Establishment and development of patch reefs in the intracratonic Ordovician sequence near Chicoutimi, Quebec |
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Authors: | TOM L Harland RON K Pickerill DENIS Fillion |
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Institution: | Poroperm-Geochem Limited, Chester CH4 8RD, England;Department of Geology, University of New Brunswick, Fredericton, New Brunswick, Canada E3B 5A3. |
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Abstract: | Patch reefs occur near the top of the transgressive sequence of Ordovician Trenton Group limestones in the Chicoutimi area of Quebec, eastern Canada. Despite their small sue, these reefs comprise diverse assemblages dominated by bryozoans, corals, stromatoporoids and receptaculitid algae. Pelmatozoans and gastropods are also conspicuous. The reefs were initiated and grew in a fully marine, open shelf setting. Available substrates varied from loose skeletal lenses to soft, firm or hardened bioturbated wackestones, and the earliest stages of reef growth reflect this heterogeneity. Loose or less firm substrates were colonised by bryozoans and pelmatozoans and/or by receptaculitids, which, together with accessory organisms, stabilised the sediments and provided the basis for further reef development. The resultant firmer, slightly elevated substrates provided sites for attachment of stromatoporoids and colonial corals which spread over earlier reef organisms and sediments and dominated the later stages of reef growth. On hardened areas of sediment, stromatoporoids and corals colonised the surface directly and the early stabilising stage of reef growth is absent. The compositions and developmental stages of these Trenton Group reefs are comparable with those seen in broadly contemporaneous and often larger reefs elsewhere, and are among the earliest in which corals played an important role. |
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Keywords: | Reefs palaeoecology Anthozoa algae Bryozoa Gastropoda Pelmatozoa Stromatoporoidea Ordovician Canada Quebec |
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