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  • 1
    Publication Date: 2001-01-01
    Description: The Mesozoic and Cenozoic history of the Porcupine Basin may be broadly summarized as a Jurassic synrift phase, followed by Cretaceous and Cenozoic post-rift subsidence. Two periods, Early Cretaceous and Early Eocene times, do not fit the simple pattern of post-rift subsidence and are characterized by increased sedimentation. We recognize distinctive sedimentological responses to the basin flanks being either exposed or submerged, and infer that transient regional uplift caused the Early Eocene event. Modelling subsidence histories of wells and of the Porcupine Bank allows quantification of the magnitude and timing of anomalous uplift and subsidence. Transient uplift of 300-600 m occurred at the Paleocene-Eocene boundary, followed by subsidence of 500-800 m after Early Eocene time, over a period with a minimum length of 25 Ma and a maximum of 55 Ma. Renewed rifting is unlikely to be responsible for the Paleogene subsidence because it cannot account for the preceding uplift, and significant normal faults of Paleogene age are absent. A Paleogene uplift-subsidence cycle has also been noted in the basins surrounding Scotland and along Hatton continental margin. One way to explain regional subsidence between Eocene time and the present is that the European plate moved off the topographic swell above the Iceland plume following continental separation between Greenland and Europe in Early Eocene time. Another possibility is that an anomalously hot layer c. 50 km thick was emplaced beneath the entire region just before the onset of sea-floor spreading in Early Eocene time and was then dissipated by convection following continental separation. A Cretaceous transient uplift-subsidence cycle that shares many similarities with the Paleogene cycle is also recognized. Immediately following Late Jurassic rifting, 200-700 m transient uplift occurred in Early Cretaceous time, followed by 0-500 m subsidence coeval with the onset of sea-floor spreading at the Goban Spur margin. The Cretaceous uplift-subsidence cycle might also be caused by anomalously hot mantle.
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  • 2
    Publication Date: 2002-01-01
    Description: The Cenozoic development of the North Atlantic province has been dramatically influenced by the behaviour of the Iceland Plume, whose striking dominance is manifest by long-wavelength free-air gravity anomalies and by oceanic bathymetric anomalies. Here, we use these anomalies to estimate the amplitude and wavelength of present-day dynamic uplift associated with this plume. Maximum dynamic support in the North Atlantic is 1.5-2 km at Iceland itself. Most of Greenland is currently experiencing dynamic support of 0.5-1 km, whereas the NW European shelf is generally supported by 〈0.5 km. The proto-Iceland Plume had an equally dramatic effect on the Early Cenozoic palaeogeography of the North Atlantic margins, as we illustrate with a study of plume-related uplift, denudation and sedimentation on the continental shelf encompassing Britain and Ireland. We infer that during Paleocene time a hot subvertical sheet of asthenosphere welled up beneath an axis running from the Faroes through the Irish Sea towards Lundy, generating a welt of magmatic underplating of the crust which is known to exist beneath this axis. Transient and permanent uplift associated with this magmatic injection caused regional denudation, and consequently large amounts of clastic sediment have been shed into surrounding basins during Cenozoic time. Mass balance calculations indicate agreement between the volume of denuded material and the volume of Cenozoic sediments deposited offshore in the northern North Sea Basin and the Rockall Trough. The volume of material denuded from Britain and Ireland is probably insufficient to account for the sediment in the Faroe-Shetland Basin and an excess of sediment has been supplied to the Porcupine Basin. We emphasize the value of combining observations from both oceanic and continental realms to elucidate the evolution of the Iceland Plume through space and time.
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  • 3
    Publication Date: 2019-02-01
    Description: Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( 〉  800 ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼  50  Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 ×  CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
    Type: Article , PeerReviewed
    Format: text
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  • 4
    Publication Date: 2017-01-04
    Description: Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 16 (2015): 3414–3435, doi:10.1002/2015GC005947.
    Description: Overflow of Northern Component Water, the precursor of North Atlantic Deep Water, appears to have varied during Neogene times. It has been suggested that this variation is moderated by transient behavior of the Icelandic mantle plume, which has influenced North Atlantic bathymetry through time. Thus pathways and intensities of bottom currents that control deposition of contourite drifts could be affected by mantle processes. Here, we present regional seismic reflection profiles that cross sedimentary accumulations (Björn, Gardar, Eirik, and Hatton Drifts). Prominent reflections were mapped and calibrated using a combination of boreholes and legacy seismic profiles. Interpreted seismic profiles were used to reconstruct solid sedimentation rates. Björn Drift began to accumulate in late Miocene times. Its average sedimentation rate decreased at ∼2.5 Ma and increased again at ∼0.75 Ma. In contrast, Eirik Drift started to accumulate in early Miocene times. Its average sedimentation rate increased at ∼5.5 Ma and decreased at ∼2.2 Ma. In both cases, there is a good correlation between sedimentation rates, inferred Northern Component Water overflow, and the variation of Icelandic plume temperature independently obtained from the geometry of diachronous V-shaped ridges. Between 5.5 and 2.5 Ma, the plume cooled, which probably caused subsidence of the Greenland-Iceland-Scotland Ridge, allowing drift accumulation to increase. When the plume became hotter at 2.5 Ma, drift accumulation rate fell. We infer that deep-water current strength is modulated by fluctuating dynamic support of the Greenland-Scotland Ridge. Our results highlight the potential link between mantle convective processes and ocean circulation.
    Description: Natural Environment Research Council Grant Number: NE/G007632/1; The University of Cambridge Girdler Fund; BP Exploration
    Description: 2016-04-15
    Keywords: Contourite ; Drift ; Iceland ; Plume
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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  • 5
    Publication Date: 2018-05-14
    Description: Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of [publisher] for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 122 (2017): 8675–8708, doi:10.1002/2017JB014225.
    Description: In the North Atlantic Ocean, the geometry of diachronous V-shaped features that straddle the Reykjanes Ridge is often attributed to thermal pulses which advect away from the center of the Iceland plume. Recently, two alternative hypotheses have been proposed: rift propagation and buoyant mantle upwelling. Here we evaluate these different proposals using basin-wide geophysical and geochemical observations. The centerpiece of our analysis is a pair of seismic reflection profiles oriented parallel to flow lines that span the North Atlantic Ocean. V-shaped ridges and troughs are mapped on both Neogene and Paleogene oceanic crust, enabling a detailed chronology of activity to be established for the last 50 million years. Estimates of the cumulative horizontal displacement across normal faults help to discriminate between brittle and magmatic modes of plate separation, suggesting that crustal architecture is sensitive to the changing planform of the plume. Water-loaded residual depth measurements are used to estimate crustal thickness and to infer mantle potential temperature which varies by ±25°C on timescales of 3–8 Ma. This variation is consistent with the range of temperatures inferred from geochemical modeling of dredged basaltic rocks along the ridge axis itself, from changes in Neogene deep-water circulation, and from the regional record of episodic Cenozoic magmatism. We conclude that radial propagation of transient thermal anomalies within an asthenospheric channel that is 150 ± 50 km thick best accounts for the available geophysical and geochemical observations.
    Description: NERC Grant Number: NE/G007632/1; Girdler Fund, University of Cambridge; BP Exploration
    Description: 2018-05-14
    Keywords: Iceland plume ; V-shaped ridges ; Mantle convection ; Oceanic crust
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 6
    Publication Date: 2017-03-14
    Description: Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC〈sub〉71〈/sub〉BM devices Scientific Reports, Published online: 13 March 2017; doi:10.1038/srep44269
    Electronic ISSN: 2045-2322
    Topics: Natural Sciences in General
    Published by Springer Nature
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  • 7
    Publication Date: 2012-11-01
    Description: The topographies of Africa and Antarctica form patterns of interlocking swells. The relationship between topography and gravity indicates that these swells are dynamically supported by mantle convection, with swell diameters of 1850 ± 450 km and full heights between 800 and 1800 m. The implication is that mantle convection not only supports swells surrounding hotspots but also influences topography across the entire surface areas of Africa and Antarctica. We investigate whether dynamically supported swells are also observed throughout the geological record, focusing on intensively studied Mesozoic–Cenozoic sedimentary rocks around Britain and Ireland. Vertical motions of Britain and Ireland, a typical piece of continental lithosphere far from a destructive plate boundary, have been demonstrably affected by dynamic support for over half of the past 200 Ma period. The diameters and maximum heights of the Mesozoic British swells and the modern African and Antarctic swells are similar. The ancient British swells grew in 5–10 Ma and decayed over 20–30 Ma, suggesting vertical motion rates comparable with those estimated from geomorphological studies of Africa. Igneous production rate and swell height are not correlated in the modern and the geological records. Mantle convection should be considered as a common control on regional sea level.
    Print ISSN: 0016-7649
    Topics: Geosciences
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  • 8
    Publication Date: 2017-02-23
    Description: Past warm periods provide an opportunity to evaluate climate models under extreme forcing scenarios, in particular high ( 〉 800ppmv) atmospheric CO2 concentrations. Although a post hoc intercomparison of Eocene ( ∼ 50 Ma) climate model simulations and geological data has been carried out previously, models of past high-CO2 periods have never been evaluated in a consistent framework. Here, we present an experimental design for climate model simulations of three warm periods within the early Eocene and the latest Paleocene (the EECO, PETM, and pre-PETM). Together with the CMIP6 pre-industrial control and abrupt 4 × CO2 simulations, and additional sensitivity studies, these form the first phase of DeepMIP – the Deep-time Model Intercomparison Project, itself a group within the wider Paleoclimate Modelling Intercomparison Project (PMIP). The experimental design specifies and provides guidance on boundary conditions associated with palaeogeography, greenhouse gases, astronomical configuration, solar constant, land surface processes, and aerosols. Initial conditions, simulation length, and output variables are also specified. Finally, we explain how the geological data sets, which will be used to evaluate the simulations, will be developed.
    Print ISSN: 1991-959X
    Electronic ISSN: 1991-9603
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 9
  • 10
    Publication Date: 2017-11-01
    Print ISSN: 2169-9313
    Electronic ISSN: 2169-9356
    Topics: Geosciences , Physics
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