Confocal Laser Scanning Microscopy and Raman (and Fluorescence) Spectroscopic Imagery of Permineralized Cambrian and Neoproterozoic Fossils

Abstract

Among all problems confronting the study of permineralized (petrified) ­fossils—the most life-like remnants preserved in the fossil record—two stand out, the need for (1) accurate documentation of their three-dimensional morphology, and (2) direct analysis of their chemical composition and that of their embedding mineral matrix. These problems can be addressed effectively by the use of two techniques recently introduced to paleontology: confocal laser scanning microscopy (CLSM), and Raman (and fluorescence) spectroscopic imagery. Both of these techniques, which are non-intrusive and non-destructive, can provide data by which to characterize, in situ and at submicron resolution, the cellular and organismal morphology of thin section-embedded organic-walled fossils. The techniques are complementary: CLSM detects laser-induced fluorescence emitted from the carbonaceous kerogen of which such fossils are composed, whereas Raman and fluorescence spectroscopic imagery provide direct analyses of the molecular-structural composition of such kerogen and its embedding mineral matrix as well as providing a means to assess quantitatively the geochemical maturity of the preserved organics. The paleontological usefulness of these techniques is illustrated here by studies of fossils from four Early Cambrian and late Neoproterozoic units: (1) a lowermost Cambrian ctenophore (“comb jelly”) embryo from the Kuanchuanpu Formation of Shaanxi Province, China; (2) scale ­fossils (Chilodictyon) from the ∼750-Ma-old Lower Tindir Group of Yukon Territory, Canada; (3) acritarchs and cyanobacteria from the ∼775-Ma-old Chichkan Formation of southern Kazakhstan; and (4) cyanobacteria from the ∼800-Ma-old Bitter Springs Formation of central Australia. Use of these techniques for studies of permineralized fossils can provide information in three dimensions at high spatial resolution about their morphology and cellular anatomy, taphonomy and fidelity of preservation, composition and mode of preservation, and show that they are both indigenous to and syngenetic with the formation of the rocks in which they occur.