Synchrotron Rapid Scanning X-ray Fluorescence Research Articles

Decimeter-scale mapping of carbonate-controlled trace element distribution in Neoarchean cuspate stromatolites

Ancient stromatolites can provide key insights into the early evolution of life on Earth. Neoarchean fenestrate stromatolites from the ∼2520 Ma Upper Nauga Formation (Transvaal Supergroup, South Africa) preserve cuspate morphologies. They possess clearly delineated support and drape structures interpreted as dolomitized microbial mat material. Petrographic observations show that the biogenic structures are composed of planar-s to non-planar ferroan dolomite, encased in ferroan calcite, including herringbone calcite textures. The cuspate stromatolites were analyzed using Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) and more conventional techniques to determine: (i) whether element distributions could be distinguished in ancient stromatolites at both cm to dm scales, (ii) whether element distributions show variation between biogenic and abiogenic textures, and (iii) the sample’s paragenesis. The distributions of Ca, Fe, Mn, Pb, Cu, As, Br, Al, Si, P, and S directly correspond to dolomitized stromatolitic structures and show trace element distributions are principally controlled by calcite and dolomite occurrence. Dolomite formation was mainly driven by seawater-derived fluids given the high concentrations of Fe and retention of marine shale-normalized rare earth element and yttrium (REY SN ) patterns, however the spatial association of dolomite to stromatolite structures may reflect microbially-influenced mineral nucleation. Given the complexity of this sample’s paragenetic evolution, trace metal distributions cannot be conclusively tied to specific metabolic pathways, bioaccumulation or passive binding, however, the results show SRS-XRF can be used for quantifiable, spatial, in-situ investigation of ancient microbialites.

Bioturbating animals control the mobility of redox-sensitive trace elements in organic-rich mudstone

Bioturbating animals modify the original mineralogy, porosity, organic content, and fabric of mud, thus affecting the burial diagenetic pathways of potential hydrocarbon source, seal, and reservoir rocks. High-sensitivity, synchrotron rapid scanning X-ray fluorescence elemental mapping reveals that producers of phycosiphoniform burrows systematically partition redox-sensitive trace elements (i.e., Fe, V, Cr, Mn, Co, Ni, Cu, and As) in fine-grained siliciclastic rocks. Systematic differences in organic carbon content (total organic carbon >1.5 wt%) and quality (Δ13Corg~0.6‰) are measured between the burrow core and host sediment. The relative enrichment of redox-sensitive elements in the burrow core does not correlate with significant neo-formation of early diagenetic pyrite (via trace metal pyritization), but is best explained by physical concentration of clay- and silt-sized components. A measured loss (~–15%) of the large-ionic-radius elements Sr and Ba from both burrow halo and core is most likely associated with the release of Sr and Ba to pore waters during biological (in vivo) weathering of silt- to clay-sized lithic components and feldspar. In conclusion, this newly documented effect has significant potential to inform the interpretation of geochemical proxy and rock property data, particularly from shales, where elemental analyses are commonly employed to predict reservoir quality and support paleoenvironmental analysis.

Synchrotron imaging reveals bone healing and remodelling strategies in extinct and extant vertebrates.

Current understanding of bone healing and remodelling strategies in vertebrates has traditionally relied on morphological observations through the histological analysis of thin sections. However, chemical analysis may also be used in such interpretations, as different elements are known to be absorbed and used by bone for different physiological purposes such as growth and healing. These chemical signatures are beyond the detection limit of most laboratory-based analytical techniques (e.g. scanning electron microscopy). However, synchrotron rapid scanning–X-ray fluorescence (SRS–XRF) is an elemental mapping technique that uniquely combines high sensitivity (ppm), excellent sample resolution (20–100 µm) and the ability to scan large specimens (decimetre scale) approximately 3000 times faster than other mapping techniques. Here, we use SRS–XRF combined with microfocus elemental mapping (2–20 µm) to determine the distribution and concentration of trace elements within pathological and normal bone of both extant and extinct archosaurs (Cathartes aura and Allosaurus fragilis). Results reveal discrete chemical inventories within different bone tissue types and preservation modes. Chemical inventories also revealed detail of histological features not observable in thin section, including fine structures within the interface between pathological and normal bone as well as woven texture within pathological tissue.

Leaf metallome preserved over 50 million years.

Large-scale Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) elemental mapping and X-ray absorption spectroscopy are applied here to fossil leaf material from the 50 Mya Green River Formation (USA) in order to improve our understanding of the chemistry of fossilized plant remains. SRS-XRF of fossilized animals has previously shown that bioaccumulated trace metals and sulfur compounds may be preserved in their original distributions and these elements can also act as biomarkers for specific biosynthetic pathways. Similar spatially resolved chemical data for fossilized plants is sparsely represented in the literature despite the multitude of other chemical studies performed. Here, synchrotron data from multiple specimens consistently show that fossil leaves possess chemical inventories consisting of organometallic and organosulfur compounds that: (1) map discretely within the fossils, (2) resolve fine scale biological structures, and (3) are distinct from embedding sedimentary matrices. Additionally, the chemical distributions in fossil leaves are directly comparable to those of extant leaves. This evidence strongly suggests that a significant fraction of the chemical inventory of the examined fossil leaf material is derived from the living organisms and that original bioaccumulated elements have been preserved in situ for 50 million years. Chemical information of this kind has so far been unknown for fossilized plants and could for the first time allow the metallome of extinct flora to be studied.

Synchrotron-based chemical imaging reveals plumage patterns in a 150 million year old early bird

Charles Darwin acknowledged the importance of colour in the natural selection of bird plumage. Colour can indicate age, sex, and diet, as well as play roles in camouflage, mating and establishing territories. Feather and integument colour depend on both chemical and structural characteristics and so melanosome structure and trace metal biomarkers can be used to infer colour and pigment patterns in a range of extant and fossil organisms. In this study, three key specimens of Archaeopteryx were subjected to non-destructive chemical analysis in order to investigate the potential preservation of original pigmentation in early fossil feathers. Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) maps are combined with sulphur X-ray Absorption Near Edge Structure (XANES) spectroscopy to provide the first map of organic sulphur distribution within whole fossils, and demonstrate that organically derived endogenous compounds are present. The distribution of trace-metals and organic sulphur in Archaeopteryx strongly suggests that remnants of endogenous eumelanin pigment have been preserved in the feathers of this iconic fossil. These distributions are used here to predict the complete feather pigment pattern and show that the distal tips and outer vanes of feathers were more heavily pigmented than inner vanes, contrary to recent studies. This pigment adaptation might have impacted upon the structural and mechanical properties of early feathers, steering plumage evolution in Archaeopteryx and other feathered theropod dinosaurs.

Mapping prehistoric ghosts in the synchrotron

The detailed chemical analysis of fossils has the potential to reveal great insight to the composition, preserva- tion and biochemistry of ancient life. Such analyses would ideally identify, quantify, and spatially resolve the chemical composition of preserved bone and soft tissue structures, but also the embedding matrix. Mapping the chemistry of a fos- sil in situ can place constraints on mass transfer between the enclosing matrix and the preserved organism(s), and there- fore aid in distinguishing taphonomic processes from origi- nal chemical zonation remnant within the fossils themselves. Conventional analytical methods, such as scanning electron microscopy (SEM) and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) have serious limitations in this case, primarily, an inability to provide large (i.e., decime- ter) scale chemical maps. Additionally, vacuum chamber size and the need for destructive sampling preclude anal- ysis of large and precious fossil specimens. However, the recent development of Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) at the Stanford Synchrotron Radi- ation Lightsource (SSRL) allows the non-destructive chem- ical analysis and imaging of major, minor, and trace element concentrations of large paleontological and archeological specimens in rapid scanning times. Here we present elemen- tal maps of a fossil reptile produced using the new SRS-XRF method. Our results unequivocally show that preserved bio- logical structures are not simply impressions or carbonized remains, but possess a remnant of the original organismal biochemistry. We show that SRS-XRF is a powerful new tool for the study of paleontological and archaeological sam- ples.

Imaging of stroke: a comparison between X-ray fluorescence and magnetic resonance imaging methods

A dual imaging approach, combining magnetic resonance imaging to localize lesions and synchrotron rapid scanning X-ray fluorescence (XRF) mapping to localize and quantify calcium, iron and zinc was used to examine one case of recent stroke with hemorrhage and two cases of ischemia 3 and 7 years before death with the latter showing superficial necrosis. In hemorrhagic lesions, more Fe is found accompanied with less Zn. In chronic ischemic lesions, Fe, Zn and Ca are lower indicating that these elements are removed as the normal tissue dies and scar tissue forms. Both susceptibility and T2* maps were calculated to visualize iron in hemorrhages and validated by XRF Ca and Fe maps. The former was superior for imaging iron in hemorrhagic transformation and necrosis but did not capture ischemic lesions. In contrast, T2* could not differentiate Ca from Fe in necrotic tissue but did capture ischemic lesions, complementing the susceptibility mapping. The spatial localization, accurate quantitative data and elemental differentiation shown here could also be valuable for imaging other brain tissue damage with abnormal Ca and Fe content.

Chemical Mapping of Paleontological and Archeological Artifacts with Synchrotron X-Rays

The application of the recently developed synchrotron rapid scanning X-ray fluorescence (SRS-XRF) technique to the mapping of large objects is the focus of this review. We discuss the advantages of SRS-XRF over traditional systems and the use of other synchrotron radiation (SR) techniques to provide corroborating spectroscopic and diffraction analyses during the same analytical session. After reviewing routine techniques used to analyze precious specimens, we present several case studies that show how SR-based methods have been successfully applied in archeology and paleontology. For example, SRS-XRF imaging of a seventh-century Qur'ān palimpsest and an overpainted original opera score from Luigi Cherubini is described. We also review the recent discovery of soft-tissue residue in fossils of Archaeopteryx and an ancient reptile, as well as work that has successfully resolved the remnants of pigment in Confuciusornis sanctus, a 120-million-year-old fossil of the oldest documented bird with a fully derived avian beak.

Infrared mapping resolves soft tissue preservation in 50 million year-old reptile skin

Non-destructive Fourier Transform InfraRed (FTIR) mapping of Eocene aged fossil reptile skin shows that biological control on the distribution of endogenous organic components within fossilized soft tissue can be resolved. Mapped organic functional units within this approximately 50 Myr old specimen from the Green River Formation (USA) include amide and sulphur compounds. These compounds are most probably derived from the original beta keratin present in the skin because fossil leaf- and other non-skin-derived organic matter from the same geological formation do not show intense amide or thiol absorption bands. Maps and spectra from the fossil are directly comparable to extant reptile skin. Furthermore, infrared results are corroborated by several additional quantitative methods including Synchrotron Rapid Scanning X-Ray Fluorescence (SRS-XRF) and Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS). All results combine to clearly show that the organic compound inventory of the fossil skin is different from the embedding sedimentary matrix and fossil plant material. A new taphonomic model involving ternary complexation between keratin-derived organic molecules, divalent trace metals and silicate surfaces is presented to explain the survival of the observed compounds. X-ray diffraction shows that suitable minerals for complex formation are present. Previously, this study would only have been possible with major destructive sampling. Non-destructive FTIR imaging methods are thus shown to be a valuable tool for understanding the taphonomy of high-fidelity preservation, and furthermore, may provide insight into the biochemistry of extinct organisms.

Archaeopteryx feathers and bone chemistry fully revealed via synchrotron imaging

Evolution of flight in maniraptoran dinosaurs is marked by the acquisition of distinct avian characters, such as feathers, as seen in Archaeopteryx from the Solnhofen limestone. These rare fossils were pivotal in confirming the dinosauria-avian lineage. One of the key derived avian characters is the possession of feathers, details of which were remarkably preserved in the Lagerstätte environment. These structures were previously simply assumed to be impressions; however, a detailed chemical analysis has, until now, never been completed on any Archaeopteryx specimen. Here we present chemical imaging via synchrotron rapid scanning X-ray fluorescence (SRS-XRF) of the Thermopolis Archaeopteryx, which shows that portions of the feathers are not impressions but are in fact remnant body fossil structures, maintaining elemental compositions that are completely different from the embedding geological matrix. Our results indicate phosphorous and sulfur retention in soft tissue as well as trace metal (Zn and Cu) retention in bone. Other previously unknown chemical details of Archaeopteryx are also revealed in this study including: bone chemistry, taphonomy (fossilization process), and curation artifacts. SRS-XRF represents a major advancement in the study of the life chemistry and fossilization processes of Archaeopteryx and other extinct organisms because it is now practical to image the chemistry of large specimens rapidly at concentration levels of parts per million. This technique has wider application to the archaeological, forensic, and biological sciences, enabling the mapping of "unseen" compounds critical to understanding biological structures, modes of preservation, and environmental context.

Synchrotron X-ray Fluorescence Reveals Abnormal Metal Distributions in Brain and Spinal Cord in Spinocerebellar Ataxia: A Case Report

For the first time, synchrotron rapid-scanning X-ray fluorescence (RS-XRF) was used to simultaneously localize and quantify iron, copper, and zinc in spinal cord and brain in a case of spinocerebellar ataxia (SCA). In the normal medulla, a previously undescribed copper enrichment was seen associated with spinocerebellar fibers and amiculum olivae. This region was virtually devoid of all metals in the SCA case. Regions with neuronal loss and gliosis in the cerebellar cortex, inferior olivary, and dentate nuclei and areas showing loss of myelinated fibers were also low in all metals in SCA compared to control. In contrast, the ventral columns of the spinal cord that exhibited only moderate myelin pallor had increased metal levels. Iron and zinc were also elevated in the globus pallidus pars externa in SCA relative to control. We hypothesize that metals increase as part of the initial neurodegenerative process, but once degeneration is advanced, the metal levels drop. This implies a role for multiple metals in SCA neurodegeneration, but further study is required to establish a causative role. We suggest that if these findings are generally true of at least some cases of SCA, not only iron but also copper and zinc should be considered as possible therapeutic targets.

Iron, Copper, and Zinc Distribution of the Cerebellum

Synchrotron rapid-scanning X-ray fluorescence (RS-XRF) is employed for the first time to simultaneously map iron, copper, and zinc in the normal cerebellum. The cerebellum is a major repository of metals that are essential to normal function. Therefore, mapping the normal metal distribution is an important first step towards understanding how multiple metals may induce oxidative damage, protein aggregation, and neurotoxicity leading to cerebellar degeneration in a wide range of diseases. We found that cerebellar white and grey matter could be sharply defined based upon the unique metal content of each region. The dentate nucleus was particularly metal-rich with copper localized to the periphery and iron and zinc abundant centrally. We discuss how RS-XRF metal mapping in the normal brain may yield important clues to the mechanisms of degeneration in the dentate nucleus.