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Horseshoe crabs as a group are renowned for their morphological conservatism punctuated by marked shifts in morphology associated with the occupation of non-marine environments and have been suggested to exhibit a consistent developmental trajectory throughout their evolutionary history. Here, we report a new species of horseshoe crab from the Ordovician (Late Sandbian) of Kingston, Ontario, Canada, from juvenile and adult material. This new species provides critical insight into the ontogeny and morphology of the earliest horseshoe crabs, indicating that at least some Palaeozoic forms had freely articulating tergites anterior to the fused thoracetron and an opisthosoma comprising 13 segments. [ABSTRACT FROM AUTHOR]

The Potsdam Group is a Cambrian to Lower Ordovician siliciclastic unit that crops out along the southeastern margins of the Ottawa graben. From its base upward, the Potsdam consists of the Ausable, Hannawa Falls, and Keeseville formations. In addition, the Potsdam is subdivided into three allounits: allounit 1 comprises the Ausable and Hannawa Falls, and allounits 2 and 3, respectively, the lower and upper parts of the Keeseville. Allounit 1 records Early to Middle Cambrian syn-rift arkosic fluvial sedimentation (Ausable Formation) with interfingering mudstone, arkose, and dolostone of the marine Altona Member recording transgression of the easternmost part of the Ottawa graben. Rift sedimentation was followed by a Middle Cambrian climate change resulting in local quartzose aeolian sedimentation (Hannawa Falls Formation). Allounit 1 sedimentation termination coincided with latest(?) Middle Cambrian tectonic reactivation of parts of the Ottawa graben. Allounit 2 (lower Keeseville) records mainly Upper Cambrian quartzose fluvial sedimentation, with transgression of the northern Ottawa graben resulting in deposition of mixed carbonate-siliciclastic strata of the marine Rivière Aux Outardes Member. Sedimentation was then terminated by an earliest Ordovician regression and unconformity development. Allounit 3 (upper Keeseville) records diachronous transgression across the Ottawa graben that by the Arenigian culminated in mixed carbonate-siliciclastic, shallow marine sedimentation (Theresa Formation). The contact separating the Potsdam Group and Theresa Formation is conformable, except locally in parts of the northern Ottawa graben where the presence of localized islands and (or) coastal salients resulted in subaerial exposure and erosion of the uppermost Potsdam strata, and accordingly unconformity development. [ABSTRACT FROM AUTHOR]

A diverse mid-Darriwilian trilobite fauna from the Table Cove Formation, western Newfoundland, has long been known on the basis of calcareous specimens from the west coast of the Great Northern Peninsula. Discovery of silicified faunas in localities on the east coast provides additional morphological information for previously known species, and also reveals the presence of multiple new genera and species. Many of these species are important, as they represent some of the earliest Laurentian members of the diversifying Whiterock Fauna, and seem phylogenetically near to the base of their respective clades. The concept of Sphaerexochinae is restricted to the genus Sphaerexochus itself, with the possible inclusion of Newfoundlandops n. gen. (type species N. karimae n. sp.), which shares with Sphaerexochus potential synapomorphies including the structure of the hypostome and the presence of fine granular sculpture on the librigenal border and field. Most of the Early and Middle Ordovician taxa with three pygidial segments previously classified as Sphaerexochinae by many authors are reassigned to Acanthoparyphinae on the basis of multiple putative synapomorphies. Other new cheirurid genera from the Table Cove Formation are the pilekiine Harebayaspis n. gen. (type species H. plurima n. sp.), and the deiphonine Mainbrookia n. gen. (type species M. becki n. sp.). Other species revised or described include the cheirurine Laneites polydorus (Billings, 1865), and the acanthoparyphines Cydonocephalus tiffanyae n. sp., Kawina stougei n. sp., and Kawina? sp.

The Middle to Upper Ordovician foreland succession of the Ottawa Embayment in central Canada is divided into nine transgressive‐regressive sequences that defines net deepening of a platform succession over ~15 m.y. from peritidal to outer ramp settings, then a return to peritidal conditions over ~3 m.y. related to basin filling by orogen‐derived siliciclastics. With a backdrop of net eustatic rise through the Middle to Late Ordovician, there are several different expressions of structural influence on sequence development in the embayment. During the Middle Ordovician (Darriwilian), foreland‐basin initiation was marked by regional onlap with abundant synsedimentary deformation across a faulted trailing‐margin platform interior; subsequent craton‐interior uplift resulted in voluminous influx of siliciclastics contemporary with local structurally influenced local channelization; then, a formation of a platform‐interior shale basin defines continued intrabasin tectonism. During the Late Ordovician (Sandbian, early Katian), structural influence was superimposed on sea‐level rise as indicated by renewed local development of a platform‐interior shale basin; differential subsidence and thickness variation of platform carbonate successions; abrupt deepening across shallow‐water shoal facies; and, micrograben development coincident with foreland‐platform drowning. These stratigraphic patterns are far‐field expressions of distal orogen development amplified in the platform interior through basement reactivation along an inherited buried Precambrian fault system. Comparison of Upper Ordovician (Sandbian‐lower Katian) sequence stratigraphy in the Ottawa Embayment with eustatic frameworks defined for the Appalachian Basin reveals greater regional variation associated with Sandbian sequences compared to regional commonality in base level through the early Katian. [ABSTRACT FROM AUTHOR]

Abstract: The Lower Ordovician sequence on the Ella Ø Island in Northeast (N-E) Greenland is a thick shallow marine platform carbonate sequence (∼1415m thick) and constitutes the major part of the Kong Oscar Fjord Group. It consists, from bottom to top, of the Antiklinalbugt, Septembersø, and Cape Weber formations, which are believed to be respectively coeval with the Watts Bight, Boat Harbour, and Catoche formations of the St. George Group in western Newfoundland, Canada. Samples were collected from outcrops at high-resolution intervals and micritic materials were extracted by microdrilling after screening their petrographic and geochemical criteria to evaluate the degree of preservation. The δ 13C and δ 18O values of well preserved micrite microsamples range from −5.2‰ to 0.5‰ (VPDB) and from −10.3‰ to−6.5‰ (VPDB), respectively. The δ 13Ccarb profile of the sequence reveals few negative shifts, which vary between ∼2 and 4.7‰ and are associated with unconformities/disconformities, thus reflecting the effect of significant sea-level changes. The δ 13C shifts can be correlated with counterparts on the St. George Group and also on the global Lower Ordovician δ 13C profiles around the early Tremadoc (∼2.3‰) and late Tremadoc–early Arenig (∼4.7‰). [Copyright &y& Elsevier]

There are few body fossil biotas known from early Paleozoic accretionary shorelines, and very few examples of Ordovician soft-bodied assemblages. This study documents two recently discovered biotas from separate sedimentary basins in Manitoba, Canada, that provide unique information about tropical shoreline communities shortly before the Late Ordovician extinction event. Each site represents a distinct depositional environment, but they share biotic elements, including eurypterids, xiphosurids, and large problematic tubes. The William Lake biota, representing more restricted conditions, includes jellyfish that are among the best hydromedusan body fossils known. Rocks at the Airport Cove site, deposited under more open circulation, contain scolecodonts and noncalcified algae. These biotas have some parallels with the recently described Middle Ordovician Winneshiek Lagerstätte, but are also similar to some Late Silurian assemblages. Considered together, early Paleozoic marginal marine deposits are a rich but as yet poorly known source of paleobiodiversity data. [ABSTRACT FROM AUTHOR]

Small Ordovician sedimentary outliers, including Brent Crater, within the northern Ottawa–Bonnechere graben are remnants of a once expansive Upper Ordovician sedimentary cover extending across the southern Canadian Shield. Facies successions along with updated macrofossil and conodont biostratigraphy, and isotope (C, O, Sr) chemostratigraphy provide additional insights into the terrestrial-to-marine transformation, carbonate-platform development, and oceanographic communication across the southern Laurentian platform. Four of the outliers document Sandbian shoreline-to-nearshore deposition: near Deux Rivières, Manitou Islands, the upper part of the Brent Crater sedimentary fill, and at nearby Cedar Lake. Marine transgression initially reworked local fine-grained to boulder-rich regolith within high-energy shoreface siliciclastic environments that gave way to low- to high-energy inner carbonate-ramp setting. Continued transgression resulted in more offshore rhythmic and diverse lithofacies successions defining mixed heterozoan, photozoan, and microbial productivity and marine isotope (C, Sr) signatures, but δ13C excursions suggest periods of greater mixing of terrestrial and marine carbon reservoirs. Lower Katian strata are preserved near Lake Nipissing and characterize deepening from high-energy ooid-heterozoan skeletal shoals to deeper water mid-ramp siliciclastics and skeletal carbonates, host to a Cruziana ichnofacies. An upsection decline in δ13C values through this succession may identify deposition during the post-peak decline of the global Guttenberg δ13C excursion. This lithic succession fits well with contemporary expansion of heterozoan skeletal lithofacies across the Laurentian platform, yet the presence of ooids identifies prevailing warm waters within the platform interior during early stages of transgression. [ABSTRACT FROM AUTHOR]

The Upper Ordovician stratigraphy in southern Ontario represents the clastic foredeep associated with the Appalachian Taconic Orogeny transitioning northwest into coeval carbonate platform facies. Ten measured and sampled sections in both the Collingwood area and on Manitoulin Island, Lake Huron, provide two relatively complete composite sections (277 and 95 m, respectively) through the marine part of the sequence. A total of 100 2 kg samples collected for a conodont biostratigraphic study yielded 77 215 well-preserved specimens. Taxonomic study of the fauna, illustrated herein, identified 34 species representing 22 genera and three taxa in open nomenclature. Taxonomic revisions are made to five species of and one of ; a new species, , is established. The fauna primarily represents the Midcontinent Province with incursions from the North Atlantic Province primarily in the Collingwood area. Four conodont zones are recognized that help refine the ages for the Upper Ordovician upper Lindsay (Collingwood Member), Blue Mountain, Georgian Bay, and Queenston formations. In particular, the Collingwood Member of the Lindsay Formation, a regionally distributed organic-rich shale of hydrocarbon source rock potential, is demonstrated to lie within the Zone of North Atlantic Province and the Zone of Midcontinent Province and to be early Richmondian age. [ABSTRACT FROM AUTHOR]

Abstract: The end Ordovician was a critical period in Earth history. It was a time of global climatic change with large-scale continental glaciations. A wealth of recent work has documented the stratigraphical records from the near-field areas, i.e., from various Gondwanan continental relics where glaciation was more severely felt. There is an urgent need to re-examine the stratigraphic record from the far-field areas at greater levels of resolution than it has been hitherto possible in order to understand the timing, duration, and character at the glaciation centred around the Ordovician/Silurian (O/S) boundary. One of the best exposed and most complete stratigraphic records from paleotropical areas near the boundary is on Anticosti Island in eastern Canada. The east–west trending, ∼200km long Ellis Bay (Hirnantian) outcrop belt, with superb coastal exposures at both ends of Anticosti Island, is slightly oblique to the paleoshoreline with near-shore siliciclastic-dominated facies restricted to the eastern part of the island and more offshore carbonate-dominated facies present along the central and western parts. These mixed carbonate–siliciclastic facies accumulated along a storm-dominated beach-to-offshore profile. They are organized into a stacked set of shallowing-upward offshore to shoreline facies successions (typically coarsening upward) separated by deepening upward facies successions (typically fining upward) formed during intervening transgressions. High-frequency glacio-eustatic fluctuations were the dominant control on the development of TR sequences observed in the Ellis Bay succession of Anticosti Island, although tectonic subsidence had a substantial secondary effect on thickness. Five TR sequences are recognized allowing for precise correlation along the Ellis Bay outcrop belt. In the eastern sections, relatively thin TR sequences are locally bounded by unconformities. A typical sequence begins with thin transgressive limestone overlain by a maximum flooding, calcareous shale grading up into regressive, storm-influenced, proximal to transitional zone fine sandstone/grainstone and shale, which are sharply overlain by shoreface to foreshore sandstone/grainstone. In the central and western sections, the thicker TR sequences have more symmetrical transgressive–regressive components reflecting greater subsidence compensated by a higher carbonate sediment supply. Two discrete glacial periods are recognized during the deposition of the Hirnantian Ellis Bay succession with the younger one recording large sea level changes (>50m in magnitude) caused by the development of very large ice sheets over western Gondwana. Abundant ice conditions on the globe during the end Ordovician, and the resulting high-amplitude eustasy, appear to have left distinctive stratigraphical imprints on mixed, paleotropical, siliciclastic–carbonate ramps. [Copyright &y& Elsevier]

The conodont fauna from nine sections across a platform-to-basin transect in northeastern British Columbia includes species of Early Ordovician (Tremadocian) to Early Silurian (Llandovery) age. A collection of 9,110 conodont elements was recovered from 205 samples taken from nine stratigraphic sections that preserve the platform succession of the Kechika, Skoki, Beaverfoot, McCusker and Nonda Formations and their off-shelf equivalents, the Ospika, Robb, Kenny and Laurier Formations of the Road River Group. The fauna is assigned to 106 species representing 67 genera; the Ordovician species are representative of two faunal realms. One new genus, left in open nomenclature, is described. Five new species include Drepanoistodus latus and four new species left in open nomenclature assigned to the following genera: Walliserodus, Multioistodus?, Pseudooneolodus, and Belodina. The Midcontinent Realm zones recognized include, in ascending order, the Acodus kechikaensis, Oepikodus communis, Jumudontus gananda, Tripodus laevis to Plectodina aculeata zones, Phragmodus undatus and Gamachignathus ensifer? zones. Zonal species of the Atlantic Realm are Microzarkodina flabellum, Eoplacognathus suecicus, Baltoniodus variabilis, Pygodus anserinus, and Amorphognathus tvaerensis. The Silurian fauna, of lower diversity than the Ordovician fauna, is representative of the Distomodus staurognathoides and Pterospathodus amorphognathoides zones. [ABSTRACT FROM AUTHOR]

The largest known trilobite fossil, a virtually complete articulated dorsal shield of the asaphid Isotelus rex new species, has been recovered from Upper Ordovician (Cincinnatian, Richmondian) nearshore carbonates of the Churchill River Group in northern Manitoba. At over 700 mm in length, it is almost 70 percent longer than the largest previously documented complete trilobite, and provides the first unequivocal evidence of maximum trilobite length in excess of one-half metre. Comparisons with other fossil and extant members of the phylum suggest that in terms of maximum linear dimensions it was among the biggest arthropods ever to have lived. Sediments of the Churchill River Group were deposited in an equatorial epeiric setting and the extremely large size of I. rex n. sp. thus marks a striking example of low-latitude gigantism, in sharp contrast to the widespread phenomenon of "polar gigantism" in many modern marine benthic arthropods. Lack of extensive epibiontic colonization of the exoskeletal surface and the presence of large distinctive trace fossils in the same unit suggest that I. rex n. sp. may have been a semi-infaunal predator and scavenger that employed a shallow furrowing and probing mode of benthic feeding. The extinction of the isotelines (and virtually the entire asaphide lineage) at the end of the Ordovician cannot be related to the near contemporaneous achievement of exceptionally large adult size in some representatives. Failure to survive the terminal Ordovician extinction event was most likely a consequence of a pelagic larval life-style that proved ill-adapted to the rapid onset of global climatic cooling and loss of tropical shelf habitats. [ABSTRACT FROM AUTHOR]

Six modifications to the hinge occur in strophomenoid brachiopods from Anticosti Island: (1) overhanging socket ridges; (2) posterolateral socket ridges along the interarea articulate with grooves on the posterior of teeth; (3) anteromedian dental notches articulate with the crests of socket ridges; (4) dental crenulations on the surfaces of teeth mesh with socket ridges; (5) denticles extend laterally to the cardinal extremities; and (6) the margin of the ventral interarea fits into a long socket along the dorsal interarea forming a lateral tooth. Denticulate hinges and dental notches that typify Silurian and Devonian strophomenids begin in the fauna of the Ellis Bay Formation. Thus the most important interval of strophomenid faunal turnover was at the base of the Gamachian (the base of the Hirnantian) and not at the Ordovician–Silurian boundary. Muscle attachment pads in the delthyrial cavity do not correspond to the positions of either the adductor or diductor muscle scars. Pedicle adjustor muscles in modern brachiopods occupy this position. The round gap between the median fold of the pseudodeltidium and groove on chilidium is proposed as the point of emergence of the pedicle muscle. The tiny foramen, commonly sealed early in growth, is suggested to be part of a neanic water-intake system, active before the growth of the cardinal process in ephebic shells. Once the cardinal process appeared, the foramen was blocked. Recurring types of strophomenid ornamentation, such as posteriorly steepened rugae and checkerboard ornamentation, may have served as a plow to redistribute sediment as the shell was pulled backwards along the pedicle.Six modifications de la charnière sont présentes dans les Brachiopodes strophoménoïdés de l'Île d'Anticosti: (1) la présence de crêtes fossulaires surplombantes, (2) les crêtes fossulaires postéro-latérales le long de l'interaréa sont articulées avec des rainures sur la partie postérieure des dents, (3) des échancrures antéro-médianes s'articulent avec les crêtes fossulaires, (4) des crénulations sur la surface des dents s'engrènent avec les crêtes fossulaires, (5) des denticules sont présentes latéralement jusqu'aux extrémités cardinales et (6) la marge de l'interaréa ventral s'insère dans une longue fossette le long de l'interaréa dorsal, formant une dent latérale. Les charnières denticulées et les échancrures dentales typiques des strophoménidés du Silurien et du Dévonien débutent dans la faune de la Formation d'Ellis Bay. Ainsi, le changement faunique le plus important des strophoménidés se situe à la base du Gamachien (base de l'Hirnantien) et non pas à la limite Ordovicien–Silurien. Les cicatrices des muscles dans la cavité delthyriale ne correspondent pas aux positions des muscles adducteurs ou diducteurs. Les muscles ajusteurs pédonculaires occupent cet endroit dans les Brachiopodes modernes. Le trou rond entre le pli médian du pseudodeltidium et le sillon sur le chillidium est proposé comme point d'émergence du muscle pédonculaire. Le petit foramen, généralement calfaté pendant la croissance précoce, est suggéré comme faisant partie du système néanique d'inspiration d'eau, fonctionnel avant la croissance du processus cardinal dans les coquilles éphébiques. Une fois le processus cardinal apparu, le foramen était bouché. Certains types périodiques d'ornementation de strophoménidés, tels les rugae postérieurement plus abruptes et l'ornementation en damier, auraient pu servir de charrue pour redistribuer les sédiments quand la coquille était tirée vers l'arrière le long du pédoncule.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Rock-Eval pyrolysis and molecular organic geochemical analyses as well as organic petrographic observations were carried out on a rare black shale xenolith core drilled from a Late Jurassic-Early Cretaceous kimberlite on the Hall Peninsula in southern Baffin Island, Canada. The results are compared with those of outcrop shale samples from the Upper Ordovician Amadjuak Formation, the only organic-rich shale deposit discovered so far in the region. The shale xenolith is found to be organic-rich and thermally mature at the stage of peak oil generation, and contain type II organic matter similar to that of the immature Amadjuak shale. Discounting the differing thermal maturation effect, similar depositional environments and original organic inputs are suggested for both the shale xenolith and the Upper Ordovician shale based on their bulk, molecular and isotopic signatures as well as organic maceral assemblages. The present study cannot exclude the possibility of the shale xenolith being originated from an organic-rich Lower Silurian deposit, as suggested by previous Re Os isotope dating study. It is clear, however, that depending on their areal distribution and thickness, the lithostratigraphic unit from which the organic-rich black shale xenolith is derived would make an excellent petroleum source rock in the study area. • Black shale xenolith in a Jurassic-Cretaceous kimberlite on Baffin Island is very organic-rich. • It likely originated in a depositional environment similar to that of the organic-rich Ordovician shale from the region. • Organic matter in the shale xenolith is originally Type II kerogen. • The shale xenolith is thermally mature at peak oil generation. [ABSTRACT FROM AUTHOR]

Presents a description of a Tremadoc fauna, based on an examination of the lowermost Ordovician cherts from the Little Port Complex in western Newfoundland. What Ordovician radiolarians; Indication of the ease that the abundance of radiolarians in chert can be extracted; Discussion on the Little Port Complex fauna.

The dolomudstone of the Stonewall Formation was deposited on the present-day northeastern side of the low-relief, relatively shallow, tropical Williston Basin of central Laurentia during the latest Ordovician. This unit hosts a geographically widespread carbonate conglomerate, up to 0.5 m thick and consisting of rudstone to floatstone, that thins and eventually disappears westward and southward. The bed contains dolomudstone intraclasts in a variably argillaceous dolomudstone matrix and varies in composition laterally and vertically. Intraclasts range from millimetres to centimetres in size, are spheroidal to tabular to irregular in shape, and are angular to rounded. They record incipient microcrystalline calcite precipitation in localised domains in lime mud that began just below the sediment–water interface, forming lightly cemented nodules in an unconsolidated matrix, and indicate exhumation and deposition by a single, short-duration, high-energy but variable event that fragmented and abraded many of the nodules and washed in clay and lime mud. The composite nature of the bed in terms of varying proportion of intraclasts versus mud, and range of intraclast size with variable rounding and sorting, suggest that the event fluctuated in intensity and current direction. We interpret this bed as having been formed by a succession of tsunami waves and backwash that scoured the sea bottom and reworked the nodules, and brought in suspended illite from shallow water and the adjacent land surface. Despite drainage from tsunami-inundated coastal areas, the absence of allochthonous quartz sand and silt suggests that there was no sediment of this size stored there. Backwash transport may also have played a role in the formation of argillaceous marker beds which have been attributed previously to sea level fall and subaerial exposure. Other anomalous beds that punctuate shallow epeiric sea successions may also be tsunami deposits, especially if the ambient paleoclimate and bathymetry were not conducive to generating or leaving a signal of major storms, and sea level fluctuation can be discounted. [ABSTRACT FROM AUTHOR]

Discusses the origin of the two paleokarsts within the Lower Ordovician Beekmantown Group dolostones in Ontario and Quebec. Methodology used to determine the paleokarsts origins; Regional structure of Paleozoic strata in eastern Ontario; Distribution and characteristics of paleokarst.

Middle to Late Ordovician subtidal carbonates in the Manitoulin Island area of Ontario are predominantly limestone in compositton, but non-ferroan and ferroan dolomite is a common cement as well as a selective or locally pervasive replacement phase. Integration of field, petrographic, geochemical {δ[sup 13]C, δ[sup 18]O) and fluid inclusion data indicates that lithification of these carbonates occurred during burial diagenesis, with much of the alteration controlled by regional fracturing and hydrothermal influences. Aqueous (type 1) fluid inclusion s in early calcite (pre-dolomite) and dolomite are saline (> 29 wt% NaCl eq.) solutions with Ca and/or Mg in excess of Na and display homogenization temperatures with modes of 95 and 101°C, respectively. These temperatures can be explained by significantly more burial than can be accounted for either by the available stratigraphic information or by an unusually high palaeogeothermal gradient, which also is not well supported The fluid inclusion temperatures are interpreted to have resulted from hydrothermal fluids which circulated during the burial diagenesis of these strata. Type 1 inclusions in late (post-dolomite) calcite are less saline (<19 wt% NaCl eq.) and have a biracial distribution of homogenization temperatures with a relatively well defined low temperature peak similar to those in early calcite and dolomite and a broad higher temperature grouping with a mode at 183°C. A small proportion of methane and light hydrocarbon-bearing fluid inclusions (type 2) are present in all stages of carbonate. Dolomitizing fluids were derived from burial compaction of argillaceous sediments in the more central earls of the Michigan Basin and the updip migration of these brines along fractures to the basin margin where the carbonates of the Manitoulin Island area were dolomitized. Alternatively, migration of dolomitizing brines downward from the overlying pervasively dolomitized Silurian sequence into... [ABSTRACT FROM AUTHOR]

Abstract: Upper Cambrian to Lower Ordovician pelagic carbonate rocks of the Cow Head Group in western Newfoundland (Canada) were sampled for the study of their radiolarian fauna. Well-preserved and diverse faunal assemblages were obtained from a number of levels of the Shallow Bay and Green Point formations. Three different assemblages, including a total of five families, eight genera and 20 species, are recognized in three different sections situated on a palaeobathymetric profile. The various recognized assemblages are compared with previous studies conducted on the Cow Head Group; they improve considerably our understanding of the pattern of changes in radiolarian diversity during the Cambrian–Ordovician transition. The Radiolarian biotic record of western Newfoundland unveils a two step faunal change across the Cambrian–Ordovician transitional interval: one situated at the base of the uppermost Cambrian Stage 10 and the second at a poorly constrained interval situated towards the top of the same Stage 10. These biotic changes consist of genus-level selective extinctions, as well as within-clade species faunal turnover (i.e. Echidnina, Paleospiculum), decrease of species abundance, species extinction and within-clade episodes of species diversification (i.e. Protoentactinia, Parechidnina). [Copyright &y& Elsevier]

Multiple latest Ordovician (Rawtheyan–Hirnantian) glaciations in central Africa, with concomitant global sea-level lowstands and cooler, restricted, equatorial carbonate shelves and ramps, interrupted by warmer interstadial highstands, had a dramatic global impact on the tropical shallow-water reef ecosystem and carbonate production. With the Ordovician-Silurian boundary strata on Anticosti Island as a global standard for a carbonate shelf-ramp setting, the latest Ordovician and earliest Silurian reveal three reef phases, ended by three extinctions. The first extinction, towards the end of the Rawtheyan, affected the last "Richmondian"-type reefs (Vaureal Formation, Mill Bay Member). The second extinction was less pronounced, ending with reefs at the base of the Prinsta Member (Ellis Bay Formation), interpreted as the top of the Normalograptusextraordinarius graptolite Subzone. The third and most severe extinction phase capped the Laframboise patch reef complex (Ellis Bay Formation), at the top of the Normalograptuspersculptus Zone. In the paleotropics, the Hirnantian interglacials showed higher biodiversity than either the preceding Rawtheyan or following Rhuddanian (early Llandovery) warm intervals, a feature perhaps achieved by high innovation rates via introduction of "Silurian" reef biotas during the Hirnantian. The Anticosti reef succession is compared with latest Ordovician reefs from northwestern Europe (Baltic Basin and U.K.), the northwestern margins of Gondwana (Spain and Austria), the Urals, Siberia, Kazakhstan, northeast Russia, and China. Reefs show a global decline from the late Caradoc through late Ashgill, marked by hiatuses towards the O–S boundary. A protracted 3–4 million-year recovery phase for Early Silurian tropical marine biotas, generally without reefs, marked the succeeding Rhuddanian; full reef recovery was delayed until the mid-Aeronian.Les dernières glaciations multiples à l'Ordovicien (Rawtheyen–Hirnantien) en Afrique centrale, en même temps que des bas niveaux globaux de la mer, des rampes et des plates-formes carbonatées plus froides et restreintes à l'équateur, interrompues par des hauts niveaux interstadiaires plus tempérés, ont eu un impact global dramatique sur l'écosystème des récifs tropicaux de faible profondeur et sur la production de carbonate. En prenant les strates de l'île d'Anticosti à la limite Ordovicien-Silurien comme une norme globale pour un milieu de rampe-plate-forme, l'Ordovicien terminal et le début du Silurien révèlent trois phases de récifs qui se sont terminées par trois extinctions. La première extinction, vers la fin du Rawtheyen, a affecté les derniers récifs de type « Richmond » (Formation Vaureal, membre de Mill Bay). La deuxième extinction était moins prononcée et s'est terminée avec des récifs à la base du membre Prinsta (Formation d'Ellis Bay), lesquels sont interprétés comme le sommet de la sous-zone du graptolite Normalograptus extraordinarius. La troisième et la plus sévère des phases d'extinction a coiffé le complexe de l'ensemble récifal Laframboise (Formation d'Ellis Bay), au sommet de la zone Normalograptus persculptus. À la hauteur des paléotropiques, les interglaciaires Hirnantien montraient une plus grande biodiversité que les intervalles tempérés du Rawtheyen qui le précédait ou du Rhuddien (Llandovérien précoce) qui le suivait, une caractéristique qui a pu être atteinte par des taux d'innovation élevés par l'introduction de biotes récifaux « siluriens » au cours de l'Hirnantien. La succession récifale Anticosti est comparée aux derniers récifs ordoviciens du nord-ouest de l'Europe (bassin baltique, Royaume-Uni), aux marges nord-ouest du Gondwana (Espagne, Autriche), de l'Oural, de la Sibérie, du Kazakhstan, du nord-est de la Russie et de la Chine. Les récifs montrent un déclin global à partir du Caradocien tardif et durant l'Ashgillien tardif lequel est marqué par des hiatus vers la limite O–S. Une phase prolongée de 3–4 Ma pour les biotes marins tropicaux du Silurien précoce, généralement sans récif, a marqué le Rhuddien qui a suivi : le rétablissement complet des récifs a été retardé jusqu'à l'Aeronien moyen.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Abstract: Rich palynological assemblages have been recovered from deposits of Hirnantian age in Anticosti Island (Québec, Canada), and in borehole Valga-10 in southern Estonia. The assemblages are well preserved, and include acritarchs, chitinozoans, and cryptospores. The age of the deposits is well constrained by means of palynomorphs (acritarchs and chitinozoans) as well as sequence stratigraphic and chemostratigraphic correlations. Cryptospore assemblages from the two localities are similar and are also broadly comparable to the few known coeval assemblages described elsewhere. They include 11 genera and 20 species, and testify to the presence of an extended and diverse flora during Hirnantian times in Laurentia and, for the first time, also in Baltica. The present findings contribute to an improved knowledge of origin and early development of vegetative cover. The recovery of diverse and abundant cryptospores in Hirnantian deposits may be related to increased input of land-derived sediment during the global sea-level fall linked to the Late Ordovician glaciation, but it also demonstrates that the early land plants may have tolerated a wide range of climatic conditions. [Copyright &y& Elsevier]

The Appalachian Forelands and Platform NATMAP project in eastern Canada is a multi-discipline and multi-organization research endeavour aimed at the understanding of the evolution and architecture of the ancient continental margin of Laurentia. The Canadian Journal of Earth Sciences special issue presents some recent research progress for our knowledge of the Cambrian-Ordovician segment of that ancient margin. [ABSTRACT FROM AUTHOR]

Late Ordovician (Turinian–Chatfieldian) drowning of a mixed carbonate–siliciclastic platform within the Taconic Orogen (Newfoundland Appalachians) is recorded by net deepening of an initial warm, shallow-water platform succession (Lourdes Formation) culminating in a metre-scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits. Composition of transported material suggests that seaward drowning was coupled with back-stepping of a high-energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine-transported siliciclastic sediments (Winterhouse Formation). In the new offshore shelf setting, a sparse reciprocal stratigraphy of fine- to very coarse-grained phosphatic carbonate and mixed sediment is interpreted to document gravity-flow deposition downgradient from either a sustained or episodically developed high-energy cool-water carbonate source along the inner shelf. Transported carbonate was cemented rapidly at temperatures no warmer than 16 °C–23 °C, possibly within a seasonal oceanic thermocline. An upsection decrease in abundance of carbonate by the early Edenian is associated with a dramatic increase in siliciclastic supply. The Turinian–Edenian succession of platform drowning, oceanographic transition to cool-water carbonate production, and, later, its termination by increased siliciclastic supply reflects a first-order tectonic control proximal to uplift within the Taconic Orogen. Similar structural and oceanographic changes along the contemporary distal Laurentian margin provides the basis, with improved biostratigraphic control, for future analysis of the significance of proximal–distal stratigraphies in response to regional foreland tectonism. [ABSTRACT FROM AUTHOR]

Three stages of carbonate-platform development are preserved in the upper Turinian – lower Chatfieldian succession of the Ottawa Group in the Ottawa Embayment and represent deposition along the Late Ordovician Taconic foreland interior of paleo-southern Laurentia. Compared with contemporary stratigraphy in the adjacent northern Appalachian (southern Ontario, New York state) and western Quebec basins, the intermediate Stage 2 succession, which brackets the Turinian–Chatfieldian boundary, preserves embayment-specific stratigraphic patterns. These include: (i) dramatic west-to-east thickening of the upper Turinian Watertown Formation that defines differential subsidence along the present axis of the embayment, (ii) post-Watertown base-level fall defined by appearance of shoreface siliciclastics, (iii) early Chatfieldian marine transgression represented by the proposed L’Orignal Formation that is coeval with but lithologically distinct from the Selby Formation in the northern Appalachian Basin, and (iv) platform segmentation that resulted in a depositional mosaic of shallow banks (Rockland Formation) and equivalent deeper water mico-seaways (lower Hull Formation). The latter event immediately follows accumulation of the Millbrig bentonite, here dated at 453.36 ± 0.38 Ma. Bracketing these local stratigraphic patterns are the bounding stages (1 and 3) represented by the upper Turinian Lowville Formation and middle Chatfieldian Hull Formation, respectively, that contain facies attributes in common with the adjacent basins and characterize inter-regional depositional systems of first warm, then cooler oceanographic conditions. Stage 2 identifies a structurally controlled transition between these end-member stages: a far-field response in the foreland interior, localized along the axis of a late Precambrian fault system, to contemporary change in subsidence rates and tectonomagmatic events along the Laurentian margin. [ABSTRACT FROM AUTHOR]

Terfelt, F, Bagnoli, G. & Stouge, S. 2011: Re-evaluation of the conodont Iapetognathus and implications for the base of the Ordovician System GSSP. Lethaia, Vol. 45, pp. 227-237. In 2000, the International Union of Geological Sciences (IUGS) ratified the decision from the International Working Group on the Cambrian-Ordovician Boundary (COBWG) to place the Global boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System in the Green Point section, Newfoundland, Canada, at a point coinciding with the first appearance of the conodont Iapetognathus fluctivagus. However, a restudy of the conodont successions from Green Point shows that this species is not present at the boundary interval, and as a consequence the section does not fulfil the biostratigraphical requirements of a GSSP. The GSSP horizon as now defined is based on a level part-way through the range of I. preaengensis- a species with lower first appearance datum (FAD). The true FAD of I. fluctivagus is above the FAD of planktonic graptolites and well above the FAD of I. preaengensis. As a consequence of these problems, a restudy of the GSSP section and the other sections in the Cow Head Group is necessary. A redefinition of the GSSP horizon is suggested. The following four alternative horizons have potential as new horizons for the GSSP level: the FAD of Cordylodus intermedius; the FAD of Cordylodus andresi; the FAD of Eoconodontus notchpeakensis; and the FAD of the agnostoid Lotagnostus americanus. □ Boundary, Cambrian, conodont, Global boundary Stratotype Section Point, Iapetognathus, Ordovician. [ABSTRACT FROM AUTHOR]

Positive δ13C carb excursions are correlated through an upper Turinian to lower Chatfieldian carbonate-platform succession along the axis of the Ottawa Embayment and into outliers of the northern Ottawa-Bonnechere graben in central Canada. Successive Turinian excursions (E1 and E2) are lithostratigraphically constrained by erosional surfaces and hosted within the Watertown and overlying L'Orignal formations, respectively, the latter coeval with the Selby Formation in the adjacent northern Appalachian Basin. The excursions coincide with periods of regional transgression, but geographic patterns of 13C depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions, respectively. Differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas, with preferential C org recycling with stratigraphic condensation. By early Chatfieldian time, segmentation of the once regional carbonate platform (L'Orignal Formation) produced a regional mosaic of low-energy muddy carbonate banks (Rockland Formation) and a deeper water platform (lower Hull Formation) settings subject to fluctuating high to low energy current flow. Excursion E3 occurs in both successions, but 13C enrichment is associated only with the bank-top muddy facies. This may identify preferential photosynthetic drawdown of 12C across the bank tops due to limited seawater exchange across the bank-deeper platform boundaries. Excursions E1 to E3, and a younger excursion (E4) in the Hull Formation, are correlated with varying confidence with excursions across southern Laurentia, excursion E3 being the local expression of the Guttenberg δ13C excursion. Our study supports local modulation of regional, if not global, δ13C excursions arising from structurally controlled changes in oceanography and productivity. • Turinian and early Chatfieldian δ13C excursions occur in the Ottawa Embayment. • Lithostratigraphic constraints reveal local excursion truncation, notably the GICE. • Lateral variation in excursion magnitude reflects local syndepositional controls. • Local controls modulate regional to global isotopic signals. [ABSTRACT FROM AUTHOR]

Epipunctae, a new type of shell perforation, are well developed in typical taxa of the family Plaesiomyidae, a group of common orthide brachiopods from Laurentia and some other tropically located tectonic plates of Late Ordovician age. These minute, prominently elongate, tubular structures are similar to endopunctae in size and density, but differ in being oblique, intersecting the shell surface at a relatively low angle, and being confined largely to the outer portion of the shell wall. The tubules are similar in orientation to aditicules within the same shells but are much smaller and denser, usually aligned along fine growth lines and arranged in crude longitudinal columns. Exceptionally preserved phosphatic molds of bundled setal canals inside epipunctae and aditicules, described for the first time in this paper, are direct evidence that these two types of tubular structures of different sizes had the same function of housing sensory setae along the shell margin, but both the setae and the tubules became abandoned in the outer portion of the shell wall through burial by the secondary shell layer when the shell margin migrated forward. Epipunctae have been found so far only in plaesiomyid shells, but aditicules are common in many groups of the order Orthida. The taxonomic value of epipunctae is shown by a reassessment of Pionorthis Schuchert and Cooper, 1932. The hypotype previously regarded widely, but erroneously, as the archetype of `Orthis sola' Billings, 1866, the type species of Pionorthis, is allied to Plaesioinys Hall and Clarke, 1892. It bears the characteristic epipunctae. The holotype of Orthis solo is a dalmanelloid shell with true punctae, assignable to Mendacella Cooper, 1930. This warrants rejection of the genus Pionorthis. [ABSTRACT FROM AUTHOR]

Middle Ordovician (late Dapingian-Darriwilian) conodonts from the Shallow Bay and Green Point formations, Cow Head Group, and the Lower Head Formation are recorded from three sections in Gros Morne National Park. The collection was investigated to clarify local age relationships between the uppermost part of the Cow Head Group and the interbedded to overlying sediments of the Lower Head Formation. Conodonts from St. Pauls Inlet North section indicate a middle Dapingian age for the upper lower Bed 13, latest Dapingian to early Darriwilian age for the upper Bed 13, an early Darriwilian (Dw 1) age for the top beds or Bed 15 of the Shallow Bay Formation at Lower Head, and the Lower Head Formation is referred to the Darriwilian. The uppermost part of the lower Bed 13 contains Periodon hankensis n. sp., Gothodus sp. A, and Diaphorodus delicatus followed by Periodon macrodentatus, Ansella longicuspica, Erraticodon n. sp. A, and Spinodus wardi n. sp. in the lowermost part of upper Bed 13. The fauna with P. macrodentatus is referred to the newly established Periodon macrodentatus conodont (phylo-)Zone, which is used for global correlation. The uppermost fauna in the Cow Head Group, i.e., Bed 15, includes Histiodella holodentata, Nealeodus martinpointensis, Oistodella pulchra, Dzikodus peavyi, and Yangtzeplacognathus n. sp. A , which are included in the Histiodella holodentata conodont (Bio-)Subzone of the Periodon macrodentatus Zone. Nealeodus is a new genus introduced here; Periodon hankensis n. sp. and Spinodus wardi n. sp. are new species described from the beds 13 and 15, respectively, in the Cow Head Group; Drepanodus aff. D. giganteus, Drepanodus aff. D. robustus, Erraticodon n. sp. A, Protopanderodus cf. P. cooperi, P. cf. P. varicostatus, and Yangtzeplacognathus n. sp. A are taxa referred to in open nomenclature. [ABSTRACT FROM AUTHOR]

The Kamouraska Formation is an uppermost Cambrian - lowermost Ordovician quartz-arenite-dominated unit of controversial origin deposited on the southeastern slope of Laurentia bordering the Iapetus Ocean. It is exposed in the Quebec Appalachians on the south shore of the St. Lawrence Estuary. The formation consists of basal polymictic conglomerate and overlying massive sheet-like quartz arenite. The conglomerate beds are reversely and reversely to normally graded. The quartz arenite beds are generally massive, although they may show coarse-tail grading. Beds containing full or partial Bouma sequences are rare. Paleoflow directions from ripple-cross lamination, ripple marks on bed surfaces, and sole marks point towards southeast, south, and southwest. The clastic sediments of the Kamouraska were transported into the deep sea by sediment gravity flows that evolved from hyperconcentrated to concentrated density flows, and then to turbidity currents. The depositional environment is interpreted to have been a southwest-trending meandering submarine canyon. The exposed part of the canyon deposits is slightly oblique to the strike of slope. If correct, our interpretation establishes the preservation of continental-slope deposits in more distal deep-water siliciclastic sedimentary rocks of the Taconian orogen in Quebec, which traditionally have been interpreted as submarine-fan and (or) basin-plain deposits. The orientation of a canyon near parallel-to strike of the slope may have been controlled by syn-depositional growth faults. The coarsest hyperconcentrated flows, which deposited the conglomerate, were restricted to the deepest parts of the canyon during its early stages of development, whereas the concentrated density flows that deposited the massive quartz-arenite beds covered a wider area. [ABSTRACT FROM AUTHOR]

The age of the upper McKay Group based on conodont biostratigraphy is latest Cambrian (Cordylodus proavus Zone) to late Early Ordovician (middle Floian; Oepikodus communis Zone). A collection of 12 940 conodont elements was recovered from 306 samples of upper McKay Group strata exposed in the Western Main Ranges of the southern Canadian Rocky Mountains, southeastern British Columbia. The conodont fauna is assigned to 53 species representing 30 genera. Twelve zones are recognized, two of which are cosmopolitan: Cordylodus proavus Zone and Iapetognathus Zone. Seven Midcontinent Realm zones, in ascending order, include Polycostatus falsioneotensis, Rossodus tenuis, Rossodus manitouensis, low diversity interval, Scolopodus subrex, and Acodus kechikaensis zones, and Tropodus sweeti Subzone (of the Oepikodus communis Zone). Three Atlantic Realm zones, in ascending order, include Cordylodus angulatus, Acodus deltatus, and Paroistodus proteus zones. The zonation for the upper McKay Group establishes correlation with the Survey Peak Formation and lower Outram Formation of the Bow Platform, and with the Kechika Formation and lower Skoki Formation of the Macdonald Platform and Kechika Trough in the northern Rocky Mountains. The McKay Group represents deposition during post-rift thermal subsidence of the margin, although its thickness, abrupt transition to black shale of the overlying Glenogle Formation, and intercalation of volcanogenic rocks imply a history of differential subsidence similar to that of the northern Cordillera, probably related to periodic extension. [ABSTRACT FROM AUTHOR]

Multivariate analytical methods, which have been used effectively in work on scleractinian corals, were applied to tabulate corals. The study involved discrimination and characterization of closely related species of Catenipora from the Selkirk Member, Red River Formation, in Manitoba. Ten morphological characters measured in transverse sections of 37 coralla were tested to perform cluster analyses. Results of correlation analysis and principal component analysis indicated that five of the characters would be suitable: tabularium area, corallite length, corallite width, tabularium length, and tabularium width. A cluster analysis was performed on the raw data matrix coordinated with 37 coralla by the five selected morphological characters. The characters were standardized to mean 0 and variance 1, and squared Euclidean distances among the coralla were calculated. The unweighted pair-group method using arithmetic average was also employed for clustering the coralla. Four morphospecies were consequently extracted from the dendrogram, which was based on the variation of the five morphological characters, and were confirmed by two types of discriminant analysis. Morphospecies A, B, and D have distinctive ranges in variation of all characters except corallite length. Morphospecies C appears to be an intermediate form, in which the ranges of variation of all five morphological characters partially overlap with those of morphospecies A and/or B. Another cluster analysis, including eight type specimens of Ordovician species previously reported from Manitoba, was performed on the data matrix coordinated with 45 coralla by the five morphological characters. Based on this analysis and morphological comparisons, morphospecies A-C are identified as C. rubra Sinclair and Bolton in Sinclair, 1955, C. foerstei Nelson, 1963, and C. robusta (Wilson, 1926) of Nelson, 1963 (= C. cf. robusta herein), respectively. Morphospecies D is equated with both C. agglomeratiformis (Whitfield, 1900) of Nelson, 1963 and C. aequabilis (Teichert, 1937) of Nelson, 1963 (=C. cf. agglomeratiformis herein). The result of cluster analysis based on the five selected morphological characters demonstrates efficiency in distinguishing closely related species of Catenipora from southern Manitoba. The same procedure should also be applicable to other cateniform corals. [ABSTRACT FROM AUTHOR]

An unusually large specimen of the rare digitate to bladed Aulocopella winnipegensis Rauff and three relatively normal sized specimens of ashtray-shaped Hudsonospongia? sp. constitute the first record of demosponges from the Upper Ordovician Beaverfoot Formation in southeastern British Columbia and the first record of these taxa from western Canada. Gross form and canal structure are well preserved, but dolomitization and (or) coarse microsphaeroidal silicification have obliterated spicules and other structural details. We interpret these sponges as epifaunal recliners, without means of attachment to the substrate, a life mode rarely encountered in the modern sponge biota. [ABSTRACT FROM AUTHOR]

The name "Jens Munk Archipelago" is proposed for a cluster of small monadnocks that rise a maximum of 45 m above present sea level on the shores of Hudson Bay in the Churchill area of northern Manitoba. Resistant Precambrian quartzite formed shoals and islands during the Late Ordovician and Early Silurian periods. Outcrop control in the present tundra environment of the Hudson Bay Lowlands is spotty at best, but the quartzitic monadnocks are fringed by Upper Ordovician and Lower Silurian ramp deposits, mainly carbonate in composition. Five isolated outliers of Ordovician-Silurian strata are described, and the location of four other potential outliers is indicated. Ramp dip at any one site generally ranges from 10° to 15°, and the surviving ramps on opposite flanks of paleoislands suggest preservation of near synsedimentary conditions. Extensive conglomerates of reworked quartzite are most abundant on a northern exposure within the islands. Ripple marks and oriented cephalopod debris are related to a vigorous long-shore current generated by northeasterly trade winds that emanated from a subtropical high-pressure cell in the Northern Hemisphere. A paleogeographic reconstruction links the Jens Munk Archipelago of Manitoba to a larger landmass with a Precambrian quartzite core centered over northern Saskatchewan. The general paleoecology of the Jens Munk Archipelago conforms to patterns of windward and leeward facies preserved on other paleoislands of various ages. [ABSTRACT FROM AUTHOR]

Identifies middle Ordovician gastropods that occur in the Anomalorthis brachiopod zone in the Orthidiella brachiopod zone of the Shallow Bay Formation of the Cow Head Group. Systematic paleontology; Correlation of autochthonous and allochthonous beds of Whiterockian age in Western Newfoundland.

Examines morphologically fairly diverse siliceous sponge spicules of Middle Ordovician age from western Newfoundland. Recognition of demosponge and hexatinellid representatives; Comparison between older and younger lithistid dendroclones; Implications of the specimens for the morphologically conservative nature of the spicular skeleton.

The Timiskaming Paleozoic oudier on the central Canadian Shield preserves a thin distal portion of the once extensive Taconic deep-water shale succession that extended across eastern Laurentia. Within this succession, a thin (5 cm) lithic and phosphatic sandstone occurs a few meters above the top of the buried shallow-water carbonate platform, and contains abundant (40-60%) euhedral dolomite, rare fluorite, pyrite-cemented shale microbreccia, and crystal mosaics of subhedral dolomite with pyritic veinlets. The dolomite formed local cement, and precipitated very near the sediment-water interface as illustrated by a relatively uncompacted sandstone framework and a 3-dimensional fabric of clay particles trapped by dolomite growth. The majority of dolomite has planar crystal faces, with ferroan (4.1 ± 0.3 mol% FeCO3) crystal cores and non-ferroan (0.9 ± 0.2 mol% FeCO3) rims. Fluid inclusions, too small (< 2 µm) for reliable microthermic analysis, are mostly liquid, which, in keeping with interpreted near-surface diagenesis, as well as temperature-controlled dolomite-crystal roughening models, may indicate that formation temperatures were no more than ~60 to 80°C. δ13CPDB values (~1.2 %) are similar to a Late Ordovician seawater composition, but δ18OPDB values (-4.8 to -5.2 %) are too negative compared to the expected values for contemporary deep-marine dolomite. Combining the regional paleoceanographic framework with diagenetic constraints and revised models for Late Ordovician seawater temperature and δ18O compositions, the dolomite is interpreted to be a proxy for a low-temperature (at least ~50°C) hydrothermal anomaly near the sediment-water interface. Fragments of shale microbreccia, pyrite veinlets, and subhedral dolomite, along with the region's structural history, allow speculation that this event coincided with local reactivation of a Precambrian fault, part of an ancestral fault system now manifest regionally by an extension of the Ottawa-Bonnechère Graben. Late Ordovician craton-interior tectonism, in a region previously considered tectonically stable at this time, is defined by local response of inherited Precambrian structure driven by, but distal to, Taconic orogenesis. [ABSTRACT FROM AUTHOR]

Upper Cambrian to Middle Ordovician mafic volcanic rocks of the Donjek assemblage comprise the oldest exposed units of the Alexander terrane in the Saint Elias Mountains of northwestern Canada. In this study, we use the geochemical and geological characteristics of these rocks to decipher their tectonic setting, petrogenetic history, and relationship to the early Paleozoic Descon arc system of the Alexander terrane in southeastern Alaska. Donjek assemblage volcanic rocks are subdivided into three geochemical types: transitional basalt (type I), light rare earth- enriched island-arc tholeiite to calc-alkaline basalt (type II), and enriched mid-ocean ridge basalt to ocean-island basalt (type III). Simple petrogenetic models illustrate that the basalts were generated by the decompressional partial melting of enriched asthenospheric mantle and variably mixed with depleted mantle and subduction-related components. Analogous geochemical signatures for modern Sumisu Rift and Okinawa Trough lavas imply that the Donjek assemblage basalts erupted during the rifting of the Descon arc. This model provides a new comparative framework for terranes of Siberian, Baltican, and Caledonian affinity in the North American Cordillera and, in particular, suggests a paleogeographic connection to rift-related magmatism in the Seward Peninsula region of the Arctic Alaska-Chukotka terrane. [ABSTRACT FROM AUTHOR]

In situ LA-ICP-MS U–Pb geochronology has been performed on apatite and zircon within thermally recrystallized clast-laden and clast-poor impact melt rocks from the Brent impact structure. A total of 377 laser analyses on 120 impact melt-grown (n = 9) and impact-recrystallized zircon grains (n = 111) were obtained, from which a concordia age of 452.8 ± 2.7 Ma (MSWD 0.57, n = 11), and a weighted average mean 206Pb/238U age of 453.2 ± 2.9 Ma (MSWD 0.60) (n = 11) are calculated. A total of 300 laser analyses from 100 relict apatite grains were obtained, with an unanchored regression through all data yielding a lower intercept age of 453.2 ± 6.0 Ma (MSWD 5.8, n = 300), that overlaps within error of zircon. 207Pb/206Pb ratios obtained from feldspar clasts within clast-laden impact melt retain the same initial Pb composition as the target rocks from which they are derived, while feldspars that crystallized from impact melt have 207Pb/206Pb ratios indicative of isotopic re-equilibration between basement lithologies of two different ages. A similar variability in 207Pb/206Pb is recorded by apatite. This provides evidence for the involvement of Neoproterozoic Lake Nipissing alkaline suite, as well as Mesoproterozoic Grenville gneisses in the production of impact melt at Brent. Recrystallized apatite grains exhibit enrichments in light rare earth elements (LREEs) along neoblast grain boundaries, indicative of trace element substitution and phase precipitation during impact-induced recrystallization. An age of 452.8 ± 2.7 Ma from zircon and 453.2 ± 6.0 Ma from apatite places the impact event in the Late Ordovician, at or near the Sandbian–Katian boundary, confirming Brent's involvement in the Middle to Late Ordovician crater cluster event—a period of enhanced impactor flux to Earth related to the L-Chondrite parent body disruption. [ABSTRACT FROM AUTHOR]

Petrography, geochemistry (stable and radiogenic isotopes), and fluid inclusion microthermometry of matrix dolomite, fracture-filling calcite, and saddle dolomite in Ordovician to Devonian carbonates from southwestern Ontario, Canada, provide useful insights into fluid flow evolution during diagenesis. The calculated δ18Ofluid, ΣREE, and REESN patterns of matrix and saddle dolomite suggest diverse fluids were involved in dolomitization and/or recrystallization of dolomite. The 87Sr/86Sr ratios of dolomite of each succession vary from values in the range of coeval seawater to values more radiogenic than corresponding seawater, which indicate diagenetic fluids were influenced by significant water/rock interaction. High salinities (22.4-26.3 wt. % NaCl + CaCl2) of Silurian and Ordovician dolomite-hosted fluid inclusions indicate involvement of saline waters from dissolution of Silurian evaporites. High fluid inclusion homogenization temperatures (>100°C) in all samples from Devonian to Ordovician show temperatures higher than maximum burial (60-90°C) of their host strata and suggest involvement of hydrothermal fluids in precipitation and/or recrystallization of dolomite. A thermal anomaly over the mid-continent rift during Devonian to Mississippian time likely was the source of excess heat in the basin. Thermal buoyancy resulting from this anomaly was the driving force for migration of hydrothermal fluids through regional aquifers from the center of the Michigan Basin toward its margin. The decreasing trend of homogenization temperatures from the basin center toward its margin further supports the interpreted migration of hydrothermal fluids from the basin center toward its margin. Hydrocarbon-bearing fluid inclusions in late-stage Devonian to Ordovician calcite cements with high homogenization temperatures (>80°C) and their 13C-depleted values (approaching −32‰ PDB) indicate the close relationship between hydrothermal fluids and hydrocarbon migration. [ABSTRACT FROM AUTHOR]

The article examines an Ordovician evaporite trough that contains salt diapirs in the northern part of the Kara Sea. It provides a concept about the Early Paleozoic Paleogeography of the North Kara region and substantiates the age of salts. It discusses the determination of evaporite age which can be estimated based on correlation to the analogs from Severnaya Zemlya. The article also offers additional information on Ordovician evaporites in the Arctic region, which are also developed within the Arctic sector of Canada.

Hundreds of shell borings of different origin and displaying variable patterns were found in strophomenide, pentameride, and orthide brachiopods of five Paleozoic localities in northern and eastern Canada. The borings were analyzed using simple statistics as well as cluster and nonmetric multidimensional scaling analyses. At the Ordovician Anticosti Island locality, all borings are parasitic or post-mortem in origin, while at the Wenlock–Ludlow Baillie-Hamilton Island, almost all borings are predatory. At the remaining three localities, borings represent a mix of predatory, parasitic, and post-mortem domichnial borings in all three brachiopod taxa, the proportions of which were controlled largely by brachiopod shell morphology and paleoecology. For the strophomenides, predatory borings can be segregated from parasitic and post-mortem domichnial using simple and multivariate statistical analyses. Sowerbyella-type strophomenides have a higher proportion of predatory borings at the Lochkovian localities than at the Ordovician localities, while the reverse is true for the Strophomena-type strophomenides. In pentamerides and orthides, very few predatory borings are identified; most borings were emplaced by parasitic or post-mortem domichnial borers. In pentamerides, this is due to the internal structure of the shells, which elevated the muscles of the organism above the shell floor, rendering them inaccessible to boring predators. In orthides, more deliberate defense mechanisms such as toxins or external ornamentation may have deterred predation. This study indicates that throughout the Paleozoic interactions between borers and brachiopods were complex but can be elucidated using a large sample size and statistical analyses. [ABSTRACT FROM AUTHOR]

The Philipsburg tectonic slice is bounded to the west by a northeast–southwest-trending thrust fault (Logan’s Line) and preserves 10 formations of Middle (?) to Late Cambrian (Milton, Rock River, and Strites Pond formations), Early Ordovician (Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations), and early Middle Ordovician (Luke Hill, Solomons Corner, and Corey formations) age. The strata were previously assigned to the Philipsburg Group. Early correlations between the Philipsburg succession and coeval strata of the St. Lawrence Platform were mainly based on sparse macrofauna and inferred stratigraphic position. Unconformities at the Cambrian–Ordovician and Early Ordovician – Middle Ordovician boundaries occurring in autochthonous St. Lawrence Platform and the allochthonous Philipsburg succession (Philipsburg tectonic slice) highlight new stratigraphic interpretations between the inner-shelf (St. Lawrence Platform) and the outer-shelf (Philipsburg) successions. The succession in the Philipsburg tectonic slice is divided into three new groups. The Middle (?) to Upper Cambrian Missisquoi Group (new) includes the Milton, Rock River, and Strites Pond formations. The upper boundary of the Missisquoi Group is defined by the upper unconformable contact between the Upper Cambrian Strites Pond Formation and overlying Lower Ordovician Wallace Creek Formation. The Missisquoi Group correlates with the Potsdam Group of the St. Lawrence Platform. The Lower Ordovician School House Hill Group (new) includes the Wallace Creek, Morgan Corner, Hastings Creek, and Naylor Ledge formations. The upper boundary of this group is marked by a regionally extensive unconformity at the top of the Naylor Ledge Formation and correlates with the younger Beekmantown-topping unconformity. The School House Hill Group is correlative with the lower to upper part of the Beekmantown Group (Theresa Formation and the Ogdensburg Member of the Beauharnois Formation) of the St. Lawrence Platform. The Middle Ordovician Fox Hill Group (new) consists of the Luke Hill, Solomons Corner, and Corey formations. This group correlates with the uppermost part of the Beekmantown Group (Huntingdon Member of the Beauharnois Formation and the Carillon Formation). [ABSTRACT FROM AUTHOR]

Current paleogeographic reconstructions extend Late Ordovician Taconic-derived siliciclastics across the central Canadian craton prior to the terminal Ordovician glacioeustatic lowstand. Revision of the Late Ordovician Dawson Point Formation of the Timiskaming outlier greatly reduces the distribution of these siliciclastics, and documents a greater spread of shallow-water carbonate of Richmondian age. As revised, the Dawson Point Formation contains two informal members: a deep-water graptolitic shale that grades upward into shallow-water siliciclastic redbeds, and an upper member of shallow-water, muddy, crinoidal limestone with interbedded shale, likely representing low-energy shoals on a muddy shelf. Deep-water shale accumulation began in the upper manitoulinensis graptolite Zone following foundering of the regional foreland carbonate platform. Basin development documents a northward-younging (~1 million years) from southern Ontario foreland basins, in keeping with regional tectonic-driven transgression along eastern North America. The shale-to-carbonate succession of the Dawson Point Formation correlates with the Georgian Bay Formation on Manitoulin Island, wherein the upper carbonate-dominated divisions of both formations are equivalent to the siliciclastic Queenston Formation of southern Ontario. In absence of additional biostratigraphic information, the upper member of the Dawson Point Formation is likely Richmondian (or late Ashgillian) in age. The revised Late Ordovician history of the Timiskaming outlier may identify a once significant volume of shallow-water carbonate across the central Canadian craton, with related sequestration of carbon dioxide possibly aiding global cooling. Erosion of the carbonate, driven by developing glacioeustatic lowstand conditions, was likely contemporaneous with early Hirnantian peritidal deposition of the uppermost Queenston Formation in southern Ontario. [ABSTRACT FROM AUTHOR]

Four graptolite biozones are recorded from the Arenig portion of the Road River Group in the Richardson and Mackenzie mountains in the Yukon and Northwest Territories. In ascending order, these zones are Tetragraptus approximatus, Pendeograptus fruticosus, Didymograptus bifidus, and Parisograptus caduceus australis (new). The Castlemainian stage may be represented by nongraptolitic massive bedded chert. The Arenig–Llanvirn boundary is drawn below the first occurrence of Undulograptus austrodentatus. Fifty-four graptolite taxa are present, and 16 of these species and subspecies are recorded for the first time in this deep-water biotope, namely, Didymograptus? cf. adamantinus, D. asperus, D. dilatans, D. cf. kurcki, D. validus communis, Holmograptus aff. leptograptoides, H. sp. A, Isograptus? sp. nov. A, I. ? dilemma, Keblograptus geminus, Pseudisograptus manubriatus harrisi, Ps. m. koi, Ps. m. janus, Ps. cf. tau, Xiphograptus lofuensis, and Zygograptus cf. abnormis. [ABSTRACT FROM AUTHOR]

A collection of 60,886 conodonts was recovered from 141 samples of the Outram, Skoki and Owen Creek Formations (Lower to Middle Ordovician) that outcrop through the Wilcox Pass section, Jasper National Park, Alberta, Canada. This section represents the standard reference section for the Lower-Middle Ordovician of the Southern Canadian Cordillera. The well preserved fauna is assigned to 75 species representing 48 genera. The species are representative of both the Midcontinent and Atlantic faunal realms, but dominantly the former. Nine Midcontinent Realm zones are recognized in the upwards shallowing carbonate platform succession including the Scolopodus subrex, Acodus kechikaensis, Oepikodus communis, Jumudontus gananda, Tripodus laevis, Histiodella altifrons, Histiodella sinuosa, Histiodella holodentata, and Phragmodus "pre-flexuosus" zones. Zones recognized that are characteristic of the Atlantic Realm include Paroistodus proteus, Paracordylodus gracilis, Oepikodus evae, Paroistodus originalis, and Microzarkodina flabellum. A new genus, Filodontus, is proposed for elements assigned previously to the form genus "Scolopodus" filosus. A new species, Leptochirognathus wilcoxi, is described and one new species, left in open nomenclature, is assigned to Rossodus?. [ABSTRACT FROM AUTHOR]

Comparison of litho-, bio-, and chemostratigraphy in two cores from the northeastern margin of the Michigan Basin (Manitoulin Island) and from within the Ottawa Embayment (eastern Ontario) identifies interbasinal differences of Late Ordovician platform foundering linked to Taconic orogenesis. Graptolite biostratigraphy defines an east-to-west younging (late Edenian to early Maysvillian) of platform burial. A regional unconformity likely caps the platform succession. In both basins, an increased supply of mafic material appears during the final stages of platform collapse, with the accumulation of organic-rich (<8%), petroliferous shales (Collingwood Member -- Michigan Basin; Eastview Member -- Ottawa Embayment). Both units preserve evidence for deposition coincident with increased dysoxic to possible anoxic bottom-water conditions, but the Collingwood Member accumulated under a relatively stable paleoceanographic environment. Rhythmic interbedding with platform limestone in eastern Ontario, combined with evidence for fluctuating paleoproductivity, suggests the depositional environment of the Eastview Member was more sensitive to higher order controls affiliated with tectonic, oceanographic, and (or) sea level variation. Such interbasinal differences likely reflect a greater rate of subsidence in the Manitoulin region transforming platform sedimentation to a distal ramp facies. In eastern Ontario, a lesser rate of subsidence maintained a shallower water, but open margin, setting. Burial of the Upper Ordovician platform, as preserved in eastern Ontario, occurred during peak dysoxic conditions, with deposition of a hemipelagic facies (Billings Formation) that marks the peak supply of clay-size mafic-derived sediment. Bottom-water ventilation occurred only with appearance of abundant Taconic-derived distal turbidites. An equivalent hemipelagic facies appears to be absent from the Manitoulin region. However, equivalent resedimented deposits are represented by the Blue M [ABSTRACT FROM AUTHOR]

The Taconian Humber Zone stretches from western Newfoundland to southern Quebec. The Early Cambrian slope succession in Newfoundland is found in the Curling Group, whereas in Quebec, various units were deposited during that first time slice. Biostratigraphic data allow correlation of the Curling Group with the Labrador Group in Newfoundland and with the newly time-constrained slope succession in Quebec. The end of the rift drift transition is marked by a sea-level lowstand at the end of the Early Cambrian. The Middle Cambrian to latest Early Ordovician passive margin history recorded five cyclic sea-level fluctuations. Three of these cycles are recorded in the shallow-marine Middle to Late Cambrian platform (Port au Port Group) and slope sediments preserved in the Cow Head and Northern Head groups in Newfoundland. The biostratigraphic information assists correlation with Cambrian passive margin units in Quebec. Major sea-level lowstands are recognized along the continental margin in early-middle Late Cambrian (Steptoan) and in late Late Cambrian (Sunwaptan). Even if the Quebec succession can be tied with its Newfoundland correlative, some significant differences in the nature of Upper Cambrian slope conglomerates argue for a tectonic control on the depth of erosion of the Cambrian continental margin. The Lower Ordovician record of the passive margin consists of two depositional cycles (Tremadocian-Arenigian) separated by a sea-level lowstand. This last event is well expressed in platform succession and is also recognized in conglomerate units found in the slope succession. [ABSTRACT FROM AUTHOR]

A few specimens of the ornate anthaspidellid demosponge, Archaeoscyphia pulchra (Bassler), have been collected from the Lower Ordovician Outram Formation or Skoki Formation, from a saddle at the head of South Rice Brook in northeastern British Columbia. This is the first report of the flanged-appearing annulate, steeply obconical sponge in western Canada, although it has been reported from the Mingan Islands of Quebec and was initially described from Nevada, in the western United States. The taxon has also been reported as other species of Archaeoscyphia from Ordovician rocks of Missouri and from the San Juan region of Argentina.Quelques spécimens de Démosponges anthaspidellides ornées, Archaeoscyphia pulchra (Bassler) ont été recueillis dans la Formation d'Outram ou de Skoki (Ordovicien inférieur); ils proviennent d'un col à la tête du ruisseau South Rice dans le nord-est de la Colombie-Britannique. Ce rapport est le premier sur l'éponge étroitement obconique, annelée et à apparence de collerette dans l'ouest du Canada, bien qu'elle ait été rapportée aux îles Mingan, au Québec, et que la description initiale provienne du Nevada, dans l'ouest des États-Unis. Le taxon a aussi été rapporté en tant que d'autres espèces d'Archaeoscyphia trouvées dans des roches ordoviciennes du Missouri et de la région de San Juan, en Argentine.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]