385 results found
Dobb EM, Magee C, Jackson CA-L, et al., 2024, Impact of igneous intrusion and associated ground deformation on the stratigraphic record, Geological Society, London, Special Publications, Vol: 525, ISSN: 0305-8719
<jats:title>Abstract</jats:title> <jats:p>The geomorphology and sediment systems of volcanic areas can be influenced by uplift (forced folding) related to subsurface migration and accumulation of magma. Seismic geomorphological analysis presents a unique tool to study how surface morphology and subsurface magma dynamics relate, given seismic reflection data can image buried landscapes and underlying intrusions in 3D at resolutions of only a few metres–decametres. However, differential compaction of the sedimentary sequence above incompressible igneous intrusions during burial modifies palaeosurface morphology. Here we use 3D seismic reflection data from offshore NW Australia to explore how the stratigraphic record of igneous intrusion and associated ground deformation can be unravelled. We focus on a forced fold that likely formed in the Early Cretaceous to accommodate intrusion of magma, but which was later amplified by burial-related differential compaction of the host sedimentary sequence. We show how: (1) marine channels and clinoforms may be deflected by syn-depositional intrusion-induced forced folds; and (2) differential compaction can locally change clinoforms depth post-deposition, potentially leading to erroneous interpretation of shoreline trajectories. Our results demonstrate seismic geomorphological analysis can help us better understand how magma emplacement translates into ground deformation, and how this shapes the landform of volcanic regions.</jats:p>
Nakken L, Chiarella D, Jackson CAL, 2023, Late Jurassic rift physiography of the Froan Basin and Frøya High, offshore Mid-Norway: Development of a syn-rift shallow marine system, Basin Research, Vol: 35, Pages: 1908-1932, ISSN: 0950-091X
The Froan Basin and Frøya High are two major structural elements located on the Mid-Norwegian Continental Shelf and are separated from the Halten Terrace by major west-dipping normal fault zones. Compared to the Halten Terrace, the Froan Basin and Frøya High are relatively under-explored and remain poorly understood in terms of their Late Jurassic tectono-stratigraphic evolution. Upper Jurassic, shallow marine, syn-rift deposits (i.e. Rogn Formation) are present locally, but their source, delivery system and depositional environment are not yet well understood. Improving our understanding of how fault activity and rift-shoulder uplift influenced rift physiography and paleowater depths is crucial when developing depositional models in this region. In this study, we present a model of the Late Jurassic rift physiography of the Froan Basin and Frøya High based on seismic reflection and well data and reverse subsidence modelling. We show that during the Late Jurassic to Early Cretaceous, major footwall uplift caused the Frøya High and the western margin of the central Froan Basin to be subaerially exposed, forming an intra-rift footwall island. Shallow marine areas to the east, immediately adjacent to the footwall island, accumulated sediment supplied from the uplifted and partially eroded footwall. In contrast, the Trøndelag Platform, north of the Froan Basin and Frøya High, remained submerged throughout the rift episode. We therefore suggest that the extent of the shallow marine system was controlled by the magnitude of footwall uplift along the western margin of the basin and that sediment dispersal was influenced by the coastal paleogeomorphology of the back-tilted footwall.
Amarante F, Kuchle J, Jackson C, et al., 2023, The cryptic stratigraphic record of the syn- to post-rift transition in the offshore Campos Basin, SE Brazil
<jats:p>Rift basins typically comprise three main tectono-stratigraphic stages; pre-, syn-, and post-rift. The syn-rift stage is often characterised by the deposition of asymmetric wedges of growth strata that record differential subsidence caused by active normal faulting. The subsequent post-rift stage is defined by long-wavelength subsidence driven by lithospheric cooling, and is typified by the deposition of broadly tabular stratal packages that drape any rift-related relief. The stratigraphic contact between syn- and post-rift rocks is often thought to be represented by an erosional unconformity. However, the late syn-rift to early post-rift stratigraphic record is commonly far more complex since: (i) the associated tectonic transition is not instantaneous; (ii) net-subsidence may be punctuated by transient periods of uplift; and (iii) strain often migrates oceanward during rifting until continental breakup is achieved with crustal rupture. The Eastern Brazilian marginal basins have not historically used the tripartite scheme outlined above, with the post-pre-rift interval instead being subdivided into rift, sag, and passive margin tectono-stratigraphic stages. The sag stage has been previously described as late syn-rift, early post-rift, or as a transition between the two, with the passive margin stage being equivalent to the classically defined post-rift, drift stage. Two (rather than one) erosional unconformities are also identified within the rift-to-sag succession. In this work, we use 2D and 3D seismic reflection and borehole data to discuss the expression of and controls on the syn- to post-rift transition in the shallow and deep water domains of the south-central Campos Basin, southeast Brazil. We identified three seismic-stratigraphic sequences bounded by unconformities. The lower pre-salt interval is characterised by wedge-shaped packages of reflections that thicken towards graben and half-graben-bounding normal faults. This stage ends with a de
Osagiede EE, Nixon CW, Gawthorpe R, et al., 2023, Topological Characterization of a Fault Network Along the Northern North Sea Rift Margin, Tectonics, Vol: 42, ISSN: 0278-7407
The factors that control the spatial variation of the topological characteristics of normal fault networks at the rift-scale are poorly understood. Here, we use 3D seismic reflection data from the northern North Sea to investigate the spatial variation of the geometry, topology, and strain heterogeneity of the Late Jurassic normal fault network along the rift margin. Our results show that fault orientation varies spatially along the rift margin. Normal faults within fault blocks that are adjacent to the North Viking Graben exhibits dominant N-S and NE-SW strikes that are sub-parallel to the graben axis and associated step-over, whereas in fault blocks farther from the graben, there is a dominant NW-SE strike. Furthermore, we identify two broad topological domains within the fault network: (a) dominated by isolated nodes, partially connected branches, and low fault connectivity, and (b) dominated by abutting nodes, fully connected branches, and moderate to high fault connectivity. These topological domains correlate with previous sub-division of the rift margin in the northern North Sea into platform and sub-platform structural domains, respectively. There is also a positive correlation between the spatial variability of the fault orientations and intensity, with the fault network connectivity, highlighting the relationship between normal fault geometry and topology. We conclude that the across and along-strike variation in strain, presence of pre-existing structures, and accommodation zone-related deformation are key factors influencing the spatial variation of fault network properties at the rift scale.
Martinez-Doñate A, Kane IA, Hodgson DM, et al., 2023, Stratigraphic change in flow transformation processes recorded in early post-rift deep-marine intraslope lobe complexes, Sedimentology, Vol: 70, Pages: 1379-1412, ISSN: 0037-0746
The Early Jurassic Los Molles Formation in the Neuquén Basin of western Argentina is a rare example of well-exposed syn-rift to post-rift stratigraphy. In the Chachil Graben, the onset of the early post-rift stage is marked by drowning of a carbonate system and the development of two deep-marine intraslope lobe complexes. This field-based study in the Chachil Graben involved field mapping and correlating eleven stratigraphic logs, and petrographic analysis to document how grain size and texture within intraslope lobe sandstones change from the lobe centre to their frontal pinch-out. Eight different bed-scale facies are identified and inferred to be formed by turbulent (turbidites; Type A and B beds), transient turbulent–laminar (transitional flow deposits; Type C, D, E and F beds), laminar gravity flows (debrites; Type G) and post-depositional clastic injections (injectites; Type H beds). Fifteen lobes form two stacked lobe complexes that show stratigraphic evolution from a lower argillaceous sandstone-dominated lobe complex, built by transitional flow deposits, to an upper coarser-grained, sandier lobe complex largely constructed by turbidites. Petrographic analysis quantified sandstone mineralogy, matrix content, grain size and sorting, revealing that both lobe complexes are volcanic arc-sourced. This study proposes that the differences in the character of the two lobe complexes are due to maturation of sediment transport routes through progressive healing of the intraslope relief, with a concomitant decrease in substrate erosion and flow bulking. Also proposed here is a model for intraslope lobe complex development that accounts for the impact of flow-confinement on flow behaviour and transformation induced by the inherited topography. Bed type distribution suggests that high-density flows terminate more abruptly against confining slopes and produce greater depositional variability than lower-density flows. This integrated petrographic, architectural
Alghuraybi A, Bell R, Jackson C, 2023, A snapshot of the earliest stages of normal fault growth, Tektonika, Vol: 1, Pages: 11-31, ISSN: 2976-548X
Observations of how faults lengthen and accrue displacement during the very earliest stages of their growth are limited, reflecting the fact that the early syn-kinematic sediments that record this growth are often deeply buried and difficult to image with geophysical data. Here, we use borehole and high-quality 3D seismic reflection data from SW Barents Sea, offshore Norway to quantify the lateral propagation (c. 0.38 – 3.4 mm/year) and displacement accumulation (c. 0.0062 – 0.025 mm/year) rates (averaged over 6.2 Myr) for several long (up to 43 km), moderate displacement (up to 155 m), syn-kinematic faults that we argue provide a unique, essentially ‘fossilised’ snapshot of the earliest stage of fault growth. We show that lateral propagation rates were up to 300 times faster than displacement rates during the initial ~25% of fault lifespan, suggesting that these faults lengthened much more rapidly than they accrued displacement. Our inference of rapid lengthening is also supported by geometric observations including: (i) low Dmax/Lmax (<0.01) scaling relationships, ii) high (>5) length/height aspect ratios, iii) broad, bell-shaped throw-length profiles, and iv) hangingwall depocenters forming during deposition of the first seismically detectable stratigraphic unit spanning the length of the fault. We suggest that the high ratio between lateral propagation rate and displacement rate is likely due to relative immaturity of the studied fault system, an interpretation that supports the ‘constant-length’ fault growth model. Our results highlight the need to document both displacement and lateral propagation rates to further our understanding of how faults evolve across various temporal and spatial scales.
Andrews B, Mildon Z, Jackson C, 2023, The impact of human factors and measurement obliquity when extracting geological slip-rate from seismically imaged normal faults.
<jats:p>Seismic reflection datasets can help unpick the long term (i.e., 100 kyr to Ma) slip history of active normal faults (e.g., Nicol et al., 2005). To constrain slip-rate from seismically imaged normal faults you measure the across-fault offset of stratigraphic markers of known age. &#160;Ideally, this is undertaken parallel to the slip-vector, i.e., orthogonal to fault-strike. In many active systems this is not possible with only non-optimally orientated 2D surveys available. Here we assess how obliquity effects continuous and discontinuous fault properties (throw, heave, dip, displacement) extracted from normal faults imaged in a 3D seismic cube. We targeted &#8216;straight&#8217; faults and extracted cut off data from sequentially oblique sample lines ranging from &#177;50&#730;, comparing oblique data to that extracted from optimally orientated lines. Additionally, repeat picks were undertaken on two horizons to investigate the relative importance of measurement obliquity and human error.Oblique measurements showed different along-fault profiles compared to orientated sample lines. This causes some datasets to be statistically different, with >100 % difference occasionally observed. Continuous deformation is more prone to obliquity errors, with the measurement of an apparent dip causing heave, and therefore displacement and dip, to display large differences at high obliquity. The dip of horizons close to the fault and localised complexity at the sample location (e.g., nearby faults) are also important factors. Differences regularly exceed 20% at high obliquity and we therefore suggest obliquity should not exceed 15&#730; and were this is not possible measurements are corrected using fault cut offs and local fault strike.For repeats picks, the shape of along-fault profiles is similar; however, subtle differences exist. Variability depends on the fault and fault parameter, with greater differences o
Wrona T, Whittaker AC, Bell RE, et al., 2023, Rift kinematics preserved in deep-time erosional landscape below the northern North Sea, Basin Research, Vol: 35, Pages: 744-761, ISSN: 0950-091X
Our understanding of continental rifting is, in large parts, derived from the stratigraphic record. This record is, however, incomplete as it does not often capture the geomorphic and erosional signal of rifting. New 3D seismic reflection data reveal a Late Permian-Early Triassic landscape incised into the pre-rift basement of the northern North Sea. This landscape, which covers at least 542 km2, preserves a drainage system bound by two major tectonic faults. A quantitative geomorphic analysis of the drainage system reveals 68 catchments, with channel steepness and knickpoint analysis of catchment-hosted palaeo-rivers showing that the landscape preserved a >2 Myr long period of transient tectonics. We interpret that this landscape records a punctuated uplift of the footwall of a major rift-related normal fault (Vette Fault) at the onset of rifting. The landscape was preserved by a combination of relatively rapid subsidence in the hangingwall of a younger fault (Øygarden Fault) and burial by post-incision sediments. As such, we show how and why erosional landscapes are preserved in the stratigraphic record, and how they can help us understand the tectono-stratigraphic evolution of ancient continental rifts.
Amarante F, Jackson C, Pichel L, 2023, Post-salt magmatism in the Campos Basin, offshore SE Brazil: style, distribution, and relationship to salt tectonics
<jats:p>Substantial magmatism occurred during the development of the marginal basins of the central and southern South Atlantic. Situated on the Brazilian side of the central segment, the Campos and Santos basin represent a transitional margin, located between the magma-rich margin in the north and the magma-poor margin in the south. In addition to magmatism associated with the initiation of continental rifting, the southeast Brazilian basins experienced three main magmatic events; one during the early post-rift (i.e., sag stage) and two during the late post-rift (i.e., passive margin stage), both occurring after deposition of a thick, late Aptian salt layer. The products of post-salt, intrusive and extrusive magmatism in the southern Campos Basin are imaged in seismic reflection data and have been directly penetrated by boreholes, yet they remain poorly understood in terms of their style, detailed geometry, and distribution. Furthermore, the temporal, spatial and possibly genetic relationships between these post-salt igneous products and salt-tectonics are largely unknown. Documenting these possible salt-magma interactions is important to understanding the tectono-stratigraphic evolution of Campos Basin and other salt-bearing passive margin basins subject to magmatic activity. We use 2D and 3D seismic reflection and borehole data from the southeastern Campos Basin, offshore Brazil to map and characterize post-salt igneous sills and volcanoes, and to understand the interaction between salt tectonics and igneous products. We identified 99 sills emplaced within uppermost Aptian-to-Maastrichtian strata, 83 emplaced above the salt and 16 intra-salt, and 15 volcanoes within Upper Cretaceous-to-lower Paleogene strata, associated with a >310 km² lava field. We also identify four, subsalt-sourced, vent-like structures, which vary in age from Paleogene to Late Cretaceous. Salt and overburden structures define a domain of extensional deformation on a base-sa
<jats:p>Geography, Earth and Environmental Science (GEES) research will play a vital role in addressing the grand challenges of the 21st century, contributing to many of the UN sustainable development goals and the global energy transition. However, geoscience knowledge cannot be successfully applied to global problems that impact people from all walks of life unless the discipline itself is equitable. There is a well-documented racial and ethnic diversity crisis in GEES subjects in the Global North1 that leads to inequities in who does environmental research. The Equator project set out to increase participation and retention of UK-domiciled Black, Asian and minority ethnic postgraduate research (PGR) students in GEES topics. Our goal was to improve equity and diversity in a research area critical to a more sustainable future; not because of a business case, or for diversity as resource- but for social justice.Equator was a six-month project, funded by the Natural Environment Research Council (NERC), that developed three evidence-based interventions targeting different barriers to racial and ethnic diversity in GEES research. To remove barriers to access, a doctoral training working group was formed to share best practice and develop recommendations to make PhD recruitment more equitable. To improve access and participation, a ring-fenced research school for ethnic minority undergraduate, masters and doctoral students was delivered. To increase retention and improve student experience, a targeted mentoring network pairing students with mentors from both industry and academia was created.Evaluation of interventions took the form of action research with a Theory of Change approach, with surveys used to capture thoughts and reflections in each of the three work packages. This occurred alongside collaborative, self-reflective inquiry within the project team and steering committee. The steering committee included grassroots organisations, higher education institut
Zhang Y, Jackson C, Darraj N, et al., 2023, Carbon dioxide storage resource use trajectories consistent with US climate change mitigation scenarios
<jats:p>To progress decarbonisation in the United States, numerous techno-economic models have been built projecting climate change mitigation scenarios that include CO2 storage deployment at annual injection rates of 0.3 – 1.7 Gt yr-1 by 2050. However, these projections do not include geological, technical, or socio-economic factors that could impede the growth of geological storage resource use. Here, we apply a growth modelling framework to evaluate CO2 storage scenarios proposed in the Net Zero America, Carbon Neutral Pathways, Long-Term Strategy, and Decarb America reports. Our modelling framework uses logistic curves to analyse the feasibility of growth trajectories under constraints imposed by the associated storage resource availability. We show that the entire storage demand for the US can be accommodated by the resources available in the Gulf Coast alone. Deployment trajectories require sustained average annual (exponential) growth at rates >10% nationally and between 3% - 20% regionally across four storage hubs. These scale-up rates are high relative to those characterising analogous, historical, large-scale energy infrastructure projects in the US (4%), suggesting that modelled projections in current reports are too aggressive in their deployment of CCS. These models could be easily constrained to more realistic deployment trajectories with the type of modelling framework we present here.</jats:p>
Magee C, Reeve MT, Jackson CA-L, et al., 2023, Reply to Alves et al. (2022) discussion on "Stratigraphic record of continental breakup, offshore NW Australia" by Reeve et al. (2022), Basin Research, Vol: 35, Pages: 483-486, ISSN: 0950-091X
Erdi A, Jackson CA-L, Soto JI, 2023, Extensional deformation of a shale-dominated delta: Tarakan Basin, offshore Indonesia, BASIN RESEARCH, ISSN: 0950-091X
Erdi A, Jackson C, Soto J, 2023, Extensional Deformation of a Shale-dominated Delta: Tarakan Basin, Offshore Indonesia
<jats:p>Deformation on shale-rich continental margins is commonly associated with thin-skinned extension above mobile shales. Normal faulting and shale mobilization are widespread on such margins, being associated with and controlled by progradation and gravitational failure of deltaic sedimentary wedges. However, due to limitations in our ability to seismically imaging these mobile shales, our understanding of how base-shale relief controls deformation, and the shape, size, and distribution of shale structures remain poorly understood. We here use 3D seismic reflection data from the Tarakan Basin, offshore Indonesia to investigate the temporal and spatial evolution of thin-skinned deformations of the Neogene sedimentary section. Our detailed seismic interpretation reveals long (≤ 74 km), concave- and convex-into-the-basin faults, dipping both basinward (eastwards) and locally landward (westwards), which detach downwards on a basal mobile shale (Middle Miocene). The base of the shale unit dips gently (< 17o) seaward, although older (Paleogene), rift-related normal faults mean a local base-shale relief is present. Our analysis of isochron (thickness map) analysis shows that supra-shale normal faulting commenced in the Middle Miocene and was accompanied by the formation of hanging wall rollover folds and associated crestal grabens, with the subsequent along- and across strike migration of strain being related to the nucleation, lateral linkage, and reactivation of individual fault systems. Updip growth faulting was also accompanied by the downslope flow of mobile shale, margin-parallel and-perpendicular differential loading, and local contraction and mobile shale-upbuilding, resulting in the growth of large, margin-parallel shale anticlines further downdip. These faults and anticlines are locally overlain by tall (≤ 5 km) mud diapirs and volcanoes. We suggest that variations in the rate of sediment loading, mobile shale flow, fault growth, and gravi
do Amarante FB, Kuchle J, Jackson CAL, et al., 2023, The cryptic stratigraphic record of the syn- to post-rift transition in the offshore Campos Basin, SE Brazil, Basin Research, ISSN: 0950-091X
Rift basins typically comprise three main tectono-stratigraphic stages; pre-, syn- and post-rift. The syn-rift stage is often characterised by the deposition of asymmetric wedges of growth strata that record differential subsidence caused by active normal faulting. The subsequent post-rift stage is defined by long-wavelength subsidence driven by lithospheric cooling and is typified by the deposition of broadly tabular stratal packages that drape any rift-related relief. The stratigraphic contact between syn- and post-rift rocks is often thought to be represented by an erosional unconformity. However, the late syn-rift to early post-rift stratigraphic record is commonly far more complex since (i) the associated tectonic transition is not instantaneous; (ii) net subsidence may be punctuated by transient periods of uplift; and (iii) strain often migrates oceanward during rifting until continental breakup is achieved with crustal rupture. Previous publications on the Eastern Brazilian marginal basins have not historically used the tripartite scheme outlined above, with the post–pre-rift interval instead being subdivided into rift, sag and passive margin tectono-stratigraphic stages. In addition, the sag stage has been previously described as late syn-rift, early post-rift or as a transition between the two, with the passive margin stage being equivalent to the classically defined post-rift, drift stage. Two (rather than one) erosional unconformities are also identified within the rift-to-sag succession. In this work, we use 2D and 3D seismic reflection and borehole data to discuss the expression of and controls on the syn- to post-rift transition in the shallow and deep water domains of the south-central Campos Basin, south-east Brazil. We identified three seismic–stratigraphic sequences bounded by unconformities, named lower and upper pre-salt and salt. The lower pre-salt interval is characterised by wedge-shaped packages of reflections that thicken towards
Joffe A, Jackson CA-L, Pichel LMM, 2022, Syn-depositional halokinesis in the Zechstein Supergroup (Lopingian) controls Triassic minibasin genesis and location, BASIN RESEARCH, ISSN: 0950-091X
Wu N, Jackson CA-L, Clare MA, et al., 2022, Diagenetic priming of submarine landslides in ooze-rich substrates, GEOLOGY, ISSN: 0091-7613
Jackson C, Evans S, Alshammasi T, 2022, Salt welding during canopy advance and shortening in the Green Canyon Area, northern Gulf of Mexico
<jats:p>Welds form due to tectonically-induced thinning and/or dissolution of salt, with their composition and completeness thought to at least partly reflect their structural position within the salt-tectonic system. Despite their importance as seals or migration pathways for accumulations of hydrocarbons and CO2, we have relatively few published examples of drilled subsurface welds; such examples would allow us to improve our understanding of the processes and products of welding, and to test analytical models of the underlying mechanics. In this study we integrate 3D seismic reflection and borehole data from the Green Canyon Area of the northern Gulf of Mexico, USA to characterize the geophysical and geological expression of a tertiary weld, as well as its broader salt-tectonic context. These data show although it appears complete on seismic reflection data, the weld contains 124 ft (c. 38 m) of pure halite. This thickness is consistent with the predictions of analytical models, and with observations from other natural examples of subsurface welds. Our observations also support a model whereby compositional fractionation of salt occurs as the salt-tectonic system evolves; in this model, less mobile and/or denser units, if originally present, are typically stranded within the deeper, autochthonous level, trapped in primary welds, or near the basal root of diapirs, whereas less viscous and/or less dense units form the cores of these diapirs and, potentially, genetically related allochthonous sheets and canopies. We also show that shearing of the weld during downslope translation of the overlying minibasin did not lead to complete welding.</jats:p>
Joffe A, Jackson C, Pichel L, 2022, Syn-Depositional Halokinesis in the Zechstein Supergroup (Lopingian) Controls Triassic Minibasin Genesis and Location
<jats:p>Salt tectonics is typically caused by the flow of mobile evaporites in response to post-depositional gravity gliding and/or differential loading by overburden sediments. This situation is considerably more complex near the margins of salt basins, where carbonate and clastic rocks may be deposited at the same time and interbedded with more mobile evaporitic strata. In these cases, syn-depositional salt flow may occur due to density differences in the deposited lithologies, although our understanding of this and related processes is relatively poor. We here use 3D seismic reflection and borehole data from the Devil’s Hole Horst, West Central Shelf, offshore UK to understand the genesis, geometry and kinematic evolution of intra-Zechstein Supergroup (Lopingian) minibasins and their effect on post-depositional salt deformation. We show that immobile, pinnacle-to-barrier-like, carbonate build-ups and anhydrite are largely restricted to intra-basin highs, whereas mobile halite, which flowed to form large diapirs, dominates in the deep basin. At the transition between the intra-basin highs and the deep basin, a belt of intra-Zechstein minibasins occur, forming due to the subsidence of relatively dense anhydrite into underlying halite. Depending on primary halite thickness, these intra-Zechstein minibasins created topographic lows, dictating the position for nucleation and subsequent down-building of Triassic minibasins. Our study refines the original depositional model for the Zechstein Supergroup in the Central North Sea, with the results also helping us better understand the style and distribution of syn-depositional salt flow on other layered evaporitic sequences and the role intra-salt heterogeneity and related deformation may have in the associated petroleum plays.</jats:p>
Wu N, Jackson C, Clare M, et al., 2022, Diagenetic priming of submarine landslides in ooze-rich substrates
<jats:p>Oozes are the most widespread deep-sea sediment in the global ocean, but very little is known about how changes in their physical properties during burial impact slope stability and related geohazards. Here, we use 3D seismic reflection, geochemical, and petrophysical data acquired both within and adjacent to 13 large (in total c. 6330 km2) submarine slides on the Exmouth Plateau, NW Shelf, Australia, to investigate how the pre-slide physical properties of oozes control slope failure and emplacement processes. Our integrated dataset allows potential slide surfaces to be detected within ooze successions; a crucial advance for improved submarine geohazard assessment. Moreover, we demonstrate that the interplay of tectonics, ocean current activity, and silica diagenesis can prime multiple slides on very low gradient slopes in tropical, oceanic basins. Therefore, the diagenetic state of silica-rich sediments must be considered to improve slope stability assessments.</jats:p>
Erdi A, Jackson C, 2022, Salt-detached strike-slip faulting, Outer Kwanza Basin, Offshore Angola
<jats:p>We here use a 3D seismic reflection dataset from Outer Kwanza Basin, offshore Angola to examine the structure and growth of salt-detached strike-slip faults. The faults occur in four, up to 13.8 km-long, NE-trending arrays that are physically linked by restraining bend and releasing stepovers, and which presently overlie Aptian salt and base-salt relief related to pre-salt faulting. We suggest that these faults formed to accommodate along-margin variations in the rate and magnitude of differential seaward translation and salt diapirism, which commenced in the Early Cretaceous. We illustrate that the arrays grew by tip propagation of isolated fault segments, some of which linked during the Albian-Cenomanian (i.e., 113-100.5 Ma, or the initial 11-13% of their deformation history). Some arrays then reached their near-final length within the subsequent ca. 77 Ma, or the next 69-81% of their deformation history), while others attained this later, during the subsequent ca. 18 Ma (i.e., after 95% of their deformation history). During this time, the segments formed and then breached releasing and restraining stepovers, with the arrays as a whole growing by alternating periods of lengthening, throw accumulation, and inactivity. Our results also show that scatter in the D-L scaling of strike-slip faults reflect the propagation, interaction, and linkage of individual segments.</jats:p>
Joffe A, Jackson C, Steinberg J, et al., 2022, Origin and kinematics of a basin-scale, non-polygonal, layer-bound normal fault system in the Levant Basin, eastern Mediterranean
<jats:p>Polygonal, layer-bound normal faults can extend over very large areas (>2,000,000 km2) of sedimentary basins. Best developed in very fine-grained rocks, these faults are thought to form during early burial in response to a range of diagenetic processes, including compaction and water expulsion. Local deviations from this idealised polygonal pattern are common; however, basin-scale, layer-bound faults with non-polygonal map-view are not well-documented and accordingly, their genesis is not well-understood. In this study we use 3D seismic reflection data, biostratigraphy, and well-logs from the Southern Levant Basin, offshore Israel, to develop an age-constrained seismic-stratigraphic framework and determine the geometry and kinematics of such basin-scale fault system. The faults tip-out downwards along an Eocene Unconformity, but unlike layer-bound faults in the Northern Levant Basin, they do not reach the base of the Messinian evaporites, instead tipping-out upwards at the top Langhian. On average, the faults in the Southern Levant Basin are 6.3 km long, have an average throw of 120 m, and consistently strike NW-SE. Throw-depth plots, accompanied by thickness changes, indicate the faults nucleated as syn-depositional faults in a mudstone-dominated unit, and are spatially and kinematically associated with a WSW-ESE-striking strike-slip fault. Unlike true polygonal faults, these faults propagated through ~2 km-thick sandstone-dominated Oligocene-Miocene strata. Whereas previous studies from the Northern Levant Basin associate fault nucleation and growth with burial-related diagenesis, the sandstone-dominated character of the Oligocene-Miocene suggests that this process cannot be readily applied to the Southern Levant Basin. Instead, we highlight potential tectonic events that occurred during and may have triggered thin-skinned extension at times of fault growth. Layer-bound normal faults therefore should be considered in the geodynamic and structu
<jats:p>Submarine landslides (slides) are ubiquitous on continental margins. They can pose a major hazard by triggering tsunami and damaging essential submarine infrastructure. Slide volume, which is a key parameter in hazard assessment, can change after initiation through substrate and/or water entrainment. However, the erosive capacity of slides is uncertain. Here, we quantify slide erosivity by determining the ratio of deposited (Vd) to initially evacuated (Ve) sediment volumes. Slides that gain volume through erosion = Vd/Ve&gt;1. We apply this method to a large (500 km3), seismically imaged slide offshore NW Australia, and review Vd/Ve ratios for other large slides worldwide. Nine of the 11 slides have Vd/Ve&gt;1 (median value=2), showing that emplaced volumes increased after initial failure. The Gorgon Slide is the most erosive slide currently documented (Vd/Ve=13), possibly reflecting its passage across a highly erodible carbonate ooze substrate. This new approach to quantifying erosion is important for hazard assessments as substrate-flow interactions control slide speed and run-out distance. The variations in slide volume also have important implications for submarine infrastructure impact assessments, including more robust tsunami modelling.</jats:p>
Erdi A, Jackson CA-L, 2022, Salt-Detached Strike-Slip Faulting, Outer Kwanza Basin, Offshore Angola, TECTONICS, Vol: 41, ISSN: 0278-7407
Pichel LM, Ferrer O, Jackson CA-L, et al., 2022, Physical modelling of the interplay between salt-detached gravity gliding and spreading across complex rift topography, Santos Basin, offshore Brazil, BASIN RESEARCH, Vol: 34, Pages: 2042-2063, ISSN: 0950-091X
Steventon M, Jackson C, Johnson H, et al., 2022, Evolution of a sand-rich submarine channel-lobe system and impact of mass-transport and transitional flow deposits on reservoir heterogeneity: Magnus Field, northern North Sea
<jats:p>The geometry, distribution, and rock properties (i.e. porosity and permeability) of turbidite reservoirs, and the processes associated with turbidity current deposition, are relatively well known. However, less attention has been given to the equivalent properties resulting from laminar sediment gravity-flow deposition, with most research limited to cogenetic turbidite-debrites (i.e. transitional flow deposits) or subsurface studies that focus predominantly on seismic-scale mass-transport deposits (MTDs). Thus, we have a limited understanding of sub-seismic MTDs ability to act as hydraulic seals and their effect on hydrocarbon production, and/or carbon storage and sequestration. We investigate the gap between seismically resolvable and sub-seismic MTDs and transitional flow deposits on long-term reservoir performance in this analysis of a small (<10 km radius submarine fan system), Late Jurassic, sandstone-rich stacked turbidite reservoir (Magnus Field, northern North Sea), which is supported by a relatively long (c. 37 years) and well-documented production history. We use core, petrophysical logs, pore fluid pressure, quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN), and 3D seismic-reflection datasets to quantify the type and distribution of sedimentary facies and rock properties. A range of sediment gravity deposits are recognised: (i) thick-/thin- bedded, structureless and structured turbidite sandstone, constituting the primary productive reservoir facies (c. porosity = 22%, permeability = 500 mD), (ii) a range of transitional flow deposits, and (iii) heterogeneous mud-rich sandstone interpreted as debrites (c. porosity = <10%, volume of clay = 35%, up to 18 m thick). Results from this study show that over the production timescale of the Magnus Field, debrites act as barriers, compartmentalising the reservoir into two parts (upper and lower reservoir), and transitional flow deposits act as baffles, impact
Steventon M, Jackson C, Hodgson D, et al., 2022, Lateral variability of shelf-edge, slope and basin-floor deposits, Santos Basin, offshore Brazil
<jats:p>Construction of continental margins is driven by sediment transported across the shelf to the shelf-edge, where it is reworked by wave-, tide- and river-influenced processes within deltas and flanking clastic shorelines. Stalling of continental margin progradation often results in degradation of the outer shelf to upper slope, with re-sedimentation to the lower slope and basin-floor via a range of sediment gravity-flows and mass-movement processes. Our understanding of how these processes contribute to the long-term development of continental margins has typically been limited to observations from broadly two-dimensional, subsurface and outcrop datasets. Consequently, the three-dimensional, particularly along-strike variability in process regime and margin evolution is poorly constrained and often underappreciated. We use a large (90 km by 30 km, parallel to depositional strike and dip, respectively) post-stack time-migrated 3D seismic-reflection dataset to investigate along-strike variations in shelf margin progradation and outer-shelf to upper-slope collapse in the Santos Basin, offshore SE Brazil. Early Palaeogene to Eocene progradation of the shelf margin is recorded by spectacularly imaged, SE-dipping clinoforms. Periodic failure of the outer-shelf and upper slope formed c.30 km-wide (parallel to shelf margin strike) slump scars, which resulted in a strongly scalloped upper slope. Margin collapse caused (1) the emplacement of slope-attached mass-transport complexes (MTCs) (up to ca. 375 m thick, 12+ km long, 20 km wide) on the proximal basin-floor, and (2) accommodation creation on the outer shelf to upper slope. This newly formed accommodation was infilled by shelf-edge-delta clinoforms (up to 685 m thick), that nucleated and prograded basinward from the margin-collapse headwall scarp, downlapping onto the underlying slump scar and/or MTCs. Trajectory analysis of the shelf-edge deltas suggests that slope degradation-created accommodation was gene
Pan S, Naliboff J, Bell R, et al., 2022, Bridging spatiotemporal scales of normal fault growth during continental extension using high-resolution 3D numerical models, G3: Geochemistry, Geophysics, Geosystems: an electronic journal of the earth sciences, Vol: 23, Pages: 1-16, ISSN: 1525-2027
Continental extension is accommodated by the development of kilometer-scale normal faults, which grow during meter-scale slip events that occur over millions of years. However, reconstructing the entire lifespan of a fault remains challenging due to a lack of observational data with spatiotemporal scales that span the early stage (<106 yrs) of fault growth. Using three-dimensional numerical simulations of continental extension and novel methods for extracting the locations of faults, we quantitatively examine the key factors controlling the growth of rift-scale fault networks over 104–106 yrs. Early formed faults (<100 kyrs from initiation) exhibit scaling ratios consistent with those characterizing individual earthquake ruptures, before evolving to be geometrically and kinematically similar to more mature structures developed in natural fault networks. Whereas finite fault lengths are rapidly established (<100 kyrs), active deformation is transient, migrating both along- and across-strike. Competing stress interactions determine the distribution of active strain, which oscillates between being distributed and localized. Higher rates of extension (10 mm yr−1) lead to more prominent stress redistributions through time, promoting episodic localized slip events. Our findings demonstrate that normal fault growth and the related occurrence of cumulative slip is more complex than that currently inferred from displacement patterns on now-inactive structures, which only provide a space- and time-averaged picture of fault kinematics and related seismic hazard.
Duffy O, Dooley T, Hudec M, et al., 2022, Principles of Shortening in Salt Basins Containing Isolated Minibasins
<jats:p>Shortening styles in salt-influenced basins can vary markedly, with the volume and distribution of salt prior to shortening being a key control. Here we use a suite of physical models to examine styles of thin-skinned regional shortening in settings where the pre-shortening structure comprised minibasins surrounded by salt (‘isolated-minibasin’ provinces). Our models show that the high volume of mechanically-weak salt localizes lateral regional shortening, with shortening inducing salt flow towards the foreland that subsequently contributes to three key processes - translation, tilting and rotation of minibasins. First, we demonstrate that the flowing salt pushes against minibasins, propelling them in the regional shortening direction. Minibasin translation is enhanced by fast-flowing salt streams and impeded by basal friction due to welding and base-salt buttresses. Second, we show how minibasin tilt directions and magnitudes vary spatially and temporally during regional shortening. Minibasins tilt away from zones of pressurized salt, the locations of which may shift due to changes in salt flow regimes. Tilt directions may also change as minibasins pivot on primary welds, or due to forces associated with minibasin collision. Third, minibasins can rotate around sub-vertical axes during regional shortening. We speculate that this rotation is caused by a combination of: i) traction imparted on the minibasin boundary by differential horizontal flow of adjacent salt; and ii) pivoting on primary and secondary welds. We synthesize our results in a series of 3-D conceptual models, before we compare and contrast regional shortening styles and processes in salt-influenced basins with different pre-shortening salt configurations. Our findings contribute to the understanding of the geometry and kinematics of shortened salt basins, as well as a deeper understanding of the tectono-stratigraphic evolution of minibasins.</jats:p>
Abu C, Jackson CA-L, Francis M, 2022, Strike-slip overprinting of initial co-axial shortening within the toe region of a submarine landslide and a model for basal shear surface growth: a case study from the Angoche Basin, offshore Mozambique, JOURNAL OF THE GEOLOGICAL SOCIETY, Vol: 179, ISSN: 0016-7649
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