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.     

Devonian spore assemblages of China

Data available show that there are many genera and species of Devonian spores in China (together with acritarchs, chitinozoans and scolecodonts) which are commonly well-preserved, especially in South China where they are also better studied. This permits their use for correlation in detailed stratigraphical studies.On the basis of the study on Devonian spores for the past twenty years it is suggested that eight Devonian spore assemblage zones may be recognised in China, with four zones for the Lower Devonian, two zones for the Middle Devonian and two zones for the Upper Devonian. Each zone is characterised by a distinctive suite of miospores.The spore assemblages of China may be correlated basically with those in Great Britain, Federal Germany, Spitsbergen, U.S.S.R., and North America.     

Biostratigraphy, biodiversity and palaeoenvironments of the chitinozoans and associated palynomorphs from the Upper Ordovician of the Central Anti-Atlas, Morocco

The range, abundance and diversity of Upper Ordovician chitinozoans and of various other organic-walled microfossils (i.e., acritarchs, leiospheres, scolecodonts) have been documented in the Bou-Ingarf section, Central Anti-Atlas, Morocco. The goal of this study is to provide a refined biostratigraphic scheme for the Lower Ktaoua, the Upper Tiouririne, the Upper Ktaoua and the Lower Second Bani formations in order to locate the initial effects of the Late Ordovician glaciation on the composition of assemblages of organic-walled microfossils. Five Late Ordovician chitinozoan biozones belonging to the North Gondwana zonation are identified. During the late Caradoc and early Ashgill, no significant changes in chitinozoan assemblages are recorded that could be attributed to any dramatic climatic and/or environmental events. The almost absence of phytoplanktonic elements (acritarchs and leiospheres) and of cryptospores in the fistulosa/barbata and in the nigerica biozones are interpreted as resulting of lower offshore environmental conditions. The reappearance of a variety of palynomorphs in the lower part of the elongata biozone does not indicate drastic climatic changes but more likely a shallowing trend of the marine environment and an increased primary production, possibly related to a cooling of the surface water masses subsequently to early effects of a general climatic cooling. The first obvious evidence of the Late Ordovician glaciation occurs in the lower part of the elongata biozone, at the base of the sandy member topping the Lower Second Bani Formation. This sandy deposit is interpreted as the result of a dramatic fall of the sea level due to the development of the Hirnantian ice cap on Gondwana. This short-lived glaciation ended when the northern Gondwanan ice cap melted during the upper part of the elongata and the oulebsiri biozones. A biological crisis affected both the chitinozoans and the acritarchs just after this glaciation, i.e., in the latest Hirnantian.     

Acritarchs from the Dadas Formationin Southeast Turkey

Dadas Formation in Southeast Turkey yields abundant well preserved acritarchs, chitinozoans, tasmanites and scolecodonts. Encountered acritarchs suggest Upper Llandoverian-Ludlovian age for this formation. The acritarch association of the Dadas Formation resembles to the Middle Silurian assemblages of Tunisia and Libya. Thus Southeast Turkey falls in the Transitional-Iberian realm of Neoveryhachium carminae facies.     

Paleoecology,biostratigraphy and biogeography of late Silurian to early Devonian acritarchs and prasinophycean phycomata in well A161, Western Libya,North Africa

Diverse and well preserved acritarch and prasinophycean phycomata assemblages were recovered from the late Silurian to Lower Devonian strata of well A161 in western Libya, and four distinct acritarch biozones are recognized, based on the stratigraphic distribution of 156 species. The palynoflora is independently dated by means of chitinozoans, and allows discussion of the evolution of acritarchs and prasinophyte phycomata across the Ludlow–Přı́dolı́ boundary in relation to probable major climatic change, as well as in the early and middle Přı́dolı́, and the lower Lochkovian. Correlations are proposed with the British Isles, Baltica, and Algerian Sahara. Sedimentation occurred in shallow high-energy conditions throughout, but with periodic rise of sea level. The changes in marine to terrestrial palynomorph ratios through the section document the relationship between marine palynomorph assemblages and sea surface conditions in these marginal marine environments. The major drift of Gondwana towards low latitudes during the Ludlow–Přı́dolı́ transition seems to have been the driving force behind homogenization of assemblages on the two sides of the Rheic ocean, and explains the similarities between phytoplanktonic assemblages of the north Gondwanan margin and the South of Baltica. The data suggest that the Rheic ocean was almost closed by the late Silurian, and had become restricted to a moderately deep sea. In the Lochkovian the microflora are strongly facies-dependent and delineate more restricted provinces such as the Ibarmaghian domain in the sense of Plusquellec (1987) including the Maghreb and Ibero–Armorican areas.Nine new species are described: Arkonia nova, Arkonia paulumstriata, ?Cymatiosphaera florida, Cymatiosphaera nimia, Dactylofusa hispidusa, Disparifusa quasibernesgae, Evittia areolata, Multiplicisphaeridium verticisum, and ?Villosacapsula steemansii. In addition, three new combinations are suggested: Visbysphaera bonita (Cramer) comb. nov., Visbysphaera jardinei (Cramer) comb. nov. and Visbysphaera albanega (Cramer et al.) comb. nov.     

Late Devonian Acritarchs from the Gneudna formation in the Western Carnarvon basin,Western Australia

The Gneudna Formation is a Late Devonian(Frasnian) sequence of marine calcareous sediments that occurs in the Carnarvon Basin, Western Australia. The present palynological study is based upon subsurface silty strata from a borehole (Pelican Hill or Bibbawarra Bore) that was drilled early this century near the western coastal limit of the Carnarvon Basin.The subject strata have previously been attributed to the Gneudna Formation on lithostratigraphic grounds. They contain a rich and varied assemblage of marine microphytoplankton (acritarchs), associated with trilete miospores of which Geminospora lemurataBalme, 1962 is the dominant form. Forty-seven species of acritarchs are recognizable in the palynoflora, which corresponds very closely with that described recently (Playford & Dring, 1981) from the Gneudna Formation in the vicinity of its type section on the opposite (eastern) side of the Carnarvon Basin. The apparently parochial complexion of the Gneudna acritarch suite is probably illusory, insofar as early Late Devonian acritarchs have not been studied extensively or intensively from either the northern or southern hemispheres.The following new species of acritarchs areformally instituted herein: Elektoriskos villosa, Lophosphaeridium pelicanensis, and Pterospermella tenellula.     

Palynostratigraphic,palynofacies, organic geochemical and palaeoenvironmental analysis of the Silurian Tanezzuft Formation in the Ghadames Basin of north-west Libya

Two palynofacies associations are documented from the Silurian Tanezzuft Formation in the Ghadames Basin. These are characteristic of the basal ‘Hot Shale’ and the overlying deposits, referred to here as the Cold Shale. The former reflects deposition in distal suboxic anoxic conditions and is dominated by highly oil-prone amorphous organic matter (AOM) typical of deposition in generally anoxic, restricted marine basins. Only a few acritarchs, prasinophyte algae and chitinozoans occur in association: virtually no spores or cryptospores were recorded. Thick-walled prasinophytes are most numerous in this part of the Tanezzuft Formation in both the Ghadames and Murzuq basins, suggesting enhanced surface water productivity. Deposition took place after the melting of the Late Ordovician ice sheets, which led to a major marine transgression. The palynofacies recorded from the overlying ‘Cold Shale’ deposits indicate deposition in distal shelf and basin conditions that were also relatively anoxic. They contain more palynomorphs, especially acritarchs, and generally less AOM. The phytoplankton assemblages are dominated by simple and thin-walled prasinophyte algae (leiospheres), suggesting dysoxic–anoxic conditions. Overall the middle and the upper parts of the Tanezzuft Formation are regarded as being deposited in distal dysoxic–anoxic shelf, distal dysoxic–oxic shelf and distal suboxic–anoxic basin respectively. Because chitinozoans are very rare, age determinations of the samples investigated are based mainly on acritarchs. The Hot Shale is dated as early-mid Rhuddanian (early Llandovery) whereas the rest of the formation is considered to late Rhuddanian–Telychian in age. As documented previously from other samples of the Tanezzuft Formation in both the Ghadames and Murzuq basins, the Hot Shale has a very high TOC content and excellent source potential for liquid hydrocarbons, whereas rest of the formation is less rich in organic matter with larger terrestrial and oxidized components and hence reduced potential for sourcing hydrocarbons (both oil and gas).     

Progress in Irish lower palaeozoic palynology

Knowledge of Lower Palaeozoic palynomorphs in Ireland has improved greatly during the last decade, and acritarchs of most epochs from Vendian to Wenlock, together with Ordovician and Silurian chitinozoa and Silurian miospores, are now known. The present state of knowledge is summarised in terms of a number of distinctive palynological assemblages.     

新疆哈密地区晚泥盆世疑源类化石的发现及地质意义

从新疆哈密地区石城子北剖面7件样品获得分异度较高、有机质壁显著炭化保存的疑源类化石,根据其形态特征,共鉴定出14个形态属和15个形态种(其中8个未定种,3个比较种)。结合国内外古生代晚泥盆世已知疑源类组合进行比较,清楚表明当前获得的疑源类组合代表了晚泥盆世海洋微体浮游植物群面貌。我国涉及晚古生代疑源类生物地层的调查研究相对薄弱,而有关晚泥盆世疑源类化石的发现和报道更为匮乏,当前疑源类化石的发现,填补和丰富了新疆乃至国内晚泥盆世疑源类化石研究资料。该发现佐证了关于卡拉麦里洋在早石炭世闭合的认识;作为基础食物链的海洋微体浮游植物是重要成烃生物,晚泥盆世疑源类的保存预示研究区域具有石油、天然气勘察的前景。     

新疆若羌石灰华中的植物化石及古环境*

根据首次从富阳西湖组发现的孢子及其垂直分布特征,划分出下段 LH 组合和上段 DP 组合,分别归入晚泥盆世法门晚期(斯图年期)和早石炭世早期(杜内早期),即泥盆-石炭系界线通过西湖组内部,与江苏五通组类似.     

Biostratigraphy,biodiversity and palaeogeography of late Silurian chitinozoans from A1-61 borehole (north–western Libya)

High resolution biostratigraphic investigation of well preserved and highly diversified chitinozoan assemblages from core samples collected in the upper part of the Alternances Gréso-argileuses Formation (late Silurian) in well A1-61 (Tripolitania, north–western Libya) is undertaken. The chitinozoan assemblages document the range of several Pridolian taxa selected as index species for the global Silurian chitinozoan biozonation. Distribution of important accompanying species is also discussed. The abundance and the diversity of these chitinozoans are quantified and collated with the local environmental trends as deduced from the lithology, sedimentary features and from the associated organic walled microfossils (i.e. scolecodonts, eurypterid fragments, acritarchs, spores, leiospheres, cuticles and plant debris). The palaeogeographic distribution of late Silurian chitinozoans is discussed with a particular attention paid to a very distinctive chitinozoan assemblage characterising the middle part of the Pridoli of the Ibarmaghian Domain in northern Gondwana regions. Systematic notes, including detailed biometric investigations and SEM illustrations, are provided for selected taxa of taxonomic interest and useful for regional or more long distance correlation.     

Cryptospore Assemblages from the Ordovician/silurian Boundary in the Puna Region, North-west Argentina

Palynomorph assemblages have been recovered from deposits believed to straddle the Ordovician/Silurian boundary, from the upper member of the Salar del Rincón Formation, in the Puna region of north-west Argentina. The palynomorph assemblages are dominated by terrestrial cryptospores, but also contain marine elements (acritarchs, prasinophycean algae and chitinozoans). The cryptospore assemblages are similar in composition to those described from coeval deposits worldwide, suggesting that the producers were cosmopolitan and tolerated a wide range of climatic conditions. They are correlated with the Imperfectotriletes spp. Interval Biozone (sub-biozone α) of the Imperfectotriletes spp.- Laevolancis divellomedia Assemblage Biozone, indicating a Hirnantian (latest Ordovician) age. Acritarchs include late Ordovician species such as Eupoikilosusa striata and Villosacapsula cf. setosapellicula , that coexist with the Llandovery species Dactylofusa estillis. Based on lithological and palynological evidence, an early Llandovery, or a late Hirnantian (post-glacial) age is proposed for the basal part of the upper member of the Salar del Rincón Formation.     

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.     

Ordovician chitinozoans and acritarchs from southern and southeastern Turkey

Revision of the lithostratigraphy of Ordovician deposits in southern and southeastern Turkey led to a re-evaluation of the age assignments of formations identified in the subsurface and at outcrop. Previous datings were based on macrofauna (mainly trilobites and graptolites). The present paper focuses exclusively on organic-walled microfossils (chitinozoans and acritarchs), which provide numerous chronostratigraphical improvements, especially in successions barren or poor in macrofossils. Close to 200 samples were collected in the Taurus chain (i.e. from Kemer, Seydisehir, Ovacik, Kozan, to Sariz regions in southern Turkey) and in the Border Folds (Mardin and Hakkari regions), usually regarded as part of the Arabian Plate in palaeogeographical reconstructions. Many samples are productive and yield chitinozoans and/or acritarchs of extremely variable preservation, depending on their geographical and geological location. In the Taurus chain, the material is “coalified” and frequently fragmented whereas, in the Border Folds, maturation of the organic matter is much lower and preservation of the microfossils is good to excellent. Several Ordovician chitinozoan biozones (northern Gondwana zonation) as well as diagnostic acritarch assemblages are identified in southern and southeastern Turkey. These Ordovician formations are assigned here to the new global stages of the Ordovician chronostratigraphical scale. The Seydisehir (upper part), Sobova, and Kilgen Lake (lower part) formations are referred to the Darriwilian. The Kilgen Lake (upper part), Sort Tepe, and Bedinan formations are attributed to the Sandbian and to the Katian, and the Halevikdere Formation (glacio-marine part) is assigned to the Hirnantian. Reworking of Early Ordovician acritarchs is documented in pre-glacial and in glacial Late Ordovician deposits. They indicate that active erosive processes occurred during the Middle and Late Ordovician sedimentation. The organic-walled microfossils recorded in the Ordovician of south and southeastern Turkey belong to the northern Gondwana realm. Interestingly however, some Baltoscandian influences are noted in the Border Folds during Early Late Ordovician.     

腕足动物Planovatirostrum Sartenaer,1970的古生态特征

小嘴贝类腕足动物Planovatirostrum形态奇特,在我国,目前仅在新疆北部和布克赛尔蒙古族自治县和什托洛盖镇北10余公里处七里沟剖面洪古勒楞组中段底部层位中发现,化石大致呈簇状密集或花斑状分布。经过对产Planovatirostrum planoovale岩性、岩相和生物相的综合分析得知,这段地层是一套深水相沉积,P.pla-noovale生活在水体宁静、海水较深的软质基底上。     

Palynological correlation of the upper devonian and lower carboniferous in central Ireland

Miospore assemblages assigned to the PL, NV, CM and Pu Zones have been recorded from a number of boreholes which penetrated Upper Devonian and Lower Carboniferous (Tournaisian and early Visean) rocks in central Ireland. The palynomorphs occur in both marine and non-marine successions, permitting correlation between these two facies. The boundary between the PC and CM Zones has been located within three sections. The palynological data suggest that the base of the marine sequence is of mid-Tournaisian (Tn2) age at Ballyvergin in the south of the area described and of uppermost Tournaisian (Tn3) or earliest Visean age around Clew Bay in the northwest.     

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.     

The effects of the final stages of the Late Ordovician glaciation on marine palynomorphs (chitinozoans, acritarchs, leiospheres) in well Nl-2 (NE Algerian Sahara)

Palynomorph assemblages, especially chitinozoans and acritarchs, from the Upper Ordovician of well Nl-2 (north-east of the Algerian Sahara) are studied in order to precisely date the ultimate effects of the Late Ordovician glaciation and to document the impact of this major climatic stress on the diversity of the palynoplankton. References are made to stable isotope excursions and to global eustatic sea level variations in order to improve the local age determination. The Hassi el Hadjar Formation, i.e. glacio-marine diamictites, is interpreted as a transgressive event resulting from the melting of the northern Gondwana ice cap. It yields poorly preserved and moderately diverse chitinozoans of late Hirnantian age. Acritarchs are more abundant in the lower part of these "microconglomeratic clays", but display a low diversity and are badly preserved throughout the whole formation. Reworked individuals are recorded in both groups. The marine sediments of the M'Kratta Formation of latest Hirnantian age contain better preserved, more abundant and more diverse palynomorph assemblages, especially in the Upper Member. The composition of this palynoplankton indicates a fairly good faunal and phytoplankton recovery after the early Hirnantian climatic stress.The extinction of the Ordovician forms, and the appearance of Silurian type taxa occur only in the uppermost Hirnantian, i.e. following with a slight delay the glacial event. The overlying black shales of Wenlock age (lower part of the Oued Mehaiguène Formation) are indicative of marine anoxic environments. They yield a virtually exclusive, but enormous number of Tasmanacea. The very peculiar composition of this palynoplankton seems to be independent of the Late Ordovician glaciation and is most likely related to the factors that, later, generated and maintained anoxic conditions in this area.A new species of chitinozoan, Spinachitina oulebsiri sp. nov. from the latest Hirnantian M'Kratta Formation, is described and illustrated.     

江汉盆地古新世的介形类

该文首次报道了江汉盆地可能属于古新世的非海相地层及其中的介形类化石,计有17属30种(其中新种3个),隶属于3个超科。该介形类动物群自下而上可分为:1.Porpocypris(?)-Paraily-ocypris-Cypridea组合;2.Sinocypris-Eucypris-Limnocythere组合。第2组合完全可与广东南雄盆地罗佛寨组的介形类化石群对比,时代可能为古新世晚期;第1组合的介形类是否可与广东南雄盆地上湖组的化石对比的问题,还有待今后发现更为可靠的Porpocypris属的代表分子来解决,这里暂置于古新世早、中期。