Lower Ordovician conodonts from the St. George Group of Port au Port Peninsula, Western Newfoundland

Ji, Zailiang (1989) Lower Ordovician conodonts from the St. George Group of Port au Port Peninsula, Western Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF (Migrated (PDF/A Conversion) from original format: (application/pdf)) - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (21MB) [English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. (Original Version)

Abstract

The St. George Group on the Port au Port Peninsula of western Newfoundland is little deformed, well exposed and provides a nearly complete sequence through the Lower Ordovician. The about 600 m thick succession records two depositional megacycles, and is divided into four formations in ascending order, the Watts Bight, Boat Harbour, Catoche and Aguathuna formations. -- Over 45,000 conodonts have been recovered from 432 3.5 kg samples from 10 sections comprising two composite sections through the St. George Group. The conodonts show excellent preservation with a low conodont Colour Alteration Index (CAI) of 1. Detailed taxonomic study of these faunas has permitted major revision to the reconstruction of Lower Ordovician multielement apparatuses, new interpretation of the phylogenetic relationships of Lower Ordovician, Midcontinent Province conodonts, and the establishment of a new and more refined Lower Ordovician conodont zonation for the Midcontinent Province. -- One of the major objectives of this study is to examine the Lower Ordovician conodont taxonomy. Seventy-five multielement species, representing 28 genera, have been described and illustrated, among them 7 new genera, 33 new species and 70 newly reconstructed multielement species. The new genera are Glyptodontus, Loxodentatus, Loxoqnathus, Polycostatus, Striatodontus, Stultodontus and Tricostatus. The new species are: Acodus primus, Clavohamulus lonqicuspis, C. neoelonqatus, C. reniformis, C. sphearicus, Cristodus ethinatoni, Drepanodus nowlani, Glyptoconus felicitii, G. multiplicatus, G. priscus, Glyptodontus constrictus, G. expansus, G. tumidus, Loxodentatus bipinnatus, Loxognathus phyllodus, Loxodus latibasis, Macerodus crassatus, M. gracilis, M. wattsbightensis, Polycostatus falsioneotensis, P. minutus, Protopanderodus prolatus, Scolopodus subrex, Stritodontus lanceolatus, S. prolificus, S retractus, S. teridontus, Stultodontus ovatus, S. pygmaeus, Teridontus obesus, Tricostatus glyptus, Utahconus longipinnatus and Variabiloconus neobassleri. -- Three apparatus types, apparatus Type I, II and III, are redefined. Type I apparatuses consist of only a and e elements, and are characterized by stubby coniforms and extremely flattened forms. Type II apparatuses have three element morphotypes including a, c and e elements. Type III apparatuses contain four or five skeletal morphotypes: a, b, c, e and, commonly f elements. -- Following the taxonomic study, the local, regional and global stratigraphic range of the taxa were examined to help interpret evolutionary lineages. Nearly twenty such lineages have been recognized. Most are closely related to the Teridontus lineage, and belong to the Teridontus evolutionary complex. The evolutionary relationships of multielement taxa in the Teridontus complex show that the Teridontus lineage spread widely, evolving into both the Clavohamulus and Semiacontiodus lineages during the latest Cambrian. The latter probably produced the Variabiloconus and Polycostatus lineages during the earliest Tremadoc. Two important lineages, Glyptoconus and Striatodontus, appear suddenly, spreading widely, and diversifing rapidly during the early and middle Arenig. The late Tremadoc extinction is one of the most profound crises in conodont evolutionary history. This extinction leads to the demise of more than seven lineages including over 35 species. -- The conodonts recovered indicate that the St. George Group ranges in age from earliest Canadian to the earliest Whiterockian. Eight conodont Assemblage Zones have been established for the shallow-water (SW) facies of the typical Midcontinent Province. Six deeper-water (DW) conodont Assemblage or Lineage Zones have been recognized or redefined, and include some taxa with affinities to the North Atlantic Province. All the SW Assemblage Zones represent limited stratigraphic intervals in the Lower Ordovician, most can be recognized with other low latitude cratons, such as Australia, Siberia, and North China. In contrast, the DW Assemblage or Lineage Zones can be correlated through the critical biostratigraphic tie-points with the North Atlantic Province zonation.

Actions (login required)

View Item