Conodont Faunas Research Articles

Ordovician limestone in Hälsingland, Sweden

Limestone boulders of Early and Middle Ordovician age occur along the Baltic coast of Sweden from c. 59°N to c. 62.5°N, apparently at a considerable distance from any known source rocks on land. We have investigated a limestone block from Lake Kultebo, at 61°N, not far inland. The conodont elements enclosed in the rock are of Mid-Ordovician age and show that the block could not have been transported any considerable distance from the west, as has previously been suggested. The new finds of presumed glacially transported boulders of Early Ordovician age confirm earlier reports of such rocks in the area. The conodont faunas here indicate that the boulders could well have been derived locally, e.g., from the floor of the SW Gulf of Bothnia, the northern part of the Baltic Sea. We conclude that at least as far as 61°N, there are probably larger areas of parautochtonous Lower and Middle Ordovician rocks than was earlier assumed.

A Cordylodus fauna from the SW Gulf of Bothnia, Sweden

A conodont fauna including several species of Cordylodus was retrieved from two glacial siltstone boulders found on the shore of Lilltuppen, a small island immediately off the Swedish coast in the Gulf of Bothnia at c. 61°N, 17°E. The erratics are remnants of a poorly known level in the Swedish stratigraphic succession. They probably derive from a nearby point on the floor of the Baltic Sea and constitute an example of an “eastern facies”, reminiscent of part of the Kallavere Formation in northern Estonia. The conodont fauna closely resembles that of the Maardu Member of the Kallavere Formation, and indicates a position in the Cordylodus lindstromi conodont zone just at the Cambrian–Ordovician boundary.

LATE ORDOVICIAN TO EARLY SILURIAN CONODONT FAUNAS FROM THE KOLYMA TERRANE, OMULEV MOUNTAINS, NORTHEAST RUSSIA, AND THEIR PALEOBIOGEOGRAPHIC AFFINITY

The Late Ordovician and Early Silurian conodont faunas of northeast Russia are described, based on 39 conodont-bearing samples collected from Kanyon, Padun, Tirekhtyakh, Maut, and lower Sandugan Formations at Mirny Creek and Ina River sections, Omulev Mountains. The faunas are represented by a total of 776 identifiable conodont specimens assigned to 35 species representing 25 genera, among which a new species, Periodon mirnyensis, is established. Based on graptolite zones at the same locality and other conodont faunas worldwide, the faunas are assigned to the Caradocian, early Ashgillian, late Ashigillian, early Llandovery, and late Llandovery. The Ordovician faunas belong to outer platform to upper slope facies with a North Atlantic Realm affinity; the Silurian faunas are from slope and basin facies. The conodont faunas are the first to be described from the Kolyma Terrane, which has an enigmatic paleogeographic position during the Early Paleozoic.

The first discovery of Permian conodont fauna from peri-Gondwana cool water facies in Tibet, China

The Angjie Formation and Xiala Formation, present in the Shiquanhe area of Gar County in the western part of Gangdise, Tibet, belong to the Gangdise stratigraphic subregion. Conodonts have been found in the Angjie Formation, and they permit an age determination of Early to Middle Permian for that formation. The age of the Xiala Formation could be late Middle Permian. Whether the Late Permian marine deposits are present in this area still needs to be determined, but it is possible that the lower part of the Xiala Formation overlaps partly the upper part of the Angjie Formation. More importantly, the study has brought about a finding of typical peri-Gondwana cool water facies conodonts, namely, Vjalovognathus sp. nov. x. This is the first report and brief description of a conodont fauna from peri-Gondowana cool water facies in China. It indicates that the Gangdise stratigraphic subregion can be subdivided; the western part belongs to peri-Gondwana cool water facies, and the eastern part belongs to Tethys.

FRASNIAN (UPPER DEVONIAN) CONODONT SUCCESSION AT HORSE SPRING AND CORRELATIVE SECTIONS, CANNING BASIN, WESTERN AUSTRALIA

The Horse Spring conodont succession in the Canning Basin replicates zones 6 through 13 of the thirteen-fold Frasnian zonation. Horse Spring, together with other Canning Basin sections, demonstrates the widespread application of the zonation. Furthermore, the recently formalized three-fold subdivision of Zone 13, which has been recognized in the Montagne Noire, Moroccan Meseta, and northern Ontario, is developed at Horse Spring and other Canning Basin sections.The Canning Basin Frasnian is noteworthy for the high quality of preservation of the conodont faunas, the extremely low CAI values, and the abundance of elements in most collections. The emphasis in this paper is on the taxonomy of Frasnian Palmatolepis. Newly described species are: Palmatolepis beckeri, P. feisti, P. housei, P. klugi, P. nicolli, P. playfordi, P. uyenoi, and Polygnathus kirchgasseri. Complete and partial multielement apparatuses have been reconstructed for Palmatolepis playfordi and P. nicolli.

First record of Hindeodus– Isarcicella population in Lower Triassic of Slovenia

This study documents the Permian–Triassic Boundary in the Žiri area of western Slovenia. A paleontological study of the Lukač section, northwest of Žiri, resulted in the recovery of a variety of microfossils. This report documents the conodont fauna recovered from the section. This is the first report of the Hindeodus– Isarcicella population in Slovenia and it provides important new biostratigraphic data for the definition of the Permian–Triassic Boundary. Hindeodus parvus has been recovered, and its first appearance in the lowermost Werfen Formation indicates the base of the Triassic Period. Based on the conodont taxa H. parvus, Hindeodus typicalis, Hindeodus sp., Isarcicella isarcica, Isarcicella lobata, Isarcicella staeschei, Isarcicella turgida, and Isarcicella sp. A, at least three faunas can be distinguished, and they make possible a worldwide correlation.

Conodont biostratigraphic control on transitional marine to non-marine Permian–Triassic boundary sequences in Yunnan–Guizhou, China

The recovery of conodonts associated with ash beds and magnetostratigraphy in the key Zhongzhai Section, near Langdai, Liuzhi, Guizhou Province, provides precise and definitive control on the position of the Permian–Triassic boundary in the transition from marine to non-marine facies of western Guizhou and eastern Yunnan Provinces of southwestern China. In the Zhongzhai Section the boundary interval consists of a lower limestone, 20 cm thick, that contains fragments of Hindeodus sp. and Clarkina sp. This is overlain by a 50 cm thick black shale bed containing an abundant brachiopod fauna, but only a single conodont fragment. This bed is in turn overlain by a 23 cm thick limestone that contains Clarkina meishanensis, Merrillina ultima, Hindeodus changxingensis, H. praeparvus and H. eurypyge. Directly over this limestone is a 5 cm thick ash bed followed by a 10 cm thick black shale, which is overlain by a second, upper, ash bed that is 3 cm thick. On top of the upper ash bed is a 20 cm thick silty limestone containing an abundant dwarf conodont fauna, dominated by Hindeodus, and containing H. parvus but also including Clarkina tulongensis. The Permian–Triassic boundary is placed at the level of the black shale located between the two ash beds.

Stratigraphic distribution of selected acritarchs in the Ordovician subsurface, Canning Basin, Western Australia

Palynological investigation of 80 core samples from four boreholes, drilled through the Lower to Middle Ordovician marine sections of the central-northeastern Canning Basin, northwestern Australia, reveals diverse acritarch associations including a number of stratigraphically significant species. The stratigraphic succession studied, embracing the Willara Formation and conformably overlying Goldwyer Formation, has been independently dated as early Arenig to Llanvirn by conodont faunas ( Oepikodus communis through Phragmodus- Plectodina zonal interval). Nine morphologically distinctive acritarch species have relatively narrow vertical ranges within the study interval and likely constitute serviceable palynostratigraphic indices for the Ordovician in and possibly beyond the Western Australian study area. Three new species, Comasphaeridium setaricum, Polyancistrodorus kunzeanensis, and Stelomorpha calix, are established; and one new combination, Baltisphaeridium variocavatum (Playford and Martin, 1984), is proposed. Other stratigraphically significant species include Petaloferidium comptum Playford and Martin, 1984 and Peteinosphaeridium sp. cf. P. exornatum Tongiorgi et al., 1995; together with Dorsennidium symmetricum (Lu, 1987) Sarjeant and Stancliffe, 1994, Peteinosphaeridium coronula Yin et al., 1998, and Striatotheca rarirrugulata (Cramer et al., 1974) Eisenack et al., 1976, which are found for the first time in Australia. The vertical distribution, and hence the stratigraphic utility, of each of the above species is documented through the studied sections.

Graptolite–conodont biostratigraphy and biofacies of the Middle Ordovician Cerro Viejo succession, San Juan Precordillera, Argentina

High resolution graptolite–conodont biostratigraphy and biofacies analysis have been carried out for the lower member of the Los Azules Formation exposed in the Cerro Viejo area, San Juan Precordillera, western Argentina. The rock succession is composed of alternating rich fossiliferous argillites and virtually barren volcanic ash beds (K-bentonites) of Darriwilian (Da2) age. Graptolite and conodont collections from the Los Azules and Amarilla creeks sections are studied. Graptolites are the most common fossils in the lower member of the Los Azules Formation and represent the Undulograptus dentatus and Holmograptus lentus zones. A diverse conodont fauna recovered from the uppermost limestones of the underlying San Juan Formation, and conodont elements preserved on bedding plane surfaces in the lower Los Azules Formation, indicate the Lenodus variabilis and Eoplacognathus suecicus zones. Micaceous siltstone with Bergstroemograptus crawfordi (Harris) and abundant biserial graptolites close to the top of the lower member is notable. This bed yielded the first specimens of Polonodus magnum Albanesi. This species precedes the entrance of Pygodus anitae Bergström, which is typical from the upper part of the E. suecicus Zone. Characteristic graptolites of the Diplograptus? decoratus Zone (Da3) or equivalent faunas were not recorded in the studied sections suggesting the presence of a hiatus between the lower and middle members, which may indicate a critical event in the history of the basin. A rich conodont assemblage dominated by planktic–pelagic forms ( Periodon– Paroistodus– Protopanderodus– Drepanoistodus), an abundant shelly fauna, and scarce graptolites are recorded in the upper San Juan Limestone. After drowning of carbonate platform the conodont diversity dramatically dropped becoming graptolites the dominant elements of the faunas in the lower member of the Los Azules Formation. The Periodon– Pygodus biofacies represents a low diversity deep-water conodont community present both in the upper part of the lower member and the middle member. Graptolite faunas represent the isograptid biofacies, including pandemic and Pacific forms of the epipelagic and deep-water biotopes. They are related to a transgressive event that diachronically flooded the Precordilleran carbonate platform during the early Middle Ordovician.

AGE AND GEOCHEMISTRY OF MIDDLE TO LATE CARNIAN BASALTS FROM THE ALAKIRÇAY NAPPE (ANTALYA NAPPES, SW TURKEY): IMPLICATIONS FOR THE EVOLUTION OF THE SOUTHERN BRANCH OF NEOTETHYS

The geochemical features of spilitic basalts and the radiolarian fauna of associated pelagic sediments have been studied from two different sections of the Alakircay Nappe of the Antalya Nappes, SW Turkey. The first section in Cukurkoy is located in the eastern part of the Antalya Gulf and includes thick spilitic basalts, overlain by an alternation of mudstone, marl and pelagic cherty limestone. Radiolarian data from the cherty limestone in this unit reveals a middle Carnian age for this section. The second section in Yaylakuzdere is situated in the western part of the Antalya Gulf. In this section, thick pillow basalts are overlain by a succession of limestone/cherty limestone and shale beds. The age of the limestones interlayered with the pillow basalts was assigned to the late Carnian, whereas the basal part of the overlying cherty limestones was dated as latest Carnian/earliest Norian by conodont and radiolarian faunas. The pillow lavas in the Cukurkoy and Yaylakuzdere regions consist of within-plate type alkaline basalts and display multi-element pattern similar to typical oceanic island basalts (OIB). Low La/Yb, Zr/Y and La/Nb < 1 ratios are also indicative for an OIB-like deep mantle source. These alkaline basalts have not suffered interactions with a subducted slab and/or continental crust due to presence of high HFSE abundance, the lack of depletion in Nb and Ta that are characteristics of subduction and/or crustal contamination processes. Based on this data, it can be concluded that alkaline volcanism in these two regions of the Antalya Nappes have been probably generated by a small OIBtype mantle plume during the middle - late Carnian time interval, in the advanced stages of rifting of the Antalya Nappes successions in the southern branch of Neotethys. This data reveals the generation of a rift basin before middle Carnian for this ocean.

High-resolution Late Silurian correlations between Gotland, Sweden, and the Broken River region, NE Australia: Lithologies, conodonts and isotopes

High-resolution correlations, partly with a precision better than 10 ka, are achieved between late Ludfordian sequences on Gotland, Sweden (on Baltica), and a section (COG) through the Coral Gardens Formation along the Broken River, northeastern Australia (on Gondwana), despite these sections having been on different palaeocontinents facing different oceans. The interval is characterised by rapid, very large faunal, isotopic, and lithologic changes. Lithologies are remarkably similar in the two areas, consisting of, in order from below: marls with thin limestone beds, flaggy limestones, oncoidal crinoidal limestone, oncoidal marls, terrigenous clastics (silty clay, mudstone, sandstone), oolite, and cliff-/gorge-forming limestones. Further, independent correlation dates several of the lithological changes as coeval. The δ 13C excursion in whole rock carbonates is one of the three largest ones known during the Phanerozoic. The increase in δ 13C is very similar in the two areas, from below + 1‰ to c. + 9‰ VPDB though two Gotland samples yielded + 9.71‰ and + 10.54‰ (the corresponding COG interval included fewer carbonate layers than needed to definitely exclude that this difference is due to a lack of suitable rocks for sampling). Compared with the lithologies and the δ 13C curves, the conodont faunas display some divergence, but key taxa permit precise correlations for much of the studied interval. The conodont assemblages change stepwise from very diverse in the Polygnathoides siluricus Zone to a low diversity fauna dominated markedly by a single taxon (Upper Icriodontid Subzone), returning abruptly to a comparatively diverse Ozarkodina snajdri Zone fauna. A method resembling graphic correlation in some respects is used to propose a similarly high-resolution correlation through a longer interval for future testing.

Triassic–Jurassic boundary events inferred from integrated stratigraphy of the Csővár section, Hungary

Processes and causes of biotic and environmental change at the Triassic–Jurassic transition remain controversial, partly because of a scarcity of Triassic–Jurassic boundary sections studied in detail. Continuous marine strata spanning the boundary are exposed at Csővár, Hungary, where new integrated stratigraphic data were obtained from multidisciplinary investigations to help reconstruct the end-Triassic and Early Jurassic events. Boundary strata are predominantly slope to basinal carbonates deposited in a periplatform basin. The position of the system boundary is constrained by radiolarian, foraminiferan, conodont and ammonoid biostratigraphy. Pronounced radiolarian turnover is observed between assemblages assigned to the Late Rhaetian Globolaxtorum tozeri zone and the Early Hettangian Canoptum merum zone. Benthic foraminifera suffered lesser extinction. Successive conodont faunas of the latest Rhaetian Misikella posthersteini and Misikella ultima zones record a marked drop in diversity and abundance but sporadic survivors persist into the earliest Hettangian. The extinction is also recorded in a reduction of biogenic components in carbonates. Decline of benthic and planktic biota is followed by a negative δ 13C carb excursion of up to − 6‰ that is composed of short-term fluctuations revealed by dense sampling. Carbon and oxygen isotope ratios are positively correlated in the lower part of the section and appear to reflect primary variations. Drivers of the stable isotope trends are interpreted as warming in excess of + 10 °C and concomitant episodic, short-term perturbations of the global carbon cycle, possibly due to methane release from gas–hydrate dissociation induced by rapid climatic events. The main biotic and isotopic events occurred within a single sedimentary cycle but sea-level does not appear to have exerted a critical influence on these changes. The Triassic–Jurassic boundary crisis appears a short but not instantaneous event.

Biostratigraphy and event stratigraphy in Iran around the Permian–Triassic Boundary (PTB): Implications for the causes of the PTB biotic crisis

The conodont succession and stratigraphic events around the Permian–Triassic boundary (PTB) have been investigated in detail in the open sea deposits of Iran (Abadeh and Shahreza in central Iran, and Jolfa and Zal in northwestern Iran). This investigation produced a very detailed conodont zonation from the Clarkina nodosa Zone up to the Isarcicella isarcica Zone. All significant events have been accurately located and dated within this zonation, and the duration of most of these conodont zones has been calculated by cross-correlation with continental lake deposits that display obvious Milankovitch cyclicity. The unusually short duration of all conodont zones in the interval from the C. nodosa up to the Hindeodus parvus Zone indicates that there was persistent high ecological stress during this time interval. Most of the conodont zones can be accurately correlated with South China. In the interval from the C. hauschkei Zone to the H. parvus Zone, even correlation with the Arctic is possible. Within three thin stratigraphic intervals, the Changhsingian (Dorashamian) warm water conodont fauna of the C. subcarinata lineage is replaced by a cool water fauna with small H. typicalis, rare Merrillina sp., and cool water Clarkina that have very widely spaced denticles. The uppermost cool water fauna horizon comprises the lower C. zhangi Zone and can be accurately correlated with continental beds by recognition of a short reversed magnetozone below the long uppermost Permian–lowermost Triassic normal magnetozone. In Iran and Transcaucasia, this short reversed zone comprises the upper C. changxingensis– C. deflecta Zone and most of the C. zhangi Zone. Its top lies 50 cm below the top of the Paratirolites Limestone (s.s.) in the Dorasham 2 section, which is at the beginning of the upper quarter of the C. zhangi Zone. In the Germanic Basin, this short palaeomagnetic interval comprises the lower and the basal part of the upper Fulda Formation. On the Russian Platform, the Nedubrovo Formation belongs to this short reversed magnetic interval. In its upper part (corresponding to the top of the lower C. zhangi Zone, see above) there is a fallout of mafic tuffs from the Siberian Trap event that originated about 3000 km away in eruption centres in the Siberian Tungusska Basin. In the Germanic Basin and in Iran, this horizon contains volcanic microsphaerules. Thus, a direct correlation can be made between the immigration of a cool water fauna into the tropical realm and an exceptionally strong interval of explosive activity during the Siberian Trap volcanic episode. These faunal changes are the same as those found at the base of the Boundary Clay, suggesting that a short cooling event at this horizon also was due to intense volcanism. Additional influence by a bolide impact cannot be excluded. Most of the events in the interval from the C. nodosa up to the I. isarcica Zone (upper Changhsingian to middle Gangetian) in the Iranian sections can be also observed in other marine sections (e.g., in Meishan) and even in continental sections of the Germanic Basin. Of particular significance is the fact that, in the investigated Iranian sections, the PTB lies either in red sediments or in light grey sediments (as in Abadeh) that contain an ostracod fauna indicative of highly oxygenated bottom waters. Therefore, anoxia cannot be the reason for the PTB extinction event in this region, even though anoxia does cause locally or regionally elsewhere an overprint on the extinction event.

Ordovician conodonts of the Tarim Region, Xinjiang, China: Occurrence and use as paleoenvironment indicators

A review of the distribution of different Ordovician conodont faunas in eight areas of the Tarim Region shows that these conodont faunas can be classified into the North China and South China types. The North China type is characterized by Aurilobodus leptosomatus, A. aurilobodus, A. simplex, Tangshanodus tanshanensis, Loxodus dissectus, Parasseratognathus paltodiformis, Microcoelodus symmetricus, Belodina compressa, B. confluens, Pseudobelodina dispansa, Yaoxianognathus yaoxianensis, and Taoqupognathus blandus. These were adapted to shallow, warm-water environments. The South China type is represented by the genera Amorphognathus, Baltoniodus, Cahabagnathus, Eoplacognathus, Lenodus, Microzarkodina, Oepikodus, Paroistodus, Paracordylodus, Periodon, Polonodus, and Pygodus, which were adapted to outer shelf, deeper, and colder water environments. Using the general pattern of conodont distribution, it is possible to interpret the various depositional environments and to reconstruct broad changes in palaeogeography of the Tarim Region during Ordovician time. In general, during Tremadocian to early Middle Ordovician time, most of the Tarim Region was a shallow semi-restricted platform that became deeper towards the north and east, with an open platform in Kalping and in the northern part of Taklimakan Desert. A slope and deep basin existed in the current Tianshan Mountains region. The Tarim sea was shallow during the Early Ordovician and became deeper during “Caradocian” (Sandbian and Early Katian) time, to become shallow again during “Ashgillian” (Late Katian) time, with the exception of part of central Taklimakan, which was a land area during “Caradocian” (Sandbian and Early Katian) time.

Upper Devonian-Lower Carboniferous conodonts from Chiang Dao cherts, Northern Thailand

In Northern Thailand, radiolarites (radiolarian cherts) are very common and their study provides an important tool to understand the regional geology and moreover to localise the suture zone(s). Some of these deep and distal oceanic series yield conodonts which provide to obtain precise age datings. The present work is focused on the Upper Devonian and Lower Carboniferous conodonts from the Chiang Dao area (Chiang Mai province). The conodont faunas from these oceanic cherts display juvenile characters which are interpreted to be a result from a constraining environment.

Silurian to Mississippian series of the eastern Catalan Pyrenees (Spain), updated by conodonts, foraminifers and algae

Stratigraphic sections and microfossils samples from the upper part of the “Graptolitic Shales- Orthoceras Limestones” and from the Camprodon Formation lying in the area of Camprodon, eastern Pyrenees, Spain, have been studied. Some beds at the top of the “Graptolitic Shales- Orthoceras Limestones” correspond to the Torres Member of the Rueda Formation, and conodont faunas, indicating a Lochkovian age, are described. The Camprodon Fm. is interpreted to be turbidites deposited in deep sea fans, although slope deposits prevail in the eastern sections. One reworked carbonate clast from the Camprodon Fm. provided a valuable early Ludlow conodont fauna, from the Kockelella crassa Zone, reported for the first time in the Iberian Peninsula. Late Devonian conodonts and late Visean (Asbian-Brigantian) foraminifers and algae were also obtained from reworked limestone clasts, and latest Visean or Serpukhovian foraminifers from the sandstone matrix in the Camprodon Fm. The studied microfossils suggest a late Mississippian age for the Camprodon Fm. instead of the previously assigned late Silurian-Lochkovian age. This age must be considered when discussing the distribution of the Culm Facies in the Pyrenees and the significance of the contact between the Camprodon Fm. and the underlying “Graptolitic Shales”.

A latest Llandovery to latest Ludlow high-resolution biostratigraphy based on the Silurian of Gotland—a summary

A succession of 26 conodont zones and 63 successive subzones and conodont faunas have been identified in the exposed latest Landovery to latest Ludlow strata of Gotland, Sweden. All zones, and several of the subzones and faunas, have been identified elsewhere on Baltica, as well as on other palaeocontinents, indicating that this zonation serves well as the standard zonation for calcareous successions. The average duration of the 24 Wenlock and Ludlow zones was 396±208 ka, using the latest radiometric timescale. However, most zones and subzones formed during the widely recognised Silurian oceanic events correspond to less time per unit—in the order of 30 to 100 ka—and most of those formed during intervening episodes correspond to a few 100 ka. The average duration of the 61 Wenlock and Ludlow zones, subzones, and faunas was only 156±82 ka, i.e., among the highest biostratigraphical resolution available for Phanerozoic epochs. On Gotland the combined known maximum thickness of the strata has increased to more than 750 m.

THE LOWER TRIASSIC SHALLOW MARINE SUCCESSION IN GORSKI KOTAR REGION (EXTERNAL DINARIDES, CROATIA): LITHOFACIES AND CONODONT DATING

The paper aims to present Lower Triassic lithofacies definition and first conodont fauna of Gorski Kotar region, Croatia. The depositional environment is envisaged as shallow marine realm of a passive continental margin. Sedimentary complex differentiates in predominantly carbonate sedimentation that characterises the beginning of deposition with upward increasing trend of terrigeneous influx. Lithofacial units have been defined as oolitic bar facies, lagoonal facies, shoreface-offshore facies, ooid-sandy shoal facies, restricted bay facies and flat-pebble conglomerate facies.The following conodont taxa were collected: Ellisonia sp., Foliella gardenae, Hadrodontina sp., Hindeodus parvus, Hindeodus sp., Pachycladina obliqua, ?Parachirognathus sp., Platyvillosus costatus and Pl. hamadai. The oldest strata yield Hindeodus parvus marking lowermost Triassic. The biostratigraphical data enable recognition of the parvus-isarcicella zones, obliqua Zone and Platyvillosus Subzone. The finds of Hindeodus parvus, Platyvillosus costatus and Pl. hamadai represent their first records in the External Dinarides and enable correlation of the Early Triassic conodont faunas of the Western Tethyan realm.

Correlation of Mississippian (Upper Viséan) foraminiferan, conodont, miospore and ammonoid zonal schemes, and correlation with the Asbian–Brigantian boundary in northwest Ireland

AbstractThe microbiota of the upper Viséan (Asbian–Brigantian) rocks in the Lough Allen Basin in northwest Ireland is analysed. The Middle Mississippian sequence studied extends from the upper part of the Dartry Limestone/Bricklieve Limestone formations of the Tyrone Group to the Carraun Shale Formation of the Leitrim Group. The rocks have been traditionally dated by ammonoid faunas representing the B2a to P2c subzones. The Meenymore Formation (base of the Leitrim Group) also contains conodont faunas of the informal partial‐range Mestognathus bipluti zone. The upper Brigantian Lochriea nodosa Conodont Zone was recognized by previous authors in the middle of the Carraun Shale Formation (Ardvarney Limestone Member), where it coincides with upper Brigantian ammonoids of the Lusitanoceras granosus Subzone (P2a). Foraminifera and algae in the top of the Dartry Limestone Formation are assigned to the upper Cf6γ Foraminifera Subzone (highest Asbian), whereas those in the Meenymore Formation belong to the lower Cf6δ Foraminifera Subzone (lower Brigantian). The Dartry Limestone Formation–Meenymore Formation boundary is thus correlated with the Asbian–Brigantian boundary in northwest Ireland. For the first time, based on new data, a correlation between the ammonoid, miospore, foraminiferan and conodont zonal schemes is demonstrated. The foraminiferans and algae, conodonts and ammonoids are compared with those from other basins in Ireland, northern England, and the German Rhenish Massif. Historically, the Asbian–Brigantian boundary has been correlated with several levels within the P1a Ammonoid Subzone. However, the new integrated biostratigraphical data indicate that the Asbian–Brigantian boundary in northwest Ireland is probably located within the B2a Ammonoid Subzone and the NM Miospore Zone, but the scarcity of ammonoids in the Tyrone Group precludes an accurate placement of that boundary within this subzone. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Conodonts of the Kiviõli Member, Viivikonna Formation (Upper Ordovician) in the Kohtla section, Estonia

Conodont faunas from the kukersites and kukersitic limestones of the Kivioli Member are similar to coeval collections from other sedimentary facies and there are no taxa endemic to this unusual environment. The presence of Amorphognathus tvaerensis and the absence of Pygodus anserinus suggest that the lower part of the Kukruse Stage is referable to the A. tvaerensis conodont Biozone and that the base of the Upper Ordovician lies at or beneath the base of the Kukruse Stage.