First Appearance Datums (FADs) of selected acritarch taxa and correlation between Lower and Middle Ordovician

Abstract

First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long‐distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity.

Palaeoecology of Cambrian–Ordovician acritarchs from China: evidence for a progressive invasion of the marine habitats

“…Recent research not only included the revision of the classification and taxonomy of the acritarchs (e.g. [39]), but also established their precise stratigraphic correlation framework [40]. Regarding palaeobiodiversity, various Palaeozoic acritarch diversity curves have been published [20], and it is shown that there are obvious differences in the diversity curves of different regions or different intervals.…”

Stratigraphic correlations between the Brabant Massif and the Stavelot, Rocroi and Givonne inliers (Belgium) and geological implications

“…The acritarch associations of Zone 9 can also be assigned to the Frankea hamata-Striatotheca rarrigulata Biozone, even if not all typical acritarch species are present. This is all the more likely as Servais et al (2017), in a synthesis of the First Appearance Datum (FADs) of selected acritarch taxa from the Middle Ordovician, place the FAD of the genus Frankea in the upper part of the Dapingian (stage slice Dp3; Servais et al, 2017, fig. 4), that of the genus Arkonia in the first half of the Darriwilian (provisional stage slice Dw1).…”

“…A . The genus Frankea is considered to have its first appearance in the upper Dapingian (stage slice Dp3; Servais et al, 2017).…”

Biostratigraphy and palaeogeographic implications of Ordovician and Silurian chitinozoa from the High Zagros Mountains, Northern Persian Gulf, Iran

“…These acritarch species have been described in more detail in Ghavidel-Syooki et al (2014). Their successive appearances and short stratigraphic ranges have essential applications in northern Gondwana biostratigraphy (Vecoli and Le Hérissé 2004; Servais et al 2018; Ghavidel-Syooki 2021).…”