sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

quantifying measurement uncertainty of thirty meter shear wave velocity thirty meter shear wave velocity v s 30 is commonly used to estimate near surface conditions for site classification seismic site response liquefaction analysis and other geotechnical earthquake engineering application quantifying the uncertainty in v s 30 measurements is important for determining the accuracy and precision of this geophysical test this study gathers existing available comparative and blind shear wave velocity tests to evaluate the apparent or observable intra and intermethod variability presented in this article are estimates of v s 30 uncertainty for the invasive methods of downhole suspension logging and seismic cone penetration testing the noninvasive method of spectral analysis of surface waves and the method of shear wave velocity correlated geologic units discussed is the issue of soil disturbance with respect to invasive methods and how this may result in measurement bias results of this study indicate that uncertainty of shear wave velocity measurements are on the order of 1 3 coefficient of variation standard deviation mean for downhole suspension logging and seismic cone penetration testing 5 6 coefficient of variation for spectral analysis of surface waves and 20 35 coefficient of variation for shear wave velocity correlated geologic units presented here are procedures for propagating the uncertainty and or bias in forward analyses

ichnology of a paleopolar river dominated shallow marine deltaic succession in the mackellar sea the mackellar formation lower permian central transantarctic mountains antarctica abstract the lower permian mackellar formation in the beardmore glacier area of the central transantarctic mountains antarctica was deposited between 80 and 85 s paleolatitude previous studies suggest that mackellar formation strata were deposited in either a large glacial lake or inland sea our study identified 30 ichnogenera from turnabout ridge and buckley island of which 1 none are exclusively freshwater forms 2 20 ichnogenera are found in freshwater brackish and marine settings and 3 10 ichnogenera are exclusively found in marine settings combining ichnologic evidence with sedimentologic observations suggests that the mackellar formation was deposited in a river dominated delta in a fully marine to brackish marine setting trace fossil associations are grouped into the arenicolites phycodes lingulichnus arenicolites planolites kouphichnium phycodes teichichnus arenicolites and planolites teichichnus phycodes ichnocoenoses of a mixed skolithos cruziana ichnofacies these associations are characteristic of epi and endobenthic worms arthropods and mollusks with the vast majority of the traces being diminutive in diameter and length and exhibit shallow 10 mm penetration depths these ichnocoenoses occur in paleoenvironments that include the prodelta distal to proximal delta front including mouth bars and subaqueous terminal distributary channels the diminutive morphology shallow penetration depth low bed ichnodiversity high overall ichnodiversity and sedimentologic characteristics are indicative of benthic organisms in a marine deltaic environment with short lived communities composed of small bodied organisms stressed by high freshwater input and high sedimentation rates

seismic property characterization of lithotypes cropping out in the siracusa urban area italy the town of siracusa is located in the south eastern coast of sicily southern italy in a wide inlet engraved into a limestone formation this lithotype which is overlaid by soft sediments such as sandy clays and detritus can be considered as the local bedrock present study aims to investigate on the dynamic properties of main lithotypes outcropping in the study area and their relationships with the local seismic response non invasive seismic prospecting techniques using the vertical component of surface waves masw and remi were adopted as well as ambient noise measurements processed through the nakamura technique the best solution for the experimental dispersion curves was selected using the neighbourhood algorithm and information about the deeper part of the estimated shear wave profiles was obtained by considering the ellipticity of the fundamental peak moreover a cluster analysis was performed to subdivide into homogeneous groups the experimental noise spectral ratios results obtained pointed out that the use of combined different methods provides a robust way to characterize the investigated soils and to reduce the problems linked to the non uniqueness of solutions during the interpretation of geophysical data

hvnsr survey in historical downtown l aquila central italy site resonance properties vs subsoil model abstract this paper presents and discusses the results of a detailed seismic noise survey carried out in historical downtown l aquila after the earthquake of 6 apr 2009 m w 6 3 seismic noise data were interpreted through numerical simulations with the support of a subsoil model characterised by four main units from the top to the bottom i soft soils anthropogenic filling material and terra rossa ii l aquila breccia iii l aquila pelite and sand and iv the meso cenozoic carbonate bedrock the hvnsr analysis permitted the identification of two peaks f0 and f1 nearly everywhere f0 0 4 0 7 hz is due to the superposition of l aquila pelite and sand on the carbonate bedrock at 200 300 m below ground level f1 3 15 hz is caused by shallower impedance contrasts due to 3 20 m thick soft sediments overlying l aquila breccia and by the weathering profile of l aquila breccia a numerical simulation was carried out for three different models characterised by i lithology lateral variation in the first 100 m of thickness due to the substitution from north to south of l aquila breccia with l aquila pelite and sand ii the thickness variation of soft top soil onto l aquila breccia and iii the presence of a weathered layer in the upper part of the l aquila breccia the numerical simulation results fit the experimental seismic noise data a spatial correlation between areal distributions of severe damages with that of f1 resonance frequency is found so it follows that the severe damage during the l aquila earthquake of 6 apr 2009 could have been caused by the seismic local effect of the soft top soil and the weathering profile of l aquila breccia

reassessment of the problematic burgess shale sponge takakkawia lineata walcott 1920 the monotypic burgess shale sponge genus takakkawia walcott 1920 has been previously assigned to the protomonaxonida despite showing several unique features a reassessment of the genus including restudy of previously described material and the addition of new material that includes partially disarticulated specimens has allowed a greatly modified understanding of its structure the sponge possessed four primary columns each divided into two of highly modified spicules with an outer organic layer extended into a unique complex flange that shows a fine microstructure the flanges within one column overlap to give the impression of radial fins and each column is surmounted by an enlarged marginal spicule of similar morphology multi rayed spicules are present both within the primary column architecture and as marginalia lining the osculum the architecture most closely resembles metaxyspongia wu et al 2005 which is placed into the takakkawiidae this restudy supports an interpretation of the family as a very early branching sponge lineage diverging within the early stem group of silicea or prior to the separation of calcarea and silicea resume le genre d eponge monotypique du schiste de burgess takakkawia walcott 1920 a deja ete affecte aux protomonaxonides et ce malgre le fait qu il presente plusieurs caracteres uniques une reevaluation du genre incluant un re examen de materiel deja decrit et l ajout de nouveau materiel dont des specimens partiellement desarticules a considerable ment modifie la comprehension de sa structure l eponge possedait quatre colonnes primaires chacune etant divisee en deux de spicules fortement modifies dotes d une couche organique externe se prolongeant en une frange complexe et parti culiere presentant de fines microstructures les franges au sein d une meme colonne se superposent pour donner l impres sion d ailettes radiales et chaque colonne est surmontee d un spicule marginal plus grand que les autres mais de morphologie semblable des spicules a plusieurs rayons sont presents dans l architecture des colonnes et comme elements marginaux bordant l oscule l architecture s apparente le plus a metaxyspongia wu et al 2005 qui est affecte aux takak kawiides le present reexamen appuie une interpretation voulant que cette famille constitue une lignee d eponges represen tant un embranchement tres precoce divergeant a l interieur du groupe souche precoce des silicea ou avant la separation des calcarea et des silicea traduit par la redaction

wavefield polarization in fault zones of the western flank of mt etna observations and fracture orientation modelling ambient noise measurements performed on the western flank of mt etna are analyzed to infer the occurrence of directional amplification effects in fault zones the data were recorded along short 500 m profiles crossing the ragalna fault system ambient noise records were processed to compute the horizontal to vertical noise spectral ratio as a function of frequency and direction of motion wavefield polarization was investigated in the time frequency domain as well peaks of the spectral ratios generally fall in the frequency band 1 0 6 0 hz pointing out directional amplifications that are also confirmed by the results of the time frequency analysis the largest amplification occurring with high angle to the fault strike a variation of the frequency of the spectral peak is observed between the two sides of the fault possibly related to a damage fault asymmetry measurements performed several kilometers away from the fault zone do not show behavior that is as systematic as in the fault zone and this suggests that the observed directional effects can be ascribed to the fault fabric we relate the polarization effect to compliance anisotropy in the fault zone where the presence of predominantly oriented fractures makes the normal component of ground motion larger than the transversal one in order to test the direction and the type of fractures that are expected in the fault zone we modeled the brittle deformation pattern of the investigated fault theoretical results are in good agreement with field observations of the fracture strike

study of the h v spectral ratio method for determining average shear wave velocities in the mississippi embayment abstract the shear wave velocity v s structure of the deep sediments in the mississippi embayment is of interest to engineers and seismologists due to its influence on seismic wave propagation and site response during an earthquake although the shallow v s structure top 30 to 60 m is generally well characterized information on the v s structure at greater depths to 1000 m in some regions is very limited past studies have developed relationships between the average v s v s ave of post paleozoic sediments in the embayment as a function of sediment thickness one of these studies used converted body wave arrivals while the other used ambient noise measurements processed with the horizontal to vertical spectral ratio hvsr method interestingly these two approaches yielded relationships that differed by about 25 to 30 the objective of this study is to investigate the cause of the discrepancy between these relationships and identify the more reliable relationship for the v s structure in the mississippi embayment experimental measurements of ambient noise were performed at eleven deep soil sites in the mississippi embayment and analyzed using the hvsr method the results from the experimental study yielded v s ave values that were consistent with findings from the previous hvsr study however simulations of body and surface wave propagation performed using estimated full depth v s profiles at each site showed that the methodology used to develop the velocity thickness relationship specifically the approximate relationship used to relate site frequency sediment thickness and v s produces an overestimation of the true v s ave for the profile by 25 to 30

ambient noise measurements for preliminary site effects characterization in the urban area of florence italy abstract environmental noise measurements and borehole data were used for a preliminary seismic characterization of the plio quaternary sedimentary basin underlying the city of florence italy an extensive survey of ambient vibrations was conducted by using the seismic noise horizontal to vertical h v spectral ratio technique hvsr to map the fundamental resonance frequency of the sedimentary cover in order to use this information to infer main features of the basin subsurface geometry an estimate of the s wave velocity profile in the sediment layer was obtained from array noise recordings along with information on resonance frequency and direct measurements of the sediment thickness available at 23 borehole sites a first order reconstruction of the seismic bedrock topography in the area was provided which shows a good consistency with available geological log data from these pieces of information a preliminary soil classification of the whole area was attempted in order to identify situations where possible seismic amplification effects are expected during future earthquakes and where more accurate investigations are needed to parameterize the local seismic response

widespread preservation of small carbonaceous fossils scfs in the early cambrian of north greenland the early cambrian ca 518 ma sirius passet lagerstatte of north greenland is one of the most celebrated sites bearing fossils of soft bodied organisms and provides key insights into the cambria

characterization of kerogenous films and taphonomic modes of the sirius passet lagerstatte greenland the sirius passet lagerstatte northern greenland is an exceptionally well preserved early cambrian faunal community containing a diverse array of stem group euarthropods lobopodians worms sponges and the iconic halkieria material collected in situ during recent expeditions has yielded a range of fossil specimens that are preserved as two dimensional reflective films here we document in detail for the first time from the sirius passet compressed kerogenous fossil films characteristic of burgess shale type bst preservation the carbon structure and the taphonomic mode associated with these films were investigated using raman spectroscopy our analysis confirms that these reflective films are kerogenous showing a higher d1 disordered band and g graphite band intensity and area indicating a greater concentration of disordered carbon compared to the surrounding matrix the spectral characteristics of the fossils denote moderately ordered kerogenous matter indicating that the transitional buen formation that hosts the sirius passet was thermally altered at a peak temperature of 409 50 c phyllosilicate minerals are associated with the films but they are not anatomical or taxon specific suggesting that the higher thermal maturation of the kerogen in the sirius passet produced a uniform distribution of minerals this is unlike the kerogenous films in the burgess shale lagerstatte british columbia canada that have been metamorphosed at a lower temperature of 335 50 c and typically show an anatomically specific phyllosilicate distribution preservation as kerogenous films however is not continuous and the presence of other taphonomic modes not indicative of bst preservation suggests that the sirius passet represents a unique and complex deposit

cambrian burgess shale type deposits share a common mode of fossilization although cambrian burgess shale type bst biotas are fundamental to understanding the radiation of metazoans the nature of their extraordinary preservation remains controversial there remains disagreement about the importance of the role of early mineral replication of soft tissues versus the conservation of primary organic remains most prior work focused on soft bodied fossils from the two most important bst biotas those of the burgess shale canada and maotianshan shale chengjiang china fossils from these two deposits do not provide ideal candidates for specimen level taphonomic study because they have been altered the burgess shale by greenschist facies metamorphism and the maotianshan shale by intensive subsurface weathering elemental mapping of soft bodied fossils from 11 other bst deposits worldwide demonstrates that bst preservation represents a single major taphonomic pathway that may share a common cause wherever it occurs the conservation of organic tissues and not early authigenic mineralization is the primary mechanism responsible for the preservation of bst assemblages early authigenic mineral replacement preserves certain anatomical features of some specimens but the preservation of non biomineralized bst fossils requires suppression of the processes that normally lead to the degradation of organic remains in marine environments

ubiquitous burgess shale style clay templates in low grade metamorphic mudrocks despite the burgess shale s british columbia canada paleobiological importance there is little consensus regarding its taphonomy its organic fossils are preserved as compressions associated with phyllosilicate fi lms clay templates debate focuses on whether these templates were fundamental in exceptional preservation or if they formed in metamorphism meaning that it is important to establish the timing of their formation relative to decay an early diagenetic origin has been proposed based on anatomy specifi c variations in their composition purportedly refl ecting contrasts in decay however we demonstrate that these films bear a remarkable similarity to those that occur on organic fossils in graptolitic mudrocks and form as a normal product of low grade metamorphism such phyllosilicates may also occur within voids created by volume loss in maturation a process that may have aided their formation in bedding plane assemblages from graptolitic mudrocks different taxa are associated with distinct phyllosilicates this likely refl ects stepwise maturation of their constituent kerogens in an evolving hydrothermal fl uid with different hyllosilicates forming as each taxon progressively underwent maturation these observations provide an analogue for the distribution and composition of phyllosilicates on burgess shale fossils which we interpret as refl ecting variations in the maturation of their constituent tissues thus their clay templates seem unremarkable forming too late to account for exceptional preservation

the middle cambrian burgess shale and its relationship to the stephen formation in the southern canadian rocky mountains the burgess shale has been an anomalous geologic unit ever since walcott named it in 1911 as the geographic equivalent of the ogygopsis shale in the middle cambrian stephen formation of southeastern british columbia but it has never been recognized outside of its type locality so its status relative to the stephen formation remained uncertain the geologic setting of the burgess shale was determined by aitken and fritz in 1968 when they recognized the cathedral escarpment and divided the stephen formation into a thin platformal succession on top of the escarpment and a thick basinal succession which included walcott s burgess shale in front fieldwork by royal ontario museum parties between 1982 and 1997 has now demonstrated that the thin and thick stephen successions lie within different facies belts and should be regarded as separate formations the stephen shale formation is part of the middle carbonate belt succession whereas the name burgess shale formation is applied to the thick basinal

sedimentation of the phyllopod bed within the cambrian burgess shale formation of british columbia we provide the most detailed sedimentological log to date through the phyllopod bed of the mid cambrian burgess shale formation of british columbia based on millimetre scale logging of a suite of thin sections the sedimentary facies is dominated by alternations of homogeneous mudstone and a coarser grained laminated variably sandy and shelly mudstone that is locally micronodular most boundaries between these two lithologies are gradational and discrete fining upwards turbidite units were rarely recognized such a pattern is interpreted to indicate rapid sedimentation of up to decimetre thick units at this location from pulsatory quasi continuous density currents consistent with earlier proposals of exceptional preservation through rapid burial the density currents responsible were probably largely akin to mud rich slurries helping explain the transport and entombment of the fossils the homogeneous mudstone units are characterized by numerous distinctive lenses of pyrite framboids or subeuhedral crystals previously interpreted as small ripples their 3d shape however suggests an origin as subspherical early diagenetic aggregates their present morphology is consistent with the high levels of compaction inferred from the preservation of fossils

elemental mapping of exceptionally preserved carbonaceous compression fossils abstract elemental mapping offers rapid qualitative analysis of the mineralogy of exceptionally preserved fossils and importantly can be undertaken on unprepared samples the results of such analyses are sensitive to several variables including the operating conditions particularly accelerating voltage and the composition of the material analysed the higher the accelerating voltage employed and the lower the atomic number of the material impacted by the electron beam the larger the excitation volume in effect a greater thickness of the specimen that contributes to the resultant elemental map fossil non biomineralised arthropods are commonly preserved as carbonaceous compresssions the cuticle is organically preserved and in hand specimen essentially two dimensional the external and internal surfaces of this cuticle may be coated by authigenic minerals examples include arthropods from the middle cambrian burgess shale exceptional fauna it is theoretically possible that the proportion of the total counts generated by a thin surficial film of low atomic number e g a carbonaceous cuticle will be insufficient to distinguish it as a peak above the background spectrum i e it will be effectively transparent in elemental maps simulated energy dispersive x ray spectra for a windowless ed detector suggest that at an accelerating voltage of 15 kev a carbon layer less than about 0 2 m thick will be undetectable and at 5 kev a layer less than a few hundred angstroms thick these values will increase if the energy dispersive spectrometer is fitted with a super ultra thin window

greenschist facies metamorphism of the burgess shale and its implications for models of fossil formation and preservation metamorphosed silty mudstones of the burgess shale and stephen shale formations record a poly metamorphic history an early greenschist facies event associated with burial by paleozoic strata produced a nearly ubiquitous bedding parallel cleavage s1 tectonic exhumation during the formation of the southern canadian rocky mountains produced a domainal subgreenschist facies retrograde overprint in which a high angle crenulation cleavage s2 was developed whereas all rocks have experienced these two events the degree of deformation and fossil pre servation varies with position relative to the cathedral escarpment this paleosubmarine cliff resulted in a zone of reduced deformation within adjacent strata by buttressing them during burial and deflecting deformation during orogenesis fossil bearing strata are composed of a typical greenschist assemblage of muscovite chlorite quartz albite are devoid of clays and contain an average of 0 28 organic carbon this typical metamudstone assemblage is consiste

microtremor observations of deep sediment resonance in metropolitan memphis tennessee we measured site resonance periods throughout metropolitan memphis tennessee the site resonance was derived from recordings of ambient microtremor and is a direct measurement of seismic ground shaking in the memphis metropolitan area the period t0 in s is predicted by the empirical relation t0 0 39899 7 8922 10 3h 3 0634 10 6h2 350 h 1100 m where h is the thickness in m of the unconsolidated sediments that overly hard paleozoic rocks assuming that a quarter wavelength relationship governs the relationship between resonant period sediment thickness and average shear wave speed we estimate the average shear wave speed of unconsolidated sediments as a function of sediment thicknesses vs 521 15 0 37459h 350 h 1100 m the scatter in the observations and discordance with earlier work suggests that caution is warranted in applying these values of wave speed indiscriminately to sites in the absence of further detailed work

a study of the seismic response of the city of benevento southern italy through a combined analysis of seismological and geological data abstract a previous analysis improta l g di giulio and a rovelli 2005 variations of local seismic response in benevento southern italy using earthquakes and ambient noise recordings j seism 9 191 210 of small magnitude earthquakes recorded at 12 sites within the city of benevento has stressed the significant role played by near surface geology in causing variability of the ground motion in this paper we extend the study of the seismic response from 12 sites to the entire urban area based on inferences from the comparison at the 12 sites between earthquake and ambient vibration results we have collected ambient noise at about 100 sites within the city intensifying measurements across the main shallow geological variations we use borehole data to interpret ambient noise h v spectral ratios in terms of near surface geology comparing h v curves to theoretical transfer functions of 1d models along five well constrained profiles on the basis of geological geotechnical and seismic data we identify three main typologies of seismic response in the city each type of response is associated to zones sharing common soil conditions and similar soil classes according to building codes for seismic design moreover we find that the spatial variation of the seismic response in the ancient town area is consistent with the damage pattern produced by a very destructive well documented historical earthquake that struck the city in 1688 causing mcs intensity of ix x in benevento finally we use ground motions recorded during the experiment by improta et al improta l g di giulio and a rovelli 2005 variations of local seismic response in benevento southern italy using earthquakes and ambient noise recordings j seism 9 191 210 to generate synthetic seismograms of moderate to strong mw 5 7 molise 2002 and ms 6 9 1980 irpinia earthquakes we calibrate the random summation technique by ordaz et al ordaz m j arboleda and s k singh 1995 a scheme of random summation of an empirical green s function to estimate ground motions for future large earthquakes bull seism soc am 85 1635 1647 using recordings of these earthquakes available in benevento after a satisfactory fit between observed and synthetic seismograms we compute response spectra at different sites and speculate on effects of the geology class at large level of shaking including soil nonlinearity we find that large discrepancies from design spectra prescribed by seismic codes can occur for a wide sector of benevento especially for periods

site effect evaluation in the basin of santiago de chile using ambient noise measurements summary we performed extensive ambient vibration measurements in the basin of santiago de chile chile and we look for testing the reliability of the horizontal to vertical amplitude spectra ratio method h v as a tool to provide qualitative and quantitative information of site effects in complex geological media the interpretation of the h v data was carried out conformably to the sesame project consensus criteria and outlines three major patterns 1 clear peaked h v curves related to sharp underground velocity contrast 2 h v peak of low amplitude and flat curve related to weak contrast and 3 broad h v peak indicating the presence of strong lateral variations of underground structure h v measurements however reveal a discrepancy between the computed soil resonance frequencies and the expected building resonance therefore not leading to a straight interpretation of the intensity distribution derived from observed damage to one storey houses in santiago after the 1985 valparaiso earthquake indeed the h v technique mostly maps the first fundamental frequency however it fails to show higher resonance modes in the case of the city of santiago this method works well for assessing the seismic hazard for high rise buildings but is questionable for smaller structures as is the case of a great percentage of constructions in the city

a new hypothesis for organic preservation of burgess shale taxa in the middle cambrian wheeler formation house range utah cambrian konservat lagerstatten are the most significant fossil deposits for our understanding of the initiation of phanerozoic life although many modes of preservation may occur these deposits most frequently contain nonmineralized fossils preserved in the form of kerogenized carbon films a rare yet important taphonomic pathway that has not previously been explained for any unit by a comprehensive model the middle cambrian wheeler formation of utah one of these lagerstatten contains abundant kerogenized preservation of nonmineralized tissues which occurs within a distinctive taphofacies that accumulated under the following conditions 1 domination of the siliciclastic fraction by clay sized particles 2 close proximity to a carbonate platform which resulted in mixed carbonate clay sediments 3 a well developed oxygen minimum precluding benthic colonization and burrowing and 4 relative proximity to oxic bottom waters facilitating transport of organisms from a habitable environment to one that favored their preservation we propose that preservation of nonmineralized tissues in the wheeler formation may have resulted from a combination of influences that reduced permeability and thus lowered oxidant flux which in turn may have restricted microbial decomposition of some nonmineralized tissues those influences include near bottom anoxia preventing sediment irrigation by restriction of bioturbation reducing conditions near the sediment water interface that may have acted to deflocculate aggregations of clay minerals resulting in low permeability face to face contacts early diagenetic pore occluding carbonate cements and an absence of coarse grains such as silt skeletonized microfossils fecal pellets or bioclasts this model may be applicable to kerogenized preservation of macrofossils in other fossil lagerstatten

seismic zonation of barcelona based on numerical simulation of site effects seismic responses of different sites of barcelona have been investigated through numerical modelling geological maps and geotechnical data available from drillings for buildings and infrastructures have been used to determine the dynamical properties of the soils through different correlations between standard geotechnical data and dynamical parameters obtained in other regions an estimation of the depth of the palaeozoic basement has been obtained through an inversion of a detailed gravity survey a 1 d equivalent linear method has been used to compute complete transfer functions and other spectral responses such as psa and psv for various damping values with the purpose of classifying zones with similar behaviour given the uncertainties associated with the input data a montecarlo s simulation process has been carried out four zones characterized by their corresponding transfer function and by pga amplifications are proposed the numerical results are compared with those previously obtained through microtremor measurements showing that predominant periods derived from nakamura s technique should be taken carefully

new burgess shale fossil sites reveal middle cambrian faunal complex soft bodied and lightly sclerotized burgess shale fossils have been found at more than a dozen new localities in an area extending for 20 kilometers along the front of the cathedral escarpment in the middle cambrian stephen formation of the canadian rockies five different fossil assemblages from four stratigraphic levels have been recognized these assemblages represent distinct penecontemporaneous marine communities that together make up a normal fore reef faunal complex

multiscale characterization of pyritized plant tissues in blueschist facies metamorphic rocks pyritized plant tissues with well preserved morphology were studied in rocks from vanoise western alps france that experienced high pressure low temperature metamorphic conditions in the blueschist facies during the alpine orogeny organic and inorganic phases composing these fossils were characterized down to the nanometer scale by raman microspectroscopy scanning transmission x ray microscopy and transmission electron microscopy the graphitic but disordered organic matter composing these fossils is chemically and structurally homogeneous and mostly contains aromatic functional groups its original chemistry remains undefined likely because it was significantly transformed by diagenetic processes and or thermal degradation during metamorphism various mineral phases are closely associated with this organic matter including sulphides such as pyrite and pyrrhotite carbonates such as ankerite and calcite and iron oxides a tentative time sequence of formation of these diverse mineral phases relative to organic matter decay is proposed the absence of traces of organic matter sulphurization the pervasive pyritization of the vascular tissues and the presence of ankerite suggest that the depositional diagenetic environment of these metasediments was likely rich in reactive iron fe sulphides and ankerite likely precipitated early and might have promoted the preservation of the fossilized biological soft tissues by providing mechanical resistance to compaction during diagenesis and subsequent metamorphism in contrast iron oxides which form rims of 100 nm in thickness at the interface between organic matter and fe sulphides may result from metamorphic processes this study illustrates that it may be possible in some instances to deconvolve metamorphic from diagenetic imprints and opens new avenues to better constrain processes that may allow the preservation of organic fossils during diagenesis and metamorphism

the initiation and growth of gullies in madagascar are humans to blame abstract lavaka madagascar s unusual gullies require thick lateritic regolith on smoothly convex hills and they are initiated locally by a variety of cultural and natural proximate causes such as paths roads defensive trenches around hillforts steep fields unchanneled to slightly concentrated storm run off springs mass movements etc growth continues by rain attack incision by run off earthfalls caused by wetting and drying cycles and especially basal sapping by diffuse groundwater flow above bedrock somewhat in that order lavaka are less directly permitted and promoted by 1 hardening of exposed laterite surfaces which creates a hard soft hard profile from bedrock to laterite which favors incision relative to lateral erosion 2 the superimposition of concave run off profiles onto convex hills and locally 3 re equilibration of watersheds after stream piracy and faulting run off and hardening are interrelated with devegetation because hardening results from exposure following devegetation because both hardening and devegetation increase run off relative to infiltration and because hardening rain attack and run off impede vegetation devegetation is certainly worsened by harmful human activities such as range burning forest cutting and or overgrazing but tectonism and natural climatic aridification are probably ultimately more important given that many lavaka are simply a natural part of the landscape s evolution and that some lavaka clearly predate primary uncut rain forest

middle cambrian carbonate platform collapse southeastern canadian rocky mountains regional erosion features termed megatruncation surfaces at the seaward margin of a middle cambrian carbonate platform in southeastern british columbia are inferred to be the proximal parts of gravity slide scars comparable in scale and morphology to modern examples in the caribbean region the surfaces truncate up to 200 m of outer platform strata and have low angle to near vertical headwalls they can be traced a minimum of 56 km along depositional strike and appear to extend at least 8 km basinward of the platform edge they therefore profoundly affect regional stratigraphy

faster better shear wave velocity to 100 meters depth from refraction microtremor arrays current techniques of estimating shallow shear velocities for assessment of earthquake site response are too costly for use at most construction sites they require large sources to be effective in noisy urban settings or specialized independent recorders laid out in an extensive array this work shows that microtremor noise recordings made on 200 m long lines of seismic refraction equipment can estimate shear velocity with 20 accuracy often to 100 m depths the combination of commonly available equipment simple recording with no source a wavefield transformation data processing technique and an interactive rayleigh wave dispersion modeling tool exploits the most effective aspects of the microtremor spectral analysis of surface wave sasw and multichannel analysis of surface wave masw techniques the slowness frequency wavefield transformation is particularly effective in allowing accurate picking of rayleigh wave phase velocity dispersion curves despite the presence of waves propagating across the linear array at high apparent velocities higher mode rayleigh waves body waves air waves and incoherent noise two locations illustrate the application of this technique in detail coincident with a large accelerometer microtremor array in reno nevada and atop a borehole logged for shear velocity in newhall california refraction equipment could duplicate microtremor results above 3 hz but could not estimate velocities deeper than 100 m refraction microtremor cannot duplicate the detail in the velocity profile yielded by a suspension logger but can match the average velocity of 10 to 20 m depth intervals and suggest structure below the 100 m logged depth of the hole eight additional examples from southern california and new zealand demonstrate that the refraction microtremor technique quickly produces good results from a wide range of hard and soft sites

evaluation of site effect within the tectonic basin in the northern side of ankara abstract this study mainly concentrates on the determination of site effects for the plio quaternary and especially alluvial soils of the cubuk district and its close vicinity in ankara turkey in the study area particularly in the vicinity of the asymmetric graben that has formed due to the tectonic activities along the ne sw trending normal faults a microtremor survey was implemented to identify the local site response under a possible seismic event the results were compared and correlated by using passive and active surface wave measurements engineering geological and geotechnical deep borehole logs along with information on local geology and geological tectonic setting regarding the microtremor results larger fundamental periods were acquired than expected over the area and the effect of the tectonic deformation on the stiffness of the soils was also observed at either the h v curves or the shear wave velocity profiles the results have demonstrated that geotechnical information down to a depth of 30 m may not be compared with the h v parameters the h v amplitudes were not always accompanied with the higher periods in the quaternary sediments this could be due to the basin and basin edge effects observed particularly at the center and boundary of the basin respectively additionally the microtremor survey showed that the spectral ratio amplitudes derived by the h v ratio are debatable and are not a direct indicator of local soil behavior under a seismic excitation

caracas venezuela site effect determination with microtremors caracas 1967 earthquake caused heavy damage to multi story buildings in 1995 184 microtremor measurement points were performed over the city the measurement grid was more or less dense and covered the main part of the alluvial basin as well as surrounding rock basement for each point the horizontal record spectrum was divided by the vertical one h v ratio subsequently the strongest value ao of this ratio in a given frequency band was kept as well as the frequency fo where it occurred spatial interpolations of ao and fo were performed among all points of palos grandes district a map was plotted representing a single surface where ao is relief and fo is represented by grey gradation an alluvion thickness h map can be compared with this result damaged buildings are located on the same map fo decreases until 0 6 hz when alluvion thickness h increases fo values fit with frequencies previously predicted from computation and with 1967 earthquake observations moreover interpolation surfaces show that amplification ao of h v on microtremor is quite low above rock but is high on the south part of the basin the maximum occurs over the non urbanized zone however the other area where ao is higher than 5 roughly corresponds to the location of the four collapsed buildings furthermore the estimated natural frequency of these buildings was around fo graphics showing h fo and ao evolution through the basin were composed links between all these values are noticeable fo is claimed to be very similar to the resonance frequency of soil as for ao it could be a fairly relevant sign of damage seriousness microtremor technique is an economic tool and it allows measurement grid as dense as desired h v ratio processing followed by interpolation of maximum values provides precise and useful information about expected site effect

cambrian burgess shale animals replicated in clay minerals although the evolutionary importance of the burgess shale is universally acknowledged there is disagreement on the mode of preservation of the fossils after burial elemental mapping demonstrates that the relative abundance of elements varies between different anatomical features of the specimens these differences reflect the compositions of the minerals that replicated the decaying organism which were controlled by contrasts in tissue chemistry delicate morphological details are replicated in the elemental maps showing that authigenic mineralization was fundamental to preserving these fossils even though some organic remains are also present

local site characterization and seismic zonation study by utilizing active and passive surface wave methods a case study for the northern side of ankara turkey abstract this study encompasses dynamic soil characterization and site classification zonation mapping of the plio quaternary and especially quaternary alluvial sediments based on the current seismic codes the study area is located in the cubuk district and its surrounding area that is situated towards the north of ankara the capital of turkey the project site is located in a region which has the potential of being seriously affected by probable seismic events occurring along the cubuk fault zone the cubuk fault zone is thought to be a continuation of the dodurga fault zone and a sub fault belt of the north anatolian fault system that is one of the most prominent fault systems in turkey with a significant earthquake potential sediment characteristics were determined and soil profiles were characterized by surface wave methods at different locations non invasive seismic methods were used to obtain a shear wave velocity profile at 41 sites and two measurements were taken at each site for passive and active surface wave methods the multichannel analysis of surface wave method masw and the microtremor array method mam which gave comparable results were used as active and passive surface wave methods respectively by combining these two techniques the shear wave velocity profile of the site was obtained additionally the mam survey alone was implemented at 10 of the sites especially to get information on the deeper parts of the soil profiles the geological characteristics of these sedimentary units were compared with the geological and geotechnical boring and seismic site characterization studies to classify the soil deposits therefore the average shear wave velocity results and the variable characteristics of the seismic data along the soil profiles were correlated with these boring studies this was performed to develop site categories which took site conditions into account according to the design codes of ibc international building code 2006 and tsc turkish seismic code 1998 consequently the regional site classification map of the north of the cubuk basin considering site classes was assessed based on the average shear wave velocity vs30 results in ibc 2006 and the shear wave velocity data and thickness of the surface layer based on the vs values in the tsc

use of microtremor in liquefaction hazard mapping this study shows how microtremor measurements can be used as an aid to liquefaction hazard mapping and zonation as demonstrated in laoag city northern philippines from microtremor measurements qualitative information on subsoil conditions was obtained and a site classification map was generated the map was combined with the geomorphology based liquefaction susceptibility map to produce an integrated liquefaction hazard zonation map this integrated map is deemed to be more accurate in depicting relative liquefaction susceptibility since it combines information on the distribution of potentially liquefiable soils in terms of geology and grain characteristics with information on the stiffness and thickness of these soils with information about the thickness of the deposits an idea of the severity of liquefaction related damage can also be gathered since thicker deposits relate to more serious damage plots of historical liquefaction cases as well as borehole data and resistivity profiles in the study area support the validity of the integrated map the use of microtremor therefore constitutes an effective and inexpensive approach to liquefaction hazard zonation and as such is very useful in less developed countries like the philippines and other areas where funds for more rigorous investigations are not always available

lateral heterogeneities and microtremors limitations of hvsr and spac based studies for site response abstract we report a site effect study carried out in a small alluvial valley nari basin in ulleung island republic of korea in that small valley a permanent broad band array of five stations records ground motion continuously in addition we performed microtremor measurements using two arrays of stations a small aperture array 60 m and a medium aperture one 500 m ambient vibration was also recorded at 38 points inside the basin the records were analyzed using horizontal to vertical spectral ratios hvsr to estimate dominant frequency and maximum amplification and the spatial autocorrelation spac method to estimate the subsoil structure via phase velocity dispersion curves nari basin is clearly a 3d structure but it was expected that a laterally irregular model might be built from the interpolation of several 1d models dominant frequency maps based on results from hvsr suggest a simple sedimentary structure with mostly smooth lateral variations in contrast maximum amplification distribution is very irregular and shows no correlation with dominant frequency in the case of nari it seems that the complexity of the basin structure cancels the usefulness of hvsr we could estimate a phase velocity dispersion curve for 81 of the station pairs recording simultaneously ambient vibration in our arrays in all the cases the resulting dispersion curve had a simple shape suggesting that the subsoil structure consists of a single layer over a half space however the dispersion curves are incompatible among them even for different station pairs covering the same path something impossible if the subsoil structure were 1d it seems that the passive methods we have used in nari basin are not adapted to its structure this makes a tomography unfeasible and we are unable to propose a subsoil structure for nari basin our results show that surface wave dispersion may be estimated using the spac method even when the medium is far from 1d we believe that this problem is enhanced by the small size of this basin which amplifies the effect of lateral heterogeneities

microtremors hvsr and its correlation with surface geology and damage observed after the 2010 maule earthquake mw 8 8 at talca and curico central chile nowadays microtremors horizontal to vertical spectral ratio hvsr has been extensively used in the estimation of the predominant vibration frequency of soils mainly for microzonation purposes in the present study we show results from extensive microtremor measurements performed at the cities of talca and curico central chile we found a strong correlation between surface geology and microtremors hvsr even in complex geological settings considering the damage produced by the 2010 maule earthquake mw 8 8 we also estimated high density macroseismic intensities at these cities with values ranging from vi up to viii on the msk64 scale we believe that the main responsible of these variations are the surface geological conditions also reflected in the variations of the resonance frequencies of the soils the evidence presented here supports the use of microtremors hvsr in combination with surface geology to improve seismic microzonation studies particularly in an andean context

in situ benthos and paleo oxygenation in the middle cambrian burgess shale british columbia canada the middle cambrian burgess shale was deposited under variable levels of oxygenation during periods of oxygenation low diversity shell beds were formed and the muds were colonized by infauna under these circumstances pyrite was restricted to anoxic microenvironments and formed small 1 mm discrete aggregated masses soft bodied organisms were preserved under low oxygen conditions typified by evenly dispersed pyrite and an absence of trace fossils and shell beds

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

organic carbon losses during burial and thermal maturation of normal marine shales the percentage of organic carbon lost during the burial diagenesis of normal marine shales those originally deposited in oxygenated bottom waters can be estimated by using the ratio of organic carbon c to pyrite sulfur s and assuming that the mean initial burial value of c s for such sediments has been approximately constant since the devonian plots of mean c s vs vitrinite reflectance r sub 0 for some sedimentary basins of jurassic and carboniferous age show a monotonic decrease of c s with increasing r sub 0 macrofossils

geochemical evidence for oxygenated bottom waters during deposition of fossiliferous strata of the burgess shale formation abstract deciphering the oxygenation potential of bottom waters during deposition of the fossiliferous strata of the burgess shale is key to understanding the paleoecology of the organisms preserved as fossils and the processes involved in their preservation methods of paleo redox determination that are based upon trace fossils organic carbon content or size analysis of pyrite framboids are problematic when applied to the burgess shale fortunately patterns in redox sensitive trace elements hold great potential for determining paleo redox conditions for these greenschist facies rocks because they are independent of both age and metamorphic grade four burgess shale type bst fossil bearing sections were studied three lie within the burgess shale formation whereas one lies within the slightly younger duchesnay unit of the middle chancellor formation the geochemical proxies of seawater redox conditions that were used are mo u th v cr v v ni ni co and v sc each of these redox sensitive indices suggests that oxygenated conditions prevailed in the overlying seawater during deposition of beds within which bst preservation developed non fossiliferous beds at the base of the mt stephen trilobite beds yield three geochemical indices v v ni v sc ni co that indicate deposition under dysoxic to anoxic conditions thus the only beds to have been deposited under anoxic conditions are barren of fossils of soft bodied taxa further contradicting the notion that bottom water anoxia is a factor in bst preservation the laminated nature of the burgess shale and evidence for subsurface anoxia coupled with evidence for oxygenated bottom waters presence of bacterial mats and surficial trace fossils suggest that the burgess shale was deposited in the exaerobic zone oxic anoxic boundary at the water sediment interface implications of this reinterpretation of the depositional environment of the burgess shale include 1 taphonomic models for bst preservation must account for the presence of oxygen in bottom waters 2 paleoecological interpretations of the burgess shale need to account for a probable autochthonous benthic component in what is a complex assemblage of fossils that includes elements derived from the platform and 3 the possibility of burgess shale communities based upon chemosynthesis and or bacteria grazing must be considered

the paleoredox setting of burgess shale type deposits abstract burgess shale type bst biotas occur globally in lower and middle cambrian shales and were preserved under specific and exceptional circumstances among the circumstances surrounding fossilization benthic redox conditions have been the subject of particular disagreement while most authors have assumed that the sites of preservation were anoxic and therefore inhospitable to metazoans several have recently argued that bst assemblages were preserved in situ under habitable benthic conditions here we use field and laboratory intensive fine scale methods to investigate the paleoredox settings of fossil assemblages in two burgess shale type deposits the wheeler and marjum formations of western utah cambrian series 3 and review recently published data for other principal burgess shale type deposits in the wheeler and marjum formations fossil assemblages and ichnofabrics were evaluated at the millimeter scale an ichnological model was then applied to reconstruct relative paleo oxygen content of bottom waters at a bed to bed scale through multiple intervals sampled continuously this approach permits fine scale evaluation of the relationships of discrete fossil assemblages to paleoredox conditions over 7800 individual beds were logged in this study these data demonstrate that the wheeler and marjum formations were deposited under dynamic benthic redox conditions in both deposits beds representing deposition under dysoxic conditions may be interbedded at the millimeter centimeter scale with those representing deposition under anoxic conditions although the beds deposited under both types of redox conditions may be richly fossiliferous the distribution of fossil assemblages within the wheeler and marjum formations was regulated by dissolved oxygen content of bottom waters as a first order control bst preservation occurs within a microfacies inferred to represent deposition under anoxic conditions and contains transported fossils along a recognizable proximal distal gradient under dysoxic benthic conditions assemblages of skeletonized body fossils dominated by trilobites occur in both formations in the wheeler formation the junction of these two benthic redox environments is characterized by dense monospecific associations of the opportunistic trilobite elrathia kingii but a comparable exaerobic taxon does not appear to be present in the marjum formation these results demonstrate the control of near bottom anoxia over preservation of bst assemblages in both formations and are consistent with the findings from the burgess shale and the chengjiang

magnetic properties of synthetic analogues of pyrrhotite ore in the grain size range 1 24 µm summary iron and sulphur in proportions appropriate to fe 7 s 8 were reacted in evacuated quartz tubes for 24 hr at 500 c quenching produces predominantly hexagonal pyrrhotite whereas further prolonged annealing at 250 c produces monoclinic pyrrhotite we mainly report the properties of material cooled from 500 ca t 10 c min 1 which is predominantly monoclinic but probably contains hexagonal pyrrhotite together with pyrite fes 2 this material which we refer to as non ideal pyrrhotite may be a better analogue of pyrrhotite ore than ideal synthetic monoclinic pyrrhotite the samples were characterized by x ray mossbauer evect and thermomagnetic analyses the slow cooled non ideal monoclinic pyrrhotite exhibits thermal stability intermediate between monoclinic and hexagonal pyrrhotites one striking observation is that the deviation from ideal monoclinic pyrrhotite increases with decreasing particle size particles about 1 mm in size have a low saturation magnetization value of about 6 am2 kg 1 indicating a lower concentration of ferrimagnetic monoclinic pyrrhotite saturation magnetization 18 am2 kg 1 than particles of about 6 mm and above saturation magnetization 12 am2 kg 1 on the other hand magnetization process parameters coercive force ratio of saturation remanence to saturation magnetization coercive force of remanence median destructive and inductive fields the magnetic susceptibility follow well behaved power law dependences on particle size similar to monoclinic pyrrhotite magnetic domain patterns in the slow cooled non ideal pyrrhotite are similar in type and style to those observed in synthetic monoclinic pyrrhotite and in natural pyrrhotite particles in rocks dynamic observations of domain walls in changing external alternating and direct magnetic fields are consistent with macroscopic obser vations of magnetization change with field the critical size for the monodomain multidomain transition in synthetic monoclinic pyrrhotite at about 1 mm is essentially the same as that previously determined for natural pyrrhotite grains in rocks the observations suggest that the domain walls lie normal to the c axis of the structure consistent with the known magnetocrystalline anisotropy symmetry of monoclinic pyrrhotite the type and style of the magnetic microstructures of hexagonal pyrrhotite are quite diverent from those of monoclinic pyrrhotite the domain patterns are on a much smaller scale wavy and sometimes resemble those of a hexagonal material such as magnetoplumbite or cobalt

microtremor survey in talchir india to ascertain its basin characteristics in terms of predominant frequency by nakamura s ratio technique abstract the talchir basin one of india s oldest basins has been a subject of interest because of its rich coal deposits the maximum thickness of the basin is about 1500 m beyond the basin is the hard metamorphic rocks of precambrian age the ambient noise survey data have been analyzed for the talchir basin using nakamura s technique of horizontal vertical spectral ratio hvsr to ascertain the basin structure in terms of the predominant frequency the predominant frequency varies from 0 25 hz to 7 8 hz but a major portion of the basin comes under the range of 0 3 hz 2 4 hz while on the metamorphic rocks it is as high as 7 8 hz the variation in predominant frequency shows a good correlation with the sediment thickness of the basin the results have been compared with the previous studies by other researchers and it shows consistency with the northerly dip of the basin the present study has also been compared with the results of the synthetic seismogram that was performed for the talchir basin the predominant frequency obtained from hvsr technique complements well with the frequency at which the peak response spectra ratio is observed the present study of the predominant frequency identifies quite well the characteristics of talchir basin and is in good agreement with the synthetic ground motion modeling of the region

sequence stratigraphy cyclic facies and lagerstatten in the middle cambrian wheeler and marjum formations great basin utah abstract recurrent taphofacies including conservation lagerstatten are identified within a spectrum of facies in fourth order sequences in the middle cambrian wheeler and marjum formations of the drum mountains and house range west central utah these sequences are 3 20 m thick and commence with sharply based compact oncolitic oolitic or pelletal pack and grainstones with sharply defined corroded and mineralized upper contacts that record drowning discontinuities and early transgressive systems tracts tsts overlying intervals of calcareous shale and thin bedded wacke to packstones with abundant disarticulated polymerid and agnostoid trilobites represent late tsts these are commonly followed by lavender gray mudstones rich in sponge spicules and comminuted fossil debris that reflect condensed maximum flooding zones the overlying early highstand hst intervals of black fissile shales are typically barren except for indistinct circular carbonized algae but in rare instances include soft bodied animal remains a combination of lower dysoxic anoxic conditions with a fluctuating oxycline and relatively rapid episodic influx of fine grained detrital sediment favored repeated burial and preservation of abundant organic detritus and rarely soft bodied animals interbedded dark gray shales include abundant articulated agnostoid trilobites and diminutive polymerids e g jenkinsonia overlying platy calcareous bedding planes covered with articulated bodies and molts of the polymerid elrathia indicate rapid blanketing of undisturbed seafloors by calcareous mud layers these beds grade upward successively into interbedded sparsely fossiliferous platy to flaggy shale and thin pale gray weathering calcisiltites and burrow mottled to nodular limestones recording late hst to falling stage fsst carbonate shedding thin calcisiltites include fossil debris and articulated larger polymerid trilobites and the eocrinoid gogia preserved by obrutionary deposits the repeated recurrence of these patterns provides the rudiments of a predictive model that not only explains the differing modes of preservation but may also aid in prospecting for new lagerstatten

a new burgess shale type assemblage from the thin stephen formation of the southern canadian rockies a new burgess shale type assemblage from the stephen formation of the southern canadian rocky mountains is described herein it occurs near stanley glacier in kootenay national park 40 km southeast of the type area near field british columbia while at least a dozen burgess shale localities are known from the thick stephen formation the stanley glacier locality represents the first discovery of burgess shale type fossils from the thin stephen formation the cathedral escarpment an important regional paleotopographic feature has been considered important to the paleoecologic set ting and the preservation of the burgess shale biota however the stanley glacier assemblage was preserved in a distal ramp setting in a region where no evidence of an escarpment is present the low diversity assemblage contains eight new soft bodied taxa including the anomalocaridid stanleycaris hirpex n gen n sp new genus new species pelagic or nektobenthic predators represent the most diverse group whereas in relative abundance the assemblage is dominated by typical cambrian shelly benthic taxa the low diversity of both the benthic taxa and the ichnofauna which includes diminutive trace fossils associated with carapaces of soft bodied arthropods suggests a paleoenvironment with restrictive conditions the stanley glacier assemblage expands the temporal and geographic range of the burgess shale biota in the southern canadian rockies and suggests that burgess shale type assemblages may be common in the thin ste phen formation which is regionally widespread

microtremor measurements in the city of palermo italy analysis of the correlation between local geology and damage abstract this study presents the results of 90 seismic ambient noise measurements in palermo the main city of sicily italy the dataset has been processed using the horizontal to vertical spectral ratio hvnsr technique and interpreted in terms of local geology which is characterized by the presence of alluvial sediments of two riverbeds masked by urbanization since the seventeenth century hvnsrs show significant variations in the study area when the transition stiff to soft is crossed a typical spectral peak appears in the hvnsrs mostly in the frequency band 1 2 hz and exceeding a factor of 3 in amplitude using available information on subsurface geological structure we compute theoretical 1d and 2d transfer functions the resonance frequencies of soft soils obtained by hvnsr are well reproduced by the fundamental frequencies from numerical modeling the distribution of frequency peaks of hvnsr and their amplitudes are also compared with the local damage caused by historical earthquakes previous studies demonstrated that damage variations in palermo were controlled more by near surface geology than building vulnerability a uniform vulnerability is an ideal condition to test statistical methods and their capability in seeking correlation between hvnsr and potential damage due to local geological conditions we apply two well established multivariate statistical methodologies factor analysis and canonical correlation to the hvnsr dataset and macroseismic data damage grades of the european macroseismic scale through these analyses we quantify the significance of the correlation between the hvnsr peak in the low medium frequency range 0 5 3 hz and the occurrence of the highest damage grades this approach allows us 1 to estimate the threshold value in the resulting linear combination of the hvnsr amplitudes which separates zones of light damage from zones of significant damage and therefore 2 to improve the spatial definition of potentially high hazard zones through a denser grid of microtremor measurements

the distinction between caledonian burial and regional metamorphism in metapelites from north wales an analysis of isocryst patterns in snowdonia and ll n three prograde stages in metapelites gwna group to wenlock are recognized stage i with white mica crystallinity values 0 43 2 stage ii 0 43 0 26 2 stage iii isocrysts at 0 03 2 intervals are drawn separately for pelites above and below the sub arenig unconformity approximately concordant isocryst patterns characterize the unconformity in the northwestern and southeastern limbs of the snowdonia syncline whereas discordant patterns are developed northwest of the aber dinlle fault and at the closure of the ynyscynhaiarn anticline the contrasting patterns are the result of a pre arenig burial metamorphism in post tremadoc pelites belts of steep metamorphic gradient coincide with belts of high strain and a broad area of higher grade caradoc pelites coincides with the core of the snowdonia syncline the later metamorphism is related to caledonian deformation rather than to burial pelite alteration adjacent to small intermediate to acid plutons suggests emplacement before the caledonian regional metamorphism a close correlation exists between metabasite zones and metapelite stages

taphonomic traits of clay hosted early cambrian burgess shale type fossil lagerstatten in south china abstract the chengjiang and guanshan fossil lagerstatten of yunnan represent key fossil deposits to understand and reconstruct early metazoan evolution despite extensive studies on the systematics of taxa from these lagerstatten the major mechanisms of exceptional soft tissue preservation at these fossil lagerstatten have remained controversial the chengjiang and guanshan fossil lagerstatten represent typical burgess shale type deposits influenced by late alteration and weathering that led to some major transformations in clay and iron minerals as well as dissolution of dolomite and skeletal biominerals the detailed geochemical screening of various fossil groups such as brachiopods priapulids arthropods and sponges indicates a more complex preservational history than hitherto supposed besides oxidation processes during sub recent recent weathering clay mineral formation and or alteration carbonization phosphatization and pyritization played key roles in the preservation of various metazoans the chengjiang fossil lagerstatte is characterized by the existence of clay dominated background beds bgbs and event beds ebs fossil preservation varies considerably in the two different depositional settings with soft tissue preservation occurring preferentially in ebs whereas skeletal accumulations are typical of bgbs the samples were analyzed and classified into three groups with different degrees of alteration and fundamentally different chemistries the specific clay mineral composition shows increasing chlorite and goethite decreasing kaolinite 2m1 mica and dolomite and a rise in the chemical alteration of mudstones it also indicates slight variations between the primary types of beds eb bgb hinting at variations in the source of clastics or the hydrochemical environment during the deposition of strata furthermore the geochemical paleoredox proxy data indicate that dysoxic or anoxic conditions were not permanently present during the deposition of ebs and bgbs in the chengjiang and guanshan fossil lagerstatten we consider that rapid deposition in finest claystones had a greater influence on the preservation of highly volatile tissues than the presence of bottom water anoxia even though bottom water anoxia and microbial sealing may further increase the probability of soft tissue preservation using different geochemical proxies such as various redox indicators and iron speciation statistics on framboid sizes classical geological observation and clay mineralogy we show that iron mineral precipitation onto organic carcasses of the chengjiang type fossils is mostly confined to later diagenetic processes and thus is not crucial for the early fixation of easily decayable tissues in burgess shale type faunas

investigation of 3 d basin structures in the izmit bay area turkey by single station microtremor and gravimetric methods summary we investigate 3 d basin structures and site resonance frequencies in the izmit bay area of turkey by new geophysical surveys based on 239 single station microtremor and 405 point gravity measurements a fundamental resonance frequency map of the izmit bay was produced from the main peak in the horizontal to vertical component spectral ratio hvsr of microtremors the hvsr analysis of the microtremor data reveals single double broad peaked or no peak type hvsr curves varying in accordance with the surface geology and spatial extent of the three basins present in the izmit bay area in the deepest sections of the izmit golcuk and derince basins of the izmit bay the fundamental resonance frequencies are dominantly 0 24 0 30 hz these resonance frequencies should be taken into consideration along with higher mode frequencies to construct earthquake resistant structures in the izmit bay area the 3 d gravimetric bedrock depth map of the izmit basin shows that the basin has an asymmetric shape with its deepest section coinciding with the surface trace of the north anatolian fault the northern shoulder of the basin has a gentle dip on the kocaeli peneplain side and the southern shoulder is much steeper and it is bounded by the samanli mountains we derive a power law relationship that correlates the fundamental site resonance frequencies with the sedimentary cover thickness obtained from the gravity and shear wave velocity data in the izmit bay we use this relationship to estimate bedrock depths beneath golcuk and derince basins our estimation of maximum basin depths is 1400 m for the izmit and is 800 m for the golcuk and derince basins finally we have analysed a converted sp phase from a local earthquake recording made at site cmp to calculate and verify the sediment thickness estimations obtained from our gravimetric and microtremor analyses this calculation shows close agreement with that of the gravimetric and microtremor results our results show that the basins in the izmit bay area have a very thick sedimentary cover with very low shear velocities underlined by hard bedrock forming a sharp impedance contrast we anticipate that these results will be a key contribution to the quantitative assessment of seismic hazard for the izmit bay area before the occurrence of strong earthquakes in the marmara region

exceptional preservation of fossil plant spores in high pressure metamorphic rocks it is commonly believed that high grade metamorphism erases all traces of fossils and more generally of biogenicity in rocks to address this issue we report in this study x ray spectromicroscopy raman microspectroscopy and electron microscopy observations at the nm scale of fossil lycophytes megaspores found in triassic metasedimentary rocks from the french alps these rocks have undergone high pressure metamorphic conditions not vert similar 14 kbar not vert similar 360 c during the alpine orogeny corresponding to a burial of not vert similar 35 km during subduction despite such metamorphism the fossil megaspores are remarkably well preserved texturally an unusual mineralogical zonation consisting of magnetite ankerite and calcite is superposed on the structures of the spore walls in parallel chemical heterogeneities of the organic matter om composing the spore walls were detected we discuss different interpretations for our observations in particular a scenario in which these features are remnants of the original structural heterogeneities in the spores and provide insights on the fossilization processes under high grade metamorphic conditions whatever the processes leading to such heterogeneities our observations oppose the usual assumption that high grade metamorphism erases all indications of biogenicity in rocks and open new avenues for investigation at the nm scale of the evolution of organic matter during diagenesis and metamorphism

microtremor hvsr study for assessing site effects in the bovec basin nw slovenia related to 1998 mw5 6 and 2004 mw5 2 earthquakes abstract the bovec basin which is filled with glacial and fluvial sediments has recently been struck by two strong earthquakes 1998 and 2004 which caused extensive damage vii viii ems 98 strong site effects resulted in large variations in damage to buildings in the area which could not be explained by the surface variations in quaternary sediments the microtremor horizontal to vertical spectral ratio hvrs method was therefore applied to a 200 m dense grid of free field measurements to assess the fundamental frequency of the sediments large variations in the sediment frequency 3 22 hz were obtained with most of the observed values in the range 6 12 hz the observed frequencies cannot be related to the total thickness of quaternary sediments sand gravel but can be explained by the presence of conglomerate or lithified moraine at shallow depths the results were compared also with the velocity structure derived from seismic refraction data microtremor measurements performed in several two and some three and four storey houses masonry with rc floors which prevail in the bovec basin have shown that the main building frequencies in the area are in the range 7 11 hz this indicates that damage to houses in both earthquakes in some parts of the basin was enhanced by site amplification and soil structure resonance areas of possible soil structure resonance were identified in the settlements bovec brdo bovec mala vas cezsoca and kal koritnica considerable changes in fundamental frequencies within short distances were established in the town of bovec their values are as high as 22 hz in the central part of the town but diminish to 6 11 hz in the adjacent brdo and mala vas districts this is in agreement with the distribution of damage in both earthquakes which was considerably higher in brdo and mala vas although the houses in the central part of the town are older microtremor investigations have proved an effective tool for assessment of site effects in cases of complex geological structure commonly encountered in young alpine basins filled with glaciofluvial sediments which are partly cemented lithified layers can considerably change the fundamental frequency and consequently the site effects by taking additional measurements in buildings possible soil structure resonance can be identified

high resolution geochemical evidence for oxic bottom waters in three cambrian burgess shale type deposits abstract the cambrian radiation of complex animals is a fundamental event in the history of life on earth much of our understanding of this event is made possible through the study of exceptionally preserved fossils in burgess shale type bst deposits based on bioturbation levels in bst deposits they are often interpreted as representing restricted oxygen settings this study tests the low oxygen interpretation through analysis of geochemical paleoredox proxies and bioturbation levels in three bst deposits the early cambrian maotianshan shale china the middle cambrian wheeler shale usa and the middle cambrian spence shale usa results from 96 samples show fine scale geochemical evidence for oxic bottom water conditions during the deposition of these three bst deposits trace element paleoredox indices pi give consistent oxic signals in all three shales in addition total organic carbon toc and total sulfur ts levels in the spence shale are extremely low the average c s ratio is 3 1 comparable to values for modern oxic marine water bioturbation levels in all three shales are low with rare development of minimal to moderate horizontal bioturbation while short term oxygen fluctuations or poikiloaerobic conditions could still have sporadically existed in these settings this study shows that these bst deposits were deposited in a dominantly oxic paleoredox setting evidence for low bioturbation levels coupled with paleoredox geochemistry indicative of oxic bottom waters suggests that pervasive exaerobic conditions with an oxic water column positioned above oxygen depleted sediment pore waters may have existed in many cambrian bst deposit paleoenvironments