a new approach to the opening of the eastern mediterranean sea and the origin of the hellenic subduction zone part 1 the eastern mediterranean sea we identify long transform faults that frame the eastern mediterranean sea and that were active during jurassic and probably the early cretaceous during the opening of the central atlantic ocean

crust mantle boundary in the central fennoscandian shield constraints from wide angle p and s wave velocity models and new results of reflection profiling in finland 1 our paper presents analysis of the crust mantle boundary in the central fennoscandian shield based on new p and s wave two dimensional velocity models of the sveka 81 sveka 91 and fennia wide angle reflection and refraction profiles and on results of a new seismic reflection experiment in finland finnish reflection experiment fire in this area the crust is extremely thick 50 60 km and the moho boundary is difficult to detect using methods based on interpretation of p waves only near vertical profiling and wide angle experiments however the s wave reflections from the moho boundary sms are frequently more pronounced in wide angle data than the p wave reflections pmp in order to infer the crust mantle transition we developed new p and s wave velocity models using reprocessing of the old data and compared them to record sections of collocated reflection profiles and to published values of vp and vp vs for the main types of lower crustal and upper mantle rocks on the basis of the lateral variations of vp vp vs and reflectivity in the lower crust and upper mantle three main types of the crust mantle boundary were distinguished the first type corresponds to eclogitized lower crust that overlies peridotitic upper mantle in this case the moho coincides with the lithological crust mantle boundary the second type corresponds to lower crust composed of mafic garnet granulites overlying the peridotitic upper mantle for which the moho and the lithologic crust mantle boundary coincide as well the third type corresponds to the mafic garnet granulites underlain by a layer of eclogitic upper mantle in the latter case the lithological crust mantle boundary is deeper than the moho

tectonic evolution of the palmyra zone syria the palmyra foldbelt extends approximately 350 km northeast from its intersection with the dead sea transform near damascus the surface expression of this feature is a southeast verging fold and thrust belt that brings rocks as old as triassic to the surface in fault contact with upper cretaceous and tertiary rocks the palmyra region is first recognized as a subsiding trough from at least triassic and possibly permian time through middle tertiary this subsidence increases south westward reaching a reported maximum of 6 km of sediment north of damascus and is related to right lateral motion along the eastern margin of the opening southern branch of the neotethys sea as the cimmerian continent moved northward away from northeast africa during permian triassic time extension and subsidence continued through the jurassic and cretaceous interrupted by uplift and erosion from late jurassic to early cretaceous in the northeastern part of the zone compression and inversion of the palmyra zone begin during miocene time with the initiation of left lateral displacement on the dead sea transform system related to the continued opening of the red sea and the failure of the gulf of suez rift system approximately 105 km of offset are reported for the dead sea transform along themore jordan israel border segment while 60 km are reported in syria north of lebanon the palmyra foldbelt accommodates this discrepancy through oblique shortening possibly utilizing pre existing extensional fault systems less

the mamonia complex sw cyprus revisited remnant of late triassic intra oceanic volcanism along the tethyan southwestern passive margin upper triassic volcanic and sedimentary rocks of the mamonia complex in southwestern cyprus are exposed in erosional windows through the post cretaceous cover where the mamonia complex is tectonically imbricated with the troodos and akamas ophiolitic suites most of these upper triassic volcanic rocks have been considered to represent remnants of triassic oceanic crust and its associated seamounts new nd and pb isotopic data show that the whole mamonia volcanic suite exhibits features of oceanic island basalts oib four rock types have been distinguished on the basis of the petrology and chemistry of the rocks volcanism began with the eruption of depleted olivine tholeiites type 1 and oceanic island tholeiites type 2 associated with deep basin siliceous and or calcareous sediments the tholeiites were followed by highly phyric alkali basalts type 3 interbedded with pelagic halobia bearing limestones or white reefal limestones strongly lree enriched trachytes type 4 were emplaced during the final stage of volcanic activity nd and pb isotopic ratios suggest that tholeiites and mildly alkali basalts derived from partial melting of heterogeneous enriched mantle sources fractional crystallization alone cannot account for the derivation of trachytes from alkaline basalts the trachytes could have been derived from the partial melting at depth of mafic material which shares with the alkali basalts similar trace element and isotopic compositions this is corroborated by the rather similar isotopic compositions of the alkali basalts and trachytes the correlations observed between incompatible elements nb th and varepsilon nd and pb isotopic initial ratios suggest that the mamonia suite was derived from the mixing of a depleted mantle dmm and an enriched component of high 238u 204pb himu type models using both nd and pb isotopic initial ratios suggest that the depleted tholeiites type 1 derived from a dmm source contaminated by an enriched mantle type 2 component em2 and that the oceanic tholeiites type 2 alkali basalts type 3 and trachytes type 4 were derived from the mixing of the enriched mantle source of the depleted tholeiites with a himu component none of the mamonia volcanic rocks show evidence of crustal contamination the upper triassic within plate volcanism likely erupted in a small southerly neotethyan basin located north of the eratosthenes seamount and likely floored by oceanic crust

permian early mesozoic tectonism and continental margin formation in israel and its implications for the history of the eastern mediterranean summary the early mesozoic tectonic reorganization of the tethys region also affected the levant area here two processes were superimposed a the pattern of long wavelength vertical motions of the arabo nubian platform changed in the late permian when israel and nearby areas began to subside b rifting occurred in this subsiding area probably in several phases late anisian and ladinian carnian norian and liassic differential movements reached 2 3 km and magmatism occurred in the liassic and perhaps also in the triassic the tectonism was strongly felt up to 50 km landward of the present coast the crust was thinned and modified under the present continental margin and in the main rifts passive margin conditions were established in late liassic times over the previously faulted area later in the jurassic a carbonate shelf was constructed along this subsiding margin its basinward edge was 1 1 5 km high which shows that the adjacent se mediterranean was already a deep sea hence this basin and its passive margin are considered to have been shaped by the early mesozoic rifting which is recognized in israel the rifting process probably signifies oblique separation of the tauride block from the levant part of gondwana

geologic structure and neotectonics of the north african continental margin south of sicily abstract marine geological and geophysical data together with drilling information indicate that the north african passive continental margin has been subjected to extension and wrenching after it collided with the northern part of sicily the area of the tripolitania basin jarrafa trough melita and medina bank and the ragusa malta plateau has formed part of a sinking passive margin since the dispersal of gondwanaland at about 180 my ago as observed from geohistory diagrams a record of rifting in a nw se direction accompanied by dextral shear along the southern troughs is observed in seismic reflection data the rifting started during the neocomian and lasted until the eocene when activity became minor a pre middle miocene period of northward subduction of oceanic crust is inferred from the geology in ne sicily uplift of the northern part of the african margin after collision in the middle miocene is seen in wells in southern sicily after the messinian a rift and dextral shear zone established itself across the african margin from the strait of sicily to the medina ridge in the lonian basin the zone is marked by up to 1 7 km deep grabens narrow active wrench faulted channels volcanic fissures and local uplifted keilhorsts such as malta this zone which varies in width from 100 to 35 km forms the southern boundary of a microplate which includes sicily we speculate that the present motion of this microplate is partly due to the eastward movement of the calabrian arc with the sicilian block over the last remaining oceanic lithosphere in the eastern mediterranean

ammonoid diversity and disparity track episodes of chaotic carbon cycling during the early mesozoic episodes of mass extinction represent the largest events of biodiversity loss known in the geologic record and may provide tests of biodiversity ecosystem stability hypotheses here we present the first correlation between ammonoid diversity and disparity and ecosystem stability as represented by stable carbon isotopic records spanning the end permian through end triassic mass extinctions ammonoid generic richness from a single biogeographic realm shows that nearly all taxa disappeared coincident with major carbon isotopic shifts to lighter values the intervals following these two major mass extinctions were characterized by multiple positive negative couplets of chaotic carbon cycling and were composed of low richness ammonoid faunas characterized by higher proportions of passively floating non swimming morphotypes than before or after in contrast richness was highest during intervals of stable carbon isotope values we propose that these chaotic carbon episodes reflect the breakdown of functional redundancy in the ecosystem and that the post extinction carbon cycle did not stabilize until redundancy was restored

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

mantle dynamics in the mediterranean the mediterranean offers a unique opportunity to study the driving forces of tectonic deformation within a complex mobile belt lithospheric dynamics are affected by slab rollback and collision of two large slowly moving plates forcing fragments of continental and oceanic lithosphere to interact this paper reviews the rich and growing set of constraints from geological reconstructions geodetic data and crustal and upper mantle heterogeneity imaged by structural seismology we proceed to discuss a conceptual and quantitative framework for the causes of surface deformation exploring existing and newly developed tectonic and numerical geodynamic models we illustrate the role of mantle convection on surface geology a coherent picture emerges which can be outlined by two almost symmetric upper mantle convection cells the downwellings are found in the center of the mediterranean and are associated with the descent of the tyrrhenian and the hellenic slabs during plate convergence these slabs migrated backward with respect to the eurasian upper plate inducing a return flow of the asthenosphere from the backarc regions towards the subduction zones this flow can be found at large distance from the subduction zones and is at present expressed in two upwellings beneath anatolia and eastern iberia this convection system provides an explanation for the general pattern of seismic anisotropy in the mediterranean first order anatolia and adria microplate kinematics and may contribute to the high elevation of scarcely deformed areas such as anatolia and eastern iberia more generally the mediterranean is an illustration of how upper mantle small scale convection leads to intraplate deformation and complex plate boundary reconfiguration at the westernmost terminus of the tethyan collision

the end triassic mass extinction record of williston lake british columbia abstract triassic jurassic boundary sections on the shore of lake williston british columbia record a spectrum of depositional environments from the western canadian continental margin a primarily deep water anoxic record of deposition indicated by v v ni v cr th u indices and pyrite framboid and facies data is seen throughout the late triassic early jurassic norian hettangian interval in a section at black bear ridge abundant monotis bivalve populations in norian strata are interpreted to have lived on the seabed during transient oxygenation events that punctuated the background anoxic conditions monotis went extinct around the norian rhaetian boundary and the deep water assemblages are subsequently dominated by thin shelled pectinids an intra rhaetian sea level fall generated a major hiatus in the proximal black bear ridge section whilst distinctive lowstand strata were developed in the more distal and more complete ne parle pas point and pardonet creek sections these consist of shallow water phosphatic ooid sand facies that contain diverse bivalves the majority of the infaunal bivalves but not the epifaunal ones disappeared at the acme of the regression this is the end triassic mass extinction event and it occurred shortly before a terminal triassic flooding event this transgressive event is associated with a rapid negative shift of 13corg values interpreted to be the initial isotope excursion of hesselbo et al hesselbo s p robinson s a surlyk f piasecki s 2002 terrestrial and marine extinction at the triassic jurassic boundary synchronized with major carbon cycle perturbation a link to initiation of massive volcanism geology 30 251 254 the rhaetian record of williston lake thus records an extinction of shallow water infaunal bivalves during a lowstand prior to the development of a transgressive record that is associated with a major negative c isotope

geodetic evidence for low coupling on the hellenic subduction plate interface we develop a block model for the aegean and surrounding areas constrained by global positioning system gps in order to investigate the degree of coupling on the hellenic subduction interface i e the fraction of the motion across the plate boundary accommodated by elastic strain accumulation we use previously published models and seismicity to define the geometry of the interface separating the down going nubian slab from the overriding aegean this model provides a good fit to the gps observations for the 200 000 km2 aegean block the wrms of the residual velocities is 1 4 mm yr for 80 gps velocity estimates approximately the 95 level of the gps velocity uncertainties we investigate the degree of coupling on the seismically active plate interface the hellenic trench splay fault believed to be the source of the 365 ad great crete earthquake and tsunami and the kephalonia transform fault by comparing the modeled gps residual velocity field for a range of coupling values the gps observations are almost insensitive to coupling on the kephalonia transform fault because of the vertical dip of the fault that creates interseismic deformation only close to the fault where few gps sites exist the absence of resolvable shortening of the leading edge of the aegean plate precludes coupling of more than 0 2 20 of the full nubia aegean convergence rate on the modeled plate interface because of the shallow dip of the plate interface and trench splay fault and high rate of convergence if these boundaries were fully coupled high elastic strain rates would be expected to extend well into the overriding aegean plate based on our preferred value for the degree of coupling 0 1 and assuming characteristic earthquake behavior we estimate a recurrence time for great earthquakes with slip similar to that for the 365 crete event of 5700 8300 yr consistent with the absence of subsequent great earthquakes on this segment of the subduction zone

origin and emplacement of the late cretaceous baer bassit ophiolite and its metamorphic sole in nw syria abstract the baer bassit ophiolite of inferred late cretaceous age was emplaced from the south tethys ocean onto the leading edge of the arabian continental margin in latest cretaceous maastrichtian time dismembered sequences in different thrust sheets can be correlated to produce a complete ophiolite sequence with a metamorphic sole at the base overlain in turn by upper mantle tectonite rare cumulates massive and layered gabbros localized high level plagiogranites sheeted dykes basic extrusives and minor fe mn sediments umbers the restored ophiolite sequence is similar to that of the more intact troodos and hatay ophiolites but dissimilar to oman the baer bassit extrusives are magnesian and strongly depleted comparable to primitive island arc tholeiites and some boninitic lavas which favours a subduction related origin a well developed metamorphic sole is divisible into high grade amphibolite facies assemblages in the north and lower grade greenschist facies assemblages in the centre of the region but no complete inverted metamorphic gradient is preserved in any one local area the protoliths of both the high grade amphibolites and lower grade rocks greenschists are interpreted as alkali basalts and pelagic sediments including chert similar to the volcanic rocks in an underlying unmetamorphosed melange the metamorphic fabrics progressively evolved from ductile to brittle during tectonic transport towards the southeast most of the metamorphic fabrics evolved during intense shearing but some of the alkaline metabasites apparently were metamorphosed under relatively static strain conditions the apparent absence of preserved inverted metamorphic gradients in baer bassit may reflect a complex deformation history during emplacement alternatively differing p t conditions may be recorded at different depths at the base of the over riding mantle wedge during emplacement the front of the ophiolite was tectonically imbricated and overthrust by the main ultramafic slab bassit massif the thickest massif baer is underlain by a high grade metamorphic sole and was internally shortened but without thrust duplication of the entire ophiolite sequence following covering by late maastrichtian palaeogene marine calcareous sediments the area was subjected to mid tertiary regional folding this was followed by neogene dominantly left lateral strike slip deformation along the african eurasian plate boundary extending from south of cyprus to the dead sea transform fault as a result the originally emplaced thrust sheets were dissected into three main composite units baer bassit and the southeastern units separated by strongly faulted and sheared ophiolitic blocks and unmetamorphosed volcanic sedimentary melange

bridging onshore and offshore present day kinematics of central and eastern mediterranean implications for crustal dynamics and mantle flow we present a new kinematic and strain model of an area encompassing the calabrian and hellenic subduction zones western anatolia and the balkans using haines and holt s 1993 method we derive continuous velocity and strain rate fields by interpolating geodetic velocities including recent gps data in the balkans relative motion between stable eurasia and the western aegean sea is gradually accommodated by distributed n s extension from southern balkans to the eastern corinth gulf so that the westward propagation of the north anatolian fault naf throughout continental greece or peloponnesus is not required we thus propose that the naf terminates in north aegean and that n s extension localized in the corinth gulf and distributed in southern balkans is due to the retreat of the hellenic slab the motion of the hyblean plateau apulia peninsula south adriatic sea ionian basin and sirte plain can be minimized by a single rigid rotation around a pole located in the sirte plain compatible with the opening the pelagian rifts 2 2 5 mm yr and seismotectonics in libya we interpret the trenchward ultraslow motion of the calabrian arc 2 2 5 mm yr as pure collapse the calabrian subduction being now inactive in the absolute plate motion reference frame our modeled velocity field depicts two toroidal crustal patterns located at both ends of the hellenic subduction zone clockwise in nw greece and counter clockwise in western anatolia we suggest the nw greece toroidal pattern is the surface expression of a slab tear and consequent toroidal asthenospheric flow

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

geochronological constraints on post extinction recovery of the ammonoids and carbon cycle perturbations during the early jurassic abstract this paper presents the first quantitative study of the early jurassic recovery of ammonoids after the end triassic mass extinction based on detailed u pb id tims isotope dilution thermal ionization mass spectrometry geochronology from ash bed zircons placed within a clear phylogenetical and biochronological framework at the subzonal and species level this study was triggered by the discovery of a rich peruvian succession of ammonites deposited concomitantly with an unusually large number of ash beds two major phases of rediversification are observed during the psiloceras spelae and angulaticeras zones that correspond to positive peaks in the 13corg curve providing a possible link between biodiversity and the global carbon cycle in the case of the post extinction recovery the development of the earliest hettangian ammonites occurs within the genus psiloceras which begins with the occurrence of p spelae and then explodes into worldwide development of smooth psiloceratids of the psiloceras planorbis group s l this rapid biodiversification likely occurred less than 100 ka after the end triassic crisis the genus psiloceras occupied all the possible ecological niches worldwide from the pacific deep waters to the nw european shallow deposits and also in some rare tethyan occurrences like at germig in tibet this global dispersion allowed the differentiation of the group in several major phyla the schlotheimiidae discamphiceratinae arietitidae and lytocerataceae which were the roots of all other jurassic and cretaceous ammonites

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

a mechanism to thin the continental lithosphere at magma poor margins crustal thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults instead of multiple normal faults through exhumation of mid crustal and mantle material where continental plates break apart slip along multiple normal faults provides the required space for the earth s crust to thin and subside1 after initial rifting however the displacement on normal faults observed at the sea floor seems not to match the inferred extension2 here we show that crustal thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust 10 km by exhumation of mid crustal and mantle material this transitional crust is capped by sub horizontal detachment surfaces over distances exceeding 100 km with little visible deformation our rift model is based on numerical experiments constrained by geological and geophysical observations from the alpine tethys and iberia newfoundland margins3 4 5 6 7 8 9 furthermore we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust the presence of such lower crustal gabbros is well constrained for the alpine tethys system4 9 initial decoupling of upper crustal deformation from lower crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution this is achieved in our models by the formation of weak ductile shear zones

early evolution of the silicoflagellates during the cretaceous abstract recent studies of santonian and campanian sediments from several sites in northern canada identified two new silicoflagellate genera many new and unusual species a santonian assemblage of variramus and abundant specimens of the poorly known genus cornua this allowed a reassessment of variramus with information from three new species and transfer of v loperi into the new genus schulzyocha along with five new species that form an unusual assemblage in the early campanian a second new and unusual genus umpiocha and two new species of cornua provide knowledge of a previously unknown diversity of silicoflagellates in the santonian the first appearance of lyramula is now dated as early campanian the occurrence of c poretzkajae in early campanian offers new information on the early history and timing of the transition from cornua to corbisema sediments from higher in the campanian show development of corbisema apical plates and unusual new skeletal morphologies of arctyocha these and other discoveries present an improved understanding of early silicoflagellate evolution most of the recently described species lack a basal ring though many of the skeletal morphologies allow for interpretation of a basal plane variramus lacks an obvious basal plane suggesting a more primitive skeletal symmetry which is interpreted to have given rise to lyramula also lacking an apparent basal plane and not known to produce double skeletons recent discoveries of rare double skeletons for corbisema schulzyocha and vallacerta show the skeletons rotated with respect to known cenozoic configurations this information along with a better understanding of cornua and knowledge of the enigmatic umpiocha provides an opportunity to fill part of the 35 40 million year gap between the previously known albian and late campanian maastrichtian silicoflagellate occurrences these new interpretations of early silicoflagellate evolution are presented in the context of studies by deflandre gleser and other previous research

comment on the organic carbon isotopic and paleontological record across the triassic jurassic boundary at the candidate gssp section at ferguson hill muller canyon nevada usa by ward et al 2007

carbon isotope stratigraphy and ammonite faunal turnover for the middle jurassic in the southern iberian palaeomargin variations in the stable carbon isotope ratio of marine and continental sediments can reflect changes in sink and flux modifications of the palaeocarbon cycle here we report carbon isotope compositions of middle jurassic marine carbonates from the betic cordillera southern spain which represents an ideal region to link the stable carbon isotope curves directly to ammonite zones and subzones and thereby for the first time achieve an accurate chronostratigraphic calibration the five sections studied represent basin and high swell deposits of the southern iberian palaeomargin we find a similar 13 c of carbonates between different oceanic areas suggesting a homogeneous carbon isotope oceanic reservoir through the middle jurassic the aalenian bajocian transition is a critical period in ammonite evolution hence the early jurassic fauna are replaced by new ammonite families which become dominant throughout the middle and late jurassic for this reason we compared the 13 c values of carbonates with ammonite diversity and extinction rates at different taxonomical levels in order to explore the possible relationship between the carbon cycle and ammonite evolution the carbon isotope values of carbonates are not exactly linearly correlated with the extinction rate and ammonite diversity but the main faunal turnovers follow minimum 13 c values where extinct taxa are replaced by new ones likewise radiation episodes are associated with increasing 13 c values and with transgressive sea level rise all these data support the idea that perturbations in the global carbon cycle reflect rapid palaeoenvironmental changes we made detailed analyses of these faunal turnovers using them as a proxy to identify major palaeoenvironmental crises in their ecosystems forced by modification in the carbon cycle

lithosphere tearing at step faults response to edges of subduction zones abstract slab edges are a relatively common feature in plate tectonics two prominent examples are the northern end of the tonga subduction zone and the southern end of the new hebrides subduction zone near such horizontal terminations of subduction trenches ongoing tearing of oceanic lithosphere is a geometric consequence we refer to such kinks in the plate boundary as a subduction transform edge propagator or step other steps are the north and south ends of the lesser antilles trench the north end of the south sandwich trench the south end of the vrancea trench and both ends of the calabria trench volcanism near steps is distinct from typical arc volcanism in some cases slab edges appear to coincide with mantle plumes using 3d mechanical models we establish that step faults are stable plate tectonic features in most circumstances in the probably rare cases that the resistance to fault propagation is high slab break off will occur relative motion along the transform segment of the plate boundary often is non uniform and the step is not a transform plate boundary in the rigid plate tectonics sense of the phrase step propagation may result in substantial deformation rotation topography and sedimentary basins with a very specific time space evolution surface velocities are substantially affected by nearby steps

oceanic core complex development at the ultraslow spreading mid cayman spreading center roughly a third of the global mid ocean ridge system spreads at 6 km spreading centers and thought to accrete some of the thinnest 3 km crust the mcsc generates end member mid ocean ridge basalt compositions and hosts recently discovered hydrothermal vents multibeam bathymetric data reveal that axial depth varies along the mcsc with intraridge rift walls defined by kilometer scale escarpments and massifs dredging and near bottom work has imaged and sampled predominantly basaltic lavas from the greatest axial depths and 15 peridotite surrounded by gabbroic rocks from the prominent massifs the gabbroic rocks exhibit wide compositional variation troctolites to ferrogabbros and in many places contain high temperature amphibolite to granulite facies shear zones gabbroic compositions primarily reflect the accumulation of near liquidus phases that crystallized from a range of basaltic melts as well as from interactions with interstitial melts in a subaxial mush zone magnetization variations inverted from aeromagnetic data are consistent with a discontinuous distribution of basaltic lavas and structurally asymmetric spreading these observations support an oceanic core complex model for mcsc seafloor spreading potentially making it a type example of ultraslow seafloor spreading through mush zone and detachment fault crustal processes

high resolution ammonite and carbon isotope stratigraphy across the triassic jurassic boundary at new york canyon nevada the triassic jurassic boundary is generally considered as one of the major extinctions in the history of phanerozoic the high resolution ammonite correlations and carbon isotope marine record in the new york canyon area allow to distinguish two negative carbon excursions across this boundary with different paleoenvironmental meanings the late rhaetian negative excursion is related to the extinction and regressive phase the early hettangian 13corg negative excursion is associated with a major floristic turnover and major ammonite and radiolarian radiation the end triassic extinction early jurassic recovery is fully compatible with a volcanism triggered crisis probably related to the central atlantic magmatic province the main environmental stress might have been generated by repeated release of so2 gas heavy metals emissions darkening and subsequent cooling this phase was followed by a major long term co2 accumulation during the early hettangian with development of nutrient rich marine waters favouring the recovery of productivity and deposition of black shales

deformation pattern in the central mediterranean and behavior of the african adriatic promontory abstract the adriatic platform has been described in the literature both as an africa promontory moving in close connection with the main continent and as an independent microplate this evident incongruity is mainly due to the wide spectrum of kinematic hypotheses proposed on the basis of paleomagnetic data and to the fact that the adriatic africa transition is not marked by any clear decoupling fracture or by any interruption of lithological facies along the marginal belts apennines maghrebides and dinarides hellenides in this work it is argued that the counterclockwise rotation of the adriatic plate driven by africa pushing beneath the calabrian arc and southern tyrrhenian may coherently account for all major plio quatemary events in the central mediterranean

pacific microplate and the pangea supercontinent in the early to middle jurassic new biostratigraphic data based on radiolarians recovered from deep within the oceanic crustal section of ocean drilling program hole 801c in the western pacific along with existing radiometric information date this oceanic crust as late bajocian early bathonian 170 165 ma the overlying basal sediments at hole 801c are essentially identical in age middle bathonian 164 162 ma to the basal sediments at deep sea drilling program hole 534a in the central atlantic we estimate the time of formation of the pacific plate as 175 170 ma and the time of initial separation of the pangea supercontinent in the central atlantic as 190 180 ma we also identify a time of extensive subduction zone magmatism 175 159 ma at the eastern and western edges of pangea we suggest that the initial plate separation of pangea increased subduction rates at its outer margins and altered the plate boundaries in the pacific superocean leading to formation of the pacific plate

reinitialization of evolutionary clocks during sublethal environmental stress in some invertebrates this paper describes the influence of high environmental stress on evolutionary trends in some selected mesozoic ammonite lineages and some protists during extinction periods many ammonoids are affected by drastic simplifications of their shell geometry ornamentation and suture line we observe that relatively tightly coiled ammonites can give rise to highly evolute forms or uncoiled heteromorphs with simple ornamentation and almost ceratitic suture line a phenomenon called proteromorphosis such simplifications often correspond to a reappearance of ancestral geometries primitive ornamentation evolute coiling or uncoiling which suggest that the evolutionary clock of these organisms can be reinitialized by extreme sublethal environmental stress such as giant volcanism including its consequences on diverse pollutions and on climatic changes and major regressive events

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

anomalously fast convergence of india and eurasia caused by double subduction prior to collision with eurasia the indian plate rapidly accelerated northwards numerical simulations show that the combined pull of two slabs in two parallel north dipping subduction systems could have caused this pulse of rapid movement

paleotemperature variations of early jurassic seawater recorded in geochemical trends of belemnites from the basque cantabrian basin northern spain abstract here we present new o isotope mg ca and sr ca data of early jurassic belemnites from the basque cantabrian basin of northern spain a succession deposited in a periodically anoxic restricted hemipelagic basin nearly 200 pliensbachian lower toarcian belemnites were collected and examined using optical cathodoluminescence and chemical techniques to constrain the effects of potential diagenetic alteration after a precise diagenetic screening of samples 176 belemnites were selected to provide records of changes in seawater geochemistry and temperature the records show a fairly good correlation of 18o with mg ca ratios r 0 65 and a weak correlation of 18o with sr ca ratios r 0 34 the oxygen isotope data if interpreted in terms of paleotemperature have revealed a period of relatively uniform and warm seawater temperatures during the early pliensbachian followed by a sharp temperature drop during the late pliensbachian earliest toarcian the onset of this cooler period occurred within the protogrammoceras celebratum subzone and the coolest seawater temperatures were reached at the end pliensbachian pleuroceras spinatum zone this was followed by a rapid seawater warming during the harpoceras serpentinus zone of the early toarcian in addition the data set provides new information regarding paleoceanographic conditions for anoxic events in a critical region of connection between the boreal and tethys realms it is the background to relatively high 18o values that prevailed during the anoxic episodes concerning the impact of the early toarcian anoxic event in northern spain the detected 18o and mg ca excursions reached their minimum and maximum respectively during the lower h serpentinus zone while the anoxic black shale interval developed earlier during the upper dactylioceras tenuicostatum lowermost h serpentinus zones