Acritarch Elektoriskos? williereae (G. & M. Deflandre, 1965) Vanguestaine, 1979 emend. nov. from the Upper Ordovician of the Siberian Platform: New Morphological and Stratigraphic Data

E G Raevskaya,A V Dronov

doi:10.1134/s0869593821060071

Abstract

The morphology of acritarch species Elektoriskos? williereae (G. & M. Deflandre, 1965) Vanguestaine, 1979, previously considered as a Silurian index of the Llandovery, has been clarified, the diagnosis emended, and the stratigraphic distribution expanded. According to new data, the first appearance of E.? williereae was confined to the upper part of the Baksan Horizon near the boundary of the Sandbian and Katian stages of the Upper Ordovician. Co-occurrence of E.? williereae with representatives of the genera Gordonirundum, Nirundella, Peteinosphaeridium, and Sacculidium is a distinct, well-recognizable palynological characteristic of the Katian deposits of the Siberian Platform which can serve for identification, dating, and correlation of the acritarch-bearing strata. Morphological variations in E.? williereae are a stable diagnostic feature of the species that distinguishes it from other taxa. It is possible that the species was sensitive to paleoenvironments and, probably, highly adaptive, which allowed it, remaining almost unchanged, to overcome the global Late Ordovician cooling, which became fatal for many other groups of organisms.

Highlights

The stratigraphic significance of acritarchs, especially for the Early Paleozoic and, above all, for the Ordovician, the period of maximum diversity and abundance of these microfossils in all sedimentary basins of the world, is beyond doubt
Since the group was created artificially, the acritarch species was defined as a set of unicellular vesicles with certain common morphological features, and the genus was defined as an artificial category that unites species with similar external characteristics (Downie et al, 1963)
Many of the species attributed to different genera, upon closer study, reveal a common morphological structure, while the species that seem similar at first sight, belong to different taxa

Summary

Introduction

The stratigraphic significance of acritarchs, especially for the Early Paleozoic and, above all, for the Ordovician, the period of maximum diversity and abundance of these microfossils in all sedimentary basins of the world, is beyond doubt. Since the group was created artificially, the acritarch species was defined as a set of unicellular vesicles with certain common morphological features, and the genus was defined as an artificial category that unites species with similar external characteristics (Downie et al, 1963). This classification, based solely on the morphology of microfossils, is undoubtedly subjective. Almost every acritarch morphotype identified at the first stages of the study became a new species especially following the improvement of technical equipment. The imperfection of the acritarch classification, stemming from the nature of this group, is a constant subject of discussion (Fatka and Brocke, 2008; Li et al, 2014; Servais, 1995; Servais et al, 2007, 2008; etc.)

Objectives

Discussion

Conclusion