Microfossils and Sedimentary Environments of the Zherba Basin: Upper Vendian of the Patom Highland of Siberia

Abstract

In the Upper Vendian deposits of the Zherba Formation of the Siberian Patom Basin, an association of organic-walled microfossils was described for the first time. The microfossils differ markedly from each other in the type of preservation. One group of microfossils includes highly corroded filamentous and rare spheromorphic acritarchs. The other group is represented exclusively by spheromorphic and acanthomorphic acritarchs with well-preserved vesicles, which are identical to microfossils from the underlying Lower Vendian Ura Formation. The performed facies analysis showed the coastal-continental and shallow-water-shelf environments of the Zherba basin, which existed under low sea level conditions and deep continental erosion in adjacent uplifts. Under such conditions, the ancient Ura microfossils contained within fine-grained lithoclastics could enter the sedimentation zone inhabited by primitive shallow-water communities. The processes of large-scale recycling throughout almost the entire Zherba time led to the mixing of taphocenoses of different ages, represented by ecologically and taxonomically contrasting associations of microorganisms.