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.     

Organic-walled microfossils from Cambrian Stage IV in the Jiaobang section,eastern Guizhou,China

The lower Cambrian succession in the Jiaobang section, Jianhe County, eastern Guizhou, China, includes, in ascending order, the Bianmachong, Balang, and Tsinghsutung formations, with a total thickness of about 645 m. Twenty-six morphological genera (including one new genus) are identified from the Balang and the underlying Bianmachong formations, many of which are common and widely distributed. Six acritarch assemblages are discerned in the Balang Formation. They are, in ascending order, the Adara alea‒Skiagia ornata, the Acrum radiale‒Pterospermella velata, the Comasphaeridium molliculum‒Solisphaeridium baltoscandium, the Corrugasphaera perfecta n. sp.‒Pterospermella vinctusa n. sp., the Acrum novum‒Heliosphaeridium oligum, and the Acrum membranosum‒Adarve diafanum acritarch assemblages. An obvious change of organic-walled microfossil assemblages occurred in the interval between 84 m and 98 m from the bottom of the Balang Formation which roughly corresponds to the boundary between the Oryctacarella duyunensis trilobite Zone and the overlying Arthricocephalus chauveaui trilobite Zone. In addition, organic-walled microfossils are scarce in about 24 m thick from the bottom of the Balang Formation. One new genus and five new species including Plagasphaera balangensis n. gen. n. sp., Asteridium tubulus n. sp., Cymatiosphaera spina n. sp., Corrugasphaera perfecta n. sp., and Pterospermella vinctusa n. sp. are described.     

Marine influence and incursion in the Gondwana basins of Orissa, India: A review

The Permian–Triassic succession of the Indian Gondwana Sequence was previously considered to have been deposited in a fluviatile-lacustrine environment. Similarly, earlier Lower Gondwanas of Orissa State (a major part of the Mahanadi Master basin) were considered entirely fresh water deposits. Faunal evidence is still scanty in this master basin. Ichnology and palynology along with a few sedimentary records are reviewed and analysed for inferring marine signature. The marine nature of the Talchir, Karharbari, Barakar, Barren Measures and Kamthi sediments of three major basins (Talcher, Ib River and Athgarh) in Orissa State was predicted on the basis of typical marine ichnofossils. Most of these sediments also contain acritarchs reflecting marine marginal environment throughout the Permian. Moreover, evidence of wave activity, salinity raise and discovery of phosphorite in Permian sediments also strengthen this view.Hence, the previous model of continental facies for the Lower Gondwanas is found to be incorrect. The ichnofossils (Skolithos and Cruziana ichno-facies), acritarchs (Foveofusa, Leiosphaeridia, Greinervillites, etc.) and other palynofossils of marine origin can be utilized as a tool for palaeoenvironmental reconstruction. In the Gondwana basins of Orissa (Mahanadi Master basin), consistent occurrence of marine acritarchs and trace fossils with some typical sedimentary structures such as wave ripples has been studied and reviewed from the Talchir (Early Permian) to Upper Kamthi (Triassic) formations at various time intervals. Here marine incursion could have occurred due to the well known global transgressions during Permian and Triassic.     

Billingen (Lower Arenig/Lower Ordovician) acritarchs from the East European Platform and their palaeobiogeographic significance

Billingen (Lower Arenig/Lower Ordovician) sediments of the St. Petersburg region, northwest Russia and the Leba area, northern Poland of the East European Craton yield acritarch assemblages, which are largely homogenous though displaying minor compositional differences that probably reflect a gradient from inner to outer shelf environments. Comparison with coeval acritarch microflora from the Yangtze Platform, South China, shows an overall similarity between Baltoscandian and South Chinese phytoplankton. The widespread uniformity in the fossil microphytoplankton may be related to the extensive global 'evae' sea-level transgression, which characterized the Billingen time. This suggests that during the Tremadoc through early Arenig times, acritarch assemblages displayed essentially an undifferentiated cold-water and oceanic character along the whole margin of Perigondwana in the South, as well as on the South Chinese and Baltic platforms, at middle latitudes (Mediterranean oceanic Realm). Despite this overall similarity, however, some typical taxa of the high-latitude Mediterranean Province (Arbusculidium, Coryphidium and Striatotheca) occur in South China, but are absent in Baltica. This discrepancy is explained as caused by differences in climatic and physiographic conditions that prevailed at the two palaeocontinents at this time. The inferred pattern of oceanic circulation during the Lower Ordovician is consistent with the palynological evidence of a prevailing warmer climate in Baltica than in South China, although the two palaeocontinents occupied the same palaeolatitudinal position.     

Marine microplankton and calcareous nannofossil palaeoecology of the Toarcian stratotype

In the Bifrons to Aalensis Ammonite Zones of the Vrines section (Toarcian stratotype), woody phytoclasts, nonsaccate pollen grains, and marine assemblages (dinoflagellate cysts, acritarchs, and foraminiferal linings) dominate the palynofacies. The dinoflagellate cyst assemblage is cosmopolitan with minor Boreal influences, characterized by relatively high quantities of Micrhystridium, Baltisphaeridium, Mendicodinium spinosum, Nannoceratopsis, and the Parvocysta suite, dominating in turn the marine assemblages. Marine assemblage compositions, both dinoflagellate cysts and acritarchs, and calcareous nannofossil abundances are different in marl and limestone lithotypes of the Vrines section. Calcareous nannofossils are generally more abundant in marls than in limestones, they display however a cyclic pattern of semiquantitative abundances in phase with lithological cycles. Although a diagenetic overprint cannot be completely excluded to explain such a difference, it seems likely that these dissimilarities are in part primary, the results of variations in terms of proximality-distality, and climatic fluctuations. A mean duration of 117.6 Kyr per marl-limestone alternation, and the stacking of four marl-limestone alternations for 470.6 Kyr, suggest a control by the Earth's two orbital eccentricity cycles. It is likely that the palaeoenvironmental conditions, which influenced the formation of marl-limestone alternations, also controlled the variations in marine phytoplankton assemblages.     

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.     

Correlating the global Cambrian–Ordovician boundary: Precise comparison of the Xiaoyangqiao section,Dayangcha, North China with the Green Point GSSP section,Newfoundland, Canada

The Cambrian–Ordovician boundary interval exposed at the Xiaoyangqiao section, North China is presented. The distribution of stratigraphically important fossils in the Xiaoyangqiao section revealed several nearly coeval graptolite, conodont, trilobite, and acritarch bioevents in the uppermost Cambrian–lowermost Ordovician carbonate-siliciclastic sedimentary sequence. The precise correlation to the Green Point GSSP section, western Newfoundland, Canada allows for the identification of the corresponding GSSP level in the Xiaoyangqiao section. The combined data from the Xiaoyangqiao section and the Green Point GSSP section provide a series of events that all can be applied as proxies for identification of the Cambrian–Ordovician boundary horizon outside the GSSP. Based on this, the Xiaoyangqiao section, Dayangcha, is here strongly recommended as a candidate for an Auxiliary Boundary Stratigraphic Section and Point section (ASSP) for the base of the Ordovician System, because it provides one of the best and most complete Cambrian–Ordovician transitions in the world and because the first planktic graptolites are from the Xiaoyangqiao section.     

Ediacaran acanthomorphic acritarchs from the Outer Krol Belt,Lesser Himalaya,India: Their significance for global correlation

Large acanthomorphic acritarchs have been previously reported from the Ediacaran successions of the Pachmunda and Krol Hill synclines in the Outer Krol Belt of Lesser Himalaya, India. Thin sections of chert from Krol ‘A’ Formation in Khanog and Rajgarh synclines, Outer Krol Belt, record an equally well developed and diversified assemblage of Ediacaran large acanthomorphic acritarchs. This assemblage contains specimens belonging to seven genera and ten species, identified as: Appendisphaera fragilis, A. grandis, Asterocapsoides sp. A, Asterocapsoides sp. B, Cavaspina acuminata, C. basiconica, Eotylotopalla dactylos, Knollisphaeridium sp., Papillomembrana sp., and Weissiella cf. grandistella. It also contains five unnamed forms, viz. A, B, C, D, and E. The Krol acritarch assemblage shows a close resemblance with the Upper Doushantuo or Tanarium anozos–Tanarium conoideum assemblage of China. However, the absence of biostratigraphically important markers such as Tanarium anozos and T. conoideum from the Krol assemblage, so far, makes it difficult to establish a definite biostratigraphic correlation between the two assemblages. The current observations from this new locality provide additional data for regional and global biostratigraphic correlation, and significantly increase the purview of Ediacaran sequences for global biostratigraphic zonation.     

中国贵州东部乌溜-曾家崖剖面早—中寒武世凯里组疑源类(英文)

我国贵州东部乌溜-曾家崖凯里组剖面作为世界早-中寒武世界线层型侯选剖面,产出良好保存的大型无脊椎动物化石(尤其是三叶虫)。因此,更加详细研究该剖面海洋疑源类的生物地层非常重要,将提供围绕界线的生物和环境变化的细微记录。乌溜-曾家崖剖面凯里组的疑源类划分两个组合,它们是凯里组0-52m的Leiomarginata si mplex-Fi mbriaglomerella membranacea组合和52-140m的Cristallinium cambriense-Heliosphaeridiumnodosum-Globosphaeridiumcerinum组合。140-214m仅有很少疑源类标本,可能因为凯里组上部以白云岩为主,不适宜有机壁微体化石的保存。距凯里组底部往上约52m处疑源类组合出现重大变化,无疑为解释沉积环境提供重要资料。两疑源类组合间界线,位于52.3-52.7m,此稍低于被三叶虫Oryctocephalusindicus首现所指示的全球寒武系第5阶潜在层型剖面界线。     

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.