Abstract
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.
Highlights
The roughly three million year long, end-Ordovician mass extinction was marked by at least three major glacial episodes on the North Gondwana Platform, extending fromMorocco to Oman, and including Spain and Portugal [1]
Telychian of Anticosti, whereas in Estonia its oldest occurrence is in the Wenlock
The East Point reef bases occur as outcrops at relatively few localities, and reef foundations were variable from reef to reef
Summary
The roughly three million year long, end-Ordovician (late Katian-Hirnantian) mass extinction was marked by at least three major glacial episodes on the North Gondwana Platform, extending from. In areas on the continental margins of Laurentia, with inner to mid-shelf facies, reefs developed within the mid to late Hirnantian [5,6] leaving a record of the coral and stromatoporoid faunas of the end Ordovician [7]. This Hirnantian reef fauna essentially vanished with only a few hold-overs, such as the phaceloid reef-builder Palaeophyllum. This paper is a contribution to the theme of recovery of reef taxa and reefs after the end Ordovician mass extinction events, as seen in the Anticosti Basin of eastern Laurentia It records the transitional coral and stromatoporoid fauna, and associated reef inhabitants that marked reefs of Aeronian All samples mentioned or illustrated in this study are in the repository of the Geological Survey of Canada, Ottawa, with catalogued samples denoted by the prefix GSC, and locality numbers preceded by the letter “A”
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