Deep-Water Stratigraphic Evolution of the Nanaimo Group, Hornby and Denman Islands, British Columbia

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2016 Deep-Water Stratigraphic Evolution of The Nanaimo Group, Hornby and Denman Islands, British Columbia

Bain, Heather

Bain, H. (2016). Deep-Water Stratigraphic Evolution of The Nanaimo Group, Hornby and Denman Islands, British Columbia (Unpublished master's thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/25535 http://hdl.handle.net/11023/3342 master thesis

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Deep-Water Stratigraphic Evolution of The Nanaimo Group, Hornby and Denman

Islands, British Columbia

Heather Alexandra Bain

A THESIS

SUBMITTED TO THE FACULTY OF GRADUATE STUDIES

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE

DEGREE OF MASTER OF SCIENCE

GRADUATE PROGRAM IN GEOLOGY AND GEOPHYSICS

CALGARY, ALBERTA

SEPTEMBER, 2016

Deep-water slope strata of the Late Cretaceous Nanaimo Group at Hornby and

Denman islands, British Columbia, Canada record evidence for a breadth of submarine channel processes. Detailed observations at the scale of facies and stratigraphic architecture provide criteria for recognition and interpretation of long-lived slope channel systems, emphasizing a disparate relationship between stratigraphic and geomorphic surfaces. The composite submarine channel system deposit documented is 19.5 km wide and 1500 m thick, which formed and filled over ~15 Ma. Facies scale analyses highlight conglomeratic channel fill juxtaposed against thin-bedded out-of-channel deposits.

Evidence that the channel system was maintained through a variety of processes over a protracted period includes identification of stratigraphic products that record degradational terraces, cyclic steps, mass transport deposition, nested erosion surfaces, and fine- and coarse-grained channel fill deposits. The thesis establishes the Nanaimo

Group as an ideal unit to investigate the record of deep-water sediment transfer through slope channels.

ii ACKNOWLEDGEMENTS

I would like to recognize and sincerely thank Dr. Stephen Hubbard for his

academic and professional guidance over the past couple of years. It’s amazing that one

small conversation during an undergraduate geology field school has transpired into one

of the best decisions of my life. I am thankful for the various opportunities he has

provided including a field excursion to Chile, attending numerous conferences and for his

patience through out the work terms I completed. His mentorship has instilled a powerful

work ethic, commitment to excellence and a passion for geology that I will take with me

through the next phase of my life.

Funding for this research was graciously provided by an NSERC Discovery grant

to Dr. Stephen Hubbard as well as student funding from the University of Calgary. To my

colleagues at the Centre for Applied Basin Studies (CABS) at the University of Calgary

including Danny Coutts, Rebecca Englert, Aaron Reimchen, Paul Durkin, Ben Daniels, Nick

Zajac, Emma Percy, David Cronkwright, Dillon Newit, Raymond Van, Garrett Quinn and

Adam Coderre thank you for your insightful geologic discussions, outdoor adventures and

most importantly friendship over the past couple of years.

I could not have completed this degree without the unwavering support that I am so grateful

to have received in my personal life. To my parents Don and Helen Bain for their constant love and support in any endeavor that I take on and encourage me to continually follow my dreams. To my brother and sister-in-law Brian and Kristine Bain, who have been

exceptional role models in academics, lifestyle, and creating a remarkable work-life

balance. To my partner and best friend Ian Gray, who endured the stressful moments that

develop during a graduate degree and encouraged me with patience and understanding in

the pursuit of my passion. To the Gray’s who accepted me into their family and

iii constantly supported me throughout my degree. To my amazing best friends Kristen

Barton, Kaitlyn Amatto, Rebecca Mayhew and Courtney Leinweber, for their acceptance of numerous geological factoids on the many adventures we have taken and reminded me to take a step back from planning and appreciate the moment. I am forever indebted to the people in my life.

iv TABLE OF CONTENTS

Abstract ii Acknowledgements iii Table of Contents v List of Figures vii List of Tables viii

CHAPTER ONE: INTRODUCTION 1 Project Motivation 1 Nanaimo Basin 3 Stratigraphy – Nanaimo Group 4 Deep-water Gravity Processes 6 Turbulent Flow 6 Liquefied Flow 6 Grain Flow 8 Cohesive Flow 8 Thesis Organization 8 References 9

CHAPTER TWO: STRATIGRAPHIC EVOLUTION OF A LONG-LIVED SUBMARINE CHANNEL SYSTEM IN THE LATE CRETACEOUS NANAIMO GROUP, BRITISH COLUMBIA, CANADA 13 Introduction 13 Study Area and Geologic Setting 16 Methodology 20 Lithofacies Results 22 Stratigraphic Results 22 Cedar District Formation 25 De Courcy Formation 29 Northumberland Formation 30 Geoffrey Formation 31 Spray Formation 34 Gabriola Formation 38 Nanaimo Group Depositional Setting Interpretation 39 Discussion: The Origins of Conduit-bounding Stratigraphic Surfaces 43 Conclusions 49 References 50

CHAPTER THREE: OUTCROP EVIDENCE FOR PROTRACTED SEDIMENT TRANSFER INA COMPOSITE SUBMARINE CHANNEL MARGIN DEPOSIT, HORNBY ISLAND, CANADA 60 Introduction 60 Background Geology and Study Area 62 Methodology 64 Architectural Elements 66

v Third-order Architectural Elements 68 Fourth-order Architectural Elements 71 Fifth-order Architectural Elements 78 Discussion: Evidence for Knickpoint Erosion in Deep-water Outcrops 81 Conclusions 84 References 85

CHAPTER FOUR: CONCLUSIONS AND FUTURE WORK 92 Future Work 94 References 97

APPENDIX 100

vi LIST OF FIGURES

Figure 1.1 - Strait of Georgia Regional Study Area 2 Figure 1.2 - Deep-water Gravity Flow Processes 7

Figure 2.1 - Evolutionary models of conduit stratigraphy 15 Figure 2.2 – Map of Study Area 16 Figure 2.3 – Stratigraphic Chart of the Nanaimo Group 17 Figure 2.4 – Geological Map of Hornby and Denman islands 19 Figure 2.5 – Maps of Paleoflow and Injection Rose Diagrams 21 Figure 2.6 – Lithofacies of the Nanaimo Group 26 Figure 2.7 – Sedimentological Characteristics of the Cedar District Formation 27 Figure 2.8 – Stratigraphic Sections of the Nanaimo Group 28 Figure 2.9 – Sedimentological Characteristics of the Northumberland and Geoffrey Formations 32 Figure 2.10 – Submarine Channel Fill, Geoffrey Formation 33 Figure 2.11 – Sedimentological Characteristics of the Spray and Gabriola Formations 36 Figure 2.12 – Cross-Section of Channel System 40 Figure 2.13 – Lateral Facies Transitions From Channelform Axes to Margin 42 Figure 2.14 – Modern Analog 44 Figure 2.15 – Depositional Evolution of the Nanaimo Group Channel Evolution 47

Figure 3.1 – Stratigraphic Architectural Elements 60 Figure 3.2 – Map of Study Area 61 Figure 3.3 – Stratigraphic Chart of the Nanaimo Group 63 Figure 3.4 – Background Geology 64 Figure 3.5 – Geology Map of Downes Point 65 Figure 3.6 – Overview of Architectural Elements Classification 67 Figure 3.7 – Cross Section of Downes Point 68 Figure 3.8 – Photos of Third-Order Architectural Elements 69 Figure 3.9 – Photos of Fourth-Order Architectural Elements 75 Figure 3.10 – Schematic Block Diagram 79 Figure 3.11 – Knickpoint Morphology 83

Figure 4.1 – Modern Submarine Canyons 95

vii LIST OF TABLES

Table - 2.1 Lithofacies 23 Table - 3.1 Third-order Elements 70 Table - 4.1 Canyon size related to respective river input 96

viii CHAPTER ONE: INTRODUCTION

PROJECT MOTIVATION

Deep-water submarine channel systems are important conduits for immense volumes of sediment from continental margins to the deep ocean (Mutti and Normark, 1987; Kolla et al., 2001; Deptuck et al., 2003; Mayall et al., 2006; Covault et al., 2012; Sylvester et al., 2012). Deep-water environments are diverse and complex, but unlike other depositional environments the processes that govern sediment dispersal are rarely observed (Sumner and Paull, 2014). Continental slopes are commonly inaccessible or inhospitable for the observation of gravity flows as they distribute sediment tens to hundreds of kilometers down slope at high velocities. As such, physical models and numerical simulations are utilized to decipher gravity flow processes that produce the stratigraphic products observed in ancient examples at the Earth’s surface (Cartigny et al., 2014; Jackson, 2014; de Leeuw et al., 2016). The Gulf Islands of British Columbia, Canada, contain well-exposed outcrops of a coarse grained submarine conduit, facilitating interpretations of formative high-energy processes that formed the subsequent stratigraphic product (Fig. 1.1 A). The motivation behind this thesis is to: (i) decipher the depositional environment preserved on Hornby and Denman islands (Fig. 1.1); (ii) reconstruct channel evolution and provide insight to paleogeographic interpretations, and (iii) link sedimentological process to the rock record. This was accomplished by conducting a large-scale analysis of outcrops on Hornby and Denman islands, as well as detailed observations at select outcrop locations. Hornby and Denman islands expose a unique outcrop orientation as the structural dip is 180° from the paleoflow direction (Fig. 1.1B).This results in the ability to view topographic features and lithological variations in a strike-oriented cross-section.

1 o A 50

Comox

St Nanaimo Group r Gulf Islands Comox Basin ait Thesis study area of G e Vancouver Island o Vancouver Nanaimo rg ia 49o Nanaimo Basin Int’l border

Pa ci c Oc ean 50 km 125o 124o

B Paleoow N Denman Dip Direction Island (aligned with paleoow)

Hornby Island

5 km

Figure 1.1 Strait of Georgia Regional Study Area. (A) Regional map of straight of Georgia on the west coast of Canada. The Nanaimo Group deposits outcrop in the locations coloured in dark gray on the eastern side of Vancouver Island and on the Gulf Islands. The Nanaimo Group was originally separated into a northern Comox basin and a southern Nanaimo Basin, but has since been amalgamated into a greater Nanaimo Basin. (B) Satellite image from GoogleEarth Pro of the thesis study area - Hornby and Denman islands.

2 NANAIMO BASIN

The Strait of Georgia is located between the west coast of mainland British Columbia, Canada and Vancouver Island (Fig. 1.1A). The Strait of Georgia is characterized by outcropping sedimentary rocks attributed to the Nanaimo Basin, a forearc basin formed during the Late Jurassic to Early Cretaceous as a product of accretion of the exotic Insular terrane onto the North American continent (Mustard, 1994). An alternating compressional to transpressional tectonic regime from the Jurassic and Holocene formed the Coast Mountains to the east of the Strait of Georgia on the mainland (Mustard, 1994). The definition of the Nanaimo Basin has undergone multiple nomenclature changes and distinctions over the past forty years. Previously this region was proposed to constitute two basins, a southern Nanaimo Basin and a northern Comox Basin (Fig. 1.1A) (Fiske, 1977; Allmaras, 1979; England, 1990; England and Hiscott, 1992; Cathyl- Bickford and Hoffman, 1998). It was then defined by one basin denoted Georgia Basin (Mustard, 1994; England and Bustin, 1998; Enkin et al., 2001), and finally to one large all encompassing Nanaimo Basin (Katnick and Mustard 2003). Beyond nomenclature, the tectonic regime of the basin has also provided contention with three main hypotheses: a strike-slip basin (Pacht, 1980; 1984), a foreland basin (Brandon, 1988; Mustard, 1994) and a forearc basin (Muller and Jeletzky, 1970; England, 1990). The strike slip model was disproven as the transcurrent faults that were interpreted by Pacht (1980) were since interpreted to be Tertiary in age, after sedimentation ceased in the basin. This thesis supports a fore-arc interpretation, however, it is perhaps not crucial to identify the basin type but to understand that the sediments studied here were deposited in a large broad depression adjacent to an active magmatic arc. The Nanaimo Basin has been extensively researched in many areas. Muller and Jeletzky (1970) determined a regional lithostratigraphic and biostratigraphic correlation that was further revised by Ward (1978), England (1990), and Mustard (1994). Basin

3 wide synthesis was put forth by Pacht (1980) and England (1990). Further studies have been conducted on specific topics surrounding the basin such as structural controls on sedimentation (England and Calon, 1991; England and Bustin, 1998; Journeay and Morrison, 1999), biostratigraphy (Haggart, 1994; Haggart et al., 2005 and sediment provenance (Mahoney et al., 1999; Katnick and Mustard, 2003; Treptau, 2002).

STRATIGRAPHY – NANAIMO GROUP

The Nanaimo Group is a 4 km thick siliciclastic succession that was previously interpreted to span the Turonian (Haggart, 1991) to Maastrichtian (McGugan 1979); however, indicates that it is as young as the Danian (Coutts et al., 2015). The deposits unconformably overlie the Coast Mountain Batholith (Mustard, 1994). The Nanaimo Group is exposed on the Gulf Islands and the eastern side of Vancouver Island (Fig. 1.1). The group comprises eleven formations with the Lower Nanaimo Group composed of non-marine to marginal marine deposits, overlain by deep-water deposits of the Upper Nanaimo Group. The group is largely composed of intercalated sandstone/siltstone; a majority of the Gulf Islands are largely composed of coarse-grained deep-water deposits that form topographic highs (England and Hiscott, 1992; Bain and Hubbard, 2016). Conversely intertidal bays and passes are underlain by fine-grained deposits.The basin’s sediment is sourced from the Coast Mountain Batholith located on the east side of the basin (Mustard, 1994; Mahoney et al., 1999; Katnick and Mustard, 2003). The nomenclature of the Nanaimo Group has been widely discussed (Muller Jeletsky, 1970; Ward, 1978; England, 1990; McGugan 1990; Mustard, 1994;) this thesis adopts the Nanaimo Group nomenclature from Katnick and Mustard, (2003). Interest in the Nanaimo Group was developed in 1852 as a coalmine prospect on Vancouver Island. The name of the Nanaimo Group was proposed by Dawson (1887; 1890) who interpreted the Lower Nanaimo Group deposits on Vancouver Island to have a fluvial to marine origin. A unified stratigraphic nomenclature of formations was created

4 by Muller and Jeletsky (1970) through a regional mapping endeavor. Other detailed work was conducted on the southern Gulf Islands (Fig. 1.1A). More relevant to this thesis, pointed research was completed on Hornby and Denman islands by Fiske (1977) and Allmaras (1979) (Fig. 1.1B). The units were initially interpreted to be deposited in a fluvial-deltaic environment with four separate transgressive cycles. Both Fiske (1977) and Allmaras (1979) compiled geological maps of Hornby Island and interpreted a western sediment source from the Wrangellia terrane, part of the Insular Superterrane. Their studies provided further evidence for a fluvial and deltaic depositional environment.The first interpretation of a deep-water depositional environment was made by Pacht (1980) who attributed coarse-grained facies of the Upper Nanaimo Group to be submarine fan deposition. Furthering this interpretation England (1990) interpreted deposits of the Southern Gulf Islands to be submarine channel in origin. Mustard (1994) added that the units were actually associated with an easterly-derived sediment source (Coast Mountain Batholith) through sandstone composition and detrital zircon dating. Katnick (2001 unpublished M.Sc. thesis) characterized the stratigraphy on Denman and Hornby islands specifically, focusing on a more detailed evaluation of the stratigraphic facies and provenance. Large faults initially interpreted by Muller and Jeletzky (1970) from lithological juxtaposition of conglomerate and siltstone, were disproven by Katnick (2001) and Katnick and Mustard (2003); they demonstrated that they were formed depositionally related contacts in a submarine fan environment. The work presented in this thesis hones the submarine depositional environment and interprets the deposits on Hornby and Denman islands to have been deposited in a large-scale submarine conduit.

5 DEEP-WATER GRAVITY FLOW PROCESSES

The deep-water deposits of the Nanaimo Group were deposited through a myriad of gravity flow processes. The most common deposits on the islands are turbidites that deposited from turbulent flows, but other deposits from liquefied flows, grain flows and cohesive flows are also present (Fig. 1.2A). As such, a brief description of these processes is provided below.

TURBULENT FLOW

In turbulent flows, grains are suspended by fluid turbulence that is strongly influenced by concentration of grains (Lowe, 1982). High concentrations of grains are more likely to experience grain interactions that generate dispersive pressure. Figure 1.2B depicts the shape and turbulent movement within a turbidity current. Large clasts are transported at the bottom of the flow and small particles are suspended in a cloud at the top of the flow. There are two types of turbidity currents that are distinguishable in outcrop: (i) low-density (Bouma sequence Tc-e, Fig. 1.2 C) and (ii) high-density (Ta- b, Fig. 1.2C). Lowe (1982) classified high-density turbidite deposits based on grain size and created respective categories for sandstone and conglomerate. Sandstones are classified as: (i) S3 - Massive to graded fine to coarse-grained sandstone, deposited through suspension. (ii) S2 - Inversely graded fine to coarse grained sandstone deposited by a traction carpet, and; (iii) S1 – sediment deposited through traction or rolling along the base of the turbidity current (Fig. 1.2D). The scheme used to classify conglomeratic deposits is similar, however the main grain sizes range from pebbles to boulders and are denoted by a ‘R’ instead of an ‘S’.

LIQUEFIED FLOW Liquefied flows are the product of pore fluid escaping from the bottom of the laminar flow as grains settle out of suspension (Lowe, 1982; Fig. 1.2A).These flows can

6 A Flow behaviour Sediment Gravity Flow

Fluidal ow Plastic ow

Flow behaviour Turbulent Liqueed Grain Cohesive Flow ow ow debris ow Low- & High- concentration suspensions

Dominant grain supported mechanism “Hindered Fluid settling” Grain Matrix turbulence by escaping interaction strength pore uid

Sedimentation Traction & Suspension Frictional Cohesive mechanism suspension sedimentation freezing freezing

B relative velocity prole ambient water turbulent suspension ow head clouds thrusted backwards ow tail

large clast transport 10 cm slope at base of ow

C D

S3 Te

Td S Tc 2

Tb S1

R Ta 3

Figure 1.2 Deep-water gravity flow processes. (A) Sediment gravity-flow behaviour as determined by their sediment composition and concentration, as well as dominant grain-support mechanism. Note that individual flows vary spatially and temporally (modified from Middleton and Hampton, 1976). (B) Downstream variation in process. (C-D) One- dimensional stratigraphic product of turbidity currents. Bouma Sequence in C records deposition from low- to high- density turbidity currents; Lowe Sequence in D records deposition from high-density turbidity currents.

7 accelerate into turbidity currents and the deposit will have a non-graded parallel laminat- ed bottom with a turbidite deposit on top.

GRAIN FLOW

Grain flows are supported through dispersive pressures that are the result of grain-to-grain interactions (Lowe, 1982; Fig. 1.2A). Grains are kept in suspension and pore water acts as a lubricant between grains but does not add any cohesive strength to the flow. Grain flows deposits solidify through frictional freezing as transported grains interlock.

COHESIVE DEBRIS FLOW

Grains within a cohesive flow are suspended by sediment-water matrix, not through dispersive pressures from grain-to-grain interactions (Lowe, 1982; Fig. 1.2A). Large pebbles or cobbles in the flow may be in grain-to-grain contact, but small sand and silt-sized particles are buoyantly floating within a matrix. As the matrix of the flow is a mixture of sediment and water the flow is held together through the cohesive strength of the matrix and the flow moves en-mass.

THESIS ORGANIZATION

This thesis is the first in a larger study of the Nanaimo Group with the objective to characterize the Gulf Islands and reconstruct a paleogeographic history from the deep- water deposits. The thesis is organized into two individual papers with an additional appendix that includes supplementary measured sections. Chapter 2 features the results of a field-based study on Hornby and Denman islands that deciphers submarine conduit deposits and their paleogeographic implications. A 19.5 km wide and 1.5 km thick stratigraphic package records a protracted history of sediment transfer through a long- lived submarine channel system. This paper has been published in sedimentary Geology

8 (Bain and Hubbard, 2016). Chapter 3 investigates stratigraphic and facies relationships at the edge of a mapped submarine conduit deposit at Hornby Island in order to deduce formative processes. REFERENCES Allmaras, J.M. 1979. Stratigraphy and sedimentology of the Cretaceous Nanaimo Group, Denman Island, British Columbia. M.Sc. thesis, Oregon State, University, Corvallis, Oregon. Brandon, M.T., Cowan, D.S., Vance, J.A., 1988. The Late Cretaceous San Juan thrust system, San Juan Islands, Washington. Geological Society of America, Special paper 221, 81. Cartigny, J.B., Ventra, D., Postma, G., van Den Berg, J.J., 2014. Morphodynamics and sedimentary structures of bedforms under supercritical-flow conditions: New insights from flume experiments. Sedimentology 61, 712-748. Cathyl-Bickford, C.G., Hoffman, G.L. 1998. Geological maps of the Nanaimo and Comox Coalfields, British Columbia Ministry of Energy and Mines, Open File 1998-7, 14 maps, scale 1:20,000. Coutts, D., Matthews, W., Guest, B., Hubbard, S.M., 2015. The Implications of Detrital Zircon Maximum Depositional Age (MDA) from Large Sample Datasets. AGU Fall meeting December 14-18. San Fransisco. Covault, J.B., Shelef, E., Traer, M., Hubbard, S.M., Romans, B.W., Fildani, A., 2012. Deep-water channel run-out length: insights from seafloor geomorphology. Journal of Sedimentary Research 82, 21-36. Dawson, G.M., 1887. Report on a geological examination of the northern part of Vancouver Island and adjacent coasts; Geological Survey of Canada, Annual Report, 1888, 2, 1-107. Dawson, G.M., 1890. Notes on the Cretaceous of the British Columbia region: the Nanaimo Group. American Journal of Science 39, 180-183. de Leeuw, J., Eggenhuisen, J.T., Cartigny, M.J.B., 2016. Morphodynamics of submarine channel inception revealed by new experimental approach. Nature Communications 7, 1-7. Deptuck, M.E., Steffens, G.S., Barton, M., Pirmez, C., 2003. Architecture and evolution of upper fan channel-belts on the Niger Delta slope and in the Arabian Sea. Marine and Petroleum Geology 20, 649- 676. England, T.D.J. 1990. Late Cretaceous to Paleogene structural evolution of the Georgia Basin, southwestern British Columbia- PhD Thesis, Memorial University, St. John’s Newfoundland. England, T.D.J., Calon, T.J., 1991. The Cowichan fold and thrust system, Vancouver Island, southwestern British Columbia. Geological Society of America Bulletin 103, 336-362.

9 England, T.D.J., Hiscott, R.N., 1992. Lithostratigraphy and deep-water setting of the upper Nanaimo Group (Upper Cretaceous), outer Gulf Islands of southwestern British Columbia. Canadian Journal of Earth Sciences 29, 574–595. England, T.D.J., Bustin, R.M. 1998. Architecture of the Georgia Basin southwestern British Columbia. Bulletin of Canadian Petroleum Geology 46, 288-320. Enkin, R.J., Baker, J, Mustard, P.S., 2001. Paleomagnetism of the Upper Cretaceous Nanaimo Group, southwestern, Canadian Cordillera. Canadian Journal of Earth Science 38, 1403-1422. Fiske, D.A., 1977. Stratigraphy, sedimentology and structure of the Late Cretaceous Nanaimo Group, Hornby Island, British Columbia, Canada. M.Sc. thesis, Oregon State University, Corvallis, Oregon. Haggart, J.W., 1991. A new assessment of the age of the basal Nanaimo Group, Gulf Islands, British Columbia in Current Research, Part E; Geological Survey of Canada, Paper 91-1E, p. 77-82. Haggart, J.W., 1994. Turonian (Upper Cretaceous) strata and biochronology of southern Gulf Islands, British Columbia; in Current Research 1994-A; Geological Survey of Canada, p. 159-164. Haggart, J.W. 1994. Turonian (Upper Cretaceous) strata and biochronology of southern Gulf Islands, British Columbia. In Current research, Geological Survey of Canada, Paper 1994-A, pp.159–164. Haggart, J.W., Ward, P.D., Orr, W., 2005. Turonian (Upper Cretaceous) lithostratigraphy and biochronology, southern Gulf Islands, British Columbia, and northern San Juan Islands, Washington State. Canadian Journal of Earth Science 42, 2001-2020. Jackson, A.A. (2014) Characterizing static reservoir connectivity of deep-water slope deposits using detailed outcrop-based facies models, Tres Pasos Formation, Magallanes basin, Chilean Patagonia. M.Sc. Thesis, University of Utah, Salt Lake City, UT. Journeay, J.M., Morrison, J., 1999. Field investigation of Cenozoic structures in the northern Cascadia forearc, southwestern British Columbia. Geological Survey of Canada Current Research 99-1A, 239- 250. Katnick, D.C., Mustard, P.S., 2003. Geology of Denman and Hornby islands, British Columbia: implications for Nanaimo Basin evolution and formal definition of the Geoffrey and Spray formations, Upper Cretaceous Nanaimo Group. Canadian Journal of Earth Sciences 40, 375-392. Kolla, V., Bourges, P.H., Urruty, J.M., Safa, P., 2001. Evolution of deep-water Tertiary sinuous channels offshore Angola (west Africa) and implications for reservoir architecture. American Association of Petroleum Geologists Bulletin 85, 1373-1405. Lowe, D.R. 1982. Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents. Journal of Sedimentary Petrology 52, 279–297.

10 Mahoney, J.B., Mustard, P.S., Haggart, J.W., Friedman, R.M., Fanning, M.C., McNicoll, V.J., 1999. Archean zircons in Cretaceous strata of the western Canadian Cordillera: The ‘’Baja B.C.’’ hypothesis fails a ‘’crucial test’’. Geology 27, 195-198. Mayall, M., Jones, E., Casey, M., 2006. Turbidite channel reservoirs – key elements in facies prediction and effective development. Marine and Petroleum Geology 23, 821-841. McGugan, A., 1979. Biostratigraphy and Paleoecology of Upper Cretaceous (Campanian and Maestrichtian) formaninifera from the upper Lambert, Northumberland, and Spray formations. Canadian Journal of Earth Sciences 16, 2263-2274. McGugan, A., 1990. Upper Cretaceous (Santonian-lower Campanian) foraminiferal biostratigraphy of the Nanaimo Group, subsurface of the Parksville area, eastern Vancouver Island; Bulletin of Canadian Petroleum Geology 38, 28-28. Muller, J.E. and Jeletzky, J.A., 1970. Geology of the Upper Cretaceous Nanaimo Group, Vancouver Island and Gulf Islands, British Columbia, Geological Survey of Canada, Paper 69-25, 24 Mustard, P.S., 1994. The Upper Cretaceous Nanaimo Group, Georgia Basin. In: Monger, J.W.H. (Eds.), Geology and Geological Hazards of the Vancouver region, southwestern British Columbia. Geological Survey of Canada Bulletin 481, pp. 27-95. Mutti, E., Normark, W.R., 1987. Comparing examples of modern and ancient turbidite systems: problems and concepts, in Legget, J.K., and Zuffa, G.G., eds., Deep Water Clastic Deposits: Models and Case Histories. Marine Clastic Sedimentology, p. 1-38. Pacht, J.A. 1980. Sedimentology and petrology of the Late Cretaceous Nanaimo Group in the Nanaimo Basin, Washington and British Columbia: Implications for Late Cretaceous tectonics - Ph.D thesis. Ohio State University, Columbus, Ohio. Pacht, J.A. 1984. Petrologic evolution and paleogeography of the Late Cretaceous Nanaimo Basin, Washington and British Columbia: implications for Cretaceous tectonics. Geological Society of America Bulletin 95, 766-788. Sumner, E.J., Paull, C.K., 2014. Swept away by a turbidity current in Mendocino submarine canyon, California. Geophysics Research Letters 41, 7611-7618. Sylvester, Z., Deptuck, M.E., Prather, B.E., Pirmez, C., O’Byrne, C., 2012. Seismic stratigraphy of a shelf-edge delta and linked submarine channels in the Northeastern Gulf of Mexico: in Prather, M.E., Deptuck, M.E., Mohrig, D., van Hoorn, B., and Wynn, R., eds., Application of the Principles of Seismic Geomorphology to Continental-Slope and Base-of-Slope Systems: Case Studies from Seafloor and Near-Seafloor Analogues: SEPM, Special Publication 99, p. 31-59. Treptau, K., 2002. An integrated sedimentological-ichnological paleoecological assessment of the Upper Campanian Cedar District Formation, Upper Cretaceous Nanaimo Group, Southwest British Columbia.

11 M.Sc. Thesis, Simon Fraser University, Burnaby, Canada. Ward, P.D. 1978. Revisions to the stratigraphy and biochronology of the Upper Cretaceous Nanaimo Group, British Columbia and Washington State. Canadian Journal of Earth Sciences 15, 405-423.

12 CHAPTER TWO: STRATIGRAPHIC EVOLUTION OF A LONG-LIVED SUBMARINE CHANNEL SYSTEM IN THE LATE CRETACEOUS NANAIMO GROUP, BRITISH COLUMBIA, CANADA

INTRODUCTION

Submarine canyons and channels facilitate the ultimate phase of sediment transport within a sedimentary routing system prior to deposition in submarine fan lobes (Normark, 1970; Shepard, 1981; Normark and Carlson, 2003; Paull et al., 2011; Peakall and Sumner, 2015). These submarine conduits are often zones of coarse sediment bypass, sculpted by erosion and later filled by fine-grained sediment that derives from relatively quiescent conditions that persist when the conduit is inactive (Shepard, 1981; Mutti and Normark, 1987; Beaubouef et al., 1999; Hubbard et al., 2014; Stevenson et al., 2015). However, significant volumes of coarse-grained sediment can accumulate as a result of various processes. Ponding of turbidity currents on rugose slopes within deep-sea sediment-routing systems, for example, is a commonly ascribed mechanism for sand and gravel sedimentation (Clark and Pickering, 1996; Prather, 2003; Cronin et al., 2005; McHargue et al., 2011). Bed load transport is also responsible for sand and gravel deposition within channelized slope seascapes (Piper and Kontopoulos, 1994; Pickering et al., 2001; Covault et al., 2014; Postma et al., 2014). In the stratigraphic record, submarine channel fills commonly coalesce spatially and temporally (e.g., Deptuck et al., 2003; Hodgson et al., 2011; Macauley and Hubbard, 2013), providing insight into up-dip and down-dip sediment-routing system segments (Romans and Graham, 2011). The lateral mobility of long-lived channel systems is often limited by structural control, or establishment of degradational or constructional channel margin relief, which can suppress or even prohibit avulsions (Deptuck et al., 2007; Clark and Cartwright, 2009; Mayall et al., 2010). Deducing the paleogeographic context or controls on sediment transfer in ancient,

13 large-scale deep-water conduits relies on accurate interpretations of the stratigraphic record. Long-lived conduits can be established through deep incision of submarine canyons, with bathymetric relief of hundreds to >1000 meters (e.g., Normark and Carlson, 2003; Williams et al., 1998) (Fig. 2.1A). Alternatively, a combination of erosion events followed by aggradation of channel floor and levee deposits can yield a broadly comparable stratigraphic product through protracted evolution of channels with more subdued bathymetric relief (e.g., Deptuck et al., 2003, 2007; Sylvester et al., 2011) (Fig. 2.1B). Despite differences in formative geomorphic elements on the paleo-seafloor, differentiating the outcropping stratigraphic architecture of these systems is non- trivial (cf., Gamberi et al., 2013) and has implications for understanding the frequency and magnitude of controlling processes such as mountain building and denudation or eustatic sea-level fluctuations (Posamentier and Kolla, 2003; Mountjoy et al., 2009; Hodgson et al., 2011; Di Celma et al., 2014). In end-member scenarios, down-cutting of deep submarine canyons is generally attributed to allocyclic controls (Posamentier et al., 1991), whereas development of a channel-levee complex may be largely driven by autocyclic processes (Sylvester et al., 2011). Detailed characterization of out-of- channel strata, including background upper slope units or levee deposits, can be used to differentiate channelized depositional systems (e.g., Hansen et al., 2015). However, both are often dominated by dilute turbidity current deposits, making bed-scale observations inconclusive in some instances. At a broader scale, levee tapering away from channel axes can be diagnostic of overbank processes, but outcrops are rarely extensive enough to capture km-scale patterns known from seafloor data (e.g., Fig. 2.1B), and the relief of these features is often muted due to differential compaction in both outcrop and subsurface datasets. In this study, outcrops of Late Cretaceous deep-water strata (Nanaimo Group) from western British Columbia, Canada (Fig. 2.2) provide a unique perspective of a long-lived (~15 Ma) deep-sea sedimentary conduit, recorded in 1.5 km of strata over

14 an along-strike distance of ~20 km. Canyon-channel systems of this magnitude can be characterized from seismic and bathymetric datasets (Barnard, 1978; Normark and Carlson, 2003; Von Rad and Tahir, 1997; Ferry et al., 2004; Hubbard et al., 2009; Catterall et al., 2010; Kolla et al., 2012), however, their scale makes them difficult to preserve and interpret from outcrop – the units of the Nanaimo Group may represent the largest ancient, composite submarine canyon-channel system exposed and recognized at the Earth’s surface. We use sedimentological evidence for erosion, sediment bypass and deposition, as well as stratigraphic evidence including stacked channel bodies to interpret the evolution of the depositional system. A primary objective is to deduce a most plausible origin for the submarine conduit-bounding stratigraphic surface, in consideration of deeply incised canyon versus relatively low-relief submarine channel modern analogs (Fig. 2.1). We emphasize that high-relief geomorphic channels from the modern seafloor are often not appropriate analogs to similarly scaled stratigraphic channelforms. These stratigraphic products are commonly generated from the evolution of lower relief channel systems, and are therefore highly composite in nature. This has

A Time 1 B

Time 2

Time 3

100-1000 m

1-15 km

Figure 2.1 Evolutionary models to account for development of submarine conduit stratigraphy. (A) Submarine canyon is largely incised during Time 1 and subsequently fills with mass-transport deposits and turbidite channels. (B) Channel- levee complex is established by early erosion, mass-wasting and levee construction and evolves through aggradation of deposits associated with low-relief geomorphic channels. In both A and B channelform stratigraphic surfaces bound the composite conduit fills, however they form under the influence of distinct processes (i.e., early incision versus protracted erosion and aggradation).

15 significant implications for interpretation of such features in the stratigraphic record, and particularly controls on sediment transfer in ancient source-to-sink systems.

STUDY AREA AND GEOLOGICAL SETTING

The geological history of the western North American Cordillera was shaped by Mesozoic–Paleogene accretion of allochthonous terranes onto the margin of the continent (Price and Monger, 2000). Since the Early Jurassic, the Canadian Cordillera has grown laterally by ~500 km through addition of terranes as a result of protracted subduction at the western margin of the North American Plate (Monger et al., 1982). The composite Insular Superterrane, of which the studied Nanaimo Group strata are a part, docked onto the western margin of North America by the Late Jurassic or Early Cretaceous (Monger et al., 1982). Following accretion, lateral strike-slip movement displaced units northwards

50o

Comox CANADA BC Northern Gulf Study area Islands S area in Fig. 2.4 tr ait

of Vancouver Island G e Vancouver Nanaimo o rg ia 49o Southern Gulf Int’l border Islands USA Pa ci c Nanaimo Group Oc ean outcrop belt 50 km 125o 124o Figure 2.2 Map of the study area including Upper Cretaceous Nanaimo Group outcrop distribution on Vancouver Island and the Gulf islands in the Straight of Georgia (modified from Mustard, 1994). The study area (Hornby and Denman islands) is located within the outlined black box. Inset map provides the location of the study area in British Columbia (BC), Canada.

16 into the Eocene (Mustard, 1994; Irving et al., 1996; Monger and Price, 1996; Ward et al., 1997; Mahoney et al., 1999). The Nanaimo Group consists of a 4 km-thick succession of Late Cretaceous siliciclastic sedimentary rocks that were deposited in the northwest-southeast trending Nanaimo Basin (Mustard, 1994) (Fig. 2.2). The basin has been interpreted both as a fore-arc (Muller and Jeletzky, 1970; England, 1990) and a peripheral foreland (Mustard, 1994). The Nanaimo Group unconformably overlies Paleozoic through Jurassic sedimentary and volcanic basement of the Insular Superterrane (Mustard, 1994; Greene et al., 2010), consisting of a series of lithostratigraphic units that record an overall transition from non-marine to marginal-marine and deep-marine settings (Mustard, 1994; Katnick and Mustard, 2003) (Fig. 2.3). The Nanaimo Group crops out on the eastern margin of

Time This Depositional Architecture Scale Study Gabriola Spray

Geo rey

Maastrichtian ? Northumberland

De Courcy (deep-water strata) (deep-water Upper Cedar District Hornby & DenmanHornby Islands Trent River

Campanian Tsable Mbr. Lower Puntledge Mbr.

Santonian Comox marine strata) Vancouver Island Vancouver (non- to marginal- (non- to

Figure 2.3 Stratigraphic chart of the Nanaimo Group, with nomenclature and ages on Hornby and Denman islands adapted from Katnick and Mustard (2003). The lower part of the stratigraphic column adapted from England (1990).

17 Vancouver Island, and on the Gulf Islands within the Strait of Georgia, British Columbia, Canada (Fig. 2.2). Deep-water strata on Hornby and Denman islands are the focus of this study. In this area, strata dip shallowly to the northeast, and previous work has demonstrated that paleoflow was 180° from the dip direction towards the west-southwest (Katnick and Mustard, 2003). Therefore, a stretched depositional strike-oriented cross-section perspective is evident in map view (Fig. 2.4). At Hornby and Denman islands the upper Nanaimo Group (Campanian to Maastrichtian) alternates between the siltstone- and mudstone-dominated Cedar District, Northumberland and Spray formations, and thick- bedded sandstone and conglomerate of the De Courcy, Geoffrey and Gabriola formations (Mustard, 1994; Katnick and Mustard, 2003) (Figs. 2.3, 2.4). The lateral and vertical juxtaposition of resistant sandstone and conglomerate adjacent to recessive siltstone and mudstone provides a strong influence on topographic relief. For example, the 300 m high Mount Geoffrey on Hornby Island is composed primarily of resistant conglomerates of the Geoffrey Formation, whereas intertidal areas are often underlain by recessive, fine- grained formations (Fig. 2.4). Pacht (1980) attributed coarse-grained facies of the Nanaimo Group to submarine fan deposits. Mustard et al. (1995) and Mahoney et al. (1999) analyzed sandstone mineral composition and detrital zircon age spectra, and interpreted a Coast Mountains sediment source from the east. Katnick and Mustard (2003) undertook a thorough sedimentology study on Denman and Hornby islands, reinforcing the eastern sediment source interpretation with sandstone and clast composition analyses. They also demonstrated that large faults interpreted by Muller and Jeletzky (1970) were in fact stratigraphic contacts. Rowe et al. (2002) measured parallel, sub-vertical clastic intrusions on the southwest shoreline of Hornby Island and interpreted that they formed during gravitational failure of a deep-water channel margin. We build on this work, with an emphasis on deducing a

18 B 7

6 4 9 A 6 7 12 6 10 6 9 7 Tribune Bay Intertidal Outline Island Outline 6 Elevation 11 8 300 m 8

7 5 9 49o35’ Denman Island 8 0 m 13 10 Third Geo rey Ridge 5 km Upper Geo rey Ridge Lower Geo rey Ridge

Fig. 2.9A Grassy Denman Pt. Collishaw Pt. Point Hornby Island

Fig. 2.8A Ferry Terminal Whaling Stn. Bay Phipps Pt. Fig. 2.7A

Spray Pt. Fig. 2.8B Mt. (Fig. 2.11A-B) Geo rey Helliwell Fig. 2.11C x GABRIOLA FM Dunlap Pt. Water well Gravelly Bay 49o30’ Downes Pt. Quaternary SPRAY FM Conglomerate-dominated Fig. 2.9B-C Fig. 2.8C GEOFFREY FM Sandstone-dominated Norman Pt. CEDAR DISTRICT FM NORTHUMBERLAND FM Sandstone and Siltstone Fig. 2.7D Boyle Pt. Siltstone-dominated DE COURCY FM MTD Fig. 2.7C

5 km 124o50’ 124o40’

Figure 2.4 (A) Geological map of Hornby and Denman islands constrained by outcrops and water wells. (B) Digital elevation model of the islands, as well as representative strike and dip measurements. A large northwest-southeast trending ridge on Denman Island and Mount Geoffrey on Hornby Island are highlighted in darker grey. The topographic highs are defined by resistant coarse-grained conglomerate and sandstone.

19 comprehensive deep-water deposition and stratigraphic evolution history for the Nanaimo Group.

METHODOLOGY

Exposures of the Nanaimo Group persist in the intertidal zone as well as isolated outcrops inland on Hornby and Denman islands. Approximately 1000 m of stratigraphy was measured at cm to dm-scale, documenting key sedimentary features such as grain size, grain sorting, primary sedimentary structures, bedding thickness and bedding contacts, which form the basis for lithofacies delineation. The distribution of strata is documented in a geological map of the islands (Fig. 2.4). This map is augmented with data from water wells (Government of British Columbia, 2015); the first lithologic unit encountered in each well was tabulated and plotted in order to constrain stratigraphic correlations between outcrop locations. Two thousand and sixty eight paleoflow indicators were measured from sole marks, the elongate edges of scours, imbricated clasts, ripple-marks, and cross- stratification (Fig. 2.5A). Sandstone injectites are locally abundant, and 420 strike orientations were measured in order to constrain stresses in the paleoslope setting (Fig. 2.5B). Photomosaics and high-resolution satellite images were used to interpret stratigraphic architecture and further aid interpretations. Thousands of data points were collected with a differential global positioning system (dGPS) that achieves < 50 cm resolution in x, y and z directions. The dGPS was used to survey features such as small- scale architectural boundaries of stratigraphic units, vertical and lateral facies transitions, locations of measured sections, formation-scale contacts, and topographic variations; the dataset forms the basis of a high-resolution digital elevation model (Fig. 2.4).

20 A n =50 Mapped units: Features measured:

n Quaternary n =50 n=3 =50 Conglomerate-dominated Imbricated Clasts Sandstone-dominated Sole Marks n=1 Sandstone and Siltstone Ripples + Cross Straticaiton Siltstone Scours n n =50 =50 MTD

n =50 n =37 n n=1 n =50 =34 n n n =50 =50 =50 n=8 n n n=6 n=13 =50 =50 n =50 n=3 n n =50 =50 n n=8 =50 n =50 n=4 n n =50 n=7 =50 n n=11 =50 n=7 n n n=10 =50 =50 n =50 n =23 n=5 n=2 n n=5 =60 n=4 n=3 n=12 n n n =42 n n =50 =50 =50 =50 n=7 n n=2 =50 n n =50 =50 n =50 n =50 n=3

n=2 n=13 n 5 km n =50 =50 n=3 n n =50 n =50 =50

B C All Paleo ow

n=150 n=93 n=84 n=2089 n=267

n=19 n=13 n=92 n=100 n=128 n=108 n=29 n=108

n=15 n=10 n=61 n=165

n=14 n=100 n=128 n=74 n=25

n=21 n=87 n=22 n=7 n=61 n=40 5 km n=5 n=100 n=13 n=151 5 km n=150 n=41 n=7

Figure 2.5 (A) Paleoflow rose diagrams distinguished by location and feature measured, overlain on geological map from Fig. 2.4A. (B) Simplified paleoflow featuring rose diagrams grouped based on location and stratigraphic position; note that the arithmetic mean for all 2089 measurements is 227° (southwest). (C) Clastic injection measurements, which are generally oriented parallel (40 -70°) or perpendicular (110-140°) to the inferred paleoslope (based on paleoflow trend).

21 LITHOFACIES RESULTS

Ten lithofacies are distinguished in the study area, and their detailed descriptions and process-based interpretations are provided in Table 2.1. Each of the lithofacies is attributed to sediment gravity flow processes, based on bed-scale characteristics (Fig. 2.6) (cf., Bouma, 1962; Lowe, 1982; Mulder and Alexander, 2001; Talling et al., 2012; Postma et al., 2014). Thick-bedded conglomerate (L1) and sandstone (L3) are attributed to high concentration turbidity currents and bedload transport. Chaotically bedded matrix-supported conglomerate (L2), sandstone (L9), and mudstone with sandstone (L10) are interpreted to derive from mass-transport processes. Sandstone of L4 crosscuts strata and was emplaced during clastic intrusion events (cf., Duranti and Hurst, 2004). Thin- bedded sandstone with pebbles (L5) records lag deposits from largely bypassing currents (cf., Mutti and Normark, 1987). Thinly bedded siltstone and sandstone (L7) record deposition from dilute, low-density turbidity currents. Thinly interbedded siltstone and muddy sandstone are considered as the product of hybrid flows (Haughton et al., 2009). In general, these facies-scale interpretations are consistent with a deep-water setting, as presented by Rowe et al. (2002) and Katnick and Mustard (2003).

STRATIGRAPHIC RESULTS

The six previously defined formations are described from oldest to youngest, including their location, nature of contacts with adjacent formations, lithology, internal stratigraphic surfaces, and paleoflow, as well as other notable characteristics that inform paleoenvironmental interpretations.

22 Table 2.1 Lithofacies on Hornby and Denman islands. Lithofacies Lithology Grading Thickness Physical Lithological Basal Turbidite Process Structures Accessories Contact Division Interpretation Character

L1 – Clast- Clast-supported Typically Beds Structureless or Rounded, poor to Sharp to Ta or R3, High concentration Supported granule to cobble ungraded, with thickness: planar well-sorted undulating, with rare R1 turbidity currents, Conglomerate conglomerate with rare normal 0.2 - 5 m laminations. extrabasinal clasts, often loaded. bedload transport, medium to very grading. Thickness: Commonly 1-30 cm in diameter cyclic steps. coarse matrix <7 m imbricated. with an average of 5 cm.

L2 – Matrix- Matrix-supported Disorganized, Beds: 0.2 m None Extrabasinal clasts Planar to None Coherent debris flow supported granule to pebble structureless – 6m 1-10cm in diameter undulating Conglomerate conglomerate with Thickness: with an average od very fine sand to <6 m 3 cm. Intrabasinal cobble sized clasts sandstone fragments

L3 – Thick- Fine to very- Normally Beds: 0.2 – Commonly Extrabasinal granule Planar to Ta or S3 High concentration bedded coarse sandstone graded from 5m structureless to pebble clasts undulating, turbidity currents, sandstone occasional Thickness: planar, low angle and/or intrabasinal commonly bedload transport, granule to <10m cross mudstone clasts amalgamated cyclic steps. pebble matrix stratification. (0.05m to 1.5m supported base Flame structures, diameter) in lags. to fine sole marks, dish sandstone structures often present

L4 – Sandstone Medium sandstone None Thickness: Rare planar Mudstone clasts, Undulating. None Rapid, remobilization of injections 2 – 120 cm bedding more commonly 1-4 Commonly fluids and sand often c, but reaches up to vertical (90°) through fractures due to 15 cm in diameter. with less overpressure common sub- vertical (16° to 78°)

L5 – Thin Medium to very None Beds: 1cm None Matrix (sands) Undulating Ta High density turbidity bedded coarse sandstone – 10 cm supported currents, traction and sandstone with (sand), 1 extrabasinal suspension deposition. pebbles cm – 40 cm granules and (siltstone) pebbles (<1.5cm) 23 Table 2.1 Lithofacies on Hornby and Denman islands (continued). Lithofacies Lithology Grading Thickness Physical Lithological Basal Turbidit Process Structures Accessories Contact e Interpretation Character Division

L6 - Thinly Siltstone, very Normally graded Beds: 1cm – Ripples, flame None Planar Tc, Td, Te Low density turbidity interbedded fine to fine from fine 20cm (sand) structures, sole current, traction and siltstone and sandstone sandstone at the Thickness: <6m marks, planar suspension sandstone base to siltstone laminations, deposition. wavy laminations. Lenticular and planar sandstone beds. L7 - Thinly Siltstone, very- Graded from a Beds: 10-50 cm Ripples, flame None Planar None Slurry/hybrid flows interbedded fine to medium clean sandstone sandstone, 5-30 structures, soft siltstone and sandstone at the base to a cm siltstone sediment muddy muddy Thickness: < 9 m deformation, sandstone sandstone and wavy to planar capped by laminations siltstone L8 – Siltstone Predominately Structureless Beds: < 1cm Ripples, wavy Rare chert clasts 1cm- Planar sharp Td, Te Suspension with limited siltstone with siltstone. sand laminations, 5cm to deposition, low sandstone beds limited very fine Normally graded Siltstone < 20cm planar Gradational density turbidity sandstone from very fine Thickness: < laminations current sandstone when 10m present.

L9 – Chaotically Mudstone or Normally grades Beds: < 7m Contorted, Intrabasinal mudstone Sharp None Slumping or rafting bedded sandstone similar to L3 Thickness: 22m overturned clasts <1m in sandstone matrix. Fine to sandstone diameter. Intrabasinal coarse grained blocks. sandstone blocks up sandstone to 30 m in diameter. blocks/beds Extrabasinal clasts up to 20cm with a 5cm average.

L10 - Mudstone, None Thickness: up to Contorted Rare floating Sharp None Mass wasting Chaotically siltstone, fine to 18 m thick mudstone fabric extrabasinal granules bedded medium grained and sandstone and pebbles. mudstone with sandstone beds 24 sandstone beds CEDAR DISTRICT FORMATION Description

The Campanian Cedar District Formation is primarily exposed on the western side of Denman Island (Fig. 2.4); it is sharply overlain by the De Courcy Formation. The Cedar District Formation is mostly composed of mudstone with isolated layers of very fine-grained sandstone (L8; Figs. 2.6H, 2.7). On the northwest extent of Denman Island it is characterized by chaotically bedded mudstone with thin sandstone beds (L10; Fig. 2.6I). The oldest strata present near the western Ferry Terminal (Fig. 2.4), contain thick mudstone beds with broad undulating erosion surfaces mantled by thin layers of coarse- grained sandstone and granules (L5; Figs. 2.6E, 2.8A). Paleoflow indicators are limited, however cross-stratification was measured in two localities (Fig. 2.5A); in one instance, paleoflow is clearly southward, consistent with previous measurements on Denman Island (Katnick and Mustard, 2003). In the other case, cross-stratification verges to the north-northeast, ~180° from other measurements, associated with the fill of scours at least 6 m long (Figs. 2.7A, B). Vertical to sub-vertical injectites composed of medium-grained sandstone (L4; Fig. 2.6D) were observed in 7 distinct localities, striking 40-140° (Figs. 2.5B, 2.7C).

Interpretation

Fine-grained facies of the Cedar District Formation were deposited by turbidity currents, with chaotically bedded units the result of mass wasting processes (Table 1). Thin coarse-grained sandstone beds with granules at the lowest stratigraphic level represent high-energy lag deposits, and are evidence for significant sediment bypass (cf., Stevenson et al., 2015) (Fig. 2.8A). Mudstone associated with lag units is possibly derived from the tails of bypassing currents; as such, the fine-grained component of the facies association does not record quiescent conditions on the paleo-seafloor (cf. Mutti and Normark, 1987; Hubbard et al., 2014). Consistent with this interpretation

25 A B C

10 cm 10 cm 1 m

D E F

5 cm 3 cm 10 cm

G H I

5 cm 5 cm 10 cm

Figure 2.6 Lithofacies of the Nanaimo Group. (A) L1, clast-supported conglomerate. (B) L2, matrix-supported conglomerate with mudstone-dominated matrix. (C) L3, thick-bedded sandstone. (D) L4, cross-sectional (bedding plane) perspective of a vertical sandstone injectite. (E) L5, mudstone with erosional surfaces (dashed white lines) overlain by pebble lags. (F) L6, thinly interbedded siltstone and sandstone. (G) L7, muddy sandstone bed with erosive base indicated with dashed black line. (H) L8, thinly interbedded siltstone with limited sandstone. (I) L10, chaotically bedded unit overlain by concordant, horizontally bedded units. are the presence of broad, up-dip propagating cross-strata (cf., Pickering et al., 2001; Kostic, 2011) (Figs. 2.7 A, B). Up-dip migrating bedforms attributed to super-critical flow are commonly described from the floors of high-gradient submarine channels (e.g., Cartigny et al., 2011; Kostic, 2011; Covault et al., 2014; Postma et al., 2014; Pemberton et al., 2016). Thin-bedded units composed of Bouma-type turbidites accumulated under

26 A

B bar migration direction conduit paleo ow

n=3

migration is to the northeast, up paleoslope

C N

5 m

1 m

Figure 2.7 Sedimentologic and stratigraphic characteristics of the Cedar District Formation. (A) Photograph and (B) line-drawing trace of interbedded sandstone and mudstone characterized by back-set stratification (i.e., beds dip up paleoslope) at the base of the stratigraphic succession at Denman Ferry Terminal, Denman Island. (B) Line-drawing trace of area outlined by black box in Part A. (C) Vertical sandstone injections in mudstone at Boyle Point, Denman Island. (D) Thinly interbedded sandstone and siltstone (Lithofacies - L8) at the western end of Denman Island. Outcrop locations indicated on Fig. 2.4A.

27 relatively quiescent conditions on distal levees or the background slope (Figueiredo et al., 2010) (Fig. 2.7D). The thick section of chaotically bedded deposits at the northwest end of Denman Island is located laterally juxtaposed against coarse-grained deposits of the De Courcy Formation, representing a stratigraphic relationship consistent with submarine channel margin processes (cf., Deptuck et al., 2003) (Fig. 2.4).

A B C pebble lag 20 L8 L5 45 L10

20 20 L3

L6 L10 L8 15 L3

Northumberland Fm 40 40 L3 De Courcy Fm.

15 L6 15 L3 mudstone- mudstone contact L10 between MTD and concordant beds

35 35 L5 scour draped by thin conglomerate lag 10 10

scour draped by coarse-grained 5 sandstone and L10 mudstone rip-up clasts 30 30 L6 L8

5 5

L3 0 m m ss vf f m c vc g p c L1

Conglomerate 25 25 Sandstone L2 0 m 0 m Siltstone m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c Dish structures Soft-sediment Planar Ripples Sandstone clasts Mudstone deformation strati cation clasts

Figure 2.8 Representative stratigraphic sections of the Nanaimo Group. (A) Interbedded mudstone with coarse sandstone–pebble lags in the Cedar District Formation near the Denman Ferry Terminal. These lags record sediment bypass. (B) Fining upward from coarse-grained conglomerate, to thick amalgamated sandstone, to interbedded sandstone and siltstone beds at the east side of Denman Island. Upwards fining records the lateral migration and vertical aggradation of the channel system. (C) Thinly interbedded siltstone with sandstone transitioning upwards to chaotically bedded mudstone and sandstone on the south side of Hornby Island. Outcrop locations indicated on Fig. 2.4A.

28 Clastic injectites are widespread in deep-water strata (Huuse et al., 2003; Hurst et al., 2005; Cobain et al., 2015). Fluid mobilization in unconsolidated sediments requires overpressure, seal failure and fluidization of a clastic horizon (Jolly and Lonergan, 2002). The orientations of injectites are commonly linked to the stress and strain orientation present during emplacement; they have been shown to be accordant with paleo fault networks (e.g., Huuse et al., 2003; Bureau et al., 2013), and in some instances have been related to extension on paleoslopes (e.g., Rowe et al., 2002). Based on paleoflow measurements on Hornby and Denman islands, the paleoslope verged to the southwest- west (Fig. 2.5A), which is roughly parallel or perpendicular to the two main populations of injectites in the Cedar District Formation (Figs. 2.5B, 2.7C).

DE COURCY FORMATION Description

Prominent, resistant ridges that trend northwest-southeast along the axis of Denman Island are composed of the De Courcy Formation (Fig. 2.4). The De Courcy Formation is also exposed at Norman Point on the southwestern tip of Hornby Island. The formation sharply overlies, and is locally in lateral contact with the Cedar District Formation on Denman Island (Fig. 2.4). Two lithologies are dominant, including amalgamated clast-supported conglomerate (L1; Fig. 2.6A) and amalgamated thick- bedded, fine to coarse-grained sandstone (L3; Fig. 2.6C) (Table 1). Commonly, the resistant conglomerate and sandstone units overlie broad (>3 km) concave-up erosional surfaces (Fig. 2.4). Matrix-supported conglomerate (L2; Fig. 2.6B) is locally present amongst beds of L1. The De Courcy Formation exhibits upward fining from conglomerate (L1) to interbedded sandstone (L3), and lastly thinly interbedded sandstone and siltstone (L6) on the eastern edge of Denman Island, north of the Gravelly Bay Ferry Terminal (Fig. 2.8B). South to southwesterly paleoflow was dominant, based on measurements of imbricated clasts and the edges of scour surfaces (Fig. 2.5A).

29 Clastic injectites are locally persistent at the edges of thick sandstone and conglomerate channelform bodies (Fig. 2.5B).

Interpretation

Broad channelform sedimentary bodies composed of conglomerate and sandstone laterally juxtaposed against fine-grained units of the Cedar District Formation are consistent with composite channel fill deposits (e.g., Morris and Busby-Spera, 1990; Crane and Lowe, 2008; Jobe et al., 2010). Chaotically bedded facies (L10) of the Cedar District Formation lateral to the De Courcy Formation on the northwest edge of the island record slumping of submarine conduit margins (cf. Deptuck et al., 2003; Jobe et al., 2011; Micallef et al., 2014) (Fig. 2.4). Upward-fining packages like that observed on the east side of Denman Island (Fig. 2.8B) are commonly associated with the coupled lateral migration and aggradation of a channelized depocentre through time (e.g., Schwarz and Arnott, 2007; Hubbard et al., 2009). Widespread injectite complexes are common to the margins of channelized turbidite systems (e.g., Duranti and Hurst, 2004; Hubbard et al., 2007; Jackson et al., 2011) (Fig. 2.5B).

NORTHUMBERLAND FORMATION Description

The Northumberland Formation is present on both Denman and Hornby islands (Fig. 2.4), where it has yielded a broad diversity of fossils (Ludvigsen and Beard, 1997). On the eastern side of Denman Island, it gradationally overlies the De Courcy Formation (Fig. 2.8B). The formation is composed of siltstone with rare thin sandstone beds (L6, L8) on the western side of Hornby Island. At Collishaw Point, L8 is overlain by chaotically bedded sandstone (L9) of the Geoffrey Formation across a sharp contact (Figs. 2.4, 2.9A). On the southeastern edge of Hornby Island, the Northumberland Formation consists of interstratified siltstone (L8) and overlying mudstone-dominated

30 chaotically bedded deposits (L10) (Fig. 2.8C). The youngest deposits of the formation are present adjacent to coarse-grained facies of the Geoffrey Formation (Fig. 2.4). Paleoflow indicators were not observed in the formation. Injectites (L4) were measured at Phipps Point (Fig. 2.4) on the western side of Hornby Island, including two main populations, striking 120-130° and 60-70° (Fig. 2.5B).

Interpretation

Siltstone-dominated strata (L6, L8) of the Northumberland Formation are largely attributable to low density turbidity currents, although evidence for mass-wasting processes (L9) is locally significant. The presence of turbiditic fine-grained deposits lateral to Geoffrey Formation conglomerate and sandstone suggests two plausible origins: (1) slope strata subsequently eroded into by submarine channels (e.g., Surpless et al., 2009); or (2) channel-overbank strata (e.g., Kane and Hodgson, 2011). Mass-wasting deposits and widespread clastic injectites are consistent with both interpretations.

GEOFFREY FORMATION Description

The resistant Geoffrey Formation is located solely on Hornby Island and is best exposed on the northern part of the island at Grassy Point, at the peak of Mt. Geoffrey, and on the southeast shoreline at Downes Point (Fig. 2.4). The formation defines two prominent ridges on the western side of the island that trend roughly north-northwest to southeast (Fig. 2.4B), both of which comprise broad (up to 6 km) channelform architectural bodies in strike view (Fig. 2.4). A third, more subdued channelform unit is exposed on the east side of the island at Downes Point, which is 2-3 km wide (Fig. 2.4B). Characteristic lithologies of the formation include amalgamated stratified clast-supported conglomerate (L1) and thick-bedded sandstone (L3), with matrix-supported conglomerate a minor component (L2) (Figs. 2.6A-C, 2.9).

31 A Coherent, tilted beds

Beds at regional Brecciated strike and dip

2 m Direction of conduit axis B

1 m

paleo ow

Figure 2.9 Sedimentologic and stratigraphic characteristics of the Northumberland and Geoffrey formations. (A) Slump block tilted southwards towards the center of the submarine conduit axis, Collishaw Point. (B) Conglomerate and sandstone channel axis deposits of the Geoffrey Formation at Downes Point. (C) Photograph and (D) line-drawing trace of scour-based sandstone characterized by low angle cross-stratified sandstone at Downes Point. Outcrop locations indicated on Fig. 2.4A.

The basal contact of the formation is overlain by L9 on the north side of the island to the east of Collishaw Point (Figs. 2.4, 2.9A). Facies L9 consists of blocks of coherently bedded sandstone and mudstone that is discordant to regional bedding, which are up to 30 m in diameter (e.g., Figs. 2.10A, B). Lateral facies transitions are particularly well

32 exposed at Downes Point, where interbedded sandstone and mudstone (L3, L5), stratified conglomerate (L1), and chaotically bedded sandstone (L9) onlaps a steep concave-up stratigraphic surface (Fig. 2.10A). The base of the formation in the vicinity of Downes Point includes stratified conglomeratic lag deposits (Fig. 2.9B) and thinly interbedded sandstone and siltstone associated with broad, wavy erosion surfaces (Fig. 2.10C). Sandstone-dominated units are characterized by undulose scour surfaces overlain by cross-stratified lithofacies, where low-angle cross stratification is characteristic (Figs. 2.9 C, D). Southward to westward paleoflow was measured; the two prominent ridges on the western side of Hornby Island are characterized by distinct paleoflow trends (Fig. 2.5A). Imbricated clasts from the lower ridge indicate average flow to 272° (n=150) versus 236° (n=176) for the upper ridge. The third coarse-grained unit that defines Downes Point on the east side of Hornby island is characterized by average paleoflow to 227° (n=164).

A 15 A’

10 A B

0 m ss vff m c vc g p c

0 m ss vf f m c vc g p c

15 30 25 m

0 m ss vf f m c vc g p c

10 30

0 m ss vf f m c vc g p c

5 25

0 20 m ss vf f m c vc g p c

0 m ss vf f m c vc g p c

10 5 B

0 m ss vf f m c vc g p c

0 m ss vff m c vc g p c conduit margin conduit base slump blocks derived from margin 10 m Conglomerate-dominated Debris ow deposits 50 m Sandstone-dominated Slump-block-dominated Siltstone-dominated

thin-bedded scour ll

scour surface

Figure 2.10 The base and edge of a submarine channel fill in the Geoffrey Formation at Downes Point, Hornby Island. (A) Strike-oriented stratigraphic cross-section documenting the transition between channel axis at left and margin at right, highlighting a series of nested erosion surfaces and evidence for mass-wasting. (B) Satellite image of overturned slump block ~25 m in diameter exposed on the land surface. Location indicated in Part A. (C) Scour at the base of the submarine conduit (just left of strata featured in Part A) infilled with thinly interbedded mudstone and sandstone. Downes Point location indicated on Fig. 2.4A.

33 Injectites are prevalent in thinly interbedded sandstone and siltstone at Downes Point (Rowe et al., 2002). Interpretation

Conglomerate and sandstone facies are attributed to high-density turbidity flows; clast imbrication and planar stratification is consistent with bedload transport of clasts beneath turbidity currents (e.g., Hughes Clarke et al., 2006). Postma et al. (2014) recently suggested that broad, low angle stratification could be attributable to cyclic steps, which record hydraulic jumps at the base of steep submarine conduits (Cartigny et al., 2011; Fildani et al., 2013; Pemberton et al., 2016) (Fig. 2.9C). The blocks of coherently bedded sandstone and mudstone up to 30 m in diameter, as well as chaotically bedded sandstone prevalent overlying the base of the broad conglomerate- and sandstone- prone channelform sedimentary bodies, are evidence for mass failure of a submarine channel margin (cf., Deptuck et al., 2003; Sultan et al., 2007; Almeida et al., 2015) (Fig. 2.10). This is consistent with the interpretation of Rowe et al. (2002), who used slump orientations, paleoflow indicators and injectite measurements from Downes Point to conclude that the outcrop featured a submarine channel margin deposit. The three ridge- forming conglomeratic channelform bodies of the Geoffrey Formation that transect Hornby Island (Fig. 2.4B) are considered to represent composite submarine conduit fills (e.g., Campion et al., 2000; Beaubouef, 2004; Jobe et al., 2010).Variable paleoflow amongst these composite channelform bodies is attributed to the sinuous nature of successive submarine channel complexes (e.g., Crane and Lowe., 2008; Macauley and Hubbard, 2013).

SPRAY FORMATION

Description

The Spray Formation is best exposed along the intertidal zone on the southeast side of Hornby Island between Downes Point and the eastern extent of Tribune Bay

34 (Fig. 2.4). At this locality, the underlying Geoffrey Formation normally grades upward from conglomerate (L1) to thinly interbedded sandstone and siltstone (L6), and finally to fine-grained units of the Spray Formation (Fig. 2.4). Notably, this exposure of the Spray Formation is exposed lateral (to the southeast) to Geoffrey Formation strata that crop out on the north side of Hornby Island (Fig. 2.4). On the southeast side of Hornby Island, the Spray Formation is dominantly comprised of interbedded siltstone and sandstone (L6) as well as siltstone beds with limited sandstone beds (L8) (Fig. 2.6). Commonly, sandstone beds are tabular; however, lenticular concave upward surfaces define sedimentary packages that are up to 30-50 m wide and 3-4 m thick, which truncate underlying strata. The resistant peninsula at Spray Point records a unique outcrop of the formation, where lateral facies shift from thick- bedded and amalgamated sandstone to thinly interbedded sandstone and siltstone over <10 m (Figs. 2.11A, B); these transitions are present within channelform sedimentary bodies up to 12 m thick and >100 m wide. Truncation surfaces are locally overlain by siltstone beds, and grain-size profiles through the sedimentary bodies are characterized by upward bed-thickening towards their margins (Fig. 2.11B). Sole marks at the base of the formation indicate southward paleoflow, whereas current ripples and elongated edges of scour surfaces at the upper part of the section indicate west-northwest paleoflow (Fig. 2.5A). The exposure of Spray Formation on the north side of Hornby Island east of Grassy Point consists of a thick succession of matrix-supported conglomerate (L2) and chaotically bedded units (L9, L10). Thick-bedded sandstone (F3), as well as rare clast- supported conglomerate (L1) and thinly interbedded siltstone and sandstone (F6), are also present. Imbricated clast measurements indicate paleoflow was to the west-northwest (Fig. 2.5A).

35 Non-amalgamated to amalgamated bed transition A

1 m

B Upward bed thickening Upward 2 m

Inclined strati cation

2 m

Figure 2.11 Sedimentologic and stratigraphic characteristics of the Spray and Gabriola formations. (A, B) Transitions from channel axial thick-bedded amalgamated sandstone to marginal non-amalgamated to amalgamated sandstone and siltstone at Spray Point. Paleoflow was into the plane of the page, to the west. (C) Stratified conglomerate of the Gabriola Formation at Helliwell Park; paleoflow was southwestward, out of the plane of the photograph. Outcrop locations indicated on Fig. 2.4A.

36 Interpretation

Matrix-supported conglomerate, thick-bedded sandstone, and rare clast-supported conglomerate of the Spray Formation on the north side of Hornby Island are consistent with deposition in submarine channel axes (Jobe et al., 2010; Hodgson et al., 2011). The thick section of the formation on the southeast side of the island, with thin-bedded strata punctuated by sandstone-dominated scour fills records sedimentation lateral to the primary axis of sediment transport, in an off-axis or perhaps out-of-channel setting such as an internal levee or terrace (cf., Deptuck et al., 2003; Kane and Hodgson, 2011; Figueiredo et al., 2013; Hansen et al., 2015). Consistent with this interpretation, paleoflow in this thin-bedded strata is southward, diverging ~90 degrees from paleoflow measurements in channel axis deposits (Kane et al., 2010). The sandy channelform bodies exposed at Spray Point contain characteristics of submarine channel fills, including amalgamated sandstone in their axes that transition rapidly to thinly interbedded facies towards their margins (cf., Campion et al., 2005; Pyles et al., 2010; Hubbard et al., 2014). The top of Geoffrey Formation on the north side of Hornby Island is in a stratigraphic position that is: (A) above that of the Geoffrey Formation exposed at Downes Point; and (B) lateral to the Spray Formation between Downes and Spray Point (Fig. 2.4). We interpret this relationship to be the product of a complex multi-phase history of submarine conduit excavation, filling, and lateral migration (cf., Morris and Busby-Spera, 1990; Beaubeouef, 2004; Sylvester et al., 2011). These observations demonstrate that the lithostratigraphic delineation of the Nanaimo Group was complicated by the discontinuous (channelized) nature of units; the complex stratigraphic relationships likely led to early interpretations of extensive faults in the study area (Muller and Jeletzky, 1970).

37 GABRIOLA FORMATION Description

The Maastrichtian Gabriola Formation is exposed on the eastern side of Hornby Island (Fig. 2.4). The formation exhibits an overall coarsening upward trend; conspicuously, the peninsula composed of the formation defines a channelform shape (Fig. 2.4). Basal deposits that crop out on the eastern edge of Tribune Bay consist of tabular, thinly interbedded siltstone and sandstone (L6, L8). These transition upwards across a sharply defined stratigraphic surface to thick-bedded sandstone deposits (L3). Locally, truncation surfaces with > 1 m of relief are overlain by thinly interbedded siltstone and muddy sandstone (L7). The sandstone-dominated strata (L3) are up to 40 m thick; this unit is sharply overlain by thick-bedded, clast-supported conglomerate (L1), which dominates the upper two-thirds of the Gabriola Formation (Fig. 2.11C). Imbricated clasts indicate that paleoflow was westwards (261°) (Fig. 2.5A).

Interpretation

The resistant coarse-grained deposits of the Gabriola Formation comprise a composite channelform body approximately 5 km wide and 250 m thick, which is incised into underlying fine-grained units of the Spray Formation. Similarly scaled composite submarine channel bodies have been widely observed in outcrops of the Late Cretaceous Magallanes foreland basin of southern Chile (e.g., Beaubouef, 2004; Crane and Lowe., 2008; Hubbard et al., 2008; Jobe et al., 2010), Early Cretaceous fore-arc basin strata of the Great Valley Group, California (e.g., Campion et al., 2000), and Late Cretaceous fore-arc units of the Rosario Group, Baja California (Morris and Busby-Spera, 1990; Kane et al., 2007). Bed-scale observations are indicative of dominant traction transport of sand and gravel beneath turbidity currents; sediment bypass was evidently significant (Stevenson et al., 2015). Stratified sandstone and conglomerate, as well as widespread

38 scours, are also consistent with supercritical flow in high-gradient submarine channels (e.g., Postma et al., 2014).

NANAIMO GROUP DEPOSITIONAL SETTING INTERPRETATION

A 3-D model of Hornby and Denman islands, consisting of the geological map from Fig. 2.4A draped on topography, is oriented such that an ideal depositional strike perspective of the units exposed is observed, with paleoflow out of the plane (Figs. 2.12A, B). This highlights the lateral transitions of composite, resistant channelform sedimentary bodies towards the center of the islands, to more recessive lithologies at island edges. A stratigraphic cross-section is constructed from this perspective, projecting data from both islands onto a single plane (Fig. 2.12C). While Katnick and Mustard (2003) reported a proximal submarine fan setting, the numerous channelform bodies demonstrated in this study more specifically suggest a slope conduit setting for the Nanaimo Group on Hornby and Denman islands. Here we summarize bed-scale and stratigraphic architecture observations that corroborate this interpretation. At the bed scale, evidence for significant sediment bypass includes scour surfaces draped by pebble lags and mudstone beds (Fig. 2.8A), sedimentary structures including back-set stratification (Figs. 2.7A, B), imbricated clasts and high-energy cross-stratification (Figs. 2.9 B, D), and an abundance of conglomerate beds (Mutti and Normark, 1987; Postma et al., 2014; Stevenson et al., 2015). Out-of-channel facies are recorded by fine-grained units adjacent to coarse-grained channel bodies (Fig. 2.13), which are commonly dominated by interbedded facies (Figs. 2.4, 2.7D, 2.8C). Bed- scale characteristics broadly support an out-of-channel interpretation, which can include internal levee, terrace, external levee or background slope environments (Hubbard et al., 2009; Figuieredo et al., 2010; Kane and Hodgson, 2011; Hansen et al., 2015).

39 Prominent ridges A

600 m GPS Points N 3x VE Island outlines

600 m N 3x VE

Island outlines Gabriola Fm 1500 C Spray Fm 1250 1000 Northumberland Fm Geo rey Fm 750 500 De Courcy Fm 250 Cedar District Fm 0 m 0 km 5 km 10 km 15 km 20 km

Channel Fill Deposits Out-of-Channel Deposits

D Composite Channelforms (Channel Complexes) Composite Channelforms (Channel Complex-Sets)

Conglomerate-dominated Fig. 2.13A-D Sandstone-dominated Sandstone and Siltstone Siltstone-dominated Fig. 2.13E-H MTD 5 km

Figure 2.12 Strike-oriented stratigraphic cross-section of the channel system mapped in the Nanaimo Group at Hornby and Denman islands. (A) Perspective satellite image of the islands draped over the digital elevation model (image courtesy of Google Earth). Average paleoflow was out of the plane of the image. (B) Image from (A) draped with geological map from Fig. 4, highlighting the link between topographic highs and coarse-grained channel fill deposits. (C) Interpreted cross-section of the channel system based on mapping, and particularly perspective in Part B. Dashed red lines encapsulate composite units (i.e., channel complex sets of Sprague et al., 2002), loosely defined by groupings of thick amalgamated coarse-grained channelform units mapped on the islands (Fig. 4). (D) Geological map overlain with interpreted channel complex set boundaries from Part C. Note the presence of mass-transport deposits (MTDs) at the edges of the interpreted, highly composite surfaces.

40 At the scale of stratigraphic architectural elements, a submarine canyon or channel complex interpretation for Nanaimo Group strata is supported by a series of observations: (1) Lateral juxtaposition of conglomerate- and sandstone-filled channel bodies against thin-bedded fine-grained units (Figs. 12, 13). Dilute turbidity current deposits (Fig. 2.7D) and mass transport deposits are consistent with a slope setting, including levees or internal levees (Figueiredo et al., 2010; Kane and Hodgson, 2011). Along-strike exposures of thin-bedded units that are 600-800 m long between Dunlop and Downes points, as well as at Collishaw Point, on Hornby Island (Fig. 2.4) are unfortunately not long enough to observe any km-scale architectural changes such as levee tapering away from channel axes (cf., Dykstra et al., 2012). It is plausible that key thickness changes were muted by stratal compaction and are too subtle to detect in intertidal exposures. (2) Evidence for slumping at channel margins suggests conduit wall failure (Deptuck et al., 2003; DiCelma et al., 2013; Micallef et al., 2014) (Figs. 2.9A, 2.10B). (3) The presence of numerous channel bodies (Fig. 2.12) that collectively comprise larger, more composite features is evidence for prolonged sediment transfer (cf., Morris and Busby-Spera, 1990; Deptuck et al., 2003; Anderson et al., 2006; Di Celma et al., 2011; McHargue et al., 2011; Sylvester et al., 2011; Fildani et al., 2013). Following the scheme for submarine channel stratal hierarchy of Sprague et al. (2002) and Beaubouef (2004), composite bodies include channel complexes and channel complex sets. Channel complexes are composed of two or more channel elements, whereas a channel complex-set contains two or more channel complexes (Sprague et al., 2002; Di Celma et al., 2011; Macauley and Hubbard, 2013). Interpreted channel complex sets are defined by dashed red lines in Figure 2.12C and D, each of which comprise mappable channel complexes that are generally 80-120 m thick and 1-4 km wide. The lithostratigraphic units can consist of multiple channel complex sets (e.g., De Courcy Formation), or a single channel complex set (e.g., Gabriola Formation) (Fig. 2.12C). The coarse-grained formations of the Nanaimo Group at Hornby and Denman

41 A B C D

40 cm 50 cm 60 cm 40 cm

Channel Out-of-Channel E F G H

10 cm 120 cm 15 cm 75 cm

Figure 2.13 Lateral facies transitions from channelform axes to margins. (A-D) Gabriola Formation example from Helliwell Park including: (A) Conglomeratic lag deposits and cross-stratified sandstone; (B) Mudstone-clast conglomerate; (C) Thick-bedded sandstone; and (D) Thinly interbedded sandstone and mudstone attributed to proximal levee-overbank deposition. (E-F) Geoffrey Formation example from Downes Point including: (E) Clast-supported conglomerate with well-developed clast imbrication; (F) Amalgamated thick-bedded sandstone beds with pebble lags; (G) Ripple-dominated fine-grained sandstone; and (H) Thinly interbedded sandstone and mudstone attributed to channel margin deposition. The locations of the two transects are indicated on Fig. 2.12D. 42 islands define an along-strike transect almost 20 km long and 1.5 km thick (Fig. 2.12). The formations do not project along strike, as most are in sharp lateral contact with fine-grained units (Figs. 2.12, 2.13). We suggest that the present surface morphology of Hornby and Denman islands, and the lack of resistant coarse-grained outcrops of similar age for at least 65 km to the south along the outcrop trend (Fig. 2.2), is largely controlled by the paleogeographic extent of coarse-grained submarine conduit deposits. A stable up-dip topographic landscape affiliated with a fixed point source for sediment-gravity flows is interpreted, consistent with examples of submarine channel systems that have persisted for >5-10 Ma (e.g., Williams et al., 1998; Ferry et al., 2004; Hubbard et al., 2009). Long-lived submarine channel systems are invariably associated with substantial down-dip sediment accumulations within submarine fans (Damuth and Flood, 1985; Covault et al., 2012). Unfortunately, up- and down-dip outcrops from the ancient depositional system are not preserved, and the paleogeographic–tectonic setting for the Nanaimo Group has been widely debated (Irving et al., 1996; Mahoney et al., 1999). The tectonostratigraphic terrane that includes the Nanaimo basin is thought to have translated northwards along the margin of North America from between a few hundred to ~2000 km (Irving et al., 1996; Monger and Price, 1996; Ward et al., 1997). Our interpretation of a long-lived submarine conduit can provide added insight into the timing of translation. For example, the observations presented support an interpretation that northward movement likely occurred after the depositional system was abandoned (or perhaps even that fault movement instigated abandonment).

DISCUSSION: THE ORIGINS OF CONDUIT-BOUNDING STRATIGRAPHIC SURFACES

In considering a modern analog for the Nanaimo Group, our initial intuition was to seek submarine canyons of a similar scale to the composite, strike-oriented cross-

43 A

Topographic surfaces Stratigraphic surface 0 Willapa Astoria

Amazon Bengal Indus 1

Zaire Navarin depth (km)water Bering Monterey V.E. = 48.5x Banderas

50 km Envelope surrounding composite Nanaimo Gp. channel stratigraphy 2 (Composite erosional surface of Sylvester et al., 2011)

B Sea oor Channel thalweg (Kolla et al., 2012

Fine-grained out-of-channel deposits

Coarse-grained channel ll Composite erosional surface

100 ms

5 km

Figure 2.14 Modern analog considerations for the Nanaimo Group. (A) Cross-sectional profiles across subma-rine canyons from various continental margins (modified from Normark and Carlson, 2003; Alvarez, 2007). The scale and aspect ratio of submarine canyons are comparable to the interpreted composite erosional surface that bounds the entire Nanaimo Group channel system (at right, in red). However, we interpret the strata of the Nanaimo Group to have accumulated through evolution of a multi-phase, degradational-aggradational slope channel complex (as in Part B). (B) Strike-oriented seismic reflection profile of the upper Bengal Fan channel system (modified from Kolla et al., 2012). High amplitude and discontinuous seismic reflections (i.e., coarse-grained channel fill) comprise a series of composite sedimentary bodies 5-15 km across, which are a product of the migration and aggradation of channels generally <1000 m wide (i.e., channel thalweg). section preserved at Hornby and Denman islands (i.e., 20 km wide x 1.5 km deep) (Fig. 2.12C). Canyons of this size are common, particularly in tectonically active settings such as fore-arc basins (Nelson et al., 1970; Normark and Carlson, 2003) (Fig. 2.14A). However, these modern canyons remain largely unfilled or their fill is under studied, making comparison to the ancient record problematic. The fill of ancient canyons of similar scale are commonly dominated by mudstones, with variably preserved internal

44 large-scale channelform bodies, 500-2000 m wide and 25-100 m thick (Williams et al., 1998; Anderson et al., 2006). Other canyons are characterized by abundant coarse- grained fill (e.g., Ferry et al., 2004; Ambrose et al., 2005; Jobe et al., 2011). The observation of laterally stacked channel complex and complex-set fills at the base of the succession at Denman Island (composite width = 18 km and thickness = 500-700 m), followed by vertically aligned and aggradational channel complex and complex-set fills at the top of the succession at Hornby Island (composite width = 8 km and thickness = 1000 m), records a trend comparable to that of numerous multi-phase degradational-aggradational submarine channel complex deposits observed globally (e.g., Deptuck et al., 2003; Posamentier and Kolla, 2003; Porter et al., 2006; Wynn et al., 2007; Cross et al., 2009; Jobe et al., 2010; Hodgson et al., 2011; McHargue et al., 2011; Janocko et al., 2013; Macauley and Hubbard, 2013) (cf., Figs. 1B, 12C). McHargue et al. (2011) postulated that this pattern is controlled by long-term, possibly allogenic cyclicity with the first phase controlled by waxing energy (elevated erosion and sediment bypass) and the later by an overall waning of formative currents. Hodgson et al. (2011) added that this pattern of channel stacking was controlled by systematic accommodation development, with early degradational channels attributed to low accommodation, and subsequent highly aggradational channels linked to levee build-up and increased accommodation (cf., Peakall et al., 2000; Kneller et al., 2003). The lateral mobility of late stage channels is limited by bounding high-relief levees. This patterned stratigraphic expression of channel fills recorded in the Nanaimo Group outcrop is strong support for the presence of a multi-phase degradational-aggradational channel system deposit rather than that of a submarine canyon fill. In cases of multi-phase degradational-aggradational slope channel complexes, the composite width and thickness of coarse-grained channelform bodies (i.e., channel complexes and complex sets) in the sedimentary record bears little resemblance to the morphology of the conduit that existed at the seafloor (cf., Deptuck et al., 2003; Strong

45 and Paola, 2005; Sylvester et al., 2011) (Figs. 2.1B and 2.14B). Specifically, the active channel through which coarse-grained sediment is transferred (i.e., thalweg) is much smaller than the stratigraphic channelform bodies (Fig. 2.14B). This can make the search for a modern analog to deposits like those exposed in the Nanaimo Group particularly challenging (Gamberi et al., 2013). At Hornby Island, the smallest channel fills are 10-15 m thick and presumably no more than a few hundred meters wide (Fig. 2.11A,B); these are comparable to channel elements observed in the rock record by Mutti and Normark (1987), McHargue et al. (2011) and Fildani et al. (2013). Similarly-scaled modern seafloor examples include the Lucia Chica channel system (Maier et al., 2012), upper Redondo Fan channels (Normark et al., 2009), and the thalweg of channels observed on the Niger Delta slope (Jobe et al., 2015) and proximal Bengal Fan (Fig. 2.14B). Conglomerate-prone channelform units in the Nanaimo Group are generally >1-2 km wide (Fig. 2.12). These units approximately scale to large submarine conduits, such as the Stromboli slope valley of the Tyrrhenian Sea (Gamberi and Marani, 2007) and the present-day Congo Fan channel system (Babonneau et al., 2010). Notably, the width of these Nanaimo Group units may have been controlled by lateral channel migration, leaving a diachronous stratigraphic product that is broader than the formative geomorphic channels (e.g., Abreu et al., 2003; Schwarz and Arnott, 2007; Babonneau et al., 2010; Sylvester et al., 2011; Maier et al., 2012; Janocko et al., 2013). Inclined stratigraphic surfaces within conglomeratic channel fill up to 15 m thick are rarely preserved, however these indicate that lateral channel migration may have been an important process (Fig. 2.11C). Deptuck et al. (2003) and Sylvester et al. (2011) have demonstrated, through seismic interpretation and stratigraphic modeling, that the composite basal erosional surfaces of large submarine channelforms commonly form through protracted processes and are highly diachronous in nature (Fig. 2.15A). Despite this, it can be tempting to interpret these stratigraphic surfaces as paleo-topographic, or chronostratigraphic

46 during evolution the of conduit the (indicated by dashed red lines ineach successive evolutionary stage). interpretation, diachronous highly the erosional that surface bounds entire the system is generated at various stages 1500 mthickand almostacross 20km by migrating and aggrading geomorphic channels up to 200mdeep. In such an inPartlabeled A).(D)Stages of interpreted channel system evolution, highlighting generation the of acomposite unit system with composite erosional that surface bounds entire the system identified (reddashed line analogous to surface interpreted 12Cidentified inFig. for reference to C Parts and D. (C) Interpreted sketch the of Nanaimo Group channel (B) Simplifiedthrough cross-section the Nanaimo Group channel system,scale andwith channel complexboundaries entire system (red dashed line) diachronous, is highly formed through phases of incision as well construction. as levee recording insubmarine atrend observed channel systems globally. The composite erosionalthat surface bounds the defined seismic amplitudeby high arelaterally stacked section base thetheand at of more aggradational upwards, through acomposite channel system from Indus the Fanfrom (modified Sylvesteral., et 2011). Internal channel forms Figure 2.15Depositional evolution of Nanaimo the Group channel system. (A)Strike-oriented reflection seismic profile C A D B channel ll(inyellow) Mass-transport deposit Mass-transport

1000 m 200 ms Coarse-grained Composite erosional surface Inner leveeInner lines from Fig. 2.12C Reference red 0 km 5 km 10 km 15 km Stages ofcomposite erosional 20 km surface generation (inred) surface 1500 1000 0 m 500 Same scaleasinPart B Same External levee External channel forms Internal

Time 47 horizons (e.g., Kolla et al., 2012) (Fig. 2.14A). We propose that the Nanaimo Group channel system studied formed through cyclic erosion, sedimentation and aggradation (Fig. 2.1B) rather than through the infilling of a 1500 m incision surface on the paleoseafloor (Fig. 2.1A) (cf., Sylvester et al., 2011). This interpretation demonstrates how the composite erosional surface was formed during a series of stages as the channel system evolved (Fig. 2.15D). The relatively simplistic explanation does not require particularly large sea-level fluctuations or disparate spans of time to account for early stage erosion (canyon incision) and sediment bypass versus late stage aggradation of conduit fill (Fig. 2.15). Based on our analysis, however, we note that differentiation between highly composite versus geomorphic surfaces in the outcrop record can be particularly challenging. The inherent uncertainty in stratigraphic interpretation (whether outcrop- or subsurface-based) has implications for understanding the fundamental controls on the stratigraphic record (e.g., timing and magnitude of relative sea-level fluctuations). At the facies scale, it is evident that numerous sedimentary processes sculpted the interpreted composite erosional surface that envelops coarse-grained channel units of the Nanaimo Group (Fig. 2.15C); the varied stratigraphic expression of formative processes adds to the challenge of local-scale delineation (and regional-scale interpretation) of the surface. Mudstone-prone strata punctuated by scours and overlying pebble lags (Fig. 2.8A), as well as back-set stratification (Fig. 2.7A) characterize the base of the sequence (upper Cedar District Formation; Fig. 2.12C). Coarse-grained channel fills and thin- bedded out-of-channel strata (levee or background slope) are juxtaposed across high- relief incision surfaces towards the edge of the conduit in numerous localities (Figs. 2.12 and 2.13). These incision surfaces are often associated with mass-transport deposits, which record failure and maintenance of channel walls across the study area (Fig. 2.12D); specific examples are presented from near Collishaw Point (Fig. 2.9A), northeast of Norman Point (Fig. 2.8C), and Downes Point (Fig. 2.10). Numerous phases of incision

48 are preserved by nested erosion surfaces towards the edges of large-scale submarine channel systems (Sylvester et al., 2011) (e.g., Fig. 2.15A); this is consistent with observations of the channel margin at Downes Point, where terraces are also interpreted (Fig. 2.10A). These detailed observations augment the interpretation of a multi-phase submarine channel system in the Nanaimo Group at Hornby and Denman islands, and more broadly, provide stratigraphic and sedimentological criteria for their recognition and interpretation in other basins globally.

CONCLUSIONS

Deep-water strata of the Late Cretaceous Nanaimo Group exposed on Denman and Hornby islands, British Columbia, Canada record a protracted history of sediment transfer through a long-lived submarine channel system. The stratigraphic product of sediment transfer is recorded in a strike-oriented cross-section 1.5 km thick and 19.5 km wide. In- channel facies including stratified conglomerate and sandstone are juxtaposed laterally against thin-bedded out-of-channel deposits and mass-transport deposits. These facies comprise a series of composite, conglomerate-prone channelform bodies that stratigraphically stack in two distinct phases, including an early phase of lateral migration and a later phase of vertical aggradation. This evolutionary trend compares to composite multi-phase degradational-aggradational submarine channel complexes observed on continental margins from around the world. Long-lived submarine conduits that transect continental slopes can be instigated and maintained through: (1) deep incision of canyons with bathymetric relief hundreds of meters or more, or (2) a combination of erosion of the continental slope and aggradation during the protracted evolution of channels with more subdued bathymetric relief. Both of these end members can yield a broadly comparable product in the outcrop record, making selection of modern analogs challenging. Stratigraphic interpretation of

49 these disparate end-members, however, has significant implications for understanding the frequency and magnitude of controlling processes such as mountain building and denudation or eustatic sea-level fluctuations. The immense channel system deposit studied in the Cretaceous Nanaimo Group represents a composite stratigraphic product 1500 m thick, which formed through migration and aggradation of geomorphic channels that were 200-2000 m wide and 20-200 m deep. REFERENCES

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59 CHAPTER THREE: OUTCROP EVIDENCE FOR PROTRACTED SEDIMENT TRANSFER IN A COMPOSITE SUBMARINE CHANNEL MARGIN DEPOSIT, HORNBY ISLAND, CANADA

INTRODUCTION

Submarine channels are important segments of sediment-routing systems through which significant volumes of sediment are transported to the deep ocean (McHargue and Webb, 1986; Hubscher et al., 1997; Kolla et al., 2012 ). Recent emphasis has been placed on protracted processes associated with their maintenance from both modern settings and stratigraphic datasets (Paull et al., 2005; Pyles et al., 2010; Conway et al., 2012; Covault et al., 2014; Hubbard et al., 2014). Maintaining a submarine conduit involves a variety of processes including turbidity current erosion and sediment bypass, mass-wasting of channel walls, and deposition from collapsing flows. The morphological products of these processes can include cyclic steps (Cartigny et al., 2011), scours (Macdonald et al., 2011), degradational terraces (Babonneau et al., 2010), inner levees (Deptuck et al., 2003), and ponded sand accumulations (Cronin et al., 2005) (Fig. 3.1). Stratigraphically, these processes manifest in a variety of ways (e.g., Elliot, 2000; Kane and Hodgson, 2011; Fildani et al., 2013; Hubbard et al., 2014; Hansen et al., 2015; Postma et al., 2015). At channel margins, diachronous surfaces are expected in the stratigraphic record as a result of innumerable erosion, mass failure and deposition events that sculpt the seascape over decades, millennia, or longer (de Ruig and Hubbard, 2006; Sylvester et al., 2011).

Internal Levee Internal Levee

Channel Fill

External Levee External Levee Degradational Terrace Parallel Erosion Surfaces Mass Failure Terrace

Figure 3.1 Schematic image of stratigraphic architectural elements of a submarine channel system including external levees, internal levees, degradational terrace, parallel erosion surfaces, mass failure terraces and channel fill in yellow.

60 In some instances, composite channel margins may consist of a series of closely spaced, nested parallel to sub-parallel erosion surfaces at the edges of channel form sedimentary bodies (Figs. 3.1) (Beaubouef et al., 1999; Deptuck et al., 2003). These nested erosion surfaces can bound degradational terraces, which have recently been attributed to knickpoint migration in seismic (Heinio and Davies, 2007) and modern seafloor (Hughes- Clarke et al., 2015) datasets. A knickpoint is broadly defined as a steep gradient between lower gradient sections along a channel; submarine channels adjust their profile to obtain slope equilibrium, which can occur via erosion upstream of a knickpoint and deposition downstream (Pirmez et al., 2000; Kneller, 2003). We examine a submarine channel outcrop of the Late Cretaceous Geoffrey Formation on Hornby Island, British Columbia, Canada (Fig. 3.2) in order to deduce the stratigraphic expression of submarine channel maintenance towards the edge of a conduit. The high-quality outcrops provide a unique, high-resolution perspective of the deposits of supercritical flows, degradational terrace development, channel margin mass-failure, innumerable erosion events, and sedimentation from gravity flows.The primary objective

CANADA BC Comox Study area Texada

Denman Hornby Lasqueti Figure 3.2 Map of the Study area including Upper Cretaceous Downes Point Nanaimo Group outcrop distribution on Vancouver Island Strait of Georgia and the Gulf islands in the Strait of Georgia (modified from Mustard, 1994). The study area (Downes Nanaimo Group Point, Hornby Island is outlined by the black box). Inset map provides the location of the study area in 10 km British Columbia, Canada. Nanaimo

61 for the work is to hone recognition criteria for facies- and stratigraphic architecture- scale characteristics of composite submarine channel margins with particular emphasis on products of knickpoint migration, which are widely interpreted from seismic datasets on continental margins globally.

BACKGROUND GEOLOGY AND STUDY AREA

The Late Cretaceous Nanaimo Group is a 4 km thick forearc basin succession that unconformably overlies Paleozoic – Jurassic allochtonous sedimentary and volcanic units of the Insular Superterrane, which docked onto the western margin of North America by the Late Jurassic-Early Cretaceous (Monger et al., 1982; Mustard 1994; Price and Monger 2000; Greene et al, 2010). The northwest-southeast trending basin formed adjacent to a volcanic arc, now represented by the Coast Mountain Batholith. The Nanaimo Group crops out in the Strait of Georgia, British Columbia, Canada between Vancouver and Vancouver Island (Fig. 3.2), consisting of a series of formations that transition upward from non-marine to marginal-marine, and finally deep-marine units (Fig. 3.3) (Mustard, 1994; Katnick and Mustard, 2003). In this study, we consider deep- water strata of the Campanian Geoffrey Formation, located on Hornby Island, a Northern Gulf Island situated between the two towns of Nanaimo and Comox (Fig. 3.2). The deposits on Hornby Island were previously interpreted to have been deposited in a deep- water proximal fan setting (Katnick and Mustard 2003), or more specifically, a submarine channel environment (Rowe et al., 2002; Bain and Hubbard 2016). Strata of Hornby Island dip shallowly towards the northeast with paleoflow orientation in an opposing direction towards the southwest (Katnick and Mustard, 2003; Bain and Hubbard 2016); this exposes a unique depositional strike cross-section perspective in map view (Fig. 3.4A). Hornby Island strata, along with older units exposed

62 Formation Age 2000 Gabriola

Spray Gabriola Maast 71.3 Geoffrey Northumberland De Courcy 1600 Cedar District Spray Protection

Campanian Pender Extension 83.5 1200 Haslam Geoffrey

Comox Point Downes 93.5 Santonian

800 Northumb.

DeCourcy Figure 3.3 Stratigraphic 400 Chart of the Nanaimo Group modified from Mustard 1994. (A) Stratigraphic chart of the entire Nanaimo group succession. (B) Stratigraphy

Cedar District and corresponding lithological 0 meters classification on Hornby and Denman islands. The red dashed box outlines cobble pebble

boulder stratigraphy on Downes Point, mudstone sandstone the main focus of this paper.

on Denman Island directly toward the west, comprise a composite slope conduit deposit ~20 km wide and 1.5 km thick (Fig. 3.4A,B; Bain and Hubbard 2016). The conduit routed sediment for over ~15 Ma, with early channel fills laterally stacked, followed by a transition upwards to vertically stacked channel fills (Bain and Hubbard 2016).This shift from laterally to vertically stacked channel deposits is a pattern described globally (Deptuck et al., 2003; Posamentier and Kolla 2003; Cross et al., 2009; Hodgson et al., 2011; McHargue et al., 2011; Macauley and Hubbard, 2013). The context for the analysis in this study is therefore broadly relevant to submarine channel systems as a whole.

63 A

Intertidal Outline Island Outline

Paleoow Denman Island

6 4 6 Hornby Island 7 6

Mt. Spray Pt. Geo rey x 8 Dunlop Pt. Water well 8 SPRAY FM Downes Pt. Quaternary Conglomerate-dominated 9 GEOFFREY FM Sandstone-dominated Norman Pt. 5 NORTHUMBERLANDStudy Area FM Sandstone and Siltstone Siltstone-dominated MTD

5 km

Strata exposed on Hornby Island B

Figure 3.4 (A) Geological map of Hornby and Denman islands constrained by outcrops and water wells. (B) Interpreted sketch of the Nanaimo Group channel system.

METHODOLOGY

The study focuses on an outcrop transect between Norman Point and Spray Point on the southeast shore of Hornby island, augmented by data from 165 water wells (Fig. 3.5). A series of 30 measured sections characterizes 650 m of strata at cm- dm scale. These sections document sedimentologic features such as grain size, grain

64 sorting, sedimentary structures, bed thickness, bed character and nature of bed contacts. Photomosaics and high-resolution satellite images were used to constrain stratigraphic observations. A differential global positioning system (dGPS) unit was used to collect thousands of data points with a resolution less than 50 cm in x, y and z coordinates. Stratigraphic surfaces including architectural elements, their boundaries, and measured

50 m 0 m

S26 S25

W62 S24

W51 S23 W83 8

W81 S22 W60 S51 Overbank S21 deposits W86 W89 3.9E n=2 S20 S19 S18 3.9F

8 n=3 S17 10 9

n=50 100 m W87 W112 S16 n=50 Vupper 3.9I, J S15 S6 S14 S12 V S5 lower W203 S4 S7 S13 S11 Cross-section 3.9H location (right) 3.9K S3a S3b S8 S10 Fifth Order Architectural S2 S9 S1 3.9G A’ Element Surface n=13 17 Scours W190 9 3.9B 3.9C,D 12 5 Slump/Rafted n=50 Blocks Canyon margin 9 failure zone

50 m S50 19

Water wells 0 m 3.9A Axial comglomerate deposits S49 Sandstone A Siltstone and sandstone lled scours MTD Siltstone 5 W203Water wells or measured sections in Cross-section cross-section location (left) N 250 m Satellite photo of Downes Point

Figure 3.5 Traced satellite image from GoogleEarth Pro highlighting the stratigraphy below and above Downes Point including strike and dip measurements, paleoflow rose diagrams, elevation, water wells and measured section locations. Water well locations are represented by coloured in circles, and water wells used in figure 3.7 are outlines in black. Note, the cross section location for figure 3.7 is outlined.

65 section locations were surveyed; this augmented 3D visualization and interpretation. 163 paleoflow indicators were measured including solemarks and imbricated clasts.

ARCHITECTURAL ELEMENTS

Deep-water depositional systems are commonly associated with repeated stratigraphic patterns, and architectural element schemes are commonly employed to organize observations and basic interpretations. The outcrop-based hierarchy used in this study was developed by Ghosh and Lowe (1993), and has since been implemented by numerous authors (e.g., Hickson and Lowe, 2002; Anderson et al., 2006; Crane and Lowe 2008; Hubbard et al., 2008; Slomka and Eyles, 2013; DiCelma et al., 2014). Based on Bain and Hubbard (2016), the outcrop of interest covers the margin of a significant submarine conduit fill, which locally fines upwards overall from a basal erosion surface to thin-bedded channel abandonment deposits. The outcrop includes almost 600 m of section exposed over an along-strike distance of >1000 m (Fig. 3.3). Six hierarchical levels describe Geoffrey and Spray formations stratigraphy, from small-scale sedimentary structures to large-scale stratigraphic surfaces (Fig. 3.6). First-order architectural elements are sedimentary structures that occur within an individual sedimentation unit, for example a division of the Bouma sequence (Bouma, 1962). Second-order architectural elements are individual sedimentation units that form during a single gravity flow event. First and second order architectural elements are not described in detail individually in this study, but are included in third-order architectural element descriptions. Third-order architectural elements comprise successions of stacked similar sedimentation units (i.e., lithofacies). Fourth-order architectural elements group reoccurring, genetically related third-order architectural elements (i.e., lithofacies associations). At this order, deposits can be linked to basic depositional settings, such as inner levee or channel fill. Fifth order architectural elements comprise one or more fourth-order elements that are typically

66 separated by erosional surfaces. In this study, fifth-order elements are defined by a concave-up (channel form) basal erosion surface (cf. Hubbard et al., 2008). The largest order architectural element considered (6th order) is composed of a succession of 5th order channelform bodies defined at its edges by recessive fine-grained units. In this study, seven third-order architectural elements are described based on lithologic character (Fig.3.7B). Four fourth order and one-fifth order architectural element are also identified (Fig.3.7C). Based on the scale of strata studied, it is important

1st order 2nd order 3rd order 4th order 5th order architectural architectural architectural architectural architectural element element element element element

Tc Tb IIItcss

S1/Ta

IV3 Turbidite V1 IIIcsc

IV1 R1

Planar bedding Clasts MTD Trough Cross-bedding

6th order architectural element

V3 V2

VI1

Figure 3.6 Overview of the architectural element scheme utilized in this study. First-order architectural elements are the smallest scale of observations (e.g. Individual beds). Second‐order architectural elements are individual sedimentation units that form during a single gravity flow event. Third-order architectural elements comprise successions of stacked similar sedimentation units (i.e., lithofacies). Fourth-order architectural elements group reoccurring, genetically related third-order architectural elements (i.e., lithofacies associations). Fifth-order architectural elements comprise fourth- order elements that are typically separated by erosional surfaces. Sixth order elements contain a group of fifth‐order elements.

67 to consider that fifth order and larger architectural elements are most likely the smallest scale of stratigraphy detectable in most seismic data; this is critical for comparisons between the outcrop and subsurface datasets (e.g., Abreu et al., 2003; Janocko et al., 2013).

Third-order Architectural Elements Third-order architectural elements in the outcrop include: clast supported conglomerate (IIIcsc) (Fig. 3.8A); matrix supported conglomerate (IIImsc) (Fig. 3.8B); thick-bedded sandstone (IIIts) (Fig. 3.8C); thick-bedded cross stratified sandstone

S26 5 S25

0 m ss vf f m c vc g p c 5 S24 0 m ss vf f m c vc g p c A 5 S23

10 0 m ss vf f m c vc g p c W5151 5 20 S52 600 m

0 m ss vf f m c vc g p c

10 20 S22 62

15 W62 15

25 60

0 m ss vf f m c vc g p c

10 W60 10 55 S21

5 5 50 S20

0 m ss vf f m c vc g p c 0 m ss vf f m c vc g p c

0 m ss vf f m c vc g p c

83 W83 30

15 5

10 0 m ss vf f m c vc g p c

W81 20

5 15 S19 5

0 m ss vf f m c vc g p c 0 m ss vf f m c vc g p c 10

10 Channel Fill 10 5 S18

15 5 5

0 m ss vf f m c vc g p c

0 m ss vf m c vc g p c 0 m ss vf f m c vc g p c f

5 3.9F

0 m ss vf f m c vc g p c 3.9E 5

0 m ss vf f m c vc g p c S17

10 W8686 S16

0 m ss vf f m c vc g p c

40 70 400 m

25 55 S16 A’

W112 15 11 45 W114 89 W89 114 50

10 40

45 40 3.9H

35 5

35 40 S15

30 0 m ss vf f m c vc g p c S14 30 5

0 m ss vf f m c vc g p c

25 Channel Migration 0 m ss vf f m c vc g p c 30

25 S1335 S11

20 87

20 W87 30

20 15 S12 20

Second fth order fth order Third 3.9D

5 10

25 3.9C

5 0 m ss vf f m c vc g p c

S10 15

0 m ss vf f m c vc g p c 20 3.9K

5 0 m ss vf f m c vc g p c

5 S9 25 0 m ss vf f m c vc g p c S520 S8 10 30

S7 0 m ss vf f m c vc g p c

0 m ss vf f m c vc g p c 70 S6 20

15 10

5 25 Coherent sandstone

10 3.9B 10

10 5

0 20 m ss vff m c vc g p c

5 5

60 S4

5 0 m ss vf f m c vc g p c 3.9G 5 15 10 beds 0 m ss vf f m c vc g p c Channel Migration 0 m ss vf f m c vc g p c

S36 55 S3a 5 0 m ss vf f m c vc g p c

0 m ss vf f m c vc g p c 10

5 55 15

0 m ss vf f m c vc g p c

0 m ss vf f m c vc g p c 50 10

45 S2 S3b S1 20

5 0 m ss vff m c vc g p c 20 45 5

0 m ss vf f m c vc g p c 40 15 0 m ss vf f m c vc g p c 200 m

35 10 3.9I,J

35 10

30 5

203 25 W203

0 m ss vf f m c vc g p c

20 25 0 m ss vf f m c vc g p c 20 W190 Scours

15 20

40 15 Progressive failure

10 15

35 10 Slump blocks derived

5 10

30 of canyon margin 5

0 m ss vf f m c vc g p c 5 from canyon margin

25 0 m ss vf f m c vc g p c deposits

0 m ss vf f m c vc g p c

10 First fth order First

5 Channel package

S50 0 m ss vf f m c vc g p c 25 bounding surface Conglomerate 20

15 Sandstone 10 3.9A S49 5 Siltstone

15 0 m ss vf f m c vc g p c

10 Conduit base Debris ow

5 0 m ss vf f m c vc g p c Slump-block 0 m Fifth order bounding surface 1250 m 1000 m 750 m 500 m 250 m 0 m

B Third Order Elements (III) C Fourth Order Elements (IV)

A’ A’

IV3 Unde ned IIIcbs IIIts IIIss IV1 IV4 IIImsc IIItcss IIIscss IV2 IIIcsc

Figure 3.7 Cross-sections of stratigraphy surrounding Downes Point. Note, cross-section location, water well and measured section locations are on figure 3.5. (A) Stratigraphic cross section highlighting lithology and key sedimentologic characteristics. (B) Cross section of thirdorder architectural elements. (C) Cross-section of fourthorder architectural elements.

68 A B C IIIcsc Incision

IIItcss

IIIss

IIImsc

E F

25 m

Figure 3.8 Photos of third-order architectural elements preserved on Downes and Dunlop Point. (A) clast supported conglomerate (IIIcsc). (B) matrix supported conglomerate (IIImsc) incised by thick‐bedded cross-stratified sandstone. (C) thick-bedded sandstone (IIIts) and thick-bedded cross-stratified sandstone (IIItcss). (D) thinly inter‐bedded siltstone and cross-stratified sandstone (IIIscss). (E) thinly inter-bedded siltstone and sandstone (IIIss) and thinly interbedded siltstone and cross-stratified sandstone (IIIscss). (F) chaotically bedded sandstone (IIIcbs).

69 Table 3.1 Third-order architectural elements. Lithofacies Lithology Grading Thickness Physical Lithological Basal Contact Process Structures Accessories Character Interpretation IIIcsc – Clast- Clast-supported Typically ungraded, Beds thickness: Structureless with Rounded, poor to well-sorted Sharp to undulating, High density turbidity Supported granule to cobble with rare normal 0.2 - 5 m rare planar extrabasinal clasts, 1-30 cm often loaded. current with Conglomerate conglomerate with grading. Thickness: <7 m laminations. in diameter with an average suspension and medium to very Commonly of 5 cm. traction sedimentation. coarse matrix imbricated. IIImsc - Matrix Matrix-supported Disorganized, Beds: 0.2 m – 6m None Extrabasinal clasts 1-10cm in Planar to undulating Coherent debris flow Supported granule to pebble structureless Thickness: <6 m diameter with an average od Conglomerate conglomerate with 3 cm. Intrabasinal sandstone very fine sand to fragments cobble sized clasts

IIIts - Thick-bedded Fine to very-coarse Normally graded Beds: 0.2 – 5m Commonly Extrabasinal granule to Planar to undulating, High density turbidity sandstone sandstone from occasional Thickness: <10m structureless. pebble clasts and/or commonly currents, deposited out granule to pebble Flame structures, intrabasinal mudstone clasts amalgamated of suspension matrix supported sole marks, dish (0.05m to 1.5m diameter) in sedimentation. base to fine structures often lags. sandstone present

IIItcss – Thick- Fine to very-coarse Normally graded Beds: 0.2m – 5 m Cross stratified Extrabasinal granule to Concave, Sharp Traction deposition in bedded Cross sandstone from occasional Thickness: .Flame structures, pebble clasts and/or high density, sand rich Stratified sandstone granule to pebble sole marks, dish intrabasinal mudstone clasts turbidity currents matrix supported structures often (0.05m to 1.5m diameter) in base to fine present lags. sandstone

IIIss– Thinly Siltstone, very fine Normally graded Beds: 1cm – 20cm Ripples, flame None Planar Low density turbidity interbedded siltstone to fine sandstone from fine sandstone (sand) structures, sole current, traction and and sandstone at the base to Thickness: <6m marks, planar suspension deposition. siltstone laminations, wavy laminations. Lenticular and planar sandstone beds. IIIscss - Thinly Siltstone, very fine Cross Stratified None Concave, Sharp High-energy turbidity interbedded siltstone to medium current that experience and cross stratified sandstone super-critical flow sandstone parameters

IIIcbs - Chaotically Mudstone or Normally grades Beds: < 7m Contorted, Intrabasinal mudstone clasts Sharp Slumping or rafting bedded sandstone sandstone matrix. similar to L3 Thickness: 22m overturned <1m in diameter. Fine to coarse sandstone blocks. Intrabasinal sandstone blocks grained sandstone up to 30 m in diameter. blocks/beds Extrabasinal clasts up to 70 20cm with a 5cm average. (IIItcss) (Fig. 3.8C); thinly inter-bedded siltstone and sandstone (IIIss) (Fig. 3.8E); thinly inter-bedded siltstone and cross stratified sandstone (IIIscss) (Figs. 3.8D, E); and chaotically bedded sandstone and mudstone (IIIcbs) (Fig. 3.8F). All seven third order elements are outlined in Figure 3.7B. Descriptions and process-based interpretations of each third order element are presented in Table 3.1.

Fourth-order architectural elements

The fourth order architectural elements described include IV1-IV4. IV1 consists of thick-bedded sandstone (IIItcss and IIIts) interbedded with siltstone (IIIss) and

chaotically bedded deposits (IIIcbs). IV2 deposits comprise siltstone with intermittent thin, laterally continuous (IIIss) and discontinuous sandstone deposits (IIIscss). IV3 is composed of thick-bedded conglomerate (IIIcsc) and sandstone (IIItcss) with rare matrix supported conglomerate (IIImsc) and siltstone (IIIss) deposits. IV4 includes interbedded lenticular stratified sandstone (IIIscss), thinly interbedded sandstone and mudstone (IIIss), and thin chaotically bedded sandstone and mudstone (IIIcbs). The distribution of fourth order architectural elements are indicated in Figure 3.7C.

IV1 – Conduit Margin and Base

Observations

This fourth order architectural element is composed of a series of third order elements. Mudstone-dominated chaotically bedded deposits with rare extrabasinal clasts and contorted intrabasinal sandstone clasts (IIImsc) dominate the base of the succession (Figs. 3.7, 3.9A). Discordant blocks of bedded strata up to 30 m in diameter within a mudstone or fine-grained sandstone matrix (IIImsc and IIIcbs) are preserved at the northeast part of the section on Downes Point (Figs. 3.7, 3.9B); these deposits transition upwards to thick-bedded sandstone (IIItcss and IIIts) (Figs. 3.7, 3.9C), with thinly interbedded siltstone beds (IIIss) towards the eastern extent of the outcrop (Figs. 3.7C, 3.9B). At this location, tabular bedding is normally faulted towards the west, or paleo-conduit

71 axis (Figs. 3.9C-D); beyond the zone of faulting, the tabular beds are replaced laterally by chaotically bedded strata dominated by discordant blocks (Fig. 3.9B). Both the tabular and chaotically bedded units are characterized by similar lithological characteristics. Furthermore, at the top of the succession tabular beds extend across the outcrop and are not faulted. These relationships are documented at the easternmost extent of the cross- section on Fig. 3.7A.

Interpretation

Chaotically bedded deposits are interpreted to have formed as a result of mass wasting as gravity flows sculpted the seascape and caused mass-failure of channel banks. Contorted and bent sandstone beds (Fig. 3.9A) are suggestive that the deposits were not entirely consolidated at the time of mass wasting. The westward transition from tabular sandstone, to faulted sandstone, and ultimately to chaotically bedded strata dominated by discordant blocks, records mass-failure of the ancient conduit margin. The tabular beds were buried and consolidated, before presumably being exhumed and undercut by turbidity currents, causing mass-failure of rafted sediment blocks into the channel. Due to the relatively large size of the blocks it is reasonable to interpret a proximal source, with little transportation. The synsedimentary origin of faults is supported by the presence of undeformed beds at the top of the succession.

IV2 – Overbank Deposits

Observations

IV2 is comprised dominantly of thin-bedded tabular siltstone and sandstone (IIIss); sandstone bodies up to 2 m thick and 30 m wide are locally defined by underlying basal discontinuous erosion surfaces (IIIscss) (Figs. 3.9E,F, 3.8C). This fourth order architectural element is present adjacent to deposits of IV3 (coarse-grained channel fill), with a notable decrease in grain size distally, away from the coarse grained strata.

72 Interpretation

IV2 is interpreted as an overbank deposit formed in an environment adjacent to the main channel fairway, such as a levee or internal levee (Deptuck et al., 2003; Hubbard et al., 2008; Kane and Hodgson, 2011). The depositional setting experienced low-energy flows interrupted by punctuated high-energy currents perhaps recording periods when channel banks were breached. High-energy scours interbedded with sandstone within a dominantly siltstone succession is a characteristic feature of breached confining levees (Flood et al., 1995; Hickson and Lowe, 2002; Hubbard et al., 2008). Thin tabular sandstone beds transition away from adjacent channel fill deposits to thinner and higher mud content units, recording an overall lateral decrease in energy away from the active conduit (Kane et al., 2007).

IV3 – Channel Fill (Coarse Grained)

Observation

IV3 composes a significant portion of the resistant deposits that define Downes Point (Figs. 3.7C, 3.9 G, H). This element is primarily composed of thick-bedded, clast-supported conglomerate (IIIcsc) deposits (Fig. 3.8A) and thick-bedded sandstone (IIIts and IIItcss) (Figs. 3.8B, C), with rare matrix supported conglomerate (IIImsc).

Coarse-grained deposits of IV3 are separated laterally from deposits of IV1 and IV2 across concave up erosional surfaces (Fig. 3.9G).

Interpretation

Deposits of IV3 are interpreted as channel fill deposits largely composed of conglomerate characterized by evidence of bedload transport (Figs. 3.9 G, H), as well as sandstone deposited from collapsing turbidity currents (Lowe, 1982; Hickson and Lowe, 2002; Hubbard et al., 2008). The coarse-grained deposits of Downes Point collectively define a channelform shape, consistent with numerous deep-water channel fill outcrops (e.g., Juniper Ridge – Hickson et al., 2002; Monterey Formation – Surpless et al., 2009;

73 Cerro Toro - Beauboeuf et al., 2004; Rosario Formation – Kane et al., 2009). Notably, the composite channelform expression at the outcrop is composed of a series of smaller channel fills (cf. Sprague et al., 2002; Mayall et al., 2006; Deptuck et al., 2007; Fildani et al., 2013).

IV4 – Channel Fill (Fine Grained)

Observation

IV4 is volumetrically small compared to the other elements, comprised primarily of scour surfaces draped by mudstone (IIIss), thin mass-wasting deposits including overturned beds (IIIcbs), and overlying stratified sandstone (IIIscss) (Figs. 3.7A,C, 3.9 I, J). The sandstone units locally contain scours with backsets, dipping at approximately

180° from the regional paleoflow direction, towards the northeast. IV4 is commonly

stratigraphically below or laterally adjacent to deposits of IV3 (Fig. 3.9 K)

Interpretation

IV4 is interpreted to be the deposits preserved from scouring, high-energy turbidity currents. Although abundant siltstone is present, it is commonly observed draping scours, attributed to the tail of high energy flows that largely bypass th e area (cf. Hubbard et al., 2014; Stevenson et al., 2015). Backset stratification is characteristic of high-energy supercritical flows, which have been recently recognized in numerous outcropping slope channel deposits (e.g., Postma et al., 2014; Pemberton et al., 2016;

74 A Chaotic bedding

1 m

B Slump blocks

C Normal faults Coherent Beds Channel axis

Rafted Blocks

75 E

1 m Up-section

G Channel axis Northwest view

Incisions

Rafted Blocks Sandstone beds

North view H Channel axis

Base channel incision

Rafted Blocks

76 I

MTD

10 cm Siltstone scour drape

Siltstone drape

10 cm

scours

Fig. 3.9I,J

Fifth order boundary

Sandstone thinning

Channel axis

Figure 3.9 Photos of fourth-order architectural elements. (A) IV1- contorted intrabasinal sandstone clasts (IIImsc) on Norman Point. (B) IV1 - discordant blocks of bedded strata up to 30 m in diameter within a mudstone or fine- grained sandstone matrix (IIImsc and IIIcbs), preserved at the base of the conduit to the northeast part of the section on Downes Point. (C-D) IV1-tabular thick-bedded sandstone (IIItcss and IIIts) with inter-bedded thin siltstone beds

(IIIss). The beds are normally faulted towards the paleo-conduit axis (left of page), Downes Point. (E) 2IV - siltstone with thin-bedded tabular sandstone beds (IIIss) sandstone bodies up to 2 m thick and 30 m wide are locally defined by underlying scour surfaces (IIIscss), Dunlop Point. (F) IV2 - bedded siltstone (IIIss), Dunlop Point. (G-H) IV3 - thick- bedded, clast-supported conglomerate (IIIcsc) deposits and thick-bedded sandstone (IIIts and IIItcss), Downes Point.

(I-K) IV4 - scour surfaces draped by mudstone (IIIss), thin mass-wasting deposits including overturned beds overlying cross-stratified sandstone (IIIscss), Downes Point.

77 Bain and Hubbard, 2016) The presence of these deposits directly beneath and adjacent to channel fill deposits is perhaps suggestive that they record processes of erosion that ultimately set the template for subsequent channelization (e.g. Fildani et al., 2006; Catteral et al., 2010; Fildani et al., 2013).

Fifth Order Architectural Element Fifth order architectural elements contain one or more fourth order elements (Ghosh and Lowe, 1993). Three fifth order elements are identified in the outcrop (Figs. 3.5, 3.7A). The oldest fifth order element is demarcated at the base of the succession by

a channelform erosion surface overlain by contorted siltstone-dominated MTDs (IV1) and bedded siltstone (IIIss) (Fig. 3.7A). Overlying the siltstone, thick-bedded channel fill

deposits (IV3) are abundant, which lap-out onto a steep erosion surface to the southeast.

This erosion surface is locally mantled by matrix-supported conglomerate (IIImsc, IV1). Capping the element are interbedded siltstone and sandstone turbidites (IIIss) attributed to overbank processes, as well as numerous conglomeratic channel fill bodies that transition to thick-bedded sandstone and thin-bedded deposits at their margin (Fig. 3.8). The second fifth order element (Fig. 3.7A) is similarly defined at its base by a channelform erosion

surface that is locally overlain by mass wasting deposits (IV1); abundant rafted blocks transition to thick-bedded tabular sandstone (IIItcss and IIIts) at the conduit edge (Fig. 3.7). At the western edge of the outcrop, however, the basal deposits consist of stratified

scour fill deposits (IV4). A series of channelform bodies in-filled with conglomerate (IV3) dominate the upper part of the succession. A third fifth order element is dominated by thinly interbedded turbidites with isolated sandstone bodies (IV2), which is attributed to channel overbank processes (i.e., internal levee). The genetically related channel fill is located to the northwest of the study area, and is not a focus of this analysis (Fig. 3.4A; Bain and Hubbard, 2016). In general, the development of fifth order elements is initiated by channel inception, presumably related to channel avulsion (Fig. 3.10A)(cf. McHargue et al.,

78 A Channel Incision

B Ponding of Sand

C Reincision and Failure of Channel Wall

D Channel Reactivation

E Channel Abandonment

Active Channel Channel migration

Figure 3.10 Schematic block diagram depicting a fifth order (V2) stratigraphic evolution of Downes Point channel system. (A) Fifth order element initiated by channel inception, likely related to channel avulsion. Initial channel fill consists of debris flows derived from up-slope, and traction structured conglomerate that was presumably linked to abundant bypass. (B) Conduit infilled with conglomerate and a tabular package of thick-bedded turbidites at the margin. We speculate that emplacement of downslope MTD deposits in the channel altered the slope equilibrium, facilitating ponding and backfilling at this local. (C) Erosion of the ponded strata occurred, presumably from an associated down-dip knickpoint’s upstream migration. As high-energy currents largely sculpted the channel, the deposits were eroded and undercut, resulting in mass-wasting and the deposition of chaotically bedded blocks of sandstone and an degradational terrace. (D) Continued gravity flows eroded into mass wasted, chaotically bedded sandstone, followed by deposition of coarse-grained channel fills. (E) Lateral channel stacking patterns are preserved by the vertical succession of coarse-grained channel fill. The succession records a lateral migration of the channel system, abandoning the area.

79 2011). A channel fairway is carved into the seafloor, with the products of channel inception typically associated with low preservation potential due to successive high- energy currents (Fildani et al., 2013). Initial channel fill consists of debris flows derived from up-slope, and traction structured conglomerate that was presumably linked to

abundant bypass (Stevenson et al., 2015). Fine-grained channel fill (IV4) deposits also overlie the deeply scoured basal channel erosion surface. The thinly interbedded sandstone and siltstone (IIIss, IIIscss) is associated with scours up to 1 m deep and 5 m long, as well as abundant cross-stratification, including backsets locally (Fig. 3.7D, 3.9I, J). These deposits are also interpreted to be product of largely bypassing turbidity currents (Postma et al. 2014). Subsequently, the conduit is largely infilled with conglomerate and a tabular package of thick-bedded turbidites at the margin, in the case of the second fifth order architectural element (Fig. 3.7A).The lack of sedimentary structures in these tabular beds is consistent with collapsing high-density turbidity currents within the channel setting (e.g., Anderson et al., 2006; Bernhardt et al., 2012). We speculate that emplacement of downslope MTD deposits in the channel altered the slope equilibrium, facilitating ponding and backfilling (Fig. 3.10B) (Clark and Pickering, 1996; Postma et al., 2009; McHargue et al., 2011). As the obstruction within the channel was overcome, a knickpoint migrated up-conduit, eroding the ponded sandstone deposits within the channel axis (cf. Heinio and Davies, 2007). The remnant sandstone strata was left as a degradational terrace at the conduit margin on the southeast side of Downes Point (Fig. 3.9C). As high-energy currents largely sculpted the channel, the thick-bedded terrace sandstone (IIIts) was eroded and undercut, resulting in mass-wasting and the deposition

of chaotically bedded blocks of sandstone (IIIcbs, IV1) across the channel setting (Fig. 3.10C). Blocks 1-30 m in diameter slumped into the newly formed accommodation space (Fig. 3.9B). To the east, sandstone beds of the terrace tilt in the direction of the channel axis and are characterized by faulting, but were not fully detached or slumped into the

80 channel (Figs. 3.9C, D). This collection of observations records the arrested development of retrogressive channel margin failure. Following mass wasting, continued gravity flows eroded into mass wasted, chaotically bedded sandstone (IIIcbs) in the axis of the conduit (Fig. 3.9G). Deposition of channel fills (IV3) composed of coarse-grained pebble- to cobble-sized extra-basinal clasts (IIIcsc) on-lap basal concave-up erosion surfaces (Figs. 3.9G,H, 3.10D). Evidence for sediment bypass is still prevalent including imbricated conglomerate (Mutti and Normark, 1987; Stevenson et al., 2015)(Fig. 3.8A). Lateral channel stacking patterns are preserved by the vertical succession of coarse-grained channel fill (IV3), overlying thick- bedded sandstone (IIIts), and interbedded sandstone and siltstone (IIIss); this pattern records the migration of channels westward (Fig. 3.10E).

DISCUSSION: EVIDENCE FOR KNICKPOINT EROSION IN DEEP-WATER OUTCROPS

From submarine channel inception to eventual abandonment, associated processes are recorded by a breadth of products in the stratigraphic record. Composite conduit-defining erosion surfaces, channel thalweg lags, drapes and bedform deposits, aggradational and degradational terraces, and back-filled axis deposits are evidence of protracted erosion, sediment bypass and deposition (Mutti and Normark, 1987; Hubbard et al., 2014; Hansen et al., 2015). The longevity of submarine channels, over centuries, millennia, or longer, has not been directly measured; undoubtedly, we collectively underestimate the duration of channel processes when interpreting the rock record. Even without direct dating methods to specifically constrain channel evolution, we are biased by products of filling rather than bypass or throughput. This is understandable, as the preservation potential of deposits of protracted sediment transfer processes is inherently low. Recent seafloor analysis has emphasized various ways in which a conduit

81 is maintained during extended periods of net sediment bypass (e.g, Conway et al., 2012; Hughes-Clarke, 2016). Mass-wasting of channel banks (Bernhardt et al., 2015), knickpoint migration (Heinio and Davies, 2007), bar development (Hughes-Clarke, 2016) and localized erosion or deposition (Conway et al., 2012) are all critical processes. The products of many of these processes have not been a focus, per se, and therefore are poorly constrained from the outcrop record. The Nanaimo Group at Downes Point provides a unique opportunity to consider the stratigraphic expression of a degradational terrace that could be attributed to knickpoint migration. Knickpoints are commonly associated with river systems and generate as a result in base level change, sediment flux and bedrock resistance (Howard et al., 1994). A knickpoint is defined in fluvial systems as a steep gradient between lower gradient sections along a channel (Howard et al., 1994). Although deep-water depositional environments are very distinct from fluvial systems, the products of knickpoint migration have been interpreted in deep-water datasets (Fig. 3.11) (e.g., Pirmez et al., 2000; Adeogba et al., 2005; Mitchell, 2006; Gee and Gawthorpe, 2006; Heinio and Davies, 2007; Micallef et al., 2014). In submarine systems, channels are constantly adjusting their profile to obtain slope equilibrium via turbidity current erosion (Figs. 3.11A,B) (Pirmez et al., 2000; Kneller, 2003). Several models have been proposed that indicate submarine erosion occurs upstream of a knickpoint and sediment deposition occurs downstream (Pirmez et al., 2000). Knickpoints may form due to various factors, including salt uplift of the seafloor, tectonic activity or the emplacement of mass-wasting deposits, blocking the channel fairway. In the later case for example, undercutting of terrace or levee deposits by erosion can cause the conduit margin to collapse into the channel. At this point, flows will divert around the mass-failure deposits (Kukowski et al., 2001; Smith, 2004) unless the channel is dammed (Bernhardt et al. 2015). Damming has a reactive response upslope, as flows rapidly decelerate and pond (Fig. 3.11C) (Bernhardt et al., 2012). Eventually, flows fill

82 Knickpoint

Figure 3.11 Knickpoint Morphology, Niger Delta (modified from Heinio and Davies, 2007). (A) seafloor map highlighting a knickpoint within a channel system. (B) Seismic line oriented parallel to the thalweg profile across knick point. (C) Seismic line perpendicular to the channel system, upstream of the knickpoint. Notice deposition has occurred below the current channel thalweg. (D) Seismic line perpendicular to the channel system, downstream of the knickpoint. Note the cut or degradational terrace downstream of the knickpoint representing upstream knickpoint migration. the accommodation and the channel re-incises via up-channel knickpoint migration (cf. Greene et al., 2002; Mitchell, 2006; Heinio and Davies, 2007; Paull et al., 2011; Bernhardt et al., 2015). The result of knickpoint migration is degradational terraces, potentially formed of the ponded sediments (Fig. 3.11D) (Heinio and Davies, 2007).

83 With a dearth of outcropping deposits attributed to knickpoint processes, the exposure on Downes Point is perhaps significant, providing a template from which to interpret other deep-water sedimentary successions. Critical observations include: (1) characterization of typical channel fill deposits, in this case widespread traction- structured conglomerate and sandstone (Figs. 3.9G, H); (2) evidence for conduit margin instability including mass-wasting deposits and clastic injections (Figs. 3.9 B-D) (cf. Rowe et al., 2002); (3) an anomalous thick-bedded tabular sandstone package adjacent to conduit margin (Fig. 3.9D); and (4) evidence for 75 m of incision, including retrogressive failure of previously deposited terrace deposits (Fig. 3.7A). In the two-dimensional outcrop, direct evidence for damming of the paleo-channel cannot be documented, although the propensity for channel margin instability through the Geoffrey Formation (Katnick and Mustard, 2003; Bain and Hubbard, 2016) supports the hypothesis that mass-failure was an important mechanism of channel maintenance. Evidence for ponding of turbidity currents within the channel is consistent with back-filling against the intra- conduit blockage. Lastly, the preservation of these units as a degradational terrace is critical to the interpretation. It is important to distinguish aggradational terraces or internal levees, which are derived from the tops of thalweg-focused turbidity currents and comprised of thin-bedded turbidites (Hansen et al., 2015), from units characterized by evidence for ponding. The relationship between tabular suspension deposits and conglomeratic channel axis deposits across a significant erosion surface (in this case with up to 75 m of relief) is observed in seismic datasets (e.g., Heino and Davies, 2007; Sylvester and Covault, 2016), and is likely more widely prevalent in the outcrop record, particularly if knickpoint migration is critical to submarine channel maintenance.

CONCLUSION Recent emphasis has been placed on protracted processes associated with submarine channel maintenance from both modern settings and stratigraphic datasets.

84 The Late Cretaceous deep-water outcrop deposits of the Geoffrey Formation on Downes Point, Hornby Island, offers a unique prospective to observe protracted erosion, substrate instability, knickpoint migration and deposition towards the edge of a large-scale conduit. Key features of a conduit margin on Downes Point include degradational terraces, cyclic steps, mass transport deposits, nested erosion surfaces, and fine- and coarse-grained channel fill deposits. An anomalous, tabular thick-bedded sandstone sheet is preserved, which is attributed to flow deceleration caused by downstream damming of the channel axis by mass transport deposits. This tabular unit was subsequently incised, and the product is interpreted as a remnant degradational terrace deposit. Degradational terraces are rarely interpreted from outcrops and, therefore, this example provides a unique stratigraphic record of knickpoint migration in submarine channel settings.

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90 West Texas, U.S.A. Journal of Sedimentary Research 80, 67–96. Rowe, C.A., Mustard, P.S., Mahoney, B., Katnick, D.C., 2002. Oriented clastic dike swarms as indicators of paleoslope. An example from the Upper Cretaceous Nanaimo Group. Journal of Sedimentary Research 72, 192-200. Slomka, J.M., Eyles, C.H., 2013. Characterizing heterogeneity in a glaciofluvial deposit using architectural elements, Limehouse, Ontario, Canada. Canadian Journal of Earth Sciences 50, 911-929. Smith, R., 2004. Silled sub-basins to connected tortuous corridors; sediment distribution systems on topographically complex sub-aqueous slopes. In: Lomas, S.A., and Joseph, P., (Eds.), Confined Turbidite Systems. Geological Society London 222, 23-43. Sprague, A. R., Patterson, P.E., Hill, R.E., Jones, C.R., Campion, K.M., Van Wagoner, J.C., Sullivan, M.D., Larue, D.K., Feldman, H.R., Demko, T.M., Wellner, R.W., Geslin, J.K., 2002. The Physical stratigraphy of Fluvial strata: A Hierarchical Approach to the Analysis of Genetically Related Stratigraphic Elements for Improved Reservoir Prediction. (Abstract) AAPG Annual Meeting. Stevenson, C.J., Jackson, C.A-L., Hodgson, D.M., Hubbard, S.M., Eggenhuisen, J.T., 2015. Sediment bypass in deep-water systems. Journal of Sedimentary Research 85, 1058-1081. Surpless, K. D., Ward, R.B., Graham, S.A., 2009. Evolution and stratigraphic architecture of marine slope gully complexes: Monterey Formation (Miocene), Gaviota Beach, California. Marine and Petroleum Geology 26, 269-288. Sylvester, Z., Pirmez, C., Cantelli, A., 2011. A model of submarine channel-levee evolution based on channel trajectories: implications for stratigraphic architecture. Marine and Petroleum Geology 28, 716-727.

91 CHAPTER FOUR: CONCLUSIONS AND FUTURE WORK

Large conduits on continental margins focus sediment transfer to the deep-sea, characterized by evidence for protracted erosion and sedimentary bypass (Mutti and Normark, 1987; Hubbard et al., 2014; Stevenson et al., 2015). Deep-water slopes are highly inhospitable, limiting the direct measurement of gravity flow processes that occur in the axis or margin of a conduit (Sumner and Paull, 2014). As a result, outcrop observations and interpretations improve the understanding of processes shape submarine conduits. In the axis of these conduits, high-energy flows persist, resulting in coarse- grained channel fill deposits that dominate the stratigraphic record (Hughes Clarke et al., 2006). Conversely, at the margins of these conduits, the preservation potential for a more complete record of erosion, sediment bypass, and deposition is higher (Kane and Hodgson, 2011). Analyzing stratigraphic products in outcrop along with seismic and bathymetric data, our understanding of sedimentology processes of the deep-water slope realm will advance. The Late Cretaceous Upper Nanaimo Group on Hornby and Denman islands was deposited in a deep-water environment. Strata of both islands constitute the record of a single submarine conduit, the product of which is 19.5 km wide and 1.5 km thick. Geologically recent ice age and modern ocean erosion biases outcrops to resistant coarse- grained deposits. Lateral and vertical facies shifts are rapid in outcrop; conglomerate and sandstone (in-channel) deposits juxtapose both thin-bedded over bank (out-of-channel) and fine-grained mass transport deposits. The basal conduit deposits on the west side of Denman Island constitute siltstone-dominated strata with evidence for high-energy (e.g., lags, scours, back-set stratification) that are indicative of conduit inception (Fildani et al., 2013). Strata above is dominated by coarse-grained thick-bedded conglomerate and sandstone channel fill, which onlap nested erosion surfaces. Channelforms on Denman Island are characterized by lateral channel migration. Coarse-grained channel fill deposits

92 also dominate Hornby Island, however, the stacking pattern evolves into one dominated by vertical channel aggradation. Channel fill stacking patterns that evolve from lateral migration-dominated to vertical aggradation-dominated are common in ancient datasets around the world (Deptuck et al., 2003; Hodgson et al., 2011). Two different deep-water submarine channel environments deliver sediment from the continent to a basin and produce similar stratigraphic products. (1) Submarine canyons characterized by a single deep-incision of the seas scape that is ultimately filled by gravity flow deposits, and (2) slope channel systems that experience punctuated erosion and aggradation. Submarine canyons have deep bathymetric relief on the seafloor, and slope channel systems exhibit much more shallow relief. Although these two end-members are distinct on the seafloor, their stratigraphic products are not easy to distinguish. Protracted aggradation of lower relief leveed channels can results in highly diachronous stratigraphic surfaces in the rock record that encapsulate turbiditic packages up to 20 km across and 1.5 km thick. The Upper Nanaimo group on Hornby and Denman islands formed through erosion, sedimentation and aggradation in a series of stages as a channel system evolved; it did not form in by filling a 1.5 km deep incision in the slope.This interpretation does not require a mechanism to incise a 1.5 km deep conduit on the seafloor; rather, more subdued controlling parameters related to allogenic (e.g., sea-level, sedimentation, tectonic) and autogenic processes are interpreted. Based on this investigation, however, it is evident that differentiation between highly composite versus geomorphic surfaces in outcrop exposures can be particularly perplexing. The processes that sculpt submarine conduits are numerous, related to erosion, sediment bypass, mass-wasting and deposition. Many of these processes have been widely deduced from outcropping stratigraphic products. Some, however, have not. For example, knickpoint migration has been observed in modern submarine channels (e.g., Hughes Clarke et al, 2015) and interpreted from seismic data (e.g., Heinio and Davies,

93 2007). In this thesis, detailed analysis of a submarine conduit margin exposed on Hornby Island reveals strata attributed to channel erosion as a result of knickpoint migration. The conduit edge exposed at Downes Point is characterized by evidence for channel inception (e.g., scours, cyclic steps), and subsequent bypass and deposition of course-grained sediment. Following inception, initial channel fills consists of mass wasted upslope deposits carried by debris flows. Due to a downstream, channel thalweg blockages during channel evolution, subsequent flows decelerated and deposited a tabular sheet of thick-bedded sandstone. Later high-energy currents carved into the ponded sandstone and re-established the channel. Undercutting at the channel margin resulted in mass-wasting. The conduit edge was greatly impacted by the generation and migration of a channel knickpoint. Direct outcrop evidence for a knickpoint is difficult to demonstrate, however the deeply incised ponded sandstone deposits is a strong indicator of intrachannel ponding. The remnant ponded sandstone is a degradational terrace deposit, recording upstream migration of a knickpoint. The stratigraphic and sedimentologic observations provide initial criteria for recognition of knickpoint processes in the stratigraphic record.

FUTURE WORK

The submarine conduit system expressed at Hornby and Denman islands is substantial in terms of scale and sediment caliber (Fig. 4.1). A logical consideration is whether a substantial submarine conduit can be linked to a significant catchment, and particularly one that may have been previously defined from coeval Late Cretaceous rocks from along the western North America margin. To date, the up-dip strata to the Nanaimo Group rocks have not been identified. Unfortunately, a clear relationship between submarine canyon size and subaerial feeder system scale is not evident (Shepard 1973). Comparing the size of four modern canyons (Astoria, Willapa, Monterey,

94 A N Cook Strait Nicholson Canyon Canyon A’ Wairarapa A Canyon

North Honeycomb Palliser Pahaoa Canyon Canyon Canyon Opouawe Canyon

A A’ 0 Elevation (m) Elevation -500 25 m 0 10 20 30 Distance (km)

B Willapa Canyon Astoria Canyon N

A’

A Guide Canyon

A A’ -400 Elevation (m) Elevation

-800 0 10 20 30 40 50 Distance (km) 25 m

Figure 4.1 Modern submarine canyons. (A) Cook Strait Canyon off of the east coast of New Zealand. (B) Willapa and Astoria Canyons off of the west coast of Oregon, USA. Images courtesy of GeoMapApp.

95 Canyon Canyon Canyon Area Length Q TSS TDS River Name 3 2 3 Name Width (km) Depth (m) (10 km ) (km) (km /yr) (Mt/yr) (Mt/yr) Willapa 15 800 Columbia 670 2000 240 9.7 21 Astoria 8 500 Columbia 670 2000 240 9.7 21

Nicholson 8 600 Hutt 0.43 56 0.68 0.13 - Wairarapa 9 600 Ruamahanga 2.3 100 2.5 0.6 -

Monterey 23 1400 Pajaro 3.1 - 0.08 0.3 -

Monterey 23 1400 Salinas 11 280 0.3 2.3 0.17

Table 4.1 Canyon size related to respective river input. Five different canyon sizes are compared to their river catchment size, flux and total suspended and dissolved solids. There is no correlation between the size of the canyon to the size of the river. The green highlighted area represents the largest canyon and the blue area represents the largest present day river. (Fluvial data collected from Milliman and Farnsworth 2011).

and Cook Strait Canyon) with their catchment length and sediment flux reveals little correlation (Table 4.1). It is notable that catchment area and sediment flux of sediment into submarine canyons reflect present day measurements (Milliman and Farnsworth 2011), however most canyons were largely active only during sea-level low stand, under the influence of a substantially different global climate. Normark and Carlson (2003) documented a link between high-relief mountainous catchment areas and sediment transport to the world’s largest submarine fans. Therefore, the recognition of submarine conduit fill in the Nanaimo Group on Hornby and Denman islands can perhaps only further support a previously proposed model for a tectonically active, mountainous catchment (e.g., Mustard 1994). Modern canyon or slope channel systems along continental margins in a forearc setting have multiple point sources from the active tectonic mountainous catchment. Two examples previously mentioned in Oregon and New Zealand both have multiple canyons feeding sediment into the ocean (Fig. 4.1). These analogues perhaps provide insight into the paleogeographic reconstruction of the continental margin during the Late Cretaceous time period. Future work on the Gulf Islands to the south of Hornby and Denman islands should emphasize identification of additional conduits along strike of the ancient basin

96 margin. Based upon preliminary reviews of geological work completed on the southern Gulf Islands (England et al., 1990, Coutts et al., 2015), it is reasonable to predict that those islands make up similar channelized environments that stem from multiple input sources. Future work by Daniel Coutts (Gabriola and Valdes islands) and Rebecca Englert (Galiano and Mayne islands) will provide more insight into the overall the depositional setting of the Upper Nanaimo Group, with paleogeographic implications of for the size of catchment that supplied these long-lived channel systems along the forearc margin. Another area of future work on Denman and Hornby islands are clastic injections. Injections form through natural hydraulic fractures as an over pressured zone attempts to stabilize, breaching the stratigraphic seal (Lorenz et al., 1991; Cosgrove, 2001; Jolly and Lonergan, 2002). Clastic intrusion provide insight into paleostresses active on the slope. Chapter two has multiple rose diagrams that represent clastic injectite orientations. The examples shown are only a portion of the intrusions on the islands and their detailed interpretation was beyond focus of this thesis. An interesting project might be to relate the injections on the islands to other injectites found in deep-water environments and analyze relationships between conduit size, location in conduit, sediment caliber or allocylic processes related to tectonically active environments. Furthermore, they may provide important insight into basin history (i.e., fluid flow, etc.) Work from this thesis provides a basis for the Nanaimo Group project to advance further understanding of coarse-grained high-energy deep-water systems. Paleogeographic implications of a long-lived stationary channel system provide insight into reconstructing the geological evolution of the North American Cordilleran.

REFERENCES

Cosgrove, J.W., 2001. Hydraulic fracturing during the formation and deformation of a basin: a factor in the dewatering of low-permeability sediments. AAPG Bulletin 85, 737–748. Coutts, D., Matthews, W., Guest, B., Hubbard, S.M., 2015. The Implications of Detrital Zircon Maximum

97 Depositional Age (MDA) from Large Sample Datasets. AGU Fall meeting December 14-18. San Francisco. Deptuck, M.E., Steffens, G.S., Barton, M., Pirmez, C., 2003. Architecture and evolution of upper fan channel-belts on the Niger Delta slope and in the Arabian Sea. Marine and Petroleum Geology 20, 649- 676. England, T.D.J. 1990. Late Cretaceous to Paleocene structural evolution of the Georgia Basin, southwestern British Columbia- PhD Thesis, Memorial University, St. John’s Newfoundland. Fildani, A., Hubbard, S.M., Covault, J.A., Maier, K.L., Romans, B.W., Traer, M., Rowland, J.C., 2013. Erosion at inception of deep-sea channels. Marine and Petroleum Geology 41, 48-61. Hodgson, D.M., Di Celma, C.N., Brunt, R.L., Flint, S.S., 2011. Submarine slope degradation, aggradation and the stratigraphic evolution of channel-levee systems. Journal of the Geological Society of London 168, 625-628. Hubbard, S.M., Covault, J.A., Fildani, A., Romans, B.R., 2014. Sediment transfer and deposition in slope channels: Deciphering the record of enigmatic deep-sea processes from outcrop. Geological Society of America Bulletin 126, 857-871. Hughes Clarke, J.E., Shor, A.N., Piper, D.J.W., Mayer, L.A., 2006. Large-scale current-induced erosion and deposition in the path of the 1929 Grand Banks turbidity current. Sedimentology 37, 613-629. Jolly, R.J.H., Lonergan, L., 2002. Mechanisms and controls on the formation of sand intrusions. Journal of the Geological Society, London 159, 605-617. Kane, I.A., Hodgson, D.M., 2011. Sedimentological criteria to differentiate submarine channel levee subenvironments: Exhumed examples from the Rosario Fm. (Upper Cretaceous) of Baja California, Mexico, and the Fort Brown Fm. (Permian), Karoo Basin, S. Africa. Marine and Petroleum Geology 28, 807-823. Lorenz, J.C., Teufel, L.W., Warpinsky, N.R., 1991. Regional fractures I. A mechanism for the formation of regional fractures at depth in flat lying reservoirs. AAPG Bulletin 75, 823–826. Milliman, J.D., and Farnsworth, K.L. 2011. River discharge to the coastal ocean. Cambridge University Press, New York. Mustard, P.S., 1994. The Upper Cretaceous Nanaimo Group, Georgia Basin. In: Monger, J.W.H. (Eds.), Geology and Geological Hazards of the Vancouver region, southwestern British Columbia. Geological Survey of Canada Bulletin 481, pp. 27-95. Mutti, E., Normark, W.R., 1987. Comparing examples of modern and ancient turbidite systems: problems and concepts. In: Legett, J.K., Zuffa, G.G. (Eds.), Marine Clastic Sedimentology: Concepts and Case Studies. Graham and Trotman, London, pp. 1-38.

98 Shepard, F.P., 1981. Submarine canyons: multiple causes and long term persistence. AAPG Bulletin 65, 1062–1077. Stevenson, C.J., Jackson, C.A-L., Hodgson, D.M., Hubbard, S.M., Eggenhuisen, J.T., 2015. Sediment bypass in deep-water systems. Journal of Sedimentary Research 85, 1058-1081. Sumner, E.J., Paull, C.K., 2014. Swept away by a turbidity current in Mendocino submarine canyon, California. Geophysics Research Letters 41, 7611-7618.

99 APPENDIX A

MEASURED SECTIONS

100 Measured Section Legend

Dish structures Soft-sediment Planar Ripples deformation strati cation

Sandstone clasts Mudstone clasts

101 S34 S33 S32 Spray Point S31 S30 S28 Tribune Bay S29 S27

S26 S24 S25 S23

S51 Dunlop Point S19 S21S22 S18 S20 S16 S17 S14 S15 S13 S5 S7 S3a S8 S2 S6 S11 S4 S9 S12 S1 S10 S36 S3b Downes Point

S50

S49 Norman Point

Measured section locations - Southeast Hornby Island

102 Collishaw Pt. Grassy Point S40 S42 S38 S41 S37 S39 S43 S45 Tralee Point S44 S47 S52 S47 S48 Phipps Pt. S53

Measured section locations - North Hornby Island 103 S53

Whaling Station Bay

S55

Helliwell Park S54 Tribune Bay

S56

Measured section locations - East Hornby Island

104 Denman Pt.

SDLH

Ferry Terminal

SDE SMR

Gravelly Bay

SBP

Boyle Point

Measured section locations - Denman Island

105 S1 - Downes Point Bottom: 10 U 381056.558 m E 5484264.09 m N Top: 10 U 381062.225 m E 5484284.807 m N

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

106 S2 - Downes Point Bottom: 10 U 381141.343 m E 5484329.15 m N Top: 10 U 381141.343 m E 5484332.47 m N

0 m ss vf f m c vc g p c

107 S3 - Downes Point Bottom: 10 U 381173.497 m E 5484359.9 m N Top: 10 U 381158.301 m E 5484371.47 m N

0 m ss vf f m c vc g p c

108 S4 - Downes Point Bottom: 10 U 381187.548 m E 5484361.78 m N Top: 10 U 381159.585 m E 5484371.14 m N

0 m ss vf f m c vc g p c

109 S5 - Downes Point Bottom: 10 U 381265.75 m E 5484432.11 m N Top: 10 U 381273.398 m E 5484455.34 m N

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

110 S6 - Downes Point Bottom: 10 U 381321.46 m E 5484434.09 m N Top: 10 U 381312.862 m E 5484481.96 m N

0 m ss vf f m c vc g p c

111 S7 - Downes Point Bottom: 10 U 381418.423 m E 5484473.58 m N Top: 10 U 381413.616 m E 5484498.32 m N

0 m ss vf f m c vc g p c

112 S8 - Downes Point Bottom: 10 U 381524.857 m E 5484436.14 m N Top: 10 U 381524.857 m E 5484436.14 m N

10 30

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

113 S9 - Downes Point Bottom: 10 U 381608.65 m E 5484312.61 m N Top: 10 U 381613.304 m E 5484348.75 m N

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

114 S10 - Downes Point Bottom: 10 U 381697.932 m E 5484289.19 m N Top: 10 U 381689.334 m E 5484339.05 m N

5 25

0 m ss vf f m c vc g p c m ss vf f m c vc g p c

115 S11 - Downes Point Bottom: 10 U 381865.272 m E 5484381.69 m N Top: 10 U 381945.548 m E 5484443.82 m N

0 m ss vf f m c vc g p c

116 S12 - Downes Point Bottom: 10 U 381730.298 m E 5484339.63 m N Top: 10 U 381745.275 m E 5484502.9 m N

15 35

10 30

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

117 S13 - Downes Point Bottom: 10 U 381791.597 m E 5484345.69 m N Top: 10 U 381776.695 m E 5484443.27 m N

0 m ss vf f m c vc g p c

118 S14 - Downes Point Bottom: 10 U 381711.752 m E 5484483.33 m N Top: 10 U 381710.926 m E 5481711.752 m N

0 m ss vf f m c vc g p c

119 S15 - Downes Point Bottom: 10 U 381657.867m E 5484506.44 m N Top: 10 U 381653.322 m E 5484535.94 m N

0 m ss vf f m c vc g p c

120 S16 - Downes Point

20 40

15 35

10 30

5 25 45

0 20 40 m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c

121 S17 - Downes Point Bottom: 10 U 381453.941 m E 5484841.76 m N Top: 10 U 381400.168 m E 5484923.01 m N

0 m ss vf f m c vc g p c

122 S18 - Dunlop Point Bottom: 10 U 381421.854 m E 5484964.09 m N Top: 10 U 381481.22 m E 5485041.99 m N

0 m ss vf f m c vc g p c

123 S19 - Dunlop Point Bottom: 10 U 381505.432 m E 5484994.91 m N Top: 10 U 381533.962 m E 5485088.02 m N

0 m ss vf f m c vc g p c

124 S20 - Dunlop Point Bottom: 10 U 381614.499 m E 5485041.3 m N Top: 10 U 381723.343 m E 5485272.12 m N

15 35

10 30

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

125 S21 - Dunlop Point Bottom: 10 U 381758.832 m E 5485065.26 m N Top: 10 U 381830.957 m E 5485333.32 m N

10 30

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

126 S22 - Dunlop Point Bottom: 10 U 381944.638 m E 5485249.28 m N Top: 10 U 381970.906 m E 5485441.83 m N

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

127 S23 - Dunlop Point Bottom: 10 U 381918.76 m E 5485450.97 m N Top: 10 U 381905.317 m E 5485549.64 m N

0 m ss vf f m c vc g p c

128 S24 - Dunlop Point Bottom: 10 U 381811.87 m E 5485559.83 m N Top: 10 U 381811.963 m E 5485620.83m N

0 m ss vf f m c vc g p c

129 S25 - Dunlop Point Bottom: 10 U 381724.93 m E 5485624.13 m N Top: 10 U 381719.419 m E 5485694.66 m N

0 m ss vf f m c vc g p c

130 S26 - Dunlop Point Bottom: 10 U 381660.941 m E 5485666.91 m N Top: 10 U 381656.912 m E 5485731.98 m N

0 m ss vf f m c vc g p c

131 S27 - Dunlop Point Bottom: 10 U 381334.399 m E 548594.22 m N Top: 10 U 381377.147 m E 5485987.15 m N

0 m ss vf mf vcc g p c

132 S28 - Dunlop Point Bottom: 10 U 381180.422 m E 5486243.57 m N Top: 10 U 381208.096m E 5486280.75 m N

0 m ss vf mf vcc g p c

133 S29 - Dunlop Point Bottom: 10 U 381234.142 m E 5486145.09 m N Top: 10 U 381257.153m E 5486205.71 m N

0 m ss vf mf vcc g p c

134 S30 - Spray Point Bottom: 10 U 381093.291 m E 5486443.55 m N Top: 10 U 381100.418 m E 5486492.16 m N

0 m ss vf mf vcc g p c

135 S31 - Spray Point Bottom: 10 U 381422.881 m E 5486692.79 m N Top: 10 U 381454.013 m E 5486744.7 m N

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

136 S32 - Spray Point Bottom: 10 U 381302.767 m E 5486823.96 m N Top: 10 U 381321.222 m E 5486841.97 m N

0 m ss vf f m c vc g p c

137 S33 - Spray Point Bottom: 10 U 381473.948 m E 5486831.09 m N Top: 10 U 381473.948 m E 5486831.09 m N

0 m ss vf mf vcc g p c

138 S34 - Spray Point Bottom: 10 U 381345.351 m E 5486949.8 m N Top: 10 U 381345.351 m E 5486949.8 m N

0 m ss vf mf vcc g p c

139 S36 - Mt. Geo rey Bottom: 10 U 5484035.641 m E 380076.611 m N Top: 10 U 5484075.756 m E 380224.727 m N

20 40 60

15 35 50

10 30 45

5 25 45

0 20 40 m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c

140 S37 - Collishaw Point Bottom: 10 U 377233.762 m E 5489676.08 m N Top: 10 U 377279.822 m E 5489694.06 m N

0 m ss vf mf vcc g p c

141 S38 - Collishaw Point Bottom: 10 U 377662.242 m E 5489978.8 m N Top: 10 U 377662.242 m E 5489978.8 m N

0 m ss vf mf vccg p c

142 S39 - Collishaw Point Bottom: 10 U 378345.69 m E 5490072.05 m N Top: 10 U 378345.69 m E 5490072.05 m N

0 m ss vf mf vcc g p c

143 S40 - Collishaw Point Bottom: 10 U 378544.955 m E 5490151.55 m N Top: 10 U 378603.357 m E 5490101.57 m N

0 m ss vf mf vcc g p c

144 S41 - Collishaw Point Bottom: 10 U 378623.585 m E 5490120.69 m N Top: 10 U 378772.574 m E 5490065.59 m N

0 20 m ss vf mf vcc g p c m ss vf mf vccg p c

145 S42 - Grassy Point Bottom: 10 U 378895.729 m E 5490113.27 m N Top: 10 U 3789029.449 m E 5490063.42 m N

0 m ss vf mf vcc g p c

146 S43 - Grassy Point Bottom: 10 U 379613.414 m E 5489624.69 m N Top: 10 U 379742.487 m E 5489494.79 m N

0 m ss vf mf vcc g p c

147 S45 - East of Grassy Point Bottom: 10 U 379922.025 m E 5489518.28 m N Top: 10 U 379881.538 m E 5489477.77 m N

0 m ss vf f m c vc g p c

148 S47 - Trallee Point Bottom: 10 U 380201.857 m E 5489201.4 m N Top: 10 U 381029.275 m E 5488878.49 m N

40 20

15 35 55

30 10 50

5 25 45

0 20 40 m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c

149 S48 - Tralee Point Bottom: 10 U 381166.197 m E 5488997.23m N Top: 10 U 381343.243 m E 5488719.84 m N

0 m ss vf f m c vc g p c

150 S49 - Norman Point

Bottom: 10 U 380052.184 m E 5483637.83 m N Top: 10 U 380115.258 m E 5483765.28 m N

0 m ss vf f m c vc g p c

151 S50 - Norman Point Bottom: 10 U 380218.703 m E 5483742.51 m N Top: 10 U 380295.185 m E 5483950.31 m N

5 25

0 20 m ss vf mf vcc g p c m ss vf mf vccg p c

152 S51 - Dunlop Point Bottom: 10 U 382029.255 m E 5485240.04 m N Top: 10 U 382032.781 m E 5485398.75 m N

0 m ss vf mf vcc g p c

153 S52 - Collishaw Point Bottom: 10 U 376409.358 m E 5488980.56 m N Top: 10 U 376510.152 m E 5489088.28 m N

0 m ss vf mf vcc g p c

154 S53 - East of Tralee Point Bottom: 10 U 381701.715 m E 5488617.12 m N Top: 10 U 382406.274 m E 5488442.37 m N

20 40

15 35

10 30

5 25 45

0 20 40 m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c

155 S54 - Helliwell Cli Bottom: 10 U 5486564.23 m E 382847.701 m N Top: 10 U 5486590.023m E 382830.518 m N

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

156 S55 - Whaling Station Bay Bottom: 10 U 5487210.206 m E 383628.872 m N Top: 10 U 5487544.473 m E 383482.422 m N

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

157 S56 - Helliwell Cli Bottom: 10 U 5486104.40 m E 5383684.01 m N Top: 10 U 5486096.889 m E 383738.643 m N

0 m ss vf f m c vc g p c

158 S57 - Helliwell

0 m ss vf f m c vc g p c

159 SBP - Boyle Point Denman Bottom: 10 U 377905.124 m E 5481937.47 m N Top: 10 U 377905.124 m E 5481937.47 m N

5 25

0 20 m ss vf f m c vc g p c m ss vf f m c vc g p c

160 SDE - Denman East Bottom: 10 U 374063.959 m E 5485900.43 m N Top: 10 U 373797.24 m E 5486556.43 m N

20 40

15 35

10 30

5 25 45

0 20 40 m ss vf f m c vc g p c m ss vf f m c vc g p c m ss vf f m c vc g p c

161 SDLH - Denman Lighthouse Bottom: 10 U 367566.108 m E 5488911.18 m N Top: 10 U 367804.559 m E 5488911.18 m N

0 m ss vf f m c vc g p c

162 SMR - Denman Millard Road Bottom: 10 U 370509.147 m E 5486254.84 m N Top: 10 U 370522.644 m E 5486278.54m N

0 m ss vf f m c vc g p c

163