from orogenic hinterlands to mediterranean style back arc basins a comparative analysis hinterland plateaux and mediterranean style back arc basins both form behind active subduction zones or collisional megathrusts and share many characteristics 1 early crustal thickening to about twice normal continental thickness 2 thin lithospheric mantle 3 mixed magmatism including asthenospheric lithospheric and crustal melts 4 late stage horizontal extension accompanied by vertical shortening horizontal extension and vertical shortening are driven by high gravitational potential energy gpe contrasts between the hinterland and surrounding lithosphere which may reach 7 10 12 n m 1 equivalent to about 2 5 times the ridge push force if extension is rapid relative to the rate of lithospheric cooling gpe may remain positive even as extension continues declining to the mid ocean ridge value as crustal thickness approaches zero this suggests that hinterland plateaux could ultimately evolve into oceanic back arc basins the rate direction and amount of extension and the rate of vertical shortening depend on the plate boundary conditions and the gpe of the surrounding lithosphere vertical shortening in tibet is limited by work required to deform the surrounding asian lithosphere whereas mediterranean back arc basins can extend at the expense of regions of thin continental or oceanic crust

benthic assemblage composition on subtidal reefs along a latitudinal gradient in western australia at regional scales the distribution of species and the structure of assemblages vary with latitude within many marine and terrestrial systems the oligotrophic coastal waters of western australia wa support highly speciose and endemic assemblages yet spatial patterns in benthic structure are currently poorly known we examined benthic assemblage composition along a latitudinal gradient of 28 5 33 5 s and a depth gradient of 14 62 m on subtidal reefs in warm temperate wa we surveyed benthos using a remotely triggered digital stills camera in total we sampled macroalgae and sessile invertebrates at 201 sites spread across four locations percent cover of coarse taxonomic groups and dominant species was estimated from over 2000 photoquadrat samples we recorded significant differences in benthic assemblage composition between locations and along depth gradients within each location however the magnitude of change with depth was not consistent between locations and shifts in assemblage composition along the depth gradients were not as pronounced as expected the percent cover of all dominant benthic groupings differed between locations and several key taxa such as the kelp scytothalia dorycarpa brown foliose macroalgae hard corals and sponges changed predictably along the latitudinal gradient our study adopted a coarse taxonomic but assemblage wide approach to describing macrobenthic assemblages and clear differences between locations and depths were detected the surveys have provided baseline data on broad scale ecosystem structure against which to detect future ecological change

spatial variation patterns of subtidal seaweed assemblages along a subtropical oceanic archipelago thermal gradient vs herbivore pressure abstract the structure and composition of subtidal rocky seaweed assemblages were studied at 69 sites on the canary islands northeastern atlantic this group of islands are situated at the southern boundary of the warm temperate region and adjacent to the cold waters from the northwest african coastal upwelling which creates a difference of almost 2 c in surface seawater temperature from the eastern to the western islands this thermal variation allows an examination of the transition between the warm temperate and the tropical regions along this longitudinal gradient together with the hypothesised fucales dominated assemblages towards the eastern islands in contrast to the dictyotales dominated assemblages towards the western ones environmental and biological parameters were considered in order to investigate which were the main factors explaining spatial variation along the gradient in a multi scaled approach although seventy nine macroalgae were identified 87 63 of the total mean cover was due to six taxa lobophora variegata nongeniculate corallines canistrocarpus cervicornis jania adhaerens cystoseira abies marina and pseudolithoderma adriaticum at a large scale sea urchin density explained the highest variation in seaweed assemblages 26 94 and its pattern of distribution across the islands the expected pattern of distribution according to the upwelling distance only occurred in restricted areas of the canarian archipelago in absence of herbivore pressure and habitat degradation spatial variations within islands medium scale were mainly related to wave exposure while at a small scale these were mostly due to the degree of sedimentation

formation and deformation of hyperextended rift systems insights from rift domain mapping in the bay of biscay pyrenees the bay of biscay and the pyrenees correspond to a lower cretaceous rift system including both oceanic and hyperextended rift domains the transition from preserved oceanic and rift domains in the west to their complete inversion in the east enables us to study the progressive reactivation of a hyperextended rift system we use seismic interpretation gravity inversion and field mapping to identify and map former rift domains and their subsequent reactivation we propose a new map and sections across the system illustrating the progressive integration of the rift domains into the orogen this study aims to provide insights on the formation of hyperextended rift systems and discuss their role during reactivation two spatially and temporally distinct rift systems can be distinguished the bay of biscay parentis and the pyrenean basque cantabrian rifts while the offshore bay of biscay represent a former mature oceanic domain the fossil remnants of hyperextended domains preserved onshore in the pyrenean cantabrian orogen record distributed extensional deformation partitioned between strongly segmented rift basins reactivation initiated in the exhumed mantle domain before it affected the hyperthinned domain both domains accommodated most of the shortening the final architecture of the orogen is acquired once the conjugate necking domains became involved in collisional processes the complex 3 d architecture of the initial rift system may partly explain the heterogeneous reactivation of the overall system these results have important implications for the formation and reactivation of hyperextended rift systems and for the restoration of the bay of biscay and pyrenean domains

cenozoic deformation of iberia a model for intraplate mountain building and basin development based on analogue modeling 1 inferences from analogue models support lithospheric folding as the primary response to large scale shortening manifested in the present day topography of iberia this process was active from the late oligocene early miocene during the alpine orogeny and was probably enhanced by reactivation of inherited variscan faults the modeling results confirm the dependence of fold wavelength on convergence rate and hence the strength of the layers of the lithosphere such that fold wavelength is longest for fast convergence rates favoring whole lithosphere folding folding is associated with the formation of dominantly pop up type mountain ranges in the brittle crust and thickening of the ductile layers in the synforms of the buckle folds by flow the mountain ranges are represented by upper crustal pop ups forming the main topographic relief the wavelengths of the topographic uplifts both in model and nature suggest mechanical decoupling between crust and mantle moreover our modeling results suggest that buckling in iberia took place under rheological conditions where the lithospheric mantle is stronger than the lower crust the presence of an indenter inducing oblique shortening in response to the opening of the king s trough in the north western corner of the atlantic iberian margin controls the spacing and obliquity of structures this leads to the transfer of the deformation from the moving walls towards the inner part of the model creating oblique structures in both brittle and ductile layers the effect of the indenter together with an increase on the convergence rate produced more complex brittle structures these results show close similarities to observations on the general shape and distribution of mountain ranges and basins in iberia including the spanish central system and toledo mountains

the mediterranean mare nostrum of earth sciences the mediterranean area is one of the most appealing natural laboratories in the world to study geodynamic and paleoclimatic processes on different scales consequently the mediterranean sea can be considered as the mare nostrum our sea of earth sciences its semi enclosed land locked configuration in a convergent setting between africa in europe in combination with its latitudinal position makes the mediterranean extremely suitable to study both fundamental plate tectonic processes and astronomically induced oscillations in climate for many years to come the mediterranean will certainly remain a fascinating area where an integrated and multi disciplinary approach will increasingly contribute to our understanding of geological geophysical geodetical and geochemical processes in an accurate and high resolution time frame

evolution of retreating subduction boundaries formed during continental collision retreating subduction boundaries formed where the rate of subduction exceeds the rate of overall plate convergence appear to be commonly developed features within regions of early or incomplete continent continent collision they are characterized by regional extension within the overriding plate and at their leading edge by thin skinned arcuate thrust belts that are concave towards the overriding plate as is illustrated by examples from the mediterranean region the formation of retreating subduction boundaries is intimately related to the process of continental collision during the early stages of collision retreating subduction boundaries are commonly formed by lateral ejection from zones of crustal shortening along the main collision boundary retreating plate boundaries can also form before the main collision and the associated thrust belts emplaced as precollisional accretionary assemblages because the driving mechanism for retreating subduction boundaries appears to be gravity acting on a dense subducted slab slab pull subduction usually ceases when and only when thick buoyant continental crust enters the subduction zone thus differences in the evolution and duration of retreating subduction systems can be largely attributed to the size and configuration of the deep water regions available to be subducted in some cases retreating subduction boundaries may escape into the open ocean where they form nearly isolated local tectonic systems in these systems the rate of subduction is approximately compensated by the rate of upper plate extension and migration of the system across the oceanic region may be very rapid for example the horseshoe seamounts located about 800 km offshore in the eastern north atlantic may be the active expression of an east dipping westwardly migrating retreating subduction boundary that has evolved from the betic cordillera rif system active in miocene time and may now be progressing across the atlantic at approximately 50 mm yr an analogous situation may be represented by the scotia arc system a westward dipping retreating subduction system located between the south american and antarctic plates which may have escaped into the south atlantic ocean from a zone of crustal shortening in the andes and is now progressing across the atlantic at a rate of about 80 mm yr

tectonosedimentary evolution related to extreme crustal thinning ahead of a propagating ocean example of the western pyrenees 1 in this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme crustal thinning in a transtensional setting ahead of a propagating ocean in the western pyrenees the labourd mauleon area situated in the western pyrenees at the termination of the v shaped bay of biscay is an ideal natural laboratory to study how such complex basins evolve in time and space because of a mild inversion of the basin during pyrenean compression the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field the basin shows a complex polyphase evolution that starts with left lateral dominated transtension in latest jurassic early aptian time this event is overprinted by a late aptian early albian extension that is related to the counterclockwise rotation of iberia away from europe leading to the opening of the bay of biscay during this stage the late triassic to jurassic carbonate platform was stretched salt migrated and detachment faults exhumed upper and lower crustal and mantle rocks to the seafloor the final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by n40 to n60 transfer faults the sedimentary architecture is characterized by late aptian synrift sediments e g urgonian limestones that were deposited in fault bounded basins and are overlain by thick latest aptian to albo cenomanian sediments e g flysch noir that define a sag sequence the complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic thermal event that postdates mantle exhumation

the deep seismic reflection marconi 3 profile role of extensional mesozoic structure during the pyrenean contractional deformation at the eastern part of the bay of biscay abstract the new marconi 3 deep seismic profile allows recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution it denotes that the easternmost part of the bay of biscay consists of a thick wedge of uppermost cretaceous to cenozoic synorogenic sediments lying unconformably on the top of a thinned continental crust with the mesozoic parentis basin to the north and the coeval landes high to the south the parentis basin appears as a major half graben bounded southwards by a north dipping planar fault it is filled by a thick sequence of jurassic upper cretaceous carbonates affected by salt domes and squeezed diapirs made up of triassic evaporites and mudstones these salt tectonic structures also affect the overlying uppermost cretaceous to lower miocene synorogenic deposits which are folded upon these structures the landes high includes a thin pre upper cretaceous cover tilted to the south in the basque shelf it is deformed by a basement involving thrust wedge emplaced during the late eocene miocene that constitutes the north pyrenean contractional front geometric relationships and thickness variations depict that this overall structure results from the following mesozoic extensional stage which includes a late jurassic late aptian syn rift stage in which the parentis basin formed and an albian early late cretaceous post rift stage in which diapirs of triassic evaporites grew close to this major fault compressive deformational stage coeval to the pyrenean orogeny which led to 1 the development of a latest cretaceous up to middle miocene foreland basin and 2 from late eocene the formation of a basement involving thrust wedge in the innermost foreland basin the squeezing of the diapiric structures formed previously in the parentis basin and later middle miocene the partial inversion of some pre existent faults located in the southern parentis basin margin this geodynamic evolution together with the structure of the area evidences that the extensional structure resulting from the opening of the bay of biscay played an important role both in the location of the north pyrenean front and in the north pyrenean foreland contractional deformation features specially the lack of significant inversion structures in the parentis basin despite that it belongs to a severely thinned crustal area before the alpine compression denotes that the mesozoic landes high acted as an important buffer for the propagation of the pyrenean contractional deformation to the north this deformational buffer was active until early miocene and probably vanished afterwards during the last stages of pyrenean orogen development when some basement faults reactivated in the parentis basin

the midcontinent rift in the lake superior region with emphasis on its geodynamic evolution abstract the midcontinent rift is a middle proterozoic continental rift which records about 15 m y of extension subsidence and voluminous volcanism in the period 1109 1094 ma in the central part of north america during that time the crust was nearly totally separated and as much as 25 km of subaerial basalts accumulated in a deep central depression following extension and volcanism a longer period of subsidence resulted in development of a post rift sedimentary basin in which as much a 8 km of fluvial and lacustrine clastic rocks were deposited partial inversion of the central depression occurred about 30 50 m y after extension to produce the current configuration of a central horst composed mostly of thick volcanic accumulations between shallower flanking basins

three dimensional gravity and magnetic modeling of crustal indentation and wedging in the western pyrenees cantabrian mountains 1 the complex crustal structure of the boundary zone between the iberian and european plates from the western pyrenees to the cantabrian mountains is probed by three dimensional 3 d gravity and magnetic modeling constrained by deep seismic profiles the 3 d modeling results support the presence of a continuous iberian crustal root and suggest that the geometry of the orogenic belt that formed in latest cretaceous tertiary times along the northern margin of iberia was conditioned by oblique structures separating areas characterized by different tectonic styles in the western pyrenees and the basque cantabrian basin a thick mesozoic basin presently incorporated to the pyrenean cantabrian belt the relatively narrow thinning of the crust inherited from the mesozoic rifting stage conditioned a structural style in which portions of the southward indenting european lower crust are interpreted to be back thrusted toward the north and uplifted to shallow depths promoting the appearance of significant potential field anomalies in the basque cantabrian basin the strongest aeromagnetic anomaly of the whole iberian mainland is superimposed on the eastern part of a well defined positive gravity anomaly similar in amplitude and wavelength to those located along the north pyrenean zone these observations suggest that the eastern part of the dense lower crustal causative body is strongly magnetized and may correspond to a gabbroic cumulate originated in the axis of the ancient mesozoic rift to the west tertiary compression affected the north iberian cantabrian passive continental margin whose geometry and inherited structures conditioned the formation of a double crustal delamination and the uplift of the cantabrian mountains

intraplate deformation and basin formation during the tertiary within the northern iberian plate origin and evolution of the almazan basin the tertiary almazan basin was a topographic high during the mesozoic rifting at the northern part of the iberian plate it was bordered by two mesozoic basins 1 the castilian basin with a maximum thickness of more than 2000 m to the south and 2 the cameros basin with a maximum thickness of 9000 m to the north to the east the almazan basin is bordered by paleozoic rocks of the nw se trending aragonian range which underwent little subsidence during the mesozoic the two mesozoic basins show an e w direction during the tertiary nne ssw compression mainly late eocene early miocene both mesozoic basins were inverted and uplifted and the almazan basin with an overall synclinal geometry was filled with syn tectonic terrestrial sediments reaching a maximum thickness of 3500 m deformation during the tertiary was strongly controlled by preexisting structures both mesozoic extensional faults and reactivated variscan folds the depocenter of the tertiary basin migrated southward during the paleogene this migration is consistent with a piggyback transport of the whole basin northward due to the movement on the underlying crustal scale north verging cameros thrust the geometry and sedimentary evolution of the almazan thick skinned piggyback basin was controlled by the uplift associated with the main crustal scale thrust which was the main source area and was separated from the foreland basin since the early stages of filling late eocene this makes the main difference with thin skinned piggyback basins controlled by the foreland thrust belt and separated from the foreland basin only at their late stages

iberian plate kinematics a jumping plate boundary between eurasia and africa the rotation of iberia and its relation to the formation of the pyrenees has been difficult to decipher because of the lack of detailed sea floor spreading data although several models have been proposed1 7 here we use detailed aeromagnetic measurements from the sea floor offshore of the grand banks of newfoundland to show that iberia moved as part of the african plate from late cretaceous to mid eocene time with a plate boundary extending westward from the bay of biscay when motion along this boundary ceased a boundary linking extension in the king s trough to compression along the pyrenees came into existence finally since the late oligocene iberia has been part of the eurasian plate with the boundary between eurasia and africa situated along the azores gibraltar fracture zone

magnetostratigraphic biostratigraphic and stable isotope stratigraphy of an upper miocene drill core from the sale briqueterie northwestern morocco a high resolution chronology for the messinian stage we report a high resolution stable isotope carbonate magnetostratigraphic and biostratigraphic record from a 175 m drill core from the sale briqueterie which is part of the bou regreg section in northwestern morocco the sale drill core spans the interval from paleomagnetic chron c4n partim to c3r earliest gilbert which represents the time leading up to and including the isolation and desiccation of the mediterranean i e the messinian salinity crisis during chrons c3an and c3ar 6 935 to 5 894 ma the isotope and carbonate signals display quasi periodic variations with estimated periods of 40 and 100 kyr respectively we interpret the 40 kyr 18o variations as reflecting changes in global ice volume caused by obliquity induced changes 41 kyr in solar insolation in polar regions the 100 kyr carbonate variations probably represent long term modulation of the amplitude of the precessional cycle 21 kyr which is not resolved by our sampling frequency the cyclic nature of the oxygen isotope signal permits us to extend the isotope nomenclature of shackleton et al 1994a from stage tg24 in chron c3r earliest gilbert to stage c3ar 18o 18 at the base of chron c3ar 6 935 ma a major change in paleoceanographic conditions is recorded across the tortonian messinian boundary which we correlate to chron c3bn at 7 04 ma benthic foraminiferal 18o values increased by an average of 0 4 in two steps at 7 17 ma and 6 8 ma and 13c values decreased by 0 7 0 8 between 7 1 and 6 8 ma representing the late miocene carbon shift the first step in 18o values coincides with an inferred reversal in deep water circulation through the rifian corridor and the second correlates with the base of the tripoli formation and onset of crisis conditions in the mediterranean we suggest that the increase in 18o values represents at least in part an increase in global ice volume that lowered sea level and contributed to the establishment of a negative water budget in the mediterranean average 18o values remained high throughout most of chrons c3ar and c3an reaching maximum 18o values during isotope stages tg20 and 22 in chron c3r earliest gilbert the glacio eustatic falls associated with these events may have resulted in the complete isolation of the mediterranean from the world ocean shackleton et al 1994a following stage tg12 in the sale record there exists a trend toward progressively lower 18o values that may represent a series of marine transgressions that eventually reflooded the mediterranean and ended the salinity crisis

a critical re evaluation of the miocene pliocene boundary as defined in the mediterranean abstract a critical re evaluation of the miocene pliocene m p boundary as defined informally in the mediterranean is presented we show that ages reported earlier for this boundary ranging from 4 81 to 4 93 ma do not imply any diachroneity of the basal zanclean lithohorizon which reflects the pliocene flooding of the mediterranean and defines the m p boundary these ages most likely represent an artefact resulting from intraformational variations in sedimentation rate and inconsistent interpretation of coluor variations in terms of sedimentary cycles the best estimate for the age of this boundary arrives at 4 86 ma if the conventional geomagnetic polarity time scale gpts of berggren et al 1 is used and at 5 16 ma if the new gpts of cande and kent 2 is used an age of 5 32 ma is obtained if the astronomically calibrated time scale of hilgen 3 is adhered to because of its presumably global paleoclimatological significance the m p boundary as currently defined in the mediterranean is preferred to a redefinition of this boundary at the gilbert chron 5 boundary in a continous open marine sequence outside the mediterranean in addition this redefinition would lead to unnecessary confusion in global chronostratigraphy

decoding the mediterranean salinity crisis this historical narrative traces the steps to unravel over a span of 40 years an extraordinary event in which 5 of the dissolved salt of the oceans of the world was extracted in a fraction of a million years to form a deposit more than 1 million km 3 in volume a buried abyssal salt layer was identified with reflection profiling and sampled during the deep sea drilling project leg 13 the dolomite gypsum anhydrite and halite in the drill cores paint a surprising picture of a mediterranean desert lying more than 3 km below the atlantic ocean with brine pools that shrank and expanded by the evaporative power of the sun the desert drowned suddenly when the gibraltar barrier gave way the explanation of deep basin shallow water desiccation and the notion of a catastrophic zanclean flood had a mixed reception however the hypothesis became broadly accepted following subsequent drilling expeditions nevertheless as experts examined the evaporate facies and sequences of equivalent age in the terrestrial outcrops weaknesses appeared in the concept of repeated flooding and drying to account for the magnitude of the deposits the rosetta stone used to decipher conflicting interpretations turns out not to be the deposits but the erosion surfaces that enclose them these surfaces and their detritus formed in response to the drop in base level during evaporative drawdown extend to the basin floor evaporative drawdown began halfway through the salinity crisis when influx from the atlantic no longer kept up with evaporation prior to that time a million years passed as a sea of brine concentrated towards halite precipitation during the later part of this interval more than 14 cyclic beds of gypsum accumulated along shallow margins modulated by orbital forcing the thick salt on the deep seabed precipitated in just the next few cycles when drawdown commenced and the brine volume shrank upon closure of the atlantic spillway the remnants of the briny sea transformed into salt pans and endorheic lakes fed from watersheds of eurasia and africa the revised model of evaporative concentration now has shallow margin shallow water and deep basin deep water precursors to desiccation

the role of the bay of biscay mesozoic extensional structure in the configuration of the pyrenean orogen constraints from the marconi deep seismic reflection survey 1 seismic interpretation of the marconi deep seismic survey enables recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution the new data denotes that two domains with different pyrenean and north foreland structures exist in the bay of biscay in the eastern or basque parentis domain the north pyrenean front is located close to the spanish coast and the northern foreland of the pyrenees is constituted by a continental crust thinned by a north dipping fault that induced the formation of the early cretaceous parentis basin in the western or cantabrian domain the north pyrenean front is shifted to the north and deforms a narrower and deeper foreland basin which lies on the top of a transitional crust formed from the exhumation of lithospheric mantle along a south dipping extensional low angle fault during the early cretaceous the transition between these two domains corresponds to a soft transfer zone linking the shifted north pyrenean fronts and a north to wnw directed thrust that places the continental crust of the landes plateau over the transitional crust of the bay of biscay abyssal plain comparison between this structure and regional data enables characterization of the extensional rift system developed between iberia and eurasia during the late jurassic and cretaceous and recognizes that this rift system controlled not only the location and features of the pyrenean thrust sheets but also the overall structure of this orogen

a seismic geotraverse across the iberian variscides orogenic shortening collisional magmatism and orocline development 1 a crustal geotraverse through the iberian variscides is presented by integrating the available geological and seismic profiling data different modes of orogenic shortening are identified with varying degrees of coupling between upper and lower crust in northern and southern regions of the geotraverse a decoupling in the middle crust permits the lower crust to subduct underthrust thus compensating for strong upper crustal shortening this behavior does not result in great crustal thickening except in sectors of crustal underthrusting in southern central iberia moderate upper crustal shortening is due to a mechanically strong lower crust impeded to subduct underthrust in this region shortening is partitioned between upper and lower crust deformation being distributed in the upper crust while localized at major fault zones in the lower crust finally the central region of the geotraverse northern central iberia shows a coupled crustal deformation having given way to the largest orogenic thickening in the iberian variscides the thermal maturity of this much thickened crust originated voluminous crustal melting and concomitant normal fault detachments developed while shortening dominated in other regions theoretical models suggest that compressive stresses may prevail in the lower crust beneath the extending upper crust thus explaining the efficient syncollisional exhumation in this part of the orogen a particular feature of the iberian variscan geotraverse is the great importance of out of section mass movements mainly left lateral shear zones concentrated in two suture boundaries which displaced to the nw present coordinates central and northern iberia with respect to southern iberia

rift related inheritance in orogens a case study from the austroalpine nappes in central alps se switzerland and n italy the austroalpine nappe systems in se switzerland and n italy preserve remnants of the adriatic rifted margin based on new maps and cross sections we suggest that the complex structure of the campo grosina languard and bernina nappes is inherited largely from jurassic rifting we propose a classification of the austroalpine domain into upper middle and lower austroalpine nappes that is new because it is based primarily on the rift related jurassic structure and paleogeography of these nappes based on the alpine structures and pre alpine rift related geometry of the lower bernina and middle campo grosina languard austroalpine nappes we restore these nappes to their original positions along the former margin as a means of understanding the formation and emplacement of the nappes during initial reactivation of the alpine tethyan margin the campo and grosina languard nappes can be interpreted as remnants of a former necking zone that comprised pre rift upper and middle crust these nappes were juxtaposed with the mesozoic cover of the bernina nappe during jurassic rifting we find evidence for low angle detachment faults and extensional allochthons in the bernina nappe similar to those previously described in the err nappe and explain their role during subsequent reactivation our observations reveal a strong control of rift related structures during the subsequent alpine reactivation on all scales of the former distal margin two zones of intense deformation referred to as the albula zebru and lunghin mortirolo movement zones have been reactivated during alpine deformation and cannot be described as simple monophase faults or shear zones we propose a tectonic model for the austroalpine nappe systems that link inherited rift related structures with present day alpine structures in conclusion we believe that apart from the direct regional implications the results of this paper are of general interest in understanding the control of rift structures during reactivation of distal rifted margins

the discovery of scapolite marbles in the biscay synclinorium basque cantabrian basin western pyrenees geodynamic implications we report the presence of scapolite marbles in the biscay synclinorium of the basque cantabrian basin the link between the mainland pyrenees and the north iberian palaeomargin from their microstructures and mineral assemblages these marbles are correlated with similar marbles formed during the cretaceous metamorphism representative of the north pyrenean zone their setting in an area with northward verging structures leads us to propose a new location of the north pyrenean fault through the basque cantabrian basin available geophysical information gravity and magnetic anomalies is better explained with this new proposal which elucidates a major outstanding matter of pyrenean geology

metallogenic relationships to tectonic evolution the lachlan orogen australia abstract placing ore formation within the overall tectonic framework of an evolving orogenic system provides important constraints for the development of plate tectonic models distinct metallogenic associations across the palaeozoic lachlan orogen in se australia are interpreted to be the manifestation of interactions between several microplates and three accretionary complexes in an oceanic back arc setting in the ordovician significant orogenic gold deposits formed within a developing accretionary wedge along the pacific margin of gondwana at the same time major porphyry cu au systems formed in an oceanic island arc outboard of an evolved magmatic arc that in turn gave rise to granite related sn w deposits in the early silurian during the ongoing evolution of the orogen in the late silurian to early devonian sediment hosted cu au and pb zn deposits formed in short lived intra arc basins whereas a developing fore arc system provided the conditions for the formation of several volcanogenic massive sulphide deposits inversion of these basins and accretion to the australian continental margin triggered another pulse of orogenic gold mineralisation during the final consolidation of the orogenic belt in the middle to late devonian

displacement transfer from borders to interior of a plate a crustal transect of iberia abstract a n s crustal transect of the whole iberian plate is presented the displacement transfer during the alpine deformation from the border ranges cantabrian and betic chains toward the interior ones was analyzed by means of balanced crustal sections inconsistencies in shortening values between upper and middle lower crust in the cantabrian mountains basque cantabrian zone imply a mid crustal detachment transferring orogenic shortening southward toward the spanish central system depending on the shortening value attributed to the central system this mid crustal detachment could involve the entire iberian plate connecting the cantabrian mountains and the betic chain the very small crustal root in the central system can be explained as a result of the tectonic load caused by the upper crustal shortening that was transferred from the border ranges we conclude that a simple shear model rather than a pure shear with lithospheric folding better explains the whole iberia deformation finally the total alpine shortening of the iberian plate is estimated between 267 and 292 km

stable isotope stratigraphy of latest miocene sequences in northwest morocco the bou regreg section oxygen and carbon isotopic ratios of foraminifers were measured from outcrop and drill core sequences from the bou regreg section northwest morocco this composite section was located at the western end of the rifian corridor during the late miocene and thus potentially contains a record of water exchange between the atlantic and mediterranean during the late tortonian and messinian stages here we correlate isotopic and sedimentologic events in the bou regreg section with mediterranean and deep sea sequences during the time leading up to and including the deposition of the messinian evaporites the late miocene chron 6 carbon shift was identified in two moroccan sequences providing a valuable 6 3 ma datum level in both sections the carbon shift coincides with the first occurrence of globorotalia conomiozea and the tortonian messinian boundary near this boundary a major faunal turnover occurred in ostracod planktonic foraminiferal and nannofossil assemblages that indicates a cooling of surface and deep water in the rifian corridor at 6 1 ma just above the tortonian messinian boundary mean 18o values of benthic foraminifers increased by 0 4 0 5 suggesting decreased temperature and or increased continental ice volume the faunal and isotopic changes are interpreted as reflecting a reversal in the direction of deep water flow through the rifian corridor that occurred between 6 3 and 6 1 ma at this time cold nutrient rich waters filled the mediterranean basins from intermediate depths of the atlantic and the production of mediterranean outflow water ceased the upwelling of nutrient rich atlantic intermediate water stimulated productivity in the mediterranean which led to the deposition of organic rich strata such as those found in the tripoli formation at 5 5 ma coincident with a coiling shift in neogloboquadrina acostaensis the variability of the benthic 18o signal increased markedly and strong color variations appeared in the sediments alternating between red and blue marls these isotopic and sedimentologic changes at bou regreg represented markedly fluctuating oceanographic conditions in the rifian corridor between 5 5 and 4 8 ma we speculate that these cycles were related to sea level variations that controlled the periodic influx of marine water into the mediterranean during the time of evaporite deposition the onset of these cycles occurred at 5 5 ma and is correlated to a eustatic fall in sea level at the base of the caliza tosca formation in carmona spain and to the base of the lowermost evaporite unit in the mediterranean e g calcare di base in sicily in this proposed scenario the duration of the messinian salinity crisis was 700 000 years and lasted between 5 5 and 4 8 ma

imaging the crustal structure of the central iberian zone variscan belt the alcudia deep seismic reflection transect alcudia is a 230 km long vertical incidence deep seismic reflection transect acquired in spring 2007 across the southern central iberian zone part of the pre mesozoic gondwana paleocontinent of the variscan orogen of spain the carefully designed acquisition parameters resulted in a 20 s twtt deep 60 90 fold high resolution seismic reflection transect the processed image shows a weakly reflective upper crust the scarce reflectivity matching structures identified at surface a thick highly reflective and laminated lower crust and a flat moho located at 10 s twtt 30 km depth the transect can be divided into three segments with different structural styles in the lower crust in the central segment the lower crust is imaged by regular horizontal and parallel reflectors whereas in the northern and southern segments it displays oblique reflectors interpreted as an important thrust north and tectonic wedging involving the mantle south the alcudia seismic image shows that in an intracontinental orogenic crust far from the suture zones the upper and lower crust may react differently to shortening in different sectors which is taken as evidence for decoupling the interpreted structures as deduced from surface geology and the seismic image show that deformation was distributed homogeneously in the upper crust whereas it was concentrated in wedge thrust structures at specific sectors in the lower crust the seismic image also shows the location of late variscan faults in spatial association with the lower crustal thickened areas

seismic image of the cantabrian mountains in the western extension of the pyrenees from integrated escin reflection and refraction data abstract integrated analysis of normal incidence and large aperture seismic reflection data collected in 1992 and 1993 within the spanish escin and complementary projects provide a first complete n s crustal transect across the northern iberian peninsula and continental margin images of the crustal structure of the cantabrian mountains and their transition to the duero basin and to the cantabrian margin are obtained from a a 65 km long vertical reflection profile escin 2 on land b a 200 km long reversed refraction profile and c wide angle recordings of the marine escin 4 profile consistent results between reflectivity pattern and velocity depth distribution reveal important lateral variations in the deep structure the reflective crust imaged in the escin 2 profile changes its attitude from sub horizontal beneath the duero basin to north dipping beyond the mountain front basement thrusts are observed in the upper crust merging into a detachment at 6 s twt and may have triggered the alpine uplift of the range the moho is identified at the bottom of the reflective lower crust and deepens from 12 to 15 s at the northern end of the profile about 35 km inland modelling of the refraction data laterally extends the seismic image and provides evidence for variscan crustal features beneath the duero basin northwards the velocity in the lower crust decreases and the moho constrained by the wide angle data from profile escin 2 deepens to about 60 km ending abruptly at the shoreline the velocity depth model is constrained along the asturian platform up to the continental slope where the crust mantle boundary is located at 24 km depth this margin moho shows a progressive deepening southwards and extends to the coast where it is found at 30 km depth the present seismic data support an important alpine reworking and thickening of the crust under the cantabrian mountains the onshore offshore transition is marked by an imbrication of two crusts of very different thicknesses this signature offers a strong parallelism with the one previously observed further east across the pyrenees in the ecors seismic profile

extension of the astronomically calibrated polarity time scale to the miocene pliocene boundary the early pleistocene to late pliocene astronomically calibrated time scale of shackleton et al 1 and hilgen 2 is extended to the miocene pliocene boundary this is done by correlating the detailed record of caco3 cycles in the trubi and the lower part of the overlying narbone formation rossello composite section sicily to the astronomical record using 1 inferred phase relations between these caco3 cycles and the corresponding orbital cycles of precession and eccentricity and 2 calibration points provided by the previously established astronomical calibration of sapropelitic layers which occur in the topmost part of the caco3 record 2 this correlation allows all small scale caco3 cycles in the rossello composite section to be coded after the correlative precession peak and to be dated astronomically with an accuracy of 1 ky in combination with the available high resolution magnetostratigraphy it further allows the construction of an astronomically calibrated geomagnetic polarity time scale for the major part of the gilbert and gauss chrons this new time scale gives ages for the reversal boundaries of the kaena 3 04 3 11 ma and mammoth 3 22 3 33 ma the gilbert gauss chron boundary 3 58 ma and the reversal boundaries of the cochiti 4 18 4 29 ma nunivak 4 48 4 62 ma sidufjall 4 80 4 89 ma and thvera 4 98 5 23 ma these ages are significantly older than the ages given by conventional time scales age discrepancies gradually increase with increasing age the age of 5 32 ma for the miocene pliocene boundary as defined by the base of the trubi on sicily is almost 0 5 m y 9 5 older than the presently accepted age of 4 86 ma 3 these considerable discrepancies with the conventional time scale can either be explained by an consistent error in the decay constants used in k ar radiometric dating or more likely by diffusional loss of radiogenic argon

the madrid basin and the central system a tectonostratigraphic analysis from 2d seismic lines abstract data from deep boreholes seismic surveys and surface geology are used to reconstruct the sedimentary infilling of the cenozoic madrid basin eight main depositional sequences and seismic units are recognised from the paleogene the latter four of these sedimentary sequences were deposited in a continental environment under the influence of tectonic activity in the central system the toledo mountains the iberian chain and the sierra de altomira the sedimentary infill shows an overall coarsening upward trend from upper cretaceous formations to syn tectonic conglomerate deposits followed by a fining upward sequence and moderate reactivation of some faults during the late miocene pliocene the syn tectonic sediments are oligocene early miocene in age the foredeep is oriented northeast southwest and shows a sediment thickness of up to 3800 m in areas close to the central system several types of tectonic structures are recognised including imbricate thrust systems thrust triangle zones fault propagation folds back thrust systems and pop up structures the frontal thrusts were subjected to significant erosion and late miocene sediments onlap the anticlines of the onshore foreland nw se trending positive flower structures have been recognised in the eastern part of the basin the total northwest southeast shortening across the contact between the madrid basin and the central system is approximately 5 km of which 2 3 km occurred across the southern border thrust the simultaneous basement uplift of the central system and the tectonic escape of the sierra de altomira have been interpreted as a consequence of constrictive deformation within the pyrenean foreland of the iberian microplate

unit stratotypes for global stages the neogene perspective abstract recent developments in integrated high resolution stratigraphy and astronomical tuning of continuous deep marine successions invalidate arguments against the designation of unit stratotypes for global stages the basic building blocks of the standard global chronostratigraphic scale gcs for the late neogene global stratotype section and point gssp sections may also serve as unit stratotypes covering the interval from the base of a stage up to the level that time stratigraphically correlates with the base of the next younger stage in a continuous and well tuned deep marine succession the added value of such sections as unit stratotype lies in the integrated high resolution stratigraphy and astronomical tuning which combined provides an excellent age control with an unprecedented resolution precision and accuracy within the entire stage as such they form the backbone of the new integrated late neogene time scale and provide the basis for reconstructing earth s history in this way a stage is also defined by its content and not only by its boundaries our unit stratotype concept strengthens the importance of time rock units by allowing the introduction of astronomically defined chronozones as formal chronostratigraphic units thereby arguing against the elimination of the dual classification of chronostratigraphy and geochronology extending this concept to older time intervals requires that well tuned continuous deep marine sections are employed thus necessitating the employment of multiple hole i odp sites for defining remaining stages and stage boundaries in at least the cenozoic and cretaceous and possibly the entire mesozoic evidently the construction of the geological time scale including the gcs should be based on the most appropriate sections available while where possible taking the historical concept of global stages into account

initiation of an active margin at the north iberian continent ocean transition 1 the north iberian or cantabrian margin located at the southern flank of the bay of biscay underwent successive tectonic regimes of rifting passive margin and compression from mesozoic to tertiary times a complete crustal cross section of the north iberian margin from the abyssal plain to the shoreline and a reconstruction of its undeformed upper cretaceous structure are presented here it is constrained after the compilation and interpretation of different geophysical data sets recently available in the area the reflective pattern is provided by deep seismic reflection profile escin 4 complemented by commercial profiles and well information from the north iberian platform and the velocity depth control comes from an onshore offshore wide angle seismic profile tested also with gravity modeling the detailed cross section of the meso tertiary basins that fill the platform and abyssal plain shows structures from the three main tectonic events 1 normal faults and asymmetric basins from the permian to lower cretaceous extensional stage 2 upper cretaceous sediments deposited under stable conditions during the passive margin period and 3 inverted faults thrusts and folds related to the tertiary compression the deep structure of the crust beneath the margin is poorly constrained from escin 4 profile that shows reflectivity in the lower crust only at a small area under the platform however the corresponding wide angle experiment provides a conspicuous image of the moho that shows a continued deepening toward the continent on the basis of the geophysical results we propose a new model for this margin where the lower crust is detached and underthrusted to the south as a result of the partial closure of the bay of biscay an interpreted mesozoic crustal scale extensional detachment could be the weakness zone that allowed the lower crust to slide southward under the upper crust resulting in the indentation of the cantabrian margin lower crust into the iberian crust plate convergence stopped at an early stage making this a unique area to study the initial stages of deformation of a passive margin

mesozoic extensional tectonics stratigraphy and crustal evolution during the alpine cycle of the eastern iberian basin abstract sequence stratigraphy subsidence analysis and the integration of the basin fill data allow to the identification of four successive evolutionary stages in the basins of the eastern iberian margin during mesozoic extension 1 triassic rift late permian hettangian 2 early and middle jurassic postrift sinemurian oxfordian 3 late jurassic and early cretaceous rift kimmeridgian middle albian and 4 late cretaceous postrift late albian maastrichtian the present day crustal structure of the eastern iberian range and evidence of its evolution are deduced from the analysis of a new gravity map and other geophysical data a regional gravity low along the iberian range is interpreted in terms of crustal thickening beneath the orogen as a result of the collision between the ebro block and the iberian plate during the paleogene the boundary between these blocks coincides with a magnetic lineament that is interpreted as an inherited signature of the thinning that occurred during mesozoic extension a geodynamic scenario for the crustal evolution of the eastern part of the iberian peninsula based on the evaluation of mesozoic extensional tectonics and an analysis of the available geophysical data includes three main successive evolutionary stages 1 1 mesozoic crustal thinning 2 2 paleogene crustal thickening 3 3 neogene crustal thinning based on new geological and geophysical arguments this study offers an alternative and a more complete geodynamic history of the eastern iberian basins related to the evolution of the iberian plate and the central north atlantic

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

intraplate deformation in the nw iberian chain mesozoic extension and tertiary contractional inversion the iberian chain developed within the iberian plate during the palaeogene and early miocene as a result of convergence between the african and eurasian plates it is a fold and thrust belt which involves the hercynian basement and the mesozoic and cenozoic cover a generalized cross section of the nw part of the chain of 195 km length is presented mesozoic basins developed on the hercynian basement display thickness variations across normal faults that bounded them and that can be recognized in the field the tertiary contraction deformed and inverted the mesozoic basins and it is inferred to have produced a thrust sheet about 5 km thick in its frontal northeastern part which thickens to the sw the total tertiary shortening in the section is 66 6 km 26 the structure and the crustal shortening and thickening of the iberian chain are explained by a major upper crustal thrust system with simple flat and ramp geometry which may branch to the pyrenees or the betics this is combined with internal deformation of the thrust sheet the contribution of the iberian chain shortening to the convergence of the african and eurasian plates during the tertiary is about one half of that of the pyrenees and should be taken into account in any reconstruction of the kinematics of these plates

high resolution moho topography map beneath iberia and northern morocco from receiver function analysis abstract crustal thickness maps at regional scales are typically compiled using estimations inferred from different geophysical datasets providing a variable coverage of the investigated area consequently spurious effects related to changes in data resolution or artifacts in grid interpolation may affect significant zones of those maps the topoiberia iberarray broad band seismic network covering the iberian peninsula and northern morocco with stations distributed on a regular 60 60 km grid provides a unique opportunity to avoid such technical problems and to obtain a crustal thickness map derived from a same method sampling evenly all the region data from more than 340 stations has been gathered and analyzed using the p to s conversion phases at the moho discontinuity receiver functions the crustal thickness has been inferred applying the classical h stacking technique though in regions of complex crustal structure we have preferred to estimate the thickness directly from the arrival time of the converted phase at some sites the topography of the moho discontinuity is strongly correlated with tectonic processes the investigated area extending from the sahara platform to the bay of biscay has a great geodynamic diversity including north to south crustal imbrication in the pyrenean and cantabrian range a large and relatively undisturbed variscan massif in the center of iberia and areas of complex and still not completely understood geodynamics in the alboran crust domain and the atlas range the crustal thickness map reflects this diversity showing variations reaching 30 km between the thickest and thinnest zones of continental crust the final map has an overall similarity with previous estimations of the crustal thickness using independent data as those coming from more sparse deep seismic sounding profiles but provides further constraints at regional scale

centrifuge modelling of folding in high grade rocks during rifting centrifuge modelling is used to simulate the progressive development of structures in a simplified crustal profile during rifting this paper focuses on folding of ductile layers representing the middle to lower crust displacement along a pre existing cut in the layer representing mantle lithosphere creates a broad shear zone in overlying ductile layers and an asymmetric rift in upper layers the footwall of the mantle lithosphere layer and overlying shear zone are rotated to sub horizontal during rise of the basal ductile layer representing asthenosphere as an isostatic response to thinning in the extended model synthetic and antithetic faults develop in models with thicker ductile crustal layers although upper semi brittle layers representing upper crust constitute a simple fault bounded or sag basin the underlying ductile layers are complexly folded open upright folds developed over the crest of the footwall mantle lithosphere layer are tightened and increased in amplitude as they progressively rotate to a recumbent attitude refolding occurs during rise of the basal ductile material representing asthenosphere and from boudinage of overlying competent layers this study suggests that regional scale folds in some high grade terrains previously interpreted as evolving in a convergent margin tectonic setting may instead be produced as a result of flow of the ductile crust during rifting

sequential faulting explains the asymmetry and extension discrepancy of conjugate margins rifted continental margins are the sites that record the thinning and break up of continents to form new oceans cesar ranero and marta perez gussinye use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this to crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy in which crustal thinning appears to be greater than the extension caused by brittle faulting by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins these authors use seismic imaging to accurately measure fault extension at the conjugate west iberia and newfoundland margins and compare this with crustal thinning they use these observations to create a balanced kinematic model of rifting that resolves the extension discrepancy where crustal thinning seems to be greater than the extension caused by brittle faulting during early extension cold continental lithosphere thins and subsides creating rift basins if extension continues to final break up the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins although basins and margins are ubiquitous structures the deformation processes leading from moderately extended basins to highly stretched margins are unclear as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1 2 3 4 this extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2 but that does not readily explain the typical asymmetric structure of conjugate margins5 6 in cross section one margin displays gradual thinning accompanied by large faults and the conjugate margin displays abrupt thinning but smaller scale faulting5 whole crust detachments active from early in the rifting could in theory create both thinning and asymmetry1 but are mechanically problematical furthermore the extension discrepancy occurs at both conjugate margins leading to the apparent contradiction that both seem to be upper plates to a detachment fault7 8 alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic resolution faulting9 invisible deformation along top basement 100 km scale detachments8 or the structural complexity of cross cutting arrays of faults3 here we use depth migrated seismic images to accurately measure fault extension and compare it with crustal thinning the observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault controlled crustal thinning which progresses from a rift basin to the asymmetric structure and extreme thinning of conjugate rifted margins contrary to current wisdom the observations support the idea that thinning is to a first degree explained by simple andersonian faulting that is unambiguously visible in seismic data

triassic paleomagnetism from the western pyrenees revisited implications for the iberian eurasian mesozoic plate boundary since the pioneering studies of van der voo tectonophysics 7 1969 5 and van der voo and boessenkool j geophys res 78 1973 5118 paleomagnetism of permo triassic redbeds and volcanics from the western pyrenees has furnished important contributions for delineating the mesozoic boundary between the iberian and eurasian plates in this paper we present a new paleomagnetic study focussed on triassic red beds 23 sites of the paleozoic basque massifs pbm the aim of this study is to complement previous studies done in those massifs to better constrain the complex kinematics of the western pyrenees two stable magnetic components have been isolated 1 a dual polarity pre folding magnetisation carried by specular hematite and 2 a secondary normal polarity component also carried by hematite our data confirm both the origin and the rotation pattern of the primary remanence described in previous works nevertheless field tests performed on the secondary component do not confirm the earlier interpretations by schott and peres tectonophysics 156 1988 75 as they indicate a synfolding nature of the remagnetisation instead of a post folding origin we consider that the secondary component is better explained if a cretaceous age is considered the presence of such remagnetisation in the western pyrenees strengthens the widespread occurrence of similar remagnetisation events reported in northern iberia in connection with the extensional tectonic events that occurred during cretaceous times a comparison of the rotations recorded by the triassic component and by the remagnetisation indicate that the paleozoic units underwent variable tectonic rotations before the remagnetisation was acquired most likely in connection with the counterclockwise rotation of iberia with respect to eurasia these results favour that the mesozoic plate boundary between the iberian and eurasian plates was a wide domain of distributed deformation and therefore contradict previous interpretations claiming for a discrete plate boundary

continental rift development in precambrian and phanerozoic europe europrobe and the dnieper donets rift and polish trough basins abstract upper crustal structure and lower crustal and mantle character of the european continental lithosphere differ significantly from west to east the processes of rifting of phanerozoic western europe s hotter thinner crust compared with the more stable thicker 45 vs 30 km proterozoic crust of the east european craton is being investigated by europrobe case studies of western and eastern european sedimentary basins the dnieper donets basin transects the southwestern part of the east european platform in a nw se direction lying between the ukrainian shield and the voronezh massif rifting took place from early frasnian until perhaps the late visean and was accompanied by major volcanic activity the distribution of both was affected by pre existing basement fault systems the syn and post rift sedimentary succession may be as thick as 20 km in the donets trough basin evolution and the present crustal geometry have been much affected by inversion during the permian in association with uralian orogenesis tectonic events of bathonian oxfordian 168 154 ma and turonian santonian 91 84 ma age are also recorded in the basin stratigraphy the polish trough lies along the boundary between the phanerozoic and proterozoic european crustal domains coincident with the trans european suture zone the presence of this rheological boundary may be paramount in structurally controlling the position of the trough tectonic subsidence analysis indicates an initial late rotliegendes early triassic syn rift phase of development subsequently episodes of increased tectonic subsidence rate occurred during the oxfordian tithonian 157 146 ma and beginning in the cenomanian 95 90 ma the oxfordian tithonian episode is likely the signature of a second extensional event correlated with intensification of rifting within the arctic north atlantic rift system while the cenomanian and later is a precursor to mild compressional intraplate orogenic movements present day crustal structure reflects the docking of phanerozoic crust against the proterozoic during palaeozoic orogenies permo carboniferous wrenching and transtensional modifications leading to formation of the polish trough as well as modifications during the late cretaceous early tertiary inversion process

integrated stratigraphy and astrochronology of the messinian gssp at oued akrech atlantic morocco a much improved high resolution integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy cyclostratigraphy is presented for the classic section of oued akrech atlantic morocco straddling the tortonian messinian boundary magnetobiostratigraphic correlations with time equivalent and astronomically dated sections in the mediterranean indicate that cyclic alternations of indurated light beige coloured marls and softer more clayey and reddish coloured marls are dominantly precession controlled characteristic sedimentary cycle patterns in particular those reflecting precession obliquity interference allow for one possible tuning thus providing accurate astronomical ages for cycles calcareous plankton events and magnetic reversals the tuning further indicates that the reddish layers are the equivalent of sapropels in the mediterranean the messinian global boundary stratotype section and point gssp has recently been formally defined at the base of the reddish layer of cycle no 15 in section oued akrech this level coincides closely with the first regular occurrence of the globorotalia miotumida group and is astronomically dated at 7 251 ma the global correlation potential is guaranteed by the straightforward calibration of the oued akrech magnetostratigraphy to the geomagnetic polarity time scale locating the gssp within c3br 1r in the marine realm the calcareous nannofossil genus amaurolithus provides a series of extremely useful events to delimit the boundary on a global scale the astronomical tuning guarantees a direct first order calibration of the messinian gssp to the standard geological time scale once as anticipated the late miocene part of the astronomical time scale has been incorporated fl 2000 elsevier science b v all rights reserved

orthogonal folding of extensional detachments structure and origin of the sierra nevada elongated dome betics se spain 1 a close relationship of the kinematics and timing between low angle extensional faulting and upright folding is established for the miocene detachment systems in the hinterland of the betics in southeastern spain folding accompanied tectonic denudation developing elongated domes with fold axes both parallel and perpendicular to the direction of extension the geometry kinematics and tectonic evolution of two major sequentially developed extensional fault systems have been characterized in several e w elongated mountain ranges of the central betics on the basis of new cartographic and structural data and a comprehensive revision of other available geological and geophysical observations the extensional systems have an average wsw direction of extension and led to exhumation of the two lower metamorphic complexes of the betics the nevado filabride and the alpujarride during the middle and upper miocene serravallian to tortonian the extended domain contains a core complex with distal and proximal antiformal hinges separated by around 60 km and with a fold amplitude of 6 km measured parallel to the direction of extension the total amount of extension across the core complex is about 109 116 km corresponding to a stretching factor of 3 5 3 9 estimated using the distance between fold axial surfaces and a geometrical model accomplishing footwall deformation during tectonic denudation via subvertical simple shear the elongated domal and basinal geometry of the detachments and their respective footwalls is due to the interference between two sets of orthogonal large scale open folds trending n s and e w longitudinal n s trending folds are interpreted as isostatic folds i e folds that developed in response to differential unloading of the extensional detachment footwalls inducing ductile flow in the middle crust these folds formed in a rolling hinge anticline in which rotation migrates westward through the footwall as it is progressively unroofed in contrast e w trending folds being subparallel to the direction of extension have a contractional origin and progressively affect to the west the isostatically readjusted segments of the detachments once they are inactive orthogonal folding occurred since the serravallian to lower pliocene extension is still active from the rolling hinge anticline in sierra nevada to the west the middle miocene to pliocene tectonic evolution of the sierra nevada elongated dome at the core of the betic hinterland is another example of the coexistence of extension and contraction during continued overall convergence and mountain building

fifteen degrees of separation latitudinal gradients of rocky intertidal biota along the california current the region of the eastern north pacific coastline dominated by the california current was surveyed annually from 2001 2003 to examine 1 benthic macro invertebrate and algal populations 2 the magnitude and patterns of key environmental variables and 3 how dynamic populations and communities of macroalgae and invertebrates respond to spatial differences in nearshore geomorphology wave dynamics and oceanography of the coastal shelf we used a highly replicated spatially nested sampling design consisting of 144 shore segments bedrock platforms longer than 50 m with three replicate segments per sit e 1 km three sites per area 10 km and sixteen areas 10 km grouped into six domains hundreds of kilometers results suggest that 1 low zone diversity was higher at northern latitudes when measured at segment site and area scales but at domain scales there were more species at southern latitudes 2 community structure showed high fidelity to geographic location with community similarity inversely related to separation distance and the only regional scale biological discontinuity in community structure was centered near pt conception and 3 wave runup was the most significant physical parameter affecting overall community structure however tidal range precipitation air and water temperature upwelling salinity and sand were significant mechanisms forcing differences in community structure within the region

model of distributed deformation block rotations and crustal thickening for the formation of the spanish central system abstract the spanish central system constitutes an important morphostructural intraplate feature of iberia that resulted from a concentration of crustal strain derived from stresses applied on the boundaries of the betics and pyrenees we propose a tectonic model in which the deformation of this zone was produced by a mid late mesozoic shear zone a type of secondary plate boundary that absorbed part of the iberia eurasia relative motion the deformation within this e w shear zone was compensated by means of block rotations that resulted from the reorganization of multiple and previous faults and fractures the subsequent n s africa eurasia convergence was partly accommodated within this intraplate zone of weakness this caused a concentration of strain that was responsible for the homogeneous thickening of the lower crust and for the blocking of block rotations and forced uplifting of the upper crust

the age of the miocene pliocene boundary in the capo rossello area sicily detailed correlations of magnetostratigraphy biostratigraphy and lithostratigraphy reveal that the basal pliocene is equally complete in the eraclea minoa and capo rossello sections sicily and the singa section calabria and that in accordance with the model of the pliocene flooding event in the mediterranean the deposition of the pelagic marls of the trubi formation started synchronously on sicily and in adjacent calabria in addition the data obtained from the trubi in the eraclea minoa section allows the age of the miocene pliocene boundary to be adjusted slightly from 4 83 4 84 1 to 4 86 ma because downward extrapolation of both sedimentation rate and average duration of small scale sedimentary cycles in the trubi yields this age for the boundary in this section linearly interpolated ages for the top of the sphaeroidinellopsis acme and the first substantial increase in globorotalia margaritae the fod of this species is non existent in the mediterranean pliocene at eraclea minoa arrive at 4 74 and 4 63 ma respectively because of the detailed magnetostratigraphy and the very accurate dating of the miocene pliocene boundary it is preferable to select the eraclea minoa section as the boundary stratotype rather than the capo rossello section finally this age of 4 86 ma for the miocene pliocene boundary suggests that the beginning of the pliocene is connected with the termination of a series of latest miocene glaciations and that the re establishment of open marine conditions in the mediterranean might be of glacio eustatic origin

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

geologic map of the basque cantabrian basin and a new tectonic interpretation of the basque arc a new printable 1 200 000 bedrock geological map of the onshore basque cantabrian basin is presented aimed to contribute to future geologic developments in the central segment of the pyrenean cantabrian alpine orogenic system it is accompanied in separate appendixes by a historic report on the precedent geological maps and by a compilation above 350 bibliographic citations of maps and academic reports usually overlooked or ignored that are central to this contribution structural scrutiny of the map permits to propose a new tectonic interpretation of the basque arc implementing previously published partial reconstructions it is presented as a printable 1 400 000 tectonic map the basque arc consists of various thrust slices that can expose at the surface basement rocks palaeozoic to lower triassic and their sedimentary cover uppermost triassic to tertiary from which they are detached by intervening upper triassic evaporites and associated rocks the slice bounding thrusts are in most cases reactivated normal faults active during meso cenozoic sedimentation that can be readily related to basement discontinuities generated during the hercynian orogeny

a review of cretaceous smooth slopes extensional basins along the iberia eurasia plate boundary how pre rift salt controls the modes of continental rifting and mantle exhumation this article points out for the first time a striking correlation between the paleogeography of upper triassic deposits and the mode of crustal stretching around and inside the northern iberia plate during the cretaceous transtensional event first we propose a review of the architecture of the basins which opened during the mid cretaceous times along the iberia eurasia plate boundary similarly to the emblematic parentis basin these basins exhibit a peculiar synclinal shaped profile and are devoid of prominent block faulting the top of the basement is characterized by gentle slopes which dip symmetrically toward the center of the basins as revealed by recent comparisons with geologically constrained rifting models established from the north pyrenean zone this architecture results from the thinning of a heterogeneous continental crust under greenschist facies conditions basement deformations are thus dominantly ductile and are characterized by large scale boudinage hyper thinning and subsequent lateral extraction bulk deformation of the upper and middle crust leads to the formation of anastomosed shear zones and the development of mylonitic fabric tectonic lenses consisting of crustal material remain welded on top of the exhuming mantle the common character shared by all the pre rift sequences of the studied basins is the presence of a thick low strength upper triassic evaporites and clays layer belonging to the keuper group i e pre rift salt and clay unit in the studied basins efficient decollement along the pre rift salt and clay unit triggers mechanical decoupling and gliding of the pre rift cover that remains in the center of the basin thus during the early rifting phase the basement undergoes thinning while the pre rift cover remains preserved in the basin center in response to hyper thinning and horizontal extraction of the continental crust hot mantle is exhumed beneath the pre and syn rift cover subsequent thermal exchange i promotes ductile deformation of the basement and ii induces the development of ht lp metamorphic conditions in the pre rift sediments and at the base of the syn rift flysch levels this thermal event is well recorded in the axial portion of the pyrenean realm future north pyrenean zone as well as in the pre rift sediments of the cameros basin northern spain the architecture of the smooth slopes type basins thus contrasts with the structure of iberia newfoundland atlantic margins which are characterized by i top basement detachment faults accommodating crustal extension through rotation and translation of undeformed basement blocks and ii the individualization of continental extensional allochthons tectonically emplaced over exhumed lower crust or mantle rocks finally using recent paleogeographic reconstructions we show that the distribution of the pre rift salt and clay unit remarkably matches the distribution of the pyrenean and peri pyrenean smooth slopes type basins this allows for the first time to propose a genetic link between the distribution of evaporite bearing pre rift sedimentary formations and the development of smooth slopes basins

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

crustal structure beneath the iberian peninsula and surrounding waters a new compilation of deep seismic sounding results abstract we present here an updated compilation of crustal parameters beneath the iberian peninsula and surrounding waters inferred from extensive deep seismic exploration performed in the last three decades firstly the more relevant experiments developed in both terrestrial and marine domains are revisited together with the corresponding seismic velocity depth models published that reveal the characteristics of the different tectonic domains sampled including oceanic zones continental margins orogenic and rift belts the results are summarized in three crustal transects sketched along representative directions secondly we compiled the moho depths along all the available seismic profiles to produce a geo referred database this database has then been interpolated using kriging algorithms to obtain a continuous moho depth model in the form of a regular grid file this integrative moho map for a key area in the western mediterranean documenting the interaction between european and african plates can contribute to constrain further regional studies either at crustal lithospheric or mantle scales

the rossello composite a mediterranean and global reference section for the early to early late pliocene a high resolution magnetostratigraphy planktonic foraminiferal biostratigraphy and cyclostratigraphy is presented for the pliocene trubi marls in the punta di maiata section on sicily the integrated stratigraphy of the rossello composite section of hilgen 1 newslett stratigr 17 1987 is thereby completed this composite section provides an unprecedented high quality reference section for the early to early late pliocene containing a continuous sequence ranging from below the thvera subchron into the matuyama chron 4 86 2 45 ma the punta di maiata section extends from the sidufjall subchron of the gilbert into the gauss chron 4 50 3 30 ma linear interpolation between paleomagnetic datum planes in this section yields first order age estimates of 3 72 0 01 and 3 59 0 01 ma for the last common occurrence lco and the actual last occurrence lo of globorotalia margaritae in addition this age of 3 59 ma provides an accurate age for the zanclean piacenzian z p boundary provided the lo of g margaritae is maintained as a criterion to define this boundary in the mediterranean irrespective however of the criterion used the punta di maiata and punta piccola subsections of the rossello composite are at present the most suitable sections to be designated as stratotypes for the z p boundary the global significance of the rossello composite is further strongly enhanced by the establishment of an astronomically calibrated geomagnetic polarity time scale based on the correlation of the trubi sedimentary cycles with the astronomical record

lateral inhomogeneities of the hercynian crust in central spain abstract an azimuthal layout of deep seismic profiles has been partially completed in the central iberian massif data from two new profiles and a reinterpretation of previous profiles make possible two dimensional models for the hercynian crust in central spain from which some lateral crustal inhomogeneities can be established these inhomogeneities due to alpine intraplate tectonics coincide with the spanish central system and consist of a 5 km crustal thickening with respect to the surrounding areas

the tertiary and the quaternary are here to stay in 1989 and 2000 the international commission on stratigraphy ics published geologic time scales in which the term tertiary had been eliminated in the time scales published by the ics in 2004 the term quaternary was also eliminated the cenozoic shown as composed of two systems the paleogene and the neogene the neogene extending to the present was there any logical basis for these changes a review of the geologic literature since 1980 19 journals of extensive distribution and a considerable number of geologic maps time scales and stratigraphy textbooks as well as the georef clearly indicates that the tertiary and the quaternary have long been and are now in widespread use by geologists the world over and that their use has not declined at all during the last 25 yr they are very useful terms in geologic work essential for clear communication among geologists paleogene and neogene have received increasing use during the last 10 yr because they are also useful terms quaternary is probably the stratigraphic term most frequently used in the geologic literature tertiary is used as the pre quaternary part of the cenozoic by most geologists some however prefer to use paleogene and neogene instead of tertiary but it should not be a question of either tertiary or paleogene and neogene all three are needed as are cenozoic paleocene eocene oligocene miocene and pliocene to express various degrees of precision in stratigraphic assignation and dating all should be recognized as units of a standard geologic time scale geologists should retain a choice of what they think better fits their needs the preferred time scale therefore should have the cenozoic erathem comprising the tertiary and quaternary systems and the tertiary including the paleogene and neogene subsystems past attempts to eliminate the tertiary and quaternary have been ignored recent attempts will not succeed either the tertiary and the quaternary are here to stay certainly as long as geologists continue to use them as they have and continue to oppose the ill advised efforts to discard them from the geologic time scale

a paleomagnetic study of the basque arc basque cantabrian basin western pyrenees the basque arc constitutes the northern segment of the basque cantabrian basin in the western part of the pyrenees the main goal of the present study was to find out by means of paleomagnetic analysis if the arched shape of the basque arc has a primary origin due to the development of sedimentary basins related to the opening of the bay of biscay or a secondary origin due to rotations about vertical axes nine volcanic flows of late albian to santonian age 100 83 5 my were sampled together with 10 sedimentary sites marls limestones calcarenites and sandstones of lower jurassic to early eocene age in order to carry out paleomagnetic and rock magnetic experiments 15 paleodirections being obtained in order to analyse these results together with data from previous studies the studied area was subdivided into a western a central and an eastern sector while inclinations of all three sectors show a similar value declinations differ the western sector displays a 37 16 clockwise rotation of its mean paleodeclination the central sector is not rotated 4 9 and both sedimentary sites which make up the eastern sector show counter clockwise rotations 25 11 and 68 9 these results suggest that the shape of the basque arc does not have a primary origin but a secondary origin due to rotations about vertical axes as a result of differential shortening related to post lutetian compressive tectonics which resulted in the formation of the pyrenees

some examples and mechanical aspects of continental lithospheric folding abstract recent theoretical and observational advances in understanding the dynamics of lithosphere processes have yielded strong evidence in favour of the existence of large scale lithosphere folds intraplate compressional stresses generated by plate tectonic forces can reach magnitudes that approach the plastic buckling strength of mechanical models of lithosphere with brittle ductile rheological stratification the models predict lower plastic buckling stresses for continental lithosphere than for oceanic lithosphere intraplate folding of relatively strong oceanic lithosphere documented extensively in the northeastern indian ocean occurs where stresses are concentrated by restricted geometric and dynamic conditions resulting in unusually high stress levels several hundreds mpa on continents where geophysical data suggest that lithosphere folding may have occurred during the development of sedimentary basins in northern canada and central australia buckling stresses can have magnitudes that are of a similar order to those thought typically to occur in the lithosphere several tens mpa folding of continental lithosphere although more difficult to document is likely to be an important mechanism of large scale continental deformation in particular thinned continental lithosphere with a history of superposition of thick sedimentary successions might be the preferential locus of such folding lithosphere folding could also be a controlling factor in the near surface deformation of rifted basins as reflected by tectonic basin inversion

mediterranean neogene stratigraphy development and evolution through the centuries the mediterranean area in general and italy in particular played an important role in developing the principles of stratigraphy since the early days of geological thinking in the middle of the 19th century there was a rush to name all the intervals of the stratigraphic column at that time when invertebrate palaeontology was the principal source of information on the relative age of the rock units dozens of stage names were created for the neogene only a few of these stage names survive and are accepted worldwide as langhian serravallian tortonian messinian zanclean and piacenzian in the later part of the 19th century and in the first decades of the 20th century a wealth of new data was made available by extensive palaeontological studies but the correlation potential of the fossil faunas was constrained poorly and understood less leading to the development of a floating stratigraphy the situation improved after world war ii when micropalaeontology underwent a fast development the creation of common stratigraphic guidelines the introduction of the stratotype concept followed by the golden spike concept global stratotype section and point combined with the application of multiple stratigraphic methodologies especially palaeomagnetic stratigraphy or magnetic polarity time scale astrocyclostratigraphy or astronomical time scale resulted in new scenarios a turning point may be located around 1970 soon after the beginning of the deep sea drilling project which greatly contributed to the development of a new approach to neogene stratigraphy now all the global stratotype sections and points for the neogene stages are being defined by multiple criteria with precise definitions in terms of magnetic polarity time scale and astronomical time scale the rossello composite section in southern sicily is the template for the late neogene stratigraphy with the best time resolution provided by astronomical forcing to complete the planned study the same criteria have to be applied downwards and upwards

crustal structure of an intraplate thrust belt the iberian chain revealed by wide angle seismic magnetotelluric soundings and gravity data abstract the iberian chain is a cenozoic intraplate thrust belt located within the iberian plate unlike other belts in the iberia peninsula the scarcity of geophysical studies in this area results in a number of unknowns about its crustal structure the iberian chain crust was investigated by means of a ne sw refraction wide angle reflection seismic transect and two magnetotelluric profiles across the chain oriented along the same direction the seismic profile was designed to sample the crust by means of three shots designed to obtain a reversed profile the resulting velocity depth model shows a moderate thickening of the crust toward the central part of the profile where crustal thickness reaches values above 40 km thinning toward de sw tajo and ne ebro foreland basins the crustal thickening is concentrated in the upper crust the seismic results are in overall agreement with regional trends of bouguer gravity anomaly and the main features of the seismic model were reproduced by gravity modeling the magnetotelluric data consist of 39 sites grouped into two profiles with periods ranging from 0 01 s to 1000 s dimensionality analyses show significant 3d effects in the resistivity structure and therefore we carried out a joint 3d inversion of the full impedance tensor and magnetic transfer functions the mesozoic and cenozoic basins along the chain are well characterized by shallow high conductive zones and low velocities elongated conductors reaching mid crustal depths evidence the presence of major faults dominating the crustal structure the results from the interpretation of these complementary geophysical data sets provided the first images of the crustal structure of the iberian chain they are consistent with a cenozoic shortening responsible of the upper crust thickening as well as of the uplift of the iberian chain and the generation of its present day topography

transpressional inversion in an extensional transfer zone the saltacaballos fault northern spain abstract this paper deals with an extensional transfer zone and its main structure the saltacaballos fault developed during early cretaceous times and obliquely inverted during the alpine shortening geological mapping and structural analysis were carried out to determine the kinematic history of the deformation the saltacaballos ridge is the relay zone between two major and conjugate normal fault systems the bilbao and the la granja samano fault systems three distinct phases in the structural evolution of this transfer zone can be identified 1 during the initial stages of extensional deformation shallow water marine limestones were deposited on the relay ridge and deep water marls on the flanking depocenters at the same time submarine landslides developed on paleoslope generated either by normal drag or by a fault propagation fold related to the saltacaballos normal fault 2 with increasing displacement normal faults antithetic to the saltacaballos fault were developed probably in response to the collapse of its hanging wall 3 during the subsequent alpine compressional stage these normal faults were reactivated as dextral strike slip faults as a result of transpressional inversion whereas previous extensional fault related folds were tightened at the same time some normal faults were overturned as a consequence of passive rotation in fold limbs

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

integrated stratigraphy and astronomical tuning of the serravallian and lower tortonian at monte dei corvi middle upper miocene northern italy an integrated stratigraphy calcareous plankton biostratigraphy magnetostratigraphy and cyclostratigraphy is presented for the serravallian and lower tortonian part middle upper miocene of the monte dei corvi section located in northern italy the detailed biostratigraphic analysis showed that both the discoaster kugleri acme and the first influx of neogloboquadrina acostaensis are recorded at monte dei corvi these events which passed unobserved in previous studies play an important role in delineating the serravallian tortonian boundary thermal and alternating field demagnetization revealed a characteristic low temperature component marked by dual polarities the resultant magnetostratigraphy for the upper part of the section can be unambiguously calibrated to the gpts ranging from c5n 2n up to c4r 2r unfortunately the lower part of the section including the serravallian tortonian boundary interval did not produce a reliable magnetostratigraphy despite the fact that some short reversed intervals and a single normal interval are recorded using sedimentary cycle patterns in combination with the calcareous plankton biostratigraphy the section can be correlated cyclostratigraphically in detail to the partially overlapping and previously tuned section of monte gibliscemi on sicily the monte dei corvi section is dated astronomically by calibrating the basic small scale sedimentary cycles to the precession and 65 n lat summer insolation time series of the la93 solution following an initial tuning of larger scale cycles to eccentricity an almost perfect fit is found between the cycle patterns and intricate details especially precession obliquity interference in the insolation target between 8 5 and 10 ma the tuning to precession remains robust for most intervals back to the base of the section dated at 13 4 ma and shows that the section is continuous apart from a possible short hiatus in the tortonian it provides accurate astronomical ages for all sedimentary cycles calcareous plankton events polarity reversals and ash layers and marks a significant improvement of the recently proposed astronomical calibrations of the monte dei corvi section and of parallel sections in the mediterranean astronomical ages for the ancona and respighi ashbeds are significantly older than previously reported 40 ar 39 ar biotite ages even if the revised older age for the fct san dating standard of 28 02 ma is applied the astronomical dating of the magnetic reversals in the monte dei corvi section results in the completion of the astronomical polarity time scale for the last 13 myr the monte dei corvi section has recently been proposed as the stratotype section for the serravallian tortonian boundary despite the moderate to

global stages regional stages or no stages in the plio pleistocene abstract over recent decades with extended exploration of all the oceans with the study of ice cores from greenland and antarctica with all the high resolution methodologies now available for integrated stratigraphy there has been a tendency in several milieux to abandon the use of stages for the plio pleistocene we do not agree with this approach and consider the use of standard stages in the plio pleistocene as appropriate as for older parts of the phanerozoic in the hierarchy of chronostratigraphic units erathem system series stage stage is the unit of lowest rank and of widest and longest usage moreover stage is the only chronostratigraphic unit defined on the basis of a typological criterion units of higher rank are usually defined on the basis of the hierarchical principle in the plio pleistocene there are three formalized stages zanclean piacenzian and gelasian oldest to youngest all defined in the mediterranean area a small geodynamically active ocean basin where uplift of coastal areas has exposed continuous successions of deep marine plio pleistocene strata the zanclean gssp is an example of event stratigraphy the pliocene transgression marking the sudden invasion by atlantic water masses of the desiccated mediterranean terminating the messinian salinity crisis the other two plio pliocene gssps are defined using multiple criteria but mainly by reversals of the magnetic field polarity following the recent iugs ratification of the formerly pliocene gelasian stage as the oldest stage of the pleistocene formalization of younger pleistocene stages is in progress starting from the calabrian with just one name of precise and well controlled time significance and multiple criteria for global correlation one can identify a defined time interval in both terrestrial and marine realms independent of latitude bioprovincialism and historical evolution

the role of the mediterranean region in the development of sedimentary geology a historical overview the mediterranean region source of so much knowledge in the world is the site of major advances in sedimentary geology in addition to its economic and cultural richness the geological and geographic diversity of the region plus its active geological processes have long stimulated indigenous scholars along with attracting talented outsiders such as steno lyell walther kuenen and bagnold since classical hellenic times debates about the origin of fossils and the changing positions of sea level served as catalysts for studies of sediments sedimentary rocks and ancient life the presence of geologically young and easily interpreted marine shell beds in many mediterranean coastal areas adjacent to their modern analogues was a particular stimulus for progress in sedimentary geology for example the very advanced stratigraphic ideas of leonardo da vinci expressed solely in his unpublished notebooks impeding progress was the geological complexity of facies faunas and structure in the circum mediterranean alpine belts once the secrets of these were unlocked however the mediterranean region became the source of major discoveries about syn sedimentary tectonics carbonate platforms pelagic and anoxic sediments turbidites evaporites aeolian processes cyclostratigraphy magnetic stratigraphy and impact events in many of these mediterranean discoveries the critical element is the occurrence of extensive mesozoic cenozoic pelagic successions whose precise age dating was made possible by pioneering biostratgraphic studies using microfossils

cenozoic right lateral wrench tectonics in the western pyrenees spain the ubierna fault system abstract a study of macro and mesostructural deformation patterns of the southern margin of the cantabrian area western pyrenees spain has revealed a complex cenozoic tectonic framework right lateral tectonics reactivated inherited wnw ese striking faults which developed during late paleozoic and early triassic events and late jurassic to early cretaceous main rifting stage the ubierna fault represents the southern boundary of the mesozoic basin during the oligocene even eocene to present day deformation this fault and the ventaniella fault located to the south in the study area acted as right lateral slightly transpressive elements forming a 120 km long and 15 km wide overstep area here named ubierna fault system where the cumulative right lateral displacement exceeds 15 km the cenozoic tectonic framework of the ubierna fault system includes reactivation along the wnw ese faults development of negative and mostly positive flower structures branch faults strike slip duplexes and releasing and restraining bends ne sw to ene wsw striking reverse faults and contractional horsetail terminations and nnw sse striking normal faults and joints are produced by the wnw ese right lateral strike slip motion the extensional elements are well developed and deformation progression implied their incorporation in the strike slip system as right lateral faults forming part of strike slip duplexes the abundance of flower structures striking wnw ese and paralleling the main strike slip faults together with the overall uplift of the overstep area testifies for a slight compressional component at a regional scale the ubierna fault system represents the most prominent element of a cenozoic transpressional belt which incorporates the western portion of the basque cantabrian basin and the asturian massif area lateral transition between this transpressive belt and the dip slip belt located to the east occurs across an area experiencing along strike shortening which developed to accommodate the eastward extrusion of the transpressional belt

the historical record in the scaglia limestone at gubbio magnetic reversals and the cretaceous tertiary mass extinction the scaglia limestone in the umbria marche apennines well exposed in the gubbio area offered an unusual opportunity to stratigraphers it is a deepwater limestone carrying an unparalleled historical record of the late cretaceous and palaeogene undisturbed by erosional gaps the scaglia is a pelagic sediment largely composed of calcareous plankton calcareous nannofossils and planktonic foraminifera the best available tool for dating and long distance correlation in the 1970s it was recognized that these pelagic limestones carry a record of the reversals of the magnetic field abundant planktonic foraminifera made it possible to date the reversals from 80 to 50 ma and subsequent studies of related pelagic limestones allowed the micropalaeontological calibration of more than 100 myr of geomagnetic polarity stratigraphy from ca 137 to ca 23 ma some parts of the section also contain datable volcanic ash layers allowing numerical age calibration of the reversal and micropalaeontological time scales the reversal sequence determined from the italian pelagic limestones was used to date the marine magnetic anomaly sequence thus putting ages on the reconstructed maps of continental positions since the breakup of pangaea the gubbio scaglia also contains an apparently continuous record across the cretaceous tertiary boundary which was thought in the 1970s to be marked everywhere in the world by a hiatus a geochemical study of the gubbio cretaceous tertiary boundary accidentally uncovered an unexpectedly large concentration of iridium in the boundary clay providing the first evidence for a large comet or asteroid impact at the time of the cretaceous tertiary mass extinction the sudden foraminiferal extinction in the essentially complete gubbio scaglia showed that the cretaceous tertiary extinction was a catastrophic event after publication of the gubbio cretaceous tertiary iridium anomaly in 1980 a decade followed in which more and more evidence for a catastrophic impact challenged the traditional uniformitarian viewpoint of geologists in 1991 the impact site was discovered at chicxulub in the yucata n peninsula of mexico the gubbio area has thus emerged as a classical geological locality it has been critical in the development of geomagnetic reversal stratigraphy a third system for dating earth history complementing biostratigraphy and radiometric age dating gubbio was also central to the recognition that occasional catastrophic events like great impacts require a rejection of strict uniformitarianism

seismic evidence of alpine crustal thickening and wedging from the western pyrenees to the cantabrian mountains north iberia 1 the alpine collision between the iberian and european plates resulted in a complex crustal structure beneath the northern iberian peninsula as revealed from a new set of seismic refraction wide angle reflection profiles the study area is characterized by two major e w ranges the cantabrian mountains and the pyrenees which are relayed to the south by the iberian chain important variations in crustal thickness and velocity distribution are found in a 560 km long e w transect in contrast to the typical 30 to 32 km thick european variscan crust of the western end of the profile a continuous alpine crustal root is evidenced from the cantabrian mountains to the central pyrenees with a moho depth of 46 48 km locally rising to 40 km depth in between beneath the basque cantabrian basin another outstanding feature is the inferred presence of high velocities of 6 40 6 75 km s at midcrustal depths which can be associated with portions of a lower crustal wedge from the northern european domain indenting the southern iberian crust during the alpine stage of compression this indentation produces the delamination of the iberian crust with northward underthrusting of its lower half and the consequent crustal thickening the indenting wedge has a discontinuous presence along the longitudinal section as it was controlled and or affected by n s to ne sw structures further evidence of the northward subduction of the iberian plate is provided by another profile toward the aquitaine basin while a n s profile across the iberian chain reveals an alpine midcrustal thickening beneath this belt with moho depths of 42 km

a 2 5 d interpretation of the basque country magnetic anomaly northern spain geodynamical implications the basque country magnetic anomaly follows a nw se trend over the basque country northern spain with intensities up to 250 nt measured at 3000 m above sea level the paired negative part of the anomaly is located to the north and presents intensities down to 60 nt a model of the magnetic properties of the crust in the area taking into account previous geological and geophysical data indicates a wedge of material with a magnetic susceptibility of 0 07 si emplaced along a ne directed basal thrust the anomalous wedge is composed of basic and or ultrabasic cretaceous intrusives and lower crustal rocks and reaches a minimum depth which increases towards the northwest from 5 7 to 12 km according to previous works geological features of the rocks on top of the anomalous wedge indicate that during the cretaceous this zone constituted a deep marine environment which underwent important crustal thinning related to rifting the transition towards the southwest was to a normal continental platform alpine deformation gave rise to displacement on a basal thrust which can be correlated with the lower contact of the magnetic wedge and emplacement of this wedge towards the northeast the southeastern termination of the anomaly can be related to the lateral termination of the basic rocks which constitute the anomalous wedge in a transform fault related to the rifting event

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget