Sedimentology, Stratigraphy, and U-Pb Detrital Zircon Geochronology of the Mesoproterozoic Husky Creek Formation, Coppermine River Group, Nunavut, Canada

Sedimentology, stratigraphy, and U-Pb detrital zircon geochronology of the Mesoproterozoic Husky Creek Formation, Coppermine River Group, Nunavut, Canada.

Robert David Meek

A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science (MSc) in Geology

The Faculty of Graduate Studies Laurentian University Sudbury, Ontario, Canada

©Robert Meek, 2020 THESIS DEFENCE COMMITTEE/COMITÉ DE SOUTENANCE DE THÈSE Laurentian Université/Université Laurentienne Faculty of Graduate Studies/Faculté des études supérieures

Title of Thesis Titre de la thèse Sedimentology, stratigraphy, and U-Pb detrital zircon geochronology of the Mesoproterozoic Husky Creek Formation, Coppermine River Group, Nunavut, Canada.

Name of Candidate Nom du candidat Meek, Robert

Degree Diplôme Master of Science

Department/Program Date of Defence Département/Programme Geology Date de la soutenance January 08, 2019

APPROVED/APPROUVÉ

Thesis Examiners/Examinateurs de thèse:

Dr. Alessandro Ielpi (Supervisor/Directeur de thèse)

Dr. Robert H. Rainbird (Co-Supervisor/Co-directeur de thèse)

Dr. William J. Davis (Co-Supervisor/Co-directeur de thèse)

Approved for the Faculty of Graduate Studies Approuvé pour la Faculté des études supérieures Dr. David Lesbarrères Monsieur David Lesbarrères Dr. Janok Bhattacharya Dean, Faculty of Graduate Studies (External Examiner/Examinateur externe) Doyen, Faculté des études supérieures

ACCESSIBILITY CLAUSE AND PERMISSION TO USE

I, Robert Meek, hereby grant to Laurentian University and/or its agents the non-exclusive license to archive and make accessible my thesis, dissertation, or project report in whole or in part in all forms of media, now or for the duration of my copyright ownership. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also reserve the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department in which my thesis work was done. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that this copy is being made available in this form by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.

ii Abstract

The Husky Creek Formation (part of the Coppermine River Group, western Nunavut,

Canada) is a <1.23-billion-year-old siliciclastic sedimentary unit that represents the uppermost portion of the Sequence A stratigraphic subdivision – a package of Proterozoic volcanic and sedimentary rocks correlative across the Canadian Arctic. Sedimentologic indicators suggest a continental, temperate to arid depositional environment for the Husky Creek Formation, which included fluvial channel belts and floodplains subject to local aeolian winnowing. U-Pb detrital- zircon geochronology resolved derivation from rocks related to the Mackenzie Igneous Event, or recycling from older sediments such as the Hornby Bay Group. The Husky Creek Formation was deposited in the waning stages of the Mackenzie Igneous Event, in a restricted basin that was carved atop an extensive mafic volcanic plateau. A dominantly west-northwestward palaeoflow suggests that sediment transport from the core of the Laurentian craton was not significantly disrupted by crustal doming related to large-igneous-province emplacement.

Keywords

Mesoproterozoic, Coppermine River Group, Sequence A, Mackenzie Igneous Event, U-Pb detrital zircon geochronology.

iii

Co-Authorship Statement

Multiple collaborators, listed as co-authors, contributed to the work presented in this manuscript. Scientific guidance, supervision, financial support, sample collection, and assistance with laboratory analysis was provided by these co-authors. Dr. Alessandro Ielpi supervised this

MSc project.

Chapter 2 is co-authored with Dr. Alessandro Ielpi (Laurentian University) and Dr. Rob

Rainbird (Geological Survey of Canada). Fieldwork and sample collection were completed by the candidate under the supervision of both co-authors. The manuscript was completed by the candidate with guidance from Dr. Ielpi and Dr. Rainbird.

Chapter 3 is co-authored by Dr. Alessandro Ielpi (Laurentian University), Dr. Rob

Rainbird (Geological Survey of Canada), and Dr. William Davis (Geological Survey of Canada).

Fieldwork and sample collection was completed by the candidate under the supervision of Dr.

Ielpi and Dr. Rainbird. Sample preparation (crushing, milling, heavy mineral separation, Franz magnetic separation, and puck mounting) was conducted in Dr. Davis’ laboratory. Analytical techniques (backscatter electron imaging, cathode luminescence, and sensitive high-resolution ion microprobe analysis) were executed in Dr. Davis’ laboratory with the assistance of the candidate. Dr. Davis also contributed to writing a subsection of the “methods”. The first draft was written by the candidate with scientific guidance from all three co-authors. All three co- authors edited subsequent drafts of the manuscript and provided scientific input.

Acknowledgements

I would like to first and foremost thank Dr. Alessandro Ielpi for providing me with the opportunity to work on such a fantastic project. Your expertise, guidance, friendship, and patience throughout this project has made my M.Sc. experience a truly excellent one. Thank you to my co-supervisor, Dr. Rob Rainbird, for your encouragement, helpful suggestions, and insightful comments. Thank you to co-author Dr. William Davis for your geochronology expertise and edits. Thank you to Tom Pestaj and Nicole Rayner from the Geological Survey of

Canada for assistance during analytical work on the SHRIMP. Thank you to all the faculty and staff at the Harquail School of Earth Sciences. Thank you to Willard Desjardin and Elliot Wehrle for help with sample preparation. Thank you to everyone on the 2017 Coppermine expedition, especially the river guides: Jessica Harris, Chris Harris, Dylan Rollo and John McAlpine, for keeping my samples and myself afloat. I would also like to thank my fellow graduate students, including lab mates: Natasha Cyples, Lorraine Lebeau, Mollie Patzke, and Sophie Michel, for their friendship, support, and advice. Thank you to a colleague and great friend Keaton

Strongman for great times and endless geology discussions. Last but certainly not least, I would like to thank my parents, David and Dorina Meek, for their continual support and encouragement.

Table of Contents

Abstract ...... iii Co-Authorship Statement ...... iv Acknowledgements ...... v List of Tables ...... viii List of Figures ...... ix List of Appendices ...... x Chapter 1 ...... 1 Introduction to the thesis ...... 1 1.1 Statement of purpose ...... 1 1.2 Goals and research questions ...... 2 1.3 Structure of thesis ...... 3 1.4 Statement of responsibilities ...... 4 1.5 Statement of original contributions ...... 4 1.6 References ...... 5 Chapter 2 ...... 6 Sedimentology and Stratigraphy of the Mesoproterozoic Husky Creek Formation, Lower Coppermine River region, Nunavut ...... 6 2.1 Introduction ...... 6 2.2 Geologic Background ...... 7 2.3 Previous Work ...... 8 2.4 Stratigraphy ...... 9 2.5 Facies Descriptions...... 10 2.6 Facies Associations ...... 17 2.6 Stratigraphic Variations ...... 20 2.7 Palaeoflow Analysis ...... 21 2.8 Depositional Style ...... 22 2.9 Conclusions ...... 23 2.10 Acknowledgements ...... 24 2.11 References ...... 24 2.12 Figures ...... 29

Chapter 3 ...... 42 Sedimentology and Detrital Zircon Geochronology of the Mesoproterozoic Husky Creek Formation: A fluvial sandstone recording the waning stages of one of Earth’s largest magmatic episodes...... 42 3.1 Abstract ...... 42 3.2 Introduction ...... 43 3.3 Geological Setting ...... 46 3.4 Sedimentology and Petrography ...... 48 3.5 Detrital zircon geochronology ...... 50 3. 6 Discussion ...... 57 3.7 Conclusions ...... 67 3.8 Acknowledgements ...... 69 3.9 References ...... 69 3.10 Figures ...... 80 Chapter 4 ...... 101 Concluding statements ...... 101 4.1 Conclusions ...... 101 4.1.1 Sedimentology ...... 101 4.1.2 Detrital Zircon Geochronology ...... 102 4.2 Future work ...... 102 4.3 Appendices ...... 104

vii

List of Tables

Table 3-1: Geochronology sample descriptions ...... 94 Table 3-2 Husky Creek Formation sedimentary facies ...... 96

viii

List of Figures

Figure 2-1: Study Area ...... 29 Figure 2-2: Coppermine Homocline stratigraphy ...... 31 Figure 2-3: Regional geology ...... 32 Figure 2-4: Husky Creek Formation Stratigraphic Log ...... 33 Figure 2-5: Husky Creek Formation contact relationships ...... 34 Figure 2-6: Fluvial deposits ...... 36 Figure 2-7: Floodplain deposits ...... 37 Figure 2-8: Aeolian deposits ...... 38 Figure 2-9: Palaeocurrent analysis ...... 40 Figure 2-10: Depositional model ...... 41 Figure 3-1: Sequence ABC stratigraphy and study area ...... 80 Figure 3-2: Coppermine Homocline stratigraphy ...... 81 Figure 3-3: Husky Creek Formation geochronology sample stations ...... 82 Figure 3-4: Husky Creek Formation general stratigraphy and contacts...... 83 Figure 3-5: Thin section and detrital zircon petrography ...... 85 Figure 3-6: Sedimentary bedforms ...... 86 Figure 3-7: Palaeocurrent analysis ...... 88 Figure 3-8: Young Detrital Zircon Grains ...... 89 Figure 3-9: Probability density diagrams- limited recycling ...... 90 Figure 3-10: Probability density diagrams- polycyclic grains ...... 91 Figure 3-11: Husky Creek Formation source areas...... 92

List of Appendices

Appendix A: Stratigraphic log- Middle Husky Creek Formation (17-RATR-028) ...... 104 Appendix B: Stratigraphic log of the middle Husky Creek Formation (17-RATR-029) ...... 105 Appendix C: Stratigraphic log of the upper Husky Creek Formation (17-RATR-032) ...... 105 Appendix D: Kernel Density Estimate Plots ...... 105 Appendix E: U-Pb Shrimp Data...... 105

Chapter 1 Introduction to the thesis

1.1 Statement of purpose

This thesis investigates a hitherto understudied sedimentary succession in the Canadian

Arctic that has regional palaeogeographic implications as part of the regionally correlative

Sequence A stratigraphy – which is, in turn, a classic stratigraphic subdivision scheme introduced in the 1970s for the Proterozoic strata exposed in northern Canada (Young et al.,

1979). This project was completed by studying the sedimentology, stratigraphy, palaeocurrent patterns, and detrital zircon geochronology of the ~1.23 Ga Husky Creek Formation

(Coppermine River Group, Nunavut, Canada). The Husky Creek Formation is exposed along canyons carved out by the Coppermine River and its associated tributaries and consists of roughly 1900 m of red beds and basalt. The formation is exceptionally exposed in three- dimensional outcrops by the Coppermine River and is well preserved, with little alteration or weathering present. These attributes provide the opportunity to interpret surficial conditions, such as climate and local hydrologic budget, at the time the sediment of the Husky Creek

Formation was deposited. The Husky Creek Formation overlies the Copper Creek flood basalts, a major component of the Mackenzie Igneous Event, which represents, in turn, one of the largest igneous activities recorded on Earth. The mechanisms of Mesoproterozoic basin development in the area are largely unknown, and particularly its potential links with the Mackenzie Igneous

Event. Preliminary geochronology work on the Husky Creek Formation produced an enigmatic age of 1232 ± 15 Ma (Rayner and Rainbird, 2013) which postdates the Mackenzie Igneous

Event, and thus warranted an encompassing study to investigate the sedimentology and

stratigraphy of the Husky Creek Formation, the links between its deposition and the Mackenzie

Igneous Event, and the provenance of detritus sourcing during basin development.

1.2 Goals and research questions

• To further our general understanding of Mesoproterozoic terrestrial sedimentary

environments and the understanding of the regional sedimentology and stratigraphy in the

Canadian Arctic.

The Husky Creek Formation is the topmost member of Sequence A stratigraphy (Young et al., 1979), a package of sedimentary and volcanic successions that are correlative across the

Canadian Arctic. The Husky Creek Formation is exceptionally well preserved and stands as a record for terrestrial processes during and just after the Mackenzie Igneous event. Only preliminary field observations and geochronology studies have been conducted so far on this formation prior to this project (Baragar and Donaldson, 1973; Campbell, 1983; Rayner and

Rainbird, 2013). Facies analysis, palaeoflow measurements, and petrography were utilised to broadly infer the depositional environments of the formation.

• To investigate possible spatial and temporal interactions between the Husky Creek

Formation and the Mackenzie Igneous Event.

Examples of significant sedimentation events occurring contemporaneously with flood basalt magmatism are relatively limited in the geologic record. Such interaction is observed in the Miocene age Columbia River Flood Basalt Province, where flood basalts, fluvial and lacustrine sedimentary rocks are interposed (Ebinghaus et al., 2014). A Precambrian example of coeval flood basalt magmatism and sedimentation is recorded in the Natkusiak Formation flood

basalts (extrusive equivalent to the 723 Ma Franklin gabbro sills) and the fluvial quartzarenites of the Kuujjua Formation (Rainbird, 1993). The evidence of temporally closely related sedimentation and volcanism in the Husky Creek Formation sandstones and Copper Creek

Formation flood basalts allows for the interpretation of surficial conditions during the emplacement of a large igneous province. Whether and how the emplacement of such large igneous provinces affects surficial sedimentation, e.g. through crustal doming or topographic alteration in the catchment area of fluvial systems, is currently poorly constrained, particularly for the Precambrian record. Field techniques, as described above and detrital zircon geochronology, allows inference of the evolution of the Husky Creek Formation basin and its catchment area.

1.3 Structure of thesis

This thesis is organised into this introductory and three following chapters. Chapter two is written as a manuscript that has been published as a Geological Survey of Canada Open File, and entitled “Sedimentology and stratigraphy of the Mesoproterozoic Husky Creek Formation, lower Coppermine River region, Nunavut”. Chapter three is written as a manuscript to be submitted for publication in a peer-reviewed scientific journal (Elsevier’s Precambrian

Research), and entitled “Sedimentology and Detrital Zircon Geochronology of the

Mesoproterozoic Husky Creek Formation: A fluvial sandstone recording the waning stages of one of Earth’s largest magmatic episodes”. As these chapters have been or will be published as separate articles, there is some repetition of material among chapters – especially in the introduction and geological setting. This latter chapter presents the first comprehensive detrital- zircon geochronology provenance study of the Husky Creek Formation and is aimed at

characterising its sediment sources, basin characteristics, and investigating the potential influence of the Mackenzie large igneous province on sedimentation.

1.4 Statement of responsibilities

Fieldwork and sample collection was completed by the candidate between July and

August 2017 under the supervision of Drs. Ielpi, Rainbird, and Davis. For petrographic results in chapters two and three, Mr. Elliot Wehrle and Mr. Willard Desjardins at Laurentian University cut samples and prepared thin sections. For the detrital zircon geochronology results described in chapter three, samples were sent to Dr. Davis and associated laboratory personnel for separation at the Geochronology Facility of the Geological Survey of Canada and crushed by mechanical disaggregation. The samples then underwent heavy mineral separation using a Wilfley table and heavy liquids before being passed through a magnetic separator. Zircons were then cast in an epoxy puck and imaged by cathodoluminescence and backscatter electron imaging. Analysis using the sensitive high-resolution ion-microprobe (SHRIMP) was undertaken by Dr. Davis and technologist Tom Pestaj with the assistance of the candidate. Dr. Davis performed raw data corrections and is co-authoring chapter three. Chapter two was written by the candidate with editing by Dr. Ielpi and Dr. Rainbird. Chapter three was written by the candidate with edits by

Dr. Ielpi, Dr. Rainbird, and Dr. Davis.

1.5 Statement of original contributions

Original contributions made by this study are outlined in the following points below:

• Provides the first detailed description of the sedimentology and stratigraphy of the Husky

Creek Formation with the interpretation that it is the product of fluvial, floodplain, and

aeolian depositional systems.

• Documents the stratigraphy and palaeoflow patterns of the Husky Creek Formation.

• Provides the first comprehensive detrital zircon geochronology provenance study for the

Husky Creek Formation.

1.6 References

Baragar, W.R.A., Donaldson, J. A., 1973. Coppermine and Dismal Lakes map areas.

Geological Survey of Canada, Paper 71–39, 20 p.

Campbell, F.H. A., 1983. Stratigraphy of the Rae Group, Coronation Gulf Area, District of

Mackenzie. Geological Survey of Canada, Paper 83-1A, p. 43–52.

Ebinghaus, A., Hartley, A.J., Jolley, D.W., Hole, M., Millet, J., 2014. Lava-sediment

interaction and drainage-system development in a large igneous province: Columbia

River Flood Basalt Province, Washington State, U.S.A. Journal of Sedimentary Research,

vol. 84, p. 1041-1063.

Rainbird, R.H., 1993. The Sedimentary Record of Mantle Plume Uplift Preceding Eruption of

the Neoproterozoic Natkusiak Flood Basalt. The Journal of Geology, vol 101, p. 305-318.

Rayner, N.M., Rainbird, R.H., 2013. U-Pb geochronology of the Shaler Supergroup, Victoria

Island, northwest Canada: 2009-2013; Geological Survey of Canada, Open File 7419,

62 p.

Young, G.M., Jefferson, C.W., Delaney, G.D., Yeo, G.M., 1979. Middle and late Proterozoic

evolution of the northern Canadian Cordillera and Shield. Geology 7, 125–128.

Chapter 2

Sedimentology and Stratigraphy of the Mesoproterozoic Husky Creek

Formation, Lower Coppermine River region, Nunavut

R. Meek1, A. Ielpi1, R.H. Rainbird2

1Laurentian University, Harquail School of Earth Sciences, Willet Green Miller Centre, 935

Ramsey Lake Road, Sudbury, Ontario P3E 2C6

2 Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8

2.1 Introduction

This open file presents results from the “Coppermine River Transect” campaign, which consisted of field activities conducted in July and August 2017 in western Nunavut as part of the second phase of the Geo-mapping for Energy and Minerals (GEM-2) program. Research activities related to this report were led by the Geological Survey of Canada (Ottawa, Central

Canada Division), in collaboration with Laurentian University of Sudbury (Ontario). This report provides a first detailed sedimentologic and stratigraphic description and interpretation of the

Mesoproterozoic Husky Creek Formation in the Coppermine Homocline, which is best exposed along the Coppermine River and its tributaries to southwest of Kugluktuk, Nunavut.

2.2 Geologic Background

Proterozoic Stratigraphy

The Proterozoic stratigraphic record of northwestern Canada can be separated into three unconformity-bounded sedimentary successions named, from oldest to youngest, A-B-C (Young et al., 1979) (Figure 2.1). The erosional unconformity between sequences A and B is considered to reflect a tectonic disturbance accompanying amalgamation of Rodinia (1100-1050 Ma) while the Sequence B-C boundary signals the beginning of rifting and magmatism associated with

Rodinia’s breakup at approximately 720 Ma (Rainbird et al., 1996, 2017). Sequences A and B are preserved in the northern Cordillera and in a series of inliers located along the northern

Canadian mainland and Arctic islands (Figure 2.1). Sequence C is only preserved in the northern

Cordillera (Young et al., 1979; Rainbird et al., 1994, 1996). The Husky Creek Formation is in the uppermost stratigraphic unit of Sequence A in the Coppermine Homocline, being unconformably overlain by marine sandstones of the Rae Group (Figure 2.2).

The Coppermine Homocline

The Coppermine Homocline is located in western Nunavut and includes strata of the

Hornby Bay, Dismal Lakes and Coppermine River groups (Figure 2.3). The term “homocline” is here used purely for consistency with previous literature, as there is in fact evidence for gentle folding in the exposed strata. The Coppermine River Group comprises basalt flows of the Copper

Creek Formation and overlying red sandstone and siltstone of the Husky Creek Formation

(Baragar and Donaldson, 1973; Campbell, 1983; Hildebrand and Baragar, 1991; Skulski et al.,

2018). Basalt flows of the Copper Creek Formation are an important component of the

Mackenzie Large Igneous Province (Kerans, 1983; Hildebrand and Baragar, 1991; LeCheminant and Heaman,1989; Skulski et al., 2018), which also includes the Muskox intrusion and the nearly pancontinental Mackenzie dyke swarm (red lines in Figure 2.3) (Kerans, 1983; LeCheminant and

Heaman, 1989; Hildebrand and Baragar, 1991). Basalts of the Copper Creek Formation form an approximately 2.5 km-thick, stepped plateau across the Coppermine Homocline (Figure 2.3).

Two periods of deformation (an earlier easterly trending folding associated with southerly vergent thrusting; and a later, northerly trending folding) occurred after the deposition of the

Husky Creek Formation, but prior to the deposition of strata belonging to the Rae Group (Shaler

Supergroup, Sequence B; Figures 2.2 and 2.3) (Hildebrand and Baragar, 1991).

2.3 Previous Work

The Husky Creek Formation was originally described by Baragar and Donaldson (1973), with the type section recognised along the Coppermine River. These authors noted that the basalts of the Coppermine River Group are partially contemporaneous with the sandstones of the

Husky Creek Formation. Due to their compositional immaturity, the sandstones weather recessively, with exposures being limited to canyon sections along the Coppermine River, its tributaries, and areas where interbedded basaltic flows have protected the erosion of sandstone

(Baragar and Donaldson, 1973; Campbell, 1983). Further work by Campbell (1983) included the collection of palaeocurrent data from three locations along the Coppermine River. These data pointed to polymodal sediment dispersal, yet with overall southwestward transport (see below).

These aspects were interpreted to represent accumulation of the Husky Creek Formation in a southwest-trending valley, predominantly filled with volcaniclastic detritus and potentially associated pyroclastic material. U-Pb detrital zircon geochronology of a sample from near the top

of the Husky Creek Formation produced a maximum age of deposition of 1232 ±15 Ma (Rayner and Rainbird, 2013).

2.4 Stratigraphy

General Description

The Husky Creek Formation has a thickness of approximately 1900 m at the type section, a figure calculated from bedding orientation measurements plotted in a GIS environment from strata exposed along the Coppermine River. The formation thickens slightly westward of the river transect (Figure 2.3). A summary of the formation’s stratigraphy is reported in Figure 2.4, and photographs from outcrops and thin sections are reported in Figures 2.5–2.8. The Husky

Creek Formation consists largely of red lithic arenite, siltstone, and local oligomictic conglomerate layers intercalated with basalt flows (Figure 2.4). The framework of the sedimentary rocks that comprise the Husky Creek Formation consists of lithic fragments, altered plagioclase, and quartz with interstitial carbonate and Fe-oxide cement (Figure 2.6f).

Intraformational mud clasts abound throughout the entire formation. Heavy mineral bands defined by dark laminae and predominantly composed of hematite and ilmenite are common

(Figure 2.8a). The Husky Creek Formation overlies flood basalts of the Copper Creek Formation, which is interpreted to be the extrusive component of the Mackenzie Large Igneous Event (Ernst et al., 1995). The sharp but conformable contact between sandstones of the Husky Creek

Formation and the underlying lava flows of the Copper Creek Formation is undulatory at the outcrop scale, with swales 30-50 cm deep, spaced approximately10 m apart (Figure 2.5a). The uppermost basalt of the Copper Creek Formation is heavily vesiculated, with evidence for magma-sediment mingling (peperite texture) indicating that the Husky Creek Formation was

water-saturated and unlithified during eruption of the lava flow (cf. Busby-Spera and White,

1987). This indicates that there was no significant time gap between deposition of the lava and the sandstone. Similar mingling features were observed between the interbedded basalts and lithic-rich sandstones within the Husky Creek Formation, with basalt flows being heavily vesiculated near the contact peperite (Figure 2.5b). The Husky Creek Formation is unconformably overlain by grey-green, shallow marine sandstone and siltstone of the Escape

Rapids Formation (Rae Group; Figure 2.5c).

2.5 Facies Descriptions

Fourteen facies were identified and are representative of three depositional settings: fluvial channel-belt (FCB), fluvial floodplain (FFP), and aeolian (EOL). The facies were recognised in three detailed (5 cm resolution) stratigraphic columns totalling 180 m (see

Appendix A-C). The stratigraphic sections, together with bedding orientation data plotted in GIS environment, were used to construct the generalized stratigraphic column for the entire Husky

Creek Formation (Figure 2.4).

Planar-bedded Sandstone (facies 1)

Description. This facies is composed of poorly to moderately sorted, fine- to medium- grained (locally coarse-grained) lithic wacke to lithic arenite. Beds display plane-parallel lamination and in planview primary current lineation was recognised (Figure 2.6a, b). Bedding is tabular and generally between 0.1–1.0 m and up to 2.3 m thick. Mud-rich intraclasts are common in these beds and are locally imbricated. This facies commonly separates cross-bedded units.

Polygonal fracturing defined by positive relief on bedforms is locally observed.

Interpretation. Plane beds occur during upper-flow-regime waterflows and, accordingly, this facies is interpreted to represent the aggradation of upper-flow-regime traction carpets either: along channel bottoms during flood conditions; or along shallowly submerged bar tops during waning-flood stages (Cant and Walker, 1975). The presence of intraformational mud-rich clasts indicate rip-up and entrainment of mud-rich units during phases of fluvial incision (e.g., Ielpi and

Ghinassi, 2016). Alternatively, these bedforms could reflect the migration of low-relief bed waves over aggrading upper-stage plane beds (e.g. Bridge and Best, 1997).

Planar Cross-bedded Sandstone (facies 2)

Description. This facies is composed of moderately sorted medium-grained lithic wacke and lithic arenite that exhibits cross stratification (Figure 2.6d). This facies is subordinate relative to the trough cross-bedded facies (see below). Foresets are planar with angular relationship with bottomsets. Beds are tabular and 0.2-5.6 m thick. Mud-rich intraclasts are present in thinner beds.

Interpretation. This facies is interpreted to represent accretion and reworking of straight, long-crested dunes during lower- to near-transitional flow regime waterflows, or the accretion of small bar slipfaces (e.g. Todd and Went, 1991; Collinson et al., 2006) within fluvial channels.

Trough Cross-bedded Sandstone (facies 3)

Description. Trough cross-bedding is the most abundant facies in the Husky Creek

Formation. Beds are 0.2-5.5 m thick along measured sections. This facies consists of tabular beds of moderately sorted medium-grained lithic wacke-lithic arenite with intersecting trough forms

(Figure 2.6e). Mud-rich intraclasts are also common, particularly at the bases of these beds

(Figure 2.6f).

Interpretation. Trough cross bedding is interpreted to be a result of accretion of three- dimensional dunes in lower flow regime waterflow, and is the typical result of perennial discharge in relatively deep fluvial channels (Harms et al., 1975; Collinson et al., 2006).

Antidunal-bedded Sandstone (facies 4)

Description. This facies is composed of thin beds of moderately sorted, medium- to coarse-grained lithic arenite, < 30 cm thick and displaying sigmoidal cross-bedding and small- scale (~5 cm in relief) undulatory bedding. Beds scour underlying strata. Mud-rich intraclasts are also common.

Interpretation. This facies is interpreted to represent accretion and reworking of plane and antidunal beds in transitional (sigmoidal cross bedding) to upper flow regime (undulatory bedding) conditions within the fluvial channel-belt (Fielding, 2006).

Soft-sediment Deformed Sandstone (facies 5)

Description. This facies is composed of poorly to moderately sorted, fine- to medium- grained lithic arenite that displays extensive internal deformation. Internal deformation occurs in both plane beds and cross bedded units.

Interpretation. This facies is interpreted to represent gravitational destabilization that affected a water-saturated and unconsolidated sediment soon after deposition, leading to fluidization and upward water escape (Collinson et al., 2006). Fluidization may be caused by either seismicity or flow-induced sediment shearing (Owen and Santos, 2014).

Ripple Cross-laminated Sandstone (facies 6)

Description. This facies is composed of moderately to well-sorted fine- to medium- grained lithic wacke and lithic arenite with unidirectional ripple forms (Figure 2.6b). Ripple cross stratified layers (including laminae and beds) are < 5 cm thick, forming tabular cosets up to

10 m thick. Mud-rich intraclasts are also present in places. Symmetrical ripples are observed in discrete <5 cm thick beds.

Interpretation. This facies is interpreted to represent deposition and reworking in ripple- bed, lower flow regime conditions within fluvial channels (Jopling and Walker, 1968).

Symmetrical ripple forms relate to oscillatory flow from wave agitation in shallow water

(Clifton, 2006), potentially within a floodplain pond.

Massive Sandstone (facies 7)

Description. This facies is rarely observed and consists of structureless fine- to medium- grained lithic wacke- lithic arenite. Beds are thin, <10 cm thick and tabular. This facies also contains layers rich in mud intraclasts.

Interpretation. The presence of massive sandstone units is indicative of depositional freezing of laminar, high-density flows, potentially triggered by a flooding event (Reading and

Collinson, 1996) within the fluvial channel-belt. Alternatively, pedogenesic processes may have obscured primary hydrodynamic structures in a floodplain environment or a shallow channel bed subject to seasonal sub-aerial exposure (e.g. Marconato et al., 2014; Ielpi et al., 2016).

Mud-rich Sandstone with Polygonal Fractures (facies 8)

Description. This facies is composed of tabular beds of lithic-rich siltstone and fine- grained lithic wacke and arenite, which displays a faint planar lamination disrupted by polygonal fractures (Figure 2.7c). Individual fractures are recessive on outcrops and are defined by subtle grain-size variation. This facies is represented by beds <10 cm thick and seldom occurs throughout the Husky Creek Formation, although it was best observed in the lower 250 m of the stratigraphy.

Interpretation. The facies represents the deposition of fine-grained sand and silt by low- strength, shallow waterflows, likely in a channel-proximal overbank environment (cf. Fralick and

Zaniewski, 2012). The polygonal fractures that intersect the planar lamination indicates the later development of incipient desiccation structures, in response to repeated expansion and contraction due to wetting and drying of cohesive material (Reading and Collinson 1996;

Marconato et al., 2014). The facies, therefore, indicates periodic sub-aerial exposure, and possibly incipient pedogenesis (Collinson et al., 2006).

Nodule-rich Sandstone (facies 9)

Description. This facies is composed of tabular beds of medium-grained, poorly sorted, massive lithic arenite containing spherical to oblate, reddish brown, 1-5 cm nodules composed of calcite and lithic fragments (Figure 2.7a). This facies is limited to the lower Husky Creek

Formation, specifically along a zone overlying thick mudstone-siltstone deposits (Figure 2.4).

Interpretation. This facies is interpreted to represent pedogenesis on exposed banks of river channels, or nearby floodplain tracts, upon recessing water levels. The presence of nodules potentially indicates a semi-arid environment where evapotranspiration is equal to, or greater

than, precipitation with alkaline pore water both percolating down from surface to a near surface layer and being drawn up by capillary action (Collinson et al., 2006).

Sandstone with Adhesion Warts (facies 10)

Description. This facies consists of fine- to medium-grained lithic arenite with irregular warts, 5-10 mm across and with about 1 mm of relief, superimposed on the stratification planes of underlying sedimentary structures. Beds are generally <5 cm thick. This facies is also characterized by an absence of intraclasts.

Interpretation. The presence of adhesion warts superimposed on other sedimentary structures indicates that sediment was wind-blown onto older deposits while they were still damp, or in response to daily fluctuations in atmospheric humidity (Olsen et al. 1989). Owing to their irregular shape, adhesion warts are typically related to frequently changing wind directions

(Collinson et al., 2006).

Large-scale Trough Cross-bedded Sandstone (facies 11)

Description. This facies is composed of well-sorted fine- to medium-grained, moderately sorted, lithic arenite with tabular to wedge-shaped beds of intersecting trough forms (Figure

2.8d). Pin-stripe lamination (described in higher detail below) is present in bottomsets (Figure

2.8b, c). Beds are 0.3–1.2 m thick along logged sections (Appendix A, B). Additionally, this facies is characterized by an absence of intraclasts and slightly higher compositional and textural maturity in comparison to other sandstone facies.

Interpretation. This facies is interpreted to represent the migration of aeolian dunes and associated scour pits (Mountney and Thompson, 2002). Grains are still texturally and chemically

immature, suggesting that sediment was likely re-worked from fluvial deposits in a short timespan.

Pin-stripe-laminated Sandstone (Facies 12)

Description. This facies is composed of well-sorted fine- to medium-grained, lithic arenite that displays pin-stripe lamination (Figure 2.8a,c) defined by well-developed grain-size segregation (Fryberger and Schenk, 1988). Laminae are moderately well sorted and commonly inversely graded. Such sandstones have slightly higher compositional maturity in comparison to other sandstone facies. Beds are tabular, generally 10 cm thick and laterally discontinuous.

Additionally, these beds are closely associated or interbedded with facies 11. This facies is also characterized by an absence of intraclasts.

Interpretation. This facies is interpreted to represent accretion and migration of subcritically climbing wind ripples (Hunter, 1977; Fryberger and Shenk, 1988; Collinson et al.,

2006). As grains are still texturally and chemically immature, sediment was likely re-worked from fluvial deposits in a relatively short time span.

Massive Mudstone and Siltstone (facies 13)

Description. Massive, lithic-rich mudstone and siltstone form a ca. 60 m-thick bedset in the lower 125 m of the Husky Creek Formation (Figure 2.4). In the lower portion of this bedset, bladed calcite rosettes, 0.25–2.00 cm wide, have been observed (Figures 2.4, 2.6).

Interpretation. This facies originated after deposition of fine-grained fractions in a floodplain tract located far away from active channels, likely due to fallout of suspended load fed by diluted and low-energy overbank flows (Miall, 2010). The floodplain was also likely subject

to evaporative concentration of solutes (Potter et al., 2005; Collinson et al., 2006), as indicated by the occurrence of the bladed rosettes. The latter are interpreted as pseudomorphs after an evaporitic mineral, possibly aragonite, suggesting arid to temperate conditions where evaporation exceeds discharge (Potter et al., 2005).

Crudely Bedded Conglomerate (facies 14)

Description. Oligomictic, matrix-supported conglomerate with 1-40 cm angular to sub- angular clasts of mudstone, siltstone, and basalt, typifies this facies. Only crude tabular bedding is locally observed, forming beds roughly 30–50 cm thick. Clasts are angular to sub-angular, and generally fine upward throughout a bed. This facies was only observed in one location, where it directly overlies an intra-formational basalt flow. The bedset is approximately 10 m thick.

Interpretation. The facies is interpreted to represent deposition by highly concentrated and matrix-rich flows that were capable of entraining coarse detritus from locally eroded basalt

(Collinson et al., 2006). The matrix-supported and yet fining-upward character of these beds suggests that flows might have experienced a transition from plastic to viscous rheology over short transport distance (Benvenuti, 2003).

2.6 Facies Associations

Fluvial Channel-Belt Facies Association (FCB)

This facies association describes the majority of strata exposed along the Coppermine

River transect, comprising facies 1, 2, 3, 4, 5, 6, 7 and 14. Sandstones in this facies association are immature, pointing to a proximal sediment source with limited reworking and transport.

Overall, the abundance of unidirectional cross-strata and the pervasive early diagenetic

reddening supports deposition by sustained flow in a continental, oxidizing, environment – most likely a set of channel belts. Perennial discharge is indicated by the abundance of trough-cross and planar-cross beds (Facies 2 and 3), which accumulated in deeper portions of fluvial channels

(Cant and Walker, 2975; Todd and Went, 1991; Collinson et al., 2006). Ripple cross-lamination

(Facies 6) indicates deposition in low-energy environments by weaker stream flows (Jopling and

Walker, 1968). Rare massive sandstone units suggest that large flooding events seldom lead to flow-induced soft-sediment deformation. Plane-laminated sandstones (Facies 1) alternating with thin siltstone to fine sandstone beds with desiccation cracks separate large-scale cross-bedded units (Facies 2 and 3) and are interpreted to represent subaerial exposure after episodes of channel avulsion. The thickest stacks of cross-bedded sandstone observed on outcrop (~6 m) suggests as a first order approximation (e.g. Ielpi et al., 2017) that the larger channels in the

Husky Creek fluvial systems may have reached ~6 m depth, a feature that is possibly consistent with channels a few hundred metres wide (Ielpi et al., 2017). The lack of extensive three- dimensional exposures where channel-bar complexes could be observed in their entirety hampers any interpretation of fluvial planform. Furthermore, although this facies association is dominated by cross-bedded units that typically occur in perennial discharge regimes, they are commonly separated by upper-flow regime bedforms, typically plane beds. The co-occurrence of upper and lower flow regime bedforms may be interpreted as a transition from a perennial discharge regime conducive to the formation of thick cross-bedded units (facies 2 and 3) (Long, 2011) to more ephemeral discharge regimes, which produced planar laminated sandstone units (facies 1) during high-discharge stages (Long, 2011), or to supra-elevated portions of channel belts (i.e. bar tops) where shallower water favoured the establishment of supercritical flow conditions.

Fluvial-floodplain facies association (FFP)

Facies 6, 7, 8, 9, and 13 comprise the fluvial-floodplain facies association. These facies share compositional and textural similarities to the fluvial channel-belt facies association, although the detritus is generally finer grained, indicating lower flow strength at time of deposition. A roughly 60 m thick massive mudstone-siltstone unit with evaporitic pseudomorphs is a prominent feature of the lower Husky Creek Formation (facies 14), in addition to subordinate massive sandstone beds that contain pedogenic nodules along specific horizons (facies 9) (Figure

2.7b). Additionally, thin beds of weathered sandstone and mudstone with desiccation cracks and polygonal fracturing were observed throughout the formation (Facies 8). These facies are bounded by large-scale cross-bedded units associated with the fluvial channel-belt (facies 2 and

3). This association is interpreted to represent a floodplain adjacent to a channel-belt that was subject to periodic flooding and drying as well as pedogenesis along channel banks (e.g.

Marconato et al., 2014; Ielpi et al., 2018). Units in this facies association were deposited after abandonment of fluvial channels or in ephemeral floodplain lakes (Potter et al., 2005), a depositional motif that can be linked to the occurrence of stacked cross-bedded units separated by thin floodplain deposits. Aeolian deposits (see below) are found in juxtaposition with this facies association, suggesting that aeolian dune fields were proximal to the fluvial floodplains.

Aeolian Facies association (EOL)

This facies association consists of facies 10, 11 and 12; these facies are more compositionally and texturally mature than the fluvial associations described above. Irregular adhesion surfaces (Facies 10) superimposed on fluvial bedforms as well as thin, spatially limited pinstripe laminated beds (Facies 12) bounded by fluvial bedforms are representative of aeolian

re-working of fluvial derived sediment and deposition after channel abandonment. Overall, this interpretation is corroborated by the occurrence of pin-stripe lamination, a distinctive feature of aeolian deposits (Hunter, 1977; Fryberger and Schenk, 1988). Large scale (~1 m in logged sections, with exposure along the river ~5 m thick) sets of well sorted, pinstripe laminated trough cross-bedded sandstone (Facies 11) underlain by pin-stripe laminated plane parallel beds (Facies

12) are interpreted to represent aeolian deposition in dune fields (Ielpi et al., 2016). The framework sediment remains angular to sub-angular and is compositionally immature (Figure

2.8a) indicating that reworking by aeolian processes was relatively limited and the aeolian facies are generally bounded by fluvial deposits, suggesting that the dune fields were proximal to the floodplain and channel belt elements.

2.6 Stratigraphic Variations

Grain size is relatively homogenous throughout the Husky Creek Formation (Figure 2.4); that being said, a first-order coarsening upward trend can be observed throughout the formation and is shown by the presence of a mudstone near the base, sandstones mid-section and occasional gravel beds near the top of the formation (Figure 2.4). Furthermore, two smaller-scale fining-upwards trends are observed: 1) along the lowest 125 m of the formation, where medium- grained sandstones are overlain by a 60 m-thick mudstone-siltstone; and 2) along the top 200 m of the formation’s stratigraphy, where a volcaniclastic conglomerate passes upward into medium-grained sandstone (Figure 2.4). Local variations in grain size are observed where medium grained sandstone associated with the fluvial channel-belt are overlain by finer grained floodplain associated sandstone.

2.7 Palaeoflow Analysis

A total of 265 palaeoflow measurements were collected from 10 stations; 9 from outcrops along the Coppermine River and one located roughly in the center of the outcrop belt (Figure

2.9). Estimation of palaeocurrent direction was based on the azimuth of foreset dip direction in planar- and trough-cross bedded and ripple-cross laminated sandstone. The palaeoflow patterns throughout the Husky Creek Formation have high dispersion with a general indicated transport to the WNW. Individual palaeoflow stations exhibit unimodal distribution varying from WSW to

WNW, while other palaeoflow clusters are polymodal. The cumulative results thus suggest overall sediment sourcing from the ESE. This result is significant in that the source area projected from palaeoflow data roughly corresponds to the Muskox Intrusion, a possible source for the medium- to coarse-grained mafic clasts present in the Husky Creek Formation. Notably, these palaeoflow results differ from Campbell (1983) (Figure 2.9), potentially as a result of sample bias, and a higher number of bedforms measured in this study. This aspect could also indicate that sediment accumulated in a WNW trending valley as opposed to the SW trending valley proposed by Campbell (1983). Field observations suggest the outcrop exposure may not necessarily be lens-shaped, which may influence the interpretation of a valley. In agreement with both interpretations, the polymodal nature of some palaeoflow measurements is postulated to reflect fluvial transport from valley flanks (Campbell, 1983). Limited aeolian palaeoflow measurements yield a bimodal distribution, indicating prevailing winds from the SE and N

(Figure 2.9).

2.8 Depositional Style

Overall, facies and palaeoflow analysis indicates that the Husky Creek Formation is the record of a river system deposited within a valley with aeolian and floodplain deposits (Figure

2.10). This inference is supported by the potential lens shaped aspect of the formation’s outcrop belt, and the dominance of unidirectional sedimentary structures, predominantly of fluvial origin, trending towards the WNW. The cumulative palaeoflow trend indicates provenance from the interior of the Proterozoic Laurentian landmass. Little is known at this stage about the mechanisms responsible for subsidence generation in the area; loading from the extensive

Copper Creek Formation flood basalts and Husky Creek Formation basalt flows, as well as local faulting, may have contributed to basin subsidence and expansion of drainage watersheds.

Despite a first-order coarsening upwards grain-size trend observed throughout the formation’s stratigraphy, the grain size is overall homogeneous (Figure 2.4), a feature that may be related to a state of near-equilibrium between subsidence, aggradation and sediment supply (Lebeau and

Ielpi, 2017). That being said, the local occurrence of fine-grained units represents the establishment of mature floodplain tracts located away from active channels, whereas coarser volcaniclastic sediment found in association with basalt may indicate the generation of local topography in response to magma extrusion. Floodplain bedsets in the Husky Creek Formation are important indicators of the local hydrologic budget at the time of deposition. Specifically, the presence of evaporitic pseudomorphs and pedogenic nodules indicate a setting where evaporation exceeds recharge for a significant portion of the year. The observations above, coupled with the presence of adhesion structures and desiccation cracks also suggests an arid to temperate palaeoclimate (Ielpi et al., 2018). These observations suggest that the Husky Creek

Formation might have been deposited in an endorheic basin, i.e. an inland sink, or a basin in only partial communication with an open sea. The interpretation of an arid-temperate palaeoclimate may not be representative of the whole formation as mud units are abundant given the expected lack of weathering in an arid-temperate environment.

2.9 Conclusions

The Husky Creek Formation, a sandstone-dominated succession forming the topmost portion of the Coppermine Homocline, western Nunavut, represents a sedimentation event that closely followed the emplacement of a thick succession of lava flows represented by the Copper

Creek Formation, which is in turn part of the extensive Mackenzie Large Igneous Province.

Deposition in sub-aerial settings is indicated by sandstone reddening, although this could have also occurred during early diagenesis through interaction of oxidized groundwater with iron bearing minerals. The Husky Creek Formation displays abundant unidirectional flow structures, which suggest that the bulk of the formation was deposited in a terrestrial environment that includes fluvial channel-belts, floodplains, and aeolian dunes (Figure 2.10). Occurrence of both lower- and upper-flow-regime sedimentary structures points to the alternation between phases of perennial and seasonal discharge, and frequent channel avulsion is indicated by the pervasive occurrence of intraformational mud-rich clasts. Furthermore, the occurrence of desiccation cracks, pedogenic nodules, adhesion surfaces, and pin-stripe lamination of aeolian origin reinforce the interpretation of deposition in a sub-aerial environment, and specifically an endorheic setting where evaporation exceeded hydrologic recharge for part of the year. The abundance of lithic fragments with angular to sub-angular grains, with low sphericity and moderate sorting, suggests a proximal sediment source with limited transport, reworking, or

chemical weathering (Allen, 1982). The potential lens shaped aspect of the outcrop belt, and the overall trend of palaeoflow indicators support the interpretation of the Husky Creek Formation being deposited in a WNW-trending valley. In conclusion, the field observations collected in this study help refine the palaeogeographic and palaeoclimate setting of northwestern Laurentia

(present coordinates) in the late Mesoproterozoic. Forthcoming studies on the Husky Creek

Formation will focus on its provenance, which will be resolved with detrital zircon U-Pb geochronology.

2.10 Acknowledgements

RM received a financial bursary from the Research Affiliate Program of Natural

Resources Canada, and by a Discovery Grant from the Natural Sciences and Engineering

Research Council of Canada to AI. Logistical support was provided by the Geo-mapping for

Energy and Mineral Program of NRCan and by the Agouron Institute (agi.org). We thank Bill

Davis for his critical review of the paper.

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2.12 Figures

Figure 2-1: Study Area

Location of study area in western Nunavut (black box) with extent of sequence A stratigraphy highlighted in yellow (after Young et al., 1979).

Figure 2-2: Coppermine Homocline stratigraphy Generalized stratigraphy of the Coppermine Homocline. Modified from Young et al., 1979 with ages from Raynor and Rainbird, 2013 and Lecheminant and Heaman, 1989

Figure 2-3: Regional geology Regional geology of the Coppermine Homocline from Skulski et al., 2018.

Figure 2-4: Husky Creek Formation Stratigraphic Log

Generalized stratigraphic column of the Husky Creek Fm. through transect of exposed strata along the Coppermine River. (FCB: Fluvial Channel Belt, FFP: Fluvial Flood Plain, Eol:

Aeolian)

Figure 2-5: Husky Creek Formation contact relationships

A) Contact between red lithic arenite of the Husky Creek Formation and underlying basaltic lava flows of the Copper Creek Formation. Also shown is a close-up of the contact between basalt/peperite and overlying red sandstone B) Note mingling of red sand and darker lava at contact between the Husky Creek Formation and the Copper Creek Formation. C) Dashed lines represent the extent of a basalt flow in upper Husky Creek Formation. Field of view is roughly

250 m. D) Close-up showing the globular peperites at the contact between basalt (green) and sandstone (red) in the upper Husky Creek Formation. E) Unconformable contact between grey- green shallow marine sandstones of the Escape Rapids Formation and the underlying sandstone of the Husky Creek Formation (lens cap, encircled for scale, is roughly 7 cm in diameter).

A) Plane-parallel lamination with mud-rich intraclasts. B) Plan view of bedding surface

exhibiting primary current lineation. C) Flow ripples. D) Planar-cross stratified beds. E) Trough-

cross stratified beds. F) Photomicrograph of fluvial sandstones with a framework composed of

elongate, mud-rich intraclasts, quartz, and altered volcanic rock fragments and feldspar grains.

Minor mud matrix, with Fe-oxide and calcite cement. Magnification: 1.25x, plane-polarized

light.

Figure 2-6: Fluvial deposits

Figure 2-7: Floodplain deposits

A) Horizons of pedogenic nodules (lighter brown) in massive sandstone. B) Bladed evaporitic

pseudomorph clusters in massive mudstone-siltstone. C) Desiccation cracks.

Figure 2-8: Aeolian deposits

A) Thin section scan (plane polarized light) of pinstriped, planar laminated aeolian lithic arenite.

Note the absence of mud intraclasts, and better sorting in comparison to the fluvial sandstones in

Figure 2.6h. B) Pinstripe laminated cross beds. C) Pinstripe laminated lithic arenite at the base of larger aeolian dunes. D) Adhesion warts on asymmetrical 3D ripples. E) Large-scale, trough cross stratified sandstone representing aeolian dunes that developed off the margins of abandoned channels.

Figure 2-9: Palaeocurrent analysis

(Left) Map of the Husky Creek Formation (modified from Hildebrand. 2011) with cumulative fluvial and aeolian palaeoflow

displayed in the top left and fluvial palaeoflow throughout the formation. (Right) Palaeocurrent results from Campbell 1983.

Figure 2-10: Depositional model

Depositional model inferred for the Husky Creek Formation displaying the close association of channel belt, floodplain, and aeolian elements. No scale is implied.

Chapter 3 Sedimentology and Detrital Zircon Geochronology of the

Mesoproterozoic Husky Creek Formation: A fluvial sandstone recording the waning stages of one of Earth’s largest magmatic episodes.

Robert Meek a*, Alessandro Ielpi a, Robert H. Rainbird b, William J. Davis b.

a Harquail School of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada b Geological Survey of Canada, 601 Booth Street, Ottawa, Ontario K1A 0E8, Canada

3.1 Abstract

Thick Proterozoic sedimentary and volcanic successions exposed across northwestern

Canada record supercontinent assemblage and breakup. One such sedimentary unit, the

Mesoproterozoic Husky Creek Formation, provides an opportunity to study the interaction between contemporaneous sedimentation and flood-basalt volcanism related to a large igneous event. Part of a regionally exposed volcano-sedimentary succession, known as the Coppermine

Homocline, the Husky Creek Formation overlies the Copper Creek Formation, a ca. 2.5 km thick, regionally extensive basaltic plateau that records volcanism linked to the 1.27 Ga

Mackenzie Igneous Event – one of the largest magmatic episodes in Earth’s history. The Husky

Creek Formation is approximately 1900 m thick with predominantly fluvial-channel and subordinate floodplain and aeolian strata dominated by lithic detritus intercalated with basalt flows. Sensitive high resolution ion microprobe (SHRIMP) U-Pb dating of detrital-zircon grains

collected from four stratigraphic levels of the Husky Creek Formation reveal four main age groupings: (1) a 1270 Ma peak attributed to the Mackenzie Igneous Event; (2) a 1600-2014 Ma grouping attributed to the Narakay Volcanic Compex and rock units of the Wopmay orogen; (3) a 2050- 2550 Ma grouping attributed to Thelon-Taltson orogenesis, plutonic and metamorphic rocks from the Queen Maud Block, and Arrowsmith orogenesis; and (4) a >2580 Ma grouping attributed to the detritus derived from the Archean Slave Province. Detrital zircons in groupings

2-4 are likely polycyclic grains sourced from older basins exposed elsewhere in the Canadian

Shield, e.g., the Hornby Bay or Elu basins. An upsection decrease in ca. 1270 Ma zircon grains, together with a relative increase in Palaeoproterozoic and Archean grains, is interpreted to reflect the expansion of the drainage basin as the Husky Creek Formation was being deposited. A small sub-population of sub-1270 Ma zircons share textural characteristics to the Mackenzie Igneous

Event-aged zircons, suggesting protracted volcanism. Palaeoflow patterns indicate dominant west-northwest-ward transport away from the Muskox Intrusion, a known source of 1270 Ma zircons. These results altogether suggest that the Husky Creek Formation was deposited in the waning stages of the Mackenzie Igneous Event by rivers flowing in a geographically restricted basin and carved into an extensive mafic volcanic plateau. More broadly, this paper provides insight into surface processes in the aftermath of one of Earth’s largest igneous events.

3.2 Introduction

Large igneous provinces (LIPs), and particularly continental flood basalts, have been a subject of substantial research targeting their relationship to mantle plumes and continental breakup (Ernst and Buchan, 1997). While the emplacement of LIPs might bring about significant perturbations on surface processes, their cascading effects on the development and evolution of

fluvial basins is poorly constrained (Ebinghaus et al., 2014). Although well preserved in the recent geological record, LIPs of Precambrian vintage are commonly partially or completed destroyed through ensuing erosive or tectonic processes (Ernst and Buchan, 1997). Areas where significant coeval sedimentation and LIP volcanism occur are limited in the geological record and include, e.g., the Columbia River Flood Basalt Province (Ebinghaus et al., 2014) and the

Franklin-Event-equivalent Natkusiak Formation Flood Basalts and coeval sedimentation of the

Kuujua Formation (Rainbird, 1993). On a smaller scale, sedimentary and volcano-tectonic activity have been studied in the British Paleocene Igneous Province (BPIP) (Brown et al.,

2009). The presence of coeval sedimentary and volcanic units in these areas provides the rare opportunity to infer palaeo-environmental conditions and surface processes during concurrent magmatism and deposition. Particularly, the study of sedimentary units that bound LIPs may constrain elements such as timing, subsidence and uplift associated with magmatism (Rainbird,

1993). For example, bounding sedimentary units might influence the morphology of overlying basalt flows, and the emplacement of basalt flows is likewise found to influence the distribution of overlying sedimentary facies. In the Columbia River Flood Basalt Province, sedimentary facies and settings were found to be strongly influenced by flood basalt volcanic activity and the emplacement patterns of lava flows (Ebinghaus et al., 2014). Deposits of the Kuujua Formation locally controlled the emplacement of the overlying Natkusiak lavas producing loading features in the underlying sandstones, grooves from rapid sheet flow lava deposition, and potentially preserved dune surface morphology (Rainbird, 1993).

At a larger scale – i.e., that of entire sedimentary basins or volcanic provinces – inferences on the interaction between volcanic and sedimentary processes rely on tools such as detrital-zircon geochronology. Analysis of detrital zircon has been particularly important in

testing palaeocontinental reconstructions from Precambrian continental rock records, which are inherently unsuitable for other tools such as biostratigraphy (Fedo et al., 2003). Detrital zircon provenance spectra can also be used to corroborate or test different tectonic settings, thanks to the generally different age populations displayed in basins formed due to crustal convergence or relaxation (Cawood et al., 2012).

In Laurentia, the ancestral core of North America, Greenland, and the northwestern

Highlands of Scotland (Hoffman, 1988; Whitehouse et al., 1997) applications of multigrain detrital zircon geochronology has notably led to the reconstruction of Precambrian pancontinental river systems (Rainbird et al., 2012, 2017; Krabbendam et al. 2017), which exhibited drainage patterns comparable to that of modern large-scale forelands such as the

Ganges-Brahmaputra and Amazon (Rainbird and Young, 2009). In northwest Laurentia (i.e., the modern-day northwestern Canadian Arctic) thick and correlative Palaeoproterozoic to

Neoproterozoic sedimentary and volcanic sequences are preserved (Young et al., 1979; Rainbird et al., 1992, 1994, 2017). The reconstruction of their stratigraphy has been fundamental in understanding the tectonic and palaeogeographic history of the later part of the Precambrian

(Rainbird et al., 1997; Zhao et al., 2004).

This study presents the first combined stratigraphic and U-Pb detrital zircon analysis of the Husky Creek Formation, a redbed succession that overlies volcanic rocks of the large

Mackenzie LIP (Ernst and Buchan, 1997; Skulski et al., 2018). In combination with detailed stratigraphy and facies analysis of the formation’s type section exposed along the Coppermine

River, this study addresses the depositional history, provenance and tectonic setting of the Husky

Creek Formation. Given the spatial and temporal relationship between the Husky Creek

Formation and the Copper Creek Formation (the extrusive member of the Mackenzie Igneous

Event) as well as the overlying Escape Rapids Formation, the Husky Creek Formation is uniquely positioned to reveal the surficial conditions immediately after one of the largest igneous events recorded in Earth’s history and prior to the amalgamation of the Supercontinent Rodinia.

3.3 Geological Setting

The Coppermine Homocline is located in northwestern Nunavut, 20-60 km south of the hamlet of Kuglutuk, and hosts thick and weakly deformed Proterozoic sedimentary and volcanic sequences that precede, and span part of, the amalgamation of supercontinent Rodinia (Young et al., 1979; Rainbird et al., 1992). The area has received attention spanning back to Samuel

Hearne’s expedition to the Coppermine River (1769-1772) (Hearne, 1795), and has been the site of mineral exploration for a variety of commodities including: uranium (Rice and Kyser, 2010), nickel and Platinum-group element mineralisation (Barnes and Francis, 1995), and stratiform copper (Bent, 2009). The area has also hosted a wide range of research in the fields of palaeobiology (Hordyskyi et al., 1985; Loron et al., 2018, 2019) palaeoclimatology (Ross and

Chiarenzelli, 1985), and igneous petrology (Dostal et al., 1983; Baragar et al., 1996).

Sedimentary and volcanic rocks exposed therein have correlative successions recognised across the western Canadian Arctic, and have been separated into three unconformably bounded sequences, labeled from oldest to youngest A-B-C (Young et al., 1979; Rainbird et al., 1996)

(Figure 3.1). An erosional unconformity between Sequence A and Sequence B is considered to reflect a tectonic disturbance associated with the amalgamation of supercontinent Rodinia at

1200–1070 Ma (Rainbird et al., 1996, 2017). The Sequences B-C boundary reflects rifting and magmatism (Franklin Igneous Event) associated with the breakup of Rodinia at about 720 Ma

(Rainbird et al., 1996, 2017). Sequences A and B are preserved in a series of inliers located along the northern Canadian mainland and Arctic islands as well as in the northern Cordillera (Young et al., 1979; Rainbird et al., 1994, 1996). The Husky Creek Formation is in the uppermost stratigraphic unit of Sequence A in the Coppermine Homocline, being unconformably overlain by marine sandstones of the Escape Rapids Formation (Sequence B, Rae Group; Skulski et al.,

2018).

The Coppermine Homocline includes, in ascending stratigraphic order, fluvial and shallow marine sandstones and carbonate rocks of the Hornby Bay, mainly shallow marine carbonate rocks of the Dismal Lake Group, and mafic volcanic and clastic sedimentary rocks of the Coppermine River Group (Kerans et al., 1981; Hahn et al., 2013; Rainbird et al., in prep.)

(Figure 3.2). The latter is composed of extensive basalt flows of the Copper Creek Formation, which is overlain by red sandstone and siltstone of the Husky Creek Formation (Baragar and

Donaldson, 1973; Campbell, 1983; Hildebrand and Baragar, 1991; Skulski et al., 2018). Basalt flows of the Copper Creek Formation are interpreted to be the extrusive component of the

Mackenzie Large Igneous Province (Kerans, 1983; Hildebrand and Baragar, 1991; LeCheminant and Heaman, 1989; Skulski et al., 2018). This magmatic episode, thought to represent one of the largest igneous events in Earth’s history, is also responsible for the emplacement of the Muskox intrusion and the pancontinental Mackenzie dyke swarm (Kerans, 1983; LeCheminant and

Heaman, 1989; Hildebrand and Baragar, 1991). Emplacement of all members of the Mackenzie igneous event occurred in a short timeframe, i.e. < 5 Ma (LeCheminant and Heaman, 1989;

Dupuy et al., 1992; Mackie et al., 2009). The Copper Creek Formation basalts form an approximately 2.5 km-thick, stepped plateau across the Coppermine Homocline (Skulski et al.,

2018). Campbell (1983) proposed that the Husky Creek Formation is at least partly coeval with

the Copper Creek Formation. Arkosic sandstones, siltstones and minor mudstones of the Algak

Formation and the Ekalulia Formation basalts in the Bathurst inlet area are proposed to be correlative to the Husky Creek Formation and Copper Creek Formation respectively (Campbell,

1978; Kerans et al., 1981).

3.4 Sedimentology and Petrography

Field Methods

Work on sedimentology and petrography is based on a combination of: (i) facies analysis, bed-by-bed measurement of stratigraphic sections, and collection of palaeoflow indicators based on the progradation azimuth of cross-strata; (ii) analysis and interpretation of petrofacies in thin- sectioned samples imaged though petrographic microscope. Grain size was estimated in the field by use of a particle chart, and then measured with the petrographic microscope. The dataset of field observations was collected along 18 GPS-referenced stations that were accessed through white-water canoes and helicopter over a five day period. A low-resolution section was reconstructed throughout the entire stratigraphic span of the Husky Creek Formation, and three additional sections were also measured bed-by-bed at a vertical resolution of 5 cm, totalling of

184 m of high-resolution stratigraphy. Furthermore, a total of 265 palaeoflow indicators were collected from 10 of the above stations (9 from outcrops along the Coppermine River and one located roughly in the centre of the outcrop belt).

Results

The Husky Creek Formation is predominantly composed of medium-grained lithic arenite, with subordinate lithic graywackes, mudstones, and lithic-rich conglomerates. Peperite is present at the contact between the Husky Creek Formation and the Copper Creek Formation, suggesting a limited gap in time between the two units (Meek et al., 2019). Peperite is also present at the contact between other basalt and sandstone units within the Husky Creek

Formation. The upper contact between the Husky Creek Formation and marine sandstones of the

Escape Rapids Formation (Rae Group) is unconformable and represents the boundary between

Sequence A and B (Figure 3.4). Petrographic observations from the samples used in this study are summarised in Table 3.1. The framework sediment of all samples is dominantly composed of lithic (volcanic) fragments with subordinate plagioclase and quartz. There is an increase in quartz relative to the lithic fragments between the basal sample and the other samples taken higher up in stratigraphy (transition from <20% quartz to ~30% quartz). The grains generally retain their angularity (Figure 3.5). Exotic grains such as glauconite (only two occurrences recorded) is present in sample 17-RATR-26. A detailed analysis of sedimentary facies and architecture is provided by Meek et al. (2019) with the facies summarised in Table 3.2. Three facies associations were recognised: fluvial channel-belt, fluvial floodplain, and aeolian (Figure 3.6).

The majority of strata exposed along the Coppermine River belong to the fluvial channel-belt facies association; there, a sub-equal abundance of trough-cross and planar-cross beds points to alternating episodes of perennial and seasonal discharge (Fielding et al., 2018). Cross sets are tabular to wedge shaped, commonly 1–2 m thick with a maximum measured thickness of 5.6 m

(Meek et al., 2019). Based on the work by Ielpi et al. (2017), first-order estimate of channel depth derived from bedform thickness of approximately 6 m provide an inferred channel width of 20–350 m. Subordinate fluvial floodplain facies are generally finer grained, and commonly

record evidence for sub-aerial exposure, such as evaporitic pseudomorphs, pedogenic nodules, adhesion structures, and desiccation cracks. The fluvial floodplain facies display evidence for deposition in lower flow-strength regimes with respect to the aforementioned channelised facies association; these characteristics overall point to a floodplain environment developed in a temperate climate setting where evaporation episodically exceeded recharge throughout the year

(Ielpi et al., 2018). Aeolian facies are more compositionally and texturally mature, with rounder grains, well-defined sorting, and less lithic fragments than the fluvial facies associations.

However, framework grains remain sub-angular and is compositionally immature, suggesting aeolian processes were limited and the dune fields were proximal to floodplain and channel-belt elements (Lebeau and Ielpi, 2017).

Palaeoflow

The fluvial palaeoflow patterns generally display high dispersion, with overall west- southwest to west-northwest distribution. At seven stations, palaeoflow displays unimodal distribution, while a polymodal distribution is recorded at three other stations (Figure 3.7). The cumulative results from the palaeoflow measurements indicates an average transport direction of

287.9o ± 11.1o.

3.5 Detrital zircon geochronology

Sampling Strategy and Analytical Methods

Four samples of the Husky Creek Formation, each about 5 kg in weight, were collected for detrital-zircon analysis (Figure 3.3). Two samples from the lower Husky Creek Formation

were collected, respectively, 1m directly above the unconformable contact between the Copper

Creek and Husky Creek formations (17-RATR-21), and about 60 metres stratigraphically above said contact (17-RATR-26). The third sample was collected near the formation’s stratigraphic midpoint (17-RATR-31), and the fourth sample was collected near the formation’s upper unconformable contact with the Escape Rapids Formation (17-RATR-34) (Figure 3.3). These samples were crushed by mechanical disaggregation, and then underwent heavy minerals separation using a Wilfley table followed by heavy liquid separation at the Geochronology facility of the Geological Survey of Canada in Ottawa, Ontario, Canada. Zircon was sorted using a Frantz isodynamic separator to a non-magnetic fraction at 1.8 ampere and 10-degree side- slope. Zircon grains were first selected randomly for the provenance study from each sample location and afterwards a sub population from each sample location was picked, targeting euhedral zircon grains. They were then cast in a 2.5 cm diameter epoxy mount (along with fragments of the GSC laboratory standard zircon; z6266, with 206Pb/238U age = 559 Ma (Stern and Amelin, 2003). The mid-sections of the zircon grains were exposed using 9, 6, and 1 μm diamond compound, and the internal features of the zircon grains (such as zoning, structures, alteration, etc.) were characterized in back-scattered electron mode (BSE) utilizing a Zeiss Evo

50 scanning electron microscope. The count rates at eleven masses (YbO, Zr, HfO, 204Pb, background, 206Pb, 207Pb, 208Pb, 238U, 248ThO, 254UO) were sequentially measured with a single electron multiplier corrected for a deadtime of 21 ns. Analytical procedures are modified from those described by Stern (1997) with data processing using SQUID2 (version 2.50.11.10 Ludwig

2009a). Age uncertainty in the data table (Appendix E) is reported at 1σ and in the text is reported at 2σ. The 1σ external errors of 206Pb/238U ratios reported in the data table (Appendix E) incorporate the error in calibrating the standard. Common Pb correction utilised the Pb

composition of the surface blank (Stern 1997). Yb and Hf concentration data were calculated using sensitivity factors derived from standard 6266 with values of 229 and 8200 ppm respectively. A secondary internal reference zircon (1242) was analysed to monitor accuracy of the measured 207Pb/206Pb ratios and correct for any instrumental mass bias. No mass bias was applied to the data. Isoplot v. 4.15 (Ludwig, 2009b), and KDX (Spencer et al., 2017) was used to calculate weighted means and kernel density estimates. The weighted mean errors are reported at

95% confidence intervals. Data was collected in two analytical sessions. The first session was conducted for the detrital zircon provenance study. The second session included additional internal standards while focussing on a sub-population of young zircon grains. In both sessions, a secondary zircon standard (9910, RAMBLER), used for the provenance study was interspersed between sample analyses to verify the accuracy of the U-Pb calibration. In the first session, where the z6266 standard was employed, the weighted mean 206Pb/238U age of 12 SHRIMP analyses of RAMBLER zircon returned an age of 437 ± 5 Ma (using a 95% confidence filter). In the second session, where the z6266 standard was employed, the weighted mean 206Pb/238U age of 8 SHRIMP analyses of RAMBLER zircon returned an age of 441 ± 2 Ma (using, again, a 95% confidence filter). The accepted 206Pb/238U age of Rambler is 441 Ma. Analyses of a secondary zircon standard z1242 were interspersed between sample analyses to assess the requirement of an isotopic mass fractionation correction for the 207Pb/206Pb age. In the first session the weighted mean 207Pb/206Pb age of 33 analyses of z1242 zircon returned an age of 2676 ± 3 Ma. In the second session, the weighted mean 207Pb/206Pb age of 8 analyses of z1242 zircon returned an age of 2672 ± 4 Ma. The accepted 207Pb/206Pb age of z1242 is 2679 ± 0.2 Ma (personal communication; Davis, 2019). In the second session, analyses of a secondary zircon standard

(Temora 2) were also interspersed between the sample analyses to verify the accuracy of the U-

Pb calibration. Using the calibration defined by the z6266 standard, the weighted mean

206Pb/238U age of 14 SHRIMP analyses of Temora 2 zircon is 417 ± 2 Ma (using a 95% confidence filter). The accepted 206Pb/238U age of Temora 2 is 416.5 ± 0.22 Ma (Black et al.,

2004). A spot size of 20 micrometres was used for all analyses at a beam current of 3.5 amperes and a raster time of 1.5 minutes. Probability density diagrams were constructed using

AgeDisplay (Sircombe, 2004) in order to maintain consistency with nearby studies in the region

(e.g., Rainbird et al., 2017). Kernel density estimate plots (Appendix D) were also created in the

R software, following the methods provided in Vermeesch et al. (2016).

Results

Sample 17-RATR-21, basal Husky Creek Formation. Seventy-four detrital zircon grains were analysed, of which 62 are within 5% of concordance. Under the polarized light microscope

(PLM) the zircon grains are yellow-brown to clear (Figure 3.5a). Forty-nine zircon grains are subhedral with one or more crystallographic faces preserved, 23 have no crystallographic faces preserved (anhedral) and two zircon grains are euhedral. The average grain size of the zircon grains, measured along the c-axis, is 116 µm. The smallest zircon measured has a length of 60

µm and the largest has a length of 170 µm. Thirty-seven of the analysed grains are fractured.

Back-scatter electron (BSE) and cathodoluminescence (CL) imaging of the analysed zircon grains show two large groupings of homogenous and oscillatory zoned zircon grains. A small population of convolute to chaotic zoned grains are also present. The probability density diagram

(Figures 3.9, 3.10) of this sample has a thin, dominant U-Pb detrital zircon peak around 1270 Ma as well as a minor late Palaeoproterozoic (1712, 1813, 1867, 1905, 1952 Ma) and early to mid

Palaeoproterozoic (2109, 2325, 2409, 2506 Ma) peaks. The youngest zircon grain, at 1194 ± 48

Ma (2σ), predates the group of younger zircon grains that produce the thin dominant peak around

1270 Ma and provides a maximum depositional age for the base of the Husky Creek Formation.

The oldest detrital zircon grain in this sample produced an age of 2506 ± 6 Ma (2σ).

Sample 17-RATR-26, lower Husky Creek Formation. Seventy-six zircon grains were analysed, of which 68 are within 5% concordance. Under PLM, the zircon grains are yellow brown to clear (Figure 3.5b). Several grains are coated with Fe-oxide. Forty-nine grains are anhedral, 26 grains are subhedral, and one grain is euhedral. The average grain size is 121 µm with the smallest zircon analysed having a c-axis length of 80 µm and the largest has a c-axis length of 190 µm. The majority of the zircon population is fractured with 62 out of 76 displaying one or more fractures. Oscillatory zoning is the predominant internal texture represented in this fraction of zircon grains with smaller populations of homogenous and convolute/chaotic zoned grains. The probability density diagram (Figures 3.9, 3.10) for this sample shows a strong

Palaeoproterozoic age signature. The early to mid Palaeoproterozoic is represented by a dominant peak at 2495 Ma and moderate peaks at 2213, 2322, 2373, 2404, 2459, and 2481 Ma.

The late Palaeoproterozoic is represented by four moderate to large peaks at 1832, 1890, 1929, and 2020 Ma. Notably, this sample is the stratigraphically lowermost containing Archean zircon grains. Large peaks at 2593 Ma and 2693 Ma are present in addition to multiple moderate to small peaks at 2725, 2753, 2807, 2900, and 2964 Ma. A smaller peak of 1270 Ma is also present, representing the youngest zircon grains present in the sample. The youngest zircon grain is 1209

± 118 Ma (2σ), within error of the 1270 Ma sub-population. The oldest zircon grain analysed produced a date of 2964 ± 12 Ma (2σ).

Sample 17-RATR-31, middle Husky Creek Formation. Seventy-one zircon grains were analysed, of which 65 are within 5% concordance. In plane light, the zircon grains are yellow-

brown to clear, with multiple grains coated with Fe-oxide (Figure 3.5c). Fifty-three grains are anhedral, while 18 had one or more crystallographic faces preserved. The average grain size is

108 µm, with the smallest zircon analysed having a c-axis length of 50 µm and the largest zircon having a c-axis length of 270 µm. Fifty-five of the analysed zircon grains are fractured.

Oscillatory zoning is the predominant internal texture represented in this fraction of zircon grains with smaller populations of homogenous and convolute-chaotic zoned grains. A strong component of early to mid Palaeoproterozoic ages is represented in the probability density diagram (Figures 3.9, 3.10) of this section, defined by a dominant peak at 2506 Ma as well as multiple moderate height peaks at 2086, 2125, 2167, 2281, 2331, 2368, 2385, and 2465 Ma. A strong late Palaeoproterozoic signature is represented by one large peak at 1931 Ma, and moderate peaks at 1890 and 1981 Ma (Figures 3.9, 3.10). A strong Archean signature is represented by one large peak at 2606 Ma and small to moderate peaks are present at 2543, 2587,

2664, 2695, 2790, 3017, and 3127 Ma. Mesoproterozoic ages are represented by a small peak at

1278 Ma. The zircon population of this sample differs from the others as it contains the only zircon population with a peak around 1600 Ma (1607 Ma). The youngest zircon is 1278 ± 28 Ma

(2σ) and the oldest zircon is 3127 ± 16 Ma (2σ).

Sample 17-RATR-34, upper Husky Creek Formation. Seventy-two zircon grains were analysed, of which 71 are within 5% concordance. Under the PLM, the zircon grains are clear, with a few grains coated with Fe-oxide (Figure 3.5d). A small grouping of zircon grains are yellow-brown. The average grain size is 121 µm, with a c-axis length of 40 µm and 210 µm of the smallest and largest grains respectively. Fifty-seven zircon grains in this sample have lost all crystallographic faces while 15 had one or more faces preserved. Oscillatory zoning is the predominant internal texture represented in this fraction of zircon grains with smaller populations

of homogenous and convolute-chaotic zoned grains. A strong late Palaeoproterozoic signature is represented in the detrital zircon probability density diagram (Figures 3.9, 3.10), with peaks at

1900, 1984, and 2038 Ma. The early to mid-Palaeoproterozoic is represented by minor peaks at

2236, 2322, 2344, 2391, and 2466 Ma as well as a moderate peak at 2504 Ma. A strong Archean age signature is also represented in this sample, and defined by a dominant peak at 2584 Ma and small to moderate peaks at 2554, 2707, 2895, 2917, and 3383 Ma. Finally, a minor

Mesoproterozoic age signature is represented by one minor peak at 1257 Ma. The youngest zircon date is 1198 ± 152 Ma (2σ), falling within error of the ~1270 Ma sub-population of zircon grains. The oldest zircon date is 3383 ± 24 Ma (2σ).

Pre-1270 Ma zircon grains. Seven zircon grains were dated with ± 5% concordant U-Pb ages younger than 1270 Ma – the inferred age of flood basalts in the directly underlying Copper

Creek Formation (LeCheminant and Heaman, 1989; Baragar et al., 1996). Five detrital zircons younger than 1270 Ma are present in the basal sample location (17-RATR-21). They include zircon 56.2 (1233 ± 34 Ma), zircon 76.2 (1210 ± 44 Ma), zircon 111.2 (1166 ± 88 Ma), zircon

74.2 (1227 ± 42 Ma) and two spots on zircon 71 (71.1 and 72.2) with dates, respectively, of 1194

± 58 Ma and 1230 ± 36 Ma. One detrital zircon had a U-Pb age younger than 1270 Ma in the lower Husky Creek Formation (17-RATR-26): Sample 276.2 with a U-Pb date of 1217 ± 34. No zircons younger than 1270 Ma were analysed in the middle Husky Creek Formation (17-RATR-

31). One post-1270 Ma zircon grain is present in the topmost Husky Creek Formation (17-

RATR-34): sample 124.2 with a date of 1233 ± 48 Ma. Zircon 276.2 from the lower Husky

Creek Formation (17-RATR-26) displays a ~1270 Ma core and younger rim (1217 ± 68 Ma).

This is also apparent in zircon 124.2 from the topmost Husky Creek Formation (17-RATR-34)

(Figure 3.8a, 3.8b). The other zircon grains are homogenous as observed in Figure 3.8c. The

morphology (sharply terminated) and CL response (homogenous to concentric) of these younger zircon grains are similar to that of the Mackenzie age zircons (Figure 3a-d). Although these ages are significantly younger than the published ages for the Mackenzie LIP, they cannot be currently considered as statistically valid on their own. Their variance could be a result of lead loss in the detrital zircons or an analytical uncertainty. Performing a kernel density estimate on all the younger grains from each sample population produces a normal bell curve distribution

(Figure 3.8e). The reduced chi-squared statistic, otherwise referred to as the mean square weighted deviation, can be applied to a set of data to determine the goodness of fit (Spencer et al., 2017). Both functions were plotted using KDX software (Spencer et al., 2017). In all cases, younger grains fall on the younger tail of a normal distribution function (Figure 3.8e).

Calculating the weighted mean average of all zircons in the 1150–1350 Ma range results in ages within error of the Mackenzie event (1263.78 ± 4.69 Ma, Figure 3.8e). The MSWD of 1.05 indicates that the observed values closely approach a statistically univariate normal distribution with minor geologic scatter (Spencer et al., 2017). Notably, Rayner and Rainbird (2013) produced a statistically significant date from one zircon grain with an age of 1232 ± 15 Ma (2σ, three repeated measurements), from a sample collected at the top of the Husky Creek Formation.

3. 6 Discussion

Apart from a preliminary geochronology analysis performed on a sample in its upper stratigraphy (Rayner and Rainbird, 2013), no U-Pb detrital zircon geochronology has been produced thus far for the Husky Creek Formation. Four groups of age peaks can be identified from the detrital zircon data herein, including a single peak around 1270 Ma, a group of peaks around 1750-2010 Ma, another grouping between 2100- 2580 Ma, and a fourth grouping older

than 2580 Ma. Two “end-member” provenance hypotheses are tested for the Husky Creek

Formation. In the first scenario, the formation is locally derived from the Copper Creek

Formation and its intrusive equivalents, such as the Muskox intrusion and Mackenzie dyke swarm. Accordingly, older zircon grains are sourced from polycyclic sediment sourced from the nearby exposed Hornby Bay and Dismal Lakes groups. In an alternative scenario, zircon grains are derived from a wide source area that includes, from the youngest to oldest age peaks, rocks of the Hornby Bay and Dismal Lakes groups, Wopmay orogen, Thelon-Taltson orogen,

Arrowsmith orogen, Queen Maud Block and Slave Province (Figures 3.9, 3.10). Provenance interpretations for each of the main statistically significant age groups are discussed below.

Mackenzie LIP-Related Material

The ~1270 Ma detrital-age peak is most significant in the sample from the base of the

Husky Creek Formation (17-RATR-21) and decreases in relative importance up section. These zircon grains have an age consistent with the Mackenzie Igneous Event (Lecheminant and

Heaman, 1989). Detrital zircon grains within this age range are relatively euhedral and generally retain at least one, unabraded crystallographic face, features that altogether suggest very limited transport. The CL and BSE response for ~1270 Ma zircon grains are either homogenous or concentrically zoned (Figure 3.8), textures commonly observed on magmatic zircon grains

(Corfu et al., 2003). Although a felsic component of the Mackenzie Event is not currently exposed, the preservation of crystallographic faces on the zircon grains, and the proximity to the

Copper Creek Flood basalts and Muskox Intrusion, suggests that the 1270 Ma zircon grains were likely derived from Mackenzie-related material. Additionally, the cumulative palaeocurrent data indicates sediment sourcing from the east-southeast, which is on strike with a significant portion

of the Coppermine Flood Basalts and the Muskox Intrusion. Also, a felsic component may not be strictly necessary to produce the zircon – although the quantity of zircon grains recovered is surprisingly high if derived from weathering of a mafic source, with zircon only reported to occur in trace amounts in the Muskox intrusion and the Mackenzie dikes and sills (Lecheminant and Heaman, 1989). Fluvial systems are well-adapted to concentrating heavy minerals through transport sorting, particularly in areas of increased shear stresses and turbulence (Slingerland and

Smith, 1986). Given the dominance of fluvial deposition, this is a possible mechanism for the abundance of Mackenzie-aged zircon grains.

Zircon grains dated at 1600–2010 Ma

This grouping of zircon grains is present at each stratigraphic interval sampled. It is subordinate in the basal Husky Creek Formation sample (17-RATR-21), but becomes dominant in the other 3 samples, and could potentially be a more significant source of sediment upsection, possibly related to an expansion of the catchment basin of the Husky Creek rivers. The zircon grains within the grouping are interpreted to be predominantly derived from rocks of the

Wopmay Orogen such as the Hottah terrane, Great Bear magmatic zone, and the Hepburn complex exposed to the south of the Husky Creek Formation, in addition to rocks exposed along the Coronation Margin to the west of the Coppermine Homocline (Figure 3.11). The Hottah

Terrane and Great Bear magmatic zone are a potential source of zircons between 1850–1950 Ma

(Hildebrand et al., 2010; Davis et al., 2015; Ootes et al., 2015). The Hottah Terrane includes the

~1950 Ma Holly Lake metamorphic complex, the Hottah Intrusion Complex (1930, 1913 Ma),

~1906 Ma subaerial volcanic rocks (Zebulon Formation), and the ~1895 Ma Bloom Basalts

(Ootes et al., 2015). The Great Bear magmatic zone records pan-continental arc activity at about

~1876–1869 Ma, bimodal volcanism (Sloan Group) at 1862 Ma, and post-orogenic granitoid and syenogranite plutonism (at ~1855 and ~1845 Ma, respectively; Ootes et al., 2015). The Hepburn batholith may also have contributed detritus with statistical minimum ages of 1874–1880 Ma, and a maximum age of ~1890 Ma (Hildebrand et al., 2010). Zircon grains from this age group could have also been sourced from erosion of rocks located along the Coronation Margin, which is constrained between 2014 ± 0.89 Ma (Felsic Tuff, Melville Group) and 1882.5 ± 0.95 Ma

(Fontano tuff, Recluse Group) (Hoffman et al., 2011). Magmatic units of the Taltson-Thelon

Orogen dated at 2000–1900 Ma (Zhao et al., 2002) are another potential source for zircons of this age group, although the distance between their current exposure and the Husky Creek

Formation outcrop belt – and particularly the inferred occurrence of palaeotopography related to the Wopmay orogenic edifice along the inferred transport route – makes this a less likely source given the compositional and textural immaturity of the framework sediment in the Husky Creek

Formation. Detrital ages of 1600–1880 Ma include the ~1700 and ~1600 Ma peaks in, respectively, the basal and middle Husky Creek Formation (Figures 3.9, 3.10). A potential igneous source for zircon grains of this age is the Narakay Volcanic Complex (Bowring and

Ross, 1985), although the U-Pb age therein of 1663 ± 8 Ma does not overlap with the ~1600 Ma or ~1700 Ma detrital-age peaks produced in this study. Another possible source for the zircon grains within this age range are sedimentary units within the Hornby Bay Basin. Although there is no current exposure of Hornby Bay Basin rocks to the east-southeast (i.e., consistent with palaeocurrent data; Figure 3.7), formations in the Hornby Bay Basin are correlative to units in the Elu Basin (Hahn et al., 2013) and may have previously extended into the source area of the

Husky Creek basin. Polycyclic zircon grains, i.e. grains that have been eroded and deposited multiple times, can account for all of the detrital age peaks from ~1600 Ma onwards (Rainbird et

al., in prep). The ~1600 Ma peak could potentially be attributed to the East River Formation of the Hornby Bay Group, where a suite of detrital zircon grains have an age range of 1660–1620

Ma, or the Leroux Formation, which produced a single ~1600 Ma zircon grain (Rainbird et al.,

2009, Hahn et al., 2013). Although the Hornby Bay Group is not currently exposed to the east- southeast of the current Husky Creek Formation outcrop belt, recycling of detritus can still be invoked, since the observed peaks from 1750 Ma onwards match up with the recorded peaks from the Hornby Bay Group, especially the Lady Nye Formation; the occurrence of correlative sedimentary units exposed in the Elu Basin suggests that Hornby Bay Group sediment likely extended to the east of the Coppermine area prior to being eroded; and, owing to their considerable distance from the Husky Creek Formation (Figure 3.11) and their compositional and textural immaturity of the Husky Creek sediment, it is less likely that rocks eroded from the

Wopmay Orogen contributed directly to the detritus of the Husky Creek Formation.

Zircon grains dated at 2100–2580 Ma

Similar to the previous grouping, this bracket of detrital ages transitions from a subordinate to dominant group of peaks upsection. These ages can be related to protoliths such as

Queen Maud Block granitoids and rocks akin to those exposed nowadays in the Arrowsmith and

Thelon-Taltson orogens. Palaeoproterozoic granitoids of the Queen Maud Block range in age from 2520 to 2450 Ma (Schultz et al., 2007; Tersmette, 2012), and occur in association with other un-deformed and un-metamorphosed mafic and felsic units with an age of ~2320 Ma

(Tersmette, 2012). Xenocrystic zircons from granitoids in the Thelon Tectonic Zone have been dated by Van Breeman et al. (1987) at 2400 Ma and 2200 Ma, while a more recent study found a xenocrystic zircon with an age of 2350 Ma (Tersmette, 2012). Plutonic units of the Arrowsmith

Orogen range from 2520 Ma (Orthogneiss, Northern Baffin Island) to 2070 Ma (granites at

Chinchaga and Buffalo Head in the Alberta subsurface) (Berman et al., 2013). Units of similar ages are present in the Taltson Magmatic Zone, with gneissic rocks dated at 2100–2400 Ma

(McNicoll et al., 2000). Rocks post-dating the age of Arrowsmith metamorphism in the Queen

Maud Belt could have sourced zircon grains, and include ~2320 Ma gabbro and granites, a 2210

Ma pegmatite dike, and a 2100 Ma mafic dike (Tersmette, 2012).

Given the size of the Husky Creek Formation outcrop belt, and the low textural and mineralogical maturity of its sediment, it is unlikely that these detrital zircon sources were directly contributing a significant volume of sediment. Recycling is therefore invoked again, with polycyclical grains from the sources above having been first deposited in the foredeep of the Kilohigok Basin at ~1.9 Ga, included in the Bear Creek Supergroup and the Coronation

Margin, and then exhumed and eroded again, included in the fill of the Hornby Bay Basin

(Rainbird et al., 2009; Hahn et al., 2013), and eventually redeposited as part of the Husky Creek

Formation. Palaeoproterozoic detritus likely derived from the Thelon Tectonic Zone and the western Rae craton is also present in the external zone of the Wopmay orogen (St. Onge and

Davis, 2017), and could therefore constitute another source of sediment for units in the Hornby

Bay Basin, and later the Husky Creek Formation. Zircon grains dated at 2100–2500 Ma and recycled from Neoarchean rocks are common in the Hottah Terrane (Davis et al., 2015), which constitutes another potential source area for late Palaeoproterozoic detrital zircon grains first deposited into the Hornby Bay Basin, and then incorporated in the Husky Creek Formation.

Zircon grains older than 2580 Ma

Archean zircon grains are absent from the basal Husky Creek Formation, but their proportion increases upsection, to eventually become dominant in the uppermost stratigraphy.

Detrital zircon grains from this age group match zircon grains from the Slave craton, including its Mesoarchean Cover Group (Sircombe et al., 2001) and ensuing late Neoarchean plutonic rocks (Davis and Bleeker, 1999). Direct sourcing from these areas is unlikely, based on the dominant west-northwestward palaeoflow recorded in the Husky Creek Formation (Figure 3.11).

As per younger age groups, also, the distance that these zircon grains would have travelled if directly sourced, is at odds with textural and mineralogical immaturity of the Husky Creek

Formation. As zircon grains pertaining to this age bracket are present in the Hornby Bay Group

(notably with a similarity in probability density pattern shown in this study and the Lady Nye

Formation; Rainbird et al., in prep), polycyclic sourcing of detrital grains from the Slave craton

(including its Cover Group and plutonic units), and through the Hornby Bay Group is the solution preferred to justify the occurrence of older detrital ages in the Husky Creek Formation.

Expansion of source drainage basin, and connections with the Mackenzie LIP

Moving upsection through the Husky Creek Formation, a noticeable decrease in the magnitude of the Mackenzie LIP peak is observed; such trend is paralleled by a proportional increase in zircon grains older than 1270 Ma (Figures 3.9, 3.10). Although all samples plot in the field of lithic arenites, there is a marked difference between the compositional maturity of the basal sandstone (~14% quartz) and the sandstones throughout the Husky Creek Formation’s stratigraphy (~26-32% quartz). Exotic grains such as glauconite are also present up-section. This result is also reflected in the zircon morphology, which attain more rounded shapes upsection

(Figure 3.5). A step-wise increase in the proportion of older zircon grains and compositional

maturity is observed stratigraphically, just above a first fining-upwards sequence at the base of the formation (Figure 3.5).

The prominent Mackenzie LIP-related peak and the small >1270 Ma age peaks together suggest that Mackenzie LIP-derived material was the dominant source of detritus for the Husky

Creek Formation in its early stages of deposition, together with detritus sources from the Hornby

Bay Group. A second stage of Husky Creek deposition is reflected instead by a return to sand- sized detritus, pronounced pre-Mackenzie age peaks, and the lesser proportion of Mackenzie

LIP-related ages (Figure 3.10). A third fining upwards succession is observed within the Husky

Creek Formation and occurs above an intra-formational basalt-flow unit in its upper stratigraphy, which is then overlain by a conglomerate unit that fines upwards again to a medium grained sandstone (Figure 3.10).

Although the decrease in the magnitude of Mackenzie ages may reflect a loss of a 1270

Ma zircon grain source, up-section maturation of framework sediment and addition of exotic grains is interpreted to reflect the expansion of the catchment basin of the Husky Creek rivers, which likely incised areas where strata of the Hornby Bay Group – or correlative units of the Elu

Basin – were exposed. Flood basalts exposed to the east of – and correlative with – the

Coppermine Homocline in the Elu Basin (Ekalulia Formation) are significantly thinner than the

Copper Creek Formation flood basalts (i.e., <500 m versus ~3000 m; Campbell, 1978; Skulski et al., 2018). As the cumulative palaeocurrent data indicates overall eastward sourcing, the catchment basin for the Husky Creek Formation may have not had to erode through a basalt package as thick as the Copper Creek Formation to incise Hornby Bay Group sedimentary units.

Loading from the extensive Copper Creek Formation flood basalts likely caused significant subsidence in the surrounding areas (Leng and Zhong, 2010), and may have caused the initial

accommodation for the Husky Creek Formation. Significant subsidence accompanying flood basalt eruptions has been documented elsewhere, e.g. in the Siberian Flood Basalt Province

(Czamanske et al., 1998).

Palaeogeographic reconstructions suggest that thermal uplift related to the Mackenzie

LIP emplacement was pronounced in the area south of the Elu Basin and to the east of the

Coppermine Homocline with karsts present in carbonate units prior to the emplacement of the

Coppermine River flood basalts (Rainbird and Ernst, 2001). Rifting related to Mackenzie magmatism resulted in the short-lived subsidence immediately prior to the eruption of the

Coppermine River Flood basalts (Lechemiant and Heaman, 1989), and may have also contributed to accommodation of the basal Husky Creek Formation sandstones. Although most of the fault structures mapped in the Coppermine Homocline appear to postdate the Mackenzie

LIP, it cannot be excluded that some of them experienced syn-Mackenzie LIP extensional kinematics (Baragar and Robertson, 1973; Lecheminant and Heaman, 1989), providing an additional structural solution for the generation of accommodation in the Husky Creek basin. Yet another mechanistic solution for subsidence in the area at ~1270 Ma or soon thereafter is thermal subsidence related to lithospheric cooling in the aftermath of the Mackenzie LIP (Mackenzie,

1978; Allen and Allen, 2005).

The occurrence of a topographic high south of the Elu Basin area at time of Husky Creek deposition is generally consistent with the palaeocurrent data collected in this study, which shows west-northwest dominant transport. Preliminary palaeocurrent measurements in the correlative Algak Formation in the Elu Basin also displays westward discharge (Campbell,

1978). The interpreted plume for the Mackenzie LIP centre lies to the north of the current exposure of the Husky Creek Formation (Blanchard et al., 2017), or in other words, away from

the area of major uplift. Offsetting between the plume centre and basalt field is possible as a result of plume-lithosphere interactions (Gorczyk et al., 2017), although, given the current state of knowledge, this hypothesis remains speculative.

The palaeocurrent records of the Husky Creek and Algak formations are overall consistent with the regional west-northwest-trending palaeoflow pattern observed in a number of sedimentary basins in northern Canada, including the Athabasca, Thelon, Hornby Bay, Elu, and

Amundsen basins (Rainbird and Young, 2009; Rainbird et al., 2012; Hahn et al., 2013), which has been interpreted to represent a continental-scale drainage network active at times during the

Proterozoic (Rainbird et al., 2012). By analogy with the much younger and smaller Columbia

River Flood Basalt Province, river valleys tend to be preserved during lava-flow emplacement, and drainage networks are eventually re-established along their former trajectories (Ebinghaus et al., 2014). This notion may, at least tentatively, offer an explanation to the observed palaeoflow pattern recorded in the Husky Creek Formation.

Continued magmatism in the Coppermine Homocline?

Basalt layers within the Husky Creek Formation have been interpreted to be at least partially linked to the Mackenzie LIP (Baragar and Donaldson, 1973; Campbell, 1983).

However, they do not follow the geochemical trends developed in the Copper Creek Formation, with an apparent mixing with the evolved Copper Creek Formation magma source and a new primitive magma source to produce the trends observed (Dostal et al., 1983). This shift to a new primitive source may be reflected by the presence of a sub-1270 Ma zircon grain collected in the uppermost Husky Creek Formation by Rayner and Rainbird (2013). The presence therein of a

detrital age at 1232 ± 15 Ma (2σ) suggests that some form of magmatism continued at least 40

Ma after the known age of the Mackenzie Igneous Event.

This timespan is significantly longer than the previously established 5 My maximum timeframe for the emplacement of all components of the Mackenzie LIP (Lecheminant and

Heaman, 1989; Dupuy et al., 1992; Mackie et al., 2009). Further work on such young zircon grains and the Husky Creek Formation basalts is needed to determine whether the latter are truly linked to the Mackenzie LIP. Peperite was observed at the basal contact between the Husky

Creek and Copper Creek formations flows, as well as upsection at the contact between basalt and sandstone within the Husky Creek Formation (Figure 3.4). This field evidence indicates that sedimentation and magmatism were contemporaneous, and that it took place without significant time loss (Busby-Spera and White, 1987). Basalt flows within the Husky Creek Formation do not extend laterally across the entirety of the area encompassed by the sedimentary units (Figure 3.3) and may have erupted adjacent to the fluvial system to create the peperite observed throughout the formation (Figure 3.4). Additional high-precision (i.e. TIMS) dating of protolith and detrital grains in, respectively, the Copper Creek and Husky Creek formations will help refine the timeframes of flood-basalt emplacement in the region.

3.7 Conclusions

This study collected the first detailed U-Pb detrital zircon geochronologic data on the fluvial sandstone dominated Husky Creek Formation, the topmost member of Sequence A stratigraphy. Four samples collected at different levels of stratigraphy were analysed with a sensitive high-resolution ion microprobe and their detrital zircon ages were plotted in probability density diagrams. Notably, the Husky Creek Formation contains ~1270 Ma detrital zircon grains,

which are likely derived from a component of the Mackenzie LIP. These zircon grains could have been sourced either by localised erosion of the Copper Creek Formation flood basalts, by the Muskox Intrusion, or by a felsic equivalent of the Mackenzie LIP that is no longer preserved.

Detrital zircon grains older than the Mackenzie LIP are likely recycled from Hornby Bay Group sedimentary units, or correlative units such as those nowadays exposed in the Elu Basin. Further work on the younger zircons is necessary to assess younger than 1270 Ma ages and assess the importance of the 1232 Ma age reported by Rayner and Rainbird (2013). Trace element studies on the Mackenzie LIP aged detrital zircon grains could also be used to further refine their source.

Detailed sedimentology, stratigraphy, and detrital zircon geochronology on the Algak Formation is also needed to corroborate correlations to the Husky Creek Formation, and of sedimentation coeval with the Mackenzie LIP emplacement.

About 1900 m of accommodation was created for the deposition of the Husky Creek

Formation. Accommodation was likely developed through a combination of flexure in response to crustal loading from the Copper Creek Formation flood basalts, localised faulting, and thermal subsidence ensuing the Mackenzie LIP cooling. The dominantly fluvial Husky Creek Formation reflects deposition as part of a river system trending roughly westwards, which locally eroded the

Copper Creek Formation basalts. The Copper Creek Formation flood basalts might have created significant changes to the topography of the Coppermine Homocline, yet our evidence suggests that they did not significantly alter the established westerly trend of a fluvial system established atop Laurentia at the time.

3.8 Acknowledgements

This work is part of the M.Sc. thesis of the lead author and was sponsored by a Discovery

Grant from the Natural Sciences and Engineering Research Council of Canada to AI. RM received a financial bursary from the Research Affiliate Program of Natural Resources Canada.

Logistical support was provided by the second phase of the Geo-mapping for Energy and

Mineral Program of Natural Resources Canada, and by the Agouron Institute. Tom Pestaj and

Nicole Rayner from the Geological Survey of Canada (Ottawa, Ontario) are thanked for their help with data acquisition on the SHRIMP. Willard Desjardins and Elliot Wehrle from

Laurentian University are thanked for their help with sample preparation.

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3.10 Figures

Figure 3-1: Sequence ABC stratigraphy and study area

Extent of sequence ABC stratigraphy in the Canadian Arctic and Alaska. General location of study area in western Nunavut starred.

Figure 3-2: Coppermine Homocline stratigraphy Stratigraphic section of the Coppermine Homocline modified from Young et al., 1979 with ages from Lecheminant and Heaman, 1989, Rayner and Rainbird, 2013 and Rainbird et al., 2017.

Figure 3-3: Husky Creek Formation geochronology sample stations Map of the Husky Creek Formation modified from Hildebrand 2011 with locations of geochronology sample stations.

Figure 3-4: Husky Creek Formation general stratigraphy and contacts

Generalized stratigraphic column of the Husky Creek Formation with photos of A: Peperite at the basal contact between the Husky Creek Formation red bed sandstones and the Copper Creek

Formation flood basalts. B: Peperite at the contact between red bed sandstones and basalts in the

Husky Creek Formation. Hammer (circled) is ~45 cm in length C: Unconformity between shallow marine sandstones of the Escape Rapids Formation (grey unit, < 1137 Ma ± 12 Ma, Det.

Zr.) and fluvial red bed sandstones of the Husky Creek Formation (< 1232 ± 15 Ma, Det. Zr.)

Lens cap is roughly 7 cm in diameter.

Figure 3-5: Thin section and detrital zircon petrography Petrographic thin section scans (plane-polarised light) and zircon populations for A, the basal sample 17-RATR-21, B, sample collected above the first sequence of basin fill, 17-RATR-26, C, sample collected at approximately the midpoint of the Husky Creek Formation, 17-RATR-31and

D, sample collected at the contact with the Escape Rapids Formation, 17-RATR-34.

Figure 3-6: Sedimentary bedforms

Common sedimentary bedforms observed at the Husky Creek Formation. Pencil in B, E, and H has a length of ca. 15 cm, field book dimensions in D are ca. 12 cm by 19 cm, lens cap in C and is ca. 7 cm in diameter. A-D, common bedforms of the fluvial channel belt facies association.

Upper flow regime bedforms include (A) planar bedding, (B) primary current lineations. Lower to transitional flow regime bedform include (C) flow ripples, and (D) trough cross-stratified bedforms. E-G: Fluvial flood plain facies association bedforms. (E) pedogenic nodules, (F) desiccation cracks (G) evaporite pseudomorphs. (H), Pinstripe laminated, trough cross stratified sandstones indicative of aeolian bedforms.

Figure 3-7: Palaeocurrent analysis

Palaeocurrent measurement stations and cumulative results for fluvial bedforms.

Figure 3-8: Young Detrital Zircon Grains

Cathode luminescence response of young detrital zircon grains from the Husky Creek Formation.

A) Zoned zircon from station 17-RATR-34. Roughly Mackenzie aged core and significantly younger rim. CL high surrounding the grain attributed to hydrothermal alteration. B) Zoned zircon from station 17-RATR-26. Roughly Mackenzie aged core and significantly younger rim.

Sharp contact between zones. C) Oscillatory zoned zircon collected from the base of the Husky

Creek Formation (station 17-RATR-21). D) Oscillatory zoned Mackenzie Igneous Event aged zircon. E) MSWD and KDE of the cumulative population of detrital zircon grains within 100 Ma of the published date of 1270 Ma for the Mackenzie igneous event (LeCheminant and Heaman,

1989). A MSWD value approaching one indicates that all zircons belong to the same age group.

Figure 3-9: Probability density diagrams- limited recycling

Probability density diagrams of the Husky Creek Formation. End-member interpretation of

limited recycling of detrital zircon grains.

Figure 3-10: Probability density diagrams- polycyclic grains Probability density diagrams of the Husky Creek Formation with the end-member interpretation that apart from the Mackenzie LIP zircon grains, zircon grains are recycled from Hornby Bay

Group units.

Figure 3-11: Husky Creek Formation source areas

Regional map with potential source areas for the Husky Creek Formation (modified from

Wheeler et al., 1996). Sequence B ages (720- 1137 Ma) are from Rainbird et al., 1996, 2017.

Coppermine River Group maximum depositional age from Rayner and Rainbird, 2013.

Coppermine River Group age and Muskox Intrusion age from Lechiminant and Heaman, 1989.

Hornby Bay Basin and Elu Basin ages from Hahn et al., 2013. Great Bear Magmatic Zone ages from Ootes et al., 2015. Hepburn Complex ages from Bowring et al., 1984 and Hildebrand et al.,

2010. Hottah Terrane ages from Ootes et al., 2015. Coronation margin ages from Hoffman et al.,

2011. Kilohigok Basin ages from Bowring and Grotzinger, 1992. Thelon Tectonic Zone ages from Zhao et al., 2002. Queen Maud Block ages from Schultz et al., 2007 and Tersmette, 2012.

Slave Province ages from Sircombe et al., 2001 (detrital zircons, Slave Cover Group) and Davis and Bleeker, 1999 (post-tectonic magmatic units).

3.11 Tables

Table 3-1: Geochronology sample descriptions

Sample ID Lithology/texture Framework Cement/matrix Other features Facies Association

17-RATR- Brown-red, medium Lithic fragments Carbonate cement Incipient nodule Fluvial channel belt

21 grained, intraclast-rich (hematite, filling larger pores 10%, growth

lithic arenite magnetite, Fe-oxide cement

chlorite, epidote, between smaller lithic Plane parallel

biotite, mud rich grains <5%; lamination

intraclasts) 50%; Pore space 6%

Plagioclase 20%;

Quartz 14%

17-RATR- Brown-red, medium Lithic fragments Blocky and granular Plane parallel Fluvial channel belt

26 grained, intraclast-rich (mud rich carbonate cement in lamination

lithic arenite intraclasts, larger voids 16%, Fe-

magnetite, oxide cement <5%

hematite, Pore space <1% Reverse grading

glauconite, biotite between laminae

±chlorite) 36%;

Plagioclase 18%;

Quartz 30%

17-RATR- Brown-red, medium Lithic fragments Carbonate cement Plane parallel Fluvial channel belt

31 grained, lithic arenite. mud-rich filling larger pores 14%; lamination

intraclasts, Fe-oxide cement Reverse grading

hematite, between smaller lithic between laminae

magnetite, biotite grains <1% Incipient nodule

± chlorite); 34%; Pore space 4% growth

Plagioclase 16%;

Quartz 32%

17-RATR- Brown-red, medium Lithic fragments Carbonate cement 18%, Plane parallel Fluvial channel belt

R34 grained, intraclast-rich (hematite, biotite, Fe- oxide cement <5% lamination

lithic arenite ±chlorite, mud- Pore space <1%

rich intraclasts) Moderate

40%; Plagioclase alteration and

16%; Quartz 26% weathering;

chloritized lithic

fragments

Table 3-2 Husky Creek Formation sedimentary facies

Facies Lithology Sedimentary Structures Locally preserved Facies

Additional features Association

1. Planar- Lithic Plane-parallel lamination. Mud-rich intraclasts Fluvial

bedded wacke- Primary current lineation preserved in Desiccation cracks channel-belt

sandstone arenite plan view (FCB)

2. Planar cross- Lithic Planar foresets with angular bases. Mud-rich intraclasts Fluvial

bedded wacke- channel-belt

sandstone arenite (FCB)

3. Trough cross- Lithic Trough cross stratification. Mud-rich intraclasts Fluvial

bedded wacke- channel-belt

sandstone arenite (FCB)

4. Antidunal- Lithic arenite Sigmoidal cross bedding; Mud-rich intraclasts Fluvial

bedded small scale (< 5 cm) undulatory bedding. channel-belt

sandstone (FCB)

5. Soft-sediment Lithic arenite Internal deformation and fluid escape Mud-rich intraclasts Fluvial

deformed conduits. channel-belt

sandstone (FCB)

6. Ripple cross- Lithic Unidirectional ripple forms. Symmetrical Mud-rich intraclasts Fluvial

laminated wacke- ripple forms. channel-belt

sandstone arenite (FCB)

Fluvial

floodplain

(FFP)

7. Massive Lithic None Mud-rich intraclasts Fluvial

sandstone wacke- channel-belt

arenite (FCB)

8. Weathered Lithic rich Blocky fabric. Desiccation cracks Fluvial

sandstone mudstone- (mudstone-siltstone) floodplain

siltstone, (FFP)

lithic wacke, Fluvial

lithic arenite channel-belt

(FCB)

9. Nodule-rich Lithic With blocky fabric in places. 1-5 cm calcite nodule Fluvial

sandstone wacke- floodplain

arenite (FFP)

Fluvial

channel-belt

(FCB)

10. Sandstone Lithic Adhesion structures Fluvial

with adhesion wacke- floodplain

warts arenite (FFP)

11. Large-scale Lithic arenite Plane-parallel (pinstripe laminated) beds; Aeolian (Eol)

trough reverse-graded laminae.

crossbedded

sandstones

12. Pin-stripe- Lithic arenite Plane-parallel, (pinstripe laminated) Aeolian (Eol)

laminated beds; reverse graded laminae)

sandstone

13. Massive Lithic-rich None 0.25-3.00 cm evaporite Fluvial

mudstone and mudstone- pseudomorphs floodplain

siltstone siltstone (FFP)

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14. Crudely Oligomictic Crude bedding Fluvial

bedded conglomerate channel-belt

conglomerate (FCB)

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Chapter 4

Concluding statements

4.1 Conclusions

This thesis provides the first detailed sedimentology, stratigraphy and geochronological study of the Husky Creek Formation, the topmost unit of Sequence A stratigraphy exposed in the central-western area of the Canadian Arctic. Thanks to the U-Pb geochronologic characterisation of detrital zircon grains, the sedimentary provenance of the Husky Creek Formation was also investigated for the first time. Exposed strata along the Coppermine River were the main focus of the sedimentologic fieldwork and sampling.

4.1.1 Sedimentology Abundant unidirectional flow structures, together with a general textural and compositional immaturity, altogether suggest that the bulk of the Husky Creek Formation was deposited in a terrestrial environment that included fluvial channel-belts, floodplains, and aeolian dunes. Perennial and seasonal phases of fluvial discharge are inferred to have occurred based on the presence of both lower- and upper-flow-regime sedimentary structures, while frequent channel avulsion (related to undercutting of new channels onto floodplain deposits) is indicated by the pervasive occurrence of intraformational mud-rich clasts. The occurrence of desiccation cracks, pedogenic nodules, adhesion surfaces, evaporitic pseudomorphs, and pin-stripe lamination of aeolian origin indicates an endorheic setting where evaporation might have exceeded hydrologic recharge for at least part of the year. The lens shaped aspect of the outcrop

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belt, and the overall trend of palaeoflow indicators support the interpretation of the Husky Creek

Formation being deposited in a WNW-trending valley.

4.1.2 Detrital Zircon Geochronology

Four intervals of the Husky Creek Formation were sampled for detrital zircon geochronology. Two main sediment sources contributed to the Husky Creek Formation. Detrital zircons with ages of ~1270 Ma were sourced from members of the Mackenzie Igneous Event

(i.e., either the Copper Creek Formation flood basalts, the correlative Ekalulia Formation basalts, or the Muskox Intrusion). Older detrital zircon grains are likely polycyclic grains sourced from the Hornby Bay Group sedimentary units or their correlative units in the Elu Basin. During the deposition of the Husky Creek Formation, ~1900 m of accommodation was created. Flexure from basalt loading, localised faulting, and thermal subsidence related to Mackenzie LIP cooling might have contributed to create such accommodation. By observing ~3000 m of flood basalts preserved, it is inferred that the emplacement of the Copper Creek Formation likely created significant topographic changes in the area nowadays represented by the Coppermine

Homocline. However, palaeoflow data suggests that the emplacement of such flood basalts did not significantly disrupt westward-trending fluvial drainage in Laurentia in the Mesoproterozoic.

4.2 Future work

Further efforts in facies analysis, stratigraphic reconstructions, and structural fieldwork is required to better resolve the tectonic setting of the Husky Creek Formation and correlative strata, particularly to better understand mechanisms of basin formation in relation to the

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emplacement of the Mackenzie LIP. Future work is necessary to assess with high precision the age distribution of protolith and detrital zircon grains dated at about, or younger than, 1270 Ma.

Trace element studies on the Mackenzie LIP-aged detrital zircon grains could also be used to further refine their source. On these terms, detailed sedimentology, stratigraphy, and detrital zircon geochronology on the Algak Formation would also be beneficial to more firmly establish correlations to the Husky Creek Formation, therefore shedding additional light on the interacting deposition and magmatism in the region at Mackenzie-LIP time.

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4.3 Appendices Appendix A: Stratigraphic log- Middle Husky Creek Formation (17-RATR-028)

Stratigraphic column of the middle Husky Creek Formation (17-RATR-028). FCB- fluvial

channel belt, FFP- fluvial floodplain, Eol- Aeolian. The number after F refers to the facies ie. F1-

facies 1, planar-bedded sandstone.

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Appendix B: Stratigraphic log of the middle Husky Creek Formation (17-RATR-029)

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Appendix C: Stratigraphic log of the upper Husky Creek Formation (17-RATR-032)

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Appendix D: Kernel Density Estimate Plots

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Appendix E: U-Pb Shrimp Data

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112

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