Conodont Species Research Articles

A new polygnathid conodont species from the Upper Devonian (Lower Frasnian) of the East European Platform

A new polygnathid conodont species from the Upper Devonian (Lower Frasnian) of the East European Platform

Conodont micropalaeontology of mid-Ordovician aged limestone clasts from Lower Old Red Sandstone conglomerates, Lanark and Strathmore basins, Midland Valley, Scotland

Abstract. Mid-Ordovician limestone clasts in the Lower Old Red Sandstone conglomerates of the Lanark and Strathmore basins of the Midland Valley, Scotland, were derived from a cryptic carbonate platform, now hidden beneath the Southern Uplands Allochthon. These have yielded 17 multi-element species of conodonts, which are systematically described herein and include the eponymous biozonal species Pygodus serra and Pygodus anserinus. The fauna represents an outer shelf-ocean margin biofacies, found only in Upper Ordovician conglomerates in the Southern Uplands and the Malopolska Terrane, Poland.

Designation of holotypes for new species of <i>Iapetonudus</i> Nicoll, Miller, Nowlan, Repetski and Ethington and <i>Iapetognathus</i> Landing

Abstract. In the course of publication of a large manuscript on earliest Ordovician conodont species and their utility for biostratigraphy (Nicoll et al., 1999), an error occurred, resulting in the lack of designation of holotypes for the type species of the genus Iapetonudus and some new species of Iapetognathus. Herein, we remedy this error so that the originally published specimens are regarded as fully established holotypes rather than as syntypes in the future.As the original authors of these species, we establish the following holotypes: For the species Iapetognathus fluctivagus Nicoll, Miller, Nowlan, Repetski and Ethington, we designate the Pa element illustrated on Pl. 11, fig. 6, USNM 498962. For the species Iapetognathus jilinensis Nicoll, Miller, Nowlan, Repetski and Ethington, we designate the Pa element illustrated as Pl. 14, fig. 4, USNM 498973. For the species Iapetognathus landingi Nicoll, Miller, Nowlan, Repetski and Ethington, we designate the Pa element illustrated as Pl. 20, fig. 3, USNM 498996. For the species Iapetonudus ibexensis Nicoll, Miller, Nowlan, Repetski and Ethington, we designate the Pa element illustrated as Pl. 23, fig. 3, USNM 499009.

Palynomorphs, Conodonts and Associated Graptolites from the Ordovician Los Azules Formation, Central Precordillera, Argentina

Palynomorphs and conodonts are reported from the Ordovician Los Azules Formation, Argentine Precordillera. The formation is mainly made up of argillites, shales and mudstones, and is divided into three informal members. Fourteen species of acritarchs including Gorgonisphaeridiumm granulobrachium Ottone, Lophosphaeridium ruidum Ottone, and Polygonium echinatus Ottone that are proposed as new; two species of prasinophytes, one of cryptospores and three different morphotypes of phytodebris are identified throughout the middle and upper members of the formation. Two distinct palynomorph assemblages are recognized: the Lower Los Azules Palynological Assemblage (middle member) and the Upper Los Azules Palynological Assemblage (upper member). Eight species of conodonts are preserved as casts on bedding planes of the lower shales of the middle member. This conodont association is correlated with the upper division of the Eoplacognathus suecicus Zone from the late early Llanvirn. The upper part of the middle member contains the eponymous species of the Pygodus serra Zone of Llanvirn age. A calcirudite sample from the upper member yielded a rich and diverse microfauna that includes ten conodont species representing the lower part of the Amorphognathus tvaerensis Zone (early Caradoc). Conodonts and palynomorphs confirm previous graptolite-based dating of the Los Azules Formation (early Llanvirn-early Caradoc). The palynological assemblage exhibits similarities with coeval assemblages from the Northern Hemisphere and Gondwanaland.

CONODONTS OF THE LOWERMOST TRIASSIC OF SPITI, AND NEW ZONATION BASED ON NEOGONDOLELLA SUCCESSIONS

Conodonts from the lowermost Triassic Otoceras woodwardi beds and adjacent strata of Spiti are described and compared with Permian-Triassic (P-T) boundary bed faunas from elsewhere. A new pelagic zonation based on Neogondolella is introduced: the interval characterized by N. carinata-N. taylorae is subdivided into three parts based on successive first appearances of N. meishanensis , N. krystyni Orchard n. sp. and N. discreta Orchard and Krystyn n. sp., the nominal species of three successive zones. The development of these Griesbachian species involves a progressive morphological change in the configuration of the axial part (blade-carina-cusp) of the pectiniform elements. The pelagic conodont zonation is intercalibrated with the parallel zonation based on species of Hindeodus and Isarcicella , and with ammonoid faunas from Spiti, other Himalayan localities, and the Arctic. The meishanensis Zone embraces the parvus Zone and part of the overlying staeschei Zone. Strata containing O. woodwardi in Spiti carry the indices to the staeschei and krystyni zones. The Neogondolella conodont fauna associated with Otoceras differs from that of the latest Permian Changshing Limestone of China, but resembles that from the P-T boundary transition beds at Meishan, where a meishanensis Zone of restricted scope occurs beneath the parvus datum. The faunal change which introduces the characteristic Neogondolella species of the N. carinata-N. taylorae fauna occurs at the base of the P-T boundary transition beds at Meishan, the proposed boundary stratotype. Slightly above this level, the disappearance of most Neogondolella species and the introduction of new Hindeodus species coincides with a change in conodont biofacies rather than an extinction event. In the Spiti sections, the N. carinata-N. taylorae fauna, associated at first with H. parvus (as in Selong, Tibet), persists through the entire Griesbachian. Indices of the three Neogondolella zones are also recognized in the Salt Range and the Canadian Arctic. Four new conodont species are described: Neogondolella discreta, N. kazi, N. krystyni , and N. nassichuki .

Apparatus structure of the Ordovician conodontDecoriconus peselephantis (Lindström 1955)

The Lower Ordovician conodont species first described asScolopodusl peselephantis Lindstrom 1955, has a seximembrate apparatus of laterally compressed, variously curved and flexed coniform elements. These are very small and invariably striated or multicostate. The taxon is reassigned toDecoriconus Cooper 1975, a genus hitherto known by species from Upper Ordovician and Silurian strata. These younger species share several characteristic morphological features with the older species investigated in this work. When studied in detail, it was discovered thatD. peselephantis was the first species in a lineage which also included two successive new species. Of these,D. mercurius n. sp. occurs in the middle Arenig, whileD. pesequus n. sp. ranges from the late middle Arenig and at least through the Llanvirn, possibly even into the Caradoc. These new species, which were previously included intoS.? peselephantis, are described and their geographic distribution investigated. In addition, a probable homeomorphic form ofD. peselephantis, Toxotodus? gabriellae n. sp., is diagnosed.

Biostratigraphy of the Currarie Formation on the northwestern edge of the Southern Uplands: implications for the cessation of basic volcanism

Synopsis The Currarie Formation forms part of the deep water succession near the northern margin of the Southern Uplands. It comprises red and green mudstones (distal turbidites), chert and interbedded lava and lava breccia and overlies basalt lavas. The age of the Currarie Formation is critical in providing a minimum age for the end of basic volcanism in the northernmost part of the Southern Uplands and a maximum age for the onset of northerly derived turbidite flysch. It also allows biostratigraphical correlations to be made across the Southern Upland Fault. Graptolites indicative of the lower Nemagraptus gracilis Biozone and the first record of the conodont species Protopanderodus varicostatus from the formation indicate an earliest Caradoc (early Aurelucian) age for the Currarie Formation. This dates the cessation of basic volcanism in the northernmost part of the Southern Uplands as earliest Caradoc. However, the waning of volcanism may have been diachronous, continuing into the upper TV. gracilis Biozone in the area between the Southern Upland–Glen App and Carcow faults in a succession thought to have been developed further to the south than the Currarie Formation. The onset of coarse turbidite deposition followed within the same graptolite zone marking the onset of a major phase in uplift of the Midland Valley terrane and subsidence in the Southern Uplands basin.

Age constraints on the Devonian shale-hosted Zn-Pb-Ba deposits, Gataga District, northeastern British Columbia, Canada

Sedimentary exhalative barite and barite sulfide deposits occur in Upper Devonian basinal clastic sedimentary rocks of the Earn Group of the Gataga district, northern Canadian Cordillera. The deposits formed in a stratigraphic sequence from which conodont species and assemblages range in age from the Upper triangularis Zone to the Lower praesulcata Zone of the early to late Famennian, a time span of no more than 7 m.y. At the Driftpile deposit, which is the best constrained example, conodonts bracket at least two distinct mineralization events during the middle Famennian: the older event is the Lower-Upper marginifera Zone or Trench zone and East zone, and the younger event is the Uppermost marginifera-trachytera Zone or Main zone. The other Gataga deposits, although somewhat less well defined, are roughly of these ages or somewhat younger: one barite-pyrite unit at Cirque is late Famennian (postera and expansa Zones), the youngest unit so far recognized in the Gataga district. Exhalation of metalliferous brines into the Gataga basin was of relatively short duration and episodic, and the sites of active venting probably migrated along extensional faults through time. This data allow temporal correlation of these sedimentary exhalative deposits with other Devonian-Mississippian mineralization events on the North American margin, such as other sedimentary exhalative sulfide deposits and volcanogenic sulfide deposits located on the outermost western margin of the miogeocline. The sedimentary exhalative deposits of the Kechika trough formed during a brief geologic episode within a much longer lived time span of are and back-arc rifting and sea-floor hydrothermal mineralization.

Biostratigraphic significance of the Ordovician conodont Eoplacognathus crassus Chen & Zhang, 1993

Recent reports show Eoplacognathus crassus Chen & Zhang, a previously poorly known Ordovician platform conodont species originally described from China, to be a valuable index fossil that is useful for both local and regional correlations. New information bearing on its occurrence in China forms the basis of a reassessment of the range of this species in terms of graptolite biozones. It occurs in the Pacific Province Acrograptus ellesae Biozone and the Atlantic Province Didymo-graptus artus Biozone, and it appears to have the potential to serve as an important guide fossil for a portion of the lowermost British Llanvirnian Series as well as for an interval in the lower part of the global Darri-wilian Stage.

Definition of a global boundary stratotype for the Darriwilian Stage of the Ordovician System

The International Commission on Stratigraphic Nomenclature and the IUGS Executive Committee have recently approved selection of a global stratotype section and point defining the base of the second stage of the Middle Ordovician Series. This stage is named the Darriwilian Stage after the Australian regional stage of the same name, with which it shares identical definition and scope. The base of the Darriwilian Stage is fixed at the base of the Undulograptus austrodentatus Biozone in a section through the Ningkuo Shale exposed at Huangnitang, Changshan Country, Zhejiang Province, southeast China. This boundary is defined by the first appearance datum of the U. austrodentatus within a densely sampled succession of graptolite first occurrences that facilitate precise global correlation of this boundary. conodont species are also present within this section and indicate that the base of the Darriwilian is likely to lie within the lower part of the Microzarkodina parva Biozone of the North Atlantic conodont zonal succession. Correlation of this boundary with well studied successions elsewhere indicates that it is coeval with a level in the mid Whiterockian in North America, and in the lower Fennian Stage of the upper Arenig of Wales. The base of the Darriwilian is about 467.5 +/- 3 Ma.

The lower Ordovician conodont Eoplacognathus crassus Chen & Zhang, 1993

An important species of Lower Ordovician platform conodonts, Eoplacognathus crassus Chen & Zhang, is described and illustrated. Prior to its recognition by Chen & Zhang in 1993, it was referred to other species of Lower Ordovician platform conodonts. It is now known from exceptionally well‐preserved material, which permits detailed study of the ontogenetic morphology. The species has a wide distribution in China, and has also been found in the Baltoscandian area and Poland. Its vertical range is restricted to the upper part of the Amorphognathus variabilis‐Microzarkodina flabellum Conodont Subzone and the lower part of the Asaphus “raniceps” Trilobite Zone of the Kundan Stage (Lower Ordovician) in Sweden. It was recently obtained from the very uppermost part of Undulograptus austrodentatus Graptolite Zone in south China. It is clearly an important species for international stratigraphic correlation. Zhang Jianhua, 1997: The Lower Ordovician conodont Eoplacognathus crassus Chen & Zhang, 1993. GFF, Vol. 119 (Pt. 1, March), pp. 61–65. Stockholm. ISSN 1103–5897.

Conodonts, stratigraphy, and relative sea-level changes of the Tribes Hill Formation (Lower Ordovician, east-central New York)

Tremadocian onlap is recorded by the Tribes Hill Formation. The formation is a lower Lower Ordovician (upper conodont Fauna B Interval(?)-Rossodus manitouensisZone) depositional sequence that unconformably overlies the Upper Cambrian Little Falls Formation.Depositional environments and stratigraphy indicate that the Tribes Hill was deposited on a wave-, not tide-, dominated shelf and that a uniform, “layer-cake” stratigraphy is present. The deepening-shoaling sequence of the Tribes Hill includes the: 1) Sprakers Member (new; peritidal carbonate and overlying tempestite limestone and shale); 2) Van Wie Member (new; subtidal shale and limestone); 3) Wolf Hollow Member (revised; massive carbonates with thrombolitic cap); and 4) Canyon Road Member (new; glauconitic limestone and overlying evaporitic dolostone). The shoaling half-cycle of the Tribes Hill is older than a shoaling event in western Newfoundland, and suggests epeirogenic factors in earliest Ordovician sea-level change in east Laurentia. Conodont and trilobite biofacies track lithofacies, andRossodus manitouensisZone conodonts andBellefontiaBiofacies trilobites appear in the distal, middle Tribes Hill Formation.Twenty-four conodont species are illustrated.Ansella?protoserratanew species,Iapetognathus sprakersinew species,Leukorhinion ambonodesnew genus and species, andLaurentoscandodusnew genus are described.

Upper Devonian conodonts from the Timan-Pechora region, Russia, and correlation with a Frasnian composite standard

A Frasnian composite standard provides a refined scaling for the thirteen-fold conodont zonation first developed in the Montagne Noire, France, but since replicated in North America, Australia, and now the Timan-Pechora region of Russia. Zones 4–13 are identifiable in seven cores from the Ukhta area of southern Timan and a core from the Bagan Field of the Khoreyver Basin. Scaling of the zones through graphic correlation demonstrates the diachronism in different sections of the bases of many conodont species, including those of zonally definingPalmatolepis.This can be effectively shown in a correlation diagram scaled to a composite standard based on graphic correlation, whereas it is obscured by the assumption of synchronism inherent in conventional zonal correlation charts.Newly described species occurring in the Timan-Pechora region and elsewhere areOzarkodina nonaginta, Ancyrognathus amplicavus, Mesotaxis johnsoni, Palmatolepis amplificata, P. mucronata, P. ormistoni, andP. timanensis.A number of other species described earlier from the region also occur outside Russia, mainly in Canada and Australia. Distribution patterns in the composite standard indicate close faunal connections between the Timan-Pechora, western Canada, and Western Australia.

Guadalupian (Middle Permian) Conodonts of Sponge-Bearing Limestones from the Margins of the Delaware Basin, West Texas

The Guadalupian Series (with Roadian, Wordian and Capitanian stages in ascending order) is very suitable for world-wide application as the Middle Permian standard. The conodont faunas of the Delaware Basin and its slope are dominated by pelagic forms represented by ribbed Mesogondolella restricted to the Middle Permian of intraplatform basins and to near-shore slopes of tropical open seas. The first appearance of the serrated Mesogondolella nankingensis (CHING) is important for the definition of the base of the Middle Permian (base of the Guadalupian Series = base of the Roadian Stage). Mesogondolella nankingensis evolved in a phylomorphogenetic cline from the unserrated M. idahoensis (YOUNGQUIST, HAWLEY & MILLER) through transition forms closely related to M. phosphoriensis (YOUNGQUIST, HAWLEY & MILLER). The appearance of serrated Mesogondolella is a very characteristic event in Permian conodont evolution, which can be traced in southwestern and western North America, Arctic Canada and in China. This event is very suitable for the world-wide correlation of the base of the Middle Permian Guadalupian Series. At the upper boundary of the Guadalupian, the serrated Mesogondolella shannoni WARDLAW changed in a phylomorphogenetic cline into the smooth Clarkina altudaensis KOZUR. This cline was also found in intraplatform basins of the eastern Tethys (China). For this reason, the top of the Guadalupian can be well correlated with the Tethyan scale, in which the Late Permian Lopingian Series is defined. The first appearance of Clarkina crofti KOZUR & LUCAS in the uppermost Lamar Limestone and in the uppermost Altuda Formation is very important as it is penecontemporaneously with the first appearance of C. altudaensis. This species is restricted to greater water depths. Two new conodont species, Hindeodus gulloides n. sp., and H. altudaensis n.sp. are described. Additionally, Clarkina crofti KOZUR & LUCAS n.sp. is described to avoid the use of nomina nuda, because the paper of KOZUR & LUCAS (in press) has not yet been printed.

Magnetostratigraphy of a Lower-Middle Triassic boundary section from Chios (Greece)

The Marmarotrapeza Formation at Chios Island (northern Aegean Sea, Greece) is renowned for its Lower-Middle Triassic boundary sections in a marine Tethyan setting. Two sections have been sampled bed by bed to develop a magnetostratigraphic framework for the ammonoid and conodont biostratigraphy. The boundary sections occur within a lower normal (A +)-reverse (B −)-upper normal (C +) polarity sequence. The Lower-Middle Triassic boundary, placed at the first occurrence of the ammonoid genera Aegeiceras ugra Diener, Paracrochordiceras spp., Paradanubites depressus Fantini Sestini and Japonites sp., and close to the first appearance of the conodont species Gondolella timorensis Nogami, occurs in normal polarity zone Chios C +. The overall mean direction of the reversal-bearing characteristic component, whose early acquisition is suggested by a tilt test, is D = 271.2°, I = 33.2° ( α 95 = 11.7°, k = 112.5, N = 3). The inferred paleolatitude of the sampling sites is about 18°N, consistent with either an African or stable European affinity, although the declinations suggest large-scale counter-clockwise rotations with respect to Africa or stable Europe since the Early-Middle Triassic.

Conodont and foraminiferal successions from the Triasic of Bulgaria

The Triassic sediments of Bulgaria refers to two different types: Balkanide and Tethyan. One of them – Balkanide is deposited in situ and occupy the larger part of the territory of the country – the Moesian Platform, Central and Western Balkanides with the Fore-Balkan as well as the outcrops in W – SW Bulagaria. It is characterized by ammonites and other megafossils, with predominance of Alpine-Tethyan species, from the uppermost part of Spathian – lower part of Anisian to parts of Norian. These, often rich in dark coloured clayey components rocks, Pelsonian-Longobardian in age comprise typical conodont fauna from the representatives of genus Pridaella, as well as from Tethyan genera Paragondolella, Kashmirella etc. and species of genus Sephardiella which penetrate from the Sephardic area. During the rest of the Triassic period there were unfavourable environments for conodonts. The foraminifers (U. Smithian-Norian) are represented by especially various Tethyan benthonic species characteristic for this development. The Triassic of the Eastern Balkan, presented in olistolites, as well as this from the Strandza Mt., which is with nappe origin, has typical Tethyan (“Alpine”) development. Except megafossils, during the whole Spathian – Norian interval, composed of much lighter coloured limestones and other sediments, comprise and the conodont species from the genera Neospalhodus, Gladigondolella, Paragondolella etc., typical for the Tethyan Realm. The foraminiferal assemblages are characterized by a lesser diversity of the benthonic species and by the permanent presence and prevalence in some places of the typical Tethyan representatives of Oberhausereliidae and Duostominidae. A biostratigraphic subdivision and correlation of these two types of shallow Triassic in Bulgaria has been made, and conodont and foraminiferal zonal standards have been accepted.

Multielement Conodont Species from the Louisiana Limestone (Upper Devonian) of West-Central Illinois and Northeastern Missouri, U.S.A.

Multielement Conodont Species from the Louisiana Limestone (Upper Devonian) of West-Central Illinois and Northeastern Missouri, U.S.A.

Conodont paleoecology of the Lower Ordovician St. George Group, Port au Port Peninsula, western Newfoundland

The St. George Group in western Newfoundland is nearly 600 m thick and is subdivided into the Watts Bight, Boat Harbour, Catoche, and Aguathuna Formations. The group is a nearly complete Lower Ordovician succession representing about 15–20 m.y. The depositional environment of the St. George Group is represented by three main lithofacies (supratidal, peritidal, and subtidal), expressed as two first-order cycles and five second-order cycles.In the study of St. George Group conodonts, over 70 multielement species are represented in 45,000 conodont specimens from 432 samples of 10 sections. Computer cluster analysis of most of those samples on the basis of similarity of conodont species was used to determine conodont community structure. Both the principal coordinate analysis (PCA) partitioning method and the agglomerative method (UPGMA with Bray-Curtis) were chosen for the statistical analysis. The four lithological formations and five secondary lithological cycles in the St. George Group emerge as distinct entities when the samples are clustered together on the basis of conodont data for analysis of first-order and second-order variations in community composition.Two deeper water, five shallow-water, and five intermediate communities through this time interval are recognized. The majority of conodonts from these communities are of Midcontinent Realm affinities, but some species represent strong North Atlantic Realm influxes during the transgressive periods.

Magnetostratigraphy and biostratigraphy of an Anisian-Ladinian (Middle Triassic) boundary section from Hydra (Greece)

On the island of Hydra, the Anisian/Ladinian boundary is exposed in a 24 m thick section of nodular reddish Han-Bulog Limestone. This paper is focused on the magnetostratigraphy and conodont biostratigraphy of this section. The Anisian/Ladinian boundary is defined by the First Appearance Datum (FAD) of the conodont species Gondolella trammeri Kozur (base of the Nevadites ammonoid zone), and occurs in a normal polarity zone. Microfacies analysis has distinguished a lower and upper lithofacies recording gradual shallowing from pelagic conditions to a platform margin paleoenvironment.

K-Bentonites and Graptolite Biostratigraphy in the Middle Ordovician of New York State and Quebec: A New Chronostratigraphic Model

Published correlations of the extensive set of altered vol- canic ash beds (K-bentonites) present in the upper Middle Ordovician rocks of New York State imply that the lower Climacograptus (Diplacanthograptus) spiniferus Zone, the entire Orthograptus ruedemanni Zone, and the upper Corynoides americanus Zone are coeval. Precise new information on the ranges of graptolite and conodont species and the position of zonal boundaries within key Mohawk Valley sections together with new data on the occurrence of K-bentonites provide the foundation for an alternative, integrated chronostratigraphic model for the Middle Ordovician of the Mohawk Valley and the St. Lawrence Lowland of Quebec. This alternative model rec- onciles the K-bentonite and biostratigraphic correlations, but remains to be independently tested