phytoplankton associations of the anisian peri tethys basin central europe evidence of basin evolution and palaeoenvironmental change abstract anisian lower muschelkalk phytoplankton associations of the nw tethys shelf and the northern peri tethys basin are characterized by acritarchs and prasinophytes stratigraphical and lateral variations in the distribution pattern of these phytoplankton groups were analyzed in key sections of the central basin germany the southern gate areas switzerland poland and the northwestern tethys shelf hungary with the aim to infer palaeoenvironmental changes related to the basin evolution stratigraphically maximum abundance of marine phytoplankton is recognized during phases of maximum flooding laterally a dominance of different phytoplankton groups within these intervals is documented in the central part of the basin prasinophytes reach 80 percent of the total plankton association sediments of the basin margin the gate areas and proximal shelf show high amounts of acritarchs ranging from 76 to 95 these signatures clearly reflect the basin evolution of the anisian lower muschelkalk peri tethys basin and the interaction between a restricted intracratonic basin and an open ocean generally the peri tethys basin is characterized by a stratified water column with oxygen depleted bottom waters and maximum abundance of prasinophytes during phases of transgression cooler waters from the shelf flood the restricted basin displayed in the acritarch dominated phytoplankton associations of the shelf and gate areas marginal parts of the basin are generally well oxygenated and dominated by acritarchs within the acritarch assemblage veryhachium spp is characteristic of the marginal and central parts of the basin whereas micrhystridium spp dominates shelf deposits and sediments of the gate areas respectively the present study highlights the significance of different phytoplankton associations in basin analysis and high resolution sequence stratigraphy

teleseismic evidence for a break off subducting slab under eastern turkey abstract we present seismic images of the upper mantle beneath eastern turkey determined by teleseismic tomography the data are measured precisely from seismograms recoded by the eastern turkey seismic experiment network consisting of 29 portable stations and 2 permanent stations our results show that obvious high velocity high v anomalies of up to 2 are interrupted beneath eastern turkey and subcrustal earthquakes occurred along these high v anomalies pronounced low velocity low v anomalies are visible from the arabian foreland basin in the southwest to the caucasus region in the northeast which extend down to about 400 km depth these low v anomalies are consistent with the existence of late cenozoic volcanism in the region these results provide new constraints on the geodynamic processes in the east anatolian plateau suggesting that the break off of the arabian slab may play an important role in the formation of the anatolian plateau and the volcanism in the region these processes might be related to the collision of the arabian plate with the eurasian plate

melange genesis and ophiolite emplacement related to subduction of the northern margin of the tauride anatolide continent central and western turkey the tauride anatolide continent stretching for c 900 km across western and central turkey is one of the world s best example of a subducted exhumed passive margin within a collisional orogen twelve widely separated areas were studied and correlated to develop a new plate tectonic model a metamorphosed rifted continental margin of triassic lower cretaceous age tauride anatolide platform is overlain by upper cretaceous cenomanian lower maastrichtian pelagic sediments and then by both tectonic melange subduction complexes and sedimentary melange foredeep gravity complexes the melanges are overthrust by unmetamorphosed ophiolitic rocks commonly peridotites with swarms of diabase gabbro dykes and are underlain by metamorphic soles new geochemical evidence from basaltic blocks in the melange indicates predominantly subduction influenced within plate and mid ocean ridge type settings the dykes cutting the ophiolites were probably intruded during early stage intra oceanic arc genesis the metamorphosed continental margin melanges and ophiolites in the north anatolides are correlated with unmetamorphosed equivalents in the taurides further south e g beysehir and lycian nappes oceanic crust of triassic late cretaceous age formed between the gondwana related tauride anatolide continent in the south and the eurasia related sakarya microcontinent in the north following late triassic early cretaceous passive margin subsidence the continental margin was covered by cenomanian turonian pelagic carbonates c 98 90 ma ophiolites formed in an intra oceanic subduction zone setting in response to northward subduction probably within a two stranded ocean with the inner tauride ocean in the se and the izmir ankara erzincan ocean in the north nw metamorphic soles relate to intra oceanic subduction c 95 90 ma oceanic sedimentary igneous rocks accreted to the advancing supra subduction oceanic slab the tauride anatolide continental margin then underwent diachronous collision with the trench c 85 ma deeply subducted and metamorphosed at hp lt c 80 ma accretionary ophiolitic and exhumed hp lt rocks were gravity reworked into a southward migrating flexural foredeep and progressively overridden c 70 63 ma slices of the upper part of the platform and its margin detached and were thrust southwards as the tauride lycian and beysehir nappes together with regional scale ophiolites the continental margin and melange were simultaneously exhumed during maastrichtian early paleocene 70 63 ma and transgressed by shallow water sediments beginning in the late maastrichtian in the east c 64 ma and the mid late paleocene c 60 ma further west remnant oceanic crust was consumed during early cenozoic time followed by mid eocene 45 40 ma diachronous continental collision and a second phase of regional deformation rather than being progressive there were two stages of collision first upper cretaceous ophiolite emplacement driven by continental margin subduction trench collision and secondly eocene collision of the tauride and sakarya eurasian continents

the 1971 may 12 burdur earthquake sequence sw turkey a synthesis of seismological and geological observations summary it is now widely accepted that the rapid extension observed in western turkey is mainly accommodated by large active normal faults which control the geomorphology the ne sw trending burdur acigol and baklan basins bounded by large faults form a system of half graben whose orientation is evident in both the topography and the tilting of neogene sediments adjacent to them we used long period p and sh waveforms to determine the source parameters of the two largest earthquakes of the 1971 may 12 sequence that occurred in the burdur region the main shock was followed by many aftershocks which were distributed in a broad zone elongated ne sw parallel to the long axes of the basins in the region documented surface breaks of the 1971 event suggest that the northwest dipping faults along the southern margin of the burdur basin are those which moved well exposed fault planes are found dominantly to the south of burdur lake the surface dips of these faults are greater than that of the nw dipping nodal plane obtained for the main shock combined seismological and geological observations suggest that these faults have listric geometries

the carbon isotope shift at the permian triassic boundary in the southern alps is gradual carbon isotope ratios in marine carbonate rocks have been shown to shift at some of the time boundaries associated with extinction events for example cretaceous tertiary1 and ordovician silurian2 the permian triassic boundary the greatest extinction event of the phanerozoic3 is also marked by a large 13c depletion4 5 new carbon isotope results from sections in the southern alps show that this depletion did not actually represent a single event but was a complex change that spanned perhaps a million years during the late permian and early triassic these results suggest that the permian triassic p tr extinction may have been in part gradual and in part stepwise 6 7 but was not in any case a single catastrophic event

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

global positioning system measurements of present day crustal movements in the arabia africa eurasia plate collision zone we present and interpret global positioning system gps measurements of crustal motions for the period 1988 1994 at 54 sites extending east west from the caucasus mountains of southern russia georgia and armenia to the aegean coast of turkey and north south from the southern edge of the eurasian plate pontus block to the northern edge of the arabian platform viewed from a eurasia fixed reference frame sites on the northern arabian platform move n38 13 w at 20 3 mm yr roughly consistent with the velocity implied by nuvel 1a circuit closure n23 7 w at 24 2 mm yr the motion of arabia appears to be transferred directly to the region of turkey north of the suture however eastern turkey is characterized by distributed deformation while central western turkey is characterized by coherent plate motion involving westward displacement and counterclockwise rotation of the anatolian plate internal deformation within the central part of the anatolian plate is less than 2 mm yr the anatolian plate is decoupled from eurasia along the right lateral strike slip north anatolian fault naf this different response in eastern and western turkey to the collision of arabia may result from the different boundary conditions the hellenic arc forming a free boundary to the west and the asian continent and oceanic lithosphere of the black and caspian seas forming a resistant boundary to the north and east we derive a best fitting euler vector for anatolia eurasia motion of 29 2 0 8 n 32 9 0 4 1 3 0 1 m y the mapped surface trace of the naf corresponds well to a small circle about this pole the new euler vector implies an upper bound for naf slip rate of 30 2 mm yr i e assuming all relative motion is accommodated along the naf using the nuvel 1a euler vector for arabia eurasia and the gps euler vector for anatolia eurasia we determine an arabia anatolia euler vector of 31 2 n 45 2 e 0 9 0 1 m y and an upper bound on the east anatolian fault slip rate of 15 3 mm yr the aegean trough region of western turkey deviates significantly from coherent plate rotation in addition to rotating with anatolia this region shows roughly n s extension at a rate of 14 5 mm yr taken together with satellite laser ranging results along the hellenic arc the contemporary pattern of deformation indicates increasing motions toward the arc suggesting that the westward displacement and counterclockwise rotation of anatolia is driven both by pushing from the arabian plate and by pulling or basal drag associated with the foundering african plate along the hellenic subduction zone

regional seismic wave propagation lg and sn and pn attenuation in the arabian plate and surrounding regions an edited version of this paper was published by blackwell publishing copyright 2004 blackwell publishing see also http www blackwell synergy com doi abs 10 1111 j 1365 246x 2004 02246 x http atlas geo cornell edu middleeastnorthafrica publications al damegh2004 htm

comparison of young volcanic associations of western and eastern anatolia formed under a compressional regime a review abstract turkey is characterised by widespread post oligocene volcanism in western anatolia volcanic activity began during the late oligocene early miocene in a compressional regime a widespread suite of andesitic and dacitic calc alkaline rocks was erupted in this period they were accompanied by locally developed high level granitic intrusions the abrupt change from n s compression to n s stretching in the middle miocene was accompanied by a gradual transition to alkali basaltic volcanism in eastern anatolia the collision related compressional tectonics and associated volcanic activity began in the late miocene to pliocene and continued almost without interruption into historical times one minor and two major volcanic phases may be distinguished an initial minor eruptive phase of basic and intermediate alkaline rocks was followed by widespread eruptions of andesitic and dacitic calc alkaline rocks during the pliocene partly penecontemporaneous with this a second more important major phase of volcanism involving alkaline and transitional lavas began and continued during the quaternary the calc alkaline lavas of both regions were erupted at a time when the compressional regime led to crustal thickening these lavas display many geochemical and isotopic signatures that may be interpreted in terms of contamination of magma involving continental crustal materials the alkaline lavas in both regions began during the final stage of the compressional regime and form two groups one group is geochemically and isotopically similar to the calc alkaline rocks and the other is more typically alkaline the volcanic evolution of these two regions of turkey followed a somewhat similar pattern producing highly contaminated calc alkaline lavas at the beginning and evolving towards uncontaminated alkaline lavas at the end

segmented african lithosphere beneath the anatolian region inferred from teleseismic p wave tomography summary lithospheric deformation throughout anatolia a part of the alpine himalayan orogenic belt is controlled mainly by collision related tectonic escape of the anatolian plate and subduction roll back along the aegean subduction zone we study the deeper lithosphere and mantle structure of anatolia using teleseismic finite frequency p wave traveltime tomography we use data from several temporary and permanent seismic networks deployed in the region approximately 34 000 p wave relative traveltime residuals measured in multiple frequency bands are inverted using approximate finite frequency sensitivity kernels our tomograms reveal segmented fast seismic anomalies beneath anatolia that corresponds to the subducted portion of the african lithosphere along the cyprean and the aegean trenches we identify these anomalies as the subducted aegean and the cyprus slabs that are separated from each other by a gap as wide as 300 km beneath western anatolia this gap is occupied by slow velocity perturbations that we interpret as hot upwelling asthenosphere the eastern termination of the subducting african lithosphere is located near the transition from central anatolia to the eastern anatolian plateau or arabian eurasian collision front that is underlain by large volumes of hot underplating asthenosphere marked by slow velocity perturbations our tomograms also show fast velocity perturbations at shallow depths beneath northwestern anatolia that sharply terminates towards the south at the north anatolian fault zone nafz the associated velocity contrast across the nafz persists down to a depth of 100 150 km hence our study is the first to investigate and interpret the vertical extent of deformation along this nascent transform plate boundary overall the resolved upper mantle structure of anatolia is directly related with the geology and tectonic features observed at the surface of the anatolian plate and suggest that the segmented nature of the subducted african lithosphere plays an important role in the evolution of anatolia and distribution of its tectonic provinces

a geometric technique for relocating hotspots and refining absolute plate motions an age independent geometric relationship is presented that links hotspots to the seamounts which they produce and so permits the use of undated seamounts to refine the motion of tectonic plates this technique has the potential to rigorously assess hotspot fixity and to locate extinct hotspots the present application of this method points to a recent change in pacific plate motion and suggests a relocation of the louisville hotspot to the hollister ridge south of the eltanin fracture zone

terminal ordovician extinction geochemical analysis of the ordovician silurian boundary anticosti island quebec elemental abundances including ir carbon and oxygen ratios in carbonates mineral content and thin sections have been measured in samples collected across the conodont defined ordovician silurian o s boundary exposed on anticosti island quebec the ir concentrations ranged from 5 to a maximum at the boundary of 58 parts per trillion ppt however there is no evidence on the basis of these ir results for the association of a large body earth impact with the o s extinction because the ir concentrations like those of most other trace elements are simply proportional to the clay al content in the carbonate sequence the sup 13 c sup 12 c and sup 18 o sup 16 o ratios decrease abruptly at the boundary then just as abruptly increase to a long period of higher than preboundary ratios these patterns are probably related to the salinity in the seaway which was shallowing up to boundary time and then deepened and developed patch reefs fresh water input from rivers would have been most influential during the shallow water conditions 32 references 4 figures

geochemical features of collision related volcanic rocks in central and eastern anatolia turkey in central and eastern anatolia volcanism related to continental collision occurred in neogene to quaternary times major and trace element compositions 87sr86 sr and k ar ages were determined for volcanic rocks from selected volcanoes in this region 87sr86 sr for basalts from erciyes volcano in the eastern part of central anatolia as well as ararat nemrut and karacadag volcanoes in eastern anatolia are in the range 0 7035 0 7040 these ratios are higher than those of n type morb but overlap arc volcanic rock values this suggests that the mantle source which was possibly contaminated by fluids and melts with higher87sr86 sr during the pre collisional events has similar sr isotopic compositions in wide areas of the eastern part of central anatolia and eastern anatolia even across the collision plate boundary in addition chemical compositions of the mantle source are not homogeneous with respect to hfs element contents indicating that the slab derived components resulting from past subductions are not homogeneously distributed the mantle source beneath the western part of central anatolia which corresponds to the transitional region from collision tectonics in the east to subduction tectonics in the west has different chemical and sr isotopic signatures from other parts of anatolia in the western part of central anatolia the87sr86 sr of basaltic rocks from three regions characterized by monogenetic volcanoes are in the range 0 70427 to 0 70581 and differ from region to region in spite of indistinguishable chemical compositions this indicates either source heterogeneity on a small scale or different contributions of local crustal contaminants calc alkaline lavas from ararat and kars in eastern anatolia have chemical compositions with subduction signatures inherited from pre collision subduction events in contrast the chemical and sr isotopic features of volcanic rocks from erciyes volcano in central anatolia indicate that the combined process of fractional crystallization of basaltic magma and crustal assimilation without injection of slab derived components is the dominant process generating calc alkaline andesite under the collision tectonics regime operating in this region

multiple rifting pulses and sedimentation pattern in the cameli basin southwestern anatolia turkey abstract the neotectonic development of western anatolia was characterized by the formation of numerous graben type basins which have been well documented by general mapping although the cause and timing of the neogene regional tectonic extension remain controversial previous interpretations of the origin and evolution of these neogene basins were based mainly on regional scale tectonic inferences rather than detailed basin fill analysis the present study of the terrestrial intramontane cameli basin in the western taurides combines detailed facies analysis with biostratigraphic dating mammalian and molluscan fossils and documents three pulses of crustal extension that are reflected in changes in the palaeogeography and sedimentary architecture of the basin development of the cameli graben commenced in the vallesian time early tortonian and is marked by alluvial fan fluvial and lacustrine depositional systems with freshwater molluscan fauna a second pulse of tectonic extension occurred in the late ruscinian time early middle pliocene producing a new normal fault that split the basin longitudinally into two compartments the lake environment expanded and deepened coastal peat forming mires developed and abundant mammal fauna appeared by the early villanian time middle pliocene with the lacustrine deposits onlapping the basin margin and intrabasinal fault escarpments the lacustrine environment subsequently shrank as the progradation of axial river deltas and basin margin fan deltas caused water shallowing and shoreline regression a third pulse of extension occurred at the end of villanian time late pliocene when the development of a new generation of normal faults further split the basin into still narrower half graben compartments the third pulse of rifting is estimated to have accounted for little more than 10 of the sub basinal crustal extension but caused the most striking changes in the basin palaeogeography and drainage pattern the inward development of the successive normal faults indicated a high rate crustal extension this is the first regional case study of a terrestrial neotectonic graben employing detailed sedimentary facies analysis and mammal biostratigraphy and providing a time stratigraphic framework for the rifting pulses in western anatolia

a continent wide map of 1 hz lg coda q variation across eurasia and its relation to lithospheric evolution 1 we present new maps of lg coda q qo and its frequency dependence at 1 hz that cover virtually all of eurasia qo is relatively high up to 650 or more in the east european siberian indian and kazakh platforms but is surprisingly low 300 500 in the arabian platform and western portion of the siberian platform as well as in great britain and the northwestern portion of mainland europe it is generally low throughout the tethysides orogenic belt but there too it displays substantial regional variations 150 400 most qo anomalies appear to be related to the tectonic history of the eurasian crust the four regions with lowest values coincide with four of eurasia s most active concentrations of earthquake activity observed eurasian qo values are consistent with a previously determined empirical plot of global values in which qo in any region is proportional to the time elapsed since the most recent episode of tectonic or orogenic activity there comparisons of the new qo map with maps of rayleigh wave velocity temperature subducted lithosphere and seismicity lead us to infer that lg coda wave attenuation is most easily explained by energy lost in moving fluids through permeable rock or in being scattered from fluid enhanced zones the fluids are likely to have originated by hydrothermal release from subducting lithosphere or other upper mantle heat sources anomalies in qo and other lithospheric properties in some cases extend well outside the tethysides belt and other regions where upper mantle heat sources are known to occur possible explanations include earlier episodes of subduction activity crustal deformation due to collision of the afro arabian and indian plates or broader than expected back arc activity beneath eurasia

active tectonics of the north and central aegean sea summary in this paper we examine the connection between the westward motion of turkey relative to europe and the extension in and around the aegean sea the principal new data available since the last attempt to synthesize the tectonics of this region by mckenzie 1978 are much improved focal mechanisms of earthquakes constrained by p and sh body wave modelling as well as by first motions these mechanisms show that the faulting in the western part of the aegean region is mostly extensional in nature on normal faults with a nw to wnw strike and with slip vectors directed nnw to nne there is evidence from palaeomagnetism that this western region rotates clockwise relative to stable europe in the central and eastern aegean and in nw turkey distributed right lateral strike slip is more prevalent on faults trending ne to ene and with slip vectors directed ne palaeomagnetic data in this eastern region is more ambiguous but consistent with very small or no rotations in the northern part and possibly anticlockwise rotations relative to europe in the south the strike slip faulting that enters the central aegean from the east appears to end abruptly in the sw against the nw trending normal faults of greece the kinematics of the deformation is controlled by three factors the westward motion of turkey relative to europe the continental collision between nw greece albania and the apulia adriatic platform in the west and the presence of the hellenic subduction zone to the south as the right lateral slip on the north anatolian fault enters the aegean region it splays out becoming distributed on several parallel faults the continental shortening in nw greece and albania does not allow the rotation of the western margin of the region to be rapid enough to accommodate this distributed e w right lateral shear and thus leads to e w shortening in the northern aegean which is compensated by n s extension as the southern aegean margin can move easily over the hellenic subduction zone the dynamics of the system once initiated is self sustaining being driven by the high topography in eastern turkey and by the roll back of the subducted slab beneath the southern aegean the geometry of the deformation resembles the behaviour of a system of broken slats attached to margins that rotate in spite of its extreme simplicity a simple model of such broken slats is able to reproduce quantitatively most of the features of the instantaneous velocity field in the aegean region including the slip vectors and nature of the faulting in the eastern and western parts the senses and approximate rates of rotation the overall extensional velocity across the aegean and the distribution of strain rates as seen in the seismicity and topography or bathymetry and using geodetic measurements as part of this study we re examined the relation between the surface faulting and the focal parameters determined seismologically for the three large 1981 gulf of corinth earthquakes and reassessed the evidence for associating particular earthquakes in the sequence with observed surface faulting an important result is that in one of the events there is a resolvable discrepancy between the slip vector measured at the surface and that determined from the seismic body waves

regional wave propagation in turkey and surrounding regions this paper was published by the american geophysical union agu copyright 2000 agu see also http www agu org journals gl gl0003 1999gl008375 pdf 1999gl008375 pdf http atlas geo cornell edu turkey publications gok et al 2000 htm

subduction and the depth of convection in the mediterranean mantle 1 we tie together geological data paleotectonic reconstruction plate motion and tomographic analysis to unravel the history of subduction and back arc extension of the eastern and central mediterranean in these two regions extensional processes started contemporaneously around 30 myr ago but with marked differences in the eastern region the aegean basin opened slowly 1 cm yr behind a shallow dipping slab 40 45 the corresponding high velocity anomaly extends inside the upper mantle and can be also followed in the midmantle down to a depth of at least 1500 km its descent into the midmantle initiated most probably during the late cretaceous and the trench moved northeastward following the path of the eurasian plate and under the persistent push of the african plate conversely in the central mediterranean region subduction initiated later and the motion of the subducting slab is confined to the upper mantle causing punctuated and rapid episodes of back arc extension provencal and tyrrhenian basins behind a slab that dips steeply 75 we explore the causes that control how the slab subducted and interacted with the lower more viscous part of the mantle

lg magnitudes and yield estimates for underground novaya zemlya nuclear explosions abstract lg wave amplitudes of 30 novaya zemlya underground nuclear explosions as recorded by short period seismographs in denmark finland germany norway spitsbergen and sweden are used to determine m b lg values assuming that the m b lg versus explosion yield relation derived from nevada test site data applies to all continental areas the yields of the explosions are estimated they cover a large range of values from 2 5 to 4900 kt the largest explosion since april 1976 had an estimated yield of 145 kt the m b lg values when subtracted from the m b p values can be used to estimate the m b p bias between two test sites in this way the m b p bias between novaya zemlya and the nevada test site is estimated to be 0 20 magnitude units

sequencing events across the permian triassic boundary guryul ravine kashmir india abstract the permian triassic boundary ptb section at guryul ravine kashmir india comprises a 100 m thick apparently conformable succession of mixed siliciclastic carbonate sediments deposited in a deep shelf or ramp setting this section although long important in debates concerning placement of the ptb has not previously been the focus of an integrated chemostratigraphic study in the present study samples from a 20 m thick interval straddling the ptb were analyzed for major and trace element concentrations toc tic rees and organic 13c 15n to investigate contemporaneous environmental changes the guryul ravine section exhibits a sequence of discrete events that provide potentially important information about the character and cause s of the ptb two transient negative c isotopic excursions within the upper changxingensis zone predate the late permian event horizon lpeh i e the global mass extinction event by 200 400 kyr and are associated with the onset of a major eustatic rise and with secondary extinction peaks these excursions may record minor environmental disturbances prior to the main end permian crisis supporting an intrinsic mechanism such as volcanism and climate change rather than an extrinsic mechanism such as a bolide impact the onset of a large 4 0 to 4 5 sustained negative c isotope shift marks the lpeh which is located at the zewan khunamuh formation contact 260 cm below the biostratigraphically defined ptb the guryul ravine section exhibits a stepwise extinction pattern with the largest peak between the lpeh and ptb and a secondary peak just above the ptb a pattern similar to that observed in the meishan d gssp

lg coda q variation across eurasia and its relation to crustal evolution an extensive set of broadband and short period seismograms from regional seismic events has been used to derive a tomographic image of broad scale variations of lg coda q for most of eurasia the image indicates that lg coda q at a frequency of 1 hz varies between about 200 and 1000 lowest q values 800 are found in four regions the east european shield the siberian shield the indian shield and the southwestern and oldest portion of the altaid belt the pattern of lg coda q variation across eurasia suggests that crustal q in any region is directly proportional to the length of time that has elapsed since the most recent episode of large scale compressional tectonic activity or upper mantle heating that occurred there we interpret the low q as resulting largely from hydrothermal fluids generated by tectonic activity or heating that now reside in cracks and permeable portions of the eurasian crust crustal q increases with time after that activity as fluids are lost to the surface or absorbed by retrograde metamorphism

magma generation by slab steepening and breakoff beneath a subduction accretion complex an alternative model for collision related volcanism in eastern anatolia turkey 1 eastern anatolia is regarded as one of the best examples of continental collision represented by a 2 km high plateau it displays shallow and diffuse seismicity indicating that the crust is still being actively deformed perhaps the most striking aspect of eastern anatolia is the volume and compositional variability of collision related volcanic products erupted during the neogene and quaternary time a number of models have been proposed for the genesis of this volcanism in the region however recent geophysical studies have revealed that a mantle lithosphere is almost completely absent beneath a greater portion of the region which makes us question the validity of the previous models in this paper we propose a new model for magma genesis slab steepening and breakoff beneath a large subduction accretion complex this model holds that a northward subducting oceanic lithosphere beneath the eastern anatolia accretionary prism gets steepened and eventually detached from the continental lithosphere of the bitlis poturge massif following the continent accretionary complex collision this brings the asthenospheric mantle in contact with the accretionary complex at shallow depths e g around 50 km resulting in rapid regional uplift and extensive melting which leads to collisional volcanism

lg coda q and its relation to the geology and tectonics of the middle east regional seismograms were collected to image the lateral variations of lg coda q at 1 hz q 0 and its frequency dependence in the middle east using a back projection method the data include 124 vertical component traces recorded at 10 stations during the period 1986 1996 the resulting images reveal lateral variations in both q 0 and in the turkish and iranian plateaus a highly deformed and tectonically active region q 0 ranges between about 150 and 300 with the lowest values occurring in western anatolia where extremely high heat flow has been measured the low q 0 values found in this region agree with those found in other tectonically active regions of the world throughout most of the arabian peninsula a relatively stable region q 0 varies between 350 and 450 being highest in the shield area and lowest in the eastern basins all values are considerably lower than those found in most other stable regions low q values throughout the middle east may be caused by interstitial fluids that have migrated to the crust from the upper mantle where they were probably generated by hydrothermal reactions at elevated temperatures known to occur there low q 0 values about 250 are also found in the oman folded zone a region with thick sedimentary deposits varies inversely with q 0 throughout most of the middle east with lower values 0 4 0 5 in the arabian peninsula and higher values 0 6 0 8 in iran and turkey q 0 and are both low in the oman folded zone and western anatolia

slab detachment beneath eastern anatolia a possible cause for the formation of the north anatolian fault in this paper we discuss the possibility that the north anatolian fault naf results from the deep deformation of the slab beneath the bitlis hellenic subduction zone we described the tectonic evolution of the anatolia aegean area in three main steps before during and after the formation of the naf we remark that the tectonic conditions that are assumed to have triggered the formation of the naf i e collision to the east and extension to the west was already achieved before the onset of that strike slip fault system we also highlight that the formation of the naf was accompanied by the uplift of the turkish iranian plateau and by a surge of volcanism in the eastern anatolia collisional area and probably by the acceleration of the aegean trench retreat we show tomographic images from global p wave model of piromallo and morelli c piromallo a morelli p wave tomography of the mantle under the alpine mediterranean area j geophys res 108 2003 doi 10 1029 2002jb001757 showing that the slab beneath the bitlis collisional belt is not continuous and that its possible rupture pursues to the west at least up to cyprus and possibly up to the eastern end of the hellenic trench all these observations suggest that the plate tectonic re organization occurred in the late miocene early pliocene in the region results from slab break off in the bitlis area and from its lateral propagation to the west this idea is tested in analogue laboratory experiments which confirm that the break of the slab under the collisional belt may trigger 1 the acceleration of slab retreat to the west due to the increase in slab pull force 2 the indentation of the continent in the collisional area and 3 produce the conditions that permit the lateral escape of material towards the west and the formation of the naf

continental arc volcanism and tectonic setting in central anatolia turkey abstract the neogene and quaternary volcanism of central anatolia represents the central sector of the anatolian volcanic arc related to continental collision between the afro arabian and eurasian plates it is closely associated with a complex system of tectonic depressions related to brittle deformations of transtentional type and which commenced in the late miocene the volcanism here considered can be divided into three main periods of activity separated by important deformative and erosive events the first period is represented by a mostly andesitic effusive activity the second period is characterized by the emplacement of a thick ignimbritic sequence and shows an areal distribution up to 11 000 km 2 seven ignimbrite units have been recognized the three main units were found at a distance of more than 100 km from the presumed source area geological and sedimentological data lead us to recognize the melendiz dag volcanic complex and the ciftlik caldera as the probable ignimbrites source vent during the third period great andesitic basaltic stratovolcanoes and a number of prevalently acid monogenic centres developed the relationship between the volcanic activity is clearly conditioned by the main transcurrent fault systems present in central anatolia the neogene quaternary volcanic activity prevalently developed along the ene wsw karaman sivas lineament most of the great central volcanoes developed at the intersection between the ene wsw trends and the ecemis and tuz golu transcurrent faults the structural interpretation of the quaternary monogenic centres is more difficult probably they are related to the very recent n s fault swarms which cross the anatolides and the taurus range

tomographic evidence of slab detachment beneath eastern turkey and the caucasus summary teleseismic phase readings from the eastern turkey seismic experiment etse have been inverted using teleseismic tomography in order to create a 3 d image of the underlying mantle beneath eastern turkey the aim was to investigate the existence of an upper mantle negative velocity anomaly that is used to explain the uplift of eastern anatolian plateau and the potential pieces of detached oceanic slabs related to neo tethyan subduction suggested by previous studies using teleseismic waveforms from the 29 stations of the eastern turkey seismic experiment 2926 direct p phases from 146 events were picked by using adaptive stacking techniques in order to increase the station coverage and resolve the surrounding area the phase readings from the international seismological center isc bulletin have also been added the data set consists of 9571 p and pkp phase readings of 79 stations from 503 teleseismic events this study develops the first highresolution 3 d upper mantle p wave tomographic model for this region the tomographic results show the existence of an upper mantle negative velocity anomaly to a depth of 200 km beneath the eastern anatolian accreationary complex eaac as commonly observed in the previous studies that suggest a shallow partially molten asthenosphere the slab like high velocity anomalies beneath the eaac pontides and caucasus are interpreted as the detached southern and northern neo tethys slabs

survival brachiopod faunas of the end permian mass extinction from the southern alps italy and south china eight brachiopod species in seven genera are described from the permian triassic boundary beds of south china and northern italy the brachiopods from northern italy are described for the first time and include two new species orbicoelia dolomitensis chen and spirigerella teseroi chen the permian affinity of these brachiopods and their stratigraphical position above the extinction horizon demonstrate that they are survivors from the end permian mass extinction the surviving brachiopods from south china which was located at the eastern margin of the palaeo tethys ocean are considerably abundant and diverse and are dominated by geographically widespread generalist elements adapted to a wide variety of environments they were mostly limited to the upper permian to lowest griesbachian in contrast the survivors in northern italy which was situated at the western margin of the palaeo tethys comprise elements ranging from the carboniferous to permian or widespread tethyan genera these survivors did not occur in the pre extinction western tethyan oceans but migrated into this region after the end permian extinction event disaster taxon lingula proliferated slightly earlier in western tethyan oceans than in eastern tethyan regions following the event survival brachiopods from both regions appear to have a generic affinity although they do not share any species both south chinese and italian survival faunas support the view that the survival interval is the duration when survivors are dominated by geographically widespread generalist organisms adapted to a wide variety of ecological conditions

tomographic regionalization of crustal lg q in eastern eurasia 1 we measure q of crustal lg waves in eastern eurasia using the reliable two station methods more than 5 000 spectral ratios are collected over 594 interstation paths and are used to determine values of lg q0 and q at 1 hz and its frequency dependence over these paths these values are used to derive tomographic models of laterally varying q0 and with resolutions between 4 and 10 the q0 model contains values that vary between 100 and 900 q0 are the lowest in the tibetan plateau increase to moderate levels towards the east and north and reach maxima in the siberian and eastern europe cratons q0 values correlate well with regional tectonics most values are between 0 14 and 0 50 with a mean of 0 18 these values are lower than those obtained previously using either an lg coda q method or a method of simultaneous inversion of source spectra and q

geochemical and temporal evolution of cenozoic magmatism in western turkey mantle response to collision slab break off and lithospheric tearing in an orogenic belt post collisional magmatism in western anatolia began in the eocene and has occurred in discrete pulses throughout the cenozoic as it propagated from north to south producing volcano plutonic associations with varying chemical compositions this apparent sw migration of magma tism and accompanying extension through time was a result of the thermally induced collapse of the western anatolian orogenic belt which formed during the collision of the sakarya and tauride anatolide continental blocks in the late paleocene the thermal input and melt sources for this prolonged magmatism were provided first by slab break off generated aesthenospheric flow then by lithospheric delamination related aesthenospheric flow followed by tectonic extension driven upward aesthenospheric flow the first magmatic episode is represented by eocene granitoid plutons and their extrusive carapace that are linearly distributed along the izmir ankara suture zone south of the marmara sea these suites show moderately evolved com positions enriched in incompatible elements similar to subduction zone influenced subalkaline magmas widespread oligo miocene volcanic and plutonic rocks with medium to high k calc alkaline compositions represent the next magmatic episode partial melting and assimilation fractional crystallization of enriched subcontinental lithospheric mantle derived magmas were important processes in the genesis and evolution of the parental magmas which experienced decreasing subduction influence and increasing crustal contamination during the evolution of the eocene and oligo miocene volcano plutonic rocks collision induced lithospheric slab break off provided an influx of aesthenospheric heat and melts that resulted in partial melting of the previously subduction metasomatized mantle lithosphere beneath the suture zone producing the eocene and oligo miocene igneous suites the following magmatic phase during the middle miocene 16 14 ma developed mildly alkaline bimodal volcanic rocks that show a decreasing amount of crustal contamination and subduction influence in time both melting of a subduc tion modified lithospheric mantle and aesthenospheric mantle derived melt contribution played a significant role in the generation of the magmas of these rocks this magmatic episode was attended by region wide extension that led to the formation of metamorphic core complexes and graben systems aesthenospheric upwelling caused by partial delamination of the lithospheric root beneath the western anatolian orogenic belt was likely responsible for the melt evolution of these mildly alkaline volcanics lithospheric delamination may have been caused by peeling off during slab rollback the last major phase of magmatism in the region starting c 12 ma is represented by late miocene to quaternary alkaline to super alkaline volcanic rocks that show oib like geochemical features with progressively more potassic compositions increasing toward south in time these rocks are spatially associated with major extensional fault systems that acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface the melt source for this magmatic phase carried little or no subduction component and was pro duced by the decompressional melting of aesthenospheric mantle which flowed in beneath the atte nuated continental lithosphere in the aegean extensional province this time progressive evolution of cenozoic magmatism and extension in western anatolia has been strongly controlled by the interplay between regional plate tectonic events and the mantle dynamics and provides a realistic template for post collisional magmatism and crustal extension in many orogenic belts

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

tomographic pn velocity and anisotropy structure beneath the anatolian plateau eastern turkey and the surrounding regions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017391 shtml http atlas geo cornell edu turkey publications al lazki et al 2003 htm

strangelove ocean before the cambrian explosion the palaeozoic and mesozoic eras were terminated by faunal changes involving mass extinction of the old and explosive evolution of the new fauna but the fossil record shows only a cambrian explosion at the end of the precambrian stanley speculated that the explosion was only possible after the ubiquitous algae community had been largely eliminated1 ecological niches were thus liberated for explosive evolution if the cambrian explosion were preceded by a mass mortality or by a mass extinction such an event should leave a record in the form of geochemical anomalies we have undertaken a search for geochemical anomalies at the precambrian cambrian contact we report here the discovery of a sharp negative carbon isotope shift in the carbonate of a clay immediately above a marker in the precambrian cambrian boundary the china c marker and interpret this signal as evidence of sudden decrease in fertility before the cambrian explosion of invertebrate evolution the discovery suggests that the precambrian cambrian boundary might be defined by an event marker at a palaeontologically correlative horizon

lateral variations of crustal seismic attenuation along the indepth profiles in tibet from lg q inversion 1 fourier spectra of crustal guided lg waves are collected to study seismic attenuation or q along the indepth profiles the 1 hz lg q q0 values are measured between many pairs of two stations and input to a back projection algorithm to obtain laterally varying q0 models along the indepth iii profile in central tibet the q0 model consists of low and nearly constant values of 90 these low values are consistent with abnormally high temperature as well as partial melts in the crust along the indepth ii profile in southern tibet the q0 values increase southward they are extremely low 60 over the northernmost segment but increase by a factor of 2 over a distance of 100 km between the indus yalong suture and the kangmar dome farther south and into the high himalayas q0 values are higher than 300 regional rayleigh waves observed along the northern indepth ii profile are used to infer a low velocity low q layer at midcrustal depths between 15 and 30 km in southern tibet the aqueous fluid trapped in the upper crust and a midcrust partial melting zone associated with the underthrusting of the indian lithosphere are the likely causes of the high lg attenuation in southern tibet low q rather then a systematic lg conversion along a dipping moho is the main cause of the previously observed lg blockage over paths crossing the southern tibetan boundary

the hellenic subduction zone a tomographic image and its geodynamic implications new tomographic images of the hellenic subduction zone demonstrate slab penetration in the aegean upper mantle to depths of at least 600 km beneath greece the lower part of the slab appears to be detached at a depth of about 200 km whereas it still seems to be unruptured beneath the southern aegean schematically we derive minimum time estimates for the duration of the hellenic subduction zone that range from 26 to 40 ma this is considerably longer than earlier estimates which vary between 5 and about 13 ma

seismotectonics of the southern boundary of anatolia eastern mediterranean region subduction collision and arc jumping the pattern of seismicity and fault plane solutions of earthquakes are used to outline the tectonic features of the southern boundary of anatolia in the eastern mediterranean and southeastern turkey the results of this study show that this boundary is composed of two distinct parts one in southeastern turkey and syria is a wide and complex zone of continental collision the other in the levantine basin of the eastern mediterranean is a zone of oceanic subduction in the region of continental collision three zones of seismicity are observed most of the seismic activity in this region follows the bitlis zone and is associated with a zone of thrusting and mountain building this appears to be the zone of most active deformation and plate consumption in the plate boundary region between arabia and turkey a less active zone of seismicity to the north of the bitlis zone is interpreted to have been more active in the past whereas another active zone of seismicity to the south is interpreted to be a zone which may be more active in the future as the main zone of plate consumption jumps to the south in the subduction zone of the eastern mediterranean the depth of the subducted slab and the rate of seismicity generally increase from east to west the zone of present day convergence between africa and turkey in the levantine basin can be best outlined by the northern edge of the mediterranean ridge the subduction zone in this area sequentially jumps to the south as small continental fragments collide with existing zones of subduction deep seismic activity near the gulf of antalya is associated with a detached subducted slab north of the anaximander mountains that is distinctly different from the seismic trend which is associated with present day active subduction the plate boundary between africa and turkey at the center of the levantine basin appears to have shifted to the south of the anaximander mountains and florence rise most of the focal mechanisms of the earthquakes along the entire southern boundary of anatolia indicate that n to nnw thrusting is the dominant mode of seismic deformation the present set of data is inconsistent with a major transform fault in the cyprean arc east of cyprus and in southeastern turkey

lg wave attenuation in the isparta angle and anatolian plateau turkey we estimate lg wave attenuation using local and regional seismic phases in the isparta angle and the anatolian plateau turkey the isparta angle ia is a tectonically active zone forming the boundary between the african plate and the anatolian plateau and is currently undergoing n s extensional deformation the anatolian plateau contains many intra continental faults including the north anatolian fault zone and the east anatolian fault zone as well as the menderes massif a large waveform data set was compiled from a variety of local and regional seismic networks including 121 digital seismic stations broad band and short period between 1999 and 2008 spanning the ia the anatolian plateau and azerbaijan the data set was used to determine the nature of lg wave propagation and characterize the nature of seismic attenuation within the crust of these regions lg waveforms were used to calculate the frequency dependent lg qo and lg eta a wide range of lg qo values was obtained between 52 6 and 524 227 low lg qo values 90 155 are calculated towards the north of ia iskenderun gulf and its vicinity bingol karliova izmit and its vicinity lg qo values are especially low 90 along the menderes massif and the aksehir simav fault zones this may be due to intrinsic attenuation of lg associated with the partially molten crust and young volcanism the high lg qo values 350 are probably caused by the crust not being subject to large amounts of extensional deformation like the antalya gulf and apparently being thick enough to support lg propagation relatively higher values along the border of this subduction zone and plate boundary might be related to the taurus mountain belts and bitlis zagros suture zone the lateral frequency dependency lg eta is also consistent with high tectonic activity in this region

the geodynamics of the aegean and anatolia introduction the complexity of the plate interactions and associated crustal deformation in the eastern mediterranean region is reflected in many destructive earthquakes that have occurred throughout its recorded history many of which are well documented and intensively studied the eastern mediterranean region including the surrounding areas of western turkey and greece is indeed one of the most seismically active and rapidly deforming regions within the continents fig 1 thus the region provides a unique opportunity to improve our understanding of the complexities of continental tectonics in an actively collisional orogen the major scientific observations from this natural laboratory have clearly been helping us to better understand the tectonic processes in active collision zones the mode and nature of continental growth and the causes and distribution of seismic volcanic and geomorphological events e g tsunamis and their impact on societal life and civilization the tectonic evolution of the eastern mediterranean region is dominated by the effects of subduction along the hellenic aegean arc and of continental collision in eastern turkey anatolia and the caucasus northward subduction of the african plate beneath western turkey and the aegean region is causing extension of the continental crust and volcanism in the overlying aegean extensional province eastern turkey has been experiencing crustal shortening and thickening as a result of northward motion of the arabian plate relative to eurasia and the attendant postcollisional magmatism taymaz et al 1990 1991a b mcclusky et al 2000 2003 dilek pavlides 2006 and references therein fig 2 the resulting combination of forces the pull from the subduction zone to the west and push from the convergent zone to the east is causing the turkish plate to move southwestward bounded by strike slip fault zones the north anatolian fault zone nafz to the north and the east anatolian fault zone eafz to the south interplay between dynamic effects of the relative motions of adjoining plates thus controls large scale crustal deformation and the associated seismicity and volcanism in anatolia and the aegean region taymaz et al 2004

massive volcanism at the permian triassic boundary and its impact on the isotopic composition of the ocean and atmosphere abstract bulk carbonate and conodonts from three permian triassic p t boundary sections at guryul ravine kashmir abadeh central iran and pufels bula bulla italy were investigated for 13 c and 18 o carbon isotope data highlight environmental changes across the p t boundary and show the following features 1 a gradual decrease of 4 to more than 7 starting in the late permian changhsingian c bachmanni zone with two superimposed transient positive excursions in the c meishanensis h praeparvus and the m ultima s mostleri zones 2 two 13 c minima the first at the p t boundary and a higher occasionally double minimum in the lower i isarcica zone it is unlikely that the short lived phenomena such as a breakdown in biological productivity due to catastrophic mass extinction a sudden release of oceanic methane hydrates or meteorite impact s could have been the main control on the latest permian carbon isotope curve because of its prolonged 0 5 ma duration gradual decrease and the existence of a 1 positive shift at the main extinction horizon the p t boundary 13 c trend matches in time and magnitude the eruption of the siberian traps and other contemporaneous volcanism suggesting that volcanogenic effects such as outgassed co 2 from volcanism and even more thermal metamorphism of organic rich sediments as the likely cause of the negative trend

tomographic imaging of lg and sn propagation in the middle east observations based on relatively limited data recorded by sparsely distributed stations have indicated that regional seismic phase propagation lg and sn is very complex in the middle east accurate characterization of regional seismic wave propagation in this region necessitates the use of a large number of seismic stations we have compiled a large data set of regional and local seismograms recorded in the middle east this data set comprises approximately four years of data from national short period networks in turkey and syria data from temporary broadband arrays in saudi arabia and the caspian sea region and data from gsn mednet and geofon stations in the middle east we have used this data set to decipher the character and pattern of regional seismic wave propagation we have mapped zones of blockage as well as inefficient and efficient propagation for lg pg and sn throughout the middle east two tomographic techniques have been developed in order to objectively determine regions of lithospheric attenuation in the middle east we observe evidence of major increase in lg attenuation relative to pg across the bitlis suture and the zagros fold and thrust belt corresponding to the boundary between the arabian and eurasian plates we also observe a zone of inefficient sn propagation along the dead sea fault system which coincides with low pn velocities along most of the dead sea fault system and with previous observations of poor sn propagation in western jordan our observations indicate that in the northern portion of the arabian plate south of the bitlis suture there is also a zone of inefficient sn propagation that would not have been predicted from prior measurements of relatively low pn velocities mapped high attenuation of sn correlates well with regions of cenozoic and holocene basaltic volcanism these regions of uppermost mantle shear wave attenuation most probably have anomously hot and possibly thin lithosphere

sn attenuation in the anatolian and iranian plateau and surrounding regions an edited version of this paper was published in geophysical research letters by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018020 shtml http atlas geo cornell edu turkey publications gok et al 2003 htm

stable isotope and sr2 ca2 evidence of diagenetic dedolomitization in a schizohaline environment cenomanian of northern israel abstract the cenomanian turonian upper judea group of israel comprises shallow marine hypersaline dolomites passing laterally into basinal limestones and chalks chertbearing diagenetic dedolomites characterize the transitional zone the restriction of dedolomites to a narrow zone their light 13c up to 11 and their low sr2 concentration

neotectonic intersection of the aegean and cyprus tectonic arcs extensional and strike slip faulting in the isparta angle sw turkey abstract the isparta angle and adjacent antalya bay areas constitute an important segment of the eastern mediterranean region located at the intersection of the southward convex aegean and cyprus arcs some recent tectonic maps show the isparta angle as a nw se compressional lineament extending eastwards into the kyrenia range of northern cyprus however fault data from the onshore isparta angle together with offshore shallow seismic reflection data show that the present morpho tectonic setting is dominated by extension the last phase of compression to affect the area studied in the late miocene was accompanied by regional nappe emplacement lycian nappes onshore fault planes measured from fault zones bounding both the limbs and the core of the isparta angle are oriented predominantly ne sw nw se and n s superimposed slickenfibres show that reverse faults were succeeded in turn by right lateral faults then by normal faults the fault phases are dated by stratigraphical and geomorphological evidence reverse faults date from the late miocene or earlier compressional deformation whereas the right lateral faults mainly developed during latest miocene early pliocene normal faulting dominated from the late pliocene recent an interpretation of shallow seismic reflection data shows that antalya bay is characterised by a nw se trending asymmetrical graben system that has continued to be active during the late miocene early pliocene right lateral strike slip resulted from shear along the eastern termination of a zone of extension and rotation that characterises the western aegean this shear was focused in a n s direction by inherited zones of structural weakness in the basement antalya complex the switch to ne sw extension in the late pliocene quaternary relates to a regional change in stress direction throughout the aegean region and was accompanied by strong uplift of the bey da lari region of the taurus mountains bordering the isparta angle in the west the isparta angle is the link between a the extensional province of western turkey bounded to the south by the actively subducting hellenic arc and b the uplifted anatolian plateau bounded to the south by the cyprus subduction zone understanding the miocene to recent tectonic development helps elucidate the kinematics of the region the new structural data presented lend no support for recent suggestions that the isparta angle and antalya bay represent parts of a regional compressional zone related to plate collision

isotope shifts in the late permian of the delaware basin texas precisely timed by varved sediments closely spaced samples 285 in number of varved sediments from the upper permian in delaware basin texas have been analyzed for 13ccarb 13corg 18ocarb corg ccarb and calcite dolomite 13c records a dramatic rise from 2 8 to 5 7 in only 4400 years detected in three sections across the basin extrapolating smoothly through a 600 year interruption by a local west side of the basin fresh water inflow evidenced by low 18o this continuity and low corg within the basin both indicate that the excess net deposition of corg necessary to generate the rise in 13c took place in the ocean external to the delaware basin correlation with similar records from the zechstein basin suggest that the event was world wide although this poses obvious difficulties for the carbon cycle the rate of rise of 13c and its sustained high level must imply conversions of oxidized carbon to reduced carbon that are very large depending on which reservoirs were involved

a back projection method for imaging large scale lateral variations of lg coda q with application to continental africa summary a new method is developed which uses back projection tomography to regionalize large scale lateral variations of coda q for lg waves which have traversed long continental paths successful use of this method requires precise and stable single trace measurements of lg coda q xie nuttli 1988 the method converges rapidly and requires minimal computer storage it also allows quantitative estimation of resolution and error in imaging lateral variations of coda q the spatial resolution of this method is limited by the uneven spatial coverage of the data base by our limited knowledge of lg coda generation and by the trade off between the stability and the spatial resolution of the coda q inversion the method is applied to a large set of digital lg coda data from africa where large scale lateral variations of lg coda q are found to correlate well with major tectonic features most of africa is stable and like other stable regions has relatively high coda q values the lowest values of coda q are associated with the african rift system other regions of low q values include the atlas mountains and cape fold belt regions of mesozoic and younger deformation the lateral variation of frequency dependence of lg coda q correlates in most regions with that of q at 1 hz our analysis of the spatial resolution of this method indicates that the resolving power of lg coda q imaging is comparable to that of velocity tomography using long period surface waves using empirical approaches we estimate that uncertainties in lg coda q and its power law frequency dependence parameter are less than about 60 and about 0 2 respectively for most of africa

seismotectonics of the cyprian arc summary the cyprian arc forms the plate boundary between the anatolian plate in the north and the nubian and sinai plates in the south we examine the tectonic setting and seismic activity along the arc in light of new geodetic studies indicating relative ne sw plate motions across the arc the first order tectonic variations are determined by the arc s geometry the eastern arc oriented subparallel to relative motion is dominated by transcurrent tectonism the western arc is oriented almost normal to relative plate motion and is subjected to convergent processes variations in the level and depth of seismic activity along the western arc suggest that the northwestern section of the arc represents a subduction boundary whereas the southeastern section represents a collision boundary the two tectonic domains of the western arc are separated by a ne sw trending tear fault which produces large earthquakes such as the mw 6 8 1996 paphos earthquake we compare the geometrically similar cyprian and hellenic arcs and find significant differences in the rate direction and type of convergence across the two arcs the hellenic arc is subjected mainly to subduction whereas the shorter cyprian arc is subjected to subduction collision and transcurrent tectonic processes

east anatolian high plateau as a mantle supported north south shortened domal structure an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017858 shtml http atlas geo cornell edu turkey publications sengor et al 2003 htm

the crustal structure of the east anatolian plateau turkey from receiver functions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018192 shtml http atlas geo cornell edu turkey publications zor et al 2003 htm

1 hz lg q tomography in central asia we have applied tomographic techniques to a data set of over 1700 regional distance lg amplitudes from 12 stations for paths inside a 30 by 40 region of central asia our purpose is to create high resolution path correction maps for use in regional distance source discrimination and magnitude determination as well as to study lg propagation characteristics in one of the most heterogeneous portions of the earth for 1 0 hz data tomography reduced variance 33 relative to a best fit uniform q model lgq varied with geologic region with low values in tibet the tien shan and the pamir range q 200 to 400 intermediate values in basins such as the tarim q 500 and high values for platforms and older crust q 800 the relatively efficient propagation across the tarim differs from the poor propagation that is generally observed across sedimentary basins

timing of cenozoic extensional tectonics in west turkey the timing of the transition from compressional to extensional tectonics in the late cenozoic evolution of west turkey has been constrained by k ar geochronology from acidic volcanic rocks and tourmaline leucogranite dykes in the central and east margin respectively of the gordes basin dacites and rhyolites in the centre of the gordes neogene sedimentary basin cut both the basement ophiolites of the izmir ankara suture zone and the neogene sediments on the basin s eastern margin the leucogranites cut metamorphic basement along a major ne sw trending normal fault that controls the regional structure of the basin pebbles of these leucogranites occur in adjacent neogene turfites and conglomerates k ar dates on biotites from the central volcanic rocks vary from 18 4 0 8 ma to 16 3 0 5 ma early miocene whilst muscovite from a leucogranite on the eastern margin of the basin provides ages of 24 2 0 8 ma and 21 1 1 1 ma latest oligocene to early miocene geochronological data and field relationships demonstrate that the earlier compressional regime had been replaced by extensional tectonics by latest oligocene early miocene

love wave group velocity maps of turkey and surrounding regions summary we present the analysis of a love wave dispersion study performed across turkey and the surroundings group velocity dispersion curves were obtained from the local and regional earthquakes recorded at both permanent and temporary stations operated in the region lovewave group velocity maps in the period range of 10 50 s were computed using a tomographic inversion method the study shows the existence of significantly different crustal types in the area the group velocity anomalies are associated with the major geological structures in the region low group velocities at shorter periods 10 20 s are observed in the local sedimentary basins the eastern mediterranean and the black sea the eastern anatolia region is also characterized by low group velocities while pontides and bitlis p ot urge massif display higher group velocities the central anatolia exhibits uniform velocity distribution indicating more homogenous crust the isparta angle is marked by a wedge shaped low group velocity anomaly the low velocities observed in the isparta angle are related to crustal thickening and subduction related complex high velocities observed on the maps are associated with metamorphics magmatic arcs along the orogenic belts of pontides p

late pliocene early pleistocene athalassa formation north central cyprus carbonate sand bodies in a shallow seaway between two emerging landmasses the late pliocene early pleistocene athalassa formation accumulated within the neogene mesaoria basin of northern cyprus bordered by two subdued but rising landmasses the kyrenia range to the north and the troodos ophiolitic massif to the south in the eastern part of the basin the formation is dominated by cross stratified bioclastic rich sandstones interpreted as shallow marine carbonate sand bodies the sediments are described in terms of six calcarenite facies and subfacies and one sandstone fades palaeocurrent analysis indicates that the carbonate sand bodies formed near the southern margin of the kyrenia landmass and then migrated southwards across a shallow marine platform the driving force is believed to have been storms generated by strong winds such winds during the late pliocene early quaternary were probably stronger than today in this area other factors influencing deposition of the formation include minor tectonic instability and probable eustatic sea level changes study of the athalassa formation thus provides insights into late pliocene pleistocene palaeoenvironments in the easternmost mediterranean

comet showers as a cause of mass extinctions if at least some mass extinctions are caused by impacts why do they extend over intervals of one to three million years and have a partly stepwise character the solution may be provided by multiple cometary impacts astronomical geological and palaeontological evidence is consistent with a causal connection between comet showers clusters of impact events and stepwise mass extinctions but it is too early to tell how pervasive this relationship may be

different stress states in the burdur isparta region sw turkey since late miocene times a reflection of a transient stress regime abstract the burdur isparta region is a transitional zone between two distinct neotectonic domains in turkey the burdur graben system as the northeastern part of the fethiye burdur fault zone and the kovada graben at the apex of the isparta angle each domain represents a particular stress regime fault data from unconsolidated pliocene and quaternary deposits were combined with stress states deduced from pre pliocene consolidated rocks in order to reconstruct the stress field evolution in the study area since late miocene different stress states were identified they were put in a stratigraphic framework and u th dating of fault related calcite precipitates proved to be an additional tool in constraining the history of the stress states the reconstructed history reflects a transient stress regime the evolving stress field indicates that the influence of the kovada stress regime fades through time and that the influence of the burdur stress regime is gaining importance suggesting a northeastwards progression of the fethiye burdur fault zone

neotectonic evolution of the anaximander mountains at the junction of the hellenic and cyprus arcs abstract the anaximander mountains occupying an outer arc position at the junction of the hellenic and cyprus arcs have been studied using a suite of geophysical data including multibeam swath bathymetry backscatter images seismic reflection profiles and gravity and magnetic data which support an improved description of its deformation history lithologically the western mountains can be correlated with the neritic limestones of the bey daglar unit of sw turkey the eastern mountains relate to the ophiolitic antalya nappe complex in addition to this lithological contrast a deep seated crustal difference which is best reflected in gravimetry relates to the mid tortonian aksu thrust phase after the early middle miocene eastward emplacement of the lycian nappes the serravallian tortonian stage was characterized by the development of an array of grabens with n120 e strikes which occupied a vast continental area that extended from southern aegean to southwestern turkey during the mid tortonian the last phase of thrusting marked the onset of a different kinematic regime related to the westward rotation of the anatolian platelet this late miocene change marked the start of differential subsidence that resulted in the formation of the anaximander mountains and which is reflected by an unconformity surface between the lower middle miocene and plio quaternary units the messinian quaternary period in the western part of the anaximander mountains was characterized by distributed sinistral shear parallel to n70 e which was marked by the onset of an extension on n20 e striking normal faults that formed long graben like depressions during the pliocene these basins were transected by n70 e striking sinistral strike slip fault zones although continued crustal extension suggests deformation in transtension the eastern part of the anaximander mountains is instead characterized by n150 e striking normal and or oblique normal fault zones which lack significant evidence of strike slip deformation close examination of newly calculated predicted relative plate motions between africa from nuvel 1a and anatolia from gps measurements indicates that plate motion vectors change rapidly at the junction between the hellenic and cyprus arcs because of the close proximity to the pole of anatolian rotation these calculations indicate that along both the eastern hellenic arc and the western cyprus arcs the florence rise the relative motion between the anatolian and african plates is sinistral on the southern florence rise deformation is characterized by pure left lateral faulting whereas farther northwest in the eastern anaximander mountains the component of strike slip decreases although arc normal convergence predicts the occurrence of thrust faulting southwestward trench retreat also causes an extension internal to this outer arc domain such that the preexisting n120 e striking thrust faults of the aksu phase have been reactivated as normal to oblique normal faults during the pliocene and quaternary the observed sinistral faulting on faults striking n70 e in the western mountains is consistent with the relative plate motion along the eastern hellenic arc and merges with the extensional domain in the eastern mountains

the neotectonics of the aegean an alternative view minor reverse faults in widely dispersed neogene outcrops in the central aegean have led several people to suggest that the regional extension which started in the lower pliocene or earlier was interrupted by short periods of compression the durations of these postulated compressional episodes are short compared to the time scale on which convective forces acting on the base of the lithosphere can change thus possible mechanisms for driving such motions are limited in this paper we offer alternative explanations for these observations and in particular show that these apparently compressional episodes are probably not regional in extent and may not be truly compressional in origin in some places they are more likely to be a consequence of the considerable rotation that is found in extensional terranes the plio quaternary paleogeography of the central aegean is satisfactorily explained by uplift in the footwall blocks of normal faults and does not require regional compression studies of the faulting associated with recent large earthquakes suggest that the sort of microtectonic analysis which is typically carried out on small faults in surficial sediments is more likely to reflect the internal deformation of blocks bounded by major fault structures than be a reliable indicator of regional stress patterns

scattering and attenuation of seismic waves in northeastern north america abstract the energy flux model of seismic coda developed by frankel and wennerberg 1987 is used to derive path averaged estimates of scattering and intrinsic attenuation for northeastern north america the model predicts the amplitude of the coda wave versus time as a function of frequency and a nonlinear inversion scheme is developed that allows for the estimation of and as a function of frequency by fitting the model to a narrow band pass filtered envelope of the seismic coda for each seismogram at discrete frequency points namely 1 5 10 and 20 hz the inversion is performed on seismograms from earthquakes recorded by the massachusetts institute of technology new england seismic network over a 15 year period between 1981 and 1995 preliminary results indicate that scattering is the dominant mechanism of energy dissipation and that the effects of intrinsic attenuation are secondary the scattering is strongest at 1 hz and decreases with increasing frequency the scattering is also strongest at shorter propagation distances and decreases substantially as the propagation distance increases for example at a frequency of 1 hz the value of is approximately 0 22 at an epicentral distance of 10 km and decreases rapidly to a value of approximately 0 05 at an epicentral distance of 50 km conversely intrinsic attenuation is negligible at shorter propagation distances and increases as the propagation distance increases and it does not show a strong frequency dependence one interpretation of these results is the presence of a strong scattering region at shallow depth with the scattering decreasing with increasing depth and with a subsequent increasing of intrinsic attenuation at greater depth possible mechanisms for the scattering include the presence of a weathering layer near the surface the presence of fractures in the shallow crust and topography

lower palaeozoic stratigraphy and palaeontology karadere zirze area pontus mountains northern turkey lower palaeozoic rocks in the karadere zirze area east of safranbolu pontides northern turkey range from early ordovician to silurian overlying the probably tremadoc bakacak formation are aydos formation quartzites followed conformably by the karadere formation dated as early arenig to early llanvirn by means of graptolites which are assigned to seventeen genera and include three new forms eoglyptograptus bouceki prolasiograptus haplus praecursor and undulograptus mui late arenig trilobites from the karadere formation include bergamia cyclopyge dionidella leioshumardia and seleneceme in the limestone member of the overlying ketencikdere formation uncommon trilobites suggest only a mid to late ordovician age but con odonts with colour alteration index 5 6 indicate the amorphognathus tvaerensis biozone early caradoc macrofossils are rare in the siltstone member but conodonts from the middle of the unit suggest the highest subzone of the a tvaerensis biozone the youngest visible strata are on acritarch evidence at least as high as caradoc but the ashgill is not confirmed and the contact with overlying silurian rocks is unexposed the findikli formation comprises a lower member black argillites with llandovery graptolites and acritarchs and an upper member grey shales with late wenlock graptolites overlain unconformably by devonian rocks the succession differs significantly from contemporaneous deposits in southern turkey and its affinities lie with western europe including the welsh basin

palaeoenvironment and carbon isotope stratigraphy of upper proterozoic carbonates of the yangtze platform the 13c values for phanerozoic marine carbonates display secular trends mainly in the range 1 to 2 1 these have been interpreted as primary features reflecting changes in the carbon isotope composition of dissolved bicarbonate in seawater brought about largely by variations in the proportions of carbon being sequestered in the oxidized and reduced carbon reservoirs1 2 carbon isotope trends are not as well established for the precambrian but there are indications that upper proterozoic sequences contain carbonates with unusually high 13c values3 9 here we present the results of the first carbon isotopic study of the upper proterozoic carbonate strata from the type locality of the sinian system in the yangtze gorges sections near yichang south china and discuss their implications for accumulation of organic matter we also compare the results for these chinese strata with 13c trends in other upper proterozoic cambrian sequences and assess the extent to which such isotopic data can be used to make stratigraphic correlations between widely spaced sequences

fault block rotations at the edge of a zone of continental extension southwest turkey the ne sw trending burdur acigol and baklan basins of southwest turkey are bounded by normal faults which became active in quaternary times prior to this a more widely spaced system of pliocene basins had existed each of the quaternary basins has a half graben geometry with a major nw dipping fault on its southeast side previous studies of the 1971 burdur earthquake caused by movement on the fault bounding the burdur basin have shown this fault to flatten slightly at depth deformation in the hangingwall of the fault controlling the pliocene basin in the burdur region suggests a planar fault geometry it is suggested that the pliocene fault rotated to its present shallow orientation then became inactive and acted as a detachment at depth for the more recent quaternary fault quaternary faults bounding the burdur acigol and baklan basins have a sinistral strike slip component with slip vectors indicating extension in an nw se direction this is at variance with regional n s extension in western turkey a solution for this contrast is found by invoking block rotations about vertical axes in a deforming zone between the rapidly extending aegean region to the west and the stable unstretched anatolian plateau to the east

lithospheric structure of the arabian and eurasian collision zone in eastern turkey from s wave receiver functions summary crustal and upper mantle seismic discontinuities beneath eastern turkey are imaged using teleseismic s to p converted phases three crustal phases are observed the moho with depth ranging between 30 and 55 km indicating variable tectonic regimes within this continental collision zone an upper crustal discontinuity at approximately 10 km depth and various crustal low velocity zones possibly associated with recent quaternary volcanism imaging of the upper mantle is complicated by the 3 d geometry of the region in particular due to the bitlis zagros suture zone however several upper mantle s to p converted phase are identified as being the signature of the lithosphere asthenosphere boundary lab the inferred lab for the eastern anatolian accretionary complex indicates that eastern turkey has an anomalously thin between 60 and 80 km lithosphere which is consistent with an oceanic slab detachment model the observed lab phases for the arabian shield and iranian plateau indicate that lithospheric thickness for these stable regions is on the order of 100 to 125 km thick which is typical of continental margins

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

regional heat flow in western anatolia using silica temperature estimates from thermal springs regional trends of variation of heat flow in western anatolia have been outlined using the silica temperature estimator on thermal springs silica heat flow values from 187 springs have been calculated the data are corrected for local long term mean annual surface temperature a mean value of heat flow for the western part of anatolia of 107 45 mw m 2 has been obtained which is about 60 above the world average the silica heat flow data are compared with available conventional heat flow values for this region a general agreement is observed and new patterns are recognized a close association exists between areas of high silica heat flow values above 100 mw m 2 and areas of tertiary and younger volcanism high heat flow is also observed in palaeozoic units of the menderes massif which is under tensional stress the highest heat flow estimate of 247 mw m 2 is obtained near gediz 38 57 n 29 13 2 e this area is part of a seismically active region and is located near a middle eocene subduction zone which is an area of later collision tectonics the new heat flow data from western anatolia improve our knowledge of the thermal conditions within the crust this information is important for the analysis of various geophysical and geological phenomena including seismicity

crustal attenuation within the turkish plateau and surrounding regions the lateral variations of seismic attenuation in the crust of turkey and surrounding regions have been imaged from the inversion of interstation lg q measurements this study develops the first tomographic model for lg q 0 in this region that model is consistent with previous more qualitative lg attenuation models that showed inefficient or blocked lg across the eurasian arabian plate boundary in general the northern arabian platform has low to normal lg q 0 values 250 350 whereas high q 0 values 670 800 occur in the southern arabian plate additionally we have found a dramatic decrease in lg q 0 across the bitlis suture the plate boundary between the arabian and eurasian plates beneath the turkish plateau our high to moderate lg attenuation values q 0 100 200 probably originates from both scattering and intrinsic attenuation due to the tectonic complexity and the widespread young volcanics in the region we conclude that the lowest q 0 values for the east anatolian plateau 70 100 and the portion of western turkey around the menderes massif 60 150 are probably caused by intrinsic attenuation we find low to normal lg q 0 values 150 300 beneath the part of the taurus mountains in western anatolia these higher values may be related to the nature of the crust in the tauride mountain belt we also mapped the lateral variations in lg and observed a fairly consistent negative correlation between and lg q 0 in the northern middle east

frequency dependent attenuation of coda waves in the crust in southwest anatolia turkey the attenuation of coda waves in the earth s crust in southwest sw anatolia is estimated by using the coda wave method which is based on the decrease of coda wave amplitude in time and distance a total of 159 earthquakes were recorded between 1997 and 2010 by 11 stations belonging to the koeri array the coda quality factor q c is determined from the properties of scattered coda waves in a heterogeneous medium firstly the quality factor q 0 the value of q c at 1 hz and its frequency dependency are determined from this method depending on the attenuation properties of scattered coda waves for frequencies of 1 5 3 0 6 0 8 0 12 and 20 hz secondly the attenuation coefficients are estimated the shape of the curve is controlled by the scattering and attenuation in the crustal volume sampled by the coda waves the average q c values vary from 110 15 to 1 436 202 for the frequencies above the q 0 and values vary from 63 7 to 95 10 and from 0 87 0 03 to 1 04 0 09 respectively for sw anatolia in this region the average coda q f relation is described by q c 78 9 f 0 98 0 07 and 0 012 km 1 the low q 0 and high are consistent with a region characterized by high tectonic activity the q c values were correlated with the tectonic pattern in sw anatolia

upper mantle discontinuity structure beneath east anatolian plateau turkey from receiver functions abstract imaging of seismic velocity discontinuities with receiver functions suggests a complex mantle structure beneath the east anatolian plateau by stacking all the receiver functions as a function of ray parameter we examined the moveout characteristics of the data set and tested different velocity models to fit the arrival times of converted phases from the moho and the lithosphere asthenosphere boundary and their multiples the best fitting model shows anomalously thin crust 40 km and lithosphere 65 km and low uppermost mantle velocities causing systematic delays on later discontinuity arrivals these findings are consistent with the high plateau supported by partially molten and buoyant asthenosphere the upper mantle discontinuities are all visible in different frequencies 0 15 and 0 4 hz especially the 410 km discontinuity does not show frequency dependence in amplitude and suggests a sharpness of 10 km or less spatial variations of the 410 and 660 km discontinuities reveal anticorrelated topography and distinct zones of diminished amplitude associated with a detached slab and delaminated fragments of lithospheric mantle in the south the slab becomes deeper and horizontally deflected towards the east suggesting westward migration of slab detachment and resistance to slab penetration at the 660 km discontinuity in the north the mantle transition zone is characterized by two spatially limited lithospheric fragments with complex geometry at the center of the study area the transition zone is thin 230 km suggesting excess temperature of 120 c this warm mantle anomaly most likely is due to hot material trapped within the upper mantle between slab in the south and delaminated fragments in the north

permian triassic extinction pattern revealed by foraminifers and geochemical records in the central persian gulf southern iran abstract permian triassic boundary ptb foraminifers are studied from the upper part of the dalan formation and the base of the kangan formation in four wells a b e f on and near the qatar arc persian gulf iran isotope studies including 13c and 18o values from wells b and e and 87sr 86sr ratios in wells b e and f have also been carried out to possibly provide a high resolution extinction pattern of foraminifers in the ptb interval the latter has been thoroughly investigated in iran turkey south china vietnam slovenia carnic alps and bukk mountains kashmir greenland and serbia the distribution of the last appearance of foraminiferal genera from the ptb interval in all of the wells is very similar featuring a stepwise extinction from 3 to 2 m before the boundary and compares to that observed in some of the sections from elsewhere i e south china vietnam slovenia and serbia the 13c value in wells b and e shows a negative shift at the base of a thrombolite unit immediately after the considered ptb and another negative shift at about 11 m below it in well e the thrombolite unit is assumed as earliest triassic but questionable with no supportive conodonts the 18o isotope values in wells b and e demonstrate the same negative upward trend due to dysoxic or anoxic conditions in the end permian oceans the uniform reduction without any sharp incline in the 18o profile suggests concurrent global warming the highest 87sr 86sr ratio fluctuations in wells b e and f coincide with the appearance of thrombolites changes in the profiles of carbon oxygen and strontium isotopes close to the ptb in wells b e and f seem to correspond to lithofacies variations from limestone to dolostone and a reduction in foraminiferal diversity these changes substantiate a clear perturbation in the marine environmental and global geochemistry elements through the ptb interval the 13c 18o and 87sr 86sr values obtained from the studied wells are comparable to those in other ptb stratigraphic sections in the paleo tethyan region

carbon isotope excursions and microfacies changes in marine permian triassic boundary sections in hungary abstract several permian triassic boundary sections occur in various structural units within hungary these sections represent different facies zones of the western palaeotethys margin the gardony core in the ne part of the transdanubian range typically represents the inner ramp while the balvany section in the bukk mountains of northern hungary represents an outer ramp setting the two sections have different patterns for their 13 c values the balvany section shows a continuous change towards more negative 13 c values starting at the first biotic decline followed by a sharp quasi symmetric negative peak at the second decline the appearance of the 13 c peak has no relationship to the lithology and occurs within a shale with low overall carbonate content indicating that the peak is not related to diagenesis or other secondary influences instead the shift and the peak reflect primary processes related to changes in environmental conditions the continuous shift in 13 c values is most probably related to a decrease in bioproductivity whereas the sharp peak can be attributed to an addition of c strongly depleted in 13 c to the ocean atmosphere system the most plausible model is a massive release of methane hydrate the quasi symmetric pattern suggests a rapid warming cooling cycle or physical unroofing of sediments through slope failure and releasing methane hydrate the gardony 1 core shows a continuous negative 13 c shift starting below the p t boundary however the detailed analyses revealed a sharp 13 c peak in the boundary interval just below the major biotic decline although its magnitude doesn t reach that observed in the balvany section based on careful textural examination and high resolution stable isotope microanalyses we suggest that the suppression of the 13 c peak that is common in the oolitic boundary sections is due to combined effects of condensed sedimentation sediment reworking and erosion as well as perhaps diagenesis

survival strategies of brachiopod faunas from the end permian mass extinction abstract global reviews reveal that 102 brachiopod species including 40 indeterminate species belonging to 43 genera within 27 families survived the end permian mass extinction in south china the himalayan regions southern tibet nepal salt range and kashmir southern alps italy arctic canada western usa and western australia of these the surviving brachiopods are most abundant and widespread in south china where they occur in 32 of the 42 permian triassic p t boundary sections around the world brachiopod faunas are the most abundant and diverse post extinction survivors and their appearance above the end permian mass extinction horizon somewhat masks recognition of the end permian extinction these surviving brachiopods occur in three stratal intervals corresponding to the mixed fauna beds mfb hereafter 1 3 of the p t boundary beds a sharp drop in diversity of the brachiopod faunas coincides with the widely accepted end permian mass extinction horizon the post extinction brachiopods were also affected by a subsequent crisis corresponding to the boundary between mfb 2 and mfb 3 so that most survivors were extinct approximately 0 7 ma after the end permian mass extinction the surviving brachiopods were mainly productida followed by spiriferida in particular small chonetids chonetid like productellids and smooth thin shelled ambocollid spiriferids are most abundant lingula is extraordinarily abundant and widespread approximately 0 7 ma after the greatest extinction when many regions became devoid of articulate brachiopods widespread broadly adapted and small sized taxa preferentially survived frequent intrageneric speciation of widespread widely adapted generalist genera enabled survival brachiopods to occupy rapidly and efficiently vacant ecospace in the aftermath of the end permian extinction the ecological habitats of the post extinction brachiopods are subdivided into nearshore epeiric sea restricted carbonate platform open carbonate platform ramp and outer shelf environments of these the survival brachiopods are most diverse in the open platform environments the nearshore zone provided ideal habitats for the nonarticulated brachiopods to occupy whereas the survivors in the outer shelf are predominantly chonetids and chonetid like productellids the most successful survivors the productid brachiopods are widely distributed in six types of ecological habitats and thus have no apparent preference for specific environments the end permian extinction resulted in the movement of biogeographical provinces towards the palaeo equator the brachiopods survived mostly in the palaeo equatorial provinces and along the southern margins of the palaeo tethys ocean

lateral variations of high frequency seismic wave propagation at regional distances across the turkish and iranian plateaus in this study we investigate crustal and uppermost mantle physical properties that characterize some of the continental plateaus of the middle east this is done as part of a larger effort to map and compare high frequency wave propagation at regional distances across the earth s continental plateaus thousands of short period wwssn seismograms recorded at stations located in the middle east and produced by earthquakes with epicentral distances less than about 20 were examined visually in an effort to study lateral variations of high frequency 0 5 2 hz seismic wave propagation across this area particularly to the north of the zone of continental collision between the africa arabian and eurasian plates variations of frequencies and amplitudes of sn and lg relative to p are examined and mapped throughout the region and this work is supplemented by a study of velocities of pn sn and lg sn amplitude variations are very striking in this area an important observation of this study is that sn propagates efficiently beneath a major part of the turkish and iranian plateaus sn is strongly attenuated however in the northernmost portion of the plateaus south of the black and caspian seas and in an area between the two seas these regions are characterized in general by active tectonism including volcanism faulting and folding however this active tectonism is not restricted to the areas of high sn attenuation but appears to extend beneath other parts of the iranian and turkish plateaus patterns of lateral variations in the propagation of lg are not as consistent as those for sn lg propagates efficiently across turkey iran and adjacent regions but the lg waves that cross the turkish and iranian plateaus are weak and have relatively long predominant periods of about 2 5 s the lg phase is not observed when the path of propagation crosses the southern caspian and the black seas consistent with the evidence of oceanic type crustal structure beneath these seas lg is also not observed from subcrustal events located in the hindu kush region the velocity of pn beneath most of the plateau areas and particularly in the regions of sn attenuation ranges between 8 0 and 8 2 km s velocities for sn and lg throughout the middle east are about 4 5 and 3 4 km s respectively it is possible to interpret the efficient sn propagation and the relatively normal uppermost mantle p and s velocities beneath a major part of the turkish iranian plateau as indicating a partial underthrusting of the arabian continental plate beneath the iranian and turkish continental blocks alternatively the mapped regions of efficient sn propagation and high sn attenuation may result from a differential cooling of a past thermal anomaly in this case the isostatic compensation of the plateaus could be due to an anomalously hot uppermost mantle that developed behind the mid to upper tertiary subduction zone s in this region and to a subsequent crustal shortening after the collision of the arabian and eurasian plates our results cannot uniquely confirm the validity of the above proposed models

active tectonics of the aegean region the aegean sea and its surrounding regions comprise one of the most rapidly deforming parts of the alpine himalayan mountain belt though the deformation of the belt as a whole is related to thc northward move ment of africa arabia and india relative to eurasia the tectonics of the aegean region itself is dominated by strike slip and extensional motions the actively deforming part of the aegean region is not large about 700 x 700 km2 compared with that in asia yet it has had an influence on our views of continental tectonics disproportionate to its size and comparable perhaps only to tibet fundamental contributions from the aegean have been made to many topics including