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Papers by Ken McClay

Detailed analysis of the upper four seconds of a 3D seismic set acquired in BP's largest ever sur... more Detailed analysis of the upper four seconds of a 3D seismic set acquired in BP's largest ever survey (17,000 km 2 ) in the offshore Sirt Basin, Libya, has identified two distinct depositional elements attributed to gravitational collapse events within the Late Miocene to Recent sequences. They are cohesive slump complexes, and a slide body characterised by sidewall NE-SW shear zones and headwall faults. Localised ENE-WSW oblique extensional faults, and NNW-SSE trending normal faults have also been documented.

Geological Society of America Bulletin, 1994

Sedimentary Geology, 2007

The Makran accretionary prism is regarded as one of the most extensive subduction complex on Eart... more The Makran accretionary prism is regarded as one of the most extensive subduction complex on Earth. It provides an ideal example of accretionary prism to study processes related to subduction at plate boundaries such as frontal accretion and underplating. The rear portion of the wedge is uplifted and extended by normal faulting and ductile flow. Spectacular shale diapirs and mud volcanoes are present all along the external part of the prism and can be seen on the regional 2D-seismic section presented in this study. The Himalayan Turbidites sequence is the main detachment level for the imbricate fan and extensional faults of the Makran accretionary prism. It is also assumed to be the main source for rising shale diapirs and mud volcanoes along imbricated thrusts within the wedge. Evidence of active sediment remobilization is prevalent in the mid-slope morphotectonic province of the accretionary prism. It is proposed that the initiation of diapirism appears to be spatially coincident with the onset of underplating processes in the rear portion of the prism. The rapid uplift of the prism and the onset of extensional faults favour the extrusion of overpressured sediments and fluids/gas along thrust faults on the seaward side of the prism. The extensional faults above the deep zone of underplating have been mildly inverted implying episodic alternation of compression and extension. The geometry of the growth strata preserved in the limbs of the fault propagation folds in the outer part of the Makran accretionary prism reveals limb rotation as the main folding mechanism with uplift rate of the growing folds exceeding the sedimentation rate suggesting active thrusting at the wedge front. The growth strata patterns also indicate a synchronous activity of many of the thrusts of the imbricate fan system that exhibit a sequence of thrusting propagating toward the foreland.

Tectonophysics, 1993

Salt diapirs produce highly complex deformation patterns in the surrounding overburden which are ... more Salt diapirs produce highly complex deformation patterns in the surrounding overburden which are difficult to image seismically or model numerically. To further the understanding of deformation around salt structures we have used physical models with brittle granular overburdens, ...

Geology, 2001

We present the application of the HCA (hybrid cellular automata) numerical modeling technique to ... more We present the application of the HCA (hybrid cellular automata) numerical modeling technique to the evolution of compressional fault-bend anticlines involving layers that have competency contrasts and a mechanical stratigraphy. The new modeling results show that, for competent hanging-wall layers, (1) the fault style is not preserved in the overlying fold; (2) fold development is not self-similar, and rotational growth

Tectonophysics, 1999

... Identification and characterization of inverted extensional faults are common exploration tar... more ... Identification and characterization of inverted extensional faults are common exploration targets in inverted basins. ... This paper addresses the problem of which is the most reasonable 2D algorithm to ... restored in this paper with the aid of the structural modelling software Geosec ...

Tectonics, 2000

A sandbox analog modeling research program was used to study the detailed evolution of doubly-ver... more A sandbox analog modeling research program was used to study the detailed evolution of doubly-vergent thrust wedges. High-resolution multilayers of thin alternating sand and mica layers were used in contractional Coulomb wedge experiments to simulate deformation of anisotropic, brittle upper crustal strata in doubly-vergent orogens. Experiments incorporating syntectonic sedimentation in foreland basins and in piggyback basins were also carded out. Our laboratory models evolved in two main stages: (1) initial high-velocity thrusting in the retrowedge and high-frequency together with low displacement folding and thrusting in the prowedge; and (2) low-frequency, high-displacement synchronous thrusting in the prowedge and low-velocity thrusting in the retrowedge. Transition from stage I to stage II occurred when the growing wedges reached the critical height at which they behaved as a backstop for further prowedge accretion. Addition of syntectonic sediments increased the persistence of stage I and triggered out-of-sequence thrusting in the axial zone of the experimental orogens. Thrust motion was stick-slip. Retrovergent thrusting occurred along a long-lived ramp whose lower tip was located at the subduction slot. Provergent kink bands nucleated at the subduction slot in stage I. In contrast, during the second stage of wedge evolution, kink bands nucleated in a piggyback fashion in the foreland far from the subduction slot and then evolved into high-displacement faults that remained active up until the end of the experiments, at progressively decreasing rates of thrusting. The axial zones of the model wedges were characterized by fast uplift rates during stage I due to backward translation of the belt along the retrovergent, longlived ramp and due to the localization of deformation close to the subduction slot. Outward migration of the deformation front in the prowedge region during stage II caused the progressive decrease in the rate of the wedge uplift, until it eventually stopped. Analytical models to quantify the Coulomb behavior in the wedges validated the reversal of thrust polarity with increasing shortening, triggered by the buildup of the topographic load during deformation. This thrust polarity reversal highlights problems with the classic concept of back thrusting as a reflection of a significant

Marine and Petroleum Geology, 2004

The Frampton growth anticline is part of the Atwater Valley-Southern Green Canyon frontal fold be... more The Frampton growth anticline is part of the Atwater Valley-Southern Green Canyon frontal fold belt in the deep-water northeastern Gulf of Mexico. The anticline is located basinward of the allochthonous Sigsbee Salt sheet near the Sigsbee Escarpment. The timing and mechanisms of the formation of the frontal fold have been investigated using palinspatically restored depth sections and by the analysis of the growth stratal architecture preserved on fold limbs. The Frampton anticline is cored by autochthonous Middle Jurassic Louann salt and its western limit is bounded by the Green Knoll diapir. The fold geometry varies along strike, from a symmetric box-fold in the east, to a breached detachment fold in the west. Small-wavelength salt pillows formed during the Late Jurassic-Cretaceous in response to an early contractional deformation. These precursor structures controlled the geometry of Tertiary age folding. The Green Knoll diapir, west of the Frampton anticline, influenced deformation, leading to complex interactions between segments of the fold system and associated thrust faults. A landward-vergent thrust fault accommodated shortening adjacent to the diapir whereas folding was the main mechanism of deformation in the eastern part of Frampton anticline. Analysis of growth strata indicates that the detachment anticline developed according to a progressive limb rotation kinematic model with minor hinge migration. The fold evolution model proposed in this study could be used as an analogue for less well imaged, hydrocarbon-bearing growth folds in the deep-water province of the Gulf of Mexico, particularly those that are partially obscured by overlying allochthonous salt sheets. q

Marine and Petroleum Geology, 2011

This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the East... more This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the Eastern Venezuelan Basin and the main conclusions about shale tectonic mechanisms in the area. The deformation of the foreland-fold-belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs. Three contractional episodes are proposed for the Eastern Venezuelan Basin: 1) Oligocene to middle Miocene, 2) late Miocene to Pliocene and 3) Pleistocene. The first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying Cretaceous units. The second episode produced the deformation of the Cenozoic strata into overlapping east-west-trending, convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide, break-through normal faults product of a high sedimentary load that overcomes contraction and the formation of short-displacement blind thrusts in the underlying Cretaceous units. The last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and NW-SE strike. The role of the shale tectonics in the evolution implies that shale deforms in two stages: 1) folding and 2) normal faulting of the crest of the anticline (Break through normal faulting). Folding controlled the sediment distribution during most of the Neogene strata, while the normal faulting of the anticlines represent basin potential for hydrocarbon. The best potential hydrocarbon plays in the basin are related to oblique-collision restricted basins and controlled by breakthrough normal faults and the presence of NW-SE strike faults that connect the HC source with the reservoirs. Results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds.

Marine and Petroleum Geology, 1995

The results are presented from two-dimensional, transient numerical models which incorporate temp... more The results are presented from two-dimensional, transient numerical models which incorporate temperature, rheology, sedimentation and isostasy for finite rift durations. These models are used to address the role of fault growth and resultant basin geometry in the presence of rheological heterogeneity, generated during continental lithospheric extension. The transition between brittle and plastic rheologies, within the yield strength envelope, is used

Marine and Petroleum Geology, 1996

The modern-day slope and outer shelf of the Niger Delta are characterized by fault-bounded sedime... more The modern-day slope and outer shelf of the Niger Delta are characterized by fault-bounded sedimentary depocentres and intervening shale structures, some of which are diapiric. Using two-dimensional seismic reflection data and stratigraphic information from five wells, the Neogene history of a 70 × 30 km portion of the northwestern Niger Delta shelf and slope has been examined. The shale structures were established by Late Miocene time, probably in response to lateral shale withdrawal from beneath the advancing deltaic load, combined with compressional uplift and folding of pro-delta strata. During Pliocene and Pleistocene time, these structures were buried by the prograding delta, and extensional growth faulting commenced. Stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period. Throughout the Pliocene, extension and subsidence were concentrated in a graben-like depocentre bounded by both regional and counter-regional growth faults. During the Early Pleistocene, subsidence on the regional growth fault ceased, and growth was transferred to the counter-regional growth fault set. The geometry and history of the depocentre is analogous to salt-related depocentres typical of the northern Gulf of Mexico and Atlantic margins of Brazil and Angola. To explain the history of the Niger Delta study area, a model is proposed in which the Miocene-Pleistocene sedimentary package has slid basinward, breaking up during extension, thereby creating seaward-stepping depocentres. Examples from analogue modelling studies are used to suggest possible origins for the large counter-regional growth faults.

Marine and Petroleum Geology, 2009

This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doub... more This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation. Two sets of experiments were considered: (1) the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge; and (2) the addition to the previous condition of a progradational sedimentary load. Results from the first set of experiments indicate that the foreland fold-and-thrust belt has a strong relationship with the competence of the syntectonic layers. When the competence is low, the deformation produces tight asymmetric detachment-folds. As the competence increases, the fold-and-thrust belt shows breaktrough folds with longer and better defined foreland-vergence. Results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers, and in the case of strong aggradation at the prowedge, extension and reactive diapirism form contemporaneously with the contraction. Three end-members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation: (1) outcropping foldand-thrust belt sequence, in the case of no syntectonic sedimentation; (2) long displacement blindthrust sheets, in the case of under-filled basins and (3) short displacement blind-thrust sheets, in the case of over-filled basins. All results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge, and reduce the critical taper. Results also indicate that at very high sedimentary rates and hyper-critical taper conditions the prowedge collapses. Conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation, migration, and entrapment in thrust belts in areas where seismic imaging is generally poor.

Marine and Petroleum Geology, 2009

Scaled sandbox models were used to investigate the 4D evolution of pull-apart basins formed above... more Scaled sandbox models were used to investigate the 4D evolution of pull-apart basins formed above underlapping releasing stepovers in both pure strike-slip and transtensional basement fault systems. Serial sectioning and 3D volume reconstruction permitted analysis of the full 3D fault geometries. Results show that very different pull-apart basins are developed in transtension compared to pure strike-slip. Both types of models produced elongate, sigmoidal to rhomboidal pull-apart systems, but the transtensional pull-apart basins were significantly wider and uniquely developed a basin margin of enechelon oblique-extensional faults. Dual, opposing depocentres formed in the transtensional model whereas a single, central depocentre formed in pure strike-slip. In transtension, a distinct narrow graben system formed above the principal displacement zones (PDZs). Cross-basin fault systems that linked the offset PDZs formed earlier in the transtensional models. Sequential model runs to higher PDZ displacements allowed the progressive evolution of the fault systems to be evaluated. In cross-section, transtensional pull-aparts initiated as asymmetric grabens bounded by planar oblique-extensional faults. With increasing displacement on the PDZs, basin subsidence caused these faults to become concave-upwards and lower in dip angle due to fault block collapse towards the interior of the basin. In addition, strain partitioning caused fault slip to become either predominantly extensional or strike-slip. The models compare closely with the geometries of natural pull-apart basins including the southern Dead Sea fault system and the Vienna Basin, Austria.

Marine and Petroleum Geology, 2009

A discrete-element model is used to investigate the manner in which deformation and fault activit... more A discrete-element model is used to investigate the manner in which deformation and fault activity change in space and time during the development of a doubly vergent thrust wedge in the upper crust. Deformation is a result of shortening at a subduction slot in the base of the model, a configuration which produces a dynamic backstop within the cohesionless, frictional cover material. A series of experiments with differing basal (decollement) friction are performed. The distinct manners in which thrust wedges grow, and the variability of fault development and activity in space and time, are then examined. Both predicted large-scale wedge geometries and individual fault-fold structures are similar to those observed in sandbox models, and show the complex manner in which shortening is accommodated and localized during the development of the thrust wedge. When compared to a sandbox model with similar boundary conditions, model results are strikingly similar. In all cases, deformation initiates above the subduction slot with the formation of an axial zone; the wedge is then developed by displacement on a retro-wedge thrust and propagation of deformation into the pro-wedge region. Models with low coefficients of basal friction typically develop wide, shallow wedges with distributed, spaced deformation and rather symmetric, box-like structures; whereas those with high coefficients of basal friction develop narrower, steeper wedges, consisting of a series of stacked, pro-wedge thrust sheets, and a high-displacement retro-wedge thrust. In general, fault initiation and linkage is extremely complex in our models, with several smaller faults operating until linkage occurs to form a major through-going structure. Of particular interest is the observation that many of the faults do not develop at the basal decollement and propagate upwards through the cover but rather initiate at high levels in the cover and propagate/link downwards with other, deeper structures. Results also indicate the utility of the discreteelement approach in modelling large-displacement, complex deformation of geological materials. r

Journal of Structural Geology, 1997

... Josep Poblet a , Ken McClay b , Fabrizio Storti c and Josep Anton Muñoz d. a Departament de G... more ... Josep Poblet a , Ken McClay b , Fabrizio Storti c and Josep Anton Muñoz d. a Departament de Geologia Dinàmica, Geofisica i Paleontologia, Facultat de Geologia, Universitet de Barcelona, C/Marti i Fratiquès s/n, 08071, Barcelona, Spain. ...

Journal of Structural Geology, 1999

Many studies have shown that in extensional basins discrete faulting at depth is commonly linked ... more Many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation, in particular folding, at higher levels. Such extensional fault-propagation folds are particularly common where there is a distinct mechanical ...

Journal of Structural Geology, 2003

Fault geometry is a primary control on hanging wall deformation. In order to examine their geomet... more Fault geometry is a primary control on hanging wall deformation. In order to examine their geometrical relationships, a positive inversion analogue experiment was conducted using a rigid fault surface of listric geometry. The hanging wall deformation observed on a representative vertical section was examined with conventional 2D geometric models, and was restored to its pre-inversion phase with two techniques. These results suggest that the deformation can be best approximated by inclined simple shearing (ISS). The ISS model can determine the inclination of the apparent shear plane and the amount of apparent horizontal shortening, which is equivalent to that calculated with the conventional depth-to-detachment method. This estimated apparent shortening was generally smaller than the actual amount of the experiments, probably due to tectonic compaction. q

Island Arc, 2010

Tectonic inversion is a common phenomenon in island arc settings, especially in back-arc basins. ... more Tectonic inversion is a common phenomenon in island arc settings, especially in back-arc basins. The reactivation of normal faults as thrusts, triggered by tectonic inversion, produces typical inversion fault-related folds and thrusts in the hangingwall. These hangingwall inversion geometries are affected by two factors: the geometry of the underlying master fault and the angle of inclined simple shear relative to the regional dip of strata, in the case that the deformation is approximated by simple shear. This study employed numerical simulations to analyse the influence of the antithetic shear angle on the geometry of the hangingwall and displacement along the master fault. The simulation results reveal that a steeply inclined shear vector during extension produces a narrow, steep-sided half-graben, whereas a gently inclined shear produces a wide, open basin. After tectonic inversion, a tight anticline is formed under steeply inclined shear, whereas an open anticline is formed under gently inclined shear. Antithetic shear results in reduced total displacement along the master fault, and the greater the angle between the shear direction and the regional dip, the greater the displacement along the master fault. Because the deformation geometry of syn-extension layers is affected by extension followed by contraction, a change in the shear angle during tectonic inversion produces a wide variety of deformation geometries. Comparison of the simulation results with the results of analogue modelling suggests that the shear angle decreases by 5°during the transition from extension to tectonic inversion and that such a change may be commonly observed in natural geological structures. These results highlight the benefits of numerical simulations, which can be used to readily examine a variety of constraining parameters and thereby lead to a better understanding of the mechanism of hangingwall deformation, avoiding erroneous estimates of the amount of fault displacement.

Detailed analysis of the upper four seconds of a 3D seismic set acquired in BP's largest ever sur... more Detailed analysis of the upper four seconds of a 3D seismic set acquired in BP's largest ever survey (17,000 km 2 ) in the offshore Sirt Basin, Libya, has identified two distinct depositional elements attributed to gravitational collapse events within the Late Miocene to Recent sequences. They are cohesive slump complexes, and a slide body characterised by sidewall NE-SW shear zones and headwall faults. Localised ENE-WSW oblique extensional faults, and NNW-SSE trending normal faults have also been documented.

Geological Society of America Bulletin, 1994

Sedimentary Geology, 2007

The Makran accretionary prism is regarded as one of the most extensive subduction complex on Eart... more The Makran accretionary prism is regarded as one of the most extensive subduction complex on Earth. It provides an ideal example of accretionary prism to study processes related to subduction at plate boundaries such as frontal accretion and underplating. The rear portion of the wedge is uplifted and extended by normal faulting and ductile flow. Spectacular shale diapirs and mud volcanoes are present all along the external part of the prism and can be seen on the regional 2D-seismic section presented in this study. The Himalayan Turbidites sequence is the main detachment level for the imbricate fan and extensional faults of the Makran accretionary prism. It is also assumed to be the main source for rising shale diapirs and mud volcanoes along imbricated thrusts within the wedge. Evidence of active sediment remobilization is prevalent in the mid-slope morphotectonic province of the accretionary prism. It is proposed that the initiation of diapirism appears to be spatially coincident with the onset of underplating processes in the rear portion of the prism. The rapid uplift of the prism and the onset of extensional faults favour the extrusion of overpressured sediments and fluids/gas along thrust faults on the seaward side of the prism. The extensional faults above the deep zone of underplating have been mildly inverted implying episodic alternation of compression and extension. The geometry of the growth strata preserved in the limbs of the fault propagation folds in the outer part of the Makran accretionary prism reveals limb rotation as the main folding mechanism with uplift rate of the growing folds exceeding the sedimentation rate suggesting active thrusting at the wedge front. The growth strata patterns also indicate a synchronous activity of many of the thrusts of the imbricate fan system that exhibit a sequence of thrusting propagating toward the foreland.

Tectonophysics, 1993

Salt diapirs produce highly complex deformation patterns in the surrounding overburden which are ... more Salt diapirs produce highly complex deformation patterns in the surrounding overburden which are difficult to image seismically or model numerically. To further the understanding of deformation around salt structures we have used physical models with brittle granular overburdens, ...

Geology, 2001

We present the application of the HCA (hybrid cellular automata) numerical modeling technique to ... more We present the application of the HCA (hybrid cellular automata) numerical modeling technique to the evolution of compressional fault-bend anticlines involving layers that have competency contrasts and a mechanical stratigraphy. The new modeling results show that, for competent hanging-wall layers, (1) the fault style is not preserved in the overlying fold; (2) fold development is not self-similar, and rotational growth

Tectonophysics, 1999

... Identification and characterization of inverted extensional faults are common exploration tar... more ... Identification and characterization of inverted extensional faults are common exploration targets in inverted basins. ... This paper addresses the problem of which is the most reasonable 2D algorithm to ... restored in this paper with the aid of the structural modelling software Geosec ...

Tectonics, 2000

A sandbox analog modeling research program was used to study the detailed evolution of doubly-ver... more A sandbox analog modeling research program was used to study the detailed evolution of doubly-vergent thrust wedges. High-resolution multilayers of thin alternating sand and mica layers were used in contractional Coulomb wedge experiments to simulate deformation of anisotropic, brittle upper crustal strata in doubly-vergent orogens. Experiments incorporating syntectonic sedimentation in foreland basins and in piggyback basins were also carded out. Our laboratory models evolved in two main stages: (1) initial high-velocity thrusting in the retrowedge and high-frequency together with low displacement folding and thrusting in the prowedge; and (2) low-frequency, high-displacement synchronous thrusting in the prowedge and low-velocity thrusting in the retrowedge. Transition from stage I to stage II occurred when the growing wedges reached the critical height at which they behaved as a backstop for further prowedge accretion. Addition of syntectonic sediments increased the persistence of stage I and triggered out-of-sequence thrusting in the axial zone of the experimental orogens. Thrust motion was stick-slip. Retrovergent thrusting occurred along a long-lived ramp whose lower tip was located at the subduction slot. Provergent kink bands nucleated at the subduction slot in stage I. In contrast, during the second stage of wedge evolution, kink bands nucleated in a piggyback fashion in the foreland far from the subduction slot and then evolved into high-displacement faults that remained active up until the end of the experiments, at progressively decreasing rates of thrusting. The axial zones of the model wedges were characterized by fast uplift rates during stage I due to backward translation of the belt along the retrovergent, longlived ramp and due to the localization of deformation close to the subduction slot. Outward migration of the deformation front in the prowedge region during stage II caused the progressive decrease in the rate of the wedge uplift, until it eventually stopped. Analytical models to quantify the Coulomb behavior in the wedges validated the reversal of thrust polarity with increasing shortening, triggered by the buildup of the topographic load during deformation. This thrust polarity reversal highlights problems with the classic concept of back thrusting as a reflection of a significant

Marine and Petroleum Geology, 2004

The Frampton growth anticline is part of the Atwater Valley-Southern Green Canyon frontal fold be... more The Frampton growth anticline is part of the Atwater Valley-Southern Green Canyon frontal fold belt in the deep-water northeastern Gulf of Mexico. The anticline is located basinward of the allochthonous Sigsbee Salt sheet near the Sigsbee Escarpment. The timing and mechanisms of the formation of the frontal fold have been investigated using palinspatically restored depth sections and by the analysis of the growth stratal architecture preserved on fold limbs. The Frampton anticline is cored by autochthonous Middle Jurassic Louann salt and its western limit is bounded by the Green Knoll diapir. The fold geometry varies along strike, from a symmetric box-fold in the east, to a breached detachment fold in the west. Small-wavelength salt pillows formed during the Late Jurassic-Cretaceous in response to an early contractional deformation. These precursor structures controlled the geometry of Tertiary age folding. The Green Knoll diapir, west of the Frampton anticline, influenced deformation, leading to complex interactions between segments of the fold system and associated thrust faults. A landward-vergent thrust fault accommodated shortening adjacent to the diapir whereas folding was the main mechanism of deformation in the eastern part of Frampton anticline. Analysis of growth strata indicates that the detachment anticline developed according to a progressive limb rotation kinematic model with minor hinge migration. The fold evolution model proposed in this study could be used as an analogue for less well imaged, hydrocarbon-bearing growth folds in the deep-water province of the Gulf of Mexico, particularly those that are partially obscured by overlying allochthonous salt sheets. q

Marine and Petroleum Geology, 2011

This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the East... more This paper presents a structural and stratigraphic analysis of the foreland-fold-belt of the Eastern Venezuelan Basin and the main conclusions about shale tectonic mechanisms in the area. The deformation of the foreland-fold-belt has been investigated analyzing the growth strata architecture preserved on the structure fold limbs. Three contractional episodes are proposed for the Eastern Venezuelan Basin: 1) Oligocene to middle Miocene, 2) late Miocene to Pliocene and 3) Pleistocene. The first episode produced contractional listric faults inside the shale and long displacement blind thrusts in the underlying Cretaceous units. The second episode produced the deformation of the Cenozoic strata into overlapping east-west-trending, convex northward anticlines that covers more than 200 kilometers in length and 40 kilometers wide, break-through normal faults product of a high sedimentary load that overcomes contraction and the formation of short-displacement blind thrusts in the underlying Cretaceous units. The last episode is related to an oblique compression and the formation of high angle extensional faults with dextral movement and NW-SE strike. The role of the shale tectonics in the evolution implies that shale deforms in two stages: 1) folding and 2) normal faulting of the crest of the anticline (Break through normal faulting). Folding controlled the sediment distribution during most of the Neogene strata, while the normal faulting of the anticlines represent basin potential for hydrocarbon. The best potential hydrocarbon plays in the basin are related to oblique-collision restricted basins and controlled by breakthrough normal faults and the presence of NW-SE strike faults that connect the HC source with the reservoirs. Results from this research imply that the role of sedimentation is fundamental for the overburden sand distribution and tectonic constrain of the folds.

Marine and Petroleum Geology, 1995

The results are presented from two-dimensional, transient numerical models which incorporate temp... more The results are presented from two-dimensional, transient numerical models which incorporate temperature, rheology, sedimentation and isostasy for finite rift durations. These models are used to address the role of fault growth and resultant basin geometry in the presence of rheological heterogeneity, generated during continental lithospheric extension. The transition between brittle and plastic rheologies, within the yield strength envelope, is used

Marine and Petroleum Geology, 1996

The modern-day slope and outer shelf of the Niger Delta are characterized by fault-bounded sedime... more The modern-day slope and outer shelf of the Niger Delta are characterized by fault-bounded sedimentary depocentres and intervening shale structures, some of which are diapiric. Using two-dimensional seismic reflection data and stratigraphic information from five wells, the Neogene history of a 70 × 30 km portion of the northwestern Niger Delta shelf and slope has been examined. The shale structures were established by Late Miocene time, probably in response to lateral shale withdrawal from beneath the advancing deltaic load, combined with compressional uplift and folding of pro-delta strata. During Pliocene and Pleistocene time, these structures were buried by the prograding delta, and extensional growth faulting commenced. Stacked onlap relationships and stacked erosional channels indicate that the shale structures continued to influence sedimentation patterns throughout this period. Throughout the Pliocene, extension and subsidence were concentrated in a graben-like depocentre bounded by both regional and counter-regional growth faults. During the Early Pleistocene, subsidence on the regional growth fault ceased, and growth was transferred to the counter-regional growth fault set. The geometry and history of the depocentre is analogous to salt-related depocentres typical of the northern Gulf of Mexico and Atlantic margins of Brazil and Angola. To explain the history of the Niger Delta study area, a model is proposed in which the Miocene-Pleistocene sedimentary package has slid basinward, breaking up during extension, thereby creating seaward-stepping depocentres. Examples from analogue modelling studies are used to suggest possible origins for the large counter-regional growth faults.

Marine and Petroleum Geology, 2009

This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doub... more This paper shows the evolution of time-constrained two-dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation. Two sets of experiments were considered: (1) the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge; and (2) the addition to the previous condition of a progradational sedimentary load. Results from the first set of experiments indicate that the foreland fold-and-thrust belt has a strong relationship with the competence of the syntectonic layers. When the competence is low, the deformation produces tight asymmetric detachment-folds. As the competence increases, the fold-and-thrust belt shows breaktrough folds with longer and better defined foreland-vergence. Results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers, and in the case of strong aggradation at the prowedge, extension and reactive diapirism form contemporaneously with the contraction. Three end-members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation: (1) outcropping foldand-thrust belt sequence, in the case of no syntectonic sedimentation; (2) long displacement blindthrust sheets, in the case of under-filled basins and (3) short displacement blind-thrust sheets, in the case of over-filled basins. All results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge, and reduce the critical taper. Results also indicate that at very high sedimentary rates and hyper-critical taper conditions the prowedge collapses. Conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation, migration, and entrapment in thrust belts in areas where seismic imaging is generally poor.

Marine and Petroleum Geology, 2009

Scaled sandbox models were used to investigate the 4D evolution of pull-apart basins formed above... more Scaled sandbox models were used to investigate the 4D evolution of pull-apart basins formed above underlapping releasing stepovers in both pure strike-slip and transtensional basement fault systems. Serial sectioning and 3D volume reconstruction permitted analysis of the full 3D fault geometries. Results show that very different pull-apart basins are developed in transtension compared to pure strike-slip. Both types of models produced elongate, sigmoidal to rhomboidal pull-apart systems, but the transtensional pull-apart basins were significantly wider and uniquely developed a basin margin of enechelon oblique-extensional faults. Dual, opposing depocentres formed in the transtensional model whereas a single, central depocentre formed in pure strike-slip. In transtension, a distinct narrow graben system formed above the principal displacement zones (PDZs). Cross-basin fault systems that linked the offset PDZs formed earlier in the transtensional models. Sequential model runs to higher PDZ displacements allowed the progressive evolution of the fault systems to be evaluated. In cross-section, transtensional pull-aparts initiated as asymmetric grabens bounded by planar oblique-extensional faults. With increasing displacement on the PDZs, basin subsidence caused these faults to become concave-upwards and lower in dip angle due to fault block collapse towards the interior of the basin. In addition, strain partitioning caused fault slip to become either predominantly extensional or strike-slip. The models compare closely with the geometries of natural pull-apart basins including the southern Dead Sea fault system and the Vienna Basin, Austria.

Marine and Petroleum Geology, 2009

A discrete-element model is used to investigate the manner in which deformation and fault activit... more A discrete-element model is used to investigate the manner in which deformation and fault activity change in space and time during the development of a doubly vergent thrust wedge in the upper crust. Deformation is a result of shortening at a subduction slot in the base of the model, a configuration which produces a dynamic backstop within the cohesionless, frictional cover material. A series of experiments with differing basal (decollement) friction are performed. The distinct manners in which thrust wedges grow, and the variability of fault development and activity in space and time, are then examined. Both predicted large-scale wedge geometries and individual fault-fold structures are similar to those observed in sandbox models, and show the complex manner in which shortening is accommodated and localized during the development of the thrust wedge. When compared to a sandbox model with similar boundary conditions, model results are strikingly similar. In all cases, deformation initiates above the subduction slot with the formation of an axial zone; the wedge is then developed by displacement on a retro-wedge thrust and propagation of deformation into the pro-wedge region. Models with low coefficients of basal friction typically develop wide, shallow wedges with distributed, spaced deformation and rather symmetric, box-like structures; whereas those with high coefficients of basal friction develop narrower, steeper wedges, consisting of a series of stacked, pro-wedge thrust sheets, and a high-displacement retro-wedge thrust. In general, fault initiation and linkage is extremely complex in our models, with several smaller faults operating until linkage occurs to form a major through-going structure. Of particular interest is the observation that many of the faults do not develop at the basal decollement and propagate upwards through the cover but rather initiate at high levels in the cover and propagate/link downwards with other, deeper structures. Results also indicate the utility of the discreteelement approach in modelling large-displacement, complex deformation of geological materials. r

Journal of Structural Geology, 1997

... Josep Poblet a , Ken McClay b , Fabrizio Storti c and Josep Anton Muñoz d. a Departament de G... more ... Josep Poblet a , Ken McClay b , Fabrizio Storti c and Josep Anton Muñoz d. a Departament de Geologia Dinàmica, Geofisica i Paleontologia, Facultat de Geologia, Universitet de Barcelona, C/Marti i Fratiquès s/n, 08071, Barcelona, Spain. ...

Journal of Structural Geology, 1999

Many studies have shown that in extensional basins discrete faulting at depth is commonly linked ... more Many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation, in particular folding, at higher levels. Such extensional fault-propagation folds are particularly common where there is a distinct mechanical ...

Journal of Structural Geology, 2003

Fault geometry is a primary control on hanging wall deformation. In order to examine their geomet... more Fault geometry is a primary control on hanging wall deformation. In order to examine their geometrical relationships, a positive inversion analogue experiment was conducted using a rigid fault surface of listric geometry. The hanging wall deformation observed on a representative vertical section was examined with conventional 2D geometric models, and was restored to its pre-inversion phase with two techniques. These results suggest that the deformation can be best approximated by inclined simple shearing (ISS). The ISS model can determine the inclination of the apparent shear plane and the amount of apparent horizontal shortening, which is equivalent to that calculated with the conventional depth-to-detachment method. This estimated apparent shortening was generally smaller than the actual amount of the experiments, probably due to tectonic compaction. q

Island Arc, 2010

Tectonic inversion is a common phenomenon in island arc settings, especially in back-arc basins. ... more Tectonic inversion is a common phenomenon in island arc settings, especially in back-arc basins. The reactivation of normal faults as thrusts, triggered by tectonic inversion, produces typical inversion fault-related folds and thrusts in the hangingwall. These hangingwall inversion geometries are affected by two factors: the geometry of the underlying master fault and the angle of inclined simple shear relative to the regional dip of strata, in the case that the deformation is approximated by simple shear. This study employed numerical simulations to analyse the influence of the antithetic shear angle on the geometry of the hangingwall and displacement along the master fault. The simulation results reveal that a steeply inclined shear vector during extension produces a narrow, steep-sided half-graben, whereas a gently inclined shear produces a wide, open basin. After tectonic inversion, a tight anticline is formed under steeply inclined shear, whereas an open anticline is formed under gently inclined shear. Antithetic shear results in reduced total displacement along the master fault, and the greater the angle between the shear direction and the regional dip, the greater the displacement along the master fault. Because the deformation geometry of syn-extension layers is affected by extension followed by contraction, a change in the shear angle during tectonic inversion produces a wide variety of deformation geometries. Comparison of the simulation results with the results of analogue modelling suggests that the shear angle decreases by 5°during the transition from extension to tectonic inversion and that such a change may be commonly observed in natural geological structures. These results highlight the benefits of numerical simulations, which can be used to readily examine a variety of constraining parameters and thereby lead to a better understanding of the mechanism of hangingwall deformation, avoiding erroneous estimates of the amount of fault displacement.