Confocal laser scanning microscopy and Raman imagery of the late Neoproterozoic Chichkan microbiota of South Kazakhstan

Abstract

Precambrian microbiotas, such as that permineralized in bedded and stromatolitic cherts of the late Neoproterozoic, 750- to 800-Ma-old, Chichkan Formation of South Kazakhstan, have traditionally been studied by optical microscopy only. Such studies, however, are incapable of documenting accurately either the three-dimensional morphology of such fossils or their chemical composition and that of their embedding minerals. As shown here by analyses of fossils of the Chichkan Lagerstätte, the solution to these long-standing problems is provided by two techniques recently introduced to paleontology: confocal laser scanning microscopy (CLSM) and Raman imagery. The two techniques are used together to characterize, in situ and at micron-scale resolution, the cellular and organismal morphology of the thin section-embedded organic-walled Chichkan fossils. In addition, Raman imagery is used to analyze the molecular-structural composition of the carbonaceous fossils and of their embedding mineral matrix, identify the composition of intracellular inclusions, and quantitatively assess the geochemical maturity of the Chichkan organic matter.CLSM and Raman imagery are both broadly applicable to the study of fossils, whether megascopic or microscopic and regardless of mode of preservation, and both are non-intrusive and non-destructive, factors that permit their use for analyses of archived specimens. They are especially useful for the study of microscopic fossils, as is demonstrated in this first in-depth study of diverse taxa of a single Precambrian microbiota for which they provide information in three dimensions at high spatial resolution about their organismal morphology, cellular anatomy, kerogenous composition, mode of preservation, and taphonomy and fidelity of preservation.