Ordovician Conodont Biostratigraphy Western Canadian Cordillera

Author : Kathleen Anne Stait
Publisher :
ISBN 13 :
Total Pages : pages
Book Rating : 4.:/5 (131 download)

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Download or read book Upper Canadian to Whiterockian (Ordovician) Conodont Biostratigraphy of the Upper St. George Group, Western Newfoundland written by Kathleen Anne Stait and published by . This book was released on 1989 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The St. George Group of western Newfoundland is a sequence of limestones and dolostones deposited on the North American platform margin of the Lower Ordovician Iapetus Ocean. The upper half of this sequence records a shoaling-upwards megacycle of deposition, which is found in the upper Boat Harbour, Catoche and Aguathuna formations. -- Much of this megacycle was sampled for conodonts in order to establish a refined biostratigraphy and to shed light upon lithostratigraphic problems within Catoche and Aguathuna formations. Over 130 core samples from the Daniel's Harbour mine and approximately 110 outcrop samples from localities throughout western Newfoundland yielded approximately 5,000 conodonts. -- In total, 72 species from 43 genera are herein described from the upper megacycle of the St. George Group. Striatodontus n. gen. is described, with S. kakivangus n. sp. and S. carlae (Repetski) both found in the St. George Group. Elements probably forming part of a previously unknown apparatus (?New Genus 1) are described, but remain unnamed. New species are Bergstroemognathus alus, Clavohamulus cavus, Diaphorodus gravelsensis, D. stevensi, Leptochirognathus planus, Parapanderodus aequalis and Rossodus symmetricus. In addition, species of Ansella Fåhraeus & Hunter, ?Erismodus Branson & Mehl, Protoprioniodus McTavish, ?Reutterodus Serpagli, and new species of Scalpellodus Dzik, Variabiliconus Landing et al. and the unnamed new (?) genus remain in open nomenclature pending the availability of more abundant material. -- Seven successive informal conodont assemblages are recognised within the faunal succession. These are based upon morphological changes within species of Parapanderodus Stouge and Diaphorodus Kennedy, and concurrent ranges of a number of species. -- Assemblage I correlates with North American trilobite Zone H, which is equivalent to early Midcontinent Province Fauna E of the North American conodont zonation; coeval Baltic Province conodonts are found in the Prioniodus elegans Zone. Assemblage II may correlate with the Prioniodus elegans Zone and Midcontinent Fauna E. Assemblage III is demonstrably contemporaneous with the Oepikodus evae Zone and with the shelly fossil Zone I of the North American succession, but younger assemblages can only be directly related to North American faunas. Faunas are initially of mixed Midcontinent and Baltic affinity, but shallowing of the depositional environment was accompanied by restriction of Baltic forms from uppermost Catoche and Aguathuna formations. -- Assemblage IV, at approximately the base of the Aguathuna Formation, contains the last occurrence of Oepikodus communis (Ethington & Clark) and conodonts of Canadian age interspersed with species more common within Whiterockian strata (e.g. Tripodus laevis Bradshaw). Conodonts equivalent in age to zones J and K are found in Assemblage IV. All but the longest-ranging Canadian conodonts disappear by Assemblage V, which is the first assemblage completely within the Whiterockian: early Whiterockian species include Pteracontiodus cryptodens (Mound), Diaphorodus gravelsensis n. sp. and D. stevensi n. sp. Assemblage VI, commencing with the incoming of Drepanodus sp. cf. D. gracilis (Branson & Mehl) and consisting of early Whiterockian conodonts, is of limited stratigraphic range. The succeeding Assemblage VII, with Drepanoistodus angulensis (Harris), Scandodus sinuosus Mound and Glyptoconus rectus (Stouge) at the base, later contains a diverse and abundant fauna showing affinity with conodonts correlated with shelly fossil Zone M of the Ibex area. This fauna, which continues several metres into the overlying Table Point Formation, is almost completely of Midcontinent Province aspect. It consists primarily of neurodont and lamellar forms such as Leptochirognathus quadrata Branson & Mehl, Multioistodus subdentatus Cullison, Paraprioniodus costatus Ethington & Clark, Erismodus spp. and several previously undescribed species. -- The upper St. George Group conodont succession is broken at two levels within the Aguathuna Formation: significant hiatuses separate assemblages IV and V, and assemblages VI and VII. The lower hiatus is recognized at the same level across western Newfoundland, but the upper hiatus occcurs at different levels both locally and regionally. This pattern of faunal occurrences is explained with reference to the tectonic setting of the platform margin during deposition of the Aguathuna Formation.