surface wave mapping of the crust and upper mantle in the arctic region pure path rayleigh wave group velocities for 24 regional grids inside the arctic have been obtained from 74 mixed path measurements the vertical shear wave velocity structures under these 24 grids were then determined according to their pure path group velocity dispersion data this result indicates that the crustal shear wave velocity in the arctic region is generally lower than the worldwide average in addition a typical mid ocean ridge structure was clearly shown under the nansen ridge we also found an abnormally high upper mantle shear wave velocity under the alpha ridge and makarov basin and low velocity beneath the canadian arctic islands in general our inversion result agrees with the known tectonics in the arctic region to further check the validity of our result we have computed synthetic rayleigh waves and a comparison with our observations shows very good agreement

surface wave dispersion crustal structure and sediment thickness variations across the barents shelf summary rayleigh and love wave group velocities were determined for 21 paths across the barents shelf those group velocities exhibit regional variations of 1 0 km or more at short periods depending upon the location of the path within the shelf only two different crustal shear velocity models beneath sedimentary layers are required however to explain all of the group velocity data one model pertains to most of the shelf from a longitude near the eastern coast of svalbard to novaya zemlya the other pertains to a 200 or 300km wide region at the western edge of the shelf shear velocities in the upper crust of the western region are significantly higher and the crust is much thinner than they are for the rest of the shelf that region is known to have moved to its present prosition from a point several hundred kilometres to the north during the caledonian orogeny surface wave group velocities within each of the two regions are strongly influenced by sediments which have accumulated in basins within the barents shelf some of these basins in the southern portion of the shelf may be 10 km or more in thickness

thermoremanent magnetization of the martian lithosphere 1 this paper investigates the thermoremanent magnetization trm of the martian lithosphere assuming that the upper part of the lithosphere acquired trm in the early history of the planet and in the presence of the core field the primary magnetization whereas the lower part has been gradually magnetized by the magnetic field of the upper part as it has cooled below the curie temperature secondary magnetization the secondary magnetization is relatively weak if the magnetic properties of the lower lithosphere are taken to be similar to that of the extrusive basalt near the oceanic ridge axes on earth however if the martian lower lithosphere is more magnetic e g by an order of magnitude the secondary magnetization can be significant although still weaker than the primary magnetization of the upper part such a highly magnetic lower lithosphere does not seem plausible by terrestrial standards and it remains to be confirmed whether it is geologically plausible for mars i also examine a lithospheric model with a strongly magnetic layer beneath the crust 25 times more magnetic than the extrusive basalt representing a possible ilmenite rich layer with a considerable amount of hematite ilmenite lamellae i assume that the layer was not magnetized by the core field because it was hotter than the curie temperature of the lamellae when the core dynamo was active it acquired secondary magnetization later in the presence of the magnetic field of the crust despite adopting an extraordinarily high magnetic layer which seems implausible by terrestrial standards the secondary magnetization of the layer has minor contributions to the observed magnetic anomalies in all models considered the primary magnetization is 20 30 a m and has the dominant contribution to the observed magnetic anomalies it is worth noting that the radial components of the primary and secondary magnetization are parallel whereas the tangential components are in opposite directions because the strong magnetic anomalies in the south likely arise from the tangential magnetization considering the secondary magnetization requires even stronger primary magnetization

fluorescent bands in massive corals result from terrestrial fulvic acid inputs to nearshore zone the discovery of yellow green fluorescent bands in the skeletons of massive corals from inshore waters of the great barrier reef and the temporal and spatial correlations of these bands with adjacent river flow1 prompted an investigation into the substances responsible for the phenomenon we have determined that all regions of the coral skeleton contain fulvic acids2 3 which impart a blue background fluorescence the yellow green fluorescent bands found only in inshore coral appear to result from enhanced concentrations of low relative molecular mass 10 000 fulvic acids from adjacent river input these compounds are ubiquitous and the yellow green banding phenomenon can be expected to occur in massive corals located near to significant river systems in the widely distributed genus porites4 the great age of the largest colonies1 means that extremely long highly resolvable records of coastal runoff exist throughout tropical nearshore seas

chronological control of coral records using luminescent lines and evidence for non stationary enso teleconnections in northeast australia eight multicentury porites coral cores were used to develop a 373 year chronology by cross dating techniques adapted from dendrochronology characteristic patterns of distinct luminescent lines within the coral skeletons were matched between coral cores from inshore and mid shelf reefs in the central great barrier reef australia skeleton plots of luminescent banding were produced for each core and combined into a master chronology back to ad 1615 in addition to improving dating control the luminescence master chronology provides a proxy for burdekin river runoff and queensland summer rainfall variations in the magnitude of the correlation between the luminescence master and the mann et al 2000 nino3 sea surface temperature reconstruction provides insights into the long term stability of el nino southern oscillation enso telecon nections burdekin river runoff was significantly inversely related to enso variability for much of the period from the ad 1650s to 1800 suggesting that enso related te

activators of photoluminescence in calcite evidence from high resolution laser excited luminescence spectroscopy abstract laser excited luminescence spectroscopy of a red algal biogenic calcite and a synthetic mn calcite can make the distinction between organic and trace element activators of photoluminescence organic activated photoluminescence in biogenic calcite is characterized by significant peak shifts and increasing intensity with shorter wavelength excitation and by significant decreases in intensity after heating to 400 c in contrast mn activated photoluminescence shows no peak shift greatest intensity under green excitation and limited changes after heating examination of samples with a high sensitivity spectrometer using several wavelengths of exciting light is necessary for identification of photoluminescence activators

tropical river flow and rainfall reconstructions from coral luminescence great barrier reef australia 1 rainfall and river flow in northeast queensland australia are highly seasonal and show high interannual and decadal variability that is modulated by el nino southern oscillation enso events and the pacific decadal oscillation pdo reconstructions of october september freshwater input to the great barrier reef lagoon and october september queensland rainfall are developed from visual assessment of the occurrence and intensity of luminescent lines in massive porites from up to 25 coral cores from 15 nearshore reefs regularly influenced by river flood plumes separate reconstructions are developed for four rivers herbert burdekin pioneer and fitzroy and these are used to reconstruct total annual freshwater flow into the great barrier reef 69 74 variance calibrated and an index of queensland rainfall 53 57 variance calibrated the reconstructions extend back to 1631 but are most reliable from 1661 and capture significant decadal variability the reconstructions provide insights into long term tropical rainfall and river flow variability and the behavior of enso and the pdo over several centuries significant though weak relationships are found between these reconstructions and an independent reconstruction of enso the reconstructions highlight that observations from the instrumental records of high interannual and decadal rainfall and river flow variability in northeast australia also characterize the past few centuries although there appears to be no overall trend toward wetter or drier conditions the reconstructions suggest that the variability of rainfall and river flow has increased during the twentieth century with more very wet and very dry extremes than in earlier centuries as projected for the region as a consequence of global warming

synthetic seismogram and surface wave constraints on crustal models of spitsbergen abstract seismic refraction data collected on spitsbergen in 1978 are used to obtain a crustal model assuming plane horizontal layering the observed travel times and wave forms are compared with those of synthetic seismograms computed for various published crustal models the more detailed models adequately explain some but not all of the features of the synthetics these models are adjusted utilizing travel times and wave form amplitudes until a satisfactory fit is achieved the best fitting model consists of a 4 layer crust having thicknesses of 4 1 10 0 7 4 and 5 8 km and compressional velocities of 4 65 6 21 6 30 and 6 65 km sec with increasing depth the uppermost mantle has a velocity of 7 90 km sec a comparison of observed and synthetic p n waveforms supports the existence of a thin low velocity zone beginning at a depth of about 5 km beneath the moho boundary an inversion of seismic surface wave group velocity data yields a shear wave model which is compatible with the compressional wave model

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

seasonal rainfall in the sinai desert during the late quaternary inferred from fluorescent bands in fossil corals skeletal bands of alternating high and low density in massive coral species have been used to record their growth history1 2 in the red sea living colonies of the genus porites deposit low density skeletal bands during summer and high density bands during winter3 additionally yellow green fluorescence can sometimes be seen in these massive corals imparted to them by the incorporation of humic material carried by coastal runoff4 annual banding of fluorescent sequences in living scleractinian corals has proved to be useful in the study of terrestrial runoff in the near shore environment5 6 here we report the finding of similar yellow green fluorescent bands in fossil porites from late quaternary reef terraces in southern sinai which are absent from living porites in the nearby fringing reefs the periodic sequences of the fluorescing humics were found to be superimposed on the low density sub bands of the fossil corals we interpret our observations as evidence that during the late quaternary reef forming peaks the climate was wetter than the extreme desert conditions now prevailing with a possible summer rainfall regime

high resolution isotopic records from corals using ocean temperature and mass spawning chronometers abstract we present a 6 year long 1978 1984 18 o and 13 c record from a great barrier reef pandora reef porites lutea coral based on near weekly sample intervals a sampling technique was designed to minimise any smoothing or distortion of the isotopic record due to complex coral growth calyx architecture and calcification at depth within the tissue layer the arrival time of the mid winter minimum sea surface temperature is very consistent 2 weeks near pandora reef and provides an annual time marker offering more precision than the traditional density band chronometer the improved chronology and high resolution record demonstrate that signal distortion in porites due to calcification within the tissue layer and variable intra annual coral extension is generally negligible also confirmed is that the arrival time of monsoonal floods is precisely preserved 1 week within the skeleton of porites the sensitivity of weekly sampling allows the detection of a subtle warm to cool sea surface temperature anomaly which preceded by more than one year a similar temperature anomaly associated with the 1982 83 el nin o in the east pacific sharply higher 13 c values coincide with the time of the annual coral mass spawning event in the great barrier reef recognition of this mass spawning signal should simplify the interpretation of coral 13 c records and provides an additional precise time marker with which to adjust chronologies when intra annual coral extension is not constant

nature and origin of organic matter in carbonates from speleothems marine cements and coral skeletons organic matter in speleothem calcite marine carbonate cements and aragonitic coral skeletons was studied to determine its location molecular structure functionality and effect on mineral growth sem analyses showed that inorganically precipitated carbonates incorporate during growth adsorbed organic matter between submicroscopic subunits of the crystals whereas biologically secreted carbonates incorporate biogenic tissue between the crystals molecular fluorescence spectroscopy indicated that low molecular weight fulvic acids are the most important constituents of the organic matter the fulvic acids are probably derived from soils speleothem calcite dissolved organic matter marine carbonates and biological decay products aragonitic coral skeleton

seismicity and present day tectonics of the svalbard region summary data collected by temporary seismic networks and individual stations over a 7 yr period in the svalbard archipelago are integrated and used to study the seismicity and present day tectonics of the archipelago and surrounding regions most of the continental seismic activity occurs in three concentrated zones one in heer land near the eastern coast of the island of spitsbergen and two in close proximity to one another on the island of nordaustlandet all three zones are in regions which have been devoid of major orogenic activity since the late devonian the heer land zone and at least one of the zones in nordaustlandet define active faulting which has not been identified by surface mapping the other zone in nordaustlandet occurs in the region of a mapped system of faults all branches of which are relatively minor a number of smaller concentrations and individual earthquakes occur throughout much of the archipelago and surrounding continental shelves seismicity is currently low in the region of tertiary orogenic activity in western spitsbergen a roughly linear pattern of minor activity in southern spitsbergen occurs west of the heer land zone and extends at least 50km southward the major n s faults in spitsbergen which are thought to have accomodated large displacements in devonian time are currently inactive except perhaps at the southern termini of the billefjorden and lomfjorden fault zones where they approach the heer land seismic zone earthquakes located near the western continental margin of spitsbergen may occur on segments of rifting and shearing which reflect the opening of the greenland sea during the tertiary the limited extent of the currently active zones of activity their spatial stability over several years and the lack of activity on the major faults of svalbard argue against the existence of plate boundaries along which motion is currently occurring in the svalbard region all fault plane solutions on svalbard are consistent with a stress field characterized by e w compression whereas previously published fault plane solutions for the ridge system west of svalbard indicate e w extension the magnitude of the compressive stress increases from small values near the ridge system to values sufficiently large to dominate the regional seismicity of svalbard over distances of 200 300 km

grain size dependent potential for self generation of magnetic anomalies on mars via thermoremanent magnetic acquisition and magnetic interaction of hematite and magnetite abstract early in the history of planetary evolution portions of martian crust became magnetized by dynamo generated magnetic field a lateral distribution of the secondary magnetic field generated by crustal remanent sources containing magnetic carriers of certain grain size and mineralogy is able to produce an ambient magnetic field of larger intensity than preexisting dynamo this ambient field is capable of magnetizing portions of deeper crust that cools through its blocking temperatures in an absence of dynamo we consider both magnetite fe3o4 and hematite fe2o3 as minerals contributing to the overall magnetization analysis of magnetization of magnetic minerals of various grain size and concentration reveals that magnetite grains less than 0 01 mm in size and hematite grains larger than 0 01 mm in size can become effective magnetic source capable of magnetizing magnetic minerals contained in surrounding volume preexisting crustal remanence for example 250 a m relates to 25 of multi domain hematite can trigger a self magnetizing process that can continue in the absence of magnetic dynamo and continue strengthening and or weakening magnetic anomalies on mars thickness of the primary magnetic layer and concentration of magnetic carriers allow specification of the temperature gradient required to trigger a self magnetization process

on the inversion of love and rayleigh wave dispersion and implications for earth structure and anisotropy summary various factors can make it difficult to explain observations of love and rayleigh wave dispersion with the same relatively simple isotropic model these factors include systematic errors which might occur in determinations of observed group and phase velocities lateral variations in structure along the path of travel and the attempt to explain observations with a model comprised of only a small number of thick layers the last of these factors is illustrated by an inversion of dispersion data in the central united states where shear wave anisotropy had previously been invoked as one way to explain incompatible love and rayleigh wave velocities it is shown that the data can be satisfied equally well by an isotropic model consisting of several thin layers in cases where the incompatibility of love and rayleigh wave data might be produced by intrinsic anisotropy it is necessary to invert those data using an anisotropic theory rather than by separate isotropic inversions of love and rayleigh waves inversions of fundamental mode data for a region of the pacific assuming anisotropic media in which the layers are transversely isotropic with a vertical axis of symmetry lead to models which are highly non unique even if the inversions solve only for shear velocities in the litho sphere and asthenosphere it is not possible without supplementary information to ascertain the depth interval over which anisotropy occurs or to determine the thickness of the lithosphere or asthenosphere with much precision

sedimentary basins and the blockage of lg wave propagation in the continents the phenomenon of lg blockage where lg is strongly attenuated by crustal heterogeneities poses a serious problem to ctbt monitoring because lg is an important seismic phase for discrimination this paper examines blockage in three continental regions where the lg blockages may be caused by large enclosed sedimentary basins along the propagation path the barents sea basin blocks lg propagation across the barents sea from the russian nuclear test sites at novaya zemlya to scandinavian stations also early lg waves are observed in sn codas on norsar noress and arcess recordings of novaya zemlya explosions where direct lg is blocked early lg waves may have resulted from sn to lg mode conversion at the contact between the barents basin and the kola peninsula the northern and southern caspian sea basins also block lg waves from pnes and earthquakes perhaps due to thick low velocity low q sediments replacing the granitic layer rocks in the crust lg blockage has also been observed in the western mediterranean levantine basin due to low q sediments and crustal thinning a basin capture model is proposed to explain lg blockage in sedimentary basins in this model shear waves that reverberate in the crust and constitute the lg wave train are captured delayed and attenuated by thick low velocity sediments that replace the granitic layer rocks of the upper crust along part of the propagation path sn waves which propagate below the basin would not be blocked and in fact the blocked lg waves may be diverted downward into sn waves by the low velocity sediments in the basin

multimode rayleigh wave attenuation and qβ in the crust of the barents shelf the multimode method of cheng and mitchell 1981 is used to study the attenuation properties of the crust throughout the barents shelf the sensitivity of the spectra to various source factors and to propagation factors which might characterize a shelf region are thoroughly studied for plane layered models the method is very sensitive to q in the upper crust and to q of sedimentary layers if those layers are thick and highly attenuating it is far less sensitive to q in the lower crust and to q the spectra for shallow strike slip earthquakes are very insensitive to changes in strike slip and dip angles of the fault throughout the entire period range of interest but are very sensitive to variations in focal depth except in the long period range of the fundamental mode and the short period range of the higher modes the fundamental mode but not the higher mode spectra for one path across the barents shelf are apparently distorted at short periods by lateral heterogeneities along the travel path simple two layer trial and error inversions yield a model of the barents shelf with an upper crustal q value of about 80 three layer inversions with a sedimentary layer however yield an upper crustal q of about 250 if the sediments are 1 km thick and are characterized by q values of 40 shear velocity models for the barents shelf show variations between about 3 0 and 3 6 km s in the upper crust along different paths the lower crust shows smaller regional differences but velocities vary between 3 5 and 4 0 km s through the depth range 25 35 km the variation of shear velocities in the upper mantle may correlate with those of the upper crust and vary regionally between about 4 3 and 4 8 km s

luminescence and density banding patterns in massive porites corals around the thai malay peninsula southeast asia we characterized the annual luminescent and skeletal density banding patterns in 51 massive porites corals from 15 reefs from six locations around the thai malay peninsula in southeast asia and explored the seasonal environmental cues drivers of band formation location specific recurrent annual luminescent banding patterns were found at all study locations with a brighter band occurring toward the end of the year october november december at five locations and in june one location annual density banding patterns could only be discerned at four locations and were categorized into those that formed a dense band commencing november december and those starting may june overall compared to luminescence variations in skeletal density provided a less clear signal for demarcation of annual growth increments seasonal variations in luminescence showed clearest relationships with salinity as a proxy for freshwater river runoff no convincing relationship between intra annual luminescence intensity and density variations was found which supports the notion that luminescent banding is due to inclusions of fluorophores into the coral skeleton rather than variations in skeletal architecture the relationships between seasonal density variations and significant wave height and rainfall suggest density banding in this region is likely related to wave energy or some other correlated environmental parameter s the large variability in skeletal banding patterns not only highlights the current relatively poor understanding of their nature and causes but also the need for replication in their interpretation especially in settings with complex seasonal hydrodynamic hydrological patterns such as those found around the thai malay peninsula

a 50 degree spherical harmonic model of the magnetic field of mars this paper presents a 50 degree and order spherical harmonic model of the magnetic field of mars derived at 120 km altitude using the three orthogonal components of the vector magnetic field data acquired by the mars global surveyor within the 80 to 200 km altitude range the downward continued vector magnetic field components to the surface of mars delineate details of the martian magnetic field the strong magnetic anomalies in the southern hemisphere do not show compelling evidence for magnetic lineations similar to those associated with the seafloor spreading on earth the anomalies are more or less equidimensional the magnetic signatures surrounding the impact basins hellas argyre and isidis show that the prominent magnetic anomalies are older than the impact events an average magnetization of 2 a m is estimated for the upper crust surrounding hellas basin four isolated magnetic anomalies are modeled by vertical prisms with circular cross sections of 170 to 190 km radius and 20 to 30 km thickness the magnetization of the model prisms is 5 a m more than that of the surroundings

an altitude normalized magnetic map of mars and its interpretation techniques developed for the reduction and analysisofterrestrialsatellitemagneticelddataareusedto better understand the magnetic eld observations made by mars global surveyor a global distribution of radial br magnetic eld observations and associated uncertainties is invertedfor an equivalentsource magnetization distribution and then used to generate an altitude normalized map of br at 200 km the observations are well represented by a potential function of crustal origin consistent with a rema nent origin for the martian magnetic features the correla tion between the 40546 br observations andbr calculated from the magnetization solution at observation locations is 0 978 for a magnetization distribution connedto a 50 km layer calculatedmagnetizationsrangefrom 22to 17a m we see correlations with tectonics that were only hinted at in earlier maps magnetic features appear to be truncated against valles marineris and ganges chasma suggestive of a major change in crustal properties associated with fault ing

tomographic inversion of rg wave group velocities for regional near surface velocity structure the tomographic inversion of group velocities of rg waves is a viable technique for mapping lateral variations in the lithology of sedimentary basins in order to determine a velocity structure we first use the moving window maximum entropy spectral analysis to measure the average rg wave group travel times second the group velocities within blocks subregions covering the area sampled by the rg wave propagation paths are determined by tomographic inversion third the vertical shear wave velocity profile within each block is determined from the inversion of group velocities for that block finally a structural cross section is obtained by connecting blocks located along a profile rg waves recorded from mining explosions in alabama were used in a test of the technique by modeling the paleozoic sedimentary rocks in the black warrior basin of northern alabama the high resolution of moving window maximum entropy spectral analysis allows estimation of the rg wave group velocities with a precision of better than 3 the usable frequency range of 0 5 to 1 5 hz allows determination of structures to depths of about 2 4 km with layers of 0 2 km thickness blocks of widths of 20 km or less could be resolved with appropriate data shear wave velocities in the black warrior basin range from 1 6 to 4 0 km s the layering in the velocity structure corresponds to major geologic units within units an increase in velocity to the northeast corresponds to observed facies changes

evidence of reduced mid holocene enso variance on the great barrier reef australia this study was funded by the national environmental research programme nerp tropical ecosystems hub project 1 3 characterising the cumulative impacts of global regional and local stressors on the present and past bio diversity of the gbr to j xz jmp sgs trc y xf and others and australian research council lief grant le0989067 for the purchase and installation of the mc icp ms essential for this study to jxz jmp y xf and others as well as an australian postgraduate award apa to ndl we are grateful to eric matson from the australian institute of marine science aims for technical assistance in obtaining the fossil coral cores and to hard rock earth works rod morelli and associates in townsville for allowing access to the corals we also thank st vincent s private hospital brisbane for ct scans and queensland diagnostic imaging indooroopilly for x rays we thank an anonymous reviewer for helpful comments on an earlier manuscript the data used in this study are available through the cited references figures and tables as well as in the supporting information to this manuscript

fluorescent bands in massive corals record centuries of coastal rainfall massive coral colonies on the great barrier reef grow outwards at 5 25 mm yr 1 ref 1 skeletal density varies seasonally in all massive corals from the great barrier reef and an exact temporal record of growth can be obtained by x radiography of appropriately cut sections of the colony2 3 environmental influences on coral growth have been described from such analyses4 6 this is the first report from the skeletons of massive corals of yellow green fluorescent bands which appear under long wave uv light such fluorescence is confined to corals growing within 20 km of the shore and is not present in massive corals from mid and outer shelf reefs of the central great barrier reef region the timing width and intensity of the fluorescent bands correlate strongly with summer monsoonal rainfall and coastal runoff large colonies several centuries old can provide long records of the strength and periodicity of terrestrial runoff to the tropical nearshore environment such records are potentially important to climatology meteorology agriculture civil engineering and management of the great barrier reef

cathodoluminescence in quaternary carbonate deposits abstract the cathodoluminescent oscillatory and sectoral growth zones common in crystals formed in ancient limestone successions in a variety of putative environments appear to be rare or absent from recent and pleistocene marine carbonate sequences the factors controlling cathodoluminescence and reasons for this disparity are examined the cathodoluminescent zones in the cements of ancient rocks have been interpreted as responses to variations in the redox potential of formative pore waters during crystal growth although similar cathodoluminescent behaviour is recorded from some deposits including travertines and quaternary speleothems formed in what are thought to have been strongly oxidizing environments the apparent absence of cathodoluminescence in the most recent and pleistocene marine deposits that presumably reflect deposition and diagenesis in environments that are also characteristically oxidized therefore seems anomalous the controlling influences on cathodoluminescence are reviewed together with evidence relating to observations of pleistocene marine deposits and likely conditions of formation but where it is present the mechanism s for its development remain elusive

belemnite taphonomy upper jurassic western tethys part ii fossil diagenetic analysis including combined petrographic and geochemical techniques abstract fossil diagenetic features were analyzed on 56 belemnite rostra from the pozo canada section external prebetic as well as 31 belemnite rostra from the rio segura internal prebetic both from the upper oxfordian lower kimmeridgian they mainly correspond to hibolithes and secondarily to belemnopsis fossil diagenetic processes were analyzed in each specimen using petrographic conventional cathodoluminescence epifluorescence and scanning electron microscopy and geochemical elemental and stable isotopes techniques the most common fossil diagenetic processes are dissolution calcite cementation and recrystallization of the apical zone and outer growth rings of belemnite rostra these processes may appear enhanced by fracturing and stylolite formation petrographic study also reveals that the alternation of cloudy and clear concentric growth areas displayed by many belemnite rostra corresponds to an early diagenetic feature in origin however an original concentric growth pattern is also observed under epifluorescent microscopy and bsem this growth pattern fits with changes in the mg and s content of the rostra although fossil diagenetic processes typically make specimens non suitable for paleoenvironmental interpretations microsampling of petrographically altered and non altered areas from the same specimens performed directly from thin sections after petrographic study allowed us to obtain excellent geochemical results suitable for paleoenvironmental interpretations these geochemical analyses moreover demonstrates that caution should be taken if elemental analyses are used as the most significant criteria for discriminating diagenetically altered and non altered belemnite samples

reply to the comment on the paper grain size dependent potential for self generation of magnetic anomalies on mars via thermoremanent magnetic acquisition and magnetic interaction of hematite and magnetite by gunther kletetschka norman f ness j e p connerney m h acuna p j wasilewski phys earth planet inter 148 2005 149 156 made by jafar arkani hamed

investigation of teleseismic lg blockage and scattering using regional arrays abstract incoherent beamforming and continuous frequency wavenumber polar scan analysis have been applied to study the characteristics of p coda and lg waves recorded at the regional arrays noress and arcess from presumed explosions on the northwestern russian platform and at test sites of novaya zemlya and eastern kazakh also recordings at the graefenburg array near the new geress regional array of novaya zemlya events and an eastern european platform white sea event have been compared with the norwegian array recordings of the same events the white sea explosion at distances of 14 and 22 from noress and graefenburg respectively exhibits lg rms amplitudes on incoherent beams that exceed those of sn however for explosions at novaya zemlya at 20 from noress and eastern kazakh at 30 from arcess the lg waves have much smaller amplitudes than sn in the case of novaya zemlya the lg wave is almost completely blocked at both noress and arcess but is well recorded at graefenburg this reduction of the lg amplitudes relative to those from events at longer distances cannot be accounted for by anelastic attenuation and spreading comparison of propagation paths suggests that the reduction in amplitudes may be due to blockage and scattering of lg in the barents sea analysis of sn coda waves on incoherent beams and continuous frequency wavenumber analysis polar scans suggests that they can result from lg to sn scattering from the coastline between the barents sea and scandinavia recent geologic studies have revealed significant variations in crustal structure in the barents sea basin which may cause the blockage of lg waves from novaya zemlya in the case of eastern kazakh explosions arcess incoherent beams show much reduced lg amplitudes relative to the p coda waves compared with noress even though the distance to arcess 31 is less than that to noress 38 this reduction in lg amplitude at both noress and arcess is accompanied by enhancement of p and sn coda the timing of the coda waves and the propagation paths suggest that lg waves may be partially blocked and scattered by the ural mountains and that the p and sn coda waves may result from lg to pn pn to sn sn to lg and lg to sn conversions from lateral heterogeneities in the crust beneath the urals the blockage is greater for the eastern kazakh to arcess path because it crosses the middle part of the urals whereas the eastern kazakh to noress path crosses the southern part of the urals chain these blockage effects seem to result from sudden lateral variations in shallow crustal structure such as variations in sediment thicknesses in the sedimentary basins of the russian platform and adjacent to the urals these blockage effects can be predicted from geologic studies and need to be accounted for when using lg amplitudes to estimate absolute yields of explosions and for event identification

modelling low frequency volcanic earthquakes in a viscoelastic medium with topography summary magma properties are fundamental to explain the volcanic eruption style as well as the generation and propagation of seismic waves this study focusses on magma properties and rheology and their impact on low frequency volcanic earthquakes we investigate the effects of anelasticity and topography on the amplitudes and spectra of synthetic low frequency earthquakes using a 2 d finite difference scheme we model the propagation of seismic energy initiated in a fluid filled conduit embedded in a homogeneous viscoelastic medium with topography we model intrinsic attenuation by linear viscoelastic theory and we show that volcanic media can be approximated by a standard linear solid sls for seismic frequencies above 2 hz results demonstrate that attenuation modifies both amplitudes and dispersive characteristics of low frequency earthquakes low frequency volcanic earthquakes are dispersive by nature however if attenuation is introduced their dispersion characteristics will be altered the topography modifies the amplitudes depending on the position of the seismographs at the surface this study shows that we need to take into account attenuation and topography to interpret correctly observed low frequency volcanic earthquakes it also suggests that the rheological properties of magmas may be constrained by the analysis of low frequency seismograms

nitrogen isotopic composition of organic matter from a 168 year old coral skeleton implications for coastal nutrient cycling in the great barrier reef lagoon abstract ongoing human activities are known to affect nitrogen cycling on coral reefs but the full history of anthropogenic impact is unclear due to a lack of continuous records we have used the nitrogen isotopic composition of skeleton bound organic matter cs 15 n in a coastal porites coral from magnetic island in the great barrier reef as a proxy for n cycle changes over a 168 yr period 1820 1987 ad the magnetic island inshore reef environment is considered to be relatively degraded by terrestrial runoff given prior cs 15 n studies from other regions there was an expectation of both secular change and oscillations in cs 15 n since european settlement of the mainland in the mid 1800s surprisingly cs 15 n varied by less than 1 5 despite significant land use change on the adjacent mainland over the 168 yr measurement period after 1930 cs 15 n may have responded to changes in local river runoff but the effect was weak we propose that natural buffering against riverine nitrogen load in this region between 1820 and 1987 is responsible for the observed stability in cs 15 n in addition to coral derived skeletal 15 n we also report for the first time 15 n measurements of non coral derived organic n occluded within the coral skeleton which appear to record significant changes in the nature of terrestrial n inputs in the context of previous cs 15 n records most of which yield cs 15 n changes of at least 5 the magnetic island coral suggests that the inherent down core variability of the cs 15 n proxy is less than 2 for porites

soluble humic substances from in situ precipitated microcrystalline calcium carbonate internal sediment and spar cement in a cretaceous carbonate mud mound albian carbonate mud mound limestones exposed near iraneta northern spain show a fabric and particle specific fluorescence intense fluorescence is restricted to in situ precipitated microcrystalline automicritic fabrics calcified demosponges and coralline sponges intermediate intensity derives from micritized bioclasts pellets and a rim of marine bladed cement most invertebrate skeletons late diagenetic equant cement and crosscutting zones of dolomitization are weakly to nonfluorescent internal microcrystalline sediment allomicrite and red algae debris have variable fluorescence correlation between rock fluorescence and soluble humic substances was evaluated from 3 g of automicrite allomicrite and cement time resolved laser induced fluorescence spectroscopy trlfs with ultra short pulses on two extracrystalline fractions naoh soluble and two intracrystalline fractions hcl soluble and naoh soluble showed that most of the soluble humic substances of automicrite are within the crystals but conversely are significantly enriched on outer surfaces of allomicrite spar cement is close to detection limits fluorescence lifetimes are in the range of 0 5 2 ns and 3 5 6 ns we conclude that precipitation of automicrite took place during oxidative organic matter diagenesis i e during condensation reactions of degradation products of marine biopolymers by contrast allomicrite formed by skeletal breakdown followed by ingestion organic coating and reingestion during deposit feeding a humic substance based model of marine polymer gels represents a new approach for the understanding of ancient polygenetic carbonate muds so typical of phanerozoic mud mounds in deeper water settings

transitional continental oceanic structure beneath the norwegian sea from inversion of surface wave group velocity data summary we have analysed the fundamental mode of love and rayleigh waves generated by 12 earthquakes located in the mid atlantic ridge and jan mayen fracture zone using the multiple filter analysis technique we isolated the rayleigh and love wave group velocities for periods between 10 and 50 s the surface wave propagation paths were divided into five groups and average group velocities calculated for each group the average group velocities were inverted and produced shear wave velocity models that correspond to a quasi continental oceanic structure in the greenland norwegian sea region although resolution is poor at shallow depth we obtained crustal thickness values of about 18 km in the norwegian sea area and 9 km in the region between svalbard and iceland the abnormally thick crust in the norwegian sea area is ascribed to magmatic underplating and the thermal blanketing evect of sedimentary layers maximum crustal shear velocities vary between 3 5 and 3 9 km s 1 for most paths an average lithospheric thickness of 60 km was observed which is lower than expected for oceanic type structure of similar age we also observed low shear wave velocities in the lower crust and upper mantle we suggest that high heat flow extending to depths of about 30 km beneath the surface can account for the thin lithosphere and observed low velocities anisotropy coeycients of 1 5 per cent in the shallow layers and 7 per cent in the upper mantle point to the existence of polarization anisotropy in the region