spatial and temporal variation of summer precipitation over the eastern tibetan plateau and the north atlantic oscillation abstract the interannual variability of summer precipitation over the eastern tibetan plateau etp was examined in relation to the northern hemisphere macroscale circulation patterns during the period 1961 90 summer precipitation data for 66 stations located above 2000 m msl are used in the analysis using principal component analysis it is found that the dominant spatial pattern of interannual variability of the summer precipitation is a seesaw structure between the southern and northern parts of etp correlation analysis shows that this pattern of precipitation anomalies is closely associated with the north atlantic oscillation nao further analysis based on midtropospheric geopotential height and wind data suggests the upstream zonal flow variation associated with the nao pattern as the major mechanism linking the regional precipitation fluctuation to macroscale circulation conditions during the summers of low nao index values the westerly winds between 40 and 50 n from the eastern atlantic to

modeling the effect of wave current interaction on the three dimensional wind driven circulation of the eastern irish sea abstract a high resolution 0 5 north south by 1 0 west east three dimensional hydrodynamic model of the eastern irish sea is used to examine the influence of enhanced bed friction due to wind wave effects upon the three dimensional wind induced circulation of the eastern irish sea the model uses a mixed finite difference modal approach in which a standard finite difference grid is employed in the horizontal with the galerkin method with an expansion of functions modes in the vertical giving a continuous current profile from sea surface to seabed vertical eddy viscosity within the model is a function of the flow field the model is used to examine the wind induced response of the area to spatially uniform and constant in time northerly and westerly wind stresses of 1 n m 2 the effect upon bed stresses and hence the three dimensional circulation of the region of enhanced bed turbulence due to wind wave effects is also considered using idealized wave fields changes in bed stress particularl

onset of maikop sedimentation and cessation of eocene arc volcanism in the talysh mountains azerbaijan the maikop series forms an important source rock in the former paratethys deposition is often interpreted as anoxic linked to restriction of the paratethys the pirembel formation in the talysh mountains azerbaijan is attributed to the maikop series and was deposited above the eocene volcanic peshtasar formation dating the onset of anoxia could help to distinguish glacio eustatic from tectonic causes of restriction we integrated magnetostratigraphy and biostratigraphy to date the onset of pirembel sedimentation and used geochemistry to characterize the tectonic setting of the peshtasar volcanic rocks the onset of maikop sedimentation in the talysh was determined to be 37 7 ma ruling out a link with the major sea level drop at the eocene oligocene transition 33 9 ma and favouring a tectonic cause extrapolating the average sedimentation rate 34 cm kyr suggests that the entire pirembel formation belongs to the late eocene we hypothesize that the end of volcanism is important in the transition to pirembel sedimentation the palaeomagnetic and geochemistry results for the volcanic rocks cluster in three groups suggesting three distinct episodes of volcanism volcanic sills within the eocene arkevan formation plot exactly on these groups confirming the relationship between the arkevan and peshtasar formations volcanic rocks of the talysh show continental arc signatures and may be related to an eocene volcanic belt extending towards southeastern iran

lake seasonality across the tibetan plateau and their varying relationship with regional mass changes and local hydrology the recent growth and deepening of inland lakes in the tibetan plateau tp may be a salient indicator of the consequences of climate change the seasonal dynamics of these lakes is poorly understood despite this being potentially crucial for disentangling contributions from glacier melt and precipitation which are all sensitive to climate to lake water budget using in situ observations satellite altimetry and gravimetry data we identified two patterns of lake level seasonality in the central northern and northeastern tp lake levels are characterized by considerable increases during warm seasons and decreases during cold seasons which is consistent with regional mass changes related to monsoon precipitation and evaporation in the northwestern tp however lake levels exhibit dramatic increases during both warm and cold seasons which deviate from regional mass changes this appears to be more connected with high spring snowfall and large summer glacier melt the variable lake level response to different drivers indicates heterogeneous sensitivity to climate change between the northwestern tp and other regions

lake volume and groundwater storage variations in tibetan plateau s endorheic basin the tibetan plateau tp the highest and largest plateau in the world with complex and competing cryospheric hydrologic geodynamic processes is particularly sensitive to anthropogenic warming the quantitative water mass budget in the tp is poorly known here we examine annual changes in lake area level and volume during 1970s 2015 we find that a complex pattern of lake volume changes during 1970s 2015 a slight decrease of 2 78 gt yr 1 during 1970s 1995 followed by a rapid increase of 12 53 gt yr 1 during 1996 2010 and then a recent deceleration 1 46 gt yr 1 during 2011 2015 we then estimated the recent water mass budget for the inner tp 2003 2009 including changes in terrestrial water storage lake volume glacier mass snow water equivalent swe soil moisture and permafrost the dominant components of water mass budget namely changes in lake volume 7 72 0 63 gt yr 1 and groundwater storage 5 01 1 59 gt yr 1 increased at similar rates we find that increased net precipitation contributes the majority of water supply 74 for the lake volume increase followed by glacier mass loss 13 and ground ice melt due to permafrost degradation 12 other term such as swe 1 makes a relatively small contribution these results suggest that the hydrologic cycle in the tp has intensified remarkably during recent decades

magnetosusceptibility event and cyclostratigraphy method applied to marine rocks detrital input versus carbonate productivity magnetic susceptibility data from marine rocks can be used for global correlation due to synchronous variations in global erosion we show here that the magnetic susceptibility signature found in two forms resides mainly in paramagnetic and other detrital constituents in most marine rocks the first form is a short term low magnitude high frequency cyclic climate signature that is often useful for regional correlation the second form is a longer term higher magnitude low frequency signature resulting from transgressive and regressive events that can be used for global correlation fluctuations in detrital input due to eustatic based erosion are the primary cause of events these fluctuations are driven by large scale processes such as global orogenic cycles however variations in carbonate productivity cannot be ruled out when explaining the low magnitude climate driven cyclicity also observed in magnetic susceptibility data sets

near bed turbulence and relict waveformed sand ripples observations from the inner shelf 1 results are presented from a field investigation of near bed turbulence above degrading waveformed sand ripples in 17 m water depth on the inner shelf the heights of the 50 cm wavelength primary ripples were about 5 cm at the start of the observation period and decreased by a factor of 2 within 15 days the principal degradation mechanism involved fish making pits in the seafloor near bed turbulent kinetic energy dissipation rates are estimated both from the energy spectrum and from the vertical structure function within the inertial subrange and ranged from 0 1 10 6 to 3 10 6 w kg the friction velocity u at the bed ranged from 0 3 to 0 5 cm s and the wave friction factor fw from 0 017 to 0 02 the nearbed turbulence intensities and consequently the estimated values of u2 and fw are likely too small by a factor of 2 partly to satisfy the smooth wall constraint and partly to account for the effects of small scale turbulence within the finite volume range cells of the coherent doppler system used to make the turbulence estimates finally the results indicate that the hydraulic roughness of relict ripples is likely a function of both ripple height and steepness and that the relative roughness should also depend on the near bed wave orbital excursion for modeling purposes nielsen s ripple roughness formula is recommended with a reduced proportionality constant to account for the effects of irregular wave forcing and non equilibrium ripple history

a suspended sediment stratification correction for combined wave and current flows a simple model for the near bottom combined wave and current flow over a moveable sediment bed is presented the model is an extension of the grant and madsen 1979 combined wave and current model with moveable bed effects on the physical bottom roughness included as by grant and madsen 1982 the unsteady conservation of fluid momentum and sediment mass equations which are coupled through an eddy diffusivity closure scheme are solved for the wave and current velocity profiles along with the suspended sediment concentration and transport profiles sample runs are presented to illustrate the effect of varying wave conditions on the current the mean sediment concentration and the mean sediment transport results show that for fine to medium sands self stratification of the flow can be important during storms owing to the large amount of sediment suspended by the waves and the enhanced turbulent mixing associated with the wave current interaction the theory easily can be generalized for inclusion in a full ekman layer model

modeling bottom roughness in the presence of wave generated ripples 1 near bottom wave current and microtopography measurements have been obtained at the leo 15 site off the southern coast of new jersey the measurements are used in conjunction with a recently calibrated continental shelf bottom boundary layer model to refine estimates of bottom roughness for a rippled bed under combined wave and current flows in the presence of nearly two dimensional wave generated ripples application of the grant and madsen 1979 type bottom boundary layer model produces estimates of the bottom roughness felt by the current that are several times greater than established formulations for rippled beds under waves modifying one of the primary length scales in the eddy viscosity profiles returns estimates that are more consistent with the wave roughness results application of the roughness model in conjunction with a refined empirical ripple geometry model produces highly accurate estimates of measured shear velocities and apparent roughnesses during a moderate storm the demonstrated accuracy of this simple combined roughness and ripple geometry formulation reveals its utility when considering applications of coupled bottom boundary layer shelf circulation models

momentum balances on the north carolina inner shelf four months of moored current pressure temperature conductivity wave and wind observations on the north carolina shelf indicate three dynamically distinct regions the surf zone the inner shelf between the surf zone and the 13 m isobath and the midshelf in the surf zone the along shelf momentum balance is between the cross shelf gradient of the wave radiation stress and the bottom stress the linear drag coefficient in the surf zone is about 10 times larger than seaward of the surf zone on the inner shelf the along shelf momentum balance is also frictional the along shelf wind stress and pressure gradient are balanced by bottom stress in the cross shelf momentum balance the pressure gradient is the superposition of roughly equal contributions from the coriolis force geostrophy and wave setdown from shoaling unbroken surface gravity waves at midshelf the along shelf momentum balance is less frictional and hence flow accelerations are important the cross shelf momentum balance is predominantly geostrophic because the greater depth and smaller bottom slope at midshelf reduce the importance of wave setdown the cross shelf density gradient is in thermal wind balance with the vertical shear in the along shelf flow in depths as shallow as 10 m the dominant along shelf momentum balances provide a simple estimate of the depth averaged along shelf current in terms of the measured forcing i e wind stress wave radiation stress divergence and along shelf pressure gradient that reproduces accurately the observed cross shelf variation of the depth averaged along shelf current between the surf zone and midshelf

integrated biomagnetostratigraphy of the alano section ne italy a proposal for defining the middle late eocene boundary the alano section has been presented at the international subcommission on paleogene stratigraphy isps as a potential candidate for defi ning the global boundary stratotype section and point gssp of the late eocene priabonian stage the section is located in the venetian southern alps of the veneto region ne italy which is the type area of the priabonian being exposed along the banks of the calcino torrent near the village of alano di piave it consists of 120 130 m of bathyal gray marls interrupted in the lower part by an 8 m thick package of laminated dark to black marlstones intercalated in the section there are eight prominent marker beds six of which are crystal tuff layers whereas the other two are bioclastic rudites these distinctive layers are useful for regional correlation and for an easy recognition of the various intervals of the section the section is easily accessible crops out continuously is unaffected by any structural deformation is rich in calcareous plankton and contains an expanded record of the critical interval for defi ning the gssp of the priabonian in order to further check the stratigraphic completeness of the section and constrain in time the critical interval for defi ning the priabonian stage we performed a high resolution study of integrated calcareous plankton biostratigraphy and a detailed magnetostratigraphic analysis here we present the results of these studies to open a discussion on the criteria for driving the golden spike that should define the middle eocene late eocene boundary

a numerical study of wave current interaction through surface and bottom stresses wind driven circulation in the south atlantic bight under uniform winds the influences of surface waves on ocean currents in the coastal waters of the south atlantic bight are investigated by using a coupled wave current modeling system the ocean circulation model employed is the three dimensional princeton ocean model pom and the wave model invoked is an improved third generation wave model wam the coupling procedure between the pom and the wam and the simulated coastal ocean circulation driven by uniform surface winds are presented the simulated results show that wind waves can significantly affect coastal ocean currents not only through an enhancement of wind stress but also through a modification of bottom stress wave induced wind stress increases the magnitude of currents both at the surface and near the seabed on the other hand wave induced bottom stress weakens the currents both at the sea surface and near the seabed therefore the net effect of surface wind waves on currents depends on the relative importance of current modulations by wave induced wind stress and bottom stress the results further indicate that at a fixed location the relative importance of wave induced surface and bottom shear stresses in coastal ocean circulation depends on the surface wind field for the constant wind cases considered in this study the effect of wave induced bottom stress is more significant in along shore wind conditions than in cross shore wind conditions

detrital sediment fluxes from continents to oceans abstract detrital sediment is carried from land to the sea by three agents rivers glaciers and winds the shoreline is an arbitrary boundary within the detrital sediment transport system which extends from a site of origin across areas of temporary storage to a site of long term deposition the most important of the agents moving sediment across the land is river transport estimated to be in the order of 20 10 12 kg of sediment annually at present analysis of drainage basins indicates that relief and runoff are the most important factors in determining the sediment load of rivers the competence of rivers to transport sediment is governed by the volume flow gradient and the sediment load itself today most large rivers are fed by snowmelt in highland areas runoff from rainfall in the drainage basin and groundwater inflow along the river course water is lost to evaporation and groundwater infiltration river courses can often be divided into two segments a degradational section in which the gradient is relatively steep and little temporary storage of sediment takes place and an aggradational section where the gradient is sharply reduced through meandering and where large scale temporary sediment storage forms a flood plain lakes trap sediment inland and prevent its transport to the sea today many high and mid latitude rivers are interrupted by lakes of glacial origin there are also some large areas of internal drainage that deliver no sediment to the sea the load carried by rivers has been markedly altered by human activity and may have doubled over the past few thousand years only to be reduced in the past century by the widespread construction of dams the ancient use of fire in hunting and its subsequent use in clearing land has increased erosion extensive deforestation and cultivation processes have also increased the sediment supply dam construction is a relatively new factor and affects the sediment transport system by trapping sediment before it can reach the sea the resulting lower sediment supply from rivers is at least in part compensated by increased coastal erosion glacial erosion is difficult to estimate there is an ongoing controversy whether ice sheets are effective erosive agents or not estimates of the present global flux of glacial detritus range from 0 8 50 10 12 kg annually with the lower value most probable the dust flux is in the order of 0 5 to 0 9 10 12 kg annually but may vary greatly with time

stratigraphy and geochemical characterization of the oligocene miocene maikop series implications for the paleogeography of eastern azerbaijan abstract the oligocene miocene maikop series is a world class source rock responsible for much of the oil and gas found in the south caspian basin it is composed of up to 3 km of marine mudstone and contains a nearly continuous record of deposition during progressive tectonic closure of the basin as the arabian peninsula converged northward into eurasia historically the stratigraphy of this interval has been difficult to define due to the homogenous nature of the fine grained clay dominated strata outcrop exposures in eastern azerbaijan allow direct observation and detailed sampling of the interval yielding a more comprehensive stratigraphic context and a more advanced understanding of syndepositional conditions in the eastern paratethys sea specifically the present investigation reveals that coupling field based stratigraphic characterization with geochemical analyses e g bulk elemental geochemistry rock eval pyrolysis bulk stable isotope geochemistry yields a more robust understanding of internal variations within the maikop series samples from seven sections located within the shemakha gobustan oil province reveal consistent stratigraphic and spatial geochemical trends it is proposed that the maikop series be divided into three members based on these data along with lithostratigraphic and biostratigraphic data reported herein when comparing rupelian early oligocene and chattian late oligocene strata the rupelian age strata commonly possess higher toc values more negative 15 n tot values more positive 13 c org values and higher radioactivity relative to chattian age rocks the trace metals mo and v normalized to al are positively correlated with toc with maximum values occurring at the rupelian chattian boundary and overall higher average values in the rupelian across the oligocene miocene boundary a slight drop in v al mo al ratios is observed along with drops in s and toc these results indicate that geochemical signatures of the maikop series are regional in nature and furthermore that analogous fine grained sections may be better characterized and subdivided using similar techniques in general geochemical indicators suggest that the basin was in limited communication with the tethys sea throughout the oligocene early miocene with suboxic to anoxic conditions present during the oligocene and to a lesser extent in the miocene this increased isolation was likely due to tectonic uplift to both the south and north of the study area and greatly enhanced by global sea level fluctuations these data serve as the basis for a more detailed understanding of the tectonic evolution of the region and support a standardized chemostratigraphic division of the important petroleum source interval

arabia eurasia continental collision insights from late tertiary foreland basin evolution in the alborz mountains northern iran a poorly understood lag time of 15 20 m y exists between the initial arabia eurasia continental collision in late eocene to early oligocene time and the acceleration of tectonic and sedimentary processes across the collision zone in the early to late miocene the late eocene to miocene pliocene clastic and shallow marine sedimentary rocks of the kond eyvanekey and semnan basins in the alborz mountains northern iran offer the possibility to track the evolution of this orogen in the framework of collision processes a transition from volcaniclastic submarine deposits to shallow marine evaporites and terrestrial sediments occurred shortly after 36 ma in association with reversals in sediment provenance strata tilting and erosional unroofing these events followed the termination of subduction arc magmatism and marked a changeover from an extensional to a contractional regime in response to initiation of continental collision with the subduction of stretched arabian lithosphere this early stage of collision produced topographic relief associated with shallow foreland basins suggesting that shortening and tectonic loading occurred at low rates starting from the early miocene 17 5 ma flexural subsidence in response to foreland basin initiation occurred fast sediment accumulation rates and erosional unroofing trends point to acceleration of shortening by the early miocene we suggest that the lag time between the initiation of continental collision 36 ma and the acceleration of regional deformation 20 17 5 ma reflects a two stage collision process involving the soft collision of stretched lithosphere at first and hard collision following the arrival of unstretched arabian continental lithosphere in the subduction zone

the origin of hydrocarbon source rocks in the austrian molasse basin eocene oligocene transition organic rich rocks schoneck formation from five wells representing a section across the northern paleo slope of the austrian molasse basin were studied using a multi method approach including petrography x ray diffraction organic and inorganic geochemistry and c and n isotopes of the organic material organic matter accumulation commenced during the latest eocene and was dependent on variations of currents salinity organic productivity and nutrient supply initial marl deposition and phosphorite formation under dysoxic conditions was followed by organic rich mud deposition associated with benthic and photic zone anoxia this paleoceanographic situation resembles the first isolation of the western central paratethys deposition of organic rich rocks terminated during lower oligocene time when changing current patterns and decreasing salinity caused a breakdown of water column stratification even though the schoneck formation is an excellent source rock major differences exist in the petroleum potential of the schoneck formation deposited in upper and lower basin slope settings the schoneck formation from the upper slope is characterised by toc contents up to 12 and hi values between 500 and 600 mghc gtoc in the lower slope settings toc values are generally below 2

geodynamics seismicity and seismic hazards of the caucasus abstract being a part of ongoing continental collision between the arabian and eurasian plates the caucasus region is a remarkable site of moderate to strong seismicity where devastating earthquakes caused significant losses of lives and livelihood in this article we survey geology and geodynamics of the caucasus and its surroundings magmatism and heat flow active tectonics and tectonic stresses caused by the collision and shortening gravity and density models and overview recent geodetic studies related to regional movements the tectonic development of the caucasus region in the mesozoic cenozoic times as well as the underlying dynamics controlling its development are complicated processes it is clear that the collision is responsible for a topographic uplift inversion and for the formation of the fold and thrust belts of the greater and lesser caucasus tectonic deformations in the region is influenced by the wedge shaped rigid arabian block indenting into the relatively mobile region and producing near n s compressional stress and seismicity in the caucasus regional seismicity is analysed with an attention to sub crustal seismicity under the northern foothills of the greater caucasus which origin is unclear whether the seismicity associated with a descending oceanic crust or thinned continental crust recent seismic tomography studies are in favour of the detachment of a lithospheric root beneath the lesser and greater caucasus the knowledge of geodynamics seismicity and stress regime in the caucasus region assists in an assessment of seismic hazard and risk we look finally at existing gaps in the current knowledge and identify the problems which may improve our understanding of the regional evolution active tectonics geodynamics shallow and deeper seismicity and surface manifestations of the lithosphere dynamics among the gaps are those related to uncertainties in regional geodynamic and tectonic evolution e g continental collision and associated shortening and exhumation lithosphere structure deformation and strain stress partitioning and to the lack of comprehensive datasets e g regional seismic catalogues seismic gravity and geodetic surveys

mantle vs crustal fluid sources in the gas discharges from lesser caucasus and talysh mountains azerbaijan in relation to the regional geotectonic setting abstract azerbaijan is famous for the impressive phenomenon of mud volcanism that dominates the landscape of the central sector of the country the gases released are here strongly ch4 enriched conversely the lesser caucasus to the nw host numerous thermo mineral springs into which co2 rich gas are bubbling in the talysh area located to se at the border with iran ch4 n2 and co2 rich gases are discharged the chemical and isotopic composition of the free gases from the lesser caucasus and talysh was investigated to define their origin in a particularly complex geodynamical and geological setting the co2 in the lesser caucasus was apparently associated with thermometamorphic processes affecting the jurassic and cretaceous limestones at which a minor contribution by a mantle component helium was also recognized likely related to oceanic subduction and or fluid interactions with the accreted ophiolite complex the fold zone of talysh which represents the northern extension of the iranian alborz chain produced the early and middle eocene to pleistocene volcanism that was invoked to explain the distinct chemical and isotopic composition of the discharged gases the co2 rich gases at buludul showed helium and carbon isotopic ratios that suggested mixing processes between i a crustal component produced by hydrolysis of limestones and interaction with volcano sedimentary complexes rich in organic material and ii tectonically driven mantle derived fluids the relatively high rc ra values 6 are indeed comparable with those recorded in the active volcanoes of the region indicating the presence of degassing magmas at depth finally typical hydrothermal gas compounds e g co and h2s were not detected in both the study areas unless secondary processes at shallow depth are occurring the presence of developed hydrothermal systems at regional scale is unlikely

zagros orogeny a subduction dominated process this paper presents a synthetic view of the geodynamic evolution of the zagros orogen within the frame of the arabia eurasia collision the zagros orogen and the iranian plateau preserve a record of the long standing convergence history between eurasia and arabia across the neo tethys from subduction obduction processes to present day collision from 150 to 0 ma we herein combine the results obtained on several geodynamic issues namely the location of the oceanic suture zone the age of oceanic closure and collision the magmatic and geochemical evolution of the eurasian upper plate during convergence as testified by the successive sanandaj sirjan kermanshah and urumieh dokhtar magmatic arcs the p t t history of the few zagros blueschists the convergence characteristics across the neo tethys kinematic velocities tomographic constraints subduction zones and obduction processes together with a survey of recent results gathered by others we provide lithospheric scale reconstructions of the zagros orogen from 150 to 0 ma across two sw ne transects the evolution of the zagros orogen is also compared to those of the nearby turkish and himalayan orogens in our geotectonic scenario for the zagros convergence we outline three main periods regimes 1 the mid to late cretaceous 115 85 ma corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper plate fragmentation 2 the paleocene eocene 60 40 ma witnesses slab break off major shifts in arc magmatism and distributed extension within the upper plate and 3 from the oligocene onwards 30 0 ma collision develops with a progressive sw migration of deformation and topographic build up sanandaj sirjan zone 20 15 ma high zagros 12 8 ma simply folded belt 5 0 ma and with partial slab tear at depths 10 ma to present our reconstructions underline the key role played by subduction throughout the whole convergence history we finally stress that such a long lasting subduction system with changing boundary conditions also makes the zagros orogen an ideal natural laboratory for subduction processes

quantifying the contribution of glacier meltwater in the expansion of the largest lake in tibet lake siling co is currently the largest endorheic lake in tibet and the lake surface area has expanded by about 40 since the 1970s with a remarkable acceleration after 1999 in this study a hydrologic modeling framework was established by linking the variable infiltration capacity vic land surface hydrologic model with the degree day glacier melt model over the lake siling co basin with an aim to quantify the contribution of each runoff component to changes in the lake storage we found that glacier melt contributed to less than 10 of the total water input to the lake during 1979 2013 while precipitation induced runoff in nonglacierized area was responsible for about 67 75 the mean annual water input to the lake increased by 2 15x10 9 m 3 yr 1 in 2000 2013 relative to that in 1979 1999 the amount of precipitation over the lake surface precipitation induced runoff and glacier melt runoff accounted for 13 82 and 5 of this total increase respectively suggesting that the substantial expansion of siling co in the 2000s was mostly due to the increase in precipitation induced runoff when modeling lake level changes during 1979 2013 we found that the water level rose by 14 1m when glacier melt was included and by only 10 5m a reduction of about one fourth when glacier melt was removed it is concluded that glacier melt played an important role in controlling the water level of siling co although it only contributed less than 10 of water input to the lake during 1979 2013

volcanic belts as markers of the mesozoic cenozoic active margin of eurasia abstract from the triassic to the present linear belts of calc alkaline volcanism developed along the southern margin of eurasia in the triassic the calc alkaline belt can be traced in turan fore caucasus crimea and dobrogea its development is related to the closure of the paleo tethys when fragments of gondwana iran afghanistan etc were approaching eurasia since the early jurassic calc alkaline volcanism has been related to subduction of the oceanic crust of the mesozoic tethys five stages of calc alkaline volcanic activity can be distinguished early jurassic middle jurassic early cretaceous late cretaceous paleogene and late miocene quaternary the configuration of the volcanic belts the intensity of the volcanism and the chemistry of the erupted products change considerably from stage to stage mesozoic belts were most pronounced in the pontian transcaucasian segment of the margin starting from the late cretaceous and especially in the cenozoic the volcanic belts can be continuously traced from the balkans to afghanistan most of the belts were actually island arcs formed on the fragments of the hercynian of baikalian basement and in this respect similar to the island arc of japan only the incipient island arcs of senonian age formed close to the passive margin of gondwana are the exceptions they were built on oceanic crust and are geochemically close to the mariana arc at certain times early jurassic eocene parallel chains of island arcs existed in general the situation resembled the present day convergent boundary in the western pacific as closure of the tethys proceeded island arcs gave way to marginal continental volcanic belts with wide spread development of high potassium particularly shoshonitic series peaks of volcanic activity in the bajocian late cretaceous eocene and late miocene present alternated with quiet periods and corresponded to the times when the convergence rate between africa and eurasia increased the opening of the back arc basins is reflected in outbursts of basaltic rift type volcanism these outbursts occurred in the toarcian aalenian bathonian late jurassic aptian turonian and early middle eocene

circumglobal teleconnection in the northern hemisphere summer analysis of the 56 yr ncep ncar reanalysis data reveals a recurrent circumglobal teleconnection cgt pattern in the summertime midlatitude circulation of the northern hemisphere this pattern represents the second leading empirical orthogonal function of interannual variability of the uppertropospheric circulation the cgt having a zonal wavenumber 5 structure is primarily positioned within a waveguide that is associated with the westerly jet stream the spatial phases of cgt tend to lock to preferred longitudes the geographically phase locked patterns bear close similarity during june august and september but the pattern in july shows shorter wavelengths in the north pacific north america sector the cgt is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western europe european russia india east asia and north america this implies that the cgt may be a source of climate variability and predictability in the above mentioned midlatitude regions the cgt has significant correlations with the indian summer monsoon ism and el nino southern oscillation enso however in normal ism years the cgt enso correlation disappears on the other hand in the absence of el nino or la nina the cgt ism correlation remains significant it is suggested that the ism acts as a conductor connecting the cgt and enso when the interaction between the ism and enso is active enso may influence northern china via the ism and the cgt additionally the variability of the cgt has no significant association with the arctic oscillation and the variability of the western north pacific summer monsoon the circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of india where a baroclinic circulation structure dominates two possible scenarios are proposed the abnormal ism may excite an anomalous west central asian high and downstream rossby wave train extending to the north pacific and north america on the other hand a wave train that is excited in the jet exit region of the north atlantic may affect the westcentral asian high and thus the intensity of the ism it is hypothesized that the interaction between the global wave train and the ism heat source may be instrumental in maintaining the boreal summer cgt

review and revision of cenozoic tropical planktonic foraminiferal biostratigraphy and calibration to the geomagnetic polarity and astronomical time scale planktonic foraminifera are widely utilized for the biostratigraphy of cretaceous and cenozoic marine sediments and are a fundamental component of cenozoic chronostratigraphy the recent enhancements in deep sea drilling recovery multiple coring and high resolution sampling both offshore and onshore has improved the planktonic foraminiferal calibrations to magnetostratigraphy and or modified species ranges this accumulated new information has allowed many of the planktonic foraminiferal bioevents of the cenozoic to be revised and the planktonic foraminiferal calibrations to be reassessed we incorporate these developments and amendments into the existing biostratigraphic zonal scheme in this paper we present an amended low latitude tropical and subtropical cenozoic planktonic foraminiferal zonation we compile 187 revised calibrations of planktonic foraminiferal bioevents from multiple sources for the cenozoic and have incorporated these recalibrations into a revised cenozoic planktonic foraminiferal biochronology we review and synthesize these calibrations to both the geomagnetic polarity time scale gpts of the cenozoic and astronomical time scale ats of the neogene and late paleogene on the whole these recalibrations are consistent with the previous work however in some cases they have led to major adjustments to the duration of biochrons recalibrations of the early middle eocene first appearance datums of globigerinatheka kugleri hantkenina singanoae guembelitrioides nuttalli and turborotalia frontosa have resulted in large changes in the durations of biochrons e7 e8 and e9 we have introduced upper oligocene zone o7 utilizing the biostratigraphic utility of paragloborotalia pseudokugleri for the neogene period major revisions are applied to the fohsellid lineage of the middle miocene and we have modified the criteria for recognition of zones m7 m8 and m9 with additional adjustments regarding the globigerinatella lineage to zones m2 and m3 the revised and recalibrated datums provide a major advance in biochronologic resolution and a template for future progress of the cenozoic time scale

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

wave formed structures and paleoenvironmental reconstruction clifton h e and dingier j r 1984 wave formed structures and paleoenvironmental reconstruction in b greenwood and r a davis jr editors hydrodynamics and sedimentation in wave dominated coastal environments mar geol 60 165 198 wave formed sedimentary structures can be powerful interpretive tools because they reflect not only the velocity and direction of the oscillatory currents but also the length of the horizontal component of orbital motion and the presence of velocity asymmetry within the flow several of these aspects can be related through standard wave theories to combinations of wave dimensions and water depth that have definable natural limits for a particular grain size threshold of particle movement and that of conversion from a rippled to fiat bed indicate flow velocity limits the ratio of ripple spacing to grain size provides an estimate of the length of the near bottom orbital motion the degree of velocity asymmetry is related to the asymmetry of the bedforms though it presently cannot be estimated with confidence a plot of water depth versus wave height h h diagram provides a convenient approach for showing the combination of wave parameters and water depths capable of generating any particular structure in sand of a given grain size natural limits on wave height and inferences or assumptions regarding either water depth or wave period based on geologic evidence allow refinement of the paleoenvironmental reconstruction the assumptions and the degree of approximation involved in the different techniques impose significant constraints inferences based on wave formed structures are most reliable when they are drawn in the context of other evidence such as the association of sedimentary features or progradational sequences

palaeomagnetic results from upper triassic red beds and camp lavas of the argana basin morocco abstract the continental argana basin of morocco is the trans atlantic counterpart of the extensively studied fundy hartford and newark basins in north eastern america that have provided the astrochronologically tuned geomagnetic polarity timescale gpts for the late triassic and earliest jurassic the argana red bed successions also show astronomically driven time control which allowed trans atlantic correlations and revealed that the interval towards volcanism of the central atlantic magmatic province camp is without any significant hiatuses here we present palaeomagnetic results from the cyclically bedded upper triassic red beds and the intercalated volcanics associated with camp our composite argana section comprises an interval of 3 5 4 0 ma but its magnetostratigraphic pattern does not allow a straightforward correlation to the newark gpts the continental red bed deposits of the bigoudine formation demonstrate a dominant magnetic overprint that could only be removed at temperatures above 600 c we suggest that this overprint could have been caused by a period of jurassic c 170 ma magmatism that caused pervasive overprinting of the triassic palaeomagnetic signal correlations between the sections in the tazantoute region are not straightforward hampered by the presence of a magmatic sill the camp lava sequences of tazantoute are all of normal polarity and record secular variation in a manner that agrees with short lived pulses of camp activity in morocco our results indicate that the sedimentary successions of the argana basin have the potential to evaluate the newark gpts but that detailed palaeomagnetic analyses of more suitable sections with long er cyclostratigraphic records are required

geochemical evaluation of hydrocarbons and their potential sources in the western south caspian depression republic of azerbaijan abstract the western south caspian depression located in offshore azerbaijan contains significant accumulations of oil and gas in upper tertiary fluvial deltaic sediments the active tertiary hydrocarbon system is a product of unique paleogeographic and tectonic events that led to paleogene deposition of organic rich source rocks rapid pliocene subsidence concurrent with voluminous supply of clastic sediments and development of anticlinal traps with abundant shale diapirs molecular characterization of selected oil samples indicates most of the oils are sourced from similar organic facies the molecular characteristics are consistent with oils sourced from a tertiary slightly calcareous marine clastic facies examination of oil molecular characteristics oil oil correlations molecular characteristics of selected source rock samples maturation models and potential migration pathways suggests the oil is not syngenetic but most likely sourced from deeper miocene and older marine shales most of the oils have low to moderate organic maturities vre 0 75 0 85 relative to conventional peak generation windows significant variations in oil gravity and whole oil gas chromatogram character suggest post emplacement bacterial and fractionation alteration several oils display characteristics consistent with multiple phases of trap charging the bulk of reservoired gases examined in this study have been sourced from mixed terrestrial marine kerogen generated at organic maturities of vre 0 80 1 00 with some biogenic low maturity mixing none of the gases examined were sourced from the thermal destruction of liquid hydrocarbons we postulate multi stage hydrocarbon emplacement into evolving structural traps the first phase of emplacement occurred in the middle pliocene when tectonic movement and increased subsidence initiated early trap reservoir formation hydrocarbon generation and migration late rapid subsidence from quaternary tectonic activity produced additional hydrocarbons to replenish older depleted traps and charge newly formed traps this late tectonic activity also extensively redistributed hydrocarbon accumulations degassed some that were breached by faults and destroyed other oil pools thermal disequilibrium from the rapid subsidence delayed hydrocarbon generation and increased the minimum depth required for the onset of liquid hydrocarbon generation

retrodeforming the arabia eurasia collision zone age of collision versus magnitude of continental subduction the arabia eurasia collision has been linked to global cooling the slowing of africa mediterranean extension the rifting of the red sea an increase in exhumation and sedimentation on the eurasian plate and the slowing and deformation of the arabian plate collision age estimates range from the late cretaceous to pliocene with most estimates between 35 and 20 ma we assess the consequences of these collision ages on the magnitude and location of continental consumption by compiling all documented shortening within the region and integrating this with plate kinematic reconstructions shortening estimates across the orogen allow for 350 km of neogene upper crustal contraction necessitating collision by 20 ma a 35 ma collision requires additional subduction of 400 600 km of arabian continental crust using the oman ophiolite as an analogue ophiolitic fragments preserved along the zagros suture zone permit 180 km of subduction of the arabian continental margin plus overlying ophiolites wholesale subduction of this more dense continental margin plus ophiolites would reconstruct 400 500 km of postcollisional arabia eurasia convergence consistent with a ca 27 ma initial collision age this younger arabia eurasia collision suggests a noncollisional mechanism for the slowing of africa and associated extension

the shutdown of an anoxic giant magnetostratigraphic dating of the end of the maikop sea abstract paratethys the lost sea of central eurasia was an anoxic giant during oligocene early miocene maikop series times with a size matching the modern day mediterranean sea and a history of anoxic conditions that lasted for over 20 myrs the eastern part of this realm black sea caspian sea domain holds key records for understanding the build up maintenance and collapse of anoxia in marginal seas here we show that the collapse of anoxic maikop conditions was caused by middle miocene paleogeographic changes in the paratethys gateway configuration when a mid langhian badenian tarkhanian transgression flooded and oxygenated the eastern paratethys we present an integrated magneto biostratigraphic framework for the early middle miocene tarkhanian chokrakian karaganian regional stages of the eastern paratethys and date the lithological transition from anoxic black shales of the maikop series to fossiliferous marine marls and limestones of the regional tarkhanian stage for this purpose we selected two long and time equivalent sedimentary successions exposed along the belaya and the pshekha rivers in the maikop type area in ciscaucasia southern russia we show that a significant but short marine incursion took place during the tarkhanian ending the long lasting maikop anoxia of the basin our magnetostratigraphic results reveal coherent polarity patterns which allow a straightforward correlation with the time interval 15 12 ma of the geomagnetic polarity time scale the tarkhanian flooding occurred during a relatively short normal polarity interval that correlates with c5bn resulting in an age of 14 85 ma the regional tarkhanian chokrakian stage boundary is located within c5adn at an age of 14 75 ma and the chokrakian karaganian boundary is tentatively correlated with c5acn and an age of 13 9 13 8 ma our new tarkhanian flooding age reveals a paleogeographic scenario that is different from many previous reconstructions instead of envisaging marine connections to the indian ocean we show that major changes in connectivity between the eastern and central paratethys seas have caused the influx of marine waters during the tarkhanian an increase in marine connectivity with the mediterranean during a short episode of rapid sea level rise triggered mixing and ended the widespread anoxia in the eastern paratethys the mixing episode was short lived 100 kyr as the sea level rise slowed down and connectivity degraded because of tectonic uplift in the gateway area

enso variability reflected in precipitation oxygen isotopes across the asian summer monsoon region abstract oxygen isotope signals 18 o from paleo archives are important proxies for past asian summer monsoon asm climate reconstruction however causes of interannual variation in the 18 o values of modern precipitation across the asm region remain in argument we report interannual 18 o variation in southern tibetan plateau precipitation based on long term observations at lhasa these data together with precipitation 18 o records from five global network of isotopes in precipitation gnip stations and two ice core 18 o records were used to define a regional metric of asm precipitation 18 o asmoi back trajectory analyses for rainy season precipitation events indicate that moisture sources vary little between years with relatively high and low 18 o values a result that is consistent for the south lhasa southeast bangkok and east asm regions hong kong in contrast 18 o values at these three locations are significantly correlated with convection in the estimated source regions and along transport paths these results suggest that upstream convection rather than moisture source change causes interannual variation in asm precipitation 18 o values contrasting values of the asmoi in el nino and la nina years reveal a positive isotope el nino southern oscillation enso response e g high values corresponding to warm phases which we interpret as a response to changes in regional convection we show that the isotope enso response is amplified at high elevation sites and during la nina years these findings should improve interpretations of paleo 18 o data as a proxy for past asm variation and provide new opportunities to use data from this region to study paleo enso activity

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

depositional environment and hydrocarbon source potential of the oligocene ruslar formation kamchia depression western black sea abstract the oligocene ruslar formation is a hydrocarbon source rock in the kamchia depression located in the western black sea area depositional environment and source potential of the predominantly pelitic rocks were investigated using core and cuttings samples from four offshore wells in these wells the ruslar formation is up to 500 m thick based on lithology and well logs the ruslar formation is subdivided from base to top into units i vi dysoxic to anoxic conditions and mesohaline to euhaline salinities prevailed during deposition of the ruslar formation relatively high oxygen contents occurred during early solenovian times lower part of unit ii when brackish surface water favoured nannoplankton blooms and the deposition of bright marls solenovian event anoxic conditions with photic zone anoxia were established during late oligocene times units iii and iv and probably reflect a basin wide anoxic event in the eastern paratethys during kalmykian times organic carbon content in the ruslar formation is up to 3 autochthonous aquatic and allochthonous terrigenous biomass contribute to the organic matter relatively high amounts of aquatic organic matter occur in the lower part of the ruslar formation units i and ii and in its upper part unit vi diatoms are especially abundant in the lower part of unit vi the kerogen is of type iii and ii with hi values ranging from 50 to 400 mghc gtoc units i and ii pshekian lower solenovian are characterized by a fair to good potential to produce gas and oil but potential sources for gas and oil also occur in the upper oligocene units iv vi

structure and dynamics of fluid muds on the amazon continental shelf thick layers of fluid mud occur in strong tidal flows over the inner portion of the amazon continental shelf in regions of strong salinity fronts associated with the plume discharged from the amazon river detailed shipboard profile measurements obtained in this region during a multidisciplinary amazon shelf sediment study amasseds provide an unprecedented opportunity to examine the structure and dynamics of fluid muds under natural conditions the analysis focuses on flows in which the motion is fully turbulent and suspended sediment dominates the stratification under these conditions a comparison of measurements and one dimensional model calculations indicates that vertical transport is controlled by suppression of turbulent mixing at gradient richardson numbers near 1 4 this constraint produces a distinctive vertical structure and leads to an upper bound on the total amount of suspended sediment that may be carried in a turbulent suspension by a tidal flow

langmuir supercells a mechanism for sediment resuspension and transport in shallow seas recent measurements at a cabled sea floor node in 15 meters of water off the coast of new jersey suggest that langmuir supercells langmuir circulations that achieve vertical scales equal to the water depth under extended storms are an important mechanism for major sediment resuspension events on the extensive shallow shelves off the eastern u s coast because sediment resuspension is a prelude to transport supercell events are a necessary condition for major sediment transport such events may also contribute to shelf sea exchange and to offshore gradation of benthic community structure in shallow seas

langmuir turbulence in shallow water part 1 observations during extended deployment at an ocean observatory off the coast of new jersey a bottom mounted five beam acoustic doppler current profiler measured large scale velocity structures that we interpret as langmuir circulations filling the entire water column these circulations are the large eddy structures of wind wave driven turbulent flows that occur episodically when a shallow water column experiences prolonged strong wind forcing many observational characteristics agree with former descriptions of langmuir circulations in deep water the three dimensional velocity field reveals quasi organized structures consisting of pairs of surface intensified counter rotating vortices aligned approximately downwind maximum downward velocities are stronger than upward velocities and the downwelling region of each cell defined as a pair of vortices is narrower than the upwelling region maximum downward vertical velocity occurs at or above mid depth and scales approximately with wind speed the estimated crosswind scale of cells is roughly 3 6 times their vertical scale set under these conditions by water depth the long axis of the cells appears to lie at an angle 10 20 to the right of the wind a major difference from deep water observations is strong near bottom intensification of the downwind jets found typically centred over downwelling regions accessible observational features such as cell morphology and profiles of mean velocities turbulent velocity variances and shear stress components are compared with the results of associated large eddy simulations reported in part 2 of shallow water flows driven by surface stress and the craik leibovich vortex forcing generally used to represent generation of langmuir cells a particularly sensitive diagnostic for identification of langmuir circulations as the energy containing eddies of the turbulent flow is the depth trajectory of invariants of the turbulent stress tensor plotted in the lumley triangle corresponding to realizable turbulent flows when langmuir structures are present in the observations the lumley map is distinctly different from that of surface stress driven couette flow again in agreement with the large eddy simulations les unlike the les observed velocity fields contain two distinct and significant scales of variability documented by wavelet analysis of observational records of vertical velocity variability with periods of many minutes is that expected from langmuir cells drifting past the instrument at the slowly time varying crosswind velocity shorter period variability of the order of 1 2 min has roughly the observed periodicity of surface wave groups suggesting a connection with the wave groups themselves and or the wave breaking associated with them in high wind conditions

bottom stress estimates and their prediction on the northern california continental shelf during code 1 the importance of wave current interaction abstract high quality near bottom boundary layer measurements obtained at a midshelf location 90 m water depth in the code region off northern california are described bottom tripod velocity measurements and supporting data obtained during typical spring and early summer conditions june 1981 during code 1 are analyzed to obtain bath velocity profiles and mean bottom stress and bottom roughness estimates during the time period described the mean near bottom 0 997 approximately 30 percent of the time effects induced by unsteadiness from internal waves result in some degradation of the profiles 0 96 r 0 997 the rest of the time mean stress profiles indicate the logarithmic layer is approximately a constant stress layer the near bottom flow field is composed of mean currents and oscillatory currents due to well typing mean u values estimated from measurements greater than 30 cm above the bottom have magnitudes of 0 5 1 0 cm s 1 mean stress valu

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

modeling stratified wave and current bottom boundary layers on the continental shelf the glenn and grant 1987 continental shelf bottom boundary layer model for the flow and suspended sediment concentration profiles in the constant stress layer above a noncohesive movable sediment bed has been updated the reynolds fluxes for sediment mass and fluid momentum are closed using a continuous time invariant linear eddy viscosity modified by a continuous stability parameter to represent the influence of suspended sediment induced stratification throughout the constant stress region glenn and grant 1987 use a less realistic discontinuous eddy viscosity and neglect the stratification correction in the wave boundary layer for typical model parameters the two models produce currents above the wave boundary layer that are in better agreement than the suspended sediment concentrations within the wave boundary layer the differences are much greater for both the current and the sediment concentration this leads to significant differences in the sediment transport throughout the constant stress layer sensitivities of the updated model were examined on the basis of observed wave and current data acquired during storms on the inner continental shelf comparisons between the stratified and neutral versions of the updated model indicate that the stratified version produces a total depth integrated sediment transport that can be 2 orders of magnitude less than and time averaged shear velocities that can be nearly half of that predicted by the neutral version sensitivities to grain size distributions indicate that even a small amount of finer sediment can stratify the storm driven flows sensitivities to closure constants within the range of reported values also produce up to an order of magnitude variation in sediment transport illustrating the need for dedicated field experiments to refine further estimates of these parameters

quantifying arabia eurasia convergence accommodated in the greater caucasus by paleomagnetic reconstruction since the late eocene convergence and subsequent collision between arabia and eurasia was accommodated both in the overriding eurasian plate forming the greater caucasus orogen and the iranian plateau and by subduction and accretion of the neotethys and arabian margin forming the east anatolian plateau and the zagros to quantify how much arabia eurasia convergence was accommodated in the greater caucasus region we here provide new paleomagnetic results from 97 volcanic sites 500 samples in the talysh mountains of nw iran that show 15 net clockwise rotation relative to eurasia since the eocene we apply a first order kinematic restoration of the northward convex orocline that formed to the south of the greater caucasus integrating our new data with previously published constraints on rotations of the eastern pontides and lesser caucasus this suggests that north of the talysh 120 km of convergence must have been accommodated north of the eastern pontides and lesser caucasus this is significantly more 200 280 km our reconstruction independently confirms previous caucasus convergence estimates moreover we show for the first time a sharp contrast of convergence between the lesser caucasus and the talysh this implies that the ancient paleozoic mesozoic transform plate boundary preserved between the iranian and east anatolian plateaus was likely reactivated as a right lateral transform fault since late eocene time

arabia eurasia collision and the forcing of mid cenozoic global cooling the end of the eocene greenhouse world was the most dramatic phase in the long term cooling trend of the cenozoic era here we show that the arabia eurasia collision and the closure of the tethys ocean gateway began in the late eocene at 35 ma up to 25 million years earlier than in many reconstructions we suggest that global cooling was forced by processes associated with the initial collision that reduced atmospheric co2 these are 1 waning volcanism across southwest asia 2 increased organic carbon storage in paratethyan basins e g black sea and south caspian 3 increased silicate weathering in the collision zone and 4 a shift towards modern patterns of ocean currents associated with increased vigour in circulation and organic productivity

principal bed states during sandyduck97 occurrence spectral anisotropy and the bed state storm cycle 1 results are presented from 70 days of nearly continuous in situ acoustic imagery of the nearshore sandy seabed in 3 m mean water depth at two locations separated by 40 m cross shore distance the bottom sediments were 150 m median diameter sand with nearly identical size distributions at the two locations five principal bed states were observed irregular ripples cross ripples linear transition ripples lunate megaripples and flat bed the linear transition and flat bed states were the most frequent together accounting for 68 of the total time bed state occurrence was a strong function of incident wave energy each bed state occurring within a relatively narrow range of sea and swell energies during the 12 major storm events spanned by the record the bed response was characterized by a repeatable bed state storm cycle involving four of the five principal states lunate megaripples did not appear repeatedly and thus may be a special case with no obvious dependence of bed state occurrence on prior bed state or on third moment measures of wave nonlinearity radial spectra from the rotary acoustic images indicate pronounced differences in the anisotropy of spatial scales for the different bed states and exhibit onshore offshore differences which are likely related to ripple migration

an oligocene sink for organic carbon upwelling in the paratethys a synoptic review of the organic carbon content kerogen type biogenic siliceous sediments and planktonic remains is attempted for the often anoxic oligocene early miocene sediments of the paratethys covering a large area between the rhine valley and the aral sea on this basis stratification of the sea and intensity of planktonic productivity are discussed for different parts of the paratethys the eastern parathethys and some parts of the central and western paratethys show a black sea like stable stratificatin while the bulk of the anoxic sediments in the carpathian flysch basin are interpreted to have an upwelling origin the supposed flysch ocean upwelling regime has no good recent analogue although it shows similarities with the bay of california high rate of corg burial laminated diatomaceous sediments and turbiditic intercalations and offshore nw africa abundant fresh water discharge sediments of a brackish water incursion are widespread on the bottom of the np 23 zone from earliest oligocene to early miocene a continuous narrowing of the anoxic sedimentary belt towards the east european platform is observed

geomagnetic secular variation and the statistics of palaeomagnetic directions in this study we examine the role of palaeosecular variation psv in the use of statistics for palaeomagnetic studies and we provide new reliability criteria for palaeomagnetic poles or directions we first conclude that fisher statistics should not be applied to average palaeomagnetic directions but to virtual geomagnetic pole vgp distributions instead secondly we strongly advocate that typical properties of geomagnetic field behaviour are taken into account in the assessment of palaeomagnetic data sets the latitude dependent properties e s k provide useful guidelines for the reliability of a palaeomagnetic data set a reliable assessment of these properties depends on the sufficient number of palaeomagnetic samples being taken therefore as an additional instrument of assessing data sets we provide a n dependent a95 envelope bounded by an upper limit a95max and a lower limit a95min that helps to ascertain whether or not a distribution has sufficiently well sampled psv and therefore geomagnetic field behaviour applying these criteria is indispensable for studies of geomagnetic behaviour or for studies aiming at using tk03 gad for inclination error correction through the elongation inclination e i method for palaeomagnetic studies aimed at geological reconstructions they form helpful guidelines and increase the confidence in the rocks having faithfully recorded the field an analysis of published eastern mediterranean data shows that the vast majority of studies do not conform to the van der voo criteria in particular with respect to n and a95 we have provided criteria that are on the one hand more lenient lower n may still provide relevant information and on the other hand more strict for high n the criterion of a95 16 should be adapted to a requirement of lower a95 e g a95 80

on the weakening relationship between the indian monsoon and enso analysis of the 140 year historical record suggests that the inverse relationship between the el nino southern oscillation enso and the indian summer monsoon weak monsoon arising from warm enso event has broken down in recent decades two possible reasons emerge from the analyses a southeastward shift in the walker circulation anomalies associated with enso events may lead to a reduced subsidence over the indian region thus favoring normal monsoon conditions additionally increased surface temperatures over eurasia in winter and spring which are a part of the midlatitude continental warming trend may favor the enhanced land ocean thermal gradient conducive to a strong monsoon these observations raise the possibility that the eurasian warming in recent decades helps to sustain the monsoon rainfall at a normal level despite strong enso events

tibetan plateau summer monsoon northward extent revealed by measurements of water stable isotopes a program of individual precipitation events and river water sampling and of water isotopic measurements d 18o was carried out during summer 1996 along a northeast southwest transect of the tibetan plateau the spatial distribution of both 18o and deuterium excess d d 8 18o of the precipitation reveals three distinct regions simulations with a simple isotopic model and seasonal isotopic variations measured at two extreme south and north locations support our interpretation in terms of different summer moisture origins 1 south of the himalayan mountains the moisture provided by the indian monsoon has been recycled over the indian peninsula 2 between the himalayas and the tanggula mountains the oceanic moisture is directly transported from the bay of bengal along the brahmaptra river valley 3 north of the tanggula mountains the moisture is not provided by the monsoon anymore but by continental water recycling

effects of weathering on single domain magnetite in early pliocene marine marls rock magnetic parameters are often used to recognize variations in the original magnetic mineralogy and for normalizing purposes in palaeointensity studies incipient weathering however is shown to have a profound but partly reversible influence on the rock magnetic properties of the marls of the early pliocene trubi formation in southern sicily italy the remanence in the marls resides in single domain sd magnetite grains but the remanent coercive force hcr shows a strong variation and most values observed are anomalously high hcr range 36 188 mt the enhanced coercivities are attributed to stress in the magnetite grains induced by surface oxidation at low temperature upon heating to 150 c a reduction of coercivities occurs that can be explained by a stress reduction as a result of a reduction of fe2 gradient due to a higher diffusion rate at elevated temperature after heating to 150 c coercivities are quite uniform throughout the outcrop and the values are characteristic of sd magnetite hcr range 30 38 mt the bulk susceptibility increases by 4 24 per cent and the isothermal remanent magnetization irm decreases by 5 11 per cent the increase in anhysteretic remanent magnetization arm is large 20 242 per cent the magnitude of the changes is related to the degree of weathering another effect of heating the marl samples to 150 c is a substantial reduction of the coercivities of the secondary overprint in the natural remanent magnetization after heating separation of the secondary and primary components by alternating field demagnetization is more efficient the usual difficulties of thermal demagnetization above 300 c may thus be avoided by a combination of moderate heating to 150 c and subsequent alternating field demagnetization

insights from the talysh of azerbaijan into the paleogene evolution of the south caspian region the age and mode of formation of the south caspian basin are disputed an 10 km thick predominantly middle eocene clastic and volcanic succession is exposed in the talysh mountains of azerbaijan at its western margin here high k alkali basalts pass laterally to the east and southeast into volcanogenic sandstone dominated turbidity current and debris flow deposits these southeasterly directed depositional systems accumulated in water depths generally greater than 200 m and fed directly into the western south caspian basin new ar ar ages cluster around 39 ma with an upper 1400 m thick volcanic interval being deposited in 2 2 0 2 m y we interpret that this rapid deposition and magmatism records a major back arc extensional transtensional event in the talysh north of the north dipping neotethyan subduction zone this event is recognized across much of southwest asia and may indicate a period of significant basin formation within the adjacent south caspian basin a transition into upper eocene lower oligocene strata dominated by fine grained turbidity current and hemipelagic sediments with slope instability features is interpreted to mark the end of rifting and volcanism in the talysh and the start of the arabia eurasia collision overlying oligocene coarse clastic rocks are interpreted as the erosional products of localized topography created by the further propagation of compressional deformation into the talysh region

spatial variability of the wave bottom boundary layer over movable rippled beds observations of the spatially dependent velocity field over movable bed forms subjected to slightly skewed and asymmetric regular wave forcing were collected the dynamics between the ripple elements is dominated by coherent vortices characterized by the swirling strength and evidenced in the temporal and spectral characterization within the boundary layer spectral energy in the second harmonic 3f0 is amplified at the ripple slopes and is consistent with the location of the expected strongest pressure gradients first moment and second moment velocity statistics were used to address the spatial variability of the intra ripple hydrodynamics estimates of displacement and momentum thicknesses and mom are smaller than suggested by the higher harmonics but consistently highlight areas of adverse and favorable pressure gradients shear stress and roughness estimates were inferred by fitting a logarithmic model to first moment and second moment statistics of the velocity field the maximum shields parameter was observed to peak at the stoss slope of asymmetric ripples during the strongest and shorter half wave period onshore first moment roughness estimates are similar in magnitude to bed load parameterizations provided by li et al 1997 and about a factor of 3 larger than second moment estimates assessment of the vertical transfer of horizontal momentum derived using a reynolds decomposition suggests that stresses inferred from the logarithmic law using first moment velocity statistics appropriately reproduce the mean momentum transfer for the longer and weaker offshore half wave period

sulphidic mediterranean surface waters during pliocene sapropel formation sapropels organic matter rich layers are common in neogene sediments of the eastern mediterranean sea the formation of these layers has been attributed to climate related increases in organic matter production1 2 3 and increased organic matter preservation due to oxygen depletion in more stagnant bottom waters2 3 here we report that eastern mediterranean pliocene sapropels4 contain molecular fossils of a compound isorenieratene known to be synthesized by photosynthetic green sulphur bacteria suggesting that sulphidic euxinic and therefore anoxic conditions prevailed in the photic zone of the water column these sapropels also have a high trace metal content which is probably due to the efficient scavenging of these metals by precipitating sulphides in a euxinic water column the abundance and sulphur isotope composition of pyrite are consistent with iron sulphide formation in the water column we conclude that basin wide water column euxinia occurred over substantial periods during pliocene sapropel formation in the eastern mediterranean sea and that the ultimate degradation of the increased organic matter production was strongly influential in generating and sustaining the euxinic conditions