Aspidella and water escape structures from the ca 850 Ma (Tonian) Heavitree Formation, Amadeus Basin, Central Australia

Abstract

The mid-Tonian-aged Heavitree Formation, the basal unit of the Amadeus Basin succession, has long been believed to be devoid of metazoan fossils. Since a recent review of isolated occurrences of purported metazoan traces and remains within the formation’s upper unit, however, that conclusion has been questioned and led to the identification of new fossil remains, including imprints of Aspidella reported herein. Previously, organic-looking structures encountered in rocks older than mid-Ediacaran (ca 580 Ma) were commonly interpreted as originating inorganically, primarily through water escape, but a recently examined outcrop of the upper unit of the Heavitree Formation revealed a variety of water escape structures in association with, but structurally distinct from, a suite of organic impressions.

KEY POINTS

1. Both biogenic Aspidella and abiogenic water escape structures occur within the upper member of the Tonian Heavitree Formation in the Amadeus Basin.

2. The Aspidella are structurally distinct from the water escape structures.

3. The presence of Aspidella adds to a growing list of phyla seemingly extant within the Amadeus Basin during the early Neoproterozoic.

4. Extinction of this Amadeus ‘biota’ occurred at ca 840 Ma when climatic conditions changed the basin from a conducive shallow aquatic environment to a harsh evaporitic salt pan.

Keywords:

• Neoproterozoic
• pre-Ediacaran life
• diverse metazoan fauna
• failed evolutionary attempt
• sand volcanoes

Acknowledgements

The authors thank two anonymous reviewers whose comments improved the comprehensiveness of the paper.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

The authors confirm that the data supporting the findings of this study are within the article.