Late Ediacaran organic microfossils from Finland

Sebastian Willman,Ben J Slater

doi:10.1017/s0016756821000753

Abstract

AbstractHere we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs).

Highlights

The latest part of the Ediacaran System harbours signatures for some of the most important changes in the history of the biosphere
A trace fossil record of complex horizontal burrows and trails appears from ~560 Ma, likely documenting the emergence of a bilaterian benthos (Martin et al 2000; Jensen, 2003; Chen et al 2013, 2019; Budd, 2015; Budd & Jensen, 2017)
These simple trace fossils are consistently found in association with bedding planes exhibiting microbial mat textures, and have been interpreted as representing a variety of mat-exploiting behaviours (Buatois et al 2014; Meyer et al 2014; Tarhan et al 2017; Ivantsov et al 2019b)

Summary

Introduction

The latest part of the Ediacaran System harbours signatures for some of the most important changes in the history of the biosphere. A trace fossil record of complex horizontal burrows and trails appears from ~560 Ma, likely documenting the emergence of a bilaterian benthos (Martin et al 2000; Jensen, 2003; Chen et al 2013, 2019; Budd, 2015; Budd & Jensen, 2017) These simple trace fossils are consistently found in association with bedding planes exhibiting microbial mat textures, and have been interpreted as representing a variety of mat-exploiting behaviours (Buatois et al 2014; Meyer et al 2014; Tarhan et al 2017; Ivantsov et al 2019b).

Geological setting

Materials and methods

Organic-walled fossils

Discussion

Conclusions