In situ Infrared Microspectroscopy of ∼850 Million-Year-Old Prokaryotic Fossils

Abstract

In situ infrared (IR) and Raman microspectroscopy have been conducted on Neoproterozoic, organic-walled microfossils (prokaryotic fossils) in doubly polished, petrographic thin sections in order to detect their spectral signatures. The microfossils are very well preserved and occur in black chert from the approximately 850 million-year-old Bitter Springs Formation, Northern Territory, Australia. Raman microspectroscopy on two species of microfossils, one a filament and the other a coccoid, shows disordered peaks (D peak, 1340 cm(-1)) and graphite peaks (G peak, 1600 cm(-1)), indicating that they consist of disordered carbonaceous materials. IR micro-mapping results of the filament reveal that the distributions of peak heights at 2920 cm(-1) (aliphatic CH(2)), 1585 cm(-1) (aromatic C-C), and 1370 cm(-1) (aliphatic CH(3)) match the shape of the filamentous microfossil. These results suggest that IR microspectroscopy can be used for in situ characterization of organic polar signatures that morphologically indicate microfossils embedded in chert by using doubly-polished rock (petrographic) thin section samples. Further, these methods can be applied to controversial microfossil-like structures to test their biogenic nature.

Carbonaceous biosignatures of diverse chemotrophic microbial communities from chert nodules of the Ediacaran Doushantuo Formation

“…Marshall et al, 2005;Igisu et al, 2006Igisu et al, , 2009Igisu et al, , 2014. The absorbance ratio of asymmetric stretching band of aliphatic CH 3 end-methyl versus CH 2 chain-methylene describes the branching index of carbon chains.…”

“…-band, and it has been used to describe the branching index of carbon chains in fossilized carbonaceous material (Igisu et al, 2006(Igisu et al, , 2009Qu et al, 2015). It has been proposed that the R 3/2 ratio shows systematic variations between biomass of archaeans, bacteria, and eukaryotes due to their different chemical compositions within cellular constituents, especially the membrane lipids (Igisu et al, 2009).…”

Domain‐level identification and quantification of relative prokaryotic cell abundance in microbial communities by Micro‐FTIR spectroscopy

“…Igisu and colleagues (2006; 2009) showed that specific IR absorption peaks for aliphatic methylene (CH 2 ) and aliphatic methyl (CH 3 ) groups can be potential chemical indicators for domain‐level identification of prokaryotes. From the domain‐specific lipid components (e.g.…”

Changes of aliphatic C–H bonds in cyanobacteria during experimental thermal maturation in the presence or absence of silica as evaluated by FTIR microspectroscopy

“…Recently, micro‐scale spectroscopic and geochemical analyses have been used to obtain the chemical signatures of a range of micrometer‐sized fossils (e.g., Alleon, Bernard, Le Guillou, Marin‐Carbonne et al., ; Brasier et al., ; House, Oehler, Sugitani, & Mimura, ; House et al., ; Kudryavtsev, Schopf, Agresti, & Wdowiak, ; Oehler et al., , , ; Schopf, Kudryavtsev, Agresti, Czaja, & Wdowiak, ; Schopf, Kudryavtsev, Agresti, Wdowiak, & Czaja, ; Ueno, Isozaki, & McNamara, ; Ueno, Isozaki, Yurimoto, & Maruyama, ; Wacey, Kilburn, Saunders, Cliff, & Brasier, ; Williford et al., ). In particular, transmission Fourier transform infrared (FTIR) microspectroscopy, which usually has a spatial resolution of more than ~10 μm, has been successfully used to analyze Proterozoic organic‐walled microfossils and Phanerozoic miospores (e.g., Arouri, Greenwood, & Walter, , ; Igisu, Nakashima, Ueno, Awramik, & Maruyama, ; Igisu et al., ; Marshall, Javaux, Knoll, & Walter, ; Steemans, Lepot, Marshall, Le Hérissé, & Javaux, ).…”