Beyond taxonomy: Raman spectroscopy reveals organic complexity in Precambrian-Cambrian microfossils from South China

Abstract

Raman spectroscopy offers powerful insights into the structural characteristics of carbonaceous matter and holds promise for distinguishing phylogenetically distinct fossil groups based on differences in their organic precursors, which is essential for understanding the early evolution of eukaryotes and animals. This study applies Raman spectroscopy to organic microfossils preserved in cherts from the Precambrian–Phanerozoic boundary (∼538 Ma) in the Yangtiao section, Guizhou Province, South China. Although peak metamorphic temperatures estimated from three Raman geothermometers converge around 220 °C, significant spectral variation among fossil groups likely reflect differences in organic composition. The commonly used R1 ratio does not correlate monotonically with thermal maturity in low- to medium-grade carbonaceous matter and should not be used in isolation; instead, its relationship with other Raman parameters provides a more robust framework for assessing metamorphic maturity. Principal component analysis of Raman spectra and spectral parameters reveals that acritarchs, multicellular algae, prokaryotes, and sponge tissues form a coherent cluster, while over half of the sponge spicule spectra fall outside this group. These findings highlight the influence of organic precursors on Raman signals and demonstrate the potential of Raman spectroscopy as a rapid tool for identifying possible Precambrian animal remains.