carbon isotopes as indicators of dispersal patterns in devonian mississippian shales of the appalachian basin measurement of the carbon isotopic composition of organic matter in about 200 samples from the devonian shale sequence of the eastern united states shows a definite transition from nonmarine values of around 25 through intermediate values in prodelta samples to distal basinal samples with values around 30 5 this trend matches very closely that found for paleocurrents in the sequence from sole markings on turbidite siltstone beds thus the carbon isotopes suggest that the organic matter and hence the enclosing shale had the same dispersal pattern as the silt stones furthermore the steady westward change to more marine values indicates that the cincinnati arch was never sufficiently positive to act as a source of organic matter the nonmarine carbon has an isotopic composition very similar to that of coal and so probably represents woody material the basinal values however are much lighter than modern marine plankton this may be a diagenetic effect or it may reflect a difference in the devonian plankton

seismotectonics of the sinai subplate the eastern mediterranean region summary we define the sinai subplate from a seismotectonic perspective as a distinct component in the plate tectonics of the eastern mediterranean region this is based on the tectonic characteristics of a comprehensive listing of all ml 4 recorded seismicity in the region during the 20th century on newly calculated and recalculated fault plane mechanisms of first p wave arrivals and on published solutions based on waveform inversion of broad band data the low seismicity level and scarcity of strong events in the region required a thorough search for useful data and a careful examination of the reliability of the focal solutions we gathered all available records of first p wave onsets from the iss and isc bulletins and the local seismic networks altogether we were able to calculate 48 new focal mechanisms and 33 recalculated ones of events that occurred during the years 1940 1992 with the increasing number of teleseismic and regional broad band stations in the later years we added 37 solutions based on teleseismic and regional waveform inversions of events that occurred during 1977 2001 these mechanisms enabled us to examine the seismotectonic character of the sinai subplate the strike and rake directions of the calculated mechanisms usually reflect the geometry and the large scale type of deformation observed along the boundaries of the sinai subplate the dead sea transform the cypriot arc convergent zone and the suez rift nevertheless along each of these boundaries we found anomalous solutions that attest to the complexity of the deformation processes along plate margins earthquakes along the dead sea transform exhibit mainly sinistral transtension and transpression reflecting its leaky manner and local change in the transform geometry the presence of other unexpected mechanisms near the transform however reflects the heterogeneous deformation it induces around as expected thrust mechanisms along the cypriot arc mirror its convergent nature and typical curved geometry transtension and transpressional solutions in the eastern segment of the arc reflect the sinistral shear motion between anatolia and sinai there however shear mechanisms found between cyprus and the eratosthenes seamount pose a problem regarding its collision process most intriguing of all are ml 4 thrust and shear solutions found in the gulf of suez they are associated with predominantly normal mechanisms within a rift zone and therefore constitute a unique phenomenon yet to be deciphered

fluid history during deep burial and exhumation of oil bearing volcanics hercynian belt of southern brittany france in southern brittany france the porphyroid nappe a variscan tectonic unit made of volcanic pyroclastic deposits that was involved in a low temperature high pressure prograde metamorphic path followed by exhumation and extension displays evidence for very large and distributed strains achieved through dissolution crystallization processes such distributed strains at low temperature are rather unusual in felsic lithologies recent studies have documented that these rocks deformed within a system closed to fluids this paper presents results of detailed analyses of fluid inclusions and stable isotopes within the deformed metavolcanics and their undeformed counterparts in order to document the fluid history of the tectonic unit results show that its initial thermal evolution likely occurring in a context of basin inversion involved important open system alteration with k metasomatism adularization oil impregnation and hydration during the subsequent tectonic evolution the fluids maintained a constant composition in the c h o n system within the porphyroid nappe and its para autochthon being water rich and containing hydrocarbon components likely related to oil pyrolysis oxidation atoll like fluid inclusion morphology and rare undisturbed fluid inclusions with steep isochore slopes are consistent 750 mpa with pressures estimated for the peak of metamorphism using mineral solid solution thermodynamics fluid inclusions indicate a sub isothermal retrograde path between 420 and 300 c followed by a high thermal gradient at the end of the retrograde path within the underlying para autochthonous unit only the late high temperature gradient is recorded by fluid inclusions the sub isothermal low grade path suggests fast exhumation of the unit without thermal relaxation the high geotherm observed at the end of the p t path is consistent with the post thickening extensional collapse and associated intrusion of granites documented in the area hydration and heterogeneous oil water distribution achieved in the early metasomatic evolution of the porous pyroclastic deposits are responsible for subsequent fluid confining in the porphyroid nappe and for its strongly distributed strain pattern

the structure of the dead sea basin abstract the dead sea basin is located along the left lateral transform boundary between the arabian and sinai plates its structure and history are known from surface geology drilling seismic reflection and other geophysical data the basin comprises a large pull apart almost 150 km long and mostly 8 10 km wide which is flanked by a few kilometres wide zones of normal faulting the basin formed at about 15 ma or earlier close to the beginning of the transform motion and it reached about half its present length before the end of the miocene a strong negative gravity anomaly records a thick sediment basin fill 5 km under half its length reaching a maximum of 10 km the fill includes a few km of salt ca 6 4 ma which forms several diapirs at any one time large parts of the basin subsided simultaneously but the site of fastest subsidence seems to have shifted northward sedimentation rates reached at least hundreds of metres per million years or more in the miocene and 1 km myr in later periods the basin structure is dominated by longitudinal faults intrabasinal faults which delimit the pull apart and which are the extensions of the major strike slip faults north and south of the basin and normal faults which extend along the basin margins the latter faults express a small component of extension across the basin whereas the pull apart resulted from the much larger lateral motion along the basin in addition transverse faults divide the pull apart into several segments with somewhat different histories the pull apart grew by becoming longer parallel to the transform motion at shallow levels this was probably achieved by normal slip on transverse listric faults while the fill between them was little deformed the crust under the basin was stretched and thinned during basin lengthening which caused its subsidence basin formation was accompanied by uplifting of its flanks by 1 km sparse igneous activity occurred along the basin and its flanks its presence suggests a thermal anomaly in the lower lithosphere beneath the basin and adjacent parts of the transform

the anatomy of a pull apart basin seismic reflection observations of the dead sea basin the dead sea basin dsb located along the african arabian plate boundary constitutes a good example of a pull apart basin because of its large dimensions its structural simplicity and its active subsidence a coherent three dimensional picture of the dsb has been constructed on the basis of analysis of seismic stratigraphy together with the interpretation of previously published geological and geophysical data despite the large known vertical offsets across the basin deformation takes place mainly along the transverse and longitudinal faults and the intervening sediments are relatively undeformed and are hardly tilted comparison between e w seismic lines indicate that the basin has widened by the collapse and tilting of arcuate blocks from the western margin but that its original shape is a full graben the southern and central parts of the basin are divided into equidistant segments 20 30 km long by transverse faults activity along these faults commenced only during the pleistocene long after the dead sea strike slip fault system was formed and migrated northward with time a likely scenario for the development of the dsb is one in which the basin grows northward with time by a simultaneous propagation of the southern strand of the dead sea fault and a retardation of the northern strand

shallow architecture of the wadi araba fault dead sea transform from high resolution seismic investigations in a high resolution small scale seismic experiment we investigated the shallow structure of the wadi araba fault waf the principal fault strand of the dead sea transform system between the gulf of aqaba eilat and the dead sea the experiment consisted of 8 sub parallel 1 km long seismic lines crossing the waf the recording station spacing was 5 m and the source point distance was 20 m the first break tomography yields insight into the fault structure down to a depth of about 200 m the velocity structure varies from one section to the other which were 1 to 2 km apart but destinct velocity variations along the fault are visible between several profiles the reflection seismic images show positive flower structures and indications for different sedimentary layers at the two sides of the main fault often the superficial sedimentary layers are bent upward close to the waf our results indicate that this section of the fault at shallow depths is characterized by a transpressional regime we detected a 100 to 300 m wide heterogeneous zone of deformed and displaced material which however is not characterized by low seismic velocities at a larger scale at greater depth the geophysical images indicate a blocked cross fault structure the structure revealed fault cores not wider than 10 m are consistent with scaling from wear mechanics and with the low loading to healing ratio anticipated for the fault

the origin of the bir zreir rhomb shaped graben eastern sinai the bir zreir graben a rhomb shaped depression located in eastern sinai is well exposed in three dimensions a nearly horizontal nonconformity between precambrian crystalline basement and overlying phanerozoic sediments contacts of basement plutons and a system of early miocene basaltic dikes permit very precise mapping of the local structures and the determination of vertical and horizontal displacements along faults applying the standard pull apart model to the bir zreir rhomb shaped graben predicts greater vertical separations 3 to 6 times larger than those observed an alternative model based on a rotational movement of the bir zreir block agrees more closely with field evidence it is concluded that the shape and size of the graben was determined by the original fault pattern and that its final shape was changed relatively little by later movements the rotation of the bir zreir block resulted from a combination of sinistral displacement along n s faults a change of their trend to nne and a regional e w extension the model proposed here does not require the presence of large deep gaps along the diagonal faults as in pull aparts

frasnian famennian mass extinction and cold water oceans suturing of laurussia and africa elimination of easterly tropical currents and consequent equatorial diversion of cold and possibly dysaerobic waters are suggested as prime causes of the frasnian famennian late devonian extinction these are explained by using a new paleogeographic model evidence for stepdown extinctions that took place from givetian through frasnian time is taken particularly from atrypoid brachiopods one of the most abundant representatives of the global tropical shelly marine benthos during the middle and late devonian only 5 of 17 frasnian genera or subgenera of atrypoids are known to be present in late frasnian sediments and possibly only a single genus spinatrypa was present at the frasnian famennian boundary evidence for stepdown extinction from other invertebrate and vertebrate groups in general corroborates that provided by brachiopods

shear velocity structure and azimuthal anisotropy beneath eastern north america from rayleigh wave inversion 1 we have obtained shear velocity structure beneath the northeastern united states and southeastern canada using rayleigh wave phases and amplitudes thin crust 36 42 km is observed along the atlantic coast and in the eastern appalachian orogen and thick crust 42 46 km is imaged in the western appalachians and in the western new york portion of the grenville province the variation of crustal thickness correlates well with the observed bouguer gravity anomalies in the upper mantle the high velocity continental keel of cratonic north america is present in the western part of the study area while a broad low velocity region is imaged in new england from the hudson river valley to the white mountains this low velocity anomaly is probably the consequence of past heating of the lithospheric mantle associated with the monteregian hotspot and may represent intrusion of asthenosphere into the edge of the keel in addition to lateral variations in velocity we estimate the azimuthal dependence of phase velocity strong and relatively uniform shear wave splitting is observed in the study region but at periods of 100 s or less the average azimuthal anisotropy of rayleigh waves is less than 1 and is not significantly different from zero at any individual period this small degree of azimuthal anisotropy is not consistent with a substantial contribution to shear wave splitting from fossil anisotropy in the lithosphere much of the source of the shear wave splitting must lie deeper than 200 km

preservation of elemental and isotopic source identification of sedimentary organic matter the amount and type of organic matter in the sediments of lakes and oceans contribute to their paleoenvironmental and paleoclimatological records only a small fraction of the initial aquatic organic matter survives destruction and alteration during sinking and sedimentation selective degradation modifies the character of the surviving small fraction of organic matter which becomes incorporated in bottom sediments organic matter alterations can continue to sub bottom depths of hundreds of meters corresponding to millions of years source and paleoenvironmental information nonetheless remains preserved in the molecular elemental and isotopic compositions of organic matter c n and 13c values of total organic matter in particular appear to retain paleoenvironmental information for multi myr time periods

geological structure of the eastern side of the lower jordan valley dead sea rift reflection seismic evidence abstract interpretation of recently released seismic reflection lines from the shuna eastern jericho basin combined with re analysis of the lithologic logs of the deep jv 1 and jv 2 boreholes provide new insights into the structure of the sedimentary basin that formed along the dead sea transform fault north of the dead sea in jordan we identified four major seismic boundaries in the reflection profiles the upper two were correlated with borehole stratigraphy these reflection boundaries include the top of the pan african basement r4 the base of the mesozoic r3 the base of the cretaceous r2 and the base of the post eocene section r1 the latter records sedimentation during the dead sea transform tectonic regime the total thickness attained by the older sedimentary units late cretaceous through cambrian is apparently less than 2 km we identified a subsurface structure a faulted monocline with a n s trend sub parallel to the strike of the dead sea transform that is named here al kharrar monocline the al kharrar structural ensemble is buried by syntectonic lacustrine and fluviatile sediments of the jordan valley group the structure formed as part of the dead sea transform deformation overprinting the late cretaceous syrian arc folds continued tectonic deformation is evident from the prominent unconformity at the base of post eocene syntectonic deposits that dip nw w and s away from the structural high along the nw flank of the al kharrar monocline syntectonic sediment thickness is generally less than 0 5 km while along the sw flank it thickens rapidly to nearly 1 km at the southern end of the interpreted seismic lines this rapid southern subsidence probably continues into the north end of the dead sea basin the lake s shoreline being located less than 3 km to the south young bifurcating faults with reverse slip components cutting the eastern part of the al kharrar monocline are attributed to a positive flower structure this pattern suggests strike slip with localized active compression northeast of the dead sea it may result from local transpression between fault strands that appear to be a northward continuation of the eastern boundary fault of the dead sea basin

seismic reflection across a continental transform an example from a convergent segment of the dead sea rift three seismic reflection lines in the dead sea rift in northern israel cross the transform plate boundary between arabia and the sinai block of the african plate the arabian plate edge consists of the meshoshim tilted block which we suggest to be partly a result of prerift activity in the sinai block the elevated rosh pinna saddle is faulted over the meshoshim block with a vertical separation of 2 5 3 km much of this separation is due to young reverse faulting which is related to the oblique plate boundary in this area the main fault zone transfers the motion from the western margin of the kinneret zemah graben to the eastern margin of the hula graben immediately north of lake kinneret the main fault is a 1 to 2 km wide zone of extensive deformation and a discrete main fault trace is hard to define further to the north the deformation is less extensive and is concentrated in a narrow fault zone deformation across the plate boundary is asymmetrical and while the meshoshim block is quite coherent the rosh pinna saddle is a highly faulted and deformed positive flower structure

no regional anisotropic domains in the northeastern u s appalachians a fabric frozen within the continental lithosphere should lead to regional anisotropic domains with close correlation between tectonics seismic anisotropy and shear wave travel time delays alternatively seismic anisotropy could be maintained by active deformation in the sub lithospheric mantle this scenario would predict broad spatial consistency in shear wave splitting and weak correlation between the splitting surface tectonics and travel time delays a coherent pattern of shear wave splitting is observed in the northeastern united states covering large parts of new york and new england spanning the appalachian orogen and areas underlain by the grenvillian basement the direction of fast shear wave propagation as measured from core refracted sks skks and pks phases varies systematically with event back azimuth at all sites examined and is fit well by two layers of anisotropy with subhorizontal symmetry axes relative travel time delays of shear waves that sample the region vary over 100 km length scale and correlate with surface geology tomographic images suggest lateral shear velocity variations 3 including a slow anomaly beneath the grenvillian basement exposed in the adirondack mountains there is little correlation between this horizontally rough seismic velocity and the horizontally smooth anisotropic model consistent with shear wave splitting we therefore conclude that in the northeastern us the concept of regional anisotropic domains i e distinct regions within the lithosphere characterized by coherent anisotropic properties reflective of present or past deformation does not apply

shear wave velocity structure in north america from large scale waveform inversions of surface waves a two step nonlinear and linear inversion is carried out to map the lateral heterogeneity beneath north america using surface wave data the lateral resolution for most areas of the model is of the order of several hundred kilometers the most obvious feature in the tomographic images is the rapid transition between low velocities in the tectonically active region west of the rocky mountains and high velocities in the stable central and eastern shield of north america the model also reveals smaller scale heterogeneous velocity structures a high velocity anomaly is imaged beneath the state of washington that could be explained as the subducting juan de fuca plate beneath the cascades a large low velocity structure extends along the coast from the mendocino to the rivera triple junction and to the continental interior across the southwestern united states and northwestern mexico its shape changes notably with depth this anomaly largely coincides with the part of the margin where no lithosphere is consumed since the subduction has been replaced by a transform fault evidence for a discontinuous subduction of the cocos plate along the middle american trench is found in central mexico a transition is visible from low velocities across the trans mexican volcanic belt tmvb to high velocities beneath the yucatan peninsula two elongated low velocity anomalies beneath the yellowstone plateau and the eastern snake river plain volcanic system and beneath central mexico and the tmvb seem to be associated with magmatism and partial melting another low velocity feature is seen at depths of approximately 200 km beneath florida and the atlantic coastal plain the inversion technique used is based on a linear surface wave scattering theory which gives tomographic images of the relative phase velocity perturbations in four period bands ranging from 40 to 150 s in order to find a smooth reference model a nonlinear inversion based on ray theory is first performed after correcting for the crustal thickness the phase velocity perturbations obtained from the subsequent linear waveform inversion for the different period bands are converted to a three layer model of s velocity perturbations layer 1 25 100 km layer 2 100 200 km layer 3 200 300 km we have applied this method on 275 high quality rayleigh waves recorded by a variety of instruments in north america iris usgs iris ida terrascope rstn sensitivity tests indicate that the lateral resolution is especially good in the densely sampled western continental united states mexico and the gulf of mexico

global patterns of azimuthal anisotropy and deformations in the continental mantle summary we present a summary of measurements of azimuthal anisotropy in the continental mantle based on the sks technique and performed mostly with the active participation of the authors the directions of polarization of the fast quasi shear wave and the time delays between the quasi shear waves are obtained at nearly 70 locations in all continents except antarctica these data are interpreted in terms of lattice preferred orientation of olivine which is caused by deformations in the mantle the depth interval responsible for anisotropy is unknown but the data suggest that it may reach at least 300 km the fast directions in sks do not show clear correlation with the fast directions of the teleseismic p at the same seismograph stations in the regions of present day convergence the fast direction of anisotropy usually aligns with the plate boundary this correlation implies that the direction of shortening is the same in the crust and the upper mantle in the regions of rifting the inferred direction of mantle flow usually aligns with the direction of extension in the crust outside the regions of recent tectonic activity we most likely observe a combined effect of frozen anisotropy in the subcrustal lithosphere and of recently formed anisotropy in the asthenosphere on a global scale in these regions there is a positive correlation between the absolute plate velocity directions and the fast directions of anisotropy the correlation is especially strong in central and eastern parts of north america a clear absence of any evidence of large scale azimuthal anisotropy in the data of long range refraction profiling for the upper 100 km of the mantle of that region implies that the effect in sks is generated mainly at greater depths in the asthenosphere orientation of olivine at these depths reflects recent and present day flow in the mantle rather than processes of a distant geologic past

gaussian probability estimates for large earthquake occurrence in the jordan valley dead sea rift abstract a catalog including only large earthquakes in the jordan valley segment of the dead sea rift was compiled using existing recent catalogs for this region large earthquakes in the jordan valley did not always break the entire plate boundary and in particular the last large earthquake 1927 broke only a southern segment of the valley thus the catalog was divided into northern and southern zones segments a conservative approach was used whenever the length of the epicentral area was not well constrained these data were used to estimate gaussian conditional probabilities for the occurrence of a large rupturing the plate boundary earthquake during a 50 year time window versus the time elapsed from the last large earthquake since the historical data particularly the location and extent of the epicentral areas are not always accurate the results can be used for gross estimates of the probabilities and generalized conclusions in general the analysis show that for the southern jordan valley conditional probability estimates are low mainly due to the short time which elapsed since the last large earthquake relative to the mean repeat time in the northern jordan valley acceptable probability estimates are high in addition the probability that a large earthquake would have occurred by 1986 is close to 100 such unusually high values most probably mean that some input parameters are erroneous either the mean repeat time is much larger and the region was the site of much less seismic activity than indicated in the catalog or more probably the last large earthquake is more recent than generally thought whatever the explanation the various computations clearly indicate a higher probability estimate in the northern than in the southern part of the jordan valley the results stress the need for improved studies of the historical seismic record particularly stressing accurate determination of date and rupture length of the last large earthquake

δ13c of organic carbon in the bengal fan source evolution and transport of c3 and c4 plant carbon to marine sediments carbon isotopic measurements on organic carbon oc in sediment cores from the bengal fan odp leg 116 show a dramatic 10 increase beginning ca 7 ma ago and a rapid decrease after 0 9 ma these shifts reflect changes in the mixing ratio of terrigenous carbon derived from c3 and c4 plants the rapid increase in 13c of bengal fan oc at 7 ma shows that late miocene expansion of c4 plants already documented in the siwaliks was widespread over all the himalayan foreland after 7 ma relations of 13c with sedimentological parameters show that c4 plants dominate in the foreland whereas c3 plants remain abundant in the mountain range variations in the source of the sediments and of the oc appear to be sensitive to climate hydrologic conditions in the basin major changes in the isotopic composition of the carbon flux in one of the worlds largest river systems modify the isotopic budgets of both marine dissolved carbon and the sedimentary carbon mass

anatomy of the dead sea transform does it reflect continuous changes in plate motion a new gravity map of the southern half of the dead sea transform offers the first regional view of the anatomy of this plate boundary interpreted together with auxiliary seismic and well data the map reveals a string of subsurface basins of widely varying size shape and depth along the plate boundary and relatively short 25 55 km and discontinuous fault segments we argue that this structure is a result of continuous small changes in relative plate motion however several segments must have ruptured simultaneously to produce the inferred maximum magnitude of historical earthquakes

evidence for shallow isostatic compensation of the southern rocky mountains from rayleigh wave tomography in the past decade seismologists have found that the topography in colorado correlates with seismic velocities in the upper mantle not with crustal thickness and postulated that isostatic compensation of the southern rocky mountains takes place largely in the mantle to test the validity of this hypothesis we use rayleigh wave phase and amplitude data recorded in the rocky mountain front passcal experiment to obtain crustal thickness and shear wave structure in the crust and upper mantle the thickest crust in the model is beneath one of the two most elevated regions the san juan volcanic field the other most elevated region in central colorado the sawatch range is underlain by crust of anomalously low velocity the seismically defined mantle lithosphere is thicker beneath the great plains than beneath the colorado plateau and is largely absent beneath the southern rocky mountains but the correlation of topography with mantle velocities is weaker than the correlation with crustal anomalies we construct a model that matches the observed bouguer gravity anomaly primarily with variations in crustal thickness and density by assuming that density anomalies are proportional to the observed velocity anomalies the anomalous mantle may also contribute to maintaining regional isostasy in colorado but its contribution may be much less important than the crust

the late aeronian graptolite sedgwickii event associated positive carbon isotope excursion and facies changes in the prague synform barrandian area bohemia study of the lower silurian black shale succession of the prague synform has enabled detailed insight into graptolite faunal dynamics and diversity trends from the mid aeronian diversity maximum through to the late aeronian crisis graptolite diversity decreased from 33 taxa in the lituigraptus convolutus biozone to 17 taxa in the upper part of the stimulograptus sedgwickii biozone and newly erected lituigraptus rastrum biozone the graptolite assemblages of the latter biozones exhibit low species richness along with high dominance many graptolite species that became extinct in the early part of the sedgwickii zone were promptly replaced by new forms in the later part of the sedgwickii zone however replacement of extinct species by new forms considerably decelerated the increased rate of graptolite extinction recorded in the convolutus sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in 13 c org of 2 2 compared to baseline values sea level drawdown can be inferred from siltstones and or temporary nondeposition in the middle sedgwickii zone this level also sees total organic carbon toc fluctuations and a strong positive 13 c org excursion with a peak shift of at least 7 the sedgwickii event exhibits substantial reorganization of the graptolite fauna its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre extinction assemblage associated changes in lithology toc and the pronounced 13 c org excursion suggest a relatively extended and probably multi phase period of stressed conditions that affected the pelagic realm inhabited by graptolites in the course of the late aeronian interval

tomographic inversion for the seismic velocity structure beneath northern new england using seismic refraction data the seismic velocity structure of the crust and the upper mantle beneath northern new england was investigated from the travel time data of the 1984 maine seismic refraction profile and the 1988 ontario new york new england seismic refraction profile seismic refraction experiments by using tomographic inversion techniques strong lateral seismic velocity variations were found in the upper 15 km of the crust and these variations are correlated with regional geologic and tectonic structures the grenville basement in the adirondack mountains of eastern new york is characterized by an unusually high p wave velocity of 6 7 km s in the upper 15 km of the crust this high velocity basement extends eastward below western vermont to a depth between 15 and 20 km from the surface more typical upper crustal p wave velocities of 5 6 to 6 4 km s were generally found in central and southern maine and in new hampshire and the anisotropic upper crustal zone west of penobscot bay in maine was imaged by locally slower velocities the correlation of the inversion velocity structure with the tectonic features of northern new england shows that the appalachian mountains in northern new england may extend tectonically to at least 20 km deep in the crust the velocity distribution at 20 km depth shows three northeast elongate juxtaposed belts which correspond to the connecticut valley gaspe synclinorium the bronson hill anticlinorium and the kearsarge central maine synclinorium respectively the connecticut valley gaspe and kearsarge central maine synclinoria have relatively high velocities from 6 94 to 7 12 km s while the bronson hill anticlinorium has relatively low velocities from 6 52 to 6 75 km s in the lower crust another low velocity area of 6 52 km s at 20 km depth is imaged beneath the white mountain batholith in central new hampshire and may be a lower crustal expression of this batholith upper mantle velocity structures were obtained for the grenville basement the appalachians in northern new england and the avalon terrane in southeastern maine from the long range seismic refraction data generally the older grenville lithosphere about 1100 ma in quebec has higher velocity in the upper mantle than does the younger avalon terrane no older than 650 ma in the southeastern part of northern new england the data suggest that the velocity of the upper mantle beneath the old north american craton increases stepwise with observable velocity discontinuities in depth while that beneath the avalon terrane does not increase through the first 40 km of the upper mantle the data analysis also shows that the upper mantle suture between the grenville basement and the avalon terrane occurs in a narrow belt beneath the appalachian mountains of central maine and new hampshire the did of the moho discontinuity beneath northern new england is modeled as nearly flat as 0 7 in the n57 w direction and as steep as 1 2 beneath the grenville basement

non plane geometries of seismic surface wavefields and their implications for regional surface wave tomography summary seismic surface waves exhibit much more complicated wavefields than is commonly assumed we are led to this conclusion after analysing 90 teleseismic events recorded at on average eight broad band stations in southern germany large amplitude and phase fluctuations across the network are observed which as we show are definitely not due to instrument response or calibration problems in order to give an impression of how surface wavefields may look in reality we fit wavefields to the observed network data using basis wavefields derived from hermite gaussian functions we show both amplitude and phase distributions of several events synthetic wavefields generated by acoustic finite difference computations in a random medium with realistic correlation length and rms velocity fluctuations support the interpretation that most of the observed wavefield anomalies have accumulated on the path of the wave from the source to the network even if no lateral heterogeneities existed in the region of the network the large scale features of the observed wavefields would remain nearly unaltered we also model the synthetic wavefields using hermite gaussian wavefields and achieve extremely good fits in view of the large anomalies of the wavefields we investigate their implications for the regional surface wave tomography in this method one infers regional structure from a set of measurements of phase traveltime between pairs of stations the basic assumption of the method is that the wavefield incident on the network be plane thus all observed phase traveltime anomalies are interpreted in terms of regional heterogeneous structure the consequence is a seemingly highly inconsistent data set we perform several tomographic experiments with realistic synthetic data sets our experiments indicate that regional surface wave tomography may work if there is an excellent coverage of paths crossing the region and if each path is sampled several times under realistic conditions that is on a sparse network with not much more than one velocity value per path the imaging power of surface wave tomography is very poor owing to the seeming inconsistency of the phase traveltimes variance reduction is generally low with an increasing number of traveltime data it further decreases while at the same time the imaging power increases the opposite behaviour is observed if the number of data is reduced variance reduction increases but imaging power decreases hence in connection with regional surface wave tomography high variance reduction indicates a lack of data rather than the goodness of reconstruction

tiran island an internal block at the junction of the red sea rift and dead sea transform abstract tiran island and the strait of tiran are part of a compressional segment at the southern end of the dead sea transform during the late oligocene and miocene the area was controlled by tensional tectonics at that time the tiran and shadwan islands were internal blocks within the red sea rift close to safaga the area came under a compressional regime during the last 14 to 5 m y after the dead sea transform became active when this segment began to collide with the sinai microplate around 2 5 or 1 7 m y ago tiran island began to be uplifted at an annual rate of 0 2 0 3 mm yr and was probably rotated

the association of micro earthquake clusters with mapped faults in the dead sea basin about 1100 micro earthquakes that occurred along the dead sea basin during the past 25 years express ongoing seismic activity along mostly obscured fault segments we apply seismological and statistical methods in order to associate seismic activity with geological and geophysical data and to locate and characterize active fault segments in the basin three regional 1 d velocity models and the double difference method were used for the relocation of seismic events geostatistical analysis shows that in first order the micro earthquakes reflect faulting along segments of the main longitudinal fault while seismic quiescence along historically active zones indicates locked segments and stress concentration based on waveform similarity spatial and temporal proximity we define earthquake clusters that comprise about 30 of the relocated seismicity and two thirds of the total seismic moment about 80 of the clusters are associated with n s trending faults in two cases the clusters indicate a migration of the seismicity in time and space one of which preceded the largest earthquake in our catalog m5 2 in addition to the associated longitudinal activity several clusters appear to represent faulting in east west orientation which is interpreted here as a secondary fault system

early palaeozoic palaeobiogeography of the variscan regions abstract the palaeobiogeographic method appears to be an attractive alternative for reconstruction of the palaeogeography of the variscan regions during the palaeozoic the evolution of faunal assemblages and climatic characteristics from the cambrian up to the end of the devonian demonstrates that baltica and north gondwana represent two major and independent palaeogeographic entities separated by a mid european rheic ocean which opened as early as the cambrian and closed progressively from the devonian the south armorican ocean whose closure generated the so called ligerian orogen is regarded as a branch of the rheic ocean both a tornquist s sea separating baltica from its western extension avalonia during the ordovician and a proto tethys ocean extending between southwestern europe and north africa during the devonian are excluded from our reconstructions

active tectonics along the wadi araba jordan valley transform fault a geological study has been carried out along the 200 km long wadi araba following the transform fault that separates the arabian and sinai african plates recent movements along this structure affect upper pleistocene holocene deposits and archaeological sites kinematic indicators show sinistral strike slip and oblique movements in agreement with the relative motion between the two plates other evidence of recent horizontal displacement exists along the jordan valley fault both on the dead sea lake tiberias segment and on the segment north of lake tiberias a minimum horizontal slip rate of 1 cm yr 1 has been estimated for both the southern segment of the wadi araba fault and for the southern jordan river fault the two faults can be roughly subdivided into at least four segments two in the wadi araba 80 km long each one from the dead sea to lake tiberias 130 km and one from lake tiberias to the hula graben 30 km faulting may also occur along shorter subsegments as shown by bends in the wadi araba jordan river fault and by the growth of local compression and extension features instrument recorded seismicity appears to be mainly concentrated along some of these subsegments a comparison between the observed seismic and field determined slip rates across the fault indicates possible strain accumulation during the last 2000 years

shear wave splitting in the appalachians and the urals a case for multilayered anisotropy observations of shear wave splitting in the northeastern u s appalachians and in the foredeep of the urals vary significantly with the back azimuth and incidence angle of the incoming phase these variations suggest two or more layers within the upper mantle with different anisotropic properties synthetic seismograms for simple multilayered anisotropic structures show that shear wave splitting parameters tend to vary substantially with the direction of approach relying on a subset of back azimuth and incidence angle may strongly bias the model inferred especially if the observations are averaged on the other hand the azimuthal splitting pattern provides additional constraints on vertical or lateral variation of anisotropic properties in the earth using a new error estimation technique for splitting we find that individual measurements from broadband data have errors of the order of 3 7 for the fast direction and 0 1 0 2 s for the delay of split shear waves the azimuthal variation of splitting parameters is broadly consistent throughout the appalachian terranes in the northeast united states especially for two long running stations in the northeast united states hrv harvard massachusetts and pal palisades new york observations can be separated into two distinct populations with mean fast axis azimuths of n60 e 4 and n119 e 2 delay values within each population range from near zero to 1 s azimuthal splitting variation for aru arti russia in the foredeep of uralian mountains is characterized by sharp transitions between different groups of observations using synthetic seismograms in simple structures we develop one dimensional anisotropic models under stations hrv and aru the model for hrv includes two layers of anisotropic material under an isotropic crust with fast axis azimuths n53 e and n115 e for the bottom and the top layers respectively the model for the upper mantle under aru includes a layer with a fast axis at n50 e atop a layer with fast axis azimuth n90 e our modeling confirms the need for a layer of strong anisotropy with a slow axis of symmetry in the lower crust under aru reported by levin and park 1997a our results suggest that both urals and appalachians possess a relict anisotropy in the tectosphere associated with past continental collision and accretion underlain by anisotropy with orientation similar to the local absolute plate motion suggesting an asthenospheric component to the signal

palynology organic geochemistry and carbon isotope analysis of a latest ordovician through silurian clastic succession from borehole tt1 ghadamis basin southern tunisia north africa palaeoenvironmental interpretation abstract palynological and palynofacies analyses combined with organic carbon isotope measurements have been performed on terminal ordovician through silurian clastic sediments from the north african margin of gondwana southern tunisia a first carbon isotopic signal 13corg from gondwanan silurian sedimentary sequences is presented showing interesting correlation with existing coeval isotopic curves from other areas changes in lithology palynofacies characteristics palynomorph diversity carbon isotope developments and organic geochemistry parameters appear to be all causally linked and to reflect changes in palaeoceanographic conditions in particular the detailed chronostratigraphic correlation and the observed similarities in patterns of carbon isotopic developments and palyno and litho facies changes through the study section has permitted to identify the supposedly global earliest wenlock ireviken event and late ludlow lau event isotopic excursions for the first time in high latitude gondwana this confirms that these excursions were linked to global changes in the oceanic system the present results suggest that from rhuddanian to early wenlock times an extended period of black shale deposition occurred over the north african gondwanan margin progressively transgressing from basin palaeodepressions to basin palaeohighs palynofacies and organic geochemistry support a coastal upwelling promoted productivity increase during this interval associated to a decrease in diversity of the marine microplanktonic communities the earliest wenlock strong positive isotopic shift appears associated with this protracted period of massive black shale deposition and thus of organic carbon burial on continental platforms located in high latitude settings this could well explain the apparent paradox between excessive carbonate deposition simultaneous to a carbon isotopic shift towards lighter values observed in low palaeolatitude localities laurentia and baltica the strong distinct isotope excursion occurring in late ludlow times is possibly linked to the well know lau event evidence for extensive organic carbon burial is lacking to explain this strong excursion some significant changes in the marine palynomorph communities are recorded in connection to the increase in stable isotope values 13corg additionally a strong correlation between abundance of terrestrially derived palynomorphs miospores and 13corg development is recorded which seems to support increased clastic input from a terrestrial source

teleseismic traveltimes residuals across the dead sea basin new findings of the structure of the dead sea sedimentary basin and its eastern and western bordering regions are obtained by p and pkp wave relative traveltime residuals of 644 teleseisms as recorded by the dead sea integrated research portable seismic network in the dead sea basin and its neighboring regions the lisan peninsula is characterized by relatively small teleseismic traveltime residuals of about 0 14 s in the latitude range of 31 22 31 37 and at the longitude of 35 50 slowly decreasing toward the west the largest teleseismic traveltime residuals are in the southern dead sea basin south of the lisan peninsula in the latitude range of 31 05 31 15 and along longitude 35 45 and continuing southward toward the amaziahu fault reaching values of 0 4 0 5 s there is a small positive residual at the amaziahu fault and a small negative residual south of it probably marking the southern end of the dead sea basin east and west of the dead sea basin the mean teleseismic traveltime residuals are negative with overall averages of 0 35 s and 0 45 s respectively using the teleseismic residuals we estimate the horizontal dimensions of the lisan salt diapir to be 23 km 13 km at its widest and a maximal thickness of about 7 2 km the thickness of the mount sodom salt diapir is estimated as 6 2 km

variability in the δ13c of lower palaeozoic palynomorphs implications for the interpretation of ancient marine sediments abstract we have analyzed the stable carbon isotope ratios of various organic walled microfossils preserved in marine sediments of silurian and devonian age the aim of this study is to determine the amplitude of isotopic fractionations among the different extinct palynomorph groups twenty six samples of marine palynomorphs have 13c values in the range 30 0 to 26 3 whereas two samples likely of terrestrial origin tracheids and woody tissue have the highest 13c values 24 8 and 23 3 among six sediments that only contain marine palynomorphs three show 13c variations of 0 8 1 0 and 2 5 respectively whereas the others do not show significant difference in the presence of fragments of woody tissue mixed with the marine plankton these internal isotopic variations may reach about 4 the bulk 13c values of organic matter in these ancient marine sediments are interpreted as average values which integrate in addition to chemical characteristics of surface waters e g co2 aq source and species dependent isotopic compositions the possible occurrence of such 13c heterogeneities at the scale of a sediment sample could result at least from three kinds of material fluxes 1 autotroph and heterotroph elements from the water column 2 oceanic current and river inputs and 3 selective molecular preservation related to specific biochemical structures

lithospheric assembly and modification of the se canadian shield abitibi grenville teleseismic experiment this paper presents the results of a joint lithoprobe incorporated research institutions for seismology iris program for array seismic studies of the continental lithosphere passcal teleseismic experiment that investigates portions of the grenville and superior provinces of the canadian shield along the quebec ontario border data from a 600 km long n s array of 28 broadband seismographs deployed between may and october 1996 have been supplemented with additional recordings from an earlier 1994 deployment and from stations of the canadian national seismograph network and the southern ontario seismic network relative delay times of p and s waves from 123 and 40 teleseismic events respectively have been inverted for velocity perturbations in the upper mantle and reveal a low velocity nw se striking corridor that crosses the southern portion of the line at latitude 46 n and lies between 50 and 300 km depth multievent s k s splitting results yield an average delay time of 0 57 0 22 s and a direction of fast polarization of n93 e 18 which is consistent with an earlier interpretation as being due to fossil strain fields related to the last major regional tectonic event subtle variations in splitting parameters over the low velocity corridor may suggest an associated disruption in mantle fabric profiling of radial receiver functions reveals large and abrupt variations in moho topography specifically a gradual thickening in crust from 40 to 45 km between latitudes 45 n and 46 n which is followed by an abrupt thinning to 35 km at 46 6 n some 65 km southeast of the grenville front this structure is interpreted as a subduction suture extending the full length of the front and punctuating a major pre grenvillian archean proterozoic episode of lithospheric assembly in the southeast canadian shield the low velocity mantle corridor by contrast is better explained as the extension of the monteregian white mountain new england seamount hotspot track below the craton and is here postulated to represent interaction of the great meteor plume with zones of weakness within the craton developed during earlier rifting episodes

tectonic implications of recent microearthquake data from israel and adjacent areas a recently installed seismograph network in israel enables for the first time a systematic examination of the microearthquake activity and its relation to the regional tectonics the observed microearthquake activity is widespread and not limited to the dead sea rift plate boundary in the rift itself the more seismically active parts are north of the sea of galilee and in the dead sea basin a possible seismic quiescence appears in the jordan valley to the north of the dead sea basin and may be associated with that segment of the plate boundary which broke recently 1927 thus indicating a low strain level inside israel the active nature of the carmel farah fault systems was determined its present level of seismicity appears to be comparable to that of the rift itself indicating the significance of this fault system in the active tectonics of the area the high microseismic activity on these faults and their location in densely populated areas mark them as possibly important sources of seismic hazards diffused seismicity is observed throughout much of israel although the nature of these earthquakes is not yet understood the small magnitude earthquakes near the rift are most probably part of a seismic halo around the plate boundary pronounced seismicity is also observed in the mediterranean sea off the coast of southern lebanon and northern israel this microearthquake activity decreases from north to south and to some extent from east to west whereas near the coast of northern israel and southern lebanon the microearthquake activity is relatively high in the south near the coast of the sinai peninsula it is very low this difference is attributed to a possible combination of a higher strain level in the african plate as it approaches the africa eurasia plate boundary and hinge faulting near the coast

the northern end of the dead sea basin geometry from reflection seismic evidence abstract recently released reflection seismic lines from the eastern side of the jordan river north of the dead sea were interpreted by using borehole data and incorporated with the previously published seismic lines of the eastern side of the jordan river for the first time the lines from the eastern side of the jordan river were combined with the published reflection seismic lines from the western side of the jordan river in the complete cross sections the inner deep basin is strongly asymmetric toward the jericho fault supporting the interpretation of this segment of the fault as the long lived and presently active part of the dead sea transform there is no indication for a shift of the depocenter toward a hypothetical eastern major fault with time as recently suggested rather the north eastern margin of the deep basin takes the form of a large flexure modestly faulted in the n s section along its depocenter the floor of the basin at its northern end appears to deepen continuously by roughly 0 5 km over 10 km distance without evidence of a transverse fault the asymmetric and gently dipping shape of the basin can be explained by models in which the basin is located outside the area of overlap between en echelon strike slip faults

active compressional tectonics in the jericho area dead sea rift abstract the results of several seismic reflection surveys in the jericho area north of the dead sea are described and the data are used to analyze the structure of this part of the dead sea rift in particular we describe the structure of the dead sea transform which in this area is a zone of intense deformation rather than a distinct fault plane the transform has a westerly dip away from the rift suggesting that it may have a reverse faulting component associated with the transform are several folds of which the best documented is the kalia monocline immediately north of the dead sea the kalia monocline lies along the transform and appears to be a young structure associated with it indicating that this part of the plate boundary is characterized by local compression the southerly extent of the kalia monocline is not clear presently but the available data suggest that the compressional field also characterize the northwestern part of the dead sea basin the other folds appear north of the kalia monocline and seem to be similar to it they are most probably also the result of recent compression along the transform a number of mechanisms of small earthquakes in this area are computed and several of them show thrusting suggesting that the local compression is still active

seismic anisotropy in the eastern united states deep structure of a complex continental plate we have analyzed shear wave splitting recorded by portable and permanent broadband and long period stations located in the eastern united states teleseismic shear waves sks skks and pks were used to retrieve the splitting parameters the orientation of the fast wave polarization plane and the delay time t in total 120 seismic events were processed allowing for more than 600 splitting measurements within the appalachians stations located in the western external part are characterized by t 1s and trending n50 70 e in the south and central regions and n30 40 e in the north closely following the trend of the orogenic belt in these areas the transition region between north and central is characterized by t 1 1 3 s and by e w trending that are at a high angle to the regional geologic trend measurements at two stations located in the eastern internal part of the belt indicate very weak anisotropy the large scale pattern of anisotropy is not consistent with that predicted for simple asthenospheric flow beneath the plate splitting along the southern and eastern margins of the continent is consistent with that expected for grenvillian deformation an alternative model of asthenospheric flow around the cratonic keel cannot be ruled out within the cratonic core the correlation between t and lithospheric thickness suggests a lithospheric anisotropy smaller length scale variations also argue for a significant contribution of lithospheric structures the fabric responsible for shear wave splitting may have formed during tectonic episodes that affected the eastern united states i e the grenville and appalachian orogenies and the subsequent rifting of the north atlantic ocean our observations in the western appalachians suggest that the anisotropy may be preserved since the grenvillian orogeny the absence of detectable splitting in the two stations in the eastern appalachians is attributed to the igneous intrusions related to the atlantic rifting the measurements in the transition between the northern and central southern appalachians constitute an intriguing anomaly whose e w have little obvious relation to the regional surface geology we suggest two possible causes 1 the local dominance of asthenospheric flow motivated by the proximity of a pervasive low velocity anomaly and 2 lithospheric deformation in a transcontinental strike slip fault zone active during the appalachian collision

crustal structure of the dead sea basin from local earthquake tomography summary new findings of the velocity structure of the crust across the dead sea basin are obtained by applying tomography based method to local earthquakes we use p wave traveltime of 614 earthquakes that occurred in the dead sea basin in 1983 2009 at all depths the dead sea basin is characterized by lower velocities relative to both the eastern and western sides of the basin there is significant seismic activity at a depth of about 20 km mainly in the centre and the northern part of the basin at shallow depths 15 km there is more seismic activity on the eastern side of the basin than on the western side and the northern basin is generally more active than the southern basin asymmetry is also observed in the faults that border the dead sea basin the arava fault on the eastern side with nearly vertical dip faulting appears to be a clear boundary at all depths down to about 20 km the depth extension of the jericho fault on the western side of the basin is definitely limited to less than 15 km at greater depths of 20 km or more the western side is only partially bounded by a fault the concentration of earthquakes in the central part of the basin at depths larger than 15 km suggests that the dead sea fault at those depths acts as one single fault that is located in or near the central axis of the basin the existence of a number of clusters of earthquakes that spread from shallow depths of a few kilometres up to a depth of about 22 km points to several defined faults that traverse the dead sea basin one such example is the aftershock sequence of the 2004 earthquake that occurred in the northern dead sea basin seismic activity near mt sodom is relatively low and occurs at shallow depths down to 10 km whereas at larger depths 15 km it ceases this implies that the whole structure is relatively shallow with no wide and deeper extension seismic activity near and within the lisan peninsula extends to somewhat larger depths 15 km and then it ceases the occurrence of earthquakes at large depths suggests that the upper and the lower crust are relatively cool as was also suggested by earlier studies pointing to the fact that the heat flow is significantly below the global average value

terrestrial vegetation change inferred from n alkane σ13c analysis in the marine environment abstract we report gas chromatography isotope ratio monitoring mass spectrometry gc irm ms measurements of the 13c values of individual biomarker compounds n alkanes extracted from a 3 m marine sediment core taken near the mouth of the johnstone river north queensland australia the technique allows a purely terrestrial isotope signal to be discerned despite mixing of terrestrial and marine derived carbon the results indicate that there has been a 2 increase in the 13c values of terrestrially derived n alkanes c29 c33 since clearing of the forested johnstone river drainage basin for sugarcane and pasture began in the late 19th century a much slower 1 increase in 13c values after 6 000 years bp and prior to european settlement may be related to a decrease in rainfall in the basin or to an increase in the abundance of c4 plants as a result of increased aboriginal burning the results from the sediment core are consistent with data obtained for modern river sediments from forested and cleared subcatchments within the basin and demonstrate that the 13c values of terrestrially derived n alkanes in the marine environment can be used to assess basin wide vegetation changes in adjacent river catchments on geological timescales

reconstructing the environmental conditions around the silurian ireviken event using the carbon isotope composition of bulk and palynomorph organic matter the carbon isotope composition 13c of bulk organic matter and two palynomorph groups scolecodonts and chitinozoans from the llandovery wenlock strata of gotland e sweden are compared to gain knowledge about carbon cycling in the silurian sub tropical shelf environment the 13c values of the palynomorphs are mostly lower than the 13c values of the bulk organic matter and the 13c values of the benthic scolecodonts are lower than those of the planktonic chitinozoans while the difference between bulk and palynomorph 13c may be in part a function of trophic state the lower values of the scolecodonts relative to those of chitinozoans which are assumed to live in the well mixed water column might imply an infaunal mode of life for the polychaetes that carried the scolecodonts lower 13c for the scolecodonts in the middle of the section may represent variations in primary marine productivity supported by acritarch abundance data oxidation of organic matter in the bottom waters or genera effects in general however trends between the three data sets are parallel indicating similarities in the low frequency environmentally forced controls the 13c data show a decreasing trend from the base of the section up to a horizon well below the base of the upper visby formation at this level and therefore probably several 10 kyr before the 13c increase in the carbonates the 13c organic values increase by 1 this perhaps is an expression of a changed composition of the bulk organic matter associated with the extinction events prior to the llandovery wenlock boundary

effects of chemical preparation protocols on δ13c values of plant fossil samples abstract for over a half century studies of the stable carbon isotope compositions of plant fossils have provided noteworthy conclusions about the evolution of earth climate however different preparation protocols were used prior to carbon isotope analysis of plant fossils and the accuracy of measured 13c 12c ratios may strongly depend on them we have applied the most frequently used chemical preparation protocols to frenelopsis leaves from four cretaceous localities of western europe our results indicate that procedures to extract plant fossils from sediments are not adequate to retrieve the original plant 13c values the use of schulze s reagent to bleach cuticles in paleobotany allows misleading 13c values of specimens from a same locality with positive shifts of up to 13 6 and increases intra specimen and inter specimen variances sample treatment involving hcl or hcl hf gives consistent 13c mean values for a same leaf and for leaves from a same sedimentary bed however although hf does not provide any advantage in removing potential contamination sources it alters plant fossil tissues slightly increasing the intra and inter leaf variances of 13c values our results indicate that processing plant fossils with hcl only is the most accurate and conservative way to retrieve original 13c values

the land plant δ13c record and plant evolution in the late palaeozoic abstract based on the evaluation of 1323 carbon isotope values for silurian to permian terrestrial organic carbon measured on plant fossils cuticules humic coals and bulk terrestrial organic matter tom we conclude that the temporal trend in 13ctom records variations in the global carbon cycle notably an increase in the fractional burial of light terrestrial organic matter in late palaeozoic sediments 13ctom values suggest that the late palaeozoic po2 peak could have been restricted to a time frame of 40 ma carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions no significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible the carbon isotopic composition solely reflects c3 plant metabolism

localized versus distributed shear in transform plate boundary zones the case of the dead sea transform in the jericho valley 1 continental transform plate boundaries are typically either localized along a single usually segmented major fault or distributed over a broad deformation zone in the latter shear is partitioned between major strike slip faults and intervening often rotating fault systems analog and numerical simulations suggest that such internal fault systems evolve and may be localized or delocalized depending on strain and fault zone strength this paper examines the degree and evolution of shear localization in the jericho valley section of the dead sea transform dst which is part of the africa arabia plate boundary in this section the current breadth of the transform valley and its penetrative strain field are difficult to reconcile with localized shear we integrate newly acquired high resolution reflection data reprocessed exploration reflection data both focused to 2 5 3 5 km depth relatively relocated earthquake epicenters and fault plane solutions based on p wave first arrivals and suggest reinterpretations for previously published structural and seismic data in the jericho valley and the northern dead sea basin it is found that shear in this section of the dst evolved from an early probably miocene pliocene stage of localized strike slip motion primarily along the jericho fault to a late stage pliocene recent when shear has been distributed over internal fault sets that apparently lean against a major eastern dst segment in the early stage the jericho fault formed the western boundary of a deep narrow probably pull apart basin filled by fluvial clastics and evaporites this is overlain by the late stage broad basin characterized by low energy deposition of lacustrine and fluvial sediments pliocene rock salt has apparently utilized the jericho fault zone as a conduit for diapirism causing the uplift normal faulting and surface deformation of late pleistocene and holocene sediments currently observed along the 15 km long jericho lineament on the basis of the currently observed dextral normal motion across the internal nne ne trending fault system counterclockwise rotation is expected to have occurred within the transform zone these tectonic and depositional changes were probably associated with onset of transtension across the dst related to the previously postulated shift of the africa arabia euler pole of rotation in the pliocene

structural geometry and evolution of the dead sea jordan rift system as deduced from new subsurface data abstract analysis of deep drilling data and seismic reflection surveys obtained in recent years permit establishment of a tectonic model of the dead sea jordan rift system that is in part conformable with some of the many often controversial theories on this subject but which also introduces new information negating some concepts that are widely accepted in the literature the dead sea jordan rift system is not a tensional graben between two parallel sets of faults but instead can be best defined as a sinistral transform connecting an incipient oceanic ridge the red sea with an upthrusted collision zone the taurus range the shear is caused by the opening of the red sea and the motion of the arabian sub plate away from the african plate the shearing occurs along a largely south north trending slightly arcuate une consisting of a series of en echelon left stepping left lateral strike slip master faults of varying lengths these faults characteristically die out to the north by bending outward northeast and the movement is taken up by the strike slip faults to the left i e to the west where overlap of the two faults occurs very narrow and very deep grabens have evolved in places the width being equal to the depth the narrowness of these grabens is dictated by the closeness of the overlapping segments of the successive strike slip faults this feature points to the probability that the en echelon strike slip faults have a common root zone at great depth these grabens are not typical leaky pull aparts in that they have no gravimetric magnetic or heat flow anomalies nor are they closed on all four sides by large faults their northern ends are characterized by gradually rising graben floors without major diagonal cross faults the dead sea jordan rift system sensu stricto extends over a distance of 420 km from the northern shore of the gulf of elat to the northern margin of the hula valley southward it is connected with the red sea along the gulf of elat transition zone which has elements of strike slip as well as tensional opening a northern transition zone exists between the hula valley and the taurus arc where diminishing strike slip movement is compensated by several underthrust belts the time of the beginning of the movement along the rift can be established as pre middle miocene because mid miocene sediments overlie an upper cretaceous graben floor rifting has continued intermittently to the present volcanism in the northern fifth of the rift is genetically associated with the seismically active tensional golan hauran jebel drouz wadi sirhan tectonic trend which has a north west southeast orientation and not with the north south trending dead sea jordan rift

interpretation of seismic surface waves in regional networks joint estimation of wavefield geometry and local phase velocity method and numerical tests summary teleseismic surface waves in general strongly deviate from plane waves as is evident from the analysis of surface wave data recorded with dense networks this causes conventional ray based tomographic techniques to break down if applied to network surface wave data we present a new inversion method based on the acoustic wave equation and applicable to vertical component surface wave data which successfully deals with non plane wavefield geometries the basic idea of the method is a joint estimation of the incoming wavefield and heterogeneous structure within the network region crucial to the success of the method is an adequate parametrization of the incoming wavefield which is realized using hermite gaussian basis functions additionally we apply a constraint on the wavefield parameters that expresses the idea that the samples of the wavefield taken at the station locations should be representative for the wavefield in the whole network region in this way wavefields that show stronger fluctuations in spectral amplitude than observed at the stations are rejected to represent heterogeneous structure within the network region we use an expansion into 2 d hermite gaussian functions provided that the density of stations is sufficient the proposed method retrieves heterogeneous structure in the network region very well it is not sensitive to noise or non uniform azimuthal coverage of earthquakes moreover it yields smoothed versions of the true model if the roughness of the latter has been underestimated in the inversion conversely if the true model is much smoother than anticipated inspection of the trade off between model smoothness and data misfit allows us to find the correct model the limiting factor for the inversion is the density of stations which must allow for a reliable interpolation of the observed wavefield within the network therefore in order to perform regional surface wave studies it is essential to deploy seismic stations in the region of interest itself

les crises du devonien superieur par l etude des faunes d ostracodes dans leur cadre paleogeographique abstract ostracod evolution studied at a global scale can contribute to an evaluation of the palaeobilogical crises during the late devonian the mostly pelagic entomozoidae are not affected data on benthic neritic ostracods come from the western canadian platform europe the russian platform north africa and the middle east species extinction rates vary according to provinces and areas extinction occur at the givetian frasnian lower upper frasnian and frasnian famennian boundaries only five families seem to disappear during the late devonian the appearance of new assemblages since the earlisst famennian is worldwide on platforms the thuringian ecotype ostracod assemblages underwent a major change since the early famennian it is characterized by many species with spinous carapaces and is known in the paleotethys during famennian dinantian times it is related to a glacial event in the north of the gondwana which generated cold deep water currents invading the paleotethysian basins the thuringian ecotype allows to propose a paleobathymetric model its species composition shows a double origin by evolution of early devonian roots and with lineages proceeding from circalittoral species causes of these late devonian events can be understood in a particular paleogeographic reconstruction where the paleotethys has no western faunal communication since the givetian frasnian boundary warming water associated with an oxygen deficiency eliminated several species at the givetian frasnian and lower upper frasnian boundaries a first cooling at the frasnian famennian time was sufficient to decimate species strongly adapted to the frasnian conditions the generalized regression at this time probably increased this last phenomenon

geophysical evidence of deep hydrocarbon flow in mottled zone areas dead sea transform zone the origin of unusual magnetic initially sedimentary rocks of the mottled zone mz in israel and jordan remained enigmatic for several decades until integrated characterization of the mz area was achieved by ground magnetic measurements and geologic observations along representative profiles in parallel with reprocessing and reinterpretation of available aeromagnetic and gravity data micromagnetic profiling was combined with gamma radioactivity measurements and representative samples were selected to determine rock physical properties results of field measurements reduction and transformation of geophysical fields anomaly inversion and forward modeling accompanied by geologic analysis suggest that two types of magnetic anomalies and local gravity minima in the mz areas are related to the same event i e deep hydrocarbon flow associated with fossil mud volcanism physicochemical interaction of deep hydrocarbon flow and surrounding sedimentary rocks caused widespread weak magnetization and correspo

asymmetry and basin migration in the dead sea rift the dead sea depression sensu stricto forms the deepest continental part of the dead sea rift a transfer which separates the levanthine and arabian plates it is occupied by three distinct sedimentary bodies deposited in basins whose depocenters are displaced northward with time they are the continental red beds of the hazeva formation miocene the bira lido gesher marls and the exceptionally thick rocksalt of the sedom formation pliocene early pleistocene and the successive amora lisan and dead sea evaporites and clastics early pleistocene recent lengthwise and crosswise asymmetries of these sedimentary basins and their respective depocenters are due to leftlateral shear combined with anticlockwise rotation of the arabian eastern plate steeper faulting of the crustal eastern margin than of the western sedimentary margin and modification of depositional pattern by twice filling up of basins by hazeva red beds during late miocene pause of shear and by sedom rocksalt during pliocene marine ingression

the crust mantle boundary beneath cratons and craton margins a transect across the south west margin of the kaapvaal craton lower crustal suite xenoliths occur in on craton and off craton kimberlites located across the south western margin of the kaapvaal craton southern africa rock types include mafic granulite plagioclase bearing assemblages eclogite plagioclase absent assemblages with omphacitic clinopyroxene and garnet pyroxenite orthopyroxene bearing eclogite the mafic granulites are subdivided into three groups garnet granulites cpx grt plag qtz two pyroxene garnet granulites cpx opx grt plag kyanite granulites cpx grt ky plag qtz reaction microstructures preserved in many of the granulite xenoliths involve the breakdown of plagioclase by a combination of reactions 1 cpx plag grt qtz 2 plag grt ky qtz 3 plag cpx jd rich qtz compositional zoning in minerals associated with these reactions records the continuous transition from granulite facies mineral assemblages and pressure p temperature t conditions to those of eclogite facies two distinct p t arrays are produced 1 off craton granulites away from the craton margin define a trend from 680 c 7 5 kbar to 850 c 12 kbar 2 granulite xenoliths from kimberlites near the craton margin and on craton granulites produce a trend with similar geothermal gradient but displaced to lower t by 100 c both p t fields define higher geothermal gradients than the model steady state conductive continental geotherm 40 mwm2 and are not consistent with the paleogeotherm constructed from mantle derived garnet peridotite xenoliths a model involving intrusion of basic magmas around the crust mantle boundary followed by isobaric cooling is proposed to explain the thermal history of the lower crust beneath the craton margin the model is consistent with the thermal evolution of the exposed namaqua natal mobile belt low pressure granulites and the addition of material from the mantle during the namaqua thermal event c 1150 ma the xenolith p t arrays are not interpreted as representing paleogeotherms at the time of entrainment in the host kimberlite they most likely record p t conditions frozen in during various stages of the tectonic juxtaposition of the namaqua mobile belt with the kaapvaal craton

formation of sequential basins along a strike slip fault geophysical observations from the dead sea basin abstract the dead sea basin is often cited as one of the classic examples for the evolution of pull apart basins along strike slip faults despite its significance the internal structure of the northern dead sea basin has never been addressed conclusively in order to produce the first comprehensive high resolution analysis of this area all available seismic data from the northern dead sea lake lower jordan valley land were combined results show that the northern dead sea basin is comprised of a system of tectonically controlled sub basins delimited by the converging western and eastern boundary faults of the dead sea fault valley these sub basins grow shallower and smaller to the north and are separated by structural saddles marking the location of active transverse faults the sedimentary fill within the sub basins was found to be relatively thicker than previously interpreted as a result of the findings of this study the classic model for the development of pull aparts based on the dead sea is revised the new comprehensive compilation of data produced here for the first time was used to improve upon existing conceptual models and may advance the understanding of similar basinal systems elsewhere

shear wave splitting continental keels and patterns of mantle flow in this study we investigated the origin of seismic anisotropy in the mantle beneath north america in particular we evaluated whether shear wave splitting patterns in eastern north america are better explained by anisotropy caused by lithospheric deformation anisotropy due to mantle flow beneath the lithosphere or a combination of both we examined new measurements of shear wave splitting from the missouri to massachusetts broadband seismometer array moma the north american mantle anisotropy and discontinuity experiment nomad as well as splitting parameters from several previous studies we developed a simple finite difference model that approximates mantle flow around a complex three dimensional continental lithospheric keel to evaluate potential anisotropy from mantle flow beneath the lithosphere in eastern north america we compared shear wave splitting observations to predicted splitting parameters calculated using this mantle flow model our results indicate that a significant portion of observed shear wave splitting in eastern north america can be explained by mantle flow around the continental keel however shear wave splitting patterns in a few regions of eastern north america indicate that a component of lithospheric anisotropy must exist particularly in regions containing the largest keel thicknesses for eastern north america as well as for splitting observations in australia europe and south america we favor a model in which anisotropy is controlled by a combination of both lithospheric deformation and subcontinental mantle flow

seismic characteristics and identification of negative flower structures positive flower structures and positive structural inversion negative and positive flower structures and positive inverted structures imply specific modes of formation and their distinctive characteristics make them important criteria for the identification of certain structural styles a negative flower structure from the andaman sea consists of a shallow synform bounded by upward spreading strands of a wrench fault that have mostly normal separations paralleling monoclines and oblique en echelon normal faults flank the divergent wrench fault a positive flower structure from the ardmore basin oklahoma consists of a shallow antiform displaced by the upward diverging strands of a wrench fault that have mostly reverse separations en echelon folds are present on either side of this convergent wrench fault flower structures may resemble extensional or contractional fault blocks on individual seismic profiles flower structures are identified by their unique internal fault and fold architecture by their association with a straight and throughgoing zone of deformation and by their lack of a consistent sense of separation or regional upthrown side positive structural inversion at the rambutan oil field south sumatra basin has formed a shallow anticlinorium and has partly uplifted the underlying graben deeper fault segments bounding the graben have retained their normal fault profiles but at shallow levels some of these faults have reverse separations similar changes of separation with depth may be produced by strike slip but sets of faults with listric profiles and nearby blocklike trend patterns identify the inversion as a dip slip event where correlation of reflections is uncertain or deep control is unobtainable positive inverted structures may also resemble contrational fault blocks detached normal fault assemblages and certain negative inverted structures

an isotopic study of biogeochemical relationships between carbonates and organic carbon in the greenhorn formation carbon isotopic compositions of total carbonate inoceramid carbonate micritic carbonate secondary cements total organic carbon and geoporphyrins have been measured in 76 different beds within a 17 m interval of a core through the greenhorn formation an interbedded limestone and calcareous shale unit of cretaceous age cenomanian turonian from the western interior seaway of north america results are considered in terms of variations in the processes of primary production which led to the biosynthesis of the molecular precursors of the geoporphyrins and in secondary processes those mediating the transformation of primary organic material into sedimentary total organic carbon it is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the toc isotopic record and that in these sediments toc is enriched in 13c relative to its primary precursor by 0 6 to 2 8 this enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate this correlation is attributed to effects of environmental changes on the marine foodweb these may have included increased atmospheric oxygen associated with the cenomanian turonian oceanic anoxic event the isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1 5 during the interval of deposition it is suggested that this change is due to a variation in the makeup of the community of primary producers and or to a decrease in the atmospheric abundance of co2 during the oceanic anoxic event

hotspot tracks and the early rifting of the atlantic abstract many hotspot tracks appear to become the locus of later rifting as though the heat of the hotspot weakens the lithosphere and tens of millions of years later the continents are split along these weakened lines examples are the west coast of greenland east coast of labrador madeira hotspot the south coast of mexico north coast of honduras guyana hotspot and the south coast of west africa north coast of brazil st helena hotspot a modern day analog of a possible future rift is the snake river plain where the north american continent is being pre weakened by the yellowstone hotspot track this conclusion is based on reconstructions of the motions of the continents over hotspots for the past 200 million years the relative motions of the plates are determined from magnetic anomaly isochrons in the oceans and the motion of one plate is chosen ad hoc to best fit the motions of the plates over the hotspots however once the motion of this one plate is chosen the motions of all the other plates are prescribed by the relative motion constraints in addition to the correlation between the predicted tracks and sites of later continental breakup exposed continental shields correlate with the tracks their exposure may be the result of hotspot induced uplift which has led to erosion of their former platform sediment cover

mesozoic hotspot epeirogeny in eastern north america geologic data especially conodont paleotemperatures imply that southeastern canada and new england have been elevated at least 4 km relative to the central appalachian region apatite fission track ages suggest that the uplift and consequent erosion occurred in cretaceous early tertiary time consistent with the formation of a broad swell as north america moved northwestward over the great meteor hotspot

structure of the dead sea pull apart basin from gravity analyses analyses and modeling of gravity data in the dead sea pull apart basin reveal the geometry of the basin and constrain models for its evolution the basin is located within a valley which defines the dead sea transform plate boundary between africa and arabia three hundred kilometers of continuous marine gravity data collected in a lake occupying the northern part of the basin were integrated with land gravity data from israel and jordan to provide coverage to 30 km either side of the basin free air and variable density bouguer anomaly maps a horizontal first derivative map of the bouguer anomaly and gravity models of profiles across and along the basin were used with existing geological and geophysical information to infer the structure of the basin the basin is a long 132 km narrow 7 10 km and deep 10 km full graben which is bounded by subvertical faults along its long sides the bouguer anomaly along the axis of the basin decreases gradually from both the northern and southern ends suggesting that the basin sags toward the center and is not bounded by faults at its narrow ends the surface expression of the basin is wider at its center 16 km and covers the entire width of the transform valley due to the presence of shallower blocks that dip toward the basin these blocks are interpreted to represent the widening of the basin by a passive collapse of the valley floor as the full graben deepened the collapse was probably facilitated by movement along the normal faults that bound the transform valley we present a model in which the geometry of the dead sea basin i e full graben with relative along axis symmetry may be controlled by stretching of the entire brittle and ductile crust along its long axis there is no evidence for the participation of the upper mantle in the deformation of the basin and the moho is not significantly elevated the basin is probably close to being isostatically uncompensated and thermal effects related to stretching are expected to be minimal the amount of crustal stretching calculated from this model is 21 km and the stretching factor is 1 19 if the rate of crustal stretching is similar to the rate of relative plate motion 6 mm yr the basin should be 3 5 m y old in accord with geological evidence

active faulting in the dead sea rift abstract manifestations of late quaternary and holocene faulting were studied in a 500 km long segment of the dead sea transform rift most prominent are left slip faults whose characteristic physiographic features are recognizable along most of the studied segment where these faults bend or are stepped to the left rhomb shaped grabens or pull aparts are produced forming depressions in the reverse situation compressional features such as pressure ridges domes and folds form positive topographic features such structures are combined on a variety of scales ranging from a few hundred meters long to tens of kilometers normal faults sub parallel to the left slip faults produce a trough like valley along much of the dead sea transform but are most prominent along the margins of the large rhomb grabens e g the dead sea trough they apparently record a small component of transverse extension generally their motion is slow young slip did not occur along some segments during the last few 10 4 y elsewhere throws of 10 20 m at least occurred in this period the dead sea transform is seismically active the instrumental and historic records indicate a seismic slip rate of 0 15 0 35 cm y during the last 1000 1500 y while estimates of the average pliocene pleistocene rate are 0 7 1 0 cm y either much creep takes place or the slip rate varies over periods of a few 10 3 y

composition of the crust in the grenville and appalachian provinces of north america inferred from v p v s ratios we use the ratios between p and s wave velocities vp vs derived from seismic refraction data to infer the composition of the crust in the grenville and the appalachian provinces of north america the crust exhibits vp vs increasing with depth from 1 64 to 1 84 there is a clear distinction between the grenville province average vp vs 1 81 and the appalachian province average vp vs 1 73 which persists at all depths the boundary between these provinces is east dipping extending for 100 km east of the champlain thrust in the appalachian province the increase in vp vs ratios with depth from 1 67 to 1 74 0 02 may reflect a normal decrease of silica content in the continental crust in the grenville province beneath the central granulite terrane an anomalous vp vs ratio of 1 82 0 02 is observed extending to a depth of 10 km this correlates with the abundance of ca plagioclase in the marcy anorthosite at greater depth 15 20 km where seismic lamination and high electrical conductivity is observed vp vs is 1 84 0 02 and correlates with the tahawus complex a layered mafic intrusion within the 25 km thick lower crust of the grenville province the vp vs is 1 84 0 02 and p velocity is 7 0 0 1 km s which are typical for plagioclase bearing rocks gabbro norite the high vp vs ratio in the grenville province has not been reported in crust of any other age since the grenville province contains 75 of the world s known anorthosites high vp vs ratio is related to high plagioclase we suggest that the composition of the grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid proterozoic

crustal structure of the southeastern grenville province northern new york state and eastern ontario the grenville province exposes an oblique cross section through mid lower crustal lithologies that were pervasively deformed and subjected to regional thermal overprinting during the grenvillian orogeny 1 1 ga the southeastern grenville province is divided into two subterranes by the carthage colton mylonite zone a 110 km long lineament characterized by intense ductile shear and igneous intrusion which separates the amphibolite facies metasediments of the central metasedimentary belt to the west from the granulite facies metaplutonics of the central granulite terrane to the east the recognition of distinct lithotectonic domains separated by zones of intense ductile shear in the grenville province raises questions concerning the deep structure of these subterranes and in particular the means by which the mid lower crustal rocks exposed in the grenville province were emplaced seismic refraction wide angle reflection data were acquired to investigate the deep structural interrelationships within the southeastern grenville province a travel time inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude modeling to produce a seismic velocity model of the crust in the southeastern grenville province in the central metasedimentary belt the upper crust is characterized by velocities in the range 6 3 6 4 km s and a poisson s ratio of 0 26 0 01 which are attributed to quartzofeldspathic rocks farther east in the central granulite terrane upper crustal velocities of 6 55 km s and a poisson s ratio of 0 28 0 01 are associated with the marcy anorthosite the seismic homogeneity of the upper crust in the region of the carthage colton mylonite zone suggests that this boundary is a shallow feature limited to the upper 2 3 km of the crust the deep crustal structure of the southeastern grenville province is characterized by two discrete and laterally discontinuous seismic interfaces in the central metasedimentary belt the top of the lower crust is delineated by an eastward dipping interface at 24 28 km depth in the central granulite terrane prominent en echelon reflections referred to as the tahawus complex form a gently arched dome at 17 22 km depth interpretation of the tahawus complex as a zone of layered mafic cumulates is supported by its high velocity 7 1 km s and poisson s ratio 0 27 0 02 the lower crust is characterized by a velocity of 7 0 7 2 km s and an anomalously high poisson s ratio of 0 30 0 02 which are representative of pyroxene garnet granulites in contrast velocities of 6 8 7 0 km s are modeled beneath the central granulite terrane and appear to signify a lateral change in composition the moho lies at 44 45 km depth and is characterized by pronounced en echelon reflection segments suggesting compositional interlayering around the crust mantle boundary the velocity of the upper mantle is 8 0 8 2 km s an anomalous upper mantle layer with a reversed velocity of 8 6 km s dips eastward from 50 to 60 km depth beneath the southeastern grenville province our results indicate that remnants of magmatic intrusions that mobilized and thickened the crust during the grenvillian orogeny are preserved in the mid lower crust as a layered cumulate body tahawus complex and in the upper mantle as an eclogitic lens possibly delaminated from the overthickened crust during uplift of the southeastern grenville province

mechanical aspects of pull apart basins and push up swells with applications to the dead sea transform abstract pull apart basins and push up swells are common features at steps along strike slip faults the structure of these features is examined here for two types of rheology perfect brittle and perfect ductile the stress fields derived for the step area predict that fault patterns mode of deformation and vertical displacement are different for the two rheologies these predictions are illustrated for basins and swells developed in laboratory experiments with modelling materials the structure of basins and swells along the dead sea transform is discussed here the pull apart basins display an intensively faulted southern end and a gently dipping flexure at the northern end a consistent dissimilarity appears between the structures of the eastern and western boundary faults of the basins according to the present interpretation these dissimilarities reflect a relatively ductile crust in arabia and a relatively brittle crust in sinai israel

tectonic evolution of the qumran basin from high resolution 3 5 khz seismic profiles and its implication for the evolution of the northern dead sea basin abstract the dead sea basin is a morphotectonic depression along the dead sea transform its structure can be described as a deep rhomb graben pull apart flanked by two block faulted marginal zones we have studied the recent tectonic structure of the northwestern margin of the dead sea basin in the area where the northern strike slip master fault enters the basin and approaches the western marginal zone western boundary fault for this purpose we have analyzed 3 5 khz seismic reflection profiles obtained from the northwestern corner of the dead sea the seismic profiles give insight into the recent tectonic deformation of the northwestern margin of the dead sea basin a series of 11 seismic profiles are presented and described although several deformation features can be explained in terms of gravity tectonics it is suggested that the occurrence of strike slip in this part of the dead sea basin is most likely seismic sections reveal a narrow zone of intensely deformed strata this zone gradually merges into a zone marked by a newly discovered tectonic depression the qumran basin it is speculated that both structural zones originate from strike slip along right bending faults that splay off from the jordan fault the strike slip master fault that delimits the active dead sea rhomb graben on the west fault interaction between the strike slip master fault and the normal faults bounding the transform valley seems the most plausible explanation for the origin of the right bending splays we suggest that the observed southward widening of the dead sea basin possibly results from the successive formation of secondary right bending splays to the north as the active depocenter of the dead sea basin migrates northward with time

upper mantle s velocity structure of north america we have inverted fundamental and higher mode rayleigh waveforms from 685 vertical component broadband seismograms with wave paths over north america to obtain an image of the upper mantle s velocity structure down to 660 km among the well resolved features of the new model are 1 a high velocity root beneath the north american craton which extends no deeper than 250 km except near the archean core of the craton where depths of 350 km are reached 2 a weak band of low velocity along the eastern margin of the north american craton which reaches into the transition zone 3 a low velocity slab window beneath the western united states down to a depth of 300 km 4 areas of low uppermost mantle velocity beneath the cascade volcanoes the yellowstone hotspot track the colorado plateau the sierra madre occidental and the grabens bordering the jalisco block and 5 a pronounced band of high velocities in the transition zone coinciding with the expected location of the subducted trailing fragments of the farallon plate we introduce several improvements to the method of partitioned waveform inversion which was used to compute the new model rather than to correct for an estimated depth to the mohorovicic discontinuity we leave the crustal thickness as a free though yet poorly resolved parameter in the inversion we also improve the windowing and filtering operator used to select uncontaminated waveforms

young faults in the hula pull apart basin central dead sea transform abstract the geometry and nature of structural features inside the hula pull apart basin at the central dead sea transform are presented here two systems of n s left lateral strike slip faults are located on the east and west sides of the hula basin both fault systems are composed of several segments arranged in a right stepping en echelon pattern the northern end of each segment is bent northeastward and usually merges with the next segment elevated regions and small hills appear on the northern side of each bend the strike slip faults are oblique with both vertical and horizontal components the vertical component may be normal or reverse although the hula valley is subjected to general extension the studied structures indicate local compression inside the basin normal faults striking e w comprise the northern border of the hula basin age determination of displaced travertines and basalts along the faults indicates sub recent tectonic activity and suggests migration of normal faulting towards the inner part of the basin the youngest fault displaces travertine dated at 25 300 years

seismic anisotropy beneath the continents probing the depths of geology seismic anisotropy beneath continents is analyzed from shear wave splitting recorded at more than 300 continental seismic stations anisotropy is found to be a ubiquitous property that is due to mantle deformation from past and present orogenic activity the observed coherence with crustal deformation implies that the mantle plays a major if not dominant role in orogenies no evidence is found for a continental asthenospheric decoupling zone suggesting that continents are coupled to general mantle circulation

how to relate body wave and surface wave anisotropy seismic anisotropy is one of the most efficient geological and geodynamical tools for understanding the dynamics of the earth upper mantle anisotropy is evident in seismic data sets for the last 30 years primarily from surface wave dispersion curves and body wave sks data we demonstrate in this paper that surface wave and body wave derived anisotropy can be explained by the same anisotropic parameters l gc gs in the simplest case of a horizontal fast symmetry axis one application of this method is to display the sks delay time and the corresponding azimuth which can be derived from surface wave global with a lateral resolution of around 2000 km and regional lateral resolution of 350 km anisotropy tomography a global scale comparison is disappointing since there are only a few areas where both data types are correctly retrieved at the same spatial scale same lateral resolution the anisotropy is well resolved in oceanic basins from surface waves whereas most measurements of sks splitting are available below continents however there is a good agreement between surface wave and body wave anisotropy in regions where large scale processes primarily tectonic are taking place such as the western united states and in central asia in particular we show that at high frequency 1hz the observed sks delay time and azimuth depend on the order in which s waves propagate through the layers a comparison between synthetic and observed sks phases in central asia highlights the varying sensitivity of sks waves at depth we can obtain a good correlation between synthetic and observed sks by considering anisotropy only between 80 and 200 km depth in the tomographic model rather than in the entire upper mantle however it is more difficult to explain the discrepancy between synthetic and observed sks under the eastern united states where a large scale coherent sks anisotropy is present such results call for more sophisticated sks waveform modeling and for enhanced lateral resolution in anisotropic tomographic models

seismic anisotropy tracing plate dynamics in the mantle elastic anisotropy is present where the speed of a seismic wave depends on its direction in earth9s mantle elastic anisotropy is induced by minerals that are preferentially oriented in a directional flow or deformation earthquakes generate two seismic wave types compressional p and shear s waves whose coupling in anisotropic rocks leads to scattering birefringence and waves with hybrid polarizations this varied behavior is helping geophysicists explore rock textures within earth9s mantle and crust map present day upper mantle convection and study the formation of lithospheric plates and the accretion of continents in earth history

crustal structure of the western new england appalachians and the adirondack mountains we present an interpretation of the crustal velocity structure of the new england appalachians and the adirondack mountains based on a seismic refraction wide angle reflection experiment in eastern north america extending from the adirondacks in new york state through the northern appalachians in vermont and new hampshire to central maine modeling of the eastern portion of the profile within the new england appalachians shows a subhorizontal layered crust with upper crustal velocities ranging from 5 5 to 6 2 km s a midcrustal velocity of 6 4 km s and a lower crustal velocity of approximately 6 8 km s crustal thickness increases from 36 km beneath maine to 40 km in vermont little evidence is seen for structures at depth directly related to the white mountains or the green mountains a major lateral velocity change in the upper and mid crust occurs between the appalachians and the adirondacks this boundary projecting to the surface beneath the champlain valley dips to the east beneath the green mountains and extends to a depth of 25 km below the eastern edge of the connecticut valley synclinorium in vermont the tahawus complex a series of strong horizontal reflections at 18 24 km depth beneath the adirondack highlands is seen to dip eastward beneath vermont upper crustal rocks in the adirondack mountains have poisson s ratios of 0 28 0 01 that can be correlated with the marcy anorthosite pois son s ratios of 0 24 0 01 calculated for rocks of the connecticut valley synclinorium indicate a siliceous upper crust in vermont the lower crust is considered to be best represented by intermediate to mafic granulites a high poisson s ratio 0 26 0 27 tends to support a mafic lower crust in the new england appalachians this seismic refraction wide angle reflection experiment provides further evidence for the obduction of the allochthonous western appalachian units onto grenvillian crust above a zone of detachment that penetrates at least to midcrustal depths and was the locus of successive paleozoic thrusting

the relationship between δ13c of organic matter and co2 aq in ocean surface water data from a jgofs site in the northeast atlantic ocean and a model the 13c of suspended particulate organic matter spom in surface waters increased from 22 9 to 18 1 during april 25 may 31 1989 at the jgofs north atlantic bloom experiment site nabe site 47 n 20 w during the same period nearly parallel increases in sinking pom 13c were also found although these values were usually lower than those of the corresponding spom consistent with the hypothesis that plankton 13c and co2 aq are inversely related the increases in both sinking and suspended pom 13c were highly negatively correlated with mixed layer co2 aq that generally decreased from 10 1 13 2 moles kg during the five weeks the change in spom 13c per change in co2 aq however appears to be somewhat greater than that expected from previous though less direct ocean and laboratory evidence by adapting a model of plant 13c by farquhar et al 1982 it is shown that under a constant phytoplankton demand for co2 an inverse nonlinear spom 13c response to ambient co2 aq is expected such trends are unlike the negative linear relationships indicated by data from the nabe site and or from southern hemisphere waters such differences between predicted and observed spom 13c vs co2 aq trends and among observed relationships can be reconciled however if biological co2 demand is allowed to vary this has significant implications for the use of the 13c of plankton or their organic subfractions or sedimentary remains as a proxy for past or present ocean co2 concentrations and biological productivity

seismic evidence for a fossil mantle plume beneath south america and implications for plate driving forces a teleseismic travel time study reveals the presence of a fossil plume in the deep upper mantle beneath brazil which has apparently remained geographically fixed with respect to the overly ing continent despite thousands of kilometres of plate motion this result implies that the upper mantle and lithosphere beneath south america have remained coupled since the breakup of gondwanaland and may provide an answer to the long standing question of what forces drive continental plates

paleoceanography of the cretaceous tertiary boundary event inferences from stable isotopic and other data we report the results of new stable oxygen and carbon isotope analyses on carbonate fine fraction whole rock and benthic foraminifers caco3 and coarse fraction percentage determinations and trace element sr analyses on carbonate constituents across the cretaceous tertiary k t boundary in deep sea drilling project dsdp sites 47 2 356 384 and 577 and compare them with published results from k t boundary sections in other dsdp sites we used the trace element data and scanning electron microscope examination to evaluate possible diagenetic alteration and relative preservation of the samples analyzed in this study the 18o data when interpreted as isotopic paleotemperatures indicate relative stable surface water and deepwater temperatures in the late maestrichtian followed by somewhat fluctuating temperatures in the early paleocene however there is no indication of either a significant warming or cooling at or following the k t boundary several sites do exhibit somewhat heavier 18o values by about 0 5 across the boundary which might suggest a 2 3 c cooling at most however we interpret these somewhat heavier 18o values as reflecting slightly better preservation of 18o of carbonate constitutents in relatively clay rich intervals e g lower diagentic potential characteristic of the k t boundary the 13c values of carbonate fine fraction and planktonic foraminifers indicate a major negative excursion in surface water total dissolved carbon across the boundary the surface water and deepwater 13c values from benthic foraminifers combined with calculated decreases in carbonate accumulation rates at all sites in the earliest paleocene are consistent with a major decrease in productivity across the k t boundary the decrease in caco3 accumulation rates is due not to increased rates of dissolution but to decreased production in surface waters the low productivity episode lasted at least 1 m y beyond the k t boundary crisis suggesting that hypothesized catastrophic events alone such as impact of an apollo object are not the only explanation for the observed long term decrease in productivity there is also an indication in the 13c curves from several sites that the surface water 13c decrease began in the latest maestrichtian suggesting that the decrease in productivity may have been independent of a hypothesized impact event

internal structure of the dead sea leaky transform rift in relation to plate kinematics abstract the structures along the dead sea transform rift are related to the motions of the sinai and arabia plates which border it and to the irregularities of their boundaries the total slip was 105 km left lateral but the present structures were formed mainly during the last 40 km of slip which probably occurred in the plio pleistocene along the southern half of the transform the strike slip motion takes place on en echelon faults this produces rhomb shaped grabens or pull aparts which are sometimes composite and in which there is local crustal separation thus much of the transform is leaky these structures occur in a morpho tectonic rift valley delimited by normal faults which express a small component of transverse extension along a few segments the shape of the transform is such that lateral motion produces local transverse compression the geometric relations of the structures along the transform define an eulerian pole of relative plate motions at 32 8 n 22 6 e 0 5 the older motion was somewhat different and is described by a pole located about 5 west of the above then the component of transverse extension and crustal separation was much smaller than now while local transverse compression was more important the northern half of the dead sea transform has an irregular shape and the bordering plates did not remain rigid as lateral motion continued here transverse compression is often important

shear wave splitting and implications for mantle flow beneath the melt region of the east pacific rise shear wave splitting across the fast spreading east pacific rise has been measured from records of sks and skks phases on the ocean bottom seismometers of the mantle electromagnetic and tomography melt experiment the direction of fast shear wave polarization is aligned parallel to the spreading direction delay times between fast and slow shear waves are asymmetric across the rise and off axis values on the pacific plate are twice those on the nazca plate splitting on the pacific plate may reflect anisotropy associated with spreading induced flow above a depth of about 100 km as well as a deeper contribution from warm asthenospheric return flow from the pacific superswell region

geomorphological response of the lower jordan river basin to active tectonics of the dead sea transform abstract the lower jordan river ljr basin has been shaped on an active tectonic segment of the dead sea transform dst the jordan valley fault jvf which remains relatively unexplored due to its rough terrain conditions hyper arid climate and location along a political border where minefields are common the ability to detect the morphology of the valley surface by remote sensing methods provides an opportunity to follow the complex tectonic structure of the ljr basin and the spatial and temporal geomorphic processes that have shaped the basin since its exposure in the early holocene after the desiccation of lake lisan 14 5 ky bp in this study we use gis analyses and image processing to explore the relation between the geomorphology of the ljr basin and the active tectonics of the jvf the morphometric fluvial parameters of the basin are interpreted in relation to mapped faults geophysical gravity interpolation and seismic data we introduce morphometric gravity relations that show an increasing trend of the morphometric parameters standard deviation std as a function of the gravity anomaly increase which are consistent with stream power formulation studies and seismic measurements our results show that the active tectonics of the jvf is concentrated towards the basin s center and the dead sea fault location and that at the borders of the gravity highs sinuosity slope and width changes together with recent seismic activity all suggest on tectonic uplifting and active faulting in those areas

a test of the great circle approximation in the analysis of surface waves a new way of reconstructing wave fronts is de veloped for testing the validity of the great circle approxima tion in dispersion analysis of surface waves phase and time delays between pairs of stations of an array are used to re construct the wave fronts or surfaces of equal phase this techque is applied to fundamental mode rayleigh waves recorded at the nars stations dudlag the iliha iberian lithosphere heterogeneity and anisotropy project the re sulting wave fronts are compared with the theoretical ones i e calculated assuming that the waves have traveled along the great circle path with a constant phase velocity and the angle between both fronts is calculated waves traveling mosfiy through a laterally homogeneous oceanic path before arriving to the iberian peninsula are analyzed for the fre quency range of 10 to 60 mhz these show angles up to 8 degrees between the theoretical wave fronts and the wave fronts reconstructed using the delay data this implies that we make a relative error less than 1 when calculating path averaged phase velocities ignoring the deviation of the ar rival of the wave from the great circle direction

active transform fault zone at the fringe of the dead sea basin the evolution of an asymmetric basin at the edge of a pull apart structure is studied using geophysical observations and mechanical modeling a new seismic analysis of the northern edge of the dead sea basin indicates recent subsidence folding and oblique faulting along the jericho strike slip fault a main segment of the dead sea transform fault the subvertical fault trace crosses the entire sedimentary sequence typically branching in the shallow subsurface the seismic analysis reveals the three dimensional structure of the area as an asymmetrical basin bordered on the east and on the west by long monoclinic folds the thickness of the sedimentary fill varies from 1 4 km near the present lake shores to a few hundreds of meters about 10 km northward the subsidence is partitioned between a vertical component of slip along the jericho fault and the simultaneously active monoclines bordering the basin we present a model and simulations that reconstruct the present basin structure in the uppermost part of the crust and demonstrates the generation of flexures along the basin margins without horizontal shortening we show that the basin asymmetry and the association of folds and fault can be explained as a long term ductile response of the sediments to local subsidence the asymmetry along the basin is a consequence of a later vertical displacement component on a pre existing strike slip fault our analysis points to ongoing northward propagation of the dead sea basin and provides an explanation for the structural asymmetry of the basin margins

the sources and deposition of organic matter in the late quaternary pigmy basin gulf of mexico abstract the concentration and carbon isotopic composition 13c of sedimentary organic carbon corg n c ratios and terrigenous and marine 13corg endmembers form a basis from which to address problems of late quaternary glacial interglacial climatic variability in a 208 7 m hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico while interpretations of sedimentary 13corg time series records are often not unique paired analyses of 13corg and n c are consistent with the hypothesis that the corg in the pigmy basin is a climatically determined mixture of c3 photosynthetic terrigenous and marine organic matter confirming the earlier 13corg model of sackett 1964 a high resolution 1 4 2 9 ka sample 13corg record shows that sedimentary organic carbon in interglacial oxygen isotope sub stages 1 and 5a b are enriched in 13c average 1 values are 24 2 1 2 o and 22 9 0 7 o relative to pdb respectively while glacial isotope stage values 2 are relatively depleted 25 6 0 5 concentrations of terrigenous and marine sedimentary organic carbon are calculated for the first time using 13corg and corg measurements and empirically determined terrigenous and marine 13corg endmembers the net accumulation rate of terrigenous organic carbon is 4 3 2 6 times higher in isotope stages 2 4 than in sub stages 1 and 5a b recording higher erosion rates of terrigenous organic material in glacial times the concentration and net accumulation rates of marine and terrigenous corg suggest that the nutrient bearing plume of the mississippi river may have advanced and retreated across the pigmy basin as sea level fell and rose in response to glacial interglacial sea level change

seismic anisotropy in the north eastern us as a source of significant teleseismic p traveltime anomalies summary observations of shear wave splitting in the north eastern us and southern canada provide evidence for seismic anisotropy in the lithosphere throughout most of the region s wave splitting times of the order of 1 s are found within the proterozoic grenville province and at a number of sites within the appalachian orogen as a notable exception seismic anisotropy is weak or absent in vermont and western new hampshire a transitional zone between proterozoic and palaeozoic terranes the fast direction is westerly 260 280 within the grenville province and north westerly 300 320 in the appalachians the effects of seismic anisotropy on the traveltimes of body waves are modelled in a horizontal layer characterized by an anisotropic elastic tensor of olivine simulations are made to study the influence of parameters such as the fraction of anisotropic material the angle between the tensor symmetry axis and the wave propagation direction and the type of crystallographic axis aligned in olivine grains results indicate that earth models with s wave splitting times of about 1 s should also have p traveltime anomalies positive or negative of the order of 0 2 0 3 s also alignment along either axis a or b can produce the combination of p delays between 0 25 and 0 75 s and s wave splitting times between 0 7 and 1 3 s observed in the adirondack mountains we conclude that velocity anomalies found in this region by earlier studies may in part be due to seismic anisotropy

geology and evolution of the southern dead sea fault with emphasis on subsurface structure the dead sea fault is an active transform fault linking opening in the red sea with collision in the taurus zagros mountains motion is left lateral and estimated at approximately 5 7 mm year 1 the fault is seismically active and can be divided into two distinct structural segments this study focuses on the southern segment based mainly on the wealth of geophysical data owing to transtention caused by oblique slip and the overlapping of en echelon fault strands a series of pull apart basins were formed along the fault s length these basins are long and deep reaching in places more than 10 km deep they are characterized by extensional compressional and asymmetrical structures varying in size from large scale defining the general structure of the dead sea fault valley to small scale defining the internal structure this study examines the internal structure of these basins from south to north and summarizes the state of knowledge to date

is the jericho escarpment a tectonic or a geomorphological feature active faulting and paleoseismic trenching abstract the jericho fault is considered to be the main active fault in the northern dead sea lower jordan valley in previous studies it has been identified by a prominent linear topographic escarpment that is thought to be the surface expression of this fault on land north of the dead sea in this study the paleoseismic natures of the escarpment and the fault were examined seismic activity was investigated in a series of three trenches excavated south of the fault trace on the surface these trenches show evidence for late holocene faulting a fourth trench excavated 300 m farther to the south exposed continuous finely laminated marl from the 80 ka samra formation at a depth of 2 0 6 m below the surface with no evidence of faulting this could suggest that the fault on land is segmented and that the nature of its activity changes from north to south toward the lake indeed the continuation of this fault under the waters of the dead sea reveals active faulting along a sharp segmented linear bathy

holocene seismic and tectonic activity in the dead sea area abstract the dead sea is a large active graben within the dead sea rift which is bounded by two major strike slip faults the jericho and the arava faults we investigated the young tectonic activity along the jericho fault by excavating trenches up to 3 5 m deep across its trace the trenches penetrate through late pleistocene and holocene sediments we found that a zone up to 15 m wide of disturbed sediments exists along the fault these disturbed sediments provide evidence for two periods of intensive activity or more likely for two major earthquakes that occurred during the last 2000 years the earthquakes are evident in small faults vertical throw of a few layers cracks unconformities and wide fissures we further documented evidence for recent sinistral shear along the jericho fault in deformed sediments and damage to an 8th century palace on a subsidiary fault we suggest that the two earthquakes may be correlated with the 31 b c earthquake and the 748 a d earthquake reported by the ancients