Early Llanvirn Research Articles

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.

A systematic revision ofSelenopeltis (Trilobita: Odontopleuridae) with description of new material from the Ordovician Anti Atlas region, Morocco

The name of the spinose odontopleurid trilobiteSelenopeltis Hawle & Corda, 1847, has been given to a characteristic endemic fauna inhabiting the shallow Ordovician seas around the northern margin of Gondwana. First described in detail byJoachim Barrande (1852) from Bohemia, the genus has since been identified from species in Ordovician strata in South Wales, Shropshire, Brittany, the Montagne Noire, Spain, Portugal and ?Iraq. This paper describes new material from the Anti Atlas Region of Morocco. Together with new material from Bohemia and Spain, a general description of the genus is given including details of the hypostoma illustrated for the first time in approximate position beneath the cephalon. Reliable and meaningful criteria for distinguishing the various species assigned to theSelenopeltis buchi group are lacking and there appears to be a gradual series from the earliestS. cf.buchi from the early Llanvirn of South Wales to the CaradocS. buchi from the Welsh Borderland, Bohemia and Morocco.S. macrophthalma (Kloucek, 1916) could well be the forerunner ofS. buchi which gave rise toS. vultuosa Přibyl & Vaněk, 1966 during the Caradoc of Morocco and here this species extends into the Ashgill. In BohemiaS. vultuosa is restricted to this time interval.Languedopeltis Pillet, 1988 (type speciesS. binodosus Dean, 1966) is considered a synonym ofSelenopeltis.

Assignment of the South Chinese Ordovician trilobite Calymene paronai to Neseuretus

Turvey, S.T. & Siveter, D.J., June 2007. Assignment of the South Chinese Ordovician trilobite Calymene paronai to Neseuretus. Alcheringa 31, 173‐183. ISSN 0311-5518. Calymene paronai Pellizzari, 1913 was described on the basis of an almost complete enrolled specimen from the Ordovician (probably the early Llanvirn Yangtzeella poloi Biozone) of southern Shaanxi, China. It represents one of the first Chinese trilobite species to have been established, but has been almost completely ignored by subsequent workers. This species is redescribed and reassigned to the Gondwanan inner shelf indicator calymenid Neseuretus, compared with other South Chinese taxa previously assigned to this genus, and interpreted as a senior synonym of N. concavus Lu, 1975.

Baltica: A mid Ordovician diversity hotspot

A detailed bed-by-bed study of late Early—early Mid Ordovician Eastern Baltic brachiopods has been used to construct an α-diversity curve through the upper Billingen—Kunda regional stages (Arenig–early Llanvirn). Surprisingly the main peak in diversity does not occur until the Volkhov–Kunda boundary, whereas global data indicate a peak in the mid Volkhov. On Baltica especially the orthidines show a time lag compared with the global data. This study is based more than 30 000 specimens collected from argillaceous limestones with interfingering marls at eight different localities in the East Baltic area.

Palynostratigraphy of Ordovician strata, Canning Basin, Western Australia. - Part Two: chitinozoans and biostratigraphy

This second and concluding part of a comprehensive palynological study of the Lower to Middle Ordovician succession of the central-northeastern Canning Basin completes the systematic documentation of the palynomorphs, i.e., chitinozoans, and formulates a palynostratigraphic zonation scheme embracing all three constituent formations of this investigation, viz., the Willara, Goldwyer, and Nita formations. A total of 21 species of chitinozoans (five genera), detailed systematically herein, are identified. Although chitinozoan recovery per sample proved variable, the following species occur fairly persistently in the productive samples: Belonechitina micracantha, Conochitina subcylindrica, C. poumoti, C. langei, Calpichitina windjana, and Rhabdochitina magna. Five, stratigraphically successive acritarch/prasinophyte assemblage zones, ranging in age from early Arenig through late Llanvirn, are proposed as follows (ascending order): Athabascaella rossii Assemblage Zone (corresponding to the lower Willara Formation; and dated as early-mid Arenig); Comasphaeridium setaricum Assemblage Zone (upper Willara and lowermost Goldwyer; late Arenig-earliest Llanvirn); Sacculidium aduncum Assemblage Zone (lower Goldwyer; early Llanvirn); Aremorica-nium solaris Assemblage Zone (middle and lower upper Goldwyer; mid Llanvirn); and Dactylofusa striatogranulata Assemblage Zone (upper Goldwyer and lower Nita; late Llanvirn). Four chitinozoan assemblage zones, stratigraphically coinciding (within the limits of sampling) with the acritarch/prasinophyte zones, comprise (in ascending order): Lagenochitina combazi Assemblage Zone (equivalent to the A. rossii and L. heterorhabda Assemblage Zones); Conochitina langei Assemblage Zone; Conocbitina subcylindrica Assemblage Zone; and Belonecbitina micracantha Assemblage Zone. Chronostratigraphic assignments are based principally on associated conodont and graptolite faunas. Whereas the acritarch/prasinophyte zones bear scant similarities to those established globally elsewhere, the chitinozoan zones show significant affiliations with those known from Laurentia.

The Ordovician of the Condroz Inlier, Belgium: Trilobites from the southeastern margin of Avalonia

During the Early Palaeozoic, Belgium was located in the eastern part of the microcontinent of Avalonia, which moved from high to low latitudes during the course of the Ordovician. In the Belgian Condroz Inlier (“Bande de Sambre-et-Meuse”), Ordovician trilobites have been reported from four formations: the early Llanvirn Huy Formation, the Caradoc Sart-Bernard and Oxhe formations, and the Ashgill Fosses Formation. These assemblages are some of the easternmost occurrences of trilobites in Avalonia, and they include aspects that are particularly interesting from a palaeobiogeographical standpoint. The trilobite faunas of the Huy and Sart-Bernard formations are revised in detail, while the others are discussed more briefly, having been redescribed in recent years. The Huy Formation belongs to a biofacies characteristic of the outer shelf/upper slope, and its faunas are typically Avalonian, almost identical to those recorded from the Skiddaw Group of northern England, and from the Ebbe and Remscheid anticlines in the Rhenish Massif, Germany. Pricyclopyge binodosa, which is inferred to be mesopelagic, is common to all these areas, and also occurs in Bohemia and Armorica. Placoparia cambriensis has a remarkably wide distribution in the early Llanvirn, and has been recorded from a range of biofacies across Avalonia, Armorica, Morocco and Bohemia. It is suggested that this species may have been epipelagic. Re-examination of the trilobites from the Sart-Bernard Formation has confirmed that all are conspecific with, or compare closely with Bohemian taxa. The trilobite assemblages of the Oxhe Formation are typical eastern Avalonian faunas, while the Ashgill Fosses Formation assemblage has much in common with those of other parts of Armorica, as well as with Baltica and Bohemia, attesting to the increasing proximity of Avalonia, Baltica and the Prague Basin during the latest Ordovician.

Provenance analysis and tectonic setting of the Ordovician clastic deposits in the southern Puna Basin, NW Argentina

AbstractProvenance studies on Early to Middle Ordovician clastic formations of the southern Puna basin in north‐western Argentina indicate that the sedimentary detritus is generally composed of reworked crustal material. Tremadoc quartz‐rich turbidites (Tolar Chico Formation, mean composition Qt89 F7 L4) are followed by volcaniclastic rocks and greywackes (Tolillar Formation, mean Qt33 F42 L25). These are in turn overlain by volcaniclastic deposits (mean Qt24 F30 L46) of the Diablo Formation (late Arenig–early Llanvirn) that are intercalated by lava flows. All units were deformed in the Oclóyic Orogeny during the Middle and Late Ordovician. Sandstones of the Tolar Chico Formation are characterized by Th/Sc ratios > 1, La/Sc ratios ≈ 10, whereas associated fine‐grained wackes show slightly lower values for both ratios. LREE (light rare earth elements) enrichment of the arenites is ≈ 50× chondrite, Eu/Eu* values are between 0·72 and 0·92, and flat HREE (heavy rare earth elements) patterns indicate a derivation from mostly felsic rocks of typical upper crustal composition. The εNd(t = sed) values scatter around −11 to −9. The calculated Nd‐TDM residence ages vary between 1·8 and 2·0 Ga indicating contribution by a Palaeoproterozoic crustal component. The Th/Sc and La/Sc ratios of the Tolillar Formation are lower than those of the Tolar Chico Formation. Normalized REE (rare earth elements) patterns display a similar shape to PAAS (post‐Archaean average Australian shale) but with higher abundances of HREEs. Eu/Eu* values range between 0·44 and 1·17, where the higher values reflect the abundance of plagioclase and feldspar‐bearing volcanic lithoclasts. Average εNd(t = sed) values are less negative at −5·1, and Nd‐TDM are lower at 1·6 Ga. This is consistent with characteristics of regional rocks of upper continental crust composition, which most probably represent the sources of the studied detritus. The rocks of the Diablo Formation have the lowest Th/Sc and La/Sc ratios, lower LREE abundances than the average continental crust and are slightly enriched in HREEs. Eu/Eu* values are between 0·63 and 1·17. The Nd isotopes (εNd(t = sed) = −3 to −1; TDM = 1·2 Ga) indicate that one source component was less fractionated than both the underlying Early Ordovician and the overlying Middle Ordovician units. Synsedimentary vulcanites in the Diablo Formation show the same isotopic composition. Our data indicate that the sedimentary detritus is generally composed of reworked crustal material, but that the Diablo Formation appears to contain ≈ 80% of a less fractionated component, derived from a contemporaneous continental volcanic arc. There are no data indicating an exotic detrital source or the accretion of an exotic block at this part of the Gondwana margin during the Ordovician.

MIDDLE ORDOVICIAN LITHISTID SPONGES FROM THE BACHU-KALPIN AREA, XINJIANG, NORTHWESTERN CHINA

Moderately diverse Middle Ordovician sponge faunas of Darriwilian (late Arenig to early Llanvirn) age have been discovered in outcrops in the Bachu-Kalpin area of the Tarim platform of Xinjiang, China. These are the first reported occurrences of early Paleozoic sponges from Xinjiang, China. These sponges occur in the Yijianfang and Dawangou Formations, which are of nearly the same age, but crop out in different areas of the platform margin. Fossil sponges discovered to date are the anthaspidellid lithistid sponges Archaeoscyphia minganensis (Billings, 1859); Hudsonospongia cyclostoma Raymond and Okulitch, 1940; Calycocoelia profunda sichuanensis Deng, 1990; Calycocoelia sp.; Pseudopalmatohindia sp.; Aulocopium sp.; Annulospongia tarimensis n. gen. and sp.; Rhopalocoelia kalpinensis n. sp.; Rhopalocoelia bachuensis n. sp.; and Zittelella xinjiangensis n. sp. They are preserved in reefal limestones and are associated with Calathium, cyanobacteria, and bryozoans, like in many North American assemblages.

Middle Ordovician lithistid sponges from the Bachu-Kalpin area, Xinjiang, northwestern China

Moderately diverse Middle Ordovician sponge faunas of Darriwilian (late Arenig to early Llanvirn) age have been discovered in outcrops in the Bachu-Kalpin area of the Tarim platform of Xinjiang, China. These are the first reported occurrences of early Paleozoic sponges from Xinjiang, China. These sponges occur in the Yijianfang and Dawangou Formations, which are of nearly the same age, but crop out in different areas of the platform margin. Fossil sponges discovered to date are the anthaspidellid lithistid sponges Archaeoscyphia minganensis (Billings, 1859); Hudsonospongia cyclostoma Raymond and Okulitch, 1940; Calycocoelia profunda sichuanensis Deng, 1990; Calycocoelia sp.; Pseudopalmatohindia sp.; Aulocopium sp.; Annulospongia tarimensis n. gen. and sp.; Rhopalocoelia kalpinensis n. sp.; Rhopalocoelia bachuensis n. sp.; and Zittelella xinjiangensis n. sp. They are preserved in reefal limestones and are associated with Calathium, cyanobacteria, and bryozoans, like in many North American assemblages.

Diversification patterns in the clitambonitoid brachiopods of the Ordovician of Baltoscandia

Two intervals of clitambonitoid diversification followed by major extinctions have been recorded in the Ordovician rocks of Baltoscandia, one during the Arenig and a second in the mid Caradoc. The Arenig radiation was characterized by high origination and extinction rates of both genera and species associated with the development of carbonate environments across the region. In addition the migration of numerous stocks of clitambonitoids out of Baltica to a number of other palaeocontinents occurred during this diversity peak during the Arenig, together with the spread of the majority of genera into a range of more local environments. A marked extinction in the Early Llanvirn coincided with shifts in sedimentation patterns whereas the diversity hike in the Mid Caradoc reflects the diversification of clitambonitoid species in both inner and outer shelf environments. The later Caradoc extinction coincided with an extensive eustatic regression event and the major restructuring of the ecosystem and brachiopod fauna. The final extinction of Baltic clitambonitoids in the late Ashgill was gradual and probably reflected an increasing dependence on more restricted niches.

Ordovician acritarchs of China and their utility for global palaeobiogeography

Abstract Since the 1970s, acritarch workers have recognized two distinct geographic acritarch assemblages in the Ordovician. The first assemblage occurs in the late Tremadoc in low latitude areas. This assemblage, recently redefined by Volkova [1997], has been attributed to warm-water environments. A second “Mediterranean” or “peri-Gondwanan” province, attributed to high latitudes in the southern hemisphere, can easily be recognized in late Tremadoc to Arenig acritarch assemblages. This second palaeogeographic “province”, defined by Li [1989] is distributed around the border of Gondwana in a zone reaching from Argentina through northern Africa and peri-Gondwana up to Iran, Pakistan and southern China. In the present work we propose an initial simplified, tentative model of the latitudinal distribution of selected early to middle Ordovician acritarchs. Both “provinces” are plotted on the recent palaeogeographical reconstruction of the early Ordovician of Li and Powell [2001]. It appears that the first “province” is limited to low and intermediate latitudes, i.e., to warmer water environments. However, the generally adopted interpretation that the so called “Mediterranean” or “peri-Gondwanan” geographical assemblage is principally controlled by palaeolatitudes and is considered to be typically “cold-water” has to be revised, because the distribution of this “province” appears related more to the continental arrangement along the Gondwana border than to latitudes. This distribution shows some similarities with recent investigations in Silurian acritarch palaeogeography [Le Hérissé and Gourvennec, 1995] that provides evidence that the global distribution of Silurian acritarchs is under the interdependence of continental arrangement, latitudinal position, environmental conditions and oceanic currents, and that it is not simply latitudinally controlled as previous interpretations have suggested. The Yangtze Plaform of southern China presents elements of both early to middle Ordovician “provinces”, i.e., from both the “warm-water” and the “peri-Gondwanan” geographic assemblages. The South China Plate is therefore one of the areas that shows typically mixed assemblages. Although it remains difficult to define clearly a “Baltic” province, it is important to note that between the latest Tremadoc and the early Llanvirn a clear distinction of the acritarch assemblages between peri-Gondwana and Baltica is possible.

Chitinozoa and Nd isotope stratigraphy of the Ordovician rocks in the Ebbe Anticline, NW Germany

Abstract Strongly tectonized Ordovician rocks appear in the Ebbe Anticline (Rheinisches Schiefergebirge), West Germany. These fine-grained detrital rocks of the Herscheider Schichten are divided into the Plettenberger Bänderschiefer. Unterer (Kiesberter) Tonschiefer, (Rahlenberger) Grauwackenschiefer, and the Oberer (Solinger) Tonschiefer. The scope of this investigation was to improve the dating of the entire Ordovician succession. but especially the Oberer (Solinger) Tonschiefer. We used chitinozoans. Palaeozoic microfossils of high biostratigraphic value, and Nd isotopes, which previously have been used for correlation and terrane affinity analysis. Chitinozoan preservation is poor, but some taxa could be confidentially identified to the species level. The ɛNd(t) values obtained from the Ordovician succession range from -8.0 to -9.2. Joint evaluation of chitinozoan and Nd isotope data together with previously known age-ranges suggest the following ages for the Herscheider Schichten: Plettenberger Bänderschiefer (early Abereiddian, earliest Llanvirn), Unterer (Kiesberter) Tonschiefer (early to mid Abereiddian, early Llanvirn). (Rahlenberger) Grauwackenschiefer (Aurelucian, earliest Caradoc), and Oberer (Solinger) Tonschiefer (late Caradoc). The Ebbe ɛNd(t) values are most readily compared with ɛNd(t) values from Avalonia. and we therefore support the inclusion of the Ordovician rocks of the Ebbe Anticline in that palaeocontinent.

Quantitative evaluation of microplankton palaeobiogeography in the Ordovician–Early Silurian of the northern Trans European Suture Zone: implications for the timing of the Avalonia–Baltica collision

Quantitative analysis of assemblage similarity among chitinozoan and acritarch associations recovered from various sedimentary sequences across the Trans European Suture Zone (TESZ; southern Baltic Sea and northern Germany region), permits evaluation of changes in microplankton palaeobiogeography during the Ordovician in the study area. The present data confirm strong palaeobiogeographic differences between the lower Ordovician of the Rügen area, and the coeval domains of the East European Platform (EEP), corroborating the idea that the subsurface of Rügen should be considered palaeogeographically as the eastern extension of Avalonia. Cluster analysis of chitinozoan assemblages from numerous wells in the Rügen area, and one well from the southern margin of the EEP indicates that chitinozoan bioprovincialism reached its maximum during the Llanvirn; during this period, the Rügen microplankton communities were clearly Gondwanan in character. Calculations using the coefficient of similarity support the conclusion of a high similarity between Llanvirn acritarch assemblages from the Rügen subsurface and from coeval Perigondwana localities (e.g. Tunisia). Since the early Caradoc, this Gondwanan affinity of the Rügen microfossils starts to lessen, and becomes negligible during the late Caradoc. During latest Caradoc–early Ashgill through Llandovery times the chitinozoan assemblages from either side of the TESZ are undistinguishable. If palaeobiogeographical differentiation is primarily related to palaeolatitudinal distance, then the present data support closure of the Tornquist Ocean during late Caradoc–Ashgill times. The presence of reworked Llanvirn acritarchs of Perigondwanan affinity in middle Ashgill sedimentary sequences at the southern margin of the EEP, clearly shows that by this time erosion of an uplifted area was taking place. Accordingly, the closure of the Tornquist Ocean, and consequent Avalonia–Baltica collision must have taken place during the time interval between the middle Caradoc and the early middle Ashgill (Rawtheyan). New chitinozoan data from boreholes H 2 and K 5, offshore of Rügen Island, northern Germany, allow for precise biostratigraphic dating. In the pre-Devonian part of H 2, Siphonochitina formosa indicates an Abereiddian (Early Llanvirn) age, facilitating correlation with boreholes Binz 1/73 and Lohme 2/70 of Rügen. In borehole K 5, the occurrence of Belonechitina robusta and Tanuchitina bergstroemi permits attribution of the investigated pre-Carboniferous sequence to the middle-late Caradoc, and, possibly, early Ashgill.

A new assemblage of graptolites, rhabdopleuran hemichordates and chitinous hydroids from the late Arenig (Ordovician) of the Banestan area, east-central Iran

A rich benthic and planktonic graptolite fauna is associated with encrusting rhabdopleuran hemichordates and chitinous hydrozoans in the late Arenig (Ordovician) part of the Katkoyeh Formation at Banestan, east-central Iran. New taxa described here are the dendroid graptolites Callograptus huckriedei sp. nov. and Dictyonema bitubulata sp. nov. Other dendroid graptolites Dendrograptus sp. cf. D. flexuosus J. Hall, 1865; Acanthograptus divergens Skevington, 1963; and Thallograptus ?succulentus Ruedemann, 1904 are described. The tuboid graptolite Galeograptus sp., the rhabdopleuran hemichordates Rhabdopleura sp. aff. R. primaevus (Kozlowski, 1967) and Kystodendron sp., and the chitinous hydroid Palaeotuba sp. are also described. Graptoloid graptolites described here are Aulograptus? sp., Didymograptus incertus Perner, 1895, Undulograptus formosus (Mu & Lee, 1958), and Yutagraptus sp. cf. Y. mantuanus Riva, 1994. All but two species-level taxa are described from Iran for the first time. The fauna is confirmed as being late Arenig or, less likely, early Llanvirn and thus probably correlates with the early part of the Darriwilian stage. It resembles the Atlantic cold water faunas in lacking isograptids and sinograptids.

Llanvirn-early Caradoc trilobite biofacies of western Hubei and Hunan, China

On the basis of representative collections made from seven measured sections in western Hubei and Hunan, four early Llanvirn and five late Llanvirn-early Caradoc trilobite biofacies are distinguished along a bathymetric gradient from shallow to deep outer shelf. The diversity and relative abundance of mesopelagic cyclopygids gradually increased southwards or seawards. According to the facies association exhibited in the region, the upper limit of living depth for different forms is inferred as follows: 1) more than 70 m (M. (Microparia)); 2) less than 100 m (M. (Quadratapyge), Pricyclopyge, Aspidaeglina); 3) at approximately 100 m (Cyclopyge); and 4) more than 100 m (Symphysops, Psilacella). Benthic forms were absent in the deep outer-shelf basin because of stagnant conditions. In shallower sites of the outer shelf, genera of nileids in the carbonate facies and raphiophorids in the clastic facies were relatively abundant, but some endemic forms, such as the asaphid Birmanites and remopleuridid Hexacopyge, became dominant during the late Llanvirn-early Caradoc. Rorringtoniids are mainly associated with deeper outer-shelf facies. Panderia is common in an early Llanvirn nileid fauna at Yichongqiao, Cili area, and may well indicate development of shelf carbonate buildups. A transgressive event is suggested by the sudden appearance of rich Cyclopyge in the early Caradoc at Jiuxi, Changde.

Chitinozoan faunas from the Rügen Ordovician (Rügen 5/66 and Binz 1/73 wells), NE Germany

The island of Rügen (NE Germany), situated close to the Trans-European Suture Zone (TESZ), in the southern Baltic Sea is underlain by sedimentary rocks of an Early Palaeozoic age, known only from boreholes. The wells, Rügen 5/66 and Binz 1/73, were investigated for their chitinozoan assemblages to improve the earlier biostratigraphic dating (graptolites and acritarchs) and to facilitate comparisons with other chitinozoan assemblages on both sides of the TESZ. In the lower part of the Rügen 5/66 core (3794.7–3615.8 m), Lagenochitina destombesi Elaouad-Debbaj is indicative of an early late Tremadoc age. In the upper part of the same well (3287.3–1709.7 m), the observed chitinozoan taxa suggest an age spanning the early Llanvirn to the Caradoc. The entire sampled interval of the Binz 1/73 core (5217.6–5041.8 m) is interpreted as belonging to the Siphonochitina formosa Biozone (early–early late Abereiddian, corresponding to the early Llanvirn). The chitinozoan data corroborate the earlier suggested biostratigraphic ages, based on acritarchs and graptolites. The chitinozoans from the Binz 1/73 well point to a high latitude provenance of the investigated host sediments at time of deposition.

The Margaree orthogneiss: an Ordovician, peri-Gondwanan, mafic-felsic igneous complex in southwestern Newfoundland

The igneous protoliths of the Margaree orthogneiss intruded the peri-Gondwanan rocks of the Port-aux-Basques Complex, in the southwestern corner of the Hermitage Flexure, prior to regional deformation and metamorphism. Field relationships and U–Pb geochronology indicate that the Margaree orthogneiss represents a 20 km long, mafic-felsic intrusive complex formed by amphibolite, dioritic orthogneiss, 474+14-4 Ma hornblende-bearing tonalitic orthogneiss with mafic enclaves, 472 ± 2.5 Ma and 465 ± 3 Ma biotite-bearing granitic orthogneiss, and minor ultramafic rocks. Most amphibolite have the chemistry of volcanic-arc tholeiite and are interpreted to be coeval with the intrusion of tonalitic and granitic magma with volcanic-arc geochemical signatures. Locally, mafic magmatism continued after the intrusion of the 465 Ma granite. The Margaree orthogneiss and its country rock were overprinted by upper amphibolite-facies metamorphism and deformation associated with the final closure of the Iapetus Ocean. A late-synkinematic granite dates the late stages of the high-temperature regional deformation at 417+7-4 Ma, while metamorphic titanite (411 ± 2 Ma) is interpreted to date extensive recrystallization under amphibolite-facies conditions as Early Devonian. The Margaree orthogneiss is broadly coeval with the plutons that postdate the Early Ordovician Penobscottian arc – passive margin imbrication in central and southern Newfoundland. It also coincides with the extensive late Arenig – early Llanvirn back-arc rifting event along the entire peri-Gondwanan margin of the northern Appalachians. The external position of the Port-aux-Basques Complex with respect to the back-arc elements in the Hermitage Flexure, coupled with the rock types and geochemistry of the orthogneiss, suggest formation of the Margaree orthogneiss in an arc and (or) back-arc transitional setting.

Early to early Middle Ordovician conodont biostratigraphy of the Gillberga quarry, northern Öland, Sweden

The Gillberga quarry in northern Öland provides a c. 16 m thick sequence through middle Volkhov to upper Kunda (mid-Arenig to early Llanvirn) beds. The section has been sampled for conodonts and its temporal faunal changes have been investigated on the basis of fiftynine samples yielding over 300,000 conodont elements. Conodont zones earlier recognized in south-central Sweden and ranging from the middle of the Baltoniodus navis Zone to the middle or upper part of the Microzarkodina ozarkodella Subzone of the Eoplacognathus pseudoplanus Zone were encountered at Gillberga. The temporal changes in relative frequencies of the most abundant conodont genera were calculated throughout the sequence and are presented in frequency diagrams. A new species, Microzarkodina bella, from the lower Kunda has been identified and is described.

Lower Palaeozoic stratigraphy and palaeontology, Karadere–Zirze area, Pontus Mountains, northern Turkey

Lower Palaeozoic rocks in the Karadere-Zirze area, east of Safranbolu (Pontides, northern Turkey), range from Early Ordovician to Silurian. Overlying the probably Tremadoc Bakacak Formation are Aydos Formation quartzites, followed conformably by the Karadere Formation, dated as Early Arenig to Early Llanvirn by means of graptolites which are assigned to seventeen genera and include three new forms: Eoglyptograptus bouceki, Prolasiograptus haplus praecursor and Undulograptus? mui. Late Arenig trilobites from the Karadere Formation include Bergamia, Cyclopyge, Dionidella?, Leioshumardia and Seleneceme. In the Limestone Member of the overlying Ketencikdere Formation, uncommon trilobites suggest only a mid- to late Ordovician age, but conodonts with Colour Alteration Index 5–6 indicate the Amorphognathus tvaerensis Biozone (early Caradoc). Macrofossils are rare in the Siltstone Member, but conodonts from the middle of the unit suggest the highest subzone of the A. tvaerensis Biozone; the youngest visible strata are, on acritarch evidence, at least as high as Caradoc, but the Ashgill is not confirmed and the contact with overlying Silurian rocks is unexposed. The Findikli Formation comprises: a Lower Member, black argillites with Llandovery graptolites and acritarchs; and an Upper Member, grey shales with late Wenlock graptolites, overlain unconformably by Devonian rocks. The succession differs significantly from contemporaneous deposits in southern Turkey and its affinities lie with western Europe, including the Welsh Basin.

Epizoan-sponge Interactions in the Early Ordovician of the Argentine Precordillera

Abstract Evidence for biotic interaction is not obtainable easily in the fossil record. Epizoans cemented to the skeletons of host organisms provide an opportunity to study possible host–epizoan interactions and the ecological structure of hard substratum communities. One such possibility is sponges and their associated encrusters, but few such occurrences have been documented from the fossil record. Early Ordovician limestones of the San Juan Formation in the Argentine Precordillera bear an important sponge fauna consisting mainly of demosponges. This Early Llanvirn assemblage has the highest diversity, and most sponges were subjected to epizoan encrustations. A total of nineteen species included in eleven genera of sponges were examined to record epizoans encrustations. Type and relative abundance of epizoans were compiled for each sponge species. Five kinds of epizoans were recorded: bryozoans, stemmed echinoderms, brachiopods, other sponges, and scars and borings of undetermined organisms. Crinoids an...