late quaternary submarine bedforms and ice sheet flow in gerlache strait and on the adjacent continental shelf antarctic peninsula geophysical data from gerlache strait croker passage bismarck strait and the adjacent continental shelf reveal streamlined subglacial bedforms that were produced at the bed of the antarctic peninsula ice sheet apis during the last glaciation the spatial arrangement and orientation of these bedforms record the former drainage pattern and flow dynamics of an apis outlet up flow and feeding into a palaeo ice stream in the western bransfield basin evidence suggests that together they represent a single ice flow system that drained the apis during the last glaciation the ice sheet outlet flowed north northeastwards through gerlache strait and croker passage and converged with a second more easterly ice flow tributary on the middle shelf to form the main palaeo ice stream the dominance of drumlins with low elongation ratios suggests that ice sheet outlet draining through gerlache strait was comparatively slower than the main palaeo ice stream in the western bransfield basin although the low elongation ratios may also partly reflect the lack of sediment progressive elongation of drumlins further down flow indicates that the ice sheet accelerated through croker passage and the western tributary trough and fed into the main zone of streaming flow in the western bransfield basin topography would have exerted a strong control on the development of the palaeo ice stream system but subglacial geology may also have been significant given the transition from crystalline bedrock to sedimentary strata on the inner mid shelf in the broader context the apis was drained by a number of major fast flowing outlets through cross shelf troughs to the outer continental shelf during the last glaciation copyright 2004 john wiley sons ltd

the velocity description of deformation paper 2 sediment geometries associated with fault bend and fault propagation folds abstract a general tectono sedimentary forward modelling equation is used to derive two dimensional numerical models of sediment geometries associated with developing fault bend and fault propagation folds these styles of folding are described in terms of velocity models of deformation and are linked with syn tectonic erosion transport and sedimentation the resultant two dimensional numerical models simulate pre growth and growth strata in both submarine and subaerial settings the geometries and relationships produced by the models are broadly similar to those seen in natural examples however complex stratal geometries may be generated which are significantly different to those produced by previous models growth strata associated with fault bend and fault propagation folds are also compared and the distinguishing features of each mode of folding discussed the forward models presented in this paper have predictive capabilities in terms of possible sediment geometries associated with fault bend and fault propagation folds and also in terms of the amount of deformation or erosion that a part of a structure may have undergone

visual aspects of the flanking line in severe thunderstorms abstract photographs are presented that illustrate the various forms in which flanking lines exist in nature flanking lines may appear not only as the commonly observed sloping line of cumulus congestus but also as erect towers with a vertical face and as a line of altocumulus castellanus above and parallel to a band of stratocumulus lenticularis it is suggested that the slope of the tops of the flanking line towers with respect to the ground is related to a quantity that is similar in form to the bulk richardson number and that the orientation of the flanking line is a function of the mean wind in the lowest 6 km and storm motion these hypotheses need to be verified when high resolution rapid scan visible and infrared satellite imagery become available on a daily basis

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

kinematic analysis of a large scale leading edge fold lost river range idaho abstract the mahogany creek buck creek structure within the lost river range idaho is a large scale leading edge fold which developed in late paleozoic outer shelf stratigraphy during the sevier orogeny incremental strain histories determined from antitaxial fibrous pressure shadows are used to quantify temporal variations in the magnitude and orientation of elongation as a function of structural position around the leading edge of this northward and eastward propagating blind thrust plane strain is indicated by coaxial up dip extension on cleavage planes on the backlimb of the structure the bluebird mountain formation a calcareous sandstone has deformed by flexural flow whereas the forelimb of the structure records spin through a fixed steeply plunging incremental extension direction the flat limb ahead of the anticline exhibits top to the foreland simple shear in contrast the underlying surrett canyon formation a thick bedded limestone has experienced flexural flow localized within thin zones on both limbs of the anticline samples from the anticlinal hinge zone suggests kinematic partitioning with pin lines which were variably distributed within each unit and which were temporally transient finite elongations are greatest in the hinge and above the foreland flat in the bluebird mountain formation but are negligible in the surrett canyon formation except within the mechanically active interbeds of the hanging wall and within the footwall adjacent to the fault along the northernmost exposures strain histories in the hanging wall do not vary significantly along strike while the footwall varies from undeformed in the south to penetratively deformed in the north thus the strain data are consistent with self similar along strike fold development in the hanging wall during strike parallel ramp propagation forward thrust propagation may have been blunted by a combination of fold accommodated shortening and footwall deformation to the north once the fold had tightened and fold shortening required greater differential stress forward fault propagation resumed transporting the anticline onto the upper flat with little change in hanging wall fold geometry or strain distribution

origin of terraced hillslopes on active folds in the southern san joaquin valley california abstract the northern facing forelimbs of the active san emigdio and wheeler ridge anticlines in the southern san joaquin valley ssjv are marked by numerous sharply defined terracettes terracette treads and risers are 3 5 and 7 11 m wide respectively the terracettes are discontinuous along their length with the longest being 300 m although most terminate more abruptly forming lobate mounds the terracettes form on 10 25 slopes underlain by loosely consolidated coarse conglomerate beds of the pleistocene tulare formation that dip subparallel to terracette risers soil developed on the slopes is comprised of a 1 to 2 m thick calcic bk horizon overlain by a 0 5 m thick argillic claypan bt horizon followed by 1 to 3 m thick ab and a horizons that have been extensively bioturbated a number of hypotheses have been proposed for the genesis of similar terracettes the two most viable tectonic models for our study area are based on growth of active fault bend folds and include i sediment onlap with seismic folding and ii flexural slip faulting we produced a very high resolution digital elevation model dem 1 67 m spatial resolution and 5 cm vertical accuracy using nasa s rascal raster scanning airborne lidar instrument and completed numerical modeling that we interpret to disprove both of the active fold growth models the discovery and mapping of similar terracettes on nw to ne facing hillslopes on the kettleman hills anticline and comanche point in the northern tehachapi mountains suggest that a northern facing aspect is an important factor contributing to terracette development the terracettes are also present only on hillslopes that overlie blind or emergent thrust faults we propose that a soil creep model based on flow dominant mass wasting is the most likely cause of terracette development creep is confined to the thick a and ab cumulic soil horizons that delaminate above the rigid bt claypan and occurs predominantly on northern facing slopes due to increased soil moisture retention the barrier to creep caused by the decrease in slope at the base of fold limbs leads to the development of terracettes that become more sharply defined in a downslope direction we interpret the overthickened a and ab soil horizons to form preferentially on northern facing slopes due to increased bioturbation and deposition of eolian silt strong ground motions produced by earthquakes may facilitate soil creep and thereby contribute to the overall development of the terracettes

withdrawn hydrogeochemical and isotope evidence of groundwater evolution in el guettar oasis area southwest tunisia in southern tunisia the major aquifer system is characterized by the superposition of three principal levels the upper unconfined quaternary alluvial aquifer the intermediate semi confined confined complex terminal segui beglia and zebbag formations and the continental intercalaire bou dinar and sidi aich formations which constitutes the deeper confined aquifer the hydrodynamic functioning of this aquifer system is largely influenced by tectonics gafsa and sehib faults lithologic variation and recharge conditions the tectonics has contributed to the discontinuity of the aquifer levels by creating some barriers which play the role of hydraulic sills a study of the potentiometric maps shows four principal flow directions these flow directions converge at the sill zones chott el guettar and chott djerid depressions the total mineralization evolution shows an increase from the periphery of the basin to the discharge area 1 75 tds 14 4 g l dissolution of halite gypsum and or anhydrite bearing rocks is the principal source of the salinity of the groundwater the isotopic signatures permit to classify the studied groundwaters into two different groups non evaporated groundwaters that are characterized by depleted 18o and 2h contents highlight the importance of modern recharge at higher altitude evaporated groundwaters with enriched contents reflect the significance infiltration of return flow irrigation waters and the influence of the water dam tritium data in the studied groundwaters lend support to the existence of pre 1950 and post 1960 recharge according to radiocarbon residence time estimates the deep groundwater is approximately 40 kyears old and was recharged during a period when the climate was wetter and colder based on radiocarbon content the shallow groundwater is older than 0 5 kyear and represents modern waters mixed with a limited quality of palaeo recharge moreover the insulation of certain compartments of the reservoir and inter communications between the aquifer levels seem to play a principal role in the degradation of quality of groundwater

stream networks and long term surface uplift in the new madrid seismic zone stream networks are sensitive to low rates of surface uplift and can be used to decipher the history of large earthquakes even where faults do not rupture the surface as in intraplate seismic zones statistical analysis of alluvial network data from topographic maps in the new madrid seismic zone in the central united states shows that stream segment gradients deviate the most from an estimated natural stream profile where surface uplift is greatest evidence of cumulative deformation distilled from stream network patterns represents at least several meters of differential surface uplift during holocene time which suggests that more than one cycle of surface deformation occurred

an analysis of cold season supercell storms using the synthetic dual doppler technique abstractcold season tornadic outbreaks occur with regularity in the southeastern united states however detailed analyses of parent supercell storms in the cold season environment often low cape high shear are scarce this is often because storms do not always move close enough to radars for a comprehensive single doppler analysis and significant topography or trees in the southeast make it difficult for mobile radars to operate thus limiting dual doppler coverage however during the super tuesday tornado outbreak of 5 6 february 2008 two tornadic supercell storms passed within 30 40 km of the weather surveillance radar 1988 doppler wsr 88d sites in memphis and nashville tennessee knqa and kohx respectively the relative steadiness of these storms during passage along with the large motion vector from the southwest at 20 25 m s 1 allowed the application of a synthetic dual doppler sdd analysis as such a detailed analysis of these storms was completed including examinations of low lev

river profiles along the himalayan arc as indicators of active tectonics abstract longitudinal profiles along sixteen major transverse himalayan rivers add important constraints to models of active continental subduction and its evolution these profiles are characterized by a zone of relatively high gradient that cannot be associated with differential resistence to erosion in all cases the base of the zone of increased gradients correlates with 1 the topographic front between the lesser and high himalayas 2 the narrow belt of intermediate magnitude thrust earthquakes 3 the main central thrust zone mct these features define a small circle in the central portion of the himalayan arc these correlations suggest that the discontinuity in the river profiles and the other features are controlled by a major tectonic boundary between the rising high himalayas and the lesser himalayas no sharp increases in gradient are observed near the main boundary thrust mbt except on a few rivers such as the jhelum or kundar where the mbt lies close to both the mct and the seismic belt thus it is unlikely that the mbt is a major tectonic boundary the diversion of river courses along the mbt and around anticlines in the sub himalayas has probably been caused by aggradation near the rosion deposition boundary upstream of uplifts in the mahabharat range and sub himalayas a parallel is drawn between the himalayas and new guinea based on the hypothesis that continent arc collision of the type occurring in northern australia preceded continent continent collision in the himalayas the present sedimentary tectonic phase in new guinea resembles the subathu paleocene eocene phase in the himalayas incipient counterparts of the major himalayan structures including the mct and the mbt are recognized in new guinea the drainage patterns in the himalayas and in new guinea bear a similar relation to major structures this suggests that 1 the tectonic evolution of the himalayas has been rather uniform since early stages of collision and 2 the himalayan drainage was also formed at these early stages and is therefore antecedent to the rise of the high himalayas

the dodge city tornadoes on 24 may 2016 damage survey photogrammetric analysis combined with mobile polarimetric radar data abstractpolarimetric measurements recorded by a mobile x band radar are combined with photographs of the dodge city kansas tornado to quantitatively document the evolving debris cloud an inner a

kinematics of fault related folding in a duplex lost river range idaho u s a abstract the doublespring duplex located in the lost river range of idaho is a sevier age fault related fold complex in massive limestones of the upper mississippian scott peak formation folds within the duplex closely resemble fault bend fold geometrics with open interlimb angles and low angle bed cut offs narrow widely spaced bedding parallel shear zones with well developed pressure solution cleavage alternate with massive relatively undeformed layers on fold limbs shear zones are developed only on the limbs of anticlines and have similar but unique morphologies in each of three different folds incremental strain histories reconstructed from antitaxial fibrous overgrowths and veins within the shear zones constrain the kinematics of folding shear zones experienced distributed bedding parallel simple shear flexural flow towards pins near axial surfaces while adjacent massive layers experienced rotation through an externally fixed extension direction the absence of footwall synclines and morphological differences in shear zones from adjacent folds suggest that faulting preceded folding kinematic histories of folds that have experienced different translational histories are identical and are not compatible with strain histories predicted from previous kinematic models of fault bend folding shear zone development and fiber growth is instead interpreted to have occurred during low amplitude fixed hinge buckling in response to initial resistance to translation of the thrust sheet fault bend folding with mobile axial surfaces occurred with translation of the thrust sheets once the initial resistance to translation was overcome and resulted in no penetrative strain

geometry and kinematics of fault propagation folds with variable interlimb angle abstract several conceptual approaches have been proposed to account for the development of fault propagation folds whose geometry and kinematics depend on the amount of displacement along a basal decollement level the ramp angle and the slip to propagation ratio among these the variable interlimb angle model of mitra 1990 is able to explain open and close natural folds but its application is limited because the fold geometry and bed thickness evolution rely on imposed parameters that cannot be measured directly here we use the ramp and the interlimb angles as input data to develop a forward fold model that accounts for thickness variations in the forelimb the relationship between the fold amplitude and fold wavelength is subsequently applied to construct balanced geological cross sections from surface parameters only and to propose a kinematic restoration of the folding through time the model can catter for a wide variety of folds reconstruct the deep architecture of anticlines and deduce the kinematic evolution of the folding with time we consider three natural examples to validate the variable interlimb angle model along strike thickness variation in the forelimb of the turner valley anticline in the alberta foothills of canada precisely corresponds to the theoretical values proposed by our model reconstruction at depth of the alima anticline in the southern tunisian atlas implies that the decollement level is localised in the triassic liassic series as highlighted by seismic imaging the kinematic reconstruction of the ucero anticline in the spanish castilian mountains is also in agreement with the fold geometry derived from two cross sections the variable interlimb angle model predicts that the fault propagation fold can be symmetric normal asymmetric with a greater dip value in the forelimb than in the backlimb or reverse asymmetric with greater dip in the backlimb depending on the shortening amount

l ecaille des gaux ardennes beiges un exemple d evolution tectono sedimentaire complexe lors du developpement d un pli de propagation the kinematics of internal structuration in the gaux thrust sheet charleroi coal basin belgium is explained with the help of a geometric model this model is controlled by the distribution of landelies red breccia outcrops that was syntectonically deposited probably during the namurian we suggest that the tectono sedimentary evolution was controlled by 1 the growth of a fault propagation fold 2 the formation of collapse structures and 3 localized interbed extension 1994 springer verlag

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

fault propagation folds above thrusts with constant dip abstract previous models of fault propagation folds have been extended to include the case where folding initiates above a thrust ramp of constant dip the model may be useful in analyses of fold thrust structures in thin and thick skinned compressional terrains it may be most applicable to fault propagation folds that develop as a fault propagates from a thick massive brittle unit into a thinly layered anisotropic unit

the kinematics of break thrust folds abstract the kinematics of asymmetric open to close often overturned thrust related folds are commonly explained with fault propagation or detachment fold models field observations of thrust related folds exposed in tennessee virginia wyoming and montana that exhibit this geometry indicate that models of fault propagation and detachment folds do not adequately describe the kinematics of these structures existing models of fault propagation and detachment folding employ migrating kink shaped hinges and relate fold geometry entirely to fault geometry slip and to the thickness of the basal detachment layers the models exclude the relation between fold shape and amplitude and they do not predict a correlation between competent layer thickness and fold wavelength as expected from buckling theory thrust related folds examined in this study exhibit unique distributions of fabrics in the hinges and forelimbs which demonstrate a lack of hinge migration furthermore the ratios of dominant member thickness to fold wavelenght agree with those expected for folds controlled by a single layer and they are within the expected range for folds with multiple evenly spaced harmonically deforming layers our analyses suggest these folds evolved from an initial brief stage of sinusoidal buckling to a later stage of fixed hinge kinking and thrusting thrust related folds which exhibit a geometry and mesofabric distribution suggesting this type of evolution are defined as break thrust folds

active oblique ramp faulting in the southern tunisian atlas abstract the gafsa fault is the longest and most active structure of the fold and thrust belt achieving southeastward propagation of the atlas belt of eastern north africa onto the saharan platform the gafsa fault is a 75 km long dextral oblique basement fault ramp that poses a sizable challenge in earthquake hazard assessment because the post paleozoic sedimentary cover is decoupled from its basement above the basement fault in this study we combine seismic lines interpretation tectonic geomorphology and paleoseismological investigations to assess the level of seismic hazard of this fault and evaluate its role in the geodynamic framework of the central mediterranean we show that despite a moderate instrumental and historical seismicity the fault has produced m 6 earthquakes with a return period of ca 500 5000 years during the late quaternary the latest large event having produced a surface rupture on the fault occurred around 8000 yr bp suggesting an m 6 earthquake is overdue on the fault the fault has a minimum reverse component of slip rate of 0 21 0 34 mm yr over the past 50 ka the occurrence of m 7 paleoearthquakes on the fault may be suspected but not established such very strong earthquakes would require transient coseismic linkage of the buried basement fault with the overlying listric fault ramping off the decollement layer the level of seismic hazard may be underestimated on the gafsa fault indeed given the geometry of the basement cover fault system a number of earthquakes generated in the basement would have led to coseismic surface folding instead of to surface rupture the gafsa fault is a major structure accommodating eastward extrusion spreading of the atlas belt onto the saharan and pelagian plateforms above the retreating ionian lithospheric slab

kinematics of large scale tip line folds from the high atlas thrust belt morocco abstract the kinematics of several tip line folds situated along the south atlas front near goulmima morocco is established using both forward modelling and analysis of syn folding deformation from the sahara foreland to the atlas the two successive major structures forming the mountain front in this area fit geometrically with a generalised fault propagation fold model and a model of fault propagation fold altered by late transport on the upper flat respectively field evidence shows that the two folds are developed more or less synchronously the analysis of minor structures helps address the question of migrating hinges vs fixed hinges during the fold s growth

tectonosedimentary evidence in the tunisian atlas bou arada trough insights for the geodynamic evolution and africa eurasia plate convergence the bou arada trough is an east west oriented structure located 80 km sw of tunis characterizing the central tunisian atlas this trough is filled by a thick quaternary sand and clay series and is bordered by complex systems of folds generally trending ne sw contacts between the bou arada trough and the neighbouring folds are accommodated by ne sw and nw se oriented faults in contrast to the other troughs of the tunisian atlas which are related to the pliocene quaternary orogenic period the geodynamic evolution of the bou arada trough began in the maastrichtian and has continued until the present day structural tectonosedimentary and seismic data analyses are undertaken in the study area to better understand the evolutionary scenario of this trough the results obtained show that the bou arada trough is fragmented into three nw se oriented sub basins and records a continuous history of downthrow indeed during extensional to transtensional regimes this trough has evolved in response to the two networks of perpendicular fractures whereas during compressive to transpressive periods the collapse of the bou arada trough has been induced by a pull apart mechanism using the same network of faults but with a strike slip movement the bou arada trough thus preserves a record of the convergence between the european and african plates since the maastrichtian

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with which a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and themore law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons 18 figs less

structure paleogeographic inheritance and deformation history of the southern atlas foreland fold and thrust belt of tunisia 1 structural analysis of the southern tunisian atlas was carried out using field observation seismic interpretation and cross section balancing it shows a mix of thick skinned and thin skinned tectonics with lateral variations in regional structural geometry and amounts of shortening controlled by nw se oblique ramps and tear faults it confirms the role of the late triassic early jurassic rifting inheritance in the structuring of the active foreland fold and thrust belt of the southern tunisian atlas in particular in the development of nw se oblique structures such as the gafsa fault the late triassic early jurassic structural pattern is characterized by a family of first order nw se trending normal faults dipping to the east and by second order e w trending normal faults limiting a complex system of grabens and horsts these faults have been inverted during two contractional tectonic events the first event occurred between the middle turonian and the late maastrichtian and can be correlated with the onset of the convergence between africa and eurasia the second event corresponding to the principal shortening tectonic event in the southern atlas started in the serravalian tortonian and is still active during the neogene the southern atlas foreland fold and thrust belt propagated on the evaporitic decollement level infilling the late triassic early jurassic rift the major eocene atlas event described in hinterland domains and in eastern tunisia did not deform significantly the southern tunisian atlas which corresponded in this period to a backbulge broad depozone

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding geologic note 1 this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with whi h a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and the law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons

geometry and kinematics of the south atlas front algeria and tunisia abstract the south atlas front is the structural boundary between the sahara platform and the atlas mountains it is frequently indicated as a foreland dipping monocline known as the sahara flexure earlier work generally considered that such a cover structure resulted from direct inversion of basement faults this assumption is not applicable to the studied area which is situated close to the algeria tunisia border our study demonstrates a thin skinned style characterised by ramp related folds ten parallel balanced cross sections give an interpretation for the south atlas front from negrine to gafsa about 100 km along strike the geometry at depth of each cross section is defined by forward modelling of each individual anticline the depth to detachment is defined using the geometric characteristics of the fault propagation folds well exposed along the deformation front in all sections the modelling is consistent with basal decollements located within cretaceous stratigraphic levels lateral changes of the tectonic style accommodated by tear faults are observed they seem related to lateral variations in the efficiency of the based decollement faults inducing either a jump of the decollement to another level or the development of en echelon folds the modelling predicts small rotations of cover sheets separated by large scale tear faults

kinematic implications of consequent channels on growing folds 1 as soon as a fold begins to grow above base level it becomes subject to erosion a numerical model of simultaneous fold growth and river erosion captures the early stages of channel formation and delineates the evolution of longitudinal channel profiles this numerical exploration suggests that the patterns of channel incision into growing folds can be used to guide kinematic interpretations of fold growth four types of fold limb growth are modeled limb lengthening through 1 the fold crest or 2 the fold toe 3 limb rotation and 4 curved fold limbs due to trishear folding initially the pattern of channel incision is sensitive to the kinematics of surface deformation subsequently more mature streams evolve toward similar incision patterns with deepest incision near the midpoint of the longitudinal channel profile we compare these model predictions to rough ridge on new zealand s south island where high resolution topographic data reveal the multitude of channels incised into the flanks of these folds because the opposing limbs of these folds have followed distinct deformation pathways the early sensitivity of channel incision to deformation pathway can be examined furthermore the lateral propagation of the fold through time allows for an approximate space for time substitution such that the evolution of these incision patterns can be examined from early through more mature stages this analysis indicates that the west limb of rough ridge has grown by limb lengthening through the toe and the east limb has grown primarily by lengthening through the crest

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

thick skinned tectonics within the intracontinental easternmost atlas foreland and thrust belt tunisia meso cenozoic kinematics and implications for regional geodynamics the transition zone between western and central mediterranean domains presents a key area to investigate kinematic interactions within the adjacent orogen systems such as the easternmost atlas foreland and thrust belt analysis of gravity and seismic data revealed a highly structured basement characterizing a series of structural highs and lows delimited by high angle n s e w and nw se extensional faults this basement architecture is inherited from successive extensional events related to the openings of the triassic early cretaceous tethys oceans i e alpine tethys ligurian tethys and mesogea throughout this period this mosaic of continental blocks significantly controlled the thickness and facies distributions early stages of diapirism took place along these basement faults and allowed maximum subsidence in minibasins revealed by the development of growth strata in response to the late cretaceous eocene shortenings these extensional faults have been reactivated as trasnpressional shear zones giving rise to narrow popup structures in addition gravity modeling indicates crustal thinning and deep rooted faults affecting the crust south of the zaghouan thrust and along e w transfer zones from the late miocene a drastic change in the stress regime is attributed to the effect of the adjacent sicily channel on the study area this promotes crustal thinning basin subsidence and channeling up of mantle derived helium along lithospheric scale weak zones our results give rise to new insights into the reactivation of inherited weakness zones of southern tethys margin in response to the complex interaction between african and eurasian plates accommodated by subduction rollback collision and slab segmentation

unfolding an inverse approach to fold kinematics preservedfoldshapesusuallyreveallittleabouttheirkinematicevolution syntectonic strata preserved in growth synclines in contact with a fold however can permit unfolding a sequential reconstruction of fold growth backward through time from a geometry observed at present to an initial undeformed state such reconstructions can define the kinematics of fold growth growth strata associated with anticlinal forelimbs in the ebro basin exhibit depositional tapering of beds on fold flanks and progressive limb rotation unfoldingawell dateddetachmentfolddefinesitskinematicevolutionandcoevallyvarying rates of shortening forelimb uplift and forelimb rotation interplay of these rates with sedimentation rates controls onlap and offlap relations

a fluvial record of active fault propagation folding salsomaggiore anticline northern apennines italy 1 fault propagation folds offer the potential to relate folding to underlying fault propagation and slip provided that fold kinematics can be established fluvial terraces have been recognized as kinematic indicators but precise relationships between surface uplift and various folding mechanisms remain largely unexplored this study takes advantage of a well preserved progressively deformed suite of middle pleistocene to recent fluvial terraces above a growing fault propagation fold at the apennine mountain front northern italy to constrain the recent fold kinematics and place them in the context of a longer growth history gleaned from older growth strata the geometry of straths and overlying terrace deposits defines a fixed anticlinal hinge a rolling synclinal hinge proxies for fault tip propagation rates rock uplift rates and tilting rates and how these features and rates vary over the last 800 ka along 15 km of strike length field studies are augmented with dem based quantitative geomorphic analyses that document catchment hypsometry mean anticlinal hinge elevation and long profile form notably long term rock uplift rates using incision as a proxy are uniformly correlated with fault propagation and associated synclinal hinge migration mean anticlinal hinge elevation and variations in catchment hypsometries channels that cross the forelimb at a high angle to the fold hinge generally have higher concavities but channel steepness commonly thought to reflect rock uplift is more strongly adjusted to rock type this study elucidates a new understanding of a complex fold growth history extending back at least 10 ma and provides a novel demonstration of how fluvial terraces may be utilized to constrain fault related fold kinematics

growth of wheeler ridge anticline california geomorphic evidence for fault bend folding behaviour during earthquakes abstract unique landforms which we term fold growth terraces and alluvial fan ridges are interpreted to be produced by kink band migration of the front limb of wheeler ridge anticline an active fault bend fold in the southern san joaquin valley based on a folding related model these features form by onlap of alluvium across an active axial surface along the tip of a thrust wedge structure alluvial fan ridges record the sense of slip on the underlying blind thrust which is composed of both thrust and left lateral components our model predicts formation of fold growth terraces by upward propagation of an active axial surface through onlapped alluvium during a folding event to produce a prism of translated but otherwise undeformed sediment alternative hypotheses for the terraces include flexural slip faulting solifluction and erosive processes the width of fold limb between adjacent terraces is equivalent to fault displacement at depth which we interpret to be related to slip caused by earthquakes on the underlying blind thrust earthquake magnitudes derived from the terraces are much larger than expected for the length of the active fold and thrust belt and may indicate a kinematic link with the san andreas fault that drives shortening in the region

groundwater origins and mixing pattern in the multilayer aquifer system of the gafsa south mining district a chemical and isotopic approach major ion geochemistry and environmental isotopes were used to identify the origins and the mineralisation processes of groundwater flowing within the three aquifer levels of the multilayer system of the gafsa south mining district southwestern tunisia it has been demonstrated that groundwaters are characterised by a ca mg so4 water type geochemical pattern is mainly controlled by the dissolution of halite gypsum and or anhydrite as well as by the incongruent dissolution of dolomite 18o and 2h values are much lower than the isotopic signature of regional precipitation and fall close to the meteoric water lines indicating that groundwaters have not been significantly affected by evaporation or mineral water reactions the distribution of stable and radiogenic isotopes 18o 2h 13c and 14c within the aquifer levels suggests that the deep confined aquifer receives a significant modern recharge at higher altitudes while the shallow unconfined aquifer has been mainly recharged under cooler paleoclimatic condition likely during late pleistocene and early holocene humid periods however waters from the intermediate confined unconfined aquifer have composite isotopic signatures highlighting that they are derived from a mixture of the two first end members

the geomorphologic responses to hinge migration in the fault related folds in the southern tunisian atlas in kinematic models of fault related folds hinges must be mobile during fold growth yet hinge migration has been rarely demonstrated in nature several complementary and independent geomorphological responses are presented here that indicate fold hinge migration in the southern tunisian atlas the deformation of the overlying quaternary pediment suggests recent migration of the forelimb synclinal hinge as predicted by the rafini and mercier model the uplift of the first order transverse drainage network the poor maturation and shallow incision features of limb drainage networks toward the base of the limb slope suggest that new and un eroded material was regularly uplifted from the down slope flat plains as predicted by the fault propagation fold model

geometry and structural evolution of lorbeus diapir northwestern tunisia polyphase diapirism of the north african inverted passive margin detailed geologic mapping structural analysis field cross sections new dating based on planktonic foraminifera in addition to gravity signature of lorbeus diapir are used to characterize polyphase salt diapirism this study highlights the role of inherited faulting which controls and influences the piercement efficiency and the style and geometry of the diapir and also the localization of evaporite early ascent displaying diapiric growth during extension salt was extruded along the graben axis developed within extensional regional early cretaceous tectonic associated with the north african passive margin evolution geologic data highlight reactive diapirism during albian time most extreme extension period and passive diapirism during the late cretaceous post rift stage northeastern maghreb salt province gives evidences that contractional deformations are not associated with significant diapirism during shortening the initial major graben deforms as complex anticlines where diapirs are squeezed and pinched from their feeding