Publications
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Jackson CA-L, Elliott GM, Royce-Rogers E, et al., 2019, Salt thickness and composition influence rift structural style, northern North Sea, offshore Norway, BASIN RESEARCH, Vol: 31, Pages: 514-538, ISSN: 0950-091X
Wrona T, Magee C, Fossen H, et al., 2019, 3-D seismic images of an extensive igneous sill in the lower crust, Geology, Vol: 47, Pages: 729-733, ISSN: 0091-7613
When continents rift, magmatism can produce large volumes of melt that migrate upwards from deep below the Earths surface. To understand how magmatism impacts rifting, it is critical to understand how much melt is generated and how it transits the crust. Estimating melt volumes and pathways is difficult, however, particularly in the lower crust where the resolution of geophysical techniques is limited. New broadband seismic reflection data allow us to image the three-dimensional (3-D) geometry of magma crystallized in the lower crust (17.5-22 km depth) of the northern North Sea, in an area previously considered a magma-poor rift. The sub-horizontal igneous sill is 97 km long (N-S), 62 km wide (E-W), and 180 40 m thick. We estimate that 472 161 km3of magma was emplaced within this intrusion, suggesting that the northern North Sea contains more igneous intrusions than previously thought. The signi cant areal extent of the intrusion ( 2700 km2), as well as presence of intrusive steps, indicate sills can facilitate widespread lateral magma transport in the lower crust.
Pichel LM, Jackson CA-L, Peel F, et al., 2019, Base-salt relief controls salt-tectonic structural style, Sao Paulo Plateau, Santos Basin, Brazil, BASIN RESEARCH, ISSN: 0950-091X
Qiliang S, Jackson C, Magee C, 2019, Deeply buried ancient volcanoes control hydrocarbon migration in the South China Sea, Basin Research, ISSN: 0950-091X
Seismic reflection data image now‐buried and inactive volcanoes, both onshore and along the submarine portions of continental margins. However, the impact that these volcanoes have on later, post‐eruption fluid flow events (e.g. hydrocarbon migration and accumulation) is poorly understood. Determining how buried volcanoes and their underlying plumbing systems influence subsurface fluid or gas flow, or form traps for hydrocarbon accumulations, is critical to de‐risk hydrocarbon exploration and production. Here we focus on evaluating how buried volcanoes affect the bulk permeability of hydrocarbon seals, and channel and focus hydrocarbons. We use high‐resolution 3D seismic reflection and borehole data from the northern South China Sea (SCS) to show how ~<10 km wide, ~<590 m high Miocene volcanoes, buried several kilometers (~1.9 km) below the seabed and fed by a sub‐volcanic plumbing system that exploited rift‐related faults: (i) acted as long‐lived migration pathways, and perhaps reservoirs, for hydrocarbons generated from even more deeply buried (~8‐10 km) source rocks; and (ii) instigated differential compaction and doming of the overburden during subsequent burial, producing extensional faults that breached regional seal rocks. Considering that volcanism and related deformation are both common on many magma‐rich passive margins, the interplay between the magmatic products and hydrocarbon migration documented here may be more common than currently thought. Our results demonstrate that now‐buried and inactive volcanoes can locally degrade hydrocarbon reservoir seals and control the migration of hydrocarbon‐rich fluids and gas. These fluids and gases can migrate into and be stored in shallower reservoirs, where they may then represent geohazards to drilling and impact slope stability.
Sun Q, Jackson CA-L, Magee C, et al., 2019, Extrusion dynamics of deep-water volcanoes
<jats:p>Abstract. Submarine volcanism accounts for c. 75 % of the Earth's volcanic activity. Yet difficulties with imaging their exteriors and interiors mean the extrusion dynamics and erupted volumes of deep-water volcanoes remain poorly understood. Here, we use high-resolution 3-D seismic reflection data to examine the external and internal geometry, and extrusion dynamics of two Late Miocene-Quaternary, deep-water (> 2 km emplacement depth) volcanoes buried beneath 55–330 m of sedimentary strata in the South China Sea. The volcanoes have crater-like basal contacts, which truncate underlying strata, and erupted lava flows that feed lobate lava fans. The lava flows are > 9 km long and contain lava tubes that have rugged basal contacts defined by ~ 90 ± 23 m high erosional ramps. We suggest the lava flows eroded down into and were emplaced at shallow sub-surface depths within wet, unconsolidated, near-seafloor sediments. Extrusion dynamics were likely controlled by low magma viscosities, high hydrostatic pressures, and soft, near-seabed sediments, which collectively are characteristic of deep-water environments. Because the lava flows and volcanic edifices are imaged in 3D, we calculate the lava flows account for 50–97 % of the total erupted volume. Our results indicate deep-water volcanic edifices may thus form a minor component (~ 3–50 %) of the extrusive system, and that accurate estimates of erupted volume requires knowledge of the basal surface of genetically related lava flows. We conclude that 3D seismic reflection data is a powerful tool for constraining the geometry and extrusion dynamics of buried, deep-water volcanic features; such data should be used to image and quantify extrusion dynamics of modern deep-water volcanoes. </jats:p>
Osagiede E, Rotevatn A, Gawthorpe R, et al., 2019, Pre-existing intra-basement shear zones influence growth and geometry of non-colinear normal faults, western Utsira High–Heimdal Terrace, North Sea
Sun Q, Jackson C, Magee C, et al., 2019, Deeply buried ancient volcanoes control hydrocarbon migration in the South China Sea
Lenhart A, Jackson C, Bell RE, et al., 2019, Structural architecture and composition of crystalline basement offshore west Norway, Lithosphere, Vol: 11, Pages: 273-293, ISSN: 1941-8264
Numerous studies have investigated the geodynamic history and lithological composition of the Proterozoic basement, Caledonian nappes, and Devonian extensional basins and shear zones onshore west Norway. However, the offshore continuation of these structures, into the northern North Sea, where they are suspected to have influenced the structural evolution of the North Sea rift, is largely unknown. Existing interpretations of the offshore continuation of Caledonian and Devonian structures are based on simple map-view correlations between changes in offshore fault patterns and pronounced onshore structures, without providing evidence for the presence, nature, and geometry of offshore, basement-hosted structures.By integrating three-dimensional (3-D) seismic, borehole, and onshore geological and petrophysical data, as well as two-dimensional (2-D) forward modeling of gravity and magnetic data, we reveal the structural architecture and composition of the crystalline basement on the Måløy Slope, offshore west Norway. Based on 3-D mapping of intrabasement reflection patterns, we identified three basement units that can be correlated with the Caledonian thrust belt, and the major Devonian Nordfjord-Sogn detachment zone, located only 60 km to the east, onshore mainland Norway. Similar to that observed onshore, offshore crystalline basement of the Proterozoic basement (Western Gneiss Region) and allochthons is folded into large-scale antiforms and synforms. These units are separated by the strongly corrugated Nordfjord-Sogn detachment zone. Our analyses show that different types of crystalline basement can be distinguished by their seismic reflection character, and density and magnetic properties. We speculate that the main causes of the observed intrabasement reflectivity are lithological heterogeneities and strain-induced structures such as shear and fracture zones. Our interpretation of the architecture of crystalline basement offshore west Norway has importa
Howlett DM, Ge Z, Nemec W, et al., 2019, Response of unconfined turbidity current to deep-water fold and thrust belt topography: orthogonal incidence on solitary and segmented folds, Sedimentology, ISSN: 0037-0746
Seafloor topography of deep-water folds is widely considered to have a major impact on turbidity currents and their depositional systems, but understanding the flow response to such features was limited mainly to conceptual notions inspired by small-scale laboratory experiments. High-resolution 3D numerical experiments can compensate for the lack of natural-scale flow observations. The present study combines numerical modelling of thrusts with fault-propagation folds by Trishear3D software with computational fluid dynamics simulations of a natural-scale unconfined turbidity current by MassFlow-3D™ software. The study reveals the hydraulic and depositional responses of a turbidity current (~50 m thick) to typical topographic features that it might encounter in an orthogonal incidence on a seafloor deep-water fold and thrust belt. The supercritical current (~10 m s-1) decelerated and thickened due to the hydraulic jump on the fold backlimb counter-slope, where a reverse overflow formed through current self-reflection and a reverse underflow was issued by backward squeezing of a dense near-bed sediment load. The reverse flows were re-feeding sediment to the parental current, reducing its waning rate and extending its runout. The low-efficiency current, carrying sand and silt, outran a downslope distance of >17 km with only modest deposition (<0.2 m) beyond the fold. Most of the flow volume diverted sideways along the backlimb to surround the fold and spread further downslope, with some overspill across the fold and another hydraulic jump at the forelimb toe. In the case of a segmented fold, a large part of the flow went downslope through the segment boundary. Preferential deposition (0.2–1.8 m) occurred on the fold backlimb and directly upslope, and on the forelimb slope in the case of a smaller fold. The spatial patterns of sand entrapment revealed by the study may serve as guidelines for assessing the influence of substrate folds on turbiditic sedi
Wrona T, Magee C, Fossen H, et al., 2019, 3-D seismic images of an extensive igneous sill in the lower crust
Fernandez N, Hudec M, Jackson C, et al., 2019, The competition for salt and kinematic interactions between minibasins during density-driven subsidence: observations from numerical models
Duffy O, Fernandez N, Peel F, et al., 2019, Obstructed Minibasins on a Salt-Detached Slope: An Example from above the Sigsbee Canopy, Northern Gulf of Mexico
Jackson C, Magee C, Hunt-Stewart E, 2019, Cenozoic contourites in the eastern Great Australian Bight, offshore southern Australia: implications for the onset of the Leeuwin Current, Journal of Sedimentary Research, ISSN: 1527-1404
Thermohaline oceanic currents influence global heat transfer, controlling local and global variations in climate, biodiversity, and the terrestrial biosphere. Paleoceanographic studies typically use biostratigraphic and geochemical proxies to reconstruct the dynamics of these currents in Earth’s ancient oceans, although seismic reflection data have also been successfully employed, most commonly in the North Atlantic Ocean. Here we use 2D seismic reflection data from the Ceduna Sub-basin, Great Australian Bight, offshore southern Australia to describe middle Eocene-to-Recent contourites deposited within an overall carbonate-dominated succession. These deposits comprise large (100 m wavelength by up to 50 m tall) bedforms and deep (10–90 m), wide (up to 3 km) erosional scours. The scours are particularly well-developed at one specific stratigraphic level, defining moats that encircle Middle Eocene shield volcanoes, which formed syn-depositional bathymetric highs. We suggest that sediment erosion, transport, and deposition record middle Eocene initiation of the Leeuwin Current, one of the most important ocean currents in the southern hemisphere. Deepest seabed scouring occurs within the middle of the middle Eocene-to-Recent sequence, and may reflect middle Miocene waxing of the so-called ‘proto-Leeuwin Current’, possibly driven by changes in ocean circulation patterns caused by the Miocene Global Optimum. The results of this seismic reflection-based study are consistent with results derived from other paleoceanographic proxies, thereby highlighting the continued key role seismic reflection data have in understanding the occurrence, geographical distribution, and significance of ancient ocean currents.
Magee C, Hoggett M, Jackson CA-L, et al., 2019, Burial-related compaction modifies intrusion-induced forced folds: implications for reconciling roof uplift mechanisms using seismic reflection data, Frontiers in Earth Science, Vol: 7, ISSN: 2296-6463
Space for shallow-level sills and laccoliths is commonly generated by bending and uplift of overlying rock and sediment. This so-called “roof uplift” produces forced folds, the shape and amplitude of which reflect the geometry of underlying intrusions. The surface expression of forced folds can therefore be inverted to constrain intruding magma body properties, whilst ancient forced folds provide a record of sill and laccolith emplacement. Deciphering how shallow-level intrusion translates into roof uplift is thus critical to enhancing our understanding and forecasting of magma emplacement. To-date, emplacement models and surface deformation inversions are underpinned by the consideration that roof uplift is, to a first-order, an elastic process. However, several studies have suggested inelastic processes can accommodate significant magma volumes, implying first-order roof uplift may be a function of elastic and inelastic deformation. In particular, seismic reflection images of forced folds above ancient sills and laccoliths have been used to argue that final fold amplitudes can be substantially less (by up to 85%) than the underlying intrusion thickness. Although these seismic-based observations imply elastic and inelastic deformation accommodated intrusion, these studies do not consider whether burial-related compaction has reduced the original fold amplitude. Here, we use geological (e.g., lithology) and geophysical (e.g., seismic velocity) information from the Resolution-1 borehole offshore eastern New Zealand, which intersects a forced fold and upper ~50 m of a sill imaged in 2D seismic reflection data, to decompact the folded sequence and recover its original geometry. We show the Resolution Sill is likely ~117–187 m thick, depending on the interval velocity for the entire intrusion, whereas the forced fold has an apparent maximum amplitude of ~127 m, corresponding to a sill thickness-fold amplitude discrepancy of up to 47%. Decompaction indi
Pichel LM, Jackson C, Peel FJ, et al., 2019, Effects of Pre-Salt Relief on Salt Tectonics on the São Paulo Plateau and Implications for the Albian Gap, Basin Research, ISSN: 0950-091X
Pre-salt relief has been recently shown to significantly influence salt flow, producing three-dimensionally complex strain distribution and multiphase deformation within the evaporite sequence and overburden. The São Paulo Plateau, Santos Basin, Brazil is a prolific hydrocarbon province situated downdip of the Albian Gap, characterized by > 2 km thick, mechanically layered Aptian salt, prominent basal relief and a complex framework of supra-salt structures. This study uses 3D seismic data combined with physical and kinematic models to demonstrate how gravity-driven translation above thick salt with complex basal relief generated this framework. A series of ramp-syncline basins occur above and downdip of the main pre-salt highs indicating c. 30 km of translation in the area. As the system translated downdip, salt flux variations caused by significant base-salt relief resulted in non-uniform motion of the cover with simultaneous development of extensional and contractional structures and multiphase reactivation during the Late Cretaceous-Paleocene. Contraction occurred preferentially above landward-dipping base-salt ramps and downdip of basinward-dipping base-salt ramps where motion decelerated. Extension occurred at the top of basinward-dipping ramps and base-salt plateaus, where flow accelerated. Where base-salt was broadly flat, structures evolved primarily by load-driven subsidence and diapirism. At the edge of or around smaller base-salt highs, salt structures were affected by plan-view rotation, shearing and radial flow. To the north, where earlier Albian growth occurred, deformation is marked by a polygonal plan-view framework that is also a consequence of oblique flow driven by the concave shape of the margin. The observed translation and deformation style in the area affords an improved kinematic model for the enigmatic Albian Gap located further updip. These observations contribute to the long-lived debate regarding the mechanisms of salt tectonics
Wu N, Jackson C, Johnson H, et al., 2019, Lithological, petrophysical and seal properties of mass-transport complexes (MTCs), northern Gulf of Mexico
Ge Z, Gawthorpe R, Rotevatn A, et al., 2019, Minibasin depocentre migration during diachronous salt welding, offshore Angola
Jackson C, Duffy O, Fernandez N, et al., 2019, The Stratigraphic Record of Minibasin Subsidence, Precaspian Basin, Kazakhstan
Jackson CA-L, Zhang Y, Herron D, et al., 2019, Subsurface expression of a salt weld, Gulf of Mexico, Petroleum Geoscience, Vol: 25, Pages: 102-111, ISSN: 1354-0793
Salt welds form due to salt expulsion and thinning by mechanical (e.g. salt flow) and/or chemical (e.g. salt dissolution) processes. Despite being ubiquitous in salt-bearing sedimentary basins, where they may trap large volumes of hydrocarbons, little is published on weld thickness and composition. We here use 3D seismic reflection, borehole, and biostratigraphic data from the Atwater Valley protraction area of the northern Gulf of Mexico to constrain the thickness and composition of a tertiary salt weld. Seismic data image an ‘apparent weld’ (sensu Wagner & Jackson 2011) at the base of a Plio-Pleistocene minibasin that subsided into allochthonous salt. Borehole data indicate the weld is actually ‘incomplete’, being c. 24 m thick, and containing an upper 5 m thick halite and a lower 15 m thick halite, separated by a 4 m thick mudstone. The age and origin of the intra-weld mudstone is unclear, although we speculate it is either: (i) Late Jurassic, representing material transported upwards from the autochthonous level within a feeder, and subsequently trapped as allochthonous salt thinned and welded, or, perhaps more likely; (ii) Pliocene, representing a piece of salt carapace reworked from the top of and eventually trapped in, the now locally welded sheet. We show that 3D seismic reflection data may not resolve salt weld thickness, with the presence of relatively thin remnant salt lending support to models of welding based on viscous flow. Furthermore, the halite-dominated character of the weld supports the hypothesis that tectonic purification may occur during salt flow.
Lenhart A, Jackson C, Bell R, et al., 2019, Structural architecture and composition of crystalline basement offshore west Norway
<jats:p>Numerous studies have investigated the geodynamic history and lithological composition of the Proterozoic basement, Caledonian nappes, and Devonian extensional basins and shear zones onshore west Norway. However, the offshore continuation of these structures, into the northern North Sea, where they are suspected to have influenced the structural evolution of the North Sea rift, is largely unknown. Existing interpretations of the offshore continuation of Caledonian and Devonian structures are based on simple map-view correlations between changes in offshore fault patterns and pronounced onshore structures, without providing evidence for the presence, nature, and geometry of offshore, basement-hosted structures. By integrating three-dimensional (3-D) seismic, borehole, and onshore geological and petrophysical data, as well as two-dimensional (2-D) forward modeling of gravity and magnetic data, we reveal the structural architecture and composition of the crystalline basement on the Måløy Slope, offshore west Norway. Based on 3-D mapping of intrabasement reflection patterns, we identified three basement units that can be correlated with the Caledonian thrust belt, and the major Devonian Nordfjord-Sogn detachment zone, located only 60 km to the east, onshore mainland Norway. Similar to that observed onshore, offshore crystalline basement of the Proterozoic basement (Western Gneiss Region) and allochthons is folded into large-scale antiforms and synforms. These units are separated by the strongly corrugated Nordfjord-Sogn detachment zone. Our analyses show that different types of crystalline basement can be distinguished by their seismic reflection character, and density and magnetic properties. We speculate that the main causes of the observed intrabasement reflectivity are lithological heterogeneities and strain-induced structures such as shear and fracture zones. Our interpretation of the architecture of crystalline basement offshore west Nor
Magee C, Ernst RE, Muirhead J, et al., 2019, Magma transport pathways in large igneous provinces: Lessons from combining field observations and seismic reflection data, Dyke Swarms of the World: A Modern Perspective, Editors: Srivastava, Ernst, Peng, Publisher: Springer, Pages: 45-85, ISBN: 9789811316654
Large Igneous Province (LIP) formation involves the generation, intrusion, and extrusion of significant volumes (typically > 1 Mkm3) of mainly mafic magma and is commonly associated with episodes of mantle plume activity and major plate reconfiguration. Within LIPs, magma transport through Earth’s crust over significant vertical (up to tens of kilometres) and lateral (up to thousands of kilometres) distances is facilitated by dyke swarms and sill-complexes. Unravelling how these dyke swarms and sill-complexes develop is critical to: (i) evaluating the spatial and temporal distribution of contemporaneous volcanism and hydrothermal venting, which can drive climate change; (ii) determining melt source regions and volume estimates, which shed light on the mantle processes driving LIP formation; and (iii) assessing the location and form of associated economic ore deposits. Here, we review how seismic reflection data can be used to study the structure and emplacement of sill-complexes and dyke swarms. We particularly show that seismic reflection data can reveal: (i) the connectivity of and magma flow pathways within extensive sill-complexes; (ii) how sill-complexes are spatially accommodated; (iii) changes in the vertical structure of dyke swarms; and (iv) how dyke-induced normal faults and pit chain craters can be used to locate sub-vertical dykes offshore.
Clare M, Chaytor J, Dabson O, et al., 2019, A consistent global approach for the morphometric characterization of subaqueous landslides, SUBAQUEOUS MASS MOVEMENTS AND THEIR CONSEQUENCES: ASSESSING GEOHAZARDS, ENVIRONMENTAL IMPLICATIONS AND ECONOMIC SIGNIFICANCE OF SUBAQUEOUS LANDSLIDES, Vol: 477, Pages: 455-477, ISSN: 0305-8719
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Pichel L, Jackson C, Peel F, et al., 2018, Base-Salt Relief Controls on Salt-Tectonic Structural Style, São Paulo Plateau, Santos Basin, Brazil
Jackson C, Royce-Rogers E, Elliott GM, et al., 2018, Salt thickness and composition influence rift structural style, northern North Sea, offshore Norway, Basin Research, Vol: 31, Pages: 514-538, ISSN: 0950-091X
‘Salt’ giants are typically halite‐dominated, although they invariably contain other evaporite (e.g. anhydrite, bittern salts) and non‐evaporite (e.g. carbonate, clastic) rocks. Rheological differences between these rocks mean they impact or respond to rift‐related, upper crustal deformation in different ways. Our understanding of basin‐scale lithology variations in ancient salt giants, what controls this, and how this impacts later rift‐related deformation, is poor, principally due to a lack of subsurface datasets of sufficiently regional extent. Here we use 2D seismic reflection and borehole data from offshore Norway to map compositional variations within the Zechstein Supergroup (Lopingian), relating this to the structural styles developed during Middle Jurassic‐to‐Early Cretaceous rifting. Based on the proportion of halite, we identify and map four intrasalt depositional zones (sensu Clark et al., 1998) offshore Norway. We show that, at the basin margins, the Zechstein Supergroup is carbonate‐dominated, whereas towards the basin centre, it become increasingly halite‐dominated, a trend observed in the UK sector of the North Sea Basin and in other ancient salt giants. However, we also document abrupt, large magnitude compositional and thickness variations adjacent to large, intra‐basin normal faults; for example, thin, carbonate‐dominated successions occur on fault‐bounded footwall highs, whereas thick, halite‐dominated successions occur only a few kilometres away in adjacent depocentres. It is presently unclear if this variability reflects variations in syn‐depositional relief related to flooding of an underfilled presalt (Early Permian) rift or syn‐depositional (Lopingian) rift‐related faulting. Irrespective of the underlying controls, variations in salt composition and thickness influenced the Middle Jurassic‐to‐Early Cretaceous rift structural style, with diapirism characterising hangingwall basins where autochthonous salt was thick and halite‐rich
Magee C, Jackson C, 2018, Can we relate the surface expression of dike-induced normal faults to subsurface dike geometry?
Turner CC, Cronin BT, Riley LA, et al., 2018, The South Viking Graben: Overview of Upper Jurassic Rift Geometry, Biostratigraphy, and Extent of Brae Play Submarine Fan Systems, Rift-related coarse-grained submarine fan reservoirs; the Brae Play, South Viking Graben, North Sea, Publisher: AAPG, Pages: 9-38, ISBN: 978-0-89181-395-8
The South Viking Graben (SVG) hosts many large oil and gas condensate reservoirs, some within Middle Jurassic and Cenozoic rocks, but most within thick submarine fan sandstone and conglomerate sequences of the Upper Jurassic Brae Formation and their correlative equivalents, collectively termed here the Brae Play. Regional studies carried out over the last few years (based on the extensive well database and a variety of 3-D seismic data) and the recent acquisition of extensive, high-quality, broadband 3-D seismic data across the SVG have led to better definition of the half-graben geometry and the extents of the Upper Jurassic submarine fans that host these hydrocarbon accumulations. A summary structure map, seismic sections that extend across the graben, and a 3-D image of the “Base Cretaceous” are used to illustrate the main structural features. On its western side, the top of an eroded scarp, which grades downdip into the major fault plane, can be used as the lateral limit of the postrift graben fill. The uppermost Kimmeridge Clay Formation (KCF; termed Draupne Formation in Norway), which is the top seal and dominant source rock for Brae Play fields, onlaps this eroded slope and limits the western extent of the synrift section. At depth, the top of the prerift Bathonian Sleipner Formation can be mapped along this fault margin abutting the uneroded footwall fault; this boundary defines the edge of the thickest Upper Jurassic synrift section within the graben. The top of the prerift section becomes progressively shallower to the east, where an approximate minimum limit of the graben can be defined along much of its length by the eastern limit of seismically mappable KCF (Draupne) Formation. Thick sequences of Upper Jurassic conglomerates and sandstones within the KCF (i.e., the Brae Formation) were deposited as submarine fans within the graben. Most sediment was derived from the west (i.e., the Fladen Ground Spur), but some important fan systems were fed
Jackson CAL, 2018, Growth of a Salt-Detached Normal Fault and Controls on Throw Rate Variability; Gudrun Field, South Viking Graben, Offshore Norway, Rift-related coarse-grained submarine fan reservoirs; the Brae Play, South Viking Graben, North Sea, Editors: Turner, Cronin, Publisher: AAPG, Pages: 423-444, ISBN: 978-0-89181-395-8
The growth and throw/displacement rate variability on normal faults can reflect fault interaction, plate tectonic forces and, in gravity-driven systems, variations in sediment loading. Because earthquakes may occur as faults slip, it is important to understand what processes influence throw rate variability on normal faults to be able to predict seismic hazards in extensional terranes. Furthermore, the rate of normal fault growth directly controls rift physiography, sediment erosion, dispersal and deposition, and the distribution and stratigraphic architecture of syn-rift reservoirs. Instrumental (e.g. geodetic) data may constrain the very short-term (i.e. days to years) throw rate history of normal faults, whereas palaeoearthquake data may provide important information on medium-term (i.e. 103-105 years) rates. Constraining longer-term (i.e. >106 Myr) variations typically requires the use of seismic reflection data, although their application may be problematic because of poor seismic resolution and the absence of, or poor age constraints on, coeval growth strata. In this study I use 3D seismic reflection and borehole data to constrain the growth and long-term throw rate variability on a gravity-driven, salt-detached normal fault (Middle-to-Late Jurassic) in the South Viking Graben, offshore Norway, and to assess the impact of throw rate variability on the thickness and character of syn-rift reservoirs. I recognise five kinematic phases: (i) Phase 1 (early Callovian) - fault initiation and a phase of moderate fault throw rates (0.06 mm yr-1); (ii) Phase 2 (early Callovian-to-end Callovian) - fault inactivity, during which time the fault was buried by sediment; (iii) Phase 3 (early Oxfordian-to-late Oxfordian) - fault reactivation and a phase of moderate throw rates (up to 0.03 mm yr-1); (iv) Phase 4 (late Oxfordian-to-end Oxfordian) – a marked increase in throw rate (up to 0.27 mm yr-1); and (v) Phase 5 (early Kimmeridgian-to-middle Volgian) – a decl
Narock T, Goldstein E, Jackson C, et al., 2018, Earth Science is Ready for Preprints: The First Year of EarthArXiv
Magee C, Hoggett M, Jackson C, et al., 2018, Burial-related Compaction Modifies Intrusion-induced Forced Folds: Implications for Reconciling Roof Uplift Mechanisms using Seismic Reflection Data
Bastow IA, Booth AD, Corti G, et al., 2018, The development of late-stage continental breakup: seismic reflection and borehole evidence from the Danakil Depression, Ethiopia, Tectonics, Vol: 37, Pages: 2848-2862, ISSN: 0278-7407
During continental breakup, the locus of strain shifts from a broad region of border faulting and ductile plate stretching to a narrow zone of magma intrusion in a young ocean basin. Recent studies of volcanic rifts and margins worldwide suggest this shift occurs sub‐aerially, before the onset of seafloor spreading. We test this hypothesis using recently‐acquired seismic reflection and borehole data from the Danakil Depression, Ethiopia, a unique region of transition between continental rifting and seafloor spreading. Our data, located near Dallol, ~30km northwest of the Erta'Ale Volcanic Segment (EAVS), reveal a remarkably‐thick (>1km) sequence of young (~100ka) evaporites in a basin bound by a major (≤400m throw), east‐dipping normal fault. To generate such a large amount of subsidence in such a relatively short time, we propose that upper‐crustal extension in Danakil is currently dominated by faulting, not magmatic intrusion. Given the region's markedly thinned crust (~15‐km‐thick), relative to elsewhere in Afar where magma‐assisted rifting dominates and maintains crustal thickness at ~25km, mechanical extension in Danakil is likely coupled with ductile extension of the lower‐crust and mantle lithosphere. Despite proximity to the voluminous lavas of the active EAVS, evidence for igneous material in the upper ~2km of the 6–10‐km‐wide basin is limited. Late‐stage stretching was likely aided by thermal/strain‐induced lithospheric weakening following protracted magma‐assisted rifting. Basin formation immediately prior to the onset of seafloor spreading may also explain the accumulation of thick marine‐seepage‐fed evaporite sequences akin to those observed, for example, along the South Atlantic rifted margins.
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