Conodont Assemblages Research Articles

First documentation of early Silurian conodonts from western Thailand and its geological implications

The early Silurian conodonts are firstly described and illustrated from western Thailand. Samples were collected from the Kroeng Kravia Forest Park area for conodont and lithofacies analyses. An upper Telychian Lower Pterospathodus amorphognathoides amorphognathoides Subzone is recognized for the studied succession. Three lithofacies were identified from the carbonate succession, including stromatolite–thrombolite limestone, nodular limestone, and red limestone. Both analyses on lithofacies and conodont assemblages indicate a deeper marine depositional environment. The conodont fauna in the study area is similar to that from Baoshan of Yunnan Province and Langao of Shaanxi Province in West China and resembles that from similar depositional environments in Australia, Laurentia, and peri-Gondwana, suggesting good connections among these regions by ocean currents.

Famennian conodont assemblage in the Compte section (Upper Devonian, Central Pyrenees) and its comparison with Eurasian sequences

A detailed study of the fossil assemblages of Famennian conodonts has been carried out in the Compte section in the Central Pyrenees. The studied section comprises the upper part of the Comabella Formation, the La Mena Fm and the lower part of the Barousse Fm. Fifty samples have been collected from a 11.73 m thick Famennian stratigraphic succession. Forty–seven lower–middle Famennian conodont taxa have been identified, belonging to four genera: Palmatolepis, Polygnathus, Icriodus and Mehlina. The identified conodont assemblages change through the studied section: in the lower part, Palmatolepis and Icriodus taxa are more frequent and in the overlaying strata, Palmatolepis and Polygnathus taxa are dominant. Several conodont taxa have been recorded for the first time in Central Pyrenees zone. The conodont sequence analysis suggests a lower to middle Famennian age (from the termini to mg. marginifera Zones) in the Compte section (Beds 98–120). On the other hand, a comparison of the Pyrenean conodont assemblages with those from other relevant regions has been carried out. The conodont associations from Compte shows certain similarities with those from western and eastern Europe; however, sequences from eastern and central Asian exhibit some differences.

Brachiopods from the Serpukhovian Tonka Formation of Carlin Canyon, Elko, Nevada (USA): Systematics and biostratigraphy

Systematic study of a brachiopod assemblage from the Upper Mississippian Tonka Formation in Carlin Canyon, Elko, Nevada, USA, led to the recognition of 13 species, representing 12 genera and seven orders: ?Antiquatonia sp., Flexaria sp., ?Marginatia sp., Echinoconchus sp. of the Productida, ?Orthotetes sp. of the Orthotetida, Rhipidomella sp., Schizophoria sp. of the Orthida, Cleiothyridina cf. sublamellosaHall, 1858, Composita sulcataWeller, 1914 of the Athyridida, Anthracospirifer shawi shawiGordon, 1975, Anthracospirifer aff. A. shawi of the Spiriferida, Punctospirifer sp. of the Spiriferinida, and Girtyella indianensisGirty, 1909 of the Terebratulida, with the addition of one undetermined linoproductid and one genus and possibly two undetermined species of the Delthyridina. The assemblage shares affinities with upper Chesterian (middle Serpukhovian) Carlinia phillipsi and C. amsdeniana associations from western North American units, though the presence of Composita sulcata makes it also close to uppermost Chesterian faunas (Rhipidomella nevadensis and Composita popsiensis zones, upper Serpukhovian). The recorded faunal association, in terms of composition at the genus-level, is characteristic of brachiopod Unit 16 of Carter (1990a). Unit 16 spans the middle Chesterian (Gnathodus bilineatus conodont Zone) to upper Chesterian (Rachistognathus muricatus conodont Zone), corresponding to the upper Visean–Serpukhovian interval. A monospecific Vogegnathus postcampbelli conodont assemblage from the same locality confirms a late Chesterian (Serpukhovian) age of the fauna.

Pragian conodont biostratigraphy of the western slope of the Southern Urals (Mindigulovo section)

Research subject. Pragian conodonts from the Mindigulovo section on the western slope of the South Urals. Aim. Conodont-based biostratigraphy of the Pragian deposits. Materials and methods. This study is based on the biostratigraphic method: identification of conodonts using conventional techniques, recognition of Pragian conodont associations, zonal scale proposal and correlation. Results. The Pragian beds in the Mindigulovo Section in the latitudinal flow of the Belaya River are characterized using conodonts for the first time. The following conodont-based subdivisions at the rank of beds with fauna are recognized (from bottom to top): Beds with Gondwania irregularis, Latericriodus steinachensis, Beds with Pelekysgnathus serratus, Beds with Gondwania profunda, Pseudogondwania kindlei and Beds with Polygnathus cf. pireneae. Conclusions. The recognized conodont-based units can be directly correlated with the standard zonal scale of the Pragian. The conodont assemblage studied contains taxa characterizing the Gondwania irregularis–Gondwania profunda, Pseudogondwania kindlei–Eognathodus zeravshanicus, Polygnathus pireneae lineage, also known in the Pragian successions of Australia and the South Tien Shan. The co-occurrence of the deep-water family Eognathodidae and the shallow-water Icriodontidae in the Mindigulovo Section enables the correlation of different facies sections.

Upper Triassic (middle Norian) conodont biostratigraphy succession from Qamdo, eastern Tibet

The Late Triassic is a critical period that witnessed major biological and environmental events. The geographic range and taxonomic diversity of conodonts were significantly changed during the Late Triassic, with the geographic range contracting prior to complete extinction of the group near the end of the Triassic. In the present study, we recognize for the first time a continuous middle Norian (Upper Triassic) conodont succession from the Qamdo (Changdu) area, eastern Tibet (Xizang), which was part of the North Qiangtang and Qamdo-Simao Block (NQ-QSB) located in the northeastern Tethys Ocean during the Late Triassic. Four conodont zones are established from the middle Norian (Alaunian) of the Chaiwei section in Qamdo, and in ascending order these are: the Epigondolella spiculata Zone, the Orchardella elongata Zone, the Mockina postera Zone, and the E. serrulata Zone; the neighboring Tuoba section also records these four zones, in addition to the upper lower Norian (upper Lacian) Ancyrogondolella uniformis Zone. All of these zones (except for the M. postera Zone) have been recognized for the first time in eastern Tibet. The Lacian-Alaunian boundary is tentatively placed at the level of sample CW-3 at the Chaiwei section and at the level of sample TBL-36 at the Tuoba section by the first occurrence (FO) of E. spiculata in each section. The position of the Alaunian-Sevatian boundary (ASB) is uncertain since the conodont assemblage from the top of the Bolila Formation at the study sections lacks age-diagnostic elements. The conodonts recovered from the Qamdo area have not only dated the Bolila Formation but also refined the conodont biostratigraphic zonation of the Alaunian in the study area. This allows improved correlation between the faunas of Qamdo and their counterparts elsewhere in Tibet and Europe, although the conodont zonations from these regions display lower precision than those established from North America. The Alaunian conodont faunas at Chaiwei and Tuoba appear to be dominated by juvenile specimens; this often appears to be the case in the Alaunian of the Tethyan Realm, but seems not occur in North America. This may suggest that the conodonts living in these two realms may have inhabited different ecological environments. The faunal turnover around the Lacian-Alaunian transition, with the evolution of Epigondolella, Orchardella, and Mockina from Ancyrogondolella, can be recognized in both study sections, although it is more remarkable in the Tuoba section. Although the lack of previous detailed studies of Norian conodont biostratigraphy from Tibet hampers correlation in this region and beyond, this study demonstrates the possibility of establishing high-resolution conodont biostratigraphic successions from Tibet in the future, since the conodont faunas recognized from Tibet and adjacent areas (e.g., Baoshan) suggest that relatively complete Norian strata exist in these regions. Overall, this study also provides new data to improve our understanding of conodont evolution during the Alaunian, and is significant in providing palaeontological data for studying the palaeogeographic evolution of eastern Tethyan ocean basins in the Late Triassic.

Conodonts paleobiogeographic dynamic of the Pennsylvanian epicontinental sea Itaituba-Piauí, in the northern intracratonic Brazilian basins, Western Gondwana

During the Pennsylvanian, icehouse glacioeustasy and the debasement of Western Gondwana caused widespread transgressive-regressive cycles in the Itaituba-Piauí epicontinental sea located in modern-day South America. This seaway extended from the most distal and western Solimões basin, into the medial Amazonas basin, and at times into the most eastern and restricted Parnaíba basin. These basins contain a rich variety of marine (e.g., invertebrates, conodonts, foraminifers) and continental (plant pollen-spore assemblages) fossils. This paper presents the conodonts retrieved from outcrops and wells in the Carauari (Solimões Basin), Itaituba (Amazonas Basin), and the Piauí (Parnaíba Basin) formations. The conodonts recovered from these formations include Idiognathodus, Neognathodus, Adetognathus, Idiognathoides, Diplognathodus, Declinognathodus, and Hindeodus. Biostratigraphic correlation of this Pennsylvanian conodont assemblage is possible between the three studied basins. The conodont-bearing marine units can identify transgression episodes when the Itaituba-Piauí sea inundated these basins.

First record of the late Famennian conodonts in Qamdo, Tibet and their biostratigraphic implications

Based on the conodonts recovered for the first time and some brachiopods, this study revises the age of the Wuqingna Formation in eastern Tibet to a late Famennian, challenging prior Carboniferous classification based on coral assemblages. In this study, conodonts are described for the first time from the Wuqingna Formation on the Wuqingka Mountain near Toba Town, Qamdo City in eastern Tibet. The conodont assemblage contains 6 species/subspecies (including morphotypes within open nomenclature) that belong to three genera. The conodont species Polygnathus cf. perplexus, Po. homoirregularis, Po. wuqingnaensis n. sp. and Scaphignathus peterseni suggest an age of late Famennian, probably the Palmatolepis gracilis manca Zone to the Pa. gr. expansa Zone, for the lower part of the Wuqingna Formation, which was previously assigned to the Carboniferous based on the rugose coral assemblages.

Microfossils from Middle Triassic beds near Mišji Dol, central Slovenia

Middle Triassic beds exposed along the road between Mišji Dol and Poljane pri Primskovem (Posavje Hills) comprise marlstone, tuff, volcaniclastic sandstone, and thin- to medium-bedded limestone and dolostone. The succession was logged and sampled for conodonts. A relatively rich conodont assemblage was determined, consisting of Budurovignathus gabrielae Kozur, Budurovignathus sp., Cratognathodus kochi (Huckriede), Gladigondolella malayensis Nogami, Gladigondolella tethydis Huckriede, Gladigondolella sp., Neogondolella balkanica Budurov & Stefanov, Neogondolella cf. excentrica Budurov & Stefanov, Neogondolella constricta (Mosher & Clark), Neogondolella cornuta Budurov & Stefanov, Neogondolella sp., Paragondolella excelsa Mosher, Paragondolella liebermani (Kovacs & Kozur), Paragondolella trammeri (Kozur), Paragondolella cf. alpina (Kozur & Mostler), and Paragondolella sp. The assemblage correlates with the upper Anisian and lowermost Ladinian assemblages from the Global Boundary Stratotype Section and Point (GSSP) of the Ladinian at Bagolino in the Southern Alps in northern Italy. Along with conodonts, numerous specimens of benthic foraminifera Nodobacularia? vujisici Urošević & Gaździcki were recovered from the lowermost part of the succession. Previous research on this taxon is critically evaluated.

Lower Devonian conodonts from the Xainza area, central Tibet and the Lower Devonian stage boundaries in China

We report conodont assemblages from the Dardong Formation of the Xainza area, Lhasa Block, yielding several chronostratigraphically significant conodont elements discovered from the Lhasa Block for the first time, including Gondwania profunda, Polygnathus pannonicus, P. kitabicus, P. cf. sokolovi and P. excavatus excavatus. Two conodont zones are identified, namely, the middle Pragian profunda Zone and the lower Emsian excavatus Zone. The Pragian–Emsian boundary is presumably located within the interval between bioclastic limestone beds 4 and 6 with an interbed of siltstones. Although the sparse conodont occurrences in this study precludes more precise chronostratigraphic subdivision, the Xainza area of the Lhasa Block is potentially important for recognition of Lower Devonian stage boundaries in China and deserves further conodont investigations.

Uppermost Devonian–Lower Carboniferous conodonts from the Indert Formation in the Shine Jinst area, South Mongolia

In southwestern Mongolia, conodonts from the Indert Formation at its type locality in Shine Jinst were investigated to improve regional and global correlation of the uppermost Devonian–lowermost Carboniferous. The abundance and diversity of the conodont fauna is quite low in general, whereas representatives of Siphonodella, Protognathodus, Pseudopolygnathus, Polygnathus and Bispathodus have been collected from the Indert-Uul section. Five conodont biointervals, from the Bi. costatus-Pr. kockeli Interregnum (ckI) to the Siphonodella sandbergi Zone, could be recognized from the top Heermorit Member and the lower part of the Shombon Member, while the middle and upper parts of the Shombon Member cannot be zoned based on the conodonts. Absence of index fossils Si. sulcata, Pr. kuehni and Pr. kockeli hampered precise recognition of the Devonian–Carboniferous boundary (DCB) at Indert-Uul, but this transition is well delineated by typical uppermost Famennian and Tournaisian conodont assemblages. The DCB is tentatively placed at the base of the Shombon Member, consistent with the lithological boundary and the resuming of carbonate production during the DCB transitional interval.

Conodonts and the correlation of the Lower Permian Yeso Group, New Mexico, USA

Across much of New Mexico, the Lower Permian Yeso Group is a thick and complex succession of nonmarine fluvial and eolian, evaporitic coastal sabkha and shallow, restricted to openmarine deposits.Yeso strata have long been assigned a Leonardian age because of their lateral equivalence to Leonardian strata of the Bone Spring Formation in the Delaware Basin of southeastern New Mexico-West Texas. However, Yeso strata have also failed to yield many age-diagnostic fossils.We document the first conodont assemblages from Yeso strata, from the lower part of the Los Vallos Formation of the Yeso Group in the Caballo Mountains of south-central New Mexico. These conodonts represent the Neostreptognathodus clinei-N. prayi Zone of middle Kungurian age. The conodonts from the base of the Los Vallos Formation correlate to a position near the base of the Cathedral Mountain Formation of the Leonardian stratotype and indicate that the LosValles Formation is approximately middle Leonardian in age. This correlation also establishes the age of an extensive marine transgression across much of New Mexico.

Moscovian–Kasimovian boundary conodont assemblages from the Kalinovo section, Donets Basin, Ukraine

Moscovian–Kasimovian boundary conodont assemblages from the Kalinovo section, Donets Basin, Ukraine

The middle–late Tournaisian crisis in conodont diversity: a comparison between Northeast Laurussia and Northeast Siberia

The middle–late Tournaisian (Hastarian–Ivorian) transition is marked by isotopic and sedimentological evidence of climatic cooling and glaciations accompanied by a sea level fall and changes in global ocean circulation. At this time, the extinction among conodonts was followed by its gradual recovery in the late Tournaisian–early Viséan. Siphonodellids, representing an important part of conodont assemblages in the early–middle Tournaisian, became extinct. This study aims to compare conodont diversity dynamics in Northeast Laurussia and Northeast Siberia. The materials used range in paleolatitudinal gradients from 20°N (the north of the Urals and Pechora Craton) up to 45°N (Northeast Siberia), and in paleoclimatic gradient from an equatorial to a warm subtropical climate. The middle and late Tournaisian conodont associations of these regions demonstrate a high similarity in taxonomic composition and diversity dynamics, which may suggest that the glaciation and the following decrease in temperature probably was not the direct cause of conodont extinction; instead, the changes in the food web implied by the carbon isotope compositions of conodont elements and host carbonates could have been the main driver of the crisis in conodont diversity

The Pridoli (Silurian) Lithostratigraphy and Biostratigraphy of Gorny Altai

Abstract —The paper presents new data on the upper Silurian litho- and biostratigraphy of the Gorny Altai area. Sediments within this interval store a succession of taxonomically representative middle–upper Ludfordian, lower Pridoli, and Lower Devonian (Lochkovian–Pragian) conodont assemblages. The new fauna constraints made a basis for updated correlations of the local and regional stratigraphic units at the Silurian/Devonian boundary of Gorny Altai with the stages of the International Stratigraphic Chart. The correlation results reveal a mismatch between the boundaries of the local and regional Silurian units and the respective boundaries of stages in the International Stratigraphic Chart.

Upper Eifelian and Givetian (Middle Devonian) conodont sequence at Renanué (Aragonian Pyrenees, Spain): a relevant section for Givetian Chronostratigraphy

ABSTRACT The study of 111 conodont samples has provided the first detailed biostratigraphical subdivision of the Renanué section ranging from the upper Eifelian ensensis Zone into the uppermost Givetian norrisi Zone. The conodont record supports the global threefold subdivision of the Givetian. The lower boundary of the Lower Givetian coincides with the lower boundary of the Givetian and is recognised in the uppermost 5 cm of Bed −8 with the entry of Polygnathus hemiansatus. The lower boundary of the Middle Givetian is identified in Bed 5 with the joint entry of P. varcus and P. rhenanus. Lack of Schmidtognathus precludes identification of the Upper Givetian lower boundary, but the conodont assemblage suggests its position around the lower part of Bed 55. Absence of Ancyrodella and other key taxa impeded precise identification of the Frasnian lower boundary and its earliest zones. Our lowest record of P. webbi seconds its global downwards range extension into the Upper Givetian. The uppermost local record of P. rhenanus might sustain the upward extension of its range into the latifossatus Zone.

Ordovician conodont biostratigraphy, diversity and biogeography in deep-water radiolarian cherts from Kazakhstan

Studies of conodonts from the ribbon-banded radiolarian cherts and siliceous siltstones in the Burubaital Formation in the Buruntau area (SW Balkhash region, Kazakhstan) made it possible to characterize the conodont fauna from deep-water environments in the Ordovician. The conodont assemblages from chert successions at times of high diversity document at least 53 taxa (39 species and 14 taxa identified in open nomenclature) for the entire Ordovician. Conodont biodiversity in the Floian and lower Darriwilian is comparable to the diversity of conodonts inhabiting the neritic zone of epicontinental basins and continental shelves. In the Dapingian and from the middle Darriwilian to the end of the Ordovician, the taxonomic diversity of deep-water conodonts in Kazakhstan is lower and comprises no more than five–six species in total. Stratigraphic distribution of conodonts in the Burubaital Formation sections along with their distribution in the previously studied chert localities in Kazakhstan were used as a base to estimate the succession of conodont zones in deep-water siliceous deposits. The resulting conodont zonation is based on cosmopolitan conodont species and allows broad correlation with deposits of several other paleocontinents.The pelagic habitat of the Early Ordovician oceans is subdivided into two latitudinal biogeographical units - tropical, recorded in Siberia, Laurentia and adjacent terranes, and temperate to cold climate zone, recorded in Baltoscandia, Avalonia and Western Gondwana. The low gradient between the climate of high and low latitudes confirms that the climate in the Early Ordovician was warmer than in the Middle Ordovician.

Smithian (Olenekian, Early Triassic) Conodonts from Ammonoid-Bearing Limestone Blocks at Crittenden Springs, Elko County, Nevada, USA

The ammonoid-bearing limestone blocks at the classic Crittenden Springs ammonoid site belong to the lower part of the Lower Triassic Thaynes Group. These 0.5–1.2 m thick blocks, consisting mainly of bioclastic floatstone and rudstone, contain abundant macro- and micro-fossils such as ammonoids, gastropods, bivalves and scaphopod shells, as well as conodont elements, fish and echinoid remains. Ammonoid and conodont assemblages obtained from three blocks are utilized for biostratigraphical analysis. Twelve informal Smithian ammonoid biostratigraphic intervals from a previous study are condensed into four ammonoid beds, based on the range of age-diagnostic taxa, in ascending order: Meekoceras millardense-M. aff. olivieri beds, Owenites koeneni beds, Anasibirites multiformis bed, and Condensoceras youngi bed. Conodonts recovered from the three blocks consist of 30 species distributed among 15 genera, including one newly described taxon, i.e., Guangxidella minuta Maekawa and Jenks sp. nov. The blocks are divided into two conodont interval zones, i.e., the Novispathodus ex gr. waageni Interval Zone and Nv. pingdingshanensis Interval Zone, based on the first occurrences of their eponymous taxa. Additionally, four conodont range zones, i.e., the Paullella meeki Range Zone, Guangxidella bransoni Range Zone, Scythogondolella milleri Range Zone, and Borinella buurensis Range Zone are recognized, based on the ranges of these four index species. Conodonts within these interval and range zones vary in age from middle Smithian to latest Smithian. The presence of key ammonoid and conodont taxa regarding the Smithian-Spathian boundary (SSB) such as the AW (Anasibirites and Wasatchites) and GXP (Glyptophiceras, Xenoceltites and Pseudosageceras) ammonoid assemblages and the conodonts B. buurensis, Nv. pingdingshanensis and S. milleri demonstrate that the study area is an important reference site for the SSB in the eastern Panthalassa area.

Revision of the Conodont Mockina slovakensis and Its Paleogeographic Implications for the Upper Triassic Intraplatform Basins of the Alps

Mockina slovakensis, thought to have evolved from Epigondolella praeslovakensis, is an important species of the Norian (Upper Triassic), generally considered as the representative of the uppermost Alaunian to upper Sevatian in the Tethys. The previous description of M. slovakensis was incomplete, thus has led to some misidentifications. We thus update the description of M. slovakensis and discuss its comparisons and occurrence based on the new conodont investigations in Dolomia di Forni and the data from previous literatures. The conodont assemblage in the succession of Dolomia di Forni is dominated by M. slovakensis, along with rare M. postera and E. praeslovakensis. We described two morphotypes of M. slovakensis (morphotypes A and B), on the basis of shape of the lateral profile. These two morphotypes can also be observed in the E. praeslovakensis. Moreover, M. slovakensis is usually documented as almost monospecific conodont association in intraplatform basins, thus its paleogeographic implications are also discussed.

A late Permian–Triassic trench‐slope basin in the Central Qiangtang metamorphic belt, Northern Tibet: Stratigraphy, sedimentology, syndepositional deformation and tectonic implications

AbstractRecords of sedimentation and deformation in trench‐slope basins contain valuable tectonic information about the associated oceanic subduction zone. Here, we present a multidisciplinary study on newly discovered late Permian–Triassic sedimentary successions in the >500‐km‐long Central Qiangtang metamorphic belt (CQMB) to better understand the type of basin and the concomitant tectonism. The Mayer Kangri succession contains lithofacies associations of submarine fan siliciclastic rocks, slope‐environment limestone, deep marine chert and minor olistostromes from the forearc basin. The conodont assemblages and sandstone and andesite interlayers yield continuous stratigraphic ages from the Lopingian to middle Norian. The clastic sediments had two provenances, including the epicontinental arc in the North Qiangtang block (NQB) and synchronous volcanism in the accretionary wedge. Moreover, a large suite of the Anisian–early Carnian radiolarian cherts (>30 m thick) was discovered in the Lanling area. Regionally, the CQMB shows evident spatiotemporal variations in late Permian–Triassic sedimentation, with a general depositional trend of southward deepening and getting younger. The three identified subzones include a bathyal setting, a carbonate platform setting and a deep marine setting from north to south. These observations indicate that the late Permian–Triassic sedimentary successions in the CQMB were deposited in a trench‐slope basin environment during the northward subduction of the Longmu Co–Shuanghu Tethys Ocean beneath the NQB. Generally, the CQMB and the concomitant trench‐slope basin is among the well‐preserved ancient analogs characterized by extensional tectonism. The syndepositional horst‐graben‐like structure, forearc basin‐derived olistostromes, abyssal radiolarian cherts and synchronous volcanism provide new implications for the geological evolution of the trench‐slope basin.

Conodont Biostratigraphy of the Lower Carboniferous Deep-Water Facies in the Kokshaal and Djangdjir Ranges, South Tianshan, Kyrgyzstan

On the basis of a detailed study of 39 sections in the Djangdjir and Kokshaal ranges of the South Tianshan (Kyrgyzstan), the conodont zonation of deep-water facies of the Tournaisian, Visean, and Serpukhovian stages was specified. Nine conodont zones, including three new ones, and one unit in the rank of layers with conodonts were distinguished. The deep-water character of studied facies determines the predominant occurrence of cosmopolitan conodonts, which enable the reliable correlation with coeval sections in many regions worldwide. The comparison of conodont assemblages at the specific level indicates that conodont assemblages from the South Tianshan sections are the most similar to those from the Southern Urals and South China.