Tubular microfossils from Neoproterozoic cap limestone of the Dzhetym Group, Kyrgyzstan

The Neoproterozoic microfossil record provides a window into the evolution and diversification of the marine biosphere during a dynamic interval in Earth history. Over the course of the Neoproterozoic, the Earth experienced two global glaciations followed by intense warming intervals, a potential rise in atmospheric oxygen, and perturbations to the geochemical cycles of C, Si, and Fe, among others. Generally coincident with these global environmental changes, the biosphere saw key evolutionary and ecological changes that included a rise in marine eukaryotic algae, increased diversity of the marine biosphere, and the appearance of increasingly complex organisms. Although broad evolutionary trends have been documented, further investigation of individual Neoproterozoic microfossil assemblages from across the globe are needed to better constrain evolutionary and ecological changes and how they relate to changing marine environments.

Here, we present a new microfossil assemblage preserved in black limestone of the Dzhetym Group from the Naryn Region of Kyrgyzstan that directly overlie a glacial diamictite. These microfossils are hollow, tube-shaped structures of ∼25 µm in diameter composed of silica and iron. The structures also contain kerogen that is chemically distinct from the bulk kerogen preserved in the limestone matrix. Based on the composition and morphology of the structures and their preservation by silica and iron, we suggest that they represent microfossils preserved through a previously uncharacterized taphonomic window in a carbonate-dominated Neoproterozoic marine environment. Characterization of these microfossils, as well as the taphonomic mechanisms that facilitated their preservation, expands our understanding of the Neoproterozoic marine biosphere and the potential chemical and biological processes that facilitated microfossil preservation in the aftermath of a glaciation.