Reefs during the multiple crises towards the Ordovician-Silurian boundary: Anticosti Island, eastern Canada, and worldwide

2001 ◽  
Vol 38 (2) ◽  
pp. 153-171 ◽  
Author(s):  
Paul Copper
Keyword(s):  
Patch Reef ◽  
Central Africa ◽  
Recovery Phase ◽  
Baltic Basin ◽  
Eastern Canada ◽  
Northeast Russia ◽  
Carbonate Production ◽  
Reef Recovery ◽  
Global Sea Level ◽  
Anticosti Island

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 Normalograptus extraordinarius graptolite Subzone. The third and most severe extinction phase capped the Laframboise patch reef complex (Ellis Bay Formation), at the top of the Normalograptus persculptus 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.

A Hirnantian (latest Ordovician) reefal bryozoan fauna from Anticosti Island, eastern Canada: taxonomy and chemostratigraphy

2009 ◽  
Vol 46 (3) ◽  
pp. 207-229 ◽  
Author(s):  
Andrej Ernst ◽  
Axel Munnecke
Keyword(s):  
Patch Reef ◽  
Stable Carbon Isotope ◽  
Late Ordovician ◽  
Stable Carbon ◽  
Eastern Canada ◽  
Generic Level ◽  
Rugose Corals ◽  
Stratigraphic Position ◽  
Yield Values ◽  
Anticosti Island

The Natiscotec outcrop on Anticosti Island, Canada (Ellis Bay Formation, Laframboise Member, Hirnantian, Late Ordovician), exposes a patch reef some 20–30 m in diameter, 2–3 m thick, with abundant rugose corals, as well as favositids and heliolitids. Reef capping and flanking sediments include typical Hirnantian brachiopods, such as Hirnantia , Hindella , and Eospirigerina . Within the reef peloidal microbialites encrusting bryozoan colonies are common. The bryozoan fauna includes three cystoporates, seven trepostomes, and three phylloporines. Two genera and two species are new: the cystoporate Natiscotecella tenuis n. gen. and n. sp. and the phylloporine Dilaminocladia natiscotecensis n. gen. and n. sp. Three more species are also new: the cystoporates Ceramopora clara n. sp. and Acanthoceramoporella spinigera n. sp. and the trepostome Revalotrypa honguedensis n. sp. Furthermore, we identify the three trepostomes Atactoporella aff. ortoni (Nicholson, 1874), Hallopora elegantula (Hall, 1852), and Monotrypella cf. aequalis Ulrich, 1882, and a phylloporine Parachasmatopora porkunensis Lavrentjeva, 1985. Four species are identified at generic level and in open nomenclature: the three trepostomes Lioclemella sp., Calloporella sp., and Trepostomata sp. and a phylloporine ? Ralfinella sp. The bryozoan fauna shows some affinities with the Late Ordovician fauna of Scandinavia. Stable carbon isotope investigations from brachiopod shells of the same outcrop yield values for δ13C of up to +6.7‰, which represent the highest values reported from the Anticosti succession so far. This indicates that the stratigraphic position of the outcrop is at or close to the peak of the globally recognized Hirnantian δ13C excursion.

Carbonate production rates of encruster communities on a lagoonal patch reef: Vabbinfaru reef platform, Maldives

2014 ◽  
Vol 65 (8) ◽  
pp. 720 ◽  
Author(s):  
K. M. Morgan ◽  
P. S. Kench
Keyword(s):  
Coral Cover ◽  
Patch Reef ◽  
Coralline Algae ◽  
Carbonate Production ◽  
Sedimentary Environments ◽  
Reef Health ◽  
Global Estimates ◽  
Range Of Values ◽  
Encrusting Organisms ◽  
Reef Platform

Coral reefs are formed by the growth and calcification of primary coral framework and secondary encrusting organisms. Future scenarios of reef health predict global declines in coral cover and an increase in the relative importance of encrusting organisms to gross reef calcification. Numerous coral growth studies are available; however, there are few quantitative estimates of secondary carbonate production on reefs. The present study used vertically orientated PVC pipe to generate rates of carbonate production (g cm–2 year–1) by encruster communities on Vabbinfaru reef platform, Maldives (4°18′35″N, 73°25′26″E). Maximum carbonate production by encrusters was 0.112 g cm–2 year–1 (mean ± s.d.: 0.047 ± 0.019 g cm–2 year–1). Encruster community composition was dominated by non-geniculate coralline algae (mean ± s.d.: 76 ± 14.2%), with other encrusting taxa being quantitatively unimportant to total substrate cover (mean ± s.d.: 9 ± 16.7%). Rates of encruster calcification at Vabbinfaru fell within the range of values reported for other reef-building provinces. There is a particular need for more quantitative field-based measurements of reef-organism calcification rates because such values strengthen regional and global estimates of gross carbonate production and have direct implications for net reef accretion and the development of reef sedimentary environments.

Late Ordovician sand-wave complexes on Anticosti Island, Quebec: a marine tidal embayment?

1987 ◽  
Vol 24 (9) ◽  
pp. 1821-1832 ◽  
Author(s):  
D. G. F. Long ◽  
Paul Copper
Keyword(s):  
Local Community ◽  
Late Ordovician ◽  
Sand Wave ◽  
Sand Waves ◽  
The North ◽  
Sand Ridges ◽  
Tidal Embayment ◽  
Tidal Modification ◽  
Global Sea Level ◽  
Anticosti Island

Laterally discontinuous, mixed carbonate–siliciclastic sandstones in the upper Vaureal and lower Ellis Bay formations of Anticosti Island were deposited on an equatorial carbonate ramp with a slope of less than 1°. The 10–18 m thick sandstones are interpreted as subaqueous sand-wave complexes analogous to detached parts of modern shoreface-connected sand ridges. These record storm-enhanced, tidal modification of a northerly derived shoal retreat massif that may have formed in response to recovery from global sea-level lowstands in the Late Ordovician (Ashgill: late Rawtheyan – Hirnantian). The sand-wave complexes formed within a tidal embayment that was confined by the Precambrian Shield to the north and northwest by rising tectonic highlands of the Humber Zone in Newfoundland to the east, and by active tectonic highlands in the Quebec Appalachians (Gaspésie) to the south. Paleocurrent distributions, parallel to the western margins of the Strait of Belle Isle, suggest that the north end of the embayment was closed in Late Ordovician time. Low-diversity faunas within the sand units consist mostly of sowerbyellid, strophomenid, and rhynchonellid brachiopods, bivalves, gastropods, large aulacerid stromatoporoids, and large, domed favositid corals. These "sandy fades" faunas belong to communities significantly different from those found in the laterally interfingering and overlying carbonates and shales, suggesting that the sand waves played an important role in local community modification.

scholarly journals Early Silurian brachiopods (Rhynchonellata) from the Sælabonn Formation of the Ringerike district, Norway

2006 ◽  
Vol 53 ◽  
pp. 111-126
Author(s):  
Thomsen E. ◽  
Jin J. ◽  
Harper, D.A. T.
Keyword(s):  
Early Evolution ◽  
Eastern Canada ◽  
Additional Information ◽  
Lower Silurian ◽  
Anticosti Island

A revision of Kiær’s index fossils of "Etage" 6 in the Ringerike district of Norway reveals the presence of four species: Rostricellula wadti sp. nov., Platytrochalos ringerikensis sp. nov., Platytrochalos rabbei sp. nov., and Zygospiraella duboisi. Rostricellula is a common Ordovician rhynchonellide brachiopod and is known to occur in the Lower Silurian as a holdover taxon in only a few localities worldwide. Previously, Platytrochalos was known only from the Lower Silurian (Llandoverian) rocks of Anticosti Island, eastern Canada. The occurrence of this rare genus in the Ringerike district provides additional information for the early evolution and palaeogeography of the taxonomically enigmatic family Leptocoeliidae. Zygospiraella is regarded as an index genus for the Rhuddanian, and the presence of Z. duboisi provides a useful biostratigraphic control on the age of the Sælabonn Formation.

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