TUBULAR MICROFOSSILS FROM CAP CARBONATES OF KYRGYZSTAN

The Cryogenian Period is characterized by two global glaciations, the Sturtian and Marinoan which lasted c. 55 and 5 million years, respectively. Recent studies of carbonates that cap these global glacial deposits have revealed a microbiota including testate amoeba, pyritized cyanobacteria, and possible agglutinated foraminifera. This work investigates fossils found within Neoproterozoic cap carbonates overlying glacial deposits in the Naryn region of Kyrgyzstan. One of these cap carbonates is composed of dark gray limestone and interbedded black shale that sharply overlie massive polymictic diamictite. Samples from this unit were dissolved in dilute acetic acid, filtered, and examined, and one sample was found to be fossiliferous. The tubular fossils discovered in the residues consist of gently curved and straight tubes with a consistent diameter of 30 µm and lengths that vary from approximately 100 µm to 400 µm. Analysis of SEM images of the microfossils displays hollow, smooth interiors, and rough exteriors. EDS and Raman analysis of the fossils revealed that they are primarily composed of Si and O with an iron-rich rim around the microfossils. EDS maps showed that the rock contained aluminum-silicate regions in addition to the quartz. Raman spectroscopy showed distinct peaks at ~1360 cm^-1 and ~1600 cm^-1, corresponding to disordered (D) and graphitic (G) carbon respectively which are indicative of fossil organic carbon. An additional peak at 1450 cm^-1 appears to have a heterogeneous distribution and is unique to the microfossils. This peak lies in a region typical of organic matter, but is distinct from the D and G band peaks characteristic of fossil kerogen, and may be indicative of biomarkers preserved in these tubular microfossils. This research adds to the existing Neoproterozoic fossil record and contributes to the documentation of the diversity of microorganisms that thrived in the aftermath of glaciations during this time.