Synchrotron radiation in palaeontological investigations: Examples from Brazilian fossils and its potential to South American palaeontology

摘要

Synchrotron radiation (SR) is an electromagnetic radiation produced when electrons are forced to assume a curved trajectory resulting in an emission of a bright beam of high energy photons. This phenomenon is carried out in large particle acceleration facilities called synchrotrons, which is equipped with experimental stations at the end of each spot where the beam is emitted. In an applied sense, SR allows the investigation of materials of different nature, from synthetic to biological, from macro to the nano-scale. Since fossils are typified as environmental samples (i.e. a mixture of different type of compounds), SR has become an important approach to modern palaeontology. Due to the selective nature of the fossil record, bias can occur in both, morphology and geochemistry. Therefore, palaeontologists are frequently susceptible to equivocal interpretations. To diminish this problem, the employment of analytical methods became paramount in many areas of palaeontology. However, most benchtop equipments are limited in resolution, they also require particular experimental conditions (e.g. vacuum), and complex sample preparations (e.g. extraction from rocks). In this scenario, SR is advantageous as it allows non-destructive experiments to be performed in situ in qualitative or quantitative modes, in larger areas of the samples, still maintaining high spatial resolution and low detection limits. Nonetheless, in contrast to worldwide palaeontology where SR is widely applied, this analytical approach remains still poorly explored in South America. In Brazil, only a few studies used SR to resolve palaeontological problems. This panorama contrasts with the fact that in Brazil had a 2nd generation synchrotron, the UV and Soft X-Ray Light Source (UVX), which operated for 22 years. Nevertheless, this machine was substituted by a new 4th generation synchrotron, Sirius, which has been in operation since early 2020. Among its 13 beamlines, some will be best suitable to analyse palaeontological material, both through spectroscopy and imaging at a nanoscale. Therefore, it is expected that fossils will be routinely analysed in Sirius, being able to push forward the current knowledge in palaeontology. Here, we review the application of SR to the investigation of fossilization and other challenging topics in palaeontology. In this context, a fossil beetle from the Cretaceous Crato Formation (NE Brazil) was analysed using synchrotron radiation micro-X-Ray fluorescence (SR-mu XRF). Results revealed which elements are involved in the process of fossilization and diagenesis, providing additional evidence for the preservational model of insects in this unit. Due to the high resolution and non-destructive properties, the SRtechniques have provided invaluable information on rare and delicate fossils. Considering all these aspects, it is now clear that this analytical approach has a high potential of expanding not only the frontiers of palaeontology, but also of the South American Earth sciences as a whole.