A Lower Devonian Reef Sequence And Fauna, Disappointment Bay Formation, Canadian Arctic Islands
The Disappointment Bay Formation (Emsian) on Lowther Island, N.W.T., consists of an 85-90 m thick sequence of upwards-shoaling limestones and dolomites. Within the upper two-thirds of the formation, exhumed reef mounds, about 50 m thick, are exposed. Four principal, vertically-successive reef facies...
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| Format: | Text |
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Scholarship@Western
1989
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| Online Access: | https://ir.lib.uwo.ca/digitizedtheses/1795 https://ir.lib.uwo.ca/context/digitizedtheses/article/2794/viewcontent/NL49351.PDF |
| Summary: | The Disappointment Bay Formation (Emsian) on Lowther Island, N.W.T., consists of an 85-90 m thick sequence of upwards-shoaling limestones and dolomites. Within the upper two-thirds of the formation, exhumed reef mounds, about 50 m thick, are exposed. Four principal, vertically-successive reef facies can be distinguished; a basal stromatactis mudstone-wackestone; an algally-bound wackestone; a stromatoporoid-coral framestone; a capping crinoidal grainstone. Reef growth occurred in response to passive sedimentary shoaling under static sealevel conditions, the reefs nucleating upon small mounds of aggregated brachiopods. Following stromatactis-mudstone deposition, a thick sequence of dominantly algally-bound wackestone accumulated on the reefs; ubiquitous, horizontally-disposed, large fibrous calcite cements within this facies can be demonstrated to be early replacement products after algal crusts, on the basis of overgrowth relationships, fossil inclusions, and other criteria. Steeply-dipping, reef-flank debris beds also accumulated at this time. With the transgression of mean wave-base, reef deposition changed dramatically to a stromatoporoid-coral framestone; capping crinoidal grainstones indicate reefal senescence at the end of Disappointment Bay deposition.;Disappointment Bay faunas studied include bivalves, ammonoids, bactritoids, gastropods, scaphopods, hyolithids, tentaculites, brachiopods, trilobites, ostracodes, corals, stromatoporoids, calcareous algae, and conodonts. The mollusc fauna represents the first detailed report from the Arctic Lower Devonian, and most notably includes eight bivalve species (many new), and the only ammonoids (two species) so far known from the Arctic Devonian. The tentaculite fauna, consisting of six dacryonarid and two tentaculitid species, is also the most extensive of its sort yet documented for the Arctic. While indicating considerable biostratigraphic potential for the Arctic, the Disappointment Bay tentaculites are highly endemic. Geochemical analysis of tentaculite shell ... |
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