a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

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

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

selective reverse reactivation of normal faults and deformation around reverse reactivated faults in the mesozoic of the somerset coast abstract normal faults exposed in the triassic jurassic limestones and shales of the somerset coast were formed during the mesozoic development of the bristol channel basin reverse reactivation of some of these normal faults occurred during late cretaceous to early tertiary north south contraction the contraction is also evident from thrusts and conjugate strike slip faults preferential reactivation of the normal faults is attributed to 1 decreased fault plane friction 2 domino block rotation 3 displacement magnitude and 4 fault connectivity the geometries of overlapping and underlapping zones in reactivated fault zones are dependent on the existing structural geometry two distinctive styles of displacement accommodation occur between reverse reactivated normal faults 1 formation of a network of strike slip faults conjugate about nne ssw and 2 oblique steeply dipping reverse faults interaction between strike slip and an existing fault is dependent on whether the normal fault was reactivated the range of structures related to the north south contraction has been incorporated into a single deformation model controlled by the northwards movement of the hanging wall of the quantock s head fault pure dip slip movement occurred in the centre of its curved fault trace with a sinistral component at the western tip and a dextral component of displacement and strike slip block rotations occurred at the eastern tip shortening of these blocks was achieved through development of a strike slip fault network and nw striking thrusts in an underlap zone loading of the footwall by the hanging wall block modified the local stress system to allow formation of oblique steeply dipping reverse faults

fault propagation folding in extensional settings examples of structural style and synrift sedimentary response from the suez rift sinai egypt field data from the oligocene miocene gulf of suez rift demonstrate that coeval growth faults folds and transfer zones exerted a major control on synrift stratigraphic sequence development growth folds in the suez rift are related to steeply dipping normal faults that propagated upward resulting in broad upward widening monoclines in overlying strata folding during fault propagation was accommodated by layer parallel slip and detachment along mudstone horizons as well as by normal and rare reverse secondary faults that propagated away from the master fault the eventual propagation of the master fault through to the surface left the steep limb of the monocline and most of the secondary faults in the hanging wall this evolving structural style exerted a marked control on the geometry and stacking patterns of coeval synrift sediments synrift sediments display onlap and intraformational unconformities toward the growth monoclines and buried faults whereas they diverge into broadly synclinal expanded sections away from the growth monocline continued movement across buried faults resulted in the progressive rotation of the monoclinal limb and associated synrift sediments each successively younger sequence dipping basinward at a shallower angle than the previous one the resulting synrift geometries differ significantly from stratal geometries normally anticipated adjacent to normal faults along strike variations in facies stacking patterns are also commonly associated with decreasing displacement across faults and associated folds toward low relief transfer zones data from other rift basins indicate that fault propagation folds are not unique to the gulf of suez

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

inverted turtle salt anticlines in the eastern basque cantabrian basin spain abstract halokinetic structures are sometimes masked by subsequent compression in inverted salt related basins making their study difficult the eastern basque cantabrian basin is an outstanding area to study salt tectonics and sedimentation relationships because precursor salt structures have maintained undeformed geometries after the alpine contraction phase based on the interpretation of subsurface data with surface geology a structural model of some of the area s salt structures is proposed according to the model the formation of listric faults and raft tectonics during the first extensional rifting stage resulted in the sinking and collapse of the late jurassic early cretaceous formations giving rise to a turtle back anticline structure with a semicircular geometry the upper triassic keuper salt migrated towards the outer zones of the structure and peripherial troughs were subsequently filled with albian late cretaceous post rift sediments during the eocene alpine contraction the whole area was folded and moved southwards maintaining much of the geometry of the previously formed salt anticlinal structures traditionally the presence of an nne ssw alignment of triassic diapirs in the eastern zone of the basin has been used to place the southern segment of the so called pamplona fault rather than being associated with fault these diapirs are interpreted to rise along the eastern edge of the collapsed extensional turtle structure existing below the eocene urbasa andia synclines no evidence of fault affecting the mesozoic cover series is observed in several composite profiles that cross the pamplona fault alignment it is suggested that the alignement of the triassic diapirs is due to the incidence of the later alpine compression in a previous expulsion rollover rather than the effect of a major alpine strike slip fault

displacement transfer from borders to interior of a plate a crustal transect of iberia abstract a n s crustal transect of the whole iberian plate is presented the displacement transfer during the alpine deformation from the border ranges cantabrian and betic chains toward the interior ones was analyzed by means of balanced crustal sections inconsistencies in shortening values between upper and middle lower crust in the cantabrian mountains basque cantabrian zone imply a mid crustal detachment transferring orogenic shortening southward toward the spanish central system depending on the shortening value attributed to the central system this mid crustal detachment could involve the entire iberian plate connecting the cantabrian mountains and the betic chain the very small crustal root in the central system can be explained as a result of the tectonic load caused by the upper crustal shortening that was transferred from the border ranges we conclude that a simple shear model rather than a pure shear with lithospheric folding better explains the whole iberia deformation finally the total alpine shortening of the iberian plate is estimated between 267 and 292 km

influence of a transverse basement fault on along strike variations in the geometry of an inverted normal fault case study of the mosha fault central alborz range iran abstract inverted normal faults show variations in structural geometry from footwall shortcut thrusts to hanging wall break back thrusts in the present study we evaluated along strike variations in the geometry of the mosha fault central alborz range iran detailed structural mapping within the taleqan mountains revealed that the mosha fault in the eastern part of the study area is associated with a large basement cored hanging wall anticline thrust over tertiary rocks that occur as a syncline or cut by footwall shortcut thrusts in the western part of the study area however the hanging wall consists of break back thrust sheets of paleozoic mesozoic rocks these thrust sheets occur as a duplex system and have allochthonous masses gravitationally emplaced in the foothills of the taleqan mountains curved fold axial traces and scattered intrusive bodies are observed in the valian valley area where the mosha fault is displaced across a transverse basement fault this basement fault controlled along strike variations in the geometry of the mosha fault during its evolution from a basin bounding fault to an inverted normal fault inversion of the fault in the eastern part of the study area where the fault is relatively steep involved basement rocks in the western part of the study area where the fault is relatively shallowly dipping deformation in the hanging wall is accommodated by thin skinned break back thrust sheets

fault development and stress evolution of the post hercynian asturian basin asturias and cantabria northwestern spain abstract the asturian basin an emerged part of the north iberian continental margin has been investigated in terms of fault development and stress evolution the mesozoic history of this domain is mainly linked to the extensional faulting processes which preceded the opening of the bay of biscay preserved jurassic faulted blocks and associated half graben structures bounded by wnw ese to nw se faults are related to a late jurassic kimmeridgian rifting stage this fault system seems to have played a major role during the mesozoic structuring of the basin suggesting an extension oriented approximately ne sw the cenozoic evolution is related to the iberia eurasia convergence and collision leading to compressional and subsequent extensional structures the direction of compression documented in various sites was nnw sse during an initial early middle eocene stage reoriented probably in the oligocene to ne sw this succession of stress regimes was applied to the same three major fault systems ne sw nw se and e w which were inherited from the variscan orogeny some of them having already been involved in the latest stephanian early permian rifting episode during the tertiary compressional phase the nw se trend which is believed to have controlled the late jurassic tectonic development was rejuvenated into dextral strike slip faults whereas the ne sw system moved in a sinistral sense the e w system was reactivated as reverse faults giving rise to a partial inversion of the basin

linked sequence stratigraphic and structural evolution of propagating normal faults two distinct phases in the structural evolution of normal faults can be identified in the miocene gulf of suez rift 1 an initial growth fold stage when the fault is a buried structure and 2 a subsequent surface faulting stage during the growth fold stage strata thin and become truncated toward the fault zone and are rotated and diverge away from the buried fault into growth synclines in contrast once the fault breaks surface strata form a divergent wedge which is rotated and thickens into the fault the two tectono stratigraphic styles also occur contemporaneously along the length of a single fault segment growth folding characterizes deformation around the ends of fault segments where the fault is blind whereas the center of fault segments are characterized by surface faulting these observations suggest that marked along strike variation in stratal surfaces and facies stacking patterns will occur in depositional sequences in areas of normal faulting

controls on carbonate platform evolution on active fault blocks the lower cretaceous castro urdiales platform aptian albian northern spain abstract four contrasting carbonate sequences developed in a tectonically active extensional setting in the lower cretaceous aptian albian castro urdiales platform of north spain the four carbonate phases p1 p4 early aptian late aptian earliest albian and early late albian respectively are identified across the platform to basin transition on the basis of sedimentary geometries and internal facies patterns they are vertically separated by four incipient drowning events d1 d4 middle aptian aptian albian boundary early albian and late albian the first carbonate stage p1 corresponds to a low relief carbonate platform characterized by widespread shallow marine depositional environments with a nearly flat organization the second platform stage p2 developed as a rimmed carbonate platform the third carbonate stage p3 evolved from a low relief aggradational platform substage a to a progradational offlapping platform substage b and back to a backstepped aggradational rimmed platform substage c responding to changes in differential subsidence and carbonate production at the beginning of the albian the castro urdiales carbonate platform was broken up by extensional tectonic movements with formation of fault blocks bounded by ne sw and nw se trending faults on the crests of uplifted blocks meteoric processes were active whereas grabens and half grabens acted as channel conduits for terrigenous rich deposits subsidence rates increased during the late early albian late albian the crests of rotated blocks formed paleohighs that nucleated small residual carbonate platforms carbonate stage p4 that were surrounded by deeper water basins this study suggests that the evolution of carbonate platform sequences in the lower cretaceous of castro urdiales was primarily controlled by changes in accommodation space which were most likely driven by intraplate stresses related to extension in the north spanish continental margin during the opening of the north atlantic drowning events in the castro urdiales platform coincide with major crises of cretaceous carbonate production worldwide suggesting that regional tectonism and global oceanic changes interacted to cause phases of platform demise

sandbox experiments on basin inversion testing the influence of basin orientation and basin fill analogue modelling experiments using brittle materials are performed to study the inversion of extensional structures asymmetric grabens of two different orientations are first created during a phase of extension and progressively filled they are subsequently shortened in the same direction the aim of our experiments is to determine factors affecting the style of deformation during inversion we specifically investigate variations in thickness and distribution of strong and weak layers constituting the graben fill and in initial basin orientation the main advantage of our experimental set up is that we have a complete control on graben location width infill and orientation before inversion the experiments show that shortening results only in limited reactivation of pre existing normal faults in general forward thrusts and backthrusts cut across normal faults into the footwall of the graben the forward thrusts either propagate parallel to the enveloping surface of faulted blocks or they cut across basin limiting normal faults at various angles the graben fill is mechanically extruded by displacement along forward thrusts that accommodate most of the shortening both pre existing faults and weak graben fill act as zones of weakness during inversion and determine the orientation and location of both backthrusts and forward thrusts the results of our experiments conform well to natural examples of inverted graben structures

iberian plate motions during the mesozoic abstract as more data are collected on the deep parts of the conjugate margins of canada and eurasia models of the early kinematics of iberia become better constrained in order to specify the motions during phases of continental rifting to the west and to the north of iberia we used recent data on the early oceanic spreading in the tagus abyssal plain and added simple assumptions on the geometry the tagus abyssal plain was formed after the end of continental rifting on the southwest portuguese margin in latest jurassic time before chron m 0 118 ma as a first step we close the space adjacent to the m 0 anomaly to keep open only the oldest oceanic part of the tagus plain which is assumed to be latest jurassic to earliest cretaceous in age in a second step we close this space the main results are as follows 1 1 the galicia bank slid along the southern flank of flemish cap this motion is interpreted as a strike slip motion or as a very oblique rifting 2 2 a late jurassic reconstruction of iberia and north america is obtained without considerable overlap and without large motion of microplates such as galicia bank this is possible because a large amount of continental extension occurred over a long time to the north of the grand banks and permitted early motion between north america and eurasia 3 3 a tight initial reconstruction can only be reached if strike slip motion is located between southern eurasia and northern eurasia along a shear zone following the english channel and the transform area between galicia bank and flemish cap

widespread cretaceous inversion event in northern spain evidence from subsurface and palaeomagnetic data abstract in this paper we present geological evidence of a mid cretaceous inversion event in the polientes basin northern iberian plate based on geological data analysis of seismic profiles across the basin indicates that this tectonic event resulted in the uplift of the basin depocentre and the formation of an upright gentle anticline before cenomanian times the presence of a pre alpine syntectonic remagnetization in the jurassic and lower cretaceous rocks of the polientes basin allows us to define the geometry of the basin at the time between this early inversion event and the main alpine compressional period the early inversion in the polientes basin is consistent with a transpressional tectonic setting contemporaneous with the left lateral strike slip movement of iberia with respect to europe this study shows the successful use of two approaches to unravel the geodynamic scenario of the northern iberian plate during the cretaceous which was later obliterated during the tertiary pyrenean orogeny

wavenumber spectra of pacific winds measured by the seasat scatterometer abstract vector winds measured by the seasat a satellite scatterometer sass are analyzed to determine the spatial structure of oceanic surface winds over wavelengths from 200 to 2200 km the analysis is performed in four latitudinal bands in the pacific ocean sampling characteristics of sass preclude the possibility of determining full two dimensional spectra the analysis is therefore limited to one dimensional along the satellite ground track spectra of vector wind components and kinetic energy the salient features of the results are summarized as follows i for each of the four geographic regions the spectra of meridional and zonal wind components and of kinetic energy are consistent with a power law dependence on wavenumber for midlatitude regions in both the northern and southern hemispheres the wave number dependence of kinetic energy is k 2 2 while for tropical regions in both hemisphere it is k 1 9 ii for each individual region the spectral dependence on wavenumber is nearly the same

glacial chronology and palaeoclimate in the bystra catchment western tatra mountains poland during the late pleistocene abstract deglaciation chronology of the bystra catchment western tatra mountains has been reconstructed based on 10be exposure age dating fourteen rock samples were collected from boulders located on three moraines that limit the horizontal extent of the lgm maximum advance and the lateglacial recessional stage the oldest preserved maximum moraine was dated at 15 5 0 8 ka an age that could be explained more likely by post depositional erosion of the moraine such scenario is supported by geomorphologic and palaeoclimatological evidence the younger cold stage is represented by well preserved termino lateral moraine systems in the kondratowa and sucha kasprowa valleys the distribution of the moraine ridges in both valleys suggest a complex history of deglaciation of the area the first late glacial re advance lg1 was followed by a cold oscillation lg2 that occurred at around 14 0 0 7 13 7 1 2 ka glaciers during both stages had nearly the same horizontal extent however their thickness and geometry changed significantly mainly due to local climatic conditions triggered by topography controlling the exposition to solar radiation the lg1 stage occurred probably during the pre bolling cold stage greenland stadial 2 1a however the lg2 stage can be correlated with the cooling at around 14 ka during the greenland interstadial 1 gi 1d older dryas this is the first chronological evidence of the older dryas in the tatra mountains the ela of the maximum bystra glacier was located at 1480 m a s l in accordance with the ela in the high tatra mountains during the lgm during the lg1 and lg2 stages the ela in the catchment rose up to 1520 1530 m a s l and was located approximately 100 150 m lower than in the eastern part of the massif climate modelling results show that the bystra glacier maximum advance could have advanced in the catchment when mean annual temperature was lower than today by 11 12 c and precipitation was reduced by 40 60 this is in accordance with lgm conditions previously reported for the high tatras during the lg1 and lg2 stages the temperature decrease in the study area reached 10 c and precipitation was lower by 30 compare to modern conditions this resulted in slightly higher accumulation 20 30 in the western tatra mountains compare to the high tatra mountains

extensional fault related folding northwestern red sea egypt the duwi and hamadat areas on the northwestern margin of the red sea rift system exhibit superb outcrop examples of kilometric scale extensional fault related folds in this area the nakheil and hamadat faults of the rift border fault system consist of a series of wnw and nw trending segments that link through breached relay ramps the fault hanging walls are characterised by a series of offset synclines with non linear axial traces sub parallel to the faults the synclines are doubly plunging and in the immediate hanging wall to the normal faults the strata dip sub parallel to the fault these folds result from along strike displacement variations on the individual fault segments together with extension related fault propagation folding as the faults propagated upwards through a highly anisotropic pre rift sedimentary section in the duwi area the axial traces of the synclines are offset and bend in the regions of relay ramps in the hamadat area the synclines associated with individual fault segments are separated by transverse hanging wall anticlines that formed where segment linkage occurred numerical simulations of extension related fault propagation folding using a trishear model produce geometries that closely match those of the duwi and hamadat folds the dimensions of these hanging wall synclines and their relationships to fault displacement variations indicate that they are formed by extensional fault propagation folding rather than by frictional drag along the fault surface

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

relative role of accommodation zones in controlling stratal architectural variability and facies distribution insights from the fushan depression south china sea in sedimentary basins a better understanding of the controlling effect of accommodation transfer zones on stratal architecture and facies distribution can improve the success rate of locating hydrocarbon reservoirs the fushan depression is a half graben rift sub basin located in the southeast of the beibuwan basin south china sea in this study comparative analysis of seismic reflection palaeogeomorphology fault activity and depositional facies distribution indicates that three different types of inner basin slopes i e multi level step fault slope in the western area slope flexure zone in the accommodation zone area and gentle slope in the eastern area were developed along the southern slope of the fushan depression together with a large scale accommodation zone located at the intersection of the western and eastern fault systems further analysis shows that the accommodation zone played an important role in controlling not only stratal architectural variability in the southern slope but also depositional facies distribution in the accommodation zone area during the high stand stage the deposition of depositional systems was mainly controlled by sediment supply and the nw trending transfer faults major drainage systems entered the fushan depression through the accommodation zone along the direction of sediment supply and sedimentary flow paths were parallel to the accommodation zone axis with sedimentary flows constrained to the adjacent areas of the nw trending transfer faults by contrast during the low stand stage the transfer faults had little control over depositional facies distribution and the sublacustrine fan sediments diverted away from the accommodation zone and flew down along the northeast oblique to the accommodation zone axis the flow division in the lowstand stage might be greatly influenced by flow type and topography in addition the accommodation zone area demonstrated unique hydrocarbon accumulation models different from the western and eastern areas suggesting that the future exploration should be conducted at different levels in the fushan depression

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

graben inversion in nature and experiments the inversion of crustal scale basement grabens is studied here through laboratory experiments on small scale models and available oil industry seismic lines from the southern north sea two basic configurations are considered first both the basement and the sedimentary cover are brittle and inversion does not involve any potential decollement between them second the basement and sedimentary cover are separated by a weak ductile layer e g salt which can allow decollement of the cover during both extension and later compression and inversion the second configuration is more complicated and can lead to a large variety of geological structures laboratory experiments were carried out on brittle ductile models built with sand to represent brittle layers basement and sedimentary cover and silicone putty to simulate the decollement layer between basement and cover a mechanically based classification of inversion structures is proposed the effects of some crucial parameters are investigated including obliquity between the direction of shortening and normal faults as well as strength profiles and the presence or absence of salt diapirs the experimental investigation leads to the following conclusions 1 the inversion of the graben by reactivation of normal faults implies that the angle between the direction of compression and the graben is less than 45 2 if there is a superficial decollement e g basement cover interface inversion initiates low dipping thrust faults in the cover localized at graben borders 3 salt diapirs or salt walls localized along the graben borders in the cover are preferential sites for the development of thrust faults and 4 when the cover is decoupled from the basement by a decollement layer inversion induced deformation in the cover which is partitioned between thrust faults along the graben borders and strike slip faults within the graben trending oblique to the graben borders experimental results are compared with field examples in particular from the southern north sea

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

seismic evidence of alpine crustal thickening and wedging from the western pyrenees to the cantabrian mountains north iberia 1 the alpine collision between the iberian and european plates resulted in a complex crustal structure beneath the northern iberian peninsula as revealed from a new set of seismic refraction wide angle reflection profiles the study area is characterized by two major e w ranges the cantabrian mountains and the pyrenees which are relayed to the south by the iberian chain important variations in crustal thickness and velocity distribution are found in a 560 km long e w transect in contrast to the typical 30 to 32 km thick european variscan crust of the western end of the profile a continuous alpine crustal root is evidenced from the cantabrian mountains to the central pyrenees with a moho depth of 46 48 km locally rising to 40 km depth in between beneath the basque cantabrian basin another outstanding feature is the inferred presence of high velocities of 6 40 6 75 km s at midcrustal depths which can be associated with portions of a lower crustal wedge from the northern european domain indenting the southern iberian crust during the alpine stage of compression this indentation produces the delamination of the iberian crust with northward underthrusting of its lower half and the consequent crustal thickening the indenting wedge has a discontinuous presence along the longitudinal section as it was controlled and or affected by n s to ne sw structures further evidence of the northward subduction of the iberian plate is provided by another profile toward the aquitaine basin while a n s profile across the iberian chain reveals an alpine midcrustal thickening beneath this belt with moho depths of 42 km

kinematic modelling of extensional fault propagation folding abstract many studies have shown that in extensional basins discrete faulting at depth is commonly linked to more distributed deformation in particular folding at higher levels such extensional fault propagation folds are particularly common where there is a distinct mechanical contrast between faulted basement and sedimentary cover outcrop and analogue modelling studies indicate that such folds form as upward widening zones of distributed deformation monoclines above discrete faults at depth with increasing displacement strain the folds are cut by faults as they propagate upwards into the cover to date however there has been little investigation into the kinematics of linked basement faulting and extensional fault propagation folding here we present a two dimensional kinematic model of linked basement faulting and fault propagation folding which is based upon trishear the model allows investigation of the influence of shear zone geometry and the rate of fault propagation upon the style of folds and the strains associated with them the evolution of linked basement faulting and folding predicted by the model is compared in detail to that observed in an analogue model the kinematic model reproduces well many of the features seen both in the analogue model and reported from outcrop and seismic studies