lunar global shape and polar topography derived from kaguya lalt laser altimetry a global lunar topographic map with a spatial resolution of finer than 0 5 degree has been derived using data from the laser altimeter lalt on board the japanese lunar explorer selenological and engineering explorer selene or kaguya in comparison with the previous unified lunar control network ulcn 2005 model the new map reveals unbiased lunar topography for scales finer than a few hundred kilometers spherical harmonic analysis of global topographic data for the moon earth mars and venus suggests that isostatic compensation is the prevailing lithospheric support mechanism at large scales however simple rigid support is suggested to dominate for the moon venus and mars for smaller scales which may indicate a drier lithosphere than on earth especially for the moon and venus

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

what do kinematic models imply about the constitutive properties of rocks deformed in flat ramp flat folds kinematic theories of flat ramp flat folds relate fault angles to stratal dips in a way that allows prediction of structural geometries in areas of economic or scientific interest however these geometric descriptions imply constitutive properties of rocks that might be discordant with field and laboratory measurements in this study we compare deformation resulting from kinematic and mechanical models of flat ramp flat folds with identical geometries to determine the conditions over which kinematic models may be reasonably applied to folded rocks results show that most mechanical models do not conform to the geometries predicted by the kinematic models and only low basal friction 0 1 and shallow ramps ramp angle 10 produce geometries consistent with kinematic predictions this implies that the kinematic models might be appropriate for a narrow set of geometric and basal fault friction parameters

global distribution of large lunar craters implications for resurfacing and impactor populations by using high resolution altimetric measurements of the moon we produced a catalog of all impact craters 20 kilometers in diameter on the lunar surface and analyzed their distribution and population characteristics the most densely cratered portion of the highlands reached a state of saturation equilibrium large impact events such as orientale basin locally modified the prebasin crater population to 2 basin radii from the basin center basins such as imbrium orientale and nectaris which are important stratigraphic markers in lunar history are temporally distinguishable on the basis of crater statistics the characteristics of pre and postmare crater populations support the hypothesis that there were two populations of impactors in early solar system history and that the transition occurred near the time of the orientale basin event

laboratory testing of an automatic method for determining normal fault geometry at depth abstract a general kinematic method for determining two dimensional normal fault geometries from a large number of hanging wall horizons has been tested on synthetic data and laboratory models the method assumes that the hanging wall deforms by a combination of arbitrarily inclined bulk simple shear and differential compaction it should be applicable to normal faults which do not change shape as deformation proceeds fault geometry the inclination of simple shear and compaction parameters may all be uniquely determined provided that the geometry of the hanging wall stratigraphy is accurately known prior to and after deformation testing the method on synthetic data has shown that unique solutions can be found solutions obtained using large numbers of hanging wall horizons of laboratory modelled faults are encouraging in each case the method was able to predict a fault geometry close to the fault geometry used in the laboratory model hence bulk simple shear appears to be a good approximation of hanging wall deformation the inclination of simple shear appears to be controlled by the underlying fault geometry rather than the amount of extension or the composition of the hanging wall fill in future it is hoped that a general method similar to this one can be applied routinely to depth converted seismic reflection data

vegetation changes and hydrological fluctuations in the central ebro basin ne spain since the late glacial period saline lake records abstract although the central ebro basin northeastern iberian peninsula is both the northernmost semi arid area in europe and one of the regions with the largest biodiversity it has been insufficiently studied in terms of past climate variability due to the scarcity of suitable sites for palaeoenvironmental analyses previous studies from ephemeral saline lakes in the area mainly based on palynological data show abrupt and rapid arid humid transitions throughout the last glacial cycle highlighting a complex palaeohydrological evolution new cores from two saline lakes la playa and la salineta in the los monegros area provide multi proxy records including sedimentology geochemistry and pollen indicators this study together with a detailed review of the main saline records from the central ebro basin enables us to reconstruct the main features of the palaeoclimate evolution during the last glacial cycle one of the main results of this study is the alternation of humid and dry phases as a characteristic of the climate evolution during the late glacial additionally the study suggests an important role of the increased flow from the pyrenean rivers during deglaciation in the hydrological balance of the central ebro basin the early holocene is the wettest period of the studied sequences contrasting with the aridity of the middle holocene interval which is frequently absent as a result of intense aeolian erosive processes the lack of archaeological remains associated with the middle holocene neolithic also supports increased aridity that would have impeded human settlements although anthropogenic activity partially masks the climate signal from the palynological data in the uppermost part of the studied sequences there is some sedimentological evidence for a climate change during the last 2000 yr resulting in a recovery of average saline lake levels in the central ebro basin

quaternary palaeohydrological evolution of a playa lake salada mediana central ebro basin spain this research was partly funded by the national science foundation usa under the ear 941 8657 programme and by the eead csic project number z 5 96 this is limnological research center contribution number 527

an analytical model of hanging wall and footwall deformation at ramps on normal and thrust faults abstract we determine stress strain and structural evolution for an analytical model of moderate angle 10 20 ramps developed on both normal faults normal ramps and thrust faults thrust ramps in the model a frictionless sliding surface with ramp configuration separates two incompressible isotropic viscous half spaces of different viscosity hanging wall and footwall ramps are planar but ramp flat corners are locally rounded deformation is due solely to translation across the ramp and regional extension or shortening is ignored sliding down a normal ramp causes vertical extension and horizontal shortening in both the hanging wall and the footwall this conforms with reverse faults seen in experimental models of normal ramps the stress in the footwall has the same magnitude as that in the hanging wall but the footwall strain rate is reduced in magnitude by the ratio both a hanging wall syncline and a footwall anticline form the normal ramp migrates in front of the rising footwall at a rate v ss v where v is the sliding velocity but the ramp does not change shape the continuous ramp motion in the model may correspond to the creation of an extensional duplex or chaos zone in brittle rocks at a normal ramp mean compressive stress is lowered and deviatoric stress is raised favoring local faulting and fracture sliding up a thrust ramp causes stresses strain rates and strains of the opposite sign horizontal extension and vertical shortening in both walls is consistent with normal faulting both a hanging wall anticline and a footwall syncline form passively although the deviatoric stress is raised at the ramp so is the mean compressive stress inhibiting fracturing however the mean compressive stress is lowered on the adjacent flats favoring fracturing there

sedimentary and diagenetic features in saline lake deposits of the monegros region northern spain abstract the monegros region in northern spain is marked by the occurrence of a large number of ephemeral to dry lake basins occupying small karstic depressions the lacustrine sediment fill of these basins contain various carbonate and silicate minerals whose origin and palaeoenvironmental significance is poorly understood for the present study 14 lake basins were sampled in order to establish vertical lateral and regional variations in mineralogical and textural characteristics aimed at determining the mode of formation of the various mineral phases present in nearly all basins the same sequence of three lithological units is recognized including a basal clayey unit a middle magnesite bearing and gypsum rich unit and a calcite and dolomite dominated surface unit distribution patterns of carbonate minerals indicate that magnesite is a synsedimentary precipitate dolomite formed as a diagenetic authigenic phase and calcite is partly authigenic and partly allogenic all clay minerals including sepiolite and smectite appear to be allogenic regional variations are marked by similarities between groups of neighbouring basins but no overall trend related to regional drainage patterns is recognized the middle lithological unit records a lake stage with predominantly chemical sedimentation unit ii overlying a less well documented interval corresponding to a perennial lake stage with lower salinity unit iii whereas the surface unit formed during a period with predominantly clastic sedimentation based on a comparison with other regional records the middle unit is attributed to an early holocene humid stage separated from the overlying late holocene deposits by a hiatus that corresponds to a mid holocene arid stage

arid and humid phases in southern spain during the last 4000 years the zonar lake record cordoba a multiproxy study of sediment cores from zonar lake 37 29 00 n 4 41 22 w 300 m a s l supported by 11 14c ams dates provides the first high resolution centennial scale reconstruction of past h

dynamic modeling suggests terrace zone asymmetry in the chicxulub crater is caused by target heterogeneity we investigate the cause of terrace zone asymmetry in the chicxulub impact crater using dynamic models of crater formation marine seismic data acquired across the crater show that the geometry of the crater s terrace zone a series of sedimentary megablocks that slumped into the crater from the crater rim varies significantly around the offshore half of the crater the seismic data also reveal that at the time of impact both the water depth and sediment thickness varied with azimuth around the impact site to test whether the observed heterogeneity in the pre impact target might have affected terrace zone geometry we constructed two end member models of upper target structure at chicxulub based on the seismic data at different azimuths one model representing the northwest sector had no water layer and a 3 km thick sediment layer the other model representing the northeast sector had a 2 km water layer above a 4 km sediment layer numerical models of vertical impacts into these two targets produced final craters that differ substantially in terrace zone geometry suggesting that the initial water depth and sediment thickness variations affected the structure of the terrace zone at chicxulub moreover the differences in terrace zone geometry between the two numerical models are consistent with the observed differences in the geometry of the terrace zone at different azimuths around the chicxulub crater we conclude that asymmetry in the pre impact target rocks at chicxulub is likely to be the primary cause of asymmetry in the terrace zone

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

observations at terrestrial impact structures their utility in constraining crater formation hypervelocity impact involves the near instantaneous transfer of considerable energy from the impactor to a spatially limited near surface volume of the target body local geology of the target area tends to be of secondary importance and the net result is that impacts of similar size on a given planetary body produce similar results this is the essence of the utility of observations at impact craters particularly terrestrial craters in constraining impact processes unfortunately there are few well documented results from systematic contemporaneous campaigns to characterize specific terrestrial impact structures with the full spectrum of geoscientific tools available at the time nevertheless observations of the terrestrial impact record have contributed substantially to fundamental properties of impact there is a beginning of convergence and mutual testing of observations at terrestrial impact structures and the results of modeling in particular from recent hydrocode models the terrestrial impact record provides few constraints on models of ejecta processes beyond a confirmation of the involvement of the local substrate in ejecta lithologies and shows that z models are at best first order approximations observational evidence to date suggests that the formation of interior rings is an extension of the structural uplift process that occurs at smaller complex impact structures there are however major observational gaps and cases e g vredefort where current observations and hydrocode models are apparently inconsistent it is perhaps time that the impact community as a whole considers documenting the existing observational and modeling knowledge gaps that are required to be filled to make the intellectual breakthroughs equivalent to those of the 1970s and 1980s which were fueled by observations at terrestrial impact structures filling these knowledge gaps would likely be centered on the later stages of formation of complex and ring structures and on ejecta

volumetric analysis of complex lunar craters implications for basin ring formation the transition in hypervelocity impact structures from complex craters to basins is defined by a transition in uplifted central features from peaks to peak rings volumetric and morphologic analyses of the central peaks in complex lunar craters are combined with subsurface data from terrestrial complex impact structures in an effort to characterize the crater to basin transition central peak volumes in lunar craters with rim diameters drc 80 km central peak volume is relatively reduced and a second power law relationship is defined the relative reduction in peak volume in craters with drc 80 km is associated with a relative decrease in peak height and is accompanied by the development of a concentric zone of enhanced floor roughening studies of terrestrial complex impact structures suggest that the amount of uplifted material as judged from its depth of origin continues to increase with increasing rim diameter this suggests that a redistribution of uplifted material away from a centralized peak may occur in the larger craters the volumetric and morphologic changes described occur over a rim diameter range of 51 80 km far below the previously proposed range for the crater to basin transition drc 140 175 km evidence is presented to support a crater to basin transition beginning at drc 51 80 km characterized by a relative reduction in central peak volume and the development of rings of floor roughening which are suggested to be precursors of peak ring development

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 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

influence of layering and boundary conditions on fault bend and fault propagation folding the influence of heterogeneous layering and boundary conditions on the structural development of fault bend and fault propagation folds has been investigated through petrographic study of nonscaled rock models the models are deformed in a triaxial rock deformation apparatus at room temperature and a 50 mpa confining pressure the models consist of a single layer of sandstone containing a saw cut ramp that is inclined 20 to the layering and an overlying intact thinly layered unit that is composed of limestone interlayered with lead or mica analysis of the fold thrust structures generated in sequentially shortened models with different loading conditions and layer types suggests that the mode of fold thrust interaction activated upon shortening will depend on fault zone drag bending and shearing resistance of the hanging wall shear strength of layer interfaces and loading conditions for the models these parameters may be expressed as a strength ratio describing the resistance to foreland translation relative to the resistance to internal deformation of the thrust system low strength ratios favor fault bend folding high strength ratios favor internal shortening of the sheet isotropic and thick relative to ramp height units above a propagating thrust tip will shorten primarily by faulting whereas thinly layered anisotropic units will shorten by fault propagation folding during both modes of fold thrust interaction the dips of the fold limbs increase interlimb angles decrease and imbricate faults form in the hanging wall or footwall with shortening in one model suite the imbrication is associated with a transition from fault bend folding to fault propagation folding and produces a highly asymmetric ramp anticline similar to a second mode fault bend fold or to a transported fault propagation fold the model data suggest that fault propagation folding in heterogeneously layered rock occurs by the discontinuous formation growth and linkage of faults below the growing fold amplification of the fault propagation fold is affected by the amount of slip transferred out of the deforming region imbrication and buckling the changes in the mode of fold thrust interaction and modifications in the local geometry and strain distribution that occur during shortening result from slip hardening on faults or from rotation or strain induced variations in the strength of the layers

mechanical analysis of the geometry of forced folds a mechanical model of forced folding comprised of an anisotropic cover overlying displaced rigid basement blocks is used to investigate the influence of various parameters on theoretical fold form shape and dip of basement fault strength of basement cover contact and degree of anisotropy of the cover we show that the degree of anisotropy in the cover largely influences the geometry of the forelimb of the forced fold folds produced in isotropic cover display forelimbs that taper from large dip angles near the basement cover contact to low dip angles at the ground surface in contrast dips in the forelimbs of folds in anisotropic cover are nearly uniform with depth we show that the basement cover contact and the shape of the basement fault largely influence the geometry of the backlimb backlimb rotation occurs in cover welded to the basement and in cover underlying curved basement faults in addition the kinematic features of the theoretical folds are compared with the fold geometry generated by parallel kink and trishear models folds in isotropic cover overlying straight basement faults closely resemble the fold forms produced by the trishear kinematic model while fold forms in anisotropic cover more closely resemble folds produced by parallel kink geometric constructions

scaling impact melting and crater dimensions implications for the lunar cratering record abstract the dimensions of large craters formed by impact are controlled to a large extent by gravity whereas the volume of impact melt created during the same event is essentially independent of gravity this differential scaling fosters size dependent changes in the dynamics of impact crater and basin formation as well as in the final morphologies of the resulting structures a variety of such effects can be observed in the lunar cratering record and some predictions can be made on the basis of calculations of impact melting and crater dimensions among them are the following 1 as event magnitude increases the volume of melt created relative to that of the crater will grow and more will be retained inside the rim of the crater or basin 2 the depth of melting will exceed the depth of excavation at diameters that essentially coincide with both the inflection in the depth diameter trend and the simple to complex transition 3 the volume of melt will exceed that of the transient cavity at a cavity diameter on the order of the diameter of the moon this would arguably correspond to a moon melting event 4 small lunar craters only rarely display exterior flows of impact melt because the relatively small volumes of melt created can become choked with clasts increasing the melt s viscosity and chilling it rapidly larger craters and basins should suffer little from such a process 5 deep melting near the projectile s axis of penetration during larger events will yield a progression in cen tral structure morphology with growing event magnitude this sequence should range from single peaks through multiple peaks to peak rings 6 the minimum depth of origin of central peak material should co incide with the maximum depth of melting the main central peak in a crater the size of tycho should have had a preimpact depth of close to 15 km

links between topography wind deflation lakes and dust the case of the bodele depression chad the bodele depression chad is the planet s largest single source of dust deflation from the bodele could be seen as a simple coincidence of two key prerequisites strong surface winds and a large source of suitable sediment but here we hypothesise that long term links between topography winds deflation and dust ensure the maintenance of the dust source such that these two apparently coincidental key ingredients are connected by land atmosphere processes with topography acting as the overall controlling agent we use a variety of observational and numerical techniques including a regional climate model to show that 1 contemporary deflation from the bodele is delineated by topography and a surface wind stress maximum 2 the tibesti and ennedi mountains play a key role in the generation of the erosive winds in the form of the bodele low level jet llj 3 enhanced deflation from a stronger bodele llj during drier phases for example the last glacial maximum was probably sufficient to create the shallow lake in which diatoms lived during wetter phases such as the holocene pluvial winds may therefore have helped to create the depression in which erodible diatom material accumulated instead of a simple coincidence of nature dust from the world s largest source may result from the operation of long term processes on paleo timescales which have led to ideal conditions for dust generation in the world s largest dust source similar processes plausibly operate in other dust hotspots in topographic depressions

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

how sensitive are fault slip rates in the los angeles basin to tectonic boundary conditions geodetic studies have produced different interpretations of the relative vertical thickening versus escape tectonics occurring within the los angeles basin based on calculated horizontal strain rates ranging from 56 10 9 yr contraction at n36 et o 85 10 9 yr north south contraction and 60 10 9 yr east west extension three dimensional forward mechanical models of faults in the los an geles basin are used to compare modeled slip rates and slip styles represented as the rakes of average net slip vectors under four representative horizontal strain condi tions with geologically determined late quaternary slip rates and observed slip styles the comparisons strive to identify the most mechanically viable tectonic boundary conditions for the los angeles basin the three dimensional fault surfaces used within the mechanical models have been defined by southern california earthquake center scec workers based on surface geology and subsurface data the model results suggest that northeast southwest principal contraction is inappropriate for the los angeles basin because this tectonic boundary condition produces left lateral slip along the whittier and san gabriel faults in contrast with abundant geologic evidence of right lateral slip of the four tectonic boundary conditions evaluated north south contraction accompanied by either zero or slow east west contraction gives the low est mismatch of modeled and observed fault slip style these results suggest that vertical thickening may be more predominant than escape tectonics in this region

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

extensional fault propagation folds mechanical models and observations from the modoc plateau northeastern california extensional fault propagation folds are produced by warping of material ahead of a growing normal fault we use field observations of surface breaking normal faults in the modoc plateau california in conjunction with three dimensional linear elastic boundary element computer models to address the mechanical controls on extensional fault propagation folds detailed topographic and structural maps of the near tip regions of several kilometer long faults reveal throw decreases rapidly toward the tip suggesting elliptical slip distributions fault parallel monoclinal folds are present beyond the tip with axes offset into the hanging wall and open fissures are common in the tip region parametric tests with the model show that the amplitude and form of folds at the fault terminations are influenced by slip distribution fault dip elastic properties of the rock and the presence or absence of a blind portion of the fault models reproduce the form of observed folds to first order and suggest that the faults both isolated and in relay zones are probably blind for some lateral extent beyond the surface break

structural evolution of connecting splay duplexes and their implications for critical taper an example based on geometry and kinematics of the canyon range culmination sevier belt central utah abstract critical taper in an evolving orogenic wedge can be maintained by structural thickening in the back of the wedge this is often achieved by folding and uplift of pre existing large internal thrust sheets by the continued growth and or reactivation of duplexes in the hinterland the growth of a blind imbricate complex off a lower thrust provides another mechanism for folding a higher thrust individual splays in a blind imbricate complex may have fault propagation folds and or fault bend folds associated with them if the splays reach the overlying thrust they serve as connecting splays between the lower thrust floor and the upper thrust roof thereby forming a connecting splay duplex csd this type of duplex geometry requires periodic reactivation of the pre existing roof thrust the canyon range thrust in central utah is an internal thrust that is folded into an overturned antiform synform pair and overrides its own synorogenic conglomerates the same conglomerates are infolded into the core of the synform and preserve critical timing information regarding the history of folding and thrust reactivation the folding is caused by the development of a footwall antiformal stack in the core of the canyon range antiformal culmination the geometry and timing relationships suggest that the structure grew as a csd regional timing relationships suggest that the growth of the csd and reactivation of the thrust took place during the later part of the evolution of the orogenic wedge and may have helped the wedge maintain critical taper during thrusting in the external fold and thrust belt

considerations on the chronological and causal relationships between talus flatirons and palaeoclimatic changes in central and northeastern spain abstract talus flatirons are relatively common landforms in arid and semiarid areas they are frequent in the duero tajo and ebro tertiary basins in spain the generation of a flatiron requires the alternation of periods with a prevalence of accumulation processes followed by periods with a preponderance of erosion processes in the three tertiary basins considered here talus flatirons have been found in numerous places and up to five stages of slope evolution have been recognised in some locations the second youngest stage s 2 has been dated in several places in the ebro and duero basins through 14 c the age of this stage ranges from 2529 52 to 3590 40 14 c ybp the third youngest stage s 3 has yielded dates of 27 862 444 radiocarbon years bp in the ebro basin and 28 550 130 14 c ybp in the duero basin s 4 has been dated in the ebro basin to 35 570 490 14 c ybp the s 2 slope facets correspond to the iron and bronze age cold stages the s 3 and s 4 flatirons may be correlated with the heinrich events h 3 and h 4 these dates may indicate that the accumulation periods on the slopes correspond to cold global events the dates obtained for the stages s 3 and s 4 in the central and northeastern sectors of spain and their good correlation with heinrich events suggest that flatirons could be related to climatic sequences in the upper pleistocene and holocene

late holocene drought responsible for the collapse of old world civilizations is recorded in an italian cave flowstone a severe drought in parts of low latitude northeastern africa and southwestern asia 4200 yr ago caused major disruption to ancient civilizations stable isotope trace element and organic fluorescence data from a calcite flowstone collected from the well watered alpi apuane karst of central western italy indicate that the climatic event responsible for this drought was also recorded in mid latitude europe although the timing of this event coincides with an episode of increased ice rafted debris to the subpolar north atlantic the regional ocean atmosphere response seems atypical of similar holocene ice rafting events furthermore comparison of the flowstone data with other regional proxies suggests that the most extreme part of the dry spell occurred toward the end of a longer term climate anomaly

the effect of non parallel thrust fault interaction on fold patterns the geometry of two subsurface non parallel thrust faults are systematically altered within mechanical models to determine the range of resulting fold map patterns and the effect of fault interaction on these fold patterns and ultimately to infer fault geometry from complex fold shapes multiple faults can create both complex fold patterns with more than one fold axis and single folds without evidence of a second fault fold length may not correlate to fault length when remote contraction is oblique to the faults thus contraction direction should be determined before fault length is inferred the influence of fault interaction is studied by comparing the fold pattern created by interacting faults to the fold pattern created from the superposition of folds produced by equivalent but isolated faults under small strains larger faults tend to have greater interaction but even interacting faults may not produce fold patterns notably distinct from the superposed fold patterns this suggests that fault interaction need not necessarily be considered when inferring fault geometry from fold shape in the field however under non coaxial strain conditions fold patterns may differ from those presented here

the holocene fluvial chronology of spain evidence from a newly compiled radiocarbon database abstract a critical analysis of 74 radiocarbon dates selected from a total of 102 published and unpublished dates from holocene fluvial environments in spain has identified a number of periods of increased fluvial activity in spain namely 11 170 10 230 9630 8785 7980 6860 5800 4800 3880 3085 2895 1820 1300 0 cal bp the latter period reflecting sustained fluvial response to increased human impact the radiocarbon samples were classified according to type of depositional environment a alluvial overbank b flood basin c alluvial channel gravels d fluvio torrential deposits and e slackwater flood deposits palaeofloods dates from slackwater flood deposits indicated at least five phases of increased frequency of large magnitude floods during the holocene 10 855 10 230 9530 8780 2880 2430 975 790 and 520 265 cal yr bp flood basin type deposition occurred from 7980 to 4830 cal yr bp the main clusters of dates from alluvial floodplain deposits occurred at 2750 2150 and 930 520 cal yr bp the record is discussed in relation to other palaeoenvironmental archives including pollen records of holocene vegetation change and palaeoclimatic proxies such as the north atlantic drift ice record comparison with the latter indicates that major holocene flooding coincided with cold climate phases during 9530 9280 2880 2430 and 520 265 cal yr bp a cooling phase at 10 855 10 230 and warming phases at 9030 8780 and 975 790 cal yr bp

paleohydrological fluctuations and steppe vegetation during the last glacial maximum in the central ebro valley ne spain combined analysis of sedimentary facies geochemistry and pollen from lake sediment records and sedimentological and palynological studies from slope deposits allow the characterization of vegetation and lake level status during the last glacial lgm in the central ebro valley ne spain these records show the presence of phases of increased effective moisture while regional vegetation was dominated by steppe species the longest lake record comes from la salineta one of the saline lakes in the los monegros area the other lake sequence comes from a sinkhole in the gallego river floodplain the slope deposit from valmadrid is the only periglacial deposit found in the central ebro valley our data indicate that at least for some intervals during full glacial times when cold steppe vegetation dominated the region some lakes experienced more positive water balance than today and run off was also high the data are coherent with the hypothesis that at least for some periods the ice age climate of the western mediterranean was characterized by cold winters with relatively higher effective moisture precipitation minus evaporation ratio and summer droughts increased flow from the pyrenean rivers during the early deglaciation could also have played a significant role in the paleohydrological cycle in the central ebro valley however la salineta records also show evidence for arid periods during glacial times indicating the complex evolution of hydrology and moisture availability in the central ebro valley during the lgm

numerical modeling of fold initiation at thrust ramps abstract the movement of the hangingwall over the footwall at thrust ramps produces a variety of structures found commonly at different scales in fold and thrust belts the nature of the structure depends on the relative rigidity of the hangingwall and footwall friction along the fault fault dip fault displacement and the boundary conditions of the deformation structures include fault bend style folds fault propagation style folds and wedge folds we investigate the initial stages of development of such structures using the finite difference code flac the rock layers are represented as continua with elastic plastic mohr coulomb constitutive relations and the fault and bounding bedding planes are assigned normal and shear stiffnesses and coefficients of friction under conditions with all layers compressed antisymmetric fault propagation style folds develop in both the hangingwall and footwall with rigid footwall and restricted far field slip in the hangingwall a single fault propagation style fold develops with far field displacement of the hangingwall allowed broader antisymmetric wedge folds develop if hangingwall and footwall are deformable and a single fault bend style fold develops if the footwall is rigid all structures become accentuated with increasing slip on the fault where both hangingwall and footwall are deformable the deformation reduces the ramp angle and tends to minimize distortion of the rock adjacent to the fault fault propagation style folds paired wedge folds and fault bend style folds are common in nature and small scale examples can be found in various stages of development continued slip on thrust faults may lead to the mature structures commonly seen in fold and thrust belts

constraints on the depth geometry and kinematics of blind detachment faults provided by fault propagation folds an example from the mesozoic fold belt of south china abstract the mesozoic multi layered thin skinned fault related fold belt in south china is characterized by propagation chevron folding and thrust faulting we examine the geometry and depth of blind detachment faults in this belt using faults and folds that crop out along a well defined cross section a combination of parameters such as backlimb dip angle 2 interlimb angle height of anticline h thickness of the referenced layer h0 width of the anticline ab and thickness change ratio of layering within the forelimb tf t are used to develop new equations to estimate the geometry and depth of the detachment faults in the cross section the huangdushan chevron anticline has parameters revealing a blind fault with a ramp angle of 42 and a flattened segment at a depth of 4 9 km based on existing seismic data we interpret this blind fault as a backthrust developed over an in sequence imbricated duplex of cambrian to ordovician strata a chevron anticline at qiyueshan also reveals a backthrust fault however a broad anticline in lengzhuba and a small cylindrical sinusoidal anticline in yupize reveal a flat ramp flat detachment fault with flat segments at depths of 7 4 and 3 4 km respectively suggesting that the sinian strata were thickened probably by an out of sequence imbricated duplex our results indicate that the flat ramp flat detachment fault along the bottom of the sinian strata produced the out of sequence imbricated duplex and cylindrical sinusoidal folds the in sequence imbricated duplex produced backthrusts and related chevron anticlines we consider that this fault related fold belt was produced by collision between the yangtze block and north china blocks

applicability of thin or thick skinned structural models in a region of multiple inversion episodes southern south africa abstract the deformation of the cape fold belt has been attributed to repeated structural reactivation of a mega detachment from the late proterozoic to the mesozoic 650 65 ma through the integration of onshore cross sections with observations from the offshore mesozoic extensional system this study evaluates the applicability of the mega detachment model regional scale cross sections through the permian triassic cape fold belt reveal that it comprises two main structural domains a northern domain dominated by northward verging and asymmetric folds and a southern domain comprising a series of approximately 8 km wavelength box folds the genesis of these box folds is attributed to motion on underlying high angle 45 reverse faults this variation between north and south in the fold belt is reflected by a similar variation in extensional geometry of the mesozoic normal faults as revealed by subsurface data the normal faults demonstrate a progressive increase in dip from 24 in the north to 60 in the south features commonly attributed to thin and thick skinned tectonic models are observed in both domains therefore it is not appropriate to describe the observed deformation as one of the two end members in addition the structures are inferred to have undergone at least two stages of inversion irrespective of dip this is not predicted by either end member model

facies identification within the playa lakes of the monegros desert spain from field and satellite data abstract the monegros desert and its saline wetlands called saladas literally translated as the salties are a unique european landscape of great scientific and ecological value the saladas i e playa lakes and other small saline depressions are dynamic environments changing their surface morphology on a seasonal diurnal basis in response to both climate and groundwater fluxes to depict changes in these natural systems we have identified five surface facies classes which are detectable both in the field and from remote sensing data these facies are crucial for describing and promoting the protection of these habitats remote sensing has provided worthwhile historical data and additional information that compensate for scarce field records combined field and satellite criteria are used to catalog these facies with a new conceptual integration that manages the asynchronism between the field and satellite data the catalog of facies is intended to be helpful for monitoring these wetlands and for understanding the current hydrological patterns and trends in the playa lakes this work will serve as a baseline for studying the future evolution of the saladas which may soon fall under manmade environmental forces such as increased water input from adjacent newly irrigated lands it is hoped that identification of these facies will be useful with minor adaptations in using more advanced sensors or in studying similar habitats

hydrocode simulations of chicxulub crater collapse and peak ring formation we use hydrocode modeling to investigate dynamic models for the collapse of the chicxulub impact crater our aim is to integrate the results from numerical simulations with kinematic models derived from seismic reflection and wide angle velocity data to further our understanding of the formation of large impact craters in our simulations we model the collapse of a 100 km diameter bowlshaped cavity formed in comprehensively fractured crustal material to facilitate wholesale collapse we require that the strength of the target be significantly weakened in the present model we achieve this using acoustic fluidization where strong vibrations produced by the expanding shock wave cause extreme pressure fluctuations in the target at times and positions where the overburden pressure is sufficiently counteracted the frictional resistance is reduced enabling the rock debris to flow our simulations produce a collapsed crater that contains most of the features that we observe in the seismic data at chicxulub in particular we observe a topographic peak ring formed as material that is originally part of the central uplift collapses outward and is thrust over the inwardly collapsing transient crater rim this model for peak ring generation has not been previously demonstrated by numerical simulations and predicts that the peak ring is composed of deeply derived material and that the stratigraphy within the peak ring is overturned c 2002 elsevier science usa

using vertical rock uplift patterns to constrain the three dimensional fault configuration in the los angeles basin comparison of geologic uplift patterns with results of three dimensional mechanical models provides constraints on the fault geometry compiled by the south ern california earthquake center community fault model in the northern los angeles basin california the modeled uplift matches well the geologic pattern of uplift as sociated with the santa fe springs and coyote hills segments of the puente hills thrust fault but does not match structures to the west of the san gabriel river to better match the geologic patterns in this area alternative fault configurations were tested the best match to geologic uplift is attained with a model incorporating 1 a steep blind thrust fault at the location of the los angeles segment of the puente hills thrust system following interpretations of the las cienegas fault geometry at this location 2 removal of an inferred linking fault between the raymond and holly wood faults and 3 lateral continuation of the lower elysian park fault a blind low angle detachment at 10 km depth along strike to the northwest these geometric revisions alter the connectivity of northern los angeles basin faults and significantly improve the match of model uplift pattern to geologic data model results suggest that fault connectivity may be more important in governing fault slip rate than are fault dip and fault area the preferred model alters slip rates by 0 2 mm yr for the upper elysian park hollywood lower elysian park raymond sierra madre west and verdugo faults additionally the preferred model alters the surface area of several faults in the northern los angeles basin such as the puente hills thrust and the lower elysian park fault which may have important implications for seismic hazard assess ment in the northern los angeles basin

particle tracking in ideal faulted blocks using 3d co ordinate geometry abstract this article performs particle material point tracking for ideal brittle faults with translational and rotational slip components the fault planes are considered to be planar and step like in separate cases in the latter case the hangingwall block is considered to behave ductilely for a specific choice of the three cartesian co ordinate axes dip slip fault will change two out of the three ordinates of any point in the faulted block that moves a strike slip faulting can change one out of the three ordinates on the other hand whatever be the orientation of the orthogonal co ordinate axes an oblique slip fault of any dip amount and a purely rotational fault with dip 0 90 alter all the three ordinates except the pivot point in the latter case as expected oblique slip faulting modifies the co ordinates of the shifted material points depending on both i the pitch of stretching lineation and ii the dip of the fault plane

kinematic retro modelling of a cross section through a thrust and fold belt the western irish namurian basin the western irish namurian basin winb developed into a fold and thrust belt at the front of the northward propagating variscan orogenic wedge part of this basin is well exposed along the coast of county clare ireland from a detailed study that used an integrated gps mapping approach we produced a c 50 km long balanced cross section parallel to the tectonic transport vector we sequentially decompacted and retro deformed the namurian strata in 7 stages to evaluate the palinspastic situation of the basin and the amount of shortening by using passive markers in the model and a highly detailed timescale we were able to determine that shortening of the winb from the onset of central clare group sedimentation was 7 44 or 4 07 km of which shortening due to folding accounts for c 2 64 c 1 37 km and therefore c 4 80 c 2 69 km was solely because of thrusting the rate of horizontal shortening ranges from 1 34 mm a 1 this is within typical orogenic values

quantitative measurement method for impact basin characteristics based on localized spherical harmonics abstract characteristics of impact basins are important fundamental knowledge for assessing basin forming impacts and their influence on surficial and interior structural evolutions for lunar and planetary bodies to estimate impact basin characteristics based on spherical harmonic expressions of topographic figures we propose a quantitative method that we apply it to actual lunar topographic data the estimated basin locations center are almost coincident with those determined by visual inspection however the numbers of ring structures differ from previously reported ones the relation between the ring height and the ring diameter coincides well with those reported previously some older basins show discrepancies in the height diameter relation which probably reflect the degree of degradation by subsequent small impacts we recognize a power law relation between the diameters of a ring and a neighboring ring structure that relation suggests that the formation volume and modification of the melt cavity control the formation and size of peak ring and multi ring structures these relations which are thought to reflect the mechanism of the collapse stage of basin formation impact provide helpful constraints for elucidating the long standing problem of how multi ring impact basins are formed

origin and evolution of playas and blowouts in the semiarid zone of tierra de pinares duero basin spain abstract a large number of blowouts and playas occur in the marginal sectors of the aeolian deposits located in the southern sector of the duero depression tierra de pinares in spain the blowouts are relict landforms that were developed on sand sheets by deflation during dry periods with lower vegetation cover and a deeper water table the studied blowouts form complexes of nw se and nnw sse elongated hollows with accompanying dunes up to 4 km long in the leeward margins some hollows host lakes or swampy areas related to a shallow water table the dunes formed by ne ene winds show steep windward slopes and gentle leeward slopes the studied playas with prevalent nnw sse orientations result from the aeolian excavation of terrace deposits and the underlying marly bedrock it is probable that the formation of these depressions in an initial stage was related to deflation processes affected preferentially nnw sse sandy channels perpendicular to the dominant wind direction the precipitation of salts in the playas generates aggregates of clay particles peloids that are easily removed by the wind once the bottom reached the substratum the deepening of the depressions progressed by the deflation of particles produced by weathering of the argillaceous bedrock

landform characterization using geophysics recent advances applications and emerging tools abstract this paper presents an overview of the strengths and limitations of existing and emerging geophysical tools for landform studies the objectives are to discuss recent technical developments and to provide a review of relevant recent literature with a focus on propagating field methods with terrestrial applications for various methods in this category including ground penetrating radar gpr electrical resistivity er seismics and electromagnetic em induction the technical backgrounds are introduced followed by section on novel developments relevant to landform characterization for several decades gpr has been popular for characterization of the shallow subsurface and in particular sedimentary systems novel developments in gpr include the use of multi offset systems to improve signal to noise ratios and data collection efficiency amongst others and the increased use of 3d data multi electrode er systems have become popular in recent years as they allow for relatively fast and detailed mapping novel developments include time lapse monitoring of dynamic processes as well as the use of capacitively coupled systems for fast non invasive surveys em induction methods are especially popular for fast mapping of spatial variation but can also be used to obtain information on the vertical variation in subsurface electrical conductivity in recent years several examples of the use of plane wave em for characterization of landforms have been published seismic methods for landform characterization include seismic reflection and refraction techniques and the use of surface waves a recent development is the use of passive sensing approaches the use of multiple geophysical methods which can benefit from the sensitivity to different subsurface parameters is becoming more common strategies for coupled and joint inversion of complementary datasets will once more widely available benefit the geophysical study of landforms three cases studies are presented on the use of electrical and gpr methods for characterization of landforms in the range of meters to 100 s of meters in dimension in a study of polygonal patterned ground in the saginaw lowlands michigan usa electrical resistivity tomography was used to characterize differences in subsurface texture and water content associated with polygon swale topography also a sand filled thermokarst feature was identified using electrical resistivity data the second example is on the use of constant spread traversing cst for characterization of large scale glaciotectonic deformation in the ludington ridge michigan multiple cst surveys parallel to an 60 m high cliff where broad 100 m synclines and narrow clay rich anticlines are visible illustrated that at least one of the narrow structures extended inland a third case study discusses internal structures of an eolian dune on a coastal spit in new zealand both 35 and 200 mhz gpr data which clearly identified a paleosol and internal sedimentary structures of the dune were used to improve understanding of the development of the dune which may shed light on paleo wind directions

thrust dip and thrust refraction in fault bend folds analogue models and theoretical predictions analogue models made of two layers of loose sand separated by a thin layer of micro glass beads were shortened by a rigid emerging ramp dipping at either 30 or 45 and possessing a high intermediate or null surface friction shortening resulted in formation of closely spaced back thrusts in the sand layers the dips of the back thrusts vary within a range of 30 depending on the ramp friction and 7 depending on its dip an increase in ramp friction or to a lesser extent in ramp dip decreases the thrust dips in the model the second important observation is that when friction is greater along the ramp than along the layer of glass beads then the glass beads layer acts as a separate upper ramp above which the back thrusts steepen the theory proposed to explain these observations predicts the thrust dips through a two step procedure first global equilibrium of forces in the two layers is required to yield the mean forces at stake along the ramps and thrusts second the total dissipation is minimized with respect to the dips of the back thrusts the relevant frictional properties of our analogue materials have been measured in stress conditions as close as possible to the experimental ones below 1 kpa and used with the theory to yield optimal back thrust dips that are all within 3 of the measured dips this is a surprisingly good fit when considering that we did not take into account geometric changes strain softening and dilatancy or compaction due to slip on the thrusts we conclude that this general two step theoretical procedure is validated in the context of analogue frictional materials we also propose a possible mechanism for thrust refraction and top to the foreland sense of shear observed in the hanging walls of lower flat to ramp transition in sedimentary piles that is based on the triggering of secondary upper ramps finally this mechanical approach can also be seen as complementary to the kinematic models of fold thrust structures which by definition cannot grasp the strong effects of friction on the kinematics

elliptical structure of the lunar south pole aitken basin abstract the south pole aitken basin sp a is the largest and oldest basin on the moon the basin has usually been interpreted to exhibit a degraded circular structure but here we demonstrate that the topography iron and thorium signatures of the basin are well described by ellipses with axes measuring 2400 by 2050 km and centered at 53 191 e topography abundances of iron thorium and the distribution of mare basalts are all elevated in the northern halves of the ellipses we also identify an outer topographic ellipse whose semiminor axis scales with the main topographic ellipse by approximately 2 taken together these data imply that the basin was created by an oblique impact along an azimuth of approximately 19 measured counterclockwise from longitude 191 e the geometry of the elevated central farside topography surrounding sp a suggests that it predates the impact the elliptical ring structures of sp a and their scaling relationships will help to understand the formation of large and elliptical basins elsewhere in the solar system this refined basin shape will also inform local geology geochemistry and geophysics of the region

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

the subsurface character of meteor crater arizona as determined by ground probing radar ground probing radar has provided new two dimensional stratigraphic and structural information on meteor crater arizona four 50 mhz transects inside the crater and one 100 mhz transect on a northeast radial across the exterior ejecta blanket were carried out the frequencies used were in relation to the desired depth of investigation greater than 50 m at 50 mhz and 30 m for 100 mhz the results obtained inside the crater show that the water table can be clearly detected at depths of 65 m as can the contact between the crater wall and the infilling allochthonous breccia lens in addition we were able to detect 1 point reflectors from relatively coherent blocks 1 5m within the breccia lens 2 a zone 7 m thick relatively free of point reflectors from the immediate fall back unit 3 a series of subhorizontal reflectors a few meters apart due to bedding in the post impact crater sediments and 4 five separate subhorizontal reflectors from what we interpret to be a series of postimpact paleo water table levels in the breccia lens the ejecta blanket transect indicates a 4 10 m thick ejecta layer and the underlying moenkopi formation sandstone as well as the moenkopi kaibab contact and bedding within the kaibab formation in addition reverse faults with displacements up to 4 m were detected in the bedrock as well as changes from subhorizontal to 30 in the dip of the bedrock as the crater rim is approached from the northeast beneath the ejecta blanket the total uplift observed at the crater rim is around 55 m the radar data indicate uplift effects out to a radial distance of 400 m from the rim farther than that determined from drilling 300 m the results demonstrate the utility of continuous ground probing radar cross sections in studying the near subsurface 50 m character at meteor crater this relatively rapid low cost technique can be extended to other structures but confident interpretation requires supplemental ground truth constraints

thrust fault nucleation due to heterogeneous bedding plane slip evidence from an ohio coal mine abstract shales often form the roof and floor rocks of coal mines in the appalachian basin from a geologic perspective these mines offer outstanding 3d exposures of fresh rocks otherwise only accessible via boreholes or heavily weathered surface outcrops and present an excellent opportunity to directly observe pristine in situ natural fractures in shale in carroll county ohio small thrust faults that predate mining operations are well exposed within the roof rocks and develop near areas where gradients of coal shale contacts are steepest causing ground instability we hypothesize that bedding contact surfaces served as natural displacement discontinuities that perturbed the local stress state resulting in localized thrust fault development using borehole and in mine survey data we digitally constrain bedding contact geometry to model slip along this interface and resolve related stress perturbations our modeling results suggest that inherited non planarity of contact surfaces influenced the nucleation of secondary faults simulation results as constrained by the integrated field and modeling approach taken in this study help us to better understand the relationship between subsurface stress perturbations and the formation of secondary fractures for mining purposes recognizing subsurface stress heterogeneities due to variable bedding geometry within a regional stress field can improve our predictive capabilities of underground structural hazards

late holocene evolution of playa lakes in the central ebro depression based on geophysical surveys and morpho stratigraphic analysis of lacustrine terraces abstract the origin and morpho stratigraphic evolution of the largest playa lake system la playa el pueyo in the bujaraloz sastago endorheic area located in the semiarid central sector of the ebro depression are analysed the enclosed depressions are developed on gypsiferous tertiary bedrock and show a prevalent wnw ese orientation parallel to the direction of the prevalent strong local wind cierzo yardangs have been carved in bedrock and unconsolidated terrace deposits in the leeward sector of the largest lake basins a sequence of three lacustrine terrace levels has been identified by detailed geomorphological mapping the treads of the upper middle and lower terrace levels are situated at 9 m 6 m and 0 5 m above the playa lake floors respectively seismic refraction and electrical resistivity profiles acquired in la playa reveal a thin basin fill 2 m with a planar base these data allow ruling out the genetic hypothesis for the depressions involving the collapse of large bedrock cavities and support a mixed genesis of combined widespread dissolution and subsidence by groundwater discharge and eolian deflation during dry periods the 5 m thick deposit of the middle terrace was investigated in hand dug and backhoe trenches six ams radiocarbon ages from this terrace indicate an aggradation phase between 3 9 ka and ca 2 ka these numerical ages yield a maximum average aggradation rate of 2 6 mm yr and a minimum excavation rate by wind deflation of 3 mm yr subsequent to the accumulation of the middle terrace the latter figure compares well with those calculated in several arid regions of the world using yardangs carved in palaeolake deposits the aggradation phase between 4 and 2 ka is coherent with other iberian and mediterranean records showing relatively more humid conditions after 4 ka including the iron ages and the iberian roman period

prediction of normal fault geometries a sensitivity analysis several workers have developed cross section balancing schemes for extensional structures using these geometric models structural interpreters can predict normal fault geometries at depth by specifying the shape of a folded bed in the hanging wall of a normal fault the deformation mechanism that accommodates the folding the footwall counterpart of the folded hanging wall bed and the dip and location of the fault segment between the hanging wall and footwall beds we have systematically determined how uncertainties in these input parameters affect the prediction of normal fault shape and detachment depth our sensitivity analysis shows that reasonable uncertainties in the fold shape near the normal fault the deformation mechanism the footwall correlation and the fa lt dip produce large uncertainties in the predicted fault geometry reasonable uncertainties in the fold shape far from the normal fault and the fault location however produce only small uncertainties in the predicted fault geometry our work suggests that if seismic and well data are lacking or of poor quality then geometric models cannot provide unique answers to questions about the geometry of a normal fault at depth geometric models however can provide a range of possible fault geometries

recent holocene palaeoenvironmental evolution in the central ebro basin ne spain abstract evolutionary aspects of landscape are analysed from the geomorphological palynological and archaeological study of a sector in the central ebro basin ne spain in this study we use four representative sites each of them offering different information about the evolution of the landscape in which they are located together the data allow for the reconstruction of general patterns concerning the holocene palaeoenvironmental evolution erosion processes and their genetic interpretation climatic factors alone do not explain the key features and profound transformations suffered by this landscape more likely they have been the response to the changes activated by human impact deforestation since the neolithic period has given rise to spaces of difficult bio edaphic recovery different erosive agents have been the main source of sediments that currently fill the bottoms of the depressions and plain valleys human communities since the neolithic have modified the landscape sufficiently to be recorded palynologically several phases of accumulation and incision stages have been identified post bronze regularisation iberian roman incision medieval accumulative incisive stage and actual incision the importance that the climatic factor would have had on the mentioned sites if without any human intervention in the exploitation of the environment is still subject to debate from a climatic point of view these phases are a consequence of the occurrence of dry and wet periods thus the evolution of the landscape in the ebro basin in relation to the human occupation during the upper holocene is explained by a succession of dynamic changes these fluctuations would have been due to a combination of climatic conditions conducive to the triggering of erosive processes along with the strengthening of them by humans due to their intervention in the environment

measurement and analysis of lunar basin depths from clementine altimetry altimetric profiles from the clementine lidar are used to calculate the depths of 29 large craters and basins on the moon plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre clementine studies reveals an inflection in the depth diameter d d curve in addition to the one revealed by pre clementine data this inflection occurs in the diameter range that corresponds to the morphologic transition from complex crater to basin the best empirical power law fit for basin depths is log10 d 0 41 log10 d 0 57 this relationship is characterized by a lower slope than that for complex craters demonstrating that this morphologic transition corresponds to a further decrease in the depth of an impact structure relative to its diameter with increasing size qualitative consideration of possible causes for the second inflection leads to the conclusion that it is most likely a consequence of a short term modification mechanism that influences fundamental crater morphology such as the increasing influence of gravity with diameter thicknesses of maria in the major basins are calculated by assuming that their unfilled depths would follow thed drelation results are compared with previous estimates and yield thicknesses that are generally greater than those determined by studies of flooded craters and less than those obtained from analysis of gravity

lateral heterogeneity of lunar volcanic activity according to volumes of mare basalts in the farside basins estimates for volumes of mare basalts are essential to understand the thermal conditions of the lunar mantle and its lateral heterogeneity in this study we estimated the thicknesses and volumes of mare basalts within five farside basins apollo ingenii poincare freundlich sharonov and mendel rydberg using pre mare craters buried by mare basalts and post mare craters that penetrated non penetrated mare basalts employing topographic and multiband image data obtained by selene kaguya furthermore using the grail crustal thickness model and the mare volumes estimated by this and previous studies we investigated the relationship between the volumes of the mare basalts and the crustal thicknesses the results suggest that the minimum crustal thicknesses within the basins were a dominant factor determining whether magma erupted at the surface and that the critical crustal thicknesses for magma eruption were 10 km on the farside and 20 km on the nearside the total areas of the regions in which magmas could erupt at the surface are 10 times larger on the nearside than on the farside a comparison between the mare volumes within the mare basins on the nearside and the farside shows that magma production in the farside mantle might have been 20 times smaller than that in the nearside mantle implying a stronger dichotomy than previously estimated these results suggest that the mare hemispherical asymmetry should be attributed to both the difference in the crustal thickness distribution and the difference in the quantity of magma production between the nearside and farside mantles

the geometry of listric normal faults and deformation in their hangingwalls abstract in cross sections containing listric extensional faults area balancing techniques for depth to decollement are usually based on either bed length conservation or displacement conservation listric fault geometry may be constructed from a hangingwall roll over profile using the chevron construction this construction based on conservation of heave necessitates a reduction in fault displacement with decreasing fault dip a modification of this construction utilizing conservation of fault displacement predicts a listric fault that detaches at a shallower depth a new construction based on slip lines uses fault perpendicular displacement segments to generate listric fault shape fault propagation strain may be responsible for anomalous hangingwall geometries and these can be predicted by forward modelling using either a modified chevron construction or a slip line construction

application of an automatic method for determining normal fault geometries abstract an automatic method is used to determine the geometries of normal faults on depth converted seismic reflection profiles from the gulf of mexico and from the north sea the general method has previously been tested on synthetic and sand box data and assumes that the hanging wall deforms within the plane of section by a combination of arbitrarily inclined bulk simple shear and differential compaction the range of possible solutions is systematically investigated using inverse modelling we assume that the fault surface does not significantly change shape during deformation however inversion of flexural forward models shows that when the fault surface does change shape the misfit function at an automatically determined solution is unacceptably large and featureless consequently spurious solutions obtained when the principal assumptions break down can be identified the approximations used in modelling the effects of differential compaction are justified by a range of appropriate synthetic models we reiterate that the inversion procedure is dependent upon careful identification of a two or more deformed horizons within the hanging wall and b the regional levels of deformed horizons before deformation the numerical stability of the scheme is demonstrated by inverting synthetic data to which random and systematic noise have been added the solutions we have obtained are good and indicate that the method works regardless of the scale and shape of the faults throughout we emphasize the importance of combining inverse theory with a simple kinematic model in order to investigate the solution space and the resolution of the model parameters obtained

integrating 3 d seismic data field analogs and mechanical models in the analysis of segmented normal faults in the wytch farm oil field southern england united kingdom we propose a methodology for the analysis of normal fault geometries in three dimensional 3 d seismic data sets to provide insights into the evolution of segmented normal fault systems and to improve recovery efforts in fault controlled oil fields limited seismic resolution can obscure subtle fault characteristics such as segmentation and gaps in fault continuity that are significant for oil migration and thus accurate reservoir characterization detailed seismic data analyses that incorporate principles of normal fault mechanics however can reveal evidence of fault segmentation we integrate seismic attribute analyses outcrop analog observations and numerical models of fault slip and displacement fields to augment the use of 3 d seismic data for fault interpretation we applied these techniques to the wytch farm oil field in southern england resulting in the recognition of significant lateral and to a lesser extent vertical segmentation of reservoir scale faults slip maxima on fault surfaces indicate two unambiguous segment nucleation depths controlled by the lithological heterogeneity of the faulted section faults initiated preferentially in brittle sandstone and limestone units subsequent growth and linkage of segments predominantly in the lateral direction resulted in composite fault surfaces that have long lateral dimensions and multiple slip maxima reservoir compartmentalization is greatest at the level of prevalent segment linkages which corresponds at wytch farm with the predominant hydrocarbon producing unit the sherwood sandstone at relatively shallower depths fault segments are younger and less evolved resulting in a greater degree of segmentation with intact relay zones

a genetic classification of sinkholes illustrated from evaporite paleokarst exposures in spain this contribution analyses the processes involved in the generation of sinkholes from the study of paleokarst features exposed in four spanish tertiary basins bedrock strata are subhorizontal evaporites and in three of the basins they include halite and glauberite in the subsurface our studies suggest that formation of dolines in these areas results from a wider range of subsidence processes than those included in the most recently published sinkhole classifications a new genetic classification of sinkholes applicable to both carbonate and evaporite karst areas is thus proposed with the exception of solution dolines it defines the main sinkhole types by use of two terms that refer to the material affected by downward gravitational movements cover bedrock or caprock and the main type of process involved collapse suffosion or sagging sinkholes that result from the combination of several subsidence processes and affect more than one type of material are described by combinations of the different terms with the dominant material or process followed by the secondary one e g bedrock sagging and collapse sinkhole the mechanism of collapse includes any brittle gravitational deformation of cover and bedrock material such as upward stoping of cavities by roof failure development of well defined failure planes and rock brecciation suffosion is the downward migration of cover deposits through dissolutional conduits accompanied with ductile settling sagging is the ductile flexure of sediments caused by differential corrosional lowering of the rockhead or interstratal karstification of the soluble bedrock the paleokarsts we analysed suggest that the sagging mechanism not included in previous genetic classifications plays an important role in the generation of sinkholes in evaporites moreover collapse processes are more significant in extent and rate in areas underlain by evaporites than in carbonate karst primarily due to the greater solubility of the evaporites and the lower mechanical strength and ductile rheology of gypsum and salt rocks

effects of nonplanar fault topology and mechanical interaction on fault slip distributions in the ventura basin california to assess the control of fault geometry and mechanical interactions on fault slip distributions in a complex natural system we present results from three dimensional mechanical models incorporating both nonplanar and rectangular planar representations of active faults within the ventura basin region of southern california we find that the incorporation of geologically constrained nonplanar fault surfaces into numerical models of active deformation results in a better match to available geologic slip rate data than models utilizing rectangular planar fault surfaces the model results demonstrate that nonplanar fault geometry and mechanical interactions exert a strong control on resultant slip distributions additionally we find that slip rates at most locations along the surface trace of ventura faults are not likely to rep resent average values for the entire fault surface we propose that results from three dimensional mechanical models using realistic i e nonplanar fault geometry can be used to both predict slip rates at specific locations and determine whether existing site specific slip rate estimates are representative of average fault slip rates although geo metric irregularities along fault surfaces should resist slip planar faults can have lesser slip than nonplanar faults due to the differing mechanical interactions among nearby faults in the two representations this suggests that models using simplified or planar fault geometry are likely to inaccurately simulate regional deformation we assert that detailed knowledge of three dimensional fault shape as well as the geometry and con figuration of deep fault intersections is essential for accurate seismic hazard char acterization of regions of complex faulting such as the ventura basin of southern california

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

farside gravity field of the moon from four way doppler measurements of selene kaguya the farside gravity field of the moon is improved from the tracking data of the selenological and engineering explorer selene via a relay subsatellite the new gravity field model reveals that the farside has negative anomaly rings unlike positive anomalies on the nearside several basins have large central gravity highs likely due to super isostatic dynamic uplift of the mantle other basins with highs are associated with mare fill implying basalt eruption facilitated by developed faults basin topography and mantle uplift on the farside are supported by a rigid lithosphere whereas basins on the nearside deformed substantially with eruption variable styles of compensation on the near and farsides suggest that reheating and weakening of the lithosphere on the nearside was more extensive than previously considered

geochemistry and mineral formation in the earth surface edited by r rodriguez clemente and yves tardy proceedings of the intermational meeting geochemistry of the earth surface and processes of mineral formation held in granada spain 16 22 march 1986 csic madrid 1987 893p 7000 pesetas isbn 84 00 06683 9

slip distributions on intersecting normal faults abstract slip distributions on normal faults often are asymmetric and display multiple local maxima numerically computed slip distributions from elastic models indicate that such irregular slip distributions can be caused by mechanical interaction between intersecting faults that produce local perturbations of the stress field resolved on the faults a three dimensional boundary element model based on the displacement discontinuity method has been used to analyze the mechanical interaction of faults that form y or t shaped intersections slip distributions are asymmetric with a steeper slip gradient toward the line of intersection multiple slip maxima occur depending on the angle between the faults but generally they are not located along the intersections nor at the fault centers examples of intersecting normal faults taken from oil reservoir seismic surveys and sandbox experiments have been used to confirm the application of the theoretical results despite considerable simplifications in terms of geometry and boundary conditions the computed slip distributions capture the characteristics of the observed slip distributions

evaluation analysis and prediction of geologic structures abstract balanced cross sections claim to be better because they apply a rigorous set of rules to develop the conceptual model of the structures present in an area balanced cross sections can be further improved and become more useful to understanding real physical problems by collection of additional data such as seismic reflection surveys collection of additional stratigraphic data or collection of rock fabric information the additional information validates the initial model and provides details on deformation conditions and on local rock responses to the deformation although individual cross sections are two dimensional the objective of evaluation and analysis of deformed regions should be three dimensional whenever possible to recognize the challenges of the real world subsurface system analysis derived from the hydrologic community emphasizes conceptual model development through model verification validation uncertainty quantification benchmarking and meta analysis their approach includes many steps informally used by the structural geology community but in a much more explicit way newer geological applications of structural geology would benefit from this more rigorous approach for designing and doing performance predictions as technological needs become more socially sensitive such as for carbon storage sites new areas of energy exploration in higher population density areas or for nuclear waste storage facilities

anomalous moscoviense basin single oblique impact or double impact origin 1 the moscoviense basin is the most prominent mare basalt filled impact basin on the farside highlands of the moon the moscoviense basin has been studied extensively because of its characteristic geological and mineralogical context and distinct mare volcanism the success of kaguya s direct farside gravity recovery and global laser altimetry revealed that the moscoviense basin shows unique characteristics not only for geological and mineralogical but also for the geophysical contexts we measured geomorphological features of the moscoviense basin and the asymmetry suggests an oblique impact formation process moho undulation beneath the moscoviense basin however can hardly be explained by a single oblique impact formation process we propose an alternative hypothesis for the moscoviense basin formation which is called double impact scenario this scenario simultaneously accounts for the anomalously large mantle plug asymmetric surface geo morphology and excavation of olivine rich material originally located beneath the thickest crust on the moon on the basis of a set of monte carlo simulations we statistically examine the occurrence of a small spatial separation of two nearby basins the probability of double impact as seen on the moscoviense basin where the two impacts occurred 80 km apart is estimated to be about 50

is plane strain a valid assumption in non cylindrical fault cored folds many algorithms assume plane strain to construct model and restore fault cored folds using mechanical models that allow heterogeneous transport in three dimensions we explore the distribution and magnitude of out of plane transport in plunging fault cored anticlines and provide guidelines of where plane strain should and should not be applied we developed a new technique of incrementing infinitesimal elastic strains to produce folds with aspect ratios similar to natural folds map views of displacement vectors show that in general out of plane displacement is localized near the lateral fold tips cross sections show that out of plane transport is depth dependent with out of plane displacement increasing toward the surface flexural slip surfaces compartmentalize out of plane transport within distinct mechanical units with the maximum out of plane displacement near the tops of mechanical units two dimensional models with additional frictionally slipping bed contacts suggest that freely slipping contacts can approximate the deformation of many frictionally slipping contacts we show that out of plane transport is significant in the simplest non cylindrical folds and suggest that complex non cylindrical structures should not be modeled using plane strain exclusively we also show that flexural slip surfaces exert a significant control on the magnitude and structural position of out of plane transport in our models

past hydrological events reflected in the holocene fluvial record of europe abstract a comprehensive database of radiocarbon dated fluvial units in great britain poland and spain has been compiled to investigate the relationship between environmental change flooding and holocene river dynamics following the methodology recently developed by macklin and lewin macklin m g lewin j 2003 river sediments great floods and centennial scale holocene climate change journal of quaternary science 18 101 105 radiocarbon dates in fluvial sequences that coincide with a modification in sedimentation rate or style have been highlighted allowing geomorphologically significant changes in holocene river activity to be identified data analysis has been undertaken at both national and sub national scales and on catchments of different size type and land use history multiple phases of higher flood frequency characterized by accelerated erosion and sediment deposition on floodplains are recognized and compared with a range of climate proxies the relative and varying roles of climate and land use on river dynamics are considered and the value of the database for reconstructing past hydrological events as well as for predicting river response to future environmental change is assessed

estimation of fault propagation distance from fold shape implications for earthquake hazard assessment a numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault propagation fold the propagation distance defines the initial position of the tip line at the onset of slip in the santa fe springs anticline of the los angeles basin we show that the tip line of the underlying puente hills thrust fault initiated at the same position as the 1987 magnitude 6 0 whittier narrows earthquake

models of strain variation in nappes and thrust sheets a review abstract strain within nappes and thrust sheets can be modelled using simple boundary conditions an original rectangular prism of material resting on a thrust plane is considered to be subject to various pure and simple shear components operating parallel to the thrust deformation gradient tensors are determined for the models and solutions found for the principal strains a two dimensional model considers heterogeneous simple shear combined with a stretch in the direction of shear simple shear zones arise as a special case where 1 recumbent fold nappes characteristic of gravitational collapse can be modelled with 1 and thrust sheets with layer parallel shortening and folding with differential transport of nappes gives rise to additional wrench type shears solutions for the principal strains in this type of model are found and used to interpret side wall ramps and steep zones parallel to nappe movements by including a stretch in the transport direction these differential transport models produce prolate strains 1 and oblate strains finally a brief consideration of bending strains produced in a sheet passing over a ramp indicates reversals in the shear direction during the strain history these predict possible crenulation of early thrust fabrics at ramps

origin of basin scale syn extensional synclines on the southern margin of the northern carnarvon basin western australia fault geometry exerts a dominant structural control on the deformation of hanging wall sequences during extension and contraction numerical kinematic and sandbox modelling studies have demonstrated that characteristic anticline syncline pairs are produced during the extension of ramp flat faults these features are commonly recognized in smaller fault scale structures but remain underappreciated in larger basin scale settings the lewis trough situated within the northern carnarvon basin western australia is a basin scale largely unfaulted syncline with an associated anticline along its western flank rather than the fault related graben typical of the region we present kinematic models demonstrating that a se dipping ramp flat fault geometry can produce relative highs and lows in jurassic strata as well as honouring the asymmetrical onlap pattern within the lewis trough this study indicates that the lewis trough formed during the early jurassic a period typically associated with high rates of extension and not during the late triassic fitzroy compression event this study also highlights the importance of the locker shale in partitioning deformation of the permian and mesozoic fault systems and as a diffuse zone that variably partitions displacement between stacked permian and mesozoic fault systems

the transition from complex crater to peak ring basin on the moon new observations from the lunar orbiter laser altimeter lola instrument impact craters on planetary bodies transition with increasing size from simple to complex to peak ring basins and finally to multi ring basins important to understanding the relationship between complex craters with central peaks and multi ring basins is the analysis of protobasins exhibiting a rim crest and interior ring plus a central peak and peak ring basins exhibiting a rim crest and an interior ring new data have permitted improved portrayal and classification of these transitional features on the moon we used new 128 pixel degree gridded topographic data from the lunar orbiter laser altimeter lola instrument onboard the lunar reconnaissance orbiter combined with image mosaics to conduct a survey of craters 50 km in diameter on the moon and to update the existing catalogs of lunar peak ring basins and protobasins our updated catalog includes 17 peak ring basins rim crest diameters range from 207 km to 582 km geometric mean 343 km and 3 protobasins 137 170 km geometric mean 157 km several basins inferred to be multi ring basins in prior studies apollo moscoviense grimaldi freundlich sharonov coulomb sarton and korolev are now classified as peak ring basins due to their similarities with lunar peak ring basin morphologies and absence of definitive topographic ring structures greater than two in number we also include in our catalog 23 craters exhibiting small ring like clusters of peaks 50 205 km geometric mean 81 km one humboldt exhibits a rim crest diameter and an interior morphology that may be uniquely transitional to the process of forming peak rings a power law fit to ring diameters d ring and rim crest diameters dr of peak ring basins on the

kinematics of constant arc length folding for different fold shapes abstract basic mathematical functions are applied for the two dimensional geometrical and kinematical analysis of different fold shapes relationships between different fold parameters are established and related to the bulk shortening taking place during folding under upper crustal conditions the bulk shortening taking place during constant arc length folding is mathematically related to the bulk shortening during homogenous pure shear using a particular aspect ratio which is for folding the ratio of amplitude to half wavelength and for pure shear the ratio of vertical to horizontal length of the deformed initially square body the evolution of the fold aspect ratio with bulk shortening is similar for a wide range of fold shapes and indicates that the fold aspect ratio allows a good estimate of the bulk shortening the change of the geometry of individual layers across a multilayer sequence in disharmonic folding indicates a specific kinematics of multilayer folding referred to here as wrap folding which does not require significant flexural slip nor flexural flow the kinematic analysis indicates that there is a critical value for constant arc length folding between shortening values of 30 40 depending on the fold geometry for shortening values smaller than the critical value limb rotation and fold amplitude growth are dominating for shortening larger than this value faulting boudinage and foliation development are likely the dominating deformation process during continued shortening the kinematical analysis of constant arc length folding can be used for estimating the bulk shortening taking place during multilayer folding which is an important component of the deformation of crustal rocks during the early history of shortening the bulk shortening is estimated for a natural multilayer detachment fold and the shortening estimates based on the kinematic analysis are compared and supported by numerical finite element simulations of multilayer detachment folding in power law materials

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

reconstruction of palaeoenvironmental conditions by investigation of holocene playa sediments in the ebro basin spain preliminary results endorheic basins are typical landscape elements found in several parts of the ebro basin spain mineralogical and geochemical analysis of sediment cores from the endorheic basins facilitates the reconstruction of local palaeoenvironmental and palaeoclimatic conditions during the holocene the different morphogenetic and lithological environments of the areas investigated allows one to calibrate such information first results of the analysis of the geochemistry and mineralogy of sediments from two endorheic basins within the central ebro basin indicate that the climatic conditions governing sedimentation during the holocene changed from humid and subhumid to the present subarid conditions but was interrupted by a phase of increased humidity the varying character of solid bedrock caused different weathering products which are reflected in the varying geochemical and mineralogical composition of lake deposits

transition from complex craters to multi ringed basins on terrestrial planetary bodies scale dependent role of the expanding melt cavity and progressive interaction with the displaced zone 1 the observed differences between complex craters and multi ringed basins are described and a combined transient cavity displaced zone melt cavity model is explored to account for the observations in this nested melt cavity model the increasing influence of the percentage of the target undergoing impact melting at the sub impact point with increasing size the differential melt scaling of cintala and grieve 1998 causes fundamental changes in the nature of the transient cavity its relationship to the displaced zone and its short term collapse behavior the transition from complex craters to two ring basins involves expansion of the melting front into the displaced zone formation of a two component excavation cavity and a concomitant radial expansion outward of the zone of maximum elastic rebound the short term modification stage is then dominated by the strength differences between the fluid melt in the inner cavity and rocks of the displaced zone the highly shocked rocks at the outer margin of the expanded parabolic melting front rebound to form the expanded peak ring moving upward and laterally inward easily displacing fluid melt filling the inner depression at larger sizes differential melt scaling causes the peak ring diameter to expand relatively more rapidly than the basin rim and upon collapse the increased volume of melt ponds in the rebounded melt cavity inside the expanding peak ring as the transient melt cavity further increases proportionally in size it penetrates through the base of the displaced zone with significant consequences the resulting modification stage now incorporates into the collapse process inward and upward movement along the base of the displaced zone listric failure occurs inward into the fluid melt cavity beginning at the edge of the melt cavity and extending out along the base of the displaced zone up to the base of the rim structural uplift at 1 5 crater radii this forms an additional outer ring and a resulting megaterrace modifying the radial ejecta on the collapsed rim to form a domical facies at multi ring basin scales the significantly deeper penetration that occurs in the expanding melt cavity accounts for the maximum crustal thickness decrease that occurs inside the peak ring in the final basin early onset and higher density of peak ring basins on mercury is predicted by higher mean impact velocity and differential melt scaling

the distribution of deformation in parallel fault related folds with migrating axial surfaces comparison between fault propagation and fault bend folding abstract in fault related folds that form by axial surface migration rocks undergo deformation as they pass through axial surfaces the distribution and intensity of deformation in these structures has been impacted by the history of axial surface migration upon fold initiation unique dip panels develop each with a characteristic deformation intensity depending on their history during fold growth rocks that pass through axial surfaces are transported between dip panels and accumulate additional deformation by tracking the pattern of axial surface migration in model folds we predict the distribution of relative deformation intensity in simple step parallel fault bend and fault propagation anticlines in both cases the deformation is partitioned into unique domains we call deformation panels for a given rheology of the folded multilayer deformation intensity will be homogeneously distributed in each deformation panel fold limbs are always deformed the flat crests of fault propagation anticlines are always undeformed two asymmetric deformation panels develop in fault propagation folds above ramp angles exceeding 29 for lower ramp angles an additional more intensely deformed panel develops at the transition between the crest and the forelimb deformation in the flat crests of fault bend anticlines occurs when fault displacement exceeds the length of the footwall ramp but is never found immediately hinterland of the crest to forelimb transition in environments dominated by brittle deformation our models may serve as a first order approximation of the distribution of fractures in fault related folds