Microfossil Taxa Research Articles

(261–266) Proposals to amend the Code to update regulations of the nomenclature of fossils

(261–266) Proposals to amend the <i>Code</i> to update regulations of the nomenclature of fossils

Systematic paleontology, acritarch biostratigraphy, and δ13C chemostratigraphy of the early Ediacaran Krol A Formation, Lesser Himalaya, northern India

AbstractAcritarch biostratigraphic and δ13C chemostratigraphic data from the Krol A Formation in the Solan area (Lesser Himalaya, northern India) are integrated to aid inter-basinal correlation of early–middle Ediacaran strata. We identified a prominent negative δ13C excursion (likely equivalent to EN2 in the lower Doushantuo Formation in the Yangtze Gorges area of South China), over a dozen species of acanthomorphs (including two new species—Cavaspina tiwariaeXiao n. sp.,Dictyotidium grazhdankiniiXiao n. sp.), and numerous other microfossils from an interval in the Krol A Formation. Most microfossil taxa from the Krol A and the underlying Infra-Krol formations are also present in the Doushantuo Formation. Infra-Krol acanthomorphs support a correlation with the earliest Doushantuo biozone: theAppendisphaera grandis-Weissiella grandistella-Tianzhushania spinosaAssemblage Zone. Krol A microfossils indicate a correlation with the second or (more likely, when δ13C data are considered) the third biozone in the lower Doushantuo Formation (i.e., theTanarium tuberosum-Schizofusa zangwenlongiiorTanarium conoideum-Cavaspina basiconicaAssemblage Zone). The association of acanthomorphs with EN2 in the Krol Formation fills a critical gap in South China where chert nodules, and thus acanthomorphs, are rare in the EN2 interval. Like many other Ediacaran acanthomorphs assemblages, Krol A and Doushantuo acanthomorphs are distributed in low paleolatitudes, and they may represent a distinct paleobiogeographic province in east Gondwana. The Indian data affirm the stratigraphic significance of acanthomorphs and δ13C, clarify key issues of lower Ediacaran bio- and chemostratigraphic correlation, and strengthen the basis for the study of Ediacaran eukaryote evolution and paleobiogeography.UUID:http://zoobank.org/5289fdb2-0e49-4b3b-880f-f5b21acab371.

Biostratigraphy of the Upper Devonian Khoshyeilagh Formation in NE Iran based on conodonts and other faunas

The Khoshyeilagh Formation located in the northeast of Iran yielded seven conodont species and sub-species and 19 macro- and microfossil taxa that allow recognition of two conodont biozones and one biozone based on calcareous microfossils. The latest Frasnian age (the Upper rhenana to linguiformis zones) is attributed to the topmost strata with Icriodus alternatus. Its replacement with I. cornutus indicates the Famennian (Lower triangularis to Lower crepida zones) corresponding to the Umbellina Zone. The fossil assemblages identified in the Khoshyeilagh Formation represent a shallow marine environment with a tropical climate at the time of deposition. The fossil species from the Khoshyeilagh Formation and the sedimentary basins in Algeria, Libya, Morocco, Poland, and Russia reveal a close connection between the Iranian plateau and the northern parts of Gondwana in the Late Devonian. The biofacies and lithofacies analyses show a sea-level decline at the end of Frasnian, followed by a considerable sea-level drop, as in other regions of the world. After a short time, in the Famennian, the deepening occurred in some parts of the area and the open marine facies (bioclast spicule wackestone-packstone) were deposited. This study is the first attempt to determine the Frasnian-Famennian boundary based on conodont assemblages and other fossil species such as umbellulids, tentaculites, and ostracods. The distribution of these species is interpreted in sedimentological, stratigraphic, sequence stratigraphy, and the global eustatic context. Keywords: biofacies, conodont, Frasnian-Famennian boundary, Late Devonian, NE Iran.

Authigenic anatase within 1 billion-year-old cells.

The siliciclastic ~1Ga-old strata of the Torridon Group, Scotland, contain some of the most exquisitely preserved three-dimensional organic-walled microfossils (OWMs) of the Precambrian. A very diverse microfossil assemblage is hosted in a dominantly phosphatic and clay mineral matrix, within the Diabaig and the Cailleach Head (CH) Formations. In this study, we report on several microfossil taxa within the CH Formation (Leiosphaeridia minutissima, Leiosphaeridia crassa, Synsphaeridium spp. and Myxococcoides spp.) that include populations of cells containing an optically transparent and highly refringent mineral, here identified using electron microscopy as anatase (TiO2 ). Most anatase crystals occur entirely within individual cells, surrounded by unbroken carbonaceous walls. Rarely, an anatase crystal may protrude outside a cell, interpreted to correspond to zones where the cell wall had broken down prior to anatase precipitation. Where an anatase crystal entombs an organic intracellular inclusion (ICI), the ICI is large and well preserved. These combined observations indicate that the intracellular anatase is an authigenic sedimentary phase, making this the first report of in situ precipitated anatase intimately associated with microfossils. The ability of anatase to preserve relatively large volumes of intracellular and cell wall organic material in these cells suggests that the crystallisation of anatase entombed cellular contents particularly quickly, soon after the death of the cell. This is consistent with the strong affinity of Ti for organic material, the low solubility of TiO2 , and reports of Ti occurring in living organisms. With the data currently available, we propose a mineralisation pathway for anatase involving Ti complexation with organic ligands within specific cells, leading to localised post-mortem anatase nucleation inside these cells as the complexes broke down. Further overgrowth of the anatase crystals was likely fuelled by very early diagenetic mobilisation of Ti that had been bound to more labile organic material nearby in the sediments.

Recent contributions to the standard Albian/Cenomanian boundary chronology from Hokkaido, Japan: A review for data reintegration and numerical age recalibration

The numerical age of the Albian/Cenomanian (A/C) boundary (=Early/Late Cretaceous Epoch boundary) has recently been updated using new radiometric dates from Hokkaido, Japan. Yet, an element of uncertainty still remains in the age scaling due to inaccurate chronostratigraphic contexts surrounding the tuff beds that have been geochronologically studied in the Oyubari and Soeushinai areas. To ensure stability in the Cretaceous time scale, this paper rigorously reevaluates the current status of Hokkaido A/C chronology, clarifying the limitations and making refinements via proper reintegration of published chronostratigraphic data. In the case of the Oyubari area, its A/C biostratigraphic scheme is limited by near-absence of ammonites and planktonic foraminifera at the Albian–Cenomanian transition, resulting in a large discrepancy in the proposed boundary levels based on these macro- and microfossil taxa. These problems can be solved by solid data integration aided by event- and δ13C-sratigraphy from the adjacent Ashibetsu area, wherein the A/C boundary is well documented by the superior planktonic foraminiferal record. Based on the resultant A/C boundary redefinition for the Oyubari area in conjunction with a simple linear interpolation from two published UPb ages, the A/C boundary age can be independently calibrated to be 100.8 Ma [with ±1.4 Myr uncertainty (=analytical precision)], which is consistent with that currently in use in the Geologic Time Scale 2012 (100.5 ± 0.4 Ma). In the case of the Soeushinai area, its chronostratigraphic framework is limited by rather complex geological structure and vertically/laterally variable lithologies. Moreover, the accuracy of geochronological data from this area is undermined by the fact that the dated tuff levels do not bracket the inferred A/C boundary.

Stratigraphy, palaeoenvironments and palaeoecology of the Loch Humphrey Burn lagerstätte and other Mississippian palaeobotanical localities of the Kilpatrick Hills, southwest Scotland.

Background and Aims. The largely Mississippian strata of the Kilpatrick Hills, located at the western end of the Scottish Midland Valley, enclose several macrofossil floras that together contain ca 21 organ-species of permineralised plants and ca 44 organ-species of compressed plants, here estimated to represent 25 whole-plant species (Glenarbuck = nine, Loch Humphrey Burn Lower = 11, Upper = seven). The most significant locality is the internationally important volcanigenic sequence that is reputedly intercalated within the Clyde Plateau Lava Formation at Loch Humphrey Burn, where ca 30 m of reworked tuffs and other clastic sediments enclose one of the world’s most important terrestrial lagerstätten of this period. We here explore the palaeoecology and palaeoenvironments of the locality, and elucidate its controversial age.Methods. Repeated re-excavation of key exposures allowed recognition of five main depositional units, differing in thickness from 4 m to 12 m. It also permitted detailed sampling for plant macrofossils and microfossils throughout the succession. Several approaches are integrated to re-assess the taphonomy and preservation of these exceptional plant fossils.Key Results. The deposits are rich in taxonomically diverse miospores and in toto contain at least six well-developed compression floras, together with two beds yielding nodules that enclose well-researched anatomically preserved plants permineralised in calcite. Bulk geochemistry shows that the upper nodules formed by migration of Ca with subordinate Mn and Na. Some phylogenetically important plant fossils recovered in the early 20th century have been traced to their source horizons. Trends in relative proportions of macrofossil and microfossil taxa through the sequence are only moderately congruent, perhaps reflecting the likelihood that microfossils sample the regional rather than the local flora.Conclusions. The Loch Humphrey Burn sequence encompasses a wide range of depositional environments that intercalates high-energy fluvial channels (possibly developed during flash floods in a seasonally arid environment) with lower energy flood plains and a brief lacustrine interval; all yield macrofloras typically dominated by allochthonous pteridosperms. The uppermost unit represents clastic swamps dominated by (hypo)autochthonous lycopsids and ferns s.l., and is tentatively correlated with the entire—reputedly mid-Visean—exposure at nearby Glenarbuck. Other nearby localities with rooted tree-lycopsids appear to have immediately pre-dated the onset of regional volcanism. These interpretations allow revised provenancing and dating of historical collections of key plant fossils. The late Tournaisian date previously attributed on palynological evidence to the lowest unit at Loch Humphrey Burn appears increasingly improbable when our re-appraisal of the macrofloras and microfloras is placed in the context of (a) statistical comparison with other permineralised Mississippian assemblages and (b) recent stratigraphic and geochronologic studies in the region; rather, we ascribe the entire Kilpatrick Hills sequence to the mid-Visean. Stratigraphic and palaeoenvironmental interpretations of the Mississippian rocks of the Kilpatrick Hills have especially profound implications for our understanding of the physical evolution of Scotland during the Variscan orogeny and formation of Pangea.

Organic-walled microfossils from the early Neoproterozoic Liulaobei Formation in the Huainan region of North China and their biostratigraphic significance

Biostratigraphic subdivision and correlation of early Neoproterozoic strata is hampered by the limited number of widely distributed and age diagnostic fossils. The acanthomorphic acritarch Trachyhystrichosphaera aimika, among a few other microfossil taxa, has emerged as a potential early Neoproterozoic index fossil, but its temporal and spatial ranges have not been thoroughly documented. To improve our knowledge about early Neoproterozoic biodiversity, we carried out a micropaleontological investigation of the early Neoproterozoic Liulaobei Formation in northern Anhui of North China. Our investigation using a low-manipulation maceration technique revealed a diverse assemblage of organic-walled microfossils dominated by sphaeromorphs and filaments, with relatively few acanthomorph taxa. A total of 23 taxa were recovered, including three new species (Eotylotopalla? grandis n. sp., Siphonophycus gigas n. sp., and Trachyhystrichosphaera botula n. sp.). Also present in the Liulaobei Formation are Trachyhystrichosphaera aimika (a species widely present in pre-Cryogenian Neoproterozoic and latest Mesoproterozoic rocks) and Pololeptus rugosus (a species characterized by an ellipsoidal vesicle with transverse annulations). The new data add to the growing diversity of early Neoproterozoic fossils and strengthen the basis for improved biostratigraphic correlation of early Neoproterozoic strata. Correlation with other geochronologically dated successions that contain Trachyhystrichosphaera confirms Trachyhystrichosphaera and T. aimika as promising index fossils to define and subdivide the pre-Cryogenian Neoproterozoic Era in terms of Global Boundary Stratotype Section and Point (GSSP), as opposed to current system using Global Standard Stratigraphic Age (GSSA). Available biostratigraphic data, including the occurrence of Trachyhystrichosphaera, Chuaria, Tawuia, and Sinosabellidites, suggest that the Liulaobei Formation is of pre-Cryogenian Neoproterozoic age, not Cryogenian–Ediacaran age as some have suggested in the past.

Biogeographic effects of the closing Central American Seaway on benthic Foraminifera of Venezuela

Studies of the effects of the Central American Seaway's closure on microfossil taxa and stable isotopes of foraminifera previously addressed the timing of emplacement of the Caribbean-tropical eastern Pacific sill, changes in marine nutrients, evolutionary and paleobiogeographic events associated with closure, and rates of uplift in Central America. However, there have been no quantitative studies of the transisthmian divergence of whole biotas. Here we assess biogeographic effects of the closing Central American Seaway by comparing middle Miocene to Pliocene, neritic benthic foraminiferal assemblages from Falcon State, Venezuela, to those of coeval deposits with similar paleoenvironments from Panama, Costa Rica, and Ecuador. Benthic foraminiferal assemblages from the Urumaco, Codore, Caujarao, and La Vela formations of Venezuela's central coast were compared to other Caribbean and tropical eastern Pacific assemblages with Simpson's, Dice, and Jaccard similarity coefficients. Results of the Simpson's Coefficient indicate that the Caribbean inner neritic faunas of Venezuela, Costa Rica, and Panama became significantly more similar from the late Miocene to Pliocene, as mixing with Pacific waters was reduced and modern oceanic conditions of the Caribbean Sea were established.

The Early Sarmatian bryozoan Celleporina medoborensis sp. nov. from the Medobory reefs of western Ukraine (Central Paratethys)

Moundlike, globular to hemispherical bryozoan colonies of Celleporina medoborensis sp. nov. are documented from the calcareous organodetrital, slightly marly facies of the Lower Sarmatian (Volhynian) serpulid-microbialite reefs, in the Polupanivka and Ditkivtsi quarries (Medobory Hills), located at the northeastern margin of the Carpathian Foreland Basin (Central Paratethys) in western Ukraine. The colonies of C. medoborensis are multilamellar, often with a subcircular hole and occur together with numerous cyclostome bryozoans (crisiids, tubuliporinids, branching colonies of entalophoroids) as well as schizoporellid and cryptosulid cheilostomes, accompanied by a few macro- and micro-fossil taxa. The combination of morphological characters such as: thick radial ribs in the pseudoporous, variably-shaped area of the ovicell, and one or two small adventitious oral, as well as large vicarious avicularia are the main characteristic features of species. The rich occurrence of the celleporiform colonies of C. medoborensis sp. nov. within the fine-grained calcareous sands of Polupanivka and Ditkivtsi suggests a shallow-water setting and high availability of soft substrates, probably dominated by calcareous algae upon which the bryozoans may have settled in the Medobory reef biota during the Early Sarmatian.

Microfossils from the Arymas and Debengda formations, the Riphean of the Olenek Uplift: Age and presumable nature

Studied assemblages of diverse organic-walled microfossils separated from the Arymas and Debengda formations of the Olenek Uplift include several paleobiological groups of microorganisms. Sufficiently large morphotypes of the first group are identified with remains of cyanobacteria. Morphotypes of variable spiral structure, which dwelt in association or in symbiosis with cyanobionts, are attributed to the same bacterial community. The other group includes a series of different acritarch genera whose characters suggest their affinity with green algae of the order Desmidiales. It is very likely that this group coexisted on siliciclastic shoals with large ancestral forms of the present-day brown algae. Several microfossil taxa have been known before from the Neoproterozoic deposits only. With due regard for the relatively gradual accumulation of sedimentary succession lacking large hiatuses and for the regular series of K-Ar dates characterizing three Riphean formations of the Olenek Uplift, it is possible to suggest that there was the Arymas-Debengda-Khaipakh cycle of long-lasted, almost uninterrupted sedimentation within the time span of 1250–900 Ma. It is also admissible that age ranges of some Late Precambrian microfossils are much larger than their distribution intervals postulated formerly.

Stratigraphical distribution of Cambrian fossils in the Příbram-Jince Basin (Barrandian area, Czech Republic)

The stratigraphical distribution of all the fossil taxa known from the Cambrian Přibram-Jince Basin of the Barrandian area are shown in seven tables. Crustaceans, trace fossils, macroscopical algae, and microfossil taxa have been established in the Lower Cambrian Paseky Shale Member (Holsiny-Hořice Formation). Ranges of molluscs, brachiopods, echinoderms, miomerid and polymerid trilobites, crustaceans, trace fossils, incertae sedis, foraminifers, and acritarchs have been plotted on biostratigraphical charts of the Middle Cambrian Jince Formation.

A preliminary investigation of siliceous microfossil succession in late quaternary sediments from Lake Baikal, Siberia

Siliceous microfossil assemblage succession was analyzed in a 100 m sediment core from Lake Baikal, Siberia. The core was recovered from the lake's central basin at a water depth of 365 m. Microfossil abundance varied greatly within the intervals sampled, ranging from samples devoid of siliceous microfossils to samples with up to 3.49 × 1011 microfossils g-1 sediment. Fluctuations in abundance appear to reflect trends in the marine δ18O record, with peak microfossil levels generally representing climate optima. Microfossil taxa present in sampled intervals changed considerably with core depth. Within each sample a small number of endemic diatom species dominated the assemblage. Changes in dominant endemic taxa between sampled intervals ranged from extirpation of some taxa, to shifts in quantitative abundance. Differences in microfossil composition and the association of variations in abundance with climate fluctuations suggest rapid speciation in response to major climatic excursions.