2021 Vol. 32, No. 3
Seven conodont biozones are recognized in the carbonate-dominated shelf-marine Middle Ordovician developed in the intracratonic sedimentary basins (Canning, Amadeus and Georgina) of central and north-western Australia, in the Lachlan and New England orogens of New South Wales, and in the Takaka Terrane of New Zealand. A separate scheme identifying seven conodont biozones spanning the Middle Ordovician has also been developed for siliciclastic sequences deposited in slope-basinal environments in the Lachlan Orogen in New South Wales and Victoria. This biozonal classification consisting of two parallel biostratigraphic schemes for the shelf-marine and deep-marine successions respectively has significantly increased precision in regional and global biostratigraphic correlation and laid a solid foundation for the Middle Ordovician chronostratigraphy of Australia and New Zealand. Recognition of short-ranging pandemic species as the eponymous species of the biozones also supports direct correlation with the classical conodont successions established in Baltoscandia and the North American Midcontinent, and with those of the major Chinese terranes (South and North China and Tarim). The Lachlan Orogen appears to be globally unique in enabling correlation of contemporaneous conodont faunas over a considerable spectrum of water depths and biofacies ranging from carbonate shelves, slopes to deep-water basins.
Ordovician conodonts representing 28 genera and 28 named and three unnamed species were identified from 740 chert and siliceous siltstone spot samples (> 3 000 thin sections) from deep-water turbiditic sequences of the Lachlan Orogen in central and southern New South Wales, Australia. Based on these faunas, a new conodont biozonal scheme has been established to divide the Ordovician turbiditic successions of the Lachlan Orogen into 12 superbiozones and biozones. They are (in ascending order) the Paracordylodus gracilis Superbiozone (including the Prioniodus oepiki Biozone), Periodon flabellum Superbiozone (including the Oepikodus evae Biozone in the lower part), Periodon hankensis Biozone, Periodon aculeatus Superbiozone (including the Histiodella labiosa, Histiodella holodentata, Histiodella kristinae, Pygodus serra and Pygodus anserinus biozones) and the Periodon grandis Biozone. The Pygodus anserinus Biozone is divided further into the lower and upper subbiozones. This new conodont biozonation scheme spanning the upper Tremadocian to middle Katian interval permits precise age-dating and correlation of deep-water siliciclastic rocks that characterize the Ordovician Deep-Sea Realm regionally and internationally.
Conodont elements are calcium phosphate (apatite structure) mineralized remains of the cephalic feeding apparatus of an extinct marine organism. Due to the high affinity of apatite for rare earth elements (REE) and other high field strength elements (HFSE), conodont elements were frequently assumed to be a reliable archive of sea-water composition and changes that had occurred during diagenesis. Likewise, the crystallinity index of bioapatite, i.e., the rate of crystallinity of biologically mediated apatite, should be generally linearly dependent on diagenetic alteration as the greater (and longer) the pressure and temperature to which a crystal is exposed, the greater the resulting crystallinity. In this study, we detected the uptake of HFSE in conodont elements recovered from a single stratigraphic horizon in the Upper Ordovician of Normandy (France). Assuming therefore that all the specimens have undergone an identical diagenetic history, we have assessed whether conodont taxonomy (and morphology) impacts HFSE uptake and crystallinity index. We found that all conodont elements are characterized by a clear diagenetic signature, with minor but significant differences among taxa. These distinctions are evidenced also by the crystallinity index values which show positive correlations with some elements and, accordingly, with diagenesis; however, correlations with the crystallinity index strongly depend on the method adopted for its calculation.
The Ireviken Event was the first Middle Paleozoic event consisting of synchronised faunal, isotopic and facies change to be recognised. An analysis of the conodont faunas throughout the Boree Creek/Borenore Limestone succession in the central western region of the Tasman fold belt of New South Wales (Australia) revealing all five conodont zones that comprise the event is presented. While some zonal boundaries are precise, allowing direct comparison of stratigraphic intervals on other paleo-continents, some can only be approximated. Conodont data from pre-Ireviken Event strata, in contrast, only permit the identification of a broad Telychian chronology. The identification of Wenlock post-Ireviken Event conodont zones is incomplete due to lithological variability, namely the presence of tuffaceous beds near the top of the formation and an unconformity between the Boree Creek and overlying Borenore Limestone. The Boree Creek Formation contains the only example of the Ireviken Event discovered to date from the Tasman fold belt of eastern Gondwanaland.
The age of the Silurian Lower Red Beds in the Upper Yangtze region remains debatable. Twenty-four samples were collected for conodont biostratigraphical studies from the Paiyunan Formation in the Sanbaiti Section, Huaying, Sichuan Province. The conodont fauna from the Paiyunan Formation, together with the graptolites from the underlying Lungmachi Formation, indicates that the Lower Red Beds at Sanbaiti correspond to the lower Telychian. Comparative analysis indicates that most exposures of the Lower Red Beds in the Upper Yangtze region can be assigned, in general, to the Telychian Stage, except for several localities, where the Lower Red Beds can be roughly dated as an interval between the upper Aeronian and lower Telychian.
Focusing on the Shuixiakou Section (Xikou area, Zhen'an County, Shaanxi Province, southeastern Qinling region, China), the Roadian-Wordian conodonts are investigated. More than 2 000 conodont elements including 6 genera and 14 species have been obtained. Based on these materials, the Guadalupian Jinogondolella nankingensis and J. aserrata zones have been recognized. The Roadian-Wordian boundary is tentatively defined by the first occurrence of J. aserrata in the lower part of Unit Ⅲ in the Shuixiakou Formation. The sedimentary succession of Xikou area records similar sea-level changes to those observed in Laibin area (South China). The 40 m-thick bioclastic limestone of Unit Ⅳ in this section can be correlated with the reefs of Bed 114 in Laibin area. A temperature drop indicated by δ18Oapatite values suggests this Wordian interval coincides with a period of glaciation and global regression.
Information on latest early Olenekian (latest Smithian) ammonoids is available apparently from only seven regions of the world, including South Primorye. Latest Smithian evidences on this topic are recorded from the West SMID (abbreviation from the Russian name of the quarry: "Building Materials and Details"), East SMID and Golyj Cape areas in South Primorye. This provides additional information on systematic composition of latest Smithian ammonoid, as well as conodont and brachiopod assemblages from the recently identified Shimanskyites shimanskyi Zone, located between lower Olenekian Anasibirites nevolini Zone and upper Olenekian Tirolites subcassianus Zone. There are many common ammonoid species in the Shimanskyites shimanskyi Zone and the underlying Anasibirites nevolini Zone, e.g., Prosphingitoides sp., Arctoceras septentrionale (Diener), Churkites syskoi Zakharov et Shigeta, Submeekoceras? subhhydaspis (Kiparisova), Prionites markevichi Zakharov et Smyshlyaeva, 'Anasibirites' simanenkoi Zakharov et Smyshlyaeva, Xenoceltites? subvariocostatus Zakharov et Smyshlyaeva, and Mianwaliites zimini Zakharov et Smyshlyaeva. The base of the Shimanskyites shimanskyi Zone, marked by a negative δ13Corg excursion in the Kamenushka-2 Section by our previous study, coincides with the FO (first occurrence) of ammonoids Shimanskyites shimanskyi Zakharov et Smyshlyaeva and Glyptophiceras cf. sinuatum (Waagen) and conodont Hindeodella budurovi Buryi. This zone is characterized additionally by some fossils common for the overlying upper Olenekian Tirolites subcassianus Zone: ammonoids of the genus Kamenushkaites, brachiopods Bittnerihyris margaritovi (Bittner) and Lepismatina sp. and conodont 'Neogondolella' (=?Borinella) jubata Sweet. The latest Smithian ammonoids recorded from the Shimanskyites shimanskyi Zone totally consist of 30 taxa belonging to 11 families (Sageceratidae, Ussuiriidae, Aspenitidae, Paranannitidae, Arctoceratidae, Proptychitidae, ?Galfetitidae, Prionitidae, ?Kashmiritidae, Xenoceltitidae and Palaeophyllitidae). The problems of global correlation of uppermost Smithian strata are also discussed.
The Olenekian-Anisian Boundary (OAB) interval is an important time in Earth history, reflecting the last phase of marine ecosystem recovery in the aftermath of the end-Permian mass extinction. Despite this, the Global Stratotype Section and Point (GSSP) for the base of the Anisian remains undefined. The first appearance of the conodont Chiosella timorensis has been proposed as a potential index for the boundary; however, the discovery of this conodont with ammonoids traditionally considered to be Spathian has generated doubts about its suitability. The taxonomy and relationships of early Anisian conodonts, including species of Chiosella, remain understudied, which leads to difficulties in correlation. New species of Neogondolella (N. gradinarui) and Magnigondolella (M. n. sp. D) have been recognized from the leading GSSP candidate section for the OAB at Deşli Caira, and from an additional OAB section at Guandao. Furthermore, several species previously identified in Canada and the USA can be recognized from these sections, improving correlation between Tethys and North America. One of these species may serve as a suitable alternative proxy for the OAB; for instance, N. curva appears just below the first Anisian ammonoids in Deşli Caira, and just above the first appearance of C. timorensis in both Deşli Caira and Guandao. Continued work on sections other than the candidate sections, and on the taxonomy of species outside of those traditionally proposed as indices, is required.
The Nanpanjiang Basin is a key area for paleontological and biostratigraphical study of the Middle Triassic. Herein we studied Middle Triassic conodonts from a well-exposed section, the Shaiwa Section, which is located at the northwest end of the Nanpanjiang Basin. A total of six Anisian conodont zones are recognized; in ascending order, they are: the Nicoraella germanica Zone, the Nicoraella kockeli Zone, the Paragondolella bulgarica Zone, the Neogondolella constricta Zone, the Neogondolella cornuta Zone, and the Paragondolella excelsa Zone, respectively. The first occurrence of Nicoraella kockeli defines the Bithynian-Pelsonian boundary. The Pelsonian-Illyrian boundary is defined by the first occurrence of Neogondolella constricta. The Anisian-Ladinian boundary cannot be recognized at the Shaiwa Section due to the absence of conodont indicative of the Ladinian. However, the new conodont data indicate that the uppermost strata could be very close to the boundary. The abrasion of conodont surfaces provides evidence for demonstrating reworking at the Shaiwa Section, which makes some conodonts possess a longer stratigraphic range than previously recorded. The variation in relative abundance between blade-shaped conodonts and platform conodonts indicates that segminiplanate elements probably preferred deeper and oxygenated environments whereas a restricted marine environment is more suitable for segminate elements.
The present study of Anisian (Middle Triassic) conodonts from the Kocaeli Peninsula (western Turkey) encompasses over 10 species of the families Gondolellidae and Gladigondolellidae, providing Early and Middle Triassic time constraints, Chiosella timorensis (
Lime mud (i.e., micrite) is a major component of carbonate deposits. Various mechanisms (biotic versus abiotic) have been proposed for the formation of lime mud in Earth's history. However, the detailed role that microbes play in the nucleation and subsequent precipitation of micrites remains to be resolved. Herein we undertook a detailed geobiological characterization of laminated lime mudstone from the Middle Triassic Guanling Formation in Yunnan Province, southwestern China. Morphological features, together with previous geobiological investigations, suggest that the laminated lime mudstones represent the former presence of microbial mats. These lime mudstones consist mainly of calcite, dolomite and quartz, with clay minerals and pyrites as subordinate components. In particular, micro-analysis shows copious nano-globules (65-878 nm) and capsule-shaped nano-rods in laminations. These low-Mg calcite nano-globule aggregates are closely associated with mucilaginous biofilms resembling extracellular polymeric substances (EPS). Nano-sized globules coalesce to form semi-euhedral micrite crystals. We suggest that a decaying hydrolytic destruction of the EPS by microbial communities within microbial mat leads to the precipitation of the nano-globules by enhancing alkalinity in local micro-environment. As an intermediate, these nano-globules further aggregate to form micrite crystals possibly through a dissolution-reprecipitation process.
Based on a study of 49 conodont and 57 g eochemical samples from the Upper Triassic, carbonate-dominated Dengdengqiao Formation, Qinling Basin, China, the Carnian conodonts and carbon isotope records are first reported. Two genera and four species have been identified amongst 87 conodont elements: Mosherella praebudaensis, Mo. longnanensis sp. nov., Mo. sp., and "Misikella" longidentata. The presence of Mo. praebudaensis indicates that the lower part (bed 2) of the formation is attributable to the Julian (lower Carnian) substage. A radiolarian fauna identified in a previous study belongs to the upper Carnian, but the sampling horizon is unclear. The δ13Ccarb curve shows a~1.8‰ negative excursion beginning from upper part of bed 3, but its stratigraphic location is uncertain. The Dengdengqiao Formation is clearly at least partly of Carnian age but could include younger strata. The abundant calcareous algae at the section is probably due to some transport rather than preserved in site. The unusual ecosystem with rare marine organisms may reflect long-term stressful and unfavorable conditions at Dengdengqiao.
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.
During their last phase of evolution, the pectiniform conodont elements manifested an evident trend of simplification and miniaturization. This phase started from the late Norian (Sevatian) in the Late Triassic and the evolutionary process of genus Mockina to Parvigondolella, in particular between Mockina bidentata and Parvigondolella andrusovi, is one of the most significant examples. Parvigondolella has been reported worldwide since it was first described in the early 1970s. However, it has recently been suggested that genus Parvigondolella is an ecostratigraphic morphotype of genus Mockina, and thus a phenotype controlled by the environmental conditions, and not an independent taxon. In the Pizzo Mondello Section (Sicily, Italy), transitional forms between M. bidentata and P. andrusovi have been found at different evolutionary stages. We have investigated the oceanic conditions at the time by using redox-sensitive elements (Mn, Fe, V, Cr, and Ni) and seawater temperatures from biogenetic δ18Ophos to understand the possible environmental influences on the phylogenetic evolution between Mockina and Parvigondolella. T he geochemical and isotope analyses indicate that the redox condition and temperature were stable during the evolution of genus Parvigondolella in Pizzo Mondello, confirming that genus Parvigondolella is a real taxon and not a phenotype. A new conodont species named Parvigondolella ciarapicae n. sp. is described here for the first time.
This study presents the results of the conodont biostratigraphy and microfacies analysis carried out on the pelagic limestones of the Upper Triassic Dovško Section in Slovenia, which represents the eastern part of the Slovenian Basin. The age of the section ranges from the Lacian 1 to the Alaunian 1. The Lacian part of the succession is predominantly characterized by the representatives of the genus Ancyrogondolella. Transitional morphologies towards Alaunian faunas first appear in the Lacian 3 and become common during the Lacian-Alaunian transition. This evolutionary development coincides with a shift in microfacies from a dominantly radiolarian-bearing mudstone-wackestone-packstone to a filament-dominated wackestone-packstone, and the formation of small neptunian dykes, which may reflect environmental perturbations and/or a change in basin geometry. The proliferation of the genera Epigondolella and Mockina is observed in the Alaunian part of the section, though the genus Ancyrogondolella is still present in this interval. Systematic description of the conodont taxa is provided, and seven new species and two new subspecies are established. The new advances will be of great value in further biostratigraphic studies, especially in areas without ammonoid faunas, and in the reconstruction of the paleogeography of the Slovenian Basin.
The Norian represents the longest stage of the Triassic, nevertheless, its precise subdivision is an unresolved matter. Conodonts might be useful in the establishment of an accurate biozonation to avoid common scientific misinterpretations. Understanding the Norian evolutionary trends and morphological changes of the Ancyrogondolella lineage (genus Ancyrogondolella and descendant genera Epigondolella, Orchardella and Mockina) is of key importance in this issue. The forward shifting of the pit and the posterior prolongation of the keel and the carina characterize the main trend that corresponds to the faunal turnover around the Lacian-Alaunian transition. A gradual decrease in overall element width and length can be observed from that time on, which couples with a decrease in the length of the free blade and an increase in the height of the anterior platform denticles. The presence of secondary carinae is characteristic for the mid-Lacian 1 to Alaunian 1, but their development shows no trends and has no taxonomic value. Adult specimens of the Lacian generally have an arched lower profile, whereas in the Alaunian and Sevatian the lower profile is dominantly stepped or straight. The thorough documentation of the Tethyan assemblages is needed for any detailed taxonomic and paleobiogeographic comparisons with other regions.
Almost all aspects of conodont research rely on a sound taxonomy based on comparative analysis. This is founded on hypotheses of homology which ultimately rest on knowledge of the location of elements in the apparatus. Natural assemblages—fossils that preserve the articulated remains of the conodont skeletal apparatus—provide our only direct evidence for element location, but very few are known from the Late Triassic. Here we describe fused clusters (natural assemblages) from the late Norian limestone beds of the Nanshuba Formation in Baoshan, Yunnan Province, southwestern China. Recurrent arrangements and juxtaposition of S and M elements in multiple clusters reveal the composition of the apparatus of Mockina and, probably, Parvigondolella. They indicate that these taxa had a standard 15 elements ozarkodinid apparatus, and provide new insights into the morphology of the elements occupying the P2, M and S locations of the apparatus. The apparatus comprised a single alate (hibbardelliform) S0 element, paired breviform digyrate (grodelliform) S1 and (enantiognathiform) S2 elements, paired bipennate (hindeodelliform) S3 and S4 elements, paired breviform digyrate (cypridodellifrom) M elements, paired, modified-angulate P2 elements (with reduced or lacking 'posterior' process) and segminiplanate (mockiniform and parvigondolelliform) P1 elements. Our results will allow testing of the hypothesis that Mockina, Parvigondolella and Misikella—critical taxa in Late Triassic biostratigraphy—are closely related and possessed morphologically similar elements in homologous locations.