the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications the main aim of this paper is to review middle permian through middle triassic continental successions in european secondly areas of middle late permian sedimentation the permian triassic boundary ptb and the onset of triassic sedimentation at the scale of the westernmost peri tethyan domain are defined in order to construct palaeogeographic maps of the area and to discuss the impact of tectonics climate and sediment supply on the preservation of continental sediment at the scale of the western european peri tethyan basins the upper permian is characterised by a general progradational pattern from playa lake or floodplain to fluvial environments in the northern variscan belt domain areas of sedimentation were either isolated or connected to the large basin which was occupied by the zechstein sea in the southern variscan belt during the late permian either isolated endoreic basins occurred with palaeocurrent directions indicating local sources or basins underwent erosion and or there was no deposition these basins were not connected with the tethys ocean which could be explained by a high border formed by corsica sardinia palaeorelief and even parts of the kabilia microplate the palaeoflora and sedimentary environments suggest warm and semi arid climatic conditions at the scale of the whole study area an unconformity more or less angular is observed almost everywhere between deposits of the upper permian and triassic except in the central part of the germanic basin the sedimentation gap is more developed in the southern area where in some basins upper permian sediment does not occur the large sedimentary supply erosion and or lack of deposition during the late permian as well as the variable palaeocurrent direction pattern between themiddle late permian and the early triassic indicate a period of relief rejuvenation during the late permian during the induan all the intra belt basins were under erosion and sediment was only preserved in the extra belt domains the northern and extreme southern domains in the northern domain the central part of the germanic basin sediment was preserved under the same climatic conditions as during the latest permian whereas in the extreme southern domain it was probably preserved in the tethys ocean implying a large amount of detrital components entering themarinewaters mesozoic sedimentation began in the early olenekian the ephemeral fluvial systems indicate arid climatic conditions during this period three distinct areas of sedimentation occur a northern and southern domain separated by an intra belt domain the latter accumulated sediments during the early middle permian and experienced erosion and or no deposition conditions between the middle late permian and the beginning of mesozoic sedimentation dated as anisian to hettangian at the top of the lower triassic another tectonically induced more or less angular unconformity is observed the hardegsen unconformity which is dated as intra spathian and is especially found in the north european basins this tectonic activity created new source areas and a new fluvial style with marine influences at the distal part of the systems during the anisian and ladinian continental sedimentation was characterised by a retrogradational trend in other words the fluvial system evolved into fluvio marine environments attesting to a direct influence of the tethys ocean in the southern and northern domains both at the end of the olenekian spathian and during the anisian the presence of palaeosols micro andmacrofloras indicate less arid conditions throughout this domain

non marine permian biostratigraphy and biochronology during the permian the single supercontinent pangaea stretched from pole to pole early permian glacial deposits are found in southern gondwana along the sutures of pangaea mountain ranges towered over vast tropical lowlands interior areas included dry deserts where dune sands accumulated gypsum and halite beds document the evaporation of hot shallow seas that formed the most extensive salt deposits in the geological record the permian period 251 to 299 ma encompasses nine ages stages arranged into three epochs series most of the permian marine timescale has been defined by global stratotype sections and points for the stage boundaries this volume presents new data regarding the biostratigraphy and biochronology of the non marine permian and provides a basis for temporally ordering permian geological and biotic history on land and correlating that history to events in the marine realm

diagenetic origin of carbon and oxygen isotope compositions of permian triassic boundary strata bulk carbonate 13 c and 18 o compositions of profiles across permian triassic p t boundary sections in china italy austria and iran show wide varieties of trends the 13 c depletions occur in all sections and range from 2 to 8 pdb in magnitude these excursions take place over intervals ranging from less than 0 1 to more than 40 m the 18 o values may increase or decrease toward the p t boundary but decrease sharply by 2 9 pdb at or above the boundary cross plots of 13 c and 18 o values from all sections show positive covariance wide differences in magnitudes trends and position of the excursions relative to the boundary as well as the covariance patterns suggest that p t boundary 18 o and 13 c values are partially or entirely diagenetic in origin formed in association with exposure surfaces this interpretation implies that p t boundary sections studied till date were subaerially exposed before during and after the mass extinction resulting in the removal of strata containing key information about the extinction mechanism this inference is consistent with the paleontological studies that have shown the presence of gaps at the boundary and further supported by the sharp lithologic changes observed at virtually all p t boundary sections subaerial exposures are documented by detailed sedimentologic and isotopic studies from central tethyan sections in abadeh and shah reza in iran proposed p t boundary extinction models are based on isotopic values that are diagenetic in origin and stratigraphic sections that are incomplete leading to extinction mechanisms with little physical supporting evidence

provenance constraints from detrital zircon u pb ages in the nw iberian massif implications for palaeozoic plate configuration and variscan evolution detrital zircons from pre orogenic upper ordovician to devonian low grade metasedimentary rocks have been dated by laser ablation inductively coupled plasma mass spectrometry la icp ms to 1 constrain the variations of zircon age populations within the autochthonous sequences of nw iberia 2 compare u pb detrital zircon ages with previous data 3 test the hypothesis of the armorica microplate as a peri gondwanan terrane separated from gondwana the similarity in the ages of detrital zircons found in the palaeozoic samples studied here to those published for the upper proterozoic lower cambrian and lower ordovician sediments of nw iberia argues against the separation of armorica and points to a common source area for all of the palaeozoic detrital formations of nw iberia the west african craton and the surrounding pan african belts la icp ms u pb dating of zircons from a synorogenic flysch preserved in klippen in the core of a syncline establishes a maximum depositional age for this deposit as early namurian this age is also a maximum age limit for thrusting and refolding in this part of the iberian massif correlation of the zircon age populations with published ages confirms the link between the emplacement of the allochthonous complexes of nw iberia and synorogenic sedimentation

geochemical markers of paleoenvironments weathering and provenance in permian triassic terrestrial sediments this study compares several geochemical factors major and minor rare earth elements ti al ratios and chemical index of alteration cia values in the early triassic canizar formation fm buntsandtein facies of e iberia with those of adjacent middle permian and middle triassic units alcotas and eslida fms respectively according to significant differences detected it seems that most geochemical perturbation occurred during the early triassic variations in ti al ratios suggest changes in source areas between the studied units and even within the canizar fm these provenance changes correlate with successive tectonic pulses during the opening and development of the iberian basin as they can be linked to major sedimentary surfaces and unconformities as well as major sedimentological variations ti enrichment in the lower and middle part of the canizar fm together with high sr and p concentrations may be indicative of environmental alterations related to acid meteoric waters moreover this acid alteration took place under arid conditions as reflected by cia values indicating that during the deposition of the canizar fm variable but predominantly physical weathering prevailed in contrast to the chemical weathering that took place when the alcotas and eslida formations were deposited our data along with the known fossil record of the study area indicate that during the middle late permian and early triassic conditions in this tectonically active area changed from humid to arid acid hampering biotic recovery then during late early middle triassic times the return of more humid and less acid environments promoted biotic development geochemical markers emerged as useful tools complementary to sedimentological paleontological and tectonic data for unveiling paleoenvironmental events especially in a setting of significant regional change

the beginning of the buntsandstein cycle early middle triassic in the catalan ranges ne spain sedimentary and palaeogeographic implications abstract the early middle triassic siliciclastic deposits of the catalan ranges ne spain are dominated by aeolian sediments indicating a predominance of arid climate during this time span in sharp contrast with the coeval fluvial sediments found in the castilian branch of the iberian ranges 300 km to the sw the ne sw oriented catalan basin evolved during the middle late permian as the result of widespread extension in the iberian plate this rift basin was bounded by the pyrenees ebro and montalban oropesa highs the permian early triassic age sediments of the catalan basin were deposited in three isolated subbasins montseny garraf prades separated by intrabasinal highs but linked by transversal nw se oriented faults the three subbasins show evidence of diachronic evolution with different subsidence rates and differences in their sedimentary records the buntsandstein sedimentary cycle started in the late early triassic smithian spathian in the central and southern domains garraf and prades with conglomerates of alluvial fan origin followed by fluvial and aeolian sandstones source area of the fluvial sediments was nearby paleozoic highs to the north and west in contrast with the far away source areas of the fluvial sediments in the iberian ranges to the sw these fluvial systems were interacting with migrating aeolian dune fields located towards the s which developed in the shadow areas behind the barriers formed by the paleozoic highs these highs were separating the subbasins under arid and semi arid climate conditions the dominating winds came from the east where the westernmost coast of the tethys sea was located and periods of water run off and fields of aeolian dunes development alternated some of the fluvial systems were probably evaporating as they were mixed into the interdune areas never reaching the sea from the end of the smithian to the spathian the catalan basin and neighbour peri tethys basins of the present day southern france sardinia and minorca islands constituted a geographical arch where arid and semi arid conditions represented an extension of the prevailed arid and hyper arid conditions in surrounding areas of the variscan belt harsh climatic conditions in this area prevented the life recovery in the aftermath of the permian triassic extinction event until the early anisian when more humid climate allowed for the colonisation of the area by plants amphibians and reptiles the boundary between desert areas and semi arid and or seasonal climate domains during the smithian spathian in sw europe can be precisely established in ne iberia between the catalan ebro region and the castilian branch of the iberian ranges to the sw

the transition from pangea amalgamation to fragmentation constraints from detrital zircon geochronology on west iberia paleogeography and sediment sources abstract detrital zircon u pb geochronology data from late carboniferous to triassic clastic sedimentary rocks in sw iberia were used to investigate the regional paleogeography during the transition from pangea amalgamation to break up the major u pb zircon age peaks are middle devonian to carboniferous 390 300 ma cambrian ordovician 530 440 ma cryogenian ediacaran 750 540 ma stenian tonian 1 2 0 9 ga and paleoproterozoic 2 3 1 8 ga rapid exhumation of variscan crystalline rocks at the contact between the south portuguese zone and ossa morena zone explains the abundance of late paleozoic ages in the upper carboniferous lower permian continental successions the u pb zircon data constrain the maximum depositional age of the santa susana basin to c 304 ma and the viar basin to c 297 ma the triassic sequences despite being c 100 ma younger than the variscan tectonothermal events contain low proportions of late paleozoic zircon the major peaks in all zircon spectra closely resemble those found in the adjacent basement rocks indicating small source areas mainly located near the rift shoulders longer travelled fluvial systems are postulated for the eastern portions of the algarve basin which was closer to the westward advancing tethys ocean than the rift basins of west iberia sequences that contain significant proportions of 1 2 0 9 ga zircon are probably recycled from post collisional carboniferous permian continental deposits that were more extensive than those found today

introduction to unconventional petroleum systems ben law is a consultant and sole proprietor of pangea hydrocarbon exploration llc his research interests include basin centered gas and coalbed methane systems prior to his consulting position he was a member and chief of the u s geological survey western tight gas sand project and regional coordinator of south asia for the u s geological survey world energy project he received b s and m s degrees from san diego state university california john b curtis is associate professor and director petroleum exploration and production center potential gas agency at the colorado school of mines he is an associate editor for the aapg bulletin and the mountain geologist as director of the potential gas agency he works with a team of 145 geologists geophysicists and petroleum engineers in their biennial assessment of remaining united states natural gas resources the collection of articles included in this theme issue of the aapg bulletin originated in the aapg

diagenetic effects on porosity permeability relationships in red beds of the lower triassic bunter sandstone formation in the north german basin abstract carbonate and anhydrite cement clay clasts and inter granular clay are the main components that reduce reservoir quality in the studied bunter sandstone formation the impacts of these parameters on porosity and permeability are determined by combining petrographic mineral quantification with conventional core analysis of samples from the danish part of the north german basin the depositional environments are considered because they largely control the distribution of cements clays and grain sizes the lateral variability of depositional environments is defined by the position in the basin and the proximity to the source areas the stratigraphic distribution of depositional environments is related both to local topography and to climate because high aridity promoted aeolian deposition the bunter sandstone formation has high porosity and permeability in most of the sandstone intervals in the northern north german basin the reservoir quality is good as long as the cements and clays are present as confined bodies that leave the remaining pore spaces available for flow in contrast inter granular clay and pervasive cementation hinder virtually all flow through the sandstone the ephemeral fluvial deposits have an average porosity and permeability of 20 3 and 810 md respectively and the values are 24 6 and 807 md for the aeolian sandstones excluding the unconsolidated aeolian sands which presumably have higher porosity and permeability the aeolian sandstones of the volpriehausen member have very good reservoir quality since they have a thickness of about 25 m are laterally continuous are largely clay free and the cement occurs in small amounts the sandstones of the solling member consist mainly of ephemeral fluvial deposits which generally have good reservoir quality however some intervals have high contents of inter granular clays or pervasive carbonate anhydrite or halite cement and these components reduce the permeability significantly the lateral distribution of the ephemeral fluvial sandstones is variable and therefore difficult to predict when planning a geothermal exploration well thus the volpriehausen member is the preferred target

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

u pb ages of detrital zircons from the permo triassic series of the iberian ranges a record of variable provenance during rift propagation abstractthe provenance of the permo triassic series of the talayuelas anticline iberian ranges have been studied using u pb geochronology laser ablation inductively coupled plasma mass spectrometry of detrital zircons these intracontinental siliciclastic series were formed by extensive sandy braided fluvial systems associated with ephemeral lake deposits and aeolian sediments with paleocurrents suggesting constant nw se transport directions upper permian reddish sandstones from the upper alcotas formation lopingian contain a dominant variscan zircon population 290 360 ma which indicates source areas located in the axial zone of the variscan belt in the core of the ibero armorican arc however in the lower triassic sandstones of the canizar formation olenekian the variscan zircon population is almost completely replaced by cadomian zircons 520 750 ma with important avalonian 390 520 ma mesoproterozoic 900 1750 ma eburnian 1 78 2 35 ga and post eburnian and archaean 2 4 ga zi

late permian flora and vegetation changes near the permian triassic boundary in the landete section of the alcotas formation se iberian ranges spain on the basis of rich and diverse thuringian palynomorph samples gathered from successive levels of the landete section alcotas formation se iberian ranges the succession of palynofloras and the vegetation dynamics have been studied in detail with the aid of quantitative analysis the aim of this study is to elucidate the timing and scenario of the biotic crisis during the latest permian before the actual permian triassic boundary and to determine the shape of the extinction at the local level four successive associations have been recognized through time the oldest a klausipollenites lueckisporites association this was followed by a klausipollenites falcisporites an alisporites lueckisporites and finally a re establishment of a klausipollenites lueckisporites association it is worth noting the scarcity or lack of fungal remains which indicates that in this area the fungal spike event cannot be demonstrated the palynomorph associations are dominated by non striate bisaccate pollen and verrucate spores in contrast with other palynofloras from western europe north america and continental series in eurasia the study indicated the absence of transitional floras and a dieback of diversity that ranges from 35 to 67 depending on the group population density of the 27 taxa identified underwent a significant decline ca 75 average indicating that at least at a local level the biotic crisis occurred prior to the p t boundary futhermore the quantitative analysis of the successive palynomorph assemblages allowed us to locally recognize the evolution of vegetation in which competitive exclusion and competitive release events took place

impact of rock fabric on water imbibition and salt diffusion in gas shales abstract understanding water uptake of gas shales is critical for designing fracturing and treatment fluids previous imbibition experiments on unconfined gas shales have led to several key observations the water uptake of dry shales is higher than their oil uptake furthermore water imbibition results in sample expansion and microfracture induction this study provides additional experimental data to understand the effects of rock fabric complex pore network clay swelling and osmotic potential on imbibition behavior we systematically measure and compare the imbibition rates of deionized water and oil into wet dry and confined unconfined rock samples from different shale members of the horn river basin we also measure the ion diffusion rate from shale into water during imbibition experiments the results show that initial water saturation decreases the water uptake of shale samples however it has no effect on oil imbibition rates the liquid imbibition and ion diffusion rates along the lamination are higher than those against the lamination the results also suggest that confining the shale samples decreases the water imbibition rate parallel to the lamination however it has a negligible effect on water uptake perpendicular to the lamination furthermore confining does not significantly affect the ion diffusion rates the comparative study suggests that for both confined and unconfined samples water uptake is higher than oil uptake however previous experiments on crushed shale samples show that the oil uptake of crushed packs is higher than their water uptake xu and dehghanpour 2014 the data suggest that the connected pore network of the intact samples is water wet while the majority of rock including poorly connected pores is oil wet this argument is backed by bse images and complete spreading of oil on fresh break surfaces of the rock

new u pb ages for early ordovician magmatism in central spain felsic orthogneisses occur widely in the ollo de sapo domain of the central iberian zone most of which were previously considered to represent a precambrian basement to the palaeozoic sequences of this domain however new u pb dating across the berzosa riaza shear zone sierra de guadarrama central spain indicates an early ordovician age for the most representative types of orthogneisses in the eastern part of the ollo de sapo domain dated rocks include the volcaniclastic cardoso gneiss 480 2 ma from the low medium grade hanging wall the riaza gneiss 468 8 16 ma mylonitic granite in the berzosa riaza shear zone three types of leucogneiss buitrago gneiss 488 8 10 ma megacrystic granite 482 11 14 ma aplitic vein and 482 8 9 ma gneissic leucogranite and the la morcuera granitic augen gneiss 477 4 ma in the high grade footwall the new age of the cardoso gneiss brackets to the mid late arenig the so called early ordovician sardic unconformity characteristic of the central iberian zone these new ages suggest that the broadly coeval volcanism and plutonism were closely associated with the sardic events and that these orthogneisses were part of a felsic magmatic belt which extended along the ollo de sapo domain of the central iberian zone this magmatic belt is interpreted to have been active during the early ordovician break up of the peri gondwanan margin of the iapetus ocean

oblique strain partitioning and transpression on an inverted rift the castilian branch of the iberian chain the iberian chain is a wide intraplate deformation zone formed by the tectonic inversion during the pyrenean orogeny of a permian mesozoic basin developed in the eastern part of the iberian massif the n s convergence between iberia and eurasia from the late cretaceous to the lower miocene times produced significant intraplate deformation the nw se oriented castilian branch of the iberian chain can be considered as a key zone where the proposed models for the cenozoic tectonic evolution of the iberian chain can be tested structural style of basin inversion suggests mainly strike slip displacements along previous nw se normal faults developed mostly during the mesozoic to confirm this hypothesis structural and basin evolution analysis macrostructural bouguer gravity anomaly analysis detailed mapping and paleostress inversions have been used to prove the important role of strike slip deformation in addition we demonstrate that two main folding trends almost perpendicular ne sw to e w and nw se were simultaneously active in a wide transpressive zone the two fold trends were generated by different mechanical behaviour including buckling and bending under constrictive strain conditions we propose that strain partitioning occurred with oblique compression and transpression during the cenozoic 2008 elsevier b v all rights reserved

u pb ages of detrital zircons from the internal betics a key to deciphering paleogeographic provenance and tectono stratigraphic evolution abstract zircons from the nevado filabride complex metamorphic rocks yielded 891 concordant inherited detrital ages the 342 concordant ages from the aulago fm indicate a pennsylvanian maximum depositional age while the age density distribution indicates that this formation is closely related to the cantabrian zone north of the iberian massif the dominant ediacaran and cryogenian populations at ca 596 and 788 ma respectively relate the nevado filabride complex to northern gondwana terranes a discrete mesoproterozoic zircon population at ca 1031 ma tonian late estenian population suggests that the basement of the nevado filabride complex could have been located near of the saharan metacraton and west of the east african orogen at the beginning of the paleozoic the 549 concordant ages from the tahal fm yield an early permian age for the protoliths the age density distribution pattern records erosion of rocks from the variscan belt including late variscan magmatic rocks zircon spectra differ from those of the alboran domain supporting the hypothesis that the nevado filabride complex is part of the south iberian domain furthermore data from the tahal fm are similar to those of permo triassic rocks from the iberian ranges

geochemical processes and solute transport at the seawater freshwater interface of a sandy aquifer geochemical processes occurring at a seawater freshwater interface were studied in a shallow coastal siliclastic aquifer containing minor amounts of calcite data were collected from 106 piezometers in a 120 m transect from the coastline and landward in the first 40 m from the coastline a wedge of saltwater is intruding below the freshwater aquifer the aquifer is strongly reduced with mineralization of organic matter by methanogenesis in the freshwater aquifer and sulfate reduction dominating in the most seaward part of the saline aquifer the spatial separation of cations in the aquifer indicated a slow freshening process where ca2 from freshwater displaced the marine cations na and mg2 from the exchanger complex the resulting loss of ca2 from solution decreases the saturation state for calcite and possibly causes calcite dissolution a storm flooding event was recorded where pulses of dense seawater sank through the fresh aquifer as a result the terminal electron accepting process switched from methanogenesis to sulfate reduction the pulses of sinking seawater also triggered cation exchange reactions where ca2 was expelled from the exchanger by seawater na and mg2 the released ca2 is being flushed from the aquifer by groundwater flow and this export of ca2 will in the long term cause decalcification of the sediment the water composition in the aquifer is in a transient state as the result of various processes that operate on different timescales oxidation of organic matter occurs continuously but at a rate decreasing on a geological time scale the freshening of the aquifer operates on the timescale of a few years the episodic flooding and sinking of seawater through the aquifer proceeds in the course of days to weeks but occurs irregularly with years in between

the importance of along margin terrane transport in northern gondwana insights from detrital zircon parentage in neoproterozoic rocks from iberia and brittany abstract detrital zircons from late neoproterozoic rocks of the peri gondwanan cadomian belt of sw iberia and north armorican domain of brittany record neoproterozoic ca 860 550 ma palaeoproterozoic ca 2300 1800 and archaean ca 3300 2600 ma u pb ages the absence of mesoproterozoic zircons suggests that these terranes evolved in a peri w african realm this is in contrast to other western european terranes that preserve mesoproterozoic zircons and are likely to have evolved in a peri amazonian realm such a contrast in detrital zircon populations coupled with the presence of mesoproterozoic zircons in the ordovician armorican quartzite deposited in a peri african platform is interpreted to record along margin terrane transport the change in provenance suggests that subduction was replaced by transform faults that juxtaposed amazonia derived terranes against w africa derived terranes to form the avalonia and armorica microcontinents subsequent extension along the margin resulted in the birth of the rheic ocean and the outboard drift of avalonia

tectonic evolution of a continental subduction exhumation channel variscan structure of the basal allochthonous units in nw spain a regional study starting from detailed geological mapping has been carried out in the malpica tui complex of galicia in nw spain the complex is formed by two units representing pieces of the external edge of gondwana subducted and exhumed during the variscan collision the study shows that synsubduction and early synexhumation structures in continental subduction channels tends to be obscured and even erased once exhumation is complete detailed structural analysis matched with the knowledge of the history and available data for other galician basal units have elucidated the major structures developed during the subduction exhumation process the results include evidence of the plate convergence causing early variscan continental subduction of the gondwana margin subduction was followed by exhumation driven by ductile thrusting within the subduction channel which in turn provoked crustal duplication in the subducted slab and modified the initial tectonometamorphic architecture of the subduction wedge the next step was accretion to the adjacent continental domains placing the subduction wedge on top of unsubducted parts of the gondwana margin via ductile thrusting thrusting was preceded by progressive propagation of a train of recumbent folds toward the foreland that affected the previous structural stack subsequent transference of oceanic rheic and peri gondwanan terranes to the gondwana margin took place by out of sequence thrusting followed by crustal extensional collapse and strike slip tectonics

late permian continental sediments in the se iberian ranges eastern spain petrological and mineralogical characteristics and palaeoenvironmental significance abstract a detailed mineralogical and petrological study and the analysis of paleosol profiles in continental alluvial sediments of the late permian in the se iberian ranges spain allow us to infer the significant environmental changes that occurred during this time period three parts have been distinguished in the late permian sediments alcotas formation the lower part includes abundant and well preserved carbonate paleosol profiles and fine grained sediments made up by quartz feldspar hematite and illite with scarce kaolinite the preservation of dolomicrite in some paleosols suggests that they originally developed as dolocretes in an arid to semi arid climate with marked seasonality a change towards more humid and acid conditions can be deduced from the presence of siderite and goethite in paleosols in the middle part of the alcotas formation moreover the presence of plant remains coal beds and or carbonaceous shales at the top of the middle part and the lack of carbonate paleosols in the upper part of the formation would indicate a further step towards acid conditions these conditions would increase until the early triassic as indicated by the lack of carbonates and the presence of sr rich aluminium phosphate sulphates aps minerals at the base of the triassic canizar formation which clearly indicates extreme acid conditions during the permian triassic transition of the study area

mass extinctions and sea level changes abstract review of sea level changes during the big five mass extinctions and several lesser extinction events reveals that the majority coincide with large eustatic inflexions the degree of certainty with which these eustatic oscillations are known varies considerably thus the late ordovician and end cretaceous extinctions are associated with unequivocal major regressions demonstrated from numerous widespread regions in contrast the multiple high frequency sea level changes reported for the frasnian famennian crisis based on the supposed depth preferences of conodont taxa have little support from sequence stratigraphic analyses which reveals the interval to be one of highstand the end permian mass extinction has long been related to a severe first order lowstand of sea level newell n d 1967 revolutions in the history of life geol soc am spec pap 89 63 91 based primarily on the widespread absence of latest permian ammonoid markers but field evidence reveals that the interval coincides with a major transgression newell s hypothesis that marine extinctions are related to shelf habitat loss during severe regression remains tenable for the end guadalupian and end triassic extinction events but not for other crises rapid high amplitude regressive transgressive couplets are the most frequently observed eustatic changes at times of mass extinction with the majority of extinctions occurring during the transgressive pulse when anoxic bottom waters often became extensive the ultimate cause of the sea level changes is generally unclear a glacioeustatic driving mechanism can only be convincingly demonstrated for the end ordovician and end devonian events at other times it is speculated that they may relate to the widespread regional doming and subsequent collapse caused by the impingement of superplumes and ultimate eruption on the base of the lithosphere

deducing the ancestry of terranes shrimp evidence for south america derived gondwana fragments in central europe we present here an example of how the sensitive high resolution ion microprobe shrimp zircon dating method can provide a terrane specific geochronological fingerprint for a rock and thus help to reveal major tectonic boundaries within orogens this method applied to inherited zircons in a ca 580 ma metagranitoid rock from the eastern bohemian massif has provided for the first time in the central european variscan basement unequivocal evidence for mesoproterozoic and late paleoproterozoic geologic events ca 1 2 ga 1 5 ga and 1 65 1 8 ga the recognition of such zircon ages has important consequences because it implies that parts of the precambrian section of variscan central europe were originally derived from a grenvillian cratonic province as opposed to the common assumption of an african connection a comparison with previously published shrimp data suggests however that these mesoproterozoic and late paleoproterozoic zircon ages may be restricted to the moravo silesian unit in the eastern variscides whereas the saxothuringian and moldanubian zones appear to contain a typical north african i e neoproterozoic plus eburnian inherited zircon age spectrum this finding supports new tectonic concepts according to which variscan europe is composed of a number of completely unrelated terranes with extremely different paleogeographic origins the moravo silesian unit can be best interpreted as a peri gondwana terrane which was situated in the realm of the amazonian cratonic province by the late precambrian comparable to the avalonian terranes of north america and the united kingdom

atmospheric solitary waves some applications to the morning glory of the gulf of carpentaria a mathematical model is proposed to describe atmospheric solitary waves at the interface between a shallow layer of fluid near the ground and a stationary upper layer of compressible air the lower layer is in motion relative to the ground perhaps as a result of a distant thunderstorm or a sea breeze and possesses constant vorticity the upper fluid is compressible and isothermal so that its density and pressure both decrease exponentially with height the profile and speed of the solitary wave are determined for a wave of given amplitude using a boundary integral method results are discussed in relation to the morning glory which is a remarkable meteorological phenomenon evident in the far north of australia

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

palaeoenvironmental significance of late permian palaeosols in the south eastern iberian ranges spain the late permian wuchiapingian alcotas formation in the se iberian ranges consists of one red alluvial succession where abundant soil profiles developed detailed petrographical and sedimentological studies in seven sections of the alcotas formation allow six different types of palaeosols with distinctive characteristics and different palaeogeographical distribution to be distinguished throughout the south eastern iberian basin these characteristics are in turn related to topographic climatic and tectonic controls the vertical distribution of the palaeosols is used to differentiate the formation in three parts from bottom to top showing both drastic and gradual vertical upwards palaeoenvironmental changes in the sections reconstruction of palaeoenvironmental conditions based on palaeosols provides evidence for understanding the events that occurred during the late permian some few millions of years before the well known permian triassic global crisis

provenance of triassic feldspathic sandstones in the iberian range spain significance of quartz types abstract the base of the triassic in the iberian range is represented by detrital sediments buntsandstein facies deposited initially in a continental environment finally evolving into a marine environment that is represented at the top of the sequence the lithology of this facies is dominated by arkosic sandstones the aim of this study is to reconstruct the nature and position of the source areas of these sandstones provenance research was carried out by quartz grain typology eleven stratigraphic sections were sampled the amount of interstitital matrix has been considered in selecting samples because mechanical compaction suffered by sandstones with little matrix may give rise to a significant increase in the undulosity of monocrystalline quartz the ollo de sapo gneissic formation located in the hesperian massif has been mentioned as source rocks of feldspathic sandstones in previous works in order to verify the provenance of feldspathic sandstones in artificial sands derived by grinding gneisses and sand samples collected at stream heads that drain the gneiss outcrops we followed the methodology of basu et al 1975 analytical results indicate that two different areas within the triassic basin were notably influenced by different source areas a a western zone the nearest to the gneissic source rocks where monocrystalline nonundulatory quartz grains predominate qm 5 increase sediment evolution during transport processes is markedly reflected by the increase in qm 5 ratios in the westernmost zone away from the source area low values in the above mentioned ratios in the eastern zone are interpreted as results of local influence by low ranking metamorphic source areas finally this ethod also allows for the monitoring of the evolution of sediment maturity throughout the basin

tectonic evolution of the careon ophiolite northwest spain a remnant of oceanic lithosphere in the variscan belt abstract analysis of the careon unit in the ordenes complex northwest iberian massif has supplied relevant data concerning the existence of a paleozoic oceanic lithosphere probably related to the rheic realm and the early subduction related events that were obscured along much of the variscan belt by subsequent collision tectonics the ophiolite consists of serpentinized harzburgite and dunite in the lower section and a crustal section made up of coarse grained and pegmatitic gabbros an early devonian zircon age documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10

tearing up rodinia the neoproterozoic palaeogeography of south american cratonic fragments rodinia was initially defined as a long lived supercontinent that assembled all the continental fragments around laurentia and remained stable from 1000 up to 750 ma nonetheless recent work has cast doubt on the rodinia palaeogeography and even on the timing of its assembly and break up the geochronological and palaeomagnetic databases accumulated for south america and africa in the last decade show that most of these continental fragments were not part of rodinia a wide brasiliano ocean separated most of the south american and african cratons from the laurentia amazonia rio apa west africa margin this ocean was closed between 940 and 630 ma along the pampean paraguay araguaia pharusian mobile belts moreover accretion along the south american and african platforms was a diachronous and long lived process that involved several intra oceanic and continental magmatic arcs and microcontinents this evolution started at around 1000 ma and ended at around 520 ma with the final assembly of gondwana

temporal and spatial variations in tectonic subsidence in the iberian basin eastern spain inferences from automated forward modelling of high resolution stratigraphy permian mesozoic by subsidence analysis on eighteen surface sections and 6 wells which cover large part of the iberian basin e spain and which are marked by high resolution stratigraphy of the permian triassic jurassic and cretaceous we quantify the complex permian and mesozoic tectonic subsidence history of the basin backstripping analysis of the available high resolution and high surface density of the database allows to quantify spatial and temporal patterns of tectonically driven subsidence to a much higher degree than previous studies the sections and wells have also been forward modelled with a new automated modelling technique with unlimited number of stretching phases in order to quantify variations in timing and magnitude of rifting it is demonstrated that the tectonic subsidence history in the iberian basin is characterized by pulsating periods of stretching intermitted by periods of relative tectonic quiescence and thermal subsidence the number of stretching phases appears to be much larger than found by earlier studies showing a close match with stretching phases found in other parts of the iberian peninsula and allowing a clear correlation with discrete phases in the opening of the tethys and atlantic

an early triassic evolving erg system iberian chain ne spain palaeoclimate implications the triassic buntsandstein facies in the north eastern iberian chain central eastern spain previously considered to be fluvial in origin is shown to contain an evolving erg system the preserved erg accumulation comprises a succession that represents the transition from a wadi belt via inner erg margin to a central erg system this study supports early triassic olenekian palaeoclimate models for western europe which predict extremely arid conditions for iberia the two main easterly and southerly palaeowind directions are in accordance with data from other triassic dune fields in europe and corroborate the influence of monsoonal circulation which affected precipitation in the variscan massif to the south and west

careon ophiolite nw spain suprasubduction zone setting for the youngest rheic ocean floor the careon ophiolite galicia nw iberian massif shows lithological and geochemical features suggestive of an origin in a suprasubduction zone setting as with other devonian ophiolites in the european variscan belt it was generated within a contracting rheic ocean this setting and the general absence of large silurian devonian volcanic arcs on both of the rheic ocean margins strongly suggest that this ocean was closed by intraoceanic subduction directed to the north this subduction removed the older normal n mid oceanic ridge basalt morb oceanic lithosphere and gave rise to a limited volume of new suprasubduction zone oceanic lithosphere the careon ophiolite is a key element in understanding the evolution of the rheic ocean which was the main oceanic domain that closed during the paleozoic convergence of gondwana and laurussia preceding the assembly of pangea

lower triassic sequence stratigraphy of the western part of the germanic basin west of black forest fluvial system evolution through time and space abstract the aim of this paper is to analyse the fluvial evolution of the lower triassic in the western part of the germanic basin through time and space as well as the impact of the geodynamic and climatic setting on the preservation of fluvial deposits the lower triassic crops out only in the vosges massif and the black forest so well log studies are required to realise sequence stratigraphy correlations and establish comparisons with others parts of the germanic basin in a first step we use well log data analyses to characterise the electrofacies associations in the triassic and then define the well log signatures of each formation in a second step the characterisation and recognition of genetic sequences and their stacking pattern allow us to define seven minor cycles integrated into two major cycles finally the quantification of the lithologies at different stages of basin evolution leads to the reconstruction of paleoenvironmental maps to illustrate facies evolution through space and time a comparison with cycles defined in the germanic basin allows us to propose correlations of the lower triassic on either side of the rhine graben and leads to a discussion of the evolution of fluvial systems through time and space during the scythian the fluvial style is characterised by braided fluvial systems evolving laterally into lake deposits towards the central part of the germanic basin during this stage the basin was a huge depression with very few marine connections in its extreme eastern part the stratigraphic cycles represent rhythmic fluctuations in relative lake level that could be attributed to sediment supply and or lake level variations in an arid setting four minor stratigraphic cycles are observed that are integrated within a single major stratigraphic cycle during the period of the stratigraphic base level rise of the major cycle a maximum of 233 m of sediment would represent a duration of sedimentation in the paris basin of at least 1 8 m y during the period of the stratigraphic base level fall of the major cycle a maximum of 65 m of sediment would have accumulated over 2 5 m y on the western edge of the germanic basin the top of the scythian is marked by a major sedimentary break characterised by a planation surface with preservation of the first paleosols followed by the hardegsen unconformity this unconformity is tectonically deformed leading to the development of a new sedimentation area in the west of the basin the fluvial sedimentation above this discontinuity shows a trend towards enhanced development of floodplain or lacustrine type environments at its western margin with the formation of paleosols the fluvial systems are linked with sabkhas and then with a shallow sea connected to the tethys ocean in this context the stratigraphic cycles are caused by variations in relative sea level and or sediment supply the fluvial deposits are preserved in an exoreic basin

diachronous variscan tectonothermal activity in the nw iberian massif evidence from 40ar 39ar dating of regional fabrics abstract multigrain concentrates of hornblende and muscovite together with whole rock slate phyllite samples have been dated 27 analyses using 40ar 39ar incremental release methods along a systematic traverse across the various lithotectonic structural elements which comprise northwestern sectors of the variscan iberian massif hornblende concentrates from amphibolites in the allochthonous ordenes complex yield plateau isotope correlation ages of 425 ma and 377 ma muscovite concentrates and whole rock slate phyllite from this and the cabo ortegal complex yield plateau ages which range from 367 ma to 295 ma analyses of similar material from the relative autochthon yield plateau ages between 359 ma and 275 ma muscovite concentrates from three late to post kinematic granitic stocks yield plateau ages between 309 ma and 274 ma at least seven of the 40ar 39ar analyses from metamorphic rocks record variable thermal rejuvenation of intracrystalline argon systems associated with emplacement of proximal granitic stocks the remaining analyses may be used to constrain the local age of various variscan tectonothermal events the oldest fabric ages are recorded in allochthonous units whereas the youngest fabric ages occur along the boundary between internal and external zones middle devonian ages are recorded in the allochthon and suggest a chronological continuity with deformational events in the relative autochthon where variscan deformation initiated in the upper devonian and diachronously prograded eastward the first deformational events recorded in the limit within the internal and external zones occured ca 20 25 ma later lower namurian variscan deformation systematically prograded diachronously eastward across the orogen as new crustal material was added along the front of the developing orogenic wedge however the entire orogen remained tectonically active with different structural features forming at different times and at different places an average propagation rate of ca 5 km m y is suggested by consideration of a 20 25 ma difference in correlative fabric ages and present separations

a comparison of the iberian and ebro basins during the permian and triassic eastern spain a quantitative subsidence modelling approach the permian triassic sediments of the iberian plate are a well studied case of classical buntsandstein muschelkalk keuper facies with good sedimentological interpretations and precise datings based on pollen and spore assemblages ammonoids and foraminifera synrift postrift cycles are recorded in these facies but there are only a few studies of quantitative subsidence analysis backstripping method and only a previous one using forward modelling for the quantification of synrift postrift phases of this period here we present the results obtained by the quantitative analysis of fourteen field sections and oil well electric log records in the iberian and ebro basins spain backstripping analysis showed five synrift phases of 1 to 3 million years duration followed by postrift periods for the permian triassic interval the duration however shows lateral variations and some of them are absent in the ebro basin the forward modelling analysis assuming local isostatic compensation has been applied to each observation point using one layer and two layer lithospheric configurations the second one shows a better fit between observation and model prediction in a systematic way so a two layer configuration is assumed for the sedimentary basin filling analysis lithospheric stretching factors and obtained in the forward modelling analysis are never higher than 1 2 but sometimes 1 in the same section if surficial extension is compensated by deep compression either at the roots of the rift basins or in far away zones is not yet clear but this anomaly can be explained using a simple shear extensional model for the iberian and ebro basins 2008 elsevier b v all rights reserved

permian climate development in the northern peri tethys area the lodeve basin french massif central compared in a european and global context abstract the lodeve basin which contains an exceptional long and nearly uninterrupted profile of early to late permian continental red beds is well correlated to the other european permocarboniferous basins together they cover the time span from the late pennsylvanian to the permian triassic boundary although these basins were placed within the equatorial belt for the whole permian several climatic changes are recorded in the sediments terrestrial sedimentation is governed by the interaction of climate and tectonics as well as by volcanism to a variable degree therefore small scale climatic variations of the milankovitch band are hardly discernable and if so they could not be correlated between different basins indeed larger scale climatic shifts could be identified it is shown that the shift from the carboniferous icehouse to the mesozoic warmhouse was a multi stage process this global warming resulted in a general aridisation of northern pangea indicated by outspreading playa and sabkha red beds aeolianites and evaporites several short phases of increased humidity interrupted this trend indicated by wet red beds lake sediments and coal deposits in central and southern europe these wet periods are traceable within the late stephanian lower rotliegend gzhelian asselian topmost lower rotliegend asselian sakmarian upper rotliegend i late artinskian early kungurian and upper rotliegend ii zechstein wuchiapingian the aridisation of the northern pangea which accelerated near the sakmarian artinskian transition is attributed to a reorganisation of the major ocean currents cold water currents along the western flank of the pangea indicated by the permian chert event blocks moisture transport from west onto the continent during roadian and wordian the onset of an additional cold water current along the cimmerian continents blocks moisture transport from the east both phenomena together are responsible for the maximum of aridity at the early to middle permian transition additionally the equatorial climate has been affected by an increasing seasonality within the late pennsylvanian and permian caused by the wide shifting of the zone of inter tropical convergence itc over the equator based on a new reconstruction of the pangean assembly in this paper climatic changes in the permian are interpreted and causes of the arid humid arid shifts are examined phases of higher humidity are often related to events of global impact like the waxing and waning of the gondwanan glaciation obtained in the south african karoo basin dwyka group but also regional events had strong climatic influence the zechstein transgression in the northern and southern permian basin as well as the bellerophon transgression of the southern alps caused the wet phase in the wuchiapingian

the birth of the rheic ocean early palaeozoic subsidence patterns and subsequent tectonic plate scenarios abstract new plate tectonic reconstructions of the gondwana margin suggest that the location of gondwana derived terranes should not only be guided by the models but should also consider the possible detrital input from some asian blocks hunia supposed to have been located along the cambrian gondwana margin and accreted in the silurian to the north chinese block consequently the gondwana margin has to be subdivided into a more western domain where the future avalonian blocks will be separated from gondwana by the opening rheic ocean whereas in its eastern continuation hosting the future basement areas of central europe different periods of crustal extension should be distinguished instead of applying a rather cylindrical model it is supposed that crustal extension follows a much more complex pattern where local back arcs or intra continental rifts are involved guided by the age data of magmatic rocks and the pattern of subsidence curves the following extensional events can be distinguished during the early to middle cambrian a back arc setting guided the evolution at the gondwana margin contemporaneous intra continental rift basins developed at other places related to a general post pan african extensional phase affecting africa upper cambrian formation of oceanic crust is manifested in the chamrousse area and may have lateral cryptic relics preserved in other places this is regarded as the oceanisation of some marginal basins in a context of back arc rifting these basins were closed in a mid ordovician tectonic phase related to the subduction of buoyant material mid ocean ridge since the early ordovician a new phase of extension is observed accompanied by a large scale volcanic activity erosion of the rift shoulders generated detritus armorican quartzite and the rift basins collected detrital zircons from a wide hinterland this phase heralded the opening of palaeotethys but it failed due to the silurian collision eo variscan phase of an intra oceanic arc with the gondwana margin during this time period at the eastern wing of the gondwana margin begins the drift of the future hunia microcontinents through the opening of an eastern prolongation of the already existing rheic ocean the passive margin of the remaining gondwana was composed of the galatian superterranes constituents of the future variscan basement areas remaining under the influence of crustal extension they will start their drift to laurussia since the earliest devonian during the opening of the palaeotethys ocean

magmatism and early variscan continental subduction in the northern gondwana margin recorded in zircons from the basal units of galicia nw spain in situ uranium lead dating la sf icpms and sims and lu hf isotope analyses la mc icp ms of zircon from eclogite facies rocks from the basal units of the variscan belt in galicia constrain their magmatic and metamorphic evolution and give some clues about the nature and origin of the involved basement the samples studied are two felsic gneisses two eclogites and one eclogitic gneiss of intermediate composition metatonalite oscillatory zoned zircon cores from the felsic samples gave a main clustering of u pb ages at 493 2 and 494 2 ma and some older ages that represent inherited cores zircon grains from the intermediate and one of the mafi c rocks show no inherited cores and yielded ages of 494 3 and 498 6 ma respectively interpreted as time of protolith crystallization variably developed homogeneous zircon rims in one felsic gneiss yielded an age of 372 3 ma and very tiny zircons of one eclogite gave 350 2 ma both of which we interpret as metamorphic ages the new age data demonstrate that the calc alkaline magmatic suite described in the basal unit is ca 20 ma older than the alkaline to peralkaline plutonic suite of the same unit dated at 472 2 ma rodriguez et al 2007 and thus probably represents a distinct geologic event overgrowth rims are interpreted as metamorphic on the basis of their lu hf and th u ratios the 372 3 age is considered as dating the high pressure high p metamorphism and is essentially in agreement with previous ar ar and rb sr data this high p metamorphism marks the initial early variscan subduction of the gondwana margin the inherited zircon ages and hf isotopic composition of zircons point to a considerable input of crustal material with west african craton provenance to the felsic magma

sudden changes in fluvial style across the permian triassic boundary in the eastern iberian ranges spain analysis of possible causes abstract the sedimentary record of the late permian and early triassic of the eastern iberian ranges shows four major sudden or very rapid vertical changes in fluvial style the late permian sedimentary cycle starts with the boniches formation of alluvial fan braided fluvial origin which grades vertically over within a few metres into the alcotas formation deposited by low to high sinuosity avulsion prone rivers with extensive floodplains the alcotas formation contains calcimorphic soils plant remains and pollen and spore assemblages however the upper third of the unit is devoid of all organic remains and soils and is characterized by a dominant red colour the sandstone levels were deposited by high sinuosity meandering rivers this major change took place during the late permian and is probably coeval with the emplacement of the emeishan basaltic large igneous province lip in se china rocks of the boniches and alcotas formations are separated by an angular unconformity from the overlying strata which consist of the late permian conglomeratic hoz del gallo formation of alluvial fan gravel braided fluvial origin and the sandy canizar formation of low sinuosity sandy river origin the permian triassic boundary lies probably between the upper part of the hoz del gallo formation and the first metres of the canizar formation late permian pollen and spore assemblages have been found in the hoz del gallo formation but the canizar formation is barren with the exception of an anisian middle triassic assemblage at the top tectonic extensional pulses in the iberian basin caused the changes observed between the lower and upper parts of the boniches formation at the base of the hoz del gallo formation and between the lower and upper part of this formation the changes observed in the uppermost part of the alcotas formation are not easily explained by tectonic causes nor those in the passage from the hoz del gallo formation to the canizar formation similar sedimentary characteristics of the sandy canizar formation such as amalgamated sandstone bodies erosion and reactivation surfaces dominant trough cross stratification tabular geometry absence of plant remains and pollen and spores and absence of silts and clays to those of coeval formations in places as far away as australia south africa and brazil suggest a global rather than local cause for these abrupt changes in fluvial style this global cause was probably die off of plant cover over extensive areas of the catchment related to the end of the permian mass extinction and possibly related to the emplacement of the west siberian basaltic large igneous province lip responsible for drastic atmospheric and marine changes

the vila de cruces ophiolite a remnant of the early rheic ocean in the variscan suture of galicia northwest iberian massif abstract the vila de cruces ophiolite is one of the ophiolitic units involved in the variscan suture of the northwest iberian massif this ophiolite consists of a tectonically repeated succession of greenschist facies volcanic rocks common alternations of metasediments of pelitic or siliceous character and scarce orthogneisses metagabbros and serpentinites the protolith age of a granitic orthogneiss that intruded the mafic rocks is dated at documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape 497 pm 4 end document ma u pb in

imbibition of hydraulic fracturing fluids into partially saturated shale recent studies suggest that imbibition of hydraulic fracturing fluids into partially saturated shale is an important mechanism that restricts their migration thus reducing the risk of groundwater contamination we present computations of imbibition based on an exact semianalytical solution for spontaneous imbibition these computations lead to quantitative estimates of an imbibition rate parameter a with units of lt 1 2 for shale which is related to porous medium and fluid properties and the initial water saturation our calculations suggest that significant fractions of injected fluid volumes 15 95 can be imbibed in shale gas systems whereas imbibition volumes in shale oil systems is much lower 3 27 we present a nondimensionalization of a which provides insights into the critical factors controlling imbibition and facilitates the estimation of a based on readily measured porous medium and fluid properties for a given set of medium and fluid properties a varies by less than factors of 1 8 gas nonwetting phase and 3 4 oil nonwetting phase over the range of initial water saturations reported for the marcellus shale 0 05 0 6 however for higher initial water saturations a decreases significantly the intrinsic permeability of the shale and the viscosity of the fluids are the most important properties controlling the imbibition rate

comparative evolution of the iapetus and rheic oceans a north america perspective abstract differences in the origin and evolution of the iapetan and rheic oceans profoundly affected the development of the ouachitan appalachian variscan orogen the iapetus ocean was initiated in the late neoproterozoic early cambrian by the separation of large continental landmasses laurentia baltica gondwana whereas the rheic ocean originated in the late cambrian early ordovician as the result of the separation of several ribbon continents collectively termed peri gondwanan terranes from the northern margin of gondwana compared to the classic passive margin developed along the laurentian margin of iapetus passive margin successions to the rheic ocean are more limited in extent during convergence both margins of the iapetus ocean developed western pacific type arc back arc systems whereas subduction of the rheic ocean was primarily directed beneath laurentia and was andean in style closure of iapetus involved a number of arc back arc accretionary events and had occurred by the middle silurian as a result of laurentia baltica collision to form laurussia and the accretion of the peri gondwanan terranes rheic ocean closure occurred in the carboniferous by way of continent continent collision between laurussia and gondwana with gondwana on the lower plate within iapetus the formation of ophiolites occurred early in the orogenic cycle and was followed soon after by obduction hp lt metamorphism and foreland directed thrusting that is intimately related to accretionary events these features dominate the northern appalachian orogen where ht lp metamorphism is attributed to post accretionary slab break off events in contrast hp lt metamorphism within the rheic ocean reflects a type subduction during laurussia gondwana collision and is rapidly succeeded by ht lp metamorphism attributed to orogenic collapse ophiolites are rare and were formed either very early early ordovician or very late devonian carboniferous in the evolution of the ocean the early ordovician ophiolites were not obducted until the carboniferous at least 100 million years after their protoliths were formed rheic ocean closure resulted in the formation of large scale bivergent structures within the orogen with symmetry changing on either side of the rheic suture comparison of the evolution of the iapetus and rheic oceans suggests that differences in rift configuration passive margin development and subduction zone geometry within the two oceans profoundly influenced the subsequent style of orogenesis within the ouachita appalachian variscan orogen

new lithostratigraphy for the cantabrian mountains a common tectono stratigraphic evolution for the onset of the alpine cycle in the w pyrenean realm n spain abstract the pyrenean cantabrian orogen arose through the collision of the iberian and eurasian plates mostly in cenozoic times this orogen comprises two main mountain ranges the pyrenees to the east and the cantabrian mountains to the west to date the early alpine tectono sedimentary phases preserved in the cantabrian mountains of permian and triassic age have been considered independently from the same phases in neighbouring basins of sw europe and even from the eastern part of the same orogeny the pyrenean orogeny in consequence the beginning of the alpine cycle in the cantabrian mountains has been interpreted within a specific geodynamic context far from the general evolutionary phases of the western peri tethys basins through detailed field work including geological mapping sedimentology lithostratigraphy and petrology of volcanic rocks and new palaeontological data here we define several new lithostratigraphical formations and five new tectono sedimentary cycles ts i v for the initial phases of evolution of the mesozoic basque cantabrian basin interrupted by periods of tectonic stability to complete this information we include data from an onshore borehole villabona mine and two offshore boreholes constrained by 2d reflection seismic profiles acquired in the north iberian continental platform the main tectono sedimentary cycles related to the deposition of five major identified lithostratigraphic units can be described as follows ts i late gzelian early asselian relating to the late variscan deformation and preserved in a single outcrop in all the cantabrian mountains san tirso formation this formation is constituted by medium distal alluvial fan deposits in which humid intervals predominate forming some thin coal beds ts ii asselian sakmarian a post variscan extensional phase with associated calc alkaline magmatism represented by profuse volcanic and volcanosedimentary intercalations in the early permian sedimentary basins acebal formation and small plutons in surrounding areas ts iii kungurian or reactivation of the post variscan extension leading to alluvial and lacustrine carbonate sedimentation in arid climate conditions which do not change during the rest of the permian and triassic periods sotres formation a generalized karstification in the basin represents the end of permian deposition followed by an interruption in sedimentation longer than 30 myr the permian tectono sedimentary cycles ts ii and ts iii are contemporary with variscan belt collapse and the basins are controlled by extensional reactivation of ne sw and e w variscan structures and nw se late variscan structures ts iv late anisian middle carnian renewed sedimentation in more extensive basins precursors of the great mesozoic basque cantabrian basin this cycle is represented by fluvial deposits cicera formation or buntsandstein facies which are interrupted by the first mesozoic marine ingression rueda formation or muschelkalk facies ts v norian rhaetian or shallow marine carbonate deposits transicion formation related to increasingly compartmentalized sub basins controlled by normal faults this final ts is broadly connected with different basins of the western peri tethys domain the identification of units ts i v in the cantabrian mountains along with the volcanic character of ts ii all indicate the development of a common post variscan to early alpine tectono sedimentary evolution for the whole pyrenean cantabrian realm