Prayssac, France


Prayssac, France
Time filter
Source Type

Wang Y.,CAS Nanjing Institute of Geology and Palaeontology | Jin J.,University of Western Ontario | Zhan R.,CAS Nanjing Institute of Geology and Palaeontology | Copper P.,Loupicoubas
Geology Today | Year: 2014

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. © 2014 John Wiley & Sons Ltd, The Geologists' Association & The Geological Society of London.

Copper P.,Loupicoubas | Jin J.,University of Western Ontario | Desrochers A.,University of Ottawa
Stratigraphy | Year: 2013

The type sections of the Ellis Bay Formation are revised to incorporate recent stratigraphic correlations east to west on Anticosti Island. This is one of the most complete tropical carbonate sequences spanning one of the major Phanerozoic mass extinction episodes. A richly fossiliferous benthic fauna faithfully records the change-over from the Ordovician (Richmondian, late Katian), the mass extinction around the boundary, and the recovery within the earliest Silurian (Rhuddanian, Llandovery). Critical in this revision is the Hirnantian shelly fauna that begins at or close to the base of the Ellis Bay Formation at the west end (as revised herein), and ends at the top of the reefal Laframboise Member, the O/S boundary as used herein. Equivalent strata at the east end contain Hirnantia sp. at the base of the Prinsta Member, as the basal Ellis Bay Formation, and Hirnantia sagittifera in reef-capping beds at the top of the Laframboise Member in the central area of the island. The Ellis Bay Formation is rich in typical Hirnantian brachiopods such as Eospirigerina and Hindella. The earliest Silurian recovery brachiopod fauna is usually small-shelled, composed of both Ordovician hold-over taxa (ca 30%) and new arrivals such as the pentameride Viridita, athyridide Koigia, and atrypide Zygospiraella. In this study, three new members are proposed for the 80-90m thick Ellis Bay Formation at the west end of Anticosti Island, beginning with the basal shales and limestones of the Fraise Member (overlying a recessive shaly unit of the Katian Vaureal Formation), followed by the Juncliff Member resistant limestones, and the overlying limestones and shales of the Parastro Member. The uppermost two members are correlated directly with the Lousy Cove and Laframboise members at the east end, where the same sequence is thinner and contains several discontinuities. The top of the reef-capping grainstone beds above the reefal Laframboise Member marks the major end-Ordovician extinction of Hirnantian brachiopods, stromatoporoids, corals, crinoids and nautiloids, signaled by the return to background δ18O and δ13C values. The overlying Rhuddanian Becscie Formation comprises a lower Fox Point Member of thin, evenly bedded limestones, with a low-diversity but high-abundance Rhuddanian brachiopod fauna, and an upper Chabot Member of irregularly bedded coralline, non-reefal limestones, marking the appearance of typical Silurian benthic faunas.

Copper P.,Loupicoubas | Stock C.W.,University of Alabama | Jin J.,University of Western Ontario
Journal of Paleontology | Year: 2013

A large and abundant columnar stromatoporoid, Quasiaulacera n. gen., from the Ellis Bay Formation, up to 3 m long and 40 cm in diameter, marks the Hirnantian (latest Ordovician) of Anticosti Island. Two species are present: Quasiaulacera stellata n. sp. from the basal Ellis Bay Formation (basal Prinsta Member, lower Hirnantian) along the northeastern coast of the island, and the type species Q. occidua n. sp. from the upper Ellis Bay Formation (Lousy Cove Member, upper Hirnantian) in the western carbonate facies of the island. Quasiaulacera is rare or absent in the reefal Laframboise Member (uppermost Hirnantian) of the formation. The new genus differs from Aulacera in the underlying Vaureal Formation (upper Katian) in having a large central axial zone marked by a single stack of large, convex-up cyst-plates, that is surrounded by a middle layer of small, concentric microcyst-plates, in places denticulate, and an outer layer composed of concentric laminae with dense pillars, in which microcyst-plates are either absent or rare. The outer two layers are defined by longitudinal fluting; there are no branching forms. Both species demonstrate a ball-like holdfast system, some with diameters of 30 to 70 cm, microbially cemented into the substrate. Quasiaulacera "gigantism" in the paleotropical Anticosti Basin evolved at a time of global cooling associated with the Hirnantian glaciation in south polar Gondwana, but terminated in mass extinction of the aulaceratids at the O/S boundary in Laurentia. This supports other evidence that the Hirnantian featured not only generic loss, but also innovation and migration in tropical latitudes.Copyright © 2013, The Paleontological Society.

An extensive late Aeronian patch reef swarm outcrops for 60-70 km on Anticosti Island, eastern Canada, located in the inner to mid-shelf area of a prominent tropical carbonate platform of southeastern Laurentia, at 20°-25° S paleolatitude of the southern typhoon belt. This complex, described here for the first time, includes more than 100 patch reefs, up to 60-80 m in diameter and 10 m high. Reefs are exposed three-dimensionally on present-day tidal flats, as well as inland along roads and rivers. Down the gentle 1°-2° paleoslope, the reefs grade into coral-sponge biostromes, and westerly they grade into inter-reef or deeper 'crinoidal meadow' facies. The reef builders were dominantly tabulate and rugose corals, with lesser stromatoporoids. Other components include crinoids, brachiopods, green algae (especially paleoporellids), and encrusting cyanobacteria: reefs display some of the earliest known symbiotic intergrowths of corals and stromatoporoids. Reefs were variably built on a base of crinoidal grainstones, meadows of baffling tabulate corals, brachiopod shells, or chlorophytes. These reefs mark an early phase of reef recovery after a prominent reef gap of 5-6 million years following the Ordovician/Silurian mass extinction events. The reefs feature a maximal diversity of calcifying cyanobacteria, corals and stromatoporoids, but low diversity of brachiopods, nautiloids and crinoids. Following the North American Stratigraphic Code, we define herein the Menier Formation, encompassing the lower two members of the existing Jupiter Formation. © 2012 by the authors; licensee MDPI, Basel, Switzerland.

Copper P.,Loupicoubas | Jin J.,University of Western Ontario
Newsletters on Stratigraphy | Year: 2015

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 deepwater, 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). © 2015 Gebrüder Borntraeger, Stuttgart, Germany.

Ausich W.I.,Ohio State University | Copper P.,Loupicoubas
Palaeontographica Canadiana | Year: 2010

The diverse Katian (Late Ordovician) through Llandovery (Early Silurian) crinoid fauna from Anticosti Island is described. Previously, six described species were known; with one now a nomen dubium and two others placed in open nomenclature, herein. In contrast, Katian through Llandovery Anticosti crinoids are now recognized with 49 named species assigned to 39 genera, including 41 new species and 18 new genera. Including all taxa left in open nomenclature, crinoid species-level richness is more than 60. The Anticosti Island crinoid fauna is highly endemic with 46 percent of genera only known from Anticosti Island and only three species known from elsewhere. This undoubtedly results because the temporal and geographic interval represented on Anticosti Island is extremely poorly known from elsewhere, especially in shallow-water facies with shelly faunas. The Anticosti fauna is very significant for understanding the macroevolutionary transition from the early to the middle Paleozoic Crinoid Evolutionary Faunas, which was mediated, in part, by end-Ordovician mass extinctions. Late Katian crinoid faunas from Anticosti Island are similar in composition to contemporaneous faunas elsewhere. "Silurian aspect" faunal elements are common in Anticosti Hirnantian faunas. The Rhuddanian, immediately following the end-Ordovician extinctions, contains the least diverse crinoid fauna on Anticosti Island, and this earliest Silurian fauna still retains some "Ordovician aspect" faunal elements. By the Telychian, the fauna is characteristically Silurian in composition.

Loading Loupicoubas collaborators
Loading Loupicoubas collaborators