Multielement Imaging Reveals the Diagenetic Features and Varied Water Redox Conditions of a Lacustrine Dolomite Nodule

The genesis of dolostone has long been puzzling for more than two centuries. Although much work has been done on investigating the process of dolomitization, little emphasis has been put on examining the diagenetic water redox condition with the wealthy geochemical information preserved in primary dolomite, which is believed to archive the aqueous environment as well as biotic and/or abiotic effects during formation. In situ interpretation with high resolution is a prerequisite in refined research of dolomite. Here, we reported the multielement imaging results of a lacustrine dolomite nodule with the host black shale from the Songliao Basin, northeast of China. Micro X-ray fluorescence (μ-XRF) with a spatial resolution down to 10 μm was used for in situ scanning. Two key parameter settings of the μ-XRF, including single-point exposure time and spatial resolution, were optimized to achieve a better result in a reasonable scanning time scale. The final imaging data graphically revealed dynamic variation of elemental distributions, including elements enriched in dolomite (e.g., Ca, Mg, Fe, and Mn), clastic quartz (Si), and clay minerals (e.g., Al and K) and redox-sensitive trace elements (e.g., Cr, Mo, V, and U). The well-preserved laminated structures inside the nodule and the features with a magnesium-rich core wrapped with an iron-concentric outer layer and a manganese-concentric shell together indicated its primary form as dolomite and a gradual transformation into ankerite as well as manganese-ankerite. The elemental variation indicates a varied bottom water redox condition, which involved from sulfidic to ferruginous and manganous zones. Here, we propose that the intermittent supplies of sulfate and Fe-/Mn-oxidized minerals interrupting the black shale deposition while favoring dolomitization might be brought by the oxidized and salted seawater. And this lacustrine dolomite is expected to be a potential fingerprint mineral in tracking the seawater intrusions to the Songliao Basin which happened 91 million years ago.

Evolutionary Process from Mockina bidentata to Parvigondolella andrusovi: Evidence from the Pizzo Mondello Section, Sicily, Italy

During their last phase of evolution, the pectiniform conodont elements manifested an evident trend of simplification and miniaturization. This phase started from the late Norian (Sevatian) in the Late Triassic and the evolutionary process of genus Mockina to Parvigondolella, in particular between Mockina bidentata and Parvigondolella andrusovi, is one of the most significant examples. Parvigondolella has been reported worldwide since it was first described in the early 1970s. However, it has recently been suggested that genus Parvigondolella is an ecostratigraphic morphotype of genus Mockina, and thus a phenotype controlled by the environmental conditions, and not an independent taxon. In the Pizzo Mondello Section (Sicily, Italy), transitional forms between M. bidentata and P. andrusovi have been found at different evolutionary stages. We have investigated the oceanic conditions at the time by using redox-sensitive elements (Mn, Fe, V, Cr, and Ni) and seawater temperatures from biogenetic δ18Ophos to understand the possible environmental influences on the phylogenetic evolution between Mockina and Parvigondolella. The geochemical and isotope analyses indicate that the redox condition and temperature were stable during the evolution of genus Parvigondolella in Pizzo Mondello, confirming that genus Parvigondolella is a real taxon and not a phenotype. A new conodont species named Parvigondolella ciarapicae n. sp. is described here for the first time.

Merging tTEM data and borehole lithological information to generate hydrogeologic structural models and redox conditions through Direct Sampling

<p>Detailed 3D structural information of the subsurface is fundamental for the development of both hydrological and geochemical models. This structural information is often derived from geophysical mapping results. Some parts of a catchments areas are however inaccessible for the geophysical mapping or might suffer from low data quality, which results in information gaps. Multipoint statistics can be used to remediate these data gaps and incorporate uncertainty in the construction of the hydrogeological models. This results in an ensemble of plausible 3D hydrogeological models.</p><p>This project focusses on nitrate retention mapping. The approach taken is to start from the resistivity models that are obtained from the tTEM measurement campaign. These resistivity datasets are combined with borehole lithological data from the Danish national well-database in an automated procedure that estimates resistivity-to sand/clay translator functions. This results in a clay fraction – resistivity data pair for every point in the subsurface where resistivity data is collected. These clay fraction – resistivity data pairs are converted to discrete hydrogeological units through clustering. This procedure is performed because the groundwater model that uses the end-product of this workflow, uses hydrogeological units rather than resistivity values or clay fractions to define zones of similar hydrogeological behavior.</p><p>Direct sampling is used to go from the cluster information obtained at the resistivity model location to fill out the full model volume and generate multiple plausible model realizations. This method allows, at the same time, for incorporating uncertainty through separation of data into a hard  data set for the cluster information with higher probability, and a soft data set for the cluster information with lower probability. Since the redox conditions in the subsurface are related to the hydrogeological conditions, we are using this method to co-simulate hydrogeological units and redox conditions by merging the cluster training dataset with a redox condition training dataset that is constructed based on the cluster dataset and hydrogeochemical samples that are collected across the catchment. We combine the three training images: resistivity, cluster and redox condition, to simultaneous simulate the three variables in each grid point as a vector, instead of simulating them as separate variables.  The resulting set of  3D hydrogeologic structural models and redox condition models retains the complex geostatistical spatial relationships that can exists between the different type of datasets within the training image, making them suitable for nitrate retention modeling at catchment scale.</p>

In situ filamentous communities from the Ediacaran (approx. 563 Ma) of Brazil

Precambrian filamentous microfossils are common and diverse. Nevertheless, their taxonomic assignment can be difficult owing to their overall simple shapes typically lacking in diagnostic features. Here, we report in situ communities of well-preserved, large filamentous impressions from the Ediacaran Itajaí Basin ( ca 563 Ma) of Brazil. The filaments are uniserial (unbranched) and can reach up to 200 µm in width and up to 44 mm in length. They occur as both densely packed or sparsely populated surfaces, and typically show a consistent orientation. Although simple in shape, their preferred orientation suggests they were tethered to the seafloor, and their overall flexibility (e.g. bent, folded and twisted) supports a biological (rather than sedimentary) affinity. Biometric comparisons with modern filamentous groups further support their biological affinity, suggesting links with either large sulfide-oxidizing bacteria (SOB) or eukaryotes. Other morphological and palaeoecological characteristics further corroborates their similarities with modern large filamentous SOB. Their widespread occurrence and association with complex Ediacaran macrobiota (e.g. frondose organisms, Palaeopascichnus ) suggest that they probably played an important role in the ecological dynamics of these early benthic communities by providing firm substrates for metazoans to inhabit. It is further hypothesized that the dynamic redox condition in the latest Ediacaran, with the non-continuous rise in oxygen concentration and periods of hypoxia, may have created ideal conditions for SOB to thrive.

Transient release of radioactive iodine from the fission of UF4 in 2LiF–BeF2 salt

The reaction between hot atoms of fission product iodine causes its partial release and is affected by the redox condition of FLiBe salt.

Vanadium micro-XANES determination of oxygen fugacity in olivine-hosted glass inclusion and groundmass glasses of martian primitive shergottite Yamato 980459

The redox condition of magma determines the stability and composition of crystallizing and volatile phases in martian meteorites, reflecting the evolution of the martian interior. In the current study, direct analyses on the oxidation states of V, Cr, and Fe were performed based on the X-ray absorption near-edge structure (XANES) measurements equipped with a micro-sized X-ray beam. We first applied the micro-XANES (μ-XANES) technique to the olivine-hosted glass inclusion and groundmass glass of martian meteorite Yamato 980459 (Y98), which is interpreted as representing a primary melt composition. Mass-balance calculations and XANES spectra comparisons indicated that, while chromite and pyroxene affected Cr and Fe K-edge XANES spectra, the contribution of these minerals was minimal for V. The pre-edge peak intensity of V K-edge XANES enabled the estimation of the oxygen fugacity for inclusion and groundmass glasses. The calculated oxygen fugacity (fO2) of the glass inclusions was near the Iron-Wüstite (IW) buffer (IW-0.07 ± 0.32) for the glass inclusion, whereas it was 0.9 log units more oxidized (IW+0.93 ± 0.56) for the groundmass glasses. This result suggests that the redox condition of the parent magma of Y98 evolved during magma ascent and emplacement. Since Y98 is interpreted to have evolved in a closed system, our finding suggests that fractional crystallization and/or ascent of magma potentially induces the fO2 increase. This study shows that the μ-XANES technique enables us to determine the fO2 by only measuring a single phase of glassy compounds, and thus, it is useful to discuss the redox condition of volcanic rocks even if they do not crystallize out several equilibrium phases of minerals.