Chitinozoan Assemblages Research Articles

A new chitinozoan assemblage from the Middle Devonian Los Monos Formation (sub-Andean basin, southern Bolivia) and its biozonal implications for Western Gondwana.

Chitinozoans recovered from one section of the Middle Devonian Los Monos Formation in the TCB X-1001-Tacobo borehole, sub-Andean basin of Bolivia, have been analysed. Eleven from the eighteen processed cutting samples yielded specimens that allowed taxonomic study. Eleven genera and thirty-five chitinozoan species were identified from the Los Monos Formation with four of them recorded for the first time in Western Gondwana. Ancyrochitina biconstricta, Ancyrochitina parisi, Angochitina galarzae and Ramochitina boliviensis are among the most relevant taxa restricted to Western Gondwana that support the affinity with this paleocontinent. One new species, Lagenochitina tacobensis sp. nov. is described, and Ramochitina candelariaensis sp. nov. (n. n.) is formally erected. The chitinozoan assemblage reinforces the late Eifelian-middle Givetian age previously proposed by organic-walled phytoplankton and miospores for this section of the TCB X-1001-Tacobo borehole. A new local chitinozoan biozonation based on the chitinozoan assemblages is proposed and a revision of the current chitinozoan biozonation for Western Gondwana and Bolivia is recommended.

Chitinozoan biostratigraphy of the regional Arenig Series in Wales and correlation with the global Lower–Middle Ordovician series and stages

AbstractThe Arenig Fawr area of North Wales constitutes the type area for the British Lower to Middle Ordovician Arenig Series and is complemented by sections in the Carmarthen and Whitland areas of South Wales. We describe chitinozoan assemblages from both areas in order to aid correlation of the Arenig Series in its type region with the global Ordovician series and stages. Chitinozoans recorded from Arenig Fawr provide permissive rather than conclusive evidence but suggest that the Henllan Ash Member correlates with the upper Floian Stage Slice Fl3 or lower Dapingian Stage Slice Dp1. Better results were obtained from South Wales where six chitinozoan assemblages are distinguished, ranging in age from late Tremadocian to middle Darriwilian (early Llanvirn). Most species are known from South China, Gondwana and/or Baltica where there are controls on ranges. They show that much of the lower Arenig (Moridunian) succession in South Wales correlates with the upper Floian Stage (Fl3). Correlatives of the lower and middle Floian Stage (Fl1, Fl2), if present, must be represented by the Ogof Hên Formation and lowest Carmarthen Formation. Chitinozoan assemblages from the upper Arenig Series (Fennian Stage) are more readily correlated with Gondwanan biozones and indicate correlation of the Fennian Stage with the Dapingian and lower Darriwilian (Dw1) stages. The middle Arenig Whitlandian Stage is constrained in South Wales to an interval from the uppermost Floian Stage to the basal Dapingian Stage, resulting in an inferred increased rate of sediment accumulation.

The age of the Euconochitina symmetrica Zone and implication for Lower Ordovician chitinozoan and graptolite zonations of Laurentia

An Euconochitina symmetrica Zone was defined in the G-locality at Lévis, Quebec, within an interval belonging to Zone A of Raymond that contains Paratetragraptus approximatus. The interval was consequently attributed to the Floian. E. symmetrica was also recognized in Northern Gondwana, and the species was considered an undisputed marker for the base of the Floian. During the past decades, several occurrences of E. symmetrica have been reported from Avalonia, southern China, and even from Northern Gondwana in Tremadocian strata casting doubt on the Floian age of the Zone.Revisions of the graptolites in the G locality and N section at Lévis provides a frame on which the age of the E. symmetrica Zone can be precisely documented. At both localities the E. symmetrica chitinozoan assemblage is older than the base of the Paratetragraptus approximatus graptolite Zone. Therefore, the presence of E. symmetrica can no longer be correlated with the graptolite P. approximatus Zone as it was initially suggested. It rather characterizes the upper Tremadocian Sagenograptus murrayi Zone, its upper part could however reach the Floian.An older assemblage characterized by a Lagenochitina gigas n. sp. assemblage (previously designated Lagenochitina maxima) occurs in strata correlated with the Tremadocian Aorograptus victoriae graptolite Zone.Correlation of the biostratigraphic ranges of the chitinozoan and graptolite faunas in the lower part of the Lévis Formation allowed for a better positioning of the Lower Ordovician Laurentian chitinozoan zones on the Ordovician time scale.

Preliminary palynological study of the Upper Ordovician Pin Formation in northern Indian Himalaya

The Pin Formation of the northern Indian Himalaya may contain a record of the late Katian (Late Ordovician) warming event (the Boda Event). Palynological samples collected from two members of this formation are investigated in order to evaluate the biostratigraphical potential of the different microfossil groups. Acritarchs and chitinozoans are the most abundant microfossils, but fragments of scolecodonts and melanosclerites are also present. Several of the acritarchs from the Pin Formation are long-ranging through the lower Palaeozoic, but other taxa can be compared to Upper Ordovician (Katian) assemblages described from other parts of the world. The chitinozoan assemblages, consisting of 13 species (including those in open nomenclature) belonging to seven genera, are mainly recorded from two layers. The chitinozoan assemblage collected from the sample at 87.3 m in the uppermost part of the Farka Muth Member, and that collected at 184.89 m from the Takche Member, indicate a late Katian age. This age interpretation is in accordance with conodont data from the Takche Member, a positive carbon isotopic peak from the top of a shale unit in the Takche Member, and the initial part of the rapid negative shift of the Paroveja isotopic excursion related to the Boda Event of late Katian age. Further detailed studies with a higher number of samples are needed, that describe better preserved and more diversified palynomorph assemblages, which would help to more precisely refine the Upper Ordovician biostratigraphy in this area.

Llandovery microfossils and microfacies of the Hýskov section, Prague Basin

Abstract The lower Silurian strata of the Prague Basin, as well as in many other regions, are primarily represented by black shales, with limited to no record of benthic life. In this paper, we describe an exceptional late Aeronian volcanic-carbonate succession from the Hýskov locality near Beroun, which contains a diverse and well-preserved fossil assemblage and specific microfacies features. The studied section is mostly represented by well-washed, poorly sorted skeletal grainstones, rudstones and floatstones along with volcaniclastic material. The environment is interpreted as agitated, above storm wave base, and with rapid sedimentation and burial. The collection of acid-resistant microfossils includes abundant scolecodonts, conodonts and chitinozoans, of which only the chitinozoans have previously been studied. The scolecodonts recovered represent at least 14 polychaete genera and 20 species. The fauna bears a great similarity to the early Silurian assemblages previously reported from Baltica, and some environmentally sensitive species allow constraining the assemblage to shallow-shelf settings. The recovered conodonts similarly show close affinities to Baltic faunas, and suggest a Rhuddanian – Aeronian age for the studied section. The chitinozoan assemblage, containing at least eight species, is dominated by Conochitina, and most likely belongs to the C. alargada Biozone.

A new Middle Devonian chitinozoan assemblage from northern Iberia

Chitinozoans were recovered from the Naranco, Huergas and Gustalapiedra formations of northern Spain, which yielded a diverse assemblage including 29 taxa in 9 named genera. The deposits are of early Givetian age, a time when Iberia was isolated from large continents as part of the Armorican Terrane Assemblage. The formations studied here consist of a large clastic unit interrupting carbonate deposition, with large limestone formations positioned above and below the formations analyzed here. This clastic unit includes the Kačák Event, an important global extinction event associated with anoxia in the marine realm. In this paper, the relatively well-preserved chitinozoan assemblage is described and considered from a biogeographical and stratigraphical perspective. The chitinozoan community was deposited in a short space of time and includes various taxa not previously known from the Middle Devonian, though the assemblage as a whole is attributable to the period. Only moderate similarity is seen with assemblages reported from Laurussia and Gondwana, with a slight bias towards the latter. This report adds to our knowledge of chitinozoan paleobiogeography and to other recent studies of Middle Devonian palynology in northern Iberia.

Age constraints of the Hungshihyen Formation (Early to Middle Ordovician) on the western margin of the Yangtze Platform, South China: New insights from chitinozoans

The Hungshihyen Formation represents the Lower to Middle Ordovician near-shore siliciclastic deposits on the western margin of the Yangtze Platform, South China. However, its age is still debated, largely because of insufficient studies. Here we documented the Bursachitina maotaiensis–B. qianbeiensis chitinozoan assemblage from the lower part of the Hungshihyen Formation at Songliang, Qiaojia County, eastern Yunnan Province. This assemblage is remarkably similar to an assemblage that roughly correlates to the middle part of the Corymobograptus deflexus graptolite Biozone in northern Guizhou Province, indicating that the Hungshihyen Formation at Songliang is probably of late Floian age and may extend into the early Dapingian. Additionally, a revision on the chitinozoans previously documented from the strata assigned to the same formation in the Wuding area was made according to the latest classification. The revision allows the recognition of the Euconochitina symmetrica–Eremochitina brevis assemblage, and therefore suggests a late Tremadocian age for this interval based on regional and global chitinozoan biostratigraphic correlations. Considering also its lithologic succession, we argue that the chitinozoan-bearing strata in the Wuding area previously assigned to the Hungshihyen Formation correspond most likely to the uppermost part of the underlying Tangchi Formation or the lowermost part of the Hungshihyen Formation. The base of the Hungshihyen Formation appears therefore to be diachronous in eastern Yunnan Province.

Palynological analysis of Upper Ordovician to Lower Silurian sediments from the Diyarbakir Basin, southeastern Turkey

ABSTRACT This paper reports on a palynological analysis of 41 core and 21 cutting samples from a well drilled through an Upper Ordovician–Lower Silurian sequence, belonging to the Bedinan and Dadas formations, of the Diyarbakir Basin of southeastern Turkey. The samples yield abundant and well-preserved marine palynomorphs (acritarchs, chitinozoans and scolecodonts) although non-marine palynomorphs (spores/cryptospores) are extremely rare or absent. The Upper Ordovician sediments of the Bedinan Formation have low organic content but contain abundant palynomorphs whereas the Lower Silurian sediments of the Dadas Formation have high organic content, dominated by amorphous organic matter, with relatively rare palynomorphs. Three chitinozoan assemblages are identified and attributed a late Katian (merga Biozone), Hirnantian (moussegoudaensis Biozone) and Llandovery (?alargada Biozone) age. Two acritarch assemblages are identified and attributed a Katian–Hirnantian and Llandovery (Aeronian–Telychian) age. The chitinozoan and acritarch age determinations are compatible and suggest that the Bedinan Formation is of Katian–Hirnantian age and is separated by an unconformity from the Dadas Formation that is of Llandovery (Aeronian–Telychian) age. These findings confirm the presence of an unconformity at the Ordovician–Silurian transition in the southeastern Turkey. Palynofacies analysis suggests that the Bedinan Formation accumulated on an offshore shelf that was initially well oxygenated but became increasingly anoxic, whereas the Dadas Formation accumulated in an offshore basin that was anoxic. Palynomorph assemblages recorded in the Bedinan and Dadas formations indicate northern Gondwana affinity.

Darriwilian (Middle Ordovician) chitinozoans from the Qaidam Paleoplate, northwest China

The Qaidam Paleoplate is a microcontinent that is currently part of central Asia. Its position during the Ordovician is uncertain, with paleogeographic reconstructions placing it either near South China or near North China. Ordovician microfossils such as chitinozoans have not previously been reported from the Qaidam Paleoplate. In this paper, a chitinozoan microfauna from the middle part of the Shihuigou Formation in the Dameigou section, South Qilian Mountains, Qinghai Province, northwest China is documented. The assemblage is dated as Darriwilian (Undulograptus austrodentatus and Archiclimacograptus confertus graptolite biozones) on the basis of associated graptolites. The chitinozoan fauna is well-preserved and includes several biostratigraphically and paleogeographically important chitinozoan species, such as Lagenochitina langei, L. pirum, Rhabdochitina magna, R. usitata, Conochitina turgida, C. subcylindrica, C. decipiens, Clavachitina poumoti, Belonechitina nevillensis, B. cf. uniformipunctata and B. chydaea. The assemblage contains a specimen in which the collarette of a specimen of Desmochitina sp. is attached to the aboral pole of a specimen of Lagenochitina sp., possibly indicating that a single organism could produce more than one chitinozoan morphospecies. The Conochitina turgida–C. subcylindrica Biozone is indicated by the recovered chitinozoan assemblage. Biostratigraphically important species from the Qaidam microfauna suggest faunal affinities with Laurentia (North America), eastern Gondwana (Australia) and the peri-Gondwana area (southeast China). The chitinozoan paleogeographic data indicate that the Qaidam region was at low latitude during the Middle Ordovician, and that the area was near South China. The paleogeographic information deduced from chitinozoans is consistent with that obtained from graptolites and paleomagnetic analysis in previous studies.

Chitinozoans from the upper Tremadocian (Lower Ordovician) Watch Hill Formation of the Lake District, northern England

ABSTRACTThe Global Stratotype Section and Point (GSSP) for the Lower Ordovician Floian Stage is defined by the first appearance datum (FAD) of the graptolite Tetragraptus approximatus at Diabasbrottet Quarry, Hunneberg, southern Sweden. Correlation of sections with the Floian GSSP when graptolites are absent, however, must rely on other criteria. Among other fossil groups with potential for biostratigraphical correlation at this level are chitinozoans. Here we describe a chitinozoan assemblage from the Watch Hill Formation in the Skiddaw Group of northern England. The Watch Hill Formation is dated on graptolite evidence as late Tremadocian, but the assemblage contains Euconochitina symmetrica, a species previously considered to indicate the eponymous lowermost Arenig (Floian) chitinozoan biozone in a long-established Gondwanan Ordovician biozonal scheme. The hitherto earliest Floian index species has also been reported recently from Tremadocian successions in South China and Morocco. We here confirm its extended range into the Tremadocian and its continued significance as an index species for the Tremadocian–Floian boundary interval.

Palynology of the Middle Ordovician Hawaz Formation in the Murzuq Basin, south-west Libya

ABSTRACTTwenty-nine core and seven cuttings samples were collected from two boreholes penetrating the Middle Ordovician Hawaz Formation in the Murzuq Basin, south-west Libya. The samples were palynologically analysed in order to determine age and depositional environment. The palynological assemblages contain abundant sphaeromorphs, rare but diverse acritarchs, rare chitinozoans, and relatively abundant cryptospores. A total of 26 acritarch species, five chitinozoan species and 17 cryptospore species have been identified. The acritarch and chitinozoan assemblages provide biostratigraphical age dating and indicate that the Hawaz Formation is Mid Ordovician and most likely mid Darriwilian (Llanvirn) in age. The cryptospore assemblage is typical of those from the Mid Ordovician–earliest Silurian and does not permit further age refinement. Based on palynofacies analysis, the depositional environment of the Hawaz Formation is interpreted as shallowing upward from nearshore marine inner shelf to marginal marine. The cryptospores provide rare evidence for Middle Ordovician terrestrial vegetation at this very early stage in its development.

Stratigraphic evidence for Hirnantian glaciation in the Alborz Mountain Ranges, northeastern Iran

The author examined the high-latitude Hirnantian diamictites of the Ghelli Formation and the early Silurian olive-gray shales of the Niur Formation exposed in the northeastern Alborz Mountains, Iran. These 404m thick glacial deposits can be divided into three progradational-retrogradational cycles, each potentially controlled by the regional advance and retreat of the Hirnantian ice sheet. The glaciated source area was west of the study area, in the Arabian Shield region, where numerous tunnel valleys have been reported. Time calibration was performed based on a high-quality biostratigraphic control, mainly derived from the chitinozoan biozones Tanuchitina fistulosa, Acanthochitina barbata, Armoricochitina nigerica, Ancyrochitina merga, Tanuchitina elongata, Spinachitina oulebsiri, and Spinachitina fragilis. The land-derived miospores present in most chitinozoan assemblages, often abundant, seem associated with global sea-level changes during the Late Ordovician glaciation. The Ghelli Formation's high abundance of terrestrial miospores and low abundance of marine palynomorphs suggests its deposition in a shallow marine environment. Additionally, rhythmic bedded tidalites of claystone and sandstone indicate the growth of early land plants producing cryptospores on adjacent flooded areas. Based on marine palynomorphs (chitinozoans and acritarchs), the northeastern Alborz Mountains glacial deposits were dated as Hirnantian; the Niur Formation was assigned to the earliest Llandovery (Rhuddanian). Glacial deposits and marine palynomorphs suggest the presence of Hirnantian ice caps in the Alborz Mountains, at the margin of the Arabian Plate, and indicate the peripheral extension of the Late Ordovician ice sheet. Several biostrome beds forming pelmatozoan-bryozoan mud-mounds, mainly comprising bryozoans, echinoderms, tentaculites, and subordinate trilobites, were found in the glacial deposits of the Ghelli Formation, suggesting carbonate deposition during the Hirnantian. These carbonate beds are not related to the Boda warming event, which happened over the Gondwana landmass in the Katian interval; the glacial deposits of the Alborz Mountain Ranges are thus not correlated to those of the Gondwana paleocontinent. Climatic amelioration is more likely than local reduction of clastic input to be responsible for the biostrome beds in the Glacial Member of the Ghelli Formation, namely a short-lived episode of global warming during the Hirnantian interval (the Milankovitch cycles). Four new chitinozoan species, namely Armoricochitina persianense n. sp., Tanuchitina alborzensis n. sp., Spinachitina iranense n. sp., and Hyalochitina jajarmensis n. sp., are described and illustrated. Biometric data are also provided for the Iranian S. oulebsiri and A. nigerica.

Late Ordovician (Katian) chitinozoans from northwest Saudi Arabia: Biostratigraphic and paleoenvironmental implications

Investigation of 37 samples from continuously cored intervals of the upper part of the Quwarah Member of the Qasim Formation yielded well-preserved and diverse chitinozoan assemblages. Two biozones previously defined from the North Gondwanan Domain were recognized in the examined cores: the Tanuchitina elongata and Ancyrochitina merga. One new genus, Alhajrichitina, and five new species, Alhajrichitina adamantea, Hyalochitina incomposita, Rhabdochitina curvata, Tanuchitina contracta and Tanuchitina densimura, are described. The vertical distribution of these new taxa form the basis of the Tanuchitina elongata Partial Range Subzone, Hyalochitina incomposita Total Range Subzone, Tanuchitina contracta Partial Range Subzone, and Tanuchitina densimura-Belonechitina aff. robusta Concurrent Range Subzone. Two other assemblages, T. ontariensis and Angochitina cf. curvata are also recognized from the merga Biozone. These new subzones and assemblages improve regional and local stratigraphic correlations, and the recognition of the degree of the Hirnantian glacial erosion at the top of the Quwarah Member. An evolutionary lineage is proposed for the species assigned to Alhajrichitina nov. gen., originating with the Sandbian Lagenochitina dalbyensis, through the Katian Alhajrichitina adamantea and culminating with Rhuddanian species, Alhajrichitina nuayyimensis. Three minor diversity and abundance increases are recognized within the merga–elongata biozone interval. These events could represent minor pulses of sea level rise within a progressive, overall sea level drawdown. For this upper part of the core, a general trend of decreasing diversity is recognized and may indicate an upward shallowing. This trend is compatible with diversity trends from all paleocontinents. It could be speculated that fluctuations in sea level were caused by ice advance and retreat during the initiation of Hirnantian continental glaciation south of the study area.

Palynology, microfacies and biostratigraphy across the Daleje Event (Lower Devonian, lower to upper Emsian): new insights from the offshore facies of the Prague Basin, Czech Republic

The Zlichovian/Dalejan boundary interval (Emsian, Lower Devonian) of the Pekarek Mill section was studied employing biostratigraphy (dacryoconarid tentaculites, conodonts) and palynology (chitinozoans, prasinophytes, scolecodonts) and microfacies analysis in order to shed more light on the timing and characteristics of the Daleje Event. The results of our study stress the great importance of the base of the Nowakia elegans Zone for the substage level division of the Emsian. Onset of the Daleje transgression is linked with higher terrigenous input, and coinciding changes in the chitinozoan assemblages were recorded at this level. The transgression at the base of the N. elegans Zone preceded the main transgression taking place in the N. cancellata Zone; it can be correlated with the Upper Zlichov Event. For the first time, Emsian chitinozoans and a jawed polychaete fauna are described in detail from the Prague Basin and can be correlated with other northern Gondwanan regions. The family-level composition of scolecodont assemblage confirms the dominance of paulinitids in the peri-Gondwanan realm.

Ordovician deposits of the western slope of the Southern Urals and their correlation based on conodonts and chitinozoans

Biostratigraphic subdivision and correlation of Ordovician different-facies sections on the western slope of the Southern Urals are carried out based on conodonts and chitinozoans. Upper Ordovician conodonts are defined in the West Zilair zone, in the carbonate-terrigenous section near Nabiullino Village. They belong to important cosmopolitan taxa which allow distinguishing biostratigraphic units corresponding to the North Atlantic standard conodont scale. Successions of Middle and Upper Ordovician conodont and chitinozoan assemblages are identified in the terrigenous-siliceous sections of the East Zilair zone. Middle Ordovician chitinozoans are found in the Uraltau zone, in the metamorphic rocks of the Belekei Formation of the Suvanyak complex, previously assigned to the Precambrian. Most of the taxa in the conodont and chitinozoan assemblages have a good correlation potential due to their wide geographic range. A positive 513C excursion of 3.3%c was first recorded in the Nabiullino section (West Zilair zone), suggesting the initial phase of the HICE isotopic events in the Southern Urals. The development of shallow-water conodont biofacies at the top of the section suggests a sea level fall in the Late Ordovician.

Late Ordovician (late Katian) cryptospores and chitinozoans from the Mannan-1 borehole, south Tarim Basin, China

Well-preserved cryptospore and chitinozoan assemblages were recovered from the Tierekawati Formation (late Katian, Late Ordovician) of the Mannan-1 borehole, south Tarim basin (Tarim Block), China. The chitinozoan assemblage is low in abundance and diversity (two genera, five species), and its age is restricted to the late Katian (Late Ordovician). The cryptospore assemblage consists of the tetrads (three genera, five species) and dyads (three genera, four species), with a low abundance and diversity. It has similarities to the previous records from the coeval deposits around the world. Comparison of two coeval cryptospore assemblages from two boreholes more than 300km apart within the Tarim Block shows the separate landmasses of the south and north Tarim Block were covered with much the same cryptophyte vegetation. The different elements in the vegetation might be caused by the local palaeogeography and palaeoenvironment.

Sea-level curve for the Middle to early Late Ordovician in the Armorican Massif (western France): Icehouse third-order glacio-eustatic cycles

Abstract This contribution deals with the Middle to early Late Ordovician of the Armorican Massif (western France). The aim is to reconstruct a multi-order eustatic curve from the stratigraphic record. The studied section (Crozon Peninsula area) shows sediments deposited in tidal to storm-dominated shelf environments. A sequence analysis (facies and stacking pattern analyses), combined with a gamma-ray record and a backstripping procedure, was carried out. Chitinozoan assemblages provide the biostratigraphic framework including time calibration. The stratigraphic succession is dominated by the stacking of sequences representing different orders of sea-level change i.e. very high- ( formosa and pissotensis biozones of the Darriwilian. The reconstructed sea-level curve reveals that most of the third-order cycles comprise three fourth-order cycles of assumed 400 kyr duration. This 1.2 myr duration of the Ordovician third-ordersequences suggests that they may be related to long-period obliquity cycles, an orbital forcing characteristic of icehousesequences in the late Cenozoic and the Quaternary. These results imply that the major part of the Middle and early Late Ordovician was characterized by icehouse conditions and third-orderglacio-eustatic cycles. A time calibration of the chitinozoan biozones was developed from the sequential analysis. It suggests that the early Darriwilian biozones (from henryi to calix biozones) have short durations of several 10 to several 100 kyr whereas the pissotensis Biozone has a temporal extent of several myr, extending into the early Sandbian.

Late Ordovician–earliest Silurian chitinozoans from the Qusaiba-1 core hole (North Central Saudi Arabia) and their relation to the Hirnantian glaciation

The continuously cored Qusaiba-1 drilled in North Central Saudi Arabia penetrated successively the Qalibah, Sarah and Qasim formations. Silurian graptolites and chitinozoans from the Qusaiba Member of the Qalibah Formation were previously investigated. The present study focuses on the Upper Ordovician and lowermost Silurian parts of the core hole. Part of the sample set yielded abundant and well-preserved specimens associated with eurypterid remains, scolecodonts, acritarchs and cryptospores. Other samples from glacially derived shaly sediments contain only a few fragmented chitinozoan vesicles of Middle and Late Ordovician species indicating reworking through glacial processes. Four different chitinozoan assemblages are identified. The first recorded chitinozoan assemblage is restricted to the deepest processed sample (core 56). It contains Belonechitina cf. robusta, Hercochitina sp. A, and Spinachitina cf. kourneidaensis, and taxa also represented in the second assemblage, e.g., Fungochitina spinifera and Euconochitina species. This first assemblage, however, lacks some of the diagnostic species of the second one (e.g., Acanthochitina barbata, Tanuchitina cf. elongata) and suggests a slightly older late Katian age. The second recovered chitinozoan assemblage is documented in the upper part of the Qasim Formation (cores 49–56) and in the deeper core samples referred to the lower part of the Sarah Formation (cores 45–47 from the disrupted facies of the Sarah Sandstone Member). It contains abundant and well-preserved Armoricochitina nigerica and Ancyrochitina merga associated with e.g., Euconochitina lepta, Calpichitina lenticularis, A. barbata and Desmochitina typica. In addition to these classical components, new species have been observed. This assemblage occurring in pre-glacial as well as in glacially related strata is assigned to the late Katian–earliest Hirnantian (Ashgill). The overlying productive interval, corresponding to the Baq'a Shale Member, is less productive and sometimes virtually barren of chitinozoans. This interval yields a third assemblage mainly composed of broken specimens of Angochitina cf. curvata, C. lenticularis, Cyathochitina sp., D. typica, F. spinifera, Tanuchitina fistulosa, Euconochitina gr. lepta, and even Siphonochitina formosa. Most of these forms are interpreted as glacially reworked. The youngest assemblage is restricted to three samples (core 27), which are located very close to a Silurian gamma ray peak and above the highest evidence of glacial sediments represented by the Sarah Formation. This forth assemblage contains extremely abundant chitinozoans coexisting with a few graptolite remains and inarticulate brachiopods. This chitinozoan assemblage is dominated by Cyathochitina caputoi, which is associated with Belonechitina pseudarabiensis and subordinate numbers of Ancyrochitina and Euconochitina species. The classical Late Ordovician chitinozoan taxa are no longer present and an earliest Rhuddanian age is proposed.Carbon stable isotope (δ13Cchit.) values have been measured on picked chitinozoan vesicles from the upper part of the Quwarah Member (upper Qasim Formation) and from the basal part of the Qusaiba Member (Qalibah Formation) where they register a shift towards more negative values close to the Gamma ray peak. The timing of the Late Ordovician glaciation and correlation with Hirnantian glacial events recorded in Northern Gondwana regions are briefly discussed based on the recovered chitinozoans.Four new species, i.e., Conochitina rotundata sp. nov., Belonechitina tenuicomata sp. nov., Hercochitina multiansata sp. nov., and Calpichitina bernardae sp. nov. are described, discussed and illustrated. Biometric data are provided for Acanthochitina barbata and for Armoricochitina nigerica.

Early Silurian chitinozoans from the Qusaiba type area, North Central Saudi Arabia

Sixty one core samples from three shallow core holes (Qusaiba-1, Baq'a-3 and Baq'a-4) penetrating the Qalibah Formation (Qusaiba Member) in the North Central Saudi Arabia were investigated. These core slabs corresponding to grey–greenish hemipelagic shale or silty-shale yield well-preserved and very abundant early Silurian chitinozoans. Most of the recorded chitinozoan assemblages are diverse and include several new species occurring with well-known species. An informal early Rhuddanian chitinozoan assemblage dominated by Cyathochitina caputoi is documented in the lowermost part of the Qusaiba Member. The six chitinozoan biozones defined above this basal assemblage range from Aeronian to Telychian. They are considered of regional value for northern Gondwana. From the lowest to the highest they are the Angochitina qusaibaensis (pro parte), Conochitina alargada, Angochitina hemeri, Angochitina macclurei, Tanuchitina obtusa and Euconochitina silurica biozones. The older regional biozones have been previously documented in Saudi Arabia whereas the two youngest ones, the eponymous index species of which were described from the subsurface of the Algerian Sahara, are documented for the first time in the Arabian Peninsula. Four subbiozones, of at least of regional application, are also defined in order to improve the precision of biostratigraphic correlation between Silurian lithostratigraphic units cropping out along the Arabian Shield and their counterparts in the subsurface of Central Saudi Arabia. Thanks to the closely spaced and to the regular sampling, the total range of several highly diagnostic forms as well as the interval of uncertainty between the successive chitinozoan biozones are better constrained. A hiatus with a duration of late Rhuddanian to early Aeronian separates the lowest informal chitinozoan assemblage from the qusaibaensis Biozone. A recent detailed study of the graptolites in the three cored holes provides independent chronostratigraphical control calibrating the previous chitinozoan-based age assignments. The qusaibaensis (pro parte), the alargada, and the hemeri chitinozoan biozones occur with the mid-Aeronian convolutus graptolite Biozone whereas the macclurei chitinozoan Biozone extends through the early Telychian guerichi and turriculatus graptolite biozones. The obtusa and the silurica chitinozoan biozones occur in an interval devoid of usable graptolites. They are referred to the mid–late Telychian as they do not contain typical Sheinwoodian species.Besides the abundant chitinozoans and acritarchs, sporadic occurrences of scolecodonts and of eurypterid cuticle fragments are also noted in the organic residues. The presence of eurypterids reflects a shallowing trend in the sedimentary record, which is consistent with the distribution of the graptolite remains (siculae and/or rhabdosomes). Indeed, graptolites are common throughout the Qusaiba Member, except in the youngest processed samples presaging the shallower environments prevalent in the Sharawra Member. The taphonomy of the chitinozoans (isolated vesicles, chain-like structures, clusters, coprolites) and their environmental context is briefly discussed.Fifteen new species are described and illustrated: Ancyrochitina alhajrii sp. nov., Ancyrochitina camilleae sp. nov., Armoricochitina crassicarinata sp. nov., Armoricochitina gengi sp. nov., Bursachitina baqaensis sp. nov., Conochitina viiuae sp. nov., Cutichitina minivelata sp. nov., Cyathochitina neolatipatagium sp. nov., Fungochitina merrelli sp. nov., Muscochitina olivieri sp. nov., Plectochitina alisawyiahensis sp. nov., Plectochitina alnaimi sp. nov., Plectochitina jaquelineae sp. nov., Plectochitina lucasi sp. nov., and Spinachitina geerti sp. nov.

New data of early Late Ordovician chitinozoans from the Miaopo Formation at Jieling, Yichang, central China

Chitinozoans from the uppermost Darriwilian–lower Sandbian Miaopo Formation at Jieling of western Hubei Province are reported, for the first time, including 30 species of 14 genera from 10 collections which are much more diverse and abundant than previously known. Two chitinozoan assemblages are recognized: the Laufeldochitina cf. striata Assemblage and the Eisenackitina cf. rhenana Assemblage. The L. cf. striata Assemblage is correlative to the upper Hustedograptus teretiusculus graptolite biozone. The base of the E. cf. rhenana Assemblage coincides with the base of the Nemagraptus gracilis graptolite biozone, indicating that E. cf. rhenana has the potential for recognizing the base of Upper Ordovician.