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Geological and topographic map of the southwest coast in the Gun River area. Note the upper contact (exposed around Ranga Creek), and the estimated lower western contact (covered).
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The 85-100 m thick carbonate succession of the Gun River Formation is revised on the basis of nearly continuous cliff sections measured on the northeast coast, and a re-analysis and re-measurement of the stratotype sections on the southwest coast of Anticosti island, Quebec. The Gun River Formation (Llandovery: lower Aeronian) is herein formally di...
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New Anisian (Middle Triassic) ammonoids are reported from British Columbia (BC), Canada. Eight species are reported, including one new genus and two new species: Eofrechites roopnarini gen. et sp. nov. and Parafrechites cordeyi sp. nov. New ammonoid subzones are recognized, leading to improved correlation between BC and Nevada: the Hollandites mino...
Citations
... The exposed Upper Ordovician-lower Silurian stratigraphic succession of the Anticosti Basin is nearly a kilometer thick and divided into eight formations: the Upper Ordovician Vaureal and Ellis Bay formations and the lower Silurian Becscie (Copper and Jin, 2014), Merrimack (Copper and Long, 1989), Gun River (Copper et al., 2012), Menier, Jupiter, and Chicotte formations (Copper and Jin, 2015). In this paper, we focus on the stratigraphic interval spanning the uppermost Vaureal and lowermost Ellis Bay formations. ...
Anticosti Island, eastern Canada, records an exceptionally thick and well-exposed Ordovician/Silurian boundary section that hosts a series of diverse marine invertebrate faunas across the Late Ordovician mass extinction. However, the base of the terminal Ordovician stage, the Hirnantian, has been difficult to identify on Anticosti due to the lack of a traditional Hirnantia fauna within the Upper Ordovician Ellis Bay Formation. Previously, the eponymous taxon of the Hirnantia fauna, and type species of the genus Hirnantia , H. sagittifera (M'Coy, 1851) has been reported only from the uppermost Ellis Bay Formation, leading to uncertainty as to the age of the lower Ellis Bay Formation. Here we report Hirnantia notiskuani n. sp. from the lowermost Ellis Bay Formation. This new species is similar to the type species, H. sagittifera , but is distinguished by its strongly dorsibiconvex shell in mature forms and variously developed uniplicate anterior commissure. Occurrences of these two similar species of Hirnantia , H. notiskuani and H. sagittifera , within the lower and uppermost Ellis Bay Formation, respectively, indicate a Hirnantian age for the entire Ellis Bay Formation, a finding that is supported by recent palynological and chemostratigraphic studies. Brachiopod assemblages within the Ellis Bay Formation therefore are best characterized as a unique and diverse Hirnantia fauna, consisting of genera from both the typical Hirnantia fauna and the epeiric seas of Laurentia.
UUID: http://zoobank.org/1c1dff6a-ee38-4cd3-b8bd-3d803a2774ef
... nematodes, polychaetes and other vermiform organisms) as described from the Upper Ordovician. Soft-bodied algae in the Gun River Formation were recognized by Copper et al. (2012). The Vauréal Konservat-Lagerstätte has several similarities with elements described from intervals of the Middle Triassic of Germany (Knaust, 2008(Knaust, , 2010 and Sardinia, Italy (Knaust and Costamagna, 2012). ...
A diverse benthic fauna containing exceptionally preserved soft-bodied organisms is described from the new Vauréal Konservat-Lagerstätte from the Upper Ordovician Vauréal Formation (Katian) of Anticosti Island, Canada. These fossils occur as pyritic (or goethitic, if weathered), calcitic aggregates or sediment-filled voids on micritic bedding planes of a marlstone-limestone alternation originated on a shallow tropical carbonate ramp. Many organisms are preserved in association with their traces (e.g. burrows, trails), whose changing shapes indicate increasing cohesiveness of the substrate. Rapid burial (obrution) under dysoxic bottom conditions must have favoured exceptional preservation. Although anatomical details of the organisms are often lacking due to recrystallization, members of different groups of organisms could be interpreted based on their shape and other characteristic features, including those of which represent their oldest fossil record (i.e. Acoelomorpha, Turbellaria, Nemertea, Nematoda), beside Polychaeta, Sipuncula, Ostracoda and other Arthropoda. In parallel with molecular data, which recently have changed the phylogenetic status of some clades, this soft-bodied fauna and their traces not only record their appearance but add to the understanding of their body plan and behaviour. The new Konservat-Lagerstätte provides important information about a diverse benthic community in the Late Ordovician after the Great Ordovician Biodiversification Event (GOBE), and represents a calibration point for comparison across the Late Ordovician mass extinction. Moreover, comparable Fossil-Lagerstätten are probably more common in shallow-marine carbonates than currently known but might have been simply overlooked.
... The situation for the Silurian is not much different from the one for the Devonian. Hardgrounds are reported in many studies (Tucker, 1971;Cherns, 1980;Cherns, 1982;Kershaw et al., 2006;Vinn and Wilson, 2010;Copper et al., 2012), but these authors focus on hardground biota and their palaeo-ecology and detailed descriptions of the hardground petrography are lacking. ...
Early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the Proterozoic. Hardground surfaces, however, are more commonly recorded in the Phanerozoic sedimentological archive. While ecological studies of hardground biota abound, the environmental and physico-chemical parameters leading to the development of seafloor lithification remain, in many cases, poorly understood and documented. This paper reviews published evidence on the petrography, mineralogy and geochemistry of Phanerozoic carbonate hardgrounds within a process-oriented context of their environmental controls. Hardgrounds typically develop in warm and shallow, agitated tropical waters that are saturated with respect to CaCO3, but are also reported from hemi-pelagic to bathyal realms and from cool-water, temperate settings. A range of early marine cement types are documented from present-day hardgrounds whereas (preserved) cement fabrics and related mineralogies are less diverse in early Phanerozoic hardgrounds. Carbonate hardgrounds are widespread during calcite sea periods (e.g., Ordovician and Cretaceous), as opposed to some (preservation bias?) ancient aragonite seas (e.g., Permian and Triassic). Obviously, the relation between seawater chemistry and hardground abundance and attributes is not an easy one. Here, the concept of aragonite versus calcite seas serves as a first-order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties. This spatio-temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the Devonian or Paleogene rock record contrasted by the abundance in aragonite Holocene and Recent seas. Holocene hardgrounds allow for the direct assessment of rates of, and reasons for, early subaquatic lithification and-in most cases-escaped subsequent non-marine diagenetic overprint. Conversely, studies of ancient hardgrounds are often biased by early biological and mechanical erosion, the degree of diagenetic overprint, and tectonic to orogenic processes. The formation, distribution and physical properties of hardgrounds depend on the global climatic context (greenhouse/icehouse modes), on sea-level changes, on ocean stratification, on the spatial extent of epicontinental seas and carbonate depositional environments, and on the spatially different mineralogies and rates of carbonate production. The fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric CO2. Thus, the application of lessons from modern to ancient hardground case examples is not straightforward. A holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the Phanerozoic is as yet lacking. A more critical view on secular changes in hardground formation patterns is clearly needed. Future work should rely on the combination of sedimentological, stratigraphic, palaeoecological, petrographic, and geochemical approaches. Specific emphasis should be given to time intervals (Triassic, Carboniferous, Cambrian etc.) where the bulk of reported case studies is at best scarce.
... The Gun River Formation is divided into four members, including, in ascending order, the Lachute, Innommée, Sadtop, and Macgilvray Members (Copper et al. 2012). The upper Macgilvray Member comprises thin-to medium-bedded micritic mudstone, wackestone, and shelly packstone. ...
... The preservation ranges from in situ shell pockets to imbricated coquinas, with a lithology from irregular-to nodular-bedded mudstone to shelly packstone, indicating a depositional setting near the storm wave base (upper BA3). The brachiopod community suggests a middle Aeronian (early Silurian) age (Jin 2008;Copper et al. 2012). The lower Macgrilrvay Member contains a lower-diversity and low-abundance cryptospore assemblage dominated by alete monads, Velatitetras and Laevolancis, suggesting the existence the early land plants (Richardson and Ausich 2007). ...
An exceptionally preserved noncalcified thallophytic alga, Menieria minuta gen. nov. et sp. nov. from the uppermost Gun River Formation (middle Aeronian, Lower Silurian) of Anticosti Island, eastern Canada, is characterized by a relatively delicate thallus with a central axis, lateral branches, and helically arranged, regularly and closely spaced, elongate-linguoid appendages. The algae locally constitute an important portion of the biomass in a brachiopod-dominated paleocommunity, forming an algal meadow on a relatively deepwater subtidal setting within the photic zone. This rare fossilization window suggests that such soft algal meadows may have been common during the Early Paleozoic, resembling modern sea grass meadows that are part of the carbon sink.
The Silurian climate was volatile and punctuated by multiple short-lived climate events, each associated with biotic crisis and perturbations to the global carbon cycle. In total, seven positive carbon isotopic excursions are globally recognized in the Silurian with the large excursions of the Wenlock-Ludlow interval in the Baltic succession garnering the most research; these excursions are recorded in association with cyclic facies changes and the enigmatic resurgence of microbial carbonates. Climate models, hypothesizing cycles of alternating humid and arid climate states, have been developed to explain these paired lithologic-isotopic fluctuations; however, little work has been done to test these models on lower Silurian strata. To test for the presence of δ¹³Ccarb excursions and the stratigraphic motif of proposed climate events, we developed a high-resolution integrated stratigraphic framework for the upper Hirnantian to mid-Telychian (Upper Ordovician to Llandovery) carbonate-dominated succession of Anticosti Island, by examining ~450 m of strata from a recent drill core, supplemented by ~120 m of outcrop. Four facies assemblages and three time-specific facies are identified and organized into three orders of superimposed transgressive-regressive cycles. High-resolution isotopic curves reveal the presence of four global positive carbon isotope excursions all sequentially recorded in the study interval; the HICE (peak of +5‰), Early Aeronian (peak of +2‰), Late Aeronian (peak of +6‰), and Valgu (peak of +3.5‰) excursions. Common cyclic stratigraphic trends are recognized with these δ¹³Ccarb excursions, where each excursion is associated with a shift from shale-rich to shale-poor facies, an intermediate-order transgression, and a minor δ¹⁸O excursion. These repetitive lithologic-isotopic patterns in the Llandovery succession of Anticosti Island are linked to cyclic fluctuations between low-latitude humid and arid climate states. In addition to these patterns, microbial-rich carbonates are associated with the Late Aeronian and Valgu δ¹³Ccarb excursions on Anticosti Island; this suggests a genetic link between the elevated δ¹³C values and the proliferation of calcified cyanobacteria and associated microfossils. This integrated stratigraphic model linking carbon excursions with climate and carbonate factory shifts provides an excellent framework for future studies, using a wide variety of geochemical systems, to better understand the processes that drove environmental and biodiversity changes through the Llandovery.
The subfamily Hindellinae is an early group of athyride brachiopods, characterized by a simple jugum that connects the laterally directed spiralia, which are disjunct from the crura. Four genera ( Hindella , Cryptothyrella , Koigia , and Hyattidina ) are reexamined on the basis of their internal structures, such as the crura and their connection to the hinge, the jugum, and spiralia. The internal brachidium and shell of the Aeronian genus Cryptothyrella differ substantially from those of Hindella . Elkanathyris pallula n. gen. n. sp. is recognized as a posteriorly ribbed hindellide of Aeronian age. These genera are transferred from the Meristellinae to the subfamily Hindellinae (family Hindellidae). On Anticosti Island, Hindella is confined to the Hirnantian (latest Ordovician): it became extinct at the end Ordovician during the last of several mass extinction events that also extinguished the Laframboise reefs at the top of the Ellis Bay Formation. Post-extinction recovery of athyrides was pioneered by small-shelled Koigia , which are abundant in the basal Silurian Becscie Formation. Hyattidina , with a simple brachidium, is abundant in the Aeronian and Telychian of Anticosti, but absent earlier. True meristellines, as envisioned here, first appeared in the Aeronian Gun River Formation. The revised taxonomy and stratigraphic ranges of these earliest athyrides shed light on the nature of the Ordovician–Silurian mass extinction and recovery, and help refine the biostratigraphy of the O-S boundary interval.
Refinement of the 105–115 m thick Llandovery Jupiter Formation provides a more precise view of the tropical faunal recovery and radiation on the eastern margins of Laurentia. The formation spans the late Aeronian through mid-Telychian (438–434 Ma) and preserves an ‘experimental
laboratory’ for evolution of tropical benthic communities in Laurentia, with a mixture of endemic and immigrant genera. Brachiopod communities, for the first time during the Llandovery, differentiated into those that became firmly ensconced as deeper-water inhabitants, and those that
inhabited shallower depths. Following deposition of the Aeronian coral patch reef complex (East Point Member, Menier Formation) on Anticosti Island, sealevel rise resulted in the deposition of the Richardson Member shales (basal Jupiter Formation). This featured relatively deep-water, locally
rich assemblages dominated variously by Dicoelosia, Triplesia, Striispirifer, Gotatrypa, Lissatrypa or Zygatrypa, accompanied by common graptolites. Progressive shallowing marked the overlying Cybèle Member, characterised by diverse suites of
pentamerides (e.g. Phricoclorinda, Chiastodoca, Microcardinalia, Ehlersella) and abundant atrypides (‘Gotatrypa’, Zygatrypa, Clintonella, Lissatrypa). In the Jupiter Formation, spiriferides appeared in pulses, beginning with
Striispirifer in the Richardson Member, Eospirifer in the Cybèle Member, and Cyrtia in the Pavillon Member. Corals are generally rare, locally with small favositids, heliolitids and solitary rugosans. The succeeding lower Ferrum Member reflects a shallow, quiet-water,
possibly lagoonal setting, with a less diverse benthic shelly assemblage dominated by shellbeds of large Gotatrypa. The upper Ferrum Member features the recurrence of Pentamerus, abundant Eocoelia, common crinoids, rare tabulate corals and small solitary rugosans, and
common hardgrounds. The Pavillon Member at the top of the formation is marked by the first appearance of Pentameroides and Costistricklandia, indicating a mid-Telychian age. It has diverse stromatoporoids, solitary and colonial rugose corals, including the first Telychian coral-sponge
patch reefs at South Point, a precursor to the reef-crinoid meadow ecosystem preserved in the overlying Chicotte Formation (mid–?late Telychian).
In modern marine ecosystems, sea-grass and chlorophyte meadows play an important ecological role by serving as a carbon sink. Despite their generally limited areal distribution, the high productivity of sea-grass meadows makes them an efficient assimilator of CO2. During the early Palaeozoic, complex life was virtually confined to the marine environment, with algae being one of the common carbon-fixers, alongside abundant calcifying cyanobacteria, rhodophytes, chlorophytes and charophytes, as well as non-skeletal dinoflagellates and acritarchs. Fossil and molecular data indicate that marine thallophytic algae first appeared in the Early Proterozoic and became widespread in the Palaeozoic, although their fossil record is sporadic because of their soft-bodied nature; in the absence of angiosperm sea grass and mangroves and poorly understood phytoplankton biomass, thallophytic algae were probably major primary producers. In this article, we suggest that thallophytic algae may have played a significant role as a carbon sink in the Early Silurian, analogous to modern sea-grass meadows or kelp forests, based on the well-preserved Early Silurian thallophytic algal meadow from Anticosti Island, eastern Canada.
Silurian brachiopods of Middle Llandovery (Aeronian) ages are reviewed, and 215 genera are identified here, compared with 109 in the preceding Early Llandovery (Rhuddanian), indicating a recovery-radiation interval after the end-Ordovician mass extinction. The chief regions in which they are found are the continents of South China, Avalonia-Baltica, Laurentia and Siberia, which were all at tropical latitudes with the exception of Avalonia. In addition, the very large superterrane of Gondwana, although with patchy brachiopod distribution, included temperate faunas, as well as subtropical faunas (in Iran and Afghanistan). Aeronian brachiopods greatly increased in diversity, with dominance of four major groups: orthides and strophomenides (which had flourished previously in the Rhuddanian), pentamerides and atrypides (which became dominant in the Aeronian), and many newly evolved taxa, and occupied deeper water and wider ecological niches (level bottom and reef) than those in the Rhuddanian. Each of the continents has some endemic genera, but there is a greater proportion of them in South China, where some groups (such as the pentamerides and atrypides) are more diverse and others, such as the orthides, are much less common than elsewhere. Affinity indices (AI) show that two megaunits can be recognized: South China and Avalonia-Baltica-Laurentia (ABL); Siberia seems to have been loosely connected with ABL and even more loosely to South China presumably because of its geographical separation in the Northern Hemisphere. The separation of South China from the other megaunits is further supported by cluster analysis.
