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Baltica except for Baltoscandia was subject to an early Tremadocian immigration of trilobites similar to that on other plates. In Baltoscandia the Olenid biofacies lingered on until it was replaced by the late Tremadocian Ceratopyge biofacies. For the rest of the time (Floian to mid-Darriwilian), Baltoscandia had fairly monotonous lithologies and faunas, constituting a single Asaphid biofacies with lateral variations expressed as differences largely in the relative abundance of species. In the South Urals immigration started in the earliest Tremadocian with fairly rich deep-water faunas. A poorer fauna is known from the Polar Urals. A slightly younger, sparse fauna is known from Paj-Khoj. Over most of the Ural border north of the South Urals there was a further development of first a Ceratopyge biofacies, then an eastern Asaphid biofacies, together with more siliciclastic input to the lithofacies and with fewer asaphids than in Baltoscandia. In the South Urals there was a development in the Darriwilian of a Cheirurid biofacies following the Ceratopyge biofacies. By contrast, the shelf part of the South China Plate shows a development of fifteen biofacies distinguished on the genus level, and the number of species for each biofacies is notably small. The major difference in the pattern of distribution of the biofacies probably reflects the faunal development in rather different climatic conditions, suggesting that the Yangtze block is supposedly positioned rather distant from Baltica, but still close enough to share genera inhabiting the outer shelf.

The Baltica terrane is well known as the Asaphus Province of the Ordovician World. Being situated in intermediate latitudes and surrounded by fairly wide oceans, Baltica had a benthic fauna that developed in a relatively endemic direction. The most common trilobites were the asaphids. The present study discusses how they appeared, evolved in various environments around Baltoscandia and finally disappeared. The total range of the asaphids based on data from 381 species is estimated as extending from the Furongian, latest Cambrian to the end Ordovician. The remnant Cambrian Olenid Fauna, which was adapted to black bituminous shale facies, survived into the Tremadocian. This Cambrian fauna includes the first asaphids (Promegalaspides, Niobella, ?Eoasaphus). With a shift to lighter-coloured and carbonatic sediments in the middle Tremadocian, this fauna was replaced by the immigrating Ceratopyge Fauna. The latter contains the first five widely distributed asaphid genera Promegalaspides, Niobe, Niobella, Niobina, and Asaphellus. As carbonate sedimentation became more widespread in many areas from the Floian onwards, the asaphids increased in number and formed a stabilised Asaphid Fauna during the Dapingian. In Baltoscandia a gradual development of endemism related to facies belts is observed during the Darriwilian. Records of the mud-related niobines, Megistaspis and Ptychopyge faunas, together with some other benthic macrofaunas are not found beyond the boundary of the Kunda/Aseri regional stages (middle Darriwilian). Their disappearance may be due to a catastrophic event. In contrast Asaphus s.l. survived this interval. Drift of Baltica towards lower latitudes and fluctuations in sea-level influenced the Asaphid Fauna leading to its gradual collapse by late Sandbian time. Influx of the islotelines during the early Katian gave way to a set of illaenimorph species found together with corals that are related to a reefal environment. This morph disappears prior to the Hirnantian glaciation.

Discovery of well-preserved specimens from the Nanba section in Yiyang, Hunan Province, in combination with a literature review, enabled us to re-evaluate and revise the graptolite genus Ancoragraptus. This is a genus of biradiate, multiramous anisograptids with horizontal to reclined rhabdosomes and free lower part of the metasicula and slightly isolated autothecal apertures. According to the revised definition, two species are included in Ancoragraptus, i.e., Ancoragraptus bulmani (Spjeldnæs, 1963) and Ancoragraptus psigraptoides Cho, Kim, and Jin, 2009. It is the first time that A. bulmani has been reported from China. The occurrences of Ancoragraptus reported worldwide are reviewed in the present study and found to be restricted to the lower upper Tremadocian. The restriction of Ancoragraptus in stratigraphical distribution makes it a taxon with a high potential for precise biostratigraphical correlation at both regional and global scale.

Unique find of a porambonitid brachiopod in the Sarka Formation (Darriwilian) in the Prague Basin, the Czech Republic, is described. Porambonites havliceki sp. nov. is characterized by thin shell with finely pitted radial multicostellate ornament, long parallel brachiophore plates and long dental plates. It is the earliest known representative of the family Porambonitidae in the West Gondwana. Poramborthis, an orthid-like syntrophiid genus abundant in the Tremadocian of the West Gondwana, is assumed the evolutionary ancestor of the Porambonites. Pitted multicostellate ornament is suggested synapomorphy of the porambonitid brachiopods.

Based on a large data-set, spanning the Ordovician–Early Silurian (Telychian) interval, this study explores the phylogeographic distributional pattern for higher orders of rhynchonelliformean brachiopods through four time slices: Tremadocian, Dapingian–Darriwilian, Katian and Telychian. In addition, a palaeobathymetrical analysis has been conducted for the latter two time slices to assess the phylogenetic impact of the Late Ordovician mass extinctions at various palaeowater depths. Whereas the Tremadocian time slice exhibits phylogenetically simple regions characterized by orthide and porambonitoid taxa, these increase in complexity up through the Ordovician and become dominated by the strophomenides. By the Silurian this phylogentic composition shifted once more to atrypide- and pentameride-dominated faunas.

Acritarch assemblages are described here for the first time from the Early Ordovician Yinzhubu and Ningkuo formations of the Nanba section (Yiyang region, Hunan province, South China). Independent stratigraphical control is provided by co-occurring late Tremadocian–early Floian (early Arenig) graptolite and chitinozoan biozones. A very diverse association of 33 species attributed to 23 genera is identified, and three acritarch assemblage zones are distinguished. These are comparable to coeval assemblages from several localities worldwide. During the Early Ordovician the Yiyang area was at low latitudes. The acritarch association interestingly shows a mixed character, comprising typical taxa from both cold-water and warm-water paleobioprovinces.

The Stumsnas 1 core, drilled in 2011 in the southern part of the Siljan Ring, provides new insights into the stratigraphy of the Ordovician succession in central Sweden. The core section shows evidence of the structural complications caused by the late Devonian meteorite impact in the area. In the core, about 90m of Tremadocian to Darriwilian strata are sandwiched between Proterozoic igneous basement rocks. At the lower contact, the sedimentary succession starts with glauconitic, fine-grained siliciclastics and carbonates directly resting on the weathered basement. The basal siliciclastic unit is overlain by a ca. 19-m-thick limestone succession, well-known from this part of the Baltoscandian Basin, includes strata corresponding to the Latorp Limestone through the upper Holen Formation. This succession is covered by a limestone-marl alternating sequence, representing some yet unknown deeper water facies, presumably coeval to the topmost Holen Formation through upper Dalby Limestone. The upper third of the sedimentary succession in the core includes numerous slices of partly overturned strata, including relatively thick successions of the Slandrom Formation, Fjacka Shale and Jonstorp Formation, as well as carbonate and siliciclastic units of yet unknown stratigraphic origin.

The Yichang area of Hubei Province, China provides important information on Lower to Middle Ordovician fossil faunas and is a center for research on Ordovician graptolites due to the sometimes excellent preservation of the copiously available material. New material collected during a research project on Lower to Middle Ordovician biota in the Yichang Region provided among others specimens a number of dendroid (benthic) graptolites of the genera Acanthograptus, Aspidograptus, Dendrograptus, and Koremagraptus showing unexpected and unknown structural features, useful for structural and evolutionary investigations.

The remotely located Cambro-Ordovician strata in Ny Friesland, NE Spitsbergen, Svalbard, are referred to the Oslobreen Group, which is composed of the Tokammane, Kirtonryggen and Valhallfonna formations. Herein we record the conodont succession of the Kirtonryggen and Valhallfonna formations. Collections of well-preserved conodonts (CAI 1) have been recovered from the Lower to lower Middle Ordovician interval in the region. Eight regional conodont zones are established in this preliminary study of the Oslobreen Group exposed at Hinlopenstretet, NE Svalbard. In ascending order these zones are: Rossodus manitouensis, Macerodus dianae, Oneotodus costatus, Oepikodus communis, O. evae, O. intermedius, Periodon aff. flabellum-Periodon hankensis and Periodon macrodentatus. The yield is relatively poor for the Kirtonryggen Formation, but the oldest Ordovician conodont faunas span the Tremadocian Rossodus manitouesis through Macerodus dianae zones followed by the Floian Oepikodus communis Zone. The taxa are typical of the tropical North American Midcontinent faunal province that dominated the region until open marine associations invaded the shallow shelf (i.e. Evae transgression). The pandemic Oepikodus evae becomes frequent and is succeeded by O. intermedius in abundance in the lower Valhallfonna Formation (Olenidsletta Member). The upper strata are characterised by the Periodon-Paroistodus assemblage characteristic for outer shelf and slope environments around Laurentia. In total, this formation comprises the Floian and Dapingian stages and ends in the early Darriwilian Periodon macrodentatus Zone in this region. The Ny Friesland faunas show affinities to coeval assemblages from Northeast Greenland and West Newfoundland. (Less)

The Eoplacognathus pseudoplanus Zone is defined by a conodont fauna composed by E. pseudoplanus (Viira) and Dzikodus tablepointensis (Stouge) among others in the Central Precordillera, Sierra de La Trampra region. We revised the biostratigraphical distribution and control biofacies of the conodonts D. tablepointensis and E. pseudoplanus in the Middle Ordovician of the Precordillera. This study confirms that these species has a similar biostratigraphical distribution to those of equivalent age in south-central China, Baltica and Midcontinent region. We also corroborate that the presence of D. tablepointensis is accurately positioned in the E. pseudoplanus Zone. In this paper we discuss for the first time the morphological affinities of D. tablepointensis and E. pseudoplanus elements from the Precordillera with those same species from southcentral China and Baltica. On the other hand, we review the genus "Polonodus" galerus Albanesi and propose it as Kallidontus? galerus (Albanesi), extending the biostratigraphical record of the genus Kallidontus from the late Tremadocian to middle Darriwilian. Fil: Mestre García, Ana Isabel. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Investigaciones Mineras; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina Fil: Heredia, Susana Emma. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Centro de Investigaciones de la Geosfera y Biosfera. Universidad Nacional de San Juan. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones de la Geosfera y Biosfera; Argentina. Universidad Nacional de San Juan. Facultad de Ingeniería. Instituto de Investigaciones Mineras; Argentina

The Bohemo‐Iberian regional scale for South Gondwana, involving the ‘Mediterranean Province’, comprises five regional stages (Arenigian, Oretanian, Dobrotivian, Berounian and Kralodvorian) plus the global Tremadocian and Hirnantian. The predominance of shallow‐water taxa in those high‐latitude faunas imposes serious difficulties for correlating the regional succession with the formal global chronostratigraphy because of the almost total absence of the key graptolites and conodonts defining the base of the standard series, stages and stage slices. Instead, the abundant benthic faunas (trilobites, brachiopods, molluscs, echinoderms) of South Gondwanan origin largely dominated in the area from the middle Darriwilian to the late Katian. The poleward faunal migration of originally Avalonian, Baltic, Laurentian and even Asiatic taxa during the Boda Event of global warming progressively ends with the endemicity in the region, where the ensuing benthic assemblages were severely affected by the Hirnantian glaciation. The regional scale significantly improves the precision of correlations between Ordovician strata from SW and central Europe, North Africa and a large part of the Middle East. An updated record of palaeontological data from areas where Mediterranean faunas remain practically unknown, or are still poorly investigated, is also included. Palaeobiogeographical relationships based on the distribution of faunas across South Gondwana are suggested as an improvement for positioning many territories in modern palaeogeographical reconstructions and offer a constructive approach to problems related to the pre‐Variscan and pre‐Alpine orogenic puzzles., This work has been supported by the IBEROR project (‘Iberian Ordovician chronostratigraphy and its correlation with the global scale’, ref. CGL2012‐39471/BTE) of the Spanish Ministry of Economy and Competitiveness.

The relationship of many Cambrian rhynchonelliform brachiopods is poorly understood, with many genera displaying a combination of morphological features that are taxonomically confusing. The study of middle Cambrian–early Tremadocian brachiopods is critical because this interval is sandwiched directly between the two largest radiation phases in the early Palaeozoic and provides raw data for deciphering the events leading up to the explosion of brachiopod genera in the Ordovician. Here we present a parsimony analysis of a wide selection of Cambrian and Ordovician brachiopod genera with a particular focus on the evolution and phylogeny of Billingsellida. The billingselloids were widespread by the late Cambrian and the group was originally thought to represent the ancestral stock of many Ordovician brachiopod lineages. The phylogenetic analyses portray the polytoechioids as derived billingselloids separate from the clitambonitoids that form a sister group. The Gondwanan brachiopod Roanella is interpreted as ...

Over the past 15 years, significant progress has been achieved in our understanding of Lower Palaeozoic radiolarian faunas. However, description of biogeographical patterns of Ordovician Radiolaria is hampered by the paucity of known occurrences as well as possible taphonomic influences. The distribution of all known assemblages is analysed in time and space. Lower Ordovician (especially Tremadocian) Radiolaria are known from two distinct tropical localities of Laurentia. Geographical coverage is much better for the Middle Ordovician (Darriwilian). However, data are concentrated in tropical palaeolatitudes (between 30°N and 30°S). The absence of data from mid/high-latitude localities limits any biogeographical insights. In addition to this there are taphonomic and taxonomic biases. Data are also sparse for the Upper Ordovician. However, comparison between Australian and Nevadan material of Katian age shows strong similarities, suggesting the presence of a coherent tropical radiolarian bioprovince, as in the modern ocean.

The phylogeographical evolution and the consequent changing distribution and diversity of rhynchonelliform brachiopods through the Ordovician are linked to the dynamic palaeogeography of the period. The Early Ordovician (Tremadocian and Floian) is characterized by globally low-diversity faunas with local biodiversity epicentres, notably on the South China Palaeoplate; low-latitude porambonitoid-dominated faunas with early plectambonitoid and clitambonitoid representatives, as well as high-latitude assemblages mostly dominated by orthoids, can be recognized, but many taxa are rooted in Late Cambrian stocks. The Early Ordovician displays a steady increase in rhynchonelliformean biodiversity, which was mostly driven by the increasing success of the Porambonitoidea and Orthoidea, but the billingsellids and early plectambonitoids also contributed to this expansion. During the Early to Mid Ordovician (Dapingian–Darriwilian), marine life experienced an unprecedented hike in diversity at the species, genus and family levels that firmly installed the suspension-feeding benthos as the main component of the Palaeozoic fauna. However, this may have occurred in response to an early Darriwilian annihilation of existing clades, some of which had been most successful during the Early Ordovician. New clades rapidly expanded. The continents were widely dispersed together with a large number of microcontinents and volcanic arcs related to intense magmatic and tectonic activity. Climates were warm and sea-levels were high. Pivotal to the entire diversification is the role of gamma (inter-provincial) diversity and by implication the spread of the continents and frequency of island arcs and microcontinents. The phylogeographical analysis demonstrates that this new palaeogeographical configuration was particularly well explored and utilized by the strophomenides, especially the Plectambonitoidea, which radiated rapidly during this interval. The porambonitoids, on the other hand, were still in recovery following the early Darriwilian extinctions. Orthides remained dominant, particularly at high latitudes. Biodiversity epicentres were located on most of the larger palaeoplates, as well as within the Iapetus Ocean. Provincial patterns were disrupted during the Sandbian and early Katian with the migration of many elements of the benthos into deeper-water regimes, enjoying a more cosmopolitan distribution. Later Katian faunas exhibit a partition between carbonate and clastic environments. During the latest Katian, biogeographical patterns were disrupted by polewards migrations of warm-water taxa in response to the changing climate; possibly as a consequence of low-latitude cradles being developed in, for instance, carbonate reef settings. Many clades were well established with especially the strophomenides beginning to outnumber the previously successful orthides, although this process had already begun, regionally, in the mid to late Darriwilian. At the same time, atrypoid and pentameroid clades also began to radiate in low-latitude faunas, anticipating their dominance in Silurian faunas. The Hirnantian was marked by severe extinctions particularly across orthide-strophomenide clades within the context of few, but well-defined, climatically controlled provincial belts. Supplementary material: The individual localities and a reference list for the data sources are provided at: http://www.geolsoc.org.uk/SUP18667

The biogeographical patterns shown by Ordovician linguliform and craniiform brachiopods are greatly influenced by their dominance in low-diversity associations in marginal environments. This is particularly evident in the Early Ordovician, when linguliform-dominated dysaerobic assemblages are widely distributed along the deep shelves of Gondwana, the Kazakhstanian terranes and in Baltica. By the Darriwilian, micromorphic linguliforms are characteristic components of the pantropical climatic-controlled faunas of Laurentia, Cuyania and Kazakhstanian terranes, which – in spite of separation by extensive oceans – retain a distinct similarity. Analysis of craniiform biogeographical distribution is impeded significantly by the poor state of craniide taxonomy and lack of reliable data from most regions. However, in general their biogeographical dispersion is similar to other groups of the Palaeozoic Evolutionary Fauna. Unlike the linguliforms, which are important members of the Cambrian Evolutionary Fauna, there is no convincing Cambrian craniiform record; they may have evolved and dispersed from Gondwana and associated microcontinents and island arcs. The earliest well-established record is from the late Tremadocian of temperate to high-latitude peri-Gondwana. During most of the Ordovician, they have a peri-Iapetus distribution. They are very rare or absent in tropical Gondwana, South China and Kazakhstanian terranes and are not yet documented from Siberia. The trimerellides probably evolved in tropical peri-Gondwanan island arc settings. Their dispersion and major features of biogeography mirror those of atrypides.

The Fezouata Shale (= Fezouata Formation) has produced the most complete Lower Ordovician graptolite succession known from the African continent, which was studied from 32 sections located along the western, central, and eastern Moroccan Anti-Atlas. A composite biostratigraphic and chronostratigraphic scheme is presented for the entire formation that, in ascending order, comprises the Anisograptus matanensis–Rhabdinopora flabelliformis anglica zones (uppermost lower Tremadocian), “Adelograptus” tenellus and Aorograptus victoriae zones (middle Tremadocian), Araneograptus murrayi and Hunnegraptus copiosus zones (upper Tremadocian), ?Cymatograptus protobalticus Zone (lower Floian), ?Baltograptus jacksoni Zone (middle Floian), and the Baltograptus minutus Zone plus an “Azygograptus interval” (upper Floian). Most of these zones or biozones are recorded for the first time in Africa, together with important graptolite species such as Ancoragraptus bulmani (Spjeldnaes), ?Cym. protobalticus (Monsen), ?B. jacksoni Rushton, Clonograptus multiplex (Nicholson), B. minutus (Törnquist) and Azygograptus eivionicus Elles. A correlation with the graptolite sucession from the Algerian Sahara is also suggested, reinforced by the common record of the minute anisograptid Choristograptus louhai Legrand, providing its second world occurrence in the Tremadocian of Morocco. The prior late Tremadocian dating of the Fezouata Lagerstätte is here extended to the middle Floian as revealed by the graptolite biochronology. The repeated record along the lower and middle parts of the Fezouata Formation of deep-water mesopelagic species of the genera Araneograptus — with mass occurrences of conical colonies, together with large horizontal rhabdosomes of Paratemnograptus, Paradelograptus, Clonograptus, “Tetragraptus” and Holograptus/Schizograptus do not fit the sedimentological interpretation of deposition of these strata in much shallower inshore to mid-shelf environments. This inconsistency has implications when inferring the living conditions of the Fezouata soft-bodied assemblages., This paper was financed by the project CGL2012-39471 of the Spanish Ministry of Economic Affairs and Competitivity, and is also a contribution to the projects RALI 197 of the French ANR and IGCP 591 and 653 (IUGS-UNESCO)

This study documents conodont faunas of the Fezouata Formation, recovered from the AZ-1 borehole at Adrar Zouggar Mountain and from outcrops near Zagora in south-eastern Morocco. The Fezouata Formation was deposited on the peri-Gondwanan shelf near the South Pole during Early Ordovician times. It is composed of mostly fine-grained siliciclastics and is well known for including beds displaying the exceptionally well preserved Fezouata Biota. Studies on different microfossil groups, including conodonts, increase the diversity recorded from this exceptional ecosystem. Strongly recrystallised conodont elements were extracted from the fine-grained siliciclastic sediments by diluted hydrofluoric acid (HF), which was used for isolating palynomorphs. The material is dominated by simple cone taxa such as Parapaltodus, Semiacontiodus, Scolopodus, Scalpellodus, Drepanoistodus, Acodus, Paltodus, and Cornuodus. In addition, a few elements of early Prioniodus are recovered. This composition allows an estimation of uppermost Tremadocian through basal Floian ages for the fragmented elements because characteristic elements of younger assemblages, including ramiform (e.g., Oepikodus, Baltoniodus) or coniform (e.g., Tropodus, Protopanderodus) apparatuses, have not been recorded. The association is devoid of any warm/tropical and temperate water taxa and is typical for faunas in the cold water environments of the subpolar siliciclastic shelves during Early Ordovician times. The new term of ‘subpolar faunal domain’ is proposed for these conodont associations of low diversity that occur at high southern latitudes during the Early Ordovician. Ecological implications and palaeobiogeographical relationships of the conodont faunas are discussed., The research was supported as part of the RALI project (Rise of Animal Life), funded by the ANR (Agence Nationale de la Recherche, France; grant number ANR-11-BS56-0025). G.N. Sarmiento and J.C. Gutiérrez-Marco were financed by the project CGL2012-39471/BTE of the Spanisch Ministry of Economy and Competitiveness.

Components of biodiversity are strongly scale dependent, but the relative importance of the patterns that operate at different scales and the links between them have been overlooked. To disentangle the ecological structure of Cambro‐Ordovician trilobite assemblages from the Argentine Cordillera Oriental at different scales, we explore patterns of abundance, dominance and occupancy across the onshore–offshore profile, and through three time intervals: Furongian, earliest Late Tremadocian (Tr2), latest Middle Floian–earliest Late Floian (Fl2–Fl3). At the regional scale, single taxa are overwhelming dominant in the Furongian (Parabolina) and in the earliest Late Tremadocian (Leptoplastides). Several dominants occur in the Floian, but just one (Famatinolithus) attains high occupancy and, rarely, high dominance. In contrast, only the Furongian records highly dominated local assemblages, whereas dominance distinctly decreases among Tr2 and Fl2–Fl3 ones. Thus, when both scales of analysis are combined, an unexpected scenario becomes evident: Tr2 assemblages resemble those of the Furongian at the regional scale, but mirror those of the Floian at the local scale. These results highlight a decoupling in local versus regional structures triggered by an earlier switch in dominance in local communities and a delayed change at the regional scale. Interestingly, this decrease in local dominance matches previous analyses accounting for a coeval step‐up in local evenness, suggesting that the Tr2 appears as a pivotal interval in the reorganization of communities in the Cordillera Oriental. This scenario emphasizes that biogeographical regions witnessed different regional‐scale processes, and suggests that scaling local and regional patterns provides new insights to unravel the history of biodiversity among benthic communities. Fil: Waisfeld, Beatriz Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Balseiro, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

The eoorthid brachiopod Apheoorthina is reported for the first time from the Lower Ordovician of NW Argentina. It is represented by a species similar to A. ferrigena from the Tremadocian of the Prague Basin, increasing the faunal affinities between the Central Andean Basin and the South European microcontinents, in particular the Bohemian region (Perunica). Nine out of the fourteen brachiopod genera reported from the Tremadocian of the Central Andean Basin (~64 %) are shared with the Mediterranean region, four of which (~ 28 %) have been recorded in the Prague Basin, and two (Kvania and Apheoorthina) are restricted to the Central Andes and Perunica. Dispersal pathways around Gondwana are analyzed in the light of major factors affecting large-scale distribution of brachiopods (environment, larval capacity for dispersal, oceanic currents).The presence in Apheoorthina aff. ferrigena of a well-preserved larval protegulum measuring 420 μm in width and 210 μm in length strongly suggests that this species had planktotrophic larvae capable of long-distance dispersal. According to recent oceanatmosphere general circulation models for the Ordovician Period, the Central Andean margin was dominated by the cold-water Antarctica Current. Despite the complex nonzonal pattern produced by current deflections around the peri-Gondwanan microcontinents, the general westward circulation sense favoured larval dispersal from the Andean region to North Africa, Avalonia, the Armorican Terrane Assemblage, and Perunica. On the other hand, the eastwards flowing Gondwana Current connected the North Gondwana waters with the South American epicontinental seas, which could explain the reversed migration of some brachiopods. Fil: Muñoz, Diego Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

The re-study of species previously attributed to the genus Nanorthis from the Tremadocian of north-western Argentina has led to the recognition of the new genera Gondwanorthis (type species Nanorthis calderensis Benedetto), to which the Iranian species Nanorthis bastamensis Ghobadi Pour, Kebriaee-Zadeh & Popov is also referred, and Lampazarorthis (type species Eoorthis bifurcata Harrington), which includes Nanorthis brachymyaria Benedetto and Lampazarorthis alata sp. nov. New extensive collections from the Cordillera Oriental support reassignment of the upper Tremadocian species Nanorthis purmamarcaensis to the genus Tarfaya. The species Nanorthis carinata Laurie, from Tasmania, is reassigned here to Tarfaya. According to the present taxonomic revision, Nanorthis is not cosmopolitan but is a pan-tropical genus, confined to Laurentia, the Laurentian-derived Precordillera terrane, and probably to Baltica, Siberia and Kazakhstanian terranes, whereas Gondwanorthis and Tarfaya are Gondwanan and peri-Gondwanan endemic taxa. Cladistic analysis of early orthoids, plectorthoids and dalmanelloids, including those recorded from mid to high latitude Gondwana successions, portrays Gondwanorthis and Lampazarorthis as a sister group basal to the tarfayid C heterorthid clade, whereas the South American and North African Incorthis appears as a basal member of this clade. Morphological and stratigraphical evidence provided in this study, along with the results of the cladistic analysis, supports the view that heterorthids could have arisen from the tarfayids by the end of Floian. The enlargement and incipient bilobation of the cardinal process in Tarfaya grandis leaves this species as a potential ancestor of Tissintia, which occurs in Darriwilian beds of the Central Andean Basin (Bolivia), but could have been present in this basin since the late Floian. We speculate that punctae in the Heterorthidae evolved independently from a Tarfaya-like ancestor, and that the transition from an impunctate to a punctate shell may have occurred repeatedly through rhynchonelliform evolution. Fil: Benedetto, Juan Luis Arnaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Muñoz, Diego Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

The first ever list of the regional Öland Series (Tremadocian to mid Darriwilian) trilobites and agnostids from the whole of Baltoscandia is compiled. The study includes revision of systematics as well as vertical and horizontal distribution. This is necessary because of the uneven state of knowledge, some faunas having being studied recently, others not for more than a century. Three successive faunal types are recognized: the Olenid Fauna surviving from the Cambrian in black bituminous shale facies, the immigratingCeratopygeFauna, and the stabilized Asaphid Fauna. The latter fauna collapsed in the middle of Darriwilian and gave way to a set of new post-Ölandian faunas.

Early to Middle Ordovician cherts and cherty siltstones associated with distal turbidite deposition in back-arc basins, are widespread in the Hermidale and Albury–Bega Terranes of the Lachlan Orogen in New South Wales. Study of more than 2500 bedding plane-parallel thin sections prepared to a thickness of 50 μm from these cherts enables recognition of four conodont zones that range in age from the late Tremadocian to latest Darriwilian. Comparable cherts are present in two small remnants of oceanic derivation now exposed on the coast of New South Wales, in the Narooma Terrane (Furongian to Darriwilian), and in the New England Orogen at Port Macquarie in allochthonous blocks (Late Ordovician). Associated fauna include radiolaria, sponge spicules, lingulide and acrotretide brachiopods, fragmentary graptolites, and rare filaments attributed to cyanobacteria. Some of these organisms were pelagic, or may have been attached to floating material, and hence became entrapped in siliceous ooze on the sea floor when they settled under gravity. Others (e.g. the brachiopods) may have been attached to sponges growing on the sea floor. The presence of burrows and bioturbation demonstrates that the deep-sea environment in the Middle Ordovician was well-oxygenated, though this contrasts with Lower Ordovician environments where evidence for infauna is lacking. Predominant colouration of the cherts examined in thin section ranges from honey and yellow-brown (typical of semitransparent cherts) through cream-coloured translucent lithologies to opaque varieties. Dark brown cherty rocks that show evidence of burrowing or bioturbation tend to have a higher silt component. The Ordovician is also a time of extensive chert deposition elsewhere, including terranes in Kazakhstan (commencing in the Late Cambrian); these siliceous sediments display many of the features described from eastern Australia.

The succession at Mt. Hunneberg consists of intercalated siliciclastic mudstones and carbonates of Tremadocian to Floian age. Above an unconformity with underlying Furongian shales, siliciclastic mudstones with graptolites and overlying glauconite packstones of the upper Alum Shale Formation are exposed showing a sharp top contact to the carbonates of Bjorkasholmen Formation. Above, the Toyen Shale Formation consisting of siliciclastic mudstones and intercalated carbonate beds forms the stratigraphically youngest Ordovician unit at Mt. Hunneberg. The Toyen Shale Formation is characterized by a lower marl- and carbonate-rich part, exclusively present in the southwest of Mt. Hunneberg, and an upper portion consisting of siliciclastic mudstones, extending from the Tetragraptus phyllograptoides graptolite Biozone on upwards. The siliciclastic mudstones of the Alum Shale Formation represent open shelf sediments reflecting sea-level highstands of two trans- and regressions. Overlying glauconite packstones indic...

Organic-walled microfossils (acritarchs) provide age constraints for the previously poorly dated Cambrian and Lower Ordovician turbiditic Goldenville and Halifax Groups in the northern Appalachian Meguma terrane of Nova Scotia and address controversies about stratigraphy and provenance. The oldest exposed formation of the ∼8-km-thick Goldenville Group contains the trace fossil Oldhamia , which suggests an age of late Early Cambrian, whereas the coticule-bearing uppermost formation yielded an acritarch species consistent with Middle Cambrian (Epoch 3) age. The conformably overlying ∼5-km-thick Halifax Group includes basal pyritiferous units that yielded a Late Cambrian (Furongian) assemblage of acritarch species, providing further confirmation that the underlying manganese-bearing formations are of Cambrian Epoch 3 age, and not Ordovician as recently claimed. Overlying nonpyritiferous formations contain the Early Ordovician graptolite Rhabdinopora flabelliformis flabelliformis and acritarchs of similar age. Samples collected up section from the graptolite occurrence yielded acritarch species that are indicative of the later Tremadocian and Floian. The new fossil data confirm a gap in age of ∼30 m.y. between the Halifax Group and the overlying Silurian to Lower Devonian Rockville Notch Group. The new ages are consistent with stratigraphic units defined in regional mapping and support recent interpretation of fundamental differences in depositional and tectonic environments between the northwestern and southeastern parts of the Meguma terrane. They also provide new constraints on paleogeography of the terrane by confirming age similarities to stratigraphy in north Wales, with which correlation has been proposed previously based mainly on lithological similarities.

This paper describes late Cambrian dikes and Early Ordovician volcano-sedimentary successions of the Prague Basin, Bohemian Massif, to discuss the timing and kinematics of breakup of the northern margin of Gondwana. Andesitic dikes indicate minor E–W crustal extension in the late Cambrian, whereas the Tremadocian to Dapingian lithofacies distribution and linear array of depocenters suggest opening of this Rheic Ocean rift-related basin during NW–SE pure shear-dominated extension. This kinematic change was associated with the onset of basic submarine volcanism, presumably resulting from decompression mantle melting as the amount of extension increased. We conclude from these inferences and from a comparison with other Avalonian–Cadomian terranes that the rifting along the northern Gondwana margin was a two-stage process involving one major pulse of terrane detachment in the early Cambrian and one in the Early Ordovician. While the geodynamic cause for the former phase remains unclear, but still may include effects of Cadomian subduction (roll-back, slab break-off), isostatic rebound, or mantle plume, the incipient stage of the latter phase may have been triggered by the onset of subduction of the Iapetus Ocean at around 510 Ma, followed by advanced extension broadly coeval (Tremadocian to Darriwilian) in large portions of the Avalonian–Cadomian belt. Unequal amounts of extension resulted in the separation and drift of some terranes, while other portions of the belt remained adjacent to Gondwana.

Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions, and some of them may serve as potential hydrocarbon source rocks. The present study of the Ordovician graptolite fauna from these shales, together with the yielded conodonts and chitinozoans etc., permits a refined correlation of the rocks. Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions, and the successful identification of the new graptolite material from a few drill cores within the basin, we are able to update our knowledge of the Ordovician in the regions, and draw some conclusions: (1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions, which correspond to the Nemagraptus gracilis Zone, may be related to a global sea-level rise during this time interval. (2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag (also spelled as Quruq Tagh) region in eastern Tianshan Mountains, spanning Tremadocian to mid-Katian (D. spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression. The black shales of the D. spiniferus Zone may even extend into the central Tarim Basin. (3) Three different bio- and litho-facies belts (Bachu: carbonate platform and reef belt; Kalpin-Aksu: marginal platform and upper slope belt; Wushi: slope belt) are recognized in the northwestern Tarim Basin. (4) The internationally well-correlated Saergan black shale, which has been considered to possess high potential for hydrocarbon source rock, may possess a restricted distribution in the Kalpin and Aksu areas.

In the carbonate-siliciclastic strata of West Gondwana (e.g. in the Montagne Noire, France), the aftermath of the mid Languedocian (mid Cambrian) regression is characterized by a late Languedocian major turnover of trilobite families and a Furongian–early Tremadocian radiation related to the stepwise immigration of trilobite invaders from East Gondwana under persistent transgressive conditions. The scarcity of upper Languedocian fossil accumulations in clayey substrates has inspired the sampling of the palaeogeographically most distal parts of the Iberian Chains (Spain), where diagenetic dissolution of ubiquitous hexactinellid sponge spicules has favoured the formation of siliceous concretions. These have yielded the trilobitesPeronopsiscf.insignis,Oidalagnostus trispinifer,Proampyx difformis(=Proampyx aculeatus),Bailiaspis?glabrata(=Holocephalina agrauloides, by ontogeny),Holasaphuscf.centropygeand a paradoxidid gen. et sp. indet. Despite preservation and sampling biases, the identification of this taphonomic window in offshore clayey substrates of West Gondwana allows the recognition of a strong biogeographical link with Baltica, and the correlation of the global Guzhangian Stage and theSolenopleura?brachymetopaZone of Scandinavia with part of the Mediterranean upper Languedocian Substage.

Among the Caledonides exposed in the western part of the Kyrgyz Range the Lower Ordovician volcanogenic-sedimentary, plutonic, and tuffaceous-terrigenous complexes were distinguished. Volcanogenic-sedimentary sequences are the Kentash Formation, composed of volcanic rocks, tuffs and subvolcanic bodies of dacitic, andesitic and basaltic composition, sandstones and tuffites with interlayers and lenses of limestone. On the basis of conodonts and U-Pb dating of zircon grains the age of this Formation is in the age interval between Late Tremadocian Stage and Early Darriwilian Stage. Differentiated volcanites are associated with ultramafic-gabbro massifs of the Kokkiya Complex of the Late Darriwilian age (U-Pb zirconology). Features of the chemical composition of rocks of the Kentash Formation and the Kokkiya Complex indicate that they formed in suprasubduction settings within the island arc with a thick heterogeneous basement. Tuffaceous-terrigenous deposits are presented by the olistostrome formation, and coarse-grained deposits of the Taldybulak and Kyzylkainar Formations. The formation of olistostrome formation is associated with the over-thrusting of Cambrian melanocratic complexes on terrigenous-carbonate and shale strata of the Upper Precambrian-Cambrian age. Deposits of the Taldybulak and Kyzylkainar Formations accumulated in the back-arc basin and on the island arc slope, made of rocks of the Kentash Formation.

The Yeongweol Group is a Lower Paleozoic mixed carbonate-siliciclastic sequence in the Taebaeksan Basin of Korea, and consists of five lithologic formations: Sambangsan, Machari, Wagok, Mungok, and Yeongheung in ascending order. Sequence stratigraphic interpretation of the group indicates that initial flooding in the Yeongweol area of the Taebaeksan Basin resulted in basal siliciclastic-dominated sequences of the Sambangsan Formation during the Middle Cambrian. The accelerated sea-level rise in the late Middle to early Late Cambrian generated a mixed carbonate-siliciclastic slope or deep ramp sequence of shale, grainstone and breccia intercalations, representing the lower part of the Machari Formation. The continued rise of sea level in the Late Cambrian made substantial accommodation space and activated subtidal carbonate factory, forming carbonate-dominated subtidal platform sequence in the middle and upper parts of the Machari Formation. The overlying Wagok Formation might originally be a ramp carbonate sequence of subtidal ribbon carbonates and marls with conglomerates, deposited during the normal rise of relative sea level in the late Late Cambrian. The formation was affected by unstable dolomitization shortly after the deposition during the relative sea-level fall in the latest Cambrian or earliest Ordovician. Subsequently, it was extensively dolomitized under the deep burial diagenetic condition. During the Early Ordovician (Tremadocian), global transgression (viz. Sauk) was continued, and subtidal ramp deposition was sustained in the Yeongweol platform, forming the Mungok Formation. The formation is overlain by the peritidal carbonates of the Yeongheung Formation, and is stacked by cyclic sedimentation during the Early to Middle Ordovician (Arenigian to Caradocian). The lithologic change from subtidal ramp to peritidal facies is preserved at the uppermost part of the Mungok Formation. The transition between Sauk and Tippecanoe sequences is recognized within the middle part of the Yeongheung Formation as a minimum accommodation zone. The global eustatic fall in the earliest Middle Ordovician and the ensuing rise of relative sea level during the Darrwillian to Caradocian produced broadly-prograding peritidal carbonates of shallowing-upward cyclic successions within the Yeongheung Formation. The reconstructed relative sea-level curve of the Yeongweol platform is very similar to that of the Taebaek platform. This reveals that the Yeongweol platform experienced same tectonic movements with the Taebaek platform, and consequently that both platform sequences might be located in a body or somewhere separately in the margin of the North China platform. The significant differences in lithologic and stratigraphic successions imply that the Yeongweol platform was much far from the Taebaek platform and not associated with the Taebaek platform as a single depositional system. The Yeongweol platform was probably located in relatively open shallow marine environments, whereas the Taebaek platform was a part of the restricted embayments. During the late Paleozoic to early Mesozoic amalgamations of the Korean massifs, the Yeongweol platform was probably pushed against the Taebaek platform by the complex movement, forming fragmented platform sequences of the Taebaeksan Basin.

Three conodont fossil occurrences stratigraphically above and below a rhyolitic tuff in the Lower Ordovician Crow Formation, southeast Yukon, constrain the tuff to the early Tremadocian Rossodus manitouensis Zone and possibly the Rossodus tenuis Zone. U–Pb dates were obtained from zircon from the tuff that was imaged with cathodoluminescence and chemically abraded to reduce the likelihood of dating grains that contain older components or suffered Pb loss, respectively. Six dates from grains with oscillatory parallel zoning are equivalent, with a weighted mean 206Pb/238U date of 491.04 ± 0.13 Ma. These grains are interpreted as being primary volcanic crystals, and the date is therefore taken as the depositional age of the tuff. Four other dates from grains with sector zoning are slightly older, up to 492.0 Ma, and are interpreted as inherited or recycled from earlier volcanics. The currently defined Cambrian–Ordovician boundary is inferred to be below the tuff and separated from it by at least two conodont biostratigraphic zones that are estimated to span at least 2.25 Ma based on the top of the Rhabdinopora flabelliformis parabola graptolite zone being older than the base of the Rossodus tenuis conodont zone. We interpret the evidence in southeast Yukon to suggest that the global Cambrian–Ordovician boundary is older (>493.3 Ma) than previous estimates of ∼488 and 491 Ma based upon legacy 207Pb/206Pb zircon ages.

New drill cores from the largest known impact structure in Europe, the relict of the Siljan meteorite crater, provide new possibilities to reconstruct Early Palaeozoic marine environments and ecosystems, and to document changes in sedimentary facies, sea level and palaeoclimate in Baltoscandia. The impact crater is an important target of the project "Concentric Impact Structures in the Palaeozoic" within the framework of the "Swedish Deep Drilling Program". Two core sections, Mora 001 and Solberga 1, have been analysed. The sedimentary successions of these core sections include strata of late Tremadocian through late Wenlock ages. Our preliminary studies show not only that several of the classical Palaeozoic units of Sweden are represented in the area, but also that other significantly different facies are preserved in the Siljan district. An erosional unconformity representing a substantial hiatus occurs between Middle Ordovician limestone and a Llandovery-Wenlock (Silurian) shale succession in the western part of the Siljan structure and suggests an extended period of uplift and erosion. This may be related to forebulge migration due to flexural loading by the Caledonian thrust sheet to the west. Thus, this part of Sweden, previously regarded as a stable cratonic area, presumably was affected by the Caledonian collision between Baltica and Laurentia.

A new conodont collection from the Alfarcito area of the Tilcara Range, Cordillera Oriental of northwestern Argentina, has been studied. The Santa Rosita Formation exposed in this area consists of the Tilcara, Casa Colorada, Pico de Halcon, Alfarcito, Rupasca and Humacha members, which have a combined total thickness of ca. 1100 m. The sequence is composed of interbedded shales and sandstones, including calcarenites and coquinas, mostly appearing in the upper parts of the units. An abundant fauna of conodonts (ca. 11 000 elements), associated with graptolites and trilobites, was recorded. The biostratigraphic analysis allows for the identification of the Cordylodus intermedius and C. lindstromi sensu lato zones at the base of the Alfarcito Member. The C. angulatus Zone spans the upper part of the latter unit, and the Paltodus deltifer Zone (Paltodus deltifer pristinus and P. deltifer deltifer subzones) is identified in the Rupasca and Humacha members. The new species Acanthodus raqueli, A. humachensis, Utahconus tortibasis, U. scandodiformis, U. purmamarcensis, Variabiloconus crassus, Kallidontus gondwanicus and Acodus primitivus are recorded from the two latter biozones and they are described herein. The genera Acanthodus and Variabiloconus are emended, and a new genus Tilcarodus is created to include T. humahuacensis (Albanesi and Acenolaza). Copyright © 2012 John Wiley & Sons, Ltd.

For many years the earliest record of the class Crinoidea was a single late Tremadocian genus. In the past decade, five crinoid genera were described from the early and middle Tremadocian, near the base of the Ordovician. Together these six genera represent a diverse assemblage with all but one expressing existing subclass apomorphies. Two of the recently described genera were initially assigned to their own order (plesion) Protocrinoida but not to a subclass. Here they are placed in the camerates based on apomorphies of the tegmen complex. Protocrinoids exhibit plesiomorphies unlike typical camerates. Two genera group with cladids, one expressing dendrocrinine apomorphies and the other cyathocrinine. One genus is placed within disparids, with iocrinid apomorphies.Based on its ancient age and trait mosaic, the protocrinoid Titanocrinus is designated as outgroup in a phylogenetic analysis using all other Early Ordovician and select Middle Ordovician taxa as an ingroup. Character compilation and phylogenetic analysis posit early class-level plesiomorphies inherited from an unknown ancestry but lost during subsequent crinoid evolution. Class-level apomorphies also emerge, some of which were subsequently lost and others retained. Results are generally robust and consistent with earlier subdivisions of the class, but supporting lower rank reorganizations. Strong support for the camerate branch low in the crinoid tree mirrors findings of earlier workers. Cladids branch from a series of intermediate nodes and disparids nest highest. Branching of disparids from cladids could be homoplastic.

The discovery of magnetic spherules in acid-insoluble residues from conodont samples encouraged a systematic search for Ordovician micrometeorites from northwestern Argentina. Some 220 melted micrometeorites were recovered from the magnetic fraction of six samples (total rock weight: 23 kg) from the Cordillera Oriental (Santa Rosita Formation) and 17 from five samples (total rock weight: 8.9 kg) from the Argentine Precordillera (Las Aguaditas, Gualcamayo and Las Vacas formations). The specimens resemble I-type cosmic spherules, in their chemistry and distinct dendritic and polygonal crystalline structures. They represent a flux of micrometeorites several orders of magnitude greater than present. The wide differences in spherule abundance between the Precordillera and the Cordillera Oriental samples could reflect uncertainties in the sedimentary rates or temporal variations in the flux of extraterrestrial matter to Earth. The micrometeorite-bearing formations span the late Tremadocian to the late Darriliwian (~480–460 Ma), which is consistent with a period of elevated flux of extraterrestrial material, as recorded several thousand kilometres away from coeval horizons in Scotland, Sweden and central China. Copyright © 2012 John Wiley & Sons, Ltd.

Ordovician reefs are located in the South China, Tarim, and North China blocks, in low-latitude epicontinental marine regions and mostly consist of large-scale carbonate platforms. During the Paleozoic, faunal radiation reef biota diverged and thrived in diverse paleogeographic settings. Algal reefs of the Early Ordovician, Calathium-lithistid sponge-algal reefs of the late Early Ordovician to early Middle Ordovician, and coral-stromatoporoid-algal reefs of the early Late Ordovician, indicate change from Cambrian to Paleozoic biota. Coral-stromatoporoid-algal reefs were the basic communities after 100 Ma. The macroevolution of biotic structures generally shows increased complexity; the evolution of China’s reef biota parallels that worldwide. Important aspects are: (1) The Calathium-algal reefs from the early Tremadocian Nantzinkuan Formation, Zhangjiajie, western Hunan are the pioneer reefs, and the Darriwillian Yijianfang Formation, Bachu are the relic reefs. (2) The bryozoan-dominated reefs of the late Tremadocian Fenhsiang Formation, Middle Yangtze Platform are unique. (3) The early coral-stromatoporoid-algal reefs are highly restricted in China. (4) The algal reefs from the latest Katian on the western margin of the Yangtze Platform, represent an abnormal reef-building environment during the initial stages of Gondwanan glaciations.

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14–23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan (Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three-dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal-dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal-dominated reef evolution and the ensuing development of reefs during the Middle–Late Ordovician. □Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef.

The Penobscot arc system of the northeastern Appalachians is an Early Cambrian to early Tremadocian (ca. 514- 485 Ma) ensialic to ensimatic arc-back-arc complex that developed along the margin of the peri-Gondwanan microcontinent Ganderia. Remnants of this Paleozoic arc system are best preserved in the Exploits Subzone of central Newfoundland. Cor- relative rocks in southern New Brunswick are thought to occur in the ca. 514 Ma Mosquito Lake Road Formation of the Ellsworth Group and ca. 497-493 Ma Annidale Group; however in the past, the work that has been conducted on the latter has been of a preliminary nature. New data bearing on the age and tectonic setting of the Annidale Group provides more conclusive evidence for this correlation. The Annidale Group contains subalkaline, tholeiitic to transitional, basalts to basal- tic andesites, picritic tuffs and calc-alkaline to tholeiitic felsic dome complexes that have geochemical signatures consistent with suprasubduction zone magmatism that was likely generated in a back-arc basin. New U-Pb ages establish that the Late Cambrian to Early Tremadocian Annidale Group and adjacent ca. 541 Ma volcanic rocks of the Belleisle Bay Group in the New River belt were affected by a period of younger magmatism ranging in age from ca. 479-467 Ma. This provides im- portant constraints on the timing of tectonism in the area. A ca. 479 Ma age for the Stewarton Gabbro that stitches the faulted contact between the Annidale and Belleisle Bay groups, demonstrates that structural interleaving and juxtaposition occurred during early Tremadocian time, which closely coincides with the timing of obduction of Penobscottian back-arc ophiolites onto the Ganderian margin in Newfoundland. Resume : Le systeme d'arc Penobscot du nord-est des Appalaches est un complexe d'arc-d'arriere-arc ensialique a ensima- tique datant du Cambrien precoce au Tremadocien precoce (~514-485 Ma) qui s'est developpe le long de la bordure peri- gondwannienne du microcontinent Ganderia. Des lambeaux de ce systeme d'arc paleozoique sont le mieux conserves dans la sous-zone Exploits du centre de Terre-Neuve. Des roches correlatives dans le sud du Nouveau-Brunswick seraient presen- tes dans la Formation de Mosquito Lake Road (~514 Ma) du Groupe d'Ellsworth et dans le Groupe d'Annidale (~497-493 Ma); toutefois, par le passe, le travail effectue sur ce dernier groupe n'a ete que preliminaire. De nouvelles donnees sur l'âge et l'environnement tectonique du Groupe d'Annidale fournissent des evidences plus concluantes de cette correlation. Le Groupe d'Annidale contient des basaltes a des andesites basaltiques, subalcalins, tholeiitiques a intermediaires, des tufs picritiques et des complexes de domes felsiques, calco-alcalins a tholeiitiques, possedant des signatures geochimiques qui concordent avec un magmatisme de zone de suprasubduction probablement generee dans un bassin d'arriere-arc. De nou- veaux âges U-Pb ont etabli que le Groupe d'Annidale, Cambrien tardif a Tremadocien precoce, et les roches volcaniques ad- jacentes du Groupe de Belleisle Bay (~541 Ma) dans la ceinture de New River ont ete affectes par une periode de magmatisme plus jeune, datant d'environ 479 a 467 Ma. Ces donnees fournissent des contraintes importantes sur le moment du tectonisme dans la region. Un âge d'environ 479 Ma pour le gabbro de Stewarton, qui reunit le contact de faille entre les groupes d'Annidale et de Belleisle Bay, demontre que l'imbrication et la juxtaposition structurales ont eu lieu au debut du Tremadocien, ce qui coincide de pres avec le moment de l'obduction des ophiolites d'arriere-arc de Penobscot par-dessus la bordure de Ganderia a Terre-Neuve. (Traduit par la Redaction)

New Tremadocian ostracod material from the Alborz Mountains of Iran confirms the early and widespread occurrence of the Ordovician genus Nanopsis, and the apparently simultaneous first appearance of ostracods in the fossil record at the level of the P. deltifer conodont biozone (485.5 Ma) from China to Argentina. Nanopsis pairidaeza sp. nov. adds to the pool of species diversity for the Early Ordovician, though documented Tremadocian ostracod generic diversity remains low, with only four genera. The presence of Early Ordovician ostracods in Alborz, their occurrence elsewhere in palaeocontinental Gondwana, Baltica and China coupled to their marked absence from the Tremadocian of Laurentia and Siberia, supports the notion of the earliest occurrence of ostracods centred on Gondwana/Baltica.

Cambrian-Ordovician sedimentary sequences crop out extensively in the area surrounding the Sarydzhaz River, a remote mountainous region situated in the eastern part of Kyrgyzstan. These sequences, composed essentially of fine siliciclastic lithologies, were deposited on a passive margin of the peri-Gondwanan Karatau-Naryn microplate. Palaeontological constraints for the age of these sequences are rare. Recent efforts of geological mapping in the area discovered reasonably well-preserved radiolarian and conodont faunas. The occurrence of conodonts was mentioned previously, but no taxonomic details were ever reported. Two conodont assemblages are identified from the Oldzhobai Formation; the first is dominated by Paracordylodus gracilis , which can be correlated with the upper Tremadocian to lower Floian; the second assemblage is more diverse and characterized by Prioniodus elegans , suggesting a mid Floian age. This is the first discovery of Ordovician Radiolaria from Kyrgyzstan. In spite of its rather moderately good to poor preservation, the fauna is interesting in many respects, especially due to the presence of a new radiolarian species ( Inanigutta (?) kyrgyza nov. sp.). The latter is easily identifiable by the distinctive pore pattern of its cortical shell and has therefore the potential to become in the future a biostratigraphic marker species.

The ostracod fauna from the Floian (Lower Ordovician) strata of the Cordillera Oriental, Argentina (Acoite Formation) are documented. One new genus Acoitella and four species are recognized, two of which are new (Nanopsis victoria sp. nov. and Conchoprimitia frequens sp. nov.). The diversity of the Early Ordovician ostracod faunas of the Central Andean Basin is evaluated. Compared with other regions, the ostracod diversity, at generic and specific level, of the Cordillera Oriental was comparatively high during the Tremadocian (nine species recorded) and comparatively low during the Floian (four species recorded). The taxonomic composition of the fauna is similar during the entire Early Ordovician of the Cordillera Oriental, where it displays a high percentage of soanellids. The Floian assemblages are characterized by the dominance of the eridostracan C. frequens sp. nov. with a high percentage of nondimorphic palaeocopids: Nanopsis and two genera of the Soanellidae family (Saltite and Acoitella gen nov.). An ostracod shell bed is described and interpreted to be a parautochthonous assemblage, as a result of transport within the same habitat. The composition of the fauna, with the presence of Saltite and Nanopsis, shows significant affinities with East Gondwana. Copyright © 2011 John Wiley & Sons, Ltd.

Slow subsidence and tectonic quiescence along the New York Promontory margin of Laurentia mean that the carbonate-dominated Tribes Hill and overlying Rochdale formations serve as proxies for the magnitude and timing of Tremadocian eustatic changes. Both formations are unconformity-bound, deepening–shoaling, depositional sequences that double in thickness from the craton into the parautochthonous, western Appalachian Mountains. A consistent, ‘layer cake’ succession of member-level units of the formations persists through this region. The Tribes Hill Formation (late early Tremadocian, late Skullrockian, late Fauna B–Rossodus manitouensisChron) unconformably overlies the terminal Cambrian Little Falls Formation as the lowest Ordovician unit on the New York Promontory. It was deposited during the strong early Tremadocian, or Stonehenge, transgression that inundated Laurentia, brought dysoxic/anoxic (d/a) slope water onto the shelf and led to deposition of the Schaghticoke d/a interval (black mudstone and ‘ribbon limestone’) on the Laurentian continental slope. The uniform lithofacies succession of the Tribes Hill includes a lower sand-rich member; a middle, dark grey to black mudstone that records d/a in eastern exposures; and an upper, shoaling-up carbonate highstand facies. A widespread (12000+ km2) thrombolitic interval in the highstand carbonate suggests the New York Promontory was rimmed by thrombolites during deposition of the Tribes Hill. Offlap and erosion of the Tribes Hill was followed by the relatively feeble sea-level rise of the Rochdale transgression (new) in Laurentia, and deposition of the Rochdale Formation. The Rochdale transgression, correlated with theKierograptusDrowning Interval in Baltica, marks a eustatic rise. The Rochdale Formation represents a short Early Ordovician interval (early late Tremadocian, middle–late Stairsian,Macerodus dianaeChron). It correlates with a depositional sequence that forms the middle Boat Harbour Formation in west Newfoundland and with the Rte 299 d/a interval on the east Laurentian slope. The Rochdale has a lower carbonate with abundant quartz silt (Comstock Member, new) and an upper, thrombolitic (Hawk Member, new) high-stand facies. Tribes Hill and Rochdale faunas are mollusc-rich, generally trilobite-poor, and have low diversity, Laurentian faunal province conodonts.Ulrichodina rutnikaLanding n. sp. is rare in Rochdale conodont assemblages. Trilobites are also low in diversity, but locally form coquinas in the middle Tribes Hill. The poorly preserved Rochdale trilobites include the bathyuridRandaynia, at least two hystricurid species andLeiostegium.

The Chesley Drive Group, an Upper Cambrian-Lower Ordovician mudstone-dominated unit, is part of the Ediacaran–Ordovician cover sequence on the North American part of the Avalon microcontinent. The upper Chesley Drive Group on McLeod Brook, Cape Breton Island (previously “McLeod Brook Formation”), has two lithofacies-specific Tremadocian biotas. An older low-diversity benthic assemblage (shallow burrowers,Bathysiphon, phosphatic brachiopods, asaphid trilobites) is in lower upper Tremadocian green-gray mudstone. This wave-influenced, slightly dysoxic facies hasBathysiphon–brachiopod shell lags in ripple troughs. The upper fauna (ca. 483 +/- 1 Ma) is in dysoxic-anoxic (d-a), unburrowed, dark gray-black, upper upper (but not uppermost) Tremadocian mudstone with a “mass kill” of the olenidPeltocare rotundifrons(Matthew)—a provincial trilobite in Avalonian North America that likely tolerated low oxygen bottom waters.Scandodus avalonensisLanding n. sp. andLagenochitinaaff.conifundus(Poumot), probable nektic elements and the first upper Tremadocian conodont and chitinozoan reported from Avalon, occur in diagenetic calcareous nodules in the dark gray-black mudstone. An upper Tremadocian transition from lower greenish to upper black mudstone is not exposed on McLeod Brook, but is comparable to a coeval green-black mudstone transition in Avalonian England. The successions suggest that late late Tremadocian (probable Baltic Hunnebergian Age) sea level was higher in Avalon than is suggested from successions on other paleocontinents. The Tremadocian sea-level history of Avalon was a shoaling-deepening-shoaling sequence from d-a black mudstone (lower Tremadocian), to dysoxic green mudstone (lower upper Tremadocian), and back to black mudstone (upper upper Tremadocian).ScandodusLindström is emended, with the early speciesS. avalonensisLanding n. sp. assigned to the emended Family Protopanderodontidae.TriangulodusVan Wamel is considered a junior synonym ofScandodus. Peltocare rotundifronsis emended on the basis of complete specimens.

About 500 samples from 11 Ordovician sections in South China have been analysed for their δ 13 C carb composition. Four sections are located in the Yangtze platform region, the remaining seven sections in the Jiangnan slope region. The sections span more or less the entire Ordovician, but the sample resolution in its lower part (Tremadocian to Dapingian) is lower than in its upper part (Darriwilian to Hirnantian). Overall, the data show a good correlation with the published global isotope curve. At the Cambrian–Ordovician boundary positive values are observed. In the succeeding Tremadocian the values decrease and remain negative into the early Floian. In the late Floian, the values increase to slightly positive. The correlation of Dapingian rocks between the Yangtze and the Jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the Yangtze section. In the Darriwilian a small positive excursion is observed in the Yangtze platform area, however, it is missing in the Jiangnan slope area. This excursion probably correlates with the mid-Darriwilian excursion (MDICE) reported from Baltoscandia. Both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the Shihtzupu Formation and the Pagoda Formation, i.e. most of the Sandbian is probably not represented in the Upper Yangtze region. The earliest Katian is characterised by a pronounced positive excursion correlating with the well-known global Guttenberg excursion (GICE). In the late Katian at least one additional positive excursion was determined. The precise biostratigraphy, however, is not clear, and therefore it is not known which of the known four to five remaining Katian δ 13 C excursions identified in Baltica correlate(s) with the one(s) observed in the present study, and further biostratigraphic study is required. The lower part of the Hirnantian excursion (HICE) is probably not preserved, with only small remnants of the HICE observed near the base of the Kuanyinchiao Bed.

LATE TREMADOCIAN (ORDOVICIAN) CONODONTS AND GRAPTOLITES FROM THE SIERRA DE ZENTA, CORDILLERA ORIENTAL OF JUJUY, ARGENTINA. A thick heterolithic Ordovician succession lies exposed in the Zenta Range of the Cordillera Oriental, Jujuy Province, Argentina. It is mostly siliciclastic with subordinated calcareous concretions, coquinas and calcarenites, and bears a significant conodont and graptolite fauna. The sampled localities are situated on the road running from Abra de Zenta to Santa Ana, within a wide anticline structure. Exposures of gray shales and coquinas near Abra de Santa Ana, yielded a low diversity conodont fauna that includes Acodus apex n. sp., Drepanoistodus chucaleznensis Albanesi and Acenolaza, and Drepanoistodus costatus (Abaimova), which are referred to the lower part of the Acodus deltatus — Paroistodus proteus Zone. The diagnosis of the conodont genus Acodus is emended. The A. murrayi Zone is suggested by a graptolite assemblage including Araneograptus murrayi (J. Hall), Kiaerogr...

The Ordovician is a period when novel reef ecosystems appeared along with new reef constructors and skeletal-dominated reefs. The Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area in South China contains the oldest known bryozoan reefs (lithistid sponge–bryozoan and bryozoan–pelmatozoan reefs) alongside lithistid sponge–microbial reefs. The latter are characterized by the dominance of microbialites that encrusted and bound the frame-building sponges and inter-sponge sediments. In contrast, the lithistid sponge–bryozoan and bryozoan–pelmatozoan reefs are generally characterized by bryozoans that encrusted the frame-building sponges or pelmatozoans and grew to fill the inter-frameworks. These sponges and pelmatozoans did not construct the rigid frameworks unaided; their association with bryozoans enabled the development of small skeletal-dominated reefs with rigid frameworks. Skeletal-dominated reefs, for which frame-constructing and encrusting roles are conspicuous, were largely unknown before the Early Ordovician. The appearance of skeletal organisms (specifically colonial, encrusting bryozoans) enabled the development of skeletal-dominated reefs, which were pioneers in the rise of Middle–Late Ordovician reefs. The Early Ordovician establishment of skeletal-dominated reefs at the earliest stages of the Great Ordovician Biodiversification Event would have created novel niches and biological interactions that further promoted the evolution of reef-building and -dwelling organisms, as well as ensuing reef ecosystems.

Victoria is emerging as the region where members of the Ordovician graptolite subfamily Kinnegraptinae, revised herein, reached its highest diversity, with 16 or 17 species present, grouped in the four genera Paradelograptus Erdtmann et al. (1987), Lignigraptus n. gen., Wuninograptus Ni, 1981 and Psenograptus n. gen. The biostratigraphic range of the subfamily extends over much of the Early and Middle Ordovician, from the late Tremadocian Aorograptus victoriae Biozone to the late Darriwilian Archiclimacograptus riddellensis Biozone. Species described are Paradelograptus antiquus (T.S. Hall, 1899a), P. pritchardi (T.S. Hall, 1899a), P. bulmani (Thomas, 1973), P. maletzi n. sp., P. orthae n. sp., P. cayleyi n. sp., Lignigraptus chapmani (Keble & Harris, 1934), L. sedecimus (Harris & Thomas, 1938a), L. ramulosus (Harris & Thomas, 1938a), L. erdtmanni (Rickards & Chapman, 1991), L. gnomus n. sp., L. absidatus n. sp., L. daangean n. sp., L. diabolus n. sp., Wuninograptus quadribrachiatus Ni, 1981, Psenograptus costermansin. sp., Psenograptus sp. A and Psenograptus sp. B. The term glossa is proposed for the elongate apparatuses that adorn thecal apertures of Kinnegraptus, Lignigraptus and Wuninograptus.

Radiolarians have been recovered from lowermost Arenigian rocks of the Cow Head Group in Gros Morne National Park, Newfoundland. Two new faunal assemblages include eight families, 13 genera, and 25 species. Among these, the family Neoaspiculumidae, the genusNeoaspiculum, and 11 species,Beothuka aitchisoni, B. grosmornensis, B. stougei, B.?stellata, Neoaspiculum cancellium, N. headense, N. transformum, N. laxum, N.?amplum, Proventocitum cylindricum, andP. piriforme, are new.This study elucidates the reason for the significant difference in species composition between pre-Arenigian and Arenigian radiolarian faunas. This difference does not appear to be due to mass extinction, but rather to phylogenetic evolution: most radiolarian families that flourished during pre-Arenig time were gradually but significantly reduced by the earliest Arenig. Characteristic features of the earliest Arenig assemblages that distinguish them from their Tremadocian predecessors are 1) the development of a distinctive skeletal constructional element referred to as “bandage” structure that evolved through modification of a mesh of thin bars and 2) the appearance of multiple concentric shells including a proloculus (or a microsphere), which developed from a primitive three-dimensionally interwoven meshwork or spongy shell wall. These forms, represented by beothukids, antygoporids, and inaniguttids, are rare but they appear to originate in the earliest Arenig. Transitional characteristics among those forms are developed in the Neoaspiculumidae, which flourished during the earliest Arenig.The precise biostratigraphic age of one of the assemblages was determined with the recovery of the index condontPrioniodus adamiStouge and Bagnoli, 1988 from strata belonging to theTetragraptus approximatusGraptolite Zone, which is at the base of the Arenigian.

The Meguma Terrane of Nova Scotia and the Harlech Dome of North Wales preserve similar sedimentary successions of Cambrian age. Both successions comprise a thick succession of early Cambrian sandstone turbidites, overlain by early to middle Cambrian alternating mud-rich and sand-rich units in which manganese is concentrated in two stratigraphic intervals. Above these, both successions comprise anoxic, organic-rich turbidites, shallowing upward into paler, more bioturbated Tremadocian mudstone with Rhabdinopora . Within the limited constraints of the available biostratigraphic and geochronological data, major changes in environment occurred synchronously in the two successions. Both successions show much greater similarity to each other than to adjacent successions on ‘Avalonia9. A detrital zircon analysis from the Rhinog Formation, low in the Harlech Dome succession, reveals distinct clusters of ages around 537 Ma and 2.0–2.1 Ga. A close similarity to analyses from the Meguma Terrane suggests proximity between the two terranes on the margin of Gondwana during the Cambrian Period. We suggest the term Megumia for the palaeogeographical domain that included the two successions, which was dispersed during subsequent Appalachian and Caledonian movements. These observations suggest that Megumia may have separated terranes previously regarded as parts of Avalonia. Supplementary material: U/Pb detrital zircon analytical data are available at http://www.geolsoc.org.uk/SUP18431.