Publications
401 results found
Jackson CAL, Jackson MPA, Hudec MR, et al., 2014, Erratum to Internal structure, kinematics, and growth of a salt wall: Insights from 3-D seismic data [Geology, 42, 307-310] doi:10.1130/G34865.1, Geology, Vol: 42, ISSN: 0091-7613
Mannie AS, Holgate NE, Jackson CAL, 2013, Get outside, 52 Things You Should Know About Geology, Publisher: Agile Geoscience, Pages: 30-31, ISBN: 0987959425
Zakaria AA, Johnson HD, Jackson CAL, et al., 2013, Mass Transport Complex (MTC) on NW Borneo slope; influence of thrust related folding on its stratigraphic development
Zakaria AA, Johnson HD, Jackson CAL, et al., 2013, Sedimentology of the major W crocker submarine fan system; analogue to the younger productive fans, NW Sabah basin
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Holgate NE, Mannie AS, Jackson CAL, 2013, As easy as 1D, 2D, 3D, 52 Things You Should Know About Geology, Editors: Hall, Publisher: Agile Geoscience, Pages: 18-19, ISBN: 0987959425
Jackson CAL, Lewis MM, 2013, Physiography of the North Permian Basin margin: new insights from 3D seismic reflection data, Journal of the Geological Society, Vol: 170, Pages: 857-860
3D seismic reflection data from the Egersund Basin, offshore Norway image geomorphic features that record mid-Permian, footwall degradation of basin-bounding fault systems. This ancient landscape was subsequently flooded during the pan-European, Late Permian transgression of the North Permian Salt Basin, and was fossilised beneath Zechstein Supergroup evaporites. We provide the first conclusive evidence for pre-Zechstein normal faulting in the Egersund Basin, indicating that extensional strain was shared between Permian and Late Jurassic-to-Early Cretaceous rift events.
Magee C, Briggs F, Jackson CAL, 2013, 3D seismic insights into lithological controls on igneous intrusion-induced ground deformation, Journal of the Geological Society, Vol: 170, Pages: 853-856
Ground deformation commonly precedes volcanic eruptions, although its relationship to underlying intrusion networks is complex. We use 3D seismic reflection data to examine the link between a saucer-shaped sill and an overlying forced fold formed at the contemporaneous palaeosurface. Our results highlight a disparity in size between the sill and fold, which we attribute to accommodation of magma by overburden uplift and fluid expulsion from the host rock. Sill transgression occurred in response to plastic deformation of the host rock and did not produce seismically resolvable uplift. Inversion models of ground deformation should therefore acknowledge host rock behaviour during intrusion.
Holford SP, Schofield N, Jackson CAL, et al., 2013, Impact of igneous intrusions on source and reservoir potential in prospective sedimentary basins, Western Australia Basin Symposium
Many prospective basins in rifted continental margins, including those located along the western Australian continental margin, contain extrusive and intrusive rocks generated during rifting and particularly during continental breakup. Intrusive igneous systems in rifted margin basins are typically characterized by networks of interconnected, laterally and vertically extensive sheet complexes (e.g. sills and dykes) that transgress basin stratigraphy. The presence of igneous rocks thus represents an important geological risk in hydrocarbon exploration. Constraining the distribution, timing and intrusive mechanisms of the igneous rocks is essential to reducing exploration risk. This paper focuses on two key sources of risk associated with the intrusion of igneous rocks into prospective sedimentary basins: (1) interconnected, low-permeability sheet intrusions (e.g. sills and dykes) that can compartmentalise significant volumes of source and reservoir rock, thereby reducing migration efficiencies; and (2) igneous-related hydrothermal circulation systems that can be highly mineralising and thus detrimental to reservoir quality. It is also important to highlight that igneous rocks may also be beneficial to petroleum systems. For example, the thermal effects of igneous intrusions may in some cases be sufficient to place immature source rocks within the oil window. The impacts of igneous intrusion on the prospectivity of rift basins along the western Australian continental margin are examined, with particular focus on frontier exploration areas such as the Exmouth Plateau and Browse Basin.
Jackson CA-L, Lewis MM, 2013, Physiography of the NE margin of the Permian Salt Basin: new insights from 3D seismic reflection data, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 170, Pages: 857-860, ISSN: 0016-7649
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Jackson CAL, Schofield N, Golenkov B, 2013, Geometry and controls on the development of igneous sill-related forced folds: a 2D seismic reflection case study from offshore southern Australia, Geological Society of America Bulletin, Vol: 125, Pages: 1874-1890
Emplacement of magma in the shallow subsurface can result in the development of dome–shaped folds at the Earth's surface. These so-called "forced folds" have been described in the field and in subsurface data sets, although the exact geometry of the folds and the nature of their relationship to underlying sills remain unclear and, in some cases, controversial. In this study we use high-quality, two-dimensional (2-D) seismic reflection and borehole data from the Ceduna sub-basin, offshore southern Australia, to describe the structure and infer the evolution of igneous sill–related forced folds in the Bight Basin igneous complex. Thirty-three igneous sills, which were emplaced 200–1500 m below the paleo-seabed in Upper Cretaceous rocks, are mapped in the Ceduna sub-basin. The intrusions are expressed as packages of high-amplitude reflections, which are 32–250 m thick and 7–19 km in diameter. We observe five main types of intrusion: type 1, strata-concordant sills; type 2, weakly strata-discordant, transgressive sills; type 3, saucer-shaped sills; type 4, laccoliths; and type 5, hybrid intrusions, which have geometric characteristics of intrusion types 1–3. These intrusions are overlain by dome-shaped folds, which are up to 17 km wide and display up to 210 m of relief. The edges of these folds coincide with the margins of the underlying sills and the folds display the greatest relief where the underlying sills are thickest; the folds are therefore interpreted as forced folds that formed in response to emplacement of magma in the shallow subsurface. The folds are onlapped by Lutetian (middle Eocene) strata, indicating they formed and the intrusions were emplaced during the latest Ypresian (ca. 48 Ma). We demonstrate that fold amplitude is typically less than sill thickness even for sills with very large diameter-to-depth ratios, suggesting that pure elastic bending (forced folding) of the overburden is not the only process a
Somme TO, Jackson CAL, 2013, Source-to-sink analysis of ancient sedimentary systems using a subsurface case study from the Møre-Trøndelag area of southern Norway: Part 2 – sediment dispersal and forcing mechanisms, Basin Research, Vol: 25, Pages: 512-531, ISSN: 0950-091X
The composition, volume and stratigraphic organisation of submarine fan systems deposited along continental margins are expected to reflect the landscape from which the sediment was derived. During the Late Cretaceous, the Møre-Trøndelag margin, Norwegian North Sea was dominated by the deposition of deep-marine fines; the emplacement of 11 sand-rich submarine fan systems occurred only during a c. 3 Myr period in the Turonian-Coniacian. The systems were fed by sediment that was routed through submarine canyons incised into the basin margin; the canyons are underlain by angular unconformities and are interpreted to have resulted from tectonically-induced changes in slope physiography and erosion by gravity flows. The areal extent of the onshore drainage catchments that supplied sediment to the fans has been estimated based on scaling relationships derived from modern source-to-sink systems. The results of our study suggest that the Turonian fans were sourced by drainage catchments that were up to ~3600 km2, extending more than ~100 km inland from the palaeo-shoreline. The estimated inboard catchment extent correlates to the innermost structures of a large, long-lived, basement-involved, normal fault complex. Based on our analysis we conclude that increased sediment supply to the Turonian fan systems reflects tectonic rejuvenation of the landscape, rather than eustatic sea-level or climate fluctuations. The duration of fan deposition is thus interpreted to reflect the ‘relaxation time’ of the landscape following tectonic perturbation, and fan system retrogradation and abandonment is interpreted to reflect the eventual depletion of the onshore sediment source. We demonstrate that a better understanding of the stratigraphic variability of deepwater depositional systems can be gained by taking a complete source-to-sink view of ancient sediment dispersal systems.
Zakaria AA, Johnson HD, Jackson CAL, et al., 2013, Sedimentary facies analysis and depositional model for the Palaeogene West Crocker submarine fan system, NW Borneo, Journal of Asian Earth Sciences, Vol: 76, Pages: 283-300
This study outlines a sedimentological analysis of the Palaeogene West Crocker Formation (WCF) around the Kota Kinabalu area of SW Sabah, which represents a large submarine fan depositional system within part of what was the complex and tectonically active margin of NW Borneo. The newly acquired and often extensive outcrop data summarised in this study has resulted in a more complete synthesis of the Crocker fan depositional system than has been previously possible. Seven facies (F1 to F7) have been identified which constitute three main facies groups: (1) sand-dominated facies (F1 to F3), comprise high- to low-density turbidites and form the dominant part of the WCF, (2) debris flow-dominated facies (F4 to F6) comprises mud- and sand-dominant debris flows and mass transport deposits (MTD), which form a secondary but highly distinctive part of the WCF, and (3) mudstone-dominated facies (F7), represent a subordinate part of the WCF. Analysis of the vertical facies successions (from proximal to distal), has resulted in recognition of five major genetic units: (1) Channel-levee complex; characterised by thick (30-60 m) thinning and fining upward facies succession, which are dominated in their lower part by thick-bedded (1-6 m), amalgamated high-density (Lowe-type) turbidites with rare debrite beds; the upper part is dominated low-density (Bouma-type) turbidites, without associated debrite beds. (2) Channelised lobes; characterized by 2-10 m thick, coarsening upward, which are overlain by 5-20 m thick fining upward facies successions; these successions are dominated by high-density turbidites (c. 0.5-1 m thick) and linked co-genetic turbidite-debrite beds (0.1-0.5 m thick), with subordinate mudstone facies. (3) Non-channelised lobes; comprise 5-20 m thick coarsening upward facies successions; these start with mudstone facies, which pass gradually upwards into linked co-genetic turbidite-debrite beds; sandstone bed thickness increases upwards, while the debrite caps tend
Wilson P, Elliott GM, Gawthorpe RL, et al., 2013, Geometry and segmentation of an evaporite-detached normal fault array: The southern Bremstein Fault Complex, offshore mid-Norway, Journal of Structural Geology, Vol: 51, Pages: 74-91
Geometry and segmentation of an evaporite-detached normal fault array: The southern Bremstein Fault Complex, offshore mid-Norway.
Tvedt ABM, Rotevatn A, Jackson CAL, et al., 2013, Growth of normal faults in multilayer sequences; a 3D seismic case study from the Egersund Basin, Norwegian North Sea, Journal of Structural Geology, Vol: 55, Pages: 1-20
We investigate the structural style and evolution of a salt-influenced, extensional fault array in the Egersund Basin (Norwegian North Sea) through analysis of 3D reflection seismic and well data. Analysis of fault geometry/morphology, throw distribution and syn-kinematic strata reveal an intricate but systematic style of displacement and growth, suggesting an evolution of (1) initial syn-sedimentary fault growth contemporaneous with salt mobilization initiated during the Late Triassic, (2) cessation of fault activity and burial of the stagnant fault tips, and (3) subsequent nucleation of new faults in the cover above contemporaneous salt re-mobilization initiated during the Late Cretaceous, with downward propagation and linkage with faults. Stage 3 was apparently largely controlled by salt mobilization in response to basin inversion, as reactivated faults are located where the underlying salt is thick, while the non-reactivated faults are found where salt is depleted. Based on the 3D-throw analyses, we conclude that a combination of basement faulting and salt (re-) mobilization is the driving mechanisms behind fault activation and reactivation. Even though the sub- and supra-salt faults are mainly geometrically decoupled through the salt, a kinematic coupling must have existed as sub-salt faults still affected nucleation and localization of the cover faults.
Lewis MM, Jackson CAL, Gawthorpe RL, 2013, Salt-influenced normal fault growth and forced folding; the Stavanger Fault System, North Sea, Journal of Structural Geology, Vol: 54, Pages: 156-173
Displacement ratio (Dr) is the ratio of salt thickness (Tv) to sub-salt normal fault displacement (D) (Dr = Tv /D), and it is typically used to predict the degree of geometric and kinematic linkage between sub- and supra-salt fault populations, and the overall resultant structural style in salt-influenced extensional settings. However, we currently lack natural examples of how Dr and the underlying geological controls vary, and how these may control the three-dimensional geometry and evolution of salt-influenced normal fault systems. Furthermore, it is currently unknown if kinematic coherence in salt-influenced extensional settings can be maintained over long length-scales (101-103 m) and for long periods of extension, and how this may impact the growth and geometry of large-throw (> 500 m), salt-influenced normal fault systems. In this paper we use a 3600 km2, high-quality 3D seismic reflection dataset and borehole data from the Stavanger Fault System (SFS), Egersund Basin, eastern North Sea Basin to investigate; (i) how pre-rift salt thickness (Tv) and sub-salt fault throw (T) control the structural style and evolution of a basin-bounding, salt-influenced normal fault system; and (ii) the role salt plays in maintaining kinematic coherence in normal fault systems. We demonstrate that; (i) pre-rift salt distribution (Tv), specifically its presence in the proto-footwall (i.e., when Tv > 0), is the primary control on partitioning of faulting and (forced) folding along the fault system, and the style of linkage (i.e., hard- or soft-linkage) between sub- and supra-salt fault populations; and (ii) that sub- and supra-salt fault populations represent brittle elements of single geometrically and kinematically coherent structure, which is related to the ductile translation of strain on a scale (up to 8 km) and duration (c. 65 Myr) that is significantly greater than previously documented.
Legler B, Johnson HD, Hampson GJ, et al., 2013, Facies model of a fine-grained, tide-dominated delta: lower Dir Abu Lifa Member (Eocene), Western Desert, Egypt, Sedimentology, Vol: 60, Pages: 1313-1356
Existing facies models of tide-dominated deltas largely omit fine-grained, mud-rich successions. Sedimentary facies and sequence stratigraphic analysis of the exceptionally well-preserved Late Eocene Dir Abu Lifa Member (Western Desert, Egypt) aims to bridge this gap. The succession was deposited in a structurally controlled, shallow, macrotidal embayment and deposition was supplemented by fluvial processes but lacked wave influence. The succession contains two stacked, progradational parasequence sets bounded by regionally extensive flooding surfaces. Within this succession two main genetic elements are identified: non-channelised tidal bars and tidal channels. Non-channelised tidal bars comprise coarsening-upward sand bodies, including large, downcurrent-dipping accretion surfaces, sometimes capped by palaeosols indicating emergence. Tidal channels are preserved as single-storey and multilateral bodies filled by: (i) laterally migrating, elongate tidal bars (inclined heterolithic strata, 5 to 25 m thick); (ii) forward-facing lobate bars (sigmoidal heterolithic strata, up to 10 m thick); (iii) side bars displaying oblique to vertical accretion (4 to 7 m thick); or (iv) vertically-accreting mud (1 to 4 m thick). Palaeocurrent data show that channels were swept by bidirectional tidal currents and typically were mutually evasive. Along-strike variability defines a similar large-scale architecture in both parasequence sets: a deeply scoured channel belt characterised by widespread inclined heterolithic strata is eroded from the parasequence-set top, and flanked by stacked, non-channelised tidal bars and smaller channelised bodies. The tide-dominated delta is characterised by: (i) the regressive stratigraphic context; (ii) net-progradational stratigraphic architecture within the succession; (iii) the absence of upward deepening trends and tidal ravinement surfaces; and (iv) architectural relations that demonstrate contemporaneous tidal distributary channel infill and ti
Jackson CAL, Rotevatn A, 2013, 3D seismic analysis of the structure and evolution of a salt-influenced normal fault zone: a test of competing fault growth models, Journal of Structural Geology, Vol: 54, Pages: 215-234
In this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3D seismic reflection dataset from the Suez Rift, Egypt. Our analysis indicates that the October Fault Zone is composed of two fault systems that are locally decoupled across an salt-bearing interval of Late Miocene (Messinian) age. The sub-salt system offsets pre-rift crystalline basement, and was active during the Late Oligocene-early Middle Miocene. It is composed of four, planar, NW-SE-striking segments that are hard-linked by N-S-striking segments, and up to 2 km of displacement occurs at top basement, suggesting that this fault system nucleated at or, more likely, below this structural level. The supra-salt system was active during the Pliocene-Holocene, and is composed of four, NW-SE-striking, listric fault segments, which are soft-linked by unbreached relay zones. Segments in the supra-salt fault system nucleated within Pliocene strata and have maximum throws of up to 482 m. Locally, the segments of the supra-salt fault system breach the Messinian salt to hard-link downwards with the underlying, sub-salt fault system, thus forming the upper part of a fault zone composed of: (i) a single, amalgamated fault system below the salt and (ii) a fault system composed of multiple soft-linked segments above the salt. Analysis of throw-distance (T-x) and throw-depth (T-z) plots for the supra-salt fault system, isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history. The fault tips were then effectively ‘pinned’ and the faults accumulated displacement via predominantly downward propagation. We interpret that the October Fault Zone had the following evolutionary trend; (i) growth of the sub-salt fault system during the Oligocene-to-early Middle Miocene; (ii) cessation of
Magee C, Hunt-Stewart E, Jackson CAL, 2013, Volcano growth mechanisms and the role of sub-volcanic intrusions: Insights from 2D seismic reflection data, Earth and Planetary Science Letters, Vol: 373, Pages: 41-53
Temporal and spatial changes in volcano morphology and internal architecture can determine eruption style and location. However, the relationship between the external and internal characteristics of volcanoes and sub-volcanic intrusions is often difficult to observe at outcrop or interpret uniquely from geophysical and geodetic data. We use high-quality 2D seismic reflection data from the Ceduna Sub-basin, offshore southern Australia, to quantitatively analyse 56, pristinely-preserved, Eocene-age volcanogenic mounds, and a genetically-related network of sub-volcanic sills and laccoliths. Detailed seismic mapping has allowed the 3D geometry of each mound to be reconstructed and distinct seismic facies within them to be recognised. Forty-six continental, basaltic shield volcanoes have been identified that have average flank dips of <10.31, basal diameters of 1.94–18.89 km, central summits that are 0.02–1 km high and volumes that range from 0.06 to 57.21 km3. Parallel seismic reflections within the shield volcanoes are interpreted to represent interbedded volcanic and clastic material, suggesting that a series of temporally separate eruptions emanated from a central vent. The shield volcanoes typically overlie the lateral tips of sills and we suggest that the intermittent eruption phases correspond to the incremental emplacement of discrete magma pulses within the laterally extensive sill-complex. Eight volcanogenic hydrothermal vents, which are also associated with the lateral tips of sills, were also recognised, and these appear to have formed from the seepage of intrusion-related hydrothermal fluids onto the seafloor via emplacement-induced fractures. This work highlights that deformation patterns preceding volcanic eruptions may (i) be offset from the eruption site; (ii) attributed to intrusions with complex morphologies; and/or (iii) reflect magma movement along pre-existing fracture systems. These complexities should therefore be considered in erupt
Holgate NE, Jackson CAL, Hampson GJ, et al., 2013, Sedimentology and sequence stratigraphy of the Upper Jurassic Krossfjord and Fensfjord formations, Troll Field, northern North Sea, Petroleum Geoscience, Vol: 19, Pages: 237-258
The Middle-to-Upper Jurassic Krossfjord and Fensfjord formations are secondary reservoir targets in the super-giant Troll oil and gas field, Horda Platform, offshore western Norway. The formations comprise sandstones sourced from the Norwegian mainland to the east and pinch out basinwards into the offshore shales of the Heather Formation to the west. Sedimentological analysis of cores across the Troll Field has identified six facies associations, which represent wave- and tide-dominated deltaic, shoreline and shelf depositional environments. Based on facies stacking patterns and abrupt shifts in facies, three regionally extensive flooding surfaces are identified. Facies association distributions and stratigraphic architectures are complex across the field, reflecting spatial and temporal variations in physical processes at the shoreline (e.g. wave- vs. tide- vs. fluvial-dominated), sediment supply and accommodation. The recognition of pronounced variability in facies character and stratigraphic architecture emphasize the need for a robust depositional model of the Krossfjord and Fensfjord formations in order to drive future exploration in these, and coeval, reservoirs.
Magee C, Jackson CAL, Schofield N, 2013, The influence of normal fault geometry on igneous sill emplacement and morphology, Geology, Vol: 41, Pages: 407-410
Magma flow within the subsurface is heavily influenced by the pre-existing structure of the upper crust. During continental rifting, normal faults modify the geometry of igneous networks by providing preferential pathways for the intrusion of magma. However, the mechanisms by which magma intrudes into fault planes is poorly understood. Here, we quantitatively document the relationship between fault architecture and intrusion distribution and geometry using 3D seismic reflection data from the Exmouth Sub-basin, offshore NW Australia. Inclined segments of saucer-shaped sills are observed to specifically intrude faults along positive fault-plane corrugations (i.e., convex-into-the-hangingwall). We suggest that stress field variations associated with the positive corrugations provide suitable conditions for fault reactivation as magma conduits. Pre-existing faults also modify sill geometries through the offset of stratigraphic horizons that may be preferentially intruded, potentially resulting in the formation of a new sill or the development of minor intrusive steps. This work emphasizes the importance of the pre-existing structural template in controlling the growth and final geometry of intrusive networks and, implicitly, the distribution of eruptive volcanic centers.
Lonergan L, Jamin NH, Jackson CA-L, et al., 2013, U-shaped slope gully systems and sediment waves on the passive margin of Gabon (West Africa), Marine Geology, Vol: 337, Pages: 80-97
3-D seismic reflection data has enabled the documentation of a system of remarkable modern and buried u-shaped gullies which intimately co-exist with upslope migrating sediment waves along 80 km of the Gabon continental slope. The modern gullies occur on a silty mud-dominated slope in water depths of 150–1500 m on an ~50 km wide slope with a gradient of 4.5° decreasing to 1.5°. The gully sets persist laterally for distances of at least 40 km and extend downslope for distances of up to 60 km. The gullies are u-shaped in crosssection,with a relief of 5–30 m, and widths of 50–400 m. Intriguingly, the gullies become narrower andshallower with distance down the slope, as well as increasing in number down slope. The majority of the gullies appear to be erosional but some appear to have resulted from simultaneous aggradation along inter-gully ridges and non-deposition along the adjacent gully floor. Hence, these gullies are interpreted to have formed mainly inresponse to spatially-variable deposition, rather than erosion. Upslope migrating sediment waves occur in close proximity to the gullies. Gullies cross fields of sediment waves and waves are observed to migrate up-slopelocally within both the erosional and aggradational gullies. Evidence is lacking for any slumping or headward erosion in the headwall region of the gullies, which discounts formation by very local sediment gravity flowsoriginating from shelf-edge collapse, as has been observed in other v-shaped gully systems. Based on our new data, and supported by theoretical studies on the mechanics of turbidity currents, we propose that the gulliesand related sediment waves were formed by diffuse, sheet-like, mud-rich turbidity currents that presumably originated on the shelf. Instabilities in the turbidity currents generated a wave-shaped perturbation in a crossflow direction leading to regularly spaced regions of faster and slower flow. For the non-aggradational and erosional gullies it is
Somme TO, Jackson CAL, Vaksdal M, 2013, Source-to-sink analysis of ancient sedimentary systems using a subsurface case study from the Møre-Trøndelag area of southern Norway: Part 1 - depositional setting and fan evolution, Basin Research, Vol: 25, Pages: 489-511
In this study we use seismic reflection, well and core data to investigate the role that basin physiography and sediment routing systems played on the distribution, geometry and stratigraphic architecture of Upper Cretaceous submarine fans offshore Norway. The Late Cretaceous Møre-Trøndelag margin of western Norway was characterised by steep submarine slopes (gradient of ~0,3-3º). Mudstones dominate the Upper Cretaceous slope succession although a few regionally extensive, sandstone-dominated units are developed. We focus on the most regionally extensive sandstone unit, which is of Late Turonian-to-Early Coniacian age. Mapping and visualisation of 2D and 3D seismic reflection data and analysis of well data indicates that the sandstone unit comprises a total of 11 submarine fans, which were fed by sand-rich sediment gravity flows routed through multiple upper slope canyons. Based on the internal organisation of seismic facies, four fan types have been identified: (i) Type Ia fans, which are characterised by <10 erosional channel complexes at their bases and aggradational to landward-stepping lobes in their upper parts; (ii) Type Ib fans, which are characterised by >10 erosional channel complexes at their bases and aggradational to landward-stepping lobe and mass-transport deposits near the fan apex in their upper parts; (iii) Type II fans, which are dominated by aggradational lobe deposits; and (iv) Type III fans, which are dominated by a single channel complex that passes downdip into a small terminal lobe. The different fan types are interpreted to reflect variable stratigraphic responses to source proximity and basin physiography, which is principally related to the degree of local fault reactivation and differential compaction. This variability highlights the diversity of fan types that may occur over short distances along continental margins, and demonstrates the importance of local controls in understanding the internal stratigraphic va
Reeve M, Bell RE, Jackson CA-L, et al., 2013, Origin and significance of intra-basement seismic reflections offshore western Norway, Journal of the Geological Society, Vol: 171, Pages: 1-4
We use 3D seismic data to image a series of enigmatic, SW-dipping reflection packets within pre-Mesozoic crystalline basement offshore western Norway. Based on their low-angle dip and complex reflection wave-train our preferred interpretation is that the reflection packets are the seismic expression of mylonitic zones generated by nappe emplacement during the Caledonian Orogeny. Late Jurassic faults truncate and offset these reflection packets by several hundred metres, suggesting that these faults did not exploit pre-existing basement weaknesses. Our observations suggest that older basement fabrics may not always play a significant role in determining the geometry of later fault systems.
Jackson CAL, Chua S-T, Bell RE, et al., 2013, Structural style and growth of early-stage inversion structures: insights from 3D seismic reflection data, Egersund Basin, offshore Norway, Journal of Structural Geology, Vol: 46, Pages: 167-185
High-quality three-dimensional (3D) seismic reflection and borehole data from the Egersund Basin, offshore Norway are used to characterise the structural style and determine the timing of growth of inversion-related anticlines adjacent to a segmented normal fault system. Two thick-skinned normal faults, which offset Permian clastics and evaporites, delineate the north-eastern margin of the basin. These faults strike NNW-SSE, have up to 1900 m of displacement and are separated by an ESE-dipping, c. 10 km wide relay ramp. Both of these faults display exclusively normal separation at all structural levels and tip out upwards into the upper part of the Lower Cretaceous succession. At relatively shallow structural levels in the hangingwalls of these faults, a series of open, low-amplitude, fault-parallel anticlines are developed. These anticlines, which are asymmetric and verge towards the footwalls of the adjacent faults, are interpreted to have formed in response to mild inversion of the Egersund Basin. The amplitude of and apparent shortening associated with the anticlines vary along strike, and these variations mimic the along-strike variations in throw observed on the adjacent fault segments. We suggest that this relationship can be explained by along-strike changes in the propensity of the normal faults to reactivate during shortening; wider damage zones and lower angles of internal friction, coupled with higher pore fluids pressures at the fault centre, mean that reactivation is easier at this location than at the fault tips or in the undeformed country rock. Seismic-stratigraphic analysis of growth strata indicate that the folds initiated in the latest Turonian-to-earliest Coniacian (c. 88.6 Ma) and Santonian (c. 82.6 Ma); the control on this c. 6 Myr diachroneity in the initiation of fold growth is not clear, but it may be related to strain partitioning during the early stages of shortening. Anticline growth ceased in the Maastrichtian and the inversion event is
Olafiranye K, Jackson CAL, Hodgson DM, 2013, The role of tectonics and mass-transport complex emplacement on upper slope stratigraphic evolution: a 3D seismic case study from offshore Angola, Marine and Petroleum Geology, Vol: 44, Pages: 196-216
Three dimensional seismic-reflection data of the mid-Pliocene-to-Holocene upper slope succession, offshore Angola, provide an opportunity to constrain the stratigraphic context, distribution, external morphology and internal strain within mass-transport deposits (MTDs). These data also allow an assessment of the impact that erosion and relief associated with MTDs have on upper slope stratigraphy and depositional patterns, and the role that MTDs play in achieving ‘grade’ on submarine slopes. The study area is dissected by a series of NW-SE-striking, thin-skinned, salt-detached normal faults, which bound a slope-perpendicular, intra-slope horst that divides the study area into two depocentres. Three main seismic packages and their six constituent units have been mapped across the study area and reveal that, during the initial stages of deposition, a series of MTDs were emplaced, the thickness and distribution of which are controlled by the intra-slope horst. Substantial volumes of substrate were removed and entrained into the parent flow, and significant and irregular relief (150 m) was developed along MTDs upper surface. This MTD-rich package is interpreted to document a time when the slope was above grade, degradational processes dominated and sediment was trapped on the upper slope due to tectonic accommodation. Subsequent deposition was from either turbidity currents or and suspension fallout, at a time when the slope had begun to achieve ‘grade’ and depositional processes dominated. The associated depositional units display only minimal thickness variations with respect to the intra-slope horst, which had been ‘healed’ by this time; however, the unit displays pronounced and abrupt changes in thickness due to infilling of relief at the top of the preceding MTDs. The uppermost strata document a time when the slope was at grade and constructional process (i.e. aggradation and progradation) dominated. Deposition at this time was c
Magee C, Jackson CA-L, Briggs F, 2013, Lithological controls on igneous intrusion-induced ground deformation, In press, Journal of the Geological Society of London
Jackson CA-L, 2012, Seismic reflection imaging and controls on the preservation of ancient sill-fed magmatic vents, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 169, Pages: 503-506, ISSN: 0016-7649
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- Citations: 69
Jackson CA-L, Lewis MM, 2012, Origin of an anhydrite sheath encircling a salt diapir and implications for the seismic imaging of steep-sided salt structures, Egersund Basin, Northern North Sea, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 169, Pages: 593-599, ISSN: 0016-7649
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- Citations: 28
Schofield N, Heaton L, Holford SP, et al., 2012, Seismic imaging of 'broken-bridges': linking seismic to outcrop-scale investigations of intrusive magma lobes, Journal of the Geological Society of London, Vol: 169, Pages: 421-426
Three-dimensional seismic datasets have provided unrivalled insights into magma flow within sub-volcanic systems. One of the key revelations is that sills appear to be constructed of a series of discrete magma lobes that form during the emplacement of magma into host-rock. We focus on a large sill, within the Faroe–Shetland Basin, North Atlantic, that is well imaged on seismic data, and identify the presence of ‘broken bridges’ within the sill, developed between elongate magma lobes, and reveal for the first time in three dimensions the development of broken bridges. Critically, by relating the imaged structures to key outcrop-scale examples we confirm that bridge and broken-bridge structures are oriented perpendicular to the magma flow direction. This work thus demonstrates a key link that can be made between seismic-scale investigation of intrusions and sub-seismic (outcrop-scale) processes, highlighting the seemingly scale-invariant nature of the magmatic emplacement process.
Jackson CAL, 2012, The initiation of submarine slope failure and the emplacement of mass-transport deposits in salt-related minibasins: a 3D seismic reflection case study from the Santos Basin, offshore Brazil, Geological Society of America Bulletin, Vol: 124, Pages: 746-761
3D seismic reflection data are used to characterise the seismic expression and investigate the origin of two mass transport complexes, which are contained in two salt-related minibasins on the São Paulo Plateau, offshore SE Brazil. The mass transport complex contains numerous slide blocks, which are expressed on seismic data as broadly tabular packages of weakly-deformed reflections. Individual slides blocks are up to 50 m thick and up to 1 km2 in plan-view. The slide blocks are flanked by laterally continuous reflections, which are interpreted as the seismic expression of either a thin mudstone-dominated debrite deposit or a thin interval of hemipelagic mudstones. The surface that bounds the base of the mass transport complex is planar and this suggests that the associated gravity flow event was associated with only limited erosion of the seafloor. The upper surface of the mass transport complex is very rugose and onlapped by overlying strata, indicating that the slide blocks formed seabed relief of up to 20 m. The mass transport complex occurs at the base of a unit that thins towards the margins of the studied minibasins, and the slide blocks in the mass transport complex decrease in size and density away from the salt-cored structural high that separates the two minibasins. Based on its seismic-stratigraphic context and the spatial distribution of the slide blocks which is contains, the mass transport complex is interpreted to have been derived from the failure of material of the margins of the salt-cored high in response a period of relatively rapid minibasin subsidence. The results of this study indicate that large volumes of sedimentary material may be derived from the margins of salt-related minibasins in relatively distal submarine settings. From a geohazard perspective this observation is important, as it is typically thought that the risk associated with submarine slope failure, and the transport and emplacement of large blocks, is low in relatively
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