Latest Ordovician Silurian Articulate Brachiopods And Biostratigraphy Of The Avalanche Lake Area Southwestern District Of Mackenzie Canada

Author : Ravindra S. Tipnis
Publisher :
ISBN 13 :
Total Pages : 0 pages
Book Rating : 4.:/5 (143 download)

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Download or read book Biostratigraphy and Paleontology of Late Cambrian to Late Middle Ordovician Conodonts from Southwestern District of Mackenzie, Northwest Territories written by Ravindra S. Tipnis and published by . This book was released on 1978 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ordovician strata of the South Nahanni River area occur both as a fine clastic facies in the Selwyn Basin (Rabbitkettle and Road River formations) and as carbonate facies with shelly faunas in the Root Basin (Broken Skull, Sunblood, Esbataottine, and Whittaker formations). The lithofacies are controlled by major tectonic features, namely the Redstone Arch, the Selwyn Basin and the Root Basin. Conodonts are present in rocks of both facies and are represented by distinctly dif ferent faunas. The carbonate facies of the Root Basin and the region immediately south of the Redstone Arch contains a complete record of shelly faunas of Canadian to at least Kirkfieldian age, and yields conodonts of pre dominantly Midcontinent type. A large component of the Canadian fauna consists of North Atlantic elements. Recognized here are the late Canadian Faunas D and E of Ethington and Clark (1971) and Middle Ordo vician Faunas 1-9, 10? of Sweet et al. (1971). The Broken Skull Formation generally consists of sequences of carbonates that are vari ably sandy and contains, in its highest parts, the late Canadian Faunas D and E and earliest Whiterockian Faunas 1 and ?2. The Sunblood Forma tion consists of generally resistant, red-orange-buff weathering limestones and minor dolostones and contains conodonts diagnostic of Whiterockian Faunas (?2-4) and Chazyan Faunas 5 and 6. The Esbataottine Formation proposed by Ludvigsen (1975) comprises moderately recessive, grey-buff weathering limestone and contains upper Fauna 6, Fauna 7, and lower Fauna 8. The lower Whittaker Formation consists of limestones, dolostones and shales, and contains conodonts belonging to Faunas 8, 9 nd ?10 (Rocklandian to ? early Shermanian). Conodonts from the clastic facies of the Selwyn Basin are pres ent in the Rabbitkettle and Road River formations. The thin-bedded argillaceous limestones of the Rabbitkettle Formation yield sparse but distinctive Late Cambrian ( Proconodontus Zone of Miller, 1975 to ear liest Ordovician (Faunas A, ?B) conodonts. Their biogeographic affinities are unclear. The argillaceous limestones of the Road River Formation contain a diverse and fairly rich North Atlantic type conodont fauna, including Oepikodus evae (Lindstrom), Eoplacognathus planus (Sergeeva), Pygodus serrus (Hadding) and Amorphognathus superbus (Rhodes). The restriction of the Midcontinent faunas to the carbonate de posits of the southern Mackenzie platform and that of the North Atlantic fauna to the deepwater clastic facies of the Selwyn Basin, clearly emphasizes the dependency of these two biogeographic faunas on ecologi cal factors present. Based on the study of conodonts from both the Root and Selwyn basins, the following distributional pattern emerges for the Middle Ordovician conodonts, arranged in approximate order from biofacies close to paleoshore to those farther away, on the continental slope: 'Biofacies' I, near shore dominated by 'Fibrous' conodonts; 'Biofacies' II, shallow shelf, dominated by Plectodina ; 'Biofacies' III, deep shelf, dominated by Phragmodus ; and 'Biofacies' IV, slope/basinal, dominated by Periodon/Amorphognathus . The total conodont fauna studied can be assigned to 41 multi- elemental genera, 18fom genera; 96 multielemental species , 70 foim species and one subspecies. Of these 4 multielement genera, 14 multielemental species, 3 form genera, 5 form species and one subspecies are new.