rayleigh waves normally incident at a continental boundary summary some results of a study of the propagation of monochromatic rayleigh waves normally incident on the western ocean continent boundary of the iberian peninsula are described this seismological problem is modelled in two dimensions using the finite element method for periods in the range of 1 5 to 60 0s the following results for ocean continent direction of propagation are presented i the estimate of the reflected and transmitted wavefields ii the phase velocity curves for the fundamental mode in the transition zone iii the transmission and reflection coefficients and iv the seismic energy distribution for transmitted and reflected modes experimental data from porto pto a continental station and ponta delgada pda an oceanic station were compared to ascertain the effect on rayleigh wave propagation across the continental margin comparison of the experimental amplitude ratios and transmission factor suggests a thickness of about 4 km for the sediment layer in the western oceanic zone of the iberian peninsula

anatomy of a mixed marine non marine lowstand wedge in a ramp setting the record of a barremian aptian complex relative sea level fall in the central neuquen basin argentina

reflection and transmission of surface waves at a vertical discontinuity and imaging of lateral heterogeneity using reflected fundamental rayleigh waves we present a technique for the determination of approximate reflection and transmission coefficients of surface wave modes for a vertical plane discontinuity that is simple to use it is applied to different models of lateral heterogeneity furthermore a method for the localization of lateral heterogeneity using the coda of the fundamental rayleigh mode is proposed in particular the frequency content of surface waves enables the investigation of the lower crust and the uppermost mantle lateral changes of the s wave velocity density and p wave velocity lead to the formation of the coda of the fundamental rayleigh mode that contains delayed surface waves that reach the recording station indirectly the complicated structure of the coda makes it impossible to identify reflected surface waves visually using a small number of recordings only coda waveforms of a large number of source station pairs are inverted simultaneously for experimental reflection coefficients the method is successfully tested using an ultrasonic model experiment finally it is applied to central europe and especially to the tornquist zone tz mainly using records of the german regional seismological network grsn the resulting reflection coefficients depend on frequency and give an image of the location of reflectors

correlation of early cretaceous carbon isotope stratigraphy and platform drowning events a possible link the early cretaceous carbonate carbon isotope record is marked by three positive high amplitude 1 5 excursions each covering time spans of more than 106 years they are of late valanginian hauterivian and early and late aptian age in a case study along a transect across the western tethys ocean we identified a coincidence between 13c excursions black shale formation and widespread carbonate platform drowning events we conclude that the 13c excursions reflect a change in partitioning of carbon between the organic and carbonate carbon sinks which was triggered by climate induced ecological changes in cretaceous pelagic and neritic environments episodes of intensified greenhouse climate conditions led to an increase in weathering erosion and runoff rates and to elevated nutrient transfer rates from continents into oceans the resulting increase in oceanic nutrient levels favoured marine phytoplankton production and black shale deposition while conditions for carbonate producing biotas became unfavourable partial choking of carbonate production along river influenced coasts resulted in widespread carbonate platform drowning during times of sea level rise in the valanginian and aptian widespread contemporaneous black shale deposits and drowned carbonate platforms therefore reflect the contrasting response of the marine organic and carbonate carbon pumps to nutrient enhanced phytoplankton productivity the change in marine carbon partitioning is mirrored in a shift of the 13c record towards more positive values the transition to the 13c peak values lasted up to several hundred thousand years the peaks of the excursions also covering a time span of up to several hundred thousand years reflect a new stabilisation of the carbon partitioning between carbonate and organic carbon sinks a renewed intensification of carbonate sedimentation under mesotrophic conditions was facilitated by stabilisation of the sea level rise at a high level decreasing 13c values record increasing carbonate carbon burial rates at constant or decreasing organic carbon accumulation rates these changes contributed to the stabilisation of the marine carbon budget and the global carbon cycle up to millions of years after its initial perturbation

paleoceanographic modeling of temperature salinity profiles from stable isotopic data temperature salinity t s profiles in ancient seawater can be estimated from oxygen isotopic compositions of well preserved calcitic fossils sampled from known paleodepth gradients the proposed model uses isotopic compositions of fossils to determine possible combinations of temperature and salinity during deposition given estimates of average salinity isotopic composition and net global hydrologic fractionation for ancient oceans increasing density with depth constrains those combinations to narrow ranges this graphic method superposes curves for density and isotopic composition in t s space to reveal possible ancient t s profiles application of this method to oxygen isotope data from ordovician brachiopods deposited on the eastern continental slope of north america demonstrates its usefulness and yields a stable seawater column in which brackish intermediate waters overlie warmer more saline deep waters

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

paleoenvironmental framework of dinosaur tracksites and other ichnofossils in early cretaceous mixed siliciclastic carbonate deposits in the neuquen basin northern patagonia argentina abstract the study of the uppermost section of the early cretaceous agrio formation in northern patagonia neuquen basin where dinosaur tracks assigned to cf therangospodus pandemicus are exposed tracksites i and ii evidence mixed marginal marine siliciclastic carbonate deposits the succession was divided in two intervals a lower one containing theropod tracks recorded on top of subtidal oolithic limestones with tiny wave ripples suggesting shoreline fluctuations and subaerial exposure tidal influence is recognised by fining upward and prograding cycles starting with subtidal carbonates and ending with fine grained siliciclastic deposits at the top or rarely laminites dolomitization affects subtidal deposits generated in an alkaline media stressful for tracemakers intertidal facies include abundant heterolithic deposits coquinas composed of gastropods encrusted by multilayered bryozoans and muddy levels with incipient mud cracking invertebrate ichnofossils recognized from tidally dominated deposits include arenicolites kouphichnium and rhizocorallium the upper interval is a transgressive regressive cycle that starts with dark shales deficiently oxygenated and covered by prograding sandstones and finally sand flat deposits this interval contains gyrochorte hillichnus and ophiomorpha documented in wave influenced sandstones dinosaur tracks as well as hillichnus attributed to tellinoid bivalves and kouphichnium assigned to xiphosurans imply the activity of producers rarely recorded previously as body fossils in marginal marine deposits of southern south america previous paleogeographic schemes are questioned by our analysis which shows evidence of extremely shallow and tide controlled sedimentation sometimes with subaerial exposure with high cyclicity related to a marginal marine depositional setting and lack of significant erosion by the overlying unit as traditionally was suggested

paleosalinity determination in ancient epicontinental seas a case study of the t oae in the cleveland basin uk abstract the early jurassic toarcian oceanic anoxic event t oae was marked by deposition of organic rich sediments and a pronounced negative carbon isotope excursion across the northwest european sea nwes representing a signal that was stronger regionally than globally various models for the t oae have been proposed some focusing on general atmospheric oceanic controls to reflect its global character and others emphasizing local or regional factors to account for its strong expression in the nwes in this study we evaluate watermass dynamics of the early jurassic cleveland basin uk during the t oae using a combination of paleosalinity proxies b ga sr ba and s toc these proxies suggest that brackish conditions existed prior to onset of the t oae with a shift to nearly freshwater conditions during the t oae reflecting a large increase in terrestrial runoff due to a stronger hydrological cycle possibly combined with shallowing of the marginal sill of the cleveland basin through sea level fall following the t oae basinal salinity conditions first returned to brackish and then gradually shifted to fully marine this hydrographic history accounts for low mo concentrations in t oae sediments of the cleveland basin demonstrating control by watermass restriction and local rather than global aqueous mo drawdown these findings demonstrate the importance of local hydrographic controls on the sedimentary expression of the t oae the more general significance of this study is that it highlights the need for application of paired salinity and redox proxies in order to correctly interpret paleoenvironmental variations in marginal marine basins

sedimentological evidence concerning the paleoceanography of the cretaceous western north atlantic ocean abstract black clays developed as a result of progressively intensifying intermittent anoxic conditions from the early through mid cretaceous the preservation of primary sedimentary structures of authigenic minerals such as pyrite and siderite and of significant amounts of organic carbon testify to the stagnant conditions intermittent anoxic conditions prevailed in the deepest portion of the basin resulting from vertical migration of an intrasediment anoxic interface middle aptian variegated clays within the black clay sequence at several low latitude sites suggest a widespread oxygenation event of short duration occurred there greater thicknesses of black clays accumulated in low latitudes implying that surface or intermediate depth currents redistributed the sediments south ward millimeter scale laminae characterizing the early and mid cretaceous sediments represent seasonal sediment input where seasons during the cretaceous had durations measured in years cenomanian variegated clays succeeded the black clay interval and represent deposition under totally oxygenated conditions thus the sluggish and stagnant conditions present in the early and mid cretaceous were followed by increased current activity these currents were derived from more northern latitudes as iberia was rifted from north america cooler temperatures presumably increased the oxygen capacity of the water and its ability to sink into the deep basin to relieve the stagnant conditions present the late cenomanian through late campanian was a time of widespread marine transgression resulting in the deep ocean becoming a sediment starved basin clastics and carbonates accumulated on the shelves as the calcite compensation depth ccd shallowed appreciably the late campanian through maastrichtian interval is characterized by calcium carbonate accumulation throughout much of the deep basin a significant lowering of sea level paralleled by a deepening ccd caused this sedimentation pattern

matrix material in type 3 chondrites occurrence heterogeneity and relationship with chondrules abstract matrix material in type 3 chondrites forms rims on chondrules metal sulfide aggregates ca al rich inclusions and chondritic clasts it also forms lumps up to a millimeter in size which may contain coarser silicates chondrules of all types were found with internal matrix lumps that appear to have entered the chondrules before the latter had crystallized mean concentrations of mg na al and ca in matrix occurrences show up to fivefold variations in a single chondrite variations between mean matrix compositions of individual type 3 ordinary chondrites are almost as large and partly reflect systematic differences between h l and ll matrices such variations are probably a result of nebular separation of feldspathic material and ferromagnesian silicates compositions of chondrules and their matrix rims are normally unrelated although rim compositions are correlated with those of matrix lumps inside chondrules a single chondrule was found with a composition nearly identical to that of its internal matrix lump suggesting that some chondrules may have formed from matrix material matrix lumps are as heterogeneous as chondrules but mean chondrule and matrix compositions differ even allowing for possible loss of metallic fe ni during chondrule formation since bulk compositions of matrix lumps and rims have probably not changed significantly since their formation except for fe mg exchange our matrix samples cannot represent typical chondrule precursor materials

physical properties of chondrules in different chondrite groups implications for multiple melting events in dusty environments chondrite groups cv ck cr with large average chondrule sizes have low proportions of rp plus c chondrules high proportions of enveloping compound chondrules high proportions of chondrules with thick igneous rims and relatively low proportions of type i chondrules containing sulfide in contrast chondrite groups cm co oc r eh el with smaller average chondrule sizes have the opposite properties equilibrated ck chondrites have plagioclase with relatively low na equilibrated oc r eh and el chondrites have more sodic plagioclase enveloping compound chondrules and chondrules with igneous rims formed during a remelting event after the primary chondrule was incorporated into a dustball repeated episodes of remelting after chondrules were surrounded by dust would tend to produce large chondrules rp and c chondrules formed by complete melting of their precursor assemblages remelting of rp and c chondrules surrounded by dust would tend to produce porphyritic chondrules as small dust particles mixed with the melt providing nuclei for crystallizing phenocrysts this process would tend to diminish the numbers of rp and c chondrules correlations among these chondrule physical properties suggest that chondrite groups with large chondrules were typically surrounded by thick dust rich mantles that formed in locally dusty nebular environments chondrules that were surrounded by thick dust mantles tended to cool more slowly because heat could not quickly radiate away slow cooling led to enhanced migration of sulfide to chondrule surfaces and more extensive sulfide evaporation these chondrules also lost na the plagioclase that formed from equilibrated ck chondrites was thus depleted in na

microchondrule bearing clast in the piancaldoli ll3 meteorite a new kind of type 3 chondrite and its relevance to the history of chondrules in the piancaldoli ll3 chondrite we found a mm sized clast containing 100 chondrules 0 2 64 m in apparent diameter much smaller than any previously reported that are all of the same textural type radial pyroxene fs1 17 this clast like other type 3 chondrites has a fine grained ferich opaque silicate matrix sharply defined chondrules abundant low ca clinopyroxene and minor troilite and si and cr bearing metallic fe ni however the very high modal matrix abundance 63 8 vol unique characteristics of the chondrules and absence of microscopically observable olivine indicate that the clast is a new kind of type 3 chondrite most chondrules have feo rich edges and chondrule size is inversely correlated with chondrule core feo concentration the first reported correlation of chondrule size and composition chondrules acquired fe by diffusion from fe rich matrix material during mild metamorphism possibly before final consolidation of the rock microchondrules those chondrules 100 m in diameter are also abundant in another new kind of type 3 chondrite clast in the rio negro l chondrite regolith breccia in other type 3 chondrite groups microchondrule abundance appears to be anticorrelated with mean chondrule size viz 0 02 0 04 vol in h and co chondrites and 0 006 vol in l ll and cv chondrites microchondrules probably formed by the same process that formed normal sized droplet chondrules melting of pre existing dustballs because most compound chondrules in the clast and other type 3 chondrites formed by collisions between chondrules of the same textural type we suggest that dust grains were mineralogically sorted in the nebula before aggregating into dustballs the sizes of compound chondrules and chondrule craters which resulted from collisions of similarly sized chondrules while they were plastic indicate that size sorting of dustballs occurred before chondrule formation probably by aerodynamic processes in the nebula we predict that other kinds of type 3 chondrites exist which contain chondrule abundances size ranges and proportions of textural types different from known chondrite groups

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

interference of long period seismic wavefield observed by the dense hi net array in japan 1 in order to recover small signals of long period ground motions recorded by a short period seismometer we designed a time domain recursive filter that simulates seismic waves recorded with broadband seismometers we applied the time domain filter to seismograms recorded by the dense hi net array which consists of 800 stations at intervals of approximately 20 km the effectiveness of the time domain filter is demonstrated through the comparison of broadband waveforms obtained by the filter and sts 2 true broadband seismograms from the f net at the same site good agreement is observed between filtered and true broadband waveforms with high correlation coefficients for periods of up to 100 s for waveforms from the 2007 sumatra earthquake m7 9 which occurred approximately 5000 5800 km away from japan the applicability of the time domain filter to the recovery of long period signals from the record of a short period seismometer depends on the signal to noise ratio as a result a limited bandwidth of broadband signal is recovered for smaller earthquake from the spatiotemporal variation of the long period t 20 100 s wavefield obtained by the time domain filter we newly found an anomalous phase pattern of splitting of polarity along the wavefront particularly for the relatively short period band of from 20 50 s array analysis of the dense broadband waveforms revealed multipathing of the rayleigh waves which propagated toward central japan from two directions with slightly different slowness vectors the interference of two rayleigh waves caused such splitting of wavefield

mapping the moho with seismic surface waves a review resolution analysis and recommended inversion strategies abstract the strong sensitivity of seismic surface waves to the moho is evident from a mere visual inspection of their dispersion curves or waveforms rayleigh and love waves have been used to study the earth s crust since the early days of modern seismology yet strong trade offs between the moho depth and crustal and mantle structure in surface wave inversions prompted doubts regarding their capacity to resolve the moho here we review surface wave studies of the moho with a focus on early work and then use model space mapping to establish the waves sensitivity to the moho depth and the resolution of their inversion for it if seismic wavespeeds within the crust and upper mantle are known then moho depth variations of a few kilometres produce large 1 perturbations in phase velocities however in inversions of surface wave data with no a priori information wavespeeds not known strong moho depth shear speed trade offs will mask 90 of the moho depth signal with remaining phase velocity perturbations 0 1 only in order to resolve the moho with surface waves alone errors in the data must thus be small up to 0 2 for resolving continental moho with larger errors moho depth resolution is not warranted and depends on error distribution with period an effective strategy for the inversion of surface wave data alone for the moho depth is to first constrain the crustal and upper mantle structure by inversion in a broad period range and then determine the moho depth in inversion in a narrow period range most sensitive to it with the first step results used as reference prior information on crustal and mantle structure reduces the trade offs and thus enables resolving the moho depth with noisier data such information should be used whenever available joint analysis or inversion of surface wave and other data receiver functions topography gravity can reduce uncertainties further and facilitate moho mapping

physical description of lg waves in inhomogeneous continental crust summary the view of lg waves as a superposition of seismic surface waves is very useful for explaining the amplitudes of the late parts of seismograms from regional earthquakes we have recently made computations for rayleigh waves interpreting the special attenuation of lg waves in the north sea as being caused by 1 the distribution of energy over longer time intervals combined with 2 the upwards or downwards pumping of wave energy in the diverent crustal structures combined with 3 anelastic absorption no special discussion is necessary of the claim that anelastic absorption in a particular area gives a reduction in wave amplitude whilst a physical description of the geometrical evect is warranted a physical description of the wave propagation phenomena involved is given in the present paper by classifying the mode conversion that is involved in the propagation from one crustal structure into another the physics is described via relations between the phase velocities group velocities and energy dependences on depths of the various surface wave modes that exist in the diverent crustal structures we introduce the concept of energy depth similarity a parameter that is almost as easily computed as the ratios of phase velocities or group velocities but is a far better measure of the transition character the crustal structures in question are representative of 1 the north sea and its surroundings in general and 2 the viking and central grabens in the middle of the north sea wave propagation is fundamentally diverent for diverent wave frequencies it is coherent for long period waves and incoherent for short period waves the propagation may generally be termed well behaved for wave periods longer than several seconds that is energy cross coupling between incoming and outgoing modes follows some regular pattern this regularity is highly dependent on the similarity of the two modes on either side of a discontinuity and also on the similarity of their neighbouring modes a characteristic of the regularity is that there is no mode conversion for very longperiod modes in contrast a pattern cannot be recognized for waves of shorter period and one may use the term ill behaved the lg waves in the continental crust are in the short period range because their wavelengths are short compared to thickness changes as well as to the thicknesses of crustal structures this leads to the view that lg waves are superpositions of many modes changing into even more modes at any discontinuity since rayleigh and love waves are coupled at non perpendicular incidence and the earth has many discontinuities the superposition of modes is constantly changing in relative proportions rayleigh and love modes being intermingled

palaeosalinity variations in the early cretaceous of the neuquen basin argentina evidence from oxygen isotopes and palaeoecological analysis abstract the neuquen basin is a stratigraphically and economically important early cretaceous depocentre located in west central argentina the early valanginian to early barremian succession upper vaca muerta mulichinco and agrio formations contains a rich fossil record with abundant bivalves and ammonoids palaeosalinities are determined systematically throughout the succession based on an oxygen isotope analysis of unaltered oyster shells from two localities in neuquen province a total of 188 oyster samples from 52 stratigraphic levels were processed a total of 52 mean values of 18o isotope are used to calculate palaeosalinities assuming an estimated water temperature of 25 c the observed range of palaeosalinities between the maximum and the minimum is 19 which is in conflict with published accounts of this being a fully marine succession the isotopic data are combined with independent faunal evidence to evaluate palaeosalinity variation both laterally and temporally significant fluctuations in water salinity are indicated with a clear tendency to increase from brachyhaline to euhaline and near hyperhaline conditions through time the fluctuations were probably due to dilution from normal marine water caused primarily by variations in rainfall and continental runoff in addition the presence of a volcanic island arc along the western margin of the basin may have at least partially isolated the basin from the marine waters of the pacific ocean also a gulf shaped basin may have inhibited hydrodynamic exchange with the ocean while enhancing retention of continental waters

advances in the biostratigraphy of the agrio formation lower cretaceous of the neuquen basin argentina ammonites palynomorphs and calcareous nannofossils abstract detailed stratigraphic logging and systematic studies on late valanginian early barremian ammonites from the agrio formation of the neuquen basin of west central argentina have provided a detailed local ammonite zonation here we combine the ammonite data with an initial study of calcareous nannofossils and palynomorphs from two sections to produce a provisional integrated biostratigraphy for the agrio formation while the palynomorphs are essentially of local value only especially the continental forms the nannofossils and the ammonites allow some correlations to be made with the european mediterranean standard sequences

anomalous surface waves associated with deep earthquakes generated at an ocean ridge summary broad band seismograms observed at regional distances from deep earthquakes display large amplitude rayleigh and love waves with a predominant period of about 20 s although deep earthquakes in laterally homogeneous structures do not generate such surface waves since the propagation direction of the surface waves inferred from particle motion is approximately radial and the group velocity of the surface waves observed at each station is similar it can be assumed that the surface waves have travelled close to the great circle paths back projection allows us to determine the region in which these surface waves are generated manyof the zones from which the surface waves appear to originate are located close to the norfolk ridge where crustal structure has strong lateral heterogeneity this suggests that the surface waves are generated by the interaction of body waves from the deep earthquakes with this strongly heterogeneous crustal structure in order to investigate the eiect of such heterogeneity in crustal structure on seismic wave elds we have modelled the p sv wave eld using a pseudospectral method the results show that surface waves such as those observed can be generated by ridge structures and indicate that sedimentary layer thickness plays a very important role we suggest that such unexpected surface waves from deep earthquakes may prove useful for delineating heterogeneity in shallow structure

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

isotopic signals from late jurassic early cretaceous volgian valanginian sub arctic belemnites yatria river western siberia this contribution presents the first detailed oxygen and carbon isotope record from the latest jurassic early cretaceous interval of the yatria river subpolar urals siberia isotopic compositions have been determined on well preserved belemnite samples from the genera lagonibelus cylindroteuthis and acroteuthis these new data indicate a shift to lower temperatures from the late volgian into the late valanginian with some warmer phases recognized within the ryazanian and earliest valanginian the lowest temperatures of the late valanginian consistent with subfreezing polar temperatures are coincident with an inferred eustatic sea level fall a late valanginian positive shift in carbon isotopes correlates with the carbon isotope excursion recorded from tethyan successions the most positive carbon isotope values correspond to the most positive oxygen isotope values and hence lowest palaeotemperatures in the absence of widespread valanginian organic rich black shale deposition the carbon isotope excursion may point to increased storage of organic carbon in coastal areas and or enhanced preservation within stratified waters in high latitude basins at these higher latitudes where rates of weathering were presumably much lower because of the prevalent cold climate the isotopic data may point to pulses of productivity being brought about by increased riverine nutrient transfer and also by nutrients being released by the melting of ice the correlation between positive carbon isotopes and cool climates may indicate the effectiveness of these high latitude carbon sinks and their ability to draw down atmospheric co 2 resulting in an inverse greenhouse effect

the evidence and implications of polar ice during the mesozoic abstract the mesozoic perhaps representing the longest period of warmth during phanerozoic earth history contains in general sparse and frequently equivocal evidence for polar ice although this time is undoubtedly punctuated by oscillations in climate whether sufficient to lead to polar cooling and the formation of polar ice an inviting mechanism to account for faunal and floral distribution patterns and large scale sea level change has been widely debated mesozoic evidence for glacial conditions includes abraded rock surfaces generally unsorted stone rich beds and the presence of dropstones rafted by ice within a finer grained host sediment faunal and floral evidence has also been utilised to determine the presence or absence of cold or sub freezing polar conditions together with more indirect evidence for glacial conditions derived from general circulation model gcm simulations of climate the analysis of clay mineral distributions glendonite abundance and palaeontological and sedimentological evidence for globally synchronous sea level change the extent of possible glacial environments during the mesozoic has been established by plotting published reports of glacial sediments on palaeogeographic reconstructions the general clustering of evidence at high palaeolatitudes suggests that the extent of polar ice during the mesozoic is likely to have been approximately one third the size of the present day based on such evidence a number of episodes of cold or sub freezing polar climates during the bajocian bathonian tithonian volgian valanginian and aptian are recognised evidence exists possibly also for a cold episode during the early jurassic pliensbachian although poorly constrained owing to limited biostratigraphical control the longevity of these events may be represented by a cold snap within a stage although undoubtedly the possible smearing of ages may have had the effect of lengthening and hence promoting the importance of these proposed events the climate regime of the earth during these times may be hypothesised to be characterised by a relatively steep pole to equator temperature gradient where low latitude regions are as warm or warmer than today the evidence to support such reasoning includes sharp increases in the areal distribution of both glendonites and deposits with affinities to glacial tillites and dropstones for these times coincidental falls of sea level arid events and an increased bipolarity of faunas at these times imparts further confidence that these events were of a magnitude to effect the earth as a whole

xiphosurid trackways in a lower cretaceous tidal flat in patagonia palaeoecological implications and the involvement of microbial mats in trace fossil preservation abstract lower cretaceous trackways assignable to xiphosurids were recently found in tidally influenced marginal marine deposits of the agrio formation patagonia argentina the aim of this paper is to describe these trace fossils in detail discuss their conditions of preservation make palaeoecological and taphonomic inferences from them and analyse the importance of their palaeogeographic location these trace fossils are assigned to kouphichnium and five track morphotypes are established microbially induced sedimentary structures miss are associated with the trackways scanning electron microscope sem studies document the involvement of microbial mats in the preservation of the trackways by the presence of cyanobacteria like filament sheaths the microbial mats enabled preservation of the tracks by binding and biostabilisation of the sediment surface the mostly likely producers of the trackways are from the subfamily limulinae the studied surface could represent a high tide mating ground associated with a very shallow water deposit on a warm cretaceous tidal flat these records are the first convincingly documented trackways produced by xiphosurids in the early cretaceous worldwide and the second fossil record of this group from the cretaceous in the southern hemisphere

finite element modelling of surface wave transmission across regions of subduction summary propagation of rayleigh waves across the regions of subduction of japan and of the north island of new zealand is examined in the frequency domain by the finite element method study of the japan region of subduction ese of the island of honshu has shown that for perfectly elastic 2d models although love waves decrease in velocity across the region rayleigh waves of periods of 35 60s increase slightly in velocity the material properties of the predominantly crustal material being subducted appear to slow the love waves whereas the rayleigh waves of periods of from 35 to 60 s tend to retain their oceanic velocities which are higher than the velocities of rayleigh waves of those periods for the island of honshu amplitude calculations have shown that at periods of 60 s down to 10 s love waves are increasingly forward scattered into higher love modes whereas at a period of 20s 98 per cent of the energy of rayleigh waves is transmitted as the rayleigh fundamental mode this result together with that of drake for the continental margin at berkeley california confirms the practice of using rayleigh waves at a period of approximately 20 s measured at seismographic stations near continental margins and near regions of subduction to estimate the magnitude of teleseisms study of the new zealand region of subduction se of lake taupo on the north island of new zealand has shown similar results to those for the japan region of subduction although love waves decrease in velocity across the region rayleigh waves of periods of 60 s down to 20 s increase slightly in velocity amplitude calculations have shown that at periods of 60 s down to 15 s love waves are increasingly forward scattered into higher love modes on the other hand at a period of 20 s 96 per cent of the energy of rayleigh waves is transmitted as the rayleigh fundamental mode at a period of 10 s in contrast to the results for the japan region of subduction and for the continental margin at berkeley 73 per cent of the energy of love waves is transmitted as the love fundamental mode and 97 per cent of the energy of rayleigh waves is transmitted as the rayleigh fundamental mode amplitude and phase changes of love and rayleigh waves at continental margins and in regions of subduction need to be allowed for when waveform inversions of waves which have traversed these regions are made

absence of matrix like chondrule rims in cr2 lap 02342 in numerous past papers it was concluded that the fine 1 m matrix immediately adjacent to and radially symmetric around chondrules in primitive chondrites consists of compact low porosity rims that were attached in the solar nebula we present here textural and compositional evidence that no matrix like or accretionary rims around chondrules are present in the well preserved cr2 chondrite lap 02342 fine grained matrix rich regions i e candidate rims at the edges of chondrules were studied with an electron microprobe based matrix grid technique comparison of the rims data for matrix regions near these chondrules showed the candidate rims to be compositionally heterogeneous inconsistent with origins as radially symmetric matrix like rims formed by gradual accretion this evidence together with simulations and laboratory studies indicating that accretionary processes produced highly porous aggregates strongly suggests that nebular processes did not produce compact matrix like rims around chondrules in any chondrite group

western margin and provenance of sediments of the neuquen basin argentina in the late jurassic and early cretaceous abstract the late jurassic to early cretaceous 138 117 ma sediments of the neuquen basin argentina are in part derived from a transitional to dissected magmatic arc in the west and a metamorphic highland north patagonian massif in the south to southwest the only exceptions are the sediments 128 5 ma in age which also indicate a source from a recycled orogen block of san rafael in the east modal analyses and heavy mineral analyses reflect the development of the magmatic arc with regard to both region and time in the tithonian the arc supplied debris typical of a transitional arc in the berriasian the detritus originated from a dissected arc which returned to its transitional stage in the uppermost berriasian

upper mantle beneath southeast asia from s velocity tomography 1 we present a three dimensional s velocity model of the se asian western pacific upper mantle with 400 km lateral resolution using the novel automated multimode inversion technique we processed 4038 vertical component seismograms and extracted 22 708 linear equations with uncorrelated uncertainties that constrain upper mantle structure we used time frequency windows to select signal with negligible proportion of scattered energy the windows included the fundamental rayleigh mode and s and multiple s waves the observed range of s velocity variations is the widest 17 18 in the upper 150 km of the mantle high velocity continental roots can reach beyond the present extent of the overlying archean proterozoic crust by 500 km beneath some precambrian units the roots are absent which can be attributed to deformation and gradual destruction of the ancient lithosphere at 120 150 km s velocity beneath some cratons reaches 4 8 km s this can be accounted for by thermal and compositional effects beneath the hainan island area a low velocity anomaly is observed from near the surface to the bottom of our model the hot spot type volcanism here may be caused by the deep mantle hainan plume a low velocity mantle domain underlies the south central sea of japan surrounded on the surface by intraplate volcanoes a deep seismicity gap is present near 40 n in the pacific slab subducting below and may result from a plume slab interaction a high velocity anomaly is present in the transition zone beneath the northern boundary of the yangtze craton we propose that the anomaly corresponds to subducted continental lithosphere stagnant atop the 660 km discontinuity

extension of the basin rayleigh wave amplification theory to include basin edge effects the presence of sediments near the earth s surface can significantly amplify the strength of shaking during earthquakes such basin or site amplification effects have been well documented in numerous regions yet the complex and often situational dependence of competing reasons for this amplification makes it hard to quantify in a general sense or to determine the most significant contributions simple 1d seismic profiles can be used to estimate the amplitude differences between a basin site and a hard rock reference site but this ignores any reflections or conversions at the basin edge or a resonance effect depending on the basin s geometry in this article we explore an analytic model based on coupling coefficients for surface rayleigh waves to account for the lateral discontinuities at a basin s edge datta 2018 we use this simple tool to explore the relationship between the basin s rayleigh wave amplification spectrum and various parameters such as basin depth edge slope angle and impedance contrast the step by step construction of the model allows us to quantify the contributions from various wave propagation effects with the goal of identifying situations under which various basin edge effects must be considered in addition to purely 1d estimates for the most velocity contrasts less than a factor of 5 the error made by the 1d theory in predicting maximum rayleigh wave basin amplification is under 35 for both the horizontal and the vertical components for simple basins the vertical amplification dominates at larger high frequencies and the horizontal at lower frequencies finally we demonstrate from comparisons with spectral element wavefield simulations that realistic velocity structures can be reduced to a simpler box shape for the semi analytic formulation used here with reasonable results for the purposes of estimating site amplification or microzonation an improved model that accounts for basin edge effects can be implemented without high computational cost

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

microchondrules in two unequilibrated ordinary chondrites evidence for formation by splattering from chondrules during stochastic collisions in the solar nebula the diversity of silicate glassy spherules analogous to chondrules called microchondrules and the implications for their presence in unequilibrated ordinary chondrites uocs were investigated using different electron microscope techniques our observations show that the abundance of microchondrules in uocs is much larger than the values proposed by previous studies we identified two different types of microchondrules porous and nonporous embedded within fine grained matrices and type i chondrule rims the porous microchondrules are characterized by distinctive textures and chemical compositions that have not been recognized previously additionally we show detailed textures and chemical compositions of protuberances of silicate materials connected to the chondrules and ending with microchondrules we suggest that microchondrules and protuberances formed from materials splattered from the chondrules during stochastic collisions when they were still either completely or partially molten the occurrence and distinct morphologies of microchondrules and protuberances suggest that rather than just a passive flash melting of chondrules an additional event perturbed the molten chondrules before they underwent cooling the bulk chemical compositions suggest that 1 nonporous microchondrules and protuberances were formed by splattering of materials that are compositionally similar to the bulk silicate composition of type i chondrules and 2 the porous microchondrules could represent the splattered melt products of a less evolved fine grained dust composition the preservation of protuberances and microchondrules in the rims suggests that the cooling and accretion rates were exceptionally fast and that they represent the last objects that were formed before the accretion of the parent bodies of ocs

high temperature rims around chondrules in primitive chondrites evidence for fluctuating conditions in the solar nebula abstract rims or rim sequences surrouding chondrules have been identified in carbonaceous and unequilibrated ordinary chondrites these chondrule rims include three chemical subtypes fe ca rich and fe ni metal rich rims which occur predominantly in kainsaz co3 and ferromagnesian rims which occur in kainsaz co3 allende cv3 renazzo cr2 chainpur ll3 semarkona ll3 krymaka l3 and tieschitz h3 the compositions of minerals in these rims are often drastically different from those in the underlying chondrule cores indicating that the solar nebula was chemically heterogeneous in many cases the compositions of the rims require an environment that was much more oxidizing than a solar composition gas particularly interesting is that some of the fe ca rich chondrule rims are remarkably similar to some of the rims around refractory inclusions suggesting that chondrules and refractory inclusions experienced late coeval processing the textures of the chondrule rims suggest they formed at high temperatures and that they accreted onto chondrules that had already solidified the lengthscale of the thermal heterogeneities necessary to make available hot material that could accrete to cold chondrules has been calculated to be less than 10 km implying there were localized heat sources in the solar nebula

microchondrules in ordinary chondrites implications for chondrule formation abstract previous studies of ordinary chondrites oc reported isolated microchondrules within the fine grained or clastic matrix of many type 3 samples larger sets of microchondrules have also been found as rare clasts in type 3 oc we report here another major setting for microchondrules large numbers n 100 of microchondrules 40 m in apparent diameter occur together with irregularly shaped fragments in fine grained rims around four low feo porphyritic olivine chondrules and one barred olivine chondrule these chondrules are from ll3 1 bishunpur l3 4 eet90161 l3 4 eet90261 ll3 4 piancaldoli and ll3 0 semarkona the two kinds of microchondrules observed are 1 numerous low feo radial and cryptocrystalline microchondrules consisting of low ca pyroxene and 2 relatively rare high feo olivine microchondrules both types of microchondrules are embedded in high feo fine grained matrix materials they are typically accompanied by irregularly shaped pyroxene fragments that form a continuum in composition and shape with the low feo microchondrules the pyroxene rich surfaces of the host chondrules project into the surrounding rims as peninsulas with rounded embayments consistent with remelting although on average less ferroan the peninsulas overlap the fragments and low feo microchondrules in composition and appear to have been the main source of these objects the occurrence of numerous low feo pyroxene rich microchondrules with similar textures and compositions within high feo fine grained matrix rims around normal size chondrules and the apparent remelting of the surfaces of the host chondrules indicate that the microchondrules formed after solidification of the host chondrules mainly by remelting of their pyroxene rich surfaces or possibly igneous rims the remnants of these pyroxene rich rims are preserved as peninsulas extending outward from the chondrule surface and as irregularly shaped pyroxene fragments coexisting with the microchondrules because a newly formed microchondrule cloud in the nebula would dissipate quickly due to random motions of the individual microchondrules it seems inescapable that the fine grained material which now surrounds the microchondrules was in their immediate vicinity when they formed and served as a trapping matrix the material probably occurred as a highly porous aerogel like aggregate of feo rich nebular dust the rare high feo olivine microchondrules probably formed at the same time as the low feo pyroxene microchondrules by melting adjacent portions of the porous dust

waveform inversion for lateral heterogeneities using multimode surface waves summary we propose a waveform inversion scheme that can be used to invert strong structural heterogeneities the method is based on a ray approximation for surface waves strong structural lateral variations are modelled by vertical discontinuities therefore a geologically heterogeneous region is partitioned into a number of lateral homogeneous subregions synthetic seismograms are calculated by modal summation over incident and transmitted modes with this method the complete waveforms of surface waves including mode cross branch coupling multipathing and scattering are considered in the inversion we test the method with several geophysically realistic structural models an example of waveform inversion for real data a wave path across the iberian peninsula and the oceanic structure off the french coast owing to the gibraltar earthquake ms 5 7 is presented the method allows us to obtain the information represented by different set of structures along the same source receiver minor arc through which the waves have propagated the method is applicable to different models of lateral heterogeneity in its present development it is most appropriate for inverting structures around tectonic scenarios such as continental margins grabens and discontinuities between major plates

surface waveform tomography of the turkish iranian plateau summary the middle east is a tectonically complex region consisting of terrains as diverse as precam brian shields and young orogens the dominant tectonic feature is the turkish iranian plateau a recently elevated seismically active region along the zagros bitlis suture which results from the collision of the arabian plate with eurasia in this study we use surface waveform tomography to elucidate the upper mantle shear wave velocity structure beneath the turkish iranian plateau and adjacent regions the main large scale feature in the tomographic model is a low shear wave velocity anomaly in the uppermost mantle beneath the plateau this low velocity feature correlates with a long wavelength free air gravity anomaly and with recent volcanism whose geochemistry has a lower lithospheric mantle signature seismology gravity and volcanism all suggest the presence of a thin lithosphere and warm upper mantle beneath the turkish iranian plateau the upper mantle low shear wave velocity zone the high free air gravity and the deep lithospheric source depth for the basaltic volcanism are all consistent with a partial delamination of the lithosphere as a result of earlier lithospheric thickening resulting from the continental collision

the frequency of compound chondrules and implications for chondrule formation the properties of compound chondrules and the implications that they have for the conditions and environment in which chondrules formed are investigated formulae to calculate the probability of detecting compound chondrules in thin sections are derived and applied to previous studies this reinterpretation suggests that at least 5 of chondrules are compounds a value that agrees well with studies in which whole chondrules were removed from meteorites the observation that adhering compounds tend to have small contact arcs is strengthened by application of these formulae while it has been observed that the secondaries of compound chondrules are usually smaller than their primaries these same formulae suggest that this could be an observation bias it is more likely than not that thin section analyses will identify compounds with secondaries that are smaller than their primaries a new model for chondrule collisional evolution is also developed from this model it is inferred that chondrules would have formed on average in areas of the solar nebula that had solids concentrated at least 45 times over the canonical solar value

european cretaceous shorelines stage by stage abstract inferred shorelines are presented for the twelve cretaceous stages for the area of europe and adjacent seas contained between approximately 35 and 65 n and between 15 w and 25 e there is a brief stage by stage commentary and a bibliography of source materials

multimode rayleigh wave inversion for heterogeneity and azimuthal anisotropy of the australian upper mantle summary we present an azimuthally anisotropic 3 d shear wave speed model of the australian upper mantle obtained from the dispersion of fundamental and higher modes of rayleigh waves we compare two tomographic techniques to map path average earth models into a 3 d model for heterogeneity and azimuthal anisotropy method i uses a rectangular surface cell parametrization and depth basis functions that represent independently constrained estimates of radial earth structure it performs an iterative inversion with norm damping and gradient regularization method ii uses a direct inversion of individual depth layers constrained by bayesian assumptions about the model covariance we recall that bayesian inversions and discrete regularization approaches are theoretically equivalent and with a synthetic example we show that they can give similar results the model we present here uses the discrete regularized inversion of independent path constraints of method i on an equal area grid with the exception of westernmost australia we can retrieve structure on length scales of about 250 km laterally and 50 km in the radial direction to within 0 8 per cent for the velocity 20 per cent for the anisotropic magnitude and 20 for its direction on length scales of 1000 km and longer down to about 200 km there is a good correlation between velocity heterogeneity and geologic age at shorter length scales and at depths below 200 km however this relationship breaks down the observed magnitude and direction of maximum anisotropy do not in general appear to be correlated to surface geology the pattern of anisotropy appears to be rather complex in the upper 150 km whereas a smoother pattern of fast axes is obtained at larger depth if some of the deeper directions of anisotropy are aligned with the approximately n s direction of absolute plate motion this correspondence is not everywhere obvious despite the fast 7 cm yr 1 northward motion of the australian plate more research is needed to interpret our observations in terms of continental deformation predictions of sks splitting times and directions an integrated measure of anisotropy are poorly matched by observations of shear wave birefringence

lower cretaceous berriasian aptian biostratigraphy of the neuquen basin the berriasian aptian succession in the neuquen basin is mainly marine in the lower part and non marine in the upper portion a detailed ammonite zonation is presented for the berriasian early barremian interval while some ammonite taxa are endemic others are widely distributed and there are several levels where correlation can be suggested with the standard stages and zones of the tethyan mediterranean area several nannofossil bioevents are recognized and these provide evidence for correlation with tethyan areas correlations suggested by both groups are reasonably consistent berriasian aptian palynomorphs include both terrestrial and marine forms several terrestrial assemblages can be recognized but the marine forms are mainly long ranging taxa especially in the agrio formation the geological society of london 2005

reconstruction of vertical temperature gradients in past oceans proxy data from the hauterivian early barremian early cretaceous of the boreal realm abstract a total of 25 mudstone samples from two sections in northwest germany and northeast england palaeolatitude 40 n respectively of hauterivian and early barremian age were analysed using tex86 palaeothermometry in addition the stable isotope ratio 18o 13c and trace element content mg sr fe and mn of 138 belemnite guards from the same two outcrops were determined to reconstruct past sea water temperatures the tex86 based sea surface temperatures were constantly warm 24 26 c throughout the entire hauterivian for both sections and even warmer for the early barremian 27 30 c stable water temperatures prevailed over a period of 6 4 ma in the southernmost part of the boreal realm these findings clearly support the view of warm equable conditions for the hauterivian at least for mid latitudinal settings a constant off set between higher tex86 derived temperatures and lower 18obel derived temperatures was observed this may be explained by either increased sea water salinities a deep dwelling habitat of belemnites or a combination of both a by 3 higher salinity of the sea water below the thermocline which would at least partly explain the by 2 too positive 18obel values cannot be ruled out in these epicontinental settings a habitat of the belemnites below the thermocline in perhaps 50 100 m water depth may have contributed to the positive 18obel data as well the temperature difference between the tex86 and the 18obel findings might therefore reflect a vertical temperature gradient of the water column of 4 5 c and a salinity of the subsurface waters of 38

organic facies variations in the valanginian mid hauterivian interval of the agrio formation chos malal area neuquen argentina local significance and global context

constraints on the formation age of cometary material from the nasa stardust mission we measured the 26 al 26 mg isotope systematics of a 5 m refractory particle coki returned from comet 81p wild 2 in order to relate the time scales of formation of cometary inclusions to their meteoritic counterparts the data show no evidence of radiogenic 26 mg and define an upper limit to the abundance of 26 al at the time of particle formation of 26 al 27 al 5 the absence of 26 al indicates coki formed 1 7 ma after the oldest solar system solids ca al rich inclusions cais the data presented here suggest that high temperature inner solar system material formed was subsequently transferred to the kuiper belt and incorporated into comets several million years following cai formation

approximation of surface wave mode conversion at a passive continental margin by a mode matching technique summary at a continental margin sharp structural changes cause strong lateral heterogeneity in s wave velocity p wave velocity and density therefore mode conversion of surface wave modes is expected passive continental margins may be modelled by vertical discontinuities mode conversion is then expressed in terms of re ection and transmission coe cients long period seismograms are calculated by mode summation over incident re ected and transmitted modes re ection and transmission coe cients for surface waves are approximated by a mode matching technique that is adapted to a spherical earth model an orthogonality relation for surface wave eigenfunctions on a spherical earth is given that allows one to simplify the linear system of equations for the determination of re ection and transmission coe cients transmission of fundamental love and rayleigh modes is strongly in uenced by upper crustal heterogeneity for frequencies larger than 40 hz for fundamental love modes and larger than 60 hz for fundamental rayleigh modes mode conversion to neighbouring modes can be strong but mode conversion is not necessarily con ned to neighbouring modes fundamental modes in particular can couple with more distant higher modes in synthetic seismograms calculated for epicentral distances up to 40 0 mode conversion between higher modes and fundamental modes results in shear coupled rayleigh waves

paleoceanographic changes during the early cretaceous valanginian hauterivian evidence from oxygen and carbon stable isotopes we investigated valanginian hauterivian bulk rock and belemnite samples from vocontian basin sections in southeastern france for their stable carbon and oxygen isotope signature firstly because these sections permit calibration with high resolution biostratigraphy based on ammonites and secondly because detailed isotope studies for the hauterivian are lacking the results show that 13c values for bulk rock decrease during the late valanginian early hauterivian with 1 and increase again during the late hauterivian with 1 the 18o signal for bulk rock samples is mostly disturbed by diagenesis the belemnites show carbon and oxygen isotope values that are lower and higher than bulk rock samples respectively we explain this as the result of the belemnites recording a deeper water signal with lighter 13c values and heavier 18o values implicating colder water at greater depth the overall preservation of the belemnites is very good and permits the construction of a paleo temperature trend this trend shows warm deeper water temperatures during the late early valanginian 15 c and progressively cooler temperatures during the late valanginian and early hauterivian 11 c during the late hauterivian temperatures increase again 13 c we relate this cooling trend for deeper water to a second order sea level rise which allowed for the exchange of cold boreal and warm tethyan water masses the influx of cold nutrient rich water had a profound effect on carbonate producing biota along the northern margin of the tethys during the hauterivian leading to prolonged phases of condensation and platform destruction during the early hauterivian the carbonate system along the northern tethyan margin shifted into a green water mode of carbonate production high rates of carbonate production under mesotrophic conditions also observed in other parts of the world meant that the global carbon cycle became buffered shown by the stable trends in carbon isotopes

reconstruction of jurassic bathonian palaeosalinity using stable isotopes and faunal associations abstract the bathonian is an interval from which salinity controlled benthic faunas are particularly well known this study examines late bathonian faunas from dorset uk from the wattonensis beds fuller9s earth of known marine origin the overlying elongata beds and the boueti bed marking the base of the forest marble 18 o values of belemnites belemnopsis from the wattonensis beds range from 1 4 to 0 7 and carbon isotope values range from 2 3 to 0 5 vpdb isotope values of well preserved rhynchonella from the wattonensis beds range from 2 4 to 1 3 for oxygen and 1 1 to 0 6 vpdb for carbon the 18 o data suggest high palaeotemperatures possibly up to 28 c a similar spread of data is derived from brachiopods goniorhynchia boueti from the boueti bed given the marine origin of the wattonensis beds and overlap of data the reduced faunal diversity of the boueti bed is considered unlikely to be the result of reduced salinity brachiopods therefore should not be regarded more sceptically as evidence for fully marine conditions as has been suggested the oysters praeexogyra hebridica elongata and brachiopods rhynchonella from the elongata beds have isotope values that also imply fully marine conditions and are interpreted as being indicative of slightly cooler conditions

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

the primitive matrix components of the unique carbonaceous chondrite acfer 094 a tem study the mineralogical and chemical characteristics of the fine grained matrix 53 m of the unique primitive carbonaceous chondrite acfer 094 have been investigated in detail by scanning electron microscopy sem and analytical transmission electron microscopy atem generally the fine grained matrix represents a highly unequilibrated assemblage of an amorphous material small forsteritic olivines 200 300 nm low ca pyroxenes 300 400 nm and fe ni sulfides 100 300 nm the matrix is basically unaffected by secondary processes only minor amounts of serpentine and ferrihydrite as products of hydrous alteration are present texturally the amorphous material acts as a groundmass to olivines pyroxenes and sulfides mostly exhibiting rounded or elongated morphologies only very few clastic mineral grains have been found the texture and chemical composition of the amorphous material are consistent with an origin by disequilibrium condensation in either the cooling solar nebula or a circumstellar environment as such the amorphous material may be considered as a possible precursor of matrix materials in other types of chondrites the non clastic matrix olivines fo98 99 and pyroxenes en97 100 are suggested to have formed either by condensation in the solar nebula under highly oxidizing conditions or by recrystallization from the amorphous material the formation of these grains by fragmentation of chondrule components is unlikely due to chemical and microstructural reasons rapid cooling caused the observed intergrowths of clino orthoenstatite in the mg rich matrix pyroxenes although some similarities exist comparing the fine grained matrix of acfer 094 with the matrices of the unequilibrated c03 chondrite alha77307 and the unique type 3 chondrite kakangari acfer 094 remains unique since it contains the highest measured concentrations of circumstellar sic and the second highest of diamond highest is orgueil it seems reasonable to suggested that at least parts of the amorphous material in the fine grained matrix may be of circumstellar origin

fe mn systematics of type iia chondrules in unequilibrated co cr and ordinary chondrites we have examined fe mn systematics of 34 type iia chondrules in eight highly unequilibrated co cr and ordinary chondrites using new data from this study and prior studies from our laboratory olivine grains from type iia chondrules in co chondrites and unequilibrated ordinary chondrites uoc have significantly different fe mn ratios with mean molar fe mn 99 and 44 respectively olivine analyses from both these chondrite groups show well defined trends in mn versus fe afu and molar fe mn versus fe mg diagrams in general type iia chondrules in cr chondrites have properties intermediate between those in uoc and co chondrites in most uoc and cr type iia chondrules the fe mn ratio of olivine decreases during crystallization whereas in co chondrites the fe mn ratio does not appear to change it is difficult to interpret the observed fe mn trends in terms of differing moderately volatile element depletions inherited from precursor materials instead we suggest that significant differences in the abundances of silicates and sulfides metals in the precursor material as well as open system behavior during chondrule formation were responsible for establishing the different fe mn trends using fe mn mg systematics we are able to identify relict grains in type iia chondrules which could be derived from previous generations of chondrules including chondrules from other chondrite groups and possibly chondritic reservoirs that have not been sampled previously