Geographic and stratigraphic setting

The Maly Karatau Range (Fig. 1.1) is located within the Karatau-Таlass folded zone of the Ulutau-Sinian structural belt that extends southeastward from the Ulutau Mountains of central Kazakhstan into northern China. The basinal sediments that comprise this monocline (Fig. 1.2), deposited during the Caledonian tectonic cycle, span an interval that extends from the Neoproterozoic to the mid-Paleozoic. The Neoproterozoic (Upper Riphean) to Lower Cambrian part of this succession includes six stratigraphic groups, defined and discussed in detail in numerous publications (Bezrukov, Reference Bezrukov1941; Аnkinovich, Reference Ankinovich1961; Korolev, Reference Korolev1961, Reference Korolev1971; Keller et al., Reference Keller, Korolev and Krylov1965; Krylov, Reference Krylov1967; Eganov and Sovietov, Reference Eganov and Sovietov1979; Korolev and Ogurtsova, Reference Korolev and Ogurtsova1981, Reference Korolev and Ogurtsova1982; Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981; Ogurtsova, Reference Ogurtsova1985; Eganov et al., Reference Eganov, Sovietov and Yanshin1986; Ogurtsova and Sergeev, Reference Ogurtsova and Sergeev1987, Reference Ogurtsova and Sergeev1989; Missarzhevskii, Reference Missarzhevskii1989; Sergeev, Reference Sergeev1989, Reference Sergeev1992, Reference Sergeev2006; Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989; Mambetov, Reference Mambetov1993; Popov et al., Reference Popov, Bassett, Zhemchuzhnikov, Holmer and Klishevich2009; Meert et al., Reference Meert, Gibsher, Levashova, Grice, Kamenov and Ryabinin2011). The source of the Lower Cambrian Kyrshabakta and Chulaktau microbiotas studied here is the uppermost of the six stratigraphic units, the Ediacaran through Ordovician Tamda Group.

Figure 1 (1) Map of the Maly Karatau Range showing the locations of the fossiliferous Kyrshabakta (Berkuta Member) and Chulaktau Formation cherts collected from outcrop at stratigraphic sections K-27, K-28, K-29, K-30, K-32, K-33 and K-40 shown in Fig. 2; the inset map at the upper right indicates the location of the region studied in South Kazakhstan (southwest of Astana, the filled region denoted by the arrow between the Aral Sea and Lake Balqash). (2) Generalized stratigraphic column (at right) and lithologies (at lower left) of the Neoproterozoic (Cryogenian through Ediacaran) and Cambrian deposits of the Maly Karatau Range. Abbreviations for formations: Ak=Aktogai, Ch=Chichkan, Kr=Kurgan, Ks=Kyrshabakta; Bk=Berkuta (known also as the “Lower Dolomite” and here regarded as the Berkuta Member of the Kyrshabakta Formation); Cl=Chulaktau, Sh=Shabakta. Abbreviations for Stages: ND=Nemakit-Daldynian, Tm=Tommotian, At=Atdabanian, Bt=Botomian; and, for East European Platform Regional (EEPR) Stages: Rv=Rovno, Lv=Lontova, Vr=Vergale, Rs=Rausve; E=Ediacaran system. Biostratigraphic zones of Lower Cambrian small shelly fossils and trilobites are shown at the upper right.

The Tamda Group is composed of three formations: the lowermost terrigenous-carbonate 6- to 300-m thick Kyrshabakta Formation, characterized by basal diamictites (the “Aktas tillites”; Meert et al., Reference Meert, Gibsher, Levashova, Grice, Kamenov and Ryabinin2011) and an overlying carbonate unit containing interbedded microfossiliferous chert lenses that has been referred to as the “Lower Dolomite” or “Berkuta Formation” (Korolev, Reference Korolev1971) or the “Berkuta Member” (Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981); the mid-Tamda Group siliceous-phosphate Chulaktau Formation, up to a few tens of meters in thickness; and the >3000-m-thick uppermost carbonate Shabakta Formation. For clarity, we refer to the post-glacial carbonate unit of the lowermost Tamda Group Kyrshabakta Formation, the source of one of the two fossil assemblages described here, as the “Berkuta Member.”

As discussed by Meert et al. (Reference Meert, Gibsher, Levashova, Grice, Kamenov and Ryabinin2011), deposition of the lowermost, pre-Berkuta part of the Kyrshabakta Formation commenced with sedimentation of the ~30-m thick Aktas tillites, a unit that was then overlain by a massive widespread cap-dolomite that ranges from 1–3 to 10–12 m thick (Eganov and Sovietov, Reference Eganov and Sovietov1979; Eganov et al., Reference Eganov, Sovietov and Yanshin1986). Separated by a hiatus from the cap-dolomite, deposition continued by sedimentation of a fine-grained dolomite that, in turn, was overlain by a mixed terrigenous and brownish carbonate succession documented only along the Kyrshabakata River (viz., at outcrop K-28 of the present paper). In most of the stratigraphic sections studied here—viz., the Koksu (outcrop K-27), Berkuta (K-29), Au-Sakan (K-30), Zhaanaryk (K-32), Aktogai (K-33), and Kurtlybulak (K-40) sections (Fig. 2)—the lower (pre-Berkuta) part of formation is represented either by interbedded siltstones and argillites or is missing from the succession with a 6–8 m thick part of the Berkuta sediments directly overlying tuffs of the immediately underlying Neoproterozoic Kurgan Formation of the Maly Karoy Group.

Figure 2 Stratigraphic correlation of sampled microfossiliferous cherts of the Berkuta Member of the Kyrshabakta Formation and the Chulaktau Formation at stratigraphic sections K-27, K-28, K-29, K-30, K-32, K-33, and K-40 (the geographic locations of which are specified in the text) in the part of the Maly Karatau Range shown in Fig. 1. Sample numbers with adjacent filled circles indicate the stratigraphic levels of the fossiliferous cherts studied here; symbols denoting rock types are shown in Fig. 1; Us=the Ushbass Member of the Chulaktau Formation; Bc=the B. cristata biostratigraphic zone.

The Berkuta Member of the Kyrshabakta Formation—strata assigned by Eganov and Sovietov (Reference Eganov and Sovietov1979) to the overlying Chulaktau Formation—is composed predominately of dolostone augmented by microfossil-bearing nodules of phosphorite and chert, and contains problematic stromatolites, thrombolites, and metazoan burrows. Following the suggestion of Missarzhevskii and Mambetov (Reference Missarzhevskii and Mambetov1981) and Missarzhevskii (Reference Missarzhevskii1989), we regard this microfossiliferous unit—which unconformably overlies older rocks, primarily those of the Maly Karoy Group—as the terminal member of the Kyrshabakta Formation. Sequence stratigraphy indicates that the Berkuta Member and overlying strata of the formation represent a transgressive sequence that decreases in thickness toward the Besh Tash stratigraphic section along the Tian Shan Mountains (outcrop #9 in Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981) to the southeast of the sections sampled here (Fig. 1).

The Lower Cambrian Chulaktau Formation conformably overlies the Kyrshabakta Formation and the slightly eroded surface of its uppermost Berkuta Member. Silicified phosphorites of the Chulaktau occur as reentrants infilling cracks and erosional features at the top of the Berkuta Member and as phosphatic breccias and interclastic grainstones (flat-pebble conglomerates).

Traditionally, the Chulaktau Formation has been divided into three subunits, in ascending order the Aksai, Karatau, and Ushbass Members (Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981; Mambetov, Reference Mambetov1993; Popov et al., Reference Popov, Bassett, Zhemchuzhnikov, Holmer and Klishevich2009). The Aksai (known also as the “Cherty Member”), a few centimeters to a few meters in thickness, is composed of silicified and non-silicified oolitic phosphorites interbedded with dolomites, shales and bedded cherts and contains abundant thrombolites, in some areas forming reef- or bioherm-like bodies. As documented here, silicified rocks of this unit are richly microfossiliferous.

The middle, Karatau Member of the formation—up to tens of meters thick and composed mainly of nonsilicified or partially silicified (and sporadically microfossiliferous) phosphorites interbedded with shales, cherts, and dolomites—is the principal phosphate-producing unit of the succession. Because of its economic importance, the predominantly oolitic and coarse-grained phosphorites of this unit have been described in numerous publications (e.g., Eganov and Sovietov, Reference Eganov and Sovietov1979; Baturin, Reference Baturin1978; Kholodov and Paul, Reference Kholodov and Paul1993a, Reference Kholodov and Paul1993b, Reference Kholodov and Paul1994).

In the traditional stratigraphic scheme, the immediately overlying iron and manganese oxide-rich limestones and limy dolostones of the Ushbass Member—having a maximum thickness of ~3 m and present sporadically throughout the Maly Karatau Range—have been regarded to comprise the uppermost unit of the Chulaktau Formation. Ushbass strata are overlain disconformably by cherty dolomites of the >3000-m thick Early Cambrian (Atdabanian Stage) through the Ordovician Shabakta Formation.

Opinions vary regarding the stratigraphic boundary between the Shabakta and Chulaktau formations (e.g., Eganov and Sovietov, Reference Eganov and Sovietov1979; Eganov, Reference Eganov1988; Meert et al., Reference Meert, Gibsher, Levashova, Grice, Kamenov and Ryabinin2011). Here, we follow Missarzhevskii and Mambetov (Reference Missarzhevskii and Mambetov1981), who assign the Ushbass Member to the Shabakta Formation rather than the Chulaktau, an interpretation supported by biostratigraphic data both for small shelly fossils (Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981; Missarzhevskii, Reference Missarzhevskii1989) and microfossils (Korolev and Ogurtsova, Reference Korolev and Ogurtsova1981, Reference Korolev and Ogurtsova1982; Ogurtsova, Reference Ogurtsova1985; Sergeev, Reference Sergeev1989, Reference Sergeev1992).

Chronostratigraphic nomenclature adopted here

Internationally accepted stratigraphic nomenclature for Upper Proterozoic-Lower Cambrian successions is in a state of flux. In addition to terms preferred by the International Union of Geological Sciences (IUGS), workers in Russia and central Asia commonly subdivide the lowest Cambrian into the Nemakit-Daldynian, Tommotian and Atdabanian Stages, with those in China including the widely known Meishucuanian Stage. Given this lack of uniformity and the long-established use in Kazakhstan of the Russian stratigraphic system, we use this system for the Lower Cambrian deposits of the Maly Karatau Range. For the Precambrian part of the Maly Karatau succession, we use IUGS nomenclature. We therefore place the Proterozoic-Cambrian boundary as defined by the latest Ediacaran Trichophycus pedum biostratigraphic zone, approximately correlative with the Early Cambrian–defining presence of small shelly fossils of the Protohertzina anabarica zone, and in Fig. 1.2 indicate the approximate stratigraphic relationships between such zones and the Russian and East European Platform Regional Stages.

Age of the microfossiliferous Tamda Group

A pre-Cambrian, pre-Ediacaran, late Neoproterozoic, and evidently Cryogenian, 800- to 750-Ma age of the Maly Karoy Group that underlies the microfossiliferous Tamda Group strata studied here is supported by radiometric and biostratigraphic data. U-Pb dates on zircons in tuffs of the uppermost Maly Karoy Group Kurgan Formation have yielded ages of 779±17 Ma (Sovietov, Reference Sovietov2008) and 766 ±7 Ma (Levashova et al., Reference Levashova, Meert, Gibsher, Grice and Bazhenov2011). Similarly, the composition of the chert-permineralized microbiota of the Chichkan Formation, immediately underlying the uppermost Maly Karoy Group Kurgan Formation, provides strong evidence of its late Neoproterozoic (Cryogenian) age. This assemblage contains numerous taxa typical of pre-Ediacaran Neoproterozoic deposits including vase-shaped microfossils (e.g., Melanocyrillium); morphologically complex and acanthomorphic acritarchs (e.g., Cerebrosphaera, Stictosphaeridium, Trachyhystrichosphaera, and Vandalosphaeridium); and the spiral-filamentous cyanobacterium Obruchevella exilis (Schopf et al., Reference Schopf, Kudryavtsev and Sergeev2010a; Sergeev and Schopf, Reference Sergeev and Schopf2010).

The Neoproterozoic to Cambrian organic-walled microfossils and the biozones of earliest Cambrian small shelly fossils present in Tamda Group strata, the source of the two microfossil assemblages studied here, establish its Early Cambrian age.

The lowermost strata of the Tamda Group Kyrshabakta Formation, immediately overlying those of the Maly Karoy Group, have been reported to contain terminal Neoproterozoic acritarchs of the so-called “valdaian-type” (e.g., Leiosphaeridia, Origmatosphaeridium and Protosphaeridium; Ogurtsova, Reference Ogurtsova1985). The age of these strata, the Aktas tillites, is uncertain: they may be correlatives of the Marinoan, Gaskiers or Baykonurian glacial episodes. Meert et al. (Reference Meert, Gibsher, Levashova, Grice, Kamenov and Ryabinin2011) tentatively assigned these tillites to the Marinoan glacial event that marks the end of the immediately pre-Ediacaran (pre-Vendian) Cryogenian. This interpretation was based primarily on the presence in Kyrshabakta Formation carbonates of a large negative shift in δ¹³C values (up to −9‰) that may correspond to the Shuram/Wonoka carbon isotope anomaly of approximately the same age. In contrast, Chumakov (Reference Chumakov2009, Reference Chumakov2010, Reference Chumakov2011) correlates the Aktas tillites and similarly aged glacial sequences of Kazakhstan and Kirghizia to Late Ediacaran (Vendian)-Nemakit-Daldyn Baykonurian glacial deposits and, thus, with tillites of the Luoquan Formation (North China), Hankalchough Formation (Tarim, northwestern China), Zabit Formation (East Sayan, northwestern Mongolia-southern Siberia) and the Pourpree de l’Ahnet Group (West African Craton, Algeria). Similarly, rather than correlating the negative carbon isotope excursion in the Kyrshabakta carbonates with the Shuram/Wonoka δ¹³C anomaly, Chumakov (personal communication to V.N.S.) correlates this shift to the negative δ¹³C Dounce anomaly of South China (Zhou et al., Reference Zhou, Yuan, Xiao, Chen and Xue2004) and assigns an age to this glaciation of 550–540 Ma.

Although Chumakov’s interpretation is consistent with the reported occurrence of lowermost Cambrian-defining small shelly fossils of the Protohertzina anabarica biozone in the cap dolomite immediately overlying the Aktas tillites (Mambetov, Reference Mambetov1993), subsequent searches of these strata by Missarzhevskii (personal communication to V.N.S.) were unable to confirm this finding. Eganov and Sovietov (Reference Eganov and Sovietov1979) also recorded the presence of small shelly fossils in this cap dolomite—for which, however, they did not provide taxonomic descriptions. At present, therefore, the oldest confirmed and appropriately documented occurrence of Protohertzina anabarica biozone fossils in the succession here studied is that in the Berkuta Member of the Kyrshabakta Formation (Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981).

Fossils typical of Early Cambrian Tommotian Stage faunas occur in phosphorites of the Kyrshabakta-overlying Chulaktau Formation (Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981). The two lower members of the formation, the Aksai and Karatau, correspond, respectively, to the Tiksitheca licis and Pseudorthotheca costata Tommotian faunal zones, and the uppermost Ushbass Member to the Berkutia cristata zone (which has been suggested, however, to occur in the Atdabanian Stage; Cook and Shergold, Reference Cook and Shergold2005, p. 318).

Lower units of the Chulaktau-overlying Shabakta Formation contain Late Atdabanian faunas of the Rhombocorniculum cancellatum zone (Missarzhevskii and Mambetov, Reference Missarzhevskii and Mambetov1981; Missarzhevskii, Reference Missarzhevskii1989; Mambetov, Reference Mambetov1993; Popov et al., Reference Popov, Bassett, Zhemchuzhnikov, Holmer and Klishevich2009) whereas the upper strata of the formation contain Microcornus parvulus zone small shelly fossils and, higher in the succession, trilobites of the Hebediscus orientalis, Ushbaspis limbata and Redlichia chinensis-Kootenia gimmelfarbi faunal zones of the Lower Cambrian Botomian and Toyonian Stages (Ergaliev and Pokrovskaya, Reference Ergaliev and Pokrovskaya1977; Mambetov, Reference Mambetov1993; Popov et al., Reference Popov, Bassett, Zhemchuzhnikov, Holmer and Klishevich2009).

Such fauna-based biostratigraphic data for the Early Cambrian age of the Tamda Group strata are supported by organic-walled microfossils of the Chulaktau and overlying Shabakta Formation. The Chulaktau shales contain microfossil assemblages that include such time-diagnostic acritarch taxa as Granomarginata prima, G. squamacea, and Leiomarginata simplex, indicating their temporal correlation to the Early Cambrian Lontova Regional Stage (Horizon) of the East European Platform (Korolev and Ogurtsova, Reference Korolev and Ogurtsova1981, Reference Korolev and Ogurtsova1982; Ogurtsova, Reference Ogurtsova1985; Sergeev, Reference Sergeev1989, Reference Sergeev1992). Similarly, and although none of the chert- and phosphate-permineralized Chulaktau microfossils reported here are time-diagnostic, this microbiota is dominated by the distinctive helically coiled cyanobacterium Obruchevella typical of Early Cambrian phosphorite-bearing deposits worldwide (Sergeev, Reference Sergeev1989, Reference Sergeev1992; Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989). Furthermore, acanthomorphic acritarch taxa present in the Chulaktau-overlying Shabakta Formation correspond well to those of the late Early Cambrian Vergale Regional Stage of the East European Platform.

In sum, the Early Cambrian age of Berkuta and Chulaktau microfossil assemblages described here seem firmly established by radiometric analyses of underlying deposits and by biostratigraphic data, both faunal- and microfossil-based, and from both underlying and overlying strata.

Confocal laser scanning microscopy

The history of the development of CLSM, and its principles and technical details are summarized in Claxton et al. (Reference Claxton, Fellers and Davidson2005). By suppressing the image-blurring input of out-of-focus planes above and below the focal plane analyzed, CLSM provides a crisp image of a thin in-focus plane that cannot be provided by standard optical microscopy. The laser of such systems excites fluorescence in the material analyzed, for organic-walled kerogenous fossils emitted from the interlinked polycyclic aromatic hydrocarbons, “PAHs,” of which they are primarily composed (Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005). This kerogen-derived fluorescence is then collected by the detector of the system in a wide spectral range at precisely defined depths of a rock-embedded fossil to produce its three-dimensional image at submicron lateral spatial resolution.

Raman spectroscopy

Raman spectroscopy is an analytical technique used widely in geochemistry for the identification and molecular-structural characterization of minerals (e.g., McMillan and Hofmeister, Reference McMillan and Hofmeister1988; Williams et al., Reference Williams, Nelson and Dyer1997) including graphite, the end-point of the geochemical alteration of kerogenous organics (e.g., Pasteris and Wopenka, Reference Pasteris and Wopenka1991; Wopenka and Pasteris, Reference Wopenka and Pasteris1993; Jehlička et al., Reference Jehlička, Urban and Pokorny2003). Raman can also be used to document the carbonaceous composition of geochemically less altered organic-walled fossils and the mineralogy of their enclosing matrices (Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Wdowiak and Czaja2002, Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005, Reference Schopf, Farmer, Foster, Kudryavtsev, Gallardo and Espinoza2012; Schopf and Kudryavtsev, Reference Schopf and Kudryavtsev2005, Reference Schopf and Kudryavtsev2012; Chen et al., Reference Chen, Schopf, Bottjer, Zhang, Kudryavtsev, Wang, Yang and Gao2007).

In analyses of permineralized carbonaceous matter, CLSM and Raman are complementary, both being used to measure signals derived from properties of the kerogenous materials analyzed—for CLSM, laser-induced fluorescence derived chiefly from the electronic transitions of the interlinked PAHs that predominate in kerogen (Schopf et al, Reference Schopf, Tripathi and Kudryavtsev2006); for Raman, vibrational transitions of such PAHs and their associated functional groups (Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005)—with both being applicable to specimens analyzed at depths of up to 150µm within a fossil-containing thin section. Like CLSM, Raman is capable of providing both two- and three-dimensional images of the specimens analyzed (e.g., Schopf and Kudryavtsev, Reference Schopf and Kudryavtsev2005, Reference Schopf and Kudryavtsev2010, Reference Schopf and Kudryavtsev2012; Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Wdowiak and Czaja2002, Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005). Unlike CLSM, however, Raman provides definitive molecular-structural data about the materials analyzed and for permineralized kerogen-walled fossils and associated carbonaceous matter provides a reliable index, the RIP, of its geochemical maturity (Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005).

Fluorescence spectroscopy

Unlike CLSM, which also relies on the fluorescence of the material analyzed, fluorescence spectroscopy analyzes narrow spectral ranges specific to particular luminophores. Prior to the current study, this technique had been applied to only one other fossiliferous deposit (Schopf and Kudryavtsev, Reference Schopf and Kudryavtsev2010; Cohen et al., Reference Cohen, Schopf, Butterfield, Kudryavtsev and Macdonald2011), primarily because fluorescing minerals are rarely associated with permineralized fossils. Apatite, however, prevalent in the Chulaktau cherts studied here, is an exception. Generally assumed to be nonfluorescing, apatite can be rendered laser-excitably fluorescent by the presence of the rare earth element samarium⁺³ substituting for calcium in the Ca I and II sites of the apatite lattice (Gaft et al., Reference Gaft, Reisfeld and Panczer2005, p. 142, 143, 148). Such Sm⁺³-replacement at the highly symmetric Ca I site has been shown to occur under vacuum whereas that at the low-symmetry Ca II site occurs in the presence of air (Gaft et al., Reference Gaft, Reisfeld, Panczer, Boulon, Shoval and Champagnon1997a, Reference Gaft, Reisfeld, Panczer, Shoval, Champagnon and Boulon1997b), observations that applied to fossil-associated apatite may provide evidence of its environment of formation.

Although additional studies are needed to confirm the usefulness of such substitution to establish paleoenvironmental settings, it is likely that the cause of this effect is the presence or absence of oxygen. Air is 78% nitrogen, 21% oxygen, and <1% Ar, CO₂, and other gases. The dominant component, triple-bonded N₂, has a bond-energy of 226 kcal/mol, among the highest in nature. N₂ is therefore essentially inert and was therefore originally named “azote” (meaning “without life”) by the French chemist Antoine Lavoisier, a property that explains its absence from common rock-forming minerals and its resulting accumulation in Earth’s atmosphere. In contrast, oxygen, the other principal component, is highly reactive and is soluble in apatite-depositing waters where it is present in variable concentrations that, as discussed below, are consistent with oxygen-related patterns of samarium-substitution.

Morphology, geochemistry, and permineralization of the Berkuta and Chulaktau microbiotas

As is shown in Figure 3 for five organic-walled fossils permineralized in the Chulaktau cherts, optical microscopy, confocal laser scanning microscopy, and Raman and fluorescent spectroscopic imagery can be used to analyze the same individual specimen. Because of its confocal capability and high resolution—having a lateral spatial resolution of ~0.2 µm, some 50% greater than optical microscopy—CLSM is particularly useful for documenting the morphology and fine structure of three-dimensionally sinuous fossil filaments such as the specimen of Obruchevella parva shown in Figure 3.1 through 3.5. Similarly, the capability of such CLSM images to be rotated enables them to be studied from perspectives not permitted by optical microscopy, as shown in Figure 4.3 and 4.7 for cask-like to spheroidal vesicles of Berkutaphycus elongatus new gen. and sp. permineralized in cherts of the Berkuta Member of the Kyrshabakta Formation.

Figure 3 Quartz- and apatite-permineralized organic-walled microfossils from the Chulaktau Formation shown in optical photomicrographs (1, 6, 11, 16, 21); confocal laser scanning micrographs (2, 7, 12, 17); two-dimensional Raman images documenting the spatial distribution of kerogen (3, 8, 13, 18, 22; blue, acquired at its ~1605 cm⁻¹ major Raman band); and apatite (4, 9, 14, 19, 23; red, acquired at its ~965 cm⁻¹ major Raman band); and two-dimensional spectroscopic fluorescence images showing the spatial distribution of fossil-permineralizing apatite (5, 10, 15, 20; orange, acquired in the spectral range centered at ~603 nm that includes its major fluorescence bands)—fluorescent because of the presence of Sm⁺³ replacing both Ca I and Ca II sites—and of later-emplaced fossil-encrusting apatite in which Sm⁺³-replaced Ca I sites (24; orange, acquired at ~597 nm) and Ca II sites (24; green, acquired at ~605 nm) are spatially distinct. The red rectangle in (1) denotes the part of the specimen shown in (3–5); that in (6), in (8–10); that in (11), in (13–15); and that (21), in (22–24); (16) shows the same area as that in (17–20); the arrows in (16) and (17) indicate sites of apatite nucleation. (1-5) Obruchevella parva Reitlinger, Reference Reitlinger1959, 4681-391 (102) specimen location point (p.) 11, England Finder Slide (EFS) G32[1], GINPC 202. (6–10) O. cf. meishucunensis Song, Reference Song1984, 4681-391 (102), p. 17, EFS K41[4], GINPC 197. (11–20) Tetraphycus acutus Sergeev, Reference Sergeev1989: (11-15) 4681-391 (102), p. 29, EFS R29[0], GINPC 210; (16–20) 4681-399 (103), p. 26b, EFS P31[0], GINPC 1269. (21–24) Siphonophycus solidum Golub, Reference Golub1979, 4681-1026 (273), p. 81, EFS W23[1], GINPC 1270.

Figure 4 Optical photomicrographs (1, 5, 9, 12, 15, 18), confocal laser scanning micrographs (2, 3, 6, 7, 10, 13, 16, 19), and two-dimensional Raman images showing the spatial distribution of kerogen (4, 8, 11, 14, 17, 20; blue, acquired at its ~1605 cm⁻¹ major band) of quartz-permineralized organic-walled microfossils from the Berkuta Member of the Kyrshabakta Formation. The red rectangle in (1) denotes the part of the specimen shown in (4); that in (5), in (8); that in (9), in (11); that in (12), in (14); that in (15), in (17); and that in (18), in (20). Berkutaphycus elongatus new genus and new species, (1–4) 4681-372 (115a), location point (p.) 22, England Finder Slide (EFS) N35[2], GINPC 1276; (5–8) 4681-372 (115a), p. 31, EFS P39[1], GINPC 1277; (9-11) 4681-372 (115a), p. 26, EFS R41[0], GINPC 1278; (12–14) 4681-373 (115a), p. 7, EFS K44[3], GINPC 1279; (15–17) 4681-373 (115a), p. 10, EFS M38[0], GINPC 1280; (18-20) 4681-382 (115a), p. 13, EFS T46[3], GINPC 1281.

As is typical of permineralized organic-walled fossils (e.g., Schopf and Kudryavtsev, Reference Schopf and Kudryavtsev2010; Schopf et al., Reference Schopf, Kudryavtsev and Sergeev2010a, Reference Schopf, Kudryavtsev, Tripathi and Czaja2010b, Reference Schopf, Farmer, Foster, Kudryavtsev, Gallardo and Espinoza2012), comparison of the CLSM (black and white) and Raman-kerogen images (blue) in Figures 3 and 4 shows that much of the CLSM-detected fluorescence of the Chulaktau and Berkuta specimens is derived from the PAHs of their kerogenous cell walls and associated carbonaceous components. In addition, however, Raman imagery shows that apatite has permineralized the walls of various of the Chulaktau fossils and infilled their interiors, not only of the kerogen-walled trichomes of helically coiled Obruchevella parva (Fig. 3.4) and the cellular lumina of O. cf. meishucunensis (Fig. 3.9), but also of coccoidal sheath-enclosed cells of the colonial cyanobacterium Tetraphycus acutus (Fig. 3.14 and 3.19) in which sites of apatite-nucleation are discernible both in optical (Fig. 3.16) and CLSM images (Fig. 3.17).

Raman spectra (Fig. 5.1) document the kerogenous composition of the cell walls and associated organic matter of the Berkuta and Chulaktau fossils. Analyses of these spectra to determine their Raman Index of Preservation (RIP) value—an easily calculated metric that ranges from 1 to 10 used to compare the molecular-structural composition and fidelity of preservation of kerogenous permineralized fossils in permineralized fossil assemblages (Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005)—shows them to have an RIP of ~7.5. This value indicates that the kerogen comprising the Berkuta and Chulaktau fossils is appreciably less geochemically altered (“better preserved”) than that of the carbonaceous components of numerous Proterozoic and Archean microbiotas but is more altered than that of the especially well-preserved ~800-Ma-old Bitter Springs Formation (RIP=9.0), the ~1900-Ma Gunflint Formation (RIP=8.8), and the ~750-Ma-old Berkuta- and Chulaktau-underlying Chichkan Formation (RIP=8.6; Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005, Reference Schopf, Kudryavtsev and Sergeev2010a).

Figure 5 Raman (1) and fluorescence spectra (2, 3) of quartz- and apatite-permineralized organic-walled Early Cambrian Maly Karatau Range microfossils. (1) Raman spectra of kerogen comprising permineralized fossils of the Kyrshabakta (Berkuta Member) and Chulaktau formations, in both units having an RIP value of ~7.5 (see text). The relatively prominent D band shoulder of the Chulaktau kerogen, derived largely from hydrogen situated on the periphery of the platy polycyclic aromatic hydrocarbons (PAHS) of which it is dominantly composed, indicates that that it has a somewhat higher H:C composition than the Berkuta kerogen (Schopf et al., Reference Schopf, Kudryavtsev, Agresti, Czaja and Wdowiak.2005). (2) Fluorescence spectra acquired from differing areas of the Siphonophycus solidum-encrusting apatite crystal denoted by the green arrow in Fig. 3.24 in which Sm⁺³ replaced Ca II and Ca I sites are spatially distinct. (3) Complete fluorescence spectrum of this apatite-encrusted Chulaktau specimen of S. solidum.

Like Raman spectra, fluorescence spectra (Fig. 5.2, 5.3) document the composition of the Chulaktau fossils and their associated matrix. The fluorescence spectra show also that the fossil-permineralizing and -infilling apatite of the deposit contains a mixture of Sm⁺³-replaced Ca I and Ca II lattice sites. Although the analytical uncertainty in measurement of the position of fluorescence bands is typically ≤2 nm, spectral differences between these two varieties of apatite are firmly evidenced by the position and intensity of their fluorescence bands: (1) the upper spectrum in Figure 5.2 exhibits a prominent Sm⁺³ fluorescence band at ~597 nm, corresponding to the ~598 nm band (Gaft et al., Reference Gaft, Reisfeld and Panczer2005) and ~599 nm bands (Reisfeld et al., Reference Reisfeld, Gaft, Boulon, Panczer and Jorgensen1996; Gaft et al., Reference Gaft, Reisfeld, Panczer, Boulon, Shoval and Champagnon1997a) reported for Sm⁺³ replacing the Ca I site of apatite under vacuum conditions; (2) the lower spectrum includes a prominent Sm⁺³ fluorescence band at ~605 nm that corresponds to the ~607 nm band reported for Sm⁺³-replacement of the Ca-II site of apatite exposed to air (Reisfeld et al., Reference Reisfeld, Gaft, Boulon, Panczer and Jorgensen1996; Gaft et al., Reference Gaft, Reisfeld, Panczer, Boulon, Shoval and Champagnon1997a; Gaft et al., Reference Gaft, Reisfeld and Panczer2005), a band in such fossil-associated apatite that is virtually imperceptible in the upper spectrum; and (3) the assignment of these bands to Sm⁺³ is supported by the presence of a band at ~643 nm (Fig. 5.2) that corresponds in position and relative intensity to a secondary Sm⁺³ fluorescence band reported to be situated at ~645 nm (Reisfeld et al., Reference Reisfeld, Gaft, Boulon, Panczer and Jorgensen1996; Gaft et al., Reference Gaft, Reisfeld, Panczer, Boulon, Shoval and Champagnon1997a; Gaft et al., Reference Gaft, Reisfeld and Panczer2005).

Much of the Chulaktau fossil-associated apatite (e.g., that permineralizing and infilling the fossils shown in fluorescence images in Fig. 3.5, 3.10, 3.15, and 3.20) exhibits a mixture of Sm⁺³-replaced Ca I and Ca II sites. Unmixed varieties of Sm⁺³-replaced apatite also occur. In contrast with the fossil-permineralizing and -infilling apatite (Fig. 3.1–3.20), crystals of fossil-encrusting apatite (Fig. 3.21–3.24) are mostly composed entirely of Ca I site-substituted apatite with some exhibiting peripheral zones of Ca II site-substitution (Figs. 3.24, 5.2), their euhedral form indicating that these apatite crystals were precipitated before consolidation of the surrounding sediment. Both the mode of occurrence of these encrusting apatite crystals and their unmixed rather than intermixed pattern of Sm⁺³-substitution indicate that they represent a generation of apatite-formation different from that permineralizing and infilling the fossils.

Coupled with the paleoenvironmental setting of the Chulaktau fossil-bearing cherts—and assuming that local oxygen concentrations were determinant in Sm⁺³-replacement of the calcium sites of apatite, as discussed above—the spectroscopic fluorescence data seem readily explicable. Initially, before microbial decay and disintegration of the fossils, permineralizing and infilling apatite was emplaced in the low-oxygen (dysoxic) environment of basinal waters at and near the sediment-water interface (resulting in Sm⁺³-replacement of a mixture of the Ca I and Ca II lattice sites). After burial in unconsolidated anoxic mud, permeating waters carried in phosphate that emplaced fossil-encrusting apatite crystals (and Sm⁺³-replacement of their Ca I lattice site). At some later time, presumably by an influx of oxygen-containing waters, the peripheries of some encrusting crystals became oxidized (resulting in replacement at the Ca II lattice site).

This scenario is consistent with what is now is known regarding both samarium-replacement of calcium in apatite and the paleoecology of the Chulaktau basin. Nevertheless, the use of such substitution in apatite-permineralized fossils to establish the relative oxygen-concentrations of their preservational history is a concept new to paleobiology. Confirmation of this novel interpretation will depend on additional investigations.

In summary, as with virtually all comparable permineralized microbiotas, the Early Cambrian Berkuta and Chulaktau assemblages inhabited a carbonate-precipitating shallow photic-zone environment. The localized relatively low pH produced by microbial metabolism in these benthic communities resulted in dissolution of associated carbonate and its replacement by colloidal silica that infused microbial cell walls and mucilaginous envelopes and sheaths prior to their decay and disintegration. Upwelling of phosphate-laden deep marine waters into the restricted Chulaktau basin resulted in the deposition of phosphorites and, in the benthic dysoxic parts of near-shore facies, the infusion of phosphate into partially silicified microbes and its intracellular precipitation to infill cells. After near-surface burial but before consolidation of the anoxic microbe-enclosing mud, extracellular precipitation of a later insurge of phosphate produced swaths of microbe-encrusting euhedral apatite crystals, the surfaces of some of which were subsequently oxidized by interaction with oxygen-bearing percolating waters.

It has been suggested that microbial physiology may have played an active role in the concentration and precipitation of phosphate in apatite-mineralized fossil microbes (e.g., Gerasimenko et al., Reference Gerasimenko, Goncharova, Zhegallo, Zavarzin, Zaitseva, Orleanskii, Rozanov and Ushatinskaya1996, Reference Gerasimenko, Zavarzin, Rozanov and Ushatinskaya1999; Zhegallo et al., Reference Zhegallo, Rozanov, Ushatinskaya, Hoover, Gerasimenko and Ragozina2000). Although it is plausible that an influx of dissolved phosphate into the Chulaktau basin may have promoted the proliferation of cyanobacteria, as it does in similarly shallow water settings today, the evidence presented here indicates that the infusion of silica and phosphate into the microbes that resulted in their quartz- and apatite-permineralization and -infilling were post-mortem, not under biological control. An analogous occurrence of apatite-permineralization, of essentially the same age as the Chulaktau fossils and also studied by CLSM and Raman, has been documented for a ctenophore (“comb jelly”) embryo from the ~540 million-year-old Kuanchuanpu phosphorite of China (Chen et al., Reference Chen, Schopf, Bottjer, Zhang, Kudryavtsev, Wang, Yang and Gao2007).

Mat-forming filamentous cyanobacteria

In the Chulaktau assemblage, well-preserved spiral filaments of Obruchevella are particularly abundant. Four species of Obruchevella have been detected: O. parva (Figs. 3.1–3.5, 7.1–7.7, 8.1, 8.2, 8.5, 8.6, 9.1–9.6), O. parvissima (Fig. 8.3, 8.4, 8.7, 8.8), O. delicata, and O. cf. meishucunensis (Fig. 3.6–3.10). As in genera of similarly helically coiled modern cyanobacteria (e.g., Spirulina and Arthrospira), such fossil trichomes typically exhibit little evidence of cell-defining transverse cell walls. Such septa, however, are preserved in some Chulaktau specimens of O. parva, showing their cells to be 5–10 µm in diameter. This species of Obruchevella is predominant in all Chulaktau samples here studied whereas other taxa of the genus—differentiated from O. parva by their filament diameters (viz., O. parvissima, 3–5 µm, O. delicata, 10–13 µm, and O. cf. meishucunensis, 20–22 µm)—are relatively uncommon.

Other filamentous Chulaktau cyanobacteria are here assigned to Eomicrocoleus (Fig. 11.9), Siphonophycus, Oscillatoriopis and Palaeolyngbya. Siphonophycus, most recently defined taxonomically by Butterfield et al. (Reference Butterfield, Knoll and Swett1994) and Sergeev et al. (Reference Sergeev, Sharma and Shukla2012) and interpreted to be the extracellular trichome-enclosing tubular sheaths of oscillatoriacean cyanobacteria, is represented by three species differentiated by their breadths: S. robustum (2–4 µm; Fig. 11.11); S. kestron (8-16 µm); and S. solidum (16–32 µm; Figs. 3.21–3.24, 10.7, 10.8, 10.11, 10.12). These taxa, like those of Obruchevella spp., are of common occurrence in the Chulaktau cherts. The assemblage also includes three species of Oscillatoriopsis, each exhibiting well defined rounded terminal cells and disc- or cube-shaped medial cells and differentiated by their characteristic cell diameters: Oscillatoriopsis sp. (5–7 µm), O. cuboides (13–18.5 µm; Fig. 9.7–9.9), O. longa (22-30 µm; Figs. 10.5, 10.6, 11.7, 11.8). The Chulaktau cherts also contain two species of Palaeolyngbya, characterized by its sheath-enclosed uniseriate trichomes composed of discoidal to cylindrical cells: P. sp. (6–7 µm in diameter; Fig. 11.12, 11.13) and a much broader form, P. catenata (28–35 µm in diameter; Figs. 9.10, 9.11, 10.1–10.4, 10.9, 10.10, 11.1–11.6).

Given the phototaxis of the trichomes of oscillatoriaceans and their capability by gliding motility to vacate their encompassing tubular sheaths, it is possible that various of the taxa of trichomes and sheaths of Siphonophycus, Oscillatoriopsis and Palaeolyngbya co-occurring in the Chulaktau cherts represent differing parts of single biological entities. Thus, for example, the cell size–defined 13- to 18.5-µm broad taxon Oscillatoriopsis cuboides may have been a Lyngbya-like oscillatoriacean that was originally ensheathed by 16- to 32-µm diameter Siphonophycus solidum sheaths that might also have originally enclosed the 22- to 30-µm broad cellular trichomes of O. longa. Like their modern counterparts, these taxa were evidently mat-forming, in some instances preserved in the Chulaktau cherts in eroded and redeposited rounded or subrounded mat fragments.

Colonial and single-celled chroococcacean cyanobacteria

Of the taxonomic families of coccoidal cyanobacteria identified in the Chulaktau microbiota, the mat-forming Entophysalidaceae is represented by Eoentophysalis belcherensis (Fig. 12.3, 12.6, 12.7–12.13), a taxon having spheroidal to ellipsoidal 3-to 10-µm diameter cells occuring in palmelloid colonies enclosed by multilayered envelopes. Of limited distribution in the assemblage, distinctive crustose pustular laminae like those formed by E. belcherensis in Proterozoic stromatolitic deposits (Hofmann, Reference Hofmann1976; Sergeev et al., Reference Sergeev, Knoll and Grotzinger1995, Reference Sergeev, Sharma and Shukla2012) have not been observed in the Chulaktau cherts.

Among all types of fossil coccoidal cyanobacteria represented in the Chulaktau biota, colonial members of the Chroococcaceae are particularly abundant, their affinity to this family indicated typically by their occurrence in small clusters of 2, 4 or as many as 8 close-packed and commonly individually ensheathed cells produced by cell division in two mutually perpendicular planes and surrounded by a colony-enclosing originally mucilaginous envelope. Of these, Tetraphycus acutus (Figs. 3.11–3.20, 12.4, 12.5), having a cell size-range of 10-20 µm, is especially abundant, occurring in groups of small colonies spread laterally over hundreds of square microns. Although Chulaktau specimens of the morphologically similar colonial chroococcacean Archaeophycus yunnanensis (Fig. 12.1, 12.2), characterized by 8- to 15-µm-diameter cells, may represent apatite-replaced preservational variants of Tetraphycus acutus, the individual mineralized cells of such colonies are not sheath-enclosed and are typically somewhat smaller than those of T. acutus.

The colonial chroococcacean Eoaphanocapsa molle (Fig. 14.12) exhibits multilamellated spheroidal and ellipsoidal cells 12- to 17-µm in diameter that occur in loose clusters of a few to many tens of individuals embedded in a diffuse organic matrix and surrounded by a colony-defining envelope. Eoaphanocapsa, regarded as a fossil analogue of the modern chroococcacean Aphanocapsa, provides a useful form genus for colonies of multilamellated spheroidal cells that lack evidence of a cell division pattern like that known for such fossil chroococcaceans as Gloeodiniopsis. Like colonies of modern Aphanocapsa, those of fossil Eoaphanocapsa typically occur as benthic components of mat-building microbial communities dominated by filamentous cyanobacteria, not only in the Chulaktau cherts but also in those of the Proterozoic Min’yar and Sukhaya Tunguska formations (Nyberg and Schopf, Reference Nyberg and Schopf1984; Sergeev, Reference Sergeev2006).

One additional coccoidal colonial Chulaktau taxon, Synodophycus sp. (Fig. 14.7–14.9), deserves mention. Fossils of this genus occur as tightly packed spheroidal colonies of single-walled cells 10- to 15-µm in diameter that in some instances are enclosed by multilayered envelopes. Given their simple morphology and small cell size, these fossils are probably of cyanobacterial, chroococcacean affinity. Nevertheless, morphologically similar colonies occur also in other cyanobacterial families (e.g., the Pleurocapsaceae and Entophysalidaceae) as well as among microalgal eukaryotes. Described originally from the Neoproterozoic Draken Conglomerate of Spitsbergen (Knoll, Reference Knoll1982), species of Synodophycus have been reported less commonly from permineralized microbial communities than those of the other colonial Chulaktau taxa noted above. Similarly, unlike the benthic habit of the other colonial taxa, that of the Chulaktau Synodophycus specimens has yet to be established.

Planktonic acritarchs and other unicells

Although the Berkuta and Chulaktau strata, unlike some Early Cambrian microbiotas, lack abundant spiny (acanthomorphic) acritarchs, the Chulaktau cherts contain the planktonic sphaeromorphs Leiosphaeridia minutissima (Fig. 13.10) and L. tenuissima (Fig. 13.9) as well as the problematic acanthomorphs Vandalosphaeridium koksuikum and Cymatiosphaera sp., all of probable of eukaryotic affinity. Leiosphaeridia, of broad stratigraphic range and the principal form genus of unornamented sphaeromorphic acritarch known from Proterozoic and Cambrian sediments, is commonly interpreted to be a unicellular prasinophycean (e.g., Tappan, Reference Tappan1980) or chlorophycean alga (Talyzina and Moczydłlowska, Reference Talyzina and Moczydłowska2000; Moczydłlowska, Reference Moczydłowska2010; Moczydłlowska et al., Reference Moczydłowska, Schopf and William2010). Although for most specimens of Leiosphaeridia such affinities are likely correct, some leiosphaerids exhibit wall ultrastructure seemingly unlike that of eukaryotic green algae (e.g., Javaux et al., Reference Javaux, Knoll and Walter2004). In addition to specimens permineralized in the Chulaktau cherts, carbonaceous compression-preserved vesicles assigned to Leiosphaeridia have been reported from interbedded shales of the formation (Korolev and Ogurtsova, Reference Korolev and Ogurtsova1981, Reference Korolev and Ogurtsova1982; Ogurtsova, Reference Ogurtsova1985).

Of particular interest among the acritarchs of the Chulaktau assemblage is Vandalosphaeridium koksuicum (Fig. 14.3, 14.6), a form typified by its evidently single-layered more or less spheroidal vesicles, 40- to 45-µm in diameter, in which the vesicle-defining envelope appears to be sculptured by prominent semicrescent to transverse ramparts and short appendage-like possible processes. This characteristic sculpture pattern, exhibited also by specimens reported from the underlying Neoproterozoic Chichkan Formation (Schopf et al., Reference Schopf, Kudryavtsev and Sergeev2010a; Sergeev and Schopf, Reference Sergeev and Schopf2010), coupled with the occurrence in Chulaktau and Chichkan specimens of a globular interior cyst-like body, suggests their probable chlorococcalean affinity (cf., Moczydłlowska, Reference Moczydłowska2010). A morphologically rather similar 55- to 65-µm-diameter acritarch co-occurring in the Berkuta and Chulaktau cherts is cf. Cymatiosphaera sp. (Fig. 14.1, 14.2, 14.4, 14.5). Because almost all previously described species of Cymatiosphaera have been defined on the basis of flattened compression-preserved specimens in shales, rather than three-dimensionally chert-permineralized specimens such as those studied here, we do not assign the Tamda Group specimens to a previously defined species.

Two species of the spheroidal-celled colonial or unicellular form genus Myxococcoides, M. minor and M. inornata, occur rather commonly in small colonies scattered among the benthic members of the Chulaktau assemblage, an irregular distribution suggesting that they may represent allocthonous plankton derived from overlying waters. The epithet Myxococcoides has been applied both to envelope-enclosed many-celled colonies of closely packed spherical cells such M. minor (Fig. 14.11), composed of 8.5- to 14-µm diameter cells, and to isolated cells and cell pairs like those of M. inornata (Fig. 14.10), 15–20 µm in diameter. Although all described species of Myxococcoides are plausibly chroococcacean (Сhrооcосcus- or Gloeocapsa-like) cyanobacteria, as such forms were originally interpreted (Schopf, Reference Schopf1968), some bear resemblance also to extant small-celled eukaryotic chlorophycean algae (Knoll et al., Reference Knoll, Swett and Mark1991; Knoll, Reference Knoll1996; Schopf et al., Reference Schopf, Kudryavtsev and Sergeev2010a; Sergeev and Schopf, Reference Sergeev and Schopf2010).

Filamentous microfossils of uncertain affinities

This category includes only two of the 27 taxa here reported, Botominella lineata and Berkutaphycus elongatus. Botominella lineata (Fig. 13.1–13.5) exhibits a filamentous trichome-like body composed of cell-like segments 20- to 60-µm wide and 2- to 5-µm long. Berkutaphycus elongates (Figs. 4.1–4.20, 13.6–13.8, 13.11–13.16) is a previously unreported taxon here described from the Berkuta Member of the Kyrshabakta Formation where it is evidently represented by life cycle and preservational variants and is interpreted to include 11- to 34-µm broad filamentous tubes as well as spheroidal and cask-like structures 25- to 70-µm wide and 2- to 5-µm long. Like Botominella lineata, Berkutaphycus elongatus is of uncertain affinities, resembling large-diameter cyanobacteria and some filamentous eukaryotic algae.

Type species

Eomicrocoleus crassus Horodyski and Donaldson, Reference Horodyski and Donaldson1980.

Eomicrocoleus crassus Horodyski and Donaldson, Reference Horodyski and Donaldson1980

Figure 11.9

Eomicrocoleus crassus Horodyski and Donaldson, Reference Horodyski and Donaldson1980, p. 154, figs 15A, 15B; Sergeev, Reference Sergeev2001, p. 442, fig. 9.5; Sergeev, Reference Sergeev2002, p. 559, pl. 2, fig. 6; Sergeev, Reference Sergeev2006, p. 208, pl. 18, fig. 5, pl. 25, fig. 6; Sharma, Reference Sharma2006, p. 91, fig. 10d; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 289, pl. 15, figs. 4–6, 9.

Description

Bundles of tube-like trichomes having very rare cross-walls closely grouped within a common cylindrical sheath or without a surrounding sheath. Parallel or subparallel trichomes are 2–3 µm in diameter, mostly hollow, and have psilate walls ~0.5 µm thick; trichome-encompassing common sheaths, when present, are 25–30 µm in cross-sectional diameter, up to 80 µm long, ~1 µm thick, and are typically fine-to medium-grained.

Material examined

Several well-preserved specimens.

Occurrence

Widely distributed in Proterozoic and Lower Cambrian chert-permineralized organic-walled assemblages.

Remarks

Trichomes and sheaths of the Chulaktau Formation are of slightly larger diameter than those of the type population and the bundles of trichomes commonly lack encompassing sheaths, an absence attributable to preservational alteration (Gerasimenko and Krylov, Reference Gerasimenko and Krylov1983, Sergeev et al., Reference Sergeev, Knoll and Petrov1997).

Genus Obruchevella Reitlinger, Reference Reitlinger1948, emend.

Yakschin and Luchinina, Reference Yakschin and Luchinina1981, emend. Kolosov, Reference Kolosov1984,

emend. Yankauskas, Reference Yankauskas1989, emend. Burzin, Reference Burzin1995,

emend. Nagovitsin, Reference Nagovitsin2000

Type species

Obruchevella delicata Reitlinger, Reference Reitlinger1948.

Obruchevella parva Reitlinger, Reference Reitlinger1959, emend.

Golovenok and Belova, Reference Golovenok and Belova1989, emend. Burzin, Reference Burzin1995

Figures 3.1–3.5, 7.1–7.7, 8.1, 8.2, 8.5, 8.6, 9.1–9.6

Obruchevella parva Reitlinger, Reference Reitlinger1959, p. 21, pl. 6, figs. 1, 2; Kolosov, Reference Kolosov1977, p. 73,74, pl. 6, fig. 1; 1982, pl. 16, figs. 1a, 1б; Cloud, Awramik, Morrison and Hadley, Reference Cloud, Awramik, Morrison and Hadley1979, p. 87-89, figs. 5J and 5K; Yakschin and Luchinina, Reference Yakschin and Luchinina1981, p. 30, pl. 10, figs. 1–3; Golovenok and Belova, Reference Golovenok and Belova1983, p. 1464, figs. 1B–1D; Song, Reference Song1984, p. 183, figs. 3.1–3.3, 3.8, 3.9; Sergeev, Reference Sergeev1989, pl. 2, figs. 1–3, 5, 6, 8; Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 1, figs. 1–3, 5–9, 12; Golovenok and Belova, Reference Golovenok and Belova1989, p. 193, figs. 1d–1f; Sergeev, Reference Sergeev1992, p. 89, pl. 24, figs. 5, 6, 11, pl. 25, figs. 1a, 1b, 2, 3, 5, 6a, 6b; Burzin, Reference Burzin1995, p. 10–11, 13, pl. 1, figs. 1–3, 4A, pl. 3, fig. 1; Prasad, Uniyal and Asher, Reference Prasad, Uniyal and Asher2005, p. 54, pl. 10, figs. 4, 12, Pl. 11, fig. 9; Prasad, Reference Prasad2007, pl. 1, figs. 3, 6, 15; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 296, pl. 19, figs. 1–6, 14 (for additional synonymy, see Burzin, Reference Burzin1995, Golovenok and Belova, Reference Golovenok and Belova1989, and Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2012).

Description

Empty non-tapering cylindrical tubes, rarely exhibiting cell-defining septa, coiled into regular cylindrical spirals. Tube diameters range from 5 to 10 μm; coiled spirals are 20–35 μm in breadth and up to 155 μm long. Cross-walls, when present, define cellular segments 1.5–2.0 μm in length. Tube lateral- and cross-walls are fine-grained ~0.5 μm thick.

Material examined

A few hundred well-preserved specimens.

Occurrence

Widely distributed in Ediacaran (Vendian) and Lower Cambrian microfossil assemblages.

Remarks

In the Chulacktau cherts, the permineralized spirals are commonly infilled by apatite. Golovenok and Belova (Reference Golovenok and Belova1983) described O. parva from units incorrectly assigned to the underlying Chichkan Formation, an error corrected in subsequent publications (Decision of Fifth All-union Colloquium on Precambrian Microfossils of the USSR, 1986; Ogurtsova and Sergeev, Reference Ogurtsova and Sergeev1987; Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989; Sergeev, Reference Sergeev1989, Reference Sergeev1992).

Obruchevella parvissima Song, Reference Song1984

Figure 8.3, 8.4, 8.7, 8.8

Obruchevella parvissima Song, Reference Song1984, p. 183, figs. 3.14–3.16; Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 1, fig. 11; Sergeev, Reference Sergeev1992, p. 90, pl. 25, fig. 4; Prasad, Uniyal and Asher, Reference Prasad, Uniyal and Asher2005, p. 54, pl. 11, fig. 10; Prasad, Reference Prasad2007, pl. 1, fig. 16; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 296, pl. 19, fig. 10.

Description

Thin-walled empty cylindrical tubes, coiled into loose regular spirals in which the walls of adjacent tubes are not in contact. Tube diameters range from 3 to 5 μm; the outer diameter of the spiral coils ranges from 18 to 30 μm whereas their inner boundary ranges from 12 to 20 μm. Tube walls are medium-grained, opaque, and typically ≤1.0 μm thick.

Material examined

A few well-preserved specimens.

Occurrence

Ediacaran (Vendian): Nagod Limestone Formation, India; Lower Cambrian: Yuhucun Formation, China; Chulaktau Formation, South Kazakhstan.

Obruchevella cf. O. meishucunensis Song, Reference Song1984

Figure 3.6–3.10

Obruchevella cf. O. meishucunensis Song, Reference Song1984. Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 1, fig. 11; Sergeev, Reference Sergeev1992, p. 90, pl. 24, fig. 8; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, pl. 19, fig. 7.

Description

Thin-walled empty cylindrical tubes, coiled into a loose regular spirals in which the walls of adjacent tubes are not in contact. Tube diameters range from 20 to 22 μm; the outer diameter of the spiral coils is ~120 μm whereas their inner boundary is ~80 μm. Tube walls are medium-grained, translucent, ~1.0 μm thick.

Material examined

Several not very well-preserved trichomes.

Genus Oscillatoriopsis Schopf, Reference Schopf1968, emend.

Mendelson and Schopf, Reference Mendelson and Schopf1982, emend.

Butterfield, 1994 (in Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994)

Type species

Oscillatoriopsis obtusa Schopf, Reference Schopf1968.

Oscillatoriopsis cuboides Knoll, Strother and Rossi, Reference Knoll, Strother and Rossi1988

Figure 9.7–9.9

Oscillatoriopsis cuboides Knoll, Strother, and Rossi, Reference Knoll, Strother and Rossi1988, p. 275, 276, fig. 11c; Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2012, text-fig. 42D.

Description

Solitary uniseriate unbranched cellular trichomes lacking encompassing sheaths. Terminal cells were not detected in the specimens studied; medial cells are quadrate, cask-shaped, translucent, 13.0–18.5 wide (n=6, μ=15 μm, σ=2.3, RSD=15%) and 15–23 μm long (n=6, μ=18.6 μm, σ=2.3, RSD=12%), and have a width-to-length ratio ranging from 1 to 1.5 occurring in trichomes up to 100 μm long. Cross walls are translucent, fine- to medium-grained, 0.5–1.0 μm thick.

Material examined

Two well-preserved solitary trichomes.

Occurrence

Lower Proterozoic: Duck Creek Formation, Australia; Lower Cambrian: Chulaktau Formation, South Kazakhstan.

Remarks

Oscillatoriopsis cuboides is distinguished from other species of Oscillatoriopsis by its characteristic cell dimensions and cask-shaped, cuboidal, medial cells (Knoll et al., Reference Knoll, Strother and Rossi1988; Sergeev et al., Reference Sergeev, Sharma and Shukla2012). The Chulaktau specimens are broader than trichomes described from the Paleoproterozoic Duck Creek Formation (Knoll et al., Reference Knoll, Strother and Rossi1988), having cell widths similar to those of O. longa. In assigning the Chulaktau specimens to O. cuboides, rather than to O. longa, we have followed the taxonomy of Sergeev et al. (Reference Sergeev, Sharma and Shukla2012) rather than that of Butterfield et al. (Reference Butterfield, Knoll and Swett1994).

Oscillatoriopsis longa Timofeev and Hermann, Reference Timofeev and Hermann1979, emend. Butterfield, 1994

(in Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994)

Figures 10.5, 10.6, 11.7, 11.8

Oscillatoriopsis longum Timofeev and Hermann, Reference Timofeev and Hermann1979, p. 139, pl. 29, figs. 3, 4.

Oscillatoriopsis longa Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994, p. 60, figs. 24F–24G; Dong, Xiao, Shen, Zhou, Li and Yao, Reference Dong, Xiao, Shen, Zhou, Li and Yao2009, p. 39, figs. 6.10–6.11 (For additional synonymy see Butterfield et al., Reference Butterfield, Knoll and Swett1994 and Zhang et al., Reference Zhang, Yin, Xiao and Knoll1998).

Description

Uniseriate straight to curved unbranched non-ensheathed trichomes that lack cell-defining constrictions and occur commonly as isolated individuals. Terminal cells are rounded to hemispheroidal, 12–21 μm wide (n=5) and 4–6 μm long (n=5); medial cells are disc-shaped, translucent, 23–30 μm wide (n=48, μ=26 μm, σ=1.6, RSD=6%), 4–9 μm long (n=48, μ=6 μm, σ=1.0, RSD=16%), and have a width to length ratio 4 to 8; trichome lengths range from 180 to 270 μm. Transverse cell walls are commonly indistinct whereas the trichome-defining lateral cell walls are typically distinct, translucent to opaque, fine- to medium grained, and 0.5–1.0 μm thick. Preserved remnants of degraded cytoplasm, a few micrometers wide and up to a few tens of micrometers long, occur commonly as thread-like inclusions inside the trichomes.

Material examined

A few dozen well-preserved trichomes.

Occurrence

Widely distributed in Proterozoic and Lower Cambrian microfossil assemblages.

Remarks

Oscillatoriopsis longa is distinguished from other species of Oscillatoriopsis by its characteristic cell dimensions and its trichomic breadth. Although the diameter of trichomes of O. longa from the Chulaktau Formation is up to 35 μm—appreciably broader than the 25 μm upper size limit recognized by Butterfield et al. (Reference Butterfield, Knoll and Swett1994) and Sergeev et al. (Reference Sergeev, Sharma and Shukla2012) for this taxon —similarly sized specimens of O. longa have been described from the Chulaktau-contemporaneous Yanjiahe and Yurtus formations of China (Dong et al., Reference Dong, Xiao, Shen, Zhou, Li and Yao2009). Only one other broader taxon of the genus has been reported, O. majuscula, described from a single incomplete specimen 63 μm in diameter from the Paleoproterozoic Duck Creek Formation (Knoll et al., Reference Knoll, Strother and Rossi1988) and a species, however, that was not included in the Butterfield et al. (Reference Butterfield, Knoll and Swett1994) taxonomic monograph of the genus.

Genus Palaeolyngbya Schopf, Reference Schopf1968, emend.

Butterfield, 1994 (in Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994)

Type species

Palaeolyngbya barghoorniana Schopf, Reference Schopf1968.

Palaeolyngbya catenata Hermann, Reference Hermann1974

Figures 9.10, 9.11, 10.1–10.4, 10.9, 10.10, 11.1–11.6

Palaeolyngbya catenata Hermann, Reference Hermann1974, p. 8 and 9, pl. 6, fig. 5; Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994, p. 61, figs. 25F–25G; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo2001, p. 6, pl. 1, figs. 4–6; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo.2004, p. 13, 15, pl. 2, figs. 1–3; Srivastava and Kumar, Reference Srivastava and Kumar2003, p. 30, 32, pl. 9, figs. 5, 7; Sergeev, Reference Sergeev2006, p. 207, pl. 22, figs. 4–6, pl. 27, figs. 1–3; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2008, pl. 4, fig. 5, pl. 7, fig. 12, pl. 9, fig. 4; 2012, p. 300, 301, pl. 18, figs. 1–5, 8, text-fig. 43B.

Palaeolyngbya maxima Zhang, Reference Zhang1981, p. 495, pl. 2, figs. 4, 6, 7 (for additional synonymy, see Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2012).

Description

Unbranched uniseriate trichomes having discoidal medial cells and rounded terminal cells that lack constrictions at septa and are encompassed by a prominent non-lamellated smooth sheath. Terminal cells are rounded to hemispheroidal, 22–26 μm wide and up to 7 μm long; medial cells are 28–35 μm wide (n=60, μ=32.5 μm, σ=1.7, RSD=5%) and 7–11 μm long (n=60, μ=8.5 μm, σ=1.6, RSD=18.5%), having a width-to-length ratio ranging from 3 to 5. Transverse cell walls are commonly indistinct; lateral, trichome-defining walls are translucent, fine-grained and 0.5–1.0 μm thick. Encompassing extracellular sheaths are translucent, 29–39 μm in diameter, 0.5–1.5 μm thick and up to 900 μm long.

Material examined

More than one hundred well-preserved filaments.

Occurrence

Widely distributed in Proterozoic microfossil assemblages.

Remarks

The diameter of trichomes of P. catenata in the Chulaktau assemblage ranges up to 35 μm, broader than the upper size limit previously recognized for this species (Butterfield et al., Reference Butterfield, Knoll and Swett1994; Sergeev et al., Reference Sergeev, Sharma and Shukla2012). In sheath diameter, the Chulaktau specimens span the range between P. castenata and P. hebeiensis (Zhang and Yan, Reference Zhang and Yan1984).

Palaeolyngbya sp.

Figure 11.12, 11.13

Description

Unbranched uniseriate trichomes, up to 53 μm long, exhibiting discoidal medial cells and rounded terminal cells that lack constrictions at septa and are surrounded by a prominent unilayered smooth sheath. Medial cells are 6–7 μm wide and 1–2 μm long. Transverse walls are indistinct or missing; lateral cell walls are translucent, fine-grained, 0.5–1.0 μm thick. The encompassing sheath is translucent, single-layered, ~9 μm broad and ~0.5 μm thick.

Material examined

One filament, not well preserved.

Genus Siphonophycus Schopf, Reference Schopf1968, emend.

Knoll and Golubic, Reference Knoll and Golubic1979, emend.

Knoll, Swett and Mark, Reference Knoll, Swett and Mark1991

Type species

Siphonophycus kestron Schopf, Reference Schopf1968.

Siphonophycus robustum (Schopf, Reference Schopf1968), emend.

Knoll and Golubic, Reference Knoll and Golubic1979, comb. Knoll, Swett, and Mark, Reference Knoll, Swett and Mark1991

Figure 11.11

Eomycetopsis robusta Schopf, Reference Schopf1968, p. 685, рl. 82, figs. 2, 3; рl. 83, figs. 1–4; Knoll and Golubic, Reference Knoll and Golubic1979, p. 149, figs. 4A, 4B; Mendelson and Schopf, Reference Mendelson and Schopf1982, p. 59, 60, 62, pl. 1, figs. 9, 10; Ogurtsova, Reference Ogurtsova1985, p. 97 and 98, pl. 3, figs. 4, 6, pl. 10, figs. 1–6, pl. 11, figs. 2, 3, 5, 6; pl. 12, figs. 1, 3, 5, 7; Sergeev, Reference Sergeev1992, p. 93 and 94, pl. 7, figs. 9, 10; pl. 16, figs. 3, 6, 7, 10; pl. 19, figs. 1, 5, 6, 7–10; pl. 24, fig. 7; Golovenok and Belova, Reference Golovenok and Belova1993, pl. 2, fig. е.

Eomycetopsis filiformis Schopf, Reference Schopf1968, p. 685 and 686, pl. 82, fig. 1, 4, pl. 83, figs. 5–8.

Siphonophycus robustum Knoll, Swett, and Mark, Reference Knoll, Swett and Mark1991, p. 565, figs. 10.3, 10.5; Butterfield, Knoll, and Swett, Reference Butterfield, Knoll and Swett1994, p. 64, 66, figs. 26A, 26G; Sergeev, Knoll, Kolosova, and Kolosov, Reference Sergeev, Knoll, Kolosova and Kolosov1994, pl. 3, fig. 6; Sergeev, Knoll, and Petrov, Reference Sergeev, Knoll and Petrov1997, p. 230, fig. 14A; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo2001, p. 6, pl. 1, figs. 1, 2, 7, 11, 12; Sergeev, Reference Sergeev2001, p. 442, figs. 7.8, 7.9; Sergeev, Reference Sergeev2002, pl. 2, figs. 1, 3; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo.2004, pl. 2, fig. 4; Sergeev, Reference Sergeev2006, p. 213 and 214, pl. 6, figs. 9, 10, pl. 17, fig. 1, pl. 19, figs. 8, 9, pl. 22, figs. 1, 2, 7, 8, 11, 12, pl. 25, figs. 1, 3, pl. 27, figs. 4, 5, pl. 28, fig. 2, pl. 36, figs. 1, 2, pl. 44, figs. 1–7, 13, pl. 46, figs. 7–10, pl. 48, fig. 4; Sergeev and Schopf, Reference Sergeev and Schopf2010a, p. 387, fig. 6.4; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 309, 310, pl. 21, figs. 2, 4, 8–10, text-figs. 8, 9, 16, 17 (for complete synonymy, see Butterfield, Knoll, and Swett, Reference Butterfield, Knoll and Swett1994 and Sergeev, Sharma, Shukla, Reference Sergeev, Sharma and Shukla2012).

Description

Unbranched nonseptate tubes, cylindrical to slightly compressed and 2–4 μm broad, that rarely contain degraded trichome-like fragments; tube walls, less than 0.5 μm thick, range from psilate to finely granulate. Specimens are solitary or entangled in masses of many individuals aligned subparallel to the bedding lamination.

Material examined

A few dozen well-preserved specimens.

Occurrence

Widely distributed both in chert-permineralized and compression-preserved organic-walled Proterozoic microfossil assemblages.

Remarks

Like the other Chulaktau and Berkuta species of Siphonophycus, S. robustum is distinguished by its characteristic range of diameters.

Siphonophycus solidum (Golub, Reference Golub1979), comb.

Butterfield, 1994 (in Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994)

Figures 3.21–3.24, 10.7, 10.8, 10.11, 10.12

Omalophyma solida Golub, Reference Golub1979, p. 151, pl. 31, figs. 1–4, 7.

Siphonophycus solidum Butterfield in Butterfield, Knoll, and Swett, Reference Butterfield, Knoll and Swett1994, p. 67, figs. 25H, 25I, 27D; Sergeev, Knoll, and Petrov, Reference Sergeev, Knoll and Petrov1997, p. 231, figs. 14I, 14K; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo2001, p. 8, pl. 1, figs. 1–3; Sergeev, Reference Sergeev2001, p. 442 and 443, fig. 7.7; Sergeev, Reference Sergeev2002, pl. 2, fig. 15; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo.2004, pl. 2, fig. 8; Sergeev, Reference Sergeev2006, p. 215, pl. 17, figs. 9, 10, pl. 19, fig. 7, pl. 22, figs. 1–3, pl. 25, fig. 15, pl. 28, figs. 4, 5, pl. 36, fig. 4, pl. 39, fig. 1, pl. 45, figs. 4, 7; Sergeev and Schopf, Reference Sergeev and Schopf2010, p. 387, figs. 7.6–7.8, 8.1, 8.2; Schopf, Kudryavtsev and Sergeev, 2010, figs. 2.5–2.15; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 310, pl. 18, figs. 9–11, pl. 20, figs. 4–6, 8 (for complete synonymy, see Butterfield, Knoll, and Swett, Reference Butterfield, Knoll and Swett1994 and Sergeev, Sharma, Shukla, Reference Sergeev, Sharma and Shukla2012).

Description

Unbranched solitary nonseptate tubes, cylindrical to slightly compressed and 16–32 μm broad, that rarely contain degraded trichomic fragments; tube walls, 1–2 μm thick, range from smooth to fine- or medium-grained.

Material examined

Approximately one hundred well-preserved specimens.

Occurrence

Widely distributed both in chert-permineralized and compression-preserved Proterozoic assemblages.

Remarks

The exterior surfaces of some Chulaktau specimens are encrusted by closely spaced small euhedral apatite crystals (Figs. 3.21–3.24, 5.2, 5.3).

Class Coccogoneae Thuret, Reference Thuret1875

Order Chroococcales Wettstein, Reference Wettstein1924

Family Chroococcaceae Nägeli, Reference Nägeli1849

Archaeophycus Wang, Zhang, and Guo, Reference Wang, Zhang and Guo1983

Type species

Archaeophycus yunnanensis (Song in Luo et al., Reference Luo, Jian, Wu, Song and Ouyang1982) comb. Dong et al., Reference Dong, Xiao, Shen, Zhou, Li and Yao2009.

Archaeophycus yunnanensis (Song in Luo et al., Reference Luo, Jian, Wu, Song and Ouyang1982) comb. Dong et al., Reference Dong, Xiao, Shen, Zhou, Li and Yao2009

Figure 12.1, 12.2

Tetraphycus yunnanensis Song in Luo, Jiang, Wu, Song, and Ouyang, Reference Luo, Jian, Wu, Song and Ouyang1982, p. 216, pl. 31, figs. 3, 4; Luo, Jiang, Wu, Song, Ouyang, Xing, Liu, Zhang, and Tao, Reference Luo, Jian, Wu, Song, Ouyang, Xing, Liu, Zhang and Tao1984, pl. 19, figs. 11, 12.

Archaeophycus venustus Wang, Zhang, and Guo, Reference Wang, Zhang and Guo1983, p. 153 and 154, figs. 5.10, 6.1, 8.3; Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 2, fig. 11; Sergeev, Reference Sergeev1992, pl. 26, fig. 5; Zhou, Yuan, Xiao, Chen, and Xue, Reference Zhou, Yuan, Xiao, Chen and Xue2004, p. 354, pl. 1, figs. 5–9.

?Bigeminococcus grandis Wang, Zhang, and Guo, Reference Wang, Zhang and Guo1983, p. 149–150, fig. 13.1–13.4.

Paratetraphycus giganteus Zhang Z., Reference Zhang1985, p. 166, pl. 1, figs. 1, 4, 6, 7; pl. 2, fig. 6; Zhang Y., Yin, Xiao, and Knoll, Reference Zhang, Yin, Xiao and Knoll1998, p. 46, fig. 20.4–20.8.

Tetraphycoides multa Cao, Reference Cao1985, p. 189, pl. 1, figs. 1, 2.

Archaeophycus yunnanensis Dong, Xiao, Shen, Zhou, Li, and Yao, Reference Dong, Xiao, Shen, Zhou, Li and Yao2009, p. 37, figs. 6.1–6.6.

Description

Spheroidal or polyhedral cells occurring in dyads, triads, tetrads and octets not surrounded by a common sheath that form colonial aggregates composed of a few to a few tens of individuals. Colony form varies from loose clusters of dyads and tetrads to more closely packed regularly cuboidal aggregations. Cell walls are 0.5–1.0 μm thick, transparent and medium-grained. Cell diameters range from 8 to 15 μm (n=80, μ=9 μm, δ=2, RSD=22%, DDI=3). A single opaque inclusion 1–2 μm in diameter is commonly present within each cell.

Material examined

Several hundred cells in tens of colonies.

Occurrence

Ediacaran (Vendian): Doushantuo Formation, China. Lower Cambrian: Zhujiaqing, Yanjiahe and Yurtus Formations, China; Chulaktau formation, South Kazakhstan.

Remarks

In colonial organization and cell-shape and -size, Archaeophycus yunnanensis resembles Tetraphycus acutus, the distinction between the taxa being the absence in A. yunnanensis of distinct cell- and colony-encompassing sheaths. Although the two taxa may represent preservational variants of a single species (which would demote Tetraphycus acutus to the status of a junior synonym of Archaeophycus yunnanensis), the lack of cell- and cell tetrad-encompassing sheaths is a diagnostic character of the genus Archaeophycus (Dong et al., Reference Dong, Xiao, Shen, Zhou, Li and Yao2009). Because of the absence of transitional forms between these species in the Chulaktau Formation, we elected to maintain the taxa as separate entities.

Genus Eoaphanocapsa Nyberg and Schopf, Reference Nyberg and Schopf1984

Type species

Eoaphanocapsa oparinii Nyberg and Schopf, Reference Nyberg and Schopf1984.

Eoaphanocapsa molle Sergeev, Reference Sergeev1989 (in Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989)

Figure 14.12

Eoaphanocapsa molle Sergeev in Sergeev and Ogurtsova Reference Sergeev and Ogurtsova1989, p. 65, pl. 2, fig. 9; Sergeev, Reference Sergeev1992, p. 78 and 79, pl. 26, fig. 3; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 240, pl. 4, fig. 7.

Description

Individual colonial cells, 12–17 μm in diameter, surrounded by single-layered envelopes, occurring in loose colonies commonly about 60 μm broad that are composed of tens of individuals. Cell-enclosing envelopes and cell walls are translucent, fine-grained, 0.5–1.0 μm thick. Some cells include a spot-like inclusion 1–2 μm in diameter.

Material examined

A few well-preserved colonies comprising dozens of vesicles.

Occurrence

Lower Cambrian, Chulaktau Formation, South Kazakhstan.

Genus Tetraphycus Oehler, Reference Oehler1978

Type species

T. gregalis D. Oehler, Reference Oehler1978.

Tetraphycus acutus Sergeev, Reference Sergeev1989 (in Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989), emend.

Figures 3.11–3.20, 12.4, 12.5

Tetraphycus acutus Sergeev in Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, p. 64, pl. 2, fig. 8; Sergeev, Reference Sergeev1992, p. 80, 81, pl. 26, fig. 4.

In part: Tetraphycus amplus Golovenok and Belova, Reference Golovenok and Belova1984. Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 2, figs. 6, 12; Sergeev, Reference Sergeev1992, pl. 26, figs. 1, 2.

Diagnosis (emended)

Spheroidal and polyhedral single-walled cells 10–20 μm in diameter that occur in dyads, triads and planar tetrads surrounded by a common sheath. Ensheathed tetrads may occur in closely associated groups.

Description

Spheroidal or polyhedral cells enclosed by single-layered sheaths occurring in dyads, triads and tetrads that comprise larger colonial aggregates of a few to a few tens of cell-groups. Colony morphology varies from loose clusters of tetrads to more regular cuboidal aggregations in which the tetrads commonly occur in closely packed groups encompassed in a surrounding originally mucilaginous organic matrix. Cell walls are 1–2 μm thick, translucent and course-grained; transparent outer sheaths, >0.5 μm thick, are fine-grained. Cell diameters range from 10 to 20 μm (n=28, μ=15 μm, δ=2.6, RSD=17%, DDI=3); sheath diameters range from 12 to 22 μm. A single opaque inclusion 1 to 2 μm in diameter is commonly present within individual cells.

Material examined

A few hundred vesicles in tens of colonies.

Occurrence

Lower Cambrian: Chulaktau Formation, South Kazakhstan.

Remarks

Modern counterparts exhibiting cell shapes and sizes similar to those of Tetraphycus acutus occur among chroococcacean and entophysalidacean cyanobacteria as well as chlorococcacean green algae, and planar tetrads like those of Tetraphycus are particularly common among coccoical colonial cyanobacteria. Two species of the genus, T. acutus and T. amplus, have previously been described from the Chulaktau Formation (Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989). T. amplus was originally described by from the Proterozoic Billyakh Group of the Anabar Uplift (Golovenok and Belova, Reference Golovenok and Belova1984) but was later regarded to be a junior synonym of Myxococcoides grandis (Sergeev et al., Reference Sergeev, Knoll and Grotzinger1995). We have therefore amended T. acutus to include this and other forms previously described as T. amplus.

Family Entophysalidaceae Geitler, Reference Geitler1932

Genus Eoentophysalis Hofmann, Reference Hofmann1976 emend.

Mendelson and Schopf, Reference Mendelson and Schopf1982

Type species

Eoentophysalis belcherensis Hofmann, Reference Hofmann1976.

Eoentophysalis belcherensis Hofmann, Reference Hofmann1976

Figure 12.3, 12.6–12.13

Eoentophysalis belcherensis Hofmann, Reference Hofmann1976, p. 1070, 1072, pl. 4, figs. 1–5, pl. 5, figs. 3–6, pl. 6, figs. 1–14; Hofmann and Schopf, Reference Hofmann and Schopf1983, p. 347, pl. 14-2, figs. G-J, pl. 14-6, figs. L-M, pl. 14-8, fig. C, Pl. 14-9, figs. O-Q; Sergeev, Reference Sergeev1992, p. 81 and 82, pl. 9, figs. 1–3; Sergeev, Knoll and Grotzinger, Reference Sergeev, Knoll and Grotzinger1995, p. 27 and 28, figs. 12.1–12.4, 12.6, 12.12–12.14, 17.1–17.10; Sergeev, Reference Sergeev2006, p. 196 and 197, pl. 5, figs. 1–4, 6, 12–14, pl. 8, figs. 1–10; pl. 34, figs. 1, 2, pl. 41, figs. 11–15; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 263, pl. 10, figs. 1–10 (for complete synonymy see Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2012).

Eoentophysalis sp. Sergeev, Reference Sergeev1992, pl. 26, fig. 6.

Description

Spheroidal or polyhedral cells enclosed by multilamellated envelopes and occurring in dyads, tetrads, octets that comprise colonies of a few tens of cell groups. The colonies typically are enclosed within a translucent envelope and vary from loose clusters of gloeocapsoid cells to more regular spheroidal aggregations. Outermost envelopes enclosing individual cells are fine-grained and ~0.5 μm thick; inner envelopes are medium- to coarse-grained, ~1.0 μm thick; cell diameters range from 3 to 10 μm (n=80, μ=6 μm, σ=1.5, RSD=26%, DDI=5). A single opaque inclusion 0.5–1.0 μm in diameter is commonly present within individual cells.

Material examined

Approximately 200 cells in several colonies.

Occurrence

Widely distributed in Paleo-, Meso-, Neoproterozoic, Ediacaran, and Lower Cambrian chert-permineralized organic-walled assemblages.

Remarks

A taxon particularly common in Paleo-Mesoproterozoic microbial assemblages, Eoentophysalis is morphologically highly variable, the several stages of its complex life cycle being subject to varying degrees of preservational alteration (Hofmann, Reference Hofmann1976; Golubic and Hofmann, Reference Golubic and Hofmann1976; Hofmann and Schopf, Reference Hofmann and Schopf1983; Knoll et al., Reference Knoll, Swett and Mark1991; Sergeev at al., Reference Sergeev, Knoll and Grotzinger1995, Reference Sergeev, Sharma and Shukla2012; Sergeev, Reference Sergeev2006). In many Proterozoic deposits, colonies of E. belcherensis comprise crustose stratiform laminae. However, those of the Chulaktau population occur only as isolated gloeocapsoid palmelloid colonies, presumably as a result of the dynamic, highly energetic environment evidenced by the Chulaktau phosphoites (Kholodov and Paul, Reference Kholodov and Paul1993a, Reference Kholodov and Paul1993b, Reference Kholodov and Paul1994)

Family Xenococcaceae Ercegović, Reference Ercegović1932

Genus Synodophycus Knoll, Reference Knoll1982, emend.

Knoll, Swett and Mark, Reference Knoll, Swett and Mark1991

Synodophycus sp.

Figure 14.7–14.9

Synodophycus sp. Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 2, fig. 7; Sergeev, Reference Sergeev1992, pl. 26, fig. 8.

Description

Aggregates of equidimensional 10- to 15-μm diameter cells, commonly surrounded by single or multilayered envelopes and clustered in irregular spheroidal colonies 40–50 μm across composed of 16–64 individuals. Cell walls are <0.5 μm thick, translucent and fine-grained; when present, surrounding sheaths are single- or multilayered, transparent, fine-grained and up to 2 μm thick.

Material examined

A few colonies comprising tens of individuals.

Remarks

Synodophycus has been assigned to the cyanobacterial pleurocapsalean family Xenococcaceae (Knoll et al., Reference Knoll, Swett and Mark1991). Although not a widely reported genus, many colonial fossils assigned to other cyanobacterial genera may actually be taxa of this genus.

Incertae Sedis

Genus Berkutaphycus new genus

Type species

Berkutaphycus elongatus gen. sp. nov. by monotype.

Diagnosis

Single-walled unbranched cylindrical filaments separated by cross walls into cell-like segments having lengths greater than widths. Filaments can be broken into short cylindrical bodies, cask-like fragments having rounded ends, or spheroidal vesicles. The filaments occur singly or in groups of tangled subparallel-oriented individuals.

Etymology

From the name of Berkuta settlement, situated near the source of the Kyrshabakta Formation Berkuta Member (Lower Dolomite) holotype-containing fossiliferous chert and with reference to cyanobacterial/algal affinity.

Berkutaphycus elongatus new species

Figures 4.1–4.20, 13.6–13.8, 13.11–13.16

Siphonophycus sp., Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 2, figs. 2, 3.

Palaeosiphonella sp., Sergeev and Ogurtsova, Reference Sergeev and Ogurtsova1989, pl. 2, fig. 1; Sergeev, Reference Sergeev1992, pl. 24, fig. 3.

Siphonophycus sp₄., Sergeev, Reference Sergeev1992, pl. 24, figs. 1, 2, 4, 10.

Diagnosis

Single-walled cylindrical filaments, 11–70 µm broad, commonly separated by cross- or end-walls into segments 70–80 µm long. Filaments can be broken into short cylindrical bodies 25–70 × 40–205 µm having rounded ends, or into 25- to 60-µm diameter spheroidal vesicles.

Description

Single-walled unbranched cylindrical filaments separated by cross walls into cell-like segments having lengths larger than widths. Filaments can be broken into short cylindrical bodies, cask-like fragments having rounded ends, or spheroidal vesicles. The filaments occur singly or in entangled groups of subparallel-oriented individuals. Filaments are 11–34 µm in diameter (n=80, μ=23 μm, σ=5.1, RSD=22%) and up to 500 µm long (incomplete specimen). Filament fragments, equant to more elongate cylindrical bodies, range from 25 to 70 µm in width and 40 to 205 µm in length, whereas the diameters of isolated vesicles range from 25 to 60 µm; diameters of the entire population range from 11 to 70 µm (n=85, μ=24 μm, σ=9.2, RSD=38%). Filament walls are translucent, medium-grained, and 1 to 2 µm thick. In the Berkuta cherts, the interiors of Berkutaphycus elongatus filaments commonly contain elongate or actinomorphic anthraxolite-like degraded cytoplasmic remnants.

Etymology

From the Latin elongatus referring to the elongate to the distinctive cylindrical elongate shape of the cell-like segments.

Holotype

Figure 13.11, 13.12, GINPC 192; Lower Cambrian, Nemakit-Daldynian Stage; Kyrshabakta Formation, Lower Dolomite, locality 27, the Koksu River basin.

Material examined

More than 500 well-preserved specimens.

Occurrence

Lower Cambrian: Kyrshabakta Formation (Berkuta Member), South Kazakhstan.

Remarks

The distinctive features of Berkutaphycus elongatus, such as the breakage of its filaments into elongate segments and the presence of isolated akinete-like cylindrical and spherical bodies, suggest affinity to hormogonian cyanobacteria (or, perhaps, to eukaryotic green or chrysophyte algae). The anthraxolite-like contents of the Berkuta filaments are not uncommon in metamorphosed Proterozoic deposits but are relatively rare in Cambrian and younger strata. Though this new taxon is somewhat similar to Cyanonema majus described from the Lower Cambrian of Tarim Platform of China (Dong et al., Reference Dong, Xiao, Shen, Zhou, Li and Yao2009), in the absence of a comparative study of the Chinese population it would be premature to propose a formal synonymy.

Genus Botominella Reitlinger, Reference Reitlinger1959

Type species

Botominella lineata Reitlinger, Reference Reitlinger1959.

Botominella lineata Reitlinger, Reference Reitlinger1959

Figure 13.1–13.5

Botominella lineata Reitlinger, Reference Reitlinger1959, p. 25, pl. 10, figs. 1–7.

(non) Botominella lineata Reitlinger, Reference Reitlinger1959. Sergeev, Reference Sergeev1989, pl. 1, figs. 11.

Description

Solitary, unbranched, unsheathed, nontapering filaments up to 130 μm long (complete specimen) that consist of separated short-discoidal opaque cell-like bodies that range from 2 to 5 µm in width and 20 to 60 μm in length that are separated by 1.5- to 3.5-μm gaps.

Material examined

Three well-preserved specimens.

Occurrence

Widely distributed in Lower Cambrian formations.

Remarks

Botominella lineata, first described by Reitlinger (Reference Reitlinger1959) from the Lower Cambrian Pestrocvetnaya Formation of Siberia, is known from numerous Lower Cambrian carbonate units. Similar structures, initially referred to Botominella lineata and reported from the Chulaktau-underlying Neoproterozoic Chichkan Formation (Sergeev, Reference Sergeev1989), have been interpreted to be inorganic and of nonbiological origin (Sergeev, Reference Sergeev1992, pl. 23, figs. 1–3). However, the Chulaktau specimens described here differ morphologically from these earlier reported pseudofossils and their biological origin is confirmed by Raman spectroscopy that shows them to be composed of apatite-permineralized kerogen. The morphology of the Chulaktau specimens suggests them to be either relatively broad cyanobacterial oscillatoriacean filaments or, less likely, eukaryotic (chlorophycean?) algae.

Genus Chlorogloeaopsis Maithy, Reference Maithy1975, emend.

Hofmann and Jackson, Reference Hofmann and Jackson1994

Type species

Chlorogloeaopsis zairensis Maithy, Reference Maithy1975.

Chlorogloeaopsis contexta Hermann, 1976 (in Timofeev, Hermann and Mikhailova, Reference Timofeev, Hermann and Mikhailova1976), comb. Hofmann and Jackson, Reference Hofmann and Jackson1994

Figure 11.10

Polysphaeroides contextus Hermann, 1976 in Timofeev, Hermann and Mikhailova, Reference Timofeev, Hermann and Mikhailova1976, p. 42 and 43, pl. 14, figs. 3, 4; Yankauskas, Reference Yankauskas1989, p. 119, pl. 27, figs. 10a, 10б; Hermann, Reference Hermann1990, pl. 7, fig. 8; Schopf, Reference Schopf1992c, pl. 24, figs. B₁, B₂; Sergeev, Reference Sergeev2001, p. 443, fig. 9.1–9.3; Sergeev, Reference Sergeev2006, p. 230 and 231, pl. 18, figs. 1–3.

Chlorogloeaopsis contexta Hofmann and Jackson, Reference Hofmann and Jackson1994, p. 19, figs. 12.13–12.15; Prasad, Uniyal and Asher, Reference Prasad, Uniyal and Asher2005, pl. 7, fig. 9, pl. 11, fig. 14; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, pl. 14, figs. 7–9 (see Hofmann and Jackson, Reference Hofmann and Jackson1994, p. 19 for additional synonymy).

Description

Solitary unbranched non-ensheathed nontapering filaments composed of irregularly oriented spheroidal compressed cells. Cell walls are single-layered, translucent, fine-grained, and <0.5 μm thick. Cell diameters vary from 3.5 to 4.5 μm; filament diameters range from 7.5 to 12.5 μm, having a maximum length of 50 μm.

Material examined

Three specimens, none well preserved.

Occurrence

Mesoproterozoic: Bylot Supergroup, Baffin Island, Canada. Neoproterozoic: Burovaya and Miroedikha formations, Turukhansk Uplift; Nelkan, Kumakhtinskaya, Kandykskaya and Ust’-Kirba formations, Uchur-Maya Region; Daskinskaya Formation, Yenisey Ridge, Siberia. Lower Cambrian, Chulaktau Formation, South Kazakhstan.

Remarks

The Chulaktau C. contexta specimens are probably compessed remnants of chroococcalean cyanobacterial colonies or, less likely, of stigonematalean cyanobacterial filaments or filamentous green algae.

Genus Cymatiosphaera Wetzel, Reference Wetzel1933, emend. Deflandre, Reference Deflandre1954

cf. Cymatiosphaera sp.

Figure 14.1, 14.2, 14.4, 14.5

Description

Spheroidal vesicles, subcircular in cross-section and 55 to 65 µm in diameter, having medium-grained 1- to 2-µm thick walls the surface of which is folded into distinctive polygonal fields 5–7 µm broad and 12–17 µm long.

Material examined

Two well-preserved specimens.

Remarks

Some six species of this widely occurring planktonic taxon have been reported from Lower Cambrian microfossil assemblages. However, because most such taxa have described on the basis of compression-preserved rather than permineralized specimens, it is difficult to compare them with the Chulaktau specimens recorded here to which we therefore do not assign a specific epithet.

Genus Leiosphaeridia Eisenack, Reference Eisenack1958, emend.

Downie and Sarjeant, Reference Downie and Sarjeant1963, emend.

Turner, Reference Turner1984, emend. Yankauskas, Reference Yankauskas1989

Type species

Leiosphaeridia baltica Eisenack, Reference Eisenack1958.

Leiosphaeridia minutissima (Naumova, Reference Naumova1949), emend. Yankauskas, Reference Yankauskas1989 (in Yankauskas, Reference Yankauskas1989)

Figure 13.10

Leiotriletes minutissimus Naumova, Reference Naumova1949, pl. 3, fig. 4. For complete synonymy, see Yankauskas, Reference Yankauskas1989.

Leiosphaeridia minutissima Yankauskas in Yankauskas, Reference Yankauskas1989, p. 79 and 80, pl. 9, figs. 1–4, 11; Grey, Reference Grey2005, p. 185, fig. 68D; Vorob’eva, Sergeev, and Knoll, Reference Vorob’eva, Sergeev and Knoll2009, p. 185, fig. 14.9; Sergeev, Sharma and Shukla, Reference Sergeev, Sharma and Shukla2012, p. 332 and 333, pl. 26, fig. 9.

Description

Spheroidal, solitary, single-walled vesicles 35–40 μm in diameter; walls are translucent, hyaline to fine-grained, <1 μm thick and have a smooth surface texture.

Material examined

Nine well-preserved specimens.

Occurrence

Widely distributed in Proterozoic and Paleozoic rocks.

Leiosphaeridia tenuissima Eisenack, Reference Eisenack1958

Figure 13.9

Leiosphaeridia tenuissima Eisenack, Reference Eisenack1958, pl. 1, fig. 2; Yankauskas, Reference Yankauskas1989, p. 81, pl. 9, figs. 12, 13; Butterfield in Butterfield, Knoll and Swett, Reference Butterfield, Knoll and Swett1994, p. 42, fig. 16I (for complete synonymy, see Yankauskas, Reference Yankauskas1989).

Description

Spheroidal, solitary, single-walled vesicles 70–80 μm in diameter; walls are translucent, hyaline to fine-grained, about 2-μm thick, and have a smooth surface texture.

Material examined

Four well-preserved specimens.

Occurrence

Widely distributed in Proterozoic and Paleozoic sedimentary rocks.

Remarks

Species of Leiosphaeridia are identified following a formal scheme based on envelope diameter and wall thickness (see Yankauskas, Reference Yankauskas1989, p. 24 and 25). Although some specimens of Leiosphaeridia may be empty envelopes that originally enclosed cyanobacterial colonies, the great majority are remains of eukaryotic unicellular phytoplankton.

Genus Myxococcoides Schopf, Reference Schopf1968

Type species

Myxococcoides minor Schopf, Reference Schopf1968.

Myxococcoides inornata Schopf, Reference Schopf1968

Figure 14.10

Myxococcoides inornata Schopf, Reference Schopf1968, p. 676 and 677, pl. 84, fig. 7; Sergeev, Knoll, and Petrov, Reference Sergeev, Knoll and Petrov1997, p. 234, figs. 18B, 18G; Sergeev, Reference Sergeev2001, p. 444, fig. 10.11; Sergeev and Lee Seong-Joo, Reference Sergeev and Seong-Joo.2004, p. 17, pl. 3, fig. 12; Sergeev, Reference Sergeev2006, p. 226, pl. 15, figs. 6, 7, pl. 21, fig. 1, pl. 29, fig. 18; Sergeev and Schopf, Reference Sergeev and Schopf2010, p. 393, fig. 12.3, 12.4; Schopf, Kydryavtsev and Sergeev, Reference Schopf, Kudryavtsev and Sergeev2010a, fig. 5.1–5.4; Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2012, pl. 5, fig. 8, pl. 6, fig. 9.

Description

Spheroidal cells, solitary or occurring in colonies composed of few to tens of individuals embedded in a diffuse commonly well-defined organic matrix. Cell diameters range from 15 to 20 μm; colony size is 50–70 × 100–120 μm. The single-layered cell walls are typically translucent, fine- or medium-grained, 0.5–1.0 μm thick. Some cells contain an opaque spheroidal inclusion 1–2 μm in diameter that appears to be attached to the inner surface of the cell wall.

Material examined

Tens of well-preserved cells in several colonies.

Occurrence

Widely distributed in Proterozoic chert-permineralized microfossil assemblages.

Remarks

Although Myxococcoides was established in 1968 to include colonies of simple spheroidal microfossils interpreted to be chroococcacean cyanobacteria (Schopf, Reference Schopf1968), this genus name has since been used to encompass diverse microfossils of heterogeneous origin (Green et al., Reference Green, Knoll and Swett1989; Knoll et al., Reference Knoll, Swett and Mark1991; Butterfield et al., Reference Butterfield, Knoll and Swett1994; Sergeev et al., Reference Sergeev, Knoll and Grotzinger1995, Reference Sergeev, Sharma and Shukla2012). Some such species are no doubt chroococcaceans (though this may be uncertain for the type population of M. minor; Knoll, Reference Knoll1981) whereas others also resemble small-celled chlorococcalean green algae (Green et al., Reference Green, Knoll and Swett1989; Knoll et al., Reference Knoll, Swett and Mark1991; Sergeev and Schopf, Reference Sergeev and Schopf2010). Still others have been suggested to have different affinities; for example, specimens of the relatively large-diameter taxon M. grandis have been suggested to represent the empty originally colony-enclosing envelopes of colonial prokaryotes (Fairchild, Reference Fairchild1985; Sergeev, Reference Sergeev1992, Reference Sergeev2006) or the akinetes of nostocalean cyanobacteria (Sergeev et al., Reference Sergeev, Knoll and Grotzinger1995; Reference Sergeev, Sharma and Shukla2012). Because of such uncertainty regarding the affinities of Myxococcoides taxa, M. inornata and M. minor are classified here as Incertae Sedis. To date, more than 30 species of this genus have been described.

Myxococcoides minor Schopf, Reference Schopf1968

Figure 14.11

Myxococcoides minor Schopf, Reference Schopf1968, p. 676, pl. 81, fig. 1, pl. 83, fig. 10; Schopf, Reference Schopf1992b, pl. 32, figs. H, I; Sergeev, Knoll, and Petrov, Reference Sergeev, Knoll and Petrov1997, p. 234, figs. 18C, 18D; Sergeev, Reference Sergeev2001, p. 443, fig. 8.11; Sergeev, Reference Sergeev2006, p. 225 and 226, pl. 15, figs. 2, 5; pl. 20, fig. 11; pl. 48, fig. 5; Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2008, pl. 5, fig. 8, pl. 6, fig. 9; Sergeev and Schopf, Reference Sergeev and Schopf2010, p. 393, figs 12.3, 12.4; Schopf, Kydryavtsev and Sergeev, Reference Schopf, Kudryavtsev and Sergeev2010a, figs 5.5, 5.6; Sergeev, Sharma, and Shukla, Reference Sergeev, Sharma and Shukla2012, pl. 5, fig. 8, pl. 6, fig. 9.

Description

Spheroidal closely packed cells 8.5–14.0 μm in diameter, occurring in organic matrix-embedded colonies of a few to tens of individuals, defined by single-layered fine-grained walls ~ 0.5 μm thick. Some cells contain spheroidal to irregularly shaped opaque bodies, evidently condensed cytoplasmic remnants, that partially or nearly completely infill cell lumina.

Material examined

Tens of well-preserved colonies and hundreds of individuals.

Occurrence

Widely distributed in Proterozoic chert-permineralized microfossil assemblages.

Genus Vandalosphaeridium Vidal, Reference Vidal1981

Type species

Vandalosphaeridium reticulatum (Vidal), Reference Vidal1981.

Vandalosphaeridium koksuicum Sergeev and Schopf, Reference Sergeev and Schopf2010

Figure 14.3, 14.6

Vandalosphaeridium koksuicum Sergeev and Schopf, Reference Sergeev and Schopf2010, p. 397, figs. 13.1, 13.2a, 13.2b, 13.3, 13.4a, 13.4b.

Description

Spheroidal vesicles, subcircular in cross-section, having a surface folded into numerous polygonal fields from the walls of which protrude unbranched broadly conical processes that are more or less evenly distributed across the surface. Vesicle diameters range from 40 to 45 µm (n=3, x=43); processes are commonly indistinct, evidently 5 to 7 µm long and taper from being 2–5 µm broad at their base to 1–2 µm wide in their distal parts. A globular opaque polygonal (pyrite-like) inclusion, 4–5 µm broad, is present within some vesicles.

Material examined

Three well-preserved specimens.

Occurrence

Neoproterozoic: Chichkan Formation, South Kazakhstan; Lower Cambrian, Chulaktau Formation, South Kazakhstan.

Remarks

The taxonomic status of this genus is uncertain. Described initially from the Late Neoproterozoic Visingsö Group of Sweden as a morphologically distinctive acanthomorphic acritarch (Vidal, Reference Vidal1981), Vandalosphaeridium has been reported from numerous other Neoproterozoic units including the Chulaktau-underlying Chichkan Formation (Sergeev and Schopf, Reference Sergeev and Schopf2010) and Ediacaran-age strata of Australia (Grey, Reference Grey2005). The Chulaktau taxon, Vandalosphaeridium koksuicum, exhibits distinctive broadly conical processes and differs in size and morphology from such other described species as V. reticulatum and V. varangeri. Although at least one species of the genus (V. walcottii, described from the Neoproterozoic Chuar Group of Arizona; Vidal and Ford, Reference Vidal and Ford1985) was defined on the basis of what appear to be rather poorly preserved specimens of Trachyhystrichosphaera aimika, the distinctive morphology of V. koksuicum and the occurrence in many Chichkan specimens of a vesicle-enclosed globular organic body (Sergeev and Schopf, Reference Sergeev and Schopf2010) that is similar to that of the (pyrite-replaced?) inclusions of the Chulaktau specimens, suggests that V. koksuicum is a legitimate taxon, most probably allied to planktonic chlorophycean green algae.