The diversification and extinction of Doushantuo‐Pertatataka acritarchs in South China: causes and biostratigraphic significance

Abstract

The Ediacaran Period immediately follows the last Cryogenian glaciation-the $635 Ma Marinoan or Nantuo glaciation, and it is also punctuated by another brief glaciation-the $582 Ma Gaskiers glaciation. It is possible that these glaciations may have had significant impact on Ediacaran biological evolution (e.g. the appearance or disappearance of Doushantuo-Pertatataka acritarchs). Alternative hypotheses propose that the diversification of Doushantuo-Pertatataka acritarchs was caused by the Acraman bolide impact or by emerging eumetazoans. To test these hypotheses, high-resolution geochronological and biostratigraphic data are required. The Doushantuo Formation in South China, radiometrically constrained between $635 and $551 Ma, has the potential to clarify the global picture of early-middle Ediacaran evolution. Here we present preliminary biostratigraphic data from the Doushantuo Formation in the East Yangtze Gorges area and new d 13 C chemostratigraphic data from the Doushantuo Formation at Weng'an. These and previously published palaeontological data, aided by the tool of d 13 C chemostratigraphy, indicate that the biostratigraphic record of the Doushantuo Formation is locally sensitive to the availability of specific taphonomic windows. In the East Yangtze Gorges area, Doushantuo-Pertatataka acritarchs first appeared shortly after the termination of the Nantuo glaciation and gradually diversified throughout the Doushantuo Formation. At Weng'an, however, such acritarchs first appear-abruptly and in much greater diversity-in phosphorite of the upper Doushantuo Formation, immediately above a subaerial exposure surface. Thus, the biostratigraphic pattern in the East Yangtze Gorges area permits, whereas that at Weng'an apparently disallows, a causal relationship between the Nantuo glaciation and the diversification of Doushantuo-Pertatataka acritarchs. We conclude that the biostratigraphic record is incomplete at Weng'an, where the early Ediacaran evolutionary history is not preserved. The South China data indicate that special attention has to be paid to taphonomic and palaeoenvironmental analysis before extrapolating local and regional biostratigraphic ranges to make global interpretations.It is less clear when Doushantuo-Pertatataka acritarchs disappeared. Previous investigators have variously suggested that they disappeared before, at, or after, the Gaskiers glaciation. These hypotheses are difficult to test because of the lack of sedimentary evidence for the Gaskiers glaciation in South China and other regions (e.g. South Australia) where Doushantuo-Pertatataka acritarchs are abundant. In Australia, Doushantuo-Pertatataka acritarchs are thought to have experienced a sharp decline after the Egan glaciation, which may well be equivalent to the Gaskiers glaciation. If true, then Doushantuo-Pertatataka acritarchs are largely restricted to the interval between the Nantuo and Gaskiers glaciations. This conclusion allows us to place constraints on the possible causes of the diversification and extinction of Doushant...

Doushantuo-type microfossils from latest Ediacaran phosphorites of northern Mongolia

“…Elsewhere in the world Doushantuo-Pertatataka-type acanthomorphs occur generally in rocks that predate or are synchronous with carbon isotope excursions interpreted to be equivalent to the Shuram excursion (Zhou et al, 2007;Xiao et al, 2016;Zhou et al, 2017). The similarity between the Khesen assemblage reported here and that Publisher: GSA Journal: GEOL: Geology DOI:10.1130/G39576.1 Page 8 of 17 of the older Doushantuo Formation includes the presence of Appendisphaera grandis and A. tenuis, Cavaspina ?basiconica, Megasphaera, and Variomargosphaeridium gracile (Xiao et al, 2014b).…”

“…We have reworded this sentence to read: "Elsewhere in the world Doushantuo-Pertatataka-type acanthomorphs occur generally in rocks that predate or are synchronous with carbon isotope excursions interpreted to be equivalent to the Shuram carbon isotope excursion (Zhou et al, 2007;Xiao et al, 2016;Zhou et al, 2017)" for the reasons detailed in our response to the comment on lines 162-164 above. Please see lines 157-160 in the revised manuscript.…”

Phylochronology of early metazoans: combined evidence from molecular and fossil data

“…Older reports of eukaryotic organisms are considered to be phylogenetically uncertain (Knoll 2003). On the other hand, the oldest widely accepted metazoan fossils only occur in the Doushantuo Formation, South China (Xiao et al 2000;Zhou et al 2001Zhou et al , 2007Chen et al 2004). Xiao (2004) suggested that there is no unequivocal metazoan fossils before the Neoproterozoic glaciation interval (ca.…”

The Weng'an Biota (Doushantuo Formation): an Ediacaran window on soft-bodied and multicellular microorganisms

“…2k) from Weng'an have been reviewed comprehensively by Xiao et al (2014b) and form part of the Doushantuo-Pertatataka microbiota (Zhou et al 2001(Zhou et al , 2007Liu et al 2014). The phylogenetic affinities of acritarchs are unknown and they probably represent a polyphyletic assortment of eukaryotes (Huntley et al 2006).…”