Carbon, oxygen, and strontium isotope geochemistry of the Proterozoic carbonate rocks, Bhima basin, south India: Implication for diagenesis

A carbonate dominated shallow marine Proterozoic Bhima basin consists of carbonates and clastic rocks, and is widely distributed in the northern part of the Karnataka state, south India. Limestones of the Shahabad Formation have been selected for this study and secular variations in C, O, and Sr isotope compositions are reported. δ13C values are varying from +3.50 to -1.38‰PDB. Similarly, the δ18O values recorded a range between -5.76 and -12.93‰PDB 87Sr/86Sr ratio for these limestones is varying between 0.70699 and 0.7117. Higher burial rate of organic matter could have been responsible for the positive δ13C values, which is common in the Proterozoic carbonate rocks. The δ18O values in most of the samples are similar to the average value of the Proterozoic carbonate rocks. Albeit some of the samples are modified in their original isotopic signature, which shows high negative δ18O values 1.5 and a negative trend between δ18O and 87Sr/86Sr, suggesting that the δ18O and 87Sr/86Sr isotopic signatures of Bhima carbonates have been altered by diagenesis. The post depositional diagenetic alteration is also supported by the petrographic characters of these carbonates

Shape and intrusion history of the Late Caledonian Newry Igneous Complex, Northern Ireland

The Tellus high-resolution airborne magnetic and radiometric maps define previously unmapped zones within the Newry Igneous Complex, County Down. High-precision uranium–lead zircon dating of nine rock samples from different parts of the complex provides a robust set of age constraints (c.414–407 Ma), which confirm that the different plutons of the complex young towards the south-west. Combined, these new data allow an innovative model of intrusion to be developed, with intrusion beginning in the north-east and progressing towards the south-west

Potassium Isotopic Compositions of NIST Potassium Standards and 40Ar/39Ar Mineral Standards

Knowledge of the isotopic ratios of standards, spikes, and reference materials is fundamental to the accuracy of many geochronological methods. For example, the 238U/235U ratio relevant to U-Pb geochronology was recently re-determined [1] and shown to differ significantly from the previously accepted value employed during age determinations. These underlying values are fundamental to accurate age calculations in many isotopic systems, and uncertainty in these values can represent a significant (and often unrecognized) portion of the uncertainty budget for determined ages. The potassium isotopic composition of mineral standards, or neutron flux monitors, is a critical, but often overlooked component in the calculation of K-Ar and 40Ar/39Ar ages. It is currently assumed that all terrestrial materials have abundances indistinguishable from that of NIST SRM 985 [2]; this is apparently a reasonable assumption at the 0.25per mille level (1) [3]. The 40Ar/39Ar method further relies on the assumption that standards and samples (including primary and secondary standards) have indistinguishable 40K/39K values. We will present data establishing the potassium isotopic compositions of NIST isotopic K SRM 985, elemental K SRM 999b, and 40Ar/39Ar biotite mineral standard GA1550 (sample MD-2). Stable isotopic compositions (41K/39K) were measured by the peak shoulder method with high resolution MC-ICP-MS (Thermo Scientific NEPTUNE Plus), using the accepted value of NIST isotopic SRM 985 [2] for fractionation [4] corrections [5]. 40K abundances were measured by TIMS (Thermo Scientific TRITON), using 41K/39K values from ICP-MS measurements (or, for SRM 985, values from [2]) for internal fractionation corrections. Collectively these data represent an important step towards a metrologically traceable calibration of 40K concentrations in primary 40Ar/39Ar mineral standards and improve uncertainties by ca. an order of magnitude in the potassium isotopic compositions of standards

Fe isotope exchange between Fe(II)(aq) and nanoparticulate mackinawite (FeSm) during nanoparticle growth

We detail the results of an experimental study on the kinetics of Fe isotope exchange between aqueous Fe(II)aq and nanoparticulate mackinawite (FeSm) at 25 °C and 2 °C over a one month period. The rate of isotopic exchange decreases synchronously with the growth of FeSm nanoparticles. 100% isotopic exchange between bulk FeSm and the solution is never reached and the extent of isotope exchange asymptotes to a maximum of ~ 75%. We demonstrate that particle growth driven by Ostwald ripening would produce much faster isotopic exchange than observed and would be limited by the extent of dissolution–recrystallisation. We show that Fe isotope exchange kinetics are consistent with i) FeSm nanoparticles that have a core–shell structure, in which Fe isotope mobility is restricted to exchange between the surface shell and the solution and ii) a nanoparticle growth via an aggregation–growth mechanism. We argue that because of the structure of FeSm nanoparticles, the approach to isotopic equilibrium is kinetically restricted at low temperatures. FeSm is a reactive component in diagenetic pyrite forming systems since FeSm dissolves and reacts to form pyrite. Isotopic mobility and potential equilibration between FeSm and Fe(II)aq thus have direct implications for the ultimate Fe isotope signature recorded in sedimentary pyrite

High-precision 41K/39K measurements by MC-ICP-MS indicate terrestrial variability of δ41K

Potassium is a major component in continental crust, the fourth-most abundant cation in seawater, and a key element in biological processes. Until recently, difficulties with existing analytical techniques hindered our ability to identify natural isotopic variability of potassium isotopes in terrestrial materials. However, measurement precision has greatly improved, and a range of K isotopic compositions has now been demonstrated in natural samples. In this study, we present a new technique for high-precision measurement of K isotopic ratios using high-resolution, cold plasma multi-collector mass spectrometry. We apply this technique to demonstrate natural variability in the ratio of 41K to 39K in a diverse group of geological and biological samples, including silicate and evaporite minerals, seawater, and plant and animal tissues. The total range in 41K/39K ratios is ca. 2.6‰, with a long-term external reproducibility of 0.17‰ (2σ, N=108). Seawater and seawater-derived evaporite minerals are systematically enriched in 41K compared to silicate minerals by ca. 0.6‰, a result consistent with recent findings (1, 2). Although our average bulk- silicate Earth value (-0.54‰) is indistinguishable from previously published values, we find systematic δ41K variability in some high-temperature sample suites, particularly those with evidence for the presence of fluids. The δ41K values of biological samples span a range of ca. 1.2‰ between terrestrial mammals, plants, and marine organisms. Implications of terrestrial K isotope variability for the atomic weight of K and K-based geochronology are discussed. Our results indicate that high-precision measurements of stable K isotopes, made using commercially available mass spectrometers, can provide unique insights into the chemistry of potassium in geological and biological systems

Nitrogen and Strontium Isotopes as Tools for the Reconstruction of Breastfeeding Practices and Human Behavior – A Neolithic Collective Grave in Bronocice (Poland)

Isotopic analyses are often used in biological anthropology and bioarcheology, in studies of ancient human populations. Such analyses in anthropology have been used to study migration patterns, the nutrition strategies of prehistoric populations and the weaning of infants. The main objective of this work was to investigate patterns of breastfeeding and weaning in Neolithic populations at Bronocice in Poland using nitrogen stable isotopes. Additionally, strontium isotope analysis was conducted to determine if the individuals from the collective grave (Burial XIII, Pit 36-B1) at Bronocice were of local origin. The samples consisted of skeletal remains from individuals buried in the collective grave during the early Funnel Beaker-Baden phase (3300-3100 BC). Two models have been used for reconstructing precisely the age at the start and end of weaning (Schurr’s model and WARN model). The results suggest that weaning began in the first year of life and ended at about 3 years of age

Precessional variability of 87 Sr/86 Sr in the late Miocene Sorbas Basin: An interdisciplinary study of drivers of interbasin exchange

We present the first subprecessional record of seawater 87Sr/86Sr isotope ratios for a marginal Mediterranean subbasin. The sediments contained in this interval (three precessional cycles between 6.60 and 6.55 Ma) are important because they record conditions during the transition to the Messinian Salinity Crisis (MSC; 5.97 to 5.33 Ma), an event for which many details are still poorly understood. The record, derived from planktic foraminifera of the late Miocene Sorbas Basin (SE Spain), shows brief excursions with precessional cyclicity to 87Sr/86Sr ratios higher than coeval ocean 87Sr/86Sr. The hydrologic conditions required to generate the observed record are investigated using box modeling, constrained using a new paleodepth estimate (150 to 250 m) based on benthic foraminiferal assemblages. The box model results highlight the role of climate‐driven interbasin density contrast as a significant driver of, or impediment to, exchange. The results are particularly significant in the context of the MSC, where 87Sr/86Sr excursions have been interpreted purely as a consequence of physical restriction. To replicate the observed temporal patterns of lithological variations and 87Sr/86Sr isotope excursions, the Sorbas Basin “box” must have a mainly positive hydrologic budget, in contrast with the Mediterranean's negative budget during the late Miocene. This result has implications for the assumption of synchronous deposition of specific sedimentary layers (sapropels) between marginal and open Mediterranean settings at subprecessional resolution. A net positive hydrologic budget in marginal Mediterranean subbasins may reconcile observations of freshwater inclusions in gypsum deposits

A procedural development for the analysis of ^56/54Fe and ^57/54Fe isotope ratios with new generation IsoProbe MC-ICP-MS

We have developed a procedure for iron isotope analysis using a hexapole collision cell MC-ICP-MS which is capable of Fe isotope ratio analysis using two different extraction modes. Matrix effects were minimised and the signal-to-background ratio was maximised using high-concentration samples (~ 5μg Fe) and introducing 1.8 mL/min<sup>-1</sup> Ar and 2 mL/min H<sub>2</sub> into the collision cell to decrease polyatomic interferences. The use of large intensity on the faraday cups considerably decreases the internal error of the ratios and ultimately, improves the external precision of a run. Standard bracketing correction for mass bias was possible when using hard extraction. Mass bias in soft extraction mode seems to show temporal instability that makes the standard bracketing inappropriate. The hexapole rf amplitude was decreased to 50 % to further decrease polyatomic interferences and promote the transmission of iron range masses. We routinely measure Fe isotopes with a precision of ± 0.05 ‰ and ± 0.12 ‰ (2σ) for δ<sup>56</sup>Fe and δ<sup>57</sup>Fe respectively

Nitrogen and Strontium Isotopes as Tools for the Reconstruction of Breastfeeding Practices and Human Behavior – A Neolithic Collective Grave in Bronocice (Poland)

Isotopic analyses are often used in biological anthropology and bioarcheology, in studies of ancient human populations. Such analyses in anthropology have been used to study migration patterns, the nutrition strategies of prehistoric populations and the weaning of infants. The main objective of this work was to investigate patterns of breastfeeding and weaning in Neolithic populations at Bronocice in Poland using nitrogen stable isotopes. Additionally, strontium isotope analysis was conducted to determine if the individuals from the collective grave (Burial XIII, Pit 36-B1) at Bronocice were of local origin. The samples consisted of skeletal remains from individuals buried in the collective grave during the early Funnel Beaker-Baden phase (3300-3100 BC). Two models have been used for reconstructing precisely the age at the start and end of weaning (Schurr’s model and WARN model). The results suggest that weaning began in the first year of life and ended at about 3 years of age