A sequence of temporally separated element peaks; the fingerprint of a biogeochemical event initiated by sedimentary exhalative (SEDEX) brine expulsion

<p>The Ireviken Biogeochemical Event (IBE) consists of the Ireviken Extinction Event (IEE) and is superseded by the Ireviken positive d13Ccarb Excursion (ICIE). During the Ireviken Extinction Event 80% of the conodont species and 50% of the trilobite species went extinct and Acritarchs, chitinozoans, graptolites, corals, and brachiopods communities were severely affected as well. Currently there are no indications that the Ireviken Biogeochemical event can be linked to a LIP or a bolide impact which are the usual triggers for most known biogeochemical events. The IBE has been tentatively linked to SEDEX brine expulsion, however convincing high-resolution data supporting the SEDEX brine expulsion theory was lacking.</p><p>The Altajme core from Gotland Sweden covers the entirety of the Ireviken Biogeochemical Event and using an ITRAX XRF core scanner  we were able to create a new dataset with a 1cm(~150-400 yr.) resolution. This dataset enables us to shed new light on the origin of the IBE and serves as a template for a cyclostratigraphic age model (using the detrital proxies of Ti and Al) which puts the IBE within a precise temporal framework.</p><p>The occurrence of peak values of Nb, Mn, Cu, Ba, Pb, Zn, As, Ag in the Altajme core follows the temporal sequence of element peaks which is characteristic for the cooling of a hydrothermal system. A Pb:Zn ratio of >1 and low Cu/(Zn+Pb) ratio categorises the hydrothermal system as being the sedimentary exhalative (SEDEX) brine expulsion type system. Through these results we can undoubtedly link the Ireviken Biogeochemical Event to a SEDEX brine expulsion. Numerous SEDEX style ore deposits of Proterozoic to Cenozoic age are known, but it has been difficult to connect them with similarly aged biogeochemical events.  This study demonstrates that through extremely high resolution XRF/element data we can observe the far-field signature of a SEDEX brine expulsion and thus showing us the way to recognize more biogeochemical events triggered by SEDEX brine expulsions. </p>

Application of Corrected Methods for High-Resolution XRF Core Scanning Elements in Lake Sediments

Contemporary studies emphasize theoretical and analytical aspects of monitoring water quality within lacustrine settings. The X-ray fluorescence (XRF) core scanner provides the most rapid, non-destructive high-resolution elemental measurements for unprocessed sediments. However, the analytical precision of measured elemental composition may be offset due to water content and inhomogeneities in the physical properties of the sediment. A range of calibration approaches developed specifically for converting XRF scanning intensities to element fractions has been made available. Here, two lake sediment-cores retrieved from southwest China were used to evaluate the performance of various calibration methods. In particular, the influence of sediment properties on XRF scanning intensities was assessed by redundancy analyses (RDA) and the generalized additive model (GAM). The results demonstrate that for fine-grained sediments, the impact of grain size results in only minor deviations in the XRF scanning intensities. Water content of the lake sediment was shown to be the most important factor influencing the XRF scanning intensities, especially for light elements (e.g., Al to Fe). Significant decreases in XRF scanning intensities may occur when sediment water content is greater than 47%. We recommend testing the element fractions obtained via conventional techniques throughout the core and applying the multivariate log-ratio calibration for high-resolution XRF scanning elements within lake sediments.

Artificial intelligence for discrimination of sediment facies based on high-resolution elemental and colour data from coastal sediments of the East Frisian Wadden Sea, Germany

<p>Sediment facies provide vital information for the reconstruction of past environmental variability. Due to rising interest for paleoclimate data, sediment surveys are continually growing in importance as well as the amount of sediments to be discriminated into different facies. The conventional approach is to macroscopically determine sediment structure and colour and combine them with physical and chemical information - a time-consuming task heavily relying on the experience of the scientist in charge. Today, rapidly generated and high-resolution multiproxy sediment parameters are readily available from down-core scanning techniques and provide qualitative or even quantitative physical and chemical sediment properties. In 2016, an interdisciplinary research project WASA (Wadden Sea Archive) was launched to investigate palaeo-landscapes and environments of the Wadden Sea. The project has recovered 92 up to 5 m long sediment cores from the tidal flats, channels and off-shore around the island of Norderney (East Frisian Wadden Sea, Germany). Their facies were described by the conventional approach into glacioflucial sands, moraine, peat, tidal deposits, shoreface sediments, etc. In this study, those sediments were scanned by a micro X-ray fluorescence (µ-XRF) core scanner to obtain high-resolution records of multi-elemental data (2000 µm) and optical images (47 µm). Here we propose a supervised machine-learning application for the discrimination of sediment facies using these scanning data. Thus, the invested time and the potential bias common for the conventional approach can be reduced considerably. We expect that our approach will contribute to developing a more comprehensive and time-efficient automatic sediment facies discrimination.</p><p>Keywords: the Wadden Sea, µ-XRF core scanning, machine-learning, sediment facies discrimination</p>

Obliquity pacing of Antarctic glaciations during the Quaternary

<p>Obliquity pacing of Antarctic glaciations during the Quaternary</p><p>The frequency of Antarctic glaciations during the Quaternary are not well understood. Benthic oxygen isotope records provide evidence for eccentricity paced global ice volume changes since c. 800 000 years and the ice core records (such as EPICA) also appear to have 100 000 year cycles over the last 800 000 years. However, the benthic oxygen isotope records are a global average – not an Antarctic record. Quaternary, sedimentary records proximal to the ice margin (such as the ANDRILL AND-1B record) are needed to understand better the recent glacial history of Antarctica. </p><p>Here we present results from the 6.21 m long, NBP03-01A-20PCA sedimentary record which was recovered from the outer continental margin of the Ross Embayment.</p><p>Sediments comprise mud with numerous clasts and paleomagnetic analyses revealed magnetic reversals at 4.21 m, 5.74 m, and 5.85 m depth. These reversals are correlated with C1n-C1r.1r-C1r.1n-C1r.2r geomagnetic reversals which have corresponding ages of 773 ka, 990 ka, and 1070 ka. </p><p>Time series analysis of continuous Anhysteretic Remanent Magnetisation (ARM) data, which are controlled primarily by the concentration of magnetic minerals, revealed strong obliquity paced cycles between c. 800 ka and 350 ka. The presence of obliquity cycles prompted us to carry out core scanning XRF and grain size analyses. The archive half was scanned in a itrax XRF core scanner at the Marine and Geology Repository at Oregon State University and high density grain size analyses were conducted at the University of Otago. </p><p>We identified obliquity paced cycles in the titanium elemental data over the same period which we suggest represent variations in the terrigenous material in the core. Weaker obliquity cycles are also present in the >2mm grain size fraction which we suggest is controlled by the proximity of the ice shelf front. </p><p>We suggest that the presence of obliquity paced cycles in our data series indicate that the Ross Ice Shelf calving line advance and retreat cycles were paced with obliquity until at least 350 ka and that the mid-Pleistocene transition occurred later in the Southern Hemisphere than in the North. </p>

Comparison and correction of element measurements using qualitative and quantitative X-ray fluorescence in lacustrine sediments: A case study of Lake Hurleg

Using an X-ray Fluorescence (XRF) core scanner with nondestructive and successive, the chemistry features of lacustrine sediment can be measured directly. This method of XRF core scanner measurements has been widely applied to core sediment analysis but uncertain of the precision and accuracy. Comparison of intensities obtained by XRF core scanning and the concentration measured by conventional X-ray Fluorescence, indicates effects of physical properties varied from different elements on elemental intensities in the lacustrine sediments of a core from Lake Hurleg in the northeastern Tibetan Plateau. Correlation among elements Ti and Sr between the two measurement methods of the XRF and the conventional XRF is high. Using the intensity of Cl as an indicator of water content, the element intensities of Ti and Sr in the core samples is corrected. But the correlation coefficients of Ti and Sr is litter raised. The results show that XRF core scanning is a very useful tool for measuring element concentration in sediments particularly for high intensities elements.