scholarly journals Strike-slip overprinting of initial co-axial shortening within the toe region of a submarine landslide: a case study from the Angoche Basin, offshore Mozambique

2021 ◽  
pp. jgs2021-032
Author(s):  
Clara Abu ◽  
Christopher A-L. Jackson ◽  
Malcolm Francis
Keyword(s):  
Shear Zone ◽  
Sedimentary Basins ◽  
Shear Zones ◽  
Submarine Landslides ◽  
3D Seismic ◽  
Direction Parallel ◽  
Seismic Reflection Data ◽  
Slide Mass ◽  
Reflection Data ◽  
Basal Shear

Submarine landslides (slides) are some of the most voluminous sediment gravity-flows on Earth and they dominate the stratigraphic record of many sedimentary basins. Their general kinematics and internal structure are relatively well-understood. However, how slides increase in volume and internally deform as they evolve, and how these processes relate, in time and space, to the growth of their basal (shear) zone, are poorly understood. We here use three high-resolution 3D seismic surveys from the Angoche Basin, offshore Mozambique to map strain within a shallowly buried, large, and thus seismically well-imaged slide (c. 530 km3). We document several key kinematic indicators, including broadly NW-trending lateral margins and longitudinal shears bounding and within the slide body, respectively, and broadly NE-trending symmetric pop-up blocks in the slide toe. Approximately 7 km downdip of the slide toe wall, thrusts and related folds also occur within otherwise undeformed slope material, with thrusts detaching downwards onto the downslope continuation of the basal shear zone underlying the slide body. Based on the style, trend, and distribution of these features, and their cross-cutting relationships, we propose an emplacement model involving two distinct phases of deformation: (i) bulk shortening, parallel to the overall SE-directed emplacement direction, with contractional shear strains reaching c. 8%; and (ii) the development of broadly emplacement direction-parallel shear zones that offset the earlier-formed shortening structures. We infer that the contractional strains basinward of the slide body formed due to cryptic basinward propagation of the basal shear zone ahead of and to accommodate updip sliding and shortening associated with, the entire slide mass. Our study demonstrates the value of using 3D seismic reflection data to reveal slide emplacement kinematics, especially the multiphase, non-coaxial nature of deformation, and the dynamics of basal shear zone growth.

scholarly journals Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

2018 ◽  
Vol 477 (1) ◽  
pp. 223-240 ◽  
Author(s):  
D. M. Hodgson ◽  
H. L. Brooks ◽  
A. Ortiz-Karpf ◽  
Y. Spychala ◽  
D. R. Lee ◽  
...  
Keyword(s):  
Seismic Reflection ◽  
Three Dimensional ◽  
Submarine Landslides ◽  
Seismic Reflection Data ◽  
Karoo Basin ◽  
Reflection Data ◽  
Seabed Topography ◽  
Flow Evolution ◽  
Basal Shear ◽  
Process Product

AbstractMany mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides.

scholarly journals Sigmoidal normal faults and evidence for vertical-axis block rotation in an oblique convergent margin: A 3D seismic example from offshore Colombia

2021 ◽  
Vol 40 (12) ◽  
pp. 923-930
Author(s):  
Pedro A. Galindo ◽  
Lidia Lonergan
Keyword(s):  
Shear Zone ◽  
Vertical Axis ◽  
Fault Zones ◽  
Normal Displacement ◽  
Normal Faults ◽  
3D Seismic ◽  
Block Rotation ◽  
Plan View ◽  
Seismic Reflection Data ◽  
Reflection Data

Sigmoidal fold and fault geometries are typical kinematic indicators of strike-slip fault zones. We document kilometer-scale, normal faults with sigmoidal plan-view geometries within the dextral pull-apart Bahia Basin, at the rear of the obliquely convergent South Caribbean Deformed Belt, offshore Colombia. Using 3D seismic reflection data calibrated to wells, closely spaced, low-displacement, planar normal faults are mapped within the Miocene strata. A series of seismic horizontal (time) slices and computed seismic attributes are used to interpret the 3D configuration of these faults. The closely spaced faults display an east–west trend with a progressive rotation into a northwest–southeast trend. In map view, the fault traces curve toward their tips, describing a sigmoidal-Z geometry that terminates at discrete northeast–southwest-trending fault zones. The structures observed may correspond to either tension fractures, which form theoretically at 45°, or antithetic shear fractures with normal displacement formed at 50°–70° to the boundaries of a dextral shear zone. These scenarios lead to a clockwise block rotation of between 20° and 40° within the shear zone. This study shows the first example of vertical-axis block rotations observed offshore in the western end of the South Caribbean margin and is an important example of the use of 3D seismic data to identify rotations where paleomagnetic studies are not available.

scholarly journals Seismic analysis of igneous systems in sedimentary basins and their impacts on hydrocarbon prospectivity: examples from the southern Australian margin

2012 ◽  
Vol 52 (1) ◽  
pp. 229 ◽  
Author(s):  
Simon Holford ◽  
Nick Schofield ◽  
Justin MacDonald ◽  
Ian Duddy ◽  
Paul Green
Keyword(s):  
Seismic Analysis ◽  
Sedimentary Basins ◽  
Hydrocarbon Exploration ◽  
Passive Margin ◽  
Continental Margins ◽  
3D Seismic ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Exploration Risk ◽  
Igneous Activity

The increasing availability of 3D seismic data from sedimentary basins at volcanic and non-volcanic continental margins has provided fundamental new insights into both the storage and transport of magma in the continental crust. As global hydrocarbon exploration increasingly focuses on passive margin basins with evidence for past intrusive and extrusive igneous activity, constraining the distribution, timing and pathways of magmatism in these basins is essential to reduce exploration risk. Producing and prospective Australian passive margin basins where igneous systems have been identified include the Bight, Otway, Bass, Gippsland and Sorell basins of the southern margin. This paper reviews both the impacts of volcanic activity on sedimentary basin hydrocarbon prospectivity (e.g. advective heating, reservoir compartmentalisation and diagenesis), and the styles, distribution and timing of late Cretaceous–Recent extrusive and intrusive igneous activity along basins of the southern Australian margin, providing illustrative examples based on 2D and 3D seismic reflection data.

Free gas distribution and basal shear zone development in a subaqueous landslide – Insight from 3D seismic imaging of the Tuaheni Landslide Complex, New Zealand

2018 ◽  
Vol 502 ◽  
pp. 231-243 ◽  
Author(s):  
Felix Gross ◽  
Joshu J. Mountjoy ◽  
Gareth J. Crutchley ◽  
Christoph Böttner ◽  
Stephanie Koch ◽  
...  
Keyword(s):  
New Zealand ◽  
Shear Zone ◽  
Seismic Imaging ◽  
3D Seismic ◽  
Gas Distribution ◽  
Free Gas ◽  
Zone Development ◽  
Basal Shear

Three-dimensional geometry and growth of a basement-involved fault network developed during multiphase extension, Enderby Terrace, North West Shelf of Australia

2021 ◽  
Author(s):  
Hongdan Deng ◽  
Ken McClay
Keyword(s):  
Three Dimensional ◽  
Sedimentary Basins ◽  
Fault Reactivation ◽  
Late Triassic ◽  
Seismic Reflection Data ◽  
North West ◽  
Reflection Data ◽  
Data Volume ◽  
Vertical Linkages ◽  
Fault Network

<div>Basement fault reactivation, and the growth, interaction, and linkage with new fault segments are fundamentally three-dimensional and critical for understanding the evolution of fault network development in sedimentary basins. This paper analyses the evolution of a complex, basement-involved extensional fault network on the Enderby Terrace on the eastern margin of the Dampier sub-basin, NW Shelf of Australia. A high-resolution, depth-converted, 3D seismic reflection data volume is used to show that multiphase, oblique extensional reactivation of basement-involved faults controlled the development of the fault network in the overlying strata. Oblique reactivation of the pre-existing faults initially led to the formation of overlying, en échelon Late Triassic – Middle Jurassic fault segments that, as WNW–directed rifting progressed on the margin, linked by breaching of relay ramp to form two intersecting fault systems (F1 and F2-F4). Further reactivation in the Latest Jurassic – Early Cretaceous (NNW–SSE extension) produced an additional set of en échelon fault arrays in the cover strata. The final fault network consists of main or principal faults and subordinate or splay faults, together with branch lines that link the various components. Our study shows that breaching of relay ramps and/or vertical linkages produces vertical and horizontal branch lines giving complex final fault geometries. We find that repeated activity of the basement-involved faults tends to form continuous and planar fault architectures that favor displacement transfer between the main constituent segments along strike and with depth.</div>

scholarly journals Seismic reflection data reveal the 3D structure of the newly discovered Exmouth Dyke Swarm, offshore NW Australia

2020 ◽  
Author(s):  
Craig Magee ◽  
Christopher A.-L. Jackson
Keyword(s):  
Seismic Reflection ◽  
Surface Deformation ◽  
3D Structure ◽  
Sedimentary Basins ◽  
Dyke Swarm ◽  
Normal Faults ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Dyke Swarms ◽  
Nw Australia

Abstract. Dyke swarms are common on Earth and other planetary bodies, comprising arrays of dykes that can extend for 10's to 1000's of kilometres. The vast extent of such dyke swarms, and their rapid emplacement, means they can significantly influence a variety of planetary processes, including continental break-up, crustal extension, resource accumulation, and volcanism. Determining the mechanisms driving dyke swarm emplacement is thus critical to a range of Earth Science disciplines. However, unravelling dyke swarm emplacement mechanics relies on constraining their 3D structure, which is extremely difficult given we typically cannot access their subsurface geometry at a sufficiently high enough resolution. Here we use high-quality seismic reflection data to identify and examine the 3D geometry of the newly discovered Exmouth Dyke Swarm, and associated structures (i.e. dyke-induced normal faults and pit craters), in unprecedented detail. The latest Jurassic dyke swarm is located on the Gascoyne Margin offshore NW Australia and contains numerous dykes that are > 170 km long, potentially > 500 km long. The mapped dykes are distributed radially across a 39° arc centred on the Cuvier Margin; we infer this focal area marks the source of the dyke swarm, which was likely a mantle plume. We demonstrate seismic reflection data provides unique opportunities to map and quantify dyke swarms in 3D in sedimentary basins, which can allow us to: (i) recognise dyke swarms across continental margins worldwide and incorporate them into models of basin evolution and fluid flow; (ii) test previous models and hypotheses concerning the 3D structure of dyke swarms; (iii) reveal how dyke-induced normal faults and pit craters relate to dyking; and (iv) unravel how dyking translates into surface deformation.

scholarly journals Structural and microstructural analysis of K–Mg salt layers in the Zechstein 3 of the Veendam Pillow, NE Netherlands: development of a tectonic mélange during salt flow

2017 ◽  
Vol 96 (4) ◽  
pp. 331-351 ◽  
Author(s):  
Alexander F. Raith ◽  
Janos L. Urai ◽  
Jacob Visser
Keyword(s):  
Microstructural Analysis ◽  
Shear Zones ◽  
Horizontal Shear ◽  
X Ray Diffraction ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Tectonic History ◽  
Dynamic Recrystallisation ◽  
Bulk Chemical ◽  
Tectonic Mélange

AbstractIn fully developed evaporite cycles, effective viscosity contrasts of up to five orders of magnitude are possible between different layers, but the structures and mechanics in evaporites with such extreme mechanical stratification are not well understood. The Zechstein 3 unit in the Veendam salt pillow in the Netherlands contains anhydrite, halite, carnallite and bischofite, showing this extreme mechanical stratification. The Veendam Pillow has a complex multiphase salt tectonic history as shown by seismic reflection data: salt withdrawal followed by convergent flow into the salt pillow produced ruptures and folds in the underlying Z3-anhydrite–carbonate stringer and deformed the soft Z3-1b layerWe analysed a unique carnallite- and bischofite-rich drill core from the soft Z3-1b layer by macroscale photography, bulk chemical methods, X-ray diffraction and optical microscopy. Results show high strain in the weaker bischofite- and carnallite-rich layers, with associated dynamic recrystallisation at very low differential stress, completely overprinting the original texture. Stronger layers formed by alternating beds of halite and carnallite show complex recumbent folding on different scales commonly interrupted by sub-horizontal shear zones with brittle deformation, veins and boudinage. We attribute this tectonic fragmentation to be associated with a softening of the complete Z3-1b subunit during its deformation. The result is a tectonic mélange with cm- to 10 m-size blocks with frequent folds and boudinage. We infer that these structures and processes are common in deformed, rheologically strongly stratified evaporites.

Investigating fault continuity associated with geologic carbon storage planning in the Illinois Basin

2014 ◽  
Vol 2 (1) ◽  
pp. SA151-SA162 ◽  
Author(s):  
John H. McBride ◽  
R. William Keach ◽  
Eugene E. Wolfe ◽  
Hannes E. Leetaru ◽  
Clayton K. Chandler ◽  
...  
Keyword(s):  
Carbon Storage ◽  
Seismic Reflection ◽  
Oil Field ◽  
Illinois Basin ◽  
Storage Site ◽  
3D Seismic ◽  
Seismic Attribute ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Attribute Analyses

Because the confinement of [Formula: see text] in a storage reservoir depends on a stratigraphically continuous set of seals to isolate the fluid in the reservoir, the detection of structural anomalies is critical for guiding any assessment of a potential subsurface carbon storage site. Employing a suite of 3D seismic attribute analyses (as opposed to relying upon a single attribute) maximizes the chances of identifying geologic anomalies or discontinuities (e.g., faults) that may affect the integrity of a seal that will confine the stored [Formula: see text] in the reservoir. The Illinois Basin, a major area for potential carbon storage, presents challenges for target assessment because geologic anomalies can be ambiguous and easily misinterpreted when using 2D seismic reflection data, or even 3D data, if only conventional display techniques are used. We procured a small 3D seismic reflection data set in the central part of the basin (Stewardson oil field) to experiment with different strategies for enhancing the appearance of discontinuities by integrating 3D seismic attribute analyses with conventional visualizations. Focusing on zones above and below the target interval of the Cambrian Mt. Simon Sandstone, we computed attribute traveltime slices (combined with vertical views) based on discontinuity computations, crossline-directed amplitude change, azimuth of the dip, shaded relief, and fault likelihood attributes. The results provided instructive examples of how discontinuities (e.g., subseismic scale faults) may be almost “invisible” on conventional displays but become detectable and mappable using an appropriate integration of 3D attributes. Strong discontinuities in underlying Precambrian basement rocks do not necessarily propagate upward into the target carbon storage interval. The origin of these discontinuities is uncertain, but we explored a possible strike-slip role that also explains the localization of a structural embayment developed in Lower Paleozoic strata above the basement discontinuities.

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