a tsunami deposit at the cretaceous tertiary boundary in texas at sites near the brazos river texas an iridium anomaly and the paleontologic cretaceous tertiary boundary directly overlie a sandstone bed in which coarse grained sandstone with large clasts of mudstone and reworked carbonate nodules grades upward to wave ripple laminated very fine grained sandstone this bed is the only sandstone bed in a sequence of uppermost cretaceous to lowermost paleocene mudstone that records about 1 million years of quiet water deposition in midshelf to outer shelf depths conditions for depositing such a sandstone layer at these depths are most consistent with the occurrence of a tsunami about 50 to 100 meters high the most likely source for such a tsunami at the cretaceous tertiary boundary is a bolidewater impact

barremian danian chemostratigraphic sequences of the cauvery basin india implications on scales of stratigraphic correlation abstract chemostratigraphic concepts postulate that distinct chemozones could be recognized from rock records to help correlate geographically separated strata many studies have upheld this view but were limited to classic boundaries such as cenomanian turonian or cretaceous tertiary only a few elements and isotopic compositions were made use in such studies an attempt to recognize chemozones of barremian danian strata of the cauvery basin south india through whole rock chemistry had revealed many complex signals and depositional events as expressed by bulk geochemical profiles the signals indicate major shift in sedimentation pattern from dynamic depocenter to stable depositional conditions during santonian varying sensitivities of different elements towards prevalent depositional conditions are also inferred trends of geochemical composition indicated domination of single depositional control all through the depositional history basinal configuration that limited terrestrial sediment source and episodic influx of detrital materials presence of distinct change in whole rock geochemistry across geochronological and lithostratigraphic boundaries is deciphered through a statistical tool anova these results demonstrate that visual delineation of chemozones in a long ranging rock record would be tenuous and has to be exercised with caution

interactive gravity inversion we have developed a new approach for estimating the location and geometry of several density anomalies that give rise to a complex interfering gravity field the user interactively defines the assumed outline of the true gravity sources in terms of points and line segments and the method estimates sources closest to the specified outline to achieve a match between the predicted and observed gravity fields each gravity source is assumed to be a homogeneous body with a known density contrast different density contrasts may be assigned to each source tests with synthetic data show that the method can be of use in estimating 1 multiple laterally adjacent and closely situated gravity sources 2 single gravity sources consisting of several homogeneous compartments with different density contrasts and 3 two gravity sources with different density contrasts of the same sign one totally enclosed by the other the method is also applied to three different sets of field data where the gravity sources belong to the same categories established in the tests with synthetic data the method produces solutions consistent with the known geologic attributes of the gravity sources illustrating its potential practicality

finding the shape of a local heterogeneity by means of a structural inversion with constraints various aspects of structural inversion are considered the aim of the inversion is limited to finding the shape of an isolated 2d homogeneous body although the technique may be generalized to the case of interfaces with steep fragments faults or overhangs the unknown parameters are shifts of border points the shift directions can be normal to the initial heterogeneity configuration or to another contour medium properties seismic velocities densities etc within the heterogeneity are assumed to be known the optimal shape is determined iteratively a quadratic objective function being minimized at each iteration with the conjugate gradient method special attention is paid to preventing self intersections for which purpose each unknown parameter is forced to lie within a certain predetermined interval in order to achieve this the classical conjugate gradient method has been modified accordingly three numerical examples are considered these illustrate how the developed technique can be applied to different practical problems the first example is devoted to monitoring an oil steam interface by gravity gradiometry measurements in the second example a cross hole seismic experiment is simulated it is shown that a structural inversion can restore the configuration of a local body much more accurately than traditional seismic tomography in the third example the shape of a salt dome is reconstructed by joint inversion of refracted traveltimes and gravity measurements this example demonstrates how different kinds of data used simultaneously in a structural inversion can complement each other

microstructural and chemical changes associated with cataclasis and frictional melting at shallow crustal levels the cataclasite pseudotachylyte connection in pelitic schists of the nason terrane of washington state pseudotachylyte can be demonstrated to have developed subsequent to the formation of foliation parallel cataclasite zones numerous microstructural lines of evidence point to a genetic link between pseudotachylyte and cataclasite and chemical evidence indicates that cataclasis played an important role in controlling pseudotachylyte chemistry besides optical and textural differences between the cataclasite and pseudotachylyte which may occur together there is unambiguous evidence of a melt origin for the pseudotachylyte while such evidence within the cataclasite is absent tem evidence indicates that glass is present in at least some of the veins as demonstrated by a lack of electron diffraction microlites present in the glass lack dislocations high temperature microlites of a mineralogy and composition not present in the host schist occur in various habits which depend on the distance from the vein margin also present are assimilation textures apparently quenched sulfide droplets and vesicles and amygdules in a pseudotachylyte vein studied in detail five microstructural domains occur these include vein margin cataclasite a transitional dark pseudotachylyte vein interior glass opaque and sulfide rich blebs and translucent haloes surrounding some of the blebs the cryptocrystalline cataclasite matrix grades into the dark pseudotachylyte which optically grades into the glass after adjustment for silica the host schist and cataclasite matrix are chemically very similar the dark pseudotachylyte and glass with the exception of na2o and cao are chemically quite similar to the cataclasite matrix the main difference may be the result of the segregation of the opaque plagioclase blebs thus the pseudotachylyte chemistry is strongly dependent upon the chemistry of the material comprising the cataclasite matrix which in turn is dependent on mineral susceptibility to incorporation into the cataclasite matrix fluids infiltrated along the cataclasite zones prior to pseudotachylyte generation as recorded by hydration reactions sulfide veining na2o loss and fluid inclusions this demonstrates that pseudotachylytes can form under fluid rich conditions as opposed to the commonly assumed dry conditions

gravity inversion using convexity constraint we present a constraint which incorporates in the geophysical inverse problem a priori information about the source convexity two kinds of convexity are considered directional convexity defined as the attribute of a body being intersected at most at two points by a straight line with a fixed spatial orientation and global convexity defined as the attribute of a body being intersected at most at two points by any arbitrarily oriented straight line the interpretation model consists of several juxtaposed 2 d prisms whose positions widths and physical property are established by the interpreter the depth to the top and the thickness of each prism are the parameters to be determined the directional convexity is incorporated by minimizing a functional which expresses the number of times that several lines parallel to a given direction and spaced at regular intervals intersect the interpretation model on the other hand the global convexity is introduced in an algorithmic way by constraining the dep

global comparisons of organic matter in sediments across the cretaceous tertiary boundary a tract the cretaceous tertiary k t boundary is marked by extensive changes in the sedimentary fossil record of continental and marine life organic matter in sediments from above and below the k t boundary has been studied to identify consequences of the biotic extinctions and of the changes in biological productivity which occurred at this time data from locations encompassing a variety of marine paleoenvironments were examined to assess the global extent and local expressions of these biological changes characterizations of organic matter included rock eval pyrolysis stable carbon isotope ratios and distributions of extractable biomarkers in general organic carbon concentrations are a few tenths of a percent in the chalks and marls above and below the k t boundary in some boundary clay samples concentrations up to 5 are found the elevated amounts near the boundary result from oxidation of marine organic matter consequent dissolution of carbonates and concentration of the surviving organic matter at all locations the organic matter has been microbially reworked and evidently was deposited in oxidizing environments carbon isotope shifts in open marine sediments suggest biological productivity was depressed following the k t boundary repetition of these changes at different locations verifies the global extent of the boundary event yet local variations in its expression are evident

vesicles amygdales and similar structures in fault generated pseudotachylytes amygdales in fault generated pseudotachylytes from the outer hebrides thrust scotland and the ikertoq shear belt west greenland contain mineral assemblages dominated by k spar sphene epidote quartz and carbonates respectively these contrasting assemblages indicate that vesicle infilling took place under differing environmental conditions other filled cavities resembling amygdales in form and mineralogy are recognized as replacement pseudomorphs after porphyroclasts using published data relating vesicle abundance and solubility functions for h2o and co2 to pressure a palaeoseismic depth estimate equivalent to the depth of vesiculation of about 1 6 km is inferred for the greenland pseudotachylytes described in this paper

mechanisms of shear localization in the continental lithosphere inference from the deformation microstructures of peridotites from the ivrea zone northwestern italy the ultramafic massif of balmuccia northwestern italy shows a variety of deformation fabrics including some localized shear zones that resulted in nearly complete melting pseudotachylyte a series of peridotite specimens were collected near one of the pseudotachylyte fault veins to investigate the mechanisms of shear localization the microstructural analyses show at least three deformation stages the first stage i is nearly homogeneous deformation at low stress 3 mpa and high temperature 1300 1500 k followed by localized deformation stage ii at a higher stress 60 mpa and moderate temperature 1000 1150 k and finally semi brittle deformation stage iii at a very high stress 400 mpa that resulted in the formation of pseudotachylyte the stage ii deformation resulted in relatively small strains in most areas but significant localized deformation leading to dynamic recrystallization occurred the degree of which increases systematically toward the fault zone based on this observation together with the observation that the brittle deformation post dated dynamic recrystallization we conclude that the shear localization in this locality occurred as a result of ductile deformation rather than brittle deformation various mechanisms of shear localization in the ductile regime are examined and we conclude that the grain size reduction due to dynamic recrystallization at relatively high stresses and moderate temperatures is a probable mechanism of shear localization the intermediate regime between dislocation and diffusion creep where rheology is grain size sensitive yet continuous recrystallization occurs due to dislocation creep is suggested to play an important role in shear localization in the upper mantle the conditions of shear localization due to this mechanism are examined based on the laboratory data on creep and dynamic recrystallization it is shown that shear localization occurs at relatively low temperatures and or high stresses localized deformation in the continental lithosphere will occur well below the brittle ductile transition 10 km depth down to 40 80 km depth depending upon the geothermal gradient and water fugacity

iridium sulfur isotopes and rare earth elements in the cretaceous tertiary boundary clay at stevns klint denmark microbial activity and redox controlled precipitation have been of major importance in the process of metal accumulation in the strongly ir enriched cretaceous tertiary k t boundary clay the fish clay at stevns klint in denmark two important findings support this view 1 1 kerogen recovered by leaching the fish clay in hcl and hf shows an ir concentration of 1100 ppb this represents about 50 of the ir present in the bulk sample fish clay strong organometallic complexes is the most probable carrier phase for this fraction of ir kerogen separated from the k t boundary clay at caravaca spain similarly exhibits enhanced ir concentrations 2 2 sulfur isotope analyses of metal rich pyrite spherules which occur in extreme abundance about 10 by weight in the basal fish clay give a 34s value of 32 this very low value shows that sulfide formation by anaerobic bacteria was intensive in the fish clay during early diagenesis since the pyrite spherules are major carriers of elements such as ni co as sb and zn microbial activity may have played an important role for concentrating these elements in the fish clay large amounts of rare earth elements have precipitated from sea water on fish scales analyses reveal that compared with sea water the fish clay is only about four times less enriched in sea water derived lanthanides than in ir this shows that a sea water origin is plausible for elements that are strongly enriched in the clay but whose origin cannot be accounted for by a lithogenic precursor

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

biomarker geochemistry of black shales from cretaceous oceans an overview abstract cretaceous black shales have an extensive distribution in the atlantic and other areas of the world oceans they are sediments rich in organic matter which were deposited in anoxic environments under various paleoenvironmental conditions of sedimentation the literature is reviewed briefly and some type areas are examined using biomarker geochemistry to assess the sources and maturity of the organic matter and the paleoenvironmental conditions of sedimentation these areas are the eastern angola basin the cape verde basin and eastern north atlantic the western north and south atlantic and the pacific oceans molecular marker indicators were identified in bitumens and in kerogen pyrolysates in addition bitumens were characterized by other geochemical techniques thus delineating the terrigenous versus autochthonous sources and the paleoenvironmental preservation of this organic fraction the kerogens were characterized by their elemental composition stable carbon isotope composition and by pyrolysis gc or pyrolysis gc ms including rock eval data these parameters confirmed that the organic matter in sediments of the cretaceous oceans was derived from several different sources is relatively immature and was preserved under various paleoenvironmental conditions

3d gravity inversion through an adaptive learning procedure we have developed a gravity inversion method to estimate a 3d density contrast distribution producing strongly interfering gravity anomalies the interpretation model consists of a grid of 3d vertical juxtaposed prisms in the horizontal and vertical directions iteratively our approach estimates the 3d density contrast distribution that fits the observed anomaly within the measurement errors and favors compact gravity sources closest to prespecified geometric elements such as axes and points this method retrieves the geometry of multiple gravity sources whose density contrasts positive and negative values are prescribed by the interpreter through the geometric element at the first iteration we set an initial interpretation model and specify the first guess geometric elements and their target density contrasts each geometric element operates as the first guess skeletal outline of the entire homogeneous gravity source or any of its homogeneous parts to be reconstructed from the second iteration on our method automatically redefines a new set of geometric elements the associated target density contrasts and a new interpretation model whose number of prisms increases with the iteration the iteration stops when the geometries of the estimated sources are invariant along successive iterations tests on synthetic data from geometrically complex bodies and on field data collected over a mafic ultramafic body and a volcanogenic sedimentary sequence located in the tocantins province brazil confirmed the potential of our method in producing a sharp image of multiple and adjacent bodies

2d gravity inversion of a complex interface in the presence of interfering sources we present a new semiautomatic gravity interpretation method for estimating a complex interface between two mediacontainingdensityheterogeneitiesreferredtoasinterferingsourcesthatgiverisetoacomplexandinterferinggravity field the method combines a robust fitting procedure and the constraint that the interface is very smooth near the interfering sources whose approximate horizontal coordinates aredefinedbytheuser theproposedmethoddiffersfromthe regional residual separation techniques by using no spectral contentassumptionabouttheanomalyproducedbytheinterface to be estimated i e the interface can produce a gravity response containing both low and high wavenumber features asaresult itmaybeappliedtomapthereliefofacomplex interface in a geologic setting containing either shallow ordeep seatedinterferingsources testsconductedwithsyntheticdatashowthatthemethodcanbeofutilityinestimating the basement relief of a sedimentary basin in the presence of saltlayersanddomesorinthepresenceofmaficintrusionsin the basement or in both basement and the sedimentary section the method was applied to real gravity data from two geologic settings having different kinds of interfering sources and interfaces to be interpreted 1 the interface between the upper and lower crusts over the bavali shear zone of southern india and 2 the anorthosite tonalite interface over the east bull lake gabbro anorthosite complex outcrop in ontario canada

transcrystalline shear fracturing and pseudotachylite generation in a meta anorthosite harris scotland abstract the meta anorthosite is locally deformed by brittle shear fracturing which progressively increases from isolated fractures with little cataclasite to many generations of closely spaced fractures the intervening rock being highly deformed in both a plastic and brittle way in most cases an e w compression on gently dipping to steep reverse shear planes occurs which we relate to a caledonian thrust zone in places the highly deformed rock is cut by pseudotachylite veins which locally form networks the pseudotachylite is generally intrusive but does not appear to be related to movement on major slip surfaces very locally it may have formed in situ pseudotachylite only occurs in highly deformed rock is only very occasionally deformed itself and thus generally represents at each locality the last stage of a complex deformation history as if its presence welded the rock and prevented further deformation these striking differences from the country rock gneisses in which pseudotachylite occurs on well developed fractures in very slightly deformed rock are considered to be due to the low anisotropy of the meta anorthosite to its lower shear strength and to the easy propagation and branching of the shear fractures in plagioclase the source of the heat necessary to generate the pseudotachylite melt is not clear it may come from crack propagation as well as frictional sliding

barium anomaly preceding k t boundary possible causes and implications on end cretaceous events of k t sections in cauvery basin india israel ne mexico and guatemala maastrichtian danian strata of the cauvery basin as well as selected sections of ne mexico guatemala and israel record ba anomalies away from the cretaceous tertiary boundary ktb in addition to common occurrences of geochemical and stable isotopic anomalies across the ktb ba anomalies were recorded in monotonous shallow marine sandstones of the cauvery basin south india which contain minor amounts of ba orthoclase barium anomalies were observed also in shallow marine carbonates in sections of israel ne mexico and guatemala calculation of excess ba with reference to paas post archaen average australian shale comparison of coeval geochemical anomalies depositional pattern and associated petrographic and mineralogical features of the cauvery basin revealed that while a first ba peak was related to detrital influx the second ba peak was coincident with sea level fall which in turn may have been influenced by emission of volatile hydrocarbons and resultant climatic changes in view of intrinsic involvement of ba in various geochemical processes and occurrence of ba anomalies in k t sites distributed around the world ne mexico guatemala and israel it is suggested that probable causes of such widespread ba anomalies should be taken into consideration while analyzing end cretaceous events these observations support the views espoused by many workers who have stated that the k t boundary was also accompanied by many non catastrophic events that might have contributed to environmental stress on marine fauna as a result of which selective multi stage extinctions occurred

generalized compact gravity inversion extending the compact gravity inversion technique by incorporating a priori information about the maximum compactness of the anomalous sources along several axes provides versatility thus the method may also incorporate information about limits in the axes lengths or greater concentration of mass along one or more directions the judicious combination of different constraints on the anomalous mass distribution allows the introduction of several kinds of a priori information about the arbitrary shape of the sources this method is particularly applicable to constant linear density sources such as mineralizations along faults and intruded sills dikes and laccoliths in a sedimentary basin the correct source density must be known with a maximum uncertainty of 40 percent otherwise the inversion produces thicker bodies for densities smaller than the true value and vice versa because of the limitations of the inverse gravity problem the proposed technique requires an empirical technique to analyze the sensitivity of solutions to uncertainties in the a priori information the proposed technique is based on a finite number of acceptable solutions presumably representative of the ambiguity region by using standard statistical techniques each parameter is assigned a coefficient measuring its uncertainty the known hematite and magnetite ore body shape in the vicinity of iron mountain mo was reproduced quite well using this inversion technique

stable isotope toc and caco3 record across the cretaceous tertiary boundary at el kef tunisia we report the results of stable oxygen and carbon isotope analysis of carbonate fine fraction and benthic and planktic foraminifers caco3 and toc determinations of sediments across the cretaceous tertiary k t boundary at el kef tunisia we used grain size analysis of the fine fraction carbonate to determine possible compositional effects and smearslide and scanning electron microscope examinations to evaluate possible diagenetic alteration and microfossil preservation the data suggests the following sequence of events upper maastrichtian oxygen and carbon isotope signals indicate relatively warm temperatures a decreasing thermal gradient possibly related to a shallowing sea and relatively high surface water productivity a sharp cooling appears to begin just below the k t boundary the k t boundary is characterized by a sudden 2 negative shift in fine fraction 13c a slight 0 6 enrichment in benthic 13c and a reduction of about 40 in caco3 sedimentation these data imply strongly reduced surface water productivity as also observed in numerous deep sea sequences worldwide the lower danian planktic foraminiferal zones p0 p1a is marked by generally low productivity and unstable environmental conditions as indicated by generally low but fluctuating fine fraction 13c values and low 5 15 carbonate deposition at the base of subzone p1b caco3 benthic and fine fraction 13c values increase gradually and reach near pre k t boundary levels in subzone p1c indicating initial recovery after the k t boundary event about 300 000 400 000 years after the k t boundary the prolonged low productivity episode after the k t crisis and the pre k t boundary cooling associated with a major reduction in planktic foraminiferal diversity are difficult to explain by a single k t boundary bolide impact

stereochemical studies of acyclic isoprenoids xii lipids of methanogenic bacteria and possible contributions to sediments abstract abundant volatile lipids of methanobacterium thermoautotrophicum and methanosarcina barkeri include isoprenoid hydrocarbons c30 and c15 c20 and c25 isoprenoid alcohols m barkeri contains 2 6 10 15 19 pentamethyleicosane whose relative stereochemistry is the same as found in marine sediments indicating that it is a marker of methanogenic activity the c20 c30 and c25 alkenes in m thermoautotrophicum also have a preferred sterochemistry the latter have the 2 6 10 14 18 pentamethyleicosanyl skeleton suggesting that the alkane in marine sediments may derive from methanogens the stereochemistry of squalane in a marine sediment is also compatible with an origin in methanogens in contrast the stereochemistry of pristane in m thermoautotrophicum indicates a fossil fuel contaminant origin suggesting that this and certain other alkanes reported in archaebacteria might also be of contaminant origin there is therefore little evidence at present that the pristane in immature marine sediments originates in methanogens the c15 and c20 saturated alcohols in m thermoautotrophicum have mainly the all r configuration if this is generally true for methanogens the c20 alcohol in the messel shale may originate mainly from methanogens whereas that in the green river shale may originate mainly from photosynthetic organisms

reconstruction of geologic bodies in depth associated with a sedimentary basin using gravity and magnetic data summary we present a comprehensive review of the most comm on gravity and magnetic interpretation methods to in depth retrieval of the geometry of two types of geologic bodies associated with a sedimentary basin 1 sedimentary basement relief and 2 salt bodies in reconstructing a basement topography we identify three groups of methods the automatic the spectral and the nonspectral methods the reconstruction of salt bodies geometries from gravity data usually uses the interactive forward modeling but recently gravity inversion methods have been developed to interpret this kind of geological environment

simultaneous 3d depth to basement and density contrast estimates using gravity data and depth control at few points we have developed a gravity inversion method for simultaneouslyestimatingthe3dbasementreliefofasedimentary basin and the parameters defining a presumed parabolic decay of the density contrast with depth in a sedimentary pack assumingpriorknowledgeaboutthebasementdepthatafew points thesedimentarypackisapproximatedbyagridof3d vertical prisms juxtaposed in both horizontal directions of a right handed coordinate system the prisms thicknesses representthedepthstothebasementandaretheparametersto be estimated from the gravity data to estimate the parameters defining the parabolic decay of the density contrast with depthandtoproducestabledepth to basementestimates we imposed smoothness on the basement depths and proximity between estimated and known depths at boreholes we applied our method to synthetic data from a simulated complex 3d basement relief with two sedimentary sections having distinct parabolic laws describing the density contrast variationwithdepth theresultsprovidegoodestimatesofthetrue parameters of the parabolic law of density contrast decay with depth and of the basement relief inverting the gravity data from the onshore and part of the shallow offshore almadabasinonbrazil snortheasterncoastshowsgoodcorrelationwithknownstructuralfeatures

determination of the stress conditions of the ductile to brittle regime along the asuke shear zone sw japan abstract the stress conditions of the ductile to brittle regime have been assessed along the asuke shear zone asz which strikes ne sw in the cretaceous ryoke granite terrain in sw japan along the asz pseudotachylyte and mylonitized pseudotachylyte are locally developed together with cataclasite the simultaneous operation of dislocation creep and grain size sensitive creep as indicated by the coexistence of the z maximum and relatively random c axis lattice preferred orientations as well as the sizes of dynamically recrystallized quartz grains 6 40 7 79 m in the mylonitized pseudotachylyte suggest differential stresses of 110 130 mpa at 300 c the e twin morphology twinning ratio and distribution of the glide direction on the e twin plane of the twinned calcite in the amygdules of the pseudotachylyte suggest the stress conditions of the 1 and 3 axes trend 228 and 320 and plunge 55 and 1 respectively and indicate differential stresses of 40 80 mpa at 150 200 c based on kinematic indicators in the fault rocks the stress conditions estimated from calcite twins and the cooling history of the granitic protolith the asz is inferred to have been activated under a stress state that caused sinistral normal movements before and after pseudotachylyte formation at 70 50 ma

velocity modelling and prestack depth imaging below complex salt structures a case history from on shore germany in recent years the advances in velocity model building and depth imaging have provided a better understanding of complex subsalt plays the tomographic approach to subsurface velocity modelling using interpretive processes has led to significant progress in solving subsalt imaging problems which were once considered to be impenetrable barriers we show how gravity data as an alternative data source can be integrated into iterative velocity depth model building to constrain the overburden velocity model and delineate the shape of the salt body above the target reflector in this way a structurally accurate image of subsalt reflectors is achieved

microcrystalline textures resulting from rapid crystallization in a pseudotachylite melt in a meta anorthosite the very fine grained 1 m polygonal microcrystalline texture occurring in the groundmass of pseudotachylite veins in the harris meta anorthosite and its variation with position are described and an origin by crystallization from a melt at very large undercooling suggested the intrusive nature of the veins is shown by their geometry and internal structures clasts which are almost always only plagioclase are generally concentrated towards the centres of veins flow of tens of millimetres can account for this concentration in millimetre thick veins as a result of the bagnold effect the veins are generally thin 5 m to 5 mm or more are frequently zoned and always contain transparent granules of high relief probably al rich pyroxene and opaque granules of magnetite up to a few micrometres in size the granules are either uniformly distributed in microcrystalline textures or concentrated locally giving cellular textures in some veins spherulitic or bow tie textures occur the coarsest textures are found in the centres of the thickest veins the groundmass of the pseudotachylite is never completely isotropic but consists of a mosaic of transparent plagioclase crystals decreasing in size from the centres of thick veins to less than 1 m in thin veins or in the margins of thicker veins this fine microcrystalline texture was studied by both scanning and transmission electron microscopy and consists of polyhedral crystals of regular size in the range 0 2 1 5 m which show little sign of deformation the local composition of the pseudotachylites varies little from the average compositions of the rocks in optically homogeneous veins the variation being within the compositional space defined by the minerals of the host rock this shows that homogenization of the pseudotachylite has occurred in cellular veinsdifferentiation has occurred as the compositions of the cell centres lie outside those of the minerals of the host rock this was produced by segregation of the granules pyroxene being absent from the host rock the plagioclase in the pseudotachylite is more disordered than that in the host rock all the microtextures described are absent from the associated cataclasites and cannot be due to recrystallization of a fine grained and intensely strained rock powder the physical state on and after intrusion was that of a melt and injection was followed by crystallization the melt was produced by more or less total fusion of the host rock minerals at shallow depth by heat produced during local faulting and perhaps during crack propagation the fine microcrystalline texture very closely resembles that produced during hypercooling of molten metals and alloys it thus possibly formed not by devitrification but from a melt at much greater degrees of undercooling than the spherulitic and bow tie textures

rapid 3 d forward model of potential fields with application to the palinuro seamount magnetic anomaly southern tyrrhenian sea italy 1 we show a set of forward model equations in the fourier domain for calculating the 3 d gravity and magnetic anomalies of a given 3 d distribution of density or magnetization one property of the potential field equations is that they are given by convolution products providing a very simple analytic expression in the fourier domain under this assumption the domain of the density or magnetization parameters is connected by a biunivoc relationship with the data space and potential field anomalies can be seen as filtered versions of the corresponding density or magnetization distributions a very fine spatial discretization can be obtained by using a large number of points within a unique 3 d grid where both the source distributions and field data are defined the main advantage of this formulation is that it dramatically reduces execution times providing a very fast forward model tool useful for modeling anomalies at different altitudes we use this method to evaluate an average magnetization of 8 a m for the palinuro seamount in the tyrrhenian sea southern italy thus performing a joint interpretation of morphological and newly acquired magnetic data

electron microscopy study of hyalomylonites evidence for frictional melting in landslides abstract hyalomylonites from langtang nepal and kofels otz valley austria were investigated by transmission electron microscopy tem the matrix is glassy at both localities rarely it is crystallized and devitrified to dendrites and skeletal microlites of plagioclase alkali feldspar and biotite the matrix is chemically heterogeneous with schlieren and formed by partial to almost complete melting of host rocks of granitic to granodioritic composition locally glasses with pure quartz plagioclase and alkalifeldspar composition were found from sio 2 glass minimum temperatures of 1520 c are estimated at both hyalomylonite localities melting appears to be the result of frictional heating on the gliding plane of a large landslide the host rocks were deformed in a brittle mode microstructures typical of plastic deformation at high temperatures are displayed by inclusions and were probably inherited from previous tectonic events

light dark cycles in opal rich sediments near the plio pleistocene boundary dsdp site 532 walvis ridge continental terrace diester haass l meyers p a and rothe p 1986 light dark cycles in opal rich sediments near the plio pleistocene boundary dsdp site 532 walvis ridge continental terrace mar geol 73 1 23 samples taken at 10 cm intervals from dsdp core 532b 17 contain variations in carbonate opal organic carbon and terrigenous components that correlate with light dark cycles in sediment color the core site at 1300 m water depth is well above the ccd yet the color variations appear to result largely from cyclical fluctuations in carbonate dissolution which was greater during glacial periods higher concentrations of organic carbon and of terrigenons sediment components correlate with enhanced carbonate dissolution but opal concentrations inversely correlate and suggest that biological productivity at this site diminished during glacial periods a complicated glacial interglacial picture emerges from the data in interglacial times upwelling associated with the benguela current produced abundant opaline material organic matter was fairly well preserved and carbonate was only moderately dissolved in glacial times the upwelling core shifted as sea level fell and winds intensified productivity in the waters over site 532 decreased but lateral supply of oxidizable organic matter enhanced carbonate dissolution giving rise to light dark cycles in these sediments

gravity inversion of 2d basement relief using entropic regularization we have developed a gravity interpretation method for estimating the discontinuous basement relief of a sedimentary basin the density contrast between the basement and the sediments is assumed to be known and it could be either constant or vary monotonically with depth the interpretation model consists of a set of vertical juxtaposed prisms whose thicknesses are the parameters to be estimated we used the entropic regularization that combines the minimization of the first order entropy measure with the maximization of the zeroth order entropy measure of the solution vector we validated the method by applying it to synthetic data produced by a simulated basin bordered by high angle step faults we obtained a good definition of the relief particularly of the discontinuities we also applied the method to a profile across the buyuk menderes valley in west turkey and obtained a solution exhibiting a gravity fault with large slip on the northern border of the valley when applied to the interpretation of a discontinuous basement relief the method has a better performance than the global smoothness method it is comparable to the weighted smoothness method but it does not require the a priori knowledge about the maximum basin depth

fracture geometry of pseudotachylyte generation zones a study of shear fractures formed during seismic events abstract the orientation and movement sense of shear fractures in pseudotachylyte generation zones developed in the ikertoq shear belt west greenland are described and the fracturing sequence is inferred the generation zones occur in strongly foliated gneisses and consist of concordant usually paired principal displacement shear fractures paired shears on which most melt was generated and a system of minor shear fractures minor shear fracturing was most intense between principal displacement shear fractures and most melt intruded from these paired shears inwards with respect to the zone intrusion of injection veins of pseudotachylyte off the principal displacement shear fractures is believed to be contemporaneous with minor shear fracturing in the generation zones generation zones affect intact rocks and individual principal displacement shear fractures have a maximum displacement of 4 6 m paired principal displacement shear fractures are up to 3 m apart and have a maximum observed length of 1 km in all the zones described the fracturing appears to be the result of a single episode of slip both dextral and sinistral generation zones occur within the study area and have different geometries in each case the displacement is strike slip

eigenvector analysis of gravity gradient tensor to locate geologic bodies we have developed a new method to locate geologic bodies using the gravity gradient tensor the eigenvectors of the symmetric gravity gradient tensor can be used to estimate the position of the source body as well as its strike direction for a given measurement point the eigenvector corresponding to the maximum eigenvalue points approximately toward the center of mass of the causative body for a collection of measurement points a robust least squares procedure is used to estimate the source point as the point that has the smallest sum of square distances to the lines defined by the eigenvectors and the measurement positions it s assumed that the maximum of the first vertical derivative of the vertical component of gravity vector gzz is approximately located above the center of mass observation points enclosed in a square window centered at the maximum of gzz are used to estimate the source location by increasing the size of the window the number of eigenvectors used in the robust least squares and

euler deconvolution of gravity tensor gradient data tensor euler deconvolution has been developed to help interpret gravity tensor gradient data in terms of 3 d subsurface geological structure two forms of euler deconvolution have been used in this study conventional euler deconvolution using three gradients of the vertical component of the gravity vector and tensor euler deconvolution using all tensor gradients these methods have been tested on point prism and cylindrical mass models using line and gridded data forms the methods were then applied to measured gravity tensor gradient data for the eugene island area of the gulf of mexico using gridded and ungridded data forms the results from the model and measured data show significantly improved performance of the tensor euler deconvolution method which exploits all measured tensor gradients and hence provides additional constraints on the euler solutions

gravity inversion of basement relief and estimation of density contrast variation with depth we present a method to estimate the basement relief as well as the density contrast at the surface and the hyperbolic decaying factor of the density contrast with depth assuming that the gravity anomaly and the depth to the basement at a few points are known in both cases the interpretation model is a set of vertical rectangular 2d prisms whose thicknesses are parameters to be estimated and that represent the depth to the interface separating sediments and basement the solutions to both problems are stable because of the incorporation of additional prior information about the smoothness of the estimated relief and the depth to the basement at a few locations presumably provided by boreholes the method was tested with synthetic gravity anomalies produced by simulated sedimentary basins with smooth relief providing not only well resolved estimated relief but also good estimates for the density contrasts at the surface and for the decaying factors of the density contrast with depth the method was ap

chemical heterogeneity in an enderbite hosted pseudotachylite eastern india evidence for syn deformation multi reaction melting in pseudotachylite the origin of chemical and mineralogical heterogeneity in tens of microns wide layers and domains in enderbite hosted couple of centimeters wide pseudotachylite vein is examined based on the results of bse and x ray element imaging and electron probe microanalyses of major elements of host rock minerals clasts microphenocrysts and pseudotachylite matrix the pseudotachylite layers and domains containing variable proportions of orthopyroxene and magnetite microphenocrysts continue as mantles around quartz k feldspar plagioclase and garnet clasts the clasts are chemically modified along margins and intra clast pseudotachylite injections the chemical modifications are extensive in smaller clasts 5 m diameter at least three chemically distinct layers and domains in the pseudotachylite and their fine grained matrices plot in sharply defined well segregated and non overlapping fields in feo mgo al2o3 sio2 feo cao mgo and cao na2o k2o and feo vs feo feo mgo diagrams the compositions of the layers and domains smeared between a feldspar quartz component and a ferromagnesian component of garnet fe ti oxides orthopyroxene possibly correspond to fractionated quenched melts or admixtures of microphenocrysts that cannot be resolved by the microbeam techniques employed the compositional variations are incompatible with deformation driven crystal fractionation in melt instead the layers and domains possibly are crystal melt mushes produced by syn deformation ultra high temperature 1 250 1 375 c melting reactions involving variable proportions of host rock minerals determined by time transient local phase aggregates experiencing strain the similar element variation trends in pseudotachylite examined here and those reported from anorthosite metapelite and charnockite elsewhere suggests local phase aggregate controlled multi reaction melting is a phenomenon commoner than hitherto realized in pseudotachylites

large volumes of anhydrous pseudotachylyte in the woodroffe thrust eastern musgrave ranges australia a mylonitic thrust zone at least 1 5 km thick forms a sharp contact between granulite and amphibolite facies gneisses in the eastern musgrave ranges central australia the thrust dips gently to the south and is interpreted as an extension of the woodroffe thrust which was formed about 550 ma ago mylonites at the base of the thrust grade upwards into ultramylonites which pass abruptly into a pseudotachylyte bearing zone approximately 1 km thick containing approximately 4 of pseudotachylyte veining the orientation of the veins appears to be random pseudotachylytes occur only in the granulite facies rocks and their precursors are felsic pyroxene and or garnet granofelses rotated blocks of ultramylonite are present in some of the pseudotachylytes and some pseudotachylyte veins have been plastically deformed suggesting nearly contemporaneous semiductile and brittle behaviour the matrix of the pseudotachylyte shows spectacular examples of igneous quench microstructures especially skeletal and dendritic crystals of plagioclase and feathery pyroxene dendrites also present are glass devitrification microstructures spherulites evidence of liquid flow and partly melted residual grains with former glassy rims showing different optical properties from those of the surrounding isotropic material these features confirm that the pseudotachylyte formed by melting in anhydrous conditions the matrix of the pseudotachylyte veins is less siliceous than the host rocks owing to non equilibrium melting of pyroxene garnet and plagioclase the igneous assemblages of the melt notably the crystallization of pigeonite are consistent with rapid cooling from very high temperature 1000 c melting and quenching is probably due to very local short lived rises in temperature accompanied by dilation

diverse patterns of ocean export productivity change across the cretaceous paleogene boundary new insights from biogenic barium 1 one of the best studied aspects of the k pg mass extinction is the decline and subsequent recovery of open ocean export productivity e g the flux of organic matter from the surface to deep ocean some export proxies including surface to deep water 13c gradients and carbonate sedimentation rates indicate a global decline in export productivity triggered by the extinction in contrast benthic foraminiferal and other geochemical productivity proxies suggest spatially and temporally heterogeneous k pg boundary effects here we address these conflicting export productivity patterns using new and compiled measurements of biogenic barium unlike a previous synthesis we find that the boundary effect on export productivity and the timing of recovery varied considerably between different oceanic sites the northeast and southwest atlantic southern ocean and indian ocean records saw export production plummet and remain depressed for 350 thousand to 2 million years biogenic barium and other proxies in the central pacific and some upwelling or neritic atlantic sites indicate the opposite with proxies recording either no change or increased export production in the early paleocene our results suggest that widespread declines in surface to deep ocean 13c do not record a global decrease in export productivity rather independent proxies including barium and other geochemical proxies and benthic community structure indicate that some regions were characterized by maintained or rapidly recovered organic flux from the surface ocean to the deep seafloor while other regions had profound reductions in export productivity that persisted long into the paleocene

nanosims study of seismically deformed zircon evidence of y yb ce and p redistribution and resetting of radiogenic pb lattice defects in zircon can cause trace elements redistribution and disturbance of isotopic systems this study investigates in detail how seismically induced deformation microstructures in zircon correlate with trace element and isotope re equilibration felsic mylonites with pseudotachylyte veins from the ivrea verbano zone in northern italy were studied with special focus on deformed zircon we have revealed the following post growth deformation microstructures planar deformation bands pdbs planar fractures pfs non planar fractures both healed and open and finite strain patterns pdbs are planar portions of crystal lattice that are strictly parallel to 100 crystallographic planes and are rotated to up to 3 with respect to the host grain they are from 0 5 to 1 m wide and have average spacing of 5 m pdbs originate in seismically active environment at elevated differential stress strain rate and temperature several grains in which pdbs are observed were analyzed with ion microprobe ion maps indicate redistribution of radiogenic pb isotopes associated with pdb formation isotopic redistribution preferably occurs in pdbs with larger crystallographic misorientation profiling demonstrated clear spatial correlation of pdbs with variations of ree abundances both gain and loss and possible correlations with increased and decreased hf ti and p abundances trace elements can be depleted or enriched compared to the abundance in surrounding matrix in deformed domains depending on the spacing of pdbs and the proximity of the analyzed volume to grain boundary or to detrital core 207 pb 206 pb ratio demonstrates systematic pb loss in the pdb bearing lattice domains with respect to pdb free domains in some cases pb gain is observed where the pdbs source radiogenic pb from older detrital cores our study has important implications for geochronology and microchemistry of zircon from seismically deformed sections of ivrea verbano zone and from other paleo seismic zones of the world zircon found in seismically deformed rocks near pseudotachylyte veins may demonstrate distorted and even reset isotopic ages and altered trace element abundances enhanced trace element exchange between deformed zircon and host mylonite can influence mass balance calculations for the bulk rock

origin of microlayering in worldwide distributed ir rich marine cretaceous tertiary boundary clays the three most ir rich marine cretaceous tertiary boundary clays are found in denmark spain and new zealand the clays have many features in common the most interesting being a thin basal red layer that together with an overlying organic rich zone contains enhanced concentrations of elements such as ir ni co cr zn cu as and sb at first glance the global correlation of element enrichments may seem to be strong evidence for a dust cloud origin of the basal red layers however detailed layer by layer major element analyses e g si al mg ca k and na together with studies of trace element phase partitioning reveal that the elastic allogenic fraction of the red layers at each site is predominantly locally derived water transported material and that concentrated metals exist in authigenic phases the red layers most likely represent precipitation horizons and not fallout layers metal precipitation was induced by various redox controlled processes in connection with decomposition of the abundant algal matter that settled on the end maastrichtian sea floor the concentrated trace elements derive from sea water however the ultimate origin of some of the elements may have been an earth impacting asteroid

robust 3d gravity gradient inversion by planting anomalous densities we have developed a new gravity gradient inversion method for estimating a 3d density contrast distribution defined on a grid of rectangular prisms our method consists of an iterative algorithm that does not require the solution of an equation system instead the solution grows systematically around userspecified prismatic elements called seeds with given density contrasts each seed can be assigned a different density contrast value allowing the interpretation of multiple sources with different density contrasts and that produce interfering signals in real world scenarios some sources might not be targeted for the interpretation thus we developed a robust procedure that neither requires the isolation of the signal of the targeted sources prior to the inversion nor requires substantial prior information about the nontargeted sources in our iterative algorithm the estimated sources grow by the accretion of prisms in the periphery of the current estimate in addition only the columns of the sensitivity matrix corresponding to the prisms in the periphery of the current estimate are needed for the computations therefore the individual columns of the sensitivity matrix can be calculated on demand and deleted after an accretion takes place greatly reducing the demand for computer memory and processing time tests on synthetic data show the ability of our method to correctly recover the geometry of the targeted sources even when interfering signals produced by nontargeted sources are present inverting the data from an airborne gravity gradiometry survey flown over the iron ore province of quadrilatero ferrifero southeastern brazil we estimated a compact iron ore body that is in agreement with geologic information and previous interpretations

glacial interglacial climatically forced δ 13 c variations in sedimentary organic matter sedimentary organic geochemical properties have long been used to characterize sedimentary organic matter sources1 8 but the characterizations are often not unique there are at least four plausible mechanisms to account for the large 3 6 glacial to interglacial climatic variations in the sedimentary organic carbon isotopic composition 13corg in the northern gulf of mexico they are temperature dependent c isotopic fractionation by phytoplankton mixing of c3 photosynthetic terrigenous and marine organic matter mixing of c3 and c4 photosynthetic organic matter and diagenetic alteration of the originally sedimented material in a 208 7 m deep sea drilling project hydraulic piston core dsdp 619 from the pigmy basin in the northern gulf of mexico we find that paired analyses of 13corg and n c are consistent with the hypothesis that the sedimentary organic carbon in the pigmy basin is a glacial interglacial climati cally determined mixture of c3 photosynthetic terrigenous and marine organic matter9 confirming the model of sackett5

total variation regularization for depth to basement estimate part 1 mathematical details and applications we have developed an inversion approach that estimates the basement relief of a fault bounded sedimentary basin the sedimentary pack is approximated by a grid of 3d or 2d vertical prisms juxtaposed in the horizontal directions of a right handed coordinate system the prisms thicknesses represent the depths to the basement and are the parameters to be estimated from the gravity data to obtain depth to basement estimates we introduce the total variation tv regularization as a stabilizing function this approach lets us estimate a nonsmooth basement relief because it does not penalize sharp features of the solution we have deduced a compact matrix form of the gradient vector and the hessian matrix of the approximation to the tv function that allows a regularized gauss newton minimization approach because the hessian matrix of the approximation to the tv function is ill conditioned we have modified this hessian matrix to improve its condition and to accelerate the convergence of the gauss newton algorithm tests conducted with synthetic data show that the inversion method can delineate discontinuous basements presenting large slips or sequences of small slip step faults tests on field data from the almada basin brazil and from the san jacinto graben california u s a confirm the potential of the method in detecting and locating in depth normal faults in the basement relief of a sedimentary basin

pseudotachylyte bearing strike slip duplex structures in the fort foster brittle zone s maine abstract detailed 1 60 scale mapping of the fort foster brittle zone in the mylonitic rye formation of southernmost maine has revealed the intricate internal duplex structure of a system of probable paleozoic age dextral strike slip faults that have produced abundant pseudotachylyte and minor breccia the internal configuration of this brittle zone consists of a mosaic of individual pseudotachylyte generation zones as slab duplex structures individual duplex zones are up to 100 m in length and 1 m or less in width and are defined by pairs of layer parallel slip surfaces along which frictional melts were produced these slab duplex structures are interpreted as zones of displacement transfer between long overlapping layer parallel en echelon strike slip fault surfaces contractional duplexes develop layer parallel compressional structures that tend to shorten and thicken the fault bounded slabs by the formation of lateral ramps and conjugate faults kinks and asymmetric folds extensional duplexes develop layer parallel stretching and thinning by the formation of oblique dextral shears high angle conjugate pairs and localized fault breccias the production of pseudotachylyte by friction melting along layer parallel fault surfaces in these exposures is attributed to rapid slip during paleoseismic events the rupture structures developed during these events may be characteristic of fault structure and mechanics at near focal depths in a strike slip seismogenic zone

environmental and vegetational changes recorded in sedimentary leaf wax n alkanes across the cretaceous paleogene boundary at loma capiro central cuba abstract the stable carbon isotopic compositions 13c and chain length distribution acl and n c31 n c29 n c31 of sedimentary leaf wax n alkanes were investigated across the cretaceous paleogene k pg boundary at loma capiro central cuba to reconstruct paleoenvironmental changes that are recorded in terrestrial higher plants the stratigraphic profiles of the n alkane 13c values show a negative excursion in the lowermost paleocene although its magnitude is much smaller 0 3 than the global signals 1 5 to 2 0 in the surface ocean atmospheric carbon reservoir relations between the n alkane 13c values and the c31 c29 c31 ratios exhibit two different trends suggesting that our 13c records are likely affected by two types of paleoenvironmental factors in addition to the 13c variations in the exogenous carbon reservoir rare occurrence of terrigenous organic matter that is usually transported by rivers suggests that the n alkanes at loma capiro are likely to have been transported by trade winds which recorded paleoenvironmental conditions of the northwestern part of the african continent the n alkane 13c values show a parallel decrease with the acl and c31 c29 c31 values in the first 37 000 yr following the k pg boundary such decreases are consistent with plant physiological responses to reduced net evaporation suggesting a possible influence of the impact induced warm humid condition in the early paleocene in contrast the n alkane 13c values are negatively correlated with the c31 c29 c31 ratios from 40 000 to 67 000 yr after the k pg boundary this time period matches well with that required for the recovery of terrestrial floras from the k pg mass extinction to those with diversity equivalent to the late cretaceous suggesting that the n alkane signals are also likely affected by the plant diversification process after the mass extinction

geochemical evidence for suppression of pelagic marine productivity at the cretaceous tertiary boundary the normal biologically productive ocean is characterized by a gradient of the 13c 12c ratio from surface to deep waters here we present stable isotope data from planktonic and benthic micro fossils across the cretaceous tertiary boundary in the north pacific which reveal a rapid and complete breakdown in this biologically mediated gradient the fluxes of barium a proxy for organic carbon and caco3 also decrease significantly at the time of the major marine plankton extinctions the implied substantial reduction in oceanic primary productivity persisted for 0 5 myr before the carbon isotope gradient was gradually re established in addition the stable isotope and preservational data indicate that environmental change including cooling began at least 200 kyr before the cretaceous tertiary boundary and a peak warming of 3 c occurred 600 kyr after the boundary event

distribution stereochemistry and stable isotope composition of amino acids in k t boundary sediments abstract the cretaceous tertiary k t boundary with an age of 65 million years before present is associated with the mass extinctions of dinosaurs and other terrestrial and marine organisms evidence for the k t boundary is reported in both marine and non marine stratigraphic units the presence of two exotic amino acids aminoisobutyric acid and isovaline has been reported from stevns klint denmark sediments two hypotheses have been proposed for the occurrence of aiba and i val in the stevns klint sediments 1 they are of extraterrestrial origin and 2 they are the by products of the thermal alteration of coal to test these hypotheses samples were obtained from three k t boundary sites two starkville south and raton pass located in the non marine raton basin of colorado and new mexico and one from the marine sequence at stevns klint denmark the samples were analyzed for amino acid distributions and stereochemistry bulk stable c and n isotope compositions and stable c isotope compositions of individual amino acids at the starkville south site protein and non protein amino acid components are present in the k t boundary sediments at nmol g levels and are primarily of the l configuration the non protein amino acids aiba and i val were detected in several of the sediment samples based on retention times and verified through coinjections of authentic standards protein and non protein amino acid components of the murchison meteorite are enriched in 13 c relative to terrestrial materials the 13 c values of individual amino acids in the starkville south samples are however depleted in 13 c in all samples with values ranging from 13 for glycine to 31 for l isoleucine in contrast the 13 c value for glycine in murchison is 22 also bulk organic 13 c and 15 n values for the k t boundary sediments are substantially depleted in 13 c and 15 n relative to bulk values for the murchison meteorite it is therefore suggested that the amino acids in these k t boundary sediments are primarily of terrestrial biogenic origin

petrogenesis and tectonic significance of amphibolites interlayered with metasedimentary gneisses in the ivrea zone southern alps northwest italy abstract amphibolites occurring as elongate lenses and boudins within the metasedimentary kinzigite formation of the ivrea zone are all of igneous parentage a detailed study of their trace element characteristics shows that they can be divided into two groups type 1 amphibolites occur as layers up to 100 m thick and have trace element distributions showing depletion in incompatible elements typical of normal n type mid ocean ridge basalts type 2 amphibolites occur as thinner layers and boudins and have higher levels of the more incompatible elements similar to transitional or enriched e type ocean basalts although metamorphism appears to have resulted in loss of sio 2 and variable enrichment in na k rb ba sr and locally ca the less mobile elements including the rare earth elements have preserved the primary basaltic geochemical characteristics the tectonic model which best explains the assemblage of slivers of morb like amphibolites within extremely highly deformed semi pelitic metasediments is that of an accretionary sedimentary wedge formed at a palaeozoic subduction zone

magnetic properties of fault pseudotachylytes in granites 1 we investigate the petrographic geochemical and magnetic properties of fault pseudotachylytes formed by frictional melting in granitic rocks from southern california the italian alps and kyushyu japan the main magnetic remanence carriers are mixtures of grain sizes of fine grained magnetite these ferrimagnetic grains record a stable multicomponent magnetization that consists of one or more of the following coseismic thermal remanent magnetization coseismic lightning isothermal remanent magnetization and post seismic chemical remanent magnetization fault pseudotachylytes from the three localities display contrasting magnetic properties which suggests that oxygen fugacity and host rock composition ultimately control the magnetic assemblage

three dimensional regularized focusing inversion of gravity gradient tensor component data we develop a new method for interpretation of tensor gravity field component data based on regularized focusing inversion the focusing inversion makes its possible to reconstruct a sharper image of the geological target than conventional maximum smoothness inversion this new technique can be efficiently applied for the interpretation of gravity gradiometer data which are sensitive to local density anomalies the numerical modeling and inversion results show that the resolution of the gravity method can be improved significantly if we use tensor gravity data for interpretation we also apply our method for inversion of the gradient gravity data collected by bhp billiton over the cannington ag pb zn orebody in queensland australia the comparison with the drilling results demonstrates a remarkable correlation between the density anomaly reconstructed by the gravity gradient data and the true structure of the orebody this result indicates that the emerging new geophysical technology of the airborne gravity gradient observations can improve significantly the practical effectiveness of the gravity method in mineral exploration

pseudotachylytes in the balmuccia peridotite ivrea zone as markers of the exhumation of the southern alpine continental crust terra nova 22 70 77 2010 abstract two types of pseudotachylytes are observed in the balmuccia peridotite of the ivrea zone southern alps italy a type pseudotachylytes correspond to previously studied occurrences and were formed under temperatures comprising between 550 and 900 c and pressures comprising between 0 6 and 1 2 gpa these conditions were met in the ivrea crust between 350 and 270 ma suggesting that a type pseudotachylytes were formed during variscan tectonics or permian transtensional tectonics b type pseudotachylytes post date a type pseudotachylytes textural characteristics of b type veins suggest a formation in the upper continental crust at depths of about 5 10 km or less petrological constraints indicate that the exhumation of the ivrea crust at such shallow depths was achieved later than c 70 ma thus providing a maximum age of 70 ma for b type veins pseudotachylytes appear as markers of the poly orogenic evolution of the alpine belt

elemental and stable isotope variations of organic matter from a terrestrial sequence containing the cretaceous tertiary boundary at york canyon new mexico abstract elemental and isotopic composition of organic matter from a terrestrial sequence including the palynological cretaceous tertiary k t boundary together with an ir anomaly at york canyon new mexico record information about paleoclimatological and environmental conditions six layers of coal carbonaceous shale and mudstone with high contents of organic material were selected for analysis a late cretaceous coal bed 10 m below the k t boundary and an early tertiary coal bed containing the k t iridium anomaly at its base were sampled intensively in the lower bed the isotopic ratios 13 c 12 c 15 n 14 n andd h and the elemental ratios c n andn h all varied sympathetically with one another over depth in contrast in the upper coal layer only the d h c n andn h ratios showed some coupling immediately above the k t boundary the 13 c values displayed a long term shift of 1 8 to more negative values while the hydrogen isotope ratios in these samples did not change significantly we interpret the covariations in both coal layers as sympathetic responses of the isotopic and elemental ratios to climatic and environmental changes as have been observed for younger sedimentary organic matter the long term 13 c shift during the early tertiary is similar to the trend observed for 13 c values of marine carbonates our data thus support the proposal that the carbon cycle was perturbed globally by the effects of a drastically decreased marine bioproductivity along the k t transition the uncoupling of variations in the climatically sensitive isotopic and elemental ratios seen in the early tertiary coal bed provides evidence for major geochemical and environmental changes in the york canyon area at the end of the mesozoic on the other hand the constancy of d values in the organic matter deposited at and above the k t boundary gives no indication of significant changes in the hydrologic climatic regimes as recorded in the d h ratios at the site for several thousand years following the event which produced the high ir concentrations our results provide constraints on models that have been advanced to explain that event and its consequences

joint inversion of gravity and traveltime data using a level set based structural parameterization abstractwe have developed a new level set based structural parameterization for joint inversion of gravity and traveltime data so that density contrast and seismic slowness are simultaneously recovered in the inverse problem because density contrast and slowness are different model parameters of the same survey domain we assume that they are similar in structure in terms of how each property changes and where the interface is located so that we are able to use a level set function to parameterize the common interface shared by these two model parameters the level set parameterization makes it easy to maintain the structural similarity between the two geophysical properties the inversion of gravity and traveltime data is carried out by minimizing a joint data fitting function with respect to density contrast slowness as well as the level set function an adjoint state method is used to compute the traveltime gradient efficiently we have tested our algorithm on various synthetic examples including

carbon isotope evidence for unusual plankton blooms and fluctuations of surface water co2 in strangelove ocean after terminal cretaceous event abstract a decrease in 13c kerogen by 3 and increase in 13c carbonate kerogen by 1 2 has been observed in sediments at the k t boundary substantiating the occurrence of a strangelove ocean wherein dissolved co2 was enriched in 12c because of mass mortality or reduced plankton production a subsequent increase in 13c kerogen by 7 and decrease in 13c carbonate kerogen by 5 4 indicate a dramatic reduction in pco2 this decrease could be the consequence of depletion of co2 in surface waters because of unusual plankton blooms these environmental changes which characterize the strangelove ocean occurred after the terminal cretaceous event during this time rapid fluctuations in dissolved co2 of ocean surface waters may have caused significant perturbations in atmospheric pco2 levels and consequently major instability of the global climate

late cretaceous and paroxysmal cretaceous tertiary extinctions the various geological signatures at cretaceous tertiary time including iridium and other associated elements microspherules and shock deformation features are compatible with the suggestion that the transition is marked by a period of intense volcanism the volatile emissions from this volcanism would lead to acid rain reduction in the alkalinity and ph of the surface ocean global atmospheric temperature changes and ozone layer depletion these environmental effects coupled with those related to the major sea level regression of the late cretaceous provide the framework for an explanation of the selective nature of the observed extinction record

extinction survivorship and evolution of planktic foraminifera across the cretaceous tertiary boundary at el kef tunisia an expanded sediment record at el kef shows that the k t boundary extinctions of planktic foraminifera extend over an interval from 25 cm below the geochemical boundary ir anomaly to 7 cm above species extinctions appear sequential with complex large ornate forms disappearing first and smaller less ornate forms surviving longer the 14 species extinctions below the boundary appear unrelated to an impact event cretaceous species survivorship is greater than previously assumed about 10 species survive 22 into subzone p1a globigerina eugubina all cretaceous survivors are small primitive forms which are generally smaller than their ancestors in cretaceous sediments species evolution after the k t event occurs in two pulses the first new paleocene species evolve in the basal black clay zone po immediately after the major cretaceous extinctions evolving species are small and primitive similar to cretaceous survivors the second pulse in species evolution occurs in the lower part of subzone p1b with the appearance of larger more diverse species the first major increase in carbonate sedimentation and productivity occurs at this time and signals the recoveyr of the ecosystem nearly 300 000 years after the k t event the species extinctions prior to the generally assumed impact event implied by the ir anomaly and the long recovery period of the ecosystem thereafter cannot be explained by a single impact but suggest that multiple causes may be responsible such as climatic changes volcanism a sea level drop production of warm saline bottom water and the chemical consequences associated with increased salinity

planar microstructures in zircon from paleo seismic zones pseudotachylytes resulted from frictional melts associated with ultramylonites in high grade metapelitic rocks from the ivrea verbano zone in the southern alps northern italy were studied with focus on the deformation microstructures in zircon the aims were to investigate the characteristics of zircon deformation in seismic zones and to recognize specific microstructures generated in zircon during earthquakes which could be useful for mineral dating of paleo seismic events helps to understand how seismic energy is released at depth and interacts with metamorphic processes the interior of polished zircon grains ranging from 30 to 150 m in length were investigated with optical microscope and scanning electron microscope sem techniques including secondary electron se backscattered electron bse forward scattered electron fse cathodoluminescence cl imaging and crystallographic orientation mapping by electron backscatter diffraction analysis ebsd grains were studied in situ and as separated fractions embedded in epoxy disks among different cataclastic and crystal plastic deformation microstructures in zircon we identified characteristic planar deformation bands pdbs planar fractures pfs and curviplanar fractures cfs planar deformation bands in zircon are crystallographically controlled planar lattice volumes with misorientation from the host grain which varies from 0 4 to 2 7 pdbs are usually parallel to 100 crystallographic planes have width from 0 3 to 1 m and average spacing of 5 m in 2d sections planar deformation bands appear as contrast lamellae in orientation contrast images and in ebsd maps and in rare cases can be observed with the optical microscope pdbs form in specifically oriented grains due to high differential stresses high temperatures and high strain rates generated in seismically active environment and or due to shearing in the vicinity of frictional melts discovered structures represent a result of crystal plastic deformation of zircon grains with operating dislocations having 010 glide system and misorientation axis therefore they can be classified as a new type 4 lattice distortion pattern according to the existing classification for zircon piazolo et al 2012 kovaleva et al 2014 we have demonstrated that formation of planar fractures in zircon takes place not only during impacts but also in seismically active zones we observe at least two cases of formation of pfs with 100 orientation 1 as a result of evolution of pdbs and 2 as micro cleavage this study demonstrates that planar microstructures in terrestrial zircon do not exclusively form during impact events but also as a result of seismic events at depth due to unusually high differential stress strain rate and temperature according to the new findings pdbs in zircon from the deep crust are supposed to represent newly recognized evidence of seismicity

abrupt and massive influx of terrestrial biomarkers into the marine environment at the cretaceous tertiary boundary caravaca spain the mass extinction at the cretaceous tertiary k t boundary ca 65 million years ago caused a major change in the nature and abundance of global life in earth history we present the first vertical high resolution records of molecular distributions of n fatty acids across the k t boundary at caravaca spain the results reveal that the first basal thin horizon 0 to 0 5 cm 0 k t boundary of the k t boundary clay layer showed as much as a 35 fold increase in concentrations of terrestrial longchain n fatty acids zc20 representative of an eight fold increase in mass accumulation rate compared with the subjacent cretaceous layers thereafter concentrations rapidly declined back to almost pre boundary values within 3 cm above the k t boundary the abrupt increase in supply of terrestrial organic matter into the marine environment at the k t boundary could have been caused by an enhanced riverine flux probably due to heavy rains associated with global warming combined with enhanced fragments of terrestrial higher plants withered by acid rain and or by temporal darkness and cooling d 2005 elsevier b v all rights reserved

a paleoclimatic and paleoatmospheric record from peatlands accumulating during the cretaceous paleogene boundary event western interior basin canada petrological and 13 c analyses were undertaken on contiguous specimens of coal and intercalated minor organic rich clastic sediments collected from coal seams spanning the cretaceous paleogene boundary in the alberta and saskatchewan portions of the western interior basin the generally high smectite content of the coal suggests that the original mires were largely small disconnected and rheotrophic readily receiving abundant waterborne detrital clastic material of largely volcanic origin nevertheless using the distinctive claystone that marks the cretaceous paleogene boundary as a regional datum it is possible to correlate cycles in the vitrinite and inertinite composition of the coals over 500 km estimates of peat accumulation rates suggest that the cycles in vitrinite and inertinite composition represent regional cyclic fluctuations in wildfire and oxidation of the peatlands and overlying canopy at a frequency of hundreds to thousands of years the likely causes of these fluctuations were cyclic regional scale changes in temperature the cretaceous paleogene boundary event occurred early during a phase of gradually increasing temperature and or decreasing rainfall but peak wildfire and desiccation of peat occurred up to 14 000 yr later than the cretaceous paleogene boundary and the mires did not experience significant water stress in the immediate aftermath of the extinction event a persistent 1 5 3 0 negative 13 c excursion occurs across the cretaceous paleogene boundary but it cannot be readily separated from four further negative excursions later in the earliest danian the negative carbon isotope excursion linked to the cretaceous paleogene boundary began a few hundred years before the event itself and recovery occurred within 21 k y and possibly in as little as just a few thousand years consistent with recently calibrated shallow marine 13 c records hence the atmospheric and surface ocean carbon pools were coupled at this time the absence of evidence for catastrophic change in the climatic regime at the time of the cretaceous paleogene extinction in these mires supports the notion that the negative shift in atmospheric 13 c was brought about by changes in the 13 c composition of the surface ocean this is consistent with the greater magnitude of extinction experienced by marine fauna relative to the terrestrial realm

melt origin of fault generated pseudotachylytes demonstrated by textures a petrographic and electron microprobe study of fault generated pseudotachylytes from the outer hebrides thrust zone scotland demonstrates that the textures have resulted from the primary crystallization of a clast laden melt rather than the devitrification of a glass or by crushing and cataclasis the observations are consistent with these pseudotachylytes having formed by frictional fusion followed by rapid quenching implying faulting at shallow crustal depths

gradual dinosaur extinction and simultaneous ungulate radiation in the hell creek formation dinosaur extinction in montana alberta and wyoming was a gradual process that began 7 million years before the end of the cretaceous and accelerated rapidly in the final 0 3 million years of the cretaceous during the interval of apparent competition from rapidly evolving immigrating ungulates this interval involves rapid reduction in both diversity and population density of dinosaurs the last dinosaurs known are from a channel that contains teeth of mantuan mammals seven species of dinosaurs and paleocene pollen the top of this channel is 1 3 meters above the likely position of the iridium anomaly the cretaceous tertiary boundary

gravity inversion of basement relief using approximate equality constraints on depths we present a gravity interpretation method for estimating the relief of an arbitrary interface separating two homogeneous media the upper medium is discretized into rectangular juxtaposed prisms whose thicknesses represent the depths to the interface and are the parameters to be estimated from the gravity anomaly the density contrast of each prism is assumed to be constant and known to stabilize the inversion we introduce two kinds of constraints on the depths the first one requires proximity between the observed and computed depths at isolated points such as those obtained from boreholes absolute equality constraint the second one requires that groups of depths approximately follow an established linear relationship among the depths relative equality constraint both kinds of constraints are imposed in the least squares sense we illustrate the method performance by applying it to a synthetic anomaly produced by a simulated basement relief consisting of four narrow and adjacent structural lows

3d inversion of airborne gravity gradiometry data using cokriging abstractwe developed a new method for interpretation of airborne gravity gradiometry data based on cokriging inversion the cokriging method that we evaluated minimized the theoretical estimation error variance by using auto and crosscorrelations of several variables it does not require iterations and can easily include complex a priori information moreover the smoothing effects in the inverted density structure model can be reduced to a certain extent due to the anisotropy constrain in the covariance model we compared the recovered models obtained by inverting the different combinations of gravity gradient components to understand how different component combinations contributed to the resolution of the recovered model the results indicated that including multiple components for inversion increased the resolution of the recovered density model and improved the structure delineation moreover in the case in which the parameters of the variogram model are not well chosen cokriging with multicompon

end cretaceous devastation of terrestrial flora in the boreal far east a continuous marine sedimentary sequence spanning the cretaceous tertiary k t boundary has been identified in eastern hokkaido japan on the basis of planktonic foraminifera the k t boundary is marked by a 6 10 cm thick layer of pyrite rich fossil poor greyish black claystone1 which is lithologically similar to the well known boundary clay of the classical european k t boundary sections2 4 we show here that terrestrial palyno morphs from the hokkaido section record sudden changes in the floristic composition precisely at the base of the boundary claystone layer in particular both angiosperm and gymnosperm pollen abundances decline markedly and these changes are accompanied by an abrupt rise in the proportion of fern spores return to the original moderate level of fern dominance occurs within a few centimetres above the boundary layer a sharp increase of fern spores has also been reported at the palynologically defined k t boundary in the western interior of north america5 which coincides with the top of an iridium rich clay layer6 7 the possibly synchronous occurrence of analogous floral changes at these widely separated regions implies a devastation of the land flora which although geologically brief was intercontinental in scope and which was probably caused by a major catastrophic event such as the impact of a massive meteorite7

biotic turnover in benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia abstract the cretaceous tertiary boundary section exposed near el kef tunisia is the most complete boundary sequence known to date it contains nearly 1 m of black and gray boundary clay containing planktic foraminiferal zone poa b 2 m of clayey shales of p1a globigerina eugubina zone and 4 m of shales and marls of p1b g taurica zone quantitative analysis of the benthic foraminiferal fauna suggests that deposition during the latest cretaceous occurred in an upper slope to outer shelf environment which shallowed at the k t boundary to an outer to middle shelf depth and shallowed further by p1b time to mid shelf depth a major reduction in benthic diversity occurred near the k t boundary with about 50 of the fauna disappearing diversity remained an average of 37 lower during deposition of the first 3 m of sediment above the boundary poa b p1a and productivity was very low surviving and thriving foraminifers during this interval were primarily low oxygen tolerant epifaunal and infaunal species a sharp decrease in the low oxygen tolerant fauna and appearance of a shallow mid shelf fauna at about 4 m above the boundary p1b zone signals a second regression return to higher oxygen levels and higher productivity although the environmental effects of the k t boundary event can be inferred from benthic faunas the ultimate cause remains elusive faunal changes prior to and the long recovery period after the k t boundary are difficult to explain by a single impact hypothesis

amphibolite facies pseudotachylytes in premosello metagabbro and felsic mylonites ivrea zone italy abstract pseudotachylytes solidified friction induced melts produced during seismic slip that formed under high temperature ambient conditions might retain information on earthquake mechanics beneath the brittle ductile elasto frictional viscous plastic transition in the crust thin sharply bounded pseudotachylytes and ultramylonites occur together inside the granulite facies premosello metagabbro and inside country felsic mylonites of the ivrea zone italian southern alps petrographic and microstructural data indicate that the studied pseudotachylytes and ultramylonites are coeval and developed under amphibolite facies 500 650 c metamorphic conditions the occurrence of foliated pseudotachylytes and of local remnants of cataclastic microstructures within ultramylonites suggests that pseudotachylytes might have represented planar heterogeneities for nucleation of ultramylonites the association of coeval pseudotachylyte and mylonites is interpreted as caused by cyclic stages of coseismic high strain rate transients related to downward propagation of seismic ruptures from the upper brittle crust followed by post seismic stress relaxation by ductile flow

the development of pseudotachylyte in the ivrea verbano zone of the italian alps abstract pseudotachylyte was formed as part of the retrogressive tectonometamorphic evolution of the ivrea verbano zone during its post hercynian uplift from the lower crust during the mesozoic and cenozoic the pseudotachylytes preferentially occur in mafic rocks and in paragneisses and were generated along brittle faults which locally cut older ductile shear zones fracturing and the selective melting of minerals resulted in an aphanitic matrix containing host rock fragments and newly formed minerals e g biotite quartz sericite feldspar friction melt induced hydraulic fracturing of the adjacent rocks facilitated the formation of pseudotachylyte veins the veins occur as networks or as single 0 1 m to several metres thick injections with the geometry of pull apart structures in zones with a high density of contemporaneously formed pseudotachylyte veins the fractured wall rock lost cohesion and became intrusive masses of angular to rounded fragments became mobilized when the macroscopically homogeneous pseudotachylyte matrix exceeded about 30 of the total rock volume geochemical data show that the pseudotachylytes developed from the immediately adjacent host rocks scanning and transmission electron microscopy indicate that the enrichment or depletion of individual elements in the pseudotachylyte relative to the host rock depended on the amount of selectively melted minerals that were incorporated amphiboles plagioclase quartz and or sheet silicates and on the degree of secondary alteration the development of pseudotachylyte took place in the upper crust during retrogressive metamorphism which commenced in the ductile deformation field with the formation of high temperature mylonites followed by the generation of low temperature mylonites and finally by brittle deformation

on the geometric relationship between deformation microstructures in zircon and the kinematic framework of the shear zone abstract we present novel microstructural analyses of zircon from a variety of strained rocks for the first time multiple plastically deformed zircon crystals were analyzed in a kinematic context of the respective host shear zones our aim was to derive how the orientation of zircon grains in a shear zone affects their deformation based on careful in situ observations for sampling we selected zircon bearing rocks that were deformed by simple shear samples covered a range of p t conditions and lithologies including various meta igneous and meta sedimentary gneisses microstructural analyses of zircon crystals in situ with scanning electron backscatter diffraction mapping show strong geometrical relationships between orientations of i the long axes of plastically deformed zircon crystals ii the crystallographic orientation of misorientation axes in plastically deformed zircon crystals and iii the foliation and lineation directions of the respective samples we assume that zircon crystals did not experience post deformation rigid body rotation and thus the true geometric link can be observed the relationships are the following a plastically deformed zircon crystals usually have long axes parallel to the mylonitic foliation plane b crystals with axes oriented at an angle 15 to the foliation plane are undeformed or fractured zircon crystals that have axes aligned parallel or normal to the stretching lineation within the foliation plane develop misorientation and rotation axes parallel to the 001 crystallographic direction zircon grains with the axis aligned at 30 60 to the lineation within the foliation plane often develop either two low miller indices misorientation axes or one high miller indices misorientation axis host phases have a significant influence on deformation mechanisms in a relatively soft matrix zircon is more likely to develop low miller indices misorientation axes than in a relatively strong matrix these relationships are independent of zircon s grain size and shape and reflect the strong geometric control of the macroscopic kinematic rotation axis on the crystal plastic deformation behavior of zircon and on the geometry of its slip systems we describe previously unknown rheological and crystallographic properties of zircon which suggest a tool for deriving an orientation of the plastically deformed zircon crystals with respect to the associated foliation and stretching lineation additionally relationships between zircon deformation microstructures and the macroscopic kinematic framework have implications for zircon geochronology if deformation events result in zircon distortion and as a consequence partial or complete resetting of the zircon isotopic system the age of deformation can be accurately dated