can flat ramp flat fault geometry be inferred from fold shape a comparison of kinematic and mechanical folds the inference of fault geometry from suprajacent fold shape relies on consistent and verified forward models of fault cored folds e g suites of models with differing fault boundary conditions demonstrate the range of possible folding results of kinematic fault parallel flow and mechanical boundary element method models are compared to ascertain differences in the way the two methods simulate flexure associated with slip along flat ramp flat geometry these differences are assessed by systematically altering fault parameters in each model and observing subsequent changes in the suprajacent fold shapes differences between the kinematic and mechanical fault fold relationships highlight the differences between the methods additionally a laboratory fold is simulated to determine which method might best predict fault parameters from fold shape although kinematic folds do not fully capture the three dimensional nature of geologic folds mechanical models have non unique fold fault relationships predicting fault geometry from fold shape is best accomplished by a combination of the two methods

3 d anatomy of an active fault propagation fold a multidisciplinary case study from tsaishi western caucasus georgia abstract ongoing deformation processes combining fault propagation and folding are the cause of diffuse seismicity in many areas of the world a detailed understanding of the structural evolution of tectonically active folds is crucial for the evaluation of seismic hazard this paper proposes an integrated analysis of an active fold consisting in the development of a 3d model by combination of geomorphological observations field geological structural data and seismic reflection sections our case study is the tsaishi anticline located at the southwestern tip of the rioni basin uplifted area at the foothill of greater caucasus western georgia we recognized that the fold started to form since the beginning of the middle miocene although preliminary data suggest the possibility of initial local uplift in the oligocene folding process continues up to nowadays giving rise to a south vergent anticline as shown by upwarped late quaternary river deposits the fold backlimb is affected by three main back thrusts whereas at the foot of the forelimb a main north dipping thrust comes very close to the surface based on seismic sections here field data show the presence of a 13 km long fault scarp or fold scarp along the scarp is located the epicenter of the strongest earthquake to date the ms 6 0 tsaishi earthquake that struck the area in 1614 ce based on our results we propose that the overall structure can be classified as an active fault propagation fold the recognition of its very recent growing associated with a major underlying active fault represents also a major contribution to the seismic hazard assessment of this populated area

fold evolution matrices and axial surface analysis of fault bend folds application to the medina anticline eastern cordillera colombia the medina anticline is a fault bend fold located in the hanging wall of the aguaclara fault along the southeastern thrust front of the eastern cordillera of colombia a petroleum province with giant fields we employ a modified technique of axial surface analysis using fold evolution matrices which helps define the subsurface geometry and thereby provides important constraints on trap geometry modeling of hydrocarbon migration pathways and prediction of reservoir quality

thrust sheet rotation and out of plane strains associated with oblique ramps an example from the wyoming salient u s a abstract movement over oblique thrust ramps results in local thrust sheet rotation and principal strains which deviate from the transport plane resulting folds faults and deformation fabrics are superposed on those associated with displacement on frontal ramps the south fork thrust a hangingwall imbricate of the absaroka thrust sheet sw wyoming has a steeply dipping 70 small displacement 300 m oblique ramp in the hangingwall and footwall which makes an angle of 25 to the regional transport direction two penetrative deformation events are recorded by folding stylolitic cleavage and calcite twinning strains in the deformed hangingwall and footwall the first is e to se directed layer parallel shortening prior to or during motion of the absaroka thrust sheet the second event indicates ne directed shortening unique to the oblique ramp at a high angle to ramp strike at the trailing frontal ramp oblique ramp intersection folds in the footwall and normal faults in the hangingwall reflect local strike parallel shortening and extension due to out of plane deflection of the wallrock during displacement the out of plane strains arc consistent with those predicted by kinematic and mechanical models in the hangingwall of the oblique ramp cross strike fractures and bedding are rotated 30 counterclockwise about a vertical axis with respect to structural domains to the north and south due to differential displacement on the south fork thrust stylolitic cleavage and caleite strains unique to the oblique ramp show a similar change in attitude indicating the rotation was the latest recorded stage of deformation in general if an oblique ramp is shallowly dipping the hangingwall may move from the lower flat up the ramp and onto the upper hat if an oblique ramp has a steep dip as in the case of the south fork thrust relatively greater sliding and bending resistance may impede displacement up the ramp and upper flat further transport of the thrust sheet is then accommodated by footwall deformation and hangingwall rotation

tectonic heredity and tectonic wedging along an oblique hanging wall ramp the southern termination of the misty thrust sheet southern canadian rocky mountains the misty range is a homoclinal southwest dipping panel of paleozoic carbonate rocks in the canadian rocky mountains southwest of calgary that has been juxtaposed against underlying mesozoic siliciclastic rocks along the northeast verging misty thrust fault at the south end of the misty range a steep oblique ramp marks an abrupt southward change along the hanging wall of the misty thrust from a detachment zone in the upper devonian palliser formation to another detachment zone in the jurassic fernie group this 2 km high ramp is expressed in the hanging wall rocks as a large oblique southeast plunging fold a west verging back thrust that rises from a detachment zone in the mississippian mount head formation extends across the hanging wall ramp fold and is truncated by the misty thrust the misty thrust evidently propagated southward as an oblique tectonic wedge into this detachment zone forming a triangle zone structure with the back thrust as the roof thrust as displacement on the misty thrust increased and the hanging wall ramp of the misty thrust moved into the triangle zone the back thrust was progressively back folded and became convex subsequently the lower part of the back thrust was partly overridden by the misty thrust and became overturned before becoming detached and incorporated in the misty thrust sheet the configuration and evolution of the tectonic wedge and the oblique hanging wall ramp provide a natural prototype for the interpretation of ramps that mark the lateral terminations of oil and gas reservoir structures in the foothills belt but which are concealed by overlying deformed mesozoic rocks

interpreting the geologic map expression of contractional fault related fold terminations lateral oblique ramps versus displacement gradients abstract fault related folds in contractional settings do not extend indefinitely but rather commonly terminate as plunging anticlines near the tips of the genetically related fault geologists often attribute the formation of such terminations to loss of slip on the underlying fault i e a displacement gradient to changes in fault geometry in which the fault laterally changes stratigraphic position along strike i e a lateral oblique ramp or to some combination of these mechanisms discerning between these formative mechanisms solely through the interpretation of the geologic map expression of the termination can be difficult because of the subjective nature of the criteria used e g lateral oblique ramps often are interpreted at terminations where folds plunge at steep angles where hanging wall cutoff lines trend at high angles to fault strike where stratigraphic contacts trend at high angles to fault strike etc we created pseudo three dimensional model terminations of individual fault related folds using both displacement gradients and lateral oblique ramps to determine if unique characteristics in their map expressions exist we show that map patterns of folds produced by a displacement gradient along a thrust fault of constant geometry are similar to map patterns of folds produced by constant slip on a thrust fault with a lateral oblique ramp specifically our modeling results suggest that 1 simple fault bend folds that plunge less than 20 and simple fault propagation folds that plunge less than 50 at their terminations can be created by both displacement gradients and lateral oblique ramps angles greater than these values suggest that a lateral oblique ramp may be involved in forming the termination 2 hanging wall cutoff lines at terminations that trend at angles less than about 35 to fault strike for simple fault bend and fault propagation folds also may be produced by both displacement gradients and lateral oblique ramps higher angles likely indicate the presence of a lateral oblique ramp at the termination 3 the angle at which stratigraphic contacts trend to the fault strike cannot be used to uniquely identify displacement gradients or lateral oblique ramps for simple fault related folds 4 stratigraphic separation diagrams can indicate the presence of ramps in the thrust sheet but do not uniquely differentiate between frontal ramps with displacement gradients and lateral oblique ramps and 5 actual changes in fault orientation after topographic influences have been taken into account by definition indicate a lateral oblique ramp in reality most natural fault related fold terminations probably share components of both displacement gradients and lateral oblique ramps with each structure possessing contributions from each mechanism

the effects of fault geometry and kinematic parameters on 3d fold morphology insights from 3d geometric models and comparison with the dushanzi anticline china

the unusual 3d interplay of basement fault reactivation and fault propagation fold development a case study of the laramide age stillwell anticline west texas usa abstract subsurface fault geometries have a systematic influence on folds formed above those faults we use the extraordinarily well exposed fold geometries of the laramide age stillwell anticline in west texas usa to develop a strain predictive model of fault propagation fold formation the anticline is a 10 km long nw trending ne vergent asymmetric fold system with an axis that displays a map view left stepping en echelon pattern we integrated field observations geologic and structural data cross sections and 2d kinematic modeling to establish an unusual 3d two stage model of contractional fold formation including 1 reverse reactivation of a pre existing nw striking sw dipping left stepping en echelon normal fault system in paleozoic basement rocks to generate monoclinal flexures in overlying layered cretaceous carbonate rocks and 2 the formation of a subsequent flat ramp fault system that propagated horizontally along a mechanically weak clay rich cretaceous unit before ramping up at the hinge of the pre existing monocline system strain is focused within the forelimb of the system in front of the propagating fault tip and is accommodated by a combination of interlayer slip flat ramp faulting and fracturing proximal to planes of slip this strain predictive model can be applied to similar less well exposed contractional systems worldwide and provides a new unusual example of laramide age contractional deformation

kinematics of orocline tightening in the core of an arc paleomagnetic analysis of the ponga unit cantabrian arc northern spain 1 paleomagnetic and structural analyses of the western european variscan belt wevb suggest that the most viable kinematic model for variscan deformation in northern iberia is oroclinal bending of an originally linear belt in a two stage tectonic history this history represents two regional compression phases e w in the late carboniferous and n s in the permian both in present day coordinates which resulted in the refolding about steeply plunging axes of initially north south trending thrusts and folds in the hinge zone and oroclinal tightening due to vertical axis rotation of the belt s limbs however the orocline model has yet to be critically tested in the wevb s core this study reports new paleomagnetic rock magnetic and structural data from the inner core of the wevb in order to test opposing kinematic models for the well documented fault and fold interference structures formed by late stage variscan deformation and to better understand the overall development of the wevb arc map scale structural features within the wevb core have a highly sinuous geometry characterized by transverse and thrust parallel fold systems formed by fault bend folding over footwall ramps the intersections of these two fold systems produce steeply plunging interference folds which are best exposed in the ponga thrust unit a total of 67 paleomagnetic sites were collected in the barcaliente formation of the ponga unit with emphasis placed on detailed spatial coverage of individual structural domains a multicomponent paleomagnetic remanence was measured which is interpreted to be composed of two components a low unblocking temperature recent viscous magnetization and a high unblocking temperature ancient magnetization that was acquired in the latest stephanian to early permian after initial d1 thrusting and folding bur prior to major secondary rotation rock magnetic experiments show that the characteristic remanence magnetization is carried by secondary authigenic pseudosingle domain magnetite these paleomagnetic results are used to determine the kinematics and geometry of postmagnetization deformation by restoring in situ magnetic vectors back to a defined reference direction on the basis of the restored ponga unit geometry the steeply plunging interference folds found in the wevb core are best described by a combination of secondary buckling of frontal ramp parallel hanging wall anticlines and modification of d1 lateral oblique ramps as frontal ramps during late stage north south shortening this combination of structural modification of the inner core of the wevb was necessary to accommodate oroclinal bending during the final amalgamation of pangea in the late paleozoic

geometrical modeling of fault related folds a pseudo three dimensional approach abstract area balanced cross sections of ramp anticlines and tip line folds in thin skinned fold thrust belts can be quantitatively constructed using plane strain fault bend and fault propagation fold models cross sections alone however are somewhat inadequate for interpreting along strike changes in thrust related fold geometry complex interplay between along strike changes in fault slip and fault shape determines a range of geometric configurations which are difficult to visualize without the aid of quantitative three dimensional models we extend conventional two dimensional folding theories into the third dimension by allowing for continuous variations in fault slip and fault shape along strike geometric equations relating map view angles between fold axial surface traces are derived for a case assuming a uniform fault geometry and an along strike displacement gradient the resulting folds possess no unique fold axis but rather are characterized by multiple fold hingelines each corresponding to bends in the fault for typical displacement gradients observed in the field analysis of the models suggests that discernible differences exist between map patterns of fault bend folds and fault propagation folds whereas little difference exists between map patterns of similar and parallel fault bend folds map view angles between axial surface traces for parallel fault bend folds and fault propagation folds are a function of both ramp cutoff angle and fault slip whereas these same angles for similar fault bend folds are solely a manifestation of fault slip examples assuming uniform shortening and continuously varying fault geometry along strike are also presented fault geometry is varied along strike to simulate oblique and lateral ramps depending upon model type and fault shape parameter modified resulting folds exhibit either cylindrical or non cylindrical fold geometries closure is generated by a decrease in fold amplitude where there is a decrease in ramp cutoff angle along strike or where a fault laterally cuts up section in either instance closure develops without varying shortening along strike model map patterns resemble actual thrust related fold geometries and can be compared to maps of real structures to help predict subsurface geology

an evaluation of models for the kinematic evolution of thrust and fold belts structural analysis of a transverse fault zone in the front ranges of the canadian rockies north of banff alberta abstract the prevailing piggyback conceptual model for the kinematics of thin skinned thrust and fold belts maintains that the main faults develop sequentially from the hinterland to the foreland and from the top to the bottom of the accretionary wedge moreover it presumes that when younger thrust faults originate overlying older thrust faults become inactive and are carried forward passively this appears to contradict the prevailing mechanical model for the evolution of thin skinned thrust and fold belts the critical coulomb wedge model which requires that lateral growth of the wedge must be accompanied by vertical thickening of the wedge crosscutting relationships along a transverse fault zone in the front ranges of the canadian rockies north of banff alberta and patterns of overprinting of thrust related folding on pre existing thrust sheets demonstrate substantial overlap in the times of displacement on four major thrust faults in this part of the front ranges the presumption that displacement on one major thrust fault ends when displacement on a younger underlying thrust begins is a fallacy there is no contradiction between the piggyback conceptual kinematic model and the critical coulomb wedge mechanical model for the evolution of thin skinned foreland thrust and fold belts the main faults do originate sequentially from the hinterland to the foreland and from the top to the bottom of the evolving wedge but displacement occurs simultaneously on several major faults

structural analysis using thrust fault hanging wall sequence diagrams ogden duplex wasatch range utah detailed mapping and cross section traverses provide the control for structural analysis and geometric modeling of the ogden duplex a complex thrust system exposed in the wasatch mountains east of ogden utah the structures consist of east dipping folded thrust faults basement cored horses lateral ramps and folds and tear faults the sequence of thrusting determined by means of lateral overlap of horses thrust splay relationships and a top to bottom piggyback development is willard thrust ogden thrust weber thrust and taylor thrust major decollement zones occur in the cambrian shales and limestones the tintic quartzite is the marker for determining gross geometries of horses this exposed duplex serves as a good model to illustrate the method of constructing hanging wall sequence diagram a series of longitudinal cross sections that move forward in time and space and show how a thrust system formed as it moved updip over various footwall ramps a hanging wall sequence diagram also shows the complex lateral variations in a thrust system and helps to locate lateral ramps lateral folds tear faults and other features not shown on dip oriented cross sections

centrifuge modelling of thrust faulting structural variation along strike in fold thrust belts abstract the three dimensional geometry and the kinematic evolution of fold thrust structures are investigated by analog modelling using the centrifuge technique we focus on along strike structural variation and transfer of displacement between faults and folds the total horizontal shortening across the model fold thrust belts is constant yet there are systematic variations in shortening by the mechanisms of thrusting folding and layer parallel shortening these along strike changes in structural geometry and strain mechanism are manifestations of displacement transfer the model thrust faults have different amounts of thrust displacement at different points along strike the variation is accommodated by transfer of displacement to over or underlying faults or to en echelon faults by transfer of shortening into folding or by transfer of displacement into layer parallel shortening in the models it is clear that faults nucleate at points that are localized by earlier folding of competent units faults nucleated at different points along a single fold may propagate along the fold and link together to form major thrusts the thrust displacement in such cases varies from smaller values at linkage points to larger values at nucleation points the models have a stratigraphie succession like that of the central appalachian valley and ridge province after an equivalent amount of structural shortening the models exhibit structural features analogous to those of the valley and ridge the lowest competent unit equivalent to the cambro ordovician lithotectonic unit forms a large scale duplex like that of the waynesboro sheet the middle competent unit equivalent to the siluro devonian clastic units forms anticlinoria and synclinoria like those of the martinsburg sheet these structures are spatially associated with underlying culminations and depressions that reflect respectively large and small displacements on thrusts that ramp through the lowest competent unit however in the models it appears that the amplitude of buckling of the middle unit controls the amount of displacement on underlying thrusts whereas in the appalachians the structural culminations of the middle unit are interpreted to have been caused by large displacement on underlying faults

comparison of tectonic styles in the mexican and canadian rocky mountain fold thrust belt despite the fact that most fold thrust belts around the world share many features successfully explained by the critical wedge model the details of their geometric evolution and tectonic style development are poorly understood in the classic section of the southern canadian rocky mountains the dominant tectonic style consists of imbricate thrust sheets with relatively little internal deformation of the individual slices in the mexican fold thrust belt central mexico the age of deformation the overall structural pattern and the total amount of shortening are similar but the individual thrust sheets exhibit much more internal deformation as manifest by metre scale buckle folds one of the differences between these localities is the lateral variation of facies resulting in massive platform limestone separated by thinly bedded basinal limestone in the central mexico section strain is concentrated toward the margins between platforms and basins in canada thick platform carbonates form continuous resistant units across the front range possible reasons for the differences in tectonic style between the two sections include the dominant lithology distribution of lithologies taper angle of the tectonic wedges amount of friction along the basal detachment and the degree of anisotropy of the basin facies rocks fold thrust belts are common features that developed on the edges of orogenic belts worldwide many have been well studied and their characteristic features established dahlstrom 1970 chapple 1978 boyer elliott 1982 price fermor 1985 mcclay 1992 these features include the classic notions of forward propagation of thrusts piggyback style a basal decollement and decreasing intensity of deformation towards the foreland most fold thrust belts are wedge shaped and since the mid 1980s the critical taper model of their development davis et al 1983 dahlen et al 1984 dahlen 1990 has become generally accepted analogue and numerical models have been developed that are able to capture many of the basic features of fold thrust belts and that are broadly consistent with the critical taper theory e g huiqi et al 1992 stockmal et al 2007 from early studies it has been clear that most of the large folds in fold thrust belts are intimately related genetically to the thrusts and extensive studies of thrust related folds in the field and in analogue and numerical models have established the nature of this relationship e g dahlstrom 1969 1970 elliott 1976 suppe 1983 mcclay 1992 wilkerson et al 2002 spratt et al 2004 despite the many similarities among fold thrust belts in general there are significant differences among belts and along strike within individual belts these reflect among other things differences in the strength of the basal detachment and the composition and distribution of the rocks in the fold thrust wedge in this contribution we compare basic elements of the structures developed roughly synchronously in two widely separated parts of a single orogenic belt the north american cordillera the sections we compare are a well known section across the southern canadian rocky mountains and a new section across the sierra madre oriental in central mexico the dimensions of the fold thrust belts in these two locations are similar and both sections are dominated by carbonates the structural style however is quite different we compare structures in the two locations and speculate on what may be responsible for the differences

three dimensional geometry and kinematics of the gale buckeye thrust system ouachita fold and thrust belt latimer and pittsburg counties oklahoma the gale buckeye thrust system consists of a series of blind thrusts and associated folds near the boundary between the ouachita fold and thrust belt and the arkoma basin in oklahoma a dense grid of high resolution seismic reflection data augmented by data from exploration and production wells provides a unique opportunity to analyze the three dimensional geometry and kinematics of these structures in detail results from our interpretation provide new insight into the extent style and sequence of thrusts within the gale buckeye thrust system and contrast with previous models for the region specifically we recognize two previously unmapped transverse structures in the gale buckeye thrust system a sharp left stepping zone of oblique ramps and a tear fault within the gale thrust sheet these transverse structures are spatially coincident with similar structural trends in lower paleozoic strata beneath the thrust system as well as outcropping structural trends on the surface this interpretation extends thrusts in the gale buckeye system to minimum strike lengths of 7 9 mi 11 15 km and fault length to displacement ratios of about 10 1 furthermore interpreted structural relationships suggest that the gale and buckeye thrusts formed in a backward stepping manner a new interpretation for faults in this system measurement of differential transport angles from our interpretations of the gale buckeye thrust system indicates that along strike displacement variations of the gale and buckeye thrusts are consistent with thrusts from other nonmetamorphic fold and thrust belts using the differential transport model we infer that the tear fault in the gale thrust sheet indicates a region that became segmented to accommodate excessive along strike differences in displacement in addition we use the model to explain errors in previous interpretations of the gale buckeye thrust system that resulted in the drilling of dry holes integrating realistic differential transport angles with our interpretations for extent style and sequence of thrusting provides new strategies for hydrocarbon exploration hroughout the region

altered rhyolites as oil and gas reservoirs in the minaminagaoka gas field niigata prefecture japan abstract subsurface geology and petrography of volcanic rocks of the recently discovered minaminagaoka gas field show that good reservoirs in the field are altered rhyolites of the mid miocene nanatani formation the nanatani formation is composed of mudstone lava and pyroclastic rock with a composition of rhyolite andesite and basalt rhyolites are divided into rhyolites a b b c and d according to petrographical features rhyolite a is a hyaloclastite and pumiceous tuff of glassy rhyolite rhyolites b b and d are aphyric rhyolite lavas characterized by needle like plagioclase in groundmass rhyolite c is perlite lava rhyolites b d and c are suitable for reservoirs whose pores are not primary but are secondary macroscopic druses and micropores formed by hydrothermal alteration micropores are openings among crystal grains of quartz and albite and are several tens of micrometers in size alteration of rhyolitic rocks is of hydrothermal type and is characterized by a smectite or smectite chlorite mixed layer mineral sericite albite quartz carbonate mineral assemblage in the upper zone but clay minerals in the lower zone are chlorite and sericite alteration of andesite and basalt is similar to that of rhyolite in general but in the kitafukazawa bore hole andesite and basalt below 4640 m depth have chlorite laumonite prehnite pumpellyite epidote assemblage which is correlated to the assemblage of the higher part of the laumonite subfacies of zeolite facies formation temperature of secondary quartz estimated by the measurement of the filling temperature of fluid inclusions is 150 c and is nearly the same as the present temperature at the bottom of the hole from the geological environment characteristics of alteration and paleogeotherm formation of rhyolite reservoirs and migration of oil and gas can be summarized as follows 1 formation of volcanic piles by submarine volcanism of rhyolite andesite and basalt and deposition of mudstone around the piles 2 generation of hydrocarbon in mudstone along with increasing temperature related to volcanism and 3 formation of rhyolite reservoirs by hydrothermal alteration followed by lateral migration of oil and gas into secondary pores

aspects of the three dimensional structure of the alberta foothills and front ranges ever more detailed subsurface images of the alberta foothills and front ranges obtained from improving seismic techniques coupled with an ever expanding base of information from deep wells and improved structural analysis techniques have produced an understanding of fold thrust deformation that is probably applicable to other fold thrust belts comprehensive subsurface data obtained by the petroleum industry are used to outline and analyze the three dimensional configuration of fold thrust deformation of paleozoic carbonate strata these data indicate that displacement changes smoothly along individual thrusts but displacement changes along strike may be large marked by considerable horizontal rotation 20 30 or more of hanging wall stratigraphic cutoffs relative to the footwalls stacking of thrusts with varying displacements has produced summed horizontal rotations of hanging wall cutoffs of as much as 45 50 the three dimensional trajectories of the thrusts through the stratigraphy are smooth for large distances interrupted by abrupt offsets at lateral and oblique ramps these are more common than previously realized the intersections of these ramps with other thrusts produce complex three dimensional links between thrusts with concomitant abrupt displacement changes some simple examples of these linkages are examined with a three dimensional geometric analysis the predictions of the analysis are consistent with structural geometries observed in two case studies of subsurface structures the links at lateral ramps imply simultaneous displacement on parts of the thrusts connected by the ramps since the ramps extend downdip 20 km or more displacement occurred simultaneously on structures occupying relatively interior and exterior positions in the thrust belt the smooth and long radius of curvature folding of many upper detachments indicated by reflection seismic data also is consistent with simultaneous or overlapping periods of motion on groups of thrusts distributed along regional dip most major alberta foothills thrust sheets terminate southward at lateral ramps at the paleozoic level the abrupt southwest northeast offsets at these features are most clearly apparent on a palinspastic reconstruction these offsets cause the paleozoic deformation front to step out east and northeast around the southern and eastern margins of the main arc of the foothills in contrast northward thrust terminations at the paleozoic level commonly occur at both tip lines and lateral ramps subsurface data reveal that there have been some misconceptions regarding large scale structural relationships for example the mcconnell and livingstone sheets are actually portions of the same thrust sheet as are the bighorn and nikanassin sheets when corrected for these misconceptions the data from the alberta foothills suggest that maximum displacement has a nonlinear relationship to thrust length although a linear relationship cannot be ruled out

mechanical stratigraphy as a factor controlling the development of a sandbox transfer zone a three dimensional analysis abstract in thrust belts fold fault terminations are common features of the structural architecture and can pose complicated problems to unravel in particular when two or more terminations are in close proximity such terminations usually reflect pre existing attributes amongst the many factors lateral variations in the mechanical stratigraphy can control along strike geometry and kinematics of fault related folds a displacement transfer zone was produced in a compressional sandbox model by means of two adjacent mechanically different stratigraphic domains the experiment allowed two discrete chains to develop in the different domains so that a complex structural setting occurred in the connecting area periclinal folds oblique thrust fronts and oblique ramps developed in the resulting transfer zone the interaction between periclines in the transfer zone produced lateral culminations in the folded structures the analysis of displacement across the structural domains revealed that a significant loss of slip along the faults occurred in the relay zone in this area imbricate faulting was partially replaced by layer parallel shortening a linear relationship appears to exist between the bed length of the thrust sheet and the related fault slip

displacement and deformation associated with a lateral thrust termination southern golden gate range southern nevada u s a abstract the golden gate thrust offers an excellent opportunity to study displacement and deformation at a lateral thrust tip slip across this e vergent thrust is uniformly about 2 4 km for the southern 2 km of exposed strike length and dies out to zero in the northern 5 km constant displacement and uniform hangingwall structure along the southern one third of exposed strike length suggest that along strike displacement variation and consequent deformation are localized near the lateral tip structures located at and north of the lateral tip are consistent with transpression and later uplift as slip accumulated on the thrust fold and fault orientations and calcite twinning strain record possible transpression north of the lateral tip e w striking normal faults at the thrust tip record extension that is interpreted to be the result of the uplift and translation of a structurally continuous rigid block located north of the normal faults this block is connected to and was uplifted with the crest of the hangingwall anticline and was separated by the normal faults from thrust related folding to the south the main hangingwall structure is an anticline that in southern exposures trends n s parallel to the thrust but bends westward and opens into a box fold to the north the hangingwall anticline superficially resembles a classic fault propagation fold formed by a migrating ductile bead however we are forced to reject the ductile bead hypothesis for the fold because 1 the geometry of the hangingwall anticline far from the thrust tip cannot have evolved from the geometry at the thrust tip and 2 twinned calcite strain data from along the thrust suggest that strain was homogeneous and coaxial rather than inhomogeneous and progressively non coaxial as predicted for a migrating ductile bead the three dimensional structural and kinematic relations at the lateral tip of the golden gate thrust appear to be the result of deformation around a pinned tip although the reason that the tip was pinned at its present location is unclear we interpret the thrust to have propagated relatively quickly to its ultimate extent with little initial displacement indicating that it was easier to fault the rocks than to fold them

displacement transfer at thrust terminations the saltville thrust and sinking creek anticline virginia u s a abstract the saltville thrust terminates in the core of the sinking creek anticline changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination consequently thrust displacement would be transferred into the fold we combine newly published maps and new strain and mesostructural data from the tuscarora sandstone to argue that the sinking creek anticline did perform this kinematic role we propose that the anticline developed as a fault propagation fold that experienced both decollement and anticlinal breakthrough by the saltville thrust thrust displacement was accommodated by the development of the modified fault propagation fold and by transfer to a roof flat from the decollement breakthrough new strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding consequently layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough towards the plungeout of the sinking creek anticline the displacement on the saltville thrust is transferred to a floor thrust we apply this interpretation to the termination of the st clair thrust which has a similar surface geometry where the thrust terminates into an anticline a testable implication of this proposed interpretation for the st clair thrust is that the appalachian plateau must absorb over 20 km of thrust displacement as horizontal shortening

seismic expression and kinematics of a fault related fold termination rosario structure maracaibo basin venezuela abstract fold terminations are primary features of deformed belts and are critical elements in understanding the 3 d kinematics of fault related folds typically such terminations form due to loss of displacement on the genetically related thrust fault and or to along strike change in fault attitude forming a lateral or oblique ramp to unambiguously determine the mechanism responsible for a given fault related fold termination footwall cutoffs and along strike displacement variation must be constrained reflection seismic data can provide the detail necessary to uniquely describe these features the rosario structure in the maracaibo basin venezuela is an example of a natural fault related fold that possesses a southern termination whose fold fault geometry and along strike displacement variation are constrained by industry reflection seismic and well data we interpret that the fold plunge near the southern termination is due to an along strike decrease in displacement the fault geometry associated with the southern termination changes from a flat ramp flat at the crest of the structure where displacement is greatest to simply a ramp near the lateral fault tip without forming a lateral or oblique ramp we combine these observations regarding displacement and fault geometry with the assumption that along strike spatial variations reflect temporal variations during development of a fault related fold to propose a kinematic model for the rosario structure specifically we suggest that the structure first initiated as an isolated fault ramp within the stiff carbonate and clastic units with increased shortening the fault grew to link with upper and lower detachments in the weaker shale units to create a hybridized fault bend fold our model suggests a possible explanation for the evolution of the rosario structure and also provides an alternative to existing pseudo three dimensional models for fault related fold growth that relaxes the rigidity in the assumption of along strike self similarity

distinguishing lateral folds in thrust systems examples from corbieres sw france and betic cordilleras se spain abstract folds with axes almost parallel to the mean tectonic transport direction are frequent in fold thrust belts particularly along the borders of arcuate belts such structures have been frequently explained in terms of superimposed tectonic events but in some cases they are most realistically understood in terms of lateral folds inherited from lateral footwall ramps and initiated subparallel to the tectonic transport direction in order to distinguish frontal and lateral folds we have established criteria based on field examples from two regions where folds occur parallel to the regional transport direction the betic cordilleras southern spain and the corbieres thrust front northeast pyrenees france the main differences between frontal and lateral folds concern the geometry the evolution of the structures and the modes of strain accommodation in the roof strata enveloping imbricate stacks recalling that above a duplex or even on individual horse the roof layers are thinned along sections normal to transport we examine the precise location where the extension is expressed illustrated by examples from the two regions this leads us to address some tectonic problems of these erogenic zones such as the thrust sequence and development of thrust related cleavage

computerized tomographic analysis of displacement trajectories and three dimensional fold geometry above oblique thrust ramps computerized tomographic analysis of physical models of fold thrust structures permits nondestructive systematic analysis of variations in displacement trajectories and variations in three dimensional fold geometry as a function of thrust fault geometry the authors studied models in which sand layers with embedded transport parallel marker lines were shortened incrementally up to a maximum of 24 over rigid footwall fault templates these templates simulated a right stepping oblique ramp connecting two ramps perpendicular to the shortening direction in response to movement over the oblique ramp templates overturned folds formed and marker line deflections indicative of out of plane strains developed marker lines within layers originally truncated by fault templates were deflected leftward away from the right stepping oblique ramp during deformation whereas marker lines within sand layers that originally extended across the upper flat of the fault template were deflected in a more radial pattern differences in marker line deflections imply that displacement trajectories within natural thrust sheets may vary as a function of overburden and structural position furthermore their tomographic studies graphically demonstrate that out of plane strain and differential rotation of layers within thrust sheets occur in the vicinity of oblique ramps

differential transport and continuity of thrust sheets abstract structural geologists long have strived to establish basic tenets describing the interaction between thrust displacement and lateral extent of thrust sheets individual non metamorphic thrust sheets can be partitioned into segments that exhibit linear variations in displacement along strike the differential transport between endpoints of each segment define an along strike bulk shear angle which describes the spatial rate of change in displacement along the length of the fault empirical measurements of differential transport angles for continuous thrust sheets from different north american fold thrust belts yield bulk shear angles that do not exceed 35 40 without formation of tear faults these values might thus be considered a limit for coherent behavior of continuous non metamorphic thrust sheets thereby providing constraints on three dimensional interpretations of fold thrust belts

displacement transfer at thrust terminations in southern appalachians saltville thrust as example transition from faulting to noncylindrical folding involving rapid plunge change at the fold closure is the primary displacement transfer mechanism at the northern end of the south appalachian foreland fold and thrust belt regional thrust faults including the saltville narrows and st clair terminate in regional overturned asymmetric anticlines this mechanism of displacement transfer is distinct from thrust terminations where fold complexes of smaller noncylindrical folds converge toward the end of the fault trace the saltville thrust transition to the sinking creek anticline is representative of the southern appalachian structures deformation intensity patterns reflected by cleavage development mesoscopic folding and faulting suggest that the sinking cree anticline formed due to upwarping from shear thrusting at depth laboratory deformation analogs of folds formed above ramps support this contention experimentally produced folds are asymmetric overturned structures with high strains on overturned limbs and very low strains on upright limbs a deformation sequence involving shear thrusting with subsequent break thrusting may characterize fault propagation at thrust termini this will be important for layered sedimentary sequences where thick rigid members low in the sedimentary pile are overlain by thinner interbedded mechanically anisotropic strata

complex strain patterns developed at the frontal and lateral tips to shear zones and thrust zones abstract many of the complex strain patterns seen in shear zones and thrust zones such as variable fabric orientations refolded folds and fabrics together with folds with hinges almost parallel to the main transport direction can be explained in terms of differential movement within the shear zones these strains are developed at the frontal and lateral tips of the zones as they propagate examples are taken from the moine thrust zone of scotland which show variations in strains particularly at the lateral tips the form of differential movement described here may lead to complex strain paths and non plane strain ellipsoids and the spatial variations in finite strain may be used to delineate zones of extensional and compressional flow and differential movement in the shear zones or thrusts

fault displacement distance relationships as indicators of contractional fault related folding style we present a method of using fault displacement distance profiles to distinguish fault bend shear fault bend and fault propagation folds and use these insights to guide balanced and retrodeformable interpretations of these structures we first describe the displacement profiles associated with different end member fault related folding models then provide examples of structures that are consistent with these model based predictions natural examples are imaged in high resolution two and three dimensional seismic reflection data sets from the niger delta sichuan basin sierras pampeanas and cascadia to record variations in displacement with distance updip along faults termed displacement distance profiles fault bend folds exhibit constant displacement along fault segments and changes in displacement associated with bends in faults shear fault bend folds demonstrate an increase in displacement through the shearing interval and fault propagation folds exhibit decreasing displacement toward the fault tip more complex structures are then investigated using this method demonstrating that displacement distance profiles can be used to provide insight into structures that involve multiple fault related folding processes or have changed kinematic behavior over time these interpretations are supported by comparison with the kinematics inferred from the geometry of growth strata overlying these structures collectively these analyses illustrate that the displacement distance approach can provide valuable insights into the styles of fault related folding

kinematics of thrust sheets within transverse zones a structural and paleomagnetic investigation in the appalachian thrust belt of georgia and alabama deformation styles of orogenic belts change along strike across transverse zones tzs hence the kinematics of tzs is indispensable for three dimensional restoration of thrust belts we investigate the causes of deviation in strike of fold axes and fault surfaces in two tzs of the southern appalachians using structural cross sections and paleomagnetism in the rising fawn tz of georgia hanging wall lateral ramp folds yield paleomagnetic rotations and variation in magnitude of thrust translation plunge of folds differential slip and rotations are associated with lateral ramp geometry and along strike variation in the rheology and thickness of units that host lower and upper detachment levels in alabama the internal geometry strike and paleomagnetic rotations of the helena thrust sheet change across the anniston tz these differences resulted from movement of the helena thrust sheet over different footwall blocks and sub decollement basement graben structures and from differential slip along an oblique ramp rotations of thrust sheets within tzs occur where a thrust sheet was translated over 1 an oblique lateral ramp with contrasting rock strengths at lower and upper detachment levels 2 a transverse basement fault that separates contrasting basement structural domains and 3 intersections between frontal ramps and transverse structures because of the local causes of rotations in lateral structures paleomagnetic and structural analyses of tzs are necessary for understanding the kinematics and restoration of both single thrust sheets and large scale curves in thrust belts

paleoenvironmental setting mechanism and consequence of massive organic carbon burial in the permian junggar basin nw china abstract the junggar basin in northwestern china is a typical walled sedimentary basin that has a prolonged basin evolution history from the paleozoic to cenozoic and is rich in petroleum resources permian strata reach thousands of meters in thickness and have been intensively studied for their record of regional tectonics and paleoenvironments they have also been exploited for oil and gas for the past several decades in this paper we summarize perspectives on tectonic evolution stratigraphic framework sedimentary environments and the paleoclimate of the permian junggar basin and the adjacent turpan basin further we discuss the mechanism and consequences of massive organic carbon burial based on a compilation of published radiometric dating datasets an updated chronostratigraphic framework was proposed for the junggar basin this framework constrains the ages of two main petroleum source intervals the fengcheng formation and the lucaogou and equivalent formations as early permian and middle permian respectively although a global warming and drying trend was present throughout the permian period the regional climate over the junggar basin was drier in early permian and more humid in the middle late permian with short term climatic fluctuations during the deposition of the two petroleum source intervals dry and temperate climate prevailed and evaporative lacustrine environment dominated organic matter enrichment was promoted by stable salinity stratification and limited dilution by inorganic sediments leading to one of the richest lacustrine source rock deposits in the world the average organic carbon burial rates were 11 2 gc m2 yr for the lucaogou formation and 3 5 gc m2 yr for the fengcheng formation lower than the average organic carbon burial rate in modern lakes however considering the large areas of global tectonic lakes in the permian period organic carbon burial in lacustrine environments could act as a significant carbon sink and impact the global carbon cycle and climate evolution

quaternary transfer faulting and belt front deformation at pakuashan western taiwan the arcuate pakuashan anticline is located in the outermost front units of the western foothills of taiwan this oblique feature of the deformation front is investigated in terms of combined morphostructural analysis based on imagery and digital elevation model as well as microtectonic analysis of fault slip data a subsurface structural study based on available seismic and well data was also carried out resulting in improved mapping of the neogene series and associated structures this mapping allowed construction of several along strike cross sections such combined analyses revealed that the transverse pakuashan fold is located above a major transfer fault zone this active fault zone accommodates differential westward propagation of thrust units its kinematic evolution is principally controlled by the geometry of the foreland peikang high behaving as a buttress for the west verging thrust sheets a preliminary analytical model of the oblique thrusting at pakuashan is based on similar cases studied by apotria et al 1992 it involves quaternary transfer faulting accommodating the motion of connected thrust sheets moving over oblique ramps linked to a preexisting major basement boundary the hinge fault of the peikang high this analytical modeling accounts for the occurrence of local extension at the intersection of oblique ramps in the southern pakuashan numerous complementary structural and tectonic evidences led us to establish a complete deformation model involving local rotation in southern pakuashan which caused differential slips in northern pakuashan resulting in tear faulting these evidences include large extension at the intersection of oblique ramps distributed extension in the transverse zone regional wrench deformation absence of major reorientation of local stress inside the transverse zone along strike variation of structural styles coupled with low to high uplift rate from the northern to the southern part of the pakuashan fold thus a synthetic reconstruction of the pakua transfer fault zone evolution is proposed as a typical example of active transfer faulting evolving gradually from a primary tear fault with a slight curvature to the left lateral tear fault or transfer fault that offsets two distinct frontal thrust and fold sheets

quantifying vertical axis rotation in curved orogens correlating multiple data sets with a refined weighted least squares strike test 1 map scale curvature is a fundamental feature of most contractional orogenic belts and is central to understanding the kinematic and dynamic evolution of mountain systems paleomagnetic analysis combined with detailed structural studies is the most robust means of quantifying vertical axis rotations that produce curvature over a range of temporal and spatial scales this paper explores how vertical axis rotations can best be evaluated for multiple data sets by applying a weighted least squares method to the classic strike test this refined method provides measures of best fit slope confidence interval and goodness of fit between map scale structural trend paleomagnetic rotations and deformation fabric orientations structural trend is estimated by averaging fold axial trace formation contact and bed strike data over kilometer scale areas paleomagnetic and deformation fabric site mean orientations and measurement uncertainties are estimated using vector and bootstrap statistics weighting factors are estimated from combined measurement uncertainty structural noise related to small scale block rotation and stress strain refraction and variations in restoration paths the number of sites needed to obtain a significant confidence interval in strike test slope is a function of combined uncertainty in paleomagnetic or deformation fabric directions and the total range in structural trend around a curved orogen improved estimates of strike test slope and rotation thus require systematic sampling with a wide distribution of sites evaluation of appropriate weighting factors and statistical analysis a case study is presented that highlights application of this refined method to paleomagnetic and deformation fabric data sets from the wyoming salient of the sevier thrust belt paleomagnetic data yield a strike test slope of 0 76 0 11 indicating that the wyoming salient is a progressive arc with 3 4 secondary curvature related to vertical axis rotation synchronous with large scale thrusting and 1 4 initial curvature finite strain anisotropy of magnetic susceptibility and mesoscopic structural orientations which are related to early layer parallel shortening all yield strike test slopes of 0 9 0 1 comparing these slopes with paleomagnetic results indicates that deformation fabrics had initial curvature and thus cannot be used alone to accurately estimate rotations by integrating systematic paleomagnetic and structural data using statistical analysis curvature models for the wyoming salient are closely constrained

deformation around a thrust tip in carboniferous limestone at tutt head near swansea south wales abstract the tutt head thrust zone is the tip of a forward propagating lateral ramp which links two levels of detachment within the langland mumbles anticline an early pressure solution accommodated cataclastic phase of deformation is partially overprinted by later plastic deformation involving dislocation glide dislocation climb and grain boundary sliding mechanisms two and three dimensional strain determinations indicate that displacement reduction in the tip zone is primarily accommodated by footwall extension with subsidiary contribution from hangingwall contraction localized oblique movement in the tip zone is explained by the process of tip line pinning geometrical considerations reveal the requirement for diachronous emergence of the tip line from an obstacle to propagation this enables differential displacement about a pinning point and the consequent generation of shear strain coplanar with the thrust plane such shear strains are necessarily localized and limited in magnitude the stress pattern around the thrust tip is compatible with that predicted by the elastic solution to the stress distribution around a mode ii shear crack the observation of a recognizable stress concentration suggests that quite high stress concentrations may accompany thrust tip propagation

kinematics around a large scale oblique ramp southern pyrenees spain the gavarnie thrust sheet of the southern pyrenees is bound to the east and west by 40 km long transverse zones producing a rectilinear thrust sheet within the boltana region the northwest corner of the gavarnie thrust sheet is well exposed the locale is used to characterize the strain and kinematic patterns and detailed geometry of an oblique ramp over a variety of scales the hanging wall of the gavarnie thrust fault in the area was transported toward 200 and contains two regional scale north south trending anticlines in the vicinity of the oblique ramp the strike of the gavarnie thrust fault and the trend of hanging wall fold axes are 0 180 the magnitude of shortening accommodated by regional scale fold and fault development is constant at 25 along the length of the ramp the orientation of instantaneous and finite shortening axes on meso and grain scales was inferred from the attitudes of cleavage mesoscale folds and faults carbonate mechanical twins and the geometry of finite strain finite and instantaneous shortening axes are subhorizontal and remain perpendicular to the gavarnie thrust ramp within a 10 km wide zone in the footwall and a 20 km wide zone in the hanging wall outside of the halo of footwall and hanging wall ramp deformation the principal shortening directions consistently trend 200 parallel to thrust transport directions throughout the south pyrenean thrust belt the parallelism of instantaneous and finite principal strain axes suggests that grain scale deformation was rionrotational total shortening measured within the footwall of the gavarnie thrust fault decreases from 60 adjacent to the thrust ramp to 10 approximately 10 km away from the ramp while principal shortening directions determined over scales ranging from millimeters to kilometers show a consistent pattern in the boltana region they differ by as much as 90 from tectonic convergence directions between iberia and eurasia during the alpine orogeny 80 18 ma determined from magnetic anomaly patterns in the central atlantic and bay of biscay divergence between plate convergence directions and alpine south pyrenean shortening directions suggests that 200 km of nw se convergence was apparently partitioned into the north and south pyrenean thrust zones which were shortened 167 km the iberian range which accomodated 30 km of shortening 10 km of shortening accomodated in the catalan coastal range and 100 km of right lateral strike slip accomodated within the internides

map view retrodeformation of an arcuate fold and thrust belt the jura case 1 the mechanism of arcuate mountain range formation is a matter of debate here we perform a map view restoration of a detailed three dimensional model of the jura arc a typical arcuate mountain range in the foothills of the swiss and french alps this retrodeformation is performed using the unfold surface balanced program based on a block mosaic method it results in a displacement field divergent toward the deformation front this displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30 in the southern internal jura and a corresponding vertical axis rotation or shear strain of the savoie molasse basin hinterlandward we also predict a 10 clockwise vertical axis rotation of the molasse basin in switzerland all these rotations agree with those documented by paleomagnetic data the former are taken to result from a substantial decrease in shortening at the southern jura end while the divergence of displacements is interpreted to result from variations in the detachment level distribution

a computed tomography approach for understanding 3d deformation patterns in complex folds abstract analog models are an important tool for understanding complexly folded and faulted geological structures in this paper we propose the use of x ray computed tomography to accurately reconstruct the geometry of analog models using an orthogonal reference system and to completely characterize deformation patterns within the modeled structure in 3d the rheology and radiological contrast of various different materials have been studied showing that eva sheets are a good choice to model buckling layers after considering various possibilities to define the reference system we opted to screen print two orthogonal sets of parallel lines on the surfaces using minium lead tetroxide the model was then built with gocad using a series of ct slices that can be closely spaced this kind of model allows us to reconstruct the volume distribution of strain ellipsoids and can be very accurate and useful to ascertain the orientation of folded lineations in complex structures as well as to characterize the expected deformation on the surfaces we have built a simple analog model inspired in the balzes anticline located in the external sierras southern pyrenees to illustrate the potential of the technique and to analyze the deformation patterns of this complex curved fold that has accommodated significant magnitudes of vertical axis rotation during its formation

simultaneous development of noncylindrical folds frontal ramps and transfer faults in a compressional regime experimental investigations of himalayan examples experiments were performed with modeling clay models to understand the simultaneous development of folds frontal ramps and transfer faults oblique ramps in layered sequences the models were deformed by layer parallel contraction at a late stage of deformation the models were subjected to a maximum contraction parallel to the layering and perpendicular to the early axis of maximum contraction to study the effect of the superposed deformation the experimental results reveal that a transfer fault joining two frontal thrust ramps acts as a shear zone and controls the orientation of fold hinge lines in the adjacent region hence two orientations of fold hinge lines may be observed 1 oblique to the axis of maximum compression in the vicinity of the transfer fault and 2 normal to the axis and parallel to the frontal ramps away from the transfer fault during the longitudinal fold propagation the two hinge lines may coalesce to form a fold curvature opposite to the tectonic transport direction the curvature varies along the transfer fault depending on the shear zone geometry additional fold hinge line curvatures may result during the superposed deformation both in the early and the superposed fold hinge lines all these curvatures produce a systematic pattern which can be analyzed with the help of the experimental results the fold hinge line orientation may also be used to establish an oblique ramp in field as demonstrated by examples from the lesser himalayas india