geometry and evolution of salt structures in a marginal rift basin of the gulf of mexico east texas the geometry and distribution of salt structures in the east texas basin shown in an isometric block diagram reveal that a minimum of 1 500 m of mid jurassic louann salt accumulated in a north northeast trending trough floored by thinned continental crust above a threshold thickness of 600 m salt was mobilized by 1 loading beneath a carbonate wedge 2 differential loading by prograding terrigenous clastics and 3 basin edge tilting and erosion salt structures evolved from salt pillows to active diapirs with maximum gross growth rates of 400 to 530 m m y each stage lasted 10 to 30 m y three generations of diapirs were successively activated in different areas by different forces

salt tectonics and tear faulting in the central part of the zagros fold thrust belt iran abstract the central part of the zagros fold thrust belt is characterized by a series of right lateral and left lateral transverse tear fault systems some of them being ornamented by salt diapirs of the late precambrian early cambrian hormuz evaporitic series many deep seated extensional faults mainly along n s and few along nw se and ne sw were formed or reactivated during the late precambrian early cambrian and generated horsts and grabens the extensional faults controlled deposition distribution and thickness of the hormuz series salt walls and diapirs initiated by the early paleozoic especially along the extensional faults long term halokinesis gave rise to thin sedimentary cover above the salt diapirs and aggregated considerable volume of salt into the salt stocks they created weak zones in the sedimentary cover located approximately above the former and inactive deep seated extensional faults the n s to nne ssw direction of tectonic shortening during the neogene zagros folding was sub parallel with the strikes of the salt walls and rows of diapirs variations in thickness of the hormuz series prepared differences in the basal friction on both sides of the precambrian cambrian extensional faults which facilitated the zagros deformation front to advance faster wherever the salt layer was thicker consequently a series of tear fault systems developed along the rows of salt diapirs approximately above the precambrian cambrian extensional faults therefore the present surface expressions of the tear fault systems developed within the sedimentary cover during the zagros orogeny although the direction of the zagros shortening could also potentially reactivate the basement faults as strike slip structures subsurface data and majority of the moderate large earthquakes do not support basement involvement this suggests that the tear fault systems are detached on top of the hormuz series from the deep seated precambrian cambrian extensional faults in the basement

anticline growth by shortening during crustal exhumation of the moroccan atlantic margin abstract it is unclear how the crustal scale erosional exhumation of continental domains of the moroccan atlantic margin and the excessive subsidence of its rifted domains affected the late jurassic early cretaceous post rift evolution of the margin to constrain the km scale exhumation we study the structural evolution of the jbel amsittene this anticline is located on the coastal plain of the moroccan atlantic margin and is classically considered to have been developed initially in the late cretaceous by halokinesis and by contraction during the neogene contrarily our structural analysis indicates that the anticline is a fault propagation fold verging north with triassic salts at its core and that it formed by shortening shortly after continental breakup of the central atlantic the anticline grew by nnw sse to nne ssw contraction as shown by syn tectonic wedges regional kinematic indicators and synsedimentary structures in upper jurassic to lower cretaceous rocks it grew further and tightened during the cenozoic presumably in relation to the atlas alpine contraction thus our data and interpretation suggest that tectonic drives salt in the anticline early growth which is coeval with the growth of other anticlines along the moroccan atlantic margin and widespread km scale exhumation farther onshore anticline growth due to shortening argues for intraplate far field stresses potentially linked to the geodynamic evolution of the african american and european plates

evolution of the ridges of midelt errachidia section in the high atlas revealed by paleomagnetic data new paleomagnetic data 43 sites from mesozoic sediments are contributed in this work verifying the presence of a pervasive syntectonic early cretaceous remagnetization in the easternmost area of the moroccan high atlas using the small circle intersection method we have calculated the characteristic remagnetization direction dec 337 3 inc 38 4 that fits with a 100 ma age according to the apparent polar wander path of africa the paleomagnetic vectors of remagnetization are used to obtain the geometry during the remagnetization stage 100ma of one of the most renowned geological cross sections of the high atlas the midelt errachidia profile the partial restoration of the cross section at 100ma allows us to determine the dips of the beds at the remagnetization stage in five structures ridges or anticlines our results indicate that the five ridges that configure the midelt errachidia profile were initiated to different degrees prior to wholesale compressive deformation during the cenozoic this configuration can be explained according to two different scenarios that we discuss in this paper transpression and diapirism the geological model obtained both at present and at 100ma indicates the existence of a mesozoic cover substantially decolled from the paleozoic basement what strongly contrasts with previously published transects of the same area

impact of basin structure and evaporite distribution on salt tectonics in the algarve basin southwest iberian margin abstract the sw iberian margin developed as a passive margin during mesozoic times and was later inverted during the mainly cenozoic alpine orogeny the initial syn rift deposits include a lower jurassic evaporite unit of variable thickness in the onshore this unit is observed to thicken basinward i e southward in fault controlled depocenters and salt related structures are only present in areas of thick initial evaporites in the offshore multiple salt structures cored by the lower jurassic evaporites are interpreted on seismic reflection data and from exploratory drilling offshore salt structures include the allochthonous esperanca salt nappe which extends over an area roughly 40 60 km the abundance of salt related structures and their geometry is observed to be controlled by the distribution of evaporite facies which is in turn controlled by the structure of rift related faulting this paper presents a comprehensive study of salt tectonics over the entire onshore and offshore sw iberian passive margin southern portugal and gulf of cadiz covering all aspects from initial evaporite composition and thickness to the evolution of salt related structures through mesozoic extension and cenozoic basin inversion

horizontal spatial correlation of hydraulic and reactive transport parameters as related to hierarchical sedimentary architecture at the borden research site 1 highly resolved data from the borden research site provide a unique opportunity to study the horizontal spatial bivariate correlation of hydraulic and reactive attributes affecting subsurface transport the data also allow quantitatively relating this correlation to the hierarchical sedimentary architecture of the aquifer the data include collocated samples of log permeability y the log of the perchloroethene sorption distribution coefficient and lithologic unit type the horizontal y and autosemivariograms and the y cross semivariogram have the same underlying correlation structure shape and range in the rise to a sill the common structure is not due to y point correlation or in unit spatial correlation the common structure is defined by how the proportion of lag transitions crossing different unit types i e the cross transition probability structure increases with increasing lag distance the common underlying cross transition structure contains two substructures with different correlation ranges corresponding to two scales of unit types within the sedimentary architecture for each substructure a large standard deviation in the length of units relative to the mean length gives rise to an exponential like shape and the proportions and mean length of units define the ranges the horizontal y spatial cross correlation is primarily defined by the larger scale substructure and the differences in mean and y between larger scale unit types

relationship between fluvial bounding surfaces and the permeability correlation structure results of three meter scale outcrop studies suggest a quantifiable relationship between fluvial bounding surfaces and the permeability correlation structure mapping of bounding surfaces and in situ measurements of permeability were obtained in three types of deposits a low energy channel deposit a paleosol and a high energy channel deposit for the low energy channel deposit only second order surfaces separating lithofacies were mapped the variogram exhibits anisotropic exponential behavior and an analysis of variance anova suggests that the within facies variation dominates over between facies variation the paleosol contained no internal bounding surfaces and exhibited a bellshaped variogram consistent with a smoothly varying style of heterogeneity both firstand second order bounding surfaces were mapped in the high energy channel deposit results of the anova suggest that the between facies variation dominates over the within facies variation a model of spatial correlation using superposition of independent processes acting over different scales provides a good fit to the data these three studies suggest that fluvial bounding surfaces provide a geological basis for conceptualizing and modeling heterogeneity in alluvial deposits

post miocene rifting and diapirism in the northern red sea abstract rifts and diapirs are the dominant structures in the bathyal zone of the northern red sea where commonly the diapirs ascend along normal faults associated with the rifts in this manner the diapirs form elongated features sometimes exceeding lengths of 30 km and widths of 4 km they also penetrate a sedimentary sequence about 1000 m thickness or less thicknesses generally considered to be barely adequate for the gravity conversion required to initiate diapiric motion we suggest that development of diapirs under these minimal overburden conditions was made possible by the high thermal gradients in the area resulting from the underlying attenuated continental crust and ascending mantle that prevail in the rift system of the northern red sea diapiric evolution was also dependent on the extensional tectonic regime with its numerous normal faults forming weaknesses along which the diapirs could move upwards

testing thin skinned inversion of a prerift salt bearing passive margin eastern prebetic zone se iberia abstract detailed geologic mapping combined with well and seismic data from the eastern prebetic zone se iberia reveal extensional and contractional structures that permit characterization of passive margin development and its incorporation into a thin skinned fold and thrust belt the study area is represented by nw directed ene trending folds and thrusts faults locally disrupted by the nw trending matamoros basin and the active jumilla and la rosa diapirs these structures resulted from the thin skinned inversion of the proximal part of the eastern south iberian passive margin containing prerift salt here upper jurassic to santonian thick skinned extension controlled the accumulation of sediment over mobile prerift salt this in turn defined the style of salt tectonics characterized by monoclinal drape folds suprasalt extensional faults and diapirs the structural and sedimentological analysis suggests that during extension salt localizes strain thus decoupling sub and suprasalt deformation thick skinned extension controls suprasalt deformation as well as its location and distribution which changes over time salt also localizes strain during inversion the preexisting salt structures weaker than adjacent areas preferentially absorb the contractional deformation in addition the stepped subsalt geometry that results from thick skinned extension also controls the shortening propagation therefore the degree of strain localization depends on the thickness of the suprasalt cover and on the dip of subsalt faults relative to the thin skinned transport direction

hydrogeologic facies models to delineate large scale spatial trends in glacial and glaciofluvial sediments recent interest in contaminant transport in ground water has led hydrogeologists to the conclusion that predicting the movement of solutes requires information on the distribution of spatial trends and heterogeneities in porous media description of spatial trends has long been of interest to sedimentologists who have produced a large body of geologic information on the subject in this paper facies models are used to construct conceptual models of hydrogeologic facies for glacialmeltwater stream sediment and till these hydrogeologic facies models which delineate large scale trends in heterogeneity are appropriate for use in designing hydrogeologic field tests and for estimating input to regional ground water flow and transport models this paper treats each facies as a homogeneous anisotropic hydrogeologic unit the models presented herein conceptualize the hydrogeologic relationships among facies and illustrate one method of converting the apparent chaos in nature into an orderly system that can be tested scientifically and modeled mathematically the principles used to create conceptual models of hydrogeologic facies for the types of sediment considered in this paper can be extended to other sedimentary environments it should be recognized however that such models do not address the small scale heterogeneity present within individual facies additional basic research is required to measure hydraulic conductivity variation within representative hydrogeologic facies and to develop statistical descriptions to represent the variations such detailed descriptions of hydraulic conductivity may be necessary to describe ground water flow at a local scale for analysis of contaminant transport

diapiric growth within an early jurassic rift basin the tazoult salt wall central high atlas morocco the central high atlas morocco constitutes a diapiric province that hosts a complex array of elongated diapirs and minibasins that formed during the lower jurassic rift of the atlas basin this paper aims to study the structure and growth evolution of the tazoult diapiric wall located in the central high atlas by means of structural and sedimentological fieldwork integrated with remote sensing mapping the tazoult salt wall is a 20 km long x 3 km wide ne sw trending ridge that exposes upper triassic red beds and basalts along its core the succession flanking the salt wall ranges from hettangian to bajocian ages displaying spectacular sedimentary wedges in the se and nw flanks the hettangian early sinemurian carbonates mainly crop out as blocks embedded in the core rocks the 1 km thick pliensbachian platform carbonates display large subvertical flap structures along the flanks of the tazoult salt wall with unconformities bounding tapered composite halokinetic sequences in contrast the 2 5 km thick late pliensbachian aalenian mixed deposits form tabular composite halokinetic sequences displaying small scale hook halokinetic sequences passive diapirism resulted in the lateral extrusion of the evaporite bearing rocks to form an allochthonous salt sheet towards the adjacent se amezrai minibasin the bajocian platform carbonates partially fossilized the tazoult salt wall and thus constitute a key horizon to constrain the timing of diapir growth and discriminate diapirism from alpine shortening the pliensbachian carbonate platform evolved as a long flap structure during the early growth of the tazoult salt wall well before the onset of the alpine shortening

style of atlassic tectonic deformation and geodynamic evolution of the southern tethyan margin tunisia the structure of the southern atlas fold and thrust belt of tunisia was investigated using new geologic mapping seismic reflection data together with the construction of a balanced cross section the structural architecture of the tunisian foreland consists in a mixed tectonic style with deep seated basement faults shallower decollements within sedimentary cover and salt diapirism the restoration of the cross section shows a surface shortening of 8 1 km similar to 7 3 sequential restoration of the balanced cross section has been permitted to decipher the structure and evolution of the southern tethyan margin of tunisia structural geometry and orientation of the pre existing permian to cretaceous extensional structures controlled subsequent contractional deformation within the sedimentary cover during the shortening this inherited tectonic framework controlled the development of ene trending thrust related anticlines such as the orbata and chemsi structures nw trending lateral ramp such as the gafsa and fejej faults and diapir structures as the beidha anticline the inversion of the margin can be correlated with the onset of the convergence between africa and eurasia the first phase of the orbata thrusting growth might occur in late cretaceous continuous inversion of the margin occurred during the eocene and mainly during the late miocene to present day this study underlines the predominant role of inherited basement structures acquired during the evolution of the southern tethyan margin and their influence on the geometry of the atlassic thrust belt this structural analysis provides new perspectives for future hydrocarbon exploration in this poorly explored region c 2015 elsevier ltd all rights reserved

diachronous folding and cleavage in an intraplate setting central high atlas morocco determined through the study of remagnetizations abstract remagnetizations are common in intraplate basins when remagnetizations occur at an intermediate stage between different tectonic processes they can be used for paleo geometrical reconstructions and relative dating of different structures this has a particular interest in geological frameworks where other geological time markers are absent in order to apply this methodology it is necessary to calculate the regional remagnetization direction and subsequently to use this reference direction to restore the attitude of the beds at the moment of remagnetization acquisition in this work we use this methodology for dating a pervasive cleavage whose time of formation is controversial and the associated structures in the central high atlas morocco paleomagnetic directions from 64 sites were used to calculate the remagnetization direction d 330 9 i 35 1 a n 6 107 which is coincident with the albian cenomanian ca 100 m a expected direction for nw africa this direction was used to restore the mesozoic paleo geometry of beds allowing us to analyze bedding orientation cleavage and folding relationships between the present day and the cretaceous geometry after restoration we conclude that the development of cleavage post dates remagnetization being in relation with cenozoic basin inversion however the paleo geometry shows incipient folds at cretaceous times which can be related to an intra mesozoic compressional event

a new method for analysis of variance of the hydraulic and reactive attributes of aquifers as linked to hierarchical and multiscaled sedimentary architecture this technical note presents a useful methodology for studying how the variance of hydraulic and or reactive attributes of an aquifer are linked to the multiscaled and hierarchical sedimentary architecture of the aquifer a new recursive equation is derived which quantitatively describes how the variance is related to sedimentary facies defined at all scales across an entire stratal hierarchy as compared to prior published equations that emphasize differences in means among facies populations within a hierarchical level it emphasizes differences across levels because of the hierarchical relationships among the terms of the equation we find it to be useful for conducting a holistic analysis of the relative contributions to the variance arising from all facies types defined across all scales the methodology is demonstrated using appropriate field data and is shown to be useful in defining parsimonious classification systems

halokinesis and structural evolution of the major features in eastern and southern tunisian atlas abstract the eastern and southern tunisian atlas is marked by the presence of three major faults the n s axis fault the nw se gafsa fault and the e w northern chott fault seismic lines crossing these structures show the existence of significant halokinetics that began in the early jurassic the aim of this paper is to study and better understand the triassic salt movements which are mainly linked to periods when the major basement faults were reactivated resulting in extension compression transtension or and transpression analysis of the seismic data allows us to conclude that the triassic salt migration started in the early jurassic and continued during the late jurassic and the early cretaceous although these periods are characterized by an extensional tectonic regime the synsedimentary halokinesis is accompanied by thickening and thinning of the overlying series salt remobilization was accentuated during the compressional deformation which occurred from the late tertiary to quaternary and resulted in local diapiric extrusions along the major structural features

using high resolution electrical resistivity to estimate hydraulic conductivity and improve characterization of alluvial aquifers abstract shallow alluvial aquifers are important local and regional water resources but obtaining sufficient hydrogeologic data to properly characterize their spatial extent and hydraulic conditions can often be difficult time consuming and expensive in this study we used over 40 000 measurements of electrical resistivity tomography ert data and hydraulic conductivity k data from 33 pump tests across eight shallow alluvial and glacial outwash aquifer field sites in iowa to 1 assess the relation between hydraulic k tests and electrical resistivity er in alluvial and glacial outwash systems and 2 evaluate the application of the er k relationship as input data for local scale groundwater flow modeling average field measured k across the eight sites was 95 m day and ranged from 29 to 246 m day whereas aquifer resistivity ranged from 27 to 896 ohm m both k and er were greater at the glacial outwash aquifer sites compared to the alluvial aquifer sites and a linear relationship r2 0 90 was observed between field measured k and er when incorporating all field sites we evaluated how k derived from the er k relationship compared to k estimated from pump tests and calibrated k in a local scale groundwater flow model the k estimated by the er k relationship was comparable to the k estimated from the pump tests in terms of providing reasonable values for model development utilizing the er k relationship to estimate k would save significant time compared to conducting pump tests hence estimating k from electrical resistivity can provide a non intrusive cost and time efficient way to evaluate and model alluvial aquifers

mesozoic evolution of nw africa implications for the central atlantic ocean dynamics the central atlantic ocean opened during the early jurassic and represents the oldest portion of the atlantic ocean although the american margin has been well studied the onshore evolution of its african counterpart is poorly understood we investigated the evolution of a c 1300 km transect across the reguibat shield morocco mauritania algeria in the northern west african craton using low temperature thermochronology fourteen samples were dated using apatite fission track analysis nine of these samples were also dated using u th sm he analysis fission track ages range from 118 10 to 497 61 ma with mean track lengths between 11 2 0 4 and 12 5 0 2 m u th sm he single grain ages range from 32 3 to 396 32 ma through forward and inverse thermal modelling we demonstrate that the craton underwent kilometre scale exhumation between the early middle jurassic and the late cretaceous based on our new results published data on nw africa and data from the conjugate eastern north american passive margin we show that this post rift early middle jurassic to early cretaceous exhumation affected both margins to a similar areal extent and simultaneously transient mantle dynamic support is suggested to account for the major erosional phase recorded on both margins supplementary material the method for thermal modelling the thermal modelling for all samples and the relationship between apatite chemistry and u th he ages are available at https doi org 10 6084 m9 figshare c 3770918

architecture of the sierra ladrones formation central new mexico depositional controls on the permeability correlation structure statistical models of hydrogeological heterogeneity are often used in aquifer and reservoir characterization the number of data required to estimate objectively the spatial correlation structure of permeability however is often prohibitive the objective of this study was to develop a better understanding of how information about depositional processes can be used to characterize hydrogeological heterogeneity an outcrop of the fluvial interfluvial sierra ladrones formation of new mexico was studied for this purpose on the basis of previous studies of paleogeography and our own field observations deposits of the sierra ladrones formation are interpreted as marginal ancestral rio grande flood plain and tributary deposits architectural elements were mapped over a 0 16 km sup 2 peninsular outcrop of pliocene pleistocene deposits of the central albuquerque basin geostatistical analysis of the architectural element map data indicates non orthogonal anisotropy in the horizontal direction the orientations of the strongest n30 degree w and weakest n90 degree e correlation correspond to the orientation of the tributary system and the ancestral rio grande flood plain respectively in the vertical direction the correlation structure exhibits exponential behavior corresponding to the average element thicknesses the results demonstrate that information about depositional environment can be used to help to quantify statistically subsurface heterogeneity 28 refs 9 figs 1 tab

spatial variability in river sediments and its link with river channel geometry 1 this study explores the link between spatial variability within fluvial sedimentary strata and river channel geometry this link is then used to determine the macrodispersion coefficients for solute transport in groundwater flow in river deposits in doing that we combine concepts from sedimentology geostatistics and the stochastic lagrangian theory of subsurface transport it is proposed to analyze the spatial variability of river sediments in terms of transition probabilities the transition probabilities can be determined from the averages and variances of the lengths of stratasets and their volumetric fractions using concepts developed by carle and fogg 1996 and ritzi 2000 strataset length scales are shown to correlate well with the geometry of the river channel and its bed forms and can be determined indirectly from aerial photogrammetry and more directly through surface ground penetrating radar surveys stratal dimensions can also be related using lagrangian transport analysis to macrodispersivity of subsurface transport this allows relationships between the geometry of river channels and subsurface transport parameters of associated fluvial deposits for demonstration the longitudinal macrodispersivity in a compound bar deposit in the gravelly braided sagavanirktok river was investigated

emplacement and deformation of mesozoic gabbros of the high atlas morocco paleomagnetism and magnetic fabrics a paleomagnetic and magnetic fabric study is performed in upper jurassic gabbros of the central high atlas morocco these gabbros were emplaced in the core of preexisting structures developed during the extensional stage and linked to basement faults these structures were reactivated as anticlines during the cenozoic compressional inversion gabbros from 19 out of the 33 sampled sites show a stable characteristic magnetization carried by magnetite which has been interpreted as a primary component this component shows an important dispersion due to postemplacement tectonic movements the absence of paleoposition markers in these igneous rocks precludes direct restorations a novel approach analyzing the orientation of the primary magnetization is used here to restore the magmatic bodies and to understand the deformational history recorded by these rocks paleomagnetic vectors are distributed along small circles with horizontal axes indicating horizontal axis rotations of the gabbro bodies these rotations are higher when the ratio between shales and gabbros in the core of the anticlines increases due to the uncertainties inherent to this work the igneous bodies recording strong rotations interpretations must be qualitative the magnetic fabric is carried by ferromagnetic s s minerals mimicking the magmatic fabric anisotropy of magnetic susceptibility ams axes using the rotation routine inferred from paleomagnetic results result in more tightly clustered magnetic lineations which also become horizontal and are considered in terms of magma flow trend during its emplacement nw se parallel to the general extensional direction in the western sector and ne sw parallel to the main faults in the easternmost structures

radial gravitational gliding on passive margins abstract gravitational gliding of uppermost sediments down a passive margin is possible if there is a basal layer of evaporite or other soft material to allow detachment in examples from the gulf of mexico and the brazilian margin gliding has produced three main structural domains an uppermost domain of downdip extension an intermediate domain of rigid gliding and a lowermost domain of downdip contraction domain boundaries are established by changes in slope in this paper we examine three kinds of gravitational gliding depending on the paths followed by material particles in ideal parallel gliding particle paths are parallel straight lines trending downslope this should occur where the margin is perfectly straight in ideal radial gliding particle paths are radii of a circle and the margin is shaped like a circular cone natural margins will not have ideal shapes but divergent gliding will tend to occur off coastal salients convergent gliding off coastal re entrants a simple kinematic model based on ductile behaviour illustrates some essential features of radial gliding changes in radius during divergent gliding produce strike parallel extension during convergent gliding they produce strike parallel contraction vertical strains also differ divergent gliding produces an uppermost domain of strong vertical thinning balanced by extensions in all horizontal directions similarly convergent gliding produces a lowermost domain of strong vertical thickening balanced by contractions in all horizontal directions these deformed states cannot be restored by simple techniques based on section balancing we have done three experiments using analogue materials sand to model the brittle behaviour of sediments silicone putty to model the ductile behaviour of basal layers of evaporite the experiments were properly scaled to account for gravitational forces experiment i reproduced convergent gliding above a basement with a conical upper surface strike parallel contraction was responsible for radial folds on the lower slopes the lowermost domain had a complex fold pattern indicating contraction in all horizontal directions experiment 2 reproduced divergent gliding above a basement with a pyramidal upper surface strike parallel extension produced radial rifts on the upper slopes the uppermost domain had a complex polygonal pattern of normal faults indicating extension in all horizontal directions experiment 3 also reproduced divergent gliding but due to non uniform sediment thickness we have examined the many seismic profiles both downdip and alongstrike available for the brazilian margin alongstrike profiles show structures which we attribute to strike parallel strains around the santos re entrant syn sedimentary growthfolds indicate strike parallel contraction increasing downslope this argues for a mechanism of convergent gliding in contrast around the campos salient normal growth faults and associated salt rollers indicate strike parallel extension decreasing downslope this argues for a mechanism of divergent gliding the pattern of oil fields in the campos area including the giant marlim field seems to be closely controlled by divergent gravitational gliding and associated processes radial gliding should occur on other passive margins as well especially where the coastline is sinuous structures around the western gulf of of mexico seem to indicate convergent gliding at the scale of the entire gulf structures at a smaller scale around the mississippi delta seem to indicate divergent gliding

extensional vs compressional deformation in the central high atlas salt province a paleomagnetic approach abstract in this paper we address the problem of the distinction between diapiric salt driven and compressional structures using the outstanding example of the central high atlas morocco a remagnetized component carried by magnetite has been isolated in 32 new paleomagnetic sites it is characterized by maximum unblocking temperatures around 450 c syn folding behavior and normal polarity these 33 mean paleomagnetic directions were analyzed together with other 68 from published works around the study area to construct a robust paleomagnetic dataset along a cross section perpendicular to the main structures the remagnetization direction n 100 dec 332 2 inc 34 5 6 2 2 0 a n 6 427 and the paleo dip of beds the attitude of the beds at the remagnetization occurrence were calculated through small circle methods the remagnetization can be dated as ca 100 ma because of its occurrence between the extensional and compressional periods this remagnetization offers the possibility of restore the basin to its pre inversion geometry comparison between present day and pre inversion structure allows discriminating three different evolutionary patterns i thrusted and welded salt walls mainly structured during the extensional stage ikkou ridge with steep limbs close to the salt wall core ii jurassic salt walls with weaker deformation restricted to the areas adjacent to the structure tadaghmamt and timedouine in this case cenozoic compression is limited to welding of the salt walls and buttressing of the sedimentary sequences against faults iii salt rollers gently initiated during the jurassic toumliline diapir thrusted during the cenozoic compression results show the importance of salt tectonics both during extension and compression as well as the control of the compressional features by the inherited extensional structures the performed restorations prove that paleomagnetism is a useful independent tool to obtain palinspastic restorations and to separate and quantify the imprint generated during the basinal stage from the inversional features

sequence of thrusting and syntectonic sedimentation in the eastern sub atlas thrust belt dades and mgoun valleys morocco a series of balanced cross sections across the sub atlas thrust belt and the northern ouarzazate basin are used to illustrate the structural geometry and the timing of deformation at the southern front of the high atlas mountains of morocco the selected area is among the best sedimentary records of mountain building of the entire orogenic system the study of the relationships between thrusts and synorogenic continental formations enables the unraveling of kinematic sequences and the proposal of a relative chronology of deformation active thrusting in the area occurred in a rather continuous fashion from the oligocene to the pliocene punctuated by a major erosional phase imprecisely placed in late oligocene to early miocene times detrital sedimentary facies indicate that uplift in the hinterland of the high atlas to the north of the sub atlas belt was taking place already by mid eocene times although it might have commenced locally even earlier within the sub atlas zone the exposed faults did not propagate in a simple piggy back fashion but show evidence of a complex synchronous sequence with events of fault reactivation and out of sequence thrusting

halokinetic sequences and diapiric structural kinematics in the field two day excursion to la popa basin northeastern mexico exposures of salt diapirs and flanking strata in la popa basin in the mexican states of nuevo leon and coahuila contain world class examples of salt sediment interaction that provided the basis for the concept of halokinetic sequences the basin also contains one of the first secondary salt welds described in outcrop the two day field trip described here provides an easily accessible overview of salt sediment relations within a short distance of monterrey the capital city of nuevo leon the first day constitutes an introduction to basin stratigraphy a traverse through halokinetic sequences at el papalote diapir and visits to the cretaceous paleogene boundary bed and a salt cored detachment fold near the town of hidalgo north of monterrey the second day is a visit to la popa salt weld where stops at several parts of the weld permit comparison of different structural styles developed along the weld the trip begins and ends at the marriott courtyard hotel near the monterrey airport

timing and duration of the central atlantic magmatic province in the newark and culpeper basins eastern u s a abstract new major and trace element data and 40ar 39ar plateau ages constrain the timing duration and time related geochemical evolution of the central atlantic magmatic province in the u s a newark and culpeper basins and refine correlations with basaltic lava flows from other late triassic early jurassic circum atlantic basins the precise statistically robust 40ar 39ar plateau ages were obtained on biotite and on fresh plagioclase and calculated using the latest 40k decay constants these ages are supported by a general consistency of the ca k calculated from 37ar 39ar of the plateau steps and the ca k obtained by detailed electron microprobe analyses on plagioclase phenocrysts the ages of five analyzed basalt lava flows from all three lava flow units in the newark basins and the ages of two sill samples are indistinguishable indicating a brief magmatic peak phase at 201 8 0 7 ma recalibrated 40ar 39ar plateau ages from the entire province indicate a near synchronous onset and peak volcanic activity at the triassic jurassic boundary within the circum atlantic basins from the u s a canada and morocco the early erupted magmas moroccan lower to upper basalts the fundy basin north mountain basalt and orange mountain and equivalent u s a flows yield an enriched geochemical signature e g with relatively high la yb whereas late magmas in the u s a hook mountain and hampden basalts and morocco recurrent basalt yield relatively depleted geochemical compositions low la yb a slight but significant age difference for eruption of hook mountain and hampden basalts 200 3 0 9 ma and recurrent basalts 198 2 1 1 ma is interpreted as evidence of a diachronous northward rift drift transition during break up of pangea our data indicate also a prolonged intrusive sequence that continued until about 195 ma at the palisades sill and is consistent with sporadic late camp magmatism for dykes from the south eastern u s a and for intrusions from guinea

the effect of dust radiative heating on low level frontogenesis abstract severe dust storms frequently occur over northwestern china during spring they are often associated with strong fronts in this paper numerical simulations are performed to examine the effect of dust radiative heating on surface frontogenesis the absorption and multiple scattering of the dust are included in an atmospheric radiation scheme a two dimensional primitive equation model with 20 levels in the vertical is used for idealized simulations after a 12 h integration a strong narrow front zone is created below 650 mb the horizontal potential temperature gradient reaches 6 k 100 km 1 which is three times as large as that in the initial data a direct vertical transverse circulation is established along the frontal zone which is qualitatively similar to the observations the results show positive interaction between low level frontogenesis and dust radiative heating the adiabatic frontogenesis forcing is enhanced by the feedback of the dust radiative heating these results suggest tha

characterizing the heterogeneity and correlation of perchloroethene sorption and hydraulic conductivity using a facies based approach a facies based approach was used to delineate both geochemical and physical aquifer property heterogeneity specifically the parameters considered were the sorption coefficient kd for a model organic contaminant and hydraulic conductivity k inferred from the particle size distribution subfacies sized samples were analyzed for both tetrachloroethene kd and k in a vertical core of the borden aquifer both parameters were correlated with the six sedimentary facies identified within the vertical core as a consequence of their relations to sedimentary facies significant positive correlations between ln k and ln kd which were different from the core scale correlation and different from each other were identified for some facies fades specific correlations generally resulted in improved statistics i e higher correlation coefficients and reduced confidence intervals compared to the core scale correlation the results suggest that a facies based approach can be useful in characterizing the heterogeneity of the transport properties of sedimentary aquifers

upscaling of reactive mass transport in fractured rocks with multimodal reactive mineral facies 1 this paper presents a methodology for upscaling matrix material transport parameters in fractured flow dominated systems with multimodal reactive mineral facies the upscaling method provides a theoretical and practical link between controlled experimental results at the laboratory bench scale and multikilometer field scales at which contaminant remediation and risk assessment are actually conducted as sorption reactions in matrix are in part determined by mineral properties a new conceptual model is developed to reflect the hierarchical structure of reactive mineral facies at the microform mesoform and macroform scales the conceptual model of hierarchical reactive matrix mineral facies is integrated with a dual porosity model for simulating diffusion of solutes out of fractures and sorption onto the matrix minerals by assuming that sorption reactions primarily occur in the rock matrix we develop a multimodal spatial random function for characterizing both the tortuosity physical heterogeneity and sorption coefficient chemical heterogeneity at different scales in the rock matrix the effective tortuosity at the field scale is derived by volume averaging of mass transfer coefficient for a conservative species subsequently using a sorbing species e g uranium we derive the equations for upscaling the sorption coefficients in a saturated fractured rock system for field scale simulations the effective field scale tortuosity and sorption coefficient are related to their mean variance integral scale and domain size along a pathway through a three dimensional flow field the upscaled values increase with the integral scale and are larger than their geometric mean simulations conducted with upscaled sorption coefficients and tortuousities are compared very well with high resolution monte carlo simulations capturing the parameter spatial variations results of this study can be extended to explore scaledependenceofotherimportant transportparametersforfractured rocksolutetransport citation deng h z dai a wolfsberg z lu m ye and p reimus 2010 upscaling of reactive mass transport in fractured rocks with multimodal reactive mineral facies water resour res 46 w06501 doi 10 1029 2009wr008363

halokinetic sequences in carbonate systems an example from the middle albian bakio breccias formation basque country spain in diapir flanks unconformity bounded sedimentary packages associated with gravity driven deposits controlled by the ratio between the rates of sediment accumulation and diapir growth can be interpreted in the context of halokinetic sequences the bakio breccias formation basque country spain corresponds to redeposited carbonate deposit that developed in response to the bakio diapir growth during the middle albian these deposits provide on of the rare documented example of carbonate dominated halokinetic sequences the bakio breccias formation consists of an alternation of clast and matrix supported breccias calcirudite calcarenite and marl deposited along the flanks of the diapir the description and the analysis of the bakio breccias formation lead to a new model for carbonate dominated halokinetic sequences these sequences differ from their siliciclastic counterpart because sediment accumulation rate is controlled by carbonate platform growth on the topographic relief top of the diapirs while sediments are preferentially deposited in the mini basins adjacent of the diapirs in siliciclastic settings during transgressive system tract carbonate platform are able to keep up with the sea level rise and to aggrade on top of the diapirs forming thick and resistant roof which is assumed to limit the diapir growth and thus to favour the development of halokinetic sequences with low angle unconformities wedge halokinetic sequences during late highstand system tract deposition and lowstand system tract if present platform progradation results in high sediment accumulation in the adjacent depocenters loading the autochthonous salt layer and promote diapir growth and creation of topographic relief in addition if the diapir roof reaches emersion karstification of the carbonate platform top may also favour roof destruction and diapir growth depending on the thickness of the roof developed previously and the amplitude of the sea level fall the halokinetic sequences with the emersion and the karstification of the carbonate platform may display high angle unconformities hook halokinetic sequences furthermore gravity driven deposits are assumed to be more common in carbonate dominated halokinetic sequences compared to their siliciclastic counterparts since carbonate platform aggradation creates steep slopes on the diapir margins leading to the partial collapse of the margin even when limited diapir growth occurs the carbonate dominated halokinetic sequence model proposed here is an important tool for the prediction of potential reservoir distribution seal and hydrocarbon migration in flanks of salt diapirs where carbonate platform developed

magnitude of rift related burial and orogenic contraction in the marrakech high atlas revealed by zircon u th he thermochronology and thermal modeling the atlas of morocco is a continental rift developed during the triassic jurassic and moderately inverted during the cenozoic the high atlas south of marrakech with exposures of basement and triassic early syn rift deposits has been viewed as a high during the mesozoic rifting first zircon u th he ages and thermal models obtained from 42 samples in the marrakech high atlas following two nnw sse transects across the mountain belt reveal that in contrast to previous models the triassic jurassic rift was well developed in the marrakech high atlas with more than 4 5 6 km of rift related deposits mid jurassic early cretaceous zhe cooling ages obtained indicate that rift related subsidence in the marrakech high atlas finished in the mid jurassic and was followed by a period of exhumation where 2 3 km of rock were eroded thermal models from zhe data provide the first thermochronologic clue for a late cretaceous initiation of the atlas compression driven exhumation in the inner parts of the marrakech high atlas the triassic jurassic basin reconstruction assisted by thermochronology highlights a key role of inherited basement anisotropy in rift orientation and evolution and on its subsequent inversion comparison of present day and restored sections to the rifting stage aided by thermochronology suggests minimum values of total orogenic shortening in the marrakech high atlas of 13 to 14 km 21 to 17 with exhumation of 1 to more than 5 km of rocks similar zhe ages on both sides of the tizi n test fault evince minor vertical movements along the fault during the atlas orogeny

use of sedimentological information for geometric simulation of natural porous media structure a geometric simulation method was used to develop a three dimensional highly detailed synthetic representation of point bar sediments in the wabash river system geometric simulation methods in comparison to well known second order stochastic methods offer the advantage of being more closely related to depositional processes which are often similarly conceptualized i e described in terms of shapes of discrete bed forms trends in grain size and spatial relationships of defined geologic facies multiple scales of geometric variation were defined within a sedimentologically prescribed framework and shapes of discrete geometric elements were established at each scale the selected shapes were based on published field studies including sedimentological bed form studies and trench studies in active point bar sediments the parameterization of the shapes allowed for random variability of the shape descriptors discrete shapes were then generated and assimilated by computer hydraulic conductivity values were assigned to the discrete elements based on reports of observed variations in grain size and field measurements of hydraulic conductivity the synthetic model referred to as a numerical aquifer is being used as the basis for extensive numerical experimentation to study the relationship between natural spatial structure and subsurface flow and transport

loule the anatomy of a squeezed diapir algarve basin southern portugal the loule salt diapir grew through the jurassic and early cretaceous when tight subvertical curtain folds were developed it was then squeezed during the alpine orogeny in the oligocene and miocene this produced an intense array of brittle faults veins and brittle ductile shear zones through most of the diapir the diapir exhibits more localized shear and brittle structures than any other previously described diapir the most unusual deformation structures are streaky shear vein zones a new term with an average spacing of 1 5 m and usually less than 30 cm wide they consist of a central coarse grained halite vein surrounded by parallel zones of wispy discontinuous shale streaks and recrystallized halite a new mechanism is proposed for the development of these zones where repeated pulses of fluid flow have caused extensive halite recrystallization and streaking out of unlithified mud intercalated with crystalline halite this explains the formation of wide zones of well aligned mud streaks now lithified to shale but with only small amounts of simple shear offset observed across these zones

subsidence history in basins of northern algeria abstract the tellian foreland in algeria represents a part of the southern tethyan margin during the mesozoic its tectonic evolution includes a rifting stage during the triassic and liassic times characterised by tilted blocks and early diapiric events during the liassic a post rift regime from middle jurassic up to the late cretaceous and basin inversion during the tertiary related to the african and european plates convergence the subsidence modelling supported by surface and subsurface data integration emphasises different subsidence phases 1 liassic subsidence phase under tethyan and atlantic control related to crustal thinning 2 late jurassic cretaceous and tertiary subsidence phases where the first one is linked to diapiric events and the second in eastern algeria to the effects of the rifting event developed more easterly in the gulf of gabes and sirte the last one is flexural and occurs in foreland basins during the tertiary taking into account the subsidence record of each structural domain a correlation between tectonic events and the subsidence phases can be established

spatial distributions of perchloroethylene reactive transport parameters in the borden aquifer 1 we determined the descriptive statistical and spatial geostatistical properties of the perchloroethene ln kd and the ln k of a 1 5 m thick by 10 m horizontal transect of the borden aquifer near the location of the stanford waterloo sw tracer experiment the ln kd distribution is not normal and is right skewed because of a few high values that occur localized in two regions of the transect in contrast the ln k data can be characterized by a normal distribution a linear regression of ln kd on ln k yields a statistically significant positive correlation also shown at small lags in the cross correlogram no significant vertical or horizontal trend in the ln kd data was detected the semivariogram ranges of ln k and ln kd differ from one another in the vertical direction 0 33 0 06 m and 0 20 0 04 m respectively and are much less than the horizontal ranges a few meters despite significant effort the horizontal range of ln kd remains poorly characterized because of limitations of the sample locations many of the characteristics described above do not match those assumed in prior theoretical studies that examined the importance of various aquifer characteristics on sw tracer transport we suggest that there is knowledge to be gained by revisiting the conclusions of these prior studies in light of the new information presented here

syn to post rift diapirism and minibasins of the central high atlas morocco the changing face of a mountain belt the atlas mountains are classically regarded as a failed mesozoic rift arm subject to alpine inversion folding and thrusting here we present new integrated structural and sedimentological studies that have revealed numerous early middle jurassic diapiric ridges and minibasins characterized by distinctive halokinetic structures diachroneity in halokinesis is observed across the central high atlas waning first in the sw during the early middle jurassic jbel azourki and tazoult ridges and continuing to late middle jurassic towards the ne imilchil region the halokinetic structures are readily differentiated from the effects of later alpine deformation allowing a new picture of the central high atlas to emerge the most pervasive deformation in the central high atlas is associated with early middle jurassic diapirism whereas the impact of alpine inversion is mostly focused at the basin margins this new understanding helps explain previously problematic aspects of the atlas mountains which we now recognize as an exceptionally well exposed natural laboratory for understanding the interactions between halokinesis tectonics and sedimentation

new evidence of xiphosurids from the middle jurassic of morocco palaeoenvironmental palaeoecological and palaeobiogeographical implications abstract horseshoe crabs chelicerata xiphosura from mesozoic deposits are extremely rare in the fossil record of the african continent here we report new evidence of the occurrence of xiphosurans in north africa these are horseshoe crab traces including the ichnogenera kouphichnium repichnia and selenichnites fodinichnia and or domichnia which have been discovered in middle jurassic strata of the imilchil area central high atlas morocco they are preserved on upper and lower bed surfaces of sandy limestones and marls in the upper parts of the tislit and imilchil formations late bajocian early bathonian the selenichnites traces measuring up to 30 cm in width co occur with theropod and birdlike tracks the reported kouphichnium is the first record from mesozoic deposits of morocco while selenichnites is the second occurrence in jurassic strata of africa these ichnogenera evidence different behaviour of horseshoe crabs i e selenichnites is the result of burrowing activity when searching for food in the sediment and kouphichnium is a regular locomotion trace left on the sediment surface occasionally leaving an impression of the telson the combination of sedimentological data and ichnological analysis indicates a shallow water subtidal depositional environment preceding the bathonian regression of the atlas domain palaeobiogeographically the discoveries indicate the presence of horseshoe crabs at the southern margin of the tethys furthermore they enhance our knowledge of their previously scarcely documented distribution in gondwana during the mesozoic

submarine salt glacier of northern tunisia a case of triassic salt mobility in north african cretaceous passive margin stratigraphical sedimentological and structural data and a bouguer gravity map of medjez el bab meb in northern tunisia are used to illustrate a cretaceous example of salt extrusion on a passive continental margin located just south of the teboursouk thrust front a preferential decollement surface used by the continuous tertiary shortening in this area the meb structure is a simple n40 e box anticline removing the two tertiary foldings eocene and miocene leads to the exposure of the original feature of a simple submarine salt glacier the triassic salt rocks appear as an albian interstratified body between two cretaceous series with stratigraphic normal polarity suggesting a bedding parallel extrusion at the sediment water interface of the triassic salt in cretaceous times the formation of such salt extrusions are associated with extensional faulting probably both in the cover and basement the presence of a slope and basinwards salt flow this scenario is similar to the allochthonous salt described in other salt provinces characterizing passive margins

syncline topped anticlinal ridges from the high atlas a moroccan conundrum and inspiring structures from the syrian arc israel introductionfold and thrust belts usually resultfrom superimposed folding episodes classical examples are those of theexternal western alps lemoine 1972 and provence areas in sefrance andreani et al 2010 withreferences therein where the early late cretaceous eocene folds werepartly eroded before being reactivatedby the neogene shortening event insuch classical examples early anti clines are converted into tighter anti clines or thrusts whereas latesynclines develop above early ones alonso 1989 demonstrated theoreti cally that the reactivation of exuralfolds and exural slip folds below anunconformity produces folds of thesame sense of curvature in layersabove and below the unconformity in contrast the high atlas belt o ersthree stunning examples of perchedsynclines developed on top of narrowanticline hinges in the imilchil areaeast of marrakech fig 1 all theseperched synclines correspond toupper palaeocene lower eoceneformations overlying tight elongatedanticlinal ridges made up of mesozoicrocks fig 2 these anomalous struc tures termed herein syncline toppedanticlinal ridges stars dependclearly on superimposed foldingevents as the layers forming theperched synclines overlie unconform ably the oldest formations of theanticline why the tertiary depositsdo not occur within the wide lowelevation synclines next to the tight culminating anticlines but only occurover the eroded crest of the latter this enigma has been never addressedup to now geological settingthe moroccan high atlas is the mostelevated part of the intracontinentalbelts developed in northern africa fig 1 insert through inversion offormer triassic liassic rift basinsduring the africa eurasia conver gence frizon de lamotte et al 2008 with references therein its highelevation depends on the hot mantleanomaly developed under northernmorocco during the neogene teixellet al 2005 missenard 2006 fullea et al 2010 the central highatlas cha corresponds to the deep est part of the former atlas basin underlain by a necked continentalcrust gouiza et al 2010 in contrastwith the other segments of the atlas the cha is characterized by alkaline transitional gabbroic magmatism em placed in the form of sills dykes andoutpours fig 2 saidi 1992 zayane 1992 armando 1999 lhachmi et al 2001 ibouh et al 2002 zayane et al 2002 this event occurred shortlyafter the bathonian emersion of theatlas domain fig 3 during thelatest dogger and late jurassic hail wood and mitchell 1971 armando 1999 haddoumi et al 2010 although the latest basalts emplacedduring the barremian coeval with theyoungest red beds haddoumi et al 2010 marine sedimentation resumed dur ing the aptian extending all overmorocco during the cenomanian turonian high stand regression be gan during the late cretaceous butthe earliest unconformable continen tal red beds are those of the imilchilregion herein discussed they werepreviously regarded as jurassic orcretaceous e g laville and pique 1992 or possibly triassic barberoet al 2007 but are now dated fromthe thanetian ypresian charrie reet al 2009 in both the north andsouth sub atlas zones superimposedfolding events are dated from the lateeocene early miocene and pliocene quaternary frizon de lamotte et al 2000 el har et al 2001 teson andteixell 2008 frizon de lamotteet al 2008 within the mountainbelt narrow faulted anticlinal ridgescored by triassic argillites and mag matic rocks extend between wide opensynclines fig 2 syncline topped anticlinal ridgesfrom central high atlasin the imilchil area fig 4 the tas sent and tasraft ridges north of theplateau des lacs syncline o er thebest examples of star a thirdabstract

spatial correlation of permeability in cross stratified sediment with hierarchical architecture 1 cross stratified deposits can give rise to a hierarchy of permeability modes across scales corresponding to a hierarchy of sedimentary unit types the shape of the sample semivariogram for permeability can be largely controlled by the shape of the cross transition probabilities of unit types having the greatest contrast in permeability the shape of those cross transition probabilities can be in turn largely determined by the variance of the lengths of those unit types a sufficient condition for an exponential like semivariogram is the repeated occurrence of unit types having both a contrast in permeability and a large length variance these relationships are shown through writing the identities for spatial correlation of permeability in a hierarchical and multimodal form and as a function of the transition probabilities for the sedimentary unit types these relationships are also illustrated through analyzing data representing cross stratified sediments within a point bar deposit

the impact of syn and post extension prograding sedimentation on the development of salt related rift basins and their inversion clues from analogue modelling abstract various studies have demonstrated the intrinsic interrelationship between tectonics and sedimentation in salt related rift basins during extension as well as during their inversion by compression here we present seven brittle ductile analogue models to show that the longitudinal or transverse progradation of sediment filling an elongate extensional basin has a substantial impact on the growth of diapirs and their lateral geometrical variations we use five extensional models to reveal how these prograding systems triggered diapir growth variations from proximal to distal areas relative to the sedimentary source in the models continuous passive diapir walls developed after a short period of reactive active diapiric activity during syn extensional homogeneous deposition in contrast non rectilinear diapir walls grew during longitudinal prograding sedimentation both longitudinal and transverse post extensional progradation triggered well developed passive diapirs in the proximal domains whereas incipient reactive active diapirs incipient roller like diapirs or poorly developed diapirs were generated in the distal domains depending on the modelled sedimentary pattern two models included final phases of 6 and 10 shortening associated with basin inversion by compression respectively to discriminate compressional from purely extensional geometries with the applied shortening the outward flanks of existing diapir walls steepened their dips from 8 17 to 30 50 likewise 6 of shortening narrowed the diapir walls by 32 72 with their fully closing salt welds with 10 of shortening we compare our results with the distribution of salt walls and minibasins of the central high atlas diapiric basin in morocco which was infilled with a longitudinally prograding mixed siliciclastic and carbonatic depositional sequence during the early middle jurassic with a minimum thicknesses of 2 5 4 0 km

autochthonous versus allochthonous upper triassic evaporites in the sbiba graben central tunisia abstract two dimensional seismic data and well data from the sbiba graben in central tunisia north africa reveal its asymmetrical structural geometry affected by e w n s nw se and ne sw master strike slip faults these faults have been intruded by upper triassic evaporites which can be classified into the following three types 1 sealed evaporite anticlines and domes along folded structures 2 extrusional wrinkles of salt walls at the borders of the graben related to along strike displacement of the master fault zone and 3 evaporite outpouring at the center of the graben interpreted as the result of fault and diapir movement detailed seismic stratigraphic analysis highlights a complex interplay between fault growth and evaporite movement which strongly controlled the evolution of the graben during the mesozoic tectonic stresses induced multidirectional faulting along inherited faults the vertical rising of the upper triassic evaporites was initiated locally at the intersection of master faults during regional extensional and transtensional events in the sub evaporite basement the interaction of normal faulting and evaporite diapirism caused lateral outpouring of surface piercing evaporites this phenomenon is well expressed in upper cretaceous upper cenomanian to lower turonian strata the master faults which cut the diapir at the border and the crest have caused the extrusion of evaporites the downward gravity driven flow of these evaporites across the slope surface and subsequent accumulation and preservation in mesozoic sediments is related to the fault escarpment and the adjacent fault induced depression there is an apparent relation between tectonic inheritance and inversions of the graben where interconnected deep faults and diapirs have been reactivated during extensional and contractional tectonic episodes causing evolution of the structures with the associated sedimentary lapouts several autochthonous triassic evaporites and associated fault escarpments have induced salt canopy structures

rift controlled fluvial tidal transitional series in the oukai meden sandstones high atlas of marrakesh morocco abstract the carnian formation of the oukai meden sandstones was deposited in the northwestern corner of the african craton along tectonic troughs grouped as a wsw ene rift system on the southwestern margin of the tethys red sandstones represent mainly distal braided stream deposits where very extensive sand flats with 3d dunes 2d sand waves and high regime horizontally laminated sandstones predominate the similarities in orientation between current patterns and trough border faulting the sudden large variations in the thickness of deposits and the occurrence of lateral alluvial fans along the marginal faults are all evidence of the tectonic control of sedimentation the middle part of this clastic continental rift series includes finer facies containing marine reworked or in situ fossils and tracks as well as sedimentary structures interpreted as being of tidal origin especially overlapping s shaped sets the episodic marine influxes that occur within these continental rift deposits are thought to result from the substantial downdropping of tectonic blocks and the drowning of fluviatile facies by the peritethyan marine domain to the northeast the development of marine facies was of relatively short duration and figures little in the sedimentary record butit is evidence of the earliest mesozoic onlaps of the tethys over the african craton in a carnian rift

megaflaps adjacent to salt diapirs megaflaps are steep stratal panels that extend far up the sides of diapirs or their equivalent welds they have multiple kilometer fold widths and structural relief and are thus distinct from smaller scale composite halokinetic sequences maximum dips range from near vertical to completely overturned although overturned megaflaps are associated with flaring salt there is no direct link between megaflap formation and the initiation of salt sheets strata within a megaflap are usually convergent and the lower boundary is typically concordant with the top salt the upper boundary ranges between a prominent onlap surface and a more diffuse zone of gradual rotation and thinning and growth strata likewise display both onlap and stacked wedge geometries we use quantitative cross section restoration to elucidate the origin and development of megaflaps megaflaps typically represent the relatively thin roofs of early salt structures that include single flap active diapirs passive diapirs salt pillows and salt sheets they develop during halokinetic drape folding as the minibasin sinks during contractional squeezing of the diapir and its roof or during some combination of the two the kinematics are dominated by either limb rotation or kink band migration in which roof strata move through a fold hinge into a lengthening steep megaflap both restoration results and direct field evidence suggest that internal strain is minor with little bed lengthening and thinning recognition and understanding of megaflaps are critical to successful petroleum exploration of three way truncation traps against salt megaflaps also have implications for the lateral seal of stratigraphic traps and fluid pressures in minibasins

hierarchical geostatistics and multifacies systems boise hydrogeophysical research site boise idaho 1 the geostatistical structure of a heterogeneous coarse fluvial aquifer is investigated with porosity data derived from neutron logs at a research well field boise hydrogeophysical research site or bhrs that was designed in part to support three dimensional geostatistical analysis of hydrologic and geophysical parameters recognizing that the coarse fluvial deposits include subdivisions units between bounding surfaces we adopt a hierarchical approach and examine the porosity geostatistics of the aquifer at three scales at the bhrs the saturated fluvial deposits as a whole maximum interwell spacing 80 m thickness 16 18 m are at hierarchical level 1 five subhorizontal units within these deposits four cobble dominated units and a channel sand can be traced across the central area of the bhrs and are at hierarchical level 2 and subunits patches or lenses in one of the level 2 units unit 4 are at hierarchical level 3 we use variography and porosity statistics to recognize nonstationarity at hierarchical level 1 and in one of the level 2 units unit 4 where the means and variances of porosity differences as a function of lag are not constant between distinct units and subunits respectively the geostatistical structure at level 1 is modeled with different horizontal and vertical structures that have different sills vertical sill greater than horizontal sill the difference in sills can be explained quantitatively by the summing of weighted sills from all individual units and combined units i e a given pair of different units where the weights are the proportions of data pairs contributing to the sills at each lag from the individual and combined units extension of this analysis leads to a weighted multistructure form of the variogram function whereby a global experimental variogram in a hierarchical system can be decomposed quantitatively into weighted component individual and combined unit or facies structures for any number of units or hierarchical levels such decomposition of the global horizontal variogram from the bhrs indicates that short range periodicity in that structure is due to both 1 combined unit structures associated with patches or lenses at hierarchical level 3 in unit 4 and 2 variations in thickness of unit 2 for hierarchical multifacies systems structure models fit to global horizontal and vertical experimental variograms may not be useful for subsequent stochastic modeling if the system on which the structure models are based is nonstationary

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

the inverted triassic rift of the marrakech high atlas a reappraisal of basin geometries and faulting histories the high atlas of morocco is an aborted rift developed during the triassic jurassic and moderately inverted during the cenozoic the marrakech high atlas with large exposures of basement and triassic early syn rift deposits is ideal to investigate the geometries of the deepest parts of a rift constituting a good analogue for pre salt domains it allows unraveling geometries and kinematics of the extensional and compressional structures and the influence that they exert over one another a detailed structural study of the main triassic basins and basin margin faults of the marrakech high atlas shows that only a few rift faults were reactivated during the cenozoic compressional stage in contrast to previous interpretations and emphasizes that fault reactivation cannot be taken for granted in inverted rift systems preserved extensional features demonstrate a dominant dip slip opening kinematics with strike slip playing a minor role at variance to models proposing a major strike slip component along the main basin bounding faults including faults belonging to the tizi n test fault zone a new middle triassic paleogeographic reconstruction shows that the marrakech high atlas was a narrow and segmented orthogonal rift sub perpendicular to the main regional extension direction which was nw se in contrast to the central and eastern segments of the atlas rift which developed obliquely this difference in orientation is attributed to the indented ouzellarh precambrian salient part of the west african craton which deflected the general rift trend in the area evidencing the major role of inherited lithospheric anisotropies in rift direction and evolution as for the cenozoic inversion total orogenic shortening is moderate 16 and appears accommodated by basement involved large scale folding and by newly formed shortcut and by pass thrusting with rare left lateral strike slip indicators triassic faults commonly acted as buttresses

neritic carbonate crisis during the early bajocian divergent responses to a global environmental perturbation abstract the early bajocian witnessed a global environmental perturbation characterized by faunal and floral turnovers and a positive carbon isotope excursion in italy this environmental perturbation coincided with an eutrophication event and a carbonate crisis but this has so far not been adequately reported from other settings leaving doubt about the extent and nature of these phenomena in this paper we are reporting on an extensive neritic carbonate factory demise that occurs in the upper lower bajocian of morocco more precisely in the upper propinquans lower humphriesianum zones this demise coincided with the acme of the global carbon isotope perturbation recorded by a 3 positive carbon isotope excursion in the bulk organic matter of morocco but not in the micritic phase due to the fact that the moroccan carbonate 13c record is more sensitive to local rather than global influences furthermore we observe that the lower bajocian of morocco is relatively enriched in arenitic siliciclastic deposits suggesting increased weathering and nutrient levels along the northwestern margin of africa during the early bajocian however comparison with neighboring european basins highlights the non uniqueness and different timing of the response of shallow water carbonates to the early bajocian environmental perturbations as some regions present no sign of carbonate factory crisis hence we postulate that local factors were important in mediating the response of neritic carbonate factories to this global environmental perturbation we notably highlight the role of large early bajocian sea level fluctuation as a trigger for carbonate factory change and demise in morocco

new 40 ar 39 ar dating of lower cretaceous basalts at the southern front of the central high atlas morocco insights on late mesozoic tectonics sedimentation and magmatism this study is based upon a stratigraphic and structural revision of a middle jurassic upper cretaceous mostly continental succession exposed between boumalne dades and tinghir southern morocco and aims at reconstructing the relation among sedimentary tectonic and magmatic processes that affected a portion of the central high atlas domains basalts interbedded in the continental deposits have been sampled in the two studied sites for petrographic geochemical and radiogenic isotope analyses the results of this study provide 1 a robust support to the local stratigraphic revision and to a regional lithostratigraphic correlation based on new 40ar 39ar ages ca 120 ma of the intervening basalts 2 clues for reconstructing the relation between magma emplacement in a structural setting characterized by syn depositional crustal shortening pre dating the convergent tectonic inversion of the atlasic rifted basins 3 a new and intriguing scenario indicating that the middle jurassic lower cretaceous basalts of the central high atlas could represent the first signal of the present day canary islands mantle plume impinging flattening and delaminating the base of the moroccan continental lithosphere since the jurassic and successively dragged passively by the africa plate motion to ne the tectono sedimentary and magmatic events discussed in this paper are preliminarily extended from their local scale into a peculiar geodynamic setting of a continental plate margin flanked by the opening and spreading central atlantic and nw tethys oceans it is suggested that during the late mesozoic this setting created an unprecedented condition of intraplate stress for concurrent crustal shortening related mountain uplift and thinning of continental lithosphere

linking hierarchical stratal architecture to plume spreading in a lagrangian based transport model 2 evaluation using new data from the borden site 1 a new data set collected at the well documented borden research site was used in order to evaluate a newly published but as yet untested idea for stochastic modeling ramanathan et al 2008 the new data set reveals the stratal architecture of the borden aquifer and allowed us to determine how the stratal architecture at different scales controlled the macrodispersion observed in the original natural gradient tracer test the newly published idea for modeling uses a lagrangian based model for the particle displacement variance developed from independent physically based quantifiable univariate statistics including the proportions and mean length of the strata the method for defining model parameters avoids the often equivocal step of fitting sample bivariate permeability statistics the model parameters were developed from the new data from the borden site the new data included geologic data in much greater abundance than permeability data there are two scales of unit types delineated in a hierarchy of stratal architecture their shapes are complex not simple layers or lenses the method facilitated the direct use of both geologic and permeability data which need not be collocated the dispersion model developed from these data represents the field measured particle displacement variance that occurred in the natural gradient tracer test well the contributions to time dependent macrodispersion by strata at each scale were computed and analyzed independently this analysis revealed that macrodispersion at the borden site is primarily controlled by the proportions and the mean and variance in length of larger scale strata of medium sand m and strata of fine sand and silt fz with secondary contributions by smaller scale strata types occurring within the larger scale units when sampling the pattern in the longitudinal direction m and fz couplets repeat at 10 m intervals on average with a high length variance to reach a time constant macrodispersivity the stratal length variability must be fully sampled by the plume the macrodispersivity becomes asymptotic beyond an advective distance of about 60 m corresponding to about 12 longitudinal transitions between m and fz unit types

improving permeability semivariograms with transition probability models of hierarchical sedimentary architecture derived from outcrop analog studies received 21 july 2004 revised 22 february 2005 accepted 23 march 2005 published 30 july 2005 1 as analogs for aquifers outcrops of sedimentary deposits allow sedimentary units to be mapped permeability to be measured with high resolution and sedimentary architecture to be related to the univariate and spatial bivariate statistics of permeability sedimentary deposits typically can be organized into hierarchies of unit types and associated permeability modes the types of units and the number of hierarchical levels defined on an outcrop might vary depending upon the focus of the study regardless of how the outcrop sediments are subdivided a composite bivariate statistic like the permeability semivariogram is a linear summation of the autosemivariograms and cross semivariograms for the unit types defined weighted by the proportions and transition probabilities associated with the unit types the composite sample semivariogram will not be representative unless data locations adequately define these transition probabilities data reflecting the stratal architecture can often be much more numerous than permeability measurements these lithologic data can be used to better define transition probabilities and thus improve the estimates of the composite permeability semivariogram in doing so bias created from the incomplete exposure of units can be reduced by a bayesian approach for estimating unit proportions and mean lengths we illustrate this

mid triassic to early liassic clastic evaporitic deposits over the maghreb platform abstract the development of triassic to lower liassic clastic evaporitic series over the epicratonic maghreb platform is closely associated with the eastern opening of a tethyan marine domain between africa and europe west of the platform morocco became separated from north america in late triassic times by rifting along the axis of the proto atlantic ocean in addition ne sw and ene wsw trending atlasic half grabens formed essentially in morocco as part of a late triassic early liassic atlas rifting episode this is the tectonic context in which the red bed to evaporite sequences were deposited a first depositional pattern is illustrated by the areally extensive onlapping of upper triassic clastic evaporitic series over the algerian saharan platform from the carnian to the norian distal mudflats and evaporites graded westward i e landward into proximal fluvial facies seven stratigraphic cycles formed part of a general base level rise of a major retrogradational clastic to evaporitic cycle indicative of general tectonic subsidence of the algerian platform as a whole the evaporites are thus interpreted as markers of persistent onlapping occurring at the edge of the basin as clastic influxes gradually diminished a second depositional pattern is provided by ladinian to rhaetian clastic evaporitic carbonate transgressive sequences of the atlasic domain in tunisia these terminate characteristically in marine facies in this domain intense tectonic activity was consistently offset by a high rate of evaporitic or clastic sedimentation in shallow water environments a third depositional pattern is illustrated in the moroccan high atlas in the central part of this range carnian red conglomerates and sheet like sandstones of a distal braided fluvial plain were deposited in tectonic troughs that linked together as part of a rift system episodic connections occurred with the tethyan domain to the northeast in the western high atlas an upper carnian norian sequence several hundred meters thick displays a general trend from clastics to evaporites reflecting the development of arid paleoclimatic conditions the moroccan meseta provides examples of clastic evaporitic depositional patterns within intracratonic troughs clastic filling of rift induced troughs in the oujda mountains exhibits significant facies and thickness variations ranging from local proximal alluvial and distal anastomosed channel systems through to dominant mudflat systems in the 1000 m thick series of the 60 km long khemisset basin facies range from red beds located mainly along the basin margins to salt dominated deposits in the basin center increasing accommodation controlled the deposition of evaporites and the maximum flooding surface is to be found in typical halite deposits with interbedded bands of clays at that time greater tectonic subsidence rates allowed more marked episodic marine incursions clastic evaporitic series from the passive margin of the moroccan atlantic coast are known only from bore holes and onshore and offshore seismic data recent papers have reported interesting sections across strongly subsiding grabens or tilted blocks related to predominantly ssw nne faults

deformation within an exposed salt wall recumbent folding and extrusion of evaporites in the dead sea basin abstract despite the enormous global interest in salt tectonics which is largely driven by its importance to hydrocarbon exploration direct field based studies of salt exposed at the earth s surface are rare however mount sedom located at the western side of the dead sea basin presents one such opportunity for detailed analysis of salt and the associated sedimentary and structural record of its movement the sedom salt wall is a 10 km 1 5 km n s trending ridge comprising a range of late miocene pliocene evaporites and clastics which have penetrated the overlying pleistocene clastic sequence the salt wall displays a moderate steep west dipping western margin and an overturned west dipping eastern flank the sedimentary record of passive wall growth includes sedimentary breccia horizons that locally truncate underlying beds and are interpreted to reflect sediments having been shed off the crest of the growing salt wall structurally the overturned eastern flank is marked by upturn within the overburden extending for 300 m from the salt wall deformation within the evaporites is characterised by ductile folding and boudinage while a 200 m thick clastic unit within the salt wall forms a tight recumbent fold traceable for 5 km along strike and associated with a 500 m wide inverted limb this overturned gently dipping limb is marked by ne directed folding and thrusting sedimentary injections and a remarkable attenuation of the underlying salt from 380 m to

pre existing salt structures and the folding of the zagros mountains four dimensional analogue x ray tomography imagery is used to investigate the role played by pre existing salt structures during compressive deformation initially linear salt structures evolve towards more axisymmetric diapirs depending on the diapir geometry and on its thickness relative to the sedimentary column thickness the diapirs are either 1 shortened and localize sharp overturned folds for vertical pipe like diapirs or else 2 act as preferentially oriented ramps the diapir being incorporated in the fold for pillow like diapirs the ridges have a strong effect on the lateral extent and orientation of folds they disconnect the folds formed on either side of the salt wall compressional relays between ridges allow for a folded connection between both sides the zagros mountains in southern iran offer a large variety of comparable structures associated with the hormuz salt level which acts as the regional decollement most of the salt structures have been active from the early palaeozoic until the present day the firstorder critical taper is controlled by the distribution of hormuz decollement level and by its thickness at a smaller scale the fold geometry and size are locally controlled by the pre existing salt structures which are the main source of heterogeneity in the deformation

how does resolution of sedimentary architecture data affect plume dispersion in multiscale and hierarchical systems abstract the potential impacts of the spatial resolution of sedimentary structure data on solute dispersion in heterogeneous porous formations are investigated with lagrangian based transport models the models rely on a covariance function that represent a hierarchical organization of sedimentary facies types by using facies physical properties such as volume proportions and mean length as well as auto and cross transition probabilities and their log permeability covariance a detailed sedimentary architecture data i e indicator data provides better representation of the spatial correlation structures of the global covariances through capturing its underlying structure defined by transition probabilities more accurately however the extent to which such data affect time dependent transport parameters i e dispersivity is unclear in this study we parameterize transport models using detailed collocated sedimentary architecture and permeability data from an outcrop in espanola basin nm in addition we perform global sensitivity analysis based on polynomials chaos expansion to understand the significance of parameters in the transport models the results show that dispersivity and particle displacement variance are under estimated if less resolved facies i e indicator data are used even if the global covariance structure is well captured dispersivity is sensitive to the correlation scale that is directly calculated from sedimentary architecture data and the mean log permeability however anisotropy ratio and mean log permeability are the most sensitive parameters for the transverse dispersivity