Structural and chemical heterogeneity of Proterozoic organic microfossils of the ca. 1 Ga old Angmaat Formation, Baffin Island, Canada

• Published in: Geobiology
• Main Authors: Nabhan, Sami, Kah, Linda, Mishra, Bhoopesh, Pollok, Kilian, Manning‐berg, Ashley, Zuilen, Mark
• Other Authors: Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), The University of Tennessee Knoxville, School of Chemical and Process Engineering, University of Leeds, Friedrich-Schiller-Universität = Friedrich Schiller University Jena Jena, Germany, University of Tennessee Chattanooga (UTC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Mesoproterozoic; organic microfossils; Angmaat Formation; Raman-spectroscopy; [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology; [SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry; Baffin Island; Canada; Baffin
• Online Access: https://hal.science/hal-03426869; https://hal.science/hal-03426869/document; https://hal.science/hal-03426869/file/Nabhan-2021-Geobiology-pre-proof.pdf; https://doi.org/10.1111/gbi.12463

International audience Organic microfossils in Meso-and Neoproterozoic rocks are of key importance to track the emergence and evolution of eukaryotic life. An increasing number of studies combine Raman spectroscopy with synchrotron-based methods to characterize these microfossils. A recurring observation is that Raman spectra of organic microfossils. A recurring observation is that Raman spectra of organic microfossils show negligible variation on a sample scale and that variation between different samples can be explained by differences in thermal maturation or in the biologic origin of organic precursor material. There is a paucity of work, however, that explores the extent to which the petrographic framework and diagenetic processes might in-fluence the chemical structure of organic materials. We present a detailed Raman spectroscopy- based study of a complex organic microfossil assemblage in the ca. 1 Ga old Angmaat Formation, Baffin Island, Canada. This formation contains abundant early diagenetic chert that preserves silicified microbial mats with numerous, readily identifiable organic microfossils. Individual chert beds show petrographic differences with discrete episodes of cementation and recrystallization. Raman spectroscopy reveals measurable variation of organic maturity between samples and between neigh-boring organic microfossils of the same taxonomy and taphonomic state. Scanning transmission X- ray microscopy performed on taphonomically similar coccoidal micro-fossils from the same thin section shows distinct chemical compositions, with varying ratios of aromatic compounds to ketones and phenols. Such observations imply that geochemical variation of organic matter is not necessarily coupled to thermal alteration or organic precursor material. Variation of the Raman signal across single samples is most likely linked to the diagenetic state of analyzed materials and implies an association between organic preservation and access to diagenetic fluids. Variation in the maturity of individual ...