Oxygen isotope compositions of conodonts – analytical challenges of in situ SIMS studies

Reliable deep-time environmental and climate reconstructions are needed to understand the drivers of Earthâs system evolution over geological time. Palaeozoic temperature estimates, including reconstructions of the climate change through the Ordovician, are based mainly on oxygen isotope (18O/16O; δ18OVSMOW) thermometry derived from carbonate rocks with fossils such as calcitic brachiopods and phosphatic conodonts that are often the best preserved repositories of environmental conditions. Palaeoenvironmental reconstructions are reliable only if the geochemical data is obtained using well-calibrated analytical tools. Most previous research devoted to oxygen isotope composition of conodonts has been conducted using the bulk method (gas source isotope ratio mass spectrometry (GS-IRMS)) that typically requires pooling several dozens of conodont elements for a single isotope ratio measurement. As such, studies of conodont-poor intervals and assessments of taxon-specific δ18O variability require extensive sample preparation and are challenging using the bulk method. Such challenges can be addressed by in situ secondary ion mass spectrometry (SIMS) analyses using only picogram sampling masses. However, several studies have reported inconsistencies between SIMS and GS-IRMS δ18O data for the same research material. We aim to solve this controversy by establishing a robust analytical protocol for conodont isotope analysis by SIMS. Here we present conodont data on Pterospathodus and Amorphognathus specimens extracted from Ordovician strata in Nurme and Mehikoorma-421 boreholes (Estonia). Oxygen isotope composition of conodonts was analysed by both SIMS and GS-IRMS, where we paid particular attention to four inorganic apatite reference materials in order to understand the offset between these two techniques that have been reported in the literature. While the results of GS-IRMS measurements conducted using high-temperature reduction of Ag3PO4 represent exclusively δ18O of phosphate-bound oxygen, SIMS analyses do not discriminate between different oxygen components (e.g., (PO4)3â, (SiO4)4â, (CO3)2â, and (OH)â) in apatite, inherently providing information on pooled isotope compositions. We conducted quantitative chemical analyses of selected conodont elements by electron probe microanalysis to assess to what extent matrix effects cause the offsets between the two isotope techniques. We also used scanning electron microscopy and white light optical profilometry to evaluate sample topography and porosity, which have a major impact on SIMS data quality. We collected oxygen isotope data using a CAMECA 1280-HR large geometry instrument at the Potsdam SIMS user facility over several months to determine reproducibility of the results and to optimise a routine measurement protocol. Our tests included a variety of instrumental settings, e.g., different raster parameters for both pre-sputtering and data collection, which yielded slightly differing results due to different instrumental mass fractionation. SIMS is a comparative method, and as such relies on reference materials that have been previously characterised by bulk methods, ideally provided by multiple laboratories. We noted that the inconsistent offsets between SIMS and GS-IRMS data obtained for a given conodont specimen (with SIMS δ18O values in most cases being higher) are linked to reference material measurements that are necessary for conodont data calibration and are often biased towards lighter δ18O values. Our tests show that such bias is even more significant when calibration is based on a single reference material characterised by a single GS-IRMS laboratory, which has been a common practice in past conodont studies

L'Amérique latine en 2010: une et de plus en plus plurielle

info:eu-repo/semantics/publishe

SIMS Lab Potsdam: Secondary Ion Mass Spectrometry Laboratory Potsdam

Secondary Ion Mass Spectrometry (SIMS) is among the most powerful laboratory tools available to the analytical geochemist. Its strength lies in SIMS’ ability to produce high precision trace element and isotope ratio data on sample masses as small as 100 picograms. The Helmholtz-Centre Potsdam GFZ German Research Centre for Geosciences operates a fully equipped, large geometry SIMS instrument, which is supported by a comprehensive spectrum of peripheral instrumentation. This facility operates as an open user facility which supports the needs of the global geochemical community

Inter‐laboratory Characterisation of Apatite Reference Materials for Chlorine Isotope Analysis

Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca10(PO4)6(F,Cl,OH)2 solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for 37Cl/35Cl homogeneity using SIMS followed by δ37Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10% (1s) for the five samples with > 0.5% m/m Cl and ± 0.19% (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38% between the mean 37Cl/35Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ37ClSMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 103δ37ClSMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25.Key Points: Six apatite reference materials having various Cl mass fractions were characterised for chlorine isotope ratios by SIMS and three GS‐IRMS laboratories. A small, but significant, crystal orientation effect was recorded by SIMS analyses. Correlation of instrumental mass fractionation factor with Cl mass fraction is visible along the apatite solid solution series.Narodowe Centrum NaukiDeutscher Akademischer AustauschdienstHelmholtz Recruiting InitiativeInstitute of Geological Sciences, Polish Academy of Science

Prevalence of anal symptoms in general practice: a prospective study

Abstract Background Anal disorders are largely underestimated in general practice. Studies have shown patients conceal anal symptoms leading to late diagnosis and treatment. Management by general practitioners is poorly described. The aim of this study is to assess the prevalence of anal symptoms and their management in general practice. Methods In this prospective, observational, national study set in France, all adult patients consulting their general practitioner during 2 days of consultation were included. Anal symptoms, whether spontaneously revealed or not, were systematically collected and assessed. For symptomatic patients, the obstacles to anal examination were evaluated. The general practitioner’s diagnosis was collected and a proctologist visit was systematically proposed in case of anal symptoms. If the proctologist was consulted, his or her diagnosis was collected. Results From October 2014 to April 2015, 1061 patients were included by 57 general practitioners. The prevalence of anal symptoms was 15.6% (95% CI: 14–18). However, 85% of these patients did not spontaneously share their symptoms with their doctors, despite a discomfort rating of 3 out of 10 (range 1–5). Although 65% of patients agreed to an anal examination, it was not proposed in 45% of cases with anal symptoms. Performing the examination was associated with a significantly higher diagnosis rate of 76% versus 20% (p < 0.001). Proctologist and general practitioner diagnoses were consistent in 14 out of 17 cases. Conclusions Patients’ concealed anal symptoms are significant in general practice despite the impact on quality of life. Anal examination is seldom done. Improved training of general practitioners is required to break the taboo

Correction to: Prevalence of anal symptoms in general practice: a prospective study

Following publication of the original article [1], the authors reported an error to one of the ‘study groups’ in the authorship section