scholarly journals Geometric and temporal evolution of extensional growth folds in the Barents Sea, offshore Norway: A tool to understand normal fault growth

2021 ◽  
Author(s):  
Ahmed Alghuraybi ◽  
Rebecca Bell ◽  
Chris Jackson
Keyword(s):  
Surface Deformation ◽  
Barents Sea ◽  
Temporal Evolution ◽  
Normal Fault ◽  
Normal Faults ◽  
Borehole Data ◽  
Growth Strata ◽  
Sedimentary Evolution ◽  
Extensional Strain ◽  
Fault Growth

Extensional growth folds form ahead of the tips of propagating normal faults. These folds can accommodate a considerable amount of extensional strain and they may control rift geometry. Fold-related surface deformation may also control the sedimentary evolution of syn-rift depositional systems; thus, the stratigraphic record can constrain the four-dimensional evolution of extensional growth folds, which in term provides a record of fault growth and broader rift history. Here we use high-quality 3D seismic reflection and borehole data from the SW Barents Sea, offshore northern Norway to determine the geometric and temporal evolution of extensional growth folds associated with a large, long-lived, basement-involved fault. We show that the fault grew via linkage of four segments, and that fault growth was associated with the formation of fault-parallel and fault-perpendicular folds that accommodated a substantial portion (10 – 40%) of the total extensional strain. Fault-propagation folds formed at multiple times in response to periodic burial of the causal fault, with individual folding events (c. 25 Myr and 32 Myr) lasting a considered part of the total, c. 130 Myr rift period. Our study supports previous suggestions that continuous (i.e., folding) as well as discontinuous (i.e., faulting) deformation must be explicitly considered when assessing total strain in extensional setting. We also show changes in the architecture of growth strata record alternating periods of how folding and faulting, showing how rift margins may be characterised by basinward-dipping monoclines as opposed to fault-bound scarps. Our findings have broader implications for our understanding of the structural, physiographic, and tectonostratigraphic evolution of rift basins.

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

Solid Earth ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 579-606 ◽  
Author(s):  
Craig Magee ◽  
Christopher Aiden-Lee Jackson
Keyword(s):  
Seismic Reflection ◽  
Surface Deformation ◽  
3D Structure ◽  
Dyke Swarm ◽  
Normal Faults ◽  
Borehole Data ◽  
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 laterally for tens to thousands of kilometres. The vast extent of such dyke swarms, and their presumed 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 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). Dykes are expressed in our seismic reflection data as ∼335–68 m wide, vertical zones of disruption (VZD), in which stratal reflections are dimmed and/or deflected from sub-horizontal. Borehole data reveal one ∼130 m wide VZD corresponds to an ∼18 m thick, mafic dyke, highlighting that the true geometry of the inferred dykes may not be fully captured by their seismic expression. The Late Jurassic dyke swarm is located on the Gascoyne Margin, offshore NW Australia, and contains numerous dykes that extend laterally for > 170 km, potentially up to > 500 km, with spacings typically < 10 km. Although limitations in data quality and resolution restrict mapping of the dykes at depth, our data show that they likely have heights of at least 3.5 km. The mapped dykes are distributed radially across a ∼39∘ wide arc centred on the Cuvier Margin; we infer that this focal area marks the source of the dyke swarm. We demonstrate that seismic reflection data provide unique opportunities to map and quantify dyke swarms in 3D. Because of this, we can now (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.

The temporal evolution of syn-sedimentary normal faults and the possible role of tip retreat

2020 ◽  
Author(s):  
Bailey Lathrop ◽  
Christopher Jackson ◽  
Rebecca Bell ◽  
Atle Rotevatn
Keyword(s):  
Growth Model ◽  
Temporal Evolution ◽  
Fault Model ◽  
Normal Faults ◽  
Constant Length ◽  
Final Length ◽  
Fault Growth ◽  
Stratigraphic Evolution ◽  
The Relationship

&lt;p&gt;We need to understand how normal faults grow in order to better determine the tectono-stratigraphic evolution of rifts, and the distribution and size of potentially hazardous earthquakes. The growth of normal faults is commonly described by two models: 1) the propagating fault model (isolated growth model), and 2) the constant-length model. The propagating fault model envisages a sympathetic increase between fault lengthening (L) and displacement (D), whereas the constant-length model states that faults reach their near-final length before accumulating significant displacement (Walsh et al., 2002). Several relatively recent studies agree that faults generally follow a constant-length model, or a &amp;#8220;hybrid model&amp;#8221; of the two, where most faults reach their near final length within the first 20-30% of their lives, and accrue displacement throughout. Furthermore, in the past 20 years, much research has focused on how faults grow; relatively few studies have questioned what happens to the fault geometry as it becomes inactive, i.e. do faults abruptly die, or do they more gradually become inactive by so-called tip retreat. We here use a 3D seismic reflection dataset from the Exmouth Plateau, offshore Australia to support a hybrid fault growth model for normal faults, and to also determine the relationship between length and displacement as a fault dies. We show that the studied faults grew in three distinct stages: a lengthening stage (&lt;30% of the faults life), a displacement accrual stage (30-75%), and a possible tip retreat stage (75%-end). This work has important implications in our understanding of the temporal evolution of normal faults, both how they grow and how they die.&lt;/p&gt;

Quantitative analysis of fault and fold growth in a salt-bearing transtensional basins: the Sørvestsnaget Basin, Western Barents Sea

2020 ◽  
pp. SP495-2020-123
Author(s):  
Thomas B. Kristensen ◽  
Atle Rotevatn ◽  
Maria Marvik ◽  
Gijs A. Henstra ◽  
Rob L. Gawthorpe ◽  
...  
Keyword(s):  
Barents Sea ◽  
Hanging Wall ◽  
Structural Evolution ◽  
Normal Fault ◽  
Growth Patterns ◽  
Hydrocarbon Exploration ◽  
Normal Faults ◽  
Lateral Migration ◽  
Seismic Reflection Data ◽  
Economic Implications

AbstractThe growth of faults and folds in basins formed under transtension has been less studied than in their extensional counterparts. In this study, we capitalise on 3D seismic reflection data to investigate the evolution of faults and folds that evolved coevally during sub-orthogonal partitioned extension and shortening, respectively, in the Sørvestsnaget Basin, Western Barents Sea. We use quantitative techniques to constrain the distribution of normal fault throw, shortening accommodated by folds and thrusts, and stratigraphic thickness variations, to analyse the relative temporal and spatial evolution of faults and folds. Our results show that normal faults display a similar evolution to those occurring in extensional basins, where they grew by lateral- and dip-linkage of individual fault segments as well as upward propagation. Notably, we show that shortening-related fold growth affected the fault growth patterns, skewing their throw distributions, and shifting the location of accommodation away from the evolving folds. Thus, fold amplification caused lateral migration of normal fault hanging-wall depocentres. Our results shed new light on fault and fold growth processes in transtensional basins and contributes to an improved understanding of the structural evolution of basins forming along sheared continental margins, which has economic implications for sheared-margin basins targeted for hydrocarbon exploration.

scholarly journals Repeated degradation and progradation of a submarine slope over geological timescales

2021 ◽  
Vol 91 (1) ◽  
pp. 116-145
Author(s):  
Christopher A-L. Jackson ◽  
Andrew E. McAndrew ◽  
David M. Hodgson ◽  
Tom Dreyer
Keyword(s):  
Large Scale ◽  
Normal Faults ◽  
Borehole Data ◽  
Late Mesozoic ◽  
Gravity Flows ◽  
Tectonically Active ◽  
Marine Facies ◽  
Fault Growth ◽  
Age Constraints ◽  
Lower Slope

ABSTRACT Submarine slopes prograde via accretion of sediment to clinoform foresets and degrade in response to channel or canyon incision or to mass-wasting processes. The timescales over which progradation and degradation occur, and the large-scale stratigraphic record of these processes, remain unclear due to poor age constraints in subsurface-based studies and areally limited exposures of exhumed systems. We here integrate 3D seismic reflection and borehole data to study the geometry and origin of ancient slope canyons developed in late Mesozoic strata of the Måløy Slope, offshore Norway. Slope degradation and canyon incision commenced during the late Kimmeridgian, coincident with the latter stages of rifting. Later periods of canyon formation occurred during the Aptian to Albian and the Albian to Cenomanian, during early post-rift subsidence. The canyons are straight, up to 700 m deep, and 10 km wide on the upper slope and die out downdip onto the lower slope. The canyons trend broadly perpendicular to and crosscut most of the rift-related normal faults, although syn-filling fault growth locally helped to preserve thicker canyon-fill successions. The headwalls of the oldest (late Kimmeridgian) canyons are located at a fault-controlled shelf edge, where younger canyons overstep this fault, which was inactive when they formed, extending across the paleo-shelf. Downslope, Aptian to Albian canyons either erode into the older, late Kimmeridgian to Barremian canyon fills, forming a complicated set of unconformities, or in the case of the Albian to Cenomanian canyons, die out into correlative conformities. Boreholes indicate that the canyon bases are defined by sharp, erosional surfaces, across which we observe an abrupt upward shift from shallow- to deep-marine facies (i.e., late Kimmeridgian canyons), or deep marine to deep marine facies (Aptian to Albian and Albian to Cenomanian canyons). Missing biostratigraphic zones indicate the canyons record relatively protracted periods (c. 2–17 Myr) of structurally enhanced slope degradation and sediment bypass, separated by &gt; 10 Myr periods of deposition and slope accretion. The trigger for slope degradation is unclear, but it likely reflects basinward tilting of this tectonically active margin, enhanced by incision of the slope by erosive sediment gravity flows. The results of our study have implications for the timescales over which large-scale slope progradation and degradation may occur on other tectonically active slopes, and the complex geophysical and geological record of these processes. We also show that canyon formation can cause large volumes of margin-derived sediment to bypass proximal sub-basins within rifted terranes, an important process not currently captured by marine rift-basin tectono-stratigraphic models.

scholarly journals A snapshot of the earliest stages of normal fault development

2021 ◽  
Author(s):  
Ahmed Alghuraybi ◽  
Rebecca Bell ◽  
Chris Jackson
Keyword(s):  
Seismic Reflection ◽  
Spatial Scales ◽  
Normal Fault ◽  
Normal Faults ◽  
3D Seismic ◽  
Seismic Reflection Data ◽  
Reflection Data ◽  
Temporal And Spatial ◽  
Fault Growth ◽  
Lateral Propagation

Despite decades of study, models for the growth of normal faults lack a temporal framework within which to understand how these structures accumulate displacement and lengthen through time. Here, we use borehole and high-quality 3D seismic reflection data from offshore Norway to quantify the lateral (0.2-1.8 mmyr-1) and vertical (0.004-0.02 mmyr-1) propagation rates (averaged over 12-44 Myr) for several long (up to 43 km), moderate displacement (up to 225 m) layer-bound faults that we argue provide a unique, essentially ‘fossilised’ snapshot of the earliest stage of fault growth. We show that lateral propagation rates are 90 times faster than displacement rates during the initial 25% of their lifespan suggesting that these faults lengthened much more rapidly than they accrued displacement. Although these faults have slow displacement rates compared with data compiled from 30 previous studies, they have comparable lateral propagation rates. This suggests that the unusual lateral propagation to displacement rate ratio is likely due to fault maturity, which highlights a need to document both displacement and lateral propagation rates to further our understanding of how faults evolve across various temporal and spatial scales.

Controls on gravity-driven normal fault geometry and growth in stacked deltaic settings: a case study from the Ceduna Sub-basin

2021 ◽  
Vol 61 (2) ◽  
pp. 632
Author(s):  
Monica Jimenez ◽  
Simon P. Holford ◽  
Rosalind C. King ◽  
Mark A. Bunch
Keyword(s):  
Normal Fault ◽  
Passive Margin ◽  
Seismic Survey ◽  
Normal Faults ◽  
Petroleum Systems ◽  
Kinematic Analyses ◽  
Gravity Driven ◽  
Fault Growth ◽  
Constant Growth

Kinematics of gravity-driven normal faults exerts a critical control on petroleum systems in deltaic settings but to date has not been extensively examined. The Ceduna Sub-basin (CSB) is a passive margin basin containing the White Pointer (Albian-Cenomanian) and Hammerhead (Campanian-Maastrichtian) delta systems that detach on shale layers of Albian-Cenomanian and Turonian-Coniacian ages, respectively. Here we present evidence for spatially variable fault growth styles based on interpretation of the Ceduna 3D seismic survey and fault kinematic analyses using displacement–distance, displacement–depth and expansion index methods. We identified faults that continuously grew either between the Cenomanian–Santonian or Santonian and the Maastrichtian located throughout the study area and faults that exhibit growth between the Cenomanian–Maastrichtian that are geographically separated into three areas according to their evolution histories: (i) Northern CSB faults exhibit constant growth between the Cenomanian and Maastrichtian. (ii) Central CSB faults show two dip-linkage intervals between (a) Cenomanian and Coniacian–Late Santonian, (b) Coniacian–Late Santonian and Late Santonian–Maastrichtian segments, respectively. (iii) Central and southern CSB faults exhibit dip-linkage intervals between Cenomanian–early Santonian and Late Santonian–Maastrichtian segments. Our study demonstrates a relationship between the location of the Cenomanian–Maastrichtian faults and their evolution history suggesting constant growth evolution at north and dip linkage at the central and south areas.

scholarly journals A new model for the growth of normal faults developed above pre-existing structures

Geology ◽  
2021 ◽  
Author(s):  
Emma K. Bramham ◽  
Tim J. Wright ◽  
Douglas A. Paton ◽  
David M. Hodgson
Keyword(s):  
Early Period ◽  
Normal Fault ◽  
Sedimentary Basins ◽  
Vertical Displacement ◽  
Wide Distribution ◽  
Airborne Lidar ◽  
Normal Faults ◽  
Constant Length ◽  
Existing Structures ◽  
Fault Growth

Constraining the mechanisms of normal fault growth is essential for understanding extensional tectonics. Fault growth kinematics remain debated, mainly because the very earliest phase of deformation through recent syn-kinematic deposits is rarely documented. To understand how underlying structures influence surface faulting, we examined fault growth in a 10 ka magmatically resurfaced region of the Krafla fissure swarm, Iceland. We used a high-resolution (0.5 m) digital elevation model derived from airborne lidar to measure 775 fault profiles with lengths ranging from 0.015 to 2 km. For each fault, we measured the ratio of maximum vertical displacement to length (Dmax/L) and any nondisplaced portions of the fault. We observe that many shorter faults (&lt;200 m) retain fissure-like features, with no vertical displacement for substantial parts of their displacement profiles. Typically, longer faults (&gt;200 m) are vertically displaced along most of their surface length and have Dmax/L at the upper end of the global population for comparable lengths. We hypothesize that faults initiate at the surface as fissure-like fractures in resurfaced material as a result of flexural stresses caused by displacements on underlying faults. Faults then accrue vertical displacement following a constant-length model, and grow by dip and strike linkage or lengthening when they reach a bell-shaped displacement-length profile. This hybrid growth mechanism is repeated with deposition of each subsequent syn-kinematic layer, resulting in a remarkably wide distribution of Dmax/L. Our results capture a specific early period in the fault slip-deposition cycle in a volcanic setting that may be applicable to fault growth in sedimentary basins.

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