Microfossils from the Krol ‘A’ of the Lesser Himalaya,India: Additional supporting data for its early Ediacaran age

An assemblage of microfossils of moderate diversity, with the remarkable occurrence of ECAP acritarchs, is reported from the Ediacaran Krol ‘A’ (= the Mahi Formation) succession of Lesser Himalaya, India. Microfossils occur in the chert nodules exposed in Solan district, Himachal Pradesh. Two microfossils, Barogophycus symmetricus n. gen. n. sp. and Botominella lineata are new to the well-established Krol assemblage. The paper concentrates predominantly on fossil eukaryotic filamentous and coccoidal micro-organism of simple morphology. The assemblage is dominated by remains of prokaryotic cyanobacteria and demonstrates the diversity achieved by microorganisms at the beginning of the Ediacaran Period in the aftermath of the Marinoan glaciation. Filamentous and coccoidal microorganisms differ in taxonomic composition from the Mesoproterozoic microbiotas. The Krol microfossils assemblage has biostratigraphic potential and usefulness in broadly demarcating the different levels of the Ediacaran strata. Because of the presence of ECAP acritarchs, along with the appearance of other eukaryotic microorganisms of filamentous and coccoidal morphology, the general level of the Krol ‘A’ assemblage is considered as Ediacaran.     

First record of organic-walled microfossils from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong,North China

Organic-walled microfossils offer important information on the biospheric evolution in pre-Cryogenian and provide biostratigraphic implications for many Proterozoic fossiliferous sequences that are poorly age constrained for the lack of reliable radiometric date. Recently, macroscopic carbonaceous compression fossils have been reported for the first time from the Tonian Shiwangzhuang Formation of the Tumen Group in western Shandong, North China. However, organic-walled microfossils have never been discovered from this formation up till now. To improve our knowledge about Proterozoic biodiversity in North China, we conducted a micropaleontological survey on the argillaceous limestone samples of the Shiwangzhuang Formation, which also contain macroscopic carbonaceous compression fossils, from the Baishicun section in Anqiu, western Shandong, North China. Our investigation shows that the Shiwangzhuang microfossil assemblage is dominated by smooth-walled sphaeromorphic acritarchs and cyanobacterium-like filaments and relatively low abundance of other acritarchs, including 16 taxa, such as Polysphaeroides filliformis, Ostiana microcystis, Simia annulare, ?Jacutianema sp., Arctacellularia tetragonala, Pellicularia tenera, Polythrichoides lineatus, and Navifusa actinomorpha. The Shiwangzhuang organic-walled microfossil assemblage, although consisting of long-ranging and not age diagnostic taxa, is consistent with a Tonian age suggested by macroscopic carbonaceous compression fossils, including the Chuaria-Tawuia and Sinosabellidites-Protoarenicola-Pararenicola assemblages, revealed from the same fossiliferous horizon of the Shiwangzhuang Formation and by organic-walled microfossil assemblage, including the late Mesoproterozoic to Tonian index fossil Trachyhystrichosphaera aimika, from the underlying Tongjiazhuang Formation. However, it is also worth noting that a Cryogenian or Ediacaran age cannot be completely excluded based just on the Shiwangzhuang microfossils because of their limited biostratigraphic utility.     

New graptolite,chitinozoan and acritarch records from the Pascha-Incamayo area,Cordillera Oriental,Argentina

A new fossil assemblage bearing graptolites, chitinozoans and acritarchs is analyzed based on material collected in the Pascha-Incamayo area, Salta Province, NW Argentina. The occurrence of Hunnegraptus copiosus (Lindholm, 1991), associated with specimens of the genus Tetragraptus (Salter, 1863), is highly relevant to improve the age assignment and correlate the fossil-bearing levels previously assigned to the Devendeus Formation. Different stages in the development of the index species of the Upper Tremadocian H. copiosus Biozone are described and illustrated. The precise stratigraphic ranges of the associated chitinozoans and acritarchs are discussed, according to the biostratigraphic analysis, and the stratigraphic relationships for the studied section are considered.     

Organic walled microfossils from the Neoproterozoic Owk Shale,Kurnool Group,South India

An assemblage of organic walled microfossils (OWM) of 17 taxa belonging to 10 genera is reported from the Neoproterozoic Owk Shale of the Kurnool Group, South India. The assemblage comprises sphaeromorphs, colonial aggregates, filamentous forms, spiral cylindrical filaments belonging to cyanobacteria, problematic acanthomorphic acritarchs, Netromorphic, Sphaeromorphic and Acantomorphic groups. The assemblage includes cyanobacteria: Siphonophycus kestron, S. robustum, S. typicum, S. solidum, Polytrichoides lineatus; Netromorphic acritarch: Arctacellularia tetragonala, Navifusa majensis, Jacutianema solubila; Sphaeromorphic acritarch: Ostiana microcystis, Synsphaeridium spp., Leiosphaeridia minutissima, L. tenuissima, L. crassa, L. jacutica, L. ternate; and Acanthomorphic acritarch: Cavaspina aff. C. acuminata and Variomargosphaeridium aff. V. litoschum. The age conundrum of Kurnool Group (Mesoproterozoic versus Neoproterozoic) is discussed. On the basis of the reported OWM assemblage the age of the Kurnool Group is established as Neoproterozoic.     

Environmental changes reflected by palynomorphs in the early Middle Ordovician Hanadir Member of the Qasim Formation, Saudi Arabia

Core samples from the QASIM-801 (QSIM-801) water well in the Qasim Region of central Saudi Arabia were investigated palynologically. The interval studied contains the transgressive succession from the Sajir Member of the Saq Formation to the Hanadir Member of the Qasim Formation, and yields well-preserved and abundant cryptospores, microphytoplankton (acritarchs and chlorophycean algae), and chitinozoans, indicative of a Darriwilian (Llanvirn) age. The lowermost portion of the cored interval from the upper Sajir Member consists of fine-grained sandstones deposited in tidal flat, and shallow-marine settings. It is characterized by abundant and diverse cryptospores (permanent tetrads, dyads, monads), cuticle-like phytoclasts, and a low diversity assemblage of marine palynomorphs. The upper part of the cored interval from the Hanadir Member is composed of hemipelagic to pelagic, organic-rich, graptolitic shales, and micaceous shales, of middle- to outer-shelf depositional settings, which yield abundant marine palynomorphs (acritarchs and chitinozoans). Cryptospore-bearing horizons are interspersed in the succession. Changes in the composition of palynomorph assemblages reflect higher frequency environmental changes within an overall transgressive succession. Four new acritarch species are described in open nomenclature, Tyrannus sp. A, Clypeolus sp. A,?Pulvinosphaeridium sp. A, and?Tinacula sp. A.     

Diverse small spinose acritarchs from the Ediacaran Doushantuo Formation, South China

The Ediacaran Doushantuo Formation in South China is underlain by the Cryogenian Nantuo Formation (glacial rocks) and overlain by the late Ediacaran Dengying Formation. It is characterized by well-preserved, large (normally >100 μm in size) spinose acritarchs (LSAs), which have been shown to be probably the only useful biostratigraphic tool for the global correlation of the early- and middle-Ediacaran. Acritarchs are organic microfossils normally known as single-celled eukaryotic organisms (protists). Although recent research suggests that some large spinose acritarchs may represent diapause egg cysts of metazoans, the biological affinities of the Ediacaran spinose acritarchs, especially for those displaying remarkable size ranges, are still debatable.Recently, smaller specimens of the Ediacaran spinose acritarchs have been found in cherts and phosphorites of the Doushantuo Formation in South China. Many described Ediacaran spinose acritarch taxa display large size variation (from tens to hundreds of microns in vesicle diameter), but some taxa only have smaller (<70 μm) specimens. The morphological comparison with Paleozoic counterparts indicates that some Ediacaran spinose acritarchs may have phylogenetic affinity to eukaryotic algae. More evidence, including wall ultra-structure, geochemical analysis and comparison with modern analogs, is needed to understand the biological affinity of the Ediacaran spinose acritarchs. The remarkable radiation of planktonic protists, characterized by abundant, diverse spinose acritarchs, occurred as early as in the late Neoproterozoic, i.e., 40–60 million years earlier than previously thought.     

Aeronian (Llandovery, Lower Silurian) palynomorphs and graptolites from the Lipeón Formation, Eastern Cordillera, north-west Argentina

The lower levels of the Lipeón Formation, in the Eastern Cordillera, north-west Argentina, yield a marine-dominated palynomorph assemblage, together with graptolites of mid to late mid Llandovery age (Demirastrites convolutus and probably Stimulograptus sedgwickii zones). The palynomorph assemblage is dominated by acritarchs, but also contains algae and terrestrial cryptospores. Crassiangulina variacornuta, considered a potentially good global biostratigraphical marker for the Upper Llandovery is recovered for the first time from the Silurian of Argentina. The occurrence of this species in strata not younger than late Aeronian, and independently dated by graptolites, indicates an early first appearance for Crassiangulina variacornuta, in the Lipeón Formation, below the Aeronian/Telychian boundary. The lower part of the unit corresponds to a quiet marine environment; thus supporting that Crassiangulina variacornuta is a facies-sensitive acritarch.     

Cellular preservation of excysting developmental stages of new eukaryotes from the early Ediacaran Weng’an Biota

The Ediacaran Weng’an Biota provides a unique window on marine diversity during the interval in which the fundamental animal body plans were being established. Here we describe a previously unreported component of the assemblage, millimeter-scale encysted spheres that exhibit a characteristic but simple slit-shaped excystment mechanism (Sporosphaera guizhouensis n. gen. n. sp.), reminiscent of acritarchs. The cysts contain a large inner body or numerous small discrete membrane-bounded bodies. It is possible that the inner bodies represent disaggregated cells of a multicellular body, like an embryo, but there is no evidence to support this interpretation and the occurrence of the excystment structure is not readily compatible with an embryo interpretation. Rather, we interpret the encysted organisms as multicellular stages within the lifecycle of otherwise probably unicellular eukaryotes. The developmental mode exhibited by Sporosphaera, incorporating a resting stage, implies an adaptation to adverse environmental conditions. This parallels the appearance of Large Ornamented Ediacaran Microfossils (LOEMs) which have been interpreted as diapause stages in the embryology of early animals. Sporosphaera is distinct from LOEMs by ornamentation instead of size, which may implicate that not all LOEMs are animal embryos, if any.     

Precambrian–Cambrian boundary interval occurrence and form of the enigmatic tubular body fossil Shaanxilithes ningqiangensis from the Lesser Himalaya of India

The affinity of the Ediacaran fossil Shaanxilithes ningqiangensis and putatively related forms has long been enigmatic; over the past few decades, interpretations ranging from trace fossils to algae to metazoans of uncertain phylogenetic placement have been proposed. Combined morphological and geochemical evidence from a new occurrence of S. ningqiangensis in the Krol and Tal groups of the Lesser Himalaya of India indicates that S. ningqiangensis is not a trace fossil, but rather an organic‐walled tubular body fossil of unknown taxonomic affinity. Specimens consist of compressed organic cylindrical structures, characterized by extended, overlapping or fragmented iterated units. Where specimens intersect, overlapping rather than branching or intraplanar crossing is observed. Lithologic comparisons and sequence stratigraphic data all suggest a late Ediacaran age for the uppermost Krol Group and basalmost Tal Group. By extending the biogeographical distribution of S. ningqiangensis, hitherto confined to the Ediacaran of China and potentially Siberia, to the Precambrian–Cambrian boundary interval of India, this new occurrence of S. ningqiangensis expands the biostratigraphic utility of this enigmatic fossil to the inter‐regional and intercontinental scale. Moreover, study of these new and exceptionally preserved samples may help to significantly constrain the long‐debated problem of Shaanxilithes' affinity, elucidating its ‘problematic’ status and shedding new light upon the ecology and taphonomy of one of the most significant intervals in early life history.     

Three-Dimensional Phosphatic Preservation Of Giant Acritarchs From The Terminal Proterozoic Doushantuo Formation In Guizhou And Hubei Provinces, South China

During the last two decades, a diverse assemblage of multicellular algae, spherical microfossils, bacteria and cyanobacteria (the Weng'an Biota) has been reported from the Terminal Proterozoic Doushantuo phosphorite in south China, which provides an important window for evolutionary studies of multicellular life just before the Ediacaran animal radiation. In this paper we report on three-dimensionally preserved acritarchs from the Doushantuo phosphorites at Weng'an in Guizhou Province and, for the first time, from Baokang in Hubei Province. Our assemblage contains species of the genus Meghystrichosphaeridium Zhang, Yin, Xiao and Knoll, 1998 non Chen and Liu, 1986 including M. chadianensis (Chen and Liu) Zhang, Yin, Xiao and Knoll, emend. 1998, and M. reticulatum Xiao and Knoll, 1999; the genus Echinosphaeridium Knoll, 1992 including the species E. maximum (Yin) Knoll, 1992; the new genus Bacatisphaera including the new species B. baokangensis and the new genus Castaneasphaera including the new species C. speciosa . The latter shows a marked resemblance to similarly preserved phosphatized Palaeozoic acritarchs called 'mazuelloids', consistent with a phytoplanktonic mode of life for the global Doushantuo/Pertatataka microflora (DPM).     

中国湖北秭归县庙河村早寒武世天竺山段的硅化微体化石

描述了湖北秭归县庙河村寒武系最底部(天竺山段)硅化微体化石13属16种,并论述了其地层意义.所有微体化石皆见于燧石切片中,此组合含大量小个体的具刺凝源类,以Micrhystridium ampliatum Wang为主,并与Paracymatiosphaera spp.,其它球形分子Lelosphaeridia,Favososphaeridium,Eoaperturilites及丝状体Obruchevella 和Megathrix共生,此地真正的陡山沱组是以含大量的和形态复杂的疑源类及简单的丝状体和球状化石为特征,这两个可靠的微体化石组合的发现和区分对本区及邻区震旦系-寒武系过渡层的划分和地层对比有重要意义.     

Upper Ordovician microphytoplankton of the Bill's Creek Shale and Stonington Formation,Upper Peninsula of Michigan,U.S.A.: Biostratigraphy and paleogeographic significance

An abundant, diverse, and well-preserved organic-walled microphytoplankton assemblage is described from the Upper Ordovician Bill's Creek Shale and the lower Stonington Formation (Bay de Noc Member) in the Upper Peninsula of Michigan, U.S.A. Based on graptolite and conodont evidence, the Bill's Creek Shale and Stonington Formation are Richmondian (=Ashgill) in age. The assemblage is dominated by acritarchs, which comprise 29 species (including the enigmatic palynomorph Gloeocapsomorpha prisca) assigned to 20 genera. The prasinophyte phycomata are represented by undifferentiated species of Leiosphaeridia and Tasmanites. In addition, chitinozoans are abundant, and scolecodonts and graptolite fragments are common. Paleontologic-palynologic and sedimentologic evidence indicates that the Bill's Creek Shale was deposited in a low-energy, shallow, nearshore marine environment. The overlying Bay de Noc Member of the Stonington Formation also accumulated in a low-energy, normal marine environment, but in a more offshore, somewhat deeper water setting. Both formations experienced minor transgressive and regressive episodes as indicated by fluctuations in the composition of the palynoflora. The combined Bill's Creek/Stonington acritarch assemblage closely resembles those described from the Richmondian-aged Maquoketa Shale (Missouri and Kansas), Sylvan Shale (Oklahoma), and Vauréal Formation (Anticosti Island, Québec, Canada). The overall composition of the acritarch assemblage from these four formations reflects a distinctive, recognizably Laurentian character. Nonetheless, many of the Bill's Creek/Stonington acritarchs have been reported from Upper Ordovician localities elsewhere, providing additional evidence for Late Ordovician cosmopolitanism of the marine microphytoplankton community. Additionally, the restricted stratigraphic range of many of the taxa further enhances their biostratigraphic application, both regionally and globally, and reaffirms the Richmondian (=Ashgill) age of the Bill's Creek Shale and Stonington Formation.     

Bryozoans from the Mitikha Formation (Lower Famennian, Upper Devonian) of the Kuznetsk Basin, Russia

Bryozoans from the Mitikha Formation (Lower Famennian, Upper Devonian) in the Kuznetsk depression are described for the first time. This bryozoan assemblage comprises both the well-known species Leioclema numerosum Moroz., L. ramosum Nekh., and Nicklesopora graciosa Troiz. and new taxa: L. kusmense sp. nov. and Megacanthopora glubokaensis sp. nov. The bryozoan assemblage contains some species common with the Famennian bryozoan assemblage of Kazakhstan.     

Discovery of a Charophyte locality and Biostratigraphy of the continental Eocene deposits of Oued Méridja (southwestern Algeria)

The continental deposits of Oued Méridja area (west of Bechar, southwestern Algeria) have been assigned by previous authors to the early Eocene on the basis of lacustrine gastropod fauna (Pseudoceratodes). This study reports new paleontological and biostratigraphic data from the Oued Méridja section. Recent field investigations resulted in the discovery of an important charophyte assemblage, composed of five species belonging to four genera: Maedleriella cristellata, Maedleriella aff. cristellata, Harrisichara aff. leptocera, Peckichara disermas and? Gyrogona sp. This association allows to suggest a late Thanetian to early Ypresian age for this locality.     

Early post-mortem calcified Devonian acritarchs as a source of calcispheric structures

Uniquely preserved Late Devonian calcispheres were found in a core of the deep borehole Sosnowiec IG-1 (Upper Silesia, southern Poland). These enigmatic calcareous microfossils are interpreted here as acritarchs that underwent an early post-mortem calcification. Remnants of organic walls preserved in the calcispheres suggest that they represent various acanthomorphic acritarchs, characteristic members of the Palaeozoic marine phytoplankton. Taphonomic analysis combined with the light microscope and scanning electron microscope (SEM) observations of mineral and organic components of the investigated calcispheres suggest that a complex multi-stage process led to calcification of their in vivo non-mineralized acritarch forerunners. The ubiquity of acanthomorphic calcispheres in many Devonian shallow-water limestones is a testimony to little, thus far, documented acritarch crops that must have existed over extensive areas of carbonate-producing epicontinental seas. The scarcity of acritarchs described from Devonian shallow-water limestones may thus represent a taphonomic bias rather than real rarity or absence.     

New insights on the palaeobiology and biostratigraphy of the acritarch Trachyhystrichosphaera aimika: A potential late Mesoproterozoic to Tonian index fossil

The late Mesoproterozoic to Tonian (∼1100 Ma to ∼720 Ma) witnessed a critical evolutionary transition in Earth history. Several fossil taxa, including acritarchs and vase-shaped microfossils, have been suggested as potential diagnostic fossils for this time interval. The acanthomorphic acritarch Trachyhystrichosphaera aimika has become a focus of recent biostratigraphic investigations, showing great potential to assist the definition of the Tonian Global Boundary Stratotype Section and Point (GSSP). Although T. aimika has been extensively reported in the Proterozoic sequences, little is known about its phylogenetic interpretation. Its palaeogeographic and stratigraphic distributions need to be critically scrutinized with recently emended diagnosis of the taxon and new published age constraints. In this study, we report new palaeobiological data of T. aimika specimens from the Tonian Liulaobei Formation in the Huainan region, North China, using transmitted light microscopy, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. Our analyses reveal a multilayered ultrastructure from the vesicle wall of T. aimika that has experienced advanced diagenesis to low-grade metamorphism with the peak palaeotemperature of ∼212 °C. In addition, a compilation of palaeogeographic occurrences of T. aimika shows the taxon is preserved in a wide range of palaeoenvironments and has a broad palaeogeographic distribution with a relatively limited stratigraphic range from ∼1150 Ma to ∼720 Ma, suggesting that T. aimika has great potential to become an index fossil for the late Mesoproterozoic to Tonian interval.     

Miospore stratigraphy of Lower and early Middle Devonian deposits from Tidikelt, Central Sahara, Algeria

The Tidikelt region forms an outstanding area for subsurface Lower Devonian stratigraphy in the central Algerian Sahara. Sediments from five boreholes have revealed abundant and diverse assemblages of miospores, acritarchs, chitinozoa, scolecodont and microplant remains. The miospores are moderately well preserved. Three new miospore species (Dibolisporites saharansis nov. sp. Hassan Kermandji, Acinosporites conatus nov. sp. Hassan Kermandji and Scylaspora tidikeltense nov. sp. Hassan Kermandji) are described. Miospore assemblages vary through the regressive and transgressive sequences. Seven miospore assemblage biozones, including six new miospore assemblage biozones (Scylaspora tidikeltense-Perotrilites microbaculatus, Dictyotriletes emsiensis-Emphanisporites spinaeformis, Apiculiretusispora arenorugosa-Camptozonotriletes caperatus, Verrucosisporites polygonalis-Dictyotriletes subgranifer, Emphanisporites annulatus-Geminospora svalbardiae, Hystricosporites microancyreus-Grandispora protea, Calyptosporites velatus-Rhabdosporites langii) are proposed for the Lower and early Middle Devonian rocks of Tidikelt Plateau. The combined use of distinctive, wide distribution cosmopolitan and Gondwanan forms as biozonal and species characteristics permits accurate subdivision, dating and correlation of Tidikelt successions with other similar miospore zones of the Lower Devonian of Europe, Canada and other parts of Gondwana plate. The miospore data provide new explanations to stratigraphic relationships of regional rock units, sedimentary cycles and stratigraphic hiatus. The miospore biozones are proposed as a provincial biozonation, which may also be applied to other Palaeozoic rocks of similar miospore content.     

Dickinsonia from the Ediacaran Dengying Formation in the Yangtze Gorges area,South China

Dickinsonia is an iconic fossil of the Ediacara biota (~575–539 Ma). It was previously known from siliciclastic successions of the White Sea assemblage in Australia, Baltica, and possibly India. Here we describe Dickinsonia sp. from the terminal Ediacaran Shibantan Member limestone (ca. 551–543 Ma) of the Dengying Formation in the Yangtze Gorges area of South China. The stratigraphic distribution of Ediacara-type fossils in the Shibantan Member indicates that this biota uniquely preserves both the White Sea and Nama assemblages in stratigraphic succession. The new data presented here suggests that Dickinsonia had wider paleogeographic and paleoenvironmental distributions, implying its strong dispersal capability and environmental tolerance.     

Perisphinctes orbignyi n. sp. and accompanying perisphinctid assemblage from the Lower Oxfordian (Cordatum Zone,Cordatum Subzone) in southern Poland (Zalas,Krakow region)

The paper presents preliminary characteristics of a new perisphinctid assemblage from the Lower Oxfordian section of Zalas near Krakow, regarded as the classic one for southern Poland. The assemblage is derived from strata of the Cordatum Subzone, Cordatum Zone. Two major groups of perisphinctids are differentiated. The assemblage appears similar to those described by Neumann from Cetechowitz 〚12〛, Bourseau from ‘Terres noires’ of de Beauvoisin in France 〚2〛, and Gygi from Switzerland 〚9〛. It fills very well a gap in our knowledge of this fauna from upper parts of the Lower Oxfordian and further studies should make it possible to propose and define a new biostratigraphic unit. A new ammonite species Perisphinctes (Arisphinctes?) orbignyi n. sp. is described. Its name is given to commemorate the bicentenary of the birth of Alcide d’Orbigny and his contribution to the developments of stratigraphy of the Mesozoic, especially Jurassic strata.