High-resolution Trace Element Research Articles

Semi-quantitative μLIBS mapping of germanium diffusion between metal and silicate during planetary core–mantle segregation

Understanding the distribution of elements between the cores and mantles of planetary bodies is essential for elucidating the geological and geochemical processes operating during their formation. Because the semi-metallic element Ge shows complex siderophile, chalcophile, and lithophile properties, it is particularly significant for investigating core–mantle segregation and ore deposit formation. Recent advancements in in situ microanalysis techniques, such as μLIBS, have enabled high-resolution elemental mapping of Ge and other trace elements.This study explores the application of μLIBS imaging to investigate the high-temperature/high-pressure distribution of Ge between metallic and silicate matrices analogous to planetary cores and mantles. By cross-calibrating the μLIBS intensities with electron microprobe profile analyses carried out on piston cylinder experimental samples, we produced semi-quantitative Ge maps from which we extracted Ge concentration profiles to assess Ge diffusion from the silicate to the metal. We determined, for the first time, the diffusion coefficient of Ge between metal and silicate to be D(Ge)metal = 4.03E−13 ± 3.6E−14 m2/s at 1 GPa and 1350 °C. Our results demonstrate the capability and efficiency of μLIBS for providing detailed, high-resolution (15 μm) trace element concentration data at few ppm levels, offering a time- and cost-effective alternative to conventional techniques.These findings bring insights on planetesimal differentiation and on chemical exchanges between metal and silicate phases in a magma ocean and between two different metal phases occurring at the bottom of the magma ocean during planetesimal formation.

High-resolution trace element chemistry across the Cretaceous-Tertiary boundary in Denmark

Closely spaced samples on millimeter scale across the Cretaceous-Tertiary boundary clay in Denmark were analyzed by instrumental neutron activation analysis. The results show a strong correlation between Cr and Ir while Co, Zn, As, Sb and Au are correlated with Fe. The elemental peaks for Ir-Cr and Fe are separated by 6 mm. The Fe peak is found in burrow-fillings at the lowermost part of the boundary clay. Chromite grains extracted from boundry clay in Denmark and New Zealand show a compositional common group. The composition points to an ultrabasic (kimberlitic) origin of the chromites. Tandem accelerator mass spectroscopy demonstrated, that there are no Ir carriers in addition to elemental carbon in the boundary clay from two localities in Denmark.

Thermal Budgets of Magma Storage Constrained by Diffusion Chronometry: the Cerro Galán Ignimbrite

Abstract The long-term thermochemical conditions at which large bodies of silicic magma are stored in the crust is integral to our understanding of the timing, frequency, and intensity of volcanic eruptions and provides important context for interpreting volcano monitoring data. Despite this, however, individual magmatic systems may exhibit a range of time–temperature paths, or thermal histories, that are the result of many complex and, in some cases, competing processes. This complexity contributes to an incomplete understanding of the long-term thermal evolution of magma stored within the Earth’s crust. Of recent interest to the volcanology community is the length of time large volumes of rheologically eruptible and geophysically detectable magma exist within the crust prior to their eruption. Here we use a combination of diffusion chronometry, trace element, and thermodynamic modeling to quantify the long-term thermal evolution of the 2.08 Ma, 630 km3 Cerro Galán Ignimbrite (CGI) in NW Argentina; one of the largest explosive volcanic eruptions in the recent geologic record. We find that diffusion of both Mg and Sr in plagioclase indicate that erupted magmatic material only spent decades to centuries at or above temperatures (~750°C) required to maintain significant volumes of stored eruptible magma. Calculated plagioclase equilibrium compositions reveal an array of liquids that is controlled overall by fractionation of plagioclase + biotite + sanidine, although high-resolution trace element transects record a diversity of fractionation pathways. Overall, we suggest that there is compelling evidence that the magma erupted from the CGI magmatic system spent most of its upper crustal residence in a largely uneruptible state and was rapidly remobilized shortly before eruption.

Microbial utilization of rare earth elements at cold seeps related to aerobic methane oxidation

A major breakthrough in the field of rare earth element (REE) geochemistry has been the recent discovery of their utility to microbial life, as essential metalloenzymes catalyzing the oxidation of methanol to formaldehyde. Lanthanide-dependent bacteria are thought to be ubiquitous in marine and terrestrial environments, but direct field evidence of preferential microbial utilization of REE in natural systems is still lacking. In this study, we report on the REE and trace element composition of the tube of a siboglinid worm collected at a methane seep in the Gulf of Guinea; a tube-dwelling annelid that thrives in deep-sea chemosynthetic ecosystems. High-resolution trace element profiles along the chitin tube indicate marked enrichments of lanthanum (La) and cerium (Ce) in its oxic part, resulting in REE distribution patterns that depart significantly from the ambient seawater signature. Combined with various geochemical and microbiological evidence, this observation provides direct support for an active consumption of light-REE at cold seeps, associated with the aerobic microbial oxidation of methane. To further evaluate this hypothesis, we also re-examine the available set of REE data for modern seep carbonates worldwide. While most carbonate concretions at cold seeps generally display REE distribution patterns very similar to those for reduced pore waters in marine sediments, we find that seafloor carbonate pavements composed of aragonite commonly exhibit pronounced light-REE enrichments, as inferred from high shale-normalized La/Gd ratio (>~0.8), interpreted here as possibly reflecting the signature of lanthanide-dependent methanotrophic activity. This finding opens new perspectives for revisiting REE systematics in ancient seep carbonates and other microbialites throughout the Earth's history. In particular, the geochemical imprint of aerobic methane oxidation could be possibly traced using REE in Archaean stromatolites and other archives of Precambrian seawater chemistry, potentially providing new insights into the oxygenation of early Earth's oceans and associated microbiogeochemical processes.

Identification of growth mechanisms in metamorphic garnet by high-resolution trace element mapping with LA-ICP-TOFMS

Garnet is one of the most robust and ubiquitous minerals that record element zoning during crustal metamorphism. In addition to major elements, zoning in trace elements can provide a wealth of information to document the changing conditions of garnet growth and modification. However, mapping trace elements at low concentrations, over large areas and with high resolution has remained a major challenge. We present a comprehensive investigation of the TE distribution in garnet from three Alpine samples that underwent a complex evolution at different metamorphic conditions. The TE distribution in garnet grains is mapped in 2D in thin section with a novel approach using laser ablation inductively coupled plasma time of flight mass spectrometry (LA-ICP-TOFMS) to achieve a lateral resolution of 5 µm and limits of detection for the heavy rare earth elements (REE) down to 0.2 µg/g. Comparison with major element zoning measured by electron probe microanalysis and trace elements measured by conventional LA-ICPMS spot analysis testifies to the accuracy of the measurements. Garnet in an amphibolite-facies metapelite from Campolungo, Central Alps, that recorded metamorphism to 600 °C preserves Y + REE trace element zoning that closely matches that of Ca. In this sample, there is no notable diffusive modification for trace elements. Y + REE zoning is dominated by Rayleigh fractionation in the core and by the sporadic breakdown of accessory phases producing annuli in the rim of the garnet. A granulite-facies garnet from Malenco, Eastern Central Alps, formed during subsolidus heating, followed by peritectic melting reactions up to temperatures of 800–850 °C. Major and trace element zoning are decoupled indicating diffusional resetting of major elements, whereas trace elements still largely document the growth history. Enrichment of trace elements in the garnet mantle may be related to the consumption of biotite (V, Cr) and the dissolution of zircon (Zr) and monazite (Y + REE) in the melt. Diffusion of Y + HREE at the core–mantle boundary occurred over a length scale of ~ 200 µm. Garnet in an eclogite from the Sesia Zone, Western Alps (P ~ 2 GPa, T ~ 600 °C), displays pronounced fluid-related veinlets, visible in FeO, MgO and MnO, which cross-cut the primary growth zoning. Surprisingly, complex Y + REE and Cr zoning is not affected by the veinlets, indicating that they did not form by a crack-seal mechanism but are rather related to a selective replacement process. The trace element maps provide a detailed insight into the growth and modification of garnet and thus allow assessment of equilibrium versus disequilibrium processes, and assist in determination of P–T conditions, garnet dating, diffusion modelling as well as documenting fluid-induced modifications.

Large S isotope and trace element fractionations in pyrite of uranium roll front systems result from internally-driven biogeochemical cycle

Complex pyrite textures associated with large changes in isotopic and trace element compositions are routinely assumed to be indicative of multi-faceted processes involving multiple fluid and sulfur sources. We propose that the features of ore-stage pyrite from roll front deposits across the world, revealed in exquisite detail via high-resolution trace element mapping by LA-ICP-MS, reflect the dynamic internal evolution of the biogeochemical processes responsible for sulfate reduction, rather than externally driven changes in fluid or sulfur sources through time. Upon percolation of oxidizing fluids into the reduced host-sandstones, roll front systems become self-organized, with a systematic reset of their activity cycle after each translation stage of the redox interface down dip of the aquifer. Dominantly reducing conditions at the redox interface favor the formation of biogenic framboidal pyrite (δ34S from −30.5 to −12.5‰) by bacterial sulfate reduction and the genesis of the U mineralization. As the oxidation front advances, oxidation of reduced sulfur minerals induces an increased supply of sulfate and metals in solution to the bacterial sulfate reduction zone that has similarly advanced down the flow gradient. Hence, this stage is marked by increased rates of the bacterial sulfate reduction associated with the crystallization of variably As-Co-Ni-Mo-enriched concentric pyrite (up to 10,000′s of ppm total trace contents) with moderately negative δ34S values (from −13.7 to −7.5‰). A final stage of pyrite cement with low trace element contents and heavier δ34S signature (from −6.9 to +18.8‰) marks the end of the roll front activity cycle and the transition from an open to a predominantly closed system behavior (negligible advection of fresh sulfate). Blocky pyrite cement is formed using the remaining sulfate, which now becomes quickly heavy according to a Rayleigh isotope fractionation process. This ends the cycle by depleting the nutrient supplies for the sulfate-reducing bacteria and cementing pore spaces within the host sandstone, effectively restricting fluid infiltration. This internally-driven roll front activity cycle results in systematic, large S isotope and trace element fractionation. Ultimately, the long-time evolution of the basin and fluid sources control the metal endowment and evolution of the system; these events, however, are unlikely to be preserved by the roll front, as a direct result of its hydrodynamic nature.

Last glacial climate oscillations and sudden environmental changes investigated in stalagmites from southwest Sulawesi, western Pacific

We investigated two stalagmites from the Saripa Cave and Bumi Cave in southern Sulawesi, Indonesia, using high-precision U-series dating and high-resolution trace element and C-O-Sr isotope analysis. The growth record (from 10.4 ± 0.1 ka to 77.4 ± 0.9 ka) of the Saripa Cave stalagmite (SR04-ST3) is fragmented with two major (at the top: 10.4-11.6 ka and middle: 43.8-44.7 ka sections of the stalagmite) and some short (middle and bottom sections) growth phases, interrupted by long-lasting growth hiatuses. Both the timing of the growth phases and the δ18O values for different growth phases are correlated with those of cold/dry (~22 ka and 43.8-44.7 ka) and wet/warm periods (e.g., Greenland Interstadials 12, 14, and 21) in the northern hemisphere speleothem records, displaying both anti-phase and in-phase relationships with the northern hemisphere records. This observation is unique in the Western Pacific tropical region, mostly likely because the Saripa Cave is located within the region of the latitudinally migrating Intertropical Convergence Zone (ITCZ), whereby the rainfall seasons may have changed through time depending on the mean latitude of the ITCZ. The Saripa Cave stalagmite contains textural laminae, which are here interpreted as a record of rapid environmental changes, possibly caused by volcanic eruptions at around 22.55 ka and 44.73 ka BP. The Bumi Cave record (stalagmite BC-09-3-C), on the other hand, presents very little variation in stable isotope and trace element compositions between 26.8 ka and 18.5 ka and does not seem to be influenced by any possible volcanic activity. More detailed future studies investigating millimeter- to submillimeter-scale geochemical time-series constrained by accurate ages in speleothems can be useful in unfolding the effects of eruptions and provide parallel records of climate and sudden environmental changes.

Elemental signatures of Australopithecus africanus teeth reveal seasonal dietary stress.

Reconstructing the detailed dietary behaviour of extinct hominins is challenging1-particularly for a species such as Australopithecus africanus, which has a highly variable dental morphology that suggests a broad diet2,3. The dietary responses of extinct hominins to seasonal fluctuations in food availability are poorly understood, and nursing behaviours even less so; most of the direct information currently available has been obtained from high-resolution trace-element geochemical analysis of Homo sapiens (both modern and fossil), Homo neanderthalensis4 and living apes5. Here we apply high-resolution trace-element analysis to two A.africanus specimens from Sterkfontein Member 4 (South Africa), dated to 2.6-2.1million years ago. Elemental signals indicate that A.africanus infants predominantly consumed breast milk for the first year after birth. A cyclical elemental pattern observed following the nursing sequence-comparable to the seasonal dietary signal that is seen in contemporary wild primates and other mammals-indicates irregular food availability. These results are supported by isotopic evidence for a geographical range that was dominated by nutritionally depauperate areas. Cyclical accumulation of lithium in A.africanus teeth also corroborates the idea that their range was characterized by fluctuating resources, and that they possessed physiological adaptations to this instability. This study provides insights into the dietary cycles and ecological behaviours of A.africanus in response to food availability, including the potential cyclical resurgence of milk intake during times of nutritional challenge (as observed in modern wild orangutans5). The geochemical findings for these teeth reinforce the unique place of A.africanus in the fossil record, and indicate dietary stress in specimens that date to shortly before the extinction of Australopithecus in South Africa about two million years ago.

High-resolution trace element distributions and models of trace element diffusion in enamel of Late Neolithic/Early Chalcolithic human molars from the Rioja Alavesa region (north-central Spain) help to separate biogenic from diagenetic trends

High resolution in situ trace element μXRF maps and profiles were measured on the enamel exposed in cross sections through archaeological human permanent molars from seven Late Neolithic/Early Chalcolithic funerary caves and megalithic graves of north-central Iberia. Changes in concentrations of Fe, Zn and Sr in inward direction into the enamel shed light on diagenetic and endogenous trace element concentrations in archaeological tooth enamel. Most of these profiles resemble sigmoid-shaped leaching profiles, suggesting that a combination of diffusion and advection processes govern the uptake of trace elements into the enamel from pore fluids on the outside of the tooth and in the more porous dentine. The present study shows how diffusion-advection (DA) models can be fitted to these trace element profiles to explain changes in trace element concentrations that happen during diagenesis. DA models explain a major part of the variation observed in leaching profiles into the enamel and can be used to reconstruct endogenous trace element concentrations, leaching times and leaching depth as well as trace element concentrations in ambient pore water during diagenesis. Models of trace element leaching together with trace element mapping reveal that Fe, Zn and Sr concentrations consistently increase during diagenesis, regardless of the type of burial site (i.e. funerary caves vs. megalithic graves). Profiles of Pb concentrations show much smaller concentration gradients, causing DA model fitting to be less accurate. Modelled leaching depths of 300–400 μm warrant a careful approach when sampling for endogenous archaeological tooth enamel for trace element and stable isotope analysis. Results also show that it is possible to reconstruct endogenous trace element concentrations from these samples, even without applying pretreatment procedures, because leaching of trace elements into the enamel often remains limited to the outer 300–400 μm of the enamel on archaeological timescales. Modelled leaching times are about ten times lower than the age of the samples, suggesting that the rate of trace element leaching into tooth enamel slows down or even halts during the burial period.

Characterizing the Eemian-Weichselian transition in northwestern Europe with three multiproxy speleothem archives from the Belgian Han-sur-Lesse and Remouchamps cave systems

Interglacial to glacial transitions represent the most drastic turnovers in the Quaternary climate system. Yet, millennial-scaled climate variability and stochastic internal variability that result in (inter)glacial transitions remain poorly understood. Here, three speleothems from two different cave systems in Belgium are investigated to characterize the Eemian to early Weichselian transition. The speleothems show high reproducibility for δ13C, interpreted as a proxy for past vegetation activity, controlled by type of vegetation above the cave. All three speleothems show a drastic increase in δ13C between 118 and 117 ka, reflecting a rapid change in vegetation from last interglacial temperate tree species towards glacial open-grass vegetation. This transition shows a strong affinity with the Late Eemian Aridity Pulse (LEAP) at 118 ± 1 ka, previously identified in pollen records from Western Germany. An age of 117.7 ± 0.5 ka is determined for the start of this transition in the Belgian speleothems. The speleothem records show a distinct transition in the proxies between Eemian optimum conditions and increased variability during the glacial inception and therefore the Eemian-Weichselian transition is set at 117.7 ± 0.5 ka in the speleothem records. High-resolution trace element analysis shows that the transition is initiated by a cooling pulse followed by a decrease in precipitation. Through comparison with other archives, including North-Atlantic sedimentary records, it is proposed that the transition at 117.7 ka constitutes an internal climate response caused by a substantial input of freshwater from degraded ice-sheets by the end of the Eemian (∼120-118 ka).

Trace Element Mapping of Copper- and Zinc-Rich Black Smoker Chimneys from Brothers Volcano, Kermadec Arc, Using Synchrotron Radiation XFM and LA-ICP-MS

High-resolution trace element mapping (2 µm beam) was performed by synchrotron radiation X-ray fluorescence microscopy (SXFM) on Cu- and Zn-rich chimneys from Brothers volcano, Kermadec arc. The maps cover 84- to 136-mm2 cross sections of the inner chimney walls and document the distribution of Fe, Cu, Zn, As, Se, Sr, Pb ± Ga, Au, Bi, and U. Comparative element maps were generated by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) at a lower resolution (47 µm beam), which additionally measured Co, Ni, Mo, Ag, Cd, In, Sn, Sb, Ba, Au, Tl ± V, Te, and Bi. In two Zn-rich chimneys, Cu distribution varies from Cu-bearing sphalerite with chalcopyrite disease to distinct chalcopyrite-lined channels, implying a progression of chalcopyrite replacement of sphalerite. Conversely, the two Cu-rich chimneys have different styles of massive chalcopyrite lining their conduits. The first displays elongate chalcopyrite grains that radiate into and infill the conduit; these radial grains may be related to decreased fluid flow during sealing of the chimney at both its top and bottom. The second style involves multiple, concentric chalcopyrite laminations (0.25–1 mm) inside the conduit, which progressively narrowed the orifice as they were deposited. Fine (15–40 µm) trace element rings are revealed within and between laminations that exhibit variable contents and distributions of Co, Ni, Zn, As, Se, Mo, Ag, Cd, Sn, Te, Au, Tl, Pb, Bi, and U. The presence of U in the rings specifically indicates seawater ingress into the chimney interior despite it vigorously discharging 274°C fluids at the time of sampling. During these periodic seawater incursions, rapidly changing chemical gradients within the chimney wall induce the instantaneous precipitation of metals from the vent fluid. Thus, the trace element rings are a proxy for the secular evolution of vent fluid compositions. We compared enrichment factors of trace element rings to those of fumarole condensates studied at subaerial arc and rift volcanoes and molten S pooled atop a submarine back-arc volcano. Our enrichment factors show remarkable consistency with the other volcanoes and indicate Au, Te, Bi, Cu, Ag, and Se in Brothers’ chimneys were magmatically derived.

Zircon Macrocrysts from the Drybones Bay Kimberlite Pipe (Northwest Territories, Canada): A High-Resolution Trace Element and Geochronological Study

Zircon macrocrysts in (sub)volcanic silica-undersaturated rocks are an important source of information about mantle processes and their relative timing with respect to magmatism. The present work describes variations in trace element (Sc, Ti, Y, Nb, lanthanides, Hf, Ta, Pb, Th, and U) and isotopic (U-Pb) composition of zircon from the Drybones Bay kimberlite, Northwest Territories, Canada. These data were acquired at a spatial resolution of ≤100 µm and correlated to the internal characteristics of macrocrysts (imaged using cathodoluminescence, CL). Six types of zircon were distinguished on the basis of its luminescence characteristics, with the majority of grains exhibiting more than one type of CL response. The oscillatory-zoned core and growth sectors of Drybones Bay zircon show consistent variations in rare-earth elements (REE), Hf, Th, and U. Their chondrite-normalized REE patterns are typical of macrocrystic zircon and exhibit extreme enrichment in heavy lanthanides and a positive Ce anomaly. Their Ti content decreases slightly from the core into growth sectors, but the Ti-in-zircon thermometry gives overlapping average crystallization temperatures (820 ± 26 °C to 781 ± 19 °C, respectively). There is no trace element or CL evidence for Pb loss or other forms of chemical re-equilibration. All distinct zircon types are concordant and give a U-Pb age of 445.6 ± 0.8 Ma. We interpret the examined macrocrysts as products of interaction between a shallow (<100 km) mantle source and transient kimberlitic melt.

Tracking plumbing system dynamics at the Campi Flegrei caldera, Italy: High-resolution trace element mapping of the Astroni crystal cargo

The Campi Flegrei caldera (southern Italy) is one of the most hazardous volcanic systems on Earth, having produced >60 eruptions in the past 15 ka. The caldera remains active and its potential for future eruptions is high, posing a danger to the dense population living nearby. Despite this, our understanding of pre-eruptive processes and the architecture of the sub-volcanic system are poorly constrained. Here, we combine established petrological techniques, geothermobarometric evaluation, and high-resolution trace element crystal mapping, to present a multifaceted, coherent reconstruction of the complex pre-eruptive dynamics and eruption timescales of Astroni volcano located in the eastern sector of Campi Flegrei caldera. The Astroni volcano is an important case study for investigating plumbing system processes and dynamics at Campi Flegrei caldera because it produced the most recent (ca. 4 ka ago) Plinian eruption within the caldera (Astroni 6); current long-term forecasting studies postulate that a similar sized event in this location is a probable future scenario.Geothermobarometric results indicate interaction between an evolved, shallow magma chamber, and a less evolved, deeper pocket of magma, in agreement with previous studies focused on the Astroni 6 eruption products. In addition, a range of textural and trace element zoning patterns point to a complex evolution of both magmas prior to their subsequent interaction. High-resolution trace element crystal maps reveal discrete zonations in compatible elements. These zonations, combined with knowledge of K-feldspar growth rates, highlight a recharge event in the shallow plumbing system a few hours to days before the Astroni 6 eruption.

Reconstruction of late Holocene autumn/winter precipitation variability in SW Romania from a high-resolution speleothem trace element record

We present the first high-resolution trace element (Mg/Ca, Sr/Ca, Ba/Ca) record from a stalagmite in southwestern Romania covering the last 3.6 ka, which provides the potential for quantitative climate reconstruction. Precise age control is based on three independent dating methods, in particular for the last 250 yr, where chemical lamina counting is combined with the identification of the 20th century radiocarbon bomb peak and 230Th/U dating. Long-term cave monitoring and model simulations of drip water and speleothem elemental variability indicate that precipitation-related processes are the main drivers of speleothem Mg/Ca ratios. Calibration against instrumental climate data shows a significant anti-correlation of speleothem Mg/Ca ratios with autumn/winter (October to March) precipitation (r = −0.61, p < 0.01), which is statistically robust when considering age uncertainties and auto-correlation. This relationship is used to develop a quantitative reconstruction of autumn/winter precipitation.During the late Holocene, our data suggest a heterogeneous pattern of past regional winter hydroclimate in the Carpathian/Balkan realm, along with intermittent weakening of the dominant influence of North Atlantic forcing. In agreement with other regional paleo-hydrological reconstructions, the observed variability reveals periodically occurring strong NW–SE hydro-climate gradients. We hypothesize, that this pattern is caused by shifts of the eastern edge of the area of influence of the NAO across central-eastern Europe due to the confluence of North Atlantic forcing, and other climatic features such as the East Atlantic/Western Russia (EAWR) pattern.

Volcanic crystals as time capsules of eruption history

Crystals formed prior to a volcanic event can provide evidence of processes leading to and timing of eruptions. Clinopyroxene is common in basaltic to intermediate volcanoes, however, its ability as a recorder of pre-eruptive histories has remained comparatively underexplored. Here we show that novel high-resolution trace element images of clinopyroxene track eruption triggers and timescales at Mount Etna (Sicily, Italy). Chromium (Cr) distribution in clinopyroxene from 1974 to 2014 eruptions reveals punctuated episodes of intrusion of primitive magma at depth. Magma mixing efficiently triggered volcanism (success rate up to 90%), within only 2 weeks of arrival of mafic intrusions. Clinopyroxene zonations distinguish between injections of mafic magma and regular recharges with more evolved magma, which often fail to tip the system to erupt. High Cr zonations can therefore be used to reconstruct past eruptions and inform responses to geophysical signals of volcano unrest, potentially offering an additional approach to volcano hazard monitoring.

Tropical seasonality in the late Campanian (late Cretaceous): Comparison between multiproxy records from three bivalve taxa from Oman

Geochemical proxy records from calcite shells of bivalves constitute an important archive for the reconstruction of palaeoenvironmental conditions on sub-annual timescales. However, the incorporation of these trace element and stable isotope proxies into the shell is influenced by a multitude of physiological and environmental factors that need to be disentangled to enable reliable reconstruction of palaeoclimate and palaeoenvironment. In this study, records of multiple proxies in three bivalve taxa from the same late Campanian locality in Oman are used to study the expression of various geochemical proxies in relation to each other and to the palaeoenvironment. Micro-X-Ray Fluorescence mapping allows the localization, discussion and evasion of diagenetically altered parts of the fossil shells. X-Ray Fluorescence line scanning calibrated with Laser Ablation Inductively Coupled Plasma Mass Spectrometry is used to measure trace element profiles through well-preserved calcitic parts of the shells. Records of stable carbon and oxygen isotope ratios of shell calcite are combined with these high-resolution trace element concentration profiles to study sub-annual variations in shell chemistry and reconstruct changes in the palaeoenvironment of the bivalves on a seasonal scale. Spectral analysis routines are used to detect cyclicity in stable isotope (δ18O and δ13C) and trace element (Mg/Ca, Sr/Ca, S/Ca and Zn/Ca) records. Differences in seasonal expression between these chemical proxies and between individual shells are discussed in terms of the relative influence of palaeoenvironment and potential species-specific physiological effects. Stable oxygen isotope ratios between shells suggest a local palaeotemperature seasonality of 8°C around an annual mean of 28°C, with the shell of the rudistid Torreites sanchezi milovanovici yielding slightly higher average temperatures. The discussion of the application of various Mg/Ca palaeotemperature calibrations on Mg/Ca records in these bivalve species emphasizes the complexity of using trace element proxies in extinct bivalve species. It shows that long-term changes in Mg/Ca ratios in ocean water need to be taken into account and that Mg/Ca ratios in bivalves might be influenced by vital effects. Sr/Ca and S/Ca ratios in these fossil taxa are likely controlled by growth and metabolic rates of the shell, although an influence of local salinity on strontium-to-calcium ratios cannot be excluded. Sub-annual variations in zinc concentrations in shell calcite may reflect seasonal variations in palaeoproductivity and redox conditions in the water column.

Holocene climate variability in Central Germany and a potential link to the polar North Atlantic: A replicated record from three coeval speleothems

Here, we present high-resolution trace element and stable isotope records from three coeval Holocene stalagmites from the Herbstlabyrinth cave system, Central Germany. All stalagmites were precisely dated using MC-ICPMS 230Th/U-dating. One stalagmite started to grow at 13.62 ± 0.13 ka BP, covering the late Glacial; the other two speleothems started to grow at 11.13 ± 0.08 and 10.26 ± 0.08 ka BP, respectively. The combined record covers the entire Holocene. The interpretation of the different climate proxies is supported by data from a detailed cave monitoring programme. Cold conditions during the Younger Dryas are reflected by intermittent stalagmite growth at the Herbstlabyrinth. The δ18O records are in general agreement with the NGRIP δ18O record on millennial time scales indicating that speleothem δ18O values at the Herbstlabyrinth reflect large-scale climate variability in the North Atlantic area. The 8.2 ka event is clearly visible as a pronounced negative excursion in the δ18O records. In all other proxies, it is not reflected as a major excursion. Correlation and principal component analysis enable us to disentangle the various processes affecting the stable isotope and trace element signals. Phases with higher P, Ba and U concentrations and more negative δ13C values are interpreted as reflecting more productive vegetation above the cave. The negative correlation of Mg with P, Ba and U and the positive correlation with δ13C indicate more recharge during phases of more productive vegetation, probably because of increased rainfall. The majority of the observed phases of reduced vegetation productivity and drier climate coincide with cooler periods in the polar North Atlantic as reflected by a higher abundance of hematite-stained grains (i.e. the Bond events), suggesting a close relationship between terrestrial climate in Central Europe and the polar North Atlantic.

High spatial resolution trace element determination of geological samples by laser ablation quadrupole plasma mass spectrometry: implications for glass analysis in volcanic products

Increasing the spatial resolution of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a challenge in microanalysis of geological samples. Smaller sizes for the laser beam will allow for (1) high resolution determination of trace element compositions, (2) accurate estimation of crystal/melt partition coefficients, (3) detailed characterization of diffusion profiles, and (4) analysis of fine volcanic glasses. Here, we report about the figures of merit for LA-ICP Quadrupole MS down to a spatial resolution of 5 {\mu}m. This study highlights the possibility to achieve suitable limits of detection, accuracy and precision for geological samples even at spatial resolutions of the order of 5 {\mu}m. At a beam size of 15 {\mu}m precision (measured as one sigma) and accuracy (expressed as relative deviation from the reference value) are of the order of 10%. At a smaller beam size of 8um, precision decreases to 15% for concentration above 1.7 {\mu}g g-1. As the beam size is decreased to ~5 {\mu}m, precision declines to about 15% and 20% for concentrations above 10 {\mu}g g-1 using 42Ca and 29Si as internal standard, respectively. Accuracy is better or equal to 10% and 13 % at beam sizes of 15 and 10 {\mu}m respectively. When the spatial resolution is increased to 8 {\mu}m, accuracy remains better than 15% and 20% for 42Ca and 29Si as internal standard, respectively. We employed such high-resolution techniques to volcanic glasses in ash particles of the 2010 Eyjafjallaj\"okull eruption. Our results are well consistent with the previously reported data obtained at lower spatial resolution, supporting the reliability of the method.

High-resolution trace element and stable/radiogenic isotope profiles of late Pleistocene to Holocene speleothems from Dim Cave, SW Turkey

Multiple climate-sensitive trace element/Ca and stable isotope (O and C) profiles derived from Dim Cave speleothems (S-SW Turkey) provide evidence of climatic changes and define a series of palaeohydrological conditions for the period ~10–90kyr. Dim Cave speleothem Mg/Ca, Sr/Ca, U/Ca, Ba/Ca, and Y/Ca ratios demonstrate similar patterns over glacial–interglacial scales, in agreement with δ18O and δ13C records. Three episodes of more positive moisture balance (71–63kyr, 51–40kyr, and 18–10kyr) were observed based on Y/Ca (and to a lesser extent Zr/Ca), 87Sr/86Sr ratios, calcite micromorphology, and growth rates. Increasing concentrations of Y, Zr (and U) and elevated 87Sr/86Sr ratios are attributed to enhanced levels of terrestrial input during these periods. Correlations between δ13C, δ18O and Mg/Ca during 40–18kyr (corresponding with the lowest growth rate of ~0.8mm/kyr), 63–51, and 80–71kyr (relatively low growth rates), as well as co-varying and enhanced Mg/Ca, Sr/Ca, and to a lesser extent Ba/Ca, ratios point to the prior calcite precipitation, wall rock interaction, and preferential dolomite dissolution over calcite in the host dolomitic limestone during these periods. This relationship suggests that water–rock interactions are maximised during episodes of slower drip rates of water through the karst under drier conditions. Chondrite-normalised rare earth element and yttrium (REY) patterns of the stalagmites reveal seawater signatures closely linked to the dolomitic limestone. Excluding the aragonite formation during ~80–75kyr, which is an autogenic effect, trace element/Ca ratios appear to respond to millennial scale global cooling periods such as Heinrich events.

The major and trace element glass compositions of the productive Mediterranean volcanic sources: tools for correlating distal tephra layers in and around Europe

The increasing application of cryptotephra studies is leading the identification of new tephra marker layers the sources of which in many cases may not be known or may be ambiguous. In this contribution, we discuss the controls on tephra geochemistry in the context of establishing the provenance of an unknown tephra layer. We use the RESET database (https://c14.arch.ox.ac.uk), which contains major and trace element data for a number of European silicic tephra erupted in the period 100ka to ca 10ka, to define new and modify existing tectonic setting discrimination diagrams for use with volcanic glass analyses. Bivariate plots of the elements Rb, Nb, Ta, Y and Th and K2O, SiO2, FeO and MgO can be used to identify tephra from different tectonic settings. New, detailed glass chemistry shows that tephra from the productive Neapolitan volcanic centres, Somma-Vesuvius (22–4ka activity), Campi Flegrei (60–15ka) and Ischia (75–20ka), can be separated using major elements, CaO–SiO2, Na2O/K2O–CaO and CaO–MgO. In each of these centres, the tephrostratigraphic record is characterized by the repeated occurrence of similar glass compositions, punctuated by significant changes in magma chemistry. The glass compositions of successive eruptions from Campi Flegrei are similar but there is a significant change in the composition following the Campanian Ignimbrite, and there are comparable compositional changes at Ischia following the Monte Epomeo Green Tuff eruption and at Somma-Vesuvius following the Verdoline event. Distinguishing different tephras from a single volcanic centre is more problematic, and in some instances even impossible, without good chronological and stratigraphic control and/or high-resolution trace element glass data. At Somma-Vesuvius certain major elements can be used to separate glasses from the major chronological phases (Group 1 – Pomici di Base and Verdoline; Group 2 – Mercato and Avellino), but separating tephras within a single group on the basis of glass composition can be problematic.