Ordovician Succession Research Articles

Stratigraphic restriction of stromatolites in a Middle and Upper Ordovician foreland-platform succession (Ottawa Embayment, eastern Ontario)

Stromatolites are abundant and widely distributed within two narrow stratigraphic intervals in Middle (Darriwilian) and Upper (lower Turinian) Ordovician strata of the Laurentian foreland interior in the Ottawa Embayment, eastern Ontario. These lithostratigraphic markers coincide with rapid, tectonically driven flooding of the foreland interior and may identify an opportunistic microbial response to nutrient loading with shallow (peritidal, subtidal) marine reworking of terrestrial or nutrient-rich coastal systems. The remaining (Chatfieldian–Edenian) foreland-platform succession represents deeper-water deposition in response to elevated subsidence rates along the Laurentian margin. Stromatolites are absent in this higher-energy setting, but microbial calcite is preserved as coccoid-like microencrustations on skeletal debris. Stromatolites of Darriwilian age are dolomitic, occur in the Carillon Formation, and are part of a regional (200+ km) onlap of peritidal sediment during onset of Taconic orogenesis. Stratiform to large (2 m diameter) low-relief domal stromatolites contain rhythmic laminations of inclusion-rich and -poor dolomicrospar grouped by Fe-oxide-stained erosional surfaces. Domal forms also contain thrombolitic microstructure. Patterns of lamination and stable (C, O) isotopes suggest a balance between abiotic and microbial carbonate production, likely influenced by water depth and temperature. Stromatolites of Turinian age are calcitic and form a regional (80+ km) thin (<8 m) subtidal biostromal unit in the lowermost Pamelia Formation. Their occurrence defines an abrupt vertical transition from initial intrabasinal transgressive subtidal phosphatic siliciclastics and carbonates to an interbasinal stratigraphy of peritidal lime mudstone. Arrhythmic laminations of microbial peloid packstone, with possible eukaryote alga moulds, and locally evaporitic spongiostromate microstructure identify salinity and energy as primary depositional controls. The stromatolite–?eukaryotic association is similar to some modern subtidal microstructures and is part of the reef-community diversification in the Ordovician.

Machaeridians from the Middle and Upper Ordovician of the Argentine Precordillera

The machaeridians are marine Palaeozoic annelids, which developed a dorsal skeleton composed of calcite sclerites, achieving a world‐wide distribution from the Early Ordovician to the Middle Permian. The absence of records from this group is notable in Argentina in spite of intense studies of Palaeozoic rocks. This fact can be explained by biases in sampling or because of preservation problems. Machaeridian sclerites of the families Plumulitidae and Turrilepadidae collected in Middle and Upper Ordovician rocks from the San Juan Precordillera, Argentina, are described here for the first time. Plumulites sp. is recorded in early Darriwilian strata from the Gualcamayo Formation exposed in the western flank of the Cerro La Chilca locality, and from the Las Aguaditas Formation in the Quebrada de Las Aguaditas section. Plumulitid and turrilepadid sclerites are described from the upper member of the Los Azules Formation (late Sandbian) in the Cerro Viejo de Huaco area. The material of the Los Azules Formation is the first record of turrilepadids in Sandbian rocks, which are scarce in Ordovician successions. The referred strata bear pelagic, benthic and nektobenthic faunal assemblages, constituting a similar taphocoenosis preserved in shales and calcareous silty shales related to transgressive events. The record of machaeridians expands our knowledge of the Ordovician biotas from Argentina and provides new information on the palaeobiogeographical distribution of this Palaeozoic annelid group. Copyright © 2012 John Wiley & Sons, Ltd.

Distribution and palaeoecology of Ordovician bivalves and gastropods from Girvan, SW Scotland

ABSTRACTMolluscs from the Middle and Upper Ordovician succession of Girvan, SW Scotland are common and diverse in some localities. The mollusc fauna consists mainly of gastropods, bivalves and various univalved molluscs (mimospirids and tergomyans), along with scarcer polyplacophorans, rostroconchs and cephalopods. The present study gives an overview of the distribution and palaeoecology of bivalves, gastropods and univalved molluscs and compares them with mollusc faunas worldwide. Gastropods, mimospirids and tergomyans are present from the Darriwilian (mid Llanvirn) onwards in both siliciclastic and carbonate facies, and increase in diversity through the Sandbian (Caradoc) and into the Katian (Ashgill). Bivalves first appeared in Girvan in the late Darriwilian (early Caradoc) in deep water siliciclastic facies; where they continued to be more abundant and diverse than in equivalent carbonate facies. Molluscs are initially Laurentian in aspect, though peri-Gondwanan faunal elements occur, particularly during the Sandbian. The pattern of bivalve and gastropod diversity found in the Ordovician of Girvan generally follows that of the known global diversity for these groups.

Palaeogeography and palaeoecology of early Floian (Early Ordovician) cephalopods from the Upper Fezouata Formation, Anti-Atlas, Morocco

Abstract. In the central Anti-Atlas (Morocco), the Early Ordovician succession consists of about 1000 m of fossiliferous argillites and siltstones. The Upper Fezouata Formation (Floian) contains a comparatively rich and abundant cephalopod association. A small collection of these cephalopods is described herein for the first time. The cephalopods are interpreted as autochthonous or parautochthonous, representing a fauna, which originally lived nektobenthically in the open water above the sediments or related to the sea bottom. The cephalopod associations of the Upper Fezouata Formation are similar to other contemporaneous assemblages known from higher palaeolatitudes and associated with deeper depositional settings and in siliciclastically dominated deposits. They are composed almost exclusively of slender orthocones, in this case predominantly of Destombesiceras zagorense n. gen., n. sp., which is interpreted as an early discosorid. Bathmoceras australe Teichert, 1939 and Bathmoceras taichoutense n. sp. from the Upper Fezouata Formation are at present the earliest unambiguous occurrences of bathmocerid cephalopods. Epizoans on the shell of a specimen of Rioceras are the earliest evidence of bryozoans growing as potential hitchhikers on cephalopod shells, indicating an early exploitation of a pseudoplanktonic lifestyle in this phylum. doi: 10.1002/mmng.201200004

Palaeogeography and palaeoecology of early Floian (Early Ordovician) cephalopods from the Upper Fezouata Formation, Anti-Atlas, Morocco

In the central Anti-Atlas (Morocco), the Early Ordovician succession consists of about 1000 m of fossiliferous argillites and siltstones. The Upper Fezouata Formation (Floian) contains a comparatively rich and abundant cephalopod association. A small collection of these cephalopods is described herein for the first time. The cephalopods are interpreted as autochthonous or parautochthonous, representing a fauna, which originally lived nektobenthically in the open water above the sediments or related to the sea bottom. The cephalopod associations of the Upper Fezouata Formation are similar to other contemporaneous assemblages known from higher palaeolatitudes and associated with deeper depositional settings and in siliciclastically dominated deposits. They are composed almost exclusively of slender orthocones, in this case predominantly of <i>Destombesiceras zagorense</i> n. gen., n. sp., which is interpreted as an early discosorid. <i>Bathmoceras australe</i> Teichert, 1939 and <i>Bathmoceras taichoutense</i> n. sp. from the Upper Fezouata Formation are at present the earliest unambiguous occurrences of bathmocerid cephalopods. Epizoans on the shell of a specimen of <i>Rioceras</i> are the earliest evidence of bryozoans growing as potential hitchhikers on cephalopod shells, indicating an early exploitation of a pseudoplanktonic lifestyle in this phylum. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201200004" target="_blank">10.1002/mmng.201200004</a>

Darriwilian species of Histiodella (Conodonta) in the Argentine Precordillera

Mestre, A. & Heredia, S., iFirst article. Darriwilian species of Histiodella (Conodonta) in the Argentine Precordillera. Alcheringa, 141–150. ISSN 0311-5518. The Middle Ordovician successions in the Central Precordillera of Argentina are characterized by carbonate and fine mixed carbonate/siliciclastic deposits. Two middle Darriwilian sections spanning the Eoplacognathus pseudoplanus to Eoplacognathus suecicus Zones were sampled for conodonts, among which were found species of Histiodella. We revised the biostratigraphical distribution of these species in the Middle Ordovician of the Precordillera. This study confirms that the Darriwilian species of Histiodella present in the Argentine Precordillera have a similar distribution to those of equivalent age in Newfoundland, South China and the Baltic region. On the other hand, the overlap in the ranges of H. holodentata and H. kristinae seems to be restricted to a fairly short interval in the upper part of the E. pseudoplanus Zone. We also propose that the FAD of H. kristinae Stouge is accurately positioned in the upper part of the E. pseudoplanus Zone; thus this species should not be used to define the base of the E. suecicus Zone in the Ordovician biozonation of the Argentine Precordillera. Ana Mestre [amestre@unsj.edu.ar] and Susana Heredia [sheredia@unsj.edu.ar], Conicet—Instituto de Investigaciones Mineras, Facultad de Ingeniería, Universidad Nacional de San Juan. Av. Libertador y Urquiza (5400) San Juan, Argentina. Received 16.2.2011, revised 27.4.2011, accepted 13.5.2011.

Rifting and Arc-Related Early Paleozoic Volcanism along the North Gondwana Margin: Geochemical and Geological Evidence from Sardinia (Italy)

Three series of volcanic rocks accumulated during the Cambrian to Silurian in the metasediment-dominated Variscan basement of Sardinia. They provide a record of the changing geodynamic setting of the North Gondwana margin between Upper Cambrian and earliest Silurian. A continuous Upper Cambrian–Lower Ordovician succession of felsic submarine and subaerial rocks, dominantly transitional alkaline in character (ca. 492–480 Ma), is present throughout the Variscan nappes. Trace element data, together with Nd isotope data that point to a depleted mantle source, indicate an ensialic environment. A Middle Ordovician (ca. 465 Ma) calc-alkaline bimodal suite, restricted to the external Variscan nappes, overlies the Sardic Unconformity. Negative ϵNdi values (−3.03 to −5.75) indicate that the suite is a product of arc volcanism from a variably enriched mantle. A Late Ordovician–Early Silurian (ca. 440 Ma) volcano-sedimentary cycle consists of an alkalic mafic suite in a post-Caradocian transgressive sequence. Feeder dykes cut the pre-Sardic sequence. The alkali basalts are enriched in Nb-Ta and have Zr/Nb ratios in the range 4.20–30.90 (typical of a rift environment) and positive ϵNdi values that indicate a depleted mantle source. Trachyandesite lavas have trace element contents characteristic of within-plate basalt differentiates, with evidence of minor crustal contamination.

Ediacaran to Lower Ordovician age for rocks ascribed to the Schist–Graywacke Complex (Iberian Massif, Spain): Evidence from detrital zircon SHRIMP U–Pb geochronology

New SHRIMP U–Pb ages of detrital zircon obtained from eight samples of Neoproterozoic to Lower Paleozoic graywackes, schists, microconglomerates and shales provide the maximum depositional age and a new zircon age pattern for the Schist–Graywacke Complex (SGC) from the Iberian Massif (SW Europe). The ages of the youngest zircon grains found in four samples provide a maximum depositional age of latest Ediacaran–Lower Cambrian for the complex. Lower-Middle Cambrian fossiliferous formations on top of the lithologies correctly attributed to the SGC constrain its minimum depositional age. Unexpectedly, two samples attributed to the SGC yielded Cambro-Ordovician zircon populations. These must belong to younger Lower Ordovician sedimentary successions that, up to now, have not been differentiated from those of the SGC. The new age patterns are mainly composed of Neoproterozoic (73%) and Paleoproterozoic (15%) ages, with minor Neoarchean (7%), Mesoarchean (2%), Mesoproterozoic (3%) and Cambrian (1%) ages for the latest Ediacaran–Lower Cambrian successions, and Neoproterozoic (46%) and Cambro-Ordovician (46%) ages, with minor Neoarchean (1%), Mesoarchean (0.5%), Paleoproterozoic (6%), Mesoproterozoic (0.5%) and Carboniferous (1%) ages for the Lower Ordovician successions. The presence of Mesoproterozoic zircon points to the Saharan Metacraton as a contributing source for these sediments. Cadomian granitoids could have been a local Neoproterozoic source. The Cambro-Ordovician zircons may also indicate that Cambro-Ordovician magmatism contributed as a source. Cambro-Ordovician volcanism, the most probable source of the Cambro-Ordovician zircons, would have been coeval with the deposition of the Lower Ordovician successions.

The Amadeus Basin, central Australia

The Amadeus Basin of central Australia has a depositional history spanning the Neoproterozoic to the Devonian/Carboniferous. It was initiated as part of the Neoproterozoic Centralian Superbasin, which formed in an intracratonic setting related to the break up of Rodinia. Sedimentation continued until the 580-540 Ma Petermann Orogeny, coinciding with the assembly of Gondwana, which resulted in the fragmentation of the superbasin into separate intracratonic basins. The Petermann Orogeny was focused in the Musgrave Province and the southern part of the Amadeus Basin, and involved significant N-directed shortening on large-scale structures that involved both the basement and the overlying Neoproterozoic sedimentary rocks. It significantly transformed the basin architecture, with the development of major basin features that controlled subsequent sedimentation. Deposition of Paleozoic successions was largely concentrated in sub-basins and troughs in the N of the basin, where up to 14 km is preserved. Minor events or uplifts punctuated this depositional history and account for local disconformities and absent sections. The 450-300 Ma Alice Springs Orogeny was a multi-phase, intracratonic event concentrated in the Arunta Region and the northern part of the Amadeus Basin. Like the earlier Petermann Orogeny, the Alice Springs Orogeny involved both basement and basin sedimentary rocks, but with overall S-directed movement. Synorogenic sedimentation accompanied Mid-Late Devonian uplift, with Late Devonian-Carboniferous basin inversion terminating sedimentation, and folding the youngest successions. The Amadeus Basin has known reserves of U, minor historic and recent Au production, and is prospective for base metals, especially Cu, and phosphate. The Ordovician succession supports commercial gas production, and the Neoproterozoic succession is considered prospective for oil and gas.

On the Upper Ordovician unconformity in the Pyrenees: New evidence from the La Cerdanya area

In recent years, contradictory reports about whether or not an unconformity exists at the base of the Upper Ordovician succession of the Pyrenees have been made. In the Cerdanya area (Central Pyrenees), good outcrop evidence for this unconformity is displayed at the base of the Rabassa conglomerates. In this area, the Upper Ordovician rocks overlie a tilted Cambro-Ordovician sequence, displaying an angular unconformity and indicating a break in the stratigraphic series. Moreover, the existence of such an unconformity is supported by the distribution of Variscan minor structures, suggesting that the Cambro-Ordovician and the Upper Ordovician strata initially had different orientations before the main Variscan folding.

Ordovician conodont diversity in the northern Baltic

The diversity data presented in this paper are based on recently revised collections of conodonts from outcrops (northern Estonia) and core sections of Estonia and western and northern Latvia. Based on variations in the abundance of taxa, four intervals with different general trends in diversity changes can be recognized in the Ordovician part of the succession: (1) the proavus-crassus zones and (2) crassus-anserinus zones, both intervals forming quite distinct diversity cycles; (3) the variabilis- ventilatus zones, characterized in general by stable diversity values, and (4) the ventilatus Zone-the topmost Ordovician, with a steady increase in diversity up to the ordovicicus Zone, followed by a decline during the End-Ordovician Extinction Event. Diversity was lowest in the earliest and latest Ordovician but reached maximum values at the end of the Early Ordovician radiation of conodonts, in the middle and upper Darriwilian, and just before the start of the End-Ordovician Extinction Event. Four supersequences (transgressive-regressive cycles) are proposed here for the northern Baltic Ordovician succession. The diversity changes recognized in the conodont succession demonstrate general correlation with these supersequences: boundaries between supersequences are characterized by low diversity values; diversity increases more or less rapidly in the lower, transgressive parts of the supersequences and decreases in their upper parts.

Taxonomy and biostratigraphy of Ordovician brachiopods from northeastern Ny Friesland, Spitsbergen

We describe Early and Middle Ordovician brachiopod faunas from northeastern Spitsbergen and discuss their biostratigraphical and palaeoecological implications. We recognise 60 species and 41 genera representing both linguliform and rhynchonelliform brachiopods. These include one new genus, the obolid Lenticulella with the type species Lenticulella amphora (Krause & Rowell, 1975), and 23 new species: Ectenoglossa? oviforma, Elliptoglossa vulgaris, Rosobolus? elongatus, Broeggeria obscura, Mirilingula? svalbardensis, Schizotreta marginalis, Conotreta convexa, Cyrtonotreta profilbekkiensis, Cyrtonotreta spinosa, Eurytreta subtriangularis, Hisingerella maniformis, Semitreta basisslettaensis, Semitreta pustulosa, Semitreta spitsbergensis, Numericoma? proclina, Eoconulus subquadratus, Dictyonites mugilis, Pelonomia sulcata, Leptella (Leptella) inequicostellata, Protoskenidioides promontorium, Anomalorthis rossi, Nothorthis subpyramidalis and Phragmorthis noda. The Ordovician succession contains both intertidal and deep-sea deposits with brachiopod faunas from nearly the whole range of environments. The Tremadocian is represented by a succession of low-diversity, rhynchonelli-6 · Zootaxa 3076 © 2011 Magnolia Pressform-dominated assemblages occupying shallow-marine environments. With the abrupt and large-scale drowning during the Floian, these faunas were replaced by a sparse slope fauna of micromorphic linguliforms. The outer shelf environments established in the latest Floian were occupied by a highly diverse brachiopod fauna dominated by micromorphic linguliform taxa. As the environment shifted toward the mid-shelf during the Darriwilian, however, the composition of the fauna changed to an Orthidiella-dominated assemblage of mostly rhynchonelliform taxa. The very late occurrence of the Orthidiella assemblage suggests that the Dapingian Orthidiella Zone found in America is probably diachronic. Although it includes many endemic species, the Middle Ordovician fauna shows a strong resemblance to the brachiopod fauna of Nevada. This study is based on approximately 16 500 brachiopod specimens obtained from both crack-out samples and acetic-acid-treated bulk samples.

Polyphase white mica growth in low-grade metapelites from La Cebila Metamorphic Complex (Famatinian Belt, Argentina): evidence from microstructural and XRD investigations.

Two tectono-thermal metamorphic events, M1-D1 (S1, with associated white mica and chlorite: WM1-Chl1) and M2-D2 (S2, with development of WM2-Chl2), are established from polyphase white mica growth for low-grade units from the Ordovician metasedimentary successions of La Cebila Metamorphic Complex in the Famatinian belt (western-central Argentina). The thermobarometric characterization of the M1 main event was carried out by means of clay-mineral analysis and crystallo-chemical parameter measurements. Epizonal (temperatures between 300 and 400ºC) and low-pressure conditions are suggested for M1 event, based in Kübler index values ranging from 0.23 to 0.17 Δº2θ, white mica b parameter values between 9.004 and 9.022 Å (mean of 9.014 Å, n=16) and Si contents between 3.13-3.29 a.p.f.u. Temperatures of ~180-270ºC are estimated for the M2 event, with Kübler index values ranging from 0.31 to 0.46 Δº2θ. The M1-D1 event of La Cebila could be linked to highstrain heating tectono-metamorphic Ordovician regime recorded in others complexes from Famatinian foreland region of Sierras Pampeanas.

The ordovician-silurian boundary on the western slope of the Subpolar Urals

Data obtained using different methods: paleontological, sedimentological, event stratigraphy and C-isotope chemostratigraphy of a unique succession of the Upper Ordovician and lower Silurian, located on the western slope of the Subpolar Urals, are presented in this work. The data obtained made it possible to revise some existing ideas about the texture of the Upper Ordovician succession and clarify the position of the Ordovician-Silurian boundary in the region. In addition, the Upper Ordovician Yaptiknyrd Formation was correlated with the synchronous formations in Scotland and Estonia.

Conodontes y Graptolitos del Tremadociano Tardío (Ordovícico) de la Sierra de Zenta, Cordillera Oriental de Jujuy, Argentina

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 Aceñolaza, 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), Kiaerograptus cf. K supremus Lindholm and Kiaerograptus? sp., which was collected from strata overlying the conodont-bearing levels. These conodont and graptolite faunas indicate a late Tremadocian age. Another locality on the road to Abra de Zenta, west of Santa Ana, contains Hunnegraptus cf. H. novus (Berry), Hunnegraptus spp. and Paradelograptus sp., indicating the Hunnegraptus copiosus Zone of the latest Tremadocian. The biostratigraphic succession is equivalent to that from the upper part of the Santa Rosita Formation and to the Parcha Formation exposed in other areas of the Eastern Cordillera in northwestern Argentina. The faunas contain elements of wide intercontinental distribution as well as endemic forms. The occurrence of concentrations of graptolites and lingulids showing evidence of transport in some strata indicates bottom reworking by erosive episodes in the basin.

Linking diagenesis to sequence stratigraphy in fluvial and shallow marine sandstones: Evidence from the Cambrian–Ordovician lower sandstone unit in southwestern Sinai, Egypt

By integrating diagenesis and sequence stratigraphy, the distribution of diagenetic alterations and their impact on reservoir quality was investigated within a sequence stratigraphic framework using the fluvial and shallow marine sandstones in the Cambrian–Ordovician succession of southwest Sinai. The perographic and geochemical analysis of the studied sandstone revealed that the eogenetic alterations display fairly systematic spatial and temporal distribution patterns within the lowstand system tract and transgressive system tract, as well as along the sequence stratigraphic surfaces (i.e., sequence boundaries, transgressive surfaces and parasequence boundaries). During relative sea-level fall, percolation of meteoric waters through sandstones of the LST and below sequence and parasequence boundaries resulted in extensive dissolution of detrital grains and formation of kaolinite, authigenic K-feldspar and feldspar overgrowths as well as formation of mechanical infiltrated clays around the detrital grains. During relative sea-level rise, invasion of marine water into the sandstones as a consequence of landward migration of the shoreline, as well as low sedimentation rates encountered in the TST, resulted in the formation of glauconite, apatite and pyrite. Development of pseudomatrix, which was formed by mechanical compaction of mud intraclasts, is mostly abundant along transgressive surfaces and parasequence boundaries of the TST, and is related to the abundance of mud intraclasts in the transgressive lag deposits. The types and extent of eogenetic alterations have an important impact on the distribution of the mesogenetic alterations, including the formation of quartz overgrowths and dickite. Distribution of mesogenetic quartz overgrowths in the sandstones was controlled by the distribution of mechanically infiltrated clays and the presence of eogenetic cement. Sandstones that remained poorly cemented during eodiagenesis and that have thin or discontinuous infiltrated clay rims around the detrital grains were cemented during mesodiagenesis by quartz. The absence of extensive eogenetic cements in the sandstones suggested that the partial deterioration of porosity was mainly due to mechanical compaction. Partial transformation of kaolinite to dickite, which indicates neomorphic change to a better-ordered and more stable crystal structure at the elevated temperatures during mesodiagenesis, is partially a function of distribution of kaolinite during eodiagenesis. The conceptual model developed in this study shows the diagenetic evolutionary pathways in the reservoir sandstones within a sequence stratigraphic context, which in turn provides some insights into the controls on reservoir heterogeneity.

Review and palaeoecological analysis of the late Tremadocian – early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France

The Early Ordovician successions of the southern Montagne Noire consist of a thick sequence of predominantly siliciclastic sediments of which the late Tremadocian St. Chinian Formation and the earliest Floian La Maurerie Formation contain a comparatively rich and abundant cephalopod association. The cephalopods of the St. Chinian and La Maurerie Formation are interpreted as generally authochthonous, representing a fauna which originally lived in the open water above the sediments or related to the sea bottom. The cephalopod associations of the St. Chinian and La Maurerie formations are similar to other contemporaneous assemblages known from higher palaeolatitudes and associated with deeper depositional settings. They are composed almost exclusively of longiconic orthocones, in this case predominantly of eothinoceratids and baltocerids. The occurrences of <i>Annbactrocera</i>, and <i>Bactroceras</i> in the St. Chinian Formation are at present the earliest unambiguous reports of the Orthocerida. The available data suggest an initial expansion of orthoceroid cephalopod faunas from open water habitats of high paleo-latitudes, and a subsequent expansion on the carbonate platforms during the Floian. The presence of the eothinoceratid <i>Saloceras</i> in abundance demonstrates the Gondwanan affinity of the assemblage whilst adding further support for the presence of a "<i>Saloceras realm</i>" that may have extended along the margins of East and West Gondwana at least into intermediate latitudes. The following new taxa are proposed: <i>Annbactroceras</i> n. gen., <i>Annbactroceras felinense</i> n. sp., <i>Cyclostomiceras thorali</i> n. sp., <i>Felinoceras</i> n. gen., <i>Felinoceras constrictum</i> n. sp., <i>Lobendoceras undulatum</i> n. sp., Rioceratidae n. fam., <i>Saloceras murvielense</i> n. sp., <i>Thoraloceras</i> n. gen., <i>Thoraloceras bactroceroides</i> n. sp. <br><br> doi:<a href="http://dx.doi.org/10.1002/mmng.201000013" target="_blank">10.1002/mmng.201000013</a>

Review and palaeoecological analysis of the late Tremadocian - early Floian (Early Ordovician) cephalopod fauna of the Montagne Noire, France

Abstract. The Early Ordovician successions of the southern Montagne Noire consist of a thick sequence of predominantly siliciclastic sediments of which the late Tremadocian St. Chinian Formation and the earliest Floian La Maurerie Formation contain a comparatively rich and abundant cephalopod association. The cephalopods of the St. Chinian and La Maurerie Formation are interpreted as generally authochthonous, representing a fauna which originally lived in the open water above the sediments or related to the sea bottom. The cephalopod associations of the St. Chinian and La Maurerie formations are similar to other contemporaneous assemblages known from higher palaeolatitudes and associated with deeper depositional settings. They are composed almost exclusively of longiconic orthocones, in this case predominantly of eothinoceratids and baltocerids. The occurrences of Annbactrocera, and Bactroceras in the St. Chinian Formation are at present the earliest unambiguous reports of the Orthocerida. The available data suggest an initial expansion of orthoceroid cephalopod faunas from open water habitats of high paleo-latitudes, and a subsequent expansion on the carbonate platforms during the Floian. The presence of the eothinoceratid in abundance demonstrates the Gondwanan affinity of the assemblage whilst adding further support for the presence of a Saloceras realm that may have extended along the margins of East and West Gondwana at least into intermediate latitudes. The following new taxa are proposed: Annbactroceras n. gen., Annbactroceras felinense n. sp., Cyclostomiceras thorali n. sp., Felinoceras n. gen., Felinoceras constrictum n. sp., Lobendoceras undulatum n. sp., Rioceratidae n. fam., murvielense n. sp., Thoraloceras n. gen., Thoraloceras bactroceroides n. sp. doi: 10.1002/mmng.201000013

Chitinozoan biostratigraphy of a new Upper Ordovician stratigraphic framework for Anticosti Island, Canada

Thickness and facies variations in the Upper Ordovician succession of Anticosti Island have made correlations between the western and eastern ends of the island difficult. This chitinozoan study reveals that most strata of the Ellis Bay Formation at the eastern end of the island correlate with the Vaureal Formation at the western end. In the eastern end, chitinozoans typical of the Ellis Bay Formation occur only in the upper part of the Lousy Cove Member, whereas chitinozoans diagnostic of the mid-upper Vaureal occur in the rest of the formation. Moreover, the eastern Schmitt Creek and Mill Bay members of the Vaureal Formation are older than the uppermost Vaureal eponym members in the western end. New east-west correlations, supported by geochemical, sedimentological, and sequence stratigraphic data, are proposed. Comparison with coeval Upper Ordovician successions suggests a Hirnantian age for the gamachiana Zone that occurs in the lower members of the Ellis Bay Formation. It also indicates that the Hirnantian Isotopic Carbon Excursion (HICE) on Anticosti begins in the D. anceps Zone, just below the base of the Hirnantian Stage, reaches a first peak in the lower N. extraordinarius Zone, a second modest peak high in the N. extraordinarius Zone, and a third, more important one, in the lower part of the N. persculptus Zone. These results are in agreement with the biostratigraphic and chemostratigraphic data at the Global Boundary Stratotype Section and Points (GSSPs) for the base of the Hirnantian and Silurian in south-central China and at Dob9s Linn in Scotland.

Provenance of detrital zircons from the late Neoproterozoic to Ordovician sandstones of South China: implications for its continental affinity

AbstractThe U–Pb geochronology of 687 detrital zircons from the voluminous Upper Neoproterozoic–Ordovician succession in the Wuyishan Fold Belt of South China reveals a common dominant c. 1200–950 Ma group, indicative of an outboard provenance terrane with a Grenville-age province to the southeast during the late Neoproterozoic–Early Palaeozoic. Compared with coeval samples from the Gondwanan and eastern Laurentian margins, our data show a scarcity of distinctive Gondwanan provenances (c. 650–500 Ma) and reveal some Laurentian signatures. These results argue against the peri-Gondwanan setting for South China during the late Neoproterozoic–Ordovician, instead implying a Laurentian affinity.