application of high resolution seismic techniques in the evaluation of earthquake site response ottawa valley canada abstract high resolution seismic surveys including p and s wave studies have been conducted in an area of the ottawa river valley located 80 km east of ottawa canada based on dating of paleolandslides the existence of paleoearthquake activity has been postulated in this area the target zone for the seismic survey is characterized by surface disturbance and sediment deformation p wave seismic imaging was used to map the overburden bedrock interface as well as to indicate reflecting boundaries within the overburden the area of surface disturbance was found to overlie a buried bedrock basin 8 km in diameter infilled with a maximum thickness of 180 m of unconsolidated quaternary sediments preliminary results of core logging show the presence of sand overlain by deformed fine sediments within the disturbed area shear refraction studies reveal differences in the velocity depth profiles between the disturbed area and the surrounding undisturbed areas the shear wave reflection method was used to produce a fundamental resonant period map for the area surface sediment disturbance was probably due to a combination of ground motion amplification due to the basin thick soft sediments and the presence of water saturated sand at depth

structural traverse across the sierra madre oriental fold thrust belt in east central mexico the exposed structural geometry of the sierra madre oriental foreland fold thrust belt is quantified for an 130 km long strip along the moctezuma river 21 n lat east central mexico the strip extends from the belt s leading edge in the east to its most internal continuous outcrops in the west where the cordilleran structures disappear beneath cenozoic volcanic rocks the style of deformation is controlled mainly by the geometry and lithology of two major cretaceous carbonate banks el doctor and valles san luis potosi the long dimensions of which parallel the cordilleran structural trend the exposed shortening is concentrated on the platform margins 5 km on the eastern edge of the el doctor bank and 10 to 12 km on either edge of the valles san luis potosi platform and is characterized by thrust and fold nappes the thrust faults cut across the platform margin carbonates on 20 inclined tectonic ramps that were partly steepened by imbrication or by subsequent folding but pass in the overlying mechanically weak rocks nearly parallel to bedding the interiors of the platforms appear relatively undeformed whereas the regions between the two platforms zimapan basin and between the eastern edge of the valles san luis potosi platform and the foreland are composed of flexural slip folds resulting from decoupling along several incompetent layers the exposed bulk shortening measures 41 4 km or 25 for the entire traverse retrodeformable sections of the subsurface structure down to basement result in a bulk shortening of 90 1 km or 40 the subsurface deformation model for the western part of the traverse is thin skinned and has geometry similar to that on the surface the model is very speculative in the eastern part where the areal shortening calculated for thin skinned models is much larger than is the exposed linear shortening balance was attained by inferring a blind thrust on an upper detachment in the late cretaceous which has a shortening of 20 to 30 km it could also be attained however by intrabasement decoupling in a depth of 10 to 20 km deformation is brittle in the eastern part of the belt east of the valles san luis potosi platform whereas igneous intrusion controlled higher ductility characterizes the western part of the foreland fold thrust belt

basin tectonics and erg response abstract the alignment and distribution of facies in the major erg eolian sand sea deposits in the permian and jurassic systems on the colorado plateau show remarkable coincidence with modern tectonic elements this indicates that subtle tectonic elements precursors to the present ones were coeval with ancient eolian deposition and controlled erg geometry and facies distribution no other known controls or processes were capable of producing the observed patterns facies and architectural analysis of the permian and jurassic erg deposits define several major trends across the colorado plateau the high plateaus trend parallel to and slightly east of the wasatch line is defined by a zone of thinning and facies change of several erg deposits the zuni trend lies along the zuni lineament and is coincident with facies changes or erg margins of several units the colorado trend lies along the course of the modern colorado river and a number of erg margins and several facies changes coincide with it most erg centers as defined by facies and thickness lay within paleobasins that include the circle cliffs trough holbrook black mesa and blanding basins and southern cordilleran miogeocline most erg deposits thin or pinch out across paleoarches which include the sedona monument emery and defiance arches although the exact relation between the paleostructures and facies distribution is uncertain it appears likely that some of the structural elements defined areas of greater and less sand accumulation areas of greater sand accumulation would be expected to be dominated by facies typical of erg centers and areas of lesser sand accumulation would be expected to be dominated by facies typical of the erg margin and eolian sand sheets the structures may have also formed straight margins in aqueous environments such as rivers and marine coasts straight vertically stacked facies changes are commonly associated with erg margins in the stratigraphic record early post depositional uplift of some arches may have defined straight thin edges of some eolian sequences the knowledge that subtle intrabasinal tectonic elements had an effect on eolian deposition can be used to reconstruct basin history therefore the mapping of eolian geometry and facies patterns can provide powerful information concerning the tectonic evolution of a sedimentary basin

forced folding and fracturing induced by differential compaction during post depositional inflation of sandbodies insights from numerical modelling abstract three series of numerical models based on the discrete element method were constructed to simulate forced folding and fracturing triggered by postdepositional inflation of fluidised sandbody the models consist of numerous particles that have relatively low to high interparticle bonds to represent overburden sediments with a relatively low to high cohesion and cohesionless frictionless particles to represent fluidised sands the modelling results show that normal faults were produced due to the upward inflation of sand domes and the resulting flexed overburden when the cohesion of the host sediments is low opening voids were created as a result of strata collapse when the intrusion related normal faults terminated within the host sediments as blind faults conical fractures that are aligned along sandbody margins were produced which consist of closed lower segments with a reverse displacement and opening middle upper segments with a minor to zero shear component forced folds were generated in most models with a moderate to high cohesion resulting in differential compaction in the overlying sediments that can account for the formation of fold related fractures which are either shear hybrid or pure tensile depending on their structural positions the amplitude of forced folds is closely associated with both cohesion and thickness of sediments in the overburden whilst fold wavelength is mainly controlled by sediment cohesion based on the modelling results three types of preferential sites for the storage of injected sands were suggested which are believed to be instructive for subsurface sandbody detection and prediction this study demonstrates that differential compaction induced by sand inflation can play an important role in overburden folding and fracturing

an integrated model of extrusive sand injectites in cohesionless sediments clastic injection and surface expression of subsurface sediment remobilization is a phenomenon which is becoming increasingly recognized however understanding of the physical mechanisms that control these features remains limited dominated by inference from outcrop and seismic studies here this limitation is addressed through a set of experiments focused on the development and evolution of fluidization features in non cohesive bedded sequences fluidization and the onset of piping are shown to occur progressively through a sequence of discrete phases with initial void formation development of infiltration horizons rupture and finally pipe formation critically the style of piping the stability of piping and the temporal evolution of venting are shown to exhibit considerable variability in particular pipes may either be stable or very mobile migrating laterally over large distances these produce deposits that are typically interpreted in outcrop as being the product of en masse liquefaction rather than localized dynamic fluidization these differing elements are synthesized to produce a model of sand extrudites in addition the implications of this model are explored

boiling sand springs dismal river nebraska agents for formation of vertical cylindrical structures and geomorphic change boiling motion not temperature sand springs fed by ground water moving upward along distinct conduits occur along the dismal river in the nebraska sand hills the cylindrical conduits are developed in alluvium and are as large as 10 m in diameter and 44 m deep sides of the spring conduits are firm boiling sand is overlain in several places by a clear layer of water in the spring time varying wave patterns and boils can be observed along the interface between these layers sediment within the conduits is generally well sorted although some debris is present because of their large size firm sides and persistence in time the conduits have the potential for preservation as vertical cylindrical structures comparable to those reported in sedimentary rocks of several ages the discovery of preserved structures is evidence of paleo ground water discharge and therefore the structures are a useful mapping tool for determining position in landscape evolution

concurrence of folding and remagnetization events in the monterrey salient ne mexico abstract carbonate formations from many locations reveal magnetizations that are secondary attaching a numerical age to these remagnetizations would provide information on orogenic processes to contribute to the effort of assigning an age to remagnetization events lower cretaceous formations from the monterrey salient in northeast mexico were sampled individual fold tests reveal eight site pair synfolding remagnetizations set a of eocene age the remanence is a chemical remanent magnetization crm carried by magnetite the magnetization of set b is possibly due to an early carbonate alteration that produced a remanence significantly older than folding a complexity of set b is that the site pairs reveal k versus unfolding percentage diagrams with maximum unfolding peaks at 100 to 125 an explanation of multiple deformation phases with an earlier horizontal folding phase around a non plunging horizontal axis and a later vertical axis rotation is suggested for the past 100 peaks of the b sites the latter deformation rotation about a vertical axes is revealed by a declination strike test in set a sites and site means of the full collection that deviate counterclockwise from the reference declination by combining synfolding results with published 40ar 39ar illite ages of folding fitz diaz et al 2016 remagnetization ages in set a sites of 48 52 ma are obtained the magnetization in set b sites is likely older though not well constrained interestingly prior results from the central sierra madre oriental to the south show two remagnetization events late cretaceous and early eocene in age in a succession from w to e nemkin et al 2015 the age of folding and remagnetization acquisition in set a sites along the monterrey salient are concurrent with the frontal remagnetized folds in the central sierra madre oriental thus the timing of major remagnetization in the monterrey salient occurred in the eocene

piggyback basin in the sevier orogenic belt utah implications for development of the thrust wedge timing data on a frontal thrust system indicate that the sevier thrust wedge of central utah advanced rapidly to its ultimate structural front in 30 m y between early albian and campanian time it then persisted by out of sequence thrusting for an additional 25 m y until the early eocene the key to the history of the frontal thrust is a piggyback basin that formed on the hanging wall unconformity bounded sedimentary units within the basin thin both westward and eastward onto structures generated by thrust faulting up to 860 m of upper campanian to lower eocene strata accumulated between these structures which consist of a ramp anticline in the west and a thrust duplex in the east the newly recognized interaction of coeval deposition and thrust deformation permits revised limits on the inception and longevity of the frontal thrust system

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

influence of pre tectonic carbonate facies architecture on deformation patterns of syntectonic turbidites an example from the central mexican fold thrust belt abstract the mexican fold thrust belt in central mexico excellently exposes relatively well preserved syntectonic deposits that overlay rocks with lateral lithostratigraphic changes across the belt we consider the deformational effects of these changes by investigating the geometry kinematics and strain distribution within syntectonic turbidites which are deposited on top of albian cenomanian shallow and deep water carbonate layers field observations and detailed structural analysis at different stratigraphic and structural levels of the late cretaceous syntectonic formation are compared with the deformation as a function of lithological and structural variations in the underlying carbonate units to better understand the effect of these lithostratigraphic variations on deformation kinematics strain distribution and propagation of deformation from our kinematic analyses we conclude that the syntectonic strata are pervasively affected by folding in all areas and that deformation partitioning localized shear zones at the boundaries of this unit particularly along the contact with massive carbonates at the boundaries with massive platformal carbonates the turbidites are strongly deformed by isoclinal folding with a pervasive sub horizontal axial plane cleavage and 70 60 shortening in contrast contacts with thinly bedded carbonate layers basinal facies do not show strain localization and have horizontal shortening of 50 40 that is accommodated by buckle folds with a less pervasive steeply dipping cleavage the mechanical properties variations in the underlying pre tectonic units as a function of changes in lithostratigraphy fundamentally control the deformation in the overlying syntectonic strata which is an effect that could be expected to occur in any deformed sedimentary sequence with such variations

controls on caldera structure results from analogue sandbox modeling we conducted scaled analogue sandbox models of caldera formation in order to understand the effects of chamber depth and orientation on the spatial and temporal development of calderas dry sand contained in a 1 m diameter cylinder served as a crustal rock analogue and a water filled 0 6 m diameter rubber bladder served as an analogue magma chamber scaling parameters included a length ratio l of 2 5 10 5 and a stress ratio of 1 8 2 4 10 5 in contrast to some previous analogue models the viscosity of the fluid in the chamber and its withdrawal rate were properly scaled generally deformation began with broad sagging followed by an arcuate or linear outward dipping fault that formed on one side of the caldera this fault propagated laterally around the caldera in both directions sometimes joining other faults and typically forming an overall polygonal structure as subsidence continued the caldera grew incrementally outward and progressively formed a series of concentric outward dipping faults lastly a peripheral zone of extension and pronounced sagging and commonly an inward dipping outer fault related to extension developed at the surface as the depth of the chamber increased 1 the area of faulting decreased 2 the symmetry of the caldera was affected and 3 the coherence of the subsiding block decreased tilting the chamber caused highly asymmetric subsidence to occur in this case faults formed first where the bladder was shallowest subsidence then shifted rapidly to where the bladder was deepest producing an elongate trapdoor caldera that was deepest where the bladder was deepest our experiments highlight the roles of sagging and faulting during caldera subsidence surface fault patterns both in our experiments and at natural calderas are frequently not circular the aspect ratio of the block above the magma chamber controls the shape of the caldera which is frequently polygonal the faults at natural calderas determine locations and migration of eruptive vents the degree of subsidence the style of postcal dera resurgent magmatism and the extent of hydrothermal circulation our experiments reveal details of how calderas grow outward incrementally and demonstrate that asymmetric subsidence along linear and arcuate faults is common to many calderas

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

origin of exotic clasts in the central southern apennines clues to the cenozoic fold and thrust collisional belt in the central mediterranean area

geological relationships of basalts andesites and sand injectites at the base of the parana volcanic province torres brazil abstract the cretaceous interaction of the heated giant guarani aquifer with lavas dikes and sills of the parana volcanic province is here evaluated based on the description of the large exposures in torres southernmost brazil chalcedony silicified sandstone dikes sills and breccias containing volcanic clasts in a sandstone matrix are common in the parana volcanic province sandstone layers mark either the contact between lava flows or the base of the vertically jointed massive core in torres one basaltic andesite and one andesite lava flow of the low ti gramado type and basalt and basaltic andesite sills and dikes are correlated over 10 km with rocks in the graxaim quarry scintillometric emission rates vary systematically with contents of k th and u and are characteristic of each lava or intrusive rock major and trace elements are also characteristic of each lava three large outcrops of breccias display angular amygdaloidal volcanic clasts immersed in a silicified sandstone matrix no evidence was found of high temperature 1150 c interaction of the lava with the loose erg of the botucatu formation such as fluidal volcanic clasts quenched rims or thermal recrystallization of the sand only a thin 5 mm layer of thermally modified sand is present on top of a paleodune in torres in torres the interaction of andesite with wet sand occurred after degassing of the lava because the breccia clasts are amygdaloidal all evidence points to hydrothermal processes for the formation of the breccias such as lozenge fractures filled with silicified sandstone preserved detrital characteristics of the sandstone grains and cold below 130 c contact between the volcanic rock and the sand most significant is the timing of sand intrusion because thin 1 mm dikes of silicified sandstone cut fractures in the rock and the zeolite filled amygdales the sandstone dikes sills and breccias are interpreted as a result of the ascent of overpressured heated water and its vapor from the huge underlying guarani aquifer carrying fluidized sand and continuously silicifying the intruded sand the three breccias are sills intruded into cold lava flows the description and correlation of the magmatic bodies and the field relationships of the silicified sandstones establish the stratigraphy of the parana volcanic province in torres and elucidate the processes responsible for the injection and effusion of sand in the cretaceous

experimental evidence for fluidization processes in breccia pipe formation results of small scale fiuidization spouting and channeling experiments suggest that similar processes may have been involved in the formation of many breccia pipe features various cylindrical parallel plate and boxlike model containers were filled with mixtures of particulate materials ranging from clay sized powdered kaolinitc to 1 cm gravel and each container was attached at its base to a large volume compressed air source features generated during the course of the various experimental runs are analogous to the majority of features observed in breccia pipes complex branching fracture systems developed in models containing abundant cohesive material appear to be similar to incipient crackle breccias steep walled funnel to cone shaped conduits formed readily and in some models inward dipping fractures ring fractures marginal shear folds and or downwarps and or high angle normal faults developed in adjacent material thorough mixing of heterogeneous particulate materials from throughout the stratigraphic column commonly was achieved and blocks of more cohesive materials were readily rounded and comminuted convective particle motion spouting was most effective in the mixing process and was accompanied by downwarping and fragmentation of adjacent strata downward migration of wall rock blocks along conduit margins and generation of annular zonation of conduit filling material in some systems annular size classification resulted in fine layering parallel to conduit walls crude centroclinally nested saucer bedding developed in some experiments where air fall ejecta were generated and these beds commonly were transported essentially intact downward within the pipe during a bubbling fiuidization event a gas streaming or channeling process in which finer material was elutriated or cleared out of coarser material led to the formation of channelways or chimneys which in natural systems would provide excellent avenues for introduction of later magma or hydrothermal solutions in model systems enriched in strongly cohesive clay sized particles accretionary pelletal spherules commonly were generated fluidization and related processes have been defined to describe highly controlled industrial systems problems of scale and strength of materials are significant when comparing experimental with geologic systems but the striking similarity of many features observed in both experimental and natural breccia pipe systems suggests that a similar genetic process is reasonable although many pipes clearly are not formed by fiuidization and related processes these processes may be important in the development of or some developmental stage of some breccia pipes

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

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

critical taper model of fold and thrust belts and accretionary wedges the fold and thrust belts and submarine accretionary wedges that lie along compressive plate boundaries are one of the best understood deformational features of the earth s upper crust although there is considerable natural variation among the many fold and thrust belts and accretionary wedges that have been recognized and explored several features appear to be universal in cross section fold and thrust belts and accretionary wedges occupy a wedge shaped deformed region overlying a basal detachment or decollement fault the rocks or sediments beneath this fault show very little deformation the decollement fault characteristically dips toward the interior of the mountain belt or in the case of a submarine wedge toward the island arc the topography in contrast slopes toward the toe or deformation front of the wedge deformation within the wedge is generally dominated by imbricate thrust faults verging toward the toe and related fault bend folding two north american fold and thrust belts that exhibit these features are shown in figure 1 neither of these two examples is tectonically active today the southern canadian fold and thrust belt was active during the late jurassic and cretaceous 150 100 ma whereas the southern appa lachians were deformed during the late carboniferous to permian alle ghenian orogeny 300 250 ma figure 2 shows two examples that are currently active the taiwan fold and thrust belt produced by the sub duction of the eurasian plate beneath the philippine sea plate suppe 1981 1987 and the barbados accretionary wedge produced by the sub

synapsid burrows and associated trace fossils in the lower jurassic navajo sandstone southeastern utah u s a indicates a diverse community living in a wet desert ecosystem abstract enigmatic structures in the lower jurassic navajo sandstone near moab utah occur at three localities below carbonate beds that record interdune lake deposits these structures are interpreted as mammal and therapsid burrows based on their architectural and surficial burrow morphologies type i large diameter and type ii mega diameter burrows type i burrows include sinuous tunnels y and t branched tunnels sinuous ramps and chambers and weather into mounds averaging 33 m 22 m and extend 1m above the surface type i burrows are dorsoventrally flattened in cross section averaging 9 3 cm wide and 4 2 cm high and are sand filled and structureless type i burrows mostly have smooth walls though some have scalloped walls type ii burrows are simple inclined tunnels 35 cm wide and 20 cm high and exhibit well preserved bilobate morphology along the underside of the tunnel the walls preserve a series of 3 or 4 thin 4 8 mm inclined scratch marks from the upper part of the wall and along the floor the great complexity and high density of type i burrow systems is best explained by multiple individuals living together in social groups these burrows are more complex than early triassic therapsid burrows from south africa and are most similar to burrows of extant social e g voles and eusocial mammals e g naked mole rats type ii burrows were likely constructed by therapsids based on burrow size and comparison to permian and triassic therapsid burrows from south africa and antarctica

indicators of propagation direction and relative depth in clastic injectites implications for laminar versus turbulent flow processes clastic injectites are widely recognized in deep water stratigraphic successions although their sediment transport processes propagation direction and depth of injection are poorly constrained understanding how they form is important as injectites are increasingly being recognized as significant components of sedimentary basin fills yet are not predicted by standard sedimentary facies models here analysis of features on the margins of exhumed clastic sills and dikes and clasts within them enables their genesis to be determined a diverse array of diagnostic structures is found on the margins of injectites in the karoo basin south africa where the net direction of injection and position of the parent sand are well constrained injectite margin features include mudstone clast rich surfaces planar or smooth surfaces blistered surfaces and parallel and plumose ridged surfaces combined these features are critical in distinguishing injected sands where injectites are strata concordant from those of primary deposition all features are indicative of propagation through brittle very fine grained sediments at depths where the applied shear stress is at least four times the tensile strength of the host rock additionally the presence of parallel ridges plumose ridges and steps allows local fracture propagation to be constrained and in turn injection direction the features described provide evidence that sands were injected at considerable depth in closed fractures with limited capacity for flow dilution and turbulence enhancement calculated reynolds numbers lack of erosion at injectite walls and the presence of mud clasts at the top and base of sills indicate that many flows were likely fully laminar during injection the sedimentary features of these confined relatively deep laminar flow induced injectites are very different from injectites that reach the surface and produce extrudites surface linked injectites are associated with open conduits where a greater fraction of carrier fluid to particles can be accommodated enabling highly turbulent lower concentration flows

cordilleran deformation along the eastern edge of the valles san luis potosi carbonate platform sierra madre oriental fold thrust belt east central mexico the eastern margin of the cretaceous valles san luis potosi carbonate platform hidalgo queretaro and san luis potosi states became activated during the formation of the sierra madre oriental fold thrust belt a series of thrust sheets with a minimum linear shortening of 3 to 4 km each and 10 to 12 km in total formed where the platform edge was approximately normal to the greatest principal stress trajectories as deduced from fold axes a tear fault developed where the platform edge formed an acute angle with the same stress trajectories the overthrusts cut across the competent layers of the lower cretaceous on tectonic ramps that dip 10 and became partly steepened by subsequent imbrication or folding in the mechanically weak upper cretaceous rocks the thrust faults are nearly parallel to bedding for several kilometres the location of the thrusts is controlled mainly by the lithological and thickness change of the middle cretaceous rocks from an orthotropically layered basin facies into a two to five times thicker homogeneous platform edge assemblage the bank margin was a zone of stress concentration the magnitude of the horizontal tectonic components which caused the deformation may have changed by a factor of two to five across the platform margin due to the change in cross sectional area oblique and layer parallel discrete shears and subordinate tectonic stylolites appear to have been the dominant deformational mechanisms the rocks did not suffer any measurable penetrative ductile deformation ooids present at the base of the xilitla thrust are unflattened but are marked by a closely spaced stylolitic cleavage perpendicular to bedding the deformations are bracketed by the paleontological age of the youngest strata affected by the overthrusts globotruncana contusa planktonic foraminiferal zone and by the isotopic age of a post tectonic pluton 62 2 ma and are thus of late maastrichtian paleocene age

giant sandstone pipes record basin scale liquefaction of buried dune sands in the middle jurassic of se utah giant sandstone pipes crop out over a 20 000 km2 area of se utah they range from metres to decametres in diameter and crosscut more than 100 m of continental sediments new and published observations encompassing all known pipe localities in se utah suggest that the pipes formed by upward movement of groundwater sand and sediment blocks in response to liquefaction of buried dune sands pipe formation was most likely triggered by seismicity during a phase of cordilleran shortening and regional tectonic reorganization in the late middle jurassic the depth of liquefaction recorded by the pipes far exceeds depths usually considered in earthquake engineering

origin of enigmatic sand injectite outcrops associated with non tectonic forced folding structure in bahrah area northern kuwait bay abstract this is a quantitative and qualitative study for the first time linking surface with subsurface geology to understand the occurrence and origin of enigmatic sand injectite outcrops in two sites within the bahrah coastal plain area northern kuwait bay field work observations and aerial photography were used to describe and characterize the surface geology and stratigraphy of the study area thirty one rock samples were obtained for petrographical fluid inclusions and strontium isotopes analyses 3d seismic data were also used to assess the subsurface geology of the area the petrography and microthermometry of fluid inclusions were used to understand the origin of fluids and gases associated with the formation of these sand injectites we found that these surface geological features represent surface manifestation of subsurface geological and biological activities processes therefore we proposed a near surface complex focused fluid injection mechanism model responsible for the formation of the sand pipes the model consists of five episodes episode 1 represents the development of near surface geobody paleoshoreline sealed by a shale layer episode 2 represents the entrapment of hydrocarbons that migrated laterally up dip within geobody interacting with mixed seawater intrusion and fresh groundwater episode 3 represents the effect of biodegradation biological processes of the entrapped hydrocarbons generating ch4 co2 and h2s gases episode 4 represents overpressure build up due to gas generation exceeding pore volume of geobody and forming non tectonic forced folds and polygonal to semi circular joints fractures network and episode 5 represents overpressure release triggered by external factor s seismic activities facilitating gases water and sand remobilisation through weakened zones of natural fractures

the deep structure of south central taiwan illuminated by seismic tomography and earthquake hypocenter data abstract the taiwan mountain belt is generally thought to develop above a through going basal thrust confined to within the sedimentary cover of the eurasian continental margin surface geology magnetotelluric earthquake hypocenter and seismic tomography data suggest however that crustal levels below this basal thrust are also currently being involved in the deformation here we combine seismic tomography and earthquake hypocenter data to investigate the deformation that is taking place at depth beneath south central taiwan in this paper we define the basement as any pre eocene rifting rocks and use a p wave velocity of 5 2 km s as a reference for the interface between these rocks and their sedimentary cover we found that beneath the coastal plain and the western foothills clustering of hypocenters near the basement cover interface suggests that this interface is acting as a detachment this detachment is located below the basal thrust proposed from surface geology for this part of the mountain belt inherited basement faults appear to determine the geometry of this detachment and their inversion in the alishan area result in the development of a basement uplift and a lateral structure in the thrust system above them however across the shuilikeng and the chaochou faults earthquake hypocenters define steeply dipping clusters that extend to greater than 20 km depth above which higher velocity basement rocks are uplifted beneath the hsuehshan and central ranges we interpret these clusters to form a deeply penetrating east dipping ramp that joins westward with the detachment at the basement cover interface it is not possible to define a basal thrust to the east beneath the central range

conical sandstone landforms cored with clastic pipes in glen canyon national recreation area southeastern utah abstract clusters of conical sandstone landforms many with summit weathering pits have developed on barren outcrops of the jurassic entrada sandstone in glen canyon national recreation area southeastern utah the conical landforms have developed on cylindrical bodies of fluidized sandstone clastic pipes that typically have near vertical contacts with the enclosing cross bedded eolian sandstone these landforms vary in size and shape due chiefly to differential erosion of the clastic pipe relative to the enclosing sandstone the greater resistance to weathering of the clastic pipes is due in part to their higher content of calcite cement conical pipe cored landforms develop progressively from low domes to cones as high as 70 m some of the clastic pipes have relatively soft cores and resistant contacts leading to the development of conical landforms with summit weathering pits with time the size of these pits increases as does the relief of the conical landform the summit pits are as deep as 16 m and have width depth ratios as low as 1 5 the resistant rims of these pits are due in part to calcite enriched pipe contacts sandy pit floor sediment is removed principally by strong wind rotors and vortices intense eolian activity in and near the landforms is indicated by abrasional features and pit floor sand dunes factors that promote the development of these conical landforms include i the presence of clastic pipes some with relatively soft cores ii porous friable fine grained pipe and host sandstones iii aridity iv strong winds and v virtually sediment free unvegetated bedrock outcrops

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

coal quality coal rank variation and its relation to reconstructed overburden upper cretaceous and tertiary plains coals alberta canada near surface coals in the alberta plains occur in upper cretaceous and tertiary sediments the former represented by the belly river group horseshoe canyon formation and wapiti formation and the latter by the scollard member of the paskapoo formation statistical techniques were used to document both the distribution of and the interrelationships among the components of proximate and ultimate analysis and calorific value determinations the coals discussed range in rank from subbituminous c to high volatile bituminous c these coals are variable in ash content and low in sulfur content the relationships among calorific value dry basis in kj kg and ash dry basis in and calorific value moist mineral matter free basis in kj kg and equilibrium moisture meq in were determined to be cvd 29 677 315 17 ashd and cvmmmf 31 816 442 05 meq respectively the maximum depth of coal seam burial dob in m was reconstructed on the basis of previously published graphs relating the equilibrium moisture loss to depth of coal seam burial using the relationship log10meq 1 865 0 000416 dob a least squares regression analysis of calorific value mmmf basis in k kg on the calculated depth of burial dob in m yielded the equation cvmmmf 14 748 6 25 dob indicating a coalification gradient determined on the reconstructed overburden of 6 25 kj kg m 0 82 btu lb ft of depth or overburden near surface coals in the alberta plains increase in rank toward the west southwest toward the foothills and mountains region because of progressively greater amounts of overburden that existed in that direction during the tertiary erosion has since removed between 900 and 1 900 m 3 000 and 6 200 ft of sediment with the greatest amount of removal occurring in a west southwest direction

paleogeographic and paleotectonic setting of laramide sedimentary basins in the central rocky mountain region in the rocky mountain region between central montana and central new mexico sedimentologically isolated nonmarine basins were produced by basement deformation during the laramide orogeny within the area formerly occupied by a broad late cretaceous foreland basin in which laterally continuous marine facies had accumulated previously laramide structures of varying trend and scale reflect heterogeneity of crustal strain caused by shear between the continental lithosphere and an underlying subhorizontal slab of subducted oceanic lithosphere laramide basins include perimeter basins along the cratonic periphery of the arcuate laramide province axial basins along a north south intramontane trend and ponded basins located farther west closer to the overthrust belt twelve specific stratigraphic and sedimentologic criteria for the onset duration and termination of laramide deformation allow the chronology of basin development to be inferred independently for each basin maastrichtian initiation of laramide deformation was approximately synchronous throughout the laramide province but termination of laramide deformation was systematically diachronous from north to south between early and late eocene time widespread eocene erosion surfaces truncate syntectonic laramide sequences and are overlain by largely volcanic and volcaniclastic post laramide strata of eocene age in the north and oligocene age in the south fluvial depositional systems draining toward the great plains were dominant in perimeter and axial basins but ponded basins were occupied at times by large lakes that served as regional sediment traps paleocene drainages from ponded basins also led eastward toward the continental interior but partly interconnected lakes that developed within several ponded basins by mid eocene time were either closed hydrologically or else they drained westward into the tyee paleoriver of the pacific northwest

insights into fluid flow and water rock interaction during deformation of carbonate sequences in the mexican fold thrust belt analysis of mesoscopic structures and related veins allows the history of deformation and role of fluids to be established for part of the central mexican fold thrust belt mftb the mftb developed in mostly carbonate rocks with prominent lateral facies changes associated with two platforms and two basins fluids played a key role in the deformation both physically and chemically by reducing strength and inducing extensional fracturing through raised pore pressure and by providing the medium for solution transfer on the grain scale veins preserve portions of water related to deformation as fluid inclusions lithology and lithological variations strongly control deformation styles with thrusts dominant in the platforms and folds dominant in the basins and also influence fluid behavior by controlling both porosity and permeability structural observations allow distinguishing veins dominantly calcite of several generations emplaced early during and late after deformation v1 v3 respectively 13c and 18o analyses in calcite from veins and host rock show that the veins confined within thrust slices are isotopically buffered by the host rock and differ in isotopic composition from veins emplaced along major thrusts or crosscutting thrust slices d analyses in fluid inclusions and clay minerals strongly suggest rock interaction with meteoric fluids in the west hinterland and with fluids close to smow in the less deformed eastern foreland side of the cross section by focusing on a single stratigraphic interval exposed across the width of the fold thrust belt we propose a conceptual model that explains the differences in vein rock isotopic composition the differences of in isotopic composition of aqueous fluids active during deformation and the progression of clay dehydration reactions as being related to variations in temperature and intensity of deformation in a growing tectonic wedge

quantifying frictional variations and erosion in the mexican fold thrust belt abstract the impact of frictional crustal heterogeneities and surface processes on the evolution of the ancient thin skinned mexican fold and thrust belt mftb is investigated and quantified using numerical finite element simulations these simulations explore the evolution total shortening and structural styles of deforming orogenic wedges the models include spatial lateral variations in the internal friction and the topographic erodibility k using the power law incision rule the mftb exhibits paleogeographical elements manifested as lateral facies changes across two platforms units and two sedimentary basins that show different degrees of deformation the observed kinematics of the mftb requires based on the parameters considered in this study a rheologically heterogeneous crust with at least laterally varying internal friction yet only limited syntectonic and post tectonic erosion are necessary to explain the geometries and internal total shortening constrained by field observations and interpretations application of the analytical and homogeneous critical coulomb wedge ccw theory to the mftb closely predicts the external wedge geometry but fails to predict the observed shortening of the individual litho tectonic units and structural styles

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

seismogenically induced fluidization of jurassic erg sands south central utah large bodies of fluidized sandstone occur in the jurassic entrada carmel page and navajo formations at several locations in south central utah they are most abundant in the entrada sandstone where they commonly occur in clusters have a cylindrical form and have a sharp contact with their cross bedded host rock these clastic pipes are as wide as 75 m and have exposed heights of as much as 100 m some of the entrada pipes extend well into the underlying carmel redbeds other clastic pipes in the entrada sandstone are less deformed and display various degrees of brittle to hydroplastic deformation and liquefaction clastic pipes in the page and navajo sandstones are less common but are similar in size and form to those in the entrada and carmel and probably have a similar origin some massive sandstone bodies are irregular in form and have tongue like projections into the host rock implying forcible injection of fluidized sand several pipe host contacts in the entrada sandstone display small scale ring faults where relative displacement can be clearly demonstrated pipe sandstones are invariably down faulted locally as much as 5 m at two sites carmel host rock is upwarped around the entrada pipes stratified and cross bedded breccia blocks occur in many entrada pipes and preliminary petrographic analysis indicates that at least some of these breccia blocks are derived from the host rock homogeneous pipe sandstones are also petrographically similar to their entrada host rock suggesting that some pipes originate through fluidization of the fine grained entrada fluidization of the entrada must have occurred in a water saturated environment during early diagenesis but before complete lithification most probably under considerable porewater pressure although there are no known modern analogues to these huge masses of structureless sandstone they may have a small scale modern counterpart in earthquake induced sandblows these features were most probably caused by large magnitude seismic events during the middle jurassic although other possibilities cannot be ruled out at this point

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

fault dating in the canadian rocky mountains evidence for late cretaceous and early eocene orogenic pulses fault rocks from the classic rocky mountain foreland fold and thrust belt in southwestern canada were dated by ar analysis of clay grain size fractions using x ray diffraction quantification of the detrital and authigenic component of each fraction these determinations give ages for individual faults in the area illite age analysis the resulting ages cluster around 72 and 52 ma here called the rundle and mcconnell pulses respectively challenging the traditional view of gradual forward progression of faulting and thrust belt history of the area the recognition of spatially and temporally restricted deformation episodes offers field support for theoretical models of critically stressed wedges which result in geologically reasonable strain rates for the area in addition to regional considerations this study highlights the potential of direct dating of shallow fault rocks for our understanding of upper crustal kinematics and regional tectonic analysis of ancient orogens

structure and evolution of upheaval dome a pinched off salt diapir upheaval dome canyonlands national park utah is an enigmatic structure previously attributed to underlying salt doming cryptovolcanic explosion fluid escape or meteoritic impact we propose that an overhanging diapir of partly extrusive salt was pinched off from its stem and subsequently eroded many features support this inference especially synsedimentary structures that indicate jurassic growth of the dome over at least 20 m y conversely evidence favoring other hypotheses seems sparse and equivocal in the rim syncline strata were thinned by circumferentially striking low angle extensional faults verging both inward toward the center of the dome and outward near the dome s core radial shortening produced constrictional bulk strain forming an inward verging thrust duplex and tight to isoclinal circumferentially trending folds farther inward circumferential shortening predominated radially trending growth folds and imbricate thrusts pass inward into steep clastic dikes in the dome s core we infer that abortive salt glaciers spread from a passive salt stock during late triassic and early jurassic time during middle jurassic time the allochthonous salt spread into a pancake shaped glacier inferred to be 3 km in diameter diapiric pinch off may have involved inward gravitational collapse of the country rocks which intensely constricted the center of the dome sediments in the axial shear zone beneath the glacier steepened to near vertical the central uplift is inferred to be the toe of the convergent gravity spreading system

controls on synorogenic alluvial fan architecture beartooth conglomerate palaeocene wyoming and montana late palaeocene uplift of the beartooth range in northwestern wyoming and southwestern montana generated the beartooth conglomerate along the eastern and northeastern flanks of the range systematic unroofing sequences and intraformational unconformities folds and faults in the conglomerate attest to deposition during uplift along the eastern flank at least three ancient alluvial fan systems and a braidplain system can be distinguished on the bases of petrofacies and lithofacies the two southern fans consist of 700 m of sedimentary clast conglomerate and subordinate sandstone dominated by hyperconcentratedflow and stream flow facies the next fan to the north is dominated by plutonic and metamorphic clasts and contains abundant mud matrix supported debris flow facies as well as stream flow facies the northernmost depositional system consists of arkosic channellized fluvial conglomerate and sandstone overbank mudstone and crevasse splay sandstone units palaeocurrent data indicate eastward dispersal away from the beartooth range outstanding exposure of the beartooth conglomerate allows facies to be mapped on lateral photographic mosaics a seven fold hierarchy of bounding surfaces and enclosed lithosomes exists in the beartooth conglomerate first through fourth order surfaces are analogous to first through fourth order surfaces that recently have been documented in sandy fluvial facies with one exception sediment gravity flows are bounded by first order surfaces fifth order surfaces are either erosional e g lateral migration of fanhead trench or accretionary e g aggradation of fan surface during backfilling of trench and construction of lobes on lower fan during entrenchment on upper fan some fifth order surfaces coincide with intraformational angular unconformities and are thus the result of long term fanhead entrenchment following uplift of the upper part of the fan sixth order surfaces bound individual fan packages that are several hundred metres thick and 10 km2 in area the enclosed sixth order lithosomes are distinguishable in terms of petrofacies and lithofacies a single seventh order surface bounds the entire beartooth conglomerate lower order lithosomes are produced by intrinsic processes of fan construction fifth order lithosomes can be attributed to both extrinsic and intrinsic controls sixth and seventh order lithosomes are generated by extrinsic controls

clastic pipes and mud volcanism across mars terrestrial analog evidence of past martian groundwater and subsurface fluid mobilization abstract clastic pipes are cylindrical injection features that vertically crosscut bedding with sharp contacts terrestrial pipes have cylindrical morphologies massive or radially graded interiors and raised outer rims increased grain size and subsequent cementation along the more porous edges makes the rims more resistant to weathering pipes have crosscutting relationships with other pipes due to multiple formation events or migrating eruption centers and are associated with other soft sediment deformation features terrestrial clastic pipes form via liquefaction and fluidization which require a near surface groundwater system to initiate i e sand sized sediments must be saturated for pipes to form clastic pipes cm to 1000 m diameters occur on mars across multiple time periods and terrains and are recognized in both rover and orbital imagery a conical or cylindrical geometry and massive interior core characterize these features the pipes on mars show various geomorphic expressions and are classified into five types by the presence or absence of a raised outer rim or a central pit these types are interpreted to represent the erosional evolution of pipes at different stages from their initial surface eruptive structures to their weathered remnants eroded conical hills martian pipes formed via fluidization as evidenced by 1 raised outer rims possibly indicating textural differences along the pipe edges from traction interactions of fluid suspended sediment 2 crosscutting relationships with other pipes suggesting reactivated fluidization pathways or migrating eruptive vents and 3 close spatial association between pipes and other features thought to form by soft sediment deformation e g contorted bedding integration of terrestrial analog data with the mars observations provides evidence for past martian groundwater and subsurface fluid mobilization

isotopic evidence for a young lunar magma ocean abstract mare basalt sources and ferroan anorthosite suite cumulates define a linear array on a 146sm 144nd versus 142nd 144nd isochron plot demonstrating these materials were derived from a common reservoir at 4336 31 32 ma the minimum proportion of the moon that was in isotopic equilibrium at this time is estimated to be 1 3 of its entire volume based on the geographic extent from which the analyzed samples were collected and the calculated depths from which the samples were derived scenarios in which large portions of the moon were molten to depths of many hundreds of kilometers are required to produce the observed sm nd isotopic equilibrium between the mantle and crustal rocks at 4 34 ga this is a consequence of the fact that limited heating of a solid moon above the blocking temperature of the sm nd isotopic system is insufficient to diffusively homogenize radiogenic nd throughout the mantle and crust there are three scenarios that might account for global scale isotopic equilibrium on the moon relatively late in solar system history including 1 sm nd re equilibration of a solid moon resulting from widespread melting in response to mantle overturn or a very large impact 2 early accretion of the moon followed by delayed cooling due to the presence of an additional heat source that kept a large portion of the moon molten until 4 34 ga or 3 late accretion of the moon followed by rapid cooling of the magma ocean late in solar system history neither density driven overturn of the mantle nor a large impact are likely to homogenize the mantle and crust to the extent required by the sm nd isochron likewise secondary heating mechanisms such as tidal heating or radioactive decay are not efficient enough to keep the moon molten to the depth of the mare basalt source regions for many tens to hundreds of millions of years instead the age of equilibrium between such a compositionally diverse set of rocks produced on a global scale likely records the time of primordial solidification of the moon from a magma ocean this scenario accounts for both the petrogenetic characteristics of lunar rock suites as well as their sm nd isotopic systematics it is supported by the preponderance of 4 35 ga ages obtained for other hypothetical magma ocean crystallization products such as ferroan anorthosite suite rocks and k ree and p enriched cumulates that are thought to represent flotation cumulates of the magma ocean and the last vestiges of magma ocean solidification respectively

kinematic evolution and structural styles of fold and thrust belts fold and thrust fat belts occur worldwide and have long been the focus of research of structural geologists who have devised a variety of techniques to image characterize and model their main structural features this introductory chapter reviews the principal geological features of fat belts formed in different settings emphasizing aspects related to their kinematic evolution and structural styles despite great advances challenges remain particularly in the understanding of the spatial and temporal evolution 4d of fat belts and their controlling factors these research efforts are being assisted by the growing availability to researchers of relatively new tools to collect field data high quality 3d seismic data and computer and laboratory modelling tools this volume includes technical papers presented in the conference international meeting of young researchers in structural geology and tectonics yorsget 08 held in oviedo spain together with other papers on the same theme these papers deal with fat belts in different parts of the world and cover a broad range of different aspects from detailed structural analysis of single structures to regional issues and from studies based on classical field structural geology to modelling

seismic characteristics of fluid escape pipes in sedimentary basins implications for pipe genesis abstract fluid escape pipes were first documented from 3d seismic data over a decade ago and have subsequently been identified in many petroliferous basins worldwide they are characterized on seismic data by vertical to sub vertical zones of reduced reflection continuity that have a columnar geometry in three dimensions the upper terminations of these pipes commonly coincide with pockmarks or palaeo pockmarks signifying a close connection of pipe formation with a high flux fluid expulsion process dimensions range from tens to hundreds of metres in diameter and hundreds to over a thousand metres in height and the slenderness ratio defined as height diameter ranges from 0 8 to over 20 pipes are frequently associated with sub vertical clustering of amplitude anomalies on seismic data related either to the presence of free gas or to cementation linked to the passage of hydrocarbons three mechanisms have been suggested to explain pipe genesis 1 hydraulic fracturing 2 erosional fluidisation and 3 capillary invasion we suggest a further two possible mechanisms in the form of localised collapse by volume loss and synsedimentary flow localisation we review all five mechanisms and conclude that it is unlikely that a single mechanism applies but that combinations of these processes may all occur in particular contexts fluid escape pipes may be far more widespread that currently appreciated and they may play a critical role in secondary hydrocarbon migration and in providing leakage pathways for trapped hydrocarbons through overlying seals

xrd based 40ar 39ar age correction for fine grained illite with application to folded carbonates in the monterrey salient northern mexico abstract due to their minute size 40ar 39ar analysis of illite faces significant analytical challenges including mineral characterization and especially effects of grain size and crystallography on 39ar recoil quantifying the effects of 39ar recoil requires the use of sample vacuum encapsulation during irradiation which permits the measurement of the fraction of recoiled 39ar as well as the 39ar and 40ar retained within illite crystals that are released during step heating total gas ages tga are calculated by using both recoiled and retained argon which is functionally equivalent to k ar ages while retention ages ra only involve retained ar in the crystal natural applications have shown that tga fits stratigraphic constraints of geological processes when the average illite crystallite thickness ict is smaller than 10 nm and that ra matches these constraints for icts larger than 50 nm we propose a new age correction method that takes into account the average ict and corresponding recoiled 39ar for a sample with x ray corrected ages xca lying between total gas and retention ages depending on ict this correction is particularly useful in samples containing authigenic illite formed in the anchizone with typical ict values between 10 and 50 nm in three samples containing authigenic illite from cretaceous carbonates in the monterrey salient in northern mexico there is a range in tgas among the different size fractions of 46 49 36 43 and 40 52 ma while ras range from 54 64 47 52 and 53 54 ma respectively xca calculations produce tighter age ranges for these samples of 52 5 56 45 5 48 5 and 49 52 5 ma respectively in an apparent age vs ict or 2m 1illite plot authigenic illite grains show a slope that is in general slightly positive for tga slightly negative for ra but close to zero for xca with thinner crystallites showing more dispersion than thicker ones in order to test if dispersion is due to a different formation history or the result of retention capability degassing spectra were modeled for site xca averages and overall xca average modeling shows that local site age average best match the measured spectra instead of a global average age indicating that illite growth reflects local deformation and is not the result of regional metamorphism modeling also shows that ar degassing spectra are very sensitive to grain size such that age interpretation based on ar plateaus is meaningless for most fine grained clays

kinematic modeling of cross sectional deformation sequences by computer simulation we derive a kinematic algorithm which permits simulation of postulated cross sectional deformation sequences in sedimentary rocks affected by faulting fault related folding and simple shear the transformations are to a more deformed state and are formulated analytically in terms of the less deformed configuration forward modeling lagrangian description the medium is subdivided into domains of constant dip and homogeneous displacement vector fields which are delimited by the axial planes of the fault inflections the displacement trajectory is of constant length for all the displaced particles throughout the medium and parallel to the underlying active fault segment as a consequence the deformation path is continuous but not smooth and causes an angular style of parallel folding except at the deformation front where the layer thickness is not conserved the inhomogeneity of the displacement vector field across axial planes introduces longitudinal and angular shear strains whereas the area of the medium remains constant these strains which are superposed on the externally applied simple shear make the mapping transformation unconformal we define the stratigraphic layering of the undeformed medium by an approximating body of finite quadrilateral elements evaluate the defined displacement functions for the grid nodes and graph the deformed mesh eventually we create with the algorithm synthetic deformation sequences for simple boundary conditions and try in a specific case study to match the resulting synthetics with the available observational and experimental data

large scale rotations of the chortis block honduras at the southern termination of the laramide flat slab abstract paleogeographic reconstructions place the chortis block adjacent to southern mexico in the late cretaceous and earlier time forming the tectonically disturbed southwestern tip of the north american plate this study assesses the relative motion between chortis and north america during the laramide orogeny later development of the north america caribbean plate boundaries we carried out paleomagnetic analysis of rotations and latitudinal displacement using a total of 90 sites from the atima limestone and the valle de angeles formation redbeds sampled at seven localities in honduras two secondary but ancient magnetizations post date late cretaceous folding at most localities the oldest magnetization is a chrm of high laboratory unblocking temperature in the redbeds 650 c and a moderate temperature in the limestones 500 600 c this component is wnw directed at five localities varying somewhat in declination having a consistent moderate positive inclination mean i 39 7 95 6 8 n 53 sites the age of the chrm is bracketed between 85 and 63 ma based on youngest zircon age and the age of a cross cutting dike an intermediate unblocking temperature component present in both units dec 146 2 inc 28 5 k 13 1 95 6 8 n 37 sites is interpreted as an overprint the chrm indicates an average counterclockwise rotation of 55 4 5 7 with respect to the expected direction the younger overprint was acquired between 50 and 15 ma its mean is also discordant with the expected north america direction implying some neogene rotation of chortis abundant late albian turonian zircons in valle de angeles redbeds explicitly require extending the laramide arc along western mexico into chortis a reconstruction of chortis south of mexico that takes into account 55 degrees of rotation shows a gap between both continental blocks at about 70 ma we propose a model where this gap formed by back arc extension creating the late cretaceous chontal basin at the southern termination of the laramide flat slab

paleohydrologic controls on soft sediment deformation in the navajo sandstone abstract many workers have noted the presence of contorted cross strata in the navajo sandstone and other ancient eolianites and have recognized their significance as indicators of sediment saturation during the accumulation history horowitz 1982 proposed a general model for the production of such features in ancient ergs by episodic seismically induced liquefaction of accumulated sand a key feature of that popular model is the prevalence of a flat water table characteristic of a hyper arid climatic regime during deformation under arid climatic conditions the water table is established by regional flow and liquefaction is limited to the saturated regions below the level of interdune troughs however various paleohydrological indicators from navajo sandstone outcrops point toward a broader range of water table configurations during the deformation history of that eolianite some outcrops reveal extensive deformation complexes that do not appear to have extended to the contemporary depositional surface these km scale zones of deformation affecting multiple sets of cross strata and grading upward into undeformed crossbeds may represent deep water table conditions coupled with high intensity triggers which produced exclusively intrastratal deformation such occurrences contrast with smaller scale complexes formed within the zone of interaction between the products of soft sediment deformation and surface processes of deposition and erosion the horowitz model targets the smaller scale deformation morphologies produced in this near surface environment this study examines the implications of a wet climatic regime for the horowitz deformation model it demonstrates how a contoured water table characteristic of humid climates may have facilitated deformation within active bedforms as well as in the accumulation intra dune deformation would enable deflation of deformation features during the normal course of dune migration more parsimoniously accounting for the frequent occurrence of erosionally truncated deformation structures in the navajo sandstone the production of such erosional truncations during bedform climb and aggradation of the accumulation and the dramatic fluctuations in the water table required to deposit dry eolian sand deform those deposits under saturated conditions and then dry the deformed sand to enable deflation

post paleozoic alluvial gravel transport as evidence of continental tilting in the u s cordillera the western united states contains three thin but remarkably widespread alluvial conglomeratic units that record episodes of large scale tilting across the u s cordilleran orogen in post paleozoic time these units are 1 the shinarump conglomerate of late triassic age exposed in northern arizona and adjacent parts of utah nevada and new mexico 2 lower cretaceous gravel deposits that overlie the morrison formation throughout the rocky mountain region and 3 the gravel rich parts of the miocene pliocene age ogallala group in western nebraska and adjacent southeastern wyoming paleoslopes of the rivers depositing these units were in the range of 10 24 to 10 23 based on paleohydraulic calculations however depositional thickness trends of these units are not sufficient to have generated such steep paleoslopes thus long wavelength tilting of the earth s surface must have occurred for these gravels to be transported although these units were deposited adjacent to large tectonic features including an evolving and migrating continental arc and for the ogallala group the northward propagating rio grande rift the tilting occurred over wavelengths too broad to be directly generated by these features these widespread gravel units attest to the interplay between the creation of subduction related isostatic and dynamic topography and continental sedimentation hence paleotopography as determined from calculated transport gradients of sedimentary deposits provides a

eocene sandstone intrusions in the tampen spur area norwegian north sea quad 34 imaged by 3d seismic data the eocene of the northern north sea is characterised by fine grained mudstones and isolated sandbodies three dimensional 3d seismic data reveal that the eocene mudstones are intensely deformed by polygonal faulting and contain numerous discordant amplitude anomalies the anomalies identified in the tampen spur area are similar to discordant anomalies previously described from the eocene in the south viking graben and the outer moray firth detailed mapping shows that the anomalies are often conical in three dimensions with dimensions ranging from 100 to 200 m height and a few hundred metres to a few kilometres lateral extent well calibrations show that the anomalies arise from sandstones tens of metres thick encased in mudstone the discordant amplitude anomalies are interpreted as large scale conical sandstone intrusions fed from deeper paleocene sandbodies individual conical intrusions may contain millions of cubic metres of sandstone and may provide fluid migration paths potential reservoirs and pose a drilling risk when exploring for deeper targets

geological and geophysical study of a thin skinned tectonic wedge formed during an early collisional stage the trasimeno tectonic wedge northern apennines italy the presence of a set of well known turbidite successions deposited in progressively e migrating foredeep basins and subsequently piled up with east vergence makes the northern apennines of italy paradigmatic of the evolution of deepwater fold and thrust belts this study focuses on the early apenninic collisional stage early miocene in age which led to the accretion of the turbidites of the trasimeno tectonic wedge ttw in the central part of the northern apennines based on the interpretation of previously unpublished seismic reflection profiles with new surface geology data and tectonic balancing we present a detailed tectonic reconstruction of the ttw in the study area the ttw is characterized by a w dipping shaly basal decollement located at a depth of 1 5 km the tectonic wedge is c 5 km thick at its central western part and tapers progressively eastwards to c 1 km the total shortening balanced along a 33 km long cross section is c 60 km including 20 km 40 of internal imbrication c 23 km of horizontal ene wards translation along the basal decollement and c 17 km of passive translation caused by the later shortening of footwall units deformation balancing constrained through upper aquitanian upper burdigalian c 21 16 ma biostratigraphy provides an average shortening rate of c 8 6 mm a 1 internal shortening of the ttw shows an average shortening rate of c 4 mm a 1 for this period

basement cover relations sevier orogenic belt northern utah precambrian crystalline basement and sedimentary cover rocks were deformed within a regional anticline in the wasatch range of northern utah during the cretaceous to early tertiary sevier orogeny this regional fold had a complex uplift and deformation history and is an imbricated ramp anticline that marks the transition to basement involved deformation large scale thrusting and folding within the basement cored anticline produced about 60 shortening and most of the slip on thrusts within the anticline was transferred into slip on frontal thrusts of the idaho utah wyoming thrust belt a network of ductile deformation zones ddz9s accommodated heterogeneous internal deformation of the basement and cleavage minor folds and vein arrays accommodated internal deformation of the sedimentary cover kinematics of internal deformation are consistent between basement and cover rocks in most areas and vary systematically with structural position recording early layer parallel shortening localized layer parallel shear and minor detachment of the cover and later fanning of structures during large scale folding ddz sets with opposite shear senses accommodated bulk coaxial flattening perpendicular to cleavage away from major thrust faults and ddz9s with consistent shear sense produced simple shear near major thrusts cleavage intensifies and refracts and minor folds tighten in the cover near major thrusts and glide horizons vein arrays record principal extension down the dip of cleavage minor extension parallel to the regional fold axis and differential displacements at high angles to fold axes slip on basement ddz9s produced about 5 to 20 bulk shortening subparallel to the basement cover contact shortening in the cover ranges from about 5 to 30 in most areas but reaches 65 near imbricate thrusts and along glide horizons reflecting heterogeneous simple shear principal extension is down the dip of cleavage and minor extension parallels local fold axes consistent with the geometry of mesoscopic structures

thrust timing growth of structural culminations and synorogenic sedimentation in the type sevier orogenic belt western united states most of the regional shortening in the type area of the sevier orogenic belt in central utah was accommodated by displacement on the canyon range neocomian aptian pavant aptian albian paxton cenomanian campanian and gunnison late campanian paleocene thrust systems inception of each thrust system generated synorogenic sediment associated with frontal thrust tip anticlines or triangle zones and older thrust sheets that were elevated above major ramps farther toward the hinterland the sevier culmination a large antiformal duplex cored by crystalline basement rocks developed during paxton and gunnison thrusting west of and structurally beneath the canyon range and pavant thrusts growth of the sevier culmination was coeval with reactivation of the canyon range and pavant thrust systems and produced a second culmination in proterozoic lower cambrian rocks in the canyon range these structural highs provided much of the sediment to the adjacent foreland basin from late cenomanian to late paleocene time and may have helped to maintain critical taper in the thrust belt