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

Abstract

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 lo. The 10-18 m thick sandstones are interpreted as subaqueous sand-wave complexes analogous to detached parts of modem 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 -Himantian). 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 (Gasesie) to the south. Paleocurnnt 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 facies" 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.Les strates de carbonate mixtes -g k s silicoclastiques, latkralement discontinues, dans les formations de Vaukal supkrieur et d'Ellis Bay infkrieur de l'ile d'Anticosti ont kt6 sedimentkes sur une rampe calcaire equatorial avec une pente ne dkpassant pas 1 ". Les g k s de 10 i 18 m d'kpaisseur repksentent des dunes sous-marines complexes analogues aux morceaux dktachks de cktes de sable fixkes dans la zone infratidale. 11s temoignent d'un dkrangement par les markes, accentuk par des tem$tes, qui a modelk un massif de retrait de haut-fond form6 possiblement lors de l'envahissement total de la mer par les basses-terns niveles i l'ordovicien superieur (Ashgill : Rawthkyen -Hemantien). Les complexes de dunes sous-marines formks i l'interieur d'une baie de make qui ktait confinke au nord et au nod-ouest par le Bouclier pkcambrien, h l'est par les hautes-terres tectoniquement soulev6es de la zone d'Humber dans Terre-Neuve et au sud par les hautes-terres tectoniquement actives des Appalaches du Quebec (Gaspksie). Les palkocourants distribues parallklement aux marges occidentales du dktroit de Belle Isle kvklent que l'extkmitk n o d de la baie ktait fermke durant l'ordovicien supkrieur. Les faunes peu varikes qui colonisaient les unites de sable sont repksenttes principalement par des Brachiopodes sowerbyellidks, strophomknidts et rhynchonellidks, des Bivalves, des Gastropodes, des grands Stromatoporo'ides aulacerides et des Coraux favositidks d6mks. Ces faunes de ufaci8s de sableux* appartiement h des communautks considtrablement diffkrente...

Carbon isotope chemostratigraphy in Arctic Canada: Sea-level forcing of carbonate platform weathering and implications for Hirnantian global correlation

“…This may result from the fact that the Baltic and Anticosti basins show a history of sedimentation and sea-level change that differs from those represented in Arctic Canada, Nevada, and South China. Facies analyses of successions both in the Baltic region (Dahlqvist and Calner, 2004;Kaljo et al, 2004) and Anticosti Island (Long and Copper, 1987;Long, 1993b) show that although there were one or several minor or moderate episodes of sealevel fall within the lower Hirnantian in these regions, the timing of maximum lowstand occurred in later Hirnantian time, coincident with the time of the maximum positive y 13 C excursion (see discussion of correlations above). Those authors attributed the occurrence of relatively high sea levels through the Late Ordovician in these regions to relatively high rates of subsidence, due to crustal loading resulting from nearby Caledonian-Taconic orogenic uplift.…”

A composite tectonic–eustatic origin for shelf sandstones at the Cambrian–Ordovician boundary in North Greenland

“…Klein & Ryder 1978). Similar lithofacies are figured from other cratonic sandstones interpreted to be of tidal origin (Button & Vos 1977;Tankard & Hobday 1977;Long & Copper 1987). Elsewhere the presence of reactivation surfaces and burrowed set tops indicates intermittent migration of bedforms by pulsatory or episodic current systems, although the precise nature of these systems is difficult to determine.…”

“…Like the heterolithic sandstones and mudstones this facies is also interpreted to represent local deepening, although the wave-formed structures indicate a relatively shallow water origin, as do the flat-pebble conglomerates which are interpreted to result from storm activity (cf. Sepkoski 1982;Long & Copper 1987).…”

A New Endosymbiont in Late Ordovician Tabulate Corals from Anticosti Island, Eastern Canada

“…Minor siliciclastic sediments (e.g., fine quartz sand and silt) associated with sand-wave complexes are concentrated in late Rawtheyan and Hirnantian (Ordovician) strata primarily in the northeastern region of the island. These are thought to have been derived from Precambrian highlands to the north, especially during sealevel drawdowns associated with Late Ordovician glaciation in Africa (Long and Copper, 1987a). Tectonic deformation of the sequence is slight, with few minor folds and local faults that have a displacement of a few meters or less.…”