Small shelly fossils from the Kharayutekh Formation of the Upper Vendian period in the lower reaches of the Lena River in Eastern Siberia

The study of problematic skeletal remains from the Kharayutekh Formation of the Upper Vendian period, uncovered along the right bank of the Lena River at the mouth of the Ulakhan-Ald’yarkhay Brook, revealed two distinct levels characterized by finds of small shelly fossils embedded in dark gray limestones. The first assemblage includes problematic skeletal remains with indeterminate systematic affinities, as well as two morphological types of fossil specimens attributed to the genus Tianzhushania . These specimens represent different stages in the embryonic development of this taxonomic group. In addition to Tianzhushania , the second, younger level also contains chancellorids ( Chancelloria sp.) and hyoliths ( Paragloborilus subglobosus ). The material for this study consisted of a collection of several dozen fossilized specimens, obtained through the standard process of chemical preparation, which involved dissolving limestone in a weak acetic acid solution (3–5 %). Based on the findings, it can be inferred that the Tuorasis Basin of the passive continental margin of Siberia during the Late Vendian period provided favorable conditions for the survival and evolution of the microflora discussed in this paper. These discoveries are of significant interest from both paleobiological and stratigraphical perspectives. In the future, it will be crucial to conduct more in-depth research on the morphological features and internal structures of the embryonic fossils found in the Kharayutekh Formation of the Ulakhan-Ald’yarkhay section, employing a microtomographic approach to validate their embryonic nature. Additionally, further sampling of small shelly fossils from the Kharayutekh Formation is essential to enhance the faunal attributes and strengthen the biostratigraphical foundation.