THE SOUTHERN TEFWlNATION OF THE MAIN RANGES AND WESTERN RANGES OF THE SOUTHERN CANADIAN ROCKY MOUNTAINS: STRATIGRAPHY, STRUCTURAL GEOLOGY, AND TECTONIC IMPLICATIONS
by
GORDON W. STRETCH
A thesis submitted to the Department of GeoIogicai Sciences in conformity with the requirements for the degree of Master of Science
Queen's University Kingston, Ontario, Canada April, 1997
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The Tanglefoot area straddles the southern termination of the Main Ranges and Western Ranges geologic sub-provinces of the Foreland Fold and Thrust Belt of the Canadian Cordillera. The map-area also straddles a regional, east-west. cross-strike discontinuity, across which there are profound changes in the stratigraphy, sedimentary facies, and the style and orientation of the structures of the Rocky Mountains. The stratigraphy of the Tanglefoot area is subdivided into three distinct. unconformity-bounded assemblages: the Mesoproterozoic straw the Lower Palaeozoic strata, and the Upper Palaeozoic strata. There is a profound change in the Palaeozoic stratigraphy across the Dibble Creek fault. On the south side of the fault, the Lower Palaeozoic strata comprise a thin (1 18 m - 337 m), condensed succession of Middle Cambrian cratonic platform facies rocks, which unconformably overlie Mesoproterozoic strata, and are unconformably overlain by Upper Devonian cratonic platform facies strata. On the north side of the Dibble Creek fault, shaly equivalents of the Upper Devonian Fairholme Group (?), Palliser, Exshaw, and Banff Formations overlie approximately 7 km of shaly Lower Palaeozoic rocks. The structures within the maparea are dominantly northeast-trending, and verge to the southeast, in marked contrast to the regional structurai trend of the Foreland Fo!d and Thrust Belt. The Tanglefoot area has been subdivided into three structural domains: the Montania domain, the Tanglefoot domain, and the Hughes domain. The "Fisher block", which forms the stratigraphic base of the shaly Tanglefoot domain, is a steeply- dipping, east-northeast- facing, relatively undeformed panel of Mesoproterozoic and basal Cambrian strata It is separated £kom the shale-dominated Tanglefoot domain by an important dkcollement within the Eager Formation. Above the decollement, shaly Lower Palaeozoic strata are tightly folded, with a penetrative, northwest-dipping solution cleavage. The south-trending axis cf the fan-shaped Porcupine Creek anticlinoriurn swings to southwest in the Tangiefoot area, and the fan structure terminates above the dicollement in the Eager Formation. The conspicuous southeast-verging deformation in the Tangiefoot area is the result of tectonic inversion, which involved thickening and elevation of the Tanglefoot shale basin, followed by lateral gravitational spreading to the southeast. The Mount Haley syenitoid stock, which occurs in the footwall of the Lussier River fault, appears to be deformed, and therefore is older than regional deformation. "ArP9A.r geochronology completed as part of this study gives a date of 1 1 1 Ma for the Mount Haley stock. On the west side of the Rocky Mountain trench, the Reade Lake granitoid stock plugs the St. Mary-Lussier River fault, which cuts through the Tanglefoot area. Previous work has reported a U-Pb zircon date of 94 Ma for the Reade Lake stock. Hence, upper and lower constraints are placed on the age of deformation, at 94 Ma and 11 1 Ma respectively. "...thedescription of the highlands that surround that veritable sinkhole ofdisappearing fads, the Bull Valley in the Dibble-Lime-Iron Creek section. "
-G.B.Leech. 1962 ACKNOWLEDGEMENTS
It is a pleasure to acknowledge Dr. Raymond A. Price for his generous support. patient criticism, and guidance throughout all stages of this project. I am also indebted to Dr. Doug Archibald for guiding and supervising the geochronological work on the Mount Hdey stock, for providing me with geochronological results fiom the Central Hughes
Range, for many insightfid conversations about the geology of the study area and Cordilleran tectonics, and lastly, for being a great fiend. Dr. Geoff Leech of the Geological Survey of Canada continues to provide fiesh and thoughtfid insight into the geology of the southeast Cordillera, and I thank him for his interest in this project. and for providing me with copies of his geological maps and field notes. Fossils collected during the field work for the study were identified by Dr. W.H. Fritz of the Geological Survey of Canada. At Queen's University, Dr. Hamish Sandeman assisted with the geochronological work on the Mount Haley stock, and Drs. Frank Brunton and Guy Narbonne provided assistance with certain samples. My thanks also go out to Dr. Dugald Carmichael for making his petrographic equipment available to me. I am also very gratefd to Derek Brown of the British Columbia Geological Survey for providing digitized TRIM maps of the Tanglefoot area. Assistance in the field was provided by P. Twa in 1994 and S. Bertels in 1995. In addition, visits to the Tanglefoot area by Ray Price in 1994 and 1995 and Doug Archibald in 1995 are gratemy acknowledged. A specid thank-you goes out to my father, Gord C. Stretch, for helping with the logistics of my field work, and for the cheefi companionship and outstanding camp food provided during a visit to the area in the summer of 1995. My thanks are also extended to Art, Linda, Rudy, and Frieda of the Kootenay Country Comfort Inn in Cranbrook, for their down-home generosity, hospitality, and for putting up with a certain pugnacious field assistant! Field work was hded by an NSERC research grant to Dr. R.A. Price. and personal financial support was provided by a Carl Reinhart Fellowship and a Queen's Graduate Scholarship in 1994, and by an Amoco Fellowship in 1995 and 1996.
I owe a big thank you to dl the staff and graduate students at Queen's geology department for countless geological discussions and much assistance. My closest partners in crime, Mike "Ooley" Cooley, Clark Darner, Dave Gale. Brian Martin. Ian Russell, and Karen-Jane Wright: a 'uge-big thank you for everything, and thanks for helping me relax with an occasional pop at the Grad Club. Finally, my very sincere and profound thanks are extended to Pat and Gord Stretch of Edmonton for their support, assistance, confidence and encouragement throughout all stages of this project. TABLE OF CONTENTS
Page
Abstract I ... Acknowledgements U1
Table of contents v .. . List of Figures VIlI
List of Plates x
Chapter 1 - INTRODUCTION...... 1 General Statement 1 Location Access Relief and Exposure Methodology Previous work
Chapter 2 - REGIONAL BASEMENT TECTONICS...... -6 Introduction 6 Basement tectonics and the Tanglefoot area 7
Chapter 3 - REGIONAL TECTONIC SETTTNG ...... 10
Chapter 4 - STRATIGRAPHY...... 18 Introduction 18 Mesoproterozoic strata 25 Fort Steele and Aldridge Formatons 25 Creston Formation 27 Kitchener Formation 28 Van Creek Formation 29 Nicol Creek Formation 30 Sheppard Formation 32 Gateway Formation 32 Phillips Formation 33 Lower Palaeozoic strata 34 Flathead, Gordon, and Elko Formations 34 Cranbrook Formation 37 Eager Formation 38 "Tanglefoot unit" McKay Group Glenogle Formation Mount Wilson Formation Beaverfoot Formation Upper Palaeozoic strata "basal Devonian unit" Buraais. Cedared, and Harrogate Formations Fairholme Group Palliser Fonnation "Devono-Mississippian shale unit" Cretaceous Intrusive Rocks
Chapter 5 - STRUCTURE...... Introduction The Montania domain Moyie-Dibble Creek fault The Tanglefoot domain The "Fisher block" Faulting Boulder Creek fault Porcupine Creek anticlinorium St. Mary-Lussier River fault The Hughes domain
Chapter 6 - INTRUSIVE ROCKS: SIGNIFICANCE AND GEOCHRONOLOGY...... 87 Introduction 87 The Reade Lake and Kiakho stocks 88 The Mount Haley stock 91 Petrography 91 Structures 92 Geochronology results Conclusions
Chapter 7 - DISCUSSION ...... 96 The "Tanglefoot unit": Interpretations 96 Conclusions 97
REFERENCES CITED...... 1 00 vii
Page APPENDICES ...... 106 Appendix 1 : aArP9Ar analytical methods 106 Appendix 2: Geochronology results fiom hornblende _gains 108 Appendix 3 : Geochronology results fiom a K-feldspar phenocryst 112
VITA ...... * ...... * ..-...-.*..-...-...... * 114 LIST OF FIGURES
Page
Location map, showing the Tanglefoot area with respect to the cities and towns of southeastern B.C. and southwestern AIberta -3
Location map, showing the Tanglefoot area with respect to the five morphogeological belts of the Canadian Cordillera 11
The geologic sub-provinces of the Foreland Fold and Thrust Belt; the Tanglefoot area straddles the southern termination of the Main Ranges and the Western Ranges 12
Regional geology map of the Tanglefoot area and surrounding region 15
Legend to accompany Figure 4a 16
Schematic N-SE cross-section through the Tanglefoot area, showing the stratigraphic contrast across the Dibble Creek fault 19
Map showing the location of the line of section of Figure 5a 20
Map of all the Lower Palaeozoic exposures which occur on the southeast side of the Moyie-Dibble Creek fault 21
Stratigraphic column showing the assemblage on the south (footwall) side of the Dibble Creek fault 22
Stratigraphic column showing the assemblage on the north (hanging wall) side of the Dibble Creek fault 23
Map showing the major faults and the location of named creeks, rivers. and lakes within the Tanglefoot area 27a
Map showing the structural domains of the Tanglefoot and surround- ing region 67
Equal-area projections: simplified map of the Tanglefoot area with stereonets showing the dominant orientation of structures in different parts of the map-area 71
Cross-section through the Porcupine Creek anticlinorium, north of the Tanglefoot area 82 Page
12b Location map, showing the line of section of Figure 1 la 83
13a Geology map of the Cmbrook area, showing locations of the Reade Lake and Kiakho stocks 89
13b Map showing exposures of the Reade Lake and Kiakho stocks, traces of the St. Mary and Cranbrook fauits, and isomagnetic lines 89
14 Equal-area projection of poles to the joint set which is folded across the Mount Haley stock 93 LIST OF PLATES &
Map: Geology of the Tanglefoot Area Pocket
Cross-sections to accompany Plate 1 Pocket
Olenellus "gilberti",fossilized in the lower Eager Formation 39
Bedded lime mudstone of the "Tanglefoot unit" 41
Laterally continuous, planar bedded strata of the "Tanglefoot unit" 43
Discontinuous and continuous laminaions in bedded limestone of the "Tanglefoot unit"
Carbonate debris-flow breccia within the "Tanglefoot unit"
Folded clasts within a debris-flow breccia of the "Tanglefoot unit"
The "toe" of a cohesive slump block comprising a carbonate debris- flow deposit in the "Tanglefoot unit"
Laminated, shaly lime mudstone from the upper "Tanglefoot unit"
Looking west up the Dibble Creek valley; undeforrned, northerly- dipping Fairholme Group strata constitute the valley wall
A branching, colonial rugose coral preserved in place in Fairholrne Group strata along the footwall of the Dibble Creek fault
Dolomitized burrows and surrounding halos in the Palliser Formation
View to the north of a monzonitic intrusion into McKay Group host rocks, south of the Mount Haley stock
Zone of major detachment in the lower Eager Formation
Disharmonically folded lime mudstones and shaly limestones within the "Tangle foot unit"
17 Disharmonic folding in the "Tanglefoot unit" 75 Plate Paee
18 Strong axial planar cleavage in the hinge zone of folded strata of the "Tanglefootunit" 76
19 Upright, closed, inclined anticline in the lower "Tanglefoot unit", south of the Boulder Creek fault 78
20 Tight, overturned fold ia thinly bedded strata of the upper "Tanglefoot unit" 78 INTRODUCTION
eneral Statement
The study area (the "Tanglefoot area") straddles a tectonic anomaly in the southern Canadian Cordillera. The regional structural trend of the southern Rocky Mountains is north to northwest, but the predominant structural grain of the Tanglefoot area, except for the central-west portion, is northeast-southwest. The Tanglefoot area includes the southern termination of both the Main Pages and Western Ranges geologic sub-provinces (North and Henderson, 1954) of the Rocky Mountain Foreland Fold and Thrust Belt- There are profound changes in the stratigraphy, sedimentary facies. and the style and orientation of the structures of the Rocky Mountains across a regional east- west, cross-strike discontinuity that coincides with the Moyie-Dibble Creek fault, a northwest-dipping, right-hand reverse fault. The purpose of this study has been to elucidate the stratigraphy and structural geology of the Tanglefoot area, to assess the influence of the reactivation of older structures on the stratigraphic and structural evolution of the area, and to reconstruct the palaeogeomorphological setting of the southern termination of the Main and Western Ranges of the Rocky Mountain Foreland Fold and Thrust Belt.
Locatioq
The Tanglefoot area is situated in the southern Canadian Rocky Mountains. adjacent to the Bull River (Figure 1). It comprises the western part of the Fernie 150 000 map sheet (82 GI1 I), and includes the easternmost part of the adjoining Cranbrook map sheet (82 GI12). It is approximately 25 km to 45 km northeast of Cranbrook, and 20 km Figare 1: Location map, showing the Tanglefoot area with respect to the cities and towns of southeastern B.C. and southwestern Alberta to 40 km northwest of Fernie, in the East Kootenay Valley of southeast British Columbia
Access
The Tanglefoot area is fairly easily accessible with an off-road vehicle and a good pair of hiking boots. The main access road is the Bull River forest service road; a well maintained dirt road which runs along the Bull River. and provides access to the southeast parts of the study area. The Bull-Gdbraith forest se~ceroad runs alongside Galbraith Creek, providing access to the northeast reaches of the study area on the way up to Summer Lake. It was well maintained in 1994, but washed out in June of 1995 due to flooding in the area, which made it impassable. The Tanglefoot Creek forest service road runs east-west through the central part of the study area, and the Van Creek forest service road extends hmthe Bull River to Tangiefoot Creek, through the southwest part of the study area. The western reaches of the area were accessed by hiking west up the Tanglefoot Creek, and east up the Boulder Creek road. south of Vertical Mountain in the southern Hughes Range. In addition to the maintained forest senrice roads in the Tanglefoot area there are various trails and deactivated logging roads which usually provide access to areas between the drivable roads.
Relief and Ex~osure
There is impressive relief in the Tanglefoot area, as well as a remarkable variability of terrane. The Bull River valley in the southern reaches of the area is less than 1000 m above sea level (ASL), but the peaks of Mount Fisher (the highest peak in the area), Mount Sneath, Mount Haley and Mount Patmore all exceed 2700 rn in elevation. The most dramatic relief in the area is along the western side, where thickly bedded strata of the Belt-Purcell Supergroup form the high peaks of the Steeples Range and the southern
Hughes Range. In contrast, shaly limestone and calcareous shale of the "Tanglefoot unit" underlie most of the central and east portion of the rnap-area, and are much more recessive in nature. This has resulted in rounded ridges which rarely exceed 2000 m ASL. thick, mature forests overlying the bedrock, and therefore often a paucity of outcrop. Rock exposure in the Tanglefoot area is approximately 10%; the remainder of the area hosts a wide variety of environments such as mature cedar forests, swamplands, dry grasslands. and alpine meadows.
Field work for the study was conducted during the summers of 1994 and i 995. The orientation of planar and linear fabrics in mtcrops were measured and recorded, structural, lithological, mineralogical and palaeontological samples were taken, and a geological map was produced. Field data were plotted on 1:20 000-scale digital Terrane Resource Information Management (TRIM) maps provided by the British Columbia
Geological Survey. The ensuing laboratory work, map drafting, and writing of the report was conducted at Queen's University in Kingston, Ontario. Palaeontological specimens were examined by W.H. Fritz at the Geological Survey of Canada, in Ottawa, Ontario.
Previous work
The first reconnaissance-scale mapping of the region was completed by G.B. Leech of the Geological Survey of Canada during the sumhers of 1956 and 1957. His published map and report (Leech, 1958) provide excellent regional descriptions and interpretations of the north and east-centrd parts of the Fernie map-area west half. which includes most of the Tanglefoot area Additional information was published in 1960 (Leech. 1960) on the age of the Lower Palaeozoic voIcanic rocks between Wild Horse
Creek and Summer Lake, and on Belt-Purcell strata in the Purcell and Rocky Mountains. In 1962. results of more detailed mapping in the Bull River valley were published (Leech. 1962), which focused on the southern part of the Tanglefoot area, and extended slightly Mersouth, into the Lizard Range (Leech, 1962). T.L. Thompson conducted reconnaissance-scale mapping in the Rocky Mountain Trench area of southeastern B.C., towards a 1962 Ph.D. thesis. His study area included most of the Fernie map-area west half, and he was the first to name the Middle Cambrian rocks overlying the Eager Formation north of Dibble Creek the "Tanglefoot Unit7'
(Thompson, 1962). These strata had previously been referred to as "Cambrian and (?) Ordovician undivided" (Leech, 1958, 1960). New detailed mapping of Mesoproterozoic and basal Palaeozoic rocks in the Mount Fisher area of the northeastern Belt-Purcell basin was conducted by M.E. McMechan towards a 1979 publication (McMechan, 1979), and a 1980 Ph-D. thesis. The southwest part of the Tanglefoot area is included in McMechan's "Mount Fisher area". Benvenuto and Price (1 979) provided a compilation map and regional interpretation of the tectonic and structural evolution of the Hosmer Thrust sheet. although no new mapping was conducted in the Tanglefoot area for that report. Previously published data were also compiled by Hay and Carter (1 988) and Hoy (1993), but their iepom did not include any new mapping in the Tanglefoot area. REGIONAJi BASEMENT TECTONICS
Introduction
Regional ancestral basement tectonics play a profound role in the geological rock record which is preserved in the southern Canadian Rockies, and especially the structurally anomalous Tanglefoot area Field work for this report was restricted to the
Tanglefoot area, however, the regional significance of tectonic heredity and repeated reactivation of basement-controlled faults has been emphasized by Price (1975. 198 I. 1993: 1996) and Price and Sears (in press). The Tanglefoot area straddles an important cross-strike discontiruity which follows the locus of older structures, and accordingly the previous reports on basement tectonics in the southern Canadian Rockies will be summarked here. Deformation in the Rocky Mountain Foreland FoId and Thrust Belt is "thin- skinned" (Shaw, 1963; Bally et al., 1966; Price and Mountjoy, 1970; Dahlstrom, 1970: Chappie, 1978; Price, 1981): the deformed supracrustal rocks are underlain by a gently westward-dipping, crystalline basement of Palaeoproterozoic age which is not involved in deformation (Bally ef al., 1966; Price and Mountjoy, 1970; Price, I98 1). The supercrustal strata have been horizontally shortened, vertically thickened. and displaced eastward over the edge of the ancestral North American craton on an underlying basal detachment It is important to understand that, while the Palaeoproterozoic crystalline basement was not deformed with the overlying strata, structures in the basement can become reactivated, and indirectly have great affect on later sedimentation, deformation. and preservation. Basin margin structures which were parallel with the regional trend of the continental margin produce simple hanging wall ramp antichoria, an example being the Purcell anticlinorium and the Mesoproterozoic Belt-Purcell basin (Price, 198 1). Basin margin structures which are sub-perpendicular to the regional trend of the continental margin (transverse basin margin structures) may be inherited through the re-activation of older basement structures, and thus produce cross-strike discontinuities in thin-skinned thrust and fold belts (Price, 1993).
Basement Tectonics and the Tan~lefootarea
The Tanglefoot area straddles the Crowsnest Pass deflection (Price. 1993. 1 996). within which the trend of the regional structural grain of the Foreland Fold and Thrust Belt changes from northwest to north. It also straddles the Crowsnest Pass cross-strike structural discontinuity, which is related to a 200 krn right-hand offset of the hinge line of the Lower Palaeozoic Cordilleran miogeocline and a 60 km left-hand offset in the margin of the Belt-Purcell basin (Price, 1993). This cross-strike discontinuity coincides with northeast-southwest striking basement structures which have been outlined by Bouguer gravity, total field magnetic and seismic surveys (Kanasewich et a/., 1969; Ross er al.. 1991). It has been suggested (Price. 1975) that these basement structures were reactivated as transform faults, movement along which controlled the margins, and therefore affected the stra!igraphy, of the Mesoproterozoic Belt-Purcell Supergroup, the Neoproterozoic Windermere Supergroup, and the Lower Palaeozoic North American miogeocline. The basement smcturis which have been outlined using geophysical methods extend fiom beneath the interior plains of Alberta westward for hundreds of kilometres into the Southern Canadian Rbckies (Kanasewich et a(., 1969). There, the anomalies are aligned with the location of the east-northeast-striking segments of the Moyie-Dibble Creek (NDC) and St. Mary-Lussier River (SMLR) faults in the Tanglefoot area. Contrasting stratigraphic successions on either side of both the MDC and SMLR faults indicate that they follow the locus of older (at least Neoproterozoic) structures. The antecedent structure of the MDC fault had the opposite stratigraphic separation during the Early Palaeozoic; it was downthrown to the northwest. This is indicated by
the presence of a thick sequence of Cambrian, Ordovician. and Silurian strata on the northwest side of the MDC fault, and their absence on the southeast side. In the case of the southwest-striking SMLR fault, the southwest part had the opposite stratigraphic separation (downthrown to the northwest) during Neoproterozoic time (Lis and Price. 1976), and perhaps Early Palaeozoic time as well, but the northeast part of the antecedent structure had little or no stratigraphic offset. The evidence for this occurs in the western Purcell Mountains, on the northwest side of the St. Mary fault. There, the basal Cambrian strata (Hamill Group) are underlain by at least 5 km, and possible as much as 8 km of Late f roterozoic Windermere Supergroup strata that are in turn underlain by the upper part of the Middle Proterozoic Belt-Purcell Supergroup. The strata of the
southeast side of the fault are in direct contrast: basal Cambrian strata lie directly and unconformably on the lower part of the Belt-Purcell Supergroup (Rice, 1941), which is stratigraphically more than 10 km deeper than the top of the Windermere strata that occur in the hanging wall of the St. Mary fault. Moreover, coarse. polymict conglomerates that occur at the base, near the middle, and near the top of the Windermere Supergroup northwest of the St. Mary fault contain clasts of Belt-Purcell rocks; these class indicate that the block southeast of the St. Mary fault was being uplifted and eroded, and was
contributing sediment to the Late Proterozoic Windermere Supergroup that was being deposited northwest of it cisand Price, 1976). On the east side of the Roclcy Mountain Trench, stratigraphic relationships on
either side of the SMLR fault indicate that, in Late Proterozoic time, there was little or no offset across it. This is Idicated by the fact that the basal Cambrian Cranbrook Formation lies on approximately the same stratigraphic level on either side of the fault and the Windermere Supergroup is missing on both sides. Hence. the SMLR fauit apparently follows the locus of a northeastward-trending Neoproterozoic fault that was hinged: it had more than 10 km of dip slip at the southwest end. but little or no displacement at the northeast end. Both the stratigraphic relationships across the MDC and SMLR faults and the northeast-southwest-striking geophysical anomalies suggest that the MDC and SMLR faults follow the locus of structures in the basement of the Western Canada Sedimentary Basin, which were re-activated as transform faults, and controlled the margins of the Mesoproterozoic Belt-Purcell basin, the Neoproterozoic Windennere basin, and the Early PaIaeozoic North American con",?ent.l margin. Therefore. these regional basement tectonic features played an important role in the occurrence of the Crowsnest Pass deflection, the cross-strike discontinuity, and the southeast termination of the Main Ranges and Western Ranges geologic sub-provinces. The location of the Tanglefoot area with respect to the geoiogic sub-provinces will be discussed in detail in the following chapter, "Regional Tectonic Setting". REGIONAL TECTONIC SETTING
The Rocky Mountain Foreland Fold and Thrust Belt is the easternmost of the five morphogeological belts of the Canadian Cordillera (Figure 2). It has been subdivided into four geologic sub-provinces (Bostock 1948; North and Henderson, 1954): the Foothills. the Front Ranges, the Main Ranges, and the Western Ranges (Figure 3), each of which is characterized by its structural style, its dominant level of exposure. and its physiography. The Foothills geologic sub-province forms the northeasterly margin of the Rocky Mountains. Its structurai styie is characterized by relatively flat thrust faults of listric geometry, which bifurcate into numerous splays upward. The thrust faults are often folded, along with bedding, above an underlying thrust fault or one of its imbricate splays (Price and Mountjoy, 1970). The dominant level of exposure within the Foothills is that of the Cretaceous part of the clastic wedge sequence, which, combined with the structural style, has resulted in a relatively subdued topography, characterized by linear ridges that outline the structure, and have been carved fiom the underlying resistant sandstone (ibid,). The structure of the Front Ranges geologic sub-province is dominated by a series of sub-parallel, southwest dipping thrust faults. which are relatively few in number but large in displacement, in comparison to the thrust faults of the Foothills. The level of exposure in the Front Ranges is primariIy the Devonian to Jurassic carbonate and siliciclastic rocks of the miogeocline-shelf sequence (Price and Mountjoy , 1970). The physiography of the sub-province is characterized by a series of sub-parallel. northwest trending linear mountain chains, which are separated and controlled by thrust faults, and contain steeply southwestward dipping stratigraphic successions. The Main Ranges geologic sub-province is divisible into an eastern and a western sector, on the basis of structural style, lithology, and sedimentary facies. The boundary between the two sectors was criginally thought to be a single, through-going fault, the FIgare 2: The five morphogeological belts of the Canadian Cordillera, and the location of the Tanglefoot area (from Wheeler and McFeely, 1991). Figure 3: The geologic sub-provinces of the FmhdFold and Thrust Belt (modified hrnRice, 1981). The TangIefwt area (shaded) straddles the southern termination of the Main Ranges and the Westan Ranges sub-provinces. Stephen-Dennis fault (North and Henderson, 1954); but subsequent work (Cook. 1967: Price, 1967; Price, 1967a) has shown that no such fault exists. East of Golden, the boundary between the eastern and western Main Ranges is an abrupt facies change from a carbonate shelf facies in the northeast to a shaly and slaty basin facies to the southwest (Figure 3) (Cook, 1967; Price and Mountjoy, 1970). The eastern Main Ranges are relatively flat-lying and undisturbed. compared to the Front Ranges and Footbills sub-provinces. Folds are generally broad and open. the dips on the flanks of which rarely exceed 25 degrees (North and Henderson. 1954). The eastern Main Ranges have formed in thick, highly competent. Lower Palaeozoic carbonate rocks of the northeastern miogeocline-wedge sequence, and have been carved into lo@. high-shouldered, castellated peaks such as Mounts Robson, Edith Cavell, Eisenhower, and Assiniboine (North and Henderson, 1954; Price and Mountjoy, 1970). The structures of the western Main Ranges, in contrast. developed in the thick. relatively homogeneous, and less competent Lower Palaeozoic shaly strata of the miogeocline. They are characterized by widespread, cornpiex patterns of folding, and strong to penetrative cleavage on scales down to hand-sample size (Cook. 1967; Price and Mountjoy, 1970). Individual thrust faults with large displacements are rare; instead. horizontal shortening has been taken up primarily by a more penetrative styIe of deformation. Physiographicaily, the western Main Ranges is more subdued than its counterpart to the east. The western Main Ranges comprises mountains which are generally not as high, rugged, or dramatic as the castellated peaks of the eastern Main Ranges. The structure of the southern Main Ranges is dominated by the fan-shaped Porcupine Creek anticlinorium, which contains southwest-verging structures in its southwestern limb, and northeast-verging faults and folds in its northeastern limb. The Porcupine Creek anticlinorium will be discussed in detail in the "Structure" chapter, in the section describing the Tanglefoot domain. The fan-axis of the Porcupine Creek anticlinorium constitutes the southwesterly limit of the Main Ranges geologic sub-province (Price and Mountjoy, 1970). Beyond the fan-axis, the southwest verging, southwesterly overturned foIds and fault slices constitute the Western Ranges geologic sub-province, which extends to the southwest as far as the Rocky Mountain Trench (Price and Mountjoy, 1970). The four geologic sub-provinces were originally thought to be separated from each other by individual major faults or fault zones (North and Henderson, 1954), however. the boundaries between them are not always distinct, and not everywhere marked by a specific fault or fault zone (Price and Mountjoy, 1970). Moreover. the boundary between two geologic sub-provinces is defined by different faults in different places. and therefore subject to en echelon offsets among various components in the array of overlapping thrust faults (Figure 3) (Price and Mountjoy, 1970). This is most obvious in the case with the boundary between the Foothills and the Front Ranges sub-provinces. especially south of 5 10 N latitude. The Main Ranges and Western Ranges sub-provinces end rather abruptly at a regional cross-strike discontinuity, part of which extends across the southern part of the Tanglefoot area The cross-strike discontinuity is a regional feature, extending from beneath the Interior Plains of southern Alberta westward into northeastern Washington
(Kanasewich et a/., 1969; Price, 1993, 1997). In the Tanglefoot area, the cross-strike discontinuity is marked by segments of two regionally important, north- to northwest- dipping, right-hand reverse faults, the Moyie-Dibble Creek fault and the St. Mary-Lussier River fault, which occur at approximately 490 35' N and 490 39' N respectiveiy. Both faults turn into westdipping thrust faults north of the study area (Figure 4), snd into southwest-dipping thrust faults to the southwest, in the western Purcell Mountains. Contrasting stratigraphic successions on either side of both faults indicate that they follow the locus of older smctures, as was described in detail in the previous chapter,
LEGEND FOR FIGURE 4a o [=I Km Monzonite 8 0Mr Rundle Group Meb Exshaw, Banff Forrnatlons a aDp Palliser Formation MDsh 'Devono-Mississippian shale unitn a a 0Df Fairholme Group I 0Db "basal Devonian unitn, Cedared, Burnais, Harrogate Formations rn\/ 6 Osb Beaverfoot Formation Corn McKay Group Thrust fault Crnuj Jubilee Fonnatlon (Central Hughes Range) -a!lwldw.. I Cmfge Flathead, Gordon, Elko Formatlons (Uzard Range) 9 Clce Cranbrook, Eager Formations / Transverse fault ~ehowaenwdmovrwnent 8 Pdc Gateway, Phillips, Roosville Formations N Anticline~na*on plunging dl- llPkvn Kitchener, Van Creek, and Nicol Creek Formations 0P O PC Creston Formation Pa Aldridge Formation CD :'I :'I Pfs Fort Steele Formation (Central Hughes Range)
Figure 4b: Legend to accompany Figure 4a, Regional Geology map of the Tanglefoot and surrounding area "Regional Basement Tectonics". The cross-strike discontinuity is related to a 200 km right-hand offset of the hinge line of the Corrdilleran miogeocline. and a 60 km left- hand offset of the margin of the Belt-Purcell basin (Price, 1993). The Tangle foot area also straddles the Crowsnest Pass deflection (Price. 1993). where the predominant structural grain of the southern Canadian Cordillera changes tiom northwesterly to northerly. Two regional strucnual salients within the Foreland Fold and Thrust Belt meet at a conspicuous re-entrant at Crowsnest Pass in southeast B.C. and southwest Alberta (Price et al., 1972). The structural salients are outlined by the regional trends of folds and thrust sheets in the Rocky Mountains. South of the Crowsnest Pass re-entrant, the structural grain is northwest-trending, outlining the northern Montana structurai salient, which extends 450 km into central Montana. North of the re-entrant. the structural grain is north-trending, forming the south end of an 800 km long arc. which extends northwestward to the Peace River re-entrant. The Tanglefoot area occurs in the hanging wall of the Hosmer thrust sheet, which is structurally the highest and westernmost thrust sheet of the Cordilleran Foreland Fold and Thrust Belt (Benvenuto and Price, 1979). Most of the map-area lies in the southern part of the hanging wall of the Dibble Creek fault. The extreme southern part of the study area is in the northern part of the Lizard Range, in the footwall of Dibble Creek fault (Figure 4). STRATIGRAPHY introduction
The stratigraphic succession in the Tanglefoot area can be subdivided into three ciistincq unconformity-bounded stratigraphic asszublages, which collectively span an interval of more than 1.1 billion years. They comprise the Mesoproterozoic strata. the
Lower Palaeozoic strata, and the Upper Palaeozoic strata (Rice. 1937; Leech. 1958: Benvenuto and Price, 1979). Within the Tanglefoot area, there is a profound change in the Lower Palaeozoic stratigraphy across the Dibble Creek fault (Figure 5). South of the Dibble Creek fault, a sporadically exposed (Figure 6), thin, condensed succession of Middle Cambrian cratonic platform facies strata unconformabty overlies Mesoproterozoic strata, bevels the Mesoproterozoic rocks northwestward, and is unconformably overlain by the Upper Devonian Fairholme Group (Figure 5, Figure 7). The erosional unconformity at the base of the Upper Devonian Fairholrne Group beveIs the thin, Middle Cambrian succession northwestward, and adjacent to the Dibble Creek fault, Upper Devonian rocks lie directly on Mesoproterozoic rocks of the Belt-Purcell Supergroup (Figure 5). On the north side of the fault, a sequence of Upper Devonian and Lower Mississippian shaly rocks, which are deeper water facies equivalents of the Fairholme Group, Palliser Formation. Exshaw and lower Banff Formations, unconformably overlie approximately 7 km of shaly lower
Palaeozoic strata (Figure 5, Figure 8). Thus, the Dibble Creek fault coincides with the southeast margin of a sedimentary basin in which approximately 7 km of Lower
Palaeozoic strata accumulated. This chapter will describe the stratigraphy of the region as follows: the rocks examined in outcrop and thin section for the purpose of this study will be described in LOCUS OP LOCUS OF DIBBLE CREEK DIBBLE CREEK FAULT FAULT IlKlUS OF Wi~hrerpcrt III Wth rcrpxl co BOULDER CREEK ~I~II~INaltmg fomu~vu FAULT IU hw~gtngwall ilr kur
DATUMBase 01 Falmolme Qp.
IYlrupul~reutw;l(ltm ol crlirnatul I?hm overlap wns~thc Dlhhlc Crcch VERTICAL EXAGGERATION = 3/1 I Figore Sa: Schematic cross-section through the ~~leiootand surrounding area, extending from the Top of the World area (N) to the Central Lizard Range, just north of Elko (SE) (modified from Benvenuto and Price, 1979). Note the stratigraphic contrast across the Dibble Creek fault, and the relatiouships of the major unconformities in the area. Figure 5b shows the location of the line of section. Abbreviations are the same as for Figures 4a and 4b, except Og = Glenogle Formation, and Omw = Mount Wilson Formation. Figure 5b: Location map showing the location of the Line of the schematic cross-section of Figure 5a (modified from Benvenuto and Rice, 1979). Major fault traces are: MO = Moyie fault, DC = Dibble Creek fault, STM = St Mary fault. LR = Lussier River fault, BC = Boulder Creek fault, HO = Homer thrust, RMT = Rocky Mountain Trench. I I / I CAMBRIAN EXPOSURES
Figure 6: Map of all the Lower Palaeozoic exposures which occur on the southeast (footwall) side of the Moyie-Dibble Crtek fault These strata constitute the Middle Cambrian Flathead, Gordon, Elko, and Windsor Mountain (only at Windsor Mountain, Alberta) Formations (modified from Norris and Price, 1966).
i Udshale unit Shalt and mndstoee, minor shaly lirnestont
Figure 8: Stratigraphic column showing the assemblage which occurs on the north (hanging wall) side of the Dibble Creek fault. Note the thick, shaly, lower Palaeozoic succession, and the different vertical scales in the Mesoproterozoic, Lower Palaeozoic, and Upper Palaeozoic successions. detail, and time-equivalent and correlative units in the surrounding regions, primarily to the north and southeast, will be described briefly on the basis of previously published observations and reports. Emphasis will be placed on objective descriptions. and tectono-sedimentary interpretations will be developed in the chapter on "Interpretations and Conclusions". For siliciclastic sedimentary rocks, Dott's (1964) classification schenx will be employed. For carbonate rocks, Dunham's (1962) scheme will be used; and the terminology for crystal sizes will follow Folk's (1962) scheme. Igneous rocks will be classified according to the International Union of Geological Sciences (IUGS) classification. The oldest rocks exposed in the Tanglefoot area belong to the Mesoproterozoic Belt-Purcell Supergroup, which is made up primarily of fine grained clastic and impure carbonate rocks (McMechan, 1980; Hoy, 1993). Belt-Purcell s;rata in the southern and western parts of the Tanglefoot area constitute part of the eastern limb of the crustal- scale Purcell anticlinorium, which occupies most of the Purcell Mountains (Price. 1981). In the southwestern part of the Tanglefoot area, they occur in the footwall of the Dibble Creek fault, beneath the sub-Devonian unconformity. In the western part of the Tanglefoot area, between the Dibble Creek and Boulder Creek faults. Belt-Purceil strata form a steeply-dipping, east-northeast facing homocline in the eastern Hughes Range. Most of the Tanglefoot area is underlain by shaly Lower Palaeozoic strata. The Lower Cambrian Cranbrook Formation, which forms the base of the thick, shaly sequence, unconformably overlies Mesoproterozoic Belt-Purcell rocks (Gateway and Phillips Formations) in the homocline between Dibble Creek and Boulder Creek faults. It is conformably werlain by Lower Cambrian shale of the Eager Formation, Middle and Upper (?) Cambrian shaly limestone and shale of the "Tanglefoot unit", and Cambro- Ordovician shale and limestone of the McKay Group. To the north, McKay Group strata are overlain by graptolitic shale, siltstone and limestone of the Glenogle Formation and quartz arenite of the Mount Wilson Formation, which are unconformably overlain by dolomite and limestone of the Upper Ordovician and Silurian Beaverfoot Formation (Leech, 1958; Norford 1969). To the south of the Tanglefoot area, the Lower Palaeozoic succession comprises a Middle Cambrian assemblage of cratonic platform facies strata. belonging to the Flathead, Gordon, Elko, and WiorMountain (the latter is preserved only at Windsor Mountain in southwest Alberta) Formations, which have been largely removed by pre-Upper Devonian erosion.
Upper Pdaeozoic strata, though not abundant in the Tanglefoot area are regionally very conspicuous and important. To the south, on the southeast side of the MDC fault, they comprise a cratonic platform sequence of shallow water carbonate rocks belonging to the Fairholme Group, the Palliser, Exshaw and Banff Formations. and the
Rundle Group. In the northern region, in the vicinity of Top of the World (Figure 4a), the Upper Palaeozoic succession comprises a clastic "basal Devonian unit", Lower (?) and Middle Devonian gypsum and related evaporite deposits of the Burnais Formation. Middle Devonian shale and limestone of the Harrogate Formation, and an Upper Devonian and Lower Carboniferous shde and limestone unit (Leech, 1958). The Devono-
Mississippian shaly strata (MDsh of Figure 4) are lateral equivalents of the Fairholme Group, and the Palliser, Exshaw, and Banff Formations (Savoy and Harris, 1993).
Meso~roterozoicStrata
Fort Steele and Aldridee Formations The Fort Steele Formation consists of quartz arenite and quartzwacke, and constitutes the oldest unit in the Belt-Purcell Supergroup that is exposed in the southern Canadian Rockies. It occurs northwest of the Tanglefoot area, in the central Hughes Range, immediately east of the Roclq Mountain Trench (Rice, 1937; Leech, 1958; Hoy, 1993). It consists primarily of white quartz arenite with conspicuous cross-bedding, which grades upward into quartz arenite interbedded with quartzwacke, feldspathic greywacke and dark argrllite. Hiiy (1 993) reported a thickness of greater than ZOO0 m for the Fort Steele Formation, and noted that its base is not exposed. The Aldridge Formation conformably overlies the Fort Steele Formation. and comprises a thick sequence of argillite, siltstone and fine-grained quartzwacke turbidites. The lower Aldridge Formation includes thick gabbroic sills, known as the Moyie sills (Daly, 1912). The geochronology of the sills has been problematic, because Precambrian thennai events (e.g. McMechan and Price, 1982) have reset ages of the sills, and the K-Ar dates for the sills range from 660 Ma to 1918 Ma (Hoy, 1989). However, Hoy (1 989) reported a U-Pb zircon date of 1445 +/- 11 Ma, interpreted as the minimum age of emplacement of the sills (Hey, 1989), and Anderson and Davis (1994, 1995) dated zircons from the middle of thick sills at 1467 +/- 3 and 1468 +/- 2 Ma. These dates are interpreted to be more reliable, and represent the true age of the Moyie sills. Gradational contacts between the sills and the host rock, soft-sediment deformational structures, and large scale dewatering structures indicate that the sills intruded into wet, unconsolidated sediments (Hoy, 1989). Therefore, the age of the Moyie sills defines the minimum age of deposition of the lower Aldridge Formation. The Aldridge Formation occurs northwest and west of the Tanglefoot area in the Hughes Range (Hoy, 1979; Hoy and Carter, 1988: Hay, 1993), and south of the Tanglefoot area in the southern Steeples Range (Leech, 1958; McMechan, 1980). The Ndridge Formation is reported to be 3500 m thick (McMechan, 1980) between the Boulder Creek and Dibble Creek faults. Neither the Aldridge Formation nor the Fort Steele Formation of the Belt-Purcell Supergroup are expcxd in the immediate study area, and accordingly they will not be described Merherc. Creston Formation The Creston Formation, which conformably overiies the Aldridge Formation. comprises primarily interbedded shallow-water siltstone and argillite, with local quartz arenite and rare dolomitized siltstone near the top. A northeast-plunging anticline of Creston Formation strata occurs in the extreme south part of the Tanglefoot area on the west side of the Bull River, in the vicinity of Donely Creek (Figure 9). There, outcrops weather medium grey to slightly rust coloured, and strata comprise light greenish-grey to pale green argillite and siltstone. Wavy, discontinuous laminations and dolomitic cement occur locally. Near the top of the formation, there are local layers (possibly lenses) of white to pinkish light grey quartz arenite. The layers are 1 m to 3 m thick and the quartz afenite is well sorted, and contains subrounded to rounded medium-sized quartz grains. McMechan (1979, 1980) and H6y (1993) reported that lenses of fine to coarse grained quartz arenite occur throughout the Creston Formation, and also that the interbedded siltstone and argillite are dolomitic near the top, and grade into the dolomitic siltstones of the overlying Kitchener Formation. The Creston Formation is up to 1800 m thick in the area between the Boulder Creek fault and the Dibble Creek fault (McMechan, 1980). although only the upper 30 to 40 rn of the formation is exposed in the Tanglefoot area. On the west side of Bull River, south of the mouth of Dibble Creek. the Creston Formation (and Kitchener Formation?) is intruded by a small, elliptical, gabbroic plug, which is approximately 300 m by 600 m, and could be related to the Moyie sills. It is a bufY to brown-weathering, light green and dark green speckled, medium grained, equigranular, massive altered gabbro (possibly diorite). Plagioclase, which constitutes 40% of the rock, comprises subhedral, lathe-shaped grains, commonly 2 mm to 3 mrn long, that show weak to moderate sericite plus epidote alteration. Hornblende, which constitutes 5-7% of the rock, occurs as subhedral, elongate grains 1 mrn to 2 mm long, that have been strongly chloritized. Fe-rich chlorite, which is a dominant seconw I CANYON
Figure 9: Map showing the major faults (grey rharles) and some of the namexi creeks, lakes, and rivers within the Tauglefwt area Various creeks are often referred to as geographical landmsltks in the text, especially in the "Stratigraphy"and "Structure" chapters. AU hydrological featrrres are also named on the geological map (Plate 1) mineral, constitutes 40% of the rock. It occurs as very fine grained, black masses. in stubby, prismatic shapes approximately 2 mm to 3 mm in diameter. It appears to pseudomorph anhedral to subhedral pyroxene (?) grains. which likely constituted as much as 40% of the rock prior to alteration. Clay minerals, likely vermiculite and/or smectite group (on the basis of the apparent Fe abundance in the rock), account for approximately 10% of the rock, and opaque minerals (ilrnenite, magnetite. and rare pyrite) account for the remaining 3-5%.
Kitchener Formatios The Kitchener Formation comprises dominantly carbonate and calcareous siliciclastic rocks that conformably overlie the Creston Formation. It is exposed in the southern portion of the Tanglefoot area in the footwall of the Dibble Creek fault, and further south, on the west side of the Bull River between the mouths of Donely Creek and Dibble Creek (Figure 9). It also forms part of the east-northeast-facing homoclinal succession in the area between the Boulder Creek fault and the Dibble Creek fauit. There. the Kitchener Formation is approximately 2000 m thick (McMechan, 1980; Hoy, 1993). Immediately west of the Bull River in the southern part of the map-area, only the lower Kitchener Formation is preserved, and it is truncated by the sub-Devonian unconformity. The Kitchener Formation near the Bull River consists of greyish olive-green medium-crystalline siliceous dolomitic wackestone and medium- to coarsely-crystalline siliceous dolomite, reddish brown to reddish purple dolomitic siltstone, and locally of non-dolomitic siltstone. Molartooth structure, climbing ripples, and mudcracks are abundant locally in the lower Kitchener Formation, and slightly wavy bedding is somewhat obscured by a moderate southwest-striking cleavage. The Kitchener Formation is also exposed in the footwall of the Boulder Creek fault, near the drainage divide between the headwaters of Tanglefoot Creek and Boulder Creek. These outcrops are stratigraphically near the overlying Van Creek Formation. and thus are near the top of the Kitchener Formation. Strata close to the Boulder Creek fault are sheared, and show very strong foliation that dips steeply to the nor&, and is sub- parallel or parallel to the Boulder Creek fault. Primary bedding is generally completely obliterated, and what was once dolomitic siltstone or wackestone has now been strongly silicified and sheared. However, within tens of metres to the south of the fault. dolomitic siltstone and medium-crystalline dolomite occur as laterally continuous. northwest- dipping planar bedded strata. The southern and northern occurrences of Kitchener strata in the Tanglefoot area correspond stratigraphically with McMechan's ( 1980) lower member and upper member respectively.
Van Creek Formatioq The Van Creek Formation (McMechan et al., 1980) comprises argillite. siltstone. and quartz arenite that conformably overlies the Kitchener Formation. It occurs in two regions in the Tanglefoot area, but was examined at only two locations: one in the footwall of the Boulder Creek fault, and one in the footwall of the Dibble Creek fault. In the area between the Boulder Creek fault and the Dibble Creek fault, the Van Creek Formation is 340 m to 420 m thick (McMechan, 1980). In the footwall of the Dibble Creek fault, the formation is approximately 200 m thick. In the footwall of the Boulder Creek fault, the Van Creek Formation consists of greyish-green and subordinate light grey, discontinuously laminated, non-calcareous argillite, siltstone, and very fine grained quartz arenite. Primary bedding has been completely obscured locally, and there is a paucity of other sedimentary structures at this location, likely due to its proximity to the Boulder Creek fault. In the footwall of the Dibble Creek fault, the Van Creek Formation contains non- calcareous argillite and siltstone, with lesser amounts of very fine-grained quaaz arenite. Planar, continuous laminations are abundant: wavy. discontinuous laminations are less common. Laminations are generally dark green and light green or dark green and white. and less commonly green and red. Scour-and-fill structures occur locally. and mudcracks were observed at one outcrop.
Nicol Creek Formation
The Nicol Creek Formation (McMechan et a/-.1980) conformably overlies the Van Creek Formation, and comprises dark green, amygddoidal basalt. It is equivalent to the Purcell Lava (Daly, 1912; Price. 1962) of the Belt Supergroup. and has also been called the top of the Kitchener-Siyeh Formation (Leech. 1958). and the "Mount Baker
Unit" (Benvenuto and Price, 1979). The Nicol Creek Formation was examined at two locations in the Tanglefoot area. The best exposure is in the footwail of the Dibble Creek fault south of Dibble Creek. approximately 3 to 4 km west of the Bull River. At this location. the Nicol Creek Formation consists solely of massive amygdaloidal subporphyritic mafk volcanic flows that overlie argillite and siltstone of the Van Creek Formation. Hunt (1964) conducted a geochemical analysis of the Nicol Creek Formation along the Lussier River. and found it to be basaltic in composition. Arnygdules are commoniy filled with medium- to coarse-grained quartz, locally with chlorite around the rims. They are commonly 7 to 9 mm in diameter. and rarely exceed 15 rnrn in diameter. Subhedd to euhedral plagioclase phenocrysts are usually 3 mm to 5 rnm in diameter. and have been weakly to moderately sericitized and chloritized. Fresh surfaces of the lava are dark green with white amygdules and greenish grey phenocrysts, and weathered surfaces are dark green with white to pale green amygdules. Both the Van Creek and Nicol Creek Formations are unconformably overlain by Upper Devonian rocks in the footwall of the Dibble Creek fault, where the Nicol Creek Formation is approximately 140 m thick. The second location where rocks of the Nicol Creek Formation were examined is immediately south of the Boulder Creek fault. near the southern headwaters of Tanglefoot Creek (Figure 9), where a splay fiom a westdipping normal fault has resulted in a repetition of the Van Creek-Nicol Creek sequence. At this locality, the Nicol Creek Formation is moderately to strongly foliated and altered. presumably due to its proximity to the Boulder Creek fault. Amygdules are less common and more altered: thin chlorite rims ( In larger arnygdules, the fine- to medium-grained quartz grains surround a core of red hematite. Phenocrysts were not observed at this location, although outcrop is scarce. It should be noted that only two exposures of the Nicol Creek Formation were observed in the study area, and they are not completely representative of the Nicoi Creek Formation proper. McMechan (1980) reported that, between the Dibble Creek fault and Boulder Creek fault (near Cliff Lake (Figure 9)), the formation is 600 m thick. comprising massive lava flows interbedded with green locally dolomitic siltite and argil!ite. and green volcanic sandstone and tuff. Felsic volcanic rocks fiom the Purcell Lava (equivalent to the Nicol Creek Formation) in the Purcell Mountains of Northern Montana were dated by J.N. Aleinikoff (1 996) using a sensitive high-resolution ion microprobe (SHRIMP). Two suites of zircons were dated using the U-Pb method and both gave dates of 1443 +/- 5 Ma (Aleinikoff, 1996). This date has remarkable implications regarding the rate of deposition of the Belt-Purcell Supergroup. If Anderson and Davis' (1995) age of 1468 +/- 2 Ma for the lower Aldridge Formation is accurate, then it suggests that approximately two thirds of the Belt-Purcell Supergroup (approximately 7 km of strata) were deposited in 20 - 30 Ma. She~~ardFormation The Sheppard Formation. which overlies the Nicol Creek Formation. consists of stromatolitic dolomite. argillite and siltstone. with subordinate fine-grained quartz arenite (McMechan. 1980: Soy, 1993). It is only exposed in one part of the Tanglefoot area: between Boulder Creek and Dibble Creek faults, where it forms part of the homoclinal sequence of Belt-Purcell strata. The rocks of the Sheppard Formation were not examined for this study, but the reader is referred to McMechan ( 1979. 1980). and Hoy ( 1993) who reported that the Sheppard Formation in the Tanglefoot area consists primarily of stromatolitic and oolitic dolomite. pale green. light grey and white. localI!- discontinuously laminated, thinly bedded argillite and siltstone, with lesser amounts of fine-grained. weakly dolomitic subarkosic quartz arenite. Its thickness east of Cliff Lake south of Boulder Creek fault is reported to be 125 m (McMechan. 1980; Hoy, 1993). Gatewav Formation The Gateway Formation comprises siltstone. argillite. and fine-grained quartz arenite, and conformably overlies the Sheppard Formation. It was examined at two localities in the study area: one at the sub-Cambrian unconforrnity approximately 1 km west-southwest from where the Van Creek road crosses the Tanglefoot Creek (footwall of the Boulder Creek fault), and the other in the east-northeast facing homocline of Belt- Purcell rocks between Boulder Creek fault and Dibble Creek fault. McMechan ( 1980) reported its thickness between the two faults as greater than 475 m. and Hoy (1993) reported that it is "approximately 500 rn" thick there. The Gateway Formation has similar characteristics at the two localities where it was examined, except for colour. At the northern location (footwall of Boulder Creek fault) the rocks are conspicuously purple with local green to greenish-grey laminations. and at the southern location (north of Dibble Creek), the formation is dark green with light greenish-grey, and rarely purple. thin Iayers. The strata comprise primarily siltstone. with lesser amounts of argillite and fine- to medium-wed quartz arenite. Fine laminations in the siltstone are commonly planar and continuous, and locally wavy and discontinuous. Ripple laminations, climbing ripples. and fine scour-and-fill structures are also present in the siltstone portions of the formation. Quartz arenite is less abundant than siltstone. It occurs in layers 10 cm to 35 cm thick. and is grey to purple. well indurated and fine-grained. showing low-angie cross-laminations (hummocky cross- stratification?). P hilli~sFormation The Phillips Formation. which conformably overlies the Gateway formation. consists of thin-bedded, dark red quartzite, siltstone and argillite. It is one of the most distinctive regional marker units in the Belt-Purcell Supergroup. It is exposed at only one location in the TangIefoot area - between Boulder Creek and Dibble Creek faults in the homoclinal sequence of Belt-Purcell strata - where it is truncated by the sub-Cambrian unconformity. It is similar in some respects to the underlying Gateway Formation. comprising red. maroon. and purple, thin- to very thin-bedded, very fine- to medium- grained quartz arenite. rnicaceous siltstone and argillite (McMechan. 1980: Hoy. 1993). Exposure of the Phillips Formation beneath the sub-Cambrian unconformity is poor in the study area and Mersedimentary structures are not discernible. The thickness of the entire formation was not measured as it is truncated by sub-Cambrian erosion, but there is approximately 80 m of Phillips Formation strata present beneath Cambrian rocks north of Dibble Creek. Lower Palaeozoic Strata The Lower Palaeozoic succession on the southeast side (the foonva11) of the Dibble Creek fault is only sporadically exposed (Figure 6).and completely different from that occurring on the north side of the fault. On the southeast side of the Dibble Creek fault, the Lower Palaeozoic assemblage comprises a thin (1 18 m - 337 m). condensed sequence of Middle Cambrian cratonic platform facies strata. These strata belong to the Flathead, Gordon. Elko, and Windsor Mountain (one locality only) Formations (Figures 5 and 7) (Norris and Price. 1966), and are unconformably overlapped northwestward by Upper Devonian strata. Adjacent to the Dibble Creek fault, Upper Devonian strata lie directly on Mesoproterozoic rocks of the Belt-Purcell Supergroup. In contrast. on the north side (the hanging wall) of the Dibble Creek fault the Lower Palaeozoic sequence comprises up to approximately 7 km of shaly, basinal facies strata. which are overlain b:; Upper Devonian shaiy rocks that are deeper water equivalents of the Fauholme Group. Palliser Formation. Exshaw Formation. and lower Banff Formation (Savoy and Hams. 1993). The thin. Lower Palaeozoic platformal succession on the southeast side of the Dibble Creek fault will be described first and then the correlative thick. shaly Lower Palaeozoic strata on the north side of the fault will be described. Footwall of the Dibble Creek fault Flathead. Gordon. and Elko Formations The Middle Cambrian Flathead, Gordon, and Elko Formations occur southeast of the Tanglefoot area, in the footwall of the Moyie-Dibble Creek fault system, where they constitute the entire Lower Palaeozoic sequence. They were not examined during this study, but as described by Norris and Price (1966), they are strikingly different in character from the Middle Cambrian succession that occurs in the Tanglefoot area north of the Dibble Creek fault. The Flathead Formation consists mostly of interbedded quartz arenite and quartzwacke, with subordinate greywacke and siltstone. and rests unconformably on Mesoproterozoic rocks of the Belt-Purcell Supergroup (Leech. 1958; Norris and Price- 1966). The sandstones are commonly limonitic, yellowish-grey. fine- to coarse-grained. thin- to medium-bedded, medium to coarsely crossbedded. and weather yeilowish-orange with the cross-laminations standing out in colour relief as shades of purple (Noms and Price. 1966). Conglomerates are present locally, and most commonly at the base and top of the formation (Norris and Price. 1966). The thickness of the Flathead Formation varies considerably from place to place on a regional scale. and also on an outcrop scale. The thinnest reported section of the Flathead Formation is just north of Elko, at the old Burton Mine, where Leech (1 958) reported a thickness of 2.5 m for the "Burton Formation". which has been assigned to the Flathead Formation by Norris and Price (1966). The thickest section is in the Flathead Range, where it is 46 m thick (Price, 1962). The Gordon Formation, which conformably overlies Flathead strata. consists dominantly of fissile, greyish-green, micaceous shale (Nonis and Price. 1966). Interbeds of sandstone and limestone occur throughout the formation. In the lower two-thirds of the formation. there are interbeds of resistant. yellowish-brown biogenic and glauconitic sandstones, and in the upper one-third of the formation. there are interbeds of detrital. fossiliferous limestone (Noms and Price, 1966). The Gordon Formation thickens southeastward. It is 45 m thick just southeast of the Tanglefoot area (above the old Burton mine north of Elko), it is 70 m thick in the Flathead Range near the Alberta-British Columbia border. and it is 88 m thick on Windsor Mountain in southwest Alberta (Norris and Price, 1966). The presence of a Plaeiura-PoIiella faunule in the lower Gordon Formation near Eko (Leech. 1958; Fritz and Norris, 1966) and of an Albertel la faunule 18 m above the base of the Gordon at Windsor Mountain (Noms and Price, 1966) indicates that the basal Gordon strata are of early Middle Cambrian age. The conformable. gradational contact between the underlying Flathead Formation and the Gordon Formation suggest that the FIathead is also early Middle Cambrian (Fritz and Noms. 1966). The Elko Formation comprises a relatively thin. basal zone of dark grey limestone overlain by cliE-forming dolomite (Norris and Price, 1966). The dolomite is generally medium to light grey, fine- to medium-crystalline, and commonly shows faint textural mottling which becomes etched into relief on weathered surfaces (Norris and Price. 1966). The Eko Formation rests conformably on the Gordon Formation, and near the Tanglefoot area, is overlain unconformably by the Upper Devonian Fairholme Group (Leech, 1958: 1960). The thickness of the Elko Formation varies as a result of pre-late Middle Devonian erosion. At its thickest, the formation is 155 m thick (Noms and Price. 1966). however. the entire Middle Cambrian succession is unconformably overlapped northwestward by Devonian strata, and is removed completely in the footwall of the Dibble Creek fault, where Middle Devonian strata lie dircctly on Middle Proterozoic rocks of the Belt-Purcell Supergroup (Leech, 19%). The Windsor Mountain Formation consists of dolomites and limestones which conformably overlie the Elko Formation, and are unconformably overlain by Devonian strata. The Windsor Mountain Formation was proposed by Noms and Price ( 1966) to describe the succession on Windsor and Citadel Mountains in southwestern Alberta, where it is 68 m thick (Noms and Price, 1966). The Middle Cambrian age of the formation is established by the recovery of trilobites from the lower part of the formation (Fritz and Noms, 1966), which belong to either the Glossopleura or Bathvuriscus- &athina biozones moms and Price, 1966). The Windsor Mountain Formation is absent to the west and northwest because of pre-Devonian erosion. HanPing wall of the Dibble Creek fault Cranbrook Formation North of the Dibble Creek fault. the Cranbrook Formation unconformably overlies Mesoproterozoic rocks of the Belt-Purcell Supergroup, and is overlain by the Lower Cambrian Eager Formation. The Cranbrook Formation consists of quartz arenite. quartz wacke, quartz-pebble conglomerates, and subordinate siitstone. It unconformably overlies Belt-Ekrcell rocks in the east-northeast facing homoclinal sequence in the area between the Boulder Creek fault and the Dibble Creek fault. There. the unconformity is sharp, and very slightly angular. A very low-angle northwestward truncation of beds in the underlying Gateway Formation is discernible along the unconformity, but it occurs at approximately the same level in the Belt-Purcell Supergroup - the upper Gateway Formation - for approximately 10 km southward from the Boulder Creek fault. There. the unconformity is truncated by an east-west trending fault. beyond which the Cranbrook Formation is underlain by the lower part of the Phillips Formation. A conglomerate occurs locally at the base of the Cranbrook Formation. which contains subrounded clasts primarily of fine-grained quartz arenite and siltstone. In the Tanglefoot area the Cranbrook Formation commonly contains grey, purplish grey or pinkish grey, moderately sorted quartz arenite and quarhwacke, purple and mauve, poorly sorted quartz granule grit and quartz pebble conglomerate. The Cranbrook Formation contains lesser amounts of medium- to coarsely-crystalline dolomite, local Iayers of dark siltstone, shale, and argillite. Beds are generally thick, and internal laminations are absent, but crude cross-bedding does occur locally. The Cranbrook Formation is approximately 80 m thick near the Boulder Creek fault and the Dibble Creek fault but is approximately 100 m thick between Cliff Lake and Van Creek (Fibme 9). In the footwall of the Lussier River fault in the most northwesterly pan of the Tanglefoot area, the Cranbrook Formation consists primarily of pale green and light grey siltstone and argillite. with lesser amounts of fine-grained. weakly dolomitic. subarkosic quartz arenite. Near the Lussier River fault, it is moderately brecciated and altered. Ewer Formatioq The Eager kormation, which overlies the Cranbrook Formation consists primarily of dark, recessive shale, but locally of medium-grey, calcareous shale with fine black laminations. The contact between the Eager Formation and the underlying Cranbrook quartzite is covered throughout the Tanglefoot area. Trace amounts of muscovite are visible locally in thin sections of the calcareous shales, and the muscovite flakes are oriented sub-parallel with the laminations. No other rock types were observed in the Eager Formation in the Tanglefoot area, although Leech (1 958) reported that the formation also contains limestone, and siltstone and sandstone near the base. The thickness of the Eager Formation is difficult to determine accurately because of poor exposure and tectonic thickening; however, the formation appears to be approximately 100 m near the Dibble Creek fault, where tectonic thickening is at a minimum. Fossils collected from the lower Eager Formation less than 1 km west from where Van Creek road crosses Tanglefoot Creek have been identified as Olenellus schofieldi and Olenellus "dberti" (Plate 3) (Fritz, 1995). Elsewhere in the region, Olenellus schofieldi and Olenellus "eilberti" are associated with Wanneria and Bmnia. This suggests that they belong to the medial pa.of the upper Qienellus Zone (Lochman-Balk and Wilson. 1958: Bamber et al., 1WO), and are late Early Cambrian in age (Fritz, 1995). Plate 3: Olenellus "~lberti",fossilized in the Iower Eager Formation "Tan~lefoot- untt" The "Tangle foot unit" conformably overiies the Eager Formation. and consists of shaly lime mudstone, wackestone, and packstone. carbonate breccia, and subordinate dolomite and shale. It is a unique and anomalous strati-gaphic unit which occurs between the Eager Formation and the McKay Group, and is exposed in the Tanglefoot map-area and nowhere else. The distinctive assemblage of rock types of the "Tanglefoot unit" resembles that of the Chancellor Fonnation (Cook, 1973, which occurs in the western Main Ranges to the north. in the vicinity of Vermillion Pass and Kicking Horse Pass. Deeper water rocks of the Chancellor Formation are separated &om the shallower water McKay Group by the medial Upper Cambrian Ottertail Formation, a massive. thin- to thick-bedded limestone unit (Gardner, 1977). Immediately northwest of the Tanglefoot area, in the central Hughes Range, Lower Cambrian rocks correlated with the Eager Formation are overlain unconformably by the Jubilee Formation (Leech. 1958). an unfossiliferous cliff-forming dolomite unit, of Lower (?) to Upper Cambrian age that is overlain by the McKay Group. The "Tanglefoot unit", which occurs only to the north of the Dibble Creek fault, underlies most of the map-area and accordingly, has been a primary focus of this study. It has been examined in the field and in thin section more thoroughly than the other formations in the area. The actual contact with the underlying Eager Formation is not exposed. but rocks characteristic of the two formations are interbedded over a thickness of approximately 10 m, suggesting that the contact is gradational and conformable. The most abundant rock type in the "Tanglefoot unit" is bedded lime mudstone and wackestone (Plate 4). It is dark grey to black on a fiesh surface, and weathers a distinctive bluish grey. It is normally very fine-crystalline to fine-crystalline, and rare allochems do not exceed medium-crystalline size (250p.m). Thin section analysis reveals that approximately 5% clay minerals and 2% to 5% medium-crystalline spany calcite Plate 4: Bedded lime mudstone of the "Tanglefoot unit"; hammer is 40 cm long blebs also exist with the rnicrite. Beds are planar. laterally very continuous (Plate 5). and usually around 5 cm thick but locally are up to 40 cm thick. Sedimentary structures other than primary bedding are conspicuously absent fiom most exposures. with the exception of occasional fine, continuous and discontinuous laminations (Plate 6) and rare small-scale fining-upwards sequences. The Tanglefoot unit" also contains spectacular oligornictic carbonate breccias. which are more abundant in the southern half of the study area than the northern part. The matrix of the breccias is fine-crystalline lime mudstone, dolomitic mudstone, wackestone. and occasionally silty (siliceous) wackestone. It generally weathers buff to brown, while fresh surfaces are dark grey to black. The matrix normally constitutes around 20% of the rock, although it ranges fiom 5% to 40%. The clasts of the breccia comprise conspicuous tabular slabs of limestone that are 1 cm to 30 cm long, and generally 2 to 3 cm thick. Approximately 60% of the clasts are dark grey to black. very fine-crystalline lime mudstone that weathers bluish grey, in notable contrast to the buff- brown weathering matrix (Plate 7). The remaining 40% of the clasts are locally ooid- bearing, peloidal packstone. Grains (peloids) are well rounded, moderately to well sorted. and composed of rnicrite. Thin section analysis reveals up to 2% clay as a dissolution product in sutured, sub-stylolitic seams between peloids, and locally between ooids. within the packstone clasts. There are diverse macroscopic textures within the oligomictic carbonate breccias. Some of the clasts are aligned in preferred orientations (e.g. Plate 7), some are imbricated. some are gently folded, indented, or pierced by other clasts (Plate 8). Locally, small-scale fining-upwards sequences are present within individual dasts. The oligomictic carbonate breccias in the ''Tmglefoot unit" are interpreted as debris flow deposits. Gently folded clasts within the debrites (Plate 8) indicate that slumping and massive basinward transport of sediment occurred prior to lithi fication. At Plate 5: Laterally continuous, planar bedded strata of the "Tanglefootunit"; hammer is 40 cm long Plate 6: Discontinuous and continuous laminations in a relatively thick bed of limestone belonging to the "Tanglefootunit" Plate 7: Carbonate debris-flow breccia of the "Tanglefoot unit". In the lower left-hand part of the outcrop, there has been only a small amount of basinward transport of soft sediment, resulting in large, nearly continuous, "slabs" of limestone. In the upper right- hand part, more extensive down-slope transport has resulted in a more chaotic, massive carbonate breccia. Hammer is 40 cm long Plate 8: Folded clasts in debris-flow breccia of the "Tanglefoot unit", indicating that downslope (basinward) transport occurred prior to lithification one location on the ridge between Van Creek and Bull River, the "toe" of a cohesive slump block, which overlies a syn-sedimentary slip surface, occurs in outcrop (Plate 9). Palaeoslopes can also be inferred fiom clast imbrication, and the occurrence of ripple marks and flute casts on the underside of beds. Palaeoslopes are generally northwestward, although they vary Iocaily fiom northeastward to southwestward. The third most common rock type ia the "Tanglefoot unit" is coarse-grained detrital limestone that contains peloids, ooids, and lithic grains. Small scale textures and abundances of peloids, ooids, and lithic grains vary across the entire study area, but detrital limestones can be grouped into one unit. It comprises peloidai packstone. ooid- bearing peloidal packstone, lithic peloidal grainstone, and lithic oolitic greywacke (originally a carbonate, has been strongly siliciified). It also includes rare peloidal dolomite, as diagenetic dolomitization does not change the original detrital nature of the rock. Contact relations between bedded lime mudstones and wackestones, oligomictic carbonate breccias, and peloidal limestones generally can be assigned to one of three categories: (1) conformable, with m-scale ripups of underlying carbonate sediment within the overlying sediment, (2) submarine erosiona! or scoured, with a mm-scale lag deposit at the base of a coarser grained detrital carbonate unit overlying lime mudstone or wackestone, or (3) stylolitic contacts, with a single thick stylolite between rock types. Thin section analysis of the latter contact type shows that the stylolitic surface is clay rich, forms a distinctive sutured seam, and was formed by dissolution processes. The "Tanglefoot unit" also contains relatively rare non-calcareous shale, interbedded with lime mudstone. Shale layers are dark grey to black, fissile, recessive, and rhythmically interbedded with lime mudstones. The top several metres to tens of metres of the "Tanglefoot unit" comprise a distinctive laminated shaly succession (Plate lo), which varies in thickness between approximately 25 m and 65 m. It is most commonly Plate 9: The "toe" of a cohesive slump block comprising a carbonate debris-flow deposit in the "Tanglefoot unit". Note the two major slip surfaces, which converge downslope from the slump block, and the more chaotic breccia above the upper detachment. Hammer is 40 cm long. Plate 10: Laminated, shaly lime mudstone from the upper "TangIefoot unit". View is to the north; laminations dip gently to the northwest, and cleavage dips more steeply to the northwest medium grey in colour, but is also yellowish grey. tan. or dark grey. It contains remarkably planar. continuous black laminations, which are 0.2 mm to 0.7 rnm thick. The least abundant characteristic rock type in the "Tanglefoot unit" is medium to coarsely-crystalline, recrystallized dolomite. It is bedded on a scale of 2 cm to 5 cm. locally massive. and weathers a distinctive brown to reddish brown colour. Dolomite accounts for approximately 5% of the strata of the "Tanglefoot unit". Fossils are very rare in the "Tanglefoot unit". but its age has been constrained by Early Cambrian fossils fiom the underlying Eager Formation and Late Cambrian fossils fiom the overlying McKay Group, which were collected during this study. and examined by W.H. Fritz of the Geological Survey of Canada- One fossil collection from an unspecified horizon in the "Tanglefoot unit", which was obtained by Leech in 1960. has also been examined by Fritz (1969). Leech's colIection included specimens of Acrothele sp., Ehmaniella sp.. Parkaspis sp., Paterina sp., Protos~ongiasp.. and P~chamosrus(?) sp., all of which Fritz (1969) confirmed as belonging to the upper Middle Cambrian Bathvuriscus-Elrathina Zone (Lochman-Balk and Wilson. 1958; Bamber et a[. 1970). Fritz (1969) also commented that Leech's collection suggests a correlation between the -'Tanglefoot unit" and the Stephen Formation at the type section on Mt. Stephen. Fossil data from the Eager Formation, the "Tanglefoot unit". and the McKay Group indicate that the "Tanglefoot unit" is Middle Cambrian, and possibly early Late Cambrian in age (the age of the overlying McKay Group is discussed under the next sub-heading). McKav Grou~ The McKay Group consists of thinly bedded shale and limestone (Leech. 1958). which overlie shaly limestones of the "Tanglefoot unit". Leech (1 958) examined and described a section 900 m thick in the Hughes Range to the north, which is underlain by dolomites of the Jubilee Formation. He reported that the McKay Group consists of two main lithological divisions, an upper and a lower. each of which can be subdivided into a lower shdy member and an upper cliff-forming member. consisting chiefly of limestone with lesser interbeds of shale. Fritz et al. (1991) correlated the lower shale member with the Upper Cambrian Bison Creek Formation, which overlies the Ottertail Formation in the eastern Main Ranges of the Rocky Mountains to the north. Similarly, the lower limestone member of the McKay Group has been correlated with the Mistaya Formation. and the upper division has been correlated with the Lower Ordovician Survey Peak Formation (Fritz et al., 1991). The two main lithological divisions of the McKay Group are correlative with Aitken's 6th and 7th Grand Cycles in the lower Palaeozoic of the Rockies (Aitken. 1966. 1978; Fritz er al., 1991). Rocks of the Upper Cambrian McKay Group were visited and examined at only one location during this study. Trilobites, which were collected from the McKay Group approximately 1.4 krn north of the mouth of Clay Creek. have been identified by W.H. Fritz (Fritz. 1995) as Housia ovata, belonging in the Dunderbergia-Elvinia Zone (Lochman-Balk and Wilson. 1958; Bamber et al.. 1WO), suggesting a middle Upper Cambrian age for these lower McKay Group strata (Fritz. 1995). At this location. the McKay Group consists of soft shdy limestones. remarkably clay-rich. which are thinly bedded with very thin. discontinuous laminations. They are medium-grey on a fresh surface. and weather a yelIowish-grey , with black laminations. Gardner (1977) reported on the discovery of Dunderbereia Zone fossils in the lower part of the Ottertail Formation in the Kicking Hone Pass region to the north. The presence of a Dunderbereia fauna in the lower McKay Group in the Tanglefoot area suggests that that it may be laterally correlative with the Ottertail Formation. In the Tanglefoot area, the McKay Group appears to be gradationally conformable with the "Tanglefoot unit", although the contact is covered. Immediately north of the study area on Empire State Peak, the Ordovician-Silurian Beaverfoot Formation unconformably overlies the McKay Group, and further north. in the Top of the World area (Figure 4a), the McKay Group is overlain by the Glenogle and Mount Wilson Formations. which are in turn overlain unconformably by the Beaverfoot Formation. The contact relations in the Top of the World area are illustrated in Figure 5b. Although the Glenogle, Mount Wilson, and Beaverfoot Formations do not occur within the study area they will be briefly described under the next two sub-headings in order to facilitate the discussion of the sigmficance of the changes in the Lower Palaeozoic stratigraphy fiom the north to the south side of the Dibble Creek fault. Basic volcaniclastic and volcanic or subvolcanic amygddoidal rocks occur within the mid-Lower Ordovician rocks of the McKay Group in the Top of the World area. and are unconformably overlapped by the Beaverfoot Formation (Norford and Cecile. 1994a. 1994b). G.B.Leech (1 958) described a succession of volcaniclastic and volcanic rocks near Ruault Lake, which he tentatively interpreted as overlying the Beaverfoot Formation. and therefore of Silurian (?) or Devonian (?) age. Hoy and Carter ( 1988) and Welbon and Price (1993) folIowed Leech's interpretation, which was based on the notion that the volcanic rocks occupied the core of a syncline outlined by east- and west-facing. steeply dipping panels of Beaverfoot Formation. However. it is now recognized that: ( 1 ) the "west-facing" panel of Beaverfoot Formation that lies east of the volcanic rocks is a very tight, almost vertical, syncline with Cedared and (?) Burnais Formations in its core. and (2) the volcanic rocks occur within the upper part of the McKay Group (Norford and Cecile, 1994a; R.A. Price, pers. cornrn., 1996). Glenogle Fomatioq The Lower and Middle Ordovician Glenogle Formation (Leech, 1954) conformably overlies McKay Group strata, and consists primarily of black, fossiliferous shale, with lesser amounts of black, laminated siltstone, shaly limestone, and limestone (Leech, 1954, 1958). The limestone and shaly limestone tend to form lenses and beds up to 40 cm thick in the black shales (ibid.). The most abundant fossils are graptohtes. some of which retain their original three-dimensional form (Leech 1958). The formation is just over 150 rn thick in the northern part of the Fernie map-area (Leech, 1958). but thins somewhat towards the south, partly due to regional depositional thinning towards the south, and also possibly due to an overlying disconformity that very gradually cuts down section towards the south (Leech, 1954, 1958). The Glenogle Formation is almost everywhere overlain by the Mount Wilson Formation, except for the southernmost occurrence of Glenogle strata, where the sub-Beaverfoot unconfonnity cuts downsection through the Mount Wilson, and the Beaverfoot Formation sits unconfomably on the Glenogle Formation (Figure 5) (Leech, 1958; 1960). The Glenogle Formation occurs north of Iat. 490 15' N and east of long. 1 I50 25' N. The southernmost exposure is approximately 9.5 km northeast from the northern tip of the Mount Haley stock in the northwest part of the TangIefoot area. Mount Wilson Formation The Mount Wilson Formation disconformably overlies the Glenogle Formation. and is unconfomably overlain by the Upper Ordovician strata of the Beaverfoot Formation (Leech, 1958; Norford, 1969). It consists mostly of white and yellow quartzite with some calcareous sandstone in the lower part, with an increasing proportion of cdcareous sandstone in the upper part (Leech, 1954, 1958). The only fossils recovered are hgments of crinoid stems (Leech, 1954). The distribution of the Mount Wilson Formation is very similar to that of the Glenogle Formation. Leech (1 958) reported that the thickness of the Mount Wilson Formation is approximately 6 1 rn near the north end of the Fernie map-area (Leech, 1958, 1960) (lat. 500 N), and suggested that the Mount Wilson is likely disconformable on the Glenogle. Although the two formations appear to be concordant on an outcrop scale. an unconformity is indicated by the fact that the Mount Wilson rests on different levels of Glenogle strata in different locales in the western Rockies (Leech 1958). Beaverfoot Formation The Beaverfoot Formation, which unconforrnably overlies the Mount Wilson Formation, the Glenogle Formation, and the McKay Group, consists of a competent sequence of mostly dolomite with lesser limestone, with blebs and lenses of chert throughout the formation (Leech. 1958). Norford and Cecile (1994a) also reported approximately 10 m of mafic volcanic and volcanicIastic rocks near the base of the Beaverfoot Formation near Bear Lake and Ruault Lake. Strata of the Beaverfoot Formation are thickly bedded and weather shades of grey, buff, white, and brown. often in a mottled pattern (ibid.). It is Upper Ordovician and Lower Silurian in age (Norford. I969), and exposed just north of the Tanglefoot area at several locations. The nearest exposurcs of Beaverfoot strata are: just east of Bear Lake in the footwall of the Lussier River fault (Leech. 1958, 1960; Norford and Cecile. 1994a), on the east and west shores of Ruault Lake (ibid.) on the east shore of Summer Lake (Leech, 1958, 1960). at the top of Empire State Peak (ibid.), and just north of Goat Haven f eak. approximately 4 km east of the northeast tip of the Tanglefoot area (ibid). The Beaverfoot Formation is 550 m thick east of Lussier River fault, in the Top of the World section (Leech. 1958). On a local scale, contact relations between the Beaverfoot Formation and underlying strata may appear to be conformable (Leech, 1958, 1960; Hoy and Carter. 1988), and Leech (1958) noted that at individual outcrops, the contact between Beaverfoot and underlying strata may even appear gradational. However, regional studies show the Beaverfoot Formation to be unconformable upon the McKay Group immediately north of the study area and further north, upon the Glenogle Formation and Mount Wilson Formation. UDD~~Paiaeozoic Strata "basal Devonian unit" The "basal Devonian unit" consists of conglomerate, grit. quartz wacke. siltstone. and dolomite, which marks the unconformity at the base of the Devonian section in the Tanglefoot area and vicinity. It should be noted. however, that the unit is not ubiquitous in the southern Canadian Rockies. Throughout much of the Rockies, the Fairholme Group constitutes the lowest Devonian strata, and the "basal Devonian unit" is absent (Benvenuto and Price, 1979: H6y and Carter. l988), as shown schematically in Figure 5. The stratigraphically enigmatic Burnais and Harrogate Formations (Shepard. 1926: Evans. 1933; Henderson, 1954; Leech, 1954, I%8,1960), and the Cedared Formation (BeIyea and Norford, 1967), which occur firrther north, will also be briefly described here. in order to facilitate the explanation of the outstanding problems regarding their relative ages. The "basal Devonian unity'occurs in the southern part of the Tanglefoot area. where it unconformably overlies the Mesoproterozoic Kitchener. Van Creek, Nicol Creek. and possibly Gateway Formations. The unconformity is sharp, slightly angular. and locally shows gentle but significant topography. It is overlain by a poorly sorted basal conglomerate, with clasts derived dominantly fiom the Belt-Purcell Supergroup. One of the best exposures of the "basal Devonian unit" and the underlying unconformity is on the Bull River road on the west side of the river, between the mouths of Donely Creek and Oveson Creek. There, the "basal Devonian unit" is a remarkable basal conglomerate, containing subrounded to well rounded clasts ranging in size fiom 2 mm to 25 cm in diameter, most of which are derived fiom the Mesoproterozoic Kitchener Formation. The clasts comprise fine- to medium-crystalline dolomite. silty dolomite. siltstone, argillite, shaly limestone, shale, occasional mafic volcanic rock. and rare quartzwacke and sublithic graywacke. The matrix of the conglomerate comprises fme- grained quartzwacke, which weathers rusty and purple. and is purple with white specks on a fiesh surface. The conglomerate is massive, and locally contains quartz-filled en echelon tension gash arrays. The nature of the "basal Devonian unit" varies considerably, often over a very short lateral distance. AIong the north side of Dibble Creek, in the footwall of the Dibble Creek fault, it comprises conglomerate similar to the Bull River road exposure. quartz granule grit, poorly sorted, crudely cross-bedded quartzwacke, dolomitic quartzwacke. laminated siliceous siltstone, dolomitic siltstone, and dolomite. Leech (1958) also commented on the variable lithology of the "basal Devonian unit". Primary sedimentary structures are rare except for the finer-grained rocks, where bedding and large scale cross- beds are locally present. Burnais. Cedared- and Harrogate Formations The stratigraphic position of the Burnais Formation (Henderson. 1954: Leech. 1954, l9S8), the laterally correlative Cedared Fomtion (Belyea and Norford, 1967) and the overlying (?) Harrogate Formation (Evans, 1933; Leech, 1958; Mott. 1989) and the stratigraphic relationships between the three, are not clearly understood in the Tanglefoot and surrounding area 'The name "Harrogate limestone" was originally proposed by Shepard (1926) for the youngest rocks in the Brisco Range at about 510 N, but the rocks were not described. Evans (1933) provided a description and stratigraphic section of the type exposure near Harrogate, and assigned them to the "Harrogate Formation". Henderson (1954) reported on the Bumais Formation, which underlies (?) Harrogate strata in the Stanford Range. Belyea and Norford (1967) proposed the Cedared Formation for Middle Devonian strata formerly placed in the lower part of the Hmogate Formation and in the upper part of the Beaverfoot Formation in the Beaverfoot. Brisco. and Stanford Ranges. They suggested that the Cedared Formation is laterally correlative with the Burnais Formation. The Burnais Formation, which appears to underlie (?) the Harrogate Formation. was defined by Henderson ( 1954) as comprising an unfossiliferous succession of +wsum and limestone in the Stanford Range, at about 500 15' N. The rocks are stratigraphically above Silurian strata, and beneath strata which correlate to late Middle Devonian fossiliferous beds (Henderson, 1954; Leech, 1954; 1958). Neither the top nor the base of the Bumais Formation is exposed in the Stanford Range, although Leech (1958) estimated that the formation is approximately 180 m to 2 10 m thick. Mott (1989) proposed to correlate the Burnais and Cedared Formations to the north with the "basal Devonian unit" in the Tanglefoot area. The Cedared Formation contains dolomites. dolomitic quartz arenite. and subordinate quartzite, mudstone, and argillaceous limestone. which rest unconformabl y on Lower Silurian Beaverfoot Formation (Belyea and Norford, 1967). Locally. the Cedared Formation contains a basal conglomerate which contains clasts of the underlying Beaverfoot Formation. Strata are generally thickly bedded, with diverse. light weathering colours (ibid.). The type section is 213 m thick at Hatch Creek approximately 5 krn northeast of Hanogate at latitude 5 10 N, and Belyea and Norford (1967) and Mott ( 1 989) have reported that it is conformably overlain by the Harrogate Formation. although the top contact is nowhere exposed in the type section. The Harrogate Formation consists of 21 3 m of thin-bedded, dark iimestone, with local interbeds of shaly limestone (Leech, 1958). The lower strata comprise alternating dark, dense limestone, sandy, light-coloured limestone, and well-indurated sandstone beds 5 cm to 180 cm thick. The base of the Harrogate Formation was arbitrarily placed at the lowest occurrence of the sandstone beds, which, stratigraphically, is midway between the highest Silurian and lowest Devonian fossil collections at the time. the latter which was late Middle Devonian (Evans, 1933; Leech. 1958). This corresponds with Moa (1989). who suggested that the Harrogate Formation is early Middle Devonian, and conformably overlying the Cedared and Burnais Formations. Neither the Burnais Formation nor the Cedared Formations occur in the Tanglefoot area, although Leech (1958) suggested that some of the Devonian rocks in the footwall of the Dibble Creek fauIt may be age equivalents of the Harrogate Formation. Leech (1958) discovered a few fossilized Alveolite~ex gr. A. and Favosites sp. C along the footwdl of the Dibble Creek fault, which were identified by D.J. McLaren, who noted that they also occur in the Harrogate Formation (Leech, 1958). Furthermore. striking contrasts in the tectonic fabric of the rocks of the immediate hanging wall of the Dibble Creek fault and those of the footwall prompted Leech (1958) to suggest that the fault may have been "lubricated" by Devonian gypsum. The gypsum might be correlative with the gypsum of the &mais Formation. During this study, it was established that the "basal Devonian unit" occupies the footwall of the Dibble Creek fault westward from Bull River for about 4 km. Further west, younger Devonian rocks that apparently belong to the Upper Devonian Fairholme Group occur along the footwall of Dibble Creek fault. Upper Devonian strata of the Fairholme Group also overlie the "basal Devonian unit" along Bull River, between the mouths of Dibble Creek and Lime Creek. Leech (1958) described a section of Devonian strata in the core of the Lussier syncline between Lussier River and Coyote Creek, approximately 16 km north from the northern tip of the Mount Haley stock. It includes rocks of the "bad Devonian unit". rocks of Burnais type, rocks of Harrogate age, and Upper Devonian strata. After examining more than 300 m of section in the core of the Lussier River syncline, Leech (1 958) recognized questions concerning the relationship of the Burnais and Harrogate Formations. and summarized his conclusions as follows: "The terms Burnais Formation and Harrogate Formation are used with certain reservations in referring to this sequence. The relation of the type Burnais Formation to the "basal Devonian unit" of this map-area is unknown. The term Harrogate is used in its restricted sense but it is uncertain whether all the rocks of Bumais type are older than all the fossiliferous rocks assigned to the Harrogate. Furthermore. the upper limit of the Harrogate Formation has never been defined." (Leech. 1958) Fairholme Group The Fairholme Group comprises limestone, dolomite, and argillaceous and shaly limestone which overlie the "basal Devonian unit" or the underlying Mesoproterozoic rocks in the southern part of the Tanglefoot area, in the footwall of the Dibble Creek fault. The Fairholme Group strata shown in the southern part of the map-area east of the Bull River were not examined during this study. The information given on the map (Plate 1) for the area on the east side of Bull River in the southern portion of the map-area has been compiled and interpreted fiom mapping by Leech (1962), McMechan (1979), and Benvenuto (1978). Sandstones, siltstones, and silty carbonate rocks of the Sassenach Formation (McLaren and Mountjoy, 1962; Price, 1964) overlie the Fairholme Group in the Canadian Rockies, but are included in the "Fairholme Group'' map unit in this report. Price (1964) described the relationships between the Fairholme Group and the Sassenach Formation in the Flathead-Crowsnest Pass area. Leech (1958, 1960) reported that the Fairholme Group unconformably overlies the bbbasalDevonian unit" south of the Dibble Creek fault. He also indicated that shaly rocks which are laterally equivalent to the Fairholme Group occur stratigraphically between the Harrogate Formation and shales that are lateral equivalents of the Palliser. Exshaw. and Banff Formations (Savoy and Harris. 1993). Leech reported a thickness of 407 m for the Fairholme Group in the Lizard Ra~ge,and a thickness of 238 m for the Devono-Mississippian shdy succession overlying the Bumais and Harrogate Formations to the north. Strata belonging to the Fairholme Group were examined at two locations in the Tanglefoot area: in the footwall of the Dibble Creek fault, about 4.5 km west fiom the confluence of Dibble Creek and Bull River, and also on the west side of Bull River. between Dibble Creek and Lime Creek. In the Dibble Creek valley, thick. planar beds of dolomitized fossiliferous wackestone, packstone, and boundstone form the valley wall along the north side of DibbIe Creek (Plate I I). The strata weather buff.brown. and rusty brown, and are medium to dark grey on fiesh surfaces. They are fine- to medium- crystalline, locally have a mottled texture, and occasionally contain less dolomitized nodules. Fossils include both digitate and massive Favositic corals, branching, colonial rugose corals (Plate 12), and crinoid ossicles. On the west side of the Bull River, strata from near the base of the Fairholme Group are exposed. There, they comprise mainly shaly dolomite. locally silicified. with subordinate shale and siltstone. Planar. continuous beds are generally 4 cm to 10 cm thick. Strata weather rusty, purple, buff, and tan colours, and are usually dark grey to purplish grey on fkesh &aces. A lens of columnar stromatolites is present. which is approximately 2.5 m thick near its centre, and greater than 10 m in length. Limestone belonging to the Palliser Formation (Beach, 1943) occurs only in the extreme southern part of the Tanglefoot area, on the east side of the Bull River, along Iron Creek. During this study, mapping in this area was focused on the location of the Dibble Plate 11: Looking west up the Dibble Creek valley; the creek is down and to the left, the shadows. Fairholme Group strata in the footwall of the DibbIe Creek fault dip to t north at approximately 55 degrees, sub-parallel to the fault. Fallen log is 3 m long. Plate 12: A branching, colonial rugose coral preserved in place in the Fairholme Groq indicates upright bedding in the footwall of the Dibble Creek fault. Specimen is &om d section shown in Plate 11; hammer is 40 cm long. Creek fault, and therefore the Palliser Formation was not examined in detail. Leech (1958) reported that the totaI thickness of the formation is approximately 245 m in the Lizard Range south of the study area. Along Iron Creek, the well-exposed, cliff-forming lower member of the PalIiser Formation (the Monow member (dewit and McLaren, 1950)) is composed primarily of fine- to medium-crystalline lime wackestone and mudstone. Strata weather light grey to medium grey and commonly display a massive, pitted, mottled to burrow-mottled appearance, and are dark grey and homogenous on fiesh surfaces. Bedding thickness. though often obscure on weathered surfaces, ranges fkom 15 cm to 275 cm. and averages around 100 cm. Shallow water limestone of the Palliser Formation is locaily peloidai, nodular andlor selectively dolomitized, and fossils occurring in the cliff-forming strata up Iron Creek include crinoid stems and fragments, and brachiopod (?) fragments. The Palliser Formation also contains trace fossils which weather out in relief from the more massive lime wackestone. They comprise dolomitized burrows which are 5 rnm to 10 mm in diameter, with dolomitized halos around their margins (Plate 13). "Devono-Mississimian shale unit" An important occurrence of Upper Devonian and Lower Carboniferous strata was discovered in the core of the Lussier River syncline by Leech (1958, 1960). Although it was not examined directly for this study, an understanding of its age and lithofacies is essential in understanding the paleogeography of the area The core of the Lussier syncline contains "Middle (?) and Upper Devonian" shaly strata (Leech, 1958, 1960) which are overlain by the Lower Carboniferous Badf Formation. The sequence of "Middle (?) and Upper Devonian" strata, which overlies the Harrogate Formation, consists of about 235 m of shaly limestone, with lesser limestone, shale, and minor siltstone and dolomite (Leech, 1958). Strata typically weather medium grey to dark grey, Plate 13: Dolomitized burrows and surrounding halos in the Palliser Formation, indicataing shallow-water platforma1 environment of deposition and are black on fksh &aces. The limestone is fine-grained. bedding ranges from 2.5 cm to 60 cm thick. and is usually around 30 cm thick. Savoy and Harris (1993) analyzed conodonts collected from these rocks. and concluded that the Lussier syncline contains rocks which are age-equivalent to. and represent a lateral shaly facies of the Palliser Formation and overlying strata in the southern part of the Tanglefoot area. Cretaceous Intrusive Rock Intrusive rocks are relatively rare in the Tanglefoot area. especially in comparison to the Purcell Mountains on the west side of the Rocky Mountain trench. However. a few intrusive bodies do occur in the map-area. Covered contacts usually preclude observing the exact dimensions of the intrusions. but dimensions are estimated on the basis of topographical features and air photo analysis. The igneous rocks are primarily variably altered monzonites and syenites, and are likely related to the Mount Haley stock in the northwest comer of the Tanglefoot area. The intrusive rocks will be described here. beginning with the westernmost occurrence. Near the western edge of the study area, in the footwall of the Lussier River fault. there is a small porphyritic intrusion, which is very strongly dolomitized. It is pale green to medium-grey on a fresh surface and weathers buff to rusty-brown. The intrusion was originally elliptical, but has since been folded with the country rock, and is now a rounded V-shape. It is composed of approximately 70% secondary dolomite, which constitutes the groundmass and pseudornorphs the phenocrysts of the rock. The dolomite is fme- crystalline, and replaces subhedral to euhedral, 4 mm-to 5 rnm-long feldspar and pyroxene phenocrysts. Approximately 2% to 3% of the rock comprises K-feldspar, which occurs in the centre of some of the larger phenocrysts. The rock also contains approximately 15% chlorite as a secondary mineral, as well as 12% to 13% Fe-oxides and clay minerals. Pyrite occurs as euhedral cubes and disseminated masses in trace amounts, and a single grain of spinel occurs in one of the two thin sections examined. The intrusion shows weak margin-parallel flow-banding near its periphery. The largest body of intrusive rock in the Tanglefoot area is the "J-shaped porphyritic monzonite in the extreme northwestern part of the map-area, which will hereafter be referred to as the Mount Haley stock, named after Mount Haiey. The north- south trending part of the stock is 4 krn long, and the east-west part is nearly 3 km long. Samples were taken from the Mount Hdey stock for geochronological work and accordingly the stock will be described in detail in the chapter on "Intrusive rocks, Implications and Geochronology". The smailer "J-shaped" intrusion immediately to the south of the Mount Haley stock was not examined closely during this study, but it was observed from across the Tanglefoot Creek to the south, and it can be recognized on air photos. There are striking contrasts in weathering colours and patterns between the stock and the host rock (Plate 14), which are similar to those associated with the Mount Haley stock. Leech (1958) reported that numerous dykes and small irregular bodies occur on the north side of the Mount Haley stock (approximately 1.5 km northwest of Summer Lake), and the smaller intrusive body that occurs south of Mount Haley probably also is similar in nature and composition to the Mount Haley stock. There is also a small intrusion approximately half-way between the peak just west of the headwaters of Clay Creek and the bridge where the Van Creek road crosses Tanglefoot Creek. Covered contacts preclude observing the exact dimensions of the intrusion, but it appears to occupy an area of approximately 10 000 m'. It is a strongly altered, sub-porphyritic monzonite (or gabbro?). It weathers greenish white with brown patches, and is pale green with small rusty speckles on a fresh surface. It comprises approximately 50% "phenocrysts", 40% groundmass. and 10% accessory and trace Plate 14: Northward view of the monzonitic (?) intrusion south of the Mount Haley stock, from the south side of Tanglefoot Creek. Note the contrast in weathering characteristics between recessive McKay strata above treeline on the right-hand side and at the peak, and the more resistant, blocky-weathering, intrusive rocks. constituents. The "phenocrysts" comprise fme-grained chlorite plus sericite which have replaced plagioclase, and possibly K-feldspar. phenocrysts. The 1 mrn- to 3 mm-long. fine-gained masses of chlorite and sericite pseudomorph subhedral to euhedral lathe- shaped feldspar grains. The groundmass of the rock constitutes approximately 40% of the rock. and contains chlorite and epidote in equal proportions. and traces of dolomite. Grain size is very fine. and grains are most commonly anhedrai and equant. The rock also contains 7% to 9% Fe-oxide as an alteration product. which is very fine *grained throughout the rock, and I% to 3% medium grained hornblende. as weakly chloritized. subhedral, acicular grains. Trace amounts of sphene and pyrite are also present in the rock. There is a smdl intrusion into the "Tanglefoot unit" which occurs near the top of the peak west of the headwaters of Clay Creek. It is coarse-*pained, equigranular. massive hornblende alkali feldspar quartz syenite, which is white. brown and dark green spotted on a fresh surface, and weathers brown or greyish brown. The contacts are covered, but the intrusion appears to occupy an area of approximately 20 000 m'. Alkali feldspar is the most abundant mineral. and constitutes approximately 50% of the rock as white, coarse (grains up to 6 mm long), subhedral to euhedral, lathe-shaped grains. which show weak clay alteration. Altered homblende constitutes 35% of the rock: it is dark green, coarse-grained (grains up to 9 rnm long), subhedral to euhedral. and acicular. It has been strongly altered to chlorite and dolomite, with traces of sericite, muscovite. and biotite. The rock also contains 10% quartz, as coarse, anhedral, equant. unaltered grains. The remaining 5% is a collection of accessories: sphene. Fe-rich chlorite, sericite. muscovite. apatite, and biotite. Thin section analysis revealed an interesting phenomenon in this rock: a 4 rnm by 4 mrn area rich in fibrous sillimanite surrounding 12 to 15 very small (approximately 0.5 mm) grains of blue corundum (sapphire). The interpretation is that a millimetre-scale inclusion or "microxenolith" of shaly host rock was caught up in the intrusion. It was strongly metamorphosed by the intrusion. and corundum and sillimanite were produced from the inclusion of aluminum-rich sedimentary rock. By chance. the thin section was cut through the inclusion. West from the headwaters of Clay Creek an occurrence of porphyritic andesite (possibly basalt) in the upper "Tanglefoot unit" is exposed in a single, large outcrop. It weathers brown or greyish brown, and is medium-grey with white spots and smaller green speckles on a fiesh surface. The rock is massive, with an aphanitic groundmass and medium- to coarse-grained phenocrysts. Plagioclase constitutes 85% of the rock. as phenocrysts and groundrnass. 30% of the plagioclase gains are phenocrysts; they are white, coarse grained (up to 10 mm long), subhedrai. lathe-shaped. and have been strongly carbonatized. The remaining 70% of the plagioclase is aphanitic groundrnass. Hornblende constitutes 15% of the rock as dark green, medium-grained (grains up to 5 mrn long), subhedral to euhedral, acicular grains, which have been moderately carbonatized and sericitized. Accessory minerals are sphene, apatite, and ilmenite. The "Tanglefoot unit" hosts an igneous intrusion near the top of the ridge north of Tanglefoot Creek, east of Clay Creek, and southeast from the headwaters of Green Creek. It is greenish-grey with small white spots on a fksh surface. and weathers reddish brown. The rock is altered magnetite-bearing monzogabbro (perhaps gabbro); it is fine- to mediumgrained (grains up to 2.5 m),inequigranular. and massive. Plagioclase. which is fine-grained (usually 0.5 mm grains), subhedral, and lathe-shaped, constitutes 40% of the rock. It is present in a random orientation, and has been moderately chloritized. There is less than 1% fine-grained, anhedral quartz in the rock. which is the only other recognizable primary mineral in the rock. The remainder of the rock comprises fine- grained calcite, dolomite, and chlorite replacing either pyroxenes or alkali feldspars. Introduction The structure of the Tanglefoot area is conspicuously anomalous with respect to the rest of the Rocky Mountain Foreland Fold and Thrust Belt. Within most of the map- area, the structural grain is dominantly northeast-trending (Plate 1 : map), almost perpendicular to the regional structural trend of the Foreland Fold and Thrust Belt. which is generally southeast-trending, but arcuate and southeriy-trending locally. The anomalous northeast-trending structural grain is part of a major regional cross-strike discontinuity in the southeastern Canadian Cordillera (Price, 1993). The geological structures of the Tanglefoot map-area will be described from south to north. For the purpose of this study, the region has been subdivided into three structural domains (Figure lo), on the basis of their structural style. The rocks south of the Dibble Creek fault constitute the "Montania domain", the rocks between Dibble Creek fault and the Lussier River fault cons'Jtute the "Tanglefoot domain", and the rocks northwest of the Lussier River fault constitute the "Hughes domain". The three stmcturai domains of the Tanglefoot area and surrounding region coincide with individual stratigraphic domains, because the structures which form are largely controlled by thicknesses and lithofacies during deformation. The more competent, shallow water rocks of the Montania and Hughes doriains are more resistant to ductile deformation, in contrast to the deeper water, shaly rocks of the Tanglefoot domain, which are more prone to ductile deformation. Figure 10: Map showing the structural domains ofthe Tanglefoot anx and surrounding region. Note the Tier blockn within the Tanglefoot domain, comprising an east-northeast-facing panel of Mesoproterozoic rocks beneath a decoIlement in the Eager Formation The Montania domain The Montania domain comprises rocks south of Dibble Creek fault. It corresponds with Benvenuto and Price's (1979) "Lizard segment" of the Homer Nappe. and includes the Mesoproterozoic rocks of McMechan's (1979) "Steeples Block. Between the Dibble Creek fault and the Bull Canyon fault (the southernmost fault in the Tanglefoot map-area), the region consists of a sequence of relatively competent. thickly bedded Belt-Purcell stram which have been folded into a series of northeast-plunging anticlines and synclines (leech, 1962), and is unconformably overlain by Devonian rocks along the fooouall trace of the Dibble Creek fault. During this study, only the easternmost anticline was examined. It occurs on the west side of the Bull River. between Donely Creek and Dibble Creek. The fold is upright and plunges to the north-northeast at approximately 20 degrees. Creston Formation strata are exposed in its core. and are overlain by carbonate rocks of the Kitchener Formation. Rocks of both the Creston and Kitchener Formations have a moderate to strong, spaced to penetrative cleavage that dips steeply to the west-northwest, and is axial planar to the anticline. The fold is not as tight as its trace on the map might indicate, because the hillside cuts the fold at a low. oblique angle, creating the appearance of a tight fold (Leech, 1962). Further to the southeast, beyond the Bull Canyon fault. the structure is dominated by the northwest-plunging, northeast-verging folds and faults of the Lizard Range segment of the Hosmer nappe (Leech, 1958,1960; Benvenuto and Price, 1979). Movie-Dib ble Creek fault The Dibble Creek fault is a north-dipping, right-hand reverse fault. The trace of the fault extends fiom the Bull River up Dibble Creek and down Horseshoe Creek to the Rocky Mountain trench, where it is truncated by the southwest-dipping Rocky Mountain trench normal f'ault (Leech. 1958). Its matching counterpart on the west side of the normal fault is the Moyie fault. Together, they form the regional Moyie-Dibble Creek (MDC) fault system (Figure 4a). The MDC fault changes northward fiom a northwest-trending, southwest-dipping thrust fault in northern Idaho. into a northeast- trending, northwest-dipping, right-hand reverse fault through the Purcell anticlinorium. It crosses the Rocky Mountain trench northeast of Cranbrook, and becomes the Dibble Creek fault in the Tanglefoot area. Beyond the Tanglefoot area. it becomes a north- trending, east-verging thrust fault that extends northwards up the Bull River valley (Figure 4a). The Dibble Creek fault branches into several splays in the southern Tanglefoot area between Bull River and Iron Creek (Figure 9; Plate 1: map). Previous regional studies (Leech, 1962; Benvenuto and Price, 1979; Hoy md Carter, 1988) have concluded that the lowest splay of the Dibble Creek fault extends fiom near the mouth of Dibble Creek. northeast dong the ridge between Lime Creek and Bull River (Figure 9), and continues as the north-striking Gypsum fault, which follows the upper valley of Bull River. However. new detailed mapping in the southern part of the Tanglefoot area indicates that the trace of the lowest branch of the Dibble Creek fault swings to the south down the Bull valley for approximately 3 km to near the mouth of Iron Creek (Figure 9), where it turns back to the northeast. At Iron Creek, the fault cuts upsection along a footwall ramp through "basal Devonian" rocks, the Fairholme Group, and the lower part of the Palliser Formation. The footwall follows a glide zone in the Banff Formation. The trace of the fault turns to the southeast up the valley of East Iron Creek, where it becomes the "Lizard Tear faWof Henderson and Dahlstrom (1 959), Leech (1962), and Benvenuto and Price (1 979). The small separation on this branch of the Dibble Creek fault suggests that most of the displacement occurs on the branch that follows the ridge between Bull River and Lime Creek to the north, and juxtaposes the "Tanglefoot unit" and McKay Group over the "basal Devonian unit". Another branch of the Dibble Creek fault is folded over the anticlinai duplex in which the Purcell rocks occur in the Lime Creek section (Leech. 1962), and connects to the Lizard tear fault at the south end of the ridge between Iron Creek and Lime Creek. These relationships confirm the overall interpretations of Leech, who stated that, "The essential continuity of the Dibble and Lizard faults seems undeniable in view of [their] position and relation to the rocks which are segments of the Hosmer thrust" (Leech, 1962). Similarly, Benvenuto and Price state that "The spatial relationships between the Lizard Tear fauit and the Dibble fault suggest that the southeastward displacement on them was concurrent and coupled" (Benvenuto and Price, 1979). There are profound contrasts in geological structures across the Dibble Creek fault (Leech, 1958, 1962). The most obvious on a map-scale is the change in orientation of structures (Leech, 1958, 1962). On the south side, in the immediate footwaIl of the Dibble Creek fault, the Belt-Purcell and overlying Devonian strata strike west and dip to the north, at approximately 45 to 55 degrees, and are nearly parallel with the fault (Figure 11, Plate 1 1). In contrast, on the north side, in the hanging wall. the fault is sub- perpendicular to the strike of bedding in the hanging wall, and cuts almost directly across formations (Figure 1 1) for more than 6 km westward from Bull River valley (Leech. 1958. 1962). There is also a profound contrast in intensity of deformation across the Dibble Creek fault. Strata in the immediate footwall, even tens of metres south of the fault. are only very weakly deformed. Primary sedimentary structures such as bedding, cross- bedding, and at one location, columnar stromatolites, are webpreserved and only weakly deformed, if at all. In contrast, in the hanging wall of the Dibble Creek fault, the rocks are A Olp - 51.7 Dip - 59.3 Plng - 29.7 Figure 11: Equal-- projections from the lower hemisphere: A - F = plots of poles to bedding; G = plot of poles to cleavage. A, B, C, and F show best-fit axis of cylindrical folding; D and E show mean bedding orientation; G shows mean cleavage orientation strongly deformed. A penetrative, northwest- to southwest-dipping cleavage locally completely obscures bedding in the "Tanglefoot unit" near the Dibble Creek fault. and farther north, the rocks of the "Tanglefoot unit" are tightly folded. Leech (1 9%) suggested that Devonian gypsum (Burnais Formation?) in the footwall of the fault probably provided "lubrication", which served to leave footwall strata relatively undeformed. Benvenuto and Price (1979) concluded that there were two distinct episodes of displacement on the Hosmer thrust sheet: fust the thrust sheet was displaced 8 km northeastward, and then it was displaced I2 km southeastward. It is the latter displacement which is linked to the displacement on the Dibble Creek fault. and shown schematically palinspastically restored in Figure 5. The Tan~lefootdomain The Tanglefoot domain comprises rocks north of the Dibble Creek fault, and southeast of the Lussier River fault. It is characterized by southeast-verging, northeast- plunging, closed to tight folds, and strong to penetrative northwest-dipping cleavages in shaly strata The base of the Tanglefoot domain comprises the east-northeast-facing, homocline of Belt-Purcell strata, which lies underneath a major detachment in the Eager Formation. This relatively undeformed panel occurs in the southwestern part of the Tanglefoot domain in the area between Dibble Creek and Boulder Creek faults (Figure 10). It corresponds with McMechan's (1979, 1980) "Fisher block", and will be described separately fiom the shaly, basinal facies rocks which occur above the detachment within the Eager Formation. The "Fisher block 7, The lower part of the "Fisher block" is a steeply-dipping, east-northeast-facing panel of Purcell strata (Figure 11). In this block, the Lower Cambrian Cranbrook Formation is structurally conformable with the underlying Gateway Formation. The Cranbroo k Formation and underlying Belt-Purcell strata form a relatively undeformed. steeply-dipping homoclinal panel that is only disrupted by minor offsets on a few small tramverse faults and local minor folding. An important detachment (Plate 15) occurs above the Cranbrook Formation. within the overlying shaly rocks of the Lower Cambrian Eager Formation, which separates the "Fisher block" fiom the rest of the Tanglefoot domain. The upper part of the Eager Formation and the overlying Middle Cambrian "Tanglefoot unit" are disharmonically folded above this detachment (Plates 1 and 2: map and cross sections. Plates 16 and 17). Tight folds with an associated axial planar solution cleavage are easily discernible in the shaly limestone at various scales from a map-scale of tens of kilometres, down to a scale of centimetres. Close to the detachment, the folds in the "Tanglefoot unit" commonly plunge to the east-northeast and the northeast at 30 to 40 degrees, and are generally overturned to the south-southeast and the southeast. Most are inclined, but locally they are either upright or recumbent. Axial planar cleavage is common, and locally it partially obscures bedding within the "Tanglefoot Unit" (Plate 18). The orientation of the folds swings to the north-northwest at higher stratigraphic levels, the plunge of the folds shallows to 10 to 15 degrees, and there is increasing disharmony above the detachment (Plate 1 : map). On the north side of the Boulder Creek fault, near the Lussier River fault, folds are generally uprigh~closed, and plunge to the north and north-northeast (Figure 1 1). Further east, in both the hanging wall and the footwall of the southeast-verging Galbraith Plate 15: Zone of major detachment in the lower part of the Eager Formation; hammer is 40 cm long Plate 16: Disharrnoncally folded, rhythmically bedded lime mudstones and shaly limestones of the "Tanglefoot unit". Shaly layers behave in a more ductile manner than the more competent lime mudstones, and "flow"into the cores of the folds. Hammer is 40 cm long Plate 17: Disharmonic folding within the "Tanglefootunit"; hammer is 40 cm long. Plate 18: Strong axial planar cleavage in the hinge zone of folded strata of the "Tanglefoot unit". Cleavage completely obscures bedding in the lower left-hand part of the outcrop; hammer is 40 cm long. fault, folds are closed to tight (Plates 19 and 20), commonly overturned to the east- southeast, and north-northeast-plunging . Locally in the Tanglefoot domain there is an older set of folds that are generally upright, and plunge either to the northwest or to the southeast. They are deformed by the northeast-plunging, southeast-verging folds. and are relatively rare in the Tanglefoot area. The older northwest- and southeast-trending folds (Figure 11) are most common in two areas: (1) on the north side of the Boulder Creek fault approximately 2.5 km east- northeast from the mouth of Clay Creek, and (2) approximately I .8 km north fiom where the Van Creek road crosses Tanglefoot Creek. Near the base of the "Tanglefoot unit", for approximately 2.5 km ncith fiom the Dibble Creek fault, upright folds plunge to the south and to the south-southwest at 20 to 30 degrees (Figure 11, Plate 1: map). These folds are overprinted by the more common northeast-plunging folds of the Tanglefoot domain, and intersect the latter at an angle of approximately 60 degrees. The south-plunging fold set is nearly perpendicular to the east-northeast-plungiing folds on the east side of the Bull River, in the immediate hanging wall of the Dibble Creek fault. Faulting Thrust faults marked by zones of brittle deformation are superimposed on the ductile deformation associated with the folding in the Tanglefoot domain. Fault breccia generally consists of angular fkagments of limestone supported in coarse-grained, white, sparry calcite cement. Limestone clasts within fault breccias are commonly cleaved, indicating that the ductile folding preceded the thrust faulting. Where slickensides are absent, the sense of movement on faults is often difficult to discern, and must be inferred from stratigraphic relationships. Coarse-grained, euhedral, free-growing calcite crystals Plate 19: Upright, inclined, closed anticline in the lower "Tanglefoot unit", south of the Boulder Creek fault. Hammer (near bottom of photo, slightly right of centre) is 40 cm long; outcrop is approximately 10 m high. Plate 20: Tight, overturned fold closure in thinly bedded strata of the upper "Tanglefoot unit" within fault planes indicate that faulting occurred at relatively shallow depths. Two thrust faults occur in the central part of the Tanglefoot domain. in the eastern half of the map-area. They are associated with the increased shortening and tightness of folding in the east half of the map-area relative to the west half. They are both west- northwest-dipping. and their traces are sub-parallel in the Tangle foot area The larger and more southeasterly is the Galbraith fault, which is marked by typical fault breccias. and contains an overturned, southeast-verging, folded succession of Tanglefoot strata in its hanging wall, juxtaposed over lower McKay Group rocks in its footwall. The trace of the Galbraith fault can be traced for approximately 10 krn north of the Tanglefoot area. where it dies out in Beaverfoot strata (Thompson, 1962). The smaller thrust fault occurs entirely within the "Tanglefoot unit", and is located 2 km to the northwest of the Galbraith fault. it dies out in the core of an overturned syncline in the northeastern part of the map-area suggesting that the fault is the result of synclinal breakthrough (Suppe and Medwedeff, 1990). This may occur when either a fault-propagation fold or fault- bend foid is unable to progressively grow in a compressional stress regime. and a fault breaks through the syncline, which is one of the sites of the most pre-existing fractures (ibid.). Two possible tectonic windows through the Dibble Creek fault occur in the Tanglefoot domain, between the Dibble Creek fault and the Boulder Creek faults. One occurs east of Bull River, at the confluence of the middle and north forks of Lime Creek. and the other occurs just under one kilometre southwest from the confluence of Van Creek and Bull River. The fmt was originally discovered by T.L. Thompson. and subsequently described by Leech (1962). It consists of quartz arenite and argillite that "...could belong to either the Gateway or Creston Formation" (Leech, 1962). Its contact relations are udnow~~Leech offered two possible explanations for the occurrence of Mesoproterozoic rocks: either the outcrop represents a structural window in the Hosmer thrust sheet, or else it lies southwest of the Lizard Tear fault, and is part of the Lizard Range structural panel. The absence of Lower Palaeozoic rocks between the basal Devonian rocks and the underlying Mesoproterozoic rocks suggests that these strata are part of the Lizard Range structural panel. In nearby parts of the Lizard Range panel to the southeast, the Devonian rocks unconfonnably overlie the Kitchener Formation: but just west of the mouth of Lime Creek the sub-Devonian unconformity has cut down through the Kitchener Formation almost to the Creston Formation. The second enigmatic outcrop. which occurs nearly one kilometre southwest of the confluence of Van Creek and Bull River, is a small outcrop of quartz arenite and subarkosic arenite of the "basal Devonian unit". It is exposed in a relatively new logging road cut. Its contact relations with the surrounding "Tanglefoot unit" are unknown. but it is probably a structural window in the Dibble Creek thrust sheet, because strata of the "basal Devonian unit" occur in the footwall of the Dibble Creek fault close by to the south, and the outcrop is topographically low, near both the Bull River valley and the Van Creek valley. If the outcrop is a structural window, it implies that the Dibble Creek fault plane flattens somewhat at depth, and also that there is considerable Iocal relief on the Dibble Creek fault plane Boulder Creek fault The steeply northward-dipping Boulder Creek fault has a complex history, and is poorly understood. There have been multiple episodes of movement on the fault, the youngest of which has obliterated older structures in rocks in the immediate hanging wall and footwall, and the stratigraphy in the vicinity of the Boulder Creek fault indicates conflicting displacements. First of all, the strike separation of the Midd!e Proterozoic Nicol Creek Formation (an excellent marker horizon) across the Boulder Creek fault is approximately 6 km in a left-hand sense (Figure 4a). However. the Nicol Creek Formation on the north side of the fault is overturned, dips to the west, and is in the hanging wall of the Lussier River thrust fault. South of the Boulder Creek fault. the Nicol Creek Formation is upright, dips to the east, and represents a different structural level (Leech, 1958). Secondly, along upper Tanglefoot Creek, the Boulder Creek fault is marked by more than 3 km of normal dip-slip separation (down to the north), where it juxtaposes Mesoproterozoic lower Belt-Purcell strata with Lower Palaeozoic strata (Figure 4a). Thirdly, the map-scale disharmonic folding within the "Tangle foot unit" north of the BouIder Creek fault implies that the fault is a right-hand tear fault. The disharmonic folding within the Tanglefoot unit" may be related to the detachment withh the Eager Formation, and may have occurred prior to movement on the Boulder Creek fault, The map-scale zone of detachment in the lower Eager Formation has been offset by the left-hand normal separation on the Boulder Creek fault. The latest displacement on the Boulder Creek fault may have occurred during the Tertiary normal faulting along the Rocky Mountain trench. Porcupine Creek anticlinorium The fan-shaped Porcupine Creek anticlinorium is the dominant structure of the southern Main and Western Ranges of the Foreland Fold and Thrust Belt. At its south end in the Fernie west-half map-area, between latitudes 490 45' N and 500 00' N, the anticlinoriurn consists of a broad, north-northwest-trending open syncline with steep. east-verging folds in its east flank, and steep west-verging folds and thrust faults in its west flank (Figure 12) (Leech, 1958, 1960). Just south of latitude 490 45' N, immediately north of and adjacent to the MDC fault, the south-southeast-trending axis of the fan structure swings to the southwest, and the anticlinorium terminates above the east- WEST EAST Figure 1%: Cross-section through the Porcupine Creek anticlinorium, north of the Tanglefoot area (modified from Leech, 1960; Price, 1981; Hoy and Caxter, 1988). The location of the line of section is shown in Figure 1 lb Fi12b: Location map, showing traces of the major faults in the Tanglefoot area and Central Hughes Range, and the line of cross section through the Porcupine Creek anticlinorium, which is shown in Figure 9. "TOTW = Top of the World area northeast-facing "Fisher block". It terminates in the major zone of disharmonic folding in the "Tanglefoot unit". above the decollement near the base of the underlying Eager Formation. Balkwill (1972), who originally described the Porcupine Creek anticiinorium in the region to the north (near lower Kicking Horse River). suggested that the core of the anticlinorium rests on a decollement in the slate and very thin-bedded limestone near the base of the Middle and Upper Cambrian Chancellor Fonnation (Balkwill, 1972). In the Tanglefoot area the decollement occurs in shales of the lower Eager Formation. The core of the andclinorium comprises argillaceous and shaly limestone of the Middle Cambrian "Tanglefoot unit". which are similar to the rocks of the Chancellor Formation. and it also includes shales of the Lower Cambrian Eager Formation. St. Mary-Lussier River fault The SMLR fault system is similar in certain respects to the MDC fault. The St. Mary fauit cuts across the Purcell Mountains as a northwest-dipping, right-hand reverse fault. On the east side of the Rocky Mountain Trench, it becomes the north-striking. west-dipping Lussier River fault, which, farther north in the Canal Flats area. becomes the Redwall fault (Leech, 1954). The SMLR-Redwall fault is an important regional structure: it separates west-verging thrust faults, folds, and axial planar cleavage of the western Porcupine Creek anticlinorium from east-verging deformational structures. which are more characteristic of the Purcell Mountains to the west of the Rocky Mountain Trench. In the Tanglefoot area, the Lussier fault was examined at only one locality in the northwestern comer of the map-area, where it juxtaposes the Lower Cambrian Cranbrook Fonnation over the Middle Cambrian "Tanglefoot unit". The Hu~hesdomain The Hughes domain is bounded by the Rocky Mountain trench on the west side. and the Lussier Ever-Redwall fault on the east side. It was not examined directly during this study, except for Cranbrook Formation strata in the immediate hanging wall of the Lussier River fault in the northwest comer of the Tanglefoot map-area. The structures of the Hughes domain are markedly different that those of the Tanglefoot domain and will be summarized here on the basis of work by Leech (1958. 1960), and Welbon and Price (1 99%; 1992b; 1993). The Hughes domain comprises a competent succession of dominantly north- striking, east-facing Mesoproterozoic Belt-Purcell strata unconfonnably overlain by Lower Palaeozoic carbonate platform facies rocks (Leech, 1958, 1960; Welbon and Price. 1992b). It is part of the east limb of the Purcell anticlinorium, the main part of which occurs to the west, in the hanging wall of the Rocky Mountain trench normal fault. The west-dipping Lussier River-Redwall fault separates the east-verging structures of the Hughes domain from the west-verging structures in shaly rocks of the Porcupine Creek anticlinorium in the Tanglefoot domain. The structure of the Hughes domain is dominated by faults and not folds. in contrast to the Tanglefoot domain. Three main sets of faults occur in the Hughes domain: northeast-trending transverse faults, north-trending, east-verging thrust faults. and north- trending normal faults (WeIbon and Price, 1992). The Tanglefoot map-area does not extend into the Hughes domain, but Hoy and Carter's (1988), and Welbon and Price's (1992% 1993) maps show the relationships between the three fault sets in detail. The northeast-striking tramverse faults are the oldest, and were active prior to deposition of dolomites of the Jubilee Formation (Welbon and Price, l992b). The north-striking thrust faults were activated in the Late Mesozoic with regional Cordilleran deformation, but are older than 94 Ma (Hoy and van der Heyden. 1988). The north-striking normal fauits are related to Tertiary extension, and the Rocky Mountain trench normal fault. INTRUSM ROCKS: SIGNIFICANCE AND GEOCHRONOLOGY Introduction There are numerous mid-Cretaceous @toid intrusions in the Pwcell Mountains of the eastern Omineca Belt (e.g. Reesor, 1958; Wdess et a/.. 1968: Archibald et a/.. 1983, 1984), but only a very few in the Rocky Mountain Foreland Fold and Thrust Belt. The Mount Haley stock, in the northwestern comer of the Tanglefoot area is one of the largest and easternmost syenitoid (monzonitic) intrusives in the Foreiand Belt. It was originally mapped and described by Leech (1958), who referred to it as a "granitic intrusion in an L-shape". The name "Mount Haley stock" is introduced. after Mount Haley, which occupies the west-trending segment of the intrusion. The age and structural position of the Mount Haley stock with respect to the surrounding country rock, when considered in conjunction with the larger and more numerous intrusions in the Purcells, can be used to constrain the timing of deformation in the Tanglefoot area and surrounding region. In the Purcell Mountains. wen of the Tanglefoot area two major, transverse, northeast-trending faults are intruded by Cretaceous granitoid plutons that can be used to establish the minimum age of displacement on the faults. This chapter provides a summary of the age and tectonic significance of two Cretaceous plutons in the PurcelI Mountains, and it describes the petrography, geochronology, and regional tectonic significance of the Mount Haley stock. The Reade Lake and Kiakho stocks The Reade Lake and Kiakho monzonitic stocks both occur southwest of the Mount Hdey stock, in the Purcell Mountains. The Reade Lake stock occurs on the west side of the Rocky Mountain trench approximately 10 km north of Cranbrook (Figure 13a), and the Kiakho stock occurs approximateIy 10 km west of Cranbrook. Both intrusions have important cross-cutting relationships involving two of the prominent. northeast-trending faults which are typical of the area. The Reade Lake stock is exposed only in small, scattered outcrops which were initially described by Rice (1937), and appear on maps by Leech (1958: 1960) and Hoy (1984). Although Quaternary sands and gravels cover its contacts and much of its surface area, its limits can be accurately inferred fiom a well-defined magnetic anomaly which is centred on the known exposures (Figure 13b) (Hoy and van der Heyden. 1988). The dominant phase of the Reade Lake stock is a grey, coarse-grained, porphyritic quartz monzonite (ibid.). It intrudes Mesoproterozoic rocks of the Aldridge, Creston. and Kitchener Formations, and Lower Cambrian rocks of the Eager Formation. and it cuts and seals the St. Mary fault (Figure 13a) (ibid.). Therefore, the emplacement of the Reade Lake stock postdates any movement on the St. Mary fault, and presumably its counterpart on the east side of the Rocky Mountain trench, the Lussier River fault. A U-Pb zircon date for the Reade Lake stock gives a lower intercept age of 94 Ma that has been interpreted as the minimum age for emplacement of the stock (Hoy and van der Heyden, 1988). Conventional K-Ar dates on hornblende concentrates from the Reade Lake stock range from 103 +I- 4 Ma to 143 +I- 6 Ma, probably because of variable amounts of excess %r inherited from country rock through degassing during ascent of the magma (Hiiy and van der Heyden, 1988). The Reade Lake stock plugs the St. Mary fault, therefore the minimum age for movement on the St. Mary fault, and presumably for its Figure 13: The Cranbrook area; a: Geological map, showing the locations of the Reade Lake and Kiakho stocks; the limit of the Reade Lake stock is taken as the 60 000 gamma isomagnetic line (see Figure 12b); b: Map showing exposures of the two stocks, traces of the St. Mary and Cranbrook faults, and isomagnetic lines (from H6y and van der Heyden, 1988) counterpart on the east side of the Rocky Mountain trench the Lussier River fault. is 94 Ma. The Kiakho stock, which first appeared on Schofield's (1915) map, is exposed on the heavily wooded slopes of Kiakho Creek. approximately 10 krn west-southwest of Cranbrook (Figure 13a). The contacts of the intrusion are mostly covered, but regional mapping indicates that the stock intrudes rocks of the Aldridge and Creston Formations (Hoy and van der Heyden, 1988). The dominant phase of the Kiakho stock is a light grey, mediumgrained quartz monzonite, which is mostly equipmlar, and grades locally into a sub-porphyritic phase (ibid.). The intrusion has a well-defined magnetic anomaly (Figure 13b), and cuts and seals the Cranbrook Fault without offset; therefore. the emplacement of the Kiakho stock postdates movement on the Cranbrook fault. and presumably its offset counterpart, either the Maus Mountain fault or Fisher Peak fault (Benvenuto and Price, 1979; McMechan, 1979). Conventional K-Ar dates for hornblende concentrates from the Kiakho stock give a date of 122 +/- 4 Ma (H6y and van der Heyden. 1988). This is one of the oldest. if not the oldest date obtained from the mid-Cretaceous granitoid inwives of the southeastern Ornineca Belt (Archibald et a/.,1983, 1984; D.A. Archibald. pers. comm.. 1997). and therefore it is reasonable to assume that there was excess M;\r in the hornblende. Accordingly, the K-A. date from the Kiakho stock is considered irrelevant to this study. No U-Pb zircon dates were obtahed from the Kiakho stock. The Mount Halev stock The Mount Haley stock constitutes the largest igneous body in the Tanglefoot area. It is hosted by calcareous shale and shaly limestone of the McKay Group (Leech, 1958) which has been hornfelsed to amphibolite facies. The pluton is mostly monzonite and quartz monzonite. with lesser syenite and quartz syenite. The colour on weathered surfaces is generally either pink and black speckled, white and black speckled, or a combination of pink white, and black. Fresh surfaces are pink, white. black, and shades of grey. It is commonly massive and porphyritic with interlocking grains, although in parts there is a distinctive alignment of alkali feldspar phenocrysts. Phenocrysts are coarse-grained to pegmatitic, and the groundmass is medium-grained. Different phases of igneous activity have resulted in varying cumposition and relative abundances of minerals across the pluton. White or pink alkali feldspar usually constitutes 60% to 65% of the rock, commonly as 20 mm to 30 mm long subhedral to euhedral lathe-shaped phenocrysts, which commonly show oscillatory zoning and Carlsbad twinning. White or grey piagioclase constitutes 30% to 35% of the rock, usually as a groundmass constituent. Grains are coarse (up to 4 mrn long), anhedral to subhedral. lathe-shaped, and often oscillatorily zoned, with Carlsbad and albite twinning, and pericline lamellae. Coarse grained hornblende constitutes around 5% of the rock, as anhedral to subhedral acicular grains. Locally in the pluton, anhedral, smoky quartz may constitute as much as 2% or 3% of the rock, usually with a decrease in hornblende content (Leech, 1958). Accessory minerals include sphene and epidote, and Leech (1958) reported important quantities of garnet locally in the intrusion. Structures The Mount Haley stock occupies the core of a large, north-plunging anticline (Leech, 1%8), which in the Top of the World area, becomes overturned to the west. and constitutes part of the western limb of the Porcupine Creek anticlinorium. Field work for this study included a singie traverse across the north-trending branch of the Mount Haley stock, along the ridge on the northeast side of Mount Sneath. There, the pluton contains a joint set which is folded in a fan-shaped stmcture across the pluton (Plate 1: map; Figure 14). On the eastern margin of the intrusion, the joint set dips moderately to the west: in the middle, the joint set is sub-vertical; and on the western margin, it dips moderately to the east. The joint set is also parallel with cleavage in host rocks of the McKay Group on both the east and west margins of the pluton. Hornfelsed McKay Group strata, which have been deformed, occur just east of the "heel" of the stock, and they contain a moderate to strong fi-acture cleavage. Both of these pieces of evidence suggest that the Mount Haley stock is pre- or syn-deformational. However. the relationships between the Mount Haley stock and the regional structures in the surrounding McKay Group rocks are equivocal because cross-cutting relationships between the larger structures and the stock are lacking. Tightly folded McKay Group strata have been overprinted by the contact metamorphism in the metamorphic aureole of the Mount Haley stock, close to the southern contact, near the small lake west of Mount Haley (R.A. Price, pers. cornm.. 1996). This folding may have occurred during emplacement of the stock. The small-scale structures at the contact could easily be produced in shaly strata during ascent of the stock, and then metamorphosed as heat was transferred fiom the intrusion to the surrounding wallrock. This explanation supports the argument that the Mount Haley stock is pre- or syn-deformational. Fold Axis: Azim = 194. N-9 Plng = 25.5 Poles to Planes Fold Axis: Azim = 194. N 9 Plng- 25.5 Poles to Planes- Figure 14: Equal-area projection hmthe lower hemisphere of poles to the joint set which is folded snoss the Haley stock. A: 9 poles to joints, with best-fit axis of cylinrtrical folding; B: Contour plot of same (*= mean fold axis) 40~r?~~r geochronological analyses was completed for samples taken from the Mount Haley stock. Conventional 40As/39~ranalytical methods (Appendix 1) were employed for a single, large, K-feldspar phenocryst, and laser techniques (Appendix 1) were used for concentrations of hand picked hornblende grains. The isotope correlation age of the hand-picked hornblende grains is 109.7 Ma +/- 3.4 Ma. and the plateau age is 112.4 Ma +/- 2.6 Ma (Appendix 2). The initial 'OA~/~~A~ratio of the hornblende was 363 (Appendix 3,indicating that a minor amount of excess %r was initially present in the hornblende. The results fiom the analysis of the K-feldspar gain are consistent with those from the analysis of hornblende grains. The correlation age of the K-feldspar phenocryst is 1 11.1 Ma +/- 3.8 Ma, and its plateau age is 1 1 1.4 Ma, +I- 0.6 Ma (Appendix 3). The agreement of the hornblende and K-feldspar dates (within analytical error) shows that the pluton cooled rapidly. These results show that the Mount Haley stock of the northwest part of the TangIefoot area is a high-level intrusion which is. at the oldest, Aptian. and more likely Nbian age of the Early Cretaceous epoch. Additional data, fiom rocks in the hanging wall and footwall of the Lussier River fault, were provided by D.A. Archibald. Conventional ''~r/~~~rmethods were used to date samples collected by A. W. Welbon during field work in the Central Hughes Range in 199 1 (D.A. Archibald, pers. comm., 1997). A variety of slates, both crenulated and uncrenulated. were analyzed. There are a few Cretaceous granitoid intrusives which occur in the hanging wall of the Lussier River fault (Leech, 1958; Welbon and Price, 1992a; 1993) in the region where the samples were taken, but ~!.edated samples were not hornfelsed, and suggest a deformational event or a iow-temperature overprint at approximately 1 L 0 Ma @.A. Archibald pers. comm., 1997). If this age represents the time of development of the slaty cleavage, and not a thermal overprint from emplacement of a Cretaceous granitoid. then this gives more credence to the suggestion that the Mount Haley stock is pre- or syn-deformational. Conclusions This study has shown that the age of the Mount Hdey stock is 1 11 Ma. The interpretation of field data collected for this study is that the stock is perhaps syn- deformatiod, or more likely pre-deformational, which places a I 11 Ma lower age constraint on deformation. Hiiy and van der Heyden's (1988) data show that displacement on the St. Mary fault occurred prior to 94 Ma Assuming that the age of displacement on the St. Mary fault corresponds with the age of displacement on the Lussier River fault and regional deformation in the Tanglefoot area this places upper and lower age constraints on deformation, at 94 and 1 1 1 Ma, respectively. This conchsion is supported by the occurrence of a folded porphyritic intrusion hosted by the "Tanglefoot unit" just south of the Mount Haley stock. The small. dolomitized intrusion is likely related to the Mount Haley stock. and the former is dearly folded with the country rock. The age constraints on regional deformation are also supported by the folded joint set within the Mount Haley stock, and by the occurrence of hornfelsed r~ckswhich are cleaved in the metamorphic aureole of the inmion. Furthermore, these conclusions are supported by the 40Ar/39Arplateau segment dates of t 10 Ma for slates fiom the Central Hughes Range @.A. Archibald, pers. comm., 1997), which is interpreted to represent the age of development of the slaty cleavage in the rocks, and regional deformation. DISCUSSION Tbe "Tan~lefootunitn: Interpretation The "Tanglefoot Unit", which dominates most of the map-area is primarily marine argiUaceous lime mudstone and wackestone. Deposition was primarily beIow wave base, o~cclrringas fine-grained gravity flow deposits and suspension deposits. Syn- sedimentary mass wasting events fiom the upper slope and platform environments yielded oligomictic carbonate debris flow breccias interbedded with the thick and extensive carbonate slope and distal slope deposits of the "Tanglefoot Unit". Debris flow breccias are absent in the northern part of the Tanglefoot area, and become more abundant towards the south, indicating that their source was to the south. Flute casts and ripple marks on the underside of bedding planes, clast imbrication within debris flow breccias. slump structures, and syn-sedimentary fadting all indicate an approximately northwestward palaeoslope, although it varies locally fiom northeast to southwest. Locally, clasts within oligomictic debris flow breccias are bimodal in composition. Clasts are composed of either very fmely-crystalline carbonate mud. which was derived fiom the lower slope, or peloidal carbonate sand, which is interpreted to have spilled over the rim of the carbonate platfon to the south. and been transported downslope in debris flows. The southeast margin of the Middle Cambrian shale basin roughly coincides with the trace of the Dibble Creek fault (Stretch and Price, 1996). There are two domains of folds within the "Tanglefoot Unit": a dominant domain of southeast-verging, northeast-plunging folds, and a domain of older, upright folds which plunge either to the northwest or to the southeast. Benvenuto and Price (1979) reported that the Hosmer thrust sheet was displaced first 8 km northeastward and then 12 km southeastward. The two fold orientation domains are nearly perpendicular to each other. and reflect the compressive stress fields responsible for the two displacement directions on the Hosmer thrust: The less common, northwest-southeast trending folds were produced as a result of the same compressive stress which displaced the Hosmer thrust sheet 8 km northeast, prior to its 12 km displacement to the southeast. The profound changes in the stratigraphy, and the style and orientation of structures in the Rocky Mountain Foreland Fold and Thrust Belt that occur across the MDC fault are due to reactivation of northeast-trending, Pdaeoproterozoic basement structures that controlled patterns of sedimentation and erosion during the Palaeozoic. The resulting northwest-southeast changes in the thickness and lithofacies of the Palaeozoic rocks controlled the style of deformation during the late Mesozoic and early Cenozoic evolution of the Rocky Mountain Foreland Fold and Thrust Belt. During Early Palaeozoic time, abrupt and rapid subsidence occurred north of the MDC fault. This is reflected by the Cranbrook Formation, interpreted as a shorefront or shallow-water facies succession, overlain abruptly by shales of the Eager Formation. During the Middle Cambrian and lower Upper Cambrian, rapid subsidence on the north side of the MDC fault continued, and the 'bTanglefootunit" was deposited. These deep water strata are intercolated with lower slope and debris flow deposits. which outline the southeast margin of the shale basin. The south side of the MDC fault corresponds with "Montania" (Deiss, 194 I), a southwestern eflension of the North American cratonic platform, where the entire Lower Palaeozoic assemblage is restricted to part of the Middle Cambrian. The south side of the fault hosted a shallow-water cratonic platform depositional environment, of siliciclastic sedimentation during deposition of the Flathead and Gordon Formations, and carbonate sedimentation during deposition of the Eko and Windsor Mountain Formations (Norris and Price, 1966). During the interval fiom the Upper Cambrian to the Lower Silurian. the rate of subsidence on the north side of the Dibble Creek fault decreased (assuming a constant rate of sediment supply), and the McKay Group. Glenogle Formation. Mount Wilson Formation, and Beaverfoot Formation were deposited in shallow water. Prior to Devonian sedimentation, there was a fall in relative sea-level, and a period of non-deposition and erosion. During this interval. uplift and southeastward tilting of the northwest margin of Montania resulted in the northwesn~ard-bevellingof the Middle Cambrian strata along the unconfonnity at the base of the Fairholme Group (Benvenuto and Price, 1979). The region was completely innundated in Late Devonian time, and the shallow- water carbonates of the Fairholme Group and Palliser Formation were deposited. As relative sea-level continued to rise, the upper, thinner-bedded Costigan member of the Palliser Formation accumulated, and was overlain by shales of the Exshaw and Banff Formations. During the Late Devonian and eady Mississippian, the rate of subsidence was higher on the north side of the Dibble Creek fault than it was on the south side of the fault. This is recorded by the "Devono-Mississippian shale unit" in the core of the Lussier River syncline (Leech, 1958; 1960). Deformational style in the Tangle foot area and surrounding region is controlled by stratigraphy and lithofacies. In the Montania domain and the Hughes domain, thicker. more resistent strata have deformed mainly in a brittle manner, and contain many thrust faults. Tight, overturned folds dominate the structures of the Tanglefoot domain. The anomalous southeast-verging deformational structures in the Tanglefoot domain are a product of northeastward compression, tectonic inversion (Price. 1993), and gravitational spreading. The Tanglefoot domain comprises a shale basin that was tectonically inverted during Late Cretaceous northeastward thrusting when its initial basin-shaped basal dkcollement was forced to conform with the flat, planar surface of the through-going basement. As defonnation continued, the shaly, basinal facies rocks were built up even higher as a result of ductile deformation within the Porcupine Creek anticlinorium, and the "critical taper" (Davis et a(., 1983: Dahlen et al.. 1984: Dahlen. 1990) of the western Main Ranges and Western Ranges was surpassed. 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Ham (ed.); Memoir of the American Association of Petroleum Geologists, no. 1, p. 108-12 1 Evans, C.S., 1933: Brisco-Dogtooth Map-Area, British Columbia; Geological Survey of Canada Summary Report, 1932, part AII, p. 106- 176 Folk, RL., 1962: Spectral subdivision of limestone types; iu Classification of Carbonate Rocks. W.E. Ham (ed.); Memoir of the American Association of Petroleum Geologists, no. 1, p. 62-84 Frie W.H., 1969: Report on three collections of Cambrian fossils from the Fernie map-area SE British Columbia; Geological Survey of Canada, Paleontological Report C5- 1969-WHF Fritz, W.H., 1995: Report on 7 lots of Cambrian fossils hmthe southern Canadian Rocky Mountains near Tangiefoot Creek, B.C. collected by G. Stretch (Queen's Univ.). NTS 82G: Geological Survey of Canada, Paleontological Report C 1- 1995-WHF Fritq W.H.,and Norris, D.K.. 1966: Lower Middle Cambrian correlations in the east-central Cordillera: Geological Survey of Canada, Report of Activities, Paper 66- 1, p. 105- 1 10 Fritz, W.H.,CeciIe, M.P.,Norford B.S., Morrow, D., and Geldsetzer, Ei.HJ.. 199 1: Cambrian to Middle Devonian assemblages; &Geology of the Cordilleran Orogen in Canada, H, Gabrielse and C J. Yorath (ed.); Geological Survey of Canada, no. 4. p. 15 1-2 18 (& Geological Society of America, The Geology of North America, v. G-2) Gardner, D.A.C., 1977: Structural geology and metamorphism of calcareous Lower Paleozoic slates. Blaeberry River-Redburn Creek area, near Golden, British Colurn bia; unpublished Ph.D. thesis. Queen's University Henderson, G.G.L., 1954: Geology of the Stanford Range of the Rocky Mountains. Kootenay District. British Columbia; British Columbia Department of Mines, Bulletin 35 Henderson, G.G.L., and Dahlstrom, D.C.A., 1959: First-order nappe in Canadian Rockies: American Association of Petroleum Geologists Bulletin, vol. 43, no. 3, p. 641-653 HUy, T., 1979: Geology of the Estella-Kootenay King area Hughes Range, southeastern British Columbia: B.C. Ministry of Mines and Petroleum Resources, Preliminary map 36 Hay, T., 1984: Geology of the Cranbrook sheet and Sullivan map area; British Columbia Ministry of Energy, Mines, and Petroleum Resources, Preliminary map 49 HUy, T., 1989: The age, chemistry, and tectonic setting of the Middle Proterozoic Moyie sills. Purcell Supergroup, southeastern British Columbia: Canadian Journal of Earth Sciences.vol. 26. p. 2305- 23 17 HCIy, T., 1993: Geology of the Purcell Supergroup in the Fernie west-half map area. southeastern British Columbia; BCMinistry of Energy, Mines, and Petroleum Resources. Bulletin 84. I57p. Hay, T., and Carter, G., 1988: Geology of the Fernie W 112 Map Sheet (and part of Nelson E 1/3): B.C. Ministry of Energy, Mines and Petroleum Resources, Open File Map no. 1988- 14 HCy, T., and van der Heyden, P., 1988: Geochemistry, geochronology, and tectonic implications of two quartz monzonite intrusions, Purcell Mountains. southeastern British Columbia; Canadian Journal of Earth Sciences, vol. 25, p. 106-1 15 Hunt, G., 1964: Chemical correlation of the Purcell igneous rocks; Bulletin of Canadian Petroleum Geology, vol. 12, p. 544-555 Kanasewich, E.R., Clowes, R.M., and McCloughan, C.H.. 1969: A buried Precambrian rift in Western Canada; Tectonophysics, vol. 8, p. 5 13-527 Leech, G.B., 1954: Canal Flats, British Columbia (Map and Preliminary Account); Geological Survey of Canada, Paper 54-7,3 1 p. Leech, G.B., 1958: Fernie Map Area, West Half, British Columbia; Geological Survey of Canada, Paper 58- 10, 40 p. Leech, G.B., 1960: Geology of the Fernie (West Half) Kootenay District, British Columbia: Geological Survey of Canada, Map 1 1- 1960 Leech, G.B., 1962: Structure of the Bull River Valley near Latitude 49O 35'; Joumai of the Alberta Society of Petroleum Geologists, vol. 10, no. 7, p. 396-407 Lis, M.G.,and Price. RA., 1976: Large-scale block faulting during deposition of the Windermere Supergroup (Hadrynian) in southeastern British Columbia; Report of Activities. Part A. Geological Survey of Canada, Paper 76-1A. p. 135-136 Lochman-Balk C., and Wilson, J.L., 1958: Cambrian biostratigraphy in North America: Journal of Paleontology, vol. 32, p. 312-350 McLaren, D.J., and Mountjoy, E.W.. 1962: Alexo equivalents in the Jasper region, Alberta: Geological Survey of Canada, Paper 62-23,36 p. McMechan, M.E., 1979: Geology of the Mount Fisher-Sand Creek Area: B.C. Ministry of Energy, Mines and Petroleum Resources. Preliminary Map 34 McMechan, M.E.. 1980: Stratigraphy, structure, and tectonic implications of the middle Proterozoic Purcell Supergroup in the Mount Fisher area, southeastern British Columbia; unpublished Ph.D. thesis. Queen's University McMechan, M.E., H6y. T., and Price, RA., 1980: Van Creek and Nicol Creek Formations (New): A revision of the stratigraphic nomenclature of the Middle Proterozoic Purcell Supergroup. southeastern British Columbia; BuIletin of Canadian Petroleum Geology, vol. 26. p. 542-558 McMechan, M.E., and Price, R.A., 1982: Superimposed low-grade metamorphism in the Mount Fisher area, southeastern British Columbia - implications for the East Kootenay Orogeny: Canadian Journal of Earth Sciences, vol. 19, p. 476-489. Mott, J.A., 1989: Structural and stratigraphic relations in the White River region. eastern Main Ranges. Southern Canadian Rocky Mountains. British Columbia: Unpublished Ph.D. thesis. Queen's University Norford, B.S., 1969: Ordovician and Silurian stratigraphy of the southern Rocky Mountains: Geological Survey of Canada, Bulletin 176, 90 p. Norford, B.S., and Cecile, M.f ., 1994a: Cambrian and Ordoviciaq volcanic rocks in the McKay Group and Beaverfoot Formation, Western Ranges of the Rocky Mountains, southeastern British Columbia; Current Research 1994-B; Geological Suvey of Canada p. 83-90 Norford, B.S., and Cecile, M.P., 1994b: Ordovician emplacement of the Mount Dingley Diatreme. Western Ranges of the Rocky Mountains, southeastern British Columbia: Canadian Journal of Earth Sciences, vol. 3 1, p. 149 1- 1500 Noms, D.K., and Price, RA., 1966: Middle Cambrian lithostratigraphy of southeastern Canadian Cordillera; Bulletin of Canadian Petroleum Geology, voi. 14, no. 4, p. 385-404 North, F.K., and Henderson, G.G.L., 1954: Summary of the geology of the southern Rocky Mountains of Canada; Alberta Society of Petroleum Geologists, Field Conference Guidebook, p. 15-8 1 Price, RA., 1962: Fernie map-area, east half, Alberta and British Columbia; Geological Survey of Canada, Paper 6 1-24? 65p. Price. RA., 1964: The Devonian Fairholme-Sassenach succession and evolution of reef-front geometry in the Flathead-Crowsnest Pass area Alberta and British Columbia: Bulletin of Canadian Petroleum Geology, vol. 12 (field conference guide book issue), p. 427-45 1 Price, R.A., 1967: Operation Bow-Athabasca, Alberta and British Columbia; Report of Activities. Part A, May to October, 1966, Geological Survey of Canada, Paper 67- 1. p. 106- 1 12 Price, R.A., 1967a: Golden. East Half, Maparea (82N E ID), British Columbia and Alberta; & Report of Activities, Part B. November 1966 to April 1967. Geological Survey of Canada, Paper 67-1. p. 88-9 1 Price, R.A., 1975: Recurrent displacements on basement-controlled faults across the Cordilleran rniogeocline in southern Canada; Geological Society of America Abstracts with Programs. voI. 7. p. 1234 Price, R.A., 1981: The Cordilleran foreland thrust and fold belt in the southern Canadian Rocky Mountains; Thrust and Nappe Tectonics: McClay, K.R and Price, NJ.. eds., The Geological Society of London; Special Publication no. 9, p. 427-448 Price, R.A., L993: Tectonic heredity, tectonic inversion, and cross-snike discontinuities in thrust and fold belts: An example fiom the southeastern Canadian Cordillera; Geological Society of America, Abstracts with Programs, vol. 25, no. 2 (Northeast Section), p. 71 Price, R.A., 1996: Tectonic heredity of the Crowsnest Pass cross-strike discontinuity: Mesozoic-Cenozoic tectonic inversion of Palaeozoic structures with Eocambrian Neoproterozoic. Mesoproterozoic. and Archean antecedents; iu Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) Transect and Cordilleran Tectonics Workshop Meeting, University of Calgary, Lithoprobe Report no. 50, p. 155 Price, R.A., 1997: Reactivated Alberta basement structures: The Crowsnest Pass cross-strike discontinuity, SW Alberta and SE British Columbia; Canadian Society of Petroleum GeologistsKanadian Society of Economic Geologists. Abstracts with Programs. Annual General Meeting, 1997 Price, R.A., and Mountjoy, E.W.. 1970: Geologic Structure of the Canadian Rocky Mountains benveen Bow and Athabasca Rivers - A Progress Report; & Structure of the southern Canadian Cordillera. 3.0. Wheeler (ed.), Geological Association of Canada, Special Paper no, 6, p. 7-25 Price, R.A., BaIkwill, H.R.. Charlesworth, H.A.K., Cook, D.G., and Simony, P.S., 1972: The Canadian Rockies and tectonic evolution of the southeastern Canadian Cordillera; 24th International Geological Congress, Guidebook for field excursion A 15 - C 15, p. 77-107 Price, RA., and Sears, J.W., in press: A preliminary palinspastic map of the Mesoproterozoic BeWPurceil Supergroup, Canada and U.S.A.; "Implications for the tectonic setting and structural evolution of the Purcell anticlinoriurn and the Sullivan deposity*: The Sullivan deposit and its geological environment, J.W. Lydon, T. Hby, M. Knapp, and J.F. Slack (eds.), Geological Survey of Canada, Special Volume Reesor, J.E., 1958: Dewar Creek map-area with special emphasis on the White Creek batholith. British Columbia; Geological Survey of Canada, Memoir 292, 78 p. Rice, H.M.A., 1937: Cranbrook map-area, British Columbia; Geological Survey of Canada Memoir 207. 67p. Rice, H.M.A., 1941: Nelson map-area east half, British Columbia: Geological Survey of Canada Memoir 228,86 p. "9 Roddick J.C., 1983: High precision intercalibration of 40~rp'Ar standards: Geochirnica ct Cosmochimica Acta, vol. 47. p. 887-898 Ross, G.M., Parish. RR, Villeneuve, M-E., and Bowring, S.A.. 199 1 : Geophysics and geochronolo~ of the crystalline basement of the Alberta basin, western Canada; Canadian Journal of Earth Sciences, vol. 28, p. 512-522 Savoy, L.E., and Harris, A.G.. 1993: Conodont biofacies and taphonomy along a carbonate ramp to black shale basin (latest Devonian and earliest Carboniferous), southernmost Canadian Cordillera and adjacent Montana; Canadian Journal of Earth Sciences, vol. 30, p. 2404-2422 Schofield, S.J., 1915: Geology of Cranbrook map area, British Columbia; Geological Survey of Canada. Memoir 76,245 p. Shaw, E.W., 1963: Canadian Rockies - Orientation in time and space; k Backbone of the Americas. O.E. Childs and B.W. Beebe (eds.), American Association of Petroleum Geologists, Mernoir 2. p. 23 1-242 Shepard, F.P., 1926: Further Investigations of the Rocky Mountain Trench; Journal of Geology, VOI. 34, p. 623-64 1 Steiger, RH., and Jilger, E., 1977: Subcommission on geochronology: Convention on the use of decay constants in geo- and cosmo-chronology; Earth and Planetary Science Letters, vol. 36, p. 359-362 Stretch, G.W., and Price, RA., 1996: The southeast termination of the Main Ranges geological province of the Southern Canadian Rockies near Crowsnest Pass, southeast B.C.; & Slave-h~o~thern CordiIlera Lithospheric Evolution (SNORCLE) Transect and Cordilleran Tectonics Workshop Meeting, Universiry of Calgary, L ithoprobe Report No. 50. p. 154 Suppe, J., and Medwedeff, D.A., 1990: Geometry and Kinematics of Fault-Propagation Falding; Ecologae Geologicae Helvetiae, vol. 83, p. 409-454 Thompson, T.L., 1962: Stratigraphy, tectonics, structure, and gravity in the Rocky Mountain Trench area southeastern British Columbia, Canada; unpublished Ph.D. thesis, Stanford University Wanless, R.K.. Loveridge, W.D., and Mursky, G., 1968: A geochronological study of the mite Creek batholith, southeastern British Columbia; Canadian Journal of Earth Sciences. vol. 5, p. 375-386 Welbon, A.I., and Price, R.A., 1992a: Geology of the Central Hughes Range, British Columbia: British Columbia Ministry of Energy, Mines and Petroleum Resources, Open File Map na. 1992- 17 Welbon, A.I., and Price, R.A., 1992b: Stratigraphic dating of fault systems of the Central Hughes Range, southeast British Columbia (82G/t 2); Contribution No. 5, Sullivan-Aidridge project, British Columbia Geological Survey Branch, paper 1992- 1 Welbon, A.I., and Price, R.A., 1993: Geology of the Wild Horse River-Lussier River area, S.E. British Columbia, NTS 82G/11, 12, 13, 14; British Columbia Ministry of Energy, Mines, md Petroleum Resources, Open File Map no. 1993-7 Wheeler, J.O., and McFeely, P. (comp.) 1991: Tectonic Assemblage Map of the Canadian Cordillera and adjacent parts of the United States of America; Geological Survey of Canada, Map 17 J~A,scale 1:2 000 000 APPENDICES M~r/39~rstepheating experiments were performed on IXVO mineral separates. The first was a collection of hornblende grains less than 0.5 mm in length. The hornblende grains were separated at Queen's University (Kingston. Ontario) by- first crushing and sieving rock samples, running the sieved portions through a Frantz iso- dynamic mineral separator, employing heavy liquid techniques, and finally by hand- picking grains. The second analysis was on a single K-feldspar grain, which was approximately 20 mm by 16 mm by 5 mm. It was crushed into pieces 0.5 mrn to 1 mm in diameter. The samples and flux monitors (standards) were wrapped in aluminum foil and loaded into an irradiation container, which is 1 1.5 cm long and 2.0 cm in diameter. It was then irradiated with fast neutrons in position 5C of the McMaster Nuclear Reactor (Hamilton, Ontario) for 29 hours. Groups of flux monitors (26 in total) were located at approximately 1 cm intervals along the irradiation container, and J-values for individual samples were determined by interpolation. The K- feldspar was heated in a pure-silica tube (GE2 14) using a Lindberg hace. This bakeable, ultra-high vacuum, stainless-steel, argon-extraction system is operated on- line to a substantially modified, A.E.I. MS-10 mass-spectrometer run in the static mode. Flux monitors (39 splits of intra-laboratory standards MAC-83 Bio and 9 1 JG-44 Bio) were analyzed using laser fusion. For total-hion of monitor samples and step- heating using a laser, the samples were mounted in an aluminurn sample-holder, beneath the sapphire view-port of a small stainless-steel chamber connected to an ultra-high vacuum purification system. Step-heating was accomplished by de-focusing the beam of an 8 W Lexel3500 laser to cover the entire sample and heating for approximately 2 minutes at increasing power settings. The evolved gas, after purification using an SAES CSO getter, was admitted to an on-line, MAP 216 mass spectrometer, with a Bhr Signer source and an electron multiplier (set to a gain of 100 over the Famday), and analyzed in static mode. Blanks, measured routinely, were subtracted from the subsequent sample gas-fractions. Extraction-blank volumes during this series of analyses were: 4- 1 7 x lo-". 0.2-0.9x 10-13,0.4-0.6 x 10-13.and 0.2-1.0x 10'13 cm') STP for masses 40, 39, 37, and 36. respectively. Measured argon-isotope peak heights were extrapolated to zero-time. normalized to the *~r/~~A.ratmospheric ratio (295.5), and corrected for neutron-induced "~rfrom potassium, 39~rand 36~rhm calcium, and 36~rhrn chlorine. Dates and errors were calculated using formulae given by Dalrymple et nl. (198 I), and the constants recommended by Steiger and Jager (1977). Errors shown represent the analytical precision at 20, assuming that the error in the Evalue is zero. A conservative estimate of this error in the J-value is 0.5 % and can be added for inter-sample comparison. The dates and J-values for the two additional, ha-laboratory standards are referenced to LP-6 biotite at 128.5 Ma (Roddick, 1983). ~eadix2: Geochronolo~vresults from hornblende wains D-272 : GS-556L Hbl HP maswed volunrcs are x 1E-10 cm3 NTP. All errors are 2 x standard error. 1.0 Fraction 39- Name: GordonWillianrStrrtch Place and year of birth= Ecbonton, Albcrra, 1969 Experience: UniMsity of Alberta, Junior Field AaislanS srmnner 1992 Queenls University, USc. thesis field study, summers t 994,1995 BHP Minds Canada Ltd. Contract Roja Geologist sprin~summer1996 BHP Minerals Canada Ltd., Contract Project Gdogist 1997 Awards: Am- Fellowship. 1995. 19% . NOTE TO USERS Oversize maps and charts are microfilmed in sections in the following manner: LEFT TO RIGHT, TOP TO BOTTOM, WITH SMALL OVERLAPS LOGY I LOCATION SCALE - .--.-: Dark grey to black shale; med m IAGERFM- .,-i. calcareous shale 1.2 nonzonite, quartz - (1 (1 01- CRANBROOK-- FM. Approximate Mean Declination 1988 for Centre of Map Decreasing 7.9' Annually MAPPING / COMPllATlON a ''e'8I~ImCI8t8 INTRUSIVE ROCKS Pink, black-speckled, porphyritic monzonite, qu U, monzonite, and syenite UPPER PALAEOZOIC EXSHAW, BANFF FMs. Thin-bedded, platy dolomite and limestone; sha local cherty layers, locally pyritic PALLISER FM. Buff and grey, thick-bedded lime mudstone an wackestone, locally mottled, local siltstone inter FAIRHOLME GP, Lime wackestone, packstone, boundstone; dolorr Sassenach Fm.: sandstone; siltstone; silty limesq "BASAL DEVON IAN u N IT" Purplish brown and grey sandstone; conglomerc grit LOWER PALAEOZOIC McKAY GP Cambro-Ordovician undi\ Limestone; sha e; intraformational limestone conglomerate McKAY GP. (upper ~ambrian) Cum Yellowish rey to dark grey, thin-bedded clayst shale; sha9 y limestone Medium-bedded lime mudstone; shaly limestone carbonate debris-flow breccia U calcareous shale monz~nite,quartz ),,I ),,I CRANBROOK FM. Purple, buff, and grey quartz I LIC I conglomerate, quartzwacke, ar imestone; shale; MESOPROTEROZOIC PHILLIPS FM. Dark red quartzite, micaceous mudstone and siltstone interbeds GATEWAY FM. Green dolomite, quartz wacke, dstone; dolomite le; silty limestone SHEPPARD FM. Dolomitic quartzite, sandstone; conglomerate at base ; conglomerate; NlCOL CREEK FM. Dark green, amygdaloidal, and6 flows cian undivided) VAN CREEK FM. imestone Green and greyish-green, lamir argillite KITCHENER FM. ebded claystone; Grey, reddish-brown and purpk wackestone and siltstone; siltst CRESTON FM. ~lylimestone; Light greenish-grey argillite; sil. quartz arenite LIMIT OF MAPPING / COI 'M . *- GEOLOGICAL B~.UNDARY( grey quartz arenite, quartz-pebble artzwacke, and grit BEDDING (TOPS KNOWN, CLEAVAGE (S , S, , S3 ) . LINEATION (PRIMARY, DE e, micaceous siltstone and argillite FAULT (DEFINED, APPROX THRUST FAULT (TEETH NORMAL FAULT (DOTS quartz wacke, siltstone, and argillite ANTICLINE SYNCLINE k, sandstone; oolitic dolomite; local OVERTURNED ANTICLINE ( base OVERTURNED SYNCLINE (I FM. FOSSIL OCCURRENCE - jdaloidal, andesitic to basaltic lava SCREE SLOPE ELEVATION CONTOUR A. vgreen, laminated siltstone and RIVER/STREAM wn and purple dolomite, dolomitic siltstone; siltstone ey argillite; siltstone; fine-grained Contours generated from Digital 1 :i Contour interval 100 metres Elevations in metres above Mea F MAPPING / COMPllATlON m **mDm*m**mmw**m*a ; (TOPS KNOWN, TOPS UNKNOWN, OVERTURNED) r) I IN (PRIMARY, DEFORMATIONAL) u * ST FAULT (TEETH ON HANGING WALL) a AL FAULT (DOTS ON HANGING WALL) U ?NED SYNCLINE (LOOP POINTS AT CLOSURE) _____JdL OCCURRENCE El SLOPE TREAM ------ated from Digital Elevation Model. Universal Transverse Mercator Pro) 1 I00 metres North American Datum - NAD83 letres above Mean Sea Level. UTM zone II Mercator Projection m - NAD83 PLEASE NOTE: Oversize maps and charts are filmed in seaions in the following manner: LEET TO RiGHI', TOP TO BOTTOM, WITH SMALL OVERLAPS The foilowing map or chart has been refilmed in its entirety at tke end of this dissertation (not adable on microfiche). A xerographic reproduction has been provided for paper copies and is inserted into the inside of the back cover. Black and white photographic prints ( 17" x 23") are available for an additional charge. P LATE CROSS SECT SECT ON5 P LA- P LAT E Trace of section C-D Trace of section C-D 3000 METRES 2ooc 1000 SEA LEVEl SCALE: 0 1000 2000 3000 1 I I I I I I I I I 1 I 1 I I 1 METRES NO VERTICAL EXAGGERATION 'Oml 4000 3000 - METRES 2000 Trace section Trace of section A-B IBBLE I------ SCALE: METRES NO VERTICAL EXAGGERATION Mebr, 1000 LEVEL .-7- - . ' NO VERTICAL EXAGGERAnON Mebr, Mebr,