3.a. Arctic Norway

Samples from Arctic Norway were collected during the 2016 and 2018 field expeditions of the Digermulen Early Life Research Group (DELRG). The Digermulen Peninsula in the Finnmark region of mainland Arctic Norway hosts an approximately 3-km-thick succession of mainly siliciclastic sedimentary rocks of Cryogenian–Ordovician age (e.g. Högström et al. Reference Högström, Jensen, Palacios and Ebbestad2013; Figs 1a, b, 2a, 3a). The base of the Vestertana Group contains glaciogenic diamictites of the Smalfjorden and Mortensnes formations that have been linked to the Marinoan and Gaskiers glacial intervals, respectively (Halverson et al. Reference Halverson, Hoffman, Schrag, Maloof and Rice2005). These sequences bracket the siliciclastic shallow-marine to basinal, non-glacial Nyborg Formation. Organic-walled microfossil taxa characteristic of the early Ediacaran Period (ECAP/DPA), as well as organically preserved remnants of multicellular tissue, have been documented in the upper part of the Nyborg Formation (Agić et al. Reference Agić, Högström, Jensen, Ebbestad, Meinhold, Taylor, Palacios and Høyberget2018, Reference Agić, Högström, Moczydłowska, Jensen, Palacios, Meinhold, Ebbestad, Taylor and Høyberget2019). Overlying the Mortensnes diamictite is the Stáhpogieddi Formation, which starts with sandstones and shales of the Lillevannet Member, representing a transgressive interval (Banks et al. Reference Banks, Edwards, Geddes, Hobday and Reading1971; Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b). Above lies the Indreelva Member composed of mudstones, siltstones and sandstones, which hosts an assemblage of Ediacara-type macrofossils dominated by discoidal taxa (Farmer et al. Reference Farmer, Vidal, Moczydłowska, Strauss, Ahlberg and Siedlecka1992; Högström et al. Reference Högström, Jensen, Palacios and Ebbestad2013, Reference Högström, Jensen, Ebbestad, Taylor, Høyberget, Agić, Meinhold and Palacios2017; Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b). The overlying Manndrapselva Member consists of a basal sandstone unit, followed by two upwards-coarsening cycles of red and grey mudstone and sandstone alterations and, in the second cycle, carbonate concretions and calcareous siliciclastic beds (Meinhold et al. Reference Meinhold, Jensen, Høyberget, Arslan, Ebbestad, Högström, Palacios, Agić and Taylor2019 a). The stratigraphically highest occurrence of macrofossils Palaeopascichnus and Harlaniella is c. 15 m above the carbonates, and the Ediacaran–Cambrian boundary lies close to the base of the third cycle, indicated by the occurrence of the trace fossil Treptichnus pedum (Fig. 2a; McIlroy & Brasier, Reference McIlroy, Brasier, Brasier, McIlroy and McLoughlin2017; Jensen et al. Reference Jensen, Högström, Almond, Taylor, Meinhold, Høyberget, Ebbestad, Agić and Palacios2018 a, b).

Fossiliferous samples discussed here were collected from shales and siltstones in the basal part of Indreelva Member from Árasulluokta Cove (Fig. 1a, b). Samples D16-HA-80 (70° 34.165ʼ N, 28° 07.224ʼ E) and D18-HA-20 (70° 34.174ʼ N, 28° 07.204ʼ E, just above a bed with discoidal fossils), were collected 3 m and c. 10 m above the lowest occurrence of palaeopascichnids (cf. Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b). Sample D16-HA-53 was recovered 2 m below the earliest aspidellomorphs in the Stáhpogieddi section, 6 m above the Lillevannet–Indreelva transitional beds (70° 32.534ʼ N, 28° 00.929ʼ E). The sample from the Manndrapselva Member third cycle at the Manndrapselva River section (D16-HA-77, 70° 34.575ʼ N, 28° 06.847ʼ E) was collected immediately above the quartzite marking the top of the second cycle.

3.b. Namibia

Fossiliferous samples from Namibia were collected from the Dabis Formation during the field workshop on the Ediacaran Nama Group of southern Namibia, part of the IGCP 587 programme (Xiao et al. Reference Xiao, Vickers-Rich, Narbonne, Laflamme, Darroch, Kaufman and Kriesfeld2017) on Farm Pockenbank (Figs 1c, d, 2b, 3b). The Nama Group contains c. 3 km of fluvial to marine siliciclastics and carbonates, representing a tidal to below-wave-base environment of a foreland basin (Germs et al. Reference Germs, Knoll and Vidal1986; Germs & Gresse, Reference Germs and Gresse1991). It occurs in a northern Zaris sub-basin and a southern Witputz sub-basin, separated by the Osis Ridge (Germs, Reference Germs1983). The lower part of the Nama, the Kuibis Subgroup, consists of 200 m of mature siliciclastics and carbonates, and is subdivided into the Dabis and Zaris formations (Germs, Reference Germs1983; Saylor et al. Reference Saylor, Grotzinger and Germs1995). In the Pockenbank area (Witputz sub-basin), the lowermost Kanies Member of the Dabis Formation contains predominantly arkosic sandstones with ripples and desiccation cracks indicative of shallow, fluvial environments (Germs, Reference Germs1983; Saylor et al. Reference Saylor, Grotzinger and Germs1995). The Mara Member overlies the transgressively eroded top of the Kanies Member, and contains alternating fine-grained siliciclastics and limestones with microbialites and evaporites within a shallowing-upwards sequence (Germs, Reference Germs1972 b, Reference Germs1983; Saylor et al. Reference Saylor, Grotzinger and Germs1995). Above the Mara Member are the Kliphoek and Aar members that consist of cross-stratified coarse sandstones and carbonates grainstone (Germs, Reference Germs1983; Saylor et al. Reference Saylor, Grotzinger and Germs1995; Hall et al. Reference Hall, Kaufman, Vickers-Rich, Ivantsov, Trusler, Linnemann, Hofmann, Elliott, Cui, Fedonkin and Hoffmann2013). Saylor et al. (Reference Saylor, Grotzinger and Germs1995) interpreted the Dabis Formation strata as two transgressive sequences. Some of the oldest examples of the youngest Ediacaran evolutionary assemblage – the Nama assemblage – occur in the Kliphoek/Aar members (e.g. Germs, Reference Germs1983; Narbonne et al. Reference Narbonne, Saylor and Grotzinger1997; Vickers-Rich et al. Reference Vickers-Rich, Ivantsov, Trusler, Narbonne, Hall, Wilson, Greentree, Fedonkin, Elliott, Hoffmann and Schneider2013; Maloney et al. Reference Maloney, Boag, Facciol, Gibson, Cribb, Koester, Kenchington, Racicot, Darroch and Laflamme2020). Carbonates (micrite phases) in the Mara Member (Arasab section) preserve a negative δ¹³C excursion from −6.22‰ to −0.22‰, previously correlated with the recovery from the global Shuram–Wonoka anomaly (Kaufmann et al. Reference Kaufman, Hayes, Knoll and Germs1991; Saylor et al. Reference Saylor, Grotzinger and Germs1995, Reference Saylor, Kaufman, Grotzinger and Urban1998; Grotzinger et al. Reference Grotzinger, Bowring, Saylor and Kaufman1995; Hall et al. Reference Hall, Kaufman, Vickers-Rich, Ivantsov, Trusler, Linnemann, Hofmann, Elliott, Cui, Fedonkin and Hoffmann2013; Wood et al. Reference Wood, Poulton, Prave, Hoffmann, Clarkson, Guilbaud, Lyne, Tostevin, Bowyer, Penny and Curtis2015). The excursion is not fully manifested at the locality where the microfossils were collected (cf. Vickers-Rich et al. Reference Vickers-Rich, Narbonne, Laflamme, Darroch, Kaufman and Kriesfeld2016). Sandstones of the overlying Kliphoek and Aar members include fossils in offshore-shoreface settings, characteristic environments inhabited by the late Ediacaran Nama assemblage including such taxa as Ernietta, Pteridinium and Rangea, as well as macroscopic bacterial colonies Nemiana (Narbonne et al. Reference Narbonne, Saylor and Grotzinger1997, Reference Narbonne, Xiao, Shields, Gehling, Gradstein, Ogg, Schmitz and Ogg2012; Vickers-Rich et al. Reference Vickers-Rich, Ivantsov, Trusler, Narbonne, Hall, Wilson, Greentree, Fedonkin, Elliott, Hoffmann and Schneider2013). These macrofossiliferous strata span the late Ediacaran Period: an ash bed in the Kuibis Subgroup yielded a U–Pb age of 548.8 ± 1 Ma (Grotzinger et al. Reference Grotzinger, Bowring, Saylor and Kaufman1995), and ash beds from the Spitskop Member of the overlying Urusis Formation yielded ages of 538.99 ± 0.21 Ma in the most recent study using U–Pb chemical abrasion – isotope dilution – thermal ionization imaging spectrometry (CA-ID-TIMS) dating technique (Linnemann et al. Reference Linnemann, Ovtcharova, Schaltegger, Gärtner, Hautmann, Geyer, Vickers-Rich, Rich, Plessen, Hofmann and Zieger2019).

Collection for a pilot microfossil survey was carried out from the lower Mara Member, Nama Group on Farm Pockenbank, at the Quiver section (see Vickers-Rich et al. Reference Vickers-Rich, Narbonne, Laflamme, Darroch, Kaufman and Kriesfeld2016): N16-HA-P2 c. 9 m above the base of the Mara Member (27° 08.619ʼ S, 16° 26.803ʼ E), and N16-HA-P3 immediately above a grey limestone package. These strata are overlain by grey and pink dolomite, and dark limestone at the top.

3.c. Newfoundland, Canada

The microfossiliferous Gibbett Hill Formation of the Signal Hill Group is exposed on the eastern Avalon Peninsula, Newfoundland, Canada (Sala Toledo, Reference Sala Toledo2004; Hofmann et al. Reference Hofmann, O’Brien and King2008). The Signal Hill Group overlies the fossiliferous strata of the Conception and St John’s groups, which contain some of the oldest Ediacara-type macrofossils, that is, the Avalon assemblage (Fig. 2c; Misra, Reference Misra1969; Narbonne in Fedonkin et al. Reference Fedonkin, Mikhail, Gehling, Grey, Narbonne and Vickers-Rich2007; Liu et al. Reference Liu, Kenchington and Mitchell2015; Matthews et al. Reference Matthews, Liu, Yang, McIlroy, Levell and Condon2021). Temporal constraints in the upper part of this succession are generally scarce, but the Conception Group contains a glacial diamictite (Gaskiers Formation) dated between 580.90 ± 0.40 and 579.88 ± 0.44 Ma using CA-ID-TIMS U–Pb analyses on zircon grains (Pu et al. Reference Pu, Bowring, Ramezani, Myrow, Raub, Landing, Mills, Hodgin and Macdonald2016), and the rangeomorphs from the Fermeuse Formation in the upper St John’s Group, have a maximum age of 564.13 ± 0.65 Ma (Matthews et al. Reference Matthews, Liu, Yang, McIlroy, Levell and Condon2021). A tuffite sample from the lower Fermeuse Formation yielded zircon U–Pb dates from 563.67–569.01 Ma (Matthews et al. Reference Matthews, Liu, Yang, McIlroy, Levell and Condon2021).

The overlying Signal Hill Group contains c. 1500 m of mudstones, fine-grained sandstones and ash beds (Sala Toledo, Reference Sala Toledo2004). Its oldest unit is the Cappahayden Formation, containing laminated grey siltstones. It is overlain by the Gibbett Hill Formation consisting of 760 m of green-grey sandstone, mudstone and black shales (Sala Toledo, Reference Sala Toledo2004) and deposited in a shallow-marine environment.

Rare OWM dominated by sphaeromorphs were previously reported from siliciclastics of the Drook, Mall Bay, Fermeuse and Renews Head formations in the St John’s Group (Hofmann et al. Reference Hofmann, Hill and King1979; O’Brien & King, Reference O’Brien and King2004), and the Cappahayden Formation (underlying the Gibbett Hill Formation) in the Signal Hill Group (Hofmann et al. Reference Hofmann, Hill and King1979). The microfossils in this study derive from a single sample of the ‘Brasier Shale’ outcrop in the Gibbett Hill Formation, near Ferryland, Avalon Peninsula, Newfoundland (Fig. 1e–f).

4.a. Ediacaran Indreelva Member, Stáhpogieddi Formation, Digermulen Peninsula, Norway

Out of 13 analysed samples from the Indreelva Member, 10 were barren or had very low organic content, and the rest yielded moderately well preserved OWM. These include: Granomarginata prima, G. squamacea, Leiosphaeridia crassa, L. jacutica, a tapering annulated microfossil, a lobate acritarch, fragmented SCF and aggregates of cells Symplassosphaeridium sp. A new type of flask-shaped OWM is described: Lagoenaforma collaris gen. et sp. nov. (Fig. 5a). Fragmented remains of filamentous prokaryotes and parts of rare larger SCF, as well as often torn membranous extensions of Granomarginata, are likely not a result of destructive processing because a low-manipulation acid maceration method was applied; this indicates either degradation within the sediment or transport. Leiosphaerids are the most common component of the Indreelva OWM assemblage (> 80%, Fig. 6a, b, d). There are few Granomarginata specimens; it is therefore rarer when compared with its abundance in the Cambrian strata (e.g. 3–10 counts, see Palacios et al. Reference Palacios, Högström, Ebbestad, Agić, Høyberget, Jensen, Meinhold and Talyor2020). OWM are generally scarce in the strata examined here.

The first record of G. squamacea and L. collaris in the Indreelva Member occurs in a laminated mudrock 3 m above the level hosting palaeopascichnids, and c. 10 m above the transitional beds of the Lillevannet Member (Figs 2a, 3a). Microfossils also occur c. 6 m below the first discoidal Ediacara-type macrofossils in the Indreelva Member in the Stáhpogieddi type section. Mudrock samples below the Palaeopascichnus horizon in the Árasulluokta Cove were devoid of microfossils apart from rare leiosphaerid fragments. This is likely not preservational bias because at least some OWM (leiosphaerids) are present. Granomarginata makes up 4% and L. collaris 7.5% of the Indreelva assemblage. Overall filaments and organic problematica represent nearly 10% of the assemblage. Samples from the upper part of the Indreelva Member did not yield any microfossils.

Distinct OWM are not commonly found very close to the beds containing Ediacara-type biota (Grey in Fedonkin et al. Reference Fedonkin, Mikhail, Gehling, Grey, Narbonne and Vickers-Rich2007). Although microfossils in the Indreelva Member are rare and occur sporadically, these results from the Digermulen Peninsula represent a rare distribution of acritarchs and Ediacaran macrofossils within a few metres of each other.

4.b. Ediacaran–Cambrian Manndrapselva Member, Stáhpogieddi Formation, Digermulen Peninsula, Norway

Granomarginata was previously documented higher up in the stratigraphy on the Digermulen Peninsula, in association with leiosphaerids in the third cycle of the Manndrapselva Member of the Stáhpogieddi Formation, correlated with the basal Terreneuvian (Högström et al. Reference Högström, Jensen, Palacios and Ebbestad2013), as well as in the Cambrian Series 2 to Miaolingian Duolbagáisá Formation further up in the stratigraphy (Palacios et al. Reference Palacios, Högström, Ebbestad, Agić, Høyberget, Jensen, Meinhold and Talyor2020). Only two samples (one fossiliferous) from the Manndrapselva Member below the Ediacaran–Cambrian boundary were analysed here, but no Granomarginata was recovered. Instead, these strata contain organic problematica such as a neck-bearing microfossil (Fig. 5d), as well as fragments of leiosphaerids, bacterial filaments and SCF. Palacios et al. (Reference Palacios, Ou, Högström, Jensen, Høyberget, Meinhold, Taylor, Ebbestad and Agić2017) observed lobate SCF problematica upsection in the third cycle similar to microfossils from the Gibbett Hill Formation on Newfoundland (Fig. 6c).

4.c. Mara Member assemblage, Dabis Formation, Nama Group, Farm Pockenbank, Namibia

Organic-walled microfossils recovered from the Mara Member of the Nama Group on Farm Pockenbank occur in fine sandstones/silts interbedded with limestones, deposited in a shallow-marine environment. Taxa include: Granomarginata squamacea, Lagoenaforma collaris gen. et sp. nov., Leiosphaeridia crassa, Simia annulare (Fig. 6f), Bavlinella sp. (Fig. 6h), Symplassosphaeridium sp. and vesicle fragments of smooth-walled microfossils or possible SCF (Fig. 6j). Fragments of broad filaments are rare, but similar to material identified as Vendotaenia sp. from the Kuibis Subgroup by Germs et al. (Reference Germs, Knoll and Vidal1986). The newly reported microfossils here occur below strata containing possible first occurrence of cloudinids (following an unillustrated report of Cloudina by Germs, Reference Germs1972 a; cf. Wood et al. Reference Wood, Poulton, Prave, Hoffmann, Clarkson, Guilbaud, Lyne, Tostevin, Bowyer, Penny and Curtis2015), and they are uncomformably overlain by the Kliphoek and Aar members, which contain the Ediacara-type macrofossils Ernietta (Pflug, Reference Pflug1966; Elliot et al. Reference Elliott, Trusler, Narbonne, Vickers-Rich, Morton, Hall and Schneider2016), Pteridinium (Gürich, Reference Gürich1930) and Rangea (Narbonne et al. Reference Narbonne, Saylor and Grotzinger1997; Vickers-Rich et al. Reference Vickers-Rich, Ivantsov, Trusler, Narbonne, Hall, Wilson, Greentree, Fedonkin, Elliott, Hoffmann and Schneider2013) characteristic of the late Ediacaran Nama assemblage (Narbonne et al. Reference Narbonne, Saylor and Grotzinger1997).

OWM from the weathered sediments of the Mara Member are slightly lighter in colour than the specimens from Newfoundland and Arctic Norway (thermal alteration index (TAI) = 3–4 sensu Hayes et al. Reference Hayes, Kaplan, Wedeking and Schopf1983), which indicates a lower degree of thermal alteration. Leiosphaerids make up the bulk of the OWM assemblage in the Mara Member (c. 80 % of the overall microfossil abundance). Cell aggregates Symplassosphaeridium are the next most common component. Granomarginata represents 3.5% and L. collaris 6% of the assemblage. This preliminary record of Ediacaran OWM from Namibia, despite being of low diversity, is encouraging future explorations of the late Ediacaran microfossil record hosted in the Nama Group.

4.d. Gibbett Hill Formation microfossils, Signal Hill Group, Avalon Peninsula, Newfoundland, Canada

The Gibbett Hill Formation contains rare and poorly to moderately preserved OWM. The most common component are fragments of prokaryotic filaments and leiosphaerids. As a low-manipulation acid maceration method was used, the fragmentation is likely not a result of palynological processing and could instead indicate transport. Additional microfossils include prokaryotic clusters of cells Symplassosphaeridium sp., a small carbonaceous problematicum with lateral protrusions (Unnamed Form B, Fig. 6c), a fragment of a single-celled microfossil with a spongy envelope – likely Granomarginata prima (Fig. 6l) – and a dark flask-like microfossil with an elongate neck-like structure Lagoenaforma sp. (Fig. 5e). The dark colour of the Gibbett Hill OWM indicates high thermal alteration of the organic matter. Only a single specimen of a poorly preserved Granomarginata has been recovered. However, due to the presence of the late Ediacaran organic problematica (Fig. 6c) and L. collaris, which co-occur with Granomarginata in the Ediacaran strata of Norway and Namibia, the identification of envelope-bearing microfossil from Gibbett Hill as Granomarginata is plausible. These microfossils occur hundreds of metres above the fossiliferous successions hosting some of the oldest assemblage of Ediacaran macrofossils (cf. Hofmann et al. Reference Hofmann, O’Brien and King2008; Liu et al. Reference Liu, Kenchington and Mitchell2015; Matthews et al. Reference Matthews, Liu, Yang, McIlroy, Levell and Condon2021), consistent with a broadly late Ediacaran age of the Gibbett Hill Formation.

5.a. Ediacaran Granomarginata

The lower Ediacaran strata accommodate a rich and diverse record of organically preserved microfossils of biostratigraphic importance (e.g. Zang, Reference Zang1988; Grey, Reference Grey2005; Vorob’eva et al. Reference Vorob’eva, Sergeev and Knoll2009; Sergeev et al. Reference Sergeev, Knoll and Vorob’eva2011; Willman & Moczydłowska, Reference Willman and Moczydłowska2011). On the contrary, however, the strata postdating localized short-lived glaciations, the Shuram negative carbon isotope excursion (CIE) and the first appearance of the macroscopic Ediacara-type biota are generally depauperate of microfossils, with little distinctive morphologies. The strata bearing Ediacaran macrofossils rarely contain acritarchs, mainly leiosphaerids and prokaryotes (cf. Hofmann et al. Reference Hofmann, Hill and King1979; Grey, Reference Grey2005; Leonov & Ragozina, Reference Leonov, Ragozina, Vickers-Rich and Komarower2007) in lower abundance than in older, pre-Gaskiers or pre-Shuram strata. This pattern is observed on the Digermulen Peninsula where the lower Ediacaran Nyborg Formation contains acanthomorphs (Agić et al. Reference Agić, Högström, Jensen, Ebbestad, Meinhold, Taylor, Palacios and Høyberget2018), whereas the strata above in the Stáhpogieddi Formation are mostly barren and relatively depauperate until Cambrian time. OWM assemblages of low diversity, with few eukaryotic forms, have also been reported from Argentina, Australia, Brazil, East European Platform, Namibia and Siberia (Germs et al. Reference Germs, Knoll and Vidal1986; Gaucher et al. Reference Gaucher, Boggiani, Sprechmann, Sial and Fairchild2003; Grey, Reference Grey2005; Leonov & Ragozina, Reference Leonov, Ragozina, Vickers-Rich and Komarower2007; Chiglino et al. Reference Chiglino, Gaucher, Sial and Ferreira2015; Kolesnikov et al. Reference Kolesnikov, Marusin, Nagovitsin, Maslov and Grazhdankin2015; Ragozina et al. Reference Ragozina, Dorjnamjaa, Serezhnikova, Zaitseva and Enkhbaatar2016; Arrouy et al. Reference Arrouy, Gaucher, Poiré, Xiao, Peral, Warren, Bykova and Quaglio2019; Arvestål & Willman, Reference Arvestål and Willman2020). Late Ediacaran acanthomorphic acritarchs were found in Mongolia (Anderson et al. Reference Anderson, McMahon, Macdonald, Jones and Briggs2019) and in a drillcore from Siberia (Grazhdankin et al. Reference Grazhdankin, Nagovitsin, Golubkova, Karlova, Kochnev, Rogov and Marusin2020), but these occurrences are exceptions among the generally low-diversity late Ediacaran OWM assemblages.

The organic-walled microfossil genus Granomarginata is one of the more distinguishable OWM taxa of the Terreneuvian epoch, known from units in Canada, China, the East European Platform, Finland, India, Norway, Siberia, and Spain (Moczydłowska, Reference Moczydłowska1991, Reference Moczydłowska2011; Palacios & Moczydłowska, Reference Palacios and Moczydłowska1998; Kumar & Maithy, Reference Kumar and Maithy2008; Yin et al. Reference Yin, Yang, Peng and Kong2009; Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018, Reference Palacios, Högström, Ebbestad, Agić, Høyberget, Jensen, Meinhold and Talyor2020; Slater & Willman, Reference Slater and Willman2019), and was also reported from the uppermost Ediacaran strata of India (Prasad et al. Reference Prasad, Asher and Borgohai2010) and Poland (Gunia, Reference Gunia1990; Jachowicz-Zdanowska, Reference Jachowicz-Zdanowska2011). It is a common component of the Granomarginata prima Zone of the East European Platform (EEP) (Jankauskas & Lendzion, Reference Jankauskas and Lendzion1992), the Granomarginata Zone in Newfoundland (Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018), and rare to common in abundance in Skiagia-bearing zones (e.g. Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018, Reference Palacios, Högström, Ebbestad, Agić, Høyberget, Jensen, Meinhold and Talyor2020) that characterize the latest Terreneuvian and Cambrian Series 2. The new record documented here extends its distribution deeper in time as well as to a new region: Namibia.

Granomarginata is a single-celled eukaryote consisting of a central body and an uneven equatorial extension with granular surface. Its morphology resembles a phycoma of prasinophyte algae (Moczydłowska, Reference Moczydłowska2011). Because of its widespread palaeogeographic distribution and occurrence in sediments deposited in both shallow and deep waters, it is assumed to have been a cyst of a planktonic organism. Microfossils with distinct morphological elements (e.g. processes and envelopes) provide a useful biostratigraphic tool, and the envelope-bearing Granomarginata is one of the few non-leiosphaerid acritarchs present in low-diversity microfossil assemblages of upper Ediacaran strata, in addition to organically preserved problematica (cf. Golubkova & Raevskaya, Reference Golubkova, Raevskaya, Steemans and Javaux2005; Leonov & Ragozina, Reference Leonov, Ragozina, Vickers-Rich and Komarower2007; Moczydłowska et al. Reference Moczydłowska, Budd and Agić2015; Slater et al. Reference Slater, Harvey, Bekker and Butterfield2020). Microfossils of this material differ from more ubiquitous Proterozoic envelope-bearing taxa such as Simia (also present in the Nama Group) in their fluffy, granular envelope with an uneven outline, which is likely a result of its less resistant nature compared with the central body (Naumova, Reference Naumova1960; Moczydłowska, Reference Moczydłowska1991). Although the material from Norway and Newfoundland is relatively poorly preserved, it possesses sufficient diagnostic features that fall into the preservational range of Granomarginata reported in younger, thermally altered sedimentary successions (e.g. Moczydłowska, Reference Moczydłowska2002).

Until now, Granomarginata was considered characteristic of the lower Cambrian Lontovan regional stage of the EEP (Volkova et al. Reference Volkova, Kirjanov, Piskun, Paskeviciene, Jankauskas, Urbanek and Rozanov1983; Jankauskas & Lendzion, Reference Jankauskas and Lendzion1992). Yet similarly to recent observations that the fossil record of some traditionally Cambrian groups such as SCF extends back into the Ediacaran (Slater et al. Reference Slater, Harvey, Bekker and Butterfield2020, see also Chiglino et al. Reference Chiglino, Gaucher, Sial and Ferreira2015), Granomarginata first occurs in older strata globally, albeit in lower abundance. In the lower Cambrian Chapel Island Formation on Newfoundland, Granomarginata precedes the first appearance of small process-bearing acritarchs characteristic of the early Cambrian Period, which was the rationale used for the establishment of the Granomarginata Zone (Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018). Considering our findings and previously published data on the Ediacaran Granomarginata (Gunia, Reference Gunia1990; Prasad et al. Reference Prasad, Asher and Borgohai2010; Jachowicz-Zdanowska, Reference Jachowicz-Zdanowska2011), the Granomarginata Zone could represent an extension of late Ediacaran OWM assemblages into the Cambrian. Granomarginata’s appearance on the Digermulen Peninsula is just above the beds containing the macroscopic fossil Palaeopascichnus attributed to the middle–upper Ediacaran (Fig. 2a; Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b) and below and through the horizons bearing discoidal and dickinsoniamorph Ediacara-type macrofossils in Norway (cf. Högström et al. Reference Högström, Jensen, Palacios and Ebbestad2013, Reference Högström, Jensen, Ebbestad, Taylor, Høyberget, Agić, Meinhold and Palacios2017). On Newfoundland, Granomarginata occurs in upper Ediacaran strata (Fig. 2c), in units well above formations bearing Avalon assemblage macrofossils (cf. O’Brien & King, Reference O’Brien and King2004; Matthews et al. Reference Matthews, Liu, Yang, McIlroy, Levell and Condon2021). In Namibia, Granomarginata occurs in the unit below strata bearing Cloudina (cf. Germs, Reference Germs1972a, Reference Germs1983), and in strata overlain by a member containing the late Ediacaran Nama assemblage (Fig. 2; cf. Narbonne et al. Reference Narbonne, Saylor and Grotzinger1997; Vickers-Rich et al. Reference Vickers-Rich, Ivantsov, Trusler, Narbonne, Hall, Wilson, Greentree, Fedonkin, Elliott, Hoffmann and Schneider2013; Elliot et al. Reference Elliott, Trusler, Narbonne, Vickers-Rich, Morton, Hall and Schneider2016; Maloney et al. Reference Maloney, Boag, Facciol, Gibson, Cribb, Koester, Kenchington, Racicot, Darroch and Laflamme2020). Rocks in these localities are not coeval, and we do not correlate them, but all three sequences represent the post-Shuram late Ediacaran time interval (cf. Xiao et al. Reference Xiao, Narbonne, Zhou, Laflamme, Grazhdankin, Moczydłowska-Vidal and Cui2016) and offer insights about the age range of flask-shaped microfossils and Granomarginata.

Two Granomarginata morphotypes are recognized in the present material. The type with a wider equatorial extension is consistent with the diagnosis of G. squamacea (Fig. 4a–d). The morphotype with a narrower extension (Fig. 4e, f) is consistent with G. prima. This taxon is also known from the upper Ediacaran strata of Poland (Jachowicz-Zdanowska, Reference Jachowicz-Zdanowska2011), but it is the more pervasive morphotype in younger strata, known from the Terreneuvian deposits of the Digermulen Peninsula (Högström et al. Reference Högström, Jensen, Palacios and Ebbestad2013; Palacios et al. Reference Palacios, Högström, Ebbestad, Agić, Høyberget, Jensen, Meinhold and Talyor2020), New Brunswick (Palacios et al. Reference Palacios, Jensen, Barr, White and Miller2011) and Newfoundland (Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018) in Canada, from the lower–middle Cambrian of China (Yin et al. Reference Yin, Yang, Peng and Kong2009), as well as from elsewhere on Baltica (Volkova et al. Reference Volkova, Kirjanov, Piskun, Paskeviciene, Jankauskas, Urbanek and Rozanov1983; Jankauskas & Lendzion, Reference Jankauskas and Lendzion1992), the EEP (Jachowicz-Zdanowska, Reference Jachowicz-Zdanowska2013; Szczepanik & Żylińska, Reference Szczepanik and Żylińska2016) and the eastern Cordillera (Rubinstein et al. Reference Rubinstein, Mángano and Buatois2003). In the stratigraphic correlation chart presented by Kumar & Maithy (Reference Kumar and Maithy2008), the Stáhpogieddi Formation in Norway was aligned with the Ediacaran to lowermost Cambrian Kauriyala Formation of the Lesser Himalayas in India, which also contains G. prima. It was potentially reported from the Kuibis Subgroup in Namibia by Germs et al. (Reference Germs, Knoll and Vidal1986, fig. 6i) as a ‘Comasphaeridium-like fossil’.

Granomarginata is a rare component (c. ≤ 5 specimens per slide) of the leiosphaerid-dominant palynomorph assemblage (c. 50–70 leiosphaerids per sample) in the upper Ediacaran successions studied here, where it co-occurs with rare small carbonaceous problematica. Both Granomarginata morphotypes are more common and abundant in the Fortunian Stage, and define the Granomarginata Zone. Their higher abundance (> 10 specimens per slide), along with Cambrian-characteristic taxa, can be viewed as more indicative of lower Cambrian strata (e.g. Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018). On the other hand, a low abundance of Granomarginata within a leiosphaerid-dominant assemblage, in association with flask-shaped L. collaris, is so far found in upper Ediacaran or transitional strata.

5.b. The life and times of the Granomarginata–Lagoenaforma association

The new flask-shaped microfossil Lagoenaforma (Fig. 5) was observed in the horizons containing Ediacaran Granomarginata. Flask-shaped microfossils resembling chitinozoans are common in Ordovician–Devonian strata and some non-chitinozoan flask-shaped problematica are present in Ordovician strata (e.g. Loeblich & McAdam, Reference Loeblich and MacAdam1971), but have not been previously described from the Ediacaran. L. collaris is a minor component of leiosphaerid-dominated assemblages, but in addition to Granomarginata it is one of the few OWM taxa outside of dominant simple sphaeromorphs in the upper Ediacaran (LELP assemblage). As L. collaris is currently unknown from Cambrian units, it serves as a better representative of the late Ediacaran microbiota of the two. A low-diversity OWM assemblage with G. prima occurs along with ‘flask-shaped bodies’ in the lower Cambrian Withycombe Formation, UK (Rushton & Molyneux, Reference Rushton and Molyneux1990). No microfossils were illustrated in that publication, so affinities with Lagoenaforma could not be determined. However, the presence of other soft-bodied flask-shaped microfossils higher up in the stratigraphy on the Digermulen Peninsula (A. Högström, pers. obs.) and in other upper Ediacaran – Cambrian units worldwide (Table 1; cf. Sabouri et al. Reference Sabouri, Frahani and Narimani2003), as well as agglutinated forms (Gaucher & Sprechmann, Reference Gaucher and Sprechmann1999), suggests that flask-shaped OWM may be a common component of the microbiota during this transitional interval.

We found these OWM in upper Ediacaran units with a depauperate palynomorph assemblage, but their full stratigraphic range still needs to be determined. We used information on the age of the rocks hosting Granomarginata–Lagoenaforma to assess their age range. Granomarginata and Lagoenaforma do not co-occur with the classic acanthomorphic acritarch assemblage (ECAP/DPA) in the underlying lower Ediacaran strata in Norway (H. Agić, pers. obs.), nor have they been recognized so far in the older deposits on Newfoundland (see Hofmann et al. Reference Hofmann, Hill and King1979) or elsewhere (e.g. Grey, Reference Grey2005), so we view them as constituents of the late Ediacaran OWM assemblage (LELP sensu Grey, Reference Grey2005). On Newfoundland, a flask-shaped microfossil was found in an assemblage hundreds of metres above the youngest occurrence of rangeomorphs in the St John’s Group that have a maximum age of 564.13 ± 0.65 Ma (U–Pb zircon data; Matthews et al. Reference Matthews, Liu, Yang, McIlroy, Levell and Condon2021). In Namibia Granomarginata and Lagoenaforma are found in the Mara Member, below all local occurrences of Ediacaran body fossils, and which records a negative δ¹³C excursion that has been interpreted as correlative with the Shuram–Wonoka CIE (cf. Grotzinger et al. Reference Grotzinger, Bowring, Saylor and Kaufman1995; Saylor et al. Reference Saylor, Grotzinger and Germs1995; Narbonne et al. Reference Narbonne, Saylor and Grotzinger1997). In Arctic Norway, these fossils appear immediately above the first occurrence of palaeopascichnids and below the first Ediacara-type fossils including discs and dickinsoniamorphs (Högström et al. Reference Högström, Jensen, Palacios and Ebbestad2013, Reference Högström, Jensen, Ebbestad, Taylor, Høyberget, Agić, Meinhold and Palacios2017; Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b), suggesting an age of 565–550 Ma based on radioisotopic ages that constrain similar fossils assemblages (cf. Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b; Kolesnikov et al. Reference Kolesnikov, Liu, Danelian and Grazhdankin2018; Soldatenko et al. Reference Soldatenko, El Albani, Ruzina, Fontaine, Nesterovsky, Paquette, Meunier and Ovtcharova2019). These examined units are not coeval, but their ages are mostly younger than the Shuram anomaly, the most negative carbon isotope excursion in Earth’s history and a global, synchronous event with bounding Re–Os ages of 574.0 ± 4.7 to 567.3 ± 3.0 Ma (Rooney et al. Reference Rooney, Cantine, Bergmann, Gómez-Pérez, Al Baloushi, Boag, Busch, Sperling and Strauss2020). Based on these occurrences, and depending on the age of palaeopascichnids in the Indreelva Member (see Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b), the Granomarginata–Lagoenaforma association first appeared after, or coincides with, the latest part of the Shuram excursion. It has a relatively long range to the uppermost Ediacaran, and Granomarginata becomes more common in the Cambrian strata.

The age uncertainty of the Norwegian strata presents two possibilities for the overall age range of the Granomarginata–Lagoenaforma association (Fig. 7b). The Mortensnes Formation diamictite (separated from the Indreelva Member by the Lillevannet Member, Fig. 2a) is thought to be of Ediacaran age (Halverson et al. Reference Halverson, Hoffman, Schrag, Maloof and Rice2005). A dolomite bed 20 m below the Mortensnes diamictite on the neighbouring Varanger Peninsula contains depleted δ¹³C values (< −8‰) considered ‘a likely correlative of the Shuram–Wonoka anomaly’ (Rice et al. Reference Rice, Edwards, Hansen, Arnaud and Halverson2011, p. 598), and it is thought to correlate with the Shuram CIE in the upper Johnnie Formation in Death Valley, USA (Halverson et al. Reference Halverson, Hoffman, Schrag, Maloof and Rice2005). This suggests a younger age of the Mortensnes diamictite than the Marinoan glaciation and it was correlated with the short-lived Ediacaran Gaskiers glaciation expressed in diamictites on Newfoundland. At the time that model was proposed, the Gaskiers was assumed to be near in age to the Wonoka (=Shuram) anomaly (cf. Halverson et al. Reference Halverson, Hoffman, Schrag, Maloof and Rice2005). Subsequently, the age of the Gaskiers glaciation was constrained to c. 579 Ma (Pu et al. Reference Pu, Bowring, Ramezani, Myrow, Raub, Landing, Mills, Hodgin and Macdonald2016), which is older than the recent age constraints on the Shuram–Wonoka excursion based on Re–Os geochronology of strata in Oman and NW Canada (c. 574–567 Ma, Rooney et al. Reference Rooney, Cantine, Bergmann, Gómez-Pérez, Al Baloushi, Boag, Busch, Sperling and Strauss2020) and estimates from astrochronology (c. 570–562 Ma, Gong & Li, Reference Gong and Li2020). This places the Shuram–Wonoka excursion after the Gaskiers glaciation. Accepting the interpretation that the negative δ¹³C values in the Nyborg Formation carbonates are representative of the Shuram–Wonoka anomaly, the Mortensnes diamictite could be younger than the Gaskiers and Trinity diamictites on Newfoundland, which suggests an even younger age for the base of the overlying Indreelva Member. This places it closer in age to the studied strata in Newfoundland and Namibia, and implies a narrower stratigraphic range of OWM at the end of the Ediacaran Period.

Fig. 7.

Distribution and occurrences of documented Granomarginata–Lagoenaforma in the Ediacaran Period. (a) Microfossils from the studied units occur in three distinct areas: Baltica (Indreelva Member, Vestertana Group), Avalonia (Gibbett Hill Formation, Signal Hill Group) and Nama Basin (Mara Member, Nama Group), in white. Localities with additional occurrences of Ediacaran Granomarginata or flask-shaped organic-walled microfossils are marked in black. Continental reconstruction around 550 Ma was produced using PaleoAtlas for GPlates program (Scotese, Reference Scotese2016). (b) Schematic timeline of the appearance and the stratigraphic range of Granomarginata–Lagoenaforma relative to macrofossil assemblages and major environmental events in the Ediacaran Period. The orange box represents the permissible time of the duration of the Shuram negative carbon isotope excursion, following Rooney et al. (Reference Rooney, Cantine, Bergmann, Gómez-Pérez, Al Baloushi, Boag, Busch, Sperling and Strauss2020). Fossiliferous localities are marked by black symbols. A dashed line represents the interval of age-uncertainty for each locality (see Discussion for details).

Alternatively, if the Mortensnes Formation is of Gaskiers age (Halverson et al. Reference Halverson, Hoffman, Schrag, Maloof and Rice2005) and therefore older than the Shuram excursion, the Granomarginata–Lagoenaforma association has approximately the same age constraint as Palaeopascichnus (Fig. 7b). This is supported by the presence of palaeopascichnids of a type around 565 Ma or younger in age in the Indreelva Member (Jensen et al. Reference Jensen, Högström, Høyberget, Meinhold, McIlroy, Ebbestad, Taylor, Agić and Palacios2018 b), just below the occurrence of OWM, which coincides with the later part of the permissible duration of the Shuram excursion. Moreover, the OWM and the palaeopascichnids occur prior to the appearance of dickinsoniamorphs (Högström et al. Reference Högström, Jensen, Ebbestad, Taylor, Høyberget, Agić, Meinhold and Palacios2017), whose stratigraphic range is around 558–550 Ma (Narbonne et al. Reference Narbonne, Xiao, Shields, Gehling, Gradstein, Ogg, Schmitz and Ogg2012). The older age of the Mortensnes diamictite, probably coeval with the Gaskiers and Trinity diamictites, is therefore more likely, and indicates a longer age range of Granomarginata–Lagoenaforma through late Ediacaran time.

A negative carbon isotope excursion in the Nama Group was correlated to excursions recorded in the upper Nafun (c. 550 Ma) and lower Ara groups in Oman, above the Shuram Formation (Grotzinger et al. Reference Grotzinger, Bowring, Saylor and Kaufman1995; Halverson et al. Reference Halverson, Hoffman, Schrag, Maloof and Rice2005). However, these depleted δ¹³C values in the carbonates of the Dabis Formation, including the Mara Member, have also been interpreted as heralding the end of the Shuram excursion (Hall et al. Reference Hall, Kaufman, Vickers-Rich, Ivantsov, Trusler, Linnemann, Hofmann, Elliott, Cui, Fedonkin and Hoffmann2013; Wood et al. Reference Wood, Poulton, Prave, Hoffmann, Clarkson, Guilbaud, Lyne, Tostevin, Bowyer, Penny and Curtis2015). The excursion recorded in the Mara Member elsewhere (Kaufman et al. Reference Kaufman, Hayes, Knoll and Germs1991; Wood et al. Reference Wood, Poulton, Prave, Hoffmann, Clarkson, Guilbaud, Lyne, Tostevin, Bowyer, Penny and Curtis2015) is not fully expressed in the sampled section, possibly because the Pockenbank area was on a palaeo-high compared with that of other localities that record the Shuram anomaly in full (see Vickers-Rich et al. Reference Vickers-Rich, Narbonne, Laflamme, Darroch, Kaufman and Kriesfeld2016). Additional micropalaeontological investigation is needed to evaluate the extent of the association’s range through the lower Nama Group and in relation to its chemostratigraphy.

Throughout the late Ediacaran interval, both Granomarginata and Lagoenaforma are rare in comparison to leiosphaerid and filamentous microfossils, but still more morphologically distinct than most other OWM in the upper Ediacaran strata. The association also co-occurs with the coccoid aggregate structure Bavlinella sp. (Fig. 6h), which is relatively common in Neoproterozoic strata (cf. Vidal, Reference Vidal1976) and was previously recovered from the Ediacaran strata of Namibia by Germs et al. (Reference Germs, Knoll and Vidal1986). Smooth-walled OWM (leiosphaerids; Fig. 6a, b, d) are the most abundant component of the examined assemblages, consistent with the idea that the late Ediacaran microbiota was generally of low diversity and dominated by simple leiosphaerids (Moczydłowska, Reference Moczydłowska1991; Grey, Reference Grey2005). Lophosphaeridium is another OWM best known from Cambrian strata that was also reported from the upper Ediacaran Frecheirinha Formation (Chiglino et al. Reference Chiglino, Gaucher, Sial and Ferreira2015) and Maricá and Bom Jardin groups in Brazil (Lehn et al. Reference Lehn, Horodyski and Paim2019). This taxon was not found in the present material, so it may not have been distributed globally or it may have been restricted to a specific environment, and more work is needed to assess its distribution at this time. Regardless, both Lophosphaeridium and Granomarginata first appeared during the rise of macroscopic Ediacara-type biota, and have subsequently diversified and became more prominent components of OWM assemblages in the Cambrian strata (e.g. Moczydłowska, Reference Moczydłowska1991; Palacios et al. Reference Palacios, Jensen, Barr, White and Myrow2018).

Because of the presence of taxa and fossil groups that ‘cross’ the Ediacaran–Cambrian boundary, the composition of whole assemblages may also be relevant for the OWM biostratigraphy of the Ediacaran–Cambrian transition. A leiosphaerid-dominant assemblage with Lagoenaforma in association with Granomarginata is present in multiple palaeogeographic areas and, pending further studies, has potential to be broadly used as one of the indicators of the upper series Ediacaran. However, this association may also reflect a specific environmental control.

5.c. Palaeoenvironmental implications

Our new data show that Granomarginata and Lagoenaforma are relatively rare components of the late Ediacaran microbiota, but were present on several palaeocontinents (Fig. 7a; Table 1). The studied strata in Norway, Newfoundland and Namibia are not coeval, but can be viewed as part of the upper series Ediacaran (cf. Xiao et al. Reference Xiao, Narbonne, Zhou, Laflamme, Grazhdankin, Moczydłowska-Vidal and Cui2016). Considering the palaeogeographic reconstruction for this time, the Granomarginata–Lagoenaforma association was widely dispersed (Fig. 7a), and possibly an assemblage of cosmopolitan taxa. The association could be representative of taxa occupying a specific type of environment. All strata in which this assemblage occurs (including the upper Ediacaran rocks bearing Granomarginata in India, Poland and Baltica; Prasad et al. Reference Prasad, Asher and Borgohai2010; Jachowicz-Zdanowska, Reference Jachowicz-Zdanowska2011; Arvestål & Willman, Reference Arvestål and Willman2020), represent a marine shallow-water to marginal shelf environment. Leiosphaerids are usually highly abundant in nearshore, shallow-water environments (e.g. Li et al. Reference Li, Servais, Yan and Zhu2004). They comprise most of the OWM assemblage containing Granomarginata and Lagoenaforma, so this is further indication of a shallow-water setting.

Acanthomorphic OWM characteristic of ECAP/DPA do not occur in the studied strata, although rare cases of late Ediacaran acanthomorphs are documented in Mongolia (Anderson et al. Reference Anderson, Macdonald, Jones, McMahon and Briggs2017, Reference Anderson, McMahon, Macdonald, Jones and Briggs2019) and Siberia (Grazhdankin et al. Reference Grazhdankin, Nagovitsin, Golubkova, Karlova, Kochnev, Rogov and Marusin2020). These assemblages are an exception among the depauperate OWM assemblages prevalent at this time (Grey, Reference Grey2005; Leonov & Ragozina, Reference Leonov, Ragozina, Vickers-Rich and Komarower2007). While the pre-Shuram ECAP assemblages are generally diverse (e.g. 54 taxa in the Doushantuo Formation; Xiao et al. Reference Xiao, Zhou, Liu, Wang and Yuan2014), the LELP assemblages tend to contain fewer taxa (e.g. 16 in the Lyamtsa Formation, White Sea region; Leonov & Ragozina, Reference Leonov, Ragozina, Vickers-Rich and Komarower2007), many of which are bacterial. The exceptionally preserved microfossils from the Khesen Formation in Mongolia exhibit Doushantuo-style preservation (Anderson et al. Reference Anderson, Macdonald, Jones, McMahon and Briggs2017), similar to ECAP microbiota from phosphorites of the lower Ediacaran Doushantuo Formation in China (e.g. Xiao et al. Reference Xiao, Zhou, Liu, Wang and Yuan2014). The Khesen assemblage is preserved in phosphatic grainstones, within a sediment-starved, condensed carbonate succession. The acid-extracted acanthomorphs from the Oppokun Formation in Siberia occur in a thick succession of mudstones (Grazhdankin et al. Reference Grazhdankin, Nagovitsin, Golubkova, Karlova, Kochnev, Rogov and Marusin2020), probably deposited in a low-energy environment. These occurrences in different depositional environments may result in different assemblages: nearshore shallow marine in the case of the Granomarginata–Lagoenaforma association and depauperate leiosphaerid assemblage (LELP) recognized by Grey (Reference Grey2005), or low-energy environments in the case of ECAP. The overall dearth of microfossils across the Ediacaran–Cambrian transition could also be a result of the lack of sampling for palynological analyses, or a depositional hiatus. Many relevant successions consist of mainly unsuitable lithologies for OWM preservation (especially in Australia; Grey, Reference Grey2005), although this is not the case on EEP and Baltica. The dearth of OWM could also relate to the Kotlinian Crisis: a drop in diversity of soft-bodied taxa near the increase of bioturbation and expansions of reef-builders (Kolesnikov et al. Reference Kolesnikov, Marusin, Nagovitsin, Maslov and Grazhdankin2015).

Some prasinophyte-like OWM (in addition to Granomarginata, e.g. Tasmanites and Pterosperma-like morphotypes) persisted through the Ediacaran–Cambrian transition, and it was suggested that perhaps these organisms played a role as primary producers in sustaining the metazoan ecosystem during this transitional interval (Moczydłowska, Reference Moczydłowska2011). This is difficult to reconcile with biomarker evidence for bacterially dominated primary production on Baltica and the EEP in the upper Ediacaran strata (Pehr et al. Reference Pehr, Love, Kuznetsov, Podkovyrov, Junium, Shumlyanskyy, Sokur and Bekker2018). Prasinophytes are generally successful in low diversities of other phytoplankton taxa and in an aftermath of crises, which labels them disaster-taxa (e.g. van de Schootbrugge et al. Reference van de Schootbrugge, Tremolada, Rosenthal, Bailey, Feist-Burkhardt, Brinkhuis, Pross, Kent and Falkowski2007). A community of such disaster-taxa and potential mixotrophs (flask-shaped microfossils) is therefore a likely response of eukaryotic microbiota to ecosystem perturbations (cf. Kolesnikov et al. Reference Kolesnikov, Marusin, Nagovitsin, Maslov and Grazhdankin2015; Wood et al. Reference Wood, Liu, Bowyer, Wilby, Dunn, Kenchington, Cuthill, Mitchell and Penny2019) through the late Ediacaran Period.