Palaeocast lunchtime lectures: A Doushantuo-type acritarch assemblage from the Ediacaran Biskopås Formation of southern Norway - Peter Adamson
The early Ediacaran saw the appearance of remarkably large microfossils succeeding the Cryogenian glaciations. This new microfossil biota, best known from the Doushantuo Formation of South China, includes a diverse assemblage of large (20-800 µm diameter) acanthomorphic acritarchs with potential for biostratigraphically resolving early Ediacaran time.
Doushantuo-type acritarchs have been described from Australia, China, Eastern Europe, India, Siberia, Svalbard, and Urals, but were first described from phosphorite pebbles in the Biskopås Formation, Southern Norway. Restudy of the Biskopås phosphorites has revealed eleven species of acanthomorphic acritarch, numerous colonial and solitary acritarchs, microbial filaments and microbial mats, all in close association. Significantly, the assemblage of Biskopås acritarchs is duplicated in Biozone 2 (Member III) of the Doushantuo Formation in Yangtze Gorges, illustrating close biostratigraphic correlation with South China. The absence of Tianzhushania in the Biskopås, which dominates Biozone 1 in the Doushantuo Formation, is consistent with this observation.
The Biskopås phosphorites were deposited within microbially-dominated — subsequently phosphatized — siliciclastics, which contrast markedly with the carbonate-dominated facies and early diagenetic chert nodules in the Doushantuo Formation. Although the Biskopås does not display the similarities that the Doushantuo and some shale-hosted assemblages do, taxonomic similarities between different environments support their relatively facies independent distribution.