Late Devonian Conodont Biostratigraphy of the Earn Group
Total Page：16
File Type：pdf, Size：1020Kb
LATE DEVONIAN CONODONT BIOSTRATIGRAPHY OF THE EARN GROUP WITH AGE CONSTRAINTS FOR STRATIFORM MINERAL DEPOSITS, SELWYN AND KECHIKA BASINS, NORTHERN BRITISH COLUMBIA AND YUKON By STEVEN EDWARD BRUCE IRWIN B.Sc, The University of British Columbia, 1985 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Geological Sciences) We accept this thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA January 1990 © Steven Edward Bruce Irwin, 1990 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Geological Sciences The University of British Columbia Vancouver, Canada ABSTRACT Devonian and Early Carboniferous marine clastic rocks of the Earn Group host several economically important stratiform massive sulphide and bedded barite deposits. Due to the chaotic sedimentation, considerable regional metamorphic overprint and, relative inaccessibility, little was known about the stratigraphy, the Late Devonian conodont fauna, or the age of the stratiform mineral deposits within the Earn Group. Conodont microfossils, however, are an excellent fauna for an Earn Group biostratigraphy program because of their ability to withstand both temperatures in excess of 400° C, and significant physical stress. With standard laboratory techniques conodonts were readily extracted from fine grain calcareous elastics and carbonate lenses within the Earn Group. The conodonts are described from three specific areas where the Earn Group is known to host stratiform barite and barite-lead-zinc mineral deposits: Macmillan Pass, Midway, and Gataga. As the majority of conodonts were diverse and well preserved platform elements of the genus Palmatolepis, the taxonomic studies focused on this genus; other genera including Ancyrodella, Icriodus, Klapperina, Mesotaxis, and Polygnathus were examined as part of the biostratigraphic/taxonomic studies. Previous to this study the widespread stratiform mineralization was dated as only Late Devonian. The conodont taxonomy and ii biostratigraphy in the Earn Group provide age constraints for duration and formation of the stratiform mineralization. The ability to tightly constrain the age of the stratiform mineralization adds to the knowledge of Earn Group deposition, the paleogeography of the Selwyn and Kechika Basins, and has implications for stratiform mineral exploration strategies in the Earn Group. On the basis of conodont faunal ages barite mineralization at MACMILLAN PASS apparently occurs as three different levels: 1) CATHY property - Eifelian to early Frasnian; 2) PETE, JEFF, GARY, and GHMS properties - middle to late Frasnian; 3) TEA property - Early Carboniferous. In addition, barite-lead-zinc mineralization at TOM and JASON properties likely occurs during middle to late Frasnian. In the GATAGA area barite and barite-lead-zinc mineralization have been recognized at several temporally distinct levels in the early to middle Famennian: 1) Lower rhomboidea Zone; 2) Lower marginifera Zone; 3) Upper marginifera Zone. Several other mineralized horizons are loosely constrained within the same interval. Within the MIDWAY area the stratiform barite mineralization at the EWEN and PERRY properties is of Early Carboniferous, Tournaisian age, and correlates broadly with the TEA barite in the Macmillan Pass area. In summary, events that produced stratiform barite-lead-zinc and barite mineralization in the Selwyn and Kechika Basins were not coeval. The Late Givetian and early Frasnian barite mineralization took place in the Macmillan Pass and southernmost Gataga areas. During the middle Frasnian barite and barite-lead zinc mineralization events occurred at Macmillan Pass. Several episodes of barite and/or barite-lead-zinc mineralization occurred in the Gataga area during the middle Famennian. The youngest barite mineralization events in the Earn Group took place in the Early Carboniferous, Tournaisian time at Macmillan Pass and Midway. iv TABLE OF CONTENTS Abstract ii Table of Contents v List of Tables ix List of Figures and Plates x Acknowledgements xii I. INTRODUCTION 1 A. Purpose and Scope 1 B. Regional Geology 5 C. Stratiform Mineral Deposits 9 D. Methods 13 II. UPPER DEVONIAN CONODONTS 16 A. Taxonomy 16 B. Zonation 2 0 C. Biofacies 23 D. Previous Work in Western Canada 2 6 III. REGIONAL CASE STUDIES 32 A. Macmillan Pass 37 1. Geological Setting 37 2. Stratigraphy 38 3. Biostratigraphy 43 B. Midway 52 1. Geological Setting 52 2. Stratigraphy 53 3. Biostratigraphy 58 C. Gataga 63 1. Geological Setting 63 2. Stratigraphy 65 3. Biostratigraphy 7 0 v III. REGIONAL CASE STUDIES cont'd D. Synthesis 81 1. Macmillan Pass 81 2. Midway 85 3. Gataga 88 4. Selwyn and Kechika Basins Overview 91 IV. CONCLUSIONS 94 V. SYSTEMATIC CONODONT TAXONOMY 104 Ancyrodella 106 Ancyrodella binodosa 106 Ancyrodella aff. A. binodosa 108 Ancyrodella curvata 108 Ancyrodella gigas 110 Ancyrodella ioides Ill Ancyrodella lobata 112 Ancyrodella aff. A. lobata 113 Ancyrodella nodosa 114 Ancyrodella rotundiloba 115 Klapperina 116 Klapperina disparalvea 117 Klapperina disparata 119 Klapperina disparilis 120 Klapperina ovalis 121 Mesotaxis 12 3 Mesotaxis asymmetrica 12 3 Mesotaxis dengleri 125 Mesotaxis falsiovalis 12 7 Palmatolepis 129 Palmatolepis crepida 13 0 Palmatolepis delicatula 132 Palmatolepis delicatula clarki 13 3 Palmatolepis domanicensis 134 Palmatolepis foliacea 13 5 Palmatolepis glabra 137 Palmatolepis glabra glabra 139 Palmatolepis glabra aff. P. g. glabra 139 Palmatolepis glabra acuta 14 0 Palmatolepis glabra distorta 14 2 Palmatolepis glabra lepta 14 3 Palmatolepis glabra lepta morphotype 1 144 Palmatolepis glabra lepta morphotype 2 145 Palmatolepis glabra pectinata 146 Palmatolepis glabra aff. P. g. pectinata 148 Palmatolepis glabra pectinata morphotype 1 148 Palmatolepis glabra prima 149 Palmatolepis gracilis 150 Palmatolepis gracilis gracilis 151 Palmatolepis hassi 153 vi V. SYSTEMATIC CONODONT TAXONOMY cont'd Palmatolepis klapperi 154 Palmatolepis marginifera 156 Palmatolepis marginifera marginifera 156 Palmatolepis marginifera utahensis 158 Palmatolepis minuta 159 Palmatolepis minuta minuta 161 Palmatolepis minuta loba 162 Palmatolepis perlobata 163 Palmatolepis perlobata schindewolfi 164 Palmatolepis perlobata aff. P. p. schindewolfi .... 166 Palmatolepis poolei 167 Palmatolepis proversa 168 Palmatolepis punctata 169 Palmatolepis quadrantinodosa 171 Palmatolepis quadrantinodosa quadrantinodosa 172 Palmatolepis quadrantinodosa inflexa 174 Palmatolepis quadrantinodosa inflexoidea 175 Palmatolepis quadrantinodosa n.subsp. A 177 Palmatolepis quadrantinodosalobata 178 Palmatolepis quadrantinodosalobata morphotype 1 ... 179 Palmatolepis cf. P. regularis 180 Palmatolepis rhenana 182 Palmatolepis rhomboidea 183 Palmatolepis rugosa 185 Palmatolepis rugosa trachytera 186 Palmatolepis rugosa aff. P. r. trachytera 188 Palmatolepis stoppeli 189 Palmatolepis subperlobata 190 Palmatolepis tenuipunctata 193 Palmatolepis transitans 195 Palmatolepis triangularis 196 Palmatolepis winchelli 198 Palmatolepis wolskajae 201 Palmatolepis sp. C Orchard, 1988 2 02 Palmatolepis sp. B Klapper & Foster, 1986 203 Palmatolepis n.sp. A 203 Polygnathus 205 "Polygnathus" cristatus 206 VI. BIBLIOGRAPHY 2 08 VII. PLATES 226 vii VIII. APPENDICES 252 A. Macmillan Pass localities and sample information 1. Givetian - Frasnian 252 2. Famennian 266 B. Midway localities and sample information 1. Frasnian 273 2. Famennian 275 C. Gataga localities and sample information 1. Givetian - Frasnian 282 2. Famennian 287 viii LIST OF TABLES Table I. Age ranges of important Givetian and Frasnian conodont species and subspecies in the Selwyn and Kechika Basins 3 3 Table II. Age ranges of important Famennian conodont species and subspecies in the Selwyn and Kechika Basins 35 Table III. Distribution of Frasnian conodont species in the Macmillan Pass area 242 Table IV. Distribution of Frasnian conodont species in the Midway and Gataga areas 244 Table V. Distribution of Famennian conodont species and subspecies in the Macmillan Pass and Midway area 246 Table VI. Distribution of Famennian conodont species and subspecies in the Gataga area 248 Table VII. Distribution of Famennian conodont species and subspecies in the Gataga area of northern British Columbia 250 ix LIST OF FIGURES AND PLATES Figure 1. Case study areas; Macmillan Pass, Midway, and Gataga, within the Selwyn and Kechika Basins 2 Figure 2. Generalized western Canadian Cordilleran terrane map 4 Figure 3. Regional Earn Group outcrop map with general locations of conodont sample sites 6 Figure 4. Late Devonian paleogeography of the Selwyn and Kechika Basin region 8 Figure 5. Late Devonian stratiform barite and barite- lead-zinc-silver deposits in western North American Cordillera 10 Figure 6. The revised international standard Late Devonian conodont zonation 2 0 Figure 7. Correlations of previously published Late Devonian conodont biostratigraphy studies in western Canada with Earn Group biostratigraphy 28 Figure 8. Stratigraphic section across the Macmillan