetic seismic profiles. The technique is illustrated with data from the Edoras Bank area of the Rockall Plateau, NE Atlantic, where apparently discontinuous reflectors underlying basalt flows are shown to be from continuous sedimentary horizons distorted by overlying rough horizons
The southern margin of the Rockall Plateau: stratigraphy, Tertiary volcanism and plate tectonic evolution
No full textThe geological evolution of the southwest Rockall Plateau in the area of Edoras Bank has been clarified using seismic reflection, gravity and magnetic data. Four principal reflectors are observed within the Tertiary sedimentary sequence: I, Late Miocene; II, latest Early Miocene; III, Late Eocene; IV, earliest Eocene. A period of pronounced sediment drift accumulation marks the interval I–II. Reflector III, the top of a sediment wedge prograding southward from Edoras Bank, marks a change from terrigenous to pelagic sedimentation that is probably related to subsidence of the Rockall Plateau following the separation of Greenland from Eurasia in the earliest Eocene. Reflector IV marks the top of a wedge-shaped seismically transparent layer that also thins southward away from Edoras Bank. On the basis of its seismic attributes and magnetic signature, this layer is interpreted as a volcanic sheet, formed as part of the North Atlantic Tertiary Volcanic Province during rifting of Greenland from Eurasia. The recognition of voluminous volcanic rocks south of Edoras Bank extends the known area of the Tertiary volcanic province several hundred kilometres to the south. Gravity anomaly modelling and continental reconstructions suggest that the region south of Edoras Bank is underlain by thinned continental crust. A four stage geological evolution for this region is indicated, (i) Initial rifting associated with the separation of Labrador from Greenland in the late Cretaceous is characterized by enhanced crustal thinning and subsidence in the region of a rift triple junction. (ii) Passive subsidence and accumulation of late Cretaceous and earliest Tertiary sediments followed the initiation of seafloor spreading in the Labrador Sea. (iii) Blanketing of the area by Palaeocene volcanic rocks masked pre-existing magnetic lineations, providing an explanation for some of the problems in earlier interpretations based mainly on magnetic data. (iv) Post-volcanic sedimentation, continuing to the present day
CHIMNEY (James Cook 152) multibeam bathymetry (MB710) data from Scanner Pockmark, North Sea
No full textMultibeam bathymetry data were collected around the Scanner Pockmark in the northern North Sea, by RRS James Cook (JC152) in August-September 2017 during the CHIMNEY survey (NERC grant NE/N016130/1). The multibeam data were acquired using MB710 along the seismic profiles and processed by the JC152 Science Party. Two grids are available, a larger area (10 m grid interval), and a dense (2.5 m interval) grid provides the micro bathymetry around the Scanner and Scotia pockmarks. Two jpeg images are available to see the lateral extent of the data. Please refer to CHIMNEY NERC grant reference NE/N016130/1 and this DOI when using this data.</span
Structural style of intra-plate deformation, Central Indian Ocean Basin: evidence for the role of fracture zones
No full textThe structural style of the intraplate deformation developed in the Central Indian Ocean Basin was investigated in an area (7S°E - 82°E, 0°S - 6°S) to the west of the Afanasy Nikitin seamount using an integrated data set of seismic reflection profiles from Edinburgh University and Lamont-Doherty Geological Observatory. The study area contains two fracture zones, which strike ~ 005°E to 010°E, with oceanic lithosphere (age range ~ 65-78 Ma B.P.) younging westwards across them. No evidence for recent fault activity in the oceanic basement along the fracture zones could be detected in this area, although the close association between intraplate earthquakes and fracture zones elsewhere suggests reactivation of the fracture zones at upper mantle depths in a left lateral strike-slip sense. A statistical study was carried out into the first and second orders of deformation, long wavelength basement undulations and high-angle reverse faults respectively, and the relationships between them. The orientations of the axes of the undulations vary from 065°E to 085°E while the high-angle faults strike consistently at 090°E to 100°E. The results of this analysis suggest that the high-angle faults are the result of the reactivation of two sets of pre-existing spreading-centre normal faults, one set originally facing towards the spreading centre and the other facing away. Furthermore, although the long wavelength undulations are not fault generated, the high-angIe faults have modified the basement topography causing the accentuation of some of the basement highs. The observation that the undulations are not fault-generated is consistent with them being of flexural origin (including buckling of the crust and/or lithosphere). Basement undulations are clearly discontinuous across fracture zones and the facing direction of faulting is also offset. This discontinuity, the orientation of the axes of the undulations, the presence of other strong oblique basement trends, and information from regional earthquake studies suggest that the deformation resulted from not only ~ N-S compression as a result of the continental collision between India and Asia, but also left lateral strike-slip along fracture zones caused by the difference in resistance to plate motion between the continental collision to the north and subduction at the Sunda Arc to the northeast
Sediment velocities and deep structure from wide-angle reflection data around Leg 116 sites
No full textThe reduction of six wide-angle reflection profiles shot within the two fault blocks visited by Ocean Drilling Program (ODP) Leg 116 in combination with the ODP sonic logs has produced a velocity-depth structure for this area. The sediment velocity increases from 1.6-1.7 km/s in the near surface to 3.4-3.5 km/s immediately above basement with a velocity gradient of 0.75/s. A depth converted seismic reflection profile suggests that the pre-deformational basement surface was similar to the abyssal hill topography developed in the Pacific Ocean. A velocity for the top of oceanic layer 2 of 4.1 km/s was identified as layer 2A. Assuming a velocity gradient of 0.7/s, an estimate of layer 2 thickness was obtained of 1.5 km. It is possible to interpret residual depth anomalies in terms of a layer 3 that may be thinner than for normal oceanic crust
Channels, echo character mapping and tectonics from 3.5kHz profiles, distal Bengal Fan
No full textThe distal parts of the Bengal Fan are spectacularly affected by tectonic deformation related to the diffuse plate boundary between the Indian and Australian plates. Here we use 3.5kHz and 12kHz echosounder profiles, seismic reflection profiles and piston core results to examine sedimentary processes and their relationships to tectonism within an area (78º-82ºE, 0º-6ºS) just to the south of Ocean Drilling Program Leg 116 sites.Echo character mapping was completed using echosounder data in conjunction with results from piston coring, and a total of five different echo types have been recognised. Four of these fall into the echo character classification scheme developed by Damuth (1980a), whilst the fifth is believed to represent hemiturbidite deposits. Several types of submarine channel were also identified from echosounder data and a correlation between echo type and channel location can be seen. Their abundance, erosional and/or depositional nature together with a complex meandering and bifurcation pattern across a wide region of average gradient around 1/km, are all features characteristic of a broad channel termination zone on a large elongate fan. It is clear, therefore that the Bengal Fan extends beyond 6ºS.Active faulting in the area has led to the development of an irregular topography of low rounded hillocks that interfere with incoming turbidity currents. This has resulted in ponding between highs rather than lobe construction, thinning and pinching out of turbidites against the flanks of local relief, flow lofting and hemiturbidite drape, and common small-scale slumping. In some cases uplifted channel segments can be seen abandoned and partially filled. <br/
Analysis of a strike-slip fault network using high resolution multibeam bathymetry, offshore NW Devon U.K.
No full textImaging of the sea floor offshore from Hartland Point (north Devon, U.K.), using high resolution multibeam bathymetry, reveals a strike-slip fault network. This consists of NE-trending left-lateral faults and NW-trending right-lateral faults that cut folded and steeply dipping strata (~ 60°). Faults were accurately mapped using the multibeam imagery, and lateral separations of marker beds measured along fault traces. These data are used to examine the spatial arrangement, fault displacement, and strain distribution within the network at different displacement cut-offs.At high displacement cut-offs, the fault network is dominated by a few long isolated right-lateral fault segments that bound fault blocks, but at lower displacement cut-offs shorter left-lateral and right-lateral fault segments make up fault tips and infill fault blocks. The majority (70%) of fault trace-length is taken up by small fault segments that have < 10 m displacement whereas 84% of strain is localized onto large fault segments with > 10 m displacement. The topology and relative connectivity of the network is analysed in terms of a system of fault branches between tips (I-nodes) or intersections (X or Y-nodes), the relative proportions of which reflect the connectivity of the network. Although the kinematic behaviour of the fault network is controlled by large fault segments, connectivity is very dependent on the small fault segments.A comparison with a similar, nearby, strike-slip fault network at Westward Ho! (north Devon) shows many similarities and indicates that fault networks are better connected with increasing strain and that the network becomes better connected when strain is localized within damage zones rather than on individual faults
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