an example of three dimensional analysis of thrust related tectonites abstract a spaced pressure solution cleavage related to alpine thrusts in mallorca balearic isles is deformed by several sets of shear planes and minor folds all these structures formed synchronously related to the thrust sheet movement shear plane sets show different orientations irrespective of the cleavage disposition slip along these shear planes shows that deformation did not result in plane strain minor fold axes show a wide range of orientations neither folds nor shear planes enable us to directly deduce the sense of thrust motion indicating that these criteria must be used with care previous strain characterization is required for definite conclusions to be reached

tectonic adaptation of the external zones around the curved core of an orogen the gibraltar arc abstract there is no real curvature in the external zones of the arc of gibraltar these external zones are made up by the juxtaposition of segments with nnw sse or e w trending structures juxtaposition does not result from late tectonics nor from a paleogeographic layout but only from miocene tectonics during and after the late burdigalian relative motion between europe and africa was essentially a n s convergence which accounts for the e w structural trends the nnw sse trends are the result of offset of the two main plates along sinistral strike slip fault zones that cross cut the previously mobile block of the internal zones and that shifted southward through time to explain the sharp juxtaposition of different trending structures two tectonic stages must be considered in each area of the external rif during the first one the rocks behaved plastically while during the second they could only move as a block the internal zones alboran block slid independently between europe and africa only until early burdigalian after this time they were locked in the main plates and broken together with them to allow further displacements

from extension to shortening tectonic inversion distributed in time and space in the alboran sea western mediterranean 2d seismic reflection data tied to biostratigraphical and log information from wells in the central and south eastern alboran sea have allowed us to constrain the spatial and temporal distribution of rifting and inversion normal faults tilted basement blocks and growth wedges reveal a thinned continental crust that formed in response to nw se extension to the east a secondary sw ne trend of extension affects the transitional crust adjacent to the oceanic algerian basin the maximum thickness of syn rift sediments is 3 5 km and the oldest recorded deposits are serravallian the wnw ese yusuf fault formed a buttress separating and accommodating variable extension between two different tectonic domains the thinned continental crust of alboran and the oceanic spreading of the algerian basin late tortonian to present day nw se africa eurasia plate convergence drove shortening and reactivation of some of the earlier extensional structures as reverse and strike slip faults forming complex compartmentalised sub basins tectonic inversion coexisted with the formation of new faults and folds inversion was partial along the habibas basin and al idrisi fault but complete along the alboran ridge where some sw ne trending faults were perpendicular to the recent nw se plate convergence and were reactivated as thrusts the wnw ese yusuf fault is oblique to the convergence vector and therefore reactivation is mainly expressed as transpressional deformation volcanic rocks intruded along the alboran ridge and yusuf faults during the latest stages of extension formed rheological anisotropies that localised the later inversion

a structural and palaeomagnetic study of a section through the eastern subbetic southern spain a well exposed 2 km section through the eastern subbetic immediately to the south of the crevillente wrench fault zone can be divided into an upper thrust sheet of triassic rocks a middle thrust sheet of cenomanian turonian basinal sediments and a lower thrust sheet of jurassic limestones unconformably overlain by upper cretaceous palaeocene sediments structural relationships suggest that the middle sheet overthrust the lower sheet and both units were subsequently folded and imbricated this sequence was then overthrust by the upper sheet incorporating a footwall duplex of cenomanian turonian sediments these structures can be related to the complex deformation associated with a single overthrusting event the dominant thrust transport direction is to the east strongly oblique to the overall trend of the orogen however a palaeomagnetic study isolates stable components which indicate no cumulative vertical axis rotation of the thrust sheets the section is cut by strike slip faults whose displacements appear to be relatively minor the triassic rocks of the upper thrust sheet form a highly disrupted thrust sheet extending over much of the subbetic rather than being local to the crevillente fault zone this section through the subbetic can be interpreted as the result of a major east directed thrust of basinal sediments of the median subbetic over marginal shelf facies of the internal subbetic strongly oblique to the general ese trend of the orogen the shortened sequence is cut by a later set of strike slip faults which are probably related to movement on the crevillente fault

timing and kinematics of deformation in the malaguide complex internal zone of the betic cordillera southeast spain the betic cordillera of southern spain forms the westernmost of the mediterranean alpine orogenic belts and is divided traditionally into internal and external zones in the external zone fold and thrust belt unmetamorphosed cover rocks of the iberian margin were deformed from the early miocene onward in contrast internal zone rocks are dominantly metamorphic and are generally assumed to have been deformed and metamorphosed in an alpine event resulting from late cretaceous palaeogene convergence between africa and europe in the sierra espuna at the northern edge of the internal zone in the eastern betics the uniquely preserved permo triassic to miocene stratigraphy of the unmetamorphosed malaguide complex offers a rare opportunity to date the internal zone deformation kinematic data thrust geometries and structural facing of folds suggest that the imbricate thrust stack of malaguide rocks formed as a result of nnw directed motion within present geographical coordinates a fossilized front to this thrust stack preserved beneath a thick sequence of oligocene conglomerates indicates that the timing of the thrust deformation is late eocene in age deformation propagated into the foreland basin in the late oligocene with renewed thrusting subsequently the whole stack has been folded into a n nw vergent regional recumbent fold the espuna fold during the early miocene

mapping permeability in heterogeneous aquifers using hydrologic and seismic data a new method is presented for identification of the permeability distribution in near surface aquifers in addition to using the usual sparsely sampled pressure and permeability data the method incorporates densely sampled seismic data as obtained from a reflection or tomography survey along with empirical relationships between seismic and hydraulic properties the procedure is to first estimate by hydrologic inversion a pressure field then the velocity permeability pressure relationship is used to map the inverted pressure and measured seismic data to multivalued estimates of the permeability of those the most probable value based on the hydrologic inversion is selected in synthetic case studies the tremendous increase in coverage offered by the seismic data leads to dramatically better results in terms of both accuracy and resolution an appealing feature is the use of relatively easy to acquire pressure data a second is the incorporation of geophysical data which can sample an entire aquifer remotely without the need for an expensive and invasive drilling program

unidirectional slip vectors in the western betic cordillera implications for the formation of the gibraltar arc we have investigated the kinematics of deformation in a sector of the gibraltar arc in sw spain by synthesizing lineation data from major faults the variation in structural trends and palaeomagnetically determined vertical axis rotations the kinematic data show that transport directions throughout formation of the arc were consistently wnw regardless of structural trend which varies between 050 and 350 in the study area the data suggest that this part of the gibraltar arc can be explained simply by oblique convergence with a curved indenter taken together with other published data it appears likely that the variation in thrust transport direction within the betic cordillera as a whole may be considerably less than that in the moroccan part of the arc unidirectional convergence combined with the presence of palaeomagnetic rotations implies either eycient overprinting of old rotated lineations and or a convergence rate that is much greater than the rotation rate also required is a low degree of partitioning in the thrust wedge the latter probably increases east of the study area where the structural trend becomes more oblique to the transport direction and major strike slip faults occur

east west thrusting and anomalous magnetic declinations in the sierra gorda betic cordillera southern spain abstract structural and palaeomagnetic studies in the sierra gorda sierra de loja located in the external zone of the betic cordillera indicate that westward directed thrusting is not associated with significant rotations about a vertical axis detailed mapping and slip vector analysis show that the sierra gorda is a thrust complex composed of three thrust sheets the uppermost thrust places early jurassic pelagic carbonates on top of jurassic to oligocene sediments that form a large doubly plunging footwall syncline the eastern limb of this syncline has been overturned and is tectonically thinned as a result of the overthrusting palaeomagnetic results from mesozoic and tertiary sediments both within and around the perimeter of the sierra gorda indicate that 1 the average remanence vector of the seven late jurassic localities sampled within the sierra gorda has a direction d 328 and i 38 that is not significantly different from the expected declination for the upper jurassic of stable iberia and 2 there is no significant difference between the remanences in the two upper thrust sheets indicating that differential rotation did not occur during the initiation and displacement on the thrusts in contrast the one late jurassic site that was sampled to the west of the sierra gorda is rotated like the rest of the subbetics 60 clockwise of the reference direction the unrotated directions obtained in the sierra suggest either that it has rotated in a clockwise sense concordant with the rest of the subbetic zone and has then been backrotated or that it has never rotated relative to stable iberia in the latter simpler hypothesis the unrotated declinations may be explained in terms of orthogonal convergence along an irregular continental margin

wrenching in the external zone of the betic cordilleras southern spain abstract regional structural trends in the caravaca huescar area forming the central part of the external zone in the betic cordilleras indicate that deformation of the area results from right lateral wrenching subparallel to the paleogeographic zonation the structural trends do not fit the nappe interpretation generally used elsewhere in the external zone arguments for wrenching in the area are the structural inverse symmetry with respect to a central transcurrent fault zone the crevillente fault zone the distributional pattern of stratigraphic anomalies and types of deformation and the outcrop pattern of the paleogeographic zones it is argued that certain tectonic units in the area formerly interpreted as klippes in a nappe configuration form centers of flower structures and are vertically squeezed out blocks a theoretical model is sketched illustrating the evolution of a wrench zone under the stratigraphic conditions of the studied area and resulting in its present characteristics many of the features of the caravaca huescar area are also present elsewhere in the external zone and support the idea that wrenching was a major deformational mechanism it is therefore suggested that the external zone should in general not be described in terms of a nappe structure as has been done so far but in terms of a strike slip orogen or a wrenched continental margin

kinematics of a twisted core complex oblique axis rotation in an extended terrane betic cordillera southern spain 1 the sierra de las estancias is a metamorphic core complex that developed during the late oligocene to early miocene extensional collapse of the betic cordillera structural and paleomagnetic analysis shows that the northern half of the complex has been strongly modified by rotation about an inclined axis requiring reassessment of the kinematics of the extensional phase of deformation the extensional tectonic event produced two major detachment faults associated mylonitic foliation and lineation and pervasive sets of shear bands and brittle normal faults with a top to ne shear sense an older foliation was largely transposed and reoriented during this event the regional foliation now defines a broad antiform with a steep north dipping limb and the trend of shear related lineations swings from nne to ene from the southern gently dipping limb into the north dipping limb the remanent magnetization in a suite of near vertical early miocene mafic dikes intruded into the north dipping limb has a declination of 243 and an inclination of 27 assuming that the dikes were originally vertical a rotation of approximately 50 about an inclined ssw plunging axis preserves the near vertical orientation of the dikes and brings the remanence into agreement with the expected orientation for an early miocene age correction for this rotation brings the foliation and lineation in the surrounding schists into orientations subparallel to those on the present southern limb of the antiform and the dikes into a vertical e w orientation the corrected orientation of the shear related lineation nne normal faults and dikes suggests that the original direction of extension during the late orogenic extensional event in the internal betic cordillera may therefore have been around nne ssw rather than e w as currently accepted the observed net tectonic rotation can be decomposed into a series of geologically plausible rotations involving domino style rotation due to slip on the late brittle normal faults tilting about the regional fold axis related to thrust ramping onto the iberian margin during miocene collision and a 30 clockwise rotation about a vertical axis related to oblique convergence with the iberian margin

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

evidence for internal zone unroofing from foreland basin sediments betic cordillera se spain tertiary sediments at the boundary of the internal and external zones in the eastern betic cordillera record evidence of compressive deformation in the internal zone and its subsequent exhumation sediments on the north side of the sierra espun associated with the structurally highest unit of the internal zone the malaguide complex are interpreted as a foreland or piggyback basin which formed in response to the deforming internal zone basin evolution has been reconstructed using an integrated analysis of sedimentary facies petrography heavy minerals and structural data the basin fill contains eocene shallow marine carbonate shelf ramp sediments early oligocene fan conglomerates and coralgal reefs transitional to probable slope deposits of the late oligocene and a late oligocene to mid miocene deep water sequence with pelagic faunas the provenance analyses illustrate an unroofing history of the internal zone orogenic edifice locally uplifted mesozoic to eocene carbonates at the thrust front were the source of lower oligocene conglomerates clastic detritus supplied to the late oligocene to aquitanian basinal sediments was mainly derived from the permo triassic and palaeozoic basement of the malaguide complex the presence of small amounts of first cycle metamorphic minerals indicates the start of exhumation of the deeper metamorphic alpujarride complex from the burdigalian onwards a metamorphic terrane dominated the source area of the deep water sediments and by the langhian high pressure minerals from the deepest parts of the internal zone orogenic edifice appear in the sedimentary sequence rapid exhumation recorded in the early miocene sediments may be the result of extensional exhumation of the internal zone metamorphic complexes

the malaguide alpujarride boundary a major extensional contact in the internal zone of the eastern betic cordillera se spain abstract the internal zone of the betic cordillera in southern spain was formed by thrusting and horizontal ductile shortening in the late cretaceous palaeogene but was subjected to a major phase of vertical thinning during the neogene the contact between the malaguide the structurally highest thrust complex and the underlying alpujarride complex is an example of several major tectonic contacts across which the stratigraphy has been repeated by thrusting but the metamorphic grade increases abruptly downwards detailed work in the eastern betic cordillera documents the relationships across this contact in the sierra espuna petrographic and illite crystallinity studies show that the highest imbricate thrusts of malaguide rocks have only been diagenetically altered whereas the deeper parts of the thrust stack exhibit anchizone facies metamorphism in the northern sierra de las estancias apatite fission track studies confirm that there too malaguide rocks have never been above 200 c in both areas the underlying alpujarride rocks exhibit epizone or greenschist facies metamorphism and a major fault zone with both brittle and ductile structures separates the two complexes the observed rapid increase in metamorphic grade over very small structural thicknesses suggests that part of the original metamorphic zonation has been excised across the contact thus in its present form we interpret the malaguide alpujarride boundary as an extensional contact the extensional motion took place in early middle miocene times as constrained by fission track cooling ages the fault zone at the contact is sub horizontal in the sierra espuna but in the sierra de las estancias it is mainly sub vertical kinematic data from a 5 20 m thick calcmylonite layer within the fault zone in the sierra de las estancias corrected for later tilting indicates that the extensional movement was originally directed with the top to the east northeast the interpretation of the malaguide alpujarride boundary as an extensional contact is similar to recent interpretations of the nevado filabride alpujarride contact at deeper structural levels in the central and eastern betics the identification of another major extension fault system confirms that miocene extension was widespread at all structural levels during the early middle miocene the sierra espuna and the northern margin of the sierra de las estancias lay on the boundary between the region undergoing horizontal extension in the internal zones and the alboran sea to the south and the region undergoing horizontal shortening in the external zones to the north as a result the detailed history of the alpujarride malaguide contact is complicated extensional structures cross cut structures related to earlier alpine shortening and were then affected by further shortening as convergence with the external zones continued

a stochastic approach to the characterization of lithofacies from surface seismic and well data heterogeneity of natural geologic formations strongly influences groundwater flow and contaminant migration this study presents a formal stochastic approach for the integration of surface seismic data and well data into the identification of the spatial arrangement location geometry and interconnectedness of lithofacies and incorporating this information in the estimation of the log permeability probability density function pdf to achieve this goal normal move out nmo corrections are applied to the seismic reflection data to estimate interval seismic velocities calibration curves constructed from the well logs transform these velocity estimates into a lithology indicator prior probability field from the well data and the indicator prior probability field the indicator covariance function and its associated confidence limits are computed neighboring lithology logs and the indicator covariance function are then combined to update the indicator probability field the conditional log permeability pdf is finally computed by weighting the log permeability distribution of each lithology with respect to its indicator probability field the effectiveness of the proposed procedure is shown to depend on the quality of the seismic data and the degree of correlation between seismic and hydrogeologic soil properties a synthetic case study is performed which shows that the surface seismic and well data complement each other with optimal results achieved when both types of data are incorporated into a joint identification procedure

origin of the western subbetic arc south spain palaeomagnetic and structural evidence abstract an integrated structural and palaeomagnetic study in late cretaceous eocene rocks of the western subbetic arc in the betic cordillera of southern spain shows that the change in fold trend around the arc is significantly greater than the variation in primary magnetic declination this suggests that the arcuate geometry is not primarily a consequence of differential rotation the area has experienced a regional clockwise rotation of at least 40 which was most probably imposed during oblique wnw directed convergence along the southern iberian margin in early miocene time before the arcuate structure was formed kinematic indicators associated with the arcuate folds and thrust traces arc for the most part consistently wnw directed suggesting that the arc is not primarily a result of variations in the direction of tectonic transport the arcuate structure was probably initiated without significant rotation by the wnw directed indentation of the curved western end of the alboran domain into the iberian margin and was then tightened involving up to about 35 of further rotation in different segments of the arc finally one sector in the arc was rotated anticlockwise by about 40 with respect to the rest of the region reorientating the magnetic declinations the fold trends and the kinematic indicators this rotation was associated with local sinistral shear

paleomagnetic rotations and the kinematics of the gibraltar arc paleomagnetic investigations of a mesozoic limestone sequence around the gibraltar arc show that there have been large systematic rotations about a vertical axis and imply that there must have been a significant component of westward motion within the betic rif orogenic belt rotations of the late jurassic and late cretaceous limestones in the betic cordillera of southern spain are clockwise with the exception of the unrotated sierra gorda whereas the jurassic sites in the rif mountains of morocco are rotated counterclockwise except in the area around tetuan these data are generally consistent with formation of the arc either by a westward moving alboran microplate or by extensional collapse of a collisional mountain chain the former model however fails to recognize the nonrigid nonplate like character of the alboran domain and lacks a definable driving mechanism a model of a collapsing east west elongated ridge that takes into account the obliquity of the convergence along the active margin may provide mechanisms both for the observed rotations and for the large westward component of motion and therefore can explain the geometry of the gibraltar are

repeated palaeoseismic activity of the ventas de zafarraya fault s spain and its relation with the 1884 andalusian earthquake one of the most destructive historical earthquakes m 6 7 in spain occurred in 1884 along the normal ventas de zafarraya fault located in the central betic cordilleras palaeoseismic and radiocarbon data presented in this study are the first to constrain the timing of the pre 1884 fault history in the last 10 ka these data yield a recurrence interval of between 2 and 3 ka for major earthquakes under the assumption of uniform return periods along the normal fault the holocene slip rate is estimated to be in the order of 0 35 0 05 mm year which is significantly higher than the mean slip rate of 0 17 0 03 mm year since the tortonian several of the most important deformations and secondary features such as landslides and liquefaction are related to strong ground motion and document the holocene activity of the ventas de zafarraya fault

mid crustal detachment in the betic system of southeast spain abstract the tertiary orogenic belts of eastern spain can be interpreted using the principles of thin skinned thrusting with a fundamental detachment at mid crustal level in the eastern betics the compression involves an oblique restacking of a stretched continental margin much of the shortening is transmitted on permian and triassic detachments which emerge as forward and back thrust duplexes an interpretation of the guadarrama range of central spain is presented in which significant shortening is shown on a mid crustal detachment propagating from the southeast it is suggested that this represents the external limit of a compressive system linked to the betics the pyrenees and eastern cantabrians are a separate tertiary compressive system again resulting from restacking of an extensional basin during the collision of iberia and france previous authors have proposed mid crustal detachment in the pyrenees observation of the geological map of the iberian ranges suggests a broadly similar structural origin may apply in which case the iberian ranges may represent the most external zone of a major pyrenean system again linked by a mid crustal detachment thus it is suggested that the whole of eastern spain is made up of two major compressive systems linked at mid crustal level

role of strike slip faults in the betic rifian orogeny abstract a new model for the betic rifian orogeny of the western mediterranean spain and north africa is proposed in which four strike slip faults play an important role the faults are not of the same age two faults the left lateral jebha fault to the south in morocco and principally in the mediterranean sea and the right lateral north betic fault southern spain to the north define the boundaries of the alboran block betic and rifian internal zones final movement along these faults was during the burdigalian time two other faults the left lateral nekor fault north africa to the south of the jebha fault and the right lateral crevillente fault somewhat to the north of the north betic fault define a larger alboran block including part of the betic and rifian external zones that was present during the tortonian the following sequence of events is proposed 1 a during the eocene and oligocene the african and european plates converged in a n s sense causing the breakup and overthrusting of the betic rifian and kabyle internal zones and then the movement towards the wsw of the alboran block by slip along the jebha and north betic faults 2 b by the end of burdigalian time movement along the jebha and north betic faults ceased 3 c with continued n s convergence the nekor and crevillente faults which bound a larger alboran block were formed during the mid and late miocene the arc of gibraltar the zone lying between the four major faults seems to be a result of wsw motion of a crustal block being thrust over external zones the model proposed adds to the earlier idea that tectogenesis proceeds from the interior to the exterior of an erogenic belt in the betic rifian orogeny major strike slip fracture zones shifted to the exterior of the orogenic belt as the orogeny progressed in order to relieve the stress caused by locking of the more internal faults

the internal external zone boundary in the eastern betic cordillera se spain reply abstract the internal external zone boundary iezb in the betic cordillera of southern spain separates the internal zone which was deformed and in part metamorphosed before the early miocene from the external zone which consists of the cover rocks of the iberian margin shortened to form a thin skinned fold and thrust belt in early to middle miocene times over much of its length the iezb is roughly linear trending approximately 070 it has been referred to as a major dextral strike slip zone and has even been considered as the northern boundary of a westward moving alboran microplate field and kinematic data from the eastern betic cordillera show that the iezb crops out over a 60 km distance as a gently dipping thrust with displacement to the southeast or south southeast oblique to its regional trend there is no evidence of dextral strike slip movement along the boundary new micropalaeontological studies of calcareous nannoplankton indicate that the oligo miocene basin along the boundary was the site of continuous deposition until the beginning of the middle miocene the thrust at the iezb cuts early miocene rocks and is overlapped by the middle miocene thrusting therefore occurred in this time interval the iezb is therefore unlikely to have been the dextral boundary of a westward moving alboran microplate at this time but was more likely to have been the locus of nw directed dextrally oblique convergence

geophysical hydrological identification of field permeabilities through bayesian updating a new bayesian method is developed to identify the spatial distribution of permeabilities in addition to sparsely sampled permeability and pressure data this approach incorporates densely sampled seismic velocity data along with semiempirical relationships between seismic and hydraulic soil properties the procedure consists first of performing a hydrological inversion based solely on the permeability and pressure data in light of the available seismic data the velocity permeability pressure relationships are then used to update in a bayesian sense the image of the permeability field to investigate the usefulness of this approach synthetic case studies are performed these studies demonstrate that even when the seismic data are corrupted by a significant level of error a joint geophysical hydrological inversion can produce improved images of permeability moreover this paper derives rigorously the bounds on the error that can be tolerated in seismic velocities such that they are still useful for hydrological purposes

oyster shells as recorders of short term oscillations of salinity and temperature during deposition of coral bioherms and reefs in the miocene lorca basin se spain abstract we use 18 o and 13 c of oyster shells inferred seawater 18 o w and temperature tolerance ranges of modern zooxanthellate coral communities to constrain and model paleo salinities of marginal marine waters of the miocene lorca basin spain salinities ranged from 22 to 32 psu during growth of coral bioherms and carpets of the soriana and parrilla formations and from 35 to 39 psu during deposition of the hondo formation reef complex the periods with lower modeled salinities correspond with deltaic and alluvial fan sedimentation in the area the modeling is supported by 87 sr 86 sr data and provides new insights into the evolution of the local depositional settings departures of sr isotope values from the global oceanic curve occur within the intervals with the lowest modeled salinities and the non oceanic 87 sr 86 sr preserved in individual oyster shells was probably sourced from uplifted aquitanian burdigalian limestones 87 sr 86 sr values that plot along the global ocean sr isotope curve for the late miocene indicate a tortonian age for the upper part of the soriana formation and the parrilla formation and a messinian age for the hondo formation more generally we demonstrate how the chemical analyses of oyster shells provide additional information regarding short term oscillations of salinity and temperature of seawater beyond what can be obtained by traditional paleoecological methods

geologic evolution of the betic cordilleras in the western mediterranean miocene to the present abstract the betic cordilleras were formed during the eo meso and neo alpine evolution of the western mediterranean area during the neo alpine stage the northward subduction of the african plate took place and the algerian provencal basin opened with the creation of oceanic floor associated space problems produced the expulsion and extensive stretching of the internal zones to the west which in turn disrupted and deformed the external zones of the betic and rif cordilleras these occurrences essentially took place in the burdigalian and continued with diminished intensity into the middle miocene following the suturing of the transcurrent contact between the internal and external zones important n60 90 e and nw se faults occurred the betic cordilleras are characterized as having been deformed by regional horizontal shortening compression oriented wnw ese or nw se which gradually rotated to the nnw sse in the late miocene when its most important intramontane neogene basins were formed the alboran basin with a thinned continental crust was formed as a western prolongation of the opening of the algerian provencal basin with its basic features already apparent in the burdigalian the volcanism present in the southeast of the betic cordilleras and in northeast morocco crossing the alboran basin is mainly late miocene in age it is linked to fracturing and exhibits chemistry related to the different thickness of the crust

the betic segment of the lithospheric trans alboran shear zone during the late miocene abstract the betic sinistral transcurrent shear zone betic cordilleras crosses the southeastern part of spain the study of the geodynamics of this area is approached from tectonic sedimentary magmatic and geophysical data large strike slip movements tectono sedimentary processes and magmatic events are seen at the boundary between two different lithospheric slabs they are located in a thinned compartment with a high geothermal gradient the large scale movements vertical and horizontal and the intensity of magmatic activity are the expression of the mechanical behaviour of this hot and thin crust all the geological events from the late miocene to recent are integrated in a crustal scale cross section which shows that the betic sinistral transcurrent shear zone widely affects the lithosphere it appears that subduction zones are not the only geodynamic context in which calc alkaline magmatism occurs

palaeomagnetic rotations in the eastern betic cordillera southern spain palaeomagnetic declinations from the external zones of the eastern betic cordillera southern spain and an adjacent area of the internal zone indicate variable and locally very large clockwise rotations the rotations occurred after latest oligocene times and probably before the late miocene this overlaps a period of dextrally oblique convergence during the early to middle miocene along the internal external zone boundary and within the external zone rotations in the external zone are recorded by palaeomagnetic results from 27 sites in upper jurassic ammonitico rosso facies limestones from the subbetic zone and one site of a similar age from the prebetic the sites show either two or three component behaviour the low temperature component is coincident with the present field direction the intermediate temperature component was probably acquired during miocene folding the high temperature component passes fold tests miocene age and a conglomerate test eocene early oligocene age palaeomagnetic declinations from individual tectonic blocks in the subbetic are consistent but indicate large differential rotations between blocks these blocks are underlain by low angle thrust faults which probably accommodated much of the rotation the largest rotations occur on relatively small isolated blocks of jurassic carbonates in a highly deformed triassic evaporite sequence the single site in the prebetic has not rotated significantly relative to stable iberia in malaguide rocks of the sierra espun a in the adjacent internal zone stable palaeomagnetic components were measured at one site in upper miocene sedimentary rocks at three sites in upper oligocene lower miocene red marls at one site in oligocene marls at one site in jurassic limestones and at two sites in permo triassic red beds the palaeomagnetic results suggest that about 60 of clockwise rotation occurred in the latest oligocene earliest miocene and a further 140 of clockwise rotation subsequently one site in late miocene sedimentary rocks yields unrotated declinations which if not representing an overprinted direction indicate that the rotation was complete by the end of the miocene

mode of extensional tectonics in the southeastern betics se spain implications for the tectonic evolution of the peri alboran orogenic system the gibraltar arc which closes the westernmost part of the mediterranean basin is a miocene a type subduction arc formed by the continental collision of various pre miocene terranes in the major zone of collision between the iberian and african cratons the hanging wall block known as the alboran domain has undergone more than 300 km migration from a more easterly position where it was the continuation of the alpine cretaceous paleogene orogen contemporaneous with thin skinned thrusting in the footwall the alboran domain underwent two episodes of nearly orthogonal extension in which extensional systems developed with directions of extension varying from a nnw sse system orthogonal to the belt axis in the late burdigalian langhian to a wsw directed orogen parallel one in the serravallian the superposition of these two systems resulted in a chocolate tablet megastructure this extensional pattern is not satisfactorily explained in previously proposed models for the evolution of the arc orthogonal extension is plausible in a process of the gravitational collapse of an overthickened crust nevertheless orogen parallel extension is more difficult to explain in this context we advocate that the wsw directed low angle normal faults formed during large scale extension in connection with important westward arc migration the driving force of extension in a general context of convergence is controversial and varies between a convective removal model and a delamination model constraints on both the timing and the kinematics of extension as presented in this paper seem to support the contribution of both mechanisms convective removal may have started the process but continued n s convergence could have resulted in westward tectonic escape and asymmetric lateral inflow of asthenospheric material accompanying lithospheric delamination

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in

resolving the age of madumabisa fossil vertebrates palynological evidence from the mid zambezi basin of zambia age estimates for permian rocks in the mid zambezi basin of zambia have thus far yielded ambiguous results previously studied palynoassemblages from the madumabisa formation resemble spore pollen suites from both the cistecephalus zone of north luangwa lopingian and the palynological assemblage sub zone iv h of zimbabwe proposed as guadalupian in order to improve age estimates and refine the biostratigraphy of the madumabisa formation this formation together with the underlying gwembe formation were sampled for palynomorphs assemblages from the gwembe formation are dominated by trilete spores with less common striate and non striate bisaccate pollen whereas the overlying madumabisa formation palaeoflora is composed predominantly of striate bisaccates ferns pteridosperms lycopods sphenophytes glossopterids and conifers are represented in the palynofloras the upper gwembe formation palynoassemblage can be correlated with the didecitriletes ericianus zone of backhouse 1991 the guttulapollenites hannonicus protohaploxypinus rugatus zone zone vi of aitken 1998 assemblage zone iii of the mid zambezi basin zimbabwe and biozone kk 3 in the kalahari karoo basin botswana suggesting a guadalupian wordian capitanian age the upper madumabisa formation palynoassemblage can be placed in the upper dulhuntyispora parvithola zone of backhouse 1991 app5 of price 1997 dated as wuchiapingian lopingian and correlates with assemblage 2 of the moatize minjova basin mozambique and the mckinnon member palynofloras of east antarctica it also resembles daptocephalus formerly dicynodon assemblage zone palynofloras of the lower and middle balfour formation in the karoo basin south africa and is suggested to be lopingian wuchiapingian changhsingian in age although these palynological assemblages place lower and upper age constraints on madumabisa formation vertebrate fossils uncertainty remains as to the exact correlation between the madumabisa vertebrate assemblages and the assemblage zones of the main karoo basin