Palaeometry applied to the investigation of biomineralization, environments and fossil preservation

Abstract

The relationship between life and the environment offers several perspectives in the study of the geological record, and Brazilian fossils are of worldwide importance in this discussion. Currently, the most innovative approach to test hypotheses concerning those issues is the use of Palaeometry, that is, imaging, spectroscopic, and geochemical techniques that make it possible to extract information with a high level of detail from fossils. The Ediacaran-Cambrian transition (ca. 541 Ma) was characterized by geological changes, which relate to profound transformations in the evolution of the biosphere. In this context, animals capable of synthesizing skeletons made up of minerals (biomineralizing animals from the Ediacara Biota), or actively exploring the substrate first appeared, then resulting in biological diversification. The determination of the original composition of the skeletons and the biases generated during their fossilization (taphonomy) are still little explored. In the Corumbá Group (MS), the Tamengo Formation consists of rocks deposited in a marine environment in the Ediacaran-Cambrian transition, where are found some of the first biomineralizers, such as Cloudina sp. and Corumbella werneri. In the Cambrian Period, there was the so-called 'Cambrian explosion' of life, the most expressive diversification event in the history of life on Earth, including the profusion of biomineralized groups and the development of the phyla's body plans. The beginning of the Cambrian (ca. 541 Ma) was marked by the appearance of the ichnofossil (evidence for biological activity) Treptichnus pedum, which indicates locomotion of bilateral animals within the marine substrate. This ichnofossil, which together with microbial mats are important palaeoenvironmental indicators, were recently found in the Três Marias Formation (ca. 520 Ma), Grupo Bambuí (MG). The fossils of invertebrates, vertebrates, and plants of the Crato Formation (CE), Cretaceous Period (ca. 110 Ma) are known worldwide for their exceptional state of conservation (Konservat Lagerstätte), which allows access to the morphology of these organisms with high fidelity. This project has the following objectives: investigate possible biomineralizing animals not yet described in the Tamengo Formation, to test several aspects of their biomineralization versus preservation; investigate the Cambrian environments of the Bambuí Group by means of sedimentary analysis and the investigation of ichnofossils and microbial mats; and, advance in the investigation of microbial participation in exceptional preservation using Cretaceous fossils as a model. For this purpose, paleometric imaging, spectroscopic and geochemical techniques will be used (e.g., cathodoluminescence, electron probe microanalysis, Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEM/EDS) and Electron Backscattered Diffraction (EBSD), X-ray fluorescence by energy dispersion (EDXRF), Raman micro-spectroscopy, X-ray Diffraction (XRD), and geochemical analyses indicative of redox conditions). From a palaeontological perspective, this work will shed new light on palaeoenvironmental, preservational, palaeoecological, and evolutionary issues. From the perspective of Palaeometry, the research will allow (1) to apply new forms of XRF data processing to extract palaeoenvironmental information from fossils, which will be validated by other analyses; (2) to develop analysis protocols to test hypotheses in palaeontology; and (3) to use different spectroscopic analytical techniques, exploring the advantages of each technique, and correlate the results to yield a better integration of information from the studied material. (AU)