Biostratigraphic Criteria Research Articles

PALAEONTOLOGICAL CRITERIA FOR THE IDENTIFICATION OF SEDIMENTARY BREAKS IN THE CARBONIFEROUS DEPOSITS OF THE DNIPRO-DONETS DEPRESSION (UKRAINE).

The article is devoted to the theoretical substantiation of the palaeontological methodology of searching and lateral tracing of stratigraphic breaks as potential hydrocarbon traps in the Carboniferous deposits of the Don-Dnipro Trough. Five palaeontologica criteria for the search for stratigraphic breaks are identified and described, namely: ichnological, taphonomic, palaeoecological, palaeopedological, and biostratigraphic. The biostratigraphic criteria have an advantage over the other criteria listed above, as they allow not only to record the presence of a stratigraphic break, but also to estimate its extent (=duration). However, the other criteria listed above allow detecting very short-term breaks (diastems), for which the capabilities of the biostratigraphic method is not sufficient. Palaeontological research aimed at finding stratigraphic breaks in the Carboniferous sequence of the Don-Dnipro Trough should be comprehensive and consist of taphonomic observations of fossils and their assemblages (preservation, lateral and stratigraphic distribution, etc.), palaeoecological observations of the remains of individuals and assemblages of organisms with special attention to organogenic buildups, ichnofacies analysis, study of palaeosoils as products of interaction between the biosphere and other geospheres of the Earth, biostratigraphic studies of macro- and microbiota assemblages with a priority role for microfaunistic groups and palynoflora as they are widespread in these rocks

A new model for Early Paleozoic ichnostratigraphy based on trace fossil assemblages from Brazil

Trace fossils are not generally utilized as biostratigraphic indicators due to their long stratigraphic ranges. Despite the use of intricate behavioral traces in the absence of other indicators, existing models like the Precambrian–Cambrian boundary and Cruziana stratigraphy encounter limitations due to crucial data gaps and regional constraints. To surmount these challenges, in this paper, we critically assess established models and present a new framework for Early Paleozoic strata, drawing on trace fossils from the intracratonic basins of Brazil. Our ichnostratigraphic model is calibrated using ichnological data from the Parnaíba, Paraná, and Amazonas basins, including new data. The analysis focuses on trace fossils in strata that are independently dated using chitinozoan, miospore, and acritarch biozonation. Key ichnotaxa, such as Arthrophycus and Cruziana, are identified as prominent indicators of the Llandovery Stage in Brazil. Occurrences of Heimdallia and Musculopodus in the Tianguá Formation also may be used to suggest a Llandovery interval. Notably, Bifungites, found widely across Brazilian basins, emerges as a potential ichnomarker for the Early to mid-Paleozoic interval, with a global presence throughout Cambrian to Mississippian deposits. While current ichnostratigraphic models lack robust calibration with chronostratigraphic or biostratigraphic data, our new proposed model integrates key ichnotaxa, including Bifungites, Climactichnites, Heimdallia, Oldhamia, and Musculopodus, surpassing those pre-existing zonations based on Cruziana and arthrophycids. These ichnotaxa exhibit unique features and narrow temporal ranges, meeting essential biostratigraphic criteria. Although their spatial distribution is somewhat limited, our new model, which is continually evolving with new data, holds promise for enhancing global stratigraphic correlations, particularly where independent age information is available.

Late Palaeocene to Early Eocene biostratigraphic framework from Upper Indus Basin, Pakistan, Eastern Tethys

This investigation resulted in the biostratigraphic framework of the Upper Palaeocene–Lower Eocene rocks from the Upper Indus Basin, Pakistan, Eastern Tethys. The Patala Formation of the Chinjana Nala, Surghar Range of the Upper Indus Basin, was selected for this purpose. Lithologically, the Patala Formation is composed of shale and limestone interbeds. Three different fossil groups – smaller benthic foraminifera, planktic foraminifera, and calcareous nanno‐planktons – are used to establish a biostratigraphic framework for the Patala Formation. The biozones recognized in this study include: (a) bathyal benthic biozones, BB1 and BB2 of the Late Palaeocene and Early Eocene, respectively; (b) planktic biozones, P4 and P5 of the Late Palaeocene, while E1 and E2 of the Early Eocene; and (c) Calcareous Nanno‐planktons biozones: the NP9, which is further divided into NP9a and NP9b of the Late Palaeocene and Early Eocene, respectively. These biozones have been integrated to identify the Palaeocene–Eocene (P–E) boundary interval by applying widely used biostratigraphic criteria (i.e.,Rhomboaster‐Discoaster[RD]‐assemblage of calcareous nanno‐planktons). In this study, we have considered the lithological interval between ChN/TP‐16 and ChN/TP‐17 as a marker horizon for the P–E boundary interval, which provided a basis for the correlation of locally established biozones with those established Tethys wide, that is, Pak‐DIV to part of Pak‐DVI correlated to SRX‐1 and SRX‐2, which are equivalent to BB1, P4, P5, and NP9a. Similarly, parts of the Pak‐DVI and Pak‐DVII are correlated to SRX‐3, which are equivalent to BB2, E1, E2, and NP9b within the study.

Hyperpycnites within the Devonian-Carboniferous flysch of the Carpatho-Balkanides (Kostadinovica, eastern Serbia)

This study presents new discoveries of vascular plants and the trace fossil Dictyodora liebeana (GEINITZ) from the Devonian–Carboniferous Kučaj-Zvonce flysch of the Carpatho-Balkanides and the implications of this fossil association for its sedimentary setting. The occurrence of the described plant debris in a deep-marine environment indicates the presence of hyperpycnites within the siliciclastic turbidites exposed at the Kostadinovica locality. The sedimentological data and the characteristics of the fossil material support the proposed model in which the sediment was at least partially transported by hyperpycnite currents. Furthermore, based on the assessment to similar palaeofloras from comparable formations, the age of the fossil plants can be determined as Early Carboniferous. This can be used as an additional biostratigraphic criterion given the relative abundance of vascular plants in other localities of the Kučaj-Zvonce flysch described in previous studies. The age and the depositional setting of the succession is further better constrained by the first observation of Dictyodora liebeana (GEINITZ) in the Carpatho-Balkanides of Serbia.

Towards better correlation of the Central Paratethys regional time scale with the standard geological time scale of the Miocene Epoch

AbstractDepositional sequences originating in semi-enclosed basins with endemic biota, partly or completely isolated from the open ocean, frequently do not allow biostratigraphic correlations with the standard geological time scale (GTS). The Miocene stages of the Central Paratethys represent regional chronostratigraphic units that were defined in type sections mostly on the basis of biostratigraphic criteria. The lack of accurate dating makes correlation within and between basins of this area and at global scales difficult. Although new geochronological estimates increasingly constrain the age of stage boundaries in the Paratethys, such estimates can be misleading if they do not account for diachronous boundaries between lithostratigraphic formations and for forward smearing of first appearances of index species (Signor-Lipps effect), and if they are extrapolated to whole basins. Here, we argue that (1) geochronological estimates of stage boundaries need to be based on sections with high completeness and high sediment accumulation rates, and (2) that the boundaries should preferentially correspond to conditions with sufficient marine connectivity between the Paratethys and the open ocean. The differences between the timing of origination of a given species in the source area and timing of its immigration to the Paratethys basins should be minimized during such intervals. Here, we draw attention to the definition of the Central Paratethys regional time scale, its modifications, and its present-day validity. We suggest that the regional time scale should be adjusted so that stage boundaries reflect local and regional geodynamic processes as well as the opening and closing of marine gateways. The role of eustatic sea level changes and geodynamic processes in determining the gateway formation needs to be rigorously evaluated with geochronological data and spatially-explicit biostratigraphic data so that their effects can be disentangled.

The International Stratigraphic Chart: state of the art

The International Stratigraphic Chart of the Phanerozoic is constructed by drawing lower boundaries of stratigraphic units with reference to Global Boundary Stratotype Section and Point. Some systems retain former, usually European, names of stages, whereas new sequences of stages are proposed for others, such as for Cambrian and Ordovician. The boundaries of 64 stages of 100 had been approved by the beginning of 2014. Fifty-three of these boundaries were drawn with regard to biostratigraphic criteria; one ichnological, six magnetostratigraphic, two chemo stratigraphic, one impact, and one climatic criteria. Their type sections are distributed over continents as follows: thirty-nine in Europe, twelve in Asia, nine in North America, and four in Africa. They are located in 19 countries: ten in China, nine in the United Kingdom, nine in Italy, seven in the United States, six in France, five in Spain, three in Czech, two in Morocco, two in Sweden, and one in each of several more countries. Although none is in Russia, candidates are proposed for stages of the Cambrian, Carboniferous, Permian, Triassic, and Jurassic Systems. Type sections for the Sakmarian and Artinskian have already been agreed. With the present work speed, it will take two or three decades to complete the scale construction. The General Stratigraphic Scale of Russia and the International Chart gradually converge. Their similarity at the stage level is 84%. Major disagreements exist only in the Cambrian and Permian Systems.

Maastrichtian carbon cycle changes and planktonic foraminiferal bioevents at Gebel Matulla, west-central Sinai, Egypt

Comparison between the planktonic foraminiferal bioevents from different palaeolatitudes suggests that the biostratigraphic criteria used to identify the Maastrichtian stage boundaries are problematic. A new high-resolution calibration of planktonic foraminiferal biostratigraphic, carbon-isotope, and sequence-stratigraphic criteria has been recorded for the first time from the Maastrichtian Sudr Formation at Gebel Matulla, west-central Sinai. The sedimentary successions allow the identification of prominent long-term carbon isotope events in the Maastrichtian, namely the negative excursion of the Campanian–Maastrichtian Boundary Event (CMBE), the positive excursion of the mid-Maastrichtian Event (MME), and the decline towards the Cretaceous-Palaeogene transition (KPgE). Termination of these well known δ13C events is associated with unconformities, created by eustatic sea-level changes, although the long duration argues for superimposed local tectonic control.

New data on the magnetostratigraphy of the Jurassic–Cretaceous boundary interval, Nordvik Peninsula (northern East Siberia)

The results of this study were used to identify a reversed polarity magnetozone, referred to as M17r, in Berriasian sections of the Nordvik Peninsula (northern East Siberia) within the normal polarity magnetozone (M18n) from previous studies. The new magnetozone embraces the Volgian–Ryazanian boundary (Chetaites chetae/C. sibiricus zonal boundary). It was also found that the former magnetozone M17r at Nordvik, which includes the C. sibiricus/Hectoroceras kochi zonal boundary should correspond to magnetozone M16r. Using magnetostratigraphic and biostratigraphic criteria proves that the Boreal C. sibiricus Zone is correlated with at least the major part of the Tethyan Tirnovella occitanica Zone, and the Boreal H. kochi Zone is correlated with the lower part of the Malbosiceras paramimounum Subzone of the Tethyan Fauriella boissieri Zone.

A revised sedimentary and biostratigraphical architecture for the Type Llandovery area, Central Wales

AbstractThe global standard for the Llandovery Series (early Silurian) in central Wales is re-assessed in the light of detailed geological surveying, biostratigraphical sampling and a rigorous examination of published datasets. A new sedimentary and biostratigraphical architecture is presented. Key graptolite, brachiopod, acritarch and, for the first time, chitinozoan assemblages are critically assessed. Upper Hirnantian to Aeronian strata record events that followed the Late Ordovician glacial maximum and comprise a series of progradational sequences bounded by flooding surfaces, but inferred still to be glacioeustatic in origin. Significant faunal renewals associated with many of the flooding levels underpin their potential for international recognition. Compound non-sequences are a feature of proximal parts of the system where erosion associated with fault footwall uplift was an important process. Extensive slump sheets contribute to further stratal loss and displacement in distal facies. A re-assessment of the Aeronian Stage GSSP reveals shortcomings with the biostratigraphical criteria used in its selection. Telychian portions of the succession display the disrupting effects of intra-Wenlock synsedimentary sliding; hence the relevance of key published fossil assemblages and the criteria used to erect the stage GSSP are undermined. However, the Llandovery area remains one of the best studied early Silurian successions in the world. This, together with regional considerations, supports the retention of the series standard in mid Wales where the contiguous deep-water basinal succession affords internationally cited exposure of richly graptolitic facies for the whole series and, significantly, for the post-sedgwickiiBiozone interval.

Planktonic foraminiferal and calcareous nannofossil biostratigraphy and magnetostratigraphy of the uppermost Campanian and Maastrichtian at Zumaia, northern Spain

The well-exposed and continuous uppermost Cretaceous in the coastal section of Zumaia (northern Spain) crops out as cyclic, deep-water, hemipelagic carbonate-rich sediments of significant geological interest. We present a new, high-resolution calibration of planktonic foraminiferal and calcareous nannofossil biostratigraphic datums, alongside new magnetostratigraphy. Six planktonic foraminiferal zones (Rugoglobigerina rotundata to Pseudoguembelina hariaensis) and nine nannofossil (sub)zones (UC15eTP? to UC20dTP) have been identified, encompassing the uppermost Campanian through uppermost Maastrichtian. Magnetostratigraphic data were obtained from the lower half of the section, where chrons C31r and C31n have been identified; the lithological nature of the upper part of the section provided spurious palaeomagnetic results. According to these data, the Campanian/Maastrichtian (C/M) boundary lies in Chron C31r at Zumaia. Differences between the planktonic foraminiferal and nannofossil datums at Zumaia and those from the Tercis boundary stratotype section (France) suggest that the biostratigraphic criteria used to identify the C/M boundary are problematic. We propose, therefore, two alternative, key biostratigraphic datums with which to determine the stratigraphic position of this boundary: the stratigraphic base occurrence datum (BO) of the planktonic foraminifer Pseudoguembelina palpebra and the top occurrence datum (TO) of the nannofossil Broinsonia parca subsp. constricta. The C31r/C31n magnetic polarity reversal, and the BOs of the planktonic foraminifer Racemiguembelina fructicosa and the nannofossil Lithraphidites quadratus are events that may prove useful in formally defining the lower/upper Maastrichtian boundary.

Lower Vendian microfossil assemblages of East Siberia: Significance for solving regional stratigraphic problems

Both published and original data are used for the analysis of the stratigraphic position and taxonomic characteristics for acanthomorphic microfossils of the Pertatataka type in Lower Vendian sediments of the central and southeastern Siberian Platform and its surrounding structures. Four taxonomically different microbiotas are distinguished in sections of the Nepa-Botuoba, Fore-Patom; Syugdzher, Anabar, Zhuya-Lena, and Berezovo lithotectonic zones: two diverse (Nepa and Ura) and two impoverished (Otradnino and Torga) each including diagnostic Early Vendian taxa. Beyond the Siberian Platform, genera and species characterizing these microbiotas occur in single assemblages and represent diagnostic taxa of the second (Tc-Sr-Vl) and third (Ti-Cg-Mp) zones of the acritarch scale proposed by Australian geologists as a biostratigraphic basis for subdividing the Ediacarian of the Standard stratigraphic scale (SSS). In the Russian General stratigraphic scale, the distribution of Pertatataka acritarchs corresponds to the Lower Vendian. The appearance and mass development of acanthomorphic microorganisms represents a global biological event, which should be taken into consideration as a biostratigraphic criterion for defining the Vendian System. For substantiating age, the following species among diagnostic Lower Vendian forms of East Siberia should be used: Appendisphaera grandis, “Appendisphaera” tabifica, A. tenuis, Ceratosphaeridium glaberosum, Dicrospinosphaera virgata, Multifronsphaeridium pelorium, “Polygonium” cratum, Tanarium conoideum, Variomargosphaeridium litoschum, and Talakania obscura. These taxa are readily recognizable, morphologically stable, and characterized by their wide lateral distribution and relatively narrow stratigraphic range. Their occurrence in the upper part of the Dal’nyaya Taiga Group of the Baikal-Patom region indicates that host sediments should be attributed to the Lower Vendian, not the Upper Riphean as is currently accepted.

High-resolution biostratigraphy of the Tournaisian-Visean (Carboniferous) boundary interval, Mokrá quarry, Czech Republic

This paper summarizes the results of investigations carried out in the Mokrá quarry since 2006 on the biostratigraphy of the Tournaisian-Visean (T-V) boundary interval. It also integrates previous results obtained by J. Kalvoda and collaborators. The main focus is on the boundary itself, but stratigraphically lower and higher levels have been investigated as well to provide a biostratigraphical context spanning the late Tournaisian to early Visean. This stratigraphical level has been the focus of intense international research in the recent years under the auspices of the Subcommission on Carboniferous Stratigraphy (SCCS) in order to find a new criterion and reference section (Global Stratotype Section and Point, GSSP) for the base of the Visean Stage. The appearance of Eoparastaffella simplex from its ancestor E. “ ovalis” and the Pengchong section (Guangxi, southern China) have recently been proposed by the Task Group on the Tournaisian-Visean Boundary and ratified by the SCCS as the new biostratigraphic criterion and GSSP for the base of the Visean, respectively. The sequence exposed in Mokrá is not suitable as a GSSP, notably because it is an active quarry, but it contains most of the foraminifer and conodont guides allowing a high-resolution biostratigraphy of the boundary interval. In addition, it contains abundant trilobites. For these reasons, it constitutes one of the best sections across the T-V boundary in Europe and can serve as a useful additional reference.

The upper Volgian Substage in Northeast Siberia (Nordvik Peninsula) and its Panboreal correlation based on ammonites

Section of the middle and upper Volgian substages and basal Boreal Berriasian in the Cape Urdyuk-Khaya (Nordvik Peninsula) is largely composed of dark argillites substantially enriched in Corg. Characteristic of the section is a continuous succession of ammonite, foraminiferal, ostracode, and dinocyst zones known also in the other Arctic areas. Boundaries of the upper Volgian Substage are recognizable only based on biostratigraphic criteria. The succession of the middle Volgian Taimyrosphinctes excentricus to basal Ryazanian Hectoroceras kochi zones is characterized. The range of the substage is revised. The lower Exoticus Zone, where ammonites characteristic of the Nikitini Zone upper part in the East European platform have been found, is referred to the middle Volgian Substage. Newly found ammonites are figured. Two possible positions of the Jurassic-Cretaceous boundary in the Arctic region, i.e., at the lower and upper boundaries of the Chetae Zone at the top of the upper Volgian Substage, are discussed.

Biocronoestratigrafia da Bacia de Pelotas: estado atual e aplicação na geologia do petróleo

The biostratigraphic studies of the Brazilian sedimentary basins have providing a support for the exploratory research of energetic and mineral resources, in particular at the continental margin. From new discoveries of hydrocarbon accumulations at the Santos and Campos basins, the south portion of the Brazilian continental margin were converted in an important target of the exploration. Therefore, the biostratigraphic refinement is necessary to detect gaps and to promote an increment on the precision of the lateral correlations in the delimitation and spatial analysis of the potential reservoirs. The actual stage of the bio-chronostratigraphic framework of the Pelotas Basin is presented herein, focusing on its application to the reservoir prospection. The main questions and lacunae on the knowledge are also discussed. In terms of biostratigraphy, the Pelotas Basin remains poorly evaluated, despite publication of important works on the biostratigraphy are known since the 1960’s. A comparison of biostratigraphic schemes proposed for the Tertiary section of the basin allows the inference of diverse hiatuses, identified by the absences of biozones. Hiatuses identified in the 87Sr/86Sr curve, suggest their relationship with discontinuities in the deposition. Discrepancies between the proposed schemes can be attributed to the particular resolution of the different groups used, the variations in the biostratigraphic criteria and the sampling interval, influencing the biostratigraphic resolution and therefore its potential as a correlation tool.

Biocronoestratigrafia da Bacia de Pelotas: estado atual e aplicação na geologia do petróleo

The biostratigraphic studies of the Brazilian sedimentary basins have providing a support for the exploratory research of energetic and mineral resources, in particular at the continental margin. From new discoveries of hydrocarbon accumulations at the Santos and Campos basins, the south portion of the Brazilian continental margin were converted in an important target of the exploration. Therefore, the biostratigraphic refinement is necessary to detect gaps and to promote an increment on the precision of the lateral correlations in the delimitation and spatial analysis of the potential reservoirs. The actual stage of the bio-chronostratigraphic framework of the Pelotas Basin is presented herein, focusing on its application to the reservoir prospection. The main questions and lacunae on the knowledge are also discussed. In terms of biostratigraphy, the Pelotas Basin remains poorly evaluated, despite publication of important works on the biostratigraphy are known since the 1960’s. A comparison of biostratigraphic schemes proposed for the Tertiary section of the basin allows the inference of diverse hiatuses, identified by the absences of biozones. Hiatuses identified in the 87 Sr/ 86 Sr curve, suggest their relationship with discontinuities in the deposition. Discrepancies between the proposed schemes can be attributed to the particular resolution of the different groups used, the variations in the biostratigraphic criteria and the sampling interval, influencing the biostratigraphic resolution and therefore its potential as a correlation tool.

Callovian to Lower Cretaceous pelagic carbonates in the West Balkan Mountains (Komshtitsa and Barlya sections): integrated biostratigraphy and microfacies

The Jurassic System in the West Balkan Mountains attracted the attention of the first scholars of geology and stratigraphy in Bulgaria F. Toula and V. Zlatarski more than 100 years ago. The intense field, palaeontological and stratigraphical studies of the Upper Jurassic and Lower Cretaceous pelagic carbonates in the Izdremets Syncline led to the lithostratigraphic subdivision and establishment of all stages from the Callovian to the Hauterivian as a relust of publications of I. Sapunov, I. Nachev, T. Nikolon and G. Mandov in the 60s and 70s of the last century. An integrated micropalaeontological zonation of the Tithonian, Berriasian and Valanginian was elaborated by I. Lakova, K. Stoykova and D. Ivanova. Recently, P. Tchoumatchenco divided the sections at Komshtitsa and Barlya into second- and third-order sequences. The subject of this paper is a synthesis of the existing stratigraphic knowledge of the Callovian to Valanginian pelagic carbonate succession at the sections of Komshtitsa and Barlya in the West Balkan tectonic unit, as well as a correlation with new micropalaeontological and microfacial results. A zonation on calcareous dinocysts for the Upper Jurassic is here presented and correlated to the ammonite zones in the Yavorets, Gintsi and Glozhene Formations. The used biostratigraphical criteria of determination of the stage boundaries (Callovian to Valanginian) are discussed. Six successive microfacies are determined and described: filamentous, Globuligerina-radiolarian, Saccocoma, Globochaete, calpionellid and spicule.

Data on stratotypes of the neopleistocene-holocene regional and local subdivisions in the Caspian region

Considered in the work are data characterizing stratotypes of regional and local stratigraphic subdivisions, which are distinguished in the Neopleistocene-Holocene sedimentary succession of the Caspian region. The succession is composed of sediments deposited by the Caspian transgressions and intervening continental sediments of the late Quaternary. Except for stratotypes of the Tyurkyany Horizon and Gyurgyany Formation, which are established in borehole sections, the other ones represent the well-stratified natural sections accessible for examination of their subdivisions distinguished based on biostratigraphic criteria. Mollusks of the genus Didacna Eichwald and fossil assemblages of large mammals are used to substantiate stratigraphy of marine and terrestrial deposits, respectively.

Conodont biostratigraphy and sedimentary history in the upper Tremadoc at Uuga, Cape Pakri, NW Estonia

The upper Tremadocian boundary beds at Cape Pakri, NW Estonia, consist of an extremely friable glauconitic sandstone, which presents a challenge to detailed biostratigraphy. A combination of sedimentological and biostratigraphical criteria has served to clarify the tempo and mode of the processes that formed the sandstone and explain its relationships to strata immediately below and above it. Apatitic conodont elements, which abound in all these sediments, are particularly well suited to tracing the geological history of the surrounding sediment, since they can be repeatedly included in the sediment, eroded and redeposited, often leaving telltale marks on the elements which are nevertheless identifiable. By separating the indigenous elements from those that had been redeposited, we could place the local upper boundary of the Tremadocian at slightly more than 1 m above the base of the c. 4 m-thick sandy deposit. We showed that the sandstone, where 58-97% of the conodont elements have been redeposited, had been formed during four successive phases of sand deposition. The entire sandstone unit belongs to the Paroistodus proteus Zone. In the sandy and clayey Varanguan beds of the Paltodus deltifer Zone that underlie the sandstone, less than 50% of the conodont elements had been redeposited. The upper part of the section consists of limestone beds belonging to the Oepikodus evae Zone, where the redeposited portion of the conodont elements decreases upwards.

A proposed Global Stratotype Section and Point for the base of the Viséan Stage (Carboniferous): the Pengchong section, Guangxi, South China

The first appearance of Eoparastaffella simplex in the lineage Eoparastaffella ovalis - Eoparastaffella simplex (foraminifers) has been officially approved by the Voting Members of the SCCS in early 2002 as the new biostratigraphic criterion to define the base of the Vis an. The present paper summarizes eight years of research and proposes a new Global Stratotype Section and Point from Guangxi, South China. The boundary is defined at the base of bed 85 of the Pengchong section where the first E. simplex is recorded, following more primitive Eoparastaffella. The conodont Gnathodus homopunctatus, whose cryptic first appearance has beet? used as an empirical tool for identification of the T-V boundary it? Western Europe, enters a decimetre higher in bed 86. Scaliognathus anchoralis europensis and other conodonts considered characteristic of the late Tournaisian occur below these levels.

Correlation of the Askyn River section, Southern Urals, Russia, with the Mid-Carboniferous Boundary GSSP, Bird Spring Formation, Arrow Canyon, Nevada, USA: implications for global paleoceanography

Isotopic data of unaltered low-Mg calcite brachiopods from type Bashkirian strata of the Askyn River section (southern Urals, Russia) are correlated with those from the Mid-Carboniferous Boundary Global Stratotype Section and Point (GSSP) at Arrow Canyon (southern Nevada, USA). Strontium isotope and conodont data of precisely located samples from the sub- to tropical locations spanning the Mid-Carboniferous boundary facilitate the correlation of the two sequences and support the discontinuous nature of the sequence at Askyn. Carbon isotopic trends of the two sites are generally divergent and demonstrate the influence (overprinting) of local oceanographic conditions on global parameters. Oxygen isotopes show a similar divergence for the latest Mississippian time period, with concurrence of values for the earliest Pennsylvanian at the two sites. In both instances, differences-variations in water temperature, currents, salinity and burial rate/amount of organic matter or combinations of these factors may have played roles of influencing water chemistry at the local level. It is possible to achieve global correlations at a finer scale than biozones with precisely located material from stratotype and ancillary sections, especially if a Global stratotype POINT has been identified and selected according to universally accepted biostratigraphic criteria. Consequently it is possible to resolve oceanographic influences at the local level and reconcile them with truly global oceanographic conditions and ultimately define global causes/effects such as cryospheric and tectonic events. Seawater chemistry at Arrow Canyon probably represents Panthalassan global Mid-Carboniferous oceanic conditions, supported by its similarity with data from other locations and modern global oceanographic parameters. Askyn represents Paleotethys and global oceanographic conditions, but in part, overprinted by local influences. The Mid-Carboniferous seems to be a time of expansion of the cryosphere as documented by a positive shift in seawater oxygen isotope composition of about 0.5‰ (SMOW) from the latest Mississippian (−1.2‰) to earliest Pennsylvanian (−0.7‰).