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  • Journal article
    Winsor K, Carlson AE, Caffee MW, Rood DHet al., 2015,

    Rapid last-deglacial thinning and retreat of the marine-terminating southwestern Greenland ice sheet

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 426, Pages: 1-12, ISSN: 0012-821X

    Marine-terminating outlet glaciers are a major source of modern ice loss from the Greenland Ice Sheet (GrIS), but their role in GrIS retreat during the last deglaciation is not well constrained. Here, we develop deglacial outlet glacier retreat chronologies for four regions in southwest and south Greenland to improve understanding of spatial variations in centennial- to millennial-scale ice loss under a warming climate. We calculate 10Be surface exposure ages of boulders located in fjords near the towns of Qaqortoq, Paamiut, Nuuk, and Sisimiut. Our northernmost study site, Sisimiut, deglaciated earliest at ∼18 ka to ∼15 ka with an average thinning rate of 0.1–0.3 m yr−1. Inland retreat from Sisimiut to the modern ice margin took ∼7 ka at an average retreat rate of 15–20 m yr−1. A 10Be-dated moraine ∼25 km from the modern GrIS margin deposited at ∼8 ka suggests a possible ice-margin still-stand, but this does not change overall retreat rates. After retreat from the small coastal Sisimiut fjords, the GrIS margin was mainly land-terminating in this region. In contrast, earliest exposure occurred at ∼12 ka near Qaqortoq, and 11–10 ka near Nuuk and Paamiut, with ice thinning at rates of 0.2–0.3 m yr−1 to instantaneous within measurement uncertainty. Ice retreat inland through the extensive Nuuk, Paamiut, and Qaqortoq fjord systems to near modern ice margins occurred in <1 ka, resulting in minimum retreat rates of 25–65 m yr−1 and maximum retreat rates of ∼95 m yr−1 to instantaneous within the uncertainty of our measurements. This rapid thinning and retreat of marine-terminating southwest GrIS margins is contemporaneous with an incursion of relatively warm ocean waters into the Labrador Sea and toward the southwest Greenland coast, suggesting that a warming ocean may have contributed to the more rapid retreat of marine GrIS termini in the Nuuk, Paa

  • Journal article
    Magee C, Maharaj SM, Wrona T, Jackson CA-L, Magee C, Maharaj SM, Wrona T, Jackson CA-Let al., 2015,

    Controls on the expression of igneous intrusions in seismicreflection data

    , Geosphere, Vol: 11, Pages: 1-18, ISSN: 1553-040X

    The architecture of subsurface magma plumbing systems influences a variety of igneous processes, including the physiochemical evolution of magma and extrusion sites. Seismic reflection data provides a unique opportunity to image and analyze these subvolcanic systems in three dimensions and has arguably revolutionized our understanding of magma emplacement. In particular, the observation of (1) interconnected sills, (2) transgressive sill limbs, and (3) magma flow indicators in seismic data suggest that sill complexes can facilitate significant lateral (tens to hundreds of kilometers) and vertical (<5 km) magma transport. However, it is often difficult to determine the validityof seismic interpretations of igneous features because they are rarelydrilled, and our ability to compare seismically imaged features to potential field analogues is hampered by the limited resolution of seismic data. Here we use field observations to constrain a series of novel seismic forward models that examine how different sill morphologies may be expressed in seismic data. By varying the geologic architecture (e.g., host-rock lithology and intrusion thickness) and seismic properties (e.g., frequency), the models demonstratethat seismic amplitude variations and reflection configurations can beused to constrain intrusion geometry. However, our results also highlight that stratigraphic reflections can interfere with reflections generated at the intrusive contacts, and may thus produce seismic artifacts that could be misinterpreted as real features. This study emphasizes the value of seismic data to understanding magmatic systems and demonstrates the role that synthetic seismic forward modeling can play in bridging the gap between seismic data and field observations.

  • Conference paper
    Gavin K, Jardine RJ, Karlsrud K, Lehane BMet al., 2015,

    The Effects of Pile Ageing on the Shaft Capacity of Offshore Piles in Sand.

    , International Symposium Frontiers in Offshore Geotechnics, Publisher: CRC Press, Pages: 129-151

    A number of field studies suggest that the axial capacity of driven piles in sand increases withtime. Field test programmes were performed by a number of research groups to examine this aspect of pilebehaviour. The paper presents a summary of the findings from these experiments. It also reviews laboratorypile and element testing performed to provide further insights into the mechanisms controlling pile ageing.

  • Journal article
    Lewis MM, Jackson CAL, Gawthorpe RL, 2015,

    Early synrift reservoir development on the flanks of extensional forced folds: a seismic-scale outcrop analog from the Hadahid Fault System, Suez Rift, Egypt

    , AAPG Bulletin, Vol: 99, Pages: 985-1012

    Forced folds typically develop above the tips of propagating normal faults in rifts that contain thick, prerift salt or mudstone sequences. This structural style is associated with the deposition of wedge-shaped synrift deposits that thin and onlap towards monoclinal growth folds overlying the vertically restricted fault tips. Subtle stratigraphic traps may develop on the flanks of these folds although, due to limited seismic resolution and sparse well data, the architecture, thickness and distribution of early synrift reservoirs are difficult to predict. To improve our understanding of early synrift reservoir development on the flanks of forced folds, we focus on seismic-scale outcrop analogs along the Hadahid Fault System, Suez rift, Egypt. Our data indicate that forced folding dominated during early rifting and that the onset of folding was diachronous along-strike. Fluvial systems incised the rotating monocline limbs, leading to the formation of valley-like erosional relief along the base synrift unconformity. Reservoir-prone fluvial facies are only locally developed along the forced fold flank, with their distribution related to the degree of sediment bypass downdip into the adjacent basin. Early synrift relief not filled by fluvial strata was backfilled by transgressive, tidally influenced, reservoir-prone facies, with carbonates being locally developed in areas of low clastic sediment supply. Further extension and fault-tip propagation led to amplification of the forced folds, and deposition of shallow marine-to-shelf parasequences that became thinner towards the growing folds. Although displaying greater strike continuity than the underlying fluvial or tidal reservoirs, shoreface sandstone reservoirs amalgamate onto the flanks of the forced folds and may be absent towards the fold crest. This outcrop analog helps us better understand the sub-seismic stratigraphic architecture and facies distributions of early synrift reservoirs on the flanks of extensional f

  • Journal article
    Graham GH, Jackson MD, Hampson GJ, 2015,

    Three-dimensional modeling of clinoforms in shallow-marine reservoirs: Part 2. Impact on fluid flow and hydrocarbon recovery in fluvial-dominated deltaic reservoirs

    , AAPG Bulletin, Vol: 99, Pages: 1049-1080, ISSN: 0149-1423

    © 2015. The American Association of Petroleum Geologists. All rights reserved. Permeability contrasts associated with clinoforms have been identified as an important control on fluid flow and hydrocarbon recovery in fluvial-dominated deltaic parasequences. However, they are typically neglected in subsurface reservoir models or considered in isolation in reservoir simulation experiments because clinoforms are difficult to capture using current modeling tools. A suite of three-dimensional reservoir models constructed with a novel, stochastic, surface-based clinoform-modeling algorithm and outcrop analog data (Upper Cretaceous Ferron Sandstone Member, Utah) have been used here to quantify the impact of clinoforms on fluid flow in the context of (1) uncertainties in reservoir characterization, such as the presence of channelized fluvial sandbodies and the impact of bed-scale heterogeneity on vertical permeability, and (2) reservoir engineering decisions, including oil production rate. The proportion and distribution of barriers to flow along clinoforms exert the greatest influence on hydrocarbon recovery; equivalent models that neglect these barriers overpredict recovery by up to 35%. Continuity of channelized sandbodies that cut across clinoform tops and vertical permeability within distal delta-front facies influence sweep within clinothems bounded by barriers. Sweep efficiency is reduced when producing at higher rates over shorter periods, because oil is bypassed at the toe of each clinothem. Clinoforms are difficult to detect using production data, but our results indicate that they significantly influence hydrocarbon recovery and their impact is typically larger than that of other geologic heterogeneities regardless of reservoir engineering decisions. Clinoforms should therefore be included in models of fluvial-dominated deltaic reservoirs to accurately predict hydrocarbon recovery and drainage patterns.

  • Journal article
    Molkenthin C, Scherbaum F, Griewank A, Kuehn N, Stafford PJ, Leovey Het al., 2015,

    Sensitivity of Probabilistic Seismic Hazard Obtained by Algorithmic Differentiation: A Feasibility Study

    , Bulletin of the Seismological Society of America, Vol: 105, Pages: 1810-1822, ISSN: 0037-1106

    Probabilistic seismic-hazard analysis (PSHA) is the current tool of thetrade used to estimate the future seismic demands at a site of interest. A modern PSHArepresents a complex framework that combines different models with numerous inputs.It is important to understand and assess the impact of these inputs on the modeloutput in a quantitative way. Sensitivity analysis is a valuable tool for quantifyingchanges of a model output as inputs are perturbed, identifying critical input parameters,and obtaining insight about the model behavior. Differential sensitivity analysisrelies on calculating first-order partial derivatives of the model output with respect toits inputs; however, obtaining the derivatives of complex models can be challenging.In this study, we show how differential sensitivity analysis of a complex frameworksuch as PSHA can be carried out using algorithmic/automatic differentiation(AD). AD has already been successfully applied for sensitivity analyses in variousdomains such as oceanography and aerodynamics. First, we demonstrate the feasibilityof the AD methodology by comparing AD-derived sensitivities with analyticallyderived sensitivities for a basic case of PSHA using a simple ground-motion predictionequation. Second, we derive sensitivities via AD for a more complex PSHA studyusing a stochastic simulation approach for the prediction of ground motions. The presentedapproach is general enough to accommodate more advanced PSHA studies ofgreater complexity.

  • Journal article
    Maes J, Muggeridge AH, Jackson MD, Quintard M, Lapene Aet al., 2015,

    Modelling in-situ upgrading of heavy oil using operator splitting method

    , Computational Geosciences, Vol: 20, Pages: 581-594, ISSN: 1573-1499

    The in-situ upgrading (ISU) of bitumen and oil shale is a very challenging process to model numerically because of the large number of components that need to be modelled using a system of equations that are both highly non-linear and strongly coupled. Operator splitting methods are one way of potentially improving computational performance. Each numerical operator in a process is modelled separately, allowing the best solution method to be used for the given numerical operator. A significant drawback to the approach is that decoupling the governing equations introduces an additional source of numerical error, known as the splitting error. The best splitting method for modelling a given process minimises the splitting error whilst improving computational performance compared to a fully implicit approach. Although operator splitting has been widely used for the modelling of reactive-transport problems, it has not yet been applied to the modelling of ISU. One reason is that it is not clear which operator splitting technique to use. Numerous such techniques are described in the literature and each leads to a different splitting error. While this error has been extensively analysed for linear operators for a wide range of methods, the results cannot be extended to general non-linear systems. It is therefore not clear which of these techniques is most appropriate for the modelling of ISU. In this paper, we investigate the application of various operator splitting techniques to the modelling of the ISU of bitumen and oil shale. The techniques were tested on a simplified model of the physical system in which a solid or heavy liquid component is decomposed by pyrolysis into lighter liquid and gas components. The operator splitting techniques examined include the sequential split operator (SSO), the Strang-Marchuk split operator (SMSO) and the iterative split operator (ISO). They were evaluated on various test cases by considering the evolution of the discretization error as

  • Journal article
    Armitage JJ, Ferguson DJ, Goes S, Hammond JOS, Calais E, Rychert CA, Harmon Net al., 2015,

    Upper mantle temperature and the onset of extension and break-up in Afar, Africa

    , EARTH AND PLANETARY SCIENCE LETTERS, Vol: 418, Pages: 78-90, ISSN: 0012-821X
  • Journal article
    Mostaghimi P, Percival JR, Pavlidis D, Ferrier RJ, Gomes JLMA, Gorman GJ, Jackson MD, Neethling SJ, Pain CCet al., 2015,

    Anisotropic Mesh Adaptivity and Control Volume Finite Element Methods for Numerical Simulation of Multiphase Flow in Porous Media

    , MATHEMATICAL GEOSCIENCES, Vol: 47, Pages: 417-440, ISSN: 1874-8961
  • Journal article
    Jackson CA-L, Jackson MPA, Hudec MR, Rodriguez CRet al., 2015,

    Enigmatic structures within salt walls of the Santos Basin—Part 1: Geometry and kinematics from 3D seismic reflection and well data

    , Journal of Structural Geology, Vol: 75, Pages: 135-162, ISSN: 0191-8141

    Understanding intrasalt structure may elucidate the fundamental kinematics and, ultimately, the mechanics of diapir growth. However, there have been relatively few studies of the internal structure of salt diapirs outside the mining industry because their internal parts are only partly exposed in the field and poorly imaged on seismic reflection data. This study uses 3D seismic reflection and borehole data from the São Paulo Plateau, Santos Basin, offshore Brazil to document the variability in intrasalt structural style in natural salt diapirs. We document a range of intrasalt structures that record: (i) initial diapir rise; (ii) rise of lower mobile halite through an arched and thinned roof of denser, layered evaporites, and emplacement of an intrasalt sheet or canopy; (iii) formation of synclinal flaps kinematically linked to emplacement of the intrasalt allochthonous bodies; and (iv) diapir squeezing. Most salt walls contain simple internal anticlines. Only a few salt walls contain allochthonous bodies and breakout-related flaps. All of these are in an area having a density inversion within the autochthonous salt layer, such that upper, anhydrite-rich, layered evaporites are denser than lower, more halite-rich evaporites. We thus interpret that most diapirs rose through simple fold amplification of internal salt stratigraphy but that locally, where a density inversion existed in the autochthonous salt, Rayleigh-Taylor overturn within the growing diapir resulted in the ascent of less dense evaporites into the diapir crest by breaching the internal anticline. This resulted in emplacement of high-level intrsalt allochthonous sheets underlain by breakout-related flaps and steep salt-ascension zones or feeders. Although late-stage regional shortening undoubtedly occurred on the São Paulo Plateau during the Late Cretaceous, we suggest this was only partly responsible for the complex intrasalt deformation. Although based on the Santos Basin, our kinematic

  • Journal article
    Bommer JJ, Coppersmith KJ, Coppersmith RT, Hanson KL, Mangongolo A, Neveling J, Rathje EM, Rodriguez-Marek A, Scherbaum F, Shelembe R, Stafford PJ, Strasser FOet al., 2015,

    A SSHAC Level 3 Probabilistic Seismic Hazard Analysis for a New-Build Nuclear Site in South Africa

    , EARTHQUAKE SPECTRA, Vol: 31, Pages: 661-698, ISSN: 8755-2930
  • Journal article
    Dooley TP, Jackson MPA, Jackson CA-L, Hudec MR, Rodriguez CRet al., 2015,

    Enigmatic structures within salt walls of the Santos Basin—Part 2: Mechanical explanation from physical modeling

    , Journal of Structural Geology, Vol: 75, Pages: 163-187, ISSN: 0191-8141

    Jackson et al. (this volume) used 3D seismic reflection data to describe intrasalt deformation in salt walls in the Santos Basin. They focused on the origin of enigmatic allochthonous salt sheets of older evaporites (A1 unit) emplaced above overlying stratified evaporites (A2–A4 units). Their kinematic model incorporates: (i) initial inward flow and thickening of A1 salt within the rising wall, and arching of A2–A4 overburden; (ii) breaching of the arched overburden, ascent of mobile A1 evaporites along single or multiple feeders, and emplacement of upper-wall sheets or canopies; and (iii) a component of regional shortening within the salt. This companion paper uses physical modeling to explain how and why these structures occur and proposes a mechanical basis for the kinematic model. Our first two models simulated salt having uniform internal density, with walls growing by (i) initially symmetric differential loading and (ii) initially symmetric differential loading plus shortening. These models reproduced anticlines and injection folds seen in the simpler deformed walls in the Santos Basin. However, neither model reproduced the most complex structures within the Santos evaporites, which are: (i) allochthonous intrusions, (ii) steep feeders, and (iii) recumbent synclines. Thus, differential loading and shortening alone are insufficient to generate these complex structures. In our third model, a less-dense lower evaporite (A1) was overlain by denser upper evaporites (A2–A4), similar to the density structure found by Santos Basin wellbores. The wall rose solely by differential loading. In this model, A1 breached the overlying evaporites to form vertical diapirs feeding salt sheets and salt wings in the upper part of the salt wall. Breakthrough of A1 folded A2–A4 evaporites into recumbent synclines. Model sections closely resemble Santos seismic examples, suggesting that the key to forming these complex intrasalt structures is a density inversi

  • Journal article
    Zhao Y, Liu JG, Zhang B, Hong W, Wu Y-Ret al., 2015,

    Adaptive Total Variation Regularization Based SAR Image Despeckling and Despeckling Evaluation Index

    , IEEE Transactions on Geoscience and Remote Sensing, Vol: 53, Pages: 2765-2774, ISSN: 1558-0644
  • Journal article
    Jackson MD, Percival JR, Mostaghiml P, Tollit BS, Pavlidis D, Pain CC, Gomes JLMA, El-Sheikh AH, Salinas P, Muggeridge AH, Blunt MJet al., 2015,

    Reservoir Modeling for Flow Simulation by Use of Surfaces, Adaptive Unstructured Meshes, and an Overlapping-Control-Volume Finite-Element Method

    , SPE RESERVOIR EVALUATION & ENGINEERING, Vol: 18, Pages: 115-132, ISSN: 1094-6470
  • Book chapter
    Davies DR, Goes S, Lau HCP, 2015,

    Thermally dominated deep mantle LLSVPs: A review

    , The Earth’s Heterogeneous Mantle: a geophysical, geodynamical, geochemical perspective, Editors: Khan, Deschamps, Publisher: Springer, Pages: 441-477

    The two large low shear-wave velocity provinces (LLSVPs) that dominate lower-mantle structure may hold key information on Earth’s thermal and chemical evolution. It is generally accepted that these provinces are hotter than background mantle and are likely the main source of mantle plumes. Increasingly, it is also proposed that they hold a dense (primitive and/or recycled) compositional com- ponent. The principle evidence that LLSVPs may represent thermo-chemical ‘piles’ comes from seismic constraints, including: (i) their long-wavelength nature; (ii) sharp gradients in shear-wave velocity at their margins; (iii) non-Gaussian distributions of deep mantle shear-wave velocity anomalies; (iv) anti-correlated shear-wave and bulk-sound velocity anomalies (and elevated ratios between shear- and compressional-wave velocity anomalies); (v) anti-correlated shear-wave and density anomalies; and (vi) 1-D/radial profiles of seismic velocity that deviate from those expected for an isochemical, well-mixed mantle. In addition, it has been proposed that hotspots and the reconstructed eruption sites of large ig- neous provinces correlate in location with LLSVP margins. In this paper, we review recent results which indicate that the majority of these constraints do not require thermo-chemical piles: they are equally well (or poorly) explained by thermal heterogeneity alone. Our analyses and conclusions are largely based on comparisons between imaged seismic structure and synthetic seismic structures from a set of thermal and thermo-chemical mantle convection models, which are constrained by ∼ 300 Myr of plate motion histories. Modelled physical structure (temperature, pressure and composition) is converted into seismic velocities via a thermodynamic approach that accounts for elastic, anelastic and phase con- tributions and, subsequently, a tomographic resolution filter is applied to account for the damping and geographic bias inherent to seismic imaging. Our re

  • Journal article
    Alqahtani FA, Johnson HD, Jackson CA-L, Som RBet al., 2015,

    Nature, origin and evolution of a Late Pleistocene incised valley-fill, Sunda Shelf, Southeast Asia

    , Sedimentology, Vol: 62, Pages: 1198-1232, ISSN: 1365-3091

    Shallow (<500 ms TWT/c. 500 m sub-sea) 3D seismic reflection data from a large (11500 km2), ‘merge’ survey, supplemented with high-resolution site survey data, have enabled identification and characterisation of a large (up to 18 km wide by 80 m deep) Late Pleistocene incised valley on the Sunda Shelf, offshore eastern Malaysia. The valley-fill displays five large-scale stratigraphic features: (1) it is considerably larger than other seismically-resolvable channel forms and can be traced for at least 180 km along its length within the available 3D seismic volume; (2) it is located in the axial part of the Malay Basin with a_NNW-SSE orientation, which is parallel to the maximum thickness of the underlying Oligo-Miocene succession (the main fill of the Malay Basin); (3) the youngest fill of the valley-fill is dominated by a large (up to 800 m wide and 23 m deep), high-sinuosity channel, with well-developed lateral accretion surfaces, point bars and meander loop cut-offs; (4) the immediately adjacent interfluves contain much smaller, dendritic ‘tributary’ channel systems, which drain into the larger incised valley system, and (5) a ca. 16 m thick, shell-bearing, Holocene age clay caps the valley-fill. Site survey borehole data from the abandonment part of the large meandering channel at the top of the incised valley-fill display the following: (1) pebbles, gravels and cobbles form a basal channel lag above a prominent, seismically-defined erosional surface; .(2) interbedded fine-grained sandstones and claystones, with shell fragments and terrestrially-derived organic material, form the middle part of the channel-fill; and (3) inclined heterolithic stratification (IHS), visible on high-resolution site survey seismic data, is the dominant macro-scale sedimentary structure. The interval adjacent to the incised valley comprises muds and silts with dispersed plant material and shell debris. These data document two major depositional environments

  • Journal article
    Pupim FDN, Bierman PR, Assine ML, Rood DH, Silva A, Merino ERet al., 2015,

    Erosion rates and landscape evolution of the lowlands of the Upper Paraguay river basin (Brazil) from cosmogenic Be-10

    , GEOMORPHOLOGY, Vol: 234, Pages: 151-160, ISSN: 0169-555X
  • Journal article
    Jordan JR, Kimura S, Holland PR, Jenkins A, Piggott MDet al., 2015,

    On the Conditional Frazil Ice Instability in Seawater

    , JOURNAL OF PHYSICAL OCEANOGRAPHY, Vol: 45, Pages: 1121-1138, ISSN: 0022-3670
  • Journal article
    Wyshnytzky CE, Ouimet WB, McCarthy J, Dethier DP, Shroba RR, Bierman PR, Rood DHet al., 2015,

    Meteoric Be-10, clay, and extractable iron depth profiles in the Colorado Front Range: Implications for understanding soil mixing and erosion

    , CATENA, Vol: 127, Pages: 32-45, ISSN: 0341-8162
  • Journal article
    D'Arcy M, Boluda DCR, Whittaker AC, Carpineti Aet al., 2015,

    Dating alluvial fan surfaces in Owens Valley, California, using weathering fractures in boulders

    , EARTH SURFACE PROCESSES AND LANDFORMS, Vol: 40, Pages: 487-501, ISSN: 0197-9337

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