tectonism the dominant factor in mid cretaceous deposition in the jeanne d arc basin grand banks abstract the development of stratigraphic sequences has been demonstrated to be controlled by a set of factors including variations in subsidence sediment input eustatic sea level and physiography well and seismic data from the jeanne d arc basin grand banks indicate that mid cretaceous tectonism controls at least three of these factors namely subsidence sediment input and physiography north atlantic rift tectonism was therefore the dominant factor in controlling the migration of coastal to shallow marine environments and the development of sequence stratigraphy in this basin during the mid cretaceous the avalon formation respresents a mainly barremian to early aptian regressive phase of clastic marine to marginal marine sedimentation this followed the deposition of a thick sequence of mainly marine limestones and shales of the whiterose formation above a mid valanginian sequence bounding unconformity the increased clastic input and northward progradation of coastal environments represented by the avalon formation occurred during uplift of a basement arch to the south with subsidence of the basin increasing to the north accompanied by only relatively minor faulting these features indicate that a period of epeirogenesis was initiated during the barremian continuing uplift over an expanding area at the southern end of the basin is interpreted to have resulted in the development of an angular unconformity with incised valleys this mid aptian unconformity defines the top of the whiterose avalon sequence initiation of brittle fracturing of the sedimentary package and underlying basement i e rifting in mid aptian times resulted in rapid fault controlled subsidence and fragmentation of the jeanne d arc basin this great increase in subsidence rate caused retrogradation of coastal environments across the previously developed sequence bounding unconformity despite continuing high rates of sediment input from the uplifted basin margins the transgressive siliciclastic ben nevis formation comprises two separate but related facies associations a locally preserved basal association represents interfingering back barrier environments and is herein defined as the gambo member an upper ubiquitous facies association comprises tidal inlet channel shoreface and lower shoreface offshore transition sandstones this upper facies association onlapped marine ravinement diastems above the laterally equivalent back barrier facies the rapid fault controlled subsidence and high sediment input rate of this mid aptian to late albian rift period resulted in the accumulation and preservation of very thick shoreface sandstones the transgressive sandstones were buried by laterally equivalent offshore shales of the nautilus formation flooding of the basin margins induced by the onset of thermal subsidence in latest albian or early cenomanian times marks the top of the ben nevis nautilus syn rift sequence

fault reactivation control on normal fault growth an experimental study field studies frequently emphasize how fault reactivation is involved in the deformation of the upper crust however this phenomenon is generally neglected except in inversion models in analogue and numerical models performed to study fault network growth using sand silicon analogue models we show how pre existing discontinuities can control the geometry and evolution of a younger fault network the models show that the reactivation of pre existing discontinuities and their orientation control i the evolution of the main fault orientation distribution through time ii the geometry of relay fault zones iii the geometry of small scale faulting and iv the geometry and location of fault controlled basins and depocenters these results are in good agreement with natural fault networks observed in both the gulf of suez and lake tanganyika they demonstrate that heterogeneities such as pre existing faults should be included in models designed to understand the behavior and the tectonic evolution of sedimentary basins

evaluating sand and clay models do rheological differences matter abstract dry sand and wet clay are the most frequently used materials for physical modeling of brittle deformation we present a series of experiments that shows when the two materials can be used interchangeably document the differences in deformation patterns and discuss how best to evaluate and apply results of physical models extension and shortening produce similar large scale deformation patterns in dry sand and wet clay models indicating that the two materials can be used interchangeably for analysis of gross deformation geometries there are subtle deformation features that are significantly different 1 fault propagation and fault linkage 2 fault width spacing and displacement 3 extent of deformation zone and 4 amount of folding vs faulting these differences are primarily due to the lower cohesion of sand and its larger grain size if these features are of interest the best practice would be to repeat the experiments with more than one material to ensure that rheological differences are not biasing results dry sand and wet clay produce very different results in inversion models almost all faults are reactivated in wet clay and few if any are significantly reactivated in sand models fault reactivation is attributed to high fluid pressure along the fault zone in the wet clay a situation that may be analogous to many rocks sand inversion models may be best applied to areas where most faults experience little to no reactivation while clay models best fit areas where most pre existing normal faults are reactivated

controls of listric normal fault styles in the northern gulf of mexico insights from experimental models abstract passive margins such as the gulf of mexico are characterized by two distinct styles of faulting homogenous sand shale packages in offshore texas mostly display basinward dipping listric normal faults with associated rollover structures cut by synthetic and antithetic faults the fault traces are generally long and show a linear trend stratigraphic packages with a ductile substratum salt in offshore louisiana are characterized by basinward and landward dipping short arcuate faults detaching within the salt the structures consist of a series of half grabens with the movement of salt from the front to the back of each fault block clay experimental models are used to study the controls of fault geometries in the two structural styles and their interaction to form complex transfer zones the surface of the clay cake is laser scanned to enable 3d visualization and accurate measurements of structures the results suggest that within homogeneous sand shale packages the dips of the faults and their locations are primarily dependent on the direction of the drop down of the basal detachment along pre existing discontinuities with the slope of the basal discontinuity and the direction of extension providing secondary controls on the other hand the dips of fault systems in packages underlain by a ductile substratum are primarily controlled by the slope of the basal detachment therefore the more common regional roho systems typically form above salt sheets with initial basinward slopes whereas counter regional fault systems form above salt sheets with initial landward slopes the direction of extension and the presence of small pre existing discontinuities impart only secondary controls when ductile basal units are involved the faults initiate at the head of ductile layer and propagate downslope complex transfer zones develop at the boundary of the ductile substratum due to interference between the two fault styles

influence of rift obliquity on fault population systematics results of experimental clay models abstract we use clay models to simulate how fault population systematics vary as a function of rift obliquity rift obliquity is related to the acute angle between the rift trend and the displacement direction so that the value of is inverse to the degree of obliquity the range of azimuths in a fault population increases as rift obliquity increases i e as decreases the length of the longest faults the sum of fault lengths and the width of the deformed zone all increase as rift obliquity decreases i e as increases the majority of faults in our models are segmented and have highly tortuous traces tortuosity is maximum when 30 as segments of widely varying azimuth link during fault growth significant changes occur in the fault patterns between 30 and 45 at 30 two fault populations of equal importance develop in the center of the rift zone one approximately rift parallel and the other displacement normal between 30 and 45 the number of faults more than doubles and between 45 and 60 summed fault length more than doubles fault patterns for all models are fractal with fractal dimensions that increase with increasing and that are comparable to those found in the field fault populations are not multi fractal because the cumulative frequency distributions of fault lengths do not generally follow a power law relationship an exponential distribution best describes the data for whole faults with the characteristic length increasing with increasing segment lengths also follow an exponential distribution with characteristic length varying very little with the fault patterns in our models resemble the spatial pattern of brittle deformation observed at oblique mid ocean ridge segments and are similar in geometry to those in oblique continental rift basins at the rift margins tensional stresses are modulated and reoriented by a secondary stress field related to a change in boundary conditions resulting in the formation of two distinct sub populations of faults during oblique rifting

the mechanical relationship between strike slip faults and salt diapirs in the zagros fold thrust belt analogue models are used to study the mechanical relationship between basement strike slip faults and salt diapirs displacement along a strike slip fault in 1 g models resulted in extension along pre existing jogs and the formation of oblique extensional faults where reactive diapirs were triggered in some models in the centrifuge models prescribed cuts simulating pre existing structures were reactivated during simple shear deformation of the models resulting in formation of pull apart basins which were intruded by diapirs the models show that because of the low ratio of salt to overburden thickness in the zagros 0 15 0 35 it is unlikely that diapirs have formed solely if at all as a result of movement along basement strike slip faults two mechanisms are suggested first pre kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the zagros which were later downbuilt to their current geometry by additional sedimentation second movement along the strike slip faults e g the kazerun and mangarak faults induced oblique movement along nw se zagros structures folds or thrusts resulting in the formation of pull apart basins where diapirs were eventually intruded fault plane solution of shallow earthquakes supports the second scenario which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than zagros shortening and young southwestwards

double evaporitic decollements influence of pinch out overlapping in experimental thrust wedges abstract this article focuses on how deformation and displacements are transferred between two decollements located at different stratigraphic levels by means of analogue modeling using brittle viscous sand silicone systems we present results from ten analogue models in which we varied key parameters such as the amount of horizontal offset or overlap between the pinch outs of the upper and lower decollements the total amount of shortening and the planform geometry of the upper decollement results indicate that i structures root onto the basal and upper decollement defining an inner and an outer domain and ii the offset overlap of the decollements controls the geometry of the transition zone located between the two decollements the propagation of deformation into the foreland both in space and time and the deformation style and kinematics in the different domains of the model when the pinch out of the upper decollement is at an angle with the backstop oblique structures form and the geometry and propagation mode of the structures change progressively along strike we compare our experimental results with other silicone sand analogue models and with the natural examples of the southern pyrenees where upper triassic and eocene oligocene syn tectonic evaporites acted as basal and upper decollements respectively

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

forced folding and basement detached normal faulting in the haltenbanken area offshore norway triassic evaporites affected the structural development of the haltenbanken area of offshore norway during the late jurassic and early cretaceous by mechanically isolating triassic and younger strata from older strata and basement many folds in the haltenbanken area are forced folds above basement involved normal faults forced folds formed at least in part because triassic evaporites behaved ductilely decoupling overlying strata from underlying faulted strata and basement seismic data show that these forced folds are asymmetric flexures that affect lower cretaceous jurassic and triassic strata strata beneath the traiassic evaporites are faulted some forced folds die out along strike into and are cut by basement involved normal faults folding predominated above salt swells where decoupling was enhanced whereas faulting occurred on the flanks of salt swells where salt thicknesses were reduced and decoupling was less effective many normal faults in the haltenbanken area are basement detached and flatten within the triassic evaporites seismic data show that rollover anticlines and antithetic normal faults affect lower cretaceous jurassic and triassic strata within the hanging walls of these basement detached normal faults strata beneath the evaporites are not affected by this deformation some basement detached normal faults may be secondary structures associated with forced folding others especially thosemore with large displacements may have formed in response to gravity sliding less

characteristics and deformation mechanism of salt related structures in the western kuqa depression tarim basin insights from scaled sandbox modeling abstract three scaled analog sandbox models are constructed to simulate the evolution of thick skinned shortening on broad and narrow salt basins these models simulate the evolution of the cenozoic salt salt related structures in the westernmost kuqa salt bearing depression quele area tarim basin the formation mechanism and the controlling factors of structural deformation in this area are investigated and discussed systematically model results show that the variable depositional width of the salt basin has a major controlling influence on the differential structural deformation in different longitudinal segmentations from east broad to west narrow in the western kuqa depression quele area model results also demonstrate that the early salt structure salt diapir has an important controlling role on the subsequent compressional structural deformation the pre existing thin overburden quele diapir which acts as a stress concentration zone during the subsequent shortening is deformed to the quele salt nappe on the basis of the model results it is suggested that the formation of the long distance quele allochthonous salt sheet is related with the pre existing quele diapir which displaces up paralleling the hanging wall and flows to the surface during the subsequent shortening

testing thin skinned inversion of a prerift salt bearing passive margin eastern prebetic zone se iberia abstract detailed geologic mapping combined with well and seismic data from the eastern prebetic zone se iberia reveal extensional and contractional structures that permit characterization of passive margin development and its incorporation into a thin skinned fold and thrust belt the study area is represented by nw directed ene trending folds and thrusts faults locally disrupted by the nw trending matamoros basin and the active jumilla and la rosa diapirs these structures resulted from the thin skinned inversion of the proximal part of the eastern south iberian passive margin containing prerift salt here upper jurassic to santonian thick skinned extension controlled the accumulation of sediment over mobile prerift salt this in turn defined the style of salt tectonics characterized by monoclinal drape folds suprasalt extensional faults and diapirs the structural and sedimentological analysis suggests that during extension salt localizes strain thus decoupling sub and suprasalt deformation thick skinned extension controls suprasalt deformation as well as its location and distribution which changes over time salt also localizes strain during inversion the preexisting salt structures weaker than adjacent areas preferentially absorb the contractional deformation in addition the stepped subsalt geometry that results from thick skinned extension also controls the shortening propagation therefore the degree of strain localization depends on the thickness of the suprasalt cover and on the dip of subsalt faults relative to the thin skinned transport direction

deformation pattern during normal faulting a sequential limit analysis we model in 2 d the formation and development of half graben faults above a low angle normal detachment fault the model based on a sequential limit analysis accounting for mechanical equilibrium and energy dissipation simulates the incremental deformation of a frictional cohesive and fluid saturated rock wedge above the detachment two modes of deformation gravitational collapse and tectonic collapse are revealed which compare well with the results of the critical coulomb wedge theory we additionally show that the fault and the axial surface of the half graben rotate as topographic subsidence increases this progressive rotation makes some of the footwall material being sheared and entering into the hanging wall creating a specific region called foot to hanging wall fhw the model allows introducing additional effects such as weakening of the faults once they have slipped and sedimentation in their hanging wall these processes are shown to control the size of the fhw region and the number of fault bounded blocks it eventually contains fault weakening tends to make fault rotation more discontinuous and this results in the fhw zone containing multiple blocks of intact material separated by faults by compensating the topographic subsidence of the half graben sedimentation tends to slow the fault rotation and this results in the reduction of the size of the fhw zone and of its number of fault bounded blocks we apply the new approach to reproduce the faults observed along a seismic line in the southern jeanne d arc basin grand banks offshore newfoundland there a single block exists in the hanging wall of the principal fault the model explains well this situation provided that a slow sedimentation rate in the lower jurassic is proposed followed by an increasing rate over time as the main detachment fault was growing

kinematic and geometric analysis of fault related folds in a rift setting the dannemarie basin upper rhine graben france abstract the upper rhine graben urg developed in the alpine foreland from mid eocene to pliocene as part of the west european rift system the dannemarie basin occupies the sw termination of the urg and is bordered by the vosges fault zone west and the illfurth fault zone east we constructed a 3d model of faults and principal pre and syn rift stratigraphic surfaces using all available subsurface and surface geological and geophysical data the model shows 1 syn rift strata thinning across kilometre scale fault parallel monoclinal flexures associated with basin margin faults and 2 major basin margin faults terminating laterally into major flexures sequential cross section restorations show that these flexures accommodated deposition of over 1300 m of syn rift strata salt series which is 42 63 of the basin fill these folds are interpreted as syn rift fault propagation folds that developed above normal faults their geometry is replicated in a trishear numerical model using reasonable parameter values fold development was controlled principally by 1 reactivation of favourably oriented basement faults 2 the presence of a thick viscous layer principally triassic evaporites allowing decoupling between crystalline basement and competent jurassic cover and 3 a relatively slow deformation rate

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

evolution and timing of salt diapirism in the iranian sector of the persian gulf abstract the iranian sector of the persian gulf is affected by more than 30 large diapiric structures triggered by the mobilization of the infracambrian hormuz complex an evaporite rich unit that overlies precambrian basement at the base of the sedimentary succession nineteen non piercing diapirs without any appreciable salt intrusion into the upper succession were studied in detail and retro deformed by the decompaction and unfolding of 13 seismic horizons that were identified by the interpretation of a dense grid of 2d seismic lines and calibrated by well data salt uplift had begun by the early palaeozoic and persists to the present day with major pulses of intensity during the middle triassic cenomanian late oligocene and post middle miocene the structural reconstructions and the analysis of the progressive deformation of the study diapirs do not show any link between diapiric uplift and local tectonic structures and no clear correlation with the regional geodynamic events acting at the boundary of the arabian plate on the contrary the salt uplift seems strongly influenced by the differential rate of sedimentation that affected the whole study basin more than 40 000 km 2 with a coefficient of correlation between the salt uplift rate and the differential rate of sedimentation expressed by the standard deviation of the sedimentation rate calculated over the entire basin of 0 95 this downbuilding mechanism of diapiric growth is apparently induced by differential sedimentation over long distances several tens of kilometers showing that the flow of salt affected the whole basin and not just the areas around the single diapiric structures

scandinavia s north atlantic passive margin 1 the tectonics of the eastern passive margin of the north atlantic are reexamined the scandinavian north atlantic passive margin includes not only the offshore exploration and basin domain but also large portions of the onshore domains of the scandinavian caledonides combined information from structural geology potential field data regional geology basin development and geomorphology made it possible to propose a new definition of the passive margin the rift shoulder is formed by linked faults defining the present rift flank these faults are the extensional structures located furthest to the east onshore norway sweden that can be linked to the rifting that led to the formation of the north atlantic this innermost boundary fault system ibf is formed by a set of normal west dipping crustal faults it extends over a distance exceeding 2000 km from the north sea across the caledonian mountain belt to the barents sea the passive margin width between the continent ocean boundary and the ibf ranges from 550 km in the south to over 700 km in mid norway to 165 km north of lofoten rifting and faulting on the ibf started in permo carboniferous and a succession of rift phases eventually culminated in continental breakup and the formation of the north atlantic basin development between permian and cretaceous was toward the future breakaway fault but faulting was also active on land from mesozoic to present onshore offshore crustal scale cross sections show the geometry of the passive margin the dip orientation of the major faults and the changes in crustal thickness

extensional tectonics and stratigraphy of hibernia oil field grand banks newfoundland the tectonic evolution of the grand banks involved several episodes of rifting and sequential development of the continental margin the dominant period of rifting and basin formation in the central grand banks was late callovian to aptian extensional failure of the central grand banks crust probably occurred along a shear zone that dipped gently to the west listric normal basin forming faults merge at depth with this detachment system the listric murre fault soles at 26 km 16 mi creating the very deep jeanne d arc basin cross basin transfer faults accommodated different amounts and rates of extension and resulted in the conspicuous offset pattern and funnel shaped geometry of the jeanne d arc basin the hibernia oil field is associated with one of these structural salients the stratigraphy of the jeanne d arc basin and the hibernia oil field is a direct response to this tectonic and structural framework large scale unconformity bounded sequences correspond to major plate reorganizations and zipper type opening of the atlantic ocean smaller scale adjustments to episodic extension are expressed in multiple stacking of depositional sequences the broad scale evolution of the synrift succession involved the early deposition of limestones and oil prone shales about 10 12 m y later rifting climaxed resulting in floods of coarse terrestrial material from the rift shoulders the characteristics of these depositional systems reflect a pervasive structural control affecting the distribution of facies tracts dip slip movement on basin bounding faults and c oss basin transfer fault trends were equally important a profound structural modification of the hibernia structure occurred in late barremian time when a major detachment developed within the basin fill this structural modification and associated antithetic and synthetic faulting in the hanging wall largely controlled reservoir distribution and the maturation migration and trapping of hydrocarbons

from mesozoic rifting to apennine orogeny the gran sasso range italy the apennines are a low temperature accretionary prism generated by the west directed subduction of the adriatic ionian plate whose structural origin is still to be fully understood the highest and best exposed seg ment of the apennines the gran sasso range is here documented to unravel the tectonic history of the northern tip of gondwana it is located along a ne verging salient of thrust sheets decoupling the sedimentary cover of the subducting adriatic lithosphere field mapping and structural analysis along the e w trending left lateral transpressive segment of the salient highlight the interplay of the inherited mesozoic passive margin stratigraph ic and tectonic framework with the neogene contraction the rheological differences between the massive carbonate platform and the well bedded turbiditic and pelagic limestones determined along strike undulations of the thrusts geometries and fold styles during shortening heterogeneities are due to inherited syn and post rift mesozoic tectonics the gran sasso overturned anticline shows a backlimb anomalously tilted toward the foreland and we infer this dip as being related to a deeper back thrust of a triangle zone the pinching out of the foredeep sequence on the growth anticline forelimb dates the contractional phases of the region to the late messinian from the late pliocene to present the area has been uplifted and extended about 2 km by oblique normal faults cross cutting the accretionary prism some of them are seismically active as shown by the 2009 mw 6 3 l aquila earthquake

episodic activity of a dormant fault in tectonically stable europe the rauw fault ne belgium abstract our knowledge about large earthquakes in stable continental regions comes from studies of faults that generated historical surface rupturing earthquakes or were identified by their recent imprint in the morphology here we evaluate the co seismic character and movement history of the rauw fault in belgium which lacks geomorphological expression and historical present seismicity this 55 km long normal fault with known neogene and possibly early pleistocene activity is the largest offset fault west of the active roer valley graben its trace was identified in the shallow subsurface based on high resolution geophysics all the layers within the late pliocene mol formation 3 6 to 2 59 ma are displaced 7 m vertically without growth faulting but deeper deposits show increasing offset a paleoseismic trench study revealed cryoturbated but unfaulted late glacial coversands overlying faulted layers of mol formation in between those deposits the fault tip was eroded along with evidence for individual displacement events fragmented clay gouge observed in a micromorphology sample of the main fault evidences co seismic faulting as opposed to fault creep based on optical and electron spin resonance dating and trench stratigraphy the 7 m combined displacement is bracketed to have occurred between 2 59 ma and 45 ka the regional presence of the sterksel formation alluvial terrace deposits limited to the hanging wall of the rauw fault indicates a deflection of the meuse rhine confluence 1 0 to 0 5 ma by the fault s activity suggesting that most of the offset occurred prior to at this time interval in the trench sterksel formation is eroded but reworked gravel testifies for its former presence hence the rauw fault appears as typical of plate interior context with an episodic seismic activity concentrated between 1 0 and 0 5 ma or at least between 2 59 ma to 45 ka possibly related to activity variations in the adjacent continuously active roer valley graben

an experimental study of the secondary deformation produced by oblique slip normal faulting we have used scaled clay models to define the secondary deformation produced by oblique slip normal faulting in the models the master fault beneath the clay layer dips 45 degrees and strikes at a 45 degrees angle relative to the heave direction i e the horizontal component of the displacement direction thus the master fault has both normal dip slip and strike slip components of displacement the modeling results show the following 1 the fault patterns produced by oblique slip normal faulting vary significantly with depth secondary faults that strike obliquely to the master fault trend are more abundant near the top of the clay layer whereas secondary faults that are subparallel to the master fault trend are more abundant at depth 2 a single episode of oblique slip normal faulting produces two populations of secondary faults that have different trends and ages secondary faults that strike obliquely to the master fault trend are more abundant during the early stages of the experiments whereas secondary faults that strike subparallel to the master fault trend are more abundant during the later stages of the experiments 3 relay ramps between overlapping secondary synthetic normal faults are wide and temporally persistent in oblique slip models the ramps are cut by numerous small scale normal faults that are subparallel to the ramp bounding faults cross faults are uncommon and begin to develop only during the final stages of the experiments 4 both map and cross section data are necessary to distinguish among the deformation patterns produced by strike slip oblique slip and dip slip faulting the map views of oblique slip models closely resemble those of strike slip models in both models many of the secondary faults strike obliquely to the master fault trend these map views however differ considerably from those of dip slip models in which most of the secondary faults strike subparallel to the master fault trend alternatively the cross sectional views of oblique slip models are similar to those of dip slip models in both models a highly faulted extensional forced fold develops these cross sectional views are dissimilar to those of strike slip models which show no appreciable folding and no change of regional level

discrete element modelling of hanging wall deformation along the d 1 fault system danish north sea with implications for gas chimney interpretations abstract this study uses 3d seismic mapping nncc attribute analysis and 2d sdem modelling of soft sediment deformation to analyse hanging wall deformation related to faulting across a listric fault detaching along the top of a major salt roller the computational model experiments used the overall fault and salt structure evolution as boundary conditions to predict the distribution of faults within the hanging wall the modelling successfully reproduced geometries similar to the syn and antithetic faults that are visible on seismics but it also showed the presence of well defined vertical deformation zones both in the hanging wall and the foot wall of the listric fault in the model salt movement controls the formation of the deformation zones the similarity of nncc inferred vertical chimneys and the modelled deformation zones suggests that the subtle vertical chimneys identified in the 3d seismic data might actually be related to vertical to sub vertical deformation zones caused by the presence and movement of the salt structure

structural style of buried ediacaran basins in saudi arabia on seismic reflection data abstract several isolated ediacaran basins subcrop phanerozoic strata in saudi arabia the structural styles of these subcropping basins are reviewed here based on interpretation of 2d and 3d seismic reflection data and comparison with arabian shield outcrops the basins are distinguished by layered seismic reflectors that are interpreted as sedimentary and volcanic strata due to limited well penetrations these packages cannot be directly dated but a relative chronology is established anchored by constraints from the arabian shield and regional studies most of the basins are bound by extensional faults and the basin fills show growth architectures and angular unconformities the bounding faults trend broadly north south and are interpreted to be late to post orogenic reactivations of oceanic terrane margins based on their structural characteristics in comparison with sub basins exposed on the shield the basin fills are correlated with the ediacaran jibalah group an equivalent of the omani nafun group these sub basins experienced inversion and exhumation prior to ongoing volcanism and unconformable deposition of late ediacaran to earliest cambrian kurayshah group sediments the kurayshah group is disconformably overlain by the widespread tayma group siliciclastics this disconformity correlates to the angudan unconformity in oman the kurayshah group includes a late ediacaran stratovolcano over 40 km in diameter in the eastern basins evaporitic structural styles indicate the presence of hormuz ara evaporites with local igneous intrusions that correlate at least in part to the kurayshah group the tayma group infills significant accommodation space variations and was affected by ongoing but declining differential subsidence and reactivation of the underlying basin bounding faults

analogue and numerical modelling of salt supply to a diapiric structure rising above an active basement fault salt diapirs preferably rise above basement faults in extensional basins a series of analogue and numerical models were developed in order to assess the supply of salt from the footwall and hanging wall to a diapir and to study the influence of basin inversion on the diapir development the modelling scenario was based on the klodawa salt structure evolution central poland the experiments show that the ductile material derived from the footwall constitutes the dominant portion of the diapir developed due to model extension and this material occurs both in the footwall and hanging wall parts of the diapir shortening of the analogue models resulted in thinning of the diapir and shifting its stem onto the footwall ductile material become redistributed inside the diapir however footwall material still prevails in the diapir structure results from the numerical models show that the magnitude of the basement fault governs the amount of salt supply to a diapir across the fault and that there is a differential salt supply from the hanging wall and footwall with time

extensional tectonics in the jeanne d arc basin offshore newfoundland implications for the timing of break up between grand banks and iberia

the three dimensional geometry of relay zones within segmented normal faults abstract individual normal faults are rarely single planar surfaces and often comprise arrays of fault segments arising from the earliest stages of fault propagation current models for the geometry and formation of relay zones between adjacent fault segments have been informed mainly by 2d analysis from either maps or cross sections observed in outcrop and to a lesser extent by the analysis of relay zones from 3d seismic reflection data using high quality 3d seismic reflection datasets from a selection of sedimentary basins we investigate fundamental characteristics of segmentation from the analysis of 67 normal faults with modest displacements

the structural styles and formation mechanism of salt structures in the southern precaspian basin insights from seismic data and analog modeling abstract using the seismic profiles and analog modeling this paper addresses the salt structures in the m and b blocks in the southern precaspian basin the salt structural features the formation mechanism and the controlling factors of structural deformation are investigated and discussed systematically the interpretation of the seismic profiles shows that typical salt related structures include salt wall flip flop salt diapir salt roller salt pillow dome salt weld salt withdrawal minibasin and drag structure or drape fold in addition model results demonstrate that the gravity spreading driven by progradation and aggradation is probably the primary factor in controlling the formation of the salt structures in the research area due to the differential loading driven by progradation passive salt diapir developed near the progradational front followed by the formation of intrasalt withdrawal minibasin bounded by two salt diapirs and secondary reactive triangle salt diapir or salt pillow might form within the intrasalt withdrawal minibasin model results also indicate that the pattern of the subsalt basement has important influence on the formation and evolution of salt structures salt diapirs primarily developed along the margin of the subsalt uplift basement where high shear deformation was induced by differential sedimentary loading between the uplift area and the slope area

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

fault controlled evaporite deformation in the levant basin eastern mediterranean abstract during the messinian salinity crisis a multi layered salt giant of 1 5 km thickness was precipitated in the levant basin easternmost mediterranean sea incipient deformation of this geologically young salt layer was commonly explained by gravity driven processes only based on high quality depth migrated seismic data we show for the first time how sub salt extensional faults influence the internal deformation pattern of the messinian evaporites in the levant basin extensional faulting started in the middle miocene and lasted until late messinian times we suggest faulting to have caused the development of fault propagation folds within the evaporite unit subsequently folds may have accommodated tectonic shortening at the latakia ridge and evolved into the presently observed complex intra evaporite fold pattern while fault controlled evaporite deformation is evident in the northern part of the levant basin only evaporites are increasingly influenced by nile derived differential sediment loading towards the south locally zones of reduced amplitudes in the sub salt domain terminate into phase reversed bright spots within the lower part of the evaporites indicating active fluid migration and potentially evaporite dissolution finally we present a high resolution velocity model of the messinian evaporites based on model based processing and residual moveout analysis relatively high interval velocities of acoustically transparent evaporites 3850 4240 km s are consistent with halite whereas lower velocities of reflective layers 3650 4030 km s may point towards the presence of low velocity evaporite facies like gypsum

geometric and experimental models of extensional fault bend folds the geometric models ranged from simple models of listric normal faults with continuous hanging wall deposition to complex models of normal faults with ramps and flats and footwall deposition and or erosion the inclined shear angle i e the angle between the horizontal and the shear direction was 70 in all models withjack and peterson 1993 describe the modeling technique in the experimental models a 4 cm thick layer of either wet clay or dry sand covered a flat metal base consisting of overlapping plates or precut blocks movement of the plates or blocks produced a listric normal fault in the overlying clay or sand layer we added growth layers after every centimeter of displacement withjack and callaway 2000 describe the properties of the wet clay and dry sand

bowl shaped basin related to low angle detachment during continental extension the case of the controversial neogene siena basin central italy northern apennines abstract this paper deals with the tectonic evolution of a bowl shaped neogene basin siena basin located in the inner northern apennines and developed during an articulated tectonic evolution this basin was controversially interpreted by different authors as graben half graben or thrust top basin structural and stratigraphic data from the basin substratum and filling sediments integrated with the interpretation of reflection seismic profiles and borehole logs highlight that the siena basin consists of a tectonic depression with a complex internal architecture such a basin developed on a multilayered substratum deeply affected by extensional tectonics since the middle miocene extensional detachments produced a widespread thinning of the basin substratum and superimposed on contractional structures developed during the northern apennines collisional events extensional detachments accommodated within weak horizons and gave rise to the lateral segmentation of most competent stratigraphic horizons sediments filling the siena basin mainly deposited on the ligurian units the topmost tectonic units forming the tectonic pile in the gap between two laterally segmented geological bodies made up of the triassic siliciclastic succession of the verrucano group such a lateral segmentation produced a synformal structural depression not delimited by faults filled by late serravallian late messinian marine to continental sediments which deposited during the extensional faulting from the latest early pliocene to the middle pliocene the architecture of the basin was modified by an high angle normal fault system which affected the eastern side of the basin and produced new accommodation space for marine sediments in sum the siena basin consists of a sin tectonic basin developed on the hanging wall of staircase extensional detachments later affected by high angle normal to oblique faults the latter faults defined a half graben during the latest evolution of the basin the tectonic evolution of the siena basin made it possible to point out some differences with respect to the types of bowl shaped basins related to extensional detachments and named as supradetachment basins

growth folds above propagating normal faults abstract growth folds above the upper tips of normal faults are ubiquitous in extensional settings especially during the early phases of extension and in salt rich basins as slip accumulates on the underlying normal fault the geometry and size of the fold changes these changes reflect the dip throw displacement and propagation rate of the underlying normal fault as well as the thickness and rheology of the overlying cover these changes also have a marked impact on the architecture and distribution of synkinematic sediments as well as the styles of secondary deformation accommodating strain within the growing fold here we analyse a large dataset of natural and physically and numerically modelled growth folds to i characterise their diagnostic features ii investigate the controls on their geometry size and differences and iii describe how they grow with increasing extensional strain we demonstrate that larger fault throws and a thicker and weaker cover are associated with larger growth folds in contrast small fault throws as well as thin and strong brittle cover are associated with smaller growth folds we show that the geometry and size of growth folds vary through time the width and thus the wavelength of the fold is established relatively early during fold growth whereas fold amplitude increases gradually with increasing fault throw fold width and amplitude become increasingly similar during fold evolution until the fold is breached by the underlying normal fault we also derive a number of preliminary empirical relationships between readily observable structural and stratigraphic parameters in our dataset that may help estimate the geometry and size of poorly exposed i e in the field or imaged i e in the subsurface growth folds in addition we discuss how fault growth models i e constant length vs propagating may impact the three dimensional evolution of growth folds finally our work shows that growth folds are likely more common than previously thought for example although they are well documented in areas characterised by weak ductile cover strata and low strain rates our dataset illustrates that growth folds may also occur in brittle relatively strong rocks and in regions with high strain rates however the underlying controls on fold occurrence remain elusive

surface expression of an accommodation zone within the gulf of suez rift egypt the gebel gharamul region in the western gulf of suez offers an excellent outcrop example of the structural geometries associated with an accommodation zone termination the surface expression of the accommodation zone is dominated by a basement promontory which protrudes from the rift shoulder and underlies the junction of oblique ramps from two adjacent half grabens both of which face the gulf of suez the southern half graben represents the breakaway fault of the southwest dipping tilt block domain and the northern half graben represents the collapse of the upper plate above the northeast dipping tilt block domain basement and nubian rocks in the hanging walls above the opposing low angle detachments on either side of the accommodation zone are broken by gulf parallel synthetic normal faults and orthogonal transfer faults which act as block terminations and incrementally accommodate the large scale rotation and displacement between adjacent blocks the prerift and synrift stratigraphic succession is draped over this fault template resulting in a complex and variable distribution of structures the product of an inhomogeneous stratigraphic succession within an accommodation zone

sequence stratigraphic response to aptian albian rifting in conjugate margin basins a comparison of the jeanne d arc basin offshore newfoundland and the porcupine basin offshore ireland

experiments on fault reactivation in strike slip mode abstract experiments were undertaken to investigate how faults reverse or normal in a cover sequence become reactivated when an underlying basement fault is itself reactivated in strike slip mode physical models properly scaled for gravity were deformed in a large 2 1 5 m apparatus divided into two halves one half can be moved laterally or vertically past the other models were constructed with a coulomb layer sand overlying a newtonian ductile layer silicone three different configurations of the basement fault reverse normal or vertical defined three series of experiments each consisted of 1 brittle model 6 cm of sand and 2 brittle ductile models 5 cm of sand overlying 1 cm of silicone or 4 cm of sand overlying 2 cm of silicone each model was deformed in two steps 1 a pure dip slip stage and 2 a reactivation in pure strike slip mode in surface views little reactivation was observed but in all cases the deformation imposed during the strike slip episode was localized by pre existing dip slip structures in cross sections however faults were seen reactivated at depth on the basis of these experiments we suggest that 1 a previously faulted zone can control the deformation of a strike slip zone and 2 reactivation of faults in strike slip mode can occur at depth without being visible at the surface we attribute the higher probability of reactivation at depth to the mechanical properties of the sand especially cohesion

the role of pre existing discontinuities in the development of extensional faults an analog modeling perspective abstract several mountainous regions are currently affected by syn or post orogenic active extension we investigate how a newly formed normal fault interacts with structures inherited from a previous contractional phase to this end we use analog models that adopt an innovative technique for performing a precut that mimics such inherited structures into a clay layer this clay layer is laid on top of a master fault simulated by two rigid blocks sliding along an inclined plane we carry out six experiments with variously oriented precuts and compare the results with those obtained in a reference isotropic experiment all other conditions are identical for all seven realizations fault evolution is monitored by taking closely spaced snapshots analyzed through the digital image correlation method we find that the upward propagation of the normal fault can be either accelerated or decelerated depending on the presence of a precut and its orientation such precuts can also promote or inhibit the formation of bending moment faults these interactions between master fault and precut also affect the shape of the fault related syncline anticline pair

structural analysis of a salt cored transfer zone in the south timbalier block 54 offshore gulf of mexico implications for restoration of salt related extensional structures the style of faulting in offshore louisiana gulf of mexico is characterized by short arcuate regional and counterregional growth faults which commonly form complex transfer zones above shallow miocene level salt bodies south timbalier block 54 st54 constitutes one such area where a basinward dipping regional and a landward dipping counterregional growth fault form a convergent transfer zone structural interpretation using three dimensional 3 d seismic and well data reveals that the eastern and western flanks of the structure contain salt in the footwalls of the main regional and counterregional faults the salt rises to a much shallower stratigraphic level in the central part of the transfer zone forming a symmetric salt diapir secondary antithetic and synthetic faults adjacent to the two main faults and extending into the transfer zone accommodate slip between the main faults kinematic restoration of a series of north south trending cross sections across the structure show that upslope evacuation of salt is the result of sediment loading and growth fault movement and the location of the transfer zone is possibly controlled by the allochthonous salt the entire area is characterized by down to basin movement with the major regional and counterregional faults displaying footwall and hanging wall fixed deformation respectively the presence of the crestal graben above the salt high and the timing of maximum salt evacuation from the flanks suggest that active or reactive diapirism occurred during part of the deformation history a 3 d structural model using depth converted horizons balanced cross sections and well tops accurately portrays the subsurface structure understanding the evolution of the structure in st54 provides insight on similar structures in other areas in offshore louisiana and the relationship between salt evacuation and transfer zone development

reactive surface area control of the dissolution kinetics of biogenic silica in deep sea sediments abstract flow through dissolution experiments demonstrate that the specific reactive surface area of biogenic silica decreases significantly with depth in surficial sediments of the southern ocean specific surface areas obtained from nitrogen gas bet adsorption isotherms however do not exhibit the systematic changes of the specific reactive surface area inferred from the kinetic experiments furthermore the decrease in surface reactivity of the siliceous skeleton fragments continues at depths in the sediments where there is no longer a net release of silicic acid to the pore waters thus the specific reactive surface changes most likely reflect a progressive reduction of the surface density of reactive sites aging during burial rather than the preferential dissolution of a more reactive fraction of siliceous debris deposited from the water column the observed aging of the silica surfaces has important consequences for the benthic regeneration of nutrient silicic acid from deep sea sediments

formation and inversion of salt detached ramp syncline basins results from analog modeling and application to the columbrets basin western mediterranean abstract the widespread extensional deformation that took place during jurassic to cretaceous times in western europe and the north atlantic margin resulted in the formation of several rift systems some of the resulting basins associated with these rifts show broad synclines detached on pre or syn kinematic permian or triassic salts and are filled by thick sedimentary successions the development of these salt detached ramp syncline basins has been associated to the extensional motion of ramp flat extensional sub salt faults the shape and kinematics of such faults have usually been established using the architecture of syn kinematic units and by assuming complete coupling of the hanging wall rocks therefore there are fault interpretations that do not consider the role played by the deep salt layers which clearly act as an effective detachment decoupling sub and supra salt deformations moreover the complexity of these scenarios further increases due to some of these basins which during latest cretaceous and cenozoic times were partially inverted and were often incorporated into fold and thrust belts based on analog models and using the mesozoic columbrets basin western mediterranean as a case study the aim of this research is to decipher the influence of the ramp flat extensional fault during the syncline development and the interaction with a pre kinematic salt and to infer how salt detached ramp syncline basins are subsequently inverted to achieve this goal we carried out an experimental program consisting of eight different sandbox models our results show that the main structure formed at the end of the extension is a salt detached ramp syncline and that its geometry not only depends on the dip and length of the fault panels but also on the fault displacement and salt thickness the inversion of these salt detached ramp synclines resulted in a major thick skinned fault bend anticline with minor thin skinned contractional structures

active transform fault zone at the fringe of the dead sea basin the evolution of an asymmetric basin at the edge of a pull apart structure is studied using geophysical observations and mechanical modeling a new seismic analysis of the northern edge of the dead sea basin indicates recent subsidence folding and oblique faulting along the jericho strike slip fault a main segment of the dead sea transform fault the subvertical fault trace crosses the entire sedimentary sequence typically branching in the shallow subsurface the seismic analysis reveals the three dimensional structure of the area as an asymmetrical basin bordered on the east and on the west by long monoclinic folds the thickness of the sedimentary fill varies from 1 4 km near the present lake shores to a few hundreds of meters about 10 km northward the subsidence is partitioned between a vertical component of slip along the jericho fault and the simultaneously active monoclines bordering the basin we present a model and simulations that reconstruct the present basin structure in the uppermost part of the crust and demonstrates the generation of flexures along the basin margins without horizontal shortening we show that the basin asymmetry and the association of folds and fault can be explained as a long term ductile response of the sediments to local subsidence the asymmetry along the basin is a consequence of a later vertical displacement component on a pre existing strike slip fault our analysis points to ongoing northward propagation of the dead sea basin and provides an explanation for the structural asymmetry of the basin margins

tectonic development of the mid norway continental margin abstract the area reviewed covers the mid norway continental margin between latitudes 62 n and 68 n main structural elements as defined at the base cretaceous level are the trondelag platform underlying the inner shelf the more and voring basins located beneath the outer shelf and slope and the more platform and the outer voring plateau forming a base of slope trend of highs sediments contained in the mid norway basin range in age from late palaeozoic to cenozoic the basement was consolidated during the caledonian orogenic cycle devonian and early carboniferous wrench movements along the axis of the arctic north atlantic caledonides are thought to have preceded the namurian onset of crustal extension rifting processes were intermittently active for some 270 my until crustal separation between greenland and fennoscandia was achieved during the early eocene during the evolution of the norwegian greenland sea rift system a stepwise concentration of tectonic activities to its axial zone the area of subsequent continental separation is observed during the late palaeozoic to mid jurassic a broad zone was affected by tensional faulting during the late jurassic and cretaceous the trondelag platform was little affected by faulting whilst major rift systems in the more and voring basins subsided rapidly and their shoulders became concomitantly upwarped during the latest cretaceous and early palaeogene terminal rifting phase only the western more and voring basins were affected by intrusive and extrusive igneous activity following the early eocene crustal separation and the onset of sea floor spreading in the norwegian greenland sea the voring segment of the mid norway marginal basin subsided less rapidly than the more segment during the early and mid tertiary minor compressional deformations affected the voring basin and to a lesser degree the more basin tensional forces dominated the late palaeozoic to early cenozoic evolution of the mid norway basin and effected strain mainly in the area where the crust was weakened by the previous lateral displacements the lithosphere thinned progressively and the effects of the passively upwelling hot asthenospheric material became more pronounced massive dyke invasion of the thinned crust preceded its rupture

decoupled extensional faulting and forced folding in the southern part of the roer valley graben belgium abstract during late oligocene incipient rifting the southern part of the roer valley graben was characterized by normal faulting and forced folding of its paleogene pre rift strata the 2d seismic data used in this study shows that these faults and forced folds were geometrically decoupled from faults or fault zones in the underlying triassic and older strata geometric decoupling consistently took place in an interval that comprises latest triassic to early jurassic soft claystones on top of triassic alternations of evaporites and claystones layers this mechanically weak interval probably inhibited the upward propagation of re activated underlying faults resulting in the formation of the observed forced folds monoclines in the overlying paleogene pre rift strata strain from the sub detachment faults was distributed along the mechanically weak interval towards detachment edges leading to the consistent presence of faults in the footwall domain of the supra detachment monoclines the mechanically weak interval was thereby able to maintain the kinematic coherency between geometrically decoupled under and overlying deformation throughout late oligocene rifting

3d geometries of normal faults in a brittle ductile sedimentary cover analogue modelling abstract it is well known that ductile layers play a major role in the style and location of deformation however at the scale of a single normal fault the impact of rheological layering is poorly constrained and badly understood and there is a lack of information regarding the influence of several decollement levels within a sedimentary cover on the single fault geometry under purely extensive deformation we present small scale experiments that were built with interbedded layers of brittle and ductile materials and with minimum initial constraints only a velocity discontinuity at the base of the experiment on the normal fault geometry in order to investigate the influence of controlled parameters such as extension velocity rate of extension ductile thickness and varying stratigraphy on the 3d fault geometry these experiments showed a broad spectrum of tectonic features such as grabens ramp flat ramp normal faults and reverse faults forced folds are associated with fault flats that develop in the decollement levels refraction of the fault angle one of the key points is that the normal fault geometry displays large variations in both direction and dip despite the imposed homogeneous extension this result is exclusively related to the presence of decollement levels and is not associated with any global regional variation in extension direction and or inversion

salt flow and diapirism related to extension at crustal scale abstract the analysis of the structure and history of salt diapirs in large ancient evaporitic basins such as the southeastern north sea basin suggests that diapirism is controlled by crustal scale extension laboratory experiments on small scale models designed to simulate configurations comparable to the southeastern north sea basin show that diapirs which grow in a sedimentary cover during basement extension can develop close to basement normal faults or at a significant distance from them if the displacement on the basement faults is transfered horizontally along the salt layer for given values of salt viscosity strain rate and friction coefficient in brittle rocks the pattern of salt diapirism in a particular area depends on the ratio of cover thickness to salt thickness as well as the absolute thicknesses of cover and salt layers the experiments give criteria for identifying different types of diapirs and provide models of horizontal flow in a salt layer undergoing extension and diapir development some dynamic implications of the experiments are applied to the southeastern north sea basin

the effect of cover composition on extensional faulting above re activated basement faults results from analogue modelling abstract analogue models were used to investigate differences in deformation between sedimentary cover sequences of contrasting composition above reactivated basement faults during extension two types of model arrangements were used the first represented clastic sediments directly overlying faulted basement and the second represented a basal ductile layer in an overburden overlying the same faulted basement the basement configuration consisted of faults both oblique and orthogonal to the bulk extension direction particular attention was paid to the resulting map view fault patterns in experiments without a basal ductile layer in the overburden grabens only developed in areas directly above basement faults in section cover faults above oblique basement faults curved in profile and in places exhibited reverse movement at shallow depth in experiments involving a ductile layer at the base of the overburden faults developed oblique to both the bulk extension direction and the basement faults the resulting fault pattern was influenced by both bulk extension and basement fault reactivation the results indicate that cover sequences that include thick basal ductile layers above reactivated basement faults are more likely to develop faults with strikes perpendicular to the regional extension direction compared to those without faulting in an overburden lacking a basal ductile sequence is more likely to be directly influenced by the underlying reactivated basement faults

viscosity estimates of salt in the hormuz and namakdan salt diapirs persian gulf the parabolic surface profiles of the hormuz and namakdan salt diapirs in the persian gulf suggest that they have been extruding with newtonian viscous rheologies for the last 10 4 years we derive velocity profiles for these diapirs neglecting gravitational spreading and erosion dissolution while assuming incompressible newtonian rheology of the salt fitting known rates of extrusion at specific points in its elliptical cross section the dynamic viscosity of the salt of the hormuz diapir is found to range between 10 18 and 10 21 pa s approximating its sub circular cross section to a perfect circle the range of viscosity of the salt of the namakdan diapir is obtained as 10 17 10 21 pa s these calculated viscosities fall within the range for naturally flowing salts elsewhere and for other salt diapirs but are broader than those for salts with newtonian rheology deforming at room temperatures the salts of the hormuz and namakdan diapirs are expected to exhibit a broader range of grain size which matches the limited existing data

highly extended terrains lateral segmentation of the substratum and basin development the middle late miocene radicondoli basin inner northern apennines italy 1 this paper deals with the evolution of sedimentary basins not delimited by normal faults with a substratum characterized by an upward concave shape and with infilling sediments synclinally deformed we describe the middle late miocene radicondoli basin representing an example of such bowl shaped basins its tectonic origin is controversial being related both to compression and extension these opposite interpretations bear significant consequences on the geodynamic context in which the inner northern apennines developed during the middle late miocene the results of our structural studies carried out in the substratum and infilling sediments indicate that the radicondoli basin is an example of a hanging wall basin developed in an extensional setting extensional tectonics determined the lateral segmentation of the substratum competent levels i e tuscan nappe and verrucano group and the consequent collapse of overlying less competent levels i e the ligurian units with the formation of a bowl shaped tectonic depression here the syntectonic sediments serravallian late messinian are deformed in a large syncline characterized by minor gravity driven folds with vergences toward the depocenter and traces of their axial planes parallel to the basin margins this paper highlights the role of the competence contrast during the postcollisional tectonic evolution and the influence of substratum lateral segmentation for the accommodation of syntectonic sediments

balancing sub and supra salt strain in salt influenced rifts implications for extension estimates the structural style of salt influenced rifts may differ from those formed in predominantly brittle crust salt can decouple sub and supra salt strain causing sub salt faults to be geometrically decoupled from but kinematically coupled to and responsible for supra salt forced folding salt influenced rifts thus contain more folds than their brittle counterparts an observation often ignored in extension estimates fundamental to determining whether sub and supra salt structures are kinematically coherent and the relative contributions of thin i e gravity driven and thick skinned i e whole plate stretching deformation to accommodating rift related strain is our ability to measure extension at both structural levels we here use published physical models of salt influenced extension to show that line length estimates yield more accurate values of sub and supra salt extension compared to fault heave before applying these methods to seismic data from the halten terrace offshore norway we show that given the abundance of ductile deformation in salt influenced rifts significant amounts of extension may be ignored leading to the erroneous interpretations of thin skinned gravity gliding if a system is kinematically coherent supra salt structures can help predict the occurrence and kinematics of sub salt faults that may be poorly imaged and otherwise poorly constrained

analogue benchmarks of shortening and extension experiments we report a direct comparison of scaled analogue experiments to test thereproducibility of model results among ten different experimental modelling laboratories we present results for two experimen

jurassic tectono sedimentary evolution of the northern lusitanian basin offshore portugal abstract the lusitanian basin is one of a series of rift related basins developed during the rifting that led to the break up of iberia and canada the strong influence of halokinesis on the depositional evolution of its northern sector provides an analogue for the development of other evaporite prone rift basins on atlantic type passive margins in this paper the pre valanginian evolution of the northern lusitanian basin is documented based on regional seismic stratigraphy isochron and time structure maps tied with sonic and stratigraphic data from 10 exploration wells the pre salt structure of the study area is marked by two sets of faults i a n s to ne sw striking set active throughout the jurassic period and ii a nw se striking set active during the late jurassic the latter defines five late jurassic sub basins northeast of a basin margin structure the marinha grande fault the development of half graben basins in the northern lusitanian basin during the jurassic was overprinted by halokinesis over the marinha grande fault and other major marginal basement faults halokinesis climaxed during the oxfordian kimmeridgian rifting with the formation of a 10 km long salt ridge over the marinha grande fault the ridge limited the southward progradation of fluvial deltaic units derived from hanging wall drainage systems and restricted the syn rift sediments to a 15 km long 5 km wide bowl shaped depocentre located 10 km west of the present coastline in order to better characterise the jurassic tectono sedimentary evolution of the northern lusitanian basin the interpreted seismic data is compared with physical models for extensional forced folds above active normal faults and with stratigraphic information from well and outcrop

coupling a frictional cohesive cover and a viscous substrate in a discrete element model first results of application to thick and thin skinned extensional tectonics abstract mechanical stratigraphy is now recognised as a fundamental control on the development of geological structures in the upper crust at a variety of different scales this is perhaps never more apparent than when salt is part of the crustal section being deformed the interaction of a ductile salt substratum and a brittle sedimentary cover is complex but an understanding of it is essential both from an economic and academic standpoint here i present first results of a discrete element model which combines a viscous linear newtonian substrate and a frictional cohesive cover the modelling approach is firstly presented and experimental scaling to appropriate geological timescales discussed the approach is then applied to 3 experiments simulating extensional deformation two of which are thick skinned and one is thin skinned strain rates in all experiments are c 1015 s 1 the complex manner in which salt flows in the substrate and faults develop in the cover are illustrated and their linkage evolution examined movement of the viscous substrate is the result of both couette type and poiseuille type flows and combinations thereof whilst deformation in the cover takes the form of discrete dilational faults which are not directly linked or only soft linked to any sub salt basement faults cover faults typically lose displacement towards and tip out at the cover substrate interface in addition in models with a basement fault the fault itself presents a growing and important no slip boundary which significantly affects viscous flow implications for the timing evolution of and strain within the resultant structures are discussed

plate interactions at the southern end of the rhine graben abstract the southern end of the rhine graben in the basel area originated in the early tertiary as an extensional structure it is the site of a transfer zone that connected the rhine graben with the bresse rhone grabens this transfer zone is located in an area into which a late paleozic trough projects which apparently was reactivated from the beginning of miocene to recent times three distinct phases of slight compression were superimposed on the southern end of the rhine graben the first one in the aquitanian early burdigalian is coeval with the development of the helvetic nappes and the insubric fault zone in the alps the second one in the langhian tortonian interval occurred when the external massifs and an important part of the lombardic fold thrust belt in the southern alps developed and the third pliocene to recent one is contemporaneous with the inactivation of this belt and its incorporation into the foredeep of the northern apennines in the aquitanian the forebulge of the alpine orogen is recognizable as a system of flexures that developed preferably on the margin of the late paleozoic trough the middle late miocene one gave rise to uplift of the black forest vosges domain and a river system flowing from this high to the south in the pliocene to recent one alpine rivers made their appearance flowing first to the west into the rhone system and then as the rhine to the north the pliocene to recent phase seems to be decoupled from the body of the central and southern alps

multidisciplinary approach to an extensional syncline model for the mesozoic cameros basin n spain abstract in this paper we explore the possibility of reconstructing the initial geometry of inverted basins using combined geophysical and geological methods seismic reflection profiles paleomagnetism analogue modelling and 3d geometrical analysis these techniques allow for some unknowns in the geometry and evolution of extensional sedimentary basins mainly the normal drag reverse drag geometrical problem to be solved the example chosen for checking these techniques is the cameros basin northern iberian chain formed during the late jurassic early cretaceous and inverted during the tertiary compressional stage according to the reconstruction proposed the cameros basin can be characterised as a lens shaped syncline basin with maximum thickness of deposits of about 8000 m in its depocenter gradually diminishing toward the north and south the extensional geometry of the cameros basin is defined by 1 a large scale growth syncline over the major basement fault with southward dipping beds in the northern basin margin forming a southward opening sedimentary wedge with upward decreasing dip values large scale normal drag geometry 2 roll over anticlines at the contact between the pre rift series against the normal fault limiting the basin smaller scale reverse drag geometry the combined syncline anticline syn extensional structures were characterised by means of paleomagnetic analysis of a remagnetization acquired at the time of extension analogue models indicate that the development of syncline basin geometries in extensional settings as the one interpreted for the cameros basin is closely related to the presence of a detachment level in the pre rift sequence above the main basement faults

folding in high grade rocks due to back rotation between shear zones abstract folds with a sense of asymmetry opposite to the bulk shear sense may form in high grade rocks due to back rotation between ductile shear zones layers back rotated into the shortening field can undergo additional buckle folding with progressive deformation shear zones and domains of back rotated foliation between shears rotate towards the x y flattening plane of the finite strain ellipsoid in high grade gneiss the migration of melt into shear zones may facilitate displacement along them and accentuate back rotation of material between shear zones folding during back rotation occurs when the spacing between shear zones does not increase sufficiently to accommodate the length of back rotated layers or between non parallel shear zones folds formed by back rotation between shear zones commonly have pegmatites sub parallel to their axial planes thickened overturned limbs and occur in localised packages associated shear zones have the same sense of shear on both attenuated limbs of folds formed by back rotation examples are given for folds between transcurrent and normal ductile shear zones in the albany mobile belt and leeuwin complex western australia and the dharwar craton india

the influence of basement structure on the evolution of the bicorb quesa diapir eastern betics iberian peninsula contractive thin skinned deformation above a pre existing extensional basement fault on the basis of an analysis of structural surface data in addition to previously available and new magnetotelluric data it was possible to reconstruct the evolution of bicorb quesa diapir this was initiated as a reactive diapir in relation to a basement fault the reactive diapir was rejuvenated by a thin skinned compression during the paleogene and rose during an extensional early middle miocene phase later in the middle miocene the diapir was squeezed and then in the late miocene was extensionally reactivated the current reconstruction allows us to analyse a diapir affected by a thin skinned contractional deformation located on top of a pre existing basement fault our study highlights the role played by the geometric relationship between the propagation direction of the cover deformation and the basement fault

fault patterns associated with extensional fault propagation folding abstract extensional fault propagation drape folds are a common type of structure in rift basins and a number of oil and gas fields produce from these structures the detailed geometry and trap volumes are dependent on the relationship between the basement faults and the overlying folds and associated secondary faults in the sedimentary cover experimental models were used to study the 3 d geometry and secondary fault patterns of drape folds associated with single faults and two or more intersecting faults two layer clay models consisting of stiff and soft clay were used to model the deformation zones in the basement and sedimentary cover respectively extension on single basement faults normal to the direction of extension results in the development of a deformation zone with expanding width in which the fault density initially increases and then remains approximately constant extension on terminating faults results in conical drape folds with faults oblique to the fold axis along the propagating tip basement faults oblique to the direction of extension are characterized by oblique secondary faults along the boundaries of the deformation zone which curve into a direction normal to the extension direction in the center trapdoor fault geometries associated with two or more intersecting faults result in a triangular uplift with maximum relief at the apex the difference in relief between the flanks and the apex is greatest in the case of propagating basement faults en echelon secondary faults initiate on the flanks and extend into the apex area curving into orientations that are closer to normal to the regional direction of extension the width of the fault zone and the total fault length increase with increasing extension the fault density initially increases and then remains approximately constant with increasing extension

style and sequence of deformation during extensional fault propagation folding examples from the hammam faraun and el qaa fault blocks suez rift egypt kilometre scale fault parallel folds are identified adjacent to normal faults in the oligo miocene suez rift egypt and are interpreted to have formed in response to fault propagation folding above upward propagating blind faults the geometry scale and distribution of secondary structures within the folds and their cross cutting relationships with the master faults allow the style and sequence of deformation during fault propagation folding to be established and suggest that during the initial stages of folding the proto footwall underwent extension which was accommodated by layer parallel slip in encasing mudstone horizons and linked normal faulting and block rotation in carbonate and sandstone units the proto hanging wall also contains dominantly extensional normal faults although locally where the master fault had a convex into the footwall map view trace reverse faulting and fracturing occurred secondary structures adjacent to the master fault were not all active simultaneously but initiated and died at different stages during the evolution of the fault propagation fold the results of this study confirm many key predictions of numerical and physical analogue models but also highlight several important controls on the evolution of fault propagation folds in extensional settings which existing models cannot capture such as the influence of the map view trace of the propagating fault and lateral variations in cover stratigraphy lithology and strength on the style and magnitude of secondary deformation

3d seismic characterisation of an array of blind normal faults in the levant basin eastern mediterranean the geometry throw distribution and kinematics of an array of blind normal faults were investigated using a high resolution 3d seismic dataset located in the levant basin offshore israel to establish criteria allowing true blind faults to be distinguished from minor synsedimentary faults a detailed analysis of throw distribution on the fault planes shows that the displacement exhibits a crudely concentric pattern about a maximum region located centrally on a fault plane as expected for ideal blind faults however vertical displacement profiles do not exhibit classical linear or triangular profiles but are mostly flat topped or hybrid in type comparison of unrestricted blind faults to those that interacted with a mechanical boundary or another structure suggests that such interactions significantly modify the throw spatial distribution on a fault plane to distinguish small synsedimentary faults from blind faults we use a combination of three criteria to assess whether a fault grew by blind propagation 1 plunging upper tip region and complementary pattern in the throw contours 2 presence of upper tip propagation fold and 3 absence of stratigraphic evidence that the fault interacted with the free surface

longitudinal evolution of the suez rift structure egypt abstract a three dimensional study of the structure of the suez rift has been carried out using field and subsurface data in an attempt to determine the role of transverse faults and the longitudinal evolution of the rift as in most intracontinental rifts the structure of the gulf of suez area is governed by normal faults and tilted blocks whose crests constitute the main target of exploratory wells the fault pattern consists of two major sets of trends 1 1 longitudinal faults parallel to the rift axis and created in an extensional regime where 3 was trending ene wsw and 2 2 transverse faults with a n s to nne ssw dominant trend the transverse faults are inherited passive discontinuities while most of the longitudinal faults were created during neogene times in a purely extensional regime both sets were simultaneously active producing a zigzag pattern and rhombic shaped blocks the transverse faults can show horizontal strike slip components and act as relays between major normal faults although the suez rift appears as a simple narrow elongated trough dominated by two almost symmetrical shoulders its internal structure is asymmetrical cross profiles show that all the major blocks are tilted in the same direction however the tilt direction changes twice along the rift to the north and to the south of the rift the blocks are tilted eastward while in the central part they are tilted westward to the north the change of dip is accompan ed by a graben type twist zone without transverse faulting at least in the neogene series to the south the change of dip is accompanied by a more complex structure involving both a major transverse fault and a horst type twist zone in this latter case the transverse fault does not cut through the entire rift balanced cross sections established from subsurface data show that the tilt angle and the amount of extension increase from north to south while the width of the blocks decreases indicating a pole of opening close to the northern end of the gulf minimum values for the amount of opening range from 5 km in the north to about 20 km in the south

the transition from thick skinned to thin skinned tectonics in the basque cantabrian pyrenees the burgalesa platform and surroundings interpretation of seismic data in the margins of the burgalesa platform in the basque cantabrian pyrenees has allowed proposition of a new structural model that combines different modes of deformation during oblique tectonic inversion conditioned by the distribution of triassic salts deformation was decoupled by the presence of the salt horizon between basement involved thrusts inverting formerly triassic and late jurassic early cretaceous extensional faults and a detached thrust system involving the upper triassic to neogene sedimentary package structural units experiencing different styles of deformation are not only stacked vertically above and below the salt but most importantly they change from one to the other along strike across the transversal edges of the triassic salts the burgalesa platform detached thrust system was confined between the basement involved structures of the cantabrian mountains westward and the nw tip of the iberian basement involved structures san pedro southward this together with the obliquity between the pyrenean shortening direction and the strike of the previous extensional faults mostly during the late stages of deformation determined the strike slip reactivation of the basement involved inverted faults and the lateral extrusion of the burgalesa platform detached mesozoic successions above the salt towards the se to form a prominent thrust salient oblique to the main pyrenean trend the proposed model combines thick skinned with thin skinned structural styles during oblique tectonic inversion and is consistent with the surface data including the fracture system the available subsurface data and the mechanical stratigraphy

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

transpressional inversion in an extensional transfer zone the saltacaballos fault northern spain abstract this paper deals with an extensional transfer zone and its main structure the saltacaballos fault developed during early cretaceous times and obliquely inverted during the alpine shortening geological mapping and structural analysis were carried out to determine the kinematic history of the deformation the saltacaballos ridge is the relay zone between two major and conjugate normal fault systems the bilbao and the la granja samano fault systems three distinct phases in the structural evolution of this transfer zone can be identified 1 during the initial stages of extensional deformation shallow water marine limestones were deposited on the relay ridge and deep water marls on the flanking depocenters at the same time submarine landslides developed on paleoslope generated either by normal drag or by a fault propagation fold related to the saltacaballos normal fault 2 with increasing displacement normal faults antithetic to the saltacaballos fault were developed probably in response to the collapse of its hanging wall 3 during the subsequent alpine compressional stage these normal faults were reactivated as dextral strike slip faults as a result of transpressional inversion whereas previous extensional fault related folds were tightened at the same time some normal faults were overturned as a consequence of passive rotation in fold limbs

growth of normal faults in multilayer sequences a 3d seismic case study from the egersund basin norwegian north sea abstract we investigate the structural style and evolution of a salt influenced extensional fault array in the egersund basin norwegian north sea through analysis of 3d reflection seismic and well data analysis of fault geometry morphology throw distribution and syn kinematic strata reveal an intricate but systematic style of displacement and growth suggesting an evolution of 1 initial syn sedimentary fault growth contemporaneous with salt mobilization initiated during the late triassic 2 cessation of fault activity and burial of the stagnant fault tips and 3 subsequent nucleation of new faults in the cover above contemporaneous salt re mobilization initiated during the late cretaceous with downward propagation and linkage with faults stage 3 was apparently largely controlled by salt mobilization in response to basin inversion as reactivated faults are located where the underlying salt is thick while the non reactivated faults are found where salt is depleted based on the 3d throw analyses we conclude that a combination of basement faulting and salt re mobilization is the driving mechanisms behind fault activation and reactivation even though the sub and supra salt faults are mainly geometrically decoupled through the salt a kinematic coupling must have existed as sub salt faults still affected nucleation and localization of the cover faults

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

effect of ductile and frictional decollements on style of extension abstract scaled analogue models were used to study the effect of frictional and ductile detachments on thin skinned extension models consisted of two halves one half is the ductile and the other has a frictional detachment extension occurred above two different basal configurations a stretchable rubber sheet and a folded banded sheet intended to produce homogeneous and heterogeneous extension respectively model parameters varied systematically and included the brittle ductile thickness ratio rheologies and bulk strain structures in the two halves are compared in profiles and plan views a series of graben developed above both halves of models extended above a banded sheet although there were differences in style propagation rate and width of the deformation zone between the two halves different rates of propagation of structures in the two halves led to the formation of an accommodation or transfer zone parallel to the extension direction most relay ramps and inflection of normal faults in this zone indicate differential extension between the two halves in contrast in models extended above a stretchable rubber sheet extensional structures such as horst and graben developed only above the ductile detachment model results indicate that heterogeneous mechanical stratigraphy and displacement rate have no effect on extensional structure above a rubber sheet however above 20 bulk extension deformation becomes heterogeneous along multiple sets of conjugate faults oblique to the extension direction

deformational behavior of shale interlayers in evaporite detachment horizons jura overthrust switzerland shale deformation was studied in a series of naturally strained evaporites and shales deformed at low temperatures 70 high strain rates 10 14s 1 and low pressures overburden 2 km as well as in rock samples and sintered specimens experimentally deformed in coaxial and simple shear configurations at temperatures of 20 350 c strain rates of 10 4 10 6s 1 and confining pressures of 0 1 400 mpa within naturally strained shale sulfate multilayers three deformation regimes can be recognized that are separated by the inversion of relative competence of shale and anhydrite and the onset of gypsification respectively in deeper domains strain is focused on slickensides which are often coated with sulfate that acts as a lubricant in shallower domains and especially in domains with significant access to syntectonic water strain becomes pervasive and very low strength ductile shale gypsum tectonites form experiments reveal that confining pressure and water content have a significant influence on style of deformation pervasive or focused on discrete surfaces whereas temperature and strain rate have virtually no influence on either strength or deformation style except at temperatures 200 c that cause dehydration and embrittlement

displacement rates of normal faults previous estimates of displacement rates on individual faults have been limited to neotectonic faults and averaged over time intervals of about 200 kyr or less1 2 3 4 5 these estimates have been highly variable which has led to a belief that longer term displacement rates on individual faults are likely to be variable as well here we report estimates of long term normal fault displacement rates averaged over time intervals ranging from 1 to 40 myr and based on observed decreases in displacement of progressively younger horizons intersected by syn sedimentary faults we find that displacement rates are remarkably stable over these longer time periods and within a given fault system the rates are strongly dependent on the relative size of the fault as measured by cumulative vertical displacement taken together these results indicate that faults become large relative to nearby faults by having higher displacement rates even when small rather than as a consequence of having been active for longer our analyses also show that high regional strain rates tend to be accommodated by high fault displacement rates rather than high fault densities

active normal faulting beneath a salt layer an experimental study of deformation patterns in the cover sequence scaled experimental models show that the presence of a viscous layer such as salt facilitates the development of extensional forced folds above active normal faults the geometries of the extensional forced folds and their associated secondary fault patterns depend on the thickness and viscosity of the viscous layer the thickness of the cover sequence the strength and ductility of the cover sequence and the magnitude and rate of displacement on the underlying master normal fault increasing the thickness of the viscous layer and the cohesive strength and ductility of the overburden enhances the decoupling between the deep and shallow deformation alternatively increasing the viscosity of the viscous layer the thickness of the overburden and the magnitude and rate of displacement on the master normal fault reduces the decoupling between the deep and shallow deformation enhanced decoupling facilitates the formation of broad extensional forced folds and the development of detached secondary faults both near and far from the master normal faults the model predicted deformation patterns closely resemble those observed in the gulf of suez the haltenbanken area of offshore norway and the jeanne d arc basin of the grand banks offshore southeastern canada

the influence of mechanically weak layers in controlling fault kinematics and graben configurations examples from analog experiments and the norwegian continental margin fault systems in extensional basins commonly display geometries that vary with depth reflecting depth and lithology dependent mechanical strength using an experimental approach we investigate this relationship by deploying physical analog models with stratified sequences consisting of brittle ductile sand silicone polymer sequences subject to single and polyphase deformation the experiments were used as analogs for a sandstone sequence interlayered by beds of evaporates or overpressured or unconsolidated mudstone in nature the latter being representative of decollement horizons experiments series 1 s1 using homogeneous and stratified quartz and feldspar sand produced asymmetric composite single grabens with diverse fault frequencies and fault styles for the graben margin faults for the mechanically stratified experiments with one decollement level series 2 contrasting graben configurations were produced in that the lowermost sequence was characterized by graben geometries of similar type to that of the s1 experiments whereas the sequence above the decollement was characterized by large fault blocks delineated by steepened or oversteepened faults the experiments with two decollements series 3 were displayed similarly but included graben geometries that widened upward with each level being characterized by independent fault systems the results can be used to explain strata bound fault patterns and depth dependent extension as seen in several places along the norwegian continental margin and elsewhere

global atmospheric oscillation an integrity of enso and extratropical teleconnections many researchers have recognized the long distance teleconnections between el nino southern oscillation enso events and some other processes in the global climate system happening in areas often very far from the equatorial zone of the pacific ocean in this paper we investigate similar links between enso and extratropical processes taken in their whole set for this goal we compute differences between the sea level pressure and the near surface air sea surface temperature global fields which correspond to either el nino or la nina events observed since the end of the xix century and up to the beginning of the xxi century as a result we establish that an integrity exists of enso and the extratropical teleconnections such as north atlantic oscillation nao arctic oscillation ao the northern hemisphere annular nha mode as well as the pacific north american pna pattern and their analogs in the southern hemisphere in the interannual timescale named this integrity the global atmospheric oscillation gao we define two representative indices of gao and investigate the temporal dynamics of these indices this investigation reveals that gao s extratropical components may be real irrespective of enso while the latter accompanies gao in all cases moreover in view of a general eastward propagation of the gao as a spatial structure some its extratropical components show changes of their features prior the el nino la nina begins to form using these features as fingerprints of the forthcoming evolution of enso we define another gao index for the el nino prediction with the lead time of about 1 year at last we establish that some of the cmip5 models reproduce gao reasonably well

3d seismic analysis of the structure and evolution of a salt influenced normal fault zone a test of competing fault growth models abstract in this paper we determine the structure and evolution of a normal fault system by applying qualitative and quantitative fault analysis techniques to a 3d seismic reflection dataset from the suez rift egypt our analysis indicates that the october fault zone is composed of two fault systems that are locally decoupled across a salt bearing interval of late miocene messinian age the sub salt system offsets pre rift crystalline basement and was active during the late oligocene early middle miocene it is composed of four planar nw se striking segments that are hard linked by n s striking segments and up to 2 km of displacement occurs at top basement suggesting that this fault system nucleated at or more likely below this structural level the supra salt system was active during the pliocene holocene and is composed of four nw se striking listric fault segments which are soft linked by unbreached relay zones segments in the supra salt fault system nucleated within pliocene strata and have maximum throws of up to 482 m locally the segments of the supra salt fault system breach the messinian salt to hard link downwards with the underlying sub salt fault system thus forming the upper part of a fault zone composed of i a single amalgamated fault system below the salt and ii a fault system composed of multiple soft linked segments above the salt analysis of throw distance t x and throw depth t z plots for the supra salt fault system isopach maps of the associated growth strata and backstripping of intervening relay zones indicates that these faults rapidly established their lengths during the early stages of their slip history the fault tips were then effectively pinned and the faults accumulated displacement via predominantly downward propagation we interpret that the october fault zone had the following evolutionary trend i growth of the sub salt fault system during the oligocene to early middle miocene ii cessation of activity on the sub salt fault system during the middle miocene to early pliocene iii stretching of the sub and supra salt intervals during pliocene regional extension which resulted in mild reactivation of the sub salt fault system and nucleation of the segmented supra salt fault system which at this time was geometrically decoupled from the sub salt fault system and iv pliocene to holocene growth of the supra salt fault system by downwards vertical tip line propagation which resulted in downward breaching of the salt and dip linkage with the sub salt fault system the structure of the october fault zone and the rapid establishment of supra salt fault lengths are compatible with the predictions of the coherent fault model although we note that individual segments in the supra salt array grew in accordance with the isolated fault model our study thereby indicates that both coherent and isolated fault models may be applicable to the growth of kilometre scale basin bounding faults furthermore we highlight the role that fault reactivation and dip linkage in mechanically layered sequences can play in controlling the three dimensional geometry of normal faults

intersection patterns of normal faults in the lufeng sag of pearl river mouth basin china insights from 4d physical simulations abstract interpretation of seismic data from the lufeng sag of the pearl river mouth basin prmb in the northern part of south china sea shows that different intersection patterns developed in the cover units above basement normal faults a series of analogue models are used to investigate the intersection patterns and deformation in the sedimentary cover sequences above a basement horst bounded by two non parallel faults modelling results show that during their upward propagation the basement faults may intersect within the cover sequences and form a graben above the basement horst length and width of the graben increase with cover thickness the strike and dip intersection points are controlled directly by the thickness of the cover sequences dip and strike of the basement faults and width of the basement horst the intersection point migrates along the axis of the graben toward the wide end of the basement horst when the cover sequence thickens in contrast it migrates toward the narrow end of the basement horst where both fault dip and angle of strike difference increase the intersection point moves upward with increasing width of the basement horst crest model profiles also indicate that in the presence of a ductile layer between the cover and basement such intersection patterns do not form interpretation of seismic data and model results show that the intersection pattern developed in the lufeng sag is a result of propagation of basement faults into cover units during different extension stages of the basin results of this study can be applied to many other sedimentary basins where such fault intersection patterns are likely to form when non parallel conjugate basement faults are active during sedimentation

rift margin extensional forced folds and salt tectonics in the eastern basque cantabrian rift basin western pyrenees abstract in this paper we present and discuss cretaceous extensional folds of the eastern basque cantabrian basin northern spain geometry and kinematics of folds is constrained by means of structural and sedimentological fieldwork integrated with geological mapping revealing an intimate link between coeval folding extensional faulting and salt mobilization in detail the mesozoic succession of the northwestern and southern borders of the palaeozoic bortziriak cinco villas massif eastern margin of the bcb host late albian early cenomanian syn rift forced folds the studied forced fold axes trend parallel and are located above main and inferred cretaceous syn sedimentary basement faults structural data indicate that these folds formed during the late albian early cenomanian interval the presence of upper triassic clay and evaporite outcrops along and or close to the axes of folds and their stratigraphic relationship with upper cretaceous strata indicate their halokinetic origin and extrusion during folding the trigger of salt tectonics is attributed to a basement extensional pulse during the bay of biscay pyrenean rifting related high subsidence rates allowed salt to flow towards faults forming salt walls and causing the inflation and folding of the overburden

geometry and kinematics of extensional structural wedges abstract structural wedges in the compressive environment have been recognized and studied in different locations however extension structural wedges are less well understood based on the normal fault bend folding theory and inclined shear model this paper quantitatively analyses deformations related to extensional structural wedges and builds a series of geometric models for them an extensional structural wedge is a fault block held by two or more normal faults the action of which would fold its overlying strata extensional structural wedges of different shapes will lead to different deformation results for the overlying strata and this paper illustrates both the triangular and quadrangular wedges and their related deformations this paper also discusses differences between the extensional structural wedges and the normal fault bend folding by analysing two seismic sections from langfang gu an sag east china this paper provides two natural examples of the triangular and quadrangular extensional structural wedges where the models can reasonably explain the overlying distinct highs and lows without obvious faults the establishment of a geometric model of extensional structural wedges can provide reference and theoretical bases for future quantitative analysis of deformations in the extensional environment