syn and postkinematic cement textures in fractured carbonate rocks insights from advanced cathodoluminescence imaging abstract in calcite and dolomite deposits in fractures transmitted light and optical cathodoluminescence methods detect crack seal texture in some fractures but scanning electron microscope based cathodoluminescence sem cl combined with secondary electron images and element maps reveals crack seal and cement growth textures where previous sem cl imaging methods found massive or featureless deposits in a range of fractured carbonate rocks patterns and textures of calcite and dolomite cements precipitated during and after fracture growth resemble complex accumulation patterns found in quartz in sandstone fractures suggesting that some apparent differences between carbonate mineral and quartz deposits in fractures reflect the limits of previous imaging methods advances in delineating textures in widespread carbonate mineral deposits in fractures provide evidence for growth and occlusion of fracture porosity

cathodoluminescene at low fe and mn concentrations a sims study of zones in natural calcites abstract point analyses of natural calcite cements by sims confirm the earlier suggestions that 20 ppm mn is required to activate luminescence whereas fe concentrations in excess of 1400 ppm quench it partly independently of the mn content below this fe threshold luminescence is bright at mn concentrations in excess of 225 ppm in the range 20 225 mn all types of luminescence dull luminescent and nonluminescent can occur this undifferentiated domain is evident also from a compilation of literature data the type of luminescence is not a simple function of fe and mn concentrations other parameters influence cl sinc most diagenetic calcite cements have fe and mn concentrations that place them within the field of mixed cathodoluminescence these results force reassessment of models that equate the type of luminescence with the redox state of the diagenetic environment

burrow mediated carbonate dissolution in rudist biostromes aurisina italy implications for taphonomy in tropical shallow subtidal carbonate environments abstract in upper cretaceous rudist biostromes at aurisina italy marked taphonomic loss of radiolitids by burrow mediated dissolution and mechanical disintegration illustrates the relation between synecology and early diagenesis in the fossilization of tropical shallow water bioconstructions the studied platform succession accumulated in a prevalently open lagoon with bioturbated carbonate sand rudist thickets bioclastic dunes and areas with shelly lime ooze rudist biostromes consist of radiolitids and hippuritids or of radiolitids only and have an open parautochthonous rudist fabric with a matrix of bioclastic bioturbated wackestone swirly disorientation of bioclasts records early softground bioturbation later firmground burrows comprise an irregular network of tunnels and chambers filled with bioclastic packstone to grainstone the size geometry and sediment fill of the firmground burrows suggest that they were produced by crustaceans radiolitid preservation ranges from complete to relictic radiolitid relicts formed by a spalling and or dissolution of the cellular boxwork ostracum of the attached valve leaving calcite tubes built by a distinct thin ostracal shell layer or b dissolution of the entire shell leaving the sedimentary fills of the intertabular spaces of the attached valve as a diagnostic vestige or c shell dissolution within the firm sediment with subsequent filling of the biomould by bioclastic wackestone to packstone to grainstone loss of radiolitids produced a taphonomic bias towards rudists with non cellular ostracum locally taphonomic loss produced ghost biostromes composed nearly entirely of faint radiolitid relicts shell dissolution resulted from chemical gradients in the sediment within and near the burrows and from enhanced microboring and microbial infestation dissolution of radiolitids was favoured by the combined effects of chemical instability of hypostracal aragonite and by the structure of the calcitic boxwork ostracum of thin walled cells some biostromes are intercalated with or are capped or overlain within a short vertical distance by a hardly recognizable emersion surface as a consequence of the shallow depth of biostrome accumulation taphonomic loss by dissolution is widespread in open parautochthonous rudist fabrics and confirms actuogeological results of other authors that bioturbation mediates carbonate dissolution also under shallow tropical waters supersaturated for calcium carbonate the amount of carbonate dissolved upon burrowing of the biostrome matrix is hardly quantifiable but by analogy to recent carbonate environments may have been large within bioconstructions deep tiered burrowing occurred at least since the carboniferous taphonomic loss by dissolution thus may have been active in the fossilization of tropical shallow water mounds and biostromes over much of phanerozoic times

exploring the impact of diagenesis on isotope geochemical and microstructural alteration features in biogenic aragonite for the quaternary and neogene aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment conversely pre neogene aragonite is often diagenetically altered and calcite archives are studied instead nevertheless the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material here experiments were performed to understand biogenic aragonite alteration processes and products shell subsamples of the bivalve arctica islandica were exposed to hydrothermal alteration thermal boundary conditions were set at 100 degrees c 175 degrees c and 200 degrees c these comparably high temperatures were chosen to shorten experimental durations subsamples were exposed to different o 18 depleted fluids for durations between two and twenty weeks alteration was documented using x ray diffraction cathodoluminescence fluorescence and scanning electron microscopy as well as conventional and clumped isotope analyses experiments performed at 100 degrees c show redistribution and darkening of organic matter but lack evidence for diagenetic alteration except in delta 47 which show the effects of annealing processes at 175 degrees c valves undergo significant aragonite to calcite transformation and neomorphism the delta o 18 signature supports transformation via dissolution and reprecipitation but isotopic exchange is limited by fluid migration through the subsamples individual growth increments in these subsamples exhibit bright orange luminescence at 200 degrees c valves are fully transformed to calcite and exhibit purple blue luminescence with orange bands the delta o 18 and delta 47 signatures reveal exchange with the aqueous fluid whereas delta c 13 remains unaltered in all experiments indicating a carbonate buffered system clumped isotope temperatures in high temperature experiments show compositions in broad agreement with the measured temperature experimentally induced alteration patterns are comparable with individual features present in pleistocene shells this study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits the limitations of a study restricted to a single test organism are acknowledged and call for refined follow up experiments

ree activated cathodoluminescence of calcite and dolomite high resolution spectrometric analysis of cl emission hrs cl abstract cathodoluminescence cl investigations of phanerozoic marine limestones sinter calcites and saddle dolomites of hydrothermal veins indicate that in contrast to previous knowledge rare earth element ree activated cl in sediments is common the methods of high resolution spectrometric analysis of cl emission hrs cl combined with hot cathode cl microscopy are able to prove qualitatively some ree below the detection limits of electron microprobe and proton induced x ray emission analysis pixe our investigations document sm3 dy3 tb3 and probably ho3 activated cl in calcite and eu3 activated cl in a saddle dolomite of hydrothermal veins sometimes the ree activated cl is hidden by dominant mn 2 emission in such cases the ree emission spectrum may be obtained by subtracting a spectrum of luminescence produced only by mn2 the occurrence of only one ree in natural samples is uncommon in all observed samples ree are present in groups

a two stage rifting in the basins of the corsica sardinian straits abstract a set of seismic and field data from the corsica sardinian straits allowed us to define three well separated oligocene deep basins the castelsardo and porto torres basins forming the northern end of the sardinian graben and the bonifacio basin on the continental shelf of the bonifacio straits a seismostratigraphic investigation of these three basins revealed two major tectonic events a first oligocene to middle aquitanian rifting phase followed by oceanic spreading in the western mediterranean and then a second rifting event between corsica and sardinia in lower burdigalian time the first rifting is noticed in the three basins but the second one only in the porto torres and castelsardo basins

oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater one hundred and two articulate brachiopods and twenty one marine cements from ordovician strata were analyzed for oxygen and carbon isotopes these together with 200 previously published analyses of ordovician brachiopods mostly of upper ordovician age define a general trend of increasing 18o values with decreasing age from a minimum of 10 5 in the earliest ordovician to a maximum of 1 5 at the ordovician silurian boundary the 13c values show a general positive correlation with 18o and increase from 2 5 in the earliest ordovician to as high as 7 at the ordovician silurian boundary the magnitudes of ordovician excursions for both 18o and 13c are similar to those reported previously for the entire phanerozoic different genera of brachiopods from the same stratigraphie level did not yield any large differences in their isotopic compositions suggesting that vital effects did not influence decisively the isotope values of the studied skeletal parts petrographic examination and trace element analyses indicate that brachiopod shells from llandeilo to ashgill strata are well preserved and thus may have retained their primary isotopic signatures the same criteria for the tremadoc arenig and some llanvirn brachiopods suggest partial diagenetic alteration of 18o values in these samples but this does not preclude their utility as a recorder of a primary 13c signal the observed 18o trend for the well preserved portion of the record may reflect progressive cooling during ordovician perhaps complemented by a changing 18o values of seawater the latter could have been a consequence of a net increase in the rate of high temperature water rock interaction relative to its low temperature counterpart as indicated also by the large coeval decrease of marine 87sr86sr superimposed on the above long term 18o trend is a positive excursion of about 2 at the end of the ordovician probably reflecting a large expansion of polar ice caps the magnitude of this excursion indicates a degree of glaciation comparable to that at the height of the quaternary glacial episodes the secular 13c trend may reflect a progressive increase in marine organic productivity and or enhanced organic deposition in the ordovician oceans particularly noticeable at the time of the terminal ordovician glaciation

belemnite biomineralization development and geochemistry the complex rostrum of neohibolites minimus abstract belemnites a group of extinct coleoid cephalopods were important components of mesozoic marine ecosystems their calcitic rostra are extensively used in biostratigraphy and geochemistry the preservation state of the rostra is a crucial factor for the interpretation of their geochemical data however their preservation is difficult to assess since no modern cephalopod forms calcitic rostra the biomineralization process of the rostrum which functioned as an internal skeleton is poorly understood for most species this also applies for the epirostrum a late ontogenetic extension of the rostrum which is only present in some belemnite species the primary structure and function of this character are still being debated controversially we have investigated the microstructure stable isotope 13 c 18 o and elemental composition mg ca sr ca fe ca mn ca of both ortho and epirostra of the belemnite species neohibolites minimus early cretaceous albian for comparison we studied argonauts argonauta argo these recent octopuses build a calcitic shell ortho and epirostra of n minimus show microstructural and geochemical differences cathodoluminescence microscopy and the microstructures of belemnites and argonauts indicate that blue orange luminescent growth lines in the studied belemnites are largely a primary biomineralization phenomenon and not solely due to diagenesis based in part on analogy to argonaut shell we suggest that the inner part of the belemnite epirostrum is a continuation of an originally organic apical line the development and evolution of the epirostrum as a potential sexually selected character is discussed well preserved epirostrum calcite has higher element ca ratios than the calcite of the orthorostrum suggesting a vital effect affecting these values we further found evidence for vital effects on the stable isotope signatures due to metabolic and kinetic fractionation our findings suggest a complex mineralization process of the studied rostra different microstructures with distinctive geochemical signatures occur in a single belemnite species vital effects played an important role in the rostrum geochemistry complicating the application of the rostra as paleoclimatic archives

video cathodoluminescence microscopy of diagenetic cements and its applications abstract diagenetic studies of sedimentary rocks using cold cathodoluminescence cl microscopy have been severely limited because of the very low intensity of visible luminescent emissions which required long photographic exposure times and because of the difficulty in obtaining quantitative data from cl observations the solution to this problem is to fit the microscope with a high sensitivity digital colour video camera linked to a computer with image enhancement and image analysis software the new technique described in this paper produces digital cl images of consistent high quality both quickly and cheaply controls the capture and editing of cl images to reveal detailed textural information even from minerals exhibiting low level luminescence such as quartz acquires quantitative information on pore systems and the abundance of cement zones from cl images examples are presented to demonstrate the high quality of images produced in this way and the range of uses to which the new technique can be applied the ability to image exactly the same field of view in both plane polarised light and cl is a particular advantage image analysis techniques have been developed to give a statistical characterisation of both pore systems and cement phases that infill them the abundance of contrasting cement zones seen in cl can be measured and the abundance of cement phases can be mapped across a reservoir the history of porosity occlusion can be reconstructed quantitatively and integrated with burial history and hydrocarbon migration porosity can be measured accurately and since the technique obtains data on pore geometry as well as abundance the pore system can be characterised by pore size distributions and pseudo capillary pressure curves this also opens the possibility of estimating permeability from thin sections

application of redox sensitive proxies and carbonate clumped isotopes to mesozoic and palaeozoic radiaxial fibrous calcite cements abstract ancient marine radiaxial calcite cements are commonly exploited as archives of marine porewater properties based on the argument that they lack metabolic effects often assigned to biogenic carbonates here we critically test the significance of conventional versus with respect to these fabrics less conventional proxy data from pennsylvanian triassic and cretaceous case examples conventional proxies include cathodoluminescence carbon and oxygen isotope ratios main and trace elemental concentrations less conventionally applied proxies are clumped isotope 47 redox sensitive and rare earth elements sampled across a succession of triassic radiaxial fibrous calcites radiaxial calcites are subdivided in three groups based on their luminescence characteristics non luminescent patchy luminescent and bright luminescent luminescence patterns are in fair agreement with isotope ratios in particular with those of oxygen the data fall into or are close to the range of reconstructed marine seawater values and often plot to the positive end member of the isotopic range these results disagree with the commonly held view that isotope data from luminescent cements reflect a priori non marine values further evidence for this comes from ree concentration patterns and cerium anomalies suggesting normal marine porewater values for all except the very last generation of radiaxial calcites this implies that luminescent radiaxial calcites must not necessarily represent significant diagenetic resetting kinetic effects during precipitation and different activator elements must be considered marine and earliest burial porewater temperatures of 12 26 c are suggested by conventional calcite 18 o thermometry conversely the application of the clumped isotope thermometer to the same radiaxial calcites suggests temperatures of 180 200 c reflecting solid state resetting of fully cemented limestones under a low water rock ratio redox sensitive elements particularly zn cd u and cu are affected by kinetic processes overriding fluid eh manganese concentrations and ce anomaly data point to gradually decreasing marine porewater oxygen levels from outer to inner cement fringes judging from ree patterns and ce anomalies the cement layers in the central portions of the pore filling cement succession witnessed the end of marine precipitation and the onset of shallow marine diagenesis consequently radiaxial calcite precipitation is suggested to continue in the early shallow marine burial domain this study underscores the potential of radiaxial calcite successions as archives of marine porewater to shallow burial diagenetic pathways the combination of conventional and less conventional proxies is a clear strength of this study and documents that abiogenic carbonate archives are often underexplored

ion microprobe analysis of trace elements in calcite with an application to the cathodoluminescence zonation of limestone cements from the lower carboniferous of south wales u k ion microprobe analysis offers high spatial resolution 10 m and low detection limits for many elements in calcite detection limits are likely to be instrument dependent the values given here are specific to the instrument used a modified aei im 20 and more recent instrument designs should give lower detection limits li na and k signals have been observed and detection limits are estimated to be 10 ppm the detection limit for pb is in the range 10 50 ppm zn and ba suffer from significant molecular interferences which impose higher detection limits mg fe mn and sr were standardised against three chemically analysed calcites detection limits in the range 1 5 ppm were obtained for mg mn and sr but fe is subject to interference by a hydride species so that the detection limit is determined by vacuum conditions calcite cements in sections cut from a lower carboniferous limestone from south wales can be divided texturally into four zones analyses were made for mg fe mn and sr only sr differs among the zones mn is the main activator of cathodoluminescence cl in these cements when the fe content is up to 1600 ppm there is a positive relationship between cl intensity and mn content fe acts as a suppressor of cl intensity for a given mn concentration the cl intensity decreases as the fe content increases for fe contents 1600 ppm the cl intensity may be negatively related to the mn concentration when the mn content is below 125 150 ppm the fe content has little discernible effect on the cl intensity in these cements non luminescence can only be predicted with confidence if the mn concentration is below 25 ppm there is no critical concentration of fe up to 7000 ppm or critical fe mn ratio in the range 0 26 which always causes mn bearing locations to become extinct with respect to cl the present data are compared with those from the literature and a diagram is constructed which represents the region of fe mn composition space where luminescence can occur conflicting evidence regarding the relative importance of fe mn ratio and absolute fe and mn concentrations can be reconciled both concentrations and fe mn ratio are involved in controlling luminescence

the control of cathodoluminescence in dolomite by iron and manganese variations in the cathodoluminescent properties of carbonates are usually attributed to differing proportions of manganese mn2 as the most important activator and iron fe2 as the main inhibitor of luminescence interactions between manganese and iron concentrations and the luminescent properties of dolomite are demonstrated by petrographic and chemical analyses of 86 samples of dolomite representing a range of depositional environments and ages cambrian to cretaceous and a wide geographical distribution north america and europe iron and manganese are positively correlated in the dolomites with the former showing a greater range of variation very small amounts of manganese are sufficient to activate the luminescence and as little as 100 ppm mn2 is present in highly luminescing samples the intensity of luminescence is not proportional to the manganese concentration iron begins to quench luminescence as its concentration reaches 10 000 ppm above that level luminescence is rapidly lost and total extinction occurs among samples containing more than 15 000 ppm fe2 regardless of the manganese concentration

quantitative aspects of mn activated cathodoluminescence of natural and synthetic aragonite the cathodoluminescence analyses of the trigonal carbonates calcite and dolomite have been applied intensively in sedimentary petrology for a long time and the properties of these minerals are well known but much less attention has been paid to aragonite in this study the cathodoluminescence behaviour and the trace element composition of natural and synthetic aragonite have been studied employing trace element analyses proton induced x ray emission and luminescence spectroscopy aragonite doped with mn2 has been synthesized in a nh4 mg2 ca2 cl solution in contact with a co2 h2o nh3 atmosphere the low effective distribution coefficients indicate a rapid growth of the crystals of millimetre size which occurred within hours or days the natural aragonite samples contain mn fe and sr in different concentrations the mn bearing aragonites exhibit a bright green luminescence which is caused by a strong emission band at 575 nm with a half width of about 84 nm the luminescence intensity shows a strong positive correlation with mn in aragonite when fe and mn do not exceed 2000 p p m the intensity is depressed if the concentration of these elements exceeds the critical values in the shell of a recent unio sp the luminescence intensity deviates from the linear correlation although the trace element contents are not too high this is probably an effect of quenching by organic material between the crystallites of the biogenic aragonite

cathodoluminescence in diagenetic calcites the roles of fe and mn as deduced from electron probe and spectrophotometric measurements quantitative spectrophotometric measurements of cathodoluminescence cl intensities of calcite cements from the mississippian lake valley formation are compared with mn and fe electron microprobe analyses of the same calcites cl intensities of these calcites show excellent positive correlation with mn concentrations at approximately constant fe mn ratio and within narrow ranges of fe contents r 0 76 to 0 97 our data suggest that fe mn ratios may control the maximum cl intensity of calcite below this maximum at constant fe mn ratios cl intensity can vary significantly and is controlled mainly by absolute concentrations of mn and fe cl intensities are therefore a function both of absolute concentrations of mn and fe and of fe mn ratios the data further suggest that cl intensities in calcites with low fe concentrations 1 000 ppm are more sensitive to mn activation than to fe quenching cl spectra on the calcites show no evidence of rare earth element activators visual estimates of cl intensities of these calcite cements compare moderately well with intensities measured with the spectrophotometer spectrophotometrically measured cl intensities of calcites in any single visually estimated category bright moderate dull non luminescent overlap with those from adjacent categories thus spectrophotometric measurements are distinctly superior to the visual estimates our data indicate that calcites with more than about 100 ppm mn will luminesce even in the presence of moderate amounts of fe in the absence of detectable fe calcites with about 150 to 650 ppm mn have moderate cl and those with mn contents greater than about 700 ppm have bright cl in the presence of detectable fe the amount of mn required to impart moderate or bright cl increases with fe content furthermore fe does not extinguish mn activated cl up to about 10 000 ppm fe the maximum of our data these results are in general agreement with the electron microprobe study of grover and read 1983 in partial agreement with the data of frank et al 1982 and in poor agreement with the data of fairchild 1983 considering the poor precision of the electron probe at low element concentrations 100 ppm our data are reasonably consistent with the published ion microprobe and atomic absorption data mason 1987 ten have and heijnen 1985 richter and zinkernagel 1981 which imply that mn concentrations in the 30 to 50 ppm range are sufficient to activate cathodoluminescence in calcites

isolating coccoliths from sediment for geochemical analysis 1 trace element analysis of open marine sedimentary carbonates provides a wealth of paleoclimate data at present the majority of this data is obtained from foraminifera tests complications regarding the variability of conditions experienced by foraminifera throughout test formation and the influence of diagenetic processes on sample chemistry limit the value of foraminifera samples in certain situations coccoliths the calcium carbonate plates produced by coccolithophores represent a second major pelagic open marine carbonate source with the potential to provide a wide range of valuable trace element proxy data but which have until now been unavailable for analysis of many trace elements because of clay contamination here we describe a novel technique which utilizes fast sorting flow cytometry to enable the production of clay free sedimentary coccolith samples

did anoxia terminate ediacaran benthic communities evidence from early diagenesis abstract the ediacaran oceanic redox landscape was heterogeneous where many basins had a shallow and highly dynamic chemocline above anoxic ferruginous or euxinic or low oxygen manganous waters seawater mmg ca ratio was also high promoting early diagenetic dolomitisation how the benthos responded to these conditions is fundamental to understanding their ecological dynamics here we utilise redox sensitive elements in early marine carbonate cements to investigate possible water column redox controls on the distribution and growth of the oldest metazoan communities skeletal communities in the zaris sub basin of the nama group namibia 550 547 ma grew in shallow waters where fine grained carbonate sediment often shows evidence of early dolomitisation mid ramp cloudina reefs are composed of open highly porous structures that formed multiple successive assemblages each assemblage is terminated by thin reef cements show a paragenetic sequence from synsedimentary to early marine cement and final burial which we infer were precipitated under dynamic redox conditions first acicular pseudomorphed aragonite cement formed under oxic conditions low fe and mn next the presence of iron rich dolomicrite sediment often associated with a recrystallised ferroan dolomite crust suggests that originally aragonitic or calcitic sediment and a high mg precursor cement were preferentially dolomitised dolomitisation may have been enhanced either via upwelling of deeper water anoxic ferruginous seawater or by later fluid remobilisation from adjacent shales a following mn rich calcite cement is inferred to be early marine due to its inclusion rich fibrous form and well preserved cl zonation the final blocky cement precipitated under oxic conditions probably during shallow burial the cements likely record a general shallow to deeper water transect from oxic shallow waters to low oxygen manganous waters then to oxic shallow burial conditions we hypothesize that cloudina reef communities were terminated by episodic sediment incursions during short term transgressive cycles possibly accompanied by upwelled anoxic ferruginous and dolomitising waters although the timing for this is poorly constrained more generally such incursions may have terminated ediacaran benthic communities that grew close to the chemocline

improved methodology for identification of goktepe white marble and the understanding of its use a comparison with carrara marble abstract the provenance of marbles used for ancient statuary and architecture is of utmost importance for archaeologists art historians and archaeometrists the aim of this paper is to provide a comprehensive characterisation of the white marble exploited in antiquity in goktepe mugla province turkey to increase the reliability for identifying this marble in ancient artefacts a campaign of interdisciplinary archaeological and geological fieldwork undertaken by the marmora asiatica project is based on a multi method approach and on a representative set of samples used for the archaeometric analyses petrographic investigation showed that the goktepe marble is more variable with regard to fabrics and grain size than previously suggested whereas it is generally non luminescent and dolomite free stable c and o isotope and elemental analyses confirmed the results reported so far we also report for the first time for goktepe white marble the results of sr isotope measurements which in combination with elemental ratios e g sr mg and mn sr and 18o values greatly improve the discrimination among goktepe carrara and other fine grained white marbles applicability of these proxies was tested on artefacts from hadrian s villa for which carrara and goktepe provenance had been proposed the paper also reports new archaeological findings and results of estimates of stone extracted from the quarries which allowed for a recontextualization of the significance of quarries at goktepe high resolution topographic measurements performed for the first time with the use of a 3 d laser scanner combined with geological field study allowed for precise calculation of the volume of the white variety extracted in antiquity estimates of 17000 m3 is almost a half less than previously suggested moreover a careful study of the existing literature showed that in some instances assignment of white marble artefacts to the goktepe quarries may not be accurate verification of provenance for those problematic artefacts and a more reliable identification of goktepe marbles in the future can be achieved by application of the set of analyses proposed in this work which has a higher discrimination potential

magnetic fabrics rock magnetism cathodoluminescence and petrography of apparently undeformed bambui carbonates from sao francisco basin minas gerais state se brazil an integrated study abstract magnetic measurements were performed on apparently undeformed limestones and carbonate shales from 44 sites in nearly horizontal stratigraphic layers mainly from the basal units of the neoproterozoic bambui group in the southern part of the sao francisco basin rock magnetism cathodoluminescence transmitted and reflected light microscopy analyses reveal that there is a mix of ferromagnetic minerals mainly magnetite and pyrrhotite in most sites in some sites however the ferromagnetic minerals are magnetite and hematite fine grained pyrrhotite and pyrite accompany rare fine grained graphite and probably amorphous carbon in some of stylolites while pyrrhotite is also present as larger interstitial masses in coarse grained domains outside but close to the stylolites magnetic fabrics were determined applying both anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence magnetization aar the aar tensor was less well defined than the ams fabric due to the low ferromagnetic mineral content the analysis at the individual site scale defines three ams fabric types the first type two sites shows k min perpendicular to the bedding plane while k max and k int are scattered within bedding plane itself this fabric is usually interpreted as primary sedimentary compactional typical of totally undeformed sediments the second type shows the three well clustered ams axes with k min still perpendicular to the bedding plane this fabric is the most important since it was found in the majority of the sites the third type two sites is characterized by well clustered k max in the bedding plane while k min and k int are distributed along a girdle the second and third fabric types are interpreted as combinations of sedimentary compactional and tectonic contributions at the earliest and at a slightly later stage of deformation respectively ams represents the contribution of all the rock forming minerals while aar isolates the contribution of remanence bearing minerals from the matrix minerals however rock magnetism shown that anhysteretic remanence only reaches grains with coercivity k max and a max respectively in general k max is well developed and follows the trend of the main regional thrusts fold axes and faults generated in the first deformational phase while a max follows both this trend and that of structural lineaments formed during the second deformational phase these deformation phases arose from the compression which occurred during the evolution of the brasilia fold belt during the last stages of the brasiliano event the magnetic fabrics of the apparently undeformed bambui limestones are typical of very weakly deformed sediments in which the depositional compaction fabric has been partly overprinted by a tectonic one with minimum susceptibility direction remaining perpendicular to bedding this result is in agreement with the textures given by the petrographic observations

low limit of mn2 activated cathodoluminescence of calcite state of the art in the literature the lower limit for mn2 activated cathodoluminescence cl of calcite is variously reputed to over a very wide range of values above 10 ppm mn our spectroscopic investigations of the cl response in natural calcite reveal that below 10 ppm manganese content mn2 activation is also present using the quantitative high resolution spectral analysis of cl qhrs cl an activation by mn2 in the range of 700 ppb is proved which cannot be determined visually so if not quenched the minimum mn2 content for mn2 activation is one atom in the irradiated calcite crystal lattice volume as the intrinsic background blue luminescence is used to determine non altered biogenic calcite the limit of mn2 activation plays an important role in the interpretation of diagenetic processes our results of spectroscopic analyses require a revision of current opinions about the diagenesis of calcite as revealed by cl investigation

evaluation of shark tooth diagenesis screening methods and the application of their stable oxygen isotope data for palaeoenvironmental reconstructions the 18o po4 of shark teeth can be used as a geochemical proxy for the palaeoenvironment during tooth mineralization a well preserved state of the teeth is necessary for this approach we used polarization cathodoluminescence cl and scanning electron microscopy to investigate two fossil shark teeth sphenodus nitidus from the late jurassic nusplingen plattenkalk the data are compared with those for two recent shark teeth hemipristis elongata lamiopsis temminckii 18o po4 of six further jurassic shark teeth was measured and is compared with 18o data from co occurring belemnite rostra and carbonate sediments the enameloid of both the fossil and the recent shark teeth shows orange red cl which is due to incorporation of mn during biomineralization the 18o po4 values of the fossil enameloid are constant around 21 50 v smow whereas those of the fossil dentine are more negative with values around 20 v smow which indicates that the enameloid is well preserved palaeotemperatures calculated from the enameloid are like those derived from belemnites we demonstrate that cl microscopy should only be used cautiously as a diagenesis screening method for fossil biophosphates geochemical and microstructural analyses of tissue types with different susceptibility to diagenetic alteration on the other hand provide an effective way to identify well preserved tissues supplementary material polarization microscopy images energy dispersive x ray data and cathodoluminescence spectra are available at https doi org 10 6084 m9 figshare c 4373720

differentiation of environments of dolomite formation lower cretaceous of central tunisia combined field sedimentological mineralogical isotopic and geochemical study of the lower cretaceous dolomites of central tunisia has demonstrated considerable diversity in origin environments of dolomite formation include deep phreatic karst lacustrine and evaporitic sabkha all four groups of dolomite are composed of non stoichiometric and or disordered crystals which are more or less rich in calcium and in iron petrographic fabrics are of three types replacement recrystallization and cementation these three fabrics are proposed among the various criteria for the different environments of dolomitization average isotope 18 o and 13 c contents for these four dolomite groups range from 10 5 to 0 4 o pdb and 3 9 to 3 7 o respectively the distribution of strontium is related both to the degree of recrystallization and to the palaeosalinity ferrous iron also very common is regarded as an indicator of relatively deep reducing conditions mainly in meteoric groundwaters sodium distribution is related to inclusions within the dolomite its distribution being relatively constant in all four groups it cannot be regarded as a reliable criterion for palaeosalinity of dolomitizing fluids this study confirms that dolomitization may occur under widely different palaeoenvironments either at the surface or during burial with the exception of the sabkha environment dolomitizing fluids seem to have been essentially meteoric

dynamics of cementation in response to oil charge evidence from a cretaceous carbonate field u a e abstract oil charge is thought to inhibit the growth of cements within subsurface pore systems we explore this phenomenon in a giant cretaceous carbonate field from u a e where the oil filled crest porosity ranges from 10 to 50 and permeability from 0 08 to 830 md but coeval water leg porosity is reduced to 10 to 23 and permeability to 0 1 to 4 md only 5 of primary interparticle pores 30 m diameter in the crest are fully cemented compared to 99 of pores in the water leg syntaxial calcite burial cements 10 m diameter in the oil leg show 12 cathodoluminescence zones with oil inclusions n 27 occurring in four of the five final zones mean in situ ion microprobe 18ovpdb data from the oil leg cements range from 1 2 in the oldest zone decreasing to 10 3 in zone 11 returning to 7 7 in the final zone the oldest distinguishable cement zone in the water leg shows highly variable 18o from 3 6 to 9 3 with a mean of 7 3 and with subsequent zones decreasing to a mean value of 9 4 for the youngest cement zone decreasing 18o values are interpreted as indicating increasing temperature reflecting burial and the evolution of pore water composition broadly similar trends in the oil and water legs suggest precipitation under the same general conditions unlike the oil leg cements the final zone in the water leg occludes nearly all remaining pore space the 18ovpdb of bulk micrite from the water leg shows an average of 7 4 n 9 compared to 6 2 n 10 from the oil leg suggesting the precipitation of further micrite cement at greater burial depths we infer that burial cementation slowed in the presence of oil due to a reduction of potential nucleation sites as well as porewater and solute movement within weakly oil wet pores whereas continued flow and solute movement through all pores including the micropores

comment on oxygen and carbon isotopic composition of ordovician brachiopods implications for coeval seawater by h qing and j veizer

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

how to overcome imaging problems associated with carbonate minerals on sem based cathodoluminescence systems on sem based cathodoluminescence systems scanned cl methods are needed to overcome image quality problems caused by persistent luminescence of carbonate minerals an effective solution to the persistence problem is to acquire images using only the shorter wavelengths most easily done by using a broadband short wavelength uv blue range filter the filter used provides 80 to 90 transmissivity in the range of 385 to 495 nm and some transmissivity as low as 350 nm the filter allows transmission of the relatively nonpersistent uv violet luminescence present in most carbonates in the range of 350 to 425 nm but blocks the common orange red wavelength luminescence found in carbonates the lack of imaging problems in subsequent images shows that persistent luminescence in carbonates is primarily in the orange red wavelengths cathodoluminescence images produced using a short wavelength filter are comparable in detail to those obtained from conventional light microscope based cathodoluminescence systems in almost all examples features visible in the orange red wavelengths show corresponding variations in luminescence in the shorter wavelengths

imaging of cathodoluminescence zoning in calcite by scanning electron microscopy and hyperspectral mapping abstract imaging of cathodoluminescence cl emission from carbonate minerals by scanning electron microscopy sem is problematic owing to the slow rate at which cl decays from each point as the electron beam is scanned over an area the phenomenon of phosphorescence using sem cl and a newly developed electron probe based technique of hyperspectral mapping we have evaluated methods that have been proposed to overcome phosphorescence with the dwell time technique the duration of time that the electron beam is static is increased such that cl emission from a given point makes a negligible contribution to the total signal from subsequent points the dwell time required to form sharp sem cl images of calcite that has a high intensity of luminescence at orange wavelengths is equal to or greater than 6 4 milliseconds whereas calcite that luminesces predominantly at ultraviolet to blue wavelengths can be imaged using submillisecond dwell times by using longer dwell times 1000 ms cl and x ray spectra can also be acquired from each point to form hyperspectral maps the limited wavelength imaging technique employs optical filters to excise slowly decaying long wavelength emission so that the image is formed only using the more rapidly decaying ultraviolet to blue wavelengths allowing shorter dwell times to be used both techniques have some disadvantages the main drawback of the dwell time technique is the long period of time required to acquire high resolution images whereas the success of limited wavelength imaging may depend on the sensitivity of the cl detector being used cl images and emission spectra acquired by hyperspectral mapping also show that there is a nonlinear relationship between luminescence intensity variations at ultraviolet to blue wavelengths and intensity variations at orange wavelengths indicating that short wavelength emission is an imperfect proxy for zoning at longer wavelengths additionally we have been unable to identify the controls on spatial variations in the intensity of ultraviolet to blue luminescence although our data discount fe2 concentrations as being the sole determinant by using hyperspectral mapping in combination with electron probe microanalysis to obtain cl and x ray spectra from the same micrometer sized volume of a material it is now possible to understand and quantify the controls on activation and quenching of cl in calcite and other minerals such as apatite and zircon

cathodoluminescence in calcite cements new insights on pb and zn sensitizing mn activation and fe quenching at low trace element concentrations abstract the role of pb and zn as sensitizers of cathodolumines cl in sedimentary carbonates is still speculative as is the relationship between mn fe and cl intensity at low concentrations of mn and fe we address these questions using calcite cements from the lower oligocene suwannee formation of florida which have mean mn pb zn and fe concentrations less than 45 ppm only a small fraction of these cements exhibit visible cl but when present the luminescence is orange to reddish orange trace element contents were measured using a synchrotron x ray fluorescence microprobe and cl intensity was approximated by spot metered photomicrograph exposure times based on mn and fe contents four cement populations can be defined group i is luminescent calcite with mn 25 ppm and molar mn fe 1 8 group ii contains both luminescent and nonluminescent cements all with mn 25 ppm molar mn fe 25 ppm molar mn fe 100 ppm group iv is nonluminescent calcite with mn 25 ppm and variable fe these groupings and statistical analyses of the data mann whitney tests and factor analyses confirm that 25 ppm mn is necessary to initiate visible cl and that mn is the sole control on cl intensity when mn and fe contents are very low 100 ppm the data also establish 100 ppm fe as a new minimum for the quenching of cl when mn is below 200 ppm there is no evidence in our data that pb or zn concentrations in tens of parts per million either activate or sensitize cl the mann whitney test shows that there is no statistical evidence at the 95 confidence level to indicate that luminescent and nonluminescent cements reflect different populations of pb and zn except for group ii cements that have more pb in nonluminescent cements than in otherwise chemically equivalent luminescent cements factor analysis shows that cl intensity in all luminescent cements is unrelated to pb or zn concentrations given that pb or zn sensitizing is lacking in low mn calcites like the suwannee cements it is hard to imagine how these elements could play a significant role in calcites containing even more mn as is typical of most sedimentary carbonates

new insights into geochemical behaviour in ancient marine carbonates upper jurassic ammonitico rosso novel proxies for interpreting sea level dynamics and palaeoceanography elemental concentrations in phanerozoic sea water are known to fluctuate both in time and space with regard to carbonates precipitated from marine fluids elemental concentrations in the carbonate crystal lattice are affected by a complex array of equilibrium and non equilibrium as well as post depositional alteration processes to assess the potential of carbonate elemental chemostratigraphy seven upper jurassic sections were investigated along a proximal to distal transect across the south east iberian palaeomargin the aim was to explore stratigraphic and spatial variations in calcium strontium magnesium iron and manganese elemental abundances the epicontinental geochemical record is influenced by the combination of continental runoff and a significant diagenetic overprint in contrast the epioceanic geochemical record agrees with reconstructed open marine sea water values reflecting a moderate degree of syn depositional to early marine pore water diagenesis establishing a fair degree of preservation of matrix micrite a thorough statistical approach was applied and elemental associations tested for their environmental significance principal component and hierarchical cluster analyses revealed a persistent relation between carbonate magnesium iron and strontium abundances processes related to early diagenetic nodulation in ammonitico rosso facies most probably account for the incorporation of these elements in the calcium carbonate lattice the clear decoupling of carbonate manganese abundance with respect to the remaining elements is documented and related to high sea floor spreading rates and hydrothermal activity during the late jurassic the investigation of potential time fluctuation of geochemical patterns was approached through variogram computation the observed temporal behaviour is most likely to be forced by relative sea level dynamics reflecting late jurassic palaeoceanographic conditions and potential planetary interactions the data obtained in this study highlight the utility of elemental data from carbonate matrix micrites as geochemical proxies for studying the influence of remote trigger factors