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The upper Cambrian Yancannia Formation is a small and isolated basement exposure situated in the southern Thomson Orogen, northwestern New South Wales. Understanding the geology of the Yancannia Formation is important, as it offers a rare glimpse of the composition and structure of the mostly covered basement rocks of the southern Thomson Orogen. It consists of deformed fine-grained, lithic-rich, turbiditic metasediments, suggesting deposition in a proximal, low-energy deep-marine environment. A 497 ± 13 Ma U-Pb detrital zircon date provides its maximum depositional age, the same as previously published for a tuff horizon in a correlative unit. Analysis of sedimentological, geochronological and geophysical data confirms the Yancannia Formation belongs to the Warratta Group. The Warratta Group exhibits many similarities to the Teltawongee Group in the adjacent Delamerian Orogen, including similar provenance, sedimentology and deep-water turbiditic depositional environment. Additionally, there is no sedimentological evidence for deposition of the Warratta Group following the ca 500 Ma Delamerian Orogeny, which suggests that the Warratta Group is syn-Delamerian. However, no geochronological or structural evidence for Delamerian orogenesis was observed in the Warratta Group, suggesting that the group was either unaffected by Delamerian orogenesis, or that no conclusive record remains. The provenance signature of the Warratta Group also bears strong similarities with the upper Cambrian Stawell Zone Saint Arnaud Group in the western Lachlan Orogen. Units east of Yancannia have similar provenance signatures to the Lower Ordovician Girilambone Group of the Lachlan Orogen, suggesting equivalents exist in the southern Thomson Orogen. These are likely to be the Thomson beds, deposited in a deep-marine setting outboard of the Delamerian continental margin. Structural analysis from a ∼10 km, semi-continuous, across-strike section indicates a major, kilometre-scale, upright, shallow northwest-trending, doubly plunging anticline dominates the Yancannia region. This D1 structure was associated with tight-to-isoclinal folding, penetrative cleavage and abundant quartz veining of probable Benambran age. Later dextral transpressional deformation (D2) produced a sporadic, weak cleavage and dextral faulting, possibly of Bindian age. Major south-directed thrusting (D3) on the adjacent Olepoloko Fault occurred in the early Carboniferous and appears to pre-date a later deformation event (D4), which was associated with kink folding. [ABSTRACT FROM AUTHOR]

Microbial carbonates were major components of early Paleozoic reefs until coral-stromatoporoid-bryozoan reefs appeared in the mid-Ordovician. Microbial reefs were augmented by archaeocyath sponges for ~15 Myr in the early Cambrian, by lithistid sponges for the remaining ~25 Myr of the Cambrian, and then by lithistid, calathiid and pulchrilaminid sponges for the first ~25 Myr of the Ordovician. The factors responsible for mid–late Cambrian microbial-lithistid sponge reef dominance remain unclear. Although oxygen increase appears to have significantly contributed to the early Cambrian ‘Explosion’ of marine animal life, it was followed by a prolonged period dominated by ‘greenhouse’ conditions, as sea-level rose and CO 2 increased. The mid–late Cambrian was unusually warm, and these elevated temperatures can be expected to have lowered oxygen solubility, and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia. Greenhouse conditions would also have stimulated carbonate platform development, locally further limiting shallow-water circulation. Low marine oxygenation has been linked to episodic extinctions of phytoplankton, trilobites and other metazoans during the mid–late Cambrian. We propose that this tendency to dysoxia-hypoxia in shallow marine environments also limited many metazoan reef-builders. In contrast, during the mid–late Cambrian, the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs. These conditions ameliorated during the Ordovician, as temperature decline promoted ocean ventilation. The prolonged time gap occupied by low diversity reefs between the ‘Cambrian Explosion’ and the ‘Great Ordovician Biodiversification Event’ reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments. [ABSTRACT FROM AUTHOR]

The Middle Ordovician Kelimoli Formation carbonate reservoirs in the northern Tianhuan area, Ordos Basin, China are main exploration targets. Subsurface core samples, logging, drilling and production data from the area were used to characterise the carbonate reservoir and to construct a genetic model for exploration. The sedimentary facies identified include trough-continental rise, upper-lower slope, platform margin reef-shoal, open platform and evaporation-restricted platform. The slope and platform margin facies are potential zones for high-quality reservoirs. Porosity in the study area comprises intergrain, intercrystal, intragrain and intracrystal pores, fractures and vughs. The Sr/Ba (0.40-4.87) and V/(V + Ni) (0.64-0.97) ratios indicate deposition in a brackish water-dominated environment under reducing conditions, associated with sea-level fluctuations during the deposition of the Kelimoli Formation. The Sr/Ba, V/(V + Ni), 87Sr/86Sr ratios, δ18O values and crystal texture of dolomite samples suggest that meteoric water was involved in the diagenetic fluid in the near-surface depositional environment. Isotopes (δ13C and δ18O) and trace elements (Fe and Mn) allowed the identification of seepage-reflux and mixed-water dolomitisation. The crystal textures of the samples consist of micritic, bioclastic and reefal limestones, and dolomite with gypsum, which were easily dissolved during the early diagenetic stage. The epidiagenetic stage was the key period for the development of high-quality reservoirs because of large-scale bedding-parallel karstification from meteoric water. The reservoir zones, dominated by partially filled and unfilled vughs, and fractures, are favourable exploration targets in the northern Tianhuan area. [ABSTRACT FROM AUTHOR]

Conodont δ18O is increasingly used to reconstruct Paleozoic-Triassic seawater temperature changes. Less attention has been paid to δ18O variation in time slices across paleoenvironments, within sample assemblages, or for reconstructing the thermal structure of Paleozoic oceans. Furthermore, there have been few independent tests of conodont ecologic models based on biofacies and lithofacies distributions. Here we present the first test of ecologic models for conodonts based on δ18O values of a Laurentian Lower Ordovician (Floian) shelf edge-upper slope assemblage in debrites of the proximal lower slope Shallow Bay Formation, Cow Head Group, western Newfoundland. Nine species yield a 1.6-1.8‰ intra-sample δ18O variability based on mixed tissue and white matter-only analyses, equivalent to an ~7-8 °C range. Linear mixed models demonstrate statistically significant differences between the δ18O of some species, supporting the interpretation that an isotopic and temperature gradient is preserved. By considering conodont δ18O in a geologic context, we propose an integrated paleoecologic and paleoceanographic model with species tiered pelagically through the water column, and confirm the utility of conodonts for water-mass characterization within Paleozoic oceans. [ABSTRACT FROM AUTHOR]

The Tazhong Low Rise has abundant hydrocarbon resources in the Yingshan Formation of Lower Ordovician, where dolomite has been demonstrated to be a significant target for carbonate hydrocarbon exploration. Using optical observation and geochemical tests, three types of dolomite can be used as replacement and cement products. D1 dolomite is silt or fine crystalline, and has the fluid inclusions of low Th (71.4 °C) and corresponding salinity (9.89 wt% NaCl). In addition, geochemical data indicate that D1 dolomite was formed with shallow burial fluids and was intensely affected by weathering karst in the middle Ordovician, which served as a mixing-zone for dolomitisation. D2 dolomite of medium-coarse grain has similar geochemical characteristics as D1 dolomite except that it has higher diagenetic temperature and negative δO, suggesting that it generally developed in a deep burial environment. The cathodoluminescence showed two zonal structures in D1 dolomite, while at least three zonal structures in D2 dolomite were influenced by multiple burial diagenetic fluids. The D3 dolomite has a saddle structure with medium-coarse crystalline, high contents of Mn, Ba, Fe, and Sr, high Th (140 °C), high salinity (20.36 wt% NaCl), and negative δO (-10.1 to-7.8‰). Meanwhile, D3 dolomite is distributed near faults and fractures that are accompanied by hydrothermal minerals and is obviously influenced by hydrothermal fluids. [ABSTRACT FROM AUTHOR]

We present here a comprehensive and updated review on the gneissic Ollo de Sapo Formation (OSF) in the Iberian Massif and discuss multiple aspects (lithostratigraphy, petrography, geochemistry, geochronology, and partial melting relationships) of its evolution through time. These aspects arise from the superposition of a multi-magmatic Cambro-Ordovician assemblage and a complex Variscan metamorphic overprint. The OSF comprises plutonic, subvolcanic, volcanic, and volcaniclastic units of fel and peraluminous compositions and calcalkaline affinity of the Upper Cambrian to the Lower Ordovician age (495–470 Ma), which crops out at the core of a 600-km-long antiform in the Ollo de Sapo Domain of the Iberian Massif and are overlain by the Armorican Quartzite. The most striking petrographic features of the OSF are the large phenocrysts of K-feldspar, plagioclase, and blue quartz, giving the name “Ollo de Sapo” (toad's eyes), and the large fraction of inherited zircons of Ediacaran or older ages. Geochemical and petrographic indicators point to a medium-P, high-T melting event of Neoproterozoic metasedimentary rocks, most probably the Schist and Greywacke Complex, and a subsequent rapid ascent of melts. Augen gneisses of mostly plutonic origin, of similar age, petrography, and geochemistry and emplaced in the same sedimentary sequences in the Iberian Massif but in lower stratigraphic levels than the classical Ollo de Sapo Domain, also exist. These plutonic augen gneisses are considered to be genetically related to the OSF. The magmatic event that produced the OSF and the equivalent augen gneisses in the Iberian Massif, as well as other augen gneisses present in the European Variscan Belts, has been supposedly related to the opening of the Rheic Ocean in the northern margin of Gondwana. The Variscan metamorphism affected the OSF and the equivalent augen gneisses to variable degrees, from low-grade to anatectic conditions, in a clockwise P-T-t path, that produced its characteristic gneissic foliation. No model for the generation of the OSF has been unanimously accepted yet because of several, and often contradictory, geodynamic scenarios suggested by the petrographic and geochemical characteristics, further complicated by current debates on the paleogeography of northern Gondwana terranes. The stepwise investigation of this complex formation allows at present a general review of its evolution through time, a review that is presented here. [ABSTRACT FROM AUTHOR]

Hirnantian (latest Ordovician) localities containing echinoderm fossils are rare; the few that have been discovered primarily contain disarticulated crinoid ossicles. Therefore, relatively little is known about echinoderm evolutionary dynamics across the Late Ordovician - early Silurian boundary, especially noncrinoid echinoderms. New diploporitan echinoderms, Holocystites salmoensis and an unidentified holocystitid, from reefal facies of the Upper Ordovician Ellis Bay Formation of Anticosti Island provide a critical data point concerning diploporitan biogeography and evolutionary pathways undertaken during the Ordovician and Silurian. These fossils also provide a crucial link in understanding the ancestry of the Silurian Holocystites Fauna, an unusual diploporitan fauna from the middle Silurian of North America, whose origination dates back at least 15 million years earlier than previously thought with the discovery of taxa described here. New fossil data such as these stress the importance of uncovering new localities from underrepresented times and places in Earth's history, so that these evolutionary transitions can be better understood. [ABSTRACT FROM AUTHOR]

Stratigraphic units exposed on Akpatok Island, Ungava Bay, Nunavut, were previously recognized as Boas River and Akpatok formations; their biostratigraphic ages and correlations, in particular the stratigraphic position and age of the organic rich 'Boas River' Formation, were largely based on limited data. New detailed field observations have recognized three stratigraphic units, namely the Amadjuak, Akpatok, and Foster Bay formations, in which extensive microfossil sampling recovered over 22 000 conodont elements from 66 productive samples from both outcrops and rubble at over 20 localities in four areas. Four Upper Ordovician conodont zones and one unzoned interval are established for the three redefined formations: Belodina confluens and Oulodus velicuspis Interval zones are confined to the exposed Amadjuak Formation and correlated to Edenian and Maysvillian; Amorphognathus ordovicicus - Plegagnathus dartoni Concurrent-range Zone occurs with the Akpatok Formation and correlated to lower Richmondian; Rhipidognathus symmetricus Taxon-range Zone is retained in the Foster Bay Formation and correlated to upper Richmondian; and an 'Unzoned Interval' is defined between the last two zones in the lower Foster Bay Formation. The conodont Amorphognathus ordovicicus occurs in both Akpatok and lower Foster Bay formations, and it is also recovered from the bituminous, argillaceous limestone rubble, based on which the stratigraphic position of the previously named 'Boas River' Formation is most likely positioned within the lower Foster Bay Formation. The biostratigraphy and lithostratigraphy are combined with geographic information systems (GIS) to establish the thicknesses of the three formations and revise the geologic map of the island. [ABSTRACT FROM AUTHOR]

The Ordovician acritarch genusBarakellaCramer & Díez 1977 and two species,B. felixandB. fortunata, bearing characteristic anastomosing filamentous elements at one pole were first described from the subsurface of the Kasba Tadla Basin, Morocco. Subsequently, another species was described from the South Chinese Ordovician and was later attributed to the genus asBarakella rara. New material from the type locality in Morocco and additional sections in South China are used for a review of the genusBarakella. Based on this review, including statistical analysis,Barakella rarais considered a junior synonym ofBarakella felix.Barakellais a useful taxon for biostratigraphical applications in the Ordovician. Its first appearance datum (FAD) lies in the early Floian (Early Ordovician, time slices 2a–2b) in both South China and Wales. Except for a doubtful record from Sweden, all records ofBarakellaare from the peri-Gondwana margin, making the genus an indicator of the peri-Gondwana palaeoprovince. The appearance ofBarakellain South China indicates thatBarakellapossibly originated in shallow-water nearshore environments, and later spread to offshore environments. [ABSTRACT FROM AUTHOR]

This contribution deals with the record of the Ordovician genus Pygodus in Cuyania, Argentina. Several classical sections have been sampled for conodonts in the Precordillera and the San Rafael Block, involving diverse sedimentary deposits: coarse clastic rocks with carbonate cement, carbonate beds intercalated in fine clastic deposits, green shale, and black carbonate deposits. The recovered species of this genus are Pygodus lunnensis Zhang, P. anitae Bergström, P. serra (Hadding), P. protoanserinus Zhang and P. anserinus Lamont & Lindström. These key conodonts indicate middle to upper Darriwilian – lower Sandbian age for the bearing strata. The species P. protoanserinus is recorded for the first time from the Precordillera. Detailed observations were made on specimens of P. anitae, P. lunnensis and P. protoanserinus; the two last species are described for the first time from Cuyania. [ABSTRACT FROM AUTHOR]

Two assemblages from the Ordovician rocks of the Arctic region contain exclusively trepostome bryozoans. The first assemblage from the Yunoyaga Formation (Middle Ordovician) of Maly Oleniy Island, Novaya Zemlya, containsMonticulipora mammulatad’Orbigny, 1850 andNicholsonella vaupeliformisModzalevskaya, 1955. Both species possess thick-branched ramose colonies characteristic for rather high energy environments. The second assemblage comes from two localities of the Stroinaya Formation (Upper Ordovician) of the October Revolution Island containing the single speciesAmplexopora angustaAstrova, 1965. The monospecific bryozoan fauna of branched, rarely encrusting growth forms and sedimentological characteristics of embedding rocks (floatstone) suggest low energy conditions in deeper environments, apparently accompanied by high salinity conditions. [ABSTRACT FROM AUTHOR]

The 186-m-thick Shiyanhe Formation exposed at the Sigang section, Neixiang area, Henan Province, central China has been investigated for conodonts. The collected 33 samples yielded 8858 conodont specimens. The conodonts are referred to 15 genera and 34 species, but four species cannot be positively identified and one taxon is kept in open nomenclature. The Oulodus ulrichi , the Oulodus robustus , the Aphelognathus grandis and the Aphelognathus divergens conodont biozones are introduced and the conodont fauna and biozones of the Shiyanhe Formation are referred to the Katian Stage (Stage slices Ka2–Ka4) of the Upper Ordovician. The presence of biostratigraphically important species of the genera Aphelognathus , Oulodus and Yaoxianognathus allows for the recognition of the previously defined local conodont biozones that were established from the studied section. Regionally, the Shiyanhe Formation fauna is relatively similar to the contemporaneous faunas from the Tarim terrane in western China and from the southwestern margin of the North China Platform. However, the faunal composition also shows a close affinity to the North American Midcontinent Province and correlation to North America is clear. The conodont fauna is dominated by the species of Aphelognathus , Belodina , Drepanoistodus , Oulodus , Panderodus , Phragmodus , “ Plectodina ” and Yaoxianognathus . The Aphelognathus – Oulodus biofacies, the “ Plectodina ” biofacies, the Panderodus biofacies, the Drepanoistodus biofacies and the Phragmodus biofacies have been established using multivariate statistical techniques on the conodont assemblage. As their turnovers were related to sea-level changes, the conodont biofacies are used to demonstrate the transgressive-regressive pattern in the studied section. [ABSTRACT FROM AUTHOR]

This paper presents outcrop, petrographic, geochemical, well log and seismic data which together characterise the T 8 0 unconformity that occurs between the carbonate-dominated Ordovician and Cambrian successions in the Tarim Basin, NW China. In the region the T 8 0 unconformity represents the Cambrian-Ordovician transition surface controlled by both large-scale tectonic movements and sea level changes. The unconformity had a major influence on platform-margin architectures and depositional environments in the Palaeozoic carbonates below and above the unconformity. Seismic profiles show that a progradational ramp platform margin developed in the Upper Cambrian below the T 8 0 unconformity, while a retrogradational rimmed platform margin developed in the Lower Ordovician above the T 8 0 unconformity. The Upper Cambrian carbonates are dolomitized whereas limestones dominate in the Lower Ordovician strata. At four measured outcrop sections near the northwestern margin of the basin (Yingshan, Yonganba, Penglaiba and Shuinichang), extensive dissolution porosity from karstification is developed below the T 8 0 unconformity surface. The unconformity is associated with various geochemical anomalies. δ 13 C and δ 18 O ratios in the dolomitized Upper Cambrian strata immediately below the unconformity surface display negative excursions, paired with significantly reduced concentrations of major and trace elements such as, K, Ti, Sr, Fe, Ca, Si, Cl and S, while Mg and Ba are enriched relative to the Ordovician strata above. Furthermore, it is proposed that changes in the natural gamma radiation and Sr element concentrations can be used as a new tool for the identification and correlation of the Cambrian-Ordovician boundary, especially where diagnostic fossil markers are missing. [ABSTRACT FROM AUTHOR]

The long time interval after Pander's (1856) original conodont study can in terms of Ordovician conodont biostratigraphical research be subdivided into three periods, namely the Pioneer Period (1856-1955), the Transition Period (1955-1971) and the Modern Period (1971-Recent). During the pre-1920s, the few published conodont investigations were restricted to Europe and North America and were not concerned about the potential use of conodonts as guide fossils. Although primarily of taxonomic nature, the pioneer studies by Branson & Mehl, Stauffer and Furnish during the 1930s represent the beginning of the use of conodonts in Ordovician biostratigraphy. However, no formal zones were introduced until Lindström (1955) proposed four conodont zones in the Lower Ordovician of Sweden, which marks the end of the Pioneer Period. Because Lindström's zone classification was not followed by similar work outside Baltoscandia, the time interval up to the late 1960s can be regarded as a Transition Period. A milestone symposium volume, entitled 'Symposium on Conodont Biostratigraphy' and published in 1971, summarized much new information on Ordovician conodont biostratigraphy and is taken as the beginning of the Modern Period of Ordovician conodont biostratigraphy. In this volume, the Baltoscandic Ordovician was subdivided into named conodont zones, whereas the North American Ordovician succession was classified into a series of lettered or numbered faunas. Although most of the latter did not receive zone names until 1984, this classification has been used widely in North America. The Middle and Upper Ordovician Baltoscandic zone classification, which was largely based on evolutionary species changes in lineages and hence includes phylozones, has subsequently undergone only minor changes and has been used slightly modified also in some other regions, such as New Zealand, China and eastern North America. The great importance of conodonts in Ordovician biostratigraphy is shown by the fact that conodonts are used for the definition of two of the seven global stages, and seven of the 20 stage slices, now recognized within this system. [ABSTRACT FROM AUTHOR]

The Ordovician Mweelrea Formation is part of the basin fill of the South Mayo Trough in western Ireland and records progradation of alluvial facies northwestward across shallow- and marginal-marine Mweelrea 'passage beds' to marine Glenummera Formation facies. Early in Mweelrea Formation sedimentation, the first of a series of ignimbrites was emplaced, causing a disruption in this progradation. The preserved thickness of the ignimbrite is up to ca. 12 m, and the sedimentary response varied depending on the environment that was affected. Eastern exposures of the Mweelrea Formation are coarse grained and represent fluvial facies. Emplacement of the ignimbrite caused overlying sediment to become richer in feldspar as well as coarser grained; heavy-mineral laminations are common here and in many supra-ignimbrite exposures, but the depositional style was unchanged. The ignimbrite overlies decreasing thickness of fluvial sandstone towards the west to where it directly overlies shoreline and shallow-marine passage beds. Here, sandstone that overlies the ignimbrite is fluvial, indicating that emplacement of the ignimbrite brought about an abrupt progradation. At the westernmost outcrops of Mweelrea Formation, the ignimbrite lies at the contact with the underlying marine Glenummera Formation. Marine sedimentation continued after emplacement of the ignimbrite, although a coarse conglomerate horizon immediately overlying the ignimbrite together with development of a delta suggests that sediment input was vastly increased. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Moroccodiscus smithi represents a new cyclocystoid genus and species based on moldic specimens from the Middle Ordovician Taddrist Formation (Darriwilian) of SE Morocco. This represents the earliest articulated member of the Cyclocystoidea and is the first complete cyclocystoid described from the Ordovician of Gondwana, as well as the first cyclocystoid ever recorded from Africa. The anatomy and morphology of this new species were studied using a combination of conventional paleontological methods and nondestructive X-ray computed tomography. Because Moroccodiscus differs from other cyclocystoids, in particular by lacking cupules attached to the marginal ossicles, it is assigned to the new family Moroccodiscidae. This new taxon illustrates the relatively poorly known early diversification of these enigmatic extinct echinoderms and sheds light on the mode of life of cyclocystoids, including injuries to plate circlets during early ontogeny and folding of these disk-like specimens at the time of death. The overall thecal shape was very similar in cyclocystoids and many domal edrioasteroids, probably because they were both sessile or attached, benthic, suspension feeders. However, many oral surface, ambulacral, and marginal ring features had become very different, indicating that these two groups had either converged because of similar life modes or were only distantly related sister groups. [ABSTRACT FROM AUTHOR]

We present revision of the taxonomy and palaeoecology of the Ordovician aristocystitid Lepidocalix pulcher from the Zaouïa of Stita (Great Kabylia, Algeria). An emended diagnosis is proposed, highlighting the four-fold ambulacral system and the typical thecal plating organised in circlets. Lepidocalix is here assigned to the subfamily Calicinae of the family Aristocystitidae. The latex casts show fitted sutures between plates, slightly abraded spines, and well-preserved oral surface. The thecal plates possess up to three dipores, each, included into the spines. The presence of such covered diplopores would have reduced the respiration rate, by restricting their exchange surface area. The spines covering the dipores are not articulated and they could have a protective role. Lepidocalix is interpreted as stationary epifauna, probably using iceberg strategy to be stabilized into the soft substrate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Gastropoda, Tergomya, and Paragastropoda (GTP) are a small but recognizable part of the collective Fezouata biota from the Lower Ordovician (Tremadocian–Floian) Fezouata Formation in Morocco. GTP range through the sequence but become more abundant and diverse in the stratigraphically higher and shallower marine parts of the succession. About 200 rock samples in existing collections have GTP but usually each slab contains several specimens so the number of individual is many times higher. A total of seven species are recognized of which four were known earlier. Gastropods are represented by the planispiral bellerophontoid Sinuites sp., recognized for the first time in the Tremadocian part of the succession, and the anisostrophic, nearly planispiral Lesueurilla prima (Barrande in Perner). Tergomyans are most abundant, dominated by the genus Carcassonnella with Carcassonnella courtessolei Horný and Peel, Carcassonnella vizcainoi Horný and Peel, and Carcassonnella sp. The latter encompass several specimens from different localities and stratigraphical levels, and may represent one of the named species or new varieties. Carcassonnella is for the first time recorded in the Tremadocian part of the succession. A second tergomyan is Thoralispira laevis (Thoral), while paragastropoda are represented by Pelecyogyra fezouataensis Ebbestad and Lefebvre. In the peri-Gondwana area Carcassonnella , Thoralispira , and Lesueurilla are considered signature taxa, and the Fezouata GTP compare closely with those of Montagne Noire, France, both in composition and distribution. The Bohemian fauna is slightly younger (Floian–Darriwilian) with different species, except for Lesueurilla prima . The latter may have a wider distribution, being tentatively recognized in the Lower Ordovician of Argentina and Spain. [ABSTRACT FROM AUTHOR]

Hyolithids are an extinct group of early lophotrochozoans with an external skeleton consisting of a conical conch, an externally fitting operculum, and a pair of long, lateral spines named helens. Their phylogenetic position within the lophotrochozoans is unclear, but traditionally they have been regarded as molluscs. Although hyolithids occur in Konservat-Lagerstätten, their soft-part preservation had so far been restricted to the gut. The few known examples suggested that a simple U-shaped gut was characteristic of the group, but new occurrences show a diversity of gut configurations suggesting certain ecological diversity within the group. Here is reported an exceptionally preserved hyolithid specimen from the Ordovician Fezouata Konservat-Lagerstätte of Morocco with a relatively complete gut possibly including an oesophagus, a mouth and a faecal string. Uniquely for hyoliths, other soft parts, likely those associated with the inner surface of the operculum, appear to be preserved as well protruding from the aperture. The anatomy of the preserved soft parts is in accordance with inferences from skeletal anatomy suggesting that hyolithid soft parts did not extend much beyond the aperture, and that only the internal portion of the helens was associated with soft tissues. It is also compatible with lophotrochozoan affinities, but molluscan apomorphies, such as a foot or a radula are not present in the specimen. Taken together, the newly available information suggests that hyolithids may have had a relatively generalized feeding organ, which could adapt to various feeding modes in the suspension-detritus-deposit feeding spectrum. A specialized deposit feeding strategy would be at odds with what is known about hyolithid functional morphology, therefore the presence of a sediment-like infill in the posterior part of the gut of the presently described specimen is puzzling and, as it has been suggested for some Chengjiang taxa, may represent a taphonomic “artefact”. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The Lower Ordovician Fezouata Lagerstätte from Morocco (central Anti-Atlas, Zagora area) has yielded abundant and diverse soft-bodied fossils. Most described taxa were epibenthic or pelagic, so that little is known about the endobenthic components of the fauna. Here we report the discovery of a locally abundant element of the biota, a palaeoscolecid worm, which may have played an important ecological role in the community. Palaeoscolecids had a long, annulated body with an eversible tooth-bearing pharynx. They probably represent stem priapulids, but unlike them, they were protected by biomineralized (phosphatic) microscopic plates covering most of the body. These sclerites are commonly found isolated within SSF assemblages, thus considerably extending the fossil record of the group that ranges from the Cambrian Series 2 (Stage 3) to the upper Silurian. Like priapulids, palaeoscolecids might have been important bioturbators, contributing to the substrate colonization in the lower Palaeozoic. The discovery of abundant material (38 specimens) in the Fezouata Shale (Lower Ordovician, Morocco) allows us to reconsider their possible lifestyle, habitat and feeding habits. All the specimens belong to Palaeoscolex ? tenensis , a species previously only known from a fragment of cuticle from the Floian of Bohemia (Czech Republic). Some exhibit remains of the gut and aboral spines, features that are highly informative with regard to the ecology of these extinct organisms, but rarely preserved. The phosphatic nature of the plates is demonstrated by compositional analyses and interpreted with regard to the diagenetic context of the Fezouata Shale as primary. We also hypothesize that (at least) some palaeoscolecids were makers of Tomaculum -type ichnofossils, which are elongate clusters of faecal pellets, and show that they ingested a notable amount of sediment during the normal course of feeding. The presence of Palaeoscolex ? tenensis in the Lower Ordovician of Morocco further documents the great faunal similarities between Perunica and northern Gondwana at that time. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Trilobites are a major component of both biomineralized and soft-bodied assemblages of the Fezouata Biota, central Anti-Atlas, Morocco. Trilobite taxa of the Fezouata Shale (Tremadocian–Floian) in the Zagora area are typical of Lower Ordovician communities from shallow shelf environments, and show strong affinities with Early Ordovician assemblages from the Montagne Noire (southern France). Dramatic variations in both taxonomic composition and taphonomic attributes, together with the sedimentological facies changes, allow us to discriminate the palaeoenvironmental versus stratigraphic control on trilobite assemblages. Three communities are described along an onshore–offshore profile, namely the pilekiid-bavarillid, Agerina and raphiophorid biofacies. Additionally, three stratigraphic assemblages are identified: assemblage 1 is confined to the late Tremadocian, assemblage 2 ranges from late Tremadocian to middle Floian and assemblage 3 is restricted to the Floian. The higher diversity of some levels is explained by storm-induced inputs of debris from taxa living in adjacent environments. Additionally, control of relative seal level variation on some peculiarities of the trilobite fauna (specific endemicity, lack of some expected taxa) is evidenced in the Fezouata Shale. Finally, temporary dysoxic events are highlighted by preliminary geochemical analyses, probably allowing episodic exceptional preservation. [ABSTRACT FROM AUTHOR]

Early Ordovician bivalves are rare worldwide; thus discovery of any new bivalve fauna of this age presents an exceptional event. A new abundant bivalve fauna from the Fezouata Formation of Morocco includes nine genera; Alococoncha ?, Babinka , Cardiolaria ?, Coxiconchia , Ekaterodonta , Glyptarca , Cienagomya ?, Praenucula ?, and Redonia . Modern evaluation of the recently collected bivalves as an important infaunal element substantially supplements our knowledge of the fossil assemblage of the Fezouta Formation. Bivalves from the Fezouata Formation show close affinities with assemblages of comparable age known from the Montagne Noire as well as with Middle Ordovician bivalve faunas from Perunica, Iberia, Avalonia and Australia. Some genera are in common with Early Ordovician bivalves from South American West Gondwana (Argentina and Bolivia). During the Early Ordovician, the migration of the bivalves was limited only to Gondwana and peri-Gondwanan terrains. The Montagne Noire and Morocco played an important role in the distribution of important groups of bivalves to other regions of European peri-Gondwana (Armorica, Perunica, Iberia) and probably similarly during the Middle Ordovician for the expansion of bivalves through Avalonia to other continents like Baltica and Laurentia. Quantitatively, the Early Ordovician bivalve fauna of Morocco is dominated by heteroconchs associated with protobranchs and pteriomorphs. The dominance of heteroconchs and poor evidence of pteriomorphs are conspicuous here and both of these features characterise a high latitude bivalve fauna. Exclusively infaunal burrowers (filter feeders and deposit feeders) are present in siliciclastic facies of the Fezouata Formation. The genus Redonia completely dominates the Early Ordovician bivalve fauna of Morocco. Functional morphology of muscle scars in Early Ordovician and Cambrian bivalves is compared. Two conspicuous complex muscular systems, decisive for an efficient burrowing, appear already in the Early Ordovician. Myophoric buttress in Early Ordovician protobranchs and heteroconchs seems to be an important character for serving as the attachment point for muscles, which helped to hold the visceral sac during burrowing. [ABSTRACT FROM AUTHOR]

Carbonates of western Newfoundland span the Cambro-Ordovician interval and preserve a record of slope-basinal deposition in the Cow Head Group near Cow Head. This unit consists of conglomerates and ribbon and laminated limestone interbedded with shale that is well exposed in sea cliffs at Cow Head Peninsula. These conglomerates, although prevalent throughout the section, vary in thickness and abundance stratigraphically and record both local disruption and large-scale episodic sedimentation events. Microfacies drilled for carbon isotope (δ 13 C carb ) analysis of conglomerates reveal isotopic heterogeneity within individual samples, in some cases more than 1‰. While this might be an expected outcome of drilling multiple areas of a heterogeneous conglomerate hand sample, permil-level variability was observed both between individual clasts in a sample, between different parts of the same matrix, and between a clast and its surrounding matrix. No associated variation in δ 18 O carb or trace element distributions exists to suggest that this δ 13 C carb variability is the result of later-stage meteoric diagenesis. The δ 13 C carb variability suggests multiple sources of dissolved inorganic carbon (DIC) associated with carbonate precipitation for phases within these individual samples. These data indicate that processes such as local organic matter remineralization and early authigenic carbonate precipitation during lithification at the sediment–water interface (SWI) are either contributing to or controlling δ 13 C carb values in Cambrian carbonates, perhaps more so than at other intervals in Earth history. [ABSTRACT FROM AUTHOR]

The ‘Great Ordovician Biodiversification Event’ comprises the rapid diversification of marine organisms during the Ordovician Period. It is now clear that this adaptive radiation started for some organisms already in the Cambrian and continued for others beyond the end of the Ordovician, making the ‘Great Ordovician Biodiversification Event’ part of a long-term late Proterozoic and Early Palaeozoic radiation, that in part is expressed by the fossil record as the ‘Cambrian Explosion.’ A significant diversification of different groups of the plankton is observed in the late Cambrian–Early Ordovician interval, leading to the subsequent ‘Ordovician Plankton Revolution.’ The possible causes of this ‘plankton revolution’ are currently debated. They include changes in palaeoclimate, palaeogeography or tectonic and volcanic activity, as well as a modified nutrient supply. In this context, the Steptoean Positive Carbon Isotope Excursion δ 13 C carb (SPICE) event in the late Cambrian (Paibian Stage, Furongian Series) has been related to a major increase in atmospheric O 2 (from 10–18% to some 20 – 29%) and to increased oceanic nutrient availability. Here we analyze the diversification of the planktonic groups during the late Cambrian and Early Ordovician, in particular in relation to the SPICE event. Our analyses include the changing diversities of the phytoplankton (acritarchs), diverse groups of zooplankton (e.g., radiolarians, graptolites, chitinozoans) and the switch to a planktonic mode of life of fossil groups (e.g., arthropods, molluscs) that were part of the Cambrian benthos and that later occupied pelagic niches. In addition, we focus also on data indicating evidence for a late Cambrian to Ordovician origin of planktotrophy in invertebrate larvae. It can be concluded that none of the diversifications of the different planktonic organisms can be related directly to the SPICE event. However, a long term (10–20 million years) oxygenation pulse related to the SPICE event might have fuelled the explosion of phytoplankton diversity observed in the latest Cambrian–Early Ordovician that led to completely modified trophic structures permitting an increase in diversity and abundance of plankton-feeding groups during the Ordovician. [ABSTRACT FROM AUTHOR]

Paired measurements of bulk carbonate (δ 13 C carb ), organic matter (δ 13 C org ), and their difference (Δ 13 C) can be used to estimate changes in isotopic fractionation through time as a function of O 2 /CO 2 in the atmosphere. However, because local scale processes can also affect Δ 13 C, it is essential to compare sections from widely separated water masses. Here we present new δ 13 C org data from Ordovician carbonate rocks from the Great Basin, Oklahoma, and Appalachian Basin and compare with published δ 13 C carb records from these sections and paired δ 13 C values from other carbonate successions around North America. These new data complement previous studies that focused on Upper Ordovician δ 13 C carb excursions and now provide a composite Ordovician δ 13 C org record. New Lower Ordovician (Tremadocian Stage) δ 13 C org data range from ca. − 26 to − 28‰, decreasing throughout the Lower–Middle Ordovician (Floian–Dapingian Stages) to ca. − 29 to − 31‰. δ 13 C org values remain at their lowest throughout the Sandbian and are similar to other published Upper Ordovician (Sandbian–Katian) δ 13 C org data from North America. Δ 13 C values from well-preserved intervals generally vary between + 26 to + 28‰ throughout the Lower to Middle Ordovician (Tremadocian to early Darriwilian), but increase to + 31‰ during the mid–late Darriwilian and mid Sandbian, similar to published data from younger Late Ordovician positive δ 13 C excursions known as the Guttenberg (GICE) and Hirnantian (HICE) events. The overall Δ 13 C trend shows a ~ 3‰ increase throughout the Early–Middle Ordovician and coincides with a previously interpreted period of ocean cooling and some of the earliest pulses of global biodiversity of marine invertebrates and planktonic organisms. Modeling studies predict that p CO 2 decreased during this time, suggesting that the effect of p CO 2 on Δ 13 C may have been overwhelmed by other controls, such as an in increase in p O 2 or a higher O 2 /CO 2 ratio during this biodiversification event. [ABSTRACT FROM AUTHOR]

The Tarim Basin, located in NW-China, represents one of China's major palaeoplates. Its palaeogeographic position in the Ordovician, however, is debated. In this study we present biostratigraphically controlled stable carbon isotope data from some 600 samples spanning almost the entire Ordovician in order to provide a tool that can be used for future chemostratigraphic correlations. The data correlate well with results from South China, and several major global δ 13 C excursions such as the MDICE (Dw2/3), SAICE (Sa2), GICE (Ka1), and Whitewater excursion (Ka4) are documented for the first time from the Tarim Basin. Major sedimentary gaps are detected in the lower Floian between the Penglaiba and Yinshan formations, in the upper Darriwilian to lower Sandbian between the Dawangou and Saergan (or Kanling) formations, and in the latest Sandbian between the Kanling and Qilang formations as well as between the Tumuxiuke and Lianglitag formations. Three scenarios for the depositional history of the late Darriwilian to early Sandbian Saergan Formation, which represents an important hydrocarbon source rock in the Tarim Basin, are discussed with respect to their bio- and chemostratigraphic implications. The mid-upper Ordovician rocks recording high δ 13 C values have been deposited during transgressive or highstand intervals, whereas the regressive intervals are mostly missing. This results in a stacking of several positive excursions, and thus chemostratigraphic correlation without biostratigraphic control might produce misleading results, especially for shallow-water carbonates. [ABSTRACT FROM AUTHOR]

Middle–Late Ordovician sequences from the Appalachian Basin and Arbuckle Mountain regions of North America were analyzed for carbonate-associated sulfate (δ 34 S CAS ) and pyrite (δ 34 S pyr ) paired with carbonate (δ 13 C carb ) and organic matter (δ 13 C org ) chemostratigraphy. Two major negative drops in δ 34 S CAS (12‰ excursions) are recognized: the older decline in δ 34 S CAS occurs within the Histiodella holodentata–Phragmodus polonicus Conodont Zones and the younger drop is within the Cahabagnathus sweeti–Amorphognathus tvaerensis ( Baltoniodus gerdae subzone) Zones. These overall these negative shifts in δ 34 S CAS have an antithetical relationship with positive shifts in δ 34 S pyr (~+ 10‰) and δ 13 C carb (~+ 2‰) recorded in the same successions. The older negative δ 34 S CAS shift is coincident with the widely documented mid-Darriwilian δ 13 C excursion (MDICE), and the younger negative δ 34 S CAS shift is coincident with another positive δ 13 C carb shift in the early Sandbian. Geochemical modeling of these sulfur isotope shifts suggests that a decrease in the global rate of pyrite burial or isotope fractionation between seawater sulfate and sedimentary pyrite could account for these negative δ 34 S CAS trends. Additionally, a substantial increase in the weathering flux of pyrite to the global oceans could also explain these secular sulfur isotope trends. While increased crustal weathering is broadly consistent with a sea-level lowstand, and the seawater 87 Sr/ 86 Sr isotope record of change in continental weathering in the late Darriwilian Stage of the Ordovician, geologic and geochemical proxy evidence do not support distinct pulses of continental weathering required to generate two separate negative shifts in δ 34 S CAS . These antithetical isotope trends may be best explained by changes in the marine redox state that significantly reduced microbially mediated pyrite burial and organic matter remineralization rates. Pulses of oceanic ventilation would have expanded habitable environments for marine organisms, and thus is broadly consistent with major increases in biodiversification during this period of the Ordovician. [ABSTRACT FROM AUTHOR]

Patterns of change in the isotope composition of sulfur-bearing minerals play a key role in reconstructing the marine sulfur cycle. Determining marine sulfate concentration, in particular, is critical to understanding the linkages between oxygenation of the Earth's atmosphere and oceans, and the history of life. Much of our current understanding of marine oxygenation relies on a traditional single reservoir model, wherein the isotopic composition of marine sulfate is controlled primarily by burial of sedimentary pyrite. Utility of this model is limited, however, during times of persistent marine euxinia, which marks a fundamental decoupling between oxic and anoxic marine sulfur reservoirs. At these times, short-term fluxes that act between the two reservoirs (e.g., sulfate reduction and sulfide oxidation processes) often dominate over the long term fluxes (e.g., weathering and pyrite burial) that control the single reservoir ocean model. Ordovician strata from Argentina, western Newfoundland, and South China illustrate how the marine sulfur cycle is affected by the presence of a persistent euxinic reservoir. Regional euxinic reservoirs remain generally stable from the Floian through the Dapingian, despite evidence for periodic short-term oxygenation events. Dramatic reorganization of the marine sulfur cycle in the early Darriwilian, however, reflects dynamic disequilibrium between oxic and anoxic (euxinic) marine reservoirs, driven by ocean ventilation. Ventilation resulted in a rapid change in the isotopic composition of marine sulfate in surface oceans, and ultimately led to the near depletion of hydrogen sulfide within the anoxic reservoir, as marked by formation of superheavy pyrite. Ventilation occurred coincident with a decline in sea surface temperatures and may represent the onset of climatic change that ultimately led to late Ordovician glaciation. [ABSTRACT FROM AUTHOR]

Shallow water carbonate shelf strata of the Ely Springs Dolostone accumulated on the western Laurentian margin as relative sea level fluctuated during the Late Ordovician icehouse. The Ely Springs Dolostone is divided into four upper Katian depositional sequences and one Hirnantian sequence. Here we present new carbon isotope data from the Ely Springs in the context of the sequence stratigraphic architecture. These data derive from a shelf transect of five stratigraphic sections exposed in the eastern Great Basin, USA and provide records of carbon cycling on the Laurentian margin prior to and during the Hirnantian glacial maximum. The δ 13 C values range between − 2‰ and + 4‰ at each section, and chemostratigraphic tie points occur in all sections of the transect. Intrabasinal correlations based on the δ 13 C records are consistent with correlations derived from sequence stratigraphy and conodont biostratigraphy. The Ely Springs Dolostone carbon isotope curve can also be correlated with the late Katian (Cincinnatian) composite derived from epicontinental deposits of the Laurentian midcontinent. The globally documented Hirnantian positive carbon isotope excursion (commonly referred to as “HICE”) occurs within the uppermost depositional sequence immediately below a regional unconformity coinciding with peak glacial conditions on Gondwana. The late Katian Elkhorn and Waynseville δ 13 C excursions are also present in the Ely Springs Dolostone carbon isotope record. The peak value of the Hirnantian carbon excursion increases from 2.6‰ to 3.8‰ across the shallow shelf and reaches 7.3‰ in coeval limestones of the Hanson Creek Formation deposited in a deep dysoxic setting. This lateral gradient is not the result of changes to the δ 13 C of weathered carbon supplied by rivers, as previously proposed; it may be instead related to authigenic carbonate cement precipitation during early diagenesis of the Hanson Creek strata. That these pervasively dolomitized shallow water carbonates retain δ 13 C signatures useful for regional and global stratigraphic correlation indicates that δ 13 C chemostratigraphy may be an appropriate correlation tool for dolostones with few biostratigraphically useful fossils. [ABSTRACT FROM AUTHOR]

Analysis of 161 nodular and bedded cherts shows that shallow-water biosiliceous facies, which were common in the Lower Ordovician, had mostly retreated from peritidal–lagoonal facies to deeper settings by the Middle Ordovician. For decades, this retreat was thought to have spanned the Cambrian and Ordovician Periods. Our data suggest that the basinward shift may have taken approximately 2–14 m.y. in the late Lower to early Middle Ordovician. A likely cause for the departure of these often siliceous-sponge cherts from shallow waters was depletion of shallow-water dissolved silica (DSi). Increased use of DSi by radiolarians may have commenced in the Middle Ordovician when radiolarians increased just as a pulse of radiolarite deposition began. Siliceous sponges may have been forced to relocate to deeper waters because radiolarians depleted shallow-water DSi. Apparent low relative sea level in the Middle Ordovician may have hampered the formation and/or preservation of shallow-water cherts by reducing available shelf area to host such deposits. However, the resurgence of shelf chert in the Upper Ordovician while peritidal cherts remained virtually absent suggests that biology was critical to driving the basinward shift of cherty facies. Formation and preservation of abundant latest Darriwilian through Sandbian cherts may have been favored in deep-water settings during a possible warming interval marked by sea-level rise and extensive anoxia and euxinia that coincided with an ongoing decline in 87 Sr/ 86 Sr ratios and increased sea-floor volcanic activity that probably enriched the DSi content of deep-ocean waters. Ocean circulation associated with the onset of cooling in the Katian may have optimized chert accumulation by stimulating surface water biosiliceous productivity before DSi-rich chert-preserving anoxic basins were ventilated. As Late Ordovician glaciation intensified, deep-ocean ventilation by thermohaline sinking of oxygen-rich waters probably decreased preservation potential of biosiliceous deposits while increasing oceanic recycling of silica. [ABSTRACT FROM AUTHOR]

The rare earth element (REE) composition of bioapatite has long been used as a proxy for ancient seawater chemistry and paleomarine environmental reconstruction, based on the assumption of preservation of a hydrogenous (seawater-derived) REE signal. Recent work, however, has begun to question the provenance of REEs in conodonts, emphasizing the importance of REEs released by the lithogenous fraction of the sediment and subsequently adsorbed onto conodont apatite in the burial environment. Here, we investigate patterns of REE and trace-element abundance in conodonts and their host sediments from the Early to Late Ordovician Huanghuachang and Chenjiahe sections of Hubei Province, South China. Several lines of evidence indicate that REEs in the conodont samples were acquired mainly from clay minerals in the host sediment during burial diagenesis: (1) REEs in conodonts show a strong positive correlation to Th and other lithogenic elements; (2) conodonts and whole-rock samples show general patterns of REE and trace-element enrichment that are highly similar to each other and bear no resemblance to seawater elemental concentrations; (3) similar patterns are observed in Triassic conodonts and whole-rock samples; and (4) Y/Ho ratios in conodonts are mostly < 40 (mean ~ 33), values that are consistent with derivation of > 90% of REEs from lithogenous sources. Conodonts show pronounced middle rare earth element (MREE) enrichment, a pattern that is unambiguously of diagenetic origin owing to its association with lower Y/Ho ratios. With increasing MREE enrichment of conodont samples, U concentrations and La N /Yb N ratios shift from high to low, and Mn concentrations from low to high. These patterns suggest that conodont diagenesis was initiated at shallow burial depths under suboxic conditions (i.e., in the zone of Mn(IV) and Fe(III) reduction) but continued at greater burial depths, with most acquisition of secondary REEs at later diagenetic stages. Our findings indicate that (1) conodont apatite frequently does not preserve a recognizable hydrogenous REE signal, and (2) the results of many earlier studies in which REEs in bioapatite were used as a paleoseawater proxy may need re-evaluation. [ABSTRACT FROM AUTHOR]

A large, resistant buildup at the top of the Upper Ordovician (Hirnantian?) Red Head Rapids Formation on Southampton Island (Nunavut, Arctic Canada) is dominated by massive boundstone and cementstone facies. These massive facies have more in common with the sponge-microbial reefs that dominated worldwide in the Early Ordovician, including the following primary components: early calcified sponge material, microbial elements, and synsedimentary cement. A close spatial relationship between sponge and microbial framework elements suggests that a poorly preserved decaying sponge framework provided substrates for the attachment and development of microbes and that the microbes played essential roles as reef consolidators. Centimetre-scale colonial metazoans are present and locally intergrown with the sponge and microbial components. Other mound-dwelling invertebrates or calcareous algae are rare. Although altered now to calcite, cement fabrics suggest that aragonite was ubiquitous as seafloor precipitate. Prior to its subaerial exposure in the latest Ordovician, the Red Head Rapids Formation buildup developed on the margin of a shallow-marine evaporative epicratonic basin where a diverse community of reef-building metazoans was unable to flourish. [ABSTRACT FROM AUTHOR]

Integration of chitinozoan and conodont biozones is based on detailed collections from the Bliudziai-150 well, southern Lithuania, that penetrated upper Darriwilian - lower Sandbian sedimentary carbonate rocks. The strata accumulated at the southeastern side of the Livonian Tongue and represent the transition from shallow shelf facies of the Lithuanian shallow-water shelf facies belt to the deeper-water shelf facies belt. Systematically collected and closely spaced samples of the carbonates from the Bliudziai-150 core yielded both chitinozoans and conodonts in abundance. The chitinozoans are assigned to the Laufeldochitina striata, Laufeldochitina stentor, Angochitina curvata - Armoricochitina granulifera, Lagenochitina dalbyensis, Belonechitina hirsuta, and Spinachitina cervicornis chitinozoan biozones, and the conodonts are assigned to the Pygodus serra Zone (with three subzones), Pygodus anserinus Zone (with two subzones), and the three subzones of the Amorphognathus tvaerensis Zone. The fossils are clearly of Baltoscandian affinity, and the integrated results support existing knowledge concerning the biostratigraphy of the two groups in Baltoscandia. Thus, the studied interval is confidently assigned to the Lasnamägi, Uhaku, Kukruse, and Haljala regional stages of the East Baltic regional chronostratigraphical scheme, corresponding to the global upper Darriwilian - lower Sandbian stages (Middle to Upper Ordovician). International correlation of the chitinozoan and conodont succession is presented, and the position of the base of the international Sandbian Stage is placed at 1380.00 m in the Bliudziai-150 core. A horizon marked by multiple discontinuity surfaces represents the base of Kegel depositional sequence and coincides with the appearance of Armoricochitina granulifera, Angochitina curvata, Lagenochitina dalbyensis, and Baltoniodus gerdae in the Bliudziai-150 core. [ABSTRACT FROM AUTHOR]

The Middle-Late Ordovician Ghelli Formation in the Kopet Dagh region northeastern Alborz range of Iran is composed of siliciclastic rocks deposited in a variety of turbidite to marginal marine environments (deep marine clastic fan and related environments and prodelta, distal delta front, proximal delta front and distributary channels). The ichnology of the middle member of the Ghelli Formation is here reported. Combined sedimentological and ichnological analysis allows recognition of a tide-influenced deltaic succession in the middle member of the Ghelli Formation consisting of three main facies associations: lower distributary channels, delta front and prodelta facies. Twenty-two ichnogenera have been identified in this marginal marine succession: Arenicolites, Arthrophycus, Bergaueria, Chondrites, Conichnus, Cruziana, Cylindrichnus, Didymaulichnus, Diplichnites, Diplocraterion, Helminthopsis, Gyrochorte, Lockeia, Macaronichnus, Monomorphichnus, Palaeophycus, Planolites, Rosselia, Rusophcus, Skolithos, Teichichnus and ?Scolicia. Their distribution is clearly linked with lithofacies and depositional palaeoenvironments. The ichnological analysis reveals that the trace fossil suites developed in these environments indicate low diversity and low to moderate abundance of burrows, poor development of tiering and sporadic distribution. Low ichnodiversity and low bioturbation intensities with higher bioturbation clusters consist of facies-crossing ichnogenera, and the impoverishment of suspension-feeding trophic types indicates 'stressed', non-archetypal expression of the Cruziana ichnofacies. The periodic higher intensities of bioturbation due to variations in hydrodynamic regimes of tidal currents reflect the archetypal of the Cruziana ichnofacies (and rare Skolithos ichnofacies). [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We studied the petrogenesis of mafic igneous rocks in the Famatinian arc in the western Sierra Famatina (NW Argentina), an Early Ordovician middle-crustal section in the proto-Andean margin of Gondwana. Mafic rock types consist of amphibolite, metagabbro, and gabbro, as well as pod- and dike-like bodies of gabbro to diorite composition. Field relations together with geochemical and isotopic data for the mafic rocks of the western Sierra de Famatina (at 29°S) define two contrasting suites, which can be correlated with similar assemblages noted in other parts of the orogen. Amphibolite, metagabbro, and gabbro bodies are mostly the oldest intrusive rocks (older than 480 Ma), with the host tonalite and post-tonalite mafic dikes being slightly younger. The older mafic suite is tholeiitic to calc-alkaline and isotopically evolved, except for most of the amphibolite samples. The younger suite is calc-alkaline, typically displaying subduction-related geochemical signatures, and it is isotopically more juvenile. Whole-rock chemical composition and isotopic analyses are compatible with a progressive mixing of different isotopic reservoirs. Pyroxenite (±garnet) was likely the dominant source of the older gabbroic magmas, whereas peridotite dominated in the source of the younger suite, implying that the mafic magma experienced a progressive shift toward more juvenile compositions though time (over 20 m.y.). Pyroxenitederived melts could have been generated by lithospheric foundering followed by upwelling of primitive melts by adiabatic decompression of mantle wedge peridotite. [ABSTRACT FROM AUTHOR]

No. 10 coal seam in Wangjialing Coal Mine is threatened with floor water bursting from aquifers underlying the coal seam. A geographic information system (GIS)-based analytic hierarchy process (AHP) vulnerability index method was used to assess the floor water bursting. Based on detailed analysis of the geological and hydrogeological conditions of the mine, eight main factors were determined that control the No. 10 coal seam floor water bursting from the karstified Ordovician limestone. Subsequent to acquisition and normalization of the main controlling factor data, the sub-thematic layers of each dominating factor and the overlay layer were established using GIS for the eight factors. AHP was used to determine the weight of each main controlling factor. The GIS-based AHP vulnerable evaluation model resulted in coal floor water bursting vulnerability zoning scheme for the coal mine, which is used for taking necessary control measures to avoid water bursting. [ABSTRACT FROM AUTHOR]

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Copyright of Canadian Journal of Earth Sciences is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A diverse, typical Hirnantia brachiopod fauna from terminal Ordovician strata in Latvia extends the distribution of the Kosov Province across much of the Baltic Palaeoplate into the deeper-water facies of the East Baltic. The new data emphasise the co-occurrence of the core elements of the fauna, Eostropheodonta , Dalmanella , Cliftonia , Hindella , Plectothyrella and Hirnantia , in a siliclastic shelfal setting. The fauna has close similarities with faunas elsewhere on Baltica, including Jämtland, the Oslo Region and Västergötland and plot within the Kosov Province in analyses of the global distribution of Hirnantian assemblages. Carbonate facies, first, in Estonia (lower Hirnantian) and, second, in Oslo together with Östergötland (upper Hirnantian) support quite different faunas related to the margins of Laurentia and the Edgewood Province of the midcontinent, respectively. Stable isotope curves, when used with caution, have helped correlate the sections across the eastern Baltic into Sweden. [ABSTRACT FROM AUTHOR]

Body size is an important ecological parameter that can be understood in both evolutionary and environmental terms. We present a database of changes in overall body size in brachiopods and trilobites through the Ordovician and earliest Silurian of the Oslo Region, Norway. In contrast with global studies, the limited geographical extent of our data allows correlation with environmental parameters such as climate and water depth, and simplifies taxonomical standardization and stratigraphical correlation. In our data set there is a clear indication of increasing size both for brachiopods and trilobites during most of the Ordovician, although this could result from an unbiased random walk. The size increase is followed by a reduction in size during the latest Ordovician. Trilobites show a strong increase followed by a decrease in body size during the Middle Ordovician, while brachiopod body size peaks later, in the Late Ordovician. These changes are partly correlated with the changes in species diversity in the Oslo Region. We discuss the results in terms of two models for change in body size — Cope's rule and the Lilliput effect. Cope's rule is the theory of an increasing body size through geological time, while the Lilliput effect describes a decrease in body size in the aftermath of a mass extinction or a severe environmental disturbance. We find no clear correlations between body size and sea level. [ABSTRACT FROM AUTHOR]

The Middle Ordovician Llanfallteg Formation has yielded remains of soft-bodied organisms previously known only from Cambrian Burgess Shale-type deposits. A new arthropod Etania howellsorum gen. et sp. nov. is described here, characterized by a semi-circular cephalon, clusters of spinose endites on the endopod and exopods with ovoid distal lobes. These characters are consistent with xenopod affinities, a clade otherwise known exclusively from the Cambrian Period. The discovery of E. howellsorum demonstrates that a number of Burgess Shale-type taxa, including xenopods, survived past the Cambrian Period (albeit within a restricted environment) and may have been outcompeted during the Great Ordovician Biodiversification Event (GOBE). [ABSTRACT FROM PUBLISHER]

Much of the material of Paleozoic successions of Kotelnyi Island (New Siberian Islands) is composed of various carbonates, which accumulated in relatively shallow conditions in the Ordovician-Middle Devonian. Such deposits are widespread in synchronous sections throughout the Eastern Arctic and therefore attract attention as a potential tool for interregional correlations. In paleotectonic reconstructions, Kotelnyi Island either is included in terrain which was disconnected from the Siberian Platform in the Paleozoic or is joined to it. These different interpretations result from lack of primary evidence. This paper presents new data on stratigraphy and macroand microfauna of the Upper Ordovician and Silurian of the central regions of Kotelnyi Island. For this interval, we propose a correlation of the studied sections with those of adjacent regions. A conclusion is drawn on the basis of the similarity of lithology and fossil assemblages and also shared trends in the evolution of the sedimentary environment that the Upper Ordovician-Silurian beds of Kotelnyi Island, Taimyr, and the Siberian Platform accumulated in a single shelf basin, which apparently also extends to northeastern Chukotka. [ABSTRACT FROM AUTHOR]